ae a S poems ax there See Pe eet ets Tykes oe Ouch bat) . ert: tO rere hii et Tete Sr anal Bee IF12 Cornell University Library OF THE Rew Work State College of Agriculture 4: 47 IB. LUMA 8IoI ‘ornell University Libra 7 nA CHEMISTRY INORGANIC & ORGANIC CHEMISTRY INORGANIC & ORGANIC WITH EXPERIMENTS BY CHARLES LOUDON BLOXAM TENTH EDITION, REWRITTEN AND REVISED BY ARTHUR G BLOXAM, F.I.C. Consulting Chemist and Chartered Patent Agent AND S. JUDD LEWIS, D.Sc., F.I.C. Consulting and Analytical Chemist PHILADELPHIA P. BLAKISTON’S SON & CO 1orz2 WALNUT STREET 1913 o. 13 Ber \4 13 Agu 148 BALLANTYNE AND COMPANY TAVISTOCK STREET COVENT GARDEN Lonpon ENGLAND LT) INTRODUCTION By PROFESSOR JOHN M. THOMSON, LL.D., F.R.S. Iris with regret that I have found myself compelled by increasing College and University duties, to relinquish the share I have previously taken in the re-editing of ‘“ Bloxam’s Chemistry ’’—a pleasant task which I regarded as the natural inheritance of my professorial chair at King’s College. Fortunately, Mr. Arthur G. Bloxam, who has been my colleague for so many years in former editions, was able to continue the work, and I felt that in his hands the traditions of the book would be maintained. In this I am not disappointed. Dr. §. Judd Lewis has ably assisted in bringing the work into a more modern form, and having had the opportunity of reading the sheets as they passed through the press, I feel satisfied that the tenth edition will prove as useful a text-book for the student as its predecessors. I venture therefore to give to this edition my best wishes and recom- mendation, and to express my earnest hope for its success. JOHN MILLAR THOMSON. King’s College, London. PREFACE THE first edition of this work appeared in 1867; the preface stated that the book was intended for those studying chemistry as a branch of general education, as well as for those professionally interested in the science. This intention was undoubtedly well fulfilled, but at that time 630 pages, containing only a few passages in small type, sufficed to give a fuller account of the science of chemistry than the tenth edition can pretend to offer. In the present year of grace, to perpetuate the aim of the author appeared a task well-nigh impossible ; nevertheless, it is what the editors have endeavoured to achieve. Whenever feasible the lucid explanations (many of them those that first appeared) of the common phenomena and of experiments illustrat- ing them, have been retained so that the general reader may still be able to take the book from the shelf with a reasonable prospect of satisfying his need of information. The editors have been even more desirous of maintaining the reputation of the book as the most compendious work on chemistry in a single volume, and it is here, of course, that serious difficulty has occurred and much re- writing has been required. The development of physical chemistry has rendered necessary a re-casting of the first portion of the book for the purpose of introducing to the student the fundamental principles of this branch at the same time that he becomes familiar with the more strictly chemical principles illustrated by the experiments described. Thus, after the Introduction, Water is con- sidered, not only from the chemical point of view, but as a typical liquid in the physical sense. Then an account of the chemistry of Air, including historical features, is blended with the consideration of the physical proper- ties of Gases. There follows a chapter on Acids, Bases, and Salts. The detailed consideration of the non-metals affords illustration of the principles previously set forth, and in the chapter on General Principles, which has been largely rewritten, a more advanced treatment of the subject is adopted. The Periodic Classification is followed more closely than in previous editions, and the development of the inorganic portion of the book rather than the Vii viii PREFACE organic is only in accord with the increased attention which has been given to inorganic chemistry of late years, as evidenced by the greater bulk of literature devoted to that branch. The work has gradually acquired an encyclopedic character, and the editors have done their best to increase its value in this direction by including precise details from original memoirs, which are outside the scope of the ordinary text-book. It is hoped that the present generation of students will find the tenth edition of “ Bloxam’s Chemistry” as interesting and useful as the now grey-headed students of the past generation found the first edition. CONTENTS INTRODUCTION WATER Hydrogen, Oxygen, Solutions AIR Nitrogen, Oxygen, Carbon Dioxide, Properties of Gases, Liquefaction of Gases ACIDS, BASES, SALTS Tonie Hypothesis HYDROGEN Occlusion, Reduction, Oxidation HALOGEN GROUP Chlorine, Hydrochloric Acid, Bleaching Powder, Bromine, Iodine, Fluorine SULPHUR GROUP Oxygen, Ozone, Hydrogen Peroxide, Sulphur, Sulphuric Acid, Carbon Disulphide, Selenium, Tellurium PHOSPHORUS GROUP Nitrogen, Ammonia, Nitric Acid, Phosphorus, Phosphoric Acid, Arsenic CARBON AND BORON GROUPS Carbon, Carbon Monoxide, Hydrocarbons, Combustion, Fuel, Silicon, Silicates, Boron ARGON GROUP GENERAL PRINCIPLES AND PHYSICAL CHEMISTRY Elements, Compounds, Isomorphism, Periodic Classification, Gases, Kinetic Theory of Gases, Molecular Weights, Liquids, Solution, Electrolysis, Solids, Crystallography, Phase Rule, Chemical Energy, Thermochemistry, Valency, Spectroscopy, Radioactivity CHEMISTRY OF THE METALS 1x PAGES 1-13 14-47 48-87 88-94. 95-100 101-136 137-180 181-234 235-292 293-295 296-357 358 x CONTENTS ALKALI METAL GROUP Potassium, Sodium, Alkali Manufacture, Ammonium Salts, Lithium, Rubidium, Cesium ALKALINE EARTH METAL GROUP Barium, Strontium, Calcium, Cements, Glass, Radium, Dis- integration of Elements MAGNESIUM GROUP Magnesium, Zinc, Cadmium, Beryllium, Mercury ALUMINIUM GROUP Aluminium, Pottery, Gallium, Indium, Thallium, Metals of the Rare Earths, Cerium IRON GROUP Iron, Cobalt, Nickel, Manganese, Chromium CHROMIUM GROUP Molybdenum, Tungsten, Uranium ANTIMONY GROUP Bismuth, Antimony, Vanadium, Niobium, Tantalum TIN GROUP Tin, Alloys, Titanium, Zirconium, Thorium, Germanium, Lead COPPER, SILVER, GOLD Electroplating, Photography EIGHTH GROUP Platinum, Palladium, Rhodium, Osmium, Ruthenium, Iridium ORGANIC CHEMISTRY Ultimate Analysis, Formule, Constitution HYDROCARBONS Paraffins, Olefines, Benzenes, Isomerism ALCOHOLS, ALDEHYDES, ACIDS STEREOCHEMISTRY Melting-points, Specific Volumes KETONES, ETHERS, HALOGEN DERIVATIVES, ESTERS Oils, Terpenes METAL AND METALLOID DERIVATIVES PAGES 358-384 385-402 402-420 420-433 434-469 470-473 474-482 483-505 505-528 529-537 538 546-574 574-633 633-647 647-683 683-692 CONTENTS AMMONIA DERIVATIVES Amines, Aniline, Urea, Amido-Acids, Diazo-Compounds, Dyes CYANOGEN AND ITS COMPOUNDS Fulminates PHENOLS, QUINONES Dyes CARBOHYDRATES Sugars, Cellulose, Gums ‘GLUCOSIDES PROTEINS Amino-acids HETEROCYCLIC COMPOUNDS Pyrrol, Indigo, Pyridine, Alkaloids INDEX xi PAGES 692-721 721-743 743-760 760-778 778-784 784-794 794-822 823-878 Aluminium Antimony. Argon ‘Arsenic . Barium Bismuth . Boron Bromine . Cadmium Cesium Calcium Carbon Cerium Chlorine Chromium Cobalt Columbium! Copper Dysprosiunt Erbium Europium. Fluorine . Gadolinium Gallium Germanium Glucinum? Gold Helium Holmium Hydrogen. Indium lodine Iridium Tron Krypton . Lanthanum Lead Lithium Lutecium Magnesium Manganese Mercury ATOMIC WEIGHTS Al . Sb . A As Ba Bi B Br Cd Cs Ca Cc Ce Cl Cr Co Cb Cu Dy Er Eu F Gd Ga Ge Gl Au He Ho H In I Ir Fe Kr La Pb Li Lu Mg Mn Hg 0=16 27-1 120-2 39-88 74-96 137-37 208-0 11-0 79-92 112-40 132-81 40-07 12-00 140-25 35-46 52-0 58-97 93-5 63-57 162-5 167-7 152-0 19-0 157°3 69-9 72-5 9-1 197-2 3-99 163-5 1-008 114:8 126-92 193-1 55-84 82-92 139-0 207-10 6-94 174.0 24-32 54-93 200-6 Molybdenum Neodymium - Neon . P F . Nickel. F 3 “ Niton (radium emanation) . Nitrogen . Osmium Oxygen Palladium Phosphorus Platinum . Potassium Praseodymium . Radium Rhodium . Rubidium. Ruthenium Samarium Scandium. Selenium . Silicon Silver Sodium Strontium Sulphur Tantalum. Tellurium Terbium . Thallium Thorium . , Thulium . me Tin. Titanium . Tungsten . Uranium . Vanadium Xenon i a F Ytterbium (Neoytterbium). Yttrium . ' Zinc. Zirconium 1 Also known as Niobium, Nb. 2 Also known as Beryllium, Be. xii Mo Nd Ne Ni Nt N Os Pd Pt K Pr Ra Rb Ru Sa Sc Se Si Ag Na Sr Ta Te Tl Th Tm Sn Ti U Xe Yb Yt Zn Zr 0=16 96-0 144:3 20-2 58-68 222-4 14-01 190-9 16-00 106-7 31-04 195-2 39-10 140-6 226-4 102-9 85-45 101-7 150-4 44-1 79-2 28-3 107-88 23-00 $7-63 32-07 181-5 1275 159-2 204-0 232-4 168-5 119-0 48-1 184-0 238-5 51-0 130-2 172-0 89-0 65-37 90-6 INTRODUCTION Maw has always been familiar with certain changes which occur in the pro- perties of the materials about him, and any thoughtful consideration must have led him to classify such changes into those which are permanent, like the rusting of iron, and those which are only temporary, like the passage of water into steam and back again into water. Speaking generally, the changes which are permanent (i.e. those in which the new state persists after the cause of the change has ceased to operate) are the result of some alteration in the com- position of the material and are treated under the science of Chemistry ; while those changes which are temporary (i.e. where the substance 1 assumes its original state when the cause of the change no longer acts) occur usually without any variation in composition and are dealt with under Physics. Properties themselves are of two classes: (a) specific properties, those that persist with the body, such as weight, composition, are considered under chemistry ; (6) arbitrary or accidental properties, those which can be altered without affecting the specific properties, such as temperature, electri- cal condition, are studied under physics. Nature, however, abhors a well- defined boundary and the provinces of these two sciences frequently overlap. Chemistry has for its chief object the investigation of the nature of homo- geneous substances} as well as of the causes and nature of the permanent changes of which these substances are susceptible. The study of phenomena (Gr. =appearances) and of the forms of energy which produce them, except that form of energy known as chemical energy (v.i.), belongs to the domain of physics. Thus all our direct observations by touch, sight, hearing and pos- sibly by taste and smell also, are physical. Chemistry proper is a purely theoretical science based on our interpretation of certain physical pheno- mena. We are not conscious of any chemical change occurring except when it gives some physical demonstration, but all purely physical changes are without any chemical disturbances. It is readily conceivable that some homogeneous substances consist of only one kind of matter, while others are composed of two or more kinds. Investigation has shown this to be the case. All the devices of the scientist have failed to decompose iron into any simpler bodies; similarly zino, sulphur, phosphorus and several others. Such simple forms of matter are called Elements. Those homogeneous substances which are built up from two or more ele- ments are known as compounds or chemical compounds. In these the inherent attraction of the elements for one another is such, and the union is so peculiar and intimate, that they are said to have entered into chemical combination by reason of the chemical energy (p. 12) which they possess. Of the nature of this form of energy we have no precise knowledge. It is frequently referred to as chemical affinity, a term which is often used vaguely ; for its correct use see p. 341. A compound rarely exhibits any of those properties charac- teristic of the elements from which it is formed. Thus lime differs in every 1 Definitions.—Matter may be defined as that which has weight and occupies space. The mass of a body is the quantity of matter in the body. The unit of mass is the gram for scientific purposes, or the poundin English units. It is measured by the force with which it is attracted to the earth, 4.e. by its weight, The units are the weight of a gram and the weight of a pound. A body is any limited circumscribed portion of matter. A substance (Lat. substo = I stand under or support) is that which supports or possesses those qualities or properties which we find existing; or, it is a body if considered with reference to properties which are independent of its quantity or of its position in time and space. The term is frequently used as equivalent to homogeneous substance. A homogeneous substance is one whose specific properties are invariable. I 2 MIXTURES AND COMPOUNDS way from each of its constituents: calcium, a silver-white metal, and oxygen, one of the components of the atmosphere. When a compound is broken up by any means into two or more substances, chemical decomposition is said to occur. It will be shown later (p. 4) that absolute constancy of com- position is the criterion of a chemical compound. . If a substance is not homogeneous, ¢.g. milk, granite, it is regarded as a mixture or mechanical mixture. The composition of a mixture may vary to any degree and its properties are the mean of those of its constituents. The microscope shows that milk consists of a mixture of fat globules and a liquid medium. That granite is not a single chemical compound is ren- dered apparent by a merely superficial examination, when it is seen that there are three distinctly different substances in the granite. This at once stigma- tises the rock as a mixture, for it is never possible to see the elements in a compound. When the granite is powdered, a microscope is requisite to make its heterogeneous character visible, but by taking advantage of some essen- tial difference between the properties of the three constituent substances— as, for instance, the different rates at which they sink in water—a separation, more or less perfect, may be effected, No such differentiation of the parts of a lump of sugar can be detected. This is a pure compound, and is homogeneous, so that when it is powdered, every granule of it possesses the same properties as those of the whole mass— each dissolves in water, tastes sweet, &c. Thus, a mixture of elements or compounds is readily distinguished from a pure compound by the fact that each constituent of the mixture retains its individual properties, whereas in a pure compound the properties of its several constituents (elements) are entirely obliterated. If a portion of iron be weighed before and after it has rusted, the iron, together with its coat of rust, will be found to be heavier than the original 1ron. Since matter, in a chemical sense, is anything which possesses weight, the quantity of matter in the rust is greater than that in the iron. It must not be supposed that any matter has been created during the rusting, The iron has in fact combined with that form of matter known as oxygen, one of the gases existing in the atmosphere. s An instructive experiment can be made with copper in place of iron. Weigh accurately on an analytical balance a small porcelain crucible, place in it about half a gram of very thin copper foil, in small pieces, and weigh again; by deducting the weight of the crucible the exact weight of metal is ascertained. Now heat the crucible, open and tilted, over a small but powerful Bunsen burner for an hour (gently crushing the blackened foil into the bottom of the crucible by means of a glass rod after a few minutes, being very careful to avoid loss). The metal becomes a black powder. After cooling, weigh the crucible and its contents, and deduct the weight of the crucible ; it will be found that the black powder, copper oxide, weighs one- fourth more than the copper metal. The in- crease represents the weight of oxygen taken Fra. 1. from the atmosphere ; so that the composition of copper oxide is copper 80 per cent., oxygen 20 per cent. However often this experiment is repeated and whatever the weight of metal these proportions always recur, provided the experiment is- LAW OF THE CONSERVATION OF MASS 8 performed with due care. As absolute constancy of composition is the criterion of a chemical compound (p. 4), copper oxide must be placed in this class. Another common example of a chemical change is furnished by heating a lump of marble at a red heat. There is here no very con- spicuous alteration in the appearance of the marble, although the struc- ture of the piece is seen to have been somewhat modified. It can easily be shown, however, that there has been a permanent change wrought in the marble, for when the lump has cooled it is found to become hot again and to crumble to powder when water is poured upon it; neither of these manifestations occurs when the original marble is wetted with water. By weighing the marble before and after it has been heated, a loss of weight may be proved to have occurred during this chemical change—a quantity of matter has left the marble, but there has been no destruction of matter ; that which has left the marble has disappeared because it has been converted into the invisible or gaseous form, and has spread itself through the surrounding atmosphere. If a good specimen of marble be weighed and heated in a suitable furnace, it will be found in every experiment that the residue amounts to 56 per cent. of the weight of the marble, and that 44 per cent. has been lost. The residue is quicklime and the lost gas is carbon dioxide. ; To prove that the gaseous carbon dioxide which the marble has lost is substantial, the experiment may be performed so that the escaping gas is caught. Put a little finely pow- dered marble into a silica tube A (glass will not bear the high tem- perature necessary) (Fig. 2), con- nected with the apparatus B containing caustic potash solu- tion, which has the property of absorbing carbon dioxide gas. Weigh A and B with their con- tents separately, connect them by means of tightly fitting india- rubber tubing and weigh all together. Heat A strongly by a powerful Bunsen burner or a blowpipe for several minutes, whereby some of the marble will be decomposed; allow to cool, and weigh the whole again. The total weight will be exactly the same as before ; there has been neither gain nor loss. Now weigh A and B separ- ately ; A weighs less, but B has gained precisely the same quantity that A has lost. When copper is heated in a closed vessel containing air, the whole vessel being weighed before and after heating, no change of weight is observed, showing that, as in the case of the marble heated in the apparatus shown in Fig. 2, the total quantity of matter has not varied, although there has been a chemical change. Experiments of this kind illustrate the Law of the Conservation of Mass, first enunciated by Lavoisier (6. 1743, d. 1794) and most simply stated by saying that matter is never created or destroyed in any chemical or other process, (Compare the Law of the Conservation of Energy, p.12.) For centuries men had studied the transformations of matter without arriving at any exact knowledge, largely due to their not recognising the participation of gaseous Fie. 2. 4 LAWS OF CONSTANT PROPORTIONS substances, especially air, in many reactions ;* and so when a thajestic oak grew from a tiny acorn and could afterwards be burnt to a comparatively small quantity of ash, it appeared that matter had been created and de- stroyed respectively. We now know that broadly speaking all except the ash is derived from the atmosphere and disappears into it again when the oak is burnt. But the most serious cause of their failure was that they ascribed no significance to the weight of the material they used or to that of the pro- ducts obtained, and so they could not realise either the principle of the conservation of matter or any constancy of composition. Their work was purely qualitative, t.e. properties were examined, but without any reference to quantity. Lavoisier from 1772 investigated the increase in weight of metals during their calcination, attributing the increase to absorption of some part of the air. His experiment with mercury is a good example of his method of work (p. 49). He thus laid the foundation of quantitative chemistry—gravimetric when the proportion is by weight, volumetric when by volume. So convinced was he of the indestructibility of matter that he represented chemical reactions by equations (cf. p. 11), showing that the total weight of material taking part in, and that produced by, any reaction were equal. The experiments with copper and marble already described point to constancy of composition as characteristic of chemical compounds. Although Lavoisier performed similar experiments this idea had not gripped him. It was left for his fellow-countryman, Proust (6. 1755, d. 1826), in a long dis- cussion (1799 to 1807) with the renowned Berthollet (b. 1748, d. 1822), to prove by an extensive series of demonstrations this all-important Law of Constant Proportions ; Lvery compound contains its constituent elements always in the same proportion, from whatever source the compound may be obtained. The independent researches (about 1792) of J. B. Richter (b. 1762, d. 1807) on the formation of salts lead to the same conclusion. Proust also pointed out that when two elements combine in more than one proportion, the increase is always by leaps and not gradual. Thus he found that tin unites with oxygen to form (a) the protoxide of tin containing 88-1 per cent. tin and 11-9 per cent. oxygen, and (6) the binoxide of tin con- taining 78-8 per cent. tin and 21-2 per cent. oxygen ; but never in any inter- mediate or other proportion. Though he was so near, yet he failed to formulate the Law of Multiple Proportions: When an element unites with another in more than one proportion, the higher proportions are invariably simple multiples of the lowest. The discovery of this law is due to Dalton. Carbon and oxygen unite to form two compounds, (a) a gas, carbon monoxide, which contains 42:86 per cent. carbon and 57:14 per cent. oxygen by weight ; and (d) another gas, carbon dioxide, containing 27-27 per cent. carbon and 72°73 per cent. oxygen by weight. These two gases have very different properties, e.g. the first is inflammable and will not turn lime- water cloudy, the other is not inflammable and will cloud lime-water. It is difficult to see any relationship between the numbers so long as the com- position is expressed as parts per cent., and this explains Proust’s failure ; but a calculation shows that for each part by weight of carbon in the first gas there are 1-3 parts of oxygen, and in the second gas 2°6 parts. Thus: (a) 42°86 (b) 27:27 soe + carbon. ——_ = aE part carbon a737 1 part carbon, 5714 8 72°73 . ae I'3 4, oxygen. 737 = 26 4, oxygen. 1 Reaction and chemical reaction are used to express any chemical transformation, whether combination, decomposition, or both when occurring simultaneously. Substances are said to react whenever they bring about any chemical change in one another, LAWS OF CHEMICAL COMBINATION 5 From this it is clear that the second gas has exactly twice as much oxygen as the first in combination with the unit weight of carbon. Conversely, in carbon monoxide 1 part oxygen unites with 0°75 part carbon, while in carbon dioxide 1 part oxygen unites with 0°375 part carbon. Hence, reciprocally, the proportion of carbon in the second is one-half that in the first for the unit weight of oxygen. In either case the higher proportion is a simple multiple of the lower. A similar calculation shows that the two tin oxides of Proust are likewise related: (a) 119 parts of tin: 16.parts of oxygen; (6) 119 parts of tin: 32 parts of oxygen ; the oxygen being in the ratio 1 : 2 and the tin 2: 1. The hydrocarbons yield abundant examples of this law ; thus, quantita- tive analysis of marsh gas, olefiant gas, and acetylene shows that they have the following gravimetric compositions per cent. : Carbon Hydrogen Ratio of C: H Marsh gas. : : : . 15 25 3: Olefiant gas . ‘ ‘ . 85-7 14:3 6:1 Acetylene . ‘i ‘ : - 92:3 77 12:1 It is apparent from the ratios that the proportion of carbon that com bines with 1 part by weight of hydrogen in the second and third compounds, is a multiple of that in the first compound by a simple whole number. Another striking example is afforded by the oxides of nitrogen ; in these there are, for 100 parts of nitrogen, 57:1, 114-2, 171-3, 228-4 and 285-5 parts of oxygen respectively, figures in the ratio 1:2:3:4:5. Law of Reciprocal Proportions : The proportions by weight in which several elements combine with a given element are those in which they combine with one another ; or, they combine in some simple multiple of those proportions. Thus, sulphuretted hydrogen, sulphur dioxide, and carbon disulphide have the following gravimetric compositions : Per cent. Per cent, Sulphuretted hydrogen . Sulphur 94,1 ‘ . Hydrogen 5°9 Sulphur dioxide. ‘ Sulphur 50:0 : ‘ Oxygen 50-0 Carbon bisulphide . “ Sulphur 84:2 : ‘ Carbon 15°8 When these figures are calculated for 100 parts of sulphur in each case they become : Sulphuretted hydrogen . Sulphur 100 3 , Hydrogen 6:2 Sulphur dioxide. : Sulphur 100 4 : Oxygen 100 Carbon bisulphide . .. Sulphur 100 : : Carbon 18:7 The ratios of the proportions of C, H and O which combine with 100 parts of sulphur in the above Table are : C:H = 187: 62 or 3: I C:O = 187:100 or 8:16 H:0O0 = 62: 100 or 1:16 Now 3 compounds of carbon with hydrogen, 2 of carbon with oxygen, and 2 of hydrogen with oxygen are known, and the ratios of the elements in these compounds are : C:H = 3:1 6: 1 12:1 C:0 = 38:8 3: 16 H:O = 1:8 1: 16 Thus the ratio in which any pair of these elements combine with each other is either the same as that in which they combine with a constant mass of sulphur or is some multiple orjsubmultiple;thereof by a simple whole number. re The foregoing are known as the three Laws of Chemical Combination. 6 ATOMS AND MOLECULES Limited Divisibility of Matter.—That matter is not capable of infinite subdivision has always been regarded as a reasonable assumption, and it was a tenet of the Greek philosophers that matter consists of extremely fine patticles which could be separated from each other by an ideal process of subdivision, but when separated could not be further subdivided. These imaginary ultimate particles were termed atoms (Greek for indivisibles). This theory of the structure of matter possessed little significance until the laws of chemical combination were established, when it became apparent that in the theory there was at hand a very simple explanation of the laws. Considering water as an example, it can be scattered in exceedingly fine spray, the particles of which are, however, still visible. It can also be converted into invisible steam, which, being still matter, must consist of ultimate particles in accordance with the theory. Evidently the conversion of water into steam by heat may be regarded as a mode of subdividing the water, and the question presents itself whether the theoretical final sub- division has been attained—whether the invisible particles of steam are indeed the indivisibles of this particular form of matter. This was originally assumed to be the case, and a later study of the physical properties of gases and vapours has confirmed the assumption that any matter in a gaseous condition consists of particles which are indivisible unless they are chemically changed. The proviso in italics is necessary because steam, for instance, can be chemically decomposed by heat into hydrogen and oxygen, and what is true of a mass of steam must be true also of its ultimate particle ; in other words, the ultimate particle of steam can be split up but only if it ceases to be steam. To call such decomposable particles by the Greek name atom, meaning absolutely indivisible, appeared inappropriate, and the name “mole- cule” was invented for them. A Molecule is the smallest particle of a substance which exists, while still possessing the distinctive properties of that substance. ; . There are many gases, like hydrogen and oxygen, which have never been decomposed and their molecules might be regarded as true atoms but for the evidence which chemistry affords that these molecules must undergo scission when the gas enters into chemical reaction. This evidence, which will be appreciated later, leads to the conclusion that the molecules of most elements consist of two or more parts. No evidence of any smaller parts has ever been obtained, so that the parts of elementary molecules are regarded as the true indivisibles or atoms, and the molecules of compounds are considered as consisting of combinations of the atoms of elements. An Atom is the smallest particle of an element existing in combination, that is, as a constituent part of a molecule. The atom has no separate existence, except in a very few cases. Upon the three laws of chemical combination and the conception of the limited divisibility of matter the all-important Atomic Theory, first enun- ciated by John Dalton (6. 1766, d. 1844) during the first decade of the last century, has been built up. The new meaning which Dalton gave the old idea of an atomic constitution of matter was that each of the atoms has a weight which ts constant for those of any particular element. This constant relative weight is known asthe Atomic Weight: the consideration of how it is ascertained must be postponed for the present. The weight of an atom of hydrogen is taken as a standard and is said to be 1; that of oxygen is 16 because its atom weighs 16 times as heavy as that of hydrogen : similarly the atomic weight of carbon is found to be 12 and that of calcium 40. A natural sequence of this is to conclude that the molecules of chemical com- pounds are formed by the union of the atoms of different elements in simple ATOMIC AND MOLECULAR WEIGHTS 7 numerical proportions. Thus a molecule of water consists of 2 atoms of hydrogen and 1 of oxygen in chemical combination; that of calcium carbonate (e.g. marble) is made up of 1 atom of calcium, 1 atom of carbon, and 3 atoms of oxygen chemically combined. Thus the weight of a molecule of water is 16 for the oxygen plus 1 x 2=2 for the hydrogen, and the Molecular Weight (p. 11) of water is said to be 18, 7.c. 18 times as heavy as an atom of hydrogen. The molecular weight of calcium carbonate is 40 for the calcium plus 12 for the carbon plus 3 X 16=48 for the oxygen, i.e. 100 ; the molecular weight of a substance is equal to the sum of the weights of its constituent atoms. The Elements.—The number of different kinds of atoms, or the number of elements, is not great, only some 82 being known with certainty, but the number of compounds is practically infinite. Inthe Table (p.8) the elements are arranged in the order of their atomic weights and classified according to the Periodic Law, which will be explained later (p. 301). Those printed in heavy type are Non-Metallic elements, all the rest are Metals, the more important being distinguished by capital letters. It is difficult to formulate a satisfactory and concise definition of a metal. The chemical definition that a metal is a substance which forms at least one basic oxide which can neutralise acids to produce salts, is not sufficiently fundamental. It is better to rely on the general conception of a metal. The word is derived from the Latin metallum, a metal, mine or quarry ; probably also from the Greek meradAaw to search after. The typical metals are characterised by hardness, reflection of light, emitting a peculiar lustre generally known as “ metallic lustre,’”’ opacity, high specific gravity, malleability, rigidity, fusibility, volatility at very high temperatures, un- changed on exposure to air except superficially, insolubility in water, solu- bility in acids, solubility in other metals, when molten, forming “alloys ”’ which also have “ metallic’ properties. Several of the metals, e.g. sodium, mercury, are exceptional in certain properties, but in general there is no difficulty in deciding a substance to be a metal or not. However, there are two or three elements, e.g. arsenic, which form a transition between the metals and non-metals. As each element is studied, its position in the Table should be carefully considered with a view to discovering some relation between its properties and those of its neighbours, e.g. it will be found that all the non-metals (except hydrogen, which frequently behaves as a metal) lie on one side of a line drawn from Boron to Niton. The Symbol following the name is used as an abbreviation, but especially to signify 1 atom of the element having the atomic weight indicated by the numeral. Thus H stands for 1 atom of hydrogen having a weight of 1 unit ; O represents 1 atom of oxygen weighing 16 times as much as an atom of hydrogen. It is of interest to note that the most abundant elements are those of low atomic weight, and to observe how they are grouped together in the periodic table. The atmosphere consists of a mixture of 4 volumes nitrogen with 1 volume of oxygen; and water contains 8 parts by weight of oxygen to 1 part by weight of hydrogen. By far the greater proportion of the various materials supplied to us by animals and vegetables consists of the four elements—oxygen, hydrogen, nitrogen, and carbon ; and if we add to these the two most abundant ele- ments in the mineral world, silicon and aluminium, we have the six elements composing the bulk of all matter. It is computed that of the mineral matter of the earth’s crust oxygen constitutes 50 per cent., silicon 25-3, aluminium 7-3, iron 5, calcium 3-5, 2 MENDELEEFF’S PERIODIC TABLE 883 a BES UL kad en IN 333 or “ wnuery = urno"uT, _ vanIpey. _ (NOLIN) IN BBB 1a 80 qa 203 IL 503 3H 10% ny 261 6 NOLIN = = HIANSIa aval uINTTeqL AUNOWAN (a109) 2461 = ny a1o9 S6l = 4d ‘NONILVId $8T NN TST eL OFT ap 681 eT Lg eg eet 89 9x Ost g « s6l = II ‘WMIPNT a NELSYNAL wanyeyuey, uani199 wunueqyuey WOldva uanjse) (NONTX) I6T = 80 ‘uInyuIsQ ex Okt I 231 oL 821 as OZ ug 6IL uy SIL pO SIL 3y 80T ye NONGX ONIGOI WOIMATTAL | ANOWILINVY NIL umntpuy uunIuped (MHATIS) sol = Sy ‘YRATIS | : 901 = Pd ‘umnIpeled 96 on 86 qn 16 1Z 68 K 88 Ig sg qe 1m $8 9 sol = YX ‘wunTpoyy _ umuepqAjon, UIMIqoIN UINTUOOIZ UIntI44.A untquOIS UINIprqny (NOLdAUH) 20L = ny ‘wnTueyny Pos eg | ig 08 ag 6L sy 92 a9 BL ep 02 uz ¢9 ng +9 q & NOLdAUM | ANINOUA | WOINATAS OINGSUV urnyueUtiey), umnITey ONIZ (aadd09) 99 = 10 ‘“Weddoo 6¢ = IN “IGMOIN s¢ nid ao iQ T¢ A 8F I oP ag OF 29 68 Di Vv OF e Sf 6g = 99 ‘ETVEOO HSANVONVN | WOIKOWHO UInIpeUeA cantaezLy umnIpueog WAIDTVO WAISSVLOd (NODUY) 99 = of ‘NOUL v or | 10 ¢.c¢ s as a Ts IS 83 Iv 13 3 3 83 eN oN 03 ge NODUV ANIYOTHO anHdTAs (SnuoHdsOHd NOOITIS WAINIWOATY | NWOISANOVIN waridos (NON) oN 08 a 61 oO 9T N #1 9 aL a IL og 6 4 'T 2H + Z NOUN ONIWONTA NGYAXO NADOULIN NOduvo Nowor wn Arog moO T (NOITHH) eH % T H I soreg WOITHH . NGVOUCAH a ze igi (o%x 30) oe (oF 20) toy @o* 30) on z te ‘OU ‘ou ow qsousiEZ spunoduoo = Aw "AW "AW ‘AU "HU "HU HU _ uasoipAy qsoustH 8 4 9 Sg ¥ & z T 0 dnoip GAS LAWS 9 magnesium 2-5, sodium 2:3, potassium 2-2, and hydrogen 1. No other element is present to a greater extent than 0-3 per cent. Thus oxygen is at once the most abundant and the most widely dis- tributed. Science is again indebted to Dalton for much pioneer work in relation to gases, which, however, was confirmed and elaborated by the French savant Gay Lussac (6. 1778, d. 1850), and still further explained by the law of Avogadro (p. 10). Gay Lussac’s Law of Gaseous Volumes: When gases chemically combine or decompose, the volumes of the gases taking part in the reaction and of those produced, all stand to one another in simple numerical relation. This was merely a particular case of the Laws of Chemical Com- bination (p. 5). Many years before, the English chemist Henry Cavendish (b. 1731, d. 1810) had found that hydrogen and oxygen combine in the simple ratio of 2 volumes of the former to 1 volume of the latter and in no other. The volume of gas (steam) thus produced is always 2 volumes, thus bearing a simple ratio to each of the volumes of the gases taking part in the reaction. Again, 1 volume of hydrogen unites with 1 of chlorine to produce 2 volumes of hydrochloric acid ; if more than 1 volume of either gas is used the excess remains unaffected, mixed with the hydrochloric acid produced. There are two physical laws referring to gases which are of frequent application by the chemist. The first was enunciated in 1660 by Robert Boyle (b. 1626, d. 1691), who made the important assertion that from ex- perimental methods alone can we look for progress in all useful knowledge. It is known as Boyle’s Law: The volume of a given quantity of gas varies inversely as the pressure upon it, provided the temperature remains constant. Thus if the pressure on a gas be doubled (or trebled) the volume will be reduced to one-half (or one-third) and vice versa. The law is often expressed by saying that the product of the pressure (p) into the volume (v) ts a constant (k); pv=k (see p. 309). The second is Dalton’s Law (also known as Charles’ Law): The volume occupied by a given quantity of gas varies directly as its absolute tem- perature, provided the pressure remains constant. If 1000 c.c of air at 0° C. be heated until its temperature is 1° C., a constant pressure being main- tained, the volume will be increased to 1003-665 c.c., or the volume will be increased by = of tts volume at O° C. This increase for each degree is known as the coefficient of expansion (a) of the gas. Therefore if V be the volume of the gas at 0° and V’ its volume at any other temperature, t°, then V’= V(1 + at). If it be cooled to —1° C. it will measure 57, less, and therefore if it be cooled to —273° C. it should have no volumé at all. This last condition cannot be realised, but except at very low temperatures the law holds good. ° The temperature, —273° C., is known as the absolute zero because it is computed that a body at this temperature contains no heat at all and that any lower temperature is impossible. Several considerations lead to this conclusion. Temperatures measured from the absolute zero are called absolute temperatures and can be found by adding 273 to the reading of the Centigrade thermometer ; thus 17°C. = 17 + 273 = 290° A. A third law deducible from the last two is: The pressure of a given quan- tity of a gas varies directly as the absolute temperature, provided the volume remains constant (p. 309). The increase in pressure for each degree rise in temperature is the pressure coefficient, which, numerically, is almost precisely equal to the coefficient of expansion. As a basis for scientific purposes a gas is always measured at standard or normal temperature and pressure; conveniently abbreviated to N.T.P. 10 AVOGADRO’S HYPOTHESIS The figures are 0° C. and 760 m.m. If measured otherwise corrections must be made, see p. 74. For experimental proofs of these laws the reader is referred to any good text-book on physics. Dalton did not make any suggestion of a second kind of ultimate particle, now called a molecule (p. 6). Thus he spoke of an “atom” of water and other compounds, notwithstanding that by his hypothesis an atom is in- divisible, while by definition a compound is divisible. His studies of gases were limited to their combination by weight. Gay Lussac (1809) studied their combination by volume and experienced a difficulty in applying Dalton’s atomic theory. The difficulty was removed by Avogadro (Italian, b. 1776, d. 1856), who conceived the existence of two kinds of ultimate par- ticle ; (a) molecules which are the ultimate particles of the gas, (b) atoms of which the molecule is composed (p. 6). In 181] he suggested the hypothesis that equal volumes of different gases contain equal numbers of molecules, provided the temperature and pressure respectively of the gas are the same in each case. This follows from the synthesis (Gr.=putting together) of hydrogen chloride (hydrochloric acid gas) from hydrogen and chlorine and similar instances. When 1 volume of hydrogen containing x molecules unites with an equal volume of chlorine containing x molecules, 2 volumes of hydrogen chloride containing 2” molecules is formed. Now each molecule of hydrogen chloride cannot contain less than 1 atom of hydrogen combined with not less than 1 atom of chlorine; therefore since an atom cannot be divided there must have been at least 2% hydrogen. atoms and at least 2a chlorine atoms to produce the 2% hydrogen chloride molecules. It follows that the volume of hydrogen (or chlorine) containing x molecules must also have contained at least 2% atoms, in other words each molecule must contain at least 2 atoms. There being no particular reason to suppose that the hydrogen molecule contains more than 2 atoms, it is accepted there are only 2 atoms in the molecule. Again, 2 volumes of hydrogen and 1 volume of oxygen unite to form 2 volumes of steam (p. 9). Let it be assumed that each volume (measured in every case at the same temperature and pressure) contains 1000 molecules of gas, then 2 volumes of hydrogen will contain 2000 molecules and 1 volume of oxygen will contain 1000 molecules, and therefore. because the steam produced measures 2 volumes, 2000 molecules have been formed. Now if this is not true, assume that 1 volume of hydrogen contains some other number of molecules, say 1060 ; then 2120 molecules of hydrogen react with 1000 molecules of oxygen to produce some unknown number of molecules of steam ; that is 2-12 molecules of hydrogen react with 1 molecule of oxygen, which is at variance with the definition of a molecule (p. 6); and if 212 molecules be supposed to react with 100 molecules of oxygen the law of simple multiple proportions is violated (p. 4). It is seen that 1 molecule of oxygen is sufficient to produce 2 molecules of steam; therefore the molecule of oxygen must be composed of at least 2 atoms, for the molecule of steam cannot contain less than 1 atom of oxygen. The extraordinary similarity in the physical properties of different gases is another strong argument in favour of Avogadro’s hypothesis. The im- portance of this idea was not recognised until Cannizzaro (Italian, b. 1826, d. 1910) in 1858 revised and developed it during his researches on vapour densities (p. 11). If a suitable flask (Fig. 3) of say 500 or 1000 c.c. capacity be evacuated at the air-pump and accurately weighed and then filled with hydrogen and again weighed, the weight of a certain volume of the gas containing n mole- VAPOUR DENSITY 11 cules of hydrogen can be found. If the experiment be repeated with oxygen (care being taken that the temperature and pressure are the same as before) the weight of the same volume of gas containing the same number (n) of molecules will be ascertained and will be found to be nearly 16 (15-9) times that of the hydrogen ; therefore, since the number of molecules is the same in each case, the weight of a molecule, the Molecular Weight (p.'7), of oxygen is 16 times that of a molecule of hydrogen, and the Density! (i.e. mass per unit volume) of hydrogen being taken as the unit for gases, the density of oxygen is 16 and its molecular weight is 32. Hence, if we know the density of a gas compared with that of hydrogen we know its molecular weight and vice versa. If a substance which is liquid at ordinary temperatures, e.g. water, alcohol, chloroform, be heated so as to assume the gaseous state and its density be compared with that of hydrogen at the same temperature and pressure, the value obtained is described as the Vapour Density (p. 312) of the substance and is half the value of its molecular weight. This is the most reliable method of determining a molecular weight and is described fully at p. 312. The student should carefully observe that while the density of hydrogen is 1, the molecular weight is 2. Similarly in all other cases, the density of the gas or vapour is equal to one half the molecular weight of the substance. Much confusion will be avoided by always representing the molecular weight of the substance in the form of gas as occupying 2 volumes. Reference has been made to the meaning of the symbols (p. 7) represen- ting the various elements, and it was pointed out (p. 4) that Lavoisier in- stituted the practice of equation writing, although not with symbols in the manner to be described. In the chemical equation H, + Cl, = 2HC1 it is signified (a) on the left-hand side that a molecule of hydrogen and one of chlorine are brought together, and the + sign shows that they are not chemi- cally combined but only mechanically mixed ; this is before chemical re- action sets in; (b) on the right-hand side the product of the reaction is represented, and the writing of the H and Cl close together signifies that the elements are in chemical union with one another. H, or HH is the formula or chemical formula for the molecule of hydrogen ; similarly HCl is the formula for that of hydrogen chloride (hydrochloric acid) ; the large 2 in front signifies that 2 molecules are formed. If it were written H,Cl, it would be understood that only 1 molecule containing 4 atoms had been produced. ‘To decide which is right the density of the gas must be determined. HCl requires it to be 18-25; 1 + 35-5 = 36-5 and 36-5 + 2 = 18-25. H,Cl, requires 36-5; 2x 1+2 x 35-5 = 73 and 73—2 = 36°5. The former is found by experiment, and hence the equation as written is correct. Bak 2H O = 2H,0 Similarly, 2(1 x 2) ss (16x2) = 2(1x2416) is the equation for the formation of 2 molecules of water from 2 molecules of hydrogen and 1 of oxygen. The figures beneath the symbols are the parts by weight taking part in the reaction. The order in which the terms are written is significant: 2H,O = 2H, + O, represents the decomposition of water into its elements. ; ; i The sign —+ is frequently used to signify “ produces ”’ or “ gives rise to, sometimes with the name of the agent or substance bringing about the change written over the arrow, thus het; e.g. CaCO, beat CaO. Fie. 3. 1 Strictly the unit is one-sixteenth the mass of unit volume of oxygen at 0° and 760 mm., which is slightly gveater than the above (p. 297). . 12 ENERGY—VALENCY Following the practice of representing the volume of the molecular weight of a gas as occupying 2 volumes and representing each volume by a square, we have: 2H, + O, = 2H,0 These equations are in harmony with the atomic theory in regarding chemical reaction as consisting in the eachange of atoms in one molecule for those in another. It must be remembered that a chemical equation is only a short mode of expressing the result of an experiment, and cannot be used, like a mathemati- cal equation, to effect the solution of a problem. A chemical equation may be written to express what is likely to be the result of the action of different molecules upon each other, but it has no value until verified by experiment. Energy may be defined as ability to effect a change. It is exhibited in various forms ; potential energy (p. 341), kinetic energy, heat energy, light energy, electric energy, chemical energy (p. 1), &c. A quantity of energy is always the product of two factors ; (a) a capacity factor, such as length, volume, mass, calorie; (6) an intensity factor, such as weight, force, pressure, temperature, electromotive force. One kind may be transformed into another, for instance electrical energy into heat energy, but a given quantity of one form is always strictly equivalent to a certain quantity of another form. The Law of the Conservation of Energy (p. 341) states that energy is never created or destroyed, no matter how it may be transformed, (Compare the Law of the Conservation of Mass, p. 3.) This law is of great importance with respect to quantity of chemical energy, since no unit of chemical energy has yet been defined ; the only available means is to measure the heat, electricity or the like into or from which it is transformed. Thermochemistry is that branch of the science of chemistry dealing with the study of the thermal changes accompanying chemical reactions. Chemical changes are always attended by evolution or absorption of heat. As a general rule, the formation of compound molecules from elementary molecules evolves heat, whilst the formation of elementary molecules from compound molecules absorbs heat. Hence it will be found that the applica- tion of heat is generally required for the commencement of chemical change, in order to effect that loosening of atoms in their molecules which must precede every chemical transformation of matter. When any chemical change appears to occur without any change of temperature being observed, it is because the total heat absorbed in the destruction of the original mole- cules is equal to the total heat evolved in the construction of the new molecules. The quantity of heat evolved or absorbed in any particular reaction is always the same. Electrochemistry deals with the chemical reactions where electrical energy is concerned, and Photochemistry where light energy plays a part, as in photography. Valency (Lat. valeo =to be worth or strong) is a form of chemical energy and is expressed by the number of hydrogen atoms with which one atom of a given element (or a group of elements) can combine (or for which it can be exchanged). The hydrogen atom never combines with more than one atom of any other element. When the atom of an element combines with, or can be substituted for, 1 atom of hydrogen, the element is said to be univalent (or monad), e.g. chlorine in HCl; when with 2 atoms of hydrogen, bivalen t CHEMICAL EQUIVALENTS 13 (or diad), e.g. oxygen in H,O; when with 3, trivalent (or triad), e.g. nitro- gen in NH;; when with 4, quadrivalent (or tetrad), eg. carbon in CH,. Compounds of elements with hydrogen do not show higher valencies ; but those with oxygen, which being bivalent is equivalent to 2 atoms of hydro- gen, indicate that valency varies in value from 1 to 8, thus: univalent potassium forms K,O ; bivalent calcium, CaO ; trivalent aluminium, Al,O, ; quadrivalent carbon, CO,; quinquivalent (or pentad) nitrogen, N,.O;; sexavalent (or hexad) sulphur, SO,; septivalent (or hepiad) manganese, Mn,0,; octavalent (or octad) osmium, OsO,. Argon will not combine with any element and is non-valent. The valency is sometimes written as in Ki, Oli, Alii, &e. The variation in the valency of some elements, e.g. nitrogen (trivalent in NH, and quinquivalent in N,O;), may present difficulty to the beginner, but frequent reference to the periodic table on p. 8 as each element is studied will gradually remove this. R in the formulz in that Table stands for any one of the elements in a given group (or column). Group 8 is exceptional (p. 302). The subject is further studied on pages 300-307. The Chemical Equivalent (E) of an element is closely associated with its valency (V); indeed, the one is sometimes defined as the ratio of the other to the atomic weight (A) ; thus E == But a definition resting on this interdependence is not universally satisfactory. It is better, therefore, to define the chemical equivalent of an element (or of a group of elements) as the number of parts by weight which will combine with (or, are exchangeable for) 1 part by weight of hydrogen (p. 19), or, more strictly, with 8 parts by weight of oxygen. The time-honoured division of the science into Inorganic and Organic chemistry arose from the supposition that those substances which are pro- duced by processes of life could not be made artificially and they were classed accordingly as organic. That view has ceased to exist for three-quarters of a century, but owing to the fact that animal and vegetable substances show certain relationships not detected among mineral substances the classification is maintained. The whole of chemistry is intimately associated with physics, and those subjects which may be treated under either science are discussed in the chapter on General Principles and Physical Chemistry. WATER THE most convincing demonstration of the composition of water is afforded by resolving it into its elements by means of the electric current. This ex- periment, which is an example of analysis! as opposed to synthesis (p.10), was first performed in 1800 by Nicholson and Carlisle. The process of analysis or decomposition of chemical compounds by electricity has now be- come known as electrolysis and is of very wide application. Analysis of Water by Electrolysis,—The usual arrangement for electrolysing water is represented in Fig. 4. It consists of two tubes A and o pro- vided with stop-cocks above and in communication below with each other, and a third a which serves merely as a reservoir. In the lower part of each tube h,o is fused a platinum wire carrying a small plate of platinum called an electrode, b, c. It is not necessary for the tubes to be joined; the arrangement shown in Fig. 5 is equally effec- tive; where, moreover, the electrodes B, C are rolled into cylinders, the wires are held in position by corks and the reservoir is the large vessel A.. The enclosure of liquid with the two electrodes, whether whole as in Fig. 5 or forked as in Fig. 4, constitutes an electrolytic cell, and the liquid itself is called an electrolyte. The stop-cocks being open, Via. 4. water acidified with a little sulphuric acid is poured into the reservoir until the tubes are filled and the reservoir nearly so; the stop-cocks are then closed. If the ends of the wires outside the apparatus are now connected with the terminals of a suitable battery, a current of elec- tricity passes through the acidified water and minute bubbles of gas rapidly appear on each of the elec- trodes and, increasing in size, detach themselves and rise to the surface. If the passage of the “ current ”’ be interrupted when the tube H has become full of gas, the tube O will be only half full,? since water is a com- pound of hydrogen and oxygen in the proportion of 2 volumes of hydrogen to 1 volume of oxygen. For determining accurately the com- ° * dvddvors = (1) releasing, (2) the resolution of a whole into its parts. * nAexzpoy, amber (root of electricity) ; avous, setting free. 2 The volume of the oxygen is always found to be slightly less than one-half the volume of the hydrogen in this experiment, both because the solubility of oxygen in water is rather greater than that of hydrogen and because a small proportion of the oxygen is evolved in the condition of ozone, which occupies only two« thirds of the volume occupied by an equal weight of oxygen (see Ozone). 1 BATTERIES 15 ‘position of water, the gases should be allowed to escape for some time before the stop-cocks are closed. Corrections to the observed volume must be made for (i) temperature (p. 9), (ii) barometric pressure (p. 9), (iii) difference of height of liquid between that in each of the tubes and that in the reservoir, and (iv) the tension of aqueous vapour over the acidified water (p. 33). The two gases may be distinguished by opening the stop-cocks in suc- cession and presenting a burning match. The hydrogen will be known by its kindling with a slight detonation and burning with a very pale flame at the jet; whilst the oxygen will very much increase the brilliancy of the burning match, and if a spark left at the extremity of the match be presented to the oxygen, the spark will be kindled into a flame. A volume of oxygen weighs 16 times as much as an equal volume of hydrogen, so that if 1 volume of hydrogen be said to weigh 1 part by weight, 1 volume of oxygen will weigh 16 parts by weight. But in water the proportion of hydrogen to oxygen is 2 volumes: 1 volume. Therefore the proportion by weight of these two elements in the water must be 2 : 16, or water is a compound of hydrogen and oxygen in the proportion of 2 parts by weight of hydrogen to 16 parts by weight of oxygen. Since the atom of oxygen is believed to weigh 16 times as much as the atom of hydrogen, the simplest view of the com- position of the molecule of water is that it contains 2 atoms of hydrogen and 1 atom of oxygen ; its formula may there- fore be represented as H,0O. The Battery. It is of interest to note that the electricity in . a battery such as that shown is generated by means of chemical action ; chemical energy is transformed into electrical energy (p. 326). If plates of zine and copper fitted with wires (Fig. 6) : be placed in a vessel containing dilute sulphuric acid, or any Fia. 6. other liquid which acts unequally on the two metals, an electric current will pass from the copper to the zinc when the “circuit ’’ is ‘‘ closed,” 7.¢. when the wires are joined. Such an arrangement is known as a Voltaic cell (Volta, Italian, b. 1745, d. 1826). A number of cells joined together constitutes a battery. The zinc before use should be amalgamated by cleaning it with dilute sulphuric acid and then rubbing a little mercury over the surface, in order to protect it from corrosion by the acid when the circuit is “open,” ¢.e. when the wires are apart. On bringing the wires together hydrogen gas is liberated at the copper plate, but the action soon becomes much less vigorous due to polarisation, i.e. to the bubbles of hydrogen almost completely covering the copper so that it becomes practically a plate of hydrogen. In the Grove’s cell (G, Fig. 5) this difficulty is removed by substituting platinum for copper and using strong nitric acid which oxidises (p. 58) the hydrogen. The Grove’s battery shown consists of five cells or earthenware vessels (A, Fig. 7) filled with diluted sulphuric acid (one measure of oil of vitriol to four of water), In each of these cells is placed a bent plate of zinc (B), which has been amalgamated. Within the curved portion of this plate rests a small flat vessel of unglazed earthenware (C), filled with strong nitric acid, in which is immersed a sheet of platinum-foil (D). The platinum (D) of each cell is clamped, at its upper edge, to the zine (B) in the adjoin- ing cell (Fig. 8), so that at one end (P, Fig. 5) of the battery there is a free platinum Fic. 7. 16 VOLTAMETERS plate, and at the other (Z) a free zinc plate. These plates are connected with wires D and E, by means of the copper plates, L and K, attached to the ends of the wooden trough in which the cells are arranged. The wire, D (Fig. 4), which is connected with the last zinc plate of the battery, is often called the “ negative pole ” (—), whilst E, in connection with the last platinum plate, is called the “‘ positive pole” (+). When the connection is established by means of the wires, D and E, with the electro- lytic cell, A, the galvanic current is commonly said to pass along the wire, E, to the platinum plate, C, through the acidified water, to the platinum plate, B, and thence along the wire, D, back to the battery. Since the electricity travels into and out of the electrolytic cell by the plates, B and C, these are called the electrodes (jXexrpov, amber—root of electricity ; édos, a way). The plate, C, or way into the cell, is called the anode (ava, towards ; dd0s) or positive electrode or pole (+); the plate, B, or way out of the cell, is the cathode (xara, away from ; dédos) or negative electrode or pole (-—). During this “‘ passage of the current’ (which is only a figurative mode of expressing the transter of the electric influence), the water intervening between the plates, B and C, is decomposed, but no transmission of gas is observed between them. The products appear at the two electrodes only, which is characteristic of electro-chemical reaction, and not throughout the mass of reacting material as is usual in ordinary chemical processes. All the oxygen is attracted to the anode (+) and therefore it is said to be an electro-negative element, while all the hydrogen travels towards the cathode (—) and is described as an electro-positive element. Metals are electro-positive, non-metals electro-negative. Hydrogen, though non- metallic in most of its properties, behaves as a metal in electro-chemical and some other reactions ; its position in the periodic table (p. 8) is peculiar, as already pointed out (p. 7), and should be noted. An explanation of the part played by the sulphuric acid is omitted for the sake of simplicity. Pure water could not be decomposed except by a very much stronger battery. Ihe whole subject will recur for fuller discussion in the chapter on General Principles (p. 328). The apparatus depicted in Fig. 4 (see also p. 112) is, when the tubes are graduated, known as Hofmann’s Voltameter, an instrument for measuring quantity of elec- tricity (see p. 329), for the volume of hydrogen is strictly proportional to the quantity of electricity passed through the acidified water. Ii in place of the two tubes in Fig. 5 one tube large enough to cover both the electrodes be sub- stituted, a mixture of the two gases will be collected ; the mixture is sometimes spoken of as electrolytic gas in view of the method of its production or as deto- + nating gas because of the violence with which it explodes when a flame is applied. Another convenient form of apparatus for generating this gas is Oettel’s Voltameter (Fig. 9). It consists of a glass jar about 6 in. high and 2 in. diameter, fitted with an india- rubber stopper, through which pass a delivery tube and two wires carrying two cylindrical nickel elec- trodes immersed in a 15 per cent, solution of sodium — hydroxide, NaOH, free from chlorine. After the “————- ‘ apparatus has run for a time to free it from air and Fra. 9. to saturate the solution with the gases, it may be restarted ; the volume of mixed gases collected in the graduated receiving tube is proportional to the quantity of electricity passed through the voltameter. Analysis of Water by Means of Electric Sparks.—Another method of decomposing water by electricity consists in passing a succession of =) oul 1! ry Ul 16 I, on al oll wll 4 ANALYSIS OF WATER BY ELECTRIC SPARKS 17 ' electric sparks through steam. It is probable that in this case the decom- position is produced rather by the intense heat of the spark than by its electric influence. For this purpose, however, the galvanic battery does not suffice, since no spark can be passed through any appreciable interval between the wires of the battery—a fact which electricians refer to in the statement that, although the quantity of electricity developed by the galvanic battery is large, its electromotive force or tension or pressure is too low to allow it to dis- charge itself in sparks like the electricity from the machine or from the induction coil, which possesses a very high tension, though its quantity is small. The most convenient instrument for producing a succession of electric sparks is the induction-coil invented by Ruhmkorff, in which a current of low tension, sent from a weak battery through a coil of stout insulated wire and back to the battery, induces or excites a current of high tension in a coil of thin insulated wire of great length, wound outside the thick coil. This current is capable of discharging itself in sparks, such as are obtained from the electrical machine. Fig. 10 represents the arrangements for exhibiting this experiment. Aisa 250 c.c. flask furnished with a cork in which three holes are bored ; in one of these is inserted Fie. 10. the bent glass tube, B, which dips beneath the surface of the water in the trough, C. D and E are glass tubes, in each of which a platinum wire has been sealed so as to project about an inch at both ends of the tube. These tubes are thrust through the holes in the cork, and the wires projecting inside the flask are brought within about i, of an inch of each other, so that the spark may easily pass between them. The flask is somewhat more than half filled with water, the cork inserted, and the tube, B, allowed to dip beneath the water in the trough, the wires in D and E being connected with the thin copper wires passing from the induction-coil, F, which is connected by stout copper wires with the small battery, G. The water in the flask is boiled for about fifteen minutes, until all the air contained in the flask has been displaced by steam. When this is the case, it will be found that if a glass test-tube, H, filled with water be inverted over the orifice of the tube, B, the bubbles of steam entirely condense, with the usual sharp rattling sound, and only insignificant bubbles of air rise to the top of the test-tube. If now, whilst the boiling is still continued, the handle of the coil, F, is turned so as to cause a succession of sparks to pass through the steam in the flask, large bubbles of incondensable gas accu- mulate in the tube, H. This gas consists of the hydrogen and oxygen gases in a mixed state, having been released from their combined condition in the steam by the action of the electric sparks. The gas may be tested by closing the mouth of the tube, H, with the thumb, raising it to an upright position, and applying a lighted match, when a sharp detonation will indicate the re-combination of the gases.* Analysis of Water by Heat.—It has long been known that a very intense heat is capable of decomposing water. The temperature required for the 1 With a powerful coil, a cubic inch of explosive gas may be collected in about fifteen minutes. 2 18 ANALYSIS OF WATER BY HEAT purpose is below the melting-point of platinum, as may be shown by the apparatus represented in Fig. 11. A platinum tube, ¢, is heated by the burner, 6, the construction of which is shown at the bottom of the cut. It consists of a wide brass tube, from which the coal-gas issues through two rows of holes, between which oxygen is supplied from a gas bottle through the holes in the narrow tube, brazed into a longitudinal slit between the two rows of holes in the gas tube, o. The flask, f, containing boiling water is furnished with a perforated cork, carrying a brass tube, a, which slips into one end of the platinum tube, into the other end of which another brass tube, ¢, is slipped ; this is prolonged by a glass tube attached by india-rubber so as to deliver the gas under a small jar standing upon a bee-hive shelf in a trough. The platinum tube is not heated until the whole apparatus is full of steam, and no more bubbles of air are seen to rise through the water in the trough ; the gas burner is then lighted, and the oxygen turned on until the platinum tube is heated to a very bright red heat ; bubbles of the mixture of hydrogen and oxygen produced by the decomposition of the water may then be collected in the small jar, and afterwards exploded by applying a flame. In these experiments, the high temperature to which the steam is exposed causes its molecules to vibrate with such high velocities that the equilibrium of chemical attraction between their component atoms is disturbed, and new molecules of hydrogen and oxygen are produced. These are immediately carried out of the heated region by the current of steam. In the above cases the force of chemical attraction holding the atoms of oxygen and hydrogen together in the form of water has been overcome by the physical forces of electricity and heat respectively ; electrical energy and heat energy have been transformed into chemical energy. But water may be more easily decomposed by acting upon it with some element which has sufficient chemical energy to enable it to displace the hydrogen or the oxygen. Analysis of Water by (a) Metals which decompose it at the ordinary temperature.—Among the important metals, five, namely, Potassium, Sodium, Barium, Strontium, Calcium, have so powerful an attraction for oxygen that it is necessary to preserve them in bottles filled with some liquid free from that element, such as petroleum (composed of ‘carbon and hydro- gen) to prevent them from combining with the oxygen of the atmosphere. Oxygen enters into the composition of water and these metals are capable of decomposing water with great facility. When a piece of potassium is thrown upon water, it takes fire and burns with a fine violet flame, floating about as a melted globule upon the surface of the water, and producing in the act of combination heat sufficiently intense to kindle the hydrogen as it escapes. The violet colour of the flame is due to the presence of a little potassium in the form of vapour. The same results ensue if the potassium be placed on ice. After the experiment the water is soapy to the touch and taste, and has a remarkable action upon certain colouring-matters. Paper coloured with the yellow dye turmeric becomes brown when dipped in it, and paper coloured with red litmus ANALYSIS OF WATER BY METALS 19 becomes blue. Substances possessing these properties have been known from a very remote period as alkaline substances, apparently because they were first observed by the alchemists in the ashes of plants called kali. The alkalies are amongst the most useful of chemical agents. These alkaline properties are directly opposed to the characters of sour or acid! substances, such as vinegar or vitriol, which change blue litmus to red. If to a portion of an alkaline liquid, vinegar or dilute sulphuric acid is added gradually during constant stirring with two or three fragments of litmus paper floating about in the liquid, the paper continues blue, indicating that the liquid is still alkaline, until a certain quantity of the acid has been added, when the litmus paper assumes a tint between blue and red, showing that the alkali and the acid have neutralised one another ; the addition of one more drop of the acid turns the paper decidedly red, indicating that the liquid now contains an excess of acid. Litmus solution may with advantage be substituted for the litmus paper ; in either case the litmus is an indicator (p. 88) of the occurrence of a certain definite change in the progress of the reaction. Similarly, by adding the alkaline solution gradually to a portion of acid liquid the same neutral solution can be obtained. An alkali is a compound substance, soluble in water, turning red litmus blue and turmeric brown, and capable of neutralising an acid; see also p. 88. An acid substance may be known by its property of neutralising an alkali (either entirely or partly) and by turning blue litmus red. The minute investigation into the action of potassium upon the water would require considerable manipulative skill. It would be necessary to weigh accurately the potassium employed, to evaporate the resulting solu- tion in a silver basin (most other materials being corroded by the alkali), and after all the water had been expelled by heat, to ascertain the com- position of the residue by a chemical analysis. It would be found to contain by weight 1 part of hydrogen, 16 parts of oxygen, and 39 parts of potassium, in every 56 parts; so that if 39 parts of potassium had been treated with water, 56 parts of the alkali (caustic potash) would be obtained. Since water contains 2 parts by weight of hydrogen, combined with 16 parts by weight of oxygen, it is evident that the product of the action of potassium on water is formed by the substitution of 39 parts of potassium for 1 part of hydrogen. It is found that whenever potassium takes the place of hydrogen in a compound, 39 parts of the former are exchanged for one of the latter, and this is generally expressed by stating that 39 is the chemical equivalent of potassium (p. 13). Potassium is thus univalent (p. 12). In the cases of potassium and sodium and of some other elements the chemical equivalent has the same value as the atomic weight, but in the majority of instances this is not so. : The action of potassium upon water is an example of the production of compounds by substitution of one element for another, a mode of formation which is far more common than the production of compounds by direct: combination of their elements. : ; : If the symbol K represent 39 parts by weight of potassium, its action upon water would be represented by the chemical equation : HOH +K-= KOH +H (1 +1641) + 39 = (39+1641) +1 Water Potassium Caustic potash? 1 From dy, a point, referring to the pungency or sharpness of the acid taste. : : ? Caustic, from ical to burn, in allusion to its corrosive properties ; and potash, from its having been originally prepared from the washings of wood ashes poiled down in iron pots and decomposed by lime. 20 ANALYSIS OF WATER BY METALS But since atoms cannot exist, except in combination as molecules (p. 6), it would be strictly correct to write the equation thus : oHOH + K, = 2KOH + H;,. 2 (1-+16+1) + (2x39) =2 (3941641) + (21) Sodium has a less powerful attraction, or affinity, for oxygen than potassium has ; it does not, therefore, evolve so much heat when it combines with oxygen, for it is generally noticed that the greater the affinity between two elements the greater is the quantity of heat evolved when they combine. Thus sodium does not usually take fire when thrown upon cold water, although sufficient heat is evolved to fuse at once the metal. By holding a lighted match over the globule as it swims upon the water, the hydrogen may be kindled ; its flame is bright yellow, from the presence of the sodium. The solution is strongly alkaline from the caustic soda produced. By placing the sodium on a piece of blot- - ting paper laid on the water, it may be made to ignite the hydrogen spontane- ously, because the paper keeps the sodium stationary, and prevents it from being so rapidly cooled by the water. Several cubic inches of hydrogen may easily be collected by placing a piece of sodium as large as a pea in a small wire-gauze box, A (Fig. 12), and holding - ee an inverted cylinder, B, filled with water and standing on a bee-hive shelf. The product of the action of sodium upon water contains | part by weight of hydrogen, 16 of oxygen, and 23 of sodium, so that the 23 parts of sodium have been exchanged for, or been found chemically equivalent to, 1 part of hydrogen. A comparison with the previous experiment will show that 23 parts of sodium are chemically equivalent to 39 parts of potassium. Taking the symbol Na to represent 23 parts by weight of sodium, its action would be expressed thus: 2H,O + Na, = 2NaOH + Hg. 2H,0 + Na = 2Na0OH + H, 2(2x1416) + (2x23) = 2 (23+16+1) + (2x1) Barium, strontium, and calcium (p. 388) decompose water less rapidly than potassium and sodium do. ; (b) Metals which decompose Water at its boiling-point —The increase in molecular motion caused by heat disturbs the equilibrium of chemical attraction, so that metals which refuse to decompose water at the ordinary temperature will do so if the temperature be raised, and accordingly Mag- nesium and Manganese, which are without action up oncold water,decompose it at the boiling-point, disengaging hydrogen, and producing magnesia (MgO, a feebly alkaline earth) and oxide of manganese (MnO). (c) Metals which decompose water at a temperature above red heat —Zine Iron, Chromium, Cobalt, Nickel, Tin, Antimony, Aluminium, Lead, Bismuth, Copper—abstract the oxygen from water at high temperatures ; those at the commencement of the list requiring to be heated to redness (about 600°), and the temperature required progressively increasing until it attains whiteness for those at the end of the list. The decomposition of water by iron is of both historic and industrial interest. Lavoisier employed apparatus essentially similar to that now to ‘ This experiment sometimes ends in an explosi i i i L D c plosion. It is a wise precaution to wear m performing experiments likely to cause splashes dangerous to the ear Cee eta Fie. 12. ANALYSIS OF WATER BY NON-METALS 21 be described, when for the first time, in 1783, he demonstrated the composi- tion of water analytically. The same process has been used for producing large quantities of hydrogen for filling balloons, &c. It is, chemically speak- ing, the simplest process for preparing hydrogen in quantity, and consists in passing steam over red-hot iron. An iron tube (A, Fig. 13) is filled with iron Fie. 13. Preparation of hydrogen from steam. nails and placed in a furnace, B, where it is heated to redness by gas burners. A current of steam is then passed through it by boiling the water in the flask, C, which is connected with the iron tube by a glass tube, D, and per- forated corks. The hydrogen is collected from the glass tube, G, in cylinders, E, filled with water, and inverted in the trough, F, upon the bee-hive shelf, H, the first portions being allowed to escape, as containing air from the apparatus. The iron combines with the oxygen of the water to form the black oxide of iron (Fe,0,). which will be found in a crystalline state upon the surface of the metal. The decomposition is represented by the equation 4H,O + 3Fe = Fe,0, + 4H. The atomic weight of iron being 56, the 3Fe in the above equation repre- sents 56 x 3, or 168 parts by weight of iron. Other methods for depriving steam of its oxygen, and therefore for preparing hydrogen, will be noticed in the sequel. Metals decompose water more readily when in a very fine state of division or in a state of electrical polarisation by being placed in contact with other metals more electro-negative than themselves. Thus zinc, in contact with precipitated copper, decomposes water slowly at the ordinary temperature, hydrogen being evolved, and zinc hydrate separated in white flakes. The copper-zinc couple made by precipitating copper sulphate with zinc- foil in excess, and washing, is very useful in many operations where a slow production of hydrogen is required. ee The noble metals, as they are called, exhibit no tendency to oxidise in air, and are incapable of removing the oxygen from water, even at high tem- peratures. These metals are Mercury, Silver, Gold, Platinum. Analysis of water by non-metals.—Metals are not alone in their power of decomposing water; certain non-metals have the like power. Thus fluorine decomposes water at the ordinary temperature, combining with the hydrogen and liberating oxygen, while by passing a mixture of steam and chlorine through a red-hot tube the chlorine combines with the hydro- gen of the steam and sets free the oxygen. See p. 106. If steam be passed over red-hot carbon a mixture of hydrogen and carbon monoxide (so-called “‘ water-gas,” p. 274) is obtained. Review of the analytical methods : (a) a mixture of hydrogen and oxy- gen is liberated when electric sparks or heat is the agent of decomposition 22 HYDROGEN (b) both gases separate in the electrolytic process; (c) hydrogen only is disengaged when metals act on water ; (d) oxygen only when the non- metals fluorine or chlorine react with water. To complete the analysis where a mixture of the two constituent gases occurs it will be necessary to separate them. It can be done by removing one of them chemically or by separating both by the process of diffusion (p. 78) or by taking advantage of the greater solubility of oxygen in water (cf. air, p. 79) ; but before describing this it is desirable to examine the general properties of each of the gases separately, reverting subsequently to their systematic study. HYDROGEN ! is an invisible and, when pure, odourless gas. The most remarkable physical property of this element is its lightness ; it is the lightest of all kinds of matter, being i times as heavy as air, nm times, as heavy 1 as oxygen, and ;,5; times as heavy as water. One litre of hydrogen gas weighs 0-09 gram (or precisely 0-08990 gram) at normal temperature and pressure (p. 23) and 1 gram hydrogen measures 11-124 litres under the same conditions. Hence the molecular weight of hydrogen expressed in grams measures approximately 22°4 litres (p. 96), and it follows from what has been stated at p. 11 that the molecular weight of any gas expressed in grams measures 22°4 hitres at 0° C. and 760 mm. The lightness of hydrogen may be demonstrated by many interesting experiments. Soap bubbles or small balloons (of collodion, for example) will ascend very rapidly if inflated with hydrogen. A light beaker glass may be accurately weighed in a pair of scales ; it may then be held with its mouth downwards and the hydrogen poured up into it from another vessel. If it be then replaced upon the scale-pan with its mouth downwards, it will be found very much lighter than before. Another form of the experi- ment is represented in Fig. 14, where a light glass shade has been suspended from the balance and counterpoised ; the equilibrium becomes at once disturbed when hydrogen is poured up into the shade. If a stoppered gas jar full of hydrogen be held with its mouth downwards, and a piece of smouldering brown paper held under it, the smoke which would rise freely in the air is quite unable to rise through the hydrogen, and remains at the mouth of the jar until the stopper is re- moved, when the hydrogen quickly rises and the smoke follows it. If the weight of a given volume of purified and dried air be represented as unity, an equal volume of hydrogen, at the same temperature and pres- sure, would weigh 0-0695 ;_ this is expressed by saying that the specific gravity of hydrogen (air=1) is 0-0695. The specific gravity of a gas or vapour is the weight of a volume of it compared with that of an equal volume of some other gas, selected as a Fie. 14. standard, at the same tempera- ture and pressure. The specific gravity or density (see also p. 314) of a gas is not infrequently referred to air as a standard, but for scientific purposes hydrogen has been 1 Chief monograph on p. 95 HYDROGEN—PROPERTIES 23 almost always taken as the standard. Thus the specific gravity of air is 14-39 referred to hydrogen ; that of oxygen 15-900 (p. 57). But see also pp. 11 and 297. In ascertaining the weights of different volumes of gases, it is of the greatest importance that they should have some definite temperature and pressure, since the volume of a given weight of gas is augmented by increase of temperature and by decrease in pressure. It is usual to state the weights of gases at normal temperature and pressure, 7.e. at 0° Centigrade and 760 millimetres barometric pressure (p. 11). Ira. 15. Fie. 16. Hydrogen is one of the least soluble of gases ; 100 volumes of water dis- solve only 1-83 volumes of the gas at 15°. Chemical properties —The most conspicuous chemical property of hydro- gen is its disposition to burn in air when raised to a moderately high tempera- ture, entering into combination with the oxygen of the air to form water (p. 14). ‘i Since an atom of oxygen combines with 2 atoms of hydrogen to form water, the gases will not combine unless under the influence of some force, such as heat or elec- tricity, to assist in resolving their molecules into the constituent atoms (p. 12). On introducing a taper into an inverted jar of hydrogen (Fig. 15), the flame of the taper is extinguished, but the hydrogen burns with a pale flame at the mouth of the jar, and the taper may be rekindled at this flame by slowly withdrawing it. The lightness and combustibility of hydrogen may be illustrated simultaneously by some interesting experiments. If two equal gas cylinders be filled with hydrogen, and held with their mouths respectively upwards and downwards, it will be found on testing each with a taper after the same interval, that the hydrogen has entirely escaped from the cylinder held with its mouth upwards, whilst the other still remains nearly filled with the gas. The hydrogen may be scooped out of the jar, A (Fig. 16), with the small cylinder, B, attached to a handle. On removing B and applying a taper to it, the gas will take fire. A cylinder may be filled with hydrogen by displacement of air, if the tube from the hydrogen apparatus be passed up into it. If such a dry cylinder of hydrogen be kindled whilst held with its mouth downwards, the formation of water during the combustion of the hydrogen will be indicated by the deposition of dew upon the sides of the cylinder. By softening a piece of glass tube in the flame of a spirit-lamp, drawing it out and eee SYS filing it across in the narrowest part Fre. 18 (Fig. 18), a jet can be made from which eee the hydrogen may be burnt. This jet may be fitted by a perforated cork to any common bottle for containing the zinc and sulphuric acid (Fig. 19); see also p. 95. P 4 24 OXYGEN The hydrogen must be allowed to escape for some minutes before applying a light, because it forms an explosive mixture with the air contained in the bottle. This may be proved, without risk, by placing a little granulated zinc in a soda-water bottle (old form), pouring upon it some diluted sulphuric acid, and quickly inserting a perforated cork, carrying a piece of glass tube about three inches long and one-eighth of an inch wide. If this tube be immediately applied to a flame, the mixture of air and hydrogen will explode, and the cork and tube will be projected to a considerable distance. By inverting a small test-tube over the jet in Fig. 19, a specimen of the hydrogen may be collected, and, removing the still inverted tube of the hydrogen to a little distance, the gas may be kindled, to see if it burns quietly, before lighting the jet. A dry glass, held over the flame, will collect water, formed by the combustion of the hydrogen, until it becomes too hot to condense the vapour. If a taper is held several inches above a cylinder of hydrogen, standing with its mouth upwards, the gas is kindled with a loud explosion, because an explosive mixture of hydrogen and air is formed in and around the mouth of the cylinder. A stoppered glass jar (Fig. 20) is filled with hydrogen and supported upon three blocks ; if the hydrogen be kindled at the neck of the jar, it burns quietly until air has entered from below in sufficient proportion to form an explosive mixture, which will then explode with a loud report. The explosion of the mixture of hydrogen and air is due to the sudden expansion caused by the heat generated in the combination of the hydrogen with the oxygen throughout the mixture. After the explosion of the mixture of hydrogen and air (oxygen and nitrogen), the substances present are i steam (from the combination of the hydrogen and p oxygen) and nitrogen, which are expanded by the heat developed in the combination to a volume far greater than the vessel can contain, so that a por- tion of the gas and vapour issues very suddenly into the surrounding air, the collision with which produces the report. po llescesl If pure oxygen is substituted for air, the je _fsS explosion is more violent, because the mixture LYM 2 is not diluted with the inactive nitrogen. Se ‘= OXYGEN. Physical properties—From the~ Fis, 20. fact that it occurs in the uncombined state in the atmosphere, it will be inferred that oxygen gas is perfectly invisible and without odour. It is a little more than one-tenth heavier than air, which is expressed in the statement that its specific gravity is 1-1053 (air=1) or 15-9 (H=1). One litre of the gas weighs 1-429¢. It is more soluble in water than hydrogen (p. 14), 100 volumes dissolving 3 volumes of the gas at 15°. Chemical properties.—Oxygen is remarkable for the wide range of its chemical attraction for other elementary substances, with all of which except two, fluorine and bromine (in addition to the rare gases of the atmosphere which combine with no element), it is capable of entering into combination, and often with such energy that the reaction is accompanied by high tem- perature and light phenomena. In particular it unites with hydrogen to form water, as explained on pages 25 and 26. Substances which burn in air do so in oxygen with greatly increased brilliancy ; several experiments SYNTHESIS OF WATER 25 in illustration of this will be described in the chapter on Air; ef. the match test on p. 15. Oxygen is dealt with more fully on pp. 54 and 137. SYNTHESIS OF WATER.—By the methods already described under the analysis of water it has been abundantly proved that water is a com- pound containing hydrogen and oxygen, and in the electrolytic process (p. 14) these gases were obtained in the proportion of two volumes of the former to one of the latter ; it was also pointed out (p. 24) that orygen gas ts 15-9 times as heavy as hydrogen gas and that therefore the composition of water by weight is 2 parts hydrogen and 15-9 parts oxygen. It remains to be demonstrated that when these gases in the proportions named are caused to combine, water is produced. Volumetric methods will be first considered, and then gravimetric (p. 4). Volumetric synthesis.—The composition of water was first determined synthetically by Cavendish in 1781. He prepared a mixture of two volumes of hydrogen and one volume of oxygen and admitted it in small quantities at a time into a eudiometer? which had previously been pumped free from air, and exploded each portion in succession. In this way he treated about 3-5 litres of the gaseous mixture and obtained a few drops of liquid which he proved to be water. The demonstration may be repeated in the so-called Cavendish eudiometer (Fig. 21). This is a strong glass vessel, with a stopper firmly secured by a clamp, A, and provided with two platinum wires, P, which pass through the stopper and approach very near to each other within the eudiometer, so that the electric spark may easily pass between them. By screwing the stop-cock, B, into the plate of an air-pump, the eudiometer may be exhausted. It is then screwed on to the jar represented in Fig. 22, which con- tains a mixture of two measures of hydrogen with one measure of oxygen, standing over water. On opening the stop-cocks between the two vessels, the eudiometer becomes filled with the mixture, and the quantity which has entered is indicated by the rise of water in the jar. The glass stop-cock, C, having been closed to prevent the brass cap from being forced off by the explosion, the eudiometer is again screwed on to its foot, and an electric spark passed between the platinum wires, either from a Leyden jar or an induction coil, when the two gases will combine with 4 vivid flash of light,? attended with a very slight concussion but no noise, since there is no collision with the external air. For an instant a mist is perceived within the eudiometer, which condenses into fine drops of dew, consisting of the water formed by the combination of the gases, which was here induced by the high temperature of the electric spark. If the gases 1 So named from evdtoc, fine or clear, and «€é7pov, a measure, because an instrument upon the same principle has been used to determine the degree of purity of the atmosphere. 2 Since the steam produced at the moment of combination is here prevented from expanding, the heat which would have expanded it is saved, so that the temperature is higher and the flash of light brighter than when the combination is effected in an open vessel. 26 VOLUMETRIC SYNTHESIS OF WATER have been mixed in the exact proportion of two measures of hydrogen to one measure the eudiometer will now be again vacuous, and if it be screwed on to the of oxygen, a which may be exploded in capped jar, may be filled a second time with the mixture, the same manner. The entire disappearance of the gases may be rendered obvious to the eye by explo- ding the mixture over mercury. For this purpose the mixture of 2 volumes of hydrogen and 1 volume of oxygen may be artificially prepared, or the mixed oc gases may be collected from water itself in one of the voltameters described on page 16. The latter course is instructive as showing the re-formation of water from the products of its decomposition. The first few bubbles of the mixture of hydrogen and oxygen evolved having been allowed to escape, in order to displace the air, the gas may be collected in a Bunsen’s eudiometer (Fig. 23), which has been previously filled with mercury. This eudiometer is a cylinder of very strong glass, closed at one end, and having two stout platinum wires inserted near the closed end, the wires approaching sufficiently near to each other to allow the passage of the electric spark. Having been half filled with the mixture of hydrogen and oxygen, the eudiometer is transferred and pressed firmly down upon a stout cushion of india-rubber on the bottom of the mercury trough, and the spark passed through the mixed gases, either from a coil or a Leyden jar. The combustion occurs with violent concussion, but without noise ; and since the eudiometer is vacuous after the gases have combined, the cushion will be found to be very firmly pressed against its open end. On loosening the cushion, the mercury will be violently forced up into the eudiometer, which will be completely filled with it except for the very small volume of water produced, proving that when Fie. 23. an electric spark is passed through the mixture of 2 volumes of hydrogen and 1 volume of oxygen, no residue of gas remains. This may also be demonstrated with the siphon eudiometer (Fig. 24), by confining about a cubic inch of the explosive mixture in the closed limb, over water, and stopping the open limb securely with a cork, so as to leave a space filled with air between the cork and the water. The eudiometer must be very firmly fixed on a stand, or it will be broken by the con- cussion. After it has been proved, it may be held in the hand, as in the figure. By firing mixtures of hydrogen and oxygen, in different proportions, in the same manner, it may be shown that any excess of either gas above the ratio of 2H: O will remain uncombined after the explosion. Care is required in these experi- ments, since eudiometers are often burst by the explosion of the mixture of 2 volumes of hydrogen with 1 volume of oxygen. AEE Mm in Fig. 24. The knowledge of the volumes in which hydrogen and oxygen combine, is turned to account in the analysis of gases, to ascertain the proportion of hydrogen or oxygen contained in them. Suppose, for example, it be required to determine the amount of oxygen in a sample of atmospheric air; the latter is mixed with hydrogen, in more than sufficient quantity to combine with the largest proportion of oxygen which could be present, and when the combination has been induced by the electric spark, . the volume of gas which has disappeared (2 volumes H + 1 volume O) has only to be divided by three to give the volume of the oxygen. A bent eudiometer (Fig. 24) may be used. Having been completely filled with water (previously boiled to expel dissolved air), it is inverted in the trough, and the specimen of air is introduced (say 10 c.c.). The open limb is then closed by the thumb, and the eudiometer turned so as to transfer the air to the closed limb. A stout glass rod is thrust down the open limb, so as to displace enough water to equalise the level in both limbs, in order that the volume of the air may not be diminished by the pressure of a higher column of water in the open limb. The volume of the included air having been accurately noted, the open limb of the tube is again filled up with water, inverted in VOLUMETRIC SYNTHESIS OF WATER 27 the trough, and a quantity of hydrogen introduced, equal to about half the volume of the air. This having been transferred, as before, to the closed limb, the columns of water are again equalised, and the volume of the mixture of air and hydrogen ascer- tained. The open limb is now firmly closed with the thumb, and the electric spark passed through the mixture, either from the Leyden jar or the induction-coil. On removing the thumb, after the explosion, the volume of gas in the closed limb is found to have diminished very considerably. Enough water is poured into the open limb to equalise the level, and the volume of gas is observed. If this volume be subtracted from the volume before explosion, the volume of gas which has disappeared is ascer- tained, and one-third of this represents the oxygen, which has condensed with twice its volume of hydrogen into the form of water. Thus the numbers recorded will be: Volume of air analysed . ‘ ‘ ; 3 : . 1dce. Volume of air mixed with hydrogen . ; : 15 ,, After explosion. 2 ; 3 : ‘ . ee Ds Difference (3H and 40) 6-0 c.c. 6 divided by 3 = 2 c.c. of oxygen. In exact experiments, a correction would be required for any variation of the temperature or barometric pressure during the progress of the analysis. It will have been observed, in the experiment upon the synthesis of water in the Cavendish eudiometer, that the volume of water obtained is very small in comparison with that of the gases before combination, about 1870 volumes of the mixed gases being required to form 1 volume of liquid water, because after the chemical attraction has caused the molecules of H and O to form steam, the cohesive attraction has caused the molecules of steam to unite and form liquid water. In order to watch the effect of the chemical attraction only, we must prevent the steam from changing its state after it is produced. If the mixture of hydrogen and oxygen be measured and exploded at or above the boiling-point of water, it is found that the steam produced occu- pies two-thirds of the volume of the mixed gases, measured at the same temperature and pressure. Hence, 2 volumes of hydrogen combine with 1 volume of oxygen to form 2 volumes of aqueous vapour, at the same tempera- ture and pressure. The combination of hydrogen and oxygen in a vessel heated to the boiling-point of water is effected in the apparatus shown in Fig. 25, where the closed limb of the eudiometer is surrounded by a tube into which steam is passed from a flask connected with the wide tube by a cork and a short wide piece of bent glass tubing, jacketed with caoutchouc to prevent loss of heat. The steam escapes through the tube, t, which enters the cork at the bottom. The closed limb of the eudiometer having been filled with mercury, a small quantity of the mixture of hydrogen and oxygen obtained from the volta- meter (Fig. 9) is introduced into it through a tube passed down the open limb, the displaced mercury being run out through the tube, c, which is closed by a screw clip. The closed limb is then heated by the steam, and the mercury in the two limbs adjusted from time to time by running a little out through ¢, until the gas in the closed limb no longer expands and the level in the open limb is one or two inches lower than in the closed limb. Its ; volume is then observed, an inch more mercury poured into the open limb, which is then tightly closed by a cork, and the spark from the induction-coil (Fig. 10) is passed 1 ‘The latest researches show that the exact volume ratio is 200245 H : 10. 28 GRAVIMETRIC SYNTHESIS OF WATER by the wires ~ and +. After the explosion, the cork is removed, and the mercury in the two limbs adjusted until the difference of level is exactly the same as before sparking, when the volume of the steam will be found to be just two-thirds of the volume of the gas before the explosion. On cooling down, the steam condenses, and the mercury entirely fills the closed limb of the eudiometer, save for the minute globule of liquid water. That 2 volumes of steam should contain 2 volumes of hydrogen and 1 volume of oxygen would appear, on physical grounds, impossible, since two bodies cannot occupy the same space at the same time ; but it must be remembered that the two bodies in question have lost their individuality in consequence of their chemical combination by which they have become one body—water. The synthesis of water by weight is not easily effected with accuracy by weighing the gases themselves, on account of their large volume. It is there- fore accomplished by passing an indefinite quantity of hydrogen over a known weight of pure hot oxide of copper, when the hydrogen combines with the oxygen of the oxide to form water. The loss of weight suffered by the oxide of copper gives the amount of oxygen ; and if this be deducted from the weight of the water, that of the hydrogen will be ascertained. In this way it is shown that water contains 8 parts of oxygen to every 1 part of hydrogen. The subject will be more critically considered when dealing with the relative atomic weights of hydrogen and oxygen. The apparatus employed for this purpose is represented in Fig. 26. h is the bottle in which hydrogen is generated from diluted sulphuric acid and zinc ; the gas passes, Sie K Lege i Aa —— FS ie a LEe in p, through solution of potash, which absorbs any sulphuretted hydrogen ; then through s, containing pumice-stone (used on account of its porous character), saturated with a strong solution of silver nitrate, which removes arsenic, antimony, and phos- phorus from the hydrogen ; the gas then passes through vv, containing pumice saturated with oil of vitriol to absorb moisture. The bulb, c, with the oxide of copper, is weighed before and after the experiment, as are the globe, g, for condensing the water, and the tube, ¢, containing pumice and oil of vitriol, to absorb the aqueous vapour. Of course the bulb, c, must not be heated until the hydrogen has displaced all the air from the apparatus. As an example, 10 grams of CuO were employed, and 7-98 grams Cu were left, 2-2725 grams water being collected. 10 — 7:98 = 2-02 grams O; 2-2725 — 2-02 = 0-2525 grams H ; 2-2725: 2-02: : 100: 88-88 ; 2-2725: 0-2525::100: 11:11. 100 parts by weight of water, therefore, contain 88-88 O and 11-11 H. This is the usual method of stating the composition of a substance. To deduce the chemical formula, we must divide the amount of each constituent by its atomic weight ; 88:88 + 16 = 5-5 atomic weights of O; 11-11 + 1 =11-11 atomic weights of H. Then 5:55: 11:11 ::1 atom O: 2 atoms H. Provided the copper oxide is perfectly pure and the treatment with hydrogen is continued till all oxygen is removed, the above experiment would also serve and has been used for fixing the atomic weight of copper, for it shows that 100 parts by weight of cupric oxide contain 79:8 parts of copper and 20-2 parts of oxygen. ‘Then 20-2 : 79-8: DISTILLATION OF WATER 29 16 : 63-2; so that if cupric oxide contains 1 atom of copper to 1 atom of oxygen, the atomic weight of copper would be 63-2. Distilled Water.—For the purposes of the chemist natural water is not sufficiently pare on account of its holding in solution small variable quantities of fixed and volatile impurities. The former are those which remain behind when water is evaporated, the latter those which pass away in the steam. Lvaporation is the process of a liquid be- coming resolved into vapour. (Cf. Volatilisation, p. 33.) Distillation (Lat. distillo=to drop or trickle down) is the double process of the conver- sion of a liquid into a vapour and its re-condensation into the liquid state in another vessel (cf. Sublimation, p. 33). By applying this = ‘process to ordinary water a eee distillate is obtained which : consists of water con- taining only some of the volatile impurities (chiefly ammonia) and sufficiently pure for all ordinary scientific requirements. Fig. 27 represents the form of apparatus in common use, in which A is a copper boiler known as the still containing the water to be distilled; B the head of the still which lifts out at 6 and is connected by the neck, C, with the condensing worm, D, a block- tin pipe coiled round in the tub, E, and issuing at F. The steam from the boiler, passing into the worm, is condensed to the liquid state, the cooling being effected by the water in contact with the outside of the worm; this water, becoming heated, passes off through the pipe, G, being displaced by cold water, which is allowed to enter through H. Fie. 28. If 10 gallons of river water be taken, 8} may be distilled over, but the first half-gallon should be collected separately, as it contains ammonia and carbonic acid. ies A form of apparatus for distillation of water and other liquids is shown in Fig. 28. Ais a distilling flask, the delivery tube, B, of which fits into the tube of a Liebig’s 30 INFLUENCE OF HEAT ON WATER condenser, which consists of a glass tube, C, fitted into a glass, copper, or tinned iron jacket, D, into which a stream of cold water is passed by the inlet, E, the heated water running out through the upper outlet tube, F. The water furnished by the condensation of the steam is collected in the flask or receiver. Heat is gradually applied to the distilling flask by a Bunsen burner or gas ring. : Distilled water should be bright, colourless, odourless, essentially tasteless, and not clouded on addition of silver nitrate solution. 100 c.c. should leave on evaporation at most a scarcely visible residue. There are very numerous forms of apparatus—both laboratory and com- mercial—in use for water distillation. Sea water is frequently distilled on board ship for domestic purposes. The vapid and disagreeable taste of distilled water, which is due to its having been deprived of dissolved air during distillation, is remedied by the use of Normandy’s or other suitable still, which provides for the restoration of the expelled air (p. 42). PHYSICAL PROPERTIES.—A study of the physical properties of water, especially of the influence of heat, pressure and electricity, is of such importance to the chemist that although strictly belonging to the realm of Physics the subject must be treated here to some extent, more particularly with a view to determining those properties which are common to the majority of substances by methods which are in general use in chemical laboratories. A fuller discussion with, in some cases, descriptions of more precise methods can be found in advanced text-books on physics. Pure water is an odourless, tasteless, transparent, colourless liquid, except that in layers of considerable depth it is seen to be blue. It cannot be de- scribed either as a “ heavy” or as a “ light”’ liquid, since its density is by definition unity (v. infra). In the solid state it assumes the form of six-sided prismatic crystals. Snow consists of beautiful six-rayed stellate groupings of these crystals. The surface tension (Lat. tensio=a stretching) (p. 315) of water in contact with air is greater than that of any other pure liquid except mercury. Its viscosity (p. 316) is high among liquids of so simple molecular constitution, although low compared with many of the more complex. Refractive Index (p. 646) of water, 1-336 ; of ice, 1-310. INFLUENCE OF HEAT.—(a) Water is a bad conductor of heat ; i.e. when there is no motion in the mass of the water, heat is transferred very slowly from one part of the mass to another. A body of water becomes easily heated by convection ; i.e. heat is conveyed by portions of the body of Fic. 29. Fic. 30. Fie. 31. Fie. 32. nate stopper Regnault’s flask. Nicol’s sp. gr. tube. Perkin’s sp. gr. tube. ask. liquid moving as a result of the local application of heat. This can readily be demonstrated by placing in a flask a few crystals of potassium perman- ganate or potassium bichromate, three-quarters filling with water (carefully so as not to disturb the crystals), and applying a small flame to the bottom ; DENSITY—SPECIFIC GRAVITY 31 convection currents are set up, due to the water, which has become lighter on being heated directly by conduction at the bottom of the vessel, rising through the heavier strata. (3) Changes in state, volume and density—If a picnometer (ricvos= thick, dense) (a general term for any apparatus used in determining densities) such as one of those in Figs. 29 to 32, be filled to the mark with water successively at 0°, 2°, 4°, 6°, 8°, 10°, 15°, &c., and weighed accurately, it will be found that the higher the temperature above 4° the smaller is the weight; also that at 2° the weight is about the same as at 6° and at 0° the same as at 8°; therefore at 4° (or more accurately 3-945°) water has its maximum density and hence its smallest volume. One cubic centimetre (c.c.) of water at this temperature weighs one gram (by definition of the gram). 1 ¢.c. water at 0° weighs 0-999878 gram and therefore its density is 0-999878, but 1 c.c. ice at 0° weighs 0-91752 gram and therefore its density is 0-91752; 1 c.c. water at 15° weighs 0-999154 and therefore its density is 0-999154. The density of a solid or liquid body is the mass of a unit volume of the substance, and therefore is an absolule quantity. The specific gravity is a number expressing the weight of any volume of the substance divided by the weight of an equal volume of water ; and therefore is a relative quantity. When the standard is the weight of an equal volume of water at 4°, the specific gravity is also the density. The use of one term for the other is common and without objection in general descriptions, but where precise figures are concerned the definitions should be carefully observed. S% and 8% express the specific gravities (sp. gr.) at 15° compared with water at 15° and 4° respectively. In scientific work the density at 0°, D. , is usually determined, but in ordinary practice the specific gravity at 15°, S12. The density at ¢°, D;., can be found from the specific gravity at ¢°, S2, by multiplying by the density of water at ¢°. The specific volume of a substance is the volume occupied by unit weight of the substance. If some ice at, say, 20° below the freezing-point be heated gradually to, say, 20° above the boiling-point of water under atmospheric pressure, the following changes in state and volume occur : (i) from —20° to 0° slight expansion, 0-000057 of its volume for each degree ; (ii) at 0°, by continued application of heat, the ice melts to water at 0°, 109 (or precisely, 109-082) volumes of ice contracting to 100 volumes of water ; (iii) 0° to 4° the volume continues to become still smaller ; (iv) between 3° and 5° the volume is nearly constant,1 being smallest at 3-945° ; (v) 4° to 100° expansion is con- tinuous and averages 0-000449 of its volume at 4° for each degree ;? (vi) at 100°, by continued application of heat, the water boils, 1 volume water at 100° being converted into 1604 volumes of steam at 100°; (vii) above 100° the steam expands approximately according to the laws of gaseous expansion ; (viii) above 364-3° it behaves as a true gas. On reversing the series of temperature changes, the corresponding reversal of phenomena obtains. The one of most practical interest is the expansion (,},) on freezing, which exerts almost irresistible force, causing the breakage of strong iron vessels, bursting of water-pipes, splitting of rocks, &. These powerful mechanical effects occur during the freezing, although they may not be obviously apparent until the thaw sets in, as after the bursting of a water-pipe. Ice being lighter than water has most important effects on climate and the economy of nature generally. If ice were heavier than cold water, it would sink to the bottom of the lakes and seas, which are practically impenetrable by the sun’s rays, so that the whole mass of water would eventually solidify. Itshould also be remarked that while the temperature at which ice melts is constant, water does not always solidify at 0°, although it does so normally. Water free from air in a closed vessel or in narrow tubes, and kept perfectly still, may be 1 Thus water can be measured with accuracy most easily at about 4°. ; 3 From the Table on page:34 it will be seen that the rate of expansion per degree increases with the temperature. 32 SPECIFIC HEAT—LATENT HEAT supercooled some few degrees below zero without becoming solid. By agitation or by , dropping in a small fragment of ice solidification sets in and the temperature rises to the normal melting-point (0°). This property is exhibited by most other substances ; hence usually the melting-point (m.p.) (see also p. 642) of a body (the tempera. ture at which the solid changes into a liquid) is determined in preference to its solidi- fying-point (s.p.) (the temperature at which the liquid becomes solid). The boil- ing-point (b.p.) (see also p. 643) of a liquid is the constant temperature indicated by a thermometer immersed in the vapour of the boiling liquid, a coil of platinum wire being in the liquid to facilitate disengagement of vapour, and at a barometric pressure . of 760 mm. An apparatus which will serve is shown in Fig. 282, but the thermometer should be lowered so that the bulb is, say, 5 cm. above the surface of the liquid. ‘ The boiling-point of water is 100°. The vapour density of water is 9 (Hydrogen = 1), or 0-625 (Air =1); hence the molecular weight is 18 and therefore the formula is H,O ; and a given volume of moist air weighs less than an equal volume of it when dry. (y) Calorimetry (=measurement of quantity of heat). The calori- metric unit, known as a therm or gram-calorie, is the quantity of heat required to raise the temperature of one gram of water through 1° OC. (or, pre- cisely from 0° to 1° C.). A calorie=1000 therms. However, the term “galorie” is frequently used for “‘ gram-calorie”’ and it is often so used in this book. The specific heat of a substance is the quantity of heat, measured in gram-calories, which is necessary to raise the temperature of one gram of the substance through 1° C., hence the specific heat of water is 1. It varies, however, with the temperature: at 0° it is 1; at 30° it is least, 0-9872 ; at 51° it is unity again ; at 80°, 10182 ; at 100°, 1:0306. The specific heat of ice is 0-504, and of steam, 0-477. Usually this constant for a substance is greatest when the latter is in the liquid state. The value for all solid and liquid bodies below 100° is less than 1, except for water, liquefied ammonia (p. 184), and certain aqueous mixtures of ethyl and methyl alcohols (g.v.)._ The specific heat rises, as a general rule, with the: tem- perature (cf. carbon, p. 243), and varies with crystalline condition (cf. carbon, p. 248 ; phosphorus, pp. 211, 213). See also p. 298. It was remarked in (ii) above that ice at 0° required application of heat to convert it into water at 0°, whence it appears that the transfer of heat to a body does not always bring about a rise in temperature and that the quan- tity of heat possessed by a given weight of a substance is not necessarily proportional to its temperature. Instead, transfer of heat may cause a change of state as in the melting of ice, or the conversion of water into steam. Moreover, the absorption or loss of heat by a body without simultaneous change of temperature is a means of detecting change of state, cf. Landolt’s method of determining melting-points. If one gram of water at 0° be mixed with one gram of water at 80° (which, therefore, contains 80 calories more than the water at 0°), the temperature of the resulting mixture will be the mean of the two, 40° (because the 80 extra calories are now distributed over two grams of water) ; but if one gram of ice at 0° be dissolved in one gram of water at 80°, the temperature of the two grams of water is 0°; all the 80 extra calories of the hot water have been used up in melting the ice, without raising its temperature ; hence, one gram of water at 0° contains 80 calories more than one gram of ice at 0°. Heat which disappears into a body without raising its temperature is called latent heat (Lat. latens= lying hid). The latent heat of fusion of water is 80 (precisely 79-25) calories per gram (p. 322). Similarly, to convert one gram of water at 100° into steam at 100° requires 536-5 calories ; therefore the latent heat of vaporisa- tion of steam is 536-5 calories per gram (p. 323). This value for any liquid decreases with rise in temperature, becoming zero at the critical point (p. 35). (6) Vapour is givenfoff by water and ice at all temperatures. The VAPOUR PRESSURE OF WATER 33 quantity vaporised increases with rise of temperature and is usually deduced from the pressure exerted ; see next section. INFLUENCE OF PRESSURE.—(a) Homogeneous solids and liquids generally are not easily compressible. Ice cannot be appreciably reduced in volume even by the greatest pressure. If, however, the ice is at a tempera- ture not much below its normal melting-point, fusion may occur with con- siderable diminution in volume (ef. (ii), p. 31). The lowering of the melting- point of ice is about 0-0075° for the first additional atmosphere of pressure ; but the depression per atmosphere increases somewhat with the magnitude of the pressure. Hence, in a vacuum the melting-point is +0-0075°. Water suffers a compression of about 1 in 20,000 volumes when the atmospheric pressure is doubled. (8) Vapour pressure.—If two tubes about 1 metre long, 1 cm. diameter and closed at one end be filled with clean dry mercury and inverted in a trough of the metal (Fig. 33), the mercury will stand at the same height in both tubes as that indicated in the left-handtube. The whole apparatus, including a thermometer, should now be placed for about an hour in a room or enclosure where the temperature is that at which it is desired to conduct the experiment. The apparatus being at a temperature below 0°, a small piece of ice is passed beneath one of the tubes ; it rises to the surface and gives off water vapour? until the space above the mercury is saturated with the vapour ; simultaneously the level of the mercury falls by a small but definite amount. The difference in the heights of the mercury in the two tubes represents the pressure exerted by the saturated vapour of the substance, known as the vapour pressure of the substance at the temperature of the ex- periment. The vapour pressure increases with the tem- perature, and for each temperature there is a definite vapour pressure, for each particular substance, whether liquid or solid. (Also p. 34.) i The vapour pressure of ice at 0° is the same as that of water at 0° (see also p. 339) ; but the vapour pressure of supercooled water is somewhat greater than that of see at the same temperature (see line TX in Fig. 225, p. 339). At temperatures above 0 the water floating on the surface of the mercury is in the liquid state, and a correction must be made for the depth of the water ; if this is x mm. 5% mm. must be added to the observed height of the mercury, the specific gravity of which is 13-6. (If some other substance having a specific gravity 8 is under investigation, the correction is ze.) No such correction is required for solid bodies, e.g. ice, because the solid presses into the mercury and displaces a weight of the metal equal to that of the solid. A ae excess of the liquid or solid is necessary in order to know that the vapour is ae ; if all is vaporised the space will probably be unsaturated, t.e. it will be possible for the space to hold more of the vapour at the temperature of the experiment. The pres- sure of a saturated vapour depends on the temperature only; the pressure of an unsaturated vapour depends on both temperature and volume. ‘ iqui ilisation (Lat. volo = 1 When a solid is vaporised directly, without passing through the liquid state, volatilisation (Lat. to fly) is a to occur (et. mr p.29). Sublimation is the double process of direct cE 3 solid and condensation of the vapour directly to a solid without liquefaction (cf. distillation, ae : ee which sublime at atmospheric pressure can be melted by exposing them to a higher press’ og sean oxide). On the other hand, ice and some other substances can be sublimed or a are aes ae sublimation of iceis exemplified in the formation of hoar frost (the line TH, Fig. 225, is som en “ hoar-frost line ”) at temperatures below 0°; above 0° dew is deposited. Sublimation nee ie dale when the conditions are so adjusted that the boiling-point and melting-point are close together ; cl. point curves (Fig. 225). 3 34 DENSITY AND VAPOUR PRESSURE OF WATER At 100° the vapour pressure of water is 760 m.m., i.e. equal to the normal atmospheric pressure. 100° is also the boiling-point of water. Hence, the boiling-point of a liquid may be defined as the temperature at which the vapour pressure of the substance is equal to the normal atmospheric pres- sure ; see also p. 643. This subject can be very conveniently studied in the case of any desired liquid with apparatus used for distillation under diminished pressure (q.v.); the tempera- ture being the boiling-point as shown by the thermometer, and the vapour pressure being the pressure in the apparatus (not the amount of “vacuum ”’) as deduced from the reading of the manometer. Water will not boil at 100° if the pressure be greater than 760 mm. The variation of the vapour pressure with the temperature is generally of some mathematical order, and if the experimental figures be plotted on squared paper with the ordinates to represent pressure and the abscisse to represent temperature, a “eurve,” the vapour-pressure curve, can be drawn through the points. Fig. 35 is such a curve for water drawn through the points (x) representing the temperatures and vapour pres- sures given in the accompanying Table. In other curves the specific volume (Fig. 34) and the density (Fig. 35) respectively are plotted against the temperatures. t Temperature State Specific volume Density Vapour pressure mm, — 50° Ice 0-050 — 20° 3 0-806 | — 10° 3 1-999 - 10° Water 1-00186 0-99814 2-197 0° Ice 1-089894 0-91752 4-58 0° Water 1-000122 0-999878 4-58 2° 5 1.000028 0-999972 5:29 4° 5 1-000000 1-000000 6-11 6° I 1-000031 0-999969 7-02 8° re 1-000118 0-999882 8-06 10° ‘i 1000261 0-999739 9-94 15° 5 1-000847 0-999154 12-79 20° a 1-00173 0-99827 17-52 30° i 1-00425 0-99577 31-51 50° ne 1-01197 0-98817 91-98 70° ss 1-02261 0-97789 233-31 90° 7 1-03574 0-96549 525-47 100° 5 1-04323 0-95856 760 120° ” 1-0609 0-9426 1484 150° 7 1-093 (abt.) 0-915 (abt.) 3568 250° oe 1-27 (abt.) 0-79 (abt.) 29734 364-3 ” 3-04 0-329 147904 (crit. temp. ) (crit. volume) (crit. density) (194-6 atm.) (crit. pressure) Such curves serve many purposes, but especially they show by their regular mathematical form that the variation of the property is systematic and follows some law; they have practical utility in giving at once by inspection the other factor when the one is given; e.g. if it be required to know the vapour pressure of water at 82°, find the point 82° on the tempera- CRITICAL CONSTANTS 35 ture axis (Fig. 35) and draw a vertical line through the point to the curve ; the point on the curve where it is cut by the vertical is opposite 386 mm. on the pressure axis, hence the vapour pressure at 82° is 386 mm. Similarly, 19899 Tp Ice § ro0es x / 100 | superset pag § Water 8 Viezte, | —~| goa im a5 Pm 8 / ; "0035 3) ‘98 S S | 3 0030 8 o7 oI 8 ™" 8 % ° / x ‘0025 q g 96 -—§ 4 x / = x “0020 is Sy 95 = ve re y 8 10015 3 Ny 94 pe a 2 J S se] \s Se \a 8 - = és} 8 ge |. < ro005 \ 7 ‘92 Tee SE ° 10 20 30° Seo ‘0 20 «630° 40° 50" TEMPERATURE TEMPERATURE Srecitic Votume CURVE DENSITY CURVE Fic. 34. Fie. 35. at what temperature has water a density of 0:99? Find the point on the curve (Fig. 35) which is opposite the 0-99 position on the density axis ; it is then seen to be opposite the 45° position on the temperature axis ; there- fore water has a density of 0-99 at 45°. (y) The Triple Point: see p. 339. (6) The Critical Constants.—At any temperature not higher than 364-3° the whole of the aqueous vapour can be condensed to the liquid state by applying a pressure only slightly greater than the vapour pressure. Also, provided the temperature is kept constant, the least diminution in pressure will cause the substance to vaporise entirely. At 364-3° the vapour pressure is 147,904 mm. (194-6 atm.), the highest known. But at temperatures above 364-3° no pressure, however great, can effect liquefaction. The highest temperature at which pressure can cause a vapour to liquefy is called the critical temperature; theleast pressure which can maintain the liquid state at this temperature, i.e. the vapour pressure at the critical temperature, is called the critical pressure, and the volume occupied by one gram of the substance the critical volume. There are such constants for all substances capable of vaporisation. When a vaporised substance is below its critical temperature it is in the state of vapour and obeys the gas laws irregularly ; when above, it is a true gas. Thus vaporised water is a vapour below 364-3°, but a gas above that temperature (see also p. 315). The appearance of a liquid at its critical temperature can be seen by sealing carefully a thick walled glass tube of about 3 c.c. capacity containing 1 c.c. of ether. It is convenient to bend the sealed end into the form of a hook by which the tube may be suspended at some distance abové a flame. The ether 36 CHEMICAL PROPERTIES OF WATER will be seen to boil until it becomes difficult to detect any surface to the boiling liquid; immediately after this the liquid vanishes and the tube appears empty. It should be at once removed from the flame, whereupon the liquid suddenly reappears. The temperature at which the liquid vanishes and reappears is the critical temperature of ether (190°). (ce) At very high temperatures water is decomposed into its elements ; see p. 18.. Influence of Electricity.—The purest water conducts electricity very feebly indeed, but the passage of the current is always attended by decomposition. The matter has been referred to already (pp. 14 to 16), and will recur in the chapter on Electrolysis (p. 327). Solution, Liquid Diffusion, Dialysis, Osmose, &c., are physico- chemical properties and are dealt with in special sections. The peculiarities of water as compared with most other sub- stances are (i) that its maximum density is at a temperature some degrees above its melting-point ; (ii) that it expands on solidification. Hence, pressure has the effect of lowering the melting-point and in consequence enables the stable existence of liquid water at temperatures below that of the triple point (p. 339). (iii) Water has extreme values for several constants ; e.g. exceptionally high specific heat, the highest critical pressure, the greatest surface tension for any pure liquid. Chemical properties.—Water enters into numerous reactions, usually suffering a splitting into H and OH as was seen to be the case when water reacts with potassium or sodium (p. 20). Probably this occurs even when not so obvious; e.g. with calcium (p. 388), Ca + 2H,O= Ca(OH), + 2H; and not Ca + H,O = CaO + H, followed by CaO + H,O = Ca(OH),. The same thing takes place when water unites with such a compound as sulphur trioxide, SO,; sulphuric acid is produced which for the moment may be represented by the formula HO.SO,.H ; similarly, potassium oxide, K,0, produces potassium hydrate, HO.K,O.H, i.e. 2KOH, and ammonia, NH,, forms ammonium hydroxide, H.NH;.OH (see also p. 184). In these cases both H and OH combine with the same group of elements, but they themselves are apart. Inthe process known as hydrolysis (p. 224) the same splitting obtains. As a possible exception the decomposition of water by fluorine (p. 21) may be cited, the latter having no affinity whatever for oxygen. Under the Analysis of Water (pp. 14-21) several chemical properties of water were considered. Calcium carbide, CaC,, reacts with water with production of acetylene gas, C,H,, CaC, + 2H,O = C,H, + Ca(OH), (p. 251). The evolution of acetylene on contact of calcium carbide with a substance is evidence of the presence of water. For another test, using copper sulphate, see p. 39. Water of crystallisation, deliquescence, &c. (p. 38), are also subjects which might well be considered in this section, but they will be more conveniently treated in connection with solution. The molecular relations of water to other substances are numerous, characteristic, and frequently not easy of explanation ; solution and water of crystallisation are the chief. SOLUTION.1—A substance is commonly said to dissolve in a liquid when it disappears in the liquid ; the product is called a solution, and the liquid which effects the dissolution is the solvent. The phenomenon seems simple, but its nature is not yet fully determined. In many respects it is certainly physical, but very commonly changes occur during the process of dissolution which are distinctly chemical. Many solvents are known to the chemist, but water is the most important + A further section on “ Solution” occurs in the chapter on General Principles, p. 324. SOLUTION—DEFINITION 37 to him and also the only solvent which is of any substantial importance in the economy of nature. Of the elements, chlorine, bromine and iodine dissolve in water to some extent without apparently acting chemically upon it; gaseous elements other than chlorine dissolve to a very small extent. All other elements may be said to be insoluble in water, although some of them, like potassium and fluorine (p. 21), decompose water, yielding soluble products. Of compound substances those belonging to the class of bodies of which common salt and saltpetre are examples (Salts, p. 92) are those which most generally dissolve in water. When common saltpetre (nitre or nitrate of potash) is shaken with water, it is rapidly dissolved, the water becoming sensibly colder. If fresh portions of saltpetre are added till the water is unable to dissolve any more, it is found that 100 grams of water (at 15-5°) have dissolved about 30 grams of saltpetre. Such a solution is a cold saturated solution of saltpetre. If the solution be set aside in an open vessel, the water will slowly pass off in vapour, and the saltpetre will be gradually deposited, its particles arranging themselves in the regular geometrical shape of the six-sided prism, which is its common crystalline form. The crystals of saltpetre do not contain any water ; they are anhydrous. If saltpetre is added to boiling water, and stirred (with a glass rod) until the water (kept at 100° by standing the vessel in a bath of boiling water) refuses to dissolve any more, 100 grams of water is found to have dissolved about 240 grams ; this is a hot saturated solution. As a general rule, solids are dissolved more quickly and in larger quantity by hot water than cold. Some calcium salts are exceptions. Attention must be called to two characteristics of the solution of salt- petre which are easily verified. One is that the composition of the solution is the same throughout ; from whatever part of the solution a cubic centi- metre, say, is removed, on evaporating the water from the portion the same weight of the saltpetre remains ; the solution is homogeneous. The other characteristic is that so long as dissolution of the saltpetre can be continued, that is, until the solution becomes saturated at the temperature prevailing, the water dissolves the saltpetre in any proportion, there is no interruption in the continuity of the dissolution, or no definite proportions such as are always detected in chemical combination. These two characteristics, which are shared by all other solutions, lead to a definition of a solution as a homogeneous mixture whose composition can be varied continuously up to the saturation point for the prevailing temperature. Although this definition regards a solution as a mixture, there is a differ- ence between a solution and a mechanical mixture, which appears at once from the definition. Two substances can be mechanically mixed in any proportion (p. 2), so that the limitation of the possibility of dissolving salt- petre in water is at variance with the main feature of a mechanical mixture. Again, in examining the properties of the solution, the specific gravity for example, it is found that they are not the mean of the properties of water and saltpetre. If substance A of sp. gr. 2 is mixed in the proportion of 10: 3 by weight with sub- stance B of sp. gr. 3, the specific gravity of the mixture is the mean, 2-17 ; but when 10 grams of water (sp. gr. 1) dissolve 2 grams saltpetre (sp. gr. 2-1), the specific gravity of the solution is 1-136, not the mean, 1-096 ; therefore a contraction has taken place. The term “solution ” is applicable not only to solutions of solids in liquids, but also to those of gases in liquids, gases in solids (p. 97), liquids in liquids, liquids in solids, solids in solids. It should be noted that the definition covers all these cases 38 SOLVENT—SOLUTE—SOLUBILITY and that it recognises some relation to chemistry in the word ‘* homogeneous,” while the physical aspect appears in the words “ mixture ” and “ varied continuously.” The substance which does the dissolving is commonly called the “ solvent,”’ and the substance which is dissolved the “ solute.” These terms have no absolute value, as may be seen in such a case as that of water and phenol. If 1 part phenol be mixed with 20 parts water, a clear liquid is formed and the phenol is said to dissolve in the water ; if equal parts be shaken together, no clear solution can be obtained ; if 1 part water be mixed with 20 parts phenol a clear liquid results, and then the water is said to dissolve in the phenol. The solubility of a solid or liquid substance, or the degree to which a substance is soluble, in a given liquid, is usually expressed by the number of grams of solvent required to dissolve one gram of the substance. It varies with the temperature. The following abbreviation is convenient: Soleotay 1 in 13-5 water ; 7.e. 1 gram of the substance is soluble in 13-5 grams of cold water. Sol,;° 1 in 7-9 alcohol; i.e. 1 part by weight of the substance is dissolved by 7-9 parts by weight of alcohol at 15°. Water does not always dissolve a substance in such a manner that the substance can easily be recovered from the solution, as in the case of potas- sium nitrate just cited, but not infrequently reacts with the substance chemically, so that on crystallisation or evaporation a solid having new properties is obtained; e.g. sodium oxide, Na,O, dissolves in water with the evolution of much heat, and on evaporation a residue of sodium hydroxide NaOH (Na,O. H,0), is left, from which the water cannot be expelled even at a red heat. A full chemical reaction has occurred. So also with quicklime, CaO (see pp. 1, 389), but the water can be expelled below a red heat. An intermediate effect obtains with many substances. If crystals of sodium carbonate (washing soda) are heated, they melt, boil and dry down to an opaque white mass. The composition is unchanged except that water has been expelled. If now some of this white anhydrous sodium carbonate, Na,.CO, (powdered), be stirred into a little cold water it forms hard agglom- erations, which dissolve only slowly with evolution of heat. If some of the original crystals (powdered) be similarly treated, they dissolve rapidly with absorption of heat. On evaporating either of these solutions till a pellicle (Lat. pellicula = thin skin) forms on the surface, and setting aside to cool, clear crystals of washing soda form, containing 37-04% Na,CO, and 62:96% H,0, or Anhydrous sodium carbonate (Na,CO,) 106 parts, or one molecule ; Water (10H,O) 180 ,, or ten molecules, as expressed by the formula Na,CO;. 10H,O. Water thus associated with a substance in the formation of crystals is called water of crystallisation and always occurs in molecular proportions (see also chapter on General Principles). Water associated with a substance but not accompanied by crystal formation is not water of crystallisation. Similar observations can be made with sodium sulphate, Na,SO, and Na,S0O,.10H,0; copper sulphate, CuSO, and CuS0,.5H,0; calcium chloride, CaCl, and CaCl,.6H,O and many other substances. Thus it appears that the process of dissolving such a substance as anhy- drous sodium carbonate involves at least two stages: (a) union with a definite proportion of water to form the hydrated salt, (b) dissolution of the hydrated salt. It is very probable that the latter stage involves a loose combination of still more water with the hydrated salt; so also potassium nitrate, common salt and many others whose ordinary crystals are anhydrous are not altogether chemically free when in solution, for at low temperatures WATER OF CRYSTALLISATION 39 they crystallise with water, e.g. NaCl.2H,O at —12° (not to be confused with cryohydrates, q.v.). It is remarkable that the vqlume occupied by crystals containing water of crystal- lisation is exactly that which the water alone would occupy if it were in the form of ice. Thus, in the case of washing soda: Na,CO, = 106, 10H,O = 180-16, total = 286-16 ; hence 286:16g. Na,CO;.10H,O has the same volume as 180-l6g. ice ; knowing the molecular weight (M), and thence the weight of the water of crystallisation, the volume (V) of the ice represented can be calculated, and hence the specific gravity (M + V) of the crystals, whence the specific gravity of the soda crystals ig se a = 1-457. The specific heat of these hydrates is also in conformity with the water existing in them in the solid form. Temperature and other conditions have very marked influence in determining the form and degree of hydration of crystals. See phase rule (p. 337). The colour of a substance is frequently dependent on water of crystallisation ; e.g. blue-stone, copper sulphate, CuSO,4.5H,0, loses its blue colour and transparency on drying at 100°, becoming the white opaque, monohydrated salt, CuSO,.H,O. On moistening this the characteristic blue colour returns, due to re-formation of CuSO,4.5H,0. To ascertain whether a small globule of liquid is, or contains, water, add a speck of dried copper sulphate, when the blue colour will appear if water is present (p. 36). Several of the so-called sympathetic inks employed for writings which are invisible until heated, depend upon the change of colour produced by loss of water of crystalli- sation. Characters written with a weak solution of cobalt chloride and allowed to dry, are very nearly invisible, since the pink colour of so small a quantity of the salt is scarcely noticed ; but on warming the paper, the pink hydrated chloride of cobalt (CoCly.6Aq) loses water of crystallisation, and the blue chloride with one molecule of water is produced. On exposure to air this again absorbs water, and the writing fades away. : Some salts have so great a tendency to combine with water that they become moist and ultimately deliquesce (Lat. deliquesco=to melt away) when exposed to air. This deliquescence is exhibited in a marked degree by calcium chloride, and its great attraction for water is turned to advantage in drying air and other gases by passing them through tubes filled with the salt. Generally, deliquescent substances are capable of crystallising with water, although not always readily under normal conditions. Substances which absorb moisture from the atmosphere without liquefying (or, as with sulphuric acid, without changing their state) are hygroscopic (Gr. dypdc = wet, oxoréw = to observe). Some crystals, e.g. washing soda, gradually lose some, or all, of their water of crystal- lisation on exposure to the atmosphere, simultaneously losing their crystalline form and becoming covered with a white powder, the more or less anhydrous salt ; they are said to effloresce (Lat. = to begin to blossom). This shows how very loose the com- bination of the water with the salt is in some crystals. “Water of crystallation”’ is sometimes applied only to that portion which is expelled at 100°, while any water which remains in combina- tion above 100° is termed water of constitution. This definition is not satisfactory. Water of constitution may be more logically regarded as including (a) that which enters chemically to form an altogether new molecule, ‘e.g. Al(OH),, (Al,03.3H,O); (6) that which can be exchanged molecularly for some salt or group of elements; e.g. ordinary crystals of magnesium sulphate have the formula: MgSO,.7H,0 and leave on drying at temperatures below 200° (but above 100°) a powder having the composition : MgSO,.H,O. Moreover, MgSO,.6H,0 and MgSO,.2H,0 exist. It is not easy to decide how much is to be regarded as water of crystallisation and how much as water of constitution ; but several compounds of the typé, MgSO,.K,S0,.6H,O are known, and correspond with MgSO,.H,0.6H,0 ; further, one H,O is much more difficult to expel than any of the others. 40 CRYSTALLOGRAPHY and therefore must be differently combined ; hence this one H,O may be regarded as water of constitution. CRYSTALS, CRYSTALLISATION.—A crystal is a solid body of more or less symmetrical form, bounded by plane surfaces. Asa rule it is produced by separation from solution, by solidification of a body in the melted state or by sublimation. : The commonest method of crystallising a saline substance consists in dissolving excess of it in hot water and allowing the solution to cool slowly. At a certain stage the substance begins to separate in the crystalline form and continues to do so so long as the solution contains excess at the new temperature. The more slowly it cools, the larger and more perfect are the crystals. A hot saturated solution is not generally the best for crystallising, because it deposits the dissolved body too rapidly. Thus the hot solution of saltpetre prepared as above (p. 37) would solidify to a mass of minute crystals on cooling ; but if 100 grams of saltpetre be dissolved in 120 c.c. of boiling water, it will form crystals of 2 or 3 inches long when slowly cooled (in a covered vessel). If the solution is stirred while cooling, the crystals are very minute, having the appearance of a white powder. Some solids, however, refuse to crystallise, even from a hot saturated solution, if during cooling it be kept absolutely undisturbed. Sodium sulphate affords a good example of this. When the crystallised sulphate is added to boiling water in a flask, as long as it is dissolved, the water takes into solution more than twice its weight of the salt, yielding a solution which boils at 104:5°. If this solution is allowed to cool in the open flask, an abundant crystallisation occurs, for cold water dissolves only about one-third of its weight of crystallised sulphate. But if the flask (which should be globular) be tightly corked whilst the solution is boiling, the solution may be kept for several days without crystallising, although moved about from one place to another. In this condition the solution is said to be swper-saturated. On withdrawing the cork, the air entering the partly vacuous space above the liquid will be seen to disturb the surface slightly, and from that point beautiful prismatic crystals shoot through the liquid until the whole has become a nearly solid mass. A considerable rise of temperature is observed, consequent upon the passage from the liquid to the solid form. If the solution of sodium sulphate be somewhat weaker, con- taining exactly two-thirds of its weight of the crystals, it may be cooled without crystal- lising, even in vessels covered with glass plates ; but a touch with a glass rod will start the crystallisation immediately. The crystallisation of a supersaturated solution is provoked by contact with a crystal of the salt itself. Minute crystals of sodium sulphate are present in the floating dust of the air, and cause the crystallisation when they fall into the supersaturated solution. A perfectly clean glass rod may be dipped into the liquid without causing crystallisation, but a rod which has been exposed to air will have some particles of sodium sulphate on it, and will start crystallisation ; if the rod be heated so as to render the sodium sulphate from the dust anhydrous, it will no longer cause crystallisa- tion unless it be drawn through the hand. Air filtered through cotton-wool does not cause supersaturated solutions to crystallise. If the solution of sodium sulphate con- taining two-thirds of its weight of the crystals be allowed to cool in a flask closed by a cork furnished with two tubes plugged with cotton-wool, it will be found that, on withdrawing the plugs and blowing through one of the tubes dipping into the solution, no crystallisation occurs ; but if air be blown by a pair of bellows into the same solution, it crystallises at once (p. 73). Sodium hyposulphite (thiosulphate) and sodium acetate yield supersaturated solu- tions which are less likely to be crystallised by dust than the sodium sulphate. If a warm supersaturated solution of sodium acetate be very carefully poured upon a cold super- saturated solution of sodium hyposulphite, in a narrow cylinder, which is then covered and allowed to cool, a crystal of the hyposulphite may be dropped in without causing crystallisation till it touches the lower layer of hyposulphite solution; a crystal NATURAL WATERS 41 of sodium acetate may then be dropped in to start the crystallisation of the upper layer. Supersaturated solution of sodium acetate is used in railway foot-warmers, where the heat evolved in the crystallisation renders it four times as efficacious as the same volume of hot water. A most beautiful illustration of the power of unfiltered air to start crystallisation is afforded by a solution of alum which has been dissolved in half its weight of water at 90° and allowed to cool in a flask, the mouth of which is closed by a plug of cotton- wool. In this state it may be kept for weeks without crystallising, but, on withdrawing the plug, crystallisation is seen to start at a few points on the surface immediately under the opening of the neck, and to spread slowly from these, octahedral crystals of alum of half an inch or more in diameter being built up in a few seconds, the tempera- ture, at the same time, rising very considerably. In the laboratory, stirring is often resorted to in order to induce crystallisation, if it does not occur spontaneously. Thus it is usual to test for potassium in a solution by adding tartaric acid, which should cause the formation of minute crystals of hydro- potassium tartrate (cream of tartar), but the test seldom succeeds unless the solutions are briskly stirred together with a glass rod. The classification of crystals and crystallography generally are referred to on p. 336. WATER FROM NATURAL SOURCES.—Pure water is not found in nature. Rain is the purest form of natural water, but contains certain gases which it collects from the atmo- sphere during its fall. As soon as it reaches the earth it begins to dissolve small portions of the various solid materials with which it comes in con- tact, and thus becomes charged with salts and other substances to an extent varying, of course, with the nature of the soils and rocks which it has touched. Sea water contains a very large proportion of saline matters. : When a quantity of rain, spring, — river, or sea water is boiled in a flask furnished with a tube also filled with water, and passing under a gas cylinder standing in a trough of the same water (Fig. 37), it will be found to give off a quantity of gas which was previously held in solution by the water, and is now set free because gases are less soluble in hot than in cold water. The quantity and nature of this gas varies according to the source of the water, but it usually includes the gases existing in atmospheric air, viz. nitrogen, oxygen, and carbonic acid gas. One gallon of rain water will generally furnish about 4 cub. in. of nitrogen, 2 cub. in. of oxygen, and 1 cub. in, of carbonic acid gas. It is worthy of remark that the nitrogen and oxygen have been dissolved by the water, not in the proportions in which they exist in the atmosphere, but in proportions according with the laws of partial pressures, showing that they exist in the air in the condition of mere mechanical admixture (see p. 2). The oxygen thus carried down from the air by rain appears to be serviceable in maintaining the respiration of aquatic animals, and in conferring upon river waters a self-purifying power, by acting upon certain organic matters which would prove hurtful to animals, and converting them into harmless products of oxidation. In the cases of rivers contaminated with the sewage of towns, this action of the dissolved oxygen is of great importance. The carbonic acid dissolved in rain water also serves some useful porposes in the chemical economy of nature (see Carbonic Acid). Rain water usually contains 2 parts of 42 DRINKING WATERS ammonia and 1 part of nitric acid in 2,000,000, but considerably more in the vicinity of towns. Ordinary water for drinking, domestic, steam-boiler and other economic purposes is generally supplied by lakes, rivers, wells, and springs. The chief desiderata are that it shall be free from such bacteria and sub- stances as may be prejudicial to health, and shall contain as little dissolved mineral matter as possible, especially such as constitute hardness, i.e. soap-destroying properties, or are likely to form incrustations in boilers. It is outside the scope of this work to deal with “water analysis,” but a few remarks may be of interest to the general reader. Itis very important to have some knowledge of the origin of the supply, particularly with reference to its possible contamination with sewage or manure and its subsequent history as it drains through the subsoil into the well or directly into the river. Merely to know the proportions of the constituents is not sufficient to decide on the sanitary fitness of a water. Only after long study and experience can one rightly interpret the observations. That a water contains a, little ammonia is nothing in itself, but its presence is presumptive evidence of recent sewage contamination. During percolation through the soil the ammonia becomes oxidised to nitrites and subsequently to nitrates, and experience shows that the causes which contribute to this also destroy injurious organisms, so that when this conversion is complete, the water will probably be innocuous. In streams, the purification is largely by atmo- spheric and bacterial influence. Sodium chloride indicates sewage unless its presence can be otherwise accounted for. The organic matter contained in water may be vegetable matter dissolved from the earth with which it has come in contact, or due to the decomposition of plants, or it may be animal matter derived either from the animalcules and fish naturally existing in it, or from the sewage of towns, and, in the case of well waters, from surface drainage. A few analyses are displayed in the following Table ; the first four lines are from the Metropolitan Water Board’s report for 1910, the next two fronr Sutton’s “ Volu- metric Analysis.” Parts PER 100,000 & - g 4% Hardness nD 3 so 2 = HOO] = leslesles| 2 | Seales 9 gf d0]-3 S/-4 ow] -Z Qe vn gd s Pe ea ooldo a9 Oo aid 3 q i @ |HS/ZSIES| Ss [eS e/Sol a] al & S$ |He(/S5/08| S [Seside|/ se] a] 2 a |@ |< Be 8 SB | E! q oO oO oO a] Thames: raw water | 35-40|.0066|-0166] -23 | 1-71 | -2402 |23-00|23-40] 6-48|16-92 oe filtered ,, | 34-32]-0003]-0067| -22 | 1-72 | -0889 |21-64/21-94} 7-87|14-07 Kent Wells: highest | 58-10]-0105)-0018] -92 | 5-82 | -0111 |26-45]38-50|15-42123-08 lowest. | 29-60] 0 |-0007] -15 | 1-03 | -0041 |21-92/19-19] 4-49]15-70 Sea water .. . [8898-7] -005) — |-033 |1975-6] — | — |796-9|748-0/48-9 Sewage (varies from very foul to nearly pure water) . | 72-2)5-520) — |-003 | 10-66} — —}—-—-)}-|- The palatability of a water is largely dependent upon the quantity of dissolved gas which it contains. Thus, a water which is agreeable for drinking becomes insipid after it has been boiled and the dissolved air in this way expelled (p. 30). The presence of dissolved solid matter in the water HARD AND SOFT WATERS 43 also influences its taste, preference being generally expressed for those waters which are not exceedingly poor in such solids; it is undesirable, however, that the quantity should exceed 50 parts per 100,000 (Thames water, as sup- plied to the metropolis, contains about 35 parts per 100,000). Household experience has established a classification of the waters from natural sources into soft and hard waters—a division which depends chiefly upon the manner in which they act upon soap. If a piece of soap be gently rubbed in soft water (rain water, for example) it speedily furnishes a froth or lather, and its cleansing powers can be readily brought into action ; but if a hard water (spring water) be substituted for rain water, the soap must be rubbed for a much longer time before a lather can be produced, or its effect in cleansing rendered evident ; a number of white curdy flakes also make their appearance in the hard water, which were not seen when soft water was used. The explanation of this difference is a purely chemical one. Soap is formed by the combination of a fatty acid with an alkali; it is manufactured by boiling oil or fat with potash or soda, the former for soft, the latter for hard soaps. In the preparation of ordinary hard soap, the soda takes from the oil or fat two acids—stearic and oleic acids—which exist in abundance in most varieties of fat, and unites with them to form soap, which in chemical language would be spoken of as a mixture of stearate and oleate of sodium. When soap is rubbed in soft water until a little of it has dissolved, and some Epsom salts (magnesium sulphate) is dissolved in water, and poured into the soap water curdy flakes are produced, as when soap is rubbed in hard water, and the soap water loses its property of frothing when stirred ; the magnesium sulphate has decomposed the soap, forming sodium sulphate, which remains dissolved in the water, and insoluble curdy flakes, consisting of stearate and oleate of magnesium. Similar to the effect of the magnesium sulphate is that of hard waters ; their hardness is attributable to the presence of the different salts of calcium and magnesium, all of which decompose the soap in the manner exemplified above ; the peculiar properties of the soap in forming a lather and dissolving grease can therefore be manifested only when a sufficient quantity has been employed to decompose the whole of the salts of calcium and magnesium contained in the quantity of water operated on, and thus a considerable amount of soap must be rendered useless when hard water is employed. Thus the hardness of a water is a measure of its soap-destroying powers, and is determined by ascertaining the quantity of a soap solution of known strength required to produce a lather in 100 c.c. of the water. The hard- dess may also be determined acidimetrically. On examining the interior of a kettle in which spring, well, or river water has been boiled, it will be found to be coated more or less thickly with a fur or incrustation, generally of a brown colour, and the harder the water the more speedily will this incrustation be deposited. A chemical examination shows this deposit to consist chiefly of calcium carbonate (chalk) in the form of minute crystals, which may be discovered by the microscope ; it usually contains, in addition, some magnesium carbonate, calcium sulphate, and small quantities of oxide of iron (rust) and vegetable matter, the last two substances imparting its brown colour. In order to explain the formation of this deposit, it is necessary to become acquainted with the particular condition in which the calcium carbonate exists in natural waters ; it is hardly dissolved to any perceptible extent by pure water, though it may be dissolved in considerable quantity by water containing carbonic acid. This statement, which is of great importance in connection with natural waters, may be verified in the following manner: A little slaked lime is well shaken 44 BOILER INCRUSTATIONS up in a bottle of distilled or rain water, which is afterwards set aside for an hour or two ; as soon as that portion of the lime which has not been dissolved has subsided, the clear portion is carefully poured into a glass, and a little solution of carbonic acid in water (soda water) is added to it; the first addition of the carbonic acid to the lime water causes a milkiness, due to the formation of minute particles of calcium carbonate ; this being insoluble in the water, separates from it, or precipitates, and impairs the transparency of the liquid; a further addition of carbonic acid water renders the liquid transparent again, for the carbonic acid dissolves the calcium carbonate which has separated. If this clear solution is introduced into a flask, and boiled over the spirit- lamp or gas-flame, it again becomes turbid, for the free carbonic acid is expelled by the heat, and the calcium carbonate is deposited, not now, however, in so fine a powder as before, but in small, hard grains, which have a tendency to fix themselves firmly upon the sides of the flask, and, when examined by the microscope, are seen to consist of small crystals. In a similar manner, when natural waters are boiled, the carbonic acid gas which they contain is expelled, and the carbonates of calcium, magnesium, and iron are precipitated, since they are insoluble in water which does not contain carbonic acid. But, by the ebullition of the water, a portion of it has been dissipated in vapour, and if there be much calcium sulphate present, the quantity of water left may not be sufficient to retain the whole of the salt in solution ; calcium sulphate requires about 500 parts of cold water to dissolve it, and is nearly insoluble in water having a higher temperature than 100°, as would be the case in boilers worked under pressure, so that it would readily be deposited. It contributes much to the formation of com- pact incrustations. Should the water contain much vegetable matter, this is often deposited in an insoluble condition, the whole eventually forming together a hard compact mass, composed of successive thin layers, on the bottom and sides of the vessel in which the water has been boiled. The “ furring ” of a kettle is objectionable, chiefly in consequence of its retarding the ebullition of the water, since the deposit is a very bad conductor of heat, and there- fore impedes the transmission of heat from the fire to the water ; hence the common practice of introducing a round stone or marble into the kettle, in order, by its per- petual rolling, to prevent the particles of calcium carbonate from forming a compact layer. In steam-boilers, however, even more serious inconvenience than loss of time sometimes arises if this deposit be allowed to accumulate, and to form a thick layer of badly conducting material on the bottom of the boiler, since the latter is then liable to become red-hot and to collapse. But even though this calamity be escaped, the wear and tear of the boiler is very much increased in consequence of the formation of this deposit, since its hardness often renders it necessary to detach it with the hammer, much to the injury of the iron boiler-plates, which are also subject to increased oxida- tion and corrosion in consequence of the high temperature which the incrustation permits them to attain by preventing their contact with the water. Moreover, it is obvious that a greater expenditure of fuel is requisite in order to heat the water through such a non-conducting “boiler scale.” Many propositions have been brought forward for the prevention of these incrustations ; some substances have been used, of which the action appears to be purely mechanical, in preventing the aggregation of the deposited particles. Clay, sawdust, and other matters have been employed with this view ; but the action of sal ammoniac (ammonium chloride), which has also been found efficacious, must be explained upon purely chemical principles. When this salt is boiled with calcium carbonate, mutual decomposition ensues, producing calcium chloride and ammonium carbonate, of which salts the former is very soluble in water, while the latter passes off in vapour with the steam. The ammonium chloride, however, corrodes the metal of the boiler. Solutions of the caustic alkalies, of alkaline carbonates, arsenites, tannates, &c., are also occasionally employed to prevent the formation of incrustations TEMPORARY AND PERMANENT HARDNESS 45 in boilers, and probably act by precipitating calcium carbonate and other calcium compounds which act as nuclei, around which the fur collects as a loose deposit or mud. The deposit formed in boilers fed with sea water consists chiefly of calcium sulphate and magnesium hydrate, the latter produced by the decomposition of the magnesium chloride present in sea water. As hydrochloric acid is another product of the decom- position of magnesium chloride solution, water containing any considerable quantity of this salt is liable to corrode the plates of a boiler. The incrustations formed in cisterns and pipes by hard water are also produced by the carbonates of calcium and magnesium deposited in consequence of the escape of the free carbonic acid which held them in solution. Many interesting natural pheno- mena may be explained upon the same principle. The so-called petrifying springs, in many cases, owe their remarkable properties to the considerable quantity of calcium carbonate dissolved in carbonic acid which they contain ; when any object—a basket, for example—is repeatedly exposed to the action of these waters, it becomes coated with a compact layer of the carbonate, and thus appears to have suffered conversion into limestone. The celebrated waters of the Sprudel at Carlsbad, of San Filippo in Tuscany, and of Saint Allyre in Auvergne are the best instances of this kind. The stalactites and stalagmites,’ which are formed in many caverns or natural grottoes, afford beautiful examples of the gradual separation of calcium carbonate from water charged with carbonic acid. Each drop of water, as it trickles through the roof of the cavern, becomes surrounded with a shell of calcium carbonate, the length of which is prolonged by each drop, as it falls, till a stalactite is formed, varying in colour accord- ing to the nature of the substances which are separated from the water together with the carbonate (such as the oxides of iron and vegetable matter); and as each drop falls from the point of the stalactite upon the floor of the cavern, it deposits there another shell, which grows, like the upper one, but in the opposite direction, and forms a stalagmite, thus adorning the grotto with conical pillars of calcium carbonate, some- times, as in the case of the oriental alabaster, variegated with red and yellow, and applicable to ornamental purposes. When water which has been boiled for some time is compared with un- boiled water from the same source, it is found to have become much softer, and this can now be easily explained, for, a considerable portion of the salts of calcium and magnesium having separated from the water, the latter is not capable of decomposing so large a quantity of soap. The amount of hardness which is thus destroyed by boiling is generally spoken of as temporary hard- ness, to distinguish it from the permanent hardness due to the soluble salts of calcium and magnesium which still remain in the boiled water. It is customary with analytical chemists, in reporting upon the quality of natural waters, to express the hardness by a certain number of degrees which indicate the number of grains of chalk or calcium carbonate which would be dissolved in a gallon of water containing carbonic acid, in order to render its hardness equal to that of the water examined ; that is, to render it capable of decom- posing an equal quantity of soap. Thus, when a water is spoken of as having 16° of hardness, it is implied that 16 grains of calcium carbonate dis- solved in a gallon of water (22°8 parts per 100,000) containing carbonic acid, would render that gallon of water capable of decomposing as much soap as a gallon of the water under consideration. The utility of water for household purposes must be estimated therefore, not merely according to the total number of degrees of hardness which it exhibits, but also by the proportion of that hardness which may be regarded as temporary ; that is, which disappears when the water is boiled. Thus, the total hardness of the Thames water amounts to nearly 14°, and yet the London water-supply is quite applicable to household uses, since its hardness is reduced by boiling to about 5°. It has been ascertained that every degree of hardness in water gives rise to a waste of about 10 grains 1) From oyaAdSw, J drop ; otdAayye, a drop. 46 WATER SOFTENING of soap for every gallon of water employed, and hence the use of 100 gallons of Thames water in washing will be attended with the loss of about 2 Ib. of soap ; this loss is reduced, however, to about one-third when the temporary hardness has been destroyed by boiling. The addition of washing soda (sodium carbonate) removes the permanent hardness due to the presence of the sulphates of calcium and magnesium in the water, for both these salts are decomposed by the sodium carbonate which separates the calcium and magnesium as insoluble carbonates, whilst sodium sulphate remains dissolved in the water.! The household practice of boiling the water and adding a little washing soda is therefore very efficacious in removing the hardness. Clark’s process for softening waters depends upon the neutralisation of the free carbonic acid contained in the water by the addition of a certain quantity of lime; the calcium carbonate so produced separates together with the carbonates of calcium and magnesium, which were previously retained in solution by the free carbonic acid ; this process,. therefore, affects chiefly the temporary hardness ; moreover, the earthy carbonates which are separ- ated appear to remove from the water a portion of the organic matter which it contains, and thus effect a very important purification. The water under treatment is mixed in large tanks, with a due proportion of lime or lime-water (the quantity necessary having been determined by preliminary experiment) and the mixture allowed to settle until perfectly clear, when it is drawn off into reservoirs.” Waters which are turbid from the presence of clay in a state of suspension, are sometimes purified by the addition of a small quantity of alum or of aluminium sulphate, when the alumina is precipitated by the calcium car- bonate present in the water, and carries down with it mechanically the suspended clay, leaving the water clear. One of the most important points to be taken into account in estimating the qualities of a water is its action upon lead, since this metal is so generally employed for the storage and transmission of water, and cases frequently occur in which the health has been seriously injured by repeated small doses of compounds of lead taken in water which has been kept in a leaden cistern. If a piece of bright, freshly scraped lead be exposed to the air, it speedily becomes tarnished from the formation of a thin film of the oxide of lead, produced by the action of the atmospheric oxygen ; this oxide of lead is soluble in water to some extent, and hence, when lead is kept in contact with water, the oxygen which is dissolved in the latter acts upon the metal, and the oxide so produced is dissolved by the water ; but fortunately, different waters act with very different degrees of rapidity upon the metal, according to the nature of the substances which they contain. The film of oxide which forms upon the surface of the lead is insoluble, or nearly so, in water containing much sulphate or carbonate of calcium, so that hard waters may generally be kept without danger in leaden cisterns, but soft waters, and those which contain nitrites or nitrates, should not be drunk after contact with lead. Nearly all waters which have been stored in leaden cisterns contain a trace of the metal, and since the action of this poison, in minute doses, upon the system is so gradual that the mischief is often referred to other causes, it is much to be desired that lead should be discarded altogether for the construction of cisterns (see Lead). To detect lead in a water, fill a glass tumbler with it, place this on white paper, add a drop or two of diluted hydrochloric acid and some hydrosulphuric acid ; a dark brown tinge will be seen on looking through the water from above if lead is present. Mineral waters cannot be classified by any specific distinction from ordinary waters, for some so-called mineral waters contain less saline matter than the average domestic supply. The characters commonly associated with the term are: (a) a large proportion of mineral constituents; (b) the occurrence of some peculiar salt, e.g. a CaSO, + Na,CO3 = Na,SO, + CaCO3 : Calcium sulphate Sodium carbonate Sodium sulphate Calcium carbonate, Thames water is softened, in this way, to 3°5°, or to a lower point than by boiling. MINERAL WATERS 47 lithium salts or arsenic, or of some gas, e.g. sulphuretted hydrogen ; (c) a more or less high temperature of the water at its source. The reason of the temperature is uncertain, but in numerous cases it appears to be derived from internal terrestrial heat. Mineral springs occur in nearly all localities, especially in those of past or present volcanic activity ; in flat low-lying countries they are few, in Holland absent. Almost every element has been discovered in them, the occurrence depending on the composition of the strata with which the water has been in contact. Calcium, magnesium and sodium as carbonates, sulphates.and chlorides are the most frequent constituents. Free carbon dioxide is present in the majority, in some the quantity is more than equal to 1} times the volume of the water; then in order, nitrogen, oxygen, sulphuretted hydrogen, carburetted hydrogen and ammonia gases. The waters at Bath contain traces of radium, helium (0-1 per cent. of the dissolved gases), argon, nitrogen, and carbon dioxide gases, and calcium sulphate. Temperature about 130° F. Classification according to the nature of the predominating constituent, such as the following, is generally adopted. The temperatures of the different kinds of springs vary from cold to the maximum given. Saline (sodium chloride), 160° F.; earthy (calcium salts, &c.),140° F. ; alkaline (sodium carbonate), 170° F. ; chalybeate (usually 0-03 to 0-15 gram per litre ferrous carbonate with considerable amount of carbon dioxide ; they become brown on exposure to air, absorbing oxygen and precipitating ferric hydrate), all cold ; sulphur (sulphuretted hydrogen), 140° F. ; arsenical (traces to 0-01 gram arsenious acid per litre). The following Table is from the new “ Encyclopedia Britannica,” where a useful general résumé of the subject is to be found; see also Squire’s ‘‘ Companion to the British Pharmacopeeia.” Alkaline |Chalyb oa Purgi . aline alybeate ix-la- Urgin Parts per 1000 ce moe Vichy Schwal- Chapelle Hanya (105°8° F.)| bach ee Jénos Sodium bicarbonate . —_— — 4-883 0-0206 | 0-6449 —_ Potassium 3 ‘ — — 0-352 — — _ Magnesium 33 ‘ 0-45 0-017 0-303 0-2122 | 0-0506 — Calcium 35 4 2-38 1-06 0-434 0-2213 | 0-157 — Sodium sulphate é — _— 0-292 0-0079 | 0-2831 15-9 Potassium ,, : = = = 0-0037 | 0-1527 —_ Magnesium ,, : 2-96 0-588 —_ —_— —_ 16-0 Calcium sy, 3 0-25 0:389 —_— _— — _ Sodium sulphide : — _ — — 0-0136 _ Sodium chloride : 25-21 5°52 0-534 —_ 2-616 1:3 Potassium ,, — 0-286 — —_— = —_— Magnesium ,, 3 3-39 0-303 — _— — = Ferrous carbonate . — 0-277 _— 0-0837 _— = Silicie acid ‘ : — —= — 0-0320 — _— Gases ; Carbon dioxide = 3-19 2-6 5-35 _— 0-45 Sulphuretted hydrogen _ _— — _— trace _— Bromides and iodides also occur in sea water and not infrequently in other natural waters. The circumstance that clothes wetted with sea water never become perfectly dry is to be ascribed chiefly to the magnesium chloride present in the water, which is distinguished by its tendency to deliquesce or become damp in moist air. AIR AIR (from an Indo-European root meaning to breathe) is the gaseous mix- ture which we breathe and constitutes the ATMOSPHERE (dros, vapour, caipa, a sphere), the aeriform spheroid enveloping the earth. The word ‘air’ was used in the eighteenth century in the sense of our general word “gas.” Gas is a word derived by van Helmont (5. 1577, d. 1644) from yaog (= atmosphere). The history of the development of our knowledge of the composition of air is of great interest, the more particularly as, in view of the fact that it is only within the last twenty years that the existence of certain constituents of air has been discovered, it cannot be said that even now we are fully acquainted with this commonest form of matter. Galileo (Italian, b. 1564, d. 1642) established the material nature of air by observing the increase in weight of a copper globe filled with compressed air. His pupil, Torricelli (Italian, b. 1608, d. 1647), studied the pressure exerted by the atmosphere and invented the barometer (Bapos, weight (pressure) ; erpor, measure). The space above the mercury is still known as the “ Torri- cellian vacuum.” John Mayow (English, 6. 1645, d. 1679) in 1674 showed that air contains two kinds of aerial particles; the one supports com- bustion and life, converting venous blood into arterial, and combines with metals to form calces (Lat. cala = chalk ; an old term for the ash or powder produced by the calcining of certain metals in air); the other has not such properties. He also showed that the first kind exists in nitre, by demonstrating qualitatively and quantitatively the identity of the pro- duct obtained by burning antimony in air with that prepared by the action of the “ acid of nitre ”’ on the metal. Probably owing to his early death, Mayow’s truly scientific work was soon lost sight of, and it was only gradually during the seventeenth and eighteenth centuries that the composite nature of air was recognised. Unhappily, accurate conceptions of experimental chemistry were impossible during this period on account of an almost universal acceptance of the phlogiston theory of Stahl (b. 1660, d. 1734). He assumed phlogiston to be the characteristic constituent of all combustible bodies ; it escaped or was withdrawn when bodies were burnt or metals calcined (oxidation), and returned or was added on reproducing the metal (reduction). Stahl applied his theory to explain all kinds of reactions, even that respiration and organic decomposition are comparable with combustion. The reduction of a “calx,” eg. tin “calx,” by heating it with coal (rich in phlogiston) was explained by saying that phlogiston passed from the coal and combined with the tin “ calx ” to produce tin ; thus tin was supposed to be a compound of tin “calx” and phlogiston. Similarly, sulphur, producible from sulphuric acid and coal, was composed of the acid and phlogis- ton. This was all utterly at variance with experimental evidence, for it was well known that the calx of tin weighed more than the metal from which it was generated (cf. experiment with copper, p. 2), and that sulphur yielded more than its own weight of sulphuric acid. It was considered unnecessary to prove the actual existence of phlogis- ton, but some assumed it to be “inflammable air ” (hydrogen) in view of calces yield- ing their metals when heated in the gas. Nevertheless, all the great chemists of the day until near the end of the eighteenth century were blind to the significance of their own brilliant investigations by reason of this doctrine. In 1772 Rutherford noticed that when animals remained for some time in a confined volume of air that a quantity of “fixed air” (carbon dioxide) was produced, as shown by the clouding of lime water, and that after the latter had removed the fixed air the remaining “ mephitic air” (nitrogen) 48 AIR—HISTORICAL 49 would support neither combustion nor respiration, hence it was formerly called azote (a, privative; wn, life). In the same year Priestley (b. 1733, d. 1804) discovered nitrogen (‘‘ phlogisticated air,” as he called it) indepen- dently, but his conceptions were not so clear ; he burnt substances in air and then removed the ‘‘fixed air.” Priestley observed the diminution in the volume of air in which a metal is calcined. He prepared “ dephlogisticated air’’ (oxygen) by heating ‘‘ mer- curiatus calcinatus per se”’ (mercuric oxide) which in its turn had been obtained by heating mercury in air. This classic discovery was made on August 1, 1774. Heafterwards generated the gas by heating red lead, nitre, &. He found that a candle burnt in this new “air’’ with remarkable brilliancy, and that a mouse lived much longer in a small vessel of it than in the same vessel filled with ordinary air. By means of “ nitrous air”’ (nitric oxide) he concluded that it was some “ five times as good as common air”? (p. 201). Scheele (Swede, 6b. 1742, d. 1786) also obtained “‘ fire-air’’ by heating mercuric oxide in 1771, but did not publish his discovery until 1777. In further experiments he found that manganese dioxide on heating with sul- phuric acid yields the same gas. Cavendish’s (6. 1731, d. 1810) chief contribution to our knowledge of air was the establishment of its composition by the eudiometric method presently to be described. By a carefully recorded experiment he proved the presence of a constituent (argon) in the atmosphere, but he did not himself realise the true meaning of his experiment, which remained practically unnoticed for more than a century, when attention was called to it by Rayleigh and Ramsay. Notwithstanding that a fairly accurate knowledge of the constituents of the atmosphere had been attained, mystery still shrouded the nature of com- bustion and calcination, and it was left for Lavoisier (p. 3) to lift the veil. He recognised the supreme importance of proportions by weight and like Mayow attributed the increase in weight which a metal undergoes on calcina- tion in air to absorption of some portion of the atmosphere. Priestley visited Paris about 1775 and Lavoisier was deeply interested in an account of his experiments, and ultimately the mercuric oxide experiment took the follow- ing well-known form : He put in the retort (Fig. 38) 4 ounces of pure mercury, and over its delivery tube in the bath of mercury was placed a bell jar. The mercury in the retort was heated by the furnace to near its boiling-point (349°) for twelve days. A dark powder of mercuric oxide (the “‘calx ” of mercury) formed on the surface of the mercury in the retort ; on cooling it became red ; it was collected and found to weigh 45 grains. Meanwhile the volume of air in the retort and bell jar had been reduced from 50 to 42 or 43 cub, ins. The red powder was introduced into a tube, A (Fig. 39), with its delivery end beneath a graduated cylinder, D ; when strongly heated the powder yielded 41} grains metallic mercury and 7 or 8 cub. ins. of “ dephlogisticated Be). (oxygen), a quantity identical with that lost by the ordinary air in the previous experiment. 4 50 EARLY INVESTIGATION OF AIR The experiment proved conclusively that oxygen (i) is a constituent of the atmosphere ; (ii) is that which combines with mercury to form mercury calx ; (iii) possesses weight ; (iv) after separation from the mercury has the same volume as it had before union. The experiment also affords a very good example of the relation of heat to chemical action ; also of a reversible reaction, for under one set of conditions mercury and oxygen combine to form mercuric oxide and under other conditions mercuric oxide decomposes into mercury and oxygen. Lavoisier also determined the proportion of oxygen in air by an experi- ment which was substantially as follows : A fragment of phosphorus dried by careful pressure+ between blotting-paper is placed upon a convenient stand, A (Fig. 40), and covered with a tall jar, having an opening at the top for the insertion of a well-fitting stopper (which should be greased with a little lard), and divided into seven parts of equal capacity. The jar should be placed over the stand in such a manner that the water may occupy the two lowest spaces into which the jar is divided, leaving five spaces filled with air. The stopper of the jar is furnished with a hook, to which a piece of brass chain, B, is attached, long enough to touch the phosphorus when the stopper is inserted. The end of this chain is heated, and the stopper tightly fixed in its place. On allowing the hot chain to touch the phosphorus, the latter bursts into vivid combus- tion, filling the jar with thick white fumes, and covering its sides for a few moments with white flakes of phos- phoric anhydride. At the commencement of the ex- periment the water in the jar will be depressed, in consequence of the expansion of the air due to the heat produced in the burning of phosphorus, but presently, when the combustion begins to decline, the water rises, and continues to do so until it has ascended almost to the line C, so as to occupy the place of one fifth of the air employed in the experiment. The phosphorus will then have ceased to burn, the white flakes upon the sides of the jar will have acquired the appearance of drops of moisture, and the fumes will have gradually disappeared, until, in the course of half an hour, the air remaining in the jar will be as clear and transparent as before, the whole of the flakes having been absorbed by the water. The jar should now be sunk in water (the outer vessel should be deeper than shown in figure), so that the latter may attain to the same level without as within the jar ; the level should then be at C exactly. On removing the stopper, it will be found that the gas (nitrogen) in the jar will no longer support the combustion of a taper. Instead of using the stand and chain, the phosphorus may be placed in a small evaporating dish floating on the water, and ignited ; then immediately cover with the bell jar. . The white fumes or flakes consist essentially of phosphoric oxide or ‘phosphorus pentoxide, P20,; Py + 50, = 2P,0;. This substance has an extraordinarily strong affinity for water, and unites with it to form metaphosphoric acid, H,PO,; P,0; + H,O = 2HPO,. This constitutes the clear drops referred to, the water being attracted from the moisture contained in the enclosed air. Lavoisier observed this formation of phosphoric acid ; also of sulphurous acid when sulphur is similarly burnt. In 1776 he proved that the diamond burns in oxygen to carbon dioxide alone ; and in 1777 showed that carbon dioxide and water are the chief products of the combustion (p. 58) of organic substances. The principal conclusions which he drew from such work were (1) that the increase in the weight of a substance when burnt or calcined in * Phosphorus should always be handled with great caution, especially when touching it with the fingers, as immediately it is dry it is likely to take fire spontancously, and the heat of the hand may hasten this. In the event of a burn, lime-water or plain water (not oil) should be applied to the wound as first aid. Pho#- phorus is always stored under water to avoid danger. CLASSIFICATION OF OXIDES 51 air is equal to the decrease in the weight of the air; (2) that the product of burning a substance in air is usually an acid, but metals produce calces. So frequently does the product possess acid properties that he considered “oxygen” the characteristic element in acids, hence the name (é£vc, acid; yevvaw, I produce). This classification (amplified) remains to-day. (1) Acid-forming oxides or acid anhydrides,! produced when non-metals burn in air or oxygen, unite with water to form acids (p. 19), eg. phosphoric oxide or phosphoric anhydride, P,O,, yields with water metaphosphoric acid, HPO, or $(P,0,.H,O); sulphurous oxide or sulphurous anhydride, SO,, gives sulphurous acid, H,SO, or (SO,.H,0). (2) Basic oxides, produced when metals burn in air or oxygen, combine with water to form hydroxides or true bases, which when soluble are alkaline (p.19). In all cases they are capable of neutralising acids; e.g. sodium oxide, Na,O, produces sodium hydrate NaOH (p.19) ; calcium oxide, CaO, gives calcium hydrate, Ca(OH), (p. 389) ; ferric oxide, Fe,03, corresponds with ferric hydroxide, Fe(OH),. (3) Peroxides contain more oxygen than the basic oxides; e.g. barium oxide, BaO, is a basic oxide, barium dioxide, BaOg, is a peroxide. (4) Neutral or indifferent oxides are exemplified by water, H,O; carbon monoxide, CO ; nitrous oxide, N,O. Salts are built up by the union of oxides of kinds (1) and (2) ; e.g. P,O, + 3Na,0 = 2Na,PO,, tri-sodium phosphate; SO, + CaO = CaSO , calcium sulphite. In practice, however, acids are usually made to react with the hydroxides, water being eliminated; thus, H,PO,-+3Na0H = 2Na,;PO, + 3H,0; H,SO, + Ca(OH), = CaSO; + 2H,0. These descriptions are not sufficiently comprehensive to include all acids, bases and salts; the subject is treated in a special chapter (p. 88). The proportion of oxygen in air may be exhibited by sup- porting a stick of phosphorus upon a wire stand, A (Fig. 40a), in 5 volumes of air confined in the cylinder, B, over water. After a few hours, the phosphorus will have combined with the whole of the oxygen to form phosphorous and phosphoric acids, which are absorbed by the water, and the water will have risen in the cylinder, leaving 4 volumes of nitrogen. In proper apparatus phosphorus is frequently used in this way for the ‘precise determination of oxygen in air and other gaseous mixtures. In accurate determinations of the ratio of oxygen to nitrogen and argon in the air, it is necessary to guard against any error arising from the presence of water, carbon dioxide, and ammonia.?. With this view, Dumas and Boussingault, in 1841, to whom we are originally indebted for our exact knowledge of the composition of the air, caused it to pass through a series of tubes, A (Fig. 41), containing potash, in order 1 Anhydride, or without water, from dv, negative; vSwp, water. : : 2 , 2 It would be satisfactory, of course, to deprive the air of its argon also, in making this experiment, and thus arrive at the true proportion of nitrogen to oxygen; no method is known, however, for removing argon from a gas, It must be remembered that this gas has only recently been discovered, and Dumas and Bous- singault estimated it with the nitrogen, thus making the proportion of this constituent appear too high. 52 ANALYSIS OF ATR to remove the carbon diox’de, then through a second series, B, containing sulphuric acid, to absorb ammonia and water ; the purified air then passed through a glass tube, C, filled with bright copper heated to redness in a charcoal furnace, which removed the whole of the oxygen, whilst the nitrogen passed into the large globe, N. Both the tube (containing the copper) and the globe were carefully exhausted of air and accurately weighed before the experiment ; on connecting the globe and the tube with the purifying apparatus, and slowly opening the stop-cocks, the pressure of the external air caused it to flow through the series of tubes into the globe destined to receive the nitrogen. When a considerable quantity of air had passed in, the stop- cocks were again closed, and after cooling, the weight of the globe was accurately determined. The difference between this weight and that of the empty globe, before the experiment, gave the weight of the nitrogen which had entered the globe ; but this did not represent the whole of the nitrogen contained in the analysed air, for the tube containing the copper was still full of nitrogen at the close of the experiment. This tube, having been weighed, was attached to the air-pump, the nitrogen exhausted from it, and the tube again weighed ; the difference between the two weighings fur- nished the weight of the nitrogen remaining in the tube, and was added to the weight of that received in the globe. The oxygen was represented by the increase in weight of the exhausted tube containing the copper, which was partially converted into copper oxide, CuO, by combining with the oxygen of the air passed over it (cf. experiment, p. 2). In each of the experiments described the residual gas consists almost entirely—about 99 per cent.—of nitrogen (w7poy, nitre ; yervaw, I produce), so called from its occurrence in nitre (potassium nitrate). We have thus discovered the most characteristic distinctions between this ele- ment and oxygen. Oxygen is ever ready to combine with almost any element (p. 24) and to attack the majority of compound substances. Nitro- gen, on the contrary, is characterised by being very inert and combining directly with very few substances, e.g. magnesium and calcium metals ; but even these unite with the oxygen and leave the nitrogen when both gases are present together as in air. Therefore it may be inferred, and will be shown later, that in air the nitrogen acts as a diluent to the active oxygen. How- ever, when nitrogen has been brought into combination, the compounds, eg. nitric acid, are frequently very energetic substances. Before proceeding with the study of air generally, it will be well to have some precise knowledge of each of its two chief constituents, free nitrogen and free oxygen ; also of carbon dioxide. NITROGEN constitutes 78-06 per cent. by volume and 75-5 per cent. by weight of the atmosphere and occurs in several mineral waters and in the gaseous emanations from volcanoes (p. 95). Methods of obtaining it (mixed with argon) have been described in the preceding paragraphs. When required in larger quantity, it is more conveniently prepared by passing air from a gasholder over copper turnings heated to redness ina tube. ‘The arrangement in Fig. 13 (p. 21) is applicable if for the flask, C, be substituted a gas holder (see B, Fig. 139). If the air be passed through strong solution of ammonia contained in a wash bottle before passing over the heated copper, a short length of the latter will suffice, since the oxide formed will be reduced by the ammonia which has vaporised into the air while passing through the solu- tion; 3CuO + 2NH, = 3Cu + 3H,0 + Ny. The gas may then be passed through a wash bottle containing strong sulphuric acid to free it from water and excess of ammonia. A gasholder full of atmospheric nitrogen may be obtained as follows : Put into an empty gas holder, B (Fig. 139), the small stop-cocks being closed but the large one under the funnel being open, 5 grams pyrogallol (the so-called pyrogallic acid used in photography) for each litre capacity, and about 20 c.c. water to dissolve it; then run in acold solution made by dissolving 80 grams caustic potash in 80 c.c. water ; shake for one or two minutes, close the stop- NITROGEN 53 cock and shake occasionally during ten minutes, fill the funnel with water, and the supply of nitrogen is ready for use. On a large scale nitrogen may be obtained from liquid air (p. 86). ‘* Atmospheric nitrogen” always contains about 1 per cent. by volume ofargon. To prepare pure nitrogen some compound of the element must be decomposed ; thus, an oxide of nitrogen may be passed over red-hot copper in the same manner as with air ; the oxygen unites with the copper, liberating the nitrogen ; ora concentrated solution of ammonium nitrite may be heated in a flask fitted with a delivery tube, NH,NO, = 2H,O +.N, (Fig. 42) ; after some of the gas has been allowed to escape in order to drive out the air from the flask, the nitrogen may be collected in a fairly pure condition. It is usually more convenient to use a mixture of equal parts of potassium nitrite, KNO,, and ammonium chloride, NH,Cl, each dissolved in a little water. These salts react to form po- tassium chloride, KCl, and ammonium nitrite, NH,NO,. Some nitrogen oxides are liable to accompany the gas; their formation may be prevented by adding potassium bichromate equal in weight to that of the ammonium salt, whereby they are converted into nitric acid, which remains in the flask as a nitrate. The nitrogen may contain a little ammonia, which dissolves in the water, or may be re- moved by passing the gas through sulphuric acid if the gas is collected over mercury. Physical properties.—Nitrogen is a colourless, odourless gas, which is evident from its constituting the major part of the air we breathe. It is somewhat lighter than air, its specific gravity being 0-96737 ; that of “atmospheric nitrogen”? (which includes argon) is 0-97209. It was this difference in density which led Rayleigh in 1893 to suspect the presence of some hitherto unknown gas (argon). Its specific gravity when H = 1 is 14-009 ; one litre weighs 1-25092 grams at N.T.P. The pressure coefficient (p. 9) is very regular over a wide range of temperature and is almost pre- cisely 0-003668, or approximately ,},; (p. 9). Liquefied nitrogen boils at —195-7° at 760 mm. and has a density of 0-8042 ; at its melting-point, the density of the liquid is 0-8792. When rapidly evaporated a portion of the liquid freezes to a colourless solid, melting at —210-5°. At —252-5° the density is 1-0265. Its critical temperature is —146°, crit. press. 35 atm., crit. vol. 42-6, crit. density 0-0235. Such big variation of the density with the temperature is not uncommon with liquefied gases ; but many volatile liquids, e.g. ether, when near their boiling-points, show the same thing in a lesser degree, and even water does so to a considerable extent (p. 34). Specific heat: gas about 0-24, liquid 0-43. Latent heat of vaporisation, about 49 ; latent heat of fusion, about 12-8. Refractive index, gas 1-000297; liquid 1-2053. It is not as soluble as oxygen (p. 58). 100 c.c. water at 0° dissolve 2-35 c.c. (0-00293 grams) ; at 10°, 1-86 ¢.c. (0-00230 grams) ; at 20°, 1:54 ¢.c. (0-00189 grams) ; at 60°, 1-02 c.c. (0-00105 grams) of the gas at 766 mm. 100 c.c. alcohol at 14-5° dissolve 12:15 c.c. Many gases dissolve more freely in alcohol than in water. At low temperatures it is absorbed in large quantity by charcoal ; at 0°, 15 vols. ; at —185°, 155 vols. Chemical properties.—The inactivity of nitrogen has already been mentioned. Lithium metal combines with it readily at the ordinary temperature; calcium less readily; magnesium when heated, forming nitrides (p. 182). With hydrogen und:r the influence of the electric discharge 54 OXYGEN itformsammonia. With oxygen at ordinary temperature it does not unite ; at much higher temperatures, in flame (p. 190) or by electric spark (p. 190), they combine to give nitric oxide, NO. This occurs on the passage of lightning through the air ; atmospheric electricity is responsible for some of the com- bined nitrogen required by vegetable life. Under various conditions it is capable of combining directly with boron, silicon, titanium, zirconium, and with metallic carbides, also with acetylene, to produce hydro- cyanic acid (p. 557). Nitrogen is never absorbed by animal or vegetable organisms, save only in a few exceptional cases, notably by the micro- organisms assdciated with the roots of leguminous plants and by certain alge; also by yeast. OXYGEN constitutes 20-95 per cent. by volume, 23-12 per cent. by weight of air. It has been surmised that the terrestrial atmosphere originally contained no oxygen and that its occurrence is due to its exhalation by green plants during the process of photosynthesis, which proceeds in sunlight only. This consists in the building-up by the chlorophyll apparatus in the plant cells of some form of carbohydrate from the carbon dioxide, which is absorbed from the air, and the water present in the cells, with the simultaneous dis- engagement of an equal volume of oxygen. This was discovered more or less completely by Ingenhousz (b. 1730, d. 1799), who in 1778 published “ Experiments upon vegetables, discovering the power of purifying the air in sunshine and injuring it in the shade.” The last clause is significant of respiration (taking in oxygen and giving out carbon dioxide) in plant life, which is quite independent of photosynthesis and operates at alltimes. The oleander leaf has been found to decompose, on an average, in sunlight 1108 c.c. (67-6 cub. in.) of carbon dioxide per square metre (about 11 sq. ft.) of leaf sur- face per hour. It has been estimated that one pound of unicellular alge gives out some 420 gallons of oxygen per annum. In view of all vegetable carbon being derived in this way from the atmosphere and of the composition of the dried tissues approximating that of carbohydrates (CH,O),, the weight of oxygen exhaled annually is about equal to that of the total annual produc- tion of dry vegetable substance. Preparation.—From the atmosphere oxygen can be separated directly (a) by the fractional distillation of liquid air as explained at p. 86; this is the method now generally adopted for the preparation of oxygen on the commercial scale ; (6) by absorption by charcoal, a process which has been applied technically. One hundred litres freshly ignited wood charcoal absorb 925 litres oxygen and 705 litres nitrogen from the air; on moistening with water, 650 litres nitrogen and 350 litres oxygen are given up, leaving 575 litres oxygen and 56 litres nitrogen still in the charcoal, which can be extracted by means of an air-pump. By repeating the process nearly pure oxygen is obtained. Indirectly it is procurable by the method of Lavoisier (p. 49), which, however, is far too long and costly for use. The same principle, however—namely, the combination of the oxygen with another substance at one temperature and its evolution from this combination at a higher temperature—underlies Brin’s process, wherein barium oxide (BaQ) is heated in air to form barium dioxide (BaO,); when this latter is heated more strongly, or under diminished pressure, it gives up oxygen, again becoming BaO, thus: (1) BaO + O = BaO,; (2) BaO, = BaO + O. The regenerated barium oxide is used again. Atone time this process was largely used, but it is now being displaced by the fractional distillation of liquid air. Another process which has been used depends upon the principle that the oxides of manganese, when heated in contact with alkalies and air, are capable of absorbing oxygen from the air, and of subsequently giving it up again if heated in a current of steam : it forms an instructive experiment. OXYGEN-—-PREPARATION 55 About 4 ounces of dry sodium manganate are* introduced into a porcelain tube, ¢ (Fig. 43), fixed in a furnace.? One end of the tube is connected with a branched glass tube, so that either a current of air may be passed through it by the tube, a, or a current of steam from the flask, w. On heating the manganate in the tube to dull redness, and passing the steam over it, oxygen is evolved, and may be collected in the jar, o. 4Na,MnO, + 4H,O = 8NaHO + 2Mn,0, + 30, Sodium Caustic Manganese Manganate soda sesquioxide If the current of steam be discontinued and the air be slowly passed through the tube, a, the oxygen of the air will be absorbed, and its nitrogen may be collected in the jar, nm. 4NaHO + MnO; + 3(0 + 4N) = 2Na,MnO, + 2H,O + 6N,. Air Fia. 43. If the proper temperature be employed, the stream of gas issuing from the tube may be constantly kept up, and may be made to consist of oxygen or nitrogen accord- ingly as steam or air is passed through the tube. The current of air is regulated by the clip, c. The oxygen obtained on a large scale from the atmosphere is never free from nitrogen, which, however, does not interfere with its industrial applica- tion. Pure oxygen is more easily prepared from compounds of the element ; many of thése which are rich in oxygen part with the whole or some of their oxygen when heated to a temperature which can readily be applied. Among the oxides, peroxides (p. 51) are particularly liable to give up oxygen when heated, for instance, barium dioxide, BaO, (Brin’s process, p. 54), and manganese dioxide, MnO,, a black mineral composed of manganese and oxygen found in some parts of England, but much more abundantly in Germany and Spain. It is known by the significant name of pyrolusite, referring to the facility with which it may be decomposed by heat (zip, fire, and Xéiw, to loosen). One of the cheapest methods of preparing oxygen consists in heating small fragments of this black oxide of manganese in an iron retort, placed in a good fire, the gas being collected in jars filled with water, and standing upon the shelf of the pneumatic trough, or in a gas-holder or gas-bag, if large quantities are required. The attraction existing between manganese and oxygen is too powerful to allow the metal to part with the whole of its oxygen when heated, so that 1 A copper tube with screw-caps, into which narrow brass or copper tubes are brazed, may be advan- tageously substituted for the porcelain tube. The process is much facilitated by mixing the manganate of soda with an equal weight of oxide of copper. 3 A * The furnace here represented consists of a semi-cylindrical trough made of iron rods and filled with pieces of pumice-stone ; the tube is laid in the trough and covered with a like trough. A row of Bunsen burners springing from a tube, b, heats the furnace. 56 OXYGEN—PREPARATION only one-third of the oxygen is given off in the form of gas, a brown oxide of manganese being left in the retort: 3MnO, = Mn,O0, + Oy». Among salts containing oxygen the nitrates and chlorates part with oxygen most readily when heated. Potassium chlorate, KCIO,, furnishes by far the most convenient source of oxygen for general use in the laboratory. It is largely manufactured for fireworks, percussion-cap composition, &c. If a few crystals of this salt be heated in a test-tube over a Bunsen burner or spirit lamp (Fig. 44) they soon melt (360°) to a clear liquid, which presently begins (400°) to boil from the disengagement of bubbles of oxygen, easily recognised by introducing a wooden splint with a spark at the end into the upper part of the tube, when the wood instantly bursts into flame. If the action of heat is continued until no more oxygen is given off, the residue in the tube is the salt termed potassium chloride ; KclO, = KCl + 380 Potassium Potassium Fie. 44 chlorate chloride This simple equation does not represent all that occurs. With somewhat larger quantities it is seen that after a certain quantity of gas has been evolved the mass becomes thicker ; this is due to formation of potassium perchlorate, KClO,, an intermediate product. The reaction then becomes more vigorous, much gas is evolved, and the mass may become even red-hot, due to the process being exothermic, i.e.it gives out heat ; hence it is not desirable to apply much heat when once the reaction has set in. To ascertain what quantity of oxygen would be furnished by a given weight of the chlorate, the atomic weights must be brought into use. Referring to the table of atomic weights, it is found that K = 39, O = 16 and Cl = 35:5; hence the molecular weight of potassium chlorate is easily calculated. One atomic weight of potassium . ‘ ; . 89 a is chlorine 2 zi : : . 3855 Three atomic weights of oxygen. é ; . 48 KCIO; = 122-5 So that 122-5 grams of chlorate would yield 48 grams of oxygen. Since 16 grams of oxygen (more accurately 15-88) measure 11-11 litres (p. 22), the 48 grams will measure 33-33 litres. Hence it is found that 122-5 grams of potassium chlorate would give 33-33 litres of oxygen measured at 0° and 760 mm. Since the complete decomposition of the potassium chlorate requires a more intense heat than a glass vessel will usually endure, it is customary to mix the chlorate with about one-fifth of its weight of powdered black oxide of manganese, which enables the whole of the oxygen to be given off ata comparatively low tcmperature. The manganese oxide suffers no obvious change. Ferric oxide, copper oxide, &c., may be used instead of the manganese. Although these auxiliary substances appear to undergo no change, yet it is chiefly the higher oxides which have this property. Indifferent and decidedly basic bodies do not assist the disengagement of oxygen. The gas usually includes traces of chlorine and hydro- chloric acid when prepared from the chlorate alone, and still more when mixtures are used ; but these impurities are removed by contact of the gas with caustic soda solu- tion, either by bubbling the gas through the solution in a wash-bottle or by agitation with it in the gas-holder. A convenient arrangement for preparing and collecting oxygen for the purpose of demonstrating its properties and relations to combustions is shown in Fig. 45. A is a OXYGEN—PROPERTIES 57 Florence flask in which the glass tube, B, is fixed by a perforated cork. Cisarubber tube. The gas-jar is filled with water, and supported upon a bee-hive shelf. If pint gas-jars be used, 20 grams of potassium chlorate, mixed with 4 grams of manganese dioxide, will furnish a sufficient supply of gas for the ordinary experiments. The manganese dioxide should be thoroughly dried by mode- rately heating it in a crucible before being mixed with the chlorate. It is also advisable to test it by heating a little of it with the chlorate, since charcoal and sulphuret of anti- mony, which form very ex- plosive mixtures with chlorate Ver of potash, have sometimes ("x been sold by mistake for man- ganese dioxide. Similar danger arises from the presence of bits of paper, cotton, or other rubbish. The heat must be moderated according to the rate at which the gas is evolved, and the tube, C, must be taken out of the water before the lamp is removed, or the contraction of the gas in cooling will suck the water back into the flask. The first jar of gas will contain the air with which the flask was filled at the commencement of the experiment. The oxygen obtained will have a slight smell of chlorine. A supply of oxygen can be always available by filling the “‘ oxygen mixture ” into a long tube (say 2 or 3 cm. diam. and 40 or 50 cm. long) (Fig. 46) closed at one end and fitted with delivery tube. The tube is held horizontally and the powder is distributed over the lower side so as to leave a free gas-way above ; some loose ignited asbestos, a, keeps the mixture away from the cork (this is important, as if the hot mixture touches the cork violent combustion may ensue). By gently heating a short length from time to time the required quantity of gas can be generated when desired. A convenient method of preparing oxygen at the ordinary temperature is as follows : Half fill a two-necked Woulff’s bottle, one neck fitted with a funnel having a stop- cock and the other with a delivery tube (or use the flask and funnel in Fig. 99), with a 3 per cent. (“10 volume ”’) solution of hydrogen peroxide ; acidify strongly with diluted sulphuric acid, and run in gradually a concentrated solution of potassium permanganate through the funnel. A volume of oxygen equal to twenty times the volume of the hydrogen peroxide solution used will be generated as fast as the permanganate is added. 5H,0, + 2KMnO, + 4H,SO, = 2KHSO, + 2MnS0O, + 8H,O + 50,. Half the oxygen is derived from the hydrogen peroxide and half from the permanganate. For preparing oxygen in a Kipp’s apparatus (p. 65), a mixture of 2 parts BaOQ, and 1 part MnO, may be made into a paste with a little water and 1 part plaster of Paris. The paste is made into small blocks before it has set, and these are introduced into the Kipp’s apparatus, which is then charged with dilute HCl. ud Ee Fie. 45. Fia. 46. Physical properties.—Oxygen is a colourless, odourless gas, which may be inferred from its presence in the atmosphere. It is a little more than one-tenth (1-1053) heavier than air; its specific gravity when H =1 is 15-900. 1 litre weighs 1-429 grams at N.T.P. The pressure co- efficient is 0-003674. Liquefied oxygen (p. 86) is a very mobile liquid of faintly blue colour; it boils at — 181-5° and 760 mm. or at — 210° and 10 mm. and has a density of 1-1375. Its critical temperature is — 113-0°, critical pressure 50-0 atmospheres. Specific heat: gas, at constant volume 4-95 ; liquid, 0-347. Latent heat of vaporisation about 58 calories. 58 COMBUSTION Liquid oxygen does not conduct electricity, but it is strongly magnetic and may be withdrawn from the containing vessel by a magnet, from the sur- face of which it evaporates. It may be separated from liquid nitrogen by means of the magnet (p. 86). It cannot be solidified by its own evaporation, but exposed to the temperature of liquid hydrogen it is frozen to a pale blue crystalline solid, having a density 1-4526 at — 252-5° and a melting-point — 235°. Refractive indices: gas, 1-000271 ; liquid, 1:2235; solid, 1-2036. Oxygen is more freely soluble than nitrogen ; 100 c.c. water at 0° dissolve 4-890 c.c. (0-00695 gram); at 10°, 3-802 c.c. (0-00537 gram); at 20°, 3-102 c.c. (000434 gram) of the gas at 760 mm. 100 c.c. alcohol at 15° dissolve about 25c.c.at760mm. Molten silver dissolves ten times its volume of the gas and gives it up again on cooling. Heated solid silver, gold, platinum and palladium occlude large volumes. Charcoal absorbs it freely (pp. 54, 240). Chemical properties.—Since the chemically active constituent of air is oxygen it will be instructive frequently to compare phenomena in air with the like in pure oxygen. Oxygen is remarkable for the wide range of its chemical attraction for other elements, with all of which except two— fluorine and bromine (in addition to the argon group which do not form any compounds)—it is capable of entering into combination. With nearly all the elements oxygen combines directly ; that is, without the apparent intervention of any third substance, although, since it has been proved that perfectly dry oxygen will not combine with other elements, it must be admitted that moisture (or some other third substance) is essential to chemical reaction.? There are only seven elements (among those of practical importance) which do not unite in a direct manner with oxygen—viz. chlorine, bromine, iodine, fluorine, gold, silver, platinum. An oxide is a compound of oxygen with another element. The act of combination with oxygen, or oxidation,? is frequently a slow process, and its effects are not always perceived immediately, particularly when occurring at ordinary temperatures. Some familiar examples of oxida- tion are—the tarnishing or rusting of metals by air, the gradual decay of wood, the drying of oils in paint, the formation of vinegar from alcoholic liquids, the respiration of animals. In all these processes heat is generated ; but it is not usually noticed unless it is sufficient to render the particles of matter luminous, which is the case with combustion, the most common form of oxidation. Combustion is chemical combination attended with heat and light. Combustion in air is the chemical combination of the elements of the com- bustible (the body burnt) with the oxygen of the air (the supporter of com- bustion), attended with development of heat and light. (a) Reactions with non-metals——The combination of oxygen with hydrogen has already been discussed under water. Oxygen may be said to react with itself under electric or other influence with formation of ozone, O; (p. 138). . Nitrogen combines only at very high temperatures (p. 54). Phosphorus and arsenic oxidise in moist air at ordinary temperatures. Boron, silicon, selenium and telluriwm also combine directly at higher tem- a Most of the non-metallic oxides unite with water to form acids (p. 51). The behaviour of phosphorus affords a good illustration of oxidation. If a small. piece of phosphorus be dried by gentle pressure between blotting- ie Charcoal may be heated to redness in dry oxygen without visible combustion. Sulphur and phosphorus which inflame in moist oxygen at 260° and 60° respectively, may be distilled in the dry gas at 440°. and 290° respectively, * A wider application of this term is referred to on p. 99. OXYGEN AND PHOSPHORUS 59 paper, and exposed to the air, its particles begin to combine at once with oxygen, and the heat thus developed slightly raises the temperature of the mass. Now, heat generally encourages chemical union, so that the effect of this rise of temperature is to induce a more extensive and more vigorous com- bination of the phosphorus with the oxygen, causing a greater development of heat in a given time, until the temperature is sufficient to render the particles brilliantly luminous, and a true case of combustion results—combination (of the phosphorus with oxygen), attended with production of heat and light. In cold weather, the phosphorus seldom takes fire until rubbed, or touched with a hot wire. If a dry glass (Fig. 47) be placed over the burning phosphorus, the thick white smoke which proceeds from it may be collected in the form of snowy flakes. These flakes consist of phosphoric oxide or phosphoric anhydride (P,0;), and are composed of 80 parts by z weight (5 atoms) of oxygen, and 62 parts (2 atoms) of phosphorus (p. 50). If the white flakes are exposed to the air for a short time, they attract moisture and become little drops of meta- phosphoric acid, HPO, (cf. p. 51). During the slow combination of phosphorus with the oxygen of the air, before actual combustion commences, only 48 parts (3 atoms) of oxygen unite with 62 parts (2 atoms) of phosphorus, forming the substance called phosphorous oxide or phosphorous anhydride (P,0 3), which with water produces phosphorous acid, H;PO3. : (The endings -ows and -ic distinguish between two compounds formed by oxygen with the same element; -ous implying the smaller proportion of oxygen.) Unless the temperature of the air be rather high, the fragment of phos- phorus will not take fire spontaneously, but its combustion may always be ensured by exposing a larger surface to the action of the air. As a general rule, a fine state of division favours chemical combination, because the attractive force inducing combination operates only between substances in actual contact ; and the smaller the size of the particles, the more completely will this condition be fulfilled (cf. p. 62). Thus if a small fragment of dry phosphorus be placed in a test-tube and dissolved in a little carbon disulphide, the solution when poured upon blotting-paper (Fig. 48) will part with the solvent by evaporation, leaving the phosphorus in a very finely divided state upon the surface of the paper, where it is so rapidly attacked by the oxygen of the air that it bursts spontaneously into a blaze. Though the light emitted by phosphorus burning in air is very brilliant, it is greatly increased when pure oxygen is employed ; for since the nitrogen with which the oxygen in air is mixed takes no part in the act of combustion, it impedes and moderates the action of the oxygen. Each volume of the latter gas is mixed, in air, with four volumes of nitrogen, so that.we may suppose five times as many particles of oxygen to come into contact, in a given time, with the particles of the phosphorus immersed in the pure gas, which will account for the great augmentation of the temperature and light of the 60 OXYGEN AND SULPHUR burning mass. In air, the nitrogen molecules not only impede mechanic- ally, but also, in becoming heated, withdraw heat from the materials taking part in the combustion, so lowering the temperature. To demonstrate the brilliant combustion of phosphorus in oxygen, a piece not larger than a good-sized pea is placed in a little copper or iron cup upon an iron stand (Fig. 49), and kindled by being touched with a hot wire. The globe (of thin well-annealed glass), having been previously filled with oxygen and kept in a plate containing a little water, is placed over the burning phosphorus. It will be observed that the same white clouds of phosphoric anhydride are formed, whether phosphorus is burnt in oxygen or in air, exemplifying the fact that a substance will combine with the same proportion of oxygen whether it burns in pure oxygen or in atmospheric air. The apparent increase of heat Fic. 49. is due to the combustion of a greater weight of phosphorus in a given time and space. Although the temperature may be different the total quantity of heat produced by the combustion of a given weight of phosphorus is the same whether air or pure oxygen is employed. Sulphur (brimstone) affords an example of a non-metallic element which will not enter into combination with oxygen until its temperature has been raised very considerably. When sulphur is heated in air, it soon melts ; and when its temperature reaches 260° it takes fire, burning with a blue flame. If the burning sulphur be plunged into a jar of oxygen, the blue light will become very brilliant, but the same act of combination occurs—32 parts by weight (2 atoms) of oxygen uniting with 32 parts (1 atom) of sulphur to form sulphur dioxide gas or sulphurous anhydride (SO,), which may be recog- nised in the jar by the well-known suffocating smell of brimstone matches. The experiment is most conveniently performed by heating the sulphur in a deflagrating spoon, A (Fig. 50), which is then plunged into the jar of oxygen, its collar, B, resting upon the neck of the jar, which stands in a plate contain- ing a little water. The water absorbs a part of the sulphur dioxide, producing sulphurous acid, H,SO3. It is possible to produce, though not by simple combustion, a compound of sulphur with half as much more oxygen (SOs, sulphuric anhydride), showing that a substance does not always take wp its full share of oxygen when burnt. SO; with water forms sulphuric acid, H,SO,. The luminosity of the flame of sulphur is far inferior to that of phos- phorus, because, in the former case, there are no extremely dense particles in the flame corresponding with those of the phosphoric oxide produced in the combustion of phosphorus. Carbon, also a non-metallic element, requires the application of a higher temperature than sulphur does to induce it to enter into direct union with oxygen ; indeed, perfectly pure carbon appears to require a heat approaching whiteness to produce this effect. But charcoal (the carbon in which is OXYGEN AND METALS 61 associated with no inconsiderable proportions of hydrogen and oxygen) begins to burn in air at a much lower temperature ; and if a piece of wood charcoal, with a single spot heated to redness, be lowered into a jar of oxygen the adjacent particles will soon be raised to the combining temperature and the whole mass will glow intensely, 32 parts by weight (2 atoms) of oxygen uniting with 12 parts (1 atom) of carbon to form carbon dioxide (CO,) or carbonic anhydride, which will redden a piece of moistened blue litmus-paper suspended in the jar. It should be remembered that carbon is an essential constituent of all ordinary fuel, and carbon dioxide is always produced by its combustion. It will be noticed that the combustion of the charcoal is scarcely attended with flame ; and when pure carbon (diamond, for example) is employed, no flame whatever is produced in its combustion, because carbon is not con- verted into vapour, and all flame is vapour or gas in the act of combustion ; hence, only those substances burn with flame which are capable of yielding com- bustible gases or vapours. (6) Reactions with metals.—The oxidation of metals has already been studied in the cases of iron (p. 2), copper (pp. 2 and 52), tin (p. 48), mercury (p. 49). The metals, as a class, exhibit a greater disposition to unite directly with oxygen, though few of them will do so in their ordinary con- dition, and at the ordinary temperature. Severa] metals, such as iron and lead, are superficially oxidised when exposed to air under ordinary conditions, but this would not be the case unless the air contained water and carbonic acid gas, which favour the oxidation in a very decided manner. Among the metals which are of importance in practice, five only are oxidised by exposure to dry air at the ordinary temperature, viz. potassium, sodium, barium, strontium, and calcium, the attraction of these metals for oxygen being so powerful that they must be kept under petroleum, or some similar liquid free from oxygen. On the other hand, three of the common metals, silver, gold, and platinum, have so little attraction for oxygen that they cannot be induced to unite with it directly, even at high temperatures. When a lump of sodium is cut across with a knife, the fresh surfaces exhibit a splendid lustre, but very speedily tarnish by combining with oxygen from the air, which gives rise to a coating of sodium oxide, protecting to some extent the metal beneath from oxidation. The freshly cut sodium shines in the dark like phosphorus. Even when the attraction of the sodium for oxygen is increased by the application of heat, it is long before the mass of sodium is oxidised throughout, unless the temperature be sufficiently high to convert a portion of the sodium into vapour, which bursts through the crust of oxide, and burns with a yellow flame ; if, when this has occurred, the spoon in which the sodium is heated (see Fig. 50) be plunged into a jar of oxygen, the yellow flame will be more brilliant. Sixteen parts by weight of oxygen (1 atom) here combine with 46 parts of sodium (2 atoms) to form sodium oxide (Na,O) (not pure, p. 375), which remains in the spoon in a diffused state. When the spoon is cool, it may be placed in water, which will dissolve the oxide, converting it into the alkali, caustic soda, NaOH, Na,O + H,O = 2Na0H. Zinc serves as an example of a metal which has no disposition to combine with oxygen at the ordinary temperature,’ but is induced to unite with it by a very moderate heat. If a little zine (spelter) be melted in a ladle or crucible, and stirred about with an iron rod, it burns with a beautiful greenish flame, produced by the union of the vapour of zinc with the oxygen of the air. 1 Unless water and carbonic acid gas be present, as in common air. 62 OXYGEN AND IRON But the combustion is far more brilliant if a piece of zinc foil be made into a tassel, gently warmed at the end, dipped into a little flowers of sulphur, kindled, and let down into a jar of oxygen, when the flame of the burning sulphur will ignite the zinc, which burns with great brilliancy. On with- drawing what remains of the tassel after the combustion is over, it will be found to consist of a brittle mass, which has a fine yellow colour while hot, and becomes white as it cools. This is zinc oxide (ZnO), formed by the union of 16 parts by weight (1 atom) of oxygen with 65 parts (1 atom) of zine. fron, in its ordinary form, like zinc, is not oxidised by dry air or oxygen at the ordinary temperature ; but if it be heated even to only 260° a film of oxide of iron forms upon its surface, and as the temperature is raised, the thickness of the film increases, until eventually it bcomes so thick that it can be detached by hammering the surface as may be seen in a smith’s forge. If an iron rod as thick as the little finger be heated to whiteness at the ex- tremity, and held before the nozzle of a powerful bellows, it will burn brilliantly, throwing off sparks and dropping melted oxide of iron. If a stream of oxygen be substituted for air, the combustion is of the most brilliant description. A watch-spring (iron combined with about 1 per cent. of carbon) may be easily made to burn in oxygen by heating it in a flame till its elasticity is destroyed, and coiling it into a spiral, A (Fig. 51), one end of which is fixed, by means of a cork, in the deflagrating collar, B; if the other end be filed thin and clean, dipped into a little sulphur, kindled and immersed in a jar of oxygen, OC, standing in a plate of water, the burning sulphur will raise the temperature of the iron to the point of combustion, and the spring will be converted into molten drops of oxide. The black oxide of iron formed in all these cases is really a combination of two distinct oxides of iron, one of which contains 16 parts (1 atom) by weight of oxygen and 56 parts (1 atom) of iron, ferrous oxide, FeO, whilst the other contains 48 parts (3 atoms) of oxygen and 112 parts (2 atoms) of iron, ferric oxide, Fe,0,. The latter, combined with water, constitutes ordinary rust. © The black oxide usually contains one molecule of each oxide, so that it would be written FeO.Fe,0,, or Fe,0,. It is powerfully attracted by the magnet, and is often called magnetic oxide of iron. The abundant magnetic ore of iron, of which the loadstone is a variety, has a similar composition. Iron in a very fine state of division takes fire spontaneously in air as certainly as phosphorus does. Pyrophoric iron can be obtained by a process to be described hereafter (p. 248), as a black powder, which must be preserved in sealed tubes. When the tube is opened, and its contents thrown into the air, oxidation occurs, and is attended with a vivid glow. In this case the red oxide of iron is produced instead of the black oxide. All these oxides of sodium, zinc, iron, &c., are capable of neutralising, or partly neutralising, acids, and are therefore basic oxides or bases (see also p. 51). So general is the disposition of metals to form oxides of this class, that a metal may be defined as an element capable of forming a base by combining with oxygen (cf. p. 7). A non-metal never forms a base with oxygen, but many metals are capable also of forming acid anhydrides with oxygen ; thus, tin forms stannic anhydride (SnO,), antimony forms antimonic anhydride (Sb,0,), and it is always found that a metallic anhydride contains a larger proportion of oxygen than any of the other oxides which the metal may happen to form. Fia.£51. CARBON DIOXIDE 63 Absorption of oxygen takes place under many various conditions; by alkaline pyrogallol (p. 52), ferrous salts (p. 161), similarly by cuprous and manganous salts, by aldehydes with the formation of the corresponding acids. It unites with nitric oxide, NO, to produce the dense red-brown gas nitrogen peroxide, NO,; 2NO + O, = 2NO,. This reaction, employed by Priestley (p. 49), is one of the most reliable of all qualitative tests for free oxygen (p. 200). Nitrous oxide, N,O, kindles a glowing splint just as oxygen does, but it does not give red fumes with nitric oxide. Hemoglobin, the purple constituent of venous blood, takes up oxygen from the air drawn into the lungs during the process of respiration, gives up a nearly equal volume of carbon dioxide, which is exhaled, and becomes con- verted into the bright red oxyhemoglobin, the characteristic constituent of arterial blood. The chief application of free oxygen is for increasing the temperature of combustion (see Oxyhydrogen flame, p. 268). In medicine it is valuable for temporarily increasing the oxygenation of the blood. CARBON DIOXIDE, Carbonic anhydride or ‘‘ carbonic acid gas,” COs, is also a constant and essential constituent of the atmosphere. It was discovered by Van Helmont, by whom it was designated gas sylvestre. He showed that it was liberated from limestone and potashes by acids, from burning coal, in fermentation, and that it occurs in mineral waters, &c. We are indebted, however, to Joseph Black of Edinburgh (6. 1728, d. 1799) for the first precise investigations of its properties. He called it “fixed air,” in view of its becoming “‘ fixed ” or absorbed by alkalies and alkaline earths. The discovery of its presence in air was made by Macbride in 1764, who found that lime which had been exposed effervesced with acids. The proportion approximates 3-4 volumes in 10,000 volumes of air. It, is smaller at higher altitudes and over thesea ; over the land it is greater at night than in the day, since photosynthesis by green leaves, involving the absorption of carbon dioxide, proceeds only in sunlight (p. 54), while respira- - tion by both animals and vegetables, giving out carbon dioxide, is always going on. Nevertheless, these variations are slight and the proportion is remarkably constant under normal conditions. In large towns the contin- uous production of the gas by combustion, fermentation, respiration, &c., increases the amount somewhat above the normal locally. Fogs and some other conditions of weather also have this effect. All substances used as fuel contain a large proportion of carbon, which, in the act of combustion, combines with the oxygen of the air and escapes into the atmosphere in the form of carbon dioxide. In the process of respiration, carbon dioxide is formed from the carbon contained in the blood and in the different portions of the animal frame to which oxygen is conveyed by the blood ; the latter, in passing through the lungs, gives out, in exchange for the oxygen, a quantity of carbon dioxide produced by the union of a former supply of oxygen with the carbon of digested food, which has passed into the blood and has not been required for the repair of wasted tissue. This con- version of the carbon of the food into carbon dioxide is evidently of great importance to the economy of the animal, being concerned in the maintenance of the animal heat. : As mentioned at p. 54, the leaves of plants, under the influence of light, have the power of decomposing the carbon dioxide of the atmosphere, the carbon of which is applied to the production of vegetable compounds forming portions of the organism of the plant, and when this dies, the carbon is restored, after a lapse of time more or less considerable, to the atmosphere, in the same form, namely, that of carbon dioxide, in which it originally 6+ CARBON DIOXIDE existed there. If a plant should have been consumed as food by animals, its carbon will have been eventually converted into carbon dioxide by respiration ; the use of the plant as fuel, either soon after its death (wood), or after the lapse of time has converted it into coal, will also consign its carbon to the air in the form of carbon dioxide. Even if the plant be left to decay ° this process involves a slow conversion of its carbon into carbon dioxide by the oxygen of the air. Putrefaction (p. 182) and fermentation (p. 575) are also very important pro- cesses concerned in restoring to the air, in the form of carbon dioxide, the carbon contained in dead vegetable and animal matter. In these two pro- cesses the chemical operation is of the same kind, consisting in the resolution of a complex substance into simpler forms, produced by the agency of some minute living plant or animal. The production of carbon dioxide in combustion, respiration, and fermentation may be very easily proved by experiment. If a dry bottle be placed over a burning wax taper standing on the table (or over a gas flame), the sides of the bottle will be covered with dew from the combustion of the hydrogen in the wax (or in the gas); if now a little clear lime- water be shaken in the bottle, the milky deposit of calcium carbonate will indicate the formation of carbon dioxide; Ca(OH), (soluble) + CO, (gas) = CaCO, (insoluble) + H,0. By arranging two bottles, as represented in Fig. 52, and inspiring through the tube, A, air will bubble through the lime-water in B before entering the lungs, and will then be found to contain too little carbon dioxide to produce a milkiness, but on expiring the air it will bubble through C, and will render the lime-water in this bottle very distinctly turbid. Dissolve a little sugar in eight or ten times its weight of water in a flask provided with a cork and delivery tube (as in Fig. 37, but without the burner); add a little dried yeast, previously 2 rubbed down with water, and set aside over-night in a warm place (25° or 30°) ; fermentation will begin in the course of an hour or less, and carbon dioxide may be collected in a jar standing in a pneumatic trough. Fig. 52. In the mineral kingdom, carbon dioxide is pretty abundant. The gas issues from the earth in some places in considerable quantity, as at Nauheim, where there is said to be a spring exhaling about 1,000,000 Ibs. of the gas annually. Many spring waters, those of Seltzer and Pyrmont, for example, are very highly charged with the gas. Carbon dioxide is found in the air of soils in larger proportion than in the atmosphere, amounting to 20 or 30, and occasionally even to 600, volumes in 10,000. It increases with the temperature, and originates from the decay of vegetable matter. But in combination as calcium carbonate, CaCO,, it occurs in far larger quantity in the immense deposits of limestone, marble, and chalk, which com- pose so large a portion of the crust of the earth. The expulsion of the carbon dioxide from limestone (CaCO,) forms the object of the process of lime burning, by which the large supply of lime (CaQ) is obtained for building and other purposes. But if it be required to obtain the carbon dioxide without regard to the lime, it is better to decom- pose the carbonate with an acid. In the animal kingdom, oyster-shells contain 98 per cent., egg-shells 97 per cent., and pearls about 66 per cent. of their weight of calcium carbonate. In the vegetable kingdom, it is rare. Preparation.—The form of the calcium carbonate, and the nature of the acid employed, are by no means matters of indifference. If dilute CARBON DIOXIDE—PREPARATION 65 sulphuric acid be poured upon fragments of marble, the effervescence which occurs at first soon ceases, for the surface of the marble becomes coated with the nearly insoluble calcium sulphate, by which it is protected from further action of the acid— CaCO, + H,SO, = CaSO, + H,O + CO, Marble Sulphuric Calcium acid sulphate If the marble be finely powdered, or if powdered chalk be employed, each particle of the carbonate will be attacked, but still imperfectly. When calcium carbonate is acted upon by hydrochloric acid, there is no danger that any will escape the action of the acid, for the calcium chloride produced is one of the most soluble salts— CaCO, + 2HCl = CaCl, + H,O + CO,. Marble Hydrochloric Calcium acid chloride For the ordinary purposes of experiment, carbon dioxide is most easily obtained by the action of hydrochloric acid upon small lumps of marble contained either in a two- necked. bottle (Fig. 82) or in the centre bulb of a Kipp’s apparatus (Fig. 53). A Kipp’s apparatus can be applied to the ever-ready sup- ply of several gases. The solid body is placed in the centre globe; the reacting liquid (in this case hydrochloric acid) is poured into the top and passes down the centre tube into the bottom chamber ; then it rises into the middle globe, where it meets the solid and generates the gas. Alittle gas is allowed Fie. 53. to escape to drive out the air and then the stop-cock is closed. The evolution of gas continues, with the result that the gaseous pressure increases and drives the liquid back into the lower part and up through the centre tube into the top reservoir. All but a very little of the liquid drains away from the solid, and this can react to generate only a small excess of the gas. The apparatus then has the appearance shown in the figure, and can be set aside until wanted. The pressure of the gas is equal to that of the atmosphere plus that due to the column of acid (or other liquid) from its level in the lower part to its level in the top. To avoid possible inconvenience, no very small pieces of the solid should be used, and to prevent fragments falling through and consequent “ boiling-over,”’ a close coil of copper wire or a plate of perforated lead should fit closely round the centre tube and rest on the neck above the lower chamber. The bottom stopper must also be securely tied over. The gas should be washed by passing it through a little water in a wash- bottle and may be collected by downward displacement. When carbon dioxide is required on a large scale it is used in the form of furnace gases, which contain nitrogen from the air and CO, from the com- bustion of the fuel ; or of lime-kiln gases, the CO, in which is derived from the limestone ; or of fermenting tun gases, consisting of nearly pure CO, due to the fermentation of sugar. Properties.—In view of the many interesting experiments illustrating the parts played by this gas in the general economy, these will be described before giving the usual precise details. Carbon dioxide is an invisible gas like those already examined, but is distinguished by a peculiar pungent odour, 5 66 CARBON DIOXIDE—DENSITY | as is perceived when it effervesces out of soda-water. It is more than half as heavy again as air, its specific gravity being 1-529, which enables its collection by downward displacement and causes its accumulation in confined spaces at lower levels, e.g. in wells, vats, &c. : : The following properties and experiments should be contrasted with those described under hydrogen. The high specific gravity of CO, may be shown by pouring it into a light jar attached to a balance counterpoised by a weight in the opposite scale (Fig. 54). Another favourite illustration consists in floating a soap-bubble on the surface of a layer of the gas, generated in a large jar (Fig. 55) by pouring diluted sulphuric acid upon a few ounces of chalk made into a thin cream with water. ‘If a small balloon, made of col- lodion, be placed in the jar, A (Fig. 56), it will ascend on the admission of carbonic acid gas through the tube, B. If smouldering brown paper be held at the mouth of a jar, like that in Fig. 56, the smoke will float upon the surface of the carbon dioxide, and will sink with it on removing the stopper. The power which carbonic acid gas possesses of extinguishing flame is very important, and has received practical application in the case of burning mines which must otherwise have been flooded with water.’ Many attempts have also been made from time to time to employ this gas for subduing ordinary conflagrations, but their success has hitherto been very partial. It will be remembered that pure nitrogen is also capable of extinguishing the flame of a taper, but an abnormal proportion of this gas may be present in air without affecting the flame, whereas a taper is extinguished in air con- taining one-eighth of its volume of carbon dioxide, < and is sensibly diminished in brilliancy by a much -_ smaller proportion of the gas. A candle is extinguished in air to which 14 per cent. of Fra. 56. its volume of carbon dioxide has been added ; 22 per cent, of nitrogen must be added to produce the same effect. The corresponding figures for a coal-gas flame are 33 per cent. and 46 per cent., and for a hydrogen flame 58 per cent. and 70 per cent. ___* All gases which take no part in combustion may extinguish flame, even in the presence of air, by absorb: ing heat and reducing the temperature below the burning-point. EXTINGUISHING FLAME 67 The power of extinguishing flame, conjoined with the high density of carbon dioxide, admits of some very interesting illustrations. Carbon dioxide may be poured from come distance upon a candle, and will extinguich it at once. By using a gutter, made of thin wood or stiff paper, to conduct the gas to the flame, it may be extinguished from a distance of several feet. Carbon dioxide may be raised in a glass bucket (Fig. 57) from a large jar and poured into another jar. The transfer may be proved by testing the gas in the receiving jar before and afterwards, by the effect on a lighted taper. A wire stand with several tapers fixed at different levels may be placed in the jar, A (Fig. 58), and carbon dioxide gradually admitted through a flexible tube connected with the neck of the jar from the cistern, B, a hole in the cover of which allows air to enter it as the gas flows out ; the flame of each taper will gradually expire as the surface of the gas rises in the jar. On account of this extinguishing power of carbonic anhydride, a taper cannot continue to burn in a confined portion of air until it has exhausted the oxygen, but only until its combustion has produced a sufficient quantity of carbon dioxide to extinguish the flame. When the taper is extinguished, 100 volumes of the air contain 182 volumes of oxygen and 2} volumes of carbon dioxide. To demonstrate this, advantage may be taken of the circumstance that phosphorus will continue to burn in spite of the presence of carbon dioxide. Upon the stand, A (Fig. 59), a small piece of phosphorus is placed, and a taper attached to the stand by a wire. The cork, B, fits air-tight into the jar, and carries a piece of copper wire bent so that it may be heated by the flame of the taper. A little water is poured into the plate to prevent the entrance of any fresh air. If the taper be kindled and the jar placed over it, the flame will soon die out ; and on moving the jar so that the hot wire may touch the phosphorus, its combustion will show that a considerable amount of oxygen still remains. In the same manner, an animal can breathe in a con- fined portion of air only until he has charged it with so much carbonic anhydride that the hurtful effect of this gas begins to be felt, although a considerable quantity of oxygen still remains.. Carbon dioxide is not poisonous when taken into the stomach, but acts most injuriously when breathed, by offering an obstacle to the escape of carbon dioxide, by diffusion, from the blood of the venous circulation in the lungs, and its consequent exchange for the oxygen necessary to arterial blood. 68 CARBON DIOXIDE IN AIR Any hindrance to this interchange must impede respiration, and such hin- drance would of course be afforded by the carbon dioxide present in the air inhaled, in proportion to its quantity. There is evidently a distinction between air which has had carbon dioxide added to it and air in which there is a like amount of carbon dioxide produced by respiration. Thus air which has had its content of carbon dioxide raised to 1 per cent. by addition of the gas may be breathed with impunity, but if there be this proportion present as a result of respiration the effect on most persons would be very deleterious. There is no satisfactory explanation of this observation. It is probable that the oppressive character of a close room is due to other exhalations of the body, and is not really an effect of the carbon dioxide of the breath. It is generally agreed that the percentage of carbon dioxide in the air of a room or building is an index of the wholesomeness of the air. Thus it is considered inadvisable to breath for any length of time air containing more than 10 volumes of CO, in 10,000 volumes (0-1 per cent.). When the carbon dioxide amounts to 50 volumes per 10,000 volumes of air (0-5 per cent.) most persons are attacked by the languor and headache attending bad ventilation. A large proportion of carbon dioxide produces insensibility, and air containing 20 per cent. of its volume causes suffocation. The danger in entering old wells, cellars, vats, and other confined places, is due to the accumulation of this gas, either exhaled from the earth or produced from organic matter. The ordinary test is to introduce a candle ; it should burn as brightly in the confined space as in the external air ; should the flame become at all dim, it would be unsafe to enter, for experience has shown that combustion may continue for some time in an atmosphere dangerously charged with carbon dioxide. Accidents from choke damp and after damp in coal mines are also examples of its fatal effect. The air issuing from the lungs of a man at each expiration contains from 4 to 4:5 volumes of carbon dioxide in 100 volumes of air, and could not, therefore, be breathed again without danger. The total amount of this gas evolved by the lungs and skin amounts to about 0:7 cubic foot per hour. Adding this to the carbon dioxide already present in the air (say. 0-04 per cent.), the total should be distributed through at least 3500 cubic feet, in order that it may be breathed again with perfect safety, that is, in order that the CO,, which is regarded as the indicator, should not exceed 0-06 per cent. by volume. Hence the necessity for a constant supply of fresh air by ventilation, to dilute the expired air to such an extent that it may cease to impede respiration. This becomes the more necessary where a demand is made on the atmospheric oxygen by candles or gas-lights. An ordinary gas-burner consumes at least 3 cubic feet of gas per hour, which requires rather more than its own volume of oxygen for combustion, and produces about 1-7 cubic foot of carbon dioxide. Fortunately, a natural provision for ventilation exists in the circumstance that in the processes of respiration and combustion, the evolved gases are at a higher temperature, and thus their specific gravity is diminished by expansion, causing them to ascend and give place to fresh air. Hence the vitiated air always accumulates near the ceiling of an apartment, and it becomes necessary to afford it an outlet by opening the upper sash of the window, since the chimney ventilates immediately only the lower part of the room. These principles may be illustrated by some very simple experiments. Two quart jars (Fig. 60) are filled with carbon dioxide, and after being tested with a taper, a 4-oz. flask is lowered into each, one flask containing cold and the other hot water. After a few minutes the jar with the cold flask will still contain enough carbon dioxide to extinguish the taper, whilst the air in the other jar will support combustion brilliantly, VENTILATION 69 A tall stoppered glass jar (Fig. 61) is placed over a stand, upon which three lighted tapers are fixed at different heights. The vitiated air, rising to the top of the jar, extin- guishes the uppermost taper first and the others in succession. By quickly removing the stopper and raising the jar a little before the lowest taper has expired, the jar will be ventilated and the taper revived. A similar jar (Fig. 62), with a glass chimney fixed into the neck through a cork, is placed over a stand with two tapers, one of which is near the top of the jar and the Fie. 60. Fia. 61. Fic. 62. other beneath the aperture of the chimney ; if a crevice for the entrance of air be left between the jar and the table, the lower taper continues to burn indefinitely, whilst the upper one is soon extinguished by the CO, accumulating around it. In ordinary apartments, the incidental crevices of the doors and windows are depended upon for the entrance of fresh air, whilst the contaminated air passes out by the chimney ; but in large buildings special provision must be made for the two air currents. In mines this becomes the more necessary, since the air receives much additional contamination by the gases (marsh-gas and carbon dioxide) evolved from the workings, and by the gases produced in blasting operations. Mines are generally provided with two shafts for ventilation, under one of which (the wpcast shaft) a fire may be maintained to produce the upward current, which carries off the foul air, whilst the fresh air descends by the other (downcast shaft). The current of fresh air is forced by wooden partitions to distribute itself, and to pass through every portion of the workings. The operation of such provisions for ventilation is easily exhibited. A tall jar (Fig. 63) is fitted with a ring of cork, carrying a wide glass chimney, A. If this be placed over a taper standing in a plate of water, the accumulation of vitiated Fig. 63. air will soon extinguish the taper ; but if a second chimney, B, supported in a wire ting, be placed within the wide chimney, fresh air will enter through the interval between 1 CARBON DIOXIDE the two, and the smoke from a piece of brown paper will demonstrate the existence of the two currents, as shown by the arrows. A small box (Fig. 64) is provided with a glass chimney at eachend. In one of these, B, representing the upcast shaft, a lighted taper is suspended. A piece of smoking brown paper may be held in each chimney to show the direction of the current. On closing A with a glass plate, the taper in B will be extinguished, the entrance of fresh air being prevented. By breathing gently into A the taper will also be extinguished. The experiment may be varied by pouring carbon dioxide and oxygen alternately into A, when the taper will be extinguished and rekindled by turns. A pint bell-jar (Fig. 65) is placed over a taper standing in a tray of water. If a chimney (a common lamp-glass) be placed on the top of the jar, the flame of the taper will gradually die out, because no provision exists for the establishment of the two currents ; but on dropping a piece of tinplate or cardboard into the chimney so as to divide it, the taper will be revived, and the smoke from the brown paper will distinguish the upcast from the downcast shaft. One pint of water shaken ina vessel.containing carbon dioxide, at the ordinary pressure of the atmosphere, and at the ordinary temperature, will dissolve about 1 pint of the gas, equal in weight to nearly 16 grains. If, as in the manufacture of soda-water, the gas be confined in the vessel under a pressure equal to twice or thrice that of the atmosphere—that is, if twice or thrice the quantity of gas be compressed into the same space—the water will still dissolve 1 pint of the gas, but the weight of this pint will now be twice or thrice that of the pint of uncompressed gas, so that the water will have dissolved 32 or 48 grains of the gas, accordingly as the pressure had been doubled or trebled. As soon, however, as the pressure is removed, the com- pressed carbon dioxide will resume its former state, with the exception of that portion which the water is capable of retaining in solution under the ordinary pressure of the atmosphere. Thus, if the water had been charged with carbon dioxide under a pressure equal to thrice that of the atmo- sphere, and had therefore absorbed 48 grains of the gas, it would retain only 16 grains when the pressure was taken off, allowing 32 grains to escape in minute bubbles, producing the appearance known as effervescence. In a similar manner the waters of certain springs become charged with carbonic acid gas, under high pressure, beneath the surface of the earth, and when, upon their rising to the surface, this pressure is removed, the excess escapes with effervescence, giving rise to the sparkling appearance and sharp flavour which render spring water so agreeable (p. 42). The sparkling character of champagne, bottled beer, &c., is due to the presence in these liquids of a quantity of carbon dioxide which has been generated by fermentation subsequent to bottling, and has therefore been retained in the liquid under pressure. In the case of Seidlitz powders and soda-water powders, the effervescence caused by dissolving them in water is due to the disengagement of carbon dioxide, by the action of the tartaric acid, which composes one of the powders, upon the sodium bicarbonate composing the other powder, producing sodium tartrate and carbon dioxide. In the dry state these powders may be mixed without any chemical change, but on the addition of water reaction immediately occurs with efferves- cence. Many baking powders are mixtures of this kind, being used for imparting lightness and porosity to bread and cakes, by distending the dough with bubbles of carbon dioxide. The solubility of carbonic acid in water is of great importance in the chemistry of nature ; for this acid, brought down from the atmosphere dis- solved in rain, is able to act chemically upon rocks, such as granite, which contain alkalies—the carbonic acid attacking these, and thus slowly dis- integrating or crumbling down the rock, an effect much assisted by the mechanical action of the expansion of freezing water in the interstices of the PHYSICAL PROPERTIES, SOLUBILITY 71 rock. It appears that soils are thus formed by the slow degradation of rocks, and when these soils are capable of supporting plants, the solution of carbonic acid is again of service as a solvent for certain portions of the mineral food of the plant, which pure water could not dissolve, and the plant cannot take up except in the dissolved state. (See also p. 44.) Physical properties. — The student is recommended carefully to contrast these with the properties of nitrogen, oxygen and hydrogen ; carbon dioxide deviates not infrequently from the gas laws owing to its critical point being above the normal temperature, 0°; 7¢.e. at ordinary temperatures it is in the state of vapour (p. 35), and does not behave as a true gas. As already observed, the specific gravity of carbon dioxide is 152909 (air = 1) or 21-971 (H = 1). This is slightly higher than the theoretical, 1-5201 and 21-83, because of proximity to the critical point. Consequently there is a corresponding deviation from Avogadro’s law. One litre of CO, at N.T.P.-weighs 1-9652 grams. The pressure coefficient is about 0-00370 at N.T.P., but it increases with the pressure, being 0-003725 at 0° and 1000 mm. Ata pressure of 40 atmospheres it is 0-00945 between 6° and 63-6°. The coefficient of expansion is about 0-00373, and thus is considerably different numerically from the pressure coefficient ; this also is attributable to the gas being below its critical point ; cf. p. 35, also Hydrogen, p. 97. For the same reason this substance can be liquefied at the ordinary tempera- ture by pressure alone, viz. by 54 atmospheres (800 Ibs. per sq. in.) at 17°, or 34:3 atmospheres at 0°. (It follows from this that the gas is too com- pressible and therefore it does not obey Boyle’s Law strictly at ordinary temperatures.) It forms a colourless liquid which boils at — 78-2° at 760 mm. and having a density of 1-191 at — 60°, 0-925 at 0°, 0-772 at 20°. Its critical temperature is 31-9°, crit. press. 77 atm., crit. vol. 2-155, crit. density 0-464. By its own evaporation liquid carbon dioxide readily yields the solid in a snow- like form (p. 82). If the liquid be contained in a vessel placed in a bath of liquid air, it solidifies to an ice-like mass of density 1-6267 at — 188-8°, 1-56 at — 79°. The melting- point is —56-4° at 5-11 atm., a temperature considerably above its boiling-point, — 78-2° (see Sublimation, p. 33). Heat of vaporisation of the liquid, 57 calories ; heat of sublimation, 142-4 calories ; triple point, — 56-4° and 5-llatm. Liquid carbon dioxide dissolves a few non-metallic substances, e.g. iodine, phosphorus pentachloride, and several organic substances, e.g. alcohols, camphor, naphthalene ; it will not mix with water ; its solvent powers are much inferior to those of some other liquefied gases, eg. sulphur dioxide. By dissolving carbon dioxide snow in ether and allowing the mixture to evaporate, low temperatures (— 78°) may be attained (see also p. 83); with acetone, — 110°. The specific heat of the gas at constant pressure is about 0-20, at constant volume about 0-154, increasing with the temperature ; the ratio is about 1-3, significant of its triatomicity. 1 ¢.c. charcoal is capable of absorbing 20 or 30 cc. carbon dioxide, and for each c.c. of gas absorbed 0-31 calorie is evolved. It is absorbed by glass to a considerable extent. Solubility of Carbon Dioxide.—This is a subject of great importance in nature and of wide application, as already shown (pp. 44, 70). It is much more soluble than either of the gases so far considered. 100 c.c. water at 0° dissolve 171-3 c.c. (0-335 gram); at 5°, 142-4 c.c. (0-277 gram) ; at 10°, 119-4 c.c. (0-232 gram); at 15°, 101-9 c.c. (0-197 gram); at 20°, 87-8 c.c. (0-169 gram); at 30°, 66-5 c.c. (0-126 gram) ; at 60°, 35-9 c.c. (0-058 gram) of the gas at 760mm. The solubility varies with the pressure ; at 12-4° the following observations have been made : At a pressure of | atmo- sphere (760 mm.), 1-086 volumes are dissolved by 1 volume of water; at 5 atmospheres, 5-15 volumes ; at 10 atmospheres, 9-65 volumes ; at 20 atmo- spheres, 17-11 volumes; at 30 atmospheres, 23-25 volumes corrected to 72 COMPOSITION OF AIR N.T.P.; so that there is considerable deviation from Henry’s Law (p. 79). When 44 grams CO, dissolve in water about 5700 calories are evolved. Carbon dioxide is very soluble in alcohol, which at ordinary temperatures dissolves three times its volume ; 100c.c.at — 65° dissolve 3841 c.c. ; at 0°, 444¢.c. ; at 10°, 357c.c.; at20°,298c.c.; at 45°, 201 c.c. of the gas at 760 mm. Most organic liquids dissolve carbon dioxide very much more freely than water does (see Abegg., or Z. f. phys. chem. 37 (1901), 342); glycerin is an excep- tion, it dissolves only 3 times its volume. ; Chemical properties.—The most interesting of these in the study of air are those concerned in photosynthesis (p. 55) and the absorption of carbonic anhydride by alkalies (p. 244); others are considered under carbon . 244). : © aon dioxide may be separated from most other gases by the action of potash, which absorbs it, forming potassium carbonate, 2KOH + CO, = K,CO; + H,O. The proportion of carbon dioxide is inferred, either from the diminu- tion in volume suffered by the gas when treated with potash, or from the increase’ in weight of the latter. In the former case the gas is carefully measured over mercury (Fig. 66), with due attention to temperature and barometric pressure, and a little concentrated solution of potash is thrown up through a curved pipette or syringe, introduced into the orifice of the tube beneath the surface of the mercury. The tube is gently shaken for a few seconds to promote the absorption of the gas, and, after a few minutes’ rest, the diminution of volume is read off. Instead of solution of potash, damp potassium hydroxide in the solid state is sometimes introduced, in the form of small sticks or balls. To determine the weight of carbon dioxide in a gaseous mixture, e.g. air, a known volume of the latter is passed first through tubes, B (Fig. 272), filled with calcium chloride, or pumice-stone moistened with strong sulphuric acid to remove water-vapour, then through a bulb-apparatus, C, containing a strong solution of caustic potash, and weighed before and after the passage of the gas. A little tube, containing calcium chloride, E, must be attached to the bulb-apparatus and weighed with it, for the purpose of retaining any vapour of water which the large volume of unabsorbed gas might carry away in passing through the solution of potash. Atmospheric moisture.—Water vapour is always present and varies considerably from time to time. Its existence becomes evident by the deposition of dew on a very cold body, e.g. on the outside of a glass of ice- water. The determination of its proportion—hygrometry—is usually made by physical methods (see text-books on Heat), but chemical methods are available, e.g. by passing a known volume of air through weighted tubes filled with some substance capable of absorbing moisture, B (Fig. 41), and weighing again; the increase in weight represents the quantity of water vapour in the given volume of air. COMPOSITION OF AIR.—Methods have already been described for determining the proportions of nitrogen and oxygen (p. 26), carbon dioxide (v.s.), water vapour (v.s.) ; that for argon occurs later (p. 293). Complete analyses show that the principal components occur in very nearly constant ratios and approximate the following for dry air : Nitrogen . . j j ; - 78-08 per cent. by volume. Oxygen . : : s , . 20-95 Argon. ‘ ‘ ‘ - . 0-935 2 ” ” ” DUST "93 Carbon dioxide. ‘ ‘i F . 0-034 per cent. by volume. Ozone . ‘i a ‘ - . 0-00015 ,, 5 Nitric acid ‘ ‘ ‘ . 0:0008 ,, 5 Ammonia _ . 0-00005 ,, ‘A Aqueous vapour, though very variable, may be stated, on the average, as 1-40 per cent. by volume or 0-87 per cent. by weight. Since the atmo- sphere is the receptacle for all gaseous emanations, other substances may be discovered in it by very minute analysis, e.g. marsh-gas, sulphuretted hydro- gen, sulphur dioxide, especially in the neighbourhood of their source, the last in or near towns. Thousands of accurate determinations of the ratio of oxygen to nitrogen have been made in every quarter of the globe, over the sea, in open country, in large towns, and with only very few exceptions all the results lie between 20-90 and 21-00 per cent. for oxygen and 79-10 and 79-00 per cent. for nitro- gen (including argon). This constancy of composition led many at one time to consider air a definite compound, but this is disproved by variation in composition brought about by purely physical changes ; by diffusion (p. 75), by solution in water (p. 79), by fractionation of liquid air (p. 86), &. More- over, all the properties of air and of these variations are those which would be predicted for mixtures of these gases in such proportions ; whilst an essential feature of a chemical compound is that its properties cannot be foreseen from those of its constituents. Dust, or minute particles of solid matter, although much heavier than air, is always to be found in comparatively large quantity suspended in the atmosphere and carried by the air currents. Its presence is revealed when a beam of sunlight streams into an otherwise darker room ; in its absence the air is optically pure and the pencil of light is quite invisible, being found only by placing something in its path. Much of the dust is inorganic, being blown up from dry surfaces ; volcanoes also contribute largely. By drawing air for many hours or days through a tube loosely plugged with pyroxylin (q.v.) and then dissolving it in a mixture of ether and alcohol, a quantity of atmo- spheric dust can be separated. Iron, calcium, sodium, in combination with carbonic, sulphuric, phosphoric and hydrochloric acids, silica, &c., may be found. Sodium chloride is common in sea air. The minute crystals present in the atmosphere are capable of starting crystallisation in supersaturated solutions when exposed to the air (p. 40). Micro-organisms—bacteria, yeasts, spores of moulds, &c., animal germs— chiefly saprophytes, become diffused through the atmosphere, or, more often, are carried on the particles of dust created by the drying-up of the medium on which they have grown. In presence of moisture neither dust nor micro- organisms can get free as a rule. A hundred miles out at sea the atmosphere is practically free from solid particles, save salt. The deposit of these units into a favourable environment is of great importance in nature ; the various bacteria induce formation of ammonia (p. 182), of nitrites (p. 181), of nitrates (p. 363) ; acetic acid fermentation (q.v.), lactic acid fermentation (q.v.), &. ; and are the agents causing many diseases in man, animals and plants; yeasts bring about alcoholic fermentation (q.v.), &c.; spores, when falling on a suitable medium, germinate to produce moulds, mildews, or larger organisms. Dust particles also favour the deposition of atmospheric moisture by acting as nuclei around which the aqueous vapour can precipitate and so conduce to the formation of fog and rain. However, this result follows from other causes ; sulphur dioxide or smoke may be the means. A fall in baro- metric pressure leads to the same end if the air is sufficiently moist. This may be demonstrated by slightly reducing the pressure in a flask containing water, when a fog immediately appears in the flask. 74 PROPERTIES OF GASES The physicai properties of air are throughout the mean of those of the gases composing it. Its density in the dry state is frequently taken as a standard. Compared with hydrogen it is 14387. One litre dry purified air at N.T.P. weighs 1-2934 grams and is thus 773-22 times lighter than water. This can be arrived at by calculation : 780-8 c.c. nitrogen (1 1. weighs 1-25092 g.) weigh 0-9767 g. 209'5 ,, oxygen (ll. s,, 1-429 g¢.) Bs 0-2994 g. 9-35 ,, argon (ll. 4, 17825 g.) a 0-0166 g. 35 ,, carbon dioxide (11. ,, 1:9652 g.) 3 0-0007 g. *, 1000 ,, air (dry and purified) 35 1-2934 g. The effect of temperature and pressure on the weight of one litre of air is seen in the following Table : 0° 5° 10° 15° 20° 25° 30° 750mm. .| 1-276 1-253 1-231 1-210 1-189 1-169 1-150 760 ,, «| 1-293 1-270 1-248 1-226 1-205 1-185 1-165 TAO? 55 | LBEO 1-287 1-264 1-242 1-221 1-200 1-181 Hence, owing to the varying buoyancy of air, ordinary atmospheric changes may make a sensible difference in the apparent weight of an apparatus. These figures obtain with a constant volume of air and constitute the kind of Table generally given in works of reference; their use may be illustrated by calculating the weight of 15-3 c.c. air at 25° and 770 mm. ; 1000 c.c. at 25° and 770 mm. weigh 1-200 grams, .-. 15:3 ¢.c. weigh 1-200 x 0-0153 = 0-01836 gram. But this can be found also from the weight of one litre at N.T.P. by means of the laws given on p. 9. 1000 c.c. air at N.T.P. weigh 1-2934 grams; .-. (by Dalton’s law) at 25° and 760 mm., 273 i 9934 y —A'? ‘ ? 1000 c.c. weigh 1-2934 x 973 p25 SAMs ; and (by Boyle’s law) at 770 mm., 273 770 5 : 1-2934 x 273 4 35 X ep Stams; -. 15:3 c.c. at 25° and 770 mm. weigh 12934 x 273 < 770 x 15:3 298 x 760 x 1000 2/887 gram. Another instructive table could be derived from the changes in volume suffered by a constant weight of gas. One gram air has a volume of 773:2 c.c. at N.T.P.; at 8° and 760 mm. it measures 773-2 ae 8 = 795'8 c.c. ; at 0° and 742 mm., 773-2 x Ss = 7920 c.c.; at 8° and 742 mm., 773:2 X 281 x 760 _ 815-1 we eae vie The pressure coefficient of air is 0-003670 or = iz and the coefficient of expansion is also 0-003670. These constants vary slightly with the different a ar 1 ‘ 1 11 gases ; with perfect gases it is almost exactly 373 (precisely wea) °F 3000, and this factor is universally employed for all ordinary calculations. It may be shown that the coefficient of expansion (p. 9) of a gas at any absolute temperature, A°, is + thus at 290° A (17° C.) the gas will expand 1 300 of the volume it has at 290°A for each degree rise in temperature. DIFFUSION 75 Eg. if 151 c.c. gas at 273° A (0° C.) be heated to 290° A it will measure 17 151(1+ 373) = 160-4.c.c. Now if it be raised to 315° A (42° C.) it will 25 3 measure 160-4 (1 + 300) = 174-23 c.c., ¢.e. 151 (1 + = = 174:23¢.c. The same applies to the pressure coefficient. The inexperienced student should observe that the pressure coefficient and the coefficient of expansion of a gas as published are for the gas at O° C. unless otherwise stated, and he is advised not to attempt “short cuts ”’ in making calculations. When air or any other gas is compressed, its tem- perature is raised ; when it expands, the temperature falls (p. 85). Difference of specific gravity accounts for many interesting and important pheno- mena. In the case of oxygen and nitrogen it is well exhibited by the arrangement shown in Fig. 67. A jar of oxygen, O, is closed with a glass plate and placed upon the table. A jar of nitrogen, N, also closed with a glass plate, is placed over it, so that the two gases may come in contact when the glass plates are removed. The nitrogen floats for some seconds above the oxygen, and if a lighted taper be quickly introduced through the neck of the upper jar, it will be extinguished in passing through the nitrogen, and will be rekindled brilliantly when it reaches the oxygen in the lower jar. Similarly, a jar of oxygen may be placed over a jar of CO, and a taper let down through the oxygen, in which it will burn brilliantly, into the CO,, which extinguishes it, and if it be quickly raised again into the oxygen it will rekindle with a slight detonation. This alternate extinction and rekindling may be repeated several times. But the one gas does not remain floating upon the other very ‘long ; diffusion occurs, a perfectly uniform mixture is pro- duced and maintained, even in opposition to gravitation, as in air. Fig. 67. Diffusion is the spontaneous, mutual mixing of two or more gases, or liquids, or even solids. It is very rapid and complete with gases, is slow and often incomplete after a considerable time with liquids (p. 316), and observable in only a few cases with solids (p. 334). Only gaseous diffusion will be discussed here. In the above experiments, and in those with hydrogen (p. 76) and carbon dioxide (p. 76), the downward diffusion of the lighter gas and the upward tendency of the heavier implies a rapid movement in all directions of the molecules themselves. That this is so has been amply proved, and the kinetic theory of gases (p. 308) is based on this hypothesis ; and thence are deduced explanations of most of the phenomena of the gaseous state. That the substance of a gas fills only a very small portion of the space occupied is evident from the fact that the gaseous nitrogen which occupies 800 c.c. at ordinary temperature and pressure, has a volume of only 1 c.c. when solidi- fied ; hence at least 799 c.c. out of 800 c.c. are vacuous. It thus appears that the individual molecules of a gas have plenty of room in which to move about and when more than one kind are present the molecules of each kind can wander throughout the whole space without much interference from those of the other kind ; hence they are able spontaneously and mutually to mix or diffuse. It will be shown later that a molecule of a gas moves with the same quantity of energy, no matter what kind of molecule it is, provided the temperature is the same in all cases (p. 309); therefore, this definite quantity of energy will move a molecule of light weight, e.g. hydrogen, much faster than it will a heavy molecule, e.g. carbon dioxide ; it is an obvious inference 76 DIFFUSION EXPERIMENTS that a number of rapidly moving hydrogen molecules would distribute them- selves throughout a given space in less time than an equal number of slowly moving carbon dioxide molecules will do ; experience shows that in all cases perfect intermixture is eventually attained. This is not easily shown with gases in bulk, but that such is the case can be demonstrated by introducing some hindrance to the movements of the two gases. Various porous sub- stances exhibit this hindering property. When a diffusion tube (Fig. 68), a glass tube, A, closed at one end by a plate of plaster of Paris, B, is filled with hydrogen,’ and its open end im- mersed in water, the water rises rapidly in the tube, on account of the rapid escape of the hydrogen through the pores of the plaster. The external air Vic. 69. passes into the tube through the pores at the same time, but much less rapidly than the hydrogen passes out, so that the ascent of the column of water, C, marks the difference between the volume of hydrogen which passes out, and that of air which passes into the tube in a given time, and allows a measure- ment to be made of the rate of diffusion ; that is, of the velocity with which the gas issues as compared with the velocity with which the air enters, this velocity being always taken as unity.2. To determine the rate of diffusion it is of course necessary to maintain the water at the same level within and without the diffusion tube, so as to exclude the influence of pressure. To prove that the ascent of the hydrogen due to its lightness is not instrumental in drawing up the water in the diffusion tube, the experiment may be made as in Fig. 69, where the plate of plaster, v, is turned downwards, so that the diffusion occurs in opposition to the action of gravity. This tube is filled by passing hydrogen in through the tube, s, and allowing the air to escape through t, which is afterwards closed by a cork. The plaster of Paris, o, is tied over with caoutchouc whilst the tube is filled. On removing the cap the hydrogen diffuses out downwards and the water rises in the tube, s. If the apparatus be filled with air (the lighter gas) and a beaker of carbon dioxide (the heavier gas) surround the vessel having the plate o, the same result will happen ; but if the apparatus be filled with carbon dioxide, air will enter more rapidly than the carbon dioxide diffuses out, with the result that the liquid will be depressed and gas will escape through the tube, »s. Laboratory experience shows that a cracked jar, or a bottle with a badly fitting stopper, may often be used to retain oxygen but not hydrogen. A very striking illustration of the high rate of diffusion of hydrogen is arranged * This tube must be filled by displacement (see Fig. 17), in order not to wet the plaster. A piece of sheet caoutchouc may be tied over the plaster of Paris, so that diffusion may not commence until the sheet is removed. * Air being a mixture of nitrogen and oxygen, its rate of diffusion is intermediate between the rates of those gases ; however, since the proportions of the gases are very nearly constant, no error of any magnitude arises, LAW OF GASEOUS DIFFUSION 77 as represented in Fig. 70. A is a cylinder of porous earthenware (such as are employed in galvanic batteries) closed at one end and furnished at the other with a perforated caoutchouc stopper, through which passes a glass tube, B, about six feet long and half an inch in diameter. This tube being supported so that its lower end dips about an inch below the surface of water, a jar of coal-gas is held over the porous cylinder, when the velocity of the particles of the gas is manifested by their being forced (not only out of the mouth of the jar, C, which is open at the bottom, but also) through the pores of the earthenware jar, the air from which is violently driven out, as if by blowing, through the tube, and is seen bubbling up rapidly through the water. When the air has ceased to bubble out and a large volume of gas has entered the porous jar, the bell- jar, C, is removed, when the gas escapes so rapidly through the pores that a column of twenty to thirty inches of water is drawn rapidly up the tube, B. If the greatest height to which the water ascends be marked, and when it has returned to its former level a jar of hydrogen be held over the porous cylinder, it will be found that the above phenomena are manifested in a much higher degree, showing that coal-gas, being heavier than hydrogen, does not pass nearly so rapidly through the pores of the earthen- ware as hydrogen does. By connecting the porous cylinder, A, by means of a short piece of tube, with a two-necked bottle, like that represented in Fig. 17, and passing through a cork in the other neck, a piece of tube extending to the bottom of the bottle and drawn out to an open point at its upper extremity, water may be forced out in a stream of two or three feet in height by holding the jar of hydrogen over the porous cylinder. The idea of hindrance having once been material- ised, the question of its application to the partial separation of a mixture of gases into its com- ponents naturally arises. If the diffusion tube be filled with a mixture of hydrogen and air, the hydrogen escapes more quickly than the air ; and it is because of the possibility of separating individual gases from mixtures that diffusion is a subject of such great interest to the chemist. This process of analysis is known as atmolysis (aruds, Vapour ; Fic. 70. Avw, to loosen). Débereiner observed the phenomenon with a cracked flask in 1823, but it is to Thomas Graham (6. 1805, d. 1869) we are indebted (1832) for precise knowledge of the subject and for the Law of Diffusion of Gases that the rates of diffusion of gases vary inversely as the square roots of their relative densities (p. 309). Thus, oxygen is 16 times as heavy as hydrogen, so that the rate of diffusion of hydrogen : the rate of diffusion of oxygen :: 16: /1; in other words, hydrogen will mix with another gas four times as fast as oxygen will mix with that gas. Since the relation between the weights of equal volumes of hydrogen and air is that of 0-069 : 1, the rates of diffusion are as 1: ,/ 0-069—that is, hydrogen diffuses about 3-8 times as rapidly as atmospheric air, or 3-8 measures of hydrogen will pass out of the diffusion tube whilst one measure of air is passing in. In reviewing the analytical methods for determining the composition of water (p. 22), atmolysis was suggested for resolving the mixture of free hydrogen and free oxygen obtained in certain processes. 78 ATMOLYSIS The great difference in the rates of diffusion of the two gases may be applied in the arrangement represented in Fig. 71. A is a jar filled with a mixture of two volumes of hydrogen with one volume of oxygen, communicating through the stop-cock and flexible tube with the glass tube, B, which is fitted through a perforated cork in the bowl of the common tobacco-pipe, C, the sealing-waxed end of which dips under water in the trough, D. By opening the stop-cock and pressing the jar down in the water, the mixed gases may be forced rapidly through the pipe, and if a small cylinder, Z, be filled with them, the mixture will be found to detonate violently on the approach of a flame. But if the gas be made to pass very slowly through the pipe (at the rate of about a cubic inch per minute), the hydrogen will diffuse through the pores of the pipe so much faster than the oxygen that the gas collected in the cylinder will contain so little hydro- gen as to be no longer ex- plosive, and to exhibit the property of oxygen to re- kindle a partly extinguished match. The fact that the phenomenon of diffusion is shown by solids and liquids as well as by gases has led to the conclusion that in all three states of matter the mole- cules are in constant motion. In a solid the distance through which each molecule moves is very small because the molecules are so close together that they attract and hinder each other. It is supposed that heat increases the motion until presently the molecules are moving rapidly enough partly to counteract their attraction for each other, whereupon the solid melts to a liquid. In the liquid the molecules are still under the influence of each other so that they cannot move freely through space, which is the characteristic of gaseous molecules. By heating the liquid it eventually boils and becomes a vapour, which, when its temperature is considerably above that at which the liquid boils, has the properties of a gas. In a true gas the molecules would move without influencing each other in any regard, except in so far as they might collide and rebound like billiard- balls. They would never stick together, so to speak. It has been proved by mathematics that the ideal gas would obey the laws of Boyle and Dalton (pp. 9 and 308) accurately, but gases differ very much in the degree to which they deviate from the laws. Those gases deviate least which are the most difficult to liquefy, for they are farthest removed from the liquid state. Helium is the most perfect gas, but hydrogen is practically equal, and, being readily obtainable and the lightest of all bodies, its properties are used as general standards with which to compare those of other substances. Carbon dioxide, on the other hand, is a very imperfect gas at the ordinary temperature and pressure, for it is then not far above its liquefying point ; but it improves if its temperature is raised or its pressure reduced. Absorption and solubility of gases.—It has been seen that 100 c.c. water will dissolve 2-35 c.c. (000293 gram) nitrogen, or 4:89 c.c, (0-00695 gram) HENRY’S AND DALTON’S LAWS 79 oxygen, or 171-3 c.c. (0-335 gram) carbon dioxide at N.T.P., showing that the nature of a gas has much to do with its solubility ; and that in each case the solubility decreases with rise of temperature, the pressure remaining constant, but not according to any general law (pp. 53, 58). The absorption coefficient of a gas-is the volume of gas (reduced to N.T.P. and corrected for the vapour pressure of the solvent) dis- solved by one volume of water at the stated temperature ; e.g. that of nitrogen is 0-0235 at 0°, 0-0186 at 10°. Bunsen’s absorptiometer consists of a simple graduated tube (Fig. 9, p. 16)—in which a given volume of air-free water is shaken thoroughly with a known volume of the gas—fitted with devices necessary to maintain constant temperature and pressure during the experiment; the diminu- tion in the volume of the gas is the volume absorbed by the given quantity of water. Henry’s Law states that the weight of a gas dissolved by a given quantity of a liquid is proportional to the pressure ; or—since the volume of a mass of gas is inversely proportional to the pressure (Boyle’s Law)—the volume of a gas dissolved by a liquid is the same whatever the pressure, the temperature being constant. #.g. 100 c.c. water at 0° dissolve 2-35 c.c., i.e. 0-00293 g. nitrogen at 1 atm. pressure. ” ” ” 2-35 2 >» 0-00586 2 2” ” ” 2” ” 2-35 »» > 0:00879 ” » 3 ” The law holds good provided the pressure is not great and the temperature is well above the critical point of the gas. Carbon dioxide, therefore, does not obey very well (p. 72). When a mixture of two or more gases is to be absorbed by a liquid, the same law obtains, but each gas has to be considered separately, exactly as if the others were absent. In air there is one-fifth volume of oxygen, but it exists throughout the whole volume and exerts a pressure of one-fifth of an atmosphere ; therefore at 0° 100 c.c. water dissolve 4-89 c.c. at this reduced pressure, just as if it were at normal pressure, but the weight is proportional to the pressure, 7.e. one-fifth of 0-00695 g. = 0-00139 g. ; but obviously this is the weight of one-fifth of 4-89 c.c., 7.e. of 0-978 c.c., at N.T.P. There is also four-fifths volume of nitrogen, exerting a pressure of four-fifths of an atmosphere ; therefore at 0° 100 c.c. water dissolve 2-35 c.c. as at N.T.P., but the weight dissolved is four-fifths of 0-00293 g., 7.e. 0-002344 g., which is the weight of four-fifths of 2-35 c.c., t.e. of 1-88 ¢.c., at N.T.P. Hence we find that 100 c.c. water at 0° will dissolve 2-858 c.c. air at N.T.P., and that the mixture of dissolved gases is composed of 0-978 ¢.c. oxygen and 1-88 c.c. nitrogen, so that oxygen constitutes 34-2 per cent. by volume. Precise figures give a slightly higher result. By experiment it is 34-91 per cent. at 0°, 34-25 per cent. at 15°, argon being included with the nitrogen. By boiling or otherwise removing the gases and repeating the treatment on the “ recovered air,” a gas rich in oxygen can be obtained ; a modification of the process has technical application. These facts find expression in the second of the two following statements of Dalton’s Law of partial pressures. (a) In a mixture of gases the pressure exerted by each gas is exactly the same as the pressure which that gas would exert did it alone occupy the volume filled by the mixture. (b) When a mixture of gases dissolves in a liquid, each component dissolves in a pro- portion corresponding with its own partial pressure. When the space above the solution of a gas contains the same gas as that which is dissolved, equilibrium is established when the same quantity of gas passes from the space into the liquid, and from the liquid into the space, in unit time. If for the gas in this space there be substituted another, the dissolved gas will go on escaping from the solution until its partial pressure in the space and its pressure within the solution 80 FREEZING MACHINES adjust themselves to equality, 7.e. until a new equilibrium is established ; and the new gas will be absorbed until its gaseous pressures within and without the solution are equal. It is clear, therefore, that a few such displacements of the gas in the space will cause the liquid to part with practically all of the gas originally dissolved in it. In accurate measurements correction must be made for the pressure of the vapour of the liquid and the prevailing barometric pressure. As a further example we may calculate the weight of carbon dioxide dissolved by 87 c.c. water at 15° from air when the barometer stands at 746 mm. From the Table on page 34 the vapour pressure of water at 15° is 12:79 mm., .-. the air in the apparatus exerts a pressure of 746 — 12-79 = 733-21 mm. There is 0-034 per cent. by volume of CO, in the air, .-. the pressure of the CO, is Tes eh x ovost = 02493 mm. 100 c.c. water at 15° dissolve 0-197 gram (p. 71) CO, at 760 mm., .-. at 0-2493 mm. the quantity ; . 0-197 x 0-2493 x 87 dissolved by 87 c.c. is ese OG 0-000056 gram. Those gases which are very soluble, e.g. ammonia, hydrochloric acid sulphurous anhydride, do not obey the above laws under ordinary circum- stances. With few exceptions, gases are not so soluble in solutions as they are in the pure solvents. When a liquid freezes it gives up any gas it holds in solution, which accounts for the air bubbles in ice. When a gas dissolves in a liquid, heat is disengaged ; and the quantity so evolved is called the heat of dissolution of the gas (p. 325). Speaking broadly, the greater the solubility of a gas in water, the more easily can it be liquefied ; but the rule is not absolute. Freezing machines.—It has been seen already that when water is vaporised, a large quantity of heat is rendered latent (p. 32). This disappearance of heat occurs at any temperature whenever this change of state happens ; and there- fore, if vaporisation occurs when the water is at 0°, no external heat being applied, the consequent withdrawal of heat by the vapour from the re- mainder of the water should tend to lower the temperature and produce ice. This will be demon- strated to be the case when considering the triple point (p. 72), where reduction of pressure below 4-6 mm. brings about rapid vaporisation and simul- b taneous formation of ice. This principle is applied Fie. 72. in Carré’s freezing machine (Fig. 72), where the space above the water to be frozen in the flask, a, is exhausted by the pump and the water vapour as fast as it is producedis removed by absorption by the strong sulphuric acid mechanically agitated in the vessel, b. The water is seen to boil and freeze at one and the same time. This method of boiling a liquid under greatly reduced pressure is employed for solidifying some gases ; ¢.g. hydrogen, carbon dioxide (p. 83). * Vaporisation.—It also follows from the law of Partial Pressure that in a mixture of vapour and air the vapour exerts the same pressure as it would exert did it alone occupy the space filled by the mixture, and that, since the extent to which a liquid will evaporate depends, when the temperature is constant, solely on the pressure of its vapour, evaporation must proceed to the same extent in a vacuum and in air. Thus, at 15-3° water and its vapour are in equilibrium when the pressure of the latter is equal to 12:9 mm, of mercury, so that water will continue to evaporate until it has parted with sufficient vapour to create this Pressure in the space above it. If that space originally contained a vacuum, a pressure-gauge will show 4 pressure of 12-9 mm. when the evaporation has apparently ceased ; if the space originally contained air at 760 mm. pressure, the gauge will show a pressure of 760 + 12-9 mm. The hastening of evaporation by a draught of air is simply due to the prevention of the accumulation of vapour over the surface of the liquid; in this way the vapour pressure may be hindered from Tising to that which causes equilibrium, LIQUEFACTION AND SOLIDIFICATION OF GASES 81 Another freezing apparatus invented by Carré (Fig. 73) depends on the use of ammonia. Ammonia itself is a gas which can be liquefied by very moderate pressure at ordinary temperatures ; it is also extremely soluble in water ; 1 c.c. water at 0° dissolves 1050 c.c. of the gas at 760 mm. Such a specially strong solution is put into the boiler, A, of the apparatus, which is connected gas-tight with the receiver, B, the whole being oe of resisting a pressure of about 10 atm. On placing the boiler over a fire, the solution gives up its ammonia gas, which, not being able to escape, creates the necessary pressure and condenses to a liquid in the receiver, B, standing in cold water; most of the water in which the ammonia was dissolved remains behind in the boiler. The water to be frozen is placed in the vessel, C, immersed in spirit of wine contained in a cavity in the receiver. When the boiler is taken off the fire and plunged into cold water, the water within rapidly absorbs the ammonia gas in the . apparatus, and the pressure above the liquefied ammonia being thus greatly reduced, the liquefied gas in the receiver boils away very rapidly, withdrawing the heat necessary for its vaporisation from surrounding objects, i.e. from the water in C; the latter soon freezes. The ammonia having been re-absorbed by the water in the boiler, the process can be repeated. Seventeen grams of ammonia absorb 566] calories in vaporising at — 40°. The specific heat of liquefied ammonia between 0° and 20° is 1-02, being higher than that of water, a rare occurrence (p. 32). To refrigerate large spaces by means of liquid NH3, the gas is compressed by a pump into a coil immersed in a tank, and the liquid formed is allowed to evaporate through another coil also immersed in a tank, the gas returning to the suction side of the compression pump. Brine (which can be cooled considerably below 0° without freezing) is passed through the second tank, where it is cooled by the evaporating NH,, and then through pipes in the space to be cooled, then through the first tank, where it cools the compressed NHg, and finally back into the second tank. Carbon dioxide may be similarly employed with advantage ; for although it absorbs much less heat in passing from the liquid to the gaseous state (about 60 calories per gram at 10° as against 320 calories for ammonia) the volume to be pumped per unit weight is much less. Ether (q.v.) also is frequently applied to refrigeration. LIQUEFACTION AND SOLIDIFICATION OF GASES.—The sim- plest method of liquefying a gas is to cool it at atmospheric pressure to a temperature below that at which the liquid to be formed boils. Liquefaction then ensues just as steam condenses to water when cooled below 100° C. (see Sulphur dioxide, p. 156). By increasing the pressure on a liquid, its boiling-point is raised, hence if a gas be compressed it requires less cooling to liquefy it, for the boiling-point of the liquid to be formed is higher. Thus it is generally economical to compress the gas, as well as cool it, and this was the method by which the majority of gases were originally liquefied ; the one condition being that the temperature must be below the critical point of the substance (p. 35). Lavoisier appears to have been the first to speculate on the possibility of reducing gaseous bodies to the liquid and even to the solid state ; but it was clearly foreshadowed by Dalton. Michael Faraday (6. 1794, d. 1867) was the pioneer in the experimental study. In 1823, he packed a quantity of 6 QE "Eo WAI” Fie. 73. 82 LIQUEFACTION OF CARBON DIOXIDE chlorine hydrate (Cl.4H,O) in one end of a bent glass tube, cooled in ice, which was then strongly hermetically sealed. On placing the tube in water at 38° the crystals melt and become two layers ; the lower, amber-coloured liquid chlorine (sp. gr. 1:33), the upper, pale yellow chlorine water. On allowing the tube to cool again, the crystalline hydrate is reproduced, even at common temperatures, being more permanent under pressure. It may even be sublimed in a sealed tube. Afterwards he liquefied dry chlorine at a pressure of about 4 atmospheres. Faraday then proceeded to liquefy several other gases, e.g. carbon dioxide, sulphur dioxide (see also p. 156), sulphuretted hydrogen, hydrochloric acid, cyanogen, ammonia, &c., by subjecting the gas to the pressure caused by its continuous production in a sealed tube. Two other examples by his method may be described. (a) A small specimen of liquid carbon dioxide is easily prepared. A strong glass tube, A (Fig. 74), is selected, about 12 in. long, ,5, in. diameter in the bore, and yy in. thick in the walls. With the aid of A € eee sae “) the blow-pipe flame this tube is softened and drawn off at about an wv as inch from one end, as at B, which co-= = is thus closed, C. This operation should be performed slowly, in order ce { that the closed end may not be much thinner than the walls of the tube. When the tube has cooled, about 2 grams of powdered bicarbonate of ammonia (ordinary sesquicarbonate which has crumbled down) are tightly rammed into it with a glass rod. This part of the tube is then surrounded with a few folds of wet blotting-paper to keep it cool, and the tube is bent just beyond the carbonate of ammonia to a somewhat obtuse angle, D, The tube is then - softened at about an inch from the open end and drawn out to a narrow neck, E, through which a measured drachm of oil of vitriol is poured down # funnel-tube, so as not to touch the bicarbonate or soil the neck, which is then carefully drawn out and sealed by the blowpipe flame, as at F. The empty space in the tube should not exceed 4 cubic inch. When the tube is thoroughly cold, it is suspended by strings in such a position that the operator, having retired behind a screen at some distance, may reverse the tube, allowing the acid to flow into the limb containing the carbonate of ammonia ; or the tube may be fixed in a box which is shut up and reversed so as to bring the tube into the required position. If the tube be strong enough to resist the pressure, it will be found, after a few hours, that a layer of liquid CO, has been formed upon the surface of the solution of ammonium sulphate. By cooling the empty limb in a mixture of pounded ice and salt, or of hydrochloric acid and sodium sulphate, the liquid can be made to distil itself into this limb, leaving the ammonium sulphate in the other. In 1835 Thilorier worked with large and greatly improved apparatus on the same principle, allowing the liquefied gas—carbon dioxide, nitrous oxide, &c.—after com- pletion of the reaction, to distil over into a second vessel. By permitting the liquid to escape rapidly he obtained solid, snow-like carbon dioxide. Liquid CO, is now sold in steel cylinders provided with screw valves, like those containing compressed oxygen (Fig. 189). When the cylinder is turned on its head and the valve is opened, the liquid is ejected, and at once solidifies to carbonic acid “ snow ” (sp. gr. = about 1-4), which may be collected by surrounding the nozzle with sacking. The solid should be quickly shaken on to a sheet of paper and emptied into a beaker LIQUEFACTION OF AMMONIA 83 placed within a larger beaker, the interval being filled up by flannel. By covering the beaker with a dial glass, the solid may be kept for some time. The solid carbon dioxide evaporates without melting, for its own evaporation keeps it at a temperature below its melting-point. It produces a sharp sensation of cold when placed upon the hand, and if pressed into actual contact with the skin causes a painful frost-bite. Its rapid evaporation may be shown by placing a few fragments on the surface of water in the globe (Fig. 75), which has a tube passing down to the bottom, through which the pressure of the carbonic acid gas forces the water to a considerable height. The solid carbon dioxide is soluble in ether, and it evaporates from this solution far more rapidly, because the liquid is a better conductor of heat than the highly porous solid, and abstracts heat more rapidly from surrounding objects. It thus lowers the tem- perature to the boiling-point of CO, (— 78°) (p. 71). If a layer of ether be poured upon water and some solid carbon dioxide be thrown into it, the water is covered with a layer of ice. In 1839 Mitchell (U.S.A.) showed that by exhausting a mixture of carbonic acid snow and ether under the air-pump a temperature of — 100° was attainable, and by its aid he solidified sulphur dioxide. Later, Faraday attained — 110° by the same means. Onimmersing the bulb of a thermometer into the solution of solid carbon dioxide in ether, the mercury becomes solid, and the bulb may be hammered out into a disk. By placing a piece of filter-paper in an evaporating dish, pouring = : a pound or so of mercury into it, immersing a vire turned into SS flat. spiral at the end, covering the mercury with ether, and Fie. 75. throwing in some solid carbon dioxide, the mercury may soon be frozen into a cake. If this be suspended by the wire in a vessel of water, the mercury melts, descending in silvery streams to the bottom of the vessel, leaving a cake of ice on the wire, with icicles formed during the descent of the mercury. This experiment is rendered more effective by using an inverted gas-jar, to the neck of which is attached, by a perforated cork, « test-tube to catch the mercury. The round lid of a cardboard box gives a nice disk of frozen mercury. Even in a red-hot vessel, with prompt manipulation, the mercury may be solidified by the solution of solid carbon dioxide in ether. For this purpose a platinum dish is heated to redness over a large Bunsen burner, a few lumps of carbon dioxide are thrown into it, upon these is held a copper or platinum dish containing the mercury, in which is also held a wire to serve as a handle for withdraw- ing the mercury. Some more carbon dioxide is thrown upon the mercury, and ether is spirted on to it from a small wash-bottle. One or two additions of the carbon dioxide and ether alternately will freeze the mercury which may be withdrawn from the flames by the wire handle. (6) The liquefaction of ammonia is very easily effected by heating ammoniated silver chloride (AgCl.3NH;)in one limbof a sealed tube, the other limb of which is cooled in a freezing-mixture. A piece of stout glass tube, A (Fig. 76), about 12 inches long and 4 inch in diameter, is drawn out, at about an inch from one end, to a narrow neck. About 20 grams of silver chloride (dried at 200°) are introduced into the tube, so as to lie looselyinit. For this purpose a gutter of stiff paper, B, should be cut so as to slide loosely in the tube, the silver chloride placed upon it, and when it has been thrust into the tube (held horizontally) the latter should be turned upon its axis, so that the silver chloride may fall out of the paper, which may be then withdrawn. The tube is now drawn out to a narrow neck at about an inch from the other end, as in OC, and afterwards carefully bent, as in D, Fia. 76. 84 “ GASCADE ” METHOD eare being taken that none of the chloride falls into the short limb of the tube, which should be about 4 inches long. The tube is then supported by a holder, so that the long limb may be horizontal, and is connected by a tube and cork with an apparatus delivering dry NH., prepared by heating 80 grams of NH,Cl with an equal weight of CaO in a flask, and passing the gas, first into an empty bottle, A (Fig. 77), standing in cold water, and afterwards through a bottle, B, filled with lumps of quicklime, to absorb all aqueous vapour. The long limb of the tube must be surrounded with filtering paper, which is kept wet with cold water. The current of ammonia should be continued at a moderate rate, until the tube and its contents no longer increase in weight, Fic. 77. which will occupy about three hours — about 2-2 grams of NH, being absorbed. The longer limb is sealed by the blowpipe flame whilst the gas is still passing, and then, as quickly as possible, the shorter limb, keeping that part of the tube which is occupied by the ammoniated silver chloride still surrounded by wet paper. When the shorter limb of this tube is cooled (Fig. 78) in a mixture of ice and salt (or of 8 ounces of sodium sulphate and 4 measured ounces of common hydrochloric acid), whilst the longer limb is gently heated from end to end by waving a spirit-lamp beneath it, the NH, evolved by the heat from the ammoniated silver chloride, which partly fuses, condenses to a beautifully clear liquid in the coldlimb. When this is withdrawn from the freezing- mixture and the tube allowed to warm, the liquid ammonia boils and gradually disappears entirely, the gas being again absorbed by the silver chloride, so that the tube is ready to be used again. Fie. 78. A small quantity of liquefied ammonia may be more conveniently obtained by means ofa tube prepared as above, but containing about twelve inches of fragments of well-dried wood charcoal saturated with dry NH,. The shorter limb of the tube should be drawn out to a long narrow point before sealing. Thislimb being immersed in the freezing-mixture, the other is placed in along test-tube containing water, whichis heated to boiling. The ammonia soon returns to the charcoal when the tube cools. Thomas Andrews in 1869 studied very closely the physical changes suffered by carbon dioxide at various temperatures and pressures (p. 71) and established the long- foreshadowed conception of critical temperature and critical pressure (p. 35). In spite of all attempts, although those of Cailletet and Pictet in 1877 were not without success, it was not until 1883 that oxygen and then nitrogen were satisfactorily liquefied by Wroblewski by the “‘ cascade ”’ (or a-step-at-a- time) method. This consists in cooling the vessel, containing the gas to be condensed, with a bath of another gas already liquefied and now being rapidly evaporated under reduced pressure. This brings about a temperature below the critical point of the gas under treatment, with its consequent liquefaction ; the pressure being adequate. Then having obtained a sufficient supply of this new liquefied gas, it is used as the cooling medium in repeating the process to effect the condensation of a third gas with a still lower critical point ; and so on. The gap between nitrogen and hydrogen, however, was too great to be bridged by this method. In 1892 Dewar added interest to the subject of DEWAR’S INVESTIGATIONS 85 liquefied gases by discovering a mode by which, in spite of their low boiling- points, they may be preserved for a considerable time, thus suggesting prac- tical application, always a spur to scientific endeavour. Taking advantage of the fact that a vacuum is a very good thermal insulator, Dewar made vacuum-jacketed vessels—known as Dewar vessels—of the forms shown in Fig. 79, a and 6. If the time required for a given quantity of liquefied gas to evaporate from the simple vessel be taken as a standard, it will take five times as long for it to evaporate when the space between the walls is highly evacuated ; because conduction of heat by convection currents of the enclosed air from the outer wall to the inner no-longer exists, except so far as the vacuum is not quite perfect. Radiant heat still passes through the glass walls, but this may be cut off by silvering the inner surface of the outer wall, and thus the efficiency becomes six times as great, or thirty times in all. Still five times greater efficiency is attained by filling the vacuous a b 3 space with charcoal, which hinders direct Fic. 79. molecular bombardment from the outer to the inner wall; some other substances are also used. Metal Dewar vessels (Fig. '79c) are now made. To overcome the difficulty that gases occluded by the metal (p. 97) are gradually discharged into the jacket, a pocket in the vacuous space is filled with charcoal, by which, when the temperature is reduced by introducing the liquefied gas into the inner vessel, the gas in the jacket is so completely absorbed as to produce a vacuum more perfect than is attainable with mercury. Such vessels are made in copper, nickel, &c., with necks of some badly conducting alloy, of any size up to 20 litres or so, and are just as good as the silver-coated glass vessels. Dewar vessels are equally capable of preventing passage of heat outwards from any hot body they contain, and thus find application in the so-called “‘ thermos flasks.” The modern method of liquefying gases is founded upon the Thomson- Joule (Kelvin Joule) effect. These investigators showed that when a gas under pressure passes through a porous plug (e.g. a tight plug of cotton wool) or narrow orifice and escapes and expands into the free air on the other side, a fall in temperature occurs which is proportional to the difference between the pressures on the two sides of the plug. For a difference of 1 atmosphere at the ordinary temperature the thermal depression is about 0-25° in the case of air, but it is greater when the experiment is made at lower tempera- tures. With carbon dioxide, a less perfect gas, the fall is greater—over 1°. With hydrogen, one of the most perfect gases, a rise (0-039°) in temperature occurs. This is not really an exception. In all gases the effect in question diminishes as the temperature rises, that is, as the gas becomes more perfect, until at a certain temperature the effect changes to a rise of temperature. This is called the inversion temperature, which is about 6-75 times the critical temperature on the absolute scale ; for hydrogen it is 192-5° A, or approxi- mately 6-75 x 30° A. Above the inversion temperature a thermal increase results ; below, a depression. So slight a change as 0°25° for each atmosphere would appear to be of no value per se, even when greatly multiplied, for the liquefaction of gases ; but in 1895 Linde made a most ingenious application of the principle in his regenerative cooling process, and was able to make liquid air quickly, cheaply and in any desired quantity. One form of his apparatus is shown in Fig. 80, and is worked in the following manner. 1 Yor further notes on “ imperfect" gases, see p. 78. 86 LIQUID AIR Air compressed at some 200 atmospheres is admitted at A into a lengthy coil, B, of ~etal pipe, passing concentrically through a similarly coiled pipe, C. The other end of .e inner coil opens into a box, D, and is provided with a valve, E, One end of the outer coil also opens into the box, D, whilst the other end is connected with a com- p:essing pump, 7. The coils and box are embedded in a packing of wool, not shown in the figure, contained in the casing, H. To operate the apparatus the valve, Z, is opened until the air issues into the box, D, at a reduced pressure of some 20 atmospheres. The expanded and consequently cooled air passes up the outer coil to pump, T’, which compresses it again to 200 atmospheres and forces it through a coil of pipe round which water circulates in the cooler, J. Here it is deprived of the heat imparted to it by the work of the pump, and is passed back to the inner coil to undergo the same cycle once more. It will be seen that as the air cooled by expansion passes around the inner coil, it cools the air about to be expanded, and that each portion of air issuing from the inner coil must be colder than that which preceded it. After a time this accumulated cold becomes sufficient to lower the temperature to — 193° C., whereupon liquid air collects in box, D, and may be drawn off through tap, K, into Dewar vessels. It is found more economical not to let the gas expand to atmospheric pressure, as the smaller amount of work necessary to pump air at 20 atmospheres pressure, and the increased cooling due to the work which the expanding gas has to do in moving the expanded gas at this pressure, more than balance the extra cooling which might be obtained by expansion at a lower pressure. Since oxygen boils at a temperature some 10° higher than that at which nitrogen boils, freshly made liquid air contains nearly 50 per cent. by volume of oxygen. It is turbid from the presence of crystals of CO, ; after filtration through cotton wool it is a clear, mobile, bluish liquid, boiling at — 192°, having a density of about 0-910 and a refractive index of 1-2068 ; the boiling-point gradually rising to — 182° as the nitrogen evaporates. At a lower temperature it freezes ; but by subjecting liquid air to high exhaus- tion a magma of solid nitrogen and liquid oxygen results. from which the latter can be separated by a magnet or by rapid rotation of the vessel as in a centrifuge. The chief use of liquid air is as a source of oxygen which is oe by fractionally distilling the liquid, so that the nitrogen boils away rst. Fractional distillation is the operation of separating mixed liquids by carefully raising their temperature so as to distil first that which has the lowest boiling-point. The apparatus employed for separating oxygen and nitrogen in this manner is of LIQUEFACTION OF HYDROGEN AND HELIUM 87 the type shown in Fig. 81. Here the compressed air admitted at A passes through the inner pipes of two concentric coils, B and C, the two currents uniting again at D to pass through a coil, H, situated in the receiver, F. The valve, G, being opened, the air expands into the receiver and passes away through the outer pipe of the coil, C. Presently liquid air begins to collect in F, as in the apparatus already described, but its tempera- ture is somewhat higher than in that case because of the air passing through the coil, &, As a result nitrogen boils away from the liquid, and passing up the outer pipe of coil, B, issues at H. By opening valve, I, the liquid oxygen in the receiver may be allowed to evaporate through the outer pipe of coil, B, so as to be collected for use at the extremity, K. The valves, L, are adjusted so that the proportion of hot gas passing through each coil may be in relation to the larger proportion of nitrogen (as compared with the oxygen) passing away. With improved apparatus these principles were extended successfully to hydrogen by Dewar in 1898. With the aid of liquid air boiling in vacuo and suitable compression apparatus the hydrogen was initially cooled to — 205° at a pressure of 180 atm. and then in the apparatus condensed to the liquid state. In 1899 he obtained solid hydrogen by rapidly evaporating the liquidelement. By 1901 all the conditions of working were so far perfected that he carried 5 litres of liquid hydrogen across London. Not long before the realisation of this triumph, Ramsay discovered Helium (1895), and this proved the most refractory of all. On the same principles, using liquid hydrogen as the initial cooling medium, Onnes succeeded in condensing helium in 1908 and found its boiling-point to be 4° A (— 269° C.), crit. temp. 5° A, crit. press. 3 atm.; but it could not be solidified by evaporating the liquid at a pressure of only 2 mm. when a temperature estimated at 2° A (— 271° C.) was attained. Thus the goal of three-quarters of a century’s work was reached and the way opened for many further investigations. With comparatively large open vessels of liquid air boiling at about — 190°, and of liquid hydrogen boiling at — 252-5°, all kinds of experiments may be made at these extremely low temperatures as with an open beaker of water. On surrounding vessels containing other liquefied gases—e.g. oxygen, nitrogen—with liquid hydro- gen, the liquefied gases are solidified. Densities, specific heats, conduc- tivities and other physical properties of substances when almost deprived of heat have been determined with most instructive results. One of the most remarkable of the many interesting experiments that can be performed with liquid air consists in absorbing it by a wad of cotton wool which has been mixed with finely divided charcoal and igniting the cotton ; it burns like gun-cotton, and if fired by a small primer of mercuric fulminate it detonates with violence. It is said that this form of explosive has been used in blasting operations in excavating the Simplon tunnel. ACIDS, BASES, SALTS During his investigations of combustion, Lavoisier discovered that the sub- stances generated by burning various bodies in air were generally either (in modern language) acid oxides, or basic oxides, or occasionally neutral oxides, e.g. water, and that the union of an acid oxide with a basic oxide produces a salt. These, together with peroxides, have already received notice.(p. 51). But as there are many acids, e.g. hydrochloric acid, HCl, and salts, eg. common salt, NaCl, which contain no oxygen, it will be necessary to find more comprehensive definitions. Some of the common properties of acids and alkalies are given on p. 19 ( see also p. 345). BASES.—An inorganic base ts composed of metal (or group of atoms func- tioning as a metal, e.g. NH,) and hydroxyl ; 7.e. a metallic hydroxide, e.g. KOH, Ba(OH),, A(OH),. Those bases which are very soluble in water are spoken of as alkalies. This is the strict definition ; but the term “ base ” is frequently applied to any compound capable of neutralising an acid, either partly or entirely, and then includes the basic anhydrides or basic oxides ; but also, unfortunately, such compounds as Na,CO;, Na,SiO;, Na;PO,, and many other true salts which happen to have an alkaline reaction. Alkaline must therefore be distinguished from basic properties, although very often a substance exhibits both. An alkaline compound has the power of affecting certain natural and artificial colouring-matters in a way common to such bodies ; ¢.g. they turn red litmus to blue (p. 19) ; yellow turmeric to brown ; colourless phenolphthaléin to red ; rose methyl orange to yellow, &c. How- ever, these ‘‘ indicators ”’ show differences, e.g. sodium bicarbonate is neutral to phenolphthalein, but alkaline to methyl orange. Converse changes of colour occur on adding excess of anacid. Basic substances are not always alkaline, but they can always neutralise acids; they include the true bases, their anhydrides the basic oxides, and such intermediate compounds as 2Fe..03.H,0 (p. 453) ; Pb(OH)..PbO (p. 503); also such as ammonia itself, NH, sodamide, NaNH,, potassium zincate, Z(OK),. Some basic carbonates, e.g. SMgCO3.2Mg(OH),.7Aq. (p. 403), are almost entirely basic in their pro- perties owing to the very feeble influence of the carbonic acid contained ; they should therefore be noticed here, but are better classified as basic salts (p. 93). True bases rarely occur in nature; e.g. brucite, Mg(OH),. Several minerals deviate only slightly and are basic in most of their properties ; ¢.g. bauxite, Al,O3;.2H,O, limonite, 2Fe,03.3H,0; while many others are oxides, e.g. corundum, Al,O3, or contain some carbonate, e.g. malachite, Cu(OH),.CuCO3. Preparation.—Industrially chalk is burnt to quicklime, which with water yields the true base, calcium hydroxide, Ca(OH),. From this, sodium and potassium hydroxides (q.v.) are obtained, and thence any others desired. By electrolysis ; e.g. NaCl1—- NaOH (p. 374). By action of metals on water ; see Water. Properties.—(a) Physical. They are all opaque solids, generally having specific gravities much higher than those of acids, and having little or no odour (except ammonia and the like). Taste alkaline or slight. (b) Chemical. Reaction generally alkaline to a degree proportional to the solubility (i.e. in proportion to the concentration of hydroxyl ions (p. 94); hence, sodium hydroxide, being very soluble, is strongly alkaline, while calcium hydroxide, being not very soluble (1 in 700), is much weaker. They neutralise acids (see definitions) to form salts. Generally, on heating they give up water and form basic oxides; they do not melt; e.g. Sr(OH), = SrO + H,0; but the hydroxides of the alkali metals are not so decomposed, but melt; this ; 88 ACIDS, NATURE AND NOMENCLATURE 89 distinction is very characteristic. Heated gently with an ammonium salt, ammonia is disengaged ; this occurs not only with the hydroxides, but even with lead and mercuric oxides, The acidity of a base is measured by the number of hydroxyl groups in the molecule ; thus KOH is monacid, Zn(OH), is diacid, &c.; or by the number of hydroxyl groups with which one atom of the metal is capable of combining ; e.g. BaO is diacid, being able to form Ba(OH),. The equivalent of-a base is the number of grams of it which will neutralise one gram-molecule (the molecular weight expressed in grams) of a mono- basic acid ; e.g. 36°5 grams of HCl. ACIDS.—As the alkaline hydroxides are, par excellence, characteristic bases we may say: An inorganic acid is a compound of hydrogen, containing no basic element or group of elements, which in contact with alkaline hydroxide exchanges its hydrogen, or a portion of it, for the alkali metal. The words “containing no basic element or group of elements ” are necessary in order to exclude such compounds as NaHSO, and Zn(OH),. Eig. HCl + NaOH = NaCl + 4H,0 Hydrochloric acid Sodium hydroxide Sodium chloride Water HO, + 2KOH = K,S0O, + 2H,0 Sulphuric acid Potassium hydroxide . Potassium sulphate Water H,PO, + 2NaOH = Na HPO, + 2H,0 Phosphoric acid Sodium hydroxide Sodium phosphate Water The common nomenclature of the acids expresses the principal classifica- tion. If the acid contains oxygen its name is “ acid” ; e.g. sulphuric acid, H,SO,; chlorous acid, HClO, ; cyanic acid, HCNO. On abstracting water an acid anhydride or acid oxide (p. 51) is formed, with corresponding name ; ¢.g. H,SO, — H,0 = SO,, sulphuric anhydride ; 2HC1IO, — H,O = Cl,0,, chloric anhydride. If the acid contains no oxygen the name has the prefix ““hydro-” ; e.g. hydrosulphuric acid, H,S ; hydrochloric acid, HC); hydrocyanic acid, HCN. The termination -ic usually signifies that the characteristic element or group of elements exercises its highest valency (p. 12); -ous that the second highest valency obtains ; hypo ous, some lower, or apparently lower, valency; hence oxy-acids ending in -ic have more oxygen than those ending in-ous. Per——icis applied to certain acids containing an extraordinarily large proportion of oxygen; perchloric acid, HClO,. #.g.in nitric acid, HNOg, i.e. HO —N a. the nitrogen is exhibiting its highest valency, it is pentavalent, five ‘‘ bonds” being satisfied, two by each oxygen and one by hydroxyl; in nitrous acid, HNO,, i.e. HO — N = O, it is trivalent, the second highest ; in hyponitrous acid, (HO.N),, i.e. HO — N = N —OH, each atom of nitrogen has only one bond satisfied by other elements, but the group HO — Nis too unstable to exist, for N is never mono- valent ; so two such groups unite to produce the double molecule ;_ but this doubling does not occur in hypochlorous acid, HO — Cl, Cl being a mono- valent element. The classification is extended in terms of the basicity (p. 90). There are several derivatives (substances which can be derived or pro- duced from) of acids, whose existence and transformations are explainable only on the theory of radicles or as examples of substitution (p. 19). Just as the molecules of most elements may be regarded as consisting of two parts neither of which is capable of a separate existence, so the molecules of most compounds may be looked upon as composed of two or more parts or radicles, none of which can exist alone. For further reference to radicles, acid radicles, acid chlorides, &c., see p. 198. The occurrence of inorganic acids in nature is intimately associated with the periodic classification (p. 8). Boric acid, B(OH), (group 3) is abundant in certain regions ; silicic 90 BASICITY OF AN ACID acid also occurs, but its anhydride, silica, SiO,, is ubiquitous ; so also carbonic anhy- dride, CO, (group 4); minute quantities of nitrous and nitric acids (group 5) and of hydrosulphuric acid (group 6) are present in the atmosphere; the halogen acids (group 7) probably do not occur at all, except hydrochloric acid in volcanic gases and in the stomach. Thus inorganic acids are rarely found; on the other hand, organic acids are to be met with freely in the vegetable and animal kingdoms. Preparation.—(i) Synthetically, (a) from hydrogen and a non-metal, e.g. Hy + Cl, = 2HCl; (b) from oxygen and a non-metal producing an anhydride and subsequent treatment with water, eg. 8, + 20, = 280, and SO, + H,O = H,SO3. (ii) From silts, (a) by distillation with sulphuric acid (see hydrochloric and nitric acids) ; (2) from the barium salt of the acid and the precise quantity of sulphuric acid required (see Hypophosphorous acid, p. 222); similarly from the (c) potassium salt and hydro- fluosilicic acid (pp. 120, 117); (d) silver salt and hydrochloric acid (p. 206); (e) lead salt and sulphuretted hydrogen (p. 602). (iii) By the reaction of water with compounds of phosphorus and the like, e.g. PI, + 3HOH = P(OH), + 3HI (p. 128). (iv) By special processes. Properties.—(a) Physical. Usually colourless gases (e.g. HCl, H,S) or liquids (HNO, H,SO,); occasionally solids (e.g. B(OH),, HIO, (iodic acid). Heavier than water. With a powerfully sour taste; frequently corrosive or irritant to the skin. They conduct electricity. (b) Chemical. They affect colouring-matters with the con- verse effect observed with alkalies (p. 88 ), e.g. they turn blue litmus to red. Generally when diluted they attack metals forming salts and disengaging hydrogen, e.g. Zn + 2HCl = ZnCl, + H,; with concentrated acids more complicated reactions often occur. With rare exceptions (boric and hydrocyanic acids are the chief) they liberate carbon dioxide from alkaline carbonates and bicarbonates ; also, with the majority, hydrogen sulphide from sodium hydrosulphide. They liberate iodine when applied to a mixture of an iodide and an iodate. It is often possible to hasten or bring about chemical reaction between other substances by (apparently) the mere presence of an acid ; see Catalysis (p. 143) and Hydrolysis (p. 224). The ‘‘ Basicity of an Acid’’ corresponds with the number of hydrogen atoms in the molecule which can be exchanged for metals to form salts ; thus HCl, HNO, are monobasic ; H,S, H,SO, are dibasic ; H,PO, is tribasic, and so on. If the basicity is greater than unity the acid is frequently de- scribed as polybasic. In oxy-acids all the hydrogen exists as hydroxyl, hence the basicity is also equivalent to the number of OH groups in the molecule, e.g. NO,OH ; SO,(OH),; PO(OH)s. The basicity may usually be determined as follows: subdivide a solution of the acid into six parts; neutralise three of them with a suitable monovalent base, e.g. potas- sium hydroxide ; to one of the neutralised portions add one acid portion, to another two acid portions. Then in the resulting solutions the acid is wholly neutralised in the first, half neutralised in the second, and one-third neutralised in the third. Evaporate each on the water-bath and allow to crystallise. It may be desirable to collect the crystals, dissolve them in a little water and recrystallise. Examine the crystalline and other properties in each case; if all three products are alike, the acid is monobasic, e.g. KCl; if two kinds are found, the acid is dibasic, e.g. K,SO, and KHSO, ; if three kinds, the acid is tribasic, e.g. K;PO,, K,HPO,, KH,PO,. The experiments should be repeated with some other base, and the general properties of the acid considered in order to arrive at a satisfactory conclusion. Another method is to study the heats of neutralisation (p. 345). For this it is neces- sary to know the molecular weight of the acid. Dissolve one-tenth of its molecular weight in grams of the acid in 100 c.c. water; dissolve one-tenth of its molecular weight in grams of a monovalent base (e.g. 4 g. NaOH) in 100 c.c. water ; bring both solutions to the same temperature ; mix and observe the rise in temperature. Now add another portion of alkali and observe any fresh thermal change. If none (or very slight), all the acid was neutralised in the first instance and the acid is monobasic. If there was a rise in temperature, indicating acid still to be present, add a third portion of alkaline solution ; if the thermometer remains unaffected the acid was dibasic, for it required two equivalent portions of alkali but not three ; and so on, ORTHO- AND ANHYDRO-ACIDS 91 The equivalent of an acid is the number of grams of it which will neutralise one gram-molecule (p. 89) of a monacidic base ; e.g. KOH. Anhydro-Acids.—Attention has already been called to the theory that oxy-acids contain hydroxyl groups and that they owe their basicity to the number of these groups (p. 90). Since the group OH is monovalent it is reasonable to suppose that the atom of an element would be capable cf combining with one of these groups for each atom fixing-power or valency which the element possesses. Thus, the maximum valency of phosphorus being 5 (as seen from the chloride PCl,) the acid P(OH), might be expected to exist, although it is not known. It is customary to term such hydroxyl compounds of the elements ortho-acids, and to regard other oxy-acids as being derived from the ortho-acids by loss of water; these other oxy-acids are called anhydro-acids to express this view. According to this conception, the name orthophosphoric acid, which has been given to H;PO,, is a misnomer, for this acid is really the first anhydro- acid of true orthophosphoric, P(OH);, which is unknown. Pyro-phosphoric acid is the second and metaphosphoric acid the third anhydro-acid from trve orthophosphoric acid, as will be apparent from the following : P(OH),; — H,O = a orthophosphoric acid 2 PO(OH), P < 3a PO(OH)'S — H,O = 2 fe , pyrophosphoric acid \o(0H), PO(OH), — H,O = PO,(OH), metaphosphoric acid. Only a few ortho-acids are known, although the existence of several others is indi- cated by the fact that some of their salts (chiefly organic salts) have been isolated. The ortho-acids are generally very unstable, tending to lose water and to become anhydro- acids. Thus, orthocarbonic acid, C(OH),, has never been prepared, although several organic ortho-carbonates of the type C(OR),, in which R is an organic basic radicle, are known. It will be remembered that the anhydro-acid, CO(OH),.,( = C(OH), — H,0), carbonic acid, is supposed to exist in the aqueous solution of CO, ; but this also readily loses water, yielding the true anhydride, CO,,(—= CO(OH), — H,O). Orthosulphuric acid, 8(OH),, probably exists in an aqueous solution of sulphuric acid, for the maximum contraction which occurs when H,SO, and H,O are mixed takes place when the prc- portion of acid to water is expressed by the formula H,SO,.2H,O or H,SO,. It very readily loses water, however, when heated, and if the evaporated solution be cooled to 8° the anhydro-acid, SO(OH), or H,SO,.H,0, crystallises, which in its turn loses water when heated, becoming the most stable anhydro-acid of sulphur, H,SO, or S0,(OH),. The solution of SO, in H,SO,(H,S,0,), which melts at 35° C. and is call d anhydrosulphuric acid, must be regarded as a further anhydride of sulphuric acid : 0,(0H) BOMOHI: gies 5 80,(0H),} ~ 10 = > ‘\o,(OH) Orthosilicic acid, Si(OH),, is believed to exist in solution (p. 282), but it very easily loses water, becoming the anhydro-acid, Si0(OH),, metasilicic acid. By the loss of water from several molecules of orthosilicic acid, anhydro-acids of complex type would be produced ; thus: (OH) SiC : Si(OH) Oo a On| _ 2H,0 = siZ(OH), Si(OH), | No aie” \COH), 92 SALTS—DEFINITION The mineral silicates are undoubtedly derived from such complex silicic acids, the existence of which is, in many cases, also indicated by the isolation of acid chlorides (p. 198) corresponding with them. Orthoboric acid, B(OH),, is well known. Orthonitric acid, N(OH);, is not known; ordinary nitric acid is the anhydro-acid NO,(OH). The ortho-acid of chlorine should be Cl(OH),, for this element is heptavalent, although not towards hydrogen and some other elements and radicles ; but no anhydro- acid intermediate between this and ClO,(OH), perchloric acid, is known. Orthoiodic acid, I(OH),, is unknown ; periodic acid, IO(OH);, is the first anhydro-acid from orthoiodic acid. On reviewing the highest oxy-acids of the non-metallic elements, it will be found to be generally true that those acids are the most stable which contain the same number of hydroxyl groups in the molecule as there are hydrogen atoms in the highest hydrogen compound of the element. SALTS.—A salt is an acid in which the hydrogen has been exchanged either entirely or partly for a metal (or for a group of elements functioning as a metal, e.g. NH,), such as is produced by the interaction of an acid and a true base with elimination of water ; in the equations on p. 89, NaCl, K,SO, and Na,HPO, are salts. It is generally accepted that all salts are electrolytes. Normal salts are those in which all the hydrogen atoms are exchanged for metals, as for instance in zinc chloride, ZnCl,, normal potassium sulphate, K,SO,, normal sodium phosphate, Na,PO,. Acid salts are those in which only part of the hydrogen has been exchanged for metal as in acid potassium sulphate (potassium bisulphate), KHSO,, diacid sodium phosphate, NaH,PO,. In forming a normal salt from a divalent metal, like calcium, and a mono- basic acid, like nitric acid, it is necessary to have two molecules of the acid in order to obtain sufficient hydrogen for the metal to displace ; thus Ca will displace the H from 2(NO,.0H), forming NOE Oa. The trivalent NO,.07 NO,.O aluminium would require three molecules of nitric acid: NO,.OAl. A NO,.0” similar process of counterbalancing occurs when a dibasic acid forms a normal salt with a trivalent element ; thus, aluminium sulphate can only be formed from 2 atoms of Al'# and three molecules of H,SO,: 0. SO. os Al O S02<6 or Al,(SO,)s O—Al S0.<6/ Double salts become possible with polybasic acids and polyacidic bases. They may be derived from (a) two different metals and one acid, e.g. sodium potassium carbonate, CONG ; potassium-aluminium sulphate, a OK SO, "Be OSAl 80 6” (6) two different acids and one metal, e.g. chlorosulphide of mercury, HgCl,.2Hg8 ; (c) two different metals and two different acids, e.g. potassium- magnesium chlorosulphate, KCl.MgSO,.3H,0. The formule ascribed to SALTS—CLASSIFICATION 93 double salts are usually to be accepted with some reserve ; the last might very well be written Cl.Mg.SO,.K, 3H,O. What is definite is that the elements are. present in atomic proportions and so combined as to constitute one single saline compound which frequently is formed only under certain conditions. In other circumstances, a mixture of crystals of the two or three possible salts appears (see phase rule). In dilute solutions the properties are the same whether the double salt or the mixture was dissolved, but not always so in concentrated solutions. Crystals containing two iso- morphous salts (p. 299) can be varied continuously in composition and properties and are therefore not double salts. See also p. 299. Basic salts are particular instances of double salts, namely, where one of the acid residues is hydroxyl, e.g. in basic bismuth nitrate, Bi(OH),NO3, or oxygen, e.g. in bismuth oxychloride, BiOCl. The word “ basic” and the prefixes “ sub-”’ and “ oxy- ” are in most cases interchangeable in describing these compounds. Complex salts are produced in certain cases on mixing two or more single salts insolution ; but they differ from double salts in having the constitution of single salts ; Lig. 4KCN + Fe(CN), = K,Fe(CN), Potassium cyanide Iron cyanide Potassium ferrocyanide Potassium ferrocyanide behaves throughout as a normal salt of potassium and hydroferrocyanic acid, H,Fe(CN),; and, indeed, the latter is known. See also p. 331. : Nomenclature.—The name of a salt is derived from those of the acid represented and of the metal for which the hydrogen has been exchanged ; thus potassium nitrate, KNO,, signifies that in this salt potassium, K, is the metal which has displaced hydrogen, H, in nitric acid, HNO;. When the name of the acid ends in -ic, the name of the salt ends in -ate, except in the hydro——ic acids, for which -ide is the corresponding termination ; -ous acids give salts whose names end in -ite ; thus: Sulphuric acid gives a sulphate. Hydrochloric acid gives a chloride. Permanganic ,, » permanganate. Phosphorous ,, » phosphite. Hyponitrous ,, » hyponitrite. Very many salts occur in nature. Sodium, magnesium and other chlo- rides, bromides and iodides in sea-water ; potassium and sodium nitrates as ordinary and Chili saltpetre respectively ; calcium sulphate as gypsum ; excepting silica, most minerals which are not basic are salts. Preparation. Numerous methods are available ; among the chief are (a) by direct synthesis, e.g. 2Fe + 3Cl, = 2FeCl, (p. 455); (6) by the action of acids on metals, eg. Zn + 2HCl = ZnCl, + H,O (p. 95); (c) by union of an acid oxide with a basic oxide (p. 95), e.g. BaO + SO, = BaSO, ; (d) by neutralising an acid, either entirely or partly, with a base (supra) ; (e) by some special process, e.g. KMnO, (p. 463) ; KC1O, (p. 118); (f) by application of some form of energy, eg. by heating KNO,, KNO, is obtained (p. 364). Properties.—(a) Physical. The majority are crystalline and either transparent or translucent. A salt is usually either colourless or has a colour characteristic of one of its constituents ; e.g. nearly all ferric salts are yellowish brown and ferrous salts green ; chromates are yellow ; amongst commonly occurring salts it is seldom one finds two coloured constituents in the molecule. Generally they are more or less soluble in water, but many are practically insoluble, e.g. barium sulphate. When allowed to crystallise from water many do so with water of crystallisation (p. 38). (6) Chemical. Very various, being characterised by those of the constituent elements and radicles. We have seen that when a piece of sodium is placed on water a vigorous reaction occurs, resulting in the complete disappearance of the metal and 94 IONIC HYPOTHESIS the production of an alkaline solution (p.20). If some other liquids be used, many metals will disappear similarly ; e.g. zinc dissolves in hydro- chloric acid with evolution of hydrogen and formation of zine chloride solution; Zn + 2HCl = ZnCl, + H,. Copper treated with strong sulphuric acid gives rise to copper sulphate, CuSO,, which is soluble in water. The question naturally arises: What has become of the metal? In what con- dition is it in solution ? There is as yet no single answer which is entirely satisfactory ; but a large number of properties relative to such solutions of acids, bases, salts and other substances will be considered in the chapter on physical chemistry. The conception which explains most facts consistently and, fortunately, is very simple, is the Ionic Hypothesis! of Arrhenius (Sweden). This supposes that the salt exists in solution in two forms ; (a) a certain quantity, varying with the nature of the substance and the concen- tration of the solution, is dissociated or ionised into ions, e.g. in the case of sodium chloride into sodium Na’, and chlorine ions, Cl’. These ions are not merely atoms, but atoms in a certain electrical condition ; the sodium ions are positively charged (cations) and are represented as Na’ ; the chlorine ions are negatively charged (anions) and are written Cl’. With zinc chloride, ZnCl,, the ions are one zinc ion, Zn’, and two chlorine ions, 2Cl’. The number of dots or dashes represents the magnitude of the electric charge. The ions are frequently complex; in copper sulphate, Cu’ and SO,"; in ammonium nitrate, NH,’ and NO,’ ; in sodium hydrate, Na” and OH’. (6) The remaining portion of the compound is dissolved without any dis- sociation. Thus when a substance is in the solid state, that is when no part of it is in solution, none of it is dissociated. Conversely, when suffi- ciently diluted, all will be ionised. Hence, in a solution, 1, 5, 20 or 100 per cent. of the substance may be ionised, and the ratio of the ionised portion to the total quantity is called the degree of ionisation at the particular dilution. The subject is of interest in many ways and assists in formulating right ideas of the constitution of acids, bases and salts. Thus copper sulphate, CuSO, (a salt), can be built up from copper oxide, CuO (a basic oxide), and sulphur trioxide, SO, (an acid oxide) (cf. p. 51); also from metallic copper, by substituting one atom of copper, Cu, for two atoms of hydrogen, 2H, in sulphuric acid, H,SO,, Cu + H,SO,—+>CuSO,. Clearly, here are, groupings of two kinds : (a) SO, and an oxide, CuO; (6) SO, and a metal Cu. The former is the basis of the old dualistic system of Berzelius, which dominated chemistry in the earlier decades of the last century, and is still applied, though for convenience only, in reporting mineral analyses. But it fails to explain the properties of such compounds as NaCl, ZnCl,, where oxygen is absent ; also to account for the deposition of metals in the elec- trolysis of salts where their basic oxides might be expected. The ionic view is free from both these objections. According to the ionic hypothesis, all acids are resolvable into hydrogen tons and their respective anions ; e.g. HCl--+H’ + Cl’; H,SO, — 2H’ + 80,”; H,PO,—-3H° + PO,’ ; and the modern view is that the charac- teristic properties of acidity are due to the presence of hydrogen ions. Similarly, bases dissociate into hydroxyl ions and their respective cations ; e.g. NaOH — Na’ + OH’; Ca(OH), — Ca** + 20H’; and so alkaline pro- perties are identified with the presence of hydroxyl ions. Thus acids may be viewed as “salts” of hydrogen, and bases as hydroxyl “ salts” of the respective metals. Hence, the indicators referred to above reveal which of these two kinds of ions is present ; thus methyl orange is red in presence of hydrogen ions (acidity), but yellow when hydroxyl ions (alkalinity) predominate. * See also fuller discussion in chapter on General Principlea, HYDROGEN H. Atomic weight, 1.008 (or precisely 1.00763). HyprocEn had long been known as “ inflammable air’ but without appre- ciation of its nature when Cavendish, in 1781, first recognised it to be one of the components of water, whence its name, from tédwp, water ; yevvaws I generate. By reason of its being the lightest of all known substances, its atomic weight was adopted as a standard by Dalton, and owing to its general suitability, constant physical properties and the ease with which it can be obtained in a state of approximate purity, it has become a standard in many other respects. However, because of the difficulty of accurate comparison between so light a gas and one very many times heavier it is gradually giving place to oxygen as a standard for weight, density and the like ; see Atomic weights (p. 297). Small quantities are found in nature in the free state in volcanic gases, petroleum wells, and occluded in meteoric iron ; also it is present in coal gas to the extent of 44 per cent. In the combined state it occurs in water, in many minerals as hydrates, and as an essential constituent of nearly all organic substances. Preparation Hydrogen may be prepared by several of the processes described under the analysis of water, of which those by electrolysis, sodium and iron are useful. But the method almost universally employed as a ready means in the laboratory is that of decomposing hydrochloric acid or sulphuric acid by zinc or iron. Zinc is the more convenient. It is used either in small fragments or cuttings, or as granulated zinc, prepared by melting it in a ladle and pouring it from a height of three or four feet into a pailful of water; when thus granulated it exposes a larger surface to the action of the acid. The zinc is placed in the bottle, A (Fig. 82), covered with water, and diluted sulphuric acid? slowly poured in through the funnel tube, B, until a pretty brisk effervescence is observed. The hydrogen is unable to escape through the funnel tube, since the end of this is beneath the surface of the water, but it passes off through the bent tube, C, and is collected over Fig. 82. water as usual, the first portion being ; rejected as containing air. Before collecting hydrogen for use a small portion of it must be tested for air by filling a test-tube with the gas and, with- drawing the inverted test-tube well away from the apparatus, and applying a light, when the hydrogen will burn quietly if it is free from air. The presence of air in hydrogen forms a highly explosive mixture. By allowing the solution left in the bottle to cool in another vessel, crystals of zinc sulphate (white vitriol) may be obtained : 1 Made by adding 1 vol. strong sulphuric acid (oil of vitriol) gradually to 10 vols. water, gently agitating Meanwhile, and allowing to cool. 96 HYDROGEN PREPARATION H,SO, + Zn = ZnSO, + 4H,’ Sulphuric acid Zine Zinc sulphate Hydrogen It will be noticed that the liquid becomes very hot during the action of the acid upon the zinc, the heat being produced by the chemical combina- tion. The black flakes which separate during the dissolution of the zine are metallic lead, which is always present in the zinc of commerce, and much accelerates the evolution of hydrogen by causing galvanic action. Pure zine placed in contact with diluted sulphuric acid evolves hydrogen very slowly. By allowing a piece of platinum dipping in the acid to touch the pure zine, so as to form a galvanic couple, the reaction may be considerably hastened. A few drops of platinic chloride solution or copper sulphate solution has the same effect (the metals becoming reduced). (Also p. 21.) It is now easy to calculate how much zinc it would be necessary to dissolve in sul- phuric acid in order to obtain any desired volume, say 100 litres, of hydrogen. Referring to the equation for the preparation of hydrogen, Zn + H,SO, = H, + ZnSQ,, and remembering that Zn represents 65 parts by weight of zinc, and H, represent 2 parts by weight of hydrogen, such a problem can be solved by ordinary proportion ; thus: (2 grams H) 22-247 litres : 100 litres : : 65 grams zinc : x (i.e. 292-2 grams). -'. 292-2 grams zinc give 100 litres of hydrogen at 0° C. and 760 mm. Bar. Iron might be used instead of zinc, and the solution, when evaporated, would then deposit crystals of ferrous sulphate, FeSO,4.7H,0 (green vitriol or copperas), H,SO, + Fe = FeSO, + Hy. To provide a constant supply of hydrogen, zinc, granulated or, better, in the form of sticks, is placed in the centre globe of a Kipp’s apparatus (p. 65) and a mixture of 1 volume hydrochloric acid and 2 volumes water is put into the reservoir ; zinc chloride is produced, Zn + 2HCl = ZnCl, + H,. Hydrogen so prepared from ordinary material is never quite pure ; sul- phuretted hydrogen, H,S, and arsenuretted hydrogen, AsH,, due to traces of sulphur and arsenic in the zinc, being the most common ; these and some other impurities may be removed as described on page 28. When prepared from iron the gas usually has a peculiar, disagreeable smell due to traces of hydrocarbons of the olefine series. When pure hydrogen is required, mag- nesium and pure acid or the aluminium process may be used. If dry gas is wanted, it must be collected over dry mercury. Aluminium (14 kilos) and caustic soda (24 kilos) were used with water to generate hydrogen (1 kilo) for war balloons in the Russo-Japanese campaign. The material is the lightest and most suitable for transport. The method yields very pure hydrogen. 6NaOH + 2Al = Al,(ONa), + 3H3. Properties —(a) Physical. Hydrogen is a colourless, tasteless and, when pure, odourless gas ; remarkable for its extreme lightness, in demonstration of which several experiments have been described already (pp. 22, 24, 76, 77). 1 litre weighs 0-08990 gram (or in round figures 0-09 gram) ; therefore, 1 gram occupies 11-1235 litres and since the atomic weight is 1-00763, the molecular volume, 1.e. the volume occupied by the molecular weight (2-01526) expressed in grams, is 22-4167 litres. From Avogadro’s hypothesis (p. 10) it follows that the molecular volumes of all gases are equal, and by experiment they are very nearly so ; the mean corrected value which can be used in all calculations save where great accuracy is required is 22-412 litres, with which cde 144 3 1 referred to oxygen 0-0629, i.e. 1B9 ° hydrogen itself has been taken as the hydrogen agrees very well. Its density referred to air is 0-0695, i.e. * In this equation the exccss of water which must be added to dissolve the zinc sulphate is not set down. Hydrogen could not be prepared according to the equation as it stands, because the zine sulphate would collect round the metal and prevent further action. To meet the difficulty the equation may be written: ee + Zn = Zn80,.Aq + H,; or H,80, + Zn + «H,0 = ZnSO, + H, + aH,0; the former being preferable, LIQUID HYDROGEN—OCCLUSION 97 standard for density for scientific purposes and still is with certain limita- tions ; but inasmuch as the modern standard for atomic weights is O = 16, the corresponding standard of density must also be O = 16. It has been stated that the density of a gas is one-half of its molecular weight (p. 11). Using the modern atomic weights which are given in this book, this is true when O=16; eg. mol. wt. of NH; = 14-01 + (3 x 1-008) = 17-034; .. density = 8-517. The extremely low density of hydrogen makes it the most rapidly diffusible of all gases (p. 77). Its coefficient of expansion is 0-0036613 or we 3° It conducts heat seven times as well as air does. Its specific heat at constant pressure is 3-4, whence its molecular heat is 6-8 ; at constant volume 2-4 and 4-8 respectively ; therefore the ratio is 6-8 : 4-8 = 1-41 (p. 310). The specific heat of liquid hydrogen is 3-4, the same as that of the gas at constant pressure. Refractive index: gas, 1-000139 ; liquid, 1-12. Liquid hydrogen (p. 87) is obtained as a colourless, transparent fluid which drops well and shows a clearly visible meniscus, although its surface tension is only giz that of water and = that of liquid air. Its density is less than 0-07, the lightest liquid known, six times lighter than liquid methane, which is the next. At its boiling-point its density is only fifty-five times that of the vapour it gives off ; whereas with liquid oxygen it is 258 ; nitrogen, 177; water, 1604. It boils at — 252-5° at 760 mm. ; crit. temp., — 243°; crit. press., 15 atm. Latent heat of vaporisation is 121 ; of fusion, 16 or less. It is a non-conductor of electricity and is non-magnetic. Solid hydrogen is frothy, ice-like in appearance, density 0-077 at — 260°, melts at — 256-5°. By its evaporation a temperature of — 260° (13° A) is attainable and can be maintained. Hydrogen gas is sparingly soluble in water: 100 c.c. water at 0° dissolve 2-148 c.c. (0-000192 g.); at 10°, 1-955 c.c. (0-000174 g.); at 15°, 1-883 c.c. (0-000167 g.); at 20°, 1-819 c.c. (0-000160 g.); at 25°, 1-754 c.c. (0-000153 g.) of the gas at 760 mm. In alcohol it is much more soluble ; 100 c.c. alcohol at 0° dissolve 6-925 c.c.; at 15°, 6-725 c.c, at 760 mm. A notable property of hydrogen is the ease with which it is absorbed or dissolved by metals. That solids can dissolve gases has already been stated (p. 85) ; the phenomenon as exhibited by metals was called the occlusion of gases (Lat. occludere, to shut up) by Graham, who studied the extent to which hydrogen is occluded by the metal palladium. Absorption of various gases is exhibited by several metals, but of none more than of hydrogen by most of the metals of the eighth group of elements (p. 8), especially palladium and platinum. Some other metals take up hydrogen, e.g. magnesium, alumi- nium, silver, although in much smaller proportions. Heated sodium and potassium absorb large quantities of hydrogen, but in these and some other cases definite com- pounds, hydrides, appear to be formed. The order is not the same for other gases ; silver is one of the best metallic solvents of oxygen (p, 518). See also Carbon monoxide (p. 248) and Charcoal (p. 240). The phenomena of ocelusion generally occur more readily when the metal is heated and allowed to cool in the gas ; when treated in this way hammered palladium absorks some 600 times its volume of hydrogen, though fused palladium does not absorb so much. When a metal containing occluded gas is strongly heated (particularly in a vacuum or in an atmosphere of another gas), the occluded gas is given off, just as a gas dissolved in water is expelled when the solution is heated. Palladium absorbs most hydrogen when it is used as the cathode in an electrolytic cell containing dilute acid (p. 15). In this case the metal may take up about 900 times its volume, and in doing so it increases about 1-5 per cent. in length. This expansion forms one basis of experi- mental methods for demonstrating the occlusion. A palladium wire (24 inches) is passed through the bottom cork of a vertical glass tube containing dilute sulphuric acid, and is there made fast ; the other end of the wire is attached to a long rod, pivoted hori- zontally to serve as an index. The wire is attached to the zinc of a Grove’s battery, the platinum of the battery being attached to a platinum wire which also passes through the glass tube. During the electrolysis of the dilute sulphuric acid the index descends, 7 98 CHEMICAL PROPERTIES OF HYDROGEN showing thatthe wire is increasing in length ; the non-recovery of the index when the electrolysis is stopped shows that the expansion was not a mere thermal effect. It was supposed that palladium saturated with hydrogen is a compound of the formula Pd,H,, but the properties show it to be merely a solid solution. The term hydrogenium was applied by Graham to the hydrogen occluded by palladium ; he found that hydrogen in this state is magnetic. The hydrogenised palladium is a far more active reducing agent than is free hydrogen, for it reduces chlorates to chlorides and nitrates to nitrites. At low pressures there is evidence of the hydrogen being monatomic. If the whole of the hydrogen be regarded as being occluded, its specific gravity in this condition would be 0-62, and its atomic heat 5-88. The absorption of 1 gram of hydrogen by palladium black evolves 4370 gram units of heat. At atmospheric pressure no absorption of hydrogen by palladium occurs above 145°, but at higher pressures the absorption occurs at much higher temperatures. Spongy platinum absorbs 110 vols. hydrogen at ordinary temperatures, and the heat of occlusion is 6880 calories per gram of hydrogen ; the evolution of heat during occlusion indicates some change of state. Vessels made of these and other metals, e.g. iron, capable of dissolving hydrogen, allow the gas to pass through the walls quite easily when hot, but not when éold, showing that the passage is not due to any- thing akin to porosity in the metal; further, various metals are ‘‘ permeable” to certain gases only ; e.g. nitrogen will not pass through palladium, and thus a means of separating mixed gases is afforded. Both hydrogen and oxygen are absorbed by finely divided platinum and palladium. This finds application in the automatic gas- lighters. The hydrogen in the coal-gas impinges on the metal already saturated with oxygen from the atmosphere, and the two gases combine so rapidly and energetically that the necessary temperature for igniting the gas is almost instantly attained ; see Catalysis (p. 143). Finely divided nickel finds application in organic chemistry. (b) Chemical. In its chemical relations to other elements, hydrogen is diametrically opposed to oxygen. Whereas the latter combines directly with the greater number of the elements, hydrogen enters into direct com- bination with very few ; all the metals form compounds with oxygen, but very few combinations of metals with hydrogen have been obtained. The most obvious chemical property is its burning in air or oxygen with a pale blue very hot flame producing its oxide, Water ; and the chemistry of water is to be viewed as a part of the chemistry of hydrogen. See also the oxy-hydrogen blowpipe (p: 268). The combustion of hydrogen produces a greater heating effect than that of an equal weight of any other combustible body. It has been determined that 1 gram of hydrogen, in the act of combining with 8 grams of oxygen, produces enough heat to raise 34,462 grams of water from 0° to1°. The temperature of the hydrogen flame is probably about 2000°. Notwith- standing its high temperature, the flame of hydrogen is almost devoid of illuminating power, on account of the absence of solid particles. There is also a second oxygen compound, hydrogen peroxide (p. 142). As will be seen later, hydrogen unites with fluorine very energetically even at — 210°, and with chlorine at ordinary temperatures, slowly in the dark but with explosion in sunlight. With bromine, iodine, and the elements of the sulphur group (that is, the periodic group containing sulphur ; p. 8), higher temperatures are neces- sary to bring about combination ; with nitrogen, producing ammonia, NHsg, a still higher temperature or the silent electrie discharge ; with carbon, producing methane, CH,, 1200°. Direct union with the other non-metals of the 4th and 5th groups (p. 8) does not occur normally. The periodic classification again finds expression in the fact that the hydrogen compounds of the elements of the 7th group are strong acids: hydrofluoric, HF ; hydrochloric, HCl; hydrobromic, HBr; hydriodic, HI; those of the 6th group being weak acids, sulphuretted hydrogen, H,S, &c. ; those of the 5th group being basic, ammonia, NHg, &c. ; those of the 4th group being neutral, methane, CHy, &c. With only afew metals does hydrogen combine directly, e.g. sodium (p. 375), calcium (p. 388), producing Hydrides, a name given especially to compounds of REDUCTION AND OXIDATION 99 hydrogen with metals, but also extended to those with non-metals ; but hydrides can also be made otherwise ; see Copperhydride (p. 312), Antimony hydride (p. 478), hydro- carbons generally, &c. Reduction and Oxidation.—When hydrochloric acid gas reacts with sodium metal, there is no doubt that single atoms of hydrogen are separated momentarily according to the equation HCl + Na = NaCl + H; but because the free atoms possess so much chemical energy, and if there is nothing else present wherewith they may combine, they combine with one another, forming molecules, H, (p. 10). If, however, another substance is present it will probably attract the free hydrogen atoms, for the tendency of elements is to combine with others of widely different properties (p. 113). This is probably why such very small quantities of free elements are met with in nature. If some ferric chloride, FeCl, is put into the hydrogen generating-flask along with the zinc and acid, the yellow colour of the solution soon gives place to a pale green, and the solution then contains ferrous chloride, FeCl,, but no ferric salt. The nascent hydrogen—i.e. hydrogen in the atomic state at the moment of its generation—has robbed the ferric chloride of a part of its chlorine and combined with it to form hydrochloric acid in preference to forming hydrogen molecules; FeCl, + H = FelCl, + HCl. At the same time the valency of the iron has been “‘ reduced ”’ from trivalent to divalent, Such a reduction of ferric chloride does not occur if the chloride be mixed with HCl in another vessel and the hydrogen from the flask bubbled through it—a fact which it is sought to explain by saying that the hydrogen atoms have had time to combine together to form molecules before they come into contact with the ferric chloride. Except in the nascent condition hydrogen exerts a reducing action at ordinary temperature only in very few cases. At high temperatures, how- ever, its attraction for oxygen renders it a useful reducing agent. Originally the term reduction was limited to the operation of depriving a substance of oxygen either wholly, as when a metallic oxide is reduced to metal, like the reduction of copper oxide by hydrogen (p. 28), or partially, as when a higher oxide is reduced to a lower oxide, like Fe,0, to FeO. Since in a lower oxide the valency of the element combined with the oxygen is nearly always lower than in the higher oxide, the term reduction was ex- tended to all cases in which a compound of an element is transformed into a like compound accompanied by a lowering of the valency of the element. Reduction may be said to occur, therefore, (a) when the valency of the more electro-positive element or group present in the molecule is decreased, eg. FetiCl, — FeiiCl, ; (6) when oxygen or other electro-negative element or group is withdrawn from the molecule, e.g. SnO0,-—- Sn; (c) when hydrogen or other electro-positive element or group is added to the molecule, e.g. Hgl, — Hg,],. 3 ‘ Oxidation is the reverse of reduction and occurs when oxygen is acquired by an element or compound or when the valency of an element in a compound is increased. It is to be observed that reduction and oxidation, so far as they refer to withdrawal and acquisition of oxygen, always occur simultaneously, for the “reducing agent ’’—the substance which effects reduction—is oxidised to the same extent as that to which the other is reduced ; thus in the foregoing instance the hydrogen is oxidised, and therefore the copper oxide may be regarded as an “ oxidising agent ” ; conversely, an oxidising agent is itself correspondingly’reduced. The process is described as one of “ oxidation ” or “ reduction’ according to the object in view. It must be understood, however, that the terms oxidising agent and reducing agent are confined to 100 CLASSIFICATION OF HYDROGEN bodies which show a wide téndency to impart oxygen to, or withdraw oxygen from, other bodies ; in this sense copper oxide is not generally classed as an oxidising agent. Several substances act as typical reducing agents, such as sulphuretted hydrogen, potassium cyanide, and sulphurous acid. The changes concerned in their action will be noticed in the proper places. Whether a substance is a reducing or an oxidising agent depends on the nature of that with which it reacts. However, in general hydrogen, carbon, the metals, the lower oxygen acids and their salts are reducing agents, while oxygen, the halogens, most of the higher oxygen acids and their salts and peroxides are oxidising agents. Oxidation is as typically produced by nascent oxygen as reduction is typically effected by nascent hydrogen. When a substance evolves oxygen the latter is monatomic in the nascent state and very active, just as is the case with hydrogen; so that other substances present are very readily oxidised. H.g. when chromium oxide, Cr.0,, is fused with potassium ni- trate, KNOg, the latter yields its oxygen readily (p. 364), (a) raising the valency of the chromium, Cri to Cri, (6) adding oxygen, Cr.0, —+ 2CrO, ; thus, using alkaline carbonate to take up the chromic acid as it is formed, 2Cr,03 + 4(Na,0.CO,) + 60 = 4CO, + 4(Na.0.CrO,) (sodium chromate). Determinations of hydrogen in its compounds are usually made by converting it into water and from the weight thereof calculating the pro- portion of hydrogen (pp. 28, 538). Atomic Weight.—This most important factor is considered on p. 297. Classification of Hydrogen.—The question was long discussed as to whether hydrogen is essentially metallic or non-metallic in character. Its peculiar position in the periodic table has already been noticed ‘(p. 7); also that in electrolysis it is electro-positive like a metal (p. 14) and that in acids hydrogen plays the part which in salts is taken by metals. Further, its ready absorption by palladium without destroying the metallic properties favoured the view that hydrogen may be a metal. On the other hand, recent researches on the solid element have shown it to possess no metallic properties, it is even a non-conductor of electricity. Its oxide is neutral and not basic as are those of the metals, and its compounds with non-metals are acids, not salts. In organic chemistry it behaves even more as a non-metal and is readily exchangeable for other non-metals, e.g. CH, + Cl, = CH,Cl + HCl; but it can also be exchanged for metals. More- over, it is sometimes “ mobile,” shifting from one part of the molecule to another (p. 736). So that the balance is strongly in favour of regarding hydrogen as non-metallic. THE HALOGEN (SEVENTH) GROUP FLUORINE, CHLORINE, Bromine, IODINE CHLORINE, Cl. Atomic weight = 35.46. Molecule = Cl,. CHLORINE is never found in the uncombined state, but is very abundant in the mineral world and in sea-water in the forms of sodium chloride (common salt), potassium chloride and magnesium chloride. In thé first two forms it is also an important constituent of the fluids of the animal body, but as it is not found in sufficient proportion in vegetable food, or in the solid parts of animal food, a quantity of salt must be added to these in order to form a wholesome diet. Sodium chloride is indispensable as a raw material for several of the most useful arts, such as the manufacture of soaps and glass, bleaching, &c. ; in fact, it is the source of three of the most generally useful chemical products, viz. chlorine, hydrochloric acid, and soda. About the middle of the seventeenth century, a German chemist named Glauber (6. 1604, d. 1668) distilled some common salt with sulphuric acid, and obtained a strongly acid liquid (hydrochloric acid) to which he gave the name muriatic acid (from muria, brine); this was proved to be identical with the acid long known to the alchemist as spirit of salt (obtained by dis- tilling salt with clay). The saline mass which was left after the experiment was then termed Glauber’s salt, but afterwards received its present name of sodium sulphate. It was undoubtedly a natural inference from this experiment that common salt was composed of muriatic acid and soda and that the sulphuric acid had a greater attraction for the soda than the muriatic acid had, which was there- fore displaced by it. In accordance with this view, common salt was called muriate of soda without further question. In 1774 Scheele distilled muriatic acid with manganese ore and- obtained chlorine, although it was not recognised as an element (being thought to contain oxygen), until in 1811 Davy established its elementary nature and gave itits present name. The dis- covery that muriatic acid was free from oxy- gen led at once to the correct view of thenature of common salt, namely, that it is formed from HCl by substitution of Na for H, and contro- verted Lavoisier’s theory that oxygen was essential to acid properties.? ee Preparation.—There are many processes, but most of them depend on the oxidation of hydrochloric acid by withdrawing the hy- drogen. (a) The reagent most commonly employed is manganese dioxide, MnO, Fre. 82. (pyrolusite). Thirty grams of the oxide in granular form or coarse powder are placed ina flask fitted with thistle funnel and delivery tube (Fig. 84) (or in a distilling flask, Fig. 85), 110 c.c. common hydrochloric acid are poured in through the funnel and the flask j ‘ i i ive than when it 1 However, it will be seen that hydrochloric acid when anhydrous is very much less active is in the presence of water (p. 112) or oxygen (p. 112), so that oxygen, either free or combined as water, appears to be very generally associated with acid a ee al | Maye 102 CHLORINE—PREPARATION heated by means of a water bath; if heated by a naked flame there is risk of breakage. The gas is steadily disengaged and is collected, after passage through a wash-bottle, by downward displacement, passing the delivery to the bottom of the dry bottle or cylinder and covering the mouth with a piece of perforated cardboard, as shown in the figure; or, with considerable loss due to solubility, over water in the usual way (Fig. 82). It cannot be collected over mercury as it combines with it. The wash- bottle may contain water or, better, strong solution of copper sulphate, CuSO, + 2HCl = CuCl, + H,SO,, to remove any hydrochloric acid gas carried over, or strong sulphuric acid to dry the gas, or may be dispensed with when not required. The pipette in the middle neck of the bottle acts as a safety-valve in cases where undue variation in pressure may occur. The observed reaction is represented by the equation MnO, + 4HCl = MnCl, + 2H,O + Cl,; but there is no doubt that it occurs in two stages. It is instructive to regard the reaction as consisting in the oxidation of the HCl by the excess of oxygen in the manganese peroxide, 7.e. the oxygen in excess of that required to form the basic oxide MnO. Thus it might be supposed that at the tem- perature used oxygen is first liberated and then oxidises HCI—(1) MnO.O + 2HCl = MnCl, + H,O + 0; (2) 2HCl1+ O=H,0 + Cl. It isa characteristic of peroxides that they liberate chlorine from HCl in this manner, the excess of oxygen, commonly called the ‘“‘ available oxygen,” over that which may be termed the “ basic oxygen,” serving to oxidise the hydrogen in the acid. It must be admitted, however, that the change, at all events in the case of man- ganese peroxide, is probably the formation in the first instance of a higher chloride, which subsequently breaks up into the lower chloride and chlorine. (1) MnO, + 4HCl = MnCl, + 2H,0, (2) MnCl, = MnCl, + Clg, for cold hydro- chloric acid and manganese dioxide form a dark brownish-green solution which on heating evolves chlorine ; also manganese tetrachloride, MnCl,, prepared by other means, decomposes at 100° into manganese dichloride, MnCl, and chlorine (p. 112), If it is desired to liberate chlorine from common salt, sulphuric acid must be present. (6) 40 g. common salt previously mixed with 30 g. manganese dioxide may be heated with a cold mixture of 44 c.c. strong sulphuric acid with ( az 110 cc. water; 2NaCl + MnO, + 3H,80O, = 2NaHSO, + (= MnSO, + 2H,0 + Ch. The preparation of chlorine should be conducted G in a well-acting fume chamber or in the open air or as ‘a in the following experiment, on account of its distress- ingly suffocating effect on the lungs. Smelling L_ , ®mmonia and sprinkling it about the room are the most ready means of relief. It is advisable to keep other jars ready to receive any excess of gas instead of allowing itto escape. The process may be stopped by substituting cold water for the hot water in the bath. (c) By far the most convenient arrangement for the usual small requirements of the laboratory is the following. Concentrated hydrochloric acid is allowed to drop from the funnel, A (Fig. 84), on to crystals of potassium permanganate contained in the flask, B. Chlorine is generated immediately, and the flow can be regulated by adjusting ihe supply of acid. The apparatus in which the chlorine gas is to be used is placed in the space, C, and any excess escapes by the tubes, D and E, which may be of any required length, into the open air outside the building. The bottle (2 oz.), F, contains either water or concentrated sulphuric acid. With the pipette (50 c.c., with the bottom cut aslant), G, dipping into the water as shown in the figure, the chlorine cannot escape through the trap thus formed and therefore passes on to C, but on raising the pipette above the surface of the water the gas ceases to pass through O, but escapes through G and E into the air. By this means the flow of gas is always under complete control, Fia. 84. CHLORINE—PROPERTIES 103 On closing the stop-cock of A, the evolution of gas decreases until all the acid which has run in has been used up. Just before disconnecting the apparatus for cleaning, the flask, B, may be filled with water (or much better, solution of sodium thio- sulphate to destroy the odour) through A, so saving unnecessary inconvenience. A perfectly regular stream of chlorine can be maintained for a long time and the gas is pure, provided pure materials are used ; 10 to 15 g. permanganate and 40 to 80 c.c. acid will give a good current of gas for an hour or two. On warming the flask, still more chlorine can be obtained. s Manganese dioxide (ordinary or precipitated) may be used in place of permanganate if the flask, B, be immersed in a boiling-water bath. (d) In Weldon’s manganese recovery process for the manufacture of chlorine, the manganese is made to act as a carrier of oxygen from the atmosphere to the hydrogen of the HCl, setting the Cl free. For this purpose the chloride of manganese obtained in the above process (a) is decomposed by lime ; MnCl, + CaO = CaCl, + MnO. By mixing the MnO with more lime and blowing air through the mixture, MnO, is repro- duced and may be employed for decomposing a fresh quantity of HCl. (e) In Deacon’s process, a mixture of air and hydrochloric acid gas is passed over hot fire-brick which has been soaked in solution of copper sulphate and sodium sulphate and dried. The final result is expressed by the equation 4HCl + (4N, + O,) = 2H,O + 2Cl, + (4N,), so that the chlorine obtained is mixed with twice its volume of nitrogen, which does not interfere seriously with its useful application. The action of the copper-salt has not been clearly explained, but the salt appears to act by absorbing the water formed and then discharging it again. The reaction proceeds, but less rapidly and less completely in absence of the salt, the heated porous bricks having a similar catalytic effect. The (f) Weldon-Pechiney process consists in mixing MgO with concentrated MgCl, solution, whereby magnesium oxychloride (5Mg0.4MgCl,) is produced. This can be dried without losing HCl, which is not possible with MgCl, itself ; and when the dried mass is heated in air at 1000°, it gives up its chlorine in exchange for oxygen. The MgO thus left is used again. (g) The electrolytic process constitutes the chief modern source of chlorine. It receives notice in the section on alkali industry. __Proaperties.—(a) Physical. Both the physical and chemical properties of chlorine are more striking than those of the elements hitherto considered. Its colour is greenish-yellow (whence its name—yAwpds, pale green), easily observed in- daylight or in the light of burning magnesium ; its odour is characteristic and insupportable. It is 24 times heavier than air (sp. gr. 2-4501); its sp. gr. = 2°1438 (0 = 16). One litre weighs 3°1674 grams. Its specific heat is 0-1155 at constant pressure, 0-08731 at constant volume. Refractive index, gas, 1000772 ; liquid, 1-367. It may be reduced to an amber-yellow liquid by cooling it to — 34° (its boiling-point), or by a pressure of 8:5 atm. at 125°; Sjo.5 = 1-429. Crit. temp. = 146°; crit. press. = 93-5 atm. When properly dried, liquefied chlorine can be kept, and is sold, in steel cylinders. At — 102° it forms yellow-white crystals. It is much more soluble in water than oxygen is. 100 c.c. water at 0° dissolve 461 c.c. (1-46 grams) ; at 10°, 310 c.c. (0-997 gram) ; at 20°, 226 c.c. (0-729 gram) of the gas at 760 m.m. A saturated solution, made by bubbling the gas through water, constitutes the laboratory reagent and commercial article known as chlorine water, liquor chlori. On cooling this greenish-yellow solution to 0°, yellow crystals of chlorine hydrate, Cl,.8H,0, separate, the liquid becoming colourless. This hydrate affords a convenient source of liquid chlorine (p. 82). When water in the pneumatic trough, over which chlorine is being collected, happens to be very cold, the gas is often so foggy as to be quite opaque, in consequence of the deposition of minute crystals of the hydrate. For the influence of light see p. 105. It is sparingly soluble in solution of sodium chloride ; cf. I and KI (p. 126). (b) Chemical. The most characteristic chemical feature of chlorine is its powerful attraction for other elements, with nearly all of which, except 104 CHLORINE—PROPERTIES carbon, nitrogen, oxygen, the argon group and, probably, bromine, it combines directly with ease, forming Chlorides (p. 113). With iodine; sulphur, selenium; phosphorus, powdered arsenic, antimony, bismuth ; silicon; boron; hydrogen, it unites at the ordinary temperature with the phenomena of combustion. Many compounds unite with it under various conditions, e.g. carbon monoxide, nitric oxide, ethylene, &c.; with a very large number metalepsis occurs (p. 106); with some, decomposition (p. 107), while on others it appears to act indirectly through nascent oxygen ; see bleaching, disinfection. With few exceptions the relationship of chlorine to other substances is discussed in connection with the respective substances. The presence of moisture appears to be as essential for the combination of chlorine with other elements as it is for the combination of oxygen with other elements. Thus sodium may be fused in absolutely dry chlorine gas without alteration, while in ordinary chlorine violent combustion occurs. When the sodium is heated to redness in the dry gas it burns explosively. A piece of dry phosphorus in a deflagrating spoon, immersed in a bottle of chlorine (Fig. 85), takes fire spontaneously, combining with the chlorine to form phosphorous Fie. 87. chloride, Puls. A tall glass shade may be placed over the bottle, which should stand in a plate containing water, so that the fumes may not escape into the air. If phosphorus be placed in a bottle of oxygen, to which a small quantity of chlorine has been added, it will burst out after a minute or two into most brilliant combustion. Powdered antimony metal sprinkled into a bottle of chlorine (Fig. 86) descends in a brilliant shower of white sparks, the antimony burning in the chlorine to form antimonious chloride (SbCl). A little water should be placed at the bottom of the bottle to prevent it from being cracked. If a flask, provided with a stop-cock (Fig. 87), be filled with leaves of Dutch metal (an alloy of copper and zinc resembling gold-leaf), exhausted of air, and screwed on to a capped jar of chlorine standing over water, on opening the stop-cocks so that the chlorine may enter the flask, the metal burns with a red light, forming thick yellow fumes containing cupric chloride (CuCl,) and zine chloride (ZnCl,). A gold leaf sus- pended in chlorine is not immediately attacked, but gradually becomes auric chloride (AuCl,). These are cases of combustion (p. 58), and many other experiments similar to those made with air or oxygen may be performed with chlorine—in particular the reciprocal combustion experiment (p. 264), the product being hydrochloric acid instead of water. Hydrogen and Chlorine.—The most important useful applications of chlorine depend upon its powerful chemical attraction for hydrogen. The two gases may be mixed without combining, if kept in the dark; but when the mixture is exposed to light, they combine to form hydrogen chloride CHLORINE AND HYDROGEN 105 (HCl) with a rapidity proportionate to the intensity of the actinic rays (or rays capable of inducing chemical change) in the light employed. Exposed to gas-light or ordinary diffused daylight, the H and Cl combine slowly ; but direct sunlight causes sudden combination, attended with explosion, result- ing from the expansion which the hydrogen chloride formed suffers by the heat evolved in the act of combination (22,000 gram units per 36-5 grams of HClformed). The light of magnesium burning in air, and some other artifi- cial lights, also cause sudden combination. The gases also combine at about 300°, and explode on application of a lighted taper. The presence of zir- conium metal at 40°, tin, &c., will induce explosion at comparatively low temperatures, probably due to the heat evolved by the metal being attacked by the chlorine. Two pint gas-bottles should be ground so that their mouths may be fitted accu- rately to each other, and filled respectively with dry hydrogen and dry chlorine, both gases having been dried by passing through oil of vitriol and collected, the hydrogen by upward and the chlorine by downward displacement of air. The mouths should be slightly greased before the bottles are filled with gas, and afterwards closed with glass plates. On placing the bottles together and removing the plates so that the gases may come in contact (see Fig. 136), the yellow colour of the chlorine will be permanent so long as the mixture is kept in the dark, but on exposure to diffused daylight the colour will gradually disappear, the hydrochloric acid gas being colourless. Strong daylight or sunlight would cause explosion (supra). If the bottles be now closed with glass plates, the small quantity of gas which escapes during the operation will be seen to fume strongly in air, a property not possessed either by hydrogen or chlorine ; and when the necks of the bottles are immersed in water and the glass plates withdrawn, the water will absorb the gas and be forced into the bottles so as to fill them, with the exception of a small space occupied by the air accidentally admitted, showing that the volume of hydrochloric acid gas is equal to the sum of the volumes of the hydrogen and chlorine. If the water be tinged with blue litmus, it will be strongly reddened as it enters the bottles. The sudden union of the gases with explosion may be safely exhibited in a Florence flask. The flask is filled with water, which is then poured out into a measure. Exactly half the water is returned to the flask, and its level in the latter carefully marked with a diamond or file. The flask, having been again filled with water, is closed with the thumb and inverted in the pneumatic trough, so that hydrogen may be passed up into it to displace one-half of the water. A short-necked funnel is then inserted, under the water, into the neck of the flask, and chlorine rapidly decanted up from a gas-bottle (Fig. 88) until the rest of the water has been displaced. The flask is now raised from the water and quickly closed with a cork (Fig. 89), through which pass two gutta- Fre. 88. percha-covered copper wires, the ends of which have been stripped and brought suffi- ciently near to each other to allow of the passage of the electric spark within the flask. The ends external to the flask are also stripped and bent into hooks, for convenient connection with the conducting wires. The flask is placed upon the ground, and covered with a wooden box to prevent the pieces from flying about. On connecting the copper wires with the conducting wires from an induction coil or an electrical machine, it 106 METALEPSIS will be heard, on passing the spark, that the mixture has violently exploded; on raising the box, it will be found filled with strong fumes of hydrochloric acid, and a heap of small fragments of glass will represent the flask. A flask filled in the same way with the mixture of hydrogen and chlorine may be attached to the end of a long stick and thrust out into the sunlight, when it explodes with great violence. To illustrate the direct combination of H and Cl under the influence of artificial light, a strong half-pint gas cylinder is half filled with H, over water, then filled up quickly with Cl, also over water, closed with a thin plate of mica, placed mouth upwards on the table, and a piece of burning magnesium tape held close to the side of the cylinder ; the lightness of the mica plate obviates any danger. A mixture of H and Cl which is to be exploded by light must be substantially free from certain other gases, particularly oxygen and easily reducible gases or vapours like nitrogen chloride (which is formed if ammonia gains access to the gases), for such admixtures greatly inhibit the photo-chemical action and diminish the sensitiveness of the mixture to light. . The attraction of chlorine for hydrogen enables it to decompose water. Chlorine-water may be preserved in the dark without change; but when exposed to light, it loses the smell of chlorine and becomes converted into weak hydrochloric acid, the oxygen being liberated ; H,O + Cl, = 2HCl + O.1 The decomposition is much more rapid at a red heat, so that oxygen is obtained in abundance by passing a mixture of chlorine and steam through a red-hot tube. For this experiment a porcelain tube is used, loosely filled with fragments of broken porcelain, to expose a large heated surface. This tube is gradually heated to redness in a gas furnace (Fig. 80). One end of it receives the mixture of chlorine with steam, obtained by passing the chlorine evolved from hydrochloric acid and manganese dioxide in A, through a flask, B, of boiling water. The other end of the tube is connected with a bottle, C, containing solution of potash, to absorb any excess of chlorine and the hydro- chloric acid formed ; from this bottle the oxygen is collected over the pneumatic trough. The combination of hydrogen with chlorine. may obviously be regarded as the substitution of an atom of chlorine for an atom of hydrogen in a mole- cule of hydrogen, HH + CICL = HCl + HCl, the atom of hydrogen sub- stituted having been removed as HCl. Thus viewed it becomes typical of a large number of cases in which two atoms of chlorine react with a hydrogen compound, one of them bearing away a hydrogen atom in the form of HCl whilst the other takes the place of the hydrogen thus removed. Such a sub- stitution of chlorine for hydrogen accompanied by the simultaneous forma- tion of hydrochloric acid is known as metalepsis,? and is a very common reaction of chlorine with hydrocarbons ; since the formation of hydrogen 1A portion of this oxygen becomes hypochlorous acid (HCI10), chloric acid (HC10,) and perchloric acid (HCI1O,), particularly if the light be not very intense. 2 A term introduced by Dumas in 1834, metdéAnyis, exchange. BLEACHING 107 chloride is initiated by light it is not surprising that metalepsis is aided by this agency. (Cf. Iodine, p. 129.) When equal volumes of marsh gas, methane (CH,), and chlorine are mixed and exposed to diffused daylight the volume of the mixture remains unaltered, but after a time the yellow colour of the chlorine is no longer observed,and the gas is found to consist of equal volumes of methyl chloride and hydrogen chloride, CH, + Cl, = CH,Cl + HCl. The metalepsis may be carried further by mixing methyl chloride with more chlorine, CH,Cl + Cl, = CH,Cl, + HCl. Again, CH,Cly, methylene dichloride, with Cl, will yield chloroform, CHC],; CH,Cl, + Cl, = CHCl, + HCl, and this with Cl, will yield carbon tetrachloride, CCl,; CHCl, + Cle = CCl, + HCl. By mixing 1 volume of marsh gas with its own volume of CO,, to prevent violent action, and adding four volumes of chlorine, an oily mixture, containing chiefly CHCl, and CCl,, is formed under the influence of sunlight. If no CO, is used and the sunlight is direct, explosion occurs, the Cl removes the whole of the H, and carbon is deposited ; CH, + 2Cl, = C + 4HCl. Since water is decomposed by chlorine, it is not surprising that most other hydrogen compounds are attacked by it. Ammonia (NH,) is acted on with great violence. If a stream of ammonia gas issuing from a tube con- nected with a flask in which strong solution of ammonia is heated be passed into a bottle of chlorine, it takes fire immediately, burning with a peculiar flame, and yielding thick white clouds of ammonium chloride ; 4NH, + 3Cl= 3NH,Cl1+N. A piece of folded filter-paper dipped in strong ammonia, and immersed in a bottle of chlorine, will exhibit the same effect. When chlorine is allowed to act upon ammonium chloride its operation is less violent, and one of the most explosive substances, nitrogen chloride, NCl,, is produced (p. 208). Many of the compounds of hydrogen with carbon are also decomposed with violence by chlorine. When a piece of folded filter-paper is dipped into oil of turpentine, C,,H,,, and afterwards into a bottle of chlorine, it bursts into a red flame, liberating voluminous clouds of carbon and hydrochloric acid. Acetylene, C,H,, explodes spontaneously with chlorine when exposed to light (p. 255). When a lighted taper is immersed in pure chlorine, it is extinguished ; but if a little air be present, it continues to burn with a small red flame, the hydrogen only of the wax combining with the chlorine, whilst the carbon separates in black smoke, mixed with hydrochloric acid fumes. A mixture of chlorine with an equal volume of oxygen burns up much of the carbon, with a very pretty effect. When chlorine is brought in contact with the flame of a spirit-lamp, it renders the flame luminous by causing the separation of solid particles of carbon (p. 261). Chlorine sometimes combines directly by addition with hydrocarbons, as in the case of olefiant gas (p. 256). The attraction of chlorine for hydrogen enables the moist gas to act as an oxidising agent. Thus, if marsh gas and chlorine be mixed in the presence of water, and exposed to daylight, the water is decomposed, its hydrogen combining with the chlorine, and its oxygen with the carbon of the marsh gas; CH, + 2H,O + 4Cl, = CO, + 8HCL. Bleaching.—The powerful bleaching effect of chlorine upon organic colouring-matters is now easily understood. If a solution of chlorine in water be poured into solution of indigo (sulphindigotic acid), the blue colour of the indigo is discharged, and gives place to a comparatively light yellow colour. The presence of water is essential to the bleaching of indigo by chlorine, the dry gas not affecting the colour of dry indigo. The indigo is first oxidised at the expense of the water and converted into isatin, which is then acted upon by the chlorine and converted by metalepsis into chlor- isatin, having a brownish-yellow colour— CigHioN20, (Indigo) + 2H,O + 2Cl = 20,H,NO, (Isatin) + 4HCl Hits C*#H,NO, (Jsatin) + Cl = (©,H,CINO, (Chlorisatin) + HCl 108 DISINFECTION BY CHLORINE Nearly all vegetable and animal colouring-matters contain carbon, hydrogen, nitrogen and oxygen, and are converted by moist chlorine into products of oxidation or chlorination which happen to be colourless, or nearly so. It might be thought that, since water is decomposed by chlorine only in light, chlorine would not behave as an oxidising agent in the dark. Bleach- ing by chlorine can, however, proceed in the absence of light because the colouring-matter, being ready to combine with oxygen, exerts attraction on the oxygen of the water, sufficiently powerful to weaken the union between the H and O so that the chlorine can effect the decomposition. That dry chlorine will net bleach may be shown by shaking some oil of vitriol in a bottle of the gas and allowing it to stand for an hour or two, so that the acid may remove the whole of the moisture. A piece of crimson paper dried at a moderate heat and suspended in the bottle while warm, remains unbleached for hours; but a similar piece suspended in a bottle of moist chlorine is bleached almost immediately. If characters be written on crimson paper witha wet brush, and the paper placed in a jar beside a bottle of chlorine (Fig. 91), it will be found on removing the stopper that white characters soon make their appearance on the red ground. : When a collection of coloured linen or cotton fabrics, or of artificial flowers, is exposed to the action of moist chlorine or of chlorine-water, those which are dyed with organic colouring- matters are bleached at once, whilst the mineral colours for the Fic. 91. most part remain unaltered. Green leaves immersed in chlorine acquire a rich autumnal brown tint, and are eventually bleached. All flowers are very readily bleached by the gas. Chlorine is very extensively employed for bleaching linen and cotton, the gas acting upon the colouring-matter without affecting the fibre ; but silk and wool present much less resistance to chemical action, and would be a. injured by chlorine, so that they are always bleached by sulphurous acid gas. Neither chlorine itself nor its solution in water can be very conveniently used for bleaching on the large scale, on account of the irritating effect of the gas, so that it is usual to employ it in the form of bleaching powder, chloride of lime, from which it can be easily liberated as it is wanted (p. 116). Disinfecting Properties are exhibited by chlorine and by compounds which yield it easily, e.g. bleaching powder. The explanation of this also probably depends on the withdrawal of hydrogen from the moisture present in the air or in the offensive and objectionable bodies and the simul- taneous purifying action of nascent oxygen. Chlorine substitution may also occur under certain conditions. Applications.—Chlorine is chiefly used for making bleaching powder and the chlorates used in explosives ; it is also applied in certain processes for extracting gold from its ores and in making certain chlorinated organic bodies for the dyestuff industry. HYDROCHLORIC ACID, or Hydrogen Chloride, HCl = 36-47.—Basil Valentine (15th cent.) was the first to describe this acid, which he obtained by heating a mixture of common salt and ferrous sulphate ; he also records its action on metals and their oxides and prepared aqua regia. Glauber next prepared it from common salt and sulphuric acid in 1648 (p. 101), followed by Priestley, who, having introduced the method of collecting gases over mercury, was thus enabled in 1772 to separate hydrochloric acid gas, as well as other gases which cannot be collected over water, e.g. ammonia, ae dioxide, silicon fluoride, Davy in 1811 established its composition p. 101). HYDROCHLORIC ACID 109 This acid is found in nature among the gases emanating from active voleanoes, and occasionally in the spring and river waters of volcanic dis- tricts. It is also a constituent of the gastric juice. Preparation.—The only process in general use, either experimental or technical, is the interaction of sulphuric acid and common salt ; the sodium of the salt being exchanged for the hydrogen of the acid. NaCl + H,SO, = HCl + NaHSO, (sodium hydrogen sulphate). 20 g. common salt (previously dried in an oven) are introduced into a dry flask (Fig. 92), to which has been fitted, by means of a perforated cork, a tube bent twice at right angles, to allow the gas to be collected by downward displacement. 30c.c. strong Fig. 92. Fie. 93. sulphuric acid are poured upon the salt, and the cork having been inserted, the flask is very gently heated, in order to promote the disengagement of the hydrochloric acid gas, which is collected in a perfectly dry bottle, the mouth whereof, when full, may be covered with a glass plate smeared with a little grease. The bottle will be known to be filled with gas by the abundant escape of the dense fumes which hydrogen chloride, itself transparent, produces by condensing the moisture of the air; for since the gas is heavier than air (sp. gr. 1-267), it will not escape in any quantity from the bottle until all the air has been buoyed out. While being filled, the bottle may be closed with a perforated card. If apparatus suitable for completing the reaction at a red heat be employed, only some 10 ¢.c. concentrated sulphuric acid is required and the whole of the hydrogen in the H,SO, can be converted into HCl, as is done in the manufacture of salt-cake (p. 369); 2NaCl + H,SO, = 2HCl + Na,.SO, (sodium sulphate). Common salt in powder sometimes froths to a very inconvenient extent with sul- phuric acid ; it is therefore often preferable to employ fragments of rock salt or of fused salt, prepared by fusing the common salt in a clay crucible and pouring it on to a clean dry stone. A very convenient source from which to procure the gas is the concentrated solution commonly known as “‘ hydrochloric acid.” (a) This may be heated ina flask, and the gas dried by passing through a bottle filled with fragments of pumice-stone wetted with concentrated sulphuric acid, being collected over the mercurial trough (Fig. 93). (6) Or the gas may be prepared by dropping strong sulphuric acid from a funnel pro- vided with a stop-cock into commercial strong hydrochloric acid. The apparatus may take the form shown in Fig. 99, the U-tube being omitted. : The acid is produced in enormous quantities in making salt-cake at the alkali works (see Alkali), and the manufacturer is compelled to condense the gas in water, for it is found to wither up the vegetation in the neighbourhood. Hargreave’s process for making hydrochloric acid is described under Alkali, “ Hydrochloric acid,” the solution of the gas, also called muriatic acid, occurs in commerce in two forms, (a) the crude, yellow liquid commonly known as “ spirit of salt,” which is made at the alkali works (q.v.). It generally 110 HYDROCHLORIC ACID—SOLUBILITY contains a little ferric chloride, FeCl,, to which the colour is due, also traces of arsenic, sulphuric acid, &c. (6) The pure acid, prepared for laboratory and medicinal use. On the small scale the gas prepared as above may be passed into a small bottle containing a very little water, to wash the gas or remove any sodium sulphate which may splash over, and then into a bottle about two-thirds filled with distilled water, the tube delivering the gas passing only about ;3, inch below the surface, so that the heavy solution of hydrochloric acid may fall to the bottom and fresh water may be presented to the gas (Fig. 94). The thistle funnel serves not only to receive the sul- phuric acid, but also to admit air in the event of the water in the absorbing bottle rising into the delivery tube, owing to the extreme solubility of the gas ; cf. experiment, described below. Pure solution of hydrochloric acid is some- times prepared on a large scale by allowing con- centrated sulphuric acid to run into the common hydrochloric acid, when the gas is evolved and is washed and passed into water. Properties.—(a) Physical, Hydrogen chloride is a colourless gas of suffocating, pungent odour, but not nearly so distress- ingly irritant as chlorine, It is rather more than one-quarter heavier than air, sp. gr. = 1:267 (air = 1); sp. gr. = 1147 (O = 16). One litre weighs 1-63915 grams. It is more difficult to liquefy than is to be expected from its great solubility ; a temperature of — 83-7° (its boiling-point) being necessary at 760 mm.; or, at the ordinary temperature, a pressure of 40 atm. Crit. temp, = 52°3°; crit. press. = 86 atm. The sp. gr. of the liquefied gas is 0-91. It can be solidified; m.-pt. — 112.5°. The most obvious property of the gas, observed also with the minute quantity of gas given off on opening a bottle of the ordinary hydrochloric acid of commerce, is the formation of fumes when it comes into contact with the air, although the gas itself is transparent ; this is due to its condensing with the moisture of the air. Its powerful attraction for water is a very important property of the gas, and is applied in organic chemistry. The energy of the attraction is so great that when 36-47 grams of the gas dissolve in water, 17,200 gram-calories are evolved. It is one of the most soluble gases, water dissolving some 450 times its volume at ordinary temperatures. The solution does not obey Henry’s law. It is also soluble in alcohol. The rapid absorption of hydrochloric acid by water is well shown by filling a globular flask (Fig. 95) with the gas, turning it mouth downwards into a capsule of mercury which is placed in a large basin. If this basin be filled with water, it cannot come into HYDROCHLORIC ACID—SOLUTIONS 111 contact with the gas until the mouth of the flask is raised out of the mercury, when the water will rush into the flask and completely fill it. If a rapid stream of the gas is passed into a small bottle of water, it is absorbed so rapidly that no bubble escapes from the surface until the water is nearly saturated (Fig. 96). In the following Table the student should notice (a) the very large volumes of gas dissolved, (b) the increase in volume of the liquid, (c) the comparatively high specific gravity of the solution, although the specific gravity of the liquefied gas is only 0-91. Dissolve HCl at 760 mm. Producing a solution 100 c.c. water cooled to 15° | Weight at 15° ee Sp. gr. at 15° | Containing HCl By weight at 0° 52,520 c.c. 85-5 g. 151 c.e. 1-2257(0°)| 45-15 per cent. x. 3° 48,030 ,, 78-4 ,, 146 ,, 1-2185 43-83 ae » 14° 46,240 ,, 7533 ,, 145 ,, 1-2074 42-83 95 5, 18° 45,120 ,, 73°8 ,, 144 ,, 1-2064 42-34 sy ee. 43,500 ,, 71-0 ,, 142 ,, 1-2014 41-54 Si » 60° 33,870 ,, 56:1 ,, 132 ,, 1-183 35-94 2 », 110° 15,670 ,, 25:7 ,, 114 ,, 1-101 20-24 26 The specific gravities, S%, of solutions at 15° correspond with the following respec- tive acid strengths: 1-050, 10-17 per cent. ; 1-100, 20-01 per cent. ; 1-150, 29-57 per cent. ; 1-200, 39-11 per cent. The ordinary hydrochloric acid of commerce has a specific gravity of about 1-16 and eontains about 31-5 per cent. of the gas. An acid of sp. gr. 1-20, 39 per cent., is also on the market. At — 18°, the strongest solutions deposit crystals of HCl.2H,0O. An acid of 20-24 per cent. has the composition represented by the formula HC].8H,O and distils unchanged at 110° and 760 mm. Thus a definite molecular hydrate appears to be formed, and this view was held until it was shown that many such distillates of constant composition are obtainable, but that they vary in composition with the magni- tude of the pressure, e.g. at 50 mm. 23-2 per cent., at 2500 mm. 18-0 per cent. It is a mere accident that at the atmospheric pressure the composition coincides with a mole- cular formula. When a stronger acid is distilled it evolves abundance of HCl gas until the strength of the liquid is reduced to 20-24 per cent. ; weaker acids lose water until the percentage is raised to 20-24 per cent. Afterwards the remaining 20-24 per cent. liquid distils unchanged at 110°. (b) Chemical, Hydrochloric acid is a very stable compound, few reagents affecting it except oxidising agents with elimination of chlorine (p. 102) and most of the metals with disengagement of hydrogen. Those metals which have the strongest attraction for oxygen will also generally have the strongest attraction for chlorine, so that in respect to their capability of decomposing hydrochloric acid they may be ranked in pretty nearly the same order as in their action upon water (p. 18). Since, however, the attraction of chlorine for the metals is generally superior to that of oxygen, the metals are more easily attacked by hydrochloric acid than by water, the metal taking the place of the hydrogen, and a chloride of the metal being formed. When potassium or sodium is exposed to hydrochloric acid gas, it immediately becomes coated with a white crust of chloride, which partly protects the metal from the action of the gas ; but when these metals are heated to fusion in hydrochloric acid gas, they burn vividly ; Na + HCl = NaCl + H. The metals of the platinum group, Cu, Ag, and Au in the Ist group, and the heavy netals Hg, Pb, Bi, are attacked either not at all or only very slightly. But silver, which does not decompose water at any temperature, is dissolved, though very slowly, by boiling concentrated hydrochloric acid, the chloride of silver formed being soluble 112 HYDROCHLORIC ACID—COMPOSITION in the strong acid, though it may be precipitated by adding water. Gold and platinum are attacked only if free chlorine be present, and this occurs with the fuming acid in presence of air and light ; also all the metals of the platinum group are attacked in the cold or on heating them to 150° in a mixture of hydrochloric acid gas and oxygen. The dzy pure gas, as also the liquefied gas, has comparatively little action even upon those metals which decompose its aqueous solutions most energetically. 3 The action of hydrochloric acid upon metallic oxides generally produces water and a chloride of the metal, in which each atom of oxygen in the oxide has been displaced by 2 atoms of chlorine. Thus, silver oxide acted on by hydrochloric acid gas gives water and silver chloride ; Ag.O + 2HCl = H,0 + 2AgCl. Suboxide of copper (cuprous oxide) yields water and subchloride of copper (cuprous chloride); Cu,0 + 2HCl = H,O + Cu,Cly. Ferric oxide gives water and ferric chloride; Fe,0,; + 6HCl = 3H,O + 2FeCl5. With zine oxide, water and zinc chloride are obtained ; ZnO + 2HCl = H,O + ZnCh. Antimonious oxide is converted into water and antimonious chloride; Sb,0, + 6HCl = 3H,0 + 28bC]. Most basic oxides have a corresponding chloride which is stable, asin the foregoing examples, and these oxides do not evolve chlorine on reaction with hydrochloric acid. But peroxides frequently have no corresponding chloride which is stable ; a chloride containing less chlorine than is equivalent to the oxygen is formed, the hydrogen of the acid becomes oxidised, and the excess of chlorine is disengaged in the free state. Thus, when manganese sesquioxide and dioxide are heated with hydrochloric acid— Mn,0; + 6HCl = 3H,0 + 2MnCl, + Cl, MnO, + 4HCl = 2H,0 + MnCl, + Cl, It would seem that MngCl, and MnCl,, corresponding with Mn,O, and MnO, respec- tively, are first formed and that these decompose into the stable chloride, MnCly, and chlorine (p. 102). On the other hand, basic manganese oxide, MnO, dissolves without evolution of chlorine ; MnO + 2HCl = MnCl, + H,0. Acid oxides not infrequently liberate chlorine ; there is no chloride cor- responding with chromic anhydride ; e.g. 2CrO, + 12HCl = 6H,O + 3(1, + 2CrCl; (chromic chloride). The acid oxides Cl,0 (p. 114) and Mn,0, (from 3 acid and KMn0O,) (p. 102) also do so. When ordinary hydrochloric acid in partly filled bottles is exposed to light, small quantities of free chlorine are generated. The composition of hydrogen chloride may be demonstrated in two ways: (i) By electrolysis, as in the case of water (p. 14). The apparatus represented in Fig. 4 requires a little altera- tion when it is to be used for the electrolysis of hydrochloric acid, and generally takes the form shown in Fig. 97. As chlorine attacks platinum, the electrodes are of carbon, which cannot be sealed in glass but must pass through corks. Strong hydro- chloric acid is poured into the bulb until both limbs are filled with the acid ; the stop-cocks are left open and the wires from the electrodes are connected with the poles of a battery of five ae or six Grove’s cells. The gases are allowed to escape until the Fia. 97. liquid is saturated with chlorine and so cannot dissolve any more, this gas being sufficiently soluble in water to vitiate the experiment. The stop-cocks are then closed and the gases allowed to collect. The pro- portion of chlorine is, however, always too small, owing to the difficulty of completely saturating the liquid with it. By dissolving as much common salt in the hydrochloric acid as it will take up, a better result is obtained. (ii) By determining the density and one of the constituents.—Partly fill a CHLORIDES 113 graduated tube (Fig. 66), provided with dry mercury, with dry hydrochloric acid gas, asin Fig. 93, p. 109. Adjust the position of the tube so that the level of the mercury is the same within and without the tube. Read the volume. Cut a fresh pellet of sodium metal and immediately—while it is perfectly free from hydroxide—pass it beneath the tube so that it rises into the gas. On gently agitating the tube, the gas diminishes in volume, and after a time it is found, on reading the volume as before, that there has been a contraction to one-half the original volume, and that the remaining gas has all the pro- perties of pure hydrogen. From this, according to Avogadro’s law, it tollows that the number of molecules of hydrogen obtained is one-half of the number of molecules of hydrogen chloride used ; therefore, since there are only two atoms in a molecule of hydrogen, and there are twice as many hydrochloric acid molecules as there are hydrogen molecules, there can be only one hydrogen atom in each molecule of hydrogen chloride. So far, we do not know how many atoms of chlorine exist in the molecule. This is found by weighing a known volume of the gas and determining its density ; it is 18-235, .. its molecular weight is 36-47 (p. 11). One molecule con- tains one atom of hydrogen, i.e. 1-008 parts by weight, .-. there are 36-47 — 1:008 = 35-46 parts by weight of chlorine in the molecule ; but 35-46 is the atomic weight of chlorine, .-. there is one atom of chlorine in the molecule ; .. the composition is represented by the formula, HCl. Chlorides—The majority of metallic chlorides are solids which volatilise easily, but AuCl, and PtCly, &c., are decomposed at higher temperatures and SnCl,, TiCl, SbCl, are liquids. Most are soluble in water, but TIC, PbCl, only in hot water ; AgCl, Hg,Cl,, CugCl, are insoluble ; BiCl,, SbCl; react with water giving oxychlorides, BiOClI, SbOCI ; TiCl, with water gives titanic acid. Concentrated solutions of some decompose when heated, e.g. MgClp, AICl,. The majority, except those of the alkalies and alkaline earths, are reduced on heating in hydrogen, and most are decomposed by hot H,SOx. With MnO, and H,SO, they evolve Cl., by which test, and by the precipitate of AgCl (p. 520) produced on adding AgNO, to a solution of a soluble chloride, the presence of a chloride may be proved ; also by the formation of chromyl chloride (p. 468) on distilling a mixture of a chloride, H,SO, and K,Cr20,. Most of the non-metallic chlorides are volatile fuming liquids of low boiling-point, easily decomposed by water, with formation of a hydrogen halide. For acid chlorides, see p. 198. COMPOUNDS OF CHLORINE WITH OXYGEN It is worthy of notice that, whilst chlorine and hydrogen so readily unite, there is no method by which chlorine can be made to combine in a direct manner with oxygen, the compounds of these elements having been hitherto obtained only by indirect processes. An excellent illustration is thus afforded of the fact, that the more closely substances resemble each other in their chemical relations the less will be their tendency to combine ; for chlorine and oxygen are both highly electro-negative bodies, and therefore, having both a powerful attraction for the electro-positive hydrogen, their attraction for each other is of a very low order. . Three oxides of chlorine, C1,0, ClO, and Cl,0,, and four oxyacids of chlorine, HCIO, HC1O,, HCIO,, and HCI1O,, are known. a These series are interesting as illustrating the widest variation in valency. The chlorine atom is seen to be mono-, tri-, tetra-, penta- and hepta- valent. Similar, though less complete, series are exhibited by bromine and iodine, 114 CHLORINE OXIDES Chlorine monoxide Chlorine peroxide Chlorine heptoxide 0 0 ¥ f cl — 0 — cli 0=Ccl*¥=~0 oSavi — 0 - cio o7 | No H.0 HO H20 5 L.. 1 49 f HO — cr HO-—-Chi=O HO—- ar HO — avriZ9 No : Hypochlorous acid Chlorous acid Chloric acid Perchloric acid C\(OH) Cl(OH); —H,O ClOH); —2H,0 Cl(OH); — 3H,0 The acids are first viewed as formed from their anhydrides by reaction with water, then, in the last line, as ortho- and anhydro- acids respectively 4 (p. 91). Chlorine Monoxide or Hypochlorous Anhydride, Cl,O, is of some practical interest in connection with chloride of lime, chloride of soda, and other bleaching compounds. It is prepared by passing dry chlorine over dry precipitated mercuric oxide, and condensing the product in a tube sur- rounded with a mixture of ice and salt ; 2HgO + 2Cl,= HgO.HgCl, + C1,0. Thus obtained, it is a dark brown liquid which boils at 6°, evolving a yellow gas thrice as heavy as air, and having a very powerful and peculiar odour. This gas is remarkably explosive, the heat of the hand having been known to cause its separation into its constituents. As might be expected, most substances which have any attrac- tion for oxygen or chlorine, and therefore raise the temperature of the gas by com- bining with a portion of its oxygen or chlorine, decompose the gas, sometimes with explosive violence. It evolves heat (17,800 gram-calories for 87 g.) in its decomposition, and is therefore an endothermic compound (p. 347). Endothermic compounds can gene- rally be exploded by a shock, mechanical or by a sudden rise of temperature. 1 vol. of chlorine monoxide is entirely decomposed by 2 vols. of hydrochloric acid, yielding water and chlorine; Cl,O + 2HCl = H,O + 2Cl, (p. 112). Chlorine monoxide is a powerful bleaching agent, both its chlorine and oxygen acting upon colouring-matters in the manner explained at p. 107. Hypochlorous Acid, Cl.OH, is formed when the anhydride dissolves in water; Cl,O + H,O =2ClOH. 100c.c. water at 0° dissolves 20,000 c.c. (78 gram:) of the gas (corrected to 0° and 760 mm.), evolving 9000 gram- calories. This strong solution is orange-yellow. The pure acid has not been separated. A solution of the acid may be very readily prepared by shaking mercuric oxide with water in a bottle of chlorine as long as the gas is absorbed. The greater part of the mercuric chloride which is produced combines with the excess of oxide to form a brown insoluble oxychloride, HgO.HgCl,, whilst the hypochlorous acid and a little mercuric chloride remain in solution. Also by passing Cl into CaCO, suspended in water ; CaCO; + H,O + 2Cl, = CaCl, + 2HClO + CO,. Hypochlorous acid is such a very weak acid that it does not attack the carbonate. By distilling these latter solutions, pure dilute, colourless, aqueous acid may be obtained ; also by distilling a filtered solution of bleaching powder, Cl.Ca.OCl, or other hypochlorite, with boric acid, or very dilute nitric or other acid, which will displace the OCI residue but not the Cl. Hypochlorous acid is formed when a weak solution of hydrogen peroxide is added to a large excess of chlorine water; Cl, + H,0, = 2HCIO. But with an excess of the per- oxide, oxygen is liberated ; HClO + H,O, = HCl + H,O + 0,. Solutions of the acid are most powerful oxidising and bleaching agents, * The representation of Cl as tetravalent in C10, is rather at variance with theory, for it is not usual for an element of odd valency to assume even valency, and vice versd. Nitrogen peroxide, NO, or N,O,, is similar and produces two acids—nitrous, HO — Nii 0, and nitric, HO — wig on contact with water. Nitrogen peroxide. however, forms double molecules, N,0, (p. 204), so that the valencies of the nitrogen and the production of nitrous and nitric acids can be explained in the formula 0 = Nii — 0 — nx ; @ like explanation is not available for chlorine peroxide, as Cl,0, is yot known. Cf. p. 119. HYPOCHLORITES 115 since the acid readily decomposes into HCl and 0; it erases writing ink immediately, and does not corrode the paper if it be carefully washed. Printing ink, which contains lamp-black, is not bleached by hypochlorous acid, so that this solution is very useful for removing ink-stains from books, engravings, &c. For the same weight of Clit is twice as effective as chlorine water, since nascent oxygen is the actual bleaching agent : 2HClO = HCl + 20 H,O + Cl, = 2HCl + O. The action of some metals and tneir oxides upon solution of hypochlorous acid is instructive. Iron seizes upon the oxygen, whilst. the chlorine is liberated ; copper takes both the oxygen and chlorine ; whilst silver combines with the chlorine, and libe- rates oxygen. Mercury yields, on shaking, the brown mercuric oxychloride. This distinguishes solution of HClO from chlorine water. Oxide of lead (PbO) removes the oxygen, becoming peroxide of lead (PbO,) and liberating chlorine, but oxide of silver converts the chlorine into chloride of silver, and liberates the oxygen; Ag,O + Cl,0 = 2AgCl + Op. Hypochlorites, or salts of hypochlorous acid, are obtained in solution (i) by neutralising the acid with bases ; (ii) by passing chlorine into a cold solution of a base ; (iii) in the case of calcium especially, by treating the moistened solid base with chlorine. They are almost unknown in the pure state. There are two compounds of great economic importance : chlorinated soda and chlorinated lime. Chlorinated soda, sodium hypochlorite, chloride of soda may be prepared (a) by passing chlorine into cold solution of sodium hydroxide, whereby a solution containing sodium hypochlorite and sodium chloride is obtained ; 2NaOH + Cl, = NaOCl + NaCl + HOH; the hypochlorite may be sup- posed to be formed by metalepsis (p. 106) with the hydroxide, NaOH +Cl,= NaOCl + HCl, the hydrochloric acid thus produced being neutralised by another portion of NaOH. (5) by electrolysis of brine (see Electrolytic bleach). (c) Another mode of preparation is to triturate chlorinated lime with water, add solution of sodium carbonate and filter; CaClO.Cl + Na,CO, = NaCl + NaOCl + CaCO 3. Excess of alkali is necessary for pre- serving these solutions. The sodium compound is never, in ordinary prac- tice, prepared in solid form. Berthollet’s researches (1785) upon the bleaching action of chlorine and the hypochlorites led to the manufaeture of Hau de Javelle (1789), originally made by passing chlorine into potash, but now displaced by solution of hypochlorite of soda ; the latter is also sometimes called Hau de Labarraque. A few years later (1799) Tennant made bleaching powder. Chlorinated lime, bleaching powder, chloride of lime is prepared by passing chlorine gas into boxes of lead or stone in which a quantity of moist slaked lime is spread out. The temperature is not allowed to rise above 25°, which is ensured by acting upon the fresh lime with chlorine diluted by air. The lime absorbs nearly half its weight of chlorine, and forms a white powder, which has a very peculiar smell, somewhat different from that of chlorine. The formula of chloride of lime is generally written CaCl.OCl. Dry calcium hypochlorite is now manufactured by acting on milk of lime with chlorine and concentrating the solution at a low temperature under diminished pressure so as to crystallise the hypochlorite. Chloride of lime is liable to decomposition when kept, evolving oxygen, and becoming converted into calcium chloride, which attracts moisture greedily, and renders the bleaching powder deliquescent. It has been known to shatter the glass bottle in which it was preserved, in consequence of the accumulation of oxygen; CaOCl, = CaCl, + O. When rapidly made and hastily packed, it has been known to become so hot as to set fire to the casks, 116 BLEACHING—DISINFECTION Heat and sunlight favour these changes. Old chloride of lime always con- tains calcium chlorate ; 6CaOCl, = 5CaCl, +-Ca(ClO3)>. It is only partially soluble in water, the insoluble portion containing calcium hydroxide in a form similar to that in which it is obtained on simi- larly treating calcium oxychloride, Ca(OH)Cl, whence presence of the latter in bleaching powder is assumed. The constitution of chlorinated lime is not known with certainty. It is, however, generally conceded that the principal and essential constituent is calcium chlorohypochlorite, Ca.OCI.Cl, probably formed thus: Ca(OH), + Cl, = Ca.OCLCl + H,O; but some lime always remains apparently unattacked. Practically, the constitution of the powder itself is of less importance than that of the solution obtained by treating it with water, which is generally admitted to contain calcium hypochlorite, Ca(OCl),, and calcium chloride, CaCl,, with some calcium hydroxide, Ca(OH), ; 2CaCl(OCl) = CaCl, + Ca(OCl), ; but the powder cannot contain any appreciable quantity of calcium chloride, since it is not deliquescent and alcohol extracts very little. Action of acids.—If an alkaline solution of any hypochlorite be added to blue litmus it exerts little bleaching action ; but the blue colour is discharged if either a weak acid be added—e.g. very dilute mineral acid, boric acid (p. 114), carbonic acid (for instance, by breathing into it through a glass tube), thus liberating bypochlorous acid, NaOCl + HNO, = HOCI + NaNO,; or a strong acid be added, eg. dilute sulphuric acid, dilute hydrochloric acid, thus liberating chlorine, Ca(OCl), + CaCl, + 2H,SO, = 2CaSO, + 2H,O + 2Cl,. In the latter case the strong acid liberates the powerful hydrochloric acid as wellas the feeble hypochlorous acid, and these react to generate chlorine ; HCl + HOC] = H,0 + Cl,. It should be noticed that in the case of bleaching powder the whole of the chlorine existing in the powder as Ca.OCI.Cl is thus liberated, and the determination of such ‘available chlorine” (about 37 per cent. in good samples) is the means of valuing the powder. Bleaching and Disinfecting Properties (see also pp. 107, 108).—When chloride of lime is used for bleaching on the large scale, the stuff to be bleached is first thoroughly cleansed from any grease or weaver’s dressing by boiling it in lime-water and in a weak solution of soda, and is then immersed in a weak solution of the chloride of lime. This, by itself, however, exerts very little action upon the natural colouring-matter of the fibre, and the stuff is therefore next immersed in very dilute sulphuric acid, when the colouring-matter is so far altered as to become soluble in the alkaline solution in which the fabric is next immersed, and a repetition of these pro- cesses, followed by a thorough rinsing, generally perfects the bleaching. The property possessed by acids of liberating chlorine from the chloride of lime is applied, in calico-printing, to the production of white patterns upon a red ground. The stuff having been dyed with Turkey-red, the pattern is imprinted upon it with a discharge consisting of an acid (tartaric, phosphoric, or arsenic) thickened with gum. On passing the fabric through a bath of weak chloride of lime, the colour is discharged only at those parts to which the acid has been applied, and where, consequently, chlorine is liberated. Chloride of lime is one of the most convenient forms in which to apply chlorine for the purposes of fumigating and disinfecting. If a cloth saturated with the solution be suspended in the air, the carbonic acid gas in the latter causes a slow evolution of hypochlorous acid, which is even a more powerful disinfectant than chlorine itself. In extreme cases, where a rapid evolution of chlorine is required, the bleaching powder is placed in a plate, and diluted sulphuric acid is poured over it, or the powder may be mixed with half its weight of powdered alum in a plate, when a pretty rapid and regular escape of chlorine will ensue. When the solution of a hypochlorite is boiled, it undergoes self-oxidation, that is, one part of the hypochlorite loses oxygen, becoming chloride, whilst CHLORIC ACID 117 the remainder is oxidised by this oxygen to chlorate ; 3KCIO = KCIO, + 2KCl. This change is turned to practical account in the manufacture of potassium chlorate. It is much hindered by the presence of an excess of alkali. The solution of hypochlorous acid itself, when exposed to light, is decomposed into chloric acid and free chlorine ; 5HCIO = HClO, + 2H,0 + 2Cl,. Metallic oxides, particularly MnO, and Co,Og, in small quantities liberate the whole of its oxygen from a warm solution of chlorinated lime. Large quantities of oxygen are easily obtained by adding a few drops of solution of cobalt nitrate to solutions of chloride of lime, and applying a gentle heat. This reaction has not yet been clearly explained. Ammonia and tts salts are decomposed on warming with solutions of hypochlorites, with evolution of nitrogen ; 3Ca(OCl), + 4NH, = 3CaCl, + 6H,O + 2N,. Chloric Acid, HClO, or ClO,(OH).—This acid is appropriately studied here, since its salts are usually obtained by the decomposition of the hypo- chlorites ; indeed hypochlorous acid itself yields chloric acid on exposure to light (supra). It was discovered by Berthollet in 1786. It may be procured by decomposing a solution of potassium chlorate with hydrofluo- silicic acid, when the potassium is deposited as an insoluble silico-fluoride, and chloric acid is found in the solution; 2KClO, + H,SiF, = 2HCIO, + K,SiF,. The excess of H,SiF, can be removed as SiF, by adding a little silica before concentrating. Chloric acid can also be prepared by adding the precise equivalent of dilute sulphuric acid to a solution of barium chlorate (p. 90) and decanting ; Ba(ClO,), + H,SO, = 2HCIO, + BaSO,. On evaporating the solution below 38°, or in vacuo over sulphuric acid, it may be concentrated to a yellow liquid with a peculiar pungent smell ; a 40 per cent. acid (HC1O;.7H,0) is, with care, obtainable. In its chemical characters, chloric acid bears a very strong resemblance to nitric acid, but is far more easily decomposed. It cannot even be kept unchanged for any length of time, and at temperatures above 40° or in light it is decomposed into perchloric acid, chlorine, and oxygen ; 4HC1O, = 2HC1O, + H,O + Cl, + 30. Chloric acid is one of the most powerful oxidising agents: a drop of it will set fire to paper or alcohol, and it oxidises phosphorus (even the amor- phous variety) with explosive violence. Like hypochlorous acid it will oxidise hydrochloric acid; HClO, + 5HCl = 3H,0 + 3Cl,.1 Yet it dis- solves Zn with evolution of H. Potassium Chlorate, KCIO,, is the only chlorate of any great practical importance. Most methods of obtaining it depend on the intermediate formation of hypochlorite and the self-oxidation of this on heating as already described (supra). The two stages may be combined by passing chlorine into hot, not too strong, solution of alkali; 6KOH + 3Cl, = KClO, + 5KCl + 3H,O. Potassium carbonate may be employed and the following proportions will be found convenient for the preparation of potas- sium chlorate, as a laboratory experiment. 20 g. of potassium carbonate are dissolved, in a beaker, with 60 c.c. of water, and chlorine is passed through a rather wide bent tube into the solution. At first no action appears to occur, although the solution absorbs the chlorine, because the first portion of that gas converts the potassium carbonate into a mixture of potassium hypochlorite, potassium chloride, and potassium bicarbonate, some crystals of which will probably be deposited ; 2K,CO, + Clp + H,O = KCl + KOC] + 2KHCO;. On continuing to pass chlorine, these crystals redissolve, and brick effervescence is caused by the expulsion of the CO,; 2KHCO, + Cl, = KCl + KOC] + H,O + 2CO,. When this Perchloric acid and chiorinue peroxide are also produced, 118 POTASSIUM CHLORATE effervescence has ceased, and the chlorine is no longer absorbed by the liquid, the change is complete, the ultimate result being represented by the equation K,CO, + Cl = KCl + KOC + CO,. The solution (which often has a pink colour, due to a little potassium ferrate) is now poured into a dish, boiled for two or three minutes, filtered, if necessary, from any impurities (silica, &c.) derived from the potassium carbonate, and set aside to crystallise. The ebullition converts the potassium hypochlorite into chlorate and chloride ; 3KOCI = KCIO, + 2KCIl. The latter, being soluble in about 3 times its weight of cold water, is retained in the solution, whilst the chlorate, which would require about 16 times its weight of cold water to hold it dissolved, is deposited. in brilliant rhomboidal tables. These crystals may be collected on a filter, and purified from. the adhering solution of potassium chloride by pressure between successive portions of filter-paper. If they be free from chloride, their solution in water will not be changed by silver nitrate, which would yield a milky precipitate of silver chloride if potassium chloride were present. Should this be the case, the crystals must be re- dissolved in a smal]! quantity of boiling water and recrystallised. The above processes for preparing potassium chlorate are far from economical, since five-sixths of the potash are converted into chloride, being employed merely to furnish oxygen to convert the chlorine into chloric acid. In manufacturing the chlorate upon the large scale, a much cheaper material, lime, is used to furnish the oxygen. The lime is mixed with water, and saturated with chlorine gas in closed leaden tanks ; 2Ca(OH), + 2Cl, = Ca(OCl), + CaCl, + 2H,O. The liquid is boiled down, when the calcium hypochlorite is decomposed into calcium chlorate and chloride ; 3Ca(OCl), = Ca(ClO,), + 2CaCl,. The calcium chlorate is now decomposed by boiling with potassium chloride, when it yields calcium chloride which remains in solution, and potassium chlorate which crystallises as the solution cools; Ca(ClO3), + 2KCl = CaCl, + 2KCIO3. Chlorate of potash is also made electrolytically as mentioned in the section on potassium. Potassium chlorate forms colourless monoclinic crystals, with a cool saline taste. Sol,5.5° 1 in 16-53 water ; sp. gr. of solution 1-0380; Sol,o9. 1 in 2 water ; Sol,,.4) 1 in 1700 alcohol. When heated it melts and then decom- poses with formation of chloride and perchlorate of potassium and evolution of oxygen (p. 121). The decomposition KClO, = KCl + 30 is exothermic, 9700 gram-calories being evolved per gram molecule of potassium chlorate. If the chlorate be heated to the point at which it begins to decompose, and a little ferric oxide be thrown into it, the heat evolved is so intense as to bring the mass to a red heat, although the ferric oxide is not oxidised. This evolu- tion of heat must of course contribute to increase the energy of explosive mixtures containing the chlorate, and may be accounted for on the supposi- tion that the heat evolved by the combination of the K with the Cl to form KCl exceeds that which is absorbed in effecting the chemical decomposition of the chlorate. If the fused, but not decomposed, pure salt be dropped on to an intensely hot surface, or if it be suddenly heated to a very high tempera- ture, it becomes explosive per se ; otherwise it is not an explosive per se. The same principle applies to picric acid and some other substances. The chlorates resemble the nitrates in their oxidising power, but generally act at lower temperatures, in consequence of the greater facility with which the chlorates part with their oxygen. At high temperatures the chlorates act violently upon combustible bodies. Potassium chlorate is largely employed as a source of oxygen (p. 56), as the oxygen-supplying ingredient in many explosive and pyrotechnic com- positions, in the manufacture of matches, and in medicine. A grain or two of potassium chlorate, rubbed in a mortar with a little sulphur, detonates violently, evolving a powerful odour of chloride of sulphur. If a little powdered chlorate be mixed on a card with some black antimony sulphide CHLORINE DIOXIDE 119 and wrapped up in paper, the mixture will detonate when struck with a hammer. The earliest lucifer matches were tipped with a mixture of potassium chlorate, antimony sulphide, and starch, and were kindled by drawing them briskly through a doubled piece of sand-paper. A mixture of potassium chlorate and lead ferrocyanide is used in toy detonating crackers. A little potassium chlorate sprinkled upon red-hot coal causes a. very violent defla- gration. If a little of the chlorate be melted in a deflagrating spoon and plunged into a bottle or flask containing coal gas, the salt burns with great brilliancy, its oxygen combining with the carbon and hydrogen in the gas, which becomes in this case the supporter of combustion. Potassium chlorate is much used in the manufacture of fireworks, especially as an ingredient of coloured fire compositions, which generally consist of potassium chlorate mixed with sulphur, and some metallic compound, to produce the desired colour in the flame. White gunpowder is a mixture of two parts of potassium chlorate with one part of dried yellow prussiate of potash and one part of sugar, which explodes very easily under friction or percussion. With strong sulphuric acid, chlorates evolve chlorine peroxide (infra) ; with the dilute acid, chloric acid (supra) ; with concentrated hydrochloric acid, euchlorine ; with oxalic acid at 70°, chlorine peroxide and carbon dioxide. Euchlorine, the deep yellow, dangerously explosive gas evolved by the action of strong HCl upon KCl03, appears to be a mixture of chlorine peroxide with chlorine. It is resolved by explosionsinto 2 vols. Cl and 1 vol. O. Mercurous chloride absorbs Cl from it, leaving ClO,. Hence its production may be explained by the equation, 4KCl0, + 12HCl = 4KCl + 6H,0 + 3010, + 9Cl. Chlorine Dioxide or Chlorine Peroxide, ClO,, discovered by Davy in 1815, is dangerous to prepare andexamine on account of its great instability and violently explosive character. It is obtained by the action of strong sulphuric and other acids upon potassium chlorate (supra) ; 3KCI1O, + 2H,SO, = KC1O, + 2KHSO, + 2Cl0, + H,0. On a small scale, chlorine peroxide may be prepared with safety by pouring a little strong sulphuric acid upon one or two crystals of potassium chlorate, in a test-tube supported in a holder. The crystals at once acquire a red colour, which gradually diffuses itself through the liquid, and the bright yellow gas collects in the tube. If heat be applied, the gas will explode, and the colour and odour of chlorine will be substituted for those of chlorine peroxide. If the chlorate employed in this experiment contains potassium chloride, explosion often happens in the cold, since the hydrochloric acid evolved by the action of the acid upon that salt. decomposes a part of the chlorine peroxide, and thus provokes the decomposition of the remainder. It is a bright yellow gas, with a chlorous and somewhat aromatic smell, and sp. gr. 2-32 (air = 1); condensable to a red, very explosive liquid (b.pt. 99°); it has been solidified, m.pt. — 79°. The gas is gradually decomposed into its elements by exposure to light, and a temperature of 60° causes it to decompose with violent explosion into a mixture of chlorine and oxygen, the volume of which is one and a half times that of the com- pound. ClO, is easily absorbed by water, forming chlorous and chloric acids (p. 114); the solution has powerful bleaching properties. Combustible bodies, such as sulphur and phosphorus, decompose the gas, as might be expected, with great violence. This powerful oxidising action of chlorine peroxide upon combustible substances appears to be the cause of the property possessed by mixtures of such substances with potassium chlorate, to inflame when, touched with strong sulphuric acid. 120 PERCHLORIC ACID If a few crystals of potassium chlorate be thrown into a glass of water (Fig. 98), one or two small fragments of phosphorus dropped upon them, and some strong sul- phuric acid poured down a funnel tube to the bottom of the glass, the chlorine peroxide will inflame the phosphorus with bright flashes of light and slight detonations. Powdered sugar mixed with potassium chlorate on paper will burn brilliantly when touched with a glass rod dipped in strong sulphuric acid. Matches may be prepared, which inflame when moistened with sulphuric acid, by dipping the end of splinters of wood in melted sulphur, and, when cool, tipping them with a mixture of 0-3 gram of sugar and 1 gram of potassium chlorate made into a paste with 4 drops of water. When dry, they may be fired by dipping them into a bottle containing asbestos moistened with strong sulphuric acid. These matches, under the names of Eupyrion and Vesta matches, were used before the intro- duction of phosphorus into general use. The Promethean light was an ornamental scented paper spill, one end of which contained a small glass bulb of sulphuric acid surrounded with a mixture of chlorate and sugar, which inflamed when the end of the spill was struck or squeezed, so as to break the bulb containing the sulphuric acid. The paper was waxed in order to make it inflame more easily. Percussion fuses, &c., have been often constructed upon a similar principle. Chlorous Acid, HClO, or CIO(OH), is contained, together with chloric acid, in the aqueous solution of chlorine peroxide (2C10, + H,O = HClO, + HClO,) which thus resembles nitric peroxide in not being a ‘separate anhydride (p. 114). The chlorous acid may be separated by neutralising the solution with potash and evaporating until the potassium chlorate crystallises, leaving the chlorite (KCIO,) in solution. The Na salt may be obtained by treating solution of ClO, with NayOz ; 2Cl0, + Na,O, = 2NaClO, + Op. AgNO, precipitates yellow AgClO,. Little is known about the acid or its salts ; they readily undergo self-oxidation, like hypochlorous acid and its salts, yielding chloric acid and chlorates. Chlorine Heptoxide, presumably Cl,0,, is obtained by dropping perchloric acid on to phosphoric anhydride cooled below — 10° and after a day or two warming, the retort until the heptoxide distils. It is a colourless volatile oil, boiling at 82°. and easily exploded. It is probably perchloric anhydride ; with water it forms per- chloric acid (infrd). With iodine it forms an oxide of iodine and liberates chlorine (p- 129). A similar reaction with bromine does not occur. Perchloric Acid, HClO, or ClO,(OH), is obtained by evaporating, at a boiling heat, the solution of chloric acid obtained by decomposing potassium chlorate with hydrofluosilicic acid (p. 117), when the chloric acid is decomposed into perchloric acid, chlorine, and oxygen ; 4HCIO, = 2HCI0, + H,O + Cl, + 30. The pure acid is best obtained by distilling potassium perchlorate (see below) with four times its weight of strong H,SO, in a vacuum. At 56 mm. pressure it boils at 39°. It is also formed from KCI0O, and H,SO,. See Chlorine dioxide. The pure perchloric acid is a colourless, very heavy liquid (sp. gr. 1-764 at 22°), which soon becomes yellow from decomposition. It cannot be kept for any length of time, but it is more stable than any of the other oxyacids of chlorine. When heated, it decomposes, often with explosion. In its oxidising properties it is more powertul than chloric acid. It burns the skin in a very serious manner, and sets fire to paper, charcoal, &c., with explosive violence. This want of stability, however, belongs only to the pure acid. If water be added to it, heat is evolved, and a crystalline acid, HC1O,.H,0, melting at 50°, may be obtained. Diluted perchloric acid is much more stable than the pure acid ; it does not even bleach, but reddens litmus in the ordinary way. It dissolves Zn with evolution of H, 7 BROMINE 121 Perchlorates are formed by heating chlorates, e.g. 2KCIO, = KClO, + KCl + Oz, and at higher temperatures are themselves decomposed into chlorides and oxygen, e.g. KClO, = KCl + 20, (p. 56). They are all soluble in water, but the potassium (Soloia, 1 in 150) and rubidium salts only sparingly. In the solid form they are dis- tinguished from chlorates by not yielding a yellow gas (C10,) when treated with strong sulphuric acid. Neither perchloric acid nor any of its salts is applied to any useful purpose. Potassium erchlordte crystals are isomorphous with those of potassium permanganate, KMnO, ; further Mn,0, (p. 462) exists, comparable in properties with Cl,0,; thus showing close relationship between non-metallic Cl and metallic Mn, both members of the 7th group (p. 8). BROMINE, Br = 79.92 It generally happens that elements between which any strong family likeness exists are found associated in nature. This remark particularly applies to the three elements—chlorine, bromine, and iodine—all of which are found in sea-water, though the first predominates to such an extent that the others for long escaped notice. Bromine was brought to light in the year 1826 by Balard in the examination of bittern, which is the liquid remain- ing after the sodium chloride and some other salts have been made to crystallise by evaporating sea-water, which contains bromine in the forms of bromide of magnesium and bromide of sodium.! It has also been ex- tracted from the waters of certain mineral springs, as those of Kreuznach and Kissingen, which contain much larger quantities of bromine, combined with potassium, sodium or magnesium. Now, almost the sole sources of bromine are the mother-liquors of the salt-works at Stassfurt, and certain saline springs in the United States. As a mineral it occurs in bromargyrite, AgBr (p. 521). In extracting the bromine from these waters, advantage is taken of the circumstance that chlorine displaces bromine from its combinations with the metals. After most of the other salts, such as sodium chloride, sodium sul- phate and magnesium sulphate, which are less soluble than the bromides, have been separated from the water by evaporation and crystallisation, the remaining liquid, containing about 0-3 per cent. of bromine, is run down a tower packed with earthenware balls, where it meets a current of steam conveying chlorine which has been passed into it from a chlorine still. The bromine is liberated from the bromides, the chief of which is magnesium bromide (MgBr, + Cl, = MgCl, + Br,), and passes as vapour from the top of the tower through a condenser in which it is condensed to the liquid state. The chief impurity in the crude bromine thus obtained is chlorine. This is removed by shaking the crude product with potassium or other bromide, 2KBr + Clp = 2KC] + Br, ; and the bromine is distilled away from the KCl. Hydrobromic acid, cyanogen bromide, bromoform, sulphur, also occur as impurities in crude bromine. To illustrate on a small scale the manufacture of bromine, chlorine water may be added to a dilute solution of potassium bromide, which will at once become orange from the liberation of the bromine, KBr + Cl = KCl + Br. The bromine thus set free exists now diffused through a large volume of water, which cannot be separated from it in the usual way, by evaporation, because bromine is itself very volatile. An ingenious expedient is therefore resorted to, of shaking the orange liquid briskly with ether, which has a greater solvent power for bromine than is possessed by water, and therefore abstracts it from the aqueous solution: since ether does not mix to any great extent with water, it now rises to the surface of the liquid, forming a layer of a beautiful orange colour, due to the bromine which it holds in solution. This orange layer is carefully separated and shaken with solution of potash, which immediately destroys 4-9 grams of magnesium bromide per gallon have been found in the water of the Irish Sea. 122 BROMINE—PROPERTIES the colour by combining with the bromine, leaving the ether to rise to the surface in a pure state and fit to be employed for abstracting the bromine from a fresh portion of the water. The action of the bromine upon potash is precisely similar to that of chlorine ; 6KOH + 3Br, = 5KBr + KBrO,; + 3H,0. ; After the solution of potash has been several times shaken with the ethereal solu- tion of bromine, and has become highly charged with this element, it is evaporated so as to expel the water, leaving a solid residue containing potassium bromide and bromate. This saline mass is strongly heated to decompose the bromate and convert it into bromide ; KBrO, = KBr + 30. From this salt the bromine is extracted by distilling it with manganese dioxide and sulphuric acid, when the bromine is liberated and condensed in a receiver kept cold by iced water; 2KBr + MnO, + 2H,80, = K,SO,+MnS0O,+ 2H,O0 + Brz. Cf. preparation of Cl (p. 102). Properties.—If these are compared with those of chlorine on the one hand and with those of iodine on the other, it will be found in most cases that bromine occupies a position between these two elements ; e.g. Clis gaseous ; Br, liquid ; I, solid ; HClis very stable ; HBr, stable ; HI, not very stable ; see also pp. 135, 315. (a) Physical. The aspect of bromine is totally different from that of any other element, for it distils over in the liquid condition, and preserves that form at ordinary temperatures, being the only liquid non-metallic element. Its dark red-brown colour, and the peculiar orange colour of the vapour which it exhales continually, are also characteristic ; but, above all, its extra- ordinary and disagreeable odour, from which it derives its name (Spamozs, a stench), leaves no doubt of its identity. The odour has some slight resemblance to that of chlorine, but is far more intolerable, often giving rise to great pain, and sometimes even to bleeding at the nose. The vapour is 54 (5-54) times as heavy as air, .. sp. gr. = 79-70 (H = 1), corresponding approximately with the molecular weight, 159-94, whence the molecular formula is Br, ; it is less at high temperatures, indicating some dissociation into atoms (p. 312). Sp. heat at const. press. = 0-05504 ; at const. vol. = 0-04251. The liquid has a sp. gr. at 0° (%) of 3-1883; at 15° it is about 3-0. Bpt.,59°. Sp. heat, 0-1071. Lat. heat of fusion, 16-185 ; of vaporisation, 45-6. It freezes to a brown crystalline solid; m.pt., — 7-05°. It dissolves in 30 parts by weight of water at 15°; 100 grams solution contain 3-226 grams bromine. The solution is known as bromine water ; it is stable in the dark, but generates hydrobromic acid in the light ; it has bleaching properties, but less powerful than those of chlorine water. By cooling the aqueous solution, crystals of bromine hydrate, Br,.8 (or 10) H,0, are formed ; sp. gr., 1-49 ; decomposes at + 6-2° ; comparable with chlorine hydrate (p. 103). The solubility is slightly increased by the presence of potassium bromide. Bromine is readily soluble in glycerin, alcohol, ether, chloroform, carbon disulphide, &c., but the solvents are gradually decom- posed. Kieselguhr or the like saturated with bromine, about 75 per cent. by weight, is sold as ‘‘ bromum solidificatum ”’ for antiseptic purposes. (b) Chemical. In general, bromine combines with other elements and compounds to form bromides, corresponding with the chlorides, but the reactions are usually less vigorous. The inferiority of bromine to chlorine in chemical energy is well exemplified in its relations to hydrogen ; for the vapour of bromine mixed with hydrogen will not explode under the action of flame or of the electric spark, like the mixture of chlorine and hydrogen. But if hydrogen which has bubbled through warm bromine, and therefore carries a quantity of the vapour, is passed through a red-hot tube, the hydride (hydrobromic acid) is formed; more easily if the tube contain a platinum helix. If for the tube be substituted a jet and the issuing hydrogen lighted, dense fumes of hydrobromic acid will appear; H, + Br, = 2HBr, HYDROBROMIC ACID 123 Phosphorus reacts violently, even detonates, in liquid bromine, and takes fire in the vapour, producing phosphorus bromides (p. 224). Potassium re- acts energetically, but sodium is said to require a temperature of 200°. Bromine is displaced from its compounds by free chlorine, but free bromine displaces iodine (p. 127). Bromine is a powerful oxidiser ; ¢.g. it oxidises H,8, 8O,,P (infra). Bromine itself reacts violently with ammonia solution with evolution of nitrogen; cf. p. 186; with bromine water the action is mild; 3Br, + 8NH,; = 6NH,Br + N,. Free bromine is used to determine the unsaturated hydrocarbons, especially ethylene, in coal gas; also in many laboratory and technical operations in organic chemistry, where it is frequently more tractable than chlorine, although the cheaper and more abundant chlorine answers most purposes for which bromine might otherwise be employed. Considerable quantities are consumed in the manufacture of artificial dyestufts. Hydrobromic Acid or Hydrogen Bromide, HBr = 80:93. When it is attempted to prepare this acid by distilling bromide of sodium or potassium with sulphuric acid (as in the preparation of hydrochloric acid) the inferior stability of hydrobromic acid is shown by the decomposition of a part of it, the hydrogen being oxidised by the sulphuric acid, and the bromine set free; 2HBr + H,SO, = 2H,O + SO,+ Br,. If a strong solution of phosphoric acid be employed instead of the sulphuric, pure hydrobromic acid may be obtained. But the most instructive method of obtaining hydrobromic acid consists in attacking water with bromine and phosphorus simultaneously, when the phosphorus takes the oxygen of the water, forming phosphoric acid, and the bromine combines with the hydrogen to form hydrobromic acid; 3H,O + Br; + P = HPO, + 5HBr. Metaphosphoric acid The experiment may be made in’ the apparatus shown in Fig. 99. 20 grams of red phosphorus are introduced into the flask and are covered with 40 c.c. of water. 120 grams (40 c.c.) of bromine are allowed to fall, drop by drop, from the stop-cock funnel into the flask. The hy- drogen bromide is passed through a U-tube containing fragments of glass mixed with moist red phosphorus, to absorb bromine, and is collected by downward displacement. After a time the flask may be gently heated. The aqueous acid may be obtained directly by passing sulphuretted hydro- gen into bromine covered by water, filtering, and dis- tilling ; Br, + H,S = 2HBr +8. Also, very pure, by ‘passing sulphur dioxide into the water covering a Os layer of bromine until the Eds whole is pale yellow; Br, + SO, + 2H,O = 2HBr + H,S0,; distil in a current of air, and finally over barium bromide, BaBr,, which absorbs traces of other acids, ; : Properties.—(a) Physical. Hydrobromic acid, like HCl, is a colourless gas, fuming strongly in the air, of pungent suffocating odour. At 800° it 124 HYPOBROMITES—BROMATES dissociates partially into its elements (p. 345). The liquefied gas boils at — 73°, and the crystalline solid melts at — 88°5°. It is very soluble; 100 c.c. water at 0° dissolve 61,160 c.c. (221-2 grams) at 760 mm., the solution contains 68-87 per cent. HBr and has a sp. gr. 1-78; at 25°, 53,210 c.c, (193 grams), 65-88 per cent.; at 14° a 49 per cent. acid has sp. gr. 1-502; 25 per cent., 1-206; 10 per cent., 1:073. A 47-8 per cent. acid distils un- changed at 126° and 760 mm. ‘The solution decomposes in presence of air and light, bromine being liberated. This change occurs to a much greater extent than with the corresponding change of HCl. (6) Chemical. Generally similar to those of hydrochloric acid, but less energetic. Chlorine either dry or in solution liberates bromine from hydro- bromic acid and its salts, the bromides ; 2K Br + Cl, = 2KCl + Br, (p. 121); with an excess of chlorine the yellow or red colour of the bromine is destroyed (see below). No compound comparable with chromyl chloride (p. 113) exists ; a distinction of much value in anlaysis. The bromides, KBr, NaBr, NH, Brare used in medicine as sedatives, and in photography, in which art AgBr and CdBr, also are used. In solubility and crystalline form the bro- mides simulate the chlorides. Oxy-Acids of Bromine.—A series of these exists, although their anhydrides— the oxides of bromine—are unknown. Hypobromous acid, BrOH, is obtained in very unstable pale-yellow solution by shaking precipitated mercuric oxide with bromine water, followed by distillation in vacuo at, say, 40°. Hypobromites may be formed by shaking bromine with dilute solu- tions of alkalies, and brominated lime by treating lime with bromine. All these have strong bleaching properties, like hypochlorites (p. 116). Sodiwm hypobromite solution made by dissolving 10 g. NaOH in 25 c.c. water and, when cold, adding 1 c.c. Bro, is used in determinations of ammonia in its salts, &.; 2NH, + 3NaOBr = 3H,0 + 3NaBr + N,; also of urea in urine; CO(NH,). + 3NaOBr = 3H,O + 3NaBr + CO, + Nz; the volume of nitrogen evolved is measured and its equivalent of ammonia or urea calculated. : Bromous acid, BrO(OH), is said to be obtained by adding Br to saturated solution of AgNOs. Bromic acid, BrO.(OH), may be prepared by methods described under chloric acid, of which it is an analogue ; also by passing chlorine into bromine water ; Br, + 5Cl, + 6H,0 = 2HBrO, + 10HCI. Potassium bromate, KBrO, (p. 122), is used with the bromide to generate bromine, for instance, in Koppenschauer’s method for phenol assays; 5NaBr + NaBrO, + 6H,SO,= 6NaHSO,+3H,0 + 6Br. The bromates are decomposed by heat into bromides and oxygen; thus 2KBrO, = 2KBr + 30, ; cf. chlorates (p. 118); but there is no intermediate formation of perbromate (p. 121). IODINE, I = 126.92 Iodine is contained in sea-water in even smaller quantity than bromine, is, and appears to be present as calciwm iodate, Ca(IO3),, of which 4 parts are contained in a million of sea-water,! but the iodine appears to be utilised by certain varieties of sea-weed, which extract it from the sea-water, and con- centrate it in their tissues. The ash remaining after seaweed has been burnt was long used, under the name of kelp, in soap-making, because it contains a considerable quantity of sodium carbonate ; and in the year 1811, Courtois, a soap-boiler of Paris, being engaged in the manufacture of soda from kelp, obtained from the waste liquors a substance which possessed properties ; The iodate may be detected in sea water by shaking with carbon disulphide and a little of the water in which phosphorus has been kept ; the phosphorous acid reduces the iodate, liberating iodine, which dissolves in the CS, with a rose colour. It has been shown that the amount of iodine (2:3 milligrams. per litre) in sea water is constant at all depths, but while it is in inorganic combination at great depths it is organically com- bined near the surface . IODINE—MANUFACTURE ~ 125 different from those of any form of matter with which he was acquainted. He transferred it to a French chemist, Clement, who satisfied himself that it was really a new substance ; and Gay-Lussac and Davy having examined it still more closely, it took its rank among the non-metallic elementary substances, under the name of iodine (ioedjs, violet-coloured), conferred upon it in allusion to the magnificent violet colour of its vapour. The history of the discovery of iodine affords a very instructive example of the advantage of training persons engaged in manufactures to habits of accurate observation, and, if possible, of accurate chemical observation ; for had Courtois passed over this new substance as accidental or of no conse- quence, the community would have lost, at least for some time, the benefits derived from the discovery of iodine. For some years the new element was known only as a chemical curiosity, but its detection as the active constituent in burnt sponge, which had long been used in some particular maladies, led to its regular employment in medicine ; and more recently its use in photography and in the manufacture of artificial dyestuffs, &c., has created a large demand. Although the production of iodine from kelp is a dead industry, a brief description of it may be given as an excellent example of how an element may be extracted from an enormously preponderating mass of other matter. The sea-weed 1 is spread cut to dry, and burnt in shallow pits at as low a temperature as possible ; for the sodium iodide is converted into vapour and lost if the temperature is very high. The ash, which is in a half-fused state, is broken up and treated with hot water, which dissolves about half, leaving a residue consisting of calcium carbonate and sulphate, sand, &c. The whole of the sodium iodide is contained in the portion dissolved by the water, but is mixed with much larger quantities of sulphate, car- bonate,hyposulphite, sulphide and bromide : of sodium, together with sulphate and Fia. 100. chloride of potassium. A portion of the water is expelled by evaporation, when the sulphate and carbonate of sodium and chloride of potassium, being far less soluble than the iodide of sodium, crystallise. In order to decompose the hyposulphite and sulphide of sodium, the liquid is mixed with an eighth of its bulk of oil of vitriol, which decomposes these salts, evolving sulphurous and hydrosulphuric acid gases, with deposition of sulphur, and forming sodium sulphate, ‘which is deposited in crystals. The liquor thus prepared is next mixed with a suitable proportion of manganese dioxide and heated in an iron still lined with lead (Fig. 100), when the iodine is evolved as a magnificent purple vapour, which condenses in the bottle-shaped glass or stoneware receivers (aludels) in the form of dark grey scales with metallic lustre, and having considerable resemblance to black lead. The liberation of the iodine is explained by the following equation: 2NaI + MnO, + 2H,SO, = Na,SO, + MnSO, + 2H,0+ Ij. When no more iodine passes over, more manganese dioxide is added, and the bromine then distils. The quantity of bromine obtained is about one-tenth that of the iodine. A ton of kelp yields about 10 lbs. of iodine. The crude iodine is resublimed to purify it. A more modern treatment of sea-weed for extracting iodine consists in heating the weed directly with dilute H,SO, and precipitating the iodine from the liquor by adding an oxidising agent such as sodium nitrite. Todine is now imported from Chili and Peru, where it is obtained from caliche, the crude nitrate of soda found in certain districts of those countries. ; The Laminaria digitata, or deep sea tangle, contains most iodine, amounting to 0°45 per cent. of the Tied weed. 126 IODINE—PROPERTIES In this mineral the iodine (about 0-1 per cent.) occurs as sodium iodate (NalO,) which remains dissolved in the water from which the sodium nitrate has been recrystallised for the market. These mother liquors, containing about 22 per cent. of NaIO,, are mixed with a solution containing sodium sulphite (Na,SO,) and sodium hydrogen sulphite (NaHSO,;), when the iodine is precipitated according to the equation, 2NalO, + 3Na,SO, + 2NaHSO;= 5Na,8O,+1,+H,0. The precipitate is drained, pressed, and resublimed.. Or cupric sulphate and sulphur dioxide are added to the mother liquor whereby cuprous iodide, Cul (p. 514), is precipitated; first the iodate, NaIO,, is reduced to iodide, NaI, by the sulphurous acid; NalO,; + 3H,SO, = NaI + 3H,SO,; then 2CuSO, +'4NaI = 2CuI + I, + 2Na,.S8O, and H,SO, + H,O + I, = H,SO, + 2HI. Notice that the copper is reduced by the iodide. This reaction is employed in analysis to separate iodides from bromides and chlorides. The cuprous iodide yields potassium iodide, KI, on treatment with potassium carbonate. Besides non-volatile matter (sand and calcium sulphate), which may be eliminated by resublimation, commercial iodine is liable to contain chlorine, bromine, and cyanogen iodide. It may be freed from these volatile impurities by dissolving it in a strong solution of potassium iodide, precipitating it by the addition of water and resubliming the dried precipitate after it has been mixed with barium oxide to complete its desiccation. Properties.—(a) Physical. The features of this element are extremely well marked ; its metallic lustre, peculiar odour, high specific gravity (4-933), and power to stain the skin, &c., brown, sufficiently distinguish it from all others, and the effect of heat upon it is very striking, in first easily fusing it (at 114-2°), and afterwards converting it (boiling-point, 184-35°) into a most exquisitely purple vapour, which is nearly nine times as heavy as air (sp. gr. 8-72), and condenses upon a cool surface in shining scales. However, the vapour becomes indigo-blue at very high temperatures due to partial dis- sociation of the diatomic into monatomic molecules, I, — 21, with conse- quent reduction in vapour density (see also p. 312). Specific heat, 0-0541. Latent heat of fusion, 11-7 ; of vaporisation, 23-95 gram-calories. Iodine is sparingly soluble in water, 1 in about 5000, forming a light brown solution, iodine water. It gives a solution with about 10 parts by weight of 90 per cent. alcohol, from which a great part is thrown out on adding water. Solu- tions of alkali iodides dissolve iodine freely, when e.g. a 1-80 per cent. solution of KI dissolves 1-17 per cent. iodine, sp. gr. of solution is 1-0234 at 8°; a 7-2 per cent. KT solution dissolves 6-03 per cent. of I, sp. gr. 1-1112; a 12-64 per cent. KT solution dissolves 12-06 per cent. of I, sp. gr. 1:2293. Alcoholic solutions of iodine with potassium iodide are used in medicine ; Liquor Iodi Fortis (12 per cent.) ; Tinctura Iodi (24 per cent.). One gram iodine dis- solves in 4 c.c. ether, or in 65 c.c. glycerin. All these solutions are dark red-brown. If an extremely weak aqueous solution of iodine be shaken with a little carbon disulphide, the latter will remove the iodine from the solution, and, on standing, will fall to the bottom of the liquid, having a beautiful rose colour. Benzene, chloroform and carbon disulphide dissolve it abun- dantly, producing fine violet-red solutions, which deposit the iodine, if allowed to evaporate spontaneously, in minute rhombic octahedral crystals aggregated into very beautiful fern-like forms. By dissolving a large quan- tity of iodine in carbon disulphide, a solution is obtained which is perfectly opaque to rays of light, though it allows heat rays to pass freely, and is there- fore of great value in physical experiments. A solution of iodine in carbon tetrachloride is also used for the same purpose. (6) Chemical. In general, iodine is the least active of the halogens, except in relation to oxygen, but it combines with most of the elements IODOMETRY 127 directly under some circumstances. For hydrogen it has comparatively little affinity ; however, in a red-hot tube, or at 450° or even lower, especially in the presence of finely divided platinum, hydriodic acid, HI, isformed. With F it yields iodine pentafluoride, IF; (p. 180); with Cl, a fairly stable mono- chloride, IC] (p. 130), and a feeble trichloride, ICI, (p. 130) ; with Br, a feeble monobromide, [Br (p. 131) ; warmed with 8, sulphur monoiodide, 8,1, (p. 177). P melts and then inflames ; Sb burns in the vapour. Heated with Hg it combines rapidly ; but in the cold, 200g. Hg + 127g. I moistened with alcohol and triturated well in a mortar produce the green mercurous iodide, Hg,I, (p. 418), or 200g. Hg + 254g. I, the red mercuric iodide, HgI, (p. 418). Iron wire and iodine warmed, and then boiled, with water give a solution of ferrous todide, Fel, (p. 455). Unlike chlorine and bromine it is attacked by nitric acid; in the cold to form todine tetroxide ; on boiling, todic acid (p. 130) is formed ; also it is oxidised by ozone. Iodine, in the uncombined state, dyes starch a beautiful blue colour, as may be proved by dissolving a very little of the element in water, and adding to the cold solution a little thin starch, or by placing a minute frag- ment of iodine in a stoppered bottle and suspending in it a piece of paper dipped in thin starch. This test, however, though sensitive to the smallest quantity of free iodine, gives no indication whatever with iodine in com- bination ; in order, therefore, to test for iodine, a little starch-paste is added to the suspected liquid, and then a drop of a weak solution of chlorine (or bromine, cf. p. 123), which will set free the iodine, and cause the production of the blue colour. It is necessary, however, carefully to avoid adding too much chlorine, since it would immediately destroy the colour of the iodised starch: if this has been done, a very little sulphurous acid will bring back the blue tint, which will be again bleached by more sulphurous acid.1 Alkalies or reducing agents also bleach it, due to combining with the iodine, and the colour of a mixture of the iodised starch with water is removed by heating to 80°, but returns in great measure when the solution cools. How- ever, free iodine, in the complete absence of an iodide—added, or formed from a part of the free iodine—will not give a proper blue. If a drop of fresh iodine water is added to fresh starch paste no blue colour is produced ; but on adding a trace of ‘an iodide, a full blue appears. The compound (C.4H 490 a91,) formed from starch and free iodine is colourless or pale blue ; but with an iodide a blue compound is formed (Cy4H 4 Oa l4. KI). The union must be a very loose one, for on shaking the blue iodised starch for some time with CS,, the blue colour is removed, and the red solution of iodine in CS, is obtained. This delicate test for iodine has enabled the chemist to show that the element is widely distributed in very small quantities. It has been found in the floating matter of the air, in various fungi, in forest trees, in the animal body, particularly the thyroid gland, in several mineral waters, and in a few minerals ; but never in the free state. Iodometry.—Since the quantity of iodine required to produce a full colour is so very small, starch paste is used as an indicator of the occurrence of a certain definite change in the progress of some reactions, namely, where the appearance or disappearance of free iodine is the determining factor, and hence the reaction is much employed in volumetric analysis. Sodium thiosulphate, Na2S.Oz, is used for titrating the iodine (which may be liberated in a variety of ways), the action being one of mild oxidation by the iodine ; 2Na,S,0, + I, = 2NaI + Na2S,O, (sodium tetrathionate). Chlorine and bromine oxidise the thiosulphate much more strongly, to sulphate. Free * The following equations explain these changes * i () KI+ C= KQ+1I (2) 14+ 3H,0 + 5Cl = HIO, + 5HCl (8) 2HIO, + 5H,80, = 5H,SO, + I, + H,0 (4) I, + H,0 + H,S0, = 2HI + H,80 Chlorine does not liberate iodine from iodates, the iodine having the greater affinity for oxygen. 128 HYDRIODIC ACID iodine also oxidises arsenious to arsenic acid, sulphurous to sulphuric acid, formaldehyde to formic acid, &c. Hydriodic Acid or Hydrogen Iodide; HI = 127-93.—Iodine vapour combines with hydrogen to form hydrogen iodide (supra). The gas is best prepared by the interaction of water, iodine, and phosphorus ; P + 51 + 4HOH. = PO(OH), + 5HI, or, if a smaller proportion of iodine be used, P + 3I + 3HOH = P(OH), + 3HI; or from phosphorus tri-iodide, PI,, and water; cf. HBr (p. 123). 6-5 grams of potassium iodide are dissolved in 3 c.c. of water in a retort (Fig. 101), and 13 grams of iodine are added ; when this has dissolved, 0-65 gram of red phosphorus is introduced, and the mixture heated very gradually, the gas being collected by downward displacement in stoppered bottles, which must be placed in readi- ness, as the gas comes off very rapidly. These quantities will fill four pint bottles with the gas, The aqueous solution of hydriodic acid is most conveniently prepared by passing hydro- sulphuric acid gas through water in which Se finely powdered iodine is suspended, H,S + Fre. 101. I, = 2HI +S, the separated sulphur being filtered off, and the solution boiled to expel the excess of hydrosulphuric acid. By this method it is not possible to obtain a solution of HI of greater sp. gr. than 1-56 (50 per cent. HI), for a strong solution of hydriodic acid reduces sulphur to H,S. Hence, the reaction is reversible. The iodine is able to decompose the H,S only by virtue of the fact that the HI produced has an affinity for the water ; since this affinity diminishes as the liquid grows stronger, a period is soon reached when the dissolution of the HI in the water can no longer supply enough energy to enable the iodine to decompose the H,S. In other words, the reaction occurs only so long as it is exothermic, which will be the case until the heat produced by the dissolution of the HI is only equal to that absorbed in the decomposition of the H,S by the iodine. Properties.—(a) Physical. Hydrogen iodide is very similar in its pro- perties to hydrogen chloride and bromide. It is a colourless, pungent gas, fuming strongly in moist air ; very heavy, sp. gr. 4:38 (air = 1). At — 35-7° (b.pt.) it assumes the liquid, and at — 51-5° (m.pt.) the crystalline solid state. At high temperatures it dissociates into its elements ; to the extent of 16-4 per cent. at 290°; 19-5 per cent. at 394°; 21-4 per cent. at 448°; see also p. 315. Itis readily absorbed by water ; 100 c.c. at 10° dissolve 42,500 c.c. of the gas. A 10 per cent. acid has a sp. gr. 1:077; 30 per cent., 1-271; 47 per cent., 1-508 ; 57-35 per cent., 1-700 ; when saturated at 0°, sp. gr. = 1-99 ; about 90 percent. A 57 percent. acid distils (in hydrogen) unchanged at 126° and 760 mm. ; cf. HCl (p. 111). (b) Chemical. Although in the main the chemical properties of HI are similar to those of HCl and HBr, yet some well-marked differences are ex- hibited. The colourless aqueous acid is far more prone to decomposition by air and light than HCl or HBr is ; it very soon becomes deeply coloured with liberated iodine; 4HI + O, = 2H,0 + 2I,. This is an instance of its gentle yet powerful reducing properties. It is even capable of reducing sulphuric acid to hydrosulphuric acid, H,SO, + 8HI = H,S + 4H,0 + 41, so that when potassium iodide is heated with concentrated sulphuric acid, hydrosulphuric acid is evolved in considerable quantity. It will be remem- bered that HCl does not reduce H,SO,, whilst HBr reduces it to H,S80; only. Also while free iodine oxidises arsenious acid to arsenic acid, hydriodic acid effects the converse reduction. IODINE OXIDES 129 In organic chemistry, hydriodic acid is often employed for introducing hydrogen into a compound ; thus, by heating benzene with hydriodic acid it may be made to take up 6 atoms of hydrogen ; C,H, + 6HI = C,H,, + 3I,. Since the attraction of iodine for hydrogen is so feeble, metalepsis does not occur between this halogen and hydrocarbons. The circumstance that the organic compounds containing iodine are generally much less volatile, and therefore more manageable, than those of chlorine and bromine, leads to the extensive employment of this element in researches upon organic substances. Iodides are produced by the interaction of this acid with the metals and bases, or of iodine with the respective elements (p. 127) ; cf. chlorides (p. 113). In crystalline form and solubility they are similar to the chlorides and bro- mides. Some of them are remarkable for their beautiful colours; Hg,I, (p.418) is green ; HgI, (p. 418), scarlet ; PbI, (p. 505), beautiful golden scales ; AgI (p. 521), yellow ; BiOI, brick-red ; AsI, (p. 234), orange ; but all these, except the last, are nearly or quite insoluble in water; most other metallic iodides are soluble and colourless, or have a colour characteristic of the metal ; even HgI, dissolved in alcohol or with KI in water is nearly colourless. All the above-mentioned iodides, as well as KI, Nal, NH,I, are used in medicine ; AgI, KI, NH,I, Cdl, are applied in photography. Inacid or neutral solution I is liberated from iodides by iodic acid (p. 130), orby Clor Br (supra). With gaseous HI this may be shown in pretty fashion by placing a bottle of Cl or Br vapour diluted with air over one containing HI, as in Fig. 136; the HI is instantly decomposed, with separation of the beautiful purple vapour of iodine. Iodine Oxides and Oxy-Acids.—Iodine undoubtedly shows greater affinity for oxygen than chlorine does ; a statement depending largely on the facts that (a) iodine unites directly with ozonised oxygen, (6) iodine is attacked by nitric acid, (c) the heats of formation of the iodates and period- ates are greater than those of the chlorates and perchlorates, pointing to greater stability of the former; (d) iodine displaces chlorine from KCIO;, C1,0,, &e. (g.v.) ; on the other hand it must be observed that of chlorine three oxides and four oxy-acids are known: Cl,0, ClO,, Cl,0,; ClOH, Cl0.OH, ClO,0H, Cl10,0H ; while of iodine only two oxides, I,0;, I,0,;, and two oxy-acids, IO,.0H, 103.0H, with a feeble third, IOH, have been prepared. Bromine is inferior to either in this respect, while fluorine has no such com- pounds. Cf. p. 135. Hypoiodous acid, IOH, is probably formed when an alcoholic solution of iodine is treated with mercuric oxide. Hypoiodites are formed together with iodides when iodine is dissolved in alkali; they are very unstable, yielding iodates even in the cold, or easily on heating ; they have bleaching pro- perties ; cf. hypochlorites (p. 115). Iodine Tetroxide or Dioxide, I,0,.—Rub dry finely divided iodine with 10 or 12 parts of cold nitric acid, sp. gr. 1-5, renewing the acid if necessary, till the iodine is converted completely into a voluminous yellow powder. Or, heat 1 part iodic acid with 5 parts H,SO, conc. tilliodine vapour begins to appear ; much oxygen is evolved (cf. ClO,, p. 119). It is a sulphur- yellow powder, unaltered by air, water or alcohol. The oxide produced by the action of ozone on iodine may be the tetroxide ; it is a yellow deliquescent powder. Iodine Pentoxide, I,0;, is the anhydride of iodic acid, and is obtained by heating the latter to 170°; 2(10,.0H) — H,O =I,0;; or by heating paraperiodic acid to 130°; 210(0H), =1,0;+5H,0+0,. It is a white powder, sp. gr. 4-487, decomposing slowly at 180°, readily at 300°, 9 130 IODIC AND PERIODIC ACIDS into iodine and oxygen. Soluble in water, forming iodic acid. It oxidises combustible bodies, but not with any great violence. Iodic Acid, HIO, or 10,(OH), is most easily prepared by boiling 1 part iodine with 10 parts of the strongest nitric acid in a long-necked flask, when it is dissolved in the form of iodic acid, which is left, on completely evapora- ting the nitric acid, as a white mass ; 3] + 5HNO, = 3HIO, + 5NO + H,0. This may be purified by dissolving in water and crystallising, when the iodic acid forms white hexagonaltables. Also by gradually adding iodine (3 parts) to baryta (2 parts) dissolved in boiling water (4 parts); sparingly soluble barium iodate is formed which is separated and then decomposed with the exact equivalent of dilute sulphuric acid. Potassium iodide may be oxidised directly to iodate, KIO3, by potassium permanganate. Todic acid is far more stable than chloric and bromic acids. By heat it yields iodic anhydride (supra). The formation of an anhydride by heat from a monobasic acid is very uncommon ; but cf. HNO, and NO; ; neverthe- less, the basicity of iodic acid is not satisfactorily settled, as it differs materi- ally from its analogues, and from other monobasic acids. Its solutions first redden litmus, and afterwards bleach it by oxidation. Some combustibles deflagrate with it. Several substances reduce it with liberation of iodine ; e.g. (a) hydriodic acid, HIO, + 5HI = 31, + 3H,0; (6) sulphur dioxide (p. 127). Its salts, the todates, are less soluble in water than are the chlorates and bromates, which they resemble in their oxidising action upon combustible bodies. They are all decomposed by heat, evolving oxygen, and sometimes even iodine, showing how much inferior this element is to chlorine and bromine in its attraction for metals. Sodium and calcium iodates occur in nature (p. 124). Iodic acid forms acid potassium salts, KIO,.HIO, and KIO,.2HIO,. Periodates.—The periodates (such as AgIO,), analogous to the perchlorates, are known, but the simple acid HIO, has not been isolated. Paraperiodic acid, H,10, or IO(OH),, is prepared as follows: Chlorine is passed through a solution of sodium iodate containing NaOH, whereupon the salt I0(OH)3(ONa), ‘crystallises from the solution; NaIO; + 3NaOH + Cl, = 2NaCl + I10(0H),(ONa),. This sodium salt is dissolved in HNO; and AgNO, is added ; a brown precipitate of Ag,HIO, is obtained. When this is dissolved in HNO, and the solution is evaporated red crystals of AgI0,.H,0 separate, and by treating these with water, H;IO, passes into solution, whilst Ag,I,0,.3H,O remains undissolved. Paraperiodic acid crystallises from this solution in colourless prisms ; it decomposes when heated, yielding H,O, O and I,0,. A solution of the acid is a powerful oxidant. The periodates are referable to four types, termed respectively, the meta-salts, from the acid HIO, or I0,(0H) ; the meso-salts, from the acid H,10, or I0,(OH), ; the para-salts, from the acid H,IO, or IO(OH),; and the dimeso-salts, from the acid H,1,0, or 210,(0H); — H,O0. It thus happens that a large number of these salts are known ; they are sparingly soluble. Iodine Halides.—Jodine pentafluoride, IF;, formed by passing F over dry Tina platinum boat in a tube, is a colourless liquid, which fumes in the air, b.pt. 97°; it forms a camphor-like mass at + 8°; it reacts very energetically with many substances, but it can be distilled in hydrogen. With water: 2IF, + 5H,0= 1,0; + 10HF. lodine forms two compounds with chlorine, monochloride (Cl) and trichloride (ICl,). The former is obtained by passing dry chlorine over dry iodine until it becomes 4 red-brown liquid; sp. gr. 3-28, b.pt.101°. This solidifies when cooled and then melts at 13-9°, but it is unstable, readily passing to another form which melts at 27-2°. The trichloride forms fine red needle-like crystals; it is produced when iodine or hydriodic acid gas is acted upon with an excess of chlorine. The chlorides of iodine are decomposed by water, yielding HIO,, HCl, and iodine. From the aqueous cee of ICl, ether extracts a yellow volatile compound having the composition FLUORINE 131 Iodine bromide, IBr, is a crystalline solid resembling iodine, fusing at 36°, and subliming with partial decomposition. Water decomposes it, iodine being separated. Iodonium Compounds.—The existence of certain organic compounds suggests that iodine is able to form a base on the type of ammonia. When this base is isolated it will probably have the formula IH,(OH), iodonium hydrowide, being the analogue of hydroxylamine NH, (OH). See Diphenyliodonium hydroxide, (CgHs)gI.0H. FLUORINE, F = 19.0 The most ornamental mineral substance occurring in any abundance in this country is known as fluor spar, Derbyshire spar, or blue John, calcium fluoride, and is found with several beautiful shades of colour—blue, purple, violet or green, and sometimes perfectly colourless, either in large masses or in crystals, which have the form of a cube or of some figure derived from it. The use of this mineral as a flux in smelting ores dates from a very remote period, and from this use the name fluor appears to have been originally derived ; it was applied by Schwanhardt in 1670 to the etching of glass, but we have no record of its chemical examination until 1764, when Margraf found his glass retort powerfully corroded in distilling this mineral with sulphuric acid ; Scheele (1771) used a tin retort and announced that fluor spar contained lime and fluoric acid. But though this chemist had fallen into the error to which analysts are continually liable, of mistaking products for educts, his experiments, as they were afterwards perfected by Gay-Lussac and Thénard, deserve particular consideration. Fluorine is one of the most widely distributed elements ; this follows from its constant occurrence, in proportions varying from traces up to 2 per cent. or even more of calcium fluoride, both in vegetable tissues and in the bones and teeth of man and of the lower animals. Calcium fluoride is found in quantity in many parts of the world; kryolite (ypvoc, frost), a double fluoride of aluminium and sodium, AIF,.3NaF, is abundant in Greenland and is valuable as a source of aluminium. The topaz contains fluorine, but in what form of combination is not certain ; its other constituents are alumina and silica. Tourmaline also contains fluorine, together with alumina, silica, and FeO. In such minerals it is probable that the F is substituted for part of the O. Magnesium fluoride (MgF,) forms the crystalline mineral Sellaite which is found in Savoy. Fluorides are also found, though in very small quantity, in sea water. Before describing the free element it will be convenient to study its chief acid. Hydrofluoric Acid, Hydrogen Fluoride, HF or H oe —If powdered fluor spar be mixed with twice its weight of oil of vitriol, and heated in a leaden retort (Fig. 102), the neck of which fits tightly into a leaden condensing-tube, cooled in a mixture of ice and salt, a colourless liquid distils over, and the residue in the retort is found to consist of cal- cium sulphate ;1 CaF,+H,SO,=CaSO,+2HF. The colourless liquid (hydrofluoric acid) so ob- tained is very strong, nearly anhydrous, and Fra. 102. possesses most remarkable properties ; it is powerfully acid, fumes strongly in the air, and has a most pungent, irritating odour. If the air is at all warm the liquid begins to boil when taken out of the freezing-mixture. Should the operator have the 1 The mineral kryolite (fluoride of aluminium and sodium) may be advantageously substituted for fluor Spar, being more easily obtained in a pure state. 132 HYDROFLUORIC ACID misfortune to allow a drop to fall upon his hand, it will produce a very painful sore, even its vapour producing pain under the finger-nails ; the presence of even traces in the atmosphere is very irritant to the eyes and throat. Its attraction for water is so great, that the acid evolves much heat when diluted with water. But its most surprising property is that of rapidly corroding glass, which has already been alluded to as noticed by Margraf. Experiment soon proved that great analogy existed between the properties of this new acid and those of hydrochloric acid ; and Ampére was led to believe that the acid was a hydrogen acid, containing a new salt radicle, which he named, fluorine ; the name of the acid was then changed from “ fluoric ” to “ hydro- fluoric ” acid. This liquid has since been proved by Fremy (1854) to be a solution of hydrofluoric acid in water ; for if it be distilled with phosphoric anhydride which retains the water, dry liquid hydrofluoric acid passes over. Pure anhydrous hydrogen fluoride is best prepared by heating dry potassium hydrogen fluoride (KHF,) to redness in a platinum still. It is then obtained as a colourless, mobile liquid, which fumes strongly, like hydro- chloric acid, on coming into contact with moist air, and boils at 19-4°. It has the sp. gr. 0-9879 at 12-5° and solidifies at — 102-5°. The variation of the density of its vapour with temperature naturally raises the question of the molecular magnitude of this compound and it has, indeed, been the subject of many investigations. At its boiling-point (19-4°) the density of the vapour corresponds with the formula H,F, (nearly) ; at 32°, HF, ; at 60° and above HF (approximately). However, the variation is continuous, there is no interruption as evidence of the existence of H,F, molecules at 32° ; it appears, therefore, to be a case of simple dissociation of H,F, molecules into HF mole- cules, and that at 32° the degree of dissociation (p. 340) is such (334 per cent.) that the density is the same as it would be if H,F, existed. If this were all, the subject might perhaps be dismissed as an extreme case of the irregularities observed with all vapours at or near their boiling-points ; but in solution, hydrogen fluoride behaves as a dibasic acid, H,F,, which is deduced from conductivity (p. 330), cryoscopic (p. 320), and other determinations ; a view strengthened by the formation of acid salts, e.g. KHF,, a property not shared by any other halogen acid. The anhydrous acid scarcely affects metals, excepting potassium and sodium, and has little action on glass. It combines eagerly with sulphuric and phosphoric anhydrides, with great evolution of heat, producing fluorsulphonic acid, HSO,F, and phosphorus oxyfluoride, POF, (p. 223); analogous but less vigorous reactions occur with hydro- chloric acid. Also it combines energetically with the fluorides of potassium, sodium and ammonium, forming the acid fluorides, KHF,, NaHF,, NH,HF,. It does not conduct electricity, and acts as a solvent for a variety of sub- stanees. It unites with water eagerly, 20 grams (mol. wt.) of the liquid acid evolving 4560 gram-calories when mixed with much water, the same weight in the gaseous form evolving 11,800 gram-calories ; whence the heat of vaporisation of the anhydrous acid is + 4560 — 11,800 = — 7240 gram- calories. Since hydrogen fluoride is miscible with water in all proportions and the specific gravities of the solutions are greater than that either of water or of the anhydrous acid, there is one solution heavier than any other ; hence the more concentrated acids increase in specific gravity on dilution ; cf. acetic acid (q.v.); thus the very concentrated acid obtained in the calcium fluoride process has a sp. gr. 1-06, but increases in sp. gr. to 1-15 on addition of water. An acid of 10 per cent. has a sp. gr. 1-038 ; 25 per cent., 1-089 ; 50 per cent., 1-157. An acid of sp. gr. (D'8°) 1-138, 43-2 per cent., distils unchanged. at FLUORINE 133 111° and 750 mm. (cf. HCl, p. 111). In titrations, phenolphthalein and rosolic acid are the best indicators. The aqueous acid is an active reagent ; it dissolves all the metals except gold, platinum, silver, mercury and, to a certain degree, lead ; strange to say, it has but little action on magnesium ; fluorides are formed, as also by its reaction with all the metallic oxides. Solutions of the acid or its salts do not give precipitates with silver nitrate, silver fluoride being soluble ; but they give with calcium salts a gelatinous precipitate of calcium fluoride which is practically insoluble (sol. 1 in 26,000) ; similarly with barium. In these, fluorine contrasts most signally with the other halogens ; AgCl, AgBr, AgI being insoluble, while CaCl,, CaBr,, Cal, are unusually soluble. The con- trast is again exemplified in what is the most remarkable and valuable pro- perty of hydrofluoric acid and its salts, namely, attacking silica in any com- pound, however refractory it may be, forming silicon tetrafluoride, SiF,, which being a gas, removes the silicon from that with which it was combined. This receives three most important applications: (a) In chemical analysis. When sand or flint reduced to powder is digested in a leaden or platinum vessel with hydrofluoric acid, it is gradually dissolved ; and if the solution be evaporated, the whole of the silica will be found to have disappeared in the form of gaseous silicon tetrafluoride ; SiO, + 4HF = SiF, + 2H,O. If the silica be combined with a base, the metal will be left as a fluoride decom- posable by sulphuric or hydrochloric acid. (6) The use of fluor spar as a flux. The fluorine combines with part of the silica, forming SiF,, which es- capes as a gas, SiO, + 2CaF, = 2CaO + SiF,; and the lime combines with other silica to form a vitreous slag. (c) The etching of glass. Ordinary glass consists of silicate of sodium or potassium combined with silicate of calcium or lead. The hydrofluoric acid attacks and removes the silica, and thus eats its way into the glass. In order to demonstrate the action of this acid upon glass, a glass plate is warmed sufficiently to melt wax, a piece of which is then rubbed over it, until the glass is covered with a thin and pretty uniform coating. Upon this a word or drawing may be engraved with a sharp point so that the lines shall expose the glass. The glass plate is then placed, wax downwards, over a leaden or platinum dish containing a mixture of fluor spar and strong sulphuric acid, exposed to a very gentle heat, and allowed to remain for a quarter of an hour ; the plate is then gently warmed to melt the wax, which may be wiped off with a little tow, when it will be found that the hydrofluoric acid evolved from the mixture has corroded those portions of the glass from which the graver had removed the wax. This process is applied to the marking of glass instruments, and in analysis to the detection of fluorides in unknown mixtures, the mixture, of course, being used in place of the fluor spar. ; The solution of hydrofluoric acid etches glass without deadening the surface, as is the case with the vapour; but a solution of fluoride of potassium or ammonium mixed with sulphuric acid does produce a dead surface, and is much used for engraving on glass. An ink sold for writing on glass with a steel pen is composed of barium and ammonium fluorides and sulphuric acid. Solutions of fluorides of the alkali metals, &c., attack glass slowly. The preservation of the acid, ammonium fluoride, &c., in glass vessels is, therefore, impossible, unless, indeed, they are perfectly coated with paraffin wax. Gutta-percha bottles are most usually employed ; also leaden vessels. Bottles made of ceresin or platinum are the best, and these are not attacked by the anhydrous acid, which is the case with gutta-percha. The fluorides, borofluorides (p.'291), silicofluorides (p. 288), &c., have antiseptic and (for food, &c.) preservative properties ; especially they hinder lactic acid fermentation. They have peculiar physiological properties. Fluorine was for nearly a century the quest of many investigators, including Davy. The element is isolated on heating the tetrafluorides of 134 FLUORINE—ISOLATION lead or cerium, PbF,, CeF,, just as chlorine is evolved from tetrachlorides ; indeed, recently (1894) Brauner has obtained fluorine from potassium fluor- plumbate, 3KF.HF.PbF, ; hydrofluoric acid is given off at 200°, and fluorine at 230-250°. But the earlier methods failed, owing to the great attraction which fluorine possesses for other elements, e.g. those of which the apparatus was made, until Moissan, in 1886, prepared very pure hydro- gen fluoride, and discovered that an alloy of platinum with 10 per cent. of iridium would withstand the attack of fluorine. He succeeded in electro- lysing HF with liberation of fluorine at the anode in quantity sufficient for the properties of the element to be examined. Fig. 103 illustrates the electrolytic cell used by Moissan. The U-tube, A, is made of the aforesaid alloy or of copper, but the electrodes, B, must be made of the alloy ; they pass through stoppers, C, made of fluor spar, which insulates them from the metal of the U-tube. The cell contains pure liquid hydrogen fluoride, having about 20 per cent. of potassium fluoride dissolved in it (to make the acid conduct electricity), and is im- mersed in a bath of methyl chloride whereby it is cooled to — 23°; a cur- 4 rent from twenty-five Bunsen’s cells is passed through the liquid. The liber- ated gases escape by the side tubes, D, the hydrogen being set free at the negative electrode and the fluorine at the positive electrode. To free the fluorine from HF it is passed over dry KF. Fluorine is a greenish-yellow gas, but paler and yellower than chlorine. Its odour recalls that of hypochlorous acid, but even traces of the gas are exceedingly irritant and destructive to the mucous membrane ; these properties are probably those of hydrofluoric acid and strongly ozonised oxygen, which are instantly produced on contact of fluorine with water ; fluorine is therefore known only in the anhydrous condition. It can be condensed to a pale yellow liquid which boils at — 187°; density, 1-14; non-magnetic. When frozen it forms a yellow-white crystal- line mass, m.-pt. — 233°, which on contact with liquid hydrogen at — 252°5° explodes violently. Thus at all temperatures, even in the dark, it shows unparalleled affinity for hydrogen, forming hydrofluoric acid and evolving per 20 grams of HF formed 39,000 gram-calories. With some other elements also it displays extraordinary energy ; thus, with sulphur, liquid fluorine at — 187° bursts into flame, producing sulphur hexafluoride, SF, (p. 177), and with selenium it detonates ; with iodine at — 187° it does not react, but it does so with inflammation at ordinary temperatures to form iodine penta- fluoride, TF; (p. 130). Liquid fluorine is miscible in all proportions with liquid air, but an explosive body is formed on passing gaseous fluorine into liquid air. It instantly decomposes, not only water, but alcohol, ether, turpentine and numerous other organic substances, seizing upon the hydrogen and frequently causing inflammation; similarly with many inorganic bodies containing hydrogen ; e.g. hydrogen chloride explodes with it, forming HF and Cl; similarly with HBr and HI, : : Fia. 3. THE HALOGEN GROUP 135 Nearly all the non-metals take fire in it at 15° ; but not elements of the Argon group, Cl, O2, O3, Ne ; N20, NO2, CO, COp. With Br it forms BrF, ; 1 —+ IF, (supra); S— SF, (p. 134); Se —. SeF,; NO —+ NO,F (p. 199); P— PF;; P (in excess) —> PF; (p. 223); P.O, 4het Pr, and POF; (p. 223); PCI; or PCl, —> PF; + Cl; As—— AsF; (p. 233) ; C (not diamond) —> CF, (p. 250) ; CCl, — CF, + Cl ; Si— Sik, (p. 286) ; B—+ BF, (p. 291). Sb takes fire in F at ordinary tempera- ture, thus behaving like a non-metal. There are no oxides or oxy-acids of fluorine, but several compounds containing both oxygen and fluorine are known. Most of the metals, except Sb, are only feebly attacked at ordinary temperatures, the surface—in some cases at least, e.g. Al, Hg—becoming covered with a protecting film of fluoride ; hence, fluorine can be preserved over mercury if it is kept still. At a red heat Al, Fe, and many others burn energetically in the gas; Sn at 100°. Gold and platinum are not attacked below 300° ; contrast the action of chlorine. Glass, if perfectly dry and clean, is not attacked. General Review of the Halogens—Fluorine, Chlorine, Bromine, Iodine. —The many comparisons already made throughout this section must have impressed the reader that these four elements compose a natural group. They have been considered in the order of their atomic weights, therefore in the order of their positions in the periodic table (p. 8), except that fluorine, which should have been taken first, has been left till last ; first, because a study of chlorine serves better for introducing the group ; secondly, because fluorine is the least typical of the group. They are usually styled the halogens, from their tendency to produce salts resembling sea salt in their composition (dds, the sea), and such salts are called haloid salts. These elements are also called salt-radicles, from their property of forming salts by direct union with the metals. Each of these radicles is monatomic, and combines with an equal volume of hydrogen to form an acid which occupies the joint volumes of its constituents. Well-marked gradation of their physical and chemical properties is shown in nearly every instance, depending on the atomic weight, as is evident from the following Table. Fluorine Chlorine Bromine Iodine ~ Atomic weight . ‘ 19 35-5 80 127 State at ord. temp. : Gas Gas Liquid Solid Colour—liquid . . | Pale yellow | Amber yellow Red Black “a gas. ’ . | Pale green- Yellowish- Red Violet yellow green Boiling-point , ; — 187° — 34° 59° 184° Melting-point é ‘ — 233° — 102° —7 114° Element liberated . With extreme! Without More easily | Very easily difficulty difficulty than Cl Reaction with H, : Violent Energetic Fair Weak Hydride (gaseous) ; HE HCl HBr HI » boiling-point . + 19-4° — 83-7° — 73° — 87-5° » melting-point .} — 102-5° — 112-5° — 88-5° — 51-5° » heat of forma- 38,500 20,000 12,300 400 tion (gaseous) Metalepsis . j . | Occurs, but | Occurs freely | Occurs feebly | Does not too violently occur Affinity for oxygen. None Fair Weak Strong Silver salt, soluble in . Water Very dilute NH,| Strong NH; Insoluble 136 THE HALOGEN GROUP Fluorine stands apart in several particulars : (a) it shows very little range of valency ; it is univalent in perhaps all cases except in compounds of the type H,F,, where it is probably trivalent, whereas Cl, Br, I exercise several valencies ; while F, on account of its extraordinary energy, tends to discover the higher valencies of other elements ; e.g. pentavalency of I comes to light in IF,, and the hexavalency of Sin SF,. (b) Compounds of the type H,F,, KHF, are not found with any of the other halogens ; the hydride appears to be dibasic, H,F,, in solution, whereas the others are monobasic, HCl, HBr, HI. (c) The silver salt, AgF, is soluble ; but AgCl, AgBr, AgI are in- soluble in water. (d) The calcium salt, CaF,, is insoluble ; but CaCl,, CaBr,, Cal, are very soluble in water. (¢) HF and other F compounds attack glass porcelain and other silica-containing substances ; Cl, Br, I compounds have no special affinity for silicon. The very high boiling-point of HF is probably due to association, forming molecules H,F, (p. 132). It is noteworthy that these halogen elements are par excellence acid elements ; that is to say, not only their oxygen compounds but their hydro- gen compounds exhibit acid properties. Their potassium salts all crystallise in the same (cubical) form. Similar gradation, though often not so well defined, will be observed with each of the other groups (columns, p. 8) of the periodic system. THE SULPHUR (SIXTH) GROUP OxyGeEN, SULPHUR, SELENIUM, TELLURIUM OXYGEN, O = 16 In the periodic classification (p. 8) this element occupies the first place in the sixth group. The consideration of its preparation and properties has, however, formed an important feature of the introductory portion of this work (p. 54), and but little remains to be added. Oxygen is now used as a standard substance in several respects ; in particu- lar, one-sixteenth of its atomic weight is the present unit for atomic weight. Consequently, one-sixteenth of the density of oxygen gas is the corresponding unit of density for gases ; see pages 97, 297. Oxygen possesses enormous energy, although less than that of fluorine ; as with the latter, therefore, its compounds are very stable and the element cannot often be liberated by displacement by other elements. Nearly all methods of preparing it depend on the decomposition of some compound by the application of energy—e.g. heat, electricity, light—without the interven- tion of a second substance. Much the same may be said of fluorine. — Oxygen gas is often more active at pressures less than atmospheric ; eg. in the oxidation of phosphorus (see p. 212), arsenic, nickel carbonyl, aldehyde, &c.; and detonating gas ignites at 540° and 360 mm., or at 620° and 760 mm. To prove the presence of oxygen in a compound is frequently a matter of considerable difficulty, for there is no characteristic reaction of general appli- cation. It was owing to this that mixtures of oxides of uranium, vanadium, zirconium, &c., with the elements themselves have been considered to be pure for many years. Usually decomposition of the substance is attempted by some reagent likely to yield a known oxygen compound ; ¢.g. by heating with carbon or hydrogen, when, if carbon dioxide or water is produced, oxygen must have been present. Otherwise, the percentage of each other element in the’substance is determined, and if the sum of these does not amount to 100 per cent. the difference is attributed to oxygen ; this is the regular course in organic chemistry. Tetravalent Oxygen.—We have seen that Cl, Br, I, though usually univalent, may assume tri-, penta-, or hepta-valency. Similarly, it will be shown that §, Se, Te, usually divalent, are often tetra- or hexa-valent. These belonging to the same group as oxygen, tetravalent oxygen was long suspected and substantially proved, but its existence was not satisfactorily established until Collie and Tickle in 1899 H showed that the salts of dimethylpyrone, eg. X = og (qg.v.) are true analogues Cl H of the salts of dimethylpyridone, e.g. X’ = nN ; this led to the conclusion that cl basic oxygen occurs in a number of compounds which could be referred to the hypothetical type, oxonium hydroxide, OH;.OH, comparable with iodonium hydroxide, 1H,.0H (p. 131), sulphonium hydroxide, SH;.0OH, ammonium hydroxide, NH,.OH. There is also a suggestion that oxygen is trivalent in oxonium ; see Valency (p. 351). Other instances of tetravalent oxygen are afforded by ozone, O = O = O, hydrogen peroxide, H,O: O, some metallic peroxides, eg. BaO = O, many hydrates, &ec. ; see Valency. The grouping O': O” : is probably more common and more stable than 137 138 ALLOTROPY that of two tetravalent oxygen atoms, just as in the case of nitrogen compounds the grouping N'#: Nv: is more common and stable than two quinquevalent nitrogen atoms. Allotropy (from gAXos, another; rpom}, turn, change) is the term applied by Berzelius to the persistent modifications in properties which some elements assume under various conditions, without loss of chemical identity. It rarely occurs among the metals, although several instances will be dis- cussed later. About half the non-metals have allotropic modifications. The argon and halogen (7th) groups do not show allotropy, but it is to be noted in each element of the sulphur (6th) group. The changes occur very easily and are not very persistent. E.g. oxygen exists not only in the form com- monly known by that name, but also in a very active, strong-smelling form called ozone (see below). Phosphorus and arsenic, possibly nitrogen (also antimony) in the 5th group have allotropes, but the changes occur less easily, i.e. the modifications are more stable ; this applies in still greater degree to carbon, silicon (also tin) (4th) and boron (8rd group). Allotropic change conforms with the Phase Rule (q.v.). Isomesism refers to similar phenomena amongst compounds ; it is very frequently observed in organic chemistry ; see p. 562. The expression “‘ modification ’’ is also used where only slight, though definite, differences are exhibited ; e.g. in the iodine monochlorides (p. 130). OZONE, O, = 48, is merely an allotrope of oxygen ; its formation was observed by Van Marum in 1785, but we are indebted to Schénbein (1840) for our earliest thorough knowledge of this form of matter, his name for which he derived from éZay, to smell. On account of its very powerful oxidising properties it is also called “active oxygen.” Minute quantities—about z7o0000 —Of it are usually present in the atmosphere ; much less in towns than in the country or over the sea ; and by its odour one part in two millions of air can be detected. It is produced from oxygen by heating it at a very high temperature ; by the passage of lightning ; by the influence of cathode rays, ultra-violet light and electric discharges. We have already noticed its formation during the electrolysis of water (p. 14), especially if the platinum electrode is very small (better if it consists of wires exposed only at their ends), the proportion vary- ing from a trace to 23 per cent., according to conditions ; also in the decom- position of water by fluorine ; yield 10 or 12 per cent. (p. 134). Its formation when oxygen is strongly heated, say to 2000°, accounts for the fact that it can be detected in the air in contact with any high temperature flame by quickly Fia. 104. removing the air from the flame, as proved by the following experiments. The air- regulator of a Bunsen burner should be set so as just to cause all luminosity to dis- appear from a small flame without excess of air ; then (a) hold a porcelain evaporating basin, wet on the outside, close to the flame (Fig. 104) for a fraction of a second only, and smell it immediately ; the odour of ozone will be observed. Direotly the basin OZONE 139 gets warm the experiment fails. (b) Suck gently through a tube 2 or 3 mm. bore held 5 mm. above the burner and 5 mm. to the side of the flame (the end (1) and side (2) positions of the tube are shown in the figure) ; the taste and odour of ozone are evident so long as the tube is cool. (c) Blow air from a bellows across the flame, sufficiently hard nearly to extinguish it, and momentarily hold a large beaker in position to receive the products ; the latter smell of ozone. The explanation is that ozone is formed from the oxygen of the air in contact with the hottest part of the flame, and if it is with- drawn and instantly cooled it can be collected, but at intermediate temperatures it is readily destroyed. The same principle in the formation of ozone, rapid heating followed by rapid cooling, is demonstrated in its production by submerging platinum heated electrically to a white heat in liquid air or liquid oxygen. By placing a freshly scraped stick of phosphorus (scraped under water to avoid inflammation) at the bottom of a quart bottle, with enough water to cover half of it, and loosely covering the bottle with a glass plate, enough ozone may be accumulated in a few minutes to be readily recognised by the odour and iodised starch (infra). The process is best at 24°. The water at the bottom of the bottle is found to contain, besides the phosphorous and phosphoric acids formed by the slow oxidation of the phosphorus, some hydrogen dioxide, probably due to the interaction of water and ozone. Preparation.—Ozone mixed with an excess of oxygen (or oxygen and nitrogen) is obtained by submitting dry oxygen (or air) to the silent electric discharge (electrising). The construction of the apparatus will be readily understood from Fig.105. The outside cylinder and the innermost tube are filled with dilute sulphuric acid, which serves the double purpose of conducting the electricity and keeping down the temperature of the oxygen or air. When the wires are connected with the poles of an in- duction-coil the two portions of dilute sulphuric acid are oppositely electrified, so that the space between the two liquids is submitted to the high pressure electrical dis- charge necessary for the resolution of the oxygen mole- cules into their atoms, and the recombination of these to form molecules of ozone. Through this space the air or oxygen is passed in the direction of the arrows, This induction-tube must be made of thin glass, and the space between the inner and the outer tube must be as narrow as possible. The ordinary chemical test for ozone is a damp mixture of starch paste with potas. sium iodide. If this mixture be brushed over strips of white cartridge paper, these will remain unchanged in ordinary air ; but when they are exposed to ozonised air (such as that which has passed through the induction-tube), they will immediately assume a blue colour. The ozone sets free the iodine from the KI, which has the specific property of imparting a blue colour to starch. Papers impregnated with manganese sulphate, lead acetate, or thallous oxide, become brown, in the first two cases from the formation of the peroxide of the metal and in the last case from the formation of thallic oxide, under the influence of ozone. The proportion of ozone formed depends upon the intensity and frequency of the electric discharge, the pressure, and the temperature, the last named having the greatest influence. Five per cent. at 20° is a good yield ; at lower temperatures the results are better, e.g. 10-4 per cent. at — 73°; but a 90 per cent. yield has been obtained at the temperature of liquid air. By liquefying ozonised oxygen, by cooling it to the tem- perature of liquid air and then allowing the oxygen to evaporate away from the higher boiling ozone, concentrations of 80-90 per cent., or even more, are attainable. In the silent electric discharge both ultraviolet and cathode rays are produced, and 140 OZONE—PROPERTIES inasmuch as these rays are otherwise used to ozonise oxygen, e.g. by the ultraviolet light of the mercury arc lamp, it has ee suggested that the above process depends on a light effect. There are numerous electrical aera for ozonising air; the odour of ozone is perceived in working many forms of electrical apparatus. Pr oper ties.—(a) Physical. Viewed casually, ozone, or rather ozonised oxygen, is a colourless gas, but in thick layers or when highly compressed it has a blue colour. It has been suggested that the blue colour of the sky is due to our regarding it through the ozonised atmosphere. Its odour is peculiar and, when highly diluted with air, refreshing ; but in a more con- centrated state it causes difficulty of breathing, attacks the mucous membrane, and is even poisonous. Indeed, a 5 per cent. atmosphere is a powerful germi- cide, and it has been applied to the sterilisation of water. Its density is computed to be 23°89 (O = 16), rather less than the theoretical. Cooled by liquid air it condenses to an intense indigo-blue liquid, density about 1°6, which is more magnetic than liquid oxygen and boils at about — 120°, but as it approaches the boiling-point it explodes violently ; it also explodes on touching anything oxidisable. It is freely soluble in ether and in certain oils, particularly turpentine oil, but not very soluble in water ; 100 c.c. dissolve 0°83 c.c. at 1°, reacting with it to produce a little hydrogen peroxide. Much H,O, cannot accumulate because H,O, and O; are incompatible ; H,O, + O; = H,0 + 20,. (b) Chemical. Ozone is very unstable, resolving itself into one and a half times its volume of ordinary oxygen, 20, = 30,, slowly under atmospheric conditions, and the more readily the higher the temperature, until on passing it through a tube heated to 250° or 300° it is entirely and rapidly broken down ; iodised starch paper held in the gas issuing from the tube will remain unaffected ; the presence of many substances, e.g. MnO, or even broken glass, assists the instability. Over sulphuric acid, or in sealed tubes, it may be preserved for some weeks ; it is also more stable in presence of water vapour than in its absence. Perfectly dry it is not very active and will not attack even potassium iodide, colours, &c. Traces of water are essential to its activity ; and then it proves itself to be one of the most powerful oxidisers. It is often distinguished from oxygen by reacting at ordinary temperatures where higher temperatures are necessary for the latter ; or by activity where the latter is inert ; e.g. with potassium iodide. If ozonised air be passed into a flask with a little mercury at the bottom, the surface of the mercury will soon become tarnished by the formation of oxide, and when the mercury is shaken round the flask it will adhere to the sides, which is not the case with pure mercury. It is stated that if both the mercury and the ozone be dry, the gas will be converted into oxygén, but the mercury will not be oxidised. Bright silver- foil becomes tarnished with a film of black silver peroxide (p. 519). All metals except platinum and gold are oxidised by ozone, usually to their highest oxides. The non- metals are not generally attacked very vigorously. Phosphorus takes fire in it, arsenic and nitrogen (all in the 5th group) are oxidised ; iodine also (p. 129). H, F, Cl, Br, §, Se, C, are among those not attacked. HCl, HBr, HI are oxidised, yielding H,O + Cl, Br, I; H,SO; + H,SO,; H,S—-+ H,0 +8; white Pb(OH),—> brown PbO, ; black CuS —~ pale blue CuSO, ; black PbS —» white PbSO,. Organic bodies are frequently strongly oxidised by it. It bleaches many vegetable colours; also blood. If ozonised air be passed into a very dilute solution of indigo (sulphindigotic acid), the blue colour will soon disappear, since the ozone oxidises the indigo and gives rise to products which, in a diluted state, are nearly colourless, Ordi- nary oxygen is incapable of bleaching indigo in this manner. If the ozone is passed through a tube of vulcanised caoutchouc, this will soon be perforated by the corrosive effect of the ozone, whilst ordinary oxygen would be without effect upon it. Pyrogallol is at first turned brown, then entirely destroyed. Several explosives, e.g. nitroglycerin, OZONE—CONSTITUTION 141 explode in its presence. Ozone is an endothermic substance, and its formation from oxygen, 30, = 20g, is attended by the absorption of 59,200 calories. Ozonides are formed by the action of ozone on many organic bodies. The substance under investigation is dissolved in chloroform and ozonised oxygen, often diluted with carbon dioxide to avoid violent or explosive action, is passed into the solution at a low temperature. Unsaturated hydrocarbons and alcohols combine with three atoms of oxygen, forming ozonides, which are usually thick oils or syrups and often explosive ; they liberate I from KI, bleach KMnOy,, indigo, &c. They contain the fe —C: C: group Oe | derived from O; and || . With ethylene, C,H, the action is so O-C: C;: violent as to yield formaldehyde, H.CHO, and formic acid, H.COOH. These ozonides and the “‘ ozonide-peroxides ” are of considerable interest in organic investigations ; see Organic Chemistry. Constitution of Ozone.—The facts that ozone can be produced in pure oxygen and that its formation is accompanied by a contraction in volume, lead to the conclusion that ozone is a condensed form of oxygen. When the ozonised oxygen has been heated it is found to have expanded to exactly the same volume which the pure oxygen occu- pied, and no longer to contain any ozone. By introducing turpentine into the ozonised gas all the ozone is absorbed, and a measurement of the contraction caused by this absorption reveals the fact that the volume which has disappeared is twice the volume of the contraction effected by ozonising the oxygen. Thus, if n ¢.c. of gas disappeared when the oxygen was ozonised, 2 n c.c. will be absorbed by the turpentine. Therefore 3 vols. of the original oxygen must have become 2 vols. of ozone, and if the gas had been heated, instead of having been treated with turpentine, these 2 vols. of ozone would have expanded again to 3 vols. of oxygen. If 1 atom of oxygen be regarded as occupying 1 volume, then 1 molecule (2 atoms) must occupy 2 vols. ; so that in pro- ducing ozone 1 molecule of oxygen has been combined with 1 atom of oxygen, forming a molecule of ozone, OOs. When a neutral solution of potassium iodide is introduced into ozonised oxygen, there is no contraction in volume, and yet all the ozone is destroyed ; at the same time iodine is liberated from the potassium iodide. If the quantity of this iodine be deter- mined, it is found to be as much as would (under other circumstances) be liberated by a volume of oxygen identical with the volume which disappeared when the oxygen was ozonised. The explanation of these observations is easy if the above view of the con- stitution of ozone be adopted ; for the facts may be expressed by the equation ; OO, (2 vols.) + 2KI + HOH = 2KOH + I, + Oz (2 vols.) showing that it is the third atom of oxygen in the molecule of ozone which has liberated the iodine. If the solution of potassium iodide be acidified (and thus converted virtually into a solution of hydriodic acid), twice as much iodine will be liberated and the volume of the ozone will be reduced to one-half : OO, (2 vols.) + 4HI = 2H,0 + 21, + O (1 vol.) Titration of the iodine liberated by a known volume of ozonised air, with sodium thio- sulphate, is the practical method for determining the proportion of ozone. The statement that ozone has the formula O; conveys no explanation as to why it is so much more active than ordinary oxygen, O,. Usually the atom of oxygen is divalent and the molecular formula may well be expressed as O = O, although, seeing that oxygen is sometimes tetravalent, it might be O = O. Since ozone has a density of 24, and therefore a molecular weight of 48, the structure of its molecule might Oo—O O=0 well be represented by \_“ or possibly \/ ; and if it has such a symmetrical O O structure, it is to be expected that each of the three atoms would take a similar and equal share in a reaction, just as with O,- But it is usually found with ozone that only one of the three atoms is peculiarly active, while the other two escape as ordinary oxygen. Hence it is inferred that the atoms in the molecule arrange themselves in some asymmetrical manner. When mercury is shaken with a measured volume of ozonised oxygen, the metal is 142 HYDROGEN PEROXIDE oxidised,"and the weight of oxygen absorbed can be ascertained and found to be one- third of the weight of the ozone converted ; yet the volume of gas remains unchanged, an equal volume of O, having replaced the O3;; Hg + O3 (2 vols.) = HgO + 0, (2 vols.). Similarly with the potassium iodide experiment. There is therefore something about the third atom difterent from the other two. It is expressed in such an arrange- Oo ment as “\, or O = O = O, the latter, harmonising with present views as to the structure of hydrogen peroxide, H,O=0O, being the more probable. The reactions of ozone with the latter and with barium peroxide, BaO= 0, are interesting : = H,O + 20,. = BaO + 20. There being in each cavdlesehe an oxygen ‘ape, which is active and easily separable, these unite to form a more stable molecule, Og, leaving on the one hand another Q,, and on the other a more stable oxide, H,O or BaO. These formule assume oxygen to be both tetravalent and divalent in the same molecule. HYDROGEN PEROXIDE or DIOXIDE, H,0, = 34°02, was discovered by Thénard in 1815 asa product of the action of acids on barium peroxide, BaO,. It occurs fairly regularly in air in very minute quantity (about 40 billionths of 1 per cent.). Its presence is attributed to the union of oxygen with the traces of hydrogen found in air, under the influence of sunlight ; consequently it is found in rain and snow. It is formed transitorily in a variety of reactions and probably so in the synthesis of water; H, + O, = H,0, then H,O, + H, = 2H,0. H,O, is frequently produced when sub- stances are oxidised by free oxygen in presence of water ; thus it is invariably to be detected in water in which lead has been exposed to the air. Some essential oils, e.g. turpentine, form peroxides on exposure to air, which with water yield hydrogen peroxide. Preparation.—The original process of Thénard is still the one most generally followed. Pure hydrate of barium peroxide, BaO,.8H,O (p. 386), is added gradually to dilute sulphuric acid (20 per cent.), kept cool until the liquid is only very slightly acid ;1 BaO, + H,SO, = BaSO, + H,O,. The product contains some 3 per cent. H,O,, and constitutes the ‘“‘10-volume” article of commerce ; 1 c.c. of this treated in a nitrometer with KMn0O, solu- tion acidified by H,SO, evolves 20 c.c. of oxygen—10 c.c. from the H,0, and 10 c.c. from the KMnO,; 2KMnO, + 3H,SO, + 5H,0, = K,S0, + 2MnSO, + 8H,0 + 50,. By evaporating this solution below 70° it may be concentrated to 45 or 50%. On shaking this with pure ether and carefully evaporating, or distilling in vacuo, the ether, a 70% solution is obtained; and this can be fractionally distilled in vacuo (10-60 mm.) when the water comes over first and then between 81° and 85° a 90 per cent. solu- tion ; by careful repeated fractionation a 99-5 per cent. solution is attainable. Adopting special precautions, a practically pure, 100 per cent., preparation has been made.” In all these operations, as well as in preservation of the products, one must very carefully avoid overheating, alkalinity, traces of heavy metals, suspended particles, dust, &c., otherwise rapid decomposition sets in, sometimes so suddenly as to cause energetic explosion. With the more concentrated solu- tions, great caution must be exercised, especially if ether has been used in any part of the process. The weaker solutions are in no sense dangerous. Preservatives, usually acids, are frequently added to commercial solutions} + If the H,SO, were added to the BaO,.8H,0, instead of as recommended, the H,0, would be decom posed by the remaining BaO, as fast as it was formed. ? The preparation sold as perhydrol and frequently referred to as 100 per cent. H,0, contains 30 ee cent, and yields 100 times its volume of oxygen by the usual test, HYDROGEN PEROXIDE 143 phosphoric acid, 0-6 per cent., also acetanilide, have been especially recom- mended. parated by acidifying the liquid with hydrochloric acid and adding excess of hydro- silphuric acid, which precipitates the cadmium sulphide only. On filtering the solution and adding ammonia, the zine sulphide is precipitated. Those sulphides which are soluble in the alkalies are often designated sulphur-acids, whilst the sulphides of the alkalies are sulphur-bases. These two classes of sulphides combine to form sulphur-salts analogous in compo- sition to the oxygen-salts of the same metals. Thus, there have been crystallised the salts— Sodium sulphostannate . : ‘ @ . Na,Sn8, » sulphantimonate ‘ : ‘ . NaSbS8, » Ssulpharsenate . 2 ‘ . NagAsS, Speaking generally, those metals which give feebly acid oxides also give feebly acid sulphides, whilst the sulphides, which correspond with powerful bases, are themselves basic, for H,S is not capable of completely neutralising © the alkalies. Hydrogen sulphide is a powerful reducing agent ; e.g. FeCl, —> FeCl, ; H,CrO, —> Cr,0;; HO.NO —~+» NH, (p. 153); &c. The action of air upon the sulphides of the metals is often turned to account in chemical manufactures. At the ordinary temperature the sulphides of those metals which form alkaline oxides (such as sodium and calcium), when exposed to the air in the presence of water, yield sulphite and thiosulphate (hyposulphite). This change is sometimes turned to account for the manu- facture of sodium thiosulphate. When the metal forms a less powerful base with oxygen, the sulphide is often converted into-sulphate by exposure to moist air; thus, CuS + 20, = CuSO,, which is taken advantage of for the separation of copper from its ores. The black ferrous sulphide (FeS), when exposed to moist air, becomes converted into red ferric oxide, with separation of sulphur, 2FeS + 30 = Fe,0, + S3, a change which enables the gas manufacturer to revive, by the action of air, the ferric oxide employed for removing the sulphuretted hydrogen from coal gas. When roasted in air at a high temperature, the sulphides corresponding with the more powerful bases are converted into sulphates ; thus, ZnS + 20, = ZnSO,, which explains the production of zinc sulphate by roasting blende. But in most cases part of the sulphur is converted into sulphurous . acid gas at the same time. Cuprous sulphide, for instance, is partly con- SULPHUR DIOXIDE 155 verted into cupric oxide by roasting, Cu,S + 20, = 2CuO + SO,, a change of great importance in the extraction of copper from its ores. Hydrogen Persulphide.—The composition of this substance is not yet satis- factorily ascertained. The similarity of its chemical properties to those of hydrogen peroxide prompts the idea that its formula may be HS... Some analyses, however, seem to lead to the formula H,§,, but since the persulphide is a liquid capable of dis- solving free sulphur, which is not easily separated from it, there is much difficulty in determining the exact proportion of this element with which the hydrogen is combined. When equal weights of slaked lime and sulphur are boiled with water, an orange- coloured liquid is formed, which contains calcium thiosulphate, calcium disulphide, and calcium pentasulphide (CaS;). When HCl is added to the filtered solution an abundant precipitation of sulphur occurs and much HS is evolved: CaS, + 2HCl = CaCl, + H,S +S. But if the solution be poured by degrees into a slightly warm mixture of HCl with twice its bulk of water and constantly stirred, a yellow heavy oily liquid collects at the bottom, which is the hydrogen persulphide: CaS, + 2HCl = H,8,(?) + CaCl. The acid having been kept in excess, the persulphide has been preserved from the decomposition which it suffered in the presence of the alkaline solution in the former experiment. The hydrogen persulphide very closely resembles the peroxide in the facility with which it may be decomposed into hydrosulphuric acid and sulphur ; it undergoes spontaneous decomposition even in sealed tubes, and the hydrosulphuric acid then becomes liquefied by its own pressure ; it rapidly decomposes at higher temperatures. Most of the sub- stances the contact of which promotes the decomposition of H,O, have the same effect upon the persulphide. This compound gives off a vapour of peculiar odour, which affects the eyes ; of course, its vapour is mixed with H,S resulting from its decom- position. Its specific gravity is 1-73. OXIDES OF SULPHUR. Only two important compounds of sulphur with oxygen have been ob- tained in the separate state—viz. sulphurous anhydride (SO,) and sulphuric anhydride (SO,). Sulphur sesqguioxide (S,03) and persulphuric oxide (S07) also exist. Sulphur Dioxide or Sulphurous Anhydride, SO, = 64:07.—In nature, sulphur dioxide (sulphurous acid gas) is rarely met with, but it exists in the gases issuing from volcanoes. Although constantly discharged into the air of towns by the combustion of coal (containing sulphur), it is so easily oxidised and converted into sulphuric acid that no considerable quantity is ever found in the atmosphere. Sulphurous acid gas has been already mentioned as almost the sole product of the combustion of sulphur in dry air or oxygen (p. 60), but it is generally prepared in the laboratory from sulphuric acid by heating it with metallic copper: 2H,SO, + Cu = CuSO, + 2H,0 + SO,. 20 grams of copper clippings are heated in a flask (Fig. 114, A) with 110c.c. of strong H,S0,, the gas being conducted by a bent tube down to the bottom of a dry bottle closed with a perforated card (see Fig. 92, p. 109). Some time elapses before the gas is evolved, for sulphuric acid attacks copper only at a high temperature ; but when the evolution of gas fairly begins it proceeds very rapidly, so that it is necessary to remove the flame from under the flask. The gas will contain suspended particles of sulphuric acid, which renders it turbid. When the operation is finished and the flask has been allowed to cool, it will be found to contain a grey crystalline powder at the bottom of a brown liquid. The latter is the excess of H,SO, used, and retains very little copper, since cupric sulphate is insoluble in the strong acid. If the liquid be poured off, and the flask filled up with water and set aside for some time, the crystalline powder will dissolve, forming a blue solution of sulphate of copper, yielding that salt in fine prismatic crystals by evapora- tion and cooling. The dark powder, remaining undissolved after extracting the whole of the sulphate, consists chiefly of cuprous sulphide (Cu,S), the production of which 156 SULPHUR DIOXIDE—LIQUID is interesting, as showing how far the de-oxidising effect of the copper may be carried in this experiment. 5 Instead of copper, charcoal or sulphur may be similarly employed : C + 2H,80, = 2H,O + CO, + 280,; S + 2H,SO, = 380, + 2H,0 (p. 169). Sulphur dioxide is a very heavy (sp. gr. 2-262; 11. weighs 2-9266 grams) colourless gas, characterised by its odour of burning brimstone. It con- denses to a clear liquid at — 18° (the temperature of a mixture of ice and salt) even at the ordinary pressure of the air, and has been frozen to a colour- less crystalline solid at — 76°. The liquid has the sp. gr. 1-4 at 15° and boils at —8°. At the ordinary temperature it exerts a pressure of about 2-5 atmospheres. As would be anticipated from its comparatively high boiling-point, SO, forms a very imperfect gas (p, 78). The cold produced by the evaporation of the liquefied gas is about 6500 cals. per gram-mol., and the liquid i D__ finds application in some forms of freezing- B machines. The critical temperature is 157°, and the critical pressure 79 atmo- spheres. The liquefaction of the gas is easily c Or ‘48 exhibited in the following way. In the = flask A (Fig. 114), the SO, is generated Fie. 114. from Cu and H,SO,, passed through con- centrated H,SO, in B to dry it, and then into the U-tube C, surrounded by a mixture of ice and salt, where it con- denses to the liquid state; the exit D allows the escape of any uncon- densed gas into a flue. Liquid sulphur dioxide is a convenient agent for producing (by its rapid evapora- tion) the low temperature — 39° required to effect the solidification of mercury. A small globule of this metal may readily be frozen by dropping some liquid sulphur dioxide upon it in a watch-glass placed in a strong draught of air. The tube containing the sulphur dioxide should be held in a woollen cloth or glove. The attractive experi- ment of freezing water in a red-hot crucible may also be made with the liquid. A plati- num crucible being heated to redness, and some liquid sulphur dioxide poured into it from a tube which has been cooled for half an hour in ice and salt, the liquid becomes surrounded with an atmosphere of sulphurous acid gas, which prevents its contact with the metal (assumes the spheroidal state), and its temperature is reduced by its own evaporation to so low a degree that a little water allowed to flow into it will at once become converted into opaque ice. Liquid SO, is now sold in glass “ siphons ” similar to those in which soda-water is supplied, and these form a convenient store of the gas. ; ! Sulphurous acid gas is very easily absorbed by water, as may be shown by pouring a little water into a bottle of the gas, quickly closing the bottle with the palm of the hand, and shaking it violently, when the diminished pressure due to the absorption of the gas will cause the bottle to be sustained against the hand by the pressure of the atmosphere. Water absorbs 79-79 times its bulk of the gas at 0°; 47-27 at 15°; 32-78 at 25°. The solution is known as and is believed to contain Sulphurous Acid, H,SO,, formed by the reaction H,O + SO, = H,SO,, but this body has not been obtained in the separate state. If the solution be exposed to a low temperature, a crystal- lised hydrate, H,SO,.14H,0, is obtained; this melts at 2°. When the solution of sulphurous acid is kept for some time in a bottle containing air, its smell gradually disappears, the acid absorbing oxygen and becoming con- verted into sulphuric acid. Sulphur dioxide, like carbon dioxide, possesses in a high degree the power DE Ral USES OF SULPHUR DIOXIDE 157 of extinguishing flame. A taper is at once extinguished in a bottle of the gas, even when containing a considerable proportion of air. One of the best methods of extinguishing burning soot in a chimney consists in passing up sulphurous acid gas by burning a few ounces of sulphur in a pan placed over the fire. The principal uses of sulphur dioxide depend upon its property of bleach- ing many animal and vegetable colouring-matters. Although a far less powerful bleaching agent than chlorine, it is preferred for bleaching silks, straw, wool, sponge, isinglass, baskets, &c., which would be injured by the great chemical energy of chlorine. The articles to be bleached are moistened with water and suspended in a chamber in which sulphurous acid gas is produced by combustion of sulphur. The colouring-matters do not appear in general to be decomposed by the acid, but rather to form colourless combina- tions with it, for in course of time the original colour often reappears, as is seen in straw, flannel, &c., which become yellow from age, the sulphurous acid probably being oxidised into sulphuric acid. Stains of fruit and port wine on linen are conveniently removed by solution of sulphurous acid. Hops are sulphured by exposure to fumes of burning sulphur with the object of improving their appearance. The red solution obtained by boiling a few chips of logwood with ordinary water (dis- tilled water does not give so fine a colour) serves to illustrate the bleaching properties of sulphurous acid. A few drops of the solution of the acid will at once change the red colour of the solution to a light yellow ; but that the colouring power is suspended, and not destroyed, may be shown by dividtng the yellow liquid into two parts and adding to them, respectively, potash and diluted sulphuric acid, which will restore the colour in a modified form. To contrast this with the complete decomposition of the colouring- matter, a little sulphurous acid may be added to a weak solution of potassium permanganate, when the splendid red solution at once becomes perfectly colourless, and neither acid nor alkali can effect its restoration. If a bunch of damp coloured flowers be suspended in a bell-jar over a crucible containing a little burning sulphur (Fig. 115), many of the flowers will be completely Fie. 115. Fra. 116. bleached by the sulphurous acid ; and by plunging them afterwards into diluted sul- phuric acid and ammonia, their colours may be partly restored with some very curious modifications. Another very useful property of sulphurous acid is that of arresting fermentation (or putrefaction), apparently by killing the vegetable or animal growth which is the cause of the fermentation. This is commonly designated the antiseptic or antizymotic property of sulphurous acid, and is turned to account when casks for wine and beer are sulphured in order to prevent the action of any substance contained in the pores of the wood, and capable of exciting fermentation upon the fresh liquor to be introduced. Tf a little solution of sugar be fermented with yeast in a flask provided with a funnel tube (Fig. 116), a solution of sulphurous acid poured in through the latter at once arrests the fermentation. The salts of sulphurous acid (sulphites) 158 SULPHUROUS ACID are also occasionally used to arrest fermentation, in the manufacture of sugar for instance. Clothes are sometimes fumigated with sulphurous acid gas to destroy vermin, and the air of rooms is disinfected by burning sulphur in it, 4 Ibs. of sulphur being recommended for every 1000 cubic feet of space. The disposition of sulphurous acid to absorb oxygen and pass into sul- phuric acid renders it a powerful de-oxidising or reducing agent. Solutions of silver and gold are reduced to the metallic state by sulphurous acid and sulphites. As usual, however, the reducing power of sulphur dioxide is only a comparative phenomenon. Towards several substances the acid behaves as an oxidising agent, a noteworthy case being its reaction with hydrogen sulphide, which (in presence of water) occurs in the sense of the equation, 2H,S + SO, = 2H,0 + 38. Other examples of the reducing action of sulphurous acid are H,SO, + H,O + I, = 2HI + H,SO,; 2HgCl, + H,SO,; + H,O = 2HCl + H,SO, + HgpCl. But it is itself reduced by nascent hydrogen (e.g. on mixing together a sulphite, dilute hydro- chloric acid, and zinc) to hydrogen sulphide: H,SO,; + 6H’ = H,S + 3H,0. An aqueous solution of stannous chloride gives a precipitate of stannic sulphide with sulphurous acid. If a solution of sulphurous acid be heated for some time in a sealed tube at 150°, one portion of the acid de-oxidises another, sulphur is separated, and sulphuric acid formed: 3H,SO; = 2H,SO, + H,O +S. SO, and NH; combine to form two solid compounds: (NH3),8O, and NH3.S8Ox. The unsaturated character of SO, finds illustration in the fact that chlorine com- bines with an equal volume of the gas, under the influence of bright sunshine or in presence of charcoal, to produce a colourless liquid, the vapour of which is very acrid and irritating to the eyes. This is the chloranhydride (p. 198) of sulphuric acid, sulphuryl chloride, SOgClp. Its decomposition by water occurs in two stages: (1) SO,Cl, + H,0 = S0,.C1.0H + HCl; (2) SO,.Cl1.OH + H,O = SO,.0H.OH + HCl; the final products being sulphuric and hydrochloric acids, so that the formula SO,.0H.OH for sulphuric acid is justified. The chloride of thionyl,! or sulphurosyl chloride, SOCI,, is a colourless volatile liquid obtained by the action of sulphurous acid gas on phosphorus pentachloride. It is decomposed by water, yielding hydrochloric and sulphurous acids, being the chloranhydride of the latter. Potassium and sodium, when heated in sulphur dioxide, burn vividly, producing the oxides and sulphides of the metals. Iron, lead, tin, and zinc are also converted into oxides and sulphides when heated in the gas: SO, + 3Zn = ZnS + 2Zn0. Lead peroxide, PbOg, is the best absorbent for SO, with which it combines (with incandescence in the pure gas) to form lead sulphate : PbO, +SO, = PbSO,. That sulphur dioxide contains its own volume of oxygen is best shown by burning sulphur in a given volume of oxygen in the apparatus represented in Fig. 117. The stopper, A, having been removed, mercury is poured into the open limb of the U-tube until it stands at a point just Fra. 117. below the bulb, B, the air in which is then displaced by oxygen. A pellet of sulphur is placed in the metal spoon attached to the stopper and the latter is inserted directly the tube delivering the oxygen has been removed. A platinum helix rests upon the sulphur and is now heated to redness by a current of electricity passed through the wires attached to the spoon and the helix. When the sulphur has burntitself out and the apparatus has cooled, it will ‘be found that the Oetov, sulphur. SULPHITES 159 volume of gas has not varied, show ng that the SO, produced contains its own volume of oxygen. To relieve the pressure produced by the heat of the combustion, it is well to diminish the initial pressure, after the gas has been measured, by drawing off some of the mercury through the stop-cock,C. From the molecular weight, i.e. from the density, the proportion of S may then be deduced. Sulphites.—The acid character of sulphurous acid is rather feeble, although stronger than that of carbonic acid. There is much general resem- blance between the sulphites and carbonates in point of solubility, the sul- phites of the alkali metals being the only salts of sulphurous acid which are freely soluble in water. Sulphurous acid, SO(OH),, being dibasic like car- bonic acid, forms two classes of salts, the normal sulphites (for example, sodium sulphite, Na,SO;) and acid sulphites (as hydrogen potassium sulphite, KHSO,). Aldehydes, certain ketones, &c., form compounds with the acid sulphites. Sodium sulphite is extensively manufactured for the use of the paper- maker, who employs it as an antichlore for killing the bleach, that is, neutralis- ing the excess of chlorine after bleaching the rags with chloride of lime (see p. 116): Na,SO, + H,O + Cl, = Na,SO, + 2HCl. It is prepared by passing sulphurous acid gas over damp crystals of sodium carbonate, when CO, is expelled, and sodium sulphite formed, which is dissolved in water and crystallised. It forms oblique prisms, having the composition Na,SO,.7 Aq, which effloresce in the air, becoming opaque, and slowly absorbing oxygen, passing into sodium sulphate (Na,SO,). Its solution is slightly alkaline to test-papers. For the manufacture of sodium sulphite the SO, is obtained either by the combustion of sulphur or by heating sulphuric acid with charcoal : 2H,SO, + C = 2H,O + CO, + 280,. The carbon dioxide does not inter- fere with this application of the sulphur dioxide. The existence of sulphurosyl chloride, SO.Cl,, and its behaviour with water justify the formula SO(OH), for sulphurous acid. There is some evidence, derived from organic chemistry (see Sulphonic Acids), that the metallic sulphites are not derived from O OH SO(OH),, but from an acid of the form ys , which may be regarded as of \a the parent substance of the sulphonic acids, and may therefore be termed sulphonic acid. The potassium sulphite is supposed to be O,8.OK.K, and not SO.OK.OK. Two potassium-sodium sulphites have been prepared which differ in properties and appear to be O,8.0K.Na and O,8.ONa.K respectively. Solutions of the sulphites absorb nitric oxide in the cold, yielding nitrosulphites, such as the potassium salt K,SO,.2NO. At higher temperatures the sulphites reduce NO to N,0. Pyrosulphites, derived from hypothetical pyrosulphurous acid, H,8,0;, crystallise from hot strong solutions of bisulphites, 2KHSO, = K,8,0; + H,0. Possibly they are compounds of normal sulphites with SO2: K,SO3.SO,. The K salt is known commercially as potassium metabisulphite. Sulphur Trioxide or Sulphuric Anhydride, SO, = 80-07.—Sulphur dioxide and oxygen combine to form sulphur trioxide when passed through a tube containing heated platinum or certain metallic oxides, such as those of iron and chromium, the action of which in promoting the combination is not thoroughly understood. The reaction is exothermic, evolving some 103,240 cals. per 80 grams of SO, formed. The combination may be shown by passing oxygen from the tube, A (Fig. 118), connected with a gas-holder, through a strong solution of sulphurous acid, B, so that it may take up a quantity of SO, ; afterwards through a tube, C, containing pumice- stone soaked with oil of vitriol to remove the water ; and then through a bulb, D 160 SULPHURIC ANHYDRIDE containing platinised asbestos (p. 201) heated to near but not above 450°. The mixture of the gases issuing into the air is quite invisible, but when the bulb is gently heated combination occurs, and dense white clouds are formed in the air, from the combination of the sulphuric anhydride (SO,) produced, with the atmospheric moisture. The clouds are best shown by conducting them, through a bent tube attached to D, into a large flask. The process is applied technically ; see the “ contact process,”’ p. 165. An interesting method of obtaining the sulphuric anhydride consists in pouring 2 parts by weight of oil of vitriol Fic. 118. over 3 parts of phosphoric anhydride, contained in a retort cooled in ice and salt, and afterwards distilling at a gentle heat, when the phosphoric anhydride, having a greater affinity for water than SO, has, retains water, and the SO, may be condensed in a cooled receiver: 3H,8O, + P.O, = 2H,PO, + 3803. Some SO, is also formed in the combustion of sulphur (p. 147). Pure sulphur trioxide, prepared by repeated distillation out of contact with moisture, is a mobile liquid which crystallises, when cooled, in long transparent prisms like nitre, which fuse at 14-8° and boil at 46°. At tem- peratures below 25° these crystals easily change, especially if they have absorbed a little water, into an opaque, fibrous, crystalline mass which does not fuse, but vaporises at about 50°, the vapour condensing again to the prismatic variety, which melts at 14-8°. The formula of the fibrous form appears to be 8,O,, and it is much less active than the prismatic form (SO,). Published figures and details of description of SO, vary very much. When sulphuric acid in small quantity is added to SO, it dissolves it, and on cooling to 8° crystals of H,SO,.3SO0, are deposited. When more H,SOQ, is added, it forms pyrosulphuric acid, H,SO,.80, or H,S,0, (m.-pt. 35°). SO, can dis- solve much SQ,. When exposed to air, sulphur trioxide emits strong white fumes, its vapour combining with the moisture of the air. It soon deliquesces and becomes sulphuric acid: SO; + H,O = H,S0,. When thrown into water it hisses like red-hot iron, from the sudden formation of steam. The heat evolved is very great; 39,170 cals. per 80 grams of SO, dissolved. The vapour is decomposed into SO, and O, when passed through a red-hot tube ; but if the tube contain platinum, or another “‘ contact substance,” the vapour is only in a dissociated state, for the SO, and O re-combine on cooling in contact with the platinum. Phosphorus burns in its vapour, combining with the oxygen and liberating sulphur. Baryta glows when heated in the vapour, combining with it to form barium sulphate, unless both be quite dry. Sulphuric anhydride mixes in all proportions with sulphuric acid, the mixture being known as fuming sulphuric acid (also p. 161). The melting- point of the mixture varies with the percentage of SO, init ; that containing 80 per cent. is the most convenient for use, as it remains liquid at ordinary temperature. Fuming sulphuric acid (olewm) finds extended application in Organic Chemistry for making sulphonic acids (q.v.). By gently warming it, much SO, can be distilled from it for small experiments. Sulphur dis- solves it with formation of blue sulphur sesquiowide, 8,0, (p. 170). The pyrosulphuric acid, or anhydrosulphuric acid, H,8,0z, referred to akove, contains 45 per cent. of SO, and is solid at ordinary temperature ; it may be regarded as 803 which has insufficient water to form H3;SO, (H4S,0g), and since the acid chloride 8.0;Cle SULPHURIC ACID—HISTORY 161 (formed by the action of excess of PCl; on H,SOQ,) exists, its constitution may be repre- OH Cl OSC 0,84 sented as O , the chloride being No. An acid containing a larger Ons 0s OH Na proportion of SO, remains liquid at low temperatures. Sulphuric anhydride is capable of combining with olefiant gas (C,H,) and similar hydrocarbons, and absorbs these from mixtures of gases. In the analysis of coal gas, a fragment of coke wetted with fuming sulphuric acid is passed up into a measured volume of the gas standing over mercury to absorb these illuminating hydrocarbons. SO; also combines with HCl, forming SO,.Cl.OH, which may also be obtained by distilling sulphuric acid with phosphoric chloride— 380,(0H). + PC], = 3(80, Cl.OH) + PO..OH + 2HCI. Sulphuric Acid or Hydrogen Sulphate, H,SO, or SO,(OH), = 98-08.— More than four centuries ago the alchemist Basil Valentine subjected sulphate of iron, green vitriol as it was then called, to distillation and obtained an acid liquid which he named oii of vitriol. The process discovered by this laborious monk is even now in use at Nordhausen, in Saxony, and the Nordhausen oil of vitriol was at one time an important article of commerce. The crystals of ferrous sulphate (FeSO,.7H,O) exposed to the air absorb oxygen, and become basic ferric sulphate : 6FeSO, + 30 = 2Fe,(SO,)3.Fe.03. When this salt is partially dried, and distilled in earthenware retorts, a mixture of sulphuric acid and sulphuric anhydride distils over, and consti- tutes Nordhausen or fuming sulphuric acid (see also p. 160) : Fe,(SO,), + 2H,O = Fe,0, + 2H,SO, + 80O,. The ferric oxide (Fe,0;) which is left in the retorts is the red powder known as colcothar, which is used for polishing plate-glass and metals. The green vitriol employed for preparing the Nordhausen acid was obtained from iron pyrites (FeS,). A particular variety of this mineral, white pyrites (or efflorescent pyrites), when exposed to moist air, undergoes oxidation, yielding ferrous sulphate and sulphuric acid: FeS, + H,O + 70 = FeSO, + H,SO,. Large masses of this variety of pyrites in mineralogical cabinets may often be seen broken up into small fragments, and covered with an acid efflorescence of ferrous sulphate from this cause. Ordinary iron pyrites is not oxidised by exposure to the air unless it be first subjected to distillation in order to separate a portion of the sulphur which it contains. The first step towards the discovery of the process which, until within the last few years, has been the only profitable one by which this acid could be manufactured on a large scale was also made by Valentine, when he pre- pared his oleum sulphuris per campanum, by burning sulphur under a bell- glass over water, and evaporating the acid liquid thus obtained. The same experimenter also made a very important advance when he burnt a mixture of sulphur, antimony sulphide, and nitre under a bell-glass placed over water ; but it was not until the middle of the eighteenth century that it was suggested by some French chemists to burn the sulphur and nitre alone over water ; aprocess by which the acid appears actually to have been manufactured upon a pretty large scale. The substitution of large chambers of lead for glass vessels by Dr. Roebuck was a great improvement on the process, and about the year 1770 the preparation of the acid formed an important branch of manufacture ; since then the process has been steadily improving until, at the present time, a very large quantity is manufactured by this method. II ‘ 162 SULPHURIC ACID—MANUFACTURE The diminution in the price of oil of vitriol well exhibits the progress of improvement in its production, for the original oil of sulphur appears to have been sold for about half a crown an ounce, and that prepared by burning sulphur with nitre in glass vessels at the same price per pound; but when leaden chambers were introduced, the price fell to a shilling per pound, and at present oil of vitriol can be purchased at the rate of five farthings per ound. The description of the present “‘ chamber process’ of manufacture will be better understood after a description of it on an experimental scale. The fundamental reaction is represented by the equation SO, + O + H,0 = H,S80,; and we have seen that SO, in water does take up oxygen from the air, though slowly, and produces .H,SO,. In the manufacturing process nitrogen oxides are applied so as to hasten the oxidation. Nitric oxide, NO, together with air, producing nitrogen peroxide NO,, or nitrogen trioxide, N,O, (see p. 200), is introduced into an atmosphere containing steam, so that nitrous acid, HNO,, is produced: NO + NO, + H,O = 2HNO,, or NO, + H,O =2HNO,. This then reacts with the oxygen of the air and the SO, also introduced, with the result that H,SO, is formed and NO liberated ; for equations, seep. 165. The NO thus regenerated serves to convert more SO,, O, and H,O into H,SO,. Nitrogen oxides so act as “ carriers” of the oxygen of the air to the _$O,, and theoretically a smalk quantity could convert an unlimited quantity of SO, into H,SO,. The large glass flask or globe, A (Fig. 119), is the “chamber” into which five tubes are fitted. Through these are led respectively (a) SO,, generated in flask B from copper and concentrated sulphuric Fie. 119. acid ; (6) NO, generated in flask C from copper and diluted nitric acid (sp. gr. 1-2); (c) steam from flask D ; (d) air from a gas-holder through E; the fifth tube, F, serves as an outlet to a flue. If, at first, precautions are taken not to introduce moisture, and NO and air be admitted into the large flask, red fumes of NO, and N,0, are formed as usual ; if now SO, be led in, the colour remains unchanged, showing that no action occurs, but as soon as a very little steam is allowed to enter, the red colour disappears, and “chamber crystals ” (nitrosulphonic acid, SO,.OH.ONO) (p. 165) form on the walls of the flask. On admitting more steam these crystals disappear, but the red fumes reappear, due to decom- position of the crystals by the water, with consequent formation of sulphuric acid and nitrous anhydride: 280,.0H.ONO + H,O = 2H,SO, + N,0,. On suitably adjusting the proportions of injected gases, the formation of sulphuric acid may be rendered continuous. The process employed for the manufacture of English oil of vitriol will now be easily understood. A series of chambers (about 100 ft. x 20 ft. x 20 ft., shown in transverse section at F, Fig. 120) is constructed of leaden plates, the edges of which are united by autogenous soldering (that is, by fusing together their edges without solder, which would be rapidly corroded by the acid vapours). The bottom or saucer, G, of the chamber is not attached to the upper portion or curtain, F’, the sulphuric acid which collects in the saucer serving to seal SULPHURIC ACID—CHAMBER PROCESS 163 the communication between the interior of the chamber and the outer air. A framework of timber supports the curtain. The sulphur dioxide is generated by burning iron pyrites! or sulphur in suitable furnaces, A, adjoining the chambers, and so arranged that the gas produced may be mixed with about the proper quantity of air to furnish the oxygen required for its conversion into sulphuric acid. Nitric acid vapour is evolved from a mixture of sodium nitrate and oil of vitriol (see p. 192) contained in iron nitre pots, C, which are heated by being i ili ae Hn | placed in the flue, B, leading from the pyrites burners to the chamber, so that the nitric acid is carried into the chambers with the current of sulphurous acid gas and air (through D). Jets of steam are introduced at different parts of the chambers from an adjacent boiler. The sulphur dioxide acts upon the nitric acid vapour, in the presence of the water, forming nitric oxide and sulphuric acid, which rains down into the water on the floor of the chambers. If the NO were permitted to escape from the chambers, and a fresh quantity of nitric acid vapour introduced to oxidise another portion of sulphur dioxide, 2 molecules (170 parts BD weight) of sodium nitrate would be required to furnish the nitric acid for the conversion of 2 atoms (64 parts by weight) of sulphur, whereas, in prac- tice, only 4 parts by weight of nitrate are employed for 96 parts of eulphne, The nitrogen of the air takes no part in the change ; and since the a consumed in converting the sulphur into sulphuric acid is accompanied by four times its volume of nitrogen, there is a very large accumulation of this 1 2F eS, + 110 = Fe,0, + 4803, 164 SULPHURIC ACID~MANUFACTURE gas in the chambers, and provision must be made for its removal in order to ‘allow space for those gases which take part in the change. The obvious plan would appear to be the erection of a simple chimney for the escape of the nitrogen at the end of the chamber opposite to that at which the sulphurous acid gas and air enter it, and this plan was formerly adopted; but the nitrogen carries off with it a portion of the oxides of nitrogen which are so valuable in the chamber, and to save this the escaping nitrogen is now generally passed through a lead-lined tower (Gay-Lussac’s tower), H, filled with perforated stoneware plates, through which oil of vitriol (sp. gr. 1-72) is allowed to trickle: the oil of vitriol absorbs the nitrogen oxides, and flows into a cistern (acid egg), whence it is forced up, by air pressure, to a cistern, K, at the top of another tower (Glover’s tower), E, packed with acid- proof bricks, through which the hot SO, and air are made to pass as they enter, when they take up the nitrogen oxides from the “nitrous vitriol,” and carry them into the chamber. Over 50 per cent. of the weight of sodium nitrate used is thus saved. The sulphuric acid is allowed to collect on the floor of the chamber until it has a specific gravity of about 1-6, and contains 70 per cent. of H,SO,. If it were allowed to become more concentrated than this, it would both attack the lead and absorb some of the oxides of nitrogen in the chamber, so that it is now drawn off. This acid, chamber acid, is quite strong enough for some of the applications of sulphuric acid, particularly for that which consumes the largest quantity in this country, viz. the conversion of common salt into sodium sulphate as a preliminary step in the manufacture of carbonate of soda. To save the expense of transporting the acid for this purpose, the vitriol chambers form part of the plant of the alkali works. To convert this weak acid into the ordinary oil of vitriol of commerce, it is run off into shallow leaden pans set in brickwork and supported on iron bars over the flue of a furnace, where it is heated until so much water has evaporated that the specific gravity of the acid has increased to 1:72. The concentration cannot be carried further in leaden pans, because the strong acid acts upon the lead, and converts it into sulphate— 2H,S0, + Pb = PbSO, + 2H,0 + S0,. When a Glover’s tower is used the whole of the chamber acid is passed down the tower together with the nitrous vitriol. The chamber acid is thus concentrated by the heat of the furnace gases to sp. gr. 1-72 and the gases are at the same time cooled. The acid of 1:72 sp. gr. contains about 80 per cent. of H,SO,, and is largely employed for making superphosphate of lime, and in other rough chemical manufactures. It is technically called brown acid (brown oil of vitriol, B.O.V.), having acquired a brown colour from organic matter acci- dentally present in it. To convert this brown acid into commercial oil of vitriol, it is boiled down either in glass retorts or platinum stills, when water distils, accompanied by a little sulphuric acid, and the acid in the retort becomes colourless, the brown carbonaceous matter being oxidised by the strong H,SO,, with forma- tion of CO, and SO,. When dense white fumes of oil of vitriol begin to pass over, showing that all the superfluous water has been expelled, the acid is drawn off by a siphon. The strongest acid obtainable by this process still contains about 2 per cent. of water, formed by the decomposition of some of the H,SO, into H,O and SOs, the latter escaping as vapour. The cost of the acid is very much increased by this concentration. It cannot be conducted in open vessels, partly on account of the loss of sulphuric acid, partly because concentrated sulphuric acid absorbs moisture from the air even at the boiling-point. SULPHURIC ACID—THEORY 165 The loss by breakage of the glass retorts is very considerable, although it is reduced as far as possible by heating them in sand and keeping them always at about the same temperature by supplying them with hot acid. But the boiling-point of the concen- trated acid is very high (338°), and the retorts consequently become so hot that a current of cold air or an accidental splash of acid will frequently crack them at once. Moreover, the acid boils with succussion or violent bumping, caused by sudden bursts of vapour, which endanger the safety of the retort. With platinum stills the risk of fracture is avoided and the concentration may be conducted more rapidly, the brown acid being admitted at the top and the oil of vitriol drawn off by a platinum siphon from the bottom of the still, which is protected from the open fire by an iron jacket. But since a platinum still costs £2000 or £3000, the interest upon its value increases the cost of production of the acid. It is stated to be economical to protect the platinum from the slight action of the vitriol on it by a lining of gold, which is less attacked. When the perfectly pure acid is required, it is actually distilled so as to leave the solid impurities (sulphate of lead, &c.) in the retort. Some fragments of rock crystal should be introduced into the retort to moderate the bursts of vapour, and heat applied by a ring gas-burner with somewhat divergent jets. Commercial sulphuric acid is liable to contain nitrogen oxides, lead sulphate, arsenic (from the iron pyrites burnt in the kilns), and iron. Arsenic-free acid may be made by passing H,S through the diluted acid, filtering off the precipitate of Ar,Ss, and concentrating. It is generally made, however, by using sulphur in the kilns in place of pyrites. Nitrogen oxides are eliminated by adding a little ammonium sulphate during concentration: NO + NO, + (NH,).S0O, = 2N2 + H.SO, + 3H,0. To eliminate iron and lead sulphate the acid must be distilled. There has been much discussion as to the nature of the reactions occurring in the chamber-process. Lunge’s theory is that the principal reactions are (a) the formation of nitrosulphonic acid (chamber crystals) : 280, + NO; + 0, + H,O = 280,.0H.ONO; and (6) its subsequent decomposition by water, 280,.0H.ONO + H,O = 2H,S0, + N,0,; the regenerated N,O, becoming available for renewed action. But the theory of Raschig appears more probable. He assumes (a) the formation of nitrous acid: 2NO + H,O + O = 2HNO,; (6) that of nitrososulphonic acid, HNO, + SO, = ON.SO,.0H ; (c) from this and more nitrous acid the a of hydroxyl- aminomonosulphonic acid, ON.SO,.0H + HNO, = O: NC +NO; SO,.0H (d) the breaking down of the last, O : NC = H,SO, + NO; the NO SO,.0H produced then recommences the process automatically. For many years it has been the dream of the sulphuric acid maker to combine sulphur dioxide and atmospheric oxygen, by the method described at p. 160 for making sulphuric anhydride, and to absorb the product in water to obtain sulphuric acid. In such a process the “ contact substance ” has the same function as that of the nitric oxide in the chamber-process, that is to say, it acts as a carrier of oxygen from the air to the sulphur dioxide, although in what manner is unknown. The contact-substance has the great advantage over nitric oxide that, being a solid, it requires less room jn which to do its work, and is not liable to loss by leakage. Thus the unit of plant might be expected to be considerably smaller in a ‘“ contact-process for making sulphuric acid than in the chamber-process. An economy of greater importance than the saving of interest on plant, however, consists in the possibility of making by the contact-process strong sulphuric acid, or even a fuming acid, at once, thus eliminating the cost of concentration ; for it is obvious that by adjusting the proportion of water by which the sulphuric 166 SULPHURIC ACID—CONTACT PROCESS anhydride is absorbed, an acid of any degree of concentration may be obtained. Unfortunately, there are several conditions which affect unfavourably the combination of SO, and O in the contact-process. The only contact-substance which has proved so far sufficiently active in inducing the combination is platinum, most economically used by spreading it over a large sur- face as in the form known as platinised asbestos (p. 201). The activity of this material, however, rapidly diminishes if the gases contain impurities, because these are either deposited on the plati- num or they combine with it and render it ineffective. Such im- purities are said to ‘‘ poison ”’ the metal, and the worst of them in this respect are compounds of arsenic, phosphorus, and mercury. The first of these is nearly always present in the pyrites burnt for the production of SO,, and, passing into the gases, is sufficient, to- gether with the dust arising from the pyrites burners, to render the platinum useless in a very short time. It was the necessity for constantly renewing the platinum by dissolving it from the asbestos by aqua-regia, and again pre- cipitating it thereon, that pre- vented the success of the contact- process in the past. Another difficulty to be met in the contact-process (or catalytic process) arises from the fact that the heat evolved when SO, and O combine (p. 159) is apt to ac- cumulate until the temperature of the contact-substance is so high that much of the SO; produced is decomposed again into SO, and O, or these gases never combine. The demand for strong and fuming sulphuric acid by the manufacturers of artificial dye- stuffs and other organic prepara- ——aee tions having increased rapidly oe during the last few years, strenuous efforts have again been made to produce the acid by the contact-process ; and by rigorous care in purifying the sulphur dioxide and air before they enter the chamber containing the contact-substance, and by careful regulation of ; Pre: 121. SULPHURIC ACID—PROPERTIES 167 the temperature of the latter, great success has been attained. Indeed, it is claimed that so much as 96 per cent. of the SO, may be converted into SO,, and there is little reason to doubt that the process will ultimately displace the chamber-process. Sulphur dioxide is produced in a pyrites burner as in the chamber-process, sufficient air for its conversion into SO, being drawn in through the burner. This mixture of gases is then thoroughly washed, dried, and passed into a chamber containing platinised asbestos spread on shelves. At first the chamber must be artificially heated to a temperature of about 250° to 300° in order to induce the combination, but after this has once set in, it becomes necessary to withdraw the artificial heat and to circulate the gases which are to be combined, around the contact-chamber in order that they may equalise the temperature therein, and prevent it from rising at any one point to that at which decomposition of the SO, occurs ; the sulphuric anhydride is finally absorbed in water to produce sulphuric acid. Fig. 121 illustrates the kind of plant used in the contact-process for the manufac- ture of sulphuric acid. The gases from the pyrites kiln, A, pass through a dust chamber, B, where they are submitted to the action of steam-jets in order to mix them, and at the same time to dilute the sulphuric acid, which is always produced during the com- bustion in the pyrites burner, so that afterwards it may not attack the metal of the apparatus. The gases next pass through lead pipes, C, exposed to the atmosphere, in order to cool them below 100°, and then up through washing towers, D, supplied with water. As the presence of moisture in the gases leads to formation of H,SO, in the contact-chamber, which damages the platinum, the gases are next dried in a tower, E, supplied with strong sulphuric acid. To ensure continued activity of the platinum, it is desirable to watch carefully over the purity of the gases entering the contact- chamber ; for this purpose they are passed through a long box, F, having glass ends so that the operative can observe from one end a light burning at the other, and thus determine whether the gases are free from suspended matter. A periodical chemical testing of the gases is also made by passing some of them through water, which is afterwards analysed for arsenic and other impurities. The contact-chamber, G (which is drawn to an exaggerated scale for the sake of clearness), contains columns of perforated shelves on which platinised asbestos is spread. At first the chamber is heated by the gas-jets, g, the products of combustion of which pass up the flue, h. The cold gases, being admitted at 7, and passing around the columns of shelves, become heated by transmission through the walls of the flue and enter the columns, as indicated by the arrows, at a temperature high enough to combine under the influence of the platinum. The gas-jets may now be turned off, for the heat of combination is communicated to the gases as they pass around the columns, and the whole apparatus may be maintained at the most favourable temperature for combination, about 350°. The SO; produced is absorbed by water in a series of vessels like H. No means of circulating the gases is shown in the figure, but this is best effected by pumps. Properties of oil of vitriol—The properties of concentrated sulphuric acid are very characteristic. Its great weight (sp. gr. 1-84),1 freedom from odour and oily appearance distinguish it from any other liquid commonly met with, which is fortunate because it is difficult to preserve a label upon the bottles of this powerfully corrosive acid. Although, if absolutely pure, it is perfectly colourless, the ordinary acid used in the laboratory has a peculiar grey colour, due to traces of organic matter. Its high boiling-point, 338°, has been noticed already ; it must be added that vapour of H,SO, is not evolved by ebullition but the products of its dissociation, HO + S03. When acid of 100 per cent. strength is heated it begins (apparently) to 1 i ining 97:7° i . gr., 18413; that of 98%, 18412; 99%, 1-8408 ; 99-47%, 1.8895 3 100%, 1.8884 ; amongst the linte wade 90%, 1:820; 80%, tise; 70%, 1-616; 50%, 1-390: 30%, 1-221; 10%, 1-069, 168 SULPHURIC ACID—HYDRATES boil at 290° and loses SO; until its strength has fallen to 98 per cent., when both water and SO, distil over and condense together in the receiver. The vapour is perfectly transparent in the vessel in which the acid is boiled ; as soon as it issues into the air it condenses into voluminous dense clouds of a most irritating description. Even a drop of the acid evaporated in an open dish will fill a large space with these clouds. Oil of vitriol solidifies when cooled to about — 34°, though pure H,SO, melts at 10-5°. Oil of vitriol rapidly corrodes the skin and other organic textures upon which it falls, usually charring or blackening them at the same time. Poured upon a piece of wood, the latter speedily assumes a dark brown colour ; and if a few lumps of sugar be dissolved in a very little water, and stirred with oil of vitriol, there is a violent action, and a semi-solid black mass is produced. This property of sulphuric acid is turned to account in the manufacture of black- ing, in which treacle and oil of vitriol are employed. These effects are to be ascribed to the powerful attraction of oil of vitriol for water. Cellulose (CgH,,0;) (which composes the bulk of wood, paper, and linen) and sugar (C,,H,.0,,) may be regarded, for the purpose of this explanation, as composed of carbon associated with 5 and 11 molecules of water respectively, and any cause tending to remove the water would tend to liberate the carbon. The great attraction of this acid for water is shown by the high tempera- ture (often exceeding the boiling-point of water) produced on mixing oil of vitriol with water, which renders it necessary to be careful in diluting the acid. The water should be placed in a jug and the oil of vitriol poured into it in a thin stream, a glass rod being used to mix the acid with the water as it flows in. Ordinary oil of vitriol becomes turbid when mixed with water, from the separation of lead sulphate (formed from the evaporating pans), which is soluble in the concentrated but not in the diluted acid, so that if the latter be allowed to stand for a few hours the lead sulphate settles to the bottom, and the clear acid may be poured off free from lead. Diluted sulphuric acid has a smaller bulk than is occupied by the acid and water before mixing. The heat evolved on combining 1 gram-molecule of H2SO, with 1 gram-molecule of water amounts to 69-7 gram-calories. Decreasing quantities of heat are evolved for successive additions of water, until 200 gram-molecules of water have been added. The heat thus evolved may be regarded as equivalent to a chemical affinity exerted between the acid and water ; several compounds of sulphuric acid with water have been crystallised. The most notable of these is H,S0,.H,O, corresponding with an acid of sp. gr. 1-78 ; itis called dihydrated sulphuric acid, (SO;.2H,O)—in contradis- tinction to the typical monohydrated sulphuric acid, (SO,.H,O)—which solidifies to a mass of ice-like crystals at 8°, and on this account is called glacial sulphuric acid. When sold instead of oil of vitriol it may be recognised by its freezing in winter. The hydrate H,SO,.2H,O corresponds with the maximum contraction which occurs when H,SO, and water are mixed, and with an acid of sp. gr. 1-63; it is called trihydrated sulphuric acid or orthosulphuric acid + S(OH)g. The so-called “ solidified sulphuric acid” is sodium hydrogen sulphate saturated with sulphuric acid. Even when largely diluted, sulphuric acid corrodes textile fabrics very rapidly, and though the acid be too dilute to appear to injure them at first, it will be found that the water evaporates by degrees, leaving the acid in a more concentrated state, and the fibre is then perfectly rotten. The same result ensues at once on the application of heat; thus, if characters be written on paper with the diluted acid, they will remain invisible until the paper is held to the fire, when the acid will char the paper, and the writing will appear intensely black. If oil of vitriol be left exposed to the air in an open vessel, it very soon increases largely in bulk from the absorption of water, and a flat dish of oil SULPHURIC ACID—CONSTITUTION 169 of vitriol under a glass shade (Fig. 122) is frequently employed in the labora- tory for drying substances without the assistance of heat. The drying is much accelerated by placing the dish on the plate of an air-pump and ex- hausting the air from the shade, so as to effect the drying in vacuo. Tt will be remembered also that oil of vitriol is in constant use for drying gases. At a red heat, the vapour of oil of vitriol is decomposed into water, sulphur dioxide, and oxygen: H,SO, = H,O + SO, + O. When sulphur is boiled with oil of vitriol, the latter gradually dissolves the melted : sulphur, converting it into sulphur dioxide (p. 156)— : ‘ S + 2H,SO, = 380, + 2H,0. All ordinary metals are acted upon by concentrated sulphuric acid when heated, except gold and platinum (the latter does not quite escape when long boiled with the acid), the metal being oxidised by one portion of the acid, which is thus converted into sulphur dioxide, the metal oxide reacting with another part of the sulphuric acid to form a sulphate. Thus, when silver is boiled with strong sulphuric acid, it is converted into silver sulphate, which is soluble in hot water— Ags + 2H,SO, = Ag,SO, + 2H,O + SOv. Should the silver contain any gold, this is left behind in the form of a dark powder. Sulphuric acid is extensively employed for the separation or parting of silver and gold. If the sulphuric acid contains nitric acid, it dissolves a considerable quantity of gold, which separates again in the form of a purple powder when the acid is diluted with water, the sulphate of gold formed being reduced by the nitrous acid when the solution is diluted. Some of the uses of sulphuric acid depend upon its specific action on certain organic substances, the nature of which has not yet been clearly explained. Of this kind is the conversion of paper into vegetable parchment by immersion in a cool mixture of two measures of oil of vitriol and one measure of water, and subsequent washing. The conversion is not attended by any change in the weight of the paper. Proof of the composition of sulphuric acid.—10 grams of sulphuric acid are neutralised by 22-7 grams of PbO, when heated, giving off 1-82 grams of H,O and leaving 30-9 grams of lead sulphate. Hence sulphuric acid contains 2-02 per cent. of H. 10 grams galena (PbS), containing 8-66 Pb and 1-34 8, when converted into lead sulphate (PbSO,) by nitric acid, yield 12-68 grams. Hence 12-68 grams lead sulphate contain 1-348, and 2-68 O being the difference between the lead sulphate and the lead sulphide. The 30-9 grams of lead sulphate furnished by 10 grams of sulphuric acid would therefore contain 3-26 S and 6-52 O, so that 100 parts of sulphuric acid contain 2-02 H, 32-6 8, and 65-2 O, which numbers correspond with a formula containing 2 atoms of H, 1 atom of §, and 4 atoms of O. The molecular weight of sulphuric acid cannot be deduced from the sp. gr. of its vapour because it is dissociated into H,O and SO . But it yields with KOH two salts, one containing an atom of K and an atom of H, and the other containing 2 atoms of K. Hence these salts must be KHSO, and K,SO,, and the molecule of the acid must be H,SO, ; it is therefore a dibasic acid. Even at ordinary temperatures sulphuric acid displaces most other acids from their salts ; many cases will be remembered in which this power of sulphuric acid is turned to account. cw So great is the acid energy of sulphuric acid that when it is allowed to act on an indifferent or acid metallic oxide, it causes the separation of a part of the oxygen, and reacts with the basic oxide so produced. Advantage is 170 PERSULPHATES sometimes taken of this circumstance for the preparation of oxygen; for instance, when manganese dioxide is heated with sulphuric acid, sulphate of manganese is produced, and oxygen disengaged: MnO, + H,SO, = MnSO, + O + H,0. Again, if chromic anhydride be treated in the same way, chromic sulphate will be produced, with liberation of oxygen— 2Cr0, + 3H,S0, = Crp.880, + 30 + 3H,0. A mixture of potassium bichromate (K,0.2CrO,;) and sulphuric acid is sometimes used as a source of oxygen. Sulphates.—Sulphuric acid is a dibasic acid, that is, it contains 2 atoms of hydrogen which may be exchanged for a metal. In normal sul- phates both atoms of H are so exchanged, as in K,SO,, the normal potassium sulphate. When only a part of the H is exchanged, acid sulphates are pro- duced ; thus KHSO, is acid potassium sulphate, which is very useful in blowpipe and metallurgical chemistry, because, when heated, it yields normal potassium sulphate and sulphuric acid: 2KHSO, = K,SO, + H,SO,. When the two atoms of H in H,SO, are exchanged for different metals, double sulphates are formed ; potassium alum, KAl(SO,)o, is an example of this class, in which one-fourth of the H in 2H,SO, is exchanged for potassium, and the other three atoms by triatomic aluminium (see also p. 92). In consequence of the tendency of sulphuric acid to break up into sulphur dioxide and oxygen at a high temperature, most of the sulphates are decomposed by heat ; cupric sulphate, for example, when very strongly heated, leaves cupric oxide, whilst sulphur dioxide and oxygen escape: CuSO, = CuO + SO, + O. Ferrous sulphate is more easily decomposed, some of the SO, escaping decomposition, whilst the remainder breaks up into SO, and O, the latter oxidising the ferrous oxide which would otherwise be left: 2FeSO, = Fe,03 + SO, + SOs (see also p. 161). The normal sulphates of potassium, sodium, barium, strontium, calcium, and lead are not decomposed by heat, and sulphate of magnesium is only partly decomposed at a very high temperature. When a sulphate of an alkali or alkaline earth metal is heated with charcoal, the carbon removes the whole of the oxygen, and a sulphide of the metal remains, thus : K,SO, (potassium sulphate) + 4C = K,S (potassium sulphide) + 4CO. Hydrogen, ata high temperature, effects a similar reduction. Even at the ordinary temperature, calcium sulphate in solution is sometimes de- oxidised by organic matter ; this may occasionally be noticed in well and river waters when kept in closed vessels; they acquire a strong smell of hydrogen sulphide, in consequence of the conversion of a part of the calcium sulphate into sulphide by the organic constituents of the water, and the subsequent decomposition of the calcium sulphide by the carbonic acid present in the water. Sulphur Sesquioxide, S,03, is an unstable, blue, crystalline solid, obtained by the gradual addition of sulphur to sulphuric anhydride in the cold. It dissolves in fuming sulphuric acid to a blue liquid, but is decomposed by water, alcohol, or ether, sulphur being liberated (see p. 160). Persulphuric Anhydride, S,Q,, is a crystalline compound formed by electrising (p. 139) a mixture of SO, and O. It is also produced by the interaction of hydrogen dioxide and H,SO,. It is very volatile and unstable, but its solution in fairly concen- trated sulphuric acid possesses oxidising properties and probably contains persulphuric acid, H2S.0,. Such a solution is formed at the anode during the electrolysis of sul- phuric acid of medium strength, and its presence is to be detected in the ordinary lead electric accumulator. The persulphates are easily prepared by the electrolysis of solu- tions of the sulphates in dilute sulphuric acid. To prepare potassium persulphate, K,8.03, a saturated solution of KHSOQ, is contained in a platinum dish, kept cool ;. a porous pot containing dilute H,SO, is immersed in the solution, and in this a platinum wire is introduced to serve as a cathode ; the platinum dish is made the anode. By continuing the electrolysis (current = 2-3 amperes) for some time, crystals of K,8.0, THIOSULPHATES 17) are deposited in the dish. When dried and heated they evolve SO, and O, K,SO, being left. Barium chloride gives no precipitate with a solution of a persulphate until heated, when the BaS,0, decompuses, BaSO, being precipitated. The persulphates behave as oxidising agents in solution, and find application as bleaching agents, although the use of the ammonium salt as a ‘“‘ reducer ”’ in photography can hardly be explained by reference to its oxidising power. The constitutional formula is OH.SO,.0.0.S0,.0H. It has been found that when a persulphate is treated with strong H,SO, the solution rapidly liberates iodine from an iodide, whereas persulphuric acid does so only slowly. Hence such a solution (Caro’s‘ucid) is supposed to contain permonosulphuric acid, H,SO;, or OH.SO0,0.0H. By the interaction of 100 per cent. hydrogen peroxide and sulphur trioxide, a nearly pure (92-3 per cent.) Caro’s acid has been obtained. This strong acid is stable below 0°. With catalytic agents, e.g. finely divided platinum, it decomposes with explosive violence. The acid is also formed on mixing strong H,O, sol. and H,SO, cone.: H,O, + H,SO, = H.SO,; + HO. Including the oxyacids of sulphur already described the following are known : Sulphurous ‘ : ‘ ‘ 5 g : . H,80, Sulphuric z ‘ ; : ‘ ‘ ‘ ; . H,S80, Thiosulphuric (formerly hyposulphurous) . . H,8.03 Hydrosulphurous : ; F : : 5 . H.S8.04 Dithionic P : ; i : ; : ‘ - HyS820¢ Trithionic ; : : ‘ ‘ ¥ , Z 2306 Tetrathionic . j ‘ ‘ ‘ ‘ a a . H,840, Pentathionic . 4 é ‘ , ‘ ‘ , . H,S8,0.¢ Thiosulphuric Acid (H,S,0, or SO,.0H.SH).—This acid has not been obtained in the separate state; but many salts are known which are evidently derived from it, and such salts are called thiosulphates, or popularly hyposulphites. The sodium thiosulphate is by far the most important of these salts, being very largely employed in photography, under the name of hyposulphite, and as a substitute for sodium sulphite as an antichlore. The simplest method of preparing it consists in digesting powdered roll sulphur with solution of sodium sulphite (Na,SO,), when the latter dissolves an atom of sulphur and becomes thiosulphate (Na,S,0,), which crystallises from the solution, when sufficiently evaporated, in fine prismatic crystals, having the formula Na,S,0,;.5H,0. On a large scale, sodium thiosulphate is more economically prepared from the calcium thiosulphate obtained by exposing the refuse (tank-waste or soda-waste) of the alkali works to the air for some days. This refuse contains a large proportion of calcium sulphide, which becomes converted into thiosulphate by oxidation ; 2CaS +20, +H,0= CaS,03 + Ca(OH),. The thiosulphate is dissolved out by water, and solution mixed with sodium car- bonate, when calcium carbonate is precipitated and sodium thiosulphate remains in solution ; CaS,0, + Na,CO, = CaCO, + NapS,03. The most remarkable and useful property of the sodium thiosulphate is that of dissolving the chloride and iodide of silver, which are insoluble in water and most other liquids ; hence its use in photography. On mixing a solution of silver nitrate with one of sodium chloride, a white preci- pitate of silver chloride is obtained, the separation of which is promoted by stirring the liquid; AgNO, + NaCl = AgCl + NaNO;. The precipitate may be allowed to. settle and washed twice or thrice by decantation. One portion of the silver chloride is transferred to another glass, mixed with water, and solution of sodium thiosulphate added by degrees. The silver chloride is very easily dissolved, yielding an intensely sweet solution, which contains the thiosulphate of sodium and silver, produced by double decomposition between the silver chloride and sodium thiosulphate ; s 172 SODIUM THIOSULPHATE 2AgCl + 3Na,8.0, = AgNa4(S203)3 + 2NaCl. The sodium silver thiosulphate may be obtained in crystals from the solution. When the silver chloride is acted on by a weaker solution of the thiosulphate, another thiosulphate of sodium and silver is formed, which is very insoluble in water ; AgCl + Na,S,0; = NaCl + NaAgS,03. Hence the necessity for using a strong solu- tion of the hyposulphite in fixing photographic prints. If the other portion of the silver chloride be exposed to the action of light, and especially of direct sunlight, it assumes by degrees a dark slate colour, possibly from the formation of silver subchloride; 4AgCl + H,O = SAc.C1 + HCl + HOC) By treating this darkened silver chloride with the hyposulphite, as before, the unaltered silver chloride will be entirely dissolved, but the subchloride will be decomposed into monochloride, which dissolves in the hyposulphite, and metallic silver, which is left in a very finely divided state as a black powder. The application of these facts in photography is well illustrated by the following experiments: A sheet of paper is soaked for a minute or two in a solution of 1 gram of common salt in 30 c.c. of water contained in a flat dish. It is then dried, and soaked for three minutes in a solu- tion of 5 grams of silver nitrate in 30c.c. of water. The paper thus becomes impreg- nated with silver chloride formed by the decomposition between the sodium chloride and the silver nitrate. It is now hung up in a dark place to dry. If a piece of lace, or a fern leaf, or an engraving on thin paper, with well-marked contrast of light and shade, be laid upon a sheet of the prepared paper, pressed down upon it by a plate of glass, and exposed for a short time to sunlight, a perfect representation of the object will be obtained, those parts of the sensitive paper to which the light had access having been darkened by the formation of silver subchloride, whilst those parts which were protected from the light remain unchanged. But if this photographic print were again exposed to the action of light, it would soon be obliterated, the unaltered silver chloride in the white parts being acted on by light in its turn. The print is therefore fixed by soaking it for a short time in a saturated solution of sodium thiosulphate, which dissolves the white unaltered silver chloride entirely and decomposes the subchloride formed by the action of light, leaving the black, finely divided metallic silver in the paper. The print should now be washed for two or three hours in a gentle stream of water, to remove all the silver thiosulphate, when it will be quite permanent. The power of sodium thiosulphate to dissolve silver chloride has also been turned to account for extracting silver from its ores, in which it is occasionally present in the form of chloride. The behaviour of solution of sodium thiosulphate with powerful acids explains the circumstance that the thiosulphuric acid has not been isolated, for if the solution be mixed with a little dilute sulphuric or hydrochloric acid it remains clear for a few seconds, and then becomes suddenly turbid from the separation of sulphur, at the same time evolving a powerful odour of sulphur dioxide ; H,S,0, = H,O + 8+ 80,. This disposition of the thio- sulphuric acid to break up into sulphur dioxide and sulphur also explains the precipitation of metallic sulphides, which often occurs when sodium thiosulphate is added to the acid solutions of the metals. Thus, if an acid solution of antimonious chloride (obtained by boiling crude antimony ore, Sb.83, with hydrochloric acid) be added to a boiling solution of sodium thiosulphate, the sulphur, separated from the thiosulphuric acid, combines with the antimony to form a fine orange-red precipitate of antimonious sulphide (Sb,S3), a pigment known as antimony vermilion. Lead thiosul- phate dissolved in sodium thiosulphate is used as a hair-dye, depositing the black lead sulphide. A solution of sodium thiosulphate bleaches iodine solution, becoming changed into a solution of sodium tetrathionate ; 2Na,S8,0, + I, = 2NaI + Na,8,0,. Potassium permanganate oxidises it to the same product ; also by electrolysis, tetrathionate is formed. When crystals of sodium thiosulphate are heated in the air, they first fuse in their SULPHUR OXY-ACIDS 173 water of crystallisation, then dry up to a white mass, which burns with a blue flame, leaving a residue of sodium sulphate. If heated out of contact with air, sodium penta- sulphide will be left with the sodium sulphate ; 4(Na,8,03.5H,O) =20H,O + 3Na,S8O, + Na,§;. Some of the reactions of sodium thiosulphate become more intelligible when the salt is represented as sodium sulphate, SO,(ONa)o, in which an atom of sulphur has displaced an atom of oxygen, SO,.ONa.SNa. Hydrosulphurous Acid (H,8,0,4).—In an aqueous solution of sulphurous acid zine dissolves, forming a yellow solution, without the usual evolution of hydrogen ; the solution contains zinc hydrosulphite ; 2H,SO; + Zn = Zn8,0, + 2H,O. The solution bleaches organic colours, even Prussian blue, and reduces the salts of silver, mercury, and copper to the metallic state ; it is used in the indigo vat for reducing the indigo. It is very unstable, soon becoming colourless zine sulphite ; Zn8,0, + O + H,O = ZnSO, + H,SOs. ‘ The sodium salt, NagS.04, is obtained by digesting zinc in solution of NaHSO, ; 2NaHSO, + Zn = NagS.O, + Zn(OH),. It forms needle-like crystals very soluble in water, insoluble in strong alcohol, and becoming NaHSOs, by absorption of oxygen from the air. By decomposing the sodium hydrosulphite with oxalic acid, H,S,0, is obtained as an orange-yellow unstable liquid. Dithionic Acid, or Hyposulphuric Acid (H28,0,), was discovered by Welter and Gay Lussac in 1819. To prepare a solution of the acid, manganese dioxide in a state of fine division is suspended in water and exposed to a current of sulphur dioxide, the water being kept very cold whilst the gas is passing. A solution of manganese dithionate is thus obtained ; 280, + MnO, = MnS,0,. Some manganese sulphate is always formed at the same time ; SO, + MnO, = MnSO,, and if the temperature be allowed to rise this will be produced in large quantity. The solution containing the sulphate and dithionate is decomposed by solution of baryta (baryta-water), when manganous oxide is precipitated, together with barium sulphate, and barium dithionate is left in solution. To the filtered solution dilute sul- phuric acid is carefully added until all the barium is precipitated as BaSO,, when the solution of dithionic acid is filtered and evaporated in vacuo over oil of vitriol. It is a colourless, inodorous liquid, which is decomposed, when heated, into sulphuric acid and sulphur dioxide ; H,S,0, = H,SO, + SO. Oxidising agents (HNO3;, Cl, &c.) convert it into H,SO,. The dithionates are not of any practical importance ; they are all soluble, and are decomposed by heat, leaving sulphates and evolving sulphur dioxide. They are dis- tinguished from the thiosulphates in that they evolve SO, when heated with HCl, without depositing sulphur. Trithionic Acid (H,830,) is also a practically unimportant acid. It is prepared from the potassium trithionate which is formed by boiling a strong solution of potassium bisulphite with sulphur until the solution becomes colourless, and filtering the hot solution from any undissolved sulphur ; 6KHSO; + 8 = 2K,8,0, + K,SO, + 3H,0. The solution deposits potassium trithionate in prismatic crystals. By dissolving these in water and decomposing the solution with perchloric acid, the potassium is precipitated as perchlorate and a solution of trithionic acid is produced, from which the acid has been obtained in crystals. It is, however, very unstable, being easily re- solved into sulphur dioxide, sulphuric acid, and free sulphur ; H,8,05 = H,SO, + SO, + §. te Acid (H,S,0g) is rather more stable than the preceding acid, though equally devoid of practical importance. It is formed when barium thiosulphate, sus- pended in a little water, is treated with iodine, when the tetrathionate is obtained in crystals ; 2(BaS,0,) + I, = Bal, + BaS40¢.- (Compare the action of iodine on sodium thiosulphate, p. 172.) By exactly precipitating the barium from a solution of BaS4Og by dilute H,SO,, a solution of tetrathionic acid may be obtained. When boiled, it is decomposed into sulphuric acid, sulphur dioxide, and free sulphur; H,8,0,5 = So. ee oa ot ferric chloride is added to sodium thiosulphate, a fine purple colour is at first produced, which speedily vanishes, leaving a colourless solution. The purple colour appears to be due to the formation of the ferric thiosulphate, which speedily 174 CARBON DISULPHIDE decomposes, the ultimate result being expressed by the equation Fe,Cl, + 2(Na.S,0,) = Na.S,0, + 2FeCl, + 2NaCl. Pentathionic Acid (H,S;O,) possesses some interest as resulting from the action of hydrogen sulphide upon sulphurous acid, when much sulphur is deposited and pentathionic acid remains in solution; 5H,S + 5H,SO; = H,8,0, + 9H,O + 58. Besides pentathionic acid, a colloidal form of sulphur, sulphuric acid, tetrathionic acid, and hexathionic acid (?) are found in the solution. To obtain a concentrated solution of the acid, H,S and SO, are passed alternately through the same portion of water until a large deposition of sulphur has occurred. This is allowed some hours to settle ; the clear liquid poured off and the solution concentrated by evaporation, first over a water-bath and finally, in vacuo, over oil of vitriol ; for a concentrated solution of pentathionic acid is decomposed by heat into H,SO, and SQ,, with separation of sul- phur; H,8,0, = H,SO, + SO, + 38. Carbon Disulphide, CS, = 76:14.—This important compound (also called bisulphuret of carbon) is found in small quantity among the products of destructive distillation of coal, and is very largely manufactured for use as a solvent for sulphur, phosphorus, caoutchouc, fatty matters, &c. It is one of the few compounds of carbon which can be obtained by the direct Fic. 123. union of their elements, and is prepared by passing vapour of sulphur over charcoal heated to redness. The combination is endo- thermic. In small quantity carbon disulphide is easily prepared in a combustion-tube about two feet long and half an inch in diameter (Fig. 123). This tube is closed at one end, and a few fragments of sulphur Fic. 124. dropped into it so as to occupy two or three inches. The rest of the tube is filled up with small fragments of recently calcined wood charcoal. The tube is placed in a combustion-furnace (Fig. 272) and its open end connected bya perforated cork with a glass tube, which dips just below the surface of water contained in a bottle placed in a vessel of very cold water. The part of the tube which contains the charcoal is heated first, and when it is red-hot the end containing the sulphur is heated, so that the vapour of sulphur may be slowly passed over the red-hot charcoal. The disulphide, being insoluble in water and much heavier (sp. gr. 1-292 at 0°), is depo- sited beneath the water in the receiver. To purify it from the water and the excess of sulphur which is deposited with it, the water is carefully drawn off with a small siphon, the CS, transferred to a flask, and a few fragments of calcium chloride dropped into it to absorb the water. A condenser is attached to the flask (Fig. 124) by a perforated cork, and the flask is gently heated in a water-bath, when the CS, distils over as a perfectly colourless liquid. The inflammability of the disulphide renders great care necessary. The water-bath is supplied with hot water from a kettle as required ; it is advisable not to apply a flame, since any escaping vapour may take fire. The com- mercial article can be purified by distilling it over mercury or mercuric chloride. On a large scale, a fire-clay or cast-iron retort is filled with fragments of charcoal and heated to redness, pieces of sulphur being occasionally dropped in through an earthenware tube passing to the bottom of the retort. When very large quantities are made, coke is employed, and the vapour of sulphur CARBON DISULPHIDE 175 is obtained from iron pyrites. The carbon disulphide is possessed of some very remarkable properties : it is a brilliant liquid of sp. gr. 1-292 at 0°, the light passing through which at certain angles is partly decomposed into its component coloured rays before it reaches the eye. These properties are dependent upon its high refractive and dispersive powers, which are turned to great advantage in optical experiments, especially in spectrum analysis, where the rays emanating from a coloured flame are analysed by passing them through a prismatic bottle filled with carbon disulphide. It is also highly diathermic, that is, it allows rays of heat to pass through it with comparatively little loss, so that if it be rendered opaque to light by dissolving iodine in it, the rays of light emanating from a luminous object may be arrested, whilst the calorific rays are allowed to pass. Carbon disulphide is a very volatile liquid readily evaporating at the ordinary temperature, and boiling at 47°. Its vapour, when diluted with air, has a disgusting and exaggerated odour, recalling sulphuretted hydrogen, but the smell at the mouth of the bottle is ethereal and not unpleasant if the disulphide has been carefully purified. The rapid evaporation of carbon disulphide is, of course, productive of great cold. If a. few drops be placed in a watch-glass and blown upon, they soon pass off in vapour, and the temperature of the glass is so reduced that some of the disulphide is frozen ; 1 this melts when the glass is placed in the palm of the hand. If a glass plate be covered with water, a watch-glass containing carbon disulphide placed on it, and evaporation promoted by blowing through a tube, the watch-glass will be frozen on to the plate, so that the latter may be lifted up by it. The carbon disulphide is exceedingly inflammable ; it takes fire at a tem- perature far below that required to inflame ordinary combustible bodies, and burns with a bright blue flame, producing carbon dioxide and sulphur dioxide (CS, + 30, = CO, + 2SO,), and having a great tendency to deposit sulphur unless the supply of air be very good. If a little carbon disulphide be dropped into a small beaker, it may be inflamed by holding in its vapour a test-tube containing oil heated to about 150°, which will be found incapable of firing gunpowder or of inflaming any ordinary combustible substance. The abundance of sulphur separated in the flame of carbon disulphide enables it to burn iron by converting it into sulphide. If some carbon disulphide be boiled in a test-tube provided with a piece of glass tube from which the vapour may be burnt and a piece of thin iron wire be held in the flame (Fig. 125), it will burn with vivid scintil- lation, the fusible ferrous sulphide dropping off. Carbon disulphide is endothermic (p. 114), 76 grams of the liquid absorbing 19,610 gram-calories in its formation ; like most other endothermic gases (C2H,, C,Ne, N20, &c.), it may be suddenly decomposed into its elements by a violent shock. This experiment is performed by detona- ting 0-05 gram of mercuric fulminate, by means of an electric spark, in an inclined tube open at one end, in Fic. 125. which a paper saturated with carbon disulphide has been suspended. After the explosion the carbon and sulphur are seen deposited on the walls of the tube. The vapour of CS, acts very injuriously if breathed for any length of time, producing symptoms somewhat resembling those caused by H,S. Its poison- ous properties have been turned to account for killing insects in grain without injuring the grain. 1 This solid matter is probably a cryohydrate, 2CS,.H,0. Dry CS, melts at —1 3°, 176 CARBON SULPHIDES The chief application of carbon disulphide depends upon its power of dissolving the oils and fats. After as much oil as possible has been extracted from seeds and fruits by pressure, a fresh quantity is obtained by treating the pressed cake with carbon disulphide, which is afterwards recovered by distillation from the oil. Carbon disulphide has often been made a starting-point in the attempts to produce organic compounds by synthesis. If it be mixed with hydrogen sulphide (by passing that gas through a bottle containing the disulphide gently warmed), and passed over copper-turnings heated to redness in a porcelain tube, olefiant gas will be produced ; 2CS, + 2H,S + 6Cu = 6CuS + C,H. Marsh gas may be obtained in the same way. When passed through a red- hot tube the vapour of CS, is decomposed into C and 8. The action of carbon disulphide upon ammonia is practically important for the easy production of ammonium sulphocyanide, which is formed when the disulphide is dissolved in alcohol, and acted on by ammonia with the aid of heat ; CS, + 2NH; = HLS + NH,CNS. ; Carbon disulphide is often called sulphocarbonic or thiocarbonic anhydride to emphasise its analogy to carbonic anhydride ; it combines with some of the sulphur- bases to form sulphocarbonates or thiocarbonates, which correspond with the carbonates, containing sulphur in place of oxygen. When a solution of potassium hydrosulphide is mixed with an excess of carbon disulphide, potassium thiocarbonate is obtained in orange-yellow crystals. Compare KSH + CS, = KHCS, and KOH + CO, = KHCO,. Even the hydrogen compound corresponding in composition with the unknown H,CQ; may be obtained as a yellow oily liquid by decomposing potassium thiocarbonate with hydrochloric acid; K,CS; + 2HCl = H,CS, + 2KCl. Potassium thiocarbonate is applied for the destruction of the phylloxera insect which infests vines. As would be expected, the thiocarbonates, when boiled with water, exchange their sulphur for oxygen, becoming carbonates; K,CS,; + 3H,O0 = K,CO, + 3H,8. Small quantities of CS, may be identified by dissolving in alcoholic potash and adding cupric sulphate, which gives a yellow precipitate of cwprous xanthate, CugS .CS.OC,H;. The carbon disulphide vapour in coal gas is one of the most injurious of the impu- rities, and one of the most difficult to remove with economy. It is especially injurious because, when burning in the presence of aqueous vapour, a part of its sulphur is converted into sulphuric acid, the corrosive effects of which are so damaging. Several processes have been devised for its removal, but that which is now almost universally adopted consists in absorbing it in lime which has already become saturated with H,S in the course of the purification of the gas, and thus contains calcium hydrosulphide, Ca(SH),. This compound combines with the CS, to form calcium thiocarbonate, Ca(SH). +CS, = CaCS, + HS. Carbon monosulphide (CS) is produced under the influence of the silent electrical discharge on carbon disulphide vapour at low pressures. The monosulphide, as collected in a U-tube cooled by liquid air, is at first white, but soon becomes brown, especially on rise in temperature. The brown substance is a polymer, (CS), and is probably the same as that deposited by the action of light on CS, ; also by contact of iron with CS,, 20S, + Fe = FeS, + 20S; HCl dissolves the FeS,, leaving the (CS), as a red-brown powder of sp. gr. 1-66; slightly soluble in hot ether and CS, ; soluble in boiling HNO, and in boiling strong potash. Heated with sulphur it yields CS,. Tricarbon disulphide (C382) has been obtained by boiling CS, in a flask, the upper portion of which contains an electric arc, and condensing the vapour, after it has been thus heated, so that it may fall back into the flask. It is a deep red liquid (sp. gr. ] 27) which has a very irritating odour. When heated it is changed to a black mass of the same percentage composition. Carbon Oxysulphide, COS = 60-07.—This compound, which may be regarded as CO, in which S has been substituted for O, is formed when a mixture of carbonic oxide with sulphur vapour is acted on by electric sparks, or passed through a red-hot porcelain tube ; also when carbon disulphide vapour is passed over white-hot clay, and when CdS is heated in COCl.. SULPHUR CHLORIDES 177 It is easily prepared by gently heating potassium sulphocyanide, KCNS, with oil of vitriol diluted with four-fifths of its volume of water, and collecting the gas over mercury. The action of the sulphuric acid upon the sulphocyanide produces hydro- sulphocyanic acid ; KCNS + H,SO, = HCNS + KHS0O,; which is then decomposed by the water in the presence of the excess of sulphuric acid into COS ahd NH, the latter combining with the sulphuric acid; HCNS + H,O = NH; + COS. The gas has a peculiar, disagreeable odour, recalling that of carbon disulphide ; it is more than twice as heavy as air (sp. gr. 2-11) and is very infammable, burning with a blue flame and yielding CO, and SO. Potash absorbs and decomposes it, yielding carbonate and sulphide of potassium; COS + 4KOH = K,S + K,CO, + 2H,O0. Ammonia absorbs it freely, and, on evaporation, evolves H,S and deposits crystals of urea ; COS + 2NH, = HS + CO(NHe)o. Chlorides of Sulphur.—The subchloride, or sulphur monochloride, S,Cl, = 135-06, is the most important of these, since it is employed in the process of vulcanising caoutchouc. It is very easily prepared by passing dry chlorine over sulphur very gently heated in a retort (Fig. 126); the sulphur quickly melts, and the sulphur monochloride distils over into the receiver asa yellow volatile liquid, boiling at 138°, which has a most peculiar odour. It fumes strongly in air, the moisture decomposing it, forming hydrochloric and sulphurous acids, and caus- ing a deposit of sulphur upon the neck of the bottle; 28,Cl, + 3HOH = 4HCl = + SO(OH), + 38. Fie. 126. When poured into water it sinks (sp. gr. 1-709 at 0°) and slowly decomposes ; the solution contains, besides hydrochloric and sulphurous acids, some of the acids containing a larger proportion of sulphur. If phosphorus dissolved in carbon disulphide be mixed with sulphur monochloride, the liquid will take fire on addition of ammonia. The specific gravity of the vapour is 4-7, showing that it is 68 times as heavy as hydrogen and therefore has the formula S.Cl.. Sulphur dichloride (SClz) is a far less stable compound than the preceding chloride from which it is obtained by the action of an excess of chlorine. It is a dark red fuming liquid which solidifies at — 80°, easily resolved, even by sunlight, into free chlorine and sulphur monochloride. Sulphur tetrachloride (SCl,) has been obtained, by treating the dichloride with liquid chlorine in sealed tubes, as an unstable solid, m.pt. — 31°. It forms compounds with chlorides of other elements. ; Corresponding bromides and iodides of sulphur are known. Of these the di- iodide (SI,) is a crystalline unstable substance, produced by the direct union of its elements and occasionally employed in veterinary medicine under the name of black sulphur. Sulphur heaafluoride (SF,) is formed on passing fluorine over sulphur ina copper tube. It is a colourless, odourless gas having a density of 5-03, solidifying to white crystals at — 55°. Its most remarkable property is its inertness, in which it simulates nitrogen. It will not react with hydrogen even when heated, though it does so when sparked. Sodium can be melted - it, but not more strongly heated, without change. 12 178 SELENIUM SELENIUM, Se = 79.2. Selenium (Ze\jvn, the moon) is a rare element, very closely allied to sulphur in ite natural history, physical characters, and chemical relations to other bodies. It is found sparingly in the free state associated with some varieties of native sulphur, but more commonly in combination with metals, forming selenides, which are found together with the sulphides. The iron pyrites of Fahlun, in Sweden, is especially remarkable for the presence of selenium, and was the source whence this element was first obtained. The Fahlun pyrites is employed for the manufacture of oil of vitriol, and in the leaden chambers a reddish-brown deposit is found, which was analysed by Berzelius in 1817 and found to contain the new element. In order to extract selenium from the seleniferous deposit of the vitriol works, this may be boiled with sulphuric acid diluted with an equal volume of water, and nitric acid added in small portions until the oxidation is completed, when no more red fumes will escape. The solution, containing selenious and selenic acids, is largely diluted with water, filtered from the undissolved matters, mixed with about one-fourth of its bulk of hydrochloric acid, and somewhat concentrated by evaporation, when the hydrochloric acid reduces the selenic to selenious acid— H,Se0, + 2HCl = H,SeO;, + H,O + Ch. A current of sulphurous acid gas is now passed through the solution, when the selenium is precipitated in fine red flakes, which collect into 4 dense black mass when the liquid is gently heated ; H,SeO3; + H,O + 280, = 2H,SO, + Se. The proportion of selenium in the deposit from the leaden chambers is variable. The author has obtained 3 per cent. by this process. Like sulphur, selenium exists in an amorphous and a crystalline form, and more than one of the latter appear to exist. Amorphous selenium is the red precipitate formed by precipitating the element, either as described above or by adding an acid to a solu- tion of it in potassium cyanide. When kept at 100° for some time this form of selenium suddenly changes into the grey crystalline variety with much evolution of heat. Amor- phous selenium has sp. gr. 4-26 and is soluble in CS, ; it becomes plastic a little above 100°, and if melted and cooled quickly it forms a vitreous mass (sp. gr. 4-28), still amor- phous, but if carefully cooled so that it may superfuse it solidifies to the grey crystalline form (sp. gr. 4-8) ; but when less carefully cooled it solidifies to a mass of red monoclinic prisms isomorphous with monoclinic sulphur and of sp. gr. 4-47. These crystalline forms are insoluble in CS,. Amorphous and monoclinic selenium are very poor conductors of electricity, but the grey crystalline form is a fair conductor and a better one in light than in darkness, a property which is applied in apparatus for seeing at a distance. Selenium boils at 680°, and its vapour shows much the same variation in density as that exhibited by sulphur. Selenium is less combustible than sulphur ; when heated in air it burns with a blue flame and emits a peculiar odour like that of putrid horse-radish, which appears to be due to the formation of a little selenietted hydrogen from the moisture of the air. The odour serves for the detection of selenium compounds when they are heated on charcoal. When heated with oil of vitriol, selenium forms a green solution which deposits the selenium again when poured into water. Selenium dioxide (SeO,), corresponding with sulphur dioxide, is the product of combustion of selenium in oxygen. It is best obtained by dissolving selenium in boiling nitric acid (which would convert sulphur into sulphuric acid) and evaporating to dry- ness, when the selenium dioxide remains as a white hygroscopic solid which sublimes in needle-like crystals when heated. When dissolved in water it yields selenious acid, SeO(OH)s, which can be crystallised. Selenic acid (H»8eO, or SeO,(OH),). = Petaasinn selenate is formed when selenium is oxidised by fused nitre ; 2KNO, + Se = K,SeO, + 2NO. By dissolving the potas- sium selenate in water and adding lead nitrate, a precipitate of lead selenate (PbSeQ,) is obtained, and if this be suspended in water and decomposed by passing hydrosulphuric acid gas, lead will be removed as insoluble sulphide and a solution of selenic acid will be obtained; PbSeO, + H.S = H,SeO, + PbS. This solution may be evaporated TELLURIUM 179 till it has a sp. gr. of 2-6 (when it very closely resembles oil of vitriol) and heated in a vacuum at 180° so long as any distils over ; the residue will crystallise on cooling. The crystals (sp. gr. 2-95) melt at 58° and are deliquescent ; the hydrate, H,SeO,.H,O melts at 25°. It is decomposed at 260° into H,O, SeO,, and O. It oxidises the metals as oil of vitriol does, and even dissolves gold. The selenates closely resemble the sul- phates, but they are decomposed when heated with hydrochloric acid, chlorine being evolved and selenious acid produced. They are isomorphous with the sulphates (p. 299). Hydroselenic acid, or selenietted hydrogen (H»Se), is the analogue of sulphuretted hydrogen, and is produced by a similar process, by treating ferrous selenide, FeSe, with acid. It is even more offensive and poisonous than that gas, and acts in w similar way upon metallic solutions, precipitating the selenides. There are two chlorides of selenium: the monochloride, Se,Clp, obtained by the action of chlorine on selenium, a brown volatile liquid of sp. gr. 2-9, decomposed by water, corresponding with sulphur monochloride; and the tetrachloride, SeCl, a yellow crystalline solid, yielding on contact with water selenium oxychloride, SeOCle, a yellow liquid, b.-pt. 179-5°. Notwithstanding the resemblance between the two elements, sulphides of selenium are known, probably SeS, and SeS;. The former is obtained as a yellow precipitate when hydrogen sulphide is passed into solution of selenious acid. TELLURIUM, Te=127.5. Tellurium (from éellus, the earth) was discovered by Kaproth in 1798, and is connected with selenium by analogies stronger than those which connect that element with sulphur. It is even less frequently met with than selenium, being found chiefly in certain Transylvanian gold ores. It occasionally occurs in an uncombined form, but more frequently in combination with metals. It has recently been found in Colorado, masses of native tellurium up to 12 kilos in weight having been met with ; also coloradoite, or mercuric telluride, HgTe. Bismuth telluride, or tetradymite, BigTe;, has been found in California, and lead telluride, or altaite, in North Carolina. Foliated or graphic tellurium, or sylvanite, is a black material con- taining the tellurides of silver and gold. Arsenical pyrites sometimes contains tellurium, apparently as TeS.. Tellurium is extracted from the foliated ore by a process similar to that for obtaining selenium. From bismuth telluride it is procured by strongly heating the ore with a mixture of potassium carbonate and charcoal, when potassium telluride is formed, which dissolves in water to a purple-red solution, wherefrom tellurium is deposited on exposure to air; K,Te + O + H,O = 2KOH + Te. It is purified by sublimation in hydrogen, when it is deposited as white lustrous hexagonal rhombohedra, isomorphous with 8 and Se. ; Considerable quantities of tellurium are now obtainable from the sludge deposited in the electrolytic cells in which copper is refined, the crude metal having collected the tellurium contained in the original ore. Tellurium much more nearly resembles the metals than the non-metals in its physical properties (sp. gr. 6-2), and is on that account often classed among the former, but it is not capable of forming a true basic oxide. In appearance it is very similar to bicmuth (with which it is so frequently found), having a pinkish metallic lustre and being, lke that metal, crystalline and brittle. When precipitated it is a black amorphous powder, which becomes crystalline, with evolution of much heat, when warmed. The two allo- tropes exhibit different specific heats. It fuses at 455° and boils, yielding a yellow vapour, of normal vapour density, at 1390°. When heated in air it burns with a blue flame edged with green, and emits fumes of tellurium dioxide (TeO.) and a peculiar odour. ‘Like selenium, tellurium is dissolved by strong sulphuric acid, yielding a purple- red solution, from which water precipitates it unchanged. The oxides of tellurium correspond in composition with those of sulphur. Tellurous acid (H,TeO,) is precipitated when a solution of tellurium in dilute nitric acid is poured into water. If the nitric solution is boiled, a white crystalline precipitate of tellurous anhydride, TeO., sp. gr. 5-8, is obtained, but when the solution is evaporated a well- 180 SULPHUR GROUP—REVIEW crystallised basic nitrate, Te.03(OH)NO;, separates. Unlike selenious acid, tellurous acid is sparingly soluble in water. The anhydride is easily fusible, forming a yellow glass, which becomes white on cooling, and may be sublimed unchanged. Tellurous acid is rather a feeble acid, and with some of the stronger acids the anhydride forms soluble compounds in which it takes the part of a very feeble base. Telluric acid (H,TeO,4) is also a feeble acid obtained by oxidising tellurium with nitre, precipitating the potassium tellurate with barium chloride, and decomposing the barium tellurate with sulphuric acid. On evaporating the solution, crystals of telluric acid (H,TeO,.2H,O) are obtained, which become H,TeO, at a moderate heat, and when heated nearly to redness are converted into an orange-yellow powder, which is the anhydride, TeO . In this state it is insoluble in water, acids, and alkalies. When strongly heated it evolves oxygen and becomes tellurous anhydride. The tellurates are unstable salts which are converted into tellurites when heated. Solutions of alkali tellurates yield a precipitate of tellurium when boiled with alkali carbonates and glucose. Telluretted hydrogen or hydrotelluric acid (HgTe) exhibits in the strongest manner the chemical analogy of tellurium with selenium and sulphur. It is a gas of dreadful odour and similar to H,S in most of its properties. When its aqueous solution is exposed to the air, it yields a brown deposit of tellurium. When passed into metallic solutions it precipitates the tellurides. The gas is prepared by decomposing telluride of zinc with hydrochloric acid, or from its elements directly. The most characteristic property of tellurium compounds is that of furnishing the purple solution of potassium telluride when fused with potassium carbonate and char- coal and treated with water ; in the total absence of oxygen, however, the solution is colourless. Two solid chlorides of telluriwm have been obtained ; TeCl, is a black solid with a violet-coloured vapour, and is decomposed by water into tellurium and TeCl,. The latter may be obtained as a white crystalline volatile solid, decomposed by much water into hydrochloric and tellurous acids. Carbon telluride (CTeg) is known. The atomic weight of tellurium is of exceptional interest as it is slightly higher than that of iodine, and so clashes with the periodic classification. Numerous exhaustive researches have failed to remove the difficulty. Review of the Sulphur Group of Elements.—The four elements— oxygen, sulphur, selenium, and tellurium—exhibit a relation of a similar character to that observed between the members of the chlorine group, both in their physical and chemical properties. Oxygen stands somewhat apart, just as fluorine did among the halogens, but its compounds with other elements are similar in constitution to those of the other three. Their position in the sixth group signifies their hexavalency, which is apparent in the trioxides, &c. ; oxygen, however, does not form hexavalent compounds. In the dioxides, &c., they are quadrivalent, as oxygen and sulphur are also in the oxonium and sulphoniwm compounds (q.v.). In the hydrides, &c., they are bivalent. Sulphur is a pale yellow solid, easily fusible and volatile, without any trace of metallic lustre, and of sp. gr. 2-05, melting at 115° and boiling at 444°. Selenium is either a red powder or a lustrous mass appearing black, but transmitting red light through thin layers, of sp. gr. 4-8, melting-point 217°, and boiling-point 680°. Tellurium has a brilliant metallic lustre, sp. gr. 6-2, melting-point 455°, and boiling-point 1390°. Oxygen (atomic weight, 16) is by far the most energetic of the group, but of the remainder, sulphur (atomic weight, 32) has the most. powerful attrac- tion for oxygen, hydrogen, and the metals. Selenium (atomic weight, 79) ranks next in the order of chemical energy. Tellurium (atomic weight, 127-5) has a less powerful attraction for oxygen, hydrogen, and the metals than either sulphur or selenium has. This element appears to stand on neutral ground between the non-metallic bodies and the less electro-positive metals. Allotropy, which is not found amongst the halogens, is well marked. THE PHOSPHORUS (FIFTH) GROUP Nirrocen, PHosrpHorus, ARSENIC. NITROGEN, N = 14.01. NiTROGEN was early recognised as the characteristic element contained in nitre, whence its name (p. 52) ; and also in the free state as that constituent of air occurring in greatest proportion. The free element has already been dealt with under “ Air,” so that it now remains to describe its compounds. A chemically “active” modification of nitrogen has recently been described by R. J. Strutt. It is produced when ordinary nitrogen is subjected to the Leyden jar discharge, and glows for a short time after it has left the region of the discharge while it returns to the normal condition, presumably during the recombination of dissociated atoms. It combines with phosphorus, converting much of it into red phosphorus. It has a large electrical conductivity and combines with other elements and compounds, developing their line spectra. Nitric oxide reacts with glowing nitrogen, forming nitrogen peroxide (probably 2NO + N = NO, + Ng). Hydrogen is not affected by it. In the combined state nitrogen is one of the four elements found through- out the animal and vegetable kingdoms, especially in proteid or albuminoid and ammonia-like bodies. Vast quantities occur as nitre or saltpetre, potassium nitrate (KNO,) widely distributed in soils, forming incrustations on the surface in India and elsewhere during the dry season ; as cubic nitre or Chili saltpetre, sodium nitrate (NaNO,), in S. America ; as ammonium compounds, widely distributed, and in coal. But in each of these the com- pound is the product of bacterial or other life, so that ultimately nearly all nitrogen compounds originate in biochemical activity. The cycle in nature is represented in the following diagram : Leguminous plants with the help of bacteria Organic Atmo- : ————— nitrogen spheric Atmospheric _ Nitric _Vegetable compounds nitrogen electricity me life in plants Denitrifying micro- | and animals organisms r and other disintegrat- ing influences Changes in viegetable and animal organi/sms, followed Nitratilon b cs A intel y by decomposition by micro- : rganis hs organjisms ore es i Conversion into Nitrous nitrous acid Am- acid by micro- monia organisms Fic. 127. It would appear that at least two micro-organisms are concerned in nitrification, i.e. the production of nitrates. The one induces the formation of nitrites from the ammonia, whilst the other induces oxidation of these to nitrates. Nitrification can occur only when some basic substance, like calcium carbonate, is present to neutralise the acids produced ; being dependent on a micro-organism, it can proceed only at temperatures which are not inhibitory to the life of the organism (between 0° and 55°). Darkness fayours the process, 181 182 AMMONIA—OCCURRENCE In the mineral kingdom proper nitrogen is practically unknown, except as ammonia of volcanic origin. Its position in the fifth group declares its pentavalency, but it is even more frequently trivalent. It forms compounds, nitrides, with the majority of the elements, those with hydrogen and the metals, e.g. NH, LiN;, being usually exothermic, though Hg,N, is an exception, while those with electro-negative elements, e.g. CpNe, NO, NCl3, are frequently endothermic. The temperature at which nitrides are formed varies greatly ; Mg,Np, CasNo, ALN, below 800°, but the nitrides of Fe, Cu, &., above 1250°. Several of them are magnetic ; Mn,N, is almost as much so as iron, Somewhat’ similar results follow the heating of metals in ammonia. In contrast with the inertness of nitrogen itself, the compounds usually exhibit very pronounced and peculiar properties. Many of them affect the organs of smell and taste and physiologically act most powerfully, e.g. ammonia, pyridine, nitric acid, the alkaloids, while in numerous instances the compounds are metastable, and the majority of explosives depend on some link with nitrogen. In organic chemistry nitrogen exercises more markedly than any other element except carbon the capacity for com- bining with itself, forming “‘ chains ” and “rings ” of N-atoms (see Organic Chemistry) It is the fundamental element in most organic dyestuffs. It shows asymmetry (g.v.). All the nitrogen in any compound may be recovered either as free nitrogen or as ammonia. Compounpbs oF NITROGEN witH HYDROGEN. Ammonia, NH, = 17-03, belongs to organic rather than to inorganic nature. Its mineral sources are chiefly volcanic ; ammonium sulphate is found in Tuscan boric acid, and occurs as mascagnine in the form of an efflorescence on recent lavas. It is generally a product of the decomposition of nitrogenous matter. Dead animal and vegetable matters yield it in putrefaction. Bones furnish it by destructive distillation ; so does coal, the fossilised plant. Its compounds are found in beds of guano (the excrement of sea-fowl), and the most important of them, sal ammoniac, was first made in Egypt from the dung of camels. The proportion of ammonia existing in atmospheric air is so small that it is difficult to determine it with precision; it appears, however, not to exceed 5 milligrams in a cubic metre, for although ammonia is constantly sent forth into the air by the putrefaction of animal and vegetable substances containing nitrogen, it is soon absorbed by water, and even by earth and other porous solids. Rain water contains from 1 to 2 parts per million of am- monia. With the aid of certain micro-organisms in the soil, certain families of plants, especially the Leguminose, can utilise the uncombined nitrogen of the atmosphere as food for their growth, but for a large number of plants the chief supply of nitrogen is that contained in the ammonia, nitrites, and nitrates contained in the air, the soil, and the water. During the life of an animal, it restores to the air the nitrogen which formed part of its wasted organs, mainly as urea and uric acid in the urine, the nitrogen of these being eventually converted into ammonia when the excretion undergoes putrefac- tion. Dead animal and vegetable matter, when putrefying, restores its nitrogen to the air, chiefly in the forms of ammonia and substances closely allied to it, but partly also, it is said, in the free state ; when such matter is burnt all the nitrogen is liberated in an uncombined condition. Ammonia appears to be formed from atmospheric nitrogen by the growth of fungi (which evolve hydrogen) and by the decay of wood. Nitrogen is also slowly absorbed from air by sawdust mixed with lime and by glucose mixed with soda, the nitrogen being evolved as ammonia when these materials are afterwards heated with soda-lime. Ammonia may be produced by the com- bination of nitrogen and hydrogen, induced by electric discharge, on account AMMONIA—PREPARATION 183 of “ionisation ” of the gases and not on account of temperature, but its formation soon stops unless it is absorbed by an acid as fast as it is produced, because when 6 per cent. of the mixed gases has become converted into ammonia the compound begins to be decomposed by the electric sparks.1 The chief commercial source of ammonia is the ammoniacal liquor resulting as a by-product from the destructive distillation of coal for the manufacture of gas.?_ This liquor contains ammonia in combination with carbonic and hydrosulphuric acids. To recover the ammonia the liquor is heated with lime in a still; the ammonia and hydrosulphuric acid are thus expelled and are conducted into a covered tank containing sulphuric acid or hydrochloric acid, which absorbs the ammonia and allows the hydrosulphuric acid to escape through a pipe in the cover of the tank, to be burnt, or otherwise disposed of, in order that it may not cause a nuisance by its evil odour and poisonous properties. Ammonium sulphate or chloride (according to which acid has been used) crystallises from the acid in the tank. The former is sold as a manure ; the latter is generally used for making pureammonia. The crys- tals of ammonium chloride are moderately heated in an iron pan to deprive them of tar, and are finally purified by sublimation (p. 33), that is, by con- verting them into vapour and allowing this vapour to condense again into the solid form. For this purpose the crystals are heated in a cylindrical iron vessel covered with an iron dome lined with fireclay. The ammonium chloride rises in vapour below a red heat, and condenses upon the dome in the form of the fibrous cake known in commerce as sal ammoniac. To obtain ammonia from this salt, an ounce of it is reduced to coarse powder, and rapidly mixed with 2 oz. of powdered quicklime. The mixture is gently heated in a dry flask (Fig. 128), and the gas, being little more than half as heavy as air, may be collected in dry bottles by displacement of Fie. 128. air, the bottles being allowed to rest upon a piece of tin plate which is per- forated for the nai of the tube. To ascertain when the bottles are filled, a piece of red litmus-paper may be held at some little distance above the mouth, when it will at once acquire a blue colour if the ammonia escapes. The bottles should be closed with greased stoppers. The action is explained by the following equation : QNH,Cl + CaO = CaCl + H,O + 2NH; Ammonium Lime. Calcium Ammonia. chloride. chloride. 1 The heat evolvedin the combination N + H, = NH, isonly 1195 gram-calories; hence it is not surprising ion is difficult to realise. 2 : : my Coualderable quantities of ammonia are now being recovered from the products of combustion obtained from blast furnaces (q.v.), in which, of course, it originates from the distillation of coal. The ovens in which coke is manufactured are also furnishing ammonia. 184 AMMONIA—PROPERTIES The readiest method of obtaining gaseous ammonia for the study of its properties consists in gently heating the strongest solution, the liquor ammonie fortis of commerce (p. 185), in # retort or flask provided with a bent tube for collecting the gas by dis- placement (Fig. 129). The gas is evolved from the solution at a very low temperature, and may be collected unaccompanied by steam. Other technical sources of ammonia are (a) by the hydrolysis of cyanamide (q.v.) by the action of alkalies ; (b) destructive distillation of nitrogenous organic matter, e.g. town refuse ; (c) by electric processes which are essentially synthetic, e.g. by submitting a mixture-of nitrogen and producer gas (hydrogen and carbon monoxide) to the action of non-luminous electrical discharges in the presence of steam and spongy platinu~ at temperatures below 80°. Ammonia is a colourless gas of very pungent characteristic odour, having an alkaline reaction on moistened red litmus-paper. It is much lighter than air; sp. gr. 0-597; 1 1. weighs 0-771 gram; it can easily be reduced to the liquid state (p. 81), when it has a sp. gr. of 0-69 at — 40°; 0-636 at 0° ; 0-623 at 10°. At 10° a pressure of 6} atm. suffices for its liquefaction. Boiling-point, — 33-5°. Crit. temp., 130° ; crit. press., 115 atm. Its specific heat is remarkably high (see p. 32) and varies greatly with the temperature : at — 46° to — 26° it is 0-894; at 0°, 1-118; at 20°, 1-161; at 70°, 1-269. Its high specific heat in conjunction with its great volatility makes liquid ammonia a most effectual freezing agent; see p. 81. As with water, the specific heat of the vapour approximates one-half the values for the liquid. Like water, it is an excellent solvent ; e.g. it dissolves salts, iodine, sulphur, phosphorus, &c. ; it conducts electricity very badly, and ionises strongly sub- stances dissolved in it ; but sometimes forming compounds ; e.g. it dissolves potassium and sodium, forming blue solutions containing KH,N.NH,K and NaH,N.NH,Na. At low temperatures it solidifies to white crystals which melt at — 77°. Ammonia is absorbed by water in greater proportion by volume than any other common gas, 1 vol. of water absorbing more than 700 vols. of ammonia at the ordinary temperature, and becoming 14 vols. of solution of ammonia. During the dissolution of the gas much more heat is evolved than corresponds with the heat of liquefaction of the gas ; } this excess of heat can be attributed only to chemical combination ; but no definite compound of ammonia with water has been obtained, and the gas gradually escapes on exposing the solution to the air. It is usual, however, to assume that ammonium hydrate has been formed; NH, + H,O = NH,OH (p. 187). As is the case with all solutions of gases, the quantity of ammonia retained by the water is dependent upon the temperature and pressure ; the escape of the gas from the solution is attended with great production of cold, much heat becoming latent in the conversion of the ammonia from the liquid to the gaseous state. The rapid absorption of the gas by water is well shown in the manner described under hydrochloric acid ; see p. 110. That the amount of ammonia in solution varies with the pressure may be proved by filling a barometer tube, over 30 in. long, with mercury to within an inch of the top, filling it up with strong ammonia, closing the mouth of the tube, and inverting it with its mouth under mercury ; on removing the finger the diminished pressure caused by the gravitation of the column of mercury in the tube will cause the solution of ammonia to boil, from the escape of a large quantity of the gas, which will rapidly depress the mercury. If the pressure be now increased by gradually depressing the tube in a tall cylinder of mercury (Fig. 130), the water will again absorb the ammoniacal gas. To exhibit the easy expulsion of the ammoniacal gas from water by heat, a mode- rately thick glass tube, about 12 in. long and 4 in. in diameter, may be nearly filled with mercury and then filled up with strong solution of ammonia ; on closing it with * Seventeen grams of ammonia evolve 20,300 gram-units of heat when dissolved in excess of water. AMMONIA—SOLUTION 185 the thumb and inverting it into a vessel of mercury (Fig. 131), the solution will, of course, rise above the mercury to the closed end of the tube. By grasping this end of the tube in the hand, a considerable quantity of gas may be expelled, and the mercury will be depressed. If a little hot water be poured over the top of the tube, the latter will become filled with ammoniacal gas, which will be absorbed again by the water when the tube is allowed to cool, the mercury returning to fill the tube. Solution of ammonia, which is an article of commerce, may be prepared by conducting the gas into water contained in a two-necked bottle, the second neck being connected with a tube passing into another bottle containing water, in which any escaping ammonia may be condensed. The strength of the solution is inferred from its specific gravity, which is lower in proportion as the quantity of ammonia in the solution is greater. Thus at 15° a solution of sp. gr. 0-880 contains 35-60% of ammonia (the liquor ammonie fortis of commerce) ; sp. gr. 0-888, 32-5% (this is the liquor ammonie fortis of the British Pharmacopeeia, which, however, gives the sp. gr. as 0-891); sp. gr. 0-925, 20-18%; sp. gr. 0-959, 10% (liquor ammonie, : B.P.), still known as spirit of hartshorn from the cir- cumstance that at one time it was obtained for medicinal purposes by distilling shav- ings of that Fie. 131. Fie. 132. material. For trade purposes the specific gravity is taken with an ordinary hydrometer (Fig. 132) graduated in decimals of specific gravity, or with an ammonia meter, which is the same instrument marked with the percentages of ammonia indicated instead of the usual specific gravity decimals. Ammonia is very soluble in alcohol. In 100% alcohol at 20° the saturated solution contains 7-5% of the gas and has a sp. gr. 0-791 ; 90% alcohol at 20°, 10:2%, sp. gr. 0-795. This last solution is a commercial article. Other alcohols, acetone, benzene, &c., also dissolve ammonia freely. Ammonia is feebly combustible in atmospheric air, as may be seen by holding a taper just within the mouth of an inverted bottle of the gas, which burns with a peculiar livid flickering light around the flame, but will not con- tinue to burn when the flame is removed, because the temperature produced by such a feeble combustion of the hydrogen in air is not high enough to continue the decomposition of the ammonia. During its combustion the hydrogen.is converted into water, and the nitrogen set free. In oxygen, however, ammonia burns with a continuous flame. This is very well shown by surrounding a tube delivering a stream of ammonia (obtained by heating strong solution of ammonia in a retort) with a much wider tube open at both ends (Fig. 133) through which oxygen is passed by holding a flexible tube 186 AMMONIA—COMPOSITION from a gas-bag or gas-holder underneathit. On kindling the stream of ammonia it will give a steady flame of 10 in. to 12 in. long. The elements of ammonia are easily separated from each other by passing the gas through a red-hot tube (even at 450° some decomposition occurs), or Fic. 133. Fre. 134. still more readily by exposing it to the action of the high temperature of the electric spark, when the volume of the gas rapidly increases until it is doubled, 2 vols. of ammonia being decomposed into 1 vol. of nitrogen and 3 vols. of hydrogen, showing that the molecule of ammonia probably contains atoms of N and H in the proportion of 1 : 3. For this experiment a measured volume of NH; is confined over mercury (Fig. 134), in a tube through which platinum wires are sealed for the passage of the spark from an induction-coil. The volume of the gas is doubled in a few minutes, and if the tube be furnished with a stop-cock, A, the presence of free hydrogen may be shown by filling the open limb with mercury and kindling the gas as it issues from the jet. The decomposition ceases when only 3 per cent. of ammonia remains (p. 183). Another method of demonstrating that ammonia is formed from 1 vol. N and 3 vols. H takes advantage of the fact that. when chlorine reacts with ammonia the hydrogen of the latter combines with the former to make hydrogen chloride, HCl, which may readily be absorbed by water, leaving the nitrogen. The tube, A (Fig. 135), graduated into three equal parts, is filled with chlorine. A strong solution of ammonia having been poured into the funnel, B, the stop-cock is opened so that some of the NH; may enter the tube. A violent reac- tion ensues, and white fumes of ammonium chloride, NH,Cl, are formed, due to the combination of the HCl produced with excess of NH3;. More ammonia is now admitted, and the tube is shaken. Owing to the fact that the NH,Cl pro- duced is a solid and dissolves in the water, the pressure in the tube is now below that of the atmosphere, so that when the bent tube, C, dipping into water, is attached to the funnel and the stop-cock is opened, water rushes in to fill two-thirds of the tube. The remaining gas is found to be nitrogen. Fie. 135. 2NH, + 3Cl, = 6HCl + N,. As might be expected from its powerfully alkaline character, ammonia AMMONIUM AMALGAM 187 exhibits a strong attraction for acids, which it neutralises perfectly. If a ‘bottle of ammonia gas, closed with a glass plate, be inverted over a similar bottle of hydrochloric acid gas, and the glass plates withdrawn (Fig. 136), the gases combine, unless they are perfectly dry (cf. p. 58), with disengagement of much heat, forming a white solid ammonium chloride (NH,Cl), in which the acid and alkali have neutralised each other. Again, if ammonia be added to diluted sulphuric acid, the latter will be entirely neutralised, and on evaporating the solution, crystals of ammonium sulphate, (NH,),SO,, may be obtained. The salts thus produced by neutralising the acids with solution of ammonia bear a strong resemblance to those formed by neutralising the same acids with solutions of potash and soda, a circumstance which would encourage the idea that the solution of ammonia must contain an alkaline hydroxide (NH,OH), similar to KOH or NaOH. It is difficult to believe that the solution of ammonia does really contain ammonium hydroxide (NH; + H,0 = NH,OH), when we find it evolving ammonia so easily, although at 0° the amount of ammonia dissolved approaches that required for this formula ; but it is equally difficult, upon any other hypothesis, to explain the close resenitilance between the salts obtained by neutralising acids with this solution and those furnished by potash and soda. _ Berzelius was the first to make an experiment which appeared strongly to favour this view. The negative pole of a galvanic battery was placed in contact with mercury at the bottom of a vessel containing a strong solution of ammonia, in which the positive ‘pole of the battery was immersed. Oxygen was disengaged at this pole, whilst the mercury in contact with the negative pole swelled to four or five times its original bulk and became a soft solid mass, still preserving, however, its metallic appearance! At a very low temperature the mass becomes dark grey and crystalline. So far the result of the experiment resembles that obtained when potassium hydroxide is decomposed under similar circumstances, the oxygen separating at the positive pole and the potas- ‘sium at the negative, where it combines with the mercury. Beyond this, however, the analogy does not hold; for in the latter case the metallic potassium can be readily separated from the mercury, whilst in the former all attempts to isolate the ammonium have failed, for the soft solid mass resolves itself, almost immediately after its prepara- tion, into mercury, ammonia (NH;), and hydrogen, 1 vol. of hydrogen being sepa- rated for 2 vols. of ammonia. This would also tend to support the conclusion that a substance having the composition NH, + H or NH, had united with the mercury ; and since the latter is not known to unite with any non-metallic substance without losing its metallic appearance, it would be fair to conclude that the soft solid was really an amalgam of ammonium. However, the increase in the weight of the mercury is 0 slight, and the “amalgam,” whether obtained by this or by other methods, is <0 unstable, that it would appear safer to attribute the swelling of the mercury to a physical change caused by the presence of the ammonia and hydrogen gases. This view is sup- ported by the observation that when the amalgam is subjected to pressure its volume varies nearly in the inverse ratio of the pressure. The ordinary mode of exhibiting the production of the so-called amalgam of ammo- nium consists in acting upon the ammonium chloride (NH,Cl) with sodium amalgam. A little pure mercury is heated in a test-tube and a pellet of sodium thrown into it, when combination occurs with great energy. When the amalgam is nearly cool it may be poured into a larger tube containing a moderately strong solution of ammonium chloride ; the amalgam at once swells to many times its bulk, forming a soft solid li ghter than the water, which may be shaken out of the tube as a cylindrical mass, rapidly effervescing with evolution of NH, + H, and soon recovering the original volume and liquid condition of the mercury. 1 This experiment is more conveniently made with a strong solution of ammonium sulphate in a common ‘plate. A sheet of platinum connected with the positive pole of the battery (five or six Grove’s cells) is immersed in the solution, and a piece of filter-paper is laid upon it, on which is a globule of mercury ; the negative pole is plunged into the latter. Fie. 136. 188 DISSOCIATION Ammonia is easily expelled from its salts by an alkali, so that an ammo- nium salt is easily detected by heating the suspected substance with caustic soda, when the odour of ammonia will be perceived : NH,Cl + NaOH = NaCl + NH; + H,0. When an ammonium salt is heated it is split up into ammonia and the acid from which it is formed, ammonium chloride, for example, becoming ammonia and hydrogen chloride, NH,Cl = NH, + HCl; 1 but if these pro- ducts be allowed to cool together, they combine again to produce the original salts. This behaviour furnishes an example of the phenomenon called dissociation, which differs from decomposition in that the constituents into which a Gompound is disséciated by heat recombine if they are allowed to cool together ; the products of the decomposition of a compound, on the other hand, do not so re-combine. The dissociation of ammonium chloride may be demonstrated by taking advantage of the low specific gravity of NH, as compared with that of HCl (NH; is 17/2 = 8-5, and H.Cl 36-5/2 = 18-25 times heavier than H). On this account NH, diffuses more rapidly than HCl. A fragment of ammonium chloride is placed in a narrow test-tube with a plug of asbestos at a little distance above it, a piece of red litmus-paper is placed in the tube, and the ammonium chloride and the asbestos are heated ; the NH3, being lighter, diffuses through the asbestos before the HCl does and blues the red litmus- paper, but soon afterwards the HCl diffuses through and the litmus is again reddened. The volatility of ammonia and of the ammonium salts renders a solution of the gas useful as an alkali in cases, such as in analysis, where the fixed alkalies, potash and soda, would be objectionable on account of their non- valatility. -Ammonia finds application in making sodium carbonate (g.v.) and, as already explained, in freezing-machines. Although free nitrogen and hydrogen can only with difficulty be made to form ammonia by direct combination, this compound is often produced when combined nitrogen meets with nascent hydrogen. .g., if iron-filings be shaken with a little water in a bottle of air, so that they may cling round the sides of the bottle, and a piece of red litmus-paper be suspended between the stopper and the neck, it will be found to have assumed a blue colour in the course of a few hours, and ammonia may be distinctly detected in the rust whichis produced. It appears that the water is decom- posed by the iron in the presence of the carbonic acid of the air and water, and that the hydrogen liberated enters at once into combination with nitrogen, to form ammonia. In many ways besides those mentioned above, ammonia simulates water. It is to be noted that while water is H.O.H, ammonia is H.NH.H ; and it will be found in a surprisingly large number of instances, especially in organic compounds, that to compounds containing an NH-group there is a corresponding one containing an O-atom similarly situated in the molecule. Compare the amines R.NH, or R.NH.H (e.g. C.H;.NH.H, ethylamine) with the alcohols, R.O.H. (e.g. C,H;.0.H, ethyl alcohol) ; R stands for any radicle ; also the metallic amides, e.g. Na.NH.H, sodamide, with the hydroxides, eg. Na.O.H, sodium hydroxide; N,NH (p. 189) with N,O (p. 200). Not infrequently the H of the NH-group is exchanged for metals (p. 189). Ammonia has a tendency to combine as a whole with many metallic salts, much as water does ; a typical compound of this sort is CuSO,.5NH3. It readily loses ammonia when heated. Compare CuSO,.5H,O ; see also p. 513. There are numerous compounds of very various nature having the con- stitution of ammonia with one or more of its hydrogen atoms exchanged for some other element or radicle. Thus by passing dry ammonia over gently heated sodium, sodamide, NaNHg, is formed ; potassamide, KNH,, is simi- larly prepared. These are white waxy substances which melt (at 155° and 270° respectively) to greenish liquids and partly sublime; at a red heat they are converted into their elements. Water immediately decomposes them, yielding NaOH, or KOH and NH. It is customary to apply the term * Ammonium chloride does not dissociate if perfectly dry, HYDRAZINE 189 amide to these metallic derivatives, but otherwise amide is understood to signify a compound in which an acid radicle takes the place of a hydrogen atom in ammonia ; or one in which NH, is substituted for OH inanacid; e.g. CH,CO.OH acetic acid, CH,;CO.NH, acetamide ; HO.SO,.OH sulphuric acid, NH,.SO,.NH, sulphamide ; see also p. 224 and Amides. If the sub- stituent is basic, the compound is an amine ; e.g. CH,;.OH methyl alcohol, CH,.NH, methylamine. Hydrazine, NH,.NH, = 32-05, may be regarded as a combination of two unsaturated amidogen, NH,, groups, or radicles (cf. p. 197). Hydrazine is a product of reduction of hyponitrous acid (p. 206). To prepare hydrazine, 30 grams of potassium diazomethanedisulphonate (q.v.) is added in fine powder to a solution made by first saturating a 20 per cent. solution of KOH with SO, and then adding 10 grams of KOH. The mixture is warmed until colourless, heated to boiling with 150 c.c. of dil. H,SO, (1 : 5), filtered and cooled, whereupon hydrazine sulphate, NoH,.H2SO, crystallises, The sulphate is dissolved in a very little water and mixed with the exact quantity of KOH to convert the H,SO, into K,SO,, and with sufficient absolute alcohol to precipitate all the K,SO,. After filtration the alcohol is distilled and the temperature is raised to 118°, whereupon hydrazine hydrate, NoH,.H,O, distils. This is added to a retort containing BaO, heated for some hours at 110°, and finally distilled under diminished pressure in a current of hydrogen, when anhydrous hydrazine distils. A large quantity of hydrazine sulphate must be used for a successful result. Hydrazine is a colourless liquid of sp. gr. 1-013; it boils at 113-5° and melts at 1-4°. It dissolves in water, evolving much heat (37,800 cals. per gram-molecule), forming a hydrate, N,H,.2H,O, which passes into N,H,.H,O if the water is evaporated. The latter hydrate is remarkably stable, resem- bling the caustic alkalies in many respects, but of even more caustic properties ; it is a colourless fuming liquid of sp. gr. 1-03, melts at — 40° and boils at 120°. It is powerfully alkaline and corrodes cork, rubber, and even glass when heated, so that these materials must be avoided in its manufacture ; hydra- zine itself, however, does not attack glass. With acids hydrazine hydrate yields two classes of salts, e.g. N,H,.HCl and N,H,.2HCl; those with one molecular proportion of acid are the more stable. Hydrazine and its compounds are powerful reducing agents. Azoimide or hydrazoic acid,t N,H = 42-03.—When hydrazine hydrate is treated with nitrous acid in a cooled dilute solution it is converted into azoimide, ce H,N.NH, + NO.OH = <>NH + 2HOH. This compound is a colour- less liquid (b,-pt. 30° ; m.-pt. — 80°), characterised by its explosiveness and its foul odour. It is distinguished from the other compounds of nitrogen with hydrogen by its acid properties. It dissolves many metals with evolution of hydrogen and production of metallic azoimides, such as Zn‘i (Nz)p. It is noticeable that most nitrogen compounds in which the nitrogen is not present as NH2, or an equivalent group, have an acid character. ; ; Azoimide is obtained in only small quantity by the above reaction. Tt is most conveniently prepared by the interaction between sodamide and nitrous oxide, sodium azoimide, from which the free acid can be obtained, being produced ; NH,Na + N20 = N,Na + HO. Sodium is gently heated in a porcelain boat contained in a combustion tube through which dry ammonia is passed ; _when the metal has been completely converted into sodamide, a current of dry N20 is substituted for the NH3, the temperature being raised to about 200°. The sodium azoimide is transferred to a flask and distilled with dilute sulphuric acid. To the dilute solution of N,H which distils over silver nitrate is added, whereby silver azoimide, N, Ag, is precipitated ina white crystalline form. This is washed and distilled with dilute HSO,. A solution containing 27 per cent. of N3H is thus obtained ; it is fractionally distilled, and the + This compound has also been termed hydrogen nitride, but the name is unsuitable, 190 NITROGEN OXIDES first fraction, below 45°, is dried over calcium chloride and redistilled. The pure acid is a water-white, mobile liquid, b.-pt. 37°, m.-pt. — 80°. The 27 per cent. solution is a slightly viscid liquid, specifically heavier than water ; it evolves NH at the ordinary temperature, and the vapour gives thick clouds when in contact with ammonia. The acid corrodes the skin and produces giddiness and headache when inhaled. Most of the salts crystallise well, those of silver and mercurous mercury being insoluble ; they are all explosive, except those of the alkali metals. There is a remarkable similarity between azoimide and hydrochloric acid, which extends even to their salts, which resemble each other in solubility and crystalline form ; indeed, in the case of sodium azoimide the resemblance extends to the salt taste. Silver azoimide may conveniently be obtained by cautiously warming 1-5 grams of hydrazine sulphate with 4 c.c. of nitric acid of sp. gr. 1-3 and passing the NsH which is evolved into a solution of AgNO3. Lodo-azoimide, N3I, is produced by digesting an aqueous suspension of silver azoimide with an ethereal solution of iodine. It is a colourless, very explosive solid, with an odour recalling that of iodine cyanide. _ Hydroxylamine, NH,OH, forms a link between the compounds of nitrogen with hydrogen and those of nitrogen with oxygen ; see p. 206. Compounps oF NITROGEN WITH OXYGEN. Though these elements under ordinary conditions exhibit no attraction for each other, six compounds, which contain them in different proportions, have been obtained, viz. N,0, NO, N,O;, NO, (N,0,), N,0;. When a succession of strong electric sparks is passed through air (especially if mixed with oxygen) in a dry flask, a red gas, nitric peroxide (NO,) is formed ; if water be present this is absorbed and converted into nitrous and nitric acids; 2NO, + H,O = HNO, + HNO,. If the experiment be made in a U-tibe having one limb surmounted by a stoppered globe into which platinum wires are sealed (Fig. 137) filled with water coloured with blue litmus, the latter will soon be reddened by the acid formed and the air will diminish considerably in volume, eventually losing its power of supporting combustion owing to removal of oxygen. When a few inches of magnesium tape are burnt in a gas-jar of air, red fumes may be perceived on looking down ‘the jar at the close of the combustion, and the presence of N20, or NO, may be shown by drawing the residual air through a mixture of potas- = ~ sium iodide with a little starch and, acetic acid, when the Fic. 137. iodine is set free and blues the starch. This renders it probable that the electric spark causes the combination of nitrogen and oxygen on account of its high temperature. When ozonised air (p. 139) is passed into water, nitric acid is found in solution. Rain water contains about one part per million of nitric acid, in the form of nitrates. When hydrogen, mixed with a small quantity of nitrogen, is burnt, the water collected from it is found to have an acid taste and reaction, due to thé presence of a little nitric acid, produced by the combination of the nitrogen with the oxygen of the air under the influence of the intense heat of the nydrogen flame. : Since all the compounds of nitrogen and oxygen are obtained, in practice, from nitric acid, the chemical history of that substance may conveniently precede that of the oxides of nitrogen. ; , Production of nitrous and nitric acids from ammonia.—lf a few drops of a strong solution of ammonia are poured into a pint bottle, and ozonised air (from the tube for ozonising by induction, Fig. 105) is passed into the bottle, NITROGEN WITH OXYGEN 191 thick white clouds speedily form, consisting of ammonium nitrite (NH,NO,), the nitrous acid having been produced by the oxidation of the ammonia at the expense of the ozonised oxygen— 2NH, + 0; = H,O + NH,NO,. ey If copper filings be shaken with a solution of ammonia in a bottle of air white fumes will also be produced, together with a deep blue solution containing copper oxide and ammonium nitrite ; the act of oxidation of the copper appearing to have induced a simultaneous oxidation of the ammonia. A coil of thin platinum wire made round a pencil, if heated ===# to redness at the lower end and suspended in a flask (Fig. 138) Fig, 138. with a little strong ammonia at the bottom, will continue to glow for a great length of time, in consequence of the combination of the ammonia with the oxygen of the air at its surface, attended with great evo- lution of heat. Thick white clouds of NH,NO, are formed, and frequently red vapour of nitrous anhydride (N,O,) itself. A coil of thin copper wire acts in a similar manner. When a tube delivering oxygen is passed down to the bottom of the flask, the action is far more energetic, the heat of the platinum rising to whiteness, whereupon an explosion of the mixture of ammonia and oxygen ensues. After the explosion the action recommences, so that the explosion repeats itself as often as may be wished. It is unattended with danger if the mouth of the flask be pretty large, but it is advisable to surround the flask with a cylinder of coarse wire gauze. By regulating the stream of oxygen, the bubbles of that gas may be made to burn as they pass through the ammonia at the bottom of the flask. The oxidation of ammonia may also be shown by the arrangement represented in Fig. 139. Airis slowly passed from the glass gas-holder, B, through very weak ammonia in the bottle, a, into a hard glass tube having a piece of red litmus- paper at 6 anda plug of platinised asbestos in the centre, heated by a gas-burner ; a piece of blue litmus-paper is placed at c, and the tube is connected with a large globe, d. The red litmus at 6 is changed to blue by the ammonia, whilst the blue litmus at ¢ is reddened by the nitrous acid produced in its oxidation, and clouds of ammonium nitrite, accom- panied by red nitrous fumes, appear in d. To obtain all the results in perfection, small quanti- ties of am- monia must be successively : introduced Fie. 139. into a. In the presence of strong bases, and of porous materials to favour the change, ammonia may suffer further oxidation to nitric acid, which acts on the base to form a nitrate ; thus, 2NH, + CaO + 40, = Ca(NOg), (calcium nitrate) + 3H,0. . ee : It has already been seen that the rapid oxidation (combustion) of ammonia produces nitrogen and water. ; : Nitric Acid, or hydrogen nitrate, HNO; = 63-01. This most important acid is obtained from saltpetre, which is found as an incrustation upon the surface of the soil in hot and dry climates, as in some parts of India and Peru. The salt imported into this country from Bengal and Oude consists 192 NITRIC ACID of potassium nitrate (KNO,), whilst the Peruvian or Chilian saltpetre is sodium nitrate, or “nitrate” (NaNO,). Either of these will serve for the preparation of nitric acid. On the small scale, in the laboratory, nitric acid is prepared by distilling potassium nitrate with an equal weight (or more) of concentrated sulphuric acid. As an experiment, 100 grams of powdered nitre, thoroughly dried, are introduced into a stoppered retort (Fig. 140) and 70 c.c. of concentrated sulphuric acid poured upon it. Ags soon as the acid has soaked into the nitre, a gradually increasing heat is applied by an Argand burner, when the acid distils. It must be preserved in a stoppered bottle. When the acid has ceased distilling, the retort should be allowed to cool and filled with water. On heating for some time the saline residue will dissolve. The solution may mn : = then be poured into an evaporating dish and evapo- = eh =" rated to a small bulk. On allowing the concentrated Fre. 140 pe solution to cool, crystals of bisulphate of potash ; . or potassium hydrogen sulphate (KHSO,) are de- posited, w salt which is very useful in many metallurgical and analytical operations. The decomposition of KNO, by an equal weight of H,SO, is explained by the equation—KNO, + H,SO, = HNO; + KHSO,. It would appear at first sight that one-half of the sulphuric acid might be dispensed with, inasmuch as 1 mol. could be made to decompose 2 mols. of potassium nitrate, 2KNO, + H,SO, = 2HNO, + K,SO,, but it is found that when a smaller quantity of sulphuric acid is used, so high a temperature is required to decompose completely the saltpetre (the above equation then representing only the first stage of the action) that much of the nitric acid is decomposed ; and the normal potassium sulphate (K,SO,), which would be the final result, is not nearly so easily dissolved out of the retort by water as is the bisulphate. For the preparation of large Fie. 141. quantities of nitric acid, sodium nitrate is substituted for potassium nitrate, it being much cheaper, and furnishing a larger proportion of nitric acid. The decomposition of the sodium nitrate can be represented by the above equation if Na be substituted for K, and on comparing the equations it will be seen that 85 parts by weight of NaNO, yield the same quantity of HNOs as that yielded by 101 parts by weight of KNO;. The sodium nitrate is introduced into an iron retort (A, Fig. 141) and about five- sixths of its weight of sulphuric acid is poured upon it through the funnel. The retort is heated by the furnace, when the nitric acid passes off in vapour and is condensed in NITRIC ACID—PROPERTIES 193 the stoneware bottle (bombonne), D, and reflux worm condenser, E, contained in a tub of water. The strongest acid is thus collected in this bottle, but much uncondensed vapour and steam pass through pipe, F, into further bottles, G, in which a dilute acid is collected. The tower, H, containing perforated stoneware plates through which water trickles, condenses the vapours still uncondensed. The commercial acid is liable to contain chlorine, hydrochloric acid, and iodic acid (from sodium chloride and iodate in the nitrate), sulphuric acid, sodium sulphate, nitrogen oxides, and iron. It is purified by redistillation, the middle portion of the distillate being pure. In the preparation of nitric acid it will be observed at the beginning and towards the end of the operation that the retort becomes filled with a red vapour. This is due to the decomposition by heat of a portion of the colour- less vapour of nitric acid into water, oxygen, and nitric peroxide, 2HNO, = H,O + O + 2NO,, this last forming the red vapour, a portion of which is absorbed by the nitric acid, and gives it a yellow colour (red fuming nitric acid). The pure nitric acid is colourless, but if exposed to sunlight it becomes yellow, a portion suffering this decomposition. In consequence of the accu- mulation of the oxygen in the upper part of the bottle, the stopper is often forced out suddenly when the bottle is opened, and care must be taken that drops of this very corrosive acid be not spirted into the face. _ The strongest nitric acid (obtained by distilling perfectly dry nitre with an equal weight of pure oil of vitriol, and collecting the middle portion of the acid separately from the first and last portions, which are somewhat weaker) emits very thick grey fumes when exposed to damp air, because its vapour, though itself transparent, absorbs water very readily from the air, and con- denses into very minute drops of dilute nitric acid which compose the fumes. The weaker acids commonly sold in the shops do not fume so strongly. A cri- terion of the strength is afforded by the specific gravity. Thus the strongest acid, 100 per cent. HNOs, has the sp. gr. 152.1 The concentrated nitric acid usually sold by the operative chemist (double aquafortis) has the sp. gr. 1-42, and contains 70 percent. of HNO,. Acidum nitricum dilutum, B.P., contains 17-44 per cent., sp. gr. 1-101. At the present time many attempts, more or less successful, are being made to utilise atmospheric nitrogen, oxygen, and water for the manufacture of nitric acid by means of electricity or flame, a temperature of over 1200° being desirable. When hydrogen or coal-gas burns in air, small quantities of nitrous and nitric acids are pro- duced, apparently by the oxidation of atmospheric nitrogen ; and by suitably modify- ing the conditions, much as was described under ozone, nitrogen oxides are produced, and these yield nitrites and nitrates on absorption by alkalies. Better success attends the use of electricity. The mixture of gases is exposed to the temperature of the elec- tric arc and combination is effected, but it is necessary to cool and remove the product so quickly as to avoid its subsequent decomposition through remaining in the heated region. The acid gases are absorbed by alkali, and the nitrate produced is distilled with sulphuric acid for nitric acid as above ; seealsop.190. It has recently been shown that at 2000° nitrogen can reduce steam, forming nitric oxide and hydrogen. A very characteristic property of nitric acid is that of staining the skin yellow. It produces the same effect upon most animal and vegetable matters, especially if they contain nitrogen. The application of this in dye- ing silk a fast yellow colour may be seen by dipping a skein of white silk in warm dilute nitric acid, and afterwards immersing it in dilute ammonia, which converts the yellow colour into brilliant orange. When other acids are spilt upon the clothes a red stain is produced, and a little ammonia restores the original colour ; but nitric acid stains are yellow, and ammonia intensifies 1 It is extremely difficult to obtain the HNO, free from any extraneous water, as it undergoes decom+ position not only when vaporised at the boiling-point, but even at ordinary temperatures. Distillation in a vacuum is more successful, 13 194 NITRIC ACID—ACTION ON METALS instead of removing them, though it prevents the cloth from being eaten into holes. When nitric acid is heated it begins to boil at 86°, but it cannot be dis- tilled unchanged, for a considerable quantity is decomposed into nitric peroxide, oxygen, and water, the first two passing off in the gaseous form, whilst the water remains in the retort with the nitric acid, which thus becomes gradually more and more dilute, until it contains 70 per cent. of HNO , when it passes over unchanged, at the temperature of 120°. The sp. gr. of this acid is 1-42 ; its composition corresponds approximately with the hydrate 2HNO,.3H,0. If an acid weaker than this be submitted to distillation, water will pass off until acid of this strength is obtained, when it distils unchanged. A similar result is obtained when dry air is passed through strong or weak nitric acid at 15°; an acid of 64 per cent. strength (corre- sponding with HNO,.2H,0) is produced in either case. Cf. HCl. The specific gravity of the vapour of nitric acid, at 86°, has been deter- mined as 29-6 (H = 1), which is sufficiently near to half of 63 to warrant the formula HNO, for the molecule of nitric acid (p. 11). The facility with which nitric acid parts with a portion of its oxygen renders it very valuable as an oxidising agent. Comparatively few substances which are capable of forming compounds with oxygen can escape oxidation when treated with nitric acid. A small piece of phosphorus dropped into a porcelain dish containing the strongest nitric acid (and placed at some distance to avoid danger) is soon attacked by the acid, generally with such violence as to burst into flame, and sometimes to shatter the dish ; the product is phosphoric acid, the highest state of oxidation of phosphorus. * When sulphur is heated with nitric acid, it is actually oxidised to a greater extent than when burnt in pure oxygen, for in this case it is converted into sulphurous anhydride (SO,), whilst nitric acid converts it into sulphuric acid, H,SO,. Charcoal, which is so unalterable by most chemical agents at the ordinary temperature, is oxidised by nitric acid. If the strongest nitric acid be poured upon finely powdered charcoal, the latter takes fire at once. Even iodine, which is not oxidised by free oxygen, is converted into iodic acid (HIO,) by nitric acid. But it is especially in the case of metals that the oxidising powers of nitric acid are called into useful application. If a little black oxide of copper be heated in a test-tube with nitric acid, it dissolves, without evolution of gas, yielding a blue solution, which contains copper nitrate, 2HNO,; + CuO = H,0 + Cu(NO,)>. But when nitric acid is poured upon metallic copper (copper turnings) very violent action ensues, red fumes are abundantly evolved, and the metal dissolves in the form of copper nitrate, nitric oxide being formed, 8HNO, + 3Cu = 3Cu(NO;), + 4H,0 + 2NO. The nitric oxide itself is colourless, but as soon as it comes into contact with the oxygen of the air it is converted into the red nitric peroxide, NO + O = NO. A certain amount of nitric peroxide is always produced directly by the action of copper on nitric acid, the proportion depending upon the concentration of the acid and the ratio of acid to copper. When excess of concentrated nitric acid is used the gas consists of NO, (with about 10 per cent. of N03) and contains no NO; on the other hand, when the acid is diluted with twice its volume of water nearly pure NO is evolved. It has been shown that nitric acid which is free from nitrous acid (always present in commercial samples) has a very tardy, if any, action on many metals, so that it would seem as if the oxidation were really effected by the nitrous acid. A very small quantity of this suffices to start the action, because the nitric oy*’> produced reduces THE NITROMETER 195 another portion of the nitric acid to nitrous acid, thus serving as a carrier of oxygen from the nitric acid to the metal. By the action of metals on nitric acid of various strengths all the reduction products of nitric acid—namely, the oxides of nitrogen, nitrogen, hydroxylamine, hyponitrous acid, and ammonia—can be obtained ; see also p. 205. Those metals whose attraction for oxygen is feeble (those which do not decompose water, or only do so at w very high temperature, p. 21) do not reduce HNO, to a lower state of oxidation than NO ; those metals which decompose water at a red heat yield all the reduction products ; whilst those which decompose water either at the ordinary temperature or below a red heat yield even hydrogen. The nature of the products varies with the state of dilu- tion and with the temperature. Silver behaves like copper with nitric acid. Iron evolves nearly pure NO when dissolved in nitric acid diluted with either 1 part or 12 parts of water. Zinc with 1 : 2 strength of acid (hot or cold) evolves nearly equal volumes of NO and N,0, but with the strong acid it evolves scarcely any NO, but a mixture of about 2 vols. N,O and 1 vol. N; with dilute nitric acid zinc yields ammonia (which of course remains combined with the nitric acid in the form of ammonium nitrate), possibly produced by the nascent hydrogen, liberated by the dissolution of the metal in the acid (just as when zinc is dissolved in dilute sulphuric acid), on the nitric acid, HNO; + 8H = 3H,0 + NH3. Though all the metals in common use, except gold and platinum, are oxidised by nitric acid, they are not all dissolved ; aluminium is superficially oxidised but not further attacked ; tin and antimony are left by the acid in the state of insoluble oxides, which possess acid properties and-do not unite with nitric acid. When concentrated nitric acid is poured upon tin, no action is observed ;+ Lut on adding a little water, NO, is evolved in abundance and the tin is converted into a white powder, metastannic acid. On stirring this white mixture with slaked lime the smell of ammonia is perceived, this gas having been liberated from ammonium nitrate by the lime. Thus tin reduces even moderately strong nitric acid to ammonia. When a solution of potassium nitrate is mixed with a strong solution of caustic potash and heated with granulated zinc, ammonia is abundantly disengaged, being produced by the nascent hydrogen from the action of the zinc upon the caustic potash. Aluminium acts thus even in dilute solutions. Nitric acid is completely reduced, yielding only nitric oxide, when shaken with strong sulphuric acid and mercury. On this fact is based the ap- plication of the nitrometer (Fig. 142) for estimating the quantity of a nitrate present in a substance. The apparatus is filled with mercury by opening the stop-cock and pouring the metal into the open limb, The stop-cock having been closed, the right- hand limb is lowered so that the mercury in it may be at a lower level than that in the other limb. The solution to be tested is poured into the cup and sucked into the graduated limb by opening the stop-cock until all liquid has passed through, care being taken not to admit air. Oil of vitriol is next Fra. 142. sucked in, in a similar manner, and the closed limb is thoroughly shaken to mix the mercury with the solution and acid. Nitric oxide is rapidly evolved, and when no more is seen to collect in the graduated tube, the mercury is brought to the same level in each limb, as shown in the cut, and the volume of nitric oxide is read by means of the graduations on the tube. The stop-cock has two This is often noticed in the case of strong nitric acid, and is possibly to be explained by supposing that the nitrous acid present is rapidly used up and cannot be re-formed in such a concentrated acid (see above), The strongest nitric acid which has been obtained is without action on chalk, even when boiled therewith 196 NITRATES holes bored in it, so that the apparatus may be washed out through the small tube beside the cup. The weight of nitric acid present may be calculated from the volume of nitric oxide measured, for 63 grams of nitric acid (HNOs) yield 22-24 litres of nitric oxide (NO) at 760 mm. pressure and 0°. The ordinary ready method of ascertaining whether a trinket is made of gold consists in touching it with a glass stopper wetted with nitric acid, which leaves gold untouched but colours base alloys blue, from the formation of copper nitrate. The touch-stone allows this mode of testing to be applied with great accuracy. It consists of a species of black basalt, obtained chiefly from Silesia. If a piece of gold be drawn across its surface a golden streak is left, which is not affected by moistening with nitric acid ; whilst the streak left by brass, or any similar base alloy, is rapidly dissolved by the acid. Experience enables an operator to determine, by means of the touch-stone, pretty nearly the amount of gold present in the alloy, comparison being made with the streaks left by alloys of known composition. Nitrates.—Its powerful action on bases places nitric acid among the strongest of the acids, though the disposition of its elements to assume the gaseous state at high temperatures, conjoined with the feeble attraction existing between nitrogen and oxygen, causes its salts to be decomposed, without exception, by heat. The nature of the decomposition varies with the metal contained in the nitrate. The nitrates of alkali metals are first converted into nitrites by the action of heat; thus KNO, gives KNO, and O; the nitrites themselves being eventually decomposed, evolving nitrogen and oxygen, and leaving the oxide of the metal. The nitrates of copper and lead evolve nitric peroxide (NO) and oxygen, the oxides being left. The nitrate of mercury leaves red oxide of mercury, which is decomposed at a higher tem- perature into mercury and oxygen. Ammonium nitrate splits up into nitrous oxide and water (p. 200). Comparatively few of the nitrates are in common use ; they will be men- tioned under the metals of which they are the salts. Nearly all nitrates are soluble in water ; bismuth oxynitrate and urea nitrate are the most notable exceptions. The oxidising effects of nitric acid are shared to some extent by the nitrates. A mixture of nitrate of lead with charcoal explodes when sharply struck, from the sudden evolution of carbonic acid gas, produced by the oxidation of the carbon. If a few crystals of copper nitrate be sprinkled with water and quickly wrapped up in tinfoil, the latter will, after a time, be so violently oxidised as to emit brilliant sparks. But in the case of the nitrates of alkali metals, the oxidation occurs only at a high temperature. If a little nitre be fused in an earthen crucible or an iron ladle, and, when it is at a red heat, some powdered charcoal, and afterwards some flowers of sulphur, be thrown into it, the energy of the combustion will testify to the violence of the oxida- tion. In this manner the carbon is converted into potassium carbonate (K,COg) and the sulphur into potassium sulphate (K,SO,). Determination of the composition of nitric acid.—10 grams of pure lead oxide is mixed with 5 grams of absolute HNO; and some water, and the mixture is gently heated as long as vapour of water escapes; PbO + 2HNO; = H,O + Pb(NO3)o. Say that the residue weighs 14-27 grams ; then From the weight of lead oxide and nitric acid . . 15-00 grams Deduct weight of lead oxide and lead nitrate . . 14:27 4, Water which has been expelled chemically . 0-73 gram 73 corresponding with 7 or 0-08 gram H. 9 The mixture of lead nitrate and excess of lead oxide is then strongly heated in tube containing copper, when Pb(NO 3). + 5Cu = PbO + 5CuO0 + N,; the nitrogen is collected and measured. Say that 884-7 c.c. of N are obtained ; these weigh 884-7 x rite gtam = 1-11 gram, since 11110 cc, of N weigh 14 grams. RADICLES 197 Hence we find, in 5 grams of nitric acid, 1-11 grams N, 0-08 gram H, and, by difference, 3-91 grams O. Dividing these numbers by the atomic weights, 14, 1, and 16, we obtain 0-08 atom of N, 0-08 atom of H, and 0-24 atom of O, or 1 atom of H to 1 atom of N and 3 atoms of O. This would give, for the molecule of nitric acid, HNO,:, 1 + 14 + 48 = 63, a result agreeing with that obtained from the specific gravity of its vapour ; see p. 194. : Action of nitric acid on organic substances.—The oxidising action of nitric acid on some organic substances is so powerful as to be attended with inflammation ; if a little of the strongest acid be placed in a porcelain capsule, and a few drops of oil of turpentine be poured into it from a test-tube fixed to the end of a long stick, the turpentine takes fire with a sort of explosion. By boiling some of the strongest acid in a test-tube (Fig. 143) the mouth of which is loosely stopped with a plug of raw silk or of horse-hair, the latter may be made to take fire and burn brilliantly in the vapour of nitric acid. In many cases the products of the action of nitric acid exhibit a most interesting relation to the substances from which they have been produced, one or more atoms of the hydrogen of the original compound having been removed in the form of water by the oxygen of the nitric acid, whilst the spaces thus left vacant have been filled by the NO, group formed by the deoxidation of the nitric acid, pro- ducing what is termed a nitro-substitution compound. A very simple ex- ample of this displacement of H by NO, is afforded by the action of nitric acid upon benzene. A little concentrated nitric acid js placed in a flask, and benzene cautiously dropped into it; a violent action ensues, and the acid becomes of a deep red colour ; if the contents of the flask be now poured into a large vessel of water, a heavy yellow oily liquid is separated, having a powerful odour, like that of bitter almond oil. This substance, which is used to a considerable extent in perfumery under the name of essence of Mirbane, is called nitro-benzene, and its formula, C,H;(NO,), at once exhibits its relation to benzene, C,H. To understand the nature of this reaction the theory of radicles and of substitution must be appreciated. A radicle consists of an unsaturated group of elements, such as behaves in a@ manner similar to a single atom. Their unsaturated nature may be realised by considering some saturated molecule to be deprived of one of its H atoms ; ¢.g. in methane, CH, or H—C-——H, the carbon atom which is normally | H tetravalent (p. 13) is in union with four hydrogen atoms and the compound is said to be saturated, because it has no. valency bonds disengaged ; it cannot combine with any further atom. Now if one hydrogen atom be H removed the remaining —C—H or —CHz, methyl, has one valency bond free ; i it is ready to combine with any other atom or group of atoms ; it is an un- saturated group called a radicle. CH, has no separate existence, but it is present in numerous molecules. Attempts to separate it succeed only momentarily, for, if it cannot combine with anything else, two CH, groups 198 ACID CHLORIDES unite to form C,H,, i.e. CH,—CH,;. This doubling occurs with many radicles. Atoms ave perfectly comparable. If sodium react with hydro- chloric acid, Na + HCl = NaCl + H, hydrogen atoms are undoubtedly liberated (see p. 99), but the single atoms being unsaturated, H—, two instantly combine to form the molecule H,. The term “radicle” usually signifies a well-defined group of the character described, and the names of the individuals generally end in -yl ; e.g. methyl, sulphuryl. Other groupings are described merely as groups; e.g. the CO group. The group left on abstracting hydrogen from a molecule of acid is often described as an acid residue ; e.g. NO,;SO,. The part played by such an “atomic complex ” under the particular circumstances must decide its description ; e.g. SO, is the formula for a stable compound, sulphur dioxide (p. 155) ; but SO, is an acid radicle in SO,(OH),, sulphuric acid, and merely a group in SO,. Et,, ethyl sulphone. An acid radicle is that portion of the molecule of an oxyacid remaining after abstracting the hydroxyl; thus SO,, sulphuryl [H,SO, —(OH), = SO,], is the acid radicle of sulphuric acid ; NOg, nitroxyl [HNO,—OH = NO,] is that of nitric acid. Their significance will be better realised in studying derivatives in which some element or group of elements is substituted for hydroxyl; e.g. chlorine in the acid chlorides or chloranhydrides ; thus SO,.Cl,, sulphuryl chloride (p. 199); NO.CIl, nitrosyl chloride (p. 158). The reaction which most generally produces an acid chloride is that between an oxyacid and phosphoric chloride, PCl; (see Phosphorus) ; if R represent the group of atoms combined with OH in an acid, this reaction may be expressed by the equation, R-OH + PCl,;= R-Cl + POCI, + HCl; or, since the acid.residue may be combined with several OH groups, R(OH), + nPCl, = RCL, + nPOCI, + nHCl. It is from this fact, namely, that for every atom of chlorine introduced into an acid by the action of phosphoric chloride one atom of oxygen and one atom of hydrogen are removed (as POCI, and HCl respectively), that the inference is drawn that the hydrogen in an oxyacid exists in the form of hydroxyl groups. For it is obvious that a monovalent atom like Cl can be substituted only for another monovalent atom or a monovalent radicle, so that if O and H are together exchanged for Cl they must be present as —OH ; were they present independently of each other they would represent three atom-fixing powers (—O— and H—) and could not be exchanged for the monovalent atom Cl. It will be found, particularly in organic chemistry, that acids frequently contain O and H, for which Cl cannot be substituted, and therefore exist in some relationship to the molecule other than that represented by —OH. The characteristic behaviour of acid chlorides, is that when brought into contact with water they exchange their chlorine for hydroxyl, and are con- verted into the acids from which they were derived; RCl, +nHOH = R(OH), +nHCl. It is because these chlorides form acids in this way, when brought in contact with water, that they are also termed chloranhydrides. These principles are of great significance in organic chemistry. It is noteworthy that whilst the acid chlorides yield acid hydroxides and hydrochloric acid by treatment with water, the basic hydroxides, such as NaOH, Ca(OH),, yield basic chlorides and water by treatment with hydro- chloric acid ; thus it is instructive to compare the reactions : NO-Cl + HOH NO-OH + HCl, and NaOH + HCl NaCl + HOH. It is characteristic of radicles and many other groups to persist unchanged through numerous reactions unless the latter are so drastic as to break up the radicle ; thus if OH or CH, or SO, oxists in one of the reacting substances AQUA REGIA Lvy it may usually be found in one of the products. It follows that a large number of chemical changes, particularly in organic chemistry, are to be explained as exchanges between the radicles of compounds, in the same way that many are to be explained as exchanges between the elementary atoms constituting the simpler compounds; compare KI + HCl = KCl + HI with H'C,H; + NO,OH = NO,C,H,; + H:'OH; the latter representing an exchange of the radicle C,H, of benzene (C,H,) for the OH radicle of a acid, the nitroxyl radicle having been substituted for hydrogen in the enzene. Various acid halides associated with nitric and nitrous acids are known. Nitroxyl Fluoride, or nitryl fluoride, NO,F, the acid fluoride of nitric acid, is a colourless gas, formed by the action of nitric oxide on fluorine at — 180°; m.-pt. — 139°, b.-pt. — 63-5°. Decomposed by water into HF and HNO,. Nitroxyl Chloride, or nitryl chloride, NO,Cl, has been said to result from the action of Cl on NOg, but its existence appears to be doubtful. Nitrosyl Fluoride, NOF, the acid fluoride of nitrous acid ; it is a colourless gas generated by decomposing silver fluoride with nitrosyl chloride. Nitrosy! Chloride, NOCI, is synthesised in the interaction of NO (2 vols.) and Cl, (1 vol.) ; it isan important constituent of aqua regia (v.i.) and may be separated therefrom by distillation. But it is best prepared by heating to 85° nitrosulphonic acid (infra) with sodium chloride ; NO-HSO, + NaCl =NO:Cl + NaHSO,. It is a red gas condensable by a freezing mixture to a red liquid boiling at — 5-6 ; S_13°, 1-42 ; solidifying on further cooling to a yellow mass, melting at — 61°; crit. temp., 163-5°. It dissociates above 700°. It has a very peculiar odour and forms with water nitrous and hydrochloric acids, NO-Cl + H‘OH = NO-OH + HCl. When nitrosyl chloride is passed into oil of vitriol at 0°, crystals of nitrosulphonic acid (“chamber crystals”) (p. 162) are deposited; NO-Cl + SO,-OH-OH = HCl + SO0,,OH-ONO. Nitro-sulphonic Acid, also known as nitrosyl sulphate, may also be obtained by passing SO, into nitric acid, or NO, into sulphuric acid, or by burning a mixture of 1 part of sulphur and 3 parts of nitre in moist air. Aqua regia, nitrohydrochloric acid, nitromuriatic acid.—The first name was applied in the fourteenth century to the product of the action of nitric acid upon ammonium chloride. It is now given to the mixture of 1 measure of nitric and 3 measures of hydrochloric acid, which is employed for dissolving gold, platinum, and other metals which are not soluble in the separate acids. A little gold leaf placed in hydrochloric and nitric acids contained in separate glasses remains unaffected even on warming the acids ; but if the contents of the glasses be mixed, the gold will be immediately dissolved by the chlorine, which is liberated in the action of the acids upon each other; HNO, + 3HCl = 2H,0 + NOC] + Cl,. It is a very powerful oxidiser and is very destructive to organic substances. Anhydrous Nitric Acid or Nitric Anhydride, N,O;, is obtained by gently heating silver nitrate in a slow current of chlorine, great care being taken to exclude every trace of water; 2AgNO, + Cl, = 2AgCl + O + N,0;. It may also be obtained by adding anhydrous phosphoric acid to the strongest HNO, cooled in snow and salt, and carefully distilling at as low a temperature as pos- sible. The distillate separates into two layers, the lower of which is a compound, 2N,0;.H,0, called dinitric acid ; the upper layer is separated and cooled. The anhy- dride is condensed as a crystalline solid, sp. gr. greater than 1-64. It forms transparent colourless prisms which melt at 30° and boil at 47°. By a slightly higher temperature it is readily decomposed ; and it has been said to decompose even at the ordinary temperature, in sealed tubes which were shattered by the evolved gas. It is more stable in the dark. When the anhydride is brought in contact with water, much heat is evolved and nitric acid, H,O.N,O;, is produced. The specific gravity of the vapour of nitric anhydride being unknown, it is only a surmise that its molecule is represented by N2O;. - S 200 OXIDES OF NITROGEN Nitrous Oxide or laughing gas, N,O = 44:02, is prepared by heating ammonium nitrate, when it is resolved with evolution of heat into water and nitrous oxide ; NH,NO, = 2H,0 + N,0. To obtain nitrous oxide, 30 grams of ammonium nitrate may be gently heated in a small retort; it melts, boils, and gradually disappears in the forms of steam and nitrous oxide. The latter may be collected with slight loss over water. If the tem- perature be too high, the gas may contain nitric oxide and nitrogen ; NH,NO, = NO + N + 2H,0. Moreover, since 80 grams (1 gram-molecule) of NH,NO, evolve some 31,000 gram-units of heat when decomposed into H,O and NO, explosion is liable to occur. To purify the gas, it should be passed through a strong solution of ferrous sulphate to absorb the nitric oxide, and afterwards through potash to absorb acid vapours. Nitrous oxide is colourless, but has a slight odour and a sweetish taste. Its characteristic anesthetic property is well known. It accelerates the com- bustion of a taper like oxygen itself, and will even kindle into flame a spark at the end of a match, for it is readily decomposed into N, and O by the temperature of burning wood. For a test distinguishing it from oxygen and for a comparison with nitric oxide, see the latter. When C is burnt into CO, by 2N,0, it evolves 36,000 more units of heat than when burnt in O, showing that heat is evolved in the decomposition of the N,O, amounting to 18,000 units per molecule ; this compound is therefore endothermic. Nitrous oxide can readily be distinguished from oxygen by shaking it with water, which absorbs, at the ordinary temperature, about three-fourths of its volume of the nitrous oxide. It is absorbed in larger quantity by alcohol. It is also much heavier than oxygen, its sp. gr. being 1-53, and is liquefied by a pressure of 40 atmo- spheres at 7°, and solidified at — 115°. The liquid is sold in wrought-iron bottles for use as an anesthetic in dental surgery. In small doses it has an intoxicating effect, whence its title of ‘laughing gas.” The liquid nitrous oxide has a very low refractive index ; its sp. gr. is 0-94 at 0° and it boils at — 90°. A lighted match thrown into the liquid burns with great bril- liancy. When it is mixed with carbon disulphide and evaporated in vacuo, the tem- perature falls to— 140°. The critical temperature of N,O is 39°, and the critical pressure is 73 atm. Nitric Oxide, NO = 30-01, is usually obtained by the action of copper upon diluted nitric acid (see p. 194). Twenty grams of copper turnings or clippings are introduced into a retort and 85c.c. of a mixture of concentrated nitric acid with an equal volume of water are poured upon them. A very gentle heat may be applied to assist the action, and the gas may be collected over water (see Fig. 170), which absorbs the red fumes (NO2) formed by the union of the NO with the oxygen of the air contained in the retort. The nitric oxide thus prepared generally contains nitrous oxide. Pure nitric oxide may be obtained by heating in a retort 6-5 grams potassium nitrate, 65 grams of ferrous sulphate, and 85 c.c. of dilute sulphuric acid (1 vol. + 3 vols. water), which will yield about 1133 c.c. of gas; 2KNO, + 6FeSO, + 4H,SO, = K,S8O, + 3Feg(SO,)3 + 2NO + 4H,0. Nitric oxide is distinguished from all other gases by the production of a red gas, when the colourless nitric oxide is allowed to come in contact with uncombined oxygen, the presence of which, in mixtures of gases, may be readily detected by adding a little nitric oxide. The red gas consists chiefly of nitric peroxide (NO,) when the oxygen is in excess, otherwise it contains also some nitrous anhydride (N,O;). The combination of nitric oxide with oxygen may be exhibited by decanting litre of oxygen, under water, into a tall jar filled with water coloured with blue litmus, and adding to it 4 litre of nitric oxide (Fig. 144). Strong red fumes are immediately produced, and on gently agitating the cylinder the fumes are absorbed by the water, reddening NITRIC OXIDE 201 the litmus. The oxygen will now have been reduced to half its volume, and if another 4 litre of nitric oxide be added the remainder of the oxygen will be absorbed, showing that 2 vols. of nitric oxide combine with 1 vol. of oxygen, forming nitric peroxide, which is absorbed by the water. In presence of water and excess of oxygen, NO is entirely converted into nitric acid; 2NO + H,O + 30 = 2HNO3. : Tl The addition of nitric oxide to atmospheric “os air was one of the earliest methods employed for removing the oxygen in order to determine the composition of air ; but important variations he were observed in the results, in consequence : = of the occasional formation of N.O3 in addition | {ht \ NN yan to the NOp. fl lh ae lr == In all its properties nitric oxide is very different from nitrous oxide. Itis much “= lighter, having almost exactly the same Fig. 144, specific gravity as air, viz. 1-038 (1 1. weighs 1-340 grams), and is not dissolved to an important extent by water. It is more difficult to liquefy, for its crit. temp. is — 93-6°; its crit. press., 71:2 atm. ; its b.pt.is — 153-6° ; it solidifies to a snow-like mass at — 167°. Even at very low temperatures the formula is NO, not N,O,. When a lighted taper is immersed in nitric oxide it is extinguished, although this gas contains twice as much oxygen as nitrous oxide, which so much accelerates the combustion of a taper, for the elements are held together by a stronger attraction in the nitric oxide, so that its oxygen is not so readily available for the support of combustion.1 Even phosphorus, when just kindled, is extinguished in nitric oxide, but when allowed to attain to full combustion in air, and, therefore, to a temperature high enough to decompose the nitric oxide into N and O, it burns with extreme brilliancy in the gas. Indeed, nitric oxide appears to be the least easy of decomposition of the whole series of oxides of nitrogen, which accounts for its being the most common product of the decomposition of the other oxides. Nitrous oxide itself, when passed through a red-hot tube, is partly converted into nitric oxide; and when a taper burns in a bottle of nitrous oxide, the upper part of the bottle is often filled with a red gas, indicating the formation of nitric oxide, and its oxidation by the air entering the bottle. The difference in the stability of the two gases is also shown by their behaviour with hydrogen. A mixture of nitrous oxide with an equal volume of hydrogen explodes when in contact with flame, yielding steam and nitrogen, but a mixture of equal volumes of nitric oxide and hydrogen burns quietly in air, the hydrogen not decomposing the nitric oxide except at the temperature of a strong electric spark. An 2 excess of hydrogen, however, is capable of decom- e. z= = osing nitric oxide, ammonia and water being os ie. Hag. 145, If 2 vols. of nitric oxide are mixed with 5 vols. of hydrogen and the gas passed through a tube having a bulb filled with platinised asbestos (Fig. 145),? the mixture issuing from the orifice of the tube produces the red gas by contact with the air, and will strongly redden blue litmus ; but if the platinised ss a \) S 1 = tt ——— lh 1 The nitric oxide prepared from copper and nitric acid sometimes contains so much nitrous oxide that a taper burns in it brilliantly. ‘ ; 2 Asbestos which has been wetted with solution of platinic chloride, dried, and heated to redness, to reduce the platinum to the metallic state. 4 202 NITROUS ANHYDRIDE asbestos is heated with a spirit-lamp, the hydrogen, encouraged by the action of the platinum (p. 98), decomposes the nitric oxide, and strongly alkaline vapours of ammonia are produced, restoring the blue colour to the reddened litmus ; NO + 5H= NH, + HO. It will be remembered that when oxygen is in excess ammonia is con- verted, under the influence of platinum, into water and nitrous acid (p. 191). NO is readily absorbed by ferrous salts, with which it forms dark brown solutions. If a little solution of ferrous sulphate (FeSO,) be shaken in a cylinder of nitric oxide closed with a glass plate, the gas will be immediately absorbed and the solution will become dark brown. On applying heat, the brown compound is decomposed. When shaken with moist ferrous hydroxide, NO is reduced to N,O and N. In the presence of caustic soda, sodium hyponitrite (Na,N,O,) and ammonia are also produced. By employing a large excess of soda, one-fifth of the nitric oxide may be converted into the hyponitrite. Nitrous Anhydride, N,O, or NO.NO, = 76-02, and Nitrous Acid, NO.OH = 47-01.—Ammonium nitrite is said to exist in minute quantity in rain water, and nitrites are oc- casionally found in well waters, where they have probably been ' formed by the oxidation of am- monia (p. 42). Small quantities of ammonium nitrite appear to be formed by the combustion in air of gases containing hydrogen, this element uniting with the atmo- spheric oxygen and nitrogen (p. 190). Nitrous anhydride may be ob- ae tained by heating starch with F ; nitric acid, but the most con- 1c. 146. : 3 . venient process consists in gently heating nitric acid (sp. gr. 1:35) with an equal weight of white arsenic, and passing the gas, first through « U-tube (Fig. 146) surrounded with cold water, to condense undecomposed nitric acid, then through a similar tube contain- ing calcium chloride to absorb aqueous vapour, and afterwards into a U-tube surrounded with ice. Through a small tube opening into the bend of this U-tube, the condensed nitrous anhydride drops into a tube drawn out to a narrow neck, so that it may be drawn off and sealed by the hlowpipe— 4HNO, + AsyO, + 4H,0 = 4H,As0, + 2N,03. White arsenic. Arsenic acid. The white arsenic is here used merely as a reducing agent to remove oxygen from the nitric acid. N.2O, is the anhydride of nitrous acid, HNO, (H20.N203) ; this acid is so unstable that it immediately breaks up into H,O and NO, ; 2HNO, = H,O + N,O3. The object of the above reaction, therefore, is to remove 2 atoms of oxygen from 2 molecules of nitric acid; 2HNO; = H,O + N20; + Og. White arsenic, As,Og, is arsenious anhydride and readily oxidises to arsenic anhydride, As4O,9, which then combines with water to form arsenic acid, 6H,0.As,0,9(= 4H,AsO,). Hence 1 mole- cule of white arsenic combines with 4 atoms of oxygen, and will therefore reduce A molecules of nitric acid. The student should endeavour to sift in this manner all chemical equations which appear to him complex. Nitrous anhydride is also prepared by decomposing the acid nitrosyl sulphate (see Aqua regia) with a little water; 2NOHSO, + H,O = 2H,SO, + N.O3. Tf the gas liberated in these reactions be cooled to — 20°, a pure indigo- blue liquid, supposed to be N,O,, is formed; but if the temperature be allowed to rise the colour becomes dirty and the liquid is a mixture of nitro- gen tetroxide (nitric peroxide), N,O,, and nitrous anhydride. It boils below NITROUS ACID 203 the ordinary temperature, giving a red gas which consists of equal volumes of nitric oxide and nitric peroxide, the proportion of the latter gradually increasing until the remaining liquid has the green colour and the composition of N,O,. It thus seems that usually N,O, can exist only at low temperatures and in the liquid condition. However, gaseous trioxide is obtainable by volatilising the liquid into perfectly dry nitrogen, moisture being necessary for dissociation (cf. Ammonium chloride, p. 188). N,O, molecules appear to exist. The liquid is readily obtained, although not quite pure, by passing nitric oxide into cooled liquid nitrogen tetroxide. But when equal volumes of NO and NO, gases are mixed, no contraction occurs, as would be i ei if they combined to N,0,; NO (2 vols.) + NO, (2 vols.) = N,O, vols.). Water at about 0° dissolves N,O;, yielding a blue solution, which, as the temperature rises, becomes a solution of nitric acid, nitric oxide escaping with effervescence ; 3N,0, + H,O = 2HNO, + 4NO. The blue solution is believed to contain nitrous acid, HNO, or NO.OH ; N,0; + H,O = 2HNO,; but this compound has not been obtained in a pure state. A very dilute solution of the acid may be preserved for some time, and even distilled, without decomposition. For the nitrous acid of commerce, see p. 204. Nitrous acid is often generated in situ’ (see p. 207). The salts of nitrous acid, or nitrites, are interesting on account of their production from the alkali nitrates by the action of heat (p. 196). When potassium nitrate is fused in a fireclay crucible and heated to redness, it evolves bubbles of oxygen and slowly becomes potassium nitrite (KNO,). The heat may be continued until a.portion removed on the end of an iron rod and dissolved in water gives a strongly alkaline solution. The fused mass may then be poured upon a dry stone, and, when cool, broken into fragments and preserved in a stoppered bottle. On heating a fragment of the nitrite with dilute H,SO, red vapours are disengaged, but these contain little nitrous acid, the greater part of this being decomposed by the water into HNO; and NO. When nitrous acid acts on ammonia, both compounds are decomposed, water and nitrogen being produced ; NH, + HNO, = Nz + 2H,0. When solutions of nitrites are heated in contact with air, they gradually absorb oxygen, becoming converted into solutions of nitrates. Nitrous acid may be regarded as a solution of NO and NO, in water (H,0.N,O; or H,O.NO.NO,). The former tends to combine with oxygen to form NOs, and the latter tends to part with oxygen to form NO, so that nitrous acid can behave, according to circumstances, either as a reducing agent or an oxidising agent. Obviously any compound capable of parting with oxygen to NO cannot obtain oxygen under the same circumstances from NO. Nitrous acid reduces potassium permanganate, but oxidises ferrous sulphate. It will also oxidise the hydrogen of hydriodic acid (HI), thereby liberating the iodine ; since a very small quantity of the latter can be detected by taking advantage of its property of bluing starch, the addition of hydriodic acid (KI and H,SO,) to nitrous acid (KNO, + H,SO,) forms a very delicate test for the latter; HI + NO.OH = H.OH +1+ NO. Nitric Peroxide, NO, = 46-01, or Nitrogen Tetroxide, N,O, = 92-02. —By passing a mixture of nitric oxide with half its volume of oxygen, free from every trace of moisture, into a perfectly dry tube cooled in a mixture of ice and salt, the dark red gas is condensed into colourless prismatic crystals which melt at —12° into a nearly colourless liquid. This gradually becomes yellow as the temperature rises, and at 15° has a deep orange colour. It is very volatile, boiling at 22° to a red-brown vapour,which was long mistaken for a permanent gas, on account of the great difficulty of condensing it when once mixed with air or oxygen. Nitric peroxide is also obtained, mixed with one-fourth of its volume of oxygen, by heating lead nitrate (Fig, 147); Pb(NO;), = PbO + 2NO, + O. 204 NITRIC PEROXIDE The vapour of nitric peroxide is much heavier than atmospheric air. Its vapour density diminishes as the temperature rises. At 140° the gas is twenty- three times as heavy as hydrogen, showing its molecular weight to be 46. This variation in density, in conjunction with the other changes with increase of temperature, leads to the belief that the molecule of nitric peroxide at low temperatures (in its liquid state) is N,O,, and becomes dis- sociated into 2NO, at high temperatures. At 500° the gas becomes nearly colourless, being almost entirely dissociated into NO and O. NO, is absorbed by many finely divided metals, forming unstable compounds called nitro-metals, which yield most of the reactions of NO». Nitro-copper, CugNOz2, is obtained when NO, is passed over freshly reduced Cu at 30°. By mixing N,O; with the green liquid obtained by condensing the vapours from the action of HNO, on As,Og, the N,O3 contained in the liquid is converted into N204 ; N20; + N203 = 2N204. Its colour varies with the temperature, becoming very dark at 30°. The smell of the vapour is very characteristic. The vapour supports the com- bustion of strongly burning charcoal or phosphorus, and oxidises most of the metals, potassium taking fire in it spontaneously. Nitric peroxide must, therefore, rank as a powerful oxidising agent, and it is the presence of this substance in considerable proportion in the red fuming nitric acid that imparts to it higher oxidising powers than those of the colourless nitric acid. This red acid, the so-called nitrous acid of commerce, is prepared by intro- ducing sulphur into the retorts containing the mixture of sodium nitrate and sulphuric acid employed in the preparation of the nitric acid, a portion of which is deoxidised by the sulphur and: converted into nitric peroxide. Water in excess immediately decomposes nitric peroxide into nitrous acid and nitric acid, 2NO, + H,O = HNO, + HNO,, so that the peroxide is not an independent anhydride ; cf. Cl0,, p. 120. When water is gradually added to liquid nitric peroxide, the liquid effervesces from escape of nitric oxide, and becomes green, blue, and ultimately colourless ; 3NO, + H,O = NO + 2HNO,. When red nitric acid is gradually diluted with water, it under- goes similar changes, always becoming colourless at last. The nitric acid which has been used in a Grove’s battery has a green colour, from the large amount of nitric peroxide which has accumulated in it, in consequence of the decomposition of the acid by the hydrogen disengaged during the action of the battery ; H’ + HNO; = H,O + NO,. Similar colours are obtained by passing nitric oxide into nitric acid of different degrees of concentration, apparently because nitric peroxide is formed and dissolved by the acid. When silver, mercury, and some other metals are dissolved in cold nitric acid, a green or blue colour is often produced, leading a novice to suspect the presence of copper, the colour being really caused by the dissolution, in the unaltered nitric acid, of the nitric peroxide, produced by the de-oxidation of another portion. Constitution and Analysis of the Nitrogen Oxides.—The facility with which nitrous anhydride and nitric peroxide can be decomposed with formation of nitric oxide renders it probable that they really con- tain this group of elements as the radicle nitrosyl, NO. To express this they may plausibly be represented as formed on the same plan as that on which a molecule of water is formed. Just as in H—O—H, the two atoms of hydrogen are linked together by the diatomic oxygen, so in nitrous anhydride, O—=N—O—N=O, two molecules of nitric oxide are linked together by the atom of oxygen, whilst in nitric peroxide (N,O,) a molecule of Fic. 147. NO is bound up with a molecule of NO,, thus, o=N—0—NC . Ifnitric O ANALYSIS OF NITROGEN OXIDES 205 O O anhydride be represented by Nn—o—n@ , it is easy to understand 0% No the behaviour of these three oxides with the alkalies. Thus, by the action of nitrous anhydride on caustic potash, potassium nitrite, K—O—-N=O, in which K is substituted for O : N—, is formed, whilst nitric anhydride gives potassium nitrate, K—O—NO,, and nitric peroxide gives a mixture of both salts. The remaining oxide of nitrogen, N,O, may be represented as Such formule as the above are termed structural formule, since they essay to represent the way in which the molecule is built up, so far as it is possible to represent a three-dimensional structure on one plane. They must be written with due regard to the valency of the elements ; thus nitrogen should appear either as trivalent or pentavalent, for its atom-linking power has generally one or other of these values. They must also be written with regard to the constitution of the compound, that is, the relationships which the various atoms show towards each other; thus, since there is evidence that the nitrogen atom and two of the oxygen atoms in nitric acid behave as the radicle NO,, no structural formula failing to represent the N as directly attached to 2 oxygen atoms could be accepted. All the oxides of nitrogen are endothermic compounds (p. 347), which accounts for the indisposition of N and O to combine directly. The following equations represent the number of calories or gram-units of heat (p. 32) evolved by the decomposition of one gram-molecule (the molecular weight expressed in grams) of N,O, NO, and NO, : N20 = No + O 4+ 18,000 cals. NO =N +0 + 21,500 ,, NO, = N + Og + 7,650 ”? The general principle upon which the composition of these oxides has been determined is the decomposition of a measured volume of the gaseous oxide either by heat alone, or by burning some oxidisable substance in it, and measuring and analysing the volume of the gases or gas obtained. Thus, when nitrous oxide is passed through a red-hot tube, its volume is increased by one-half, the gas becoming a mixture of 1 vol. O and 2 vols. N. This shows that the ratio of atoms of nitrogen to oxygen in the gas is 2:1. That the formula is N,O, not NOx, is decided by the specific gravity of the gas. When a known volume of nitric oxide is passed over a weighed quantity of red-hot copper and the nitrogen which passes on is collected and measured, it is found that for every 16 parts by weight of oxygen absorbed by the copper (judged from its gain of weight) 11-2 litres of nitrogen are collected; but this volume of nitrogen weighs 14 grams (p. 22), so that the nitric oxide must contain O: N = 16: 14, or 1 atom of oxygen to 1 atom of nitrogen. That the formula is NO, not N2Os, follows from the specific gravity of the gas. The other oxides of nitrogen are similarly analysed. Reduction Products of Nitric Acid—By the action of nascent hydrogen, that is, hydrogen at the moment of its liberation (p. 99}, nitric acid, the most highly oxidised nitrogen compound, may be made to yield successive reduction products until the most highly hydrogenised nitrogen compound, ammonia, is formed. The reduction may be regarded as occur- ring in the following stages, although to realise such progressive steps is difficult, if not impossible, in practice. The first stage of the reduction will be nitrous acid, NO,,OH + 2H= NO-OH + H,0. In the second stage, N-OH would be expected to be produced, but in a compound of this formula 206 HYPONITROUS ACID only one of the atom-linking powers of the nitrogen would be satisfied ; hence this group of atoms is incapable of a separate existence, but, if produced, immediately combines with a like group, forming hyponitrous acid, HO-N : N-OH. The third stage of the reduction consists in the introduction of hydrogen into the hyponitrous acid, whereby the molecule is made to yield either two molecules of a compound called hydroxylamine, HO-N : N-OH + Por 4H = HO-NC + NOB, or 1 molecule of a compound called hydra- H H zine, HO-N:N-OH + 6H = H,N: NH, + 2HOH. The final stage of the reduction transforms the hydroxylamine into ammonia. See also p. 195. Hyponitrous Acid, HO.N:N.OH. Nitrous oxide might be expected to be the anhydride of this acid, N,0 + H,O = H,N,O., but an aqueous solution of this gas does not contain hyponitrous acid. The hyponitrites are obtained by reducing solu- tions of the nitrates or nitrites by the nascent hydrogen generated when sodium amal- gam is introduced into the solution. Thus, a solution of sodium hyponitrite is obtained when sodium amalgam is added, little by little, to a strong solution of sodium nitrate, or nitrite, kept cool. The hyponitrite most easily obtained in a pure condition is the silver salt, AgyN2Oo, which is a yellow precipitate formed when silver nitrate is added to the solution of sodium hyponitrite. The precipitate dissolves in ammonia and in dilute nitric acid, but, is precipitated unchanged by neutralising the solvent ; it is insoluble in acetic acid. By adding hydrochloric acid to the silver salt, hyponitrous acid passes into the solution and silver chloride remains undissolved ; the solution is colourless and acid to litmus, but it will not liberate carbon dioxide from the alkali carbonates ; when kept it decomposes with formation of N.O0 and H,0. By adding the silver salt to a solution of HCl in ether, filtering and evaporating the ethereal solu- tion, crystals of HzN,O, are obtained; they are very explosive, like other compounds containing the group -‘N: N-. In acid solution potassium permanganate oxidises hypo- nitrous acid to nitric acid, but in alkaline solution a nitrite is formed. The formation of hyponitrous acid by the reduction of nitric oxide in presence of water has been mentioned at p. 202; another reaction by which it is produced will be mentioned below. The acid properties of NO,: OH are stronger than those of NO: OH, which in their turn are stronger than those of HO:-N: N- OH. It would thus seem that NO, is a stronger acid radicle than NO, and that the two hydroxyl groups in hyponitrous acid do not compensate in acid-producing power for the absence of an oxy-nitrogen group. Since there are two OH groups in hyponitrous acid, this is a dibasic acid (p. 90). Hydroxylamine, NH,:OH, may be obtained by the reduction of nitric acid, but is better prepared by passing nitric oxide through a series of flasks containing tin and strong hydrochloric acid. The hydrogen evolved from the metal and acid (the evolution is generally hastened by the addition of a few drops of platinic chloride, the platinum of which deposits on the tin and forms a galvanic couple) may be regarded as converting the NO into NH,OH. The hydroxylamine, being possessed of basic properties, combines with the hydrochloric acid and remains in the solution as hydroxyl- amine hydrochloride, NH,OH- HCl, together with stannous chloride. The tin is preci- pitated by the addition of HS ; the SnS is filtered off and the filtrate evaporated, when the hydroxylamine hydrochloride crystallises. To obtain free hydroxylamine, the hydrochloride is dissolved in methyl alcohol and a solution of sodium in the same solvent is added ; sodium chloride is precipitated and is filtered off ; the filtrate is then distilled under reduced pressure, when methyl alcohol passes over, followed by hydroxylamine. In this process the sodium methoxide, CH,;ONa, contained in the solution of sodium in methyl alcohol, reacts with the hydroxylamine hydrochloride, forming sodium chloride, hydroxylamine, and methyl alcohol ; NH, OH: HCl + CH;0Na = NH,OH + CH,0H + NaCl. Sodium hydroxide cannot be substituted for the methoxide because water would be one of the products, and this decomposes the hydroxylamine. : Hydroxylamine crystallises in white needles, melts at 33°, and boils at 58° under 22 mm. pressure, but explodes when heated to 90° under ordinary pressure. It is DIAZO-REACTION 207 odourless and has an alkaline reaction ; when exposed to air it deliquesces and ulti- mately evaporates ; even in sealed tubes it slowly undergoes decomposition. Hydroxylamine and its salts are very easily oxidised to nitrous oxide and water so that they reduce cupric oxide in alkaline solutions to cuprous oxide, 4CuO + 2NH,.0OH = 2Cu,0 + N,O + 3H,O. Ferrous hydroxide, however, is oxidised by hydroxylamine, which is thereby reduced to ammonia ; on the other hand, an acid ferric solution is reduced by hydroxylamine. An aqueous solution of the hydrochloride is used as a photographic developer. The free base combines with many metallic salts in the same way that water and ammonia do. : Hydroxylamine may be regarded as derived from water, substituting NH, for H; or as ammonia in which H is exchanged for OH. But it exhibits basic properties as shown in the formation of salts with acids, and so its formula would appear to be H NH,: 0, forming salts of the oxonium type, e.g. with HCl, NH,: og . Zine, cal- Cl cium, &c., can displace hydrogen from it just as from an acid, forming hydroxylamates, e.g. Ca(ONH,). No doubt it is tautomeric (see Taulomerism). When nitrous acid is brought in contact with an amide (p. 189) at the ordinary temperature (in aqueous solution), the amidogen group is exchanged for the hydroxy] of the nitrous acid, and the NH, thus removed reacts with the NO of the acid to form N, and H,O. Thus the simplest amide, hydrogen amide or ammonia, NH,'H, reacts with nitrous acid to form hydrogen hydroxyl or water ; NH,-H + NO-OH = HO-H + N, + H-OH, as already observed (p. 203). This reaction is typical of one which is very commonly em- ployed in organic chemistry for substituting OH for NH,. When it is applied to hydroxylamine, or hydroxyl-amide, NH,-OH, it does not occur on exactly the same lines, possibly because hydroxy]-hydroxyl, HO-OH (ef. p. 145), which would be the product, is too unstable to be formed under the circum- stances. The actual reaction between nitrous acid and hydroxylamine at ordinary temperatures may be represented by the equation NH,OH + NO-OH = HOH + N,0 + HOH. Since nitrous acid cannot be preserved in aqueous solution its application for such reactions is effected by generating it at the moment when it is required by dissolving sodium nitrite in the solution to be treated, and adding an acid to liberate nitrous acid from the nitrite. In the case of a large number of amides, particularly those derived from organic compounds, when the aqueous solution of the amide is kept cool by ice, no nitrogen is evolved on the addition of nitrous acid. This is because the nitrogen of the amidogen and of the nitrous acid remain combined to- gether to form a group, ‘N : N-, in which each nitrogen atom is able to attach to itself a monovalent element or radicle. Such a nitrogen group is called a diazo-group, and compounds containing it are called diazo-compounds (q.v.). To exemplify the diazo-reaction the following hypothetical equa- tion for the reaction of ammonia on nitrous acid at a low temperature may be written: HN: H, + 0:NOH = HN: NOH + H,0. The diazo-compound represented by the formula HN : N-OH has not been obtained, but it will be seen that hyponitrous acid may be regarded as formed on this type, HO being exchanged for the left-hand hydrogen atom. A comparison of the formula for hydroxylamine with that for ammonia will at once lead to the conclusion that the reaction between nitrous acid and hydroxylamine at a low temperature should produce hyponitrous acid ; this is the case, for by mixing cold dilute solutions of hydroxylamine hydrochloride and sodium nitrite, sodium chloride and hydroxylamine nitrite are formed, the latter immediately passing into hyponitrous acid ; by adding acetic acid and silver nitrate the yellow silver hyponitrite is precipitated: (1) HO-NH,.HCl + 208 NITROGEN CHLORIDE NaO-NO = NaCl + HO-NH,,HO-NO; (2) HO-NH,,HO-NO = HON: N-OH + HOH. The diazo-compounds which contain hydroxyl readily de- compose when the temperature is raised, the products of the decomposition being the same as those produced by the interaction of the original amide with nitrous acid at a high temperature. Thus, if the above experiment be conducted at a high temperature (above 50°) nitrous oxide is rapidly evolved, and no hyponitrous acid can be detected in the solution. Nitrogen sulphides.—Two compounds of nitrogen and sulphur are known. Nitrogen tetrasulphide (N84) is produced when chloride of sulphur, dissolved in benzene, is acted on by gaseous ammonia, 16NH; + 68,Cl, = 12NH,Cl + N,S8, + 88. The precipitate obtained is washed with water to remove NH,Cl and is then frac- tionally crystallised from CS, to separate the N,S, and §, the latter being the more soluble. This substance forms orange crystals which melt at 158°, and is remarkable fer its sparing solubility, its irritating odour, and its explosibility when struck or sharply heated, its elements being held together by a very feeble attraction. Sp. gr. 2-2. Nitrogen pentasulphide, N2S5, is a red oil obtained by heating the tetrasulphide dissolved in CSg, in a sealed tube at 100°, distilling the CS, and extracting the residue with ether, which leaves the N.S; on evaporation. Its sp. er. is 1-9 and it melts at 10°. It resembles iodine in odour and burns the skin. Compounpbs oF NITROGEN WITH HALOGENS. There are several halogen-substituted ammonias, all of which are very violent explosives ; they are very unstable. Nitrogen fluoride is no doubt formed at the negative pole when ammonium fluoride solution is electrolysed ; the oily drops produced explode with great violence. Nitrogen Chloride is the name usually given to the very explosive compound discovered by Dulong in 1811 produced by the action of chlorine on ammonium chloride in aqueous solution. The oily liquid thus produced is a mixture of compounds which have been formed from the NH,Cl by the substitution of chlorine for hydrogen; probably NH,Cl, NHCl,, NCl,. Nitrogen chloride, NCl;, is the most explosive constituent of the mixture, and can be isolated by a process attended with considerable danger. Electro- lysis of concentrated ammonium chloride solution is a good method. It is a yellow, heavy, oily liquid (sp. gr. 1-65), which volatilises easily, yielding a vapour of very characteristic odour, which affects the eyes. When heated to about 93° it explodes with great violence, emitting a loud report and a flash of light. Its instability is attributable to the feeble attraction which holds its elements together, and the violence of the explosion to the sudden expansion of a small volume of the liquid into a large volume of nitrogen and chlorine. It is said to absorb 38,478 gram-units of heat per gram-molecule in the process of formation and would therefore disengage that amount of heat in the act of decomposition. As might be expected, its explosion is at once brought about by contact with sub- stances which have an attraction for chlorine, such as phosphorus and arsenic; the oils and fats cause its explosion, probably by virtue of their hydrogen ; oil of turpentine explodes it with greater certainty than the fixed oils. Alkalies also decompose it vio- lently ; whilst acids, having no action upon the chlorine, are not so liable to explode it. At 71° this substance has actually been distilled without explosion. Although practically unimportant, the violently explosive properties of this sub- stance render it so interesting that it may be well to give some directions for its safe preparation, which may be effected by the action of solution of hypochlorous acid upon ammonium chloride. Fifty grains of red oxide of mercury are very finely powdered and thrown into a pint bottle of chlorine together with 4 oz. of water. The stopper is replaced and the NITROGEN IODIDE 209 bottle well shaken, loosening the stopper occasionally, as long as the chlorine is absorbed, The solution of hypochlorous acid thus produced is filtered from the residual mercuric oxychloride and poured into a clean thumb-glass (Fig. 148). A lump of ammonium chloride weighing 20 grains is then dropped into the solution, and the glass is placed under a stout wooden box. After the lapse of twenty minutes, the chloride of nitrogen may be exploded by inserting, through a hole in the box, a stick dipped in turpentine, fixed at right angles to a longer stick. = = The glass will be shattered into very small fragments. ‘Tia. 148 Nitrogen bromide is believed to be the nature of the dark ex- plosive oil which separates when potassium bromide acts on nitrogen chloride. Nitrogen Iodide.—The action of chlorine, bromine, and iodine upon ammonia exemplifies the difference in their attraction for hydrogen ; for whilst chlorine and bromine, acting upon ammonia, cause the liberation of a certain amount of nitrogen, iodine simply removes part of the hydrogen, and itself fills up the vacancies thus occasioned, no nitrogen being liberated, the hydriodic acid thus formed combining with more ammonia to form ammo- nium iodide. Nitrogen iodide, NI;, or rather a mixture of NI;, NI;.NH3, NI,.2NH;, NI,.3NHg, &c., is formed at the same time. It appears that when iodine is dissolved in dilute ammonia NH,I and hypotodous acid are formed; NH; + I, + H,O = NH,I + HOI. The hypoiodous acid then reacts with more ammonia to form nitrogen iodide ; NH, + 3HOI = NI; + 3H,0. By another theory the nitrogen iodide, alleged to have the formula N,H3lI3, is formed as a decomposition product of ammonium hypoiodite ; 3NH,OI = N.H,I, + NH, + 2H,0. The hypoiodite would be formed when iodine is dissolved in excess of ammonia; I, + 2NH, + H,O = NH,I + NH,OI. To prepare nitrogen iodide 1-3 grams of iodine are rubbed to powder in a mortar and mixed with 14 ¢.c. of strong ammonia ; the mortar is covered with a glass plate, and after about half an hour the nitrogen iodide is collected in separate portions upon four filters, which are allowed to drain and spread out to dry. The brown solution contains iodine dissolved in ammonium iodide. Another method consists in dissolving iodine in a mixture of hydrochloric with a little nitric acid, with the aid of heat, and adding ammonia, which decomposes the ICI in solution and gives a black precipitate of nitrogen iodide. When dry NH; gas is passed over iodine the two combine, several compounds, such as (NHg),I, being formed. The iodide is a black powder which explodes with a loud report even when touched with a feather, the violence of the explosion being accounted for by the sudden evolution of a large volume of gas and vapour from a small volume of solid. Even when allowed to fall from the height of a few feet upon the surface of water, it explodes if perfectly dry. In the moist state it slowly undergoes decomposition. The compound NI;.NH, forms copper- red crystals of sp. gr. 3-5 which are exceedingly explosive. PHOSPHORUS, P= 31.05. This element is never known to occur uncombined in nature, but is found abundantly in the form of phosphate of lime or tricaleie diphosphate, 3CaO.P,0, or Ca,(PO,)2, which is contained in the minerals coprolite, phos- phorite, and apatite, and occurs diffused, though generally in small propor- tion, through all soils upon which plants will grow ; for phosphorus, probably in this form, is an essential constituent of the food of plants, and especially of the cereal plants, which form so large a proportion of the food of animals. The seeds of such plants are especially rich in the phosphates of calcium and magnesium. Animals feeding upon these plants still further accumulate the phos- 14 210 - PHOSPHORUS phorus, for it enters, chiefly in the form of calcium phosphate, into the composition of almost every solid and liquid in the animal body, and is especially abundant in the bones, which contain about three-fifths of their weight of calcium phosphate. Composition of the Bones of Oxen, Fat. : : : : 5-4 Calcium fluoride ‘ . 12 Nitrogenous matter. . 28-6 Calcium carbonate ‘ . 73 Calcium phosphate ~ . . 56-5 Magnesium phosphate . . 10 What is here termed nitrogenous matter is a cartilaginous substance, converted into gelatine when the bones are heated with water under pressure, and containing C, H, N and O. It was formerly the custom to get rid of this by burning the bones in an open fire, but the increased demand for chemical products, and the diminished supply of bones, have taught economy, so that the cartilaginous matter is now dissolved out by heating the bones with water at a high pressure for the manufacture of glue ; or the bones are subjected to destructive distillation, so as to save the ammonia which they evolve, and the bone charcoal thus produced is used by the sugar-refiner until its decolorising powers are exhausted, when it is heated in contact with air to burn away the charcoal, and leave the bone-ash, consisting chiefly of calcium phosphate, Ca3(PO,4)o, and valuable as a manure. Originally, phosphorus was made from bone-ash, but now the cheaper calcium phosphate of mineral origin is employed as the raw material. The coprolites, or other phosphates, are ground to powder and mixed with enough chamber acid (H,SO,) to convert the calcium into sulphate and to liberate the phosphoric acid ; Ca,(PO,). + 3H,SO, = 3CaSO, + 2H;PO,. The liquor is evaporated and the solution of phosphoric acid separated from the calcium sulphate by filtration. This solution is further evaporated to a syrup, absorbed by charcoal and dried, during which the phosphoric acid loses water, becoming metaphosphoric acid, H,PO, = HPO, + 2H,0. It is now only necessary to distil the mixture of charcoal and metaphosphoric acid in bottle-shaped fireclay retorts set in a furnace. The phosphorus distils, hydrogen and carbon monoxide being evolved at the same time (4HPO, + 12C = 12CO + P, + 2H,), and is condensed under warm water in which it melts. It is far from pure, having a mahogany colour; to eliminate this it is remelted with a mixture of sulphuric acid and potassium bichromate ; the impurities are thus oxidised and the phosphorus becomes yellow. It is cast into sticks or wedges which are packed in tins, containing water, for the market. The yield is only 70 per cent. of the theoretical yield. Instead of liberating the phosphoric acid from the calcium phosphate by sulphuric acid as described above, advantage may be taken of the fact that at very high temperatures silicic anhydride (SiO,), being less volatile than phosphoric anhydride (P,O;), can expel the latter from its combination with lime, although a less powerfully acid oxide; Ca,(PO,), + 3Si0, = 3CaSiO, + P,O;. The temperature of the electric furnace (p. 252), how- ever, is essential for this reaction; accordingly, on a commercial scale a mixture of calcium phosphate, sand (SiO,) and coke (C) is heated in such a furnace provided with an arrangement for collecting the phosphorus which distils from the mixture. The carbon of the coke reduces the P,O; liberated according to the above equation ; P,O, + 5C = P, + 5CO. An electric furnace for the distillation of phosphorus is shown in Fig. 149. The mixture, a, of ground calcium, phosphate, sand, and coke is charged through the pipe, b, and is heated by radiation from the graphite rod, c, fitted into carbon blocks, d. These are connected by copper rods, e, with the poles of a dynamo, the current heating YELLOW PHOSPHORUS 211 the rod, ¢, to a white heat, The heated mixture, a, evolves phosphorus vapour which passes to a condenser through pipe g. The slag is removed through pipe f. On a small scale, for the sake of illustration, phosphorus may be prepared by a process which has also been successfully employed for its manufacture in quantity, and consists in heating a mixture of bone-ash and charcoal in a stream of hydrochloric acid gas; Ze Ca,(PO,)p + 6HCL + 8C = 3CaCl, + 8CO + 3H, LD 4 Py. ge A mixture of equal weights of well-dried char- coal and bone-ash, both in fine powder, is intro- duced into a porcelain tube, and placed in a gas- furnace. One end of the tube is connected with a flask evolving HCl (p. 109), and the other is cemented with putty into a bent tube for convey- pee ing the phosphorus into a vessel of water. On we ms A Li yA . . . [= heating the porcelain tube to bright redness, (f AIA, x Ly, ZY y Y phosphorus distils in abundance, The hydro- CO i, gen and carbonic oxide inflame as they escape yy LL A into the air, from their containing phosphorus vapour, Fie. 149. E, in yyy poy sunugiee My ELL Lid VLA Commercial phosphorus usually contains La Acdsee LLM ZAZA arsenic, from which it may be freed completely by twice distilling with steam in an atmosphere of CO,. Pure ordinary, or Vitreous, or Yellow Phosphorus is almost colourless and transparent, but when exposed to light, and especially to direct sunlight, it gradually acquires an opaque red colour, from its conversion into the allotropic variety known as red phosphorus. By tying bands of black cloth round a stick of phosphorus and exposing it, under water, to the action of sunlight, alternate zones of red may be produced. Even though the phosphorus be screened from light, it will not remain unchanged unless the water be kept quite free from air, which irregularly corrodes the surface of the phosphorus, rendering it white and opaque. This action is accelerated by exposure to light. The vapour of phosphorus is 62 times as heavy as hydrogen, so that its atom occupies only half a volume, if the atom of hydrogen be taken to occupy 1 volume; and the molecule of phosphorus occupying 2 volumes, would consist of 4 atoms (P,) instead of 2. At very high temperatures the specific gravity of phosphorus vapour diminishes, showing a tendency to conform with the ordinary law of volumes. By the surface tension method (p. 316) it is found that in the liquid state also the formula is P,. Ordinary phosphorus is slowly vaporised at common tempera- tures, and emits in the air white fumes with a peculiar alliaceous odour, which appear phosphorescent in the dark. It boils at 278°, yielding a colourless vapour. The specific heat is 0-18; whence the atomic heat is 5-59. The most remarkable character of ordinary phosphorus is its easy. inflammability. It inevitably takes fire in air when heated a little above its. melting-point, 44 5°, the white flame burning with a brilliance, which becomes insupportable when the combustion is in oxygen (p. 60), and evolving dense white clouds of phosphoric anhydride. When a piece 3 dry phosphorus is exposed to the air, it combines slowly with oxygen,’ and its temperature often becomes so much elevated during this slow combustion, that it melts and takes fire, especially if the combustion be encouraged by the warmth of the hand or by friction. Hence, ordinary phosphorus must never be 1 The white fumes evolved by phosphorus in moist air are said to consist partly of ammonium nitrate formed by the action of the ozonised oxygen (p. 139) upon the air and aqueous vapour. , WW NY 212 PHOSPHORESCENCE handled or cut in the dry state, but always under water, for it causes most painful burns. The slow oxidation of phosphorus is attended with that peculiar luminous appearance which is termed phosphorescence (pas, light, pépw, to bear), but this glow is not seen in pure oxygen, except under diminished pressure, or in air containing a minute proportion of olefiant gas or oil of turpentine ; nor will phosphorus glow in compressed air at the ordinary temperature. It will be remembered that the slow oxidation of phosphorus in moist air is attended with the formation of ozone. The glow of phosphorus, which may be regarded as an incipient flame, is in some way connected with this ozone (possibly produced during the oxidation of the phosphorus to P,O; ; P, + 30, = P,O, + O and O, + O = O,;). When phosphorus is exposed to pure oxygen at the ordinary pressure, oxidation seems to proceed very slowly at the ordinary temperature ; but at an elevated temperature (25°), or in oxygen at diminished pressure,’ the phosphorus is oxidised with formation of P,O, (and ozone) and P,O,. This latter oxide is readily oxidised to P,O,; and phosphoresces during the change, particularly in the presence of ozone. Moisture is essential to the oxidation (and the glow) of phosphorus at any pressure. If a small stick of phosphorus be carefully dried with filtering paper, and dropped into a cylinder of oxygen, which is afterwards covered with a glass plate, no luminosity will be observed in « darkened room until the cylinder is placed under the air-pump receiver, and the air slowly exhausted. When the oxygen has thus been rarefied to about one-fifth of its former density, the phosphorescence will be seen. A similar effect may be produced by covering the cylinder of oxygen containing the phosphorus (having removed the glass plate) with another cylinder, about four times its size (Fig. 150), filled with carbonic acid gas, which will gradually dilute the oxygen and produce the phos- phorescence. By suspending—in a bottle of air containing : a strongly luminous piece of phosphorus—a piece of paper Fic. 150. with a drop of oil of turpentine upon it, the glow may be almost instantaneously destroyed. A small tube of olefiant gas or coal gas dropped into the bottle will also extinguish the luminosity. * The characteristic behaviour of phosphorus in air is best observed when the phos- phorus is in a finely divided state. The experiment described on p. 59 (Fig. 48) will serve as an illustration. The luminosity of phosphorus vapour is seen to advantage when a piece of phos- phorus is boiled with water in a narrow-necked flask or retort, or a test-tube with a cork and narrow tube. The steam charged with vapour of phosphorus has all the appearance of a blue flame, in a darkened room, but of course combustibles are not inflamed by it, since its temperature is not higher than 100°. Phosphorus may be distilled, with perfect safety, in an atmosphere of carbon dioxide, the neck of the retort being allowed to dip under water in the receiver. Advantage is taken of the fact that phosphorus distils in steam and renders it luminous in testing for this poison in organic liquids. Very small quantities may thus be detected. Conversely, the glow of phosphorus vapour may serve as a delicate test for oxygen, as it can be detected until the last trace of this gas has disappeared. If phosphorus be dissolved in olive oil, at a gentle heat, the solution is strongly phosphorescent when shaken in a bottle containing air, or rubbed upon the hand. Characters may be written on paper with a stick of phosphorus held in a thickly folded piece of damp paper (having a vessel of water at hand into which to plunge the 1 It will be remembered that the pressure of the oxygen in the air is only about one-fifth of the total pres- sure, so that air contains oxygen at diminished pressure. The extent to which the pressure must be diminished for the production of the glow depends on the temperature. ? Chappuis finds that when phosphorus is suspended in oxygen, the space glows for a short time en adding a little oxygen. RED PHOSPHORUS 213 phosphorus if it should take fire). When the paper is held with its back to the fire, or to a hot iron, in a darkened room, a twinkling combustion of the finely divided phos- phorus ensues and the letters are burnt into the paper. Phosphorus which has been partly oxidised is even more easily inflamed than pure phosphorus. If a few small pieces of phosphorus be placed in a dry stoppered bottle, gently warmed till they melt, and then shaken round the sides of the bottle so as to become partly converted into red oxide of phosphorus, it will be found, long after the bottle is cold, to be spontaneously inflammable, so that if a wooden match tipped with sulphur be rubbed against it, the phosphorus which it takes up will ignite when the match is brought into the air, kindling the sulphur, which will inflame the wood. This was one of the earliest forms in which phosphorus was employed for the purpose of procuring an instantaneous light, If the stopper be greased, the phosphorus may be preserved unchanged for a long time. In the last experiment, if the wood had not been tipped with sulphur, the phosphorus would not have kindled it, the flame of phosphorus generally being unable to ignite solid combustibles, because it deposits upon them a coating of P,O;, which protects them from the action of air. Hence, in the manufacture of lucifer matches, the wood is first tipped with sulphur, or wax, or paraffin, which easily give off combustible vapours to be kindled by the flame of the phosphorus composition, and thus to inflame the wood. Although ordinary phosphorus is of a decidedly glassy or vitreous struc- ture, it may be obtained in dodecahedral crystals, by allowing its solution in carbon disulphide to evaporate in an atmosphere of carbon dioxide, or by fusing it in a tube exhausted by a Sprengel pump, and letting it cool in the dark. The conversion of ordinary phosphorus into red phosphorus is one of the most striking instances of allotropic modification. When phosphorus is heated for a considerable length of time to about 232° in vacuo, or in an atmosphere in which it cannot burn, it becomes converted into an infusible mass of red phosphorus, 27,000 gram units of heat being evolved for every 31 grams converted. This form of phosphorus differs as widely from the vitreous form as graphite differs from diamond. It is only slowly oxidised in warm moist air, evolves no vapour, is not luminous, cannot be inflamed by friction, or even by any heat short of 260°. When it is heated above 350° it slowly sublimes as yellow phosphorus. By heating vitreous phos- phorus in an exhausted and sealed tube te about 500°, it is converted into a violet- black fused mass with cavities containing crystals. Red phosphorus is insoluble in the solvents for ordinary phosphorus. The two varieties also differ greatly in specific gravity, that of the ordinary phosphorus being 1-83, and of the red variety 2-34 , but commercial specimens 2-14 to 2-29. Of the two, the red variety is the better conductor of electricity. Specific heat of red phosphorus is 0-17. The conversion of vitreous into red phos- phorus, or amorphous phosphorus as it was called before it was proved to be microscopically crystalline, may be effected by heating it in a flask (A, Fig. 151) placed in an oil-bath (B), maintained at a temperature ranging from 232° to 238°, the flask being furnished with a bent ttibe (C) dipping into mercury, and with another tube (D) for supplying CO,, dried by passing over calcium chloride. The flask should be thoroughly filled with CO, before applying heat, and the tube deliver- ing it may then be closed with a small clamp (E). After exposure to heat for about forty hours, but little ordinary phosphorus will remain, and this may be removed by allowing the mass to remain in contact with carbon disulphide for some hours, and 214 PHOSPHORUS—CHEMICAL PROPERTIES subsequently washing it with fresh disulphide till the latter leaves no phosphorus when evaporated. On the large scale, the red phosphorus is prepared by heating about 200 lbs. of vitreous phosphorus to 232° in an iron boiler. After three or four weeks the phosphorus is found to be converted into a hard red brittle mass, which is ground by mill-stones under water, and separated from the ordinary phosphorus by heating the powder with a solution of calcium chloride of 1-9 sp. gr. at 50°; the vitreous phosphorus melts and floats, whereas the red phosphorus (sp. gr. above 1-9) sinks. The temperature requires careful regulation, for if it be allowed to rise above 260°, the red phosphorus resumes the vitreous condition. This reconversion may be shown by heating a little red phos- phorus in a narrow test-tube, when drops of vitreous phosphorus condense on the cool part of the tube. The colour of different specimens of red phosphorus varies consider- ably, depending upon the temperature at which the conversion has been effected ; that prepared on the large scale is usually of a dark purplish colour, but it may be obtained of a bright scarlet colour. Rhombohedral crystals of the red phosphorus, resembling crystals of arsenic in form and metallic appearance, have been obtained by fusing phosphorus with lead, and dissolving out the latter with diluted nitric acid (sp. gr. 1-1). Similar crystals have been obtained by heating red phosphorus to 530° in a vacuous tube. Ordinary phosphorus is very poisonous (0-1 gram being fatal), whilst red phosphorus appears to be harmless. The former is employed, mixed with fatty substances, for poisoning rats and beetles. Cases are, unhappily, not very rare, of children being poisoned by sucking the phosphorus composi- tion on lucifer matches. The vapour of phosphorus also produces a very injurious effect upon the persons engaged in the manufacture of lucifer matches, resulting in the decay of the lower jaw-bone. The evil is much mitigated by good ventilation, or by diffusing turpentine vapour through the air of the workroom, and attempts have been made to obviate it entirely by substituting red phosphorus for the ordinary variety, but, as might be expected, the matches thus made are not so sensitive to friction as those in which the vitreous phosphorus is used. The difference between the twu varieties of phosphorus, in respect to chemical energy, is seen when they are placed in contact with a little iodine on a plate, when the ordinary phosphorus undergoes combustion and the red phosphorus remains unaltered. Ordinary phosphorus, when moist, is capable of direct union with oxygen, chlorine, bromine, iodine, sulphur, and most of the metals, with which it forms phosphides or phosphurets. Even gold and platinum unite with this element when heated, so that crucibles of these metals are liable to corrosion when heated in contact with a phosphate in the presence of a reducing agent, such as carbon. Thus the inside of a platinum dish or crucible is roughened when vegetable or animal substances containing phosphates are incinerated in it. The presence of small quantities of phosphorus in iron or copper produces considerable effect upon the physical qualities of these metals. Phosphorus has the property, a very remarkable one in a non-metal, of precipitating some metals from their solutions in the metallic state. If a stick of phosphorus be placed in a solution of sulphate of copper, it becomes coated with metallic copper, the phosphorus appropriating the oxygen. This has been turned to advantage in copying very delicate objects by the electrotype process, for by exposing them to the action of a solution of phosphorus in ether or carbon disulphide, and afterwards to that of a solu- tion of copper, they acquire the requisite conducting metallic film, even on their finest filaments. Solutions of silver and gold are reduced in a similar manner by phosphorus. By floating very minute scales of ordinary phosphorus upon a dilute solution of chloride of gold, the metal will be reduced in the form of an extremely thin film, which LUCIFER MATCHES 215 may be raised upon a glass piate, and will be found to have various shades of green and violet by transmitted light, dependent upon its thickness, whilst its thickest part exhibits the ordinary colour of the metal to reflected light. By heating the films on the plate, various shades of amethyst and ruby are developed. Lucifer Matches are made by tipping the wood with sulphur, or wax, or paraffin, to convey the flame, and afterwards with the match composition, which is generally composed of an oxidising agent, usually saltpetre or potassium chlorate, phosphorus, red lead, and glue, and depends for its action on the easy inflammation, by friction, of phosphorus when mixed with an oxidising agent, the glue serving only to bind the composition together and attach it to the wood. The composition used by different makers varies much in the nature and proportions of the ingredients. In this country, potassium chlorate is most commonly employed as the oxidising agent, such matches usually kindling with a slight detonation; but the German manufacturers prefer either potassium nitrate or lead nitrate, together with lead dioxide or red lead, which produce silent matches. Sulphide of antimony (which is inflamed by friction with potassium chlorate, see p. 118) is also used in those compositions in which a part of the phosphorus is employed in the red form, and fine sand or powdered glass is very commonly added to increase the susceptibility of the mixture to inflammation by friction. The match composition is coloured either with ultramarine blue, Prussian blue, or vermilion. In preparing the composition, the glue and the nitre or chlorate are dissolved in hot water, the phosphorus then added and care- fully stirred in until intimately mixed, the whole being kept at a temperature of about 38°. The fine sand and colouring-matter are then added, and when the mixture is complete, it is spread out upon a stone slab heated by steam, and the sulphured ends of the matches are dipped into it. The safety matches, which refuse to ignite unless rubbed upon the sides of the box, are tipped with a mixture of antimony sulphide, potassium chlorate and powdered glass, which is not sufficiently sensitive to be ignited by any ordinary friction, but inflames at once when rubbed upon the red phosphorus mixed with glass, which coats the rubber on the sides of the box. In many countries, including Great Britain, it is now illegal to make lucifer matches with white phosphorus. The most successful substitute is phosphorus sesquisulphide, P,S, (p. 223). One composition contains per cent.: P,S;, 6; KCIO,, 24; ZnO, 6; Fe,0,, 6; glass powder, 6; glue, 18; water, 34. For illustration, very excellent matches may be made upon the small scale in the following manner. The slips of wood are dipped in melted sulphur so as to acquire a slight coating. Two grams of gelatine or isinglass are dissolved in 5 c.c. of water in a porcelain dish placed upon a steam-bath ; 1-3 grams of ordinary phosphorus are then added, and well mixed in with a piece of wood ; to this mixture are added, in succession, 1 gram of red lead and 2-3 grams of powdered potassium chlorate. The sulphured matches are dipped into this paste, and left to dry in the air. To make the safety matches: 1 gram of powdered potassium chlorate and 1 gram of antimony sulphide are made into a paste with a few drops of a warm solution of 2 grams of gelatine in 5 c.c. of water, the sulphured matches being tipped with this composition. The rubber is prepared with 2 grams of red phosphorus, and | gram of finely powdered glass, mixed with the solution of gelatine, and painted on paper or cardboard with a brush. A very sensitive detonating composition formerly used for igniting percussion shells, may be prepared with care in the following manner: 0-2 gram of powdered potassium chlorate is moistened on a plate with 6 drops of spirit of wine, 0-2 gram of powdered red phosphorus is added, and the whole mixed, at arm’s length, with a 216 HYDROGEN PHOSPHIDE bone-knife, avoiding great pressure. The mixture, which should be quite moist, is spread in small portions upon ten or twelve pieces of filtering-paper, and left in a safe place to dry. If one of these be gently pressed with a stick, it explodes with great violence. It is dangerous to press it with the blade of a knife, as the latter is commonly broken, and the pieces projected with considerable force. A stick dipped in oil of vitriol of course explodes it immediately. If a bullet be placed very lightly upon one of the pellets, and the paper tenderly wrapped round it, a percussion shell may be extem- porised, which explodes with a loud report when dropped upon the floor. The detonating toys known as amorces fulminantes are made by enclosing this com- position between two pieces of thin paper. 1000 of them contain 70 grains of the composition, CoMPOUNDS OF PHOSPHORUS WiTH HyDROGEN, Although phosphorus and hydrogen do not combine directly, there are three compounds of these elements producible by processes of substitution, viz., PH,, gas; P,H,, liquid; P,H,, solid. Gaseous Hydrogen Phosphide, or Phosphoretted Hydrogen, or Phosphine, PH, = 34:06, is by far the most important of these. It is produced by the action of heat upon phosphorous acid (p. 221), and when prepared by this process, it is a colourless gas, with a most powerful odour of putrid fish, inflaming on the approach of a light, and burning with a brilliant white flame, producing thick clouds of phosphorus pentoxide. It is slightly heavier than air (sp. gr. 1-176), and has been liquefied at — 90° and solidified at — 133°; it boils at — 86-2°. The gas dissolves in 9 vols. water. The ordinary method of preparing this gas for experimental purposes consists in boiling phosphorus with a strong solution of potash, when water is decomposed, its hydrogen combining with one part of the phosphorus, and its oxygen with another part forming hypophosphorous acid, which unites with the potash— P, + 3KOH + 3H,0 = PH, + 3PH,0(OK). A few fragments of phosphorus are introduced into a small retort (Fig. 152), which is then nearly filled with a strong solution of potash (45 grams of stick potash in 100 ¢.c. of water), and heated. The extremity of the neck of the retort should not be plunged under water until the spontaneously inflammable gas is seen burning at the orifice, and the retort must not be placed close to the face of the operator, since ex- plosions sometimes happen in preparing the gas, and the boiling potash produces dangerous effects. The gas may be collected in small jars filled with water, taking care that no bubble of air is left in them. It contains hydrogen phosphide mixed with free hydrogen, the latter being formed from the de-oxidation of water by the potassium hypo- phosphite. As each bubble of this gas escapes into the air through the water of the pneumatic trough, it burns with a vivid white flame, pro- ducing beautiful wreaths of smoke (phosphoric anhydride), resembling the gunner’s rings some- times seen in firing cannon. Small bubbles some times escape without spontaneously inflaming. If a bubble be sent up into a jar of oxygen, the flash of light is extremely vivid, and the jar must be a strong one to resist the concussion. It is advisable to add a trace of chlorine to the oxygen, to ensure the inflammation of each bubble, for suksequent inflammation of an accumulation of the gas would shatter the jar. It is stated that phosphoretted hydrogen may be added to pure oxygen without PHOSPHORIC ACID 217 ignition until the pressure is reduced, when explosion suddenly occurs (compare the phenomenon of phosphorescence, p. 212). If the phosphoretted hydrogen be passed through a tube cooled in a freezing-mixture of ice and salt, the gas escaping from the tube is found to have lost its spontaneous inflammability, although it takes fire on contact with flame. The cold tube contains the Liquid Hydrogen Phosphide (P.H,), which was present in the gas in the state of vapour, and caused its spontaneous inflammability, for as soon as the liquid comes in contact with air it takes fire ; 0-2 per cent. of the P,H, will make PH; spontaneously inflammable at ordinary temperatures ; when pure, 149° is necessary. When exposed to light, the liquid phosphide is decomposed into the gaseous phosphide, and a yellow Solid Hydrogen Phosphide (P,,H,), which is not spontaneously inflammable ; 15P,H, = PyH, + 18PH3. It is for this reason that the spontaneously inflammable gas loses that property when kept (unless in the dark), depositing the solid phosphide upon the sides of the jar. Pure PHg is evolved from PH,I (infra) by KOH. Cf. NH,I+KOH. By passing a few drops of oil of turpentine up through the water into a jar of the spontaneously inflammable gas, this property is entirely destroyed. Hydrogen phosphide, when passed through solutions of some of the metals, pre- cipitates their phosphides. For example, with cupric sulphate it gives a black pre- cipitate of cupric phosphide ; 3CuSO, + 2PH, = 3H,SO, + P2Cu; (cf. H,8). When this black precipitate is heated with solution of potassium cyanide, it evolves self-lighting hydrogen phosphide.! In fact, this is one of the easiest and safest methods of preparing this gas; for the cupric phosphide is readily obtained by simply boiling phosphorus in a solution of cupric sulphate. Phosphine is absorbed by strong sulphuric acid, and, after a time, acts upon it with great evolution of heat, SO, being formed and sulphur deposited: Sulphur decomposes it in sunshine ; 2PH, + 8S, = P.S, + 3H.S. The spontaneously inflammable hydrogen phosphide may also be obtained by throwing fragments of calcium phosphide into water ; this substance is prepared by passing vapour of phosphorus over red-hot quicklime, or simply by heating small lumps of quicklime to bright redness in a crucible and throwing in fragments of phosphorus, closing the crucible immediately. The dark brown mass thus obtained is a mixture of pyrophosphate and phosphide of calcium, of somewhat variable composition. The calcium phosphide has been used in life-buoys for indicating by the flare their position on the water. : Phosphine has great pretensions to rank as the chemical analogue of ammonia, for although it has no alkaline properties, it is capable of combin- ing with hydrobromic and hydriodic acids to form crystalline compounds such as phosphonium iodide, PH,I, analogous to ammonium bromide and iodide ; these compounds, however, are decomposed by water. It will be seen hereinafter, that when the hydrogen in phosphine is displaced by certain compound radicles, such as ethyl, powerful organic bases are produced ; see ethyl phosphines. When phosphine is decomposed by a succession of electric sparks, 2 volumes of the gas yield 3 volumes of hydrogen, the phosphorus being deposited in the red form. Compounps oF PHOSPHORUS WITH OXYGEN. _ Four oxides of phosphorus are known, their formule being P,O, P,O,, P,O,, and P,O,;. Of these P,O, and P,O, are anhydrides, the others are neutral oxides. It will be convenient to consider phosphoric acid and its anhydride first. Phosphoric Acids and Phosphates.—The phosphates are by far the most important of the compounds of phosphorus. They have been already noticed as almost the only forms of combination in which that element is met with in nature, and as indispensable ingredients in the food of plants 2 Cuprie cyanide and potassium phosphide being formed and the latter decomposed by water, giving hydrogen phosphide and potassium hypophosphite, 218 PHOSPHORIC ACID—PREPARATION and animals. No other mineral substance can bear comparison with calcium phosphate as a measure of the capability of a country to support animal life. Phosphoric acid itself is very useful in calico-printing and in some other arts. The mineral sources of this acid appear to be phosphorite, coprolite, and apatite, all consisting essentially of calcium phosphate, Ca,(PO,),, but associated in each case with calcium fluoride, which is also contained, with calcium phosphate, in bones, and would appear to indicate an organic origin for these minerals. Phosphorite is an earthy-looking substance, forming large deposits in Estremadura. Apatite (from azraraw, to cheat, in allusion to mistakes in its early analysis) occurs in prismatic crystals, and is met with in the Cornish tin-veins. Both these minerals are largely imported from Spain, Norway, and Florida, for use in this country as a manure. Coprolites («dapos, dung, (Bos, a stone, from the idea that they were petrified dung) are rounded nodules of calcium phosphate, which are found abundantly in this country. Large quantities of phosphates of calcium and magnesium are imported in the form of guano, the partially decomposed excrement of sea fowl. Phosphoric acid is obtained from bone-ash, or mineral phosphate, by decomposing it with sulphuric acid, so as to remove as much of the lime as possible in the form of sulphate, which is strained off, and the acid liquid neutralised with ammonium carbonate, which precipitates any unchanged calcium phosphate, and converts the phosphoric acid into ammonium phosphate. On evaporating the solution, and heating the ammonium phosphate, ammonia and water are expelled, and metaphosphoric acid (HPO,) is left in a fused state, solidifying to a glass on cooling. Thus prepared, however, it always retains some ammonia. This method of preparing phosphoric acid is illustrative of one very generally employed in the preparation of those acids which cannot be dis- tilled. In the case of most of the acids heretofore considered, advantage is taken of their great volatility, compared with that of sulphuric acid, to obtain them from their sodium salts. It is possible to liberate phosphoric acid from its sodium salt by the action of sulphuric acid ; but since phos- phoric acid is not more volatile than sulphuric acid, it is difficult to separate the sodium sulphate produced by the combination of the sulphuric acid with the sodium of the sodium phosphate, from the phosphoric acid, both of them remaining in solution. In such cases advantage is taken of the insolubility of calcium sulphate or of barium sulphate ; when a calcium or barium salt of the required acid is treated with sulphuric acid, calcium sulphate or barium sulphate is precipitated, and may be separated by filtration from the solution containing the desired acid. The treatment of a lead salt of the acid with hydrosulphuric acid, whereby lead sulphide is precipitated,.is another method for preparing acids, based on the same principle. Pure phosphoric acid is prepared by oxidising phosphorus with dilute nitric acid (sp. gr. 1-197) and evaporating the solution unti] the phosphoric acid begins to volatilise in white fumes ; 5HNO, + 3P = 3HPO; + HO + 5NO.! Some phosphorous acid is formed at an intermediate stage. A transparent glass (glacial phosphoric acid) is thus obtained, which eagerly absorbs moisture from the air, and becomes liquid. That which is sold in sticks contains much sodium metaphosphate. The addition of a little bromine greatly facilitates the action of nitric acid upon ! Orthophosphoric acid is first formed, 5NO,.OH + 8P + 2HOH = 3PO(OH), -+ 5NO; but this loses water duirng the evaporation, producing metaphosphoric acid; PO(OH), — H,O = PO,(OH), , PHOSPHORIC ANHYDRIDE 219- phosphorus, apparently by forming the phosphorus pentabromide, which is then decom-: posed by water; PBr,; + 4H,O = H,;PO, + 5HBr. The hydrobromic acid being then acted on by nitric acid, bromine is set free to act upon a fresh quantity of phos-. phorus; 3HBr + HNO, = 3Br + 2H,0 + NO. When iodine is also added, the action is still better. 28 grams of phosphorus are placed in 170 c.c. of water and 0-32 gram of iodine is added ;_ then; drop by drop, 1:94 grams of bromine. When the action is over, 170 c.c. of HNOs (sp. gr. 1-42) are added, and the vessel is placed in cold water. When the phosphorus has dissolved, the solution is evaporated till its temperature rises to about 204° in order to expel the excess of nitric acid, the bromine, and the iodine. Strong solutions of phosphoric acid are heavy syrupy liquids; at 17-5°, a 92-99 per: cent. acid has a sp. gr. 1-800 ; 88-85 per cent., 1-750 (the strongest commercial) ; 66-3 per cent., 1-493 (acidum phosphoricum conc. B.P.) ; 13-8 per cent., 1-080 (acid. phos. dil.; B.P.). Phosphoric acid has powerful solvent properties ; it dissolves silicon, silica (from porcelain and glass apparatus), zirconium, carborundu:n, &c. The strong acids, on dilution and standing, frequently deposit silica. Phosphoric Anhydride, or Phosphorus Pentoxide. P,O,;, or PO, is prepared by burning phosphorus in dry air. : When required in considerable quantity, the anhydride is prepared by burning the phosphorus in a small porcelain dish (A, Fig. 153) placed under a bell-jar which fits in a groove containing mer- cury and surrounding a glass funnel. Airis drawn through the apparatus by an aspirator attached to the tube C, the empty bottle serving to catch the P,O; carried over by the current. A drying-tube, con- taining pumice moistened with oil of vitriol, is attached to the lateral neck of the bell-jar in order to dry the entering air. When all the phosphorus has been burnt the bell may be removed, and the P,0, swept down the stem of the funnel into a dry = bottle. A small quantity of Fie. 153. phosphoric anhydride is more conveniently prepared by burning phosphorus under a large bell-jar, as shown in Fig. 47. — Phosphoric anhydride as thus prepared is amorphous ; it may be fused at a very high temperature, and even sublimed, when it condenses as micro- scopic crystals. Its great feature is its attraction for water ; left exposed to the air for a very short time it deliquesces entirely, becoming converted into phosphoric acid. It is often used by chemists as a de-hydrating agent, and will remove water even from oil of vitriol (p. 160). When thrown into water it hisses like a red-hot iron, but does not entirely dissolve at once, a few flakes of metaphosphoric acid (?) remaining suspended in the liquid for some time. The commercial anhydride is apt to contain lower oxides of phosphorus, and even red phosphorus. The solution obtained by dissolving phosphoric anhydride in water contains monohydrated phosphoric acid or metaphosphoric acid (H,0.P,05 or HPO,) the analogue of nitric acid. If a little silver nitrate be added to a portion of it, a transparent gelatinous precipitate is formed, which is the silver metaphosphate (AgNO, + HPO, = HNO, + AgPOQ,). Jf the solution of metaphosphoric acid is heated in a flask for a short 220 METAPHOSPHORIC ACID time it loses the property of yielding a precipitate with silver nitrate, unless one or two drops of ammonia be added to neutralise it, when an opaque white precipitate of silver pyrophosphate (2Ag,0.P,0, or Ag,P,0,) is obtained, for the metaphosphoric acid has now been converted into the dihydrated or pyrophesphoric acid (2H,O.P,0; or H,P,0,). The formation of the precipitate is thus expressed— H,P.0, + 4AgNO, + 4NH, = Ag,P,0, + 4NH,NO,. When the solution of pyrophosphoric acid is mixed with more water and boiled for a long time, it gives, when tested with silver nitrate and a little ammonia, a yellow precipitate of silver orthophosphate (3Ag,0.P,0; or Ag,PO,) ; the phosphoric acid having become convertedi nto trihydrated phosphoric acid or orthophosphoric acid (3H,0.P,0, or H,PO,), and acting upon the silver nitrate in the presence of ammonia, thus H,PO, + 3AgNO, + 3NH, = Ag,PO, + 3NH,NO,. The reverse changes occur when orthophosphoric acid is heated, this becoming pyrophosphoric acid at 300°, and metaphosphoric acid at a red heat. The pyrophosphoric acid (H,P,0,) cannot be obtained by the above process without an admixture of one of the other acids, but it has been obtained in crystals by decomposing the lead pyrophosphate (Pb,P,0,) with hydrosulphuric acid, and evaporating the filtered solution in vacuo over oil of vitriol. Trihydrated phosphoric acid may also be obtained in prismatic crystals, by evaporating its solution in a similar way. This acid is also called ortho- phosphoric acid (dp00s, true), and common phosphoric acid, in allusion to the circumstance that the phosphates found in nature and commonly met with and employed in the arts are the salts of this acid. Metaphosphoric acid is distinguished from the other two acids by the fact that it coagulates white of egg (albumin). It will be perceived, from their formule, that metaphosphoric, HPO ;, orthophos- phoric, H,;PO,, and pyrophosphoric, H,P,0,, acids are respectively monobasic, tribasic, and tetrabasic acids. The normal sodium salts of these acids are, respectively, meta- phosphate, NaPO 3, orthophosphate, Na;PO,, and pyrophosphate, Na,P,0;. The hydrogen in orthophosphoric and pyrophosphoric acids may be only partly exchanged for a metal; thus there are two other orthophosphates of sodium, viz. hydrogen- disodium phosphate, HNa,PO,, and dihydrogen-sodium phosphate, H,NaPOQ,. The phosphates commonly met with are all derived from orthophosphoric acid : for example, bone-ash, or tricalcium orthophosphate, Ca3(PO,).; superphosphate, or monocalcium orthophosphate, CaH,(PO4)2 ; common phosphate of soda, or hydrogen- disodium orthophosphate, HNa PO, ; microcosmic salt, or hydrogen-ammonium sodium orthophosphate, HNH,Na(PO,). Pyrophosphates and metaphosphates may be obtained by the action of heat on the orthohydrogen phosphates. Thus, if a crystal of the common rhombic sodium phosphate (HNa,PO,.12Aq) be heated gently in a crucible, it melts in its water of crystallisation, and gradually dries up to a white mass, the composition of which, if not heated beyond 149°, will be NagHPO,. A little of this white mass dissolved in water gives a solution alkaline to red litmus-paper; and if silver nitrate (itself neutral to test-papers) is added to it, a yellow precipitate of silver orthophosphate is obtained, and the solution becomes strongly acid— Na,HPO, + 3AgNO; = Ag,;PO, + 2NaNO, + HNO. If the dried sodium phosphate be now strongly heated over a lamp it will lose water, and become pyrophosphate (mip, fire) ; 2NagHPO, = H,O + Na,P.O,. On dissolving this in water, the solution will be alkaline, and will give with silver nitrate a white precipitate and a neutral solution ; Na,P,0, + 4AgNO, = Ag,P,0, + 4NaNO3. Microcosmic salt (NaNH,HPO,.4Aq), when dissolved in water, yields an alkaline PHOSPHOROUS ACID “221 solution which gives a yellow precipitate with silver nitrate, the liquid becoming acid ; NaNH,HPO, + 3AgNO; = Ag,;PO, + NaNO; + NH,NO; + HNO3. But if the salt be heated in a crucible, it fuses, evolving water and ammonia, and leaving a transparent glass of sodium metaphosphate ; NaNH,HPO, = H,O + NH, + NaPOs, which may be dissolved by soaking in water, yielding a slightly acid solution, which gives a white gelatinous precipitate with silver nitrate, the liquid being neutral ; NaPO, + AgNO, = AgPO, + NaNO;. All the phosphates may be converted into orthophosphates, by fusing them with an alkali, or by boiling them for some time with a dilute acid. For ferric pyrophosphate and its interesting derivatives, sze p. 455. Phosphorous anhydride (P,Og) is a product of the slow combustion of phosphorus, and, by carefully regulating the combustion, may be made to constitute 50 per cent. of the oxides produced, the remainder being P,O;. It is prepared by drawing a slow current of air over ignited phosphorus and causing the product to pass, first through a tube maintained at about 60°, a temperature at which P,0; condenses, and then through a U-tube surrounded by a freezing-mixture wherein the P,Q, solidifies. It forms feathery crystals which melt at 22-5°; it boils at 173°, and is decomposed at higher temperatures (in a sealed tube) according to the equation 2P,0, = 3P,0,4 + Po. It dissolves slowly in cold water, forming phosphorous acid, P,Og + 6HOH = 4P(OH)), ; hot water decomposes it with great violence. It burns in oxygen, forming P,O;, and in chlorine, forming POC], and PO,C1(?). Its combustion in oxygen is attended by all the phenomena of phosphorescence shown by phosphorus, but no ozone is produced. Phosphorus tetroxide, P2O,4, corresponding with N2O,, is obtained as a very deliques- cent crystalline sublimate by heating P,O, to about 440° in a sealed tube filled with CO, ; the white P,O, becomes orange, from the production of red phosphorus, and P20, sublimes in deliquescent colourless crystals, When dissolved in water it is con- verted into a mixture of phosphorous and orthophosphorio acids, just as nitric peroxide, N,0,, is converted into nitrous and nitric acids ; P20, + 3H,0 = H,PO, + H;P03. Phosphorous acid, H;PO3; or P(OH)3;, or PHO(OH),, is obtained in solution, mixed with phosphoric acid, when sticks of phosphorus arranged in separate tubes open at both ends and placed in a funnel over a bottle, are exposed under a bell-jar, open at the top, to air saturated with aqueous vapour. To obtain the pure acid, chlorine is very slowly passed through phosphorus fused under water, when the phos- phorous chloride first formed is decomposed by the water into phosphorous and hydro- chloric acids; PCl; + 3H,0 = P(OH),; + 3HCl. The hydrochloric acid is expelled by a moderate heat, when the phosphorous acid is deposited in prismatic crystals. When heated, it is decomposed into phosphoric acid and gaseous phosphoretted hydrogen ; 4H;PO3, = 3H3PO, + PH3. Solution of phosphorous acid gradually absorbs oxygen from the air, becoming phosphoric acid. This tendency to absorb oxygen causes it to act as a reducing-agent upon many solutions ; thus it precipitates finely divided metallic silver from a solution of the nitrate, by which its presence may be recognised in the water in which ordinary phosphorus has been kept. The solution of phosphorous acid even reduces sulphurous acid, producing sulphuretted hydrogen and sulphur, the latter being formed by the action of the sulphuretted hydrogen upon the sulphurous acid ; H,SO; + 3H;PO; = 3H,PO, + HS. .Some metals dissolve in it, evolving PH;, If solution of phosphorous acid be poured into a hydrogen apparatus, some PH, is formed which imparts a fine green tint to the hydrogen flame. It is doubtful whether phosphorous acid is dibasic or tribasic, that is, whether it contains two or three hydroxyl groups. In the former case its formula should be PHO(OH), ; in the latter, P(OH)3. The former is the more probable in most reactions ; but as the salt Na,;PO, has been prepared, the formula P(OH),; is indicated ; it is supported by the reaction between PCl, and HOH. Hypophosphorous acid, H;PO, or PH,O(OH).—When phosphorus is boiled with barium hydroxide and water, the latter is decomposed, its hydrogen.combining with 1 It has been remarked that the pliancy of the acid character of phosphoric acid particularly fits it to take part in the vital phenomena, It may be regarded as three acids in one, 999 SULPHIDES OF PHOSPHORUS part of the phosphorus to form hydrogen phosphide (spontaneously inflammable), which escapes, whilst the oxygen of the water unites with another part of the phosphorus, forming hypophosphorous acid, which acts on the baryta to form barium hypophosphite ; this may be obtained, by evaporating the solution, in crystals having the composition (PH,0.0),Ba. The action of phosphorus upon barium hydroxide may be represented by the equation— 3Ba(OH), + 6H,0 + 2P, = 3(PH,0.0),Ba + 2PH3. Barium hydroxide. Barium hypophosphite. Some barium orthophosphate is also formed at the same time, as the result of a secondary reaction. By dissolving the barium hypophosphite in water, and decomposing it with the requisite quantity of sulphuric acid, so as to precipitate the barium as sulphate, a solu- tion is obtained which may be concentrated by careful evaporation. If this hypo- phosphorous acid be heated, it evolves hydrogen phosphide, and becomes converted into phosphoric acid ; 2H,PO, = H,P0, + PH;. When exposed to the air it absorbs oxygen, and becomes converted into phosphorous and phosphoric acids. It is a more powerful reducing-agent than phosphorous acid. The latter acid does not reduce a solution of cupric sulphate, but hypophosphorous acid, when gently warmed with it, gives a brown precipitate of cuprous hydride (CuH), which is decomposed by boiling, evolving H and leaving Cu. When heated, the hypophosphites evolve hydrogen phosphide, and are converted into phosphates. The sodium hypophosphite, PH,0.ONa, is used in medicine; its solution has been known to explode with great violence during evaporation, probably from a sudden disengagement of hydrogen phosphide. Hypophosphites, when boiled with caustic alkalies, are converted into phosphates, hydrogen being evolved ; phosphites are unchanged. Calcium hypophosphite, (PH,0-O)s:Ca, is the chief medicinal agent. Hypophosphoric acid, H4P,0, or PO(OH),.PO(OH)., exists in the water in which phosphorus has been kept. The following is a summary of the acids formed by phosphorus with oxygen and hydrogen ; Hypophosphorous acid. : , ‘ ‘ . PH,0(OH) Hypophosphoric _,, , 3 ‘ : ‘ . P,0.(0OH),4 Phosphorous % ; ‘ : : ‘ . P(OH)s Metaphosphoric _,, . ‘ : ‘ ‘ . PO,.(OH) Orthophosphoric _,, ‘ ‘ ‘ ‘ ‘ . PO(OH); Pyrophosphoric __,, ‘ ‘ . : . P,03(OH), Suboxide of phosphorus, P,O, is precipitated as a white powder by passing air into a solution of vitreous phosphorus in carbon tetrachloride gently warmed. It is stable in water but is slowly oxidised by moist air. It has been prepared as a substitute for vitreous phosphorus in lucifer matches. The sulphides of phosphorus may be formed by the direct combination of their elements. Yellow phosphorus liquefies when mixed with sulphur (an operation not unattended by danger), and the liquid dissolves as much as 25 per cent. of sulphur. It fumes in air and readily ignites, but it appears to be only a solution of sulphur in phosphorus, which, like most other solutions, has a lower melting-point than that of the solyent (phosphorus). When a mixture of red phosphorus and sulphur is heated, combination occurs, and P,S8,, PoS3, PS, or P85, PS, or P.S; is formed according to the proportions used. A clay crucible is heated by a bunsen burner and a mixture of red phosphorus (31 parts) and sulphur (48 parts) is added by degrees, the crucible being covered after each addition until the reaction is over. The crucible is allowed to cool until the mass is about to solidify, and the phosphorus trisulphide is then poured on to aniron plate. Itis a dirty yellow crystalline mass of sp. gr. 2-0 and melting-point 167°. Phosphorus pentasulphide, PSs, is similarly prepared and melts at 275° and boils at 530° ; from CS, it separates in nearly colourless crystals. Both sulphides deliquesce in air, being decomposed into oxyacids of phosphorus with evolution of HS, and both are used in organic chemistry for substituting S for O, CHLORIDES OF PHOSPHORUS 223 PS; combines with alkali sulphides, forming thiophosphates ; 3K,S + P.S; = 2K; PS,. Phosphorus sesquisulphide, P,Ss, is important as the substitute for vitreous phos- phorus in the modern match industry. It melts at 142°, CoMPouUNDS oF PHOSPHORUS WITH HALOGENS. Phosphorus trifluoride, PF, is a colourless gas obtained by the inter- action of phosphorus trichloride and arsenic trifluoride. Sparked with half its volume of oxygen, it explodes, forming phosphoryl fluoride, POF;. Phosphorus pentafluoride, PF;, results from the action of fluorine on phosphorus trifluoride or of arsenic trifluoride on phosphorus pentachloride. It is a colourless gas which fumes strongly in moist air. Two chlorides of phosphorus are known. The trichloride or phosphorous chloride (PCI), the acid chloride of phosphorous acid, is prepared by acting upon phosphorus with perfectly dry chlorine in the apparatus employed (p. 177) for preparing the chloride of sulphur. Red phosphorus may be used, and the product redistilled with a little vitreous phosphorus to decompose any PCl;. Phosphorous chloride distils over very easily (boiling-point, 76°), as a colourless, pungent liquid (sp. gr. 1-61), which fumes strongly in air, its vapour decomposing the moisture of the air and producing hydro- chloric acid fumes. In contact with water the liquid is immediately decomposed, yielding hydrochloric and phosphorous acids, as described for the preparation of the latter acid (p. 221). Its analogy to phosphorous anhydride is shown by its absorbing oxygen when boiled in the presence of that gas, and forming the phosphorus oxychloride or phosphoryl chloride POCl;, the acid chloride of phosphoric acid. It also absorbs chlorine with avidity, becoming converted,into pentachloride of phosphorus or phosphoric chloride (PCl;). This compound, however, is more conveniently prepared by passing chlorine through a solution of phosphorus in carbon disulphide, carefully cooled. On evaporation, the pentachloride of phosphorus is deposited in white prismatic crystals, which volatilise below 100°, and fume when exposed to air, from the production of hydrochloric acid. When PCI, is heated above 148° it is dissociated into PCl, and Clo, but this may be prevented by volatilising it in an atmosphere of PCl;, and thus its vapour density has been determined (p. 346). When thrown into water, it is decom- posed into phosphoric and hydrochloric acids ; PCl; + 4H,O = H;PO, + 5HCl. But if it be allowed to deliquesce in air, only a partial decomposition occurs, and the phos- phorus oxychloride is formed; PCl; + H,O = POC], + 2HCl. The same compound is obtained by distilling P.O, with NaCl; 2P,0; + 3NaCl = POC], + 3NaPOs3. This oxychloride may also be produced by heating phosphoric chloride with phos- phoric anhydride ; P,0; + 3PCl; = 5POCl;. A more instructive method of preparing it consists in distilling the phosphoric chloride with crystallised boric acid ; 3PCl, + 2B(OH); = 3POCI],; + 6HCl + B,O3. Some of the organic acids (succinic, for example) may be converted into anhydrides, as the boric acid is in this case, by distilling with phosphoric chloride. The phosphorus oxychloride distils over (boiling-point, 107°) as a heavy (sp. gr. 1-7) colourless fuming liquid of pungent odour. Of course, it is decomposed by water, yielding hydrochloric and phosphoric acids. It will be found of the greatest use in effecting certain trans- formations in organic substances. Pyrophosphoryl cnloride, P303Cly, the acid chloride of pyrophosphoric acid, is a product of the action of NO, on PCl;. It is a fuming liquid. The analogy between water and hydrosulphuric acid would lead to the expectation that a sulphochloride of phosphorus or thiophosphoryl chloride (PSCl;), corresponding with the oxychloride, would be formed by the action of hydrosulphuric acid upon phosphoric chloride ; PCl; + H,S = PSCl, + 2HCl. It is a colourless fuming liquid (boiling-point 125°, sp. gr. 1-68), which is slowly decomposed by water, giving phos- phoric,hy drochloric, and hydrosulphuric acids ; PSCl; + 4H,O =H, PO, + 3HC1+H,S8. When attacked by solution of soda, it loses its chlorine to the sodium, and acquires the equivalent of oxygen, a sodium thiophosphate (Na,PO,8 .12H,0) being deposited in crystals. This salt evidently corresponds in composition with sodium orthophosphate 224. PHOSPHORUS AMIDES (Na; P0,.12H,0), and its production is expressed by the equation—PSCl; + 6NaOH = 3NaCl + NasPO,8 + 3H,0. Salts of similar composition may be obtained with other metallic oxides. ; The bromides and orybromide of phosphorus correspond with the chlorine compounds. Iodine in the solid state combines very energetically with phosphorus, but if the two elements be brought together in a state of solution in carbon disulphide, a more ‘moderate action ensues, and two iodides of phosphorus may be obtained in crystals ; a tri-iodide (Pl,) corresponding with the trichloride, and phosphorus di-iodide (P214), which has no analogue either among the oxygen, chlorine, or bromine compounds of phosphorus. P,I, forms orange-red crystals, which are decomposed by water, with separation of red phosphorus ; 3P,I, + 12H,0 = 12HI + P, + 4P(OH)3. Phosphorus subiodide, P4I, is produced by the action of dry I on P in CS, solution ; with alkalies it forms P,OH. The addition of a very small quantity of iodine to ordinary phosphorus, fused in a flask filled with CO, materially accelerates its conversion into the red form (p. 213), and allows the change to be effected at a much lower temperature than that required when the phosphorus is heated alone, probably because successive portions of vitreous phosphorus combine with the iodine to form an unstable iodide, which is in turn decom- posed by the heat into red phosphorus and iodine. Phosphorus amides.—A general reaction between ammonia and an acid chloride is the production of the amide corresponding with the acid whose chloride is being treated, see p. 198. The amide of an acid contains NH, (amidogen) in place of the hydroxy] of the acid ; the reaction may be regarded as consisting of an exchange of Cl for NH,; thus, the action of ammonia on phosphoryl chloride produces the amide of “‘ orthophosphoric acid,” PO(NH,)3, called phospho-triamide. The change may be written PO-Cl, + 3NH,-H = PO(NH,), + 3HCl, but it will not occur unless excess of ammonia be present to combine with the liberated HCl, so that the actual reaction is POC], + 6NH, = 3NH,Cl + PO(NH,);. When an amide is boiled with an acid or an alkali it reacts with the water, producing the acid from which it is derived, and ammonia. Such a decomposition by water is termed hydrolysis ; PO(NH,), -+ 3HOH = PO(OH); + 3NH3. If an acid be present the NH, will immediately become an ammonium salt. If an alkali be present the ammonia will be evolved and the alkali will combine with the phosphoric acid. If melbher acid nor alkali be present the change will not proceed far. If the sulphochloride, PSCl,, be substituted fox the oxychloride and treated with ammonia, the corresponding sulphosphotriamide, PS(NHg)s, is obtained. The action of ammonia on phosphoric chloride yields chlorophosphamide, PCl3(NHo)o ; PCl; + 2NH; = 2HCl + PCl;(NH)3, and phospham, PN.H, a white solid which is the analogue of azoimide, N;H. When chlorophosphamide is boiled with water, a very stable insoluble substance is obtained, which is phosphodiamide ; NgH,PCl, + H,O = 3HCl + N,H3PO (phospho- diamide). When heated, it evolves ammonia and becomes phosphonitrile, the analogue of nitrous oxide ; N2,H;PO = NH; + NPO. The phosphamides may be regarded as being derived from the ammonium ortho- phosphates by the abstraction of 3H,O ; thus— (NH4)3PO, minus 5H,0 N;H,PO or PO(NH,)3, Phosphotriamide. (NH4)2HPO, ,, 7 N,H,PO or PO(NH,)NH, Phosphamide-imide. NH4HoPO, ” ” NPO, Phosphonitrile. Nitrogen chlorophosphide, N’,P’’’;Clg, is obtained by distilling phosphoric chloride with ammonium chloride ; 3PCl,; + 3NH,Cl = N,P;Cl, + 12HCl. It forms colourless rhombic prisms, melting at 114° and insoluble in water, but slowly decomposed by it ; 2P,N;Clg + 15H,O — 12HCl + 3P,03;(NH2)q(OH)2, pyrophosphodiamic acid, or pyro- I tl ll SOURCES OF ARSENIC 225 phosphoric acid,. P.0;(OH)4, in which two NH, groups have been substituted for two OH groups. ARSENIC, As =74.96.1 This element is often classed among the metals, because it has a metallic lustre and conducts electricity, but it is not capable of forming a base with oxygen, and the chemical character and composition of its compounds connect it-in the closest manner with phosphorus. In its mode of occurrence in nature it more nearly resembles the sulphur group of elements, for it is occasionally found in the uncombined state (native arsenic), but far more abundantly in combination with various metals, forming arsenides, which frequently accompany the sulphides of the same metals, The following are.some of the chief arsenides and arsenio- sulphides found in the mineral kingdom , Kupfernickel NiAs Mispickel or Arsenical nickel NiAs, | Arsenical pyrites } Fes: sii Tin-white cobalt CoAsp | Cobalt-glance CoSg.CoAss Arsenical iron Fe, As; Nickel-glance NiS..NiAs, But arsenic also occurs, like the metals, in combination with sulphur ; thus we have red orpiment or realgar, As,S,, and yellow orpiment, As,S,. It is from these minerals that arsenic derives its name (aporevixov, orpiment). The sulphides of arsenic are also found in combination with other sulphides ; thus Proustite is a compound of the sulphides of silver and arsenic (3Ag,S.As)S3) ; Tennantite contains sulphide of arsenic combined with the sulphides of iron and copper ; and grey copper ore is composed of sulphide of arsenic with sulphides of copper, silver, zinc, iron, and antimony. In an oxidised form arsenic is found in condurrite, which contains arsenious anhydride (As,0,) and cuprous oxide. Cobalt-bloom consists of cobalt arsenate, Co,(AsO,)o. Arsenical pyrites is one of the principal sources of arsenic and its com- pounds, though a considerable quantity is also obtained in the form of arsenious oxide as a secondary product in the working of certain ores, especially those of copper, tin, cobalt, and nickel. The substance used in the arts under the name of “ arsenic’ is really the arsenious oxide (As,0,) ; pure arsenic itself has very few useful applica- tions, so that it is not the subject of an extensive manufacture. Arsenic can be extracted from mispickel (Fe,8,As,) by heating it in earthen cylinders fitted with iron receivers in which the arsenic condenses as a metallic-looking crust, the heat expelling it from the mineral in the form of vapour. On a small scale it may be obtained by heating a mixture of white arsenic with half ts weight of recently calcined charcoal in a crucible, the mixture being covered with two or three inches of charcoal in very small fragments, and the crucible so placed that this charcoal may be heated to redness first, in order to ensure the reduction of any oxide which might escape from below. In order to collect the arsenic, another crucible, having a small hole drilled through the bottom for the escape of gas, is cemented on to the first, in an inverted position, with fire-clay, and protected from the fire by an iron plate with a hole in it for the crucible. The reduction of arsenious anhydride by charcoal is thus represented—As,0, + 6C = As, + 6C0. ; For the sake of illustration, a small quantity of arsenic may be prepared from white arsenic by a method commonly employed in testing for that substance. A small tube of German glass is drawn out to a narrow point (A, Fig. 154), and sealed with the aid of the blow-pipe. A very minute quantity of white arsenic is introduced into the point of the tube, and a few fragments of charcoal are placed in the tube itself at B. The charcoal is heated to redness with a blow-pipe flame, and the point is then heated so as 1 The specific gravity of the vapour of arsenic, like that of phosphorus, indicates that 74-5 parts by weight only occupy half a volume. Hence the molecule of arsenic must be represented as As, = 2 volumes ; but at very high temperatures a disposition to conform with the law is shown by a diminution in the vapour density, I5 2 226 ARSENIC—PROPERTIES to drive the white arsenic in vapour over the red-hot charcoal, when a shining black ring of arsenic (C) will be deposited upon the cooler portion of the tube. The arsenic thus obtained is a brittle mass of a dark steel-grey colour and brilliant metallic lustre (sp. gr. 5°73). It vaporises at 180° without melting unless it is heated in a sealed tube under the pressure of its own vapour, when it melts at 480°. It is not changed by ex- posure to air, unless powdered and - moistened, when it is slowly con- verted into As,O,. When heated in air it oxidises rapidly at about 71°, giving off white fumes of arsenious oxide and a characteristic garlic odour (recalling that of phos- phorus), which is also produced when arsenical pyrites is struck with a hammer or pick. At a red heat it burns in air with a bluish-white flame, and in oxygen with great brilliancy. It is not dissolved by water or any simple solvent, but is oxidised and dissolved by nitric acid. In its chemical relations to other elements, arsenic much resembles phos- phorus, undergoing spontaneous combustion in chlorine, and easily combin- ing with sulphur. Like phosphorus also, it combines with many metals, even with platinum, to form arsenides, and its presence often affects materially the properties of the useful metals. Pure arsenic does not produce symptoms of poisoning till a considerable period after its administration, being probably first oxidised in the stomach and intestines, and converted into arsenious acid. Arsenic vapour is colourless, but when rapidly cooled it appears yellow owing to the condensation of a cloud of minute yellow crystals which are an allotropic modification of arsenic (sp. gr. 3-88), soluble in CS, and remark- ably sensitive to light, which converts it into the black variety. Its formula in CS, solution is As,. When arsenic is sublimed ina tube filled with hydrogen, ordinary grey crystalline arsenic condenses on the warmer part of the tube, but on the cooler part, black amorphous arsenic is deposited, of sp. gr. only 4-7. This is not so easily oxidised in moist air as the crystalline variety. At 360° it evolves heat and becomes converted into crystalline arsenic.’ The vapour density of arsenic corresponds with As, below 800°, with As, above 1700°. Compare phosphorus, p. 211. Hydrogen Arsenide, Arsenetted Hydrogen, or Arsine, AsH, = 78. —The only compound of arsenic and hydrogen the existence of which has been satisfactorily established is that which corresponds with ammonia and phosphine. It is prepared by the action of sulphuric acid diluted with three parts of water upon the zinc arsenide, obtained by heating equal weights of zine and arsenic in an earthen retort; Zn,As, + 3H,SO, = 2AsH, + 3ZnSO,. The gas is so poisonous in its character that its prepara- tion in the pure state is attended with danger. It has a sickly alliaceous odour, and may be liquefied at — 55° and solidified at — 119°. It is inflammable, burning with a peculiar, livid flame, producing water and fumes of arsenious oxide; 4AsH, + 60, = As,O,+6H,O. The chief interest attaching to this gas depends upon the circumstance that its produc- Reduction of arsenious oxide. 1 Another amorphous variety of arsenic has been described as a brownish-black powder of sp. gr. 37 Doubt has been expressed concerning the amorphous character of this allotrope of arsenic, @e ARSENIC—DETECTION 227 tion allows of the detection of very minute quantities of arsenic in cases of poisoning. The application of this test, known as Marsh’s test, is the safest method of preparing arsenetted hydrogen in order to study its properties, for it is obtained so largely diluted with free hydrogen that it ceases to be so very dangerous. Some fragments of granu- lated zinc are introduced into a half-pint bottle (Fig. 155), provided with a funnel tube (A), and a narrow tube (B) bent at right angles and drawn out to a jet at the extremity ; this tube should be made of hard glass, so that it may not fuse easily. The bottle having been about one-third filled with water, a little diluted sulphuric acid is poured down the funnel-tube so as to cause a moderate evolution of hydrogen, and after about five minutes (to allow the escape of the air) the hydrogen is kindled at the jet. If a few drops of a solution obtained by boiling white arsenic with water be now poured down the funnel, arsenetted hydrogen will be evolved together with the hydrogen ; As,Og + 12Zn + 12H,SO, = 4AsH, + 12ZnSO, + 6H,0. Fie. 155. =f) Fie. 156. The- hydrogen flame will now acquire the livid hue above referred to, anda white smoke of As,O, will rise from it. If a piece of glass or porcelain be depressed upon the flame (Fig. 156), it will acquire a brown coating of arsenic, just as carbon would be deposited from an ordinary gas-flame. Arsenetted hydrogen is easily decomposed by heat (230°) so that if the glass tube through which it passes be heated with a spirit-lamp (Fig. 157) a dark mirror of arsenic will be deposited a little in front of the heated part, and the flame of the gas will lose its livid hue. These deposits of arsenic are extremely thin, so that a very minute quantity of arsenic is required to form them, thus rendering the test one of extraordinary delicacy. It must be remembered, however, that both sulphuric acid and zinc are liable to contain arsenic, so that it is essential to employ specially purified reagents when testing for small quantities. An electrolytic test for arsenic may also be employed which depends upon the circumstance that when a fairly powerful galvanic current is passed through an acid liquid containing arsenic, arsenetted hydrogen is evolved at the negative terminal along with the hydrogen of the decomposed water. : Arsenetted hydrogen, like phosphoretted hydrogen and sulphuretted hydrogen, causes dark precipitates in many metallic solutions. Silver nitrate is reduced to the metallic state by AsH, ; ASH, + 6AgNO, + 3H,0 = H;AsO3 + 6HNO; + 3Agy. A piece of filter-paper, spotted with silver nitrate solu- tion, will have the spots blackened if held before the tube from which the gas issues. The simplest test (Gutzeit’s test) for arsenic in wall-paper, &c., is to drop a piece of the paper into a test-tube containing some zinc and sulphuric acid, and to cover the mouth of the tube with a piece of paper wetted with silver nitrate, which will be stained if arsenic be present. The purity of the materials should be tested first in the same way, and the absence of sulphur, which blackens silver nitrate, should be proved by lead acetate, which is not blackened by arsenetted hydrogen. Hydrogen phosphide, hydrogen arsenide, and ammonia constitute a group of hydrogen compounds having certain properties in common. They are all possessed of peculiar odours, that of ammonia being the most powerful and that of hydrogen arsenide the least. Ammonia is power- fully alkaline, phosphine exhibits some tendency to play an alkaline part, 228 WHITE ARSENIC whilst arsine seems devoid of alkaline disposition. They are all inflammable, ammonia being the least so of the group, and are decomposed by heat, ammonia least easily, and hydrogen arsenide most easily. They are all producible from their corresponding oxygen compounds, viz. N,O3, P,O6., and As,O,, by the action of nascent hydrogen (e.g. by contact with zinc and diluted sulphuric acid). All three are the prototypes of various organic bases (q.v.) which contain some compound radicle in place of the hydrogen, thus— NH, is the prototype of triethylamine N(C.Hs)3 3 * 7 triethylphosphine P(C.Hs5)3 AsH3 sa, ‘5 triethylarsine As(C2H5)3 Arsonium compounds are known, e.g. (CH;),AsCl; cf. Ammonium. The compound As,H,, analogous with NH, and P,H,, has not been obtained, but its derivative As,(CH,.),, kakodyl, is well known. Oxides of Arsenic.—Arsenic forms two oxides, corresponding with phosphorous and phosphoric anhydrides, viz. As,O, and As,Os. Arsenious oxide, As,O, = 396.—Unlike phosphorus, arsenic, when burning in air, combines with oxygen to form only its lower oxide. Arsenious oxide, or white arsenic, is a very useful substance in many branches of industry. It is employed in the manufacture of glass, and of several colour- ing-matters. A large quantity is consumed also for the preparation of arsenic acid and arsenate of soda ; it is, indeed, the source from which nearly all the compounds of arsenic are procured. Small quantities of crystalline arsenious oxide are occasionally found associated with the ores of nickel and cobalt. White arsenic is manufactured by roasting the arsenical pyrites, chiefly obtained from the mines of Silesia, in muffles or ovens, through which air is allowed to pass, when the arsenic is converted into As,O,, and the sulphur into SO,, which are conducted into large chambers wherein the As,O, is deposited as a very fine powder. The iron of the pyrites is left partly as oxide, and partly as sulphate of iron. The removal of the As,O, from the condensing-chambers is a very unwholesome operation, owing to its dusty and very poisonous character. The workmen are cased in leather, and protect their mouths and noses with damp cloths, so as to avoid inhaling the fine powder. This crude white arsenic is subjected to a second sublimation on a smaller scale in iron vessels, when it is obtained in the form of a semi- transparent glassy mass known as vitreous arsenious acid, which gradually becomes opaque from crystallisation when kept, and ultimately resembles porcelain. The white arsenic sold in the shops is a fine powder, dangerously resembling flour in appearance, but so much heavier (sp. gr. 3-7) that it ought not to be mistaken for it. When examined under the microscope it appears in the form of irregular glassy fragments, mixed with octahedral _erystals. White arsenic softens when gently heated, but does not fuse (unless in a sealed tube), being converted into vapour at 220°, and depositing in brilliant octahedral crystals upon a cool surface. The experiment may be made in a small tube sealed at one end, the upper part of which should be slightly warmed before heating the arsenious oxide, so as to prevent too rapid condensation, which is unfavourable to the formation of distinct crystals. The octahedra are best examined with a binocular microscope. By saturating a boiling solution of KOH with As,O,, and allowing the liquid to cool, prismatic crystals (sp. gr. 4:00) separate. Thus As,O, is both amorphous and dimorphous, the amorphous form (sp. gr. 3-71) being con- densed from the vapour on a hot surface, the octahedral (sp. gr. 3-65) condens- ing on a cool surface, and the prismatic crystallising as described above. ARSENIOUS OXIDE 229 When crystallised from water both the other forms become octahedral. The change from amorphous to crystalline arsenious oxide is attended by -evolution of heat. At 700° the vapour density conforms with the formula As,Og, but at 1800°, As,Oz. The solubility of different specimens of white arsenic varies widely. Cold water takes up very little, and that slowly ; amorphous, 1 in 108; octahedral, 1 in 355; or after prolonged boiling, amorphous, 1 in 27; octa- hedral, 1 in 59, are representative figures. When thrown into water, white arsenic exhibits great repulsion for the particles of that liquid, and collects in a characteristic manner round little bubbles of air forming small white globes which are not wetted by the water. Even if stirred, with the water, and_ allowed to remain in contact with it for some hours, a pint of water (20 oz.) would not take up more than 20 grains. I£ boiling water be poured upon powdered white arsenic, and allowed to remain in contact with it till cold, it will dissolve about orth of its weight (22 grains in a pint). When powdered white arsenic is boiled with water for two or three hours, 100 parts by weight of water may be made to dissolve 11-5 parts, and when the solution is allowed to cool, about 9 parts will be deposited in octahedral crystals, leaving 2-5 parts dissolved in 100 of water (219 grains in a pint). This great increase in the solubility of the arsenious oxide by long boiling with water is usually attributed to the conversion of the opaque or crystalline variety, which always composes the powder, into the vitreous modification, which is the more soluble in water (1 part in 27 of water). Water, heated with white arsenic in a sealed tube, may be made to dissolve its own weight of it; as the solution cools, it first deposits prismatic crystals, and afterwards the ordinary octahedral form. The solution is very feebly acid to blue litmus-paper. Glycerin dissolves As,O, easily when heated. White arsenic dissolves abundantly in hot hydrochloric acid (a part of it being converted into arsenious chloride), and as the solution cools, part of the oxide is deposited in large octahedral crystals. The formation of these crystals is attended by flashes of light, visible in a darkened room. This experiment, which is exceedingly beautiful, is best performed by boiling 60 grams of arsenious oxide in 500 c.c. of a mixture of equal volumes of strong hydro- chloric acid and water in a flask, and allowing the solution to cool slowly ; after a time the crystals begin to form, a flash of light accompanying the formation of each, and the effect may be enhanced by carefully shaking the flask. It is said that it is only the vitreous form which exhibits this phenomenon ; but the same solution will generally serve for the above experiment any number of times if it be reheated, although the arsenious oxide has, of course, been deposited in the crystalline form ; it is, however, remarkable that the experiment sometimes unaccountably fails. Solutions of the alkalies readily dissolve arsenious oxide, forming alkali arsenites, the solutions of which are capable of dissolving arsenious oxide more easily than water can, and deposit it in crystals on cooling (see above). On adding a small quantity of hydrochloric acid to the solution of the alkali arsenite, a white precipitate of arsenious oxide is formed. This common poison may fortunately be easily recognised by sprinkling it upon a red-hot coal, when a strong odour of garlic is perceptible, due to the reduction of the As,O, by the heated carbon ; the vapour of white arsenic, or that of arsenic, is itself inodorous. The sparing solubility of white arsenic in water is very unfavourable to its action as a poison, for, when thrown into ordinary liquids, it is dissolved in very small quantity, the greater part of it collecting at the bottom. Even when taken into the stomach in a solid state, its want of solubility delays its operation sufficiently to give a better chance of antidotal treatment than in the case of most other common poisons. Its sparing insolubility is indicated by its being almost tasteless. Although so little as 2-5 grains of white arsenic have been known to prove fatal, the exhibition of gradually increasing doses will so inure the system 230 “ ARSENITES to the poison that comparatively large quantities can be administered at frequent intervals. When exhibited in this manner, white arsenic appears to have a remarkable effect on the animal body. Grooms occasionally, employ it to improve the appearance of horses, and in Styria, it seems, it is taken by men and women for the same purpose, apparently favouring the secretion of fat. It is said that a continuance of the custom develops a craving for this drug, and enables it to be taken without immediate danger, though the ultimate consequences are very serious. The antidote to the poison is ferric hydroxide, made by mixing magnesia with ferric chloride solution ; this acts by rendering the arsenic insoluble. The very general distribution of arsenic through the mineral kingdom makes it necessary that the analyst should ever be on the watch for this insidious poison. As has been seen already the arsenic in ordinary pyrites finds its way into the sulphuric acid made therefrom, and then into the commercial hydrochloric acid distilled with aid of this sulphuric acid. The use of sulphuric acid containing arsenic for converting starch into glucose subsequently used in making beer has been the cause of many deaths in the district consuming the beer. This beverage appears to be liable also to contain arsenic derived, it is alleged, from pyrites in the fuel used to dry the malt, from which the beer is brewed. White arsenic has the property of preventing the putrefaction of skin and similar substances, and is occasionally employed for the preservation of objects of natural history, &c. Arsenites.—Arsenious acid, properly so-called, has not yet been obtained in the separate state. The aqueous solution of white arsenic, when neutral- ised exactly with ammonia, yields, with silver nitrate, a yellow precipitate having the composition Ag’,AsO, ; with cupric sulphate, a green precipitate ° having the composition Cu’’HAsO, ; with zinc sulphate, a white precipitate containing Zn’’,(AsO3),; and with magnesium sulphate, a white precipitate of Mg’”HAsO;. It would appear, therefore, that the arsenious acid from which these salts are derived is a tribasic acid having the formula H,AsO,, or As(OH);, corresponding with phosphorous acid. Arsenious acid does not destroy the alkaline reaction of the alkalies, and it does not decompose the alkaline carbonates unless heat is applied, proving it to be a feeble acid. The ammonium arsenite is very unstable, evolving ammonia freely when exposed to the air. When arsenious oxide is dissolved in a hot solution of ammonia, octahedral crystals of it are deposited on cooling, notwithstanding the presence of ammonia in large excess. The alkali arsenites are more correctly metarsenites, for they are derived from HAsO,, or AsO(OH), metarsenious acid ; the potassium metarsenite is KAsO,, in solution (Fowler’s solution) it is used in medicine. When the carbonates of potassium and sodium are fused with an excess of arsenious oxide, brilliant transparent glasses (K,As,07, and Na,As,0,) are obtained which are similar in composition to glass of borax (Na.B,0,). If an alkali arsenite be fused in contact with platinum, the latter is easily melted, combining with a small proportion of arsenic to form a fusible platinum arsenide, a portion of the arsenite being converted into arsenate. The alkali arsenates (from arsenic acid, H;AsO,) are so much more stable than the arsenites that the latter exhibit a great tendency to pass into the former, with separation of arsenic. The arsenites of potassium and sodium in solution are sometimes employed as sheep-dipping compositions ; and an arsenical soap, composed of potassium arsenite, soap, and camphor, is used by naturalists to preserve the skins of animals. Sodium arsenite is also occasionally employed for preventing incrustations in steam boilers, being prepared for that purpose by dissolving 2 molecular proportions of white arsenic and 1 molecular proportion of sodium carbonate, o ? ARSENIC ACID 231 Scheele’s green is an arsenite of copper (CuHAsO,) prepared by dissolving white arsenic in a solution of potassium carbonate, and decomposing the arsenite of potassium thus produced by adding sulphate of copper, when the arsenite of copper is precipitated. This poisonous colour has been used to impart a bright green tint to paper hangings, but it is injurious to the health of the occupants of rooms thus decorated, since the arsenite ‘of copper is often easily rubbed off the paper, and diffused through the air in the form of a fine dust, a small portion of which is inhaled with every breath. The presence of the arsenite of copper in « sample of such paper is readily proved by soaking it in a little ammonia, which will dissolve the arsenite of copper to a blue liquid, the presence of arsenic in which may be shown by acidifying it with a little pure hydrochloric acid, and boiling with one or two strips of pure copper, which will become covered with a steel-grey coating of arsenide of copper. On washing the copper, drying it on filter-paper, and heating it in a small tube (Fig. 158), the arsenic will be converted | into arsenious oxide, which will deposit in brilliant octahedral crystals on the cool part of the tube. It is obvious that, to avoid mistakes, the ammonia, hydrochloric acid, and copper should be examined Fra. 158. in precisely the same way, without the suspected paper, so as to render it certain that the arsenic is not derived from them. Eimerald-green (Paris green) is a combination of arsenite and acetate of copper obtained by mixing hot solutions of equal weights of white arsenic and acetate of copper. Both Scheele’s green and Paris green are used as insecticides on growing crops. Arsenic acid, H,AsO, or AsO(OH),.—Arsenic acid is prepared by oxidising white arsenic with three-fourths of its weight of nitric acid of sp. gr. 1:35, when it dissolves with evolution of much heat and abundant red fumes of nitrous anhydride— As,O, + 4HNO, + 4H,0 = 2N,0, + 4H,As0,. After cooling, the solution deposits very deliquescent prismatic crystals containing H,;AsO,.H,0. When heated to 100°, these melt, and the liquid deposits needle-like crystals of ortho-arsenic acid, H,AsO,, corresponding with orthophosphoric ; at 180°, 2H,AsO, = H,O + H,As,0,, pyro-arsenic acid, corresponding with pyrophosphoric ; at 206°, H,As,0, = H,O + 2HAsO,, metarsenic acid, corresponding with metaphosphoric ; but here the resem- blance ceases, for at 260°, 2HAsO, = H,O + As,O,;, whereas HPO, may be vaporised without decomposition. When metarsenic and pyro-arsenic acids are dissolved in water, they at once become ortho-arsenic acid. The “meta- and pyro-arsenates are known only in the solid state. As,O, is decomposed at a red heat into As,O,, and oxygen. Arsenic anhydride, As,O, (sp. gr., 4:3), has very much less attraction for water than has the phosphoric anhydride with which it corresponds; it deliquesces slowly in air, and dissolves rather reluctantly in water. Neither does it appear that its combinations with water differ from each other, like the phosphoric acids, in the salts to which they give rise, arsenic acid forming tribasic salts only, like common phosphoric acid. The arsenates correspond very closely with the orthophosphates, with which they are isomorphous (p. 299). Thus the three arsenates of sodium are similar in 232 YELLOW ARSENIC composition to the three orthophosphates, the formule being Na,AsO,.12Aq; Na,HAsO,.12Aq ; and 2(NaH,AsO,).Aq. The common sodium arsenate, Na,HAsO,.7Aq, is largely used by calico- printers as a substitute for the dung-baths formerly employed, since, like the common sodium phosphate, it possesses the feebly alkaline properties required in that particular part of the process. It is manufactured by combining arsenious oxide with soda, and heating the resulting arsenite with sodium nitrate, from which it acquires oxygen, becoming converted into sodium arsenate. Calcium arsenate, 2CaHAsO,.7H,0, has been found in crystalline crusts at Joachimsthal. Arsenio-siderite and xantho-siderite are calcium ferric arsenates. Arsenic acid is used by the calico-printer as an acid and by the dye- stuff maker as an oxidant. It is a much more powerful acid than arsenious acid, being comparable, in this respect, with phosphoric acid. It is less stable than phosphoric acid, and acts as an oxidising agent. Sulphurous acid, which is without action on phosphoric, reduces arsenic acid to arsenious acid; H,AsO, + H,SO, = H,As0O; + H,S0O,. Sulphides of Arsenic.—There are three well-known sulphides of arsenic, having the composition As,S,, As,S;, and As,S,, the two former being found in nature. Realgar, As.S,, is a beautiful mineral, crystallised in orange-red prisms ; but the red orpiment used in the arts is generally prepared by heating a mixture of white arsenic and sulphur, when sulphurous acid gas escapes, and an orange-coloured mass of realgar is left. Another process for preparing it consists in distilling arsenical pyrites with sulphur or with iron pyrites ; FeS,.FeAs, + 2Fe8, = 4FeS + As,S,. The realgar distils, and condenses to a red transparent solid. Realgar burns in air with a blue flame, yielding arsenious and sulphurous oxides. If it be thrown into melted saltpetre, it burns with a brilliant white flame, being converted into arsenate and sulphate of potassium. This brilliant flame renders realgar an important ingredient in Indian fire and similar compositions for fireworks and signal lights. A mixture of one part of red orpiment with 3-5 parts of sublimed sulphur and 14 parts of nitre is used for signal light composition. Realgar is not easily attacked by acids ; nitric acid, however, dissolves it, with the aid of heat, forming arsenic acid and sulphuric acid, with separation of part of the sulphur in the free state. Alkalies (KOH for example) partly dissolve it, leaving a dark brown substance, which appears to contain free arsenic ; 3As,S. = 2As,8, -+- Asp. When exposed to air realgar is partly oxidised and converted into a mixture of As)S, and As,O.. Yellow orpiment, or arsenious sulphide, As.S,, is found native in yellow prismatic crystals. The pigment known as King’s yellow is a mixture of arsenious sulphide and arsenious anhydride, prepared by subliming excess of sulphur with white arsenic; 98 + As,O, = 2As,8, + 880,. It is, of course, very poisonous. This substance, like realgar, is not much affected by acids, excepting nitric acid ; but it dissolves entirely in potash, forming potassium arsenite and thioarsenite ; 6KOH + As,S, = K,AsS, + K,;AsO, + 3H,0.1_ Ammonia also dissolves it easily, forming a colourless solution which is employed for dyeing yellow, since, if a piece of stuff be dipped into it and exposed to air, the ammonia will volatilise, leaving the yellow orpiment behind. When As,§, is boiled with a strong solution of sodium carbonate, HS is evolved and As,8, is deposited as a crystalline powder. The formation of the characteristic yellow sulphide is turned to account in testing + Since the metarsenite, KAsO,, is the only potassium arsenite which has been prepared, and the metathioarsentie, KAsS., appears to exist in the solution, the reaction is better expressed by the equation, 2As,8, + 4KOH = KAsO, + 38KAsS, + 25,0. ARSENIOUS CHLORIDE 233 for arsenic; if a solution prepared by boiling white arsenic with distilled water be mixed with a solution of hydrosulphuric acid, a bright yellow liquid is produced, which looks opaque by reflected, but transparent by transmitted, light, and may be passed through a filter without leaving any solid matter behind. This solution probably contains a soluble colloidal form of arsenious sulphide ; this is, however, rendered in- soluble by evaporation. The addition of a little hydrochloric acid, or of sal-ammoniac, and many other neutral salts, will also cause a separation of the sulphide from this solution ; even the addition of hard water will have that effect. If the solution of arsenious acid be acidified with hydrochloric acid before adding the hydrosulphuric acid, the bright yellow sulphide is precipitated at once, and may be distinguished from any other similar precipitate by its ready solubility in solution of ammonium carbonate. Arsenic sulphide, As,8s, possesses far less practical importance than the preceding sulphides ; it may be obtained by fusing As,S, with sulphur, when it forms an orange- coloured glass, easily fusible, and capable of being sublimed without change. When hydrosulphuric acid gas is passed slowly through solution of arsenic acid, very little, if any, arsenic sulphide is formed, a white precipitate of sulphur being first obtained, the hydrogen reducing the arsenic acid to arsenious acid;1 H,AsO, + H,S = H;AsO; + H,O +8; and if the passage of the gas be continued, the arsenious acid is decomposed, and arsenious sulphide is precipitated ; these changes are much accele- rated by heat. But a rapid current of HS passed through a solution of arsenic acid in presence of much free hydrochloric acid throws down pure arsenic sulphide. If a solu- tion of sodium arsenate be saturated with HS, it is converted into sodium thioarsenate, Na,AsS,. On adding hydrochloric acid to this solution, a bright yellow precipitate of arsenic sulphide is obtained. Cuprous sulpharsenate, or Clarite (CugAsS4), is found in the Black Forest. ; Selenium forms corresponding compounds, e.g. As,Se;, As,Se;, AseSeoS3. Arsenic halides.—Arsenic trifluoride, AsF3, resembles the trichloride, but is much more volatile (b.-p. 63°). It may be obtained by distilling 4 parts of arsenious oxide with 5 of fluor spar and 10 of strong sulphuric acid, in a leaden retort (see p. 131) ; sp. gr. 2-73. It does not attack glass unless water be present, which decomposes it into arsenious and hydrofluoric acids. PCl, converts it into PF, and AsCl,. Arsenic pentafluoride, AsF;, by action of F on AsF;. Itisa gas and forms several double compounds, e.g. 2(AsF;.KF).H,0. Arsenic trichloride, or Arsenious chloride.—Only one compound of chlorine with arsenic is well known. The trichloride, AsCl;, may be formed by the direct union of its elements, but the simplest laboratory pro- cess for procuring it consists in heating white arsenic in dry chlorine, in a tubulated retort (A, Fig. 159). The arsenious anhydride soon melts, and the trichloride distils, leaving a melted mass in the flask, which is a brilliantly transparent glass when cool; its composition varies somewhat with the temperature used, but appears to be essentially As,0,.As,0;. The same vitreous compound may be obtained by fusing arsenious and arsenic oxides together. The reaction may be represented by the equa- ae tion— Fie. 159. 11A8,0, + 12Cl, = 8AsCl; + 6(As,O¢.A8205). Arsenic trichloride bears a great general resemblance to phosphorus trichloride ; it is a heavy (sp. gr. 2-2, b.p. 130-2°, solidifies at — 18°), pungent, fuming liquid, decomposed by the moisture of the air, its vapours depositing a white coating upon the objects in its immediate neighbourhood. When poured into water it deposits arsenious oxide ; 4AsCl, + 6H,O = As,O, + 12HC1; but when dissolved in the smallest possible quantity of water it deposits crystals of the formula AsOC1.H,O or AsCl(OH)>. When white arsenic is dissolved in hydrochloric acid, arsenious chloride is formed, 1 Under some conditions the solution remains clear at first, sulphozyarsenic acid being formed which is decomposed by more H,§ with precipitation of As.S;. (1) H,AsO, + H,S = H,As0,8 + H,0; (2) 2H,A80,8 + 3H,8 = As,8, + 6H,0. 234 ARSENIC HALIDES As,0, + 12HCl = 4AsCl, + 6H,O, and remains undecomposed by the water in the presence of strong hydrochloric acid, but if water be added, arsenious oxide is precipi- tated. When the solution in hydrochloric acid is distilled, the arsenious chloride distils over, and this is sometimes a convenient method of separating arsenic from articles of food, &c., in testing for that poison. When heated in dry hydrochloric acid gas, white arsenic yields a glassy compound, which contains As,0,.2AsOCI; 3As,0, + 4HCl = 2(As,0,.2AsOCl) + 2H,O. AsCl,; and AsH, decompose each other, yielding 3HCl and As, AsCl,; and NH; (gas) at — 35° produce arsenamide, As(NHg),. Arsenic pentachloride, AsCl;, has been obtained by passing Cl, into AsCl, at the temperature of solid CO,, but not by more ordinary methods. It is a liquid which dissociates readily into AsCl, and Cl». Arsenic tribromide much resembles the chloride in its chemical characters, but is a solid crystalline substance, fusing at 25° and boiling at 220°. Arsenic tri-iodide, or arsenious iodide (AsI3), is remarkable for not being decomposed by water, like the corresponding phosphorus compound. When obtained by heating together arsenic and iodine, it sublimes in brick-red flakes, which, if prepared on a large scale, hang in long lamine, like sea-weed. It may be dissolved in boiling water, and crystallises unchanged. It may even be prepared by heating 3 parts of arsenic with 10 of iodine and 100 of water, when the solution deposits red crystals of the hydrated tri-iodide, from which the water may be expelled by a gentle heat. AsI, is precipitated as a golden crystalline powder on mixing a hot solution of As,O, in HCl with a strong solution of KI. Sp. gr. 4:39; m.-pt., 146°; vaporises at 400°. Arsenic di-iodide, AsolIy, is obtained by heating 1 part of arsenic and 2 parts of iodine in a sealed tube to 230°, and crystallising from CS, in an atmosphere of CO,. It forms red prismatic crystals which become black when treated with water, according to the equation 3As.I, = 4AsI, + 2As. When iodine is dissolved in a solution of arsenious acid, this is oxidised to arsenic acid; H,AsO, + H,O + I, = H,AsO, + 2HI. When the solution is concentrated by evaporation, the change is reversed, and iodine liberated. Review of Nitrogen, Phosphorus, and Arsenic.—These elements are connected together by the general analogy of their hydrogen and oxygen compounds, the last two members of the group being far more closely con- nected with each other than with nitrogen. With the metals they are connected through arsenic, the hydrogen-compound of which is very similar in properties, and probably in composition, to antimonetted hydrogen ; arsenious oxide (As,O,) is also capable of occupying the place of antimonious oxide (Sb,0,) in certain salts of that oxide ; and the sulphides of antimony correspond in composition, and in some of their properties, with those of arsenic. One form of arsenious oxide (the prismatic) is isomorphous with native oxide of antimony, and this oxide may be obtained in octahedra, the ordinary form of arsenious oxide, so that these oxides are isodimorphous. These elements are also connected with the oxygen group through sulphur, selenium, and tellurium, the relations of which to hydrogen and the metals are somewhat similar to those of phosphorus and arsenic. . THE CARBON (FOURTH) GROUP CARBON, SILICON, together with THE BORON (THIRD) GROUP BORON. THE three elements, Carbon, Silicon, Boron, exhibit great similarity among themselves. Some of their many analogies are mentioned at p. 292. CARBON, C = 12.00. Carbon is one of the most widely distributed elements. Its presence in the animal and vegetable world is universal ; but also in the mineral kingdom it is scarcely less ubiquitous, being the characteristic element of carbonates, which form so much of the crust of the earth, and of their anhydride, carbon dioxide, which is diffused throughout the atmosphere. There are also enormous mineral stores of hydrocarbons (petroleum, asphalt, &c.), coal, &c., consisting chiefly of carbon. In the free state it appears in three allotropic modifications, diamond, graphite, amorphous carbon, so very different in physical properties and yet identical in chemical composition. However, the investigation of the specific heats and other physical constants of these three varieties indicates that the diamond molecule contains more atoms than the graphite molecule contains, and that the charcoal molecule is less complex than either. The chemistry of this element provides one of the most fascinating fields of study in the whole realm of science ; organic chemistry is merely one, though the largest, part of the field. Organic chemistry is so compre- hensive that it is dealt with as a separate division of chemistry, and its study has excelled all others in revealing the inner nature of the world around us ; not only with regard to composition and molecular structure of both organic and inorganic bodies, but also in prompting physical and biological inquiry. Diamond is the purest form of carbon found in nature. Apart from its great beauty and rarity, the diamond possesses a special interest for the chemist, from its having perplexed philosophers up to the middle of the eighteenth century, notwithstanding the simplicity of the experiments re- quired to demonstrate its true nature. The first idea of it appears to have been obtained by Newton, when he perceived its great power of refracting light, and thence inferred that, like other bodies possessing that property in a high degree, it would prove to be combustible (‘an unctuous substance coagulated ”). When the prediction was verified, the burning of diamonds was exhibited as a marvellous experiment, but no accurate observations appear to have been made till 1772, when Lavoisier ascertained, by burning diamonds suspended in the focus of a burning-glass in a confined portion of oxygen, that they were entirely converted into carbon dioxide gas. In more recent times this experiment has been repeated with the utmost pre- caution, and the diamond has been clearly demonstrated to consist of carbon. in a crystallised state. A still more important result of this experiment was the exact determination of the composition of carbon dioxide, without which it would not be possible to ascertain exactly the proportion of carbon in any of its numerous compounds, since it is always weighed in that form, a . 236 COMBUSTION OF DIAMONDS The classical experiments upon the synthesis of carbon dioxide were conducted with the arrangement represented in Fig. 160. Within a porcelain tube, A, which is iS atte! Bat DRAKE Fic. 160. heated to redness in a charcoal fire, was placed a little platinum tray, accurately weighed and containing a weighed quantity of fragments of diamond. One end of the tube was connected with a gasholder, B, containing oxygeu, which was thoroughly purified by passing through the tube, C, containing potash (to absorb any carbonic acid gas and chlorine which it might contain), and dried by passing over pumice soaked with concentrated sulphuric acid in D and E. To the other end of the porcelain tube, A, there was attached a glass tube, F, also heated in a furnace and containing copper oxide, to convert into carbon dioxide (CO,) any carbon monoxide (CO) which might have been formed in the combustion of the diamond. The CO, was then passed over pumice soaked with sulphuric acid in G, to remove any traces of moisture, and after- wards into a weighed bulb-apparatus, H, containing solution of potash, and two weighed tubes, I, K, containing, respectively, solid potash and sulphuric acid on pumice, to guard against the escape of aqueous vapour taken up by the excess of oxygen in its passage through the bulbs, H. The increase of weight in H, I, K, represented the CO, formed in the combustion of an amount of diamond indicated by the loss of weight suffered by the platinum tray, and the difference between the diamond consumed and the CO, formed would express the amount of oxygen which had combined with the carbon. A large number of experiments conducted in this manner, both with diamond and graphite, showed that 12 parts of carbon furnished 44 parts of CO,, and consumed, therefore, 32 parts of oxygen. A convenient arrangement for burning a diamond in oxygen is shown in Fig. 161. The diamond is supported in a short helix of platinum wire, A, which is attached to the copper wires, B B, passing through the cork, C, and connected with the terminal wires of a Grove’s © battery of five or six cells. The globe having been filled with oxygen === by passing the gas down into it till 4 match indicates that excess of Fie. 161. oxygen is streaming out of the globe, the cork is inserted and the wires connected with the battery. When the heat developed in the platinum coil by the passage of the current has raised the diamond to a full red heat, the con- nection with the battery may be interrupted, and the diamond will continue to burn with steady and intense brilliancy. Although the diamond, when preserved from contact with the air, may be heated very strongly in a furnace, without suffering any change, it is not proof against the intense heat of the electric arc ; if the arc be directed upon GRAPHITE 237 the diamond in a vessel exhausted of air, the diamond becomes converted into a black coke-like mass which closely resembles graphite in its properties. However, recent experiments contradict the conversion of diamond into graphite by heat. Diamonds are chiefly obtained from Golconda, Borneo, Kimberley in South Africa, and the Brazils. They usually occur in sandstone rock or in mica slate. The hardness of the diamond renders it necessary to employ diamond-dust for the purpose of cutting and polishing it, which is effected with the aid of a revolving disc of steel, to the surface of which the diamond- dust is applied in the form of a paste made with oil. The crystal in its natural state is best fitted for the purpose of the glazier, for its edges are usually somewhat curved, and the angle formed by these cuts the glass deeply, while the angle formed by straight edges, like those of an ordinary jeweller’s dia- mond, is only adapted for scratching or writing upon glass. Drills with diamond points have been employed in tunnelling through hard rocks. The diamond-dust used for polishing, &c., is obtained from a dark amorphous diamond (Carbonado) found at Bahia in the Brazils; 1000 oz. annually are said to have been occasionally obtained from this source. When burnt, the diamond always leaves a minute proportion of ash of a yellowish colour in which silica and oxide of iron have been detected. A genuine diamond may be known by its combining the three qualities of extreme hardness, enabling it to scratch hardened steel, high specific gravity (3-52), and insolubility in hydrofluoric acid. Sapphire (Al,0,) is nearly as hard as diamond, but its specific gravity is about 4. Artificial diamonds have been made by dissolving amorphous carbon in molten iron heated to nearly 3000° in the electric furnace, and suddenly cooling the metal by pouring it into molten lead. In this way only the surface of the globules of iron is immediately solidified. The interior expands as it cools and creates that pressure on the carbon it contains which appears to be essential to the formation of diamond. By dissolving the iron in acids the diamonds are left. They are never comparable with the natural product. Graphite (ypadu, to write), plumbago, blacklead, occurs in scaly, crystalline, grey-black, soft masses which mark paper readily. Even in the thinnest laminz it is completely opaque, yet like diamond it is one of the bodies most transparent to X-rays. It is found in many parts of the world ; the deposits at Borrowdale in Cumberland are exceptionally pure, but nearly equal are certain deposits in Ceylon, Canada and Siberia, the com- position averaging C, 99-8 per cent. ; H, 0°12 per cent. ; ash, 0-02 per cent. ; but other mines in the same countries yield much inferior material ; e.g. one from Canada, C, 76-35 per cent. ; H, 0-70 per cent. ; ash, 23-4 percent. The ash frequently includes the oxides of iron and manganese, silica, and sometimes titanic oxide. The crude graphite is purified by hand sorting, mechanical devices, and by chemical refining ; e.g. by extracting with acid or soda. Inferior kinds of graphite are treated by Brodie’s process. The graphite is heated with 2 parts of sulphuric acid and jth or ,},th of potassium chlorate. A part of the graphite is thus oxidised and converted into graphitic acid, QyyH,O;. When the graphite go treated is washed, dried, and heated to redness, the graphitic acid is decomposed, evolving steam and carbonic oxide gas, which swells up the graphite to a light volu- minous powder which can be separated from the heavy earthy impurities by floating it in water. When much silica is present in the graphite, a little sodium fluoride is added after the potassium chlorate has been decomposed. as There is a strong tendency for all forms of carbon to assume the graphitic modifica- tion at very high temperatures. Hence graphite is the most stable allotrope. The deposit of carbon on the walls of gas retorts is converted more or less into graphite, 238 WOOD CHARCOAL Molten iron dissolves carbon, and this separates as graphite as the iron cools; the scales are called kish (see Grey cast-iron). Graphite is regularly formed in the electric furnace. According to Acheson, the formation is facilitated by the presence of small proportions of various substances, e.g. SiO,, Al,O3, Fe,03, MgO, CaO; carbides appear to be formed temporarily, but as the process continues these other elements distil into the cooler parts of the apparatus, leaving a graphite of any desired degree of purity. Graphite has many applications: for pencils; for protecting iron sur- faces from rust, as in grate polishes ; as a lubricant for machinery ; for facing or imparting a glazed surface to gunpowder ; for making refractory articles. Graphite crucibles present advantages of economy in heat by reason of their conductivity, being on this account some five times more economical than clay crucibles in steel work ; they prevent oxidation and withstand sudden changes of temperature. The crucibles are composed of graphite about 50 per cent., clay, &c., 50 per cent. (Anthracite and the other varieties of coal will be described in a separate section.) Amorphous carbon is a term which comprehends all non-crystalline varieties ; e.g. lamp-black, charcoal, anthracite, &c. Lamp-black is the soot obtained from the imperfect combustion of oily, fatty, resinous, and tarry matters (or of highly bituminous coal), from which source it derives the small quantities of “ oil,” nitrogen and sulphur which it contains. The fatty oils and greases give the blacks which are purest and best in colour. Vegetable black is the lighter “fraction,” of finest texture and blackest hue, which is deposited in the chamber furthest removed from the fire. It contains about 99 per cent. carbon, against some 94 per cent. in lamp-black. The uses of this substance, as an ingredient of pigments, of printing-ink and of blacking, depend evidently more upon its black colour than upon its chemical properties. Wood charcoal.—If a piece of wood be heated in an ordinary fire, it is speedily consumed, with the exception of a grey ash consisting of the incom- bustible mineral substances which it contained ; if the experiment were performed in such a manner that the products of combustion of the wood could be collected, these would be found to consist of carbon dioxide and water ; woody fibre is composed of carbon, hydrogen and oxygen in the proportion represented by the formula C,H,,0,;, and when it is burnt the oxygen, in conjunction with more oxygen derived from the air, converts the carbon and hydrogen into carbon dioxide and water. But if the wood be heated in a glass tube closed at one end, it will be found impossible to reduce it as before to an ash, for a mass of charcoal will remain, having the same form as that of the piece of wood; in this case, the oxygen of the air not having been allowed free access to the wood, no true combustion has occurred, but the wood has undergone destructive distillation, a process simulating distillation in method, but differing in that the material placed in the still or retort is decomposed, giving rise to a distillate containing substances not existing in the original material. The vapours issuing from the mouth of the tube are acid to blue litmus- paper; they have a peculiar odour, and readily take fire on contact with flame. During the destructive distillation the hydrogen and oxygen of the wood are for the most part expelled in the forms of wood naphtha, pyro- ligneous acid, carbon dioxide, carbon monoxide, water, &c., leaving a resi- due containing a much larger proportion of carbon than that contained by the original wood. The charcoal which is left is not pure carbon, but con- tains considerable quantities of oxygen and hydrogen with a little nitrogen, RES PRODUCTION OF CHARCOAL 239 and the mineral matter or ash of the wood. The nature of the distillate is further described under Methyl Alcohol. On the small scale, the operation may be conducted in a glass retort, as shown in Fig. 162, where the water, tar, and naphtha are deposited in the globular receiver, and the inflammable gases are collected over water. This illustrates the modern method of destructively distilling wood. The retort takes the form of an iron cylinder set hori- zontally in a furnace and having a pipe spring- ing from its upper part to convey the pro- ducts toa condenser. The gases are generally burnt in the furnace to contribute to the heating of the retort. Fig. 163 shows a pair of such retorts, a, about 9 ft. x 1 ft. set in a furnace, b, having a grate, c, the products of combustion from which pass around the retorts and escape by flues, d. The billets of wood are packed into a cage, e, so that the charcoal can I (| iy iy DN oaf ar WZ ZU) SHMSSTSEOSS ESATA SS SS readily be withdrawn from the retort. The products of distillation pass through a pipe, f, into a condenser consisting of a zigzag copper pipe, g, in a water-tank, h. The liquid condensed flows through a seal trap and the gases pass through pipe, 7, back to the furnace. The original process of preparing charcoal consisted in applying the heat developed by the combustion of a portion of the wood to effect the charring of the rest. With this view the billets of wood are built into a heap (Fig. 164) around stakes driven into the ground, Za > a passage being left so that the heap Ani ir » may be kindled in the centre. This APN aR — ~ covered with turf and sand, except for a few inches around the base, where it * is left uncovered to give vent to the vapour of water expelled from the wood Fie. 164. in the first stage of the process. When the heap has been kindled in the centre, the passage left for this purpose is carefully closed up. After the combus- tion has proceeded for some time, and it is judged that the wood is perfectly dried, the open space at the base is also closed, and the heap left to smoulder for three or four weeks, when the wood is perfectly carbonised. += is ATTEN greststze ransom fo Mt) 240 CHARCOAL—PROPERTIES Upon an average, 22 parts of charcoal are obtained by this process from 100 of wood.. Much attention has been paid to the manufacture of charcoal for gunpowder (a mixture of charcoal, sulphur and saltpetre), and it has been found that the higher the temperature to which the charcoal is exposed in its preparation, the larger the proportion of hydrogen and oxygen expelled, and the more nearly does the charcoal approach in composition to pure carbon ; but it is not found advantageous in practice to employ so high a temperature, since it yields a dense charcoal of difficult combusti- bility and therefore less fitted for the manufacture of powder. The average composi- tion of wood, exclusive of ash, is in 100 parts—50 parts carbon, 6 parts hydrogen, and 44 parts oxygen. The composition of the charcoal prepared at different temperatures is given in the following Table : Obani Carbon. Hydrogen. Oxygen. Ash. 270° 71-0 4:60 23-00 1-40 363° 80-1 3-71 14-55 1:64 476° 85-8 3-13 9-47 1-60 519° 86-2 3-11 9-11 1-58 The proportion of the ash left by different charcoals varies considerably, but it seldom exceeds 2 per cent. This ash consists chiefly of the carbonates of potassium and calcium ; it also contains calcium phosphate, magnesium carbonate, silicate and sulphate of potassium, chloride of sodium, and the oxides of iron and manganese. The charcoal is kept for about a fortnight before being ground for making gunpowder, for if ground when fresh, before it has absorbed moisture and oxygen from the air, it is liable to spontaneous combustion. The infusibility of the charcoal left by wood accounts for its very great porosity, upon which some of its most remarkable and useful properties depend. The application of charcoal for the purpose of “ sweetening ”’ fish and other food in a state of incipient putrefaction has long been practised, and charcoal has been employed for deodorising all kinds of putrefying and offensive animal or vegetable matter. This property of charcoal depends upon its power of absorbing into its pores very considerable quantities of gases, especially of those which are easily absorbed by water. Thus, 1 cub. in. of charcoal is capable of absorbing about 100 cub. in. of ammonia gas and 50 cub. in. of sulphuretted hydrogen, both of which are conspicuous among the offensive products of putrefaction. This condensation of gases by charcoal is a physical effect, and does not involve a chemical combination of the charcoal with the gas; it is exhibited most powerfully by charcoal which has been recently heated to redness in a closed vessel, and cooled out of contact with air by plunging it under mercury. The precise nature of the occlusion (p. 97) has been a matter of discussion. Some view it as a case of solution, where the gas is dissolved by the carbon just as hydrogen is by palladium (p. 97); others regard it as an instance of adsorption, supposing the gas to be condensed only on the surface within the pores of the charcoal. The first view is supported by the fact that the phenomena observed with charcoal are in general similar to those with metals. Eventually, the offensive gases absorbed by the charcoal are chemically acted on by the oxygen of the air in its pores. A cubic inch of wood charcoal absorbs nearly 10 cub. in. of oxygen, and when the charcoal containing the gas thus condensed is presented to another gas which is capable of under- going oxidation, this latter gas is oxidised and converted into inodorous CHARCOAL—ABSORPTION OF GASES 241 products. Thus, if charcoal be exposed to the action of air containing sul- phuretted hydrogen gas (H,S), it condenses within its pores both this gas and the atmospheric oxygen, which slowly converts the H,S into sulphuric acid (H,SO,). The presence of so much air in charcoal renders it, like wood, apparently lighter than water; when powdered it sinks in water, its true specific gravity varying from 1-4 to 1-9. ‘The great porosity of wood charcoal is strikingly exhibited by attaching a piece of lead to a stick of charcoal (Fig. 165), so as to sink it in a cylinder of water, which is then placed under the receiver of the air-pump. On exhausting the air, innumerable bubbles start from the pores of the charcoal, causing brick effervescence. If a glass tube 16in. or 18 in. long be thoroughly filled with ammonia gas (Fig. 166), supported in a trough Fic. 165. _ Fic. 166. containing mercury, and a small stick of recently calcined charcoal introduced through the mercury into the tube, the charcoal will absorb the ammonia so rapidly that the mercury will soon be forced up and fill the tube, carrying the charcoal up with it. On removing the charcoal and placing it upon the hand, a sensation of cold will be perceived from the rapid escape of ammonia, perceptible by its odour. By exposing a fragment of recently calcined wood charcoal for a few minutes under a jar filled with H,S, so that the charcoal may become saturated with the gas, and then covering it with a jar of oxygen, the latter gas will act upon the former with such energy that the charcoal will burst into vivid combustion. The jar must not be closed air-tight at the bottom, or the sudden expansion may burst it. Charcoal in powder exposed in a porcelain crucible may also be employed in the same way. It should be pretty strongly heated in the covered crucible, and allowed to beconie nearly cool before being exposed to the H,S. Charcoal prepared from hard woods absorbs the largest volume of gas. Thus char- coal made from the shell of the coco-nut will absorb 170 times its volume of ammonia gas and 18 times its volume of oxygen, although its pores are quite invisible and its fracture exhibits a semi-metallic lustre. At very low temperatures the absorbing power is greatly intensified ; see p. 85. For an instance of selective absorption, see p. 54. As the gases which are evolved in putrefaction are of a poisonous charac- ter, the power of wood charcoal to remove them acquires great practical importance, and is applied in very many cases; the charcoal in coarse powder is thickly strewn over matters from which the effluvium proceeds, or is exposed in shallow trays to the air to be sweetened, as in the wards of hos- pitals, &e. A respirator consisting of a box of wire gauze containing charcoal has been found to afford protection against poisonous gases and vapours. Water is often filtered through charcoal in order to free it from noxious and putrescent organic matters which it sometimes contains. For all such uses the charcoal should have been recently heated to redness in a covered vessel, in order to expel the moisture which it attracts when exposed to the air; and the charcoal which has lost its power of absorption will be found to regain it in great measure when heated to redness. ‘ L 242 ANIMAL CHARCOAL This power of absorption which charcoal possesses is not confined to gases, for many liquid and solid substances are capable of being removed by that agent from their solution in water. This is most readily traced in the case of substances which impart a colour to the solution, such colour often being removed by the charcoal; if port wine or infusion of logwood be shaken with powdered charcoal (especially if the latter has been recently heated to redness in a closed crucible), the liquid, when passed through filter-paper, will be found to have lost its colour ; the colouring-matter, however, seems merely to have adhered to the charcoal, for it may be extracted from the latter by treatment with a weak alkaline liquid. Animal charcoal or bone-black possesses these decolorising and deodorising properties in still greater degree. When bone, the composition of which is given on p. 210, is heated in a retort without access of air, the animal matter undergoes destructive distillation, the gréater part of the hydrogen, nitrogen, oxygen, and some of the carbon giving rise to ammonia, combustible gases, and oily vapours, the chief product of which is known as bone oil or Dippel’s oil (q.v.). An intimate mixture of carbon and the earthy ingredients of the bone remains and constitutes ‘animal charcoal.” If a fragment of bone or a shaving of horn be heated in a glass tube closed at one end, the vapours which are evolved will be found strongly alkaline to test-papers, while those furnished by the wood were acid ; this difference is to be ascribed . mainly to the presence of nitrogen in the bone, wood being nearly free from that element ; it will be found to hold good, as a general rule, that the products of the destructive distillation of animal and vegetable matters containing much nitrogen are alkaline, from the presence of ammonia (NH;,) and similar compounds, while those furnished by non-nitrogenous substances possess acid characters. The above distillation process is not often practised. To obtain animal charcoal, the crushed bones are heated in covered crucibles arranged in a furnace, the escaping vaporous products being consumed so as to provide most of the necessary heat. The yield is about 60 per cent. Bone- black varies in composition, but carbon 16 per cent., ash 78 per cent., water 6 per cent., may be cited as usual; it is thus much poorer in carbon than vegetable charcoal is. The consequence of the presence of so large an amount of earthy matter must be to extend the particles of carbon over a larger area, and thus to expose a greater surface for the adhesion of colouring- matters, &c. This may partly help to explain the very great superiority of bone-black to wood charcoal as a decolorising agent, and the explanation derives support from the circumstance that when animal charcoal is deprived of its earthy matter, for chemical uses, by washing with hydrochloric acid, its decolorising power is very considerably reduced. The application of this variety of charcoal is not confined to the chemical laboratory, but extends to manufacturing processes. The sugar refiner decolorises his syrup by filtering it through a layer of animal charcoal, and the distiller employs charcoal to remove the fusel oil with which distilled spirits are frequently contaminated. Properties.—The three modifications are so graded in most of their physical properties that some tabulated scheme becomes instructive (see Table, p. 243). Carbon is remarkable, among elementary bodies, for its indisposition to enter directly into combination with the other elements, whence it follows that most of the compounds of carbon have to be obtained by indirect pro- cesses. This element appears, indeed, to be incapable of uniting with any other except fluorine at the ordinary temperature, and this circumstance is occasionally turned to useful account, as when the ends of wooden stakes are charred before being plunged into the earth, where the action of the atmo- CARBON ALLOTROPES 243 spheric oxygen, which, in the presence of moisture, would be very active in effecting the decay of wood, is resisted by the charcoal into which the external layer has been converted. The use of black-lead to protect metallic surfaces from rust is another application of the same principle. At a high tempera- ture, however, carbon combines readily with oxygen, sulphur, and with some of the metals, and, at a very high temperature, even with hydrogen and nitrogen. The tendency of carbon to combine with oxygen under the influence of heat is shown when a piece of charcoal is strongly heated at one point ; the carbon at this point at once combines with the oxygen of = Diamond. Graphite. Amorphous. Colour . 2 Colourless. ~ Black-grey. Black. Aspect . ‘ i Brilliant. Metallic lustre. Dull. Transparency ‘ Transparent. Completely opaque. | Completely opaque. Crystalline forny Well defined. Imperfectly defined. None. Hardness . 4 Hardest of all Soft. None. known substances. Specific gravity . 3-518 2:25 1-4 to 2-0 Conducts electricity | Non-conductor. Good conductor. Varies with kind. ss heat : Badly. Well. Fair. Specific heat at 15°. 0-1128 0-1604 0:2040 Atomic ,, ig 1-35 1-95 2-45 Specific heat at 200° 0-2791 0-297 = 9 > 980° 0-459 0-467 — Heat of combustion 94,310 cals. 94,810 cals. 97,650 cals. (12g.) In O, begins to form 720° 570° 200° CO, In O, forms CO, freely 790° 600° _— Ignites . ; ; 800°-850° 690° 300°-400° Attacked by chemi- | None, except by | As diamond, but | In several reac- cals burning in Oy. | oxidisable to gra- tions. phitic acid. the surrounding air (forming carbon dioxide), and the heat developed by this combustion raises the neighbouring particles of carbon to the tempera- ture at which the element unites with oxygen, and thus the combustion is gradually propagated throughout the mass, which is ultimately converted entirely into carbon dioxide, nothing remaining but the white ash, composed of the mineral substances derived from the wood used for preparing the charcoal. It is worthy of remark that if charcoal had been a better conduc- tor of heat, it would not have been so easily kindled, since the heat applied to any point of the mass would have been rapidly diffused over its whole bulk, and this point could not have attained the high temperature requisite for its ignition, until the whole mass had been heated nearly to the same degree ; this is actually found to be the case in charcoal which has been very strongly heated (out of contact with air), when its conducting power is greatly improved and it kindles with very great difficulty. The attraction possessed by carbon for oxygen at a high temperature is turned to account in metallurgic operations, when coal and charcoal are employed for extracting the metals from their compounds with oxygen. 1 Easily reducible oxides, such as oxide of lead, give carbon dioxide when heated with charcoal ; 2Pb0 + C = Phe + CO,, but oxides which are not easily reducible, such as oxide of zinc, give carbonic oxide ; ZnO + C= CO + Zn. 244 CARBONIC ACID GAS With boron, silicon, and most metals it forms carbides at the temperature of the electric furnace. The unchangeable solidity of carbon is another remarkable feature. Only at the temperature (3600°) attainable in the electric furnace can carbon be vaporised ; even then it does not appear to pass through the liquid condition. Melted iron and some other fused metals dissolve carbon, but beyond these there is no solvent by the aid of which carbon may be brought into the liquid form by the process of dissolution ; for although charcoal gradually disappears when boiled with sulphuric and nitric acids, it does not enter into simple solution, but is converted, as has been seen, into carbon dioxide. It is worthy of note that graphite is the final form of any kind of carbon which is submitted to a high temperature. Thus it is common to heat carbon rods or plates which are to be used as electrodes, and must therefore have the best possible electrical conductivity and power of resisting chemical attack, to the highest attainable tem- peratures in order to “‘ graphitise ’’ them. Pure carbon is prepared with some difficulty ; the charcoal obtained by heating some pure organic substance containing C, H, and O, such as white sugar-candy, in a closed crucible, is heated in a porcelain tube, as strongly as possible, in a current of dry chlorine gas until no more HCl is produced. The residue in the tube is nearly pure carbon. The carbon deposited when acetylene is passed through a red-hot tube is a very pure form. COMPOUNDS OF CARBON WITH OXYGEN. Three oxides of carbon are known, carbon monoxide, CO, carbon dioxide, CO,, carbon suboxide, C30, ; also two acids may be considered here, carbonic acid, H,COg, met with in the form of its salts, and percarbonic acid, H,C,0,. Carbon Dioxide, CO, = 44, has already been described in detail (p. 63) except with regard to certain chemical properties. Its relationship with carbon monoxide is considered under the latter. The method of proving the composition of carbon dioxide by weight is given at p. 236; its composition by volume at p. 249. Carbonates.—Although so ready to combine with the alkalies and alkaline earths (as shown in the absorption of CO, by potash and by lime-water), carbonic acid must be classed among the weaker acids. It does not neutralise the alkalies completely, and it may be displaced from its salts by most other acids. Its action upon the colouring-matter of litmus is feeble and transient. If a solution of carbonic acid be added to blue infusion of litmus, a wine-red liquid is produced, which becomes blue again when boiled, losing its carbonic acid ; whilst litmus reddened by sulphuric, hydrochloric, or nitric acid acquires a brighter red colour, which is permanent on boiling. On forcing CO, into solution of litmus at several atmospheres pressure a bright red colour is produced ; but this is not permanent. With each of the alkalies carbonic acid forms two well-defined salts, the carbonate and bicarbonate. Thus, the carbonates of potassium and sodium are represented by the formule, K,CO; and Na,CO;, whilst the bicarbonates are KHCO, and NaHCO,. The existence of the latter salts would favour the belief in the existence of the dibasic acid, H,CO,, although this has not yet been obtained in the separate state. Basic carbonates are also fairly common. White lead, 2PbCO;.Pb(OH),, magnesium carbonate, 3MgCO,.Mg(OH),, bismuth oxycarbonate, (BiO),CO,, are familiar examples. Perfectly dry carbon dioxide is not absorbed by pure quicklime (CaO) until it is heated to 350°-400°. Two hard glass tubes closed at one end, and bent as in Fig. 167, are perfectly dried, and filled, over mercury, with well-dried carbonic acid gas. Frag- ments of lime are taken, whilst red-hot, out of a crucible, cooled under the mercury, inserted into the tubes, and transferred to the upper end. No absorption of the gas CARBONIC OXIDE 245 occurs, though the tubes be left for some days; but if one of them be heated by a Bunsen burner, the CO, is rapidly absorbed, and the mercury is forced up into the tube. To demonstrate the presence of carbon in carbon dioxide, a pellet of potassium is introduced into a bulb-tube, through which a current of the gas (dried by passing through oil of vitriol or over calcium chloride) is flowing, and the heat of a spirit-lamp Fie. 167. Fie. 168. is applied to the bulb. The metal soon burns in the gas, leaving the carbon as a black mass in the bulb (Fig. 168). The potassium remains in the form of potassium carbonate ; 3CO, + 4K = 2K,C0, + C. If slices of sodium are arranged in a test-tube in alter- nate layers with dried chalk (calcium carbonate), and strongly heated with a spirit- lamp, vivid combustion ensues and much carbon is separated; CaCO, + 4Na = CaO + 2Na,O + C. When CO, is submitted to the action of electric sparks in an apparatus such as that shown in Fig. 137 it expands slightly, having been partially (about one-third) converted into CO + O, but if the sparking is continued, the mixture explodes to form COs, restoring the original volume of the gas. By conducting the sparking in presence of a piece of phosphorus all the CO, may be decomposed, because the phosphorus combines with the oxygen and CO, cannot be re-formed. In a partial vacuum in which the pressure of the CO, is only 5 mm. nearly 70 per cent. of the CO, may be decomposed in this way. ; Carbon Monoxide, carbonic oxide, CO = 28, is one of the very few substances in which carbon appears to be divalent. Acceptance of the tetravalency of carbon as one of the fundamental principles in organic chemistry makes the exceptions of great interest. The molecular refraction of CO points to the oxygen being tetravalent, and therefore the carbon also, whence the formula would be C = O, and not C = O. The combustion of potassium or sodium in carbon dioxide deprives the gas of all its oxygen, but other metals, which are not endowed with so power- ful an attraction for oxygen, do not carry the decomposition of carbon dioxide to its final limit ; thus, iron, zinc and magnesium at a high tempera- ture deprive the gas of only one-half of its oxygen, a result which may also be brought about at a red heat by carbon itself. When an iron tube filled with fragments of charcoal is heated to redness in a furnace (Fig. 13), and carbon dioxide is passed through it, the gas which issues from the other extremity of the tube takes fire on the approach of a taper, and burns with a beautiful blue lambent flame, similar to that which is often observed to play over the surface of a clear fire. Both flames, in fact, are due to the same gas, and in both cases this gas is produced by the same chemical change, for, in the tube, the carbon dioxide yields half of its oxygen to the charcoal, both becoming converted into carbonic oxide ; CO, + C = 2CO. In the fire the carbon dioxide is formed by the combustion of the carbon of the 246 REVERBERATORY FURNACE fuel in the oxygen of the air entering at the bottom of the grate; and this CO,, in passing over the layer of heated carbon in the upper part of the fire is partly converted into carbonic oxide, which inflames when it meets with the oxygen in the air above the surface of the fuel, and burns with its characteristic blue flame, reproducing carbon dioxide (cf. Producer-gas, p. 274).1. The carbon monoxide occupies twice the volume of the carbon dioxide from which it was produced. This conversion of carbon dioxide into carbon monoxide is of great importance, on account of its extensive application in metallurgic operations. It is often desirable, for instance, that a flame should be made to play over the surface of an ore placed on the bed or hearth of a re- verberatory furnace WY (Fig. 169). This ob- 4, ject is easily attained Uf when the coal affords a large quantity of in- flammable gas; but ‘with anthracite coal, which burns with very little flame, and is frequently employed in such furnaces, it is necessary to pile a high column of coal upon the grate, so that the carbon dioxide formed beneath may be converted into carbonic oxide in passing over the heated coal above, and when this gas enters the hearth of the furnace, into which air is admitted, it burns with a flame which spreads over the surface of the ore. It is frequently advan- tageous to make carbon monoxide in this way in a grate (producer) at some distance from the furnace and to conduct it thither through pipes (see Chemistry of Fuel). The temperature of the flame of carbonic oxide burning in air is estimated at about 1400°. The attraction of carbonic oxide for oxygen is turned to account in removing that element from combination with iron in its ores, as will be seen hereinafter. A very instructive process for obtaining carbonic oxide consists in heating crystal- lised oxalic acid with three times its weight of oil of vitriol. If the gas be collected over water (Fig. 170), and one of the jars be shaken with a little lime-water, the milkiness imparted to the latter will indicate abund- ance of carbon dioxide; whilst, on removing the glass plate and applying a light, the car- bonic oxide will burn with its characteristic blue flame. The gas thus obtained is a mixture of equal volumes of carbonic oxide and carbon dioxide. Crystallised oxalic acid is represented by the formula C,H,O,.2Aq, and if the water of crystallisation be left out of consideration, its decomposition may be represented by the equation C,.H,0, = H,O + CO + COs, the * change being determined by the attraction of the oil of vitriol for water. To obtain pure CO, the mixture of gases must be passed through a bottle containing solution of potash, to absorb the CO, (Fig. 171). + It is stated that when the temperature of a fuel in a furnace has attained 1000°, the carbon burns directly to CO. When carbon is heated in partially dried oxygen, CO alone is produced, showing that: this is the first product of the combustion ; it remains CO because the oxygen is too dry to burn it to the dioxide (p. 248). The carbon of gaseous carbon compounds burns first to CO, which is further oxidised to CO,. YY Fie. 169. Li Fie. 170. CARBONIC OXIDE—PROPERTIES 247 But pure CO is much more easily obtained by the action of sulphuric acid upon crystallised potassium ferrocyanide (yellow prussiate of potash) at a moderate heat. Since the gas contains small quantities of sulphur dioxide and carbon dioxide, it must Fig. 171. be passed through solution of potash if it be required perfectly pure. The chemical change which occurs in this process is expressed thus : K,Fe(CN), + 6H,O + 6H,80, = 6CO + 2K,S0O, + 3(NH,).SO, + FeSQ,. Potassium Potassium Ammonium Ferrous ferrocyanide. sulphate. sulphate. swphate, Ten grams of crystallised ferrocyanide, with 135 grams (73 c.c.) of sulphuric acid (sp. gr. 1-84) and 13 grams of water, give about 34 litres of CO. If the heating is continued after the evolution of CO has ceased, much sulphur dioxide is disengaged (2FeSO, + 2H,SO, = Fe,(SO,)3 + 2H2O + SOg). Carbonic oxide is a colourless, odourless gas, and, unlike carbon dioxide, is sparingly soluble in water, 1 in 40 vols. at 15°, but very soluble in ammo- niacal solutions of cuprous salts. It is lighter than air (sp. gr. 0-967). In its chemical relations it is an indifferent oxide, that is, it has neither acid nor basic properties. It is liquid below — 190° (its boiling-point), and solid at — 211° (its melting-point). Its critical temperature is — 140°. These constants approximate to the corresponding constants for nitrogen, of equal molecular weight. It forms many addition products which are evidence of its unsaturated or feebly saturated constitution ; e.g. with oxygen it forms carbon dioxide, and the reaction is reversible. To demonstrate the production of CO, during the combustion of CO, a jar of the gas is closed with a glass plate, and after placing it upon the table, the plate is slipped aside and a little lime-water quickly poured into the jar. On shaking, no milki- ness indicative of carbonic acid gas should be perceived. The plate is then removed and the gas kindled. On replacing the plate and shaking the jar, an abundant precipi- tation of calcium carbonate occurs. Carbonic oxide forms an explosive mixture with half its volume of oxygen. When CO is passed through a red-hot porcelain tube, a portion of it is decomposed into CO, and carbon ; and when the experiment is conducted without special arrange- ments, the CO is reproduced as the temperature of the gas falls.1. But by passing through the centre of the porcelain tube a brass tube, through which cold water is kept running, the decomposition has been demonstrated by the deposition of carbon upon the cooled tube, and by collecting the CO, formed. Carbon dioxide is also decomposed by intense 1 It is stated that CO heated at 500° always contains a little CO,, but no carbon is deposited. If this be true, a lower oxide of carbon must be supposed to be formed. 248 ADDITION PRODUCTS OF CARBONIC OXIDE heat into CO and O ; but if these gases be allowed to cool down slowly in contact, they recombine. ; The reducing action of CO upon metallic oxides, at high temperatures, may be illus- trated by passing the pure gas from a bag or gasholder first through a bottle of lime- water (B, Fig. 172), to prove the absence of COs, then over oxide of copper, contained in the tube, C, and afterwards again through lime-water in D. When enough gas has been passed to expel the air, heat may be applied to the tube by the gauze-burner, E, when the formation of CO, will be im- mediately shown by the second por- tion of lime-water, and the black oxide of copper will be reduced to red metallic copper. If precipitated peroxide of iron be substituted for oxide of copper, iron in the state of black powder will be left, and, if allowed to cool in the stream of gas, will take fire when it is shaken out into the air, becoming reconverted into the peroxide (tron pyro- phorus). Dry carbon monoxide will not combine with dry oxygen unless the mixture of gases be very strongly heated. This fact is an instance of the influence which water vapour exercises in chemical combination (cf. p. 332). Fie. 172. It follows that dry CO will not burn in dry air or dry oxygen. To demonstrate this fact, CO is passed through strong sulphuric acid and kindled at a jet; the flame is introduced into an inverted gas-jar containing ordinary air to show that the combustion will continue in such a vessel ; the air in a similar jar is now dried by shaking strong sulphuric acid in it, the acid is quickly poured out, and the flame introduced into the inverted jar, whereupon combustion ceases. Judging by analogy with other elements, whose combination with 2 atoms of oxygen produces twice as much heat as their combination with 1 atom, the conversion of C into CO, should produce twice as much heat as its conversion into CO. When C, in the form of charcoal, burns to form CO., each gram of C produces 8080 gram-units of heat; or C, 12 grams, + Op, 32 grams, = CO, + 96,960 units of heat. Now carbon cannot be burnt directly to form CO, but when CO burns to form CO,, 1 gram of CO produces 2408 units of heat ; or CO, 28 grams, + 0,16 grams, = CO, + 67,284 units of heat. In the first equation, 16 grams of O produce 48,480 units, and in the second 67,284 units of heat. But in the first case solid carbon is converted into gas, a change of state which must absorb much of the heat produced. If the C were in the state of gas to begin with, in both cases, it is probable that we should have O, 16 grams, + C, 12 grams, = CO + 67,284 units of heat, and O., 32 grams, + C, 12 grams, = COg + 134,568 units of heat, so that 1 gram of C would give 11,214 units of heat when burnt to CO,. But when 1 gram of solid C burns to CO, it gives only 8080 units of heat : hence 11,214 — 8080, or 3134 units, represent the heat required to convert 1 gram of solid carbon into gas. See also Thermochemistry. Other addition products are (a) carbonyl chloride, COC], (p. 249), by direct union with chlorine ; (6) carbonic oxide is absorbed by potassium hydrate at 100°, potassium formate being produced ; CO + KOH =HCOOK ; (c) if carbonic oxide be passed over soda-lime in a glass tube heated by a gas furnace, sodium carbonate is formed, and hydrogen liberated ; CO + 2Na0OH = Na,CO; + H,; (d) very interesting volatile compounds are produced by treating certain metals with CO; see nickel carbonyl (p. 460), cobalt carbonyl (p. 458), wron carbonyl (p. 456). Carbonic oxide is very poisonous; and it appears that the accidents which too frequently occur from burning charcoal or coke in braziers and chafing-dishes in close rooms result from the poisonous effects of the small quantity of carbonic oxide which is produced and escapes combustion, since the amount of carbonic acid gas thus diffused through the air is not sufficient, COMPOSITION OF THE OXIDES OF CARBON 249 in most cases, to account for the fatal result. The carbonic oxide formed in cast-iron stoves diffuses through the hot metal into the air of a room. It is certainly fatal to breathe air containing 1 per cent. of CO, and it is said that so little as 0-05 per cent. may prove fatal. Its occurrence in some mines and in after-damp is of vital significance, and it is a most injurious constituent of tobacco-smoke. It is absorbed by the blood, exhibiting in the complexion the peculiar rose colour of carboryhemoglobin. By matching the colour produced in a 0-5 per cent. solution of blood against carmine solution under standard conditions, the CO in 100 c.c. of air may be accurately determined when only 0-01 per cent. or even less of CO is present. With large quantities of air very accurate assays of minute proportions of CO may be made by passing the air over iodine pentoxide at 200° and titrating the liberated iodine. The poisonous character of carbon monoxide is raised as an objection to the pro- posed use of this gas for purposes of illumination. The character of the flame of car- bonic oxide would appear to afford little promise of its utility as an illuminating agent ; but that it is possible so to employ it is easily demonstrated by kindling a jet of the gas which has been passed through a wide tube containing a, little cotton moistened with rectified coal naphtha (benzene), when the carbon monoxide will be found to burn with a very luminous flame ; cf. the similar experiment with hydrogen, p. 263. The carbonic oxide destined to be employed for illuminating purposes is prepared by passing steam over white hot coke, a mixture of carbon monoxide and hydrogen known as water-gas (p. 274) being thus produced ; C + H,O = CO + Hy. Since neither hydrogen nor carbon monoxide is possessed of any odour, this mixtwe would not be detected in the atmosphere of a room where there was a leaky gas-pipe, and the presence of the poisonous carbon monoxide would remain unsuspected. Thus it becomes incumbent upon those supplying such gas to dwelling-houses to render it, by mixing some gas or vapour with it, at least as odorous as is ordinary coal-gas, an escape of which is so easily detected. The application of water-gas in this country, for illuminating purposes, is at present limited to its admixture with coal-gas, for which purpose it is rendered luminous by hydrocarbons obtained from the destructive distillation of petroleum. Composition by volume of carbon monoxide and carbon dioxide.—When carbon burns in oxygen, the volume of the carbon dioxide produced is exactly equal to that of the oxygen, so that 1 vol. of oxygen furnishes 1 vol. of carbon dioxide, or, since equal volumes of gases contain the same number of molecules (p. 10), a molecule of carbon dioxide contains the atoms of a molecule of oxygen. When 1 vol. of carbon dioxide (containing 1 vol. of oxygen) is passed over heated carbon, it yields 2 vols. of carbonic oxide; hence 2 vols., or 1 molecule, of this gas contain 1 vol., or half a molecule of oxygen. In each case the molecular weight is ascertained by determining the density of the gas. Carbon Suboxide, C;0, or OC: C: CO, is a colourless gas of intolerable odour and very reactive, obtained by dehydrating malonic acid with phosphorus pentoxide at 300° ; CH,(COOH), = C302 + 2H,O. It burns with a blue flame and separation of carbon. At + 7° it liquefies ; sp. gr. at 0°, 1-11. Solidified, it melts at — 107°. Percarbonic Acid, HyC,0, or O=C CH,.CH,OH —+ CH,.CH(OH), —» CO +H,0 + H.CHO —> Ethane. Ethyl! alcohol. —K—KwKa_—ooeee Formaldehyde. CH,CHO + H,O Acetaldehyde. Formic acid. Carbonic acid. H.COOH —+ CO(OH), Cae SSS ova _ CO + H,O0 CO, + HO H,C : CH, —> H,C : CH(OH) —> HO.CH : CH.OH Ethylene. Vinyl] alcohol. ooo Formic acid. ‘Carbonic acid. 2H.CHO. —>» H.COOH—> CO(OH), Formaldehyde. Qo —_—_—". CO +H,O0 CO, + H,0. In explosive combustion a similar, though not identical, series of reactions appears to occur. Other researches show that at 1230° water-vapour is reduced by carbon monoxide, and that the reaction is reversible; 3CO + 2H,0 = 2CO, + 2H, + CO; also that at 1300°, CO, is reduced ; CO, + 3H, CO + H,O + 2H,. Formic acid is also formed. From the above and from what has already been said about the formation of ozone (p. 138) and nitrogen oxides (p. 193), the process of combustion in an ordinary gas flame must be very complex, although the ultimate products may be simply carbon dioxide and water. During the burning of more complex gases and fuels the reactions must be very much more complicated. FUEL. Whilst any combustible substance is applicable for the purpose of pro- ducing heat, theforms of fuel actually in use are dependent for their calorific 1 W. A."Bone,’ Brit, Assoc. Report, 1910, or Chemical News, 1910, 102, 259, 309. COMPOSITION OF COAL 271 value on the combustion of carbon and hydrogen.1 A Table showing the composition of the principal fuels will be found on p. 279. Coal.—The various substances which are classed together under the name of coal are characterised by the presence of carbon as a largely pre- dominant constituent, associated with smaller quantities of hydrogen, oxygen, nitrogen, sulphur, and certain mineral matters which compose the ash. Coal appears to have been formed by a peculiar decomposition or fermentation of buried vegetable matter, resulting in the separation of a large proportion of its hydrogen in the form of marsh-gas (CH,) and similar compounds, and of its oxygen in the form of carbon dioxide, some of the carbon accumulating in the residue. Thus, cellulose (C,H,,0;), which constitutes the bulk of woody fibre, might be imagined to decompose according to the equation 2C,H,,0, = 5CH, + 5CO, + C,, and the occur- ‘rence of marsh-gas, and of the paraffin hydrocarbons of similar composition, as well as of carbonic acid gas, in connection with deposits of coal, supports this view of its formation. Marsh-gas and carbon dioxide are the ordinary products of the fermentation of vegetable matter, and a spontaneous carboni- sation is often witnessed in the “heating ’”’ of damp hay. But just as the action of heat upon wood produces a charcoal containing small quantities of the other organic elements, so the carbonising process by which the plants have been transformed into coal has left behind some of the hydrogen, oxygen and nitrogen ; the last, as well probably as a little of the sulphur, having been derived from the vegetable albumin and similar substances which are always present in plants. The chief part of the sulphur is gene- rally present in the form of iron pyrites (FeS,), derived from some extraneous source. The examination of a peat-bog is very instructive with reference to the formation of coal, as affording examples of vegetable matter in every stage of decomposition, from that in which the organised structure is still clearly visible, to the black carbonaceous mass which requires only con- solidation by pressure in order to resemble a true coal. In some cases an important part in the formation of coal may have been played by slow oxida- tion or decay of the vegetable matter at the expense of atmospheric oxygen held in solution by water ; since the hydrogen of the compound would be removed by oxidation occurring at a low temperature, giving rise to a gradual increase in the percentage of carbon. The three principal varieties of coal—lignite, bituminous coal, and anthracite—present us with the material in different stages of carbonisation, the lignite, or brown coal, presenting indications of organised structure and containing considerable proportions of hydrogen and oxygen, while anthracite often contains little else than carbon and the mineral matter or ash. The following Table shows the progressive diminution in the propor- tions of hydrogen and oxygen in the passage from wood to anthracite : Carbon. Hydrogen. Oxygen. Wood 3 ‘ i : . 100 a 12-18 ns 83-07 Peat 2 : ‘ ‘ . 100 se 9-85 as 55-67 Lignite : 100 a 8-37 ax 42-42 Bituminous coal : : . 100 6-12 oe 21-23 Anthracite : 3 ‘ . 100 as 2°84 es 1-74 The combustion of coal is a somewhat complex process, in consequence of the rearrangement which its elements undergo when the coal is subjected to the action of heat. As soon as a flame is applied to kindle the coal, the heated portion is 1 The student will meet with a few cases in which the combustion of other elements affords heat for useful purposes, so that such elements are fuels under the particular conditions. For example, the sulphur in pyrites or the aluminium in the mixture known as thermite may be regarded as fuel. 272 COKE destructively distilled, evolving various combustible gases and vapours, which take fire and convey the heat to remoter portions of the coal. Whilst the elements of the exterior portion of coal are undergoing combustion, the heat thus evolved is submitting the interior of the mass to destructive distilla- tion, producing various compounds of carbon and hydrogen. Some of these products, such as marsh-gas (CH,) and olefiant gas (C,H,), burn without smoke ; while others, like benzene (CsH,) and naphthalene (C,)H,), which contain a very large proportion of carbon, undergo partial combustion, and a considerable quantity of carbon, not meeting with enough heated oxygen in the vicinity to burn it entirely, escapes in a very finely divided state as smoke or soot, which is deposited in the chimney, mixed with a little ammo- nium carbonate and sma!! quantities of other products of the distillation of coal. When the gas has been expelled from the coal, there remains a mass of coke or cinder, which burns with a steady glow until the whole of its carbon is consumed, and leaves an ash, consisting of the mineral substances present in the coal.1 The final results of the perfect combustion of coal would be carbon dioxide, water, nitrogen, a little sulphur dioxide and ash. The production of smoke in a furnace supplied with coal may be prevented by charging the coal in small quantities at a time in front of the fire, so that the highly carbonaceous vapours must come in contact with a large volume of heated air before reaching the chimney. In arrangements for consuming the smoke, hot air is judiciously admitted at the back of the fire, in order to meet and consume the heated carbonaceous particles before they pass into the chimney. The difference in the composition of the several varieties of coal (p. 271) gives rise to a great difference in their mode of burning. The lignites furnish a much larger quantity of gas under the action of heat (and therefore burn with more flame) than the other varieties, leaving a coke which retains the form of the original coal; while bituminous coal softens and cakes together—a useful property, since it allows even the dust of such coal to be burnt, if the fire be judiciously managed. Anthracite (stone coal or Welsh coal) is much less easily combustible than either of the others, and, since it yields but little gas when heated, it usually burns with little flame or smoke. This variety of coal is so compact that it will not usually burn in ordinary grates, but it is much employed for boiler furnaces. Jet resembles cannel coal in composition. Accidents occasionally arise from the spontaneous combustion of coal. This appears to be due, in most cases, to the development of heat by the slow combination of some constituents of the coal with atmospheric oxygen, and unless due provision be made for the escape of the heat, its accumulation may raise the temperature to a dangerous degree. The oxidation is more likely to occur if, e.g. by careless loading of coal in a ship, much pulverisa- tion of the fuel has occurred (cf. p. 59). Coke is the residue left by destructively distilling coal, an operation which is conducted in coke-ovens when the object is to produce coke for metallurgical use, and in retorts when the object is to produce coal-gas, the coke being then a by-product. There is no essential difference between the coke-oven and the retort save that the former is considerably the larger of the two, thus distilling a greater weight of coal and producing a denser coke. As all the volatile portions of the coal have been expelled by the distillation, coke burns without flame, or smoke, but is correspondingly difficult to ignite. + This ash consists chiefly of silica, alumina, and peroxide of iron. When lime is present in the ash, it is liable to fuse into a rough glass or clinker, which adheres to the grate bars and causes much inconvenience. COAL-GAS 273 Wood and Charcoal have already received attention. In this country the use of the former as fuel is limited to its application for kindling less inflammable fuel such as coal. Charcoal is useful in cases where a fuel devoid of sulphur is desirable ; it stands in the same relation to wood that coke does to coal, as has already been explained (p. 238). Petroleum finds an increasing application as fuel, particularly the residues from the fractional distillation of the oil (see Organic Chemistry) for obtaining illuminating oils, Such residues are known as astatki, and when sprayed into a furnace burn with a high heating effect. An advantage of this form of fuel is its freedom from ash. The petrol burnt in motor-car engines is obtained from petroleum. Gaseous Fuel.—The fact that combustible gases can be burnt without the production of smoke and ash renders them formidable competitors of coal, notwithstanding that for an equal heating effect they are more costly. But the more important function of gaseous fuel is as a source of power by its combustion in the cylinder of a gas-engine. So far as domestic heating is concerned coal-gas is still the sole gaseous fuel used; an air-gas flame (p. 266) is caused to play upon some incombustible and infusible substance like asbestos or fireclay, so that the heat of the flame, which is a feeble radiator, may be converted into the radiant heat of a red-hot solid. The cooling of the flame by contact with the solid necessarily checks the combus- tion, giving rise to such gases as carbon monoxide and acetylene, which are unwholesome to breathe. A flue for carrying away the products of the combustion is therefore essential, but this is less necessary where the gas is allowed to burn with a luminous flame, the radiation from which is consider- able, while the combustion is practically complete. Coal-gas.—For the manufacture of coal-gas and its many by-products the reader is referred to a text-book on Technical Chemistry. Essentially it follows the lines of the destructive distillation of wood (p. 239), but the importance of the many interests involved has led to numerous refinements. The destructive distillation of coal may be exhibited with the arrangement repre- sented in Fig. 200. The solid and liquid products (tar, ammoniacal liquor, &c.) are Fia. 200. Fic. 201. condensed in a globular receiver, A. The first bent tube contains, in one limb, B, « piece of red litmus-paper to detect ammonia ; and in the other, C, a piece of paper impregnated with lead acetate, which will be blackened by the sulphuretted hydrogen. The second bent tube, D, contains enough lime-water to fill the bend, which will be rendered milky by the carbonic acid gas. The gas is collected over water in the jar, E, which is furnished with a jet from which the gas may be burnt when forced out by depressing the jar in water. The presence of acetylene in coal-gas may be shown by passing the gas from the supply-pipe (A, Fig. 201), first through a bottle, B, containing a little ammonia, then through a bent tube, C, with enough water to fill the bend, and a piece of bright sheet copper immersed in the water in each limb. After a short time the bright red flakes of the copper acetylide will be seen in the water. The chief constituents of coal-gas are hydrogen about 44 per cent., 18 274 GAS PRODUCERS marsh-gas about 40 per cent., carbon monoxide about 6-2 per cent., ethylene, &c., 5 or 6 per cent., nitrogen 4 or 5 per cent.; see also p. 280. The ethylene, together with small quantities of acetylene, benzene, and other unsaturated hydrocarbons, is the illuminating constituent. Vapours of petroleum and other suitable hydrocarbons are often added to the gas to “enrich ”’ it, 7.e. to increase its illuminating power. The sp. gr. is about 0-4 (air = 1), and is higher the higher the illuminating value of the gas. Traces of hydrogen sulphide and carbon disulphide are usually present in the crude gas, but are removed as much as possible in the purifiers, and are objectionable on account of their burning to SO, which leads to the forma- tion of sulphuric acid, so injurious to pictures, furniture, &c. Producer-gas.—In the manufacture of coal-gas some 70 per cent. of the carbon of the coal is left in the retort as coke. It is possible to convert nearly the whole of this carbon from the coal into combustible gas by taking advantage of the fact that CO, is reduced to CO by red-hot carbon, CO, + C = 2CO. The producer in which this change is effected consists of a deep grate into which the fuel is fed from above, the air entering below the charge ; ef. formation of CO in ordinary fires, p. 245. Producers are generally supplied with a blast of air to accelerate the combustion. Sometimes the air is sucked through the burning fuel (suction gas producer), particularly when the producer is to feed a gas-engine, the suction strokes of which may be used for the purpose. Fig. 202 shows «a modern blast pro- ducer. The body, 6, is an iron cylinder, through the double wall of which water is circulated for cooling it. The fuel is fed through hopper, a. The body is stationary and is supported in a circular trough, g ; the latter is mounted on ball bearings, f, and rotated by a worm, k, engaging a circular rack, h, on the trough. The grate, c, fixed to the trough, is in the form of a tower, and is constructed of annular bars, d, arranged eccentrically so that as the grate revolves with the trough the fuel is kept in movement. The blast is introduced through the grate by pipe n, == and the gas leaves the producer by pipe f. Water in the trough seals the body, and the ashes are removed by a fixed inclined YO plate (not shown) which extends into the trough so that the ashes ride up it as the F trough rotates. edocs The bottom portion of the fuel burns to CO,, which is reduced to CO! by the hot fuel in the top of the producer ; this escapes through a flue to the furnace in which it is to be burnt. Of course, producer-gas is far from pure CO; it must necessarily contain the nitrogen of the air which supplied the oxygen, and, in addition to this, some CO, and the products of the destructive distillation of tke coal, when this is used, are present. Water-gas.—A gas of more than double the heating effect of producer- gas can be obtained from the original fuel by converting it into water-gas. Its production depends on the fact that when steam is passed over heated carbon, a mixture of hydrogen and carbon monoxide is obtained, C + H,O = 2 See foot-note, p. 246. ce oo FUEL—CALORIFIC VALUE 275 CO + H,. Since this reaction is endothermic, the temperature of the carbon must be maintained if the production of the gas is to continue. In practice water-gas is made by passing steam into a producer which is already at work, until the temperature has so far fallen that the steam is no longer decomposed. The fuel is then again brought up to the required temperature by a draught of air (producer-gas being formed during this stage of the process), and steam is again turned in. Water-gas always contains some carbon dioxide, the quantity being greater the lower the temperature of the coke. This is because at lower temperatures the coke burns in steam to carbon dioxide, not to carbon monoxide ; C + 2H,O = CO, + 2H,. Water-gas usually consists of about 50 per cent. of H, 40 per cent. of CO, 5 per cent. of CO,, and 5 per cent. of N (from air and the coke). See also p. 280. It will be obvious that by blowing an appropriate mixture of steam and air into a producer, a mixture of water-gas and producer-gas (semi-water-gas, Dowson gas, and Mond gas) can be continuously produced. Calorific Value of Fuel.—For all practical purposes it may be stated that the amount of heat generated by the combustion of a given weight of fuel depends upon the weights of carbon and hydrogen respectively which enter into combination with the oxygen of the air when the fuel burns. It has been ascertained by experiment that 1 gram of carbon (in the form in which it exists in wood-charcoal), when combining with oxygen to form CO,, produces a quantity of heat which is capable of raising 8080 grams of water from 0° to 1° C. This is usually expressed by saying that the calorific value of carbon is 8080, or that carbon produces 8080 units of heat during its combustion to CO,. If the fuel, therefore, consisted of pure carbon, it would merely be necessary to multiply its weight by 8080 to ascertain its calorific value. One gram of hydrogen during its conversion into water by combustion evolves enough heat to raise 34,400 grams of water from 0° to 1° C., so that the calorific value of hydrogen is 34,400. If the fuel consisted of carbon and hydrogen only, its calorific value would be calculated by multiplying the weight of the carbon in 1 gram of the fuel by 8080, and that of the hydrogen by 34,400, when the sum of the products would represent the theoretical calorific value. But if the fuel contains oxygen already combined with it, the calorific value will be dimin- ished, since less oxygen will be required from the air. For example, 1 gram of wood contains 0-5 gram of carbon, 0-06 of hydrogen, and 0-44 of oxygen. Now, oxygen combines with one-eighth of its weight of hydrogen to form water, so that the 0-44 gram of oxygen will convert 0-44 + 8 = 0-055 gram of the hydrogen into water, without evolution of available heat, leaving only 0-005 gram available for the production of heat. The calorific value of the wood, therefore, would be represented by the sum of 0-005 x 34400 ( = 172) and 0-5 x 8080 ( = 4040), which would amount to 4212; or 1 gram of wood should raise 4212 grams of water from 0° to 1°. These considerations lead to the following general formula for calculating the calorific value of a fuel containing carbon, hydrogen and oxygen where c, h and o respectively represent the carbon, hydrogen and oxygen in 1 gram of fuel. ; : The calorific value (or number of grams of water which might be heated 0 by the fuel fiom 0° to 1°) = 8080.6 + 34400 (h —§). The calorific value of a coal, as determined by experiment in a calorimeter, is 276 CALORIMETERS generally higher than that calculated by the above formula.t This arises from lack of knowledge as to how the elements of the coal are combined together. A convenient form of calorimeter, known as Mahler’s bomb, is shown in Fig. 203, and to a smaller scale in position for use in Fig. 204. The weighed substance to be burnt (or the mixture the reaction between the constituents of which is to be started by heat) is placed in a platinum boat, C (Fig. 203), attached by metal rods to the cover Fie. 2)4. of the steel bottle, B. The cover is screwed on to the bottle, the joint being made tight by means of a lead washer, P. The bomb is now connected at N with a tube leading from a bottle of compressed oxygen and having a pressure gauge inserted in it, and is filled with oxygen under pressure by slowly turning the screw valve, R, and closing it again when the pressure gauge marks 5-10 atmospheres. The bomb is now placed in the calorimeter chamber, D, containing a known weight of water, and surrounded by an air-jacket, H, itself surrounded by a water-jacket, A. One of the rods that support the tray, C, passes through an insulating plug, Z, in the cover of the bottle, B, while the other is in electrical contact with the bottle. Thus, by connecting the end of the insulated wire with one pole of a battery, and the bottle with the other pole, an electric current may be passed through the tray, C (or through a platinum spiral embedded in the substance, Fig. 203), so as to heat it sufficiently to ignite the substance to be burnt. (The quantity of electric current used for this purpose may be measured, and the heat thus introduced into the calorimeter may be calculated from the known equivalency of electric energy and heat energy.) The battery is cut off as soon as ignition has occurred, and the stirrer, S, having been set in motion, the thermometer, 7, is read at intervals, note being taken of the highest point attained and the time occupied in attaining it. If all the heat of the combustion (or reaction) passed into the water of the calori- meter the calculation of the result would be easy ; for the weight of the water multiplied by the rise of temperature would represent the heat of combustion. As, however, the whole apparatus shares the heat with the water in the calorimeter chamber, the capacity of the apparatus for heat must be ascertained. This is best effected by burning a known weight of a substance of known calorific value (naphthalene,? for example) in the bomb, and observing how much of the total heat passes into the water in the calorimeter ; the difference between this quantity and the known total heat is the amount of heat absorbed by the apparatus, and when divided by the rise of temperature shows the heat capacity of the apparatus. Suppose that 1 gram of coal has been burnt in the manner described, that the + Results more in accord with the practical value are claimed to be obtained from the following formula, where Q = quantity of heat, C’ = carbon left as coke on distilling the coal, and C’= carbon contained in the volatile products: Q = 8080 C’ + 11214 C” + 34462 H. If much O be present, one-eighth of its weight must be deducted from the H. 2 One gram evolves 96,920 gram-units of heat. FUEL—CALORIFIC INTENSITY 277 weight of water in the calorimeter is w grams, that the rise of temperature observed is t° C, and that the heat capacity of the apparatus is k gram-units ; then the heat of combustion of 1 gram of coal is wt + kt. In accurate work a correction must be made for the heat lost by radiation and convection from the calorimeter during the time occupied by the experiment ; for the methods of making this correction a text-book on Physics must be consulted. In the case of compounds of carbon and hydrogen, it has been observed that even when they have the same composition in 100 parts, they have not of necessity the same calorific value, the latter being affected by the difference in the arrangement of the component atoms of the compound, which causes a difference in the quantity of heat absorbed during its decomposition. Thus, olefiant gas (C,H) and cetylene (C,,H3,) have the same percentage composi- tion, and their calculated calorific values would be identical, but the former is found to produce 11,858 units of heats, and the latter only 11,055. It must be remembered that the calorific value of a fuel represents the actual amount of heat which a given weight of it is capable of producing, and is quite independent of the manner in which the fuel is burnt. Thus, a hundredweight of coal will produce precisely the same amount of heat in an ordinary grate as in a wind-furnace, though in the former case the fire will scarcely be capable of melting copper, and in the latter it will melt steel. The difference resides in the temperature or calorific intensity of the two fires : in the wind-furnace, through which a rapid draught of air is maintained by a chimney, a much greater weight of atmospheric oxygen is brought into contact with the fuel in a given time, so that, in that time, a greater weight of fuel will be consumed and more heat will be produced ; hence the fire will have a higher temperature, for the temperature represents, not the quantity of heat present in a given mass of matter, but the intensity or extent to which that heat is accumulated at any particular point. In the case of the wind-furnace here cited, a further advantage is gained from the circum- stance that the rapid draught of air allows a given weight of fuel to be con- sumed in a smaller space, and, of course, the smaller the area over which a given quantity of heat is distributed, the higher is the temperature within that area (as exemplified in the use of the common burning-glass). In some of the practical applications of fuel, such as heating steam boilers and warm- ing buildings, it is the calorific value of the fuel which chiefly concerns us ; but the case is different where metals are to be melted, or chemical changes to be brought about by the application of a very high temperature, for it is then the calorific intensity, or actual temperature of the burning mass, which has to be considered. No accurate method has yet been devised for determining by direct experiment the calorific intensity of fuel, nor can this value be ascertained properly by calculation owing to lack of complete data. It will be instructive, however; to consider how some idea of calorific intensity may be obtained from the calorific value. Let it be required to calculate the calorific intensity, or actual temperature, of carbon burning in pure oxygen gas. Twelve grams of carbon combine with 32 grams of oxygen, producing 44 grams of CO,; hence 1 gram of carbon combines with 2-67 grams of oxygen, producing 3-67 grams of CO,. It has been seen above that, supposing the water would bear such an elevation of temperature, and its specific heat would remain constant, the 1 gram of carbon would raise 1 gram of water from 0° to 8080°. If the specific heat (or heat required to raise 1 gram through 1°) of CO, were the same as that of water, 8080° divided by 3-67 would represent the temperature to which the 3-67 grams of CO, would be raised, and therefore the temperature to which the solid carbon producing it would be raised in the act of combustion. But the specific heat of carbonic acid gas is only 278 FUEL—CALORIFIC INTENSITY 0-2163, so that a given amount of heat would raise 1 gram of CO, to nearly five times as high a temperature as that to which it would raise 1 gram of water. Dividing 8080 units of heat (available for raising the temperature of the CO.) by 0-2163 (the quantity of heat required to raise 1 gram of CO, through 1°), we obtain 37355 for the number of degrees through which 1 gram of CO, might be raised by the combustion of 1 gram of carbon. But there are 3-67 grams of CO, formed in the com- bustion, so that the above number of degrees must be divided by 3-67 in order to obtain the actual temperature of the CO, at the instant of its production, that is, the temperature of the burning mass. The calorific intensity of carbon burning in pure oxygen is therefore (37355° + 3-67 =) 10178°. But if the carbon be burnt in air, the temperature will be far lower, because the nitrogen of the air will absorb a part of the heat, to which it contributes nothing. The 2-67 grams of oxygen required to burn 1 gram of carbon would be mixed, in air, with 8-93 grams of nitrogen, so that the 8080 units of heat would be distributed over 3-67 grams of CO, and 8-93 grams of nitrogen. Since the specific heat of CO, is 0-2163, the product of 3-67 x 0-2163 (or 0-794) repre- sents the quantity of heat required to raise the 3-67 grams of CO, from 0° to 1°. The specific heat of nitrogen is 0-2438 ; hence 8-93 x 0-:2438 (or 2-177) represents the quantity of heat required to raise the 8-93 grams of atmospheric nitrogen from 0° to 1°. Adding together these products, we find that 0-794 + 2-177 = 2-971 represents the quantity of heat required to raise both the nitrogen and carbonic acid gas from 0° to 1°, Dividing the 8080° by 2-971, we obtain 2720° for the number of degrees through which these gases would be raised in the combustion, 7.e. for the calorific intensity of carbon burning in air. By heating the air before it enters the furnace (as in the hot- blast iron furnace), of course the calorific intensity would be increased ; thus, if the air be introduced into the furnace at a temperature of 300°, it might be stated, without serious error, that the temperature producible in the furnace would be 3020° (2720 + 300°). The temperature might be further increased by diminishing the area of com- bustion, as by employing very compact fuel and increasing the pressure of the blast, In calculating the calorific intensity of hydrogen burning in air, from its calorific value, it must be remembered that, in the experimental determination of the latter number, the steam produced in the combustion was condensed to the liquid form, so that its latent heat was added to the number representing the calorific value of the hydrogen ; but the latent heat of the steam must be deducted in calculating the calorific intensity, because the steam goes off from the burning mass and carries its latent heat with it. One gram of hydrogen, burning in air, combines with 8 grams of oxygen, producing 9 grams of steam, leaving 26-77 grams of atmospheric nitrogen and evolving 34400 units of heat. It has been experimentally determined that the latent heat of steam is 537, that is, 1 gram of water, in becoming steam, absorbs 537 units of heat (or as much heat as would raise 537 grams of water from 0° to 1°) without rising in temperature as indicated by the thermometer. The 9 grams of water produced by the combustion of 1 gram of hydrogen will absorb, or render latent, 537 x 9 = 4833 units of heat. Deducting this quantity from the 34400 units evolved in the combustion of 1 gram of hydrogen, there remain 29567 units of heat available for raising the temperature of the 9 grams of steam and 26-77 grams of atmospheric nitrogen. The specific heat of steam being 0-480, the number (0-480 x 9 =) 4:32 represents the quantity of heat required to raise the 9 grams of steam through 1°; and the specific heat of nitrogen (0-2438) multiplied by its weight (26-77 grams) gives 6-53 units of heat required to raise the 26-77 grams of nitrogen through 1°. By dividing the available heat (29567 units) by the joint quantities required to raise the steam and nitrogen through 1° C (4:32 + 6-53 = 10-85), we obtain the number 2725° for the calorific intensity of hydrogen burning in air. The actual calorific intensity of the fuel is not so high as it should be accordin’ to theory, because a part of the carbon and hydrogen is converted into gas by destructive distillation of the fuel, and this gas is not actually 1 Jt is here assumed that the specific heat of gases is constant as the temperature rises ; «sa fact it increases. The specific heat of steam is calculated to be doubled, and that of CO, to be more than doubled, at 1200°. FURNACES 279 burnt in the fire, so that its calorific intensity is not added to that of the burning solid mass. Again, a portion of the carbon is converted into carbonic oxide, especially if the supply of air be imperfect, and much less heat is produced than if the carbon were converted into carbon dioxide ; although it is true that this carbonic oxide may be consumed above tke fire by supplying air to it, the heat thus produced does not increase the calorific intensity or temperature of the fire itself. One gram of carbon furnishes 2-33 grams of CO, which evolve, in their combustion, 5599 units of heat. But if the 1 gram of carbon had been converted at once into CO, it would have evolved 8080 units of heat, so that 8080 — 5599,-or 2481, represents the heat evolved during the conversion of 1 gram of carbon into CO, showing that a con- siderable loss of heat in the fire is caused by an imperfect supply of air. It has been already pointed out that the formation of CO is sometimes encouraged with a view to the production of a flame from non-flaming coal, such as anthracite. The actual calorific intensity of fuel is diminished by the heat consumed in bringing the portion of fuel yet unconsumed, as well as the surrounding parts of the grate, up to the temperature of the fire. In all ordinary fires and furnaces, a large amount of heat is wasted in the current of heated products of combustion escaping from the chimney. Of course, a portion of this heat is necessary in order to produce the draught of the chimney. In boiler furnaces it is found that, for this purpose, the temperature of the air escaping from the chimney must not be lower than from 250° to 300°. If the fuel could be consumed by supplying only so much air as contains the requisite quantity of oxygen, a great saving might be effected, but in practice about twice the calculated quantity of air must be supplied in order to effect the removal of the products of combustion with sufficient rapidity. Much economy of fuel results from the use of furnaces constructed on the principle of Siemens’ regenerative furnace, in which the waste heat of the products of combustion is absorbed by a quantity of fire-bricks, and employed to heat the air before it enters the furnace, two chambers of fire- bricks doing duty alternately, for absorbing the heat from the issuing gas, and for imparting heat to the entering air, the current being reversed by a valve as soon as the fire-bricks are strongly heated (p.446). This system is best adapted for the use of gaseous fuel which can also be heated by the hot fire-bricks before its combustion, a very high temperature being thus attainable. The following Table shows the percentage composition of samples of the principal varieties of fuel together with their calorific values : = ©. 1 0. N. 8. Ash. ae Wood (oak) . ‘ . | 50-18 6-08 | 42-64 | 0-10 — 1-00 3,000 Peat . ‘ : . | 54:38 | 5-08 | 29-54 | 1-31 — 8-69 4,000 Lignite. ‘ és 66°32 5-63 | 22-86 | 0-56 2-36 2-27 5,000 Bituminous coal _ . . | 78-57 5-29 | 12-88 | 1-84 0-39 1-03 8,250 Wigan cannel . . | 80-06 | 5-53) 8-09 | 2-12 | 1-50 | 2-70 8,750 Charcoal : : . | 81-97 | 2-30 | 14-15 — = 1-60 8,000 Anthracite. : . | 90-39 | 3-28) 2-98} 0-83 | 0-91 | 1-61 9,000 Coke . : . | 92-48 | 0-47] 0-93] 0-73 | 1-14 | 4:27 8,000 Petroleum . : . | 85-00 | 13-00 | 2:00} — = — 11,000 280 SILICA = H. | cH, | co | c4H,'] co, N. 0. ae Coalpaa pNewoastl ae oe *} 43:99] 39:36) 642] 412] — | 540] 040 |) oo conmel (4072 apse] age) se | — | oan) a | em Producer-gas _| 2-20] 7-40] 22:80| — | 3-60 | 63-50] 0-50 | 28,000 Water-gas 4s-00| — |41-.00| — | 600] 500) — | 74,000 Mondgas . —. | 29-00 2-00/11-00] — |16-00| 42.00} — | 40,000 SILICON, Si = 28.3. Next to oxygen, silicon is by far the most abundant element, although it is not found in nature in the free state. It always occurs either as silica, its oxide SiO,, or as silica in combination with various basic oxides, 7.c. as silicates. Hence it will be convenient to study silica before the element itself. Silica, SiO, = 60-3.—The purest natural form of silica is the trans- parent and colourless variety of quartz known as rock crystal, the most widely diffused ornament of the mineral world, often seen crystallised in beautiful six-sided prisms, terminated by six-sided pyramids (Fig. 205), which are always easily distinguished by their great hardness, scratching » glass almost as readily as the > diamond. Coloured of a delicate purple,probably by a little organic matter, these crystals are known Fie. 208. as amethysts, and when of a brown colour as Cairngorm stones or Scotch pebbles. Losing its transparency and crystalline structure, we meet with silica in the form of chalcedony and of carnelian, usually coloured, in the latter, with oxide of iron. Hardly any substance has so great a share in the lapidary’s art as silica, for in addition to the above instances of its value for ornamental purposes, we find it constituting jasper, agate, cat’s eye, onyx, so much prized for cameos, opal, and some other precious stones. In opal the silica is combined with water. Sand, of which the whiter varieties are nearly pure silica, appears to have been formed by the disintegration of siliceous rocks, and has generally a yellow or brown colour, due to the presence of oxide of iron. The resistance offered by silica to all impressions has become proverbial in the case of flint, which consists essentially of that substance coloured with some impurity. Flints are generally found in compact masses, distributed in regular beds throughout the chalk formation ; their hardness, which even exceeds that of quartz, rendered them useful, before the days of matches, for striking sparks with steel ; small particles of metal are thus detached, and are so heated by the percussion as to continue to burn in the air, and to inflame tinder or gunpowder upon which they are allowed to fall. The part taken by silica in natural operations appears to be chiefly a mechanical one, for which its stability under ordinary influences peculiarly fits it, for it is found to constitute the great bulk of the soil which serves as a support and food-reservoir for land plants, and enters largely into the composition of the greater number of rocks. But that this substance is not altogether excluded from any share in life is shown by its presence in the shining outer sheath of the stems of equisetum, diatoms, grasses 1 Including benzene vapour, acetylene, &c. Gram-units per cubic foot (28-315 litres), SILICIC ACID 281 and cereals, particularly in the hard external coating of the Dutch rush used for polish- ing, and in the joints of the bamboo, where it forms the greater part of the matter known as tabasheer. This alone would lead to the inference that silica could not be absolutely insoluble, since the capillary vessels of plants are known to be capable of absorbing only such substances as are in a state of solution. Many natural waters also present us with silica in a dissolved state, and often in considerable quantity, as, for example, in the geysers of Iceland, which deposit a coating of silica upon the earth around their borders. Pure water, however, has no solvent action upon the natural varieties of silica. The action of an alkali is required to bring it into a soluble form. To effect this upon the small scale, some white sand is very finely powdered (in an agate mortar), mixed with about four times its weight of —7>SS dried sodium carbonate, placed Wi upon a piece of platinum foil fff slightly bent up (Fig. 206), and fused by directing the flame of a blowpipe upon the under side of the foil. Effervescence will be observed, due to the aN ee escape of carbonic acid gas. a The piece of platinum foil, when cool, may be placed in a little warm water, and allowed to soak for some time, when the mass will gradually dissolve, forming a solution of sodium silicate, decidedly alkaline to test-papers. If a portion of the solution of sodium silicate in water be poured into a test-tube, and two or three drops of hydrochloric acid added to it, with occasional agitation, effervescence will be produced by the expulsion of any carbonic acid gas still remaining, and the solution will be converted into a gelatinous mass by the separation of silicic acid. But if another portion of the solution be poured into an excess of dilute hydrochloric acid (i.e. into enough to render the solution distinctly acid), the silicic acid will remain dissolved in the water, together with the sodium chloride formed. In order to separate the sodium chloride from the silicic acid, the process of dialysis! must be adopted ; see also p. 77. Dialysis is the separation of dissolved substances from each other by taking advantage of the different rates at which they pass through moist diaphragms or septa. It isfound that those substances which erystallise (crystalloids) and the mineral acids pass through such septa ina solution faster than do amorphous substances (colloids). If the mixed solution of sodium chloride and silicic acid were poured upon an ordinary paper filter, it would pass through without alteration ; but if parchment paper be employed, which is not pervious to water, although readily moistened by it, none of the liquid will pass through. = If the cone of parchment paper be supported upon a vessel filled with é ZE= distilled water (Fig. 207), so that the water may be in contact with the “Fie. 207, outer surface of the cone, the hydrochloric acid and the sodium chloride will pass through the substance of the parchment paper, and the water charged with them may be seen descending in dense streams from the outside of the cone. After a few hours, especially if the water be changed occasionally, the whole of the hydrochloric acid and sodium chloride will have passed through, and a pure solution of silicic acid in water will remain in the cone. The most useful form of dialyser is a parchment-paper tube (Fig. 208), which is bent in the form of a U, filled with the solution to be dialysed, and suspended in the 1 From dadvw, to part asunder. 282 SILICA—CRYSTALLINE FORMS cylinder containing water, which is preferably kept in slow circulation by filling the funnel and allowing the siphon to act slowly. This solution remaining in the dialyser is believed to contain the ortho- silicic acid, 2H,O.SiO,, or H,Si0O,, or Si(OH),. It is very feebly acid to blue litmus-paper, and not perceptibly sour to the taste. It has a great tendency to set into a jelly in consequence of the sudden separation of silicicacid. If it be slowly evaporated ina dish, it soon solidifies ; but, by conducting the evapora- tion in a flask so as to prevent any drying of the silicic acid at the edges of the liquid, it may be concentrated until it contains 14 per cent. of silicic acid. When this solution is kept,evenin a stoppered or corked bottle, it sets into a transparent gelatinous mass, which gradually shrinks and separates from the water. When sulphuric evaporated, in vacuo, over acid, it gives a transparent lustrous glass which is composed of 22 per cent. of water and 78 percent. of silica (H,O.SiO,). This is also the composition of the gelatinous precipitate produced by acids in the solution of sodium silicate. It is some- times written H,SiO, or SiO(OH),, and called metasilicic acid. This behaviour of silicic acid is typical of collcids ; they can generally exist in solution (the hydrosol form), but are apt to separate as a jelly (the hydrogel form) from such solutions. See also Colloidal Solutions (p. 383). The hydrated silica cannot be redissolved in water, and is soluble to only a slight extent in hydrochloric acid. If it be heated to expel the water, pure silica NP remains as a white voluminous powder insoluble both in water and in hydrochloric acid, but dissolved when 1 boiled with solution of potash or soda, or their car- ae eee, ORE: fo Silica in the naturally crystallised form, as rock crystal and quartz, is insoluble in boiling solutions of the alkalies, and in all acids except hydro-fluoric; but amorphous silica (such as opal and tripoli) is readily dissolved by boiling alkalies. These represent, in fact, two distinct modifications of silica, which may be said to be dimorphous.1 Quartz has a sp. gr. 2-65 and is optically active. A transparent piece of rock crystal may be heated to bright redness without change, but if it be powdered previously to being heated, its specific gravity is diminished from 2-6 to 2-4, and it becomes soluble in boiling alkalies, having been converted into the amorphous modification. The natural forms of amorphous silica of sp. gr. 2-2 are always hydrated, and even some of the varieties of sp. gr. 2-6, such as flint, agate, and chalcedony, contain a little water, pointing to the aqueous origin of all silica. Silica has no definite melting-point. When it is heated by the oxy- hydrogen blowpipe or in the electric furnace at about 2000° it becomes viscous and can be worked like glass, but its boiling-point is so little above, this temperature that further accession of heat volatilises the silica instead of producing greater fluidity. The manufacture of vessels, tubes, &c., of silica, as a substitute for glass, has become an important industry and is’ 1 Tf tridymite—a mineral which occurs in anhydrous hexagonal crystals, has a sp. gr. of 2:3, and is not attacked by alkalies—be regarded as the type of another crystalline variety of silica, this must be said to be trimcrphous, MINERAL SILICATES 283 again mentioned in the section on Glass. Such vessels are of particular value in the chemical laboratory and works on account of the high tempera- ture and rapid change of temperature which they can withstand without fusion or fracture. When the viscous or plastic silica is cooled fairly rapidly, as in the said manufacture, it remains in the amorphous condition in which it resembles a true glass ; if slowly cooled, however, it becomes a mass of crystals, losing its transparency, Itis instructive to compare it with sulphur in this respect, although the amorphous phase is incom- parably more permanent. Possibly natural forms of crystalline silica have been pro- duced by the slow cooling of viscous silica, but to the chemist an aqueous origin seems more probable, as stated above. Crystals of quartz have been obtained artificially by prolonged action of water upon glass at a high temperature under pressure. Silicates.—The silicates form by far the greatest number of minerals. Talc, asbestos, olivine, serpentine are silicates of magnesium ; clay, slate, fuller’s earth, pumice-stone, of aluminium ; mica, felspar, of aluminium and potassium ; the various garnets, of a diacidic oxide in union with a triacidic oxide, e.g. 6CaO.3S8i0, + 2A1,0,.38i0,. The formule are usually not simple, but derived from various polysilicic acids, i.e. compounds of SiO, with nH,O (p. 91). Manufactured silicates are familiar in the forms of glass, porcelain, &c. None but the silicates of the alkali metals (e.g. sodium silicate, commonly known as water glass) is soluble in water. The acid properties of silicic acid are so feeble that it is a matter of great difficulty to determine the proportion of any base which is required to react with it in order to form a chemically neutral salt. Like carbonic acid, it does not destroy the action of the alkalies upon test-papers, and we are therefore deprived of this method of ascertaining the proportion _ of alkali which neutralises it in a chemical sense. In attempting to ascertain the quantity of alkali with which silica combines, from that of the carbon dioxide which it expels when heated with an alkali carbonate, it is found that the proportion of carbon dioxide expelled varies considerably, according to the temperature and the proportion of alkali carbonate employed. The limits of the reaction, however, appear to be the formation of the alkali metasilicate on the one hand and the alkali orthosilicate on the other : SiO, + Na,CO,; = CO, + Na,SiO, (metasilicate). SiO, + 2Na,CO,; = 2CO, + Na,SiO, (orthosilicate). By heating silica with sodium hydroxide (NaOH), it is found that 60 parts of silica expel 36 parts of water, however much NaOH is employed, and the same proportion of water is expelled from barium hydroxide, Ba(OH),, when heated with silica. The formula SiO, represents 60 parts by weight of silica, and 36 parts represent 2 molecules of water. Hence it would appear that the action of silica upon sodium hydroxide is represented by the equation—4NaOH + SiO, = Na,SiO, + 2H,0; and that upon barium hydroxide by 2Ba(OH), + SiO, = Ba,SiO, + 2H,O: and since it is found that several of the crystal- lised mineral silicates contain a quantity of metal equivalent to 4H, it is usual to represent silicic acid as a tetrabasic acid, H,S8iO,, containing 4 atoms of hydrogen exchangeable for metals. The circumstance that silica is not capable of being converted into vapour at a high temperature enables it to decompose the salts of many acids which, at*ordinary temperatures, are able to displace silicic acid. The feebly acid character of SiO, will recall that of CO,. Other comparison between these analogues is hardly possible on account of their different physical conditions. 284 SILICON Silicon has been obtained in two allotropic modifications, amorphous and crystalline. Silica and the silicates, as observed in their natural and manufactured forms, are so remarkably resistant to chemical attack that the separation of the element may be expected to present difficulty. In 1813, however, Davy obtained an impure specimen by decomposing the oxide by the action of potassium. It has since been produced, far more easily, by converting the silica into potassium silicofluoride (K,SiF,), and decomposing this at a high temperature with potassium or sodium, which combines with the fluorine to form a salt capable of being dissolved out by water, leaving the silicon in the form of a brown powder, amorphous silicon. A fairly pure product is obtained by heating a mixture of pure silica, pure magnesium metal, and a little magnesium oxide; SiO, + 2Mg = 2Mg0 + Si. The experiment may be made (with caution) in a test-tube. Amorphous silicon occurs as a brown insoluble, hygroscopic powder; sp. gr. 2°35. Unlike carbon, its analogue, silicon is fusible at a temperature somewhat above the melting-point of cast iron; on cooling, it forms a brilliant metallic-looking mass, which may be obtained, by certain processes, crystallised in octahedra so hard as to scratch glass like a diamond. It is volatilised in the electric furnace. It burns brilliantly in oxygen, but not completely, for it becomes coated with silica, which is fused by the intense heat of the combustion ; also in fluorine, forming silicon tetrafluoride, SiF,. It resists the action of all acids, except hydrofluoric, which it decomposes, forming silicon fluoride, and evolving hydrogen (Si + 4HF = SiF, + 2H,). It is also dissolved by solution of potash, with evolution of hydrogen, and formation of potas- sium silicate. When heated with the blowpipe on platinum foil, it eats a hole through the metal, with which it forms the fusible platinum silicide. Crystallised silicon is obtained by strongly heating a mixture of alu- minium (125 g.) and potassium silicofluoride, K,SiF,, (40 g.) in an iron crucible; 3K,SiF, + 4Al = 6KF + 4AlF, + 3Si. The excess of melted aluminium dissolves the liberated silicon and lets it separate in the crystalline form on cooling. The aluminium is removed by acids. Silicon is soluble in some other metals, especially silver. Crystallised silicon occurs in nearly black opaque scales or crystals, very hard, and having a metallic lustre ; sp. gr. 2°49. It conducts electricity, though amorphous silicon is a non- conductor; cf. Graphite and Amorphous Carbon. Chemically it behaves similarly to amorphous silicon, though it is less readily reactive. It does not easily dissolve in hydrofluoric acid unless nitric acid be also present. In their chemical relations to other substances there is much resemblance between silicon and carbon. Silicon, however, is capable of displacing carbon, for if potassium carbonate be fused with silicon, the latter is dis- solved, forming potassium silicate, and carbon is separated. Silicon also resembles carbon in its disposition to unite with certain metals to form compounds which have a metallic appearance. Thus silicon is found together with carbon in cast-iron, and it unites directly with aluminium zinc, and platinum, to form compounds resembling metallic alloys. Nitrogen enters into direct union with silicon at a high temperature, though it refuses to unite with carbon except in the presence of alkalies. The most important analogy between carbon and silicon from a theoretical point of view resides in the fact that each of them combines with hydrogen in the proportion of 1 atom of the element to 4 atoms of a showing that each is a tetravalent element. Silicon Carbide, SiC.—As might be expected from their aitaiiaity: carbon and silicon do not combine easily. At the temperature of the electric furnace (3500°), however, the compound SiC is produced in the form of CARBORUNDUM 285 colourless, transparent hexagonal plates of sp. gr. 3:12. In hardness (9-5) it is surpassed by the diamond only ; it scratches ruby and steel easily, and on this account is made on a considerable scale for use as an abrasive material under the name carborundum, which is generally dark coloured from im- purities. It resists the attack of all acids, but succumbs to fused alkali ; it does not oxidise even at a white heat ; but at 2200° it begins to dissociate. In the manufacture of carborundum the electric furnace consists of a brick box, having a carbon electrode projecting into each end. The bottom of the box having been covered up to the level of the electrodes with a mixture of sand, coke, and a little salt, a layer of crushed coke of the same cross-section as the electrodes is built up between the electrodes. The furnace is then filled with the aforesaid mixture. When the electric current is supplied to the electrodes the layer of coke between them attains a very high temperature owing to the resistance it offers to the passage of the current, and the radiation from this hot core causes the carbon in the charge to reduce the silica and to combine with the silicon for a certain distance around the core ; SiO, + 3C = SiC + 2C0. Silicon dicarbide, SiCz, is obtained by passing ethylene over silicon at a full white heat. Szloxicon is a refractory powder prepared somewhat similarly to carborundum ; its chief constituent is Si,C,0. Silicon borides, SiB; and SiBg, are produced by fusing the elements together in an electric furnace. Various silicon nitrides have been described ; probably Si;N, is known as a definite compound. These nitrogen derivatives readily yield ammonia on treatment with water. Better known are the compounds containing both nitrogen and hydrogen. Silicon amide, Si(NHg2)4, is formed by the interaction of liquid ammonia and silicon tetrachloride. Above 0° it loses ammonia and becomes silicon imide, Si(NH)o. CompounbDs oF SILICON wiTH HyprocreNn, Hatocens, ALKYLs, &c. These are of exceptional interest in that they are analogous to the hydro- carbons and their haloid and alkyl derivatives, and show most clearly the close relationship between silicon and carbon. Generally these compounds are unstable, oxidise readily, inflame spontaneously in the air, and are decomposed by water. Optically active compounds containing an asym- metric silicon atom are known. Silicon rarely combines with itself, the best-known cases being silicoethane, H,Si—SiH;, and silico-oxalic acid, HO.OSi—SiO.OH ; but in the higher chlorides, e.g. SisCle, Si;Cly., SigClyg, and a few other cases, longer chains are indicated. The following are selected for comparison. See also Organic Chemistry. Silicomethane SiHy. Methane CH,. Silicoethane Si,H,. Ethane CLHg. Silicoacetylene SigHg. Acetylene CH. Silicon tetrachloride SiCl,. Carbontetrachloride CCl. Disilicon hexachloride SigCl,. Hexachlorethane CoC]. Silicochloroform SiHC]. Chloroform CHCl. Silicoheptane SiH(C,Hs)3. Heptane CH(C,Hs)3. Triphenylsilicane SiH(C,H;)s.- Triphenylmethane CH(C,Hs5)s- Triethylsilicol (C,H;);8i0OH. Triethylearbinol (C.H;)sC.OH. Diethylsilicon oxide (CyH;)2Si0. Diethyl ketone (C,H; )2CO. , Silicoacetic acid CH,.SiO0.OH. Acetic acid CH; .CO.OH. Silico-oxalic acid (SiO .OH),. Oxalic acid (CO.OH)p. Silicon hydride, silicomethane, SiHy, may be formed by the direct union of its elements at the temperature of the electric arc. It is usually prepared by decomposing magnesium silicide, Mg,Si (made by heating magnesium with silica), with dilute HCl. It isa colour- less gas which, unlike CHy, ignites spontaneously in air, burning with a brilliant white flame which emits clouds of silica and deposits a brown film of silicon upon a,cold surface. It decomposes into its elements at 400°. When warmed under reduced pressure it explodes easily. The spontaneous inflammability is due to the presence of a little 286 SILICON TETRAFLUORIDE silicoethane, SigHg, which is left on liquefying the whole gas and allowing the silico- ethane (also hydrogen) to boil away (cf. PH). It is a colourless liquid ; b.-pt. + 52°. Silicon Tetrachloride, SiCl,, unlike the chlorides of carbon, may be formed by the direct union of silicon with chlorine at a high tempera- ture ; but it is best prepared by passing dry chlorine over a mixture of silica and charcoal, heated to redness in a porcelain tube connected with a receiver kept cool by a freezing-mixture. Neither C nor Cl separately attacks the silica, but when they are employed together, the combined attractions of the carbon for the oxygen and the chlorine for the silicon decompose the silica ; SiO, + 2C + 2Cl, = SiCl, + 2CO. The tetrachloride is a colourless, heavy, volatile liquid (sp. gr. 1-52, b.-pt. 59°), and fumes when exposed to air, the moisture of which decom- poses it, yielding hydrochloric acid and silicic acid; SiCl, + 4HOH = Si(OH), + 4HCI. Silicon hexachloride, Cl,8:—SiCl,, is produced when SiCl, is passed over fused silicon at a very high temperature. It forms colourless crystals melting at — 1° and boiling at 147°. Cold water decomposes it with formation of silico-oralic acid, Cl,Si: SiC]; + 4HOH = HOOSi-SiOOH + 6HCI. The chlorides of silicon are of theoretical importance as forming the starting-point of a number of silicon compounds which are the analogues of organic carbon compounds, C taking the place of Si. Silicon tetrabromide, SiBry, is a colourless liquid of sp. gr. 2-82, b.pt. 150°, and m.pt. — 12°. Silicon tetraiodide, Sil,, crystallises in colourless octahedra, melts at 120°, and boils at 290°. Silico-Chloroform, SiHCl,, so called from its analogy with chloroform, CHCl,, is obtained when silicon is heated in hydrogen chloride; Si + 3HCl = SiHCl, + H,. It is a colourless liquid which boils at 33°, has a sp. gr. 1-344, and, unlike most chlorine compounds (including chloroform), is inflammable, burning with a greenish flame, and producing SiO, and HCl. Corresponding compounds of F, Br, and I are also known. Silicon Tetrafluoride, SiF,—If a mixture of powdered fluor spar and glass be heated, in a test-tube or small flask, with concentrated sul- phuric acid, a gas is evolved which has a very pungent odour, and produces thick white fumes in contact with the air :1 it might at first be mistaken for hydrofluoric acid, but a glass rod or tube moistened with water and exposed to the gas becomes coated with a white film, which proves, on examination, to be silica. This result originated the belief that the gas consisted of fluoric (now hydrofluoric) acid and silica ; but Davy corrected this view by showing that it really contained no oxygen and consisted solely of silicon and fluorine. The gas is now called silicon tetrafluoride, and represents silica in which the oxygen has been displaced by fluorine: the change of places between these two elements in the above experiment is represented by the equation— 2CaF, + SiO, + 2H,SO, = 2CaSO, + SiF, + 2H,0. The formation of the crust of silica upon the wetted surface of the glass is due to a reaction between the tetrafluoride and the water, in which the oxygen and fluorine again change places; SiF, + 2H,O = SiO, + 4HF? Since this latter equation shows that hydrofluoric acid is again formed, it would be expected that the glass beneath the deposit of silica would be found corroded by the acid; this, however, is not the case, and when the experi- 1 SiF, becomes solid at — 102°, and, at a higher temperature, evaporates without fusing. 2 It will be noticed that the proportion of SiF, to H,O in this equation, representing the decomposition of the gas by water, is the same as that in the preceding equation, representing the evolution of the gas together with water, so that the equations seem to contradict each other. In reality it depends on the actual masses of water and other substances present, ard also on the temperature, whether SiF, and H,O can exist together or will at once decompose each other. The excess of sulphuric acid used in the manufacture of SiF, will com- bine with the water, and will prevent it from decomposing the SiF,. HYDROFLUOSILICIC ACID 287 ment is repeatéd upon a somewhat larger scale, so that the water which has attacked the gas may be examined, it is found to hold in solution, not hydrofluoric acid, but an acid which has little action upon glass, and is composed of hydrofluoric acid and silicon fluoride, the hydrofluoric acid produced when water acts on the fluoride having combined with a portion of ae latter to produce the new acid, 2HF.SiF,, or H,SiF 4, hydrofluosilicic acid. For the preparation of s‘licon tetrafluoride, 30 grams of fluor spar and an equa weight of powdered glass; are mixed together, and heated in a flask, with 200 c.c. of oil of vitriol, the gas being collected in dry bottles by downward displacement (see Fig. 92). Ifa little of the gas be poured from one of the bottles into a flask filled up to the neck with water, the surface of the latter will become covered with a layer of silica, so that if the flask be quickly inverted, the water will not pour from it and will seem to have been frozen. In a similar manner, a small tube filled with water and lowered into a bottle of the gas will appear to have been frozen when withdrawn. A stalactite of silica some inches in length may be obtained by allowing water to drip gently from a pointed tube into a bottle of the gas. Characters written on glass with a wet brush are rendered opaque by pouring some of the gas upon them. The fact that silica is so easily volatilised in the form of SiF, is of immense service in analytical chemistry for ‘‘ opening up” mineral silicates. By heating the silicate with H,SO, and HF in a platinum vessel all the silica may be expelled, leaving the bases in the form of sulphates. Hydrofluosilicic Acid, H,SiF,—This acid is obtained in solution by passing silicon tetrafluoride into water; 3SiF, + 2H,O = 2H,SiF, + SiO,. The gas must not be passed directly into the water, lest the separated silica should stop the orifice of the tube, to prevent which the latter should dip into a little mercury at the bottom of the water, when each bubble, as it rises through the mercury into the water, will become surrounded with an envelope of gelatinous silica, and if the bubbles be Ee very regular, they may even form tubes / of silica extending through the whole height of the water. bis li Crystals of H,SiF,.2Aq have been ob- a f tained by passing SiF, into solution of : i For preparing hydrofluosilicic acid, it will be found convenient to employ a gallon stoneware _ bottle (Fig. 209), furnished with a wide tube =SEpilu, dipping into a cup of mercury placed at the —— oe bottom of the water. Five hundred grams of Fra. 209. finely powdered fluor spar, an equal weight of fine sand, and 2 litres of oil of vitriol are introduced into the bottle, which is gently heated upon a sand-bath, the gas being passed into about 3 litres of water. After six or seven hours the water will have become pasty, from the separation of gelatinous silica. It is poured upon a filter, and when the liquid has drained through as far as possible, the filter is wrung in a cloth, to extract the remainder of the acid solution, which will have a sp. gr. of about 1-078. A dilute solution of hydrofluosilicic acid may be concentrated by evapora- tion up to a certain point, when it begins to decompose, evolving fumes of SiF,, HF remaining in solution and volatilising in its turn if the heat be continued. Of course, the solution corrodes glass and porcelain when evaporated in them. If the solution of hydrofiuosilicic acid be neutralised with potash and stirred, a very 288 BORIC ACID characteristic crystalline precipitate of potassium silico-fluoride (potassium fluosilicate), K,SiF,, is formed ; H,SiF, + 2KHO = K,SiF, + 2H,0. But if an excess of potash be employed, a precipitate of gelatinous silica will be separated, potassium fluoride remaining in the solution : H,SiF, + 6KHO = 6KF + 4H,0 + SiO,. One of the chief uses of hydrofluosilicic acid is to separate the potassium from its combination with certain acids, in order to obtain these in the separate state (p. 90). Tin and lead, which belong to the same group of elements as silicon (see Periodic Law), form fluostannates and fluoplumbates, such as Na,SnF, or 2NaF.SnF,, and K,PbF, or 2KF.PbF,, analogous to the fluosilicates. Silicon disulphide, SiSj, corresponding with carbon disulphide, is obtained by burning silicon in sulphur vapour, or by passing vapour of carbon disulphide over a mixture of silica and charcoal, in the form of colourless volatile needles. Unlike the carbon compound, it is a solid, absorbing moisture when exposed to air and soluble in water, which gradually decomposes it into silica and hydrogen sulphide. When heated in air it burns slowly, yielding silica and sulphur dioxide. Silicon monosulphide, SiS, is obtained by heating ferrosilicon with sulphur in an electric are furnace. BORON, B = I1.0. The element itself does not possess much importance ; it is found only in combination with oxygen in the mineral world, whence very small quantities find their way into some plants, such as the grape-vine, and into sea-water. The oxide will be considered first. Boric Anhydride, or anhydrous boric acid, B,O; = 70.—A saline substance called borax (Na.B,0,.10Aq) has long been used in medicine, in working metals, and in making imitations of precious stones ; this substance was originally imported from India and Thibet, where it was obtained in crystals from the waters of certain lakes, and came into this country under the native name of tincal, consisting of impure borax, surrounded with a peculiar soapy substance. Nowadays the chief source of borax is the bed of a dried-up lake in the Sierra Nevada. In 1702, in the course of one of those experiments to which, though empirical in their nature, scientific chemistry is now so deeply indebted, Homberg happened to distil a mixture of borax and green vitriol (ferrous sulphate), when he obtained a new substance in pearly plates, which was found useful in medicine, and received the name of sedative salt. A quarter of a century later Lemery found that this substance might be separated from borax by employing sulphuric acid instead of ferrous sulphate, and that it possessed acid properties, whence it was called boracic acid, now abbreviated to boric acid. Much more recently this acid has been obtained in a free state from natural sources, and is now imported into this country from the volcanic districts in the north of Italy, where it issues from the earth in the form of vapour, accompanied by violent jets of steam, which are known in the neigh- bourhood as soffioni. It would appear easy enough, by adopting arrange- ments for the condensation of this steam, to obtain the boric acid which accompanies it, but it is found necessary to cause the steam to deposit its boric acid by passing it through water, for which purpose basins of brick- work (lagunes, Fig. 210) are built up around the soffioni, and are kept filled with water from the neighbouring springs or brooks ; this water is allowed to flow successively into the different lagunes, which are built upon a declivity for that purpose, and it thus becomes impregnated with about 1 per cent. of boric acid. The necessity for expelling a large proportion of this water, in order to obtain the boric acid in crystals, formed for a long time a great obstacle to the success of this branch of industry in a country where fuel is BORIC ACID 289 very expensive. In 1817, however, Larderello conceived the project of evaporating this water by the steam-heat afforded by the soffioni the mselves, and several hundred tons of boric acid are now annually produced in this manner. The evaporation is conducted in shallow leaden evaporating-pans (A, Fig. 210), under which the steam from the soffioni is conducted th rough Fia. 210. the flues, F, constructed for that purpose. As the demand for boric acid increased on account of the immense consumption of borax in porcelain manufacture, the experiment was made, with success, of boring into the volcanic strata, and thus producing artificial soffioni, yielding boric acid. . The crystals of boric acid, as imported from these sources, contain salts of ammonia and other impurities. They dissolve in about three times their weight of boiling water, and crystallise on cooling, since they require 26 parts of cold water to dissolve them. These crystals have the sp. gr. 1-435 and are 3H,O.B,0, (or H;BO;3, or B(OH),;). If they are sharply heated in a retort they distil partly unchanged, together with the water derived from the decomposition of another part ; but if they be not heated above 100° they effloresce and become H,0.B,03.1 When heated for a long time to 140° this becomes H,O.2B,03, sometimes written H,B,0,, and called pyroboric acid, whilst H,O.B,0; is HBO,, metaboric acid, and the crystals, H;BO,; or B(OH),, are orthoboric acid. When pyroboric acid is heated further, the whole of the water passes off, carrying with it a little boric acid, and the B,O, fuses to a glass, which remains perfectly transparent on cooling (vitreous boric acid). This is slowly volatilised by the continued action of a very high temperature. It dissolves very slowly in water. Boric acid is an antiseptic, i.e. it hinders putrefaction, and is applied, either alone or in com- bination with glycerin, for the preservation of milk, meat, and other foods. It is also said to kill grass. A characteristic property of boric acid is that of imparting a green colour to flames. Its presence may thus be detected in the steam issuing from a boiling solution of boric acid in water; for if a spirit-flame or a piece of burning paper is held in the steam, the flame acquires a green tint, especially at the edges. The colour is more distinctly seen when the crystallised boric acid is heated on platinum foil in a spirit flame or an air-gas flame ; and still better when the crystals are dissolved in boiling alcohol and the solution burnt on a plate. The presence of boric acid in borax may be ascertained by mixing the solution of borax with strong sulphuric acid to liberate the boric acid, and adding enough alcohol to make the 1 According to Hehner, boric acid can be completely volatilised at 100° without at any stage having the composition H,0.B,03;. 19 290 BORATES mixture burn ; or by moistening the borax with glycerin, when it gives a green flame in the Bunsen burner. Another peculiar property of boric acid is its action upon tur- meric. If a piece of turmeric paper be dipped in solution of boric acid and dried at a gentle heat, it assumes a fine brown-red colour, which is changed to green or blue by potash or its carbonate. In applying this test to borax, the solution is slightly acidified with hydrochloric acid, to set free the boric acid, before dipping the paper. In the presence of oxalic acid the test is more delicate, especially when a mixture of the sub- stance in solution with small quantities of tincture of turmeric, hydrochloric acid and oxalic acid is evaporated in the water-bath. Borates—Boric acid, like carbonic, must be classed among the feeble acids. It colours litmus violet only, like carbonic acid, and does not neu- tralise the action of the alkalies upon test-papers. At high temperatures, fused boric anhydride combines with the alkalies and metallic oxides to form transparent glassy borates, which have, in many cases, very brilliant colours, and upon this property depend the chief uses of boric acid in the arts. Unlike the silicates, the borates are comparatively rare in the mineral world. No very familiar mineral substance, except borax, contains boric acid. A double borate of sodium and calcium, called boro-natrocalcite, Na,.B,0,.(CaB,0,)..18H,O, is imported from Peru for the manufacture of borax, and the mineral known as boracite is a magnesium borate. The mineral tourmaline, an aluminium-ferrous silicate, contains a considerable proportion of B,O;, apparently substituted for part of the Al,Qs. In determining the proportion of base which boric acid requires to form a chemi- cally neutral salt, the same difficulties are met with as in the case of silicic acid (p. 283) ; but since it is found that 70 parts of boric anhydride (the weight represented by B,O,) displace 54 parts of water (3 molecules) from sodium hydroxide and from barium hydroxide, each employed in excess, it would appear that the boric acid requires 3 molecules of an alkali fully to satisfy its acid character, 6NaOH + B03 = 2Na3BO; + 3H,O. Hence, boric acid is a tribasic acid represented by the formula H;BO,, which is the composition of the crystallised acid, but the formule of the common borates cannot be made to accord with this view. The only orthoborate yet obtained is Mg;(BOs)o. The acid character of boron oxide (B,O3) is so feeble as compared with that of such anhydrides as SO, and P.O; that boron oxide can even behave as a feeble base towards these powerful acid oxides, forming salts such as B,O3.P,0;. This is interesting in view of the fact that boron occurs above aluminium in the third periodic group. By treating borates with H,O, or with sodium peroxide and water, or by electro- lysing them as for the production of persulphates (p. 170), various perborates such as Na;BO, are obtained. They are stable in the solid state, but unstable in solution, and rapidly lose oxygen. Boron.—It was in the year 1808 that Gay-Lussac and Thénard suc- ceeded, by fusing boric anhydride with potassium, in isolating boron. The element is more easily prepared by fusing magnesium with an excess of boric acid and treating the product successively with alkalies and acids. The amorphous boron thus obtained is a maroon-coloured powder of sp. gr. 2-45. It is infusible, burns with a green flame at 700°, and isa very poor conductor of electricity. This form of boron is attacked by hot concentrated mineral acids ; it behaves like charcoal in its tendency to absorb gases. The so-called diamond of boron (which is not pure boron, but approximates the composition C,B,,A1;) is obtained by very strongly heating amorphous boron with aluminium, extracting the aluminium from the mass with hydro- chloric acid, and afterwards separating the crystals of mixed boron and aluminium from those of boron by boiling with nitric acid. These crystals are brilliant transparent octahedra (sp. gr. 2-68), which are sometimes nearly colourless, and resemble the diamond in their power of refracting light and in their hardness, which is so great that they will scratch rubies, and will BORON TRICHLORIDE 291 even wear away the surface of the diamond.! This form of boron cannot be attacked by any acid, but is dissolved by fused alkalies. It undergoes only superficial conversion into boric anhydride when heated to whiteness in oxygen. Boron unites with several metals to form borides. Manganese mono- boride, MnB, is strongly magnetic ; the diboride, MnB,, is not so; see p. 351. Boron Hydrides.—By melting together boric acid and excess of magnesium, an impure magnesium boride, Mg,B,, is obtained, which with hydrochloric acid evolves a mixture of hydrogen and boron hydrides, the chief of which has the formula B,H;. This is stable, insoluble in water, burns with a green flame, and is decomposed by electric sparks with separation of boron. Some BH, also occurs in the gas. Boron Nitride, BN.—Boron shows greater disposition to combine with nitrogen than is manifested by most other elements. It absorbs nitrogen readily when heated to redness, forming a white infusible, insoluble, stable powder, the boron nitride. Itis also obtained by heating to redness anhydrous borax with twice its weight of ammonium chloride and extracting with dilute HCl, which leaves the nitride undissolved. When heated in steam it yields boric acid and ammonia; BN + 3H,0 = H,BO,; + NH3. When heated in air it phosphoresces greenish. Boron carbide, CBg, is produced when boron and carbon are heated together in the electric furnace, best in the presence of silver, which dissolves both elements and enables the carbide to crystallise. It is black and remarkably hard, ranking next to diamond in this respect ; sp. gr. 2-53. It burns in oxygen at a high temperature, and is attacked by fused alkalies, but not by acids. Another carbide, B,C,, is formed on heating boric anhydride and carbon in the electric furnace. Boron Trichloride, BCl,.— Boron burns when heated at 410° in chlorine, forming the trichloride, which is more conveniently prepared by heating a mixture of boric acid and charcoal in chlorine; B,O, + 3C + 3Cl, = 2BCl, + 3CO. It is a liquid of sp. gr. 1-4 and boils at 17°. It is the chloranhydride (p. 198) of metaboric acid, being decomposed by water thus: BCl, + 3H,0 = B(OH), + 3HCl. It has a remarkable tendency to combine with other chlorides. Boron trifluoride (BF3) may be prepared by strongly heating a mixture of powdered boric anhydride with twice its weight of fluor spar in an iron tube ; 3CaF, + B,O; = 3CaO + 2BF3. The boron fluoride is a gas which fumes strongly in moist air, like the silicon fluoride. It is absorbed eagerly by water, with evolution of heat. One volume of water at 0° is capable of dissolving 1057 volumes of boron fluoride, producing a corrosive heavy liquid (sp. gr. 1-77), which fumes in air and chars organic substances on account of its attraction for water. This solution is known as fluoboric or borofluoric acid, and its formation is explained by the equation 2BF,; + 3H,O = B,0;.6HF (fluoboric acid). ae the solution is heated, it evolves boron fluoride, until its specific gravity is reduced to 1-58, when it distils unchanged. Hydrofluoboric acid is obtained in solution by adding a large quantity of water to fluoboric acid; 2(B,0,.6HF) = H,BO; + 3H,0 + 3HBF, (hydrofluoboric acid). The hydrogen of this acid may be exchanged for metals to form borofluorides, which have been applied as antiseptics. Ammonium borofluoride, NH,BF,, is produced when boron nitride is heated with hydrofluoric acid. Boron trisulphide, B83, is made by strongly heating boron in H,S ; it forms white needles, melts at 310°, and yields B(OH)3 and H,S when in contact with water. Boron pentasulphide, B.S5, is a white crystalline powder (m.-pt. 390°) made by heating BI, with S in CS, at 60°. It is decomposed by water into B(OH)s, H2S, and 8. 1 The author has known them to cut through the bottom of the beaker used in separating them from the aluminium. 292 REVIEW OF CARBON, SILICON AND BORON Review of Carbon, Silicon, and Boron.—These elements possess many properties in common. They all exist in the amorphous and the crystalline forms; all are incapable of being converted into vapour except at the tempera- ture of the electric furnace ; all exhibit a want of disposition to dissolve ; all form feeble acid oxides by direct union with oxygen, for which the order of their affinity is boron, silicon, carbon ; and all unite with several of the metals to form compounds which resemble each other. Boron and silicon are capable of direct union with nitrogen, and so is carbon if an alkali be present. Modern researches show that silicon can be substituted for carbon in numerous organic compounds (see p. 285), -but boron does not share this faculty and is further distinguished by trivalency as compared with carbon and silicon, which are quadrivalent. THE ARGON GROUP Hetrum, Arcon, Neon, Krypton, Xrnon, Niron. Iv is remarkable that until a few years ago no member of this group had been recognised, save helium spectroscopically in the sun’s corona, and that in the meantime all appear to have been discovered except one, perhaps, coronium (p. 304). The story of one is the story of all, for they are all colour- less, odourless gases, which are monatomic, as shown by the ratio of their specific heats being about 1-66 (p. 310), and so far as is yet known they are entirely devoid of all chemical affinity ; they have resisted all attempts to combine them with other elements ; they are non-valent ; hence they are found in the atmosphere and rarely elsewhere ; and are frequently referred to as the “rare gases of the atmosphere ’’; also as the “ inactive gases.” Further interest attaches to them in that some at least—helium, niton— have been obtained as products of the disintegration of elements of higher atomic weight (p.401). The non-existence of their oxides finds expression in the specific gravity curves described at p. 307. Rayleigh (1894) found that whereas 1 litre of nitrogen prepared from compounds of the element, such as from an oxide of nitrogen by passing it over red-hot copper, weighs 1-2505 grams, 1 litre of nitrogen prepared by depriving purified air of its oxygen weighs 1-2572 grams. Cavendish had long before recorded that when oxygen is added in small doses to atmospheric nitrogen through which electric sparks are passed and which is contained in a vessel also containing alkali to absorb the oxides of nitrogen produced, a small residue of gas is left which cannot be caused to combine with oxygen under the influence of the sparks. It has now been proved that Cavendish’s residue is not obtainable when nitrogen other than that from the atmosphere is used, and that it is this residue which makes atmospheric nitrogen about 4 per cent. heavier than other nitrogen, as observed by Rayleigh. The latter, in conjunction with Ramsay, examined the gas and concluded that it was an element so devoid of any tendency to combine with other elements, and therefore of chemical energy, that it might aptly be termed argon (a, without, tpyov, work). Argon, A = 39-88, is prepared by passing air first over caustic potash to absorb carbon dioxide, then through strong sulphuric acid to absorb aqueous vapour, and finally over red-hot calcium, magnesium, or lithium, which combines with the oxygen of the air to form calcium, magnesium, or lithium oxide and with the nitrogen to form calcium, magnesium, or lithium nitride. As the combination of nitrogen with any of these metals does not occur rapidly, the passage of the gas through the red-hot tube containing the metal must be repeated several times before the argon is pure. A modification of Cavendish’s experiment also serves for obtaining argon. A large inverted flask (50 litres) is closed with a rubber cork through which pass five glass tubes. Through two of these are passed conducting wires terminating within the flask in platinum electrodes, and connected at their other ends with the poles of an apparatus (an electrical transformer supplied with 40 ampéres at 30 volts), yielding electric current at very high pressure (6000 volts). A third tube serves for the introduction of a jet of caustic soda solution which plays against the side of the flask ; a fourth tube serves to remove this solution as it runs down into the neck. Through the fifth tube a mixture of 11 vols. oxygen and 9 vols. air is introduced continuously into the flask. When the 293 294 ARGON transformer is set to work, an “ electric flame ” plays between the electrodes, and is probably an actual flame of burning nitrogen, for the latter rapidly disappears, being dissolved as oxides of nitrogen in the alkali. About 20 litres of the gases may be com- bined per hour, and finally a mixture of argon and oxygen is obtained from which the latter may be absorbed by admitting pyrogallic acid. The argon amounts to 0-935 per cent. by volume of the air. It is a colourless gas, without odour. It is 19-94 times as heavy as hydrogen, so that its molecular weight is 39-88. The atomic weight is higher than that of potassium and so falls out of harmony in the periodic arrangement. Recently, argon has been fractionally crystallised, but all the different fractions have the same density. 1 litre weighs 1-7825g. Argon boils at — 186-1° and melts at — 187-9° ; its critical temperature is — 117-4° and its critical pressure 53 atm.; hence, at the ordinary temperature, it is far removed from the liquid state and obeys the gas laws well. 100 vols. of water dissolve 4 vols. of argon at 15°; the gas is thus 24 times as soluble as nitrogen and is found in the water from several mineral springs. The ratio of its specific heats was found to be 1-61, a fair approximation to 1-66, the theoretical figure for monatomic gases. Physiologically it is inactive. Helium, He = 3-99.—When argon was discovered, search was made for it in places other than the atmosphere, and while submitting to spectrum analysis (q.v.) some gas obtained by heating the rare mineral cleveite, Ramsay (1895) detected a bright yellow line coinciding with that first detected (1868) in the spectrum of the luminous atmosphere which is seen surrounding the sun when he is eclipsed. The line had been ascribed to an element, provisionally named helium (#)tos, the sun), but as no terres- trial matter had shown the same spectrum, it was concluded that the element was non- existent on the earth. Ramsay’s gas is no doubt the same matter as had been termed helium. It is obtain- able from several other minerals, besides cleveite, by heating them, particularly such as contain uranium ; the mineral is placed in a glass tube, which is then exhausted by a mercury vacuum pump and heated, the gas being collected by pumping it out of the tube. The helium is generally only a fraction of the total gas evolved, and must be separated from the other gases as argon is. It has been identified as accompanying argon in the water from the King’s Well at Bath. It is present in the atmosphere to the extent of 4 parts per 1,000,000. Helium is colourless, odourless, and exceedingly light, being only twice as heavy as hydrogen ; its sp. gr. is 0-139 (air = 1). It is not very soluble in water, 100 vols. of water dissolving about 1-4 vols. at 15°, and is very difficult to liquefy ; see p. 87. It is supposed that helium exists in minerals in a state of combination, but the gas has not yet been caused to combine with any other element ; hence its atomic weight is not chemically known. It is a product of the disintegration of radium and some other elements (see Radium). The ratio of its specific heats is 1-66, the theoretical figure for a monatomic gas, so that its atomic weight should be identical with its mole- cular weight, namely, 3:99. It is used for filling low temperature gas thermometers. Neon (Ne = 20-2), Krypton (Kr = 82-92), and Xenon (Xe = 130-2).—When a vessel containing crude argon, as it is prepared from the atmosphere, is cooled by immersion in liquid air, the gas liquefies, and on allowing the temperature to rise the first portion which boils off is a mixture of helium and another gas, neon, the density of which is 10-1. The next gas to distil is argon, and the residue is a mixture of yet two other gases, krypton, of density 41-46, and xenon, of density 65-1 (O = 16). By several such fractional distillations the argon, krypton, and xenon are completely separated, and are recognised by their characteristic spectra. Helium and neon are separated by cooling them by liquid hydrogen, when the neon freezes. All these gases are supposed to have monatomic molecules. The amounts of neon, krypton, and xenon in the air are exceedingly small, about 1 in 81,000 ; 20,000,000 ; 170,000,000 respectively. Neon when shaken with mercury emits a peculiar scarlet light, which is intensified by electric excitement. Niton (Nt = 222-4), or radium emanation, is one of the products of the disintegra- NITON 295 tion of radium, and is itself an ephemeral element (p. 356); its average life is but five and a half days. Like all the other gases of this group, it was discovered by Ramsay, and its study is a triumph of manipulative skill, for the quantity employed in any experiment never exceeded 0-1 cu. mm. or 0-0001 ¢.c. Helium is also one of the dis- integration products of radium, and it is to be noted that the difference between the atomic weight of radium (226-4) and that of niton (222-4) is 4, which is the atomic weight of helium. Its solubility in water varies greatly with the temperature ; at 0° it is 0-51 vol., at 14° 0-303, at 40° 0-153, but it obeys Henry’s law. It is much more soluble in most organic liquids. Several other properties of Niton are described at p. 401. GENERAL PRINCIPLES AND PHYSICAL CHEMISTRY Ir is only after numerous facts have been observed and accurately described that it is possible to define those fundamental principles on which a science is built up. This is the modern inductive method of investigation, proceeding from the particular to the general, of which Roger Bacon (b. 1214, d. 1294) and Robert Boyle (seventeenth century) were the early apostles ; but with the ancients, among whom Aristotle was a leader, deduction was the process, seeking to explain details by some preconceived idea. The deductive method is sometimes most fruitful, and is exemplified by the atomic hypo- thesis on which the whole science of chemistry is based ; but conclusions by this method require the widest possible confirmation before they can be trusted. In studying the preceding chapters the student will have gathered a number of such observed facts, and in the present chapter attention will be drawn to general principles; these are of necessity associated with the science of physics because chemical changes are commonly manifested by physical phenomena. Hence this chapter must treat of physical chemistry, albeit only in outline, for this branch of the science has now expanded into a separate study dealt with in its own text-books. The Elements.—The conception of an element that it is not capable of being resolved into any simpler forms of matter still remains true with respect to all ordinary analytical methods. However, for some decades there was an ever-deepening impression in the mind of the scientist that the chemical elements were but various forms of one and the same kind of matter, and that transmutation of one element into another should be possible. Demonstration of such views was conceivable if sufficient energy could be suitably concentrated on each atom to be disintegrated. Except with scant success, man has not been able to attain the necessary concentra- tion of any of the usual forms of energy, but he has recently discovered a new form of energy in the radio-active elements (qg.v.) and has found the only reasonable explanation of the behaviour of these elements in the supposition that some atoms undergo disintegration into atoms of another element ; see Radio-activity (p. 356). There are numerous speculations as to the nature of the various atoms, but most agree that the evidence afforded by radio-active elements is in favour of the atom consisting of a principal structure, having a weight nearly equal to that of the whole atom in union with a certain small number of exceedingly minute particles of negative electricity, called electrons, which are capable of separation and transfer to other atomic nuclei. However, the disintegration hypothesis is at present in its infancy and is such a special department of research that it rarely concerns the chemist even in his most advanced theories, so that the definitions given in the earlier chapters remain valid. The Atomic Weight of an element is a property of prime signifi- cance, not only because of its use in connection with the composition of molecules, but also because its magnitude is associated with most of the properties of the elements.. It is a relative value, for the actual weight of a single atom (about 0:02 x 1018 milligram in the case of hydrogen) is 296 ATOMIC WEIGHTS 297 not a practical unit, nor was it computed until comparatively recent times. Dalton adopted the atomic weight of hydrogen as a standard (H = 1), and this would still be continued but for the fact that not many atomic weights are compared experimentally with that of hydrogen, and so when a re- determination is made of the atomic weight of an element, such as oxygen, chlorine or silver, which is used as an intermediate standard, all other values dependent on this one must be revised. For instance, mercury forms no compound with hydrogen, hence the proportion in which it combines with oxygen (25 with 2) is determined, and from this the atomic weight compared with hydrogen calculated (25 x 16 + 2 = 200). This would be perfectly satisfactory if the atomic weight of oxygen were known with certainty. But unfortunately the accepted figures during the last thirty years vary between 15-864 and 16-00, whence the corresponding values for mercury are 198-3 and 200. Most of the atomic weights are determined by forming or decomposing some compound of the element with either oxygen, chlorine or silver; ¢.g. copper with oxygen (p. 28). The ratio of the atomic weights of these is known with precision, whence the ratio of the required value to 16 (O = 16) is obtained directly by experiment or through the medium of the trust- worthy ratios, Cl:O or Ag: 0. An incidental advantage is that several of the atomic weights are actually or very nearly whole numbers, whereas when H = 1 inconvenient fractions prevail. The experimental determination of atomic weights is conducted on the lines of ordinary quantitative analysis, but the most exacting and extra- ordinary precautions are taken to ensure absolute purity of all materials used and of the product to be weighed ; it is equally necessary to guard against the most trivial losses or gains. The exceptionally accurate chemical process of so-called atomic weight determination ascertains only the chemical equivalent of the element. It is found, for instance, that 16 parts by weight of oxygen combine with 24-32 parts of magnesium. From this the formula of the compound may be Mg,0, Mg,0, MgO, Mg,O,, &c., according to the atomic weight of magne- sium. The chemical equivalent is always some simple submultiple of the atomic weight, so that if the multiple, which is equal to the valency, can be found the atomic weight becomes known. Except in certain cases, e.g. NH (p. 189), which have been satisfactorily explained there has never been evidence that in any compound of hydrogen the ratio between the number of atoms of H and the other element, X, is less than 3:1. That is to say, compounds of the formula HX,, HX,, &c., are not known, except as aforesaid ; they are limited to the form HX. On the other hand, compounds of the types H,X, H,X, H,X are quite common. From this it is evident that (1) the atomic weight cannot be less than the equivalent ; (2) the atomic weight of an element forming the compound, HX, must be identical with the equivalent; and (3) the atomic weights of elements forming H,X, H,X, and H,X, respectively, must be twice, thrice, ‘ and four times the equivalents respectively. There are several ways of arriving at these values, either through some property of the element itself, or through the molecular weight of its com- pounds. The first course may be followed (a) by determining both the molecular weight, M, of the element in the gaseous state and the atomicity, n, of the molecule, i.e. the number of atoms in the molecule. Then the atomic weight = M/n. Means of deducing both these factors are given below. The atomic weights of the rare gases were so determined (p. 311). (o) By the Relationship between Specific Heats and Atomic Weights.—It was observed by Dulong and Petit (1819) from a study 298 SPECIFIC HEATS of the solid elements of known atomic weight that although the specific heats of the elements per se exhibit no regularity, they all give approximately the same value when multiplied by their respective atomic weights; e.g. if 0-2934 calorie be the quantity of heat required to raise the temperature of 1 g. of sodium through 1°, 0-2934 x 23, i.e. 6-75 calories, will represent the quantity of heat necessary to raise the temperature of one atomic weight in grams (23 g.) of sodium through 1°. In the same way 0-2032 x 31, or 6:3 calories, is the quantity of heat required to raise the temperature of one atomic weight in grams of phosphorus through 1°; and 0-03095 x 207-1, or 6-41 calories, for the atomic weight in grams of lead. These products, 6-75, 6:3, 6-41, are substantially the same. If the solid elements be arranged in the order of their atomic weights as in the Table on p. 8 it will be observed that their specific heats decrease in reciprocal proportion to the increase of the atomic weights ; and therefore if the specific heat, H, be multiplied by the atomic weight, A, the product, AH, the atomic heat, is approximately constant ; it is about 6-4 (5-9 to 6-7). The quantity of heat necessary to raise the temperature of one atomic weight of any solid element through 1° (at ordinary temperatures) is approximately the same. For “ one atomic weight” may be substituted “ one atom.” From this it follows that if the specitic heat of an element is known its atomic weight is also approximately known; for since specific heat x 6-4 specific heat’ ge ane specific heat of iron is 0-1163; .-. atomic weight is about 6-4 + 0-1163 = 55-03. The chemical equivalent of iron as found: by the accurate chemical process is 18-613, whence the chemical equivalent is evidently one-third of the atomic weight, 7.e. the latter is 18-613 x 3 = 55-84. Dulong and Petit’s original statement was: “The atoms of all the elements have exactly the same capacity for heat’ ; but the expectation that some set of conditions would be discovered under which all atomic heats would be “‘ exactly the same ” has not so far been realised, and is even approached only at ordinary temperatures. Recent investigations reveal much greater irregularities at both higher and lower temperatures, so that the so-called ‘‘law ”’ is an empirical rule ; nevertheless, at ordinary tempera- ture, or slightly above, the statement is true for all solid elements except the three similar non-metals, boron, carbon, silicon, and therefore is very significant and of much practical value. To illustrate the great variation of specific heat with tem- perature the figures for platinum are quoted: at — 173°, 0-275; + 127°, 0-0328; 427°, 0-0372 ; 727°, 0-0409 ; 1227°, 00461. At or near the melting-points and in the liquid state all the elements give very different figures from those for solids. atomic weight = 6-4, the atomic weight = When it is difficult or not possible to determine the specific heat of an element in the solid state, advantage may be taken of Neumann and Kopp’s law, which is an extension of the last. It states that the specific heat of a compound multiplied by its molecular weight, which is the molecular heat, is equal to the sum of the atomic heats of the elements composing the molecule. From this it follows that the molecular heat = 6-4 x n, where n is the number of atoms in the molecule. Thus, the specific heat of solid chlorine is not known, but if the specific heats of the chlorides of potassium, sodium, and rubidium are multiplied by the molecular weights of these chlorides, the product in each case approaches very nearly to the number 12-69. Supposing these chlorides to contain 1 atom of each of their constituents, then, by subtracting the mean atomic heat (6-65) of the three metals from the mean molecular heat (12-69) of the three chlorides, a value (6-04) for the atomic heat of solid chlorine will, according to the above generalisation, be obtained. The specific heat of barium has not been determined, so that its atomic weight has not been ascertained directly by this method ; but the specific heat of barium chloride ISOMORPHISM 299 is 0-09. Barium chloride contains 68-5 parts of barium for every 35-5 parts of chlorine ; if 68-5 be the atomic weight of barium, the formula for the chloride will be BaCl, and its molecular heat 0-09 x 104 = 9-36; this only allows an atomic heat of 3:36 for barium, because that of chlorine is 6. If the atomic weight of barium be 137 the formula for the chloride will be BaCl,, and the molecular heat will be 208 x 0-09 = 18-72 ; this will allow an atomic heat of 6-72 for barium, for two atomic heats of chlorine must be subtracted from 18-72. As 6-72 is more nearly normal for the atomic heat than is 3-16, the atomic weight of barium may be taken as 137. The laws relating to the specific heats of gaseous elements and compounds are given on p. 310. The molecular heat of a compound is thus seen to be an additive property, being the sum of the properties of the component atoms. A few other properties, e.g. specific volume, specific refraction, are additive, and they reveal an independence of the atoms in the molecule which suggests the idea that chemical combination results from a mechanical fitting together of atoms rather than an interlocking. (Cf. Barlow and Pope’s views, p. 335.) Additive properties then belong to atoms, not to molecules ; they give no clue to molecular weight. However, no property, except weight, is perfectly additive. Colligative properties (colligo, I bind together) depend on the number of molecules concerned, and not on their nature or magnitude. With gases, density or molecular weight, specific heat, velocity of diffusion are colligative properties. Constitutive properties depend on the arrange- ment of the atoms in the molecule, and are exemplified in optical rotation, isomerism, isomorphism, &c. For specific and arbitrary properties, see p.l. (c) Isomorphism.—The third method consists in studying the general chemical analogies of the element with some other element of known valency for the purpose of deciding the unknown valency. The principle of isomorphism, originally stated by Mitscherlich (1821), is that certain elements may be substituted for each other in their crystalline compounds without alteration of the form of the crystals. Such elements are said to be isomorphous with each other, and the crystalline compounds, in which the substitution occurs, are said to be isomorphous compounds. It is assumed that the one element is substituted for the other atom for atom, and therefore quantitatively in the ratio of their atomic weights ; whence, the substituted quantities being found by analysis, the unknown atomic weight can be calculated. The chief conditions of application are (a) that the two salts crystallise together in any proportion, forming mixed crystals (cf. Double Salts, p. 92) ; (6) close similarity of crystalline form ; absolute identity of shape is very rarely, if ever, found; (c) the crystals of one of the substances to be compared should be capable of growing in a saturated solution of the other. Thus aluminium, chromium and iron are isomorphous elements because they all form alums of the type KR’’’(SO,),.12H,0 (where R’”’ is Fe, Al or Cr), which crystallise in octahedra, and are capable of forming mixed crystals. For example, when a mixture of solutions of aluminium alum and chromium alum is allowed to crystallise, the crystals contain both aluminium and chromium in proportion varying with the conditions of crystallisation. Supposing that the valency of chromium were unknown it could be deduced from this isomorphism with aluminium. For the valency of aluminium is three, hence it is probable that the valency of chromium is also three, in which case the atomic weight of the metal is thrice its equivalent. Tutton has made a comprehensive study of the alkali sulphates and selenates, as well as of many other series of isomorphous salts, and finds that for the elements belonging to the same group in the periodic classifica- 300 ATOMIC WEIGHTS tion (1) the crystals of the different members of an isomorphous series exhibit slight but real differences in their interfacial angles ; (2) the physical pro- perties of the crystals, such as their optical rotation and thermal constants, are also functions of the-atomic weights of the elements of the same family group; (3) specific chemical exchanges are accompanied by clearly defined changes in crystal structure along equally specific directions, e.g. when the metal K in the sulphate, K,SO,, or selenate, K,SeO,, is exchanged for Rb or Cs, the vertical axis is elongated; when the non-metal S is exchanged for Se, the metal remaining the same, expansion occurs in the horizontal plane. Tutton makes the following generalisation : The whole of the pro- perties, morphological and physical, of the crystals of an isomorphous series of salts are functions of the atomic weights of the interchangeable chemical elements of the same family group which give rise to the series ; see also p. 335. (d) By Reference to the Periodic Classification. See p. 301. The second course, namely, deducing the atomic weight of an element through the molecular weights or other properties of its compounds, is usually followed where it is not possible to determine the vapour density of the element itself; and confirmation by such methods is always very important. In the sequel many ways of determining the molecular weight of a compound will be described; here the application of this constant for determining the atomic weight of an element will be considered. This method is best explained by an example. The vapour density of a compound of nitrogen is ascertained, as described at p. 313, to be 15, so that the molecular weight of the compound is 30 (p. 11). Gravimetric analysis shows that the compound contains 45-16 per cent. of nitrogen. Hence 30 parts by weight of it contain 13-55 parts of this element, that is to say, one molecule of the compound contains ” atoms of nitrogen weighing 13-55. If nis 1, then 13-55 is approximately the atomic weight of nitrogen ; if n is 2, the atomic weight is 6-77, andsoon. It is impossible to decide the value of m from this experiment ; all that can be said is that by hypothesis it cannot be less than 1, so that the atomic weight of nitrogen, according to this experiment, cannot be greater than 13-55 or a number very near this. Supposing, however, that many other compounds of nitrogen have been submitted to similar experiments, and it has been found that in none of them does the molecular weight contain less than 13-55 parts of nitrogen, the presumption is large that this is indeed the approximate atomic weight. As an example of the application of some of these methods, the following experi- ments may be supposed to have been performed with a view of ascertaining the atomic weight of cadmium : (1) 0-7232 gram of cadmium bromide ! was dissolved in water,:and the bromine was exactly precipitated by adding a solution of silver nitrate (with the precautions neces- sary to an accurate result). This solution was made by dissolving 10 grams of pure silver in 1 litre of dilute nitric acid, and 57-43 c.c. were required for the precipitation. Hence 0-5743 gram of silver will combine with the bromine in 0-7232 gram of cadmium bromide ; but from the careful synthesis of silver bromide, it is known that this weight of silver will combine with 0-4254 gram of Br ; therefore the 0-7232 gram of cadmium bromide contains 0-2978 gram of Cd combined with 0-4254 gram of Br. Since the 0-2978 x 80 0-4254 that is, the number of parts by weight of Cd which will combine with one equivalent of Br. The atomic weight of cadmium must, therefore, be 56 x n, where n is a small integer. (2) The vapour density of cadmium bromide was found to be 136, therefore its molecular weight is 272; but, according to the above analysis, this number of grams equivalent of bromine is 80, = 56 will be the equivalent of cadmium— 1 It will be evident that the analysis of any compound of the element with another element of well-estab shed equivalent will serve to fix the equivalent of the first element. THE PERIODIC LAW 301 will contain 112 grams of Cd and 160 grams of Br, for these elements are present in the ratio 56: 80. It follows that the atomic weight of cadmium cannot be greater than 112, or m cannot be greater than 2. (3) A piece of cadmium weighing 100 grams was heated in boiling water until it had attained the temperature of the water (100°); it was then transferred to a calorimeter containing 100 grams of water at 0°. The temperature of this water (allowing for the heat left in the calorimeter) rose to 5-3°. Therefore the 100 grams of cadmium, in cooling from 100° to 5-3°, have lost 100 x 5:3 = 530 gram-units of heat,! so that in cooling through 1° the 100 grams would lose a = 5-6 units, or 1 gram would lose 0-056 unit—that is, the specific heat of cadmium is 0-056. But the specific heat x atomic weight will probably = 6-4, so that the atomic weight of cadmium should be 0-056 = 113 (nearly). This is approximately 56 x 2, therefore n is probably 2. (4) Many cadmium salts are found to crystallise together with zinc salts, being isomorphous with them ; but zinc is divalent, therefore cadmium is probably also divalent, in which case its atomic weight must be twice its equivalent, or 112. The atomic weights of the elements having been determined and there being a speculation that all substances are but different forms of one original kind of matter, “ protyle,” it is natural to suppose that the atomic weights are multiples of the least of them, that of hydrogen, or of some simple fraction thereof. This was Prout’s hypo- thesis (1815). It has been proved untenable, but it stimulated much enthusiasm for many years to ascertain the true atomic weights ; in particular it inspired the brilliant work of Stas. But although we know of no mathematical function enabling us to calculate one atomie weight from others, their sequence is such as to reveal an order and classification as wonderful as any of which Nature has yet permitted us to learn the secret. Classification of the Elements—the Periodic Law.—It has been shown already that the elements may be classified into groups com- posed of individuals possessing similar chemical properties. Newlands, in 1864, pointed out that when the elements are arranged in the order of their atomic weights, this similarity is seen to exist between every eighth element, the first being similar to the eighth, the second to the ninth, and so on (law of octaves). In 1869 Mendeléeff and Lothar Meyer made a similar discovery. In seeking for a basis for a classification of the elements, it is natural that the chemist should turn to the most strictly chemical property of the elements, namely, their tendency to combine with each other. Mendeléeff has pointed out that the limit to this tendency is expressed by saying that one equivalent of an element never combines with more than eight equiva- lents of another element. If oxygen and hydrogen be taken as typical elements, it will be noticed that there are never more than four atoms of oxygen or four atoms of hydrogen united to one atom of an element. Further- more, the sum of the equivalents of O and H, which can combine with one atom of an element, is always eight. Thus, if an element R forms as its highest salt-forming oxide? a compound of the type, RO”,, it will form a hydride RH’,; if an oxide, RO’’;, a hydride, RH’,, and so on. For example, N forms N,O, as its maximum oxide—that is, a compound of five equivalents of oxygen with one atom of nitrogen—and its maximum hydride is NH; ; S forms SO, (6 equivalents of oxygen) and SH,. Cl forms CIH, so that its highest salt-forming oxide should be Cl,0, (7 equivalents of O to 1 atom of Cl). It follows that there are eight types of higher salt-forming oxides, viz. : R,0, R,0,, R203, R204, R2O;, R204, R07, and R,O3. Those elements which form higher salt-forming oxides of the same type 1 No allowance is here made for the slight altcration in the specific heat of water with Tise of temperature 2 Capable of behaving as an acid anhydride or as a base. 302 THE PERIODIC LAW are alone analogous. If this proposition be admitted, the elements must be classified in eight groups. Such a classification reveals the fact that when the elements are arranged in the order of their atomic weights, they follow the same order as that of their higher oxides, so that the valency of the elements towards oxygen returns to the same value at every eighth element, that is, periodically. This return is noticeable in the case of all other properties of the elements which have been accurately examined, that is to say, the properties of the elements are periodic functions of their atomic weights. In general terms, if the elements be arranged in the order of their atomic weights, the properties of consecutive elements will be found to differ, but the properties will return to approximately the same value at definite periods. Such an arrangement of the elements is shown in the Table on p. 8. It will be found that elements in the same group, and in even series, are completely similar to each other, as, for example, Ca, Sr and Ba ; this is also the case with the elements in the same group and in odd series, such as P, AsandSb. The members of the odd series, however, do not so closely resemble those of the even series, though in the same group. Thus, K and Cu have far fewer properties in common than have K and Rb. It seems, then, that the periodic return of properties to the same value occurs only - after two series have been traversed, so that each period of the Table is constituted by two series; thus, Ca, Sr and Ba resemble each other very closely ; so also do Zn, Cd and Hg. It will be seen that since this is the case, each group must consist of two sub-groups or families indicated in the Table by the setting of the symbols in two vertical lines in each group. These references to families do not apply to the first two series ; thus Be is more nearly allied to Mg than to Ca ; while Mg has much in common with Zn. These two series constitute two whole short periods, and their symbols are placed over those in the Table to which they show most simi- larity. These members are sometimes termed typical elements. Such a Table is not entirely satisfactory, chiefly because there are several elements with atomic weights between 140 (Ce) and 181 (Ta), having pro- perties which will not harmonise with the present simple arrangement, and consequently the case is not met by interpolating two extra series as is frequently done. The eighth group requires analysis ; its elements are not all octavalent. It is indeed a compound group in which the metals show valency decreasing in double stages. ‘Thus, Ru“iO,, Rh“iO,, PdivO,, (Ag#O), Ag’,0; Os"#0,, Ir“O,, PtivO, (Au’O), Au’,0. Fe, CO, Ni do not exhibit the same well- marked gradation. Cu, Ag, Au are usually placed in the first group because they are capable of monovalency and no other more suitable elements are known. They are sometimes placed in the eighth group, where they fill a more natural position, leaving blanks in. the first. A few vacancies occur where elements are believed to exist, but to be as yet unknown, e.g. after Mo comes Ru, but the latter cannot be placed in the seventh group, where it finds no kinship ; its oxide is RuO, and therefore it falls naturally into the eighth group. Credence is afforded to the view that such vacancies will ultimately be filled by the fact that the number of such blanks was larger when the Table was first drawn up, some of these spaces having been filled since by the discovery of elements (such as Ga, Ge, and Sc) the atomic weights of which showed that they were the missing elements. It is interesting to note that niton, the best known of the ephemeral elements, conforms with the scheme. No place had been provided for the argon group until its discovery. While argon alone was known there was much discussion as to its relation APPLICATIONS OF THE PERIODIC LAW 303 to other elements ; but the later recognition of its analogues leaves no question as to the interpolation of a new non-valent group. It should be noticed that the elements of this group are in the same sequence whether placed after the halogens or before the alkali metals ; both are shown in the Table. If the Table be wound slightly askew round a cylinder so that Ne is preceded by F and followed by Na, the whole of the elements appear on one helix; and it is to be observed that the members of this inactive group come as neutral elements between the highly electro-negative halogens and the strongly electro-positive alkali metals. Thus the non-valent and the eighth groups provide against a sudden drop from hepta- to mono- valency. There are four pairs of elements whose atomic weights, as at present known, do not comply with the sequence: A, K; Co, Ni; Te, I; Nd, Pr. It would, however, be illogical to reverse their positions, e.g. to put K in the A group. The Periodic Table has found numerous applications: (1) It has served to enable chemists to foretell the existence and properties of elements which have subsequently been discovered ; (2) it has afforded a means for deciding the atomic weights of some elements ; (3) it assists in the comparative study of nearly all compounds. An example of the first of these is the prophecy by Mendeléeff of the existence and properties of germanium; the principle upon which such predictions are made is that the properties of an element are approximately the mean of those of the four elements which immediately surround it. There was a vacancy in the Table between Si and Sn ; Mendeléeff termed the element which had to be discovered to fill the gap, ekasilicon (eka is ‘‘ one ’ in Sanscrit). According to the above principle, ekasilicon when discovered should have properties identical with the mean of those of Si, As, Sn, and Ga ; but Ga was itself unknown at the time, so Mendeléeff had to use Zn as a member of the quorum. The mean of the atomic weights of these four elements is 71-5, so that this would be the atomic weight of ekasilicon ; that found for germanium is 72. Ekasilicon (Es) would probably form two oxides, EsO and EsOg, an acid oxide ; for although SiO was not then known, SnO was known, and both SiO, and SnO, are stable acid oxides ; GeOQg., an acid oxide, is well known, and GeO probably exists. EsCl, and EsCl, should exist, because SnCl, and SnCl, exist, but EsCl, should be less stable than SnCl,, for SiCl, is not known. As a fact, both GeCl, and GeCl, exist, the former being less stable than SnCl,. Further, the boiling-point of EsCl, should be the mean of those of SnCly and SiCl,—namely, 88-5° ; it is found to be 86°. The second application of the Table is illustrated by the fixation of the atomic weight of beryllium. Beryllium was at one time considered to be trivalent owing to its similarity in some respects to aluminium. Its chemical equivalent is 4-55, and so its atomic weight was believed to be 13-65. But this is out of harmony with the periodic classification, for there is no vacant place in the Table between carbon and nitrogen, whose valencies and properties are well known. There was, however, a vacancy in the second group above magnesium with which beryllium showed much analogy, and this was appropriate to an atomic weight of 9-1 (the mean of 7 for Li and 11 for B), equal to twice the chemical equivalent of beryllium. The proposal to make this change was fully justified later by finding the vapour density of beryllium chloride to be 40, corresponding with a molecular weight of 80, 7.e. 9 for Be + 71 tor 2Cl ; hence its formula is BeCl,. Were the metal trivalent, its chloride would be BeCl;, with a molecular weight 120 and vapour density 60. The atomic weights of indium, uranium, and others have been similarly established. For Be and Al, see also p. 650. A new arrangement has been introduced by Werner, which avoids many of the objections associated with the Table of Mendeléeff, while retaining its important merits, An inspection of the Table, pp. 304, 305 (modified from Werner’s), comprises four pairs of series. The first is at present vacant, but it is anticipated that the space above He will be occupied by coroniwm, with an atomic weight of about 0-4, which was discovered in the sun’s coronal atmosphere by Young. There are expectations of a new halogen having an atomic weight of 2-8 or 3 in the second series. Each of these series has 3 members, In the third and fourth series there are 3 + 5 = 8 clements which are the 304 THE PERIODIC LAW “typical ” elements (p. 302). In the fifth and sixth series 3 + 5 + 10 = 18 elements occur. Those families whose symbols are on the left hand of each group in the Table on p. 8 are here separated to the left hand en masse, while those on the right hand of the groups remain under the typical elements. The seventh series has3+ 5 + 10+ 15 = 33 members. The fifteen new ones are the ‘rare earths ’’ between Ce and Ta, for which no place was found in the older Table owing to their all being trivalent. If these are omitted and the two parts of the Table closed together, the Table on p. 8 is reproduced in a modified and extended form. Only three elements in the eighth series are known at present, and these are the three strongly radio-active elements. The chief advantages of this mode of tabulation are (a) that it provides for all the elements, including the rare earths, in a natural and thoroughly systematic manner ; (b) that the members of the eighth group, together with Cu, Ag, Au, fall into place without having to make some strained provision for the monovalent group. The periodic classification, whether with the old or the new arrangement, opens up in marvellous manner the regular and recurring gradation of the properties both of the elements and of their compounds. Many of these are discussed in the reviews of the various groups, e.g. the halogen group (p. 135); but also in numerous other places, e.g. pp. 384, 398, 419. Unfortunately, present knowledge of the properties is very imperfect, so that the exact nature of the inter-relationships is not easily dis- K Ca, Se Ti 39-1 | 40-07 | 44-1 | 48-1 Rb Sr Y Zr 85-45 | 87-63 | 89-0 | 90-6 Cs Ba La Ce Nd Pr = Sa Eu Ga Tb Dy Ho Er 132-81] 187-37} 139-0 | 140-25] 144-3] 140-6 | 150-4 | 152-0 | 157-3 | 159-2 | 162-5 | 163-5 | 167-7 Ra Th “~ [226-4] ~ | 232-4 R,O0 | RO | R,0;/ RO, R, 0, Tm | Yb 168-5 | 172-0 covered. The main features of a recent study ! of the specific gravities of the elements and of their highest oxides may be reviewed briefly as an example of more detailed treatment. The very clearly defined regularity and periodicity are displayed in four curves (p. 306). This work was undertaken to decide on a theoretical basis the density of zirconium, which had been declared at 4-2 and 6-4 by two sets of observers. In this way the latter value was proved to be of the right order, for the former falls wide of the line through Ti and Ce in every case. The curves, however, have another interest in that they harmonise with the last-mentioned classification better than they do with the usual Table (p. 8). In selecting figures for drawing these curves, that for the density of the element or of its oxide at a temperature far below the melting-point was preferred in order to know that the substance was in a properly stable, solid condition, and not, as has often been done, at the melting-point, where a small variation in temperature seriously affects the result; also the most stable and, where possible, crystalline modification was chosen. In curve A (p. 306) the densities of the elements are plotted against the atomic weights. The two short periods of the typical elements form two distinctive waves, followed by those of the two long periods and of the one very long one in which the rare earths occupy half the ascent; then a long steep ascent equally spaced by Ra, Th, and U, which suggests that homologues of the rare earths are not to be expected. Just as in the Table, the most electro-positive elements, the alkali metals, begin the periods, and the strongly electro-negative elements, the halogens (save the argon group), end them ; so that both these extremes have the lowest densities, while the eighth group have the highest. Curve B is the atomic volume curve of Lothar Meyer. The atomic volume of 1 See “‘ Studien iiber daz elementare Zirkonium.” Dissertation by S. Judd Lewis, 1909. PERIODIC LAW 305 an element (or number of unit volumes in the atomic weight) is the quotient obtained by dividing the atomic weight by the specific gravity. Those elements which are most chemically active have the lowest specific gravities and therefore the highest atomic volumes ; thus it is found that the atomic volume falls from the beginning to the middle of a period, but rises again from the middle to the end ; for instance, the atomic volume of K is 45, of Ni 6-7, and of Br23. In the same family the atomic volume rises with the atomic weight, e.g. Li = 12, Na = 24, K = 45, Rb = 56, Cs = 56. It should be noted that the lines joining up the members of a family are not straight, but bowed slightly. Similar relations are maintained between the molecular volumes (molecular weight divided by specific gravity) of the oxides and of some other compounds of the elements. The same periodic fluctuation is to be noted in the melting-points, the electro- positiveness, the brittleness and the ductility of the elements, and extends to the colour of their salts. If, therefore, the atomic volumes be plotted on a curve, the same curve will apply to many other of the properties. In curve C the specific gravities of the highest oxides are plotted against the atomic weights ; e.g. one series of oxides are Na,O, MgO, Al,O;, SiO,, P.O;, SO;, Cl,O,. The elements of the same family form oxides which, when bases, are of the same order of basicity, and, when acid oxides, of the same order of acidity ; this is well illus- trated by K, Rb, Cs; Ca, Sr, Ba; P, As, Sb. This curve presents great regularity, Lu 174-0 — | (Cn) Q@) & —_ He 3:99 Be B Cc N 0 F Ne 9-1 11-0 | 12-0 | 14-01 16 19-0 20-2 Mg Al Si P 8s cl A 24:32 | 27-1 | 28-3 | 31-04] 32-07 | 35-46 | 39-88 | Vv Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 51-0 | 52-0 | 54-93 | 55-84 | 58-97 | 58-68 | 63-57 | 65-37] 69-9 | 72-5 | 74:96] 79-2 | 79-92 | 82-92 f Nb Mo Ru Rh Pd Ag Cd In Sn Sb Te I Xe 93°5 | 96-0 “™ | 101-7 | 102°9 | 106-7 | 107°88] 112°4] 114°8 | 119-0 | 120°2 | 127°5 | 126-92 | 130-2 Ta Ww Os Ir Pt Au Hg Tl Pb Bi —_ os Nt 1815 |184-0| ~ | 190-9 | 193-1 | 195-2 | 197-2 | 200-6 | 204-0 | 207-1 | 208-0 222°4 U ~~ | 238-5 t R,0,| RO; | R.0,| RO, | RO; | RO, | (RO)| RO | R,0,) RO, | RO; | RO; | R,O,} — f but the rare earths between Ce and Ta intrude on the sequence, as indeed they do in all other arrangements. The depression in the middle of each long period occupied by the acid oxides of the metals of highest valency is noticeable. The densities of several of the highest oxides are not known, which is shown by dotted lines. The gaps between. the halogens and the alkali metals are worthy of remark. On both sides of the gap the curves are directed downwards, indicating that the oxides of the rare gases have densities which are very small or zero, 7.e. they probably have no oxides. This accords with the chemical evidence, for they form no compounds whatever. In curve D the ratio of the density of an element to the density of its oxide is plotted against its atomic weight ; e.g. the density of Ca is 1:55 and that of its oxide, CaO, is 3-4; hence the ratio is 1-55/3-4, 7.e. 0-46, which is the abscissa plotted against the atomic weight of Ca at the 40 ordinate. The curve is consistently periodic and shows remarkable interruptions in the positions for the rare gases, pointing again to- the non-existence of their oxides. The acid-oxide-forming elements, whether metallic or non-metallic, engage the upper parts of the ascending portions.’ It follows that if one factor of the ratio is known, the other‘is easily calculated ; see the example below. Across each curve are drawn a solid line through Zn, Cd, Hg, representing the families to the right of the Tables, and a chain line through Ca, Sr, Ba, representing those to the left. Similar lines can be drawn for all the families, but the number is limited for the sake of clearness. In each case the solid lines are bowed ; in A, C, and D the chain lines are straight, signifying some systematic difference between the densities of those families on the right and those on the left. The typical elements lie between but usually nearer the solid lines, as might be expected from the Tables. 1 The density, 12-7, which is generally accepted for niobium, Nb (also called columbium,Cb), makes this meta to be the only one which seriously deviates from the curves; a density of about 8 might have been expected. 20 305 PERIODIC LAW 20 30 40 30 0 80 Otto tee BO 0 PO B.Aromirc Votume CURVE aD & 8 Atomic Volume 8.5 C OxipE~ DENSITY CURVE o a a a a a a He Ne a” a ie D. Ratio CuRVE 0 \ ' Col ‘ ate Ratio —» Ho Se de Fie 211. COMPOUNDS 307 In illustration of the use of these curves, it will be interesting to deduce the den- sities of radium and radium oxide, neither of which has yet been determined experi- mentally. In A the chain line through Ca, Sr, Ba, the homologues of Ra, cuts the 226-4 (atomic weight of Ra) ordinate on the 5:95 abscissa ; whence the density of Ra is 5-95. On repeating the observation in C, the density of RaO is found to be 7-6. Similarly, in D the ratio of the density of Ra to that of RaO is 0-86, whence the density of Ra is 7-6 x 0-86 = 6-68, giving with the result from A a mean of 6-3. Niton, or radium emanation, has in the liquid state a density of about 5-7 (5:6 to 5:8). We have also the densities of the rare gases, the homologues of Nt, in the liquefied condition, and can compare these with the densities of the alkaline earth metals, the homologues of Ra. ; Sp. ar. (liquid). (a) Sp. gr. (solid). (8) Ratio £ A 15 Ca” 1-55 1-06 Kr 2-155 Sr 2-54 118 Xe 3°52 Ba 3°78 1-07 Nt 5-7 Ra ss — The mean ratio is 1-1 ; employing this, the density of Ra is 5-7 x 1-1, i.e. 6-27, Thus by three independent methods the density of radium metal is found to be not far from 6-3. The density of radium oxide is 7-6 by C and, adopting 6-3 for Ra, 6-3 +- 0-86 = 7:4 by D; mean = 75. Compounds.—Composition is the first factor to be ascertained in the investigation of an unknown substance. Usually an accurate deter- mination of each element, either by analysis or by synthesis, is necessary or desirable, but sometimes much less is sufficient, e.g. if it be found that a substance is pure, an exhaustive qualitative search reveals nothing but sodium and chlorine, and the molecular weight proves to be 58-5, the sub- stance can be nothing but sodium chloride with the formula NaCl. From the elementary composition an empirical! formula, stating merely the least possible relative numbers of atoms, may be derived by dividing the percent- age of each element present by its atomic weight, e.g. from the following : Na, 14:3 per cent.; 8, 9-97 per cent. ; O, 69-56 per cent. ; H, 6.17 per cent.— we gat Na, 14:3/23 = 0-6218; S, 9-97/32:07 = 0-3110; O, 69-56/16 = 4-348 ; H, 6-17/1-:008 = 6-124. Each quotient represents the same fraction of the relative number of atoms present, whence, if each is divided by the lowest, in this case 0-3110 for 8, we get the actual number of atoms 0-6218 _ 2-8 0-3110 _ 1: * OSLO ~~? "O-3110 ~~? = 20, i.e. Na,SO,,Hy5. But this conveys a in the simplest or empirical formula: Na oO 4348 ||. 6-124 70-3110 — > 0-3110 very inadequate idea of the nature of the compound.” The molecule cannot be smaller than that represented, because there is only one sulphur atom, but the molecule may be two or three times as large, Na,8,O,,Hy9 or Na,S304H 6. Hence to decide the size of the molecule, 7.c. the molecular weight, is the next thing to be done. It will be convenient to approach this and some other problems through the avenue of physico-chemical pro- -perties, taking in order those referring to (a) gases; (5) liquids ; (c) solids. It is also usually possible to ascertain how the atoms are arranged inter se in the molecule, and even how they are relatively arranged in space. (a) GASES. Most of the gaseous properties of practical interest have been described already ; the gas laws—Boyle’s, Dalton’s (p. 9); Avogadro’s hypothesis (p. 10); density (p. 11); Gay Lussac’s law of gaseous volumes (p. 9); 1 Gk, eurecpia, experimental. : 2 This example is further considered on p. 352. For another instance see Alcohol (p. 540). 308 KINETIC THEORY OF GASES while the chapters on Air and Hydrogen contribute a further study of the general subject. A remarkable fact is that most of the physicat properties are independent of the chemical nature of the gas, and this enables the subject to be treated mathematically. Although this treatment applies first of all to ideal gases (p. 78), it has been invaluable in revealing in what manner and to what extent the various gases deviate from the ideal, and opened the way to discovering their inner nature. In the section on diffusion (p. 75) reference is made to the Kinetic Theory of Gases.' This explains the various physical gaseous phenomena on certain assump- tions: The molecules of a gas behave as smooth perfectly elastic spheres. and are in constant and rapid motion in straight lines, and continue moving in the same direction until they are reflected by striking each other or the walls of the containing vessel. The prodigious number of impacts against the sides of the vessel give rise to the pressure of the gas, whilst the tempera- ture of the gas is a measure of the velocity of motion of the molecules. Now by heating a gas its pressure is increased, and if the pressure is due to the motion of the molecules, it follows that increase of the tempera- ture of the gas means increase of molecular motion, since the number and mass of the molecules remain unchanged. Conversely, cooling a gas decreases its pressure, and therefore also its molecular motion. Gases can be liquefied by merely cooling them, that is, by depriving their molecules of motion to a sufficient extent. It is further assumed that the molecules are on an average so far separated from one another that their mutual attractions or repulsions are negligible, and that the ‘‘ mean free path,” 7.e. the average distance travelled between successive collisions, is great compared with the dimensions of the molecule, so that collisions are comparatively rare, though actually many millions of impacts occur every second. A mathematical expression for the pressure of a gas may be deduced from considera- tion of molecules moving in a hollow cube. Let a molecule of mass m in such a vessel be moving in any direction with velocity w; this can be resolved into three compo- nents (x, y, 2) in directions parallel to the sides of the cube and according to the prin- ciple of the resolution of velocities, w®= a?+ y?+2?. When the molecule moving towards the side of the cube with velocity x strikes the side, it exerts a force equivalent to its momentum, which is mz, not only at the impact but when it rebounds, making a total change of momentum of 2m. If lis the distance that the molecule has to move: from one side of the cube to the other, that is, the length of the side of the cube, this force is repeated w/1 times every unit of time. Thus the force exerted in unit time becomes 2mxa x x/l = 2mz?/l. What is true of component x applies to the other com- ponents, so the expression becomes 2m(a?+ y?+ 27)/l = 2mw?/l, and for the whole number n of the molecules, 2nmw*/l. The pressure p of a gas is expressed per unit area, so the foregoing expression must be divided by 6/?, the number of units of surface in 2nmw? 6B * . ‘ nmw of the cube, so the expression may be written py = 3 oF for unit volume p = mnw? (p. 9). 2 : 3 : : 2 5 i ee It is more instructive to write this formula p = 3 a for = is the kinetic: energy of the moving molecule and nmw?/2 that of all the molecules. Now if p is varied. by altering the temperature of the gas, this variation can be due only to the variation of the kinetic energy of the molecules, for is constant. Hence the temperature of a gas must be a measure of its kinetic energy, and if unit volumes of two gases have the- ’ Kunots = motion. the six sides of a cube; hence the final formula is p = B is the volume (v): This proves Boyle’s law ; pv = k when the temperature, 7.e. when w, is constant ” GASES 309 same temperature they must also have the same kinetic energy, or mw?/2 = MW? /2, ‘The third law on p. 9 is thus established, and from this Dalton’s law. Let the unit volumes be also at the same pressure, then n a = NY a or since mw = m,w,? by the previous equation, n = 7, that is to say, when gases are at the same temperature and pressure the number of molecules in unit volume® is the same (Avogadro’s hypothesis). vi The mass of a volume of gas must be the product of the mass of each molecule and the number of molecules ; hence mn in the foregoing equations is the mass of the gas. Taking 1 gram of hydrogen which measures 11,1231¢.c. at 760 mm. pressure and 0° C., mn will be 1, and we have pu = w?/3 or w = /3pv. The pressure of 760 mm. of mercury in absolute units is 76 x 13-6 x 980-6 = 1,013,230 dynes per sq. cm. Hence the rate w at which the hydrogen molecules move is— J/3 x 1,013,230 x 11,123 em, per second, or 1838 metres per second. The mass of unit volume is identical with density, hence for mn in the foregoing equations might be written d, and it will be obvious that if » and v are constant w must vary inversely as ,/d. That is to say, the velocity of the molecules of a gas varies inversely as the square root of the density of the gas. Since in equal volumes of two gases at the same temperature and pressure mnw? = m,n,w,?, it follows that dw* = dw? ; that is to say, the rates of movement of the molecules of different gases vary inversely as the square roots of their specific gravities. (Graham’s law of diffusion, p. 77.) or maw = mnwW,?, mw mus a : 5— varies with the absolute temperature of the gas, we Si 2 ince pu =3 yz and may write po = RT, where R is a constant and T the absolute temperature. R is called the “ gaseous con- stant,” and is proportional to the mass of a gas ; for when p or v is doubled, R also is doubled. If v = the gaseous molecular volume, 22,412! ¢.c. (V) (p. 96), » = 760 mm. of mercury, t.e. 1033 g. per sq. cm. (i.e. 76 x 13-59), and T = 273 (0° C.), then R = 84,678 ; which is just 2J, 7.e. twice the mechanical equivalent of heat, 42,350. Hence in many calculations where molecular quantities and gram-calories are involved, pv = 2T. It should be observed that in developing the foregoing dynamical theory for an ideal gas, no account is made of the fact that the molecules occupy a certain, though very small, volume (5), and that the space available for being inhabited (v—b) by a given molecule is less by this amount (6) than the total volume (v) occupied by the gas. Suppose 1000 c.c. of space to be inhabited by 1 c.c. of molecules, 999 c.c. are vacant and only I c.c. (0), the ‘“‘ co-volume,”’ is filled. When the pressure is doubled, the vacant space is halved, and we have 499-5 c.c. vacant and 1 c.c. filled, total 500-5 c.c. ; there- fore p (v — b) = RT is more correct. » Another consideration is that the molecules ought, according to mechanical laws, to exercise some attraction for each other, however small this may be. With all gases except hydrogen and helium this is found to be the case. In the interior of a volume of gas the mutual attractions may be neglected, inasmuch as the average pull is equal in all directions ; but at the confines of the gas a molecule is attracted back by its neighbours, and there is no opposing force, resulting in a condition akin to surface tension. Hence the gas does not exert so much pressure on the walls of the containing vessel as it ought. If the value of this inward attraction when the gas occupies unit volume is denoted by a, it is a/v? when the volume is v ; whence p + a/v’ is the corrected pressure. These results are summed up in van der Waal’s equation— (p+ %) @—b) = RT ‘This accords closely with experimental evidence obtained with various gases, even when far from ideal. ; Van der Waal’s equation is a cubic in », and at the critical point (p. 35) the three + 11,123 c.c. is the volume of 1 gram of hydrogen; 22,112 c.c, is the volume of 2°0152 grams (H,) (H=1 0076.) 310 GASES—SPECIFIC HEATS 8 re ; critical pressure = : a roots are equal, whence critical temperature = T, =o7- Ro? Pp, = air ; critical volume = v, = 3b (= three times the volume of the molecules ; 4.e. three times the “ limiting volume ”’ of the liquid under indefinitely great pressure ; but the volume of a liquid under ordinary conditions, when well below its boiling-point, is nearly as small as the limiting volume (p. 334). Conversely, the critical density is about one-third of the ordinary specific gravity). The critical temperature may be defined (but see also p. 35) as that at which a gas has been so compressed by pressure and its liquid so expanded by heat that they both have the same density and mix in all proportions. There is no abrupt alteration ; there is a continuous passage between the liquid and gaseous states ; there is “ Continuity of State” (see also Liquefaction of Gases, p. 81); indeed, it has been recently shown by Jaffé and others that perfectly pure liquid hexane, sulphur dioxide, &c., exhibit most of the properties of a dense gas. The Atomicity of Gaseous Molecules, i.e. the number of atoms composing the molecule, is evident if its molecular formula is known, e.g. N, is diatomic, CO, is triatomic. It is possible, however, to deduce the atomicity without reference to the chemical nature of the gas. When a gas is compressed its temperature is raised, although no heat is supplied, e.g. when working a bicycle pump ; and if allowed to expand, the gas cools although no heat is abstracted (cf. p. 85). If the gram-molecular volume, 22,412 ¢.c. (1 mol. as it is also called), of a gas at 0° be heated to 1°, it will require a certain quantity of heat, the molecular heat at constant volume, Cv, provided it is confined in a vessel so that it cannot expand ; the pressure is increased, but that is immaterial here. If the same quantity be contained in a vessel so that its volume may increase, but the pressure remain constant, more heat will be necessary to effect the same rise in temperature, and the total quantity is the molecular heat at constant pressure, Cp. (cf.p.311). The increase in volume will be 22,412 ~ 273 =82 c.c. (p. 91). Suppose the gas to be at the bottom of the vessel, open at the top and with an area of 82sq.cm. The gas in expanding would have to lift the atmosphere covering this area through a height of | cm. The atmosphere exerts a pressure of 1033 g. per sq. cm. (p. 309), .. of 1083 x 82 = 84,700 g. on 82 sq.cm.; .. the work done in lifting the atmosphere through a height of 1 cm. is 84,700 gram-centimetres ; but 42,350 gram- centimetres is the mechanical equivalent, J, of 1 calorie (p. 309); .°. the extra heat required to cause 22,412 c.c. to expand to 22,494 c.c. is 2 calories ; and hence Cp = Cv + 2. The heat required to raise the temperature is expended in increasing the kinetic energy of the molecules, proportional to mw?/2; that necessary for expansion is used in doing external work, proportional to mw?/3 ; hence Cu: Cp :: mw? /2: (mw? /2 + mw?/3)::3:5::1:1-66 5 orCp: Cu: : 1-66:1 in the case of an ideal gas. The ratio Cp: Cv is usually signified by y. In gases that are known to have diatomic molecules, y = 1-4—that is, the specific heat at constant volume is more than it would be in the ideal gas. The assumption is that in a diatomic gas the atoms in the molecule have a movement relative to each other, an intra-molecular motion, which is increased by heat. Thus heat would be absorbed which would not increase the kinetic energy of the moving molecules, Tf the ratio Cp : Cu for any particular gas be calculated, it will be found generally to approximate one of four values: 1-66 if its molecules are mon- atomic, 1-40 if diatomic, 1-25 if triatomic, less than 1-25 if polyatcmic. This is displaved in the following Table : KUNDT’S TUBE 31 Gas. Formula. Cp. Cv. Cp/Cv (y).| Atomicity. Argon . y ? ’ A — — 1-66 1 Mercury ‘ . Hg — — 1-66 1 Hydrogen. 3 : Hy . 6-82 4-82 1-41 2 Air. : . |(Ng + O2)] 6-86 4-86 1-405 2 Carbon monoxide : co 6-86 4-86 1-405 2 » dioxide. CO, 9-55 7-55 1-26 3 Nitrous oxide ‘ N,O 9-94 7-94 1:25 3 Phosphorus . : Py 13-4 11-4 1-175 | (4) poly- atomic ee trichloride ‘ PC, 18-6 16-6 1-12 (4), Ethylether. . . .(|(CsH;),.0 | 355 | 335 | 1:06 | (15) _,, Chlorine, bromine, iodine . | Cl, Br, I,] Exceptional. 1:3 2 The Ratio of the Specific Heats of a Gas, y (i.e. for 1 gram), is therefore a constant of value in ascertaining the atomicity of the gas. Experimentally, Cp is easily determined, but Cv presents difficulty ; fortunately the ratio (y) can be found quite easily by a few methods. It can be deduced from the velocity of sound () in a gas. Compare the following velocities with the figures in the foregoing Table : (diatomic) air, 332 ; CO, 337 ; (triatomic) CO,, 259 ; N20, 260 metres per second. The usual laboratory method of determining p or y is by means of Kundt’s tube, such as is shown in Fig. 212. It comprises a glass rod (carrying an echoing plate =P Fie. 212. to increase the sensitiveness), fused at the middle into a glass tube, } in. bore and 18 in. long, containing a little dry lycopodium. When the exposed end of the rod is stroked with a wet cloth it vibrates, and the vibrations thus set up in the gas distribute the lycopodium in small heaps at regular intervals (nodes) along the tube ; the length, 1, of an interval is equal to half a wave-length of sound under the prevailing conditions. p= ./yp/d, where pis the pressure and d the density of the gas. If = velocity of sound in air, and py = that in the given gas, and d, d,, M, My, y, y1, J, 4, be the respective 2 2 densities, molecular weights, constants, and lengths, y, =y ot or yy = yee . Kundt and Warburg found for air and mercury (where y for air = 1-405) that y,; = 1-405 x 1-1863 ; .*. y, for Hg = 1-66; .-. Hg-vapour is monatomic. At high temperatures specially prepared silica may be used instead of the lycopodium. When argon was discovered in atmospheric nitrogen, the possibility of its being triatomic nitrogen, N3, had to be considered ; if it were such, y would be about 1-25 ; but y for argon is 1-66, hence it is monatomic, and if monatomic it must be elementary. Equal volumes of gases contain equal numbers of molecules and expand equally for equal rise in temperature (not for absorption of equal quantities of heat), so that it would be expected that equal volumes would have equal specific heats. This is approximately realised with diatomic (sp. ht. for vol., 0-238) and triatomic (0-33) gases ; with polyatomic gases it is variable and much higher. The vapour density of some elements decreases as the temperature rises ; thus, sulphur vapour at 480° has a density of 95-1, which, divided by 32, the atomic weight of sulphur, gives 8S, as the molecular symbol; but at 1000° the density falls to 32-1, giving S, for the molecular symbol. It is supposed that in such cases the molecule suffers a dissociation as the temperature rises quite analogous to that which undoubtedly occurs in the case of many compound molecules, and noticed at p. 188. 312 DETERMINATION OF MOLECULAR WEIGHT The elements may be classified in this respect as follows: (1) Those whose vapour densities are identical with their atomic weights at all temperatures ;1 H, O, and N are the chief of these. Since M = 2D, the molecular weights of these atoms must be twice their atomic weights, and the molecule must therefore contain 2 atoms ; it is diatomic at all temperatures. (2) Those whose vapour densities are identical with their atomic weights at low temperatures, but become one-half at high temperatures. These are Cl, Br, I; their molecules are diatomic at low temperatures, but monatomic at high temperatures. (3) Those whose vapour densities are one-half of their atomic weights at all temperatures, so that their molecular weights are identical with their atomic weights at all temperatures. These are Na, K, Zn, Cd, Hg, A, He. Their mole- cules are monatomic at all temperatures. (4) Those whose vapour densities are twice their atomic weights at low temperatures, but identical with them at high temperatures. Such are P, As, Sb. Since M = 2D, the molecular weights of each of these gaseous elements must be four times their atomic weight at low temperatures, but only twice at high temperatures. They are tetratomic at low, but diatomic at high, temperatures. (5) Those whose vapour densities are a greater multiple than twice their atomic weights at low temperatures, becoming equal to their atomic weights at high temperatures.. Sulphur is the only example. Molecular Weights of Volatile Substances.—If the substance is a gas its molecular weight can be found simply by determining its density as described on p. 11, and doubling the result. The density of oxygen, 16, is the standard. If a volatile liquid or solid is the subject of investigation, there are three principal methods of determining vapour density (p. 11), of which Victor Meyer’s is the one commonly employed. (a) Dumas’ method is essentially the same as that for gases, namely, the weighing of a known volume of vapour at known temperature and pressure. The flask, of 300 or 400 c.c. capacity, usually has the form shown in Fig. 213. After weighing it full of air, introduce a few cubic centimetres of the liquid and immerse the flask entirely, except a portion of the finely drawn-out tube, in an oil- bath heated to a temperature several degrees above the boiling-point of the liquid ; the liquid boils and expels the air. When no more vapour issues from the orifice, ascertained by finding that nothing con- denses on a cold body held before it, it is assumed that all the remain- ing substance is in the gaseous state ; then seal the tube with a blow- pipe and observe the temperature of the bath (¢°) and the height of the barometer (6 mm.). Allow the bath to cool, clean the outside of the Fic. 213. bulb and weigh it. The increase in weight (w,) is the difference between the weight of the vapour (w,) at ¢° and b mm. and an equal volume of air (w3)att;°andd;mm. Having scratched the tube near the end with a file, break off the end of the tube under boiled water ; the water will rush in and fill the bulb, the sub- stance having condensed to the liquid state again ; weigh it full of water together with the end broken off. The weight of water in grams equals the volume of the bulb in c.c. (wv). v x 0-0012934 x (273 + t,) x by 273 x 760 Be ass cand W, = W, + w3. Hence we know the volume (v) and the weight (w,) of the vapour at z° and 6 mm. The weight of v c.c. of oxygen at t? and b mm. can be calculated ; 1-429 x (273 +t) xb a le = w, grams. From this the vapour density is 16w, + w,, and vw c.c. of air at t,° and bymm. weigh the molecular weight 32w, + wy. For substances which volatilise at temperatures above that at which glass becomes soft, globes made of porcelain must be employed ; these are sealed by the oxy-hydrogen blowpipe. (6) Hofmann’s method involves measuring the volume of vapour ‘pro- 1 The temperatures referred to in this classification range from 100° to 1700°. VICTOR MEYER’S METHOD 313 duced by heating a given weight of the substance in a barometer tube kept at a known temperature several degrees above the volatilising point of the substance and correcting for pressure. (c) Victor Meyer's method likewise measures the volume of vapour produced by a given weight of substance, but differs from the last in not making the measurement directly. In this, a weighed quantity of the sub- stance is converted into vapour in a vessel containing air (or some other gas), and the volume of air displaced by the vapour is collected and measured. It is not necessary to know the temperature of the heated vapour since the air displaced is at the same temperature as the vapour attains. The dis- placed air is measured at the prevailing atmospheric temperature and pressure, but it then occupies the same volume as the substance would occupy were it possible for it to exist as a vapour under the same conditions. Take, for example, the determination of the vapour density of alcohol, which boils at 783°. The vaporising-tube (b, Fig. 214), well closed by a cork, e, is heated in the cylinder of boiling water, a, so long as any bubbles of air pass from the opening of the delivery-tube, d, through the water in the trough. The end of the delivery-tube is then inserted into the graduated tube, f, which is full of water. About 0-1 gram of alcohol is weighed out into a small tube, which is dropped into the opening of the vaporising- tube, this being then quickly corked. A little asbestos is placed at the bottom of the vaporising-tube, c, to prevent breakage. The alcohol vapour expels a volume of air equal to its own, and this is collected in the tube, f, and accurately measured, with the usual corrections for temperature and pressure. The volume of a known weight of alcohol in the form of vapour having been thus ascertained, the vapour density may be calculated. For example, 0-1 gram of alcohol expelled a volume of air which measured 48-5 c.c. when corrected to 0° and 760 mm. bar. Hence, supposing that alcohol could retain the state of vapour at that temperature and pressure, 48-5 c.c. of alcohol vapour would weigh 0-1 gram. Now, 48-5 c.c. of oxygen at 0° and 760 mm. weighs 09-0693 gram, so that the vapour density of alcohol is 0-1 x 16 0-0693 For substances which can be volatilised only at very high temperatures porcelain must be substituted for glass, and a liquid of high boiling-point must be used in the bath surrounding the vaporising-tube. = 23, and its molecular weight is 23 x 2 = 46. = Inasmuch as Avogadro’s law is true only of the ideal gas, the foregoing method of determining Fic. 214. molecular weights can give accurate results only with gases which are far removed in temperature from the boiling-point of the corresponding liquids, and thus approach perfection. A criterion for the degree of gaseous character is the amount by which a gas deviates from Boyle’s law; if, for instance, on doubling the pressure on 1000 c.c. the volume becomes 400 c.c. instead of 500 c.c., the gas is far removed from perfection. Another criterion is the behaviour of the gas when heated ; if 1000 c.c. at 0° (273° absolute) expand to 2100 c.c. instead of 2000 c.c. when heated +0 273° (546° absolute), the molecules of the gas must have been consider- ably under the influence of each other at the lower temperature, for the 314 DISSOCIATION volume of a true gas must vary proportionally to the absolute temperature. Tf on heating the gas in question beyond 273° its volume increases in direct proportion to the absolute temperature, it may be concluded that at these higher temperatures the gas is nearly a true gas. Now hydrogen expands like a true gas, so that if the specific gravity! of a gas which expands more rapidly than a true gas (hydrogen) is determined at different temperatures it is found not to be constant, but to grow less as the temperature rises. For example, at 273°, 1000 c.c. of hydrogen contain 1/2 the matter contained in 1000 c.c. at 0°, whereas in 1000 c.c. of the gas cited above (as expanding to 2100 c.c. at 273°) there is at 273° only 1/2-1 the matter that is contained in 1000 c.c. at 0°. Hence if the specific gravity were x at 0° it would be only x — 2/21 at 273°. It follows that in order to apply Avogadro’s law to determine the vapour density of a substance the observations should be made at successively higher temperatures until the value remains constant. In most cases the fall in vapour density with rise of temperature is very slight, but in some it is very considerable ; cf. Sulphur, p. 150. It is supposed that in the case of sulphur and certain other substances there is more in this decrease of vapour density than a mere improvement of gaseous character. We have seen (p. 297) that the determination of vapour density for ascertaining molecular weights is used solely as an indication as to which of two values is correct ; for this method lacks the accuracy attainable by that which is particularly the chemist’s own—gravimetric analysis. Advantage is taken of the ‘‘ imperfection ’’ of gases in those processes for liquefying gases which depend upon the “ Kelvin-Joule effect”; see p. 85; Dissociation.—The only difficulty in following the foregoing steps for determining the molecular formula for a compound, provided that this is volatile, is in the doubt which sometimes exists whether the vapour or gas into which the compound is converted by heat is indeed the same com- pound. The gas produced by the vaporisation may consist of products of decomposition or of dissociation of the compound. The difference between these two phenomena has already been explained (p. 188). An example will make clear how dissociation affects the determination of molecular formule. The ultimate analysis of ammonium chloride shows that its empirical formula is NH,Cl, and this must be the minimum molecular formula, because the molecule cannot contain less than 1 atom of N or 1 atom of Cl. A deter- mination of the vapour density of ammonium chloride, however, gives the number 13-35, corresponding with molecular weight 26-7. Now, the formula NH,Cl corresponds with molecular weight 14 + 1 x 4+ 35-5 = 53-5, or double that found from the vapour density, which indeed corresponds with the impossible formula N,H,Cl,. ; The experiment cited at p. 188 shows that the vapour of ammonium chloride consists not of this compound, but of a mixture of ammonia, NH, and hydrogen chloride, HCl. That is, instead of being composed of NH,Cl molecules, the vapour consists of a mixture of NH, + HCl molecules. Unless the vapour itself had been tested this change would not have been detected, for it is a dissociation, not a decomposition, so that when the vapour is 1 Density is distinct from specific gravity. Of course the former decreases with rise of temperature because it is the ratio between the weight of a volume of the gas at the particular temperature and pressure and that of an equal volume of the standard gas at standard temperature and pressure. The specific gravity is deter- mined by weighing both gases at the same temperature, whatever that may be, and should be a constant. Vapour and gas densities refer, when not otherwise stated, to the values corrected to 0° and 760 mm., so that they are then numerically equal to the specific gravities. Compare these terms when referring to liquids and solids (p. 31). The unit for density in the one casc is the weight of 1 c.c. water at 4°, in the other one-sixtcenth the weight of 1 ¢.c. oxygen at 0° and 760 mm. LIQUIDS 315 ‘ cooled the ammonium chloride is re-formed just as water is obtained again when the steam from it is condensed. Ammonium chloride is found to be produced when equal volumes of NH, and HCl are mixed. Hence the dissociated vapour of ammonium chloride must consist of equal volumes of these gases. Now a mixture of gases in equal volumes always has a vapour density which is the mean of the vapour densities of the constituent gases. In this case the vapour density of NH, being 8-5, and that of HCl 18-2, that of the mixture would be half the sum of these values, or 13:35. If the ammonium chloride is perfectly anhydrous, no dissociation occurs and the normal vapour density, 26-7, is observed. The reaction is obviously “ reversible’ according to conditions, and is represented by the equation NH,Cl— NH, + HCl, where the reversed arrows show that the process may be one of dissociation from left to right, or one of association from right to left. Other well-known examples are nitrogen tetroxide, N,O,, which breaks up into two molecules of nitric peroxide, NO,; N,O, — NO, + NO,, and the dissociation of hydriodie acid into hydrogen and iodine, 2HI = H, + I,.. The subject is further considered at p. 345. (6) LIQUIDS. The general properties of liquids have been exemplified in the chapter on Water and the study has been extended in considering many acids and other liquids, and it has been seen that a liquid may be either a pure substance or a solution of one substance—gaseous, liquid, or solid—in another. Two gases may combine to form a liquid, e.g. ethylene and chlorine, producing ethylene dichloride (p. 256). Again, two solids may unite to form a liquid, e.g. equal parts of chloral hydrate and camphor when rubbed together in a mortar. Further, there is continuity of state from the gaseous to the liquid state (p. 310). The molecules of a liquid are considerably under the influence cf one another; the attraction is equal in all directions in the body of a liquid, and so the molecules move with a certain measure of freedom ; but the attraction is so great that the mass does not occupy uniformly the whole of the space inhabited as a gas does, with the result that collections of molecules fall by gravity to the bottom of the containing vessel. At the upper surface, molecules are attracted inwards and side- ways by neighbouring molecules, while there is no force enabling them to escape from the surface except the momentum they themselves possess. The escape of these molecules into the atmosphere constitutes the evapora- tion of the liquid. When the space is confined, it soon becomes saturated with these vapour molecules, and evaporation apparently ceases. This happens when as many molecules of vapour attach themselves to the surface of the liquid as escape from it in unit time. As the temperature of the liquid is raised, the motion of the molecules becomes more rapid, and the latter are less and less influenced by each other, with the result that evaporation increases, which happens in spite of the fact that the vapour pressure, and therefore the number of particles striking the surface in unit time, is increased; hence, eventually (at the critical point) the number of particles leaving the surface is so much greater than those striking the surface that the latter ceases to be capable of existence. The resultant of the forces of attraction at the surface is the surface tension (infra) ; capillarity is another expression of the same energy. The difference of molecular concentration above and below the surface of a liquid 316 SURFACE TENSION is so great, and the surface tension maintains such a smooth surface, that* the latter becomes clearly visible and takes a well-defined form, called a meniscus (unvicxoc, a little moon). At the critical temperature these conditions break down and the meniscus disappears. The viscosity, or internal friction, of a liquid may be defined as the resistance which the smallest particles offer to their sliding past each other, and depends on the intermolecular attraction within the body of the liquid. The viscosity is commonly measured by the time taken for a certain volume of the given liquid to flow through a narrow orifice as compared with the time taken by the same volume of a standard liquid in the same apparatus. Its deter- mination under standard conditions is of practical importance in the study of lubricating oils. The liquid is viscous or thick when the viscosity is great, or mobile when thin and moves or flows freely. Diffusion takes place in liquids as it does in gases (p. 75), but not so generally, e.g. water and oil do not perceptibly diffuse into one another ; nor is it nearly so rapid as in gases. If a layer of water be superposed on a layer of copper sulphate solution, the salt diffuses slowly upwards, although it takes months or even years to complete the process. This is further evidence that the molecules of liquids are in a state of constant motion, though vastly slower than in the case of gases. Liquids are only very slightly compressible (cf. Water, p. 33), which follows from their approach to the limiting volumes (p. 310), while change of temperature effects but little alteration of volume, in both of which properties they contrast with gases. As with gases, when pressure is applied to a liquid, it is transmitted in all directions uniformly. Molecular Weight of a Pure Liquid.—In order to determine the magnitude of the molecules in a pure liquid physical methods alone are available, since on addition of a second substance the liquid is no longer pure. The surface tension (p. 315) affords most information; Ramsay and Shields (1893) have developed the subject to a precise knowledge, although it was first recognised by Eotvés (1886). Surface tension, y, is a force tending to contract the surface of a liquid ; its magni- tude is specific for each liquid and varies with the temperature and with the nature of the adjacent gas or vapour. For present purposes, determinations are made only when the liquid is in contact with its own saturated vapour, and the unit of surface is the “ molecular area,” V3, containing at each unit of surface the same number of mole- cules, whatever the liquid may be. (If V is the molecular volume, V+ is the length of one edge of a cube whose volume is V, and Vi is (ges) “pV (liquid) +v% the area of one face.) The temperature, 0, Fic. 215. is “measured downwards from the critical point, Tc, of the liquid under examina- tion, i.e. 9 = Te — t, where ¢ is that observed on the. ordinary Centigrade ther- mometer. Then yVi = 0, which is of the same form as pV = RT (p. 309). At Tc the liquid has no surface tension (supra), therefore y= 0; just as with a gas at 0° A, p=. Hence we get the two parallel statements: (a) In all normal gases, at temperatures equally removed from the absolute zero, the product of the pressure into the molecular volume is the same ; (6) in all normal liquids, at temperatures equally removed from their critical points, the product of the surface tension into the molecular area is the same. Lig, Ether, To = 194-5°,t= 40° .. @ = 154-5, y V3 = 317-1 ergs. Benzene, ,, 288°5°, ,, 130°". ,, 1585, ,, 3198 ,, 317-1 319-8 ee 154:5 = 2-05 and 1585 2-02 respectively. Tel T 9 OSMOTIC PRESSURE 317 The average value of the constant & is 2-12. Experimentally the surface tension (y) and the specific volume (v) (i.e. the reciprocal of the density) are determined at two temperatures, ft; and ta. Then if Mv instead of V represent the molecular volume, y1(M2 )? — ye(Mv,)# a eho k (tg— ty) i gt m1 t18 — yo vot £.g. in the case of carbon disulphide : w= f 2-12 (46-1 — 19-4) — = 133-58/1- 2648 — 29-41/1-2238/ — Sl: which approximates 76, corresponding with the simple formula CSo Most neutral, indifferent, pure liquids—e.g. esters, carbon tetrachloride, phosphorus tri- chloride—are similarly found to have the smallest possible molecular weights. With certain liquids, which are otherwise abnormal, M is found to be much too great; e.g. with water at 5° it is 18 x 3-81; ethyl alcohol, 46 x 2-74; glycol alcohol, 62 x 2-92 ; signifying that in water “ molecular aggregates’ of 4 molecules (i.e, 4H,0) predomi- nate, and in the two alcohols, of 3 molecules (i.e. 3C,H,OH and 3C,H,(OH),). Molecular Weights of Non-Volatile Substances in Solution.—There are four principal methods of determination depending upon the influence which the molecules of the dissolved substance have on many of the physical properties of the solvent: (i) osmotic pressure; (ii) depression of the freezing-point of the solvent ; (iii) lowering of the vapour pressure of the solvent ; (iv) elevation of the boiling-point of the solvent. (i) Osmotic Pressure.—When two liquids are separated by a mem- brane which is “‘ permeable ” to at least one of them, a process of diffusion from one liquid to the other through the membrane will occur. Their rates of diffusion will, in general, be different, and the migration of one may be so slow that the membrane may be considered ‘‘ impermeable ”” to it. The current thus set up is called ‘‘ Osmosis ’’ (wouos, impulse), and the force impelling it ‘‘ Osmotic Pressure.’’ : In vegetable life osmosis plays an important part in the transport of water and of substances in solution through the membrane dividing one living cell from another, and Pfeffer in 1870, in the interests of plant physio- logy, attempted to measure the force exerted in such a process. Membranes of very various nature may be used, e.g. bladder tied over one end of an open tube, vegetable membranes, &c., but for experimental purposes Pfeffer preferred films of copper ferrocyanide deposited in the pores of unglazed earthenware pots; these are impermeable to sugar, the substance with which he experimented, as well as to most other solutes. The films are very delicate, but when of so very small an area and supported all round by the walls of the pores, they can resist considerable pressure. The principal phenomena may be observed in the simple arrangement shown in Fig. 216. P is a small biscuit porcelain battery cell, the top, T, of which has been dipped in paraffin-wax ; it is then filled with a 3 per cent. solution of copper sulphate, and placed nearly to the top in a 3 per cent. solution of potassium ferrocyanide, and allowed to stand some hours. The two solutions meet in the wall of the cell, with the result that a continuous sheet of copper ferrocyanide is deposited. After thorough washing, the cell is fitted with an india-rubber cork, R, carrying the manometer tube, M, and filled to M with sugar solution, and immersed in a bath of distilled water. During several hours or some days the liquid in the manometer slowly rises until a maximum is reached, corresponding with the osmotic pressure of the solution. Water has passed from the bath into the cell, but no sugar has passed outwards, An obvious fault in this arrangement is that the incoming water dilutes the solu- 318 OSMOTIC PRESSURE tion, so causing diminution of osmotic action ; further, unless the solution be dilute, the manometer may have to be of great length owing to the magnitude of the pressure. Morse’s new cell, designed to obviate this difficulty, is seen in Fig. 217. The specially made porous cell, ¢, is glazed above the line, b ; the upper part of the closed manometer, SS x £8 SS | led bask . hd is LP) z fee Rh SSIS 2 Fie. 216. Fic. 217. m, contains mercury, and the solution to be tested completely fills the lower part and the cell. An enlargement, e, of the manometer is embedded in Wood’s metal, w, surrounded by a brass cone, s, which is cushioned into the cell by the india-rubber cone, r, tied very tightly at top and bottom, t, t, to prevent any deformation and con- sequent change in volume of the rubber ; the whole is held together by the brass collar, 1, and nut, n. The whole arrangement is designed to maintain absolutely constant volume under great pressure, for with certain solutions the osmotic pressure may attain 20 or even 30 atmospheres. However, it is usual and more satisfactory to work with dilute solutions which exert only moderate pressure. The sealed end of the manometer is filled with air and the pressure is measured by observing the diminution in volume of the air. Pfeffer’s experiments showed hm that the osmotic pressure is ‘specific for each substance, and that for a given substance it is proportional to the concentration of the solution, e.g. a 1 per cent. solution of cane sugar exerts a pressure of 535 mm.; 2 per cent., 1016 mm.; 4 per cent., 2082 mm. ; 6 per cent., 3075 mm. ; provided the temperature is the same in each case (cf. Boyle's Law). He also observed that the osmotic pressure increases with the temperature. But it was van’t Hoff who, from a study of Pfeffer’s figures, discovered the close analogy between osmotic and gaseous pressure, and that the increase of osmotic pressure with rise of temperature is approxi- mately the same as the increase of gaseous pressure under the same change. Indeed, he showed that just as one may calculate the molecular weight of a gas from the weight of it occupying a certain volume at known temperature and pressure, so also one may deduce the molecular weight of a substance in solution by a similar employment of the osmotic pressure in conjunction with the temperature and pressure. An example will make this clear. Al per cent. solution of cane sugar exerts an osmotic pressure of 512 mm. at 14-15°. It is evident that in this solution 1 g. sugar is distributed through a volume of 100 c.c. Now suppose it were possible for the sugar to assume the gaseous state at the ordinary temperature ; then, according to gas laws, if 1 g. occupies 100 c.c. at 14:15°, it will 100 x 273 x 512 % 22,412 oCeuPY 73 4 14-15) x 760 = 64-06 c.c. at 0° and 760 mm. ; whence 406 8 VAN’T HOFF’S LAW 319 345-4 g., will occupy 22,412 c.c., the volume which the molecular weight in grams of any gas occupies at N.T.P. (p. 22) ; hence the molecular weight of cane sugar is about 345-4, Actually it is 342-2. How closely the osmotic pressure varies as the absolute temperature may be seen from the following figures for a 1 per cent. solution of cane sugar (cf. Third Law, p. 9): Temperature. Sees pies Ne eee Difference. 279-8° A. (6-8° C.) 504-7 509-3 — 46 286-2° (13-2° ) 525-2 522-2 + 3-0 295° (22°) 547-9 537-3 + 9-4 309° (36°) 566-9 563-0 + 3-9 Since similar observations have been made with a variety of substances, the following generalisation may be deduced: The osmotic pressure is identical with the gaseous pressure which the weight of dissolved substance would exert at the same temperature, if it were in the state of gas and occupied the volume filled by the solution. We may, therefore, repeat the fundamental gas equation, PV = RT, where P stands for osmotic instead of gaseous pressure ; however, the former frequently differs slightly from the latter, and hence R is proportionately varied. Gases at high concentration—that is, at high pressure—do not obey the laws of Boyle and Dalton properly. The same is true for solutions at high concentration ; hence it is better to work with dilute solutions. It might be expected that van der Waal’s equation would apply here. The same principles apply, but not the equation in its usual form. Thus, if v be the volume of the solution and 6 the volume of the solute, v — b is the volume of the solvent, corre- sponding with the volume of empty space (v — b) in the case of gases. This correction frequently improves matters, but in a solution there are unknown factors of association between the molecules of the solute and some of those of the solvent, which stand in the way of expressing all in one general equation. Since Avogadro’s law is deducible mathematically from those of Boyle and Dalton, and since dilute solutions appear to be controlled by the last- named laws, it seemed probable that an Avogadro’s law should exist for dilute solutions. This was first pointed out by van’t Hoff, whose law of osmotic pressure is thus stated: Equal volumes of different solutions, at the same temperature and osmotic pressure, contain equal numbers of -molecules of dissolved substance (cf. p. 10). ; : Solutions which exert equal osmotic pressure are said to be tsosmotic or asotonic. Just as the relation between the weights of the molecules of two gases can be deduced from Avogadro’s law (p. 10), so can the relation between the weights of the molecules of two dissolved solids be deduced from van't Hoff’s law. For it follows from this law that when equal volumes of two solutions are isotonic, and at the same temperature, the weight of dissolved solid in the one is as much heavier than the weight of the dissolved solid in the other, as the molecular weight of the first solid is heavier than the molecular weight of the second. ; The applicability of the measurement of osmotic pressure to the deter- mination of molecular weights will now be easily understood. A solution of the solid whose molecular weight is unknown may be diluted, or strengthened, until its osmotic pressure is identical with that of a solution containing a known weight of a solid whose molecular weight is known. 320 THE CRYOSCOPIC METHOD The ratio between the weights of the solids in one litre of each solution ‘is then the ratio between the molecular weights of the solids. Example.—A solution of a substance of unknown molecular weight was diluted until its osmotic pressure was found to be identical with that of a solution of sugar in water (at the same temperature). The weight of solid in 1 litre of each solution was then determined ; that in the sugar solution was 1 gram ; that in the other solution was 1-5 grams. By van’t Hoff’s law these weights must have the same ratio to each other as have the molecular weights of the substances. Let x be the unknown mol. wt. ; the mol. wt. of sugar is 342, therefore : 3842: a¢::1:15 0ra2 = 342 x 1:5. The nature of the mechanism of osmosis is still an open question. Ramsay’s hypothesis is the most probable, namely, that osmosis is due to the tendency to bring about an equal concentration of the solvent on the two sides of the diaphragm. The solvent molecules will pass into the vessel and out of the vessel; but since there are more of these molecules in unit volume outside the vessel than there are inside (on account of the presence of the dissolved molecules), more of the solvent will pass into the vessel in unit time than will pass out, and equilibrium will only be established when a certain pressure, compensating for this difference between the number of solvent molecules in unit volume, has been established inside the vessel. When equilibrium is established, the ‘“‘ gaseous”’ pressure of the solute, which is extra to that of the solvent, can be measured. If the manometer be open and mercury be poured into the limb, water may be made to pass out of the cell from the sugar solution. Dialysis (8:a, through ; Avorc, loosening or separating) is the separa- tion of crystalloids from colloids by osmosis ; see p. 281. The measurement of osmotic pressure is neither easy nor readily capable of great accuracy ; it is not, therefore, well adapted for the determination of molecular weights. There are, however, other methods of determining whether solutions contain the same number of dissolved molecules in equal volumes, which, owing to the ease and accuracy in making the required measurements, are much adopted for checking, and even determining, the molecular weights of substances which cannot be volatilised. Three of these will now be considered. (ii) Depression of the Freezing-Point of the Solvent; also known as the cryoscopic method and as Raoult’s method.—Blagden in 1788 dis- covered, empirically, that the freezing-point of a solution is always lower than that of the solvent, and that the depression is directly proportional to the weight of substance in solution. Thus, if 1 gram of a solid in a litre of water lowers the freezing-point by 0-1°, 2 grams will lower it 0:2°. De Coppet in 1871 observed that, comparing different substances, the depression is usually inversely proportional to the molecular weight of the solute. However, these and other observers confined their attention almost exclu- sively to aqueous solutions of salts which, as is now known, exhibit most irregularity ; and so they were not able to deduce much of theoretical significance. Raoult, about 1883, extended the inquiry, using organic solvents and solutes, and found it to be a general law that when molecular quantities of different substances are dissolved in the same amount of a solvent, they lower the freezing-point of the solvent to the same extent. This may now be expressed by saying that isotonic solutions in the same solvent have the same freezing-point. If Raoult’s generalisation (italicised above) be true, there will be a certain cryoscopic constant, C, for every solvent, representing the amount of BECKMANN’S APPARATUS 321 depression in the freezing-point of that solvent caused by the presence of 1 gram-molecule of any substance in 100 grams of the solvent. Thus, it is found that in the case of many substances a solution of 1 gram-molecule of the substance in 1000 grams of water freezes at — 1-9°; consequently a solution of 1 gram-molecule in 100 grams of water should freeze at — 19°, and the constant, C, for water is 19. Similarly for benzene it is 51; for acetic acid, 39; for phenol, 74; and soon. All these constants are calcu- lated for one molecular weight in grams of the substance dissolved in 100 g. of the solvent, although solutions of such concentration are never used in the experimental process. A little consideration will show that when the constant for a solvent is known, it should be possible to determine the molecular weight of a substance by ascertaining the depression of the freezing-point of a solution of the substance in that solvent. The method of determination by Beckmann’s apparatus is as follows: A known weight of the solvent is introduced into a long test-tube (Fig. 218) which has a side neck closed by a cork ; a cork in the mouth of the test-tube carries a thermometer of special construction, graduated to 0-01°, and a stirrer. The test-tube is passed through the cork of a wider test-tube (to serve as an air jacket, which shall prevent too rapid a change of temperature), which is immersed in a bath also provided with a stirrer and at a temperature several degrees below the freezing-point of the solvent. The bulb of the thermometer being immersed in the solvent, the stirrer is continually agitated until the solvent begins to freeze, where- upon the temperature is noted. The tube is then withdrawn from the bath, the solvent allowed to melt, and the weighed quantity of substance added through the side neck. When this has dissolved, the freezing-point of the solution is determined as before. The difference from the first reading is the required “depression.” Since superfusion of the solution may occur, it is sometimes necessary to add a crystal of a previously frozen solution (of the same strength) in order to induce solidification. The Beckmann thermometer consists of a very large bulb and long capillary tube, registering some 6 degrees divided into 1/100ths, surmounted by a small reservoir into which, and from which, mercury may be transferred so that the quantity in the bulb and capillary is correct for the desired range of tempera- ture. This apparently loose adjustment is explained by the fact that the instrument is used for determining only differences of temperature. A couple of examples will illustrate the principle. (a) 10-2 g. Fic. 218. water were introduced into the tube and cooled until crystals of ice began to freeze out; the thermometer registered 2-671°. The ice was allowed to melt and 0-1072 g. urea was added and dissolved, and the freezing-point determined as before, 2-336°. Therefore, the depression was 0:335°. Now if 19° be the constant for water, the molecular weight found for ureais0-1072 x ae x = 59-62, which is afair approximation to 60-05, the actual figure for CO(NHg),._ If, on the other hand, it is required to find the cryoscopic constant for water, i.e. the depression which would occur if 1 molecular weight in grams (60-05 in the case of urea) were dissolved in ae 5 ee 0-1072 ~ 100 (b) The constant for benzene was given by Raoult as 49° ; usually, however, it is found to be about 51° or 52°, which is more in accord with the figure deduced by theory, 51°. 8-8 g. pure benzene were weighed into the tube and the freezing-point determined ; the thermometer read 4-203°; 0-1102 g. camphor was added and dissolved, and the 2I 100 g. water, we have 0-335° x 322 VAPOUR PRESSURE OF SOLUTIONS new freezing-point determined, 3-772° ; therefore the depression was 0-431° ; whence the molecular weight of camphor is 0-1102 x ca x = = 151-1. Raoult found great divergences with certain classes of compounds, especially with saline compounds, acids and bases in aqueous solution. With those named the depression was nearly twice as great as anticipated when dilute solutions were employed, indicating a molecular weight only half that found by other methods, ¢.g. instead of KCl, the impossible formula K,Cl, was indicated. These cases are explainable on the more recent hypothesis of ionisation (p. 327), by which it appears that KCl scarcely exists in dilute solution, it being ionised into K’ and Cl’ ions, so that there are twice as many “‘ molecules ” or ions as there would be if the compound KCl remained ; and therefore the mean ‘“‘ molecular”? weight appears as but little more than half the normal. With strong solutions the irregularities were even more perplexing, but these also find elucidation under the ionic theory. In the meantime van’t Hoff showed that the constant, C, for any solvent may be deduced theoretically from its latent heat of fusion, L, and its melting-point, T, in absolute degrees, and the factor 0-02 ; thus C = 0-02 T?/L. Taking water, for instance, C = 0:02 x 2732/79-25 = 18-8: hence the normal value is about 19. Occasionally, twice the normal molecular weight is indicated, showing that in the liquid state the solute consists of particles composed of 2 ordinary molecules, e.g. benzoic acid in benzene gives a molecular depression of only 25-4 instead of 51, showing that the number of particles is only one-half the normal; hence the particles contain 2C,H,O, instead of C,H,O,. In this way much light is thrown on the nature of sub- stances in solution. The process is of exceptionally wide application. Ramsay proved that N,Og, and not N,Og, is the formula of nitrogen trioxide, by applying the method to its solution in liquefied nitrogen peroxide, NOg. Wedekind has determined the rate at which certain compounds break up in bromoform solution, by observing the rate of increase of the depression with the time. Molten tin has been used as the solvent in investigating the molecular magnitude of metallic particles. A complication common to this and the kindred methods is the not infrequent association of certain molecular quantities of the solvent with the particles of solute, whether they exist as ordinary molecules or as ions, e.g. experimental data point to the formation of hydrates such as O,>H».0,, .5H,O for cane sugar, when the substance is dissolved in water. This, however, does not seriously affect the determination of molecular weight, because the number of particles is the same whether the formula is CieHo201, or CypH»201,.5H,0 ; but it does reduce the quantity of free solvent by the scarcely significant weight of it which has entered into union. The subject recurs in the consideration of the hydration of the solute (p. 324) and the hydration of ions (p. 331). (iii) The Lowering of the Vapour Pressure of a solvent by the presence of a.substance in solution is controlled by laws which are wholly similar to those which apply to the lowering of the freezing-point of a solvent by the presence of a dissolved substance. Since the vapour pressure varies with the temperature it is necessary to add that the lowering is always the same fraction of the vapour pressure of the pure solvent, whatever the temperature. Inasmuch as the boiling-point of a liquid is that temperature at which the pressure of its vapour is equal to the pressure of the atmosphere, the presence of a dissolved substance must raise the boiling-point of a solution part passu with lowering its vapour pressure. (iv) Elevation of the Boiling-Point of the Solvent. The Lbulliscopic Method.—The principle on which this method depends is the same as in the three preceding, namely, that the influence of the solute on a property of the given solvent is proportional to the concentration. If » grams BOILING-POINT OF SOLUTIONS 323 of a substance are dissolved in 100 g. of a solvent, the boiling-point of the solution will be ¢° higher than that of the pure solvent ; if 2n grams are used, the elevation will be 2é°, and so on. If the molecular weight in grams is employed, the boiling-point will be raised by a constant amount, C°, strictly comparable with that observed in the cryoscopic method, and generally subject to the same exceptions. The constant for water is 5-2°; acetic acid, 38-8 (see also p. 604) ; benzene, 26-7° ; chloroform, 39°; acetone, 16-7°; &c. The experimental values may be controlled on theoretical bases, just as the cryoscopic constants may (p. 322). C = 0-02 T?/L, where L is the latent heat of vaporisation of the solvent and T its boiling-point in absolute degrees ; e.g. in the case of water, C = 0-02 x 373°/536:5 = 5-2. There are two experimental methods in general use. (a) Beckmann’s, in which a weighed quantity of the pure solvent is first boiled in a special test-tube fitted with reflux } e condenser and heated by a special arrangement to avoid overheating; the boiling-point is de- termined by a Beckmann thermometer (p. 321), the bulb of which is wholly immersed in the II| 27 liquid. A known weight of the substance to be El examined is added, the boiling repeated, and the thermometer read again. The difference between the two readings is the “‘ elevation.” Example.—8-646 g. benzene were used and its boiling-point as registered on the thermometer was 1-393°; 0-1540 g. naphthalene was added and. dissolved, and the boiling repeated; the thermometer now read 1-766°, therefore the elevation was 0-373°; whence the molecular weight found is 0-154 x 100 26-7 646 * 0375 7 127-5. By theory Ci>Hg requires 128-06. (6) Landsberger’s. In this, the solution is heated to its boiling-point by passing into it a stream of vapour of the pure solvent, both solution and solvent ultimately bciling at the same barometric pressure. The heat necessary for ~ the solution to attain its boiling-point, which is y, ll higher than that of the solvent, is derived from hi the latent heat of that portion of the injected Fie. 219. vapour which becomes condensed. The apparatus is shown in Fig. 219. The tube, NV, containing the solvent is surrounded by a jacket filled with the vapour of the solvent at its boiling-point. This vapour is generated in the flask, A, and is passed through the tube, B, provided with disiributing holes at its lower end, into the inner tube, N, which contains another porticn of the solvent. When the latter has been heated by the vapour to its boiling-point, the vapour passes uncondensed through the liquid solvent and through the hole, H, thus sur- rounding the tube, NV, and passing into the condenser, C. The temperature is now noted by the ordinary thermometer (graduated in fifths or tenths of a degree), 7’; the tube, V, is emptied and the operation repeated after the addition to some of the solvent (about 5 to 7 c.c.) of a weighed quantity of the substance (about 4 per cent. of the weight of the solvent), the molecular weight of which is to be determined. The tube, NV, whose weight when empty is known, is now weighed to ascertain the weight of solvent con- taining the known weight of the substance under investigation. The molecular eleva- tion of the boiling-point of the solvent, C, having been determined by the use of a substance of known molecular weight, the molecular weight of the substance is i Sia ip Ml — 324 SOLUTIONS calculated in the manner described above. It is to be noted that the stream of vapour must be stopped at the moment of reading the thermometer, otherwise the concen- tration of the solution indicated by the elevation will not correspond with the weight of solvent found. Several modifications of the process have been proposed. Solution.—The peculiar intermediate position which solution occupies between chemical combination on the one hand and physical mixture on the other has already been defined (p. 37). Several theories have been propounded to explain under one theme the many and varied phenomena associated with the familiar process of dissolution and the state of solution, but a completely satisfactory explanation is still wanting, although our knowledge at the present time is very far in advance of what it was a few years ago. The simplest case of solution, where one substance forms a homogeneous mixture with another without any manifestation of either chemical or physical change other than that the product exhibits the means of the properties of its components, can differ very little from a purely physical mixture. Such seems to be approached when two hydrocarbons of the same series form a homogeneous mixture. But even hydrocarbons are not without influence on each other, for triphenylmethane separates from benzene solution as crystals containing benzene of crystallisation, CH(C,H;)3.C.Hg. Similarly, from thiophene with thiophen of crystallisation, CH(C,H;)3.C,H,S. Several other organic solvents are known to form well-defined crystals with the substances they hold in solution, ¢.g. salicylide (q.v.) takes up chloroform of crystallisation (C;H,0,)4.(CHCl;),. Alcohol of crystallisation with salts is well known, e.g. LiCl.4C,H;OH, CaCl,.4C,H;O0H, Mg(NO,),.6C,H,OH. Water of crystallisation is very common (p. 39). The separate existence of such compounds and the equilibrium which these solids sustain with the liquids from which they have crystallised (p. 341) constitute one of the best proofs we have of the existence of such combinations between the solute and a part of the solvent in solutions ; for such equilibrium proves the existence of the same combination in the solution. Further evidence of the same thing is afforded in preparing the medicinal granulated sulphate of iron. Aqueous solution of ferrous sulphate is allowed to trickle into alcohol, when minute granular crystals of FeSO,.7H,O separate, signifying that some such association of FeSO, and H,O existed in the aqueous solution. From this a solution appears to consist of a homogeneous mixture of the solute in combination with a portion of the solvent and the remainder of the solvent which is ‘free.’ It is the free solvent which is studied in the processes described on pp. 317 to 323, and it is only from observation of changes therein that the state of the solute, whether combined with a portion of the solvent or not, is conjectured. By these methods the degree of hydration is given, but only indirectly from the collateral factor, measurement of the active mass of the free solvent. The results are generally satisfactory, but only so far as they are confirmed in the main by other considerations. Aqueous solutions engage by far the most attention, not only because of their greater practical importance, but also because water reacts in many ways with the solute, hydrating it, ionising it, hydrating the ions produced, and so on; whence it is often possible to learn much regarding the nature of the solute. : Hydration of the solute is strongly indicated by the changes in colour which solutions of some copper and cobalt salts undergo with alteration of physical circumstances. For instance, an acid solution of cobalt chloride (p. 457) is red when cold, but blue when hot, a difference which corresponds with the changes in colour of the solids with the degree of hydration ; CoCl,.6H,O (red), CoCl,.2H,O (blue), CoCl, (blue). HEAT OF DISSOLUTION 325 The argument for some union is again supported by the change in volume which usually occurs on dissolution (cf. p. 37). Contraction is the more common, and in some cases it is so great that the volume of the solution is smaller than that of the water used in its preparation. In not a few cases there is no appreciable change, e.g. on mixing many hydrocarbons, dissolving camphor in spirit, sugar in water, &c. In a very few instances the solution measures more than the sum of the volumes of its separate constituents, é.g. ammonium chloride in water. Thermal change is another phenomenon generally accompanying dissolu- tion. Avoiding those cases where ordinary chemical reaction occurs, as in SO, + H,O = H,S0O,, we find that thermal changes may arise from at least four causes : (a) Heat evolved or absorbed due to change of state. When a gas is dissolved, heat is disengaged (p. 80), since it is changed from the gaseous to the liquid state, hence the evolution of heat will be equal to the latent heat of vaporisation of the solute; similarly when a solid dissolves in a liquid, it assumes the liquid state, and this change effects the absorption of a quantity of heat equal to the latent heat of fusion of the substance, e.g. the molecular heat of fusion of naphthalene is — 4-6 cals. ; its molecular heat of dissolution in benzene is about the same, — 4-7 cals. (b) Heat of hydration, when water is the solvent, or more generally, heat of combination with the solvent, eg. in the formation of the complexes, H,SO,.H,0, LiCl.4C,H;,OH, CH(C,H;),.C,H, (p. 324); usually heat is evolved. (c) Heat of ionisation ; the separation of a salt, e.g. KCl, into its ions, K’ and Cl’, is accompanied by a thermal change. (d) Heat of dilution ; it frequently happens that heat is disengaged on diluting a strong solution, e.g. KOH. The heat of dissolution is the thermal change occurring when a substance is dissolved in a liquid, and is often a composite quantity, being the resultant of the changes just described as well as of any others which a particular case may provide. For instance, when anhydrous calcium chloride, CaCl,, is dissolved in water, (a) it is hydrated to CaCl,.6H,O with evolution of heat ; (6) it is then liquefied with absorption of heat ; (c) it is ionised in solution, CaCl, — Ca’ + 2Cl’, to a degree varying with the dilution ; (d) it is diluted, involving further thermal change. Hence, the heat of dissolution, though often referred to, is a very arbitrary quantity, and figures would appear to be of but little significance except when some parallel series are under comparison, e.g. the chlorides and bromides of the alkali metals. Change of state, evolution or absorption of heat, association of the solute with the solvent are not the only outstanding phenomena of dissolution. Again, putting aside such obviously chemical reactions as occur in the dissolu- tion of sodium in water, there are chemical differences to be accounted for on grounds other than merely elemental composition. A 4 per cent. solution of chloroform, CHCI,, in water will give no precipitate of silver chloride on adding silver nitrate, yet a 4 per cent. solution of hydrochloric acid, contain- ing nearly the same proportion of chlorine, gives immediately, under the same conditions, a copious precipitate of silver chloride. Evidently the chlorine is bound in some way in the first instance, whereas in the second it is free to be attacked by silver. Indeed, the explanation does not lie in the fact that one is a typical chloride and the other a compound of different constitution. Methyl chloride, CH,Cl, and ammonium chloride, NH,Cl, are both chlorides and similar in type, yet the first is inactive towards silver salt, whereas the other responds to the test just as hydrochloric acid does. If a variety of solutions be submitted to the influence of the electric current, it will be found that little or no result follows in the majority of 326 ELECTROCHEMISTRY those solutions which are indifferent to ordinary chemical reagents, as with chloroform and methyl] chloride, but with those which do react a separation of one constituent element or group will usually occur at one of the electrodes and another constituent at the other electrode; cf. 2HCl — H, + Cl, (p. 112). This then is further evidence of some kind of freedom in the latter which does not obtain in the former. The nature of this freedom was ever a matter of discussion until Arrhenius propounded his ionic theory (p. 94), which is now generally, though not universally, accepted (see p. 331). The theory that many mole- cules are dissociated by being dissolved finds its chief support in a study of the phenomena which accompany the conversion of chemical energy into electrical energy and vice versa, i.e. in the study of Electrochemistry, which will therefore receive attention here. The chemical action which is most frequently employed to develop chemical energy for conversion into electrical energy is that involved in the dissolution of zinc in an acid, generally dilute sulphuric acid. If a piece of commercial zinc be immersed in dilute sulphuric acid, it dissolves, and the greater part of the quantity of heat which is developed is equivalent to the chemical energy of the reaction with the zinc. If the zinc and acid be perfectly pure no action will occur ; but if a piece of platinum be immersed in the acid and be made to touch the zinc, whether beneath or above the surface of the acid, action will begin and heat will be developed ; the hydro- gen will no longer appear to be evolved from the zine, but will rise from the surface of the platinum. In the case of both the impure zinc and the zine + platinum, the chemical energy has to a great extent passed through the stage of electrical energy before it has become heat energy.+ If the platinum and zinc be connected with a wire outside the acid, the electrical energy will ‘“‘ flow” through the wire and may be utilised before it becomes converted into heat energy. Such a “ voltaic cell’ and the polarisation to which it is subject have already been described (p. 15). The total amount of electrical energy developed by a galvanic’ cell in unit time depends on the amount of chemical energy occurring in the cell in that time, and upon the nature of the plates which are used in the cell. The first of these conditions is measured (in the zinc cell) by the amount of zine which dissolves, and is therefore related to the size of the zinc plate.? The influence of the nature of the plates may be summed up by saying that the greater the antithesis between the plates, in respect of the ease with which they are attacked by the exciting medium of the cell, the greater will be the total amount of electrical energy obtained from the cell. Thus, when dilute sul- phuric acid is the exciting medium, the plates should consist of a metal which is, in a high degree, attackable by this acid, and one which is highly resistant ; zinc and plati- num are the metals, among those which are sufficiently cheap for use, which best fulfil these conditions ; zinc and copper are frequently used, but since copper has a greater tendency to dissolve in sulphuric acid than platinum has, this “ couple ” is not capable of giving so great a total of electrical energy as that yielded by a zinc-platinum couple. It will be obvious, however, that in the event of an exciting medium which has more action on platinum than on copper being used, the zinc-copper couple may transcend the zine-platinum couple. Since it is a sine qua non that the plates used in a battery should be conductors of electricity, the non-metals, with a few exceptions (the most notable of which is carbon), are put out of court for this purpose. It thus appears that quantity of chemical energy can be equated to quantity of electrical energy. The former cannot be measured directly (p. 341) ; the latter has for its unit the joule or volt-cowlomb, which is the product of the unit quantity of electricity 1 The impure zine contains foreign metals which, by contact with the zinc, enable the latter to dissolve, with generation of electrical energy, just as the platinum enables the pure zinc to dissolve. 2 If the zine plate be badly amalgamated (p. 15) the impurities in it will develop minor electric currents, causing evolution of hydrogen “‘ from the zinc,”’ and the amount of electrical energy thus developed will be unava lable for external use, and will be directly converted into heat. ELECTROLYSIS 327 called a coulomb (capacity factor), into the unit of electrical pressure or electromotive force (E.M.F.) called a volt (intensity factor) (p. 12). The joule, again, is equivalent to 0-24 gram-calorie, so that chemical, electrical and heat energies can be equated inter se. The quantity of electrical energy varies with the quantity of chemical action, i.e. with the quantity of zinc dissolved, i.e. with the size of the plates ; the intensity varies with the nature of the plates. Electrolysis.—The converse transformation of electrical energy into chemical analysis has been observed in the electrolytic cell (pp. 14, 112). There is no essential difference in the arrangement of a voltaic cell from that of an electrolytic cell. In the former, the chemical system generates electrical energy availiable for application outside the cell; in the latter, electrical energy is supplied from some external source to be converted into chemical energy inside the cell. A lead accumulator may be viewed as an electrolytic cell when it is being charged, and as a voltaic cell when being discharged. The word electrolysis is used to signify the decomposition of a compound by the passage through it, or its solution, of the electric current (p. 14). Any compound which can be thus decomposed is termed an electrolyte, and the portions into which it is decomposed are termed ions. An electrolyte must be a compound, but all compounds are not electrolytes. Compounds may be classified with regard to their relation to the electric current into (1) conductors which are not electrolytes ; (2) conductors which are electro- lytes ; and (3) non-conductors. The ionisation or electrolytic dissociation which a salt or similar body suffers on dissolution in water and certain other liquids has already been described (p. 94); also the electrical condition of the ions (p. 94). Ions are so named because, when electricity is passed through the liquid in which they exist, they travel (i#y, to travel) either with the electric current or in the opposite direction. They are differentiated into cations (+) when they are positively charged and go with the current towards the cathode, and the negatively charged anions (—), which are attracted to the ancde. The former include hydrogen and the metals, the latter the non-metals and acid residues (cf. p. 94). It is this migration of ions to the respective electrodes and their discharge there which constitute electrolysis. It was at one time thought that the electricity obtained the matter with which it was to move in the electrolyte by tearing asunder the molecules. This, however, would be inconsistent with the fact that even the smallest electrical pressure will exert some electrolysis. It has only recently been realised that the molecules in an electrolyte must be regarded as being already ionised, nearly completely in dilute solutions, and to a certain extent in all electrolytes. The free ions exist already in the electrolytic medium, each bearing its charge of electricity. According to present views, atoms are complexes built up of electrons (p. 206), and each ion consists of an atom or atomic complex into which enter either one or more electrons in excess of those in the ordinary atomic condition (anions), or there is a deficiency of one or more electrons from the normal number (cations). The electron being the unit charge of negative electricity, it moves by attraction towards the anode, and if it is associated with an atom or atomic complex forming an anion, it carries with it the atom or atoms it charges. On the other hand, an atom which has lost an electron constitutes a positively charged ion (cation), and by reason of its deficiency of negative electric charge is attracted to the cathode. When a cation arrives at the cathode, it takes up an electron from the latter and an electrically neutral atom or residue results and is discharged producing the substance in that state with which we are familiar. Similarly, when an anion arrives at the anode it gives up its charge to the anode, and the atom or atoms separate uncharged. It is simpler and usual, however, to describe the anions as negatively charged ions, 328 LAWS OF ELECTROLYSIS eg. Cl + ©), or Cl’, and the cations as positively charged ions, é.g. Na — © or Na + GO) or Na: © is the symbol for an electron or negative charge ; then &) conveniently represents a positive charge. The ions of an electrolyte are either atoms or radicles electrically charged ; thus, when an aqueous solution of HCl is electrolysed, the ions are H’ and Cl’, these being chemically equivalent ; the H atoms move towards the cathode, each carrying its charge of positive electricity ; the Cl atoms,move towards the anode, each carrying its negative charge. In the case of an aqueous solution of K,SO,, the ions are 2K’ and SO,” these being chemi- cally equivalent ; each K atom carries one positive charge, whilst the SO, radicle carries two negative charges. When the ions arrive at the electrode the charges (electrons) are neutralised, and the discharged ions either appear in the free state (when the atoms immediately combine to form molecules), or they react with the water or with the electrode ; in the latter case the final products of the electrolysis will be the products of these reactions. In the case of hydrochloric acid electrolysed by carbon electrodes, molecules of hydrogen and chlorine are evolved. In the case of potassium sulphate electrolysed with carbon or platinum electrodes, the final products are hydrogen at the cathode and oxygen at the anode ; for the potassium atoms, so soon as they are discharged at the cathode, react with the water in the well-known manner, producing 2KOH and H,, whilst the SO,, when it is discharged, reacts with the water, producing H,SO, and O. The 2KOH and H,SO, left in solution speedily neutralise each other, re-forming potassium sulphate, the total quantity of which thus suffers no diminution during the electrolysis. If, however, the electrolytic cell be divided by a porous diaphragm, the acid and alkaline products may be kept apart, a fact applied in the manufacture of alkali.t It will now be realised that the electrolysis of water described on p. 14 is the electrolysis of dilute sulphuric acid. Water is such an exceedingly poor electrolyte that it requires refined apparatus to detect its conductivity at all. When dilute sulphuric acid is electrolysed, hydrogen is liberated at the cathode and SO, at the anode, where it at once reacts with the water to form H,SO, and O. When copper sulphate solution is electrolysed with platinum electrodes the ions are Cu’ and SO,’’.. The copper is deposited on the cathode and oxygen is evolved at the anode, owing to the reaction between discharged SO, and water. If the anode be made of some mats¢rial which is more easily attacked by SO, than is water, this will react with SO,. Thus, a copper anode will be dissolved by combining with the SO,, and the quantity of copper which will pass into solution will be exactly equal to that deposited on the cathode ; this fact is applied in the process of electro-plating (see Silver). Faraday (6. 1794, d. 1867) formulated two laws of electrolysis: (i) The amount of any substance liberated is proportional to the quantity of elec- tricity passed through the electrolyte (cf. Voliameters, pp. 16, 329) ; (ii) the weights of different substances liberated by the same quantity of electricity are proportional to their chemical equivalents. For example, if the same current of electricity be passed through electrolytic cells containing sulphuric acid and silver nitrate respectively, there will be 108 g. of silver deposited on the cathode of the one cell for every 1 g. of hydrogen liberated at the cathode of the other cell, these quantities of silver and hydrogen being chemically equivalent. So also there will be 48 g. of SO, discharged at the anode of the one cell, and 62 g. of NO, at the anode of the other cell. See alkali industry. ELECTROCHEMICAL EQUIVALENTS 329 Hence, in general, the electro-chemical equivalent is the same as the chemical equivalent. We have seen already that the quantity of hydrogen liberated is strictly propor- tional to the quantity of electricity passed through the solution, and two forms of water or hydrogen voltameter have been described (p. 16). It follows from Faraday’s second law that the quantity of electricity may be equally well measured by weighing the silver deposited instead of observing the volume of hydrogen liberated ; and, indeed, such a silver voltameter affords the most accurate means of measurement. Richards employs the following arrangement (Fig. 220). The current passes through a silver wire to a rod of pure silver, A, which serves as anode, then through the electrolyte, a freshly prepared 10 per cent. AgNO, solu- tion, to the platinum crucible, C, which forms the cathode. The thin porous pot, P, is not essential, but it prevents diffusion. 8, S are glass supports. The silver is deposited in a crystalline form on the platinum, and after thorough washing and drying is weighed with the crucible. Every 0-001118 g. silver is equivalent to 1 coulomb. If this weight be divided into the atomic weight of silver, 107-88, the quotient, 96,540, is the number of coulombs required for the deposition of 1 gram equivalent of silver, and therefore of any substance. But this is only one factor of the electrical energy required, for the latter is the product of the quantity of current x the pres- sure at which it is delivered. The pressure necessary for electro- ~%, lysing any particular electrolyte depends on the chemical affinity of Fie. 220 the ions for each other. If now the heat equivalent to this chemical aa affinity be known, the electrical energy can be calculated, because 1 unit of electrical energy (joule) is equal to 0-24 gram-unit of heat, The joule = 1 coulomb x 1 volt (the unit of pressure). Leta be the heat equivalent to the affinity between 1 gram equiva- lent of each of theions; this will be equal to a/0-24 joules. But the quantity of current necessary to effect the electrolysis is 96,540 coulombs, so that the electrical energy must be made up of 96,540 coulombs x x volts; thus the equation a/0-24 = 96540 x x is obtained, from which the value of x, the voltage necessary for the electrolysis, may be calculated. The value ascertained in this manner is, of course, open to the same uncertainty as that which surrounds the value for the heat equivalent to the affinity (p. 348). Since some elements have two chemical equivalents, ions composed of them will have two electro-chemical equivalents. Thus, copper in cupric chloride has an electro-chemical equivalent of 31-5, this proportion being deposited for every 1 part of hydrogen evolved in a sulphuric acid cell ; but copper in cuprous chloride has an electro-chemical equivalent of 63, The converse of Faraday’s law is equally true ; that is to say, the chemical change of chemically equivalent quantities of ions gives rise to the same quantity of electric current. Thus, in a galvanic cell the same quantity of current will be generated, whether 32-5 parts of zinc or 28 parts of iron be dissolved in acid. Attempts are made to catalogue the elements in the order of their decreasing electro- positiveness ; that is, in such an order that if a compound of any two elements be submitted to electrolysis, the one which comes first in the list will behave as the cation. It is obvious that such an electro-chemical list must differ according to the conditions of the electrolysis, such as whether the compound be present in an acid or an alkaline elec- trolytic medium, &c. In nearly all cases, however, the metals precede the non-metals in these lists, and when the list is drawn up with reference to electrolysis in neutral or acid solution, the metals follow each other in the order of their affinity for oxygen. From what was stated with regard to the use of metals as battery plates, it will be obvious that that metal which has least affinity for oxygen, and is, therefore, least readily attacked by acids, will generally be best suited for the resistant plate in a cell. 330 IONISATION Weare now in a position to appreciate better the nature of the electrolytic dissociation or ionisation which obtains in most solutions. Since the elec- tricity is conveyed by the ions to the electrodes it follows that the conduc- tivity of the liquid will be proportional to (a) the number of ions in 1 unit volume ; (b) the charges carried by the ions; (c) the velocity with which the ions move, 4.e. their mobility ; (d) the reciprocal of the potential gradient ; the latter being the fall in voltage over each unit distance between the electrodes. If the potential gradient is the same, determination of the conductivity will throw light on the magnitude of the other factors. In order to avoid polarisation, alternating currents are employed in conductivity measurements, the general arrangement being that of Wheatstone’s bridge (Fig. 221). Tis a very small induction coil worked by a cingle Leclanché cell ; the current passes to a and divides there into one portion through abe and another through adc, both returning ogether from cto I. But some current will a a pass through the telephone receiver, T, be- I tween b and d, and cause a buzzing or singing + noise, unless the resistances in the system are such that ab: b¢::ad:cd. In ab a suitable resistance is provided by the resistance box, R ; in be is placed the electrolytic cell, E, containing the liquid to be investigated ; cda is the usual slide-wire of the bridge, the two resistances, cd, da, being proportional to the lengths and adjusted by moving the contact piece, d, until no sound is emitted by the telephone. The resistances in ab, cd, da being thus determined, that of the liquid in the cell in be can be calculated ; bc = ab x cd/ad. The temperature must be constant and the positions of the electrodes the same through the whole series of experiments to be compared. The cells usually hold only a few cubic centimetres and are very various in form. If the passage of an electric current through an electrolyte depends upon the presence of ions, a saline solution should offer a lower resistance to this passage the more perfect the ionisation of the dissolved salt. Hence the conductivity of a dilute solution, in which ionisation is more perfect, should be proportionally better than that of one which is stronger, and therefore less ionised. This is found to be the case ; as the dilution of a saline solution is increased the conductivity tends to become constant. Judging by conductivity, ionisation appears to be practically complete when 1 gram-equivalent of a salt is dissolved in 1000 litres of water ; the degree of ionisation at any other dilution is equal to the ratio of the molecular conductivity (the conduc- tivity calculated, from the observed value, for a solution containing 1 gram-molecule per litre) at this dilution to the molecular conductivity at a dilution of 1000 litres. This statement only applies to good electrolytes ; poor electrolytes do not attain a constant conductivity at any dilution at which it is practicable to make the necessary measurements. The degree of ionisation may also be calculated from measurements of osmotic pressure, for this is proportional to the ionisation. If N be the number of ultimate particles present when the osmotic pressure is P, and Nt the number when it is Pt, then P: P! = N: N!. The number of ultimate particles present at any degree of ionisa- tion depends on the nature of the dissolved substance ; for this may split up into n ions: in the case of H,SO,, n = 3; in-the case of KyFeCy,, n = 5. If ionisation were complete, the original number of molecules, N, would become nN. Let x be the frac- tion of the total number of molecules ionised, then 1 — x will be the fraction left un- ionised, The total number of unionised molecules will be N(1 — x), and Na will be ionised. But Na molecules become nNz ions, so that the total number of ultimate particles in the ionised solution will be N(1 — x) + nNa, and this is the value of N! Pi —P Pay It is found in many cases that during electrolysis the concentration of the electro- in the above equation. Therefore P: P! = N:N(1 — 2a) + nNa. Whence x = ELECTROLYTES 331 lyte at the anode (or cathode) becomes greater than that at the cathode (or anode). This can only be explained by assuming that the anions (or cations) move faster through the liquid than the cations (or anions) do. This difference in the rate of migration of the ions is also indicated by the fact that the conductivity of solutions containing equivalent quantities of various salts which are ionised in the same degree is different. When a solution of KCl is electrolysed, the concentration at the electrodes remains practically the same, so that the ions of K and Cl move at nearly the same rate ; but the equivalent conductivity of NaCl solution of equivalent strength is only about 65 per cent. of that of KCl solution ; hence the sodium ion must migrate at only 65 per cent. of the speed of the potassium ion. The solutions of all substances which are electrolytes show abnormal osmotic pressures, abnormal depressions of the freezing-point, &c. This supports the theory that many salts, acids, and bases are dissociated when they are dissolved. It must be remembered, however, that the dissociation is always into ions, and not necessarily of the same character as the dissocia- tion effected by heat ; nor is it always in accordance with what might be expected from the chemical formula, e.g. H,S —+ H’ + SH’, which, how- ever, is comparable with H,O—~ H' + OH’. Again, 2CdI, probably ionises into Cd’’ and CdIj’. Complex ions frequently result from the reaction of two or more salts to form a complex salt, e.g. K,Fe(CN),— 4K’ + Fe(CN),’” (cf. p. 93). See also the Cobalt Compounds, p. 458. On the other hand, a double salt on dissolution breaks up into the ions of its components, e.g. K,SO,, MgSO, —> 2K’ + Mg’’ + 280,’ (cf. p. 98). It has been shown that the solute generally unites with a portion of the solvent (p. 324), and it is natural to inquire whether there is any similar combination of solvent with ions. Such has been demonstrated from a study of transfer and other measurements, and the degree to which hydration of tons occurs can be determined. The theory of ionisation affords the best explanation of chemical reactions in solution. The analytical tests for metals and acid radicles are the re- actions of the ions, e.g. 2Ag’ + 2NO; + Ca’’ + 2Cl’ = 2AgCl + 2NO’; + Ca" *; or, representing the hydration of the ions, 2Ag’ .nH,O + 2NO’;.pH,0 + Ca’’.gH,O + 2Cl’.rH,O = 2AgCl + Ca’“gH,O + 2NO3pH,O + 2(n + 7) H,O. If a reaction occurs in a dilute solution which will not occur in a strong one it is because there are no ions in the strong solution, the salt not having been ionised therein. It is supposed that those solutions which are not electrolytes contain no ionised molecules ; thus, sugar, a solution of which is not an electrolyte, does not suffer ionisation when dissolved. Non-aqueous solutions as a class are not good conductors of electricity ; but in a few, e.g. liquefied ammonia, liquefied sulphur dioxide, hydrocyanic acid, ionisation of salts occurs equally well as in water. The nature of the ionisation is not always the same as in water. Fused salts conduct electricity very well with separation of the metal at the cathode (see p. 375). There are other theories of solution. For example, Armstrong seeks to explain the phenomena of aqueous solution without assumption of ionisa- tion. He considers water to be a complex mixture of active molecules— which are either monad “ hydrone,”’ H,0, or “ hydronol ” (hydrone-hydrol), H HOC —and inactive molecules consisting of ‘‘ polyhydrones ”’ or asso- OH H,O — OH,, H,0 — OH, ciated molecules, e.g. H,O : OH,, Sy | | . That water OH, H,0 — OH, consists of such complexes has already been referred to (p. 317). 332 EFFECT OF SOLVENTS He contends that dissolution involves associative and distributive changes in the molecules of the solvent which are necessary precursors of all chemical interchanges effected in such solutions. There is a constant play amongst the molecules, (H,O)n = nH,O. The influence of this lends itselfto the formation of such complexes as, in the case of HCl, H H (a) HOC (6) HO (c) H,O : CIE; Cl OH and it is to be noticed how the “ residual affinity” of the negative elements becomes operative; and how in the active form (a) Cl has only one valency satisfied, and in (b) O has only two, leaving in each case the other valencies open to action. In the closed system (c) the two extra valencies of both Cl and O are satisfied, and the complex remains inactive until it is modified into one of the others. Presumably an equilibrium amongst these forms would establish itself. The reader is referred to Armstrong’s papers in the Proceedings of the Royal Society for 1907, 1908; also to Washburn’s papers (on ionic principles) in the Technology Quarterly, vol. xxi., for detailed discussion of the theories advanced by the two chief schools, Werner’s ideas on the constitution of inorganic compounds also contribute to the study of solution ; see p. 353. From what has been said above on the theory of solution and the evidence in support ot it, it will be seen that a solvent has an effect upon a soluble substance which may be well compared with the effect of heat on a volatile substance. Just as there are many substances which resist in a high degree the disgregating action of heat, so there are many which resist that of solvents. Equally noteworthy is the similarity which exists between the influence of solvents and of heat on chemical change: reactions occur between substances in solution which have no tendency to happen between the solid substances, however finely these may be divided and however intimately they may be mixed ; so, also, reactions occur at an elevated temperature which are impos- sible at low temperatures. It is also worth while to call attention to the fact that the presence of the best solvent, water, will enable a smaller stress to convert the potential energy of a mixture into the kinetic energy represented by the combination of its constituents than would otherwise be the case ; thus, as has been already stated, a mixture of carbon monoxide and oxygen requires a far greater stress in the form of high-pressure heat (high temperature) to start combination when it is perfectly dry than when moisture is present. Many cases have been cited in which the presence of water enables a chemical change to be brought about by heat of moderate temperature, e.g. the combustion of carbon (p. 58); there is not sufficient evidence to show whether or not the stress of a much higher temperature will render these changes, also, independent of moisture. There are, however, many changes, which are capable of occurring at the ordinary temperature, that are dependent on the presence of water. It is also a fact that many substances which are excellent electrolytes when dissolved in water have an almost infinite electrical resistance when anhydrous ; in other words, these substances require the presence of water in order that they may become partially ionised. On the basis of this latter observation it has been suggested that an electrolytic medium, that is, one in which ionisation has occurred, is essential for chemical change; on this hypo- thesis the fact that anhydrous HCl will not attack calcium oxide would be explained by stating that it is only the ions of HCl which can enter into reaction with CaO. A very little water should suffice for the reaction, since, when the first formed ions have been removed by reaction with the CaO, further ionisation could occur. The discovery of other third substances which shall have a similar influence to that of water is of interest to the chemist ;! anhydrous ammonia may be cited as an example. 1 A tendency to return to the old view that chemical energy is to be regarded as due to a difference of electrical potential between elements seems at present prevalent, and it must be admitted that support for such a view is derived from the observations of Baker, who shows that when electrodes, carrying high-pressure electricity, are introduced into a mixture of hydrogen and oxygen, sufficiently dry to hinder combination, the gas around the “ positive ” electrode is richer in oxygen than that around the opposite electrode. COLLOIDAL SOLUTIONS 333 As a final word on this subject, attention must be called to the fact that high heat pressure and high electrical pressure are not alone in inducing chemical change ; it has been shown that high mechanical pressure is in many cases effective (such as in decomposing moist silver chloride), and the influence of another form of energy, the shorter wave-lengths of light, in inducing the numerous changes on which the art of photography depends, is well known. Colloidal Solutions are those which contain in true or in pseudo- solution substances which dialyse either not at all or only extremely slowly. Such substances, ‘‘ colloids,” are usually amorphous (see p. 281), and exert an extremely small osmotic pressure. Gelatin or glue (cdAAa, glue, hence the name “colloid,” glue-like), albumen, starch, dextrin, are colloids ; but also various substances, such as many of the elements, Au, Ag, S, Se, B ; oxides, SiO, (p. 281), ZrO (p. 492); sulphides, As,S, (p. 233), can assume the colloidal state. Many colloidal solutions consist of the solvent and the “ sol’ (hydrosol if in water) in the form of such extremely minute particles that they are not removable by filter-paper and may not settle out even in the course of months or years. The particles are not visible under the most powerful microscope, but their number, nature, and ‘‘ brownian ’”’ movement can be studied with the wltramicroscope. In this the light from an electric are is concentrated to the highest intensity on the particles in the solution, so that the light reflected by the particles is sufficient to become visible through a microscope. E.g.1c.c. of a colloidal solution containing 0-08 mgm. ZrO was found to contain 14,000,000,000 particles. Frequently the particles are in an electrically charged state, and in a suitable cell are attracted towards the corresponding electrode ; also they are precipitated by a colloidal solution having a charge of the opposite sign. With most electrolytes the speed of precipitation of the colloid (e.g. ZrO) is a function of the atomic weight of the metal in the added electrolyte, but regularities of different order are observed in other cases. The sols of Pt, Au, &c., show a catalytic activity similar to that of some enzymes, and like the latter they are rendered inactive by the presence of substances which are poisonous to living organisms. The solid obtained on evaporation is still a “‘sol’’ if it again forms the colloidal solution on mixing with the solvent, or a “gel”’ (hydrogel if from water) otherwise. (c) SOLIDS. When a gas assumes the liquid state there is no abrupt alteration, but a continuous passage from one into the other (p. 35); but when a gas or liquid is solidified the change is much more sharply defined, and there is a strong demarcation between the properties of the fluid and those of the solid. While general distinctions are clear enough, there is no definition which quite satisfactorily divides fluids from solids. Glass, which is amor- phous, has properties usually associated with liquids, while some liquids contain ‘liquid crystals’ (p. 337) and so are comparable with solids. Solids may be conveniently classified into (a) amorphous (auopgoc, shapeless), having no crystalline structure; and (b) crystalline (xevaTtaAXog, ice, crystal), solid matter in its most perfectly developed and organised form. A crystal is a more or less symmetrical, geometrical solid, commonly bounded by plane surfaces, called planes or faces. The terms used to describe crystals are those generally employed in geometry and in the same sense ; the study of the subject is termed crystallography. Systematic study of amorphous solids is difficult and not much is known of the relationship between the properties of their molecules and those of their larger masses, but those which form “ colloidal solutions” (supra) 334 SOLIDS are amenable to closer investigation. Very fruitful has been the attention paid to crystalline solids. Although one of the typical properties of a solid is rigidity, there can be no doubt that its molecules are in a state of motion, but very different from that in the case of a liquid. That there is some movement follows from diffusion phenomena ; e.g. if pieces of lead and gold are left in contact for a term of years, traces of each will be found to have diffused into the other. Again, the changes at ordinary temperatures of monoclinic into rhombic sulphur, and of ordinary tin into grey tin, imply considerable molecular agitation which may be regarded as limited to a species of oscillation. At one time the impression prevailed that the molecules in a solid do not fill the whole space occupied by the body, that there is in fact much empty space; but at the present time the emphasis is on the other alternative ; indeed, some are disposed to the view that there is no vacant space at all in a solid, or even ina liquid. With regard to the latter it has been shown already how closely the volume of a liquid under ordinary conditions approximates the limiting volume (p. 310). There would thus appear to be no such condition as porosity of the solid substance itself ; while even permeability (p. 98) is probably dependent on some chemical property. Richards ! (see also p. 567) has studied the compressibility of solids, which is smaller than in the case of liquids, and has arrived at the conclusion that the atoms themselves are compressible, and that the slight diminution in volume, which occurs under great pressure, is not a measure of a reduction of interatomic space as formerly supposed. He finds also that the formation of a compound of a compressible element is attended with greater decrease in volume than the formation of a similar compound of a less compressible element, other things being equal. This premises that the satisfying of each valence of an atom would cause a depression on the atomic surface, owing to the pressure exerted by the affinity at that spot. The shape of an atom is not known, but it answers most, if not all, purposes’ to imagine it to be spherical ; also perfectly elastic and capable of impressions, like a solid india-rubber ball (see also p. 335). It is a fair assumption that every known solid has at some time in some way been deposited from a fluid phase. Metals were molten, minerals were once liquid per se or in solution, vegetable and animal tissues have been deposited from solution, while others have been condensed from the vaporous state. In the liquid phase their molecules were without great attraction for one another, so that they were free to assume that shape produced by their own internal forces ; in general, that configuration which occupies least space. At temperatures not far removed from that at which some solid could separate, mutual influence increases, so that the molecules are apt to associate, forming groups, which perhaps do not arrange themselves together in any special manner ; but molecules may arrange themselves so definitely as to form “ liquid crystals’ (p. 337). It is probable that such an arranging process in the liquid immediately precedes the act of actual crystallisation when the solid phase of any crystallisable substance is assumed. In the former case, where such arrangement does not occur the separated solid is amorphous, and then the sharp line of demarcation between liquid and solid disappears. The process of crystallisation involves a close-packing of the molecules into a homogeneous assemblage of perfectly definite geometrical form. Constraining forces act in certain directions in each molecule so that the molecules fit closely against each neighbour and build up the crystal; thus ‘the whole of the volume occupied by a crystalline structure is partitioned into polyhedra, which lie packed together in such a manner as to fill the ' See Faraday Lecture, 1911, by Prof. T. W. Richards, of Harvard, U.S.A STEREOCHEMISTRY 335 whole of the volume without interstices.” Now since the crystal has the same geometrical properties whatever its size, it is conceivable that a single molecule in the crystal is distorted or deformed to assume the same shape as the crystal, although the form is not necessarily the same when the constraining forces are removed, for instance, when the crystal is melted or dissolved. ‘‘ The varying amount of deformation which has to be effected in the molecules of different substances during crystallisation may well be a responsible factor in determining the very different speeds of crystallisation observed amongst chemical substances.” But since the deformation is conceived to be but slight, it follows that the form of an independent molecule is not very different from that of the crystal it has helped to “build up, and that the relative arrangement of the atoms in the molecule suffers no change. Hence, every molecule has some stereometric (orepedc, solid) properties, t.e. it has an arrangement of the atoms, in consequence of which it exhibits various properties which are specific and perfectly definite, though not necessarily equal, in each of the three dimensions of space. Barlow and Pope conceive that within the molecule “each chemical atom present in a compound occupies a distinct portion of space by virtue of an influence which it exerts uniformly in every direction.” The subject, Stereochemistry, is as wide as chemistry itself, but the term is used with special reference to the study of those compounds which exhibit optical properties, and of isomers whose differing constitution finds explanation on no other hypothesis (p. 633, &c.). Ordinary salts and the like are not often the subject of stereo- chemical investigation, but Tutton makes the following observations on potassium sulphate. The length of the vertical axis of the crystal is a function of the metal, and the dimensions of the equatorial plane are con- K trolled by the sulphur or its analogue (see p. 300) ; whence it would | ‘appear that the 2 atoms of potassium lie on the vertical axis, while the O sulphur occupies a central position. This conforms with the structural a. formula usually accepted, as shown in the margin. The changes re- ae ferred to on p. 300 also demonstrate that specific atoms and their i; chemical substituents are definitely localised in the architecture of the molecule. It thus becomes possible to study the mechanics of A the molecules through observations of their crystal aggregates. Barlow and Pope! employ the geometrical conception not only to explain crystal structure, but also to find a geometrical basis for the study of valency. They assume that valency is a function of the relative volume of the sphere of atomic influence in the given molecule, so that in the Periodic Table (p. 8) an atom of any element in a given vertical column, or group, occupies approximately the same volume, but in a given hori- zontal series the volume occupied by an atom is propor- tional to the valency ; thus a calcium atom occupies the same volume as a strontium atom, but twice the volume of a potassium atom and two-thirds the volume of an aluminium atom. They give the following picture of the benzene, CyHg, molecule and of the close-packing of the molecules to form a crystal, There are 6 atoms of carbon of valency 4 and there- fore of volume 4, and 6 atoms of hydrogen of valency 1 and therefore of volume 1. They are to be so arranged as to harmonise with the chemical properties of benzene and to be able to aggregate into the form of a benzene crystal without undue deformation. Six spheres each of volume 4 (carbon) are placed in con- tact so that their centres lie at the apices of a regular octahedron (Fig. 222) ; six spheres each of volume 1 (hydrogen) (not shown in figure) are then placed in six of the eight similar hollows lying round the octahedral group in such a manner that the two un- occupied hollows are diametrically opposite each other. The molecules are then piled vertically so that the large and small spheres are sym- metrically alternated. Columns thus built up are placed in contact side by side, all + See papers by Barlow and Pope, Jour. Chem. Soc. 1906, T; 1675. Fic. 222. 336 CRYSTALLOGRAPHY being similarly orientated. The contiguous molecules are at slightly different levels to enable close-packing. It is assumed that a general pressure set up by the constraining forces brings about a still closer packing and some contraction, causing a slight dis- tortion or deformation of the molecules, and so eliminating more or less completely interstitial spaces. Crystallography (pp. 38 to 41, 299, 334) has become an exact and extensive science, and a subject of paramount interest to the chemist. Crystal form is becoming more and more identified with chemical constitution. As we have seen already, the beautiful symmetry of crystal architecture is but an expression of the equally well-defined stereometry of the molecule. There are seven styles or systems of symmetry (cupmerpia, due proportion), and they are analysed into two elements of symmetry, viz. planes of symmetry and axes of symmetry. The former implies that a plane can be described in a crystal, such that symmetry on its two sides obtains with respect both to the number of faces on the two sides of the plane of symmetry and to the magnitude of the angles between every face and each other face next to it. The angular measurements are made with a gonio- meter (ywria, a corner). In the ideal case the forms of the parts on the two sides of the plane of symmetry bear to one another the relationship of object and image, as in a mirror. But the relative sizes of the faces are not con- sidered in the definition ; hence, unless the crystal is more or less true to the ideal, the symmetry is often not at once evident. An axis of symmetry is the line of intersection of two or more planes of symmetry. Just as the parts about a plane of symmetry are repeated by reflection, as in a mirror, so parts may be repeated by rotation about an axis. (os When a crystal has to be rotated through 180° in order to present an exactly similar figure as it does in the first position (Fig. 223a), it has a digonal axis of symmetry, ie 4 or an axis of twofold symmetry, for two Fig. 223. such rotations bring the crystal back to identity and not merely to similarity. When a rotation of 120° suffices for similarity (Fig. 2236), and three such rotations are necessary for identity, the axis is trigonal ; when four rotations of 90° obtain, tetragonal (Fig. 223c) ; when six rotations of 60°, hexagonal. The seven crystal systems are: (1) Cubic, having three equal axes at right angles to each other (Fig. 224). The normal group includes the cube or hexahedron, the cubic octahedron, and as a form of lower symmetry the éetra- hedron. (2) Tetragonal, with two equal and one unequal rectangular axes of symmetry. (3) Rhombic, having three unequal rectangular axes of sym- metry. (4) Monoclinic, having one plane of symmetry and one axis of digonal symmetry. Of the-three unequal axes, two only are at right angles. (5) Triclinic, having neither planes nor axes of symmetry, but there may be symmetry about a central point. (6) T'rigonal or rhombohedral, charac- terised by a single trigonal axis of symmetry. The essential forms have the habit of the rhombohedron, which is a polyhedron bounded by six equal rhombuses. (7) Hexagonal, having a single hexagonal axis of symmetry. Each system includes several classes, the total for the seven systems amounting to 32, e.g. there are prismatic, pyramidal, octahedral, and other forms in the various systems.! : The student is advised to prepare specimens of crystals for himself. Place a cover- glass over 1 or 2 drops of a slightly supersaturated solution of the substance on a micro- 1 Want of space forbids giving more than an outline of this extremely interesting subject. The works of Tutton, ‘‘ Crystals’ (popular) or ‘ Crystallography and Practical Crystal Measurement’ (comprehensive), should be consulted. THE PHASE RULE 337 scope slip, and when crystallisation has started examine under a low-power ; or a good pocket lens may suffice. Precipitates, sublimates, &c., obtained in the course of ordinary laboratory work will generally afford most interesting and instructive results. The thermal and optical properties of a crystal are usually different along its several axes, Liquid crystals or flowing crystals (pp. 333, 334) have been observed by Lehmann and others in cholesterol acetate, para-azoxy-anisoil, ammonium oleate, and several Fic. 224. other liquids, especially in those whose chemical structure is that of a long chain. The substance possesses all the mechanical properties of a liquid, but the liquid shows double refraction as a solid crystal does ; and hence the molecules have marshalled themselves into some definite arrangement, such as that obtaining in an ordinary crystal ; e.g. para-azoxy-anisoil melts at 114° to a turbid liquid which exhibits strong double refraction. At 134-1° the turbidity and double refraction suddenly disappear, accompanied by increase in volume ; but in either state its molecular weight corre- sponds with the simple formula, so that there is no association. THE PHASE RULE In the foregoing chapters several instances have been noticed where some phenomenon or process arrives at a state of equilibrium and the whole system remains entirely unchanged so long as the conditions are unaltered. For example, when water is introduced into the Torricellian vacuum, the mercury falls through a certain height due to the pressure of the water vapour, which is perfectly definite, and no variation in the height of the mercury occurs as long as the prevailing temperature suffers no change. Equilibrium is established ; and this independently of the volume, whether absolute or relative, either of the water or of the vapour, so long as some liquid water remains. On raising the temperature, the equilibrium is disturbed, the amount of vapour per unit volume is increased, and the mercury falls still further until equilibrium is restored (p. 33). This is a physical instance, but in the dissociation of calcium carbonate (p. 347) equilibrium is attained on a chemical reaction arriving at a state of balance, i.e. when, at the prevailing temperature and pressure, as much CaCO, is formed from CaO and CO, in unit time as CaCO, is dissociated in the same time. In either case, the conditions of equilibrium may be studied by aid 22 338 PHASES—COMPONENTS of the Phase Rule; and it may be well to warn the reader at once that the phase rule has nothing to do with systems which are in a state of change it operates only while there is equilibrium. The phase rule applies to cases of equilibrium in heterogeneous systems, i.e. in systems where there are two or more physically distinct and mechani- cally separable portions called phases. The phases themselves are homogeneous, i.e. each possesses in every part of itself identical physical and chemical properties, though it need not be homogeneous in the chemical sense ; a mixture of gases or a solution may constitute a phase. The six phases mentioned above, ice, water, steam, CaCO,, CaO, COs, are all physi- cally distinct and mechanically separable, but each is itself homogeneous. The components of a system are chosen from among the constituents or substances composing the phases, but their numbers are not usually equal. In the system, ice—water—steam, there is only one component, H,0; in the system, CaCO,;—CaO—CO,, there are only two, CaO and CO,. In systems containing Na,SO,—Na,SO,.7H,0—Na,80,.10H,0— solutions of these—H,0, there are only two components, Na,SO, and H,0. There may be several ways of determining the number of components, but the required number is the least possible, which can be used to express the composition of the several phases. Again, in a system containing the sulphates and chlorides of sodium and potassium in aqueous solution there are four (not five) components ; for suppose there to be sufficient Na to take up all the SO, (or all the Cl), the components are Na,SO,, NaCl, KCl, H,O (or NaCl, Na,SO,, K,SO,, H,O). The number of components has nothing to do with the chemical distribution. The phases of a system are subject to three independently variable factors: temperature, pressure, concentration (variation in “‘ concentra- tion’ very frequently signifies variation in composition of a phase). The variability of a system, or the number of these variables which may be varied without disturbing equilibrium, is the number of the degrees of freedom. The Phase Rule of Willard Gibbs (about 1878) is expressed in the equation P+ F—=C+ 2, or F=C+ 2 —P, where P is the number of phases, F the number of degrees of freedom, and C the number of components. In the system there is (are) the system is expressed by Ice—water—vapour no degree(s) of freedom ;_ non-variant = z - i 4G 2528 Ice—water ; or ice— CH1P=2 vapour ;orwater— } 1 ss a univariant { ~ “1 a ey vapour Bet Bs Rae ane Ice; or water;or BS vy ‘C=1,P=1 vapour sj 2 a a paraae { - F=14+2-1=2 CaCO,—Ca0—COn, sd, » — univariant [O~ BPS The phase rule may appear arbitrary, but it was worked out by Gibbs in conformity with the laws of thermodynamics and has proved very useful in studying similarities and dissimilarities of all kinds of systems in equili- brium and opened the way for discovering new properties of the substances concerned. It has also received application in technical chemistry, as in discovering the conditions for separating the salts of the Stassfurt deposits. Some typical examples will now be considered. (a) Systems of one component.—(a) Water. The phase rule is applicable to the equilibrium represented by any point on the curves on p. 35; e.g. in the vapour- pressure curve, C= 1, P= 2,..F=1+4+2—2=1, i.e. the system is univariant. Under ordinary circumstances at 0° a new phase (ice) appears, and the system, becomes TRIPLE POINT 339 non-variant: F=1+2—3=0. The gaseous phase, however, is not chemically homogencous, and its pressure is derived from 4-58 mm. due to vapour pressure and 755-42 mm. due to air (that is, assuming the normal pressure). As the pressure of the air is accidental and variable, it is desirable to eliminate it. When this is done, the pressure being 1 atmosphere less, ice melts at 0-00745° (p. 33), and the vapour then exerts a pressure of 4-60 mm. (the vapour pressure of ice is the same as that of water at this temperature ; see also p. 34). The saturated vapour, water, and ice are all at the same time in equilibrium ; and so water may be seen to freeze and boil simul- taneously in the same vessel—a phenomenon which may be observed in some forms of ice-making machinery (p. 80). Curves may be drawn representing (a) vapour pressures of water, ST (Fig. 225); (6) vapour pressures of ice, HT ; (c) liquefaction pressures of ice, IT; also (d) the vapour pressures of supercooled water, TX, which is a con- tinuation of that, ST, at higher temperatures. The figure is diagrammatic and not drawn to scale. The point, T, representing the above-named temperature and pressure where the three phases (p. 338) of water are in equilibrium is called the Triple Point. A study of the curves will show that, starting from this point, any increase of pressure causes water to form, ice melts, and vapour is condensed ; decrease of pressure brings Pressure x Hee e Temperature __ Temperature Fic. 225. Fie. 226. Triple point curve of water, a substance which Triple point curve of a substance which expands on solidifying. contracts on solidifying. about vaporisation, so also does increase of temperature ; lowering of temperature causes ice formation. Water is exceptional in having its melting-point lowered by pressure. Usually the maximum density of a substance in the liquid state is at its melting-point and it con- tracts on solidification ; pressure raises the melting-point and stability of the liquid state is not possible at temperatures below that of the triple point ; compare Figs. 225 and 226, observing how the melting curve rises towards the left in the former, indica- ting reduction of melting-point by increase of pressure, while in the latter the rise towards the right signifies the reverse effect. Under a pressure of 1 atmosphere, paraffin wax melts at 46-3° ” ”? 85 ” ” 2”? 48-9° $5 SS 100 Fe #3 a 49-9° 3 - 1 5 sulphur » 116° ” ” 519 2? 9 ” 136-2° » ss; 192 0 » » —- 141-5° (b) Sulphur.—There are several allotropic modifications of this element (p. 148), and a discussion of them in the light of the phase rule is of peculiar interest. Ordinary sulphur consists of rhombic octahedral crystals which melt at 115°. It exerts a very small vapour pressure represented by the vapour-pressure curve, AF (Fig. 227), the dotted portion of which, OF, indicates that rhombic sulphur is metastable between 95-6° and 115°. Butif the rhombic crystals are kept for an hour or two at any temperature between 95-6° and 115°, they change their crystalline form and become monoclinic ; where- upon, if the change is complete, they do not melt below 120°. GB is the vapour-pressure curve of solid monoclinic sulphur, the dotted portion, GO, signifying that monoclinic sulphur is not stable below 95:6°. Both rhombic and monoclinic sulphur are stable at 95-6°, the Transition Point, which marks the limit of stability between two 340 PHASES OF SULPHUR systems ; but below this only the rhombic, above only the monoclinic, is stable. At 95-6° they both have the same vapour pressure, so that O is a triple point comparable with Tin Fig. 225 ; the chief distinction from the latter is that the phases are solid— solid—vapour, instead, of solid—liquid —vapour. FC is the vapour-pressure curve of liquid sulphur, the dotted portion, FB, indicating instability between 115° and 120°. If the investigation is conducted under greatly increased pressure, the transition occurs at a higher tempera- ture and the two melting-points are - also raised, until when the pressure is 1288 atmospheres all three tempera- tures coincide at 151°. OD represents the variation of the transition point, FD the change of melting-point of rhombic sulphur, and BD that of monoclinic sulphur with rise of pressure. At still higher pressures — | rhombic sulphur alone is stable, as shown by DE, which is a prolongation of the rhombic sulphur line, FD. The following Tables display the Rhombree Pa TCSSUPEC | 1 w56 7510" ‘ar Temperature Fig. 227. chief features as expressed by the phase rule; Areas—Bivariant systems. C=1,P=1,...F= 2. AODE Rhombic EDBC Liquid OBD Monoclinic AOBC Vapour. Curves—Univariant systems. C=1,P=2,..F=1. OD Rhombic, monoclinic BD Monoclinic, liquid DE, (FD) Rhombic, liquid OB, (OG) Monoclinic, vapour AO, (OF) Rhombic, vapour BC, (FB) Liquid, vapour. Triple points—Non-variant systems. C=1,P=3,..F=0. D Rhombic, monoclinic, liquid (F) Rhombic, liquid, vapour O BRhombic, monoclinic, vapour B. Monoclinic, liquid, vapour. (c) Tin, (d) Phosphorus, are capable of similar treatment. Reluctance to form new phases, when the formation becomes possible, is very common; but it obtains with reference to the first appearance only of the new phase ; e.g. the transition of rhombic into monoclinic sulphur does not occur readily just above 95-6° until some of the new phase has been formed or introduced. Air-free water may be heated above 100° without boiling until a bubble of steam, however small, has formed in the liquid ; then equilibrium is established with violent rapidity, giving rise to the well-known phenomenon of “ bumping.” Supercooled water and supersaturated solutions, pending the introduction of a suitable crystal, exhibit the same restraint. The phase existing under these strained conditions, before the new phase appears, is in a metastable condition (uera, change). (3) Systems of two components.—In accordance with the phase rule, P+ F=C +2, F is greater than before, since for the same number of phases C = 2 instead of 1. The third variable, ‘‘ concentration ” of the components, becomes operative. Disso- ciation affords many examples in point (pp. 314, 345). (a) Ammonium chloride is a good instance (p. 314). When dissociated per seit con- stitutes two phases in a one-component system, for the concentration is the same whether undissociated solid or dissociated vapour. But when an excess of one of the constituents is present it becomes a two-component system, however it is expressed ; (a) nNH, + mHCl; (b) »NH,Cl + mHCl; (c) nNH,Cl + mNH;; (d) nNH,Cl- mNH,; (e) nNH,Cl — mHCl. In any case the least number of components is two. Any of the pairs may be used, but the first is chosen as the simplest and it avoids negative formule. CHEMICAL ENERGY 341 (5) Phosphorus pentachloride (p. 346), (c) calciwm carbonate (p. 347), are other examples which might be considered here. (¢) Chlorine Hydrate.—Where there are two components in a system, three phases may be in equilibrium at different temperatures: C = 2,P = 3,..F=2+2—3=1; but when the two components are in four phases, only one condition of equili- brium is possible: C = 2, P= 4,... F=0. Such a case is presented by the two components, chlorine and water. Chlorine hydrate separates at 9-6° C. if the pressure of the chlorine is that of the atmosphere ; by raising the pressure, the temperature at which the hydrate separates is raised, and a new temperature is established at each pressure ; this is an interdependence similar to that in the case of evaporation, that is to say, the three-phase system Cl,—Cl.4H,O—H,0 is in equilibrium at different temperatures. As soon, however, as ice begins to separate (at 0-24° C.) a fourth phase is introduced, and equilibrium between the four is possible only at this temperature, the pressure being 244 mm. (e) Cryohydrates (xpvoc, frost)—When a solution of common salt is cooled well below 0° a hydrate, NaCl.2H,0, crystallises out ; and on further reducing the .tem- _ perature these crystals continue to separate, until at — 22° the whole solidifies as one mass, without any simultaneous thermal change. The definiteness of the temperature, the “cryohydric point,” and the fact that the result is attained without regard to the strength of the solution used, led Guthrie to believe that he had discovered in this and many similar instances a new series of definite hydrates ; but more recent research with the microscope has shown these “ cryohydrates ” to be mixtures of saline and ice crystals. At the cryohydric point there is a non-variant system of four phases, salt— ice—solution—vapour: F=2+4+2-—4=0. (y) Systems of three components. See Iron and Steam (p. 343). Several examples of the phase rule arise in the next few pages. THE MEASUREMENT OF CHEMICAL ENERGY. The direct measurement of chemical energy is not at present possible, for as yet no unit thereof has been defined (p. 12). Its capacity factor appears to be the known chemical equivalent, and the intensity factor the “chemical affinity ” or “‘ chemical intensity,” of which we have but little quantitative knowledge. Probably chemical energy is best compared with potential energy, for it appears to depend upon the position of the matter in which it resides. Thus a mixture of hydrogen and oxygen may be said to possess a potential energy due to the position of close proximity of the mole- cules ; for, just as the potential energy of a stone on the edge of a cliff requires an impulse in order to convert it into another form of energy—the kinetic energy of its fall to the foot of the cliff—so the potential energy of a mixture of hydrogen and oxygen requires an impulse, such as the heat of an electric spark, in order to convert it into another form of energy—heat energy. ; The potential energy of a stone on a cliff is measured by multiplying the force which impels the stone to fall to the foot of the cliff by the space through which it has to fall, so that potential energy = force x space. It is not necessary to know the force impelling the stone to fall, or the space through which it falls, in order to ascertain the potential energy of a stone on a cliff. If the stone be allowed to fall, and steps be taken to receive it in such a manner that all the heat generated by its impact with the earth is measured, then, by the principle of the Conservation of Energy1 (p. 12), the potential energy can be calculated from this heat, which is exactly equivalent to it. (The mechanical equivalent of heat is: 1 gram-unit of heat = the energy represented by 1 gram falling through 42,350 centimetres. ) It should be equally possible to measure the chemical energy of a mixture of hydrogen with oxygen by ascertaining the quantity of heat evolved during the combination of the gases, and although this method would not necessarily measure the chemical 1 This principle may be expressed thus: In any space the total quantity of energy remains the same, although the energy may be transferred from one part of the space to another, or transformed from one kind of energy into another. An example of the principle is furnished by the firing of a mixture of H, + Oina vessel from which loss of heat is impossible. There is the same quantity of energy in the vessel before the explosion and after it, but after the explosion the energy is in the form of heat energy instead of chemical energy. 342 REVERSIBLE REACTIONS energy of the hydrogen uniting with the oxygen, yet the value obtained would probably be proportional to this energy. Whether a reaction will occur or not depends on the difference between the inten- sity factors, i.e. between the chemical affinities, of the various substances present ; just as the fall of the stone depends on whether there is any difference between the height of the stone and that of the place to which it may fall. There are two methods by which a force may be directly measured: (1) A force of known magnitude may be brought into opposition with the force to be measured in such a manner that the two are in equilibrium. The two forces will then be equal. Such a method may be called a static method, and would be employed if a force of known value were brought to bear upon a falling stone so as to bring it to rest ; the force of the stone would then be equal to the opposing force. (2) By measuring the velocity of a moving mass in successive seconds, the force impelling the motion is measured by the change which occurs in this velocity. This may be called a kinetic method. The attempts which have been made to measure chemical affinity involve methods analogous to these two methods of measuring dynamical force. The attempt to measure the chemical energy of chemical reactions by ascertaining their heat changes, and thus to obtain measurements which may be regarded as proportional to chemical affinity, has been made to a much greater extent than have attempts to apply the static or the kinetic method ; the measurement of chemical energy by measuring thermal changes will be considered under Thermochemistry, p. 347. Static Method of measuring Chemical Energy.—For practical purposes chemical reactions may be classified into complete and reversible reactions. The former class includes those changes in which the whole of the reacting substances is converted into the products of the reaction ; for example, when a mixture of equal volumes of H, and Cl, is fired, the two gases combine completely and are entirely converted into HCl. A reversible reaction is of such a nature that the products of the reaction will, under a slight alteration of conditions, react with each other to re-form the original substances. Thus, when steam and iron are heated together (p. 21), a reaction expressed by the equation 3Fe + 4H,O = Fe,0, + 4H, _ occurs ; but it is equally true that when hydrogen and Fe,0, are heated together the reaction Fe,0, + 4H, = 4H,O + 3Fe occurs. Now either of these reactions may be carried to approximate completion under certain conditions ; thus by passing steam over red-hot iron the whole of the iron ‘can be converted into Fe,0,; so also by passing hydrogen over Fe,O, at the same temperature the whole of this can be reduced to metallic iron. But if iron and steam be heated together in a closed vessel, the iron will never be completely oxidised. This is because the reaction is reversible— that is to say, as soon as any Fe,0, and H are produced these tend to react with each other to form H,O and Fe; in other words, the reaction 3Fe + 4H,O = Fe,0, + 4H, can occur in either direction at the same time, a fact expressed by the substitution of = for = in the equation. It hag been seen, however, that by passing steam over red-hot iron the latter can be completely oxidised—that is to say, the equation 3Fe + 4H,0= Fe,0, + 4H, can be realised. This is only possible because one of the products of the reaction (the hydrogen) is in such a physical condition that it can be removed from the sphere of action (the tube in which the reaction is performed) ; indeed, for the complete oxidation of the iron a large excess of steam over that indicated as necessary by the equation (72 parts of steam for 168 parts of iron) must be passed through the apparatus containing the iron in order to sweep away the hydrogen. If the hydrogen could not be removed in this manner, the completion of the reaction would be impossible. The same remarks, mutatis mutandis, apply to the complete reduction of Fe,0, by hydrogen. A reversible reaction can become complete only when one of the products MASS ACTION 343 of the reaction is removed from the sphere of action. Under any other conditions the vessel in which the reaction is proceeding will contain some of each of the reacting substances, and some of each of the products of the reaction. The question naturally arises, When iron and steam are heated in a closed vessel, so that nothing can escape from the sphere of avtion, how far will the reaction proceed ? How much iron oxide and hydrogen will be produced ? How much steam and iron will be left 2 Fully to appreciate the state of the case it must be realised that both the reactions expressed by the equation 3Fe + 4H,0 = Fe,0, + 4H, are proceeding at the same time and during the whole time, and that if the temperature be kept constant a period will soon be reached when the amount of iron oxidised per unit time will be exactly equivalent to the amount of iron oxide reduced per unit time. When this state of affairs prevails the equation in the direction repre- sented by the arrow —~, which may conveniently be termed the equation representing the positive change, will be realised to exactly the same extent as the equation represented by the arrow <— (the negative change) is realised, per second. This is called the equilibrium stage of the reversible reaction, and when it is attained an analysis of the contents of the vessel will show the same proportions of iron, steam, iron oxide, and hydrogen to be present, however long the vessel is maintained at the same temperature. An altera- tion in the temperature will cause an alteration in the extent to which either the positive or negative change will occur per second ; so that with every such change of temperature a new equilibrium stage will be established, and an analysis will show new proportions between the quantities of the four substances present. There is another factor besides temperature which influences the quantity of each of the substances present at the equilibrium stage of a reversible reaction. This is the mass of any one of the substances. Thus, if iron and steam be heated in the proportion represented by the equation (168 parts of iron: 72 parts of steam) at any given temperature, exactly the same quantities of iron oxide and hydrogen will be produced as would remain undecomposed if iron oxide and hydrogen were heated in the proportion represented by the equation (232 parts of Fe,0,: 8 parts of hydrogen), at the same temperature. If the proportion of either of the constituents on the left hand of the equation be increased, the positive change will have occurred to a greater extent—that is, more Fe,0, and H, will have been produced—when the equilibrium stage is reached than was the case with the former proportion. If the proportion of either of the substances on the right hand of the equation be increased, the negative change will occur to a greater extent than before. Since Fe and Fe,0, are solids, while hydrogen and steam are gases, the system is in this case heterogeneous, and of the four substances only the H,O and H can intermix. Hence, here, an altera- tion of the proportion of Fe or Fe,0, has but little effect upon the change. According to the phase rule, there are here three components, Fe—O—H, and three phases, Fe—Fe,0,—gaseous mixture (H and H,0); hence C=3,P =3,..F = 2, ie. the system is bivariant. This mass action is of great importance in chemical change, and may be generally expressed by stating that in a homogeneous system chemical change is proportional to the active mass of each of the substances taking part in the reaction. By active mass is meant the number of molecules of the substance in unit volume, such as gram-molecules per litre. From a practical point of view mass action frequently influences chemical change, a large mass compensating a feeble affinity, it being possible for reactions to proceed 344 COEFFICIENTS OF AFFINITY which, considering the relative affinities, could not occur unless one of the products were sufficiently insoluble to be removed from the homogeneous system. Such a case will be met in the description of the manufacture of caustic soda, where the compara- tively feeble affinity of lime for CO, is nevertheless sufficient to allow the reaction NagCO, + Ca(OH), = 2NaOH + CaCO, to occur in solution, because the CaCO, immediately separates from the liquid and the reaction in the left-hand direction cannot, in consequence, occur so rapidly as that in the right-hand direction. Nevertheless care must be taken that the active mass of the NaOH does not increase too much, for then even the precipitated CaCO, will be attacked to reproduce Na,CO; and Ca(OH).. In other words, the solution must not be too concentrated. It is not difficult to imagine the mechanism of this mass action ; the greater the number of molecules in a given space the more frequently will they come into contact with each other, and, since chemical change appears to occur only between molecules in contact, the greater will be the amount of chemical change induced. In the case of steam and red-hot iron, it is obvious that the greater the number of steam molecules present, the more frequently these will come into contact with the iron, and the more oxide of iron, and consequently hydrogen, will be produced. Compare also ammonium chloride, p. 346. The subject of dissociation furnishes numerous examples of mass action. The chemical equilibrium between two opposing reactions, such as those concerned in the action of steam on red-hot iron, should serve as a static method for determining chemical energy. For the equilibrium is between two chemical affinities, the one tending to produce the positive change, the other tending to produce the negative change ; and the amount of each change must be proportional to the affinity which produces it ; so that by analytically determining the quantities of substances present, and therefore the extent of the reaction at the equilibrium stage, it should be possible to form a comparison between these affinities. The action of steam on red-hot iron does not lend itself to the application of this method, as the system is heterogeneous. But a number of double decompositions has been studied from this point of view; théy are reversible reactions and are mostly between organic compounds, so that in this place it will be useful to express them by the general form AB + CD== AC + BD. The opposing forces which bring about the equilibrium. of such a change are the sum of the affinities of A for C and B for D (say &) against the sum of the affinities of A for B and C for D (say k’). The amount of chemical change which has occurred at the equilibrium stage is proportional to the active masses of the reacting substances, and, presumably, also to these coefficients of affinity, k and k’. The amount of chemical change can be measured by chemical analysis. Suppose AB and CD be mixed in the proportion of 1 gram-molecule of each ; then, when equilibrium has been attained, there will be present a fraction of a gram- molecule of AC, BD, AB, and CD respectively ; and the fraction will be the same for AC and for BD, and also the same for AB and CD. Let this fraction of AC and BD be x, then that of AB and CD must be 1 — 2, for 1 gram-molecule was originally taken. The active masses of AC and BD, tending to produce the negative change, are x and «x, and their total effect may be represented as xz or x. The affinity tending to produce the negative change is k’, so that the total force producing the negative change is k’ x, The active masses of AB and CD are 1 — x and 1 — 2, and the affinity is k ; there- fore the total force tending to produce the positive change is k(1 — x)?. When the equilibrium stage is reached these two forces are equal to each other, whence k(1 — x)? = k’x? or k/k’ = x?/(1 — ~)®. Thus the ratio k/k’ can be determined, for x is determinable by analysis. For example, when acetic acid and ethyl alcohol are heated together, ethyl acetate and water are produced, the reaction being reversible. When 2: is determined (after no more change appears to occur), it is found to be 2, whence, by the above formula, k/k’ = 4. By this static method the relative affinity, avidity, or ‘* strength” of acids for bases has been determined. The principle of the method is to mix equivalent quantities of two acids with a quantity of base insufficient to saturate both, and to determine what AVIDITY OF ACIDS 345 proportion of the base each acid will acquire. Thus, when NaOH (one equivalent) is mixed with HNO, and }H,SO, (of each, one equivalent), « equivalents (here, « = #) of the soda combine with the nitric acid and 1 — x equivalent (here, 1 — x = 4) with the sulphuric acid, showing that the avidity, &, of the nitric acid is twice as great as that, k’, of the sulphuric acid. If the avidity of nitric acid be taken as 1, that of sulphuric acid is 0-5; for k/h’ = 2?/(1 — a2)? = 4/1... a/(1 — x) = 2/1. The avidity of an acid may be defined as the proportion of base which that acid will appropriate when equivalent quantities of the acid, a base, and HNO, are mixed in aqueous solution. It is independent of the nature of the base. The following order of avidities is probably correct: HNO,;=1; HCl=1; HBr=0-89; HI=0-79; H,SO, = 0-5. Thus, in solutions of equivalent concentration, HNO, and HCl must be accounted stronger acids than H,SO, ; but the greater volatility of the first two will enable H,SO, to expel them when heated with their salts. One method of experimental determination of avidity is to compare the heats of neutralisation. Thus if q, calories be the quantity of heat evolved when one equivalent of the acid HA, is neutralised by one equivalent of NaOH (hence q, is the “ heat of neutralisation” of HA,), and similarly q, for the acid HA, ; then if one equivalent of each HA,, HA,, and NaOH be mixed, x equivalent of the NaOH will unite with HA, and 1 — x equivalent with HA,, and the evolution of heat will be Q calories ; then Q = xq, + (1 —)q,, whence « = (Q — q@)/(q; —Q). This should be carefully contrasted and compared with the method for determining the basicity of an acid by heat of neutralisation (p. 90). Another method (kinetic) is given below. Kinetic Method of measuring Chemical Energy.—This method of measuring chemical affinity consists in determining the amount of chemical change which occurs in unit time, not waiting for equilibrium to occur. This value is termed the coefficient of velocity of the change, and the greater this coefficient of velocity the greater the force inducing the change. Most changes are too rapid for any determination of the coefficient of velocity, but in the class of changes known as hydrolysis (p. 224) such a measurement is possible because the change occurs with only moderate rapidity in the presence of an acid Thus, when cane-sugar is boiled with water it is very slowly converted into invert sugar; Cy2Ho.0) + HOH = 2C,H,,0,; but in the presence of a dilute acid the change is much more rapid, and can be measured by determining the amount of invert sugar produced. The action of the acid is not understood, but is generally ascribed to a predisposing affinity of the acid for the invert sugar ; this means that the invert sugar is the more readily produced because of the tendency which the acid has to form an unstable compound with it ; such a compound must be soon decomposed again, because to all appearances the same amount of free acid remains in the solution after the hydro- lysis as was there before. Different acids have a different influence on the rate of the hydrolysis of cane- sugar, &c., and it is reasonable to suppose that this rapidity of action is in some way proportional to the avidity of the acid. By determining the velocity of hydrolysis— that is, the amount of cane-sugar which has been hydrolysed per minute—when different acids are present, the avidities of the acids may be compared. The mathematical calculations involved are somewhat complex, and cannot be discussed here. The method yields values for the avidities of acids which are in the same order of magnitude as those determined by the thermochemical method. A little consideration of the definition of Dissociation (p. 188) will show that that phenomenon belongs to the same class as the reversible re- actions, such as the action of steam on red-hot iron discussed above. When ammonium chloride is heated to a given temperature in an evacuated space, it will vaporise and dissociate until it exerts a pressure, 1 Recently, certain phenomena have been noted which seem to indicate that dissociation of a compound can occur in the reverse sense to that usually observed, namely, as the compound cools. The behaviour of Tgthenium tetroxide (g.v.) may be cited as an example. Further search for phenomena of this kina is needed. 346 DISSOCIATION the dissociation pressure which is definite for equilibrium at that tempera- ture. But if one of the products of dissociation—either HCl or NH;—be introduced, the volume remaining unchanged, dissociation will be retarded. For suppose there to be in unit volume ” molecules of NH, and n molecules of HCl. Hach molecule of NH, has » chances of meeting and combining with a molecule of HCl in unit time, but » molecules of NH, have this chance ; hence there are n? chances of the formation of an NH,Cl molecule in unit time ; and since there is equilibrium the same number of molecules of NH,Cl are dissociated into NH, and HCl in the same time. I a further n molecules of HCl be introduced into the same space, other things being equal, the chances of association are doubled, while the rate of dissociation remains unchanged; hence the Degree of Dissociation, %.e. the ratio of the dissociated portion to the whole of the given substance in the state of vapour, is decreased. The contemplation of the case of phosphorus pentachloride will render this more evident. When this compound is heated above 300° it dissociates to a very large extent into PCl, + Cl,, a fact discovered by attempting to deter- mine the vapour density of PCl;. The amount of dissociation depends on the temperature and on the active masses of the substances present. The equili- brium between the positive and negative changes of the reversible reaction PCl, — PCl, + Cl, occurs when the same quantity of PCl, is dissociated and associated in unit time, and this will vary for every temperature. Since PCl;, PCl;, Cl, each represents 2 vols., the total active mass tending to produce the negative change is twice as great as the active mass tending to produce the positive change. If the vessel containing the three substances at the equilibrium stage be diminished in size—that is, if the pressure be increased—the active masses of all three will be increased ; for there will now be more of each in unit volume. Suppose the pressure to have been trebled, the active mass of each will have been trebled ; but the negative change is proportional to the active masses of PCl, and Cl,, so that it will have become ninefold, whilst the positive change is dependent only on the active mass of the PCI, and will therefore have been trebled only. Conse- quently the negative change will predominate over the positive change, and a new equilibrium will be established—in other words, the dissociation will be diminished. Similar reasoning may be applied to all cases of the dissocia- tion of gases, when it will be found that if the products of dissociation have a larger total volume than the volume of the substance undergoing dissocia- tion, an increase of pressure will diminish the dissociation, whilst a diminution of pressure will increase it. The effect of introducing one of the products of the dissociation into the vessel at the equilibrium stage would be to increase the active mass of that product and to increase the negative change—that is to cause associa- tion. Thus, if PCl, were introduced there would immediately be a reproduc- tion of PCl;. Advantage may be taken of this to prevent dissociation from becoming apparent ; for instance, if PCl; be heated in a vessel containing PCl,, dissociation will not be manifest untila much higher temperature than when PCI, is heated alone. The extent to which PCI, has undergone dissociation is calculated from the observed vapour density. Let x be the percentage of molecules which have undergone disso- ciation ; then 100 — x is the percentage still associated. But the x molecules have become 2x molecules when dissociated. Therefore 100 molecules have become 100 — a + 2x = 100 + x molecules after partial dissociation, so that the volume is increased in the ratio 100 :100 +. The vapour density, however, has decreased inversely to the volume. If d be the vapour density before, and D that after, partial 100 (d — D) dissociation, then 100: 100 + 2::D:dorz= ——_ . THERMOCHEMISTRY 347 The phenomena associated with evaporation and the law of partial pressures exhibit much similarity to those described above (see p. 79). The case of the dissociation of calcium carbonate by heat is closely analogous to that of evaporation. The reversible change CaCO, 2. CaO + CO, reaches equilibrium when the pressure of the CO, has attained a certain value depending on the temperature. Since the pressure of the CO, is a measure of the weight of it in unit volume, the equilibrium is reached when the product, CO,, has a certain active mass dependent on the tempera- ture. Thus at 740° the equilibrium pressure is 255 mm., and when this has been attained no further dissociation can occur ; if the calcium carbonate be heated in a vessel exposed to the open air, the CO, will gradually diffuse away and its partial pressure will be reduced below 255 mm., so that the change will continue. By exposing the heated mass to a draught of air, the admixture of the CO, with the surrounding atmosphere, and therefore the completion of the dissociation, will be more rapid. I£ the pressure of the CO, be not allowed to rise to 255 mm., the complete conversion of CaCO, to CaO can be effected at a correspondingly lower temperature. Thermochemistry (p. 12).—The prime object of the study is to obtain relative measurements of the changes in chemical energy accompany- ing reactions. But, more widely, it properly includes the study of specific heats (pp. 298, 311), thermal change occurring on allotropic modification (p. 149), heats of hydration (pp. 38, 325), dilution, ionisation, dissolution, &c. (p. 325), so far as they are related to the chemical nature of the substances concerned. Heat of neutralisation (p. 345) and heat of combustion are clearly comprehended in the prime object. Attention has been called in the preceding pages to some of the principles of thermochemistry, but they may aptly be summarised here. (1) Every chemical change is accompanied by a thermal change, which is a constant quantity. (2) The thermal change occurring during the combination of elements to form a compound is called the heat of formation of the compound. It is generally a positive quantity—that is, heat is evolved: the compound is exothermic. Sometimes, however, it is a negative quantity—that is, heat is absorbed: the compound is endothermic. (3) The thermal change occur- ring during the decomposition of a compound is called the heat of decomposi- tion of the compound. (4) The heat of decomposition of a compound is identical with, but of opposite sign to, the heat of formation of that com- ound. The last proposition follows from the principle of the conservation of energy (see footnote, p. 341). The potential energy of a mixture of elements js lost to the system in the form of heat energy when the elements combine ; and in order that the elements may be again imbued with the same potential energy, heat energy or some other form of energy must be restored to the system. @ The measurement of the thermal changes of chemical reactions is effected by causing the reaction to occur in a closed apparatus, a calorimeter, such as that described at p. 276. The heat of formation of a compound is expressed thus : H,Cl = 22,000, meaning that the combination of 1 gram of hydrogen with 35:5 grams of chlorine evolves 22,000 gram-units of heat. Again, N,O, = — 7700 means that when 14 grams of nitrogen combine with 32 grams of oxygen 7700 gram-units of heat are absorbed. Again, H,0,SO; = 21,320 means that when 18 grams of water combine with 80 grams of SO, 21,320 gram-units of heat are evolved. The heat of decomposition is expressed similarly, but with reversed signs, thus: — H,Cl = — 22,000; — N,O, = + 7700. The value obtained in a calorimeter for the thermal change of a reaction i 348 THERMOCHEMICAL DATA is not necessarily the thermal change due to that chemical reaction whose heat is to be measured. Allowance must frequently be made for secondary chemical reactions and for changes of physical state. Two examples may be quoted in order to make this clear : (1) 80 grams of SO, were mixed with a large excess of water (the quantity being known) with the view of ascertaining the thermal change 803,H,0. The value obtained was 39,177; but this obviously includes two thermal changes: (a) that due to the combination of 80 grams of SO, with 18 grams of H,0, and (b) that due to the combina- tion of the H,SO, produced with an excess of water. When sulphuric acid is diluted with water in a calorimeter, it is found that heat continues to be evolved until the weight of water amounts to about thirty-six times that of the sulphuric acid (corre- sponding with the formula H,SO,.200H,O) ; this thermal change amounts to 17,857 gram-units per 98 grams of H,SO,, and must be subtracted from that observed on mixing 80 grams of SO, with a large excess of water in order to arrive at the value S03,H,0. This now becomes 21,320. A similar action of excess of water has to be taken into account in many cases, and it is customary to use the symbol Aq for such an excess. Thus, SO3,Aq = 39,177 means that when SO, is dissolved in so much water that the addition of a further quantity will produce no further thermal change, 39,177 gram-units of heat are evolved. (2) 0-1 gram of hydrogen and 0-8 gram of oxygen were mixed and fired in a calori- meter, the final temperature of which was 20°. The gram-units of heat evolved by the reaction (calculated from the rise of temperature) amounted to 3418, This corresponds with H,,0 = 68,360. But since we know of at least three sources from which this thermal change is derived, this value cannot be regarded as expressing the amount of heat energy equivalent to the chemical energy of the combination. The first source is the chemical energy of the combination. The second and third sources are due to the change of aggregation which occurs after the gases have combined. The steam produced by the combination of H, + O occupies two-thirds of the volume previously occupied by the mixed gases ; now the contraction of the volume of a gas always involves a transformation of some of the kinetic energy of the gas into heat energy ; in other words, heat is evolved by the contraction. It is unreasonable to suppose that the condensation of H, + O into steam is an exception to this rule, so that the heat evolved by this condensation must be allowed for in the present case ; a value for it, however, can only be calculated when the kinetic energy of the molecules of hydrogen and oxygen and that of the molecules of steam are known. The method by which these kinetic energies are calculated cannot be given here ; suffice it to say that the difference between the kinetic energy of 18 grams of H, + O and that of 18 grams of steam has been calculated to be equivalent to 193 gram-units of heat. Of much greater importance than the above item is the difference between the kinetic energies of steam molecules at 100° and water molecules at the same tempera- ture. This difference is well known, and is expressed by the heat of condensation of steam. One gram of steam at 100° evolves 536-5 gram-units of heat in becoming water at 100°. Therefore 18 grams will evolve 9666 gram-units. In the calorimeter the water formed by the reaction does not remain at 100°, but cools to 20° before the temperature of the outside water in the calorimeter is measured. In cooling from 100° to 20°, 1 gram of water loses 80 gram-units of heat (supposing that the specific heat of water is constant over this range of temperature) ; therefore 18 grams of water lose 1440 gram-units. From these remarks it will be seen that of the total 68,360 gram-units evolved by the reaction in the calorimeter, 11,299 are due to the changes of aggregation, namely, 193 to the contraction of H, + O to steam, 9666 to the condensation of the steam to - water at 100°, and 1440 to the cooling of water from 100° to 20°. By deducting these 11,299 units from the total, 57,061 gram-units are obtained as the thermal equivalent of the potential chemical energy of a mixture of hydrogen and oxygen, rendered kinetic by the combination, It must be remembered that even when every allowance has been made for such secondary reactions and such changes of aggregation, it is by no means certain that the thermal value obtained represents the energy of DETERMINATION OF HEATS OF FORMATION 349 combination of the atoms concerned in the chemical change. If the hypothesis be adopted that the molecules of hydrogen and oxygen, for example, must be separated into their constituent atoms before combination can occur, it must be admitted that some energy is absorbed in this preliminary process. This energy will become potential in the atoms, and may or may not be completely rendered kinetic, and therefore evolved as heat, when the atoms combine to form molecules of water. Thus it may happen that the heat evolved in the combination of hydrogen and oxygen is only the excess of that due to the combination of the atoms of H and O over that absorbed by the decomposition of the molecules of H and O into atoms. It will be obvious, however, that for all practical purposes, such as for the calculation of the calorific value of a gaseous fuel (see Fuel), the calorimetrical value for the combination of hydrogen and oxygen is a perfectly correct one, inasmuch as the gases employed in the experiment are in the same condition as those used in practice. The heat of formation of many compounds cannot be directly deter- mined because the compounds are not formed by the direct combinations of their elements. In such cases the value is calculated by methods which can receive but short notice here. The principle underlying one of these methods is that the thermal change of any reaction in which a compound AB is concerned must be smaller or greater! than the thermal change of a reaction, having the same products, in which the constituents A and B are concerned, by the heat of formation of AB. For example, the combustion of CH, is ther- mally expressed thus: CH,,0, = 211,930 gram-units ; but it is supposed that the mechanism of this combustion consists in the decomposition of CH, into its elements, which are then burnt, and it will be at once evident that in the two reactions, CH, + O, = CO, + 2H,O and C+ H,+ 0,= CO, + 2H,0, the heat evolved in the latter will differ from that evolved in the former by an amount representing the heat of decomposition of CH,. Now C,0, = 96,960 gram-units when solid carbon is burnt, and H,,0, = 136,720 gram-units for gaseous hydrogen; therefore (C + H,),0,= 96,960 + 136,720 = 233,680 gram-units. But CH,,0, = 211,930, that is, the heat of combustion of the constituents of CH, exceeds that of CH, itself by 21,750; consequently CH, must have absorbed this amount of heat in being decomposed into its elements before these were burnt. Thus it is concluded that marsh-gas is an exothermic compound, and that C,H, = 21,750 gram-units, supposing that the gas were produced from solid carbon and gaseous hydrogen. Another instance : N,O cannot be formed directly from its elements, but the heat of combustion of carbon in the gas is easily determined, and it is found that the reaction C + 2N,0 = CO, + N, evolves 133,900 gram- units. Now this reaction involves the decomposition of 2N,O and the formation of CO,, so that the heat evolved should be smaller or greater than that evolved in the reaction of C + O, = CO, by the heat of decomposition of 2N,0. Since C,O, = 96,960, the heat of decomposition of 2N,0 must be 133,900 — 96,960 = 36,940 gram-units, and that of N,O must be 18,470 gram-units ; in other words, nitrous oxide evolves heat in its decomposition, and is therefore an endothermic compound, or N,,O = — 18,470. Another method for indirectly determining the heat of formation of a compound depends upon the fact that the total energy change in a reaction is the same whether the reaction occurs in one stage or in several. This is only an application of the principle of the conservation of energy; the total energy of a stone falling to the earth is the same whether the fall occur 1 According as AB is exothermic or endothermic. 350 APPLICATION OF THERMOCHEMICAL DATA in one stage or in several. An example of the method is furnished by the determination of the heat of formation of H,SO,. This compound cannot be made from its elements directly, but the heat of the reaction H,O + SO, + O = H,SO, is determinable, and that of H, + O = H,0, and of 8 + 0, = SO,, are well known. The total heat evolved in the Gonmaiial of H, 50, will be the same whether the change is in one stage, H, + S + 0, = H,SO ne or in three, viz. (1) H, + O=H,0 + 68,360 ; (2) 8S + 0, = S80, + 71,080 ; (3) H,O + SO, + 0 = H,SO, + 53,480 ; consequently H,,8,0, = 68,360 + 71,080 + 53,480 = 192,920. From what has been said, it will be apparent that the thermal changes of chemical reactions, as they are at present determined, cannot be regarded with certainty as equivalent to the total chemical energy concerned in the reaction. They cannot, therefore, be said to be an absolute measure of the chemical affinity of elements for each other. Nevertheless, the thermochemical data which have been accumulated, and are to be found in most books of chemical constants, are useful aids to the chemist when it is remembered (1) that endothermic reactions rarely occur save by the application of external energy (generally applied in the form of heat energy); (2) that of two exothermic reactions, that is more likely to occur, under ordinary conditions, which is the more exothermic ; and (3) that of two exothermic compounds that which is the more exothermic is the more stable. For example, it is seen from the thermal values Ca,O = 132,000 and C,O, = 96,960 that it is not probable that carbon will reduce CaO at any but a very high temperature ; for the reaction 2CaO + C = CO, + Ca, is highly endothermic, since it involves the heat of decomposition of 2CaO ( — 264,000), and the heat of formation of CO,, leaving a balance of — 167,040 gram-units. As a fact the reaction does not occur at any temperature hitherto attained, for although in the manufacture of calcium carbide reduction of CaO may be said to occur, it must be aided by the affinity of Ca for C at the high temperature used. Again, in any competition between chlorine and bromine for hydrogen, chlorine may be expected to prevail, for H,Cl = 22,000 and H,Br = 13,500. HCl is the more stable of these two because it is the more exothermic. In attempting to use thermal data as a guide for prophesying what will occur in a chemical reaction, it must not be forgotten that they have nearly all been determined at an initial and final temperature of about 20°, and are true only for the elements in their usual condition at this temperature. There is no reason to suppose that the thermal change at a high temperature is the same as it isat 20°. Thus it has been shown that the heat formation of hydrogen iodide is negative at low temperatures, but positive at 400°. Structural arrangement of the atoms within the molecuie influences the heat of formation, e.g. ethylamine (NH,CH,CH,), 92-53 cals. ; dimethyl- amine (CH,.NH.CH,), 87:74; again, in the three C,;H,O compounds, dimethyl ketone (CH,.CO.CH,), 172-40; propionic aldehyde (CH;.CH,. CHO), 168-93; allyl alcohol (CH, : CH.CH,OH), 144-89. But where no great structural difference exists the heats of formation of isomers are the same, eg. ethylene dichloride (CH,Cl.CH,Cl), 296-36; ethylidene chloride (CH,.CHCIl,), 296-41 ; showing the four valencies of carbon to be identical. The union of two carbon atoms by simple or double bonds is exothermic, but by triple bonds, as in acetylene, endothermic. Magneto-chemistry.—During the past few years it has been recognised that some connection exists between the magnetic properties of compounds and their chemical constitution! Passing by the metals iron, cobalt and nickel, the magnetic oxides of iron (Fe,0,) and chromium (Cr,;O,) have long been known. It has now been shown that these and other similar mixed oxides owe their magnetism to the presence of a metallo-acid group » See ‘‘ Magnetochemie,” by E. Wedekind, Berlin, 1911. . VALENCY 351 in combination with a basic oxide, e.g. in the ferrites, FeO. Fe,0,; CoO. Fe,05. Manganese, which per se is not magnetic, forms strongly magnetic com- pounds, especially in trivalent combinations. Manganese mono-boride, MnB, is not only strongly magnetic, but is capable of considerable permanent magnetism, 7.e. magnetic needles may be made of it. On the other hand, the diboride, MnB,, has no marked magnetic properties. Manganese nitrides are magnetic, so also MnP, MnAs, MnSb, MnBi. The magnetisability of compounds of a particular element varies inversely as the valency exerted by the element, e.g. VO is much more magnetic than V,O;. Solid and liquid oxygen and ozone are magnetic (q.v.). P. Weiss has enunciated a ‘‘ magneton” theory comparable with the electron theory. Molecular Structure, Valency.—In previous pages the chemical nature of a substance has been studied so far that its composition and its molecular weight have been determined. A large number of properties have also been discussed, and it now remains to consider how a formula can be derived which will display all the facts which have been ascertained and harmonise with the general conceptions of the atomic theory. This subject is of para- mount importance in organic chemistry, and such examples will be discussed when dealing with that branch. In inorganic chemistry it has not been of so great interest from the practical standpoint to know the precise structure of a molecule, and there are peculiar difficulties in ascertaining the atomic arrangement, but the subject is one of the chief questions at the present time ; it becomes so in seeking to arrive at the distribution of valencies in a molecule. The definition of valency already given (p. 12) conveys the general idea of valency, and no difficulty is experienced while dealing with many of the simplest formule, but when molecular magnitude and various reactions are considered doubt frequently arises. For instance, if the formula of ferric chloride be FeCl,, Fe is clearly trivalent; but if Fe,Cl,, Fe may be tetravalent, thus Cl,Fe:FeCl,. Experimentally it is found that the vapour density corresponds with FeCl, at high, and Fe,Cl, at low, temperatures. However, the latter can be explained on the assumption that two molecules of FeCl, associate by bringing into play the auxiliary valencies of the chlorine Cl = Cl atoms, thus Fe/ Cl = CL\Fe, so maintaining the trivalency of ferric Sal = cl” iron. By “auxiliary ” valencies is understood the valencies of which the atom is capable, other than the “ principal” valencies which it exercises in the ordinary way. ; Variation in valency has been amply exemplified by the halogens ; and it is somewhat curious to find them combining inter se in proportions other than atom to atom, e.g. IF;, ICl,; but a similar condition prevails in the sulphur group. It is, therefore, important to keep an open mind with regard to the valency of a particular atom in a molecule, remembering that the same atom has auxiliary valencies as well as principal. But, as with all other chemical theory, it is imperative to ascertain the valency by experimental investigation, in this case by determination of the arrange- ment of the atoms in the molecule or by other known principles, and not to assign valencies arbitrarily or by speculation. The structure of a molecule generally includes one or more groups which are common to several related substances, and can be transferred by well- known methods. Sulphuric acid, for example, can be derived in several ways from sulphur dioxide, and in many reactions it eliminates this gas, so that a group composed of 1 atom of sulphur and 2 atoms of oxygen 352 MOLECULAR STRUCTURE probably forms an integral part in sulphuric acid. There is no reason to suppose any difference between the values of the 2 oxygen atoms in SO,, so that the structural formula may be written O = 8 = O, in which 8 is tetravalent, as it is in many other compounds, and O divalent. The arrange- ment S=O=0O, though equally satisfactory from the standpoint of valency, implies a difference in properties of the 2 oxygen atoms and an instability which is contrary to experience (cf. H, = O = O, p. 144). SO, will combine with Cl, forming SO,Cl,, or with O forming SO. There is no reason to suppose any essential difference between the third O O and either of the first two O atoms, whence the formula \gZ ; 8S O becoming hexavalent, as it is in SF, (p. 177), according with its position in the periodic classification. Nevertheless there would appear to exist a state of strain, for one of the oxygens is easily lost or attacked. A special configuration, instead of one in a single plane, affords some explanation. The six valencies of sulphur may be assumed to be regularly arranged as the axes of an octahedron : OH a Meyers Fig. 228. (a) represents SO,, (b) SO,Cl,, (c) and (c’) SO3, (d) H,SO,. The stereo metric arrangement of (a), (6), and (d) receives experimental support in the case of the alkali salts (p. 335). That H,SO, contains two OH groups is indicated analytically in the usual way, viz. by reaction with PCl;, when SO,Cl, is produced, i.e. 20H have given place to 2Cl. Hence H,SO, contains one SO, group and two OH groups, therefore its constitutional formula is SO,(0H)p. f In the example on p. 307, Na,SO,,H,) was deduced. On heating the crystalline substance it gives up 55-9 percent. of its weight of water (H,O = 18), leaving 44-1 per cent. of a white solid whose empirical formula is Na,SO, (= 142); whence the formula of the first substance is 55-9 /18 = 3:103 H,O + 44-:1/142 = 0-3103 Na,SO,, or Na,SO,.10H,O. On allowing the anhydrous powder (44:1 parts) and the necessary water (55-9 parts) to combine, the clear crystals are reproduced. Evidently the water— water of crystallisation—is much more loosely bound to the Na,SO, than are the elements in the latter bound together. Both Na,SO, and H,O are saturated compounds, 7.e. all the principal valencies of each atom have been engaged. The question arises as to how such molecules can combine to form new complexes. Are they as molecules bound to one another ? or do the molecules open up in some way, allowing the atoms to rearrange themselves into a new single complex ? Such problems are engaging much attention at the present time. We have seen that water of crystallisation is not only very easily driven off, but that it exists in such a form that it has the same specific gravity and the same specific heat as ice ; therefore deep penetration into the saline molecule is not indicated. Probably the two combine by the oxygen becoming tetravalent, just as in the complexes of water itself. THE SPECTROSCOPE 353 Ammonia and water behave very similarly in many respects and are frequently found in association or exchangeable inter se. Werner gives the following series of salts, all of which are known excepting the sixth : H,0 (H,0) (H20 [Cr(NHg).}Cle [Gr 20 Jot, [ore Jo. Lora Ja, (H20)4 (H,0 Lotti Jes [oN [Os [Cx(H,0), ICs Spectroscopy.—Heated solids have their molecules vibrating in so many phases that they give rise to waves in the luminiferous ether which are of every possible wave-length ; consequently a heated solid gives a continuous spectrum in which the red is more prominent at lower tempera- tures. Heated gases, on the other hand, have their molecules vibrating in such a way that they give out waves of comparatively few wave-lengths. By passing the light emitted from a hot gas through a prism the wave- lengths are separated and take up their proper positions in the spectrum— i.e. somewhere in the violet, indigo, blue, green, yellow, orange, red—in accordance with the length of the wave between the limits 766 millionths of a millimetre for red, and 396 millionths of a millimetre for violet. Of all the wave-lengths from a given gas a few will be more visible than -the rest; so that there are characteristic lines in the spectrum for the gas of each element. Thus heated sodium vapour gives rise to two very prominent wave-lengths (589-5 and 588-9 millionths of a millimetre) which give the sensation of yellow light. When the white light emanating from an ordinary flame is allowed to pass through the narrow slit at the end of the collimator of a spectroscope Fic. 229. (Fig. 229),1 and is transmitted through a prism of flint glass, a continuous spectrum composed of overlapping images of the slit in all the colours which make up white light will be perceived through the telescope ; but if a Bunsen flame be employed, all will be dark but for a single bright yellow line in 1 This form of instrument has been found to be well suited to the general work required of a spectroscope in a chemical laboratory. Hither one or two prisms can be used, and the central table is arranged 80 as to take the levelling screws of a reflection grating. The instrument is well adapted for determination of refractive indices and dispersive powers. 23 354 THE SPECTROGRAPH the place where the brightest yellow was seen in the continuous spectrum ; this line is due to the accidental presence of a little sodium in the flame, from the dust in the air, and it becomes very intense if a little sodium chloride be held in the flame on a loop of platinum wire. By comparing the spectra of the flames containing vapours of the metals with a map of the wave-lengths in the solar spectrum (Fig. 230), the exact position of the Violet. Indigo. Blue Grecn. Yellow. Orange. Red. eo OO rrr nnn Oa an a, eigpesed) 3 z . 8 ‘ g§ : = 8 s 5 Be EE OB. g : fs cebf ESE § 3S & "8 eS ss 88 BEE 2 ae 8 3 ‘BEB Fea See SG ge 8 x BES sane 858 4 & & & oad AQ ks Xe ak Na L Kk Fic. 230. various colours may be noted, and thus, if several metals are present in the same flame, they may still be distinguished by the colours and positions of their bright lines. Thus, if a mixture of the chlorides of potassium, sodium, and lithium be taken upon a loop of platinum wire and held in the flame, the dull red line of potassium (K, Fig. 230) is seen close to one end of the spectrum ; at some distance from it the bright red band, L, of lithium ; at about the same distance from this, the pale yellow lithium line ; and close to this the bright yellow sodium lines, Na; whilst near the other end of the spectrum is the feeble violet line of potassium, &. The chlorides of the metals are most suitable for this experiment on account of their volatility. Since a very little vapour (z9y500 mgm. in the case of Na) can be de- tected by its characteristic wave-lengths, the use of the spectroscope furnishes an extremely delicate test for many elements, especially the metals. It is only certain elements which give well-defined flame spectra. But if a compound of any metal, also of certain non-metals, be introduced into an electric arc, an arc spectrum is obtained which, though visible, is often very rich in ultra-violet rays. Indeed, some elements give ultra-violet rays only. To observe these it is necessary to use quartz only for the prism and lenses in the instrument, since glass is too opaque to ultra-violet rays; and since the eye is not sensitive to these rays, the spectrum is photographed, whereby the positions of the lines and their significance are determined. The whole instrument is described as a quartz spectrograph. The character of the spectrum of a gas differs with the temperature and pressure. Increased temperature increases its complexity, the bright lines becoming more numerous and broader. The same effect is produced by increased pressure, which probably increases the collisions between the molecules, and thus gives rise to a larger number of phases of vibration. Thus, H, + O fired in a closed space gives a continuous spectrum. ABSORPTION SPECTRA 355 Hence arises the custom of examining the spectrum of a gas at much diminished pressure in a Geissler tube (Fig. 231). This consists of a tube very much constricted at the middle part of its length and having electrodes of aluminium sealed through the glass. The tube is first exhausted by the air-pump, and then a small quantity of the gas to be examined, sufficient to create a pressure of a few millimetres, is admitted. The electrodes are connected with the terminals of a powerful induction coil, and the spectroscope is directed to the constricted part of the tube for examination of the spectrum of the gas. When the vapour whose spectrum is to be examined is heated by contact with a flame (as in the method for obtaining the spectra of metallic vapours described above), chemical reactions will frequently render the spectrum different from that observed by volatilising the substance and heating the vapour by electric sparks (spark spectrum). Thus, when cupric chloride is introduced into the Bunsen flame, the reducing action of the gases causes the spectrum to contain a blue line / due to cuprous chloride, a green line due to cuprous oxide, and a red | line due to copper, together with the other, fainter lines characteristic of these vapours. Fia. 231, A gas will absorb those wave-lengths from the spectrum which it will itself emit when heated. Thus, if white light be passed through sodium vapour and then through a prism, black lines eee KX J Nana in the position of wave-lengths 589-5 and 588-9 <_ millionths of a millimetre will appear in the Rants spectrum. The black lines in the solar spectrum are Fra. 232. presumed to be due to the light passing through gaseous elements surrounding the sun. Such absorption spectra are also exhibited by some solutions, such as solutions of didymium salts, of blood, and of many dyes. Analytical use may be made of these for identifying the substance in solution. The quartz spectrogragh referred to above has been used also for investigating the absorp- tion spectra of organic liquids. Light is passed through the liquid con- tained in a tube having quartz ends and then through the instrument. The photograph (or spectrogram) shows that rays of certain wave- lengths have been ab- sorbed, and by this means valuable infor- mation relative to the constitution of the com- pound may be derived. Another method for obtaining a character- istic spectrum is to ex- pose the substance in a Fig. 233. vacuous glass bulb (Fig. 232) to a high-pressure electrical discharge (from an induction coil) delivered from two platinum electrodes, attached to wires of the same metal sealed through the glass. Many substances phosphoresce under this treatment, and 356 RADIOACTIVE SUBSTANCES when the light thus emitted is viewed through a spectroscope it exhibits bright bands which serve to identify the substance. A pump capable of creating, ina very short time, a sufficiently high vacuum for the observation of such phosphorescence is shown in Fig. 233. ° RADIOACTIVITY—DISINTEGRATION HYPOTHESIS. The study of the phosphorescence referred to in the preceding paragraph led Crookes some forty years ago to the discovery that when the electric discharge is passed through a highly evacuated space rays (since called cathode rays) proceed at right angles from the cathode in straight lines and cause strong fluorescence where they impinge on the glass walls of the tube. Shadows follow any interposed body, but it was shown that the rays are material and, therefore, not comparable with ordinary light, for they rotate vanes of mica lightly poised inside the tube and show the remarkable property of being deviated by a magnet. Bombardment of any object, even the glass of the tube, by the cathode ray particles results in the absorp- tion of the particles and the causation of pulses of an electro-magnetic nature ; the pulses are known as the X-rays, discovered by Réntgen in 1895. The latter are, therefore, not material; they do not illuminate objects in the ordinary way, but they cause certain substances, notably platino-cyanide of barium, to fluoresce strongly; they affect photographic plates, as is applied in radiography, and ionise gases, as shown by rendering the gases for the time being capable of conducting electricity ; they are not affected by the magnet. In the light of these discoveries Becquerel reinvestigated the fluorescent properties of uranium, placing portions of uranium salts which had been exposed to sunlight in opaque wrappers over a photographic plate, which was thereby affected. But he soon found that this element and its com- pounds emit also other rays which are not connected with fluorescence ; when in fact the uranium has not been exposed to sunlight. A new property of matter, Radioactivity, was thus revealed, and a new era of scientific inquiry opened. Radioactive substances, of which the element radium is especially cha- racteristic, emit several kinds of rays. The (3-rays are material and identical in type with the cathode rays, but they travel at a far higher speed and so have a much greater power of penetrating matter; they are the most powerful of all the rays in affecting photographic plates; they consist of negative electrons, each weighing about z455 of the weight of an atom of hydrogen. The y-rays are similar in properties to the X-rays; they are not material and are not deviated by a magnet; they constitute only a small portion of the total radiation. The a-rays are the most active in ionising air; they consist of particles like the cathode and /3-rays, but exhibit three important differences: (i) They are slightly deviated by a magnet in the opposite direction to the cathode and /3-rays ; (ii) they carry a positive electric charge, whereas the cathode and /3-rays are negatively charged ; (iii) the mass of the particles is about four times as great as that of an atom of hydrogen. 6-rays are similar to (3-rays except that the speed of the particles is only one-fiftieth of that of the S-ray particles. They are all capable of penetrating substances opaque to light, in the following order: y, 3, a, 6. Not only “rays,” but also radioactive disintegration products or ‘‘ emana- tions,’ having the properties of gases, are discharged by the radioactive elements, and they appear to be without electrical charge. The emanations soon lose their radioactivity, half of it in thirty minutes in the case of radium TRANSMUTATION OF ELEMENTS 357 emanation, or in one minute in the case of thorium emanation. They them- selves are in a state of disintegration and ultimately produce helium or some other of the inactive gases. This, then, demonstrates the transmutation of one element into another. Some few instances have now been recorded by Ramsay: Ra — He; Th — He; Ra — Nt; Cu—-Li; Th — C; Zr — OC. But the emanations are also elements, so that a considerable number of cases is known. It is to be noted that in every case an element of high atomic weight yields one of low atomic weight, the very opposite of the medieval dream of transmuting baser elements of low atomic weight into gold of high atomic weight. The new science of radioactivity, the science of the “ephemeral elements,” reveals new vistas for speculation and research. Those elements with which we are familiar are merely those which are stable or are in a state of change so slow that their existence seems eternal. It is outside the scope of this work to do more than introduce these phenomena of radioactivity which reveal the ultimate structure of matter. CHEMISTRY OF THE METALS THE definition of a metal has already been discussed and characteristics of this class of elements considered at p. 7. It will also be noticed that the metals are but little disposed to form combinations with hydrogen ; but that they evince very powerful attraction for the chlorine group of elements, with which they form, as a rule, compounds soluble, without apparent decomposition, in water. ALKALI METAL (FIRST) GROUP Liraitum, Sopium, Porasstum, Rusriprium, Ca&stum, CoPPER, SILvER, GoLp. Of these the first five resemble each other very closely and are considered here. The other three, copper, silver, and gold, have such resemblance to metals of other groups that they are best considered later. POTASSIUM, K = 39.10. Potassium is found in abundance, as potassium chloride and sulphate, in certain salt-mines (see below), and is contained in granite, of which it forms about 5 or 6 per cent. The indispensable alkali, potash, appears to have been originally derived from the granite rocks, where it exists, in com- bination with silica and alumina, in the well-known minerals felspar and mica. These rocks having, in course of time, disintegrated to form soils for the support of plants, the potash has been converted into a soluble state, and has passed into the plants as a necessary portion of their food. In the plant the potash is found to have entered into various forms of combination ; thus most plants contain sulphate and chloride of potassium ; but the greater portion of the potassium exists in the form of salts of certain vegetable acids formed in the plant, and when the latter is burnt these salts are decomposed by the heat, leaving the potassium in the form of carbonate. Potassium Carbonate, or carbonate of potash, K,CO,.—When the ashes of plants are treated with water, the salts of potassium are dissolved, those of calcium and magnesium being left. On separating the aqueous solution and evaporating it to a certain point, a great deal of the potassium sulphate, being much less soluble, is deposited, and the carbonate remains in the solu- tion ; this is evaporated to dryness, when the carbonate is left, mixed with much potassium chloride, and some sulphate ; this mixture was formerly imported from countries where wood (containing about 0-5 per cent. of K,O) is abundant, under the name of potashes, used in the manufacture of soap and glass. The further purified material is known as pearlash, but this is still far.from being pure potassium carbonate, which is now made by first passing CO, through an aqueous solution of potassium chloride at 20° contain- ing magnesium carbonate (the hydrate MgCO,.3H,0 is found to be the most active form for the purpose) : 3MgCO, + 2KCl + CO, + 5H,0 = 2MgKH(CO,),.4H,0 + MgCl. The double carbonate is sparingly soluble, and having been separated from the solution of magnesium chloride, it is then decomposed by warming it with 358 CAUSTIC POTASH 359 water under pressure into K,CO, and] MgCO, (the conditions being carefully selected to obtain the aforesaid hydrate). The solution of K,CO, is sepa- rated from the insoluble MgCO, and evaporated. ~ Other sources of K,CO, are now of minor importance; the principal are: (1) potassium chloride, which is converted first into sulphate and then into the carbonate by @ process similar to that by which sodium chloride is converted first into sulphate and then into carbonate (see Alkali M anufacture) ; (2) the residue left after the sugar has been extracted from the sugar beet, which residue is worked up for the potassium carbonate it contains by first charring it, extracting it with water, and fractionally erystallising the solution obtained ; the sulphate and chloride of potassium crystallise first, leaving the K,CO, in the mother liquor ; and (3) the fleeces of sheep, which contain about 50 per cent. of fatty matter (swint or yolk), rich in potassium combined with an organic acid; when the fleece is washed with water this salt is dissolved out, and on evaporating the liquid and burning the residue this is converted into potassium carbonate. : Potassium carbonate is deliquescent and soluble in its own weight of cold water, yielding a strongly alkaline solution. It may be crystallised in prisms, K,CO,.2H,0. It is insoluble in alcohol, melts at about 890°, and has sp. gr. 2-3. Bicarbonate of potash, or hydropotassium carbonate, KHCO,, sometimes sold as “carbonate”? and used in medicine, is made by saturating moist K,CO, with CO,, or by passing CO, through a strong solution of K,CO, (in three parts of water). It forms prismatic crystals (sp. gr. 2°17) which are much less alkaline and less soluble in water (30-4 per cent. at 15°) than is the normal carbonate, into which they are converted by heat; 2KHCO, = K,CO,+ ee CO,. The aqueous solution of KHCO, gradually loses CO, when oiled. Caustic. Potash, or Potassium Hydroxide, KOH.—Potassium car- bonate was formerly called potash, and was supposed to be an elementary substance. It was known that its alkaline qualities were rendered far more powerful by treating it with lime, which caused it to be termed mild alkali, in order to distinguish it from the caustic alkali obtained by means of lime and possessed of very powerful corrosive properties. The caustic potash, so largely employed by the soap-maker, is obtained by adding slaked lime (Ca(OH),) to a boiling solution of the potassium carbonate, in not less than 12 parts of water, when calcium carbonate is deposited at the bottom of the vessel, whilst potassium hydrate remains in the clear solution; K,CO; + Ca(OH), = CaCO, + 2KOH. If the solution be too strong, the lime will not decompose the carbonate, for the reaction is reversible (p. 344). When the solution is evaporated, the potassium hydroxide remains as a clear oily liquid, which solidifies to a white mass (sp. gr. 2:04) as it cools, and forms the fused potash of commerce, which is often cast into cylindrical sticks for more convenient use.1_ In soap-making, however, the potash lye is used directly, and on the Continent is now made almost solely by electro- lysis of KCl solution, the process resembling that for making caustic soda (p. 373). Potassium hydroxide is vaporised at high temperatures without decom- position. It readily absorbs water and CO, from the air. Half its weight of water suffices to dissolve it, with great evolution of heat. A strong solution deposits hydrated crystals. Alcohol dissolves it easily, but leaves the chief impurity (carbonate) undissolved ; hence the use of alcohol in purifying the substance. The potassium hydroxide is the most powerful alkaline substance in ordinary use, and is much used by the chemist, generally in 1 These have sometimes a greenish colour, due to the presence of some potassium manganate. 360 COLOURED FLAME TEST solution, the strength of which is inferred from its specific gravity, which increases with the concentration. Potassium.—Of the composition of potassium hydroxide nothing was known till the year 1807, when Davy succeeded in decomposing it by the galvanic battery; this experiment, which deserves particular notice as being the first of a series resulting in the discovery of so many important metals, was made in the following manner : A fragment of potassium hydroxide, which, in its dry state, does not conduct electricity, was allowed to become slightly moist by exposure to the air, and placed upon a plate of platinum attached to the copper end of a very powerful galvanic battery : when the wire connected with the zinc end was made to touch the surface of the hydrate, some small metallic globules resembling mercury made their appearance at the extremity of this (negative) wire, at which the hydrogen contained in the hydroxide was also eliminated, whilst bubbles of ‘oxygen were separated on the surface of the platinum plate connected with the positive wire (see p. 328). By allowing the negative wire to dip into a little mercury contained in a cavity at the surface of the potash, a com- bination of potassium with mercury was obtained, and the mercury was afterwards separated by distillation. This process, however, furnished the metal in very small quantities, and, though it was obtained with greater facility a year or two afterwards by decomposing potassium hydroxide with white-hot iron, some years elapsed before any considerable quantity of potassium was prepared by the method, which was long practised, of distilling in an iron retort an intimate mixture of potassium carbonate and carbon, obtained by calcining cream of tartar; in this process the oxygen of the carbonate is removed by the carbon in the form of carbonic oxide (K,CO, + C. = Ky + 3CO). The metal thus prepared requires re-distillation in order to decompose the explosive compound of potassium with carbon monoxide, K,(CO),g, which it always contains. Potassium is now made by electrolysing fused caustic potash in a manner similar to that adopted for preparing sodium (p. 375); the operation is more difficult, however, owing to the greater tendency of the metal to disseminate itself through the fused mass in small particles. This difficulty is overcome by surrounding the cathode with a cylinder of magnesite. Some of the most striking properties of this metal have already been referred to (p. 19); its softness, causing it to be easily cut like wax, the rapidity with which its silvery surface tarnishes when exposed to the air, its great lightness (sp. gr 0-8624), causing it to float upon water, and its ‘taking fire when in contact with that liquid, sufficiently distinguish it from other metals. It fuses at 62-5° and boils at a low red heat (757°), yielding a green vapour; if air be present, it burns with a violet-coloured flame, the oxide K,O, being the chief product. In dry air or oxy- gen the metal may be dis- tilled unchanged. The property of burning with this peculiar violet- coloured flame is charac- teristic of potassium, and Fig. 234. allows it to be recognised in its compounds. If a solution of potassium nitrate (saltpetre) in water be mixed with enough spirit of wine to allow of its being inflamed, the flame will have a peculiar lilac colour. This colour may also be developed by exposing a very minute particle of saltpetre, taken on the end of a heated platinum wire, to the reducing (inner) blowpipe flame (Fig. 234), when the potassium, being reduced to the metallic state and passing CHLORATE OF POTASH 361 into the oxidising (outer) flame in the state of vapour, imparts to that flame a lilac tinge. The difficulty and expense attending the preparation of potassiuin have prevented its receiving any application except in purely chemical operations, where its attraction for oxygen, chlorine, and other electro-negative elements is often turned to account. Potassium hydride, KH, is obtained when potassium is heated in hydrogen to about 350°, and the mass is treated with liquid ammonia to dissolve unchanged potas- sium. It forms white crystals stable in air, but decomposed by water. Oxides of Potassium.—K,O is formed when K is heated in dry oxygen under diminished pressure. Potassium tetrowide, KyQ,, is the yellow powder obtained when the metal is heated in air or oxygen; it 1s decomposcd by water, yielding KOH and HO, and evolving O. Sp. gr. of K2O is 2-656. Potassium chloride (KCl) is an important natural source of this metal, occurring substantially pure as sylvine, but in much larger quantity in combination with magnesium chloride as the mineral carnallite (KC1.MgCl,. 6H,O), an immense saline deposit overlying the rock-salt in the salt-mines of Stassfurt, in Saxony. Carnallite resembles rock-salt in appearance, but is very deliquescent. It yields a magma of KCl crystals when treated with water; this is recrystallised. Potassium chloride crystallises in anhydrous cubes of sp. gr. 1-99 ; it dissolves in about three times its weight of water and is insoluble in alcohol; it melts at 775.° It is now the raw material for the manufacture of most potassium salts. Potassium chlorate, KCl1O,, is prepared as described at p. 118. It is also made by electrolysing a neutral saturated solution of KCl, the tempera- ture being allowed to rise above 40°; the electrolyte is kept agitated to mix the chJorine liberated at the anode with the KOH formed at the cathode ; these react in accordance with the equation given at p. 117. The chlorate is crystallised and the KCl returned to the electrolytic cell. The chlorate crystallises in four-sided tables (sp. gr. 2-34), soluble in 16 parts of cold and 2 parts of boiling water. It fuses at 360°, and is decomposed at 400°, when it gives off oxygen, and leaves, at first, a mixture of chloride and perchlorate, and lastly chloride only; 2KCIO, = KCIO, + KCl + 0,. Its action on combustible bodies and consequent useful applications have been described at p. 118. Potassium perchlorate, KClO,, is remarkable for its sparing solubility, for it requires 70 parts of cold water to dissolve it. It is prepared by heating KCIO, until 12 grams have evolved a litre of oxygen, as shown in the above equation ; the mass is boiled with just enough water to dissolve it, and the solution, on cooling, deposits erystals of KClO, (sp. gr. 2-52), leaving the KCl in solution. The perchlorate is decomposed above 400° into KCl and 0,4. Potassium bromide, KBr (m.-pt. 740°), forms cubical crystals (sp. gr. 2-75) soluble in about 2 parts of water at ordinary temperature. It is much used in medicine and photography. It is made by the method referred to on p. 122. Potassium iodide, KI, is prepared by adding iodine in small quantities to solution of potash till it is coloured slightly brown, when a mixture of potassium iodide and iodate is obtained; 6KOH + I, = KIO, + 5KI + 3H,0. The solution is evaporated to dryness, the residue mixed with one-tenth of its weight of powdered charcoal, thrown in small quantities into a red-hot iron crucible, and fused; KIO, + C,; = KI + 3CO. The fused mass is dissolved in hot water, filtered, evaporated till a film appears upon the surface, and set aside to crystallise. It is also made by digesting iron filings with iodine and water, and decomposing the solution of ferrous iodide, which is formed, with potassium carbonate. Potassium iodide forms cubical crystals (sp. gr. 3-07) very soluble in 362 SALTPETRE water (1 in 0-7), but sparingly soluble in alcohol. It is of the greatest importance in medicine, in chemical analysis, and in photography. It melts at 680°. Potassium iodate, KIO , is useful in testing for SO2, and may be prepared for that purpose by mixing 3 grams of iodine with an equal weight of potassium chlorate in fine powder, adding, in a flask, about 14 o.c. of nitric acid, and digesting till the colour disappears. The liquid is then boiled for a minute, poured into a dish, evaporated to dryness, and moderately heated, when it leaves a mixture of potassium iodate and little potassium chloride, which may be dissolved in water. SO, at once liberates iodine from it, which gives a blue colour to starch. Potassium fluoride, KF (m.-pt. 860°), is prepared by neutralising HF with K,CO,. Crystallised by slow evaporation of a cold solution, it gives KF .2H,O, but above 35° it yields cubes of KF. It is deliquescent and easily soluble ; the solution corrodes glass. It combines with HF, forming KF.FH, which is employed for the preparation of pure HF. Potassium sulphide, K.S, is obtained as a red crystalline mass by heating K,SO, in hydrogen. Solution of K,S is prepared by saturating solution of KOH with H,S, and adding an equal quantity of KOH. From the solution colourless crystals of K,8.5H,O may be obtained ; they deliquesce in air and are decomposed by the CO, therein with evolution of H,S. Potassium hydrogen sulphide, KSH, may be formed by saturating a strong solution of KOH with H,S and evaporating im vacuo, when colourless deliquescent crystals, 2KSH.H,O, separate. On exposure to air the solution of KHS evolves H,S owing to the action of CO, ; if the air be free from CO, the solution is oxidised to potassium thiosulphate, K,S.03. Potassium sulphate, K,SO,, is found in certain salt-mines, in the mineral kainit, K,8O,.MgSO,.MgCl,.6Aq. A strong solution of this is de- composed by adding KCl, whereupon all the MgSO, becomes MgCl,, and on cooling the hot liquor the K,SO, crystallises in rhombic prisms (sp. gr. 2-66) which are rather sparingly soluble in cold water (1 in 10), but easily in boiling water (lin 4). It is also obtained as a by-product in some chemical manu- factures, and is used in making alum. It melts at 1066°. Kainit is largely used as an artificial manure. Bisulphate of potash, or hydrogen-potassium sulphate, KHSO,, is obtained as the residue in the preparation of nitric acid from saltpetre. It is more fusible (200°) and more soluble in water (1 in 2-5) than the normal sulphateis. Its solution is strongly acid. Much water decomposes it into sulphuric acid and K,SO,. When heated, it decomposes in two stages: (1) 2KHSO, = H,0 + K,8,0, (pyrosulphate or anhydrosulphate) ; (2) K,8,0, = K,80, + SO;. This evolution of SO; makes the bisulphate very useful in chemical operations for decomposing minerals at high tempera- tures. Its sp. gr. is 2°35. Potassium persulphate, K,S,0,, is made by electrolysing a saturated solution of KHSO, (p. 170), or by mixing strong solutions of ammonium persulphate and K,CO; ; in both cases K,8,0, separates, being sparingly soluble (1 in 60). This salt is now of importance as a source of persulphuric acid for making HO, (p. 1438). Potassium nitrate (KNO,), niére or saltpetre, isfound in India, especially in Bengal and Oude, and other hot climates, where it sometimes appears in the dry season as a white incrustation on the surface of the soil, and is sometimes mixed with the soil to some depth. The nitre is extracted from the earth by treating it with water, and the solution is evaporated, at first by the heat of the sun, and afterwards by artificial heat, when the impure crystals are obtained, which are packed in bags and sent to this country as grough (or impure) saltpetre. It contains a quantity of extraneous matter varying from 1 to 10 per cent., and consisting of the chlorides of NITRE-HEAPS 363 potassium and sodium, sulphates of potassium, sodium, and calcium, vegetable matter from the soil, sand, and moisture. The number represent- ing the percentage of impurity present is usually termed the refraction of the nitre, in allusion to the old method of estimating it by casting the melted nitre into a cake and examining its fracture, the appearance of which varies according to the amount of foreign matter present. Potassium nitrate is also made by decomposing sodium nitrate with potassium chloride ; under proper conditions of temperature and concentra- tion NaCl is precipitated and KNO, remains in solution. It is a general rule that when two salts in solution are mixed which are capable of forming, by exchange of their metals, a salt which is less soluble in the liquid, that salt will be produced and separated. In this case, of the four salts which can be formed from the ions K, Na, Cl, and NO,, KNO, is the most soluble and NaCl the least soluble at temperatures near 100°, as is shown by the solubility curves (Fig. 235). The method usually adopted is to add the potassium chloride by degrees to the boiling solu- tion of sodium nitrate, to remove the sodium chloride with a perforated ladle in proportion as it is deposited, and after allowing the liquid to rest for some time to deposit suspended impurities, to run it out into the crystallising pans. The crystals are washed with a saturated solution of KNO,. Potassium nitrate was at one time prepared Grams ir /00Grams Water from the nitrates obtained in nitre-heaps, which 0 20° 40° eo" 00" consist of accumulations of vegetable and animal TEMPERATURES refuse, with limestone, old mortar, ashes, &c. Fic. 235. These heaps are constructed upon an impermeable clay floor under a shed to protect them from rain. One side of the heap is usually vertical and exposed to the prevailing wind, the other side being cut into steps or terraces. They are occasionally moistened with stable drainings, which are allowed to run into grooves cut in the steps at the back of the heap. In such a mass, at an atmospheric temperature between 15° and 20°, nitrates of the various metals present in the heap are slowly formed, and, being dissolved by the moisture, are left by it, as it evaporateson the vertical side, in the form of an efflorescence. When this has accumulated in sufficient quantity it is scraped off, together with a few inches of the nitrified earth, and extracted with water, which dissolves the nitrates, whilst the undissolved earth is built up again on the terraced back of the heap. After two or three years the heap is entirely broken up and reconstructed. The principal nitrates which are found dissolved in the water are those of potassium, calcium, magnesium, and ammonium, the last three of which may be converted into potassium nitrate by decomposing them with potassium carbonate. The formation of nitrates in these heaps is probably the result of chemical changes similar to those which occur in the soils in which nitre is naturally formed, the nitrates being produced by the oxidation, under the influence of the nitrifying organism (p. 181), of ammonia evolved by the putrefaction of the nitrogenised matters which the heaps contain. The oxidation is much promoted by the presence of the strongly alkaline lime and of the porous materials capable of absorbing ammonia and presenting it under circumstances favourable to oxidation. In refining saltpetre for the manufacture of gunpowder, the impure (grough) salt is dissolved in about an equal weight of boiling water in a copper boiler, the solution run through cloth filters to remove insoluble matter, and allowed to crystallise in a shallow V-shaped wooden trough lined with copper. Whilst cooling, the solution is kept in continual agita- tion with wooden stirrers, in order- that the saltpetre may be deposited in 364 POTASSIUM NITRATE the minute crystals known as saltpetre flour, and not in the large prisms which are formed when the solution is allowed to crystallise tranquilly, and contain within them cavities enclosing some of the impure liquor from which the saltpetre has been crystallised. The saltpetre, being so much less soluble in cold than in hot water, is, in great part, deposited as the liquid cools, whilst the chlorides and other impurities, being present in small proportion and not presenting the same disparity in their solubility at different temperatures, are retained in the liquid. The saltpetre flour is drained and washed with two or three successive small quantities of water ; it is then allowed to drain thoroughly, and in that state, containing from 3 to 6 per cent. of water, according to the season, is ready to be transferred to the incorporating mill (p. 365) or to a hot-air oven, where it is dried if not required for immediate use. The impurities most objectionable in saltpetre for gunpowder are KCl and NaCl, . which absorb moisture from the air. Potassium perchlorate, KCl0,, is also liable to be present in the saltpetre, and is said to have led to spontaneous explosion of powder made with such saltpetre. Potassium nitrate is usually distinguishable by the long striated ‘or grooved six-sided prismatic form (sp. gr. 2-09) in which it crystallises (though it may also be obtained in rhombohedral crystals like those of sodium nitrate), and by the deflagration which it produces when thrown on red-hot coals. It is very soluble in boiling water (1 in 0-4), but less soluble in cold water (1 in 4). It is insoluble in alcohol. It fuses at 339° to a colourless liquid, which solidifies on cooling to a translucent brittle crystalline mass. The sal prunelle of the shops consists of nitre which has been fused and cast into balls. Ata red heat it effervesces from the escape of bubbles of oxygen, and is converted into potassium nitrite (KNO,), which is itselt decomposed by a higher temperature, evolving nitrogen and oxygen, and leaving a mixture of potassium oxides. The fused salt attacks all oxidisable bodies and the potassium oxide attacks siliceous bodies, so that it is difficult to find a vessel capable of resisting it at a high temperature: Platinum gives way, but gold is less corroded. In contact with any combustible body it decomposes with great rapidity, five-sixths of its oxygen being available for the oxidation of the combustible substance, and the nitrogen being evolved in a free state ; thus, in contact with carbon, the complete decomposition of the nitre may be represented by the equation 2KNO,+C,= K,CO; + CO, + CO +N,. Since a large quantity of material may be thus burnt in a very small space and in a short time, the temperature pro- duced is much higher than that obtained by burning the combustible in the ordinary way. The sp. gr. of saltpetre is 2-09, so that l c.c. weighs 2-09 grams. Since 202 grams (2 molecules) of nitre contain 80 grams (5 atoms) of oxygen available for the oxidation of combustible bodies, 2-09 grams (or 1 ¢.c. of nitre) would contain slightly more than 0-8 gram (or 555 c.c.) of available oxygen, a volume which would be contained in about 2700 c.c. of air ; hence 1 vol. of saltpetre represents, in its power of supporting combustion, 2700 volumes of atmospheric air. It also enables some combustible substances to burn without actual flame, as is exemplified by its use in touch-paper or slow portfire, which consists of paper soaked in a weak solution of saltpetre and dried, the combustion taking place between the solid combustible and the solid oxygen in the nitre instead of between gases as in the case of flame. If a continuous design be traced on foolscap paper with a brush dipped in a solution of 30 grams of saltpetre in 100 grams of water, and allowed to dry, and one part of the pattern be touched with a red-hot iron, the pattern will gradually burn its way out, the other portion of the paper remaining unaffected. A mixture of 6 grams of KNO,, 2 of sulphur, and 2 of moderately fine dried sawdust (Baumé’s flux) will deflagrate with sufficient intensity to fuse a small silver coin into a globule ; the mixture may be GUNPOWDER 365 pressed down in a walnut-shell or a sniall porcelain crucible, and the coin buried in it, the flame of a lamp being applied outside until deflagration begins. Pulvis fulminans (white gunpowder) is a mixture of 3 parts of KNOs, 1 part of sulphur, and 2 of K,COsg, all carefully dried ; when it is heated on an iron plate no action occurs till it melts, when it explodes very violently.1 " Gunpowder is a very intimate mixture of saltpetre, sulphur, and char- coal, which do not act upon each other at the ordinary temperature, but, when heated together, arrange themselves into new forms, evolving a very large amount of gas. The great attention that has been paid to the manufacture of gun- powder is due to the fact that until recently it was the sole explosive avail- able for warfare. Now, however, it may be said to be displaced by the various forms of “ smokeless powders,” which are all products of nitration (p. 197) of organic substances. Gunpowder is now made almost solely for use as a blasting explosive for mining. The proportions of the ingredients of gunpowder have been varied some- what in different countries, the saltpetre ranging from 74 to 77 per cent., the charcoal from 12 to 16 per cent., and the sulphur from 9 to 12-5 per cent. English military powder contains 75 per cent. of nitre, 15 per cent. of char- coal, and 10 per cent. of sulphur. Mining powder contains about 67 per cent. of nitre, 19 per cent. of charcoal, and 14 per cent. of sulphur. The powdered ingredients are first roughly mixed in a revolving drum having mixing arms turning in*an opposite direction, and the mixture is then subjected to the action of an incorporating mill. This consists of two cast-iron rollers (edge runners) mounted on axles of different lengths which are arms extending at right angles from a vertical shaft ; as the latter is revolved the rollers roll in different circular paths on a cast-iron bed. The mixture fed on to this bed and continuously kept moist by a sprinkler is subjected by the rollers to an intermixing similar to that produced in a pestle and mortar. The mill-cake thus formed is broken up and submitted to very high pressure to make a press-cake, which is subsequently granulated between toothed rollers. Good gunpowder is composed of hard angular grains, which do not soil the fingers, and have a perfectly uniform dark grey colour. Its sp. gr. varies between 1-67 and 1:84. When exposed to air of average dryness, gunpowder absorbs from 0-5 to 1 per cent. of water. In damp air it absorbs a much larger proportion, and becomes deteriorated in consequence of the saltpetre being dissolved, and crystallising upon the surface of the grains. Actual contact with water dissolves the saltpetre and disin- tegrates the grains. When very gradually heated in air, gunpowder begins to lose sulphur, even at 100°, this ingredient passing off rapidly as the temperature rises, so that the greater part of it may be expelled without inflaming the powder, especially if the powder be heated in carbonic acid gas or hydrogen, to prevent contact with air. If gunpowder be suddenly heated to 315° in air, it explodes, the sulphur probably inflaming first ; but out of contact with air a higher temperature is required to inflame it. The ignition of gunpowder by flame is not ensured unless the flame be flashed among the grains of powder ; it often takes some time to ignite powder with the flame of a piece of burning paper or stick, but contact with a red-hot solid body inflames it at once. Very fortunately, it is difficult to explode gunpowder by concussion, though it has been found possible to do so, especially on iron, and accidents appear to have been caused in this way by the iron edge-runners in the incorporating mill, when the workmen have neglected the special precautions which are laid down for them. The use of stone upon iron in the incorporation is avoided, because of the great risk of producing sparks, and copper is employed in the various fittings of a powder-mill wherever it is possible. / The electric spark is, of course, capable of firing gunpowder, though it is not easy to ensure the inflammation of a charge by sucha spark unless its conducting power 1 Probably 2KNO, + K,CO; + 8, = K,80, + K,8 + CO. + NO+NO,. The NOand NO, would probably be decomposed into their elements by the high temperature attained. 366 EXPLOSION OF GUNPOWDER is slightly improved by mixing it with a little graphite, or by keeping it a little moist, which may be effected by introducing a minute quantity of calcium chloride. The importance which formerly attended the study of the products of explosion of gunpowder now no longer obtains, but certain phenomena connected with the explosion are typical of explosives generally, and may receive attention. Approxi- mately, when gunpowder explodes, the mixture of nitre, sulphur, and charcoal is resolved into a mixture of potassium carbonate, potassium sulphate, carbon dioxide, and nitrogen, the last two being gases, the elastic force of which, when expanded by the heat of the combustion, accounts for the mechanical effect of the explosion. The gas evolved by the explosion of 1 gram of black powder measures 280 c.c. at 0° and 760 mm. ; the heat developed is about 700 gram-calories. The period over which the combustion of a given weight of powder extends depends upon the area of surface over which it can be kindled ; thus a single piece of powder weighing 10 grains, even if it were instantaneously kindled over its entire surface, could not evolve so much gas in a given time as if it had been broken into ten separate grains, each of which was kindled at the same instant, since the inside-of the large fragment can be kindled only from the outside. Upon this principle a given weight of powder in large grains occupies a longer period in its explosion than the same weight in small grains, so that the large-grain powder is best fitted for ordnance, where the ball is very heavy, and the time occupied in moving it permits the whole of the charge to be fired before the ball has left the muzzle, whilst in small arms with light projectiles a finer-grained and more quickly burning charge is required. If the fine-grain powder were used in cannon, the whole of the gas might be evolved before the containing space had been sensibly enlarged by the movement of the heavy projectile, and the gun would be subjected to an unnecessary strain ; on the other hand, a large-grain powder in a musket would evolve its gas so slowly that the ball might be expelled with little velocity by the first half of it, and the remainder would be wasted. There is good reason to believe that even under the most favourable circumstances a large proportion of every charge of powder is discharged unexploded from the muzzle of the gun and is therefore wasted. In blasting rocks and other mining operations, the space within which the powder is confined is absolutely incapable of enlargement until the gas evolved by the combustion has attained sufficient pressure to do the whole work, that is, to rend the rock asunder. Accordingly, a slowly burning charge will produce the. effect, since the rock must give way when the gas attains a certain pressure, whether that happen in one second or in ten. Indeed, a slowly burning charge is advantageous, as being less liable to shatter the rock or coal, and bringing it away in larger masses with less danger. Barium nitrate and sodium nitrate are sometimes substituted for a part of the potassium nitrate in mining powder, the combustion being thus retarded. The same charge of the same powder produces very different results when heated in different ways. If 5 grains of gunpowder be placed in a wide test-tube and fired by passing a heated wire into the tube, a slight puff only is perceived ; but if the same amount of powder be heated in the tube bya spirit lamp, it will explode with a loud report, and perhaps shatter the tube (a copper or brass tube is safer). In the first place, the combustion is propagated slowly from the particle first touched by the wire ; in the second, all the particles are raised at once to pretty nearly the same temperature, and as soon as one explodes, all the rest follow instantaneously. The white smoke arising from the explosion of gunpowder consists chiefly of the sulphate and carbonate of potassium in a very finely divided state : it seems probable that at the instant of explosion they are converted into vapour, and are afterwards deposited in a state of minute division as the temperature falls. From this it will be obvious that a powder that is required to be smokeless must be free from such saline products of explosion (see Nitro-glycerine). From the circumstance that the combustion of gunpowder is independent of any supply of oxygen from the air, it might be supposed that it would be as easily inflamed tn vacuo as under ordinary atmospheric pressure. This is not found to be the case, however, for a mechanical reason, viz. that the flame from the particles which are first ignited escapes so rapidly into the vacuous space that it does not inflame the more remote particles. For a similar reason, charges of powder in fuses are found to burn more slowly under diminished atmospheric pressure, the flame (or heated gas) SODIUM—SOURCES 367 escaping more rapidly and igniting less of the remaining charge in a given time. It has been determined that if a fuse be charged so as to burn for thirty seconds under ordinary atmospheric pressure (30 in. barometer), each diminution of 1 in. in barometric pres- sure will cause a delay of one second in the combustion of the charge, so that the fuse will burn for thirty-one seconds when the barometer stands at 29 in. SODIUM, Na = 23.00. Sodium is often found, in place of potassium, in various minerals, but we are far more abundantly supplied with it in the form of common salt (sodium chloride, NaCl), occurring not only in the solid state, as rock salt, but dissolved in sea water, and in smaller quantity in the waters derived from most lakes, rivers, and springs. Sodium also occurs abundantly as the silicate in albite, which is the form of felspar (p. 425) containing sodium in place of potassium ; as the fluoride in cryolite (p. 131); as the nitrate in Chili saltpetre (p. 379); and as the sulphate in glauberite (p. 376). It is noteworthy that the absorptive power of the soil for potassium salts is much greater than for sodium salts, a fact closely connected with the necessity for potassium compounds in plant food and with the accumulation of salt in the ocean. Rock-salt forms very considerable deposits in many regions; in this country the most important is situated at Northwich, in Cheshire, where very large quantities are extracted by mining. Wielitzka, in Poland, is celebrated for an extensive salt-mine, in which there are a chapel and dwelling-rooms, with furniture made of this rock. Extensive beds of rock- salt also occur in France, Germany, Hungary, Spain, Abyssinia, and Mexico. Perfectly pure specimens form beautiful colourless cubes, and are styled sal gemme ; but ordinary rock-salt is only partially transparent, and exhibits a rusty colour, due to the presence of iron. The Stassfurt salt contains about 1-5 per cent. CaSO,, 0-5 per cent. MgSO,, and 1 percent. H,O. In some places the salt is extracted by boring a hole into the rock and filling it with water, which is pumped up when saturated with salt, and evaporated in boilers, the minute crystals of salt being removed as they are deposited. At Droitwich, in Worcestershire, the salt is obtained by evaporation from the waters of certain salt springs. In some parts of France and Germany the water from the salt springs contains so little salt that it would not pay for the fuel necessary to evaporate the water, and a very ingenious plan is adopted by which the proportion of water is greatly reduced without the application of artificial heat. For this purpose a lofty scaffolding is erected and filled with bundles of brushwood, over which the salt water is allowed to flow, having been raised to the top of the scaffolding by pumps. In trickling over the brushwood this water exposes a large surface to the action of the wind, and a considerable evaporation occurs, so that a much stronger brine is collected in the reservoir beneath the scaffolding ; by several repetitions of the operation, the proportion of water is so far dimin- ished that the rest may be economically evaporated by artificial heat. In England the brine (containing about 22 per cent. of salt) is run into large pans and rapidly boiled for about thirty hours, fresh brine being allowed to flow in continually, so as to maintain the liquid at the same level in the boiler. During this ebullition a. considerable deposit, composed of the sulphates of calcium and sodium, is formed, and raked out by the workmen. When a film of crystals of salt begins to form upon the surface the fire is lowered, and the temperature of the brine allowed to fall to about 82°, at which temperature it is maintained for several days whilst the salt is crystal- lising. The crystals are afterwards drained, and dried by exposure to air. The grain of the salt is regulated by the temperature at which it crystallises, 368 COMMON SALT the size of the crystals increasing as the temperature falls. The coarsest crystals thus obtained are known in commerce as bay-salit. It is not possible to extract the whole of the salt in this way, since the last portions which crystallise will always be contaminated with other salts present in the brine ; but the mother-liquor is not wasted, for after as much salt as possible has been obtained, it is made to yield sodium sulphate (Glauber’s salt), magne- sium sulphate (Epsom salts), bromine, and iodine. Vacuum pans (see Sugar) are now being substituted for the open pans in boiling down the brine. The process adopted for extracting the salt from sea water (the composition of which is given at p. 47) depends upon the climate. In Russia, shallow pits are dug upon the shore, in which the sea water is allowed to freeze, when a great portion of the water separates in the form of pure ice, leaving a solution of salt sufficiently strong to pay for evaporation. Where the climate is sufficiently warm, the sea water is allowed to run very slowly through a series of shallow pits upon the shore, where it becomes concentrated by spontaneous evaporation, and is afterwards allowed to remain for some time in reservoirs in which the salt is deposited. Before being sent into the market, it is allowed to drain for a long time, in a sheltered situation, when the magnesium chloride with which it is contaminated deliquesces in the moisture of the air anddrainsaway. The bittern, or liquor remaining after the salt has been extracted, is employed to furnish magnesia and bromine. In another process the spontaneous evaporation is allowed to proceed until the sp. gr. is 1-24, whereby the water deposits about four-fifths of its sodium chloride. It is then mixed with one-tenth of its volume of water, and artificially cooled to — 17°, when it deposits a quantity of sodium sulphate, due to the decomposition of part of the remaining NaCl by the MgSO,. The mother-liquor is evaporated till its sp. gr. is 1:33, a fresh quantity of sodium chloride being deposited during the evaporation. When the liquid cools, it deposits carnallite, which is worked up for KCl (p. 361). This process is instructive as affording another instance of the principle underlying the separation of salts from solutions containing a number of ions, noticed under potassium nitrate (p. 361). The great tendency observed in ordinary table salt to become damp when exposed to the air is due chiefly to the presence of small quantities of chlorides of magnesium and calcium, for pure sodium chloride has a very much smaller disposition to attract atmospheric moisture, although it is very easily dissolved by water, 22 parts by weight being able to dissolve 1 part of salt. The saturated: solution contains 26-4 per cent., has a sp. gr. of about 1-2, and boils at 107-5°. In the history of the useful applications of common salt is to be found one of the best illustrations of the influence of chemical research upon the development of the resources of a country, and a capital example of a manufacturing process not based, as such processes usually are, upon mere experience, independent of any knowledge of chemical principles, but upon a direct and intentional application of these to the attainment of a particular ehbject. Until the last quarter of the eighteenth century the uses of common salt were limited to culinary and agricultural purposes, and to the glazing of the coarser kinds of earthenware, whilst a substance far more useful in the arts, carbonate of soda, was imported chiefly from Spain under the name of barilla, which was the ash obtained by burning a marine plant known as the salsola soda. But this ash contained only about one-fourth of its weight of carbonate of soda, so that this latter substance was thus imported at a great expense, and the manufactures of soap and glass, to which it is indispensable, were proportionately fettered. ALKALI MANUFACTURE 369 During the wars of the French Revolution the price of barilla had risen so considerably that it was deemed advisable by Napoleon to offer a premium for the discovery of a process by which the carbonate of soda could be manu- factured at home, and to this circumstance we are indebted for the discovery (1791), by Leblanc, of the process, which is only now being superseded, for the manufacture of carbonate of soda from common salt, a discovery which placed this substance at once among the most important raw materials with which a country could be furnished. The Leblanc process of manufacturing Sodium carbonate consists of two distinct operations: (1) The heating of salt with sulphuric acid to produce sodium sulphate and hydrochloric acid (p. 109), and (2) the conversion of the sodium sulphate into carbonate by heating it with lime- stone and coal. The existence of a high duty upon salt prevented the establishment of this process in England until 1824, when the removal of the tax enabled Muspratt to undertake the manufacture with reasonable hope of success. The important influence which the process has exerted upon the progress of the useful arts in this country will be easily understood. The three raw materials, salt, coal, and limestone, we possess in abundance. The sulphuric acid, when the process was first introduced, bore a high price, but the demand created for this acid gave rise to so many improvements in its manufacture that its price has been very greatly diminished—a circum- stance which has, of course, produced a most beneficial effect upon all branches of industry in which the acid is used. The hydrochloric acid obtained as a secondary product has been applied for the manufacture of chlorine and therefore of bleaching powder (p. 115), and the important arts of bleaching and calico-printing have thence received a considerable impulse. The manufactures of soap and glass, which probably create the greatest demand for sodium carbonate, have been increased and improved beyond all precedent by the production of alkali from native sources. While these benefits remain the Leblanc process may be said to be nearly dead, and it is now responsible for only a small proportion of the world’s production of alkali, having been displaced by the ammonia-soda process perfected by Solvay in 1866. However, this latter process, which will pre- sently be explained, does not produce hydrochloric acid, and therefore bleach- ing powder is not obtainable as an accessory product. Thus for long the Leblanc process had the advantage in this respect, but within the last few years even this advantage has been swept away by the development of a third process of converting salt into alkali, namely, the electrolysis of a solu- tion of salt; this produces chlorine directly, whereas in the Leblanc process the hydrochloric acid must be subjected to an oxidising process for liberating the chlorine (p. 102). For these reasons the second step of the Leblanc process—the decom- position of sodium sulphate by coal and limestone—is limited to a few English works. Nevertheless the manufacture of sodium sulphate and hydrochloric acid by the first step of the process is still fairly general, because it is a cheaper operation than the manufacture of sodium carbonate by the ammonia-soda process, and the glass-maker has found that he can substitute the sulphate for the carbonate in making many kinds of glass. Moreover there is an increasing market for hydrochloric acid, which is not produced by the electrolytic process. In the salt-cake process, as the manufacture of sodium sulphate is called, salt is introduced into the iron pan, A, of a salt-cake furnace, shown in longitudinal section in Fig. 236, where it is mixed with an equal weight of H,SO, (sp. gr. 1-72) and heated by the products of combustion from grate, G, which first pass over the brick roaster, D 24, 370 SALT-CAKE PROCESS (virtually a muffle), then down two lateral vertical flues shown in dotted lines and along two lateral horizontal flues into the middle flue, H. From here the hot gases pass through flue, C, in which pan, A, is set, and thence to the chimney flue. Much HCl is expelled and escapes through the flue B, whence it passes to the bottom of a tower -~f OQ N N 4 N iPr, | F NN YL, LO CO~ORK NN y \ KEE ASSES 4 D 4 A. CASSASSSSSSSSSSSSNNS NSS — SSNS y Cie.) L MLE 14 Yff Z Fria. 236. built of sandstone plates and packed with coke down which water trickles ; as the gases ascend the tower (which is connected at the top with a chimney) the water absorbs the HCl from them, forming the muriatic acid of commerce (p. 109). When the reaction in pan, A, slackens, the door, F, is raised and the charge pushed over into the roaster, D. The conversion of the salt into sulphate is here completed, the remaining HCl being drawn through five, H, to the condensing towers. The fact that the gases drawn off from the furnace contain seldom more than 10 per cent. by volume of HCl renders the condensation very difficult ; for even very soluble gases (which do not obey the law of partial pressures) are dissolved with difficulty from large volumes of other gases. On the Continent the gases are passed through a number of large earthenware Woulfe’s bottles (bombonnes), arranged in series and also connected by pipes other than those which conduct the gases, so that a current of water can be passed through the series in direction opposite that of the current of gases. This is an example of systematic working. The chemistry of the foregoing operation is discussed at p. 109. A considerable quantity of Na,SO, is made by heating the NaHSO, from the nitric acid stills (p. 192) with NaCl in specially- constructed furnaces, the HCl gas produced being of high concentration. Hargreaves’ process converts NaCl into NagSO, by passing the mixture of sulphur dioxide and air obtained from pyrites kilns (A, Fig. 120), and steam through a series of large iron cylinders containing cakes made of moist salt and kept at 500°. The reaction is 2NaCl + H,O + SO, + O = Na,SO, + 2HCl. The change which occurs when sodium sulphate is heated with coal and limestone to convert it into sodium carbonate may be regarded as consisting in (1) reduction of the sulphate to sulphide by the carbon of the coal— Na,SO, + C, = NaS + 2CO,; (2) a double decomposition between the sodium sulphide and limestone, producing sodium carbonate and calcium sulphide—Na,S + CaCO; = Na,CO, + CaS. The mass is leached with water, which dissolves the sodium carbonate and leaves the calcium sulphide, this being sparingly soluble in a strong solution of sodium carbonate; it constitutes alkali-waste, hereinafter mentiond. <4 As all the materials are not fused in the heating operation the CaCO, and C_must be considerably in excess of the proportions indicated by the equations, and the product is black (black ash) from the presence of coal. The mixture of ground salt cake (10 parts), limestone (10 parts), and small coal (4 to 6 parts) is heated in a black-ash furnace, which is ALKALI WASTE 371 either like a reverberatory furnace (Fig. 169, p. 246), or a large iron cylinder revolving on a horizontal axis and heated internally by furnace gases passing through it. The lixiviation of the black ash is facilitated by the presence of CaO in the mass formed from the excess of CaCO, used (this is another reason for using an excess) and is carried out systematically in tanks. The liquor is separated from the solid tank-waste (alkali waste) and air is blown through it to oxidise some Na,S which has escaped conversict into Na,CO;. The liquor is then evaporated and the residue calcined to obtain sodo ash. But this is by no means pure sodium carbonate, for it contains, in addition to a considerable quantity of common salt and sodium sulphate, a certain amount of caustic soda, formed by the action of the lime upon the Na,CO 3. In order to purify it, the crude soda ash is mixed with small coal or sawdust and again heated, when the carbonic acid gas formed from the carbonaceous matter converts the caustic soda into carbonate, and on dissolving the mass in water and evaporating the solution it deposits oblique rhombic prisms of common washing soda, having the composition Na,CO,.10Aq (soda crystals). It should be the object of the chemical manufacturer to utilise his raw materials in such a manner that none of the elements in them shall ultimately remain in an unmarketable form, and the course of the manufacture should be so directed that all products accessory to the main output are either saleable or adapted to be used again in the process. In the Leblanc process there is a product, practically equal in quantity to the soda produced, which cannot be sold and cannot be returned directly to the process, namely, the alkali waste (p. 370). Huge heaps of this material collected around the alkali works and became a source of offence owing to the slow decomposition of the CaS by the atmosphere with evolution of HS. Chance’s process for the recovery of sulphur from alkali waste, which came into use about 1885, removed this trouble from the Leblanc process by not only obtaining sulphur in a marketable form from the waste, but also converting the calcium into carbonate suitable for use instead of limestone in the black-ash furnace (v.s.). The process depends upon the fact that when CO, is passed into the alkali waste made into a cream with water, H,S is evolved and CaCO, remains ; CaS + H,O + CO, = CaCO; + H,S. The H,S is mixed with air sufficient only to realise the equation, H,S + O =H,0 + 8, and the mixture is passed over heated inert material, whereupon sulphur is sublimed. The alkali waste consists chiefly of CaS and CaCO3, but contains some caustic lime ; the mixture of waste and water is charged into tall iron cylinders through which lime- kiln gases are passed in succession. The CaO is first converted into CaCO, and the CaS into Ca(SH)s, excess of CO, converting the latter into CaCO, with evolution of H,S. The gases escaping from the last cylinder are mixed with the proper proportion of air and passed into a Claus kiln, a brick chamber containing lumps of hematite (iron oxide) which have to be heated to redness at the start, but are afterwards kept hot by the chemical reaction. The chamber is connected with condensing chambers in which the sulphur (about 80 per cent. of that in the CaS) is deposited. The sulphur recovered represents some 70 per cent. of that used for making the sulphuric acid required in the first stage of the process, and may, of course, be burnt on the works for making acid instead of buying pyrites (p. 163), although its sale as a separate product is generally more profitable. Hence the sulphur has become merely an auxiliary agent and may be used repeatedly, suffering, however, a considerable loss at each cycle. As sulphuric acid it converts the salt into a form (Na,SO,) which after reduction can undergo double decomposition with CaCOs. The Ammonia-Soda Process uses ammonia instead of sulphur as auxiliary agent ; this is much more expensive than sulphur, but fortunately it is capable of much more complete recovery. The process may be said to consist in a double decomposition in strong aqueous solution between 372 AMMONIA-SODA PROCESS sodium chloride and ~ ammonium bicarbonate; NaCl + NH,HCO, = NaHCO, + NH,Cl, sodium bicarbonate being precipitated. Ammonia is passed into a solution of salt until the liquid contains almost exactly one equivalent of NH, to one equivalent of NaCl, whereupon CO, is passed in as long as it is absorbed. There are thus present in the solution the ions Na’, NH’,, Cl’,and HCO’,, and since the least soluble combination at the temperature is NaHCOs, this is precipitated (cf. p. 363). The CO, is obtained by heating limestone and the CaO simultaneously formed is heated with the liquor containing NH Cl, from which the NaHCO, has been separated; the ammonia thus obtained—2NH,Cl + CaO = 2NH, + CaCl, + H,O—is returned to the process and a solution of calcium chloride (CaCl,) remains as a waste product, the utilisation of which remains a problem. The NaHCO, is calcined to convert it into Na,CO,; 2NaHCO, = Na,CO, + H,O + CO,. The CO, from this operation is returned to the process. The fact that the main reaction occurs without the necessity for heating renders the actual process much more economical than the Leblanc process ; there is also the advantage that, being a wet method, the operations are comparatively simple and manual labour is reduced to a minimum. The brine pumped from the wells contains magnesium salts and other salts ; lime is added to remove these, and the excess of lime is precipitated by ammonium carbonate. The liquor is then saturated with salt by addition of pure salt and ammonia is passed in from the ammonia stills until the solution contains slightly more than one equivalent per equivalent of NaCl, because, owing to increase in volume due to dissolution of the NHsg, more salt must afterwards be added to saturate the solution. The liquor is now m2de to flow down a vertical iron cylinder containing perforated shelves, the temperature within which is kept at about 35° C. by absorbing the heat of the reaction by water cooling. Lime-kiln gases (and gases from the calcination of the NaHCO3) are pumped up the cylinder and meet the descending liquor, from which the NaHCO, is deposited, collecting on the shelves, whence it falls as a sludge to the bottom of the cylinder. As might be anticipated, the reaction is far from complete and the liquor from which the NaHCO, has separated still contains ammonium carbonate and sodium chloride. It is first distilled alone to recover the ammonium carbonate and then with lime to liberate the NH, from the NH,Cl, as aforesaid. The liquor from the stills contains the unchanged NaCl (amounting to about one-third of that in the original liquor) and CaCly. It is a waste product and is run into the nearest stream. Soda crystals are made from the NaHCO, by boiling it with water and sufficient lime to realise the equation 2NaHCO, + CaO = NagCO, + H,O + CaCO 3. The liquor is then filtered and allowed to crystallise. Sodium Carbonate, washing soda, Na,CO;.10Aq.—The crystals (mono- clinic) of sodium carbonate are easily distinguished by their property of efflorescing in dry air (p. 39), and by their alkaline taste, which is much milder than that of potassium carbonate, this being, moreover, a deliquescent salt. The crystals (sp. gr. 1-44) are very soluble in water, requiring only 2 parts of cold water ; the solution is strongly alkaline to test-papers. The maximum solubility is at 35°, when 1 part Na,CO,.10H,0 dissolves in 0-75 part of water; the solubility then decreases slightly up to 105°, when the solution boils. At 32° the 10-hydrate passes into Na,CO,.7H,O, which separates as rhombic crystals if the liquid saturated at this temperature is cooled. At 35° the 7-hydrate passes into Na,CO,.H,O (crystal carbonate), which separates from cooled solutions saturated above this temperature. The ordinary soda crystals fuse at 50°, evolve steam, and deposit the mono- hydrate as a granular powder. At a higher temperature they become Na,CO; (sp. gr. 2:47), which melts at 850°. The mineral natron found at the soda lakes of Egypt is Na,CO;.10Aq. The chief impurities in soda CAUSTIC SODA 373 crystals are NaCl and Na,SO,; soda ash (p. 371) may contain in addition NaOH and Na,§. Bicarbonate of soda, or hydrogen sodium carbonate, NaHCO, (sp. gr. 2-21), is the substance commonly used in medicine as carbonate of soda. The crude product of the ammonia-soda process contains ammonium salts and is recrystallised for the market. The Leblanc makers produce it by saturating soda crystals with CO,. It forms small prismatic crystals much less easily dissolved by water (1 in 12, at 15°) than the carbonate. The solution is much less alkaline. When the solution is heated it evolves CO,, and crystals of the sesquicarbonate, Na,CO,.NaHCO,.2Aq, may be obtained from it. A similar salt is the mineral Trona. It has been seen that, when strongly heated, 2NaHCO, = Na,CO, + CO, + H,0. Potassium sodium carbonate, KNaCO,.6Aq, may be crystallised from a mixture of solutions of the carbonates. Sodium Hydroxide, caustic soda, NuOH.—The soap-maker is the largest consumer of this chemical ; originally he made for himself the liquor (soda lye) which he required, by boiling a solution of the carbonate with calcium hydroxide (slaked lime); Na,CO, + Ca(OH), = 2NaOH + CaCO . Since the demand for caustic soda has greatly increased for other industries the solid is now made in large quantity. The Leblanc process has some advan- tage over the ammonia-soda process for this purpose, since the black ash (p. 370) contains a considerable proportion of its soda as NaOH, so that less lime is required for causticising (as represented in the above equation) the liquor obtained by leaching black ash than for similarly treating a solu- tion made by dissolving ammonia-soda in water. The caustic liquor is evaporated until it solidifies on cooling, at which stage it is poured into iron pans, broken up when solid and packed in iron drums. The causticising reaction is reversible and is the less complete the stronger the solution, hence the liquor is seldom worked at greater strength than will yield a caustic lye containing 13 per cent. of NaOH ; thus evaporation is the chief cost of the process. The first part of the concentration is now done in multiple effect apparatus, the rest in open pans. In the Leblanc works the tank liquor (from the black ash) is purified from sulphides before it is causticised, partly by blowing air through it, which oxidises the sulphides, and partly by addition of zinc oxide, which precipitates zinc sulphide. The other salts (carbonate, sulphate, and chloride) crystallise during the concentration and may be fished out ; the last traces of sulphide are oxidised by the addition cf a little NaNO, to the melted NaOH before it is cast. The NaNO, is the source of the nitrate and nitrite generally found in commercially pure caustic soda. According to the grade made, the solid contains from 4 to 40 per cent. of water. The bicarbonate produced by the ammonia-soda process is converted into NaOH by mixing it with ferric oxide and heating the mixture to a red heat. CO, and H,O escape and sodium ferrite (Na,0.Fe,0, = NaFeQ,) is formed. This is decomposed by a small excess of water, yielding a concentrated soda lye and Fe,03. Electrolytic Production of Alkali.—The electrolysis of a solution of an alkali chloride yields a solution of caustic alkali at the cathode and free chlorine at the anode, and the development of the dynamo has rendered this method of producing alkali and chlorine practicable, particularly in localities where water-power is available for driving the dynamo. Caustic soda is produced in considerable quantity in this country by the Castner- Kellner electrolytic process, and both soda lye and potash lye are made in large quantity on the Continent by other electrolytic processes, the pro- cedure being almost identical for the two alkalies. When fused NaCl is electrolysed Na is produced at the cathode and Cl at the anode; in aqueous solution, however, hydrogen is the cathode product, which is explained by supposing that when the Na” ion is discharged 374 ELECTROLYTIC MANUFACTURE OF ALKALI at the cathode it reacts with water to form NaOH and H. Now, the heat of formation of salt is Na,Cl — 97,7001 (p. 347), and the electrical energy necessary to separate the elements of anhydrous salt must be equivalent to this heat energy. On the other hand, the action of sodium on water is exothermic, viz. Na + HOH = NaOH + H + 43,000, so that the electrical energy required to electrolyse the aqueous solution of salt is less than that required for fused salt by an amount equivalent to 43,000 heat- units. Thus the electrolysis of fused salt requires more power than that of the aqueous solution and is only practised where natural water-power is available. Since one equivalent of Na yields one equivalent of NaOH, the same quantity of electricity is required whether Na or NaOH appears at the cathode (p. 329), but the pressure at which this is supplied (the voltage of the current) must be greater when Na is the cathode product; how this pressure is calculated from the thermal data is explained at p. 329. When a solution of salt is electrolysed the caustic soda collecting in solution around the cathode is liable to mix with the saturated solution of chlorine collecting around the anode, forming a solution of sodium hypochlorite and chloride (p. 115). This intermixture is sometimes encouraged to produce electrolytic bleach, but in the manu facture of soda and chlorine it must be prevented as far as possible, and this constitutes the chief difficulty of the process. The methods of overcoming the difficulty fall under three heads : (1) In the diaphragm processes the electrolytic cell is partitioned by a diaphragm which is pervious to the current-carrying ions, but substantially impervious to the liquid The iron cathode is in one compartment, in which the NaOH collects, and the carbon anode is in the other, which is closed and provided with a pipe for leading the evolved chlorine to lime chambers (p. 115). The cathcde compartment may also be closed and the hydrogen collected for the purposes for which it is useful. In prac- tice a number of such cells are operated in parallel, and a slow current of brine is passed through them ; the chief trouble is to find a suitable material for the diaphragm, as few substances resist for long the attack of caustic alkali and chlorine. After about one-third of the salt has become NaOH the process ceases to be economical, as the NaOH begins to be uselessly electrolysed with evolution of oxygen at the anode. (2) The mercury process, or Castner-Kellner process, avoids the use of a diaphragm by employing mercury as an intermediate electrode. A vat isdivided by an impervious transverse partition which allows passage beneath it for a layer of mercury. The anode compartment contains brine and the cathode compartment, NaOH solution. In the anode compartment chlorine is liberated at the anode and the mercury acts as a cathode and dissolves the sodium liberated at its surface. The vat is rocked on a transverse axis so that the mercury in the anode compartment periodically flows under the partition into the cathode compartment, where it acts as an anode; the OH ions produced by the clectrolysis of the NaOH in this compartment combine with the Na contained in the mercury, forming NaOH, which dissolves. At the cathode the Na ions react with the water to form NaOH, and H is evolved. The method presents the advantage that the soda lye obtained is substantially free from chloride. (3) In the bell process the attempt is made to electrolyse the brine as fast as it enters the cell, and, by placing the anode very close to the surface, to ensure escape of the chlorine before interaction with the NaOH occurs. A Jong narrow bell with an escape pipe for the Cl dips in the liquid in the cell ; the anode is a carbon plate almost co-exten- sive with the space within the bell, and is close to the surface of the liquid ; the iron cathodes are outside the bell. The brine flows through a long perforated pipe just beneath the surface of the liquid above the anode, and the NaOH solution flows away from the same level without the bell. In this way a diaphragm is avoided as the layer of saturated chlorine solution floats on the caustic lye. The objection to a diaphragm is the increase which it causes in the electrical resistance of the cell and therefore in consumption of power. 1 It is rather less than this for salt at the temperature of its fusing-point. SODIUM 375. Sodium hydroxide resembles KOH in most respects, but is a less powerful alkali, and when exposed for long to air it yields a dry mass (Na,CO,) instead of a deliquescent mass (K,CO,). As the pure compound is never met with, its physical constants are not of much importance. The commercial grades have a sp. gr. about 2-1 and melt below 300°. A saturated solution at 12° contains 103 parts of NaOH and 100 parts of water ; its sp. gr. is about 1-5. The common impurities are carbonate, chloride, sulphate, and nitrite of sodium, sometimes accompanied by zinc oxide; an alcoholic solution is substantially free from these, but usually not from nitrogen compounds ; however, that made from metallic sodium is obtainable free from N. Sodium.—Owing to their similarity potash and soda were confounded together by the earlier chemists, and it was not till 1736 that Du Hamel pointed out the difference between them. The discovery of potassium naturally led Davy to that of sodium, which can be obtained by processes exactly similar to those adopted for procuring potassium, to which it will be remembered sodium presents very great similarity in properties (p. 20). Sodium, however, is readily distinguished from potassium by its burning with a yellow flame, which serves to characterise it even when in combination. Sodium is manufactured by electrolysing fused caustic soda in an iron vessel kept hot by a suitable furnace. Sodium and hydrogen are separated at the cathode and oxygen at the anode. The liberated sodium attacks the NaOH at temperatures above 400°, so that the operation is conducted at 310°-330°. The iron cathode is surrounded by iron wire gauze terminating at the surface of the liquid in an inverted pot, in which the sodium and hydrogen collect as they rise through the liquid. The anode is an iron cylinder surrounding the gauze. The object of the latter is really that of a porous diaphragm to keep the cathode and anode products apart ; the reason why a material with such large pores can be used is because the fused sodium has a high surface tension and will not pass through the gauze. When sufficient sodium has collected in the inverted pot, the bottom of this is removed and the metal ladled out. Sodium is a whiter metal than potassium ; its sp. gr. is 0-9724; it melts at 97°, and boils at 877°. When heated in air, it gives a mixture of Na,O and Na,O,, which is converted into NaOH by water, O being evolved from the Na,O.. Sodium is not attacked by perfectly dry chlorine, dry bromine, or dry oxygen, but if a trace of aqueous vapour be present, combination occurs with violence. When mixed with 10 to 30 per cent. of its weight of potas- sium, sodium yields an alloy which is liquid at temperatures above 0° and is used for filling thermometers. Sodium is far less costly than potassium, and is used on the large scale for making sodium peroxide. An amalgam of sodium (p. 187) is also employed with advantage in extracting gold and silver from their ores. Sodium hydride is similar to the potassium compound (p. 361). Sodium peroxide, NagQ.,, is manufactured by causing slices of sodium, disposed on trays of aluminium (which is not attacked), to pass through a hot (300°) tunnel which is traversed in the contrary direction by a current of dry air, freed from CO,. It is a yellowish-white powder much used as an oxidising and bleaching agent. Water at ordinary temperature dissolves it with evolution of oxygen and formation of NaOH. If water is added gradually to Na,O, it dissolves, and the solution yields crystals of Na,O,.8H,0. Sodiwm oxide, Na,O, has a sp. gr. 2-314. Sodium chloride, NaCl, forms rock salt and table salt, the latter consist- ing of minute crystals formed by boiling down the water of brine springs (see p. 367). It forms cubical (rarely octahedral), anhydrous crystals of sp. gr. 2-16, and is almost equally soluble in hot and cold water ; 100 parts of water at 15° dissolve 36 parts of salt, at 100° 39 parts. It is insoluble 376 GLAUBER’S SALT in alcohol. It melts at 772°, and is afterwards vaporised. Prismatic erystals of NaCl.2Aq are deposited from a saturated solution cooled to — 10°. Needles of NaCl.2Aq are obtained from a solution of salt in hot HCl. For the behaviour of salt with ice, see p. 341. Sodium fluoride, NaF, made by fusing fluor spar (CaF,) with Na,CO;, is used for softening boiler-feed waters. It crystallises in cubes or octahedra (sp. gr. 2°76) ; 100 parts of water dissolve 4 parts at 15°. Sodium sulphide, Na,S.9H,0, is made by heating sodium sulphate with small coal; the mass is leached and the liquor evaporated to crystallisation. It is used for removing hair from skins and in making sulphurised dyestuffs. In the latter case it is generally applied as polysulphide made by dissolving sulphur in its aqueous solution or by melting it with sulphur. The crystals (prisms or octahedra) dissolve in about seven times their weight of water at 15°. For the pentasulphide, see p. 377. Sodium sulphate is found anhydrous as Thénardite. Glauber’s salt, Na,SO,.10Aq, made by crystallising salt cake, forms monoclinic prisms which effloresce in air, fuse at 33°, and become anhydrous at 100°. Itis more soluble in water at 32-4° than at any other temperature, 100 parts of water dis- solving 115 parts of the crystals. bh O This temperature, 32-4°, is the transition point (p. 339) of the phases Na,SO,.10Aq s ttiti tt tj , and Na,SO,; when the crys- +5 10 [5 20 25 30 35 40 45 50 55 60 tals are fused there is always Te emperature a little Na,SO, remaining as Fia. 237. a solid in the liquid; so also «when the solution saturated at 324° is heated, Na,SO, is deposited. The solubility curve (Fig. 237) illustrates the change and shows how the solubility of Na,SO, diminishes with rise of temperature. The tendency of the crystals to form supersaturated solutions has already been noticed (p. 40). When the supersaturated solution is cooled to 5° crystals of Na,SO,.7Aq may be obtained ; the solution is still supersaturated with the 10-hydrate, however, as is shown by adding a crystal of the latter, whereupon the equilibrium is upset by separation of some 10-hydrate ; some of the 7-hydrate will dissolve and immediately crystallise as 10-hydrate, this continuing until the whole is crystallised in this form. The crystals of Na,SO,.10Aq, with half their weight of strong HCl, form an excellent freezing-mixture, giving the same temperature as ice and salt (= 18° ¢, 0 F). Anhydrous Na,S8O, (sp. gr. 2°67) melts at 880°; the double salt Na,SO,.K,SO, crystallises in plates (plate sulphate) from hot water, a flash of light accompanying the separation of each crystal. Glauberite is Na,Ca(SO,4)., and is nearly insoluble in water. Sodium bisulphate, hydrogen sodium sulphate, NaHSO,, crystallises in prisms with 1Aq. It is more fusible and more easily decomposed by heat than is KHSO,. Itis decomposed by alcohol into H,SO, and Na,SO,, which remains undissolved. When moderately heated, 2NaHSO, = H,O + Na,§,0, (pyrosulphate), decomposed at a red heat into Na,SO, and SO 3. Sodium pyrosulphate is also formed when NaCl is heated with SO, ; 2NaCl + 380, = Na,S,0, + SO,Cly. Sodium sulphite crystallises in prisms, Na,SO,;.7Aq (sp. gr. 1-59), which effloresce in air and slowly absorb oxygen, becoming Na,SO,; they — Grams Na, SQ 10 uO, SODIUM HYPOSULPHITE 377 dissolve readily in water (1 in 2 at 18°), and from the saturated solution the anhydrous salt crystallises at 22°, the transition point. Dry Na,SO, does not absorb oxygen from the air. The hydrated salt is made by crystallising a solution prepared by saturating one-half of a solution of Na,CO, with SO, and adding the other half, (1) Na,CO, + 280, + H,O = 2NaHSO; + CO,; (2) 2NaHSO, + Na,CO, = 2Na,SO, + H,O + CO,. Both sodium sulphite and sodium bisulphite (sodium hydrogen sulphite, NaHSO,) are much used by the paper-maker and the calico bleacher, as antichlore, for killing the bleach—that is, neutralising the excess of chlorine left in the material which has been bleached with chloride of lime (p. 116) ; Na,SO, + H,O + Cl=Na,SO,+2HCl. The solution of the normal sulphite is slightly alkaline ; that of the acid salt is acid. Sodium thiosulphate or hyposulphite crystallises in glassy prisms, Na,S,0;.5Aq. The mode of preparing it from sodium sulphite has been referred to on p.171. On a large scale it is made from the calcium thio- sulphate obtained by exposing tank waste (p. 371) to the air for some days. The calcium sulphide in the waste becomes oxidised to thiosulphate ; 2CaS + 20, + H,0 = CaS,0, + Ca(OH),. The thiosulphate may be leached out with water and the liquor mixed with sodium sulphate, which precipitates calcium sulphate, leaving sodium thiosulphate in the solution, which is then crystallised ; CaS,0,; + Na,SO, = CaSO, + NapS,05. The step of leaching and precipitating is avoided in thé actual manufacture by mixing the tank waste with sodium sulphate before it is exposed to the air ; NagS,0, is then formed either in the mass or as soon as this is leached with water. As tank waste is rapidly disappearing (p. 369) other sources of Na,S,0, are being sought. An interesting process is the passage of SO, through a solution of Na,§ ; 380, + 2Na,S = 2Na.8,0, + 8. As avoiding the elimination of sulphur the reaction between sodium bisulphite and sodium hydrogen sulphide solutions is preferable ; 2NaHS + 4NaHSO,; = 2Na,8,0, + 3H,0. Anhydrous Na,§,03 is made by first heating anhydrous Na,S in H,S to make NaHS and then heating this in a current of air first at 100° and afterwards at 150°; 2NaHS + 20, = Na,S,03, + H,0. . The crystals do not change in air and dissolve in 0-6 part of water at 20°. They melt at 56° and become anhydrous at 100°; when further heated in air the white mass burns with a blue flame, leaving a residue of Na,SO,. When heated out of contact with air sodium pentasulphide is left with the sulphate ; 4Na,S,0, = 3Na,8O, + Na,§;,. The application of hyposulphite in photography has been explained at p. 171. It is also used as an antichlore (see above); the chlorine oxidises it to sulphate ; Na,8,0, + 4Cl, + 5H,O = 2NaCl + 2H,SO, + 6HCI. Iodine, however, converts it into sodium tetrathionate (p. 127). Sodium hydrosu'phite, Na.S.0,.2H,0, is made by dissolving SO, in a strong solu- tion of NaHSO, and reducing the mixture with zinc dust ; NaHSO, + SO, + Zn = ZnSO, + Na S,0, + H,O. Milk of lime is added to precipitate ZnO and CaSO,, and the liquor is saturated with salt at 50° and cooled to crystallise the hydrosulphite ; by saturating a concentrated solution of the crystals at 50° with NaOH the anhydrous salt is precipitated as a fine powder which may be washed with alcohol. The hydro- sulphite is a very powerful reducing agent (p. 173) used mainly for reducing indigo in preparing the dye-vats of this dyestuff (q.v.). In aqueous solution it decomposes more or less rapidly into Na,S.03; and NaHSO;, and becomes NagSO, on exposure to air. Sodium phosphate, hydrogen disodium phosphate, HNa,PO,, crystallises in prisms (sp. gr. 1-537), Na,HPO,.12Aq, which effloresce in air and dissolve easily in water (9°3 in 100 at 20°) to an alkaline solution. When heated, they fuse at 35°; at a red heat, 2Na,HPO, = H,O + Na,P,0, (pyro- phosphate). When crystallised above 36° it is Na,HPO,.7Aq (cf. Na,SO,). 378 BORAX Na,HPO, occurs in the blood and in urine. It is prepared by decom- posing a mineral phosphate, which contains Ca,(PO,)., with H,SO,, so as to obtain the insoluble CaSO, and a solution of impure H;PO,. This is de- composed by Na,CO,, the solution filtered from the small quantity of CaCQg, evaporated, and crystallised ; H,PO, + Na,CO, = Na,HPO, + H,O + CO,. Sodium arsenate, HNa,AsO,, forms crystals with 12Aq (sp. gr. 1-72) isomorphous with those of the phosphate, but the salt as commonly sold contains 7Aq. It is made by dissolving white arsenic in caustic scda, adding sodium nitrate,evaporating to dryness, heating the residue to redness, and dissolving in ‘water: (1) As,O, + 12NaOH = 4Na,AsO, + 6H,0 ; (2) Na,AsO, + NaNO, = Na,AsO, + NaNO,; (3) NazAsO, + H,O = Na,HAsO, + NaOH. Borax, disodium tetraborate, Na.O.2B,03, or sodium pyroborate, Na.B,0,. —-The occurrence of this salt in nature has already been noticed (p. 288). But little borax is now made from tincal, the bulk being derived from the deposits of California, Nevada, and Chili. In the North American districts the principal minerals are colemanite, Ca,0.3B,0,;.3Aq, and pandermite, Ca,0.2B,0,.4Aq, which occur partly as superficial deposits and partly in strata needing to be mined. The South American material is chiefly boronatrocalcite, Na,B,0,.2CaB,0,.18H,O. The boracic earth dug or mined in California contains about 35 per cent. B,O3, and is the chief source of borax, which is made from it by boiling the finely ground earth with a solution containing Na,CO, equivalent to the B,O,; present, settling and crystallising the liquor. The crystallisation is conducted in iron tanks 20 ft. x 6ft. x 6ft., across which are laid iron bars having wires depending into the tank. The borax crystallises on the wires and on the sides and bottom of the tank; the crystals on the wires are pure, but those on the surfaces of the tank have to be recrystallised. : Owing to the prolonged boiling necessary for decomposing the calcium borate with Na,.COs3, it is profitable, when fuel is scarce, to liberate all the boric acid as such by treating the earth with SO, (p. 290) and to dissolve the acid in Na,CO, to make borax. The common form of borax consists of prisms, Na,B,0,.10Aq (sp. gr. 1-694). They effloresce and become opaque when exposed to air, and may readily be distinguished by their behaviour when heated, for they fuse easily and intumesce most vigorously, swelling up to a white spongy mass of many times their original bulk ; this mass afterwards fuses to a clear liquid which forms a transparent glassy mass on cooling (vitrified borax), and since this glass is capable of dissolving many metallic oxides with great readiness (borax being, by constitution, an acid salt, and therefore ready to combine with more base), it is much used in the metallurgic arts. Large quantities of borax are also employed in glazing stoneware. Octahedral borax, Na,B,0,.5Aq (sp. gr. 1-815), crystallises from a solution of borax above 60°, or below this from a supersaturated solution in absence of nuclei of the prismatic form. Solution of borax is alkaline to litmus and when dilute dissolves iodine to a colourless solution, but on concentration the iodine is precipitated ; probably the borax is decomposed in the dilute solution into boric acid and soda, which converts the iodine into iodide and iodate ; on concentrating, the boric acid liberates hydriodic and iodic acids, which react with each other, separating iodine (p. 130). One hundred of water dissolve 1-6 of Na,B,O, at 10°, and 52-3 at 100°. Sodium Perborate, NaBO,.4Aq.—This salt has become important as a convenient source of oxygen. It is made by mixing borax solution with one equivalent of NaOH (whereby sodiwm metaborate, NaBO,, is formed) and an excess of H,O, solution ; on cooling, the perborate crystallises. One hundred parts cf water dissolve 2-55 of NaBO, at 15°; the solution is NITRATE OF SODA 379 alkaline and behaves like a solution of hydrogen peroxide in respect of its active oxygen. As the salt contains some 10 per cent. of available oxygen as against the 3 per cent. in ordinary H,O, solution, it is more economical to transport and has found considerable application as a bleaching agent. It is also valuable as an antiseptic in surgery. When boric acid is mixed with Na,O, in cold water a clear solution is at first formed, but this soon becomes turbid from separation of a salt which . has been called perboraz, and is assumed to have the formula, Na,B,O,.10Aq, but when recrystallised the first crystals contain more oxygen than corre- sponds with this formula. Sodium nitrate, or nitrate of soda, NaNOg, also known as Peruvian or Chili saltpetre, is found in Peru and Chili in beds beneath the surface soil. The dug-out earth is known as caliche and contains from 10 to 65 per cent. NaNO;, much NaCl, and some KNO,, NalIO,, and NaClO,; it is leached with water, and the liquor is crystallised. The commercial nitrate thus obtained contains 95 per cent. NaNO,, also NaCl, KNO,, and NaClO,. It crystallises in rhombohedra, resembling cubes ; hence it is sometimes called cubical saltpetre, as distinct from prismatic saltpetre (KNO,). It is too hygroscopic to be substituted for potassium nitrate in gunpowder ; more- over, it is less powerful in its oxidising action upon combustible bodies at a high temperature. It is, however, used for making potassium nitrate (p. 363). By far its largest use is as a manure, for supplying nitrogen, for which purpose it should be free from perchlorate—a plant poison. Large quantities are also used for making nitric acid. It melts at 313°; 100 of water dissolve 88 of NaNO, at 20° and 175 at 100°. Its sp. gr. is 2-265. Sodium nitrite, NaNO,, is much used for diazotising organic amines (p. 207). It is made by heating NaNO, to 420°in an iron vessel and stirring the molten mass with metallic lead; NaNO; + Pb = NaNO, + PbO. It crystallises in colourless deli- quescent prisms very soluble in water (83 in 100 at 15°) ; the solution of the commercial salt is generally alkaline owing to the presence of a small quantity of caustic soda, but the pure salt is neutral. It is also made by absorbing in NaOH the nitrous gases (NO, + NO) made by the action of electric discharges on air (p. 190). Sodium Silicate——A combination of soda with silica has long been used, under the name of soluble glass, for imparting a fire-proof character to wood and other materials, and, more recently, for producing artificial stone for building purposes, and for a peculiar kind of permanent fresco- painting (stereochromy), the results of which are intended to withstand exposure to the weather. Sodium metasilicate has been obtained in prismatic crystals, Na,SiO,.8Aq, by dis- solving amorphous silica in NaOH. It is soluble in water, and the solution is decomposed by CO,. A solution of amorphous SiO, in hot aqueous Na,COz gelatinises on cooling. Soluble glass varies in composition between Na,O.2SiO, and Na,O.48i0,. It is usually prepared by fusing 2 parts of sand with 1 part of carbonate of soda and 0-1 part of charcoal. The silicic acid, combining with the soda, disengages CO., the expulsion of which is facilitated bythe presence of charcoal, which converts it into CO. The mass thus formed is scarcely affected by cold water, but dissolves when boiled with water, yielding a strongly alkaline liquid. A concentrated very viscid solution is sold as water-glass and is used, among other purposes, for preserving eggs. In using this substance for rendering wood fire-proof, a rather weak solution is first applied to the wood, and over this a coating of limewash is laid ; a second coating of soluble glass (in a more concentrated solution) is then applied. The wood so prepared is, of course, charred, as usual, by the application of heat, but its inflammability is remarkably diminished. For the manufacture of Ransome’s artificial stone, the soluble glass is prepared by heating flints, under pressure, with a strong solution of caustic soda, toa temperature between 150° and 200°, when the silica constituting the flint combines with the soda. 380 AMMONIUM SULPHATE Finely divided sand is moistened with this solution, pressed into moulds, dried, and exposed to a high temperature, when the silicate of soda fuses and cements the grains of sand together into a mass of artificial sandstone, to which any required colour may be imparted by mixing metallic oxides with the sand before it is moulded. Silicate of soda is also sometimes used as a dung-substitute in calico-printing (q.v.). Sodium chlorate, NaClO,, resembles KC10;, but dissolves in its own weight of water at 15°, and is on this account preferred for some purposes. It is made by elec- trolysing solution of NaCl as described for making KClO, from KCl (p. 361). It melts at 261°. SALTS OF AMMONIUM. The great chemical resemblance between some of the salts formed by neutralising acids with ammonia, and the salts of potassium and sodium, has been already pointed out as affording a reason for the hypothesis of the existence of a compound metal, ammonium (NH,), equivalent in its functions to potassium and sodium (p. 187). Ammonium nitrate, NH,NO,, is prepared by allowing nitric acid to flow into ammonia solution, well cooled, and subsequently crystallising. It crystallises in four forms, the commonest being six-sided prisms (sp. gr. 1-7) like those of KNO,, but they are deliquescent and very soluble in water (150 in 100 at 12°, 870 in 100 at 100°) ; it absorbs one-third of its weight of ammonia and becomes liquid, the ammonia being expelled again at 25°. When gently heated, it melts at 166°, and is decomposed at 180°, when it boils and passes off entirely as water and nitrous oxide (q.v.); NH,NO; = 2H,0 + N,0. If sharply heated, as by throwing it on a red-hot surface, it deflagrates. If very carefully heated, it may be sublimed. It is largely used for making explosives. . Ammonium nitrate can be exploded by means of a detonator, the change NH,NO; = N, + 2H,0 + O evolving some 300 cals. per gram of NH,NO,;; since there is free oxygen among the products the explosion is more violent if some combustible (naphtha- lene, for example) be mixed with the nitrate. The temperature of the explosion is low compared with that of the explosion of gunpowder or dynamite, and is accompanied by comparatively little flame. Hence explosives having NH,NO, as their basis belong to the class of safety explosives and can be used with less danger in fiery mines (p. 258) than dynamite. NH,NO; is also made from (NH4).80, and NaNO, in like manner to that in which KNO; is made from KCl and NaNO, ; the product is not pure enough for explosives. In two or three German factories NH,NO, is made by passing a mixture of air and more NH, than it can oxidise over platinum sponge heated to 308° ; nitric and nitrous acids are formed (p. 191) which combine with the excess of NH. Ammonium sulphate, (NH,),SO, (sp. gr. 1-77), is mainly used as an artificial manure, competing with sodium nitrate (p. 379). It is made by passing the gases and vapours distilled from the ammoniacal liquor of the gas works (p. 183) into H,SO, of about 55 per cent. strength ; the solid salt separates from the acid and is removed, drained, and washed with a little water. When required pure, it is reerystallised. It is isomorphous with K,SO,. One hundred of water dissolve 76-3 at 20° and 97-5 at 100° ; insoluble in alcohol. When heated it begins to lose NH, below 100°, and at about 300° becomes NH ,HSO,, which decomposes at higher temperatures, yielding NH;, SO,, H,O and N. Even the solution of (NH,),SO, loses NH, slowly when boiled. Textile fabrics which have been dipped in its solution and dried, no longer burn with flames when ignited. In volcanic districts (NH,),SO, is found as the mineral mascagnine. The crystals occa- sionally noticed on windows of rooms in which coal-gas (containing sulphur) is burnt are (NH,),SO,. Commercial Ammonium carbonate, also called smelling salts, or Preston SAL AMMONIAC 381 salis, is largely used in medicine, and by bakers and confectioners for impart- ing lightness or porosity to cakes, &c. It is prepared by bringing together NH;, CO,, and steam at about 70° in a leaden chamber ; as the gases cool the ammonium carbonate collects as a transparent fibrous mass which is generally resublimed in iron vessels surmounted by leaden domes. Even if the gases are in the proportion for forming thenormal carbonate, (NH,),COs, this salt is not produced, the product consisting of the acid carbonate or ammonium bicarbonate, NH,HCO,, formed from the carbonate by loss of NH,—CO(ONH,)(ONH,) = CO(ONH,)(OH) + NH,—and ammonium carbamate, formed from the carbonate by loss of H,O—CO(ONH,)(ONH,) = CO(ONH,)(NH,) + H,0. The commercial carbonate is usually a mixture of 2 mols. of the former to 1 of the latter. By treating it with strong alcohol, the carbamate is dissolved and the hydrogen ammonium carbonate left. When exposed to the air it smells of ammonia, and gradually becomes NH,HCO,, the carbamate being decomposed and volatilised ; CO(ONH,) (NH,) = CO, + 2NH;. On treating the commercial carbonate with a little water, the NH,HCO, is left undissolved, whilst the carbamate is con- verted into normal carbonate and dissolved ; CO(ONH,)(NH,) + H,O = (NH,),CO3. Sal volatile is an alcoholic solution of commercial ammonium carbonate. By saturating ammonia solution with CO,, crystals of ammonium sesquicarbonate, (NH,).CO, .2NH,HCOs, are obtained. Ammonium carbonate, (NH4)2COsg, is obtained in crystals by treating the commercial carbonate with strong ammonia. The crystals contain 1Aq. They are deliquescent in air, and evolve NH3, as in the above equation. The ammonium carbamate is deposited as a white solid when ammonia gas is mixed with carbonic acid gas, unless both be quite dry. It may be obtained in crystals by passing CO, and NH; into the strongest solution of ammonia. Its aqueous solution, when freshly prepared, is not precipitated by calcium chloride, but the calcium carbonate is deposited on standing or heating. When ammonium carbamate is heated in a sealed tube at 130° it is decomposed into ammonium carbonate and urea ; 2NH,CO,NH, = (NH,4)2CO, + CO(NHg)s. Carbamic acid, HCO,NHg, has not been isolated ; its relation to carbonic acid is seen by a comparison of their formule ; carbonic acid, CO.OH.OH ; carbamic acid, CO.OH.NH,; and that of urea (carbamide), CO.NH,.NH,. Other carbamates have been obtained by passing CO, through strongly ammoniacal solutions of different bases, and precipitating the carbamates by alcohol. When potassium carbamate is heated, it yields water and potassium cyanate ; KCO,NH, = KCNO + H,0. Carbamates are remarkable for evolving nitrogen when treated with a mixture of soda and sodium hypobromite, but not with the hypochlorite; thus: 2(CO.NH,.ONa) + 3NaOBr + 2NaOH = 2CO(ONa), + 3NaBr + 3H,0 + Ng. If solution of sodiwm carbamate be mixed with sodium hypochlorite and soda, no nitrogen is evolved until a soluble bromide is added, a reaction which will indicate bromides even in dilute solutions. The solution of sodium carbamate may be prepared by dissolving ammonium carbamate in a strong solution of soda, and evaporating over strong sulphuric acid. Ammonium Chloride, NH,Cl.—The combination of gaseous HCl and NH, has already been noticed (p. 187). The chloride is made by mixing the distillate from the ammonia still (p. 183) with hydrochloric acid and boiling down to obtain crude crystals of NH,Cl. These are either recrystal- lised and sold as a crystalline powder (muriate of ammonia), or sublimed in earthen pans surmounted by iron domes. This form is called sal ammoniac and constitutes very tough translucent fibrous masses, generally of the shape of the condensing dome and often striped brown from the presence of iron oxide. Its sp. gr. is 1:53; it has no smell of ammonia. It dissolves in 382 AMMONIUM SULPHIDE 3 parts of cold water (33-3 in 100 at 10°), and rather more than 1 part of boiling water (77-3 in 100). As the hot solution cools it deposits beautiful fern-like crystallisations composed of minute cubes and octahedra. The dissolution of NH,Cl in water lowers the temperature very considerably, which renders the salt very useful in freezing-mixtures. A mixture of equal weights of sal ammoniac and nitre, dissolved in its own weight of water, lowers the temperature of the latter from 10° to — 12°. The solution of ammonium chloride in water is slightly acid to blue litmus-paper. When NH,(Cl is heated it vaporises at a temperature below redness without fusing ; the vapour forms thick white clouds in the air, and may be condensed as a white crust upon a cold surface ; but it is said that it cannot be sublimed without some loss, a portion being decomposed into HCl, H,and N. For the dissocia- tion of this salt when heated, see p. 314. When ammonium chloride is heated with metallic oxides, the hydro- chloric acid often converts the oxide into a chloride which is either fusible or volatile, and this leads to one of the chief uses of the salt, namely, for cleansing the surfaces of metals previously to soldering them. Even those metallic oxides which are destitute of basic properties, such as antimonic and stannic oxides, are convertible into chlorides by the action of sal am- moniac at a high temperature. Electric batteries of the Leclanché type consume a large portion of the NH,Cl that is sold. Ammonium chloride is found in volcanic districts, and is present in very small quantity in sea water. Ammonium sulphide, (NH,),S, has been obtained in colourless crystals by mixing hydrosulphuric acid gas with twice its volume of ammonia gas in a vessel cooled by a mixture of ice and salt... It is a very unstable com- pound, decomposing in solution into free ammonia and ammonium hydro- sulphide, NH,HS, which may also be obtained in solution by saturating with H,S at 0° strong ammonia diluted with four times its volume of water. Solution of ammonium sulphide, prepared by mixing the “ hydrosulphide ” (made by saturating ammonia solution with H,S) with an equal volume of ammonia, is much used in analytical chemistry, and is supposed to contain (NH,),.S8. The solution has a very disagreeable odour. When a strong solution of ammonia is saturated with hydrogen sulphide at 0° a colourless solution is formed, from which colourless crystals separate, the composition of which varies with the strength of the ammonia, but may be expressed by the general formula, (NH4),8.cNH,HS. The solution soon becomes yellow in contact with the air, from the formation of ammonium polysulphides of the form (NH,4).8z ; eventually the solution deposits sulphur and becomes colourless, thiosulphate, sulphite, and sulphate of ammonium being formed. When the freshly prepared colourless solution is mixed with an acid, the solution remains clear, H,S being evolved with effer- vescence ; NH,HS + HCl = NH,CI + H,S and (NH,),§ + 2HCl = 2NH,Cl + HS; but if the solution be yellow, a milky precipitate of sulphur is produced, from the decomposition of the polysulphides ; (NH4)oS, + 2HCl = 2NH,Cl + HS + Sz -3. The fresh solution gives a black precipitate of lead sulphide when solution of lead acetate is added to it, but after it has been kept till it is of a dark yellow or red colour it gives a red precipitate of the persulphide of lead. Ammonium polysulphides are the chief constituents of Boyle’s fuming liquor, a fetid yellow liquid obtained by distilling sal ammoniac with sulphur andlime. They are sometimes deposited in yellow crystals from this liquid. By dissolving sulphur in ammonium disulphide, orange-yellow prismatic crystals of ammonium pentasulphide, (NH,).8;, may be obtained. Ammonium bromide (NH,Br) and Ammonium iodide (NH,]I) are useful in photo- graphy. They are both colourless crystalline salts, but the iodide is very liable to 1 When the NH, is in large excess a volatile Jiquid, (NH,).8.2NH,, is formed, the vapcur of which is very poisonous. LITHIUM 383 become yellow or brown, from the separation of iodine, unless kept dry and in the dark. Both salts are extremely soluble in water. Microcosmic salt, phosphorus salt, or hydrogen sodium ammonium phosphate, HNaNH,PO,.4Aq, is found in putrid urine and in guano. It is prepared by mixing hot strong solutions of ammonium chloride and sodium phosphate; NagHPO, + NH,Cl = HNaNH,PO, + NaCl. It forms prismatic crystals which are very soluble and fusible, boiling violently when further heated, and finally leaving a transparent glass of sodium metaphosphate, which is valuable in blowpipe work for dissolving metallic oxides ; NaNH,HPO, = NH; + H,O + NaPOs. LITHIUM, Li = 6.94. This comparatively rare metal is obtained chiefly from the minerals lepidolite (Xeric, @ scale) or lithia-mica, containing silicate of alumina with fluorides of potassium and lithium ; petalite (wéradov, @ leaf), silicate of soda, lithia and alumina; and triphane or spodumene (oroddc, ashes), which has a similar composition, but contains rather more lithium (3-8 per cent.). Its name (from \/Ouc, a stone) was bestowed in the belief that it existed only in the mineral kingdom, but recent investigation has detected it in minute proportion in the ashes of tobacco and other plants. The water of a hot spring in Clifford United Mines, in Cornwall, contains 26 grains of lithium chloride per gallon. The oxide of lithium cannot be reduced by carbon, and the metal is obtained by decomposing fused lithium chloride, or an acetone or pyridine solution of the salt, by a galvanic current. It is remarkable as the lightest solid known (sp. gr. 0-534 at 20°). It bears a general resemblance to potassium and sodium, but it is harder and less easily oxidised than those metals. It decomposes water rapidly at the ordinary tem- perature, but does not inflame upon it. It melts at 186°, but cannot be distilled. It burns in air at 200°, and when heated combines readily with nitrogen, forming NLi;, or with hydrogen, forming LiH. Lithium bears some resemblance to calcium as well as to potassium and sodium. Thus it forms an oxide, Li,O (sp. gr. 1-80), when it burns, which is earthy, and dissolves only gradually in water, unlike oxides of K and Na. The hydroxide LiOH, obtained by causticising the carbonate with lime, is less soluble (13 in 100) than KOH and NaOH and isa less powerful alkali. Another leaning towards the calcium group of metals is seen in the sparing solubility of lithium phosphate, LizPO, (1in 2500), and carbonate, Li,CO; (1-4 in 100). The latter, however, is not decomposed by heat as calcium carbonate is, but melts at 700°; it is made from lepidolite by fusing the mineral, powdering it, boiling with HCl and HNOs, and precipitating the iron, lime, &c., by Na,CO, ; the filtrate contains NaCl, KCl and LiCl; it is concentrated and mixed with Na,CO, to precipitate the Li,CO,. The “‘lithia ” used as a remedy for gout is a mixture of lithium carbonate and citric acid, the latter dissolving the former as lithium citrate with effervescence when the mixture is put in water. The compounds of lithium impart a red colour to a flame. RUBIDIUM and CA@SIUM. Rb = 85.45,Cs = 132.81. These elements were discovered in 1860 by Bunsen and Kirchhoff during the analysis of a certain spring water which contained these metals in so minute quantity (2 or 3 grains in a ton) that they would certainly have escaped observation if the analysis had been conducted in the ordinary way. The discovery of these metals, as well as of three others (thallium, indium, gallium), to be mentioned hereafter, was the result of the application of the method of spectrum analysis (see p. 354). When examining with the spectroscope the alkali chlorides extracted from the spring water, Bunsen and Kirchhoff observed two red and two blue bands in the spectrum which they could not ascribe to any known substance, and which they ultimately traced to the two new metals, rubidium (rubidus, dark red) and cesium (cesius, sky- blue), which may be isolated by the electrolysis of their fused salts (chloride and cyanide respectively), or by distilling them from a mixture of their hydroxides with magnesium, 384 REVIEW OF ALKALI METALS Rubidium (m.-pt. 38-5° ; sp. gr. 1-53) has since been found in small quantity in carnallite, in lepidolite (about 1 per cent.), and in the ashes of many plants. This metal is closely related in properties to potassium, but is more easily fusible and convertible into vapour (b.-pt. 696°), and actually surpasses that metal in its attraction for oxygen, rubidium taking fire spontaneously in air, forming RbO,. It burns on water with exactly the same flame as potassium. Its hydroxide is a powerful alkali, like potash, and its salts are isomorphous with, and more soluble than, those of potassium. The double chloride of platinum and potassium is eight times as soluble in boiling water as the corresponding salt of rubidium, which is taken advantage of in separating these two allied metals. Rubidium forms stable and sparingly soluble double salts with many halides ; thus the borofiuoride, RbBF,, requires 100 parts of boiling water to dissolve it. Cesium (m.-pt. 26-5 ; sp. gr. 2-38), the softest of metals, appears to be even more highly electro-positive than rubidium, forming a strong alkali, cesium hydroxide, and salts which are isomorphous with those of potassium. Cwsium carbonate, however, is soluble in alcohol, which does not dissolve the carbonates of potassium and rubidium. Moreover, the cesium bitartrate is nine times as soluble in water as the rubidium bitartrate is. It boils at 670°. Cesium sulphate is very deliquescent. Cesium has been found in lepidolite ; and the rare mineral polluz, found in Elba, and resembling felspar in composition, contains as much as 32 per cent. The alum of the island of Vulcano is mentioned as a rich source of cesium and rubidium. Both rubidium and cesium show a remarkable tendency to combine with halogens as though they were trivalent or pentavalent, forming such compounds as RbICI,, CsI;, and RbIBrs. Review of the Group of Alkali Metals.—Cesium, rubidium, potas- sium, sodium and lithium constitute a group of elements conspicuous for their highly electro-positive character, the powerfully alkaline nature of their hydroxides, and the general solubility of their salts. Their chemical charac- ters and {unctions are directly opposite to those of the electro-negative group containing fluorine, chlorine, bromine and iodine, and, like those elements, they exhibit a gradation of properties. The order in which they are named above and in the following Table is that of decreasing electro-positiveness, and just as iodine, the least electro-negative of the halogens, has the highest atomic weight, so cesium, the heaviest of the-alkali metals, is the least electro-negative : Cs Rb K Na Li Atomic weight . 132-8 85-4 39-1 23-0 6-9 Specific gravity . 2-28 1-58 0-86 0-97 0-53 Melting-point . 26:5° 38-5° 62-5° 97° 186° Like the halogens they are monovalent elements. While the halogens are typically acidic elements, the alkali metals are typically basic, and the combination of an element of the one group with an element of the other is a typical salt, devoid of either acidic or basic properties. In some of their salts a similar gradational relation is observed ; the carbonates, for example, of cesium, rubidium, and potassium are highly deliquescent, absorbing water greedily from the air, while carbonate of sodium is not deliquescent, and carbonate of lithium is sparingly soluble in water. The difficult solubility of the carbonate and phosphate of lithium constitutes the connecting link between this and the succeeding group of metals, the carbonates and phosphates of which are insoluble in water. ALKALINE EARTH METAL [SECOND (i)] GROUP Catcium, Strontium, Barium, Rapium. BARIUM, Ba = 137.37. Barium, so named from the great weight of its compounds (Bagis, heavy), is found in considerable abundance in the north of England, in two minerals known as witherite (barium carbonate, BaCO,) and heavy spar, barytes, or cawk (barium sulphate, BaSO,). Witherite is found in large masses in the lead mines at Alston Moor, and at Anglesark in Lancashire. It was originally mistaken, on account of its great weight (sp. gr. 4-5), for an ore of lead. All salts of barium are poisonous. The metal itself is isolated by electrolysing fused barium chloride or heating it with sodium, but it is difficult to purify and exact knowledge as to its properties is scanty. Itis pale yellow and malleable, of sp. gr. between 3°75 and 4-0 ; it is easily oxidised by air, and rapidly decomposes water at common temperatures. It requires a high temperature to fuse it. Barium and its salts impart a green colour to a flame. Such compounds of barium as are used in the arts are chiefly prepared from heavy spar, which is remarkable for its insolubility in water and acids. In order to prepare other compounds of barium from this refractory mineral, it is ground to powder and strongly heated in contact with charcoal or some other carbonaceous substance, which removes the oxygen from the mineral in the form of carbonic oxide, thus converting the barium sulphate into Barium sulphide; BaSO,+C,=4CO + BaS. This latter compound yields a solution with water from which other barium compounds can readily be prepared. The artificial Barium sulphate (sp. gr. 4:5), which is used by painters instead of white lead, under the name of permanent white (blanc fixe), and is employed for glazing cards, is prepared by mixing the solution of barium sulphide (containing Ba(SH), and Ba(OH),) with dilute sulphuric acid, when the barium sulphate separates as a white precipitate, which is collected, washed and dried—Ba(OH), + H,SO, =2H,0 + BaSOQ,. Barium sulphate is remarkable for its insolubility in water and acids, and is the form in which either barium or sulphur is determined in quantita- tive analysis. It dissolves in hot strong H,SO,, and the solution on cooling deposits crystals of acid barium sulphate, BaH,(SO,4)o. The artificial Barium carbonate (sp. gr. 4:275), which is used in the manufacture of some kinds of glass, is prepared by passing carbonic acid gas through a solution of barium sulphide, when the carbonate is precipitated ; Ba(SH), + Ba(OH), + 2CO, = 2H,S + 2BaCO,; some sulphur generally accompanies the BaCO, and is removed by boiling the precipitate with Ba(OH),. It is not decomposed into BaO and CO, below a temperature near a white heat. In preparing compounds of barium from heavy spar on the small scale it is better to convert the sulphate into barium carbonate. Fifty parts of the finely powdered sulphate are mixed with 100 of dried Na,CO;, 600 of powdered nitre, and 100 of very finely powdered charcoal. The mixture is placed in a heap upon a brick or iron plate, and kindled with a match, when the heat evolved by the combustion of the charcoal in the oxygen of the nitre fuses the mass, producing barium carbonate and sodium sulphate ; BaSO, + Na.CO; = Na,SO, + BaCO3. The mass is thrown into boiling water, which dissolves the Na,SO, and leaves the BaCO;. The latter may be allowed to settle and washed several times, by decantation, with distilled water, until the washings 25 386 BARIUM SALTS no longer yield a precipitate with barium chloride, showing that the whole of the Na,8O,4 has been washed away. Barium oxide or Baryta, BaO, may be obtained by strongly heating a mixture of barium carbonate and charcoal, BaCO, + C = BaO + 2CO, but is now generally prepared by heating the -nitrate, Ba(NO3),= BaO + 2NO, + O. It isa heavy grey solid of sp. gr. between 4:7 and 5-7 according to the mode of preparation; it combines with water with great evolution of heat to form barium hydroxide. It is chiefly used for making Barium dioxide or peroxide, BaO,, into which it is readily converted when heated in air (free from CO,) at 600-700° (see Brin’s Oxygen Process, p. 54). Barium hydroxide, Ba(OH),, is present in an aqueous solution of barium sulphide, which is decomposed by water; 2BaS + 2H,O = Ba(SH), + Ba(OH),. By mixing the solution with zinc oxide the sulphur is precipitated as ZnS and a solution of Ba(OH), remains, which may be crystallised. It forms prisms, Ba(OH),.8Aq (sp. gr. 1-656). Crystallised barium hydroxide melts in its water of crystallisation at 78°. It may be produced by adding 113 grams of powdered barium nitrate to 340 c.c. of a boiling solution of NaOH, containing 85 grams of commercial caustic soda in 567 c.c. of water ; the solution becomes turbid from the separation of barium carbonate produced froin the sodium carbonate in the caustic soda ; it is boiled for some minutes and then filtered ; on partial cooling, some crystals of undecomposed barium nitrate are deposited, and if the clear liquid be poured off into another vessel and stirred, it deposits abundant crystals of the octohydrate ; these effloresce and become opaque when exposed to air, becoming Ba(OH),.Aq ; when heated to redness they become pure, Ba(OH),, which fuses, but is not decomposed when further heated. The hydroxide is moderately soluble in cold water (baryta water), but much more soluble in hot water (100 of water contain 2-89 of BaO at 15° and 90-77 at 80°) ; the solution is strongly alkaline and absorbs carbonic acid gas from the air, depositing barium carbonate. The hydroxide is used in some processes of sugar refining. Barium chloride, which is the barium compound most commonly employed in the laboratory, may be obtained by dissolving the carbonate in diluted hydrochloric acid, and evaporating the solution ; on cooling, the chloride is deposited in tabular crystals, BaCl,.2Aq (sp. gr. 3-0). The crystals are easily soluble in water (about 1 in 3 at 15°), but insoluble in alcohol and in strong acids. On the large scale, barium chloride is generally manufactured by heating an intimate mixture of heavy spar and small coal with a strong solution of calcium chloride in a furnace similar to the black ash furnace (p. 370). The following reactions occur ; (1) BaSO, + Cy = BaS + 400 ; (2) BaS + CaCl, = BaCl, + CaS. The mass is leached with water and the solution crystallised. Barium nitrate, Ba(NO,),, is manufactured by mixing strong solutions of BaCl, and NaNO;, when Ba(NO,), is precipitated, being the least soluble combination. A more productive method consists in heating BaCO, (witherite) with solution of NaNO, under pressure. It crystallises in octa- hedra (sp. gr. 3-23) and is comparatively sparingly soluble in water (9-2 in 100 at 20°, and 32-2 in 100 at 100°). When heated it melts (593°) and is decomposed, leaving a grey porous mass of baryta. It is an ingredient in some kinds of blasting powder and is used in making fireworks. Barium chlorate, Ba(ClO3)2, is employed in the manufacture of fireworks, being prepared for that purpose by dissolving the artificial barium carbonate in solution of chloric acid ; it forms beautiful shining tabular crystals. When mixed with com- bustible substances, such as charcoal and sulphur, it imparts a brilliant green colour to the flame of the burning mixture (see p. 385). STRONTIUM NITRATE 387 STRONTIUM, Sr = 87.63. Strontium is less abundant than barium, and occurs in nature in similar forms of combination. Strontianite (strontium carbonate, SrCO,) was first discovered in the lead mines of Strontian in Argyllshire, and has since been found in small quantity in some mineral waters. Celestine (so called from the blue tint of many specimens) is Strontium sulphate (SrSO,) and is found in beautiful rhombic crystals associated with the native sulphur in Sicily, and is also met with in this country. Celestine is lighter than heavy spar, its sp. gr. being 3-92 ; that of the precipitated SrSO, is 3-71. The sulphate is very sparingly soluble in water, but more so than BaSOQ,. It is easily converted into SrCO, by cold alkaline carbonate solution, which is not the case with BaSO,. It is reduced to sulphide (which is soluble in water) by calcination with carbonaceous matter. : Strontium metal is obtained by electrolysing the fused chloride ; it is a white metal (sp. gr. 2-54), melts about 800°, and is soft enough to be cut easily by a knife. It burns when heated in air or carbon dioxide, the flame being bright crimson, which is the colour imparted to a flame by strontium compounds generally. The most important strontium compounds are the nitrate and the hydroxide, the former being used for fireworks and the latter in sugar refining. Strontium nitrate, Sr(NO,),, is made by dissolving strontianite in nitric acid. It crystallises from hot strong solutions in anhydrous octa- hedra (sp. gr. 2:93), easily soluble in water (59 in 100 at 10°, 101 in 100 at 100°). Cold solutions deposit prisms of Sr(NO,),.4Aq (sp. gr. 2-25). The salt melts at 645°, and decomposes when further heated, leaving Strontium oxide, or strontia, SrO, sp. gr. 46, which resembles baryta, but does not com- bine with oxygen when heated. The dioxide is precipitated as SrO,.8Aq when an aqueous solution of strontia is mixed with H,O,. Strontium hydroxide, Sr(OH),.—Strontium carbonate is decomposed by heat into SrO and CO, more easily than BaCO,, though less easily than CaCO,, and it is practicable to burn the carbonate to oxide in specially fired kilns ; the oxide is slaked with water, much heat being evolved, and the solution (which is strongly alkaline) is crystallised, yielding lamine, Sr(OH),.8Aq (sp. gr. 1-396), which dissolve sparingly in cold water (1-23 in 100 at 10°), but more freely in hot (47-71 in 100 at 100°). It is much more soluble in a solution of sugar. At 100° the crystals become Sr(OH), (sp. gr. 3-625), and at 700°, SrO. Strontium chloride, SrCl,, differs from BaCl, in being deliquescent and soluble in alcohol. It crystallises in prisms, SrCl,.6Aq, soluble in about 2 parts of cold water. CALCIUM, Ca = 40.07. No other metal is so largely employed in a state of combination as is calcium, for its oxide, lime (CaO), occupies among bases much the same position as that which sulphuric acid holds among the acids, and is used, directly or indirectly, in most of the arts and manufactures. Like barium and strontium, calcium is found, though far more abun- dantly than these, in the mineral kingdom, in the forms of carbonate and sulphate, but it also occurs in large quantity as calcium fluoride (p. 131), and less frequently in the form of phosphate (p. 209); the silicate is an abundant constituent of many rocks. Calcium, moreover, is found in all animals and vegetables, and its presence in their food, in one form or other, is an essential condition of their existence. 388 CALCIUM CARBONATE Metallic calcium is made by electrolysing the fused chloride in a vessel which is in effect a carbon crucible which serves as the anode. A high current density is required at the cathode. At Bitterfeld the latter is a metal rod, which at first dips just below the surface of the fused chloride ; the melting- point of calcium being slightly above that of the chloride, the metal separates on the rod as a solid ; the rod is slowly withdrawn, whereupon the calcium adhering to it becomes the cathode, so that a long stick of the metal can be formed. The metal isnowacom- mercial article in this form, the best samples containing over 99 per cent. of Ca. The pure metal may be obtained by distilling the sticks in a vacuum. . It is a silver-white metal becoming yellow in air, melts at 800°, and has sp. gr. 155. The commercial metal is grey and slightly heavier. It resembles aluminium in hardness, but at 400° is soft as lead. It decomposes water slowly (probably because of the sparing solubility of Ca(OH),) with evo- lution of hydrogen. It oxidises slowly in air at the ordinary temperature, but when heated to its melting-point it burns with a very brilliant white light, being converted into lime (calx) mixed with Calcium nitride, Ca,N,; the presence of the latter causes evolution of NH, when the mass is mixed with water. The ease with which it combines with nitrogen, and indeed all other gases except those of the argon group, when heated renders it useful for making high vacua. Calcium hydride, CaH,, made by heating the metal with hydrogen, is a useful source of hydrogen for airships, as it decomposes water thus—CaH, + 2H,0 = Ca(OH), + 2H,. It has been sold under the name hydrolithe. Calcium salts impart a red colour to a colourless flame. Calcium carbonate, or Carbonate of lime (CaCO, or CaO.CO,), from which practically all the manufactured compounds of lime are derived, constitutes the different varieties of limestone which are met with in such abundance. Chalk is calcium carbonate in an amorphous or uncrystallised state ; it is known to the agriculturist as mild lime. Limestone consists of minute crystals of cale spar (see below). The oolite limestone, of which the Bath and Portland building stones are composed, is so called from its resemblance to the roe of fish (wév, an egg). Marble, in its different varieties, is also an assemblage of minute crystals of calc spar, sometimes variegated by the presence of oxides of iron and manganese, or of bituminous matter. This last constituent gives the colour to black marble. Calcium carbonate is dimorphous ; it is found in large transparent rhombohedral crystals, known as calcareous spar, calc spar, or Iceland spar, and calcite (sp. gr. 2-7), and remarkable for their power of doubly refracting light; and in six-sided prisms, termed aragonite (sp. gr. 2-94). When heated to about 1000° under such conditions that no escape of CO, is possible, calcium carbonate is fused to a mass resembling marble. The attention of the crystallographer has long been directed to these two crystalline forms of calcium carbonate, on account of the circumstance that if a prism of aragonite be heated it breaks up into a number of minute rhombohedra of calc spar. Satin spar is a variety of calcium carbonate. When slowly deposited from its solution in carbonic acid, calcium carbonate gives six-sided prisms of CaCO,.5Aq. Precipitated calcium carbonate is amorphous, and is the least stable of the three forms and hence the most soluble (20 mgms. per litre). When heated to a high temperature it becomes aragonite, but when kept at moderate temperatures, in contact with the liquid from which it was precipitated, it becomes calcite. Calcium carbonate is a chief constituent of the shells of fishes and of egg-shells, so that, except calcium phosphate, no mineral compound has so large a share in the composition of animal frames. Corals also consist chiefly of calcium carbonate derived from the skeletons of innumerable minute insects. The mineral gaylussite is a double carbonate of calcium and sodium (CaCO3.Na.CO;.5Aq), and is scarcely affected LIME-BURNING 389 by water unless previously heated, when water dissolves out the sodium carbonate. Baryta-calcite is a double carbonate of barium and calcium (BaCO;.CaCOs). The presence of calcium carbonate in spring waters and the solubility [ this compound in a solution of carbon dioxide have already been considered p. 44). Lime or Calcium Oxide (CaO).—The process by which lime is obtained from the carbonate has been already alluded to under the name of lime- burning. Ata red heat calcium carbonate begins to decompose into CaO and CO, ; but unless the CO, be removed, it prevents further decomposition, so that marble or chalk cannot be completely decomposed in a covered crucible, and a limekiln must have a good draught to carry off the CQ,. At 812° the dissociation pressure (p. 346) of CaCO, is 753 mm., and this is the best temperature for lime-burning. A kiln is commonly employed of the form of an inverted cone of brick- work (Fig. 238), and into this limestone and fuel are thrown in alternate layers. The former, losing its CO, before it arrives at the bottom of the furnace, is raked out in the form of burnt or quick lime (CaO), whilst its place is supplied by a fresh layer of limestone thrown in at the top of the kiln. Fig. 239 represents another form of kiln, in which the limestone is supported upon an arch built with large lumps of the stone above the fire, which is kept burning for about three days and nights, until the whole of the limestone is decomposed. Lime is generally sold in lumps having roughly the form of the original broken limestone ; they are greyish white and porous. The sp. gr. of pure CaO varies with the nature of the CaCO, from which it is made and the temperature of burning ; it averages about 3-3. Lime melts in the electric furnace and solidifies to a crystalline mass. The usual test of the quality of commercial lime consists in sprinkling it with water, with which it should eagerly combine, evolving much heat,! swelling to about 24 times its bulk, and crumbling to a light white powder of calcium hydrate (slaked lime), Ca(OH)o. Lime which behaves in this manner is termed fat lime; whereas, if it be found to slake feebly, it is pronounced a poor lime, and is known to contain a considerable pro- portion of foreign substances, such as silica, alumina, magnesia, &c. Lime is said to be overburnt when it contains hard cinder-like masses of silicate of lime, formed by the combination of the silica, which is generally found in limestone, with a portion of the lime, under the influence of excessive heat in the kiln. Air-slaked lime has slaked by simple exposure taair ; it has absorbed CO, as well as H,O and contains 57 per cent. CaCO, and 43 per cent. Ca(OH),. As stated at p. 244, dry CaO does not absorb CO, unless heated to nearly 400°. 1 The sudden slaking of a large quantity of lime may beacause of fire. A rise of temperature to 150° frequently occurs. Fifty-six grams of CaO evolve 15,540 cals. when slaked. 390 BUILDING STONES Calcium hydroxide, Ca(OH),, is much less soluble in water than is barium or strontium hydroxide ; its sp. gr.isabout 2. It requires 700 parts of cold water to dissolve it, and twice as much hot water, so that lime-water always gives a precipitate when boiled. The solution is strongly alkaline, and readily absorbs CO, from the air, which precipitates CaCO;. When lime-water is evaporated in vacuo over H,SO,, it deposits small crystals of Ca(OH),. Ca(OH), is easily converted into CaO by heat, its dissociation pressure being 760 mm. at 450°. Itis used in manufacturing chemistry as the cheapest alkaline substance. The Chemistry of Building Materials is closely connected with lime- stone and lime. Chemical principles would lead to the selection of pure silica (quartz, rock-crystal) as the most durable of building materials, since it is not attacked by any of the substances likely to be present in the atmosphere ; but even if it could be obtained in sufficiently large masses for the purpose, its great hardness presents an obstacle to its being hewn into the required forms. Of the building stones actually employed, granite, basalt, and porphyry are the most lasting, on account of their capability of resisting fora great length of time the action of water and of atmospheric carbonic acid; but their hardness makes them so difficult to work as to prevent their employment except for the construction of pavements, bridges, &c., where the work is massive and straightforward and much resistance to wear-and-tear is required. The millstone grit is also a very durable stone, consisting chiefly of silica, and employed for the foundations of houses. Freestone is a term applied to any stone which is soft enough to be wrought with hammer and chisel, or cut with a saw ; it includes the different varieties of sandstone and limestone. The Yorkshire flags employed for paving are siliceous stones of this description. The Craigleith sandstone, which is one of the freestones used in London, contains about 98 per cent. of silica, together with some calcium carbonate. The building stones in most general use are the different varieties of calcium carbonate. The durability of these is in proportion to their compact structure ; thus marble, being the most compact, has been found to resist for many centuries the action of the atmosphere, whilst the more porous limestones are corroded at the surface in a very short time. Portland stone, of which St. Paul’s and Somerset House are built, and Bath stone are among the most durable of these ; but they are all slowly corroded by exposure to the atmosphere. The chief cause of this corrosion appears to be the mechanical disintegration caused by the expansion in freezing of the water absorbed in the pores of the stone. In order to determine the relative extent to which different stones are liable to be disintegrated by frost, a piece of the stone may be saturated with water and alternately frozen and thawed. Magnesium limestones (dolomite) (carbonate of calcium with carbonate of magnesium) are much valued for ornamental architecture, on account of the ease with which they may be carved, and are said to be more durable in proportion as they approach the composition expressed by the formula CaCO;.MgCO,.1 The magnesium limestone from Bolsover Moor, of which the Houses of Parliament are built, contains 50 per cent. of calcium carbonate, 40 of magnesium carbonate, with some silica and alumina. It is probable that a slow corrosion of the surface of limestone is effected by the carbonic acid continually deposited in aqueous solution from the air; and it is certain that in the atmosphere of towns the limestone is attacked by the sulphuric acid which Any excess of calcium carbonate above that required by this formula may be dissolved out by treating the powdered magnesium limestone with weak acetic acid PORTLAND CEMENT 391 results from the combustion of coal and the operations of chemical works. The Houses of Parliament have suffered severely, probably from this cause. Many processes have been recommended for the preservation of building stones, such as water-proofing them by the application of oily and resinous substances, and coating or impregnating them with solution of soluble glass and similar matters. Purbeck, Ancaster, and Caen stones are well-known limestones employed for building. The mortar employed for building is composed of 1 part of freshly slaked lime and 3 parts of sand intimately mixed with enough water to form a uniform paste. The hardening of such a composition appears to be due, in the first instance, to the absorption of carbon dioxide from the air, by which a portion of the lime is converted into calcium carbonate, and this, uniting with the unaltered calcium hydrate, forms a solid layer, adhering closely to the two surfaces of brick or stone, which it cements together. In the course of time the lime would act upon the silica, producing calcium silicate, and this chemical action would render the adhesion more perfect. The chief use of the sand here, as in the manufacture of pottery (q¢.v.), is to prevent excessive shrinking during the drying of the mortar. In constructions which are exposed to the action of water, mortars of peculiar composition are employed. These hydraulic mortars, or cements, as they are termed, are prepared by calcining mixtures of calcium carbonate with from 10 to 30 per cent. of clay, when carbonic acid gas is expelled, and the lime combines with a portion of the silica and alumina from the clay, producing tricalcium silicate, 3CaO.SiO,, and tricalcium aluminate, 3CaO.Al,0;. When the calcined mass is ground to powder and mixed with water these silicates com- g l bine with water to f form hydrated sili- c a cates (with liberation = ha Pah pp nn J of free lime), which j eee slew | dissolve in the water le AS 7b and immediately yy crystallise again (in } af the manner described MYC Yj for the setting of ! plaster of Paris), thus Fra. 240. causing the cement to set. Roman cement is prepared by calcining a limestone containing about 25 per cent. of clay, and hardens in a very short time after mixing with water. For Portland cement (so called from its resembling Portland stone) a mixture of river-mud (chiefly clay) and limestone is calcined at a very high temperature. Fig. 240 shows a rotary kiln for burning cement. This type of furnace is also used in many cases for roasting ores, and generally for heating finely divided material. The jron cylinder, a, some 150 feet long and 6 feet diameter, is mounted at an angle to the horizontal on rollers, b, and is rotated by a pinion (not shown) driven by power and engag- ing the circular rack, c. The cylinder is lined with fire-brick suitable for resisting the attack of the hot cement material, and is heated by coal dust injected by air under pressure through a pipe, d. The mixture of calcium carbonate and clay is fed through a hopper, e, and falls down the pipe, f, into the upper end of the cylinder, the rotation of which causes the mixture to travel to the lower end, whence it falls down a fixed shoot, g, into the upper end of a rotating cylinder, h, through which it travels to be dis- charged into a wagon, 7. The chamber, &, at the upper end collects dust and is con- nected, for instance at the top, by a flue, J, with a chimney-stack. This draws a current of air into the open end of the smaller cylinder, the cement clinker being thereby cooled, 392 PLASTER OF PARIS and up the larger cylinder, so that the CO, is carried away. The reaction between the lime and clay occurs about four-fifths down the larger cylinder, the CaCO, being burnt to CaO at a higher level. Hydraulic cements are mixed for use with sand before they are wetted with water. Concrete is a mixture of hydraulic cement (1 vol.) with sand (2 vols.) and small gravel (4 vols.), the last being known as the “ aggregate.” Scott's cement is a mixture of quick-lime with a small proportion of calcium sulphate. Calcium peroxide, CaO, is precipitated in combination with 8H,0, when solution of sodium peroxide is added to one of a calcium salt. Calcium nitrate, Ca(NO,),.4Aq, differs from those of Ba and Sr by being deliquescent, much more soluble in water, and soluble in alcohol. It occurs in well-waters and in soils, the NO, having been formed by oxida- tion of NH,;. The anhydrous salt melts at 561° and its sp. gr. is 2-36. Calcium nitrate is one of the products of the factories which make nitric acid from oxides of nitrogen produced by burning atmospheric nitrogen (p. 193). The gases containing NO, are absorbed in milk of lime, yielding a mixture of calcium nitrate and nitrite ; the solution is mixed with nitric acid (from another absorption tower) and heated to convert the nitrite into nitrate, Ca(NO.)2 +2HNO;=Ca(NO3). + NO, + NO + H,0, the gases being led back to the absorption apparatus, and the liquor evaporated to crys- tallise the nitrate. Or the liquor containing nitrate and nitrite is evaporated and the solid heated to 280°-300° in gases containing NO, and air, which converts the nitrite into nitrate, Ca(NOg)2 + 2NO2. = Ca(NOs3). + 2NO; the NO becomes NO, by com- bining with atmospheric oxygen and acts on another portion of the nitrite. The calcium nitrate is used as a manure, but as it is too deliquescent it is preferred to convert it into the basic nitrate, CaNO,0H, by mixing the concentrated liquor with lime just before it solidifies. Calcium sulphate, or Sulphate of lime, in combination with water (CaSO,.2H,0), is met with in nature, both in the form of transparent prisms of selenite, and in opaque and semi-opaque masses known as alabaster and gypsum (sp. gr. 2-32). Itis this latter form which yields plaster of Paris (sp. gr. 2-6-2-75), for when heated to between 120° and 130° it loses three-fourths of its water, becoming 2CaSO,.H,O, and if the mass be then powdered, and mixed with water, the powder recombines with water to form a hard mass, having substantially the composition of the original gypsum. In the preparation of plaster of Paris, a number of large lumps of gypsum are built up into a series of arches, upon which the rest of the gypsum is sup- ported ; under these arches the fuel is burnt, and its flame is allowed to traverse the gypsum, care being taken that the temperature does not rise too high, lest the gypsum be overburnt and set very slowly with water. When the operation is supposed to be completed, the lumps are carefully sorted, and those which appear to have been properly calcined are ground to a very fine powder. When this powder is mixed with about its own weight of water to a cream, and poured into a mould, the minute particles of calcium sulphate combine with water as aforesaid, and this act of combination is attended with a slight expansion which forces the plaster into the finest lines of the mould. According to recent research the action of heat on gypsum is as follows : The transition-point from CaSO,.2H,O to 2CaSO,.H,O is 107°, at which tem- perature the pressure of the water vapour from the gypsum is higher than that of the vapour from water itself at this temperature. It follows that when gypsum is heated in a sealed tube the water vapour condenses, and the gypsum becomes a magma of plaster of Parisin water. The change at 107° is exceedingly slow, so that the gypsum- burner is obliged to use a considerably higher temperature than this. The setting is due to the fact that a small portion of the plaster (2CaSO,.H,O) dissolves in the water, crystallising again immediately as CaSO,.2H,0, thus leaving CALCIUM CHLORIDE 393 the water free to dissolve another portion of 2CaSO,.H,0, which crystallises in its turn as CaSO,.2H,O. Thus the mass soon becomes one of interlaced crystals of CaSO,.2H,O. An addition of one-tenth of lime to the plaster hardens it and accelerates the setting. Above 130° plaster of Paris gradually loses its water, yielding nearly anhydrous CaSO, (sp. gr. 2-44), which when powdered sets slowly with water ; it has been called “soluble ” anhydrite because, although nearly identical in composition with the mineral anhydrite (sp. gr. 2-96), which is anhydrous CaSQ,, it differs therefrom in its speed of setting, for, notwithstanding that this is slow compared with that of plaster of Paris, it is much more rapid than that of anhydrite.1_ The setting of soluble anhydrite appears to be similar to that of plaster of Paris ; the slowness may possibly be due to the absence of any nucleus of undecomposed CaSO,.2H,O ; compare the behaviour of anhydrous Na,SO,, which will remain as a powder under water until a crystal of the hydrated salt is added, whereupon the whole mass solidifies. At temperatures between 400° and 750° the gypsum is completely dehydrated and resembles anhydrite, being quite useless as plaster. When, however, the temperature is raised to about 1000° a slight decomposition occurs, SO; (or SO, + O) being lost, so that the mass contains a little CaO. This product (sp. gr. 2:8-2-9) when powdered sets slowly, but much more rapidly than anhydrite, though apparently without much crystallisation ; when set it is much harder and stronger than plaster of Paris, and has greater resistance to weather ; it is therefore a more useful building material, and is produced for this purpose, particularly for pavement, whence its name flooring plaster. The addition of alum to this variety of plaster hastens the setting, which then occurs with crystallisation. At very high temperatures CaSO, = CaO + SO, + O. Stucco consists of plaster of Paris (occasionally coloured) mixed with a solution of size. Plaster of Paris is much damaged by long exposure to moist air, from which it regains a portion of its water, and its property of setting is so far diminished. Preci- pitated calcium sulphate is used by paper-makers under the name of pearl hardener. Calcium sulphate is useful in the farmyard and stables for absorbing the ammonia of the decomposing excrements, which would otherwise be lost to the manure. Calcium sulphate is contained in most natural waters, and is one of the chief causes of the permanent hardness which is not removed by boiling. It is much more soluble in water than is strontium sulphate, so that sulphates will precipitate calcium only from strong solutions. The aqueous solution of CaSO, precipitates barium salts immediately, but strontium salts only after an interval, on account of the greater solubility of SrSO,. The calcium sulphate is more soluble in water at 35° than at any other temperature, 1 part of CaSO, then dissolving in about 400 parts of water. It is in- soluble in aleohol. Boiling HCl dissolves it, and deposits it in needles on cooling. Calcium chloride (CaCl,) has been mentioned as contained in the residue left in the preparation of ammonia. The pure salt may be obtained by dissolving pure CaCO, in HCl, and evaporating the solution, when pris- matic crystals of CaCl,.6Aq (sp. gr. 1-65) are obtained, which dissolve in two-thirds of their weight of water at 20°. These melt at 30-2°, and at about 200° are converted into a white porous mass of CaCl,.2Aq, which is much used for drying gases. At 802° fused calcium chloride, free from water, is left; this is very useful for removing water from some liquids. When heated in air, it evolves chlorine and becomes alkaline. A saturated (305 per cent.) solution of CaCl, boils at 178°, and is sometimes used as a convenient bath for obtaining a temperature above 100°. When mixed with three-fourths of its weight of snow CaCl,.6H,O forms a cryohydrate, reducing the temperature to — 55°. In consequence of the attraction of calcium chloride for water it rapidly becomes liquid in air, and surfaces 1 A bed of anhydrite, when exposed to the air in a railway cutting, has been known to increase in bulk by absorbing water to such an extent as to disturb the stability of the sides of the cutting. 394 SUPERPHOSPHATE OF LIME wetted with a solution of the salt never get dry. Calcium chloride is easily soluble in alcohol. One gram-molecule CaCl, evolves 18,723 cals. in excess of water and 17,555 in excess of alcohol. A mass of fused CaCl, .6H,0 at 30-2° contains 102-7 of CaCl, and 100 of HO ; if its temperature be raised it can dissolve more CaCl,. Between 30-2° and 45-3° the saturated solution contains CaCl,.4Aq, for this is deposited on cooling. A solution saturated at temperatures between 45-3° and 178° deposits CaCl,.2Aq. When saturated above this temperature, under pressure, the solution contains CaCl,.Aq. When Ca(OH), is boiled with a strong solution of calcium chloride, it is dissolved and the filtered solution deposits prismatic crystals of calcium oxychloride, CaCl, .3CaO.15Aq, which are decomposed by water. Chloride of lime (chlorinated lime); seep. 115. Calcium fluoride, CaF,, occurs chiefly as fluor spar (sp. gr. 3-183) (p. 131), often beautifully crystallised. Many specimens of it decrepitate and emit a phosphorescent light when heated. It fuses at 1330°, and is used in metallurgy as a flux, since it attacks silica at a high temperature. Calcium fluoride is slightly soluble in hot HCl, and is reprecipitated by NH3. It is obtained as a gelatinous precipitate insoluble in acetic acid when CaCl, is added to an alkali fluoride. It is almost insoluble in water (16 mgms. per litre). Artificial teeth are made of calcium fluoride. In minute pro- portions calcium fluoride is a normal constituent of bones and teeth. Calcium sulphide (CaS) is present in Balmain’s luminous paint. Its property of shining in the dark after exposure to a bright light was observed by Canton in 1761 ; his so-called phosphorus was obtained by strongly heating oyster-shells with sulphur. The phosphorescence is not due to slow oxidation, since a specimen which has been kept for more than a century in a sealed tube still exhibits it ; it does not appear to be a property of the pure sulphide. It dissolves in water, but there is a partial decom- position into calcium hydrosulphide, Ca(SH),, and Ca(OH),. A solution of Ca(SH), is used as a depilatory. Calcium phosphate, Ca,(PO,),, occurs in the minerals apatite, phos- phorite, sombrerite, and coprolite ; in the first two it is combined with calcium fluoride, forming 3Ca;(PO,),.CaF,, and this is also contained in bone-ash, of which Ca,(PO,), forms the larger proportion (80 per cent.). This is sold as a non-mercurial plate powder, under the name of white rouge. Calcium phosphate is nearly insoluble in water, but slightly soluble in water contain- ing CO,; it is dissolved by HCl or HNO,, and is precipitated again by ammonia. When CaCl, is added to Na,HPO,, a gelatinous precipitate is obtained, which becomes crystalline after a short time. The gelatinous precipitate dissolves easily in acetic acid, but the crystalline precipitate does not, and if the solution of the gelatinous precipitate in very little acetic acid be allowed to stand, or briskly stirred, it deposits crystals of CaHPO,.2Aq. This salt is found in calculi in the sturgeon. Tetra-hydrogen calcium phosphate, CaH,(PO,),, commonly called Super- phosphate of lime, is made by decomposing Ca;(PO,), with sulphuric acid ; Ca,(PO,). + 2H,SO,= CaH,(PO,), + 2CaSO, ; the calcium sulphate is filtered off, and the superphosphate is left in solution. The pure super- phosphate may be prepared by dissolving bone-ash in HCl, precipitating with ammonia, and digesting the washed precipitate of Ca,(PO,). with H,PO,; Ca;(PO,). + 4H;,PO, = 3CaH,(PO,),. On allowing the solution to evaporate spontaneously, the salt crystallises in rhomboidal plates contain- ing a molecule of water. It is dissolved by a small quantity of water, but it is decomposed and precipitated by much water, or by boiling ; CaH,(PO,), =H;PO, + CaHPO,. The commercial superphosphate manure is a damp mixture of CaH,(PO,)> and CALCIUM CARBIDE 395 CaSO,, prepared by mixing ground mineral phosphates with sulphuric acid. It is valued by the agriculturist for the large amount of soluble phosphate (17 to 20 per cent.) which it contains; in course of time the proportion of this decreases, and the phosphate is said to have reverted to the insoluble form, owing to the action of the super- phosphate upon some undecomposed Ca,(PO,)2 remaining in the compound, resulting in the formation of the insoluble hydrocalcium phosphate—CaH,(PO,)p + Cag(POx). = 4CaHPO,. Another cause for this retrogression of the superphosphate which has been prepared from mineral phosphates is the presence of the sulphates of aluminium, magnesium, and iron, which gradually convert the phosphoric acid into insoluble forms. Calcium pyrophosphate, CazP,0,, when exposed for several hours to a dull red heat, forms a perfectly transparent glass of sp. gr. 2-6, which may be worked into prisms and lenses like ordinary glass, its refractive power being equal to that of crown glass. It is not acted on by acids in the cold, and even resists HF. Calcium ammonium arsenate, CaNH,AsO,.7Aq, is obtained as a white precipitate by mixing CaCl, with excess of NH, and adding arsenic acid. The precipitate is gela- tinous at first, but changes rapidly into fine needles, especially if stirred. It is slightly soluble in water, but almost insoluble in ammonia. Dried in vacuo, over sulphuric acid, it becomes CagsNH,H,(AsO,)3.3Aq. Dried at 100°, it has the formula CagNH4H,(AsO,),.3Aq. Heated to redness, it becomes calcium pyro-arsenate, CagAs,0,. Calcium ortho-arsenate, Caz(AsO4)z, and metarsenate, Ca(AsOz)o, have also been obtained. Calcium Carbide, CaC,—Some of the properties of this substance have been described at p. 251. Its manufacture is conducted by feeding a mixture of 100 parts of quicklime with 70 parts of coke, both in pieces about the size of a nut, between the poles of an electric arc, when the materials fuse, having reacted to form calcium carbide ; CaO + 3C = CaQ, + CO — 105,350 cals. The temperature at which this reaction occurs appears to be about 1600°. Several forms of electric furnace have been devised for this manufacture ; one of them consists of an iron truck contained in a brickwork chamber, and having suspended in it a bundle of carbon rods. The latter are connected with one pole of the dynamo, the truck being connected with the other pole, and thus conducting the current to the charge it contains, which forms the actual electrode and protects the truck from the heat. The truck is run out of the furnace and another substituted for it as soon as it is full of the carbide. Pure calcium carbide forms colourless transparent crystals, but the commercial preduct (about 80 per cent. of CaCg) is a grey opaque.crystalline substance of sp. gr. 2-2, which is decomposed by aqueous vapour so that it smells of impure acetylene when exposed to the atmosphere (p. 251). In addition to its use for making acetylene, it is heated with nitrogen for producing calciwm cyanamide (q.v.), and has found some application as a reducing agent in metallurgy. Calcium silicide, CaSig, is now made on a large scale by heating a mixture of lime and silicon or ferro-silicon in an electric furnace. It has a white metallic appearance and is very slowly attacked by water with evolution of hydrogen. It is used as a reducing agent in the metallurgy of iron. Calcium silicates are found associated with other silicates in many materials. They are also constituents of most forms of glass, which will therefore receive attention here. Glass.—The most valuable property of glass, after its transparency and permanence, is that of assuming a viscid or plastic consistence when fused, which allows it to be so easily fashioned into the various shapes required for use or ornament. Since it has been discovered that rock crystal and sand share this property (p. 282) and can be worked after fusion in the electric furnace by the methods of the glass-blower on a manufacturing scale, it has become apparent that the definition of glass should be extended. Formerly this material was defined as an amorphous mixture of two or more silicates, one of which is a silicate of an alkali metal, the other a silicate of calcium, barium, iron, lead, or zinc. Now it would be more correct to define glass as amorphous 396 GLASS silica containing embedded in it invisible crystals of silica or of one or more silicates. ‘ Silica-glass ware is made with the aid of an electric resistance furnace, such as is illustrated in Fig. 241 in longitudinal section. The carbon rod, a, constituting the pet resistance is fixed to one of the electrodes, b, but is merely inserted into the other. The electrodes protrude through the re- movable ends of the box, c, which is filled with glass-maker’s sand. A current is fed to the electrodes, and the rod, a, becoming very highly heated, a cylindrical mass of on fae Ge ee TONE OGL ie aan perenne: ee it, represented by eee parallel continuous lines in the figure, becomes fused to a viscous mass. The electrodes are now withdrawn by causing their carriers, d, to travel along the guides, e. Owing to the formation of silica vapour (or it may be of carbon monoxide due to the reaction of silica with the carbon) around the rod, a, the plastic mass is not in contact with the latter, which is withdrawn together with the electrode whereto it is attached. The ends of the box having been removed so that the sand falls away from the ends of the plastic cylinder, the latter is taken out by suitable tongs and blown by the usual glass-making methods. The most remarkable property of silica-glass is its low coefficient of expansion (0-00000054, or one-eighteenth that of platinum), to which its capacity for withstanding sudden changes of temperature without fracture is due. The material far surpasses glass as an insulator of electricity, especially in a moist atmosphere. It exceeds ordinary glass in resistance to acids (except HF), but is, of course, susceptible to attack of alkalies; it is proposed to overcome this latter disqualification by electro- plating silica vessels internally with gold or platinum. Silica-glass is exceptionally transparent to ultra-violet rays ; its general transparency is liable to be impaired by the presence of small bubbles, assumed to be due to the formation of vapour during the fusion of the silica ; the addition of oxide of titanium or zirconium is said to yield a more transparent product by raising the boiling-point. Typical glass may be said to correspond with the formula M,0.Ca0.6Si0,, where M is an alkali metal. The different kinds of glass may, however, vary considerably from this formula. Since silica is the constituent of glass which resists both heat and chemical action, the more of this the glass contains the more permanent and difficult to work the glass becomes. If silica be fused with an equal weight of carbonate of potassium or sodium, a transparent glassy mass is obtained, but this is slowly dissolved by water, and would therefore be incapable of resisting the action of the weather ; if a small proportion of lime or baryta, or of the oxides of iron, lead, or zinc, be added, the glass becomes far less easily affected by atmo- spheric influences. The composition of glass is varied according to the particular purpose for which it is intended, the materials selected being fused in large clay crucibles placed in reverberatory furnaces, and heated by a coal fire or by producer-gas, or in a fireclay tank in a regenerative furnace. Ordinary window glass is a soda glass, essentially composed of sodium silicate and calcium silicate, containing 1 mol. (13-3 per cent.) of soda, 1 mol. (12:9 per cent.) of lime, and 5 mols. (69-1 per cent.) of silica ; it also usually contains a little alumina. This variety of glass is manu- factured by fusing sand (100 parts) with chalk (35) and soda-ash (35); a considerable quantity of broken window glass is always fused up at the same time. Of course, CO, is expelled from the chalk and the Na,CO; in the gaseous state ; and in order that this may not cause the contents of the crucible to froth over during the fusion, the materials are first fritted together, as it is termed, at a temperature insufficient to liquefy them, when GLASS 397 the CO, is evolved gradually, and the fusion afterwards occurs without effervescence. ; Sodium sulphate is frequently employed instead of the carbonate, when it is usual to add a small proportion of charcoal in order to facilitate the decomposition of the sulphate by removing part of its oxygen (Na,SO, + SiO, + C = Na,SiO, + SO, + CO). Before the glass is worked into sheets it is allowed to remain at rest for some time in the fused state, so that the air-bubbles may escape, and the glass-gall or scum (con- sisting chiefly of sodium sulphate and sodium chloride) which rises to the surface is removed. Plate glass is also chiefly a silicate of sodium and calcium, but it contains, in addition, a considerable quantity of silicate of potassium (74 per cent. of SiO,, 12 of Na,O, 5-5 of K,0, and 5-5 of CaO). The purest white sand is selected, and great care is taken to exclude impurities. Crown glass, used for optical purposes, contains no sodium, since that metal has the property of imparting a greenish tint to glass, which is not the case with potassium, This variety of glass, therefore, is prepared by fusing sand with potassium carbonate and chalk in such proportions that the glass may contain 1 mol. (22 per cent.) of K,0, 1 mol. (12-5 per cent.) of CaO, and 4 mols. (62 per cent.) of Si0,. Bohemian glass, also w potash glass (silicate of K,0 and CaO), is less fusible than soda glass, and less easily attacked by acids ; hence its use for chemical vessels. The alkali silicate in glass being the more soluble in water the richer it is in alkali, a glass containing a high percentage of silica is the more generally useful for chemical vessels, particularly as it is less fusible than that poorer in this constituent. It is only comparatively recently, however, that furnaces attaining the high temperatures necessary for working glass rich in silica have been used. Acid solutions attack glass less than water does, while alkali produces the most effect. By steaming the glass for some time its surface becomes more resistant. Glass containing both alkalies is more easily attacked than that containing only one. The glass of which wine bottles are made is of much cheaper and commoner description, consisting chiefly of calcium silicate, but containing, in addition, small quantities of the silicates of sodium, of aluminium, and of iron, to the last of which it owes its dark colour. Flint glass, which is used for table glass and for ornamental purposes, is a double silicate of potassium and lead, containing 1 mol. (13-67 per cent.) of K,O, 1 mol. (33-28 per cent.) of PbO, and 6 mols. (51-93 per cent.) of SiO,. It is prepared by fusing 300 parts of the purest white sand with 200 parts of minium (red oxide of lead), 100 parts of refined pearl-ash, and 30 parts of nitre. The fusion is effected in crucibles covered in at the top to prevent the access of the flame, which would reduce a portion of the lead to the metallic state. The nitre is added in order to oxidise any acci- dental impurities which might reduce the lead. The presence of the lead in glass very much increases its fusibility, and renders it much softer, so that it may be more easily cut into ornamental forms ; it also greatly increases its lustre and beauty. Barium has also the effect of increasing the fusibility of glass, and zinc, like lead, increases its brilliancy and refracting power, on which account it is employed in some kinds of glass for optical purposes. Glass of this description is also made by substituting boric oxide for a portion of the silica. All glass articles must be annealed by being slowly cooled, otherwise they are liable to spontaneous fracture, due to the excessive strains produced in the structure of the glass. This practical experience is in accord with the modern conception that glass is a network of crystalline silicates and silica filled in with amorphous silicates and silica, this amorphous matter having the properties of a liquid of very high viscosity. The 398 COLOURED GLASS more quickly the plastic mass of glass is cooled the higher the proportion of the amor- phous matter to the crystals. When sufficiently slowly cooled the mass becomes so crystalline that it is opaque and very hard, resembling porcelain (Réaumur’s porcelain) ; this change, which is shared by silica (p. 283), is more marked in some varieties of glass than in others and is known as devitrification ; the devitrified glass is restored to its original transparent condition when fused and normally cooled. A temperature short of the melting-point will suffice to cause devitrification, and the phenomenon is frequently to be seen in lamp chimneys. By smearing glass with thick glue and allowing the glue to dry, the surface of the glass is torn by the contracting glue, and the crystalline network becomes apparent. The viscosity of the amorphous material is shown by the fact that a glass rod supported only at its ends will bend in the course of time, and the analogy with a liquid is shown by the high surface tension of glass, which is the greater the more rapidly the glass has been cooled—that is, the larger the proportion of the amorphous matter. _ By allowing fused glass to drop into water, very clear and hard masses (Rupert's drops) are obtained the surface tension of which is so great that a scratch will cause the mass to break into many pieces. Toughened glass is less drastically cooled, the glass vessel being heated to its softening-point and immersed in oil or steam at 200° ; its specific gravity is increased and it is hardened, but it is liable to break up when its surface is scratched, and sometimes apparently spontaneously. In producing coloured glass, advantage is taken of the property of glass of dissolving many metallic oxides with production of peculiar colours. It has been mentioned above that bottle glass owes its green colour to the presence of iron ; and since this metal is generally found in small quantity in sand, and even in chalk, it occasionally happens that a glass which is required to be perfectly colourless turns out to have a slight green tinge. In order to avoid this, a small quantity of some oxidising agent is usually added to convert the ferrous oxide into ferric oxide, which does not impart any colour when present in minute proportion. A little nitre is sometimes added for this purpose, or some white arsenic, which yields its oxygen to the ferrous oxide, and escapes in the form of vapour of arsenic ; red oxide of lead (Pb304) may also be employed, and is reduced to oxide of lead (PbO), which remains in the glass. Manganese dioxide (glass maker’s soap) is often added as an oxidising agent, being reduced to the state of manganous oxide (MnO), which does not colour the glass; but care is then taken not to add too much of the dioxide, for a very minute quantity of this substance imparts a beautiful amethyst-purple colour to glass. Suboxide of copper is used to produce a red glass, and the finest ruby glass is obtained by the addition of alittle gold. The oxides of antimony impart a yellow colour to glass ; a peculiar brown-yellow shade is given by charcoal in a fine state of division, and sesqui- oxide of uranium produces a fine greenish-yellow glass. Green glass is coloured either by oxide of copper or sesquioxide of chromium, whilst oxide of cobalt gives a magnificent blue colour. For black glass a mixture of the oxides of cobalt and manganese is employed. The white enamel glass is a flint glass, containing about 10 per cent. of binoxide of tin. Bone-ash is also used to impart this appearance to glass. The trisation of glass, giving it the tints of mother-of-pearl, is effected by corroding its surface with hydrochloric acid of 15 per cent. strength, under heat and pressure. Cryolite is employed in making opal-glass containing 64 per cent. of silica, 17 of alumina, 16 of lead oxide, and 3 of potash. Review of the Metals of the Alkaline Earths.—These three metals show a much closer relationship to each other than to the metals of the second sub-group or than these latter show among themselves. Like the metals of the first group, the electro-positiveness decreases with diminishing atomic weight, as is indicated by a comparison of many of their compounds. Thus the heat of formation of the anhydrous chloride, of the hydroxide from the oxide, and of the carbonate from the oxide all diminish as the atomic weight decreases.! * It is proper to add that so far as published data can be trusted, the reverse appears to be the case with the heat of formation of the oxides. . RADIUM 399 Cals. Cals. Cals. Ba, Cl, . 194,740 BaO,H,O . 22,300 BaO,CO, . 62,220 Sr,Cl. . 184,450 SrO,H,O . 17,700 Sr0,CO, . 55,770 Ca,Cl, . - 169,820 Ca0,H,O . 15,540 Ca0,CO, . 42,520 These figures are in accord with the facts already noticed, namely, that BaCO, and Ba(OH), require a very high temperature for their decomposition, while the corresponding Sr and Ca compounds are decomposed at successively lower temperatures. With the exception of the hydroxides and the fluorides, the solubility of most of the inorganic compounds of these metals at 18° increases as the atomic weight of the metal decreases. The manner in which these metals are associated in nature is not without significance : if two of them are found in the same mineral they will usually be those which stand next to each other in the group; thus strontium carbonate is found together with barium carbonate in witherite, whilst calcium carbonate is associated with strontium sulphate in celestine. Again, strontium carbonate is often found with calcium carbonate in aragonite. Such facts lend support to the hypotheses of Crookes and others as to the possible evolution of the elements. RADIUM, Ra = 226.4. Having invented a particularly sensitive means for detecting the ionising effect (p. 356) on air of the then recently discovered radiations of uranium and thorium, P. and 8. Curie found (1898) that certain minerals containing one or other of these elements are relatively considerably more active in this respect than either of the elements or of any of their compounds. It appeared, therefore, that the activity could not be due wholly to the known element, and a search was made for some new “radioactive ” substance. The pitchblende (p. 472) which is mined at Joachimstahl in Bohemia proved particularly active, and analysis of the mineral, accompanied by tests of each precipitate and residue in respect of its ionising power (the test consisting, in general terms, in ascertaining whether the material brought near a charged electro- scope hastens the discharge thereof, and with what degree of rapidity), showed that the active matter remained with the barium sulphate left after the numerous other consti- tuents of the mineral had been removed. It was concluded that the active substance was a metal forming an insoluble sulphate, and on converting the barium sulphate into chloride and fractionally crystallising, a small amount of an exceedingly active chloride, less soluble than barium chloride, was obtained. The metal with which the chloride was assumed to correspond was termed radium. The extraction of radium salts from pitchblende is very cumbersome, owing to the fact that there is only about 1 part of radium in 10 million parts of the ore. Modern improvements have reduced the operation to one of weeks, but details of the process are not disclosed. At Joachimstahl the pitchblende is heated with Na,CO, and then leached with water and dil. H,SO, to extract the uranium oxide from it; the residue was formerly discarded, but is now worked up for radium. A recent account states that 1-05 grams of substantially pure RaCl, were obtained from 10,000 kilos of the residue, the work occupying two years. The residue contains most of the metals as sulphates ; it is heated with NaOH solution, the undissolved portion is washed and heated with HCI; the sulphates which remain insoluble are digested with NagCO,, and the carbonates thus formed are dissolved in HCl. The sulphates (of Ba, Sr, Ca, Pb) are now precipitated by adding H,SO, and are again converted into carbonates and dissolved in HCl; the lead is precipitated with H,S and the solution evaporated to dryness, the CaCl, is extracted by strong HCl, and the remaining chlorides (about 20 grams) are fractionally crystallised, RaCl, being the least soluble. The substitution of HBr for HCl in this process is recommended, the bromides being more easily fractionated than the chlorides The total quantity of radium compounds which has been handled by chemists is so small that little is known of the chemical properties of the element. The chloride, 400 RADIUM EMANATION free from BaCl,, obtained as the final fraction of the process of extraction, gives a characteristic spectrum and closely resembles barium chloride ; assuming that it is the chloride of a metal, the equivalent of the latter is 113-2. As there is a vacancy in the second group of the Periodic Table for a metal having this equivalent, and as all the compounds resemble closely the corresponding compounds of barium, it may be accepted that the active chloride is the chloride of a metal belonging to the barium group and of atomic weight 226-4. Commercial radium preparations consist of a barium salt containing more or less radium salt (generally RaCl, or RaBr,) and are valued by their degree of radioactivity ; they are used purely for this property, which is not materially affected by the presence of the inert barium salt. Metallic radium has been isolated on @ very small scale by electrolysing a solution of radium chloride with a mercury cathode, drying the amalgam thus formed and dis- tilling the mercury from it in a current of hydrogen. It isa shining white metal, melting and volatilising at 700° ; it becomes black in air, probably owing to formation of nitride, and blackens white paper. It decomposes water. Radium salts resemble those of barium, but are rather less soluble ; they impart a red colour to a Bunsen flame. The oxide is soluble in water. In addition to emitting constantly a-, 3-, and y- radiations (p. 356), radium and its compounds evolve a gas, termed radium emanation, which in a short period changes into solid matter. Some of this gas remains occluded in the radium compound, which is therefore also mixed with the said solid matter. The proportion of these matters which are not strictly radium is larger in the commercial radium preparations than in pure radium compounds, because the inert material present helps to occlude the gas. Hence, if the properties of a radium compound are to be studied, the compound must either be strongly heated or be dissolved in water, and the solution evaporated rapidly to dryness, in order to expel this gas and other matter ; the study must then be con- ducted quickly because the evolution of gas continues. It is not likely that the presence of these other matters in the radium compound would affect the value of the ordinary physical constants, or the chemical behaviour, of the compound, because 1 gram of radium does not appear to contain more than 0-6 cubic millimetre and a correspondingly smaller proportion of other matter when in radioactive equilibrium (infra). But here it is a question of the radioactivity of the material, a property which can be tested and measured with a delicacy exceeding even that of the spectro- scope. Raa and its compounds always have a temperature higher than that of the surrounding atmosphere. Measurements show that 1 gram of radium would evolve 118 gram-calories per hour. This remarkable fact must be supposed to be due to an exothermic change occurring in the radium and having for its result the radioactivity and the evolution of emanation. When deprived of emanation, &c., radium preparations appear to emit only a-rays, but a little /3-radiation can be detected, which is taken to mean that one of the products (probably the first, called RaX) into which radium breaks up has not been eliminated. After a short period the preparation recovers the same radioactivity which it had before it was treated to deprive it of emanation, &c. In this condition it is said to be in radioactive equilibrium—that is to say, the state in which the same number of atoms of each of the ephemeral “ disintegration products ” is being formed and broken up per second. It has been calculated that in this condition over 98 per cent. of the total energy evolved by the preparation is in the form of a-rays, which consist of streams of a-particles (p. 356). It has been shown from electrical considerations that the a-particles must be four times as heavy as a hydrogen atom ; this is the atomic weight of helium, and since helium is a constant companion of radium in minerals, and radium preparations constantly evolve helium, it is concluded that the a-particle is an atom of helium. One gram of radium (as chloride) in radioactive equilibrium evolves helium at the very slow rate of 0-156 c.c. per annum, and diminution of the radioactivity of radium preparations has not been perceptible since they were known. The process of disintegration is evidently very slow, and on the assumption that each a-particle represents one disin- tegrated atom of radium free from emanation, &c., and on the basis of electrical DISINTEGRATION OF RADIUM 401 measurements, it has been calculated that the probability of life of a radium atom is 2500 years. : Radium preparations are used in medicine for the healing effect of their rays, and their application for causing the discharge of electricity from places where friction generates it undesirably has been suggested. Niton, Nt, 222-4, is the name now given to radium emanation. Although this matter has been examined only in very minute quantity, there is sufficient evidence that it is a gas obeying the usual laws and of density 111-2. The most remarkable properties of the gas are its luminosity (which renders radium preparations luminous), its radio- activity, its power of decomposing water, and its spontaneous disintegration. It is best obtained by withdrawing the gases from a solution of a radium salt ; these contain chiefly H, + O (produced by decomposition of the water by the niton) and a slight excess of H. Numerous operations carried out on a minute scale are necessary to obtain the fraction of a cubic millimetre of niton contained in the gases. Niton has a characteristic spectrum, which indicates its elementary character ; in spite of its power to produce certain chemical changes, it doesnot appear to have any chemical affinity, and this resemblance to gases of the argon group leads to the supposition that its molecules are monatomic. Niton is further described as a member of the argon group ; p. 294; and in other respects at p. 357. Among the chemical changes effected by niton, its action on glass is very noticeable, producing in the glass first a pale violet, then dark purple, and finally complete opacity. The action of niton on water has been mentioned ; nitrous oxide is produced by its action on air ; lubricants are rapidly destroyed by it. It is still doubtful whether the experiments of Ramsay and Cameron are conclusive that niton transforms certain elements into others with liberation of neon or helium—for instance, copper into lithium and thorium into carbon (p. 294). That niton is a constituent of the atmosphere seems probable in view of the very wide distribution of radioactive substances in minute traces, and the fact that highly negatively charged wires suspended in the atmosphere become radioactive from depo- sition of disintegration products of niton is confirmatory. The radioactivity of niton rapidly diminishes, having faJlen to half its value in 3-85 days, and this diminution is accompanied by a conversion of the gas into a solid, radioactive deposit, called radium A. It is impossible here to do more than indicate the results which have attended the investigation of the changes of radioactivity occurring in radium A. They show that the material undergoes successive disintegration into products which can be separated chemically in that certain compounds (BaSQ,, Ca(OH),) precipitated in solution containing the products carry down one in preference to others ; or they can be separated by electrolysis or by heat. The following list shows what is believed at present to be the disintegration series of the radium elements; one atom of each changes into one atom of that next after it in the list, and in the case of those marked a the loss of an a-particle (atom of helium) accompanies the change. (3 and y mark the products which yield these rays and the numbers give the average life of the atom; Ra (a, 2500 years), RaX ?, Niton (a, 5-57 days), RaA (a, 4:3 mins.), RaB (3, 38-5 mins.), Ra, (a, B, y, 28-2 mins.), RaC, (3, y, 1-9 mins.), RaD (6, 24 years), RaE ((, y, 7-25 days), RaF (a, 202 days), RaG. RaF is identical with the original polonium, an active substance which accompanies the bismuth precipitated in working up pitchblende for radium. Since the loss of each a-particle means a diminution of 4 in the atomic weight, RaG should have an atomic weight of 20 units less than that of radium, or 206-4 ; this is so near that of lead that it is supposed that RaG is lead (cf. the fact that RaF resembles bismuth). Radium occurs almost exclusively in minerals containing uranium, and in amount which is substantially a constant fraction of that of the uranium in the mineral ; this leads to the supposition that radium is itself a disintegration product of uranium. But the immediate parent of radium appears to be Ionium, a radioactive (a-rays) substance separated from pitchblende together with actinium and changing into radium at a measurable rate. Actinium is separated from pitchblende together with the rare earths and is probably an element related to these. It gives rise to a succession of radioactive disintegration 26 402 MAGNESIUM products and a gaseous emanation, which rapidly becomes a solid deposit of further disintegration products. For further information as to the actinium series and, indeed, the whole subject of the radioactive elements, the reader is referred to the several monographs now published. Uranium and thorium, the only other elements having well-marked radioactivity, will be dealt with in their proper places. Potassium and rubidium show slight radio- activity. MAGNESIUM [SECOND (ii)] GROUP. BEeRyYLLIUM, MaGnesium, Zinc, Capmium, Mercury. MAGNESIUM, Mg=24.32. Magnesium is found, like calcium, though less abundantly, in each of the three natural kingdoms. Among minerals containing this metal, those with which we are most familiar are certain combinations of silica and magnesia (silicates of magnesium) known by the names of talc, steatite or French chalk, asbestos, and meerschaum, which always contains water. Magnesite is a carbonate of magnesium. Most of the minerals containing magnesium have a remarkably soapy feel. The compounds of magnesium, which are employed in medicine, are derived either from the mineral dolo- mite (magnesium limestone), which contains the carbonates of magnesium and calcium, or from the magnesium sulphate which is obtained from sea- water, the waters of many mineral springs, and the Stassfurt deposits (p. 361). Magnesium is an essential element in chlorophyll (q¢.v.) and so becomes one of the most important of all metallic elements in biological synthesis. Metallic magnesium is important as a source of light. When the extremity of a ribbon of this metal is heated in a flame, it takes fire, and burns with a dazzling white light, becoming magnesia (MgO). If the burn- ing wire be plunged into a bottle of oxygen, the combustion is still more brilliant. The light emitted by burning magnesium contains a larger propor- tion of chemically active rays than any other artificial source of light contains, a circumstance turned to advantage for the production of photographic pictures, for which purpose the powdered metal is blown through a flame producing a flash of very short duration but intense luminosity. Attempts have been made to introduce magnesium as an illuminating agent for general purposes, but the large quantity of solid magnesia produced in its com- bustion forms a very serious obstacle to its use. The metal is obtained by electrolysing fused carnallite (p. 361), which, when melted, loses its water and becomes KCl.MgCl,. The operation resembles that described for the production of calcium (p. 388), the magnesium being obtained similarly in sticks. This electrolysis has displaced the older method of reducing MgCl, by fusing it with sodium. In most of its physical and chemical characters magnesium resembles zinc, though its colour more nearly approaches that of silver ; in ductility and malleability it also surpasses zinc. It is nearly as light, however, as calcium, its specific gravity being 1°75. It oxidises slowly in moist air, but is sufficiently stable to form a constituent of certain alloys, such as magnalium (Al with 10 per cent. Mg) and electron, useful for their lightness. Itfuses at 633° and boils about 1100°, so that it may be distilled like zinc. Its sp. ht. at 0° is 0°2456. Cold water has scarcely any action upon magnesium ; 1A wire of 0°33 millimetre diameter gives a light of 74 candle-power. Although the illuminating power of the sun’s rays is 524 times that of burning Mg, their chemical activity is only five times as great. The heat of combustion is Mg,O=143,400 cals. the temperature of burning magnesium appears to be about 1340° MAGNESIA 403 even when boiled, it oxidises the metal slowly, owing, no doubt to the insolubility of the oxide which forms on the surface. Acids, which rapidly dissolve such oxide, attack the metal violently. Solution of NH,Cl,-in which the oxide is also soluble (owing to the tendency of the magnesium salts to form double salts with those of ammonium), likewise dissolves the metal; 4NH,Cl + Mg = (NH,).MgCl, + H, + 2NH;. Magnesium is one of the elements which unite directly with nitrogen at a high temperature. The Magnesium nitride, Mg,Nz, is a greenish-grey powder, evidently composed after the type 2NHsg, for the action of water upon it gives rise to magnesia and ammonia ; Mg,N. + 3H,0 = 2NH; + 3MgO. If a foot of Mg tape be burnt in air, the residue evolves much NH, when boiled with water. When heated in CO the nitride yields cyanogen, Mg,N. + 3CO = 3MgO + 2CN + C. Magnesium is a powerful reducing agent, not only at high temperatures at which it removes oxygen from almost all other oxides, including the alkalies and alkaline earths, but at the ordinary temperature in solutions of metal salts, nearly all the heavy metals being readily reduced from neutral solutions. Magnesia, MgO, occurs, crystallised in octahedra, as the mineral peri- clase. It is prepared by decomposing magnesium carbonate by heat, and is a white powder, very bulky and apparently light, although its sp. gr. is 3°19 when it has been heated at 350°, and 3°57 when it has been heated to a white heat. It is very infusible (so that it is used for making basic fire- bricks), and is very little soluble in water (1 in 55,000), yielding an alkaline solution. It forms with the water Magnesium hydroxide, Mg(OH),, but with much less evolution of heat than in the case of the alkaline earths ; if excess of water be avoided the mass sets like plaster of Paris. The hydroxide (which occurs crystallised as brucite) is precipitated by alkalies from solutions of magnesium salts ; it slowly absorbs CO, from air and is easily decomposed by heat into MgO and H,0; it is used in extracting sugar from the beet. MgO dissolves easily in acids, but is a feeble base, as shown by its tendency to form basic salts, and the tendency of its normal salts to form double salts with the salts of the alkalies, indicating that there is a residual acidity about the magnesium salt, satisfied by the alkaline ten- dency of the alkali salt. Magnesium carbonate, MgCO,, is found as magnesite, which is imported from Greece. It is unaffected by water, and does not effervesce so briskly with acids as do the other carbonates. It is easily decomposed by heat into MgO and CO,. When a salt of magnesium is precipitated by an alkali carbonate, the precipitate is not the normal carbonate, as in the cases of Ba, Sr, and Ca, but a basic carbonate, or a compound of the carbonate and hydroxide. Ordinary magnesia alba, or light carbonate of magnesia, is prepared by precipitating magnesium sulphate with sodium carbonate, and boiling ; it generally has the compo- sition 5MgCO,.2Mg(OH),.7Aq. In preparing the heavy carbonate, the mixed solutions are evaporated to dryness, and the sodium sulphate washed out of the residue by water, These light and heavy carbonates, when calcined, yield light and heavy magnesia, the former having 33 times the bulk of the latter. Magnesium carbonate, like CaCOg, is soluble in carbonic acid, and is present in most natural waters, causing temporary hardness, the MgCO, being precipitated by boiling. When magnesia alba is dissolved in carbonic acid water, and the solution exposed to air at temperatures above 16°, needles of MgCO, .3Aq are deposited ; below that temperature the crystals are MgCO;.5H,0. If boiled with water the crystals lose CO, and become a basic carbonate. Dolomite, or magnesium limestone, is a mixture of magnesium carbonate and calcium carbonate in variable proportions. Magnesium carbonate is prepared from it by heating it sufficiently to decompose the MgCO3, and exposing it, under pressure, to the action of water and CO,, when the MgO is dissolved and the CaCO; is left. By passing 404 EPSOM SALTS steam through the solution the basic magnesium carbonate is precipitated. Or the dolomite may be completely burnt and mixed with a 10 per cent. solution of sugar, which dissolves the CaO, but leaves the MgO. Pearl spar is a crystalline form of the double carbonate, MgCa(CO3)9. Magnesium sulphate, so well known as Epsom salts, is sometimes prepared by calcining dolomite to expel the CO,, washing the residual mixture of CaO and MgO with water to remove part of the lime, and treating it with sulphuric acid, which converts the calcium and magnesium into sulphates ; and since CaSO, is almost insoluble in water, it is readily separated from the MgSO, which passes into the solution, and is obtained by evaporation in prismatic crystals (sp. gr. 1°68), having the composition MgSO,.7Aq. Epsom salts are now made from Kieserite, MgSO,.H,0, found in the Stass- furt salt beds. This is almost insoluble in water, but, when kept in contact with it, is slowly converted into MgSO,.7Aq. The preparation of Epsom salts from sea-water has already been alluded to (p. 368). In some parts of Spain magnesium sulphate is found in large quantities (like nitre in hot climates) as an efflorescence upon the surface of the soil. This sulphate, as well as that contained in well-waters, appears to have been produced by the action of the calcium sulphate, originally present in the water, upon magnesian limestone rocks ; MgO; + CaSO, = MgSO, + CaCO. The crystals MgSO,.7H,0 fuse easily, and become MgSO,.H,0 at 150°. The last H,0 can only be expelled at above 200°, and has been termed the water of constitution ; but see p. 39. The anhydrous MgSO, (sp. gr. 2-65) becomes MgO at a white heat. The water of constitution in MgSO,.H,0.6Aq may be displaced by the sulphate of an alkali metal without alteration of crystalline form ; a double sulphate of magne- sium and potassium (MgSO,.K,S0,.6Aq) and a similar salt of ammonium may be thus obtained. The mineral polyhalite (roduc, many, dc, salt) is a remarkable salt, containing MgS0O,.K,80,.2CaSO,.2H,0.1 Water decomposes it into its constituent salts. Epsom salts dissolve very easily in water (68 in 100 at 15°), but not in alcohol. If the aqueous solution be mixed with enough alcohol to render it turbid, small oily drops separate, from which small crystals presently shoot out, and the liquid becomes, by degrees, a pasty mass of very light needles closely interlaced. These contain 7H,O. An aqueous solution crystallised at above 70° deposits MgSO,.6Aq; at 0° crystals of MgSO,.12 Aq are formed. Penta- and tetra-hydrates are also known. Magnesium phosphate, Mg,(PO,)., is contained in bones and in some seeds. MgHPO,.7Aq is the precipitate produced by NagHPO, with magnesium salts ; it is de- composed by boiling with water ; 3MgHPO, = H;PO,4 + Mg3(PO,4)o. MgNH,PO,.6Aq is deposited in crystals from alkaline urine, and forms triple phosphate calculi. It is precipitated by Na,HPO, from a magnesium salt to which NH, has been added ; MgSO, + NH; + NagHPO, = Na,SO, + MgNH,PO,. Ammonium chloride should be added first to prevent the separation of Mg(OH),. The precipitation is much promoted by stirring ; the MgNH,P0, is sparingly soluble in water, and almost insoluble in ammonia ; when it is heated to redness, 2MgNH,PO, = Mg.P.0, + 2NH; + H,0. In quantitative analysis, Mg and P are generally determined in this form. Magnesium-ammonium arsenate, MgNH,AsO,.6H,0, is very similar, and is used in determining arsenic. Magnesium borate and chloride compose the mineral boracite, (MgO .8B,0; .MgCl., found in the Stassfurt salt mines. a Serpentine, 28i0,.3(Mg,Fe)O, and olivine, SiO,.3(Mg,Fe)O, are silicates of magnesia and ferrous oxide. Some of the varieties of serpentine are used for preparing the compounds of magnesium, being easily decomposed by acids with separation of silica. The minerals asbestos, meerschaum, steatite, and talc consist chiefly of magnesium silicates. Magnesium chloride occurs in sea-water, in brine-springs, in many 1 Polyhalite is found in the salt-beds of Stassfurt. Kainite, occurring in the same locality, ig K,80,.Mg80O4.MgCl,.6Aq, : . i GALVANISED IRON 405 natural waters, and’ in the minerals carnallite (p. 361) and bischofite, MgCl,.6Aq, which is the composition of the crystals (sp. gr. 1:56) that separate from concentrated solutions of the salt. It is easily obtained in solution by neutralising hydrochloric acid with magnesia or its carbonate ; but if this solution be evaporated in order to obtain the dry chloride, a considerable quantity of the salt is decomposed by the water at the close of the evaporation, leaving much magnesia mixed with the chloride (MgCl, + H,O = 2HCl + MgO). This decomposition may be prevented by mixing the solution with 3 parts of chloride of ammonium for every part of magnesia, when a double salt, MgCl,.2NH,Cl, is formed, which may be evaporated to dryness without decomposition, and leaves fused anhydrous magnesium chloride (m.pt. 708°) when further heated, the ammonium chloride being volatilised. When MgCl, is heated to a high temperature in’air the oxygen displaces some of the chlorine, an oxychloride being produced and free Cl evolved. The magnesium chloride absorbs moisture very rapidly from the air, and is very soluble in water. Like all the soluble salts of. magnesium, it has a decidedly bitter taste. When magnesia is moistened with a strong solution of magnesium chloride, heat is evolved and the mixture, Sorel’s cement, sets into a hard mass like plaster of Paris, apparently from the formation of an oxychloride. It may be mixed with several times its weight of sand, and will bind the sand firmly together. Xylolith is a mixture of Sorel’s cement and sawdust. The ammonium magnesium chloride, NH,Cl.MgCl,.Aq, is not decomposed by ammonia, which therefore gives no precipitate in solutions of magnesium to which NH, Cl has been added in sufficient quantity. ZINC, Zn = 65.37. Zine occupies a high position among useful metals, being peculiarly fitted, on account of its lightness, for the construction of gutters, water- pipes, and roofs of buildings, and possessing for these purposes a great advantage over lead, since the specific gravity of the latter metal is about 11:5, whilst that of zinc is only 7:15. For such applications as these, where great strength is not required, zinc is preferable to iron, on account of its superior malleability ; for although a bar of zinc breaks under the hammer at the ordinary temperature, it becomes so malleable at 120° as to admit of being rolled into thin sheets. This malleability of zinc when heated was discovered only in the commencement of the last century, until which time the sole use of the metal was in the manufacture of brass. When zinc is heated to 200° it again becomes brittle, and may be powdered in a mortar. The easy fusibility of zinc renders it easy to be cast into blocks for use in certain printing processes ; indeed, zinc is surpassed in fusibility (among the metals in ordinary use) by only tin and lead, its melting-point being below a red heat (419°). Zinc is also less liable than iron to corrosion under the influence of moist air, for although a bright surface of zinc soon tarnishes when exposed to the air, it merely becomes covered with a thin film of zinc oxide (passing gradually into basic carbonate, by absorption of CO, from the air) which protects the metal from further action. The great strength of iron has been ingeniously combined with the durability of zine, in the so-called galvanised iron, which is made by coating clean iron with melted zinc, thus affording a protection much needed in and - around large towns, where the sulphurous and sulphuric acids arising from the combustion of coal, and the acid emanations from various factories, greatly accelerate the corrosion of unprotected iron. The iron plates to be coated are first thoroughly cleansed by a process which will be more particularly noticed in the manufacture of tin-plate, and are then dipped 406 ZINC ORES into a vessel of melted zinc, the surface of which is coated with sal ammoniac in order to dissolve the zinc oxide which forms upon the surface of the metal, and might adhere to the iron plate so as to prevent its becoming uniformly coated with the zinc! A more firmly adherent coating of zine is obtained by first depositing a thin film of tin upon the surface of the iron plate by galvanic action, and hence the name galvanised iron. Of late years small articles have been zinced by immersion in a neutral solution of zine sulphate into which an electric current is passed. The ores of zinc are found pretty abundantly in England, chiefly in the Mendip Hills in Somersetshire, at Alston Moor in Cumberland, in Cornwall and Derbyshire, and ore is brought here from Italy and Africa ; but the greater part of the zinc used in this country is imported from Belgium and Germany, being derived from the ores of Transylvania, Hungary, and Silesia. Metallic zinc is never met with in nature. Its chief ores are calamine or zine carbonate (ZnCO,), blende or zinc sulphide (ZnS), and red zinc ore, in which zine oxide (ZnO) is associated with the oxides of iron and manganese. Calamine (sp. gr. about 4-4) is so called from its tendency to form masses resembling 7 a bundle of reeds (calamus, a reed). It is found in considerable quantities in Somerset- shire, Cumberland, and Derbyshire. A compound of zinc carbonate with zinc hydroxide, ZnCO,.2Zn(OH),, is found abundantly in Spain. The mineral known as electric calamine (hemimorphite) is a silicate of zinc (2Z2n0.Si0,.H,O), which becomes electrified when heated. Blende (sp. gr. about 4) derives its name from the German blenden, to dazzle, in allusion to the brilliancy of its crystals, which are generally almost black (black jack) from the presence of iron sulphide, the true colour of pure zinc sulphide being white. Blende is found in Cornwall, Cumberland, Derbyshire, Wales, and the Isle of Man, and is generally associated with galena or lead sulphide, which is always carefully picked out of the ore before smelting it, since it would become converted into lead oxide, which corrodes the earthen retorts employed in the process. For various reasons it is not economical to smelt zinc ores containing less than 40 per cent. of zinc. Hence the poorer ores are subjected to processes of ore concentration or ore dressing, with the object of separating, as far as it is profitable to do so, the zine mineral from the other minerals with which it is mixed in the ore. These processes are applied to the finely ground ore and are numerous, but may be classified into : (1) Water concentration, depending mainly on the difference of specific gravity of the various minerals ; the ore is mixed with water and caused to flow over a slightly inclined shaking table, the lighter particles (siliceous gangue, oxide of iron, &c.) being carried farther along the table than the heavier metalliferous particles ; or the ore is suspended in water in a vessel which is given a jigging motion so that the heavier particles settle first, the lighter forming an upper layer which can be skimmed off. (2) Magnetic concentration, depending on the power of the magnet to attract certain minerals ; the ore is spread on a band which travels over the pole of a magnet ; the particles least attracted travel farthest. Ferruginous minerals are most easily separated from non-ferruginous by this method, but since the common iron minerals are only feebly magnetic until they have been roasted (which converts the iron compounds into the magnetic oxide ; see Iron), a preliminary roasting is generally necessary. (3) Elec- trostatic concentration, depending on the different capacity of minerals for conducting electricity ; the ore is made to travel over a surface highly charged with electricity ; particles which are good conductors rapidly acquire a charge and are repelled, thus leaving the surface first. (4) Flotation, which depends primarily on the fact that par- ticles of siliceous gangue are more easily wetted by water than particles of metalliferous minerals are ; thus if a mixture of such particles is very gently deposited on a surface of water, the gangue is wetted first and sinks directly, the metalliferous particles remain- ing afloat for a longer period ; if the mixed particles are oiled this effect is enhanced because the oil adheres to the metalliferous matter but not to the gangue, and being oiled the metalliferous particles float all the longer; moreover such oiled particles ! The sal ammoniac acts upon the heated zinc according to the equation Zn-+2NH,Cl = ZnCl, +2NH,+H,, and the zinc chloride which is formed dissolves the oxide from the surface of the metal, producing zinc oxychloride, ZINC—EXTRACTION 407 appear to have the power of attaching to themselves bubbles of gas which may be liberated from the water by heat or reduction of pressure, or produced in the water by action of an acid on the particles themselves. It is on this last phenomenon that the most successful process depends ; the mixture of ore and water (pulp) is mixed with any cheap oil and caused to flow upwards through a vessel in which the pressure is kept below that of the atmosphere ; the air dissolved in the water separates under tke reduced pressure and, attaching itself in minute bubbles to the oiled metalliferous particles, floats them to the surface of the water, where they flow away with the lattcr, the gangue remaining in the vessel. Before extracting the metal from these ores, they are subjected to a preliminary treatment which brings them both to the condition of zinc oxide.1 For this purpose the calamine is simply calcined in a reverberatory furnace, in order to expel carbonic acid gas; but the blende is roasted for ten or twelve hours, with constant stirring, so as to expose fresh surfaces to the air, when the sulphur passes off in the form of SO,, and its place is taken by the oxygen, the ZnS becoming ZnO. The extraction of the metal from this zinc oxide depends upon the circumstance that zinc is capable of being distilled at a bright red heat, its boiling-point being about 930° C. The oxide is mixed with coal dust in excess of the amount represented by the equation ZnO + C = Zn + CO, and the mixture is heated to 1100°— 1300° in fireclay retorts, the zinc vapour passing into receivers in which it condenses to liquid metal. The excess of carbon is needed to ensure that CO, shall not be present (see footnote), and the temperature must be high because the reaction is highly endothermic. The decomposition of ZnO absorbs 85,000 cals., while the formation of CO evolves 29,000 cals., leaving 56,000 cals. to be supplied by externally heating the retorts. The facility with which this metal passes off in the form of vapour is seen when it is melted in a ladle over a brisk fire, for at a bright red heat abundance of vapour rises from it, which, taking fire in the air, burns with a brilliant greenish-white light, throwing off into the air numerous white flakes of light zinc oxide (the philosopher’s wool, or nil album of the old chemists). Zinc may be distilled on the small scale in a graphite crucible (A, Fig. 242) about 5 in. high and 3 in. in diameter. A hole is drilled through the bottom with a round file, and into this is fitted a piece of wrought-iron gas-pipe, B, about 9 in. long and 1 in. wide, so as to reach nearly to the top of the inside of the crucible. Any crevices between the pipe and the sides of the hole are carefully stopped with fireclay moistened with solution of borax. A few ounces of zinc are introduced into the crucible, the cover of which is then cemented on with fireclay, mixed with a little borax, the hole in the cover being also stopped with fireclay. The crucible having been kept for several hours in a warm place, so that the clay may dry, it is placed in a cylindrical furnace with a hole at the bottom, through which the iron pipe may pass, and a lateral opening, into which is inserted an iron tube, C, connected with a forge bellows. Some lighted charcoal is thrown into the furnace, and when this has been blown into a blaze, the furnace is filled up with coke broken into small pieces. The fire is then blown till the zinc distils freely into a vessel of water placed for its reception. Four ounces of zinc may be easily distilled in half an hour. This experiment illustrates the original English method of extracting zinc, the mixture of roasted zinc ore and coke being heated in crucibles like that shown in Fig. 242. In modern practice retorts about 4 ft. long and 8 in. in diameter are charged with a mixture of the roasted ore with half its weight of small coal, and are heated in a gas-fired furnace. 1 For the reason that the sulphide cannot be reduced to metal by carbon and that the CO, of the carbonate would oxidise the zinc as soon as this was liberated in the distillation process. 408 ZINC—DISTILLATION Fig. 243 illustrates a modern zinc furnace heated by producer-gas (p. 274) on the regenerative principle (p. 279). The furnace is divided by a fire-brick partition, a, having projections for supporting the rear ends of the fireclay cylindrical retorts, b, the front ends of which are supported on iron plates, c, held in an iron frame. The mixture of ore and coal having been charged into a retort, a clay. , receiver, open at each end, d, is luted into the mouth of the latter anda pot, e, is stuck on to the end ofthe receiver. The partition, a, has flues; f, ports, g, which open into the chamber on each side. The gas regenerators, h, h’, and air-regenerators, 4, 7’, are worked 14 as described for a steel furnace at p. 446—that is to say, during one Ig 7 ~ c period producer-gasis passing up a “ the hot regenerator, h, and air up en / 4 the hot regenerator, 7, to pass ja z : / through flues, f, and ports, g, into the left-hand chamber where they burn to heat the retorts ; the pro- ducts of combustion pass over the top of the partition, down the Y right-hand chamber, and through S HQ a& the regenerators, h’ and 7’, which they heat. During the next period the direction of air, gas and pro- Fic. 243. ducts is reversed. The distilled zine collects in the receivers, d, and pots, e. The zinc which collects in the receivers is cast into ingots which constitute the commercial spelter. This contains lead (1-3 per cent., carried over by the zinc vapour), cadmium, arsenic, and iron (dissolved by the molten zinc from iron ladles used in casting, &c.). To refine the metal it is melted in a reverberatory furnace (p. 246) having an inclined hearth terminating in a sump. The lead melts first and runs to the bottom of the sump, next comes a thin layer of hard zinc (containing iron), then the purified zinc, still containing about 1 per cent. of lead which remains dissolved. The purified metal is ladled into ingot moulds. Zinc free from lead must be made from ores free from this metal. A mass of porous refractory material (charcoal, fire-brick) placed in the front end of the zinc retort is said to stop the lead from being carried into the receiver by the vapour of zinc. Arsenic may be removed from zinc by melting it and adding 0-2 per cent. of sodium, whereupon the arsenic forms a compound with the Na and Zn which rises to the surface and can be skimmed off. Since blende can be oxidised by careful roasting to zinc sulphate, which is freely soluble in water, many attempts have been made to deposit electrolytically the zinc from such solutions. Several difficulties, chiefly the large amount of electric power required, prevent such processes from competing with the operation of smelting except when there is a good market for very pure zinc. Better success has attended the elec- trolysis of zinc chloride solution, originally undertaken at the ammonia-soda works as a method of recovering chlorine from the CaCl, liquor (p. 372). By mixing the liquor with ore roasted to ZnO and saturating it with CO, CaCO, is produced and ZnCl, passes into solution; the electrolysis of this yields chlorine at the anode, which is absorbed by lime in bleaching powder chambers or boxes (p. 115), and zinc at the cathode. Ingots of zinc, when broken across, exhibit a beautiful crystalline ZINC WHITE 409 fracture which, taken in conjunction with the bluish colour of the metal, enables it to be easily identified. Zine being easily dissolved by diluted acids, it is necessary to be careful in employing this metal for culinary purposes, since its soluble salts are poisonous, It will be remembered that the action of diluted sulphuric acid upon zine is employed for the preparation of hydrogen. Pure zinc, however, evolves hydrogen very slowly, since it becomes covered with a number of hydrogen bubbles which protect it from further action ; but if a piece of copper or platinum be made to touch the zinc beneath the acid, these metals, being electro-negative towards the zinc, will attract the electro-positive hydrogen, leaving the zinc free from bubbles, and exposed on all points to the action of the acid, so that a continuous disengagement of hydrogen is maintained. As a curious illustration of this, a thin sheet of platinum or silver foil may be shown to sink in diluted sulphuric acid, until it comes in contact with a piece of zinc, when the bubbles of hydrogen bring it up to the surface. The lead, iron, &c., met with in commercial zinc are electro-negative to the zinc, and thus serve to maintain a constant evolution of hydrogen. See also p. 96. Zinc also dissolves in boiling solutions of potash and soda, evolving hydrogen and forming alkali zincates; 2KOH + Zn = Zn(OK), + H,. Even solution of ammonia dissolves it slowly. When heated with Ca(OH), it evolves hydrogen. A coating of metallic zinc may be deposited upon copper by slow galvanic action, if the copper be immersed in a concentrated solution of potash, at the boiling-point of water, in contact with metallic zinc, when a portion of the latter is dissolved in the form of oxide, with evolution of hydrogen, and is afterwards precipitated, on the surface of the copper. Zinc-dust is metallic zinc (containing zine oxide, cadmium, &c.) which has condensed in a fine powder in smelting the ores. It is very useful in the laboratory as a reducing agent. Zinc Oxide (ZnO).—Zinc forms but one oxide, which is known in com- merce as zinc white or Chinese white, and is prepared by allowing the vapour of the metal to burn in earthen chambers through which a current of air is maintained. It is practically insoluble in water (1 in 55,400 ; the solution is distinctly alkaline to litmus), and is sometimes used for painting in place of white lead (q.v.), over which it has the advantages of not injuring the health of the persons using it, and of being unaffected by sulphuretted hydrogen, an important consideration in manufacturing towns where that substance is so abundantly supplied to the atmosphere. Unfortunately, however, the zinc oxide paint has less covering power and is more liable to peel off than white lead paint. The zinc oxide has the characteristic property of becoming yellow when heated, and white again as it cools. Its sp.gr.is 5-78. It is sometimes used in the manufacture of glass for optical purposes. At the temperature of the electric arc it is volatile. Zinc hydroxide, Zn(OH),, is precipitated in a gelatinous state when caustic alkalies are added to solutions containing zinc; the precipitate dissolves in excess of alkali, and, if this be not too great, is reprecipitated by boiling. The alkaline solution is said to contain an alkali zincate, e.g. K2ZnOg. Ammonia does not precipitate zine hydroxide from solutions containing ammonium salts, since zinc resembles magne- sium in forming double salts containing ammonium. Zinc hydroxide is easily decomposed by heat ; Zn(OH), = ZnO + H,0. Zinc Nitride, Zng,Nj.—When zinc diamine Zn(NHg2)2, made by action of NH, on zinc ethide (q.v.), is heated, out of contact with air, it gives zinc nitride ; 3Zn(NHz)2 = ZngsN2 + 4NH3. The nitride decomposes with water, evolving much heat ; Zn,N, + 3H,0 = 2NH, + 3Zn0. Zinc carbonate, ZnCO;, as found in nature (calamine, Smithsonite), forms rhombo- hedral crystals. The place of part of the zinc in the mineral is often taken by iso- 410 ZINC SALTS morphous metals, such as cadmium, magnesium, and ferrousiron. ZnCO; is precipitated when ZnSO, is boiled with KHCO, ; ZnSO, +2KHCO;=ZnCO, + K,S0, +H,0 +COz. The normal alkali carbonates precipitate basic carbonates of variable composition (as is the case with magnesium). The precipitate produced by ammonium carbonate is soluble in excess. The carbonate is substantially insoluble in water, but is more soluble in water containing COp. - It is easily decomposed by heat into ZnO and CO,. Zine chloride, ZnCl,,is prepared by dissolving Zn or ZnO in HCl, and evaporating.1 If the solution contains a little HCl in excess, it deposits octahedral crystals of ZnCl,.H,O. The solution, like that of MgCl,, under- goes partial decomposition when evaporated, leaving an oxychloride ; when this residue is distilled, ZnCl, passes over. It may also be obtained by distilling a mixture of zinc sulphate and sodium chloride. Zinc chloride is a deliquescent solid (sp. gr. 2:9), very soluble in water, alcohol, and ether ; it melts at 290° and boils at 730°. Its attraction for water renders it a powerful caustic, and it is used as such in surgery. A strong solution of ZnCl, dissolves much ZnO, and if the solution of oxychloride thus formed be mixed with water, precipitates are obtained which contain Zn(OH)Cl and Zn(OH),. Solution of ZnCl, dissolves paper and cotton, and the oxy- chloride dissolves-wool and silk. This is sometimes useful in examining textile fabrics. When zinc oxide is moistened with a strong solution of zinc chloride, an oxychloride is formed, which soon sets into a hard mass, which has been used as a stopping for teeth. Burnett's disinfecting fluid is a solution of zine chloride, and is capable of absorbing H,S, NHs3, and other offensive products of putrefaction, as well as of arresting the decomposition of wood and animal substances. Zinc chloride is also used in soldering to cleanse the metallic surface, and the careless use of this-poisonous salt in soldering tins of preserved food has frequently caused accidents. Zinc chloride is sometimes made from pyrites containing blende. This is burnt as usual to furnish SO, for the manufacture of sulphuric acid, when the Zn§ is converted into ZnSO, which is extracted from the spent pyrites by water, and decomposed with sodium chloride, when Na,SO, is deposited in crystals, leaving ZnCl, in solution. Zinc Sulphate, or white vitriol, ZnSO,.7H,O, bears a dangerous resemblance to Epsom salts ; it melts at 50°, loses its water of crystallisation at 100°, and is decomposed at a high temperature into ZnO, sulphur dioxide, and oxygen, the residue being yellow when hot and white when cold. The crystals dissolve in twice their weight of water at 15°; at temperatures above 40° the sulphate crystallises from the solution as ZnSO,.6H,0, which is isomorphous with the corresponding salt of magnesium. Like the magnesium sulphate, it forms double sulphates,in which one H,0 is exchanged for alkali sulphates. ZnSO,.K,80,.6Aq and ZnSO,.(NH,),80,.6Aq are isomorphous with the Mg double salts. Like all other truly isomorphous salts, the sulphates of magnesium and zinc crystallise together from their mixed solutions. It is made on the large scale by roasting blende (ZnS) at a low red heat, when it combines with O from the air to form ZnSO,, which is dissolved out by water and crystallised. It has a metallic, nauseous taste, and is used medicinally and in dyeing. Zinc Sulphide, ZnS.—Blende is usually crystallised in octahedra or dodecahedra (p. 406). When precipitated by a soluble sulphide from a solution of a zine salt the sulphide is perfectly white, but it darkens some- what when exposed to air and light. An intimate mixture of zinc-dust with half its weight of flowers of sulphur burns like gunpowder when kindled with a match, leaving a bulky mass of 1 Ifiron be present, it may be separated by adding a little chlorine water to pcroxidise it, and precipita- ting it as hydrated Fe,0, by adding zinc carbonate. CADMIUM 411 ZnS, which is primrose-yellow while hot, and white on cooling. Zinc sulphide is insoluble in water, in alkalies, and in acetic acid, but dissolves in HCl and in HNO. It may be sublimed in colourless crystals by strongly heating in a current of H,S. It is used as a pigment in the form of lithopone, a mixture of BaSO, and ZnS made by adding barium sulphide to a solution of zinc sulphate. CADMIUM, Cd = 112.40. This metal is found in small quantities (0-1-0-3 per cent.) in the ores of zinc, its presence being indicated during the extraction of that metal (p. 408) by the appearance of a brown flame (brown blaze) at the commencement of the distillation, before the characteristic zinc flame is seen at the orifice of the receiver. Cadmium is more easily vaporised than zinc, boiling at 778°, and the bulk of it is found in the first portions of the zinc-dust which condenses. This may contain about 5 per cent. of Cd which is isolated by repeated fractional distillation with coke. Although resembling zinc in its volatility and its chemical relations, in appearance it is much more similar to tin, and emits a crackling sound like that metal when bent. Like tin, also, it is malleable and ductile at the ordinary temperature, and becomes brittle at about 82°. It is slightly heavier than zinc, sp. gr. 8-65, and has a lower melting-point, 321°, so that it is useful for making fusible alloys. An alloy (Wood’s metal) of 3 parts of cadmium with 16 of bismuth, 8 of lead, and 4 of tin fuses at 60°. In its behaviour with acids and alkalies cadmium is similar to zinc, but the metal is easily distinguished from all others by its yielding a characteristic chestnut-brown oxide, CdO, when heated in air ; this is insoluble in water, but soluble in acids and, sparingly, in alkalies; sp. gr.8-1. The suboxides Cd,O and Cd,0 have been prepared. An amalgam of cadmium and mercury is used by dentists for stopping teeth, for while it is plastic when freshly made it rapidly hardens. Cadmium is also electro-deposited as an alloy with silver instead of ordinary electro- plating. In the manufacture of silver-plate the addition of 0-5 per cent. of Cd to the silver is found useful. ; Cadmium sulphide, CdS, occurs as the rare mineral greenockite. The artificially prepared sulphide, made by adding H,S to a solution of a cad- mium salt, has a bright yellow colour and is used as a pigment (cadmia or cadmium yellow) ; when precipitated from a hot acid solution it is orange- red, a difference which has been supposed to be due to allotropy, although this does not seem to be well established. It is insoluble in dilute HCl and in NH,, but soluble in strong HCl. Cadmium chloride, CdCl,.2Aq, effloresces in air, whilst zine chloride deliquesces; Moreover, it may be dried without undergoing partial decomposition. The anhydrous salt (sp. gr. 4-05) melts about 570° and boils at 964°, thus resembling ZnClp. It dissolves in about three-quarters of its weight of water at 20°. Cadmium bromide, CdBr..4Aq, and the iodide, CdI,, are used in photography. Cadmium sulphate, 3CdS0O,.8Aq, is much less soluble than zinc sulphate. 7 BERYLLIUM or GLUCINUM, Be or G1 = 9.1. This comparatively rare metal (which derives one of its names from the swect taste of its salts, yAv«ic, sweet) is found associated with silica and alumina in the emerald, which is a double silicate of AlpO, and BeO (Al,03 .3BeO .6Si0.), and appears to owe its colour to the presence of a minute quantity of chromium oxide. The more common mineral, beryl or aquamarine, has a similar composition, but is of a paler green colour, apparently caused by iron. Chrysoberyl consists of Al,03.BeO, also coloured by iron, The earlier analysts of these minerals mistook the beryllium oxide for alumina, 412 MERCURY—PROPERTIES which it resembles in forming a gelatinous precipitate on adding ammonia to its solutions, but it is a stronger base than alumina, and is therefore capable of displacing ammonia from its salts, and of being dissolved by them. Ammonium carbonate is employed to separate the beryllium oxide from alumina, since it dissolves the former in the cold, forming a double carbonate of beryllium and ammonium, from which the beryllium carbonate is precipitated on boiling. Beryllium oxide, BeO (sp. gr. 3-025), is inter- mediate in properties between alumina and magnesia, resembling the latter in its tendency to absorb carbonic acid from the air, and to form soluble double salts with the salts of ammonium, and so much resembling alumina in the gelatinous form of its hydrate, its solubility in alkalies, and the sweet astringent taste of its salts that it was formerly regarded as a sesquioxide like alumina. However, it does not form double salts of the type of alum (q.v.), and the formula of its chloride, BeCla, is fully estab- lished by determination of vapour density ; hence there is now no doubt that it isa divalent element. The oxide dissolves in caustic alkalies forming alkali beryllates (e.g. B2(OK),), analogous to the zincates. The metal itself is very similar to aluminium ; it is prepared by electrolysing the fused double fluoride, NaF.BeF,. Its specific gravity is 1-93, and it melts at about 1000°. It is not seriously oxidised by air, and does not decompose water. In general chemical behaviour it resembles aluminium. The atomic weight of beryllium is discussed on p. 304, and an interesting com- pound is described at p. 650. MERCURY, Hg = 200.60. Mercury (quicksilver), which chemically belongs to the magnesium group of metals, is conspicuous among metals by its fluidity, and among liquids by its not wetting or adhering to most solids, such as glass, a property of great value in making philosophical instruments. It is the only metal which is liquid at the ordinary temperature, and since it does not freeze until — 38-8°, this metal is particularly adapted for the construction of thermometers and barometers. Its high boiling-point (357°) and low specific heat (0-033) also recommend it for the former purpose, as its high specific gravity (13-54) does for the latter, a column of about 30 in. in height being able to counterpoise a column of the atmosphere having the same sectional area. The symbol for mercury is derived from the Latin name for this element, hydrargyrum (béwp, water, referring to its fluidity, dpyupos, silver). Solid mercury at — 38°85° has the sp. gr. 14:193, and at — 188°, 14°383 ; the solid is malleable (p. 83). Mercury is not met with in this country, but is obtained from Idria (Austria), Almaden (Spain), China, and New Almaden (California). It occurs in these mines partly in the metallic state, diffused in minute globules or collected in cavities, but chiefly in the state of cinnabar, which is mercuric sulphide, HgS (sp. gr. 8-1). Since mercuric oxide dissociates at 400°, the roasting of the sulphide produces the metal instead of the oxide; HgS + 0, + Hg + S0,. This is an exothermic reaction, and when the ore is sufficiently rich in HgS the operation consists in starting the combustion and adjusting the air supply to permit it to continue, as in the case of burning pyrites (p. 163). The mercury is volatilised and is condensed—a matter of some difficulty owing to the dilution of the vapour with SO, and atmospheric nitrogen. Generally, however, it is necessary to provide heat by burning fuel ; if the ore is small it is roasted in a shaft furnace fitted with shelves or baffle plates down which the ore slides, meeting the ascending gases from a fire-grate ; but when it is coarser (above 30 mm. diameter) the ore is mixed with the fuel and charged into an ordinary shaft furnace. In either case the furnace is connected with an efficient condensing plant. A shaft furnace (some 20 ft. high) for the purpose is shown in Fig. 244 in vertical MERCURY—PURIFICATION 413 section and in horizontal section (Fig. 245). The furnace having been started by a charge of burning fuel, the cover, a, dipping at its edges into a water seal, is removed, and the mixture of ore and charcoal is charged into the shaft through the hopper normally closed by the cone, 6. The residual ore is withdrawn through the shoots, ¢, and air for com- bustion and roasting is admitted through the hollow wedge, d, which extends into the shaft so that the air may be preheated by the hot walls of the wedge. The condensers, e, are stoneware pipes cooled by water, the liquid mercury and the stupp, as the condensed fumes are called, collecting in troughs, f. Ores containing as little 0-4 per cent. Hg may La be successfully treated. The whole installation is kept under slightly reduced internal pres- b Le sure by fans which draw the air i in at dand the products through the condensers, thus preventing escape of the poisonous mercury vapour into the surrounding air. The mercury contained in a SSS nS Fig. 244. Fic. 245. fine state of division in the stupp is for the greater part squeezed out of it by pressure, the residue being returned to the furnace. Distillation of a mixture of the ore with lime or iron, to retain the sulphur, was at one time practised, but has been abandoned ; 4HgS + 4CaO = 3CaS + CaSO, + 4Hg. The mercury found in commerce is never perfectly pure, as may be shown by scattering a little upon a clean glass plate, when it ‘at/s or leaves a track upon the glass, which is not the case with pure mercury. Its chief impurity is lead, which may be removed by exposing it in a thin layer to the action of nitric acid diluted with two measures of water, which should cover its surface, and be allowed to remain in contact with it for a day or two with occasional stirring. The lead is far more easily oxidised and dissolved than the mercury, though a little of this also passes into solution. The mercury is afterwards well washed with water and dried, first with blotting-paper, and then by gentle heat. Mercury is easily freed from mechanical impurities by squeezing it through a duster. Zine, tin, and bismuth are sometimes present in the mercury of commerce, and may be partly removed, as oxides, by shaking the mercury in a large bottle with a little powdered loaf-sugar for a few minutes, and straining through cloth. The sugar appears to act mechanically by subdividing the mercury. ; The most ready and good method for cleaning mercury is as follows; Nearly fill a long burette with diluted nitric acid, and let a very fine stream of the mercury trickle through it from a dry filter paper pierced with a pin-hole. The process may be repeated with water to ensure freedom from acid. In its chemical properties mercury much resembles silver, being un- affected by ordinary air and tarnished by air containing H,S. In course of time, however, it becomes oxidised, as may be seen in old instruments containing mercury and air ; itis slowly oxidised when heated in air (p. 49), which is not the case with silver. It also appears to undergo a partial oxidation when reduced to a fine state of subdivision, as in those medicinal preparations of the metal which are made by triturating it with various substances which have no chemical action upon it, until globules of the 414 USES OF MERCURY metal are no longer visible. Blue pill and grey powder, or hydrargyrum cum cretd, afford examples of this, and probably owe much of their medicinal activity to the presence of one of the oxides of mercury. Nitric acid (containing nitrous acid) dissolves mercury, and converts it into two nitrates—mercurous, HgNO,, corresponding with AgNOg, and mercuric, Hg(NO,),. Hot concentrated sulphuric acid also converts it into mercurous (Hg,SO,) and mercuric (HgSO,) sulphates. Mercury is precipitated from solutions of its salts by reducing agents, stannous chloride, for example, in what looks like a dark grey powder ; but if this be boiled in the liquid, the minute globules of which it is composed gradually unite into fluid mercury. Conversely, if mercury be diligently triturated with chalk or grease, it may be divided into extremely minute globules which behave like a powder. Uses of Mercury:—Formerly all looking-glasses were “silvered”’ by an amalgam of tin and mercury; now the glass is truly silvered (p. 517). The application of the amalgam of tin is as follows: A sheet of tinfoil of the same size as the glass to be silvered is laid perfectly level upon a table, and rubbed over with metallic mercury, a thin layer of which is afterwards poured upon it. The glass is then carefully slid on to the table, so that its edge may carry before it part of the superfluous mercury with the impurities upon its surface ; heavy weights are laid upon the glass, so as to squeeze out the excess of mercury, and in a few days the combination of tin and mercury is found to have adhered firmly to the glass ; this coating usually contains about 1 part of mercury and 4 parts of tin. In this and all other arts in which mercury is used (such as barometer-making) much suffering is experienced by the operatives from the poisonous action of the mercury. The readiness with which mercury unites with or dissolves most other metals to form amalgams is one of its most striking properties, and is turned to account for the extraction of silver and gold from their ores. The attrac- tion of the latter metal for mercury is seen in the readiness with which it becomes coated with a silvery layer of mercury whenever it is brought in contact with that metal, and if a piece of gold leaf be suspended at a little distance above the surface of mercury, it will be found, after a time, silvered by the vapour of the metal, which rises slowly even at the ordinary tempera- ture. From the surface of rings which have been accidentally whitened by mercury it may be removed by a moderate heat, or by warm dilute nitric acid, but the gold will afterwards require burnishing. Amalgams are made either by dissolving the respective metals in mercury, or by electrolysing an aqueous solution of the metal with mercury as the cathode (cf. electrolytic soda, p. 374). Most of the metals appear to form definite compounds with mercury. Zinc plates are amalgamated, as already explained (p. 15), for use in the galvanic battery. An amalgam of 6 parts of mercury with 1 part of zinc and 1 of tin is used to promote the action of frictional electrical machines. The addition of a little amalgam of sodium to metallic mercury gives it the power of adhering much more readily to other metals, even to iron. Such an addition has been recommended in all cases where metallic surfaces have to be amalgamated, and espe- cially in the extraction of silver and gold from their ores by means of mercury. Gold amalgam and cadmium amalgam are used by dentists. Sodium amalgam, in contact -with water, forms a convenient source of nascent (atomic) hydrogen. Tron and platinum are the only metals in ordinary use which can be employed in con- tact with mercury without being corroded by it. Mercury, however, adheres to platinum. A very beautiful crystallisation of the amalgam of silver (Arbor Diane) may be obtained in long prisms having the composition Ag,Hg,, by dissolving 400 grains of silver nitrate in 40 measured ounces of water, adding 160 minims of concentrated nitric acid, and 1840 grains of mercury ; in the course of a day or two crystals of 2in. or 3 in. in length will be deposited, MERCURY OXIDES 415 Oxides of Mercury.—TI'wo oxides of mercury are known—the sub- oxide, Hg,O, and the oxide, HgO; both combine with acids to form salts. Mercurous oxide, Hg,0, is obtained by decomposing calomel with solution of potash, and washing with water ; Hg,Cl, + 2KOH = Hg,0+2KCI+H,0. It is very easily decomposed, by exposure to light or to a gentle heat, into mercuric oxide and metallic mercury Red oxide of mercury, or mercuric oxide (HgO), is formed upon the surface of mercury when heated (237°) for some time in contact with air. The oxide is black while hot, but becomes red on cooling. It is used, under the name of red precipitate, in ointments, and is prepared for this purpose by dissolving mercury in nitric acid, evaporating the solution to dryness, triturating the mercuric nitrate with an equal weight of mercury, and heating as long as acid fumes are evolved; Hg(NO,), + Hg, = 3HgO + N,O3. The name nitric oxide of mercury refers to this process. It is thus obtained, after cooling, asa brilliant red crystalline powder (sp. gr. 11-2), which becomes nearly black when heated, and is resolved into its elements at a red heat. It dissolves slightly in water, and the solution has a very feeble alkaline reaction. A bright yellow modification of the oxide, also crystalline, is precipitated when a solution of corrosive sublimate is decomposed by potash (HgCl, + 2KOH = HgO + 2KCl + H,0) ; the yellow variety is chemically more active than the red, into which it changes if boiled long in the liquid wherein it was precipitated. A strong solution of NH; converts HgO into a yellowish-white powder (sp. gr. 4:08), HO.H, dihydroxymercurammonium hydroxide, NH,.OH, which is a strong base HO.He” (Millon’s base) absorbing CO, from the air and combining readily with acids. Light decomposes it, and, when dry, friction in a mortar causes it to detonate slightly, recalling fulminating silver (p. 519). By exposure over lime in NH, gas it loses H,O and becomes Hg of \NE, .OH, a dark yellow powder. This change involves a remarkable increase ae of specific gravity to 7-42, and of stability, the compound decomposing very easily, though quietly, into HgO and NH, ; in an atmosphere of NH3, however, at 125° the Hg decomposition is not so deep-seated, the compound Ds .OH being produced, which Hg is dark brown and very explosive (sp. gr. 8-52), a property which it loses together with some of its colour on exposure to air. This last substance appears to be that formerly called mercury nitride, produced by heating HgO in NH. Millon’s base will deprive all soluble and most insoluble salts of their acids; thus it will remove sulphates and chlorides from impure soda solution. The salts are of the type Hg of NH, x, where X is a monobasic acid radical. Ep” ‘ The oxygen acid salts are not of great practical importance. Mercurous nitrate, HgNO,Aq, is obtained when mercury is dissolved in cold HNO, diluted with 5 vols. of water. The prismatic crystals which are sometimes sold as protonitrate of mercury consist of a basic nitrate, Hgg0.6HgNO,.H,O, prepared by acting with dilute nitric acid upon mercury in excess. When this salt is powdered in a mortar with a little common salt, it becomes black from the separation of mercurous oxide, Hg,O .6HgNO;.H,O + 6NaCl = 6NaNO,; + 6HgCl + Hg,0 + H,0 ; but the normal nitrate is not blackened (HgNO, + NaCl = HgCl + NaNOs3). Mer- curous nitrate is soluble in a little hot water (the hot solution dissolves calomel), but much water decomposes it into nitric acid and a basic nitrate : 2Hg(NO,) + H,O = Hg,NO,.0H + HNO. 416 CORROSIVE SUBLIMATE Mercuric nitrate, 2Hg(NO,),.Aq, is formed when mercury is dissolved in an excess of strong HNOs,, and the solution boiled until it is no longer precipitated by NaCl. Water decomposes it, precipitating a yellow basic nitrate, which leaves HgO when long washed with water. Mercuric nitrate stains the skin red. When HNO, is heated with an excess of HgO, the solution, on cooling, deposits crystals of a basic mercuric nitrate ; Hg.(NO3)3.0H.Aq. Mercurous sulphate (Hg,SO,) is precipitated as a white crystalline powder when dilute sulphuric acid is added to a solution of mercurous nitrate. Mercuric sulphate (HgSO,) is obtained by heating 2 parts by weight of mercury with 3 parts of oil of vitriol, and evaporating to dryness. Mercurous sulphate is first produced, and is oxidised by the excess of sulphuric acid. It forms a white crystalline powder, which becomes brown-yellow when heated, and white again on cooling. It is decomposed by water into a soluble acid sulphate, and an insoluble yellow basic sulphate of mercury, HgSO,.2HgO, known as turbith or turpeth ‘mineral, said to have been so named from its resembling in its medicinal effects the root of Convolvulus turpethum. Chlorides of Mercury.—The chlorides are the most important of the compounds of mercury, one chloride being calomel (HgCl) and the other corrosive sublimate (HgCl,). Vapour of mercury burns in chlorine gas, corrosive sublimate being produced. Mercuric chloride or Corrosive sublimate, is manufactured by heating 2 parts by weight of mercury with 3 parts of strong H,SO,, and evapor- ating to dryness, to obtain mercuric sulphate— Hg + 2H,SO, = HgSO, + 2H,0 + S80z, which is mixed with 14 parts of common salt and heated in glass vessels (HgSO, + 2NaCl =Na,SO, + HgCl,), when sodium sulphate is left, and the corrosive sublimate is converted into vapour, condensing on the cooler part of the vessel in lustrous colourless masses, which are very heavy (sp. gr. 5:4), and have a crystalline fracture. It fuses very easily (288°) to a perfectly colourless liquid, which boils at 303°, emitting an extremely acrid vapour, which destroys the sense of smell for some time. This vapour condenses in fine needles, or sometimes in octahedra. One hundred of water dissolve 6-57 of HgCl, at 10° and 53-96 at 100°, so that the hot solution readily deposits long four-sided prismatic crystals of the salt. It is remark able that alcohol and ether dissolve corrosive sublimate much more easily than water does, boiling alcohol dissolving about an equal weight of the chloride, and cold ether taking up one-third of its weight. By shaking the aqueous solution with ether, the greater part of the HgCl, is removed, and remains dissolved in the ether which rises to the surface. An aqueous solu- tion of NH,Cl dissolves HgCl, more easily than pure water does, a soluble double chloride (sal alembroth) being formed, which may be obtained in tabular crystals ; HgCl,.2NH,Cl.H,0 ; many surgical dressings, lotions, &c., depend on this compound for their antiseptic properties. Corrosive sub- limate is a very powerful poison ; a solution of it in water containing sal ammoniac is a very efficacious bug-poison. Sulphuric acid does not decompose mercuric chloride, though it attacks mercurous chloride. Hydrochloric acid combines with it, forming crystalline compounds, HCl.HgCl, and HCl.2HgCle, which lose HCl when exposed to air. A crystalline compound, HgCl,.H,SO,4, is formed by the action of hydrochloric acid on mercuric sulphate. ‘i The poisonous properties of corrosive sublimate make it a most powerful anti- septic, and are very marked, so little as three grains having been known to cause death in the case of a child. The white of egg is commonly administered as an antidote, because it is known to form an insoluble compound with HgClp, so as to render the poison dnert in the stomach. The compound of albumin with HgCl, is also much less liable to putrefaction than albumin itself, and hence corrosive sublimate is sometimes employed CALOMEL 4\i7 for preserving anatomical preparations and for preventing the decay of wood (by com- bining with the vegetable albumin of the sap). HgCl, unites with many other chlorides to form soluble double salts, and with mercuric oxide, forming several oxychlorides which have no useful applications. White precipitate, employed for destroying vermin, is deposited when a solution of corrosive sublimate is poured into an excess of solution of ammonia : HgCl, + 2NH; = NH,Cl + NH,Hg’Cl (white precipitate). The true constitution of white precipitate is still a matter of doubt ; the view that it represents ammonium chloride, NH,Cl, in which half of the hydrogen has been dis- placed by Hg, is convenient though questionable. When boiled with potash NH,HgCl + KOH = NH, + HgO + KCl. If it be boiled with water, it is only partly decomposed in a similar manner, leaving a yellow powder having the composition (NH,HgCl).Hg0, produced according to the equation 2(NH,HgCl) + H,O = NH,Cl + (NH,HeCl).Hg0O. A compound corresponding with this yellow powder, but containing mercuric chloride in place of oxide, is precipitated when ammonia is gradually added to solution of HgCly in large excess, the result being a compound of white precipitate with a molecule of undecomposed mercuric chloride (NH,HgCl).HgClo. If white precipitate be heated to about 315°, it evolves NH, and HgCls, leaving a red crystalline powder which is insoluble in water and in diluted acids, and is un- changed by boiling with potash ; it may be represented as a compound of mercuric chloride with ammonia in which the whole of the hydrogen has been displaced by mercury, N,Hg;.2HgCle. When strongly heated, white precipitate yields a sublimate of calomel ; 3NH,Hg”Cl = 3HgCl + N + 2NH3. When solution of HgCl, is added to a hot solution of NH,Cl mixed with NH, a crystalline deposit is obtained on cooling the liquid ; this is also obtained when ammo- niacal mercuric chloride is precipitated by an alkaline carbonate; it is known as fusible white precipitate, and may conveniently be represented as 2 mols. of NH,Cl, in which one-fourth of the kydrogen has been displaced by Hg, its composition being N,H,HgCl,. The same compound is formed when white precipitate is boiled with solution of sal ammoniac ; NH,HgCl + NH,Cl = N,H,HgCh. Mercurous chloride, or calomel (HgCl), unlike corrosive sublimate, is insoluble in water, so that it is precipitated when HCl or a soluble chloride is added to mercurous nitrate. The simplest mode of manufacturing it consists in intimately mixing corrosive sublimate with mercury in the pro- portion represented by the equation HgCl, + Hg = 2HgCl, a little water being added to prevent dust, drying the mixture thoroughly, and subliming it. But it is more commonly made by adding mercury to the materials employed in the preparation of corrosive sublimate in the proportion repre- sented by the equation HgSO, + Hg + 2NaCl = 2HgCl + Na,SO,. The calomel condenses as a translucent, fibrous cake on the cool part of the subliming vessel. For medicinal purposes, the calomel is obtained in a very fine state of division by conducting the vapour into a large chamber so as to precipitate it in a fine powder by contact with a large volume of cold air. Steam is sometimes introduced to promote its fine subdivision. Sublimed calomel always contains some corrosive sublimate, so that it must be thoroughly washed with water before being employed in medicine. When perfectly pure calomel is sublimed, a little is always decomposed during the process into metallic mercury and corrosive sublimate. Calomel is met with either as a semi-transparent fibrous mass, or an amorphous powder, with a slightly yellow tinge. Light slowly decomposes it, turning it grey from separation of mercury. It is heavier than corrosive sublimate (sp. gr. 7:18), and does not fuse before subliming ; it may be obtained in four-sided prisms by slow sublimation. Dilute acids will not dissolve it, but boiling HNO, gradually converts it into HgCl, and Hg(NO,),, “7 418 MERCURIC SULPHIDE which pass into solution. Boiling HCl turns it grey, some mercury being separated, and HgCl, dissolved. Mercuric nitrate dissolves calomel, forming mercuric chloride and mercurous nitrate. Alkaline solutions convert it into black mercurous oxide, as is seen in black-wash, made by treating calomel with lime water; 2HgCl + Ca(OH), = Hg.O + CaCl, + H,0. Solution of ammonia converts it into a grey substance, which is probably a mixture of white precipitate and Hg (p. 417). Calomel is found as horn quicksilver at Idria and Almaden, crystallised in rhombic prisms. It is asserted that calomel is dissociated by heat into Hg and Hg(Cle, so that its vapour density does not decide its molecular weight. When, however, the vaporisation is performed in presence of HgCly, so that the dissociation is hindered (p. 346), the vapour density is found to be about 117-5, showing that HgCl is most probably the molecular formula for calomel. The presence of metallic mercury in calomel vapour is shown by the deposition of minute globules of mercury on a cold tube coated with gold immersed in the vapour at 440°. Mercurous iodide, Hgl, is a green unstable substance, formed when iodine is triturated with an excess of mercury and a little alcohol, or by precipitating mercurous nitrate with potassium iodide. It owes its green colour to the presence of excess of mercury ; when precipitated in a solution containing HNO, it is yellow. Witn care, it may be sublimed in yellow crystals, isomorphous with mercurous chloride, but if sharply heated it is decomposed into Hg and HgI,. Potassium iodide decomposes it in a similar way, dissolving the mercuric iodide. When mercuric chloride is boiled with HCl and copper the solution gives with KI a dark red precipitate of mercuroso-mercuric todide, insoluble in excess of KI. Mercuric iodide, or todine scarlet, HgI,, is the bright red precipitate produced by KI in HgCl,. At the moment of precipitation it is yellow, rapidly becoming fawn- coloured and red. When the dry mercuric iodide is heated, it becomes bright yellow at temperatures above 126° (with increase of volume), and remains so on cooling until touched with a hard body, when it becomes red again, the colour spreading from the point touched ; under the microscope, the red iodide is seen to be octahedral and the yellow to consist of rhombic tables. When the yellow iodide is heated, it fuses easily (238°), becomes brown, and is converted into a colourless vapour which condenses in yellow crystals on a cold surface. A very beautiful experiment is made by gently heating HglI, in a large porcelain crucible covered with a dial-glass ; the yellow iodide is deposited in crystals projecting from the under surface of the glass, and if this be placed on the table with the crystals upwards, and some of these be touched with a needle, the red spots appear like poppies among corn, and the blush gradually spreads over the entire field, attended by a rustling movement caused by the change in crystalline form. The transformation of the yellow Hgl, into the red HgI, evolves 3000 gram-units of heat. Mercuric iodide dissolves in hot alcohol, and crystallises in red octahedra. Ether also dissolvesit. Itis freely soluble in solutions of mercuric chloride and potassium iodide. The latter yields yellow prisms of 2(HgI,.KI).3Aq. The solution of this salt mixed with potash forms Nessler’s solution, which gives a brown precipitate with very minute quantities of ammonia : 2HgI, + 3KOH + NH, = NHg,I.H,O + 3KI + 2H,0. Mercuric Sulphide, HgS.—This is the only sulphide which is stable at ordinary temperature, the black substance (Hthiop’s mineral) formed under conditions which might be expected to produce a mercurous sulphide being a mixture of HgS and Hg. The native mercuric sulphide, or cinnabar, is found sometimes in amorphous masses, sometimes crystallised in six- sided prisms varying in colour from dark brown to bright red. It may be distinguished from most other minerals by its great weight (sp. gr. 8-1), and by its red colour when scraped with a knife. Neither HCl nor HNO,, sepa- rately, will dissolve it, but a mixture of the two dissolves it as mercuric chloride, with separation of sulphur. Some specimens of cinnabar have a bright red colour, so that they only require grinding and levigating to be VERMILION 419 used as vermilion ; and if the brown cinnabar in powder be heated for some time at 49° with a solution of sulphur in potash, it is converted into vermilion. Of the artificial mercuric sulphide there are two varieties—the black, which is precipitated when HgCl, is added to hydrosulphuric acid or a soluble sulphide, and the red (vermilion), into which the black variety is converted by sublimation, or by prolonged contact with solutions of alkali sulphides containing excess of sulphur, though, so far as is known, the conversion is effected without chemical change. In Idria and Holland 6 parts of mercury and 1 of sulphur are well agitated together in revolving casks for several hours, and the black sulphide thus obtained is sublimed in tall earthen pots closed with iron plates, when the vermilion is deposited in the upper part of the pots, and is afterwards ground and levigated. One of the wet processes for making vermilion consists in triturating 300 parts of mercury with 114 parts of sulphur for two or three hours and digesting the black product, at about 49°, with 75 parts of caustic potash and 400 of water until it has acquired a fine red colour. The vermilion made by the dry process is the more highly prized. The permanence of vermilion paint is, of course, attributable to the circumstance that it resists the action of light, oxygen, CO,, aqueous vapour, and even of the H,S and SO, which contaminate the air of towns, whereas the red paints containing lead are blackened by H,S, and all vegetable and animal reds are liable to be bleached by atmospheric oxygen and by SOp. The black mercuric sulphide (sp. gr. 7-5) is quickly converted into the red form (sp. gr. 8-1) by boiling it with freshly prepared ammonium polysulphide (made by saturating ammonia with H,S and dissolving sulphur in the liquid, gently warmed, until it has a dark sherry colour) ; it appears that the black form is more soluble than the red, so that when the polysulphide solution becomes saturated with the black form it is supersaturated with the red, which therefore separates ; another portion of the black then dissolves, and so on, until the conversion is complete. If the black sulphide be boiled with K,S and KOH, it is dissolved, and the solution deposits white needles of HgS.K,S.5H,0, which are decomposed by water. When the black precipitated mercuric sulphide is boiled with solution of corrosive sublimate, it is converted into a white chlorosulphide of mercury, HgCl,.2HgS, which is also formed when a small quantity of hydrosulphuric acid is added to corrosive sublimate, becoming yellow, brown, and black on adding more HS. Vermilion may be prepared by adding HgCl, to a slight excess of dilute NH, nearly dissolving the precipitate in sodium thiosulphate, and heating, when a bright yeliow precipitate is obtained, which becomes bright red on boiling. By suspending HgS in air-free water and passing H,S, a dark-coloured solution of colloidal mercuric sulphide can be obtained. Review of the Magnesium Group of Metals.—As in the case of the metals of the first group, the melting-point.falls with rise of atomic weight, and the same is true of the boiling-points. Unlike these metals, however, and also the alkaline earth metals, the electro-positiveness decreases with increasing atomic weight. a Be Mg Zn Cd Hg Atomic weight . 9-10 24-32 65-37 112-40 200-60 Melting-point. . 1000° 623° 419° 321° — 39° Boiling-point . . — 1100° 930° 778° 357° Specific gravity . 1-93 1-75 7:15 8-65 13-54 H.F. of MCI, . | 155,000 151,000 97,200 93,240 53,300 H.F.of MO. . — 144,000 85,430 65,780 21,500 Their oxides are practically insoluble in water, and are less basic as tke molecular weight’ increases, and much less basic than the alkaline carths, as indicated by the tendency to form double salts and, in the case of Be, 420 CLAY Zn and Cd, to dissolve in alkalies. The carbonates are easily decomposed by heat; the sulphates are more easily decomposed than those of the metals of the preceding groups and appear to decrease in stability with rise of molecular weight. The stability and insolubility of the sulphides increases with the atomic weight, a gradation which finds application in the usual analytical scheme. The vapour density of Zn, Cd and Hg has been determined and has been found to agree with a monatomic constitution of the vapours. ALUMINIUM [THIRD (ii)] GROUP. ALUMINIUM, GALLIuM, Inprum, THALLIUM. ALUMINIUM, Al = 27.1. Aluminium is distinguished among metals, as silicon is among non. metallic bodies, for its immense abundance in the solid mineral portion of the earth, to which, indeed, it is almost entirely confined, for it is present in vegetables and animals in so small a quantity that it can scarcely be regarded as forming one of their necessary components. Church has, how- ever, found it in certain cryptogamous plants, especially in the Lycopodiums ; the ash of Lycopodium alpinum yielding one-third of its weight of alumina. One of the oldest rocks, which appears to have originally formed the basis of the solid structure of the globe, is that known as granite. This mineral, which derives its name from its conspicuous granular structure, is a mixture, in variable proportions, of quartz, felspar and mica, tinged of various colours by the presence of small quantities of the oxides of iron and manganese. Quartz, which forms the translucent or transparent grains in the sania, consists simply of silica; felspar, the dull, cream-coloured, opaque part, is a combination of silica with oxides of aluminium and potassium, of the composition K,0.3S8i0,.A1,03;.Si0,. Mica, so named from the glittering scales which it forms in the granite, is also a double silicate of alumina and potash, K,0.3A1,0,.48i0,, but the Al,O, is very frequently displaced by He,0, and the K,O by MgO. By the long-continued action of air and water the granite is gradually disintegrated, an effect which must be ascribed to a concurrence of mechanical and chemical causes. Mechanically, the rock is continually worn down by variations of temperature, and by the freezing of water within its minute pores, the rock being gradually split by the expansion attendant upon the passage of water into ice. Chemically, the action of water containing CO, would tend to remove the potash from the felspar and mica in the form of carbonate of potash, whilst the silicate of alumina and the quartz would subsequently be separated by the action of water; the former, being more finely subdivided and somewhat lighter, would be soon washed away from the quartz, and, when again deposited, would constitute clay, the purest form of which is kaolin (Al,O,.2Si0,.2H,0). Although clay, therefore, always consists mainly of silicate of alumina, it generally contiins some uncombined 8i0,, together with variable propor- tions of lime, oxide of iron, &c., which give rise to the numerous varieties of clay. Thus a pure Chinese kaolin contains— H,O SiO, Al,O3 Fe,03 MgO Alkalies Per cent. . . 11-2 50-5 33-7 1:8 0-8 1-9 whilst Stourbridge fireclay contains about 85 per cent. of this clay-substance and some 15 per cent. of silica as quartz. ALUMINIUM—PROPERTIES 421 ‘The silicate of alumina also constitutes the chief portion of several other very important mineral substances, among which may be mentioned slate, fuller’s earth, and pumice-stone. Marl is clay containing a considerable quantity of carbonate of lime. Loam is also an impure variety of clay. The different varieties of ochre, as well as wmber and sienna, are simply clays coloured by the oxides of iron and manganese. Notwithstanding the abundance of aluminium in the form of clay, it is only comparatively recently that the metal has been extracted in quantity sufficient to make it of practical importance. Originally the metal was prepared by fusing the chloride, preferably in the form of the double chloride AICI,NaCl, with sodium, which abstracted the chlorine. Now, however, aluminium is prepared by the electrolysis of a bath of fused cryolite (the double fluoride of aluminium and sodium, Na,AlF,), containing aluminium oxide (alumina, Al,O,), dissolved in it; the metal is deposited around the cathode, oxygen being evolved at the anode (Fig. 246). The iron box, a, is lined with graphite blocks, 6, which serve as cathode, being supplicd with current through terminals, c. The anode is a bundle of carbon rods, d. The bath of fused cryolite, e, is kept melted by the heat generated by its electrical resistance, and is fed with Al,O, through openings, f, whenever its resistance rises, showing that but little Al,03 remains to be electrolysed. The temperature d is about 900° and the molten Al remains at the bottom of the bath, than which it is slightly heavier. It is tapped by withdrawing the plug, g. The Al,O; for this process is obtained from bauxite, a mineral found at Baux, near Arles, in the South of France, and in Antrim, Ireland. @ It may contain alumina 56 per cent., ferric oxide 3, silica 12, titanic acid 3, and water 26. To obtain Al,O; from it, itis roasted to oxidise any organic matter and ferrous oxide, and heated under pressure with caustic soda solution, whereby the alumina is dissolved as sodium aluminate, 3Na,0.Al,0;. After filtra- Fig. 246. tion a small proportion of alumina is : added to the liquid and the whole is agitated. In the course of thirty-six hours the greater part of the Al,O; is deposited from the solution, recalling the separation of a salt from a supersaturated solution by addition of anucleus. The liquor from which the alumina has been separated is used for extracting another portion of the ignited bauxite. The deposited alumina is filtered, washed, and heated to expel water. Aluminium is a white metal, less fusible than tin and zinc, but more so than silver, its fusing-point being 657°.1 It is not volatile at a white heat. It is easily rolled and drawn. It is much more sonorous than most other metals. A bar of it suspended from a string, and struck with a hammer, emits a clear musical sound. It is remarkable as being the lightest metal (sp. gr. 2-583) capable of resisting the action of air even in the presence of moisture. This lightness, combined with its considerable tensile strength, renders the metal useful in many cases where the saving of weight or a large bulk for a given weight is of importance. The fact that it cannot easily be soldered militates against some uses; autogenous soldering (p. 162) is possible. It is also applied for ornamental purposes, for, though not so brilliant as silver, it is not blackened by H,S. Aluminium leaf has largely displaced silver leaf as a decorative material and is capable of being printed on fabrics ; aluminium paint is a like application. The chief impurities in commercial aluminium are iron and silicon. 1 Jt is not easily fuged before the blowpipe, as its surface becomes covered with infysible oxide. ZZ 4 Y LL a g We 0 422 ALUMINIUM ALLOYS Another characteristic feature of aluminium is its comparative resist ance to the action of nitric acid even at a boiling heat. No other metal commonly met with, except platinum and gold, is capable of resisting the action of nitric acid to the same extent. Hydrochloric acid, however which will not attack gold and platinum, dissolves aluminium with facility, converting it into aluminium chloride (AICI;), with disengagement of hydrogen. Dilute H,SO, attacks it slowly. Solutions of alkalies also easily dissolve it, forming the so-called aluminates ; thus, 3NaOH + Al = Al(ONa)3-+3H (see p. 96). Even when very strongly heated in air, aluminium is oxidised to a very slight extent, probably because the coating of alumina which is formed remains infusible and protects the metal beneath it. For a similar reason, apparently, aluminium decomposes steam but slowly, even at a high temperature. The resistance of the metal to chemical attack is of much importance in connection with its‘use for cooking utensils. It appears that pure aluminium is sufficiently resistant to vegetable and animal juices, but vessels made of the metal should be used with circum- spection. When aluminium is rubbed with a solution of mercuric chloride it becomes amal- gamated with mercury on the surface and is then remarkably active, decomposing water at the ordinary temperature with violence, and serving as a useful neutral reducing agent. —~ Powdered aluminium (made by shaking the molten metal in a box until it solidifies) burns with ease like powdered magnesium. The heat of combustion is Al,,03; = 360,000 cals., and the temperature produced is very high. Indeed, if the oxygen be supplied by an admixture of a metallic oxide the temperature becomes comparable with that of the electric arc, and even highly refractory metals are both reduced and melted when their oxides are mixed with powdered aluminium and the mixture is ignited.? A mixture of ferric oxide and aluminium powder is used under the name “ thermite,”’ for the production of local high temperatures ; the mixture is ignited in a crucible by a fuse composed of a mixture of barium peroxide and aluminium powder, and when the combustion is over,the white-hot molten iron with its superincumbent layer of molten aluminium is poured on to the surface to be heated, such as two rails which are to be butt-jointed by fusing the ends together. When the mixture is ignited on an iron plate it fuses its way through the metal. Aluminium alloys are numerous. In some, Al is the principal constituent, the other metal or metals being added to increase the strength of the metal without appre- ciably diminishing its lightness ; for instance, an alloy of 94 per cent. of Al and 6 per cent. of Cu has three or four times the tensile strength of Al. Magnalium, containing about 90 per cent. of Al and 10 per cent. of Mg, is even lighter than the pure metal, and is more easily worked. Alloys of Al and Zn are of this class. In other cases the Al may be regarded as the auxiliary metal imparting strength to the alloy ; the most important example is aluminium bronze (90 per cent. Cu, 10 per cent. Al), very similar to gold in appearance, but almost as strong as iron. It is noteworthy that Al does not dissolve in cold mercury or in molten lead, both of which dissolve nearly all other metals. Aluminium is much used in the iron industry, particularly as an addition to molten steel just before it is poured, for the purpose of reducing any oxide which may be present. Aluminium sulphate, Al,(SO,)3, is the commonest compound of alu- minium used in the arts, and is best known in the form of the double sulphate KAI(SO,),.12Aq, commonly known as alum. Aluminium sulphate may be made from any pure form of clay, such as kaolin, by heating it under pressure with H,SO, of 78 per cent. strength insufficient in quantity to dissolve the Al,O3, under which condition the SiO, of the clay is not appreciably dissolved. The hot liquor is run through ' A mixture of aluminium powder and sodium peroxide ignites spontaneously when moistened, ALUM 423 a filter press and allowed to cool, when it sets to a crystalline cake known as alum cake. Although the sulphate can be obtained as crystals, Al,(SO,4)3.18Aq?, the extreme solubility of these (107 in 100 of H,O at 20° and 87 at 0°) renders it difficult to recrystallise the alum cake for the purpose of freeing it from ferric sulphate, which even in small proportion is fatal to its use in dyeing. For this reason the alum cake is converted into alum (which can be very easily crystallised) by mixing the solution of the cake with potassium sulphate and carefully crystallising ; K,SO, + Al,(8O4)3 = 2KAI(SO,),. The crystals of alum are regular octahedra, of sp. gr. 1-7; 15 parts dissolve in 100 of H,O at 20°, and 357 in 100 at 100°.2. Alum is insoluble in alcohol. When heated it melts (92:5°) and swells up to a light porous mass of burnt alum, having lost its water. 2 Of late years the production of alum has diminished owing to the discovery of bauxite as a source of alumina and its compounds. As explained on p. 421, this mineral can be treated with caustic soda to dissolve the Al,O3, and since Fe,03, the impurity to be avoided in aluminium sulphate, is insoluble in alkalies, the Al,O; obtained yields a sulphate of desired purity when dissolved in H,S8O,, the solution being evaporated until it sets on cooling. A somewhat cheaper method consists in heating the bauxite with H,SO, of 50 per cent. strength, which dissolves the Al,O3 before the Fe,03; the product contains less than 0-1 per cent. of iron oxide, but for the dyer even this may be too much, and is removed by careful precipitation as prussian blue by addition of potassium ferrocyanide before the liquor crystallises. The mineral alunite or alum stone, K(A10)3(SO,4)..3H,0, found in volcanic deposits in Italy, is the oldest source of alum. This material is burnt at 600° and allowed to weather, after which alum can be leached from it. There being excess of alumina in the mineral, a little of it dissolves in the liquor, and this has the curious effect of causing the crystals to separate in the form of cubes (cubic alum) so long as the temperature is below 40°. Both aluminium sulphate and alum solutions are acid to test papers and possess the astringent taste characteristic of aluminium salts. By the dyer and calico-printer they are used for producing a precipitate of alumina in the fibres of a yarn or fabric for the purpose of fixing or mordanting the dyestufi—that is to say, advantage is taken of the fact that alumina has a special attraction for the particles of dyestuff in a solution thereof, holding them (as adsorption compounds) in a condition insoluble in water, so that subsequent washing of the dyed fabric does not remove the colour. Several methods of applying these salts as mordants are practised. One consists in adding Na,CO, solution by degrees to a solution of alum as long as the precipitate of aluminium hydroxide at first formed is redissolved on stirring ; the solution constitutes basic alum, and a fabric dipped in it becomes impreg- nated with the hydrated alumina. The application of these salts in making lakes by adding an alkali to a solution of one of them containing a dyestuff so as to precipitate hydrated alumina, depends on the same principle, which may be illustrated by mixing a solution of alum with infusion of logwood and adding a little ammonia, whereupon a purplish-red lake will be precipitated, leaving the liquid colour- less. The paper-maker uses aluminium sulphate in conjunction with rosin to precipitate a compound of alumina and the rosin (aluminium resinate) on the fibres of the paper, and thus to size the latter, 7.e. make it less absorbent of water. 1 According to Mendeléeff, the pure salt crystallises with 16Aq and is not hygroscopic; impurities increase the water to 18Aq and the salt’ becomes hygroscopic. 2 When a supersaturated solution (p. 40) of these crystals is concentrated in a flask, stoppered with cotton- wool, until a film of solid appears on the surface of the liquor, the solution sets, on cooling, to a mass of prismatic crystals. By carefully removing the cotton-wool and introducing a crystal of the ordinary, octahedral alum, the whole of the already solidified substance may be made to break up, the prismatic crystals, being transformed into the octahedral variety with much evolution of heat, 424 ALUMINA For these several purposes ammonia-alum is as usefulas potash-alum and is made by substituting (NH,),SO, for K,SO, in the manufacture. It has the formula (NH,)Al(SO,),.12Aq and is isomorphous with KAl(SO,),.12Aq. These two alums are typical of a whole series of double sulphates, all isomorphous with each other and of the general formula M’M’’’(SO,),.12Aq, in which M’ stands for any alkali metal, Ag or Tl, and M’” for Al, Cr, Fe, Mn, Ga. They are all known as alums. If the type be doubled, M’,M’”,(SO,),.24Aq, Mg, Zn, or Cu’ may be substituted for M’, without change of ‘crystalline form, namely, that of the regular octahedron. The solubilities of the alkali alums decrease as the atomic weight of the alkali metal increases. Thus at about 17° 100 of water dissolve of the alum from Na, 50; NH,,17; K, 13; Rb, 2:27; Cs, 0-62. Alumina.—When ammonia-alum is strongly heated it leaves a white insoluble earthy substance which is alumina itself (Al,0,), and differs widely from the metallic oxides which have been hitherto considered by the feebly basic character which it exhibits.1 Not only is alumina destitute of alkaline properties, but it is not even capable of entirely neutralising the acids, and hence both aluminium sulphate and alum are exceedingly acid salts. Indeed, alumina has feebly acid properties towards the powerful bases, forming aluminates, such as sodium aluminate, 3Na,0.Al,03. Pure crystallised alumina is found in nature as the mineral corundum, distinguished by its extreme hardness, in which it ranks next to the diamond. An opaque and impure variety of corundum constitutes the very useful substance emery. The ruby, oriental amethyst, and sapphire consist of nearly pure alumina ; spinel is a compound of magnesia with alumina, MgO.Al,0,; whilst in the topaz the alumina is associated with silica and aluminium fluoride. In these forms the alumina is insoluble in acids, but it may be rendered soluble by fusion with acid potassium sulphate, or with alkali hydroxides. The sp. gr. of alumina varies from 3-7 to 4:1, the latter value being the sp. gr. of the natural crystalline varieties. The manufacture of Al,O3; from bauxite has been described on p. 421. Artificial corundum has been made by fusing alumina either in the electric furnace or by the combustion of aluminium (p. 422) and allowing the fused mass to cool. Artificial rubies are now a commercial article, being made by feeding finely powdered Al,03, containing 4 small proportion of chromium oxide, into an oxy-gas blowpipe flame directed against a cone of pure Al,O, ; the fine particles melt together on the cone and form globules of ruby, which are afterwards cut. Several others of this family of precious stones have been made. Aluminium Hydrates.—Several of these occur in nature: hydrargillite, Al,O;.3H,0, may be regarded as the true hydroxide, Alo(OH),; the purest form of bauzite is Al,O3.2H,0 (sp. gr. 2:6) ; diaspore, AloO,.H,O (sp. gr. 3-4), so named from its falling to powder when heated (S:armopa, dispersion), may be regarded as the type of the spinels. Ifa little alum is dissolved in warm water and some ammonia added to the Solution, the alumina precipitates as a semi-transparent gelatinous mass of the hydrate, Al,(OH),.2H,0, nearly insoluble in ammonia, but soluble in caustic alkalies. Being on the border-line between acids and bases, alumina shares with other like bodies the colloidal characteristic of existing in the hydrosol and hydrogel forms (p. 282). By adding ammonia to a solution of AlCl, until a slight permanent precipitate is formed, and dialy- sing (p. 281) the solution, the hydrosol of alumina is left on the dialyser ; this still contains some chlorine ions, but they cannot be detected until the hydrosol has been destroyed by adding ammonia. Almost any electrolyte added to the hydrosol will convert it into the jelly consisting of the hydrogel. When washed and dried the jelly shrinks very much and forms a mass resembling gum. It is to this colloidal character that alumina owes its power of adsorption, turned to account in dyeing and printing (p. 423). 1 The great absorption and disappearance of heat during the evaporation of the water and ammonia from this alum have led to its employment for filling the space between the double walls of fireproof safes, which may become red-hot outside, whilst the inside is kept below the scorching point of paper, ZEOLITES 425 Aluminium Chloride, AlCl;.—Apart from its use in making certain organic com- pounds, the anhydrous salt is chiefly of chemical interest. An instructive method of making it consists in strongly heating an intimate mixture of alumina and charcoal in a porcelain tube through which a stream of well-dried chlorine is passed ; the oxygen of the alumina is abstracted by the charcoal to form carbonic oxide, whilst the chlorine combines with the aluminium, yielding aluminium chloride, which passes off in vapour and may be condensed, in an appropriate receiver, as a white crystalline solid ; Al,Oz + 3C + 3Cly = 2AlCl, + 3CO. It is more easily made by heating the mete] in Cl or HCl gas. AICI; sublimes at 183°, and is volatile even at the ordinary temperature ; since it is decomposed by moisture into Al,O, and HCl, it fumes in moist air. It is remarkable for the numerous double compounds which it forms, a property that it shares with the other halides of aluminium and to which its power of acting as a catalytic agent in numerous reactions is probably due. It melts under pressure at 193°. By dissolving alumina in HCl and evaporating, needles of AlCl; .6H,Q are obtained, but they are decomposed, when heated, into Al,O3, 6HCI, and 9H,O. An impure solution of aluminium chloride made in this way is sold, chiefly for use in the wool industry. Mineral Silicates of Alumina.—Many of the chemical formule of minerals which contain silicates of alumina associated with the silicates of other metallic oxides are complicated from the circumstance that iron often takes the place of a part of the aluminium, which is possible because Fe,0; is isomorphous with Al,03, and therefore capable of taking its place without altering the crystalline form and general character of the mineral. In a similar manner, the other metals present in the mineral may be ex- changed for isomorphous representatives ; thus there are two well-known felspars, potash-felspar (orthoclase) and soda-felspar (albite), having the formule K,0.A1,0;.68i0, and Na,O.Al,0,.6S8i0,. These minerals are sometimes mingled in one and the same crystal (potash-albite or pericline) without bearing any definite equivalent proportion to each other; the formula of such a mineral would be written [KNa],0.Al,0,.68i0,. Porphyry has the same chemical composition as felspar. Mica includes the two minerals muscovite, K,0.3A],0;.48i0,, and bivtite, 3MgO. Al,0, .3Si0,. Garnet is essentially a double silicate of alumina and lime, but often contains magnesium, iron, or manganese in place of part of the calcium, and iron in place of part of the aluminium, being written 3[CaMgFeMn]O.[AlFe],0,.38i0,. This mineral is sometimes formed artificially in the slag of the iron blast-furnaces. Chlorite has the composition 6[MgFe]O. [AlFe],0; .38i0..4H,0. Basalt isa felspathic rock containing crystals of augite ([Fe,Mg]O.SiO.) and magnetic oxide of iron. Cyanite, kyanite, or disthene is Al,03.SiO. ; a crystal of this is said to point north and south when freely suspended. Gneiss is chemically composed like granite, but the mica is arranged in regular layers. Trap rock contains felspar together with hornblende, ({FeO.?MgO)SiOg. Hornblende is sometimes found in the place of mica in syenitic granite. Lava, from volcanoes, consists essentially of ferrous, calcium, and aluminium silicates ; the presence of a considerable proportion of potassium and of phosphoric acid renders the soil formed by the weathering of lava very fertile. Zeolites are of the general form [RO,R,OJAI,0,.nS8i0, + vH,O. They are practically insoluble in water, but comparatively easily attacked by acids. They are notable for the ease with which they exchange their base for another ; for instance, if a weak solution of CaCl, is filtered through a mass of natrolite, Na,O.Al,0,.3S8i0, + 2H,0, it is converted into a solu- tion of 2NaCl, all the calcium having remained as CaO in the natrolite in place of an equivalent quantity of Na,O. The reverse change can readily be effected, Na,O being fixed from a solution of NaCl. This property of zeolites, which is closely connected with the power of soils to absorb bases, 423 ULTRAMARINE particularly K,0, has been applied to several purposes, notably for soften- ing water. Artificial zeolites are made for such uses, under the name permutites, by fusing clay with alkali and silica in correct proportions and extracting with water; the zeolite remains undissolved. Lapis lazuli, the valuable mineral which furnishes the natural ultra- marine used in painting, consists chiefly of silica and alumina, which con- stitute respectively 45 and 25 per cent. of it, but there are also present 10 per cent. of soda, 6 per cent. of sulphuric acid, about 3 per cent. of sulphur, and a somewhat smaller quantity of iron, together with a variable proportion of lime. Thecause of its blue colour is not understood, since neither of its predominant constituents is concerned in the production of such a colour in other cases. In consequence of the rarity of the mineral, the natural ultramarine has a very high price, but the artificial ultramarine is manu- factured in very large quantities at a low cost, and forms a very good imita- tion. One of the processes for preparing it consists in heating to bright redness in a covered crucible, for three or four hours, an intimate mixture of 100 parts of pure white clay (kaolin), 100 of dried carbonate of soda, 60 of sulphur, and 12 of charcoal. This would be expected to yield a mixture of silicate of soda, aluminate of soda, and sulphide of sodium, the two first being white, and the last yellow or brown, but the mass is found to have a green colour (green ultramarine). It is finely powdered, washed with water, dried, mixed with a fifth of its weight of sulphur, and gently roasted in a thin layer till the sulphur has burnt off, this operation being repeated, with fresh additions of sulphur, until the residue has a fine blue colour. In the opinion of some chemists, the presence of a small proportion of iron is essential to the blue colour, whilst others believe the colour to be due to sodium sulphide or thiosulphate, or both.t Ultramarine is a very permanent colour.under ordinary conditions of exposures to the air and light, but acids bleach it at once, with separation of gelatinous silica and evolution of sulphuretted hydrogen. Blue writing- paper is often coloured with ultramarine, so that its colour is discharged by acids falling upon it in the laboratory. Chlorine also bleaches ultra- marine. Starch is often coloured blue with this substance. Aluminium phosphate, AlPO,, is found naturally in several forms. It occurs in large quantities in the West Indian islands. Turquoise is a hydrated aluminium phosphate, owing its colour to the presence of oxide of copper.2 Wavellite has the composition 3Al,0;.2P,0;.12H.O. A gelatinous precipitate of AIPO, is formed when NagHPO, is added to solution of alum. It is soluble in HCl and in potash, but insoluble in acetic acid, which distinguishes it from aluminium hydroxide. Pottery, Porcelain, and Bricks.—The manufacture of these articles is frequently termed the clay industries, since clay of one kind or another is the basis of the industry in each case: the subject is therefore conveniently considered as an appendix to the chemistry of aluminium compounds. The manufacture of pottery obviously belongs to an early period of civilisation, since the raw material, clay, would at once suggest, by its plastic properties, the possibility of working it into useful vessels, and the applica- tion of heat would naturally be had recourse to in order to dry and harden it. Indeed, at the first glance, it would appear that this manufacture did not involve the application of chemical principles, but consisted simply in fashioning the clay by mere mechanical dexterity into the required form. It is found, however, at the outset that the name of clay is applied to a large class of minerals, differing very considerably in composition, and possessing 1 Heumann assigns to ultramarine the formula 2Na,Al,Si,0,.Na,S,. Knapp attributes the blue colour to the presence of a modification of sulphur which is only blue when spread over a large surface ; in this case acids would bleach the colour by destroying the surface. Potassium ultramarine, in which K takes the place of Na, is also blue, whilst silver ultramarine, in which Ag is substituted for the Na, is yellow. 2 False or bone turquoise is fossil ivory, owing its colour to the presence of the natural blue phosphate of iron. Redonda phosphate consists chiefly of AlPO,. POTTERY AND PORCELAIN 427 in common the two characteristic features of plasticity and a predominance of aluminium silicate. The basis of all clays is the silicate Al,O,.28i0,.2H.O, containing 39-5 per cent. of Al,O3. This has been called the “ clay-substance,”’ and the more there is of it in the clay, the more valuable the latter. A mineral silicate of alumina containing more than 39-5 per cant. Al,O3 is not a clay. The origin of the plasticity of clay is still obscure. Most observers attribute it to the amorphous character of the particles of the clay- substance and their extreme finenes3, characteristics which make the moist clay behave as a colloid. Against this view is the fact that the purest forms of kaolin (p. 420), which contains most clay-substance, are not particularly plastic ; moreover, recent researches throw doubt on the amorphous character of the clay-substance. The plasticity can be increased by addition of colloidal substances like hydrated ferric oxide or hydrated silica ; humic acid (the organic matter in soil) is also added for the purpose. Another property of clay all-important to the potter is its power of shrinking-and hardening when it is baked or “fired.” This property appears to be related to plasticity, since the most plastic clays shrink the most; indeed, so much is this the case that the better clays require to be mixed with some infusible diluent such as sand in order that vessels shaped from the clay may not lose their shape or crack when fired in the pottery kiln. The great infusibility of true clay in conjunction with its shrinkage when heated would render the fired pottery porous ; in the majority of cases this, of course, is not desired, and for making porcelain and stoneware a further addition is made to the clay and sand of some substance which fuses at the temperature at which the ware is fired. Felspar (p. 420) isa suitable flux for the purpose, but many artificial mixtures containing alkali and silica are used. The presence of the flux determines the production of a body which is clinkered throughout, but a cheaper method consists in omitting the flux and firing the mixture of clay and diluent to make a porous body, and to waterproof the ware by re-firing it after applying to its surface the flux, which fuses at the temperature of this second firing and forms a glaze. The best variety of porcelain is made from substantially pure kaolin (Cornish clay), which is not as plastic as scme of the less pure clays and is therefore more troublesome to work. Porcelain is glazed to present a perfectly smooth surface, unless biscuit ware is required. A distinction is drawn between hard porcelain, the constituents of which are such that the ware is exceedingly infusible, and soft porcelain, which is more easily fused, The manufacture of Berlin hard porcelain from a mixture of 55 parts of kaolin, 22-5 of quartz, and 22-5 of felspar may serve as an example. These materials are ground with water before being mixed, and the coarser particles are allowed to subside ; the creamy fluids containing the finer particles in suspension are then mixed in the proper proportions (to form a slip) and allowed to settle ; the paste deposited at the bottom is drained, thoroughly kneaded, and stored away for some months in a damp place, by which its texture is considerably improved, for some obscure reason. It is then moulded into the required forms, either on a potter’s wheel or by pressing, and dried by simple exposure to the air. The vessels are packed in cylindrical cases (saggers) of very refractory clay, which are arranged in a furnace or kiln of peculiar construction, and very gradually heated at about 900°. When sufficiently baked, the biscuit porcelain has to be glazed, and great care is taken that the glaze may possess the same expansibility by heat as the ware itself, for otherwise it would crack in all directions as the glazed ware cooled. The glaze employed is a mixture of felspar, quartz, kaolin, marble, and broken porcelain very finely ground, and suspended in water. When the porous ware is dipped into this mixture, it absorbs the water, and retains a thin coating of the mixture of quartz and felspar upon its surface. It is now again fired, this time at 1450°, when the glaze fuses, partly penetrating the ware, partly remaining as a varnish upon the surface, and the body of the ware clinkers. When the ware is required to have some uniform colour, a mineral pigment capable of resisting very high temperatures is mixed with the glaze ; but coloured designs are 428 EARTHENWARE—BRICKS painted upon the ware after glazing, the ware being then baked a third time in order to fix the colours. These colours are glasses coloured with metallic oxides, and ground up with oil of turpentine, so that they may be painted in the ordinary way upon the surface of the ware ; when the latter is again heated in the kiln the coloured glass fuses, and thus contracts firm adhesion with the ware. Gold is applied either in the form of precipitated metallic gold, or of fulminating gold, being ground up in either care with oil of turpentine, burnt in, and burnished. English soft porcelain is made from Cornish clay mixed with less pure and therefore more plastic clay, such as China stone, which contains much felspar ; bone ash is generally the diluent ; a little sodium carbonate, borax, and binoxide of tin are sometimes added, the last improving the colour of the ware. It is burnt at about 1300°, and is glazed by a second firing at a lower temperature, the glaze being generally a lead glaze (p. 397) and therefore comparatively fusible. To avoid the use of lead, boric acid glazes have been recently introduced. Stoneware is made from less pure materials, and is covered with a glaze of sodium silicate, in a very simple manner, by a process known as salt-glazing. The ware is coated with a thin film of sand by dipping it in a mixture of fine sand and water, and is then intensely heated in a kiln into which a quantity of damp salt is presently thrown. The water is decomposed, its hydrogen taking the chlorine of the salt’ to form hydro- chloric acid, and its oxygen converting the sodium into soda, which combines with the sand to form sodium silicate ; this fuses into a glass upon the surface of the ware. Pipkins and similar earthenware vessels are made of common clay mixed with a certain proportion of marl and of sand. They are glazed with a mixture of 4 or 5 parts of clay with 6 or 7 parts of litharge. The colour of this ware is due to the presence of ferric oxide. Earthenware articles are frequently cast instead of being moulded so that plasticity of the clay is not so important (p. 427). The slip is run into a plaster-of-Paris mould, which absorbs the water, leaving the article ready for drying and firing, when the mould is taken to pieces. The chief chemical interest here resides in the discovery that the amount of water in the slip can be much reduced if a little alkali be present, particularly if humic acid be added as well ; the particles of clay appear to be emulsified with the water so that sufficiently fluid slips can be made even when the proportion of diluent (sand) is large, whereby it becomes possible to cast large articles like gas retorts. Addition of acid to the alkaline slip stiffens it, recalling the behaviour of colloid solutions (p. 333). Bricks and tiles are also made from common clay mixed, if necessary, with sand ; such common clay contains sufficient fusible material to sinter the bricks. These are very often grey, or blue, or yellow, before baking, and become red under the action of heat, since the iron, which is originally present as carbonate (FeCOg), becomes converted into the red peroxide (Fe,03) by the atmospheric oxygen.1 For the manufacture of the refractory bricks for lining furnaces, of glass-pots, crucibles for making cast steel, &c., a pure and therefore infusible clay is employed, to which a certain quantity of broken pots of the same material is added to prevent the articles from shrinking whilst being dried. Dinas fire-bricks are made from a peculiar siliceous material found in the Vale of Neath, and containing alumina with about 98 per cent. of silica. The ground rock is mixed with 1 per cent. of lime and a little water before moulding. These bricks are expanded by heat, whilst ordinary fire-bricks contract. Blue bricks are glazed by sprinkling with iron scurf, a mixture of particles of stone and iron produced by the wear of the siliceous grindstones employed in grinding gun- barrels, &c. When the bricks are fired, a glaze of silicate of iron is formed upon them. GALLIUM, Ga = 69.9. This metal is found in very small quantities (0-002 per cent.) in certain ores of zinc, particularly in the blende from Bensberg in the Pyrenees; also in most specim ns of bauxite and in certain clay ironstones and the iron smelted therefrom. Its discovery in 1875 lent great support to the periodic law, since its properties coincide with th se prophesied by Mend léeff for an unknown element to follow Al in his Table (p. 8). 4 The efflorescence frequently noticed on bricks consists mainly of sulphate and chloride of sodium, which existed in the origina] clay ; the former salt is frequently formed when iron pyrites is a constituent of the clay, GALLIUM—INDIUM 429 The powdered ore is treated with aqua regia, care being taken that the blende is in excess, $0 that the nitric acid may be destroyed as far as possible. Lumps of zinc are immersed in the cooled filtrate from the undissolved ore,whereupon all metals appreciably electro-negative to zinc are precipitated ; the filtrate from these is mixed with more zine and boiled for some hours so that the acid may be completely neutralised by the zine and basic salts of Al, Zn, and Ga precipitated. They are dissolved in HCl, ammonium acetate is added, and the Ga and Zn are precipitated by H,S. The sulphides are dissolved in HCl, H.S is boiled off, and a deficiency of Na,CO, added to precipitate Ga (which is less basic than Zn) as carbonate. The carbonate is dissolved in H,SO, and excess of NH; is added; Ga,Q, is precipitated, any ZnO present being soluble in NH. orn ae is dissolved in KOH and the solution electrolysed to deposit Ga on the cathode. Gallium is a hard white metal of sp. gr. 5-95 remarkable for its low fusing-point (30°) so that it melts with the heat of the hand. It will remain liquid when cooled far below this temperature, but solidifies when touched with a piece of the solid metal. It is not oxidised by dry air until heated nearly to redness, and the oxidation is then only superficial. Dilute HNO, scarcely attacks it in the cold, but dissolves it on heating. Both HCl and KOH dissolve it, with evolution of hydrogen. Gallium oxide, GayQ3, left on igniting the nitrate, is white. When heated in hydrogen a part sublimes, and the rest is converted into a bluish-grey substance, which appears to be gallium sub-oxide, GaO. Two chlorides, GaCl, and GaCls, exist ; they are very fusible and deliquescent ; they boil at 535° and 220° respectively. GaCl, is oxidised to GaCl, by potassium permanganate solution. GaCl, decomposes water, evolving a gas not fully identified, possibly GaH3. Gallium sulphate, Gap(SO,4)3. is very soluble in water ; the solution deposits a basic salt when boiled and dissolves it again on cooling. It combines with (NH,),SO, to form an alum, the solution of which is also precipitated by boiling. Ammonia precipitates solutions of gallium, but the precipitate is more easily soluble in excess than in the case of aluminium. Ammonium sulphide precipitates Ga,S8, only if zine be present, when ZnS is precipitated at the same time. Potash gives a precipitate which dissolves easily in excess. Potassium ferrocyanide produces a white precipitate, similar to that yielded by zinc. The most delicate test for gallium (which led to its discovery) is the production of two violet bands in the spectrum, when an induction spark passes from the positive terminal of a secondary coil to the surface of the solution under examination, into which the negative terminal of the coil is made to dip. INDIUM, In = 114.8. Indium was discovered (1865) with aid of the spectroscope in a specimen of blende from Freiberg and is present in several zinc ores, whence some of it passes into the zine distilled. Its proportion in the ore seldom exceeds 0-1 per cent. Its name refers to an indigo-blue line in the spectrum. From Freiberg zinc it is extracted by boiling the metal with HCl in deficiency of that necessary to dissolve the whole. The indium remains in the residue, which is dissolved in HNO, and treated with H,S, whereby all the metals are precipitated except In, Zn, and Fe. The solution is oxidised and precipitated by NH; ; In,0, and Fe.0, are precipitated. The precipitate is dissolved in HCl and mixed with alcohol and pyridine ; after a time a characteristic compound of InCl, with pyridine crystallises. This may be decomposed into In(OH), by heating with water, and the ignited hydroxide reduced by hydrogen. Or the pyridine compound may be dissolved in excess of pyridine and electrolysed. Indium is a white metal, very soft, of sp. gr. 7-12 and m.pt. 155°. It dissolves in dilute acids with evolution of H and forming salts of the type InX;. The types InX and InX, are also known. InCl, is the final product of the action of Cl on a heated mixture of In,O, and C. InCl, is made by heating In in HCl gas, and InCl by heating InCl, with In. All three have been volatilised and their vapour densities determined. Both the lower chlorides are decomposed by water, yielding In and InCl,. InOCl is a sparingly soluble, white powder. The fluoride forms strongly doubly refractive glistening crystals which are moderately soluble. 430 THALLIUM In,(SO,)3 crystallises with 9H,O, and forms an alum with NH,, Cs, and Rb, but not with K or Na. NH, produces, in solutions of indium, a white precipitate, In(OH)3 ; insoluble in excess. -(NH,).CO, gives a precipitate soluble in excess and reprecipitated by boiling. When ignited, In(OH), yields In,0;, which is brown when hot, but yellow when cold. When this is heated in hydrogen, InO is produced. At a bright red heat indium burrs with a violet-blue flame, yielding In,O; ; sp. gr. 7:18. In,S3 is a yellowish precipitate thrown down by HS from feebly acid solutions of indium. InS is a volatile, black- brown powder. THALLIUM, TI = 204.0.. The atomic weight of this metal brings it into the Al group of the Periodic Table. The element shows remarkable resemblance to the alkali metals and silver on the one hand, and to the heavy metals, of which lead is a type, on the other hand. It is hardly less rare than gallium and indium, but like them is widely distributed. Only ore wineral (Crookesite, a copper selenide) contains it in considerable proportion (16 per cent.) ; it occurs in many specimens of pyrites and blende, and in traces in company with alkali metals in several of their natural compounds. It is better known than Ga and In because it becomes concentrated in the products volatilised in pyrites kilns (p. 167) and is deposited as a constituent of the flue-dust of these kilns ; indeed, it was in such a deposit that Crookes discovered the element in 1861 by the green line in its spectrum, which resembles one of the barium lines, but does not coincide therewith ; he named it thallium from 6addéc, a young shoot, in allusion to the vernal green of the line. From the flue-dust the metal is extracted by a simple process, but a large quantity of dust must be operated on to obtain any considerable amount of the metal. The dust is boiled with water and the solution mixed with NaCl, which precipitates thatlous chloride ; this is heated with H,SO, to obtain acid thallous sulphate, which may be recrystallised and either electrolysed or decomposed by zinc in aqueous solution, the deposited metal being subsequently fused under potassium cyanide. In appearance and softness thallium is very similar to lead ; sp. gr. 11-85, m.-pt. 290°, b.-pt. about 1700°. It tarnishes in air more rapidly than lead does, and the streak which it makes on paper soon becomes yellowish, being converted into Tl,O ; the tar- nished metal has an alkaline taste, 11,0 being soluble, and also becomes bright when immersed in water, which does not attack thallium when free from air. Dilute H,SO, acts on thallium, evolving hydrogen ; HCl has much less action ; hot dilute HNO, dissolves it, and on cooling thallous nitrate crystallises in needles. The metal burns in oxygen with a beautiful green flame. It decomposes steam at a red heat. Thallium forms salts of the types T1X and T1X3. The former (thallous salts) resemble the alkali salts in many respects and are frequently isomorphous therewith, although generally less soluble. The thallic salts are much less stable than the thallous salts, showing a tendency to form basic salts when treated with water, and being very easily reduced to the corresponding thallous salts. Thallous oxide, Tl,0, is a black powder made by oxidising the metal at a com- paratively low temperature; Thallic oxide, Tl,03, is formed when the metal burns. Both are basic oxides. TI,O combines readily with water to form thallous hydroxide, TIOH, which is a strong alkali and very soluble in water. If granulated thallium be exposed to moist air in a warm place it absorbs oxygen and COs. On boiling with water and filtering, the alkaline solution deposits white needles of thallous carbonate, Tl,CO;, and afterwards yellow needles of TIOH. Thallous hydroxide, however, is by no means so powerful a base as potash, and also differs from the alkalies in becoming’ Tl,0 at 100° or even at 15° in vacuo. Thallic oxide is a powerful oxidising agent ; it is obtained as a brown or black crystalline powder by action of H,Q, on alkaline solu- tions of thallous salts. It begins to lose oxygen at 100° and is completely converted into TI,0 at a red heat. Thallous chloride, TICl, resembles lead chloride, being precipitated by adding HC! to a solution of a thallous salt, and being dissolved, though less freely, by boiling water (1 in 490), from which it crystallises on cooling (1 in 3000). It melts at 430° and boils at 708°. Thallous iodide, TII, obtained as a yellow precipitate on adding KI to a thallous salt, fuses at 439° to.a red liquid which remains red after solidifying, RARE EARTHS 431 but changes to yellow after a time ; when spread on paper the yellow iodide becomes red when heated (168°) and remains red on cooling, but becomes yellow when rubbed with a hard body. 'Thallous iodide shows a great tendency to pass through the filter when washed. The sulphide, TI.S, is a dark precipitate formed on adding (NH,),S to a solution of « thallous or thallic salt. ‘The sulphate, TI,S0, (m.-pt. 632°), is iso- morphous with K,SO,, and forms an alum, TIAI(SO4)2.12Aq. It is to be remarked that thailic sulphate, Tl,(SO4)3, does not form an alum in which Tl’” takes the place of Al’. Thallous silicate can take the place of alkali silicate in glass; flint glass made from thallous carbonate, red lead, and sand has a higher sp. gr. (5-6) and refractive index, and is harder and more fusible, than ordinary flint glass. Thallous salts are oxidised by permanganate and other oxidants to thallic salts, but there is a tendency to formation of thallo-thallic compounds. Salts of thallium, like those of lead, are poisonous. Review of the Aluminium Group of Metals.—It is not so easy to trace the relationship between Al, Ga, In, and Tl as in the case of the preceding groups, because the chemical behaviour of Ga and In is still but little known. The last three metals are closely related by their spectra, and their melting- ponts rise with increase of atomic weight; that of Al, however, is the highest. Al Ga In Tl Atomic weight . 27-1 69-9 114-8 204-0 Melting-point 657° 30° 176° 290° Specific gravity . 2-7 5-9 74 11-8 Chlorides. ; — _— InCl TICl — GaCl, InCl, _ AlCl, GaCl InCl, TIC, As the atomic weight rises there is an increasing tendency for the metal to assume a lower valency (cf. chlorides) and, correspondingly, for the typical oxide, R,O;, to become less stable ; indeed, in the case of thallium, T],0 appears to be more stable than Tl,0;. This is probably a reason why the tendency of the metal to form an alum in which it plays a trivalent part decreases as the atomic weight increases. METALS OF THE RARE EARTHS These elements comprise the third (i) group, scandium, yttrium, lanthanum, together with the long series of little-known elements having lanthanum for its first member and, at present, lutecium for the last ; see Table on p. 304. They are all trivalent and form oxides of the general formula M,O3, but the characteristic oxide of cerium is CeO, so that it may equally well be considered as a member of the fourth group, zirconium, cerium, thorium, all of which were at one time included under the rare earth metals. However, for sake of convenience, cerium is dealt with here. The rare earths are a series of basic oxides, remarkably similar in properties, occurring in nature always in association with each other in rare minerals which contain them chiefly as silicates, phosphates, carbonates, or fluorides. They are commonly dis- tinguished as Cerite Earths and Yttria Earths. The former comprise lanthana, ceria, praseodymia, neodymia, and samaria, while the latter include scandia, yttria, europia, gadolinia, terbia, dysprosia, holma, erbia, thulia, and ytterbia. These are all the oxides which can at present be regarded as known constituents of the rare earths, although from time to time others have been alleged to have been isolated. The principal minerals yielding cerite earths are cerite (Sweden) and orthite (Sweden, Ural, and U.S.A.), which contain the earths mainly as silicates ; monazite (widely distributed), mainly as phosphates ; and eschynite (Norway), mainly as niobates. The chief yttria earth minerals are gadolinite (Norway) and yttralite, mainly as silicates ; xenotim (Norway, Brazil), mainly as phosphates ; yttrotantalite (Scandinavia), eumenite (Norway), and samarskite (Ural, Canada), mainly as niobates and tantalates. The rare earths are characterised by the insolubility of their oxalates, even in acid solution, and by the ease with which their anhydrous sulphates form supersaturated 432 CERIUM solutions at 0°, which deposit crystallised hydrates when heated. It is upon these characteristics that the extraction of the earths from the minerals is mostly based. The powdered mineral is heated carefully with H,SO, so as to obtain a mixture containing the sulphates of the rare earths in an anhydrous state. The mass is quickly powdered and introduced into ice-water, wherein the rare earth sulphates dissolve. The acidified solution is treated with H,S to separate heavy metals, iron is oxidised, and oxalic acid is added to precipitate the rare earth oxalates. If the sulphate solution is strong enough, the two groups may be partially separated by heating it, when the hydrated sulphates of the cerite earths crystallise. The separation of the rare earths from each other presents a most difficult problem owing to the great chemical similarity between them; there are no group reagents or specific reagents for these earths, such as exist for the oxides of metals of other groups. Cerium alone stands apart in that it forms a peroxide by means of which it can be separated (v.i.). The mixture of the remaining earths must be subjected to some process which takes advantage of the very small differences existing in the basicity of the oxides or in the solubility of their salts. The basicity of the oxides diminishes in the following order :—La, Pr, Nd, Ceili Yt, Sa, Gd, Tb, Ho, Er, Tm, Yb, Sc, Ce”. By adding ammonia or an alkali to a solution of the mixed oxides in HCl in successive portions in deficiency of the amount required to precipitate the whole of the oxides—in other words, by subjecting the solution to fractional precipitation by an alkali—a series of precipitates is obtained the first of which contains the least basic oxides and the others successively the more basic oxides. By many repetitions of the process there is finally obtained a series of fractions which show by their respective spectra that they consist of individual oxides. A less practicable application of the difference of basicity consists in heating the oxides with nitric acid and decomposing the dry nitrates by fractional heating ; the nitrates of the feeblest bases decompose at the lowest temperature, and the oxides may be separated by washing, leaving a solution of nitrates which may be evaporated and heated at a slightly higher temperature to decompose the salts of the next feeble bases and so on, the process being repeated on each fraction until separation is complete. The difference in solubility of the salts is taken advantage of by repeated fractional crystallisation of the nitrates, double sulphates, oxalates, or others. Although, as stated above, provision is made in the periodic tables for the metals of the rare earths, and much has been written as to the position of these elements in the system, until further knowledge of the properties of the metals themselves has accrued the matter must remain one of doubt. There is now no lack of easily obtained material on which to work, since the larger part of the monazite sand worked up for thoria (g.v.) consists of rare earths and is a waste product. Cerium, Ce = 140-25.—The characteristic oxide is CeO,, and this metal is a member of Group IV. The salts of this oxide differ considerably in solubility from the salts of the oxides of the other rare earths ; thus a good method of separating ceria consists in heating with HNO, the mass of ignited oxalates (p. 431), which contains the Ce as CeO, and mixing the solution with NH,NO,. The mixture is evaporated until red crystals of ceric ammonium nitrate begin to separate. The liquid is then allowed to cool, and the crystals are recrystallised several times from nitric acid. The metal is obtained by electrolysing fused cerous chloride. It has the appearance of iron when bright, but gradually becomes yellow from superficial oxidation. After long exposure to the air this coating is remarkably pyrophoric, causing sparks if the metal is filed. A useful application is made of this property in producing a shower of sparks adapted to kindle a wick saturated with petrol (cigar-lighters), or even to form a signal light, the flashes being very brilliant. An alloy of Ce with 30 per cent. Fe is better than the pure metal for such purposes. Cerium is about as hard as tin, and is ductile and malleable ; sp. gr. 7:04, m.pt. 623° ; heat of combustion 225,000 cals. ; it ignites in air at 150°-180° and gives a more intense light than Mg. It decomposes water very slowly, and is easily soluble in dilute acids. Cerous oxide, CegO03, has not been obtained with certainty, but the cerous salts of the type MX, are more stable than the ceric calts, MX4, corresponding with the stable ceric oxide, CeOy. The cerous hydroxide, Ce(OH)s, is a white precipitate produced by NH, in a solution of a cerous salt ; it becomes lilac by absorbing oxygen from the air, RARE EARTH METALS 433 and eventually yellow Ce(OH),; it is a stronger base than CeQ,, which, however, has no acid properties. Ceric oxide (sp. gr. 6°74) is white and insoluble in all acids except strong H,SO,; it becomes yellow when heated. Cerous salts are colourless and taste like the Al salts. Cerous chloride, CeCls, is made by heating Ce(OH), with HCl and NH,Cl until the latter has volatilised. The nitrate, Ce(NO3)3.6H,O, is used in making incandescent gas mantles. The ceric salts are yellow or red, and are easily reduced to cerous salts ; some of them are used in the dyeing industry. No ceric chloride is known, but the fluoride, CeF,.4H,O, has been made ; it yields a gas containing free F when strongly heated. Cerium peroxide, CeOz, is obtained as a hydrate by adding H,O, and NH; to a solution of a cerous salt. Lanthanum, La = 139-0.—The oxide lanthana, La,Q3, is a strong base which absorbs H,O and CO, from the air, and evolves much heat when slaked with water. It is white and soluble in acids, yielding the corresponding salts, which are colourless and taste like the Al salts. The metal is made by electrolysing the fused chloride, LaCl, ; it is iron-grey in appearance and is readily oxidised by air ; sp. gr. 6-15, m.pt. 810°, malleable and ductile ; it possesses pyrophoric properties like cerium. Sp. gr. of LagO; = 6:48. Praseodymium, Pr = 140-6.—By fractional precipitation with a base, praseodymia and neodymia cannot be separated, so that for long they were considered to be a single base, didymia ; by fractionally crystallising the nitrate of this base Welsbach (1885) showed that it consisted of the said two bases, the neodymium salt being the more soluble. Metallic praseodymium, made by electrolysing the fused chloride, PrClg, is pale yellow, harder than cerium, and of sp. gr. 6-47. It remains long unchanged in air and melts at 940°. By heating the oxalate a black oxide, of composition depending on the temperature, is obtained ; the formula, however, is always short of that corresponding with PrO., but a black peroxide of this formula can be made by heating the nitrate with KNO3. The basic oxide, Pr.O 3, is a light green powder made by heating the black oxide in hydrogen ; it dissolves in acids, yielding light green salts which have a characteristic absorption spectrum. Neodymium, Nd = 144-3, closely resembles praseodymium, but yields red salts having a characteristic absorption spectrum. The metal, obtained by electrolysis of the fused chloride, NdCl,, resembles praseodymium and bas sp. gr. 6-95 and m.-pt. 840° ; it dissolves in acids, but is not attacked by alkalies. Apparently there is only one oxide, Nd,O3, which is a light blue powder. Samarium, Sa = 150-4.—Little is known concerning this metal. Its high melting- point (1300°-1400°) renders difficult the isolation of it by electrolysing the fused chloride ; but it has been obtained in this manner as a white metal becoming yellow in air ; its sp. gr. is 7-75. The oxide, Sa 03, is white. Scandium, Sc = 44-1, Yttrium, Yt = 89-0, Europium, Eu = 152-0, Gadolinium, Gd = 157-3, Terbium, Tb = 159-2, Dysprosium, Dy = 162-5, Holmium, Ho = 163:5, Erbium, Er = 167-7, Thulium, Tm = 168-5, and Ytterbium, Yb = 172-0, and Lutecium = 174:0, have not yet been obtained in the metallic state. Doubt still hangs over the individuality of some of the corresponding oxides, all of which appear to be of the form R,O3. For a detailed account of these rare earths the reader must consult a more exhaustive treatise than the present. 28 IRON GROUP Iron, Copatt, Nicken (E1ieutH Group); ManGanEsE (SeventH Group); CaRromium (SixtH GRovp). Tue iron series shows well-marked gradation of properties to a high degree beginning with chromium capable of forming strong acids, and ending with nickel devoid of such properties. This gradation follows from titanium (fourth group) and vanadium (fifth group) and continues beyond nickel in copper (also of the eighth group, and having nickel for its closest ally, although it differs too much from iron to be included here). It is to be noted that while the treatment of the metals in this book is usually in accordance with the “‘ groups ” of the periodic system, it is according to the “ series ”’ in the cases of those typified by iron, palladium and platinum. A study of the periodic table (p. 304) will reveal the justification for this. IRON, Fe = 55.84. This most useful of all metals is one of those most widely and abundantly diffused in nature. It is to be found in nearly all forms of rock, clay, sand, and earth, its presence in these being commonly indicated by their colours, for iron is the commonest of natural mineral colouring ingredients. It is also found, though in small proportion, in plants, and in the bodies of animals, especially in the blood, which contains about 0-05 per cent. of iron in very intimate association with its colouring-matter. But iron is very rarely found in the metallic state in nature, being almost invariably combined either with oxygen or sulphur. Metallic iron is met with, however, in the meteorites or metallic masses, sometimes of enormous size, and of unknown origin, which occasionally fall upon the earth. Of these, iron is the chief component, but there are also generally present cobalt, nickel, chromium, manganese, copper, tin, magnesium, carbon, phosphorus, and sulphur. The chief forms of combination in which iron is found in sufficient abundance to render them available as sources of the metal are shown in the following Table : Ores of Iron. Common name. Chemical name. Composition. Magnetic iron ore . . | Ferroso-ferric oxide . ‘ . | FegO4 Red hematite : : Sxecalar icon | Ferric oxide ‘ ‘ . . | Fe,03 Brown hematite . . | Ferric hydrate . Fi . . | 2Fe,0,.3H,0 Spathic iron ore. . | Ferrous carbonate : 3 . | FeCO, Clay ironstone ; . | Ferrous carbonate with clay Black-band . 2 . | Ferrous carbonate with clay and bituminous matter Iron pyrites . . | Bisulphide of iron ‘ ri . | FeS, These ores are frequently associated with extraneous minerals, some of the constituents of which are productive of injury to the quality of the iron. It is worthy of notice that scarcely one of the ores of iron is entirely 434 IRON ORES 435 free from sulphur and phosphorus, substances which will be seen to have a very serious influence on the quality of the iron extracted from the ores, and the presence of which increases the difficulty of obtaining the metal in a marketable condition. _ The following Table illustrates the general composition of the most important English ores of iron, with reference to the proportions of iron, and of those substances which materially influence the character of the iron extracted from the ore—viz, manganese (present as oxide or carbonate), phosphorus (present as phosphates), and sulphur (present as bisulphide of iron). The maximum and minimum quantities found in each ore are specified : British Iron Ores. Oxide ot Phosphoric | Bisulphide No. of In 100 parts, Tron. manganese, anhydride, of iron samples a: Mno. P05. (pyrites). | analysed. Clay ironstone from coal | Max. Min. Max. Min. | Max. | Min. | Max. | Min. measures 3 . | 43-30] 20-95] 3:30] 0-46} 1-42) 0-07] 1-21} — | 77 Clay ironstone from the lias - : . | 49-17] 17-34] 1:30] — | 5-05] — | 1-60} —} 12 Brown hematite . . | 63:04] 11-98] 1-60} trace} 3-17) — | 0-30; — | 23 Red hematite . . | 69:10] 47-47] 1-13] trace] trace] trace} 0-06) — 5 Spathic ore x . | 49°78] 13-98! 12-64] 1-93] 0-22] — | 0-11; — 6 Magnetic ore p a 57-01 0-14 0-10 0-07 1 From this Table it will be gathered that,among the most abundant of the iron ores of this country, red haematite is the richest and purest, while the brown hematite often contains considerable proportions of sulphur and phosphorus, and the spathic ore, though containing little sulphur and phosphorus, often contains much manganese. The argillaceous ores, or clay ironstones found in the lias, contain more phosphorus than those from the coal-measures ; and these latter, as a general rule, contain more sulphur (pyrites) than the former, although the maximum in the Table does not show this. Clay ironstone is the ore from which the largest quantity of iron is extracted in England, since it is found abundantly in the coal-measures of Staffordshire, Shropshire, and South Wales; and it is a circumstance of great importance in the economy of English iron-smelting that the coal and limestone required in the smelting process, and even the fireclay employed in the construction of the furnace, are found in the immediate vicinity of the ore. Black-band is the clay ironstone found in the coalfields of Scotland, and often contains between 20 and 30 per cent. of bituminous matter, which contributes to the economy of fuel in smelting it. Red hematite (Fe,0,) is the most characteristic of the ores of iron, occurring in hard, shining, rounded masses (sp. gr. 5-0), with a peculiar fibrous structure and a dark red- brown colour, whence the ore derives its name (aiya, blood). It is found in con- siderable quantities in Lancashire, Cornwall, Spain, Algiers and U.S.A. Red ochre is a soft variety of this ore, containing a little clay. Brown hematite (2Fe,0,.3H,0) is found chiefly in Northamptonshire, Spain, and Luxemburg, and is the source of most of the German, Belgian and French irons. Pea iron ore and yellow ochre are varieties of brown hematite. The Scotch ore, called kidney-form clay ironstone, is really an ore of this class. Being phosphoric, the brown hematites are the chief ores used in the basic process (q.v.). Specular iron ore (FegO3) (oligist ore or iron-glance) is very different from red hematite in appearance, having a steel-grey colour, and. a brilliant metallic lustre. The island of 436 IRON—PROPERTIES Elba, Brazil, Canada and Central India are the chief localities where this ore is found. The excellent quality of the iron smelted from this ore is due partly to the purity of the ore, and partly to the circumstance that charcoal, and not coal, is employed in smelting it. Magnetic iron ore (Fe304), of which the loadstone is a variety, has a more granular structure and a dark iron-grey colour (sp. gr. 5:1). It forms mountainous masses in Sweden and at Lake Superior, and is also found in Russia. It yields an excellent iron. Iron sand, a peculiar heavy black sand of metallic lustre, consists in great measure of the magnetic ore, but contains a very large proportion of titanium. It is found abun- dantly in India, Nova Scotia, and New Zealand ; but its fine state of division prevents it from being largely available as a source of iron. Spathic iron ore (FeCO,) is found in abundance in Saxony, and often contains a considerable quantity of manganese carbonate, which influences the character of the metal extracted from it. The oolitic tron ore, occurring in the Northampton oolite, contains both hydrated sesquioxide and carbonate of iron, together with clay. Tron pyrites (FeS,) is remarkable for its yellow colour, its brilliant metallic lustre, and crystalline structure, being generally found either in distinct cubical or dodeca- hedral crystals, or in rounded nodules of radiated structure. It was formerly disregarded as a source of iron, on account of the difficulty of separating the sulphur ; but an inferior quality of the metal has been extracted from the residue left after burning the pyrites in the manufacture of oil of vitriol (p. 163), the residue being first well roasted in a lime-kiln to remove as much as possible of the remaining sulphur. Tron owes the high position which it occupies among useful metals to a combination of valuable qualities not met with in any other metal. Although possessing at least twice as great tenacity or strength (100 tons per sq. in. for hard steel wire) as the strongest of the other metals commonly used in the metallic state, itis yet one of the lightest, its sp. gr. being only 7-7, and is therefore particularly well adapted for the construction of bridges and large edifices, as well as for ships and carriages. It is the least yielding or,malleable of the metals in common use, and can therefore be relied upon for affording a rigid support; and yet its ductility is such that it admits of being rolled into the thinnest sheets and drawn into the finest wire. Being one of the least fusible of useful metals, it is applicable to the construction of fire-grates and furnaces. Iron as known in industry, however, is not the pure metal, but consists of the element containing in combination or admixture small proportions of one or more other elements, of which carbon is always one ; the percentage and form of this carbon are the chief factors in determining whether the industrial metal is malleable iron, steel, or cast iron. Although heated iron oxide is easily reducible to metal, the production of pure iron by thermal reduction is practically impossible owing to the facility with which the hot metal dissolves or combines with the reducing agent. Pure iron is obtainable by electrolysis of a ferrous salt conducted with low current density so as to avoid liberation of hydrogen, which is readily occluded by the metal. Itissilvery white, of sp. gr. 7-86 and m.-pt. 1505°. It is soft and ductile, which properties, however, are much modified by the presence of other elements, particularly carbon, as wellas by molecular rearrangements which occur in the structure of the metal when subjected to certain changes of temperature. Such rearrangements are detected by observing the rate at which molten iron cools after it has solidified ; the rate is uniform until the temperature is 900°, when heat is evidently evolved in the mass, for there is a pause in the rate of cooling, which, however, becomes uniform again until the temperature is 780°, when there is another pause. It is believed that these pauses represent transition-points of one allotropic form of the element into another, the change being exothermic, Iron above 900° is called y-iron, IRON AND CARBON 437 that between 900° and 780° is B-iron, while below this temperature we have a-iron ; this last form is magnetic, the others are not. It may be assumed that when iron is slowly cooled there is time for the whole of it to become a-iron, whereas when it is rapidly cooled much y- and (3-iron will have escaped transformation ; this is the modern explanation why annealed (p. 450) iron is softer and more ductile than iron which has been more rapidly cooled. This behaviour of iron on cooling becomes much more marked when the metal contains carbon. The relationship between iron and carbon has been minutely studied, as it is upon this that the marked difference in the properties of the industrial forms of iron depends. Molten iron can take up 6°5 per cent. of carbon ; when the iron cools, some of this carbon separates in the mass as graphite, some remains as tron carbide, Fe,C (cementite), and some as a solid solution of iron carbide in iron (martensite). The proportion of the carbon which assumes any one of these forms depends both on the mode of cooling and on the presence of other elements. For instance, the presence of silicon (which molten iron can dissolve in all proportions) causes a more copious separation of graphite, while that of manganese (also soluble a in all proportions) diminishes the separation. When iron contain- ing these three forms of carbon is dissolved in dilute H,SO,, the graphite and iron carbide remain undissolved, while the carbon which is in solid solution is evolved as hydro-carbons, the latter imparting the disagreeable smell to the hydrogen liberated from the acid. In the diagram Fig. 247, the zero line represents pure iron, having a solidifying-point of 1505° (a) and ~ the transition-points 900° (b) and TEMES GUN 780° (c). When the iron contains. Fi. 247. carbon, as the proportion of carbon increases the metal begins to solidify at lower temperatures lying on the line a-e, the solidifying portion being poorer in carbon than the mother-liquor ; the solid portion consists of the homogeneous mixture of y-iron and cementite (Fe,C), called martensite, and the percentages of carbon and corresponding solidifying-points lie on the line a-d. This continues until the metal contains 4-2 per cent. of C, when it solidifies as a whole at 1130°, the eutectic-point, e(p. 486). The line a-d-f represents the temperatures below which the iron is solid, whatever its content of carbon ; the lowest melting-point is 1130°. If the iron contains more carbon than 4-2 per cent. there is separation of cementite, as the metal cools until the temperature is 1130° (line g-e). When the metal containing more than 2 per cent. C is kept for some time at 1130° graphite separates until the dissolved C has fallen to 2 per cent. (line e-d). When the solid metal containing 2 per cent. C is cooled, cementite separates, leaving the martensite poorer in carbon (line d-h) until the temperature is 700° and the carbon 0-95 per cent. (point h). This is a second eutectic-point, and there is no further change, the metal consisting of a eutectic mixture of cementite and a-iron, called perlite. If iron containing less than 0-95 C is cooled /3-iron separates at 900° and a-iron at 780°, until the eutectic-point, h, is again reached (line b-h). These changes are rendered evident by the methods of metallography (p. 486) ; the polished surface of the sample of metal is etched with a solution of iodine in potassium iodide or of hydrochloric acid in alcohol and viewed by reflected light through the microscope. The eutectics appear uniform in colour, the separated carbon alloys presenting dark or light patches on the uniform ground. Temperature C ete & G00 500005 10 15 2025 30 438 THE BLAST FURNACE Metallurgy of Iron.—The ore is frequently roasted or calcined as the first step towards the extraction of the metal, in order to expel H,O and CO,. The ore is sometimes built, together with a certain amount of small coal, into long pyramidal heaps ; black-band often contains so much bitu- minous matter that any other fuel is unnecessary. These heaps are kindled in several places, and allowed to burn slowly until all the fuel is consumed, whereby the ore is made more porous, and more accessible to the reducing gases of the smelting furnace. If the ore contained much sulphur, a part of it would be expelled by the roasting (p. 163). The FeCO, is converted into Fe,O3, which, being a feebler base than FeO, is less likely to combine with silica and form a fusible slag. More commonly the calcination is effected in kilns resembling lime- kilns, and it is often altogether omitted as a separate process, the expulsion of the water and carbonic acid gas being then effected in the smelting furnace itself as the ore descends. The calcined ore is smelted in a huge blast-furnace, A (Fig. 248), from 60 to 100 ft. high, encased in iron, and lined internally with fire-brick. oe 7 abo oeoo o he oo ‘ VA ee SS See op eee OS i i 7 | a Vv. EDF Winn £3) ABC$HISS Fic, 248. Since it would be impossible to obtain a sufficiently high temperature with the natural draught of this furnace, air is forced into it at the bottom, under a pressure of 3 to 7 1b. upon the square inch, through tuyére or twyer pipes, H, the nozzles, G, of which pass through apertures in the sides of the furnace. As the nitrogen of the air thus forced through the furnace carries away much heat with it, a hot-blast is found to economise fuel. To heat the blast the air is passed over fire-bricks which have been raised to a high temperature by the combustion of some of the gases which escape from the furnace (see below). In this way the temperature of the blast is frequently raised to ae and that of the furnace when the combustion is most vigorous to METALLURGY OF IRON 439 It would be very easy to reduce to the metallic state the oxide of iron contained in the calcined ore by simply throwing it into this furnace, together with a proper quantity of coal, coke, or charcoal ; but the metallic iron fuses with so great difficulty that it is impossible to separate it from the clay or gangue, as it is called unless this latter is brought into a liquid state ; and even then the fusion of the iron, which is necessary for complete separation, is only effected after it has formed a more easily fusible com- pound with a small proportion of carbon derived from the fuel. Now, clay is even more difficult to fuse than iron, so that it is necessary to add, in the smelting of the ore, some substance capable of forming with the clay a combination which is fusible at the temperature of the furnace. If clay (aluminium silicate) be mixed with limestone (CaCO,), and exposed to a high temperature, CO, is expelled from the limestone, and the lime unites with the clay, forming a double silicate of alumina and lime, which melts completely, and, when cool, solidifies to a glass or slag. The limestone acts as a flux, inducing the clay to flow in the liquid state. In order, there- fore, that the clay may be readily separated from the metallic iron, the charge or burden of the furnace must comprise a certain proportion of lime-stone. When it has been started, the blast-furnace is kept in constant work for years until in want of repair. A wood fire having been kindled in it, the stack or body of the furnace is filled with coke, and as soon as this has burnt down to some distance below the top opening or throat, a layer of the mixture of calcined ore with the requisite proportion of limestone is thrown upon it; over this there is placed another layer of coke, then a second layer of the mixture of ore and flux, and so on, in alternate layers, until the furnace has been filled ; when the layers sink, fresh quantities of fuel, ore, and flux are added, so that the furnace is kept constantly full. As the air enters from the tuyére pipes into the bottom of the furnace the carbon of the fuel is burnt to CO,; the latter, passing over the red-hot fuel in the widest part or boshes B of the furnace, becomes CO (see p. 245). It is this carbonic oxide, amounting to some 33 per cent. of the gases, which reduces the calcined ore to the metallic state when it comes in contact with it at that part of the throat of the furnace where the ore has already attained a red heat. In effecting this reduction the CO is of course oxidised to CO,. The metallic iron, being infusible at the temperatures at which it is reduced, remains disseminated through the gangue of the ore, and as it descends into a hotter region of the furnace some of it reduces CO, liberating carbon with which the rest of the iron combines to form cast iron. At this stage the clay or gangue of the ore is attacked by the lime which has been produced from the calcination of the limestone flux at a somewhat higher point in the furnace, and a fusible slag of silicate of lime and alumina is formed. This melts and liberates the disseminated cast iron at the hottest portion, C, of the furnace, just above the tuyéres. The cast iron now melts and runs together, collecting in the crucible or cavity, D, for its reception at the bottom of the furnace. The slag, which has five or six times the bulk of the iron, is allowed to accumulate in the crucible, and to run over its edge down the incline upon which the blast-furnace is built; but when a sufficient quantity of cast iron has collected at the bottom of the crucible, it is run out through a hole provided for the purpose, either into channels made in a bed of sand, or into iron moulds, where it is cast into rough semi-cylindrical masses called pigs, whence cast iron is also spoken of as pig-tron. A Cleveland furnace consumes, in the course of twenty-four hours, about 70 tons of coke, 200 tons of ore, 40 tons of limestone, and 300 tons of air. The cast iron, about 70 tons, is run off from the crucible once or twice in twelve hours. The average yield from calcined clay ironstone is 35 per cent. of iron. 440 BLAST-FURNACE SLAG In view of the enormous quantity of air passed through the furnace it pays to dry the air fed to the blowing engines by causing it to travel through refrigerators which cool it to — 5°; this reduces the volume of air to be pumped for a given weight of oxygen and avoids the cooling action which the moisture has on the contents of the furnace. The gases escaping from the blast-furnace are highly inflammable, for they contain as much as 25 per cent. of CO ;1 the throat is closed, when the furnace has been charged, by a bell, #, and the gases, which are at a temperature of about 250°, are made to pass through a flue into the stoves, L, where they are burnt in flues, M, in order to heat the brickwork, N, which is subsequently to raise the temperature of the blast. When one stove has been heated the combustible gases are turned into another stove and an air blast is passed through the first one from pipe, R, in a direction contrary to that in which the combustible gases previously travelled. The pipe, P, conducts the blast to the tuyéres, and the products of combustion leave the stove by flue, O. About 40 per cent. of the blast-furnace gases are thus used, the rest being burnt in gas-engines to supply power for the blowing engines, &c, When coal is used as fuel it is sometimes profitable to pass the gases through cooling apparatus before they are burnt, in order to condense the tar and ammonia which they centain. Although the bulk of the nitrogen present in the air escapes unchanged from the furnace, it is not improbable that a portion of it contributes to the formation of the cyanide of potassium (KCN) which is produced in the lower part of the furnace, the potassium being furnished by the ashes of the fuel. Cyanogen is generally found in the escaping gases. The blast-furnace slag is essentially a glass composed of a double silicate of aluminium and calcium, the composition of which varies much with the nature of the earthy matters in the ore and the composition of the flux. Its colour is generally grey, streaked with blue, green, or brown. The nature of the flux employed must, of course, be modified according to the composition of the gangue present in the ore. Where this consists of clay (silicate of alumina )—that is, is acid in character—the addition of lime (which is sometimes added in the form of limestone and sometimes as quicklime) will provide for the formation of the double silicate of alumina and lime. But if the iron ore happened already to contain limestone, a basic gangue, an addition of clay would be necessary, or if quartz were present, consisting of silica only, both lime and alumina (in the form of clay) will be necessary as a flux. It is sometimes found economical to employ a mixture of ores containing different kinds of gangue, so that one may serve as a flux to the other. If a proper proportion of lime were not added, a portion of the oxide of iron would serve as the base to combine with the silica and be carried off in the slag ; but if too large a quantity of lime be employed, it will diminish the fusibility of the slag, and prevent the complete separation of the iron from the earthy matter. The most easily fusible slag which can be formed by the action of lime upon clay has the composition 6CaO.Al,0;.9S8i0,; but in English furnaces, where coal and coke are employed, it is found necessary to use a larger proportion of lime to convert the sulphur of the fuel into calcium sulphide, so that the slag commonly has a composition more nearly represented by the formula 12CaO.2Al,0;.9SiOo. Iron, manganese, and “magnesium are commonly found occupying the place of a portion of the calcium, and an ordinary composition of blast-furnace slag per 100 parts is: Silica ; ; : ‘ . 43:07 Oxide of manganese (MnO) . 1:37 Alumina . ‘ : : . 14:85 Potash (K,0) . : ; . 184 Lime : : 5 F . 28-92 Sulphide of calcium . 5‘ . 1-90 Magnesia . ‘ ‘ ‘ . 5:87 Phosphoric oxide (P,0;) . . trace Oxide of iron (FeO). : 2:35 From 10 to 30 cwt. of slag are produced per ton of cast iron smelted. The gases from a coke-fed furnace contain in 100 vols.: N, 60; CO., 12; CO, 24; H,2; CH4, 2 vols. CAST IRON 441 These slags are sometimes run from the blast-furnace into iron moulds, in which they are cast into blocks for rough building purposes. The presence of a considerable proportion of potash has led to experiments upon their employment as a manure, for which purpose they have been blown out, when liquid, into a finely divided frothy condition fit for grinding and applying to the soil. They are also used for making cement. By blowing air through the slag, it is converted into a substance resemblirg spun glass, and used, under the name of slag wool or mineral cotton, for packing round steam-pipes, &c. The product of the blast-furnace, cast iron, is, essentially, composed of iron with from 2 to 5 per cent. of carbon, but always contains other sub- stances, derived either from the ore or from the fuel employed in smelting it. Considering the energetic deoxidising action in the blast-furnace, it is not surprising that portions of the various oxygen compounds exposed to it should part with their oxygen, and that the elements thus liberated should find their way into the cast iron. Thus silica is reduced, and the silicon found in cast iron sometimes amounts to 3 or 4 per cent. Hematite pig is usually rich in silicon, from the presence of silica in an easily reducible condition in the ore. Sulphur and phosphorus are also generally present in cast iron, but in very much smaller proportion ; their presence diminishes its tenacity, and the smelter endeavours to exclude them as far as possible, though a small quantity of phosphorus appears to be rather advantageous for some castings, since it augments the fusibility and fluidity of the cast iron. The sulphur is chiefly derived from the coal or coke employed in smelting, and for this reason charcoal would be preferable to any other fuel if it could be obtained at a sufficiently cheap rate. The ironworks of some parts of Kurope enjoy a great advantage in this respect over those of England. The phosphorus is derived chiefly from the phosphates existing in the ore or in the flux.1_ The proportion of phosphorus taken up by the cast iron increases with the temperature of the blast-furnace. Manganese, amounting to 1 or 2 per cent., is often met with in cast iron; its presence generally enables the iron to hold more carbon and less sulphur. Other metals, such as chromium, cobalt, &c., are also occasionally present, though in such small quantities as to be of no importance in practice. The properties of cast iron vary with the nature of the ore smelted and the conditions in the furnace. A siliceous ore smelted with a large propor- tion of coke at a high temperature produces a grey iron, mainly because much silicon is reduced, and the presence of this determines the separation in the form of graphite of much of the carbon which has been dissolved by the iron (p. 437); this graphite imparts a grey appearance to the metal. When the proportion of coke in the furnace is small, the temperature com- paratively low, and the ore not particularly siliceous, the product is white iron, the carbon having remained as cementite (p. 437) in the metal on cooling. An intermediate variety is mottled iron, which has the appearance of a mixture of the grey and white varieties. These distinctions are best seen in the surface of the fracture when the metal is broken. Grey iron is comparatively soft so that it may be turned ina lathe, whilst the white iron is extremely hard, and of higher specific gravity, 7-5, that of grey iron being 7-1. Again, although white iron fuses at a lower tempera- ture (1130°) than grey iron (1200°), the latter is far more liquid when fused, and is therefore much better fitted for casting. Mottled iron surpasses the other forms in tenacity and is used where this quality is particularly desirable. Although the presence of uncombined carbon is the chief point which distinguishes grey from white iron, other differences are commonly observed in the composition of the two varieties. While containing less silicon than grey iron, white iron has a larger + It appears to exist in the iron, at least in some cases, as Fe,P. 442 PIG IRON proportion of sulphur. The average composition of the three varieties is shown in the following Table : Grey. ‘Mottled. White. Iron ‘ ‘ ; és 90-42 92-75 94-04 Combined carbon . Ps 2 0-20 0:75 3-20 Graphitic carbon. 5: : 3:30 2-90 — Silicon 4 : , : 3-50 1-00 0-64 Sulphur ; : ; ‘ 0-02 0-15 0-20 Phosphorus. 2 ‘ ‘ 0:98 1-60 1-32 Manganese. ‘ : : 1-58 0-47 0-60 As might be expected, it is not easy to tell where a cast iron ceases to be grey and begins to be mottled, or where the mottled iron ends and white iron begins. There are, in fact, eight grades of cast iron in commerce, distinguished by the numbers ] to 8, of which No. 1 is dark grey and contains the largest proportion of graphite, which diminishes in the succeeding numbers up to No. 8, which is the whitest iron, the inter- mediate numbers being more or less mottled. The extra consumption of fuel, of course, renders the grey iron more expensive. When a furnace is worked with a low charge of fuel to produce a white iron, a larger quantity of iron is lost in the slag, sometimes amounting to 5 per cent. of the metal, whilst the average loss in producing grey iron does not exceed 2 per cent. Ores con- taining a large proportion of manganese are generally found to yield a white iron. White iron is usually used for conversion into malleable iron, whilst grey iron is used as foundry-iron (for making castings) and for conversion into steel. When grey iron is melted its graphite is dissolved, and if it be poured into a cold iron mould (chiil-casting) so as to solidify it as rapidly as possible, the external portion of the casting will present much of the hardness and appearance of white iron, the sudden cooling having prevented the separation of the graphite (cf. p. 437). It is a common practice to produce compound castings, that portion of the mould where chilling and consequent hardness is required being made of thick cast iron, and the other part, which is to give a tougher and a softer casting, of sand. When white pig-iron, melted ata high temperature, is slowly cooled, it becomes grey (cf. p. 437). When grey iron is remelted in the foundry for casting it becomes harder, both because some of the silicon is eliminated by oxidation, causing a corresponding amount of the graphite to pass into combination, and because sulphur is absorbed from the fuel with which the iron is melted. By the use of ores containing an unusually large proportion of any of the foreign constituents which enter into the reduced iron, the blast-furnace may be made to produce special irons, which have particular applications. Thus, ferro-silicon (iron rich in silicon), used for converting white iron into grey iron, ferro-manganese (iron containing 68 to 80 per cent. of Mn ; spiegel-eisen contains about 10 per cent. of Mn), and ferro-chromium (containing 60 to 70 per cent. of Cr) are made ; the last two are used in steel-making. Pig-iron has a very limited application as a building material on account of its low tensile strength (7 tons per sq. in.) and its lack of malleability. For constructional use it must be converted into malleable iron, which possesses a high tensile strength (such as 30 tons per sq. in.) and is capable of being forged. The process consists in removing the Si, P and § of the pig-iron and reducing the content of C to below 2 per cent. It is rendered possible by the fact that the impurities are more readily oxidised than is the iron, and this oxidation may be effected either by mixing the hot iron with iron oxide, or by blowing air through the molten metal. The C is thus evolved PUDDLING 443 in the form of CO, whilst the Si and P are oxidised to SiO, and P,O,, both of which oxides are capable of uniting with a base (FeO or CaO) and of being removed as slag. Production of Malleable Iron.—Before the development and main- tenance of very high temperatures was understood, it was customary to heat the iron until it became pasty and to mix it with iron oxide whilst in this condition (a process known as puddling); the impurities, oxidised at the expense of the ferric oxide, were then squeezed out of the iron by working the pasty mass under the hammer. The product was known as wrought tron, and, since it was not necessary to finish the iron in a fused condition, it was possible to reduce the carbon to a very low percentage, for it will be remembered that it is the presence of this element which lowers the fusing- point of iron (p. 439). At the present day it is possible to keep iron containing very little carbon in a state of fusion, so that the iron oxide can be mixed with it in this condition and the decarburised iron can be cast into ingots prior to being rolled into plates or bars (Siemens-Martin process). Instead of iron oxide, air is frequently used as the oxidant, in which case it is blown through the molten iron, the heat generated by the oxidation of the im- purities serving to keep the metal in fusion (Bessemer process). By this method also the metal is obtained in the form of cast ingots. The original distinction between cast iron, wrought iron, and steel lay in their content of carbon. Cast iron contains 3 to 5 per cent. of C, wrought iron under 0-1 per cent., and steel 0-5 to 2:0 percent. The term ingot iron is now employed to signify all iron made by methods involving fusion, and includes all grades of refined iron except the very softest and the very hardest (hard steel); the expression mild steel is nearly synonymous with ingot iron. Puddling.—With pig-iron containing much graphite and silicon, namely, grey iron, the puddling process is preceded by a refining process, consisting essentially in melting the iron under conditions which remove most of the silicon and thus cause the carbon to remain dissolved in the solidified metal— indeed, to transform the grey iron into white iron. The refinery is a rectangular trough (33 by 24 ft.) with double walls of cast iron, between which cold water is kept circulating to prevent their fusion, and usually lincd with fireclay ; on each side of it are arranged tuyéres for blowing air on to the contents of the trough. Coke having been kindled in this furnace, the pigs of iron are introduced and the blast turned on ; the metal melts and trickles down through the fuel to the bottom of the refinery, a portion of the iron being oxidised by the blast. When the whole of the metal has been fused, the air is still allowed to play upon its surface, and after about two hours the metal is run out into a cast-iron mould kept cold by water in order to chill the metal and obtain a brittle plate of refined iron. The composition of the slag (or finery cinder) may be generally expressed by the formula 2FeO .SiO,, the silica having been derived from the silicon of the cast iron. A typical sample of refined iron will contain, per cent., Fe, 95-14 ; C, 3:07; Si, 0-63; S, 0-16; P, 0-73; Mn, trace ; slag, 0-44. The carbon, therefore, is not nearly so much diminished as the silicon. The practical advantage of refining the iron resides in the fact that the white iron passes through a pasty stage before it melts, so that it is better fitted than grey iron for puddling. The puddling process is carried out in a reverberatory furnace (Figs. 249, 250) connected with a tall chimney provided with a damper, so as to admit of a very perfect regulation of the draught. The hearth is composed of fire-brick or of cast-iron plates, covered with a layer of very infusible slag, and since the metal is to attain a very high temperature in this furnace (estimated at 1300°), the latter is usually encased in iron so as to prevent 444 THE PUDDLING-FURNACE any entrance of cold air through chinks in the brickwork. The fine metal is broken up and heaped upon the hearth of this furnace, together with about one-fifth of its weight of iron scales (black oxide of iron, Fe,O,) and of hammer-slag (basic silicate of iron, obtained in subsequent operations), which are added in order to assist in oxidising the impurities. When the metal has fused, the mass is well stirred or puddled, so that the oxide of . iron may be brought into contact with every part of ‘the metal, to oxidise the impurities. The metal now appears to boil, in conse- quence of the escape of CO, and in about an hour from starting the puddling, so much of the carbon has been removed that the fusibility of the metal is considerably diminished, and it assumes a granular sandy or dry state, spongy masses of pure Fre/249. iron separating or coming to Puddling-furnace (elevation), nature in the fused mass. The puddling is continued until the whole has assumed this granular appearance, and the damper is now gradually raised so as to increase the temperature and soften the particles of iron, in order that they may be collected into a mass; the more easily to effect this a part of the slag is run off through the floss-hole. The workman then collects some of the iron upon the end of the paddle, and rolls it about on the hearth until he has collected a rough ball of iron weighing about half a hundredweight. When all the iron has-been collected in this way the doors are closed to raise the interior of the furnace to a very high temperature, and after.a short time, when the balls are sufficiently heated, they are removed from the furnace and placed under a steam- hammer, which squeezes out the liquid slag and forces the particles of iron to cohere into a con- tinuous oblong mass or bloom, which is then passed between rollers, by which it is extended into bars. These bars, muddled, of No, 1 ee oe bar), are always hard Fig. 250. ‘ Puddling-furnas tion). and brittle, and are ain Rima (peerore not fitforuse. In order to improve the tenacity of the iron the rough bars are cut up into short lengths, which are made into bundles, and, after being raised to a high temperature in the reheating furnace, are passed through rollers, which weld the several bars into one compound bar, to be subse- quently passed through other rollers until it has acquired the desired dimen- sions. By thus fagoting or piling the bars their texture is rendered far more uniform, and they are made to assume a fibrous structure—which BAR-IRON 445 greatly increases their strength (merchant bar, or No. 2 bar). To obtain the best, or No. 3 bar, or wire-iron, these bars are doubled upon themselves, raised to a welding heat, and again passed between rollers. These repeated rollings have the effect of thoroughly squeezing out the slag which is mechani- cally entangled among the particles of iron in the rough bar, and would produce flaws if allowed to remain in the metal. A slight improvement appears also to be effected in the chemical composition of the iron during the rolling, some of the C, Si, P and § still retained by the puddled iron becoming oxidised, and passing away as gas and slag. The impurities in the finished iron are due chiefly to the slag which the rolling operation fails to expel ; they are as follows (per cent.) : Cc Si Mn P 8 Puddled bar. ‘ : 0-10 0-13 0-08 0-35 0-05 Finished wrought iron ‘ 0-06 0-04 0-08 0-20 0-05 The yield of iron by the puddling process is about 90 to 94 per cent. of the iron charged. When grey pig-iron is puddled without undergoing the refining process, it becomes much more liquid than white pig or refined iron, and the process is sometimes described as the pig-boiling process, whilst refined iron undergoes dry puddling. In the latter the oxygen of the air has more share in the decarburising of the iron than it has in the former. Formerly it was sometimes the custom to make a puddiled steel, by arresting the puddling process at an earlier stage than usual, so as to leave a proportion of carbon varying from 0-3 to 1 per cent. Even the best bar-iron contains from 0-1 to 0-2 per cent. of C, together with minute proportions of Si, S and P. Perfectly pure iron is inferior in hardness and tenacity to that which contains a small proportion of carbon, Bar-iron is liable to two important defects, which are technically known as cold- shortness and red-shortness. Cold-short iron is brittle at ordinary temperatures, and appears to owe this to the presence of phosphorus, of which element 0-5 per cent. is sufficient materially to diminish the tenacity of the iron. When the iron is liable to brittleness at a red heat it is termed red-short iron, and a very little sulphur is sufficient to affect the quality of the iron in this respect. The best bar-iron, if broken slowly, always exhibits a fibrous structure, the particles of iron being arranged in parallel lines, probably due to the rolling operation. This appears to contribute greatly to the strength of the iron, for when it is wanting, and the bar is composed of a fused mass of crystals, it is weaker in proportion to the size of the crystals. The presence of phosphorus is said to favour the formation of large crystals and hence to produce cold-shortness. Considering the difficult fusibility of bar-iron, it is fortunate that it possesses the property of being welded—that is, of being united by hammering when softened by heat. It is customary first to sprinkle the heated bars with sand or clay in order to convert the superficial oxide of iron into a liquid silicate, which will be forced out from between them by hammering or rolling, leaving the clean metallic surfaces to adhere. In the open-hearth or Siemens-Martin process for producing malleable iron (ingot iron or mild steel) the metal is finished in a fused state. This became possible as a result of Siemens’ invention of regenerative firing (p. 279), the metal being melted in what is really a reverberatory furnace fired on this principle. Fig. 251 is a diagrammatic vertical section showing the principle of the construction ; ais the hearth, which is saucer-shaped and made of iron plates kept cool by circulation of air beneath them and lined with ganister, a fairly pure sand ; a tamping-hole, tem- porarily stopped with clay, is provided at the lower part of the hearth for drawing off the molten metal ; b, c, d, eare regenerators (p. 408), and b’, c’, d’, e’ are the flues leading thereto respectively ; b’ and e’ are branches of a flue connected with the producer (p. 274), and c’, d’ are branches of a flue open to the outer air ; each of the flues is 446 THE OPEN-HEARTH PROCESS also connected with the chimney-stack. During the first period the draught of the chimney draws producer-gas up b and air up ¢, the mixture burning above hearth a, and the products of combustion escaping through d, d’, and e, e’, on their way to the chimney, heating to a high temperature the chequer brickwork. At the end of the period a valve is turned to cut a f off flue b’ from the producer and open it to the chimney, while at the same time cutting off flue e’ from the chimney and opening it to the producer; a second valve is turned simultaneously to cut off flues c’ and d’ from the air and chimney respectively and connect them with the chimney and air respectively. The gas now passes up e and the é air up d, both becoming heated by the brickwork before they burn in the furnace; the pro- ducts pass down 6 and c, which now become hot. The valves are o 7 Z / / then again turned over, and so Db Cc C aa e€ on. The working doors of the Fa. 251. furnace are marked f. When the pigs have been thoroughly melted, scraps of iron plate, which, since they are of no other value, may be used to dilute the impure iron, are stirred in, and these are followed by an appropriate quantity of iron oxide, generally hematite. The oxidation of the impurities in the iron is effected in part by the oxygen of the hematite and in part by the excess of oxygen in the flame used to heat the hearth, the temperature of which is about 1500°. When the aspect of a test piece withdrawn and hammered by the furnaceman indicates that the process is complete (in 8 to 10 hours), the tamping-hole of the hearth is unstopped, the metal run into a ladle, and thence into ingot-moulds. In this process the Si and P are removed, chiefly in the form of iron silicate and phosphate, as slag, which floats on the surface of the metal, and in order that the removal of the phosphorus may be complete the oxidation must be carried sufficiently far to oxidise nearly the whole of the carbon in the iron, producing a very soft metal. Since for most purposes this product would be too soft, it is customary to bring up the carbon content of the metal in the ladle by the addition of a small quantity of ferro-manganese (p. 442) rich in carbon, which immediately melts and mixes with the charge. The yield by this process is about 95 per cent. of the iron charged into the furnace. Various additions to the finished steel are made for the purpose of producing sound ingots, particularly Si in the form of ferro-silicon (p. 442), Al in the form of ferro- aluminium and Ti in the form of ferro-tiianium. They appear to act by reducing iron oxide and preventing formation of CO, and consequently blow-holes, during cooling. There are several modifications of the process, for which text-books on metallurgy must be consulted. Here it may be mentioned that when pig-iron rich in phosphorus (phosphoric pig) is treated, the hearth is lined with basic material and lime is added to combine with the P,0, produced by oxidation of the P (basic open-hearth process). In the Bessemer process for producing malleable iron, the molten pig- iron is run into a large vessel called a converter (a, Fig. 252), made of iron plates lined with ganister and suspended on trunnions. Through the bottom of the vessel are a number of passages, 6, about } in. in diameter, through which air is blown at a pressure of 20 or 25 lb. per sq. in., being supplied to the air chest, ¢, by a pipe led through one of the trunnions. The converter THE BESSEMER PROCESS 447 is first heated by a. little burning coke, and is then turned into the position shown in dotted lines, the blast having been started. The molten charge (15 to 25 tons) is then run froma cupola furnace, d (or direct from a blast- furnace, or from a vessel called a mixer, when the products of blast-furnaces worked under different conditions are to be mixed), down a gutter, e, irito the converter. The latter is now turned back into its erect ad os) position and the oper- N ‘ ation begins. The i @ fan ¥ f silicon and man- 7 \ P| 3 ;\ ganese burn first in ducing « very'hien UMMM temperature, then the carbon is converted pam oa into CO, which burns with a long flame at Tih iY], the mouth of the con- i verter, and a little of Fig. 252. the iron is burnt to oxide, which forms a slag with the silica and is carried up as a froth to the surface of the liquid iron. The blast of air, or blow, is continued for about twenty minutes, when the disappearance of the flame of CO indi- cates the completion of the process; the purified iron is in a perfectly liquid condition owing to the high temperature (1580°) produced by the combustion of the Si and Mn, so that the metal may be run out into the ladle, f, by tilting the converter into a position in which the mouth is somewhat lower than is shown in dotted lines. From the ladle the metal is run into ingot-moulds, g. As in the case of the Siemens-Martin process, the desired hardness is imparted to the metal by the addition of ferro-manganese to the converter just before the iron is poured, or to the ladle. The yield is about 85 per cent. In the original Bessemer process (now known as the acid process) the converter was lined, as described above, with ganister (sand) ; this rendered the method applicable only to such grades of pig-iron as were fairly free from phosphorus, because the most efficient means of removing this element, namely, the admixture of the strong base lime with the charge, was impossible, on account of the ease with which lime combines with silica, destroying the lining of the furnace. It is now customary to line con- verters which are to be used for phosphoric pig with a basic material, namely, a mixture of magnesia and lime, made by calcining dolomite. This basic Bessemer process (known in Germany as the Thomas process) is conducted as described above, save that lime to the extent of 15 to 20 per cent. of the charge of iron is thrown into the converter before the iron is runin. This lime combines with the P,O; produced by the oxidation of the phosphorus, as well as with the silica produced by the oxidation of the silicon. The basic slag formed in this way is useful as a manure, for the sake of its phosphorus. The following percentage compositions illustrate the effect of the two processes : 1 It contains 15 to 20 per cent. of P.O, chiefly as the compound 4CaO.P,0,, which is more soluble | in saline solutions than is the ordinary phosphate 3CaO.P,0;. The content of P,0, may be raised by adding the lime to the converter in two portions and tilting the converter to pour off the first, siliceous slag before the second portion of lime is added. == RAT NS b Yf 448 TOOL STEEL Cc Si Mn 8 P Acid Bessemer pig. . 857 2:26 0:04 0-10 0-07 After blow . , . 0-19 trace trace 010 0-07 After ferromanganese . 0-37 trace 0-54 0:09 0:05 Basic Bessemer pig . 857 1:70 O71 0:06 1:57 After blow . ‘ . trace — trace 0:05 0-08 After ferromanganese . 012 0:03 0:27 0-04 0-02 In the acid process Si is the chief fuel for developing the heat necessary to keep the charge fused, and it is difficult to bessemerise pig containing only 1 per cent. Si. Hence grey iron is the best grade for the acid-lined converter. On the other hand, P is the fuel in the basic process and should amount to 1-5 per cent. ; since the lining is basic the charge should not be rich in Si, and a white iron produced from phosphoric ore is used. Owing to the fact that bar-iron is not fused whilst ingot iron is com- pletely fused in the process of its manufacture, the main difference between these two forms is that ingot iron does not show the fibrous structure of bar-iron, and is, moreover, free from particles of intermixed slag. Ingot iron is liable to the same defects as bar-iron, and these are due to the same causes. Manufacture of Tool-Steel (Hard Steel).—Steel differs from bar-iron in pos- sessing the property of becoming much harder when heated to redness, and then suddenly cooled by being plunged into water. Perfectly pure iron obtained by the electrotype process is not hardened by sudden cooling ; but all bar- iron which contains carbon exhibits this property in a greater or smaller degree according to the proportion of carbon present. Iron does not become decidedly steely, however, until the carbon amounts to 0-25 per cent. The term steel was formerly applied only to iron containing enough carbon (not less than 0-75 per cent.) to harden it sufficiently for cutting implements, but all iron containing more than 0-2 per cent. of carbon is now referred to as (mild) steel. The hardest steel contains about 1-2 per cent. of carbon, and when the proportion reaches 1-5 per cent. the metal begins to assume the properties of white cast iron. Bar-iron may, therefore, be converted into hard steel by the addition of about 1 per cent. of carbon, and, conversely, cast iron is converted into-mild steel when the quantity of carbon contained in it is reduced to from 0-2 to 0-5 per cent.? Since the presence of even the small quantities of impurities, other than carbon, which cannot be eliminated by the above processes for making ingot iron are fatal to the best hard steel, this material must be made from the best bar-iron. The process is-known as cementation, the bars of iron being imbedded in charcoal and exposed for several days to a high temperature. During this period carbon is taken up by the iron from the charcoal in a manner the chemistry of which is obscure. The operation is effected in large chests of fire-brick or stone, about 10 or 12 ft. long by 3 ft. wide and 3 ft. deep. T'wo of these chests are built into a dome-shaped furnace so that the flame may circulate round them, and the furnace is surrounded with a conical jacket of brickwork in order to allow a steady temperature to be maintained in it for some days. The charcoal is ground so as to pass through a sieve of }-in. mesh, and spread in an even layer upon the bottom of the chests. Upon this the bars of iron, which must be of the best quality, are laid in regular order, small intervals being left between them, which are afterwards filled in with the charcoal powder, with a layer of which the bars are now covered ; over this more bars are laid, then another layer of charcoal, and so on until the chest is filled. Each chest holds five or six tons of bars. 1 Many metallurgists are of opinion that manganese has an influence similar to that of carbon in converting iron into steel, CAST STEEL 449 One of the bars is allowed to project through an opening in the end of the chest, so that the workmen may withdraw it from time to time and judge of the progress of the opera- tion. The whole is covered in with a layer of about 6 in. of damp clay or sand, or grinder’s waste (silica and oxide of iron). The fire is carefully and gradually lighted, lest the chests should be split by too sudden application of heat, and the temperature is eventually raised to about 1000°, at which it is maintained for a period varying with the quality of steel which it is desired to obtain. Six or eight days suffice to produce steel of moderate hardness ; but the process is continued for three or four days longer if very hard steel be required. The a is gradually extinguished, so that the chests are about ten days in cooling own. ‘ As a result of the process the bars are covered with large blisters, obviously produced by some gas raising the softened surface of the metal in its attempt to escape. The gas is probably CO produced by the action of the carbon upon particles of slag accidentally present in the bar. On breaking the bars across, the fracture is found to have a finely granular structure, instead of the fibrous appearance exhibited by bar-iron. The iron has combined with about 1 per cent. of carbon, which is found to have penetrated to the very centre of the bar. It is this transmission of the solid carbon through the solid mass of iron which is implied by the term cementation. Probably CO is formed from the small quantity of atmospheric oxygen in the chest, and one-half of the carbon is removed from this CO by the iron, which it converts into steel, leaving CO, (2CO — C = CO.) to be reconverted into CO by taking up more carbon from the charcoal (CO, + C = 2CO), which it transfers again to the iron. Experiment has shown that soft iron is capable of absorbing mechanically 4:15 vols. of CO at a low red heat, so that the action of the gas upon the metal may occur throughout the substance of the bar. The CO is retained unaltered by the iron after cooling, unless the bar is raised to the temperature required for the production of steel. The blistered steel obtained by this process is, as would be expected, far from uniform either in composition or in texture ; some portions of the bar contain more carbon than others, and the interior contains numerous cavities. In order to improve its quality it is subjected to a process of fagoting similar to that mentioned in the case of bar-iron ; the bars of blistered steel, being cut into short lengths, are made up into bundles, which are raised to a welding heat, and placed under a steam-hammer. The bars before being hammered are sprinkled with sand, which combines with the oxide of iron upon the surface, and forms a vitreous layer which protects the bar from further oxidation. The hammered steel is much denser and more uniform in composition ; its tenacity, malleability, and ductility are greatly increased, and it is fitted for the manufacture of shears, files, and other tools. It is commonly known as shear steel. Double shear steel is obtained by breaking the tilted bars in two, and welding these into a compound bar. The best variety of steel, being perfectly homogeneous in composition, is that known as cast steel or crucible steel, to obtain which about 50 lb. of blistered steel are broken into fragments, and fused in a fireclay or plumbago crucible, heated in a regenerative furnace, the surface of the metal being protected from oxidation by a little glass melted upon it. The fused steel is cast into ingots, several crucibles being emptied simultaneously into the same mould. Tool-steel may contain about 1-2 per cent. C, 0-15 per cent. Si and 0-1 per cent. Mn ; it should be free from S and P. Cast steel is far superior in density and hardness to shear steel, but since it is exceed- ingly brittle at a red heat, great care is necessary in forging it. The soundness of steel ingots is often impaired by minute bubbles or blow-holes, formed by CO or H, the former produced by the action of the carburised iron on a portion of oxidised iron, the latter by the decomposition of moisture in the air. To obviate this, the steel is sometimes subjected to a pressure of several tons on the square inch while it is solidifying (Whit- worth’s steel). Some small instruments, such as keys, gun-locks, &c., which are exposed to con- siderable wear-and-tear by friction, and require the external hardness of steel without its brittleness, are forged from bar-iron, and converted externally into steel by the 29 450 TEMPERING STEEL process of case-hardening, which consists in heating them in contact with some sub- stance containing carbon (such as bone-dust, yellow prussiate of potash, &c.), and afterwards chilling in water. A process which is the reverse of this is adopted in order to increase the tenacity of stirrups, bits, and similar articles made of cast iron; by heating them for some hours in contact with oxide of iron or manganese, their carbon and silicon are removed in the forms of carbonic oxide and silica, and they become converted into malleable cast iron. A similar effect is produced by heating in sand, the air between its grains affording the required oxygen. After the tool-steel has been forged into the shape of any implement, it is hardened by being heated to redness, and suddenly chilled in cold water, or oil, or mercury. It can thus be rendered nearly as hard as diamond, at the same time increasing slightly in volume (sp. gr. of cast steel, 7:93 ; after hardening, 7:66), and considerably in tensile strength, but diminishing in ductility. If the hardened steel be heated to redness and allowed to cool slowly, it is again converted into soft steel, but by heating it to a tempera- ture short of a red heat its hardness may be proportionally reduced. This is taken advantage of in annealing the steel or “letting it down ” to the proper temper. The very hardest steel is almost as brittle as glass, and totally unfit for any ordinary use; but by heating it to a given temperature and allowing it to cool, its elasticity may be increased to the desired extent, without reducing its hardness below that required for the implement in hand. On heating a steel blade gradually over a flame, it will acquire a light yellow colour when its temperature reaches 220°, from the formation of a thin film of oxide ; as the temperature rises, the thickness of the film increases, and at 243° a decided yellow colour is seen, which assumes a brown shade at 255°, becomes purple at 277°, and blue at 288°. Ata still higher temperature the film of oxide becomes so thick as to be black and opaque. Steel which has been heated to 220°, and allowed to cool slowly, is said to be tempered to the yellow, and is hard enough to take a very fine cutting edge ; whilst, if tempered to the blue, at 288°, it is too soft to take a very keen edge, but has a very high degree of elasticity. The following Table indicates the tempering heats for various implements : 220° to 230° . Straw-yellow . Razors, lancets. 243° ‘ . Yellow . Penknives. 255° 2 . Brown-yellow . Large shears for cutting metal. 265° ‘ . Brown-purple . Clasp-knives. 277° : . Purple. Table-knives. 288° Blue ‘ Watch-springs, sword-blades. If a knife-blade be heated to redness its temper is spoilt, for it is converted into soft steel. In general the steel implements are ground after being tempered, so that they are not seen of the colours mentioned above, except in the case of watch-springs. A steel blade may be easily distinguished from iron by placing a drop of diluted nitric acid upon it, when a dark stain is produced upon the steel, from the separation of the carbon. The hardening of steel by quenching is no doubt due to the prevention by the rapid cooling of the passage of the carbon into the several forms in which it can exist in the metal as described at p. 437. Thus when the quenching is from 1000° it will be seen from the curve (p. 437) that the martensite does not become perlite when the carbon content is 1-2 per cent. This view is confirmed by the behaviour of steel when dissolved in acids. If hardened steel be dissolved in dilute HCl or H,SO,, nearly the whole of the carbon is evolved as hydrocarbons ; but when the temper has been let down, so that the steel is completely softened, the carbon is left, on dissolution of the metal in acid, as a dark powder consisting of cementite, Fe,C. Steel which has been partially tempered in the manner described 1 Chilling in oil cools the steel less suddenly, on account of the lower specific heat of oil, and therefore does not render it so hard and brittle. It is often spoken of as toughening. ELECTRIC REFINING OF IRON 451 above is found to contain the carbon both in the invisible form, which yields hydro- carbons when the metal is dissolved in acids, and in the form of carbide disseminated as grey scales throughout the mass. Manganese, nickel, chromium, and tungsten, respectively, in steel appear to make it hard however it is cooled, and are used for making specially hard steel. Manganese steel containing 12 per cent. of that metal is non-magnetic, until it has been heated for some hours at 500° to 600°, when it becomes magnetic ; if it then be heated above 800° and quickly cooled it again becomes non-magnetic. Steel containing 21 per cent. of nickel is non-magnetic at ordinary temperature, but magnetic when heated above 500° and cooled slowly. Direct Extraction of Malleable Iron from the Ore’—Where very rich and pure ores of iron, such as hematite and magnetic iron ore, are obtainable, and fuel is abundant, the metal is sometimes extracted without being converted into cast iron. It is probable that the iron of antiquity was extracted in this way, for it is doubtful whether cast iron was known to the ancients, and the slag left from old ironworks does not indicate the use of any flux. For such direct extraction the ore is heated in a crucible with charcoal, the combustion being urged by a blast of air from a tuyére pipe. The spongy mass of bar-iron thus obtained is hammered as in the puddling process. The wrought iron produced always contains a larger proportion of carbon than puddled iron, and is therefore somewhat steely in character. In India the native smelters produce iron or steel at will by this process. Attention has been attracted of late years to this direct extraction owing to the development of the electric furnace. The heat developed in such furnaces is so concentrated that the high temperatures necessary are attain- able without the aid of combustion urged by a blast. So far, however, the electric smelting of iron has not been extended to other than the purest ores, the comparative rarity of which diminishes the importance of the subject. Of greater moment is the electric refining of iron obtained from the blast-furnace or Bessemer converter; and here the question resolves itself into one of electrical conditions rather than chemistry, since the changes involved are really similar to those described under the puddling and open-hearth processes. The furnace used may be compared with a large shallow crucible, and is heated by the electric arc (p. 252) or by resist- ances (p. 251), or by the induction method in which the liquid metal to be heated is arranged as a ring around a large electro-magnet, so that it becomes the secondary conductor of a transformer and is heated by the current induced in it. Extraction of tron on the small scale.—In the laboratory iron may be extracted from hematite in the following manner: A fireclay crucible, about 3 in. high, is filled with charcoal powder, rammed down in successive layers; a smooth conical cavity is scooped in the charcoal, and a mixture of 8 grams red hematite, 2 grams chalk, and 2 grams pipeclay is introduced into it ; the mixture is covered with a layer of charcoal, and a lid placed on the crucible, which Tae is heated in a Fletcher’s injector furnace (Fig. Fic. 253. 253), which is an air-gas blast arrangement, for about half an hour. On breaking the cold crucible a button of cast iron will be obtained. Chemical Properties of Iron.—The preparation and properties of pure iron have been noticed at p. 436. In its ordinary condition iron is unaffected by perfectly dry air, but in presence of moisture and carbon dioxide it is gradually converted into hydrated ferric oxide (2Fe,0,.3H,0) SS SS 452 RUSTING OF IRON or rust.1 The actual mechanism of this common change is still obscure to chemists. The easiest explanation is that the iron is attacked by the carbonic acid forming ferrous carbonate (Fe + H,CO; = FeCO, + H,), which is then oxidised (2FeCO, + O = Fe,0; + CO,), the liberated CO, combining with more water to attack a fresh portion of iron. Since iron does not rust in water containing an alkali it has been supposed that a free acid is essential to the phenomenon of rusting. Certainly, pure iron will not rust in pure water if the air is free from COg, but electrolytes other than acids induce rusting of ordinary iron, and it appears probable that pure iron will not rust under any conditions. This gives rise to the theory that rusting is purely electrolytic, the lack of perfect uniformity in the composition or physical constitution of different parts of a piece of industrial iron causing one part to be electro-negative to another and thus to produce electrolysis of water containing an electrolyte, with consequent oxidation of the part acting as anode ; to account for the effect of alkalies in preventing rusting it is necessary, under this theory, to suppose that they render iron passive (v.i.), an explana- tion not quite satisfactory. It is to be noted that ordinary rust always evolves NH; when boiled with alkali. That a solution of iron (probably FeCO, dissolved in H,CO;) is formed during rusting is shown by the fact that when iron nails are driven into a new oaken fence a black streak is soon observed descending from each nail, caused by the formation of tannate of iron (ink) by the action of the tannic acid in the wood upon the solution of iron produced from the nails. The diffusion of tron-mould stains through the fibre of wet linen by contact with a nail is also evidence of the formation of a solution of iron. The iron in chalybeate waters (p. 47) is generally present in the form of carbonate dissolved in carbonic acid, and hence the rusty deposit which is formed when they are exposed to the air. Paint is the common protective for pre- venting rusting. Tinning and zincing are noticed in the sections on Tin and Zinc respectively. Concentrated H,SO, and HNO, do not act upon iron at the ordinary temperature, though they dissolve it rapidly when diluted. Even when boiling, strong sulphuric acid acts upon it but slowly. When iron has been immersed in strong nitric acid (sp. gr. 1-45), it is found to be unattacked ? when subsequently placed in HNO, of sp. gr. 1-35, unless previously wiped ; it is then said to have assumed the passive state. If iron wire be placed in HNO, of sp. gr. 1-35, it is attacked immediately ; but if a piece of gold or platinum be made to touch it beneath the acid, the iron assumes the passive state, and the action ceases at once. A state similar to this, the cause of which has not yet been satisfactorily explained, is sometimes assumed by the other metals, though in a less marked degree. In the case of iron it has been attributed to the formation of a coating of the magnetic oxide, which is sparingly soluble in strong HNO ,. It is destroyed if the acid containing the iron is placed in a magnetic field. Ferrum redactum is iron in powder obtained by reducing Fe,0; with H ata red heat in aniron tube. It always contains some Fe,Oy,. Iron is remarkable for its two series of fairly stable salts, the ferrous (con- taining divalent iron) and ferric (containing trivalent iron) (p. 351), the former acting as reducing agents and the latter as oxidising agents. Ferrous iron resembles magnesium and zinc in its disposition to form double salts with salts of ammonium, hence its solutions are imperfectly precipitated by ammonia ; but ferric iron resembles aluminium, and is completely precipi- tated. Nitric acid, chloric acid, and chlorine will always convert ferrous into ferric salts, and ensure complete precipitation by ammonia. 1 Most samples of rust are magnetic, indicating the presence of the magnetic oxide. 2 It is doubtful whether the iron ever remains quite unattacked, although no gas is evolved. The presence of oxides of nitrogen in the strong HNO, appears to be necessary for inducing the passivity, TRON OXIDES 453 Oxides of Iron.—Three compounds of iron with oxygen are known in the separate state: FeO, Fe,0,, Fe,03. Ferrous oxide, FeO, is obtained by heating ferric oxide to 500° in dry hydrogen ; Fe,0; + H, = H,O + 2FeO. It is obtained as a grey powder, which readily absorbs O from the air, taking fire and becoming Fe,0,. It is a basic oxide, yielding ferrous salts. In the finely divided state it decomposes water. Ferrous hydroxide, Fe(OH)s, is precipitated by alkalies from the ferrous salts. When pure it forms a white precipitate, but if air be present it becomes green from the production of hydrated ferroso-ferric oxide, and ultimately brown ferric hydroxide. These changes are best seen,when potash or ammonia is added to the ferrous salt ob- tained by shaking iron turnings or filings with a strong solution of sulphurous acid. This disposition of the ferrous hydroxide to absorb oxygen is turned to advantage when a mixture of ferrous sulphate with lime or potash isemployed for converting blue into white indigo. Ferrous hydroxide was used by the early investigators for absorbing oxygen in gas analysis. Ferric oxide, or peroxide of iron, Fe,O3, occurs as specular iron ore in six-sided crystals, and in hematite (p. 435). In commerce it is sold under the names colcothar, jeweller’s rouge, and Venetian red, which are obtained by the calcination of the green sulphate of iron ; 2FeSO, = Fe,0, + SO, + SOs. The ferric hydroxide obtained by decomposing a solution of ferric chloride with an alkali forms a brown gelatinous precipitate, which is easily dissolved by acids. When freshly precipitated and well washed it dissolves in a solution of ferric chloride, forming a basic chloride which by dialysis is slowly decomposed, HCl passing through the dialyser and a blood-red colloidal solution of Fe(OH), being left in the dialyser: “‘ dialysed iron.” When dried at 100° the hydroxide becomes 2Fe,0;.H,O. If a hot solution of a ferric salt be precipitated by an alkali, and the precipitate dried over sulphuric acid, it becomes Fe.(OH),.Fe,03, which is the composition of iron-rust and of some brown hematites. When either of the hydroxides is heated to dull redness it exhibits a sudden glow (recalesces), and is converted into a modification of Fe,03, which is dissolved with great difficulty by acids, althoughit has the same compositionas the soluble form which has not been strongly heated. By boiling the ferric hydroxide made by oxidising ferrous oxide for a long time with water, it becomes Fe,03.H,O, which is difficultly soluble in acids, and when heated does not show the phenomenon of recalescence. When the ferric oxide is heated to whiteness it loses oxygen, and is converted into magnetic oxide of iron; 3Fe,0; = 2Fe,0, + O. Ferric oxide, like alumina, is a weak base, and even exhibits some tendency to play the part of an acid towards strong bases, though not in so marked a degree as alumina. When heated in a stream of H or CO, it yields Fe,0, at 350°, pyrophoric FeO at 500°, and metallic iron at from 700° to 800°. Magnetic or Black Oxide of Iron (ferroso-ferric oxide), Fe,O,, is generally regarded as a compound of ferrous oxide with ferric oxide, FeO.Fe,03, a view confirmed by the occurrence of a number of minerals having the same crystalline form as the native magnetic oxide of iron, in which the iron, or part of it, is displaced by other metals. Thus, spinel is MgO.Al,0O,; Franklinite, ZnO.Fe,03; chrome-iron ore, FeO.Cr,0; ; pleonaste, MgO.Fe,0,; Gahnite, ZnO.Al,0;. This oxide is produced by the action of air or steam upon iron at a high temperature (p. 21). The hydrate Fe,0,.H,O is obtained as a black crystalline powder by mixing 1 mol. of ferrous sulphate with 1 mol. of ferric sulphate, and pouring the mixture into a slight excess of solution of NH;, which is afterwards boiled with it. With acids the oxide yields mixtures of ferrous and ferric salts, so that it is not an independent base. See also Magnetochemistry, p. 350. The very stable character of Fe,0, has led to its application for protecting iron from rust, When superheated steam is passed over the red-hot metal, as 454 GREEN VITRIOL a very dense, strongly adherent film of Fe,0, is produced, which effectually protects the metal (Barff’s process). A similar coating is produced by the action of a mixture of air and carbonic acid gas (Bower’s process). Ferric acid, H,FeO,, has not been obtained in the free state, but some of its salts are known.1 When iron filings are strongly heated with nitre, and the mass treated with a little water, a fine purple solution of potassium ferrate is obtained. A better method of preparing this salt consists in suspending 1 part of freshly precipitated ferric hydrate in 50 parts of water, adding 30 parts of solid KOH and passing chlorine till a slight effervescence begins; Fe,03; + 3Cl, + lJOKOH = 6KCI + 2(K,FeO,) + 5H,0; the ferrate forms a black precipitate, being insoluble in the strongly alkaline solution, though it dissolves in pure water to form a purple solution, which is decomposed even by dilution, oxygen escaping and hydrated ferric oxide being precipitated. A similar decomposition happens on boiling a strong solution, or on adding an acid with a view to liberate the ferric acid. The ferrates of barium, strontium, and calcium are obtained as fine red precipitates when solutions of their salts are mixed with potassium ferrate. As a lecture experiment the ferrate is readily prepared by dissolving a fragment of KOH in a little solution of FeCl,, adding a few drops of bromine and gently heating. On dissolving the cold mass in water, a fine red solution is obtained, which gives a red granular precipitate with BaCl,. The pink solution obtained by boiling some samples of chloride of lime with water contains calcium ferrate, and gives a pink precipitate with BaCl,. Ferrous carbonate, FeCO3, or spathic iron ore, or siderite, is found in rhombohedral crystals associated with the carbonates of Ca, Mg, and Mn, which are isomorphous with it. If ferrum redactum (p. 452) be suspended in water, and a stream of CO, be passed for some time, a solution of FeCO3 in carbonic acid is obtained, which, when filtered, is colourless, becomes rusty when exposed to air, and gives, when boiled, an abundant precipitate of FeCO;, which is nearly white, and becomes green when exposed to air. Na,.CO, added to a ferrous salt gives a white precipitate if all air be excluded ; otherwise oxygen is absorbed, and a dingy green precipitate containing Fe,O, is formed. See also chalybeate waters (pp. 47, 452) and rust (p. 452). The substance sold as ferric carbonate, obtained by precipitating a ferric salt with sodium carbonate, is mainly ferric hydrate, since weak bases like Fe,0, do not form carbonates. Ferrous sulphate, copperas, green vitriol, or sulphate of iron, is easily obtained by heating 1 part of iron wire with 1} parts of strong sulphuric acid mixed with 4 times its weight of water, until the whole of the metal is dissolved, and allowing the solution to cool and crystallise. Its manufacture on the large scale by the oxidation of iron pyrites has been already referred to (p. 161). It forms fine green monoclinic crystals (sp. gr. 1-88) having the composition FeSO,.7H,O. Rhombic crystals, isomorphous with the sulphates Zn and Mg, can also be obtained. The colour of the crystals varies somewhat, from the occasional presence of small quantities of ferric sulphate, Fe,(SO,)3. They dissolve in 2 parts of cold water and 0:3 part of boiling water, yielding a pale green solution. When the commercial sulphate of iron is boiled with water it yields a brown muddy solution, in consequence of the decomposition of the ferric sulphate contained in it, with precipitation of a basic sulphate. FeSO, or FeO.SO, has a great tendency to absorb oxygen, and to become Fe,(SO,), or Fe,03.380, and is thus useful as a reducing agent. For example, it is employed for precipitating gold in the metallic state from its solutions. But its chief use is for the manufacture of ink and black dyes by its action upon vegetable infusions containing tannic acid, such as that of nut-galls. Crystals of FeSO,.5H,0, isomorphous with CuSO,.5H,0, may be obtained by dropping a crystal of cupric sulphate into a supersaturated solution of ferrous 1 The common ferrates correspond with an anhydride, FeO,. Lately a barium perferrate corresponding with-FeO, has been prepared, a fact important from the point of view of the periodic law (p. 301). ’ FERRIC CHLORIDE 455 sulphate. As in the case of MgS0,.7H,O (p. 404), one molecule of the H,O in FeSO,.7H,O may be exchanged for other sulphates ; thus, ammonium ferrous sulphate, FeSO, .(NH,).SO,.6H,0, is well known. The salt FeSO,.80, is obtained in minute prismatic crystals when a saturated solution of ferrous sulphate is added to an excess of strong sulphuric acid. Ferric sulphate, Feo(8O,4)3, is found in Chili as a white silky crystalline mineral, coqguimbite, having the composition Fe,(SQ,)3.9Aq. Iron alwms, constructed on the type of the common alums (p. 424), with Fe’” in place of A (e.g. NH, .Fe’’’(804)2.12H.0), are commercial salts. Ferrous phosphate, Fe3(PO,)s, and arsenate, Fe;(AsO,)o, are used in medicine, being prepared by precipitating ferrous sulphate with a mixture of sodium acetate and sodium phosphate or arsenate. The acetate is used so that the resulting liquid may contain free acetic acid instead of the free sulphuric formed by the H in the sodium salt ; 3FeSO, + 2Na,HPO, = Fes(P04). + 2Na,SO, + H,SO,. Both the phosphate and arsenate are white when perfectly pure, but they become blue when exposed to air, from the production of a little ferroso-ferric salt. The precipitated ferric phosphate is 2FePO,.5Aq. Ferrous phosphate is found in the mineral Vivianite or native Prussian blue, Fe3(PO4)..8Aq. When ferric pyrophosphate, Fe,(P,07)3, is dissolved in sodium pyrophosphate solution there is slowly deposited a violet crystalline salt, sodium ferripyrophosphate, NagFe.(P,0,)3.9Aq, in which the iron does not give the usual reactions ; this masking of the iron is analogous to that which occurs in the ferrocyanides, and the complex Fe,(P,07)3 behaves like an acid radical ; the corresponding silver salt and the acid, H,Fe(P20,)3, have been prepared. The sodium ferropyrophosphate, NagFe,(P20,)s, is similarly made ; it is a powerful reducing agent. Ferrous chloride, FeCl, sublimes in colourless six-sided scales when iron is heated in HCl gas. It is deliquescent, and crystallises from water in pale green crystals, FeCl,.4Aq, which are oxidised by air. Its solution is prepared by dissolving iron in dilute HCl. Ferric chloride, or perchloride of iron, FeCl,, sublimes in beautiful dark green crystalline scales when iron wire is heated in a glass tube through which a current of dry chlorine is passed. The crystals deliquesce rapidly in air. FeCl, may be obtained in solution by dissolving iron in HCl, and converting the ferrous chloride (FeCl,) thus formed into ferric chloride by the action of HNO, and HCl (p. 199). A strong solution yields crystals of FeCl,.6Aq. The aqueous solution reddens litmus. The crystals are decomposed by heat, leaving an oxychloride. The solution of FeCl, has been recommended in some cases as a disinfectant, being easily reduced to FeCl,, and thus affording chlorine to oxidise unstable organic matters (p. 116). In contact with paper FeCl, becomes reduced to FeCl, when exposed to light. A solution of perchloride of iron in alcohol is used in medicine under the name of tincture of tron. It is also soluble in ether and benzene. At 400° the vapour density of ferric chloride is 165, corresponding with the formula Fe,Cl,, but at higher temperatures it approaches 82-5, corresponding with FeCl, (p. 314). Solution of ferric chloride dissolves a very large quantity of pure freshly precipitated ferric oxide (p. 453), 9 mols. Fe.03 being dissolved by 2 mols. FeCl;. The solution of ferric oxychloride thus obtained has a very dark red colour, and yields a very copious brown precipitate with common water, or any solution containing even a trace of a sulphate. When the aqueous solution of FeCl, is heated, it dissociates into a similar soluble hydroxide and HCl. Ferrous iodide, Fel,, is prepared by digesting fine iron wire with twice its weight of iodine and about 8 parts of water for some time, afterwards boiling till the red colour has disappeared, filtering, and evaporating in contact with clean iron. It forms green cystals, FeI,.5Aq, which are deliquescent and very soluble in water. The solution absorbs oxygen from the air, and deposits a brown precipitate unless kept in 456 COBALT ORES contact with clean iron or mixed with strong syrup. Ferric iodide, Fel, is not known. On mixing solutions of FeCl, and KI, Fel, and free I are produced. Ferrous bromide, FeBrg, is similarly prepared from Fe and Br. Ferrous sulphide, FeS, is formed when a red-hot bar of iron is rubbed with a stick of sulphur, the fused FeS running off in globules, and is prepared as described at p. 151. It is obtained as a black precipitate when an alkaline sulphide is added to a ferrous salt. It is easily oxidised when exposed to air in a moist state, and dissolves readily in HCl, being indeed the only black sulphide which dissolves easily in dilute HCl. It is used in the laboratory for making H,8. Magnetic pyrites, Fe,Ss, is found in yellow six-sided crystals. Iron pyrites, or mundic, FeS,, forms yellow cubes or octahedra of sp. gr. 5-2. It is formed by the slow reduction of FeSO, by organic matter, and its presence in coal appears to be accounted for in this way. Minute crystals of iron pyrites are sometimes found as rough casts of organic substances. It burns when heated, yielding Fe,0, and SO, (p.163). Sulphur may be obtained from it by distillation (p. 147). FeS, is insoluble in HCl, which distinguishes it from FeS. It may be dissolved by HNO. Radiated pyrites, or white pyrites, or marcasite, has the same composition, but its sp. gr. is only 4-8. Some kinds of pyrites explode with considerable violence when heated, and create. much alarm when they occur in household coal; these have been found to contain small cavities filled with highly compressed (probably liquid) CO, which expands suddenly when heated. Compact yellow iron pyrites is not oxidised by exposure to air, but white pyrites is easily converted into ferrous sulphate and sulphuric acid. Even yellow pyrites in minute crystals diffused through clay will behave in the same way. The FeS, may be obtained artificially by heating iron with excess of sulphur to a temperature below redness, or by heating ferric oxide or hydrate moderately i in a stream of H,8 as long as it increases in weight. Iron carbonyls.—When finely divided iron, prepared by heating ferrous oxalate in a current of hydrogen, is allowed to remain in the cold in contact with CO, a compound, Fe(CO),;, tron pentacarbonyl, is formed and can be distilled from the unaltered iron at 120° and condensed in a receiver surrounded by ice and salt. It is an amber- coloured liquid of sp. gr. 1-46; it boils at 102-5° and crystallises below — 21°; at 216° it is decomposed into Fe and CO. It dissolves in many organic solvents, and is slowly decomposed with precipitation of Fe,(OH), on exposure to air. When exposed to sunlight it deposits lustrous orange hexagonal plates of diferro-nondcarbonyl, which are stable in dry air; 2Fe(CO); = Fe.(CO), + CO. The reverse change occurs in the dark, and at 100° the nonacarbonyl is decomposed with separation of iron ; 2Fe.(CO)y = 3Fe(CO); + Fe + 3CO. The sp. er. of the crystals is 2-085. Tron carbonyl has been detected in coal-gas which has been compressed in iron cylinders. (Cf. nickel carbonyl, p. 460) COBALT, Co = 58.97. Some of the compounds of cobalt are of considerable importance in the arts, on account of their brilliant and permanent colours. It is generally found in combination with arsenic and sulphur, forming tin-white cobalt, CoAs,, and cobalt glance, CoAs,.Co8,, but its ores also generally contain nickel, copper, iron, manganese, and bismuth. The metal itself is obtained by strongly heating cobalt oxide with char- coal*in the manner to be described for preparing nickel from its oxide, or by heating the oxide with aluminium powder (p. 422). In its properties it closely resembles iron, but it is said to surpass iron in tenacity. It is magnetic. It is heavier than iron, sp. gr. 8-75, and melts at 1530°. It has been substituted for nickel in plating goods which are usually nickel-plated. Three oxides of cobalt, corresponding with those of iron, are known: cobaltous ovide, CoO; cobaltic oxide, CogO3 ; and cobalto-cobaltic oxide, Coz3O, or CoO .Co,0g. The first of these, CoO, is a brown powder left when Co(OH). is ignited in absence of air; it is a basic oxide, dissolving in acids to form cobaltous salts. When heated in COBALT SALTS 457 air it oxidises to CoO.Co,03. When heated in the electric furnace it melts and forms rose-coloured crystals. Cobaltic oxide is left as a black powder when cobaltous nitrate is gently heated. It is a feeble base, and the cobaltic salts are very unstable ; thus the oxide dissolves in cold HCl, yielding a brown solution of cobaltic chloride, CogClg, which is easily decom- posed when heated, evolving Cl, and leaving 2CoClz. When Co,0, is heated it becomcs CoO .Co,03. It is doubtful whether a cobalt dioxide, CoO,, exists, but when Co.C, is fused with MgO in the electric furnace, red crystals of MgCoO, are obtained. Cobalto-cobaltic oxide ,Co 304, is the commercial oxide of cobalt employed for painting on porcelain, and for preparing other commercial cobalt products. It is a black powder, which evolves chlorine when boiled with HCl, yielding a solution of CoCl,. It is generally prepared as a by-product in the manu- facture of nickel from its arsenical ores (see Nickel). Co,0, is not an se base, but gives cobaltous and cobaltic salts when dissolved in acids. Cobaltous hydroxide, Co(OH),, is obtained by adding potash in excess to a solution of a cobaltous salt, and boiling. The blue precipitate produced at first is a basic salt which becomes converted into the red hydroxide on boiling with excess of potash. If air be allowed access it oxidises the red precipitate, converting it into brown cobaltic hydroxide. Co(OH), dissolves in ammonia, giving a fine red solution, which absorbs oxygen from the air and becomes brown. Cobaltic hydroxide, Co,(OH).,, forms the black precipi- tate when the solution of a hypochlorite or hypobromite is added to one of a cobaltous salt. Cobaltous nitrate, Co(NO,),.6Aq, obtained by dissolving cobalt oxide in HNO, and crystallising, forms red prisms, which become blue when their water is expelled, and black Co,O, on further heating. Cobalt-yellow or potassium-cobaltic nitrite, KeCo'”’,(NO,)y., is obtained as a yellow precipitate when cobaltous nitrate is acidified with acetic acid, and potassium nitrite added ; the acetic acid liberates nitrous acid, which oxidises the cobaltous salt; 2Co’’(NO,), + lOKNO, + 4HNO, = K,Co’”’,(NO.)12 + 4KNO, + 2NO + 2H,0. It forms a yellow crystalline precipitate, slightly soluble in water, and not decomposed by cold HCl or HNO;. Caustic alkalies decompose it, separating Co,(OH),. Cobaltous chloride (CoCl,), obtained by dissolving any of the oxides in hydrochloric acid, forms red prisms, CoCl,.6Aq, which become blue CoCl,.2Aq at 120°, and at 140° CoCl,, which may be sublimed in dark blue scales in a current of chlorine. If strong hydrochloric acid be added to a red solution of this salt, it becomes blue ; if enough water be now added to render it pink, the blue colour may be produced at pleasure by boiling, the solution first passing through a neutral tint.1_ Chloride (muriate) of cobalt is employed as a sympathetic ink, for characters written with its pink solution are nearly invisible until they are held before the fire, when they become blue and resume their original pink colour if exposed to the air; a little chloride of iron causes a green colour. Cobaltous sulphide (CoS) is obtained as a black precipitate when an alkali sulphide is added to a solution of a salt of cobalt. It differs from FeS by being insoluble in HCl. A cobaltic sulphide (Co.83) is found in grey octahedra, forming cobalt pyrites. The disulphide (CoS,) has been obtained artificially. Cobaltous sulphate, CoSO,.7H,0, is found as cobalé vitriol. It forms red prisms isomorphous with ferrous sulphate. It does not become blue when dried, and bears a high temperature without decomposing. COobaltic sulphate and cobaltic alums have been prepared. Cobaltous arsenate, or cobalt bloom, Co3(AsO4)2.8Aq, is found in pink needles. 1 A solution containing so small a quantity as 0-015 per cent. of cobalt will give a distinct blue colour when boiled with an equal bulk of strong hydrochloric acid. 458 COBALT PIGMENTS Cobalt di-arsenide, CoAse, is found crystallised as tin-white cobalt and spetss cobalt, in which it is associated with the isomorphous arsenides of nickel and iron, so ‘that it is written [CoNiFe]As,. CoAs, is also found in nature. The blue colour known as smalt consists of cobaltous silicate, associated with potassium silicate, and is prepared by roasting the cobalt ore so as to convert the bulk of the cobalt into oxide, leaving, however, a considerable quantity of arsenic and sulphur still in the ore. The residue is then fused in a crucible with ground quartz and carbonate of potash, when a blue glass is formed, containing cobalt silicate and potassium silicate ; whilst the iron, nickel, and copper, combined with arsenic and sulphur, collect at the bottom of the crucible and form a fused mass of metallic appearance known as speiss, which is employed as a source of nickel. The molten glass is poured into cold water, so that it may be more easily reduced to the fine powder in which the smalt is sold. If the cobalt ore destined for smalt be over- roasted, so as to convert the iron into oxide, this will pass into the smalt as a silicate, injuring its colour. Smalt much resembles ultramarine, but is not bleached by acids. Zaffre is prepared by roasting a mixture of cobalt ore with two or three parts of sand. Thénard’s blue, or cobalt ultramarine, consists of cobalt phosphate and aluminium phosphate, and is prepared by mixing precipitated alumina with cobalt phosphate and calcining in a covered crucible. The phosphate is obtained by precipitating a solution of cobalt nitrate with phosphate of potassium or sodium. Rinmann’s green is prepared by calcining the precipitate produced by sodium carbonate in a mixture of cobalt sulphate with zinc sulphate. It is a compound of the oxides of cobalt and zinc. The relations of ammonia to the cobalt salts are very remarkable and characteristic, the NH, combining both with cobaltous and cobaltic salts to form compounds which behave like salts, known as cobaltosamine and cobaltamine salts. When NH; is added to the solution of a cobaltous salt, air being excluded, a cobalt- osamine salt of the general type CoX,.6NH;H,0, where X is an acid radicle, is formed. When these are exposed to the air they undergo oxidation, yielding oxycobaltamine salts of the type CoOX,.5NH,;H,0, in which the cobalt may be regarded as tetrad, corresponding with the oxide CoO,; these salts lose oxygen, becoming cobaltamine salts, when their solutions are heated. If the cobaltosamine solution be fairly dilute when it is exposed to the air, the oxy-salt will not be formed, and on addition of an acid w cobaltamine salt will be separated. These are of six types, represented by CoX,.nNH;, where n = 1, 2, 3, 4, 5, or 6; they are all coloured salts and distinguished by prefixes signifying the colour characteristic of the series—for example, xantho- (yellow), luteo- (yellow), roseo-, purpureo-, croceo- (saffron), and fusco- (brown). Cobalt carbonyl, Cog(CO)g.—The cobalt oxide made by heating the oxalate is reduced by hydrogen at 300° under 5 atm. pressure, and the cobalt is heated in CO under 40 atm. pressure. When the gas coming away from the apparatus is cooled, orange crystals of the carbonyl are deposited. Their sp. gr. is 1-73, and m.-pt. 51°. Above 52° the carbonyl is decomposed into Co(CO)3, a black crystalline body decomposed into Co and CO above 60°. Cobalt resembles iron in many respects, but the cobaltic compounds are much less stable than the ferric compounds. Cobaltous compounds are oxidised to cobaltic compounds only in solutions which are neutral or alkaline, while ferrous compounds are easily oxidised in acid solutions. Both metals form remarkable compounds with potassium and cyanogen, iron forming the ferrocyanide, K,Fe’’Cy,, and ferricyanide, K,Fe’’Cy,, while cobalt forms the cobalticyanide, K,Co'Cy, (see Cyanides). NICKEL, Ni = 58.68. Nickel is very similar to cobalt and closely resembles iron, but is much less attacked by air and water. It is somewhat heavier than iron, its sp. gr. NICKEL—EXTRACTION 459 being 8-8, and slightly more fusible than pure iron, its m.-pt, being 1470°. It is magnetic at ordinary temperatures, but not above 250°. Its main application is in the form of alloys, those with copper being remarkable for their whiteness, hardness, and high electrical resistance. The nickel coins used in most foreign countries consist of Cu 75 per cent. and Ni 25 per cent. German silver is brass whitened by the presence of nickel to the extent of from 6-30 per cent. (p. 510). Nickel steel (steel with 3-5 per cent. Ni) is much used as armour-plating for ships on account of its hardness. Several special copper-nickel alloys are made for use as electrical resistances, e.g. con- stantan, Cu 60, Ni 40; platinoid, Cu 60, Nil4, Zn 24,W2; manganin, Cu 84, Ni12, Mn 4. An alloy (Monel metal) containing Ni 70 and Cu 30 is made by smelting nickel-copper ores, and is remarkable for its tensile strength and hardness. The alloys of steel with 25—- 50 per cent. of nickel are remarkable for their low coefficient of thermal expansion ; for this reason platinite (Fe 54, Ni 46) can be sealed into glass without breaking the joint as it cools, so that this alloy can be substituted for platinum for the purpose. Iron containing 25 per cent. Ni is very feebly magnetic ; if cooled to — 40° it becomes decidedly magnetic and remains so until heated to 600°. Nickel can easily be electro-plated on other metals as a lustrous film, only slowly tarnished by the atmosphere. The metal itself is not much used ; dishes and crucibles made of it are useful in the laboratory, since they resist fused alkalies. The commercial metal contains about 99 per cent. Ni, the rest being Fe, Cu, S and Si. The chief ores of nickel are garnierite, a silicate of nickel and magne- sium found in New Caledonia, and the Sudbury ore (Canada), which is a magnetic iron pyrites containing 3-8 per cent. Ni. The first of these ores contains a little cobalt, but the second is free from that metal. The Saxon and Bohemian ores of nickel contain Co, As, 8 and Fe ; the chief are kupfer- nickel, NiAs, nickel glance, NiAs,.NiS,, and nickel blende, NiS. In the extraction of nickel advantage is taken of the ease with which iron sulphide can be roasted to oxide, and the oxide fluxed as ferrous silicate by fusion with silica (cf. metallurgy of copper), leaving a matte of nickel sulphide. In the case of garnierite, which is practically free from sulphur, fusion with gypsum and coke for converting the nickel and iron into sulphide is a preliminary step. The matte obtained from garnierite is free from copper and merely requires to be roasted to oxide (NiS + 30 = NiO + SO,), which is then reduced by making it into a paste with charcoal, cutting the paste into cubes and heating these to a very high temperature. The roasted matte from the sulphide ores always contains copper oxide, which must be separated from the nickel oxide before reduction if pure nickel is required, but may be reduced with the nickel if the metal is to be used for making copper alloys. The mixture of oxides of nickel and copper may be treated with dil. H,SO,, which will dissolve the CuO, leaving the NiO. The Orford process for treating nickel matte depends on the fact that fused sodium sulphide dissolves copper and iron sulphides, but not nickel sulphide. The matte is fused with salt cake and coke (potential Na.§, see p. 370), and the fused mass allowed to settle so that it may deposit the Ni8. The arsenical nickel ores are treated as described above for the removal of iron, and the speiss thus obtained, consisting essentially of nickel and arsenic, but containing a little cobalt and copper, is treated by a wet method for the separation of the cobalt. This is effected by roasting the speiss to expel most of the arsenic, dissolving in HCl, peroxidising the solution by bleaching-powder, and neutralising with chalk ; in this way the iron is precipitated as basic ferric carbonate, and the remaining arsenic as ferric arsenate. H,S is passed through the solution to precipitate bismuth and copper as sulphides, leaving cobalt and nickel in solution. The latter, having been boiled to expel the excess of H,§, is neutralised with lime and mixed with bleaching-powder, which precipitates the cobalt as Co,03, leaving NiO in solution, from which it may be 460 NICKEL COMPOUNDS precipitated by adding lime ; it is reduced as described above. The Co,03 becomes Co30, when ignited. Mond’s process for extracting nickel depends on the fact that when the finely divided metal is heated in a current of CO at 50°-100° it is volati- lised in the form of nickel carbonyl (see below), and thus separated from any other metals, &c., which may accompany it. The nickel carbonyl vapour is then heated in another vessel, whereby it is decomposed and deposits its nickel. In practice the finely divided roasted matte or speiss is caused to descend a tower containing hollow shelves heated internally by hot gas to 250°, where it meets an ascend- ing stream of water-gas. The oxides are thus reduced to metal, and the material is next conveyed to the top of a second tower, not heated, in descending which it meets a current of gas rich in CO and at a temperature of 50°. Nickel carbonyl is produced and carried forward as vapour by the gas into an apparatus in which a mass of granules of nickel is kept in motion so that the granules perpetually roll over each other and are prevented from cohering. The temperature of this apparatus being about 200°, the carbonyl deposits its nickel on the granules, while its CO passes on to be used again in the second tower for volatilising more nickel. By keeping the temperature of the volatilising tower as low as possible, the production of iron carbonyl (p. 456) is avoided. The oxides of nickel correspond in composition with those of cobalt. The salts formed by nickelous oxide (NiO) are usually green, and give bright green solutions. The hydroxide has a characteristic apple-green colour, and does not absorb oxygen from the air like the cobaltous hydroxide. It dissolves in ammonia to a blue solution unchanged by air. The greater facility with which the cobalt is converted into sesquioxide has been applied (as above described) to effect the separation of the two metals. NiO has been found native in octahedral crystals, which have also been obtained accidentally in a copper-smelting furnace ; it melts in the electric arc and crystallises on cooling. Nickelic oxide, NigQg, is a black precipitate, formed by action of an alkaline solution of a hypochlorite on a solution of # nickel salt. Ni,;0, is obtained in microscopic octahedral crystals of metallic appearance by passing moist oxygen over NiCl, at about 400°. It is converted into NiO when heated, and dissolves in hydrochloric acid with evolution of chlorine. Nickel sulphate (NiSO,.7H,O) forms fine green prismatic crystals soluble in their own weight of cold water; one molecule of water in the salt may be displaced by K,SO, or (NH,),SO,. Nickel ammonium sulphate, NiSO,.(NH,),SO,.6H,O, is used in electro-plating with nickel. It is almost insoluble in ammonium sulphate solution. Nickel sulphate may be obtained by dissolving nickel in dil. H,SO,. Itis isomorphous with the sulphates of Mg, Zn, Fe and Co. When NH, is added to its solution it produces a green precipitate of a basic salt, which dissolves in excess of NH; to a violet solution, depositing violet crystals of NiSO,.4NH,.2H,0. Four sulphides of nickel are known: Ni,S, NiS, Ni,;S4, and NiS,. NiS is found native as capillary pyrites, and is obtained as a black precipitate by the action of an alkaline sulphide on a salt of nickel ; like cobalt sulphide, it is insoluble in HCl; but ammonium disulphide dissolves it to a dark brown liquid. Nickel carbonyl, Ni(CO),, is a colourless liquid (sp. gr. 1-3) which boils at 43° and crystallises at — 25°. It is prepared by passing dry CO through a tube containing finely divided nickel which has been reduced from NiO by heating it in hydrogen at 400°. The Ni(CO), is condensed from the excess of CO used by passing the gas through a tube surrounded by ice and salt. It is insoluble in water, but dissolves in alcohol, benzene and chloroform. Its vapour is decomposed at 150° into CO and Ni, which is deposited in the form of a mirror on the sides of the vessel ; it is a powerful MANGANESE OXIDES 461 reducing agent. Theoretically it is of great importance as furnishing a volatile com- pound, by means of which the atomic weight of nickel can be determined. Nickel is farther removed from iron than cobalt is ; its peroxide, Ni,O., shows no disposition to form salts, and it does not form any compound corresponding with ferro- or cobalti-cyanides. It has far less colouring power than cobalt, and its salts are commonly green. In many respects nickel more nearly resembles copper than iron. Nickel salts are poisonous. MANGANESE, Mn = 54.93. ; Manganese much resembles iron in several particulars relating both to its physical and chemical characters, and is often found associated, in small quantities, with the compounds of that metal. It is found chiefly as pyro- lusite, MnO, (sp. gr. 4-2), braunite, Mn,O,, and manganese spar, MnCQs. In very small proportion it appears to be a normal constituent of fresh- water mussels. The metal is not used as such, but forms a constituent of some useful alloys, notably spiegel-eisen and ferro-manganese, which contain iron, Manganese and carbon, and are largely used in the production of steel (p. 442). It is obtained either by reducing one of the oxides with charcoal at a very high temperature—when a fused mass, composed of manganese combined with a little carbon (corresponding with cast iron), is obtained and may be freed from carbon by a second fusion in contact with manganous oxide—by reducing MnCl, with magnesium, or by igniting a mixture of aluminium powder and manganese oxide (p. 422). Manganese is grey with a red tinge, hard and brittle, sp. gr. 7°39; m,-pt. 1245°. It is more easily oxidised than iron, so that it decomposes water when slightly warmed (p. 20). It is not magnetic unless cooled to — 20°. It appears to be more volatile than iron. 2 Manganese dissolves easily with evolution of hydrogen in dil. HCl or H,SO,. It resembles iron in its tendency to combine with carbon at a high temperature to form a compound corresponding with cast iron, and in this form the manganese is not oxidised by air. Oxides of Manganese, MnO, Mn,0;, Mn,0,, MnO,, MnO,, Mn,0,.— The first two are bases, the last two anhydrides. Manganese dioxide or peroxide, MnO,, is the chief form in which this metal is found in nature, and is the source from which all other compounds of manganese are obtained. Pyrolusite occurs in steel-grey prismatic crystals, but psilomelane is amorphous, and wad is a hydrated form. In commerce pyrolusite is known as black manganese, or simply “manganese,” and is largely imported from Germany, Spain, &c., for use in making steel, bleaching-powder and glass. It is also used as a cheap source of oxygen (p. 55). Itis an indifferent oxide, and does not combine with acids. Strong HCl, however, dissolves it, giving a brown solution from which water precipitates a brown oxychloride. If the brown solution, which probably contains Mn,Cl, and MnCl, (p. 112), be heated, it evolves Cl, and becomes colourless MnCl,. Nitric acid is almost without action on MnO,. Strong H,SO, evolves oxygen from it; MnO, + H,SO,= MnSO, + H,O + 0. Even dilute H,SO, effects the same change if some substance ready to combine with oxygen is added, such as ferrous sulphate or oxalic acid. Hence a mixture of MnO, and H,SO, is much used as an oxidising agent, and it will be seen from the above equation that only half the oxygen in the MnO, is available for purposes of oxidation. The com- mercial black oxide is therefore valued by ascertaining how much FeSO, a given weight of it will oxidise in the presence of dil. H,SO,— 2(FeO.SO,) + MnOg + 2(H,0.S03) = Fe,05.(S05)5 + Mn0.S0, + 2H,0, 462 MANGANESE ACIDS It is easily dissolved by H,SO3, the latter being oxidised to H,8Q,. When heated in hydrogen, the oxides of manganese are not reduced to the metal, like those of iron, but are converted into MnO. Manganous oxide, MnO, obtained in this way, is a greenish powder. It has been obtained in transparent emerald-green crystals. It easily absorbs oxygen from the air. It is a basic oxide, dissolving in acids to form the manganous salts. It has been found native in a manganiferous dolomite. Manganous hydroxide, Mn(OH)s, is obtained as a white precipitate when an alkali is added to a manganous salt, out of contact with air. When exposed to air it rapidly becomes brown, forming manganic hydroxide. Manganic oxide, or manganese sesquioxide, Mn,O3, is found in the mineral braunite in octahedral crystals. By its general appearance it might be mistaken for MnO,, but it dissolves in moderately strong sulphuric acid, forming a red solution of manganic sulphate, Mno(SOq)3, showing that it is a feebly basic oxide. It may be obtained by heating any of the oxides of manganese to redness in a current of oxygen, while Mn3;0, is formed when any one of the oxides is heated in air. When MnO, in very small quantity is added to melted glass it imparts a purple colour, which is probably due to the formation of a manganic silicate. The amethyst is believed by some to owe its colour to the same cause. Manganic hydroxide, Mn,0.(0H)., may be regarded as MngOz, in which O has been exchanged for (OH)s, or as Mn,03.H,O. It is found in dark grey prismatic crystals, as manganite, associated with MnO., from which it differs by giving a brown instead of a black streak on unglazed earthenware. Moreover, on boiling it with dil. HN O3, part of it is dissolved as manganous nitrate, leaving a hydrated manganese dioxide, which dissolves to a brown solution when thoroughly washed. A hydrated manganese dioxide is also precipitated when chloride of lime is added to a manganese salt. Red oxide of manganese, Mn,Oq, is the most stable of the oxides of this metal, and is formed when any of the others is heated in air. Thus obtained, it has a brown or reddish colour; but it is found in nature as the black mineral hausmannite. In composition it resembles the magnetic oxide of iron, but it seems probable that the true formula is 2MnO.MnOg, for when treated with dil. HNO, it leaves the black hydrated dioxide. Strong H,SO, dissolves it to a red liquid containing manganous and manganic sulphates. Dil. H,SO, leaves MnO, undissolved. HCl dissolves it when heated, evolving Cl and leaving MnCl. : MnO;, or manganic anhydride, is formed in small quantity by dropping a solution of potassium permanganate in concentrated H,SO, wpon dry Na,CO3, and condensing the pink cloud which arises, in a tube cooled by ice and salt. It is a red amorphous mass, yielding manganic acid in contact with water. Permanganic anhydride, Mn,O,, is a red oily liquid formed when potassium per- manganate is decomposed by strong sulphuric acid ; K,Mn,0, + 2H,80, = 2KH80, + Mn,0, + H,0. It decomposes slowly, even at common temperatures, evolving oxygen, together with violet vapour of Mn,0,. When heated, it decomposes with explosion. It is a most powerful oxidising agent, setting fire to most combustible bodies. In contact with water, it yields permanganic acid, H,Mn.Oxg. Manganic acid, H,Mn0O,, has not been isolated, but several manganates are known, which are isomorphous with the chromates and sulphates. Potassium manganate, K,MnO,, is formed when MnO, is fused with potash; 3MnO, + 2KOH = K,MnO, + Mn,0, + H,O. If an oxidising agent, such as air or nitre, be present, the Mn,O, is also converted into K,MnO, ; Mn,0O, + 4KOH + 30 = 2K,Mn0O, + 2H,O. The extraction of oxygen from air upon this principle has been described at p. 55. Sodium manganate, Na,MnO,, obtained by heating manganese dioxide with sodium hydroxide under free exposure to air, is employed in a state of solution in water, as a convenient disinfecting fluid. It is also used as a bleaching agent, and in the preparation of oxygen at a cheap rate. The manganates of potassium and sodium dissolve in water containing potash PERMANGANATE 463 or soda, forming green liquids, but when dissolved in pure water they are decomposed, yielding the red permanganates— 38Na,MnO,4 + 2H,O = NagMn.0, + MnO, + 4Na0H. Barium manganate forms the pigment known as Cassel green. Manganous acid, of which MnO, would be the anhydride, might be expected to exist, but is not known. When Mn(OH), is oxidised in presence of an alkali, the brown substance produced contains more or less of the alkali combined with MnO,. These compounds are known as manganites—e.g. CaO .MnOg. Permanganic acid, HyMngOx, has been obtained in a hydrated crystalline state by decomposing BaMn,O, with H,SO,, and evaporating the solution in vacuo. It isa brown substance, easily dissolving in water to a red liquid, which is decomposed at about 32°, evolving oxygen, and depositing MnQ,. Potassium permanganate, K2Mn20s, forms rhombic prisms (sp. gr. 2-71) isomorphous with the perchlorate, KC10,, on which account it is some- times written KMnO,. It dissolves in 20 parts of cold water, forming a purple solution, which becomes green K,MnO, by contact with many substances capable of taking up oxygen. When crystallised permanganate is heated to 240° it gives manganate ; K,Mn,O, = K,MnO, + MnO, + O,. It is largely used in many chemical operations. In order to prepare it, 4 parts of finely powdered manganese dioxide are intimately mixed with 3} parts of KCIO, and 5 parts of KOH dissolved in a very little water. The pasty mass is dried, and heated to dull redness for some time in an iron tray or earthen crucible. The potassium chlorate imparts the required oxygen. On treating the cool mass with water, potassium manganate is dissolved, forming a dark green solution. This is diluted with water and a stream of CO, passed through it so long as any change of colour is observed ; 3K,Mn0, + 2CO, = K,Mn,0, + MnO, + 2K;CO3. The precipitated MnO, is allowed to settle, and the clear red solution poured off and evaporated to a small bulk. On cooling, it deposits prismatic crystals of the permanganate (K,Mn,Og), which are red by transmitted light, but reflect a dark green colour. The K,CO 3, being much more soluble in water, is left in the solution. Potassium permanganate is remarkable for its great colouring power, a very small quantity of the salt producing an intense purplish-red colour in a large quantity of water. Its solution in water is very easily decom- posed and bleached by substances having an attraction for oxygen, such as sulphurous acid or a ferrous salt. If a very small piece of iron wire be dissolved in diluted sulphuric acid, the solution of ferrous sulphate so produced will decolorise a large volume of weak solution of the perman- ganate, being converted into ferric sulphate— K,Mn,0, + 10FeSO, + 8H,SO, = K,SO, + 2MnSO, + 5¥Fe.(SO,4)3 + 8H,0 or K,0.Mn,0, + 10(FeO.80,) + 8(H,0.80;) = K,0.80, + 2(MnO.SOg) + 5(Fe203.380,) + 8H,0 —which shows that the molecule of K,Mn,0, has 5 atoms of oxygen available for purposes of oxidation. This decomposition forms the basis of a valuable method for determining iron in quantitative analysis. Many organic substances are easily oxidised by potassium perman- ganate, and this is the case especially with the offensive emanations from putrescent organic matter. Hence its solution is extensively used as a disinfectant in cases where a solid or liquid substance is to be deodorised ; a similar solution is sold as Condy’s fluid. The oxidising power of the permanganate is effectively illustrated by pouring a little glycerin into a cavity made in a small heap of the powdered crystals on a porcelain crucible lid; the glycerin slowly sinks into the powder, and after a minute or two bursts into flame. An alkaline solution of the permanganate is sometimes used as an oxidising agent, 464 MANGANESE SULPHATE since it parts with oxygen when boiled with oxidisable substances, becoming first green from the production of manganate ; K,Mn,0, + 2KOH = 2K,Mn0, + H,O + O; and then brown from deposition of MnO, ; K,.Mn0O, + H,O = 2KOH + MnO, + O. Sodium permanganate, NagMn.Og, is often used as a disinfectant, being cheaper than the potassium salt. It is made by heating MnO, with NaOH, in a flat vessel exposed to air for 48 hours to dull redness ; the mass is boiled with water to convert the manganate into permanganate ; 3Na,MnO,+2H,0=Na,Mn,03 + MnO, +4Na0H. There appear to be three chlorides of manganese, corresponding with three of the oxides, viz., MnCl,, Mn,Cl, and MnCl, (p. 461) ; but only the first is easily obtainable in the pure state, the others readily decomposing with evolution of chlorine. There is also some evidence of the existence of a chloride, MnCl,. By dissolving potassium permanganate in oil of vitriol, and adding fragments of fused NaCl, « remarkable greenish-yellow gas is obtained, which gives purple fumes with moist air, and is decomposed by water, yielding a red solution which contains HCl and permanganic acid. The gas, therefore, must contain Mn and Cl, and is some- times regarded as the perchloride (MnCl,) ; but it is more probably an oxychloride of manganese (see Chlorochromic acid). Care is required in its preparation, which is sometimes attended with explosion. The manganous chloride, MnCl, is obtained in large quantity as a waste product in the preparation of chlorine for the manufacture of bleaching-powder (p. 115). Since there is no useful application for it, the manufacturer sometimes reconverts it into the black oxide by Weldon’s process. As the native binoxide always contains iron, the liquor obtained by treating it with HCl contains FeCl; mixed with MnCl. In order to separate the iron, advantage is taken of the fact that sesquioxides are weaker bases than the protoxides, so that if a small proportion of lime or chalk be added to the solution, the iron may be precipitated as oxide without decomposing the chloride of manganese ; 2FeCl, + 3CaO = Fe,03 + 3CaCly. After separating the Fe,O3, an excess of lime is added and air blown through the mixture at about 65°, when the white precipitate of MnO, formed at first, absorbs the oxygen, and becomes a black compound of MnO, with lime, which is used over again for the preparation of chlorine. Unless the lime is added in excess, only MnO .MnO, is formed, so that the excess of lime displaces the MnO and allows it to be converted into MnO,. In another process Weldon employs magnesia instead of lime, with a view to recovering afterwards the chlorine from the chloride of magnesium, in the form of hydrochloric acid (see p. 405), and using the magnesia over again. Manganous sulphate is prepared by adding strong H,SO, to MnOg, heating the paste to redness to decompose any ferric sulphate, extracting with water, precipitating the last traces of iron by adding manganous carbonate, filtering, and crystallising. When crystallised at temperatures below 6°, MnSO,.7Aq, isomorphous with FeSO,.7Aq, is formed; between 7° and 20°, the crystals are MnSOQ,.5Aq, isomorphous with CuSO,.5A4q; between 20° and 30° the crystals are MnSO,.4Aq, which is the chief constituent of the commercial salt ; 100 of water dissolve 64 of MnSO,4.4Aq at 20°. Manganous sulphate is employed by the dyer and calico-printer in the production of black and brown colours. Manganous sulphide, MnS, occurs as manganese blende in steel-grey masses. It may be obtained as a greenish powder by heating any of the oxides of manganese in a current of H,S. When precipitated by alkali sulphides from manganese salts, it has a pink colour and contains water. When the pink precipitate is boiled with an excess of alkali sulphide, it becomes a green crystalline powder, 3MnS.H,O. The MnS has a tendency to form soluble compounds with the alkali sulphides, so that a solution of manganese often requires boiling with (NH,).S before a precipitate is formed. It dissolves easily in HCl. The disulphide, MnSg, is found, in regular crystals, as Hauerite, in Hungary. Manganese, though more nearly allied to iron than to any other metal, is parted from it by the greater stability of the manganous salts, which are less easily oxidised than the ferrous salts, as well as by the far greater stability CHROME IRON ORE 465 of the manganates than of the ferrates, and by the existence of permanga- nates, which have no parallel in the iron series. The chlorides of manganese give a green colour to a flame. CHROMIUM, Cr = 52.0. This metal derives its name from yooua, colour, in allusion to the varied colours of its compounds, upon which their uses in the arts chiefly depend. It is comparatively seldom met with, its principal ore being the chrome: tron ore, FeQ.Cr,O3 (sp. gr. 4:4), which is remarkable for its resistance to the action of acids and other chemical agents, and is chiefly found in Cali: fornia, Canada, Rhodesia and Asia Minor. By smelting this ore as an iron ore in a blast-furnace an alloy of iron and chromium (12-40 per cent.), called ferrochrome, is produced ; this is used as an addition to steel for imparting special. properties to the metal (p. 442). Metallic chromium is sometimes used as an addition to other alloys, in which case it is required free from iron, so that the Cr,0, must be separated from the ore before reduction. For reducing the oxide with carbon the temperature of the electric furnace is best, but the metal produced always contains carbon. A purer metal is obtained by reducing the oxide with aluminium (p. 422). It has a grey colour, sp. gr. 6-92, and m.pt, about 2000°. It is hard, takes a fine polish, and is not easily attacked by air or acids, in which it readily assumes a passive condition (p. 452); HCl dissolves it to chromous chloride, CrCl,. At high temperatures alkali hydroxides attack Cr, evolving H and pro- ducing chromate. By heating chromic chloride in sodium vapour the metal has been obtained in octahedral crystals insoluble even in aqua regia. Oxides of Chromium.—Three oxides of chromium are known in the separate state: chromic oxide, Cr,O3, chromium dioxide, CrO,, and chromic anhydride, CrO,. Monoxide of chromium or chromous oxide, CrO, is known in the hydrated state, and perchromic acid, H,Cr,Og, is believed to exist in solution. The chromous salts correspond with the ferrous salts, but are much more susceptible of oxidation. In order to separate the chromium from chrome iron ore for the manu- facture of chromium compounds, advantage is taken of the fact that in presence of a base the basic oxide Cr,O0, is readily oxidised to the acid oxide CrO3, which combines with the base to form a chromate. The ground ore (1 part) is mixed with CaCO, (1 part) and Na,CO, (1 part), and the mixture is heated strongly in a reverberatory furnace in a current of air, the charge being stirred to ensure full exposure to the air. A mixture of the bases is used because CaCO, alone gives a mass which is infusible and in which, therefore, the reaction is very slow; Na,CO, alone gives a mass which is too fusible for thorough exposure to air; the mixture gives a plastic mass. The CaCO, becomes CaO at the temperature used, and the oxidation occurs according to the equations— 2(FeO.Cr,03) + 4CaO +70 = 4(Ca0.CrO,) + Fe05. 2(FeO.Crs05) + 4(Na,0.COz) + 70 = 4(Na,0.CrO,) + Fe,03 + 4C0>. The mass containing the calcium and sodium chromates and Fe,O, is heated with a solution of Na,CO;, which decomposes the calcium chromate, forming CaCO, (which remains undissolved together with the Fe,0,) and sodium chromate, so that the whole of the chromium passes into solution in this form. As the latter is not easily crystallisable and therefore not readily purified, it is converted into bichromate by concentrating the liquor, filtered from the CaCO, and Fe,O,, until its sp. gr. is 1-5 and adding H,SO, ; at this concentration Na,SO, is precipitated and the solution is further 30 466 CHROMATES evaporated until sodium bichromate, Na,Cr,0,.2H,O, crystallises in red deliquescent prisms soluble in their own weight of water— 2(Na.0.CrO3) + H,SO, = Na,SO, + Na,gO.2CrO,; + H20. The normal sodium chromate, Na,CrO,.10H,O, is made like potassium chromate (v.i.); it is isomorphous with Na,SO,.10H,0. Potassium bichromate, K,Cr,0,, is made by mixing solutions of sodium bichromate and potassium chloride of concentration suitable for precipita- ting the sparingly soluble K,Cr,O,; or by substituting K,CO, for Na,CO, in the treatment of chrome iron ore described above. It forms red tabular crystals (sp. gr. 2-7) soluble in 10 parts of cold water to an acid solution ; it melts at about 400° and then decomposes— 2K.Cr20, = KeCrO, + Cre03 + 30. In acid solution it is a powerful oxidising agent, being reduced to the green chromium salts; the loss of oxygen to the reducing agent may he repre- sented, for example, by the equation— K,0.2Cr0, + 4(H,0.S03;) = K,0.80, + Cr203.(SO3)3 + 30 + 4H,0. As is usual in such cases, if HCl be the acid, chlorine is evolved instead of oxygen; K,Cr,0, + 14HCl = 2KCl 4+ 2CrCl, + 7H,O + 3Cl,. Even at ordinary temperatures in aqueous solution the bichromates have an oxi- dising action in presence of light, and it is on this that their application in photography for converting gelatine into a product insoluble in water is based. By pouring a cold saturated ‘solution of the bichromate into strong H,SO,, with constant stirring chromic anhydride, CrO;, commonly called chromic acid, is obtained on cooling in the form of fine crimson needles (sp. gr. 2:82), which must be freed from the mother-liquor by absorption on a porous plate, since they are very soluble in water and are reduced, even by filter-paper, to the green oxide Cr,0,;; the crystals deliquesce in air. The anhydride melts at 190° and decomposes at 250° into Cr,0, + 30. The acid H,CrO,, of which the chromates appear to be the salts, is not known. Potassium chromate, K,0.CrO, or K,CrO,, is formed by adding potassium carbonate to the red solution of the bichromate until its red colour is changed to a fine yellow, when it is evaporated and allowed to crystallise. It forms yellow prismatic crystals (sp. gr. 2-7) isomorphous with those of potassium sulphate, and is five times as soluble in water as the bichromate is, yielding an alkaline solution, which is partly decomposed by evaporation, with formation of the bichromate. Acids, even carbonic, change its solution from yellow to red, from production of bichromate. It becomes red when heated, and yellow again on cooling, and fuses without decomposition. Potassium chromate has been found in some yellow samples of saltpetre from Chili. No compound corresponding with KHSO, is known. Potassium trichromate, K,0.3CrO3: red crystals formed by adding HNO; to K,Cr,07. Barium chromate, BaCrO,, is used in painting, as yellow ultramarine, being preci- pitated by potassium chromate from barium chloride ; it is insoluble in acetic acid. 1,000,000 parts of H,O dissolve 15 parts of BaCrO, at 18°. Chrome yellow is the lead chromate, PbCrO4, prepared by mixing dilute sclutions of lead acetate and potassium chromate. The precipitate is insoluble in acetic acid. it is largely used in painting and calico-printing, and by the chemist as a source of oxygen for the analysis of organic substances, since, when heated, it fuses to a brown mass, which evolves oxygen at a red heat. In prismatic crystals it forms the rather rare red lead ore of Siberia, in which Cr was first discovered. CHROME ALUM 467 Orange chrome is a basic lead chromate, PbCrO,.PbO, and may be obtained by boiling the yellow chromate with lime ; 2(PbCrO,) + CaO = PbCrO,.PbO + CaCrO,, The calico-printer dyes the stuff with yellow chromate of lead, and converts it into orange chromate by a bath of lime-water. Chrome orange is also made by precipitating a lead salt with a weak alkaline solution of potassium chromate, which gives a mixture of the two chromates of lead. Silver chromate, AgsCrO4, is obtained as a red crystalline precipitate when AgNO, is added to K,CrO,. When K,Cr,0, is added gradually to AgNOg, a scarlet precipitate of silver bichromate, Ag.Cr20,, is obtained ; and if this be boiled with water, it leaves Ag,CrO, in dark green crystals, which become red when powdered. The colour of the ruby (crystallised alumina) appears to be due to the presence of a small proportion of chromic anhydride. Chromic oxide, Cr,03, is valuable as a green colour, especially for glass and porcelain, since it is not decomposed by heat. Being extremely hard, it is used in making razor-strops. It is prepared by heating K,Cr,0, (4 parts) with starch (1 part), the carbon of which removes oxygen, leaving a mixture of Cr.O, and K,CO,, the latter of which may be removed by washing with water. If sulphur be substituted for the starch, K,SO, will be formed, which may also be removed by water. When hydrated chromic oxide is strongly heated, it loses its water and exhibits a sudden glow, becoming darker in colour, and insoluble in acids which previously dissolved it easily ; in this respect it resembles alumina and ferric oxide. Like these oxides, the chromic oxide is a feeble base ; it is remarkable for forming two classes of salts, having the same composition, but differing in the colour of their solutions and in some other properties. Thus, there are two modifications of the chromic sulphate—the green sulphate, Cr,(SO,)3.6Aq, and the violet sulphate, Cr,(SO,4)3.9Aq. The solution of the latter conducts electricity well and gives the reactions of a sulphate, but when boiled it becomes green, conducts badly, and gives no precipitate with BaCl,. Chrome alum forms dark purple octahedra (KCr’’’(SO,),.12Aq) which contain the violet modifica- tion of the sulphate ; and if its solution in water be boiled, its purple colour changes to green, and the solution refuses to crystallise1 It is obtained as a secondary product in certain chemical manufactures, and may be prepared by the action of SO, on a mixture of potassium bichromate and sulphuric acid; K,Cr,0, + H,SO, + 380, = 2KCr(80,), + H,0. The anhydrous chromic sulphate forms red crystals, which are insoluble in water and acids. Guignet’s green, used in painting and calico-printing, is hydrated Cr.03, prepared by heating K,Cr,0, with 3 parts of boric acid (when oxygen is evolved) and washing the product until it is free from potassium borate; it generally retains a little boric acid, perhaps as chromic borate. Cr,03 combines with the oxides of the magnesium group of metals to form very insoluble and infusible compounds, crystallising in octahedra, eg. ZnO.Cr,03, MnO.Cr,0,, FeO.Cr203, which have been termed chromites, and are isomorphous with the spinels (p. 424). Crystallised Cr.03 (sp. gr. 5:2), prepared by passing chromyl chloride (p, 468) through a red-hot tube, is isomorphous with Al,O3 and Fe,03. Chromic hydroxide, Cr.(OH)g, is thrown down by alkalies from solutions of chromic salts, such as chrome alum, as a greenish-blue precipitate. It dissulves sparingly in ammonia to a pink solution, from which chromic oxide is precipitated by boiling. Potash dissolves it to a fine green solution, which becomes gelatinous when boiled, from precipitation of chromic oxide. It yields a hydrosol by the dialysis of its solution in CrCl. "Ghnotidtiin dioxide, CrOz. When K,Cr,0, is reduced by NO or sodium thiosulphate, a brown precipitate is obtained ; this is a compound of water with CrO,, which is left, on heating to 250°, as a black powder, evolving oxygen at 300°, becoming Cr,03. It may be regarded as chromic chromate, Cr.03.CrO3(=3CrOz2). 1 Exposure to cold, it is said, again converts it into the crystallisable violet form. 468 CHROMIUM CHLORIDES Chromous oxide, CrO, is not known in the pure state, but is precipitated as a brown hydrate when chromous chloride is decomposed by potash. It absorbs oxygen even more readily than ferrous oxide does, becoming converted into CrO .Cr,.03, corresponding in composition with the magnetic oxide of iron. Chromous oxide is a feeble base ; a double sulphate, KpCr’“(SO4)2.6Aq, is known, isomorphous with the corresponding iron salt, KgFe’(SO4)2.6Aq ; it has a blue colour, and gives a blue solution, which becomes green when exposed to air. Perchromic acid, H,CreOg, is believed to exist in the blue solution obtained by the action of H,O, upon solution of chromic acid, but neither the acid nor its salts have been obtained in a separate state (p. 144). A sodiwm perchromate, NagCr20,, .28H,0, crystallises from a solution made by adding Na,O, to a thin paste of Cro(OH)¢ in water. Acids decompose it, the blue colour of perchromic acid being first produced. Chlorides of Chromium.—The chromic chloride, CrCl3, is obtained as vapour by passing dry chlorine over a mixture of Cr,0, with charcoal, heated to redness in a glass tube ; it condenses upon the cooler part of the tube in shining leaflets, having a fine violet colour. When heated in air, it is decomposed, evolving Cl, and leaving Cr,03. Very soluble green crystals of CrCl,;.6Aq may be obtained, but the water cannot be expelled without decomposing the chloride. Cold water does not affect violet CrCl,, but boiling water slowly dissolves it to a green solution resembling that obtained by dissolving Cr.0; in HCl. If a little chromous chloride be added to water in which CrCl, is suspended the latter dissolves quickly and with evolution of heat, yielding the green solution, which becomes violet after some time. Only two-thirds of the Cl is precipitated from the green solution by AgNO, when this is first added. Chromous chloride, CrCly, is obtained by heating CrCl; in hydrogen. It is white and dissolves in water to form a blue solution, which absorbs oxygen from the air, becoming green. A solution of chromic chloride or.sulphate, mixed with HCl, is reduced to chromous chloride by metallic zinc, the liquid becoming greenish blue and giving a pink precipitate of chromous acetate on addition of ammonium acetate, becoming blue when shaken with air. Chromous chloride resembles ferrous chloride in absorbing NO to form a brown compound. Chromyl chloride, CrO,Clz, or chromic oxychloride, formerly called chlorochromic acid, bears the same relation to CrO, that sulphuryl chloride, SO.Clp, bears to SO3. It is a brown-red liquid (sp. gr. 1-92, b.-pt. 118°), obtained by distilling 10 parts of NaCl and 17 of K,Cr.0,, previously fused together and broken into fragments, with 40 parts of oil of vitriol : K,Cr,0, + 4NaCl + SH,S0, = K,SO, + 2Na,SO, + 3H,O0 + 2Cr0,Cl. It much resembles bromine in appearance, and fumes very strongly in air, the moisture of which decomposes its red vapour; CrO,Cl, + 2H,O = H,CrO, + 2HCl. Itisa very powerful oxidising and chlorinating agent, and inflames ammonia and alcohol when brought in contact with them. It is occasionally used to illustrate the nature of illu- minating flames ; for if hydrogen be passed through a bottle containing a few drops of it, the gas becomes charged with its vapour, and, if kindled, burns with a brilliant white flame, which deposits a beautiful green film of chromic oxide upon a cold surface. When heated, in a sealed tube, to 190°, it is converted into a black solid body, according to the equation 3CrOgClp = 2Cl, + CrCl,.2CrO3. When K,Cr,0, is gently warmed with HCl, the solution deposits red prisms of KClCrO;, formerly known as potassium chloro- chromate, which may be regarded as CrO,Cl(OK), being derived from the at present unknown Cr0,Cl(OH), corresponding with SO,Cl(OH). Chromic sulphide, Cra83, is formed when H,8 is passed over chromic oxide heated to redness. It forms black lustrous scales resembling graphite. By fusing Cr.(OH), with Na,CO, and sulphur, sodium thiochromite, NagCro8,, is obtained as a dark red body insoluble in water, and not easily attacked by HCl or H,S0,. Thiochromites of other metals have also been obtained. Chromium salts form a series of amines analogous to the cobaltamines (p. 458). Chromium is nearly allied to iron by its property of forming chromous and chromic salts, and to manganese through the chromates which corre- REVIEW OF THE IRON SERIES 469 spond and are isomorphous with the manganates, and rival them in colour. Soluble chromium compounds are very poisonous. Review of the Iron Series of Metals.—Many points of resemblance will have been noticed in the chemical history of these metals. Their atomic weights are very close together. They are all capable of decomposing water at a red heat, and easily displace hydrogen from hydrochloric acid. Each of them forms a base of the type MO, and these oxides produce salts which have the same crystalline form. All these oxides, except that of nickel, easily absorb oxygen from the air, and aré converted into sesquioxides, M,0,. The sesquioxide of nickel is very feebly basic, whilst that of cobalt is slightly more basic ; the sesquioxide of manganese is a stronger base, and the basic properties of the sesquioxides of chromium and iron are very decided. Nickel does not exhibit any tendency to form a well-marked acid oxide, but the existence of an acid oxide of cobalt is suspected ; and iron, manganese, and chromium form undoubted acid oxides of the type MO,. Nickel is known to form only one compound with chlorine ; cobalt and manganese form, in addition to their protochlorides, very unstable perchlorides known only in solution, but iron and chromium form very stable volatile perchlorides. The metals composing this group are all divalent in their protoxides and the corresponding salts, and are found associated in natural minerals ; this is especially the case with iron, manga- nese, cobalt and nickel. They all require a very high temperature for their fusion. Iron and chromium connect this group with aluminium, their sesquioxides being isomorphous with alumina, and their perchlorides volatile, like aluminium chloride. In the Periodic Table (p. 8) Cr falls in Group VI, since its highest salt-forming oxide is CrO,; Mn forms salts corresponding with Mn,O, (permanganates), and is therefore in Group VII ; Fe, Co, and Ni are placed in Group VIII, although the characteristic oxides have yet to be discovered. CHROMIUM (SIXTH) GROUP. CHromium (p. 465), MotyppEenum, Tunesten, Uranium. MOLYBDENUM, Mo = 96.0. Tuts metal derives its name from podvSava, lead, on account of the resemblance of its chief ore, molybdenite, to black lead. Molybdenite, or molybdenum glance, is the disulphide, MoS,, and is found chiefly in Bohemia, Italy, and the United States ; it may be recognised by its remarkable similarity to plumbago, and by its giving a blue solution when boiled with strong sulphuric acid. It is chiefly employed for the prepara- tion of ammonium molybdate, which is used in testing for phosphoric acid. For this purpose the disulphide is roasted in air at a dull red heat, when SO, is evolved, and molybdic anhydride, MoO3, mixed with oxide of iron is left. The residue is digested with strong ammonia, which dissolves the former as ammonium molybdate obtain- able in prismatic crystals (NH,HMo0Q,) on evaporation. When excess of ammonium molybdate is added to a phosphate dissolved in dilute nitric acid, a yellow precipitate of ammonium phosphomolybdate+ is produced, containing molybdic and phosphoric acids combined with ammonia, by the formation of which very minute quantities of phosphoric acid can be detected. If HCl be added in small quantity to a strong solution of ammonium molybdate, the molybdic acid is precipitated, but it is dissolved by an excess of HCl, and if the solution be dialysed, the molybdic acid, HgMoQ,, is obtained in the form of an aqueous solution which reddens blue litmus, has an astringent taste, and leaves a soluble gum-like residue when evaporated. Besides this simple acid, salts of many ecmplex acids are known, recalling the polysilicates. Molybdic anhydride (sp. gr. 4-50) fuses at a red heat to a yellow glass, and may be sublimed in a current of air in shining needles. In contact with dilute HCl and Zn it is converted into a blue compound of the vomposition MoO,.2Mo00; (molybdenum molybdate), which is soluble in water, but is precipitated on adding a saline solution. Molybdate of lead, PbMoO,, is found as a yellow crystalline mineral (Wulfenite). When MoQ, is heated in hydrogen it is successively reduced to MoO, and MoO, and finally to metal. The molybdic oxide, MoOg, is basic, and forms dark red-brown salts. Molybdous oxide, MoO, is obtained by adding an alkalito the solution made by the prolonged action of Zn uponan HCl solution of molybdic acid. It is a black, basic oxide which absorbs oxygen from the air. Metallic molybdenum is obtained by methods similar to those described for chro- mium. It is a white, very hard, lustrous metal. Itssp. gr. is 9-01, and its melting-point is 1800°-2000°. At 600° it oxidises slowly in air and volatilises as MoOg ; it is also attacked by halogens at this temperature, but not violently. It decomposes steam when hot and is oxidised by hot strong H,SO,, by nitric acid and by fused alkalies from which it evolves H, but it isnot attacked by HCl. The resemblance to iron extends to its relation to carbon, with which it may be combined by cementation (p. 448) to form a metal of steely properties, capable of being tempered by quenching from 300°. With a larger proportion of carbon it forms a metal capable of being cast, and containing the carbide Mo,C ; the sp. gr. of such metal is about 8-7. When heated in chlorine Mo yields molybdenum pentachloride, MoCl;, which forms a red vapour, and condenses in crystals resembling iodine, soluble in water. A sub- chloride, Mo3Clg, trichloride, MoCls, tetrachloride, MoCl,, and several oxychlorides are also known. The trisulphide, MoS;, and tetrasulphide, MoS,4, of molybdenum are soluble in alkali sulphides. In addition to the natural sources of molybdenum above mentioned, there may be noticed molybdic ochre (impure MoO ;), and the difficultly fusible masses called bear, from the copper works in Saxony, which contain a large amount of molybdenum combined with iron, copper, cobalt and nickel. Molybdenum has been detected in the mud deposited by the Buxton thermal water. 1 Its composition varies with the conditions ; it is commonly 6NH,.P,0,.24Mo0O;. 470 TUNGSTEN COMPOUNDS 471 TUNGSTEN, W = 184.0. Tungsten is chiefly found in the mineral wolfram, which occurs, often associated with tin-stone, in farge brown shining prismatic crystals, which are even heavier than tin-stone (sp. gr. 7-3), from which circumstance the metal derives its name, tungsten, in Swedish, meaning heavy stone. The symbol (W) used for tungsten is derived from the Latin name wolframium. Wolfram contains the tungstates of iron and man- ganese in variable proportions, and may be regarded as an isomorphous mixture of tungstates of iron and manganese, (MnFe)WO,. Scheelite, tungstate of calcium, CaWO,, and a tungstate of copper are also found. Sodium tungstate, Na,.WO,.2H,0, is employed by calico-printers as a mordant, and is sometimes applied to muslin in order to render it non-inflammable. It is obtained by fusing wolfram with Na,CO,, an operation to which tin ores containing this mineral in large quantity are sometimes submitted previously to smelting them. Water extracts the sodium tungstate, which may be crystallised in rhomboidal plates. When a solution of this salt is mixed with an excess of hydrochloric acid, white hydrated tungstic acid, H,WO,.Aq, is precipitated, while hot solutions give a yellow precipitate of H,WO,; but if dilute HCl be carefully added to a 5 per cent. solution of sodium tungstate in sufficient proportion to neutralise the alkali, and the solution be then dialysed (p. 281), the NaCl passes through, and a pure aqueous solution of tungstic acid is left in the dialyser. This solution is unchanged by boiling, and when evaporated to dryness, vitreous seales, like gelatine, are left, which adhere very strongly to the dish, and redissolve in one-fourth of their weight of water, forming a solution of the very high specific gravity 3-2, which is, therefore, able to float glass. The solution has a bitter and astringent taste, and decomposes NagCO, with effervescence. It becomes green when exposed to air, from the deoxidising action of organic dust. When tungstic acid is heated it loses water, and becomes of a straw-yellow colour, and insoluble in acids. There are at least two modifications of tungstic acid, which bear to each other a relation similar to that between stannic and metastannic acids (g.v.). Barium tungstate has been employed as a substitute for white lead in painting. The most characteristic property of tungstic acid is that of yielding a blue oxide (WO,.2WO;) when placed in contact with HCl and metallic zine. A very remarkable compound containing tungstic acid and soda is obtained when sodium ditungstate, NagW.07.4H.0, is fused with tin. If the fused mass be treated with strong KOH, to remove free tungstic acid, washed with water, and treated with HCl, yellow, lustrous, cubical crystals (sp. gr. 6-6), probably NagO.WO,..2W0Os3, are obtained, which are remarkable, among sodium compounds, for their resistance to the action of water, of alkalies, and of all acids except HF, and among salts for their conduc- tivity for electricity. This salt is called gold- or saffron-bronze. The corresponding potassium salt is violet- or magenta-bronze. The tungstoborates are remarkable salts, containing WO, and B,O;, combined with metallic oxides. Their solutions have a very high specific gravity ; that of cadmium tungstoborate has the sp. gr. 3-6, and is used for mechanically separating minerals of different specific gravities. Thus, a diamond (sp. gr. 3-5) would float ; whilst a white sapphire (sp. gr. 4-0) would sink in the solution. Tungstosilicates also exist. Tungsten trioxide (twngstic anhydride), WOg, is a powder (sp. gr. 6-34) obtained by decomposing metallic tungstates with HNO;, and heating the tungstic acid thus precipitated. It is orange when hot and yellow when cold. The tungsten dioxide, WO, appears to be an indifferent oxide, and is obtained by reducing tungstic anhydride with hydrogen at a low red heat, when it forms a brown powder, which is dissolved by boiling in solution of potash, hydrogen being evolved, and potassium tungstate formed. Tungsten trioxide can be reduced to metallic tungsten by carbon or hydrogen at a high temperature. The product remains a powder, however, owing to the very high melting-point (about 3000°) of the metal. It can be melted in the clectric furnace and the massive tungsten thus obtained is iron grey and of sp. gr. 18-7. The main application of the metal is for hardening steel, for which purpose the metallic powder (about 5 per cent.) may be introduced into the molten steel. For its other application, namely, as filaments for electric incandescent lamps, an alloy of tungsten and some 472 URANIUM 2 or 3 per cent. of nickel is first produced by reducing a mixture of the oxides ul u temperature above the melting-point of nickel. This alloy is drawn into filaments, which are then heated by passage of electric current through them until the nickel has been volatilised. The metal is attacked slowly by strong mineral acids. When tungsten is heated in chlorine, the tungstic chloride, WCl,, sublimes in bronze-coloured needles. When gently heated in hydrogen, it is converted into the tetrachloride, WCl,, but if its vapour be mixed with hydrogen and passed through a glass tube heated to redness, metallic tungsten is obtained in a form in which it is not dissolved even by aqua regia, though it may be converted into potassium tungstate by potassium hypochlorite mixed with potash in excess. WCl, is also obtained in steel-blue needles, together with WOC], and WO,Cl, by the action of PC]; on WOs. By action of HF at low temperatures, WClg yields WF, tungsten hexafluoride, a very active gas, distinguished by being the heaviest gas known. Tungsten disulphide, WSo, is a black crystalline substance rescmbling plumbago, obtained by heating a mixture of potassium ditungstate with sulphur, and washing with hot water. Tungsten trisulphide, WSs, is a sulphur-acid, obtainable as a brown precipitate by dissolving tungstic acid in an alkaline sulphide, and precipitating by an acid. Both MoO, and WO; form a number of complex salts with the alkali oxides and the pentoxides of As, Pand V. These are the tungsto- and molybdo- arsenates, phosphates, and vanadates. URANIUM, U = 238.5. This metal occurs in the pitchblende, UO,.2U0Oy (sp. gr. 7:2), of Cornwall. It is not used in the metallic state, but in the form of the black oxide, UO..UOs3, and of sodium uranate, Na,U,07.6H,O (uranium yellow), for imparting black and yellow colours respectively to glass and porcelain.t The latter compound is prepared from pitchblende by roasting the mineral with lime, decomposing the calcium uranate thus formed with sulphuric acid, and treating the solution of uranyl sulphate with sodium carbonate. ‘This precipitates the foreign metals and the Na,U,0,, which redissolves in the excess of sodium carbonate, and is precipitated by neutralisation with sulphuric acid and boiling. Uranium forms two oxides, UO», a basic oxide known as uranyl, and UOg, an acid oxide. Pitchblende (the green oxide) and the black oxide may be regarded as uranyl diuranate and uranyl uranate respectively. A remarkable characteristic of uranium is that it does not form salts which can be regarded as acids wherein U has displaced H, but always forms salts of the type UO.X, or U(OH),X5. This gave rise to the original mistake by which UO, was believed to be metallic uranium. Of the uranyl (also called uranic) salts, the nitrate, UO(NO3)2.6H,O, and acetate, UO,Aco.2H,0, are used as laboratory reagents, and in photographic printing, for which they are fitted by the fact that they are reduced by light in contact with organic matter to uranous salts, corre- sponding with the base, UO. These latter salts have been but little studied, but they give a brown precipitate with potassium ferricyanide, by which means the photographic print may be developed. Some organic salts of uranyl are decomposed by light without reduction ; thus the oxalate in water evolves CO and COs, leaving a precipitate of uranyl hydroxide, UO2(OH)o. Sodium peruranate, NagUO,.10H,0, is obtained by the addition of sodium peroxide to a solution of a uranyl salt. Uranium tetrachloride, UCl, (which is volatile, so that its vapour density is known), and uranyl chloride, UO2Cle, have been prepared. UCI, and UCI, are also known. Metallic uranium is prepared by reducing UC], with sodium. It is white and malleable ; sp. gr. 18-685 ; dissolves in acids evolving hydrogen. When reduced from the oxide by carbon it contains 5 to 13 per cent. of C, is very hard, and melts at a tem- perature higher than the melting-point of platinum ; the carbide which it contains decomposes water at the ordinary temperature, yielding hydrocarbons. The phenomenon of radioactivity (p. 356) was first observed in uranium salts. a-, 3-, and y-rays are emitted, the a-rays being due to uranium itself and the others to its disintegration product uranium X, which can be separated from the uranium 1 “ Uranium glass” exhibits a strong greenish-yellow fluorescence, REVIEW OF THE CHROMIUM GROUP 473 salt solution by adding excess of ammonium carbonate, whereupon traces of a radio- active precipitate remain undissolved. It appears that the uranium atom loses two a-particles and becomes uranium X, the average life of which is 35-5 days, that of uranium being 8 x 109 years. What becomes of uranium X is still a matter of investigation, but, as stated at p. 401, it probably passes through one or more intermediate stages into ionium and radium. Review of the Chromium Group of Metals.—The members of this group, chromium, molybdenum, tungsten, and uranium, exhibit great similarity in their tendency to form acid oxides of the type RO,, and oxy- chlorides of the type RO,Cl,. “They also enter into the composition of many complex salts analogous to the phosphomolybdates and the borotungstates. Sulphur, selenium, and tellurium belong to the same group, and form oxyacids of the same type. ANTIMONY (FIFTH) GROUP. . Vanapium, Niopium, Antimony, Tantalum, Bismurs. BISMUTH, Bi=208.o0. Bismutu, though useful in various forms of combination, is too brittle to be employed in the pure metallic state. It is readily distinguished from other metals by its peculiar reddish lustre and its highly crystalline structure, which is very perceptible upon a freshly broken surface; large rhombo- hedra of bismuth are easily obtained by melting a few ounces in a crucible, allowing it to cool till a crust has formed upon the surface, and pouring out the portion which has not yet solidified, when the crystals are found lining the interior of the crucible. It is isomorphous with antimony. It is some- what lighter than lead (sp, gr. 9:78), more fusible (m.-pt, 268°), and more volatile at high temperatures. It is less volatile than antimony, and burns like it in air. Unlike most other metals, bismuth is found chiefly in the metallic state, disseminated in veins, through gneiss and clay-slate. The chief supply is derived from the mines of Schneeberg, in Saxony, where it is associated with the ores of cobalt. Native bismuth, together with the oxides and sulphides, is found abundantly in Bolivia and Australia, accompanied by tin-stone and sometimes by silver and gold. Formerly the metal was extracted from the masses of earthy matter through which it is distributed by simply heating the broken ore until the bismuth flowed away from the gangue. Now, the crushed ore is roasted to expel S and As and then smelted in a reverberatory-furnace with iron oxide, soda, lime, slags from a previous smelting, and coke. The bismuth forms a layer beneath the slag and is tapped. To refine it, the bismuth is melted and exposed to air, when the impurities oxidise first and are removed as dross. Commercial bismuth generally contains arsenic, copper, sulphur and silver; silver is sometimes removed by fractional crystallisation of the molten metal, bismuth rich in silver crystallising first (cf. Pattinson’s process) ; when lead is present instead of silver, pure bismuth crystallises first. Pure bismuth dissolves entirely and easily in dil. HNO, isp. gr. 1-2); but if it contains arsenic, a white deposit of bismuth arsenate is obtained. HCl and dil. H,SO, will not attack bismuth. The chief use of bismuth is in the preparation of certain alloys with other metals. Some kinds of type metal and stereotype metal contain bismuth, which confers upon them the property of expanding in the mould during solidification, so that they are forced into the finest lines of the impression. This metal is also remarkable for its tendency to lower the fusing-point of alloys, which cannot be accounted for merely by referring to the low fusing-point of the metal itself. Thus, an alloy of 2 parts bismuth, 1 part lead and 1 part tin fuses below the temperature of boiling water, although the most fusible of the three metals, tin, melts at 232°. An alloy of this kind is used for soldering pewter. Wood’s fusible alloy consists of 4 of Bi, 2 of Pb, 1 of Sn and 1 of Cd; it melts at 60-5°. Bismuth is also employed, together with antimony, in the construction of thermo-electric piles. Oxides of Bismuth.—There are two oxides of well-established com- position, BiO and Bi,O,; two others are generally described as being 474 BISMUTH OXIDES 475 Bi,O, and Bi,O;, but there is some doubt whether these formule are correct. Bismuth suboxide, BiO, is a black powder obtained by heating bismuth oxalate in CO.. When bismuthic chloride mixed with stannous chloride is added to an excess of potash, a black precipitate is obtained, alleged by some to be the suboxide, by others metallic bismuth. Bismuth oxide, Bi,O;, is the basic and most important oxide. It is formed when bismuth is heated in air, or when bismuth nitrate is decomposed by heat, and is a yellow powder (sp. gr. about 9) becoming brown when heated, and fuses easily. Bismuth oxide forms the rare mineral bismuth-ochre. It is obtained in fine needles by precipitating a boiling solution of a bismuth salt with potash. Bismuthic anhydride, Bi.Os, is formed when Bi,O, is suspended in a strong solution of KOH through which Cl is passed, when « brown substance is formed which, when treated with warm strong HNOg, yields bismuthic acid (HBiO ) as a red powder, which becomes brown at 120°, losing H,O and becoming Bi,O;. When further heated, it loses O and becomes Bi,O, or Bi,O;.Bi,0;. When heated with acids it also evolve s O, and forms salts of Bi,O,. Bismuth hydroxide, Bi(OH),, is obtained as a white precipitate when a caustic alkali is added to a bismuth salt ; it does not dissolve in excess of alkali. Acted on by chlorine in the alkaline liquid, it becomes dark brown HBiO3. It is soluble in glycerin. At 100° it becomes BiOOH. Bismuth oxycarbonate, (BigQ2CO3)2H20, obtained by the interaction of bismuth nitrate and ammonium carbonate, is used in medicine. Bismuthite, which is, next to native bismuth, the most important of the bismuth ores, is composed of 3Bi,0;.CO,.H,O. Bismuth oxide, Bi,O,, is a very feeble base, and the normal salts of the form of BiX, are easily decomposed by water with the production of insoluble basic salts. This is one of the characteristic properties of the salts of bismuth and is illustrated by the preparation of the only two salts of bismuth which are known in the arts, viz. the basic nitrate (trisnitrate of bismuth, or flake-white) and the oxychloride of bismuth (pearl-white). If bismuth be dissolved in nitric acid, it becomes bismuth nitrate, Bi(NO3)., and this may be obtained in prismatic crystals containing 5Aq. If the solu- tion be mixed with a large quantity of water, it deposits a precipitate of flake-white, Bi(NO3)3.2Bi(OH),;, or Bi(OH),NO,, the remainder of the nitric acid being left in the solution ; Bi(NO,), + 2H,O= Bi(OH),NO, + 2HNO,. The basic nitrate, when long washed, becomes Bi(OH),. It is a crystalline powder, which is acid to moist test-paper. It is used as a paint and cosmetic, and in enamelling porcelain ; also in medicine. Pearl-white has the composition 6BiOCl. Aq, and is obtained by dissolving bismuth in nitric acid, and pouring the solution into water in which common salt has been dissolved. Bismuth chloride, BiCl3, distils over when Bi is heated in a current of dry Cl; it is a deliquescent, fusible (m.-pt. 225°), volatile (b.-pt. 447°), crystalline solid (sp. gr. 5-6), easily dissolved by a small quantity of water, but decomposed by much water, with formation of the oxychloride; BiCl; + H,O = BiOCl + 2HCl. This compound is so insoluble in water that nearly every trace of bismuth may be precipitated from a moderately acid solution of the trichloride by adding much water. Bismuth tri-iodide, Bil,, is obtained as a dark brown precipitate (sp. gr. 5-6) when potassium iodide is added to a solution of a bismuth salt. If the solution be dilute or very acid, a red or yellow colour is produced, without precipitation, and if a solution of a lead salt be added to this, a brown or red precipitate of a double iodide of Bi and Pb is produced, which dissolves in hot dilute HCl, and separates in minute crystals, like bronze powder, on cooling. Bil; melts at 439°. Bismuthous sulphide, Bi,Sg, is sometimes found in nature, but more frequently bismuthic sulphide, Bi,S3, or bismuth glance, which occurs in dark grey lustrous prisms 476 ANTIMONY—EXTRACTION isomorphous with native Sb.S3. Bi,S, is also obtained as a brown precipitate by the action of H,S on bismuth salts ; it is not soluble in dil. H,SO, or HCl, but dissolves easily in HNO. Bolivite is an oxysulphide, Bi,S, . Bi,O3. ANTIMONY, Sb = 120.2. Antimony is nearly allied to bismuth in its physical and chemical cha- racters. It is even harder and more brittle than that metal, being easily reduced to powder. Its highly crystalline structure is another very well- marked feature, and is at once perceived upon the surface of an ingot of antimony, where it is exhibited in beautiful fern-like markings (star anti- mony). Its crystals belong to the same system (the rhombohedral) as those of bismuth and arsenic. It is much lighter than bismuth (sp. gr. 6-7), and requires a higher temperature (630°) to fuse it, though it is more easily converted into vapour (b.-pt. 1300°), so that, when strongly heated in air, it emits a thick white smoke, the vapour being oxidised. Like bismuth, it is but little affected by HCl or dil. H,SO,, but HNO, oxidises it, though it dissolves very little of the metal, the greater part being left in the form of oxide. The best method of dissolving antimony is to boil it with HCl and to add HNO,, or some other oxidising agent, by degrees. The metal decomposes steam at a red heat. Antimony is found as metal to some extent in Australia, but occurs chiefly as sulphide, Sb,S,—grey antimony ore or stubnite (sp. gr. 4:6)—- which-is mined in Australia, Borneo, Japan, Germany, France, Italy and Hungary. The ore contains about 50 per cent. Sb and is generally reduced by heating it with iron, which has an affinity for sulphur stronger than that of antimony ; Sb,S, + 3Fe = 3FeS + 28b. The ground ore mixed with refuse iron (such as tin-plate clippings) is heated to fusion in a crucible ; the iron sulphide collects as a fused slag upon the surface of the molten antimony. This regulus of antimony contains about 10 per cent. of iron and is refined by melting it with sufficient Sb,S, to convert the iron into sulphide. To eliminate sulphur and obtain star antimony the product must be fused with an alkali sulphide which dissolves the Sb.83, producing a slag consisting of 3Na28.Sb,8, (crocus of antimony). When the ore is not rich enough for direct fusion with iron it is heated in a crucible in order to melt the Sb.8, (liquation process), so that it may flow away from the gangue and collect at the bottom of the crucible, whence it is tapped ; this concentrated sulphide is called crude antimony. In some places the antimony ore is roasted to convert the bulk of it into oxide, which is then heated with fresh ore, in order that the mixture may undergo “ self- reduction ” ; 2Sb,8,; + 3Sb,0, = 10Sb + 6S8O,. Antimony i is now obtained by leaching the ore with a solution of sodium sulphide, whereby the Sb,§; is dissolved. The solution is then electrolysed, Sb being deposited on the cathode, leaving a solution of sodium sulphide to be used for leaching more ore. When tartar-emetic is strongly heated in a closed crucible, an alloy of antimony and potassium is obtained which decomposes water rapidly, and becomes hot when exposed to air. Zine and iron precipitate antimony from acid solutions as a fine black powder (antimony black or iron black) used for ene plaster casts the appearance of iron or steel. The brittleness of antimony renders it useless in the metallic state, except for the construction of thermc-electric piles, where it is in cenjunc- tion with bismuth. Antimony is employed, however, to harden several useful alloys, such as type-metal, shrapnel-shell builets, Britannia metal, and pewter. Explosive antimony.—The ordinary crystalline form of antimony may be obtained by electrolysing a solution containing about 7 per cent. of antimonious chloride ; but ANTIMONY OXIDES 477 in some cases the antimony is deposited from very strong solutions in a condition having properties very different from those of ordinary antimony. One part of tartar-emetic is dissolved in 4 parts of a strong solution of antimony trichloride, and the solution is slowly electrolysed with Sb anode and Pt cathode. The deposit of antimony which forms upon the cathode has a brilliant metallic appearance, but differs from the ordinary metal. Its sp. gr. is 5-78. If it be gently heated, scratched, or sharply struck, its temperature rises suddenly to about 200°, and it becomes converted into a form more nearly resembling crystalline antimony. At the same time, however, thick fumes of antimony trichloride are evolved, for this substance is always present in this antimony to the amount of 5 or 6 per cent. The evolution of heat amounts to about 19 gram calories per gram of metal. It cannot bo said with certainty that this form of antimony is amorphous, as was originally supposed. Amorphous antimony exists in black and yellow modifications, the former (sp. gr. 5-3) being obtained by cooling antimony vapour rapidly, and the latter by action of chlorine on liquid antimonietted hydrogen at — 100°. Both varieties easily become crystalline antimony when heated. Antimonious oxide, or antimony trioxide, Sb,O,, is formed when antimony burns in air (flowers of antimony), and is made on a large scale by roasting either the metal or the sulphide in air, for use in medicinal antimony preparations and as a white pigment. It is sold as a crystalline powder consisting of rhombic prisms (sp. gr. 5-6) isomorphous with the rarer form of arsenious oxide (p. 228); when this form is slowly sublimed in a non-oxidising atmosphere it condenses as regular octahedra (sp. gr. 5:3) isomorphous with octahedral arsenious oxide. In nature the rhombic form occurs as white antimony ore (valentinite, ewitéle), and the octahedral as senarmontite. It becomes yellow when heated and melts at a dark red heat ; when heated in air it smoulders, becoming oxidised to the tetroxide, Sb,0,, which isinfusible. Sb,O, may be obtained by oxidising antimony with very weak HNO,, or, better, by boiling antimony oxychloride with a strong solution of sodium carbonate ; 4SbOCI + 2Na,CO, = 8b,0, + 4NaCl+2CO,. The oxide is insoluble in water, but strong acids dissolve it, forming salts, though its basic properties are feeble and its salts rather ill-defined. Indeed, salts of the type SbX, are unstable, passing into salts which appear to contain the monatomic group SbO, antimonyl, the most important of which is the organic salt, tartar-emetic, SbO. KC,H,O,(p. 631), made by dissolving Sb,O, in a hot solution of potassium hydrogen tartrate, HKC,H,O,. Towards strong bases Sb,O, behaves like an acid anhydride (antimonious anhydride, cf. N,0,); thus potash and soda dissolve it, forming antimonites. Two crystal- lised sodium antimonites are known, the normal, NaSbO,.6Aq, and the acid, NaSbO,.2HSbO, ; the former is sparingly soluble, the latter almost insoluble in water. Antimony tetroxide, Sb,0,, is important because it is the product of the action of heat upon either Sb,4O, (in air) or Sb,O;, so that antimony is often weighed in this form in quantitative analysis. It is readily obtained by boiling antimony with HNO , evaporating to dryness, and heating the residue to redness. It is yellow while hot, and becomes white on cooling. It is infusible, non-volatile, and of sp. gr. 6-7. Antimony ash, obtained by roasting the grey sulphide in air, consists chiefly of Sb,0,, and is used for preparing other antimony compounds. Thus, tartar-emetic may be obtained by boiling Sb,0, with acid potassium tartrate ; Sb.0, + HKC,H,0, = SbO.KC,H,0, + HSbO, (antimonic acid). This leads to the belief that Sb,O, is really antimonyl antimonate, SbO.SbO3. In some cases, noweyet the oxide behaves as a mixture of Sb,O, and Sb,0,. The presence of Sb,O4 in Sb,O, can be detected by dissolving in HCl sad addr KI, when iodine will be liberated : Sb,0, + 2KI + SHC] = 28bCl, + 2KCl + 4H,0 + I}. 478 ANTIMONIETTED HYDROGEN Antimonic oxide, or antimony pentoxide, Sb,O0;, is formed when anti- mony is oxidised by HNO,, and the product well washed and dried at 280°. It is a yellow powder (sp. gr. 6-5). It will be remembered that As,O; may be obtained in a similar way, but not P,O;. Sb,O; is a pale yellow amor- phous powder, insoluble in water, and decomposed at 300°, leaving Sb,O,. It is dissolved by KOH, forming the antimonate, KSbO3. Three antimonic acids, corresponding with the phosphoric acids, viz. orthantimonic acid, H,SbO,, pyroantimonic acid, H,Sb,O,, and metantimonic acid, HSbOs, are known. Potassium metantimonate, KSbOs, is made by gradually adding 1 part of powdered antimony to 4 parts of nitre fused in a clay crucible. The mass is powdered and washed with warm water to remove the excess of nitre and the potassium nitrite, when the anhydrous potassium antimonate is left; and on boiling this for an hour or two with water, it becomes hydrated, and dissolves. The solution, when evaporated, leaves a gummy mass of the hydrated salt. This dissolves in warm water, and is decomposed by boiling for some time, yielding an acid antimonate, K,Hp(SbOg3)g.9Aq (?). (See also potassium pyroantimonate.) Sodium metantimonate, 2NaSbO,.7Aq, is prepared like the potassium salt. Ammonium metantimonate, NH,SbOs;, is obtained as a crystalline powder insoluble in water, by dissolving HSbO, in warm ammonia. A basic lead antimonate is used in oil-painting as Naples yellow. Potassium pyroantimonate (formerly metantimonate), K,ySb,07, is made by fusing the metantimonate with potash, in a silver crucible; 2KSbO,; + 2KOH = K,8b,0, + H,O. On dissolving in water and evaporating, crystals of the pyroanti- monate are obtained, but water decomposes these into potash and ‘‘ potassium dimet- antimonate,” K,H,Sb.0,.6Aq, which forms a crystalline powder. It is sparingly soluble in cold water, but dissolves in warm water. The solution forms a valuable test for sodium, which it precipitates in the form of NagH,Sb,0,.6Aq. When long kept, the solution of ‘‘ potassium dimetantimonate ”’ becomes converted into metantimonate, which does not precipitate sodium; K,Sb,0, + H,O = 2KSbO, + 2KOH. Acids precipitate metantimonic acid, which dissolves in HCl. Nearly all metallic solutions yield precipitates with the “ potassium dimetantimonate,” so that all other metals must be removed from the solution before testing for sodium. Antimonietted hydrogen, or hydrogen antimonide, SbH;, is obtained, mixed with H, when an alloy of Sb with Zn is attacked by dil. H,SO,. When the gas is passed through a U-tube cooled by liquid air the SbH, solidifies, and by cautiously raising the temperature the solid may be melted (m.-pt. — 91-:5°) and the liquid boiled (b.-pt. —18°) to obtain the pure gas. It is very poisonous, has a characteristic smell, and decomposes at 15° into Sb and H, at a rate depending on the nature of the vessel containing it, and much increased when a little Sb has once deposited. It is endothermic and may be exploded by an electric spark. Oxygen decomposes it even at —90°, yellow antimony (p. 477) being formed ; at 15° the oxidation to H,O and Sb is gradual. Even oxides of nitrogen oxidise the gas at 15° ; with chlorine it explodes ; sulphur decomposes it, forming H,S and orange Sb,8,. Water dissolves one-fifth of its volume, alcohol 15 times, and CS, 250 times its volume, The gas is also produced, mixed with much H, when a solution of an antimony salt (tartar cmetic, for example) is poured into a hydrogen apparatus containing Zn and dilute H,SO, (p. 227). Its production forms the most delicate test for antimony, as in the parallel case of arsenic. The one cannot be mistaken for the other, however, if the following differences be observed. The SbH, burns to Sb,0, and H,O with a greenish flame, which deposits w soot-black spot upon a porcelain crucible lid (Fig. 156). This spot dissolves when a drop of yellow ammonium sulphide is placed on it with a glass rod, and on evaporation gives an orange film of Sb.83. When the tube through which the gas passes is heated to 150° (Fig. 157), metallic antimony is deposited at the heated part, and not beyond ANTIMONY CHLORIDES 479 it, like arsenic. When the gas is passed into silver nitrate, the antimony is precipitated as black silver antimonide ; SbH,; + 3AgNO; = SbAgs + 83HNO, (whereas arsenic passes into solution as arsenious acid, and gives a black precipitate of metallic silver). Chlorine and antimony combine readily, evolving heat and light; the chlorides are among the most important compounds of this metal. Antimony trichloride, or antimonious chloride, SbCl,, may be pre- pared by dissolving powdered antimony sulphide (100 grams) in commercial hydrochloric acid (500 c.c.), adding gradually potassium chlorate (4 grams), filtering from sulphur and distilling. HCl distils first, then a solution of SbCl,, and finally SbCl, itself, which forms white crystals in the receiver. The trichloride is a soft crystalline solid, whence its old name of butter of antimony. lt fuses at 73° and boils at 223°. It may be dissolved in a small quantity of water, but a large quantity decomposes it, forming a bulky white precipitate, which is an oxychloride of antimony (antimonyl chloride) ; SbCl, + H,O = 2HCl + SbOCI; this is a decomposition similar to that which occurs with PCl,, AsCl,, and BiCl,. By long washing, 4SbOCl + 2H,O = 4HCl + Sb,0,. When hot water is added to a hot solution of SbCl, in HCl minute prismatic needles are deposited containing Sb,Cl,0,;, and formerly called powder of Algaroth. The same body.is formed when SbOCI is heated; 5SbOC] = SbCl, + Sb,Cl,0O,. Antimony tri- chloride is occasionally used in surgery as a caustic ; it also serves as a bronze for gun-barrels, upon which it deposits a film of antimony. It is a solvent for many bodies and is used in the cryoscopic determination of molecular weights. It dissolves in several organic solvents. With many salts SbCl, forms double salts—for instance, 3KC1.SbCl, ; hence in presence of alkali chloride water does not precipitate SbOCl from solutions of SbCl,. Antimony pentachloride, or antimonic chloride, SbCl;, is prepared by heating coarsely powdered antimony in a retort, through which a stream of dry chlorine is passed (Fig. 126), the neck of the retort being fitted into an adapter, which serves to condense the pentachloride. The pure penta- chloride is a colourless fuming liquid (sp. gr. 2-346) of a very suffocating odour ; it combines energetically with a small quantity of water, forming a crystalline hydrate, SbCl,.4Aq, but an excess of water decomposes it into hydrochloric and pyroantimonic acids, the latter forming a white precipitate ; 28bCl; + 7H,O = 10OHCI + H,Sb,0,. Pentachloride of antimony is employed by the chemist as a chlorinating agent ; thus, olefiant gas, C,H,, when passed through it, is converted into Dutch liquid, C,H,Clo, and carbonic oxide into phosgene gas, the pentachloride of antimony being converted into trichloride. SbCl, is partially dissociated into SbCl; and Cl, at 140°, and com- pletely at 200°, and can only be distilled in chlorine. It forms many double compounds with both inorganic and organic substances. With HCl it combines to form meta- chlorantimonic acid, HSbCl, ; a number of corresponding salts are obtained by com- bining SbCl, with metal chlorides. SbCl, is the analogue of PCl,, and a chlorosulphide of antimony, SbCI,8, corresponding with chlorosulphide of phosphorus, is obtained as a white crystalline solid by the action of H,S upon SbCl;. Antimonious sulphide, or antimony trisulphide, Sb,85, has been noticed as the chief ore of antimony, The mineral is of a dark grey colour and metallic lustre, occurring in masses which are made up of long prismatic needles. It fuses easily (m.-pt. 555°), and may be sublimed unchanged out of contact with air. This grey crystalline form may be made by gradually introducing a mixture of powdered Sb and § into a red-hot crucible and fusing the mass under a layer of salt. When melted and suddenly cooled the grey variety forms a dark brown or violet amorphous mass of sp. gr. 4-28, which is not a conductor of electricity, whereas the grey form conducts. 480 ANTIMONY SULPHIDES ~The sulphide is easily recognised by heating it, in powder, with HCl, when it evolves the odour of H,S, and if the solution be poured into water it deposits a second amotphous form as an orange precipitate (p. 152). This orange sulphide (sp. gr. 4:12), which is a compound of Sb,S, with water, is also obtained by adding H,§ to a solution of a salt of antimony acidified with HCl. It may be converted into the grey sulphide at 210°, and becomes black when boiled with HCl in a current of CO,. The orange variety consti- tutes the untimony vermilion (p. 172). Native Sb,S, is employed, in conjunc- tion with potassium chlorate, in the friction-tube for firing cannon ; it is also used in percussion caps, together with potassium chlorate and mercuric fulminate. Its property of deflagrating with a bluish-white flame, when heated with nitre, renders it useful in compositions for coloured fires. The molten sulphide is a good solvent for other metal sulphides. Glass of antimony is a transparent red mass obtained by roasting the sulphide in air and fusing the product ; it contains about 8 parts of oxide and 1 part of sulphide. Itis used for colouring glass yellow. Red antimony ore is an oxysulphide of antimony, Sb,0,.2Sb,8,. Antimonic sulphide, or antimony pentasulphide, Sb,S;, is obtained as a bright orange-red precipitate by the rapid action of H,8 upon a solu- tion of pentachloride of antimony in HCl; it is decomposed by heat into Sb,8, and 8,. When boiled with hydrochloric acid, Sb.8; + 6HCl = 28bCl, + 3H.S + 8,, showing the trivalence of antimony to be stronger than the pentavalence. It is prepared on a large scale under the name of golden sulphuret of antimony by boiling Sb,S8, with KOH and 8, and adding acid to the solution of potassium thioantimonate (liver of antimony) thus obtained. It is used for vulcanising india-rubber. When H,§ acts slowly on SbCl, a mixture of Sb.S;, Sb.83, and § is obtained. In presence of CrCl, more Sb,83 is formed. When exposed to light under water or boiled with water, Sb.S; yields black crystalline Sb.8, and S. Both Sb,8; and Sb,S, are dissolved by the alkali sulphides, forming thiometanti- monites (from HSbS8,) and thioantimonates (from H,SbS,) respectively. Thus, like the sulphide of arsenic, they dissolve in alkalies, yielding the appropriate oxy-salts and thio-salts ; for example, 28b,8; + 4KOH = 3KSbS, + KSbO, + 2H,0, and 48b.8,; + 24KOH = 5K,SbS, + 3K,SbO, + 12H,0. When the solutions are acidified, all the Sb is precipitated again as sulphide. Even metallic antimony in powder is dissolved when gently heated with solution of potassium sulphide in which sulphur has been dissolved, any lead or iron which may be present being left in the residue, so that the antimony may be tested by this process as to its freedom from those metals. Mineral kermes is a variable mixture of oxide and sulphide of antimony, which is deposited as a reddish-brown powder from the solution obtained by boiling Sb.S 3 with potash or soda. It was formerly much valued for medicinal purposes. Kermes was the Arabic name of an insect used in dyeing scarlet. Schlippe’s salt is the sodium thioantimonate, Na,SbS,.9H,O, and may be obtained in fine transparent tetrahedral crystals by dissolving Sb,S, in NaOH and adding sulphur. This salt is sometimes used in photography. Antimonious sulphate, Sbe(SO,z)3, is formed when antimony is boiled with strong H,80,. It crystallises in needles, which are decomposed by water into a soluble sulphate and an insoluble basic sulphate. VANADIUM,! V = 51.0. Compounds of this metal are widely distributed, occurring in many minerals in proportions less than 0-5 per cent. The workable ores, however, are not very numerous : vanadinite, 3Pb3(VO4)2.PbCl, (Cheshire, Russia); roscoelite, a vanadium-aluminium silicate ; descloisite, a vanadate of lead (Mexico, Chili); and the vanadium sulphide of Peru are the chief ores. The extraction from the ore depends on the fact that the 1 Vanadis, a Scandinavian deity. VANADIUM COMPOUNDS 48] vanadium oxide present in the ore or produced by roasting it is easily converted into sodium vanadate by fusion, or even leaching, with soda ; this salt is dissolved in water, neutralised, and treated with a salt of Ba, Fe or Pb, to precipitate the corresponding vanadate. By treatment with acid the vanadate yields vanadic anhydride, V.O;, which is the chief commercial product ; it may be purified by dissolving in NH, and crystallising the ammonium metavanadate, NH,VO3, and decomposing this by heat, when the anhydride is left as a brick-red, fusible solid (m.-pt. 658°), which crystallises on cooling, and dissolves sparingly in water to a yellow solution. Much vanadic anhydride is prepared from the slag of the Creusot steel works, which contains about 2 per cent. of it. Metallic vanadium is not made on a large scale ; small quantities are made by heating rods made of a plastic mixture of V0, and paraffin in powdered charcoal and then passing an electric current through the rod in a vacuum. It is silver white, sp. gr. 5-5, m.-pt. 1680°. It is insoluble in HCl, but soluble in HNO,. Fused NaOH converts it into sodium vanadate. It is not oxidised by air and does not decompose water. Although undoubtedly belonging to the fifth periodic group, vanadium shows a more extended range of valency than the other elements of the group. VCle, VCls, and VCl, are known, and though VCl,; has not been prepared, the oxychloride, VOCs, is a fuming yellow liquid (vanadyl trichloride). This variable valency of vanadium gives rise to an extensive series of compounds, for which, as well as for other features of this most interesting element, a more complete treatise than the present must be consulted. The lowest oxide, VO, vanadyl, was originally mistaken for the metal ; it is a heavy black powder made by reducing VOCI,;, and is basic, dissolving in dilute acids to lavender-blue solutions. These vanadous salts rapidly absorb oxygen to form vanadic salts and are powerful reducing agents. The production of blue compounds by the action of reducing agents in solutions containing vanadium forms a test for the metal. The most delicate test is H,O., which gives a red-brown colour to a solution containing vanadium. V.03 is a black crystalline body resembling plumbago, and capable of conducting electricity, obtained by heating vanadic anhydride in a current of hydrogen ; it is insoluble in acids, and combines with bases to form vanadites, RVO . V2.0, is produced when V,0, is heated in air ; it dissolves in acids forming salts of vanadyl, VO, which are mostly blue, and in alkalies forming hypovanadates, RyV4O9. Vanadic anhydride, V,0;, forms purple and green compounds with the above oxides. Meta- vanadic acid, HVOs, crystallises in beautiful golden scales. Ammonium metavanadate is used as an oxygen-carrier for blacks in calico-printing, in conjunction with chlorates and aniline hydrochloride. In addition to VOCI, already mentioned, the oxychlorides, V,0,Cl, VOCI, and VOC, have also been obtained. There are two vanadium nitrides, VN and VNo. A series of vanadium alums of the type M’,S0,. V2(SO4)3. 24H20 is known. Vanadium enters into certain useful alloys, being generally reduced for the purpose from V.O; in contact with the other metal (e.g. steel) in an electric furnace. Vanadium compounds are very poisonous. NIOBIUM,? Nb = 93.5, and TANTALUM, Ta = 181.5. These metals occur together as niobates and tantalates respectively in several rare minerals, of which columbite and tantalite, found chiefly in the United States, are the most important and consist of mixed niobates and tantalates of iron and manganese, the niobate preponderating in columbite and the tantalate in tantalite. By fusing the mineral with KHSO,, treating with water, digesting the insoluble residue with (NH,).5 (to remove Sn and W), and with HCl to remove FeS, a mixture of Nb 20; and Ta,0; is obtained. This is dissolved in HF, and KHF, is added ; on concentrating, K,TaF, crystallises first, and is followed by K,NbOF; ; each yields the corresponding pentoxide when boiled with much water. Niobium (or columbiwm) is obtained by heating rods made of Nb,O,, paraffin, and carbon powder to about 1700° to reduce the oxide to Nb,O, ; the rods are then heated 1 Niobe, daughter of Tantalus, 31 482 TANTALUM in a vacuum with an alternating electric current to dissociate the oxide and leave a dull grey mass of niobium. It melts at 1950°; sp. gr. 12-7; fairly ductile ; not so hard as soft steel ; malleable ata redheat. It is stable in air at ordinary temperature and only partially oxidises when heated. Even aqua regia does not attack it, HF being the only solvent for it. Fused alkalies or KNO, dissolve the metal to form niobate. It does not tend to form alloys, except one with Fe, which is very hard. Tantalum is nowa commercial product for making electric lamp filaments. K,TaF, is heated with sodium, yielding a metallic powder containing oxide ; this is purified by pressing it into the form of rods, which are heated in a vacuum in the electric arc, whereby the oxide is volatilised. The pure metal is silver grey, very ductile, sp. gr. 16-64, m.-pt. 2250° ; small proportions of C or H make the metal hard and brittle, a form well suited for dental instruments.. The red-hot metal (in form of powder) decomposes water. HF is the only acid which attacks it, and that slowly, but rapidly in contact with platinum. When heated to redness thin wires burn, but thick wires are oxidised only on the surface. NbCl;, NbCl;, and NbOCI, are known, but only TaCl,. Both metals form dioxides, NbO,, TaOg, and the acid pentoxides ; Nb, O;, sp. gr. 4:57 ; Ta.O,, sp. gr. 7:35. Review of the Antimony Group of Metals.—The metals Bi, Sb, Ta, Nb, and V belong to the group of elements which includes N, P, and As. All these are characterised by their acid pentoxides. Ta, Nb, and V do not form hydrides analogous to PH;, nor is BiH, known. Many points of resemblance may be noted between vanadium and chromium, whilst niobium and tantalum recall tungsten. TIN (FOURTH) GROUP. TrraNiumM, GERMANIUM, ZIRconIuM, Tin, Cerium, Leap, TuHorrum. TIN, Sn = 119.0, Tin is by no means so widely diffused as most of the other metals which are largely used, and is scarcely ever found in the metallic state in nature. Its only important ore is that known as tin-stone, which is dioxide of tin, SnO,, and is generally found as masses in lodes or veins traversing quartz, granite, or slate. It is usually associated with arsenical iron pyrites, and with a mineral called wolfram, which is a tungstate of iron and manganese. Tin-stone is sometimes found in alluvial soils in the form of detached rounded masses ; it is then called stream tin ore, and is much purer than that found in veins, for it has undergone a natural process of oxidation and levigation exactly similar to the artificial treatment of the impure ore. These detached masses of stream tin ore are not unfrequently rectangular prisms with pyramidal terminations. The mines of Malacca, Biliton, Banca, Australia and Bolivia furnish the largest supplies of tin ; Cornwall is still a large producer, and Bohemia and Saxony also furnish the ore. At the Cornish tin-works the purer portions of the ore are picked out by hand, and the residue, which contains quartz and other earthy impurities, together with copper pyrites and arsenical iron pyrites, and seldom more than 2 per cent. of tin, is reduced to a coarse powder in the stamping-mills, and washed in a stream of water. The tin- stone, being extremely hard, is not reduced to so fine a powder as the pyritic minerals associated with it, and these latter are therefore more readily carried away by the stream of water than is the tin-stone. The removal of the foreign matters from the ore is also much favoured by the high specific gravity of the SnO,, which is 6-5, whilst that of sand or quartz is only 2-7, so that the latter would be carried off by a stream which would not disturb the former. So easily and completely can this separation be effected that a sand containing less than 1 per cent. of tin-stone is found capable of being economically treated. Tn order to expel any arsenic and sulphur which may still remain in the washed ore, it is roasted in quantities of 8 or 10 cwt. in a reverberatory furnace, when the sulphur is disengaged in the form of sulphur dioxide, and the arsenic in that of arsenious oxide, the iron being left in the state of ferric oxide, and the copper partly as sulphate, partly as unaltered sulphide. To complete the oxidation of the insoluble copper sulphide, and its conversion into the soluble sulphate, the roasted ore is moistened with water and exposed to the air for some days, after which the whole of the copper may be removed by again washing with water. _A second washing in a stream of water also removes the ferric oxide in a state of suspension, and this is much more easily effected than when the iron was in the form of pyrites, since the difference between the specific gravity of pyrites (5:0) and that of the tin-stone (6-5) is far less than the difference between the specific gravity of ferric oxide and that of tin- stone. The ore thus purified (black tin) contains between 60 and 70 per ceni. of tin; it is mixed very intimately with about $th of powdered coal, and a little lime or fluor spar, to form a fusible slag with the siliceous impurities, 483 484 TIN—-PROPERTIES and reduced in a reverberatory furnace (Fig. 169), a comparatively easy task since SnO, readily parts with its oxygen to carbon at a red heat. The temperature is raised slowly—for instance, in the course of six hours—lest a por- tion of the oxide of tin should combine with the silica to form a silicate, from which the metal would be reduced with difficulty. The doors of the furnace are kept shut, so as to exclude the air and favour the reducing action of the carbon upon the SnOg, the oxygen of which it converts into CO, leaving the metallic tin to accumulate upon the hearth beneath the layer of slag. When the reduction is deemed complete, the mass is well stirred with an iron paddle to separate the metal from the slag ; the latter is run out first, and the tin is then drawn off into an iron pan, where it is allowed to remain at rest for the dross to vise to the surface, and is ladled out into ingot moulds. The slags are carefully sorted, those which contain much oxide of tin being worked up with the next charge of ore, whilst those in which globules of tin are disseminated are crushed, so that the metal may be separated by washing in a stream of water. The metal contains small proportions of Fe, As, Cu, W, Sb, Biand 8. In order to purify it from these, it is submitted to a process of liquation, in which the easy fusibility of tin is taken advantage of ; the ingots are piled into a hollow heap near the fire-bridge of a reverberatory furnace, and gradually heated to the fusing-point, when the greater portion of the tin flows into an outer basin, whilst the remainder is converted into SnO,, which remains as dross upon the hearth, together with the oxides of iron, copper and tungsten, the arsenic having passed off in the form of arsenious oxide. The specific gravity of tin being very low (7-3), any dross which may still remain mingled with it does not separate very readily ; to obviate this, the molten metal is well agitated by stirring with wet wooden poles, or by lowering billets of wet wood into it, when the evolved bubbles of steam carry the impurities up to the surface in a kind of froth ; after resting for a time it is skimmed and ladled into ingot moulds (block tin). It is found that, in consequence of the lightness of the metal, and its tendency to separate from the other metals with which it is contaminated, the ingots which are cast from the metal first ladled out of the pot are purer than those from the bottom ; this is shown by striking the hot ingots with a hammer, when they break up into the irregular prismatic fragments known as dropped or grain tin, the impure metal not exhibiting this extreme brittleness at a high temperature. The tin imported from Banca is celebrated for its purity (Straits tin). When the tin ore contains wolfram, [FeMn]W0O,, which has sp. gr. 7-3, this remains behind with the prepared tin ore, and must be removed before smelting by fusion with sodium carbonate in a reverberatory furnace, when the tungstic acid is converted into sodium tungstate, which is dissolved out by water, and crystallised. Properties of Tin.—Tin is remarkable for its lustre and whiteness, in which it rivals silver, but is at once distinguished from the latter by its greater fusibility, and by its oxidising when heated in air. It is the most fusible of the metals in common use (231°), much lighter than silver, sp. gr. 7-29, and emits a curious grating sound when bent; it is harder than lead, but softer than zinc ; very malleable, particularly at 100° (tin-foil), brittle at 200°, vaporised only at very high temperatures. It has the lowest tenacity of all the metals in common use, only one other common metal, lead, being more difficult to draw into wire at the common temperature. Tin may, however, be drawn at 100°. Only gold, silver and copper surpass it in malleability. Tin decomposes steam at a red heat. It is scarcely affected by air or water at common temperatures,! and is therefore used for tinning other metals. Tin is easily soluble in strong hydrochloric acid, which distin- guishes it from silver, and it is converted into a white nearly insoluble powder by nitric acid, which distinguishes it from all other metals except antimony. Exposure to extreme cold converts tin into a modification which has 1 Crystalline tin deposited upon zinc from neutral stannous chloride, and powdered tin, made by shaking molten tin in a wooden box, oxidise to a considerable extent at the ordinary temperature ; when heated, the superficial oxide prevents the tin from fusing, and it burns like tinder. TIN-PLATE 485 lost its reflecting surface, and has thus acquired a grey appearance (grey tun). A spontaneous disintegration of the tin may even occur from this cause,’ the metal falling to powder. The sp. gr. of grey tin is 5-85. The transition temperature of these enantiotropic forms of tin is 20°, so that the grey form must become white when heated above this temperature ; but the change from white to grey below 20° is very slow until the temperature has fallen considerably lower. The conversion is most rapid at — 48°, and is accelerated by contact with grey tin already formed, or with stannic chloride. Thus the ordinary form of tin is metastable, but becomes stable at 20° ; it remains so until the temperature is 161°, when there is a second transition, the tetragonal crystalline form passing to rhombic. Thus there are three allotropes of tin. Tin-foil is made from bars of the best tin, which are hammered down to a certain thinness, then cut up, laid upon each other, and again beaten till extended to the required degree. Lead coated on each side with tin and hammered, yields an inferior variety. Tin-plate is made by coating sheets of iron with a layer of tin ; to effect this, the sheets, cleaned from oxide, are dipped into melted tin, a coating of which adheres to the iron when the sheet is withdrawn. ‘Tin, being un- altered by exposure to air at the ordinary temperature, effectually protects the iron from rust as long as the coating of tin is perfect, but as soon as a portion of the tin is removed so as to leave the iron exposed, corrosion occurs very rapidly, because the two metals form a galvanic couple, which decom- poses the water (charged with CO,) deposited upon them from the air, and the iron, having the greater attraction for oxygen, is the metal attacked. In the case of galvanised iron (coated with zinc), on the contrary, the zinc would be the metal attacked, and hence the greater durability of this materia] under certain conditions. Detinning tin-plate (see Stannic chloride). Terne-plate is iron coated with an alloy of tin and lead. In tinning the interior of copper vessels, in order to prevent the contamination of food with the copper, the surface is first thoroughly cleaned from oxide by heating it and rubbing over it a little sal-ammoniac, which decomposes any oxide of copper, converting it into the volatile chloride of copper; CuO +2NH,Cl=CuCl, + HO +2NHs. A little resin is then sprinkled upon the metallic surface to protect it from oxidation, and the melted tin is spread over it with tow. Alloys.—The term alloy is applied to any homogeneous mass consisting of two or more metals. In the majority of cases it is not possible to detect the properties of the individual metals in such a mass, so that the alloy cannot be regarded as a mere mixture. In many cases, on the other hand, the alteration of properties induced in one metal by the addition of another does not show any definite relationship with the mass of the added metal, as would be the case if such alteration were wholly due to chemical combina- tion. The difficulty thus experienced in assigning the phenomenon of alloy- formation to its proper position in the classes of change, usually distinguished as physical and chemical, is parallel to that experienced in assigning the phenomenon of solution to one of these two classes (p. 37). It has thus become customary to regard alloys as solidified solutions, which in some cases are analogous to what has been already termed a simple solution—that is, the alloy shows no evidence of containing a chemical compound—and in other cases are analogous to those solutions which undoubtedly contain a compound of the solvent with the dissolved substance in a state of simple solution. 1 The disintegration of the tin pipes of church organs, observed in cold climates, has been attributed to the conversion of the tin into the grey modification by the cold, perhaps aided by the vibrations to which the pipes are subjected, 486 \ ALLOYS Two important pieces of evidence in favour of these views must be quoted. (1) In many instances, when one metal is alloyed in small proportion with another, the freezing-point of the preponderating metal is lowered to an extent which is in accord with the laws controlling the lowering of the freezing-point of a solvent by a dissolved solid (p. 320). This indicates that the alloy is but a solidified solution. (2) When a compound plate (of copper and zinc, for instance), consisting of one metal closely attached to another, is used as the attackable plate of a galvanic cell, the electro-motive force of the cell is that which would be produced were the more attackable of these metals (zinc, for instance) alone used as the attackable plate. When an alloy is thus treated, the E.M.F. isin some cases that which would be produced by the more attackable constituent, and is in some cases different from this. Identity of the E.M.F. with that of the more attackable metal indicates that the alloy is a solidified simple solution, whereas a difference from this value can only be due to the existence of a compound in the alloy. The tendency for metals to alloy with each other is by no means universal. When the molten metals are miscible and the mixture is cooled slowly, one or other of the metals usually separates until a certain proportion Percentage of Cu -—— between the metals has 100, 90 80 7 60 JO 40 SO 20 oO been attained, whereupon a homogeneous mixture or eutectic solidifies. This is illustrated by the curve for Cu and Ag (Fig. 254, copied from Ost’s ‘‘ Chemische Technologie”). The eutectic-point, c, of the curve is at 778° and at 28 per cent. Cu and 72 per cent. Ag. If Cu is present in excess of this proportion and the molten alloy is 0 10 20 50 40 50 60 70 60 90 100 cooled, Cu separates as re- — Percentage of Qg presented by line a-c until Fig. 254. the eutectic composition is attained, when the whole solidifies as ‘* mixed crystals.” The like occurs, as repre- sented by line b-c, when Ag is in excess of 72 per cent. The microscopic examination of a polished surface of an alloy frequently affords much information as to the nature of the mixture, and by etching the surface with suitable acid agents the eutectic may be attacked more or less than the individual crystalline or amorphous particles, rendering the latter distinct under the microscope. This study is known as Metallography. Alloys are industrially made by mixing the constituent metals in a melted condition, although they have been also prepared both by strongly compress- ing a mixture of the powdered metals at the ordinary temperature, and by electrolysing a solution containing salts of the constituent metals; the metallic deposit obtained by the latter method consists, in some cases, of an alloy. Alloys of Tin.—Tin is the chief metal used for making white alloys, some of which resemble silver in appearance. Britannia metal consists chiefly of tin, 90 per cent., hardened by antimony, 8 per cent., and copper. Base silver coin consists chiefly of tin. Pewter consists of 4 parts of tin and 1 part of lead. Lead and tin form a eutectic mixture (supra) melting at 180° and containing 37 per cent. Sn, and solders consist of this with either Sn or Pb in excess, which ensures the necessary pasty condition of the alloy when its temperature is between the m.-pt. of the prevailing metal and 180°. The solder employed for tin-wares is an alloy of tin and lead in various TIN ALLOYS 487 proportions, sometimes 2: 1 (fine solder), sometimes 1 : 1 (common solder), and sometimes 1 : 2 (coarse solder). In applying solder, it is essential that the surfaces to be united be quite free from oxide, which would prevent adhesion of the solder; this is ensured by the application of sal-ammoniac, or of HCl, or sometimes of powdered borax, remarkable for its ready fusibility and its solvent power for the metallic oxides. Gun-metal is an alloy of 91-84 parts of copper with 9-16 of tin, especially valuable for its tenacity, hardness and fusibility. In preparing this alloy, it is usual to melt the tin in the first place with twice its weight of copper, when a white, hard, and extremely brittle alloy (hard metal, apparently a chemical compound having the formula SnCu,) is obtained. The remainder of the copper is fused in a deoxidising flame on the hearth of a reverberatory furnace, and the hard metal thoroughly mixed with it, long wooden stirrers being employed. A quantity of old gun-metal is usually melted with the copper, and facilitates the mixing of the metals. When the metals are thoroughly mixed, the oxide is removed from the surface and the gun-metal is run into moulds made of loam, the stirring being continued during the running, in order to prevent the separation, to which this alloy is very liable, of a white alloy containing a larger proportion of tin (probably SnCu, or SnCug), which has a lower specific gravity, and would collect chiefly in the upper part of the casting (forming tin-spots). : Bronze is essentially an alloy of copper and tin, containing more tin than gun-metal contains ; its composition is varied according to its application, small quantities of zinc and lead being often added to it. Bronze is affected by changes of temperature, in a manner precisely the reverse of that in which steel is influenced, for it becomes hard and brittle when allowed to cool slowly, but soft and malleable when quickly cooled, a property which the ancients applied in the manufacture of weapons. Bronze coin (substi- tuted for the copper coinage) is composed of 95 copper, 4 tin and 1 zinc. Manganese-bronze, an alloy of ordinary bronze containing Mn, is said to rival bar-iron in tenacity and extensibility ; it is used for ships’ propellers. Phosphor-bronze contains about 4 per cent. of phosphorus added as tin phosphide. Bell-metal is an alloy of about 4 parts of copper and 1 of tin, to which lead and zinc are sometimes added. The metal'of which musical instruments are made generally contains the same proportions of copper and tin as bell-metal. Speculum metal, employed for reflectors in optical instruments, consists of 2 parts of copper and 1 of tin, to which a little Zn, As and Ag are sometimes added to harden it and render it susceptible of a high polish. A superior kind of type-metal is composed of 1 part of Sn, 1 of Sb and 2 of Pb. Tin is not dissolved by HNO,, but is converted into a white powder, metastannic acid ; HCl dissolves it with the aid of heat, evolving hydrogen ; but the best solvent for tin is a mixture of HCl with a little HNO,;. When the metal is acted upon by HCl, it assumes a crystalline appearance, which has been turned to account for ornamenting tin-plate. Ifa piece of common tin-plate be rubbed over with tow dipped in a warm mixture of HCl and HNO,, its surface is very prettily diversified (moiré métallique) ; it is usual to cover the surface with a coloured transparent varnish. A mixture of 1 vol. H,SO,, 2 vols. HNO, and 3 vols. H,O dissolves tin in the cold, evolving nearly pure nitrous oxide. The solution yields a precipitate when heated. Poured into boiling water, all the tin is thrown down as metastannic acid. H Commercial tin is liable to contain minute quantities of Pb, Fe, Cu, As, Sb, Bi, Au, Mo and W. Pure tin may be precipitated in crystals by the feeble galvanic current excited by immersing a plate of tin in a strong 1 It is customary to kill the hydrochloric acid by dissolving some zinc in it, The chloride of zinc is probably useful in protecting the work from oxidation, 488 SODIUM STANNATE solution of stannous chloride, covered with a layer of water, so that the metal may be in contact with both layers of liquid. Oxides of Tin.—Two oxides of this metal are known—stannous oxide SnO, and stannic oxide, SnO,. Stannous oxide, SnO, is a substance of little practical importance, obtained by grinding stannous chloride with sodium carbonate, heating the mixture until it is black, and washing with water. It is a black powder which burns when heated in air, becoming SnO,. It is a feebly basic oxide, and therefore dissolves in acids ; it may also be dissolved by a strong solution of potash, but is then easily decomposed into metallic tin and stannic oxide, which combines with the potash. By heating tin with caustic soda a “‘ stannite’’ of soda is obtained ; this is substituted for stannate of soda, into which it is converted, with precipitation of tin, by boiling. Stannic oxide, SnO,, or dioxide (binoxide) of tin, has been mentioned as the chief ore of tin, and is formed when tin is heated in air. The natural form occurs in very hard square prisms, usually coloured brown by ferric oxide. In its insolubility in acids it resembles crystallised silica, and, like that substance, it forms, when fused with alkalies or their carbonates, compounds which are soluble in water; these are termed stannates. The artificial, amorphous SnO, dissolves in hot strong H,SO,, and is precipitated on adding water. It is easily reduced when heated in hydrogen, and is converted into SnCl, when heated in HCl gas. It melts at 1127°. Sp. gr. 6-71. Sodium stannate, Na,O.8n0O,, is prepared, on the large scale, for use as a mordant by calico-printers. The prepared tin ore (p. 483) is heated with solution of caustic soda, and boiled down till the temperature rises to 315° ; or the tin ore is fused with sodium nitrate, when oxides of nitrogen are expelled. It crystallises easily in hexagonal tables having the composi- tion Na,SnO,.3Aq, which dissolve easily in cold water, and are partly deposited again when the solution is heated. Prismatic crystals have been obtained of Na,SnO,.10Aq, like Na,CO,;.10Aq. Most normal alkali salts cause a separation of sodium stannate from its aqueous solution. The solution of sodium stannate is, like the silicate, strongly alkaline, and when neutralised by an acid yields a precipitate of stannic acid, H,SnO,, or Sn0(OH),, which may be obtained as a hydrosol and a hydrogel exactly as described for silicic acid (p. 282). The great similarity between stannic and silicic acids is here very remarkable. When heated, stannic acid is converted into SnO,. An interesting mode of making Na,SnO, is by heating tin with NaOH and lead oxide; Sn + 2NaOH + 2PbO = Na,SnO,; + Phe + H,O. Thus Sn displaces Pb in presence of alkali, whereas Pb displaces Sn in presence of acids. Stannic or metastannic acid, H,SnO, (dried at 100°), is obtained as a white crystalline hydrate when tin is oxidised by nitric acid. When heated, it assumes a yellowish colour, and a hardness resembling that of powdered tin-stone ; in this form it constitutes putty powder, used for polishing; as found in commerce, it generally contains much oxide of lead. Metastannic acid is insoluble in water and diluted acids, but when boiled with dilute HCl it combines with some of the acid, and when the excess of HCl has been removed by washing, the compound passes into solution, from which it is reprecipitated by HCl, or by boiling. When fused with alkali it is converted into a soluble stannate, but if boiled with solution of potash it is dissolved in the form of potassium metastannate, which will not crystallise like the stannate, but is obtained as a granular precipitate by dissolving KOH in its solution. This precipitate has the composition K,Sn,0,,.44q ; it is very soluble in water, and is strongly alkaline. When it is heated to expel the water, it is decomposed, and the potash may be washed out with water, leaving SnO,. The sodium salt, Na.Sn,0,, .4Aq, hag also been obtained as a sparingly soluble crystalline powder, by the action of cold TIN CHLQRIDES 489 NaOH on metastannic acid. It is claimed that the precipitate formed by alkalies in stannic chloride is orthostannic acid, Sn(OH),. Stannate of tin is obtained as a yellowish hydrate by boiling stannous chloride with ferric hydroxide; Fe,0, + 2SnCl, = SnSnO, + 2FeCl. It is sometimes written Sn,.03, and called sesguioxide of tin. . Chlorides of Tin.—The two chlorides of tin correspond in composition with the oxides. Stannous chloride, or protochloride of tin, SnCl,, is much used by dyers and calico-printers, and is prepared by dissolving tin (grain tin) in hydrochloric acid, when it is deposited, on cooling, in lustrous prismatic needles (SnCl,.2Aq) known as tin crystals or salts of tin. In vacuo, over H,SO,, they become SnCl, (m.-pt. 250°). The dissolution of the tin is gene- rally effected in a copper vessel, in order to accelerate the-action by forming a voltaic couple, of which the tin is the attacked metal. When gently heated, the crystals lose their water, and are partly decomposed, some hydrochloric acid being evolved (SnCl, + H,O = SnO + 2HCl); at a higher temperature (b.pt. 606°) the anhydrous chloride may be distilled. The crystallised chloride dissolves in about one-third of its weight of water, but if much water be added, a precipitate of stannous hydroxychloride, 28n(OH)Cl. Aq, is formed, which dissolves on adding HCl. A moderately dilute solution of SnCl, absorbs oxygen from the air, and deposits the hydroxy- chloride, leaving SnCl, in solution ; 3SnCl,+ H,O+0 = SnCl,+2Sn(OH)Cl. If the solution contains much free HCl it remains clear, being entirely con- verted into SnCl,. A strong solution of the chloride is not oxidised by the air, and the weak solution may be longer preserved in contact with metallic tin. Stannous chloride has a great attraction for chlorine as well as for oxygen, and is frequently employed as a de-oxidising or de-chlorinating agent. Tin may be precipitated from stannous chloride by the action of zinc, in the form of minute crystals. A very beautiful tin tree is obtained by dissolving granulated tin in strong HCl, with the aid of heat, in the pro- portion of 8 measured oz. of acid to 1000 grs. of tin, diluting the solution with four times its bulk of water, and introducing a piece of zinc. Stannous chloride is also obtained by heating tin in HCl gas, or by distilling tin with mercuric chloride; Sn + HgCl, =SnCl, + Hg. The mercury distils, leaving the stannous chloride as a transparent vitreous mass. Stannic chloride, or tetrachloride of tin, SnCl,, is obtained in solution when tin is heated with hydrochloric and nitric acids ; for the use of the dyer, the solution (nitromuriate of tin) is generally made with ammonium chloride and nitric acid. The anhydrous tetrachloride is obtained by heating tin in a current of dry chlorine, when combination occurs with combustion, and the tetrachloride distils as a heavy (sp. gr. 2:28) colourless volatile liquid (b.-pt. 114°), giving suffocating white fumes in the air. When it is mixed with a little water, there is energetic combination, and three crystalline compounds may be produced, containing 3, 5, and 8 mols. H,O respectively. A large quantity of water causes precipitation of stannic acid. The com- mercial crystals are SnCl,.5Aq. The anhydrous chloride is also obtained by distilling tin with an excess of mercuric chloride; Sn + 2HgCl, = SnCl, + Hg, ; but here, the result is opposite to that in the case of stannous chloride, as the stannic chloride distils before the mercury. Stannic chloride forms crystallisable double salts with the alkali chlorides. Pink salt, used by dyers, is a compound of stannic chloride with ammonium chloride, 2NH,C1.SnCl,; it is colourless, but is used in dyeing red with madder. The compound 2HCI.SnCl,.6Aq has been obtained in crystals. Much stannic chloride is now made in detinning the scrap discarded by the tin-plate can maker. This carries about 3 per cent. of its weight of tin. It is compressed into 490 TIN SVLPHIDES bundles which are thoroughly dried and packed in iron cylinders into which chlorine is forced. The heat evolved by the combination of the chlorine with the tin is absorbed by cooling the cylinder, and when the pressure within the latter remains constant, showing that no more Cl is being absorbed, the cylinder is evacuated, the vapour of SnCl, being condensed. The detinned iron can be used directly in the steel furnaces (p. 446). Stannic bromide, SnBr,, is crystalline, fuses at 30° and boils at 201°. It dissolves in water without immediate decomposition. Stannous sulphide, SnS, may be easily prepared by heating tin with sulphur, when it forms a grey crystalline mass (sp. gr. 5:27), which melts at a red heat and expands when it solidifies. It is also obtained as a dark brown precipitate by the action of H,S upon a solution of SnCl,. Stannous sulphide is not dissolved by alkalies unless some sulphur be added, which converts it into stannic sulphide. It dissolves in hot strong HCl. Stannic sulphide, SnS., is commonly known as mosaic gold or bronze powder,! and is used for decorative purposes. It cannot be made by heating tin with sulphur, because it is decomposed by heat into SnS and 8, It is prepared by a curious process, which was devised in 1771, and must have been the result of a number of trials. Twelve parts by weight of tin are dissolved in 6 parts of mercury ; the brittle amalgam thus obtained is powdered and mixed with 7 parts of sulphur and 6 of sal-ammoniac. The mixture is introduced into a long-necked flask, which is gently heated in a sand-bath as long as any smell of H,S is evolved ; the temperature is then raised to dull redness until no more fumes are disengaged. The mosaic gold is found in beautiful yellow scales at the bottom of the flask, and sulphide of mercury and calomel are deposited in the neck. The mercury appears to be used for effecting the fine subdivision of the tin, and the sal-ammoniac to keep down the temperature (by its volatilisation) below the point at which the Sn8, is converted into Sn8. Mosaic gold, like gold itself, is not dissolved by hydrochloric or nitric acid, but easily by aqua regia. Alkalies also dissolve it when heated. On adding H,S to a solution of stannic chloride, the stannic sulphide is obtained as a yellow precipitate, which is sometimes formed only on boiling. It dissolves easily in alkalies and alkali sulphides, forming thiostannates. The sodium salt, NagSnS; .2H,0, has been crystallised in yellow octahedra. When fused with iodine, SnS, forms SnS,I,, a fusible yellow body which does not lose iodine when heated, and dissolves in carbon disulphide, forming a brown solution which deposits red crystals like potassium bichromate ; these are decomposed by boiling with water, yielding SnO,, sulphur, iodine and HI. Tin pyrites contains either SnS or Sn§g, or both, accompanied by sulphides of copper and iron. Tin is very closely connected with silicon by the composition, hardness, and insolubility of SnO,, and by the characters of SnCl,. Among metals it is conspicuous by the feebly basic character of its oxides and by the powerful reducing properties of SnCl,. TITANIUM, Ti = 48.1. This metal stands in close chemical] relationship to tin ; it is very widely distributed, in small proportion particularly, in iron ores and clays, although no very important practical application has hitherto been found for it. The form in which it is generally found is titanic oxide (or anhydride), TiO, which occurs uncombined in the miverals rutile (sp. gr. 4-25), anatase, and brookite, the first of which is isomorphous with tin-stone, and is extremely hard, like that mineral, while the second crystallises in the quadratic system and the third in the rhombic. The mineral perowskite is (CaFe)TiO, ; titanite or sphene is CaO0.TiOg.SiO, (sp. gr. 3-5). In combination with oxide of iron, titanic oxide is found in titanic iron ore (sp. gr. 4:5), tron-sand, iserine, or menaccanite (found originally in Menaccan, in Cornwall), which resembles gunpowder in appearance, and is now imported in abundance from Nova Scotia and New Zealand. Some specimens of this mineral contain 40 per cent. of titanic oxide as FeO.TiOg. To extract TiO, from 1 A bronze powder is also made by powdering finely laminated alloys of copper and zinc, a little oil being used to prevent oxidation. TITANIUM 491 it,.the finely ground mineral is fused with three parts of K,CO3, when CO, is expellcd and potassium titanate, K,TiO,, formed ; on washing the mass with hot water, this salt is decomposed, a part of its alkali being removed by the water, and an acid titanate left, mixed with the gxide ofiron. This is dissolved in HCl, and the solution evaporated to dryness, when the titanic oxide and any silica which may be present are converted into the insoluble modifications, and are left on digesting the residue again with dilute hydrochloric acid ; the residue is washed with water by decantation (for titanic oxide easily passes through the filter), dried, and fused at a gentle heat with KHSO,. This forms a soluble compound with the titanic oxide, which may be extracted by cold water, leaving the silica undissolved. The solution containing the titanic oxide is mixed with about twenty times its volume of water, and boiled for some time, when the TiO, is separated as a white precipitate, exhibiting a great disposition to cling as a film to the surface of the flask in which the solution is boiled, and giving it the appearance of being corroded. The titanic oxide becomes yellow when strongly heated, and white again on cooling ; it melts at 1560°; it does not dissolve in solution of potash, like silica, but when fused with potash it forms a titanate, which is decomposed by water ; the acid titanate of potassium which is left may be dissolved in HCl, and if the solution be neutralised with ammonium carbonate, hydrated titanic acid, Ti(OH),, is precipi- tated, very much resembling alumina in appearance. By dissolving the gelatinous hydrate in cold HCl, and dialysing, a solution of titanic acid in water is obtained, which is liable to gelatinise spontaneously if it contains more than 1 per cent. of the acid. Titanic acid is employed in the manufacture of artificial teeth, and for imparting a straw-yellow tint to the glaze of porcelain. © be Metallic titanium has not yet been prepared in a pure state; prismatic crystals are obtained by passing vapour of TiCl, over heated sodium, but they contain sodium ; reduction of TiO, by carbon in the electric furnace yields a metal containing about 2 per cent. of carbon, Hence the properties of the metal are not fully known. A so-called amorphous titanium, obtained by heating potassium titanofluoride, K,TiFs, with sodium, has a sp. gr. 3-6 ; the metal containing 2 per cent. C, 4:87. These impure metals are stable in air at ordinary temperature, but burn to TiO, at 600°; their melting-point is very high. With nitrogen the metal combines with evolution of heat at 800°, to form the nitride, TiN, which is also produced by heating TiO, in NH; ; it is a very hard substance, having the appearance of bronze, yielding ammonia when heated in steam or with caustic alkali. Beautiful cubes of a copper colour, sp. gr. 4:3, and great hardness, are found adhering to the slags of blast furnaces in which titaniferous iron ores are smelted ; these consist of a compound of titanium, carbon, and nitrogen, most probably Tis;CN, (formerly called titanium nitrocyanide). A similar compound can be made by heating to whiteness in nitrogen a mixture of TiO, and charcoal. Titanium behaves towards acids like tin, and yields an insoluble metatitanic acid with HNO3. Whereas, however, tin yields no trivalent compounds, titanium is di-, tri-, and tetra-valent. Titanium dichloride, TiCl,, is obtained by reducing the tetrachloride with sodium amalgam. It is a black solid which burns when heated in air, evolving TiCl, and leaving a residue of TiO,. It volatilises in hydrogen without fusing. The statement that in contact with water it evolves H has been contradicted. Titanium trichloride, TiClz, is made by passing a mixture of hydrogen and TiCl, vapour through a red-hot tube ; it condenses on the cooler part of the tube as a violet powder. This formation is remarkable, since when the trichloride is heated in a current of hydrogen it is decom- posed into TiCl,, which volatilises, and TiClg, whichremains. TiCl; exists in the solution made by dissolving Ti in HCl, which is violet. There are two forms of the chloride, one violet, the other green. Its reducing properties resemble those of SnCl, Titanium tetrachloride, TiCl,, may be made by heating a mixture of TiO, and charcoal in a current of chlorine. It isa colourless, fuming liquid of sp. gr. 1-76, b.-pt. 136°, and m.-pt. — 23°. In absorbing H,O from the air it becomes an oxychloride, being intermediate between SnCl, and SiCl, in this respect, the former of which remains unchanged, while the latter is decomposed into SiO, and HCl. Titanium tetrafluoride, TiF,, is produced by pouring well-cooled TiC], into anhydrous HF and distilling; HF and HCl pass over first and then TiF, (b.-pt. 284°) ; on cooling, the distillate becomes a white powder. The fluotitanates, e.g. K,TiF,, are prepared by dissolving TiO, in HF and neutralising with a base, 492 ZIRCONIUM Titanic oxide, TiOg, is clearly an acid oxide, but less so than SiOg, as indicated by its solubility in acids, which shows its basic tendency. The monoxide, TiO, and the sesquioxide, Ti,O3, are known, the latter being obtainable in crystals of the same form as specular iron ore (Fe,03); both are basic. Tstanium sulphate, Tig(SO4)3, combines with alkali sulphates to form alums, TigM,(SO,)4.24H,0. Pertitanic acid, Ti0,.%H,0, exists in the yellow solution obtained by adding H,0, to a solution of a titanium compound ; it forms a yellow precipitate when TiC], is added drop by drop to a dilute solution of HO, in alcohol and is followed by ammonia. A number of its salts are known. Titanic sulphide, TiS., is not precipitated, like tin disulphide when H,S acts upon a solution containing titanium ; but if a mixture of the vapour of TiC], with H,S is passed through a red-hot tube, greenish-yellow scales of TiS,, resembling mosaic gold, are deposited. Titanous salts (salts of Ti,03) are used as reducing agents for producing discharge effects on dyed wool. Ferro-titanium, an alloy of iron with 10 to 15 per cent. of Ti, is made for special metallurgical purposes by reducing titanic iron ore. ZIRCONIUM, Zr = 90.6. This metal occurs in the form of silicate, ZrOs.SiO., in the minerals zircon (sp. gr. 4-5) and hyacinth, and the oxide zirconia, ZrOg, is abundant in Brazil as the mineral baddeleyite (sp. gr. 6). To separate ZrO, from zircon, the powdered mineral is fused with Na,CO, and the mass leached with water, whereby sodium silicate is dissolved and sodium zirconate, NagO .ZrOo, left as a white powder ; this is dissolved in H,SO,, and hydrated ZrO, precipitated by NaOH. Or the mineral may be heated with KHF, and the mass boiled with water, which dissolves potassium fluozirconate, K,ZrF,, and leaves K,SiF, ; the former is heated with H,SO, to expel HF and the solution is pre- cipitated with NH3. The metal has been described in various modifications, but these cease to be recognised as they all have been proved to be very impure. Berzelius first prepared it by heating K,ZrF, with K, and this process improved and carried out in vacuo is capable of yielding a fairly pure product, especially when Na is substituted for K. A metal content of 99-8 per cent. has been claimed, but these specimens have an extra- ordinarily high atomic heat, 7-1. Other values for the atomic heat approximate the normal. Usually, especially when K is used, the metal is oxidised during the purifi- cation to an extremely fine, intensely black powder, zirconium monozide, ZrO, sp. gr. 3-75, the so-called amorphous zirconium. It does not conduct electricity, but on heating at 1000° in vacuo its sp. gr. increases to 5-97, and it then conducts electricity, whence it. is inferred that it has changed into a mixture of Zr and ZrO. Colloidal zirconium also consists of ZrO. Attempts to reduce ZrO, with C in the electric furnace produce the carbide, ZrC, a very hard substance useful for polishing glass. The most promising method of reducing ZrO, is to heat it with filings of calcium in a very high vacuum ; after fusion in the electric furnace this metal contains about 93 per cent. of Zr. Zirconium is a silver- white metal of sp. gr. 6-39 and very high melting-point. It is stable in air at ordinary temperature, but burns when heated in air. Hot strong HCl, HNO; and aqua regia have very little action on the metal ; HF, even diluted, dissolves the metal at once. Boiling H,SO, attacks it, sometimes very violent'y. Unlike Ti and Si, Zr has little tendency to alloy with iron. For the sp. gr. of the metal, see also p. 304. Zirconides are formed with certain metals. ZrAl, constitutes the so-called crystallised zirconium, sp. gr. 4:1. Zirconium absorbs N tardily at 800°, readily above 1000°, ‘forming the nitride Zr,No, a crystalline powder, sp. gr. 6-75, which conducts electricity. The nitrides Zr,N; and Zr,.Ng are also known. Zirconium is always tetravalent, except in ZrO and ZrHy. The dioxide, ZrO, (sp. gr. 5-5), is acidic (expels CO, from fused Na,CO,), but less so than SiOx, its basic character being exhibited by the existence of the sulphate, Zr(SO4)o-4H,O. A peroxide, ZrQ3, is known. The ¢etrachloride, ZrCly, is best made by heating to 300° the carbide, ZrC, in chlorine ; it forms a white sublimate which fumes in air and reacts energetically with water to produce the oxychloride, ZrOCl. THORIA ; 493 The very high melting-point of ZrO, fits it for a substitute for lime in the lime-light and as a lining for metallurgical furnaces. THORIUM, Th = 232.4. Although a rare element, thorium in the form of thoria, ThO,, is used in large quantity for the manufacture of incandescent gas mantles (p. 267). The mineral thorite, ThO,.SiOg, and thorianite (from Ceylon), a mixture of ThO, and UOk, are the most fruitful sources of thoria, but they are rare, and the oxide is commonly prepared from monazite sand (p. 431), which is abundant, but contains only some 5 per cent. of thoria. The sand is heated with strong H,SO, and the mass treated with ice-cold water ; the thoria and rare earths dissolve as phosphates and sulphates. The solution is fractionally neutralised with MgO, whereby the phosphates of the earths (p. 432) are precipitated, the thorium phosphate being in the first fraction. This fraction is dissolved in HCl, and oxalic acid is added to the strongly acid solution ; thorium oxalate is precipitated together with small quantities of the oxalates of the other earths. By extracting the precipitate with warm Na,CO, solution, the thorium oxalate is dissolved together with those of the yttria earths, the cerite earths remaining as double carbonates ; from the solution thoria may be precipitated by adding NaOH. For the high degree of purity required in the mantle industry the thoria is dissolved in HCl, cooled, and mixed with H,SO, to produce crystals of thorium sulphate ; this is boiled with NH, and the thorium hydroxide thus obtained is dissolved in HNO, and thorium nitrate crystallised from the solution. Metallic thorium has not been obtained free from oxide. The best specimens have been produced by heating thorium tetrachloride with Na in a vacuum ; even thus accidental moisture and air cause the metal to contain some 3 per cent. of oxide. The impure metal has sp. gr. 12-16 ; it burns to oxide when heated in air. The fused metal (m.-pt. 1450°) has the appearance, softness, and ductility of platinum. All acids except aqua regia attack it very slowly. Thorium is tetravalent only. The chloride, ThCl,, is best obtained by heating ThO, in carbon tetrachloride vapour ; ThO, + 2CCl, = ThCl, + 2COCl. It sublimes in colourless prisms (m.-pt. 820°). The fluoride, ThF,, is a white precipitate which is insoluble in HF ; there is doubt whether salts of the type K,ThF, exist. The carbide, ThCy, an electric furnace product from ThO, and C, forms yellow crystals (sp. gr. 8-96) ; it decomposes water, yielding a mixture of acetylene, methane, ethylene and hydrogen. ThO, is a stronger base than ZrO,, and a feebler acid oxide, since it does not decom- pose fused Na,CO;. The anhydrous oxide (sp. gr. 10-2) does not dissolve in HCl or HNO,, but when the acid is evaporated the residue dissolves in water to an emulsion in which acids cause a curdy precipitate soluble in acids (compare metastannic acid). The anhydrous sulphate, Th(SO4)2, is soluble in water at 0°, but when the solution is heated crystals with 4H,O separate. The nitrate, Th(NO;),.12H,O, is the most important salt ; it is sold in a partly dehydrated condition ; its application in the manufacture of gas mantles has been described at p.431. It is a remarkable, and at present wnex- plained, fact that a mantle of pure thoria does not give an illumination comparable with that which it emits when it contains a trace of ceria; the proportion of ceria need be so small that an improvement in the illumination is the most delicate test for cerfa. Ordinary thoria is radioactive, emitting a-particles, and an emanation, the average life of which is 76 seconds, and which disintegrates into a-particles and a series of products ThA—ThD. A gas mantle will photograph itself if laid on a sensitive plate ina darkroom. Thorium hydroxide dissolves in excess of NH, except a fraction called mesothoria ; by dissolving this in HCl, adding a little ZrCl,, and precipitating with NH,, mesothoria-1 is carried down and mesothoria-2 remains dissolved. These are the first disintegration products of thorium, the former being inactive and the latter emitting (- and y-rays ; they are not contained in the gas mantle, having been separated in the course of manufacture. Radio-thoria accompanies commercial thoria and is the product of mesothoria-2 ; it is separated from thorium salts by precipitating BaSQ, in their solutions, which carries down the radioactive matter. It yields a-particles and thoria X ; it is separated from solutions of commercial thorium salts by adding excess of NH;, 494 LEAD when it remains dissolved. It has an average life of 5-35 days, and yields a-particles and the aforesaid emanation ; hence there are four stages between the parent thorium (average life 4 x 1019 years) and the emanation. GERMANIUM, Ge = 72.5. This occurs in argyrodite, a silver ore. It is extracted by fusing the powdered mineral with Na,CO, and S, extracting with water, neutralising the solution with H,S0,, filtering from the precipitated S, As,S, and Sb,Sg, and saturating with H,S, which precipitates white germanic sulphide, GeSg. This is roasted to oxide, from which the metal is reduced by heating with H or C. It is a white brittle metal (sp. gr. 5-47), melts about 900°, and volatilises at higher temperatures; the fused metal crystallises in octahedra. It is dissolved by H,SO, and agua regia, but not by HCl ; HNO, oxidises it to GeQg. Germanium stands between silicon and tin in the Periodic Table (p. 8), but it is more nearly related to tin than to silicon ; its existence was prophesied (ekasilicon) by Mendeléeff previously to its discovery (1885). It is both divalent and tetravalent. Germanous chloride, GeClg, is made by heating GeS (v. infra) in HCl gas ; it is a colourless liquid which fumes in air; the vapour clouds glass and turns cork intensely red. Germanic chloride, GeCl4, is obtained like stannic chloride and boils at 86°, When Ge is heated in HCl it yields germanium chloroform, GeHClz, which boils at 72°. The oxides GeO and GeO, are known. GeO, dissolves in HF and the solution yields double fluorides like K,GeF¢, similar to the silico-fluorides. Germanic oxide, GeO, (sp. gr. 4:7), is white, and sparingly soluble in water, from which it may be crystallised ; it behaves as an acid oxide. GeS, is a white precipitate obtained by adding H,S to a solution of GeO, in HCl or H,S0,. In the absence of acid it is somewhat soluble in water. It is dissolved by alkali sulphides. When reduced by hot H it yields GeS in dark grey lustrous crystals, lecomposed by potash into GeS,, which dissolves, and Ge, which separates. CERIUM, Ce = 140.25. This element in its tetravalent, ceric’ form belongs here as the analogue of zirconium and thorium ; but on account of its trivalent, cerous, function it is more conveniently considered amongst the “rare earths ” with which it exhibits the closest affinity (p. 432). LEAD, Pb= 207.10. Lead owes its usefulness in the metallic state chiefly to its softness and fusibility. The former quality allows it to be easily rolled into thin sheets and to be drawn into the form of tubes or pipes ; it is indeed the softest of the metals in common use, and at the same time the least tenacious, so that it can only be drawn with difficulty into thin wire, and is then very easily broken. The ease with which it makes a dark streak upon paper shows how readily minute particles of the metal may be abraded. Its want of elasticity also recommends it for some special uses, as for deadening a shock or preventing a rebound. In fusibility it surpasses all the other metals commonly employed in the metallic state, except tin, for it melts at 327°, and this circumstance, taken in conjunction with its high specific gravity (11-36), particularly adapts it for the manufacture of shot and bullets. For one of its extensive uses, however, as a covering for roofs, it would be better suited if it were lighter and less fusible, for in case of fire in houses so roofed the fall of the molten lead frequently aggravates the calamity. Its resistance to strong acids is turned to account in manufacturing chemistry. With the exception, perhaps, of the ores of iron, none is more abundant in this country than the chief ore of lead, galena, a sulphide of lead (PbS). This ore might at the first glance be mistaken for the metal itself, from its high specific gravity (7-5) and metallic lustre. It is found forming extensive LEAD—METALLURGY 495 veins in Cumberland, Derbyshire and Cornwall, traversing a limestone rock in the first two counties, and a clay slate in the last. The United States, Canada and Spain also furnish large supplies of this important ore. Galena presents a beautiful crystalline appearance, being often found in large isolated cubes, which readily cleave or split in directions parallel to their faces. Blende (sulphide of zinc) and copper pyrites (sulphide of copper and iron) are frequently found in the same vein with galena, and it is usually associated with quartz (silica), heavy spar (barium sulphate), or fluor spar (calcium fluoride). Con- siderable quantities of sulphide of silver are often present in galena, and in many specimens the sulphides of bismuth and antimony are found. Though the sulphide is the most abundant natural combination of lead, it is by no means the only form in which this metal is found. The metal itself is occasionally met with, though in very small quantity, and the carbonate of lead (PbCO,), white lead ore or cerussite, forms an important ore in the United States and in Spain. The sulphate of lead, anglesite (PbSO,), is also found in Australia, and is largely imported into this country to be smelted. The extraction of lead from galena is effected by one of three methods, the first of which is the oldest, and is still employed in the Flintshire works. (1) Advantage is taken of the circumstance that, in the case of many metals, when a combination of the metal with oxygen is raised to a high temperature in contact with a sulphide of the same metal, the oxygen and sulphur unite, and the metal is liberated (self-reduction), thus, PbS + 2PbO= 3Pb + SO,. Since galena, when heated with free access of air, becomes to a great extent oxidised to PbO, it will be apparent that the necessary mixture of oxide and sulphide can be obtained by roasting the galena for a certain time, namely, until two-thirds of the lead has become oxide. This change cannot be effected, however, without the simultaneous oxidation of some of the PbS into lead sulphate (PbSO,) ; fortunately, this is of no consequence, since PbS and PbSO, react with each other at a high tempera- ture, in accordance with the equation, PbSO, + PbS = Ph, + 2S5O,. It will now be understood that the essential operations in this metal- lurgical process consist in roasting the ore (PbS) in presence of air until a sufficient proportion of it has been oxidised, and in then raising the tempera- ture in order that the BT mixture of PbS, PbO and PbSO,, produced by the roasting, may react in the sense of the above equations. The ore, having been separated by water con- centration, as far as LE possible, from the foreign matters associated with it, is mixed with a small proportion of lime to flux the siliceous matter of the ore, and spread over the hearth of a reverberatory furnace (Fig. 255), the sides of which are considerably inclined towards the centre, so as to form a hollow for the reception of the molten lead. During the first or roasting stage of the smelting process the temperature is kept below that at which galena fuses. The ore is stirred from time to time, to expose fresh surfaces to the action of the air. When the roasting is sufficiently advanced, some fuel is thrown into the grate, the damper is slightly raised, and the doors of the Fie. 255. 496 LEAD SMELTING furnace are closed, so that air may be excluded and the charge heated to the tem- perature at which the oxide and sulphate of lead act upon the unaltered sulphide, furnishing metallic lead. During this part of the operation the contents of the hearth are constantly raked up towards the fire-bridge, so as to facilitate the separation of the lead, and to cause it to run down into the hollow provided for its reception, this operation being assisted by occasionally opening the doors of the furnace to chill and thus stiffen the slag. After about four hours the charge is reduced to a pretty fluid condition, the lead having accumulated at the bottom of the depressed portion of the hearth with the slag above it ; this slag consists chiefly of the silicates of lime and of oxide of lead, and would have contained a larger proportion of the latter if the lime had not been added as a flux at the commencement of the operation. In order still further to reduce the quantity of lead in the slag, more lime is now thrown into the hearth, together with a little small coal, the latter serving to reduce to the metal the PbO displaced by the lime from its com- bination with the silica. But since silicate of lime is far less fusible than silicate of lead, the effect of this addition of lime is to dry up the slags to a semi-solid mass, and it will now be seen that if the whole of the lime had been added at the commencement of the smelting, the diminished fusibility of the slag would have hindered the separation of the metallic lead. During the last hour or so the temperature is very considerably raised, and at the expiration of about six hours, when the greater portion of the lead has separated, the slag is raked out through one of the doors of the furnace, and the melted metal allowed to run out through a tap-hole in front of the lowest portion of the hearth into an iron basin, from which it is ladled into pig-moulds. The rich slags are worked up again with a fresh charge of ore. In the smelting of galena a very considerable quantity of lead is carried off in the form of vapour (lead-fume) ; and in order to condense this, the gases from the furnace pass through flues, the total length of which sometimes exceeds a mile, before being allowed to escape up the chimney. When these flues are swept, many tons of lead are recovered in the forms of PbO and PbS. (2) Ores, rich in silica, and containing other metal sulphides, are roasted until nearly free from sulphur, mixed with coke and flux (iron ore and lime), and smelted in small blast-furnaces; the lead is thus reduced from its oxide by the coke, and the gangue is fluxed as ferrous and calcium silicates. A roasting process preparatory to smelting, now commonly practised, consists in first roasting the ore with silica (if necessary) and lime and then transferring the charge to a pot carried on trunnions, and containing a fire burning in a grate. Below the latter a blast of air is introduced, and when the whole mass has become red hot this pot is tipped to discharge its contents. The result of the process is to remove nearly the whole of the sulphur from the lead, leaving the latter all in the form of oxide ; PbS + CaO +O,=PbO + CaSO,. A suitable blast-furnace is shown in cross-section in Fig. 256. It is rectangular in plan, being some 15 ft. long and 6 ft. wide at the mouth, and is about 35 ft. high. A number of twyers, a, on each side deliver a blast of air into the lower part of the shaft, which is cooled by water flowing through the space, d. The smelted metal flows into pig-moulds through channels, b, and the lead fumes WN @ pass through a flue, c, into a condensing chamber, not CZ=Zez EY =z (3) In the third process for smelting lead ores, Fie. 256. mostly adopted on the Continent, advantage is taken of the fact that iron will desulphurise galena at a high temperature; PbS + Fe = Pb+ FeS. The galena is mixed with scrap iron (or, what comes to the same thing, iron ore and coke), and charged into a small blast-furnace. SSG E\ SS SQ NW \\4 Wi LAY; NS LIN 7 PATTINSON’S DESILVERISING PROCESS 497 Some varieties of lead,- particularly those smelted from Spanish ores, are known as hard lead, their hardness being due chiefly to the presence of antimony , and since this hardness interferes materially with some of the uses of the metal, such lead is generally subjected to an improving or calcining process, in which the impurities are oxidised and removed, together with a portion of the lead, in the dross. The hard lead is fused in an iron pot (P, Fig. 257), and transferred to a shallow cast- iron pan, C. In this pan, which is set in the hearth of a reverberatory furnace, the lead is kept in fusion by the flame which traverses it from the grate, G, to the flue, F, for a period varying with the degree of impurity, from several hours to as many days, until a sample ingot shows a crystalline appearance. When sufficiently purified, the metal is run off and cast into pigs. At first sight it is not intelligible how antimony should be removed from lead by calcination, since lead is the more easily oxidised metal. The result must be ascribed to the tendency of antimony to form an acid oxide, Sb,0;, which combines with the basic oxide of lead. The dross (antimonate of lead) formed in ; this process, when reduced to the metallic state, yields an alloy of lead with 30 or 40 per cent. of antimony, which is much used for casting type furniture for printers. Extraction of Silver from Lead.—The lead extracted from galena often contains a sufficient quantity of silver to allow of its being profitably extracted. Previously to the year 1829 this was practicable only when the lead contained more than 11 oz. of silver per ton, for the only process then known for effecting the separation of the two metals was that of cupella- tion, necessitating the conversion of the whole of the lead into oxide, which has then to be separated from the silver, and again reduced to the metallic state, thus consuming so large an amount of labour that a considerable yield of silver must be obtained to pay for it. By the simple and ingenious operation known as Pattinson’s desilvering process, a very large amount of the lead can be at once separated in the metallic state with little expendi- ture of labour, thus leaving the remainder sufficiently rich in the more precious metal to defray the cost of the far more expensive process of cupella- tion, so that 2 or 3 oz. of silver per ton can be extracted with profit. Pattinson founded his process upon the observation that when lead contain- ing a small proportion of silver is melted and allowed to cool, being constantly stirred, a considerable quantity of the lead separates in the form of crystals containing a very minute proportion of silver, almost the whole of this metal being left behind in the portion still remaining liquid. _ The process, which is really one of fractional crystallisation, depends on the fact that the eutectic mixture (p. 486) of Pb and Ag contains 2-6 per cent. Ag, and melts at 303°. Hence if any alloy containing less Ag than this be cooled slowly from its melting- point to just above 303°, nearly pure lead crystallises, leaving the eutectic, which then solidifies as a whole, so that further concentration of the silver by this method is impossible. As shown in plan in Fig. 258 ten cast-iron pots are set in a row in brickwork with a furnace beneath each. A perforated ladle, a, is carried by a travelling crane, b, and, 32 Fic. 257. 498 PARKES’ DESILVERISING PROCESS working on a fulcrum, c, beside each pot, serves the whole row ; 10 to 20 tons of lead are melted in, say, pot No. 5, the metal skimmed, and the fire raked out from beneath so that the pot may gradually cool, its liquid contents being constantly agitated with a long iron stirrer. As the crystals of lead form they are fished out and well drained in the ladle a and transferred to pot No. 4. When about four-fifths of the metal has thus been removed in the crystals, the portion still remaining liquid, which retains the silver, is ladled into pot No. 6, and the pot No. 5, which is now empty, is charged with fresh argentiferous lead to be treated in the same manner. When pots Nos. 4 and 6 have received, respectively, a sufficient quantity of the crystals of lead and of the liquid part rich in silver, their contents are subjected to Fria. 258. a similar process, the crystals of lead being always passed to the next pot bearing a lower number, and the rich argentiferous alloy to the next pot bearing a higher number. As the final result of these operations, the pot No. 10, to the extreme right, becomes filled with a rich alloy of lead and silver, sometimes containing 700 ounces of silver to the ton, whilst pot No. 1, to the extreme left, contains lead in which there is not more than half an ounce of silver to the ton. This lead is cast into pigs for the market. Any copper present in the lead is also left with the silver in the liquid portion. The use of a jet of steam for stirring the bath of lead has much reduced the time and labour required in the process. This also removes the copper as oxide, and the antimony is carried off in the steam. In Parkes’ process for desilvering lead advantage is taken of the fact that fused lead only dissolves a small proportion of zine (0-6 per cent. at 360° and 3 per cent. at 650°), and that zinc alloys more readily with silver than does lead, so that when zinc (about 2 per cent.) is stirred into molten argentiferous lead at a temperature above the melting-point of zinc, the bulk of it speedily rises to the surface again, bringing with it the silver and some lead. Thus, a dross consisting of these three metals (about 5 per cent. Ag) and the oxides of zinc.and lead! is obtained. This is first liquated (p. 484) to melt out most of the lead and then distilled with carbon to recover the zinc, and the alloy of lead and silver left in the retort is cupelled (v. infra). The desilverised lead is freed from zinc by the improving process (p. 497). In order to extract the silver from the rich argentiferous lead, the latter is subjected to a process of refining, or cupellation, which is founded upon the oxidation suffered by lead when heated in air, and upon the absence of any tendency on the part of silver to combine directly with oxygen, so that by melting the lead and exposing it to a blast of air it may be oxidised, and the oxide carried away by the blast, leaving, eventually, pure silver on the cupel. The cupellation hearth (shown in horizontal section in Fig. 259) is a reverberatory furnace, the hearth of which consists of a cupel or test, a, made by ramming moist marl (formerly bone-ash) into a shallow oval iron frame having cross-bars at the bottom. 1 The addition of a little Al diminishes the amount of oxide in the dross. CUPELLATION 499 When this frame has been well filled with marl, part of the latter is scooped out, so as to form a dish of the material. The cupel, which may be about 4ft. long by 24 ft. wide by 3in. or 4in. deep, is fixed so that the flame from the grate, b, passes across it into the flues, c, and at one end, the nozzle, e, of a blowing apparatus directs a blast of air over the surface of the contents of the cupel. The alloy of lead and silver, having been previously melted in an iron pot, e, fixed by the side of the furnace, is run in through a gutter, d, until the cupel, which has previously been dried, is nearly filled with it ; a film of oxide soon makes its appear - ance upon the surface of the lead, and is fused by the high temperature. When the blast is directed upon the surface, it blows off this film of oxide, and supplies the oxygen \ WS Ee for the formation of another film upon the clean metallic surface thus exposed. A part of the oxide of lead or litharge thus formed is at first absorbed by the porous materia of the cupel, but the chief part of it is forced by the blast through channels, f, cut for the purpose in the opposite end to that at which the blast enters, and is received in an iron vessel. The door, g, permits the operation to be watched. h is the fire-door. In proportion as the lead is in this manner removed from the cupel, fresh portions are supplied from the adjoining melting-pot, and the process is continued until metal on the cupel contains about 8 per cent. of Ag. The metal is then run through a hole made in the bottom of the cupel. The removal of the lead is completed in another cupel, since some of the silver is carried off with the last portions of litharge. The appearances indicating the removal of the last portion of lead are very striking: the surface of the molten metal, which has been hitherto tarnished, becomes iridescent as the film of oxide of lead thins off, and afterwards resplendently bright, and when the cake of refined silver is allowed to cool, it throws up from its surface a variety of fantastic arborescent excrescences, caused by the escape of oxygen which has been mechanically absorbed by the fused silver, and is given off during solidification. The litharge obtained from the cupelling furnaces is reduced to the metallic state by mixing it with small coal, and heating it in a reverberatory furnace. On the small scale, lead may easily be extracted from galena by mixing 30 grm. with 45 grm. of dried Na,.CO, and 20 grm. of charcoal, introducing the mixture into a crucible, and placing in it two tenpenny nails, heads downwards. The crucible is covered and heated in a moderate fire for about half an hour. The remainder of the nails is carefully removed from the liquid mass, which is then allowed to cool, the crucible broken, and the lead extracted and weighed. In this process the sulphur of the galena is removed, partly by the sodium of the carbonate, and partly by the iron of the nails, the excess of Na,CO, serving to flux any silica in the galena. To ascertain if it contains silver, the button of lead is placed on a small bone-ash cupel (Fig. 260) and heated in a muffle (Fig. 262) until the whole of the lead is oxidised and’ absorbed into the bone-ash of the cupel, leaving the minute globule of silver. A gas muffle furnace, also capable of being used as a crucible furnace, is shown in Fig. 261. 500 LEAD—USES Small globules of lead may be conveniently cupelled on charcoal before the blowpipe by pressing some bone-ash into a cavity scooped in the charcoal, placing the lead upon its surface, and exposing it to « good oxidising flame (p. 268) as long as it decreases in size. If any copper be present, the bone-ash will show a green stain after cooling. Pure lead gives a yellow stain. Uses of Lead.—The employment of this metal for roofing, &e., has been noticed already. Its fusibility adapts it for casting type for printing, but it would be far too soft for this purpose ; accordingly, type-metal consists of an alloy of 4 parts of lead with 1 of antimony. Small shot are made of lead to which about 40 lb. of arsenic per ton has been added. The arsenic dissolves in the lead, hardening it and causing ¢ ( Fic. 262. it to form spherical drops when chilled by being dropped in the melted condi- tion from a height into water. Composition tube (‘‘ compo-pipe’”’) used by plumbers is made of lead hardened by a little antimony. Solder has been already noticed (p. 486). Leaden vessels are much used in manufacturing chemistry, on account of the resistance of this metal to the action of acids. Concentrated sulphuric,+ hydrochloric, nitric, or- hydrofluoric acid does not attack lead at the ordinary temperature. The best solvent for the metal is nitric acid of sp. gr. 1-2, since the nitrate of lead, being insoluble in an acid of greater strength, would be deposited upon the metal, which it would protect from further action. Lead is easily corroded in situations where it is brought in contact with air highly charged with carbonic acid gas, when it absorbs oxygen, forming oxide of lead, which combines with CO, and water to produce the basic carbonate of lead, PbCO;.Pb(OH),. The lead of old coffins is often found converted into a white earthy-looking brittle mass of basic carbonate, with a very thin film of metallic lead inside it. The basic carbonate is formed as a crystalline silky-looking precipitate when a piece of clean lead is left in distilled water for a few minutes. When lead is exposed to the joint action of air and of the acetic acid contained in beer, wine, cider, &c., it becomes converted into acetate of 1 It has been found that pure lead is slowly acted on by sulphuric acid, hydrogen being evolved. The presence of a little antimony almost entircly prevents the action. LEAD OXIDES 501 lead or sugar of lead, which is very poisonous. Hence the accidents arising from the reprehensible practice of sweetening cider by keeping it in contact with lead, and from the accidental presence, in beer and wine bottles, of shot which have been employed in cleansing them. The action of water upon leaden cisterns has been already noticed. Contact with air and sea- water soon converts lead into oxide and chloride. Oxides of Lead—Pb,0, PbO, Pb,O3, Pb,O,, PbO,, are known. Lead suboxide, Pb,O, is obtained by heating lead oxalate; 2PbC,0, = Pb,O + CO + 3C0,. It is a black powder which is decomposed by acids, yielding plumbic salts and metallic lead. The bright surface of lead soon tarnishes when exposed to the air, becom- ing coated with a dark film, which is believed to consist of suboxide of lead. In a very finely divided state, lead takes fire when thrown into the air, and is converted into oxide of lead. The lead pyrophorus, for exhibiting the spontaneous combustion of lead, is prepared by placing some lead tartrate in a glass tube closed at one end (Fig. 263), drawing the tube out to a narrow neck near the open end, and holding it f : nearly horizontally, whilst the lead tartrate is heated with a gas ig or spirit flame as long as any fumes are evolved; the neck is aS then fused with a blowpipe flame and drawn off. Lead tartrate, PbC,H,0,4, when heated leaves a mixture of metallic lead with charcoal, which prevents the lead from fusing into a compact mass. This mixture may be preserved unchanged in the tube for any length of time ; but when the neck is broken off and the contents scattered into the air, they inflame at once, producing thick fumes of oxide of lead. Lead tartrate is prepared by adding solution of lead acetate to a solution of tartaric acid constantly stirred, as long as a precipitate is formed. The precipitated lead tartrate is collected upon a filter, washed several times, and dried at a gentle heat. Lead oxide, PbO, is sometimes found in nature, crystallised in rhombic octahedra, and is prepared on a large scale by heating lead in air. When the metal is only moderately heated, the oxide forms a yellow powder (sp. gr. 9:2), which is known in commerce as massicot, but at a higher temperature (850°) the oxide melts, and on cooling forms a brownish scaly mass, which is called litharge (Ai@os, stone ; apyupos, silver). The litharge of commerce often has a red tint, caused by the presence of some red oxide of lead ; from 1 to 3 per cent. of finely divided metallic lead may also sometimes be found in it. Ata dull red heat litharge is dark brown, but becomes yellow on cooling. When fused it readily attacks clay crucibles, forming a fusible silicate of lead, and soon perforating the sides. When boiled with distilled water, PbO is dissolved in small quantity (69 mgm. per litre), yielding a solution which is decidedly alkaline, and becomes turbid when exposed to the air, absorbing CO,, and depositing lead carbonate. The presence of a small quantity of saline matter in the water hinders the dissolution of the oxide ; but organic matter, and especially sugar, favours it. Oxide of lead is a powerful base, and has a strong tendency to form basic salts. Hot solutions of alkali dissolve PbO readily, and deposit it in pink crystals on cool- ing ; according to some, such solutions contain sodium or potassium plumbite, KgPbO,. Litharge, from its easy combination with silica at a high temperature, is much used in the manufacture of glass, and in glazing earthenware. The assayer also employs it as a flux. A mixture of litharge with lime is sometimes applied to the hair, which it dyes of a purplish-black colour, due to the formation of lead sulphide from the sulphur existing in hair. Dhil mastic, used by builders in repairing stone, is a mixture of 1 part of massicot with 10 parts of brick-dust and enough linseed oil to form a paste ; it sets into a very hard mass, which is probably due partly to the formation of lead silicate, and partly to the drying of the linseed oil by oxidation favoured by the oxide of lead. 502 LEAD OXIDES Lead sesquiovide, Pb,O3, is obtained as a yellow precipitate by dissolving PbO in caustic soda and adding sodium hypochlorite. Cold HCl dissolves it to a yellow liquid, which slowly evolves chlorine. Nitric acid partly dissolves it, leaving a brown residue of PbO,. Heat converts it into PbO. Red lead, or minium, Pb,O,, is prepared by heating massicot in air to about 300°, when it absorbs oxygen, and becomes converted into red lead. Minium is largely used in the manufacture of glass, whence it is neces- sary that it should be free from the oxides of iron, copper, cobalt, &c., which would colour the glass. It is also employed as a common red mineral colour, and in the manufacture of lucifer matches. Red lead becomes dark brown when heated, and regains its original colour when cooled. Its sp. gr. is about88. When minium is treated with dil. HNOsg, lead nitrate, Pb(NO3),, is obtained in solution, and peroxide of lead, PbO,, is left as a brown powder, showing that minium is probably a compound of the oxide and peroxide of lead. The minium obtained by heating massicot in air till no further increase of weight is obtained has the composition 2PbO0.PbO, or Pb304, which would appear to represent pure minium; commercial minium, however, has more frequently a composition corresponding with 3PbO.PbO,, but when thisis treated with potash, PbO is dissolved out, and 2PbO.PbO, remains. Minium evolves oxygen when heated ; the dissociation pressure, however, is less than that of PbOs, showing that minium is not a mere mixture of PbO and PbO,. At 550° the dissociation pressure is} atm., so that above this tem- perature PbO cannot absorb O from the air. HCl, heated with minium, evolves chlorine by reaction with the PbO, contained in it, and leaves the white sparingly soluble PbCl,. A mixture of dilute nitric acid and sugar, or some other oxidisible body, will dissolve minium entirely as Pb(NO3)2. Glacial acetic acid dissolves minium, without evolution of gas, to a colourless liquid, which deposits PbO., when exposed to air or evaporated, or diluted ; a hot saturated solution deposits colourless crystals of lead tetracetate, Pb(CgH305)4,0n cooling. Pb,O,4crystallises from fused KNO, in small prisms. Lead peroxide, or dioxide (puce oxide of lead), PbO,, is found in the mineral kingdom as heavy lead ore, forming black, lustrous, six-sided prisms. It may be prepared from red lead by boiling it, in fine powder, with dil. HNO, washing and drying. Its sp.gr.is 94. It easilyimparts oxygen to other substances ; sulphur, mixed with six times its weight of PbO,, may be ignited by friction ; hence this oxide is a common ingredient in lucifer- match compositions. Its oxidising property is frequently turned to account in the laboratory ; for example, in absorbing sulphur dioxide from gaseous mixtures by converting it into sulphate of lead; PbO, + SO, = PbSO,. PbO, is not dissolved by dilute acids, and cannot be said to have basic properties, although certain salts of the type PbX, are known ; it is even sometimes called plumbic anhydride, for it acts upon potassium hydroxide, yielding potassium plumbate, K,PbO,;.3H,0, which has been crystallised from an alkaline solution, but is decom- posed by pure water. When CaO and PbO are heated to redness in air, caleiwm ortho- plumbate, CagPbO4, is formed; this is decomposed by CO, below 100° into CaCO, and PbO:. These changes form the basis of Kassner’s oxygen process ; for by heating the mixture of CaCO, and PbO, the latter evolves half its oxygen, after which the temperature may be raised to expel CO, (to be used again) from the CaCO. The mixture of CaO and PbO thus regenerated is put through the same cycle of operations. Pb3;0, has been regarded as lead orthoplumbate, Pb,(PbO,), and Pb,O, as lead metaplumbate, Pb(PbOs;). Lead dioxide evolves Cl from HCl when heated, and gives, at first, a brown solution (containing PbCl,) which yields a brown precipitate with ammonia, but if the solution be boiled till all the Cl is expelled, it becomes colourless PbCla, and gives a white pre- cipitate with ammonia. PbO is converted into PbO, by ozone and by hydrogen peroxide. The dioxide is not really a peroxide, because it does not yield H,O. when treated with acids. Its behaviour is that of the oxide of tetravalent lead. WHITE LEAD 503 Lead peroxide is almost the only available material for making the “‘ active mass ” for electric accumulators or storage or secondary cells. When two lead plates, one coated with PbO,, are immersed in dilute H,SO,,an electrical pressure of about 2 volts is created, and if the current be used, both plates become coated with PbSO, before the energy ceases to flow. The ultimate change may be expressed thus: Pb + PbO, + 2H,SO,4 = 2PbSO, + 2H,O. If, when this stage has been reached, current be passed into the cell in the direction opposite to that of the current which has been used, the PbSO, on the one plate will be oxidised to H,SO, and PbOs, while that on the other will be reduced to Pb and H,SO,4. Hence the cell will again be ready to deliver current, which. however, will be smaller in amount than that used to charge the cell by the inevitable loss due to resistance, &c. It will be seen that during discharge the free H,SO, dis- appears from the cell, while during charging it is liberated again ; thus by watching the indications of a hydrometer immersed in the liquid, the progress of either operation may be judged. Lead hydroxide, Pb(OH),, has not been obtained, but Pb(OH),.PbO is formed as a white precipitate when air and water, free from CO», attack lead, hydrogen peroxide being formed at the same time nearly in the proportion represented by the equation Pb + 2H,O + O2 = Pb(OH), + H2O, (compare p. 142). The same hydroxide is precipitated by alkalies from solutions of lead salts. It becomes PbO when heated at 145°. The compound Pb(OH),.2PbO crystallises in octahedra from a solution of basic lead acetate mixed with ammonia. Lead nitrate, Pb(NOg)o, crystallises in white octahedra (sp. gr. 11-5) from a solution of lead or its oxide in dilute nitric acid. It dissolves easily in water, but not in nitric acid or in alcohol. It is employed in dyeing and calico-printing. Several sparingly soluble basic lead nitrates are known. When digested with water and metallic lead, the nitrate‘gives a yellow solution, which deposits yellow scaly crystals of the compound Pb.OH.NO3.Pb.OH.NOp. Lead carbonate, PbCOg, is found in nature, as cerussite, in transparent thombic crystals isomorphous with aragonite. It may be precipitated by mixing solutions of ammonium carbonate and lead acetate, or by passing CO, into a weak solution of lead acetate. Potassium and sodium carbonates precipitate basic lead carbonates. ; White lead, or ceruse, is a basic carbonate, or combination of lead car- bonate, PbCO 3, with variable proportions of lead hydroxide, Pb(OH)>. This substance is a constant product of the corrosive action of air and water upon the metal. Its formation is, of course, very much encouraged by the presence of organic matters in a state of decay, which evolve CO). The best white lead contains about 11 per cent. of CO, and may be expressed by the formula Pb(OH),.2PbCO;. It is manufactured on the large scale by several processes, which depend, however, upon the same principle, namely, the formation of a basic lead salt, which is subsequently decomposed by CO,. The chemistry of the commonest process may be stated as follows: lead oxide, PbO, with acetic acid, HC,H,O,, yields lead acetate Pb(C,H,0,),, conveniently written PbA,. This combines with lead hydroxide, forming basic lead acetate, PbA,.2Pb(OH),.. This is decom- posed by carbonic acid gas, yielding basic lead carbonate and normal lead acetate; 3[PbA,.2Pb(OH),] + CO, = 2[2PbCO;. Pb(OH),]+3PbA,+4H,0. The normal acetate, in contact with lead, atmospheric oxygen,and water, is converted into the basic acetate; PbA, + Pb, + 0, + 2H,O = PbA,.2Pb(OH), ; this is again acted on by CO,, and the process is con- tinuous. To effect these changes, lead is exposed to the simultaneous action of air, water vapour, carbon dioxide, and acetic acid vapour. In the oldest process (still used to make the best pigment) commonly known as the Dutch process, metallic lead, in the form of square gratings cast from the purest lead, is placed over earthen pots containing a small quantity of common vinegar ; a number of these pots being built up into heaps, together with alternate layers of 804 LEAD POISONING dung or spent tan, the heaps are entirely covered up with the same material. The metal is thus exposed to conditions most favourable to its oxidation, viz. a very warm and moist atmosphere produced by the fermentation of the organic matters composing the heap, and the presence of a large quantity of acid vapour generated from the acetic acid of the vinegar. The lead is therefore soon converted into oxide, a portion of which unites with the acetic acid to form the tribasic acetate of lead, which is then decomposed by the carbonic acid gas, evolved from the fermenting dung or tan, yielding carbonate of lead, which combines with another portion of the oxide of lead and water to form the white lead. The neutral acetate of lead left after the removal of the oxide of lead from the tribasic acetate is now ready to take up an additional quantity of the oxide, and the process is thus continued until, in the course of a few weeks, the lead has become coated with a very thick crust of white lead ; the heaps are then destroyed, the crust detached, washed to remove adhering acetate of lead, ground to a paste with water, and dried. Rolled lead is not so easily converted as cast lead. Other processes for making white lead exist, but for a description of them works on technical chemistry must be consulted. White lead being very poisonous, its use by painters and others is gene- rally attended with symptoms of lead pbdisoning, arising in many cases, probably, from neglecting to wash the hands before eating, the effect of lead being cumulative, so that minute doses may show their combined action after many days. Diluted sulphuric acid and solutions of the sulphates of magnesia and the alkalies are sometimes taken internally to counteract its effect ; they are of doubtful efficacy. All paints containing lead, and cards glazed with white lead, are blackened even by minute quantities of sulphuretted hydrogen, from the production of black sulphide of lead. If the blackened surface remains exposed to the light and air, it is bleached again, the sulphide of lead (PbS) being oxidised and converted into white sulphate of lead (PbSO,), but this does not happen in the dark. A little sulphide of lead or powdered charcoal is sometimes mixed with commercial white lead to give it a bluish tint. It is probable that white lead owes a part of its value in oil-painting to the formation of a lead-salt with the fatty acid. Its “ covering” power is due to its amor- phous character, which renders it completely opaque. Pure white lead is easily soluble in acetic and dilute nitric acids. Lead sulphate, PbSO,, is found naturally as anglesite or lead vitriol, in transparent rhombic prisms (sp. gr. 6-3) isomorphous with celestine and heavy spar, and is obtained as a heavy granular precipitate when H,SO, is added to a salt of lead. Stirring much promotes the precipitation. Lead sulphate is very slightly soluble in water, 30 mgm. per litre, and even less so in dil. H,SO, and in alcohol. It is soluble in strong H,SO, and HCl, in sodium chloride and thiosulphate, and in ammonium acetate and tartrate. It fuses above 1100°. Chromates of lead (see p. 466). Lead chloride, PbCly, is found in the mineral horn lead. It is one of the few chlorides which are not readily soluble in water, and is precipitated when HCl or a soluble chloride is added to a solution of lead. Boiling water dissolves about jth of its weight of lead chloride, and deposits it in beautiful shining white needles (sp. gr. 5-8) on cooling. Cold water dissolves about ,4,th of its weight. It fuses easily (at 510°) and solidifies again to a horny mass, like fused silver chloride. It boils at 956°. Lead chloride dissolves easily in strong HCl, and is precipitated by water. The solution of lead chloride in water is precipitated by adding strong HCl; hence a dilute HCl solution, when cold, retains very little lead chloride. Like silver chloride, lead chloride is soluble in sodium thiosulphate. Several lead oxychlorides are known, formed by heating the chloride in air or steam. The minerals matlockite and mendipite are PbClp.PbO and PbCl,.2PbO resgectively. Pattinson’s oxychloride, PbCl.OH, is sometimes employed as a substitute for white lead in painting, being prepared for this purpose by decomposing finely powdered galena with concentrated HCl (PbS + 2HCl = PbCl, + H,8), washing the PbCl, with cold ; LEAD SULPHIDE 505 water, dissolving it in hot water, and adding lime-water, which precipitates the oxychloride ; 2PbCl, + Ca(OH), = 2PbCl(OH) + CaCl. Cassel yellow (Paris yellow, patent yellow, mineral yellow) is another oxychloride of lead, PbCl,.7PbO, prepared by heating a mixture of litharge and sal-ammoniac. It has a fine golden-yellow colour, is easily fused, and crystallises in octahedra on cooling. Turner’s yellow, PbCl,.3PbO, is made by allowing a strong solution of NaCl to react with PbO. Lead tetrachloride, PbCl,, probably exists in the brown solution of PbO, in cold HCl, which gives a brown precipitate of PbO, when diluted. A solution made by suspending PbCl, in water and passing chlorine may be supposed to contain chloro- plumbic acid, H,PbCl,, for with salts of rubidium and ammonium it yields yellow crystalline precipitates of Rb ,PbCl,z and (NH,).PbCl, respectively. When the latter is added to strong H,SO, a heavy oil (sp. gr. 3-18 at 0°) separates ; this is PbCl,. Lead iodide, PbI, (sp. gr. 6-16), is obtained as a bright yellow precipitate on mixing solutions of nitrate or acetate of lead and potassium iodide. If it be allowed to settle, the liquid poured off, and the precipitate dissolved in boiling water (with one or two drops of HCl), it forms a colourless solution, depositing golden scales as it cools. HI converts metallic lead into PbI,. Like mercuric iodide, PbI, dissolves in the alkali iodides. When heated, it becomes red, then black, fuses (375°), and becomes w yellow crystalline mass on cooling. It is decomposed by light with liberation of iodine. Lead sulphide, PbS, is found as galena (p. 494). It fuses at 1120°, and vaporises in a current of hydrogen, condensing in small crystals. When heated in air, it is converted into a mixture of PbO and PbSO,. Strong HCl dissolves it when heated, evolving H,S. HNO, dissolves it partly as lead nitrate, leaving some undissolved PbSO, mixed with sulphur. Lead sulphide is obtained as a black precipitate when H,§ or a soluble sulphide acts upon a solution containing lead, even in minute proportion. Galena is a good conductor of electricity. A polysulphide of lead, the composition of which has not been ascertained, is formed as a red precipitate when a solution of lead is mixed with a solution of an alkaline sulphide saturated with sulphur (or with solution of ammonium sulphide which has been kept till it has acquired a red colour). It is probably PbSs. Lead chlorosulphide, PbS .PbClo, is obtained as a bright red precipitate when hydro- sulphuric acid is added in small quantity to a solution of lead chloride in hydrochloric acid, or when freshly precipitated PbS is heated with solution of PbCl,. It is decomposed’ by hot water. Lead selenide, PbSe, occurs associated with the sulphide in some lead ores ; it much resembles galena, and has the same crystalline form. Review of the Tin Group of Metals.—These metals, Ti, Zr, Ce, Th, Ge, Sn, and Pb, belong to the group of elements which includes C and Si, the higher salt-forming oxide being RO,, which in most cases behaves as a feeble acid oxide, resembling CO, and SiO,. Their tetrafluorides have a tendency to combine with the alkali fluorides to form compounds which recall the salts of hydrofluosilicic acid, and their tetrachlorides form similar double salts with alkali chlorides (e.g. 2NH,Cl.PbCl,, 2KCl].SnCl,), which resemble the double chlorides formed by metals of the platinum group. COPPER, Cu = 63.57. Metallic copper is met with in nature more abundantly than metallic iron, though the compounds of the latter metal are of more frequent occur- rence than those of the former. A very important vein of metallic copper, of excellent quality, occurs near Lake Superior, in North America.’ Metallic copper is also sometimes found in Cornwall, and copper sand, containing metallic copper and quartz, is imported from Chili. The most important English ore of copper is copper pyrites, which is a double sulphide of copper and iron, Cu,S.Fe,8;. Known by its beautiful 506 COPPER ORES brass-yellow colour and metallic lustre, it is found in Cornwall and Devon- shire, generally associated with arsenical pyrites (FeS,.FeAs,), tin- stone (SnO,), quartz, fluor spar, and clay. A very attractive variety, found in Cornwall and Killarney, is called variegated copper ore, or peacock copper, in allusion to its rainbow colours ; its simplest formula is Cu,Fe8s. Copper glance (Cu,8) is another Cornish ore of copper, of a dark grey colour and feeble metallic lustre. Grey copper ore, also abundant in Cornwall, is essentially a compound of the sulphides of copper and iron with those of antimony and arsenic, but it often contains silver, lead, zinc, and sometimes mercury. Malachite, a basic carbonate of copper, is imported from Australia (Burra-Burra), and is also found abundantly in Siberia. Green malachite, the most beautifully veined ornamental variety, is CuCO,.Cu(OH),, and blue malachite (azwrite) is 2CuCO,.Cu(OH),. Red copper ore (Cu,O) is found in West Cornwall, and the black oxide (CuO) is abundant in the north of Chili. The wide distribution of copper leads to its presence in most soils, whence it finds its way in traces into various vegetables ; from this source a man may consume about 1 mgm. of Cu per day. The red colouring-matter (¢wracine) of the feathers of the plantain-eater (touraco) contains as much as 7 per cent. of copper. Hemocyanin, the colouring-matter of the blood of molluscs, contains Cu, just as the hemoglobin of the blood of higher animals contains Fe. Metallurgy of Copper.—Copper sulphide is capable of self-reduction— that is to say, if the sulphide be roasted until half the copper is oxidised and the mixture of sulphide and oxide be fused, metallic copper will be pro- duced; Cu,S + 2CuO = Cu,+S0,. Thus if the ore were pure copper sulphide the smelting of it would be a comparatively simple operation. As it is, however, the sulphide is always accompanied by iron sulphide, so that even if the latter lent itself to self-reduction, a mass of copper and iron would be obtained from which the copper could not be separated. The same result would occur if the ore were dead-roasted, i.e. roasted until all the sulphides had become oxides, and were then reduced with carbon. A way out of the difficulty is provided by the fact that iron sulphide is more easily oxidised than copper sulphide is, so that it is possible to convert the copper pyrites into a mixture of copper sulphide and ferrous oxide, from which the latter can be separated by fusing the mass with silica to obtain iron silicate and unchanged copper sulphide ; (1) Cu,S.Fe,8, + 30, = Cu,S + 2FeO + 350,; (2) Cu,S + 2FeO + 2810, = Cu,S + 2FeO.S8i0,. The molten mass forms two layers, the Cu,8 being beneath the silicate, so that separation is easy and the sulphide can be subjected to self-reduction, or to dead-roasting to oxide, which is then reduced by carbon, either process yielding crude copper. . All copper-smelting processes, except when oxide ores (copper oxides and carbonates), which can be reduced directly by carbon, are under treat- ment, involve this roasting to oxidise sulphide followed by fusion with silica to flux the iron oxide and obtain a copper matte (Cu,8). The differences of process depend on the richness and state of subdivision of the ore, the kind of fuel available, and other local conditions. Broadly, the processes may be distinguished by the kind of furnace employed—the reverberatory furnace, that almost exclusively used in this country, and the blast furnace used on the Continent and in America. The reverberatory furnace for copper smelting is generally of two kinds, the roasting COPPER-SMELTING FURNACES 507 furnace (shown in horizontal section in Fiz. 264, and in vertical section, drawn to a larger scale, in Fig. 169), which has a hearth, H, of large area in comparison with the grate, G, so that the temperature does not rise above the melting-point of copper sulphide, and air-admission “openings, such as O; vertical section in Fig. 265 and in horizontal section | in Fig. 266), wherein fusion; the grate is in this case large in comparison with the hearth, which fused sulphide or metal to be tapped into the tank, T, the slags being removed through a door at the end of the furnace opposite the grate. A modern form and the ore furnace (shown in the materials are heated to has a cavity, C, for collection of 4 of blast-furnace for copper Fia. 264. smelting is shown in Fig. 267. It is rectangular in cross-section and consists of an iron body, a, surrounded by a water-jacket through which water circulates. I~ Fic. 267. Fic. 265. The crucible, d, is of fire-clay and brick; e is the spout for the slag; f are twyers; g the tap-hole for the matte. The furnace may be 20 ft. to 30 ft. high. In the Welsh process, which is the oldest, the reverberatory furnace is alone used, and it is found economical not to attempt to produce a Cu,S matte in a single operation. Instead, the ore containing about 8 per cent. Cu and more FeS than corre- sponds with copper pyrites is subjected to alternate roastings and fusions so as to remove the iron fractionally ; during the roastings the iron is progressively oxidised, and during the fusions reactions occur between oxides and sulphides and silica which can happen only in the liquid or semi-liquid state. Com- monly there is (1) a roasting to expel As as AsyOg, Sb as Sb4Og, and some § as SQ, ; (2) a fusion with siliceous material in the ore-furnace to produce a coarse metal containing about 33 per cent. Cu, and corresponding in composition with copper pyrites, and a slag, FeO.SiO, ; (3) a roasting of the granulated coarse metal to complete the oxidation of the FeS ; (4)a fusion of the calcined coarse metal with siliceous materialin the ore-furnace to flux away the iron as 3FeO.2Si0., and leave a Cu,S matte or white metal containing about 77 per cent. Cu. The white metal is first roasted and then fused in the same furnace to pro- duce self-reduction and obtain blister copper (so called from its appearance, due to the escape of the last portions of SO, from the metal as it is solidifying) containing 98 per cent. Cu. When a blast-furnace is used, the first operation is still a roasting of the ore either in a reverberatory furnace or some form of roasting kiln (like a pyrites burner) for oxidising some of the iron sulphide and expelling As and Sb. The roasted ore is then mixed with coke and siliceous matter and fused in the blast-furnace. The presence of the coke constitutes the chemical difference between the processes conducted in the 508 COPPER REFINING two kinds of furnace. In the ore-furnace the reducing agent for eliminating oxygen from Fe,0, (formed by the previous roasting), to enable ferrous silicate to be produced, is the sulphur in the ore, much SO, being eliminated. In the blast-furnace CO from combustion of the coke reduces the Fe,03. The final product of the blast-furnace, like that of the first fusion in the ore-furnace, is a mixture of Cu,S and FeS, but contains about 50 per cent. of Cu. It is either subjected to further roasting and fusion in teverberatory furnaces as in the Welsh process, to produce a white metal (to be treated as in the Welsh process), or it is dead-roasted to form a mixture of CuO and Fe,Q; ; this mixture is then smelted in a blast-furnace with coke and siliceous material to reduce the Fe,0, to FeO, which is fluxed as silicate, and the CuO to metal, care being taken to adjust the constituents of the furnace charge so as to avoid the formation of copper silicate. A coarse metal of this grade may also be smelted directly to copper in a Bessemer converter, like that employed for making steel from pig-iron ; the combustion of the sulphur maintains the temperature, the iron oxide is fluxed by added silica, and the copper sulphide undergoes self-reduction. The crude or blister copper is refined either by fusion in an oxidising atmosphere, or electrolytically. In the former case the operation is con- ducted slowly in a reverberatory furnace, in which the remaining sulphur is expelled as SO, and any iron, tin, lead, &c., together with some of the copper, are oxidised and fluxed away by added silica. Cuprous oxide being soluble in copper (which it renders dry or brittle), the refined molten metal is stirred with a pole of young wood, the gases from which reduce the Cu,O and bring the copper to tough-pitch, which is about 99-6 per cent. For the electrolytic refining the metal is cast into plates which are sus- pended in a bath of copper sulphate solution, acid with H,SO,, and are made the anodes, the cathodes being thin sheets of pure copper. When a current (0-2 volt pressure) is passed through the solution from a dynamo, the anodes dissolve and the copper is deposited on the cathodes. The copper refined in this manner is almost chemically pure, but requires remelting before being hammered or rolled, on account of the crystalline condition in which it is deposited. In this process the gold, silver, and other metals (except iron, which passes into solution), which may be present in the blister copper, remain in the tanks in the form of a fine mud. For the extraction of copper from poor ores (3 per cent. Cu) a wet method is generally adopted. This is rendered economically possible by the fact that when moist copper sulphide is exposed to the air in heaps, kept constantly moist, it becomes oxidised to copper sulphate, which may be dissolved in water. Copper is recovered from the solution by introducing pig-iron, when this metal takes the place of the copper which is precipitated ; CuSO, + Fe = FeSO, + Cu. The copper precipitate thus obtained is melted and refined. Electrolytic deposition of the copper from the solution is also practised. Two other methods of dissolving the copper sulphide from the ore are employed. In the one, the ore is treated with a solution of a ferric salt containing common salt. The former converts the Cu,S of the ore into CugCly, which is dissolved by the solution of salt; Cu,S + 2FeCl, = 2FeCl, + Cu,Cl, + 8. The dissolved copper is then ,pre- cipitated by iron. In the second method (applied to the spent pyrites of the vitriol works, p. 163) the ore is submitted to a chlorinating roasting—that is to say, it is ground, mixed with NaCl, and roasted ; the copper sulphide is thus converted, first into sulphate by roasting, and then into chloride by double decomposition with the salt. The copper chloride is leached out and the copper is precipitated by iron. For the purpose of illustration, copper may be extracted from copper pyrites on the small scale in the following manner : Twenty grams of the powdered ore are mixed with an equal weight of dried borax, and fused in a covered earthen crucible (of about 8 oz. capacity) at a full red heat for about half an hour. The earthy matters associated with the ore are dissolved COPPER—PROPERTIES 509 by the borax, and the pure copper pyrites collects at the bottom of thecrucible. The contents of the latter are poured into an iron mould (scorifying mould, Fig. 268), and when the mass has set, it is dipped into water. The semi-metallic button is then easily detached from the slag by a gentle blow; it is weighed, finely powdered in an iron mortar, and introduced into an earthen crucible, which is placed obliquely over a dull fire, so that it may not become hot enough to fuse the contents, which should be stirred occasionally with an iron rod to promote the oxidation of the sulphur by theair. When the odour of SO, is no longer perceptible, the crucible is placed in a Fletcher’s injector furnace (Fig. 253), and heated a few minutes to bright red, in order to decompose the sulphates of iron and copper. When no more white fumes of SO, are perceived, the crucible is lifted from the furnace, quickly scraped, and the contents quickly trans- # ferred to an iron mortar. This mixture of CuO and Fe,0, is finely powdered, mixed Fic. 268. ‘with 60 grams of dried Na,CO, and 6 grams of powdered charcoal, returned to the crucible, covered with 20 grams of dried borax, and again heated in the furnace for twenty minutes. The crucible is then allowed to cool, and carefully broken to extract the button of metallic copper, which is weighed to ascertain the amount contained in the original ore. Properties of Copper.—The most prominent character which confers upon copper so high a rank among the useful metals is its malleability, which allows it to be readily fashioned under the hammer, and to be beaten or rolled into thin sheets ; among the metals in ordinary use, only gold and silver exceed copper in malleability, and the comparative scarcity of those metals leads to the application of copper for most purposes where great malleability is requisite. The tenacity or strength of copper is high as compared with that of metals generally, but is still only about one-half that of iron. It follows that copper is less ductile than iron, and does not admit of being so readily drawn into exceedingly thin wires. Nevertheless one of its main uses is in the form of wire for telegraphic and telephonic communication, since it is the best conductor of electricity ; in this respect it is much affected by im- purities, electrolytically refined copper being a much better conductor than that refined by furnacing. Copper melts at 1084°; its sp. gr. is 8-9; it is not so hard as iron. As one of the most sonorous of metals, copper has been used, from time immemorial, in the construction of bells and musical instruments. In conductivity for heat, copper is surpassed only by silver and gold. Copper can be obtained in octahedral crystals. When copper sulphate is heated with a very strong solution of sugar, crystalline copper is deposited. The resistance of copper to the chemical action of moist air gives it a great advantage over iron for many uses, and the circumstance that it does not decompose water in presence of dilute sulphuric acid enables it to be employed as the negative plate in galvanic couples. Nitric acid is the best solvent for copper, but the presence of nitrous acid seems to be necessary for the attack of the metal (see p. 194). HCl attacks it in presence of oxidising agents. The action of strong H,SO on Cu has been described at p. 155. A solution of common salt has no perceptible action on copper ; but in the course of time, if the air be allowed access, the metal becomes covered with a green coating of oxychloride of copper, CuCl,.38CuO.4H,0, the action probably consisting, first in the oxidation of the copper by the air, and afterwards in the decomposition of the oxide by the sodium chloride ; 4CuO + 2NaCl + H,O = CuCl,.8Cu0 + 2NaOH. 510 COPPER COOKING VESSELS The surface of the copper is thus corroded, and in the case of a copper-bottomed ship the action of sea-water not only occasions a great waste of copper but roughens the surface of the sheathing, and affords points of attachment to barnacles, &c., which injure the speed of the vessel. Many attempts have been made to obviate this incon- venience. Zinc has been fastened here and there to the outside of the copper, placing the latter in an electro-negative condition ; the copper has been coated with various compositions, but with very indifferent success. JM/untz metal, or yellow sheathing, or malleable brass, an alloy of 3 parts of copper and 2 parts of zinc, has been employed with some advantage in place of copper, for it is very much cheaper and somewhat less easily corroded ; but the difficulty is by no means overcome. Copper containing about 0-5 per cent. of phosphorus is said to be corroded by sea-water much less easily than is pure copper. Ordinary drinking water has no perceptible action on bright copper in the course of a few hours; yet it is found that within that time the water will become sterile if contained in a bright copper vessel, showing that sufficient copper must dissolve to kill the bacteria. The use of copper for culinary vessels has occasionally led to serious consequences, from the poisonous nature of its compounds, and from ignorance of the conditions under which these compounds are formed. A perfectly clean surface of metallic copper is not affected by any of the substances employed in the preparation of food, but if the metal has been allowed to remain exposed to the action of the air, it becomes covered. with a film of oxide of copper, and this subsequently combines with water and carbonic acid gas derived from the air to produce a basic carbonate of copper,! which, becoming dissolved or mixed with the food prepared in these vessels, confers upon it a poisonous character. This danger may be avoided by the use of vessels which are perfectly clean and bright, but even from these certain articles of food may become contaminated with copper, for this metal is more likely to be oxidised by the air when in contact with acids (vinegar, juices of fruits, &c.), or with fatty matters, or even with common salt; and if oxide of copper be once formed, it will be readily dissolved by such substances. Hence it is usual to coat the interior of copper vessels with tin, which is able to resist the action of the air, even in the presence of acids and saline matters. Alloys of Copper.—Copper forms a greater number of useful alloys than any other metal. Those of copper with tin (gun-metal and bronze) have been already noticed (p. 487). With from one-third its weight to its own weight of zinc, copper forms brass, much harder than copper, consider- ably cheaper, and more resisting to the atmosphere. The most important alloys of which copper is a predominant constituent are the following : Brass—55 to 72 copper, 45 to 28 zinc. Muntz metal—60 to 64 copper, 40 to 36 zinc (sp. gr. 8-2). German silver—61 copper, 19-5 zinc, 19-5 nickel (p. 459). Aich or Gedge’s metal—60 copper, 38-2 zinc, 1-8 iron. Delta metal—56 copper, 43 zinc, 1 iron. Bell-metal—78 copper, 22 tin (p. 487). Speculum metal—66-6 copper, 33-4 tin (p. 487). Bronze—75 to 90 copper, 25 to 10 tin (p. 487). Gun-metal—91 copper, 9 tin (sp. gr. 8-5) (p. 487). Bronze coinage—95 copper, | zinc, 4 tin (p. 487). Aluminium bronze—90 copper, 10 aluminium (p. 422). Brass is made by melting copper in a crucible and adding rather more than the desired proportion of zinc, the excess being required to allow for volatilisation and oxidation. The constitution of brass has not been so well ascertained as that of some other alloys. The compound Zn,Cu is 1 Often erroneously called verdigris, which is really a basic acetate of copper, COPPER ALLOYS 511 probably present, and two others of the form ZnCu and Zn ,Cumayoccur. A small quantity of tin is added to brass intended for engraving, and also to brass which is to resist the action of sea-water. When it has to be mechani- cally worked by turning, rolling, filing, &c., about 2 per cent. of lead is usually added to it. The ferruginous brasses, like Delta metal, are harder and stronger than normal brass. Brass cannot be melted without losing a portion of its zine in the form of vapour. Solder for brazing consists of equal weights of copper and zinc. In order to prevent ornamental brass- work from being tarnished by the action of air, it is either lacquered or bronzed. Lacquering consists simply in varnishing the brass with a solution of shellac in spirit, coloured with dragon’s blood. Bronzing is effected by applying a solution of arsenic or mercury, or platinum, to the surface of the brass. By the action of arsenious oxide dissolved in hydrochloric acid upon brass, the latter acquires a coating composed of arsenic and copper, which imparts a bronzed appearance, the zinc being dissolved in place of the arsenic, which combines with the copper at the surface. A mixture of mercuric chloride, HgCl,, and acetic acid is also sometimes used, when the mercury is displaced by the zinc, and precipitated upon the surface of the brass, with which it forms a bronze-like amalgam. For bronzing brass instruments, such as theodolites, levels, &c., a solution of chloride of platinum is employed, the zinc of the brass precipitating a very durable film of metallic platinum upon its surface; PtCl, + Zn, = Pt + 2ZnCl,. A very hard white alloy of 77 parts of Zn, 17 of Sn, and 6 of Cu has been employed for the bearings of the driving wheels of locomotives. Other bearing alloys consist of copper, tin, lead alloys (e.g. Cu 76-8, Sn 8-0, Pb 15-0, P 0-2), and of lead, tin, antimony, zinc and copper alloys (e.g. white metals, such as Pb 40, Sn 45-5, Sb 13, Cu 1-5). Iron and steel are coated with a closely adherent film of copper by placing them in contact with metallic zinc in an alkaline solution of oxide of copper, prepared by mixing sulphate of copper with tartrate of potash and soda, and caustic soda. The copper is thus precipitated upon the iron by slow voltaic action, the zinc being the attacked metal. By adding a solution of stannate of soda to the alkaline copper solution, a deposit of bronze may be obtained. Oxides of Copper.—Two oxides of copper are well known in the separate state, viz. the suboxide, Cu,O, and the oxide, CuO. There is some evidence of the existence of an acid oxide, CuQg. The black oxide of copper (cupric oxide), CuO, is used by the chemist in the ultimate analysis of organic substances by combustion. It is made by dissolving copper in nitric acid, evaporating, and heating the residue of cupric nitrate to dull redness, when it leaves the black oxide (sp. gr. 6:3) ; Cu(NO,), = 2NO, + 0+ CuO. At a higher temperature the oxide fuses (m.p. 1064°) into a very hard mass, losing a little oxygen. When prepared ‘in this manner it always retains nitrogen and is amorphous. It can be obtained in lustrous tetrahedra by fusing it with KOH, washing and levigat- ing away the portion which has remained amorphous. The oxide is hygro- scopic, but is not dissolved by water; acids, however, dissolve it, forming cupric salts, whence the use of oil of vitriol and nitric acid for cleansing the tarnished surface of copper; a blackened coin, for example, immersed in strong HNOg, and thoroughly washed, becomes as bright as when freshly coined. Silica dissolves CuO at a high temperature, forming cupric silicate, a reaction applied in producing a fine green colour in glass. The red oxide (cuprous oxide), Cu,O (sp. gr. 5°749), is found crystallised in regular octahedra, and is formed when copper is heated in air, that portion of the copper-scale which is in contact with the air becoming CuO, while that in contact with the metal is Cu,O. It is made by heating a mixture of 512 COPPER OXIDES 5 parts of the black oxide with 4 parts of copper filings in a closed crucible. It may also be prepared by boiling a solution of cupric sulphate with a solution containing sodium sulphite and sodium carbonate in equal quantities, when the cuprous oxide is precipitated as a reddish-yellow amorphous powder, which should be washed, by decantation, with boiled water— 2CuSO, + 2Na,CO, + Na,SO, = Cu,O0 + 3Na,SO, + 2C0,. Cu,O is precipitated in minute octahedral crystals when solution of CuSO, mixed with glucose is boiled with excess of potash; as with Fehling’s solution. Cuprous oxide is a feeble base, but its salts are not easily obtained by direct action of acids, for these generally decompose it into Cu and CuO, yielding cupric salts. In the moist state it is slowly oxidised by the air. Ammonia dissolves Cu,0, forming a solution which is perfectly colourless until it is allowed to come into contact with air, when it assumes a fine blue colour, becoming converted into an ammoniacal solution of CuO. If the blue solution be placed in a stoppered bottle (quite filled with it) with a strip of clean copper, it will gradually become colourless, the CuO being again reduced to Cu,O, a portion of the copper being dissolved. When copper filings are shaken with ammonia in a bottle of air, the same blue solution is obtained (cf. p. 191). If the blue solution be poured into a large quantity of water, a light blue precipitate of cupric hydroxide is obtained. The ammoniacal solution of cupric oxide has the unusual property of dissolv- ing paper, cotton, tow, and other varieties of cellulose, this substance being reprecipitated from the solution on adding an acid; one mode of making artificial silk is based on this precipitation. Cuprous oxide, added to glass, imparts to it a fine red colour. Cuprous hydride, CuH, is precipitated when cupric sulphate is heated with hypo- phosphorous acid ; or a strong solution of cupric sulphate may be strongly acidified with dilute sulphuric acid, solution of sodium hypophosphite added, and heated till a brown precipitate forms ; this is the hydride, which must not be further heated, as it is decomposed into its elements at 60°. HCl dissolves it easily, with brisk effervescence from escape of H, and formation of a colourless solution of cuprous chloride ; CuH + HCl= CuCl + Hg. Cupric hydroxide, Cu(OH),.—Hydrated CuO of variable composition is obtained as a blue precipitate when potash or soda is added to a cupric salt. When boiled in the liquid it becomes black CuO. It is obtained in a crystalline form, stable at 100°, by action of alkalies on several basic cupric salts. Its solubility in ammonia and the properties of the solution have been noticed above. In the presence of tartaric acid, sugar, and many other organic substances, the hydrated oxide dissolves in caustic alkali to dark blue solutions. The paint known as blue verditer is made by decomposing cupric nitrate with calcium hydroxide. Cupric acid is believed to be formed when metallic copper is fused with nitre and caustic potash, and when Cu(OH), is digested with H,O,. The mass from the former reaction yields a blue solution containing K,CuO, in water, which is very easily decom- posed with evolution of oxygen and precipitation of CuO. By adding KOH and Br to a solution containing copper a black precipitate, believed to be CuQ,, is formed even in very dilute solutions. The existence of an unstable oxide of copper, containing more than one atom of oxygen, is also rendered probable by the circumstance that CuO acts like MnO, in facilitating the decomposition of potassium chlorate by heat (p. 56). Cuprous nitride, CusN, is formed by passing ammonia over precipitated CuO at 250°. It is a dark green powder which explodes easily when heated in air. Cupric nitrate, Cu(NO,)..3Aq, crystallises in blue prisms from a solution of copper in nitric acid ; when formed below 26-4° the crystals are tables with 6Aq. It is deli- quescent and soluble in water and alcohol. When heated to 65° it becomes a green basic nitrate, Cu(NO3)..3Cu(OH)s. Cupric nitrate is used as an oxidising agent in COPPER SULPHATE 513 dyeing and calico-printing. Cupric ammonio-nitrate, Cu(NO3)2.4NHz, is deposited in dark blue crystals from a mixture of cupric nitrate with excess of ammonia. Cupric sulphate, CuSO,.5H,0.—The beautiful prismatic crystals (sp. gr. 2-28) known as blue vitriol, blue stone, blue copperas, or sulphate of copper have been already mentioned as formed from the residue in the preparation of SO, (p. 155) by dissolving copper in oil of vitriol, a process occasionally used for the manufacture of this salt. Dilute H,SO, may be used in making the sulphate by allowing the acid to trickle over granulated Cu so that atmospheric oxygen may have access to the metal. The sulphate of copper is also manufactured by roasting copper pyrites (Cu,Fe,S,) with free access of air, when it becomes partly converted into a mixture of cupric sulphate with ferrous sulphate; Cu,Fe,S, + 80, = 2FeSO, + 2CuSO,. The ferrous sulphate, however, is decomposed by the heat, leaving ferric oxide (see p. 170). When the roasted mass is treated with water, the ferric oxide is left undissolved, and the CuSO, may be obtained in crystals by evaporation. ; Since ferrous sulphate and cupric sulphate are isomorphous, they crystal- lise together (v.i.), and can be separated only by converting the ferrous into ferric sulphate by an oxidising agent such as nitric acid. The nature of the water of crystallisation in this salt has been discussed at p. 39. One hundred parts of H,O dissolve 37 parts of the crystals at 10° and 203 parts at 100°. The solution reddens litmus. Copper sulphate is largely employed by the dyer and calico-printer, and in the manufacture of pigments. It is also occasionally used in medicine, in the electrotype process, and in galvanic batteries. In agriculture it is found useful as a preservative, wheat which is to be sown being steeped in a solution of it to protect the grain from the attack of smut, and its largest application is in the vineyards, where it is used for making a copper hydrate (by mixing its solution with slaked lime) for spraying the vines to kill the phylloxera. For the last-named purpose it must be free from iron. When ammonia is added to solution of CuSO, a basic sulphate is first precipitated, which is dissolved by an excess of NH, to a dark blue liquid. On allowing this to evaporate, dark blue crystals of ammonio-cupric sulphate, CuSO,.4NH;.H,0, are deposited. They lose their ammonia when exposed to the air. CuSO, cannot easily be separated by crystallisation from the sulphates of iron, zine, and magnesium, because it forms double salts with them, which, like those sulphates, have the form MSO,.7H,0, and are isomorphous with MgSO,.7H,O (unless the CuSO, is the predominant constituent, when the salts are of the form MSO,.5H,0, and are isomorphous with CuSO,.5H,0). An instance of this is seen in the black vitriol obtained from the mother-liquor of the copper sulphate at Mansfield, and forming bluish-black crystals isomorphous with green vitriol, FeSO,.7H,O. The formula of black vitriol may be written [CuMgFeMnCoNi]S0,.7H,0, the six isomorphous metals being inter- changeable without altering the general character of the salt. Cupric arsenite (Scheele’s green), CuHAsO3, has been noticed at p. 231. It is a yellowish-green powder, insoluble in water, but easily soluble in acids and alkalies. Its solution in potash has a dark blue colour, and deposits cuprous oxide when boiled, potassium arsenate being produced. Emerald green (see p. 231). Mineral green, CuCO; .Cu(OH)p, has the same composition as natural green malachite, and is prepared by mixing hot solutions of Na,CO, and CuSQ,. When boiled in the liquid it is gradually converted into CuO. The green deposit formed on old copper by exposure to air has the same composition. The blue precipitate produced in cupric solutions by alkaline carbonates in the cold is CuCO, .Cu(OH),.Aq. Chlorides of Copper.—Cupric chloride, CuCl,, is produced by the direct union of its elements, when it forms a brown mass (sp. gr. 3-05), which fuses easily (m.-p. 498°) and is decomposed into chlorine and cuprous chloride, the latter being afterwards converted into vapour. It is very 33 514 CUPROUS CHLORIDE soluble in water, the solution being green when concentrated, and blue when diluted. It is soluble in many organic solvents ; the solution in alcohol burns with a splendid blue flame, and the chloride imparts a like colour to a gas flame. The hydrated cupric chloride, CuCl,.2H,0, is readily prepared by dissolving CuO in hot HCl, and allowing the solution to ecrystallise ; it forms green needle-like crystals (sp. gr. 2:5), which become blue when dried in vacuo. Oxychloride of copper, CuCl,.8CuO .4H,O, is found in prismatic crystals, and is called atacamite. The oxychloride formerly constituted the pigment Brunswick green, made by moistening copper with solution of HCl or NH,Cl, and exposing it to the air in order that it may absorb oxygen : 4Cu + 2HCl + 3H,0 + 202 = CuCl, .3Cu0.4H,0. It is also made by boiling cupric sulphate with chloride of lime. Modern Brunswick green consists of a mixture of Prussian blue, chromate of lead, and barium sulphate. Cuprous chloride, CuCl, is formed as a sublimate when copper is heated in HCl gas. It is also produced when fine copper turnings are shaken with strong HClin a bottle of air ; Cu, + 2HCl + O = 2CuCl +H,0. The cuprous chloride dissolves in the excess of acid to a brown solution, from which water precipitates it white, for this is one of the few chlorides insoluble in water. When exposed to light it assumes a purplish-grey tint, unless it be quite dry. Acopper plate dipped into a strong neutral solution of CuCl, acquires a thin coating of CuCl, upon which photographs may be taken. Cuprous chloride may be prepared as described on p. 254; its m.-p. is 434°; b.-p. about 1000°. Cf. AgCl of the same periodic group. If the solution in HCl be moderately diluted and set aside, it deposits tetrahedral crystals (sp. gr. 3-7) of cuprous chloride. Ammonia (free from air) dissolves CuCl to a colourless liquid which becomes dark blue by contact with air, absorbing oxygen ; it is used as a test for acetylene (p. 253). The solution may be preserved in a colourless state by keeping it in a well-stoppered bottle, quite full, with strips of clean copper. When finely divided Cu is boiled with solution of NH,Cl, the solution deposits colourless crystals of the salt, CuCl(NH;). If the solution of this salt be exposed to the air, blue crystals are deposited, having the formula 2CuCl.CuCl,.4NH;.H,O, and on further exposure a compound of this last salt with ammonium chloride is deposited. The solution of cuprous chloride in hydrochloric acid is employed for absorbing CO in the analysis of gaseous mixtures ; when this solution is exposed to air it absorbs oxygen, and deposits cupric-oxychloride. A strong solution of NH,Cl or of an alkali chloride readily dissolves CuCl, even in the cold, forming soluble double chlorides, such as CuCl.2KCl. The solution in KCl does not absorb oxygen quite so easily as that in NH,Cl. Cuprous Iodide, Cul.—When cupric sulphate is added to an iodide, cuprous iodide and iodine are precipitated, cupric iodide being unstable; CuSO, + 2KI = 2Cul +I + K,S0,4. The iodine makes the precipitate brown; but if a reducing agent be present the precipitate is pure white Cul, the iodine being reduced to HI, which reacts with more CuSQ,, and so on until all the iodine is in the form of Cul ; 2CuSO, -+ 2FeSO, + 2KI = 2Cul + Fe,(SO,)3 + K,SO,. It crystallises in tetrahedra ; sp. gr. 5-67; m.-p. 628° ; b.-p. 760°. Sulphides of Copper.—Copper has a very marked attraction for sulphur, even at the ordinary temperature. A bright surface of copper soon becomes tarnished by contact with sulphur, and H,S blackens the metal. Finely divided copper and sulphur combine slowly at the ordinary temperature, and when heated together they combine with combustion. A thick copper wire burns easily in vapour of sulphur (p. 150). Copper is even partly converted into sulphides when boiled with sulphuric acid, as in the prepara- tion of SO,. This great attraction of copper for sulphur is taken advantage of in the process of kernel roasting for extracting the copper from pyrites COPPER SULPHIDES 515 containing as little as 1 per cent. of the metal. The pyrites is roasted in large heaps (p. 147) for several weeks, when a great part of the iron is con- verted into peroxide, and the copper remains combined with sulphur, forming a hard kernel in the centre of the lumps of ore. This kernel contains about 5 per cent. of copper, and can be smelted with economy. It is easily detached from the shell, consisting of Fe,0, mixed with a little CuSO,, which is washed out with water. Cuprous sulphide, Cu,8, has been mentioned among the ores of copper and among the furnace products in smelting, when it is sometimes obtained in octahedral crystals. It is formed when H,S is passed over red-hot CuO, and when coal-gas is passed over red-hot CuS. It is not attacked by HCl, but HNO, dissolves it readily. The natural sulphide (sp. gr. 5-7) is rhombic, while the artificial sulphide (sp. gr. 5-5) is octahedral ; the change from the former to the latter occurs at 103°. Cu,S melts at 1091°. In solution of silver nitrate it deposits Ag and Ag.S and dissolves as cupric nitrate ; Cu,S + 4AgNO, = AgS + 2Ag + 2Cu(NO,)>. Cupric sulphide, CuS, occurs in nature as indigo copper or blue copper (sp. gr. 4-6), and may be obtained under certain conditions as a black precipitate by the action of H,S upon solution of cupric sulphate, but generally the precipitate is a mixture of Cu,S and 8. When this precipitate is boiled with sulphur and ammonium sulphide it is dissolved in small quantity, and the solution on cooling deposits fine scarlet needles of the NH, -salt of an acid, HCu8,, which yields a number of similar salts. When copper and sulphur are heated together in atomic-proportions to a tempera- ture below the boiling-point of sulphur (448°), CuS is produced; but at a higher temperature this is converted into Cu,8. The sulphides of copper, when exposed. to air in the presence of water, are slowly oxidised and con- verted into cupric sulphate, which is dissolved by the water. It appears to be in this way that the blue water of the copper mines is formed. By thoroughly washing CuS with dil. H,SO, and then with water, it can be made to pass into solution, but it is immediately precipitated by saline matter. CuS conducts electricity well, but Cu,S is not a conductor when free from CuS.’ Phosphide of copper, cupric phosphide, CuzP,, obtained as a black powder by boiling solution of CuSO, with phosphorus, or by passing PH; into a solution of CuSO,, has been already mentioned as a convenient source of phosphine. Another phosphide, obtained by passing vapour of Pover finely divided Cu at a high temperature, is employed in Abel’s composition for magneto-electric fuses, in conjunction with Cu,S and KCI103. Phosphide of copper employed for toughening commercial copper is made by running melted copper into a conical iron crucible lined with loam, at the bottom of which are placed sticks of phosphorus which have been coated with copper by soaking them in cold solution of CuSO,. Silicon may be made to unite with copper by strongly heating finely divided copper with silica and charcoal. A bronze-like mass is thus obtained containing about 5 per cent. Si. It is said to rival iron in ductility and tenacity, and fuses at about the same temperature as bronze. SILVER, Ag = 107.88 In silver we meet with the first metal so far considered which is not capable of undergoing oxidation in the air, and this, in conjunction with its beautiful appearance, occasions its manifold ornamental uses, which are much favoured also by the great malleability and ductility of the metal (in which it ranks only second to gold), for the former property enables it to be rolled out into thin plates or leaves, so that a small quantity of silver suffices to cover a large surface, whilst its ductility permits the wire-drawer to produce the extremely thin silver wire used in making silver lace. 516 SILVER-EXTRACTION Silver, although pretty widely diffused, is found in comparatively small quantity, and hence it bears a high value, which adapts it for a medium of currency. As might be expected from its want of direct attraction for oxygen, silver is found frequently in the metallic or native state, crystallised in cubes or octahedra, which are sometimes aggregated together, as in the silver-mines of Potosi, into arborescent or dendritic forms; it generally contains copper and gold, and sometimes mercury. Silver is more fre- quently met with, however, as sulphide (Ag,S), which is generally associated with large quantities of the sulphides of lead, antimony, and iron. The largest supplies of silver are obtained from the United States, Mexican, Peruvian, and Australian (Broken Hill) mines, but the quantity furnished by Saxony and Hungary is by no means insignificant. Silver chloride (horn silver) is found in considerable quantity in the spongy deposits of silica round the Great Salt Lake in Utah, and also in Chili and Peru. A very large proportion of the total production of silver is the metal recovered from galena in smelting it for lead as described at p. 497. When the extraction of silver from its ores is the main object the method adopted depends upon the conditions at the locality where the ore is mined. Thus, where fuel is available it is customary to smelt the ore either with lead ores or copper ores, the noble metal being eventually obtained either in solution in lead or in a copper matte. In the former case the silver is separated from the lead by cupellation (p. 499). From a copper matte the silver may be extracted by taking advantage of the fact that by carefully roasting a mixture of the sulphides of copper and silver, the copper may be completely oxidised to oxide and the silver to sulphate, so that when the roasted mass is leached with water silver sulphate passes into solution ; the metal is precipitated from this by introducing metallic copper, and the precipitate is refined by roasting it to oxidise the impurities, and fusing it. Dissolution in lead followed by cupellation frequently forms a convenient method for refining silver, but electrolytic refining of the metal on the same lines as those adopted for copper (p. 508) is becoming general ; the electrolyte is a dilute solution of silver nitrate, the crude silver cast into plates forms the anode, while sheets of pure silver constitute the cathodes. This electrolytic treatment is particularly applicable to the large amount of argenti- ferous mud which is deposited in the tanks wherein copper is electrolytically refined (p. 508). It also becomes a part of the process for winning silver from ores which contain but little copper. These are smelted with metallic copper and a flux, and by electrolysis the copper is extracted from the alloy thus produced, leaving the silver as a mud to be melted, cast, and further refined electrolytically. This process takes the place of the old method of separating copper and silver by fusing the alloy with lead and liquating (p. 484) to cause the lead to flow away from the copper, carrying the silver with it to be subsequently recovered by cupellation. Where fuel is scarce, resort is had to the use of solvents. In the old amalgamation process, now practically defunct, mercury was the solvent used. As originally practised in Mexico the process is complicated in its chemical details, but primarily depends upon the reduction of the silver from the form of chloride by means of mercury (iron being sometimes sub- stituted as a reducing agent), AgCl + Hg = HgCl + Ag, and the dissolution of the reduced silver in mercury, which is subsequently distilled, leaving the silver to be refined as described above. The solvent now commonly used is sodium cyanide in aqueous solution of about 1 percent. strength. The finely subdivided ore is stirred with the solution until the silver sulphide has dissolved as a double cyanide, from which ELECTRO-PLATING 517 silver is deposited by adding zinc to the filtered solution ; Ag,S-+-4NaCN = 2NaAg(CN), + Na,S and 2NaAg(CN), + Zn = 2NaCN + Zn(CN), + Ago. In another class of processes for extracting silver from its ores, these are roasted with NaCl, whereby the silver sulphide is first converted into sulphate by oxidation, and then into chloride by double decomposition with the NaCl (chlorinating or chloridising roasting). The silver chloride is dissolved out of the mass by means of a strong solution of NaCl, from which the silver is afterwards precipitated in the metallic state by copper, or as silver iodide, the silver iodide being reduced by zinc, and the zinc iodide used to precipitate a fresh portion of silver. Sodium thiosulphate is also employed to dissolve out the silver chloride, and the solution precipitated by sodium sulphide, the silver sulphide thus obtained being roasted to remove the sulphur and leave metallic silver. Although silver is capable of resisting the oxidising action of the atmc- sphere, it is liable to considerable loss by wear-and-tear in consequence of its softness, and is therefore always hardened, for useful purposes, by the addition of a small proportion of copper. The standard silver employed for coinage and for most articles of silver plate in this country contains, in 1000 parts, 925 of silver and 75 of copper, whilst that used in France contains 900 of silver and 100 of copper. English standard silver is said to have a fineness of 925, and French of 900. Standard. silver, for coining and other purposes, is whitened by being heated in air and immersed in dil. H,SO,, which dissolves the oxide of copper (CuO) formed by the heating, leaving a superficial film of nearly pure silver. Dead or frosted silver is produced in this manner. Owidised silver is covered with a thin film of sulphide by immersion in a solution obtained by boiling sulphur with potash. The solder employed in working silver consists of 5 parts of silver, 2 of zinc, and 6 of brass. Plated articles are manufactured from copper or one of its alloys, which has been united, by rolling, with a thin plate of silver, the adhesion of the latter being promoted by first washing the surface of the copper with a solu- tion of silver nitrate, when a film of this metal is deposited upon its surface, the copper taking the place of the silver in the solution. Electro-plating consists in covering the surface of baser metals with a coating of silver, by making them the cathode in an electrolyte made by dis- solving silver cyanide in potassium cyanide,’ the anode being a silver plate ; the current gradually decomposes the silver cyanide, and this metal is of course (see p. 327) deposited upon the cathode, whilst the cyanogen liberated at the silver plate attacks the silver, so that the solution is always maintained at the same strength, the quantity of silver dissolved at this anode being precisely equal to that deposited at the cathode. Brass and copper are sometimes silvered by rubbing them with a mixture of 10 parts of silver chloride with 1 of corrosive sublimate (mercuric chloride) and 100 of bitartrate of potash. The silver and mercury are both reduced to the metallic state by the baser metal, and an amalgam of silver is formed, which readily coats the surface. The acidity of the bitartrate of potash promotes the reduction. The surface to be silvered should always be cleansed from oxide by momentary immersion in nitric acid, and washed with water. For dry silvering, an amalgam of silver and mercury is applied to the clean surface, and the mercury is afterwards expelled by heat. Glass may be silvered with aid of certain organic substances which are capable of precipitating metallic silver from its solutions. Mirrors are made by pouring upon the surface of plates of glass a solution containing silver tartrate and ammonium tartrate. On heating the glass to a certain tempera- ture the tartrate is reduced, and the metallic silver is deposited in a closely 1 A solution of potassium cyanide in 10 parts of water, with 50 grains of silver chloride dissolved in each pint of the liquid will answer the purpose. 518 PREPARATION OF PURE SILVER adhering film. Glass globes and vases are silvered internally by a process which is exactly similar in principle. The coating is rendered more adherent by sprinkling it with a weak solution of potassio-mercuric cyanide, which amalgamates the silver. Small surfaces of glass for optical purposes may be silvered in the following manner : Dissolve 1 gram of AgNO, in 20 c.c. of distilled water, and add weak NH; carefully until the precipitate is almost entirely dissolved. Filter the solution and make it up to 100 ¢.c. with distilled water. Then dissolve 2 grams of AgNO, in a little distilled water, and add it to a litre of boiling distilled water. Add 1-66 grams of Rochelle salt (tartrate of potassium and sodium), and boil till the precipitated silver tartrate becomes grey ; filter while hot. Clean the glass to be silvered very thoroughly with HNOg, distilled water, KOH, distilled water, alcohol, distilled water ; place it in a clean glass or porcelain vessel, with the side to be silvered uppermost. Mix equal measures of the two silver solutions (cold) and pour the mixture in so as to cover the glass, which will be silvered in about an hour. After washing, it may be allowed to dry, and varnished. Very good mirrors may be made by adding ammonia to weak silver nitrate till the precipitate just redissolves, then a little potash, then ammonia till the liquid is clear, and then a very little glycerin. If a watch-glass be floated on this liquid and a gentle heat applied, a good mirror will be formed in a few minutes. Pure silver is easily obtained from standard silver by dissolving it in nitric acid with the aid of heat, diluting the solution with water, adding solution of common salt as long as it produces any fresh precipitate of silver chloride, washing the precipitate by decantation as long as the washings give a blue tinge with ammonia, and fusing the dried precipitate with half its weight of dried sodium carbonate in a brisk fire, when a button of silver will be found on breaking the crucible— 2AgCl + Na,CO, = Ag, + 2NaCl + O + CO,. The pure silver employed by Stas in his researches on atomic weights was prepared by distilling the metal. When fused in air, silver occludes oxygen (about 20 times its volume), a portion of which it evolves during solidification, causing sprouting on the surface of the partly solidified metal, and sometimes projection of portions of the mass. After cooling, it still retains oxygen, which can only be expelled by heating to about 600° in a vacuum. This may amount to 0-025 per cent. by weight, and has to be taken into consideration in determining atomic weights in terms of silver. Properties of Silver.—The brilliant whiteness of silver distinguishes it from all other metals. It is lighter than lead, its specific gravity being 10-50 ; harder than gold, but not so hard as copper; more malleable and ductile than any other metal except gold, which it surpasses in tenacity. It fuses at a somewhat lower temperature than gold or copper (960°), and is the best conductor of heat and electricity. It is comparatively easily distilled (1950°), yielding a green vapour. It is not oxidised by dry or moist air, either at the ordinary or at high temperatures, but is oxidised by ozone, and tarnished by air containing H,S, from -the production of Ag,S, which is easily removed by solution of potassium cyanide. Pure H,S does not attack silver. It is unaffected by dilute acids, with the excep- tion of nitric, and in this case the presence of nitrous acid is essential ; but hot concentrated sulphuric acid converts it into silver sulphate, and when boiled with strong HCl it dissolves to a slight extent in the form of silver chloride, which is precipitated on adding water. Strong hydriodic acid dissolves silver, evolving hydrogen ; silver iodide is precipitated on addition of water. The alkali hydroxides do not act on silver to the same extent 2 At 300° and 15 atmospheres pressure Ag absorbs as much oxygen as corresponds with the formula Agy0. SILVER NITRATE 519 as on platinum when fused with it; hence silver basins and crucibles are much used in the laboratory. Natural silver is amorphous, but the electro-deposited metal, or the metal precipitated from solution by reducing agents, is crystalline. That produced by reducing silver chloride with sugar is violet and amorphous, and becomes white and crystalline with evolution of heat at 300°. Colloidal silver is formed by the action of certain reducing agents on a solution of silver nitrate, and has lately been applied in medicine. When a solution of ferrous citrate is added to one of silver nitrate, a red solution which deposits a lilac precipitate is obtained ; this precipitate is washed with ammonium nitrate solution, and is then found to contain over 97 per cent. of silver, and to be soluble in water to a red solution. By similar methods an insoluble allotropic silver and an insoluble gold-like allotropic stlver have been obtained. The physical properties of silver deposited as a mirror seem to show that it is colloidal silver. The method of preparing colloidal solutions of metals which is known as electrical scattering is applicable to silver. It consists in forming an electric arc between two wires of the metal under water. Silver Oxide, Ag,O.—This is the only oxide which can be said with certainty to exist. It is a powerful base, comparable with the alkalies in its ability to form neutral salts. It is obtained as a brown precipitate when solution of silver nitrate is decomposed by potash, or, better, poured into an excess of lime-water. When alcoholic solutions of KOH and AgNO, are mixed at — 40° a white precipitate of silver hydroxide, AgOH, is produced ; as the temperature rises, however, it becomes dark from loss of water and formation of Ag,O. The oxide is slightly soluble in water, to which it imparts a weak alkaline reaction. At 270° it decomposes into its elements. It acts as a powerful oxidising agent. Its sp. gr. is 7-52 ; it loses a little oxygen when exposed to light. When moist freshly precipitated silver oxide is covered with a strong solution of ammonia, and allowed to stand for some hours, it becomes black, crystalline, and acquires dangerously explosive properties. The composition of this fulminating silver is not accurately known, but it is supposed to be a silver nitride, NAgs;, corresponding in composition with ammonia. The black amorphous powder produced by heating silver citrate at 100° in hydrogen was formerly called silver suboxide, Ag,O, but is now believed to be a mixture of Ag,O and Ag. The black precipitate obtained by mixing solutions of potassium persulphate and AgNO, is believed to be silver peroxide, AggO.. With ammonium persulphate there is less precipitate, and if NH, be present there is a violent evolution of nitrogen, the silver salt acting catalytically to decompose the mixture in the sense of the equation 3(NH,)oS203 + 8NH, = 6(NH,).SO, + Nz. The substance deposited on the anode during the electrolysis of silver nitrate as black octahedra, which dissolve in HNO, to a deep brown solution of strongly oxidising properties, is probably a compound of silver peroxide with AgNO. Silver nitrate, AgNO,, or lunar caustic (silver being distinguished as luna by the alchemists), is procured by dissolving silver in nitric acid, with the aid of a gentle heat, evaporating the solution to dryness, and heating the residue till it fuses in order to expel the excess of acid. It fuses at 208°. It crystallises from water in the form of colourless square tables (sp. gr. 4°3), easily soluble in water and alcohol. For use in surgery the silver nitrate is fused with 5 per cent. of potassium nitrate and poured in cylindrical moulds, so as to cast it into thin sticks of “ toughened caustic ” ; or with twice its weight of potassium nitrate to form “mitigated caustic.” The action of nitrate of silver as a caustic depends upon the facility with which it parts with oxygen, the silver being reduced to the metallic state, and the oxygen combining with the elements of the organic matter. This 520 SILVER CHLORIDE effect is very much promoted by exposure to sunlight or diffused daylight. Pure silver nitrate is not changed by exposure to light, but if organic matter be present a black deposit, containing finely divided silver, is produced. Thus the solution of silver nitrate stains the fingers black when exposed to light, but the stain may be removed by potassium cyanide, or, more safely, by tincture of iodine. If solution of silver nitrate be dropped upon paper and exposed to light, black stains will be produced and the paper corroded. Silver nitrate is a frequent constituent of marking-inks, since the deposit of metallic silver formed on exposure to light is not removable by washing. The linen is sometimes mordanted by applying «a solution of sodium carbonate before the marking-ink, when the insoluble silver carbonate is precipitated in the fibre, and is more easily blackened than the nitrate, especially if a hot iron is applied. Marking-inks without preparation are made with silver nitrate containing an excess of ammonia, which appropriates the nitric acid, and hastens the blackening on exposure to light or heat. Hair-dyes often contain AgNO;. The important use of this salt in photography has been noticed already (p. 171). In order to prepare silver nitrate from standard silver (containing copper) the metal is dissolved in moderately strong HNOsg, and the solution evaporated to dryness in a porcelain dish, when a blue residue containing the nitrates of silver and copper is obtained. The dish is now moderately heated until the residue has fused and become uniformly black, the blue Cu(NO,). being decomposed and leaving black CuO, at w temperature which is insufficient to decompose the AgNO 3. To ascertain when all the copper nitrate is decomposed, a small sample is removed on the end of a glass rod, dissolved in water, filtered, and tested with ammonia, which will produce a blue colour if any copper be in solution. The residue is treated with hot water, the solution filtered from the CuO and evaporated to crystallisation. Silver nitrate forms crystalline double salts, AgNO;.KNO, and AgNO,;.NH,NO3. It absorbs ammonia with evolution of heat, and silver ammonio-nitrate, AgNO; .2NH3, may be crystallised from a strong solution of silver nitrate saturated with ammonia. The action of chlorine on AgNO, in solution produces silver chlorate and chloride ; 6AgNO, + 3Cl, + 3H,0 = 5AgCl + AgClO; + 6HNOg. Silver nitrite, AgNOg:, is obtained as a white precipitate from KNO, and AgNO . It is soluble in hot water and crystallises in prisms. By long boiling with water it is decomposed ; 2AgNO, = AgNO, + Ag + NO. Silver hyponitrite, AgoN.O. (see p. 206). Silver carbonate, Ag,CO 3, is obtained in transparent yellow crystals when moist silver oxide is acted on by CO,. It dissolves in solution of COs, like CaCO, and is deposited in crystals when the solution is exposed to the air. It is feebly alkaline to moist test-paper. It bears heating nearly to the boiling-point of oil, and fuses just before decomposition. Silver carbonate forms a yellowish-white precipitate when silver nitrate is decomposed by an alkaline carbonate. Silver chloride, AgCl, separates, as a white curdy precipitate, when solution of hydrochloric acid or a chloride is mixed with a solution containing silver. The precipitate is brilliantly white at first, but soon becomes violet, and eventually black, if exposed to daylight, or more rapidly in sunlight, the chloride of silver being reduced to subchloride (Ag,Cl), with separation of chlorine (see p. 171). The blackening is more rapid in the presence of an excess of silver nitrate or of organic matter, upon which the liberated chlorine can act. In the presence of chlorine the blackening does not occur ; nor will perfectly dry AgCl darken. If the white silver chloride be dried in the dark and heated in a crucible, it fuses at 457° to a brownish liquid, which solidifies, on cooling, to a transparent, nearly colourless mass (sp. gr. 5-59), much resembling horn in external characters (horn silver); a strong heat converts it into vapour, but does not decompose it. If fused silver chloride be covered with HCl, and a piece of zinc placed upon it, it will be found entirely reduced, after a few hours, to a cake of metallic silver, the PHOTOGRAPHIC PLATES 521 first portion of silver having been reduced in contact with the zinc, and the remainder by the galvanic action set up by the contact of the two metals beneath the liquid. Fusion with Na,CO, reduces Ag(l, first converting it into Ag,CO;, which breaks up into Ag,, O, and CO,. Silver chloride is slightly soluble in strong HCl and in strong solutions of alkali chlorides. Potassium cyanide and ammonia readily dissolve it, and the latter solution deposits colourless crystals of the chloride when evaporated. If the ammonia be very strong the crystals are a. compound of the chloride with ammonia, 2AgCl.3NH ;. When exposed to gaseous ammonia silver chloride rapidly absorbs the gas, yielding AgCl.3NH3. From photographic fixing solutions containing sodium hyposulphite the silver cannot be precipitated by salt, because the silver chloride is soluble in the hyposulphite. A piece of sheet copper left in this for a day or two will precipitate the silver in the metallic state. Several chemists have claimed to have isolated a dark silver subchloride, to which the formule Ag,Cl and Ag,Cl; have been ascribed. The interest in this supposed subchloride arises from the fact that metallic silver cannot be found in the silver chloride which has been darkened by light, although chlorine has undoubtedly been removed. By adding a reducing agent (such as SnCl,) to an ammoniacal solution of AgCl a black precipitate is obtained, which becomes coloured pink or brown (according to the nature of the reducing agent) when it is washed with nitric acid. A number of such coloured salts has been obtained by Carey Lea from the halides of silver ; these are termed photo-salts of silver and are supposed to be identical with the products of the action of light on the silver halides ; they appear to consist of the normal silver halides with small admixtures of sub-halides. They are dissolved by ammonia with the exception of a slight residue of silver. Silver bromide, AgBr, is a rare Chilian mineral, bromargyrite. Asso- ciated with AgCl it forms the mineral embolite. It much resembles the chloride, but is yellowish and somewhat less easily dissolved by ammonia. Dry silver bromide does not absorb NH,. It melts at 420°; sp. gr. 6°35. When heated to 700° in HCl, silver bromide is converted into the chloride, but at the ordinary temperature HBr converts silver chloride into bromide. Photographic plates and printing papers are made with silver bromide, as it is more sensitive to light than the chloride is. Ammonium bromide is dissolved in a warm aqueous solution of gelatine, and a solution of silver nitrate, less than equivalent to the bromide, is poured in, the room being lighted by red light. The mixture, with the finely divided silver bromide suspended in it, is warmed for some time in order to ‘“‘ ripen’ the emulsion. By this expression it is implied that the silver bromide becomes more sensitive to light, a fact which has not been explained ; the sole effect of the ripening on the silver bromide, so far as has been observed, is the aggregation of the particles, so that they become somewhat coarser. The emulsion is now allowed to set, and washed in water to remove the ammonium nitrate produced by the interaction of the NH, Br and AgNOs, and the excess of NH,Br ; if the latter be not present during the manufacture of the emulsion wu less sensitive plate is produced. The gelatine emulsion is again melted and poured on to the plates. What has been said (p. 520) with reference to the action of light on AgCl may be applied to AgBr. The chemistry of the action and of the development of the invisible image is even yet shrouded in mystery. Silver iodide, AgI, is also found in the mineral kingdom. It is worthy of remark that silver decomposes hydriodic acid much more easily than hydrochloric acid, forming silver iodide, and evolving hydrogen. The silver iodide dissolves in hot hydriodic acid, and the solution deposits crystals of Agl.HI, which are decomposed in the air. If the hot solution be left in contact with silver, prisms of AgI are deposited. By adding silver nitrate to potassium iodide, the silver iodide is obtained as a yellow 522 SILVER SULPHIDE precipitate, which, unlike the chloride, does not dissolve in ammonia, but is bleached, forming 2AgI.NH,, which is also produced when dry silver iodide absorbs ammonia. When slowly cooled, fused AglI solidifies at 540° in the regular system, the crystals being remarkably soft, and at 146° changes to hexagonal crystals. These changes are accompanied by a change of colour from orange to pale yellow. When more rapidly cooled the melted mass contracts considerably on solidifying and on cooling, until the temperature is 116°, whereupon a sudden expansion occurs, concomitant with the passage of the red amorphous to the yellow crystalline modification. When the molten iodide is poured into cold water it becomes yellow, but remains amorphous ; its sp. gr. is 5-6. Silver iodide is the most stable of the silver halides; when exposed to light it requires a more vigorous sensitising agent (t.e. halogen-absorbent) than do the other halides in order that it may undergo photo-reduction. It dissolves in a boiling saturated solution of ‘silver nitrate, and the solution, on cooling, deposits crystals having the composition Agl.AgNO,;; these are sensitive to light since the halogen-absorbent (AgNOs) is ready to hand. The crystals are decomposed by water with separation of silver iodide. Silver fluoride, Ag¥, is deliquescent and very soluble in water, forming crystals which may contain one or two molecules of water. It fuses to a horny mass, like AgCl, but is reduced to the metallic state when heated in moist air. Ammonia also reduces it to the metallic state when heated. Fused AgF conducts the electric current without undergoing decomposition. Silver sulphide, Ag,S, is found as silver glance, which may be regarded as the chief ore of silver ; it has a metallic lustre, and is sometimes found in cubical or octa- hedral crystals. The minerals known as rosiclers or red silver ores contain sulphide of silver combined with the sulphides of arsenic and antimony. The black precipitate obtained by the action of H,S upon a solution of silver is silver sulphide. It may also be formed by heating silver with sulphur in a covered crucible. Silver sulphide is remarkable for being soft and malleable, so that medals may even be struck from it. It is not dissolved by dil. H,SO, or HCl, but HNO, dissolves it readily. Metallic silver dissolves silver sulphide when fused with it, and becomes brittle even when con- taining only 1 per cent. of the sulphide. Ag,S fuses unchanged, but when roasted in air it becomes Ag,SO,. Silver sulphate, Ag,SO,, forms a crystalline precipitate when a strong solution of silver nitrate is stirred with dilute sulphuric acid. It requires 200 parts of cold water to dissolve it. It fuses at 654°. AgHSO, has been crystallised. Silver sulphite, AgoSO3, forms a white precipitate when sulphurous acid is added to silver nitrate. Boiling with water reduces it to metallic silver : Ag,SO, + HO = Age + H,SO,. Silver orthophosphate, Ag,PO4, forms a yellow precipitate when sodium phosphate is added to silver nitrate (p. 220). It is soluble in nitric acid and in ammonia, and is thus distinguished from silver iodide. Silver arsenite, Agz,AsO3, is obtained as a yellow precipitate when ammonia is cautiously added to a mixture of silver nitrate and arsenious acid ; it is soluble in nitric acid and in ammonia. Silver arsenate, Ag,AsO,4, is a red precipitate, soluble in nitric acid and in ammonia, formed when silver nitrate is added to arsenic acid. GOLD, Au = 197.2 The individuality of gold among metals is strongly marked by its colour, its high specific gravity (19-32), its extreme malleability and ductility, its perfect resistance to air, its high conductivity for heat and electricity, its high fusing-point (1064°), its resistance to acids, and its rarity and consequent intrinsic value. Gold is one of those few metals which are always found native, and is remarkable for its wide distribution, though in small quantities, over the surface of the earth. The principal supplies of this metal are GOLD 523 derived from the Transvaal, Alaska, California, Australia, the Ural Moun- tains, Mexico, Brazil and Peru. Small quantities have been occasionally met with in our own islands, particularly at Wicklow, at Caeder Idris in Wales, Leadhills in Scotland, and in Cornwall. The mode of the occurrence of gold in the mineral kingdom resembles that of the ore of tin, for it is either found disseminated in the primitive rocks, or in alluvial deposits of sand, which appear to have been formed by the disintegration of those rocks under the continued action of torrents. In the former case the gold is often found crystallised in cubes and octa- hedra, or in forms derived from these, and sometimes aggregated together in dendritic or branch-like forms. In the alluvial deposits the gold is usually found in small scales (gold dust), but sometimes in masses of con- siderable size (nuggets), the rounded appearance of which indicates that they have been subjected to attrition. The particles of gold are extracted from the alluvial sands by taking advantage of the high specific gravity of the metal (19-32), which causes it to remain behind, whilst the sand, which is very much lighter (sp. gr. 2-6), is carried away by water, The washing is commonly performed by hand in wooden or metal bowls, in which the sand is shaken up with water, and the lighter portions dexterously poured off, so as to leave the grains of gold at the bottom of the vessel. On a somewhat larger scale the auriferous sand is washed in a cradle or inclined wooden trough, furnished with rockers, and with an opening at the lower end for the escape of the water. The sand is thrown on to a grating at the head of the cradle, which retains the large pebbles, whilst the sand and gold pass through, the former being washed away by a stream of water which is kept flowing through the trough. When the gold is disseminated through masses of quartz or other rock, it is essential to crush the latter before the gold can be separated. Stamping is the mode of crushing generally adopted, and it is more convenient to catch as much of the gold as possible in mercury, with which it readily amalga- mates, than to rely upon a washing process for the separation. With reference to this amalgamation process, the gold ore is either free-milling, t.e. gives a satisfactory yield by treatment with mercury, or refractory. In the latter case it is generally the presence of pyrites or other sulphide as an incrus- tation on the gold which hinders amalgamation, and the ore must be roasted to eliminate the sulphur before it is treated. The stamp is a mass of iron, a (Fig. 269), of about 500 kilos, lifted by a revolving cam, b, some eighty times per minute and allowed to fall from a height of 20 cm. on an iron shoe, c. Five of such stamps operate in a trough, d, charged with mercury (containing a little sodium to make it more active, or ‘“‘ quicken” it) in the space around the shoes. The ore charged into the trough is first crushed dry, then water is allowed to flow through while crushing is con- tinued until a pulp or slime of the finely subdivided ore suspended in water is produced. The larger particles of gold are caught in the mercury in the trough ; the pulp flows through a screen on the face, e, of the trough down gutters lined with amalgamated copper plates which catch much of the fine gold. The amalgam from the trough and that scraped from the H plates is squeezed through linen or wash leather, leaving behind the o& more or less solid gold amalgam, which is distilled in iron retorts to separate the mercury from the gold. The latter is fused in crucibles under borax and is then ready for the refinery ; it contains (in the Transvaal) about 85 per cent. Au, 14 per cent Ag, and 1 per cent. Cu. It is to be noted that gold is never found unaccompanied by silver and copper. c Fig. 269. The amount of gold in the ore varies greatly with the source of the ore ; about 0-5 oz. per ton is common. Only about half of it is won by amalga- 524 CHLORINATION OF GOLD ORES mation (in the Transvaal); the rest of the particles have not that bright surface which is essential for ready union with mercury, and flow away with the water containing the crushed gangue. These tailings are treated by the cyanide process, which consists in dissolving the gold in a solution of alkali cyanide and subsequently depositing it from the solution by introducing metallic zinc, or by electrolysis. Generally the tailings undergo some process of concentration (p. 406) before the treatment with cyanide. The concentrates are charged into a vat and a dilute solution (about 0-1 per cent.) of potassium or sodium cyanide is allowed to percolate through the mass. Oxygen, generally supplied by the air, is required, the reaction being represented as follows: Au, + 4NaCN + O, + 2H,0 = 2NaAu(CN), + 2NaOH + H,0,; the hydrogen peroxide at first formed acts on more gold: Au, + 4NaCN + H,O, = 2NaAu(CN). + 2NaOH. Far more NaCN is required than is indicated by these equations, much being rendered ineffective by reaction with the iron and other substances present in the tailings. The addition of cyanogen bromide, CNBr (made by action of Br on NaCN), is practised with some ores, as it aids the solvent action of the cyanide ; BrCN + 3NaCN + Aug = 2NaAu(CN), + NaBr. The solution of gold is run into vats containing zinc shavings which have been coated with lead by immersion in a lead acetate solution. The Zn takes the place of the gold, the Pb-Zn couple helping the reaction ; 2K Au(CN), + Zn= K,Zn(CN), + Aug. About 90 per cent. of the gold in the ore is recovered by the combined amalgamation and cyaniding. Refractory ores are generally treated by chlorination; the roasted and powdered ore is mixed with water in a suitable vessel into which chlorine (or bromine) is introduced. The gold dissolves as chloride (or bromide) and is precipitated from the solution by adding ferrous sulphate or sulphurous acid, or by filtration through charcoal which retains the gold; this is subsequently separated by burning the charcoal. The chlorination process yields the purest gold (95-99 per cent.), but in every case the ingots cast at the mines need refining to separate the silver and copper which are the chief impurities. This is generally effected by taking advantage of the insolubility of gold in HNO, or H,SO,, which dissolve the other metals ; but the base meta] being surrounded by the gold, the attack of the acid is excessively slow unless the base metals consti- tute at least 66 per cent. of the alloy. The crude gold is therefore first melted with about twice its weight of silver. The alloy is fused and poured into water so as to granulate it; it is then boiled in cast-iron retorts with oil of vitriol, which converts the Ag and Cu into sulphates, with evolution of SO,, whilst the gold is left untouched. The silver is precipitated from the solution of the sulphates in water by copper, copper sulphate passing into solu- tion, to be subsequently recovered by evaporation and crystallisation. This process is so effectual that even ,,th part of this metal may be profitably extracted from 100 parts of an alloy, and much gold has been obtained in this way from old silver-plate, coins, &c., which were manufactured before so perfect a process for the separation of these metals was known. On boiling old silver coins or ornaments with nitric acid, they are generally found to yield a minute proportion of gold in the form of a purple powder. If the alloy contains a large quantity of copper, it is found expedient to remove a great deal of this metal in the form of oxide by heating the alloy in a current of air. Gold which is brittle and unfit for coining, in consequence of the presence of small quantities of foreign metals, is sometimes refined by melting it with oxide of copper or with a mixture of nitre and borax, when the foreign metals, with the exception of silver, are oxidised and dissolved in the slag. Another process consists in throwing some mercuric chloride into the melting-pot and stirring it up with the metal, when its vapour converts the metallic impurities into chlorides, which are volatilised. An excellent method consists in fusing the gold with a little borax, and passing chlorine into it through a clay tube; Sb, As, &c., are carried off as chlorides, whilst the Ag, REFINING GOLD 525 also converted into chloride, rises to the surface of the gold in a fused state, afterwards solidifying into a cake, which is reduced to the metallic state by placing it between plates of wrought iron and immersing it in diluted sulphuric acid. In electrolytic refining, the crude gold is made the anode in an electrolytic cell containing a solution of gold chloride in HCl. The silver becomes AgCl, but the other metals dissolve in the acid, while the gold is deposited on the cathode. Pure gold, like pure silver, is too soft to resist the wear to which it is subjected in its ordinary uses, and it is therefore alloyed for coinage in this country with one-eleventh of its weight of copper, so that gold coin contains 1 part of copper and 11 parts of gold. The gold used for articles of jewellery is alloyed with variable proportions of copper and silver. The alloy of copper and gold is much redder than pure gold. The English sovereign contains 91-67 per cent. of gold and 8-33 per cent. of copper. Its sp. gr. is 17-157, and its weight is 123-274 grains. The Australian sovereign contains silver in place of copper, and is lighter in colour than pure gold. The degree of purity of gold is generally expressed by quoting it as of so many carats fine. Thus, pure gold is said to be 24 carats fine: English standard gold 22 carats fine, that is, contains 22 carats of gold out of the 24. Gold of 18 carats fine would contain 18 parts of gold out of the 24, or three- fourths of its weight of gold. The other legal standards are 15, 12, and 9 carat gold. The fineness sometimes refers to the quantity of gold in 1000 parts of the alloy ; thus, English coin has a fineness of 916-7, German and. American coin of 900. In order to impart to gold ornaments the appearance of pure gold, they are heated till the copper in the outer layer is oxidised, and then dipped into nitric or sulphuric acid, which dissolves the copper oxide and leaves a film of pure gold. Pure gold is easily prepared from standard or jeweller’s gold by dissolving it in a mixture of 4 vols. HCl and 1 vol. HNO;, evaporating the solution to a small bulk to expel excess of acid, diluting with a considerable quantity of water, filtering from the separated AgCl, and adding a solution of ferrous sulphate, when the gold is precipitated as a dark purple powder (2AuCl, + 6FeSO, = Au, + 2FeCl,; + 2Fe,(SO4)3), which may be collected on a filter, well washed, dried, and fused in a small clay crucible with a little borax, the crucible having been previously dipped in a hot saturated solution of borax, and dried, to prevent adhesion of the globules of gold. The precipitated gold appears, under the microscope, in cubical crystals. By employing oxalic acid instead of ferrous sulphate, and heating the solution, the gold is precipitated in a spongy state, and becomes a coherent lustrous mass under pressure. The metal is employed in this form by dentists. The genuineness of gold trinkets, &c., is generally tested by touching them with nitric acid, which attacks them if they contain a very considerable proportion of copper, producing a green stain, but this test is evidently useless if the surface be gilt. The weight is, of course, a good criterion in practised hands, but even these have been deceived by bars of platinum covered with gold. The specific gravity may be taken in doubtful cases ; that of sovereign gold is 17-157. In assaying gold, the metal is wrapped in a thin piece of paper together with about three times its weight of pure silver (quartation, see p. 524), and added to twelve times its weight of pure lead fused in a bone-ash cupel (see p. 499) placed in a mufile (or exposed to a strong oxidising blowpipe flame), when the lead and copper are oxidised, and the fused oxide of lead dissolves that of copper, both being absorbed by the cupel. When the metallic button no longer diminishes in size, it is allowed to cool, hammered into a flat disc which is annealed by being heated to redness, and rolled out to a thin plate, so that it may be rolled up by the thumb and finger into a cornette, which is boiled with nitric acid (sp. gr. 1-18) to extract the silver ; the remaining gold is washed with distilled water, and boiled with nitric acid of sp. gr. 1-28, to extract the last traces of silver, 526 GOLD LEAF after which it is again washed, heated to redness in a small crucible, and weighed. The stronger nitric acid could not be used at first, since it would be likely to break the cornette into fragments which could not be so readily washed without loss. The physical characters of gold have been referred to at the beginning of this section. In malleability and ductility it surpasses all other metals ; the former property is turned to advantage for the manufacture of gold leaf, for which purpose a bar of gold, containing 96-25 per cent. of gold, 2-5 per cent. of silver, and 1-25 per cent. of copper, is passed between rollers which extend it into the form of a riband ; this is cut up into squares, which are packed between layers of fine vellum, and beaten with a heavy hammer ; these thinner squares are then again cut up and beaten between layers of gold-beater’s skin until they are sufficiently thin. An ounce of gold may thus be spread over 100 square feet ; 282,000 of such leaves placed upon each other form a pile of only 1 inch high. These leaves will allow light to pass through them, and always appear green or blue when held up to the light, though they exhibit the ordinary colour of gold by reflected light. If a gold leaf adhering to a glass plate be heated to nearly the boiling-point of oil for some time, it becomes nearly transparent, and invisible by transmitted light, though still showing the colour of gold by reflected light ; if it be pressed with a moderately hard body, it again transmits a green light. When gold wire or leaf is deflagrated by electricity on a glass plate, the finely divided metal transmits ruby, violet, or green light, according to its thickness, though it has the golden colour by reflected light. On heating these deposits to dull redness on the glass, they all change to the ruby colour, while still golden by reflection. Pressure with a hard body changes the colour of the transmitted light from red to green. It is believed that under the conditions of these experiments the gold has passed in the colloidal state into the solid solution which constitutes the glass (p. 397). For colloidal gold always shows this play of colour. The commercial form of colloidal gold is called purple of Cassius, and is made by reducing gold chloride solution by means of stannous chloride, Ten parts of pink salt (p. 489), 1-07 parts of tin-foil, and 40 parts of water are heated together until the tin has dissolved ; 140 parts of water are then added and the solution is poured gradually into a gently heated solution of 1-34 parts of gold as chloride dissolved in 480 parts of water. The precipitate at first formed disappears on stirring, an apparently perfectly clear purple solution being obtained, from which, however, a purple powder slowly settles, especially if some saline solution be added, the liquid becoming colourless. Since the particular colour of this form of colloidal gold is in some way dependent on the presence of hydrated stannic oxide, purple of Cassius was formerly believed to be a stannate of gold. The fresh precipitate dissolves in ammonia, but the purple solution becomes blue on exposure to light and finally colourless, gold being deposited and stannic oxide left in solution. Purple of Cassius is used for painting on glass and porcelain. Other reducing agents also produce colloidal gold.t_ Thus, when a solution of gold trichloride, containing 0-04 gram of gold per litre, is shaken with a little solution of phosphorus in ether, in a chemically clean bottle, a ruby-red liquid is produced, in which the reflected colour of gold may be seen by bringing the solar rays to a focus in the liquid by a convex lens. This liquid will continue to deposit fine particles of gold for many months. The first deposits are blue by transmitted light, and the last are ruby. The supernatant liquid is eventually colourless. If a little sodium chloride be added to the ruby liquid, it transmits a blue light, and the gold which has remained suspended for six months may be deposited in a few hours. The production of the colour of colloidal gold forms the most delicate test for the metal, 1 part in 100 million parts of water being recognisable. The extreme ductility of gold is exemplified by the fact that 1 grain of gold can be drawn to a wire 166 metres long. Although fusing at about the melting-point of copper, gold is seldom cast, on account of its great contrac- tion during solidification. 1A particularly useful reagent for producing colloidal metals is a solution of an alkali ferropyrophosphate made by adding a solution of FeSO, to one of an alkali pyrophosphate. GOLD CHLORIDES 527 Gold is not affected even to the same extent as silver by exposure to the atmosphere, for H,S has no action upon it, and hence no metal is so well adapted for coating surfaces which are required to preserve their lustre. The gold is sometimes applied to the surfaces of metals in the form of an amalgam, the mercury being afterwards driven off by heat. Metals may also be gilt by means of a boiling solution prepared by dissolving gold in aqua regia, and adding an excess of bicarbonate of potash or of soda. But electro-gilding is the most common process; it resembles electroplating with silver (p. 517), a solution of gold cyanide in potassium cyanide being the electrolyte. A gold crucible is very useful in the laboratory for effecting the fusion of substances with caustic alkalies, which would corrode a platinum crucible. The only single acid which attacks gold is selenic, H,SeO,, which the gold reduces to selenious acid, H,SeO,. Aqua regia is the usual solvent. A mixture of H,SO, with HNO, dissolves the metal, the latter acid becoming reduced to nitrous acid, which precipitates the gold again in the metallic state on pouring the solution into a large volume of water. On account of its high resistance to sulphuric acid, platinum vitriol retorts are now frequently lined with gold. Fused caustic alkalies are not without action on gold, but they attack platinum more strongly. Gold forms three types of salts, AuX, AuX,, and AuXs. Oxides of Gold.—Gold cannot be directly oxidised. Three oxides have been obtained, Au,O, AuO, and Au,Q3, but none of them is of any great practical importance. Aurous oxide, Au,O, obtained by decomposing aurous chloride with potash, is a violet-coloured powder which is decomposed by hydrochloric acid ; 3Au,0 + 6HCl = 2AuCl, + 3H,0 + 4Au Auric oxide, AugQg, is obtained by gently heating auric hydroxide, Au(OH),. This is prepared by heating « weak solution of auric chloride with excess of potash, and adding sodium sulphate, when auric hydroxide is precipitated, of a brown colour like ferric hydroxide. It is very unstable, evolving oxygen when exposed to light. Nitric acid dissolves it, and it is reprecipitated by water. It dissolves in potash, and the solution yields crystals of potassium aurate, KAuO,.3Aq. By- heating Au(OH), at 160° AuO is formed. Chlorides of Gold,—Three are known: AuCl, AuCl,, AuCl,. When precipitated gold is attacked by chlorine gas at 170°, it yields gold dichloride, AuCl,, a dark red hard substance decomposed by water into AuCl and AuCl;. Auric chloride, AuCl;, may be obtained by dissolving gold in a mixture of 4 vols. HCl and 1 vol. HNOs, and evaporating on a water bath to a small bulk ; on cooling, yellow prismatic crystals of a compound of the trichloride with hydrochloric acid (AuCl,.HCl.4Aq) are deposited, from which the hydrochloric acid may be expelled by a gentle heat (not exceeding 120°), when the trichloride forms red-brown deliquescent crystals of AuCl, .2Aq, dissolving very readily in water, giving a bright yellow solution which stains the skin and other organic matter purple when exposed to light, depositing finely divided gold ; the solution appears to contain an acid, H,AuCl,0, of which the silver salt is known. Almost every substance capable of combining with oxygen reduces the gold to the metallic state. The inside of « perfectly clean flask or tube may be covered with a film of metallic gold by a dilute solution of the trichloride mixed with citric acid and NHz;, and gently heated. The facility with which it deposits metallic gold, and the resistance of the deposited metal to atmospheric action, has rendered AuCl, very useful in photography. Alcohol and ether readily dissolve the trichloride, the latter being able to extract it from its aqueous solution. Red crystals of AuCl, are sublimed when thin gold foil is heated in a current of chlorine at 300°. Trichloride of gold (like platinic chloride) forms crystallisable compounds with the alkali chlorides and with the hydrochlorides of organic bases, and affords great help to the chemist in defining these last. Awrochloride of sodiwm forms reddish-yellow prismatic crystals (NaCl. AuCl,.2Aq), which are sold for photographic purposes. Aurous chloride (AuCl) is left when the trichloride is gently heated, but is reduced 528 GOLD SULPHIDES to metallic gold at a higher temperature. Aurous chloride is sparingly soluble in water, and of a pale yellow colour. Boiling water decomposes it into metallic gold and the trichloride. Fulminating gold is obtained as a buff precipitate when ammonia is added to solution of auric chloride. It contains Au, N, H, Cl, and O, but its composition is not well established. It explodes violently when gently heated. The Sel dor of the photographer is a hyposulphite (thiosulphate) of gold aa sodium, Aup$,03.3Na,8,03.4Aq, which is obtained in fine white needles by pouring a solution of 1 part of AuCl; into a solution of 3 parts of Na.S.03, and adding alcohol, in which the double salt is insoluble. Its formation may be explained by the equation— 8Na,$,0, + 2AuCl, = Au,S.03.3Na.S.0, + 6NaCl -+ 2Na.S,0o. Since it is not decomposed by acids in the same manner as ordinary thiosulphates are, it is probably sodium aurothiosulphate, Naz;AuS,0,4.2Aq, a view supported by the preparation of a corresponding barium salt and by decomposing this with sulphuric acid, when aurothiosulphuric acid, HzAuS40g, is obtained. HNO, separates all the gold in the metallic state. The sulphides of gold are not thoroughly known. Gold does not combine directly with sulphur, but if it be heated with sulphur and alkali sulphides, it forms soluble compounds. In this way, sodium aurosulphide, NaAuS.4Aq, may be obtained in colourless prisms soluble in alcohol. It is doubtful whether the black precipitate obtained by passing H,§ into solution of AuCl; is a sulphide or metallic gold. When H,§ is added to a boiling solution of auric chloride, the metal itself is precipitated : 8AuCl, + 3H,S + 12H,O = 8Au + 24HCl + 3H,80,. A yellowish-grey brittle arsenide of gold (AuAsg) has been found in quartz in Australia. THE EIGHTH GROUP As already shown (p. 302), the eighth group of Mendeléeff’s Table (p. 8) comprehends three series of metals of descending valency. The metals of the first series, iron, cobalt, nickel, copper, have already been dealt with. The others will now be considered, for convenience, in reverse order of their group pairs, namely: Platinum and Paxuapium, Irtprum and Ruoprum, Osmium and Rursentrom, frequently all classed together as the “ Platinum Group.” These are followed by Corrsr, Stuver, and Gop, already considered. PLATINUM, Pt = 195.2 Platinum (platina, Spanish diminutive of silver) is remarkable for (1) its high specific gravity of 21-4; (2) its very high fusing-point, 1744° ; (3) its slight expansion when heated, which allows it to be sealed into glass without cracking by unequal contraction on cooling ; (4) its permanence in air at all temperatures ; (5) its resistance to the action of strong acids ; (6) its power of inducing the combination of oxygen with other bodies ; (7) its presence in nature only in the metallic state. It is found distributed in flattened grains through alluvial deposits similar to those in which gold is found ; indeed, these grains are generally accompanied by grains of gold, and of a group of very rare metals only found in platinum ores, viz. palladium, iridium, osmium, rhodium, and ruthenium. Russia furnishes the largest supply of platinum from the Ural Mountains, but smaller quantities are obtained from Brazil, Peru, Borneo, Australia, and California. The process for obtaining the platinum in a marketable form is rather a chemical than a metallurgical operation. The ore containing the grains of platinum and the associated metals is heated with hydrochloric acid to dissolve base metals, and then, in retorts, under slightly increased pressure to hasten the dissolution, with aqua regia, which dissolves palladium, rhodium, platinum, and a little iridium as chlorides. The osmium in the ore partly distils as osmic acid and partly remains undissolved as an alloy with the iridium (osmiridium), together with ruthenium, chrome iron ore, and titanic iron. The solution containing the platinum as PtCl, is neutra- lised with Na,CO,, and the palladium is precipitated as cyanide, Pd(CN),, by the addition of mercuric cyanide. The platinum is now precipitated by the addition of ammonium chloride, with which PtCl, combines to form a yellow, sparingly soluble salt (ammonium platinochloride, (NH,4),PtCl, or 2NH,C1.PtCl,).!. This precipitate is collected, washed, and heated to redness, when all its constituents, except the platinum, are expelled in the form of gas, that metal being left in the peculiar porous condition in which it is known as spongy platinum. To convert this into compact platinum it is melted ina lime furnace by means of the oxyhydrogen blowpipe (Fig. 270), whence it is poured into an ingot mould made of gas-carbon. The melted platinum absorbs oxygen, as melted silver does, and evolves it again on cooling. This method is now modified by fusing the ore with 6 parts of lead, and treating the alloy with dilute nitric acid (1:8), which dissolves most of the lead, together with copper, iron, palladium, and rhodium. The residue, containing platinum, lead, 1 When rhodium is present, the liquid from which this precipitate has been deposited will have a rose colour. The precipitate is then mixed with KHSO, and a little NH,HSO,, and heated to redness in a platinum dish; the rhodium becomes double sulphate of rhodium and potassium, which may be removed from the spongy platinum by boiling with water, 529 34, 2 530 PLATINUM—USES and iridium, is treated with dilute aqua regia, which leaves the iridium undissolved. The lead is precipitated by sulphuric acid, and the solution of platinic chloride treated as above. Another process based upon the use of lead consists in fusing the platinum ore with an equal weight of lead sulphide and the same quantity of lead oxide when the sulphur and oxygen escape as SQg, and the reduced lead dissolves the platinum, leaving undissolved a very heavy alloy of osmium and iridium, which sinks to the bottom. The upper part of the alloy of Pb and Pt is then ladled out and cupelled (p. 498), when the latter metal is left in a spongy condition, the Pb being removed in the form of oxide. Its resistance to the action of high temperatures and of most chemical agents renders platinum of the greatest service in chemical operations. Platinum stills are employed, even on the large scale, for the concentration of sulphuric acid, and platinum elec- trodes are much used in electro-chemical processes. L. In the form of basins, small crucibles, foil, and wire, 4 this metal is indispensable to the analytical chemist. Fie. 270. Unfortunately, it is softer than silver, and therefore ill-adapted for wear, and is so heavy that even small vessels must be mace very thin in order not to be too heavy for a delicate balance. Commercial platinum generally contains a little iridium, which hardens it and increases its elasticity. Its malleability and ductility are very considerable, so that it is easily rolled into thin foil and drawn into fine wires ; in ductility it is surpassed only by gold and silver. It has been drawn, by an ingenious contrivance of Wollaston’s, into wire of only sooooth of an inch in diameter, a mile of which (notwithstanding the high specific gravity of the metal) would weigh only a single grain. This remarkable extension of the metal was effected by casting a cylinder of silver around wa very_thin platinum wire obtained by the ordinary process of wire-drawing ; when the cylinder of silver, with the platinum wire in its centre, was itself drawn out into an extremely thin wire, of course the platinum core would have become incon- ceivably thin, and when the silver casing was dissolved off by nitric acid, this minute filament of platinum was left. A wide application of platinum is in the form of wire for conveying the electric current to the filament in an electric incandescent lamp. As such lamps must be vacuous the leading-in wires must be hermetically sealed in the glass, which is possible with platinum, its coefficient of expansion being near to that of glass, whereas there is considerable difference in the case of other metals, except an alloy of iron and nickel (p.459). The dentist is one of the largest users of platinum, finding it the best material for making pegs for fixing teeth. The remarkable power possessed by platinum of inducing chemical combination between oxygen and other gases has already been noticed. Even the compact metal possesses this property, as may be seen by heating a piece of platinum foil to redness in the flame of a gas-burner, rapidly extinguishing the gas, and turning it on again, when the cold stream of gas will still maintain the metal at a red heat, in consequence of the combination with atmospheric oxygen at the surface of the platinum. A similar experiment may be made by supporting a coil of platinum wire in the flame of a spirit lamp (Fig. 271), and suddenly extinguishing the flame, when the metal is intensely heated, by placing the mouth of a test-tube over it; the wire will continue to glow by inducing the combination of the spirit vapour with oxygen on its surface. By substituting a little ball of spongy platinum for the coil of platinum wire, and mixing some fragrant essential oil with the spirit, an elegant perfuming PLATINUM OXIDES 531 lamp has been contrived. Upon the same principle an instantaneous light apparatus has been made, in which a jet of hydrogen gas is kindled by impinging upon a fragment of cold spongy platinum, which at once ignites it by inducing its combination with the oxygen condensed within the pores of the metal (Dobereiner’s lamp). Spongy platinum is obtained in a very active form by heating the ammonio-chloride of platinum very gently in a stream of coal-gas or hydrogen as long as any fumes of HCl are evolved. If platinum be precipitated in the metallic state from a solution, it is obtained in the form of a powder, called platinum black, which possesses this power of promoting combination with oxygen in the highest perfection. This form of platinum may be obtained by boiling solution of platinic chloride with Rochelle salt (potassium sodium tartrate), or by dropping it into a boiling mixture of 3 vols. glycerin and 2 vols. KOH of sp. gr. 1:08, when the platinum black is precipitated, and must be filtered off, washed, and dried at a gentle heat. Platinum in this form is capable of absorbing 800 times its volume of oxygen, which does not enter into combination with it, but is simply (& condensed into its pores, and is available for combination with other }¥ bodies. A jet of hydrogen allowed to pass on toa grain or two of ‘this “S= == powder is kindled at once, and if afew particles of it be thrown into a fra. 271. mixture of hydrogen and oxygen, explosion immediately follows. A drop of alcohol is also inflamed when allowed to fall upon a little of the powder. Platinum black loses its activity after having been heated to redness. See also Occlusion, p. 97. Although platinum resists the action of hydrochloric and nitric acids, unless they are mixed, and is unaffected at the ordinary temperature by other chemical agents, it is easily attacked at high temperatures by phos- phorus, arsenic, carbon, boron, silicon, and by a large number of the metals ; the caustic alkalies and alkaline earths also corrode it when heated, so that some discretion is necessary in the use of vessels made of this costly metal. When platinum is alloyed with 10 parts of silver, both metals may be dissolved by nitric acid. Oxides of Platinum.—Platinous oxide, PtO, is obtained as a black hydrate by heating potassium platinichloride (v.7.) with NaOH. It is feebly acidic. Platinic oxide, PtOg, is characteristically an acid oxide, but is also a weak base. It is made by gently heating platinic hydroxide, Pt(OH),, obtained by boiling platinic chloride with potash, and treating the precipitate with acetic acid; this leaves a nearly white powder, Pt(OH),.2H,O. At 100° this becomes brown Pt(OH),. Acids dissolve it, forming platinic salts. Alkalies dissolve it, forming platinates. Heat reduces the oxides and hydroxides to metallic platinum. Sodium platinate, NagO.3PtO,.6Aq, may be crystallised from a solution of the hydroxide in soda. Calcium platinate is convenient for the separation of platinum from iridium, which is generally contained in the commercial metal ; for this purpose the platinum is dissolved in nitro-hydrochloric acid, the solution evaporated till it solidifies on cooling, the mixed chlorides of iridium and platinum dissolved in water, and decomposed with an excess of lime without exposure to light ; the platinum then passes into solution as calcium platinate, and the platinic acid may be separated as a calcium salt from the filtered solution by exposure to light. If platinic hydroxide be dissolved in diluted sulphuric acid and the solution mixed with excess of ammonia, a black precipitate of fulminating platinum is obtained, which detonates violently at about 204°, Chlorides of Platinum.—Platinic chloride, PtCl,, is the most useful salt of the metal, and may be prepared by dissolving scraps of platinum- foil in a mixture of 4 measures of concentrated HCl with 1 of concentrated HNO, (6-5 grams of platinum require 56 c.c. of HCl), evaporating the liquid at a gentle heat to the consistence of a syrup, redissolving in HCl, and again’ 1 When platinum leaf is heated with HCl at 150° in a sealed tube it dissolves, but the chloride is subsequently reduced by the hydrogen evolved, and the metal reappears as crystals on the sides of the tube. The same has been observed of gold and silver leaf 532 CHLOROPLATINATES evaporating to expel excess of HNO . The syrupy liquid solidifies, on cooling, to a red-brown mass, which is very deliquescent, and dissolves easily in water or alcohol to a red-brown solution. If the concentrated solution be allowed to cool before all the free HCl has been expelled, long brown pris- matic crystals of a combination of platinic chloride with HCl are obtained (PtCl,.2HCl.6Aq). If these are heated in dry HCl, the anhydrous PtCl, is obtained in a non-deliquescent condition ; it decomposes Na,CO3;, evolving CO,. Platinic chloride is remarkable for its disposition to form sparingly soluble double chlorides with the chlorides of the alkali metals and the hydrochlorides of organic bases, a property of great value to the chemist in effecting the detection and separation of these bodies. These double chlorides are generally regarded as platinichlorides (formerly platino- chlorides) or chloroplatinates, derived from hydrogen platinichloride, or chloroplatinic acid, H,PtCl,. Potassium platinichloride, 2KC1.PtCl,, forms minute yellow octahedral crystals ; those of rubidium and cesium have a similar composition and crystalline form. Sodium platinichloride differs from these in being very soluble in water and alcohol ; it may be crystallised in long red prisms, having the composition 2NaCl.PtCl,.6Aq. Ammonium platinichloride, 2NH,Cl.PtCl,, has been already noticed as the form in which platinum is precipitated in order to separate it from other metals. It crystallises, like the potassium-salt, in yellow octahedra, which are very sparingly soluble in water and insoluble in alcohol. It is the form into which nitrogen is finally converted in analysis in order to determine its weight. When heated to redness, this salt leaves a residue of spongy platinum. Silver nitrate, added in excess to platinic chloride containing HCl, precipitates all the platinum as 2AgC1.PtCl,, a yellow precipitate decomposed by water. Platinic chloride is sometimes used for browning gun-barrels, &c., under the name of muriate of platina. Platinic chloride may be heated to 230° without decomposition, but above that temperature it evolves chlorine, and is slowly converted into the platinous chloride, PtCl,, which is reduced, at a much higher temperature, to the metallic state. Platinous ehloride forms a dingy green powder, which is insoluble in water and in HNO, and H,SO,, but dissolves in hot HCl, and in solution of platinic chloride, yielding in the former a bright red, in the latter a very dark brown-red solution. Platinous chloride is capable of absorbing ethylene, C,H,. At 250° it absorbs CO and forms the crystal- line compounds PtCl,.CO, PtCl,(CO)s, and (PtCle)o(CO);, and the non-volatile compound PtCl, .2COCI, ; the first of these volatilises unchanged. The solution of PtCl, in HCl is not precipitated by KCl, but a soluble double chloride (2KC1.PtCl,) may be crystallised from the liquid. If NH,Cl be added to the hydrochloric solution, a double salt, 2NH,Cl.PtCl,, ammonium chloroplatinite or platinochloride, may be obtained in yellow crystals by evaporation. If, instead of NH,Cl, free NH, be added in excess to the boiling solution of platinous chloride in HCl, brilliant green needles (green salt of Magnus) are deposited on cooling, which contain the elements of platinous chloride and ammonia, PtClp(NH3),. This is an example of a large number of compounds containing the elements of ammonia and platinous or platinic salts, but in which neither ammonia nor platinum can be detected by ordinary reactions. Since in Magnus’s green salt half the Cl fails to react with AgNO3, the salt is supposed to have double the foregoing formula and to be a double compound of platinous chloride and a plato- NH; .NH;.Cl diammine chloride; thus, PKC NH; .NH3.Cl the salt with excess of NHz, for, on cooling, the solution deposits yellowish-white pris- matic crystals of the platodiammine chloride, Pt(NH;.NH;.Cl)..H,O. The corre- sponding sulphate can be obtained, and by treating this with Ba(OH), a powerfully alkaline solution is produced, which yields crystals of platodiammine hydroxide, Pt(NH,;.NH,;.OH).. This is a strong alkali, eagerly absorbing CO, from the air and expelling NH; from its salts ; at 110° it melts, and at a higher temperature loses NH; and H,0, becoming platosammine oxide, Pt(NH,;.NH;)O an insoluble grey solid. .PtCly. The PtCl, can be removed by boiling PALLADIUM 533 The platinum in the foregoing compounds and in others of a like kind, too many for enumeration here, is divalent. By treating the compounds with a halogen or nitric acid corresponding platinammine derivatives are formed, in which the platinum is tetravalent. Thus when the platosammine chloride, Pt(NH,.NH3)Cl,, corresponding with the foregoing oxide is suspended in boiling water and treated with Cl, it becomes chloroplatinammine chloride, Cl,Pt(NH3.NH3)Clo, a yellow crystalline substance. A series of similar derivatives containing two atoms of platinum in the molecule is known, but for a full classification of the platinum-ammonium compounds which resemble the like compounds of cobalt (p. 458) the reader is referred to the chemical dictionaries. Potassium platinonitrite, K,Pt(NO.)4, crystallises when a hot mixture of potassium nitrite and potassium platinous chloride solution is allowed to cool ; it readily combines with two atomic proportions of a halogen. The acid H,Pt(NO,), has been prepared. Platinic iodide, PtI,, is a dark brown amorphous substance which is soluble in HI, yielding a purple-red solution containing 2HI.PtI,.9Aq, which may be crystallised. Hence the dark red colour when an acid solution of PtCl, is added to potassium iodide. The sulphides of platinum correspond in composition with the oxides and chlorides and may be obtained by the action of hydrosulphuric acid upon the respective chlorides as black precipitates. PtS, combines with alkaline sulphides to form soluble compounds. K,S .3PtS.PtS, is obtained by fusing spongy platinum with KOH and sulphur. Platinum phosphide, PtP., and arsenide, PtAsy, are lustrous metallic bodies formed by direct combination at a high temperature. PALLADIUM, Pd = 106.7 This metal is found in small quantity associated with native gold and platinum. It presents a great general resemblance to platinum, but is distinguished therefrom by being far more easily oxidised, and by forming an insoluble cyanide, which is utilised in separating palladium from the platinum ores (p. 529). The cyanide yields spongy palladium when heated, which may be fused in the same manner as platinum. When alloyed with native gold, palladium is separated by fusing the alloy with silver and boiling it with nitric acid, which leaves the gold undissolved. The silver is precipitated from the solution as chloride by adding NaCl, and metallic zinc is placed in the liquid, which precipitates the palladium, lead, and copper as a black powder. This is dissolved in HNO,, and the solution mixed with an excess of NH3, which precipitates lead oxide, leaving Cu and Pd in solution. On adding HCl in slight excess a yellow precipitate of the compound PdCl,.2NH; is obtained, which leaves metallic palladium when heated. Palladium is much lighter (sp. gr. 11-9) than platinum ; it is malleable and ductile, like that metal, from which it is distinguished by being stained black by an alcoholic solution of iodine. It is capable of being highly polished and is useful for mirrors. It melts at 1500°. It is unchangeable in air unless heated, when it becomes blue from superficial oxidation, but regains its whiteness when further heated, the oxide being decomposed. Unlike platinum, it may be dissolved by nitric acid, forming palladous nitrate, Pd(NO3)2, which is sometimes employed in analysis for precipitating jodine from the iodides, in the form of black palladous iodide, PdI,. Palladium is useful, on account of its hardness, lightness, and resistance to tarnish, in the construction of philosophical instruments ; alloyed with twice its weight of silver, it is used for small weights. Its capacity for absorbing hydrogen has been already noticed (p. 97). Palladium forms three oxides. PdO is obtained in a hydrated state as a brown or black powder when a solution of Pd(NOs3)z is boiled for some time ; in this form it is soluble in acids and in alkalies, but when heated at 800° in oxygen it becomes anhydrous, green, and soluble with difficulty even in aqua regia. When a solution of .Pd(NOs). is electrolysed Pd,O, and PdO, are formed respectively as anode products according to the conditions of operation; the latter behaves as a peroxide. Palladic chloride, PdCl,, unlike platinic chloride, is very unstable, being easily decomposed, even in solution, into palladous chloride, PdCl,, and free chlorine. The latter chloride is reduced by hydrogen in the cold, and may be applied as a test for this gas. Both the 534 RHODIUM chlorides form soluble double salts with the alkali chlorides ; ammonium chloropalladite, PdCl, .2NH,Cl, has a dark green colour. PdCl is said to be formed when PdCl, is gently heated. Pulverulent palladium carbide is formed when the metal is heated in the flame of a spirit lamp, or in gaseous hydrocarbons. RHODIUM, Rh = 102.9 Rhodium, another of the metals associated with the ores of platinum, has acquired its name from the red colour of many of its salts (jd8ev, @ rose). It is obtained from the solution of the ore in aqua regia by precipitating the platinum with NH,Cl, neutra- lising with Na,CO;, adding mercuric cyanide to separate the palladium as cyanide, and evaporating the filtered solution to dryness with excess of hydrochloric acid. On treating the residue with alcohol, the double chloride of rhodium and sodium is left undissolved as a red powder. By heating this in a tube through which hydrogen is passed, the rhodium is reduced to the metallic state, and the sodium chloride may be washed out with water, leaving a grey powder of metallic rhodium, which is fused by the oxyhydrogen blowpipe at 2000°, and forms a very hard malleable metal (sp. gr. 12-1) not dissolved even by aqua regia, although this acid dissolves it in ores of platinum, because it is alloyed with other metals. If platinum be alloyed with 30 per cent. of rhodium, however, it is not affected by aqua regia, which will probably render the alloy useful for chemical vessels. Rhodium may be brought into solution by fusing it with KHSO,, when SO, escapes and a double sulphate of rhodium and potassium is formed, which gives a pink solution in water. When rhodium is melted with zinc and the alloy is boiled with an acid, the rhodium is left as a black powder which is apparently an allotropic form of the metal, for when it is heated it explodes, but remains metallic rhodium. Finely divided rhodium is oxidised, when heated in air, but whether to RhO or Rh,O3 is uncertain. Three oxides may be said to be known, namely, Rh,O;, which is left when the nitrate is gently heated ; RhO,, formed when the metal is fused with KOH and KNO,; RhO;, formed by heating the hydrated dioxide (which is a green precipitate obtained when chlorine is passed into potash containing Rh,O,) with nitric acid. BhgO; is the most stable of these ; it is not easily decomposed by heat, and is insoluble in acids, though it is a basic oxide, and its salts, which have a red colour, are obtained by indirect methods. The salts of rhodium are only of one type—RhX,;. Rhodium trichloride, RhCl,, obtained by heating the metal in chlorine, has a brownish-red colour and is insoluble ; it may, however, be obtained in a red solution by dissolving the hydrated Rh,O, in HCl. Rhodium recalls chromium in several respects ; when the red solution of rhodium chloride is boiled with a strong solution of alkali, black Rh(OH),; is thrown down; but when the alkali is added by degrees, yellow Rh(OH)3.H,O is precipitated ; this dissolves to a yellow solution in acids, which becomes red only on boiling. Like chromium, rhodium salts form a series of complex ammonium derivatives. RhCl, forms two classes of double salts with the alkali chlorides—for instance, K;RhCl,.3H,O and K,RhCl;.H,O. The sodium salt, Na;RhCl,.9H,O (red octahedra), is prepared by heating a mixture of rhodium black and NaClin a current of chlorine, dissolving and cerystallising. On boiling a solution of RhCl, with NH, in excess, a yellow ammoniated salt (RhCl, .S5NH3) may be crystallised, from which the metallic rhodium may be obtained by ignition. With sulphur rhodium combines energetically at a high temperature; a mono- sulphide and a sesquisulphide have been obtained. An alloy of gold with between 30 and 40 per cent. of rhodium has been found in Mexico. An alloy of Pt with 10 per cent. of Rh is used as one of the metals, Pt being the other, of the thermo-electric couple used as a pyrometer. OSMIUM, Os = 190.9 This metal is characterised by its yielding « very volatile acid oxide (perosmic anhydride, OsO,), the vapours of which have a very irritating odour (doy, odour). It occurs in the ores of platinum in flat scales, consisting of an alloy of osmium, iridium, ruthenium, and rhodium. This alloy is also found associated with native gold, and, being very heavy, it accumulates at the bottom of the crucible in which the gold is OSMIUM—RUTHENTIUM 535 melted. The osmium alloy is extremely hard, and has been used to tip the points of gold pens. When a grain of it happens to be present in the gold which is being coined, it often seriously injures the die. When the platinum ore is treated with aqua regia, this alloy is left undissolved, together with grains of chrome-iron ore and titanic iron. To extract osmium from this residue, it is heated in a porcelain tube through which a current of dry air is passed, when the osmium is converted into OsO,, the vapour of which is carried forward by the current of air and condensed in bottles provided to receive it. The OsO, forms colourless prismatic crystals which fuse and volatilise below the boiling-point of water, yielding a most irritating vapour, recalling chlorine. It is slowly dissolved by water, giving a solution which exhales the same odour and stains the skin black ; tincture of galls gives a blue precipitate with the solution. Its acid properties are feeble, for it neither reddens litmus nor decomposes the carbonates, and its salts are decomposed by boiling their solutions. Its solution in HCl gives a black precipitate of OsS,, with HS. By passing a mixture of CO and vapour of OsO4 through a red-hot porcelain tube, amorphous osmium is obtained, and may be converted into the crystalline form by fusing it with tin and dissolving in HCl, when blue lustrous cubical crystals of osmium are obtained, which scratch glass, and are heavier than any other body, having the specific gravity 22-48. It can be fused (2500°) in the electric are. By dissolving perosmic anhydride in potash, potassium perosmate, KOsO,, is supposed to be formed, but this has not been isolated. When alcohol is added to this solution the OsO, is presumably reduced to OsO;, for rose-coloured crystals of potassium osmate, K,0.0s0,;.2H,0, are deposited ; by treating this salt with nitric acid, osmic acid, H,O0sQ,, is obtained as a sooty-black powder, which tends to oxidise in air, yielding an odour of perosmic anhydride. The “ osmic acid ” of commerce is OsOq. When OsQ, is dissolved in solution of SO,, osmium sulphite, OsSOz, is obtained ; this is almost the only osmium oxy-salt which is known. By adding an alkali to the solution in absence of air, hydrated osmium monoxide, OsO.nH,O, is obtained as a blue-black powder soluble in HCl to a blue solution and easily oxidised. Os,03 and OsO, are obtained by heating potassium osmochloride, 3KC1.OsCl,, and osmichloride, 2KCI1.OsCl,, respectively with an alkali carbonate in absence of air. Osmium dichloride, OsCl,, and tetrachloride, OsCl, are obtained as two distinct sublimates when the metal is heated in chlorine; OsCl, is less volatile, and forms green needles, whilst OsCl, is a-dark-red powder. By mixing Os with KCl, heating the mixture in chlorine, treating the mass with water, and evaporating, red octahedra of 2KC1.OsCl, separate, whilst from the mother-liquor 3KCl.OsCl, .3H,0 is crystallised. When osmic acid is heated with HCl and alcohol and the solution is evaporated, crystals having the formula Os,Cl,.7H,O are formed ; these are red when dry, but dissolve in water and in alcohol to a green solution ; by adding KCl to the alcoholic solution, K,OsCl, is precipitated, and when the filtrate is evaporated, OsCl, .3H,O crystallises. Several compounds of osmium salts with ammonia (osmamines) are known, and a “ potassium osmiamate,”’ KNOsOs3, is obtained by the action of NH; on a solution of OsO, in KOH. RUTHENIUM, Ru = 101.7 In the process of extracting osmium from the residue left on treating the platinum ore with aqua regia, by heating in a current of air, square prismatic crystals of ruthenium dioxide, RuOg, are deposited nearer to the heated portion of the tube than the perosmic anhydride, for the dioxide is not itself volatile, being only carried forward mechanically ; or it may be that the volatile RuO, is formed in the hot part of the tube, and dissociated into RuO, and Oz, in a cooler part. When RuO, is heated in H the metal is obtained ; it can be melted (1800°) in the electric furnace, and is then a grey metal, very hard, brittle when cold but malleable when hot ; its sp. gr. is 12-06. It is insoluble in acids. When fused with zinc it yields an allotropic form similar to that described above for rhodium. When ruthenium is heated at 1000° in oxygen the volatile oxide RuO, is formed, and may be isolated if rapidly cooled, but when allowed to cool slowly it decomposes. The same oxide may be obtained by heating ruthenium with KNO, and KOH, and saturating the solution of the fused mass with chlorine, when RuQ, sublimes. It is 536 IRIDIUM soluble in water, melts at 25-5°, and sublimes easily ; at 107° it decomposes explosively. It is decomposed by light, yielding, apparently, RuO3. Its aqueous solution slowly deposits Ru gO,.eH,O, or when boiled Ru,O,.2H,O. It is reduced to metal by alcohol. The oxides RuO and Ru,0, are probably also known. Ruthenates analogous to the osmates have been prepared. RuCl, is the only chloride known with certainty ; it is made by dissolving RuO, in HCl and evaporating to dryness. It is insoluble in cold water, but dissolves in absolute alcohol to a purple-violet solution which becomes indigo-blue from absorption of water and formation of RuCl, .OH ; the solution gradually deposits Ru(OH);. Double chlorides analogous to those of osmium exist. Sulphates corresponding with RuO and Ru,Qg have been obtained. A mineral found as small lustrous granules in Borneo, and named lawrite, contains sulphides of ruthenium and osmium. IRIDIUM, Ir = 193.1 Named from Iris, the rainbow, in allusion to the varied colours of its compounds, this metal occurs in the insoluble alloy from the platinum ores. It is also sometimes found separately, and occasionally alloyed with platinum, the alloy crystallising in octahedra, which are even heavier than platinum (sp. gr. 22-4). If the insoluble osmiridium alloy left by agua regia be mixed with common salt and heated in a current of chlorine a mixture of the sodio-chlorides of the metals is obtained and may be extracted by boiling water. If the solution be evaporated and distilled with nitric acid, the osmium is distilled off as perosmic anhydride, and by adding ammonium chloride to the residual solution the iridium is precipitated as a dark red-brown ammonio-chloride, 2NH,Cl.IrCl,, which leaves metallic ‘iridium when heated. Like platinum, it then forms a grey spongy mass, but is oxidised when heated in air, and may be fused (2200°) with the oxyhydrogen blowpipe to a hard brittle mass (sp. gr. 22-4), which does not oxidise in air. Like rhodium, it is not attacked by aqua regia, unless alloyed with platinum. By fusion with zinc it yields an allotropic form similar to that described for rhodium. The product of the oxidation of finely divided iridium in air is the sesquioxide (Ir,Q3), which is a black powder used for imparting an intense black to porcelain ; it is insoluble in acids, and decomposes when heated into IrQ, and Ir with loss of oxygen. The dioxide (IrO,) and a green ftriovide (IrO3) are known. The dichloride (IrClg) and tetrachloride (IrCl,) of iridium resemble the corresponding chlorides of platinum in forming double salts with the alkali chlorides. There is also a trichloride (IrCl,), the solution of which has a green colour, and gives a yellow precipitate with mercurous nitrate, and a blue precipitate, soon becoming white with silver nitrate. Double compounds of the chloride with ammonia (iridamines) are known. Iridium resembles palladium in its disposition to combine with carbon when heated in the flame of a spirit-lamp. Salts of iridium correspond with the oxides IrO and Ir,Q3. An iridio-platinum alloy containing about 10 per cent. of iridium has been found very useful for making standard rules and weights, on account of its indestructibility, extreme rigidity, hardness, and high density. The Table on p. 537 exhibits a general view of the analytical process by which the remarkable metals associated in the ores of platinum may be separated from each other, omitting the minor details which are requisite to ensure the purity of each metal. Review of Metals of the Platinum Group.—These metals fall into two classes, according to the proximity which exists between their specific gravities and between their atomic weights, viz. Os, Ir, Pt and Ru, Rh, Pd. Gold is associated with the former class by its specific gravity, atomic weight, and insolubility, whilst silver is related to the latter class also by its atomic weight and specific gravity, and by its solubility in nitric acid, resembling that of Pd. The first member of each class (Os and Ru) gives a volatile tetroxide, whilst the highest state of oxidation of the remaining metals diminishes, thus: OsO4, IrO3, PtO, and RuOQ,, RhO;, PdO,. In the periodic classification (p. 8) they fall in the same group as Fe, Co, and Ni, with which they have several features in common, such as the marked colour of their salts, their infusibility, and their tendency to form salts in two stages of oxidation. SEPARATION OF PLATINUM METALS ANALYSIS OF THE ORE OF PLATINUM Boil with aqua regia 537 Dissolved ; PLATINUM, PALLADIUM, RHODIUM Add ammonium chloride. Undissolved ; IRIDIUM. OSMIUM, RUTHENIUM. Chrome iron ore, Titanic iron, &c. Heat in a current of dry air. Precipitated ; PLATINUM as 2NH,C1.PtCl,. Solution ; Neutralise with sodium carbonate ; add mercuric cyanide. Precipitated ; PALLADIUM as PdCyz. Solution ; Evaporate with hydrochloric acid ; treat with alcohol. Insoluble ; RHODIUM as 3NaCl.RhCl;. Volatilised ; OSMIUM as OsO,. Carried forward by the current ; RUTHENIUM as RuQ,. Residue ; Mix with sodium chloride, and heat in a current of chlorine. Treat with boiling water Dissolved ; | Residue ; IRIDIUM Titanic as iron, 2NaCl.IrCl,.| Chrome’ iron ore, &e. ORGANIC CHEMISTRY THE division of chemistry into inorganic and organic was originally intended to distinguish mineral substances from those derived from animal and vegetable life ; but since many of the latter may now be produced in the laboratory from the elements as obtained from mineral sources, it has become usual to define organic chemistry as the chemistry of the compounds of carbon, since this element is always present in the substances formerly spoken of as organic. Organic chemistry is distinguished from inorganic chiefly in being concerned with the arrangement, in different proportions or in different positions, of only four elements, carbon, hydrogen, oxygen, and nitrogen, though other elements occasionally enter into the composition of organic compounds. Perhaps the most striking difference between compounds of carbon and those of other elements is the large number of atoms contained in 1 molecule of the majority of carbon compounds. It is rare in inorganic chemistry to find a compound whose molecule contains more than 6 atoms of any one element ; yet the majority of carbon compounds contain 6 or more atoms of carbon in the molecule, so that it would appear to be a characteristic property of carbon to combine with itself. When an organic body is completely burnt in air, its carbon is oxidised to CO,, its hydrogen to H,O, and its nitrogen may be set free. If, therefore, conditions are devised for assuring the quantitative conversion of the elements into these products, the latter can be collected and weighed, and so an ultimate analysis (i.e. determination of the elements present) of the organic compound can be made. The determination of carbon and hydrogen is technically known as making a “combustion.” 1 The substance to be analysed, having been carefully dried and weighed Fie. 272. (about 0-5 gram), is placed in a small boat-shaped tray (A, Fig. 272) of porcelain or platinum, which is introduced into one end of a glass tube about 30 inches long, of which about 24 inches are filled with small fragments of carefully dried cupric oxide. The end of the tube where the boat is placed is connected with an apparatus for trans- mitting air or oxygen, which has been purified from CO, by passing through potash, and from H,O by calcium chloride. To the other end of the tube is attached, by a perforated cork, a weighed tube (B) filled with small fragments of calcium chloride to absorb H,O, and to this is joined, by a caoutchouc tube, a bulb-apparatus (C) con- taining strong potash to absorb COs, and a small guard-tube (E) with calcium chloride to 1 For exact details of the methods of organic analysis the reader must consult works on analytical chemistry. 538 ULTIMATE ORGANIC ANALYSIS 539 prevent loss of water from the potash. The potash-bulbs and guard tube are accurately weighed. The combustion-tube is supported in a combustion furnace, and that portion which contains the CuO is heated to redness. The end containing the boat is then gradually heated, so that the organic substance is slowly vaporised or decomposed. The vapour or the products of decomposition, in passing over the red-hot cupric oxide, will acquire the oxygen necessary to convert the C into CO, and the H into H,0, which are absorbed in the potash bulbs and calcium-chloride tube respectively. At the end of the process, which commonly occupies about an hour, a slow stream of pure air or oxygen is passed through, whilst the entire tube is red-hot, in order to burn any charcoal which may remain in the boat, and to carry forward all the CO, and H,O into the absorption apparatus. The weight of the CO, is given by the increase in weight of the potash bulbs (C and E), that of the H,O by the increase in weight of the calcium-chloride tube (B). , L When nitrogen is present in the substance, it may be partly converted into NOs, which would increase the weight of the absorption-apparatus. To avoid this, three or four inches of the front end of the combustion-tube are filled with perfectly bright metallic copper, which, being heated to redness, absorbs the O from the NOx, leaving N, which passes through the absorption-apparatus and escapes. When it is desired to make a de- termination of the nitrogen, the combustion-tube is arranged in the same way, but the absorption- apparatus is exchanged for a bent tube to permit Fig. 273. the collection and measurement of the gas in a graduated tube filled with strong potash. Before commencing the combustion, the air is swept out of the tube by a stream of pure COs, which is continued during the combustion, and is absorbed by the potash, the nitrogen alone being collected and measured. This is known as Dumas’ method. - Another method, Will and Varrentrap’s, of estimating nitrogen in organic substances consists in heating them with soda-lime, in a combustion tube sealed at one end and heated in a combustion furnace, when the N is evolved as NH3, which is absorbed by hydrochloric acid in the absorption bulb shown in Fig. 273, and precipitated by platinic chloride, the weight of N being calculated from that of the PtCl,.2NH,Cl obtained ; or the NH; is absorbed in a f| known quantity of acid which is after- wards titrated with a standard solution of alkali, and the quantity which has been neutralised by the evolved ammonia thus determined. Kjeldah’s method of estimating nitro- gen consists in oxidising the substance by heating it with concentrated H,SO, Fic. 274. and acid potassium sulphate (KHSO,), whereby the N is converted into NHg, which forms ammonium sulphate. The NH, is subsequently liberated by boiling with alkali, absorbed by hydrochloric acid and determined either with platinic chloride or standard alkali, as described above. Sulphur and phosphorus are estimated in organic compounds by converting them into sulphuric and phosphoric acids, respectively, by the action of powerful oxidising- agents (nitric acid, chloric acid, bromine, &c.), and determining these acids by the usual methods. The halogens are determined by oxidising the substance by heating it with fuming HNO, and AgNO, under pressure in sealed glass tubes, which for the sake of safety must be heated in a tube furnace (Fig. 274), whereby the halogen is converted into silver halide and weighed as such (Carius’ method). By heating with basic oxides, e.g. CaO, or peroxides, e.g. NagQz, the halogen, 8, P, &c., is taken up and subsequently determined in the usual way. 540 CALCULATION OF FORMULA The proportion of oxygen in an organic substance is generally ascertained by difference, that is, by deducting the sum of the weights of all the other elements from the total weight of the substance. As an example of the ultimate analysis of an organic compound, that of alcohol may be given (volatile liquids are weighed in a small glass bulb with a thin stem, the end of which is sealed for weighing, and broken off when the bulb is introduced into the combustion-tube) : ‘5 gram alcohol, burnt with cupric oxide, as above, gave -9565 gram CO, and -5869 gram H,0. Since 44 grams CO, contain 12 grams C, 4i of 9565, or -2608, is the weight of C found. Since 18 grams H,O contain 2 grams H, , of -5869, or -0652, is the weight of H found. The sum of C and H is -2608 + -0652, or -3260. Deducting this from -5 gram alcohol, we have -174 gram for the weight of O contained in it. So that -5 gram alcohol contains: ‘2608 gram carbon or 52-16 per cent. 0652 ., hydrogen or 13-04 __,, 1740 ,, oxygen or 34:80 ,, It is usual to express the results of such an analysis in an empirical formula, which gives, in the simplest form, the relative number of atoms of the elements present. To deduce the empirical formula from the percentage composition, the percentage of each element is divided by its atomic weight, and the ratio of the resulting quotients expressed in its lowest terms ; thus: 52-16 divided by 12 gives 4-34 atomic weights of carbon 13-04 we 1 ,, 13-04 23 oe hydrogen 34:80 Ps 16 sO, 2:17 55 ps oxygen If the ratio 4-34: 13-04: 2-17 be expressed in its lowest terms, it becomes 2: 6: 1, giving for the empirical formula of alcohol, C,H,0O. ‘The question now arises whether this formula is a true representation of the molecule or indivisible particle of alcohol, or whether the molecule should be written CyH,.0., or CgH,,03, or in any other form which would preserve the ratio established beyond dispute by the above analysis. To deduce the molecular formula of a compound from its empirical formula the molecular weight of the compound must be determined. The most usual methods for this and the principles underlying them have already been given (p. 312). For alcohol and volatile substances generally, the vapour density method commends itself; in other cases the cryoscopic and ebulliscopic methods. Where organic acids and bases are concerned resort is frequently had to the following chemical methods : Determination of the molecular formula of an acid.—The substance yielded, on combustion with cupric oxide, in 100 parts—carbon, 40, hydrogen, 6-66, oxygen 53-33 ; which lead to CH,O as the simplest or empirical formula of the acid. The acid was found to give only one class of salts with K and Na, showing that it contains only one atom of H exchangeable for a metal, or is monobasic (p. 90). By neutralising the acid with ammonia, and stirring with solution of silver nitrate, a crystalline silver salt was obtained, which was purified by recrystallisation from hot water, dried, weighed in a porcelain crucible of known weight, and gradually heated to redness. On again weighing the crucible after cooling, it was found to contain a quantity of metallic silver amounting to 64-66 per cent. of the weight of the salt. Now, as a general rule, a silver salt is formed from an acid by the displacement of an atom of hydrogen by an atom of silver; so that what remains of a silver salt, after deducting the silver, represents the acid itself minus a quantity of hydrogen equivalent to the silver. From the silver salt . ‘ 3 - 100-00 Deduct the silver . 3 ; . 64:66 Acid residue . , 7 7 » 85:34 MOLECULAR FORMULA 541 Then 64-66 Ag : 108 ie in one ord 6: 35-34: 59 ih residue in one of the salt molecule, To the acid residue. ‘ ‘ ; . 59 Add the hydrogen equivalent toanatomofAg 1 Molecular weight of the acid. 4 . 60 The formula CH,O represents 12 + 2 + 16 = 30. Hence the molecular formula is C,H,O2 = 60; and the silver salt is C,H, AgOp. Determination of the molecular formula of an organic base.—The substance yielded on combustion with*cupric oxide, in 100 parts, carbon 77-42, hydrogen 7-53. A deter- mination of nitrogen gave 15-05 per cent., so that there was no oxygen. These numbers lead to CgsH,N as the simplest or empirical formula of the base. By dissolving the base in hydrochloric acid and adding platinic chloride, a yellow crystalline precipitate was obtained, resembling the ammonio-platinic chloride formed when ammonia is treated in the same way. This precipitate was washed with alcohol, dried, weighed in a porcelain crucible, and heated to redness, when it left a residue of metallic platinum, which amounted to 32-72 per cent. of the weight of the salt. Asa general rule, a platinum chloride salt is formed by the combination of PtCl, with two molecules of the hydro- chloride of the base; in the case of the ammonio-platinic chloride, the formula is PtCl,.2(NH;.HCl); so that what remains of a platinum salt after deducting the platinum represents two molecules of the base + two molecules of HCl + 4 atoms of chlorine. From the platinum salt . : ; 100-00 Deduct the platinum . ; : 32-72 Remainder : ; 3 ‘ 67-28 . Pt in one molecule Base + HCl Then 32-72 Pt: 195 of the salt :: 67-28 : 400-9 + Cl Hence two mols. base + 2 mols. HCl + 4 atoms Cl = 400-9 Deduct 2HCl + 4Cl = 215-0 Weight of two molecules of the base. : . 185-9 The molecular weight of the base, therefore, is 92-95. The formula C,H,N represents 72 + 7+14= 93. This is therefore the molecular formula. The law of even numbers is sometimes a useful guide in fixing molecular formule. It may be thus expressed: The total number of atoms of monad or triad elements united with carbon in an organic compound must be an even number. The law is a result of the tetrad nature of carbon, as will be seen in the next few pages. For example, the empirical formula for glycol, deduced from ultimate analysis, is CH,;0 ; but this is an impossible formula, by the law of even numbers, and the molecular formula for glycol must be at least double this, CzH,Ox. The molecular formula having been ascertained, the question still remains as to how the atoms are disposed in the molecular structure. True, the empirical formula for either acetylene or benzene is CH, and the molecular formula of the former is C,H, as found by the density of the gas, and of the latter CsH, as deduced from the vapour density. Still, these molecular magnitudes give no clue to the specific arrangements of the atoms inter se ; but desirability of such further information is felt when it is realised that there are three pentanes each having the molecular formula C;H,,, but possessing different properties; and there are numerous cases of such tsomers (p. 553). In studying the structure of carbon compounds three fundamental principles are to be observed. (a) The carbon atom is quadrivalent, what- ever the nature of its combinations. (There are a very few doubtful excep- tions, e.g. CO, HO-N:C (fulminic acid); but these are not typical organic compounds, and it may yet prove that they are C:O, HO-'N: C.) (6) The four valencies of the carbon atom are equal and similar; see p. 546, 542 STRUCTURAL FORMULA (c) Carbon atoms can unite with one another by either one, two or three valencies, e.g. in the hydrocarbons already considered, ethane, H,C.CH;, ; ethylene, H,C: CH,; acetylene, HC : CH. All these three principles find expression in representing the carbon atom as a tetrahedron with the valencies at the apices ; and this conception is of service throughout the study. However, it must not be imagined that the shape of a carbon atom is tetrahedral. Much more probably it is an elastic sphere (see p. 335), having four symmetrically arranged valencies, which attract other atoms so strongly as to cause depressions (tetrahedrally arranged) in the surface of the sphere. Employing then the tetrahedron, these three hydrocarbons are exhibited in Fig. 275, where the single “bond” or “linking” is represented by the meeting of two apices, the a Ethane Ethylene. Acetylene. Fie. 275. double or ethylenic bond by the joining of two edges, the triple bond by the juxtaposition of two bases. : Several carbon atoms may unite to form a chain (open-chain or acyclic H H H H compounds), e.g. H — C —C — C — C— H (Butane), CH,.CH,.C : C.CH, H H H H (methyl-ethyl-acetylene), or a ring (closed-chain or cyclic compounds), e.g. H 4H H, 4H, C—C —C Ac? SoH (benzene), HCC cH, (hexahydrobenzene) ; and H #H H, 4H, the carbons in these may be united by single, double, or triple bonds as shown. Compounds having only single bonds are saturated (p. 197), being in- capable of increasing the number of atoms attached to any of the carbon atoms; in these any reaction always leads to metalepsis (p. 106), thus chlorine is substituted for hydrogen, eg. CH, + Cl, = CH,Cl + HCl. Double or triple bonds are reduced to single or double bonds by chlorine or other reagent, which combines by addition, eg. H,C:CH, + Cl, = ClIH,C-CH,Cl; HC : CH + 2H’=H,C:CH,. These changes may be shown pictorially (Figs. 276, 277) : K-BEX Ethylene. Ethylene dichloride. Fic. 276. STRUCTURAL FORMUL 543 H H 2H, pen > yf O- PK H H Acetylene. Ethylene. Fia. 277. Such compounds are said to be wnsaturated, because the carbon atoms are able to take up other atoms for which they have greater affinity than they have for one another. There are several ways of discovering the presence of double bonds, which are quite common, for instance, in fatty acids, therefore in oils ; the most usual method is to determine the bromine or iodine absorption of the substance (see p. 671 and any book on oil analysis). Since two halogen atoms are added for each double bond and the molecular weight of the substance is known, the number of double bonds in the molecule can be calculated. Numerous organic compounds have very complex formule, but in most cases these are built up from several well-known simple groups or radicles (p. 197), so that a structural or constitutional formula may be written ; ¢.g. ethyl glycollate (¢.v.) has the molecular formula C,H,O,N, which conveys no idea as to the nature of the body. But, heated with strong alkali, it evolves ammonia and ethyl alcohol and forms acetic acid (as a salt), whence it is conceivable that the radicle NH, constitutes one part of the molecule, so that the formula may be written C,H,O,.NH,; but the alcohol also points to the presence of an ethyl (C,H;) group, whence C,H,0,.C,H,;.NH, ; the formation of acetic acid suggests the presence of an acetyl (C,H,0) group, from which the complex approximates 0.C,H,0.C,H;.NH,. But here there is one H atom too many, and otherwise it is found that NH, replaces H in the C,H,0 or CH,.CO group, so that this part has the construc- tion CH,(NH,).CO. It now remains to fit the whole together in such a way that the structure or constitution arrived at accounts for all the properties of the substance ; much experience shows this to be done in the following arrangement, CH,(NH,)CO.OC,H; ; or in the graphic formula, H O H H H,N —C—C—C—CH H H H Again, to determine the structural formula of alcohol. When sodium is placed in alcohol, it is dissolved with the evolution of much hydrogen, and the alcohol is con- verted into a crystalline substance called sodium ethoxide, which has the composition C,H;ONa. Comparing this with the formula of alcohol, it is seen that Na has been substituted for one atom of H. Since the compound still contains 5H it might be supposed that by the use of an excess of Na more might be substituted for H, pro- ducing ultimately a compound C,Na,O, But this is not the case ; Na can be substituted in this way for only one of the 6 atoms of H in alcohol ; hence it is seen that one atom of the six is on a different footing from the other five. This would be expressed by writing the formula C,H;.H.O. Again, when alcohol is acted on by hydrogen chloride, and distilled at a low tempera- ture, it yields water, and a very volatile liquid known as ethyl chloride, having the composition C,H;Cl. This decomposition would be expressed by the equation, C,H;.H.O + HCl = C,H;Cl + HOH, from which it is evident that the Cl of the HCl has been exchanged for OH in the alcohol, leading to the conclusion that alcohol is made up of at least two separate groups, and that one way of writing its constitutional formula is C,H; .OH. 544 CLASSIFICATION OF ORGANIC COMPOUNDS The above-written devices are weak in that they represent everything as existing in one plane. Molecular architecture, the arrangement of the atoms in space, is usually referred to as stereochemistry (p. 633). There are two great divisions of organic compounds: (a) The acyclic, open-chain, fatty or aliphatic (adepap, fat) series, including the paraffin series of hydrocarbons, those alcohols and acids—amongst them the typically fatty acids—which are most familiar, glycerin, &c.; (b) the cyclic or closed- chain series, comprising chiefly the aromatic or carbocyclic series in which the ring is composed entirely of carbon atoms, e.g. benzene, H no SCH; \o = 0% H but also the heterocyclic series in which the ring is made up of atoms of more H H C—C than one kind, eg. pyridine, HCC »N. However, this division, C=C H #H while generally sound and very convenient in practice, shares the not un- common misfortune of having ill-defined limits, and not infrequently substances of one division are more appropriately studied in connection with those of the other. In many works on organic chemistry the fatty and aromatic compounds are dealt with in separate sections, so that the alcohols, for instance, of the two series are divorced from one another. In this book the various members of one form of compound are brought together, so that the properties of the fatty and aromatic series may be compared and contrasted directly. The majority of compounds are either hydrocarbons (composed of carbon and hydrogen only) or hydrocarbon derivatives (compounds having the constitution of hydrocarbons in which for one or more hydrogen atoms are substituted other atoms or radicles). The hydrocarbon derivatives may be regarded as compounds of hydrocarbon residues with radicles or with elements, the residue being itself a radicle derived from the hydrocarbon by displacement of one or more atoms of hydrogen. Thus CH,, methyl, is the residue derived from methane, CH,, by loss of one atom of hydrogen ; C.H,, ethyl, and C,H;, phenyl, are the like residues from ethane, C,H,, and benzene, C,H,, respectively. Those hydrocarbon residues which are derived from open-chain hydrocarbons (methyl, ethyl) are termed alkyl radicles, while those derived from closed-chain hydrocarbons (phenyl) are termed aryl radicles. The main classes of organic compounds are given below. Thesymbol R is frequently used to represent a hydrocarbon residue (alkyl or aryl), and A is used for an acid radicle or acidyl radicle, such as acetyl, CH;.CO. That part of the formula attached to the R or A is characteristic of the class, e.g. the group .CO.H is present in all aldehydes, .CO.OH in all acids, &c. (1) Hydrocarbons, R.H, e.g. ethane or ethyl hydride, C,H,.H ; benzene or phenyl hydride, C,H;.H. (2) Haloid derivatives, R.Cl, e.g. chloro-ethane or ethyl chloride, C,H;Cl; chloro-benzene or phenyl chloride, CsH;Cl. But also compounds where more than one H-atom is substituted, e.g. ethylene dibromide, C,H,Br,; triiodo- benzene, C,H,I3. (3) Alcohols, R.CH,.OH, e.g. ethyl alcohol, C,H;.0H or CH,.CH,OH ; benzyl alcohol, CgH;.CH,OH. In alcohols the OH is always in an open-chain, INVESTIGATION OF CONSTITUTION 545 even if to the latter there is, as is the case with benzyl alcohol, also attached a ring. (4) Phenols, R.OH. The .OH is attached to carbon in the ring, e.g. phenol, C.H;.OH ; cresol, CH;.C,H,.OH. Contrast H H 7 a H #H C=C C=C Va \aeé 4 a’ XY HCC = pocou H.C CC poou C—C% C—C H #H H #H Benzyl alcohol. p.Cresol. (5) Aldehydes, R.CO.H, may be viewed as alcohols deprived of two hydrogen atoms (alcohol dehydrogenatum) by oxidation, e.g. acetaldehyde, CH;.CO.H ; benzaldehyde, C,H,.CO.H. (6) Ketones, R.CO.R, are similar in constitution and properties to the aldehydes, but a second R takes the place of the characteristic H of the latter, e.g. acetone, CH;.CO.CH,; acetéphenone, CH,.CO.C,H;. (7) Acids, R.CO.OH, or A.OH, are products of the further oxidation of alcohols and aldehydes, ¢.g. acetic acid, CH;.CO.OH; benzoic acid, C,H;.CO.OH. In dibasic acids there are two carboxyl (CO.OH) groups, eg. malonic acid, CH,(CO.OH),. (8) Esters or ethereal salts or alkyl salts, R.O.A and R.X where X stands for a halogen or the like, are comparable with ordinary salts, thus cf. K.Cl and C,H;.Cl; CH,CO.OK (potassium acetate) and CH,.CO.0C3H, (propyl acetate). (9) Ethers, R.O.R, result from the dehydration of alcohols, e.g. 2C,H;.0H — H,O = C.H,;.0.C,H;, ethyl ether. (10) Ammonia derivatives, by the substitution of a radicle for H in NH;. If the substituent be an alkyl, R, an amine R.NH, is produced, e.g. CH,;.NH,, methylamine ; if an acid radicle, A, an amide, A.NH,, eg. CH,.CO.NH,, acetamide. (11) Other important classes are (a) organo-metallic compounds, RM, RM, RM, &c. ; (6) cyanogen compounds, R.CN ; (c) quinones, e.g. CgHy.O, ; the following are well-defined classes though having no very simple general formula: (d) carbohydrates, e.g. sugar; (e) glucosides, e.g. salicin ; (f) proteins. Of the means employed to investigate the constitution of organic compounds, the following are the most important: (A) Study of the reactions by which the substance is synthesised and otherwise produced. (B) Observation of the action or effect on the substance of (a) halogens, (6) dehydration, (c) hydrolysis, (d) oxidising agents (HNO,, KMnO,, CrOs, &c.), (e) reducing agents (i) acid: HI alone, metal and acid ; (ii) neutral : copper zinc couple, zinc dust and water, finely divided nickel ; (iii) alkaline : sodium as amalgam orasethoxide. (C) Determination of the presence and number of particular groups, e.g. (a) hydroxyl, ‘OH (p. 662); methoxyl, -OCH, (p. 654) ; carbonyl, :CO; amino, ‘NH,; imido, :NH; nitrile, :N; diazo-, -N:N-; hydrazo, ‘NH‘NH-‘; nitroso, ‘NO ; nitro, NO,. (D) Application of energy : (a) Mechanical energy is occasionally of interest, e.g. compressibility is related to constitution, see xylene, p. 567. (b) Heat tests are very important. Not only are changes of state at definite temperatures brought about, but at higher temperatures dissociation or decomposition often occurs in a manner suggestive of constitution, while analysis of the products usually sheds much light. Stability, reaction, &c., when limited to certain ranges of temperature, are frequently significant, e.g. benzaldoxime (p. 642), chlorination of toluene (p. 597). (c) Light plays a part in determining the constitution of a compound (cf. p. 646), also in causing isomeric change— 35 546 PARAFFINS phototropy, e.g. salicylidene-m-toluidine is yellow if kept in the dark, but orange after exposure to light. (d) Electricity has many applications. In the fatty division nearly all the reactions under electrical influence depend upon first ionising an acid ; but aromatic compounds are usually reduced, though occasionally oxidised. (E) Physical properties; most of these show continuous gradation in the various series of compounds, and are considered conveniently after suitable examples have been dealt with. (a) Crystalline form is commonly a characteristic of a body, and is often important for distinguishing isomers; these always crystallise differently. There are numerous instances of substances chemically indistinguishable occurring in two or more modifications, marked by difference of crystalline form. Crystal architecture is correlated with spatial configuration, see tartaric acid (p. 637) ; K,SO, (p. 335). HYDROCARBONS Several classes of hydrocarbons are known. A. Acyclic. (a) The paraffin or marsh-gas series, saturated ; (b) the olefine or ethyiene series, unsaturated, having double bonds; (c) the acetylene series, unsaturated, having triple bonds. B. Cyclic (carbocyclic). (d) the benzene series, unsatu- rated ; (e) the hydroaromatic series, saturated ; (f) several other cyclic series. Paraffin Series of Hydrocarbons.—The only hydrocarbon which con- tains one atom of carbon is methane or marsh gas, CH,, the more important properties of which have been already considered. It has been seen that when CH, undergoes metalepsis with chlorine, one of its H atoms is exchanged for Cl, the compound CH;Cl being produced (p. 107). Now there are several other methods of producing a compound of this formula, and, which- ever be adopted, the product always has the same properties, showing that only one compound of the formula CHCl exists. It is contrary to experience, acquired. in other cases, to suppose that all the methods of producing CH,Cl would result in the sub- stitution of Cl for the same H atom, and it may be fairly inferred that whilst one method would produce CHHHCl, another would produce CHHCIH, a third CHCIHH, and a fourth CCIHHH. In each case the substance produced is the same. It is therefore supposed that all the four H atoms in methane have an equal position with regard to the carbon atom, so that whichever is substituted the centre of gravity of the molecule will remain the same. It is in order to express, or to attempt to explain, this equality of position of the hydrogen atoms in relation to the carbon, that they are often represented on paper H H | H—C—H H Methane. He H Fie. 278. Fic. 279. as symmetrically arranged round the centre carbon atom (Fig. 278), so that whichever H is exchanged for Cl, the figure has only to be turned round in order to appear the same. On paper the atoms are, of necessity, written on the same plane,but it is not to be supposed that this represents their arrangement in the molecule. At present we have no satisfactory knowledge of the shapes of molecules, but we are obliged to think of them as having three dimensions. The most fruitful hypothesis as to the: structure of the methane molecule is that the carbon atom occupies the centre of a regular tetrahedron, the hydrogen atoms being attached to the four angles thereof, Fig. 279. Inasmuch as methane has the formula CH,, generally written as in Fig. 278, it must be regarded as a saturated compound devoid of any residual affinity such as that which causes CO (p. 248) to yield addition products. SATURATED HYDROCARBONS 547 In the case of all other hydrocarbons it is assumed that the carbon atoms are directly united together, since it does not appear to be possible for H to behave other than as a monovalent element, so that it cannot be supposed to act as an intermediary, that is, in a manner represented by the expression C-H-C. Of those hydrocarbons which have two carbon atoms, or a two- carbon nucleus, there are at least three, of which two, ethylene, C,H,, and acetylene, C,H., have received notice (pp. 255 and 251) and will be referred to again. The third is called ethane, and has the formula C,H,, which is generally represented as shown in Fig. 280, but is equally well written H,C-CH,. : The evidence for this formula is of a similar character to that for the methane formula, only one compound C,H,Cl being obtainable. If two regular tetrahedra be placed with one solid angle of each in contact, a two-carbon nucleus will be represented in which each carbon is at the centre H H of a tetrahedron, the six H atoms being at the remaining three bt angles of each tetrahedron (see Fig. 275). H—C—C—H Ethane is also a saturated hydrocarbon, for all the | | bonds of the two carbon atoms are satisfied. Passing HH to those hydrocarbons which contain three carbon ae rq. s atoms, or a three-carbon nucleus, that which is satu- rated, and therefore contains the highest number of hydrogen atoms, is C,H, called propane, and is represented as in Fig. 281, or more simply as CH, CH, CH. The evidence for this formula is derived from the methods H HH by which propane is prepared, and will be appreciated when these are described. The reasoning applied to methane will not serve H—C—C—C—H in this case, for two compounds of the formula C,;H;Cl are known, bate if as will be explained later. H H H A comparison of these three hydrocarbons will show eee that ethane may be regarded as derived from methane, nee and propane from ethane, by substituting CH, for H. By continuing this process a whole series of hydrocarbons is obtained, each of which is satu- rated and differs from the one preceding it by CH,. Thus butane, the next member of the series, is CH, CH,-CH,’CH,, pentane is CH, CH,-CH, CH,'CH;, and so on. Any series of carbon compounds, each member of which differs from the one preceding it by CH,, is called an homologous series, and the compounds are homologues of each other. It will be seen that in the homologous series under consideration, the number of hydrogen atoms must always exceed twice the number of carbon atoms by 2, and that a general formula for the series may therefore be written CrHy,+2. Since each terminal carbon atom has three hydrogen atoms attached to it, the general formula may be extended to H,C'CrHon'CH3. As already stated, hydrocarbons which conform with this general formula are termed saturated because they cannot have any free affinities by which other elements can attach themselves to the molecule. It must be under- stood that this title does not represent a mere theoretical speculation, but is the expression of actual experience, since it is found to be impossible to produce a new compound from any of these hydrocarbons save by substitu- tion ; for example, no compound containing chlorine can be obtained from methane except by exchanging one or more atoms of Cl for one or more atoms of H. On account of this inactivity the series has been called the paraffin series of hydrocarbons, the name “ paraffin” (parum, little, affinis, affinity) having been originally bestowed upon the wax-like substance obtained in the distillation of coal and peat, because of its resistance to chemical agents ; this solid was subsequently shown to consist mainly of saturated hydrocarbons. 548 PETROLEUM The paraffin hydrocarbons may be regarded as the hydrides of positive radicles of the general formula C,H2,+,, the formula for the hydrocarbons being C,H,,.,H. These radicles have been termed alkyl radicles ; they are obviously monovalent. They are designated similarly to the hydrocarbons which constitute their hydrides, the suffix -yl being substituted for -ane. The natural source of the paraffin hydrocarbons is the oil known as petroleum, mineral naphtha, or rock-oil. This is found in nearly all countries, but especially at Baku, on the Caspian Sea, the Dutch East Indies, and in Canada and Pennsylvania, and occurs in almost all geological formations. It is to be noted, however, that the Russian petroleum consists largely of hydrocarbons (naphthenes) allied to the aromatic series (q.v.), whilst that of Pennsylvania consists almost entirely of a mixture of paraffin hydrocarbons. The Pennsylvanian oil-wells discharge large volumes of gas containing H, CH,, and C,H,, which are used for heating and lighting in the neighbour- ing district. The liquid pumped out of the wells still retains a quantity of ethane in solution. It consists chiefly of members of the paraffin series, of which an abridged list is here given ; the graduated increases in melting- point, boiling-point, and specific gravity of the liquid should be noticed. Melts at Boils at Sp. gr. Methane . CH, — 186° — 164° “415 Ethane 5 . CrHe — 172° — 93° -466 Propane . CH, _— — 465° 536 Butane - CyHyo — 1° -600 Pentane . . CsHye — 36° 627 Hexane . CeAys — 69° -658 Heptane. . CrHys — 98° “700 Octane : CyHyg —_ 125° 720 Nonane CyHoo — 51° 149° 133 Decane » CyoHes — 32° 173° “746 Dodecane . » CoH — 12° 214° 173 Hexadecane » CyoHs4 + 18° 287° “115 The liquid constituents of the petroleum are separated by the process of fractional distillation, which depends upon the difference in their boiling- points. When the petroleum is heated, the hydrocarbons, ethane, propane, and butane, are evolved in the gaseous state; these are collected and subjected to the action of a condensing pump, which liquefies a portion of them, yielding the liquid sold as cymogene (sp. gr. 0-59), which is used in freezing-machines, on account of the cold pro- duced by its rapid evaporation. It consists chiefly of butane, CyHyo. The portion which first distils over requires special condensation, for it boils at 18° ; it contains a considerable proportion of pentane, and is sold as rhigolene (sp. gr. 0-62), being used as an anesthetic, and for a standard of light. The portion which distils over about 60° consists mainly of hexane, and is sold as petroleum spirit, petroleum ether, or gasolene (sp. gr. 0-66) ; it is used for dissolving india-rubber. The next fraction is chiefly heptane, and is collected until the temperature rises to 110° ; its sp. gr. is 0-7, and it is used, in some kinds of lamps, as a burning oil, and as a solvent, under the names naphtha, ligroin, and benzoline. The next fraction is collected below 150°, and is known as benzine (sp. gr. 0-74), a solvent which must not be confounded with benzene, the coal-tar product. A similar fraction is the petrol burnt in the engines of motor-cars. The kerosene oil, so much in use for paraffin lamps, is the portion which distils between 150° and 300°, and is generally refined by agitation with about 2 per cent. of sulphuric acid (which removes the olefines contained in the oil) before being sent into the market. It is unsafe to use oils of low boiling-point as illuminants in ordinary lamps, because they so easily evolve vapour which forms an explosive mixture with air, and bursts the lamp. The temperature at which the hydrocarbon evolves enough vapour to form an indammable mixture with the cir above it is termed its flash-point. No paraffin oil FRACTIONAL DISTILLATION 549 is considered safe for burning, in England, which kindles from a flame brought near to its surface when it is heated to 38°C. (100° F.) in an open vessel ; 50 ¢.c. in a teacup placed in a basin of hot water in which a thermometer is plunged, answers for a rough open test. In a closed vessel, where the vapour more rapidly accumulates in sufficient quantity, the flash-point is much lower, and no oil is considered safe which kindles at or below 23° ©. (73° F.) in a covered vessel when a flame is brought near its surface ; a small beaker filled to about 2 cm. from top, covered with a piece of tin plate having # small hole for introducing a match, may be placed in warm water for the close test. There are standard apparatus for this test. The distillation of the petroleum is finally pushed until a tarry residue is left in the retort. The distillate above 300° consists of heavy (sp. gr. 0-9) lubricating oils containing paragin-wax, which melts at about 55°, and may, therefore, be separated from the oils by freezing ; this wax contains the highest known homologues of the paraffin series. The softer varieties of paraffin are known as vaseline. Ozokerite, a crude form of which is known as ceresin, is imported from Galicia, Hungary, and Russia, for the manufacture of candles. It consists of solid hydrocarbons which appear to contain a smaller proportion of hydrogen than do the paraffin hydro- carbons ; its melting-point varies from 60° to 100°. Paraffin oils, both illuminating and lubricating, and paraffin-wax are also obtained by distilling certain minerals allied to coal, such as the Torbane Hill mineral, or Boghead cannel, found at Bathgate, in Scotland. Such shale oils contain more olefines than do the American oils. All the oils above mentioned are colourless when quite pure, although the commercial products are frequently yellow or brown. On the small scale, the process of fractional distillation for the separation of liquids of different boiling-points is conducted in a flask (A, Fig. 282) provided with a long ‘ lai Fic, 282. neck through which a thermometer (T) passes to indicate the temperature at which the liquid boils. The first portion which distils over will, of course, consist chiefly of that liquid which has the lowest boiling-point, particularly if the neck of the flask consist of a series of bulbs and thus expose a large surface to be cooled by the air ; if the receiver (R) be changed at stated intervals corresponding with a certain rise in the temperature, a series of liquids will be obtained, containing substances the boiling-points of which lie within the limits of temperature between which the liquids were collected. When these liquids are again distilled separately in the same way, a great part of each is generally found to distil over within a few degrees on either side of some particular temperature, which is the boiling-point of the substance of which that liquid 550 METHANE chiefly consists ; and if the receivers be again changed at stated intervals, a second series of distillates will be obtained, the boiling-points of which are comprised within a narrower range of temperature. It will be evident that by repeated distillations, the original mixture will eventually be resolved into a number of liquids, each distilling over entirely at about one particular temperature, which is the boiling-point of its chief sonstituent. Methane, or methyl hydride, CH,. The following must be added to she description of methane which has already been given (p. 257). To prepare the pure gas, methyl iodide is dropped slowly into a flask A (Fig. 283) containing a copper-zinc couple (p. 21) covered with dilute alcohol ; the flask is very gently heated, whereupon methane is evolved in ac- cordance with the equation — CH,I + C,H,OH + Zn = CH,H+ ZnI.0C,H,, and passes up the tube B containing granu- lated zinc which decomposes any un- changed CH,I, allowing the methane to be collected in the usual manner from the delivery tube. Methane is also formed when zinc methide is decomposed by water, Zn(CHs;), + 2HOH = Zn(OH), + 2CH,, and by the action of sodium amalgam and water (to supply H) on carbon tetra- chloride, CCl, + 8H = CH, + 4HCl, and by passing a mixture of CS, vapour and H,S (or steam) over red-hot copper, CS, + 2H,S + 8Cu = 4Cu,S + CH,. Also -. by heating a mixture of carbon monoxide - and hydrogen to 220° in presence of finely divided nickel, CO + 3H,0 = CH, + H,O. The last three methods are of great im- 3 portance, since they amount to the pre- Fic. 283. paration of the gas from its elements, and, therefore, to the synthesis of the paraffin hydrocarbons generally, for the majority of these can be built up from marsh-gas by the aid of a few elements which act as intermediaries. Methane is nearly inodorous; its sp. gr. is 0°558 (air = 1); it burns with a feebly luminous flame; 100 c.c. water at 0° dissolve 5°5 c.c., and alcohol 52 c.c. of the gas. It boils at — 164°; the sp. gr. of the liquid is 0-415 at — 164°. When methane is mixed with chlorine and exposed to sunlight, a violent reaction occurs, and often an explosion, HCl being formed, and C separated ; but when the Cl is diluted with CO, and allowed to act gradually, chlorine substitution-products are obtained. CH, + Cl,= HCl + CH,Cl monochloromethane. CH, + 2Cl, = 2HCl + CH,Cl, dichloromethane. CH, + 3Cl, = 3HCl + CHCl, chloroform. CH, + 4Cl, = 4HCl + CCl, — tetrachloromethane. The chlorine in these compounds is not precipitated by silver nitrate like the Cl in HCl and the chlorides of the metals. Ethane, or ethyl hydride, C,H, is prepared from ethyl iodide, C,H,I, just as methane is prepared from methyl iodide. It is also formed when methyl iodide is heated with zinc in a sealed tube, 2CH,I + Zn = ZnI, + CH,CH,;; hence, ethane has been termed dimethyl. However, much more methane than ethane is produced. : Ethane is evolved from the anode when a solution of potassium acetate, CH,COOK, s electrolysed; this salt dissociates into the ions CH;COO’ and K’; the former of NUCLEAL CONDENSATION 551 which breaks up into C,H, and 200g, whilst the latter reacts with the water t form KOH and H, which is evolved at the cathode ; the KOH absorbs the CO,, so that the ultimate result may be approximately represented by the equation 2CH,COOK + 2H,0 = C,H, + 2KHCO, + Hp. Ethane resembles methane in properties, but is more easily liquefied (46 atm. at 4°) ; it is about twice as soluble in alcohol as methane is. Propane, or propyl hydride, C;H,, is prepared by the action of nascent hydrogen on propyl iodide, C,H,I + 2H’= C,H, + HI. It is also formed when a mixture of ethyl iodide and methyl iodide is heated with zinc, shows that the hydrocarbon is formed by the combination of methyl with ethyl. Propane is a colourless gas which boils at — 45°. It will have been noticed that precisely similar methods serve for the preparation of methane, ethane, and propane. This is illustrative of the fact that the members of an homologous series of carbon compounds can generally be prepared from the members of another homologous series by the same reaction ; thus the series of alkyl iodides (CHI, C,H;I, C3H.I, &c.) yield the corresponding series of alkyl hydrides (hydrocarbons) by metalepsis with (nascent) hydrogen. For each series of carbon compounds, therefore, there is a number of general methods of formation. It will be noted that the hydrocarbons which are of industrial importance are either natural products, like the paraffins, or are obtained, like benzene, as products of destructive distillation, a process the mechanism of which has not yet been explained. Acetylene alone is manufactured by a process which may be said to be well understood. For the purposes of chemical investigation, however, several methods are available for preparing hydro- carbons, and are more or less generally applicable, whatever the family to which the desired hydrocarbon may belong. Nucleal synthesis or nucleal condensation is the most general of these methods. The term implies the creation of a new carbon nucleus, whether by adding another carbon atom to an existing nucleus or by converting a single bond between two carbon atoms in the molecule into a double or treble bond (intra-molecular condensation) or otherwise. In the case of the paraffins, in which the carbon atoms are always singly linked, the process must consist in subtracting carbon atoms from the existing nucleus or in adding new carbon atoms to it, and for this latter purpose two substituted hydro- carbons are treated with an agent capable of removing the substituent from each, leaving the carbon atoms of the two nuclei to combine at the points thus exposed. The equation given above for the formation of propane from ethyl or methyl] iodides illustrates the process ; in general terms RI + IR’ + Na, = 2Nal + RB-R’, in which R and R’ may be the same or different alkyl nuclei. The halogen substitution-products and sodium or zinc as the halogen remover are best suited for the method (Wurtz’s reaction). A less general method is the removal of carbon as CO, from an organic acid by heating it with alkali, as in the preparation of methane by heating sodium acetate with caustic soda (p. 258). This method is of much import- ance in the paraffin series, and is expressed by the general equation RB:COONa + NaOH = RH + NaO-COONa. In a sense it is the converse of the first method, since it forms a new carbon nucleus by removing carbon from an existing one. A similar removal of carbon dioxide from salts of organic acids may be effected by electrolysis (see ethane, p. 550), and this method is applicable 552 BUTANES to several classes of hydrocarbons. It generally involves a nucleal condensa- tion. Other methods for preparing paraffins are (1) treatment of alkyl halides with nascent hydrogen, RCl + 2H’= RH + HCl (see methane) ; (2) inter- action of alkyl iodides with zinc alkyl compounds, 2RI + ZnR’, = 2(R.R’) + ZnI, (see ethane) ; (3) by Grignard’s reaction (p. 687). Butane, C,H,,, is made by treating ethyl iodide with zinc (in large excess) in a sealed tube at 200° for three or four hours; 2C,H;I + Zn = ZnI, + C,H,o. Usually the yield of butane is small, but may be 20 or 30 per cent. ; much ethane and ethylene are simultaneously produced. Much the same results follow the use of sodium or magnesium. It is much more easily condensed to a liquid than is either of the preceding hydrocarbons, and is much more soluble in alcohol. Liquid butane (sp. gr. 0-6) boils at 1°. Since butane is prepared from ethyl iodide, it may be regarded as diethyl in the same sense that ethane is dimethyl, and therefore it is justifi- able to write its formula, CH,;-CH,-CH,-CH,, or graphically as in Fig. 284, H HH bet] H HHH H—C—C—C—H. Eh! Gl 3 bet H—C—C—C—C—H HC H Be ol. % H HHH a? NG H Normal butane. Secondary butane. Fic. 284. Fie. 285. for ethyl iodide is the iodine substitution product of ethane, CH,-CH,, and its formula is CH,CH,I. When the diad zine acts upon this, it must take the I,, which it requires to form zinc iodide, from two molecules of ethyl iodide, leaving the residues to combine and produce butane, thus : There is a second hydrocarbon of the formula 0,H,,; it is prepared by the action of nascent hydrogen on a compound called tertiary butyl todide (q.v.), CsHgl. It might be mistaken for ordinary butane but for the fact that it will not liquefy until cooled to — 17°. This second butane has been called secondary butane or isobutane (icos, equal), the first butane being termed normal butane, from norma, a rule, because it is the product of the usual general methods of formation of the paraffins, and possesses the physical properties which the hydrocarbon, C,H, , should possess from its position in the homologous series of paraffins (e.g. a boiling-point about 30° lower than the next higher member in the series). In order to explain the existence of this secondary butane it is supposed that the four carbon atoms are arranged differently from the manner in which they are arranged in the case of normal butane. A little consideration will show that the only possible second method of arrangement of the carbon atoms on one plane is that shown in Fig. 285, in which the fourth C atom is attached to the central C atom of the propane formula. The same arrangement may be expressed by the formula CH3-C(CH;)H-CH, or (CH;), : CH-CH;, and may be described as consisting of methane in which three atoms of H have been exchanged for methyl, that is as trimethylmethane. Tertiary butyl iodide has the formula CH,-C(CH,)I-CH,, and the action of nascent hydrogen in converting it into trimethylmethane, or secondary butane, is apparent. Pentane, C;H,,—Three hydrocarbons of this formwa exist; that which is made by the general methods, and, therefore, has a right to the title ISOMERIDES 553 normal pentane, is a colourless liquid, boiling at 36°. Secondary pentane, or isopentane, boils at 28°, and tertiary pentane, neopentane or tetramethyl- methane, at 9°. To account for the existence of these three hydrocarbons, it is necessary to suppose that the five carbon atoms are arranged in three different ways ; this will be found to be possible, the results being indicated in Figs. 286, 287, 288, or by the formule CH,-CH,-CH,-CH,-CH, CH,-CH,-C(CH,)H-CH3, and C(CH3),. H HH H H HCC 6-60, H,C—C—C—CH, H,C CH, Lis eK os H HUH H CH, H,C CH, Normal pentane Iso-pentane. Tertiary pentane. Fic. 286. Fic. 287. Fie. 288. ° If it were possible to arrange the five carbon atoms in a way essentially different from any of these three, a fourth pentane might be expected to exist. It will be evident that the greater the number of carbon atoms in the hydrocarbon, the greater the variety of arrangement and therefore the greater the number of possible isomerides. Thus, there may be discovered 802 compounds of the formula C,H. Isomerides are those compounds which have the same percentage composi- tion and the same molecular weight, but different properties ; see also p. 541. Polymerides have the same percentage composition, but different molecu- lar weights, e.g. C,H, and C,H, ; CH,O and C,H,,0,. Since the valency of carbon is always four, there can be only three modes in which the carbon atoms may be linked to each other, giving rise to three main classes of isomerides, which are illustrated by the three classes of paraffin hydrocarbons. Normal paraffins are those in which all the carbon atoms are united in a single chain without branches, so that the formula begins and ends with CH,, every other link being CH, (Fig. 286). Secondary paraffins or iso-paraffins have at least one branch, that is, at least one carbon atom is united with three other carbon atoms, as in Fig. 287. Tertiary paraffins or neo-paraffins, have at least one carbon atom united to four others, as in Fig. 288. The remaining hydrocarbons of the paraffin series do not need detailed consideration here. Those from hexane to pentadecane (C,,H3,.) are colour- less liquids the boiling-points of which increase, in the normal series, by about 30° for each increment of CH,. Those in the normal series, from hexadecane (C,,H;,) to pentatriacontane (C3,H,.), the highest known member, are colourless solids of which the melting-point increases by 3-4” for each increment of CH,, that of hexadecane, Cy, H,,, being 19°. UNSATURATED HyDROCARBONS Acyclic hydrocarbons which do not correspond with the general formula CrHen+. are found to be capable of combining directly with the halogens without exchanging hydrogen for them, They are, therefore, unsaturated hydrocarbons. No hydrocarbon has yet been discovered which contains an uneven number of hydrogen atoms, nor has any unsaturated hydro- carbon containing only one atom of carbon ever been isolated. To account for these facts it is supposed that all unsaturated hydrocarbons contain two or more carbon atoms which are united to each other by two or three H H atom-fixing powers, thus : ye = cd ,andH — C=C — H. : H H 1 That this is really the constitution of neo-pentane is shown by the steps for obtaining it synthetically ; acetone, H,C(CO)CHs, treated with PCls, yields H3C(CClp)CH3, and this acted on by zinc methyl, gives H3C[C(CH;)]CH, or neo-pentane. 554 OLEFINES It may be said that, in a compound, an unsaturated carbon atom cannot exist ; if there be not a sufficiency of other elements to saturate the carbon atom, it will combine by all its available atom-fixing powers with another carbon atom. The fact that no such hydrocarbon as H,0—CH, is known, is in support of this statement. Of these two carbon atoms the unsaturated one will take up an atom-fixing power of the saturated carbon atom, at the expense of one of the hydrogen atoms united to this latter, forming H,C = CHg, in which neither carbon atom can be said to be unsaturated, although the compound as a whole is unsaturated. Treatment of this compound with chlorine will open up the double linking, yielding H,C—CH,. If the compound Cl Cl were represented by the formula H,C—CHp, there would be no apparent reason why, when the compound is mixed with the proper proportion of chlorine, one carbon atom alone should not combine with Cl yielding H,C—CHg, a result which, however, has | Cl never been obtained. The same objection applies to a third possible method of repre- senting this hydrocarbon, viz. H,;C—-CH ; moreover, if this formula were correct the | Cl addition of chlorine to the hydrocarbon might be expected to produce H,C—CH, Cl whereas there is evidence that the two chlorine atoms in the compound formed by addition of chlorine to C,H, are attached to different carbon atoms. A similar line of reasoning serves for supporting the formula HC==CH for the hydrocarbon CyHp. These facts are well illustrated in the arrangement of tetrahedra on p. 542. Olefine Series of Hydrocarbons.—The Olefine hydrocarbons are un- saturated hydrocarbons containing a pair of doubly-linked carbon atoms ; they correspond in composition with the general formula C,H,,. The first three members of the homologous series are ethylene, H,C : CH, ; propylene, H,C:CH-CH,; and butylene, H,C: CH-CH,-CH,. It will be seen that the nomenclature adopted differs from that for the paraffins by the substitution of the suffix -ylene for -ane, an alternative name for the olefines being alkylenes. The olefines are found in petroleum-oil and in the products of the destruc- tive distillation of coal, wood, &c. The first three members of the series are gaseous under ordinary conditions ; the majority of the remainder are colourless liquids, but the highest members are solid. A gradation of boiling-points and melting-points is observed, similar to that existing in the paraffin series. The properties of ethylene may be considered as typical of those of the other members of this group of hydrocarbons. For diolefines, see p. 556 ; for triolefines, see p. 557. General methods for preparing olefine hydrocarbons.—(1) It is obvious that if one of the single bonds in a paraffin be converted into a double bond the corresponding olefine will be produced, e.g. propane, CH,:CH,-CHs;, will become propylene, CH:,CH:CH,. This is a nucleal condensation, and may be effected similarly to that by which new paraffins may be formed (p. 551). Thus, a dihalogen substituted paraffin may be heated with zinc, CH,Br-CH,Br + Zn = CH,: CH, + ZnBr,. For this kind of conden- sation, however, heating a monohalogen derivative with an alcoholic solution of an alkali is generally better ; in this case the halogen atom and a hydrogen atom are removed, presumably as hydrogen halide, by the alkali ; CH,-CH,Br = CH, : CH, + HBr. (2) By the dehydration of the alcohols of the paraffin series (q.v.) by strong sulphuric acid, zinc chloride, or phosphoric acid, e.g. CH,-CH,-CH,OH = CH,-CH : CH, + HOH. ETHYLENE 555 The second method frequently produces a mixture of the olefine and its polymerides (p. 558), for the olefines tend to polymerise under the influence of acids and dehydrating agents ; thus, when amylene is prepared in this way, CygHo9 and Ci;H39 are also produced. (3) The salts of some of the dicarboxylic acids (¢.v.) yield olefines when electrolysed (cf. p. 550); thus potassium succinate yields ethylene : CO,K -CH,:CH,-CO,.K + 2HOH = CH,: CH, + 2KHCO, + Hp. (4) The process of nucleal condensation may be reversed ; that is to say, a treble or double linking may be converted into a single linking by treating the compound with nascent hydrogen. Thus some of the acetylene compounds yield the corresponding olefines when so treated: CH : CH + H, = CH,: CH, (similarly, ethylene may be transformed into ethane—see above). (5) Wurtz’s reaction (p. 551) may be applied to produce new olefines by treating a mixture of a monohalogen-substituted olefine and an alkyl halide with sodium. Ethylene, or ethene, olefiant gas, C,H,, is obtained by the action of powerful dehydrating agents on alcohol; C,H,-OH — C,H, + HOH. It may be prepared, as described at p. 256, by heating alcohol with twice its volume of strong sulphuric acid ; secondary changes cause a carbonisation of the mixture, and the ethylene is accompanied by some ether vapour, and by CO, and SO,; the ether may be removed by passing the gas through strong sulphuric acid, and the dioxides by potash or soda. It is also obtained by heating an ethyl halide with a caustic alkali in alcohol, e.g. C,H;Br + KOH = C,H, + KBr + HOH. Properties of ethylene —It has a faint ethereal odour, sp. gr. 0-97, and boils at — 103°. Slightly soluble in water ; more soluble in alcohol. Burns with a bright luminous flame, which renders it very useful as an illuminating constituent of coal-gas. When mixed with chlorine, ethylene combines with it to form a fragrant liquid known as ethylene chloride or Dutch liquid, CIH,C-CH,Cl. Bromine forms a similar compound with it. Sulphuric acid slowly absorbs ethylene, forming C,H;HSO,, sulphethylic or sulphovinic acid or ethyl hydrogen sulphate, from which alcohol may be obtained by distillation with much water, and ethylene by heating it alone, C,H;HSO, + HOH = C,H,OH + H,80,; C,H;,HSO, = C,H, + H,SO,. Sulphuric anhydride absorbs ethene much more easily, and a strong solution of SO, in H,SO, (fuming sulphuric acid) is employed for absorbing it in the analysis of coal-gas. The compound formed by SO, with ethylene is crystal- line, and is termed carbyl sulphate or ethionic anhydride, C,H, (SO3).. In contact with water, this forms ethionic acid, CH,(OSO,H)-CH,(SO,H), and when this is boiled with water it yields isethionic acid, H,C,H,S,0, + H,O = H,SO, + CH,(OH)-CH,(SO,H). It will be noticed that isethionic acid has the same composition as ethyl hydrogen sulphate, but it is a more stable compound. In presence of platinum-black or finely divided nickel, ethylene combines with hydrogen to form ethane, C,H,. With HBr and HI it combines to form ethyl bromide, C,H,Br, and iodide, C,H,I, respectively. Oxidising-agents, such as nitric and chromic acids, convert ethene into oxidised bodies containing two carbon atoms, such as oxalic acid, C,H,O,, aldehyde, C,H,0, and acetic acid, C,H 40g. From the above description of the properties of ethene, it will be seen that it differs greatly from methane and the other paraffins, in the readi- ness with which it combines with other bodies, especially with chlorine, bromine, and sulphuric anhydride, forming addition-products instead of substitution-products. Experiments which may be performed with the gas will be found at p. 256. 556 ACETYLENES Propylene, C;H, or CH;:CH : CHg, occurs in small quantity in coal-gas. It may be obtained by heating glycerin with zinc-dust ; C,;H;(OH);+3Zn = C;H, +H, +3Zn0. In properties it resembles ethylene, but it is, of course, half as heavy again. It is more easily absorbed by strong sulphuric acid. Only one propylene is known, but another hydrocarbon, trimethylene, has the same formula (p. 558). Butylene, CyHg or CH3-CH,:'CH : CHg, occurs largely in the illuminating gas made by distilling the vegetable and animal oils. It is also found in the odorous hydro- carbons which are evolved when cast iron is dissolved in hydrochloric or dilute sulphuric acid. It boils at — 5°. Consideration of the formula for butylene will show that three isomerides of this hydrocarbon can exist, viz. a- or normal butylene, CHz-CH,-CH: CH, ; - or pseudo- butylene, CH;-CH: CH-CH; ; and y- or iso-butylene (CH3)oC: CHy. The butylene described above is the normal hydrocarbon. Pseudo-butylene exists in cis- and trans- modifications (see p. 641). Amylene or pentylene, C;H,9, can exist in five isomeric forms. They occur in petroleum and paraffin oil. The normal amylene, CH;-CH,-CH,°CH : CHg, boils at 40°. The moderate oxidation of the olefines, in presence of water, produces compounds in which the opened up bonds are attached to hydroxyl groups; thus, CH;:CH : CH, yields CH,-CHOH-CH,OH ; the products are alcoholic. Acetylene Series of Hydrocarbons.—The acetylene hydrocarbons are unsaturated hydrocarbons containing a pair of trebly-linked carbon atoms: they correspond in composition with the general formula C,,H.,_». The first two members of the series, acetylene, HC : CH, and allylene, H,C-C : CH, are gaseous under ordinary conditions, whilst most of the others are colourless liquids. It will be seen that the hydrocarbon, C3Hy, is capable of being represented by the two formule CH,:C : CH, and CH,: C: CHe, so that two modifications of this compound may be expected; these have been prepared, the former being called allylene and the latter allene or propadiene.1 For every true acetylene (a hydrocarbon containing a pair of trebly-linked carbon atoms) there may also be a hydrocarbon containing two pairs of doubly-linked carbon atoms. These diolefines differ con- siderably in properties from the acetylenes ; they do not form Ag and Cu compounds ; generally they are unimportant, but divinyl or erythrene, CH, : CH-CH.: CHg, is found in compressed illuminating gas, and from it erythro] can be synthesised directly (p. 591). For tsoprene (methyldivinyl), see p. 675. Acetylene, or ethine, C,H,, can be formed by the direct union of its elements ; electric sparks are passed between carbon points in an atmosphere of hydrogen. The apparatus shown in Fig. 178 is suitable, if carbon rods be substituted for copper wires. This synthesis is of the greatest interest as being the first step in the synthesis of more complex substances. Some methane is simultaneously produced, so that all organic syntheses are easily traced back to this simple experiment. The preparation and most of the properties cf acetylene have been described at p. 251. Pure acetylene may be prepared from ethylene by combining this with bromine to form ethylene bromide which is then heated with caustic potash in alcohol : BrH,C-CH,Br + 2KOH = HC : CH + 2KBr + 2HOH ; and from methane by converting this into chloroform which is then heated with sodium : HC : Cl, + 6Na + Cl, : CH = HC : CH + 6NaCl. These two reactions are typical of general methods for preparing acetylenes. 1 According to one system of nomenclature the terminations -diene, -trienc, -tetrene, &c., are used to indicate hydrocarbons coutaining 2, 3, 4, &c., double linkings respectively. ‘he position of the double bonds is indicated by the numbers of the C atoms immediately preceding them in the chain. Thus 1: 4-hexadiene is CHg: CH'CHaCH : CH-CH3. Similarly, hydrocarbons containing 2, 3, 4, &c., treble bonds terminate in -diine, -triine, -tetrine, &c., respectively. ACETYLENE 557 In the presence of platinum-black or finely divided nickel, acetylene combines with hydrogen to form ethene, C,H,. Strong sulphuric acid absorbs acetylene slowly as it does ethene ; but when the solution is mixed with water and distilled, it yields, not alcohol as with ethene, but croton- aldehyde, CsH,-CHO ; 2C,H, + H,O =C,H,O. Chromic acid oxidises acety- lene to acetic acid; C,H, + H,O +0O=C,H,0,. Alkaline potassium permanganate converts it into oxalic acid, C,H, + 40 = C,H,0,. The most remarkable feature of acetylene is the facility with which its hydrogen is displaced by metals. By heating sodium in acetylene, C,HNa, mono-sodium acetylide and C,Na,, disodium acetylide may be obtained. Cuprous acetylide, C,Cu,, has been noticed at p. 253. Silver acetylide, C,Ags, is produced as a white precipitate when acetylene is passed into ammoniacal silver nitrate ; in absence of ammonia the precipi- tate is a compound of the acetylide with silver nitrate. When acetylene is passed into antimonic chloride, kept cool, crystals of C,H,Cl,‘SbCl, are formed, which, on heating, yield the acetylene dichloride, C,H,Cl,, as a liquid smelling like chloroform, and boiling at 55°. C,H,Cl,, acetylene tetrachoride (p. 659) and C,HCl, monochloracetylene, have also been obtained. When heated in a sealed tube, acetylene is partially converted into a mixture of two liquids, benzene, C,H,, and styrolene, C,H,. By passing electric sparks through a mixture of acetylene with nitrogen, hydrocyanic acid is produced; C,H, + N, = 2HCN. Hence this acid, from which a large number of organic bodies may be derived, has been synthetised from its elementary constituents. Cuprous acetylide, in contact with zinc and solution of ammonia, yields ethylene, which is convertible into alcohol, and from this a very large number of organic compounds may be made. Allylene, or propine, CH3:C: CH, resembles acetylene, but its cuprous compound is yellow instead of red. The hydrocarbon C,H, (butine) can exist in two forms, each of which will have a pair of trebly linked carbon atoms, namely, CH,:CH,:C:CH (ethylacetylene) and CH,:C:C-CH, (crotonylene or dimethylacetylene). Crotonylene is a liquid (b.-p. 27°) ; its vapour is one of the illuminating hydro- carbons in coal-gas. It does not form any metallic derivatives, and it appears that this is generally the case with those acetylenes which have not the group -C: CH in their composition ; 7.e. where there is no “‘ basic ” H. : The other members of the series have no practical importance at present. They are prepared by treating the bromo-substitution products of the paraffins and olefines with alcoholic potash. The only other series of open-chain hydrocarbons which are known besides the three already considered are those corresponding with the general formule C,Hon_4 and CpH,_¢. The hydrocarbons of the former series must have either one pair of trebly- and one pair of doubly-linked carbon atoms, as in the formula CH;:CH: CH-C : CH (olefine-acetylenes), or three pairs of doubly-linked carbon atoms, as in CH;-CH: C: C: CH, (triolefines) ; see the olefinic terpenes (p. 676). The C,Hen-¢ Open-chain hydrocarbons must contain either two trebly-linked or four doubly-linked carbon atoms ; the treble linking is the more common, e.g. di-acetylene, CH :C-C:CH, and dipropargyl (hexadiine), CH : C-CH,:CH,:C : CH, which is isomeric with benzene. Both these hydrocarbons form copper and silver compounds like those of acetylene. The paraffins, olefines, and acetylenes are supposed to have their carbon atoms linked together in what may be termed an open chain, in which there are terminal carbon atoms, each attached to only one other carbon atom. The hydrocarbons next to be considered, notably benzene and its homo- logues, exhibit properties which show that while they are strictly unsaturated in the sense that they do not correspond with the general formula C,Hans, 558 CLOSED-CHAIN HYDROCARBONS (p. 547), they behave more like the paraffins than the olefines do towards chemical agents. The most fruitful hypothesis in explanation of this difference is that in these hydrocarbons no carbon atom is attached to only one other carbon atom. This can only be the case if the terminal carbon atoms are attached to each other, thus: C —G—CG—C: Such hydro- Ho carbons are termed closed-chain hydrocarbons, or ring or cyclic hydrocarbons —since the arrangement of the carbon atoms is usually represented in the form of a ring, eg.:C —C: :C — : Closed- chain Hydrocarbons.—It is obvious that a closed-chain hydrocarbon must contain at least three carbon atoms, and that such a one would be obtained if a hydrogen atom could be removed from each end of the propane chain, leaving the carbon bonds thus liberated to unite : CH, H,C-CH,-CH, — H, = H,C-CH,-CH, or HCC | This has not been ac- {___] CH, complished directly, but if a bromine atom is substituted for a hydrogen atom in each CH, group, producing trimethylene bromide, BrH,C-CH,-CH,Br, these bromine atoms can be removed by sodium, whereupon the gas trimethylene + or cyclopropane is formed by nucleal condensation (cf. p. 551). Several polymethylenes or cycloparaffins or alicyclic compounds of this type have been prepared in an analogous manner. Pentamethylene or CH,-CH, a | , is the most stable and is important as a CH,-CH, near relative of camphor, while hexamethylene or cyclohexane (see p. 559) is transitional between the paraffins and benzene. All these hydrocarbons are isomeric with the olefines, from which they differ in not being attacked by permanganate ; this is presumed to be conclusive that they do not contain double linking, and allies them to the saturated hydrocarbons. cyclopentane, CH Tetramethylene has not been prepared, but methyltetramethylene is known. Penta- and hexamethylene (naphthene) are found in Caucasian petroleum ; the former boils at 50°. Heptamethylene or suberene boils at 117° and is related to the acid found in cork (suberic acid). When the iodo-substitution products of these hydrocarbons are treated with potash, the iodine is removed as HI, and a double linking is introduced; for instance, CHI - CH, CH - CH, CH,“ | yields cHZ |, cyclopentene, which may be termed a \cH;—CH \\cH, CH, CH: CH cyclo-olefine. By repeating the operation, cyclopentadiene, cH’ |, is obtained ; CH: CH this is a cyclodiolefine found in crude benzene and boils at 41°. It is easily attacked and yields addition-products, indicative that it contains double linking. If the closed chain contains three double bonds it is called a cyclo-triolefine ; thus benzene is cyclo- hexatriene. There are several methods of producing nucleal condensation, besides that here given, for obtaining polymethylene derivatives ; some of these will receive notice in appropriate places. Benzene Series of Hydrocarbons.—The series was originally called the aromatic series because the first members discovered were obtained from 1 The group CHz is termed methylene. BENZENE 559 aromatic balsams and resins. Benzene itself is C,H,, and its homologues are formed from it by exchanging hydrogen for CH,; thus, toluene, C,H;CH;; xylene, C,H,(CH;),, &c. Most of the less complex members are present in coal-tar, several occur in essential oils, e.g. cymene, the terpenes, &c., while nearly all have been prepared artificially as well as many others not found in nature. When coal-tar is distilled in large iron stills the portion which has first condensed consists of water holding ammonium salts in solution, on which floats the light oil. This amounts to about 3 per cent. of the tar and contains, besides hydrocarbons, small quantities of aniline and pyridine which are removed by shaking the distillate with strong sulphuric acid, then with soda solution to remove any sulphuric acid, phenols, &c., and finally with water. If it be then fractionally distilled (p. 549), it begins to pass over below 80° and distils nearly completely below 170°. The distillate is now a colourless mobile liquid having an ethereal odour recalling that of coal-gas. By collecting separately the portions boiling below 85°, and within suitable ranges of temperature above this, and repeating the fractionation on each of the different portions, the whole is separated into fractions boiling (ap- proximately) at 80° (benzene), 110° (toluene), 137° to 148° (xylenes), 163° (mesitylene), &c.; however, the products are never quite pure. Benzene, C,H, is the lowest fraction, and is further purified by cooling it below 0° when the benzene crystallises while the other hydrocarbons remain liquid and are removed by pressure. Benzene prepared from coal- tar always contains thiophene, C,H,S (q.v.), as an impurity. , Benzene was first discovered in coal-gas by Faraday (1829) who called it phene. In 1834 Mitscherlich prepared it by distilling benzoic acid (whence the name benzene) with slaked lime (3 parts); C,H,;-CO,H + Ca(OH), = C,H, + CaCO, + H,O. This method is still adopted for preparing perfectly pure benzene. In 1845 it was found by Hofmann in coal-tar. For its synthesis see p. 560. Benzene is an ethereal liquid, having the odour of coal-gas, of which its vapour is one of the illuminating constituents. Sp. gr. 0-88; m.-p. 5-4°; b.-p. 80°. It is very inflammable, and burns witha red smoky flame ; but its vapour, when mixed with air or hydrogen (as in coal-gas), burns with a bright white flame. Benzene is slightly soluble in water, and water in benzene ; 100 vols. of water dissolve 0-82 vol. benzene and 100 vols. benzene dissolve 0-21 vol. water. It is a most useful solvent for fats, resins, caoutchouc, &c. It dissolves in alcohol and ether. It is chiefly used for conversion into aniline (p. 697). With chemical reagents benzene and its homologues yield products in which other elements or radicles are’ substituted for the hydrogen of the , ring, e.g. with halogens, C,H, + Cl, = C,H,Cl (monochlorobenzene) + HCl; with strongest nitric acid, C,H, + HNO, =C,H,NO, (nitrobenzene) + H,0; warmed and agitated with sulphuric acid, one of the hydrogens is oxidised and benzene-sulphonic acid, C,H,;.S0,.0H, is formed ; C,H, + S0,(OH), = HOH + C,H;.80,.0H ; with hydrogen dioxide, C,H, + H,O, =C,H;OH (phenol) + H,O. In this it simulates the paraffins (save that it is so easily attacked by the acids), and thus appears to be a saturated body ; so also in not reducing alkaline permanganate. However, in sunlight chlorine is added, forming C,H,Cl, ; also hydrogen is added, forming C,H,, (cyclohexane or hexahydrobenzene) when benzene is heated in a sealed tube with hydriodic acid (and phos- phorus), C,H, + 6HI = C,H,, + 3I,, so proving benzene to be unsaturated. Benzene is detected by first converting it into nitro-benzene and reducing 560 CONSTITUTION OF BENZENE this to aniline (q.v.), which is recognised by its reaction with bleaching powder. Constitution of Benzene.—This has been and is still a matter of controversy, although it has long been sufficiently well understood to allow of the unparalleled triumphs which have been made in the course of its study. The discussion centres around the difficulty of so arranging six carbon atoms and only six hydrogen atoms that the structural formula will explain the predominating saturated character of benzene and its deriva- tives, and yet account for their sometimes behaving as unsaturated com- pounds. Since all the carbons and all the hydrogens have equal properties (p. 562) the arrangement must be symmetrical in all respects ; therefore, such an arrangement as H,C:C:CH-CH:C:CH, is impossible. The relationship of the constitution of benzene to that of other closed-chain hydrocarbons has already been defined (p. 558). Acetylene, HC:CH, is producible directly from its elements (p. 556), and this on passing through a red-hot tube polymerises into benzene, so effecting the synthesis of benzene without the intervention of any other element. Molecular weight determinations show that three molecules of acetylene unite to form one of benzene, and as benzene behaves more as a saturated than as an unsaturated compound, the triple bonds are probably destroyed, and one would expect the double bonds also. However, the following equation displays the manner of the condensation : CH H HH H HH a Ge ¢2¢ cC:Cc:¢c CH 6 ere) ~ C-C:¢ - cl te Acctylene (3 mols.) Benzene (1 mol.) This is the structure suggested by Kekulé in 1867, and is the most generally satisfactory even at the present time. It would probably be accepted without question but for benzene behaving so rarely as an un- saturated compound ; see also p. 561. One would expect that the double bonds would open out in the presence of chlorine, combining with pairs of halogen atoms forming addition compounds just as is the case with ethylene ; and indeed it does so under the influence of sunlight. Compare Cc a oy oN a Gti Cl CICH, “a 7 3Cl, ais yc I a | and I _— H Cl CH, ClCH, He. aE ai SE \oZ \e i a ct Ethylene. Ethylene dichloride. Benzene. Benzene hexachloride. But the effect of chlorine under ordinary conditions is to substitute chlorine for hydrogen, in the typical case one atom only being exchanged, exactly as with the paraffins. Compare CH CCl FS os CH, Cl, CH,Cl HC CH Cl, HC CH ] — | + HCl and I | — | | + HCl CH, CH, HC CH HU CH sf SZ Mono-chloroethane CH CH Ethane. or ethyl chloride. Benzene. Mono-chlorobenzene or phenyl chloride, BENZENE FORMULA 561 Hence, the olefinic character of the double bond is suppressed. However the fourth valency of each carbon atom is disposed, whether to form ordinary double bonds or otherwise, it is certain that benzene rarely behaves in a manner comparable with that observed with the olefines. Several other syntheses from open-chain compounds support the Kekulé formula in clearly indicating double bonds, e.g. acetone, CH;.CO.CH;, on heating with concen- trated sulphuric acid loses water and condenses to mesitylene, CgH;(CHg)3, which is known to be a trimethylbenzene, with the three methyls symmetrically substituted in the benzene nucleus ; thus CH, Hy CH, co BO G y ere MN H,C CH, fs CH f=. el! H,;C—CO CO we £-CH CHs. C.CHs os KK ae eo 4 H ‘2 Mesitylene. Acetone (3 mols.). In the nucleal condensation from ethyl formyl-acetate, CHOH : CH.COOEt (Et = ethyl, C,H,;) the double bond exists beforehand ; the product, the triethyl ester of trimesic acid, CgH;(COOEt);, is known to have the constitution here given, +e, three COOEt groups substituted symmetrically in the benzene ring. COOEt Ak COOEt a wN ie | _.CH OB, c ie as hes —3H,0 ‘HC CH p-oy exer, | it wae Se gh tout COOEt C | dees COH--” or H CH Ethyl formyl-acetate (3 mols.) Triethyl ester of trimesic acid. The strain theory of Baeyer explains the varying stability of the polymethylene rings on the assumption that the four valencies of a carbon atom act in lines sym. metrically arranged (p. 541), making with each other an angle of 109° 28’ ; also that the direction of attraction can be deviated, so setting up a strain. In the pentamethylene ring the deviation (0° 44’) is smallest, consequently the strain is least and this ring is the most stable; the hexamethylene ring comes next (5° 16’), and then the tetra- methylene ring (9° 44’). Although benzene is not a polymethylene, according to this theory, it is to.be expected in the above synthesis that a six-carbon ring is formed rather than one with four or eight carbon atoms. Several other constitutional formule have been proposed. The “ diagonal ” formula of Claus (Fig. 289 (a) ), in which the opposite atoms are joined (“ para” linking), while agreeing with the saturated character, fails to show that the ring is also unsatu- rated. The “centric” formula of Armstrong and Baeyer (Fig. 289 (b) ) supposes the ’ fourth bond to be an ill-defined potential or a residual valency directed centrally. Probably o HC some dynamic formula representing 4 mobile ‘© CH 4 system in which the carbonatomsareina state yc CH of perpetual rotation and other change, would Hi H satisfy most conditions (see Collie, Jour. Chem. H Cy Soc., 71 (1897) 1013; cf. Kekule, p. 564. (2) ue. Pending a better knowledge as to the dis- position of the fourth atom-linking-power of each carbon atom, the majority of chemists prefer to omit the double bond and represent the benzene nucleus by a plain hexagon. 36 562 POSITION-ISOMERISM Position-isomerism.—Isomerides have already been defined as compounds which have the same percentage composition and the same molecular weight, but different properties. The isomerism may be due to one of three causes. (1) The isomeric compounds may be composed of different radicles, thus, the compounds C,H,-CO-C,H, and CH,-CO-C;H, are isomeric ; such isomerides are sometimes termed metamerides. (2) The isomeric compounds may consist of the same radicles, but these may be attached to different carbon atoms ; an example was met with in the case of pentane (p. 553); such isomerides may be termed position-isomerides. (3) The isomeric compounds may have the same radicles, attached to the same carbon atoms but differently situated in space with regard to each other; such cases will be met with hereinafter (lactic acids) ; these isomerides are termed stereo-isomerides ; see Stereochemistry, p. 633. Position-isomerides which are mono-substitution derivatives! of a hydrocarbon have been found to exist only in those cases where the carbon atoms in the nucleus are not all similarly united to each other. Thus, two monobromethanes, C,H,Br, have never been prepared, and it is concluded that more than one cannot exist because, since there are only two carbon atoms in the nucleus, these must be similarly united to each other. There can, however, be two monobromopropanes C;H,Br, because the carbon nucleus contains three carbon atoms, one of which is united with two other carbon atoms and two hydrogen atoms, whilst the other two are, each of them, united to only one other carbon atom and to three hydrogen atoms ; thus, the two compounds H,C-CH,-CH,Br (normal propyl bromide) and H,C-CHBr-CH, (isopropyl bromide) may be expected to be different from each other, even if only because the centre of gravity of the molecule of each is not the same, owing to the difference in the point of attachment of the bromine atom. That these two compounds exist there is no doubt, and that they have the formule above ascribed to them is rendered highly probable from the methods of their formation, which will be discussed anon. From what has been said, it will be understood that the fact that only one mono-substitution product of benzene can be found to exist, no matter what the substituting element or radicle be, is strong support in favour of the similarity of linking between all the carbon atoms, and of the sym- metrical structure of the molecule. Thus monobromobenzene, C,H,Br, can be produced in several ways, yet it always has precisely the same properties. It can, of course, be objected that it may happen that by the various methods of preparing this compound the same H atom is always exchanged for Br, so that this element is always attached to the same carbon atom, and could it be attached to some other of the six atoms a different monobromobenzene would be produced. The following line of argument, involving reactions which will be understood later, refutes this objection. Monobromobenzene is prepared by the direct action of bromine on benzene, and may have been formed by the substitution of Br for any one of the six H atoms in the benzene ring (p. 560). Assume that H (1) has been substituted, 23456 so that the product may be represented as C,BrHHHHH. By treating this with HNO,, the compound C,H,Br(NO,) is produced, and it is reasonable to admit that the second H atom, which has been exchanged for NOg, is not the same H atom as that previously exchanged for Br. Assume that H (2) has been exchanged for NOs, then 3456 the nitro-compound will be C,Br(NO,)HHHH. By treating this with nascent hydrogen (neglecting another reaction) the Br may be removed, and the H whose place it occupied ' Substitution-derivatives are mono-, di-, tri-, &c., according as the element or radicle is substituted for one, two, three, &c., hydrogen atoms. SUBSTITUTION-PRODUCTS OF BENZENE 563 ‘ : 1 3456 reinstated, so that nitrobenzene of the formula CsH(NO.)HHHH is produced. By treatment with reducing agents this is converted into an amido-substitution-derivative 1 3456 C.sH(NH,)HHHH. When this is treated, under certain conditions, with nitrous acid nee 1 3456 it yields the compound called diazobenzene, CsH(N,)HHHH, and by decomposing this 1 8456 with hydrobromic acid, monobromobenzene, CsHBrHHHH is obtained, and this is found to be identical with the bromobenzene produced directly from bromine and benzene, showing that whether H (1) or H (2) is exchanged for Br, the same substance is produced. The cases of position-isomerism among poly-substitution derivatives of hydrocarbons are very numerous. Two dibromo-derivatives of ethane are known to exist, viz. CH,Br-CH,Br and CH,-CHBr,. It has been found that there are four dibromopropanes, C,;H,Br,, and from the methods of their formation there is reason to believe that they are represented by the formule, (1) CH,Br-CH,-CH,Br, (2) CH,-CHBr-CH,Br, (3) CH,:CH,-CHBr,, and (4) CH,-CBr.-CH,. Only two other methods of writing this formula are possible, viz. (5) CH,Br-CHBr-CH, and (6) CHBr,-CH,-CH,; but in (5) the Br atoms are attached to carbon atoms, which are the same, so far as their linking to other atoms is concerned, as the carbon atoms to which the Br atoms are attached in (2), and there is the same similarity between (6) and (3). Hence, only four dibromopropanes are possible. It is evident that if the number of carbon atoms in the open-chain hydrocarbon-nucleus, or the number of substituting bromine atoms, be increased, the number of forms in which the formula can be written so that this is essentially different each time, will be increased. It has been supposed that as many isomerides may exist as there are essential differences in the formule which can be written for the compound ; whilst many isomerides, thus prophesied, have been prepared, the number remaining to be discovered is so large that some hesitancy may reasonably be shown in accepting the supposition. In the case of benzene the poly-substitution-products have been very thoroughly examined. Most of the di-substitution-products are known in three isomeric forms, but no di-substitution-product of benzene has been prepared in more than three isomeric forms. Thus, although benzene yields only one mono-substitution-product, it forms three dt-substitution-products,in each of which two atoms of hydrogen have been exchanged for radicles or for other elements. There are, then, three di-bromobenzenes, all having the formula C,H ,Br,, and therefore strictly isomeric, and yet having different properties ; so there are three di-nitro-benzenes, C,H,(NO,),, and three benzene di-sulphonic acids, C,H,(SO,H),, and such compounds form perfectly distinct series, so that if they be distinguished as a, 6, and c compounds, a-di-bromobenzene will yield a-di-nitrobenzene, and a-benzene-di-sulphonic acid, while b- and c-di-bromobenzenes will also yield their respective series of derivatives. To explain the existence of these three isomeric di-substitution-products, it is necessary to assume that different pairs of hydrogen atoms in benzene have different chemical values, and that the properties of the di-substitution- products depend upon the particular pair of hydrogen atoms exchanged. In order to investigate this it became necessary to orient (as it is termed in surveying) the plan of the benzene formula, that is, to mark the situation or bearing of its different parts. To effect this orientation of the benzene ring, it is necessary to distinguish the carbon atoms, for which purpose they are numbered consecutively as on, a watch-face (Fig. 290). . 564 SUBSTITUTION-PRODUCTS OF BENZENE The pairs of hydrogen atoms occupying places 1 and 2, 2 and 3, 3 and 4, 4 and 5, 5 and 6, 6 and 1, bear the same relation to the figure, and are there- zs fore of equal value, so that whichever pair is exchanged for “ \N__ other radicles, the same di-substitution-product will be ob- a ©@ tained. | | Again, 1 and 3,2 and 4,3 and 5,4 and 6, 5 and 1, 6 and 2, “ go being alternate atoms, bear the same relation to the figure, and ¢ their substitution would give rise to the same di-substitution- Fic. 290. product. But consecutive atoms, such as 1 and 2, or 2 and 3, have a different relation to the figure from that belonging to alternate atoms, such as 1 and 3, or 2 and 4, so that the substitution of two consecutive atoms of hydrogen would give one kind of derivative (say the a-substitution- product), and that of two alternate atoms would produce another kind (say the b-substitution-product). Lastly, the pairs 1 and 4, 2 and 5, 3 and 6, have the same relation to the figure, and, when exchanged for other radicles, would give identical products, but these would be different from the a and b products, and may be called the c-substitution-products. As the above lists exhaust all the possible pairs of hydrogen atoms, there can be only three di-substitution derivatives of benzene. Instead of using a, b and ¢ to distinguish the three isomerides, it is customary to use the prefixes ortho-, meta- and para- respectively. When adjacent hydrogen atoms in the benzene ring are exchanged for other radicles, the product is an ortho-compound ; when alternate hydrogen atoms are sub- stituted, the product is a meta-compound ; when opposite hydrogen atoms are substituted, the product is a para-compound. This is sometimes denoted by figures prefixed to the formula: thus 1 : 2-dibromobenzene is ortho- dibromobenzene ; 1:3 is meta-dibromobenzene ; and 1:4 is para-dibromo- benzene, all having the formula C,H Brg. This fact, that there are only three di-substitution-products of benzene, constitutes the main objection to Kekulé’s formula. It is not in accord with experience obtained from the open-chain compounds, that a substitution-derivative containing the sub- stituent groups attached to carbon atoms doubly linked together, should be identical with one which contains the groups attached to singly-linked carbon atoms: thus 1: 2-dinitrobenzene should differ in properties from 1: 6-dinitrobenzene, though as a fact these two compounds are identical, and four di-substitution-products are not known. Kekulé gets over this objection by supposing that the ring is in constant vibration, the double links and single links changing places every swing. Tri-substitution derivatives of benzene, in which the same radicle is sub- stituted for all three atoms of hydrogen, are found to exist in three isomeric forms; thus, there are three tribromobenzenes, C,H,Br,, distinguished as adjacent (1:2:3), symmetrical (1:3:5), and asymmetrical (1:2:4). If the substituted radicles are of two different kinds, say chlorine and bromine, six isomerides may be formed, and if three different radicles are introduced, say chlorine, bromine, and NO, ten isomerides are possible. - Tetra-substitution derivatives of benzene may also be adjacent (1: 2:3: 4), symmetrical (1:2:4:5), and asymmetrical (1:3:4:5). With a single substituted radicle, only these three isomerides are possible, but two radicles may give 20, three radicles may give 16, and four radicles may give 30 tetra- substitution-products. Evidently only one penta-substitution-product is possible with one radicle. The experimental investigation of the orientation of a benzene derivative consists in attempting to introduce fresh substituents into the nucleus, or in exchanging some substituent for hydrogen ; how this settles the orienta- tion will be understood from the following : ORIENTATION OF BENZENE DERIVATIVES 565 ___ By treating a dibromobenzene with bromine it is possible to convert it into tribromobenzenes (though this means of converting a dibromo- into a tribromo-benzene is not the most convenient). It is found that the dibromobenzene which boils at 224° yields two tribromobenzenes, whilst that which boils at 219-5° yields three tribromobenzenes, and that which boils at 219° and melts at 89° (the others melt at about 1°) yields only one tribromobenzene. Now, an inspection of the formule for the three dibromo- benzenes as written on the plane of the paper, will show that the 1 : 2- dibromobenzene can yield only two tribromobenzenes, viz. 1:2:3 and 1:2:4, since 1:2:5=1:2:4 and 1:2:6=1:2:3. Again, it will be seen that the 1: 3-dibromobenzene can yield three tribromobenzenes, viz. 1:2:3, 1:3:4 and 1:3:5 (1:3:6=1:3:4), whilst the 1:4 dibromobenzene can yield only one tribromobenzene, viz. 1 : 2:4 (or 1:3:4, or 1:4:5, or 1:4: 6, all these being identical with 1:2:4). The diagram will make this more clear : Br Br Br 4 Se a \ pr #X | yields | and | 7 Wy wr YY Br Br Br Br As i Jn ue | Br oe | ‘Br | Br = Br Br a WZ a Me a ields eal " NH Br Br It is evident that, of the three known dibromobenzenes, that must be the 1] : 2-derivative which yields two tribromo-derivatives ; that the 1 : 3- derivative which yields three tribromo-derivatives; and that the 1:4 derivative which yields only one tribromo-derivative. The orientation of tri-substitution derivatives may be similarly settled by exchanging one of the substituents for hydrogen, and thus obtaining one or more di-derivatives. If the derivative be the 1 : 2 : 3-derivative it will yield two di-derivatives, viz. 1:2 and 1:3; if it be the 1:3:5- derivative it can yield only one di-derivative. The orientation of certain derivatives, which may be called standard derivatives, having been settled by investigations involving the principle stated above, the orienta- tion of any new compound may be settled by converting it into one of these. Chief among these standards are the bromo-derivatives and the carboxylic acids (phthalic acid, &c.). Thus, the orientation of a newly discovered nitro-derivative could be settled by submitting it to a treatment (such as that indicated on p. 562) which would exchange the NO, groups for Br atoms ; a study of the properties of the bromo-derivative thus produced would decide its orientation and therefore that of the original nitrc- derivative. It is to be noticed that a polyvalent element can never be substituted for several hydrogen atoms in the benzene-nucleus ; thus, CgH,O is not known. The desire to prophesy what compound will be produced when a benzene deri- vative is treated with a substituting agent, has led to the formulation of several rules. Thus, it has been laid down that, when in a compound CgH;X, X is -NO,, ‘SO,OH or 566 TOLUENE -COOH, any new radicle entering into CsH;X will take up the meta-position to X. If X be any other group, the newly entering substituent will generally produce the para-derivative, but accompanied by a little of the ortho- and sometimes of the meta-derivative. If X be an element or radicle which forms a compound HX, capable of direct oxida- tion to HOX, the newly entering substituent will take the meta-position ; if, on the other hand, it be not so capable of oxidation, the newly entering substituent will take up the ortho- and para-positions (Crum Brown and Gibson). Thus, the introduction of asubstituent into C,H,Cl will give ortho- and para-derivatives because HClis incapable of direct oxidation to HOCI, whilst its introduction into CsH,-COOH will give a meta- derivative because HCOOH is capable of direct oxidation to HO-COOH. Homologues of Benzene.—These are derivatives of benzene containing alkyl radicles in place of hydrogen, such substituting radicles being termed side-chains. Methylbenzene (toluene), C,H;-CH5, dimethylbenzenes (xylenes), C,H,(CH;),, trimethylbenzenes, CgH3(CHs), (see Fig. 291), and tetramethyl- benzenes, C,H,(CH,),, occur in coal-tar ; numerous others, such as ethyl- benzene, O,H,-CH,-CH;, methylethylbenzene, CgH,(CH,)(CH,CH;), &c., have been prepared synthetically. CCH; CCH; HC. CCH, H CCHs HC CH H cH © CH, CH Methylbenzene 1: 2-Dimethylbenzene 1:8: 5-Trimethylben- or toluene. or orthoxylene, zene or mesitylene. Fic. 291. The residues of the benzene hydrocarbons, or aromatic or aryl radicles, are named similarly to the alkyl radicles ; thus, corresponding with methyl, ethyl, and propyl, there are phenyl, C,H;, methylphenyl or tolyl, 1 C,H ,-CH3, dimethylphenyl or xylyl, C,H,(CHs),. Isomerism among these alkylbenzenes is similar to that among other substituted benzenes, except that there may be cases of isomerism in the side-chains. Thus there is only one methylbenzene and one ethylbenzene, but there are two propylbenzenes, one containing the normal propyl! group, the other the iso-group (p. 580). These have the empirical formula C,H, which also belongs to trimethylbenzene, of which there are three isomerides, as of other tri-substitution derivatives, and to methylethylbenzene, a di- substitution-product also existing in three forms. Toluene and the aylenes are alone of any great practical importance among these homologues. Toluene, methylbenzene, phenylmethane, C,H;-CH;, is always present in commercial benzene. It was originally distilled from balsam of Tolu, and may be prepared by distilling toluic acid, C,H ,(CH,)CO,H, with lime. It resembles benzene in odour, solidifies at — 98°. It boils at 110° and its sp. gr. is 0-871. Benzene may be converted into toluene by first obtaining bromobenzene, C,H;Br, and treating this with methyl iodide and sodium, in the presence of ether, C,H; Br + Na, + ICH, = C,H,;-CH, + NaBr + Nal. Under the action of oxidising-agents, the side-chain is attacked and benzoic acid is formed ; C,H,CH, + 30 = C,H,COOH + H,0. Toluene is used chiefly for making aniline dyes and artificial oil of bitter almonds ; it is also used as a solvent. 1 Much confusion is cause] by modern nomenclature of hydrocarbon radicles. It was proposed to call radicles, such as tolyl and xylyl, alphyl radicles. Lately, however, this term has been applied to alkyl and substituted alkyl (benzyl) radicles, while tolyl, &c., have been termed aryl radicles, and benzyl, C,H, CH,, xylylene, CsH,(CH;)a, &c., have been called alpharyl or aralkyl radicles, XYLENES 567 Xylene, C,H,(CH,),, being a di-substitution-product, exists in three forms; but besides these there is a fourth hydrocarbon of the formula C,H , namely, ethylbenzene, which, however, is a metameride of xylene. The portion of the coal-tar light oil which distils at 136-141° contains about 80 per cent. of metaxylene (isoxylene) (1:3), (10 per cent. of paraxylene (1: 4), and 10 per cent. of orthoxylene (1:2). The mixture is used as a solvent. By shaking the mixture with H,SO, of 80 per cent. strength, the metaxylene is dissolved ; by treating the residue with ordinary strong H,SO,, the orthoxylene is extracted leaving the paraxylene. The action of the H,SO, is to convert the xylene into a sulphonic acid, CgH3(CH3)2‘SO.0H, from which the hydrocarbon can be obtained by dilution with water and distillation. Richards (Faraday Lecture, 1911) (cf. p. 334) concludes that of two substances otherwise similar, the less volatile one would be less compressible (for great internal pressure is implied by the difficulty of volatilisation), denser, and possess greater surface tension. He obtained the following constants for unusually pure specimens. The p-xylene froze at 13-2°, Density Surface tension Compressibility Boiling-point 20°/4° (mg/mm, 20 ) x 10° at 20 o-xylene . . 144-0° 0-8811 3-09 60-0 M- 45 ‘ . 139-0° 0-8658 2-96 63-5 P- » 136-2° 0-8611 2-92 65-2 By oxidation the methyl groups may be successively converted into COOH groups, yielding toluic acids, CgH,(CH3)(COOH), and phthalic acids, CsH,(COOH)., of each of which there are three, yielded respectively by ortho-, meta-, and paraxylene. Oxidising- agents do not act equally on the three isomerides, however. Chromic acid oxidises orthoxylene completely to CO, and H,O, but converts para- and metaxylene into para- and metaphthalic acid respectively. Dilute HNO 3 oxidises the ortho- and paraxylene to ortho- and paratoluic acid respectively, while metaxylene is not attacked. Mesitylene is 1:3: 5-trimethylbenzene, Cg,H3(CH3)3, obtained by the action of sulphuric acid on acetone (see p. 561), and by heating allylene with strong H,SO,, 3CH : C-CH; = C,H3(CH3)3 ; it boils at 163° and is metameric with cumene, or isopropylbenzene, CsH;:CH(CH3)2. Dureneis 1:2: 4: 5-tetramethylbenzene (m.-p. 79°, b.-p. 190°) and has an odour of camphor ; it is metameric with cymene or 1 : 4-methyl- isopropylbenzene, CgH,(CH3)-CH(CHs),, which is intimately associated with the terpenes and their derivatives. It is described at p. 675. The chief distinction betweeen benzene hydrocarbons and open-chain hydro- carbons resides in the ease with which the former may be converted into nitro-substitution-products by the action of strong nitric acid, and into sulphonic acids by the action of strong sulphuric acid. Moreover, the homologues of benzene easily undergo oxidation resulting in the conversion of the side chains into the group carboxyl, COOH, characteristic of acids. General methods for preparing benzene hydrocarbons are: (1) The distillation of the corresponding carboxylic acid with lime, which removes CO, from the carboxyl group: e.g. CsH,(CH3)(COOH)=C,H;-CH;+CO,. (2) The interaction of the bromo- substitution derivative and an alkyl iodide with sodium in ether : C.H,-Br + C2H;-I + Nag = CgH;-C,H; + NaI + NaBr (Fittig’s reaction, cf. the general methods for preparing paraffins, p. 551). (3) The interaction of a benzene hydrocarbon with an alkyl] halide in the presence of Al,Cl,, the precise function of which is not understood ; CsH;-CHs + 2CH,C] = C.H3(CH;)3 +2HCl. (Friedel and Craft’s reaction.) The above benzene hydrocarbons contain, as side-chains, the residues of saturated open-chain hydrocarbons. There also exist hydrocarbons containing residues of olefine and acetylene hydrocarbons ; their side-chains show full unsaturation. The olefine- benzenes correspond with the general formula C,Hen-39, and the acetylene-benzenes correspond with the general formula C,Hon—y. Cinnamene, styrolene, or styrene, CsH;-CH: CH, is phenyl-cthylene. It is obtained vy distilling cinnamic acid with lime; C,H,-CH: CH-COOH + Ca(OH), = 568 HYDROBENZENES C.H;'CH :CH, + CaCO; + H,0. It can also be prepared by distilling balsam of storax. or by distilling the resin known as dragon’s blood with zinc dust. Cinnamene is a fragrant liquid of sp. gr. 0-924, and boiling-point 145°. It is an olefine and therefore unites directly with chlorine, bromine, andiodine. When heated in a sealed tube to 200°, it becomes a transparent solid known as metacinnamene, or metastyrolene, which is polymeric with cinnamene, into which it is reconverted by distillation. When heated with hydrochloric acid to 170°, cinnamene is converted into di-cinnamene, C,gHi¢. Phenylacetylene, CgH,-C:CH, a liquid boiling at 139°, yields the explosive silver and copper derivatives characteristic of the true acetylenes (p. 557). Hydroaromatic hydrocarbons.—When heated with hydriodic acid the aromatic. hydrocarbons are converted into the corresponding hexamethylenes (p. 558); thus benzene yields hexamethylene (cyclohexane, hexahydrobenzene, benzenchexahydride, or CH,'CH, naphthene),H,C/ \CH,, while toluene yields methylhexamethylene (hexa- \\CH,-CH, CHy-CH, hydrotoluene or heptanaphthene), HO \\CH-CHs. These are colourless \CH,:CH,” liquids, boiling at 81° and 103° respectively, and occur in Caucasian petroleum. When monobromohexahydrobenzene is heated with quinoline it undergoes nucleal CH,:CH condensation, yielding tetrahydrobenzene (cyclohexene), HC’ cn, and \ cH, CH,” when the dibromo-derivative of this is similarly treated, dihydrobenzene (cyclohexa- CH-CH, diene), He CH,-CH. benzene (cyclohexatriene) is apparent, and it will be seen that cases of isomerism among the substitution derivatives should exceed those found among the corresponding benzene derivatives. For in both cases the character of the derivative may be expected to be influenced by the position of the double bond or bonds relatively to the substituent or 7 is obtained. The relation of these two compounds to CH,-CH CH,-CH, substituents. Thus HCC Nopr should differ from HC Sons, : CH,-CH, CH : CH CH:-CH, CH:,CH and HOG Dowr from oe err. Many such isomerides are CH,-CBr CH: CBr known and the nomenclature used to distinguish them consists in numbering the C atoms, as in benzene (No. 1 being always one to which a substituent is attached), and inserting the symbol A before the number of that C atom which is doubly linked to the one following it; thus the above bromo-derivatives are A 1-bromocyclohexene, A 5-bromocyclohexene, A 4, 6-orthodibromocyclohexene, and A 1, 5-orthodibromo- cyclohexene, respectively. (In the foregoing formule the direction of numbering is counter-clockwise.) Hydrocarbons containing more than one Benzene Nucleus.— These hydrocarbons can be classified into several groups: (1) Those which contain benzene nuclei directly united, such as diphenyl, C,H;-C,H;. (2) Those in which two or three nuclei are united by one carbon atom, as in diphenyl methane, C,H,CH,-C,H;, and triphenyl methane, CH(C,H;),. (3) Those which contain two benzene nuclei united by two carbon atoms, like dibenzyl, C,H;-CH,-CH,-C,H;. (4) Conjugated ring systems; those which contain condensed nuclei, as explained under naphthalene and anthra- cene. Many of the derivatives of these hydrocarbons are of importance in the arts, but, with the exception of those from naphthalene and anthracene, the hydrocarbons do not form the raw materials for making them. Diphenyl or phenylbenzene, CsH;*C,H;, is prepared by heating iodobenzene with finely divided copper at 220°; by the action of sodium on bromobenzene dissolved DIPHENYL 569. in ether ; 2CgH,;Br + Nay = (CsH,)p + 2NaBr, a mode of formation which settles its constitution. It may also be obtained by passing benzene vapour over red-hot pumice- stone ; 2C,H;H = (CgHs)2 + H,; or by distilling potassium phenol with potassium benzoate, CsH;-OK + CgH;-CO,K = (CgH5)o + K2CO, ; potassium oxalate may be substituted for benzoate, 2CgH;OK + (COOK). = (CgHs5)p + 2CO(OK),. It is also found among the last products of the distillation of coal-tar (at about 260°). Diphenyl crystallises from alcohol or ether in leafy crystals which have a pleasant odour and are insoluble in water. It fuses at 71°, and boils at 254°, When it is dissolved in glacial acetic acid, and treated with chromic acid, one of the CgH, groups is destroyed, while the other forms benzoic acid, CgH;-CO,H. It forms numerous substitution derivatives like benzene ; since it may be regarded as already being a mono-substituted benzene, containing phenyl in the place of H, its mono-substitution derivatives will be di-sub- stituted benzenes and occur in three isomeric modifications. Its di-derivatives occur in many forms, for substitution may occur in each ring. The orientation is expressed 3’ 2’ 2 3 as follows: C ¢ » Phenyltoluenes, CgH;*CgeH4*CHsg, and ditolyls, 5° 6’ 6 65 CsH4(CH,)-CgH,(CH;), are examples of mono- and di-substituted diphenyl; the 4- and 4: 4’-derivatives are the most common. By treating a mixture of 1 : 4-CgH,Bre and C,H;Br with sodium, 1: 4-diphenylbenzene, CgsH4(CgH5)o, is obtained; it melts at 205°. Diphenylmethane (benzylbenzene), CsH;*CH,*CgH;. It is obvious that toluene may be regarded as phenylmethane, CH,(C,H;), and just as toluene may be prepared by the interaction of methyl chloride and benzene in presence of Al,Clg, so diphenyl- methane, CH»(CgH5)o, can be prepared from phenylmethyl] chloride, commonly called benzyl chloride (q.v.), CsH;.CH,Cl, and benzene in presence of Al,Cl, ; C,H;H + C.H;-CH,Cl = C,H,:CH,:C,H, + HCl. It crystallises in needles which smell like the orange and dissolve in alcohol and ether ; it melts at 26° and boils at 262°. Chromic acid oxidises it to diphenyl-ketone (q.v.). When passed through a red-hot tube it undergoes the same kind of condensation as benzene does when it yields diphenyl (v.s.) under the same conditions ; the product is CeHs fluorene, | porn (p. 573). Triphenylmethane, CH(C.H;)3, is obtained by the CoHy interaction of chloroform and benzene in presence of Al,Cl,; 3CsH;H + CHCl; = CH(C,H,)3 + 3HCI. It crystallises in colourless prisms, which when formed from a benzene solution contain one molecule of benzene of crystailisation. It dissolves in hot alcohol, melts at 93°, and boils at 359°. The rosaniline dyes are derivatives of this hydrocarbon (p. 757). Dibenzyl, CsH;*CH.*CH,.:CgH;. Toluene can give rise to two hydrocarbon residues or radicles, viz. tolyl, CsH,:CH,;, and benzyl, CsH;-CH,. When the chloride of the latter ‘radicle is treated with sodium, dibenzyl is produced, 2(C,H;-CH,Cl) + Nay = CsHs:CH,:CH,:CsH, + 2NaCl. It may also be regarded as diphenylethane ; it melts at 52° and boils at 284°; when oxidised it yields benzoic acid. Diphenylethylene, or stilbene, or toluylene, CsH,:CH : CH-CgH;, is formed by treating benzal chloride (¢.v.) with sodium ; 2C,H;:CHCl, + 2Na,. = C,H,;-CH: CH-CsH; + 4NaCl. Also by par- tially oxidising toluene or dibenzyl, by passing it over hot PbO. It crystallises in prisms, melts at 125°, boils at 306°, and dissolves in hot alcohol. It contains true ethylenic linking, for the first action of bromine on it is the formation of the dibromide CsH;-CHBr-CHBr-CsH;. Diphenylacetylene or tolane, CsH,-C: C-C,H,, is formed by boiling stilbene dibromide with alcoholic potash. It melts at 60°, and behaves as an acetylene, save that, not containing a -C: CH group it yields no metallic derivative. Diphenyldiacetylene, CsH;:C : C-C : C-CgH;, is of importance as the hydrocarbon from which indigo is descended ; it melts at 88°. Conjugated Ring Systems.—Of the many various instances known, a few are of great interest. The indene, naphthalene, anthracene, phenanthrene, and fluorene groups belong here. Examples of others are (a dot signifying a carbon atom) : 570 NAPHTHALENE ea a Ps a ia. Li pee i <4 ie. pes Sa) (Ol 2) Bicycloheptane. Bicyclopentane. The figures refer to the number of carbon atoms in the bridge, the smaller part and the larger part respectively. The carbon atom at each end of the bridge is always tertiary. The atoms are orientated in a clockwise direction round the large part, then the smaller part, and finally the bridge. Pinene, camphor, 2 &c., are derived from the bicycloheptanes. ae Se «| Ls CH 2 ZN. CH, HC C— Indene, || yor occurs in coal-tar; b.-p. 178°; sp. gr. 1-040. CH SZ CH It may be synthesised from cinnamic aldehyde by reduction and condensation. /\—cH:CHCHO /“ \—CH,-CH,-CHO _ x0 CH | | = | —> 2 | by H,S0, | > CH WW Ww Oe Cinnamic aldehyde. Hydrocinnamic aldehyde. ’ HES a“ i Na Oe | > CH,, is an oil, b.-p. 177°, obtained by reducing CHa indene with sodium and alcohol. Numerous derivatives are known (e.g. p. 641). Naphthalene, C,,H,, is a crystalline hydrocarbon with an odour like coal-gas, and is occasionally deposited in gas-pipes in cold weather, causing an obstruction. It is a very common product of the action of a high tempera- ture upon substances rich in carbon ; coal and wood yield it on distillation ; marsh-gas, alcohol vapour, and ether vapour, when passed through a red- hot tube, deposit crystals of naphthalene in the cooler part. Burmese petroleum and Rangoon tar contain naphthalene. When coal-tar is distilled, the benzene hydrocarbons which distil over in the light-oil, are succeeded, as the temperature rises, by a yellow oil which is somewhat heavier than water. This, known as the middle-oil, is much more abundant than the light-oil, amounting to about 8 or 10 per cent. of the weight of the tar, and contains chiefly naphthalene and phenols. When the temperature has risen to about 200°, the distilled liquid partly solidifies on cooling, from the crystallisation of naphthalene. This portion is pressed to expel the liquid part, washed successively with caustic soda and sulphuric acid, and distilled ; or the washed naphthalene may be sublimed. Properties.—Transparent crystals, sp. gr. 1:145, melting at 79-80°, and inflammable, burning with a smoky flame. It sublimes much below its boiling-point (218°). Insoluble in water, soluble in alcohol, ether, and benzene. The peculiar odour of coal gas is largely due to naphthalene. In its chemical relations, naphthalene is closely connected with benzene, but it shows a greater disposition to form addition-products with chlorine and bromine, with which it also yields numerous substitution-products. Hydrindene, CONSTITUTION OF NAPHTHALENE 571 Naphthalene absorbs chlorine, forming a yellow liquid, naphthalene di- chloride, Cy)H,Cl,, and a crystalline solid, naphthalene tetrachloride, C,>H,Cl,. The non-existence of C,)H,Cl, is in accordance with the law of even numbers (p. 541). Naphthalene and its hydrocarbon derivatives behave in a rather characteristic way with picric acid. If they be dissolved in hot alcohol and mixed with a hot solution _ of picric acid in alcohol, stellate tufts of yellow or red needles are deposited on cooling. These consist of a compound of single molecules of the naphthalene and picric acid. Naphthalene is used for making phthalic acid, into which it is converted by oxidation ; for increasing the illuminating value of coal-gas (albo-carbon light) ; and as an insecticide. Many of its derivatives are used for making synthetic dyes. Constitution of naphthalene.—The similarity of the behaviour of naphthalene with that of benzene indicates an analogous structure for these two compounds, and since when it is oxidised naphthalene yields a benzene dicarboxylic acid CgH,(COOH),, it must be assumed to contain a benzene ring. Thus, six of the ten carbon atoms are accounted for ; two of the remaining four must be attached directly to two of the carbon atoms of the benzene ring, otherwise a dicarboxylic acid could not have been obtained by oxidation ; moreover, since the dicarboxylic acid proves to be phthalic acid, which is believed to have the carboxyl groups attached to adjacent carbon atoms of the ring, the two carbon atoms must be attached to the benzene ring in the ortho- position to each other. The two remaining carbon atoms are believed to form a closed chain with the a, oO, two just considered. Postponing, for the moment, C Zi the evidence for this belief, the formula to which it Se 2C8, gives rise may be regarded as consisting of two benzene 2 rings, so condensed together that they have two carbon atoms in common. Fig. 292 furnishes a representation BCR e we 4 pe of the structure of naphthalene (the H atoms, attached Cc one to each numbered C atom, having been omitted) and at the same time indicates the numbering of Fic. 292. the carbon atoms for purposes of orientation. To avoid the representation of ethylenic linking (cf. p. 561) many chemists omit the five double bonds in the formula. The Greek letters are sometimes used instead of the numbers, a referring to the adjacent positions, and ( to the more remote. E That naphthalene consists of two benzene-nuclei condensed as represented by the formula is supported by the following facts: When nitronaphthalene is oxidised nitrophthalic acid, CgH3(NO,)(COOH)., is produced ; from this reaction it is evident that the nitro-group in nitronaphthalene is in a benzene ring, whether there be a second benzene ring or not, and we may suppose that it occupies the position 8 in the formula (Fig. 292). By reducing the nitronaphthalene it becomes amidonaphthalene, that is the nitro-group has become an amido-group, and it is reasonable to suppose that the new group occupies the same position as the nitro-group did. Now if this amidonaphthalene be oxidised it is not an amidophthalic acid which is obtained, but simply phthalic acid itself; since an oxidising action cannot substitute H for NH, it must be concluded that it is the ring in which the NH, group was situated that has been removed by the oxidation, and yet a benzene ring compound (phthalic acid) has been left, showing that the naphthalene must contain two such rings. See also p. 804. It is found that two isomerides of every mono-substitution-product of naphthalene exist ; this is in accord with the formula, for it will be seen that whilst the carbon atoms, 1, 8, 4, and 5, are similarly situated towards the whole molecule, they are differently situated from 2, 3, 6 and 7, which, however, are similarly situated towards the molecule. When a substituent takes up any of the first-named positions, it is termed an a-derivative, whilst the other positions yield G-derivatives. It will be found that 10 di- and 14 tri-derivatives are possible ; all the mono-, di-, and tri-chloronaphthalenes are known and orientated, so that the orientation of a new derivative may be settled by its 572 ANTHRACENE conversion into one of these. The 1 : 8-derivatives are sometimes called pert-deriva- tives. The general expression for the naphthalene hydrocarbons would be CyHon_sp. Examples ‘of members of the homologous series are methyl-naphthalenes, C,p)H7*CH3, and ethyl-naphthalenes, CjpH;:C.H;. These are liquid even at low temperatures, and are constituents of coal-tar. CH, Ethene-naphthalene, or acenaphthene, Gigli” | 3 which is found in small quantity NOH, in coal-tar, is obtained by passing vapour of a-ethyl-naphthalene through a red-hot tube, when hydrogen is separated. It forms colourless prisms ; m.-p. 95°; b.-p. 277°. CH Acetylene-naphthalene, Olle || , is obtained as a fusible solid (92°) by passing CH vapour of acenaphthene over red-hot lead oxide, which removes Ho. Dinaphthyl, CjopH7'CoH,, is produced when vapour of naphthalene is passed through a red-hot tube, by the oxidising action of MnO, with H,SO, on naphthalene, and by treating C,)H,Br with Na. It forms scaly crystals, m.-p. 154°. Hydronaphthalenes.—Like the aromatic hydrocarbons, naphthalene readily forms hydrogen addition-products when treated with nascent hydrogen or hydriodic acid. These products range from dihydronaphthalene, C\oH,) to dekahydronaphthalene, C,oHig, in which all the double bonds have been converted into single bonds, so that the molecule is capable of attaching 10 atoms of H. When the hydrogenisation is in one ring only—which is the case with the di- and the tetra-hydronaphthalenes most easily obtained—the hydrogenised ring has properties resembling those of an open- chain hydrocarbon, so that the molecule is more like a phenyl derivative, having an open-side-chain, than a naphthalene. The substitution derivatives of such hydro- naphthalenes are therefore distinguished as aromatic (ar-) or alicyclic (ac-) accordingly as the substituent is in the phenyl ring or the hydrogenised ring. Thus C,H, : C,H,(NH,.) is ac-amidotetrahydronaphthalene, CgsH;(NH,): C,H is ar-amidotetrahydronaphthalene, while C,H;(NH.) : C,H7(NH.) is an ar-ac-derivative. Anthracene, C,,H,), is found, along with phenanthrene, in the green oil or anthracene oil, the last distillate from coal-tar (especially from New- castle coal), and may be distinguished from naphthalene by its being almost insoluble in alcohol and fusing only at 213°. It crystallises in colourless tables having a blue fluorescence, and boils at 351°. That fraction of the coal-tar distillate which comes over at about 360° solidifies on cooling to a mass of crude anthracene. It is freed from liquid hydrocarbons by pressure, washed with light petroleum, and purified by crystallisation from. hot benzene, or by sublimation as for naphthalene. Commercial anthracene is employed for the manufacture of alizarin. Anthracene is formed when vapour of toluene is passed through a red-hot tube containing pumice-stone to expose a large heated surface; 2C7Hg = C,,Hi9 + 3H. Lead oxide, by oxidising the H, effects the change at a lower temperature. It absorbs chlorine, forming crystals of anthracene dichloride, Cy4H Clo, and chloranthracene, Ci4H,Cl. With nitric acid, anthracene behaves in a different way from benzene and naphthalene, showing less disposition to the formation of nitro-compounds, When heated with nitric acid it undergoes oxidation and is converted into a yellow crystalline body called anthraquinone, C,4HgO. or (CgH4)o(CO)>. Constitution of anthracene.—From the fact that anthracene can be obtained syntheti- cally from benzene and tetrabromethane in the presence of Al,Clg, it is concluded that this hydrocarbon has a constitution represented by the formula CH BrCHBr CH Gat 1 SOs th Cite ein ee | See, uaape Nd She” aa PHENANTHRENE 573 The C,H, groups constitute two benzene rings (Fig. 293), whilst the central carbon atoms may be regarded as the residue of a third ring which has two carbon atoms in common with each of the other rings. By treatment with hydrogenising agents Anthracene, Anthraquinone, Fie. 293. (hydriodic acid, for example) the para-union between the central carbon atoms may CES Joy CH, formed. Support is lent to this formula for anthracene by the synthesis of anthra- quinone (q.v.). The orientation of anthracene substitution-products is expressed similarly to that of naphthalene derivatives. Three mono-substitution-products are possible—viz. the a- and /3-, like the a- and j3-naphthalene derivatives, and the y- or meso-derivatives, containing a substituent in place of the H of one of the middle carbon atoms, which may be numbered 9 and 10. Paranthracene, (Cy4Hio)2, crystallises in plates from a cold saturated solution of anthracene in benzene exposed to sunshine. It does not fuse until heated to 244°, when it is converted into anthracene. Bromine and nitric acid attack it with difficulty. Phenanthrene, C,,Hjo, is isomeric with anthracene, which it accompanies in coal-tar. It is more soluble in petroleum spirit and in alcohol than is anthracene ; the fomer solvent serves to separate it from the bulk of the crude anthracene ; the separation being finished by fractional distillation. It is used for making blacks. It melts at 99° and boils at 340°. Phenanthrene is formed when stilbene or orthoditolyl is passed through a red- hot tube ; since stilbene (p. 569) is known to contain ethylenic linked carbon and ditolyl to be a diphenyl derivative, it is concluded that phenanthrene has the constitution be opened up and dihydroanthracene or anthracene dihydride, CoH H H H H C C=C wk So 0 ee yoo H C=C H H H f ae : : _ ,. CgHy-COOH which is confirmed by the fact that its oxidation yields diphenic acid, C,H: COOH. Retene, CygHyg, is a methylisopropylphenanthrene found in wood-tar; m.-p. 98°, b.-p. 394°. Cee d picene, - : Chrysene, 6d GH and picene, C,H,—CH group Ci Hg, are similar to anthracene in properties. The former melts at 250° and boils at 448°; it is a final product in coal-tar distillation, and owes its name to its yellow colour in the crude state ; when purified it is white with a violet fluorescence. Picene melts at 364°, a higher melting-point than that of any other hydrocarbon ; it is found in the tar from lignite, and is highly insoluble. fos gy HC C——— C CH Cio Hg—CH :_, which contain the naphthylene Fluorene, | | is connected with phenanthrene through HC CH I \cu” Nort” Sca7 574 MONOHYDRIC ALCOHOLS diphenic acid (q.v.), the calcium salt of which on heating yields fluorone (diphe- CoH nylene ketone), | CO, which forms fluorene on reduction. Its condensation from diphenylmethane has already been noticed (p. 569). It is found in the last runnings (300°-305°) in coal-tar distillation and crystallises from alcohol with a blue or violet fluorescence ; m.-p. 113°, b.-p. 295°. Oxidation converts it into fluorone. DERIVATIVES OF HYDROCARBONS As has been indicated aiready, all carbon compounds may be considered as derivatives of the hydrocarbons, containing one or more elementary atoms or compound radicles in place of hydrogen, and in every compound there is a characteristic hydrocarbon radicle, which is monovalent, divalent, or trivalent accordingly as one, two, or three hydrogen atoms have been removed from a saturated hydrocarbon in order to form it. Typical hydro- carbon radicles are (CH,)’, (C,H,)”, and (C,H,)’”. I. ALCOHOLS These compounds are comparable with the metallic hydroxides, for they contain one or more (OH)’ groups, and react with acids forming water and salts containing hydrocarbon radicles. Thus, the reaction C,H,;-OH + H,SO, = C,H;HSO, + HOH is comparable with the reaction NaOH + H,SO, = NaHSO, + HOH. Just as a divalent or a trivalent metal forms a hydroxide containing two or three hydroxyl groups, so a divalent or trivalent radicle forms an alcohol containing two or three such groups, e.g. C,H,(OH),, C;H;(OH),. Hence alcohols are classified into monohydric, dihydric, trihydric, &c., accordingly as they have one, two, three, &c., OH groups. Several general methods for preparing the alcohols exist. Thus they may be formed from the halogen substitution derivatives of the corresponding hydrocarbons by treating them with moist silver oxide—C,H,I +AgOH= C,H,OH + Agl; from the ethereal salts (q.v.) by saponification— CH,-COOC,H, (ethyl acetate) + HOH = CH,;COOH + C,H;OH; from hydrocarbon derivatives containing the NH, group by treatment with nitrous acid—C,H,-NH, (ethylamine) + NO-OH = C,H,-OH + N, + HOH. This last reaction is typical of a widely applicable method for introducing an OH group into a compound, and is strictly comparable with the reaction between ammonia and nitrous acid at ordinary temperature (p. 203). Alcohols have a slightly basic tendency. They easily undergo oxida- tion, whereby hydrogen is removed with or without the introduction of an equivalent quantity of oxygen. The respective products are the alde- hydes (or ketones) and acids. Monohydric Alcohols of the Paraffin Series—These contain OH in place of one H atom in a paraffin hydrocarbon ; consequently there is an homologous series of these alcohols corresponding with the homologous series of hydrocarbons, CH, yielding CH,-OH, C,H, yielding C,H,-OH, C,H, yielding C;H,-OH, and so on. Thus, there is a general formula, CnHon+10H, for this series of alcohols. The substance originally called alcohol will be considered first. Alcohol, C,H;-OH or CH,;-CH,OH, is systematically termed ethyl alcohol. It has been already stated that it can be obtained synthetically by combining C and H to form acetylene, C,H,, which may be converted into ethene, C,H,, by nascent hydrogen; ethene can be combined with sulphuric acid to form ethyl hydrogen sulphate, C,H,-HSO,, from which ALCOHOLIC FERMENTATION 575 alcohol may be made by distillation with water. Or C,H, may be combined with HI to obtain ethyl iodide, C,H,I, which, when distilled with caustic potash, yields alcohol, C,H,I + KOH =C,H,-OH + KI. The fact that ethyl iodide (moniodoethane), CH,-CH,I, will give alcohol in this reaction justifies the formula CH,-CH,OH for this compound. In nature, alcohol is found in some unripe fruits. It occurs in coal- tar, in bone-oil, and in the products of distillation of wood and of a large variety of fermentative processes. Preparation.—Alcohol is usually made by the fermentation of glucose or grape- sugar brought about by yeast. Fora laboratory experiment, two ounces (or 60 grammes) of brown sugar may be dissolved in a pint (or 500 c.c.) of water in a flask, and about a table-spoonful of brewers’ yeast (or of German yeast rubbed up with water) added ; in a warm room, preferably at 25°, fermentation soon begins, as indicated by the froth on the surface caused by bubbles of CO,. By closing the flask with a cork furnished with a tube dipping under water, the rate of fermentation may be inferred from the escaping gas. When very little more gas is disengaged (usually after about 24 hours) the flask is fitted with a tube connected with a condenser, and the liquid distilled as long as the distillate smells strongly of alcohol. The distillate is then rectified, or submitted to a second distillation in a smaller flask or retort, when the first portion which distils over will be much richer in alcohol. This is placed in a narrow bottle, and dried potassium carbonate, in powder, is added by degrees, with frequent shaking, as long as the liquid dissolves it. On standing, two layers are formed, the lower containing the potassium carbonate dissolved in water, and the upper containing the alcohol with about 10 per cent. of water. This upper layer is transferred to a small flask or retort, and allowed to remain for some hours in contact with powdered quick-lime to remove the water; the alcohol is then distilled off in a water-bath. Yeast is a fungus (Saccharomyces cerevisie) which is amongst the germs carried by the air; when these come in contact with a liquid containing the nutriment necessary for the yeast plant, they multiply by budding into a number of round or oval cells frequently arranged in branching chains, visible under the microscope (Fig. 294). It is during this growth of the yeast that the conversion of the sugar into alcohol occurs. Pure yeast will not produce alcohol from pure sugar, because it does not contain the substances required to nourish the yeast; but when the spores are introduced into grape-juice, or infusion of malt (wort), which contain the necessary albuminous matters and phosphates, &c., they grow and cause the formation of alcohol. The crop of yeast thus raised may be used to ferment fresh por- tions of sugar, and is the more efficacious because, when it is removed from the surface of the liquid in which it has grown, it is accompanied by some of the nutrient materials. When yeast is added to a solution of cane- sugar (C,,H,.0,,) the invertase (an enzyme) contained in the yeast causes it to become invert sugar (a mixture of dextrose and levulose) by hydrolysis ; C,,H..0,, + H,O = 2C,H,,0,. The bulk of the invert sugar is then decomposed by the zymase (another enzyme contained in yeast) into alcohol and carbonic acid gas ; C,H,,0, = 2C,H,O + 2CO,; see also p. 64. About 95 per cent. of the glucose undergoes this change, and the remainder is converted into other substances, of which the most important are glycerol, C3H,;(OH)s;, (about 3 per cent.), succinic acid, C,H,(CO,H), (about 0-5 per cent.), and some of the higher members of the paraffin alcohols (collectively known as fusel oil, p. 582), which are always present in fermented alcoholic liquids. The liquid rises in temperature during fermentation, on account Fic, 294, ‘B76 ALCOHOL—PROPERTIES of the development of heat in the formation of carbon dioxide. The specific gravity of the solution decreases as the fermentation proceeds, because solution of alcohol is lighter than solution of sugar. A solution containing more than one-third of its weight of sugar is not fermented by yeast, and when the alcohol produced in the fermentation amounts to about one-sixth of the weight of the liquid, the growth of the yeast, and therefore the fermen- tation, is arrested. No fermented liquor, therefore, can contain so much as 20 per cent. of alcohol ; port wine, the strongest fermented drink, contains at most 17 per cent. The yeast does not grow, and fermentation does not occur, at temperatures below 0° C. (32° F.) or above 35° C. (95° F.), 25-30° C. being most favourable. The fermentation is also arrested by strong acids, © and by antiseptics such as common salt, kreasote, corrosive sublimate, sulphurous acid, and turpentine. Air is not essential to the fermentation, but favours it. In sweet wort (infusion of malt) the yeast increases to six or eight times its original weight. Numerous yeasts, species of Saccharomyces and Torula, are known and impart various flavours to the products of their fermentation; hence pure cultures, started from single cells of approved yeasts, are grown for both brewery and bakery purposes. On the large scale, alcohol is usually made from the starch contained in potatoes, rice and other grains. The starch, (CgH,)05) 2, is converted either into glucose, by heating it with very dilute sulphuric acid (afterwards neutralised with chalk)—when it com- bines with a molecule of water and becomes glucose, CgH,,O,—or into maltose, CyeH2.0y, by mixing it with infusion of malt, the active constituent of which is the enzyme diastase ; the glucose, or maltose, is fermented by yeast. The wash, as it is termed, is then distilled, the stills being constructed with much ingenuity, to effect the concentration of the alcohol at the least expense. Even woody fibre, paper, linen, &c., which have the same empirical formula as starch, may be converted into glucose by the action of sulphuric acid, and may thus be made to yield alcohol. New bread, made with yeast, contains about 0-3 per cent. of alcohol, and stale bread about 0-12. Properties of alcohol.—Characteristic odour and burning taste; sp. gr. of pure or absolute alcohol 0-794 at 15°. Freezes at — 112°; boiling-point 78°-3; takes fire when a flame is brought near its surface, and 3 burns with a pale, smokeless flame. Evaporates easily when exposed to the air, without combining with oxygen. Kept in a badly stoppered bottle, it absorbs water from the air. Alcohol may be mixed with water in all proportions, evolving a little heat, and giving a mixture rather smaller in bulk than the sum of its constituents. This may be shown by filling the vessel (Fig. 295) with water up to the neck joinmg the two globes, carefully filling the upper globe to the brim with (methylated) alcohol. inserting the stopper, and inverting the vessel, when the contraction of the mixture will leave a vacuum in the tube. The greatest contraction (about 3-7 per cent.) occurs when the volumes of alcohol and water are nearly equal (at 0°, 53-9 measures of alcohol to 49-8 of water). The attraction of alcohol for water affords one reason for its power Fie, 295. of preserving animal and vegetable substances from putrefaction by removing the water necessary for that change. A mixture of one molecular weight of alcohol (46) and four molecular weights of water (72) crystallises at —34°. When a weak spirit is cooled, ice separates until the compound C,H,0.4H,0 is left as the unfrozen liquid, and when the temperature reaches —34° it remains constant till the whole has solidified. E Next to water, alcohol is the most valuable simple solvent. It is especially useful for dissolving resins and alkaloids which are insoluble in water. Many salts are capable METHYLATED SPIRIT 577 of combining with alcohol, just as they do with water of crystallisation ; examples of such alcohol of crystallisation are: . LiC1.4C,H,0 ; CaCl,.4C,H,O ; MgCl,.6C,H,O ; Mg(NO3),.6C,H,O. When vapour of alcohol is passed through a red-hot tube, it is decomposed into a large number of products, among which are naphthalene, benzene, phenol, aldehyde, acetic acid, acetylene, ethene, marsh gas, carbonic oxide, and hydrogen. By oxidation alcohol is converted first into aldehyde, CH,-CHO, and then into acetic acid, CH,,;COOH. For oxidation by HNO,, see p. 616. The usual method of determining the strength of alcohol is to take its specific gravity (p. 30). Rectified spirit (alcohol 90 per cent., B.P.) has the sp. gr. 0-834, and contains 85-65 per cent. by weight of alcohol ; proof spirit (spiritus tenuior) has sp. gr. 0-91984 at 60° F. (15-5° C.), and contains about 49-24 per cent. by weight of alcohol; the strength is a purely arbitrary one fixed by Act of Parliament for Excise purposes; originally it was the weakest spirit which would answer to the old rough ‘“ proof” of firing gun- powder which has been moistened with it and kindled. Any spirit weaker than this leaves the powder too wet to explode, and is said to be below or under proof, whilst a stronger spirit is termed over proof. A spirit of 30 per cent. (or degrees), for example, over proof, is one which requires 100 measures of it to be diluted with water to 130 measures, in order to reduce it to the strength of proof spirit. A spirit of 30 per cent. below proof contains, in every 100 measures, 70 measures of proof spirit. Ordinary alcoholic liquids must be distilled before their alcoholic strength can be ascertained by specific gravity, on account of the presence of sugar, colouring-matter, &c. A measured quantity (v c.c.) of the liquid is diluted to about 120 c.c. with water rendered slightly alkaline with sodium carbonate, to retain volatile acids, and distilled in a flask connected with a good condenser until exactly 100 c.c. have been collected. The specific gravity is determined and compared with a table of alcoholic strengths, which has been prepared by ascertaining the sp. gr. of alcohol of various strengths. The percentage of alcohol indicated by the Table, multiplied by 100 and divided by »v, will be that present in the liquid under examination. The volume (v c.c.) taken may be 100 c.c. for beers, wines, &c. ; 50 c.c. for spirits. The weakest fermented alcoholic liquor is porter, which contains about 4 per cent. by weight of alcohol ; the strongest is port, which contains about 17 per cent. Distilled spirits vary greatly in strength, 50 per cent. of alcohol being about the average, though some samples contain 70 per cent. Methylated spirit is a mixture of 90 parts by weight of rectified spirit with 10 parts of purified wood-spirit added to it by the Excise in order to prevent its use for drinking. It may be distinguished by its odour, and by becoming red-brown with strong sulphuric acid. Since wood-spirit has proved an insufficient deterrent, 3 per cent. by vol. of mineral naphtha (sp. gr. 0-8) is now also added ; its presence may be recognised by the spirit becoming turbid when mixed with water. Industrial methylated spirit contains only 5 per cent. wood-spirit and no mineral naphtha. The simplest chemical test for alcohol is to add to the suspected liquid hydrochloric acid and enough potassium dichromate to colour it orange-yellow, to divide it between two test-tubes for comparison, and to heat one of them till the liquid boils ; if alcohol be present, the liquid will become green, and evolve the peculiar fragrant smell of aldehyde : 2CrO, + 6HCl + 3C,H,O = CroCly(green) + 6H,O + 3C,H,O. Alcohol may also be recognised by the production of acetic acid when its vapour is mixed with air and exposed to the action of platinum-black, which acts by favouring oxidation ; C»H,O + O, = C,H,O, (acetic acid) + H,O. If a small beaker be wetted with alcohol and inverted over a watch-glass containing a few grains of platinum-black, the liquid will soon become acid to litmus. = In contact with air and heated platinum alcohol yields much aldehyde, as well as acetic acid (see p. 530). The formation of iodoform is another useful test ; see p. 658. 37 578 HOMOLOGOUS ALCOHOLS Ethoxides or ethylates are compounds formed by the exchange of hydroxylic hydrogen in alcohol for metals; they correspond with the hydroxides, having C.Hs in place of H, eg. sodium ethoxide, C,H;.ONa, aluminium ethoxide, (C2.H;0),Als. Sodium ethoxide is used in surgery as a caustic. Water decomposes the ethoxides, yielding alcohol and hydroxides ; C,H,ONa + HOH = C,H,OH + NaOH. Barium ethoxide, (C2H,;O),Ba, is obtained by the action of anhydrous baryta on absolute alcohol. A trace of water precipitates barium hydroxide from the solution. On heating the alcoholic solution, the barium ethoxide precipitates, being less soluble in hot alcohol. Aluminium ethoxide, (CoH;0),Alg, is produced by heating aluminium in alcohol with a little iodine or stannic chloride. It melts at 135° and distils unchanged at 240° under 23 mm. pressure. Thallium ethoxide, CJH;OTI, is a liquid remarkable for its high specific gravity (3-68) and great refractive and dispersive action upon light. a The principal members of the class of monohydric alcohols derived from the hydrocarbons of the paraffin series, at present known, are shown in the following Table : Monohydric alcohols, C,Hn+1;OH. Chemical Name. Source, Formula Boiling-point.? 1. Methyl alcohol | Distillation of wood. . | CH;-OH 66° 2. Ethyl 2 Fermentation of sugar . | C,H;-OH 78° 3. Propyl ,, #3 grapes F . | C35H,-OH 97° 4. Butyl 3 a beet . : . | CyHy-OH 117° 5. Amyl BR 5 potatoes. . | C;Hy:OH 137° 6. Caproyl ,, 35 grapes ; . | CgHy3-0OH 157° 7. Cnanthyl ,, Distillation of castor oil with potash | C,H,,-OH 175° 8. Capryl ,, Essential oil of hog-weed . | CgHy7-OH 191° 9. Nonyl 2 Nonane from petroleum ‘ . | CoHy-OH 213° 10. Rutyl 55 Oil of rue . ‘ ; - | GyoHe-OH 16. Cetyl Fe Spermaceti ts : ; . | CygH33-0OH 27. Ceryl 3s Chinese wax : . é . | CogHs3-OH 30. Melissyl _,, Bees’-wax ‘ ; : - | CyoH—,;OH The usual gradation in properties attending gradation in composition among the members of homologous series, is strikingly exemplified in the alcohols. The first seven embers of the series are liquid at the ordinary temperature, possess peculiar and powerful odours, and may be easily distilled unchanged. Methyl and ethy] alcohols mix in all proportions with water, but the third member, propyl alcohol, though feebly soluble in water, is not so to an unlimited extent, while butyl alcohol is less soluble, and ~myl alcohol is very sparingly soluble, in water. Caproyl alcohol, the next member, is ir-oluble in water, while capryl alcohol is not only insoluble, but possesses an oily character, leaving a greasy stain upon paper. The last three members in the Table are solids of a wax-like character. F Those members of the series of alcohols which may be distilled without decomposing show a nearly regular increase in the boiling-point for each addition of CH, in the formula ; it will be seen from the Table that, excluding the difference between methyl and ethyl alcohols, the average difference in boiling-point is 19-5° C. for each CH, added. Methyl alcohol, carbinol, CH,-OH, is met with, in a very impure state, as wood-spirit, or pyroxylic spirit, or pyroligneous ether, or wood-naphtha. When wood is distilled, the condensed products separate into two layers, the lower of which is wood-tar, and the upper is a mixture of water with methyl alcohol, pyroligneous or acetic acid, CH,-CO,H, acetone, * Of the commonest isomeride. ? Of the normal alcohol (p. 580), METHYL ALCOHOL 579 CH,-CO-CH,, methyl acetate, CH,CO-OCH,, &c. On distilling this upper layer, the portion collected below 100° contains these bodies; on adding chalk and re-distilling, the acetic acid is retained in the still as calcium acetate, and the distillate is sold as wood-naphtha. Its yellow colour is. probably due to pyroxanthin, and the milkiness produced by adding water is due to certain oily substances which cause its peculiar odour. In order to obtain methyl alcohol, the wood-naphtha is distilled with quicklime to remove water, and heated with fragments of fused calcium chloride, which dissolves in the methyl alcohol to form a crystalline compound, CaCl,(CH,0), (methyl alcohol of crystallisation). This compound is not decomposed at 100°, the mixture is therefore poured into a retort placed in a water-bath, and heated to 100° as long as acetone and methyl-acetate distil over. An equal weight of water is then added, which decomposes the compound with CaCl,, and on continuing the distillation, methyl alcohol passes over accompanied by some water, which may be removed by contact with quicklime and distillation. Methyl alcohol is more easily obtained pure by boiling the wood-naphtha with anhydrous oxalic acid in a flask with a long condensing-tube, or a reversed condenser, until the methyl alcohol is converted into methyl oxalate, (CO-OCH;),, which separates in crystals on cooling. The crystals are collected on a filter, washed with water, and distilled with solution of potash ; (CO-OCH;), + 2KOH = (CO-OK), + 2(CH;-OH). The methyl alcohol distils over with some water, which may be removed by quicklime (also p. 669). Much methyl alcohol is now obtained by distilling the refuse of the beet-root sugar manufactory, and has become important as the source of many methyl-compounds employed in making dyes. Methyl alcohol in an impure state is used as a solvent for resins in making varnishes. Clean magnesium dissolves in absolute methyl alcohol even at ordinary temperature, evolving hydrogen and forming crystals of magnesium methoxide combined with methy] alcohol (CH,0)sMg + 3CH,OH. Properties of methyl alcohol.—Much re- sembling ethyl alcohol, with a somewhat different odour ; sp. gr. 0-7997 at 16°, b.-p. 66°; m.-p.— 95°, very inflammable, burn- ing with a pale flame. In presence of air and platinum-black, yields formic aldehyde (HCHO) and formic acid (HCO,H); CH,OH + O, = HCO,H + H,O. The formic acid may be distinguished from acetic by its property of reducing silver am- monio-nitrate to the metallic state when warmed withit. Methyl and ethy] alcohols may be distinguished by distilling them with dilute sulphuric acid and potassium dichromate, when the former yields formic acid and the latter acetaldehyde. A suitable apparatus for distilling small quantities of liquids in making such tests is shown in Fig. 296. The condenser con- sists of a vessel containing cold water and surrounded by a jacket, the lower part of which terminates in a tube. The vapour entering by the side tube condenses within the jacket. Isomerism among the monohydric alcohols——Since methyl and ethyl alcohols are mono-substitution derivatives from methane and ethane respec- | tively, it is not surprising that no position isomerides of these compounds. liso (peed 580 CLASSIFICATION OF ALCOHOLS are known (see p. 562). It has already been noticed that two mono-substitu- tion derivatives of propane are possible, namely, those which have the substituent attached to the end of the three-carbon-chain, and those in which the substituent is attached to the centre carbon atom ; the former kind is known as the normal propyl derivative, the latter as the isopropyl derivative. Thus, the general formula for a normal propyl derivative is CH,-CH,-CH,X’, whilst that for an isopropyl derivative is CH,-CHX’-CH, or X’CH: (CH; )p. Hence there is a normal propyl! alcohol and an isopropyl alcohol. Since butane may be regarded as methylpropane (a mono-substitution- product of propane) it may be expected to exist in two modifications (p. 552). The first of these, normal butane, can yield two mono-substitution deriva- tives, viz. CH,-CH,-CH,-CH,X’ and CH,-CH,-CHX’-CH,;; whilst the second, secondary butane, can also yield two mono-substitution derivatives, viz. (CH,), : CH-CH,X’ and (CH,),:CX’CH,;. Hence there should be four butyl alcohols. Pentane is methylbutane, but it exists in only three—instead of four—- modifications (p. 553) because the methylbutanes corresponding with the second and third formule given above would have the same structure. By writing the formule for a mono-substitution-product of pentane, it will be found that eight different compounds are possible, and in many cases eight are known ; eight pentyl (amyl) alcohols, for instance. All these isomeric alcohols are divided into three classes as follows : (1) Those in which the OH group is attached to a carbon atom which is itself attached to only one other carbon atom; these are called primary Jue alcohols and contain the group ie (2) Those in which the OH group is attached to a carbon atom, at is itself attached to two other cae atoms ; these are called secondary alcohols, and contain the group - 1 (3) Those in which the OH group is attached to a carbon OH : atom, itself attached to three other carbon atoms ; these are called tertiary alcohols, and contain the group : C-OH. The following list of alcohols will furnish examples of the three classes : Methyl alcohol ; . H-CH,OH Primary. Ethyl aleohol . : . CH;-CH,OH Primary. Normal propy] alcohol . CH,;-CH,-CH,OH Primary. Isopropyl alcohol .. . (CH 3). : CHOH Secondary. Normal butyl alcohol . CH;-CH,-CH,-CH,OH Primary. Primary isobutyl alcohol . (CH3).: CH-CH,OH Primary. CHs-CHy. Secondary butyl alcohol . gon Secondary. CH, Tertiary butyl alcohol . (CH), | COH 7 Tertiary. Of the eight pentyl] alcohols, 4 are primary, 3 secondary, and 1 tertiary. Greater facility in naming these numerous compounds is attained by taking methyl alcohol or carbinol as the starting-point. and supposing the alcohols to be derived from it by substitution of alcohol radicles for the hydrogen in the methyl group. Then, the primary alcohols will be mono-substitution derivatives of carbinol, as shown in the following formule : Carbinol, CH;-OH. Primary propyl alcohol, or ethyl carbinol, CH,(C,H;)-OH. Primary butyl alcohol, or propyl carbinol, CH2(C3H,)-OH. Primary iso-butyl alcohol, or iso-propyl carbinol, CH,(C3;H7)-OH (the difference here consisting in propyl, CLASSES OF ALCOHOLS DISTINGUISHED 581 CH,(CH,CH;), formed by the methylation of ethyl, CH.( CH,), and iso-propyl, CH(CHg)e, formed by the di-methylation of methyl). The secondary alcohols may be regarded as di-substitution-products of carbinol ; secondary propyl alcohol or dimethyl carbinol, CH(CH,)):OH, is evidently iden- tical with iso-propyl alcohol. Secondary butyl alcohol is ethyl methyl carbinol, CH(C.H;)(CHs)-OH. Secondary amyl alcohol is methyl propyl carbinol— CH(CH,)(C,H,)-OH. Another secondary amyl alcohol is di-ethyl carbinol, CH(C,Hs)yOH. The tertiary alcohols would be tri-substitution-products of carbinol. Tertiary butyl alcohol is trimethyl carbinol, C(CH3)3:OH. Tertiary pentyl alcohol is ethyl dimethyl carbinol, C(CyH;)(CH3)o-OH.4 The three classes of alcohols are distinguished by their behaviour under the action of oxidising-agents, which also serves to settle their constitution, When oxidised, a primary alcohol yields an aldehyde, and ultimately an acid, containing the same number of carbon atoms as the alcohol; thus, H, O g , yields acetaldehyde, cHyce , and H ethyl alcohol, CHs:C\ OH 7 ee Nous A secondary alcohol loses hydrogen by oxida- OH acetic acid, CH,:C tion just as a primary alcohol does and yields a ketone containing the same OH number of carbon atoms ; thus, secondary propyl alcohol, (CH,), : ct ; H yields di-methyl ketone, (CH,),:C: 0. A tertiary alcohol is either broken. up into two or more acids containing less carbon, or it may yield a ketone containing one atom less carbon than itself, the atom of carbon being oxidised to carbonic or formic acid; thus, tertiary butyl alcohol, C(CH,)3;'OH, yields acetone, (CH;), : CO, and formic acid, H-COOH. Another method for distinguishing between a primary, secondary, and tertiary alcohol is as follows: The alcohol is converted into the corresponding iodide by dis- tilling with iodine and phosphorus (see ethyl iodide); the iodide is distilled with a mixture of silver nitrite with dry sand (to dilute it), when the corresponding nitro- paraffin is obtained ; thus ethyl iodide yields nitro-ethane (C.H;NO.)— CH3°‘CHy-I + AgNO, = CH;-CH,-NO, + Agl. The distillate is mixed with potassium nitrite and weak potash, and dilute sulphuric acid is gradually added ; if the alcohol be primary, a red solution of the corresponding potassium nitrolate will be obtained, the nitro-paraffin having been converted into the corresponding nitrolic acid by the nitrous acid; thus, nitro-ethane yields ethylnitrolic acid— CH,-CH,-NO, + HNO, = CH3-C(NO.): NOH + H,0. Nitrolic acids are colourless, but their alkali salts have a dark red colour; they are very unstable, being decomposed into nitrous oxide and a fatty acid; thus ethylnitrolic acid yields nitrous oxide and acetic acid. If the alcohol be secondary, a blue solution of a pseudonitrol will be obtained ; thus secondary amyl alcohol, CH(CH;)(C,;H,)-OH, would yield the secondary nitro-paraffin, CH(CH;)(C;H7)-NO,, which would be con- verted by HNO, into the pseudonitrol, C(NO)(CH3)(C3H7)-NOs, giving a blue solution. If the alcohol be tertiary, no colour is produced, the tertiary nitro-paraffins being unattacked by nitrous acid. The simplest general method for preparing the alcohols consists in treating the corresponding halogen substitution derivatives of the hydrocarbons 1 According to another system, the alcohols are named by adding -ol to the name of the parent hydro- carbon; thus CH,°OH is methanol, CsH,,OHis propanol. Polyhydric alcohols are distinguished as diols, triols, &c.; CH,OH'CH,OH is ethanediol, CH,OH'CHOH'CH,OH is propanetriol, CH,OH'CH,'CH,OH is 1: 3-propanediol. - 582 FUSEL OIL with moist silver oxide, which behaves as if it were AgOH ; thus, if normal butyl bromide be so treated, it yields normal butyl alcohol, CH,-CH,-CH,-CH,Br + AgOH = CH,-CH,-CH,-CH,OH + AgBr. The secondary bromide, CH,-CH,-CHBr-CH,, yields the secondary alcohol. The tertiary bromide yields the tertiary alcohol. Another general method, similar in principle to the last, is to saponify the corresponding esters by means of alkalies, e.g. CsH,0-OC-CH, (propyl acetate) + KOH = C;H,OH (propyl alcohol) + KO-OC-:CH, (potassium acetate). This is the regular method for manufacturing glycerol (p. 589) from oils, 7.e. from its esters. As the alcohols form the basis for the production of a large number of compounds on the small scale, their general reactions will be best under- stood when these other compounds are considered. Here it may be mentioned that they dissolve alkali metals with evolution of hydrogen, forming the corresponding metallic alkyloxide or alcoholate, like C,H,-ONa. Normal propyl alcohol, or ethyl carbinol, C3H;-OH, or C,H,;-CH2-OH, is found in the latter portions of the distillate obtained in rectifying crude spirit of wine. It smells like alcohol, has the sp. gr. 0-804, and boils at 97°. When mixed with water it may be separated by saturating with calcium chloride, when the propyl alcohol rises to the surface, which would not be the case with ethyl alcohol. When oxidised, it yields propionic aldehyde, C,H;-CHO, and propionic acid, Cp,H;-CO.H. Iso-propyl alcohol, CH,-CHOH-CHs, sp. gr. -789, boils at 83°, and is obtained by reducing acetone with nascent hydrogen. The butyl alcohol, CyHy-OH, originally so-called, and mentioned in the Table at p. 578 as obtained by the fermentation of beet-root, and also by the distillation of crude spirits, is now called fermentation butyl alcohol, or primary isobutyl alcohol, (CH3)>°CH-CH,OH, to distinguish it from the normal butyl alcohol, which is the real member of this homologous series of alcohols. Fermentation butyl alcohol boils at 108°, and smells of fusel oil, which often contains it. It has sp. gr. 0-802, and is much less soluble in water than propyl alcohol is, requiring ten times its weight to dissolve it. Most salts soluble in water cause it to separate on the surface of the liquid. Normal butyl alcohol, or propyl carbinol, C;H7-CH,-OH, has sp. gr. 0-810, and boils at 117°. Itis obtained by acting upon butyl aldehyde with water and sodium amalgam, to furnish nascent hydrogen, C;H,-CHO + 2H’ = C,H,-CH,-OH. The history of amyl alcohol resembles that of butyl alcohol, the name having been originally given to the well-known offensive and poisonous liquid called fusel ozl, obtained in the distillation of spirits from fermented grain or potatoes. This contains, however, at least two isomeric alcohols, viz. isobutyl carbinol, (CH3). : CH-CHy:CH,:OH (b.p. 131°), and the “active” secondary butyl carbinol, CH; Se ee (b.-p. 127°); this latter is optically active, for it contains an CoH5 asymmetric carbon atom (*) (see stereo-isomerism). Fusel oil has the sp. gr. 0-83, and is so sparingly soluble in water that it separates from its solution in distilled spirits on dilution with water, rendering the liquid turbid. Its odour is very characteristic, and the vapour occasions coughing and a sensation of swelling of the head. On writing the formule for the possible amyl alcohols, it will be found that 4.are primary, 3 secondary, and 1 tertiary, and that 3 of them have an asymmetric carbon atom, so that each exists in a levo-, dextro-, and inactive form making 14 amy] alcohols -in all. Tertiary amyl alcohol, dimethylethyl carbinol, (CH 3)2.CoH;COH, is a liquid, b.-p. 102°, smelling of camphor, and used as a substitute for chloral as a narcotic ; it is prepared from the amyl alcohol of fusel oil. Normal hexyl alcohol, C;Hy,-CH2-OH, boiling at 157°, is not that produced by fer- mentation, but is obtained from the essential oil of an umbelliferous plant, Heracleum qviganteum, which contains hexyl butyrate, and yields the alcohol when disti led with potash, C;H;-COOC,H,, + KOH = C,H,3-OH + C,;H,-COOK. ALLYL ALCOHOL 583 The fermentation heayl alcohol, or caproyl alcohol, b.-p. 150°, is that obtained by ae fermented grape-husks; it has a more unpleasant smell than the normal alcohol. Normal capryl or octyl alcohol, CsH,7-OH, is obtained from the essential oil of the cow-parsnip or hog-weed (Heracleum spondylium), an umbelliferous plant, by distilling it with potash, which decomposes the octyl acetate, of which the oil chiefly consists, CHs-COOC,H,, + KOH = C3H,;-OH + CH;-COOK (potassium acetate). It has the sp. gr. 0-83, and boils at 199°. Cetyl alcohol, CygH ‘OH, or ethal, is obtained from spermaceti, found in the brain of the sperm-whale. This substance is cetin or cetyl palmitate, and when boiled for some time with potash dissolved in alcohol, it yields cetyl alcohol and potassium palmitate; C,,;Hs,-COOC,gH3;,; + KOH = C,gH3,-OH + C,;H,,-COOK. On mixing the alcoholic solution with water, the cetyl alcohol is precipitated in the solid state, being insoluble in water. Cetyl alcohol is a crystalline body, fusing at 50°, and boiling at 344°. See also p. 674. Ceryl alcohol, Cz7H55°OH, is prepared from Chinese wax, the produce of an insect of the cochineal tribe. It consists chiefly of cerotin or ceryl cerotate, CygH;3-COOC:7Hg,, and when fused with potash gives ceryl alcohol and potassium cerotate. By treating the fused mass with water, the cerotate is dissolved, and the ceryl alcohol is left, and may be obtained in crystals by dissolving it in ether. Its fusing-point is 79°. It occurs in flax. Recent analyses seem to show that ceryl alcohol is C.g,H;,-OH. Melissyl alcohol, or myricyl alcohol, C39Hg,-OH, is derived from bees’-wax. When this is boiled with alcohol, about one-third of its weight is left undissolved ; this is myricin or melissyl palmitate, Cy,;H3,;-COOC3,Hg,. When fused with potash it yields potassium palmitate and melissyl alcohol, which is a crystalline suis-tance, fusing at 85°. Monohydric Alcohols of the Olefine and Acetylene Serxies.— These may be regarded as formed from the olefine and acetylene hydro- ‘carbons in the same manner that the ordinary alcohols are derived from the paraffin hydrocarbons. They correspond therefore with the general formule C,H,,-,OH and C,H,,-,0H. Those which are best known are primary alcohols ; thus, allyl alcohol is CH, : CH-CH,OH, derived from propylene. The alcohol from ethylene, CH, :CH-OH, is a secondary alcohol (vinyl alcohol) and probably exists in crude ether, but it cannot be isolated because it is immediately transposed into aldehyde, CH,-CHO; this is in accord with other experience of the grouping : C : CHOH, which is always found to be unstable. The alcohols of these two classes are, of course, unsaturated compounds, and readily combine with H to form the alcohols of the preceding class. Allyl alcohol, C;H;-OH, or CH, : CH-CH,OH, is obtained by heating four parts of glycerol with one part of crystallised oxalic acid in a retort at 195°, so long as water passes over, and afterwards raising the temperature, when the allyl alcohol distils (addition of a little NH,Cl facilitates the change). The glycerol is first converted into monoformin (compare the process for formic acid, p. 602): CH,OH-CHOH-CH,OH + (COOH), = CH,OH-CHOH-CH,(OCHO) + CO. + H,0. The monoformin is then decomposed into allyl alcohol, CO, and H,0 ; CH,OH-CHOH-CH,(OCHO) = CH, : CH:CH,OH + H,0 + COs. It has a pungent smell, sp. gr. 0-856, b.-p. 966°. By very careful oxidation it yields glycerol, but when oxidised by AgsO it yields acrylic aldehyde or acrolein, CH, : CH-CHO, and acrylic acid, CH,: CH-COOH. This shows it to be a primary alcohol. Crude wood-spirit contains a little allyl alcohol. Propargyl or propinyl alcohol, CsH3-OH, or CH ! C-CH,OH, is the alcohol correspond- ing with allylene. It is obtained by boiling bromallyl alcohol (itself obtained by a some- what intricate process), CH, : CBr-CH,OH, with KOH ; CH, : CBr‘CH,OH + KOH = CH: C-CH,OH + KBr + HOH. It is a fragrant liquid of sp. gr. 0-97 and b.-p. 115° ; it burns with a luminous flame. Since it contains the CH: C group, it is capable of 584 AROMATIC ALCOHOLS yielding metallic derivatives ; cwproso-propargyl alcohol, COu: C-CH,OH is obtained as a green precipitate. Monohydric Alcohols of the Benzene Hydrocarbons.—It would seem at first sight-as though the hydroxy! compound produced by introducing OH in the place of one of the H atoms of benzene should be an alcohol. If the structure of benzene be correctly represented by the benzene ring, however, this alcohol would partake of the nature of a tertiary alcohol, since the OH would be combined to a carbon atom, itself attached by three atom-fixing powers to two other carbon atoms. As a fact, however, the hydroxy-substitution-products of the benzene hydrocarbons cannot be classed with the alcohols when the substitution occurs in the benzene nucleus. Such compounds as C,H,(OH), C,H,(OH)., CsH,(OH)(CH;,), differ to such an extent from the alcohols that they are classed apart as phenols. Only such hydroxy-derivatives of benzene hydrocarbons are alcohols (aromatic alcohols) as have OH substituted for H in the side-chain ; thus, whilst C,H ,(OH)CH, is a phenol, its isomeride, C,H,-CH,OH, is a primary alcohol, and may be termed benzyl alcohol or phenylcarbinol (pp. 544, 580). Secondary alcohols, e.g. C,H;CHOH-:CH, (from ethyl benzene), and 3 tertiary alcohols, e.g. C,H C(OH) (from isopropyl benzene), ‘CH, also exist, as in the paraffin series. For every alcohol there is an isomeric phenol, and it is possible to have a phenol-alcohol, e.g. Cg.H.(OH)-CH,OH (from hydroxytoluene), or any other substituted aromatic alcohol (Fig. 297). CHOU CH; CIL,CH OH “OH Benzyl alcohol Orthohydroxytoluene Orthohydroxybenzyl alcohol (an alcohol) (a phenol). (a phenol-alcohol). Fic. 297. Like the paraffin alcohols, the aromatic alcohols may be prepared from the halogen substituted hydrocarbons by the action of moist silver oxide or an alkali, but the substituted halogen must, of course, be in the side- chain, e.g. CsH;-CH,Cl (benzyl chloride). Benzyl alcohol, or phenylcarbinol, C5H;-CH,OH, may be obtained from benzal- dehyde (bitter-almond oil) by the action of reducing-agents ; since benzaldehyde is itself capable of undergoing oxidation, it is possible to obtain both its reduction product, benzyl alcohol, and its oxidation product, benzoic acid, by heating it with alcoholic potash ; 2C,H,-CHO ++ KOH = C,H;-CH,OH + C,H;-COOK. It can also be made from benzoic acid by the action of nascent H, generated by adding Na-amalgam to a boiling solution of the acid; CgH;-COOH + 4H’ = C,H,-CH,OH+H,0. The balsams of Tolu and of Peru and storax yield benzyl alcohol when distilled with alkalies which decompose the benzyl benzoate, C,H;-COO(C,H;CH.), and cinnamate contained in them. Benzyl alcohol is an oily liquid heavier than water (sp. gr. 1-06), boiling at 206°. Oxidising-agents convert it into benzaldehyde and benzoic acid, proving it to be a primary alcohol. Salicyl alcohol, or hydroxybenzyl alcohol, CgH4(OH)-CH,OH, shows the properties of a phenol (q.v.) as well as those of a primary alcohol, and is a type of the phenol alcohols. It is a di-substituted benzene, and therefore exists in three isomeric forms. The 1: 2-derivative was first called saligenin, made from salicin, a crystalline substance extracted from willow-bark. This substance is a glucoside, and when hydrolysed (p. 224) yields glucose (CgHj.0,) and salicyl alcohol ; CeH4(OC,H,,0;)-CH,OH + HOH = C,H,,0;(OH) + C,H,(OH)-CH,OH. 1: 2-salicyl alcohol forms tabular crystals, soluble in hot water, alcohol, and ether, CHOLESTEROL 685 fusing at 82°, and subliming at 100°. When oxidised it yields salicyl aldehyde, C,H,(OH)-CHO, and salicylic acid, CsH,(OH)-COOH. It gives an intense blue colour with ferric chloride (cf. Phenols). Cinnamyl alcohol is the primary alcohol corresponding with the unsaturated hydro- carbon cinnamene (p. 567); its formula is CsH,-CH : CH:CH,OH, phenyl allyl alcohol. It also is obtained from storax, a fragrant balsam exuded by the Styrax officinale, a tree found in Syria and Arabia, sometimes used as a pectoral remedy. When this is digested for some hours with a weak solution of soda, and the residue extracted with a mixture of ether and alcohol, needle-like crystals of styracin are obtained. This substance is cinnamyl cinnamate, CgH;-CH : CH-COO(C,H;-CH : CH:CH,), and yields cinnamy]l alcohol and potassium cinnamate when distilled with KOH ; CyHy-CsH,0, + KOH = CsHy-OH +KC,H,0.. The alcohol smells of hyacinths, melts at 33°, and boils at 250°. It dissolves spar- ingly in water, but easily in alcohol or ether. When oxidised it yields cinnamic aldehyde and cinnamic acid. Alcohols of the hydrocarbons containing more than one benzene nucleus are of minor importance. Diphenylcarbinol (benzhydrol), (CgH;),CH.OH, is a secondary alcohol obtained by reducing benzophenone (g.v.) ; it melts at 68°. Triphenylearbinol, (CgH,)3C.OH, is a tertiary alcohol, important from its relation to the “aniline dyes.” It is formed by oxidising triphenylmethane (p. 569) with chromic acid in glacial acetic acid, melts at 159° and boils at 360°. Naphthalene and anthracene alcohols also exist. Cholesterol, C,,H,,OH, is a secondary, unsaturated, monatomic alcohol very widely distributed in the animal system, being found in all forms of protoplasm. It is found in bile, as its name suggests, and it com- poses the chief part of gall-stones or biliary calculi, from which it may be extracted by boiling with alcohol. It is abundant in nerve tissues, especially in the white sheath of the nerve fibres. More frequently it occurs in the free state. Small quantities (traces to 1 per cent.) of it are to be found in all animal fats, so that its presence is evidence of the origin of the fat ; sitosterol(q.v.) is equally characteristic of vegetable fats. Egg-yolk contains 0-4 per cent. cholesterol and wool-wax several per cent. together with much isocholesterol (g.v.). Cholesterol crystallises in lamin, some with re-entering angles, from hot alcoholic solution. It is insoluble in water, soluble in six parts of. boiling alcohol (90 per cent.), sparingly in the cold. Chloroform, ether and CS, dissolve it easily. It is levo-rotatory, [a] = — 34-3° in chloroform solution. M.-p. 148°. It may be distilled unchanged in vacuo. The constitution of cholesterol is not yet settled. There is no doubt, however, that it belongs to the terpene family and that it possesses one double bond, but as recent constitutional formule are so much at variance, one is not given here. By the action of Br on its solution in CS, cholesterol dibromide, C27H,,Br.OH, is formed. On boiling with acetic anhydride (14 parts) for some time, it is converted quantitatively into cholesteryl acetate, m.-p. 114-5°. Cholesterol and its derivatives have wu tendency to form liquid crystals (q.v.). It gives characteristic colours with certain reagents. Isocholesterol, isomeric with cholesterol (q.v.), occurs in wool-wax. It is more soluble than cholesterol. M.-p. 138°, becoming much (several degrees) lower by long (several months’) exposure to light. It is dextro-rotatory ; [a]p = + 60° in ethereal solution. Sitosterol, or phytosterol, isomeric with cholesterol, is found in all seeds and fruits, and is otherwise widely distributed in the vegetable kingdom, and in the oils obtained from these sources (see Cholesterol) ; m.-p. 138°; [a]; = —26-71°. Sitosteryl acetate, m -p. about 130°. Thio-alcohols or mercaptans are analogous to the alcohols, but contain § in place of O, and as the latter are hydroxides of the alcohol radicles, so the thio-alcohols (B-SH) are the hydrosulphides. Their boiling-points are much lower than those of the corresponding alcohols. On oxidation they yield sulphonic acids. The thio-ethers, 586 SULPHONIUM COMPOUNDS RS, or sulphides of the alcohol radicles, may also be considered here: they are the analogues of the ethers, RO. Mercaptan, C,H;-SH, was named from its remarkable action on mercury com- pounds (mercurio aptum). It is made (for making sulphonal) by distilling KSH with C,H; Cl in alcoholic solution, or, on a smaller scale, with calcium sulphethylate (q.v.) : Ca(C,H,SO,4)o + 2KSH = CaSO, + K,SO, + 2(C.H;-SH). A solution of KSH is made by saturating potash of sp. gr. 1-3 with HS, and this is distilled, in a salt-and-water bath, with an equal volume of solution of calcium sul- phethylate of sp. gr. 1-3. The mercaptan forms the upper layer of the distillate, and is characterised by its powerful disagreeable odour. It is a volatile liquid, of sp. gr. 0-835, and boils at 36°. A drop exposed to the air is frozen to a crystalline mass by its own. evaporation. It burns with a blue flame. Mercaptan is sparingly soluble in water, but dissolves in alcohol and ether. It is unaffected by caustic alkalies, but alkali metals act on it as in the case of alcohol, displacing hydrogen and forming mercaptides, e.g. CoH;-SK, which are crystalline bodies soluble in water. Mercuric oxide evolves much heat with mercaptan, forming a white crystalline inodorous compound ; HgO + 2(C,H,;-SH) = H,O + (C,H;S)oHg (mercuric mercaptide). This is insoluble in water, but may be crystallised from alcohol, or from strong HCl. Potash does not decompose it. H,S converts the mercury into sulphide and reproduces mercaptan. Mercaptides (thio-ethoxides) of other metals may be precipitated by metallic salts from an alcoholic solution of mercaptan. By distilling mercuric thio-ethylate, di-ethyl sulphide or thio-ether, C.H;-S-C,H;, may be obtained; (C,H;S),Hg = (C.H;).S +HgS. This may also be prepared by distilling potassium ethylsulphate with potassium sulphide; 2KC,H;SO, + K,S = 2K,8O0, + (CoH;)o8. It resembles mercaptan, but boils at 91°. Its alcoholic solution gives, with mercuric chloride, a white crystalline precipitate of (C,H;).S-HgCly. Allyl sulphide, (C;H;)8, is the main constituent of essential oil of garlic, and occurs in several cruciferous plants. It is prepared artificially by digesting allyl iodide with potassium sulphide. It boils at 140°, dissolves sparingly in water, and behaves like ethyl sulphide. Ethyl disulphide, (C.H;)28o, is obtained when potassium disulphide and ethylsulphate are distilled. It may also be formed by heating mercaptan to 150° with sulphur ; 2(C)H;SH) + S2 = (CyH;5)2S, + HS; or by decomposing sodium mercaptide with iodine ; 2(C,H,SNa) + I, = 2NaI + (C.H;).85. It is an alliaceous liquid, boiling at 151°. Hthyl sulphoxide, (CpH;).SO, is a syrupy liquid resulting from the action of dilute nitric acid on ethyl sulphide. Ethyl sulphone, (C,H;).SOo, is a very stable crystalline body formed when ethyl sulphide is oxidised by strong nitric acid ; it fuses at 70° and boils at 248°, but sublimes at 100°. It is soluble in water and alcohol. Sulphonium Compounds.—When ethyl sulphide and ethyl iodide are heated together with a little water for some hours in a flask with an inverted condenser, the mixture, on cooling, deposits colourless prisms of tri-ethyl-sulphonium iodide, (C.H,),8-I, which are soluble in water and alcohol, but insoluble in ether. This compound is remarkable for producing a series of compounds in which the iodine may be exchanged for other negative radicles, giving rise to tri-ethyl-sulphonium salts, in which the § is quadrivalent ; thus, in the iodide, it is attached to four monad radicles, viz. 3C.H; and I. By decomposing the iodide with silver hydroxide, the tri-ethyl-sulphonium hydroxide, (C.H;)38-OH, is obtained ; it is a deliquescent crystalline body possessing the properties of a powerful caustic alkali. Compounds similar to the foregoing have been obtained from the alcohols formed by the other radicles of this series. Dihydric Alcohols, or Glycols.—The dihydric alcohols may be regarded as derived from the saturated hydrocarbons by the substitution of hydroxyl groups for two H atoms ; equally well, they may be said to be olefine hydrocarbons which have combined with two hydroxyl groups, and this is the view expressed by their nomenclature ;- ethylene glycol, C,H,(OH),, and propylene glycol, C;H,(OH),, are examples. Like the monohydric alcohols, a general method for their preparation consists in the GLYCOLS 587 treatment of the corresponding bromo-derivatives with alkalies, or, what is equivalent, an alkali carbonate, or lead hydroxide, and water. The simplest glycol would be CH,(OH), from methane; but this has never been isolated, and it appears to be a fact that no compound can exist which has two hydroxyl groups attached to one carbon atom (cf. the non- existence of carbonic acid, OC(OH), ; p. 244). The OH groups are attached to different carbon atoms. For example, ethylene glycol is CH,OH-CH,OH, not CH,-CH(OH),, and cannot exist in isomeric forms; propylene glycol may be either CH,OH-CH,-CH,-OH, or CH,-CHOH-CH,OH, the former of which contains two primary alcohol groups, and may be termed a di- primary glycol, whilst the latter is a secondary-primary glycol.2 Since disecondary, ditertiary, secondary-tertiary and primary-tertiary glycols are also possible, the cases of isomerism among the glycols are very numerous. The OH groups in the glycols are capable of the same transformations as is the OH in a monohydric alcohol ; the H in them can be exchanged for alkali metals; the hydroxyl groups can be exchanged for acid radicles, &c. Two series of such substituted glycols exist, those in which both OH groups have undergone the change, and those in which only one has been altered; thus, CH,ONa-CH,OH and CH,ONa:CH,ONa; CH,Cl-CH,OH and CH,Cl-CH,Cl. The oxidation of the glycols yields the same kind of products as those from the oxidation of the alcohols ; but since there are two alcoholic groups to be oxidised, a very large number of producté is obtainable ; for example, the two primary alcohol groups in CH,OH-CH,OH can both be oxidised to aldehyde groups, CHO-CHO, or to acid groups, COOH-COOH ; or only one of them may be so oxidised, yielding alcohol-aldehydes, CHO-CH,OH, or alcohol acids, COOH-CH,OH ; aldehyde-acids, CHO-COOH, will also be possible. If the glycol contain a secondary alcohol group (: CHOH), ketone-alcohols, ketone-aldehydes, ketone-acids, and diketones may also be prepared. Hence the glycols give rise to a very large number of derivatives, many of which are very important, although the same cannot be said of the glycols themselves. The dialcohols, alcohol-aldehydes, alcohol-acids, and alcohol-ketones, containing the group CH,OH, are frequently termed hydroxy- or oxy-deriva- tives of the corresponding paraffin compounds. Thus CH,OH-CH,OH may be regarded as hydroxyethyl alcohol (oxyethyl alcohol), i.e. ethyl alcohol, in which H has been exchanged for OH ; CH,OH-CHO as hydroxyacetic aldehyde, and CH,OH-COOH as hydroxyacetic acid. The glycols are somewhat viscid, neutral liquids. The increase in the number of OH groups in an alcohol seems to tend to increase the boiling- point, the viscidity and the solubility in water ; solubility in alcohol and ether decreases. The glycols have a sweetish taste (hence their name), a property much enhanced in glycerol and the sugars. Glycol, CH,OH-CH,OH, or ethylene glycol, is a much more artificial product than alcohol, having been discovered as lately as 1856. It is prepared by decomposing ethylene bromide with potassium carbonate. Ethylene (p. 555) is first converted into ethylene bromide by passing it slowly into 50 grams of bromine under water, well cooled, until the bromine is bleached, or nearly so. The heavy layer of ethylene bromide is shaken with a little weak potash, the upper watery layer drawn off, and 50 grams of the bromide heated with 40 of potassium carbonate, and 100 of water, for eighteen hours, in a flask provided with a reflux condenser (Fig. 298) ; when the 1 For exceptions under certain conditions, see chloral hydrate (p. 661) and muscarine (p. 701); one of the exceptions appears to be mesoxalic acid (q.v.), and generally there is a tendency for a C atom which is combined with two COOH group to hold two OH groups. 4 The glycols are either a-, B-, or y, &c., glycols accordingly as the OH groups are attached to the 1: 2, 1:38, 1:4, &€., C atoms of the chain, respectively; thus—CH,OH-CH,’CH,OH is f-propylene glycol, the a-someride being CH,,;CHOH'CH,OH. 588 GLYCEROLS bromide no longer condenses and runs back, the condenser is placed in its usual position and the contents of the flask distilled. After all the water has passed over, the flask is strongly heated by a large Bunsen burner, when the glycol distils. The reaction is expressed by the equation CpH,Bry + K,COs + H,O = C,H,(OH), + 2KBr + COs, which exemplifies the tendency of alkaline reagents, in the presence of water, to effect the substitution of hydroxy] for halogens. Glycol is a colourless liquid, less mobile than alcohol, and almost inodorous. It has a sweet taste, sp. gr. 1-125 at 0°, and the high boiling- point 197°. Its vapour is inflammable, but will not take fire at common temperatures as alcohol will. Glycol mixes with water and alcohol in all proportions, but ether dissolves it only sparingly. Sodium dissolves in glycol, as in alcohol, evolving hydrogen, and yielding monosodium glycol, CH,OH-CH,ONa, corresponding with sodium ethoxide, C,H,ONa. On heating this with more sodium, a second atom of H is displaced, yielding disodiwm glycol, CpH4(ONa)2. Water converts both compounds into glycol and sodium hydroxide. Glycol chlorhydrin is glycol in which Cl has been substituted for one hydroxyl group ; CH,OH-CH,Cl; and is prepared by saturating glycol _with HCl, and heating in a sealed tube to 100°; C,H,(OH), + HCl = C,H,-OH-Cl + HOH. It has also been obtained by the combination of ethylene, C,H,, with hypochlorous acid, CIOH. It permits the conver- Fre. 29g, sion of a dihydric into a monohydric alcohol, for it yields ethyl alcohol when acted on by the nascent hydrogen from water and sodium-amalgam ; C,H,-OH-Cl + 2H = C,H;-OH + HCl. When oxidised it yields monochloracetic acid, CH,Cl-COOH, in which it is obvious that the Cl cannot be attached to the same carbon atom as that to which the O and OH are attached (or the substance would not be an acid) ; this proves that glycol chlorhydrin must contain Cl and OH attached to different carbon atoms, and settles the constitution of glycol. The first stage in the oxidation of glycol is the formation of glycol dialdehyde, or glyoxal; the relation of this body to glycol is shown thus: glycol, CH,OH-CH,OH ; glyoxal, CHO-CHO. The further oxidation of glycol yields two acids, glycollic acid, COOH-CH,OH, and oxalic acid, COOH-COOH. The glycols from the hydrocarbons containing one or more benzene nuclei, have the hydroxyl groups in the side-chains ; they have been little studied. Hydrobenzoin, (CsHs)CHOH-CHOH(C,H;), toluylene-glycol, is derived from stilbene (p. 569) ; it crystallises in plates, and melts at 134°. An isomeride, isohydrobenzoin, melts at 119°, and occurs in two optically active and one inactive forms; both isomerides are produced when benzaldehyde (p. 597) is reduced with nascent hydrogen. The pinacones are di-tertiary glycols, obtained, together with secondary alcohols, by the action of nascent hydrogen on the ketones. Thus acetone undergoes a con- densation according to the equation, 2(CH3),CO + 2H’= (CH;).(HO)C-C(OH)(CHg)s, tetramethyl pinacone. Trihydric Alcohols, or Glycerols.— These may be regarded as derived from saturated hydrocarbons, by substituting three OH groups for three H atoms. Since two OH groups cannot remain combined with one carbon atom (p. 587), there can be no glycerol which contains fewer than three carbon atoms; thus, C,H,(OH), must be the first member of the series. The radicles of the glycerols may obviously be regarded as trivalent radicles, e.g. (C3H;)’’”’, glyceryl or propenyl. Comparatively few of the glycerols are known ; what was said with regard to isomerism, substitu- tion derivatives, and oxidation-products of the glycols, applies with even more cogency to glycerols, where there are three hydroxyl groups to be substituted and three alcoholic groups to be oxidised. It will be noted, however, that a glycerol formed from an open-chain saturated normal hydrocarbon must always contain at least one secondary alcoholic group. GLYCERIN 589 Glycerol, or Glycerin,1 C3H,(OH);, or CH,OH-CHOH-CH,OH, was discovered by Scheele in 1779 and termed by him the “‘ sweet principle ” of fats. It may be prepared from most of the natural fats, which are esters of glycerol and thence called glycerides. Glycerol is also formed during the alcoholic fermentation of sugar, and is present in small quantity in beer and wine. Previously to 1850, glycerin was made only on a laboratory scale by the process discovered by Scheele, which consisted in boiling olive oil with lead oxide (litharge, PbO) and water, when lead oleate, or lead plaster, remained, while the glycerin dissolved in the water from which it was obtained by evaporation, after precipitating the dissolved lead by H,S. Preparation of glycerin.—Glycerin is contained in the refuse liquor (spent lyes) of the soap-maker (see p. 671), being always produced when oils and fats are saponified by alkalies, and remaining in solution when the soap is separated by adding salt. The chemistry of the saponification of oils and fats will be considered under esters, to which class these bodies belong. The soap lyes are concentrated until most of the salt has crystallised and most of the water evaporated. The crude glycerin thus obtained is distilled under diminished pressure in a current of superheated steam, when water passes over first and is followed by glycerin, the temperature of the receiver being high enough to prevent much of the superheated steam from con- densing. The more or less dilute glycerin thus obtained is concentrated in a vacuum pan. Only within recent years have methods of evaporation been so far improved that it has paid the soap-maker to recover glycerin from his lyes. The candle-maker used to be the sole producer. In this industry palm-oil is decomposed by super-heared steam to obtain palmitic acid for making candles. The operation is conducted in a still, and the distillate consists of a layer of palmitic acid floating on an aqueous solution of glycerin. The latter is drawn off and concentrated as described above, the process being simplified by the absence of salt. The palmitic acid solidifies to a white cry: talline substance. Glycerol has been synthesised from propylene by combining it with chlorine to form propylene di-chloride, CH,Cl‘CHCI-CH;, which is heated with iodine chloride to convert it into propenyl tri-iodide, CH,I-CHI-CH,I ; by heating this in a sealed tube, with much water, at 160°, it is converted into glycerol; C,H,I, + 3HOH = C,H,(OH), + 3HI. This synthesis, together with the fact that glycerol can be made by oxidising allyl alcohol, CH, : CH-CH,OH, establishes the constitution of glycerol, if it be admitted that one carbon atom cannot hold two OH groups. Properties of glycerol.—It has a sweet, warm taste and resembles syruj in consistence ; sp. gr. 1-26468 at 15°; boils at 290°, but then undergoes slight decomposition. At 12-5 mm. pressure it boils at 179-5°. It is slightly volatile at 100°, but not at the ordinary temperature. If kept below 0° for some time, a strong aqeuous solution of glycerin deposits crystals, especially if a ready-made crystal be introduced ; this method was at one time practised for purifying crude glycerin; pure glycerol solidifies at — 40° to a gummy mass, which melts at 20°. It does not inflame until heated to 150°, when it burns with a flame resembling that of alcohol. It absorbs water easily from the air, and dissolves without limit in water and alcohol, but is sparingly soluble in ether ; 1 (sp. gr. 1-23) in 500. On exposure glycerin absorbs water from the air, as much as 50 per cent., and on account of its never drying, glycerin is useful in many cases when it is desired to keep any substance moist and supple. Water mixed with an equal weight of glycerin is sometimes used in gas-meters, being much 1 The systematic term glycerol may conveniently be employed whcn speaking of the chemical unit, and glycerin when referring to the substance as found in commerce. 590 POLYHYDRIC ALCOHOLS less easily frozen than water, and less liable to dry up. Glycerin is used in pharmacy, but its chief application is in making nitro-glycerin (q.v.). Glycerol possesses extensive solvent powers, like alcohol, dissolving most substances which are soluble in water, and some others, such as metallic oxides, which are insoluble in water ; glyceroxides are formed (infra). A characteristic property of glycerol is that of yielding an exceedingly pungent and irritating substance, known as acrolein, or acrylic aldehyde, C,H,-CHO, when sharply heated, or subjected to the action of dehydrating agents, CH,OH-CHOH:CH,OH = CH, : CH-CHO + 2H,0. The best test for identifying glycerol is to mix it with powdered KHSO, and heat it strongly, when the intolerable odour of acrolein is perceived. It is this substance which causes the offensive smell of smouldering candles made of tallow and other glycerides. By treatment with a mixture of nitric and sulphuric acids glycerin is converted into nitroglycerin or glyceryl trinitrate, C,H;(NO3)3, a powerfully explosive compound which will be described in the section on esters. With H,;PO,, glyceryl phosphoric acid is formed (p. 671). As glycerol contains two primary alcohol groups, CH,OH, which are known to be oxidisable first to aldehyde groups, CHO, and then to acid groups, COOH, and also a secondary alcohol group, which is oxidisable to a ketone group, CO, no fewer than 11 oxidation-products of glycerol are theoretically possible. Only six, how- ever, are at present known, namely: glyceric aldehyde, CHO-CHOH-CH,OH ; dihydroxyacetene, CH,OH:CO-CH,OH; — glyceric acid, COOH-CHOH-CH,OH ; tartronic acid, COOH-CHOH-COOH ; mesoxalic acid, COOH-C(OH),-COOH ; and hydroxypyroracemic acid, CH,OH-CO-COOH. Except the last named, all these are obtainable by the direct oxidation of glycerol. When H,O, (in presence of a small quantity of a ferrous salt) is the oxidant, a mixture of glyceric aldehyde and dihydroxyacetone is formed which was originally supposed to be a single compound, and was called “ glycerose.” Dilute nitric acid produces glyceric and tartronic acids, while oxidation with bismuth nitrate and nitre forms mesoxalic acid. More energetic oxidising-agents yield glycollic acid, CH,OH-COOH ; oxalic acid, COOH-COOH ; and glyoxylic acid, CHO-COOH. When reduced with hydriodic acid glycerol yields allyl iodide, CH,: CH-CH,I ; isopropyl iodide, CH,-CHI-CH, ; and propylene, CH,-CH : CH. Two compounds corresponding with the ethoxides may be obtained by the action of sodium ethoxide on glycerol in alcohol, sodium glyceroxide, CsH;(OH),ONa, and disodium glyceroxide, CsH;0H(ONa)>. Calcium glyceroxide, CaC3H,O3, is formed by heating to 100° CaO and anhydrous glycerol. By treating a-chlorhydrin (¢.v.) with BaO, HCl is abstracted and glycide alcohol is obtained : OF ya —HCl = of is. ; this is a colourless liquid, boiling HOC-CH,OH \\CH,OH’ e with decomposition at 162°. It combines with water to form glycerol. Tetrahydric and Higher Polyhydric Alcohols.—Alcohols containing 4, 5, 6, 7, 8, and 9 hydroxyl groups are known. The number of hydroxyl groups present in an alcohol is ascertained by heating the alcohol with acetic anhydride, (CH,CO),0, and sodium acetate, when as many acetic acid radicles (acetyl, CH,CO) enter into the composition of the alcohol, as there are hydroxyl groups in the alcohol ; for example, the compound called erythrite is known to be a tetrahydric alcohol, because it forms an acetate containing four acetyl groups ; C,H,(OH), + 4(CH;,CO),0 = C,H,(OCH,CO), + 4CH,COOH. The lowest member of each series of polyhydric alcohols must have at least as many carbon atoms as it has OH groups, otherwise one carbon atom would have to hold two hydroxyl groups, and the compound would break MANNITE 591 up (p. 587). The derivatives and oxidation-products of these alcohols are similar in constitution to those of glycol and glycerol. Most of the higher alcohols that are known are obtained from natural sources; many of them are sweet, and some were for long classed with the sugars, with which, indeed, they are closely connected. Erythrite, erythrol, or phycite, CyH (OH),, or CH,OH-[CHOH],-CH,OH, is obtained from certain lichens, such as the Roccella tinctoria, or Orchella weed, by boiling with milk of lime, filtering, precipitating the excess of lime by CO,, evaporating the filtrate to a small bulk, and treating with alcohol, when erythrite crystallises in prisms, which fuse at 126° and sublime at 300°, though not quite undecomposed. It is easily soluble in water, and has a sweet taste; sparingly soluble in cold alcohol, and insoluble in ether. In several of its reactions erythrite resembles glycerin. When it is dissolved in nitric acid, and sulphuric acid added, it yields a crystalline precipitate of nitro- erythrite or erythryl tetranitrate, CyHg(NO3)4, which is explosive like nitroglycerin. If, in the treatment of the lichen, cold milk of lime be used, the filtrate, when saturated with COg, gives a mixed precipitate of calcium carbonate and erythrin, which may be extracted by alcohol, and crystallised. Erythrin is erythrite diorsel- linate, CygH,g(OH)2(OCgH703)o, and belongs to the class of ethereal salts. It appears to exist as such in the lichen, and is decomposed into erythrite and calcium orsellinate when boiled with calcium hydroxide. Erythrite exists ready formed in certain alge, notably in Protococcus vulgaris. This natural erythrite is optically inactive. Both it and another inactive form (believed to be internally compensated—see p. 638) may be synthesised from divinyl CH, : CH:CH : CH, (p. 556) by adding Br to form two dibromides, which are stereoisomerides and can be oxidised by permanganate to corresponding bromhydrins CH,Br:[CHOH],CH,Br ; these yield the natural erythrite and its isomeride (m.-p. 72°) when treated with KOH and water. A dextro- and a levo-erythritol have also been obtained. Arabite, or arabitol, CH,OH:[(CHOH];-CH,OH, is obtained by reducing arabinose (q.v.) with nascent hydrogen. It melts at 102°. Mannite, or mannitol, CH,OH-[CHOH],-CH,OH, a hexahydric alcohol, is a sweet substance contained in manna, from which it may be extracted by boiling with alcohol, when it crystallises, on cooling, in fine needles, fusing at 166°. It is rather sparingly soluble in cold water and alcohol, but easily on heating, and is insoluble in ether. When oxidised in presence of platinum black, it yields the sugar mannose, C,H,,0, (q.v.), and when this is further oxidised it becomes mannonic acid, CH,OH:[CHOH],-CO,H. The natural mannite is dextro-rotatory ; a levo- and an inactive form are also known, as will be explained later. By treatment with nitric acid, mannite is converted into an explosive crystalline body, which is nitromannite, or mannyl hexanitrate, CgH,(NO3)., re-converted into mannitol by (NH,).8. When treated with HI, mannite becomes secondary hexyl iodide, CH,OH-CHOH-CHOH-CHOH-CHOH:-CH,OH + 11HI = CH,-CH,-CH,:CH,-CHI-CH, + 6HOH + 5]. Mannite is found among the products of the viscous fermentation of saccharine liquors, when they are said to become ropy ; beet-root juice is especially liable to this change. : Mannite is an important substance in vegetable chemistry, since it occurs not only in manna, the dried exudation of the Ornus, or manna ash, growing in the South of Europe, but also in the sap of the common ash (Fraxinus excelsior), of the larch, apple, cherry, and lime; in the leaves of the syringa and privet; in the bulbs of Cyclamen europeum (sow-bread), in the bark of the wild cinnamon, in some lichens, seaweeds, sugar-cane, mushrooms, celery, asparagus, olives, and onions. The seaweed Laminaria saccharina, or sugar-wrack, contains 12 per cent. of mannite, which is some- times found as an efflorescence on the surface of the weed. It has also been found 592 ALDEHYDES in the root of the monkshood (Aconitum napellus). The Agaricus integer, a common fungus, contains when dry about 20 per cent. of mannite. : Mannitane, CeHs(OH),0, is prepared by heating mannite to 200°; CgH,(OH), = CsH,(OH),0 + H,O. It is a viscous substance very similar to glycerol, and forming compounds when heated with the fatty acids which closely resemble the glycerides, and are saponified by alkalies in the same way. Dulcite, or dulcitol, is isomeric with mannite, and much resemblesit. It is extracted from Madagascar manna by boiling water. It is nearly twice as soluble in water as mannite is, but much less soluble in alcohol. It melts at 188°. On oxidation it yields galactose. Sorbitol, CeHg(OH)g, another isomeride of mannite, is found in the berries of the mountain ash (Sorbus aucuparia). It is more fusible (110°) than the others. It is the hexahydric alcohol corresponding with glucose and gulose. II. ALDEHYDES These compounds are the first products of the oxidation of all alcohols H, containing the primary alcoholic group HO , Which becomes O HL et ‘CY + HOH. They differ from the parent alcohols by two atoms of O hydrogen; thus, ethyl alcohol, CH,-CH,OH, yields acetic aldehyde, CH,-CHO, and so on, there being one or more aldehydes corresponding with each of the alcohols already described. They readily pass by oxidation O into the corresponding acids, the group of becoming of Fi H OH and are named after the acids into which they are converted. Since the oxidation of primary alcohols to aldehydes consists merely in the removal of H, (whence the name—al [cohol] dehyd[rogenatum]), and since the aldehyde in all its reactions appears still to contain the hydrocarbon radicle which was contained in the alcohol, the above view of the constitution of these compounds may be presumed to be correct. It is supported by the fact that when an aldehyde reacts with PCl; the oxygen atom is exchanged for two chlorine atoms, CH,-CHO + PCl, = CH,-CHCl, + POCI,, showing that the aldehyde cannot contain the O in the form of OH. For when a compound containing OH reacts with PCl,, the OH is exchanged for Cl and HCl is a product of the reaction, eg. CH,-CH,OH + PCI, = CH,-CH,Cl + POC], + HCl. Position isomerism can occur only in the radicle of the aldehyde; thus, in the general formula, R-CHO, R may occur in isomeric forms, but there are no secondary and tertiary aldehydes in the sense that there are secondary and tertiary alcohols. As already stated (p. 587), glycols of the type R-CH(OH), do not exist, although many compounds are known which might be expected to yield them under appropriate treatment; for instance, by analogy with the reaction between ethyl chloride and moist silver oxide, that between this oxide and ethylidene chloride, CH,-CHCl,, might be expected to yield ethylidene glycol CH,-CH(OH),, but as a fact yields aldehyde and water, CH,-CH(OH),, becoming CH,-;CHO + HOH. Thus the aldehydes may be regarded as the anhydrides of these unknown glycols, and it may be supposed that the latter are the true products of oxidation of the primary alcohols, being formed by the substitution of OH for a second H atom in the parent hydrocarbon ; the glycol thus formed, however, at once passes into its anhydride, the aldehyde. This view of the process of oxidation is supported by the oxidation of the aldehyde to the acid, consisting of the FORMALDEHYDE 593 substitution of OH for H. The following formule make these remarks clear, but it must be remembered that the alcohol is not formed by oxidation of the hydrocarbon : H OH O O R-CZH ROZH Roe Ro Na \a OH Hydrocarbon. Primary alcohol. Unknown glycol. Aldehyde, Acid. R H R OH R nyt R R’ HR” SH RB” OH RR” Hydrocarbon. Secondary alcohol. Unknown glycol. Icetone. The aldehydes are unsaturated in the sense that the oxygen atom is doubly linked to carbon, and they show a tendency to combine as a whole with other compounds, the aldehyde group -CH = O becoming O— cH . This tendency leads to the formation of derivatives of the aforesaid unknown glycols and to a number of nucleal condensations (p. 551), which render the aldehydes useful in building up new carbon nuclei. The chief reactions of this kind will be noticed in the description of acetic aldehyde, the behaviour of which is identical with that of the majority of aldehydes. The readiness with which the c!dehydes undergo oxidation to the corresponding acids makes them powerful reducing agents. Aldehydes from the Paraffin Alcohols.—The oxidation of the primary alcohols is not the only general reaction for preparing the aldehydes of the series. They may be obtained by distilling a dry mixture of calcium formate and the calcium salt of the acid corresponding with the aldehyde required. BOO CoH COD... C,H;COH po + fon = + 2CaC0O, HCOO C,H,COO C,H,COH Calcium formate. Calcium propionate. Propionic aldehyde. Formic aldehyde, formaldehyde, or methyl aldehyde, H:CHO, is a gas and boils at — 21°. It is formed when a mixture of methyl alcohol vapour and air is passed over a red-hot platinum wire, CH,OH + 0 = H-CHO + HOH. It is now made on a large scale by a secret process and sold in aqueous solution containing 40 per cent. under the name of formalin for use as an antiseptic and in the manufacture of dye-stuffs ; the solution has a suffocating odour and reduces ammoniacal silver nitrate. Formaldehyde is formed when a mixture of CO and H, is treated in an ozoniser (Fig. 105) and in small quantity when calcium formate is destructively distilled. By cautiously oxidising methyl alcohol with MnO, and H,SO, some of the CH,0H is oxidised to H-CHO and combines with more CH;0H to form methylal or formal (methylene dimethyl ether), CH,(OCHs)o, a liquid (b.-p. 42°) used as a soporific and as a solvent ; when this is distilled with a dilute acid it yields formaldehyde and methyl alcohol. Paraformaldehyde is a solid polymeride (CH,O)a, formed when an aqueous solution of formaldehyde is allowed to evaporate ; when heated it is converted into another polymeride, trioxymethylene or metaformaldehyde (CH,O); which melts at 171° and then becomes the gas CH,O0. By prolonged contact with lime-water formaldehyde is poly- merised to a mixture of sugars (formose), a change which may occur, through some agency, in the synthesis of sugar by plants, since formaldehyde has been found in green plants. Even.aqueous solutions contain some polymerides. Fo.maldehyde is used in synthetic chemistry for introducing the methylene group (CH) into compounds, its oxygen atom readily combining with H, and removing 38 504 ALDEHYDE—PREPARATION them as water, leaving the : CH, group to take their place, thus: R-NH, + 0: CH, = R-N: CH, + H,0. Acetic aldehyde, CH,-CHO, is obtained by distilling alcohol with potassium bichromate and sulphuric acid. This process requires much care, on account of the violence of the action and the volatility of the aldehyde. : Three parts of potassium bichromate, in crystals free from powder, are placed in a flask or retort surrounded by ice (or by a mixture of sodium sulphate crystals with half their weight of HCl), and a mixture of 2 parts of ordinary alcohol, 4 parts sulphuric acid, and 12 parts of water, also previously cooled in ice, is added. The flask or retort is then con- nected with a condenser contain- ing iced water and the refrige- rating mixture removed, when the aldehyde will generally be distilled over by the heat at- tending the reaction. The impure aldehyde thus obtained is re-distilled on the water-bath in the apparatus shown in Fig. 299. The aldehyde, freed from alcohol and aqueous vapour which condense in the inverted mae condenser, passes over and is ee dissolved in dry ether contained in the cylinders cooled by ice. The ethereal solution of aldehyde is saturated with dry ammonia, whereupon the whole of the aldehyde is separated in the form of colour- less crystals of aldehyde-ammonia, which is sparingly soluble in ether ; this is drained upon a filter, and distilled with diluted sulphuric acid in a flask or retort, heated by a water-bath, and connected with a condenser filled with ice water. The aldehyde may be freed from water by standing over fused calcium chloride, and distillation. The preparation of aldehyde illustrates the use of K,Cr,0, and H,SO, as an oxidising-agent upon organic bodies. Neglecting certain secondary reactions, the production of aldehyde may be represented by the equation : 3(CH,-CH,OH) + K,0-2Cr0, + 4(H,0-SO,) = 3(CH,-CHO) + 7H,O + K,0-SO, + Cr,05-3803. On a large scale, aldehyde is obtained as a by-product in the manu- facture of alcohol, when it comes over with the first portion of the distillate. Commercial alcohol generally contains a little aldehyde. Aldehyde may also be obtained by distilling a mixture of an acetate and. a formate (see above). Properties of aldehyde.—Sp. gr. 0-80 at 0°; boiling-point 20°-8. Alde- hyde has a peculiar acrid odour, which affects the eyes. It mixes in all proportions with water, alcohol, and ether. It has a great disposition to combine with oxygen to form acetic acid: CH,-CHO + O = CH,-COOH. Hence aldehyde acts as a reducing-agent, and one of the tests for it is the reduction of silver from its salts. If a few crystals of aldehyde-ammonia be dissolved in water, a little silver nitrate added, and a gentle heat applied, the silver will be deposited on the sides of the vessel, giving them the reflecting power of a mirror. A general test for aldehydes is their power of restoring the red colour to a solution of a salt of rosaniline which has been bleached by sulphurous acid. (Schiff’s reagent.) ALDEHYDE—REACTIONS 595 Another characteristic property of aldehydes is that of forming crystalline compounds with sodium bisulphite. If aldehyde be mixed with a saturated solution of NaHSO,, it forms a crystalline com- pound, which is the sodium salt of ethylidene glycol sulphonic acid, CH,;-CH(OH)(SO,0Na), combined with H,0; from this the aldehyde may be obtained by distillation with either acid or alkali. _ When mixed with potash, and gradually heated to boiling, most of the paraffin aldehydes yield brown-yellow substances of peculiar odour, known as aldehyde resins ; their chemical constitution is uncertain. Nascent hydrogen (water and sodium amalgam) converts aldehyde into alcohol ; CH;-CHO + 2H = CH,-CH,-OH (alcohol). Aldehyde combines with ammonia forming a compound, aldehyde- ammonia, which is probably an amine of the hypothetical ethylidene glycol, CH,-CH(OH)(NH,); with HCN to form ethylidene cyanohydrin or lactonitrile, CH,-CH(OH)(CN), which on hydrolysis (using HCl) yields, and so synthesises, lactic acid (as NH, salt), CH,;-CH(OH)(CN) + 2H,O = CH,CH(OH)-COONH,. This illustrates the application of aldehydes to synthetic purposes, forming new carbon nuclei. With alcohol it forms diethyl ethylidene ether or acetal, CH,-CH(OC,H,),, a liquid which boils at 104° and is found in old wine and in the last runnings of spirit stills. When there is no other compound with which aldehyde can combine, it tends to combine with itself or polymerise. For example, perfectly pure acetic aldehyde can be kept unchanged, but in the presence of a very little dilute acid or of zinc chloride it is converted into aldol, which is a (secondary) alcohol-aldehyde, CH3;-CHOH:CH,-CHO (hydrozy-butyric aldehyde) ; this resembles aldehyde in appearance and general reactions, but its sp. gr. is 1-120 and it does not distil unchanged ; it becomes viscous on standing. A condensation of two or more molecules in this way occurs in many other compounds, and is always termed, by analogy, an aldol condensation (cf. p. 596). By adding a drop of strong H,SO, to aldehyde, much heat is evolved and the liquid becomes specifically heavier (sp. gr. 0-99 at 20°): this liquid is paraldehyde, CeHy203, or 7/9 CHC). es fe O-CH(CH;3) It boils at 124° and melts at 10°; it is less soluble in hot water than in cold, and when distilled with dilute H,SO, it becomes aldehyde again. Metaldehyde is a stereoiso- meride of paraldehyde, produced in the same way, but at temperatures below 0°. It forms white crystals, insoluble in water, but soluble in ether and in alcohol ; it sublimes when heated to 112°, without melting, and when heated in a sealed tube at 116° it becomes aldehyde ‘again ; the crystals are said to become brittle and opaque after a time, owing to a further polymerisation to CgH,,0,° tetraldehyde. Paraldehyde and metaldehyde differ from aldehyde in not reducing silver salts and in not uniting with alkali bisulphites, ammonia, hydroxylamine, &c.; hence, they do not exhibit aldehydic properties, and, indeed, they are heterocyclic. Their stereoisomerism is supposed to depend on such an arrangement of the atoms in space (see Stereochemistry, p. 633) that certain atoms or radicles occur on one side of the plane of the ring system in the one isomer and on the other side of the plane in the other isomer, as shown in the figures, where the plane of the ring is supposed to be perpendicular to the plane of the paper. H H | H Gods H H 0O——C——O CH, | ae a: cK a De Cite DY CH, ~ ie CH, ee ge H 0 0 a=—, cis- or maleinoid- form, B—, trans- or fumaroid- forn, 596 ACROLEIN Various forms of such cis-trans isomerism are fairly common ; see also pp. 638, 641, 642, The thioaldehydes also exhibit it. Other characteristic reactions of the aldehydes are the formation of aldovimes by reaction with hydroxylamine (p. 206) : and the formation of hydrazones with phenylhydrazine ; CH,-CHO + H,: N-NHC.H; = HOH + CH,-CH : N-NHG,H, (acetaldehyde hydrazone). Stereoisomerism is exhibited by certain aldoximes (p. 642). Aldehyde, in the form of paraldehyde, and some of its derivatives, such as acetal (2.8.) are used as soporifics (cf. chloral). Aldehyde also finds application in the manu- facture of dyes. The chief known homologues of acetic aldehyde are shown in the following Table: + Chemical Name. Source. Formula. Propionic aldehyde Oxidation of propyl alcohol . : CoH;-CHO (49°) Butyric 7 33 butyl 33 , F C3H,-CHO (74°) Valeric i e amyl 7 . C,H -CHO (102°) Gopoic (Nom asmanta } Caty-CHO 28" (Enanthic a Distillation of castor oil CgHy3-CHO (155°) Caprylic 5 A 5 C,H,;;CHO (160°) Rutic 35 Oilofrue . CyH9'CHO eins Lauric 3 53 Cy,He3-CHO [445°] Myristic se : : : Cy3He7-CHO [52-5°] Palmitic A ‘ : CisH3,-CHO [58-5°] Stearic 36 : ‘ : C,7H35;-CHO [63-5°] Acetic, propionic, and butyric aldehydes occur among the products of the oxidising action of a mixture of manganese dioxide with sulphuric acid upon albumin, fibrin, and casein. Thioaldehydes, in which sulphur takes the place of oxygen, are known only in polymeric form, corresponding with the polymerised aldehydes. Trithioformaldehyde (CH,S)3 melts at 216°, trithioacetaldehyde (CH,CHS),, occurs in an a and (3 form melting at 101° and 125° respectively. Mercaptal is the thio-derivative, corresponding with acetal (p. 595). By oxidation the thio-aldehydes yield trisulphones. Aldehydes from the Olefine Alcohols.—Acrolein, or acrylic - aldehyde, CH, : CH-CHO, the aldehyde of allyl alcohol, is prepared by distilling glycerin with twice its weight of KHSO,, which abstracts the elements of two molecules of water ; C3H;(OH), = C,H,;-CHO + 2H,O. The crude acrolein is shaken with PbO, to remove SO., and rectified over CaCl, to remove the water. Acrolein is a liquid distinguished by a very powerful irritating odour. It has sp. gr. 0-84, and boils at 52°. It dissolves sparingly in water, but easily in alcohol and ether. Unlike most aldehydes, it does not combine with NaHSO, (contrast its phenyl derivative, p. 598); but°it forms a resinous body with alkali, and reduces ammoniacal AgNOs, which converts it into acrylic acid, C,H,-CO,H. Sodium amalgam and water (nascent hydrogen) convert it into allyl alcohol, C.H,-CH,OH. When kept, acrolein becomes a white solid, disacryl, probably a polymeride. HCl gas passed into acrolein converts it into a crystalline body, 3-chloropropylaldehyde, CH,Cl-CH,CHO, which, when distilled with potash, yields metacrolein, CgHy,O3 (m.-p. 45°), corresponding with paraldehyde. Crotonic aldehyde, CH,-CH : CH-CHO, is prepared by heating acetic aldehyde to 100° for two days in contact with ZnCl, and a little water. The ZnCl, acts as a dehydrating agent ; 2(CH,-CHO) = H,O + C,H;-CHO (aldehyde condensation). The unchanged aldehyde is distilled off, some water added, and the distillation continued, when water and crotonic aldehyde distil over. It has an irritating odour like acrolein, boils at 104°, and is sparingly soluble in water. When oxidised by air or silver oxide, it yields crotonic acid, C;H;-CO,H. It occurs in some kinds of fusel oil. * The boiling-points are in round brackets (...), the melting-points in square brackets [...], Centigrade scale. According to the new system the aldebydes are named like the alcohols, the termination -al being substituted for -ol (see footnote on p. 581). BITTER-ALMOND OIL 597 Aldehydes from Dihydric and Polyhydric Alcohols—These may be di- or poly-aldehydes and aldehyde-alcohols ; the latter are of much import- ance, as they include several sugars, like glucose and mannose. These compounds are not considered under this heading, however, for their near relationship to compounds in other classes will be best set forth by treating them in a separate section. The student is therefore referred to the chapter on carbohydrates for a description of the sugars. Glyoxal, or oxalic aldehyde, CHO-CHO, is prepared by slowly oxidising acetic aldehyde with dilute nitric acid. It occurs among the products of the regulated action of nitric acid on alcohol and glycol. (See p. 616.) It is a deliquescent solid, soluble, in water, alcohol, and ether, forming a crystalline compound with two mols. NaHSO,, and reducing silver nitrate, becoming oxidised to oxalic acid, CO.H-CO.H, and glyoxylic acid, CHO-CO2H. Alkalies oxidise one CHO group and reduce the other, forming glycollic acid, CH,OH-COOH (cf. benzaldehyde, p. 598). With ammonia, it yields glycosine ; 3C.H,0, + 4NH, = 6H,O + N,(C,H,)3. Glyoxal combines with 2HCN to form the nitrile of tartaric acid, CH(OH)(CN)-CH(OH)(CN). Glyceric aldehyde or glycerose, CH,0H-CHOH-CHO, is an aldehyde-alcohol obtained by the careful oxidation of glycerol (p. 590). By condensation it is converted into acrose, one of the sugars (p. 764). Aldehydes from the Aromatic Alcohols.—Benzaldehyde, benzoic aldehyde, or bitter-almond oil, C,H;-CHO, was originally made by distilling the moistened bitter-almond cake from which the fixed oil had been extracted by pressure. The cake was placed in a perforated vessel and subjected to the action of steam, which carried over the oil and deposited it as a heavy layer on standing. The bitter-almond oil does not exist ready formed in the almond, but is a product of the decomposition of the bitter substance, amygdalin, CeoH.,NO,,, of which the bitter almond contains about 5 per cent. On digesting crushed bitter almonds with water at 50° for several hours, the amygdalin, which is a glucoside, is hydrolysed under the influence of a peculiar albuminoid ferment also present in the almond and known as emulsin,! into glucose, bitter almond-oil, and hydrocyanic acid, Cy 5H,,NO,, + 2H,O = 2C,H,.0, + C;,H,O + HCN. The presence of hydrocyanic acid renders the crude oil of bitter almonds very poisonous. It may be purified either by re-distilling with lime and ferrous chloride, when the HCN is converted into a ferrocyanide ; or by shaking it with an équal volume of a strong solution of NaHSO;, which combines with the benzoic aldehyde to form a crystalline compound, from which the pure oil may be obtained by distillation with sodium carbonate. Benzaldehyde is now made artificially from toluene. When chlorine is passed into boiling toluene, preferably in sunlight, benzal chloride, C,H;-CHCL, is produced. By heating this with lime under pressure, it is converted into bitter-almond oil— C,H,-CHCl, + Ca(OH). = CaClp + H,O + CyH,-CHO. Or the chlorination of the toluene is stopped when benzyl chloride, C,H,-CH,Cl, has been formed, and this is then heated with lead nitrate— 20,H;-CH»Cl + Pb(NOs)> = 2C.H;-CHO + PbCl, + 2HNO,. Benzoic aldehyde is a colourless liquid, of characteristic odour, boiling at 179°, and of sp. gr. 1:05. It is very sparingly soluble in water, but dissolves in alcohol, and is precipitated on addition of water. It is often sold in alcoholic solution as essence of almonds. The oxidising action of air gradually converts benzoic aldehyde into crystals of benzoic acid ; 1 The terms zymase, enzyme, and hydrolyst have been applied to such unorganised ferments. If very hot water be used, the emulsin becomes inactive. 598 BENZALDEHYDE C,H;CHO + 0 =C,H;-CO,H. The presence of hydrocyanic acid retards this conversion. The aromatic aldehydes show reactions very similar to those of the fatty aldehydes. They are, however, less powerful reducing-agents, and instead of resinifying with alkalies, they are converted into the corre- sponding alcohol and acid, one part being reduced and the other oxidised : 2C,H;-CHO + KOH = C,H,;-CH,OH + C,H;-COOK (cf. glyoxal, p. 597). Moreover, with NH, they do not combine directly, but are converted into compounds like hydrobenzamide, a crystalline substance, m.-p. 110°; 3(C,H,-CHO) + 2NH, = (C,H;:CH),-N, + 3H,0. They show a remarkable tendency to condense with other compounds under influence of dehydrating agents, the aldehydic oxygen combining with two H atoms from the other compound. Thus by action of HCl gas on a mixture of benzaldehyde and acetic aldehyde, cinnamic aldehyde is formed; C,H,CHO + CH,-CHO = C,H,-CH : CH-CHO + H,0. Benzaldehyde dissolves in a strong solution of NaSO;, and if dilute H,SO, be added, drop by drop, to the solution, voluminous crystals of CgH;-CHO-NaHSO, are deposited ; these dissolve on heating but are deposited again on cooling. By reduction with Na-amalgam, benzaldehyde yields benzyl alcohol and hydrobenzoin (p. 588). Benzaldoxime exists in two forms ; see p. 642. Cuminic, or cwmic aldehyde, or cwminol, is 1: 4-isopropylbenzaldehyde, CsH4C3;H,-CHO, and occurs in the aromatic oils of cumin, caraway, and water-hemlock, all umbelli- ferous plants ; it is extracted from the oil by shaking with solution of NaHSO3;, which forms a crystalline compound with it. It is liquid, fragrant, and boils at 235°. Cinnamic aldehyde, CsH;-CH : CH-CHO, occurs in the essential oils of cinnamon and cassia, and is very similar in its chemical properties to benzaldehyde. When oxidised, it yields cinnamic acid, CgH,-CO.H. It may be obtained from benzoic and acetic aldehydes, as above mentioned. Although it is phenyl-acrolein it contrasts with acrolein (p. 596) in forming two compounds with KHSO; ; C,H,-CH : CH-CH(OH)SO,K and C,H;-CHS0,K-CH,: CH(OH)SO,K. The hydroxy-aromatic aldehydes, the type of which is salicylic aldehyde, C,H,(OH)-CHO (hydroxybenzaldehyde), have an OH attached directly to the benzene ring, and are therefore phenol aldehydes corresponding with the phenol alcohols (p. 584), from which they are formed by oxidation. The hydroxy-aromatic aldehydes are also produced by a nucleal condensa- tion between the phenols and formic acid, the latter being applied in the nascent state by heating the phenol with chloroform and aqueous alkali (Reimer’s reaction) : (a) CHCl, + 4KOH = H-COOK + 3KCl + 2H,0 Potassium formate. (b) C.H;-OH + H-COOK = C,H;(OK)-CHO + H,0. Potassium salicylaldehyde. The potassium compound is steam-distilled with dilute acid -to obtain the aldehyde. The ortho-derivative is very volatile and so is separated from para-hydroxybenzaldehyde, which is formed simultaneously. In this reaction the alkali is required to absorb the HCl which is formed when water alone is used, and which must be removed to prevent back action, the change being reversible. Salicyl aldehyde, ‘ortho-hydroxybenzaldehyde, exists in oil of spirea (meadow- sweet), and is made by oxidising saligenin (p. 584), or from phenol as described above. Its sp. gr. is 1-17, and it boils at 196°. It dissolves in alcohol, but sparingly in water. It resembles benzaldehyde in most reactions, but exhibits some characteristic of its phenol character, such as the ferric chloride coloration and the exchange of H for K by treatment with KOH forming CsH,(OK)-CHO. Like other orthohydroxyaldehydes it stains the skin yellow. FURFURAL 599 Anisic aldehyde, CgH,(OCH3)-CHO, is para-methoxybenzaldehyde, the methyl deri- vative of para-salicylic aldehyde ; it is prepared by heating the essential oils of anise and fennel (both umbelliferous plants) with dilute HNO, being formed by the oxidation of anethol (¢.v.) which these oils contain. It is a fragrant liquid, boiling at 248° ; sp. gr. 1-123. . Dihydroxybenzaldehydes are also known. The 1: 3: 4-derivative, protocatechuic aldehyde, CgH3(OH).-CHO [CHO: (OH), = 1:3:4] is obtained from pyrocatechol, CsH4(OH)s, and chloroform by Reimer’s reaction (v.s.); it melts at 153°. When methylpyrocatechol, CgH4(OH)(OCHS), is similarly treated it yields the methyl derivative of protacatechuic aldehyde, CgH;(OH)(OCH;):CHO ; this is vanillin, an aromatic substance, much used for flavouring, extracted from the pods of Vanilla planifolia, a Mexican orchidaceous plant, by boiling them with alcohol. It forms needles, melts at 80°, and sublimes. It is sparingly soluble in water. Vanillin is now made arti- ficially by oxidising coniferin, CygsH:20g, (p. 780), by chromic acid ; also from eugenol (p. 678). Coniferin is a crystalline glucoside, extracted from pinewood ; when oxidised it yields glycovanillin, the glucoside of vanillin, CsH;(OCH3)(O-C,H,,0;)-CHO, which yields glucose and vanillin on hydrolysis. Piperonal or heliotropine is methyleneprotocatechuic aldehyde, Cg.H3(O2CH2)-CHO, made by oxidising piperic acid (¢.v.). It melts at 263° and is valued for its odour of heliotrope. : Pyromucic aldehyde, furfural, or furfurol, C,H,0-CHO, is the aldehyde of / CHO) : CH ; furfurane (q.v.), ON | . It is prepared by distilling the bran of wheat, CH CH freed from starch and gluten by steeping in a cold weak solution of potash, with half its weight of sulphuric acid, previously diluted with an equal bulk of water, a current of steam being forced through the mixture ; the furfural distils over with the water, from which it may be separated by adding common salt. A hundred parts of bran yield about three of furfural. It is a product of the hydrolysis of certain carbo- hydrates, particularly such as are pentoses. It is also present in fusel oil from crude spirits. Furfural is a colourless liquid smelling of bitter almonds, of sp. gr. 1-17 and boiling-point 162°. It dissolves in twelve times its weight of water, and is freely soluble in alcohol. Strong sulphuric acid dissolves it to a purple liquid, from which water precipitates it unchanged. It becomes brown when exposed to the air. Furfural combines with NaHSO,, reduces silver, and yields an intense red colour with aniline acetate. With ammonia it behaves as an aromatic aldehyde, forming furfuramide (C4H,0-CH);No, in which three molecules of furfural have exchanged 30” for 2N’”. It is capable of all the condensation reactions of benzaldehyde. By oxidation, furfural is converted into pyromucic acid, CyH,;0-CO,H. Alcoholic solution of potash converts it into potassium pyromucate and furfuryl alcohol, C,H,0-CH,OH. Fucosol is isomeric with furfural, and is prepared, in a similar way, from certain varieties of fucus (seaweed). III. ACIDS The acids are. the second oxidation-products of the primary alcohols. H, O The group er in the alcohol is converted into OF , carboxyl, ‘ou Now in the acid, so that a general formula for an acid is R-COOH, where R is a hydrocarbon residue or radicle. This view of the constitution of acids is supported mainly by the three following facts : (1) Acids can be synthe- sised from sodium-substituted hydrocarbons and CO,, showing that the acid produced (or its sodium salt) probably contains the hydrocarhon radicle and both the oxygen atoms attached to the same carbon atom, eg. CH,Na + CO, = CH,;-COONa. (2) The monochlorohydrocarbons, e.g. CH,°CH,Cl, can be converted by double decomposition with KCN into cyanides, e.g. CH,-CH,-C: N, and when these are boiled with water the N 600 SYNTHESIS OF FATTY ACIDS is removed as NH, and the next higher acid remains; CH,-CH,-C:N + 2HOH = CH,:CH,:COOH + NH,. (3) The acids contain a hydroxyl group, for, by interaction with PCl,, they exchange O and H for Cl, hydrogen chloride being evolved (p. 592) : CH,-COOH + PCI, = CH,-COCl + POC), + HCl. It will be found that the formula H-COOH is the only formula which can be written for formic acid, the prototype of all the other acids. Two methods generally applicable for producing the acids are—(1) oxida- tion of the corresponding alcohol, R-CH,OH + O, = R-COOH + HOH, and (2) hydrolysis (p. 224) of the cyanogen derivatives of the corresponding hydrocarbons, R:CN + 2HOH = R-COOH + NHs3. Isomerism among the acids is confined to the hydrocarbon radicles in them ; thus there will be two acids of the formula C,H,-COOH, since there are two propyl! radicles. The basicity of an acid (p. 90) is found to be limited by the number of COOH groups which it contains, thus showing that it is the H in this group which is exchanged for metals to form salts. When an acid contains two CO,H groups, it is a dibasic acid, or if there are three CO,H groups, it is a tribasic acid, and so on. Acids from Monohydric Paraffin Alcohols (Acetic or Fatty Series).—The acids obtained by decomposing soap with a mineral acid were termed originally fatty acids because the soap had been made by saponifying fat. Later, the more important of them were shown to belong to the same series of acids as acetic acid, hence the term fatty acids was applied to the series. The fatty acids correspond with the general formula C,H,, + COOH and are produced, by two general methods given above, from the alcohols and cyanides of the paraffin series. An important method of obtaining fatty acids consists in treating alky] derivatives of ethyl acetoacetate (g.v.) with an alkali. This compound, CH,CO-CH,-COOC,H,. contains a C'H, group, attached to two CO groups; where this is the case Na can be substituted for the H in the CH, and by treating the sodium derivative with an alky] iodide, compounds of the type CH,;CO-CHR-COOC.H,; and CH,CO-CR.:COOC,H; are obtained. By treatment with potash these yield potassium acetate, the potassium salt of a new fatty acid and ethyl alcohol : CH,CO-CHR-COOC,H, + 2KOH = CH,COOK + CH,RCOOK + C,;H,OH CH,CO-CR,-COOC,H; + 2KOH = CH,COOK + CHR,COOK + C,H,OH In the latter case the acid contains a secondary radicle. The reaction is sometimes complicated by the formation of a ketone. The ethyl] salt of the dibasic acid malonic acid, CH,(COOH)s, also contains a CH, group attached to two CO groups, so that when it is appropriately treated, first Na or Na, and then one or two alkyl groups may be substituted for the H in the CH, group. In this way compounds of the type CHR(COOC,H;). and CR.(COOC2H;). and from these the corresponding acids CHR(COOH), and CR.(COOH), are obtained. When heated, these acids lose COz, yielding ‘acids of the acetic series. The preparation of ethyl malonate, CH,(COOC,Hs5)p, is described later ; the reactions by which it may be converted into butyric acid, for example, are as follows: CH,(COOC,H;), + CsH;,ONa = CHNa(COOC,H;), + C,H,0H CHNa(COOC,H;)2 + CoH;l = CHC,H,(COOC,H,)> + Nal CHC,H,(COOC,H;), + 2KOH = CHC,H,(COOK), + 2C,H,0H CHC,H,(COOK), + 2HCl = CHC,H,(COOH,) + 2KCI CHC H, (COOH), (heated) = CH,C,H,(COOH) + CO, As malonic acid can be made from acetic acid (p. 625) this series of reactions serves for the preparation of the homologues of acetic acid from the acid itself. FATTY ACIDS 601 The relation between (a) acetoacetic and (b) malonic acids is seen in the following formule : (a) CH3-CO-CH,:CO:COOH (b) COOH-CO-CH,-CO-COOH. The principal members of the acetic series are : Monobasic acids of the acetic series, C,H, . .CO,H. Acid. Source, Formula. M.-p. B.-p. Formic . 2 . Red ants, nettles. F H - CO,H 9° 100-6° Acetic. : . Vinegar . : ‘ CH; - CO,H 16-6° 118° Propionic. ‘ . Various fermentations . C,H; -CO,H —22° 140° Butyric . : . Rancid butter : : C3;H,:CO,.H — 65° 163° Valeric : Valerian root , CyHy -CO,H —19° 186° Caproic . : . Rancid butter : j CsHy, -CO,H — 8° 202° CGEnanthic ; . Oxidation of castor oil. C.Hi3 :CO,H —11° 223° Caprylic . : . Rancid butter ; : C,H; - CO.H 16-5° = 237° Pelargonic , . Geranium leaves. CsH,7 - CO.H 13° 254° Rutic or Capric . Rancid butter : j CyHig - CO.H 31-:3° 268° Undecylic , . Oil of rue . : » CyoHay - CO.H 29° _ Lauric . : . Bay berries . ‘ . OH; - CO.H 43-6° _— Tridecylic , . Cocoa-nut oil ; » CyHe, - CO.H 41° _— Myristic . ‘ Nutmeg-butter - Gy He, -CO.H 53-8° Pentadecylic . Agaricus integer (a fungus) C,4H»y - CO.H 51° — Palmitie . : - Palm oil ‘ ‘ - OgHs, - CO,H 62-6° — Margaric . ‘ : : i ; CyeH3, - CO.H 59-8° _— Stearic. : . Tallow . . ‘ . CH 35 -CO,H 69-3° — Arachidic. : . Earth-nut oil . ‘ CigH39 - COLH 77° — Behenic . ‘ . Oilofben . ‘ Cy,Hy3 - CO,H 81° — Cerotic . é . Beeswax ; ‘ . Cy5H5; - CO2H 77-8° _— Melissic . i : 5a : ‘ . CogHs9 - CO.H 91° — As in other homologous series, the volatility of the acids decreases as the number of carbon atoms increases, so that palmitic acid and those richer in carbon can be distilled only under diminished pressure or in a current of superheated steam. The solubility in water diminishes in the same order ; acetic acid mixes with water in all proportions while palmitic acid is quite insoluble. With the exception of formic and acetic acids they are decidedly oily in character. The acid strength also diminishes with the increase in the carbon atoms, and this is turned to account in separating the volatile fatty acids from each other by the method of partial saturation. Suppose it to be required to separate butyric and valeric acids. The mixture is divided into equal parts, one of which is exactly neutralised by soda, yielding butyrate and valerate of sodium. The other half of the acid mixture is then added, and the whole distilled. Since butyric acid is the stronger acid, it will expel the valeric acid from the sodium valerate. If the mixture contained equal mole- cules of the two acids, the distillate would contain valeric acid only, and the residue would contain the sodium butyrate. If the valeric acid preponderated, the residue would contain both valerate and butyrate, and, when distilled with sulphuric acid, would yield a fresh mixture of the acids, which could be again treated in the same way. But if butyric acid preponderated, the residue would be only sodium butyrate, while the distillate would contain both butyric and valeric acids, to be again treated by partial saturation. The non-volatile fatty acids may be separated from each other by fractional pre- cipitation, which depends on the principle that the insolubility of their barium, magnesium, and lead salts increases with the number of carbon atoms. The mixture of fatty acids is dissolved in alcohol, and is partially precipitated by an alcoholic solution of the acetate of Ba, Mg, or Pb. This precipitate will contain the acid or acids richest in carbon. It is filtered off, and another precipitate is obtained from the solution in 602 FORMIC ACID the same way. This will contain acids poorer in carbon, and so on. Each precipitate is decomposed by HCl, and the new mixture of acids so obtained is subjected to the same treatment, until the separated acid is found to have a constant melting- point. The constitution of the fatty acids is disclosed when they are subjected to electrolysis, for they then evolve one atom of carbon as CO,; thus, acetic acid yields dimethyl (ethane), CO, and H— 2(CH;:CO.H) = (CH3)2 + 2CO2 + Hy. Again, valeric acid yields dibutyl, CO, and H— 2(C4H9‘CO.H) = (CyHyg)e + 2COg + He. To prepare an acid higher in the series from one lower in the series, advantage may be taken of such reactions as the following : (1) CH,-CH,-COOH +PCl; = CH,CH,-CO-Cl + POCI, + HCl. (2) CH,-CH,-COCl.+ 4H’ = CH,CH,CH,OH + HCl. (3) 3CH,-CH,-CH,OH + PI, = 3CH,-CH»-CHyI + P(OH),. (4) CH,-CH,-CH,I + KCN = CH,-CH,-CH,-CN + KI. (5) CH,-CH,-CH,CN + 2HOH = CH,:CH,-CH,-COOH + NH;. Formic acid, H-CO,H, was originally obtained from ants, hence the name (L. formica, an ant). It occurs in nettles and other plants, in some animal fluids, and occasionally in mineral waters. It is prepared by distilling oxalic acid with glycerin. 50 grams of crystallised oxalic acid and 40 c.c. of glycerin are heated, in a 300 or 400 c.c. retort, provided with a ther- mometer and condenser, to about 80°, when the temperature gradually rises to 105°-110° and a little formic acid distils over together with the water of crystallisation of the oxalic acid, carbon dioxide is evolved ; CO,H-CO,H = H:CO,H + CO,. When the evolution of CO, ceases, and the temperature has beet allowed to fall to 80° again, a fresh quantity of oxalic acid may be introduced and the operation continued, the same glycerin serving for the conversion of a large quantity of oxalic acid. The formic acid first produced converts the glycerin into monoformin (compare allyl alcohol, p. 583)— C,H,(OH), + H-CO,H = C,H,(OH),(0-CHO) + HOH. The monoformin is then decomposed by the water of crystallisation of the oxalic acid, the equation being reversed, and glycerin is reproduced. By continuing the process, formic acid of 56 per cent. may be obtained. To prepare the pure acid, this is neutralised with lead oxide, the lead. formate crystallised, dried, and heated to 100° in a current of dry H,S; (H-CO,),Pb + H,S = 2H-CO,H + PbS. The formic acid is carefully condensed and redistilled with a little lead formate to remove H,8. Or the distillate may be neutralised by Na,CO,; and evaporated ; the sodium formate, H-COONa, is then dried and distilled with anhydrous oxalic acid. Formic acid is obtained synthetically by heating caustic alkalies to 100° in carbonic oxide; CO + KOH = H-CO,K (potassium formate) ; again, potassium, acting on carbon dioxide in presence of water, yields acid potassium carbonate and potassium formate— 2C0, + H,O + K, = KHCO, + H-CO,K. It is also produced in other reactions in which carbonic acid is acted on by reducing agents. Carbonic acid may be regarded as hydroxy-formic acid, HO-CO,H, that is, formic acid, H:CO,H, in which OH is substituted for H. When starch and other organic bodies are violently oxidised, they yield carbonic acid, but if they are gradually and quietly oxidised, they yield formic acid. The quiet oxidation of organic bodies is often effected by heating them with MnO, and dilute H,SO,. “ ACETIC ACID 603 Formic acid is also formed by oxidising methyl alcohol, and when hydro- cyanic acid, which is the nitrile of formic acid, is eee by boiling it with dilute acids, H-CN + 2HOH = H-CO,H + N Properties of formic acid.—Colourless liquid, ae slightly in air and of pungent smell; it blisters the skin. Formic acid boils at 100°-6 and melts at 9°. Its sp. gr. is 1:22 at 20°. The diluted acid boils at a higher temperature ; an acid of 77 per cent. boils at 107°. The formates are all soluble in water ; their solutions yield a red colour with ferric chloride, and reduce silver from the nitrate, when boiled with it, on account of the tendency of formic acid to become carbonic (hydroxy- formic) acid. Solid formates evolve carbonic oxide (burning with a blue flame) when heated with strong H,SO,, which removes the elements of water; H-CO,H = HOH + CO. A formate heated with excess of baryta yields the oxalate; (HCO,),Ba = (CO,),Ba + H,. Calcium formate, see p. 593. Alkali formates yield oxalates and hydrogen on gently heating (250°), 2H-COOK = (COOK), + H, ; heated strongly with excess of alkali, carbonates and hydrogen, H-COOK + KOH=K,CO, + H,; cf. acetates yielding methane, p. 258. Formic acid enters into many syntheses (sez, for example, p. 598); it is used in making some of the coal-tar dyes. Formic acid differs in some respects from the other members of the series. Thus its powerful reducing action relates it to the aldehyde acids (p. 619); indeed, if its formula be written HO-CHO it might be regarded as hydroxyformaldehyde. No acid chloride or anhydride, such as are characteristic derivatives of the higher acids of the series, can be obtained from formic acid. By loss of water it yields CO not (H-CO),0, which would be the true anhydride. When heated at 160° it breaks up into H and CO, ; the same change occurs at the ordinary temperature in contact with platinum black. Acetic acid, or methyl-formic acid, CH,-CO,H, is found either free or combined in many plants and in some animal fluids. It is obtained by the destructive distillation of wood or of sawdust, or spent dye-woods. The aqueous layer in the condenser (p. 578) is neutralised by sodium carbonate, and the methyl alcohol and acetone are distilled off. The evaporated liquor deposits impure crystals of sodium acetate which are heated to expel some tarry matters, and distilled with H,SO,, when acetic acid passes over ; CH,-CO,Na + H,SO, = CH,:CO,H + NaHSO,. The crude acid from wood is termed pyroligneous acid. Acetic acid is also made by the oxidation of alcohol for the production of vinegar ; CH,-CH,:OH (ethyl alcohol) + O, = CH,;'CO,H + H,O. But this equation cannot be realised unless some third substance be present. It was seen at p. 577 that platinum black would answer the purpose, and in some chemical works this process has been employed for making acetic acid. Weak fermented liquors, such as beer and the lighter wines, are very liable to become sour, which is never the case with distilled spirits, however much diluted. This is due to the presence in the fermented liquid of albu- minous (nitrogenised) matters and salts, which afford nourishment to a microscopic organism, termed Mycoderma aceti, which appears to convey the oxygen of the air to the alcohol. Quick vinegar process.—A weak spirit mixed with a little yeast or beetroot juice, heated to about 27°, is caused to trickle slowly from pieces of cord fixed in a perforated shelf over a quantity of wood shavings previously soaked in vinegar to impregnate them with the acetic ferment or mother of vinegar. The shavings are packed in a tall cask (Fig. 300) in which holes have been drilled in order to allow the passage of air. The oxidation of the alcohol soon raises the temperature to about 38°, which occasions a free circulation of air among the shavings. The mixture is passed three or four times 604 VINEGAR through the cask, and in about thirty-six hours the conversion into vinegar is completed. If the supply of air be insufficient, alcohol is lost in the form of aldehyde vapour, the irritating odour of which pervades the air of the factory. White-wine vinegar is prepared from light wines by a similar process. Malt vinegar is made from infusion of malt fermented by yeast with free contact of air. Vinegar contains, on an average, about 5 per cent. of acetic acid. Its aroma is due to the presence of a little acetic ether. The vinegar of commerce is allowed to be mixed with ,;),, of its weight of sulphuric acid in order to prevent it from becoming mouldy. By dis- tilling vinegar a weak acetic acid is obtained, which may be concentrated by redistilling and collecting separately the portion distilling between 110° and 120°. Pure acetic acid is prepared by distilling 5 parts by weight of fused sodium acetate with = 6 parts of concentrated sulphuric acid (see above). A fairly pure acid having been obtained, it cannot be completely purified either by frac- Fie. 300. tional distillation or by fractional freezing ; but by distilling slowly from 2 per cent. KMn0O,, using a 12-pear still-head to retain acids of higher boiling-point, a very pure acid is obtained. (Journ. Chem. Soc., 1911, T. 1432.) The acid is also produced (synthesised) when CH,Na is treated with CO, (p. 599), and when methyl cyanide, acetonitrile, is hydrolysed by boiling dilute acids; CH,-CN + 2HOH = CH,COOH + NH. Acetic acid may be produced by the reaction of zinc methyl, Zn(CH3),, with COCI, (p. 249) which yields acetyl chloride (g.v.), a compound which furnishes acetic acid when decomposed by water— Zn(CHy)p + 2COCl = 2CH,COC] + ZnCly. CH,-COC] + HOH = CH,-COOH + HCl. The group CH,-CO, which remains unchanged during the latter reaction, is termed acetyl, C,H,0, and may be regarded as ethyl, CH,-CH,, in which O” has been substituted for H,. Properties of acetic acid —Colourless, pleasant smell, blistering the skin, boiling at 118°, and giving a vapour which burns with a flame like that of alcohol. Its true melting-point is 16-6°, but it may be cooled far below this without solidifying, unless a crystal of the acid be introduced, when the whole crystallises in beautiful plates; hence the term glacial acetic acid ; 0-1 per cent. water lowers the m.-p. by 0-2014°, which corresponds with 36-3 as the cryoscopic constant (p. 321). The sp. gr. of the pure acid is 1-0515 at 18° compared with water at 4°, and the difference for each degree of temperature is 0-00123 ; at 15°/15° it is 1-0558, but the strength of the acid cannot, as in other cases, be inferred from the sp. gr., because the latter is increased by addition of water, till it reaches 1-075 at 15° (77-80 per cent. of acid), when it is diminished by more water, so that a 43 per cent. acid has the same sp. gr. as the pure acid. Acetic acid is one of the most stable of the organic acids. It is un- attacked by most oxidising agents. Highly purified acetic acid is not attacked by chlorine in the dark; but the purest commercial is. When its vapour is passed through a red-hot tube it yields several products, among which marsh gas and acetone are conspicuous. Most of its salts are soluble in water, so that it is not easily precipitated ; but if it be exactly neutralised by ammonia, and stirred with silver nitrate, a crystalline precipitate of silver acetate, CH,CO,Ag, is obtained; mercurous acetate, CH,-CO,Hg, may be obtained in a similar way. Ferric chloride added to the neutral solution gives a fine red colour, due to ferric acetate, (CH;COO),Fe,, which ACETATES 605 is precipitated as a red basic acetate on boiling. The aluminium salt behaves similarly ; hence the aluminium acetate and ferric acetate (red liquor) are much used by dyers and calico-printers as mordants, the basic acetates being deposited in the fabric, and forming insoluble compounds with colour- ing-matters. Lead acetate, or sugar of lead, (CH;COg).Pb.3Aq, is the commonest commercial acetate, and is prepared by dissolving litharge (PbO) in an excess of acetic acid, when the solution deposits prismatic crystals of the salt. On the large scale, acetic acid vapour is passed through copper vessels with perforated shelves on which litharge is placed. Lead acetate is intensely sweet and very soluble in water (14 part). Com- monly, the solution is turbid from the precipitation of lead carbonate by the carbonic acid in the water ; a drop of acetic acid clears it. The acetate is soluble in alcohol. When heated, it fuses at 75° and becomes anhydrous at 100°. The anhydrous salt melts when further heated, evolves the pleasant smell of acetone, and becomes again solid as a basic lead acetate, which is decomposed at a higher temperature, evolving CO, and acetone, and leaving a yellow residue of PbO mixed with globules of lead. ‘There are several basic lead acetates, but the only one of practical importance is the tribasic lead acetate, Goulard’s extract, (CH3'CO2)2Pb.2Pb0.H,0, which is prepared by boiling lead acetate with litharge. It forms needle-like crystals, which are very soluble in water, but insoluble in alcohol. A strong solution of the salt is not affected by the air, but a weak solution is rendered turbid by the smallest quantity of CO, in air or water. Tribasic lead acetate is very useful in the laboratory for precipitating tannin, gum, &c., from vegetable infusions in order to extract the alkaloids. Verdigris is a mixture of several basic cupric acetates prepared by acting on sheet copper with the refuse grapes of the wine-press, which yield acetic acid by oxidation of the alcohol ; the acid combines with the cupric oxide formed by the action of air upon the copper. Commercial verdigris consists chiefly of the compound (CH,-CO.),Cu.Cu0.6H,0. When this is treated with water it is only partly dissolved, the residue having the composition (CH3-CO,).Cu.2Cu0.2H,O. By dissolving verdigris in acetic acid, the normal cupric acetate may be obtained in crystals of the formula (CH3-CO,).Cu.H,O. It forms blue prisms soluble in water. Verdigris is used in the manufacture of colours, and in dyeing and calico-printing. Emerald-green or cupric aceto-arsenite, (CH3-COg),Cu.Cu3(AsO3)o.As,0g, is made by boiling verdigris with white arsenic and water. It is used for colouring wall-paper and other fabrics, and is dangerous to the makers and purchasers. Sodium acetate, CH;.CO,Na.3Aq, prepared by neutralising acetic acid with sodium carbonate, crystallises in prisms which are very soluble in water, and can yield one of the best examples of a supersaturated solution (see p. 40), which is used in foot- warmers for railway carriages, on account of the continuous evolution of heat during its crystallisation. It is four times as effective as an equal volume of water. The acetates of sodium and potassium are remarkable for their fusibility and their stability at high temperatures ; they do not carbonise so readily as do most salts of organic acids. Fused sodium acetate is frequently applied in organic chemistry, e.g. in Perkin’s reaction (7.v.). On heating with arsenic, cacodyl oxide is produced (p. 690). Potassium, sodium, and ammonium acetates combine with one and with two molecules of acetic acid to form crystalline compounds. Calcium acetate, when dissolved in water together with CaCly, yields the compound (CH,-COO),Ca.CaCl,.10Aq, which crystallises easily, and is sometimes produced for effecting the purification of crude acetic acid (Condy’s patent). Zine acetate, (CH3-COz).Zn.3Aq, is remarkable for being capable of sublimation at a moderate heat, when dried. Acetic acid is very useful in organic chemistry as a simple solvent, especially for resins and hydrocarbons, such as naphthalene and anthracene. There is an acid radicle corresponding with each alcohol radicle ; a few examples are here given : 606 ACETIC ANHYDRIDE Alcohol radicles Acid radiclest Methyl : . CH; Formyl H-CO Ethyl . CH,-CH, Acetyl . CH,-CO Propyl : . C,H,-CH, Propionyl . CoH;:CO Butyl : . CsH,-CH, Butyryl ‘ . C3H,-CO Amyl . . C,HgCHy Valeryl . . CyH,-CO lt will be seen later that the alcohol radicles combine in pairs with oxygen R to produce ethers of the type So, the two radicles being the same or different. R The acid radicles combine with oxygen in a similar manner to produce acid CH,CO: CH,C anhydrides, such as f O, acetic anhydride, pf aceto-propionic CH,CO 0,H,CO anhydride. . Acetic anhydride, or di-acetyl oxide, or anhydrous acetic acid,'(CH3-CO)20, is prepared by distilling acetyl chloride with an equal weight of perfectly anhydrous sodium acetate ; CH,COCl + CH,-COONa = (CH3:CO),0 + NaCl. It distils over as a_ colourless liquid, smelling of acetic acid, but irritating the eyes ; its sp. gr. is 1-073, and boiling- point, 137°. It is neutral in reaction. It is soluble in ether. It does not mix readily with water but dissolves slowly in it, with evolution of heat and formation of acetic acid (CH,-CO),0 + H,O = 2(CH3-COOH). Acetic anhydride may also be formed by heating lead acetate with carbon disulphide ; 2Pb(CH3°CO,). + CS = 2(CH3'CO),0 + 2PbS + CO,. Also by heating acetyl chloride with anhydrous oxalic acid ; 2C,H,;O0Cl + (COOH), = (C,H30),0 + 2HCl + CO + COx. By carefully acting on acetic anhydride with sodium amalgam and water (or snow), it has been converted into aldehyde and alcohol— (CH,-CO),0 + 4H* = 2(CH3-CHO) + H,O, and CH ;-CHO + 2H’ = CH3-CH,:OH. With HCl it yields acetyl chloride and acetic acid, (CH,CO),0 + HCl = CH,COCl + CH,;COOH. If a coil of platinum wire be immersed in acetic anhydride and heated strongly by electricity, a gas of peculiar pungent smell, keten, CH,: CO, is evolved. Chemically it is very active, forming at ordinary temperatures acetic esters with alcohols, eg. CpH,OH + CH, : CO = CH;.COOC,H;; acetamide with anhydrous ammonia, CH, : CO + NH; = CH,CO.NH,; and so is a useful acetylating agent. It is the lowest and typical member of a new and numerous class of bodies the ketens, in which a carbonyl group is doubly linked to a single C atom, the latter being also united to various radicles, e.g. phenylmethylketen, CMePh : CO, an orange-yellow liquid, b.-p. 74° (12 mm.). Many of them polymerise. Acetyl dioxide, or acetic peroxide, (CH3-CO):0z, is obtained by adding barium dioxide to an ethereal solution of acetic anhydride— 2(CH3°CO),0 + BaOy = (CH3-CO),.02 + Ba(CH3-COz)>. It melts at 30° and is insoluble in water. It explodes violently when heated, and has the powerful oxidising properties which would be expected from its chemical resemblance to hydrogen peroxide. Corresponding with the thioalcohols, the alkyl sulphides and disulphides (p. 586), there are thioacids, thioanhydrides, and thioperoxides, the oxygen outside the acid radicle having been exchanged for sulphur in each case. Thioacetic acid, CH3-COSH, is obtained by the action of P.S, on acetic acid: 5CH;-COOH + PS, = 5C,H3;0-SH + P,0;. It is a colourless, evil-smelling liquid, boiling at 93°, and sparingly soluble in water. Acetyl sulphide (thioacetic anhydride), (CH3-CO),S, is obtained by the action of P,S, on acetic anhydride, and acetyl disulphide (thioacetic peroxide), (CH3CO).S., by the action of K,S, on acetyl chloride. Propionic acid, C,H;-CO2H, is not produced upon a large scale like acetic acid. It is 1 Termed acidyl or acyl radicles, BUTYRIC ACID 607 formed in the putrefaction of various organic bodies, and in the destructive distillation of wood and of rosin. It may be separated from formic and acetic acids by saturating the mixture with: PbO, evaporating to dryness and extracting with cold water. On boiling the solution, it deposits basic lead propionate, leaving the basic lead formate and acetate in solution. From the lead salt the acid may be obtained by the action of HS or H,S0,. Sodium propionate is obtained by the action of CO upon sodium ethoxide, just as sodium formate is obtained from sodium hydroxide (see p. 602), CO + C.H;-ONa = C,H;-CO,Na. From sodium ethide and CO, (p. 686). Propionic acid, as would be expected, resembles acetic acid. Its sp. gr. is 0-996, and it boils at 140°. It has no practical importance. The propionates are mostly soluble in water, but silver propionate is sparingly soluble. Lead propionate is much more difficult to crystallise than lead acetate : Butyric acid, C;H,-CO.H. The normal acid (ethylacetic acid) is made from cane sugar by dissolving it in water (5 parts), adding a little tartaric acid (zi ,th part) boiling to convert the sucrose into glucose, and adding to the cooled liquid some putrid cheese (,1,th part) rubbed up in about thirty times its weight of milk. Some chalk (4 part) is stirred into the mixture, which is then allowed to ferment for a week at a temperature of 30°-35°. The glucose, CgH,,0,, undergoes the lactic fermentation, and is converted into lactic acid, C;Hg0 3, which is converted, by the chalk, into calcium lactate, forming a pasty mass of crystals. After a time the mass becomes liquid again, evolving bubbles of hydrogen and carbon dioxide, and forming a strong solution of calcium butyrate, produced by the butyric fermentation. When this is mixed with strong hydrochloric acid, the butyric acid rises to the surface and forms an oily layer which may be purified by distillation. The passage of lactic acid into butyric acid is_ expressed by the equation 2C;H,0, = C3H,-CO,H + 2CO, + 2Hb». Butyric acid is a strongly acid liquid, smelling like rancid butter ; sp. gr. 0.958 at 14°, m.-p. — 6-5°, b.-p. 163°. It mixes readily with water, but separates again when the water is saturated with a salt. The butyrates are rather less soluble than the acetates. Calcium butyrate is less soluble in hot water than in cold. Silver butyrate is very sparingly soluble. Butyric acid is found in the products of distillation of wood and of some other organic bodies. It exists in the perspiration of the skin, and, as a glyceride, in butter (6 per cent.) (but see p. 672), and in small quantity in a few vegetable oils. Isobutyric acid (dimethylacetic acid) (CH3),CH:-COOH boils at 155° and is made from isopropyl chloride through the cyanide reaction (p. 599). Valeric or Valerianic Acid.—Four of these are possible ; that commonly called valeric acid is isopropylacetic acid, (CH3),CH-CH,-COOH. It is prepared by oxidising amyl alcohol (fusel oil) with potassium bichromate and sulphuric acid. It is an oily liquid smelling like old cheese ; its sp. gr. is 0-95, and it boils at 174°. It is much less soluble in water than are the preceding acids, requiring thirty times its weight. The valerates are, as a rule, easily soluble in water, but the silver salt is spar- ingly soluble. Zinc valerate is used medicinally. Valeric acid occurs in valerian root, in the elder, in the berries of the guelder rose, and in many other plants ; also in some fish oils and in the perspiration. Normal caproic or hexylic acid, C;Hy,‘CO2H (sp. gr. 0:94, b.-p. 205°), is found in butter from cows and goats, and in Limburg cheese, being one cause of its odour ; it is also found in some plants, and in the perspiration. Caproic acid is formed, together with butyric and acetic acids, in the butyric fermentation described above. It dissolves very sparingly in water, and has a repulsive odour. The caproates of barium and calcium are rather sparingly soluble in water, and silver caproate is nearly insoluble. Gnanthic or normal heptylic acid, CgH,3-CO.H, is obtained by oxidising cenanthic aldehyde (cenanthol). It has a faint odour and sp. gr. 0-93; it boils at 223°. Many of the cenanthates are nearly insoluble in water. The strong solutions of the alkali cenanthates become gelatinous on cooling, like solution of soap. Normal caprylic or octylic acid, CH;(CH,)gCOOH, is found in the fusel oil from wines, in old cheese, and, as a glyceride, in butter, human fat, and cocoa-nut oil. It is the first acid of this series which is solid at common temperatures, forming needle-like crystals or scales, m.-p. 16-5°, b.-p. 237°, sp. gr. 0-910 at 20°/4°. It has an offensive 608 PALMITIC ACID smell, and is very sparingly soluble in water. The caprylates, except those of the alkalies, are sparingly soluble in water, but they dissolve in alcohol. Pelargonic or normal nonylic acid, CgH,;-COjH, was originally obtained from the essential oil of Pelargonium roseum, and is found among the products of oxidation of oleic acid by nitric acid. It is also formed when essential oil of rue (nonylmethyl- ketone) is oxidised by nitric acid. It is an oily liquid, of faint odour, crystallising at 12° and boiling at 253°. It has sp. gr. 0-91, and is insoluble in water. The pelargonates are sparingly soluble in water, except those of the alkalies. Laurie or normal dodecylic acid, C,yH23-CO2H, is obtained from a fatty substance found in the fruit of the sweet bay (Laurus nobilis) and in sassafras-nuts or pichurim beans, which are used for flavouring chocolate, and are the seeds of another of the Lauraceee (Nectandra pichury). A similar substance is found in the mango and in a variety of cochineal insect. As glyceride it forms a notable proportion of the oils of the cocoanut oil group. The fat is saponified by boiling with potash, the solution decomposed by hydrochloric acid, and the separated fatty acid distilled, when lauric acid is found in the middle fractions. The crystals of lauric acid fuse at 43-6° ; b.-p. 225° (100 mm.). It cannot be distilled at ordinary pressures without slight decomposition ; sp. gr. 0-883 at 20°/4°. Palmitic acid, n-hexadecylic acid, C,;H3,-COH, crystallises in needles (m.-p. 62-6°), and is the first of the fatty acids, properly so called, which occur as glycerides in the vegetable and animal fats, and form true soaps with the alkalies, such soaps being the salts formed by the fatty acid with the alkali-metal, characterised by easily lathering when dissolved in soft water, by being precipitated from their aqueous solutions by common salt, and by giving an oily layer of the melted fatty acid when boiled with any of the common acids. On the large scale, palmitic acid is made from palm-oil, as described at p. 589. Itis also manufactured by heating oleic acid with caustic soda, C,7H,3-COOH + 2NaOH = C,;H3,-COONa + CH,-COONa + Hy. On the small scale, palm-oil is boiled with potash, which converts it into potassium palmitate and oleate ; on adding dil. H,SO, to the solution, a mixture of palmitic and oleic acids is precipi- tated; this is washed, dried, and dissolved in hot alcohol, from which the palmitic acid crystal- lises on cooling, leaving the oleic acid in solution. It may be purified by distillation under di- minished pressure. An arrangement suitable for this operation is shown in Fig. 301. At100mm. it boils at 271-5°; at 760 mun. at 339° to 356° with some decomposition. Fig. 301. Palm-oil contains the glycerides palmitin and olein, which are saponified by the potash, with liberation of glycerin, as will be further explained under the head of esters, to which the glycerides belong. The substance known as adipocere, a wax-like mass left when animal bodies decom- pose in the earth, is a mixture of palmitates of calcium and potassium. The formation of palmitic acid from spermaceti has been explained at p. 583. Margaric acid, CygH33-CO.H, is obtained by boiling cetyl cyanide with an alkali. It crystallises like palmitic acid and fuses at 59-8°. The substance usually known as ““margaric acid ” is a mixture of stearic and palmitic acids. STEARIC ACID 609 Stearic acid, n-octadecylic acid, C,,H,,-CO,H, is an abundant constituent of many vegetable and animal fats, especially the harder ones ; it may be prepared from suet by boiling it with potash, decomposing with hydro- chloric acid the soap thus obtained, drying the separated fatty acids, and dissolving in the least possible quantity of hot alcohol. This retains the oleic acid in solution and deposits a mixture of stearic and palmitic acids on cooling ; the mixture is well pressed in blotting-paper, and repeatedly crystallised from alcohol till it fuses at 69-3°. The stearic acid exists in the suet and in most other solid fats, in the form of the glyceride stearin, mixed with palmitin and a little olein. When saponified by the potash, these yield glycerin and the stearate, palmitate, and oleate of potassium, respectively. Stearic acid has been obtained artificially by reducing oleic acid. , Stearic acid is a white crystalline solid, of the same sp. gr. as water at 11°, fusing at 69-3°, when its sp. gr. is 0-8454 (69-3°/4°), and not distilling without partial decomposition, except at low pressure or in a current of superheated steam. It is insoluble in water, but dissolves in alcohol and in ether. It burns with a luminous flame. The alkalies dissolve stearic acid on heating, forming stearates, which are components of ordinary soaps. White curd soap made from tallow and soda consists chiefly of sodium stearate, C,7H35-CO,Na, which may be crystallised from alcohol. It dissolves in a little water to a clear solution, but when this is largely diluted it deposits scaly crystals of the acid sodium stearate, (Cj7H3;-COg),HNa. Potassium stearate behaves in a similar way. The other stearates are insoluble. Those of calcium and magnesium are preci- pitated when hard water is brought in contact with soap. Magnesium stearate may be crystallised from alcohol. Stearic acid mixed with palmitic acid is the material of the so-called stearin candles. Cerotic acid, Co,H,,;COOH, occurs free in beeswax, carnaiiba wax, and as ceryl cerotate in various waxes. It is obtained by exhausting beeswax with boiling alcohol ; it is practically insoluble in cold alcohol. M.-p. 77-8°. Acids from Monohydric Olefine Alcohols (Acrylic or Oleic Series). —These correspond with the general formula C,Hen—,COOH and contain the ethylenic linking characteristic of the olefines, e.g. CH,-CH : CH-COOH, crotonic acid. They may be prepared from the corresponding alcohols and cyanogen derivatives by the general methods (p. 599), and also by two methods which recall the preparation of the olefines. These are (1) by nucleal condensation from the monohalogen substituted fatty acids, thus : CH,-CH,-CHCl-COOH + KOH = CH,:CH: CH:COOH + KCl + HOH, and (2) by dehydration of the alcohol acids (p. 615) by destructive distilla- tion ; CH,(OH)-CH,-CH,-COOH = CH, : CH-CH,-COOH + HOH. Attention must here be called to the nomenclature of isomerides among derivatives of open-chain hydrocarbons. The letters, a, 8, y, &c., are prefixed to the name of the derivative to indicate the carbon atom to which the substituent is attached, a signifying the atom next the end characteristic group, @ the next but one, y the next but two, and so on, thus : a-Chlorobutyric acid = CH3-CH,-CHCl‘COOH 3-Chlorobutyric acid = CH,-CHCl-CH,-COOH y-Chlorobutyric acid = CH,Cl-CHp-CH,-COOH It is by no means a matter of indifference whether an a, (3, or y-derivative is used in the two last-named reactions ; in both cases the /)-derivative is most easily con- verted into the acid of the olefine series. Having an ethylenic linking, the acids of the acrylic series show the property, characteristic of the olefines, of combining directly with two 39 10 OLEIC SERIES OF ACIDS atoms of bromine and with two atoms of (nascent) hydrogen. In the former case a dibromo-derivative of the corresponding fatty acid, and in the latter the fatty acid itself, is formed, the double linking being opened up in each case. kasd A characteristic reaction of the acids of this series is that when fused with an alkali they yield alkali salts of two acids of the acetic series, the rupture of the molecule generally occurring at the double linking ; thus acrylic acid, CH, :CH-COOH, yields acetate and formate, and crotonic acid yields two molecules of acetate. This reaction is not a criterion of the position of the double linking in the chain because of the influence which alkalies have in causing the double bond to shift, mere heating with aqueous alkali sufficing in many cases to convert a /y-acid (one in which the double bond is between the 3 and y carbon atoms) into an aj3-acid. Jsomerism among acids of the acrylic series may be due to variation in position of the double bonds, as, for instance, CH,-CH : CH-CH,-COOH and CH3-CH,:CH : CH-COOH, or to the substitution of a hydrocarbon radicle for H, eg. CH3-CH : C(CH;)-COOH, isomeric with the two preceding acids. There are also cases of stereoisomerism of the same kind as that between fumaric and maleic acids (q.v.). Since the polymethylenes (p. 558) are isomeric with the olefines, the monocarboxylic acids derived from them are isomeric with the acrylic acids, though they do not belong to the same series. The following are the best-known acids of the series, but although they form an homologous series, many of them differ in structure so much from the type, acrylic acid, and from each other that their physical properties cannot advantageously be compared. Acid. Source. Formula. Acrylic ‘ . Oxidation of acrolein : . CH,-CO.H Crotonic . ; é ‘ ‘ ‘ . C,H;-CO,H Angelic a . Angelica root . 5 . C,H,-CO,H Pyroterebic. . Oxidation of turpentine . . C3H»-CO.H Hypogaeic . . Earth-nut oil . ‘ j » OysHe9°-CO.H Oleic . ; . Most oils ‘ ‘ : . OH 33°CO.H Erucic 3 Rape oil ‘ * » Co,Hy:CO,H Acrylic acid, CH, : CH-CO,H, is obtained by heating acrolein, the corresponding aldehyde (p. 596) with water and silver oxide in the dark: C,H,;-CHO + Ag,O = C,H,-CO,H + Agp. It is also obtained, by the general methods given above, from {-bromopropionic and 3-hydroxypropionic acids (p. 618). It is a pungent liquid, miscible with water, and boiling at 140°. Nascent hydrogen converts it into propionic acid, C,H;-CO.H. Fused with potassium hydroxide, it yields potassium acetate and formate—CH, : CH-CO,K + KOH + H,O = CH, CO,.K + H-CO,K + Hp. While it is possible to write the formula C;H,-COOH, the next homologue to acrylic acid, in four isomeric forms, two alone are known with certainty, viz. crotonic acid, CH;:CH : CH-COOH, which occurs in a solid and a liquid modification, and methylacrylic acid, CH,: C(CH3);COOH. Vinylacetic acid, CH,:CH-CH,-COOH, is also alleged to have been obtained. Solid crotonic acid occurs in crude pyroligneous acid, and is obtained by oxidation of croton aldehyde (p. 596) with Ag,O. Its formation by heating a/3-dibromobutyric acid with KI solution indicates the position of the double linking : CH;-CHBr-CHBr-COOH + 2KI = CH,-CH : CH-COOH + 2KBr + I,. It crystallises in needles, melts at 72°, and boils at 180°, its vapour condensing in plates. It is moderately soluble in water, and has an odour like that of butyric acid, into which it is converted by nascent hydrogen. Fused KOH converts it into potassium acetate— C3H,'CO.H + 2KOH = 2(CH;CO,K) + Hp. “Liquid” crotonic or isocrotonic acid occurs in croton oil, When PCI; acts on ethylacetoacetate (q.v.) it produces B-chloro- isocrotonic acid, CH,-CCl: CH-CO.H, which, by treatment with nascent H, yields isocrotonic acid; this crystallises in needles or prisms, melts at 15°, boils at 169°, OLEIC ACID 611 and is converted into the solid acid at 180°. It appears to be a stereoisomeride of the solid acid, the relation between the two being similar to that between fumaric and maleic acids (¢.v.). Methylacrylic acid occurs in chamomile oil, and has an odour of mushrooms. It is prepared by a complicated process. It melts at 16° and boils at 160° ; nascent H converts it into isobutyric acid, whilst with fused KOH it yields propionate and formate. Angelic acid, CH3-CH : C(CH3)-COOH, is obtained by boiling angelica root (an umbelliferous plant) with lime and water, filtering, acidifying with sulphuric acid, and distilling. The acid appears to be contained in the root as an ethereal salt, which is decomposed by the lime. Chamomile flowers and some other aromatic plants also yield this acid. It crystallises in prisms, fusing at 45° and boiling at 185°. It has an aromatic odour, is soluble in hot water and in alcohol and ether. When boiled for some time, it is converted into its stereoisomeride, tiglic acid (m.-p. 64°, b.-p. 198°), which is also obtained from croton oil (Croton tiglium), and, together with angelic acid, from cumin oil (Cuminum cyminum). Fused with KOH, angelic acid yields acetate and propionate. There are several isomerides. CH,(CH,),CH Oleic acid, C,,H;,;COOH, or {| (trans- HC(CH,),COOH form), is one of the two most abundant acids occurring as glycerides in vegetable and animal oils and fats, stearic being the other; oleic pre- ponderates in the liquid oils, and stearic in the harder fats. The two acids are closely related, oleic being the olefinic unsaturated acid corresponding with the saturated stearic acid, to which the former may be reduced by means of fuming hydriodic acid and phosphorus at 200°. Pure oleic acid is a rare commodity. It may be prepared by saponifying tallow with caustic potash, precipitating the mixture of acids with lead acetate, drying, and extracting the lead oleate with ether ; this is decom- posed by shaking with hydrochloric acid, the oleic acid remaining in the ethereal layer. The liberated oleic acid is dissolved in ammonia and pre- cipitated with barium chloride. The barium oleate, after drying, is purified by crystallisation and decomposed with mineral acid. So prepared, the oleic acid is fairly though not perfectly pure. Pure oleic acid is a colourless, odourless, oily liquid ; but it turns yellow and acquires a rancid odour on exposure to light and air. At 4° it solidifies to needles which melt at 14°. Sp. gr. 0-895 at 15°. If distilled under ordinary pressure it decomposes, sebacic acid, CsH,,(COOH),, being the chief product ; but at 100 mm. it boils unchanged at 286°. It is insoluble in water, freely soluble in alcohol, even when somewhat diluted. Oleic acid is a by-product in the manufacture of candles, in which its presence would be injurious by lowering the fusing-point. It is used in greasing wool for spinning, being much more easily removed by alkalies than is olive oil, which was formerly employed. Fusion with KOH converts oleic acid into acetate and palmitate (see p. 608). This is interesting, as an isomer of oleic acid, CH,(CH,),4CH : CH-COOH, has recently been obtained from a-iodostearic acid and alcoholic KOH. The constitution of oleic acid follows from the fact that when treated with Br it yields a dibromostearic acid, which is converted by alcoholic potash into stearolic acid containing a treble linking. By oxidation stearolic acid yields two acids, each containing Cy; as acids from acetylene alcohols break up on oxidation at the treble linking, stearolic acid must contain that linking between the ninth and tenth C atoms, and this must also be the position of the double bond in oleic acid. With ozone an ozonide (see p. 141) is formed, CH, (CH,),CH_—-CH(CH,),COOH, O=O0=0 612 ACIDS FROM ACETYLENE ALCOHOLS which on heating with water breaks up into nonyl aldehyde, CH;(CH,),CHO, and nonylic acid, CH3(CH,),COOH. By the action of nitrous acid, oleic acid is converted into the stereoisomeric elaidic CH;(CHg),7.CH. acid, (cis-form), which is crystalline, and fuses at 51°. When COOH(CH,)7-CH oxidised by nitric acid, oleic acid yields several acids of the acetic and oxalic series. The alkali oleates are decomposed by much water into free alkalies and insoluble acid oleates. Sodium oleate is present in ordinary soap, and may be crystallised from absolute alcohol. Potassium oleate is the chief constituent in soft soap. Ammonium oleate forms liquid crystals (p. 337). It is sometimes employed as a mordant for the aniline dyes on cotton. Barium oleate is a crystalline powder, insoluble in water, and sparingly soluble in boiling alcohol and in hot benzene, but traces of water assist its solution in benzene ; thus benzene with 5 per cent. of 95 per cent. alcohol is a good solvent. Lead oleate, which forms the chief part of lead plaster, fuses at 80°, and solidifies on cooling to a translucent brittle mass, soluble in ether. Mercuric oleate is used in medicine. Erucic acid, CgH,7-CH : CH[CH,]},,-COOH, occurs as a glyceride in rape oil and in the fatty oils of mustard and grape seed. It fuses at 34°. When heated with phos- phorus and hydriodic acid, it gives behenic acid, Co;H43-CO.H. Heating with HNO, dil. converts it into the stereoisomeride brassidic acid (m.p. 66°). Erucic and brassidic acids are related to one another as are oleic and elaidic. Acids from Monohydric Acetylene Alcohols.—Acids of the general form, C,H2,—,COOH, may be acetylene derivatives, containing trebly linked carbon atoms, or diolefine derivatives, containing two doubly linked carbon atoms (vide infra). The acetylene acids are obtained from the acids of the oleic series by combining them with two atoms of Br to form dibromacetic acids and treating the products with alcoholic potash ; thus, aj/3-dibromopropionic acid yields propiolic acid— CH,Br-CHBr-COOH + 2KOH = CH : C-COOH + 2KBr + 2HOH. They are also obtained by heating monohalogen substituted oleic acids with alkali— CH, : CBr‘COOH + KOH = CH :C-COOH + KBr + HOH. These methods should be compared with those for obtaining acetylenes. Another method consists in heating the alkali acetylides with CO.— CH,;C : CNa + CO, = CH3C : C-COONa. Like the acetylenes, these acids combine with two or four atoms of Br or other monovalent element, and those which contain the group -C : CH yield explosive metallic derivatives (p. 557). Propiolic acid, CH : C-CO.H, corresponding with propargyl alcohol, is prepared, as its potassium salt, by heating potassium hydrogen acetylene-dicarboxylate in aqueous solution ; CO,H-C : C-CO,K = CO, + HC : C-CO,K. It melts at 6°, boils at 144°, and yields explosive metallic derivatives. Just as acety- lene polymerises to benzene (p. 560), so propiolic acid polymerises (in sunlight) te trimesic acid, CgH3(COOH)s. . Tetrolic acid, CH3°C : C-COOH, has no practical importance. It is produced when B-chlorocrotonic acid is heated at 100° with alcoholic potash. It is also formed by heating sodium allylide in carbon dioxide ; m.-p. 76°, b.-p. 203°. Sorbic acid, CH,-CH : CH-CH : CH-COOH, is a diolefinic acid, produced by boiling with acid or alkali the yellow fragrant oil obtained by distilling the juice of unripe mountain-ash berries (Sorbus). By oxidation with KMnO, it yields aldehyde and tartaric acid. Sorbic acid fuses at 134-5°, and is decomposed when distilled, unless in presence of steam. It is sparingly soluble in water, but dissolves in alcohol. Linolic acid, Cy7Hg,;-COOH, occurs as a glyceride in linseed oil, other drying oils, and in small quantity in many non-drying oils. The oil is saponified with KOH, BENZOIC ACID 613 the aqueous solution is precipitated by CaCl, and the calcium linolate extracted by ether. It is a yellowish oil, sp. gr. 0-9206, not altered by nitrous acid. Linolic acid is diolefinic, and forms a tetrabromide, CygH3.02Br,, m.-p. 114°. Palmitolic, homolinolic, and stearolic acids, CsH,7°C : C[CH,],-COOH, are acetylenic metamerides. — Linolenic acid, CygH3902, belongs to the C,H,,—;‘COsH (triolefinic) series of acids. It occurs as glyceride in linseed oil and other drying oils. The Pb and Ba salts are soluble in ether. It forms a hevabromide, m.-p. 180°. Acids from Monohydric Aromatic Alcohols (Aromatic or Benzoic Series).—These may be of two kinds : (1) Acids containing the COOH group attached to the benzene nucleus, such as benzoic acid, CgsH;-COOH, and tolwic acid, C,H ,(CH;)‘COOH. These are obtainable (a) by oxidising the hydrocarbons containing side-chains (p. 566), (b) by oxidising the corresponding alcohols or aldehydes, (c) by the action of sodium and carbon dioxide on the monohalogen substituted hydrocarbons—C,H;Br + CO, + Na, = C,H;COONa + NaBr, (d) by fusing the alkali salts of the sulphonic acids (p. 680) with alkali formate— C,H,;SO,;Na + HCOONa = C,H,COONa + NaHSO,, (e) by hydrolysis of the cyanogen substitution products of the hydrocarbons—C,H,CN + 2HOH= C,H;,COOH + NH,. (2) Acids containing the COOH group as part of the side-chain ; these may be regarded as open-chain acids in which aromatic radicles (C,H; ; C,H,(CH,), &c.) have been substituted for H, as in phenylacetic acid, C,H;-CH,COOH, and _ tolylacetic acid, C,H,(CH,)-CH,-COOH. They may be prepared by hydrolysis of the corresponding cyanogen derivatives—C,H;-CH,-CN + 2HOH — C,H,-CH,‘COOH + NH3. The aromatic acids are crystalline, volatile, sparingly soluble in water, but soluble in alcohol and ether. They show most of the reactions of the fatty acids, and like them are converted into hydrocarbons when heated with lime, which abstracts CO,. Benzoic acid, C,H,-CO.H (phenyl formic acid). This acid was originally extracted from gum benzoin, a resinous exudation from Styrax benzoin, a tree of the Malay Islands. When the gum is gently heated in an iron or earthen vessel, covered with perforated paper and surmounted by a drum of paper, the benzoic acid, which exists uncombined in the resin, rises as vapour and condenses in the drum. A better yield is obtained by boiling the benzoin with lime and water, and decomposing the filtered solution of calcium benzoate with hydrochloric acid. It is also made from the urine of cows and horses, which contains hippuric acid, easily convertible into benzoic acid (see Hippuric acid). Most benzene derivatives—hydrocarlions, alcohols; acids, &¢ —which result from the substitution of a side-chain for one H-atom in the benzene nucleus, yield benzoic acid on oxidation. But the chief source of modern benzoic acid is toluene, C,H,-CH,. This is directly convertible into benzoic acid by oxidation with nitric acid, C,H;-CH, + 2HNO, = C,H,-CO,H + 2HOH + 2NO. It is cheaper, however, to convert the toluene into benzo-trichloride by passing chlorine into it at 180°, and to heat the product with lime ; C,H;-CH; + 3Cl, = C,H;-CCl, + 3HCl; 2C,H;CCl, + 4Ca(OH), = 3CaCl, + (C,H;-CO,),Ca + 4HOH. The calcium benzoate is decomposed by hydrochloric acid, when benzoic acid separates. Much benzoic acid is obtained as a by-product in making benzaldehyde from ‘toluene (p. 597), for much of the benzaldehyde is converted into benzyl alcohol and calcium benzoate by the excess of lime used (p. 598). Benzene, C,H,, may be partly converted into benzoic acid by oxidising 614 ACID RADICLES it with MnO, and H,SO,. Addition of formic acid increases the yield of benzoic acid; C,H, + H-CO,H + O = C,H;-CO,H + H,0. Properties of benzoic acid.—It crystallises in shining needles or in feathery scales, usually having a faint aromatic odour. It fuses at 121° and boils at 249°; it volatilises when boiled with water. It is sparingly soluble in cold water (390 parts), more easily in boiling water (12 parts) ; alcohol and ether dissolve it readily (either, 22 parts). Potash and ammonia also dissolve it immediately, and it is precipitated on adding an acid. Most of the benzoates are soluble, but ferric benzoate is obtained as a buff-coloured precipitate when ferric chloride is added to a neutral benzoate. By distillation with excess of lime, benzoic acid yields benzene— C,H;-CO,H + CaO = CaCO, + CeHe. When vapour of benzoic acid is passed over heated zinc-dust, it is converted into bitter-almond oil (benzoic aldehyde)— C,H;-COsH + Zn = C,H;-CHO + Zn0. By boiling with strong HNO,, benzoic acid is converted into nitro- benzoic acids, C,H,(NO,)-CO,H, of which three exist : o-, m-, and p-. By distilling benzoic acid with PCl;, benzoyl chloride (p. 662) is obtained ; C,H,-COOH + PCI; = C,H;-COC] + POC], + HCl. This chloride bears the same relation to benzoic acid as acetyl chloride bears to acetic acid, the radicles benzoyl and acetyl being related in a similar way to benzyl and ethyl : Ethyl, CH,-CH, ; Acetyl, CH3-CO Benzyl, CsH;-CH, ; Benzoyl, CgH;-CO Ethyl hydride (ethane), CH,-CH3 Benzyl hydride (toluene), CsH;-CH, Ethyl hydroxide (alcohol), CH3-CH,-OH Benzyl hydroxide (benzyl alcohol), C,H;‘CH,OH Acetyl hydride (aldehyde), CH;-CHO Benzoyl hydride (benzaldehyde), C.H;-CHO Acetyl hydroxide (acetic acid), Benzoyl hydroxide (benzoic acid), CH,:CO-0H C,H,-CO-OH Benzoic anhydride, or dibenzoyl oxide, (CgH;-CO).0, is produced by heating benzoyl chloride with dry sodium benzoate— C,H,;COC] + CgH,-COONa = (CgH;-CO),0 + NaCl. The mass is washed with water and the anhydride crystallised from alcohol. It fuses at 42° and boils at 360°. Boiling with water converts it slowly into benzoic acid. 2 By heating benzoyl chloride with dry sodium acetate, benzoacetic anhydride is obtained ; CgH;-COCI + CH,;-COONa = (CgH;-CO)(CH3-CO)O + NaCl. Benzoic peroxide, (CgHs'CO).02, is obtained by acting on benzoyl chloride with barium dioxide; 2C,H,-COC] + BaO,g = (C.H;-CO),0, + BaCl. It may be crys- tallised from ether. Like hydrogen peroxide, it is decomposed explosively when moderately heated. Alkalies resolve it into benzoic acid and oxygen. Toluic acids, or methyl-benzoic acids, CgH4(CH3)-CO2H, are obtained by oxidising the three xylenes, CsH,(CHg)., with dilute nitric acid. The 1: 2-acid crystallises in needles, fusing at 102°, and is sparingly soluble in water. Mesitylenic acid, 1:3: 5-CgH3(CH3)o-CO2H, is prepared by oxidising mesitylene (p. 567), with dilute nitric acid. It is a crystalline volatile acid, fusing at 166° and soluble in boiling water and in alcohol. On oxidation it yields trimesic acid. Cuminic or isopropyl-benzoic acid, 1: 4 —CgH4(C3H,)-CO,H, is prepared from the aldehyde existing in Roman cumin oil, by boiling it with alcoholic solution of potash, which converts it into cuminic alcohol and potassium cuminate. On adding an acid to the aqueous solution of potassium cuminate, the cuminic acid is precipitated, and may be crystallised from alcohol ; it fuses at 117°, and may be sublimed. Phenylolefinecarboxylic acids are those in which the COOH group occurs in. an unsaturated side-chain (p. 567). Cinnamic or -phenyl-acrylic acid, CgH;CH: CH:CO2H, is prepared by boiling PERKIN’S REACTION 615 storax with soda, and decomposing the solution of sodium cinnamate with HCl, which precipitates the cinnamic acid in feathery crystals like benzoic acid, fusing at 133°, ae at 300°, and subliming undecomposed. It is soluble in boiling water and in alcohol. Its connection with acrylic acid is shown by fusing it with potash, which yields acetate and benzoate of potassium, whilst acrylic acid yields acetate and formate ; CgHs'CH : CH-CO,H + 2KOH = CH;-CO.K + C,H,:CO.K + Ho. Oxidising agents convert cinnamic acid into benzoic aldehyde (bitter-almond oil) ; C.H;-CH : CH-CO.H + 20, = CyH;-CHO + 2CO, + H,O. When distilled with excess of lime, it yields cinnamene or phenyl-ethylene (p. 567). Nascent hydrogen converts it into B-phenyl-propionic acid or hydrocinnamic acid ; CsH;-CH : CH-CO,H + 2H’ = C,H,-CH,-CH,'CO,H. Cinnamic acid may be obtained synthetically by heating benzal chloride with sodium acetate— C,H; CHCl, + CH,-COONa = C,H,;'CH : CH:COONa + 2HCl. also by Perkin’s reaction. In this, condensation occurs between an aldehyde and the sodium salt of a fatty acid; thus CsH;CH:0 + H,iCH.COONa = C,H,CH : CH.COONa + HO ; Benzaldehyde. Sodium acetate. Sodium cinnamate. the molecule of water is taken up, if not abstracted, by the anhydride of the fatty acid, which is also added. It appears that an additive compound is first formed, the carbon atom of the aldehyde group attaching itself to the a-carbon atom of the acid (cf. the aldol condensations, p. 595); but water being immediately elim- inated, an unsaturated acid is formed (cf. the condensation of acetaldehyde to crotonic aldehyde, p. 596) ; thus C.H;CHO + CH,COON: e es =e H; : a —> OsHjCHC 2) CgHs-CH : CH.COONa, CH,.COONa A variety of unsaturated acids have been synthesised in this way, see p. 623. So for cinnamic acid: benzaldehyde (30 g.), fused sodium acetate (15 g.), and acetic anhydride (45 g.) are heated together for some hours at 180° ; then the mixture is poured cautiously into water (1 or 2 1.), slightly supersaturated with Na,CO3, boiled rapidly until free from benzaldehyde, filtered, slightly supersaturated with HCl and (the total volume of hot liquid being about 900 c.c.) left to crystallise. Purify the cinnamic acid crystals by redissolving in boiling water (1 1.) and recrystallising. COOH Atropic acid, a-phenyl-acrylic acid, CgH,;:C , is produced when atropine, ‘on, the alkaloid of deadly nightshade, is boiled with baryta or with HCl. It fuses at 106°. The naphthoic acids (a and 3), C,oH7-COjH, are monocarboxylic naphthalenes, obtained by the hydrolysis of the corresponding cyanogen derivatives. Phenyl-propiolic acid, C,H,-C : C-CCOOH, m-p. 136°, obtained by boiling a- or -bromocinnamic acids with alcoholic potash, is of interest on account of its relation to indigo (p. 801). Monobasic Acids from Polyhydric Alcohols.—As already noticed (p. 587), these acids may be alcohol-acids, or aldehyde-acids if the polyatomic alcohol be a glycol, and keto-acids, or even keto-alcohol- or keto-aldehyde- acids, if the alcohol be polyhydric, in which case it must contain both primary and secondary alcohol groups. Alcohol-acids are termed hydroxy-acids, a title which is warranted by the fact that they can be prepared from the chloro-substituted open-chain acids of the foregoing series by treatment with silver oxide and water, showing that OH has been substituted for the Cl, as, for instance, when mono- 616 GLYCOLLIC ACID chloracetic acid is converted into glycollic acid ; CH,Cl:COOH + AgOH = CH,OH-COOH + AgCL It will be found that the hydrogen of the hydroxyl group in a hydroxy- acid can be exchanged for a metal, just as it is in the hydroxyl group of an alcohol, so that the acid possesses the functions of both an alcohol and an acid. Thus, the monobasic hydroxy-acids may contain two or more H atoms, which can be exchanged for a metal, although they are strictly monobasic, since they contain only one CO,H group; hence they are sometimes termed diatomic (triatomic, dc.) monobasic acids. i Of other methods available for preparing hydroxy-acids, one is the oxidation of the polyhydric alcohols; another is the oxidation of fatty acids containing the group R,CH ; such as isobutyric acid, (CH;),CH-COOH, which yelds hydroxyisobutyric acid, (CH;),C(OH)-COOH, when oxidised with alkaline permanganate. Or the olefine acids may be converted by hydrolysis into hydroxy-acids, : - CH, : CH-COOH + H,0 = CH,-CH(OH)-COOH. Again, the amido-acids may be treated with nitrous acid, CH,(NH,)-COOH (amido-acetic acid) + NO-OH = CH,(OH)-COOH + N, + H,0 (ef. p. 207). The general method of hydrolysing cyanogen derivatives is also available ; thus the aldehydes, when treated with HCN, yield cyanohydrins, such as CH,:CH(OH)-CN, and these may be hydrolysed to acids (p. 599).' The simplest hydroxy-acid, hydroxy-formic acid, HO-COOH, would be the first anhydride of orthocarbonic acid (p. 91), carbon dioxide being the second anhydride. It does not exist, probably “for the reason already given (p. 587), but if it did it might be identical with carbonic acid. When copper sulphate solution is added -to a strong solution of potassium car- bonate, a deep blue solution is obtained which is similar to, although less stable than, the solutions obtained by adding copper sulphate to other hydroxy-acids. This supports the supposition that carbonic acid is hydroxy-formic acid. Glycollic or hydroxyacetic acid, CH,OH-CO,H, is a product of the oxidation of glycol, CH,OH-CH,OH, by dil. HNO,, but is best prepared by the careful oxidation of alcohol by nitrie acid. Into a narrow glass cylinder (2 inches in diameter) pour 118 cubic centimetres of 80 per cent. alcohol ; insert a funnel tube drawn out to a fine opening, to the bottom of the vessel, and pour in 50 ¢.c. of water, so as to form a layer below the alcohol ; then pour in carefully through the funnel 126 c.c. of nitric acid of sp. gr. 1-35, to form a layer below the water. Place the vessel aside, without shaking, for about five days at about 20°, when the three layers will have mixed. Evaporate the liquid upon the water- bath, in separate portions of about 20 c.c. to a syrup, dilute it with 10 volumes of water, boil, and neutralise with powdered chalk. To the crystalline paste which forms on cooling, add an equal bulk of alcohol, and filter. The precipitate is boiled with water, and filtered, while boiling, from calcium oxalate. On cooling, the filtrate deposits calcium glyoxalate, whilst calcium glycollate remains in solution ; this is boiled with a little lime to eliminate any glyoxalate, and the filtered solution evaporated and treated with enough oxalic acid to precipitate the calcium as oxalate, leaving glycollic acid in solution. The action of nitric acid upon alcohol is of a representative character. The groups CH, and CH,-OH, contained in ethyl alcohol, are converted under the influence of oxidising-agents into CHO, characteristic of the aldehydes, and COOH, characteristic of the acids respectively. Accord- ingly, we find, among the products of the oxidation by nitric acid, acetic aldehyde, CH,-CHO ; acetic acid, CH,-COOH ; glyoxal, CHO-CHO ; glyoxylic acid, CHO-COOH ; glycollic acid, CH,-OH-COOH ; and oxalic acid, COOH-:COOH. LACTIC ACID 617 - It may be synthesised through formaldehyde and hydrocyanic acid producing the nitrile and subsequent hydrolysis : HCHO + HCN = H-CH(OH)CN *?° H,COH-COOH + NH,. Glycolic acid has been obtained by allowing the vinegar ferment, mycoderma aceti, to grow in a dilute solution of glycol. Properties of glycollic acid—Crystallises with some difficulty; fuses at 80°, and volatilises slowly at 100°. Very soluble in water, alcohol, and ether. Its anhydrides are discussed under lactic acid. As might be expected, oxidising-agents convert it into oxalic acid, from which it may be obtained by reduction. When heated with sulphuric acid it yields formic aldehyde and formic acid; CH,OH-CO,H = H-CHO + H-CO,H. The formic aldehyde is converted into formic paraldehyde, (HCOH)s, and most of the formic acid is decom- posed into H,O and CO. ’ When glycollic acid is heated with HCl it yields chloracetic acid ; CH,0OH-CO,H + HCl = CH,Cl-CO,H + H,0. With PCI, it yields chloracety] chloride, CH,C1-COCI. Hydriodic acid reduces glycollic to, acetic acid—CH,OH-CO,H + 2HI = CH;:CO,H + H,O +1. The glycollates of calcium, copper, and silver are sparingly soluble in cold water but dissolve in boiling water. — Glycollic acid occurs in unripe grapes, and in the leaves of the Virginia creeper. It can be made from glucose by oxidising it with silver oxide, in the presence of calcium carbonate to keep the solution neutral, or else the glycollic acid becomes oxalic acid. , Lactic Acids or hydroxypropionic acids, C,H,(OH)-CO,H.—Since propionic acid is CH,-CH, COOH, there can be two hydroxy-propionic acids; viz. the a-acid, CH,-CHOH-COOH, and the @-acid, CH,OH-CH,-COOH ; the former is called ethylidene lactic acid; and the latter ethylene lactic acid. Ethylidene lactic acid, CH,;CHOH-COOH, is also known as fermenta- tion lactic acid, being the acid of sour milk produced by the fermentation of the milk sugar by the lactic bacillus. As pointed out at p. 607, glucose also undergoes this fermentation, the source of the bacillus in that case being putrid cheese; the chemical change-is expressed by the equation C,H,,0, = 2C;H,O3. On a large scale a mash of starchy material, such as maize, is treated with malt to convert the starch into maltose, and is then mixed with a culture of the bacillus, chalk being stirred in for the purpose of neutralising the lactic acid as it is formed, lest it kill the bacillus. The most favourable temperature ‘is about 50°. When all the maltose has been converted, the solution of calcium lactate is treated with sul- phuric acid, the precipitated CaSO, is filtered off, and the dilute lactic acid is con- centrated in a vacuum pan to a strength of about 50 per cent., in which form it is sold for use as a mordant and as an addition to the tanning liquors in leather factories. Pure lactic acid, obtained by decomposing zinc lactate with H,§, is a colourless, strongly acid liquid which crystallises when cooled, and then melts at 18°. It can be distilled at 120° under 12 mm. pressure, but at higher temperatures it loses water, yielding a much more stable compound, . CH(CH,)CO Tactide, Of Yo, which melts at 125° and boils at 255°. \.CO(CH;)CH It is characteristic of the a-alcohol acids that they yield anhydrides from two molecules by the loss of water derived from the alcoholic groups or from the carboxylic groups, or from both. Thus from two molecules of glycollic acid may be obtained, by loss of one molecule of water, COOH-CH, -O0-CH,COOH (diglycollic acid), CH,OH:CO -O -CO-CH,OH (not known), or CH,OH-CO - 0 -CH,.COOH (glycol- glycollic acid, an ester formed from the acid and the alcohol groups respectively of 618 LACTIC ACID glycollic acid). If the first or second of these lose another mol. H,O the same compound CH,:CO will be formed, namely, of So (diglycollic anhydride) ; from the third, the sub- \cH,-co” traction of another mol. H,O yields glycolide, CH,:CO O O, of which lactide is a \co-cH,” homologue. When lactic acid is heated at 130° with dilute sulphuric acid, in a sealed tube, it yields aldehyde and formic acid; C,H,O-CO,H = CH;-CHO + H-CO,H. Oxida- tion with KMnO, converts this lactic acid into the ketonic acid, pyruvic acid, CH,;-CO-COOH. This is to be expected, since ethylidene lactic acid contains a secondary alcohol group CHOH (see p. 581). Nitric acid oxidises lactic acid to oxalic acid. Chromic acid converts it into acetic acid, CO, and H,O0. Since lactic acid is hydroxypropionic, it may be reduced to propionic acid by strong hydriodic acid ; C,H4(OH)-CO.H + 2HI = C,H;-CO,H + H,O +1. Conversely, propionic acid may be converted into lactic by the following steps : (1) CH,-CH,-CO.H + Br, = CH;-CHBr-CO.H + HBr ; (2) CH,;-CHBr-CO.H + KOH = CH;-CHOH-CO,H + KBr. Lactic acid is producible from aldehyde through its HCN derivative (p. 595). The lactates are mostly soluble; the most important of them is the zinc lactate (C2H;0-CO.)2Zn.3H,O, which is sparingly soluble in water, and is precipitated in prismatic crystals when zinc sulphate is added to lactic acid neutralised by ammonia. Salts of the type CH;-CHOM-CO.M are known: thus sodium sodiolactate, CH;-CHONa-CO.Na, is prepared by the action of sodium on sodium lactate. Ethylidene lactic acid is found in the gastric juice and in opium. Ethylidene lactic acid is also found in juice of flesh (Liebig’s extract of meat), in bile, and in the urine of persons poisoned by phosphorus. This lactic acid has been termed sarcolactic acid or paralactic acid, because it is not identical in all its properties with the fermentation lactic acid described above. The differences between the various forms of lactic acid and their stereoisomerism is fully dealt with at p. 635. Ethylene lactic acid, or 3-hydroxypropionic acid, CH,(OH)-CH,CO,H, is also found in juice of flesh, and is made by treating (-iodopropionic acid, CH,I-CH,'CO,H, with moist silver oxide. Its formula is confirmed by its formation from glycol chlorhydrin, CH,Cl-CH,OH (and therefore from ethylene, p. 588), by conversion into the cyano-hydrin, CH,CN-CH,OH, and hydrolysis of the latter. It is a syrupy mass, and is distinguished from ethylidene lactic acid by yielding no anhydrides, but acrylic acid, CH,:CH-CO,H, and water, when heated; hence it is sometimes called hydracrylic acid. This is characteristic of 6-alcohol acids, which generally yield a@-olefine acids (p. 610) when heated. When oxidised it yields carbonic and oxalic acids instead of acetic. Its zinc salt (4H,0) is very soluble in water. Hydroxybutyric acids are four in number: the a-acid, CHg-CH,-CH(OH)-CO.H, the B-acid, CH,-CH(OH)-CH»-CO.H, the y-acid, CH,OH-CH,-CH,-CO,H, and the a-iso-acid (CH). : C(OH)-CO)H. A fifth, viz. the -iso-acid (CH3)(CH,OH) : CH-CO,H is obviously possible, but is not known. The y-hydroxy-acids are very unstable, and when an attempt is made to liberate them from their salts by addition of a more powerful acid they immediately lose water, becoming ‘intramolecular anhydrides,” or lactones. These are interesting com- pounds, for they may be regarded as internally formed esters (cyclic esters), just as ethyl acetate is an externally formed ester (cf. glycolglycollic acid, p. 617). Thus, CH,:CH,OH CE CEG y-hydroxybutyric acid, | » yields butyro-lactone, | go The ; CH,:COOH CH,:CO acids containing five carbon atoms can yield 6-hydroxy acids and these lose water, HYDROXY-AROMATIC ACIDS 619 forming §-lactones. Both y- and $-lactones are fairly stable, being only partially converted into the corresponding acids by boiling water, but into salts of these acids by alkalies. a-Hydroxycaproic acid, or leucic acid ; see Leucine (p. 712). Ricinoleic acid is a hydroxy-olefinic acid (hydroxyoleic acid) characteristic of castor-oil (Olewm Ricint), of which its glyceride constitutes some 80 per cent. It is remarkable among the acids found in fixed oils in having an asymmetric carbon atom and being optically active. Further, it shows the cis-trans form of stereoisomerism, ricinelaidic acid (produced from ricinoleic acid by nitrous acid) being the isomer. C.H,3CH(OH).CH,CH C,H,3.CH(OH).CH,.CH I CH.(CH,)7.COOH COOH.(CH,),.CH Ricinoleic acid (trans-form). Ricinelatdic acid (cis-form). Pure ricinoleic acid melts at 4°-5° and ‘rotates + 6-67° in a 100 mm. tube ; sp. gr. about 0-95 at 15°. In its preparation and chemical properties it resembles oleic acid. Its glyceride, as castor-oil, is much less soluble in petroleum ether and more soluble in alcohol than any other commonly occurring oil. Polyhydroxy-monobasic Acids. —Glyceric acid, CH,OH-CHOH-CO,H, is a primary-secondary-alcohol-acid ; it has been already mentioned as an oxidation product of glycerol. When produced in this way it is optically inactive, but both an J- and a d- variety have been obtained. A number of polyhydric monobasic acids is produced by the oxidation of the sugars ; these are known as hexonic acids, CH,OH:[CHOH],:CO,H. They are stereoisomerides of each other, being either d- acids, J- acids, or 7- acids. They will receive further notice under the sugars. Aldehyde Acids.—Glyoxylic, or glyoxalic acid, CHO-CO2H, is a product of the oxidation of glycol and of alcohol. It crystallises in prisms and distils with steam. Being aldehydic in nature, it forms a crystalline compound with NaHSO, and reduces silver salts, being thereby oxidised to oxalic acid. Glycuronic acid, CHO-[CHOH],CO.H, is obtained by reducing saccharic acid (q.v.) with sodium amalgam ; it is a syrup which is readily converted into a lactone (see above). Monobasic Acids from Hydroxy-Benzenes.—The OH groups in these acids may be attached either to the benzene nucleus, in which case the acids are phenol acids, not alcohol-acids, or they may occur in the side- chain, in which case the acid is an alcohol-acid ; thus, salicylic acid is a phenol-acid, C,H,(OH)-COOH, whilst phenyl-glycollic acid is an alcohol- acid, C,H;-CHOH-COOH. The most important general reactions for obtaining the phenolic acids are as follows: (1). The sodium phenols are heated with CO, (see salicylic acid). (2) The phenols are boiled with CCl, and KOH; C,H,OH + CCl, + 5KOH = C,H,(OH)-COOK + 4KCl + 3HOH. (Cf. the method for ‘making hydroxy-aldehydes ; p. 598.) (3) The homologues of phenol are oxidised by fusion with KOH ; C,H,(OH)-CH, + 2KOH = C,H,(OK)-COOK + 3H. The alcohol-acids are made by reactions similar to those used in making the paraffin alcohol-acids. Like the alcohol-acids, the phenol-acids yield two classes of salts, e.g. C,H,(OH)-CO,Na, and C,H,(ONa)-CO,Na, the former being produced when the acid 4 is dissolved in Na,CO,, the latter when NaOH is used. Hydroxybenzoic AcidsC,H,(OH)-CO,H.—Being di-substituted benzenes, these are three in wuinber ’ The most important is the 1 : 2-acid or salicylic acid. This is prepared artificially by combining phenol with soda, and heating the product in carbonic acid gas ; Kolbe’s process. 620 SALICYLIC ACID The phenol, with half its weight of NaOH, is dissolved in a little water and evapo- rated to dryness. This sodium-phenol is powdered, placed in a flask or retort, and heated at 100° in a slow stream of dry CO, for some hours. The temperature is then raised to 180°, when phenol distils over, and continues to do so till the temperature has risen to 250° and half the phenol has passed over. The residue is dissolved in a small quantity of water, and strong HCl added to precipitate the salicylic acid, which may be purified by crystallisation from water. By dissolving phenol in soda, sodium-phenol is produced— CsH;-OH + NaOH = C.H;-ONa + HOH. When this is heated in CO,, it yields phenol and sodio-salicylate of sodium ; 2C,H,ONa + CO, = C,H;OH 4+ C,H,(ONa)-CO,Na; this last, decom- posed by HCl, yields salicylic acid— C,H,(ONa):CO,Na + 2HCl = C,H,(OH)-CO,H + 2NaCl. Tf potash be used in place of soda, the product is salicylic acid if heated to 150°, but para-hydroxybenzoic acid at 220°. Salicylic acid was formerly made from oil of winter-green (Gaultheria, a North American plant of the heath order), which is the methyl salicylate, C,H,(OH)-CO,CH, (p. 668). Its original source was salicin, a glucoside extracted from willow-bark, which yields the salicylate when fused with potash. Salicylic acid has been found in the leaves, stems, and rhizomes of some of the Violacee, and in the garden-pansy. Properties of salicylic acid.—It forms four-sided prisms which fuse at 156-85°, and sublime, if carefully heated ; but at a temperature of 200°-220° it decomposes partially into phenol and CO,; C,H,(OH)-CO,H = CO, + C,H;-OH (this change occurs more readily in presence of an alkali, to absorb the CO,), and, losing water also, salol (q.v.) is formed. It dissolves sparingly in cold water (1 in 550), more easily on boiling (1 in 9) and is soluble in alcohol and ether (1 in 2). Its solution gives an intense violet colour with ferric chloride, a reaction not exhibited by the p- and m-hydroxy- benzoic acids. It possesses antiseptic properties, and is used for the pre- servation of articles of food; also in making dyes. Sodium salicylate is a well-known anti-rheumatic. The salicylates of K and Na are crystalline ; barium salicylate (CgH,OHCO,).Ba.Aq, also crystallises, and, when boiled with baryta-water, yields a sparingly soluble salt, CgH40(CO,)Ba.2.Aq, in which the diad Ba is exchanged for the H of the hydroxyl as well as that of the carboxyl. : When POCI, acts upon salicylic acid in xylene solution, water is abstracted and O-C.H,: COO.CgH,:CO salicylide or tetrasalicylide, | | , is formed. This unites loosely : CO-C,H,0.C0.C,H,.0 with 50 per cent. chloroform, as chloroform of crystallisation (p. 324). Anisic acid, or para-methoxybenzoic acid, CsH4(OCH3)-CO.H, is metameric with oil of winter-green, and is formed by the oxidation of its aldehyde, which occurs in oil of anise (p. 599). It may be formed artificially from salicylic acid by heating its potassium salt to 220°, when it yields di-potassium parahydroxy-benzoate, which is converted into potassium anisate when treated successively with methyl iodide and caustic potash— 2(CsH4(OH)-CO,K) = CyH;-OH + CO, + CeH4(OK)-CO.K. C,H,(OK)-CO,K + 2CH,I = CgH,(OCH,)-CO,CH, (methyl anisate) + 2KI ; C,H,(OCH,)-CO,.CH, + KOH = C,H,(OCH;)-COgK (potassium anisate) + CH,-OH. Hydrochloric acid precipitates the anisic acid, which may be dissolved in alcohol and crystallised. It forms prisms fusing at 185° and subliming undecomposed. Hydroxytoluic acids or cresotinic acids CgH3(CH,)(OH)-COOH are ten in number as they are trisubstitution products with 3 different radicles. All the possible isomerides are known, GALLIC ACID 621 Protocatechuic or dihydroxybenzoic acid, CsH,(OH).-CO,H[CO.H : (OH) = 1: 3:4], is prepared by the action of fused caustic soda on the large class of bodies known as gum-resins, and acquired its name from its production in this way from catechu (Cutch or Terra japonica), a substance much used in dyeing black, extracted by boiling water from the inner bark wood of the Mimosa catechu of the East Indies ; kino, a gum-resin exuding from certain Indian and African leguminous plants, and employed in medicine as an astringent, also yields the acid. It crystallises in plates or needles containing H,O, which fuse at 199°, and are soluble in water, alcohol, and ether. Ferric chloride gives a green colour with the acid, which is changed to blue and red by alkalies. When heated, it is decomposed, yielding pyrocatechol ; CgH3(OH).:CO,.H = CO, + CgH,(OH)>. It will be found that the formation of this acid during the potash-fusion of an organic substance often throws light upon its constitution. Vanillic or 3-methyl-protocatechuic acid, CgH3(OH)(OCH3)-CO2H, is produced when vanillic aldehyde (vanillin) is exposed to moist air. It may also be made by oxidising the glucoside coniferin with potassium permanganate. It crystallises in plates, fusing at 211° and subliming unchanged. When heated in a sealed tube with dilute HCl at 160°, it yields protocatechuic acid and methyl chloride ; CgH;(O0H)(OCH;)-CO.H + HCl = CgH;(OH)2‘CO,H + CHCl. Aromatic Paraffin Alcohol-acids.— Mandelic acid or sphenylglycollic acid, C,H,;-CH(OH)-CO,H, is prepared from amygdalin (q.v.) or by the hydrolysis of the hydrocyanic compound of benzaldehyde, CsH;CH(OH)CN. It melts at 133° and is soluble in water. It exists in stereoisomeric forms, which is to be expected from the presence of an asymmetric carbon atom. Trihydroxybenzoic acids.—Of the six possible isomerides gallic acid is the most important. Gallic acid, 3:4:5 — C,H,(OH),-CO,H + is produced by the hydro- lysis of the tannin in gall-nuts (gallotannic acid), C,;,H,0,-CO, + H,O = 2C,H,(OH),-CO,H. It is therefore prepared either by boiling the tannin with dilute sulphuric acid, or by keeping the moistened powdered nut-galls some weeks in a warm place, so that they may undergo fermentation, and extracting the gallic acid with boiling water, from which it crystallises in fine needles containing H,O. It dissolves in 3 parts of boiling water and 100 of cold water. It becomes anhydrous at 100°, and melts at about 220°, yielding a crystalline sublimate of pyrogallol ; C,H,(OH),-CO,H = C,H,(OH); + CO,. Solution of gallic acid is not precipitated by H,SO, or HCl, or by gelatine. Lead acetate precipitates it, but the precipitate is soluble in acetic acid. Alum and potash give a precipitate easily soluble in potash. Copper sulphate does not precipitate it immediately. Ferric salts give a bluish-black precipitate, and the alkalies give a brown-red colour, especially on exposure to air. Gallic acid is found in several vegetable products, some of which are used in dyeing and tanning ; as in divi-divi, the fruit of a leguminous plant (Cesalpinia coriaria), in sumach, in mangoes. Gallic acid may be obtained artificially by heating di-iodosalicylic acid with solution of potassium carbonate to 140° in a sealed tube— C,HeI,(0H)-CO,H + K,CO3; + H,0 = C,H2(OH),-CO.H + 2KI + COs. When gallic acid is heated with 4 parts of strong H,SO, to 75° it gives a dark-red solution ; and if this be cooled and poured into water, a red precipitate is obtained which has the composition C,,4H,03.2Aq, or twice gallic acid, minus 2H,O. This was formerly termed rufigallic acid, but is really hexa-hydroxy-anthraquinone, C,4H»(OH)¢05, for zinc-dust reduces it to anthracene, Cy4Hjp. Ellagic acid, Cy;H;0.CO.H, is obtained by oxidising gallic acid with arsenic anhydride ; it is a yellowish crystalline powder sparingly soluble in water and alcohol. Basic bismuth gallate, CsH,(OH)3;-COOBi(OH)ps, is an antiseptic sold as dermatol. 1 In expressing orientation it is customary to assume that the characteristic group of a@ compound occupies position 1, and to name the positions ofrthe other groups relatively to this. Thus 3: 4: 6-tri- hydroxybenzoic acid means that if the CO,H group has position 1, the OH groups will be 3:4: 5. 622 TANNINS Tannic Acid or tannin.—This name has been applied to a number of plant-constituents, all of which are capable of precipitating gelatine, and therefore of more or less completely tanning hide into leather. They are also characterised by the dark blue or green colour which they give with ferrous salts; hence their use in the manufacture of inks. The tannins apparently occur in the plants as unstable glucosides, and when hydrolysed they are converted into glucoses and monobasic acids which seem to be related to the polyhydroxybenzoic acids. The only tannic acid which can be said to be thoroughly known is that obtained from gall-nuts, and com- monly called gallotannic acid, C;;H,0,-CO,H + 2H,0. 240 grams of powdered gall-nuts are digested for some hours, with frequent shaking, with 1800 cubic centimetres of ether and 150 of water. The mixture is poured into a funnel loosely plugged with cotton, and the filtered liquid allowed to stand, when it separates into two layers, the upper one being the ethereal solution of colouring- matter, &c., and the lower an aqueous solution of tannic acid, which is evaporated to dryness at a low temperature. Gallotannic acid does not crystallise, but is left, on evaporation, in brownish-white shining scales, which are very easily soluble in water, but sparingly in alcohol and in anhydrous ether. Its solution is astringent, feebly acid, and gives a bluish-black precipitate with ferric chloride. H,SO, and HCl combine with it to form white precipitates, and a solution of gela- tine precipitates a very insoluble compound with tannic acid. By hydrolysis gallotannic acid yields gallic acid (p. 621). The view that gallotannic acid is indentical with di-gallic acid— CgH2(OH)3-CO-0-CgH.(OH)2-COOH, ; which represents two molecules of gallic acid minus one molecule of water, and is produced by action of dehydrating agents (e.g. POC], at 130°) on gallic acid, cannot be correct, as tannin is optically active and so must contain an asymmetric C-atom. The constitution does not yet appear to have been settled. Albumin, starch, and most of the alkaloids are also precipitated by tannic acid. Common salt causes the separation of tannic acid from its solution. Lead acetate precipitates it as basic tannate, which is insoluble in acetic acid. Copper sulphate also precipitates it immediately. Alum and potash added to tannic acid give a preci- pitate insoluble in cold potash. Potash or ammonia added to a solution of tannic acid renders it brown, especially if shaken with air, absorption of oxygen occurring. Tannic acid acts as a reducing-agent upon alkaline cupric solutions, producing cuprous oxide. It is decomposed by heat, one of the products being pyrogallol, CgsH3(OH)s. Alcoholic solutions of tannic acid and potash yield a precipitate of potassium tannate, C,3H,O7-CO,K, and if this is dissolved in water, and BaCl, added, bariwm tannate, (CygH g07-CO2).Ba, is precipitated. The tannic acids or tannins used in commerce, in the form of extracts of various parts of plants, are slightly different in properties, and pending exact knowledge as to their constitution, they are distinguished by names implying the sources from which they are derived. Thus, querci-tannic acid is from oak-bark, quino-tannic acid from cinchona bark, caffeo-tannic acid from coffee, moritannic acid from fustic (a yellow dyewood from a tree of the Mulberry order, Morus tinctoria). Sumach, the leaves of the Rhus coriaria, a tropical plant of the Cashew order and Myrobalans, the fruit of several species of Terminalia, Indian trees, contain gallotannio acid. Myrobalans also contains ellagitannic acid, very similar to gallotannic acid, and likewise contained in divi-divi. The tannins may be classified into pyrogallol-tannins and pyrocatechol tannins, accordingly as they yield pyrogallol or pyrocatechol when heated. Those belonging to the first class yield gallic and ellagic acids when heated with alkalies, whilst those of the latter class yield protocatechuic acid, and either phloroglucol or acetic acid, by the same treatment. The deposit of ellagic acid which is formed by the oxidation of pyrogallol tannins is probably the ‘‘bloom” noticed by tanners on the surface of leather prepared by means of materials such as myrobalans, sumach, and divi-divi, ACIDS OF THE OXALIC SERIES 623 The pyrocatechol tannins are liable to deposit complex anhydrides termed phlo- baphenes,! which have a red colour ; such are the tannins of oak bark, mimosa, and valonia. Quinic or kinic acid, or hexahydrotetrahydroxybenzoic acid, CgH;(OH),4:COH, is a hydroxy-acid from hexahydrobenzene (p. 568) found in cinchona bark, in coffee and some other plants. It is crystalline, soluble, and melts at 162°. It gives pyrocatechol when distilled, and protocatechuic acid when fused with KOH. When heated with MnO, and H,SO,, it is oxidised to quinone, which sublimes in yellow needles, Hydroxyphenyl-Fatty and Olefine Acids.—These-may be regarded as phenols in which a nucleal H atom has been exchanged for an open-chain acid radicle. There are three position isomerides of each of the monohydroxyacids. 1: 2-Hydroxyphenylacetic acid, CgsH,(OH)-CH,-COOH, melts at 137°, and is important as a relative of indigo. 1: 2-Hydroxy- 3-phenylacrylic acid or 1: 2-hydroxycinnamic acid— CgH,4(OH)-CH : CH:‘COOH commonly called coumaric acid, is obtained from 1 : 2-amidocinnamic acid— C.H,(NH,)-CH : CH:COOH through the diazo-reaction; it melts at 208°. Its salts are also obtained from coumarin by heating it with alkalies. Coumarin is the lactone of coumaric acid, O——CO CHA | , and is the substance which causes the smell of hay and of the NCH : CH Tonka bean (Coumaroma odorata) from which it may be extracted by boiling with alcohol, when crystals of coumarin are deposited on cooling. It is made artificially by heating salicyl aldehyde with sodium acetate and acetic anhydride (cf. Perkin’s reaction, p. 615). The salts from coumarin are however isomeric with those prepared from coumaric acid, the origin of the isomerism being still unknown. Caffeic acid, or dihydroxy-cinnamic acid, CgH3(CH : CH-CO,H)(OH)s, [3: 4:1], is obtained by boiling with KOH the residue left on evaporating the aqueous decoction of coffee, and precipitating the solution by HCl; also by Perkin’s reaction. It cry- stallises in plates (m.p. 213°) on cooling, and is soluble in alcohol. It yields pyro- catechol when heated, and is converted into acetate and protocatechuate when fused with KOH. Piperic Acid is derived from a 3: 4-dihydroxyphenyldioletine acid, dihydroxy- cinnamenylacrylic acid, by substituting methylene, CH»g, for the two H atoms of the two OH groups; hence its formula is 3: CHC CyHa CH : CH-CH : CH-COOH. 0 Tt melts at 217° and is found as a derivative of piperidine (7.v.)in pepper. (Also p. 599.) Dibasic Acids from Paraffin Hydrocarbons (Oxalic or Succinic Series), C,H,,(COOH),.—These acids may be regarded as derived from the hydrocarbons by substitution of two COOH groups for two H atoms. They are oxidation products of diprimary glycols, as might be expected (p. 587), and are also obtainable by nucleal condensation from the fatty acids, as for instance when bromacetic acid is treated with metallic silver, producing succinic acid : HOOC-CH,'Br + Ag, + Br'(CH,-COOH = HOOC-CH,-CH,-COOH + 2AgBr. These methods are not much used, however; more important is the introduction of the CN group into a fatty acid and hydrolysis of the product. Thus, hydrolysis of cyanacetic acid, obtained from chloracetic acid by action of KCN, yields malonic acid : CH,Cl.COOH —+ CH,CN-COOH -—-+ CH,(COOH), (cf. p. 599). An analogous method is the hydrolysis of the dicyanides of the olefine radicles, CH,CN:CH,CN yielding succinic acid, for example. 1 drovds, bark ; Bay, dye. 624 OXALIC ACID Isomerism among these acids is like that among other disubstituted paraffins (p. 580). COOH The typical members of the series are malonic acid, CH, P ‘COOH. and succinic acid, CH,COOH | Acids like the former, in which the two CH,COOH carboxyls are attached to the same carbon atom, break up when heated with formation of CO, and an acid of the acetic series. Acids of the succinic type, in which the carboxyls are attached to different carbon atoms, lose CH, COW water and yield internal anhydrides, like | YO: when heated ; CH,-CO this behaviour, however, is not shown by acids in which the COOH groups are separated by more than three CH, groups. Both types lose CO, when fused with KOH, yielding an acid of the acetic series. Oxalic acid, (CO,H),, is the final product of the oxidation of glycol, and one of the products of the hydrolysis of cyanogen, CN-:CN + 4HOH = COOH-COOH + 2NH;,. It is prepared on the small scale by oxidising sugar with nitric acid, and on the large scale by oxidising sawdust with potash. Preparation of oxalic acid from sugar.—50O grams of sugar are gently heated in a flask with 250 c.c. of ordinary concentrated nitric acid, sp. gr. 1-4. After the action commences, remove the heat, when the oxidation will continue violently. On cooling, part of the oxalic acid crystallises, and more is obtained by concentrating the mother-liquor. Drain the crystals on a funnel, and dissolve them in as little boiling water as possible, so as to purify the acid by recrystallisation. It may be allowed to dry by exposure to air. Preparation of oxalic acid from sawdust.—Common pine sawdust is made into a thick paste with a solution containing KOH + 2NaOH of sp. gr. 1-35. This is spread on iron plates, dried up, and heated just short of carbonisation. Oxygen is readily absorbed from the air. The cellulose, C,H, )0;, is thus oxidised, with evolution of hydrogen, and converted into oxalic acid, which remains in the mass as oxalates of potassium and sodium. These are dissolved in water, and boiled with lime, which produces the insoluble calcium oxalate, together with solution of the caustic alkalies, which may be used again. The calcium oxalate is decomposed by dilute sulphuric acid, the solution of oxalic acid filtered from the calcium sulphate and crystallised. Strictly speaking, in carrying out this process, the fused mass is treated with a small quantity of hot water, which leaves the bulk of the sodium oxalate undissolved ; this is decomposed by lime, as stated above. The liquor, which contains but little oxalate, is boiled to dryness, the residue heated, and the alkaline carbonate causticised by lime. It is worth noting that caustic soda alone would produce very little oxalate. When potash is cheap, it may be used alone. Oxalic acid occurs in sorrel, rhubarb, and many other plants. Potas- sium oxalate is formed when potassium formate is gently heated ; 2(H-CO-OK) = H, + (CO,K),. Sodium oxalate is synthesised when sodium, mixed with sand to moderate the action, is heated at 360° in dry CO,; Na, + 2CO, = (CO,Na)p. Properties of oxalic acid.—It forms monoclinic prisms containing 2Aq, which are soluble in nine parts of cold water and in alcohol. It is a very strong acid, able to decompose the nitrates and chlorides. It is poisonous. When gently heated, the crystals effloresce, from loss of water, and begin to vaporise slowly at 100°. When sharply heated the crystallised acid melts at 101° and the anhydrous at 189°. At 165° it sublimes freely, part being decomposed into formic acid and CO,; (CO,H), = H-:CO,H + COsg. A weak solution of oxalic acid is decomposed by boiling. When heated OXALATES 635 with strong sulphuric acid, (CO,H), = CO, + CO + H,0, the CO burning on applying a flame. From twelve parts of warm oil of vitriol the acid crystallises in large rhombic octahedra, which are anhydrous. Oxalic acid, free and as its salts, is largely used in dyeing, calico-printing, and bleaching, in cleaning brass, and in removing ink and iron stains from linen. Normal potassium oxalate, (CO,K):.Aq, is moderately soluble in water. Hydro- potassium oxalate, or potassium binoxalate, or salt of sorrel, is (COj),.KH. It is also called salt of lemons, though lemons contain no oxalic acid. It dissolves in 40 parts of cold water, and has occasionally caused accidents by being mistaken for cream of tartar, potassium hydrogen tartrate, from which it is readily distinguished by the action of heat, which chars the tartrate, but not the oxalate. Trihydropotassium oxalate, or potassium quadroxalate, (COg),H,K.2Aq, is more commonly sold as salt of sorrel, and sometimes as salt of lemon. It is even less soluble than the preceding. Sodium oxalate, (CO2,Na)o, is found in various plants which grow in salt marshes, It is less soluble than potassium oxalate. The alkali oxalates, when heated, evolve CO and leave carbonates, (CO.K). = CO + CO(OK)p,. Ammonium oxalate, (CO,NH,)s.Aq, occurs in Peruvian guano. It is used in analysis for the precipitation of calcium, and crystallises, in needles, from solution of oxalic acid neutralised with ammonia. Calcium oxalate, (CO.).Ca.Aq, is often found crystallised in plant-cells. Some lichens growing on limestones contain half their weight of calcium oxalate. It is occasionally found in urine and in calculi. Calcium chloride is the. best test for oxalic acid, giving a white precipitate insoluble in acetic acid. When heated, (CO,)oCa == CO + CaCQs. Ferrous oxalate, (COz).Fe, occurs as oxalite in brown coal. Ferric oxalate, (COz)gFes, when exposed to sunlight in presence of water, evolves COs, and deposits a yellow crystalline precipitate of (CO,)2Fe.2Aq. Ferric oxalate is used in photography. The ferrous salt is brown and the ferric green, the reverse of the usual order. Potassium ferrous oxalate, (COo)4KyFe, prepared by adding potassium oxalate in excess to ferrous sulphate, is a very powerful reducing-agent, used as a photographic developer. Potassium chromic oxalate, (COz)gK3Cr.3Aq, is obtained in crystals so intensely blue as to look black, by dissolving in hot water 1 part of potassium dichromate, 2 parts of hydropotassium oxalate, and 2 parts of oxalic acid. Neither the oxalic acid nor the Cr,O, can be precipitated from this salt by the usual tests. Potassium calcium chromic oxalate, (COg)g.KCaCr.3Aq, is soluble in water, and gives a precipitate of calcium oxalate on adding calcium chloride. Barium chromic oxalate, (CO2);2Ba3Cr2.8Aq, is also a soluble salt, and, when decom- posed by sulphuric acid, yields a red solution which probably contains the acid (COs)2H Cre or H3(COz)gCr-Cr(CO2) gH. Potassium antimony oxalate, (COz)gsK,8b.6Aq, obtained by dissolving precipitated Sb,O, in hydropotassium oxalate, is used in fixing certain colours. Silver oxalate, (CO,Ag)o, is obtained as a white precipitate when silver nitrate is added to an oxalate. It explodes slightly when heated, leaving metallic silver. Manganese oxalate, (COz)2Mn, is used for mixing with drying-oils. Oxidising-agents easily convert oxalic acid into water and CO,; if a hot solution of the acid be poured on manganese dioxide, brisk effervescence is caused by the CO, produced. A similar result ensues if manganese dioxide be added to the mixture of an oxalate with dilute sulphuric acid. Nascent hydrogen reduces oxalic acid to glycollic acid ; (CO.H), + 4H° = CH,(OH)*CO,H + H,0. Malonic acid, CH,(COjH),, is prepared from chloracetic acid, CH,Cl-CO,H, by converting it into the potassium salt, and boiling this with potassium cyanide, when potassium cyanacetate, CH,(CN ):CO2K, is formed. This is boiled with potash, which converts it into potassium malonate ; CH,(CN)-CO,K + H,O + KOH = CH,(CO,K). + NHy. The excess of potash is neutralised by HCl, and calcium chloride added, which precipi. 40 626 SUCCINIC ACID tates calcium malonate ; by boiling this with the molecular proportion of oxalic acid, the calcium is left as oxalate, and the solution deposits tabular crystals of malonic acid. It fuses at 132° and afterwards decomposes into CO, and acetic acid ; CH,(CO,H), = CO, + CH;-CO,H. It will be remembered that oxalic acid is dessin: posed into COg, and formic acid, H-CO,H. Calcium malonate, like the oxalate, is very slightly soluble in water, and is found in the sugar beet ; the silver and lead salts are insoluble. Malonic acid is found among the products of oxidation of allylene, amylene, and propylene with potassium permanganate. The other acids of the malonic acid type are alkyl substitution derivatives of malonic acid, and may be built up therefrom by the treatment of its ethereal salts first with a sodium alkyloxide and then with an alkyl iodide. The series of reactions and their import have been given at p. 600. Methylmalonic acid, CHy-CH(COOH)s, is ethylidene succinic acid, isomeric with succinic acid, which is an ethylene derivative ; hence it is called tsosuccinic acid. It is prepared by hydrolysis of a-cyanopropionic acid, and from ethyl sodiomalonate and methyl iodide (see above). It should also be obtainable by treating ethylidene bromide, CH,-CHBr,, with KCN and hydrolysing the cyanide, but this leads to ordinary succinic acid. It melts at 130°, and decomposes into CO, and propionic acid. Succinic acid, C.H4(COjH)», is ethylene succinic acid, and occurs ready formed in amber, from which it was originally obtained by distillation. It is prepared by the fermentation of tartaric acid, which may be regarded as dihydroxysuccinic acid, C3H,(OH)s(CO2H)2, and becomes reduced to succinic acid. The tartaric acid is neutralised with ammonia, largely diluted, and mixed with a little potassium phosphate, magnesium sulphate, and calcium chloride, to afford mineral food for the bacteria, which soon grow if the liquid be kept warm (25°-30°). The flask should be loosely closed to exclude air. After about two months, the ammonium tartrate has become ammonium succinate and carbonate; it is boiled to expel the latter, milk of lime added, and again boiled as long as NH is expelled; the calcium succinate is decomposed by a slight deficiency of dilute H.SO,, the liquid filtered from the CaSO, and evaporated. Succinic acid crystallises in prisms, which require about 20 parts of cold or 3 parts of hot water to dissolve them. It dissolves in alcohol, but sparingly in ether. When heated, it emits vapour at 120°, fuses at 185°, and at 235° distils as water and succinic CH,:CO anhydride, | So ; the vapours provoke coughing in a remarkable way, thus CH,-CO” x affording a test for the acid. It is very stable and little affected by oxidising-agents. Fusion with KOH converts it into carbonate and propionate ; C,H,(CO.H), + 3KOH = CO(OK), + Cy.H;-CO,K + 2H,0. Calcium succinate, CzH4(COg).Ca.3Aq, is somewhat sparingly soluble in water ; it occurs in the bark of the mulberry-tree. Basic ferric succinate, Fe’’’o(CyH,O4)’’o(OH)’s, is precipitated when ferric chloride is added to a succinate ; it has a rich brown colour, and its production forms a good test for succinic acid, and is useful in quantitative analysis for separating Fe from Mn and some other metals. Malic acid is hydroxysuccinic acid, and is reduced by fermentation to succinic acid. Both malic and tartaric acid are reduced to succinic acid by the action of hydriodic acid. Succinic acid has been obtained synthetically by boiling ethene dibromide with potassium cyanide dissolved in alcohol, and boiling the ethene cyanide thus obtained with KOH dissolved in alcohol. C.H,Bry + 2KCON = C.Hy(CN). + 2KBr; and C2H4(CN). + 2KOH + 2H,0 = CyHy(CO.K). + 2NH3. Succinic acid is always produced in small quantity in the fermentation of sugar, and is therefore always present in beer, wine and vinegar. It is also produced when nitric acid oxidises fatty acids containing four or more carbon atoms. It occurs in unripe grapes, whilst ripe grapes contain tartaric (dihydroxysuccinic) acid. It is found in several plants, such as lettuce, poppies and wormwood, and in certain lignites. It has also been found in the urine of the horse, goat and rabbit. When electrolysed, succinic acid yields CgH,, CO, and H, as might be expected -from its formula, C2H,(CO.H)>. FUMARIC AND MALEIC ACIDS 627 Methylsuccinic acid, COOH-CH(CH;)-CH,-COOH, is also called pyrotartaric acid because it is formed by distilling tartaric acid (mixed with powdered pumice to diffuse the heat). The distillate is mixed with water, filtered, evaporated on the water-bath and crystallised from alcohol, It is formed from propene as succinic acid is from ethene, and crystallises in prisms which melt at 112° and decompose into water and the anhydride. Having an asymmetric carbon atom it occurs in stereoisomeric forms. Glutaric acid, COOH-CH,-CH,‘CH,-COOH, isomeric with pyrotartaric acid (and with ethylmalonic acid and dimethylmalonic acid) melts at 97°, and is obtained from trimethylene bromide (p. 659) through the KCN reaction. It yields an anhydride when heated. The higher acids of this series do not yield anhydrides ; the chief are: Adipic, CyHs(COOH)., from oxidation of oleic acid; m.+p. 153° Pimelic, C;H,9(COOH), 7 ' a is 105° Suberic, CgHy2(COOH), 5 i cork - 140° Azelaic, CrH,4(COOH), 33 35 castor oil Cs 106° Sebacic, CgH,g(COOH), », distillation of oleic acid 6 133° Brassylic, CyyH2(COOH)» », oxidation of erucic acid 5 114° Rocellic, Cy3;H39(COOH). » Rocella tinctoria 53 132° Dibasic Acids from Olefine Hydrocarbons, C,H,,—,0,.—The acids of this series are unsaturated, like those of the acrylic series, and can therefore combine with two atoms of bromine to become dibromo- derivatives of the acids of the preceding class, or with two atoms of hydrogen to become the acids of that class. Conversely, acids of this series are obtained by treating with KOH the dibromo-acids of the succinic series. The first member of the series has the formula C,H,(CO,H),, and might obviously exist in two forms, CO,H-CH : CH:COsH and CH, : C(CO,H),. The two acids fumaric and maleic, both of which have the molecular formula CO,H-CH : CH:CO,H are stereoisomerides. The acid CH, : C(COOH),, methylenemalonic acid, is known only in the form of its esters. Fumaric acid, C,H,(CO2H)., is obtained by heating malic acid at 150° as long as water distils over ; C,H,(OH)(CO.H). = C2.H,(CO.H). +H,O. The residue is treated with cold water, in which fumaric acid is almost insoluble, to extract unaltered malic acid, and the fumaric acid is crystallised from hot water or alcohol. At 200° it partly sublimes undecomposed, and the rest decomposes into water and maleic anhydride. Heated with much water at 150° it is reconverted into malic acid. NaOH at 100° slowly converts it into sodium malate. Nascent hydrogen, from water and sodium- amalgam, converts it into succinic acid, C,H,(CO,H),. Hydriodic acid effects the same change, iodine being liberated. The fumarates of barium, calcium, and lead are sparingly soluble. Silver fumarate is very insoluble, and explodes when heated. The alkali fumarates, when electrolysed, yield C,H2, CO, which forms a carbonate, and H thus justifying the formula given for the acid. Fumaric acid is found in several plants, especially in fumitory, Iceland moss, truffles, and other fungi, Fumaric acid is not oxidised by boiling with nitric acid. Maleic acid, isomeric with fumaric acid, is produced when malic acid is quickly distilled. It is crystalline, melts at 130° and is easily decomposed by heat into water and maleic anhydride. It differs from fumaric acid by its ready solubility in cold water, by the solubility of its barium and calcium salts, and by its unpleasant taste. It is con- verted into fumaric acid if heated ina sealed tube at 200°, or if boiled with dilute acids. For the stereoisomerism of these acids the reader is referred to p. 638, where its connection with that of tartaric acid is explained. Citraconic (m.-p. 91°) and mesaconic (m.-p. 202°) acids, CsHy(COOH)s, are homo- logues of maleic and fumaric acids, the former being methylmaleic acid, while the latter is methylfumaric acid ; see also p. 633. Thus they have the same relationship to each other as maleic and fumaric have. Citraconic acid, being the cis-form, yields an anhy- dride which is found in the products of destructive distillation of citric acid together with the anhydride of itaconic acid (m.-p, 161°), another isomeride which is methylene 628 PHTHALIC ACIDS succinic acid, COOH-CH,-C (: CH,)‘COOH ; hence these acids were formerly termed pyrocitric acids. If citraconic acid be heated for some time with dilute HNO; or strong HCl, it is converted into mesaconic acid. Mesaconic dissolves in about 40 parts of cold water, itaconic in about 20 parts, and citraconic in 1 part. All three are reduced by nascent H to pyrotartaric acid. They combine with the haloid acids to form isomeric substitution-products of pyrotartaric acid. Of the dibasic acids from the acetylene hydrocarbons, acetylene dicarboxylic acid, CO,H-C : C-CO,H, need alone be noticed. It is produced by heating dibro- mosuccinic acid, C,H,Br,(COjH),, with alcoholic potash, whereby 2HBr are removed. It crystallises with 2H,O, and decomposes when fused. Dibasic Acids from Aromatic Hydrocarbons.—These are obtained by oxidising benzene hydrocarbons containing side-chains. Thus, the most important of them, the three phthalic acids, CsH,(COOH),, can be prepared by oxidising the three xylenes, C,H,(CH;), and indeed most other disubstituted benzenes in which carbon is attached directly to the nucleus. 1:2-phthalic acid is the most important isomeride and is charac- terised by yielding an anhydride when heated, owing, no doubt, to the fact that the COOH groups are in the adjacent positions. It is made in large quantity, for the manufacture of dye-stuffs, by oxidising naphthalene with strong H,SO, in presence of mercury. On a small scale naphthalene tetrachloride is oxidised with HNO 3. 1 part of CyoHg is carefully mixed, on paper, with 2 parts, by weight, of KClO3, and added, in small portions, to 10 parts of strong HCl. The naphthalene tetrachloride, CypHgCly (p. 571), thus formed, is washed with water till free from acid, and allowed to dry. It is introduced into a flask and treated with strong HNO, (sp. gr. 1-45), which must be very gradually added, amounting to ten times the weight of naphthalene taken. The mixture is heated till all is dissolved, the nitric acid boiled off, and the residue distilled, when phthalic anhydride distils over and is converted into phthalic acid by dissolving fr~, COOH in hot water and crystallising ; CoH go + H,0 = CoHac . co COOH Phthalic acid crystallises in rhombic prisms or plates, which melt at 213°, and readily decompose into water and anhydride. It is sparingly soluble in cold water, but dissolves readily in hot water, in alcohol, and in ether, but not in chloroform ; it is not volatile with steam. With NH; and BaCl, it yields a precipitate of barium phthalate. When heated with lime to 340° it yields benzoate and carbonate of calcium. Chromic acid oxidises phthalic acid completely into CO, and H,0. Phthalic anhydride crystallises in long prisms, m.-p. 128°; b.-p. 284°; soluble in alcohol and benzene, slightly in water. It is used in making eosin dyes. 1: 3-Phthalic acid or isophthalic acid crystallises in needles ; it is soluble in hot water, is not precipitated by BaCl, in presence of NH3, and yields no anhydride when heated, but sublimes unchanged. 1:4-Phthalic acid, or terephthalic acid, is difficult to crystallise, and is insoluble in water, so that it is precipitated from its solutions in alkali by adding acid. The barium salt is sparingly soluble. The acid sublimes unchanged. These differences in the properties of the three phthalic acids are of importance, since the production of one or other of the acids frequently serves to decide the constitution of a benzene derivative. By treating the phthalic acids with nascent hydrogen a large number of hydrogen- addition products, hydrophthalic acids, e.g. CgHy-Hy(COOH)s, has been obtained. These are remarkable for the numerous cases of isomerism which they exhibit ; the cause of this has been traced, first, to the existence of cis- and trans-forms, as in thé case of maleic and fumaric acids, and secondly, to the different positions of the double linking between the carbon atoms of the benzene nucleus; eg. the two dihydrotere- phthalic acids (cf. p. 568), CH,-CH COCK Se-coyn and COCK CH-CH, \\CH-CH CHy CH po Oud. MALIC ACID 629 Naphthalic acids are dibasic acids from naphthalene, C,»Hg(CO,H).; six out of ten possible isomerides are known. Dibasic Hydroxy-acids.—These may be regarded as oxidation-products - of diprimary polyhydric alcohols, or, in the case of those containing a benzene nucleus, as dicarboxylic acids from phenols. Tartronic or hydroxymalonic acid, CH(OH)(CO,H)2, is formed by the action of nascent hydrogen on mesoxalic acid (see below), which is a product of the oxidation of uric acid. Its crystals melt at 158° and are then decomposed into water, CO,, and an amorphous polymer of glycolide (p. 618). Tartronic acid was first obtained by heating solution of dinitrotartaric acid ; C.H2(ONO,)o(CO2H), = CH(OH)(COzH). + N,03 + COx. It is also formed when glucose is oxidised by an alkaline cupric solution, and when glycerin is oxidised by KMnQ,. Barium tartronate, from which the acid is readily obtained, may be prepared by heating flyoxalic acid with potassium cyanide and baryta- water— CHO-CO,H + KCN + Ba(OH), + HOH = CH(OH)(CO,).Ba + KOH + NH;. Mesoxalic acid is regarded by some as dihydroxymalonic acid, C(OH)2(CO2H)., but since this compound contains two OH groups attached to one carbon atom, it is more probable that the acid is a ketonic acid of the form CO(CO,H), + HO, a view supported by the fact that it forms a compound with NaHSO3, and combines with hydroxylamine (see Ketones). It is best obtained by boiling alloxan (q.v.) with baryta water. It crystallises in deliquescent prisms with 1H,O, and melts without loss of water at 115°. Malic, or hydroxysuccinic acid, COOH:CH,-CHOH-COOH, is one of the chief natural vegetable acids, occurring in apples, gooseberries, currants, &c. It will be noted that its alcoholic C atom is asymmetric, hence it is known in the usual three optically isomeric forms (p. 636). Strong solutions of the natural acid are dextro-rotatory, though when diluted they are levo-rotatory ; a 34-24 per cent. solution is inactive. It is extracted from the juice of the unripe berries of the mountain ash. The juice is boiled, filtered, nearly neutralised with milk of lime, and boiled, when calcium malate, C2.H,(OH)(COg).Ca.Aq, is precipitated in minute crystals. This is dissolved to saturation in hot nitric acid diluted with ten times its weight of water. On cooling, crystals of hydrocalcium malate, [C.H;(OH)(CO.H)-CO,],Ca.8Aq, are deposited. These are dissolved in hot water, and decomposed by lead acetate, when lead malate is precipitated ; this is suspended in water, and H,S passed, when PbS remains precipitated, and malic acid is found in solution, from which it crystallises, though not very readily, in tufts of deliquescent needles. By boiling bromosuccinic acid, C,H;Br(COOH),:, with AgOH (silver oxide and water) the Br is exchanged for OH and inactive malic acid is produced, and so syn- thesised. The active forms are separated by crystallising the cinchonine salt of the inactive acid (cf. p. 637). The d- and I-acids are also obtained by reducing the tartaric acids (g.v.), of corresponding activity, with HI. The acid melts at 100° and at a higher temperature yields a feathery, sublimate of maleic and fumaric acids and of maleic anhydride. Oxidation with chromic acid converts it into malonic acid, fusion with potash into oxalate and acetate. Hydricdic acid reduces it to succinic acid : C,H;(OH)(COOH), + 2HI = C,H,(COOH), + H,O + Ip. Some of the salts of malic acids occur in nature. Cherries and rhubarb contain acid potassium malate, CzH,(OH)(CO,H)(CO,K), while tobacco contains acid calcium malate. Normal calcium malate is less soluble in hot water, and is therefore preci- pitated on neutralising the acid with lime-water and boiling. Lead malate forms a white precipitate containing 3Aq., distinguished by fusing under water to a gummy mass, becoming crystalline on cooling. Tartaric or dihydroxysuccinic acid, CO,H-CHOH-CHOH-CO,H, is one of the most important vegetable acids, and is often found in fruits 630 TARTARIC ACID associated with malic acid. It is prepared from argol or tartar, a crude form of acid potassium tartrate, C,H,(OH),(COOH)(COOK), deposited in crystalline crusts during the fermentation of grape-juice. This (45 ounces) is boiled with (2 gallons) water, and neutralised by adding (125 ounces) powdered chalk, which converts the hydropotassium tartrate of the argol into calcium tartrate and potassium tartrate— 20,H,O,KH + CaCO, = CyH,O,Kp + CyH,O,Ca + H,0 + COp. The potassium tartrate dissolves and the calcium tartrate precipitates. Solution of calcium chloride (134 oz. dissolved in 2 pints of water) is then added, to precipitate the potassium tartrate as calcium tartrate ; CyH,O,Ky + CaCle = CyHyOeCa + 2KCh. The calcium tartrate is strained off, washed, and heated for half an hour with dilute sulphuric acid (13 fluid ounces of acid in 3 pints of water), when calcium sulphate remains undissolved, and tartaric acid may be crystallised by evaporating the filtered solution ; CyH,O,Ca + H,SO, = C,H,OgH, + CaSO, The crude acid is dissolved in water, decolorised by animal charcoal, and again crystallised. A little sulphuric acid is generally added to promote the formation of large crystals. These often contain lead derived from the evaporating pans. a Properties of tartaric acid.—The crystals are monoclinic prisms, very soluble in water, and fairly so in alcohol, but nearly insoluble in ether. When heated rapidly to 170° it fuses, and becomes an amorphous deliques- cent mass of metatartaric acid, isomeric with it. At 145° it becomes tartralic acid, CsH,)0,;, two molecules of the acid having lost a molecule of water ; at 180° it yields tartaric anhydride, CsH,O,9. All these may be re-converted into tartaric acid by digestion with water. On further heating, it undergoes destructive distillation, yielding chiefly pyruvic and pyrotartaric acids, together with dipyrotartracetone, CsH,,0,, which has a peculiar odour, like that of burnt sugar, by which tartaric acid may be recognised. Tartaric acid exists in four stereoisomeric forms: meso-, dextro-, lcevo- tartaric acids, and the inactive mixture of the last two, known as racemic acid. These are fully discussed in the chapter on Stereochemistry (p. 633). Natural tartaric acid is dextro-rotatory and when heated with HI, in strong aqueous solution, at 120°, in a sealed tube, it is reduced to dextro- malic acid, which is again reduced to succinic acid— C,H,(0H)9(CO;H), -+ 2HI = C,H,(OH)(COjH). (malic acid) + H,O + I, And C,H;(OH)(CO,H), + 2HI = C.Hy(CO,H), (succinic acid) + H,O + Ih. Conversely, tartaric acid can be obtained by the treatment of dibromo- succinic acid with moist silver oxide, and thus synthesised. A technical synthetic process is to heat glycerol with PbO, —-> lead glycerate, and treating this with KOH —~> CH,OH.CHOH.COOK (potassium glycerate), then with CO, at 3 atm. —+ C(COOH)HOH.CHOH.COOK (cream of tartar). Fused KOH converts tartaric acid into acetate and oxalate. Boiled with nitric acid, much of it is oxidised to oxalic acid. Distilled with sul- phuric acid and MnO,,or K,Cr, O,, it yields formic acid and CO,. Salts of Tartaric Acid.—A distinguishing character of tartaric acid is the sparing solubility of the acid potassium tartrate (CHOH),COOH.COOK, which is precipitated in minute crystals when almost any potassium salt is added to tartaric acid, and the solution is stirred with a glass rod, when the precipitate attaches itself at the lines of friction. Commercially this salt is known as cream of tartar, and is prepared by recrystallising argol from hot water, which dissolves ,th of its weight, and retains only ,4,th on cooling. It is nearly insoluble in alcohol, which precipitates it from the aqueous solution, and this explains its separation from the grape-juice, as the proportion of alcohol increases during the fermentation. It dissolves easily in acids and in alkalies, which convert it into normal tartrate, (CHOH).(COOK),. When heated, it .evolves the burnt-sugar odour, and leaves a black mass of charcoal and potassium carbonate (salt of tartar). TARTAR EMETIC 631 Sodio-potassium tartrate, (CHOH),COOK.COONa.4Aq, Rochelle or Seignette’s salt, is prepared by neutralising a boiling solution of sodium carbonate with cream of tartar, when it crystallises on cooling, in fine rhombic prisms. It is used in medicine, being the chief ingredient of ‘‘ Seidlitz powders ” ; also in making Fehling’s solution (infra). Calcium tartrate, CaC,H,0,4.4Aq, occurs in grapes and in senna leaves. It is sparingly soluble in water, and is precipitated when CaCl, is added to an ammoniacal solution of a tartrate. It is soluble in potash and in ammonium chloride. Cupric tartrate, CuC,H,0,.3Aq, is sparingly soluble in water, but dissolves in alkalies to a deep blue solution, in which two atoms of the alkali metal have displaced Hg. Such a solution is often used in analysis, as alkaline cupric solution, or Fehling’s test. Tartaric acid behaves in a similar way with several other metals, retaining them in alkaline solutions when they would otherwise be precipitated as hydroxides; in the cases of Al and Fe, this is turned to account in analysis. Silver tartrate, AgoC,H,Og, is precipitated by silver nitrate from a normal tartrate ; it dissolves in ammonia, and the solution deposits metallic silver when heated, the tartaric acid being oxidised to carbonic and oxalic acids. This is taken advantage of in some processes for silvering mirrors. Potassium-antimonyl-tartrate, K(SbO)C,H,O,, or tartar emetic, is prepared by boiling cream of tartar (6 oz.) with water (2 pints) and antimonious oxide (5 oz.) ; Sb,0, + 2KHC,H,O, = 2K(SbO)C,H,O, + H,O. From the filtered solution, on cooling, the salt crystallises in rhombic prisms of the formula 2K(SbO)C,H,O,.Aq. Itis soluble in three parts of hot water and in fifteen parts of cold water. The crystals lose their water of crystallisation at 100° and when heated over 200° the emetic loses the elements of another molecule of water, and becomes KSbC,H,O,, which is recon- verted into emetic by boiling with water. When barium chloride is added to tartar-emetic, a precipitate is formed, according to the equation 2KSbOC,H,0, + BaCl, = Ba(SbOC,H,0,). + 2KCl. By decomposing this barium salt with sulphuric acid, an acid solution is obtained, which soon deposits antimonious hydroxide, but if it be neutralised with potash before decomposition occurs, it yields tartar-emetic. Hence it would seem that the emetic is the potassium salt of the acid H(SbOC,H,4O,) or C2>H2(OH)2(CO,),SbO-H, which is derived from tartaric acid by exchanging one atom of H in the (CO,H), for the monad radicle antimonyl, Sb’”0”. The emetic acid has been named tartryl antimonious acid, so that tartar- emetic would be potassium tartryl antimonite. Other tartryl-antimonites have been obtained. By dissolving Sb,O, in tartaric acid, and adding alcohol, a crystalline precipitate of antimonyl tartrate, (SbO)2C,H4O., is obtained, and this becomes tartar- emetic when boiled with normal potassium tartrate (SbO),CyH,O, + K,C,H,O, = 2KSbOC,H,O,. For the antimony in tartar-emetic, arsenic or boron may be sub- stituted. When excess of Sb,0, is boiled with solution of tartaric acid, and the liquid evaporated to a syrup, it deposits crystals of H(SbO)C,H4O¢, which is decomposed by water, and appears to be identical with the tartryl-antimonious acid. Saccharic acid, CO,H-[CHOH]-,CO,H, is obtained by oxidising sugar or starch with nitric acid, stopping short of the formation of oxalic acid. Sugar is heated with 3 parts of nitric acid of sp. gr. 1-3, till violent action begins. When no more red fumes are evolved, it is kept at 50° for some hours, diluted with two or three volumes of water, neutralised with K,CO,, and acidified strongly with acetic acid. On standing, acid potassium saccharate, C,H,04(CO.),HK, crystallises. This is dissolved in a little potash and precipitated by cadmium chloride. The precipitate of cadmium saccharate is suspended in water and decomposed by H,S, the CdS filtered off, and the solution of saccharic acid evaporated. Saccharic acid forms a deliquescent amorphous mass, soluble in alcohol and in water. Its salts are somewhat similar to those of tartaric acid, the acid salts of potassium and ammonium being sparingly soluble. Calcium saccharate, CyHg0,(COz).CaAq, is crystalline, nearly insoluble in water, but soluble in acetic acid. The stereochemistry of saccharic acid will be noticed later. Mucic acid, CO,H-[CHOH],-CO2H, stereoisomeric with saccharic acid, is prepared by oxidising gum arabic or milk sugar with nitric acid. Milk sugar is heated with 3 parts of nitric acid. of sp. gr. 1-3 until red fumes are abundant ; the heat is then removed, when the acid separates as a granular powder sparingly soluble in water and alcohol, 632 CITRIC ACID The mucates differ greatly from the saccharates, most of them being insoluble ; the acid potassium salt is more soluble than the normal salt. By boiling mucic acid with water for some time, it is converted into paramucic acid, which is isomeric with it, but more soluble in alcohol. Hydriodic acid reduces saccharic and mucic acids to adipic acid—C,H,0,(CO,H), + SHI = CsH,(CO,H). + 4H,0 + 41. Pyromucic acid, or furfurane a-monocarboxylic acid, CyH,0-CO2H, is a product of the distillation of mucic acid, and may also be obtained by boiling furfural (pyromucic aldehyde, p. 599) with silver oxide and water. It forms prismatic crystals sparingly soluble in cold water, soluble in hot water, alcohol, and ether. It may be sublimed ; m.-p. 134°. The pyromucates are very soluble. CH = C(CO,H) Meconic acid, ON yt hydrozypyrone dicarboxylic acid, is C(OH) : C(CO,H) extracted from opium by digesting it with hot water, neutralising the solution with calcium carbonate, and adding calcium chloride, which precipitates acid calcium meconate, HCaC7HO,-Aq, from which meconic acid may be crystallised by dissolving it in hot dilute HCl. It crystallises (with 3H,O) in plates, dissolving rather sparingly in cold water and ether, easily in hot water and alcohol. When heated, it loses CO,, and becomes comenic acid, Cg,H,O,;, and when further heated, hydroxypyrone (pyro- comenic acid) CgH,(OH)O. Solution of meconic acid gives a fine red colour with ferric chloride, not bleached by mercuric chloride. With silver nitrate, it gives a white precipitate of hydrodiargentic meconate, HAg,C;HO,, but if « drop of ammonia be added, and the liquid boiled, the precipitate becomes bright yellow normal silver meconate, Ag,C,HO,. Meconic acid is closely related, by its composition, to chelidonic acid, C7H4Og, an acid obtained from celandine (Chelidonium majus), which belongs to the same botanical order as the opium poppy, which yields meconic acid. Polybasic Acids.—Very few of these are of any importance. Tricarballylic acid, CH,(CO,H)-CH(CO,H)-CH,(CO,H), may be obtained by heating citric acid with hydriodic acid. It may also be built up from glycerol, C;H;(OH;), by first converting this into allyl tribromide, CsH;Br, (p. 659), and heating the tribromide with alcohol and potassium cyanide to obtain tricyanhydrin, or allyl tricyanide, C3H;(CN)3, which yields potassium tricarballylate and ammonia when boiled with potash ; C3H,;(CN)s + 3KOH + 3H,O = C,H,;(CO.K); + 3NH3. The calcium salts of tricarballylic, citric, and aconitic acids occur in the deposit formed in the stills of beet-sugar manufactories. Tricarballylic acid melts at 165° and crystallises in rhombic prisms, which are easily soluble in water and alcohol. Citric acid is a hydroxy- and camphoronic acid (p. 677) a trimethyl-derivative. Citric acid, or hydroxytricarballylic acid, CH,(CO2H)-C(OH)(CO,H)-CH»(CO2H), the most important polybasic acid, is found in many fruits, associated with malic and tartaric acids. The potassium and calcium salts are present in many vegetables and in the indigo and tobacco plants. The acid is prepared from lemon-juice. The juice is heated and chalk is added as long as effervescence occurs ; this preci- pitates part of the acid as calcium citrate, leaving the rest in solution as an acid salt ; this is precipitated by adding milk of lime, and boiling. The calcium citrate is washed with boiling water, decomposed by exactly the required quantity of dilute sulphuric acid, the liquid filtered from the calcium sulphate, and evaporated to crystallisation. It is sometimes recommended to ferment the lemon-juice with yeast for two days, and to filter before adding the chalk. It is said that the acid can also be obtained industrially by fermenting glucose with a particular fungus. The synthesis of citric acid from acetone is by the following steps: (1) Acetone treated with chlorine yields dichloracetone, CH,Cl-CO-CH,Cl, which (2) heated with strong HCN yields dichloracetone cyanhydrin, CH,Cl-C(OH)(CN)-CH,Cl ; on (3) hydro- lysis this gives dichloracetonic acid, CH,Cl-C(OH)(CO,H)-CH,Cl. (4) The two Cl atoms are now exchanged for CN by treatment with KCN; dicyanoacetonic acid is produced, CH,CN-C(OH)(CO,H)-CH,CN, which (5) by hydrolysis yields citric acid, STEREOCHEMISTRY 633 Citric acid crystallises in rhombic prisms (with 1H,O) very soluble in water and fairly so in alcohol, but little in ether ; they melt at 100°, become anhydrous at 130°, and then melt at 153°. Further heated to 175°, the acid loses water and becomes aconitic acid, C;H,(CO,H), (see below). By further heating, the aconitic acid becomes aconitic anhydride, which then loses CO, and passes into the anhydride of itaconic acid (methylene succinic acid) (COOH)CH,-C( : CH,)(COOH), which crystallises in the neck of the retort. The liquid portion of the distillate contains the anhydride of citraconic acid (methyl maleic acid) isomeric with itaconic, into which it is converted by heating its concentrated solution to 120°; see also p. 628. Oxidising agents convert citric acid into acetone and its derivatives. When dehydrated by phosphoric or concentrated sulphuric acid at 100° it does not char but yields acetone, together with CO and CO, ; C3H,(OH)(CO,H)s = 2CO, + CO + H,O + CH3-CO-CH;, (acetone). Fusion with potash converts it into acetate and oxalate— C;H,(OH)(CO,H), + 4KOH = 2(CH;-CO.K) + (CO,K). + 3H,0. Solution of citric acid, mixed with excess of lime-water, gives no precipitate in the cold, distinguishing it from tartaric and oxalic acids ; but when heated, it deposits calcium citrate, Cag(CgH,;07).-4Aq, which is more soluble in cold than in hot water, but it is insoluble in potash, which dissolves calcium tartrate ; ammonium chloride and acetic acid dissolve it. Magnesium citrate, Mg3(CgH;07)2.14Aq, is easily soluble in water. A mixture of NaHCO,, citric acid, sugar, and a little magnesium salt, rendered granular by the effect of heat on the citric acid, forms the so-called effervescent citrate of magnesia. Ferric-ammonio-citrate, Fe.(NH,z)3(CgH;07)3, dark-red scales, is used in medicine. Aconitic acid, COj.H-CH : C(CO,H):CH,:CO.H, a tribasic acid of the olefine series, is obtained by heating citric acid in a retort till oily drops appear in the neck (v.s.) and extracting the mass with ether, which leaves the unaltered citric acid undissolved. On evaporating the ether, aconitic acid is left in small crystals, easily soluble in water and alcohol. It is distinguished from citric acid by not precipitating when boiled with excess of lime-water. Aconitic acid is found in monkshood (Aconitum napellus), beet-root, and sugar-cane, and in some other plants. Trimesic acid, or 1: 3: 5-benzenetricarboxylic acid, CgsH3(CO,H)3, is produced by the oxidation of mesitylene and of mesitylenic acid. It synthesises easily from open-chain compounds (p. 561); m.-p. 300°, sublimes at about 200°. Mellitic acid, C.(COOH).,, is a hexabasic acid of the aromatic series (for it yields benzene when distilled with lime), which occurs as its aluminium salt in a mineral mellite or honey-stone. It crystallises in fine silky needles. Acrips conTAINING NitRoGEN.—See Ammonia and Cyanogen Derivatives. STEREOCHEMISTRY. Stereochemistry in its broader sense comprehends all that pertains to the spatial arrangements of the atoms within the molecule, see pp. 335- 562; but in the narrower sense it is the study of those substances which exhibit that kind of isomerism, Stereoisomerism, which depends upon differences in the arrangement of the atoms in space within the molecule, In numerous instances, sfereoisomerides are not optically active, and these are dealt with in other places, e.g. cobalt compounds (p. 458), fumaric and maleic acids and their derivatives (p. 638), oximes (p. 641), para- and meta-aldehyde (p. 595), &c. Ricinoleic acid (p. 619) and the hydrophthalic acids (p. 628) exhibit more than one kind of stereoisomerism in the same molecule. _ Interest centres chiefly in those substances which rotate a ray of polarised light. Each exists in two optically active forms—namely, one which rotates the plane of polarisation of light to the right (dextro-rotatory) and another 634 THE POLARIMETER which rotates the plane equally to the left (levo-rotatory)—and in one or more optically inactive forms. An account of the polarisation of light must be sought in a work on Physics. It may be said here that when a ray of light is passed through a certain kind of crystal (a polariser) in a certain direction, it is broken into two rays pursuing different paths. Each of these rays is of such a nature (polarised) that while it will pass through a similar crystal (the analyser) placed with its axis parallel to that of the first, it is extinguished if the second crystal be rotated through an angle of 90°. If, while the axes of the crystals are in this relative position, a solution of a dextro-rotatory compound be placed between them, the ray will pass again through the analyser (a result expressed by saying that the plane of polarisation has been rotated) and this must be turned to the right through a certain angle before the light is again extinguished ; the measure of this angle is a measure of the optical activity or rotatory power of the compound dissolved. A levo-rotatory compound produces the same effect, but in the opposite direction. The instrument whereby the rotatory power is ascertained is called a polarimeter, and is shown in Fig. 303. The essential parts of it are the prisms and lenses, the Fig. 302. A B Cc DB FH F @ Fig. 303. arrangement of which is represented in Fig. 302. The light from the lamp, shown in Fig. 303 (which burns with a non-luminous flame, made luminous by the intro- duction of a sodium compound, so that it yields light of one colour only), passes first through a plate G cut from a crystal of potassium bichromate to ensure monochromatism, then successively through a lens / to make the beam parallel, the Nicol polarising prism #, a quartz plate D covering one-half of the field of vision, the tube C, with glass énds and containing the solution to be examined, the Nicol prism analyser B, and the opera-glass combination of lenses A focusing on to the plate D. The analyser B is mounted at the centre of the graduated dial by which with the aid of verniers the rotation of B is accurately measured. According to the relative angular positions of # and B, the field viewed through A will be either of uniform shade or will have one half darker than the other, this effect being due to the quartz plate D. In using the instrument the tube C is inserted after the analyser has been rotated to produce the uniform shade ; if the solution has rotatory power the field will no longer be of uniform shade, the one half or the other being the darker accordingly as the rotation is dextro- orlevo-. The analyser is then again rotated to produce the uniform tint, and the angle of rotation is read off on the circular scale through one of the eye-pieccs. STEREOISOMERISM 633 The difference between the two readings is the angle of rotation for the given solution in the tube employed. The angle of rotation (a), in the case of any given substance, varies directly as the strength of the solution (p grams in 100 grams of liquid), its specific gravity (d) and the length of the column of liquid (2) through which the light passes. For different sub- stances the angle of rotation also varies with the specific rotatory power [a], which is found by dividing 100 times the angle of rotation by the product obtained by multi- plying together the weight of the substance in one gram of the liquid, the specific a.100. pal The “D” signifies that sodium light is used, which is the D line of the spectrum. For example, a beam of polarised light was passed through a tube with glass ends, 0-50 decimetre long, filled with turpentine, of specific gravity (at the temperature of the experiment) 0-8712, and it was requisite to turn the analyser 16° in the opposite direction to the hand of a watch in order to prevent light from reaching the eye of the observer. This would give for the specific (levo) rotatory power, 16 x 100 100 x 0-8712 x 0-5 Since p.d is the concentration (c) in grams per 100 c.c. it is often more practical when working with solutions to employ the form [a] = a.100/c.l. Any of the factors may be calculated if the others are known, e.g. 20 grams commercial cane sugar were dissolved in water and made up to 100 c.c.; this solution, contained in a 200 mm. tube, caused a rotation of 26:55°; whence the number of grams of true cane sugar a.100 26-55° x 100 [a]? 66-5° x 2 the commercial sugar contained 19-95 x 100/20 = 99-75 per cent. true cane sugar. [a] for cane sugar is 66-5°. The product of the specific rotatory power and the molecular weight (W) divided by 100 is designated the molecular rotatory power : [M] = W. [a]/100. Stereoisomerism as illustrated by ethylidene lactic acids —Two forms of this acid are known : the ordinary fermentation lactic acid which is optically, inactive (but commercial specimens are slightly active), and sarcolactic acid, which rotates the ray of polarised light to the right (dextro-rotatory). Chemically speaking, the difference is exceedingly slight, amounting mainly to a greater solubility of zinc sarcolactate (which crystallises with 2H,O) than of zinc fermentation lactate, and a smaller solubility of the calcium salt (4H,0). The physical difference between the two is considerable, for whilst the fermentation acid is inactive towards polarised light, sarcolactic acid rotates the plane of polarisation to the right. This property leads to the distinctive titles, dextro-ethylidene lactic acid for sarcolactic acid, and inactive ethylidene lactic acid for the fermentation acid. If kept in a desic- cator for some time, the dextro-acid becomes converted into an anhydride the solution of which is levo-rotatory, but the lactide obtained by heating the acid yields inactive lactic acid when dissolved. The salts of the dextro- acid are levo-rotatory. When cane sugar is fermented by means of a certain bacillus, a levo- ethylidene lactic acid is produced, the salts of which are dextro-rotatory. It seems that there are three ethylidene lactic acids, which may be distinguished as i-, d-, and lL ethylidene lactic acid respectively. But when equal weights of the d- and /- acids are mixed together the product is found to be optically inactive; hence it may be concluded that the inactive acid is made up of an equal number of molecules of the d- and I- acids which neutralise each other, so that in considering a theory to account for the existence of these three acids it is necessary to attempt to explain the isomerism of only the dextro- and levo-modifications. The theory of position isomerism, already mentioned, will not suffice to furnish an explana- gravity of the liquid, and the length of the column in decimetres. [«]> = 36-7. (See also p. 640.) in 100 c.c. of the solution: c= = 19-95 grams; whence 636 THEORY OF STEREOISOMERISM tion, because the only possible position isomeride of ethylidene lactic acid, according to the theory, is ethylene lactic acid, from which both the d- and the /- acids differ chemically. The examination of a large number of compounds which are optically activé has shown that each contains one or more carbon atoms to which are attached four different elements or radicles ; thus, in ethylidene lactic acid, CH,CHOH-COOH, the middle carbon atom has each of its atom- fixing powers satisfied by a different radicle ; viz. CH;, H, OH, and COOH. Such a carbon atom is said to be asymmetric, and it is found that an optically active compound is one which possesses one or more asymmetric carbon atoms. Several cases of isomerides differing from each other in optical activity have been noticed in the preceding pages; in each case it will be found that the accepted formula for the compound contains one or more asymmetric carbon atoms. Thus three of the 14 isomeric amyl- alcohols (p. 582) occur in the d-, I-, and i-forms; and in each the original methane carbon atom has four different radicles attached to it, namely in one—CH;, CH,-CH,, H and CH,OH; in another— CH;, CH,CH,-CH,, H and OH; and in a third—CH;, (CH,),CH, H and OH. The most fruitful hypothesis for explaining the existence of d- and L isomerides having an asymmetric carbon atom is that the four groups attached to this carbon atom are differently arranged in space, in the two isomerides, which are therefore called stereoisomerides (atepeds, solid). If the carbon atom be considered to occupy the centre of a tetrahedron in space, as suggested at p. 542, it will be found that no essentially different structures can be made, unless each corner of the tetrahedron has a different radicle attached to it. For if two tetrahedra be constructed, the corners of which are represented by A, A, A, B, or A, A, B, B, or A, A, B, C, or any combination of four letters, two or more of which are the same, it will be found to be always possible to put the one tetrahedron inside the other in such a manner that the four letters on the corners of the one shall coincide with the four letters on the corners of the other. If, however, the four corners of each be represented by the four different letters, A, B, C, c B B C Dp, it will be found possible so to Hig 30s arrange these letters that the one tetrahedron cannot be introduced into the other in such a manner that the four corners correspond. The arrangement necessary will be understood from the statement that if the observer be opposite those faces of the tetrahedra which are similarly lettered, the order of the letters on the one face will be the reverse of the order of the letters on the other face ; if the letters A, B, C, for instance, be in the order of the motion of the hands of a clock on the face of one tetrahedron they will be in the reverse order, C, B, A, on the face of the other. Such an arrangement is depicted in Fig. 304, from which it will be seen that the two arrangements bear the same relationship to each other as an object bears to its image in a mirror. It is in the above manner that Le Bel and Van’t Hoff have sought to explain why no isomerides of methane substitution-products, except of those of the type CR,R,R3Ry, exist. If the compound which is arranged in the clock-wise manner in Fig. 304 be dextro-rotatory, then that which is anticlock-wise will be levo-rotatory. The theory has been tested by investigating compounds which, by the process of their formation, ought to contain an asymmetric carbon atom, although they were known only in an inactive form. By appropriate treatment many such compounds have been resolved into a dextro- and levo-form ; the principal methods of treatment STEREOISOMERISM OF TARTARIC ACID 637 are—(1) Crystallisation from water, advantage being taken of the greater solubility of one of the active forms; in this manner the zinc-ammonium salt of i-lactic acid has been resolved into the zinc-ammonium salts of the d- and I-acids. (2) Treatment of the inactive mixture with an active compound, and crystallising the product ; thus, if the inactive compound is acid it is crystallised with an active base, such as strychnine ; if it is basic it is crystallised with an active acid, such as tartaric acid. In either case, the salt formed is separated by crystallisation into a d- and I- modi- fication, the one or the other being the more soluble. Fermentation lactic acid is split up by érystallising it with strychnine, the J-strychnine lactate separating first. (3) Fermentation of the inactive compound with some bacillus which feeds on one of the active forms rather than upon the other ; some fungi show a similar preference, e.g. penicillium (p. 638). The second method has proved the most fruitful, and by its means optically active sulphur, tin, and nitrogen compounds, containing an asymmetric 8, Sn, and N atom respectively, have been prepared. Where a compound contains more than one asymmetric carbon atom the cases of isomerism are more numerous, as exemplified by tartaric acid. Here there are two asymmetric carbon atoms and four stereoisomerides are known: d- and Ltartaric acids, d- + “tartaric acid known as racemic acid, and another inactive acid, mesotartaric acid. When natural (dextro-) tartaric acid, is heated with about one-tenth of its weight of water, in a sealed tube at 175° for some 30 hours, in the apparatus shown in Fig. 274, p. 539, it is converted into an inactive isomeride, racemic acid, which crystallises with 1H,O in triclinic prisms, melts at 202° and is much less soluble in water than dextro-tartaric acid is. By precipitating as acid potassium tartrate, the unaltered tartaric acid remaining in the mother-liquor obtained in crystallising racemic acid, there is left in solution the acid potassium salt of another inactive acid, meso- tartaric acid, which crystallises in rectangular tables (with 1H,Q).1 The differences between racemic and mesotartaric acid are sufficiently marked. The acid potassium racemate is more soluble than the tartrate, while the corresponding mesotartrate has not been crystallised. Calcium racemate, CaC,H,O,.4Aq, is less sparingly soluble than calcium tartrate and than calcium mesotartrate, CaCzH,0,.3Aq, so that calcium sulphate precipitates free racemic acid but neither of the other free acids. Calcium racemate is insoluble in ammonium chloride andin dilute acetic acid, which also fails to dissolve the mesotartrate ; the tartrate, however, is soluble in both. Racemic acid is found mixed with the tartaric acid from certain samples of argol, and its crystals may be distinguished from those of tartaric acid by the cloudy appearance which they assume at 100° due to the loss of their water of crystallisation. It has been found that racemic acid, like the inactive forms of other compounds containing an asymmetric carbon atom, can be split up by the methods referred to on this page into the dextro-tartaric acid and levo-tartaric acid, which is practically identical with the dextro-acid, save that it rotates the plane of polarisation to an equal extent to the left. The classical researches of Pasteur on sodium-ammonium racemate are the foundation of stereochemistry. The sodium-ammonium racemate, NaNH,C,H,O,, bas the same crystalline form as the tartrate, but when formed at a temperature below 28° the crystals of the racemate differ from each other in the position of a certain unsymmetrical (hemihedral) face ; this is on the right hand in the one kind and on the left hand in the other (enantio- morphous). When these are picked out, and the acid extracted from them, the right- handed crystals yield ordinary dextro-rotatory tartaric acid, whilst the left-handed crystals yield levo-tartaric acid. From a solution of cinchonine racemate, cinchonine levo-tartrate separates first. The mould penicillium glaucum consumes dextro-tartaric acid in preference to the levo-form when growing in racemic acid. 1 For obtaining mesotartaric acid the sealed tube containing the tartaric acid and water should be heated at 165° for 2 hours. : 638 INTERNAL AND EXTERNAL COMPENSATION By mixing equal weights of dextro- and levo-tartaric acid, heat is evolved and racemic acid is formed. So also calcium racemate is precipi- tated when solutions of the U- and d-calcium salts are mixed. There thus appears to be some combination of the d and] isomers. Heat is similarly generated on mixing d- and J-limonene. Three of the isomeric tartaric acids are thus accounted for, but the fourth,’ mesotartaric acid, finds no analogue among the isomerides of com- Fumaric acid, exemplifying the azial- Maleic acid, exemplifying the plane- symmetrical, trans- or fumaroid symmetrical, cis- or maleinoid configuration. . configuration. pounds containing an asymmetric carbon atom so far considered. It is not capable of being split up into active components, nor is it produced by mixing the active forms. Itis obtained practically pure by oxidising maleic acid with permanganate. It is supposed that this fourth tartaric acid owes its existence to the fact that the molecule contains two asymmetric carbon atoms, so that it is possible for the one to have its groups arranged to give dextro-rotation while the groups of the other are arranged to give levo-rotation. In this case the molecule would be internally compensated and would be optically inactive, just as the racemic acid molecule is externally compensated, consisting of two oppositely active molecules. The configurations of the various tartaric acids is well explained by reference to the olefine-carboxylic acids—fumaric and maleic (p. 627). These are not optically active. Their stereoisomerism is of the same order as that already observed in the case of paraldehyde. It is displayed in the accompanying figures and written devices. Among the arguments in favour of these arrangements are: (a) maleic H-C-CO acid very easily forms an anhydride __ || No (maleic anhydride) and H-C-CO% fumaric acid does not; hence, for some reason (as that expressed in the above spatial arrangement) the COOH groups in fumaric acid are not so related as to favour the union of their CO-groups through O. Compare the ease with which 1: 2-phthalic acid yields its anhydride, due to the proximity of the COOH groups (p. 628). (b) Fumaric acid forms racemic acid, and maleic acid gives mesotartaric acid, on oxidation by KMnO, as illustrated in the accompanying figures. Notice that fumaric acid yields d-tartaric acid on opening up from one end of the double bond, and /-tartaric acid on opening up from the other end; but maleic acid yields the same megotartaric acid in either case. This is expressed by the fact that in d- and [- tartaric acids the H, COOH and OH groups occur in the same rotatory order in both halves of the molecule, and in consequence the acids are opti- 1 A fifth acid, CO,H'C(OH),CH,CO,H, which contains two OH groups attached to the same carbon atom, has not been obtained, WRITTEN EXPRESSIONS FOR STEREOISOMERIDES 639 cally active; but in meso-tartaric acid the rotatory order is different in the two halves, so that each neutralises or compensates (internally) the optical activity of the other. Ho \W/ cooH WV Ps a, COOH d-TARTARIC ACID . cooH cooH FUMARIC ACID I-TARTARIC ACID a , MESOTARTARIC ACID COOH Heo 0H! H COOH \Y/ MALEIC ACID f ct Lex OOH H — on MESOTARTARIC ACID The student is warned that the side of the tetrahedron on which a particular atom or group appears on the paper is not necessarily a guide to the direction of the optical rotation, since the carbon atom is free to rotate about its vertical axis. If the groups about each C-atom are viewed from the central point of union, and the same order of their occurrence (e.g. H, COOH, OH) be observed in every case, it will be seen that in some cases it is clockwise (c), and in others, anticlockwise (a). In the d- acid it is (c) ‘in both cases, and in the Ll acid, (a) in both cases; therefore both parts of the molecule have the same rotatory function. But in meso-tartaric acid the two halves are opposed, (c) and (a), and therefore the molecule as a whole has no rotatory function. [The structure of malic acid (p. 629) is similar to that of tartaric acid, but there being only one asymmetric atom the case is much simpler.] The following are the usual written expressions : CO,H CO,H CO,H CO.H. CO,H HO-C-H H-C-OH HO-C-H HOCH + HCOH HCOH HOCH HO-C-H H-C-OH HO-C-H CO,H CO,H CO,H CO,H CO,H ese SY Levo-tartaric Dextro-tartaric Internally compensated Externally compensated tartaric acid. acid. or meso-tartaric acid. acid. Racemic acid, 1 As shown by the solid and dotted lines, this figure must be turned on its vertical axis before compar. ing with the figure immediately above it. 640 STEREOCHEMISTRY OF TIN It is worthy of note that in whatever manner tartaric acid is synthesised the inactive forms are produced, and it is generally the case that artificial compounds are inactive whether they contain an asymmetric carbon atom or not. This is to some extent confirmatory of the foregoing theory ; for it would seem to be an even chance which way the groups arrange themselves round the asymmetric carbon atom, so that both forms are produced in equal amounts. It is customary to speak of externally compensated compounds as racemised com- pounds and the passage of the active form into the externally compensated inactive, as racemisation. In many cases such racemisation occurs spontaneously under influences which are somewhat obscure, and the passage of an unstable active form into the more stable active form is known to occur. The sugars and allied compounds provide a host of active forms and the account given (p. 765) of their stereoisomerism should be read as a part of this chapter. Some of them show bi-rotation, i.e. the rotation of the cold, freshly made solution is different from what it is after keeping or heating. Fixed oils as a class are inactive or very feebly active, but castor- oil is anotable exception. Essential oils are usually active. Many alkaloids are powerfully active. All liquids exhibit some rotatory power for polarised light when they are under the influence of a powerful (electro) magnet, and the amount of the rotation, com- pared with that produced by water under the same conditions, is called the magnetic rotatory power. The molecular magnetic rotation obtained by multiplying the rotatory power by the molecular weight, and dividing by the specific gravity of the liquid, exhibits a definite relation to the composition of the molecule, and increases by 1-023 for each addition of CH, in homologous series. Proceeding on the same principle as in the case of specific volumes (p. 644), the atomic magnetic rotatory power of carbon is found to be 0-515, that of hydrogen, 0-254, of singly linked oxygen, 0-194, and of doubly linked oxygen, 0-263, and from these, in many cases, the molecular magnetic rotatory power of compounds may be calculated, or conversely, a knowledge of the rotatory power may be applied to determine a molecular formula. Stereochemistry of other Elements.—Until the close of the last century, no optically active solutions of compounds other than those of carbon derivatives were known. Now, compounds containing an asymmetric atom of silicon, tin, nitrogen, sulphur, selenium, have been prepared and their optical activity demonstrated. Amongst the first successful attempts were those of Pope on tin. He started with tin tetramethide, Sn(CH3)4 (p. 688), prepared from zinc methide, Zn(CH3),, and tin tetrachloride, SnCl, ; this was treated quantitatively with iodine, producing érimethyl- stannoniwm iodide, Sn(CH3)3I ; this with zinc ethide, ZnEt., yielded tin ethyl-trimethide, Sn(CH3)3.C2H;. On repeating the treatment with iodine another methyl (not ethyl) is removed and dimethyl-ethyl-stannonium iodide, Sn(CH3)o.CoH;.1, is formed, which with zine propide, Zn(C3H,)s, yields tin propyl-ethyl-dimethide. With a fresh quantity of iodine one of the two remaining methyls is removed and methyl-ethyl-propyl-stan- CHa. : Joa CH, ST in solution, and with silver hydroxide, AgOH, yields the strongly alkaline hydroxide of Me-Et-Pr-stannonium. Pope treated the iodide with the silver salt of d-camphorsulphonic acid, CyoHy;.0.SO,H ({[M]= + 50°), and obtained the Me-Et-Pr-Sn-d-camphorsul- phonate. The solution of this on crystallisation allowed first to separate a substance (m.-p. 125°-126°), [M] = + 95°, hence the d-isomer of the tin radicle forms with the d-acid the less soluble salt. The increase in [M] shows that [M] for the tin complex radicle is + 45°. The filtrate should contain the (J Sn + d A) salt, but the tin radicle racemises very easily, so that on evaporation of the mother liquor a fresh crop of the (d Sn +d A) erystals is obtained. This illustrates the lines on which much of the later work on tin, carbon, and the other elements has proceeded. Silicon like tin and carbon belongs to the tetravalent group of elements, but no compound containing a single asymmetric silicon atom appears to have been resolved nonium todide, , is formed, an oil boiling at 270°. It is ionised STEREOCHEMISTRY OF NITROGEN 641 so far. However, it is optically active with two asymmetric silicon atoms in d-l-sulpho- benzylethylisobutylsilicyt oxide, which was resolved into its optical antipodes by repeated crystallisation with d-methyl hydrindamine, a substance frequently applied to such purposes. Sulphur is in the sixth group of the periodic classification ; nevertheless, there are some organic derivatives of this element in which it appears to be tetravalent, e.g. the thetines. One of these is prepared by the action of bromacetic acid, CH,Br-COOH, on methylethylsulphide, CH,’S-C.H, ; it is inactive, and is known as methylethylthetine Br % jos bromide, i 5 CH, CH,-COOH correct, the S atom is asymmetric and the inactive compound should be capable of yielding optically active components. By applying d-camphorsulphonic acid in the manner described above, the d-form has been isolated. Selenium is optically active under the same conditions as is sulphur. Nitrogen.—The discovery of optically active nitrogen compounds has extended the theory of the connection between asymmetry and optical activity to pentavalent elements. If, in ammonium iodide, NH,I, there is substituted for each H atom a different hydrocarbon radicle, an asymmetric nitrogen compound will be produced. Such quaternary ammonium compounds are well known, and in 1899 one, benzylphenyl- allylmethylammonium iodide, N(CgH;-CH,)(CgHs)(C3Hs)(CH;)I, was resolved by Pope into optically active components by the aid of d-camphorsulphonic acid. (Also p. 697.) Several others have since been resolved, and the stereochemistry of pentavalent nitrogen is now a very wide subject. If this view of the structure of the thetine is Compounds containing two negative groups have been resolved, eg. methyl-ethyl-aniline oxychloride, Me.Et.Ph.N.OH.C1; but still more remark- able is the optical activity of its base, Me-Et.Ph.N.(OH), or Me.Et.Ph.N = O, which according to either formula shows the N to have two valencies satisfied by the same group or groups. Several instances are on record of separating a complex nitrogen compound containing one or more asymmetric N-atoms into two stereoisomers as shown by differences of various properties, but still not resolving them into optical isomers, e.g. (Me.Et.Ph.I.)N—CH,-CH, -CH,-N (I.Ph.Et.Me.) by E. and O. Wedekind. Trivalent nitrogen is not capable of optical activity, but in numerous compounds, especially the oximes, it exhibits well-marked stereoisomerism. The fundamental idea is that the three valencies are not all directed in one plane. The groups attached to N are more or less labile, as indeed all groups are, and mutually influence one another, but so differently under various conditions that sometimes one arrangement of the atoms prevails and sometimes another. For instance, in the ketoxime, CH,'C:NOH-C,H,, the OH will have a preferential gravitation towards one of the two other groups, so that it might be written either CH,C°C,H, or CH,CC,H; N-OH Ho accordingly. When the groups are quite dissimilar one modification will be much more stable than the other, and the latter may be difficult to prepare; but when they are more similar, e.g. CsH,Br'C : NOH-C,H,, both isomers are easily obtained. When compounds containing asymmetric C or N’ atoms are prepared artificially both optical antipodes are produced simultaneously, but with the trivalent N stereoisomers and the like, only that modification which is the more stable under the conditions of preparation is formed ; then this is converted into the other modification under appropriate influence. This is well illustrated by benzaldoxime (paraldehyde and metaldehyde show similar cis- trans-isomerism, p. 595 ; compare also fumaric and maleic acids, p. 638). 41 642 MELTING-POINTS Benzaldowime is produced by the interaction of benzaldehyde and hydroxylamine Two stereoisomers are known: the a- or anti- and the - or syn-form. The a- or benzantialdoxime, m.p. 35°, b.-p. 117° (14 mm.), is changed by HCl, H,SO,, or Br into the f- or benzsynaldoxime, m.-p. 125°, which on distillation under reduced pressure passes into the a-modification. Both may be converted into acetyl derivatives which are saponifiable and therefore the acetyl must be attached to the O atom. On warming these esters with Na,CO, one of them (the /3- or syn-) forms benzonitrile, indicating that the aldehydic H-atom and the acetyl group are close together ; the other regene- rates the original oxime. Hence the following configurations : C.H;-CH O,H;.-CH C,H; CH 0,H,;-CH C,H; CH C,H; °C Bae eal LS LS HO-N CH;-CO-0 HO-N N-OH NO-0C-CH; N a@ OF ansi- acetyl By or syn- acetyl benzonitrile. derivative derivative See also p. 648. The theory is supported by the fact that one of the two aldoximes nearly always loses water more easily than the other, showing that the H and OH are probably nearer to each other in the syn-aldoxime than in its isomeride. Usually, the melting-point of the syn-modification is con- siderably (30° or more) higher than that of the anti-modification. With dioximes the stereoisomerism is more elaborate. Steric hindrance, space interference, are terms implying the influence exerted by the spatial arrangement of the atoms in a molecule in hindering a reaction. Although mono-, di-, tri-, and tetra-methyl-methane are known, also mono-, di-, and tri-phenyl- methane, all attempts to prepare the tetraphenyl derivative have failed. This appears to be due to the crowding of the three large phenyl nuclei around the central methane C-atom hindering the entrance of «a fourth group. Similar difficulty attends the formation of esters fyom di-ortho-benzoic acids (Victor Meyer’s esterification law), a.e. where there is a group or heavy atom on each side of the COOH group, except under certain conditions. Numerous instances are known. Baeyer’s strain theory explains other steric phenomena ; see p. 561. Melting-points of Organic Compounds.—In order that a solid may fuse, it must first attain to a degree of temperature called the melting-point of the solid, and must then have a certain amount of motion imparted to its molecules by the transformation (into motion) of an amount of heat which is termed latent heat of fusion (p. 32). This motion enables the molecules to circulate more or less freely among themselves, and to extend themselves in a horizontal plane. The fusing-point, as indicated by the thermometer, therefore, is the temperature at which the molecules become capable of converting the heat subsequently acquired into the motion characteristic of the liquid condition. This temperature will depend upon the constitution of the molecules, which regulates their relation to adjacent molecules. If the cohesion which limits the motion of molecules in a solid mass be similar in character to the gravitation which limits the motion of masses of matter, it will be greater among those molecules which have the larger mass, that is, the highest molecular weight, and these should have the highest fusing-points, since a larger amount of progressive motion (or temperature) must be imparted to them to render them capable of acquiring the freedom of motion proper to the liquid condition. But it is by no means true that the fusing-point is always higher when the molecular weight is greater ; for palmitin, with a molecular weight of 806, fuses at 63°, while urea, with a molecular weight of 60, fuses at 130°. It may be stated, however, that in the case of homo- logous series, the fusing-point generally rises as the molecular weight increases ; thus the paraffin and olefine hydrocarbons are liquids until they contain sixteen atoms of carbon. The substitution of HO for H tends to raise the fusing-point, so that the paraffin alcohols containing more than seven carbon-atoms are solids, and this is also the case with the aldehydes. Jn the case of the metameric paraffin derivatives the fusing-point is generally higher BOILING-POINTS 643 in those compounds which contain most carbon in the form of CH, ; thus, pseudo- valeric or tertiary valeric acid, C(CH );‘COjH, fuses at about 35°, while normal valeric acid, CH [CH,],-CO,H, fuses at — 59°. Again, tertiary butyl-alcohol, C(CH3)3OH, fuses at 25°; and normal butyl-alcohol, CH3[CH,],-OH, is liquid even below 0°. In the benzene-hydrocarbons, the substitution of CH, for H raises the fusing-point ; thus, toluene, C;H,-CH3, and xylene, C,H,(CHs)s, are liquids ; but durene, CgH2(CHs3)a, fuses at 80°. In these also, when they have the same molecular weight, the fusing: point rises with the number of methyl groups directly united to carbon ; for example, amyl-toluene, C;H,:[CH2],-CH3, is liquid, while hexamethyl-benzene, C(CH3),, is solid, fusing at 164°. Even in compounds which are strictly isomeric the position of the component radicles will affect the fusing-point, the para-compound having generally the highest fusing-point ; thus, ortho-xylene and meta-xylene are liquids, but para-xylene is a solid fusing at 15°. Determination of the melting-point is one-of the most important tests of the purity of a substance ; for it follows from the cryoscopic method of molecular weight determination that a very small proportion of a second body lowers the melting-point by a considerable and definite amount. The question may arise as to whether a substance having a certain melting- point is really a given compound known to have this particular melting point, especially where other means of identification are difficult. The problem is readily solved by determining the melting-point of a mixture of the substance and the givencompound. If the melting-point is the same as before, the two substances are identical, but otherwise, a different melting- point will be found. Boiling-points of Organic Compounds.—The boiling-point of a liquid is that temperature at which its molecules are capable of converting heat into motion sufficient to enable them to overcome entirely the attraction holding them to each other, and to extend themselves in all directions through space. Under ordinary conditions, their extension is impeded by the pressure of the atmosphere upon the surface of the liquid, so that, for experimental work, the boiling-point is that temperature at which the molecules are capable of acquiring sufficient motion to overcome a pressure of 760 millimetres of mercury (at 0°). Since the boiling-point refers to a certain standard of external work, it exhibits a more definite relation to the constitution of the molecules than is the case with the fusing-point. See also p. 34. In homologous series, the boiling-point increases with the molecular weight, but the increase due to each addition of CH, varies in different series. It is most uniform in the normal primary alcohols of the paraffin series (p. 578), where each addition of CH, increases the boiling-point, on the average, by 19-5°. In the series of aldehydes derived from these alcohols (p. 596), the increase in boiling-point is also fairly regular, but it averages 26-2° for each addition of CH,. In the corresponding acids, the increase is much less uniform, but the average increase is about 19°. In the simple ketones (p. 647), the mean increase in boiling-point for each CH, added is 20-5°. In the simple ethers, the increase is 26°. In the homologous series of hydrocarbons, the increase in boiling-point for each addition of CH, is irregular, but generally diminishes as the number of carbon-atoms increases. Those hydrocarbons of the paraffin and olefine series which contain the same number of carbon-atoms exhibit a similarity in thcir boiling-points : Paraffins . . CsHy 37° CoHi, 69° CrHyg 98° CgHig 125° CygHgq 288° Olefines . . C5Hyo 35° = CgHyg 69° = C7 Hyg 99° = CgHyg 123° Cg Hyg 275° The isologous hydrocarbons of the acetylene series have higher boiling-points, and those of the benzenes are higher still— Acetylenes . COsH, 45° CegHy. 80° CrHy, 106° CgHyy 133° Cy pHi, 165° Benzenes . ‘i —_ CgHg 80-12 C,Hg 111° CgHyg 142° CyoHy4 196° The substitution of HO for H in the conversion of the paraffin hydrocarbons into alcohols increases the boiling-point greatly, but in a ratio which decreascs Missing Page SPECIFIC VOLUMES 645 of ethyl-alcohol is 62-5, or higher than that of methyl-alcohol by 20-5, which represents _ the increase due to CHg. The molecular volume of acetic acid is 64, and that of formic acid 42, giving 22 as the increase due to CH,. The mean of the three values is 21-9, and this is almost exactly the difference in the molecular volumes calculated for the homologous acids, from formic to valeric. At one time it was stated with confidence that the molecular volume depends on the number and nature of the atoms contained in the molecule rather than on their grouping ; thus, ethyl acetate, CH,-COOC,H;, has the same molecular volume as its metameride, butyric acid, C;H,;,;COOH. Recently, much doubt has been cast on this statement ; and it has been asserted that, instead of the molecular volume being the sum of the atomic volumes, it depends on the manner in which the atoms are united. The following is the evidence in favour of the older view. Octane, CgH,,, has a molecular volume = 187, and if we deduct from this (CH2)g = 176, the difference, 11, represents the molecular volume of Hy, giving 5-5 for the atomic volume of hydrogen. Cymene, CyoHy4, has the molecular volume 187 which differs from (CHg),, or 22 x 7, by 33, which represents the increase in molecular volume due to Cs, and gives 11 for the atomic volume of carbon. By deducting the volume of H, (11) from that of H,O (18-8), 7:8 is obtained for the atomic volume of oxygen. From these values the specific volumes of many molecules may be calculated and are found to agree very nearly with those obtained by dividing the molecular weight by the specific gravity of the liquid at its boiling-point ; for example— Methyl alcohol, CH,O, gives 11 + (5:5 x 4) +7-8= 40-8 instead of 42 Ethyl ,, CoH ,, (11 x2)+(55 x 6) +78= 628 ,, 625 Ether C4HyO 4, (11 x 4) + (5-5 x 10) + 7-8 = 106-8, which is correct Phenol C,H,O 4, (11x 6)+(55 x 6) +78=1068 _,, , But formic acid, CH,O,, the specific volume of which is 41-5, gives only 37-6 as the sum of 11 + (5-5 x 2) + (7:8 x 2). Again, acetone, C,H,O, with a specific volume = 77-6, gives only 73-8 (which agrees with that found for allyl-alcohol, also C;H,O) by the addition of (11 x 3) + (5:5 x 6) +78 The structural formula of acetone is (CH3).°C: O, the oxygen being doubly linked to a carbon atom, whilst in the alcohols, ethers, and phenols it is. only singly linked to a carbon atom. Deducting from the specific volume of acetone (77-6) that of C,H, (66), there remains 11-6 as the atomic volume of oxygen, when doubly linked to a carbon atom. Formic acid contains a singly linked and a doubly linked oxygen atom; hence its molecular volume should be the sum of 11 + (5:5 x 2) + 7-8 + 11-6 = 41-4, which is very nearly correct. Acetic acid, H,C(C:0)OH, gives (5:5 x 4) + (11 x 2) + 7:8 + 11-6 = 63-4, instead of 63-6. Aldehyde, H,C(C: 0)H, gives 22 + 22 + 11-6 = 55-6, instead of 56-5, whereas if its formula were H,C-O-CHg, it would give 22 + 22 + 7-8 = 51:8. The specific volume of an atom of nitrogen singly linked to carbon, as in methyl- amine, H,C—NHp, is 2-3; but when trebly linked to carbon, as in methyl cyanide, H,C—C=N, its specific volume is 17. Sulphur, singly linked to carbon, has the specific volume 23; but when doubly linked, it is 28-6. The specific volume of chlorine is 22:8, of bromine 27-8, and of iodine 37-5. There are many exceptions to the simple laws of specific volume here set forth. Thus, ethylene chloride, CIH,C.CH,Cl, and ethylidene chloride, H,C-CHCl,, which have the calculated specific volume 89-5, give, by experiment, respectively, 85-34 and 88-96, a difference too great to be ascribed to experimental errors. Benzene, and some other members of the aromatic group, also exhibit considerable deviation, the observed specific volumes being lower than those calculated. Optical Properties of Organic Compounds.—Since the phenomena of light depend upon the waves excited in the ether which fills the spaces between the molecules 646 OPTICAL PROPERTIES of matter, the motions of these molecules must exert an influence upon the optical properties of the substances which they compose. The molecular conditions which regulate the colour of compounds, by enabling them to absorb certain of the waves composing white light, and to reflect or transmit others, are not as yet understood, but colour is most commonly associated with high molecular weight. (See also Quinonoid structure, p. 757, and azo-dyestuffs, p. 718). Much attention has been devoted to the comparison of the refractive powers of liquid organic compounds, that is, to the amount of deviation from its original path which a wave of light suffers in passing through the liquid in any direction except that perpendicular to the surface. The full discussion of this subject requires the study of optics, but it may be stated that from the amount of deviation is calculated the specific refractive power of the liquid, which is closely connected with the nature of its molecules. The molecular refractive energy, or refraction-equivalent, is found by multi- plying the molecular weight by the specific refractive power. Compounds which have the same molecular weight and belong to the same or to nearly related classes of organic compounds, generally have nearly the same refraction-equivalent ; thus, the number for methyl acetate, C,H3;0.:CH3, is 28-78 and that for ethyl formate, H-CO,C,H,, is 28-61. Butyl-alcohol, CyHy-OH, gives 36-11, and ether, C.H;-O-C,H;, 36-26. Poly- meric bodies have refraction-equivalents nearly proportionate to their molecular weights ; thus, aldehyde, C,H,O, has the refraction-equivalent 18-5, butyric acid, C,HgQp, 36-6, and paraldehyde,.C,H,,03, 52-5. In the homologous alcohols and acids derived from the paraffin hydrocarbons, the refraction-equivalent increases by about 7-6 for each addition of CH, ; thus, acetic acid, C,H,O,, having the refraction-equivalent 21-1, cenanthic acid should give 21-11 + (7-6 x 5) = 59-1, which nearly agrees with that observed, 59-4. By a method similar to that explained in the case of specific volumes, the refraction- equivalents of the elements may be calculated, and they are found to be, for the wave- length corresponding with the yellow sodium line, for carbon 4-71, for hydrogen 1-47, for oxygen singly linked to carbon, 2-65, and for oxygen doubly linked, 3-33. From these numbers the refraction-equivalent of a liquid may be calculated from its formula, as in the case of its specific volume, and the result agrees very nearly, in a great many cases, with that obtained by experiment. But there is sufficient deviation to indicate that the grouping of the atoms, as well as their nature and number, influences the refraction-equivalent. Thus, in the terpenes, the observed equivalent exceeds that calculated by the constant number 3, while in the benzenes the excess amounts to 6. It would appear that when a carbon atom is doubly linked to another carbon atom, its refraction-equivalent is 5-71 instead of 4-71, so that the six doubly- linked carbon atoms in the benzene ring would explain the excess in the refraction- equivalent. When liquids having different refraction-equivalents are mixed, the refraction- equivalent of the mixture is the sum of those of its constituents, so that the proportions in which these are present may be calculated. Absorption Spectra of Organic Compounds for Chemical Rays.—The light emanating from the sun and from the electric spark is accompanied by many other waves whose period of vibration is so short that they produce no impression upon the eye, or upon the thermometer, and are detected only by their power of chemically decomposing the salts of silver and other photographic materials. The shortness of these waves causes them to suffer a greater amount of deviation or refraction than the luminous waves when the light is passed through a prism, so that their effects are chiefly perceived in that part of the spectrum which lies beyond the violet light, and is usually termed the ultra-violet. Many substances which are perfectly trans- parent are able to intercept a large proportion of these actinic waves, as they are termed, and are said to be adiactinic, whilst those which transmit them freely are diactinic. Rock crystal, or quartz, is much more diactinic than glass, and lenses and prisms of this material are used in experiments upon this subject, the light of a stream of electric sparks being allowed to pass through the slit of a spectroscope (p. 353), through a cell with quartz sides containing the liquid under examination, then through a quartz lens and prisms and afterwards received upon a sensitive photographic plate KETONES 647 upon which that portion of the ultra-violet waves which has passed through leaves its impression. See also spectrograph, p. 355. It has been shown, by such experiments, that the normal alcohols derived from the paraffins are highly diactinic, and that the corresponding acids are somewhat less so, absorbing more of the highly refrangible waves remote from the violet end of the spectrum ; the diactinic character decreasing, in both acids and alcohols, as the molecular weight increases. Benzene and its derivatives are highly adiactinic, and, when employed in strong solutions, are often capable of absorbing all the ultra- violet waves ; but when diluted to a certain extent with water or alcohol, they allow some of the waves to pass, and produce photographs of spectra exhibiting absorption bands due to this selective absorption. Since isomeric benzene derivatives exhibit very different absorption-bands, the selective absorption must be due to vibrations within the molecules, while the general absorption, which varies with the molecular weight, is caused by the vibration of the molecules themselves. There is very strong evidence that the absorption-bands in the ultra-violet spectrum are exhibited only by those compounds in which the carbon atoms form closed chains, as in benzene (p. 560) and naphthalene (p. 571), in which there are three pairs of doubly linked carbon atoms. Starch, glucose, saccharose, diastase, and gelatine are highly diactinic, and show no absorption-bands, while albumin, casein, and serin exhibit absorption-bands in dilute solution. The photographic absorption-spectra afford 4 most accurate method of identi- fying organic substances, and a most delicate test of their purity, since the absorption bands are visible in solutions of extreme dilution. IV. KETONES The relationship between an aldehyde and a ketone has already been noticed (p. 593) ; both contain a CO group, attached in the former to a hydro- carbon radicle and a hydrogen atom, as CH,-CO-H, and in the latter to two hydrocarbon radicles, as CH,-CO-CH3, acetone. Both may be regarded as formed from an acid, the aldehyde by substituting an H atom, the ketone by substituting a hydrocarbon radicle, for the OH of the COOH group. Thus both may be formed from the acid chloride, e.g. CH ,CO-Cl—the aldehyde by action of nascent hydrogen, the ketone by action of the sodium compound of a hydrocarbon radicle : CH,-CO-Cl + 2H* = CH,-:CO-H + HCl CH;-CO-Cl + CH,;Na = CH,-CO-CH, + NaCl. It has already been shown (p. 593) that the ketones are, so to speak, the aldehydes of the secondary alcohols, into which they are converted by nascent hydrogen. For the formation of ketones from esters of ketonic acids see p. 667. It was shown at p. 593 that the aldehyde of an acid can generally be obtained by distilling a mixture of a calcium salt of that acid with calcium formate. If calcium acetate is distilled with calcium formate, acetic aldehyde is produced— (CH;-CO-0),Ca + (H:CO-0).Ca = 2(CH3-CO-H) + 2(Ca0-CO,). But if calcium acetate be distilled with calcium acetate—that is, by itself— the products will be acetone and calcium carbonate— (CH,-CO-0),Ca + (CH3-CO-O),Ca = 2(CHg-CO-CH,) + 2(Ca0-CO,). Ketones are simple or mixed accordingly as the hydrocarbon radicles attached to the CO group are the same or different; thus, by distilling a mixture of calcium acetate and propionate, the mixed ketone methyl- ethyl ketone is obtained— (CH,-CO-0),Ca + (CeH,-CO-0),Ca = 2(CH,-CO-CyH,) + 2(Ca0-C0,). The ketones are less easily oxidised than the aldehydes ; for instance, 648 ACETONE they do not reduce alkaline silver solutions. By more powerful oxidants they are generally converted into two acids, the rupture of the molecule occurring at the CO group. Thus, propione, C,H,-CO-C,H,, yields propionic acid, C,H,-CO,H, and acetic acid, CH,-CO,H. As in the aldehydes, the CO group is unsaturated, so that the ketones yield a number of combinations similar to those obtained with the aldehydes. Ketoximes, R,C: NOH, like the aldoximes from aldehydes, are formed by reaction of ketones with hydroxylamine, see p. 642. The oximes show a number of cases of stereo-isomerism (see p. 641). With phenylhydrazine the ketones yield hydrazones, R,C : N-NHC,H;. Ketones containing a methyl group combine with NaHSO, to form sodium hydroxysulphonates, e.g. (CH3).°C(OH)‘SO,Na. By the action. of PCl;, the O of the CO group is exchanged for Cl, forming chlorides of the type R,CCl, in which the Cl, is easily exchanged for H, to form a secondary paraffin hydrocarbon. From their constitution, the ketones must afford many cases of isomerism (meta- merism) ; thus, propione and methyl-propyl ketone have the same ultimate composition ; so have methyl-butyl and propyl-ethyl ketones ; methyl-amyl ketone and butyrone form another pair. Moreover, each ketone of the acetic series is isomeric with the aldehyde of the acid following next in the series; thus, acetic ketone, (CH3),CO, is isomeric with propionic aldehyde, C,H;-CO-H. Acetone, or dimethyl-ketone, CH,-CO-CH;, or pyro-acetic spirit, is obtained among the products of the distillation of wood (p. 578), and may be prepared by distilling the acetate of lead, calcium, or barium, the last yielding the purest product (see the above equation). The crude distillate is shaken with a saturated solution of NaHSO, and the crystalline compound thus formed (see above) is freed from the mother-liquor and distilled with sodium carbonate, when acetone distils over, mixed with water, which is removed by fused calcium chloride. Acetone is a colourless fragrant liquid, of sp. gr. 0-80, and boiling at 56°-3. It is inflammable, burning with a luminous flame. It mixes with water, alcohol and ether. On adding solid KOH to its aqueous solution, the acetone separates and rises to the surface. It is a good solvent for certain resins and camphors, and is also used for making chloroform, iodo- form and sulphonal. It is not so powerful a reducing-agent as aldehyde, and does not reduce silver nitrate. When oxidised by KMnO, or by K,Cr,0, and H,SO, it yields acetic and carbonic acids— CH;-CO-CH, + 40° = CH,-CO-OH + CO(OH),. Acetone is formed when vapour of acetic acid is passed through a red-hot tube, and when starch, sugar, and many other organic bodies undergo destructive distillation. It occurs in the urine of diabetic patients. When acted on by dehydrating agents, such as sulphuric or hydrochloric acid or quicklime, acetone loses the elements of water, and yields condensation-products, richer in carbon; thus, two molecules of (CH3),CO, losing HO, give (CH3)oC : CH-CO-CHg, mesityl oxide, a liquid smelling of peppermint, and boiling at 130°. Three molecules of (CH3).CO, losing 2H,O, yield [(CH3).:C:CH],CO, phorone, a crystalline solid, smelling of geraniums, and boiling at 196°, whilst the loss of another H,O gives CoH, mesitylene (p. 561). Acetone peroxide, (C3HgQz)3, is formed by mixing concentrated solutions of H,0, and acetone. It forms crystals, melting at 97°, insoluble in water and explosive. An important thio-derivative of acetone is obtained by heating a mixture of acetone and mereaptan with HCl; (CH3).CO + 2C,H,SH = (CH3)oC(SC.H,;)o + HO. This is known as mercaptol and when oxidised by permanganate it yields sulphonal (acetonediethylsulphone), (CHg)eC(SO2C2H,)s, an important soporific which crystallises well and melts at 126°. PYRUVIC’ACID 649 Methyl-ethyl ketone may be obtained by the reaction between acetyl chloride and zinc ethide ; 2(CH3-CO-Cl) + Zn(C,H;). = 2(CH3-CO-C,H;) + ZnCly. It boils at 81°, and is present in small proportion in commercial acetone. When oxidised, it yields only one acid, acetic ; CH,-CO-C,H, + 30° = 2(CH,-CO-OH). Benzophenone or diphenyl ketone, (CgHs)2CO, prepared by distilling calcium benzoate, forms stable prisms which melt at 46°, and labile rhombohedra which melt at 26° ; the labile changes into the stable form on addition of a trace of the latter. Benzophenone boils at 307°. Acetophenone, methyl-phenyl ketone, CHs-CO-C,H,, from calcium acetate and benzoate, also from benzene and acetyl chloride in the presence of AlCl, (Friedel and Craft’s reaction), CgH, + CH;CO-Cl = C,H;CO-CH, + HCl; melts at 20°, boils at 202°, and is used as a hypnotic (hypnone). Methyl-nonyl ketone, CH3-CO-CyHy,, is the chief constituent of oil of rue, from which it may be precipitated by NaHSO;. It may be obtained artificially by distilling calcium acetate with calcium rutate (m.-p. 15° ; b.-p. 225°). Naphthyl-phenyl ketone, CygH7-CO-CgH,, forms a dibromide, which is useful in optical experiments, on account of its high refractive power. Ketone-alcohols, Ketone-aldehydes, Ketone-acids, Diketones.—It was shown at p. 587 that these compounds may be regarded as oxidation products of polyhydric alcohols containing a secondary alcohol group, which might be expected to become a ketonic group on oxidation (p. 581) while the primary alcohol group would yield the aldehyde or acid group. Thus from a-propylene glycol, CH,;CHOH-CH,OH, would be obtained the ketone-alcohol, CH;-CO-CH,OH, the ketone-aldehyde, CH,-CO-CHO, and the ketone-acid, CH,CO-COOH, and from -butylene glycol, CH,-CHOH-CHOH:-CH,, the diketone, CH,:CO-CO-CH,. All these com- pounds share with the ketones and aldehydes a tendency to combine and to undergo nucleal condensation ; hence many are of great value in synthetic chemistry as steps to more complex compounds. Isomerides are distinguished as a- and B-, &e., as indicated on p. 609. Ketone-alcohols or keéols are exemplified by acetylcarbinol or acetol, CH;-CO-CH,OH, which boils about 150° and is obtained by cautious oxidation of a-propylene glycol with bromine water. Several of the sugars are ketols. Pyroracemic aldehyde, or methyl glyoxal, CH3-CO-CHO, is the type of the ketone- aldehydes ; it is a volatile yellow oil. Pyroracemic acid or pyruvic acid, CH;CO-COOH, is the typical a-ketonic-acid, It is obtained by the destructive distillation of tartaric or racemic acid (p. 630), as an oxidation product of ethylidene lactic acid, CH,;-CHOH-COOH, and by hydro- lysing acetyl cyanide, CH;CO-CN. This last method, the hydrolysis of an acidyl cyanide, is a general one for preparing a-ketone-acids. It is a colourless liquid smelling of acetic acid, boiling about 167°, and soluble in water. It shows most of the reactions of a ketone and an acid ; in addition, it is a strong reducing-agent, reducing alkaline silver nitrate, probably because the CO group has COOH attached to it instead of the second hydrocarbon radicle of a ketone. Baryta water converts it into wvitic acid, a dibasic aromatic acid. With nascent H it yields lactic acid. Aceto-acetic acid, acetonecarboxylic acid, CH3-CO-CH,COOH, is the typical 3-ketone- acid, all of which are very unstable, tending to break down into COg, from the carboxyl group, and the corresponding ketone. Its ethyl ester (see Esters) is more stable than the acid and is an important compound for synthetical work ; by saponifying this ester, potassium aceto-acetetate is obtained, and from this the free acid. It is a liquid soluble in water and decomposing into acetone and CO, when heated. Levulinic acid, CH3-CO-CH,-CH,COOH, is the type of the y-ketone-acids, which are also easily broken down by heat ; but instead of losing CO, they lose H,O, yielding y-lactones (p. 618) from unsaturated hydroxy-acids, Thus, levulinic acid yields y-lactones from angelic acid ; | | | | CH,C: CH-CH,COO and CH, : C-CH,‘CH,COO. 650 ETHERS Levulinic acid is a product of the action of acids on various carbohydrates, especially levulose. It melts at 32-5° and boils at 239°, dissolves in water and is used in calico printing. Phenylglyoxylic acid or benzoyl formic acid, CsH;-CO-COOH, is produced by oxidising mandelic acid and by hydrolysing benzoylcyanide. It melts at 65°. Diacetyl, CH,CO-COCH,, is the simplest a-diketone.1 It is made by heating isonitrosomethylacetone, CH,-C(NOH)-CO-CH,, with acid, and is a greenish-yellow liquid, smelling of quinone and boiling at 87°. The /3-diketones, like acetylacetone, CH,-CO-CH,-CO-CH3, b.-p. 137°, are remarkable for forming metallic compounds, e.g. beryllium acetyl-acetone (CgH;O.)2Be, m.-p. 108°, b.-p. 270°, the vapour density of which indicates beryllium to be bivalent ; the Al compound, m.-p. 193°, b.-p. 314°, shows Al to be trivalent. The /-diketones are characterised by the group —CO—CH,—CO—., go also are acetoacetic acid and malonic acid and their esters. They all form metallic derivatives. See also pp. 303, 600, 667. The y-diketones, e.g. acetonylacetone, CH,-CO-CH,-CH,-CO-CH;, do not share this property, but are important because of the ease with which they pass into closed-chain compounds of the furfurane or pyrrol type (q.v.). V. ETHERS The ethers are derived from the alcohols by the substitution of a hydro- carbon radicle for the hydrogen in the OH group; thus, if methyl alcohol, CH,-OH, be treated with Na, the hydroxyl hydrogen is displaced by sodium, and sodium methoxide, CH,-ONa, is obtained. If this be acted on by methyl iodide—CH,-ONa + CH,I = CH,-0-CH, + NaI—the H in CH,0H is displaced by CH,, and methyl ether, CH,-O-CHsg, is formed. It will be evident that a similar reaction between sodium meth- oxide and ethyl iodide, C,H,I, would furnish the mixed ether, methyl-ethy] ether, CH,-0-C,H;, so that the number of ethers obtainable would exceed that of the alcohols. Just as the alcohols are comparable with the metallic hydroxides (p. 574), albeit far less prone to chemical change, so the ethers may be compared with the metallic oxides deprived of most of their chemical energy. This view is supported by a second general method of preparing them, namely, by heating the alkyl halides with metallic oxides, 2CH,I + Ag,O = (CH,),0 + 2AgI; and by their reaction with hot hydriodic acid to yield an iodide and water, as the alkali oxides do— K,0 + 2HI = H,O + KI; and(CH,),0 + 2HI = H,O + 2CH,I. The usual method for obtaining the ethers is by the action of sulphuric acids on alcohols, as will be explained below. The ethers are generally sparingly soluble in water, and lighter and more volatile than the corresponding alcohols. They are almost as indifferent to reagents as the hydrocarbons are, and probably for a like reason, viz. that all the hydrogen is combined with carbon. The reaction of the ethers will be gathered from those of ethyl ether. It will be remarked that the ethers derived from the alcohols of the series C,H,,;,0 form an homologous series isologous with the alcohols, that each ether is metameric with the isologous alcohol, and that the ethers containing an odd number of carbon atoms are mixed ethers. Ethers. Alcohols. Methyl : ‘ . CH;-0-CH, Ethyl. ¥ _ : . C,H; -OH Methyl-ethyl : . CH,-0-C,H, Propyl ’ j . C,H, -OH Ethyl é ‘ . CyH,-0-C.H;, . Butyl 4 ; : . C,H, -OH Ethyl-propyl 5 . C,H,-0-C3H, Amyl : ‘ ; C;Hy,-OH Propyl : s . C3;H,:0-C;H, Hexyl : ‘ : . CgH)3-OH 1 By the new system of nomenclature, ketones are named like the alcohols (see foot-note, p. 581), on being substituted for -ol. Thus, CHyCO'CH,'CH, CH, is 2-pentanon (the O being attached to the second C atom). CH, CO'CH,CO-CH, is 2: 4-pentanedion. ETHERIFICATION 651 Methyl ether, or dimethyl oxide, CHs-O-CHs, is a fragrant inflammable gas prepared by adding methyl alcohol (2 parts by weight) to cooled strong H,SOg (3 parts) and heating to about 140°, keeping up a supply of methyl alcohol, as in the preparation of ether (q.v.), the reaction being the same as in the preparation of ether, if methyl be written for ethyl. The gas may be stored for use by passing it into cooled H,SO,, which dissolves 600 volumes of it and gives it up again when mixed with water. It is condensed by cold or pressure to a liquid boiling at — 21°, and used for producing cold. Water absorbs about 37 times its volume of the gas. Ether, or sulphuric ether, C,H;-O-C,H;, is prepared by distilling alcohol with sulphuric acid. If two measures of alcohol be carefully added to one measure of strong sulphuric acid, and the mixture distilled, ether passes over together with water, and if alcohol be added from time to time,:a small quantity of sulphuric acid suffices to etherify a large quantity of alcohol. The alcohol is first converted into hydrogen ethyl sulphate, or ethyl- sulphuric acid— SO,(OH,) + C,H,-OH = $0,(0H)(OC,H,) + HOH: When this is heated to about 140° with more alcohol, it is decomposed into ether and sulphuric acid, which then acts in the same way upon a fresh quantity of alcohol— SO,(0H)(OC,H;) + C,H;-OH = C,H,-0-C,H, + 80,(OH)s. Hence the process has been termed the continuous etherification process and is carried out in the following manner : Alcohol of sp. gr. 0-83 is carefully added, with continued shaking, to an equal volume of strong sulphuric acid, cooled in a vessel of water. When the mixtureis cold,itis poured a a into a retort or flask (Fig. 305), which is connected with a reservoir of alcohol and a well- cooled condenser. The mixture is quickly heated till it boils, when its temperature will be about 140°, and alcohol is then allowed to pass in slowly from a siphon tube furnished with a stop-cock, and dipping below the liquid in the flask; the temperature should remain as nearly as possible at 140°, : which will be the case if the Fic. 305. rate of flow of the alcohol is so Continuows: etherifieation, regulated as to keep the mixture at the same level. A thermometer is fixed in the cork with its bulb in the liquid. When the total quantity of alcohol used amounts to six or seven times that originally taken, the process must be stopped, becuuse secondary reactions, attended by carbon- isation, have used up much of the sulphuric acid. The liquid collected in the receiver contains about two-thirds of its weight of ether, with about one-sixth of water, an equal quantity of alcohol, and a little sulphurous acid. It usually separates into two layers, of which the upper is ether. The whole is introduced into a narrow-stoppered bottle, and shaken with cold water, added in small portions, as long as the layer of ether on the surface increases in volume; a little potash is then added to fix SQg, and, after shaking, the upper layer of ether is drawn off, by a siphon or separator, into a flask containing lumps of fused calcium chloride, to remove water and alcohol. After standing for some hours, the ether is distilled off in a water-bath at as low a tem- perature as possible. To free it entirely from water, it must be again rectified after digestion with powdered quick-lime, and finally with bright sodium, till no more 652 ETHER—PROPERTIES hydrogen bubbles are visible. Methylated ether is prepared from methylated spirit, and is much cheaper than pure ether, for which it may usually be substituted. Tt has been found that benzene-sulphonic acid (CgsH;SO,;H) may advantageously be substituted for the sulphuric acid, as it will etherify about 100 times its weight of alcohol. The acid is melted in the flask and alcohol run in slowly, the temperature being kept about 140°. C,H,;SO,C,H, is first formed and is decomposed by more alcohol into CsH;SO,H and (C,H;),0. Theory of etherification.—The process described above for the preparation of ether had long been practised before a satisfactory explanation of it was arrived at. One of the earliest views regarded the formation of ether as a simple removal of water by the sulphuric acid from the alcohol, which was then believed to be a compound of ether and water; but against this it was urged that the water was not retained by the acid, but distilled over with the ether, and that the same acid would etherify successive additions of alcohol. Passing over the theory of catalytic action, or decom- position by contact, which was a mere statement of the facts without any real explana- tion, we come to the important observation that the first product of the action of sulphuric acid on alcohol is ethylsulphuric acid, which is decomposed, when distilled with more alcohol at 140°, into ether, water, and sulphuric acid, as in the equations given on p- 651. Very strong evidence that the above equations represent the reactions occurring in the etherification process is furnished by the following experi- ment: Amyl alcohol, C;H,,-OH, is converted by sulphuric acid into amyl- sulphuric acid, C;H,,-SO,H, which is heated in the flask (Fig. 305), whilst ethyl alcohol, C,H,-OH, is allowed to flow in from the reservoir ; this decomposes the amylsulphuric acid, yielding sulphuric acid, and amyl-ethyl ether—C,H,,SO,H 4+ C,H,-OH = C;H,,:0-C,H; + H,SO,. If the process is continued after all the amyl-ethyl ether has passed over, only ethyl ether is obtained. In this manner any mixed ether can be prepared; also p. 653. Properties of ether.—A very mobile colourless liquid with a characteristic odour; sp. gr. at 15° 0-722. It boils at 35°, evaporates very rapidly in air, producing intense cold, and yielding a very heavy vapour, of sp. gr. 2-59, which is very inflammable, forms with air an explosive mixture, and renders ether dangerous in unskilled hands. It melts at — 117-6°. It is sparingly soluble in water, so that, when shaken with it, the ether generally rises to the surface on standing, rendering it very useful for collecting certain substances, such as bromine and alkaloids, from large bulks of aqueous solutions into a small bulk of ether. Ten volumes of water dissolve one volume of ether. Thirty-four volumes of ether are required to dissolve one volume of water, so that ether, free from alcohol, could not contain much water, but commercial ether contains alcohol, which enables it to take up a larger quantity of water. Ether and alcohol may be mixed in all proportions, but the addition of much water generally brings the ether to the surface. Ether is much used in laboratories as a solvent, especially for fatty substances, resins and some alkaloids; certain inorganic salts, e.g. HgCl,, dissolve in it. The photographer uses it in making collodion. Ether containing water becomes turbid when shaken with CS, or CHCl, and that containing alcohol dissolves sufficient aniline violet to become coloured when shaken with this dye-stuff. The properties of ether admit of some interesting experiments. (1) If a little ether be evaporated by blowing upon it in a watch-glass, with a drop of water hanging from its convexity, the water will be speedily frozen. A thin beaker containing ether may be frozen to a wet table by blowing into it with the bellows. (2) A piece of tow, wool, or sponge, wetted with ether, is placed at the upper end of a sloping trough or gutter of wood or metal, over six feet long ; a match applied at the lower end fires the train of vapour. ETHER—CHEMICAL REACTIONS 653 ; (3) A jug is warmed with a little hot water, emptied, and a little ether poured into it; the vapour may be poured into a row of small beaker-glasses, each of which is afterwards tested with a taper. (4) A pneumatic trough is filled with warm water, and a small test-tube filled with ether is inverted with its mouth under the water, and quickly decanted up into a gas-jar filled with warm water, when it will be vaporised, and may be decanted through the water into other vessels, and treated like a permanent gas. Some cold water poured over the jar containing it at once proves its condensable character. Ether is also produced by the reactions given on p. 650, C,H, being substituted for CH; in the equations. Ethyl iodide, heated with a small quantity of water, under pressure, yields, first alcohol, and afterwards ether— C,H;I + HOH = C.H,-OH + HI, and C,H,I + 0,H;-OH = 0,H,-0-C,H, + HI. Other acids besides sulphuric are able to produce ether from alcohol, especially those which are non-volatile and polybasic, such as phosphoric, arsenic, and boric, which probably act in the same way as sulphuric. But certain salts, such as zinc chloride and aluminium sulphate, also generate ether from alcohol, and the explanation of this is less simple. It will be found that such salts are capable of decomposition by water, with formation of basic salts and free acid ; thus, ZnClp + HOH = ZnCl-OH + HCl, or, Al,(SO,), + 4HOH = Al,80,(OH), + 2H,S0, If these reactions occur with alcohol, C,H;-OH, instead of with HOH, the products would be C,H,Cl instead of HCl, and C.H;HSO, instead of H,SO,, and either of these would react with the excess of alcohol to produce ether. Ether may be converted into alcohol by heating it with water and a very little sulphuric acid, in a sealed tube, at 180°. The ether is probably converted at first into ethylsulphuric acid, and this into alcohol and sulphuric acid, the etherification reaction (p. 651) being reversed. When ether is acted on by hydriodic acid gas, in the cold, it yields alcohol and ethyl iodide ; (C,H;)o0 + HI = C,H,-OH + C,H,;I. If a mixed ether, such as ethyl- amyl ether, be treated in this way, the radicle containing more carbon is the one con- verted into an alcohol ; C,H,;-0-C;H,, + HI = C;H,,-OH + C,H;,I. Ordinary oxidising-agents convert ether into aldehyde and acetic acid. Ozonised oxygen converts it into formic, acetic, and oxalic acids and hydrogen peroxide. When ether vapour is passed over heated potash, hydrogen, marsh gas, and potassium carbonate are formed, potassium acetate being probably produced in the first stage of its reaction ; (Cp.H;),.0 + 2KOH + H,O = 2KC,H,0, + 4Hg. Ether enters into combination with several metallic chlorides and bromides, forming crystalline compounds ; stannic chloride combines with two molecules of ether, forming SnCl,(C,H,,0). ; aluminium bromide forms Al,Brg(C4Hy 90). : Ether is inflamed by contact with chlorine; but if it be very well cooled, and light be excluded, it yields a series of substitution-products. Monochlorether, dichlorether, and tetrachlorether are known. Perchlorinated ether, CyCl,)O, requiring sunlight for its formation, is a crystalline body (m.-p. 68°) smelling like camphor. Distilled with PCl;, ether yields C,H,;Cl and POCI;, but no HCl (cf. p. 592). Ethers from Polyhydric Alcohols.— By treating monosodium — glycol C2H,(OH)(ONa) with C,H;I, as in the general reaction (p. 650), monoethyl-glycol ether, C.H,(OH)(OC,H;) (b.-p. 127°) is obtained. If disodium glycol be similarly treated, diethyl glycol-ether, CgH4(OC.H;)2 (b.p. 123°) is obtained. Regarding the formation of an ether as the abstraction of HOH from the two OH groups of two molecules of an alcohol, glycol might be expected to form an internal CH, ether, | yo. This compound, ethylene oxide, is produced when glycol chlorhydrin CH CH,OH CHa. (p. 588) is distilled with potash: | + KOH = | wee + KCl + HOH. CH,Cl CH, It is an ethereal liquid isomeric with acetaldehyde which is ethylidene omide, CH,CHO. Ethylene oxide is characterised by its additive properties; e.g. with H,O —-+ glycol; nascent H’ —-> alcohol; usually itg passes back into glycol 654 ZEISEL’S METHOD derivatives. It is not affected by zinc alkyls. B.-p. 14°; sp. gr. 0-898 (0°). Tri- fe ee methylene oxide, CH eo boils at 50° and is similarly prepared from the CH, chlorhydrin of propylene glycol, CH,Cl-CH,-CH,OH. ; ; Glyceryl ether, CzHs-Og'CzH,, may be regarded as glycerol, C;H;(OH)s, in which glyceryl, C3H;, has been substituted for the H, of the (OH)3. It is formed when glycerin is distilled with CaCl, and is a colourless, inodorous liquid, boiling at about 170°, and of sp. gr. 1-16; it mixes with water. Its behaviour with hydriodic acid is analogous to that of ethyl ether, for it is converted into glycerol and glyceryl tri-iodide, CHI. : Whe oiaeie Ethers.—These may be either the true ethers corresponding with the aromatic alcohols, or ethers derived from phenols, which, it will be remembered, differ from the alcohols in having the OH group attached directly to the benzene nucleus. Benzyl ether, (CsH;-CHg)20, is prepared by distilling benzyl alcohol with B,O3 which removes the elements of water, 2CgH,-CH,OH — HOH = (CsH,-CHy),0. It is a P colourless liquid not mis- cible with water, and boil- ing at 296°. Diphenyl oxide, or phenyl ether, CgH;-O-CgH,, obtained by distilling phenol with aluminium chloride, forms prisms, fusing at 28° and boiling at 252°. Itsmells like the geranium leaf, and is re- markable for its stability under the influence of oxi- dising- and reducing- agents. Water does not dissolve it, but alcohol and tb ether do so. Phenyl-methyl ether, C,H,;-O-CH;, is prepared by passing methyl chloride through sodium phenol at 200°. It is a fragrant liquid, of sp. gr. 0-991, boiling at 152°. This ether is identical with anisol, obtained by dis- tilling anisic acid (p. 620) with baryta. Methyl - salicylate, or wintergreen oil, CgH4(OH)-CO,-CHs, is metameric with anisic acid, and also _ yields phenyl-methyl ether when distilled with baryta. Hy- driodic acid heated to 140° with anisol, in a sealed tube, converts it into phenol and methyl iodide ; CgH;-OCH, + HI=C,H,-OH + CH,I. This reaction is typical of the method commonly employed in determining the number of methoxy-groups (OCH;) in the molecule of a compound. It is known as Zeisel’s method, and consists in boiling a known weight (0-3 gram) of the substance with fuming hydriodic acid (10 ¢.c.) in a flask A (Fig. 306) through which a gentle current of CO, is passed. This carries the CHI, water vapour and HI through the condensing-tube B, containing a number, of aludels shown drawn to an enlarged scale Fig. 306. METHYL CHLORIDE 655 at C. The temperature of the water-bath D is regulated to ensure that the distillation shall not be too rapid, which is indicated by the thermometer HZ marking a temperature of 50°. The methyl iodide does not condense at this temperature and passes through the absorption flasks #, containing water and red phosphorus, where it leaves the HI and a little free I that it contains, and then into a wash bottle containing an alcoholic solution of silver nitrate. Here the methyl iodide is decomposed yielding a precipitate of AgI, which is collected, washed, and weighed. From its weight that of the CH;I and therefore of the OCH; in the compound taken, is calculated. The methyl ethers of the phenols are formed at the ordinary temperature when diazomethane, CH,N>, and a phenol are brought in contact, e.g. CsH;0H + CH,N2 = C.H,OCH; + Ny. They are not changed when heated with alcoholic potash. Anethol, the camphor-like substance in oil of anise, is 1: 4-propenyl-anisol, CH; CH : CH-C,H,-OCH; ; it melts at 22° and boils at 233°. Phenyl ethyl ether, CgH;-O-C,H;, or phenetol is obtained by distilling ethyl salicylate with baryta ; it boils at 172°. VI. HALOGEN DERIVATIVES Halogen Compounds from Hydrocarbons.—(A) From open-chain hydrocarbons.—It has been already noticed (p. 550) that these products result in many cases from the direct action of the halogens on the hydro- carbons, but whilst Cl and Br react thus by metalepsis with hydrocarbons, iodine seldom does so unless an absorbent for HI (e.g. HgO) be present ; this is because the metalepsis is a reversible reaction (p. 342), e.g. CH, + I, = CH,I + HI Since the unsaturated hydrocarbons generally combine with the halogen to form addition products (p. 553), which are either identical or isomeric with the di-halogen substituted saturated hydrocarbons,! some other method must generally be resorted to in order to prepare halogen substitution-products of unsaturated hydrocarbons. Thus, they are obtained either by treating the halogen substituted saturated hydro- carbons with reagents which will remove halogen hydride, or by only partially saturating still more unsaturated hydrocarbons with halogen; e.g. C,H,Cl, — HCl = C,H,Cl; C,H, + Cl, = C,H,Cl,. The halogen substitution-products from all hydrocarbons are obtain- able by the interaction of the alcohols with phosphorus halides, or, what is equivalent, with phosphorus and a halogen. Examples will be met with in the following pages. In a large number of cases the mere treatment of an alcohol with halogen hydride, particularly in the presence of a de- hydrating agent, will produce the halogen substitution-product, the reaction being of the type R-OH + HX = RX + HOH. : Methyl chloride, or monochloromethane CH,Cl, is prepared by passing HCl gas into a boiling solution of zinc chloride in twice its weight of methyl alcohol, contained in a flask connected with a reversed condenser. The methyl chloride is evolved as a gas which may be washed with a little water to remove HCl, dried by passing over calcium chloride, and condensed in tubes cooled in a mixture of ice and calcium chloride crystals. The final result is expressed by the equation CH,0H + HCl = CH,Cl + HOH. The action of the zinc chloride is little understood. Methyl chloride is an inflammable gas of ethereal odour, liquefied by a pressure of 24 atm. at 0°. Its boiling-point is — 24°. Water dissolves 4 vols. of the gas and alcohol 35 vols. 1 It will be remembered that the unsaturated hydrocarbon will also combine directly with halogen- hydrides to form substituted saturated hydrocarbons. It is to be noted that whea this is the case the halogen attaches itself to the carbon atom which has the smallest number of hydrogen atoms attached to it. Thus, from propylene, CH,-CH : CH,, and HCl, there is formed CH, CHCI‘CH,, isopropyl chloride, not CH,‘CH.-CH,Cl, 656 ETHYL IODIDE Methyl chloride may also be prepared by distilling methyl alcohol with sodium chloride and sulphuric acid. It is made on a large scale, for use in freezing-machines, from the trimethylamine obtained by distilling the refuse of the beet-sugar factories ; this is neutralised with hydrochloric acid, and heated to 260° (p. 696), when it is decomposed into trimethylamine, ammonia, and methyl chloride ; 3N(CH;)sHCl = 2N(CH;), + NH, + 3CH,Cl. Methyl chloride is very stable ; potash decomposes it with difficulty, yielding methyl alcohol and potassium chloride. It is used in the preparation of some of the aniline colours. Ethyl chloride, or monochlorethane, C,H,;Cl, is prepared by substituting ethyl for methyl alcohol in the foregoing prescription. The purified vapour is passed into 95 per cent. alcohol kept cool by water. The alcohol absorbs half its weight of ethyl chloride, which may be evolved from it by gently heating, and purified by passing through a little sulphuric acid. It is a fragrant liquid of sp. gr. 0-921 (0°), boiling at 12-5°. It is sparingly soluble in water, and burns with a bright flame edged with green. Ethyl chloride is formed when olefiant gas and HCl are heated together for some time. Its evaporation causes intense cold and so it is used as a local anesthetic. Methyl bromide, CH,Br, is prepared by acting upon methyl alcohol with phosphorus and bromine; 8CH,;0H + 3Br + P = 3CH,;Br + P(OH);. Four parts of methyl alcohol are poured on 1 part of red phosphorus in a well-cooled retort with reversed condenser, and 6 parts of bromine are gradually added. After two or three hours, heat is applied by a water-bath, and the vapour condensed by a freezing-mixture. Methyl bromide boils at 4:5°, burns feebly, and smells like chloroform; sp. gr. 1-73 (0°). Ethyl bromide, C,H;Br, may be prepared like methyl bromide, using 16 parts of absolute alcohol, 4 parts of red phosphorus, and 10 parts of bromine. It is a liquid boiling at 39°; sp. gr. 1-419. Methyl iodide, CHI, is prepared on the same principle as the bromide, 10 parts of iodine being dissolved in 4 parts of methyl alcohol, and 1 part of red phosphorus added in small portions. After heating in a water-bath for some time, the mixture is distilled. The methyl iodide is the lower layer of the distillate. It has a pleasant smell, sp. gr. 2-29, and boils at 44°. It mixes with alcohol, but not with water. When kept, it becomes brown from separation of iodine. It is converted into CH,Cl gas when heated with HgClp dissolved in ether. Hydriodic acid, at 150°, converts it into CH,. Methyl iodide is used in making aniline dyes. Methyl fluoride, CH;F, is a combustible gas obtained by heating KF with potassium methyl sulphate, KCH,S0,. Ethyl fluoride boils at — 48°. Ethyl! iodide, C,H,I, is prepared by pouring 5 parts of absolute alcohol on one part of red phosphorus in a distilling flask, adding gradually 10 parts of iodine in powder, setting aside for twelve hours, and distilling in a water- bath with a good condenser. Ethyl iodide mixed with alcohol distils over, leaving phosphoric acid in the retort (together with some phosphethylic acid formed by its action on some of the alcohol), 3C,H,OH + P + 3I = 3C,H;I + P(OH);. This distillate is shaken, in a stoppered bottle, with about an equal measure of water and enough soda to render it alkaline. The ethyl iodide collects as an oily layer at the bottom ; this is separated from the upper layer by a tap-funnel or pipette or siphon, allowed to stand with a little fused calcium chloride in coarse powder, to remove the water, and distilled. Ethyl iodide has a pleasant smell, b.-p. 72°, sp. gr. 1-93, which is lower than that of methyl iodide, and this is lower than that of methylene iodide ; the specific gravity varying with the percentage of halogen and its atomic weight. It becomes brown when kept, especially in the light, iodine being CHLOROFORM 657 liberated, and butane formed; 2C,H,I =C,H,,+1,. Ethyl iodide is sparingly dissolved by water, but readily by alcohol and ether. Ethyl iodide is a very important reagent in organic researches for intro- ducing the group C,H, into the places of other radicles. The monohalogen substitution-derivatives of the paraffins higher in the series than ethane, exist in isomeric forms exactly analogous to the isomeric alcohols (p. 579), a halogen being substituted for OH. Dihalogen derivatives of ethane can obviously exist in two modifications, CH,X-CH,X, or ethylene halides, and CH,-CHX,, ethylidene halides. The former are obtained by the direct addition of halogen to ethylene, and since by judicious treatment with moist silver oxide they can be converted into glycol halogen-hydrins (e.g. glycol chlor-hydrin, q.v.) they most probably have the formula assigned to them above ; moreover, they may be prepared from the glycols by distillation with phosphorus halides. The ethylidene halides can be obtained from aldehyde by treatment with phosphorus penta- halides (p. 592). Ethylene chloride, ethene dichloride, or Dutch liquid, CoH,Cl,, may be obtained from glycol by distilling it with PCl,— C,H,(OH), + 2PCl, = C,H,Cl, + 2POCI, + 2HC1; but it is generally prepared by allowing equal volumes of dry ethene gas and dry chlorine to pass into a large inverted globe or flask, the neck of which passes through a cork into a receiver for the condensed liquid. Ethene dichloride smells rather like chloroform ; its sp. gr. is 1-28, and it boils at 84°; it is nearly insoluble in water, but dissolves in alcohol. Ethylidene chloride, CHz,CHCl,, is best prepared by the action of COCI, on CH;-CHO, carbon dioxide being liberated ; b.-p. 60°. Ethylene bromide, or ethene dibromide, C.H4Bro, is prepared as described at p. 587. It resembles the dichloride, but its sp. gr. is 2-16, and it boils at 131°. Ethylene iodide, C2H4Iz, obtained by heating iodine in olefiant gas, forms silky needles, which may be sublimed in the gas, but are easily decomposed into CoH, and Ip. The difference in the stability of ethene chloride, bromide, and iodide is shown by the action of alcoholic solution of potash, which converts ethene dichloride into monochlorethene, or vinyl chloride, CgH,Cl, + KOH = C.H3Cl + KCl + HO; whilst the dibromide yields, in addition to the vinyl bromide, a quantity of acetylene ; C.H,Br, + 2KOH = C,H, + 2KBr + H,O; and the di-iodide is much more easily decomposed, giving very little vinyl iodide and much acetylene. Methylene iodide, CHpI,, may be obtained by heating iodoform with strong HI in a sealed tube, at about 130°, for some hours; CHI, + HI = CH,I,+],. It is a liquid remarkable for its high specific gravity, 3-328, and is used for determining the specific gravities of precious stones. It boils at 181°. Chloroform, or tri-chloromethane, CHCl,, the anesthetic, is prepared by distilling 1 part of alcohol (sp. gr. 0-834) with 10 parts of chloride of lime and 40 parts of water, at 65°, until about 14 part has passed over; the distilled liquid, consisting chiefly of water and chloroform, separates into two layers; the chloroform which is at the bottom, is drawn off, shaken with strong sulphuric acid to remove some impurities, and when it has risen to the surface it is separated and purified by distillation until it boils regularly at 61°. Chloroform is prepared from acetone in a similar manner. The action of chloride of lime on alcohol has not been clearly explained ; it might be expected that chloral would be formed at first by the oxidising and chlorinating actions, and that this would be converted into chloroform and calcium formate by the strongly alkaline calcium hydroxide in the chloride of lime (see Chloral), but much CO, is given off, causing frothing during the distillation. Probably the chloroform is produced by some such reaction as the following : 3C,H,O + 8Ca(OCl), = 2CHCI, + 8H,O + CO, + 5CaCl, + 3CaCO3. 42 658 IODOFORM Pure chloroform is more easily prepared by decomposing chloral hydrate with potash or soda. Chloroform is a very fragrant liquid of sp. gr. 1-50, and boiling-point 61-5°; solidified, it meltsat — 62°. It is very useful in the laboratory as a solvent, and is much used for extracting strychnine and other alkaloids from aqueous solutions. It is also one of the best solvents for caoutchouc. Chloroform is very slightly soluble in water (1 in 185), and gives it a sweet taste. Alcohol and ether dissolve it in all proportions. It is insoluble in glycerin. Strong sulphuric acid does not affect it or colour it, if the chloroform is pure. Aqueous solution of potash does not decompose it, but the alcoholic solution converts it into potassium chloride and potassium formate ; CHCl, + 4KOH = 3KCl + HCO-OK + 2QHOH. If Dutch liquid (C,H,Cl,) be present as an impurity in the chloroform, gaseous chlor- ethylene (C,H,Cl) is formed. Pure chloroform does not keep well, the medicinal article contains } to 1 per cent. absolute alcohol. When heated with alcoholic potash and aniline, it yields phenyl-carbamine (q.v.), the powerful odour of which renders this a delicate test for chloroform. Chloro- form of crystallisation, pp. 324, 620. Heated with alcoholic solution of ammonia in a sealed tube at 180° chloroform gives ammonium chloride and cyanide ; CHCl, + 5NH3 = 3NH,Cl + NH,-CN. When potash is present a similar reaction occurs at the ordinary temperature, CHCl, + NH, + 4KOH = KCN + 3KCl + 4H,0. Heated with potassium-amalgam, chloroform evolves acetylene ; 2CHCl, + 3K, = C,H, + 6KCl. That chloroform is really a substitution-derivative from methane is shown by its production from that gas (p. 550) and by its conversion into it when dissolved in alcohol and heated with zinc-dust; by the formation of tetrachloro- methane, CCl,, by the action of chlorine (in presence of iodine) upon chloroform, and by its formation from dichloromethane, CH,Cly, by the action of zinc and sulphuric acid. When chloroform is heated with sodium ethoxide, it is converted into orthoformic ether ; CHCl, + 3NaOC,H, = 3NaCl + CH(OC,Hs)3. Bromoform, CHBrs, is produced when bromine is added to an alcohole solution of potash. It has a general resemblance to chloroform, but boils at 151°. Crude bromine sometimes contains bromoform. Iodoform, or tri-iodo-methane, CHI, is a product of the action of iodine upon alcohol in an alkaline solution, the immediate agent being probably a hypo-iodite, whilst chloroform is produced by a hypo-chlorite. To prepare it, dissolve 32 parts of potassium carbonate in 80 parts of water, add 16 parts of alcohol of 95 per cent. and 32 parts of iodine ; heat gently till the colour of the iodine has disappeared, when iodoform will be deposited. on cooling. CH,-CH,OH + 6KOH + 41, = CHI, + HCOOK + 5KI + 5H,0. To recover the iodine left as KI, the filtrate from the iodoform is mixed with 20 parts of HCl and 2-5 parts of potassium dichromate, which liberates the iodine. The liquid is neutralised with potassium carbonate, and 32 parts more of that salt are added, together with 6 parts of iodine and 16 of alcohol ; the operations of heating and cooling are then repeated. Todoform is deposited in yellow shining hexagonal plates, of characteristic odour. It fuses at 120°, and may be sublimed with slight decomposition. It is insoluble in water, but dissolves in alcohol and ether. When boiled with potash, it is partly volatilised with the steam, and partly decomposed, yielding potassium iodide and formate. The production of CHI, on adding iodine and dilute KOH and stirring, is a very delicate test for alcohol, but many other substances, e.g. acetone, also yield it. Iodoform is used in medicine and surgery as an antiseptic. ALLYL HALIDES 659 Chloriodoform, CHIC\,, is obtained by distilling iodoform with HgCl,. It is a yellow liquid, b.-p. 131°. The corresponding Br compound has been prepared. Trichloropropane exists in several forms. The commonest of these is glyceryl trichloride or trichlorhydrin, CH,Cl-CHCI-CH,Cl ; it is obtained by the action of PCI; upon glycerin, C;H;(OH), + 3PCl; = C3;H;Cl; +3HCl + 3POCI,. It is a liquid of pleasant smell, sp. gr. 1-42, and boiling at 158°. It is sparingly soluble in water. Tribromhydrin, CsH;Brs, is a crystalline solid ; m.-p. 17°, b.-p. 220°. The iodine com- pound corresponding with this does not appear capable of existing (v. infra). Tetrachlorethane (symmetrical) or acetylene tetrachloride, ClhAHC-CHClp, is now manu- factured in large quantities and used as a cheap “ organic solvent ” for oils, resins, collodions, &c. It is produced by passing acetylene into antimony pentachloride ; also by aléernately leading currents of chlorine and acetylene into a cold mixture of sulphur chloride and 1 per cent. of reduced iron. It is a very heavy liquid, similar in odour to carbon tetrachloride ; b.-p. 147°. The unsymmetrical metamer, CCl;-CH2Cl, is also known ; b.-p. 130°. Perchlorethane ov hexachlorethane, C,Cl,, is produced by treating Dutch liquid (p. 256) with excess of chlorine in sunlight. It is a white crystalline solid, sp. gr. 2-01, m.-p. 187°, b-.p. 185°-5, 777 mm. It sublimes at ordinary temperature. By treatment with nascent hydrogen (zinc and sulphuric acid) it yields tetrachlorethylene, C,Cl,, a colourless liquid which boils at 121°. Allyl chloride, CH, : CH-CH,Cl, is obtained by distilling allyl alcohol with PCl,. It has a pungent smell, sp. gr. 0-95, and boiling-point 46° ; it is insoluble in water. Allyl bromide may be prepared by distilling allyl alcohol with KBr and H,SO,, mixed with an equal bulk of water. It is capable of combining with bromine to form glyceryl or allyl tribromide, C;H,Br3, and with HBr to form CH,Br-CH,:CH,Br, trimethylene bromide. Allyl iodide, C;H;I, is prepared from glycerin (200 parts) by adding iodine (135), filling the retort with CO, and adding, very gradually, vitreous phosphorus (40). The distilled liquid is washed with a little NaOH, and dried with CaClz. Probably, glyceryl tri-iodide is first produced; C,;H;(OH), + P + 3I = C3H;I, + P(OH); ; the tri-iodide is then decomposed into C3;H;I and I,. Allyl iodide has a very pungent odour of leeks, sp. gr. 1:8, and boiling-point 101°. It is remarkable for combining with mercury, shaken with its alcoholic solution, to form mercury allyl iodide, Hg’ C,H;I, deposited in colourless crystals, which become yellow in light, and yield HgI, and C3H;I when treated with iodine. Ag,O, in presence of H,O, substitutes OH for the I, producing HgC,H;-OH, mercury allyl hydroxide, an alkaline base. Bromine converts allyl iodide into tribromhydrin, C;H;Br;. The halogen propylenes—e.g. a-chloropropylene, CH,-CH : CHCl,—isomeric with the allyl halides, exist in a maleinoid and a fumaroid modification (p. 638). Propargyl chloride, CH : C-CH,Cl, is obtained by acting on propargyl aleohol with phosphorus chloride ; it boils at 65°. (B) Halogen Derivatives of Closed-chain Hydrocarbons.—These may be halogen substitution or addition products. The substitution may be either in the benzene or other nucleus, or in side-chains, or in both. Thus, while only one compound of the formula C,H,X exists, there are 4 of the formula C,H,X, namely, C,H,X-CH,(3) and C,H,-CH,X. Again, 3 compounds of the form C,H,X, are known, and 10 of the form C;H,X), viz. C,H, X,"CH,(6), C;sH,X-CH,X(3) and C,H;-CHX,. The nucleal substitution-products are more stable than are the open- chain hydrocarbon substitution-products. Thus, C,H;Cl will not yield C,H,OH when treated with AgOH, whilst C,H;Cl yields C,H;OH by this treatment. But the side-chain substitution-products behave as open-chain derivatives. The direct action of halogens on benzene itself produces chiefly substitu- tion-products (see p. 559). In the ‘case of its homologues, nucleal substitu- tion occurs if the action be allowed to proceed in the cold, especially in the dark and in presence of iodine; whilst at higher temperatures, and in 660 AROMATIC HALOGEN DERIVATIVES sunlight, side-chain substitution occurs. Thus, C,H,Br-CH, is formed when Br attacks cold toluene, but C,H,;-CH,Br if the temperature is higher. The treatment of phenols or alcohols with phosphorus halides, and a special reaction to be described under Diazo-compounds, also yield these halogen derivatives. The addition-products with chlorine (see also p. 559), benzene dichloride, C,H,Cl, ; tetrachloride, C,H,Cl, ; hexachloride, CgH,Cl,, are less stable than the substitution-products ; thus, the hexachloride, when heated with potash dissolved in alcohol, yields trichlorobenzene ; CeH,Cl, + 3KOH = C,H,Cl; + 3KCl + 3H,0. Chlorobenzene, or phenyl chloride, CsH;Cl, may be prepared by passing Cl into C.Hg, containing 3 per cent. of AlpClg, until the calculated gain of weight is observed ; or by the action of PCl; on phenol ; CsH;OH + PC], = CgH;Cl + POC], + HCI; it is a colourless liquid, of almond-like odour, b.-p. 132°, not decomposed by alkalies, recon- verted into benzene by nascent H’ (water and sodium amalgam). By the further action of chlorine the di-, CgH4Cle, tri-, CsH3Cly, tetra-, CsH2Cl,, penta-, CsHCI,, and hexa-, CgCl,, chlorobenzenes are formed. They are all crystalline solids. Bromobenzene (b-.p. 155°) is similarly prepared. Iodobenzene (b.-p. 188°) may be obtained by heating benzene with iodine and HIO, (to absorb HI; p. 655) at 200°. By dissolving it in CHCl, and passing Cl through the solution iodobenzene dichloride, CgHsI : Cle, is prepared ; this is of theoretical importance, since the iodine in it is trivalent ; when it is treated with NaOH it yields iodosobenzene, CgH;1: O, which is a base forming salts such as C.H;I : OCrO, ; when heated it becomes iodobenzene and iodoxybenzene, CgH;IOz, an explosive substance presumably containing pentavalent iodine. On shaking a mixture of iodo-and iodoso-benzene with moist Ag,O, a strongly alkaline solution of diphenyl-iodonium hydroxide, (CgH;).I1.OH. is formed, which forms salts (p. 131). o-and-p-Chlorotoluenes, CgH,Cl-CH;, are obtained by passing Cl into cold toluene containing iodine. Benzyl chloride, CsH;-CH,Cl (b.-p. 176°), benzal (benzylidene) chloride, CsH;-CHCl, (b.-p. 213°), and benzotrichloride or phenyl-chloroform, CgH;:CCl, (b.-p. 213°), are obtained by chlorinating boiling toluene, the Cl being passed into the liquid until the increase of weight calculated for the particular compound required has been attained. They are colourless liquids + and can be prepared by the action of PCI, on the corresponding oxygen compounds—viz. benzyl alcohol, benzoic aldehyde, and benzoic acid—into which they are converted by hydrolysis. They are intermediate products in the manu- facture of benzaldehyde from toluene (p. 597). Two of each of the monohalogen substitution products of naphthalene exist (p. 571). a-Chloro-naphthalene, CypH,Cl, is a colourless liquid (b.-p. 263°) and is the product of passing Cl into boiling naphthalene. 8-Chloro-naphthalene crystallises in lamine (m.-p. 61°; b.-p. 257°), and is obtained by treating a-naphthol, C,)H,-OH, with PCI. Ten dichloro-naphthalenes are known. When naphthalene is chlorinated in the cold, the addition-product, naphthalene tetrachloride, CyyH,Cly, is formed (p. 571); this crystallises in colourless rhombohedra, melts at 182°, and becomes C,)H,Cl, when boiled with KOH. Since it yields phthalic acid and not a chlorophthalic acid when oxidised, all the Cl atoms must be in the same benzene nucleus, and the compound must have the orientation 1: 2:3: 4 (p. 571). Anthracene dichloride, CgH4: (CHCl), : CgHy, is formed when chlorine is passed over cold anthracene, whilst at « high temperature y-chloranthracene (m.-p. 103°) and y-dichloranthracene (m.-p. 209°) are produced (p. 573) as yellow needles. The halogen derivatives from other condensed benzene nuclei are of little importance. Halogen Compounds from Aldehydes and Acids.—Chloral or tri- chloraldehyde, CCl,-CHO, is prepared by passing thoroughly dried chlorine into absolute alcohol, which must be placed in a vessel surrounded by cold water at first, because the absorption of chlorine is attended by great evolu- tion of heat. The passage of chlorine is continued for many hours, and when the absorption is slow, the alcohol is gradually heated to boiling, + Benzyl chloride and benzyl bromide have a tear-exciting odour. CHLORAL 661 the chlorine being still passed in until the liquid refuses to absorb it. The resultant reaction is represented by the equation, CH,-CH,-OH + 4Cl, = 5HCl + CCl;-CHO ; but it is very complex ; the HCl attacks part of the alcohol, forming ethyl chloride and water. On cooling, the product solidifies to a crystalline mixture of the compounds of water and alcohol with chloral, from which the latter may be obtained by distillation with sulphuric acid. On the large scale, chlorine is passed into alcohol of at least 96 per cent. for 12 or 14 days. The crude product is heated with an equal weight of strong H,SO,, in a copper vessel lined with lead. HCl escapes at first, and the chloral distils over at about 100°. ~The distillate is rectified, and mixed with water in glass flasks, when chloral hydrate, CCl,;-CHO.H,0, is formed, which is poured into porcelain basins, where jt crystallises. Chloral is a liquid of sp. gr. 1-5, and boiling-point 97°. It has a pungent, tear-exciting odour, and irritates the skin. Exposed to air, it absorbs water and forms crystals of the hydrate, which is produced at once when chloral is stirred with a few drops of water, heat being evolved. When quite pure it may be kept unchanged, but, in presence of impurities, especially of sulphuric acid, it soon becomes an opaque white mass of metachloral, which is insoluble in water, alcohol, and ether. This is probably formed by the condensation of three molecules of chloral, into which it is recon- verted at 180°. It will be remembered that aldehyde is liable to a similar’ polymerisation. Chloral also resembles aldehyde in forming crystalline compounds with NaHSO,, and in giving a mirror of silver with silver ammonio-nitrate. With ammonia it forms CCl,-CH(NH,)(OH), correspond- ing with aldehyde-ammonia. Zine and HCl substitute H, for the Cl, in chloral, converting it into aldehyde. Nitric acid oxidises it to trichloracetic acid, CCl,-CO,H, which forms deliquescent crystals and boils at 195°. When heated with KCN and H,0 it yields dichloracetic acid (b.-p. 191°), CCl,-CHO + KCN + H,0 = CHCl,-CO.H + KCl + HCN. Potash decomposes it easily, producing chloroform and _ formate ; CCl,,CHO + KOH = CCl,H + H-CO-OK. Chloral is formed when starch or sugar is distilled with HCl and MnQ,. Chloral hydrate, CCl,-CH(OH),, trichlorethylideneglycol, forms pris- matic crystals, which are very soluble in water and alcohol and have the odour of chloral. It fuses at 57°, and boils at 97°, but is dissociated into chloral and steam, which recombine on cooling. It is one of the very few compounds in which two OH-groups are attached to the same C-atom (p. 587). It is employed medicinally for procuring sleep. Chloral alcoholate, CCl,-CH(OH)(OC.H;), formed when chloral is dissolved in alcohol, crystallises like the hydrate, but is rather less soluble in water. Bromal, obtained by action of Br on alcohol, is very similar to chloral. Butyl chloral, CH,-CHCI-CCl,CHO, is a-a-/3-trichlorobutyric aldehyde, and is prepared by substituting aldehyde for alcohol in the preparation of chloral, when croton-aldehyde is first produced, and is converted into butyl chloral ; (1) 2CH,CHO = CH,-CH : CH-CHO + H,0 ; (2) CH,-CH : CH-CHO + 2Cl, = CH;-CHCI-CCl,-CHO + HCl. It is an oily liquid of pungent odour, sp. gr. 1-4, and boiling-point 164°. It combines with water to form butyl-chloral hydrate, CH3-CHCI-CCl,-CH(OH)s, which dissolves in hot water, and crystallises, on cooling, in lamine, which have a pungent odour ; m.-p. 77-8°. It is used in medicine. Halogen Compounds from Acids by Substitution of Halogen for Hydroxyl.—Acid halides. These bodies havet heir counterparts among inorganic compounds; thus, nitrosyl chloride, NOCI, is obtained by substituting Cl for OH in nitrous acid, NO-OH; and, in acetic acid, CH,-CO-OH, a similar exchange gives acetyl chloride CH,-CO-Cl. Thus, 662 ACETYL CHLORIDE they are haloidanhydrides (p. 198), or the halides of negative radicles, just as the7alkyl halides may be regarded as halides of positive radicles and compared with KCl. They are generally prepared by the action of phosphorus halides on the acids. No compound of this kind has been obtained from formic acid. Acetyl chloride, CH,-CO-Cl, or acetic chloride, is prepared by distilling acetic acid with phosphorus trichloride ; 3CH,COOH + PCl, = 3CH;-COCI + P,0, + 3HCL. To 5 parts by weight of glacial acetic acid, kept cool, are gradually added 4 parts of phosphorus trichloride, and the mixture distilled on a water- bath. The distillate may be rectified over fused sodium acetate to remove any phosphorus trichloride. The pentachloride may also be used, CH,-COOH + PCI, = CH,-CO-Cl + POCI, + HCl. Acetyl chloride is a colourless liquid, which fumes in air, and has an irritating odour ; its sp. gr. is 1-11, and it boils at 55°. Water decomposes it very energetically, yielding hydrochloric and acetic acids ; CH,-CO-Cl + HOH = CH;-CO-OH +HCl. Tf an alcohol be employed instead of water, an ester is produced, e.g. CH,-CO-Cl + C,H,-OH = CH,-CO-0C,H,; (ethyl acetate) + HCl. This mode of reaction renders acetyl chloride a most useful reagent for discovering hydroxyl growps (infra). Some other instructive reactions produce acetyl chloride, such as that between acetic anhydride (di-acetyl oxide) and phosphorus pentachloride, (C2H30),0 + PCl; = 2C,H,OCl + POC]; or between phosphorus oxychloride and sodium acetate— POC], + 2CH,COONa = 2CH,COC] + NaPO; + NaCl; it was thus that acetyl chloride was first made. By distilling sodium acetate with acetyl chloride, acetic anhydride is obtained—C,H;0-ONa + C,H,0-Cl = (C,H30),0 + NaCl. By careful treatment with sodium-amalgam and snow, ethyl alcohol has been prepared from acetyl chloride ; C,H,0Cl + 4H = C,H;OH + HCl. Acetyl bromide, CH3-CO-Br, is prepared by distilling acetic acid with bromine and phosphorus ; it resembles the chloride, but boils at 81°, and becomes yellow when kept. Acetyl iodide, CH3-CO-I, is less stable, and is prepared by distilling acetic anhydride with iodine ; it boils at 108°. Benzoyl chloride, or benzoic chloride, C,H;-CO-Cl, is prepared by distilling benzoic acid with PCl,. It is a pungent smelling liquid, of sp. gr. 1-215, and boiling-point 199°. It is decomposed by water, but more slowly than is acetyl chloride, yielding benzoic, and hydrochloric acids. It may also be obtained by the action of chlorine on bitter-almond oil (benzoic aldehyde) ; C,H,;-CO-H + Cl, = CgH;-CO-Cl + HCl. Determination of hydroxyl, OH, groups in alcohols, phenols, acids, &c., is usually made by reaction of the substance with an acid chloride and subsequent saponification. This is so when PCl;, the chloride of ortho-phosphoric acid, P(OH);, as above and on p. 592, is employed. Acetyl and benzoyl chlorides are frequently applied in various ways to this purpose, e.g. 2-2 c.c. of purified cresol, CsH,(OH)CH;, were shaken with 100 c.c. NaOH (20 percent. solution) and 12 ¢.c. benzoyl chloride and left over night. The mass was treated with water and the insoluble benzoic ester so obtained was thoroughly washed, drained, and recrystallised from alcohol and then from ether. An accurately weighed quantity of the pure dry ester was saponified (p. 664) with alcoholic alkali in the usual way (as for oils), and thus the proportion (56-97 per cent.) of benzoic acid residue (CsH;COO-) determined, from which the equivalent (15-66 per cent.) of hydroxyl (OH) was calculated. Theory requires 15-73 per cent. This is Schotten- Baumann’ s reaction, and is also a general method for the preparation of esters. Pyridine, instead of alkali, can often be used with advantage. The acid anhydrides are also used for the same purpose. When hydroxy-acids are distilled with PCl;, the alcoholic OH groups are also exchanged for Cl. Thus lactic acid yields q-chloropropionic chloride (chloro-lactyl ESTERS 663 chloride), CHg-CHCI-COCI. Salicylic acid yields 1:2-chlorobenzotc chloride (salicylic chloride). With water these chlorides yield HCl and the corresponding chloro-acid. Succinyl dichloride, CzH,4(COCI)s, is obtained by distilling succinic acid with PCI; ; C.H,(CO-OH), + 2PCl; = CeHy(COCl), + 2POCI, + 2HCl. It is a fuming liquid of sp. gr. 1-39, boiling at 190°. With water it yields HCl and succinic acid, but it is doubtful whether it is a true acid chloride, or resembles phthalyl chloride (v.1.). Fumaryl dichloride, CoH»(CO-Cl)z, is the product of the distillation of fumaric acid, C.H,(CO-OH)», and of its isomeride, maleic acid, with phosphoric chloride. It boils at 160°. Malic acid also yields fumaryl dichloride when distilled with PCI; ; C,H,(OH)(CO-OH), + 3PCl, = C,H,(CO-Cl). + 3POCI, + 4HCl. Tartaric acid, C,H.(OH).(COOH)s, heated with phosphoric chloride, is converted into chloromaleic chloride, CeHCl(CO-Cl)2, an oily liquid which yields crystals of chloro- maleic acid, CyHCl(CO-OH)s, when decomposed by water. Phthalyl dichloride is obtained by distilling phthalic acid, CgsH,(CO-OH),, with PCl;. It is a yellow, oily liquid, boiling at about 275°. It is more stable than most other compounds of this class, being slowly decomposed by water into HCl and phthalic acid. Even solution of NaOH only slowly decomposes it. It appears to gos gee have the constitution CHA De not OL , since nascent H converts CcOCcl cH. it into phthalide, OH 0, a lactone from 1:2-hydroxymethylbenzoic acid, co CH,OH-C,H,:-COOH. VII. ESTERS These compounds, formed by the substitution of a hydrocarbon radicle for the hydroxylic hydrogen in an acid, are numerous and important. They correspond in composition with the salts, but cannot properly be described as salts or ‘‘ ethereal salts,’’ since they are not ionisable (p. 94). For example : Potassium sulphate, SO,(OK),. ; methyl sulphate, SO.(OCH3)o. Potassium hydrogen sulphate, SO,(OH)(OK); methyl hydrogen sulphate, S0,(OH)(OCH,). Potassium acetate, CH;-COOK ; methyl acetate, CH3-COOCH3. It will be seen that the esters of the organic acids consist of an acidyl group and a hydrocarbon radicle united by an oxygen atom, thus resembling the ethers ; hence the name esters, or compound ethers. They may be formed (a) by heating an alcohol with an acid, whereby water is eliminated : (1) CH,;-OH +NO,-OH == NO,-OCH, + HOH. (2) CH,OH +S0,(OH), == SO,(OH)(OCH;) + HOH. (3) CH,OH + CH,COOH — CH,-COOCH, + HOH. These reactions are reversible and consequently never complete. With polybasic acids the hydrogen salts are generally obtained. In one of the most generally practised methods, the required acid is generated in situ by the action of a stronger acid on its salts in presence of the alcohol ; the ester is distilled from the mixture and then the reaction is not reversible, e.g. C,H,OH + CH,;COONa + H,SO, = CH;-COOC,H, + NaHSO, + H,0 (see p. 342). (b) From acid chlorides (or anhydrides) and alcohols, see p. 662 (important). (c) By heating a halogen derivative of a hydrocarbon with the silver salt of an acid; 2CH,I + Ag,SO, = (CH,),SO, + 2AgI. The esters exhibit. a resemblance to the metallic salts in being decom- 664 SULPHURIC ESTERS posed by the hydroxides of the alkali-metals, with formation of the alcohol corresponding with the radicle of the ester, and of a salt of the alkali-metal ; thus, ethyl acetate, heated with potash, yields ethyl alcohol and potassium acetate; CH,CO,C,H, + KOH = C,H,-OH + CH,-CO,K. A reaction of this kind is termed the saponification of the ester, because the formation of soap is effected in a similar way by the action of alkalies on the fats and oils, which are esters formed from glycerin with the higher members of the acetic series of acids. a . Many of the esters are volatile liquids, having characteristic, fruity odours, and many of them are used as flavouring and perfumery agents, also many are among the most important constituents of natural volatile oils. When treated with NH, they yield an alcohol and an acid amide: CH,-COOCH, + NH, = CH,-CONH, (acetamide) + CH,0H. Heated with water or dilute acids they are hydrolysed to the free acid and the alcohol : CH,-COOCH, + HOH = CH,-COOH + CH,-OH. With strong halogen acids they yield the free acid and the halide of the hydrocarbon radicle : CH,-COOCH, + HCl = CH,-COOH + CH,Cl. Halogen-acid Esters——Many of the halogen derivatives (p. 655) are esters and are producible by the usual methods for esters. Sulphuric Esters.—Methyl hydrogen sulphate or methylsulphuric acid, CH,HSO,. Methyl alcohol is slowly added to twice its weight of strong H,SO,, and the mixture is heated to boiling, cooled, and neutralised with BaCO3, which precipitates the excess of H,SO, as BaSO,, leaving barium methyl sulphate in solution ; this is evaporated on asteam-bath, and finally in vacwo, when square tables of Ba(CH3S04)9.2Aq crystallise. By adding an equivalent of H,SO, to a solution of these, the barium is precipitated and the solution of methylsulphuric acid may be concentrated in vacuo to a syrupy liquid. See equation 2 above. It is an unstable compound, decomposed at 130° into H,SO, and methyl sulphate, 2CH,;HSO, = (CH3).8O04 + H SO, (infra), and by boiling with water, into CH,0H and H,SO,. Heated with an alcohol, it gives the corresponding mixed ether, CH,HSO, + R-OH = CH,-0-R + H,SO, (also p. 652). The basic hydrogen in CH;HSO, may be exchanged for a metal forming methyl sulphates, which are all soluble in water. The acid is also formed by gradually adding CH;0H to well- cooled chlorosulphonic acid (a chloranhydride, cf. equation 4 above) : CH;,0H + 80,(OH)Cl = HCl + CH,HSOQ,. Methyl sulphate, (CH3),8O4, is prepared by gradually adding CH3,0H to 8 times its weight of strong H,SO, and distilling the mixture. The portion which distils at 150° is shaken with water, and the lower layer rectified over CaCl,. Much of the CH, group is, however, broken up in this process. A better result is obtained by distilling methylsulphuric acid at 130° under diminished pressure (supra). It is a liquid of peculiar odour, sp. gr. 1:32, and boiling-point 188°. It does not dissolve in water, but is slowly decomposed, yielding methyl alcohol and methylsulphuric acid. Many of its reactions resemble those of inorganic salts ; thus, if distilled with NaCl, it yields methyl] chloride, CH;Cl, and Na,SO,. With sodium formate it gives methyl formate and Na,SO,. Ethyl-sulphuric or sulphovinic acid, SO.(0H)(OC.H;), is prepared in the same way as methylsulphuric acid, employing equal weights of alcohol and sulphuric acid. It is a viscid liquid, very similar in its properties and reactions to methyl- sulphuric acid. The ethyl sulphates are soluble and easily crystallisable salts, prepared by adding the metallic carbonate to a solution made by heating alcohol with twice its weight of strong H,SO,, and, after cooling, diluting with water. The solution is then crystallised. The calcium salt is Ca(C;H;SOq)o.2Aq. Ethylsulphuric acid is formed when ethylene is absorbed by H,SO, (p. 555). Ethyl sulphate, (CoHs)2SO4, is obtained by the reaction between ethyl iodide and Ag,SO, in a sealed tube at 150°; 2C,H,T + AgoSO, = 2AgI + (C.H5).SO,4. It is a fragrant liquid, of sp. gr. 1-18, and boiling-point 208°. It does not mix with water, and is scarcely decomposed by it in the cold, but when heated with it yields alcohol SWEET SPIRIT OF NITRE 665 and ethylsulphuric acid. Heated alone it is decomposed into ethene and sulphuric acid 3 (CoH5)2SO4 => 2C,H, + H,SO,. Ethyl sulphate may also be obtained by passing vapour of SO, into well-cooled ether ; SO; + (CyH5)e0 = (C.H,).SO,. It is obtained as a secondary product in the preparation of ether, forming the bulk of the liquid called heavy oil of wine. Phenylsulphuric acid is unknown; potassium phenylsulphate, SOoOC,H;-OK, is obtained by the prolonged action of KHSO, on phenol dissolved in potash ; C.H;-OK + 280,-OH:OK = 80,-OC.H,;-OK + 80,(OK), + H,0. The product is extracted with hot alcohol, from which it crystallises in tables soluble in water. It is decomposed by exposure to moist air, or by boiling with water or dilute HCl, yielding phenol and KHSO, ; S0,-0C,H;-OK + HOH = HO-C,H, + SO,-OH-OK. Nitric Esters.—The type is ethyl nitrate or nitric ether, prepared on a small scale only lest explosion occur, from C,H;OH and HNO,, carefully purified from HNOy. 80 grams of nitric acid of sp. gr. 1:4 are heated on a steam-bath, and about 2 grams of urea nitrate are added, the urea of which decomposes any nitrous acid, 2HNO, + CO(NH,), = CO.+ 2N, + 3H,0. After a time the mixture is well cooled and 15 grams more urea nitrate are added, followed by 60 grams of alcohol of sp. gr. 0-81. By fractional distillation dilute alcohol is first obtained, and then a mixture of alcohol and nitric ether,from which the latter is separated by adding water containing a very little KOH ; the lower layer is drawn off, dried with calcium chloride, and distilled, C,H;0H + HNO, = C,H;-NO, + HOH. The nitrous acid is destroyed because it rapidly oxidises the alcohol to aldehyde and other products which react very violently with nitric acid. Ethyl nitrate has a very pleasant smell, and sp. gr. 1-11 ; it boils at 86°, and its vapour explodes when heated, from the sudden disengagement of H,O and CO,. Water dissolves it very sparingly. Alcoholic solution of potash converts it into KNO, and alcohol. Nitrous Esters.—EHthyl nitrite, CoH;NOo, is the chief product of the action of nitric acid upon alcohol, until it becomes very violent, the nitric radicle NO; being reduced to the nitrous radicle NO, by the conversion of part of the alcohol into aldehyde. To prepare pure ethyl nitrite, 100 c.c. of a solution containing 46 grams of potassium nitrite are mixed with 50 c.c. of alcohol, and the mixture allowed to run slowly into a cooled mixture of 50 c.c. of alcohol, 100 c.c. of water, and 75 grams of sulphuric acid. The ethyl nitrite is distilled over by the heat of reaction, and is condensed by ice. It is purified by shaking with a little dry potassium carbonate. Ethyl nitrite is much lighter and more volatile than the nitrate, its sp. gr. being 0-947, and its boiling-point 16°. It has a yellowish colour and a pleasant odour. Like many other nitrous and nitric esters, it may be preserved unchanged if perfectly pure, but if water or other impurities be present, it decomposes, becoming acid, evolving red vapours, and bursting the bottle. Alcoholic potash converts it into KNOg, and alcohol. Spiritus etheris nitrosi, or sweet spirit of nitre, used in medicine, is an alcoholic solution of ethyl nitrite (2} per cent.) with small quantities of aldehyde and other substances produced during the empirical process of preparation prescribed by the Pharmacopzxia. To 100 grams copper and 100 c.c. alcohol (90 per cent.) contained in a distilling flask fitted with a thermometer add 100 c.c. H,SOy, (1-84), and, after mixing, 125 c.c. HNO, (1-42). Distil 600 c.c. gently at 77°, gradually rising to 80° into a receiver already containing 1000 c.c. alcohol (90 per cent.). Allow the flask to cool, add 25 c.c. HNOg, and distil another 100 ¢c.c. Add alcohol (90 per cent.) to the contents of the receiver until it contains 2} per cent. ethyl nitrite. The strength is determined by the volume of NO evolved from a known volume in a‘ nitrometer as for metallic nitrites. The presence of aldehyde is shown by the brown colour (aldehyde-resin) which it gives when shaken with alcoholic potash. Neglecting secondary changes, the formation of the ethyl nitrite in the above process may be represented by C,H,-OH + HNO, + H,SO, + Cu = C,H;NO, + CuSO, + 2H,0. Amyl nitrite, C;H,j,NO2, may be prepared by distilling amyl alcohol with potassium 666 FORMIC ESTERS nitrite and sulphuric acid, or by passing NO 3 into amyl alcohol ; it is a yellow liquid of sp. gr. 0-877, and b.-p. 96°, insoluble in water, soluble in alcohol. It has a remarkable smell, and the peculiar effect of its vapour when inhaled has led to its employment in medicine. The vapour of amyl nitrite explodes when heated. Distilled with methyl alcohol it forms methyl nitrite and amyl alcohol. It will be noticed that the alkyl nitrites R-O-N :O are isomeric with the nitro-paraffins, R.NO, (see p. 681). Esters from polybasic acids are mainly of theoretical importance, helping to settle the number of OH groups in the acid. They are generally obtained by the action of organic acids on the chloranhydrides, such as POCl3, PCl,, AsCl3, BCl,, SiCl,, &c. Three ethyl phosphates, PO(OC,H;)3, PO(OH)(OC.Hs)2, and PO(OH)(OCH5), and an ethyl phosphite, P(OC,H;)3, are known. So also ethyl arsenite, As(OC,H5)3, b.-p. 166°; ethyl borate or boric ether, B(OCHs)3, b.-p. 119°, which burns with a green flame ; and several ethyl silicates or silicic ethers, such as Si(OC,H;)4 (b.-p. 165°), which burns with a bright flame emitting clouds of SiO,, are known. Water decomposes them into alcohol and acid. Particularly interesting is the formation of esters of acids which cannot exist in the free state. Thus ethyl carbonate, CO(OCjH;)o, b.-p. 126°, is obtained by heating silver carbonate with ethyl iodide in a sealed tube, although H,CO3 is unknown. Potassium ethyl carbonate, potassium carbethylate or carbovinate, CO(OC,H;)(OK), is precipitated in crystals when CO, is passed into a cooled solution of KOH in absolute alcohol. Again, ethyl orthocarbonate, C(OC,Hs5)4, b.-p. 159°, formed on the type of ortho- carbonic acid, C(OH), (p. 91), is obtained when chloropicrin is treated with sodium ethoxide in alcohol, CCl;NO, + 4C,H,ONa = C(OC2H;), + 3NaCl + NaNO,. Xanthic acid, CS(OC,H;)(SH), may be regarded as the acid ethyl salt of sulpho- thiocarbonic acid, HO-CS-SH,! which is not known in the free state. Xanthic acid is obtained as a potassium salt by saturating alcohol with KOH and stirring with excess of CS,; C,H,;-OH + CS, + KOH = HOH + CS(0C,H;)\(SK). This salt forms colourless crystals with a faint odour, soluble in water and alcohol, but not in ether. When it is added to dilute HCl cooled in ice, xanthic acid separates as a heavy colourless oily liquid, which is decomposed at 24° into alcohol and CS,. The characteristic reaction of the xanthates is that with cupric sulphate, which gives at first a dark-brown precipitate of cupric xanthate, rapidly decomposing into a yellow oil zanthogen persulphide, . and bright yellow flakes of cuprous xanthate, the reaction being apparently 2(CgH,O-C8»),Cu = (CxH;0-C8y),Cuy + 2(C5H;0-CSp). From this reaction the acid was named (£ar@oc, yellow). Formic Esters.—Methyl formate, HCOOCH3, is obtained by distilling sodium formate with KCH;80,; HCO,Na + KCH,SO, = HCO,CH, + KNaSQ,. It is metameric with acetic acid, CH;CO,H ; it boils at 32-5°. The whole of its hydrogen may be exchanged for chlorine, yielding ClICO,CCly, trichloromethyl chloroformate, which is decomposed by heat into 2COCly, carbonyl chloride. Ethyl formate, or formic ether, HCO,C,H; (b.-p. 55°), is prepared by distilling sodium formate (7 weights) with H,SO, (10) and alcohol (6). The distillate is freed from acid by shaking with a little lime, and redistilled. It is a fragrant liquid, used for flavouring rum. It dissolves in nine times its weight of water. Formic ether is also prepared by heating molecular proportions of alcohol and oxalic acid with glycerin for some time in a flask with a reversed condenser, and distilling (see p. 602). Acetic Esters.—Methyl acetate, CH,CO.CH, (b.-p. 57°), prepared by distilling methyl alcohol with dried lead acetate and sulphuric acid, is a fragrant liquid, lighter than water, with which it mixes freely. It is a constituent of crude wood-spirit. Ethyl acetate or acetic ether, CH,-COOC,H;.—Mix 50 ¢.c. of absolute alcohol with 50 c.c. of strong H,SO, and heat to 140° in a distilling flask with a good con- denser. Run in through a tap funnel a mixture of 400 ¢.c. of alcohol and 400 c.c. of glacial acetic acid at the rate at which the ethyl acetate distils. Neutralise the ‘ In thio-acids, the 8 which is substituted for the carbonyl O is indicated by the prefix sulpho-, the prefix thio- being confined to the 8 that is substituted for the hydroxyl O. ETHYL ACETO-ACETATE 667 distillate with Na,CO 3, separate and shake the upper layer with equal weights of water and CaCl, to extract alcohol. Separate, dry the upper layer with CaCl,, and distil. Ethyl acetate boils at 77°; its odour is characteristic ; sp. gr. 0-91; it dissolves in 11 times its weight of water, slowly decomposing into CH,COOH and C,H;OH. It mixes readily with alcohol and ether, and is useful as a solvent and for flavour- ing. Chlorine converts it into perchloracetic ether, CCl,CO,:C.Cl;, which smells of chloral. Ethyl acetate has been much studied ; see also next paragraph and p. 600. Ethyl aceto-acetate, CH,CO-CH,CO,C,H, (see Aceto-acetic acid, p. 649), is prepared by acting on dry ethyl acetate (10) with sodium (1), treating the product with a dilute acid, diluting with saturated brine and fractionally distilling in vacuo the light oil which separates. It boils at 181°. The simplest equation is— 2CH,-CO,C,H, + Nay = CH,CO-CHNaCO,C;H, + C;H,;ONa + Hp. The sodium in the ethyl sodacetoacetate being then exchanged for H by the dilute acid. But the change does not occur between pure ethyl acetate and Na ; some alcohol must be present. It is supposed, therefore, that the first step is the direct addition of sodium ethoxide, C,.H;ONa, to ethyl acetate producing the compound CH,C(OC,H;).(ONa). This is a derivative of the hypothetical orthoacetic acid, CH,C(OH)s, and with another molecule of ethyl acetate yields the ethyl sodacetoacetate and alcohol which reacts with more sodium to repeat the cycle. Ethyl acetoacetate is a colourless liquid, smelling like hay. It is sparingly soluble in water, but dissolves in alcohol, the solution giving a violet colour with FeCl, and a green crystalline precipitate, Cu(CgH )O3)., with a strong solution of copper acetate. It has an acid bias, for alkalies dissolve it and acids reprecipitate it from the solutions ; but alkali carbonates will not dissolve it. Ethyl acetoacetate is of great utility in synthetic chemistry, since through its means a variety of complex acids and ketones can be built up. This is rendered possible by two facts: (1) When ethyl acetoacetate is heated with dilute alkalies, potash or baryta, the whole of the ketone grouping splits off and persists in the product (ketone decomposition), e.g. CH,-CO-CH.CO,C,H, + 2KOH = CH,-CO-CH, + K,CO, + C,H;OH, whilst with concentrated alcoholic potash the acid grouping persists and forms the chief product (acid decomposition), e.g. CH,-CO‘CH,-CO,C,H, +2KOH = 2CH,-CO-OK + C,H,OH. (2) First one of the two methylene H atoms can be exchanged for sodium (see p. 600), but when ethyl sodacetoacetate is treated with an alkyl iodide, the sodium is exchanged for the alkyl group ; thus, ethyl ethylacetoacetate may be prepared, CH,-CO-CHNa-C0,C,H, + CyH;I =CH,-CO-CHC,H;-CO,CH, + Nal. By treating this with Na, ethyl sodethylacetoacetate, CH,-CO-CNaC,H;-CO,C.H; , is formed, and with C.H,I this becomes ethyl diethylacetoacetate, CHz-CO-C(C.H5)o"CO.CaHs. Other alkyl radicles may be substituted instead of ethyl. These substituted aceto- acetates may be represented by the general formula CH,-CO-CRR’-CO,C.H;, and such a compound yields the substituted ketone CH,-CO-CHRR’, or the substituted acid CHRR’-CO,H (together with acetic acid), accordingly as it is made to undergo the ketonic or the acidic decomposition described above. Ethyl acetoacetate combines with phenylhydrazine and hydroxylamine like a ketone (p. 648), indicating a ketone group. By reduction it yields the secondary alcohol-acid, CH,-CHOH-CH.-COjH (3-hydroxybutyric acid). It is a fact, however, that in many respects ethylacetoacetate behaves as though it were ethyl (-hydroxy- isocrotonate, CH,-COH : CH:CO,C,H;. This is explained by supposing that it can exist both in this form and in that given above, under the influence of different reagents (Tautomerism, p. 735). / When ethyl acetoacetate is heated it yields dehydracetic acid (sparingly soluble crystals, m.-p. 108°, b.-p. 269°), which is therefore in the residue in the flask from which 668 OIL OF WINTER GREEN the ester has been distilled. It is the lactone of tetra-acetic acid in its keto-form produced by the loss of alcohol to the ester ; thus, CH,.CO.CH,.CO/H: : CH.CO.CH,.COOEt —+ CH;.CO.CH,C : CH.CO.CH, es aosbl 0 éo Dehydracetic acid is of interest because it is intermediate in the passage from acetic acid to many carbo- and hetero-cyclic compounds, and is likely to explain some of the natural syntheses going on in the vegetable kingdom, e.g. (a) the lactone ring here is a pyrone ring; (b) on heating with KOH (conc.) it loses water and COs, forming orcinol, a benzene derivative ; (c) with ammonia it yields pyridine derivatives. One of the amyl acetates, CH;-CO.C;Hy1, is sold as jargonelle pear essence ; and is prepared by distilling fusel oil with acetic and sulphuric acids ; boils at 140°. Phenyl acetate, CgH;.C2H30., may be obtained by the reaction, CgH,-OH + C,H,0-Cl = C,H;-OC,H;0 + HCl, proving that phenol contains an OH group. It boils at 195°. A piece of hard glass tube becomes invisible in phenyl acetate, its index of refraction for light being the same as that of the liquid. Esters of Higher Fatty Acids.—Hthyl butyrate, or butyric ether, C3;H7-CO,C.Hs, prepared by distilling butyric acid with C,H;O0H and H,SOQx,, is sold, dissolved in alcohol, as ananas oil, or essence of pineapple, which it resembles in odour ; b.-p. 121°. Lthyl pelargonate, or pelargonic ether, CgH,7-CO,CoH;, prepared from oil of rue, is used in flavouring as quince oil, and is present in the fruit. Ethyl caprate, or capric ether, CgHy9‘CO.C.H; (b.-p. 187°), was formerly called wnanthic ether, because it is found in old wine. It is made by distilling wine-lees, and, when pure, is a colourless, fragrant, oily liquid. It is sold for flavouring. Amyl valerate, CyHo-CO.C;Hy;, or apple oil, is obtained by distilling fusel oil with sodium valerate and sulphuric acid ; its boilirig-point is 188°. The ethyl esters of acids of the acetic series containing more than ten atoms of carbon are generally prepared by dissolving the acids in alcohol and passing HCl into the solution ; probably this converts the alcohol into C,H;Cl, which acts upon the acid to form the ethyl ester ; this is deposited in crystals from the alcoholic solution. Ethyl palmitate and stearate are very fusible crystalline solids. Cetyl palmitate (m.-p. 55°) and ceryl cerotate (m.-p. 82°-5). See p. 583. Melissyl palmitate, or myricin, CysHs,:CO.C39H,, (m.-p. 72°), is the chief constituent of beeswax, insoluble in alcohol. Aromatic Esters.—Hthyl benzoate or benzoic ether, CsHs-CO.C.H;, is prepared by dissolving benzoic acid in alcohol, saturating with HCl, distilling, and mixing the distillate with water, when ethyl benzoate separates as a fragrant liquid of sp. gr. 1-05, boiling at 213°. Benzyl benzoate, CsH;-CO.C,H,, is a crystalline substance, contained in balsam of Peru ; m.-p. 20°, b.-p. 323°. Benzyl cinnamate, CgH,-CO,C;H, (cinnaméin), is present in the balsams of Peru and Tolu. Methyl salicylate, CsH,OH-CO,CHg, occurs in oil of winter-green, distilled from the leaves of Gaultheria procumbens, and was one of the first vegetable products pre- pared artificially. It is obtained by distilling methyl alcohol with sulphuric acid and salicylic acid. It is a fragrant liquid of sp. gr. 1-184, and boiling-point 220°. Ferric chloride colours it violet. On treating it with strong solution of soda, in the cold, it yields crystals of CgH,ONa-CO,CH;. When this is heated with methyl iodide in a sealed tube, it gives CsH,OCH;-CO,CHg, or methyl methylsalicylate, an oily liquid. I£ this be saponified by potash, it yields the potassium salt of methyl salicylic acid, C.H,OCH,-CO2H, a crystalline acid isomeric with methyl salicylate, but not giving the violet colour with ferric chloride. The ethyl salicylate resembles the methyl com- pound. Phenyl salicylate, C5HsOH-CO,CgH;, salol, is prepared by the action of POCI, on a mixture of salicylic acid and phenol, 2C,H,OH-COOH + 2C,;H,OH + POC], = 2CgH,OH-CO.C,H; + HPO; + 3HC1; it crystallises in tables ; m.-p. 48° It is used as an antipyretic, also as an intestinal disinfectant. It passes through the stomach unchanged, but is decomposed by the alkali of the pancreatic juice. Cinnamyl cinnamate, or styracin, CgH7-COg-CoHy, is a crystalline ester obtained from storax by treatment with soda. GLYCEROL ESTERS 669 Esters from Dibasic Organic Acids.—These may be acid or normal, both being generally obtained by distilling the anhydrous acid with an alcohol and fractionating the distillate. Methyl Oxalate, (CO,).(CH;). (b.-p. 163°), obtained by distilling CH,0H with an equal weight of anhydrous oxalic acid, solidifies in scales (m.-p. 51°) in the receiver ; when distilled with water it is hydrolysed. See also p. 579. Methyl derivatives are much more often crystalline than ethyl derivatives are. Ethyl Oxalate, or oxalic ether, (CO2°C.H;5)o, is prepared by boiling equal weights of dried oxalic acid and absolute alcohol for six hours in a retort with a reversed con- denser, and then adding water, which separates the oxalic ether as a fragrant liquid of sp. gr. 1-09, b.-p. 186°. It is hydrolysed by boiling with water, and saponified by potash. If mixed with one equivalent of potash, it yields pearly scales of potassium ethyl oxalate ; (COs-C,H;). + KOH = (CO,)2KC,H, + C,H;-OH. By decomposing this with hydrofluosilicic acid, ethyl-oxalic acid, (CO2),.HC.Hs, is obtained, but it is easily decomposed by water. With NH; ethyl oxalate yields ovamide (p. 704). By the action of sodium on an ethereal solution of ethyl oxalate and ethyl acetate, the sodium derivative of ethyl oxalacetate is obtained; this has the formula CO,C,H;-CO-CH,-CO.C.H,; (cf. acetoacetic ester), and when heated with dilute H,SO, yields pyruvic acid (p. 649). Ethyl malonate, or malunic ether, CH.(CO2°C2H;)s, is prepared by passing HCl gas into absolute alcohol, containing calcium malonate (p. 626) in suspension— CH,(CO,)2Ca + 2(C,.H;,0H) + 2HCl = CH2(CO2:CoHs)2 + CaCl, + 2HOH. After some hours’ standing, the liquid is boiled on a steam-bath, again saturated with HCl gas, the alcohol distilled off, the liquid neutralised with sodium carbonate, and mixed with water, when the malonic ether separates as a bitter aromatic liquid of sp. gr. 1-068 (18°), and boiling-point 198°. Its application for the preparation of fatty acids has been already noted (p. 600). The esters of one alcohol radicle may be converted into those of another alcohol radicle by mixing them with the alcohol in question, and adding a small quantity of a metallic alkyl oxide, the action of which has not been fully explained. Thus, methyl oxalate dissolved in ethyl alcohol, and mixed, in the cold, with a small quantity of sodium ethoxide, C,H;-ONa, becomes in great measure converted into ethyl oxalate, and, conversely, ethyl oxalate is transformed into methyl oxalate by dissolving it in methyl alcohol, and adding a minute quantity of sodium methoxide. Esters from Polyhydric Alcohols.—Glycol esters are very numerous, because either one or both of the OH groups in CpH,(OH). may be exchanged, and two different acid radicles may be introduced. None of them, however, as yet, possesses any practical importance. Glycerol Esters or Propenyl Salts.—These compounds are even more numerous than those derived from glycol, since each of the three OH groups in C3;H;(OH)3; may be exchanged for a different acid radicle. ; The glyceryl chlorides are known as chlorhydrins. «-Monochlorhydrin, CH,Cl-CHOH-CH,OH, and a-dichlorhydrin, CH,Cl-CHOH-CH,Cl, are prepared by saturating glycerol with HCl, heating for several hours at 100°, neutralising with Na,CO;, and extracting with ether. On fractionating the cthereal solution the dichlorhydrin distils first (b.p. 174°). They are liquids heavier than water, in which the mono- is more soluble than the di-chlorhydrin. The /-chlorhydrins, CH,OH-CHCI-CH,OH and CH,OH-CHCI-CH,Cl, are both obtained from allyl alcohol, the former by action of HClO, the latter by action of Cl. Trichlorhydrin is 1 : 2 : 3-tri- chloropropane (p. 659). Epichlorhydrin, CH, OH. -CH,Cl, is obtained by treating a- or }-dichlorhydrin with alkali, which removes HCl. It is a mobile liquid smelling like chloroform and insoluble in water ; sp. gr. 1-2, b.-p. 117°. It is sometimes used as a solvent. Nitroglycerin, or glyceryl trinitrate, C;H;(NOg)3, is prepared by the action of nitric acid on glycerin— C,H;(OH), + 3HNO, = C;H,(NO;); + 3H,0. Iti is a heavy oily liquid, of sp. gr. 1-6, without smell, very explosive, and 670 NITROGLYCERIN poisonous. It is insoluble in water, sparingly soluble in alcohol, but soluble in ether and in methyl alcohol. When saponified by potash, it yields glycerol and potassium nitrate. On a large scale a mixture of concentrated HNO, with twice its volume of strong H,SO, is placed in « tank lined with lead and cooled by water circulating in leaden coils. Glycerin is sprayed into the acid, care being taken that the temperature does not rise above 30°. The mixture is allowed to settle, when much of the nitroglycerin floats to the top and is run into water and washed. The lower layer is then run into water to separate the dissolved nitroglycerin, which sinks to the bottom. A little alkali is added to the last washing water to remove any trace of free acid remaining. This oil is very violent in its explosive effects. Ifa drop of nitroglycerin be placed on an anvil and struck sharply, it explodes with a very loud report, even though not free from water, and if a piece of paper moistened with a drop of it be struck, it is blown into small fragments. On the application of a flame or of a red-hot iron to nitro- glycerin, it burns quietly ; and when heated over a lamp in the open air it explodes but feebly. In a closed vessel, however, it explodes at about 182° with great violence. For blasting rocks, the nitroglycerin is poured into a hole in the rock, tamped by filling the hole with water, and exploded by the concussion caused by a detonating fuze (see below), the effect in blasting being about five times that of an equal weight of gunpowder, and much damage has occurred from the accidental explosion of nitroglycerin in course of transport. When nitroglycerin is kept, especially if it be not thoroughly washed, it decomposes, with evolution of nitrous fumes and formation of crystals’ of oxalic acid ; and it may be readily imagined that, should the accumulation of gaseous products of decomposition burst one of the bottles in a case of nitroglycerin, the concussion would explode the whole quantity. Nitroglycerin, like gun-cotton, is particularly well fitted for blasting, because it will explode with equal violence whether moisture be present or not, and it has the advantage of containing enough oxygen to convert all its carbon into carbonic acid gas. On the other hand, it is very poisonous, and is said to affect the system seriously by absorption through the skin, and the gases resulting from its explosion are exceedingly acrid. Again, its fluidity prevents its use in any but downward bore- holes. To overcome these objections, and to diminish the danger of transport, several blasting compounds have been proposed, of which nitroglycerin is the basis. Dynamite is composed of a particularly porous siliceous earth (Kteselguhr), obtained from Oberlohe in Hanover, impregnated with about 70 or 75 per cent. of nitroglycerin. Kieselguhr contains 63 per cent. of soluble silica, about 18 of organic matter, 11 of sand and clay, and 8 of water. It is incinerated to expel the organic matter, and mixed with the nitroglycerin in wooden troughs lined with lead. When used in solid rock, dynamite is six or seven times as strong as blasting-powder. Nobel’s detonators for nitroglycerin contain 7 parts of mercuric fulminate and 3 parts of potassium chlorate, pressed into small copper tubes. Blasting gelatine is made by dissolving collodion-cotton in about nine times its weight of nitroglycerin; its detonation is even more powerful than that of nitro- glycerin itself. Gelatine-dynamite consists of 65 per cent. of thinly gelatinised nitro- glycerin, 8-4 per cent. of woodmeal, 26-25 potassium nitrate, and 0-35 per cent. of soda. It is slow in detonation and is an excellent blasting-agent. Cordite is made by incorporating 58 parts of nitroglycerin with 37 parts of gun- cotton and 19-2 parts of acetone; 5 parts of vaseline are added and after this has been mixed, the compound is forced through dies, so that it assumes the form of cords from which the acetone is allowed to evaporate. Nitroglycerin is readily soluble in ether and in wood-naphtha, but somewhat less so in alcohol ; it is re-precipitated by water from these last solutions. It becomes solid at 40° F. (4:5° C.), a circumstance which is unfavourable to its use in mining operations, partly because it is then less susceptible of explosion by the detonating fuse, and partly because serious accidents have resulted from attempts to thaw the frozen nitroglycerin by heat, or to break it up with tools. It is remarkable that, when made on the small scale, the nitroglycerin may generally be cooled down to 0°F. (—18°C.) without becoming hard. This and other observations render it probable that some other substitution-product is occasionally mixed_with it. FATS AND OILS 671 Berthelot finds that, in the formation of nitric ether by the action of nitric acid upon alcohol, 5800 heat units are disengaged for each molecule of nitric acid entering into the reaction, whereas, in the formation of nitroglycerin, only 4300 heat units per molecule of nitric acid are disengaged. Less energy having been converted into heat in the latter case, more is stored up in the nitroglycerin, and hence its formidable effect as an explosive. In the formation of gun-cotton each molecule of nitric acid disengaged 11,000 heat units, to which Berthelot attributes the stability and inferior explosive effect of gun-cotton in comparison with nitroglycerin. Nitroglycerin is reconverted into glycerin by alkali sulphides with rise of tempera- ture and separation of sulphur ; C3;H;(NO3)3 + 3KHS = C;H;(OH); + 3KNO, + 38. Compare Gun-cotton. By 10 per cent. H,SO, it is hydrolysed to glycerol dinitrate. Glyceryl-sulphuric acid, CsH;(OH).SO4H, is formed with considerable evolution of heat, when glycerol is dissolved in strong sulphuric acid. The acid may be obtained as in the case of ethylsulphuric acid. It is known only in solution, being easily de- composed even by evaporation in vacuo. ‘ Glyceryl-phosphoric acid, CH.(OH).CH(OH).CH2.0PO.(OH)s, is formed by the action of 60 per cent. H,PO, (5 parts) on glycerol (6 parts) for 6 days at 105° ; also on mixing glycerol with metaphosphoric acid. Its very concentrated solution is a thick syrup. Its salts (known as glycerophosphates) are soluble and used in medicine, especially the calcium salt, also in conjunction with proteids, fats, and carbohydrates in special foods of the ‘“‘Sanatogen”’ or “‘ Ceregen”’ type, all being employed in neurasthenic and similar conditions. Glyceryl-phosphoric acid constitutes one part of the molecule of lecithin (p. 793), a substance characteristic of brain and nerve substance. When the acid is prepared from this, it is optically active, so that the artificial product is probably a racemic compound. Glyceryl arsenite, CsH;-AsO3, is obtained by dissolving white arsenic in glycerol, and heating to 250°; 4C;H;(OH), + As,O, = 4C;H;AsO, + 6HOH. It forms a yellowish glass, fusing at 50°. It is sometimes used for fixing aniline dyes, and in calico- printing. Glyceryl borate, or boroglyceride, CzxH;BOs, is prepared from boric acid and glycerol ; it also is a transparent glass, dissolving slowly in water, and has been recommended for the preservation of food. By far the most important esters are the fats and oils which are mixtures of glyceryl esters of the fatty acids, also called glycerides. Like other esters the oils and fats are easily hydrolysed into the alcohol (glycerol) and the acid. When an alkali is the hydrolytic agent the alkali salt of the fatty acid, a soap, is obtained. Thus when tallow is saponified it yields glycerol and a soap composed chiefly of alkali palmitate, stearate and oleate, from the palmitin (glyceride of palmitic acid), stearin (glyceride of stearic acid) and olein (glyceride of oleic acid) of which tallow is mainly composed : (C,;Hs;COO);C;H; + 3NaOH =,.3C,;H;,COONa + C3H;(OH)s (C,7H3;COO),C3;H; + 3NaOH = 3C,,H;,;COONa + C3H;(OH); (Cy7H,,COO),C;H, + 3NaOH = 3C,,H,;,COONa + C,H;(OH)3 Mono-, di- and tri-glycerides are known ; but generally speaking, only tri-glycerides occur in nature. Those of the lower fatty acids are present in small amount in certain fats, the most notable instances being butyric acid in butters, and then lauric acid in cocoanut oil. It is very remarkable that oils (liquid) and fats (solid)—or collectively “ fats ”—occurring in the vegetable kingdom have the same general composition as those found in animals ; they are all tri-glycerides of a certain three or four acids, and occasionally of a few other acids closely related to these. Traces of phy- tosterol (or sitosterol) are present in all vegetable fats, and cholesterol in animal fats. Waxes are allied bodies, but they differ from fats in not being glycerides ; this chemical distinction determines the characteristic properties of the waxes. The fats are classified according to (a) their origin; (b) the magnitude of their iodine value, i.e. the percentage by weight of iodine which the 672 IDENTIFICATION OF OILS oil can absorb, which indicates the proportion of unsaturated acids present (see p. 543). “ Drying”? oils, e.g. linseed oil, ‘‘ dry” more or less readily when exposed to the air in thin layers, and have a high iodine value (120 to 175); “ non-drying ”’ oils, e.g. olive-oil, will scarcely dry at all (70 to 100) ; “* semi-drying”’ oils, e.g. cotton-seed oil, are intermediate. “ Drying ” can be accelerated by small quantities of suitable agents, driers, e.g. litharge, PbO,, MnO,, Mn borate, also “ rosinates,’”’ etc., of Pb, Mn, etc. Paints usually consist of a pigment and driers suspended in a mixture of drying oil and turpentine ; the last is not entirely volatilised, but undergoes oxida- tion to a large extent and conveys oxygen to the fixed oil during the drying, and helps to form the peculiar elastic surface of the dry paint. Non-drying oils are applied to soap manufacture, illumination, lubrication, edible purposes, &c. The iodine value (p. 671), saponification value, i.e. parts per mille of KOH required to saturate the fatty acids (free and combined) contained in the fat, the Reichert value, which is a measure of the fatty acids (free and combined) which are both volatile and soluble in water, and physical constants (sp. gr., m.-p., viscosity (p. 316), refractive index, &c.) are among the most important tests for identifying an oil or ascertaining its purity. The “ acid value’ is a measure of the “ free fatty acids’ in terms of parts of KOH required to neutralise 1000 of oil, and so of the “ rancidity ” which is mainly due to the free acid ; it is often induced by enzymes, especially in presence of air, light and moisture. Details of the more important esters of glyceryl and of the oils and fats in which they occur will now be given, also those relating to waxes, but books devoted to this branch of chemistry must be consulted for fuller information. The descriptions of fatty acids (pp. 600 to 609) also contribute to this section. Monoformin, C3H;(OH)..0.0C.H, and diformin, C3H;.OH.(O.0C.H)», are produced when oxalic acid is heated with glycerin in making formic acid (p. 602). Monacetin, C3H;(OH),.0.0C0.CHs, from glacial acetic acid and glycerol, is soluble in water, sparingly in ether; sp. gr. 1-22. ; Monobutyrin and monovalerin can be similarly prepared. Monolaurin (m.-p. 59°) and higher members are obtained from a-monochlorhydrin and the potassium salt of the acid ; so also mono-olein, m.-p. 35°, sp. gr. 0-95. The di-glycerides exist in a-a and a-(3 forms. Most of them are obtainable from the corresponding di-chlorhydrin and the potassium salt of the acid. Of the “ simple ” tri-glycerides, i.e. where each glyceryl carbon is linked with a residue of the same acid, only one modification is possible, and these are formed by heating glycerol with excess of the corresponding fatty acid. In ‘“‘ mixed” tri-glycerides, two isomers are possible when two kinds of acidyl group are present, e.g. CH,A.CHA’.CH2A and CH,A.CHA.CH,A’, and three isomers with three acidyls, CH,A.CHA’.CH,A”, CH,A.CHA”.CH,A’, CH,A’.CHA.CH,A”. Most of these can be obtained by heating the appropriate diglyceride with the other acid ; or by treating a chlorodiglyceride with the potassium salt of the other acid. It is frequently difficult to decide whether an oil contains a mixed triglyceride or a mixture of simple triglycerides. In the following notes, most are described as if the latter case obtained. The process of separation of the pure triglycerides, whether simple or mixed, from fats is generally lengthy and often difficult. Tributyrin, glyceryl butyrate, C3;H;(O.C4H,O)3, sp. gr. 1-04, not solid at — 60°, b.-p. 287°, nearly insoluble in water, readily in alcohol. Its taste is very bitter, so that its existence as such in butter is doubtful. Trilaurin, C;H;(O.Cj2H230)3, sp. gr. about 0-92, m.-p. 46° ; sparingly soluble in cold alcohol, readily in ether. Tripalmitin, C;H,(0.C,7H3,0)3, m.-p. 65°, nearly insoluble in cold alcohol, sparingly in cold ether. Tristearin, C3H;(O.C,gH3;0)3, m.-p. 71-6°, is even less soluble than tripalmitin. Triolein, C3H;(0.C,sH330)3, sp. gr. 0-900, solidifies at — 5°, or at the ordinary FATS AND OILS 673 temperature on long standing. Soluble in alcohol, readily in ether. With nitrous acid it yields elatdin, and with ozone triolein-ozonide ; see Oleic acid. Oils and Fats.—The following are representative of the principal groups : Linseed oil, by pressure from the seeds of the flax, Linum usitatissimum, contains the glycerides of the unsaturated acids, linolic, linolenic, isolinolenic, and (a little) oleic 3 Sp. gr. 0-935 ; iodine value 173 to 193. It is the best drying oil and is produced in enormous quantities for paints, &c. Heated with driers for several hours at 150° (or, formerly over an open fire) it constitutes ‘“ boiled oil,” which dries more quickly than “raw”? linseed oil. Cotton seed, sesamé, almond (each from seeds), and olive (from the pulp of olives) otls, all by pressure, consist of olein (chiefly) and palmitin ; sesamé contains some linolin also. They are all edible and used in pharmacy. The first two are semi-, the last non-drying. Rape (colza) oil contains much triglyceride of erucic acid (p. 612); in the crude oil there is much mucilage, which is coagulated by shaking with H,SO, conc. (1 per cent.) and removed. It has a very low saponification value, 172 to175. It is used as a lubricant on account of its very high viscosity, and as a lamp oil. Castor oil, pressed from the seeds of Ricinus communis, is peculiar for its optical activity, high viscosity, high sp. gr. (0-96), solubility in alcohol, sparing solubility in petroleum ether, aperient properties, also for differences from most other oils in other ways; it is non-drying. It consists chiefly of the triglyceride of ricinoleic acid (see p. 619). Castor oil has many applications: in medicine, as a lubricant, in leather manufacture, for sulphonating to Turkey-red oils, with sulphur chloride it forms a ‘“‘rubber substitute’; also it is destructively distilled under diminished pressure for the preparation of ‘cognac oil,” the distillate containing undecylenic acid, CH, : CH(CH,),COOH (m.-p. 24°, b.-p. 165°), and enanthaldehyde, CH3(CH2);CHO (sp. gr. 0-827, b.-p. 155°). Cocoanut oil growp—cocoanut oil, palm oil (from palm kernels), &c. These fats are solid in the English climate, though liquid in the countries of their origin. They contain chiefly laurin and palmitin, with some olein ; also a little of the glycerides of capric and caprylic, but not butyric acids. In consequence, they give higher Reichert values than any other edible fat except butter, also, as a class, the highest saponification values (usually 250 to 260) of all fats. They require strong alkali for saponification, but are much used in the manufacture of soap and candle material, also as lubricants. Highly refined they—especially cocoanut oil—are largely used in confectionery and as “vegetable butter.” Tallow—beef and mutton, “rendered” by melting from suwet—contains various mixed triglycerides, e.g. stearodipalmitin, palmito-distearin, &c., also some tristearin. In lard the glycerides, mostly simple, are of lauric, myristic, palmitic, stearic, oleic, and linolic acids. Their specific gravities are high, 0-94. Butter is essentially the fat of cow’s milk. Its composition approximates fat 87 per cent., curd 1 per cent., salt 1 per cent., water 11 per cent. ; and that of the fat itself, butyrin (but see p. 672) 7 per cent., caproin, caprylin and caprin 1-5 per cent., olein 40 per cent., palmitin, stearin &c., 51-5 per cent. The presence of butyric acid is characteristic, and consequently the Reichert value is exceptionally high, higher than that of any other edible fat, and so is the most reliable single test for purity ; m.-p. 29-5° to 33°, sp. gF-50 0-936 to 0-940. ‘‘ Margarine’ is a mixture of refined animal (lard especially) and vegetable (cotton-seed and cocoanut) fats with milk, salt and colouring, for use as a “‘ butter substitute.” Marine animal oils—as compared with terrestrial animal oils—have high iodine values. They may be grouped into (a) fish oils (from all parts of the body), (b) liver oils, (c) blubber oils. Most of these oils are obtained by chopping up the flesh, boiling it with water, and skimming off the oil; but cod-liver oil is rendered by allowing steam to blow into the livers while as fresh as possible; the cells burst and the oil exudes. The composition of cod-liver oil is not well understood ; the glycerides of palmitic and stearic acids are included, but not oleic; two or three characteristic glycerides less saturated than olein—physetolein, jecolein, &c., variously described— constitute the chief portion ; 0-3 per cent. cholesterol is present, also traces (only) of iodine. 43 674 TURPENTINE Waxes.—Sperm and arctic sperm oils are the only liquid waxes. The former is from the head, cavities and blubber of the sperm whale. It contains only 60 to 65 per cent. fatty acids combined with monovalent aliphatic alcohols, the nature of which is not known, against 95 per cent. in the glycerides ; hence the saponification value is correspondingly low (125 to 135). Spermaceti or “ cetin”’ is composed chiefly of cetyl palmitate or cetin, Ci6H330.C0.G,,Ha1 (see also p. 583), and is the solid constituent of sperm, dolphin, shark liver, and some other fish oils ; hence all but the first are mixtures of oils and waxes. It forms lustrous white crystalline masses (sp. gr. 0-96, m.-p. 44°). Wool waa is pale yellow and peculiarly unctuous (sp. gr. 0-944, m.-p. about 39°), contains hydroxy-acid esters of cholesterol and isocholesterol, which renders the wax optically active, but the whole composition is not known. It is insoluble in water, but it can absorb 80 per cent. of its weight of water without losing its general character ; with 42 per cent. it forms the adeps lane hydrosus of the pharmaco peeia, of the “ lanolin ” type. Beeswax, secreted by the bee, consists chiefly of cerotic acid and myricin (see pp. 609, 583); sp. gr. 0-965, m.-p. 63°. Carnatiba wax is the chief vegetable wax. A hydrocarbon, ceryl and myricyl alcohols, carnatibic acid, CogH4ygQo, are the chief substances obtainable from it. Its sp. gr. (0-99) and m.-p. (85°) are very high. Terpenes, Camphors, Resins, Volatile Oils, &c.—Most of these are, or are mixtures of, substances belonging to the classes already considered : hydrocarbons (terpenes), alcohols (cineol, menthol), aldehydes (benzalde- hyde), ketones (camphor), acids (abietic acid), esters (linalyl acetate), &c. They are derivatives of one another and form a natural group. The majority of volatile or essential oils (“ volatile’ as contrasted with the fatty or “ fixed” oils) are obtained by placing the raw material with water in a still and so distilling the oil out of the drug, or by passing dry steam through the drug contained in the still ; the oil passes over with the steam and, being practically insoluble, collects either above or below the water in the receiver. The water holds traces of oil in solution, and in this way the “aromatic waters”? of pharmacy are prepared. A few ounces of freshly crushed cloves in a flask, as in the arrangement for steam- distilling aniline (Fig. 310), serve well for an experiment. Most volatile oils are optically active, and the rotation as directly observed in a 100 mm. tube, ap (not the specific rotation [a]p), is usually recorded (see also p. 634). Oil or “spirit” of turpentine, the most important of the class, however, is obtained by distilling, either alone or with water, turpentine (known as “Venice turpentine”’ if from the larch, as ‘Canada balsam’ if from Abies balsamea), the viscous exudation procured by incising the trunks of pine and some other coniferous trees. The residue in the still is colophony or common rosin. The yield is 75 to 90 per cent. rosin and 25 to 10 per cent. oil. Oil of turpentine is a colourless, spirit-like liquid of agreeable odour, sp. gr. 0-87, beginning to boil at 156°, 90 per cent. usually passing over below 165°. Dextro-rotatory (rotation about + 14° American), or levo- rotatory (rotation about — 35° French). Insoluble in water, soluble in alcohol, ether, acetone, glacial acetic acid, &c. It dissolves most fats, resins, caoutchouc, &c., and is used in preparing paints and varnishes. It absorbs oxygen from the air becoming resinous, and can convey it to other substances ; hence its superiority in paints over its cheaper substitutes. It burns with a smoky flame. Its chief constituent is pinene, both d- and i-, which accounts for the various optical properties of the oils. Camphene is also a normal component ; fenchene occurs occasionally. These unsaturated hydrocarbons, as well as dipentene, which is a mixture of d- and L- limonene, phellandrene, sylvestrene, &c., constitute the class known PINENE—CAMPHENE 675 as terpenes; they all have the formula C,,H,,, and are closely related to cymene, C,,H,, (p. 568). The three found in turpentine are bicyclic terpenes, t.e. they have conjugated rings (p. 567) and combine with 2HCI, 2HBr, 4Br, &c.; the others named are monocyclic terpenes and combine with HCl, HBr, 2Br, &c. Acyclic, “‘ olefinic terpenes,” e.g. myrcene, are also known. The terpenes are all polymerides of the formula C;H,. A hydrocarbon having this molecular formula and belonging to the diolefines (p. 556) is called isoprene (b.-p. 37°), and appears to have the constitution CH, : C(CH,)-CH : CH, (methyldivinyl) ; caoutchouc and many terpenes yield isoprene (hemiterpene) when heated, and isoprene on heating polymerises to dipentene (p. 676). Pinene may be separated by careful fractional distillation of turpentine oil; or it may be isolated from the oil, perfectly pure by chemical means, but then it is inactive ; thus, to a well-cooled mixture of 50 grams each of oil, glacial acetic acid and ethyl nitrite, add gradually 15 c.c. HCl conc. ; crystals of pinene nitrosochloride, Cyy>H,g,NOC1 or (CyoHyCl),N20., are deposited and washed with alcohol. The formation of these crystals is a characteristic test for pinene. On heating them with aniline the pinene is liberated ; C,>H,,NOC] + 2C,;H;NH, = HCl + H,O + C,H;N : NCsH,.NH, (amido- azobenzene) + Cy oHys. Methyl aniline is said to work better. It is a colourless, mobile liquid of agreeable odour ; sp. gr. {> 0-8586, b.-p. 155° to 156°, [a], = + 45° or — 43-4°. Heated to 260° ——- dipentene (monocyclic) With acid oxidising agents it yields terephthalic acid (p. 628), signifying the presence oi two alkyl groups in the 1: 4 positions ; this applies to most terpenes ; from pinene To -terebic acid, (CH3).C.CH(COOH).CH,.COO, is also formed; with alkaline KMn0O,, pinonic acid, A CBadan, COOH.CH,.CH >CH.CO.CHs, \ cH, % 2 NOE). and pinic acid, COOH.CH,.CH CH.COOH. H,SO, conc. —-> camphene. ee CH, We Dry HCl passed into well-conled pinene gives pinene hydrochloride, CyyH,,.HCl (called artificial camphor from the close resemblance of its crystals and odour to those of camphor), m.-p. 125°, b.-p. 208°; it is identical with bornyl chloride ; an intramolecular change is involved ; the chloride on heating with a feeble base (aniline) yields camphene. Pinene and camphene are bicyclo-heptane derivatives (p. 570), to which the following constitutions have been ascribed : CH; — === CHa CH, CH CH, ——.C(CH,), —— 0 CH,.C —— C(CH,), —— CH \ cH, cu 7 \eHi cn” Pinene. Camphene. Camphene occurs in turpentine, camphor and citronella oils, and, unlike pinene and fenchene (rarely found in nature), is a solid which varies somewhat in properties with its mode of preparation ; m.-p. about 51°, b.-p. about 160°, d-, J-, and i-forms, sp. gr. 50-84. It does not form a nitrosochloride. The effect of oxidation is complex. Isoborneol is obtainable from it (p. 676). The monocyclic terpenes are closely related to p-cymene (1 : 4-methyl-isopropy]- benzene) which is a frequent constituent of volatile oils. Its constitution is established by its synthesis from p-bromisopropylbenzene and methyl iodide by means of sodium. It is a colourless, pleasant smelling liquid, sp. gr. ,,- 0-860, b.-p. 175°, optically inactive. HNO, dil. and CrO, oxidise it to p-toluic acid. It is identified by conversion into p-oxyisopropylbenzoic acid (m.-p. 155°) ; heat 2 grams with 12 grams KMn0O, in 330 grams water under a reflux condenser, filter from Mn,O,, evaporate, add H,SO, dil., and recrystallise the precipitated acid from alcohol. 676 BORNEOL Limonene is very widely distributed ; the d-form in lemon, orange, and numerous other oils ; the /-form in some pine-needle and other oils. The [d + 1], racemic form, is known as dipentene produced on mixing d- and /- limonene, with slight evolution of heat (see p. 638). Isoprene, under the influence of heat, polymerises to dipentene, and so the latter is synthesised. CHa CH,=CH CH, Cia, C—CH C20n 3 No-one \C—CH, ci on, cH,7 : CH,Y \cn,—cH 4 Isoprene (2 mols.). Dipentene. The molecule has also been built up from ethyl /3-iodopropionate by Perkin and the above constitution proved. Dipentene is the most stable of the terpenes, being produced from the others by heat, HCl, &c. ; also from various terpene derivatives with the help of reagents. Its properties are in general the same as those of either of its active forms. It has a pleasant lemon-like odour, sp. gr. 15. 0-846, b.-p. 176° ; unites with 2HCl, 2HBr, 4Br, NOCI, &c. Phellandrene is present in numerous oils, especially in that from Fucalyptus amygdalina and in pine-needle oils. It is remarkable for so readily forming crystals of phellandrene nitrosite, Cy>H;gN2O3 ; from 1 c.c. oil, 2 ¢.c. glacial acetic acid, and 2 c.c. NaNO, sat. aqueous sol. (B.P. test). It is one of the least stable terpenes ; b.-~p. 171°, but at this temperature it polymerises ; sp. gr. ,;° 0-855. Probable formula: CH=CH CH — ~~ oy ie 3 10K CHC \cH—CH, CH, Sylvestrene, terpinene are other “‘ terpenes proper ” (Cy 9Hy¢). Amongst the sesquiterpenes (C\;Ho4), cadinene is the best known. It occurs in cade oil, pine-needle oils, and numerous others. It is levorotatory, [a]p = —98-56°, b.-p. 274°, sp. gr.o9° 0-918. It unites with 2HCl, NOCI, &c. Caryophyllene, CysHoq, is found in clove, copaiba, and other oils ; sp. gr. 15° 0-908, b.-p. 259° [a], —8-8°. Hydroterpenes, containing two or four more H atoms than the terpenes proper, are known, but their occurrence in nature is doubtful. Menthene, C, Hig, corresponds with menthol. “ Olefinic terpenes ” is the name proposed for certain open-chain olefines having the formula C,)Hj¢, and occurring in volatile oils. They are triolefinic (p. 557) and take up 6Br, the product corresponding with the paraffin, CjpHo9. Their oxygen derivatives, linalool, &c., are important. Myrcene, CyoHy¢, is found in oil of bay; sp. gr. 45° 0-8023, b.-p. 167°. Heated with H,SO, dil. —+ dipentene and linalool, C,o)H,,0H, which on oxidation —~> citral, CyoHi 60. The oxygen derivatives of the terpenes conform more or less with the following scheme : CH Hydrocarbon —+> alcohol — > ketone — acid Camphene — + tsoborneol —+> camphor -—»> camphoric acid Fenchene — > fenchyl alcohol —-+ fenchone -—+ apocamphoric acid Borneo! and isoborneol, C,,H,,OH, are probably stereoisomers; the former does not yield esters so easily, therefore it is probably the trans- and isoborneol the cis- modification. Both yield camphene on dehydration. With glacial acetic acid and H,SO, at 55° camphene forms isobornyl acetate, b.-p. 107°/13 mm., which with KOH —> isoborneol, m.-p. 212°. Borneol is the chief component of Borneo camphor, and with isoborneol, is produced on treating camphor in alcoholic solution with sodium. It crystallises in brilliant lamine or plates of an odour distinct from that of camphor ; m.-p. 203°, b.-p. 212°, sp. gr. 1-01; d-, - and é- forms known, [a]p= 37°6°. It oxidises to camphor and camphoric acid. Camphor, C,,H,,O (Japan or Laurel amphor), is the ketone derived from camphene and iso-borneol (q.v.). “4 is the valuable constituent of camphor oil distilled locally from the disintegrated roots and trunks of CAMPHOR 677 Cinnamomum camphora, a forest tree of Japan, Formosa, and China. Normal camphor oil is semi-solid from excess of camphor, which is removed by expression and refined by sublimation. The liquid portion is marketed as “camphor oil.” Camphor has been completely synthesised, but a descrip- tion of the process is beyond the scope of this work. The ‘‘ synthetic ‘camphor ” of commerce is made from oil of turpentine, the pinene being converted into camphene (e.g. through the hydrochloride, swpra), and this oxidised by KMnO,. Camphor occurs in colourless crystalline masses of tough granular consistence, with a great tendency to sublime even at the ordinary tempera- ture, forming clear well-defined octahedral crystals, and is of characteristic odour. Sp. gr. 0-99, m.-p. 176°, b.-p. 209°. Ordinary camphor is dextro- rotatory, [a]pn = 55-4°, but varies with the solvent; J- camphor occurs insome oils. It is soluble in 700 parts of water, in an equal weight of alcohol (90 per cent.), and is still more soluble in ether, chloroform and glacial acetic acid. It forms a liquid when triturated with chloral hydrate, men- thol, &c. Itis very inflammable, burning with a bright smoky flame. With hydroxylamine it forms a crystalline oxime, m.-p. 119°, which serves to characterise camphor and on reduction forms two isomeric bornylamines, m.-p. 163° and 180°. Distilled with P,O;, p-cymene is produced. Heated with iodine, it yields carvacrol (p. 678). HNO; oxidises it to camphoric acid, C,)H,,0,4 (monocyclic, m.-p. 187°, [alo = + 49-7° in alcohol), and on further oxidation to camphoronic acid, CyH,,0, (trimethyltricarballylic acid, p. 632, acyclic), m.-p. 139°; thus CH, CH; CH, Rees CO Rich eden H,C | oor ve do eee CHy)2 ——> d CHs)o oe CH, H,C—CH—COOH COOH en Camphor. Camphoric acid. Camphoronic acid. Fenchone is a liquid otherwise similar to camphor; the d-form occurs in fennel oil, the 7- in thuja oil. It is so stable against oxidising agents that even concentrated nitric acid or KMnO, may be applied to free it from impurities ; m.-p. 5°, sp. gr. 19° 0-946. Distilled with P,O; —-> m-cymene (cf. camphor). HNO 3 conc. oxidises it to apocamphoric acid, CyH404 (one C-atom being removed). H,C—CH —— CH, H,C—CH——_CO H,C—CH—COOH | | | C(CHs)> C(CH3)s rere C(CHs3)o A H,C—CH CH-CH, H,C—CH—COOH H,C—C(CH;)—CH, Fenchone.’ Apocamphoric acid, Cineol. Cineol or eucalyptol is a bicyclic oxide, which may be regarded as the oxide corre- sponding with cis-terpin, and is found in eucalyptus, cajeput, and other oils. It is a colourless liquid of camphor-like odour, crystallisable, m.-p. —1°, b.-p. 177°, sp. gr. 0-930. Ithas neither ketonic nor alcoholic properties. It forms loose addition products, in particular a crystallisable phosphate with HPO, (1-75), by which it may be separated from oils containing it and the proportion determined. ° CH —CH, CH; 7 eH COE) , is obtained by allowing a \cH,—CHy CH3 mixture of pinene, H,SO,, and alcohol to stand for some time, also from d- or J-limonene hydrobromide by boiling with silver oxide, ; Terpineol, CH; —C 678 THYMOL—MENTHOL From the monocyclic terpenes the following derivatives are of special interest. CH, CH,—CH,. JH Terpin cis- SoZ De HO” ~\CH,—CH, C(CH,).0H, HO fn ga C Cc CH,” \cH,—CH,” \C(CH,)20H, is a dihydric alcohol producible from dipentene through its dihydrobromide. With one molecule of water, it forms terpin hydrate, C1)Hyg(OH)2.H,O, which heated with dilute acid yields cineol, CyyH,,0. é trans- CH — CH, CH, Carvone is a ketone from limonene, cH, —c@ oH —0¢ CO — CH,” CH, b.-p. 225°, [a]p = + 62°, found in cumin and dill oils. Heated with KOH or CH — CH CH, HPO, it yields carvacrol (p. 677), CH oe Seca ,m.-p. 0°, ‘COH=CH ‘CH, CH — CH CH; b.-p. 236°, isomeric with thymol, CH,—0C ; o- cH > m.-p. 51°, ‘CH= COH CH; b.-p. 232°, which forms large crystals, occurs in thyme oil, and is used as an antiseptic. Thymo! dissolves in 1200 parts of water, freely in alcohol, &c., also in caustic alkaline aqueous solutions on account of the phenolic character. The crystals (sp. gr. 1-028) sink in cold water, but on warming they melt (sp. gr. 0-95), and rise to the surface. Of similar construction, though they are not readily convertible into one another, is the saturated , CH, — CH, x /CHs secondary alcohol, menthol, CH, —CHC fe » the CH,—CHOH CH; chief constituent of peppermint oil ; it is used in medicine ; m.-p. 42-5°, b.-p. 216°, sp. gr. {5 0-890, [a] p= — 49-6°inalcohol. It may be obtained by reducing menthone, its ketone, and is convertible into it by oxidation ; this also occurs in peppermint oil ; b.-p. 207°, sp. gr. 29° 0-895, [a]p= —28°. It forms an oxime, but not a bisulphite compound. Anethol (1 : 4-propenylanisol), CsH4.C;H;.OCHsg, is an ether (cf. anisol, p. 654), constitutes the main portion of anise oil, and gives the oil its peculiar odour and sweet taste ; m.-p. 21°, b.-p. 234°, sp. gr. 41.5° 0-999. Eugenol (1:3: 4-allylguaiacol), C,H3;.C3;H;.OCH;.OH, is the chief and charac- teristic constituent of clove oil ; it is also found in cinnamon leaf (but not in cinnamon bark), and other oils; sp. gr. 14.52 1-072, b.-p. 252°/749 mm. In alcoholic solution it strikes an intense peacock blue with FeCl,, due to the phenolic group. KMn0O, oxidises it to vanillin (p. 780). : From open-chain olefinic terpenes: Linalocl, a tertiary alcohol occurring free in several citrus and labiate oils, and as linalyl acetate in lavender, bergamot, and other oils ; b.-p. 86°/12 mm., sp. gr.s5° 0-872, d- and l-forms. It gives citral on oxidation. From its isomer, geraniol, by heating with water at 200°. Linalool (CH, )2C— CH—CH,—CH,—C(OH)(CH,;)— CH= CH, Geraniol (CH3)2C= CH—CH,—CH,—C(CH;) = CH—CH, OH. Geraniol, the main constituent of otto of rose; also in geranium, citronella and numerous other oils. It is a primary alcohol and behaves as ‘‘ geraniol of crystallisa- tion ” with CaCl (cf. ethyl alcohol) ; b.-p. 110-5°/10 mm., sp. gr. y3¢ 0-882. It oxidises to citral. : . Citral, or geranial, (CH3;)C=CH—CH,—CH,— C(CH;)=CH—CHO, is found in many oils; the value of lemon oil is determined largely by its citral content. Arti- ficially it may be obtained by oxidising linalool or geraniol with chromic acid ; b.-p. 111°/12 mm., sp. gr. 45° 0-894. It shows all the properties of an aldehyde. It is very sensitive to acids, and by a trace of HCl it is converted quantitatively into p-cymene, union occurring at the C’s marked with a dot. Such a condensation probably proceeds in plants, INDIA-RUBBER 679 Resin is the term applied to a peculiar class of solid oxidised hydro- carbons of vegetable origin, characterised by being amorphous, often vitreous in structure, fusible, insoluble in water, soluble in alcohol, usually soluble in aqueous solutions of the alkalies ; inflammable, burning with a smoky flame and frequently emitting an aromatic odour. Chemically they are very complex, their chief components being classifiable as (a) resin esters derived from peculiar resin alcohols, some of which (resinols) do not, and some (resinotannols) do, give tannin reaction with iron salts, and either peculiar resinolic acids (e.g. abietic acid) or aromatic acids (in the latter case, the resin is a balsam) ; (b) the free resinolic acids ; (c) resenes, oxy- genated compounds of unknown constitution, not attacked by alkalies. Colophony or common rosin (see p. 674), the best known, consists mainly of abietic anhydride, CyyH 60,4, or abietic acid, C,,H,,0;. Rosin is vitreous, brittle, easily pulverisable, softens at 70° to 80° and melts completely at several degrees above 100°. Sp. gr. 1-07 (about). Destructively distilled, it yields rosin spirit (sp. gr. 0-87, half of it boiling below 120°, used as a substitute for turpentine) and rosin oil (a brown viscid liquid, sp. gr. 0-98, distils above 300°, used chiefly as a lubricant). Several resins are gathered as exudations from trees, &c., e.g. benzoin, sandarac, dammar, mastic ; shellac is lac purified by melting and straining the secretion of an insect, Coccus lacca. These dissolved in spirit form spirit varnishes ; but for oil varnishes, the fossil resins are preferred, e.g. amber (contains succinic acid and on destructive distillation yields the oil of amber of pharmacy), animi, copal, kauri. Oleo-resins are natural mixtures of resin and volatile oil, e.g. turpentine, copaiba; gum-resins are natural mixtures of resin and gum, e.g. myrrh; either the gum may be dissolved out by water leaving the resin, or the resin by alcohol leaving the gum. Caoutchouc, india-rubber, is a product of the inspissation of the latex exuding on incision of several tropical plants, e.g. Hevea guianensis, Stphonia elastica, Ficus. Essentially, it consists of a polymer of isoprene, CH,.C.CH, . CH,. CH polyprene, probably I I n, and. so is allied to the CH.CH,.CH,C.CH, terpenes ; indeed, on destructive distillation it yields isoprene, dipentene and heveene, Cy9H 52 (2), b.-p. 315°. Caoutchouc is soft and elastic, softer on warming, and melts at about 120° to an oily liquid, sp. gr.0-92. It dissolves slowly in carbon disulphide, benzene, chloroform, petroleum, naphtha, turpentine, oils. It oxidises and hardens in the air. Alkalies and dilute acids are without action on it. The observation, made by Tilden in 1884, that isoprene becomes poly- merised by contact with strong acids to a substance indistinguishable from caoutchouc, has led many investigators to seek a cheap source of isoprene and an economical mode of polymerising it to obtain artificial caoutchouc. Recent investigations by W. H. Perkin and others inspire hope of success on a commercial basis. In view of the low price of natural caoutchouc, only very cheap raw material can be utilised. The fraction of fusel oil boiling at 128-130°, containing 87 per cent. of isoamyl alcohol and 13 per cent. of active amyl alcohol, is converted into chloride by dry HCl and then chlorinated, yielding -yd-dichloro-6-methylbutane, CHMe,.CHCI1.CH,Cl, and similar bodies. On passing the vapours of the fraction of this mixture boiling at 140-180° over soda-lime at 470° a distillate is obtained which is rich in isoprene. Isopropylacetylene, CHMe,.C:CH, is probably the immediate product on removal of 2HCI, and this by rearrangement becomes isoprene. This is isolated by fractional distillation and polymerised to caoutchouc by heating at €6° with 3 per 680 VULCANISED RUBBER cent. of thin sodium wire in sealed tubes for several days. The product needs purification by solvents. Vulcanised rubber, the chemical constitution of which is not understood, is pro- duced by incorporating india-rubber with 2 or 3 per cent. of sulphur, which not only greatly increases its elasticity, but prevents it from cohering under pressure, and from adhering to other surfaces unless strongly heated. It also becomes insoluble in tur- pentine and naphtha. Ordinary vulcanised rubber generally contains more sulphur than is stated above, which causes it to become brittle after a time ; for many purposes, other substances are added besides sulphur, such as lead carbonate, zinc oxide, antimony sulphide. When a sheet of caoutchouc is allowed to remain for some time in fused sulphur at 120° it absorbs 12 or 15 per cent. without any material alteration, but if it be heated for a short time to 150° it becomes vulcanised ; and when still further heated, is con- verted into the black horny substance called vulcanite or ebonite, and used for the manufacture of combs, &c., and as an electrical insulator. Vulcanised caoutchouc is sometimes made by mechanically incorporating the sulphur with india-rubber softened by heat ; or by immersing the rubber in a mixture of sulphur with chlorinated lime,or in carbon disulphide mixed with 2-5 per cent. of SpClo. It can also be made by dissolving the sulphur in turpentine, which is afterwards used to dissolve the caoutchouc ; when the turpentine has evaporated, a mixture of caout- chouc and sulphur is left, which may be easily moulded into any required shape, and afterwards vulcanised by exposure to high-pressure steam having a temperature of 140° to 150° ; however, while the pressure and steam are useful in assisting the moulding, &c., only the temperature effects the vulcanising. By treating vulcanised caoutchouc with sodium sulphite, the excess of sulphur above 2 or 3 per cent. may be dissolved out. The whole of the sulphur may be removed, and the caoutchouc devulcanised, by boiling with a 10 per cent. solution of caustic soda. Caoutchouc is by no means rare in the vegetable world, being found in the milky juices of the poppy (and thence in the opium),of the lettuce, and of the ewphorbium and asclepia families. Gutta-percha (empirical formula C,;H,), like caoutchouc, is originally a milky exudation from incisions made into the wood of the Jsonandra percha, a native of the Eastern Archipelago. The juice soon solidifies, when exposed to air, to a brown mass heavier than caoutchouc (sp. gr. 0-97) and differing widely from it by being tough and inelastic when cold, and becoming quite soft and plastic when heated nearly to the boiling-point of water. Being impervious to water, it is used as a waterproof material and for water-pipes, and its want of conducting power for electricity is turned to account for insulating telegraph cables. Gutta-percha is dissolved by those substances which dissolve caoutchouc. It is not affected by diluted acids and alkalies, and is used for keeping hydrofluoric acid. It melts easily, and is afterwards decomposed, yielding products similar to those from caoutchouc. Commercial gutta-percha contains only about 80 per cent. of the hydro- carbon, which may be dissolved out by boiling with ether. SuLPHONIC ACIDS The esters of sulphurous acid are metameric with the compounds known as the sulphonic acids ; thus, both ethyl hydrogen sulphite and ethyl sulphonic acid, have the empirical formula C,H,SO,;. The sulphonic acids, however, differ from the sulphites in that when treated with reducing-agents they yield the corresponding thio-alcohols ; thus, ethyl sulphonic acid, C,H,SO,H, yields mercaptan (ethyl thio-alcohol), C,H;SH. This reaction indicates that the sulphur in ethyl sulphonic acid is combined directly with the carbon of the ethyl group, for there can be no doubt that the S in mercaptan is so combined. The constitution of ethyl sulphonic acid is therefore probably C,H, OC,Hs. OSC , whilst that of ethyl hydrogen sulphite is os¢ : OH OH When a strong solution of sodium sulphite is heated with ethyliodide at 140°, SULPHONIC ACIDS 681 sodium ethyl sulphonate and sodium iodide are produced; NagSO; + C,H;I = C,H;‘SO,0Na + Nal. If sodium sulphite were a salt of SO(OH)s, viz. SO(ONa)., this reaction would be expected to produce ethyl sodium sulphite SO(ONa)(OC,H;).2 Since this is not the case, NagSO; must have the constitution SO.(ONa)Na;_ this constitutes the evidence referred to on p. 159. ‘ The sulphonic acids bear the same relationship to sulphuric acid, as the carboxylic acids bear to carbonic acid, that is, they contain an alcohol radicle or a hydrocarbon radicle in place of one of the OH groups. They are monobasic acids since they still retain one OH group. By partial reduction they generally yield sulphinic acids, R-SO-OH, which bear the same relationship to the SO(OH), form of sulphurous acid as the sulphonic acids bear to sulphuric acid. The sulphonic acids are also produced by oxidation of the mercaptans. Ethyl sulphinic acid, C.H;-SO-OH, is obtained as a zinc salt by the action of SO, on a cooled ethereal solution of zinc ethide ; Zn(CpH,). + 280, = (C,H;‘SO,).Zn. The acid itself is a syrupy liquid. It might be regarded as propionic acid, C,H;-CO-OH, in which tetravalent sulphur is substituted for the carbon of the carboxyl. Ethyl-sulphonic acid, C,H;-SO,-OH, is produced when ethyl-sulphinic acid, mer- captan, ethyl polysulphides, and ethyl sulphocyanate are oxidised by nitric acid ; also from C,H;I and Na,SOs3, as stated above. Ethyl-sulphonic acid is an oily liquid of sp. gr. 1-3, and may be crystallised by cooling. It forms very soluble salts, which are not easily decomposed by heat. By oxidation with HNO, it yields ethyl hydrogen sulphate. Ethionic acid has already been noticed (p. 555). It is a mixed ester and sulphonic .acid from glycol, CH,(OSO,;H;-CH,(SO3,H). By hydrolysis the ester portion is split off, H,SO, and isethionic acid or hydroxy-ethyl sulphonic acid, CH2(OH)-CH,(SO3H), being produced. It is characteristic of closed-chain compounds (at all events such as contain a benzene nucleus) that they readily yield sulphonic acids when heated with strong sulphuric acid (p. 559). These are very useful for prepar- ing other compounds, e.g. phenols (q.v.), and, on account of their solubility, for use as dye-stufis. They yield chloranhydrides (p. 198) when treated with PCl;. When benzene is warmed with H,SOy, conc., benzene sulphonic acid, CsH;-SO,0H, is produced (p. 559) ; if fuming acid (4 parts) at 275° be employed the 1:3 and1:4 benzene disulphonic acids, CgH4(SO,0H)2, are produced, used for making resorcinol. Naphthalene with H,SO, conc. at 80° produces a-, and at 180° 3-naphthalene mono- sulphonic acids. The disulphonic acids are obtainable similarly. Sulphonic acids of. most benzene hydrocarbon derivatives are easily obtainable ; some of these will receive passing mention later. NITRO-COMPOUNDS The nitrous esters are metameric with the nitro-substituted hydro- carbons ; thus, ethyl nitrite, C,H,O-N : O, is metameric with nitro-ethane, C,H,NO,. The difference in constitution represented by these two formule is justified as follows: (1) When an alkyl nitrite is treated with an alkali, it is readily converted into an alcohol and an alkali nitrite : this shows that the compound is a true ester of nitrous acid, the formula for which, as already shown (p. 205), is probably HO-N: 0. The nitro-paraffins are not affected by alkalies (but see also p. 682). (2) When a nitro-hydrocarbon is treated with a reducing-agent, it yields an amine (eg. C,H;-NH,), a compound which, since it contains only C, H and N, must contain the N attached directly to carbon. On the other hand, when an alkyl nitrite is treated with a reducing-agent it yields the corresponding alcohol and 1 E’hyl sulphite, SO(OC,H;),, is prepared by the action of SOCI, on alcohol. When heated with one equivalent of NaOH it yislds ethyl sodium sulphite; when this is treated with an acid with a view to removing the Na, it is decomposed, so that ethyl hydrogen sulphite has not been prepared. 682 NITRO-COMPOUNDS ammonia; since the alcohols contain O attached directly to carbon, the alkyl nitrite probably also contains O attached directly to carbon, in which case the N is probably not attached directly to carbon, a conclusion con- firmed by the ease with which the C and N are parted in these compounds by saponification. The nitro-compounds may be regarded as derived from nitric acid in the same way that the sulphonic acids are derived from sulphuric acid. cts With regard to the formation of the two metamers, when acyclic, it cannot be predicted whether a nitro-paraffin or an alkyl nitrite will be formed from a given metallic nitrite, until the particular reaction has been investi- gated. It is possible therefore that the nitrites are tautomeric (p. 735). CH,I and KNO, yield methyl nitrite, CH,ONO, but CH,I and AgNO, give nitromethane, CH,"NO,, although the AgNO, is prepared from AgNO, and KNO,. With AgNO,, nitro-paraffins R-NO, usually constitute the chief product accompanied by some alkyl nitrite, R-ONO. Although KNO, yields a nitrite inthe above reaction, it frequently produces nitro-paraffins, e.g. CyH,0-SO,OK (potassium sulphethylate) + KNO,—> C,H,'NO, (nitro- ethane). The nitro-paraffins can be primary, secondary, or tertiary like all other open- chain hydrocarbon substitution-products. The three forms have the same structure as the three forms of alcohols, NO, being substituted for OH (p. 580). The distinctive behaviour of the three kinds of alcohol with nitrous acid and certain properties of the nitro-paraffins have been given at p. 581. The primary and secondary nitro-paraffins contain hydrogen attached to the same carbon atom as that to which the NO, is attached ; the close proximity of the NO, to the H imparts an acid character to the latter, so that this may be exchanged for metals, such compounds as CH,;-CHNa-NOQ, and (CH3).: CNa-NO, being produced by the action of alcoholic soda on the nitro- paraffin ; compare the influence of two CO groups on a CH, group (p. 600).+ Nitro-methane boils at 101°; hydrolysis (by strong HCl at 150°) converts it into formic acid and hydroxylamine. Nitro-ethane boils at 113°; it gives a blood-red colour with ferric chloride, and burns with a luminous flame. Both are heavier than water, and their boiling-points are higher than those of the nitrous esters. T'rinitro- methane, nitroform, CH(NOg)3, is a thick colourless oil, solid below 15°, exploding violently when rapidly heated. It is an acid. On heating it with fuming HNO, and H,SOQ, tetranitromethane, C(NOp),4, is produced ; this is a crystalline mass, melting at 13° to an oil; it is very stable, does not explode ; b.-p. 126°. Trichloronitromethane or chloropicrin or nitro-chloroform, CCl;NO,, is @ product of the joint action of nitric acid and chlorine on many hydrocarbon derivatives. ‘It is best obtained by heating picric acid (q.v.) with chlorinated lime, when it disti's over as a heavy liquid, sp. gr. 1-69, b.-p. 112°, and possessed of a tear-exciting odour. Nascent H reduces it to methylamine, HCl and H,0. The nitro-hydrocarbons of the benzene series are produced by the direct action of nitric acid on the hydrocarbons, a process frequently spoken of as nitration. When the hydrocarbon has a side-chain, strong nitric acid yields a nucleal nitro- compound, but dilute acid introduces the nitro-group into the side-chain. While it is easy to introduce one or two nitro-groups into an aromatic nucleus, the direct introduction of the third is difficult, and more than three have not been introduced. The nitro-aromatic compounds having the nitro-group or groups in the nucleus are of a tertiary character, but when the group or groups are in the side-chain all three kinds may exist. Nitrobenzene, C,H,-NO,, is prepared by adding in small portions a well-cooled mixture of 1 vol. nitric acid (1-42) and 1 vol. sulphuric acid (1-84) * The salts of the primary and sccondary nitro-compounds appear to be derived from a tautomeric form, the isonitro-ccmpcund, e.g. CH,CH:NO,H ; for when treated with acids they yield a free nitro-com- Found which at first ehows reactions differing from those of the original nitro-compound, such as a coloration with FeCl,; afterwards it resumes the usual properties. NITROBENZENE 683 -to 1 vol. benzene contained in an open flask, well shaking after each addition of acid and keeping the temperature below 25° by immersing the flask in cold water. Much heat is developed, the action is energetic, and copious red fumes are evolved. Finally the mixture is heated on the water- bath to 50° for 15 minutes, agitating occasionally. C,H, + NO,-OH = C,H;NO, + H,0; the secondary reaction is not expressed in the equation. A red oil, the nitrobenzene, floats on the strong acids, but on pouring the mixture into several times its volume of water, the oily layer, sp. gr. 1-2, is at the bottom. The oil is transferred to a separating funnel, washed with dilute Na,CO, solution, then with water, removed and dried by contact with CaCl,. The yellow liquid is then fractionated. At first a little benzene passes over, which is rejected, then the nitrobenzene at 204°-207°. If the temperature has been allowed to rise much above 25° during nitration, more or less dinitrobenzene (chiefly meta-), C,H,(NO.)., will be produced ; if the temperature be 70° rising to 100°, the dinitro-derivative alone is formed (pale yellow needles, m.-p. 89-:8°, b.-p. 297°, very slightly volatile with steam). This is somewhat explosive, and the residue in the distilling flask may “blow.” The nitrobenzene may be obtained quite pure by steam-distillation (p. 698) of the crude oil, when, of course, the drying is unnecessary. It is a pale yellow liquid having the odour of bitter-almond oil, sp. gr. y5° 1-208, m.-p. 4°, b.-p. 207° ; poisonous, especially the vapour. As essence or oil of Mirbane, it is used as a perfume for soaps, &c. Techni- cally it is made by the above process and reduced to aniline, azobenzene, benzidene, &c., for dye manufacture (see p. 697). Occasionally it is used as an oxidant (see Quinoline, p. 804). The dinitrobenzenes yield the corresponding nitranilines, CgH,(NH,)(NO.), and diamidobenzenes or phenylenediamines, CgH,(NH2). when reduced. The 1: 2-derivative differs from the others in the comparative ease with which one nitro-group can be ex- changed for other radicles (e.g. for OH, forming 1: 2-nitrophenol, CsH,(OH)(NOg2), when heated with hot alkalies). Nitrotoluene, CgH,(CH;).(NO.,), is prepared from toluene by the nitrobenzene process, keeping the temperature below 20° throughout ; the product contains 35 per cent. para- (colourless prisms, m.-p. 54°, b.-p. 238°), 63 per cent. ortho- (liquid, sp. gr. 94° 1-163, b.-p. 223°), and 2 per cent. meta- (m.-p. 16°, b.-p. 230°) nitrotoluene. Dinitrotoluene, CsH3(CH;)(NOz)s[1 : 2 : 4], as for dinitrobenzene ; m.-p. 71°. Chemi- cally analogous with the benzene derivatives, yielding toluidines, &c., used for dyes. Trinitrotertiarybutyltoluene, (NOs)sCgH(CH3)C(CH3)3 [(NOz)3 : CHg : C(CH3)3=2 : 4: 6:1: 3], is obtained by nitrating various butyltoluene derivatives, and is sold as artificial musk. a-Nitronaphthalene, CyypH;NO.» Slowly sift finely powdered naphthalene (20 grams) over a mixture of HNO, (1-375) (40 grams) and H,SO, (1-84) (40 grams), rapidly agitated and kept at about 45°; after cooling and pouring away the acid, wash with hot water, dry, and recrystallise from benzene. Lemon yellow needles, sp. gr. 1:33, m.-p. 61°, b.-p. 304°. Used in the dye industry, and for destroying the fluorescence of mineral oils when used for adulterating vegetable oils. Certain other nitro-derivatives are considered under the bodies from which they are derived. : VIII. METAL AND METALLOID DERIVATIVES These compounds include those of several of the elements found on the right of Werner’s periodic Table (p. 305), also of the alkali metals, in which the valencies of the said elements are satisfied by alkyl, acid or other organic radicles. They are described by various authors as organo-mineral, organo- metallic, metallo-organic, &c., but boron and silicon alkides, for instance, cannot be described as metallic. At the extreme right of Werner’s Table stand the halogens and the sulphur group, whose compounds might have 684 METAL DERIVATIVES been considered in a separate section of the present chapter ; and it is to be noted that it is with these substances that the metallic derivatives react. In this connection, compare the sulphonium and iodonium com- pounds, as well as the usual halides. Elements in other parts of the Table do not form organic derivatives—or do not do so readily. There are three distinct classes of these compounds: (a) those of metal and alkyt radicles, e.g. zinc ethide Zn (C,H;)., by means of which the alkyl can be substituted for Cl, Br, OH, &c., in other compounds; (b) those of metal linked with the carbon of an acid radicle or other electronegative group, e.g. sodium malonic ester, CHNa(COOC,H;),, by means of which the group can be substituted for Cl, &c., in other compounds ; (c) those in which the metal is attached to nitrogen, as in the imide group. They are therefore of the highest value in effecting various syntheses ; for all that is necessary is to bring together the respective metal- and halogen-derivatives to produce any desired complex. However, there are often practical difficulties in dispensing this simple prescription, but many of these are avoided when carried out in the manner of Grignard’s reaction (infra). Another important application of these compounds is in the determination of the valency, and hence the atomic weight, of the metals, by ascertaining the vapour density of the organic derivative, e.g. Be and Al (p. 650). Compounds of the first class will be described in this chapter. Those of the second are exemplified in the @-diketone group—CO—CH,—CO— (pp. 600, 650, 667), also in those sulphones, which are similarly constituted— SO,—CH,—S0,— eg. CH,:CH:(S02°C,H;). (ethylidene diethyl sulphone) NaOH CH,-CNa(SO,C.H;). CMs! (CH3),C-(SO,C,H;), (sulphonal, p. 648). Hydrogen attached to carbon is frequently replaceable when only one CO-group is adjacent or it is absent, eg. N,:CH-CO-OC,H; (diazoacetic ester, p. 715) Na0OGHs N, : CNa-CO-OC,H,;; CH,-CHNa-NO, is from a nitro-paraffin (p. 682) ; the acetylides, e.g. C,Ag,, C,Cu, (p. 557). The third class has numerous representatives, ¢.g. C.H,(CO),NAg (silver succinimide, p. 704); NHNa:COOC,H, (sodiwm urethane, p. 707); C,H,NK (potassium pyrrol, p. 796) ; amine derivatives (p. 693), e.g. aniline (p. 697). Derivatives of the first class were discovered by Frankland in 1849 while attempting to isolate the radicles methyl, CH, and ethyl, C,H;. Those containing alkyl groups (alkides) have been best studied, and it has been found that in the case of the compounds from the more electro-negative elements the subtraction of one or more alkyl groups from the saturated compound yield monovalent or polyvalent radicles. For example, tin methide, Sn(CH,),, is a saturated alkyl derivative of Sn'Y; by treatment with iodine, one CH, is removed and Sn(CH;),I is produced. This is the iodide of a monovalent radicle, Sn(CH,),, which behaves like an alkali metal, forming a powerful base, Sn(CH;),0H, obtained by treating the iodide with NaOH. Like other monovalent radicles, such as CH;, Sn(CHs), cannot exist alone, but is known in its double form, Sn,(CH3).,, like C,H. When two alkyl groups are removed, the divalent radicle, Sn(CH3),, is produced ; this resembles a divalent metal and forms a base Sn(CH,),0 ; like CH, it exists only in the ethylenic form Sn,(CH,), (cf. Si, p. 285). Organo-mineral compounds similar to those which have been described are formed by other alcohol radicles and benzene hydrocarbon residues, and mixed compounds are obtainable. Thus, Sn(CH,).(C.H,;). may be produced by the action of zinc methide upon Sn(C,H,),Cl,; and Sn(CH,),C,H, is formed by zinc ethide with Sn(CH3),Cl. Another method is described in detail at p. 640. The most important method of producing these compounds is by the action of metals on the monohalogen substituted hydrocarbons. The ZINC ETHIDE 685 typical case is that of zine ethide, which will be considered first. Then magnesium with special reference to Grignard’s reaction, followed by Be, Hg, Al, B, (C), Si, Ge, Sn, Pb, Bi, Sb, As, P, (N). Zinc Alkides.—Zine ethide or zinc ethyl, Zn(C,H;),, is prepared in accordance with the equation Zn, + 2C,H;I = Zn(C,H;),.+ Znl.. Fifty grams of bright, freshly granulated, and well-dried zinc are placed in a flask E (Fig. 307) connected with a CO, apparatus A, the gas from which is dried by strong H,SO, in bottles B and C. The flask is also connected with the tube f of condenser F, the other end of which is sealed by mercury in D. The apparatus having been filled with COs, the cork of the flask is removed, and 25 grams of ethyl iodide (perfectly free from moisture) are in- troduced, the cork being then replaced. z CO, is again passed for a short time, and then Fic. 307. cut off by closing the nipper-tap (T), when the gas escapes through the mercury seal (G). A gentle heat is then applied by a water-bath to the flask (E) till the ethyl iodide boils briskly, the vapour being condensed in the tube (f), and running back into the flask. In about five hours the conversion is complete, and the iodide ceases to distil. The nipper-tap (T) is again opened, and a slow cur- rent of CO, is passed, the position of the condenser (F) is reversed (Fig. 308), and the tube (f) is connected by the cork (K) with the short test- tube (O) ; the longer limb of a very narrow siphon (I) of stout tube passes through a second perforation in the cork (K), the shorter limb passing into the very short test-tube (P), the cork of which is also fur- nished with the short piece of moder- Fie. 308. ately wide tube (L). For receiving and preserving the zinc ethide, a number of small tubes are prepared of the form shown in Fig. 309. The long narrow neck (R) of one of these is passed down the short tube (L) to the bottom of P, the other end (N) of the tube being connected with an apparatus for passing dry COs. The whole of the apparatus being filled with this gas, the nipper-tap is closed, and the flask (E) heated on a sand-bath, so N that the zinc ethide may distil over, a slow stream of carbonic acid gas being con- % stantly passed into P, the excess escaping Fre. 309 through L. When enough zinc ethide has Mine collected in the tube (O), a blow-pipe flame is applied to the narrow tube (N), which is drawn off and sealed ; the siphon tube (I) is then gradually pushed down, so that its longer limb may be sufficiently immersed in the zinc ethide, and the nipper-tap (T, Fig. 307) is opened, when the pressure of the carbonic acid gas forces over a part of the zinc ethyl into the tube (P). By heating the tube (M) with a spirit-lamp, so as 1 The process is said to be much accelerated if about J,th of zinc ethyl is dissolved in the ethyl iodide, 686 ZINC ALKIDES—REACTIONS to expel part of the gas, allowing it to cool, it will become partly filled with zinc ethide, and may be withdrawn and quickly sealed by the blow-pipe. The spontaneous in- flammability of the zinc ethyl, and its easy decomposition by water, render great care necessary in its preparation. If an alloy of zinc with one-fourth its weight of sodium be employed, the conversion may be effected in an hour. “The reaction in the preparation of zinc ethide really occurs in two stages ; when the ethyl iodide ceases to distil, the flask contains zinc iodo-ethide, ZnIC,Hs, as a crystalline solid, decomposed by a higher temperature into zinc ethide and zinc iodide ; 2ZnIC,H, = Zn(C2H;). + ZnI,. The action is more rapid if the zinc be polarised by copper. To effect this, CuO is reduced by heating it in a tube in a current of hydrogen or coal-gas, and 10 grams of it are mixed with 90 grams of zinc-filings in a 300 c.c. flask, which is then heated with continual shaking, until the mixture forms grey granular masses. After cooling, 87 grams of ethyl iodide are added, and the mixture heated to about 90° with the reversed condenser, till no more liquid distils back, which requires about 15 minutes ; the rest of the operation is conducted as described above, using a sand-bath or an oil-bath. Zine ethide is a colourless liquid of peculiar odour, sp. gr. 1-18, b.-p. 118°. In contact with air, it inflames spontaneously, burning with a bright greenish-blue flame, emitting a white smoke of ZnO. If a piece of porcelain be depressed upon the flame, a deposit of metallic zinc is formed, surrounded by a ring of oxide, yellow while hot and white on cooling. Dissolved in ether and treated with oxygen, it yields zinc ethoxide, Zn(OC,H;),, a white powder. Water decomposes it readily, ethane or ethyl hydride being evolved ; Zn(C,H;), + H,O = ZnO + 2(C,H;-H). When NH, is passed inta the solution of zinc ethide in ether, C,H, is evolved, and a white precipitate of zinc amide deposited— Zn(C,H,)o + 2NH; = 2(C,H,-H) + Zn(NH,)o. If 2H,O and Zn(OH), be written in the first equation, their analogy will be evident ; cf. p. 188; NH frequently acts similarly to O. Zine ethide and ethyl iodide, dissolved in ether and heated to 170°, yield butane, or di-ethyl ; Zn(C,H;). + 2C,H,I = ZnI, + 2(C,H;),. Heated with sulphur, zinc ethide is converted into zine mercaptide, Zn(SC,H;),, the analogue of zinc ethoxide and zinc hydroxide. Zinc ethide is much used in organic research, especially for effecting the substitution of C,H, for Cl, Br, I or OH. Dissolved in ether and heated with Na in a sealed tube, zinc ethide exchanges one-third of its Zn for Na, forming a crystalline compound of zinc ethide with sodium ethide, 3Zn(CoH5)o + Nag = 2(Zn(C.Hs5)o-NaC,H;) + Zn. When this is treated with dry COs, zine ethide distils, and sodiwm propionate remains ; NaC,H; + CO, = C.H;-CO.Na. Zinc methide, or zinc methyl, Zn(CH3)s, is prepared from methyl iodide, like zine ethide, which it resembles (b.-p. 46°, sp. gr. 1-38), but has a more powerful odour, pro- ducing irritation. It is more energetic in its reactions than zinc ethide, and is decom- posed, with inflammation and explosion, by water, yielding methane. Evidence of the synthetic value of the zinc alkides is afforded by the following examples ; but by substituting other alkyls for CH, either in the zine alkide or in the other reagent, corresponding changes in the product will be obtained. (1) CH.CCly.CH, + Zn(CHg)p = CH .C(CHg)o.CH, + ZnClp. Acetone dichloride. Zinc methide. Neo-pentane (hydrocarbon). Jods (2) CH,.CH: O + Zn(CH), = CH;.CHC Acetaldehyde. ‘O.Z:,CH, GRIGNARD’S REACTION 687 This product yields with 2H,O, CH;.CHOH.CH, + Zn(OH), + CH,. Secondary propyl alcohol. Methane. Cl (3) CH3.CCl: O + Zn(CHs)>. = CHy.CLOZnCHy. Acctyl chloride. \cH, This product yields with (2) 2H,0, CH,.CO.CH, + Zn(OH), + CH, + HCl. Acetone (k2tong). CH Cl (b) Zn(CH,)o, CHy.CLOZnCH, (a mn. ) \cH, \cu, Hs which with 2H,0—-+CH;.COH + Zn(OH). + CHy. \CH, Tertiary butyl aleshol. Magnesium Alkides.—The methide, Mg(CH3)o, and ethide are prepared by decom- posing CHI or C,H;I with Mg, when a solid iodide, MgCHgl, is first formed, which is decomposed when distilled in CO, ; 2MgCH,I = Mg(CH3). + MgI,. They are sponta- neously inflammable liquids, yielding Mg(OH),. and CHy, or C.Hg, with water. With magnesium it is not necessary for synthetic purposes to procure the alkides in a separate state. Following a preliminary investigation by Barbier in 1899, Grignard, in 1900, published an account of a reaction now known by his name, the essential details of which are as follows. One molecular weight in grams of an alkyl halide is added to 24 grams magnesium turnings or powder under perfectly dry ether, keeping cool, but warming eventually to finish the reaction; a magnesium alkyl halide RMgX is formed and remains dissolved in the ether; e.g. Mg + C,H,I = C,H,;.MgI (magnesium ethyl iodide). To this solution is gradually added an ethereal solution of the other reagent. If the reagent is water, a hydrocarbon will be formed; e.g. C,H;.Mg.I+ H,O =C,H, + HO.Mg I. If an aldehyde, a secondary alcohol just as with the zinc alkide, e.g. CH,CH:O + C,H;.Mg.I gen 5 : : ae 5 = CH,.CH , which with water ——> CH,.CH< (secondary O.Mg.I OH butyl alcohol). In general, the temperature should be kept at about 0° and contact with air avoided. The simplicity of working details of Grignard’s reaction offer very great advantages over the older method with the separated alkides, and the applications are much wider, and are available for manufacturing opera- tions. All the compounds R.Mg.X are soluble in ether, which is held tenaciously on evaporation ; however, other solvents may be used, but it is necessary that at least traces of ethyl, amyl or other ether, e.g. anisol, or a tertiary amine be present, if the solvent is, like benzene, an indifferent one. These catalysts appear to sever the link between the alkyl and the halogen. Beryllium ethide, Be(C,H;)2, from Be and Zn(C2H5)o, ignites spontaneously. Mercury Alkides.—Mercuric methide, Hg(CH3)2, may be obtained by the reaction between mercuric chloride and zinc methide, but better by dissolving one part of sodium in one hundred parts of mercury, and adding the amalgam, by degrees, to methyl iodide mixed with one-tenth of its volume of ethyl acetate, the action of which has not yet been explained. On distillation, the mercuric methide is obtained as a colourless liquid which is one of the heaviest known, its sp. gr. being 3-07, so that glass floats init. It is unchanged by exposure to air, but gives off a faint odour which is very poisonous. It boils at 95° and burns with a bright flame. With strong HCl, HgiCH,), + HCl = HgCH,Cl + CH,-H. 688 BORON AND SILICON ALKIDES Mercuric ethide, Hg(C.Hs)o, is prepared like the methide. It has the sp. gr. 2-4, and boils at 159°. Its vapour is decomposed at 200° into Hg and butane, but with strong H,SO, it gives ethane. Mercury ethyl chloride, HgC,H,Cl, is obtained by acting on mercuric ethide with mercuric chloride dissolved in alcohol ; Hg(C2H;)2 + HgCly = 2HgC,H;Cl; this shows it to be composed upon the mercuric type, HgCly, and not derived from the mercurous compound Hg,(C.H;)., corresponding with Hg,Cl,. The chloride is insoluble in water, hut crystallises from alcohol, and is easily sublimed. Silver oxide converts it into the mercury ethyl hydroxide, HgC,H;OH, a caustic alkaline liquid which blisters the skin. The iodide, HgC,H;I, obtained by treating Hg(C.H;). with I,, is remarkably stable, crystallising from hot caustic soda, almost without decomposition. It is hardly soluble in water or alcohol. Mercury diphenyl, (CgH;),.Hg, is formed when Na-amalgam acts on C,H;Br. It is a crystalline solid, m.-p. 120°, subliming almost unchanged, insoluble in water, and sparingly soluble in alcohol and ether, but soluble in benzene. When heated, in a sealed tube, with HgCl, and alcohol, it yields mercury-phenyl chloride, HgC,H,;Cl, which, with silver hydroxide, yields mercury-phenyl hydroxide, HgCgH;-OH, a crystalline strongly alkaline base. Aluminium methide, Al(CH3)3, and the corresponding ethide are obtaimed by de- composing mercuric methide and ethide by Al. They are spontaneously inflammable liquids, violently decomposed by water, yielding Al(OH), and methane or cthane. Their vapour densities are known. Boron Alkides.—Boron methide, B(CH3)3, formed by the action of a strong ethereal solution of Zn(CH3), upon ethyl borate, 2(C,H5)3;BO3; + 3Zn(CH3;). = 2B(CH3)3 + 3Zn(O-C.Hs5)o, is a gas with an intolerably pungent, tear-exciting odour, liquefied by three atmospheres pressure. When issuing very slowly into the air, it undergoes partial oxidation, with phosphorescence, but when it comes rapidly into contact with air, it burns with a green flame, remarkable for the immense quantity of large flakes of carbon which it emits. Boron ethide, or boron triethyl, B(C,H;)3, is prepared by passing vapour of boron chloride into zinc ethide; 2BCl; + 3Zn(C,H;). = 2B(C.H5)3 + 3ZnCl. It is a colourless liquid of irritating odour, and insoluble in water. Its sp. gr. is 0-69, and it boils at 95°. It inflames spontaneously in air, burning with a green flame, and explodes in contact with pure oxygen. Water slowly converts it into B(C,H;),0H, another spontaneously inflammable liquid. By gradual oxidation in air it becomes BC,H,;(OCjH;)2, decomposed by water, into alcohol and ethyl-boric acid, BC.H;(OH)», which is a volatile crystalline body, subliming in scales like boric acid, and having a very sweet taste and a pleasant smell; it is very soluble in water, alcohol, and ether. Silicon Alkides.—Silicon methide, Si(CH3),, produced by the action of SiC], upon Zn(CHg)o, is a liquid lighter than water, burning in air and producing a white smoke of silica. It is stable in water, and boils at 30°. Silicon ethide, or Si(CoHs),, obtained by a similar process, resembles the methide, but boils at 153°. In its chemical relations it resembles the paraffin hydrocarbons, and is sometimes called silico-nonane, the ninth member of the paraffin series, CyH29, in which silicon is exchanged for an atom of carbon. When acted on by chlorine it yields SiCgH,,Cl ; when this is heated with potassium acetate, in alcoholic solution, it yields the acetate SiCgHj9-C2H30p, and by heating this with alcoholic solution of potash, it is converted into silico-nonyl alcohol, SiCgHy9‘OH, boiling at 190°. For the corresponding hydrogen compounds, see Silicon. By acting on ethyl orthosilicate, Si(OC,H;)4, with zine ethide and sodium, silicon triethyl-ethoxide, Si(Cp.H5)5:OC.H;, silicon diethyl-diethowide, Si(CoHs)o(OCsH;)o, and silicon ethyl-triethoxide, SiCpH;(OC,H;)3, may be produced. When the last named is heated with acetyl chloride, it yields silicon ethyl trichloride, SiC,H,Cl3, which is converted by water into silico-propionic acid, CpH;-SiOOH, a solid, feeble acid. Silico- acetic acid, CH,-SiOOH, is also known. Silicic ethers, see p. 285. Germanium ethide, Ge(C,H;)4, is known. Transition between Si and Sn. Tin Alkides.—Considerable space has already been devoted to these at pp. 640 and 684. Jn tetramethide, Sn(CH3)4, composed upon the model of stannic chloride, ANTIMONY ALKIDES 689 SnCl,, is obtained by the action of an alloy of Sn, Hg and Na upon CH,I. It boils at 78°. By the action of iodine, one CHs group is removed, and tin trimethyl iodide, Sn/CH)3I, obtained ; this, acted on by NaOH, yields Sn(CH,),OH, a sparingly soluble, crystalline, volatile, alkaline base. . When CH,I is heated to 160° in a sealed tube, with tin-foil, tin dimethyl iodide, Sn(CH3)eI, is formed. It crystallises in yellow prisms soluble in water ; NH, gives a white precipitate of the base Sn(CH,),0 with the solution. Tin tetrethide, or stannic ethide, Sn(C.H;)4 (b.-p. 181°), prepared by distilling stannic chloride with zinc ethide, is remarkably stable, even when boiled with sodium. It is not precipitated by H,S8. Like the tetramethide, it yields the iodides Sn(C,H;)2I, and Sn(C,H;)3I. By treatment with Na these undergo nucleal condensation yielding a mixture of Sng(C.H;)4 and Sn,(C,H;)g. which may be separated by alcohol in which the former, stannous ethide, or tin diethide, is insoluble. It is a liquid of sp. gr. 1-56, decomposed when heated ; Sn2(C.H5)4 = Sn(C,Hs)4 + Sn. It is an unsaturated compound absorbing oxygen from the air, and forming Sn(C.H;),0, which forms crystalline salts, like Sn(C2H5)o(NO3)o. Tin hexethide, Sno(CoH;)¢, boils at 270°, decomposing into Sn(C.H;)4 and Sn. Lead Alkides.—The compounds of lead with alcohol radicles are not composed upon the model of the stable chloride, PbCl,, but upon that of PbCly, which is not known in the pure state. Lead tetramethide, Pb(CHg3)4, is formed by the action of zinc-methide upon lead chloride ; 2Zn(CH,). + 2PbCl, = 2ZnCl, + Pb(CH,;), + Pb; it distils at 110°, and has the sp. gr. 2-03. It has a faint odour, is unaffected by air, and is insoluble in water. Heated with HCl—Pb(CH;), + HCl = Pb(CH;),Cl + CH,. The chloride is crystalline, and may be sublimed ; by reaction with KI it gives colourless crystals of Pb(CH,)3;I, and when this is distilled with potash, Pb(CH3)3-OH is obtained as a strongly alkaline body smelling like oil of mustard. Lead tetrethide, Pb(C.H;)4,, and its derivatives resemble the methyl compounds. Lead tri-ethide, Pbo(C.H;),, is obtained by the action of ethyl iodide upon an alloy ofsodiumandlead. This combines with iodine in alcoholic solution, forming Pb(C.H;)gI, which yields a hydroxide, like the corresponding methyl compound. Bismuth tri-ethide, Bi(C.H;)3, is prepared by acting on ethyl iodide with an alloy of potassium and bismuth. It is a spontaneously inflammable liquid which is very unstable, depositing bismuth even below 100°, and exploding at 150°. As might be expected from the non-existence of BiCl;, bismuth tri-ethide shows no disposi- tion to combine directly with the halogens, its derivatives being formed on the model of BiCl,, No bismuth derivative corresponding with stibonium (infra) is known. Antimony Alkides, Stibines.—Antimony forms compounds with the hydrocarbon radicles, composed upon the models SbCl, and SbCl;. Stibio-trimethide, or trimethyl stibine, Sb(CH3)3, is prepared by distilling in a current of CO, methyl iodide with the potassium antimonide obtained by strongly heating tartar-emetic ; 3CH,I + K,Sb = 3KI + (CH );Sb. The powdered antimonide must be mixed with sand to moderate the action. The product is a garlic-smelling liquid, of sp. gr. 1-52, and boiling at 80°. It is insoluble in water, but dissolves in ether. By the slow action of air it is converted into Sb(CH3),0, but is liable to take fire. It com- bines with chlorine and iodine, forming Sb(CHg)3Cl, and Sb(CH3)3I2, which may be crystallised, and are formed upon the model of SbCl;. Stibio-trimethyl combines at once with methyl iodide, forming Sb(CH;),I as a white solid, crystallising in six-sided plates from hot water. When decomposed by Ag,O in presence of water, it yields a strong alkali, tetramethylstibonium hydrowide, Sb(CH,),0H, which may be crystallised, and forms crystallisable salts. Stibio-pentamethyl, Sb(CHs)s;, composed on the model of SbCl, is obtained by distilling stibio-trimethy] iodide with zinc methide. Stibio-tri-ethide, or tri-ethyl stibine, Sb(C.H;)3, is obtained like stibio-trimethide ; or by acting on antimonious chloride with zinc ethide; 2SbCl; + 3Zn(C.H5)o = 28b(CeHs)3 + 3ZnCly. It resembles the methyl compound, but boils at 158°. It is remarkable for behaving like a metal; even decomposing hydrochloric acid and 44 690 KAKODYL liberating hydrogen; Sb(C,H;),; + 2HCl = Sb(C,H;5)sClp + Hz. The chloride is an oily liquid smelling like turpentine. Its salts behave like those of the alkalies. Arsines.—While the alkyi derivatives of NH, and PH, are strongly basic, those of AsH, are not. Moreover, only the tertiary and secondary derivatives are known. The divalent radicles like As(CH3),, however, give rise to salt-forming oxides, and the radicles themselves exist in double form. Trimethyl arsine, As(CH,)3, is obtained by the action of AsCl, on zinc methide. It isastrong-smelling liquid, boiling at about 70°, and resembling P(C,H;)3, but not forming salts with the acids. Arsen-dimethyl, or kakodyl, As(CH,),, or Kd, has a special interest as having been one of the first bodies recognised as a compound radicle capable of behaving like an elementary substance, by Bunsen, 1840. The formula As(CH3), represents only one volume of vapour, so that it must be doubled to represent a molecule, conveniently termed dikakodyl. The oldest compound of kakodyl is the dikakodyl oxide, Kd,O, or alcarsin, or arsenical alcohol, named, after its discoverer, Cadet’s fuming liquid, and obtained by distilling a mixture of equal weights of white arsenic and potassium acetate— As,O, + 8CH,CO.K = 2[As(CH3)o]20 + 4COg + 4K,CO3. The distillate has a strong odour of garlic, and takes fire spontaneously, owing to the presence of dikakodyl. It is received in water, when it sinks to the bottom; sp. gr. 1-46, b.-p. 120°. It combines with acids to form salts, and dissolves in alcohol, the solution giving, with alcoholic mercuric chloride, a crystalline precipitate of Kd,O.2HgCl,. By distilling this precipitate with strong HCl in a retort filled with CO,, kakodyl chloride, KdCl is obtained as a heavy spontaneously inflammable liquid, of terrible odour. When this is heated to 100° with zinc in an atmosphere of CO,, a compound of ZnCl, with kakodyl is produced, and on treating this with water dikakodyl separates as a heavy oily liquid which boils at 170°. It inflames spontaneously in air, and when its vapour is passed through a tube heated to 400°, it is decomposed—As,(CH,;), = 2CH, + C,H, + As. When slowly oxidised by air, it is converted into Kd,O, which is afterwards converted, in presence of water, into kakodylic acid, KdO-OH, or dimethyl- arsinic acid, AsO(CH,),‘OH, 7.e. arsenic acid, AsO(OH),, in which two OH groups are exchanged for (CH3),. This acid is best prepared by oxidising Kd,O with mercuric oxide in presence of water—Kd,0 + 2HgO + H,O = 2Kd0,H + Hg,. It crystallises from the aqueous solution, and is a stable acid. The As is not precipitated by H,S, but kakodyl sulphideisformed. Its salts are used in medicine, and are remarkable for their comparative non- virulence. Sulphur dissolves in dikakodyl, forming Kd,S8, a colourless liquid of unpleasant smell, which behaves like an alkali sulphide. Kd,S, is a solid which may be crystalliscd from alcohol. Kakodyl cyanide, KCN, prepared by distilling kakodyl chloride with mercuric cyanide, forms lustrous prismatic crystals, m.p. 37°, b.p. 140°. It is nearly insoluble in water, but dissolves in alcohol. Its vapour is very poisonous. Kakodyl trichloride, As(CH3),Cl3, is composed upon the model of AsCl;, whilst the chloride, As(CH3).Cl, is formed after AsCl,. The chloride ignites in Cl, but, if it be dissolved in CSg, the action of Cl converts it into crystals of the trichloride. When this is heated, it evolves CH,Cl, and a heavy irritating liquid distils, which is arsenmethyl dichloride, AsCH;Clp, boiling at 133°, and soluble in water without decomposition. By evaporating the solution with Na,CO;, and extracting the residue with alcohol and crystallising, arsenmethyl oxide, AsCH3O, is obtained. The crystals smell like asafcetida. Mercuric oxide in the presence of water, converts the oxide into methyl- arsinic acid, ASCH;0(OH)>. PHOSPHINES 691 With methyl iodide, dikakodyl yields kakodyl iodide and tetramethyl-arsonium todide, As,(CHs)4 +'2CH,I = As(CH,)oI + As(CH;),I ; this last, when decomposed by moist silver oxide, yields the corresponding hydroxide, As(CH),OH, which is strongly alkaline, and may be crystallised. Dimethylarsine, (CH ),AsH, is a spontaneously inflammable liquid (b.-p. 36°) obtained by the action of Zn and HCl on an alcoholic solution of KdCl. The ethyl compounds of arsenic are in every respect similar to the methy! compounds. The derivatives of aromatic arsinic (arsonic) acids have become of much importance in medicine, more particularly the amino- and hydroxy-deriva- tives. They are made by heating an amine or a phenol having a free para- position with arsenic acid to about 200°; water is lost and the arsenic acid residue, AsO(OH),, enters into the para-position. Thus from aniline and arsenic acid is obtained p-aminophenylarsinic acid— NH,-C,H; + AsO(OH),; = NH,-CgH,-AsO(OH), + H,0. This was originally called arsanilic acid ; its sodium salt, NH,-CgH,-AsO(OH)ONa + 4H,0, is the therapeutic remedy known as atoxyl, and its acetyl derivative NHAc-C,H,:AsO(OH), is arsacetin, also a remedy. Mild reducing agents convert the arsinic acids into arsenoxides of the type R-AsO, in which the arsenic has become trivalent and of greater toxic effect. More drastic reduction produces compounds of the type R(OH)As-As(OH)R and R-As: As-R. (Com- pare Azo-benzene, p. 717.) Thus from atoxyl we have: p-aminophenylarsenoxide, NH2'C,H,4:AsO. 4: 4’-diaminodihydroxyarsenobenzene, NH»'CgH4-As(OH)-As(OH)-CgHy:-NHg. 4: 4’-diaminoarsenobenzene, NH,:C,H4-As : As‘CgHy-NHo. The arseno-compounds cannot be distilled or crystallised ; they are generally colloidal solids, very easily oxidised by air. p-Hydroxyphenylarsinic acid, made from phenol and arsenic acid, can be easily nitrated to 3-nitro-4-hydroxy-phenylarsinic acid, OH(NOg)-CgHz-AsO(OH),. Energetic reducing agents convert this into an arseno-benzene derivative and at the same time reduce the nitro-group, producing 3: 3’-diamino-4 : 4’dihydroxyarsenobenzene, OH(NH,)-C,H,-As : As-CgH3(NH,)OH ; the dihydrochloride is the remedy known as salvarsan. Phosphines.—These compounds being formed on the type of PHs, the analogue of NH3, are primary, secondary, and tertiary, like the alkyl- amines, as explained in the next section. Tri-ethyl phosphine, P(C,H;),, a tertiary phosphine, is prepared by very gradually dropping PCI, into a solution of zinc ethide in ether, in a retort connected with a receiver filled with CO,; a very violent action occurs—2PCl, + 3Zn(C,H;), = 3ZnCl, + 2P(C,H;)3. The upper layer of the distillate contains the excess of PCl, and ether, the lower being a com- pound of ZnCl, with triethyl phosphine, which may be separated by careful distillation with KOH in a retort filled with H. It is also obtained by heat- ing phospbonium iodide with alcohol, in a sealed tube, to 180° ; PH,I + 3C,H,OH = P(C.H,),-HI + 3HOH; the hydriodide is distilled with KOH. Tri-ethyl phosphine is a hquid of strong odour, sp. gr. 0-81, and b.-p. 127°. It behaves like a divalent metal of the calcium group, absorbing O from the air ; it becomes hot and explodes below 100°. It forms salts with the acids; its oxide, P(C,H;),0, is a very stable crystalline substance, obtained, together with ethane, by distil- ling tetrethyl-phosphonium iodide with potash ; P(C,H5)al + KOH = P(C,H;),0 + KI + C,H;H. The tetrethyl-phosphonium iodide is obtained by heating ethyl iodide with P in a sealed tube; 4C,H,I + P, = P(C,H;),l + PI,. By decomposing its aqueous solution with Ag,O, the 692 PHOSPHINES tetrethyl-phosphonium hydroxide, P(C,H;),OH, is produced, a strongly alkaline substance, which may be crystallised and is comparable with the hydroxides of the alkali metals. Tri-ethyl phosphine combines violently with methyl iodide, forming P(C,H;)3CHgI, which yields an alkaline hydroxide when decomposed with water and silver oxide. Tri-ethyl phosphine combines with sulphur, evolving heat, and forming P(C.H;),8, which crystallises in needles from solution in hot water. It also combines energetically with CS., forming a fine red crystalline compound soluble in alcohol; this reaction may be used as a test for CS, in coal gas. The methyl phosphines are similar to the ethyl compounds and are similarly prepared. The primary and secondary phosphines, ethyl-phosphine, P(C,H;)Hg, and di-ethyl phosphine, P(C,H;),H, are prepared by heating PH,I with C,H,I and ZnO, in a sealed tube for some hours ; crystalline compounds of zinc iodide with the hydriodides of ethyl-phosphine and di-ethylphosphine are first formed ; 2PH,I + 20,H,I + ZnO = H,O + Znl, + 2(P(C,H;)H>.HI), and PH,I + C,H;I+ ZnO = H,O + ZnI, + P(C,H;).H.HI. These are decomposed by distillation with water out of contact with air, when the phosphines distil over. Ethyl-phosphine is a feebly basic liquid, boiling at 25°, having an intolerable odour, insoluble in water. Di-ethyl-phosphine is also liquid, but boils at 85°, and is more strongly basic. Both compounds, being composed upon the PCl; model, are disposed to unite with other bodies to form compounds upon the PCl; model. When oxidised by nitric acid, they yield, respectively, ethyl-phosphinic acid, PO(C2H;)(OH)., and di-ethyl-phosphinic acid, PO(C.H;),0H, composed upon the model of orthophosphoric acid, PO(OH);, by the substitution of ethyl for hydroxyl. Phenylphosphine (phosphaniline), PHy-CgH;, is prepared by the action of HI on phosphenyl chloride, PCgH;Cl, ; it is a liquid of intense and repellent odour, boils at 160°, and absorbs oxygen from the air to form the soluble crystalline phenyl-phosphine oxide, CgH,PH,0. Phosphenyl chloride, PCgH;Cle, obtained when mercury diphenyl, (CgH;)oHg, is heated with PCl,, is a liquid which combines with Cl to form crystals of the tetrachloride, PC,H;Cl,. When treated with water it yields phenyl-hypophosphorous acid (phos- phenylous acid), CgH;-PHO(OH). From the tetrachloride, phenyl-phosphinic acid (phosphenylic acid), CgsHs-PO(OH),, is similarly prepared. Phosphenyl chloride and phenylphosphine react to form phosphobenzene, C.H;-P : P-C,H;, the analogue of azobenzene, CgH;-N : N-C,Hs. Amines.—These follow here quite naturally, but on account of their purely organic deportment, their occurrence in the animal and vegetable kingdoms, and the great number and variety of their derivatives, they are considered apart in the next chapter. IX. AMMONIA-DERIVATIVES The organic compounds classed under this head are derived from NH, by substitution of radicles for H, and are in many cases very nearly related to the organo-mineral compounds, since such compounds as P(CHs)3, As(CH;)3, Sb(CH);, B(CH,)s, are formed upon the type of PH;, AsHs, SbH,, and BH;, which are nearly allied to NH; ; but the strongly alkaline character of ammonia impresses special characters upon the bodies derived from it. These bodies may be divided into— (1) Amines or ammonia-bases, formed by the substitution of alcohol radicles for the hydrogen in ammonia, such as NH,-CH,, NH(CH,),, N(CH3)3. This class also includes the ammonium bases, formed by the substitution of alcohol radicles for hydrogen in ammonium hydroxide, NH,OH, such as N(CH;),0H. All these are basic, many of them powerfully so. AMINES 693 (2) Amides, derived from ammonia by the substitution of acid radicles for hydrogen, such as NH,(CH,CO), NH(CH,CO),, N(CH,CO),. These may also be regarded as formed from acids by the exchange of 1, 2 or 3 OH. groups from the COOH groups of the acid for (NH,)’, (NH)” and N’”’ respectively. They are only slightly basic compounds, since the acid radicle has nearly neutralised the basic character of the parent ammonia. (3) Amino-acids,’ derived from acids by the substitution of (NH,)’ for H in the hydrocarbon residue, such as CH,(NH,)‘COOH from CH,-COOH. These are both basic and acid in character. A compound containing the group NH, is known as an amine or an amide, one containing NH is an imide, whilst one containing N, attached to carbon only, is a nitrile. AMINES OR AMMONIA-BASES AND AMMONIUM-BASES These are called primary, secondary or tertiary, accordingly as one, two or three atoms of H in NH, have been exchanged. The quaternary bases can be derived only from NH,OH. Amines or ammonia bases Ammonium-bases Primary or Amido- Secondary or Tertiary o1 Quaternary bases Imido-bases Nitrile-bases bases NHR’, NR’; NH,R’ NR’R” NR’,OH NHR” NR” Amines are also distinguished as monamines, diamines and triamines, accordingly as they are derived fromone, two or three molecules of ammonia. The amines in the above Table are examples of monamines, and the following are examples of the other two classes : Diamines. Triamines. Primary . N,H,R” N3H,R’” Secondary . N2H2R2”; NoRe”Re’ N3H;R’”’R,’; N;H,R’R”’R’” Tertiary NR,” . N,R’R,’ NR,” ; N3R’”’Re The secondary and tertiary amines may be either simple or mixed, that is to say, the radicles R may be either the same or different. Generally speaking the amines share the properties of ammonia, forming crystalline salts with acids, which, however, differ from the ammonium salts in being soluble in alcohol. The amines containing open-chain radicles are somewhat more basic than NH3, and the basicity increases with the number of radicles, NHR, being a stronger base than NH,R, and NR, stronger than either. The amines containing aromatic radicles may have the NH,, NH, or N group attached either to the closed-chain, like NH,-C,H; or NH: (C,H;)o, or to the side-chain, like NH,'CH,'C,H; and NH: (CH,-C,H;),; those of the latter class behave in every respect like the fatty amines, but those in which the nitrogen is attached to the closed-chain show slight differences, due to the fact that a closed-chain nucleus is always somewhat more acidic than an open-chain nucleus ; thus, phenylamine (C,H;-NH,) is less basic than ethylamine (C,H,-NH,), because the basic properties of ammonia have been more neutralised by phenyl than by ethyl. For the same reason, the nucleal aromatic amines show some relationship to the amides and amino-acids 1 'Fhis term supersedes the older ‘‘ amido-acid.” 694 AMINES—PREPARATION (p. 702); for instance, they readily undergo the diazo-reaction (p. 207) characteristic of amides and amino-acids. Hence some chemists term the ‘aromatic amines amido-compounds. ‘The difference here defined is precisely similar to that between the alcohols and phenols (see Phenols). : The most generally applicable method for preparing the amines consists in reducing the corresponding nitro-compounds with nascent hydrogen. Since the nitro-compounds are more easily obtained from closed-chain than from open-chain hydrocarbons, this method is most frequently used for preparing aromatic amines; C,H,NO, + 6H’ = C,H;NH, + 2H,0. : The cyanides of hydrocarbon radicles are convertible into amines by treatment with nascent H ; C,H,-CN + 4H’ = C,H;-CH,-NHg. The open-chain amines can be prepared by heating the hydrocarbon halides with ammonia in alcohol, but the aromatic amines cannot be similarly produced from the nucleal halogen-substituted benzene hydrocarbons. For example, methylamine, NH,CH3;, dimethylamine, NH(CH3)., and tri- methylamine, N(CH,)3, in the form of their hydriodides, and tetramethyl ammonium iodide, N(CH;),I, are all obtained when a strong solution of ammonia in alcohol is heated with methyl iodide for some hours, in a sealed tube at 100°. The reactions which occur may be represented by the following equations (Me = CH,) : (1) NH, + Mel = NH,MeHI ; (2) 2NH, + 2MeI = NHMe,HI + NH,I; (3) 3NH, -+ 3MeI = NMe,HI + 2NH,I; (4) 4NH, + 4MeI = NMe,I + 3NH,I. The NH,I being nearly insoluble in alcohol separates at once and the hydriodides of the three amines crystallise on cooling, leaving the NMe,I in solution. They are distilled with KOH into a receiver cooled in ice, when a mixture of NMe,, NHMep, and a little NH,Me is condensed, much of the last escaping as gas with the NH, from the NH,I. Any NMe,I not previously separated by crystallisation remains in the retort, as it is not decomposed by KOH. The mixed amines are then digested with ethyl oxalate, when the NMe, is not acted on, and may be distilled off. The methyl- amine is converted into methyloxamide, and the dimethylamine into ethyl dimethyl- oxamate (Et = C,H;s) (cf. p. 704): COOEt CONHMe 2NH,Me + | =| COOEt CONHMe COOEt CONMe, NHMe, + | = | COOEt COOEt Water at 0° dissolves the last-named compound, and leaves the methyloxamide undis- solved. On distillation with potash, the methyloxamide yields potassium oxalate and methylamine; (CONHMe), + 2KOH = (COOK), + 2NH,Me; and the ethyl dimethyloxamate yields potassium oxalate, dimethylamine, and alcohol: C,02(NMe,)(OEt) + 2KOH = (COOK), + NHMe, + EtOH. The primary and secondary amines in which there is still ammoniacal H are capable of many of the reactions of NH, ; the tertiary amines, having no ammoniacal H, are less reactive. : On this depend the reactions which distinguish between primary, secondary and tertiary amines. The amine is treated with nitrous acid (or, what comes to the same thing, NaNO, is added to a strong solution of the amine hydrochloride). A primary amine yields the corresponding alcohol with evolution of nitrogen ; C,H;-NH, + HO-N: O = C,H,-OH +N, + HOH. + 2EtOH ; + EtOH. _METHYLAMINE 695 (Cf. the action of NH, on HNO,.) A secondary amine yields a nitrosamine, which separates in oily drops— (C,H;),.NH + HO-N: 0 = (C,H;).N-NO -+- HOH. A tertiary amine is unchanged. A primary amine can also be distinguished by the carbylamine reaction. The hydrochloride is warmed with chloroform and alcoholic KOH; the characteristically disagreeable odour of a carbylamine (q.v.) is produced ; C,H, NH, + CHCl, + 3KOH = C,H,-N: C + 3KCl + 3HOH. A nitrosamine (i.e. a secondary amine in which the H attached to C is exchanged for the nitrous radicle, NO) can be further recognised by Liebermann’s nitroso-reaction ; the suspected compound is mixed with phenol and H,SO, conc. A nitroso-compound gives a dark green solution, becoming red when diluted and blue when made alkaline. The nitrosamines are oily liquids, may be distilled, and are unaffected by acids and alkalies. See also p. 696. Another method of investigating the constitution of an amine, is to heat its alcoholic solution with methyl iodide in a sealed tube; a tertiary amine yields a substituted ammonium iodide by direct union with methyl iodide; N(C.H;)3 + CH;I = N(C,H;)3-CH3I ; a secondary amine yields an ammonium iodide containing two methyl groups ; NH(C,H;). + 2CH3,I = HI + N(C,H;)o(CH3)eI ; a primary amine yields an ammonium iodide containing three methyl groups, NH,.(C.H,;) + 3CH,I = N(C.H;)(CHg)3I + 2HI. See also Mustard-oil reaction. With organic chloranhydrides the primary and secondary amines react to form amides in which the H of the NH, group is exchanged for hydrocarbon-radicles (cf. p- 702); thus, with acetyl chloride, methylamine, NH,CH; reacts to form acetmethy’- amide—CH,CO-Cl + NH,CH,; = CH,CO-NHCH; + HCl; dimethylamine, NH(CHg)., yields acetdimethylamide, CH,;CO-N(CH3)9. The secondary amines also react with inorganic chloranhydrides to form similar substituted amides (cf. p. 224); thus, from POC], and NH(CH3;),. is obtained PO[N(CH3)o]3. Primary amines are apt to give substituted imides, such as CH,N : SO from NH,CH, and SOCl. Monamines.—Simple alkylamines are prepared as described above for methylamines. Mixed alkylamines are obtained by heating the amine of one radicle with the iodide of another (see above). The amines of methyl and ethyl are here described as typical. Methylamine, NH,CH;, is a gas (b.-p. — 6°) resembling ammonia, but more combustible and more soluble in water ; in this it surpasses all gases, one volume of water dissolving 1150 volumes of methylamine. The solution is strongly alkaline. In its reactions with metallic salts it resembies ammonia, but it dissolves aluminium hydroxide and will not dissolve the hydroxides of Cd, Ni, and Co. Its behaviour with acids and with PtCl, is similar to that of ammonia. Heated to redness it yields hydrocyanic acid, HCN, and NH,CN. Potassium converts it into potassium cyanide—2NH,CH,; + K, = 2KCN + 5Hy. Conversely, methylamine is formed by the action of nascent hydrogen on hydrocyanic acid ; HCN + 4H’= NH,CH;. It is also produced by distilling methyl isocyanate with potash (see Cyanogen). Methylamine occurs in the fruit of Mercurialis (dog-mercury), a plant of the order Euphorbiacee. Several of the alkaloids yield it when distilled with otash. Dimethylamine, NH(CH3)o, is a gas boiling at 7°, and resembling methylamine. It has been found in wood-spirit and in guano. . Trimethylamine, N(CH), is obtained on a large scale by distilling the vinasses obtained in refining beet-root sugar, which corresponds with the molasses from cane-sugar, but is not fit for food. It contains sugar, by fermentation of which alcohols are obtained, and substances containing nitrogen, particularly betaine (p. 710), which furnish ammonia and amines derived from the alcohols when distilled. By neutralising the distillate with HCl, the hydrochlorides of ammonia, trimethy]- 696 ETHYLAMINE . amine, &c., are obtained. The NH,Cl, being less soluble, is crystallised out and the N(CH3)3HCI is distilled with lime, when trimethylamine comes off as a gas which may be absorbed by water. The solution also contains dimethylamine, ethylamine, propyl- amine and butylamine. It has been used for converting KCl into K,CO,, by a process resembling the ammonia-soda process (p. 371), which depends on the fact that N aHCO, is less soluble in water than is NH,Cl; but KHCO, has about the same solubility as NH, Cl, so that trimethylamine, whose hydrochloride is much more soluble, is substituted for ammonia. Trimethylamine boils at 3-5°; it has a fish-like smell, is inflammable, and mixes easily with water. It forms salts by direct combination with acids, like ammonia. It is not unfrequently found in plants, as in the flowers of hawthorn, pear, and wild cherry, and in arnica and ergot of rye. It also occurs in the roe of the herring, and may be obtained by distilling herring-brine with lime. It is often found in the products of distillation of animal substances, together with amines containing other alcohol-radicles. Bones, when distilled, yield trimethylamine, methylamine, ethylamine, propylamine, and butylamine. The putrefaction of flour and other nitrogenous substances furnishes these ammonia-derivatives. The hydro- chloride of trimethylamine is employed for making methyl chloride on the large scale, as described on p. 656. Tetramethylammonium hydroxide, or tetramethylium hydroxide, N(CH,),OH, is prepared by decomposing the iodide with AgOH ; NMe,I + AgOH = NMe,OH + Agl. The iodide (tetramethylium iodide), obtained as already described, forms prismatic crystals, and may be purified by crystallisation from water. in which it is rather sparingly soluble. Evaporated in vacuo, the solution of the hydroxide yields a crystalline deliquesvent mass, which acts like a caustic alkali, and absorbs CO, from the air. When heated, it yields methyl alcohol and trimethylamine ; NMe,OH = NMe, + MeOH. The ammonium bases form salts with acids in the same way as the alkali hydroxides do; thus, NMe,0H + HNO, = NMe,NO, + HO; 2NMe,OH -+ H,S0, = (NMe,),8O, + 2H,0. These are not decomposed by potash, even on boiling—a distinction between the salts of amines and ammonium bases. The ethylamines may be prepared by the action of ammonia on ethy! iodide and may be separated from each other in the same way as the methyl- amines. They are prepared on a large scale by the action of NH; upon the impure ethyl chloride obtained as a secondary product in the manufacture of chloral. This is heated for an hour ina closed vessel with a saturated alcoholic solution of NH3;. The volatile matters are then distilled off, and the hydrochlorides crystallised ; on decomposing these with strong soda solution, the three ethylamines form an oily layer on the surface. They are separated as described under the methylamines. Ethylamine, NH,C,H,, is an ammoniacal inflammable liquid, of sp. gr. 0-696, and boiling-point 18-7°. It mixes with water in all proportions. It is a stronger base than ammonia, and dissolves alumina, though it does not easily dissolve cupric hydroxide. Its salts resemble those of ammonia, e.g. NH,Et.HCl, (NH,Et),H,SO,, (NH,Et.HCl),PtCl,. Di-ethylamine, NH(C.Hs5)o, is also an ammoniacal liquid, boiling at 56°, and mixing easily with water. Unlike ethylamine, it does not dissolve Zn(OH),. When its hydrochloride is distilled with potassium nitrite and a little water, ethylnitrosamine is obtained; this contains the group -NO in place of the imido-hydrogen atom, (CpH;)oN-NO (also p. 695). Di-ethylamine nitrite is probably first.formed and then decomposed—(C,H;)-NH.HONO = (C;H;)2N-NO + HOH. Ethylnitrosamine is a yellow aromatic liquid insoluble in water, of sp. gr. 0-95 and b.-p. 177°. Nascent H ANILINE 697 reconverts it into di-ethylamine—2NEt,NO + 4H’ = 2NEt,H + H,O +N,0. When it is dissolved in hydrochloric acid, and HCl gas passed into the solution,it yields nitrosyl chloride and di-ethylamine hydrochloride— NEt,NO + 2HCl = NEt.H.HCl + NOCI. Tri-ethylamine, N(C2Hs)3, differs from the other amines in having a pleasant smell, and being sparingly soluble in water. It boils at 89°. Its reaction is strongly alkaline, and it resembles ammonia in its action upon metallic salts, except that it dissolves alumina, and scarcely dissolves silver oxide, which is readily soluble in ammonia. Tetrethylammonium hydroxide, N(C.H;),-OH, is prepared like the methyl compound, which it much resembles, but crystallises rather more easily. In its chemical behaviour, it is very similar to potassium hydroxide, but it produces, in chromic salts, a precipitate of chromic hydroxide, which does not dissolve in excess. When heated to 100° it does not yield alcohol, but ethylene, water, and triethyl- amine ; N(C,H;),-OH = C,H, + H,O + N(C.H;)3. If it be heated with ethyl iodide, alcohol and tetrethylammonium iodide are formed ; NEt,OH + Etl =EtOH + NEt,I. The iodide may be obtained by the combination of N(C,H;)3 with C,H;I, just as NH4I is formed by NH; and HI, the combination producing heat. It crystallises in cubes like the alkali iodides, and becomes brown, when exposed to air, from the formation of the triodide, NEt,I;. It is very soluble in alcohol and in water, but is insoluble in solution of potash, which precipitates it from the aqueous solution, but without decomposing it. When heated, tetrethylammonium iodide undergoes dissociation, like ammonium chloride, yielding ethyl iodide, which distils over, and is followed by tri-ethylamine, these afterwards combining to reproduce the iodide. By heating a primary amine, NH2R’, successively with R”I, KOH, R’”’I, KOH and R’”’”’ I, a mixed quaternary ammonium iodide, of the form NR’R’”R’”R”’”’ I, may be obtained. The importance of such compounds to the theory of stereoisomerism has been noted at p. 641. Phenylamine, or aniline, or amidobenzene, C,H;-NH,, is prepared from nitrobenzene, C,H;-NO,, by reducing it with metallic iron in conjunc- tion with acetic or hydrochloric acid. On the large scale, the operation is conducted in a cast-iron retort provided with an agitator and a vertical condenser. 20 parts of fine cast-iron filings, some water, and 1 part of HCl are introduced into the retort, and 20 parts of nitrobenzene are allowed to flow slowly in, with constant stirring. Steam is blown into the retort through the hollow agitator, and the action continued until no more nitrobenzene volatilises and runs back from the condenser, whereupon high-pressure steam is blown in. Aniline and water distil over, the former sinking to the bottom, and the water, which retains a little aniline, being used to furnish steam for the next operation. The aniline is purified by distillation, and the iron residues are sent to the blast furnaces. In this method the HCl is required only to start the reaction, which may be represented by the equation 4CgH;NO, + 4H,O + 9Fe = 4C,H;NH, + oF e30y. The process requires care, because, if the action becomes too violent, benzene and ammonia are produced ; CgsH;-NO, + 8H’ = C,H;-H + NH, +2H,0. On the small scale tin is more convenient than iron. Granulated tin is placed in a retort with inverted condenser, and covered with strong HCl; nitrobenzene is added in small portions, and when the action has moderated, the mixture is boiled till all the nitrobenzene has disappeared ; C,H;NO, + 38nCl, + 6HCI = C,H;NH, + 38nCl, + 2H,0 ; the liquid is decanted from the excess of tin, when it deposits, on cooling, a crystalline compound of aniline hydrochloride with stannic chloride; (CsH,;NH»HCl),.SnCl,. By distilling this with excess of potash or soda in a current of superheated steam the aniline is set free. The apparatus for this purpose is shown in Fig. 310. The steam generated in the boiler passes through the coil of copper tube, which is heated by the burner, into the distillation flask, carrying the aniline with it through the condenser. Nitrobenzene may also be converted into aniline by dissolving it'in alcohol, satu- rating the solution with NH;, then with H,S gas repeatedly, as long as the latter is 698 ANILINE—PROPERTIES acted on; CsH;NO. + 3H,S = C,H;NH. + 2H,O + 38. The liquid is decanted from the S, and the alcohol and ammonium sulphide distilled off in a water-bath ; the mixture of aniline and any unaltered nitrobenzene is treated with HCl, which dissolves only the aniline ; this may be liberated by distillation with potash. Since commercial benzene contains toluene and other hydrocarbons, the aniline prepared from it contains toluidine and other bases. To purify it, the crude aniline Fie. 310. is boiled with glacial acetic acid, in a flask with a reversed condenser, when it is con- verted into acetanilide, CsH;-NH:C.H,0. This is distilled, washed with carbon disul- phide, and recrystallised from water till its melting-point is 113-5°, when pure aniline may be obtained from it by boiling with NuaOH— (1) NH,-CsH; + C,H,0-OH = NH-C,H;-C,.H,0 + HOH ; (2) NH-C,H;-C,H,0 + NaOH = NH,-C,H; + NaO-C,H;0. Aniline was originally obtained by distilling indigo, either alone or with caustic alkalies, and was named from anil, the Portuguese name for indigo. It is also found in coal tar, and in the products of distillation of bones and peat. Properties of antline.—Colourless when pure, but generally of a yellow or even brown colour, having a characteristic rather ammoniacal smell ; Sp. gr. 50 1-0275, m.-p. 8°, b.-p. 182°. When shaken with water, it appears almost insoluble, but the water dissolves about j,nd of its weight of aniline, and the latter about 1,th of its weight of water. It is easily soluble in alcohol, also in ether, which extracts it from an aqueous solution on shaking. It has no alkaline reaction, and is less strongly basic than the alkylamines, though it precipitates hydroxides of Zn, Al and Fe. Most of its salts crystallise easily. The hydrochloride, C,H;-NH,,HCI, is commercially known as aniline-salt. The oxalate, (C,H,;-NH,),,H,C.O,, is rather sparingly soluble in water. Aniline has the rare property of dissolving indigo. Many oxidising-agents produce intensely coloured products with aniline. The usual test for it is solution of chlorinated lime (bleaching-powder), which gives a purple-violet colour, changing to brown. Solutions of aniline give a bright green precipitate, (C,H;NH,),CuSO,, with CuSO,. By Caro’s reagent (a persulphate in strong H,SO,) aniline is oxidised to nitrosobenzene, C,H;-NO. Substitution products of aniline are obtained by the reduction of the corresponding nitro-compounds ; thus 1: 2-chloronitro-benzene, CgH,Cl-NOg, will yield 1 : 2-chlor- aniline, CgHyCl:.NHy. By the action of chlorine or bromine water on aniline, the trichloranilines and tribremanilines are produced, the latter form the white precipitate which bromine-water gives with aniline. Nitranilines, or nitrophenylamines, CgHyNOo-NHg, are obtained by the partial reauction of the dinitro-benzenes with NH,HS (p. 697). The presence of the acidic TOLUIDINES 699 NO, or Cl greatly reduces the basic character of aniline. Thus dinitraniline is neutral, and trinitraniline, CgH2(NO2)3-NHg, is acidic in properties. Aniline-sulphonic acid, or 1:4-amidobenzenesulphonic acid, or sulphanilic acid, C.H,(SO3H)-NH., is obtained by heating aniline with twice its weight of fuming sulphuric acid at 180° until SO, is given off. When the liquid is diluted, the acid is precipitated. Sulphanilic acid is the parent substance of several dyes. Alkylanilines.—Aniline, being a primary amine, may be converted into secondary and tertiary amines by action of iodides of other radicles. Thus, methylaniline, C.H,;-NHCHs, and dimethylaniline, CsH;N(CHs)o, are obtained by the action of methyl iodide on aniline, or by heating methyl alcohol with aniline hydrochloride, in a closed vessel, at 250°, when the hydrochlorides of the methyl bases, and water, are produced. Dimethylaniline is also prepared on a large scale by the action of methyl chloride on a heated mixture of aniline and caustic soda—2CH,Cl + CsH;NH, + 2NaOH = CsH;N(CH3)2 + 2NaCl + 2H,O. They are liquids boiling at about 190°, and used in the manufacture of certain aniline dyes. Such alkylanilines are more basic than aniline, and behave generally like phenyl-substituted open-chain amines. The dialkylanilines, however, react with nitrous acid, notwithstanding that they are tertiary amines (p. 695). The products are iso-nitrosoderivatives, i.e. the NO group is attached directly to C ; thus, tsonitroso-dimethylaniline is CgH4(NO)-N(CHs)o. Diphenylamine or phenylaniline, NH(CgH5)o, is a secondary amine obtained by heating aniline hydrochloride with aniline at 250° in a closed vessel from which the NH; is allowed to escape from time to time— C.H,;-NH,HCl + C,H;:NH, = NH(C,H;), + NH;-HC1; the excess of aniline employed decomposes the NH,Cl, so that a mixture of aniline hydrochloride and diphenylamine is left ; on adding water, the latter is left undissolved. It is a crystalline solid, soluble in alcohol and ether, and having feeble basic properties. It melts at 54° and boils at 310°. When acted on by HNO, three atoms of the phenyl hydrogen are exchanged for NOg, producing hexanitrodiphenylamine, NH(CgHo(NOg)s)o, an acid which combines with ammonia forming N(NH,)(C,H.(NObz)3)o, an orange dye, aurantia. Diphenylamine is used as a delicate test for nitrous acid, with which it gives a deep blue colour in strong sulphuric acid. The ammonia-hydrogen in aniline may be evolved by dissolving potassium in the base, when NHK-C,H; and NK,C,H; are produced. By acting on the latter with phenyl bromide (bromobenzene) the tertiary amine, triphenylamine, N(CgH5)s, is produced ; NK,C,H; + 2C,H,;Br = N(CgH5)3 + 2KBr. This compound is not basic ; it is insoluble in water, but may be crystallised from ether. The three toluidines or amido-toluenes, C,H,CH,-NH,, are metameric with methyl-aniline and benzylamine. They are prepared by reducing the nitrotoluenes, just as aniline is prepared from nitrobenzene. Ortho- toluidine resembles aniline; sp. gr. 1-0037, and boiling-point 197°. It becomes pink in air. Chlorinated lime gives it a brown colour, which is changed to red by acids. Metatoluidine is a liquid of sp. gr.,,. 0-998, and boiling at 197°. Paratoluidine, which forms about 35 per cent. of commercial toluidine, is crystalline, fusing at 45° and boiling at 198°. It is sparingly soluble in water, and is feebly alkaline ; alcohol and ether dissolve it. It is not coloured by chlorinated lime. Its basic properties are weak. Its oxalate is insoluble in ether, which dissolves orthotoluidine oxalate. When methylaniline hydrochloride is heated to 350°, it is converted into the isomeric paratoluidine hydrochloride ; C.H;-NHCH,,HCI = C,H,(CH)-NH,,HCl. This migration of a group from a side-chain into the nucleus is frequently noticed. Commercial aniline-oil is never free from toluidine, so that it gives a brown colour with chlorinated lime, as well as the violet due to aniline. Ether extracts the toluidine brown, which becomes pink by shaking the ethereal layer with acetic acid. . Urea crystallises in long prisms resembling nitre, which dissolve in an equal weight of cold water, and in five parts of cold alcohol ; it is almost insoluble in ether. When heated, urea fuses at 132°, and then forms much ammonia and some ammonium cyanate. If kept for some time at 150°, the bulk of it is converted into biwret, produced from two molecules of urea by the loss of one molecule of ammonia ; 2CO(NH,).= NH; + NH(CONH,),. When the temperature is raised to 170°, the biuret again evolves ammonia, and is converted into cyanuric acid ; 3NH(CONH,), = 3NH,; + 2(CNOH),. Urea is not alkaline, but, like many amides, it is a weak base, and, though a diamide, forms salts like a monacid base ; these are acid to litmus. The nitrate and oxalate are best known because they are sparingly soluble, and are obtained as crystalline precipitates when nitric and oxalic acids are stirred with solution of urea. The nitrate, when heated, evolves a very pungent smell, and is decomposed with almost explosive violence at 150°. Urea oxalate crystallises with 2Aq ; (NoH,CO)y.HyC,04.2Aq. Urea hydrochloride, NzH,CO.HCI, is formed, with evolution of heat, when HCl gas acts on dry urea ; it solidifies to a crystalline deliquescent mass, which is decomposed by water. Urea, like many other amides, forms compounds with the oxides of silver and mercury. 45 706 COMPOUND UREAS The compound N,H,CO.3Ag,0 is obtained as a grey crystalline powder when silver oxide is digested in solution of urea. When mercuric oxide is treated in the same way the compound N,H,CO.HgO is formed; on adding mercuric chloride to a solution of urea mixed with potash, a white precipitate of 2N,H,CO.3HgO is obtained, but if mercuric nitrate be employed, the precipitate is NoH,CO.2HgO. _ The formation of the last compound is the basis of Liebig’s method for the determination of urea. Urea also forms compounds with certain salts: the compound N,H,CO.NaCl.Aq. is obtained in crystals when urine is evaporated to a small bulk. When strong solutions of urea and AgNOg are mixed, crystals of N,H,CO. AgNO; are deposited. By mixing dilute solutions of urea and mercuric nitrate, a precipitate is formed having the formula N,H,CO(Hg0O),HNO3. E By hydrolysis urea yields ammonia and carbonic acid, hence its transformation into ammonium carbonate when urine is allowed to putrefy. ; Nitrous acid acts on urea, as on amides generally, converting the NH, into OH, and liberating N, but the (HO),CO formed is at once decomposed into H,O and CO, ; (NH,),CO + 2HNO, = 2N, + CO, + 3H,0. Hypochlorites and hypobromites (pre- pared by dissolving Br in alkalies) also expel all the nitrogen as gas— (NH,).CO + 3NaOBr + 2NaOH = N, + 3H,O + Na,CO; + 3NaBr. This method is sometimes adopted for determining urea by measuring the nitrogen. The nitrogen is also liberated when urea is boiled with potash and a large excess of potas- sium permanganate, whereas, in most other amides, the bulk of the nitrogen is oxidised to nitric acid. When chlorine is passed into fused urea, hydrochloric acid and nitrogen are evolved, and the residue is a mixture of cyanuric acid with ammonium chloride— 3N2H,CO + 3Cl = HCl + N + (CN);(HO); + 2NH,Cl. By boiling solution of urea with AgNOs, a crystalline precipitate of silver isocyanate is obtained ; N,H,CO + AgNO; = NH,NO, + AgNCO. Urea has been formed by passing NH, and CO, together through a red-hot tube ; and by passing a mixture of benzene-vapour, ammonia and air over red-hot platinum wire. Although most of the derivatives of urea behave as though they were derived from the formula CO(NH,)s, there are certain compounds which appear to be derivatives of a pseudourew of the form NH : C(NH,)(OH). Biuret or allophanamide, NH(CONH.)s, is obtained by heating urea to 150° as long as it evolves NH; freely, extracting the residue with cold water, which leaves most of the cyanuric acid undissolved, precipitating the rest by lead acetate, removing the lead by H,S, and evaporating the filtered solution, when the biuret crystallises with 1H,0. It is soluble in alcohol. Its alkaline aqueous solution gives a fine violet colour with CuSO,. When heated in HCl gas, biuret is converted into guanidine hydro- chloride ; NH(CONHg). + HCl = CO, + C(NH)(NH,).HCl. Biuret is also obtained by heating ethyl allophanate with NH,. ~ Allophanic acid has not been obtained ; when liberated from its salts, it decomposes into CO, and urea; NH,CO-NH-COOH = CO(NH2)o + COs. Ethyl allophanate is formed when urea is acted on by ethyl chlorocarbonate (prepared by saturating alcohol with carbonyl chloride) ; CO(NH,). + COCI-0C,H, = NH,CO-NH-COOC.H, + HCl. It crystallises in prisms soluble in water and alcohol. The hydrogen in urea, like that in other primary amides, may be exchanged for radicles, forming so-called compound ureas. Those containing positive radicles, such as methyl carbamide, CO(NH,)(NHCH;), and dimethyl carbamide, CO(NHCH,)s, are derived from the isocyanates of the amines, just as urea is derived from ammonium isocyanate. Those containing acid radicles, such as acetyl carbamide or acetyl urea, CO(NH,)(NHC.H,0), obtained by the action of acetyl chloride upon urea, are called ureides. Di-avetyl carbamide is formed when acetamide is heated to 50° with COCl ; 2NH,C,H;0 + COCl, = CO(NHC.H,0), + 2HCI. The action of NH, on bromacetylurea, NH»-CO-NHCH,BrCO, produces hydantoin, which is a reduction-product of alloxan (q.v.). The Br may be supposed to be exchanged for OH by the action of the ammonia solution, but hydantoin appears to be an internal anhydride of the glycolylurea which would thus be formed, NH,-CO:-NH-CH,OHCO giving NHCO-NH-CH,CO + H,0. | | CARBAMIC ACID 707 Carbanilide, or diphenyl urea, (NHC,H;).CO, is prepared by heating urea with aniline ; (NH,),CO + 2NH,C,H,; = (NHC,H;).CO + 2NH;. It is slightly soluble in water, more soluble in alcohol, melts at 235° and boils at 260°. Carbanilide is also formed when aniline is acted on by carbonyl chloride. Thiocarbamide or sulpho-urea, CS(NHg)o, is the amide of thiocarbonic acid, CS(OH),. It is obtained from ammonium (iso)thiocyanate, CS: N-NH,, by heating it to 180°, just as urea is obtained from the isocyanate. However the change is reversible, equili- brium setting in at 152°-153°, when the mixture contains 21-2 per cent. thiocyanate and 78-8 per cent. thiourea ; it is a case of dynamic isomerism (p. 735). It crystallises easily from hot water, and resembles urea in its chemical reactions ; it melts at 169°. PbO abstracts sulphur from it, converting it into cyanamide (¢.v.). Its salts appear to be derived from the tautomeric form NH : C(NH,)(SH). Thiocarbanilide, or diphenyl sulphurea, is formed when aniline is heated with carbon disulphide ; 2NH,C,H; + CS, = CS(NHC,H;). + H.S. It forms colourless crystals insoluble in water, soluble in alcohol and ether, and melts at 154°. Amic Acids.—If only one of the acid hydroxyl groups of a dibasic acid is exchanged for NH, an amic acid, like succinamic acid, CyH,(CONH,)(COOH), is obtained. These acids are primary amides, and are generally obtained by heating the acid ammonium salts of the dibasic acids, just as the normal salts yield the diamides. Or the acid esters, like ethyl hydrogen oxalate, COOH-COOC,H;, may be treated with NH3. Oxamic acid, CONH,-COOH, is prepared by heating ammonium hydrogen oxalate till it begins to give off CO, (see above). A mixture of oxamide and oxamic acid is left, from which water extracts the acid. Ammonium oxamate is formed when oxamide is boiled with solution of ammonia; (CONH,), + H,.Q = CONH,-COONH,. On adding HCl, the oxamic acid is obtained as a crystalline precipitate, sparingly soluble in water, alcohol, and ether, and converted into hydrogen ammonium oxalate by boiling with water. It fuses at 210° and decomposes, yielding oxamide, formic acid and water. Treated with PCl,, it yields oximide (COg): NH, a soluble neutral substance. Carbamic acid, CO(NH,)OH, has not been obtained in the free state, but ammonium carbamate is formed when ammonia combines with CO,; 2NH, + CO, = CO(NH,) (ONH,). The ammonium salt is best prepared by saturating absolute alcohol with dry ammonia gas, and passing dry CO, into the solution, when the ammonium carbamate crystallises. It is soluble in water, and is converted into ammonium carbonate by boiling the solution ; CO(NH,)-ONH, + H,O = CO(ONH,),. Ammonium carbamate sublimes and dissociates below 100°, and when heated in a sealed tube to 135°, yields urea and ammonium carbonate ; 2CO(NH,)-ONH, = CO(NH,), + CO(ONH,),. When ammonium carbonate is sublimed, part of it is converted into the carbamate ; CO(ONH,), = CO-NH,(ONH,) + H,0. This accounts for the presence of ammonium carbamate in the commercial carbonate (p. 381), Ethyl carbamate, or urethane, CO(NH,)OC,H;, is formed by the action of solution of ammonia upon ethyl carbonate at 100°: CO(OC,H;). + NH; = CO(NH,)OC,H; + HO-C,H;. It forms tabular crystals, soluble in water, alcohol, and ether, melts at 50°, and boils at 184°. Sodium acts on its ethereal solution, forming sodium urethane, NHNa.COOC,H;. Boiled with potash, it yields the carbonate, alcohol and ammonia ; CO(NH,)OC,H, + 2KOH = CO(OK), + NH; + HO-C,H;. Heated with ammonia, it gives alcohol and urea ; CO(NH,)OC,H; + NH; = CO(NH,). + HO-C,H;. Thiocarbamic acid, CS(NH,)SH, is obtained as an ammonium salt by acting on carbon disulphide with animonia in alcoholic solution, 2NH, + CS, = CS(NH,)SNH,, the reaction corresponding with that 708 GUANIDINE between NH, and CO,. The ammonium thiocarbamate crystallises in yellow prisms. When decomposed by HCl, it yields thiocarbamic acid as a yellow unstable crystalline body, which decomposes spontaneously ; CS(NH,)SH = H,S + HSCN (thiocyanic acid). Guanidines.—These compounds, which are of much importance on account of their physiological significance, are amidines (p. 703) of carbonic acid. Guanidine itself, the parent substance, is also called imido-urea, since it may be regarded as containing an imodo-group in the place of the oxygen of urea; thus, CO(NH,),, urea; C(NH)(NH,),, guanidine. The guanidines can be prepared synthetically by heating the hydrochloride of an amine with cyanamide dissolved in aleohol—eg. CN-NH, + NH,,HCl = C(NH)(NH,),,HCl. Guandtdine, or carbon-diamide-imide, C(NH)(NH,),, occurs in vetch seeds and sugar beet. It was so called because originally obtained by the oxidising action of KClIO, and HCl on guanine, a feeble base extracted from guano. It is prepared by heating ammonium thio- cyanate in a retort at 190° for several hours. A portion of the thiocyanate becomes thiocarbamide, which then reacts with the remaining ammonium thiocyanate yielding guanidine thiocyanate; CS(NH,), + NH3;,CNSH = C(NH)(NH,),,CNSH + H,S. This is dissolved in a little water mixed with half its weight of potassium carbonate, and evaporated to dryness, when a mixture of guanidine carbonate and potassium thiocyanate is obtained. This is boiled with alcohol, which dissolves the thiocyanate, and leaves guanidine carbonate (N;H;C),.H,CO;, which may be recrystallised from water. This is converted into guanidine sulphate, (N;H,C),.H,SO,, and decomposed by baryta-water ; the filtrate from the BaSO, is evaporated over sulphuric acid, when guanidine is obtained as a deliquescent crystalline substance, which is strongly alkaline, and absorbs CO, from the air. It is a strong monacid base, and yields well-crystallised salts. Guanidine nitrate, Nz5H,C.HNOg, like urea nitrate, is sparingly soluble in water, and crystallises in plates. Guanidine is soluble in alcohol. Its platinum salt, (N;H;C.HCl)2PtCl,, is sparingly dissolved by absolute alcohol. When hydrolysed with baryta-water, guanidine yields urea and ammonia; C(NH,),NH + H,0 = (NHz)2.CO + NH;. Heated with strong potash, it gives potassium carbonate and ammonia ; C(NH.)o(NH)” + 2KOH + H,O = C(OK),0 + 3NH;. Hot dilute H,SO,4 converts it into NH; and urea, which combine with the acid. Guanidine hydriodide is obtained when cyanogen iodide is heated with alcoholic ammonia in a sealed tube at 100° ; I-CN + 2NH, = C(NH)(NHg)o.HI. Nitroguanidine, C(NH)(NH,)(NHNO,), is obtained by nitrating guanidine, and yields amidoguanidine, C(NH)(NH2)(NHNH,), when reduced. This compound is of interest as yielding hydrazine, NH, and CO,, when hydrolysed. Hydrazoic acid (p. 189) may also be obtained from it by first treating it with nitrous acid to form diuzo-guanidine, C(NH)(NH2)(NHN : N-OH), and hydrolysing this. Diphenyl guanidine, or melaniline, C(NH-CgH5),NH, is a crystalline base produced by the action of cyanogen chloride on aniline— CLON + 2NH,C,H; = C(NH-C,H;,).NH.HCL. AmINO- OR Amrpo-Acips ! These may be prepared from the chloro-substituted acids by treatment with ammonia ; thus amido-acetic acid results from the action of ammonia on monochloracetic acid, CH,Cl-CO.H + 2NH, = CH»(NH,)-CO,H + NH;.HCl1; also by the reduction of the nitro-acids or the cyano-acids by nascent hydrogen— ' The prefixes amino-, imino-, anilino-, &c., are now often substituted for amido-, imido- anilido- & GLYCOCINE 709 CH,(NO,)-CO,H + 6H’ = CH.(NH,)-CO,H + 2H,0. CH,(CN)-COOH + 4H’ = CHs-CH,(NH,)-COOH. In the aromatic group the nitro-acids are reduced to obtain the amido-acids. They are metameric with the amides of hydroxy-acids, but are distinguished by their greater stability towards hydrolysing agents, the amido-group being more firmly held and less easily evolved as NH,. Like other ammonia derivatives they may be primary, secondary, or tertiary, as NH,(CH,COOH), NH(CH,COOH),, N(CH,COOH),, obtained from the mono-, di- and tri-chloracetic acids respectively. The open-chain derivatives may bea-, 8-, or y-amido-acids, like other open-chain substituted acids. By action of nitrous acid the NH, group is converted into an OH group, as in the case of the amines and amides, a hydroxy-acid being produced— CH,(NH,)-CO,H + NO-OH = CH,(OH):CO,H + N,+ HOH. But there is a tendency for the amido-acids to undergo the diazo-reaction (p. 207). When heated with baryta the amido-acids lose CO, and give the corre- sponding amines — CH,NH,-COOH = CH,NH, + CO,. Just as the a-hydroxy-acids form lactides by loss of water from both the COOH and the OH groups (p. 617), 40 the amido-acids are converted by dehydrating agents into bimolecular anhydrides by loss of water from the NH, and COOH groups; thus JOO Ban two mols. glycocoll, CH,NH,-COOH, yield NHC JN glycide, a diketo- CH,-CO piperazine. Further, the y- and 6-amido-acids yield internal anhydrides, lactams, corresponding with the lactones (p. 618) ; y-amidobutyric acid, CH,NH,-CH,-CH,-COOH, yields y-butyrolactam, CH,NH-CH,-CH,CO. ! ! Amidoformic acid, NH,-CO,H, is identical with carbamic acid. Glycocoll, glycocine, or glycine, is amido-acetic acid, CH,(NH,)CO,H, and is prepared by heating hippuric acid (benzoyl amido-acetic) for half an hour with 4 parts of strong HCl, which converts it into benzoic acid and glycocine hydrochloride— CH,(NHC,H;CO)-CO,.H + HCl + H,O = C,H,CO.H + CH.(NH»)CO,H.HCI. Hippuric acid. -Benzoie acid, Glyeocine hydrochloride. The solution is mixed with water and cooled, when most of the benzoic acid crystallises out ; the filtrate is evaporated to dryness on a steam-bath, the glycocine hydrochloride extracted by water, boiled with lead hydroxide, filtered from the lead oxychloride, the dissolved lead precipitated by H,§, and the filtrate evaporated, when it deposits the glycocine in transparent rhombic prisms, easily soluble in water, sparingly in alcohol, and insoluble in ether. Glycocoll has a sweet taste, fuses at 232°, evolving ammonia and methyl- amine. Its solution gives a red colour with FeCl,, and a blue with CuSO, ; if this blue solution be mixed with potash and alcohol, it deposits blue needles of the formula (NH,‘CH,:CO,),Cu.Aq. A sparingly soluble silver salt, NH,-CH,CO,Ag, may also be obtained, but these compounds do not behave like ordinary salts of the metals (cf. synthesis of hippuric acid). Like other amido-acids, glycocine plays the part of a base and an acid. It forms hydrochlorides containing, respectively, one and two molecules of glycocine, and the latter forms a crystalline platinum salt. Crystalline compounds of glycocine with salts are also known. From the behaviour of the metallic and other derivatives of glycocoll, it appears probable that the constitution of this (and of other) amido- acids is not that represented, but partakes of the nature of an intra- JER, ey Glycocoll can also be prepared by dropping strong solution of monochlor- or mono- molecular ammonia salt—CH 710 HIPPURIC ACID brom-acetic acid into strong solution of ammonia, during constant stirring, allowing to stand a day, removing excess of anfmania by passing in steam, evaporating, adding excess of freshly precipitated copper carbonate, purifying the copper glycocoll formed, and finally dissolving this in water and passing H,S to remove Cu; also by passing cyanogen into a boiling saturated aqueous solution of hydriodic acid— CN, + 2H,0 + 5HI = CH,(NH,)-CO.H + NH,I + 2]. Both methods afford a means of synthesising glycocoll, which derives its name from the fact that it may be obtained by boiling glue (or gelatine) with dilute sulphuric acid (sugar of gelatine ; yuKuc, sweet ; codda, glue). Sarcosine, or methyl glycocoll, CH,(NHCH;)-CO,H, may be obtained by heating, bromacetic acid with methylamine (in place of ammonia, which yields glycocine). It is also formed when the creatine extracted from flesh is boiled with baryta. Caffeine yields it under similar treatment. Sarcosine forms prismatic crystals, very soluble in water and of sweet taste. It is sparingly soluble in alcohol, insoluble in ether, and may be sublimed. Its reaction is neutral, but it combines with acids and bases. Betaine, or tri-methyl-glycocoll, CHa[N(CH3).]‘CO,CH3, or more probably— N(CH), i ‘ CH Can D is found in the juice of beet-root (Beta vulgaris) ( p- 695), and may be formed synthetically by the action of trimethylamine on mono-chloracetic acid— CH,CI-CO,H + N(CH), = CH,[N(CH;).}CO,CH, + HCl. Betaine hydrochloride is also obtained by the careful oxidation of choline hydrochloride (p. 701) ; N(C,H,OH)(CH,),-Cl + O2 = CHy[N(CHg)o]-CO.CH,,HCl. + H,O. Betaine is soluble in water and alcohol, and forms salts with the acids. Anilido-acetic acid or phenylglycocine, CH.(NHC,H;)-COOH, prepared from bromacetic acid and aniline, melts at 127°. It is important as the parent substance of artificial indigo. Acetylglycocine, or aceturic acid, CHa/(NHCH;CO):COOH, from acetyl chloride and silver glycocine, melts at 206°. Hippuric acid, or benzoylglycocoll, or benzamidoacetic acid, CH,(NHC,H,CO)-CO.H, is prepared from the urine of horses or cows (preferably the latter) by evaporating it to about an eighth of its bulk and adding an excess of HCl. On standing, long prisms of hippuric acid are deposited, which may be decolorised by dissolving in boiling water and adding a little chlorine- water, when the colourless acid will crystallise out on cooling. If the animal has undergone much exercise, or the urine has decomposed, benzoic acid is obtained instead of hippuric, and if a dose of henzoic acid is taken, it is found as hippuric acid in human urine, which contains naturally but a minute proportion. It may be synthesised by heating benzoyl chloride with silver glycocoll (cf. salts of glycocoll, p. 709). CH,(NH,)-CO.Ag + CgH;COCl = CH,(NHC,H,CO)-CO,H + Ag; or benzamide with chloracetic acid— CH,CI-CO,H + CesH;CO-NH, = CH,(NHC,H,CO)-CO,H + HCl. Hippuric acid crystallises in rhombic prisms, sparingly soluble in cold water, ‘soluble in hot water and in alcohol, but insoluble in ether, which distinguishes it from benzoic acid. Like benzoic, it dissolves easily in ammonia, and is precipitated, in feathery crystals, by hydrochloric acid ; but these are not dissolved on adding ether. The more complex character of hippuric acid is shown by the action of heat; for, whereas benzoic acid sublimes without decomposition, hippuric assumes a red colour, gives a small sublimate of benzoic acid and evolves hydrocyanic acid, benzamide, CgH;CO-NHp, and benzonitrile, or phenyl cyanide, CsH;-CN, which smells like bitter almonds, O, CREATINE 711 The hippurates resemble the benzoates ; in solution, they give a buff precipitate with ferric chloride. Glycocoll may be regarded as the parent substance of two physiologically important compounds, creatine and creatinine. ; When solutions of cyanamide and glycocoll are mixed, glycocyamine, or guani- doacetic acid, CHy[C( : NH)(NH,)(NH)]-CO,H, is formed. If glycocoll be regarded as an amine, NH,(CH,:CO,H), then the formation of glycocyamine is only in accord with the general method for producing guanidines (p. 708). When glycocyamine hydrochloride is heated at 160° it becomes glycocyamidine hydrochloride by loss of water— NH, NHCO < = NH: ox | +H,0. NH-CH,-CO,.H NHCH, Creatine and creatinine are methylglycocyamine and methylglycocyamidine respectively. Creatine, or methylglycocyamine (xpéas, flesh), CyH N30, or NH: C NH, NH: ce , ls obtained from chopped flesh by soaking N(CH,)-CH,-CO,H it in cold water, squeezing it- in a cloth, heating the liquid till the albumin coagulates, straining, adding baryta to precipitate phosphoric acid, and evaporating the filtrate to a syrup on the steam-bath ; on standing for some hours the creatine crystallises out. It may also be prepared from Liebig’s extract of meat by dissolving it in 20 parts of water, adding tribasic lead acetate, filtering, removing the excess of lead by H.§8, and evaporating to crystallisation. Granular crystals of creatine are sometimes met with in Liebig’s extract. The flesh of fowls yields 0-32 per cent. of creatine, that of cod fish 0-17, beef 0-07 per cent. Creatine forms prismatic crystals (with 1H,0) easily soluble in hot water, but very sparingly in alcohol and ether. It is neutral in reaction, but behaves as a feeble monacid base. Creatine nitrate, C,H,N,0,.-HNO,, erystallises in prisms. When the solutions of its salts are heated above 30°, they are converted into salts of creatinine, a stronger base containing H, and O less than creatine. When boiled with baryta water, creatine is hydrolysed to sarcosine and urea— CH,[C( : NH)(NH,)(NCH3)]‘;CO,.H + H,O0 = CO(NHe). + CH,NH(CH;)-CO2H. Creatine has been prepared synthetically by heating cyanamide with an alcoholio solution of sarcosine or methyl glycocoll, thus settling its constitution. When it is warmed with solution of sodium hypobromite, two-thirds of its nitrogen is liberated, By heating creatine in aqueous solution with mercuric oxide, it is converted into oxalio acid and methyl-guanidine, C(NH)(NH,)(NHCHs3). NH——CO c | , is prepared N(CH,):CH, by heating creatine in a water-bath amd passing a current of pure HCl over it as long as any water is formed. The hydrochloride thus obtained is dissolved in water, decomposed by lead hydroxide, the solution filtered and slowly evaporated, when it deposits prismatic crystals of C,H,;N,0.2Aq, which lose water on exposure to air, becoming opaque. If it be dissolved in cold water, and evaporated in vacuo, the original hydrated crystals are reproduced, but if it be dissolved in boiling water and the solution evaporated, it deposits tabular crystals which contain no water. The solution of these crystals when kept for some time at 60° deposits the prismatic hydrated creatinine. Creatinine is much more soluble in water than creatine is, requiring Creatinine, or methylglycocyamidine, NH : C 712 LEUCINE about 12 parts of cold water. It dissolves in about 100 parts of cold alcohol. It has an alkaline reaction, and is a strong monacid base. It is characterised by forming a sparingly soluble crystalline compound with zinc chloride, (C,H,N,0),ZnCl,. In contact with water, especially in presence of bases, creatinine is converted into creatine by hydration. When creatinine is boiled with baryta-water, it yields ammonia and methylhydantoin NHCO-N(CH;)-CH,CO. ! I Creatinine does not appear to exist as such in flesh, though it is easily produced from it by the dehydration of the creatine. A substance having the same composition as creatinine exists in considerable quantity in urine (about two grams in the urine of twenty-four hours), but its properties are not quite the same as those of the creatinine prepared from the creatine of flesh. In order to prepare urinary creatinine, the urine is mixed with one-twentieth of its volume of a cold saturated solution of sodium acetate, and with one-fourth of its volume of a cold saturated solution of mercuric chloride ; this produces an amorphous precipitate which is quickly filtered off, and the filtrate is set aside for forty-eight hours, when it deposits a granular precipitate, appearing in spheres under the microscope. This precipitate is suspended in cold water, and decom- posed by H,§, the mercuric sulphide is filtered off, and the acid filtrate evaporated over sulphuric acid, when it leaves crystals of the hydrochloride, CyH,N,0.HCl. The concentrated aqueous solution of this salt is decomposed, in the cold, with lead hydrate, when an alkaline filtrate is obtained, which has a bitter taste, and, by spontaneous evaporation, yields prismatic crystals of CsH;N,0.2H,O, which rapidly become opaque and anhydrous when exposed to air. If heat be employed during the preparation of the body, tabular crystals of C,H,N,0 are obtained, which are unchanged by exposure to air. The urinary creatinine requires 362 parts of cold alcohol to dissolve it, while flesh-creatinine requires only 102 parts. It is a more powerful reducing-agent than creatinine prepared from flesh-creatine. Propionic acid can give rise to two substituted acids (cf. p. 617), consequently there are two amido-propionic acids. The a-acid is called alanine, CH,;-CH(NH,2)-CO.H, prepared by the action of ammonia on a-chloropropionic acid. It dissolves in water and becomes ethylidene lactic acid when treated with nitrous acid. Butalanine, which occurs in the pancreas of the ox, is a-amido-isovaleric acid, (CH3). : CH-CH(NH,)-CO.H. Leucine, or a-amido-caproic acid, CH,:[CH,],-CH(NH,)-CO,H, is prepared by boiling horn shavings (1 part) with sulphuric acid (23 parts) and water (64 parts) in a reflux apparatus, for twenty-four hours. The hot liquid is neutralised by lime, filtered, and evaporated to about one-third ; it is then carefully neutralised with H,SO, and evaporated till crystals of leucine and tyrosine are deposited on cooling; by recrystallisation from water the tyrosine crystallises first. Several other animal substances yield leucine and tyrosine when boiled with dilute sulphuric acid, or fused with potash. The elastine composing the cervical ligament of the ox yields more than horn. Leucine also occurs extensively in animals and vegetables. It is found in the liver, spleen, lungs, and pancreas ; also in caterpillars and spiders ; in the white sprouts of vetch, in yeast, and in putrefying cheese. Leucine crystallises in pearly scales, moderately soluble in water, slightly in alcohol, and insoluble in ether. It fuses at 170°, and may be partly sublimed, though much of it decomposes, yielding amylamine ; CsHyo(NH,)-COsH = NH,-C,Hy, + CO. Its reaction is neutral, but it forms compounds both with acids and bases. Hydriodic acid converts it into caproic acid and ammonia— CsHio(NH»)-CO,H + 2HI = C,H,,-CO,H + NH; +I» With nitrous acid it yields leucic or hydroxy-caproic acid— CsH,o(NH,)-CO,H + HNO, = CH, (OH)-CO,H + Np + H,0. ASPARAGINE 713 Leucine is obtained synthetically from ammonia and bromocaproic acid; NH, + C;H,,)Br'CO,H = C;H,)(NH,):CO,H + HBr; also by the reaction between valeraldehyde-ammonia, HCN, HCl and H,0. C;H,)0-NH, + HCN + HCl + H,O= C;H,9(NH,):CO,H + NH,HCI. The leucine from plants appears to differ from that from animals, being optically active and existing in the usual three modifications (p. 634). Tyrosine (tupds, cheese) or 4-hydroxy-phenyl-amido-propionic acid— CH,(C,H,OH)-CH(NH,)-CO.H, is obtained, together with leucine, when albuminoid or gelatinoid bodies are boiled with dilute sulphuric acid or fused with potash. It erystallises in needles, which are sparingly soluble, even in hot water, sparingly soluble in alcohol, and insoluble in ether. It melts at 235°, and is levo-rotatory. Like leucine, it behaves both as a feeble acid and a feeble base. When its aqueous solution is boiled with mercuric nitrate it gives a yellow precipitate, which becomes red when boiled with nitric acid containing nitrous acid. With chlorine, it yields chloranil, C,Cl,0,, and with fused potash, NH, and potassium parahydroxy-benzoate and acetate ; C,H,OH-C,H,NH,-CO.H + 2KOH= NH, + C,H,OH-CO,K +CH,-CO.K + Hy. Asparagine, or amido-succinamic acid, CH,CONH,-CHNH,CO,H, is found in the shoots of asparagus and of other plants grown in the dark. It is of very frequent occurrence in plants, being found in marsh-mallow, vetches, peas, beans, mangold- wurzel, lettuces, potatoes, chestnuts, and dahlia roots. It may be extracted from the expressed juices of the plants by boiling to coagulate the albumin, filtering, and evaporating to a syrup, when the asparagine crystallises, on standing, in rhombic prisms (with 1H,O) which may be recrystallised from boiling water. It is nearly insoluble in alcohol and ether. It behaves as a weak acid and a weak base. By ferments asparagine is converted into ammonium succinate; by nitrous acid into malic acid— C,H,NH,(CO-NH,)(CO-OH) + 2HNO, = C;H,0H(CO-OH)(CO-OH) +2N, + 2H,0. From this reaction it was formally inferred that asparagine was the amide of malic acid, with which, however, it is only isomeric. Ordinary asparagine is levo-rotatory ; the dextro-form has been found in the mother-liquor from crude asparagine, and is much sweeter than ordinary asparagine. A solution of the two in equal proportions is inactive, but the asparagines are deposited from it in crystals, which are, respectively, right- and left-handed. The isomeric derivatives from each kind retain the optical properties of their source. When asparagine is boiled with acids or alkalies, it is converted into l-amidosuccinic or aspartic acid— C;H,NH,(CO-NH,)(CO-OH) + H,O = C,H;NH,(CO-OH)(CO-OH) + NH3. Aspartic acid is sparingly soluble in cold water and alcohol, but may be crystallised from hot water. Nitrous’acid substitutes OH for the NH, in aspartic acid, converting it into malic acid. Aspartic acid is found in the molasses from beetroot juice, and oceurs among the products of the action of sulphuric acid and of zine chloride upon albuminous substances. Amidobenzoic acids, Cg>H4(NH2)-CO,H. Of these the 1:2-acid or anthranilic acid is cf importance, being an oxidation product of indigo. It is prepared by reducing 1:2-nitrobenzoic acid; it sublimes in needles, melts at 145°, and dissolves in hot water; the solution tastes sweet and fluoresces blue. Methyl anthranilate (m.-p. 25:5°) in dilute solution smells like orange-blossom oil (neroli oil), of which it is a constituent. aX The internal anhydride or lactam, anthranil, CoHa, ? might be expected to NA be formed by dehydration of anthranilic acid, this being a 1 : 2-derivative (cf. p. 628) ; it cannot. be so obtained, however, but is a product of the reduction of 1 : 2-nitro- 714 AMIDOSULPHONIC ACIDS benzaldehyde. It dissolves in alkalies to form salts of anthranilic acid. By treating Cco-:0 it, or anthranilic acid, with COCl,, isatoic anhydride, CoHas » an oxidation- NH-CO product of indigo is obtained. Amidophenylacetic acids, CgH,(NH,)‘CH,COjH, are obtained by reducing the corresponding nitro-acids, but only the m- and p- acids are known in the free state'; Jerr : attempts to prepare the 1:2-acid produce oxindol, CoH Jo which is an NH internal anhydride or lactam of the acid (p. 709). The same happens in the case of 1: 2-amidophenylglyoxylic acid or isatic. acid, CeHy(NH_)-CO-CO2H, a ketonic acid ; in this case the anhydride is a lactim, isatin, CC Door. These compounds N are closely related to indigo and will receive further attention in connection with that substance. Amidosulphonic Acids.—Taurine, amido-ethyl-sulphonic acid, or amido-isethionic acid, C,H,(NH,)SO,H,. is a decomposition-product_ of taurocholic acid (q.v.) and is prepared by boiling ox-gall with dilute HCl, evaporating to dryness on the steam-bath, and treating the residue with absolute alcohol, which leaves the taurine undissolved. This is dissolved in water, from which it crystallises in large four-sided prisms sparingly soluble in cold water, and insoluble in alcohol and ether. It fuses at 240° and is decomposed. It has no acid reaction, but it forms salts with bases. When fused with KOH, it yields the acetate and sulphite of potassium— C,H,(NH,):SO,H + 3KOH = CH,-COOK + K,SO, + NH; -+ H,0 + Hy. Nitrous acid substitutes OH for the NH,, producing isethionic acid. Taurine may be synthesised by converting ethene into glycol-chlorhydrin, HO-C,H,:Cl, heating this with K,80,, to obtain potassium isethionate— HO-C,H,-Cl + K,80, = HO-C,H,S0,K + KCl; distilling the isethionate with phosphoric chloride— HO-C,H,:SO,K + PCl;=PO,Cl + HCl + KCl + Cl-C,H4-SO,Cl (tsethiontec chloride) ; heating this with water— CLC,H,:SO,Cl + HOH = HCl + Cl-C,H,:SO,:OH (chlor-ethylsulphonic acid) ; and heating this to 100° with ammonia in a sealed tube— CLC,H,-S0,-OH + 2NH, = NH,HCl + NH,-C,H,-S0,-OH (taurine). Some taurine exists as such in the bile; it has been found in the kidneys, lungs, and muscles. When solution of taurine is evaporated with potassium cyanate, it yields potassium tauro-carbamate, NH,CONH-CH,-CH,SO3K ; tauro-carbamic acid is found in the urine when taurine is taken internally ; it forms crystals easily soluble in water. Amidobenzenesulphonic acid (see p. 699). D1azo- AND AZO-COMPOUNDS Diazo-Compounds.—It has been noticed already that the amines of open-chain hydrocarbons show no tendency to undergo the diazo-reaction described on p. 207, whereas the amines of closed-chain hydrocarbons readily do so at low temperatures. It thus happens that diazo-compounds of the type R-N : N-X, where R is a positive and X a negative radicle, are only known when R is a radicle containing a benzene ring. There is, however, a tendency for the amido-acids of the open-chain series to undergo the diazo-reaction, although the diazo-acids produced appear to be differently con- structed from the true diazo-compounds, and have been isolated only as esters or as amides. : , DIAZO-COMPOUNDS 715 N Diazoacetic acid, || oH-00,H, has not been isolated, but ethyl diazoacetate, N N,CH-CO.C.H;, is precipitated as a yellow oil when the hydrochloride of ethyl amido- acetate (ethyl glycocoll) is dissolved in a little water and treated with sodium nitrite ; it boils at 143° and is decomposed by acids with evolution of nitrogen, which becomes explosively rapid if the acid be strong; it reduces hot Fehling’s solution (p. 631). Aqueous alkalies saponify the ester forming salts; the alcoholates substitute alkali metal for H in the CHN, group (p. 684). When it is slowly dissolved in strong ammonia it is converted into diazoacetamide, NXCH-CONHg, which is soluble in water and forms crystals: it detonates when suddenly heated. When attacked by halogens, ethyl diazoacetate exchanges its nitrogen for two atoms of halogen; this indicates that its constitution differs from that of diazobenzene, for instance. By reduction, ethyl diazoacetate yields NH, and glycocoll, but an intermediate product is a salt of hydraziacetic acid which yields a hydrazine salt and glyoxylic acid when treated with an acid. Strong NaOH saponifies and polymerises ethyl diazoacetate yielding the sodium salt of bisdiazoacetic acid, Og ye formerly called “ triazoacetic N:N acid.”” The acid crystallises in orange red tablés (with 2H,O) and gives a characteristic red colour with nitric acid. When heated with dilute acids it is hydrolysed to oxalic acid and hydrazine ; CO,H-CH[N,]CH-CO,H + 2H,SO, + 4H,O = 2(N.H,,H,80,) + 2(COOH)». iS Diazomethane, || De is obtained by treating various nitroso-derivatives of N methylamine such as nitrosomethylurethane, with alkalies : CO(NCH;-NO)OC,H, + NaOH = CH,N, + H,O + CO(ONa)(OC,H;) When solutions of KCN and KHSO, are mixed and allowed to remain for some days, potassium amidomethane-disulphonate, (SO,;K),: CHNHg, crystallises. If the mixture is warmed and then acidified the corresponding hydrogen potassium salt, (SO,K)(SO,H) : CHNHg, is obtained ; this yields, when treated with KNOg, potassium diazomethane disulphonate, (805K )20€ ||. the best source of hydrazine (p. 189). Diazo- N methane is a yellow, odourless, poisonous gas, yielding methylhydrazine-when reduced. Diazoethane has also been prepared. At moderately high temperatures the aromatic amines react with nitrous acid just as the fatty amines do, the NH, being exchanged for OH ; C,H;,NH, + ON-OH = C,H,OH + N, + HOH. But at low temper- atures, particularly when a salt of the amine is employed, the diazo-compound is formed as an intermediate product— C.H;-NH»,HNO, + ON-OH = C,H,-N: N-NO, + 2HOH. Aniline nitrate. Diazobenzene nitrate. The salts of diazo-compounds are usually prepared in aqueous solution, since they are only used as transition-products in the preparation of other compounds (v.t.), or for the production of azo-compounds. The amido-compound (amine) is dissolved in a dilute acid, the solution cooled in ice, and the calculated quantity of sodium nitrite added. For preparing the crystalline salts, amyl nitrite is the best nitrite and the reaction should be effected in absolute alcohol ; the amine and the amy] nitrite are dissolved in the alcohol, and an acid is added to the cooled solution ; after a few minutes the diazo- salt crystallises and may be washed with alcohol and ether ; C,H;-NH»,HCl + C;H,,NO, = CyH,-N: NCI + C;Hy,OH + HOH. Diazobenzene nitrate is best prepared by passing N,Q, (p. 202) into a thin paste of aniline nitrate and water, cooled by ice and salt, until KOH no longer precipitates 716 DIAZO-COMPOUNDS—REACTIONS aniline. A brown product is filtered off, and alcohol added to the filtrate, when the nitrate separates in colourless needles. These are soluble in water, but insoluble in ether and sparingly soluble in alcohol. At 90° or when struck, it detonates with extreme violence. By decomposing diazobenzene nitrate with potash, the compound CgH;N2:OK, diazobenzene potassoxide (potassium benzene diazotate), is obtained, in which the potassium may be exchanged for other metals, producing unstable and sometimes explosive com- pounds. By acting on the potassium compound with acetic acid, diazobenzene hydroxide, C,H;N2-OH, is obtained as a very unstable liquid. Diazobenzene butyrate is said to be identical in chemical behaviour and physiological effect, with tyrotoxicon, a poison which has been isolated from decomposing milk. The diazo-bases, e.g. C,H,-N : N-OH, have never been isolated owing to their instability. The value of the diazo-compounds in effecting chemical syntheses will be appreciated from the following typical reactions when it is remem- bered that the conversion of an aromatic hydrocarbon into a nitro-derivative, this into an amido-derivative, and the amido- into a diazo-derivative (diazotising), is easily performed. (1) For the diazo-group may be substituted a hydroxyl group by warming the compound with water, a phenol being produced ; C,H;-‘N : N-Cl + HOH = C,H;-OH + N, + HCl. (2) The diazo-group may be exchanged for a halogen or cyanogen, producing a halogen substituted hydrocarbon or a cyanide. This is best effected by warming the diazo-compound with the corresponding cuprous salt (Sandmeyer’s reaction). The cuprous salt forms a double compound with the diazo-salt which decomposes with the re-formation of the cuprous salt; C;H;:N : NCl,Cu,Cl, = C,H,-Cl + N, + Cu,Cl,. The cuprous salt need not be preformed ; thus, to produce cyanobenzene (phenyl cyanide, CgH,CN), diazobenzene chloride may be treated with a mixture of copper sulphate and potassium cyanide (potential cuprous cyanide, p. 731). Similarly, nitro- benzene may be formed when the diazobenzene chloride is treated with KNO, and freshly precipitated Cu,O (potential cuprous nitrite). Finely divided metallic copper will frequently cause the separation of nitrogen and the attachment of the acid radicle to the benzene nucleus in a diazo-salt. The cyanides can be converted into acids by hydrolysis (p. 599), so that acids may be synthesised through Sandmeyer’s reaction. (3) For the diazo-group hydregen may be substituted, the hydrocarbon being formed, by boiling the compound with alcohol— C.H;-N : NCl + C,H;OH = C,H;-H + N. + HCl + CH,-CHO. The above reactions conclusively show that diazobenzene-compounds must contain the C,H; group; that the nitrogen atoms are linked in the manner represented, is concluded from the fact that diazobenzene salts yield phenylhydrazine salts (p. 719) when reduced. C.H;-N:NCl +4H’ = C,H,-NH-NH,,HCI. On the other hand, the behaviour of solutions of the diazo-salts indicate that they are ionised by solvents in the same sense as the ammonium salts. Hence it is probable that they are really quaternary ammonium derivatives, or diazonium salts of the form CoHs\ ae N=N, corresponding with tetramethylium chloride, N = (CHa)s3, Ke ye 3/3 Cl Cl for example. The salts like CsH;N.‘OK are apt to pass, when heated, into an unstable form which cannot be coupled readily to make an azo-compound when treated with an amine or phenol (infra), as the normal salts can. These isodiazo-salts have been supposed to be really salts of the nitrosamines, of the form CgH;NK-NO. AZOBENZENE 717 Diazo-amido-compounds.—When it is attempted to prepare a diazo-compound in the absence of an acid, a diazo-amido-compound is obtained ; probably, one portion of the amine is diazotised and immediately combines with another portion. Thus, diazoamidobenzene, CgH;:N : N-NH-C,H;, is prepared by passing N,O, into a cooled solution of aniline in alcohol; diazobenzene hydroxide may be supposed to be first formed and then to combine with aniline ; CsH;-N : N-OH + NH,-CgH; = CgH;‘N : N-NHC,H, + HOH. It is also prepared by the intcraction of diazobenzene chloride and aniline, HCl being liberated, CsH;N : NCL + CgH;NH, = CyH;N: N-NHC,H; + HCl; by substituting other primary (or secondary) amines for aniline, other diazo-amido-compounds are formed, and if two molecular proportions of diazobenzene chloride to one of the amine be used, « disdiazo-amido-compound is produced: 2C,H;N : NCl + NH,C,H; = [C.H;N : N},: NCgH, + 2HCI. Diazo-amidobenzene crystallises in yellow prisms (m.-p. 96°), and is not basic ; like most other diazo-amido-compounds, it readily undergoes an intra-molecular transformation when in solution, becoming the corresponding amido-azo-compound, CeH5'‘N : N-CgH,(NH2) (v.2.). This is particularly liable to happen in the presence of an amine, so that during the preparation of diazo-amido-benzene the excess of aniline may cause the change. The diazo-amido-compounds are readily split up into diazo- benzene compounds and aniline, so that they show most of the reactions of the former compounds. Azo-Compounds.—When a nitro-compound is reduced in acid solution the corresponding amido-derivative, ¢.g. aniline, is immediately produced, but when the liquid is alkaline, there are formed, in the case of the aromatic nitro-compounds, three intermediate products, derived from two molecules of the nitro-compound. Thus, nitro-benzene in alkaline solution will yield azoxybenzene, azobenzene and hydrazobenzene, according to the reducing capacity of the agent employed. C,H;NO, COHN C,H;N C,H;NH | 0 | | CsH;NO, C,H,N” CgH,N C,H;NH 2 mols. Nitro-benzene. Azoxybenzene. Azobenzene. Hydrazobenzeue. Azoxybenzene is formed when nitrobenzene is reduced by alcoholic potash, but is best prepared by oxidising azobenzene by chromic acid in acetic acid. It crystallises in yellow needles, m.-p. 36°, insoluble in water, but soluble in alcohol. Azo-compounds may be symmetrical, like azobenzene, or mixed, like benzeneazomethane, C,H; N:N-CH,; the latter kind are produced by oxidation of the corresponding hydrazines. Azobenzene, C,H;N : NC,H,, is produced when an alcoholic solution of nitrobenzene is treated with sodium amalgam or with zinc-dust and NaOH. It is readily obtained by dissolving nitrobenzene in alcohol, adding an equal weight of KOH, and distilling, when the alcohol is oxidised to acetic acid, and the nitrobenzene reduced to azobenzene. At the end of the distillation it comes over as a dark red oil, which solidifies after a time to a crystalline mass; it is insoluble in water, but may be crystallised from alcohol or ether in beautiful red tables resembling K,Cr,0;; it melts at 68° and boils at 293°. Azobenzene is also formed when aniline is oxidised with KMnO,. It forms sub- stitution products like benzene does. Alkaline reducing-agents convert it into hydrazo- benzene, but acid reducing-agents convert it into aniline. Dyes, Dyeing.—Since the dyeing of a fabric involves the formation of an insoluble coloured substance in the fibre, it is essential that a dyestuff shall be capable of combining either with the fibre itself or with some substance (a mordant) previously fixed in the fibre, to form an insoluble compound (the dye). Most dyestuffs are capable of forming dyes with wool, and to a smaller extent with silk, without the intervention of a mordant-; the dyes thus produced are termed substantive dyes. With cotton, on the other hand; a 718 AZO-DYESTUFFS mordant is nearly always requisite, the dye obtained being called, in this case, an adjective dye. It will be seen that since a dyestuff must enter into some form of chemical combination before it can become a dye, it must be a substance possessed of a certain amount of chemical activity. Thus it happens that those substances which have been ound to be successful dyestuffs are generally either acid or basic in character ; this observation has proved of great value, since it has shown that although a compound may be useless as a dyestuff it may become useful if it be treated in such a manner that the necessary acidity or basicity be imparted to it. It is possible to impart acidity to an organic compound by the introduction of certain radicles, such as OH or SO,0H, and basicity by introducing the NH, radicle. It is, of course, only certain organic compounds 1 which can be converted into dyestuffs by the introduction of such groups ; these compounds are called chromogens, whilst the groups that lend them their dyeing capacity are called auxochromes. An acid auxochrome yields an acid dyestuff, capable of being fixed by a basic mordant (alumina, &c.) ; whilst a basic auxochrome yields a basic dyestuff, capable of being fixed by an acid mordant (tannin). That a dyestuff must be soluble in water hardly needs stating ; it will be equally obvious that a dyestuff need not be itself a coloured substance, although the insoluble compound which it forms in the fibre must be coloured. Azobenzene is a highly coloured substance, but is at the same time both chemically indifferent and insoluble in water, so that it is not a dyestuff. It is, however, a chromogen, for, by the introduction of the OH or NH, group, compounds are produced which are either dyestuffs (when soluble in water) or become dyestuffs when rendered soluble by conversion into sulphonic acids. Azo-dyestuffs are compounds containing one -N: N-: group and are -made by diazotising an amido-compound and combining the product with an amido- or hydroxy- compound (a ‘‘ dyestuff component ”’). Amido-azo-compounds are produced by the intramolecular change of diazo-amido- compounds (p. 717), especially in presence of the salt of an amine which, however, is not consumed. The change generally produces an amido-azo-compound in which the amido-group is in the para-position to the azo-group, hence if an aromatic amine is - used to prepare the diazo-amido-compound, the para-position to the amido-group should be unoccupied. p-Amido-azobenzene is prepared by heating diazo-amidobenzene (10 grams) with aniline hydrochloride (5 grams) and aniline (25 grams) at 45°, dissolving out the aniline with acetic acid and crystallising the residue from HCl. The hydrochloride thus formed is in steel-blue needles and was formerly sold as aniline yellow, a dyestuff. The hase, liberated by NH; from the hydrochloride, forms yellow needles and melts at 127°. By sulphonation it yields a mixture of mono- and di-sulphonic acids, known as acid yellow or fast yellow. It is largely used for making indulines (q.v.). By reduction, amido-azobenzene yields aniline and paraphenylenediamine. Dimethylamidoazobenzenesulphonic acid is prepared from diazo-benzcnesulphonic acid chloride and dimethylaniline— CeHa(SO3H)-N : N-Cl + CgH5-N(CH3)2 = CeH4(SO3H)-N : N-CgH,N(CH3). + HCl. The sodium salt is methyl orange (tropaeolin O, helianthin or orange III.), used in the laboratory as an indicator. 2: 4-Diamidoazobenzene, CgHs-N : N-CgH3(NHg)», is made by the action of diazo- benzene chloride on metaphenylene-diamine— CeH;N : NC] + CgH4(NHo)y = CeH;-N : N-CgH;(NHz)o + HCl. It melts at 117° and its hydrochloride is an orange yellow dyestuff called chrysoidine. The 4: 4’-diamido-azobenzene, NHg-CgeH4-N : N-CgsHy-NHp gives rise to the red basic dyestuffs, the azylines, which are the tetra-alkyl derivatives of the above compound, and are obtained by diazotising a dialkyl-p-phenylenediamine and combining the product with a dialkylaniline— NRo-CyHyN:N-Cl + CgH;NR, = NR.-C,HyN:N-C,H, NR, + HCl. Bismarck brown (phenylene brown, Manchester brown) is the hydrochloride of a mixture of bases prepared by the action of nitrous acid on metaphenyl- 1 Almost always such as contain ope or more benzene nuclei, and a special group, like the diazo-group called a shromophore. DISAZO-DYESTUFFS _ 719 enediamine (p. 701); it consists largely of the hydrochloride of triamido-azobenzene, C,H4(NH,)-N : N-C,H3(NH,)., formed by diazotising one NH, in the metaphenylene- diamine and combining the diazo-compound with another molecule of the diamine. Hydroxyazo-compounds are prepared by the interaction of a diazo-chloride and a phenol. Thus hydroxyazo-benzene is prepared from diazo-benzene chloride, and phenol ; C,H;'N : N:Cl + CsH;OH = C,H;-N : N-C,H,(OH) + HCl. They are also formed by an intra-molecular change of the azoxy-compounds, just as the amidoazo- result from the diazoamido-compounds. Dihydroxyazobenzenesulphonic acid, CgH (SO,H):-N : N-CgH,(OH), is prepared from the chloride of diazobenzenesulphonic acid and resorcinol (cf. methyl orange). Tts sodium salt is resorcin yellow. Disazo-dyestuffs.—These contain the -N: N- group twice, and are of three kinds. (1) The two Nz groups may be attached to the same benzene nucleus which also contains the auxochrome (OH or NH,). For instance, by the reaction of diazobenzene chloride on resorcinolazobenzene, resorcinoldisazobenzene is obtained— C.H;N.Cl + CgH;N.CgH3(OH). = CgH;-N : N-CgH.(OH)2:N : N-C,H,; + HCl. (2) The two N, groups may be attached to the same benzene nucleus and the auxo- chrome to another nucleus. Biebrich scarlet is a dyestuff of this type made by diazotising amidoazobenzene disulphonic acid to produce CgH4(SO3H)-N : N-CgH3(803H)-N : N-Cl, which is then combined with 3-naphthol, producing CgH,4(SO3H)-N :N-C,H3(SO3H)-N : N-C,)H,(OH). (3) The two N, groups may be attached to different nuclei. ‘To this class belong the numerous benzidine dyestuffs or tetrazo-dyestuffs, which are valuable as substan- tive dyestuffs for cotton, most others requiring « mordant. Congo-red serves as a type; benzidine, NH2-CgH, — C,H,-NHg, (p. 701), is diazotised to tetrazodiphenyl chloride, CIN : N-CgH, — CeHy-N: NCL, which is then combined with a-naphthyl- laminesulphonic acid, CyyHg(SO;H)-NH, to form congo-red, the formula for which is NH,-(SO,Na)C,)H;-N : N-CsH, — CgHy-N : N-C,9H;(SO3Na)-NHp. Trisazo colours contain three ‘N:N-: groups, and teérakisazo colours contain four ‘N : N- groups. DERIVATIVES OF HYDRAZINE AND oF AZOIMIDE Hydrazines.—These bases are derived from hydrazine (p. 189), H,N:‘NH,, by substituting a hydrocarbon radicle for H. They may be primary, R:-NH-NH,, ‘or secondary, R,:N-NH,, and symmetrical, RHN-NHR (hydrazo-compounds), or asymmetrical, RHN-NH, (hydra- zine compounds). When R is an alkyl radicle, the hydrazines are best prepared by the action of reducing-agents on the nitrosoamines ; R,:N-NO + 4H = R,:N-NH, + H,0. But the alkyl hydrazines are of very little importance at present. When R is an aromatic radicle, the hydrazines are best prepared by the reduction of the diazo- compounds. The reaction of the hydrazines with compounds containing ketonic or aldehydic oxygen has been already noticed (pp. 596, 648). Phenylhydrazine, C,H; NH-NH,, is prepared by dissolving aniline (1 part by weight) in strong HCl (20 parts), cooling by adding ice, and slowly adding an ice-cold solution of NaNO, (0-75 part), in water (4 parts). The aniline hydrochloride is thus converted into diazoben- zene chloride (p. 716). A solution of stannous chloride (4:5 parts) in an equal weight of HCl is now carefully added ; this converts the diazobenzene ‘chloride into phenylhydrazine hydrochloride, which is precipitated— C,H,N : N-Cl + 4HCl + 28nCl, = C,H;-NH-NH,,HCl + 2SnCl,. The precipitate is washed with a mixture of alcohol and ether, dissolved in. a little water, and decomposed by strong NaOH, when the hydrazine separates as an oily layer, which is freed from water by distilling with potassium carbonate. 720 PHENYLHYDRAZINE Phenylhydrazine is thus obtained as a colourless aromatic liquid of sp. gr. 1-091, and boiling-point 241°. It solidifies in a freezing mixture to tabular crystals, fusing at 23°. It is sparingly soluble in cold water, but dissolves in alcohol and ether. Phenylhydrazine is a strong reducing- agent and absorbs oxygen from air, becoming brown. It reduces alkaline cupric solution, even in the cold, precipitating yellow cuprous hydroxide, and evolving nitrogen, while aniline and benzene are found in the solution. This is a general reaction for identifying hydrazines, and may also be employed for diazo-compounds by boiling their aqueous solutions with KHSO,, to reduce them to hydrazines, and adding potash and alkaline cupric solution. It also reduces mercuric oxide in the cold, forming nitrogen, aniline, benzene, and mercury-diphenyl. It is a monacid base, and forms crystalline salts. Solution of phenylhydrazine hydrochloride, mixed with sodium acetate, forms a general test for aldehydes and ketones, with which it forms insoluble oily or crystalline compounds (hydrazones, p. 648, see also osazones), thus precipitating them from their aqueous solutions ; by warming these com- pounds with HCl they are reconverted into their parent substances. When heated with nascent hydrogen phenylhydrazine yields C,Ha;NH, and NH, a fact which settles its constitution, as well as that of the other hydrazines. It is used technically for making antipyrine (q.v.). Sodium dissolves in phenylhydrazine evolving H and forming CsH;NaN-NHb. Hydrazine yields derivatives on the same lines as NH; does, but as it has four H atoms and two N atoms, the latter allowing of dissymmetry, the number of such derivatives is even greater than that obtainable from NH 3. Moreover, the hydra- zine derivatives have a remarkable tendency to undergo internal condensation, yielding nitrogen ring compounds (cf. antipyrine). The following are the leading types : (1) Asymmetrical and secondary hydrazines ; hydrazonium and azonium com- pounds, corresponding with the amines. Hydrazobenzene or sym-diphenyl-hydrazine, C,H;HN-NHC,H; (p. 719), is prepared by dissolving azobenzene in alcohol, passing NH; and afterwards H,§ till the solution is colourless. C.H;N : NC,H, + H.S = CsH;NH-NHC,H, + 8. On adding water, the hydrazobenzene is precipitated, and may be crystallised from alcohol. It forms colourless tables (m.-p. 131°) becoming orange in air, from production of azobenzene, and smelling of camphor. A convenient method of converting azobenzene nto hydrazobenzene is to boil its alcoholic solution with zinc-dust until it is colourless. When heated, hydrazobenzene is decomposed into azobenzene and aniline— 2(CgsH;NH-NHC,H;) = CgH;N-NC,H; + 2(CgH,°H.N). When dissolved in hydrochloric or sulphuric acid, it is-converted into its metameride benzidine, NH,C,H,-CsH,NH, (p. 710). This change recalls that of a diazo-amido- compound into an amido-azo-compound (p. 717) and like the latter only occurs when the 4-positions in the benzene rings are free. Thus o- or m-hydrazotolucne yields tolidine by this intramolecular change (benzidine migration or rearrangement), but in p-hydrazotoluene only one of the NH groups shifts (semidine migration), producing C,H,NHC,H,NH», in which NH, is in the 2-position. These changes may also be compared with that of methylaniline into paratoluidine (p. 699), and it should be noted that all migrations of this type tend to produce a compound of more basic properties. Examples of other hydrazines of this class are a- and /3-ethylphenylhydrazine, C,.H;N(C,H;)-NH, and C,H; HN-NHC,H;. The former combines with C.H;Br forming diethylphenylhydrazonium bromide, CgH;N(C2H;).Br-NH>, while a/3-diethylphenyl- hydrazine, CsH;N(C.H;)-NHC,H;, combines with C,H; Br to form the azonium compound CeH;N(C.H;)2Br-NHC.H;. (2) Phenylhydrazones.—Already noticed (supra). (3) Hydrazides.—These are acidyl derivatives corresponding with the amides and prepared. analogously. For example, a-acetylphenylhydrazide, CsH;N(CH,CO)-NHg, from sodium phenylhydrazine and acetyl chloride (m.-p. 124°). CYANOGEN—HISTORY 721 Semicarbazide, NH,CO-NH-NH,, may be regarded as the hydrazide of carbamic acid, and is obtained by heating urea with hydrazine sulphate at 100°. It gives rise to many derivatives, combining with aldehydes and ketones as phenylhydrazine does ; the products are called semicarbazones. (4) Hydrazido-acids are like amido-acids and are either symmetrical, e.g. C,H;NH-NH-CH,COOH, or asymmetrical, e.g. CsH;N(NH,):CH,COOH. (5) Hydrazidines (amidoazones) are analogues of the amidines (p. 703), the NH group of the latter having been exchanged for the phenylhydrazone group, producing N-NHC,H; compounds of the type, RoC . When the NH, group is exchanged for NH, JNNHCHs the diazobenzene group, formazyl-derivatives are obtained, BK » which N : NCH; are highly coloured and may be viewed as azo-dyestuffs, prepared from diazobenzene and phenylhydrazones. (6) T'etrazones are produced when two mols. of a secondary hydrazine are oxidised with HgO— 2C.H;N(CH;)-NH, + O, = C2H,N(CH;)-N : N-(CH;)NC,H,. Azoimides.—The derivatives of azoimide, HN; (p. 189), are obtainable by the action of NH, on the diazo-perbromides. Thus, when diazobenzene bromide is brominated, C.H;-N : NBr + Br, = CgsH;-NBr-NBr,; when the perbromide is treated with N ammonia, CgH;-NBr-NBr, + NH; = 3HBr + CoH NC || (phenyl azoimide). When N heated with alcoholic potash the dinitro-phenylazoimide yields dinitrophenol and potassium azoimide, KN3. Benzoyl azoimide, C,H;CO-N3, formed when benzoyl-hydrazide, CgH;CO-NH-NHp, is diazotised, yields sodium benzoate and sodium azoimide when boiled with NaOH. X. CYANOGEN AND ITS COMPOUNDS In the beginning of the eighteenth century, a manufacturer of colours at Berlin accidentally obtained a blue powder when precipitating sulphate of iron with potash. This substance was used as a colour under the name of Prussian blue, for several years, before any explanation of its production was attempted, or even before the conditions under which it was formed were exactly determined. In 1724 it was shown that Prussian blue could be prepared by calcining dried animal matters with potashes, and mixing the aqueous solution of the calcined mass, first with sulphate of iron and afterwards with hydrochloric acid ; but the most important step towards the determination of its composition was made by Maquer, who found that, by boiling it with an alkali, Prussian blue was decomposed, yielding a residue of red oxide of iron, and a solution which reproduced the blue when mixed with a salt of iron ; hence he inferred that the calour was a compound of the oxide of iron with an acid for which the alkali had a more powerful attraction—a belief, confirmed in 1782, by Scheele’s observations, ‘that when an alkaline solution prepared for making the blue was exposed to the air, or to the action of carbonic acid, it Jost the power of furnishing the colour, but the escaping vapour struck a blue on paper impregnated with oxide of iron. Scheele also prepared this acid in a pure state, and it soon after obtained the name of prussic acid. In 1787, Berthollet found prussic acid to be composed of carbon, hydrogen and nitrogen, but he also showed that the power of the alkaline liquor to produce Prussian blue depended upon the presence of a yellow salt crystallising in octahedra, and containing prussic acid, potash and oxide of iron, though the latter was so intimately bound up with the other 46 722 CYANOGEN—PREPARATION constituents that it could not be separated by those substances which are usually employed to precipitate iron. Porrett, in 1814, applying the greatly increased resources of chemistry to the investigation of this subject, decomposed Prussian blue with baryta, and subsequently removed the baryta from the salt thus obtained by means of sulphuric acid, when he obtained a solution of the acid, which he named ferruretted chyazic acid. In 1815, Gay-Lussac, having boiled Prussian blue (or prussiate of iron as it was then called) with red oxide of mercury and water, and crystallised the so-called prussiate of mercury, exposed it, in the dry state, to the action of heat, and obtained a gas having the composition CN, which was called cyanogen, * in allusion to its connection with Prussian blue. It was then seen that the substance which had been called ferruretted chyazic acid contained iron and the elements of cyanogen, whence it was called ferro- cyame acid, and its salts were spoken of as ferrocyanates. Robiquet first obtained this acid in the crystallised state, having the composition H,C,N,Fe; and since it was found that, when brought in contact with metallic oxides, it exchanged the H, for an equivalent quantity of the metal, according to the equation, H,-C,N,Fe + 2M”O = M,”-C,N,Fe + 2H,0 it was concluded that the C,N,Fe composed a distinct group or radicle, which was named ferrocyanogen (Fey), the acid being called hydro-ferro- cyanic acid, and the salts ferrocyanides. Cyanogen and Cyanides.—Cyanogen, (CN), or NC-CN, is obtained by heating mercuric cyanide in a glass tube or retort (Fig. 311), and collect- ing the gas over mercury ; Hg(CN), = Hg + (CN),; the metallic mercury collects in globules on the cool glass. The whole of the cyanogen is not obtained, part being converted into a brown solid called paracyanogen, which is left behind. This is polymeric with cyanogen, into which it may beconverted by a high temperature. By heating together solutions of potassium cyanide and CuSO,, cyanogen is evolved; 2CuSO, + 4KCN = ee =—-Cu, (CN), + (CN), + 2K,S0,. "Hie. 311. Cyanogen is highly poisonous and is identified by its remarkable odour, and by its burning with a pink flame edged with green. Its sp. gr. is 1-806 (air = 1), and it may therefore be collected by displacement of air. It is easily liquefied by a pressure of 4 atmospheres at 15°, or 13 atmospheres at 0°. Liquid cyanogen has sp. gr. 0-87, and solidifies to a crystalline mass at — 34° and boils at — 21°. Water dissolves about 4 volumes of cyanogen, yielding a solution which soon deposits a brown flocculent substance termed azulmic acid, C,N,H;O. The solution is then found to contain ammonium salts, especially carbonate, formate and oxalate, together with urea. The first reaction between cyanogen and water, on standing, probably resembles that between chlorine and KOH in the cold, viz. Cl, + 2KOH = KCl + KCIO + H,0; the reaction in the case of cyanogen being (CN). + H,O0 = HCN + H(CN)O, producing hydrocyanic, HCN, and cyanic, HCNO, acids. The cyanic acid yields NH,HCO, by reaction with water; HCNO + 2H,0 = NH,HCO;. Hydrocyanic acid, with water, yields ammonium formate; HCN + 2H,O = HCO,NH,. Cyanogen, with water, yields ammonium oxalate ; (CN). + 4H,O = C,0,(NH,)o. Cyanic acid, with ammonia, yields urea; HCNO + NH; = (NH3),CO. The azulmic acid appears to result from a reaction between cyanogen, ammonia, and water ; 2(CN), + NH, + H,O =(C,H,N;0 ; it may be prepared by passing cyanogen into dilute ammonia, and heating in a closed vessel. When dry amnionia gas acts upon cyanogen gas, a black substance From evévcos, blue; POTASSIUM FERROCYANIDE 723 is produced, which is called hydrazulmin ; 2NH, + 2(CN). = CyHeNg. This appears to be azulmamide, for, when acted on by water, it yields azulmic acid and ammonia ; C,HeN, + H,O = C,H;N,0 + NH3. In most of its reactions, cyanogen exhibits the mutability which is generally observed in organic groups, but in some cases it exhibits a stability which allows it to be compared with the halogens. Thus, alkali metals take fire in cyanogen when gently heated, producing their respective cyanides; K, + (CN), =2KON; cyanogen, acting on solution of potash, yields potassium cyanide and cyanate ; (CN), + 2KOH = KCN + KCNO + H,0, just as chlorine yields chloride and hypochlorite. Cyanogen combines with H, under influence of the silent electric discharge, to form hydrocyanic acid, H(CN), which forms cyanides by exchanging its hydrogen for metals, just as hydrochloric acid forms chlorides ; but the cyanides of potassium and sodium are much less stable compounds than the corresponding chlorides. When boiled with water, the alkali cyanides are converted into alkali for- mates, the nitrogen being evolved as NH;, and the carbon converted into the COOH group ; KCN’” + 2H,O0 = H.COOK + NH3. The facility with which the CN group is transformed by hydrolysis into the CO,H group, is of very great importance in organic research, since it is often easy to introduce the CN group into an organic molecule, and, by afterwards converting it into CO,H, to effect the synthetical formation of an organic acid, as has been already explained (p. 599). Cyanogen is produced in small quantity by the direct union of carbon and nitrogen at the extremely high temperature of the electric spark, but to produce it in quantity, one, at least, of its elements must be in the form of a compound ; thus, if ammonia be passed over red-hot charcoal, hydrogen cyanide is produced; NH, + C=HCN + H,; again, if acetylene is mixed with nitrogen and “sparked,” hydrogen cyanide is formed, C,H, + N, = 2HCN. If one of the alkali metals be present nitrogen is much more easily converted into cyanogen; potassium cyanide may be obtained by passing nitrogen through an iron tube containing a heated mixture of charcoal and potassium—N, + C, + K, = 2KON. In place of the costly potassium, the materials for making it, viz. potassium carbonate and charcoal, may be used (see below). A better yield is obtained by employ- ing a compound of nitrogen with carbon, such as refuse horn or cuttings of hides and old leather, which are rich in nitrogen. On a large scale, potassium cyanide is made in this way, but as it cannot be crystallised easily, it is converted into the ferrocyanide, which is the source whence all cyanogen compounds are obtained. Potassium ferrocyanide, K,FeC,N,.3Aq or 4KCN.Fe’’(CN),.3Aq, yellow prussiate of potash, is manufactured by melting potashes (crude K,CO,;) mixed with iron filings in an iron vessel, and adding any cheap material containing carbon and nitrogen, such as old leather. Sometimes the animal matter is distilled for the sake of the ammonia which it will yield, and the remaining charcoal, still rich in nitrogen, is used for making ferrocyanide. The fused mass is heated with water in open boilers, when a yellow solution is obtained, which, after evaporation, deposits truncated pyramidal crystals of potassium ferrocyanide. The chemistry of this process is somewhat abstruse, but is generally explained as follows: (1) The charcoal containing nitrogen decomposes the potassium carbonate at a high temperature, producing potassium cyanide and CO; K,CO,+4C+N,=2KCN + 3C0. (2) Sulphur, derived from the animal matters, and partly from potassium sulphate present as an impurity in the potashes, combines with iron to form ferrous sulphide. (3) On treating the fused mass with water, the ferrous sulphide is dissolved 724 PRUSSIC ACID by the KON, yielding potassium sulphide and ferrocyanide ; FeS + 6KCN = K,Fe(CN), + K,S. It has been suggested to avoid the presence of K,S in the liquor (which hinders crystallisation) by melting pure K,CO, with animal charcoal, extracting the KCN from the residue by treatment with water, and digesting with finely ground spathic iron ore (FeCO;) ; FeCO; + 6KCN = K,Fe(CN), + K,CO3. The ferrocyanide dissolves in twice its weight of boiling and in four times its weight of cold water, but is insoluble in alcohol. The aqueous solution assumes a darker yellow colour when exposed to air for some time, oxygen being absorbed and potassium ferricyanide (see below) produced in small quantity. The neutral solution then becomes slightly alkaline from formation of potash. Crystallised ferrocyanide does not lose water till 60°, when it gradually becomes white and opaque. At 100° it may be dried completely, though with difficulty, unless finely powdered and heated in a current of dried air. When the undried salt is mode- rately heated, it evolves ammonia and hydrocyanic acid, and becomes brown. The thoroughly dried salt does not evolve ammonia, but fuses at a high temperature, evolving nitrogen, and leaving a residue of potassium cyanide and iron carbide ; K,C.N,Fe = N, + 4KCN + Fey. Nearly all acids decompose the ferrocyanide, evolving hydrocyanic acid, and producing compounds containing cyanogen and iron, which become blue when exposed to air, from the formation of Prussian blue and similar compounds. It is for this reason that the yellow crystals become blue and green when exposed to the air of a laboratory. Oxidising- agents convert the ferrocyanide into ferricyanide, as will be seen later. With a large number of metallic salts, the ferrocyanide gives precipitates, so that it is an indispensable test. It is also largely employed in the manu- facture of colours, and in dyeing and calico-printing. The constitution and chemical relations of the ferrocyanides will be better understood later in the history of cyanogen compounds. Hydrogen cyanide, hydrocyanic, or prussic acid, H.C : N (or HCy), is prepared, in aqueous solution, by distilling potassium ferrocyanide (prussiate of potash) with dilute H,SO,. 50 grammes of the crystallised ferrocyanide are dissolved in 200 cubic centimetres of warm water in a flask or retort connected with a good condenser. 20 c.c. of strong sulphuric acid are diluted with 60 c.c. of water, cooled, and added to the solution of ferrocyanide ; heat is applied by a ring-burner to avoid bumping, until about 140 c.c. of liquid has passed into the receiver. The potassium ferrocyanide gives up half of the cyanogen, CN, as hydrocyanic acid, leaving the remainder combined with the iron and half of the potassium as potassio-ferrous ferrocyanide, K,Fe’’.Fe’’(CN),, a yellow salt which quickly becomes blue when exposed to air, oxygen being absorbed, and Prussian blue, or ferric ferrocyanide, Fe’’’,.3Fe’’(CN),, produced. The following equation represents the preparation of hydrocyanic acid ; 2K,FeCy, + 6H,SO, = 6HCy + K,Fe’,Cy, + 6KHSO,. Hydrocyanic acid is generally used diluted, but it may be obtained anhydrous by gently heating the diluted acid in a retort connected with a condenser cooled by iced water, and receiving the distillate in a bottle cooled in ice and containing fused calcium chloride in coarse powder. This bottle is afterwards placed in a water-bath connected with a receiver cooled in ice and salt, and gently heated, when the pure hydrocyanic acid distils over. The anhydrous HCy may also be obtained by passing dry H.S gas into a long tube filled with mercuric cyanide and connected with a receiver cooled in ice and salt ; the operation must be stopped when an inch or two of mercuric cyanide remains undecomposed, to avoid contamination of the HCy with H.8 ; HgCy, + H,S = HgS + 2HCy. HYDROCYANIC ACID—PROPERTIES 725 Properties of hydrocyanic acid.—A colourless liquid, sp. gr. 0-7, which evaporates rapidly, so that a few drops in a watch-glass are solidified by the cold of evaporation, the freezing-point being — 12°. The acid boils at 25°, and its vapour burns with a purple flame. The smell of the vapour is quite characteristic, and is compared by some to a faint odour of almonds ; it generally produces a sensation of dryness at the back of the throat. The inhalation of the vapour, unless largely diluted with air, is very dangerous, and an extremely small quantity of the acid taken internally generally kills immediately. When the pure acid is mixed with an equal volume of water, a contraction ensues, amounting to about one-twentieth of the total volume, and cold is produced. The aqueous acid is decomposed when exposed to light, depositing a brown substance, whilst ammonia formate and- other products are found in solution; HCN + 2H,O = H-CO,NH,. A trace of sulphuric acid, which generally splashes over in preparing prussic acid, prevents this decomposition. Acids and alkalies, when boiled with the acid, convert the HCN into formic acid and ammonia. The acid properties of HCy are very feeble ; it hardly reddens litmus, and does not destroy the alkaline reaction of the alkalies or their carbonates. The sakts formed by displacing its hydrugen by alkali-metals are easily decomposed by water and carbonic acid, and therefore smell of HCy, but the cyanides formed by many of the metals are very stable bodies. Although HCy is so much more easily liquefied than HCl, its vapour continually escapes even from a weak aqueous solution, so that the strength is diminished every time the stopper is removed from the bottle ; it thus happens that the weak prussic acid (2 per cent.) dispensed by the druggists, is sometimes found to have become nearly pure water. Hydrocyanic acid is found in laurel-water, and in water distilled from the kernels of many stone-fruits, such as peach, apricot, and plum. In these cases it appears to be produced from amygdalin (see p. 780) or some other cyanogenetic glucoside. Hydrocyanic acid is produced synthetically by passing a succession of electric sparks through a mixture of nitrogen with an equal volume of acetylene, this being itself produced by carbon intensely heated in hydrogen (p. 556). HCy is also found among the products of distillation of coal, and occurs in imperfectly purified coal-gas. Tests for hydrocyanic acid.—Silver nitrate produces a white precipitate of silver cyanide, AgCN, which is dissolved by boiling with strong nitric acid, and precipitated in microscopic needles of AgCN.2AgNOs, on cooling. Prussian-blue test : Add potash in slight excess, to form KCy; then add ferrous sulphate solution (which always contains ferric sulphate),1 to form potassium ferrocyanide; 6KCy + FeSO, = K,Fe’Cy, + K,SO,; this acts on the ferric sulphate, and produces ferric ferrocyanide, or Prussian blue: 3K4Fe’’Cyg + 2Fe’’’s(SO4)3 = Fe’’’s(Fe’’Cye)s + 6K80,. But the excess of potash decomposes the blue ; to correct this, add excess of hydrechloric acid to neutralise the potash, the blue will be formed. Sulphocyanide test: Add yellow ammonium sulphide (which contains some disulphide), to form ammonium sulphocyanide ; HCN + (NH4)oS, = NH,CNS + NH,HS; evaporate till the smell of ammonium hydrosulphide has disappeared, and add ferric chloride, which will produce the blood-red colour of ferric sulphocyanide, bleached on adding mercuric chloride. A very fugitive purple colour is due to ammonium thiosulphate produced by the action of air, and does not indicate HCy. Potassium cyanide, KCN, or KCy, is prepared by fusing, in an iron crucible, a mixture of well-dried potassium ferrocyanide (8 parts) with dried K,CO, (3 parts) ; K,Cy,Fe + K,CO; = 5KCy + KCyO + Fe + CO,. As soon as the escape of CO, has ceased, and the metallic iron has subsided, 2 Itis well either to shake with air or to add a drop of ferric chloride to ensure the presence of ferric salt, 726 f POTASSIUM CYANIDE the clear fused mixture of cyanide and cyanate of potassium is poured into an iron mould. The presence of cyanate does not interfere with most of the uses of the cyanide ; its quantity may be diminished by adding some powdered charcoal to the mixture. A purer product is obtained, though less economically, by fusing the dried ferro- cyanide alone (see above), and crystallising the product by dissolving in hot alcohol. The purest potassium cyanide is made by passing vapour of hydrocyanic acid into solution of potash in absolute alcohol, when the cyanide is deposited in small octahedral crystals. Potassium cyanide, as met with in commerce, is in white opaque lumps, and contains about 98 per cent. of cyanide, the rest being cyanate and carbonate, When exposed to air, it deliquesces, and smells of hydrocyanic acid and ammonia, the former being produced from the cyanide, and the latter from the cyanate, by the action of water— (1) KCN + H,O = KOH + HCN. (2) KCNO + 2H,0 = NH; + KHCOg. It dissolves very readily in water, yielding a strongly alkaline solution, which evolves HCy and NH, when boiled, and becomes a solution of potas- sium formate; KCN + 2H,O = NH, + HCO,K. When the commercial cyanide is boiled with moderately strong alcohol, the cyanide, together with a little cyanate, is dissolved, and may be crystallised from the solution, while the carbonate is left undissolved. Potassium cyanide fuses at a low red heat, becoming very fluid ; it then absorbs oxygen from the air, forming cyanate. This disposition to combine with oxygen causes it to act as a powerful reducing-agent upon metallic oxides ; tin-stone is assayed by fusing it with potassium cyanide, when a button of tin collects at the bottom of the fused mass ; SnO, + 2KCy = Sn + 2KCyO. When heated with KNO, or KClO,, it causes a violent explosion, from evolution of CO: and N. Pure potassium cyanide is alkaline, but does not effervesce with acids, like the commercial cyanide. Solution of potassium cyanide dissolves silver chloride and iodide, which leads to its use in electro-plating and in photography, while its property of dissolving silver sulphide is useful in cleaning gold and silver. It is one of the most dan- gerous poisons. It is also used in gold-extraction (p. 524), for which purpose it may be made by heating K,FeCy, with sodium ; K,FeCyg + Nag = 4KCy + 2NaCy + Fe. The product is a mixture of the two cyanides which is as-effective as pure KCN. Potassium cyanide is sometimes obtained in considerable quantity from the blast- furnaces of iron-works being formed from the potassium carbonate in the ash of the fuel. Ammonium cyanide, NH,CN, may be sublimed in cubes by heating a mixture of mercuric cyanide and ammonium chloride. It dissociates, at 36°, into NH, and HCN. It is very soluble in water and alcohol, and smells of hydrocyanic acid and ammonia. When kept it becomes brown, an azulmiate being produced (p. 722). The cyanides of barium, strontium, and calcium are less soluble than the alkali cyanides, and are easily decomposed by carbonic acid. Zine cyanide, ZnCye, is pre- cipitated by KCy from ZnSO,; it dissolves in KCy, forming ZnCy.(KCy). which erystallises in octahedra. Nickel cyanide, NiCys, obtained in a similar way, forms a pale green precipitate, readily soluble in excess, forming NiCy2(KCy)s., from which hydrochloric acid reprecipitates the nickel cyanide— NiCy,(KCy), + 2HCl = NiCy, + 2KCl + 2HCy. If the solution of nickel cyanide in potassium cyanide be heated with mercuric oxide, nickel oxide is precipitated; NiCy,(KCy), + HgO = HgCy(KCy), + NiO. This reaction is important in quantitative analysis. Nickel cyanide is remarkable for its insolubility even in boiling hydrochloric acid. Cobalt cyanide, CoCys, is precipitated of a reddish-brown colour when potassium cyanide is added to cobalt nitrate ; it dissolves easily in excess of potassium cyanide, forming potassium cobaltocyanide, K4(CoCyg), which may be obtained in red deliquescent crystals by adding alcohol. This compound corresponds with potassium ferrocyanide, K,(FeCye), but is far less stable ; when exposed to air, or boiled with water, it undergoes oxidation, the cobaltous compound being converted into a cobaltic compound, the CYANIDES 727 potassium cobalticyanide—2K,(Co”’Cyg) + O + H,O = 2K,(Co’’Cy,) + 2KOH. The potassium cobalticyanide is a pale yellow salt, its solution being nearly colourless, so that the brown solution formed at first when KCy in excess is added to a cobalt salt gradually becomes pale yellow when boiled in contact with air. This solution, when mixed with hydrochloric acid in excess, yields hydro-cobalticyanic acid, H,CoCy,, which is soluble, forming a distinction between cobalt and nickel. When both metals arc present the addition of HCl to the solution in excess of KCy produces a yellowish- green precipitate of nickel cobalticyanide, Ni3(CoCyg)s, which is decomposed by boiling with potash, the nickel being precipitated as hydroxide, and the cobalt passing into solution as potassium cobalticyanide ; Ni3(CoCyg). + 6KOH = 3Ni(OH), + 2K,CoCy,. The solution of potassium cobalticyanide is not decomposed by digestion with HgO (to precipitate the NiO), but a solution of mercurous nitrate gives a white precipitate of mercurous cobalticyanide, Hg,Co,Cys, which is converted into oxide of cobalt when heated in air. The potassium cobalticyanide may be obtained in crystals ; it is analogous to, and isomorphous with, the potassium ferricyanide,.to be presently described. Hydro- cobalticyanic acid is prepared by mixing a strong solution of the potassium-salt with sulphuric acid and alcohol, when K,SO, is precipitated, and the solution yields colourless crystals of H,(CoCyg)2.H,O0, which is a very stable and powerful acid. Potassium cobalticyanide gives, with ferrous salts, a white precipitate of ferrous cobalticyanide, Fe,(CoCy,)3 ; and with cobalt salts a red precipitate of cobaltous cobalticyanide, Co”’3(Co’’’Cy¢)o.14Aq, which loses its water at 200°, and becomes blue. Cyanogen and Iron.—Ferrous cyanide, Fe(CN)s, or FeCyo, is obtained (apparently in combination with some KCy) as « red-brown precipitate, by adding potassium cyanide to a ferrous salt ; it dissolves when boiled with an excess of the cyanide, and the solution, when evaporated, deposits yellow crystals of potassium ferrocyanide— FeCy, + 4KCy = K,FeCy,. This might be regarded as 4KCy.FeCy., but the iron cannot be detected by any of the tests for that metal; thus ammonium sulphide, which produces a black precipitate in ferrous salts, does not change the ferrocyanide ; moreover, the K, may be exchanged for hydrogen or for other metals without affecting the iron and cyanogen, leading to the conclusion that the group FeCy, contains the iron in a state of intimate association with the cyanogen, so that its ordinary properties are lost. Again, the ferrocyanide is not poisonous, so that it cannot be believed to contain potassium cyanide. Hydrogen ferrocyanide, or hydroferrocyanic acid, HyFeCyg, is prepared by mixing a cold saturated solution of potassium ferrocyanide with an equal volume of strong hydrochloric acid. It forms a white crystalline precipitate, soluble in water, but not in HCl. If it be drained, dissolved in alcohol, and ether added, it may be obtained in large crystals. It is a strong acid. When exposed to air, it absorbs oxygen, and evolves hydrocyanic acid, leaving a residue of Prussian blue or ferric ferrocyanide, Fe,(FeCy,)3. The acid is decomposed by boiling its solution, into hydrocyanic acid and ferrous ferrocyanide, Fe,(FeCyg), which is white, but becomes blue when exposed to air; 3H,FeCy, = 12HCy + Fe.(FeCy,). These changes are applied to produce blue patterns in calico-printing. Hydroferrocyanic acid is tetrabasic, its four atoms of hydrogen admitting of dis- placement by a metal to form a ferrocyanide. The group FeCyg, ferrocyanogen, Fey or Cfy, is a tetrad group, consisting of ferrous iron, which is diad, Fe”, and six monad cyanogen groups, (CN)’, leaving four vacant bonds. Prussian blue or ferric ferrocyanide, Fe’’’,Fcy'’;, (Fey = FeC,N,), is prepared by adding potassium ferrocyanide to a solution of ferric chloride, or ferric sulphate ; 2Fe,Cl, + 3K,Fcy = Fe,Fcy; + 12KCl. When washed and dried, it is a dark-blue amorphous body, which assumes a coppery lustre when rubbed. It cannot be obtained perfectly free from water, always retaining about 20 per cent. (Fe,Fey + 12 Aq). On heating, the water decomposes it, hydrocyanic acid and ammonia being evolved, and ferric oxide left. The water appears essential to the blue colour, for strong sulphuric acid converts it into a white powder, becoming blue again on adding water. Strong hydrochloric acid dissolves Prussian blue, forming 728 PRUSSIAN BLUE a brown solution, which gives a blue precipitate with water. Oxalic acid dissolves it to a blue solution, used as an ink. Some ammonium salts, such as acetate and tartrate, also dissolve it. Alkalies destroy the blue colour, leaving ferric hydroxide and a solution of an alkali ferrocyanide - Fe,Fcy,; + 12KOH = 2Fe (OH), + 3K,F cy. This is turned to account, in calico-printing, for producing a buff or white pattern upon a blue ground. The stuff having been dyed blue by passing, first through solution of a ferric salt, and afterwards through potassium ferrocyanide, the pattern is discharged by an alkali, which leaves the brown ferric hydroxide capable of being removed by a dilute acid, when the stuff has been rinsed, so as to leave the design white. Prussian blue is present in large quantity in many black silks, and may be extracted by heating with hydrochloric acid, and precipitating the brown solution with water. Soluble Prussian blue, or potassio-ferric ferrocyanide, K,¥Fe’’’,(Fcy)'s, is formed when solution of ferric chloride or sulphate is poured into potassium ferrocyanide, so that the latter may be present in excess during the reaction ; Fe,Cl, + 2K,Fcy = K,Fe.Fcey. + 6KCl. This blue is insoluble in the liquid containing saline matter but dissolves as soon as the latter has been removed by washing. The addition of an acid or a salt reprecipitates it. By decomposing soluble Prussian blue with ferrous sulphate, a blue precipitate of ferroso-ferric ferrocyanide, Fe’Fe’’’,F cys, is obtained, which is erroneously called Turnbull’s blue (ferrous ferricyanide). Potassio-ferrous ferrocyanide, K,Fe’’F cy, is obtained as a white precipitate when a solution of ferrous salt quite free from ferric salt, such as a solution of ferrous hydro- sulphite (p. 173) made by dissolving iron in H,SO3, is added to potassium ferrocyanide quite free from ferricyanide ; FeS,0, + K,Fcy = K,8,0, + K,FeFcy. The precipitate is snow-white, and remains so for some time at the bottom of the liquid, but if it be exposed to air, it eagerly absorbs oxygen and becomes blue ; 6K,FeFcy + 30 = 3K,Fcy + FeyFcy3; + Fe.Q3. Oxidising-agents, such as chlorine-water and nitric acid, change it at once into Prussian blue. When potassium ferrocyanide is added to ordinary ferrous sulphate, some Prussian blue is always formed from the ferric sulphate present in the ordinary salt. In making the Prussian blue of commerce, this precipitate is oxidised by solution of chloride of lime (p. 115), and afterwards washed with dilute HCl, to remove Fe,O3. Calcium chloride gives, with potassium ferrocyanide, a white crystalline precipitate of potasstum-calcium ferrocyanide, K,CaFcy, which is insoluble in acetic acid, but dissolves in HCl, and is reprecipitated by ammonia. Potassio-barium ferrocyanide, K,BaFcy.3Aq, is similar. Manganese ferrocyanide, MnoFcy, and zinc ferrocyanide, Zn,F cy, are white precipitates. When potassium ferrocyanide is added to a zinc-salt mixed with excess of ammonia, a white crystalline precipitate of ammonio-zinc ferro- cyanide is obtained. Nickel ferrocyanide, NigFcy, is a pale green precipitate. Cobalt ferrocyanide, CogF cy, formsa pale blue-green precipitate. Uranic ferrocyanide, U,F cy, (2), is a rich brown-red precipitate. Cupric ferrocyanide, CusFcy, is also obtained as a brown-red precipitate by adding potassium ferrocyanide to cupric sulphate ; it forms the colour known as Hatchett’s brown. Its formation is a delicate test for copper, a very dilute solution giving a pink colour with the ferrocyanide. Silver ferrocyanide, Ag,F cy, is obtained as a white precipitate from silver nitrate and potassium ferrocyanide ; it is insoluble in dilute nitric acid, like silver chloride, but it is also insoluble in ammonia, which is the case with few silver salts. When boiled with nitric acid it is converted into the red-brown silver ferricyanide. which is soluble in ammonia. When silver ferrocyanide is boiled with ammonia (or KOH), it deposits metallic silver and ferric oxide, leaving silver cyanide and ammonium (or potassium) cyanide in solution— 2Ag,FeCy, + 6NH; + 3H,0 = Ag, + Fe,0, + 6AgCy + 6NH,Cy. Ferric cyanide, Fe,Cyg, is very unstable. When KCy is added to ferric chloride, the solution soon becomes turbid, depositing ferric hydroxide and evolving HCy ; Fe,Cyg + 6H,0 = Fe(OH), + 6HCy. FERRICYANIDES 729 Potassium ferricyanide, or red prussiate of ‘potash, K,Fe’’C,Ng, or 3KCN.Fe’’(CN),, is prepared by the action of chlorine upon potassium ferrocyanide ; K,Fe’’Cy, + Cl = K,Fe’’Cy, + KCl. Chlorine is passed into the solution of ferrocyanide until a little of the solution tested with ferric chloride no longer gives a blue precipitate. On the small scale, chlorine-water may be added to the ferrocyanide. The yellow colour is changed to greenish-yellow, and the solution, when evaporated and cooled, deposits dark-red prisms of the ferricyanide. It is very soluble in water. yielding a dark yellowish-green solution, but is nearly insoluble in alcohol. The aqueous solution is slowly decomposed by exposure to light, depositing a blue precipitate, and becoming partly converted into ferrocyanide. If the solution be mixed with acetic acid, and heated, it deposits a blue precipi- tate, a reaction which is turned to account in dyeing. An alkaline solution of potassium ferricyanide acts as a powerful oxidising-agent, becoming reduced to ferrocyanide ; 2K,Fe’’Cy, + 2KOH = 2K,Fe’Cy, + H,O + O. Such a solution converts chromic oxide into potassium chromate, and bleaches indigo, whence it is used as a discharge in calico-printing, for white patterns on an indigo ground. Potassium ferricyanide is also reduced to ferrocyanide when boiled with potassium cyanide— 2K,Fe’’Cy, + 2KCN + 2H,O = 2K,Fe”Cy, + HCN + NH, + CO,. Hydrogen ferricyanide, or hydroferricyanic acid, H3Fe’’’Cy¢, is obtained by decom- posing lead ferricyanide with H,SO,, not in excess. It may be crystallised in brown needles by evaporation in vacuo. Its solution is decomposed by boiling, with evolution of HCy and separation of a blue precipitate. Hydroferricyanic acid is tribasic, the 3 atoms of hydrogen being displaced by metals to form ferricyanides. Ferrous ferricyanide, or Turnbull’s blue, Fe’’,Fe’’’,Cy,2.—Whilst potassium ferro- cyanide gives a light blue precipitate with common FeSQ,, the ferricyanide gives a dark blue precipitate, resembling Prussian blue. This contains the same proportions of iron and cyanogen as the ferroso-ferric ferrocyanide, Fe’Ve’’s(Fe’’Cyg¢)sz, and it is sometimes regarded as identical with it, on the supposition that the ferrous sulphate reduces the ferricyanide to ferrocyanide. Ferric salts give no precipitate with the ferricyanide, but only a dark brown solution, probably containing ferric ferricyanide, which yields a blue precipitate of ferrous ferricyanide with reducing-agents such as H,SOs, and is used as a test. Lead ferricyanide, Pb,Fe,Cyi2.16Aq, is deposited in red-brown crystals on mixing strong solutions of lead nitrate and potassium ferricyanide. Silver ferricyanide, AgsFe.Cyj2, has been already mentioned as a red-brown precipitate formed by boiling the ferrocyanide with dilute nitric acid. Cold potash converts it into black Ag,O and potassium ferricyanide ; on boiling, the black changes to pink ; 3Ag,0 + K,Fe:Cyip = 6AgCy + 6KCy + Fe.03. The pink precipitate is a compound of AgCy with silver ferricyanide, which may also be obtained by boiling silver ferricyanide with silver oxide ; AgeFe.Cyi2 + 3Ag2.0 = Fe,0, + 12AgCy, which combines with undecomposed silver ferricyanide. On continuing to boil the silver ferricyanide with potash, the pink precipitate again becomes black, for the potassium cyanide reduces the silver ferricyanide to ferrocyanide, which is ultimately decomposed by the silver oxide, with separation of metallic silver— (1) 2AgeFe.Cy12+4KCN +4H,0 = 3Ag,FeCy, +K,4FeCy, +2HCN +2CO, + 2NH; ; (2) 4Ag,FeCy, + 2Ag,0 = AggFe.Cyy. + 12AgCy + 2FeO + Aggy. In the preparation of K,FeCyg, if an excess of chlorine be employed, the liquid when evaporated deposits a precipitate of Prussian green, which’ appears to be a compound of ferric ferrocyanide and ferricyanide, 2FeyFcy3.FeF cy, for, when boiled with potash, it yields 5 molecules of ferric hydroxide, 3 molecules of potassium ferrocyanide, and 1 molecule of potassium ferricyanide. 730 SODIUM NITROPRUSSIDE Nitroprussides.—When potassium ferricyanide is acted on by a mixture of NaNO, and acetic acid, it is converted into potassium nitro- prusside, K,Fe,Cy,)(NO),, probably according to the equation— K,FesCyj2 + 4HNO, = K,Fe,Cy,o(NO)> + 2HCy + H,O + KNO, + KNOp. If HgCl, be added to the solution, HgCy, crystallises, and, on further evapora- tion, red prisms of sodium nitroprusside are deposited— K,FesCy;. + 4NaNO, + 2HA + HgCl, = NayFe,Cy19(NO), + HgCy. + 2KCl + 2Ka + KNO, + KNO, + H,0. Sodium nitroprusside, Na,Fe,Cy,,(NO).-4Aq, is prepared by a process founded upon the above reactions (Hadow). 332 grains of potassium ferricyanide are dissolved in half a pint of boiling water and 800 grains of acetic acid are added. Into this hot solution is poured a cold solution containing 80 grains of sodium nitrite and 164 grains of mercuric chloride in half a pint of water. The solution is kept at 60° for some hours, until a little no longer gives a blue coloration with ferrous sulphate (a little more sodium nitrite and acetic acid may be added if necessary). The mixture is then boiled down till it solidifies to a thick paste on cooling ; this is squeezed in linen to drain off the solution of potassium acetate ; the mass is dissolved in boiling water, and allowed to cool, when most of the mercuric cyanide crystallises. On concentrating the red filtrate, and cooling, crystals of sodium nitroprusside are obtained, and may be purified by recrystallisation. Sodium nitroprusside was originally prepared by boiling ferrocyanide with nitric acid (Playfair). Potassium ferrocyanide, in powder, is dissolved in twice its weight of strong HNO,(1-42) mixed with an equal volume of water; effervescence occurs, from escape of CO, and N, and the odours of (CN):, HCN, and cyanic acid may be distinguished. When the salt has dissolved, the solution is heated on a steam bath till it no longer gives a blue with FeSO,. It is then allowed to cool, when KNOs crystallises, and the solution is boiled with excess of Na,CO, and filtered ; the filtrate when evaporated deposits crystals of nitroprusside. Sodium nitroprusside is very soluble in water; the solution deposits a blue precipitate when exposed to light. When its solution is rendered alkaline by soda, and boiled, the NO group exerts a reducing action, ferrous hydroxide being precipitated, and sodium ferrocyanide and nitrite remaining in solution. Alkali sulphides have also a reducing effect upon the solution, producing a fugitive violet-blue colour, even in very weak solutions, render- ing sodium nitroprusside a most delicate test for sulphur in organic com- pounds, which yield sodium sulphide when fused with sodium carbonate. The sulphur in an inch of human hair may be detected by this test. The higher (yellow) alkali sulphides should be reduced by warming with KCN solution. Alcoholic solutions of nitroprusside and sulphide of sodium yield a purple oily compound soon decomposing into ammonia and several cyanogen compounds. With silver nitrate, sodium nitroprusside gives a buff precipitate of silver nitro- prusside, Ag4FesCyo(NO)., and by decomposing this with HCl the nitroprussic acid, HyFe,Cy,o(NO)2, may be obtained, by evaporation, in vacuo, in red deliquescent prisms (with 1H,0). It is very unstable. Potassium carbonyl ferrocyanide, K;FeCOCy;, is obtained by heating a solution of K,FeCy, with CO. Chromic cyanide, CroCyg, is a pale green precipitate produced by KCy with chrome alum ; heated with excess of KCy, it yields potassium chromicyanide, K,CreCyy2, which may be obtained in yellow prisms. Manganous cyanide, MnCys, is probably contained in the greenish precipitate by KCy in manganous acetate ; an excess of KCy dissolves it to a colourless solution, from which alcohol separates blue crystals of potassium manganocyanide, K,MnCy,.3Aq, isomorphous with the ferrocyanide. When exposed to air, the solution of the man- ganocyanide absorbs oxygen, and deposits red prisms of potassium manganicyanide, K,Mn.Cy,2, isomorphous with the ferricyanide. MERCURIC CYANIDE 731 Cuprous cyanide, CugCys, is obtained as a white precipitate by boiling cupric sulphate with KCy, when cupric cyanide, CuCys, is first formed as a brown precipitate, which evolves cyanogen when boiled. Cuprous cyanide dissolves in KCy, and the solution yields colourless crystals of potassium cwpro-cyanide, K.Cu’,Cy4, which gives a precipitate of plumbic cupro-cyanide, PbCu,Cy.z, with lead acetate. By decomposing the lead salt with H,8, a solution of the corresponding acid, H,Cu,Cy,, is obtained, but this soon decomposes into 2HCy and Cu,Cyp. Silver cyanide, AgCy, is obtained as a white precipitate when hydrocyanic acid or a cyanide is added to silver nitrate. Its insolubility in water renders its formation a very delicate test for HCy (in the absence of other acids forming insoluble silver salts) and an accurate method of estimating its quantity. Silver cyanide is not altered by sunlight like silver chloride, and is dissolved when boiled with strong nitric acid, which does not dissolve the chloride. The nitric solution, when cooled, deposits flocculent masses of minute needles of the composition AgCy.2AgNO,, which detonate when heated. Silver cyanide, when heated, fuses, evolves cyanogen, and leaves a residue of silver mixed with silver paracyanide, AgC,N3. Silver cyanide dissolves in ammonia like the chloride, but the latter is deposited in microscopic octahedra, while the cyanide forms distinct needles ; a mass of silver cyanide, moistened with ammonia and warmed, becomes converted into needles. Potassium hydroxide does not decompose silver cyanide. Potassium cyanide readily dissolves silver cyanide, forming KAgCys, which may be crystallised in six-sided tables. It is used in electro-plating. Mercuric cyanide, HgCy2, is prepared by dissolving precipitated HgO in excess of solution of HCN, and evaporating, when the cyanide is deposited in four-sided prisms, which dissolve in 13 parts of cold water, and in 20 parts of alcohol (90 per cent.) ; also in ether. For its behaviour when heated, see p. 722. It is one of the most stable of the cyanides, scarcely allowing the cyanogen to be detected by the ordinary tests. Dilute H,SO, and HNO, do not decompose it, but HCl liberates HCy. KOH and NH, do not precipitate its solution. Mercuric cyanide dissolves mercuric oxide when boiled, giving an alkaline solution, which deposits needles of mercuric orycyanide, Hg,0Cy,. When solutions of mercuric cyanide and silver nitrate are mixed, the solution becomes acid, and onstirring, deposits fine needles containing Ag.Hg.NO3.Cy.2Aq. The acid reaction of the solution proves that some of the mercuric cyanide has become converted into mercuric nitrate ; the same salt may be obtained by dissolving silver cyanide in mercuric nitrate. Neither mercuric cyanide nor silver nitrate is precipitated by excess of ammonia, but a mixture of the two salts gives an abundant precipitate, containing HgCy..7AgCy.2HgO, which explodes when heated. The crystalline salt is probably AgCy.CyHgNO;.2Aq, con- taining HgCyp, in which NO, is substituted for Cy. Other crystalline compounds of the same kind are formed by HgCy,; such as NaCy.CyHgCl and KCy.CyHgl. A potassio-mercuric cyanide, KCy.CyHgCy.CyK, may be obtained in fine crystals, which may be decomposed by mercuric chloride, yielding HgCl,. HgCy. or Hg”Cy’Cl’. Mercuric cyanide was originally prepared by Scheele, when he discovered that prussic acid could be prepared from Prussian blue. This was boiled with mercuric oxide and water till the blue colour had disappeared; Fe,(FeCy,)3 + 9HgO = 9HgCy. + 2Fe,0; + 3FeO. The filtered solution was mixed with sulphuric acid, shaken with iron filings, which precipitated the mercury, and distilled to obtain hydro- cyanic acid ; HgCy, + H,SO, + Fe = 2HCy + FeSO, + Hg. Mercuric cyanide may be directly obtained from potassium ferrocyanide by boiling it with mercuric sulphate (2 parts) and water (8 parts)— 2K,FeCy, + THgSO, = 6HgCy, + 4K,804 + Feo(SO,)s + Hg. The mercurous cyanide is not known; when mercurous nitrate is decomposed by potassium cyanide, a solution of mercuric cyanide is formed, and metallic mercury is precipitated ; Hg,(NO 3), + 2KCy = HgCy, + Hg + 2KNO,. Gold Cyanides.—Potassium aurocyanide, KAu’Cys, is obtained by dissolving gold in KON solution (p. 524), or by dissolving fulminating gold (p. 528) in hot water containing pure potassium cyanide. The filtered solution deposits colourless crystals of the aurocyanide, which are very soluble in hot water. Aurous cyanide, AuCy, is 732 PLATINOCYANIDES obtained as a crystalline precipitate by adding HCl to solution of the aurocyanide of potassium. Potassium auricyanide, KAu’’Cy,, is prepared by mixing hot strong solutions of gold trichloride and potassium cyanide. It forms colourless tables (with 1H,O). With AgNO, a precipitate of silver awricyanide, AgAuCy,, is obtained, and if this be treated with HCl, avoiding excess, the silver is precipitated as AgCl, and the solution, evaporated in vacuo, yields crystals of auric cyanide, AuCy3.3Aq. Both aurocyanide and auricyanide of potassium are used in electro-gilding. Platinum Cyanides.—The cyanides of platinum have not been prepared in a pure state, but the salts known as platinocyanides exceed the ferrocyanides in the force with which they retain the platinum disguised to the ordinary tests. When KCN is strongly heated on platinum foil, the metal is attacked, and an orange-coloured mass is produced. Spongy platinum is slowly dissolved by a boiling solution of KCN, and if mixed with the solid cyanide, and heated to 600° in steam, potassium platinocyanide is formed— Pt + 4KCy + 2H,O = K,Pt’Cy, + 2KOH + Hp. When solutions of potassium vyanide and platinic chloride are boiled together till colourless, the platinocyanide is found in solution— PtCl, + 6KCN + 4H,0 = K,Pt(CN), + 4KCl + 2NH, + H,C.04. Or the ammonio-platinic chloride may be boiled with potash and a strong solution of potassium cyanide until no more ammonia is evolved. Potassium platinocyanide is also prepared by dissolving platinous chloride in solution of potassium cyanide; PtCl, + 4KCy = K,PtCy, + 2KCl. It crystallises in prisms (with 3H,0), which are yellow by transmitted light, and reflect a blue colour. They are very soluble in water. The solution is colourless, and gives a characteristic blue precipitate with mercurous nitrate. CuSO, also gives a blue precipitate, and if this be decomposed by aqueous H,§, it yields a solution of hydroplatinocyanic acid, H,PtCy,, which crystallises from ether in red prisms (with 5H,O) with a blue reflection. Barium platinocyanide, BaPtCy,.4Aq, is prepared by decomposing the cupric salt with baryta. It is dichroic, being green when looked at along the primary axis of the crystal, and yellow across it. It is remarkable for its property of becoming luminous when exposed to the Réntgen rays, in which respect it resembles, but excels, many other platinocyanides. Magnesium platinocyanide, MgPtCy,.7Aq, obtained by decomposing the barium salt with MgSOQy,, crystallises in large prisms, deep red by transmitted light, but when viewed by reflected light, the sides of the prisms exhibit a brilliant beetle-green, and the ends a deep blue or purple colour. When the red salt is gently warmed, even under water, it becomes bright yellow, from production of MgPtCy,.6Aq, which may be obtained in crystals from the solution at 71°. Heated at 100°, the yellow salt becomes white MgPtCy,.2Aq, and at about 180° it again becomes yellow, and is then anhydrous. If a little of the yellow anhydrous salt be placed on the powdered red salt (with 7Aq), it abstracts water from it, and converts it into the yellow salt with 6Aq, while it is itself changed to the white salt with 2Aq, so that a white layer is formed between two yellow layers. The yellow salt may also be obtained by crystallisation from alcohol. When the platinocyanides are attacked, in solution, by oxidising-agents, such as chlorine, bromine, or nitric acid, new salts are formed, which have a coppery lustre, and act as oxidising-agents in alkaline solutions, like the ferricyanides. These were formerly called platinicyanides, but were shown by Hadow to contain chloro-, bromo-, &c., platinocyanides. When chlorine is passed into a hot solution of potassium platino- cyanide, it deposits, on evaporation, colourless crystals of the chloroplatinocyanide, KyPtCy4Cly.2Aq. When these are treated with a strong solution of the platinocyanide, they are converted into copper-red needles of 5K,PtCy,.K,PtCy,Cly.3H,0.18Aq. This compound, when boiled with potash, yields the platinocyanide and potassium hypochlorite— 5K,PtCy,.KePtCy,Cl, + 2KOH = 6K,PtCy, + KOC] + KCl + H,0. NITRILES 733 Cyanogen Halides.—Cyanogen chloride, Ci N-Cl, is prepared by the action of chlorine upon moist mercuric cyanide, in the dark ; HgCy, + 2Cl, = HgCl, + 2CyCl. On gently heating, the cyanogen chloride passes off in vapour, and may be condensed in a tube. sur- rounded with a freezing-mixture. It is a colourless liquid, boiling at 15°, and yielding a vapour which irritates the eyes, causing tears. When exposed to light, or treated with acids, it polymerises into cyanuric chloride, Cy;Cl,;, which fuses at 146° and boils at 190°. This has also an irritating effect on the eyes. It is sparingly soluble in cold water, and is decomposed by boiling water, yielding cyanuric acid ; Cy,Cl, + 3H,0 = Cy,(OH), + 3HCl. Both these chlorides may be obtained by the action of chlorine on hydrocyanic acid. In practice cyanogen chloride is generally required in solution which is best pre- pared by dissolving 260 grams of KCN and 90 grams of crystallised ZnSO, in 8 litres of water, and passing Cl until the ZnCy, at first thrown down is nearly redissolved. Cyanogen bromide, CyBr, is obtained in crystals, mixed with KBr, when bromine is gradually added to a strong well-cooled solution of KCy. On gently heating, it sublimes in crystals, which are very volatile and cause tears. When heated in a sealed tube it becomes Cy,Br3. It melts at 52° and boils at 61°. Cyanogen iodide, Cyl, is prepared by dissolving iodine in a warm strong solution of KCy, when a crystalline mass of KI and CyI is obtained on cooling, from which the Cyl may be extracted by gently heating or by treatment with ether. It crystallises easily in colourless needles or tables, which are sparingly soluble in water, very volatile, and have a tear-exciting odour. It sometimes occurs in commercial iodine, from which it may be sublimed in a tube or flask plunged in boiling water. When heated to 100° in a sealed tube with alcoholic ammonia, it yields hydriodide of guanidine, CNI + 2NH, = CN,H;.HI. Cyanides of Hydrocarbon Radicles, or Acid Nitriles.— The term nitrile was originally applied to the final product of the removal of water from an ammonium salt (cf. p. 702); the amide being the 7° ond, of the organic ammonium salts, loses 1 mol. H,0, it passes into the O “4 group of the amides, and when this loses 1 mol. H,0, it NH intermediate product. Thus, when the group C , characteristic becomes C=N, the nitrile group. It was later found that the nitriles are identical with the cyanides of the hydrocarbon radicles. Hence there are two general lines on which these compounds may be prepared, viz. (1) by reactions which produce cyanides, such as (a) by heating the iodide of a hydrocarbon radicle with KCN in alcoholic solution, CH,I + KCN = KI + CH,CN, or (6) by distilling an alkali alkyl sulphate with KCN, KCH,SO, + KCN = CH,-CN + K,SO,; (2) by dehydrating ammonium salts or amides by distillation with P,O,, CH,-CONH, — H,O0 = CH,-CN. The ease with which the CN group reverts to the COOH group when the cyanides or nitriles are hydrolysed and the importance thus attaching to these compounds in synthetic chemistry have been dwelt upon already (p. 723). When an acid is the hydrolytic agent the ammonium salt is produced CH,-CN + 2HOH = CH,‘COONH,; but when it is an alkali the NH, is evolved, CH,-CN + HOH + KOH = NH, + CH,-COOK. The reaction shows that of two possible formule for the cyanide, H,C-C : Nand H,C-N : C, the former must be correct, since the hydrolysis’ does not part the C atoms, which must therefore be directly united in the 734 ‘ CARBAMINES cyanide. The action of nascent hydrogen on the cyanide confirms this, in \wH, Cyanogen itself is oxalonitrile, and may be obtained by dehydrating ammonium oxalate COONH,-COONH, = CN-CN + 4H,0. Hydrocyanic acid is formonitrile, obtained from ammonium formate ; HCOONH, = HCN + 2H,0. Methyl cyanide, or acetonitrile, CH,-CN, prepared as above, is a volatile liquid of pleasant odour boiling at 81°6°. Its sp. gr. is 0-8, and it is soluble in water and alcohol. The tendency for the nitrogen in the C: N group to become pentavalent, leads to the formation of crystalline compounds of CH;CN with Br, HBr, HI, etc. Certain chlorides also combine with methyl cyanide to form crystalline volatile substances, decomposed by water; such compounds are formed with PCl;,, SbCl;, and SnCl,. When methyl cyanide is acted on by sodium, part of it is decomposed with violent evolution of methyl hydride, and the remainder is polymerised to form cyanmethine (CH,)3(CN)3, an organic base, soluble in water, and having a very bitter taste. It forms prismatic crystals, which may be sublimed. An instructive reaction yielding methyl cyanide is that between diazomethane and HCN; CH,:N, + HCN = CH,CN +N. This illustrates the application of diazomethane in the formation of a number of organic compounds. Methyl cyanide is present, in small quantity, in coal-naphtha, and in the distillate from beet-sugar refuse. Ethyl cyanide, or propio-nitrile, CoH;-CN, is similarly obtained. It resembles methyl cyanide, except in being less soluble in water, and in boiling at 98°. It combines with HCl to form a sparingly soluble crystalline compound, which absorbs water from the air, and yields propionic acid and ammonium chloride. Sodium acts on ethyl cyanide in the same way as on CH,-CN : one part is decomposed, with evolution of butane (di-ethyl)—2C,H;CN + Nag = CyHyo + 2NaCN. The re- mainder is polymerised to cyanethine (CpH5)3(CN)s3. Phenyl cyanide, or benzonitrile, CsH;-CN, also called cyanobenzene, may be prepared by dehydrating ammonium benzoate, also by distilling potassium benzenesulphonate with KCN (or well-dried K,FeCy,g) ; CsH;SO,;K + KCN = C,H;-CN + K,SO,. It is a colourless liquid smelling of bitter almonds; sp. gr. 1-023, boiling at 191°. By hydrolysis it becomes ammonium benzoate. Nascent hydrogen converts it into benzylamine, CgH;CH2-NHp. Its formation from diazobenzene has already been noticed (p. 716). Benzyl cyanide, CgH;-CH,-CN, or phenyl-acetonitrile, is obtained by heating benzyl chloride with potassium cyanide and alcohol. It occurs in the essential oils of nasturtium and cress. When boiled with alkalies, it yields ammonia and phenylacetic acid, CeH,;'CHy'CO.H. Isocyanides, Isonitriles, or Carbylamines (Carbamines).—These compounds are isomeric with the cyanides of the hydrocarbon radicles, but differ from them in being much less easily attacked by alkalies and in yielding formic acid and an amine of the hydrocarbon radicle when hydrolysed by acids, methyl isocyanide, for example, yielding methylamine, H,C-NH,, and formic acid, HCOOH. This reaction shows that the C atoms in the isocyanide are not united directly, but through the N atom ; in other words, the second of the two possible formule given above for the cyanide, H,C-N : ©, must be ascribed to the isocyanide.’ The formation of two carbon compounds on hydrolysis is easily explained on this assumption ; CH,,NC + 2HOH = CH,-NH, + HCOOH. The isocyanides are obtained in small proportion together with the cyanides when the iodides of the hydrocarbon radicles are heated with KCN, but they are almost the sole products when AgCN is substituted for 1 According to Nef the isocyanides must be regarded as containing Livale.t carton, H,C-N:C. for an amine is produced—CH,-CN + 4H’ = H,C-C TAUTOMERISM 735 the KCN. The iodide and AgCN are heated in a sealed tube with ether at 140°, when a crystalline compound of the isocyanide with AgCN is formed ; this is distilled with water and KCN, whereupon the isocyanide distils ; CH,I + 2AgCN = CH,-NC,AgCN + Agl ; CH,-NC,AgCN + KCN = CH,:NC + KCN,AgCN. The term carbamine refers to the idea formerly entertained that the isocyanides were amines in which carbon is substituted for hydrogen ; thus, methyl carbamine, NC-CH;, might be regarded as methylamine, NH,CH;, in which ©” is substituted for H,. Their connection with the amines is illustrated by the fact that they can be prepared by the action of chloroform and alcoholic potash on the amines; e.g. CH,-NH, + CHCl, + 3KOH = CH,-NC + 3KCl + 3HOH. The isocyanides often accompany the cyanides of the alcohol-radicles, especially when prepared by distilling the acid ethereal salts, such as potassium ethylsulphate, with potassium cyanide. For this reason the cyanides of alcohol-radicles were formerly described as having an offensive smell, which is really characteristic of the isocyanides mixed with them. Methyl isocyanide or methyl carbamine, H3C-NO, is prepared as described above. It is lighter than water (sp. gr. 0:76) and moderately soluble in it. It has an extremely unwholesome smell, and boils at 59°. Methyl carbamine is slightly alkaline; it combines with HCl gas, forming a crystalline hydrochloride, which is decomposed by water into formic acid and methylamine hydrochloride ; H,C-NC.HCl + 2H,0 = H3;C-NH,.HCl + HCO,H. Ethyl isocyanide, or ethyl carbamine, HyC.-NC, prepared like the methyl compound, boils at 79°, and has a repulsive odour like that of hemlock. It is lighter than water, and slightly alkaline. When heated with water at 180° for some hours it is converted into ethylamine formate ; H;Cy-NC + 2H,O = H,;C,-NH,.HCO,H. Heated alone, in a sealed tube, at 230°, it is metamerised into propionitrile ; H,;C.-NC = H;C,-CN. Ethyl carbamine forms a crystalline salt with HCl, from which very strong, well cooled potash separates an oily layer of ethyl formamide ; CN-C,H; + H,O = HCO-NHC,H;. Glacial acetic acid also converts ethyl carbamine into ethyl formamide, producing acetic anhydride and much heat— CN-C,H, + 2(C,H,;0-OH) = HCO-NHC,H, + (C,H;0),0. Phenyl isocyanide, or phenyl carbamine, HjCg'NC, is prepared by mixing aniline with a saturated alcoholic solution of -potash, and gradually adding chloroform ; the distillate is treated with oxalic acid to remove aniline, with potash to remove water, and redistilled. Phenyl carbamine has a very terrible odour ; it is green by transmitted light, and shows a blue reflection. It begins to boil at 166°, but soon decomposes, being converted, at 230°, into an odourless liquid which crystallises on cooling. When heated, in a sealed tube, at 200°, phenyl carbamine slowly metamerises into phenyl cyanide, or benzonitrile, H;Cg-CN. Treated with acids, it yields formic acid and salts of phenylamine (aniline) ; H,C, NC + 2H,0 = H,C,-NH2 + HCO,H. Dynamic Isomerism, Tautomerism.—It has been seen that the cyanides of alcohol-radicles exist in two forms, as though they were derived from two hydrocyanic acids, H-C=N and HNC. It will be seen later that derivatives of cyanamide also appear to be derived from two isomerides, H,N-C : N and HN:C:NH (p. 738). Two hydrocyanic acids or two cyanamides, however, have never been prepared. It is the case with a large number of substances that, although the two isomeric forms have never been separated, the substances behave in different reactions as if they had two structural formule, either of which could be assumed according to the conditions. Such compounds are said to possess tautomeric structures. 736 DYNAMIC ISOMERISM The derivatives of one form (the stable form) are generally more stable than those of the other (the labile form or pseudo form). Tautomerism is generally connected with the migration of a H atom, as will be seen from the above examples. It is very common among ketonic compounds, in which the grouping -CH : COH: occurs, this tending to become -CH,CO- (cf. ethyl acetoacetate, p. 667); the former is the hydroxyl- or enol- form, while the latter is the keto- form. Cf. also lactams and lactims (pp. 709, 714), and amidines (p. 703). ; From the fact that the chief product of the action of CH,I on KCN is methyl cyanide, it may be supposed that potassium cyanide is a salt of H-C:N. Silver cyanide, on the other hand, must be a salt of H-N : C. for the chief product of its reaction with methyl iodide is methyl isocyanide. See also Nitroparaffins. Although the above views of tautomerism, involving the spontaneous migration or oscillation of an atom or group within the molecule, are still conceivable, it is now known that in these cases the hydrogen or other atom is not usually spontaneously mobile within the molecule, but that its mobility is dependent on the formation of a complex molecular circuit, usually brought about by some catalyst, which may be merely an impurity in the substance. Hence, the so-called instances of tautomerism must be relegated to the larger group of cases of dynamic isomerism, i.e. of a condition of equilibrium between isomers. An essential feature of the modern view of the subject is that isomeric change is not spontaneous. It has already been seen that perfectly dry pure substances will not react ; a third substance perhaps in only the minutest proportion, must be present to form a molecular circuit ; similarly, a third substance is necessary for isomeric change to occur. An ionising solvent may promote the change. Instances of iso- dynamic change are given at pp. 642, 707. : Hydroxy- and Thio-Cyanogen Compounds.—Cyanuric acid, Cy,(OH),, is obtained .by heating urea till the melted mass solidifies ; 3CO(NH,). = 3NH, + (CN),(OH)s. The residue is washed with water, dissolved in KOH, and the cyanuric acid precipitated by adding HCl. A better yield is obtained by passing dry chlorine over urea kept in fusion by a gentle heat—3CO(NH,), + 3Cl = 2NH,Cl + HCl + N + (CN),(OH)3. The residue is washed with cold water, and crystallised from hot water. Cyanuric acid crystallises in prisms containing 2Aq. It is insoluble in alcohol. It is a tribasic acid. It is probable that cyanuric acid is a closed- chain compound, and it may be represented by either of the tautomeric gh tee) NH-CO. formule COOH) o < DNS, derivatives (the N:C(OH) NH-CO cyanuric esters, ¢.g. C;N,;0;(CH;),) of both forms being known. Trisodium cyanurate, (CN),(ONa)3, is insoluble in hot solution of soda and forms a crystalline precipitate on heating solution of cyanuric acid mixed with excess of soda. Barium cyanurate, Cy;0;HBa, is obtained as a crystalline precipitate by dissolv- ing cyanuric acid in NHg, and stirring with BaCl,. It has a great tendency to deposit on the lines of friction by the stirring-rod. The most characteristic test for cyanuric acid is ammoniacal CuSQ,, which gives a violet crystalline precipitate containing Cyg(OH)4-O-Cu(NHs3). Silver cyanurate, Cy,(OAg)s, is obtained as a crystalline precipitate by adding ammonium cyanurate to silver nitrate. Cyanic acid, CyOH, is prepared by distilling cyanuric acid (dried at 100°), and condensing in a receiver surrounded by a freezing-mixture ; Cy,(OH), = 3CyOH. The cyanic acid is a colourless liquid of sp. gr. 1-14 at 0°, which smells rather like acetic acid. It cannot be kept, for when the receiver is taken out of the freezing-mixture the acid becomes turbid, and presently begins to boil explosively, being entirely converted in a few minutes into a white hard solid, known as cyamelide, which is a POTASSIUM CYANATE 759 polymeride of cyanic acid, into which it is reconverted by distillation. When cyanic acid is mixed with water heat is evolved, and the liquid becomes alkaline ; CN-OH + 2H,0 = NH,-HCO;. A compound of HCl and CNOH is obtained as a fuming liquid by acting on a cyanate with dry HCl gas. It is doubtful whether cyanic acid is HO-C: N (the nitrile of carbonic acid) or HN :C: O (carbimide). The former would be cyanic acid and the latter isocyanic acid. At one time it was supposed that derivatives of both were known, but the compounds formerly called esters of cyanic acid have been shown to have a different constitution. Potassium Cyanate.—The compound formerly so called is probably the isocyanate, K-N:C:0, since it has been found to give rise to alkyl iso- cyanates when heated with potassium alkyl sulphates. It is formed when the cyanide is oxidised by fusion in contact with air or with metallic oxides. It may be prepared by oxidising potassium ferrocyanide with potassium dichromate. Four parts of perfectly dried K,FeCy, are intimately mixed with 3 parts of K,Cr,0, ; the mixture is thrown, in small portions, into a porcelain or iron dish, heated sufficiently to kindle it. When the whole has smouldered and blackened, it is allowed to cool, introduced into a flask, boiled with strong alcohol, and filtered hot ; the isocyanate crystallises out on cooling, and the mother liquor may be employed to extract a fresh portion. Potassium isocyanate is also prepared by passing cyanogen chloride into well-cooled potash; CN-Cl + 2KOH = KNCO + KC1+H,0. It crystallises in plates; it is decomposed by moist air into KHCO, and ammonia; K-NC:0O + 2H,0 = KHCO,+NH;. It is very soluble in water, but the solution soon decomposes, especially if heated— 2K-NC: 0 + 4H,0 = CO(OK), + CO(ONH,)2. If the freshly prepared solution be mixed with dilute acetic acid, a crystalline precipitate of potassium dihydrogen cyanurate is obtained ; 3KNCO + 2HA = KH,C3N,0, + 2KA. Solution of potassium isocyanate effervesces with acids evolving CO,, together with some pungent vapour of cyanic (or isocyanic) acid, and leaving an ammonium salt in solution. Ammonium cyanate, NH,-O-CN, or 0:C:N(NH,) is prepared by mixing vapour of cyanic acid with ammonia gas in excess, when it is deposited in minute crystals, which effervesce with acids, evolving CO,. The cyanate or isocyanate is also formed when potassium iso-cyanate is decomposed by ammonium sulphate. By employing strong solutions and cooling artificially, the bulk of the potassium sulphate may be crystallised out. The isocyanate has not been crystallised, for, when its solution is evaporated, it metamerises into urea ; NH,-NC : O = (NH,),CO (p. 705). Thiocyanic acid, HSCN (sulphocyanic), is obtained by decompos- ing mercuric thiocyanate with hydrogen sulphide. It is a colourless pungent liquid, boiling below 100°, being then decomposed into hydrocyanic and persulphocyanic acids; 3CySH = HCy + Cy.8,H,. It mixes with water, but the solution soon decomposes— 3HSCN + 6H,0 = CS, + HS + NH,HCO, + (NH,4)2CO5. Thiocyanic acid and the thiocyanates give an intense blood-red colour with ferric salts, producing ferric thiocyanate; the red is bleached by HgCl,, which distinguishes it from ferric acetate and meconate. Potassium thiocyanate, or sulphocyanide, KSCN, may be obtained by direct fusion of potassium cyanide with sulphur, or by boiling sulphur with solution of the cyanide. It is best prepared by fusing dried potassium ferrocyanide (3 parts), potassium carbonate (1 part), and sulphur (2 parts), at a low red heat, in a clay crucible. The a7 738 THIOCYANATES cooled mass is extracted by hot water, evaporated, and the residue boiled with alcohol, which deposits the thiocyanate on cooling. KCy is formed by the reaction between the ferrocyanide and the carbonate (p. 725), and combines with the sulphur. Potassium thiocyanate forms prismatic crystals, which are deliquescent and very soluble in water, producing great reduction of temperature. It fuses easily, becoming a dark blue colour, which fades on cooling ; it burns when heated in air, potassium sulphate being produced. When hydrochloric acid is added to a strong solution of potassium thiocyanate, a yellow precipi- tate of persulphocyanic acid is obtained ; this may be crystallised from hot water, and yields a yellow precipitate of lead persulphocyanate, PbCy,S8,, with lead nitrate. When heated with sulphuric acid mixed with an equal volume of water, potassium thiocyanate yields carbon oxysulphide, an offensive gas which burns with a blue flame ; KSCN + 2H,SO, + H,O = KHSO, + NH,HSO, + COS. Potassium isothiocyanate, K-NCS, is said to be obtained by heating persulpho- cyanic acid with alcoholic solution of potash. The crystals are soluble in water; the solution does not give the red thiocyanate reaction with ferric salts. It is converted into normal thiocyanate by boiling or fusing. Sodiwm thiocyanate occurs in saliva. Perthiocyanogen, or pseudosulphocyanogen, C3N3S3H, is obtained as a yellow pre- cipitate when potassium thiocyanate is heated with potassium chlorate and hydro- chloric acid. It is used in dyeing (canarin). Ammonium thiocyanate is prepared by acting on carbon disulphide (7 parts by weight) dissolved in alcohol (30 parts) with strong ammonia (30 parts). After standing for a day or two, with occasional shaking, until all the CS, has dissolved, the red solu- tion is distilled down to one-third of its bulk, when it becomes colourless, filtered if necessary, and allowed to crystallise ; CS, + 4NH, = CNS-NH, + (NH,)QS. It is also made on a large scale by boiling sulphur with the solution of ammonium cyanide from the gasworks. It crystallises like the potassium salt, and is very soluble in water, producing great cold. When heated, it fuses easily, and at 170°, is meta- merised into thiocarbamide (p. 707). Lead thiocyanate, Pb(CyS)s, forms a yellow crystalline precipitate. Silver thiocyanate, AgCyS, is a white precipitate, very insoluble in water and in nitric acid, and sparingly soluble in ammonia. Mercuric thiocyanate, Hg(CyS)o, is a crystalline precipitate formed on stirring mercuric chloride with an alkali thiocyanate. It attracted much notice formerly as the toy called Pharaoh’s serpent, which was a small cylinder of the thiocyanate mixed with gum, which burnt when kindled, evolving mercury and other vapours, and swelling to a bulky vermiform mass of medlone (p. 739). Cuprous thiocyanate, Cu,(CyS)s, precipitated by potassium thiocyanate from a cuprous salt, is very insoluble in water and in cold dilute acids, so that copper is some- times precipitated in this form in quantitative analysis. Cyanogen sulphide, Cy28, is obtained by decomposing cyanogen iodide, dissolved in ether, with silver thiocyanate ; CyI + AgCyS = CyS + AglI. It is a crystalline, fusible, volatile solid, soluble in alcohol and ether, but decomposed by water ; potash converts it into cyanate and thiocyanate. Phosphorus tricyanide, Cy3P, is sublimed in tabular crystals from a mixture of silver cyanide and phosphorus trichloride, heated in a sealed tube at 140° for some hours, and distilled in a current of CO,. It inflames at a very low temperature, and is decomposed by water into hydrocyanic and phosphorous acids ; Cy,;P + 3HOH = 3CyH + P(OH)s. Cyanamide, H,N-CN, which also behaves as carbodiimide, NH: C: NH, may be obtained by fusing urea with sodium—(NH,).CO + Na = H,N-CN + NaOH + H. The mass is dissolved in water, ammonia added in excess, and silver nitrate, which gives a yellow precipitate of Ag,N-CN; this is washed, dried, covered with ether, and decomposed by H,S, when Ag.S and H,N-CN are produced, the latter dissolving in the ether, from which it may be crystallised. CYANAMIDE 739 Cyanamide may also be prepared, like other amides, by acting on NH3, dissolved in ether, with gaseous CNC]; 2NH, + CN-Cl = H,N-CN + NH,CL Another reaction which furnishes it is that between thiourea (p. 707) and freshly precipitated mercuric oxide ; (NH,),CS + HgO = H,N.CN + HgS + HO. It forms crystals soluble in water, alcohol, and ether, and melting at 40°. HCl passed into its ethereal solution gives crystals of H,N-CN,2HCl. Hydrolysis converts it into urea, and H,§ into thio-urea. With NH, it yields guanidine. In recent years cyanamide has assumed importance as an artificial manure. For this purpose a crude calcium cyanamide, CaN-CN, is produced by heating calcium carbide in an atmosphere of nitrogen in an electric furnace ; CaCy + Np = CaN.CN+C; also by heating lime or chalk with charcoal at 2000° in a current of air. The product contains 14 to 22 per cent. N, which becomes available as NH, on hydrolysis in the soil ; see also Nitrogen. Dicyanimide, HN(CN),, is produced by the action of potash on solution of potassium cyanate; 3KOCN + H,0 = (KO),CO + KOH + HN(CN). On neutralising the solution with HNO, and adding AgNOs, a precipitate of AgN(CN), is obtained. Potas- sium isocyanate, K-NCO, does not yield dicyanimide. The amides of cyanuric acid are (1) melamine or cyanuramide, C,N,(NH»)5, obtained by the action of NH, on cyanuric chloride, (2) ammeline, C3N3(NH2)2.0H, produced by boiling melamine with HCl, and (3) ammelide, U;3N;NH2(OH)s, formed by boiling melamine with KOH. Melamine crystallises from water, but the others are insoluble. When NH,SCN is heated, it loses NH; and H,§8, and is converted successively into melam, CgH,Ny,, melem, CsHgNio, and mellone, CgH;Ng, white amorphous com- pounds. Potassium mellonide, CoK3Nj3, is formed when KSCN is heated out of contact with air, CS, being evolved; this crystallises with 3Aq and yields a corresponding silver salt and free acid. Chrysean, [CN:CH(SH)],NH, is obtained by covering potassium cyanide with water in a flask, and saturating with H,S gas ; 4KCN + 5H,S = C,H;S.N, + 2K,S + NH,HS. It crystallises from boiling water in golden needles, soluble in alcohol, ether, acids, and alkalies. Its alcoholic solution is red, and changes to a fugitive green on adding a little alkali. Alkyl cyanurates and isocyanates.—The compounds formerly described as alkyl cyanates are proved to be esters of imido-carbonic acid. By the action of CNC on sodium alkyloxides, products are obtained which rapidly polymerise to alkyl cyanurates, e.g. 83CI-CN + 3CH,ONa = 3NaCl + (CH3)303C3N3. Methyl isocyanate, or methyl carbimide, H,C-NC :0, was formerly regarded as the normal cyanate, being obtained by distilling potassium methyl sulphate with potassium cyanate; KCH,SO, + K-0-CN= H,C-NC: 0 + K,SO,. It is also obtained by oxidising methyl isocyanide with mercuric oxide ; H,C-NC + HgO = H,C0-NC: O + Hg. It is a volatile liquid (b.-p. 44°) with a suffocating odour. When distilled with potash, it yields methylamine, showing that the methyl is attached to the nitrogen, and that the compound is the isocyanate: H,C-N: CO + 2KOH = H,;C-NH, + CO(OK),. Ammonia gas converts methyl isocyanate into methyl urea (H;C-NC: O + NH; = NH,:CO-NHCH,) resembling urea itself. Dimethyl urea, (NH-CH;),.CO, is formed by the action of water on methyl isocyanate ; 2(H,C-NC : 0) + H,O = (NH-CH;),CO + COp. Ethyl isocyanate, or ethyl carbimide, H,Cz-NC: O, is prepared like the methyl com- pound, which it resembles. Its sp. gr. is 0-9 and it boils at 60°. It yields ethylamine, when distilled with potash, and triethylamine with sodium ethoxide ; H,;Cy-NC: O + 2(C,:Hs-ONa) = (H;C2)3N + CO(ONa)o. Ethyl urea, NH,:CO-NHC,H;, diethyl urea, (NHC,H;).CO, and triethyl urea, (NHC,H;)N(C,H;)o"CO, have been obtained. Methyl-ethyl urea, NHCH,-CO-NHC,H,, is formed by the action of methylamine on ethyl isocyanate ; H;Co.NC:O + NH,CH; = (NHCH;)NHC,H;-CO. The isothiocyanates of the hydrocarbon radicles are called mustard oils or thiocarbimides. 740 MUSTARD OIL Allyl isothiocyanate, H,C,-NCS, is the essential oil of mustard, obtained by grinding black mustard seeds with water and distilling. It does not exist in the seed, but is produced by the decomposition of potassium myronate contained in the seed, induced by a peculiar ferment called myrosin, which decomposes the myronate into the essence of mustard, glucose, and KHSO,; KC, H,,N8,01) = H,;C,-NCS + CgH,.0, + KHSO,. The seed yields about 0-5 per cent. of the oil. The potassium myronate may be obtained from ground mustard by rendering the myrosin inactive by boiling alcohol, and then extracting the myronate with cold water. The solution is evaporated to a small bulk and mixed with alcohol, which precipitates the potassium myronate. The free acid is not known, being very unstable. Myrosin is prepared by extracting ground white mustard with cold water, evaporating the filtrate to a syrup below 40°, and adding alcohol in small quantity, when the myrosin is precipitated. It somewhat resembles albumin, being coagulated and rendered inactive by heat. Its aqueous solution, when added to potassium myronate, causes it in a few minutes to smell of mustard and become acid ; it also becomes turbid from the separation of small globular cells like those of yeast. Myrosin occurs in other plants than mustard, such as the radish, rape, cabbage, and swede, all belonging to the same natural order as mustard (Cruciferw). Mignonette root furnishes pheny] ethyl mustard oil, or phenyl ethyl isothiocyanate. Essential oil of mustard has sp. gr. 1-017, and boils at 150°. It is insoluble in water, but dissolves in alcoholand ether. It is the cause of the pungent odour of mustard paste and of its power to redden and irritate the skin. It is slowly decomposed by light, depositing a yellow precipitate. When heated with water at 100° for some time it loses sulphur and becomes crotono-nitrile, CsH;-CN, which is present in considerable quantity in commercial mustard oil. When mustard oil dissolved in alcohol is acted on by HCl and Zn, it yields allylamine ; H,C,-NCS + 4H’ = H,C,-NH, + HCHS (thioformaldehyde). By mixing mustard oil with ammonia and passing ammonia gas, allyl-thio-urea, or thio-sinamine, NH,-NH(C,H;)-CS, is obtained, forming prismatic crystals soluble in water, alcohol, and ether, and having a bitter taste. It is a weak base. When heated with lead hydroxide, it loses H,S and becomes allyl-cyanamide, NHC3H;-CN, which afterwards polymerises into sinamine, or tri-allyl melamine, (NHC3H5)3(CN)3. This is a strongly alkaline base. If allyl bromide be decomposed by ammonium thiocyanate, at a low temperature, allyl thiocyanate, H;C3:‘SCN, is formed, which has no smell of mustard. When this is heated, it boils at 161°, but the boiling-point soon falls, and a strong smell of mustard is perceived. When the boiling-point has reached 150°, the whole distils over as allyl isothiocyanate, H;C3;-NCS, or mustard oil. Allyl thiocyanate, decomposed by potash, yields potassium thiocyanate and allyl alcohol; H,;C;-SCN + KOH = H;C,-OH + K-SCN ; allyl isothiocyanate gives allylamine; H;C3-NCS + 4KOH = H,C3-NH, + K,S + CO(OK), + H,0. Mustard oil is also obtained artificially by distilling allyl iodide (p. 659) with potassium thiocyanate ; C,;H,I + KSCN = C,H;-NCS + KI. When ethyl iodide is treated in the same way, ethyl thiocyanate, CoH; YON is obtained. To obtain the ethyl isothio- cyanate, or ethyl mustard oil, or ethyl thiocarbimide, C.H;-NCS, ethylamine dissolved in alcohol is digested with carbon bisulphide, distilled nearly to dryness, and the residue in the retort boiled with solution of HgCl,. All primary amines yield the corresponding mustard oils when treated in this manner, and, since the odour is quite characteristic, the treatment with CS, and HgCl, is known as the mustard-oil test for primary bases. The mustard-oil reaction is easily explained. When CO, is combined with dry NH,, ammonium carbamate is formed ; CO, + 2NH; = CO(ONH,)(NH,). If CS, be substituted for CO, (the CS, employed in alcoholic solution), ammonium thiocarbamate is produced—CS, + 2NH, = CS(SNH,)(NH,). MERCURIC FULMINATE 741 When ethylamine is used instead of ammonia, the product is ethyl ammonium ethyl-thiocarbamate ; CS, + 2NH,(C,H;) = CS-SNH,(C,H;)NH(C,H;). On decompos- ing this with mercuric chloride, it yields the corresponding mercuric salt, which is decomposed, by boiling with water, into ethyl isothiocyanate, mercuric sulphide, and hydrogen sulphide ; Hg(CS-‘S-NHC,H;). = HgS + H,S + 2C,H,;NCS. Butyl isothiocyanate, CyHy-NCS, is the essential oil of scurvy-grass, another cruciferous plant, and is sometimes sold as mustard oil, but it has a higher boiling-point, 160°. Fulminates.—The salts known as fulminates are prepared from the fulminates of mercury and silver, obtained when those metals are treated with nitric acid and alcohol. It is still doubtful what is their constitution, but the latest researches seem to show that they are salts of the acid C : N-OH, which may be regarded as the oxime (p. 748) of CO—carbyloxime. Mercuric fulminate, (C:N-O),Hg, is prepared on a small scale with safety, by carefully observing the following directions: Dissolve 1-6 grm. of mercury in 14 c.c. of ordinary concentrated nitric acid (sp. gr. 1-42) in a half-pint beaker, covered with a dial-glass ; the dissolution may occur in the cold, or may be accelerated by gently heating. The solution contains Hg(NO,),, HNO, and HNO,. When all the mercury is dissolved, remove the beaker to a distance from any flame and pour into it, at arm’s length, 17-5 c.c. of alcohol (sp. gr. 0-87). Very brisk action soon begins, and the fulminate separates as a crystalline precipitate ; dense white fumes pour over the sides of the beaker, having the odours of nitrous ether and aldehyde ; they also contain mercury compounds and HCN, and are very poisonous. When red fumes begin to appear abundantly, some water is poured in to stop the action (which occupies only two or three minutes), and the fulminate is collected on a filter, washed with water as long as the washings taste acid, and dried by exposure to air. On a large scale the preparation is carried out under sheds. At Montreuil, 300 grams of mercury are dissolved in 3 kilos of colourless HNOs, of sp. gr. 1-4 in the cold. The solution is transferred to a retort, and 2 litres of strong alcohol are added, In summer no heat is required, and the vapours are condensed in a receiver and added to a fresh charge. When the action has ceased, the contents of the retort are poured into a shallow pan, and, when cold, the fulminate is collected in a conical earthen vessel partially plugged at the narrow end. It is washed with rain water, and drained until it contains 20 per cent. of water, being stored in that state. Mercuric fulminate, thus prepared, has a grey colour from the presence of finely divided mercury, and sometimes contains mercuric oxalate. It may be purified by dissolving it in 100 parts of boiling water, which leaves the metal and the oxalate undissolved, and deposits the fulminate on cooling in lustrous white prisms. It should not be kept in a stoppered bottle, as it would easily detonate by friction between the stopper and the neck of the bottle. The blow of a hammer causes it to detonate sharply with a bright flash and grey fumes of mercury ; HgC,N,02 = Hg + 2CO + Ng. It is also detonated by being touched with a wire heated to 195°, or by an electric spark, or by contact with strong sulphuric or nitric acid. Its sp. gr. being 4-4, a small volume of it evolves a large volume of gas; according to the above equation, the gas and vapour would occupy more than 1340 times the volume of the solid, at the ordinary temperature, and the volume at the moment of detonation would be much greater, because the fulminate evolves 403 units of heat (per unit) in its decomposition, and thig would expand the evolved gases and greatly increase their mechanical effect. It is estimated that a pressure of 48,000 atmospheres is thus produced. Fulminic acid, ©: N-OH, is isomeric with cyanic acid, and was long supposed to contain the cyanogen group. It is doubtless obtained when fulminates are treated with HCl, when a smell of HCN is perceived although none is to be detected : but the fulminic acid immediately combines with the HCl, forming chloroformoxime, CIHC : N-OH, an indication that the carbon is unsaturated, as in CO. This oxime rapidly breaks up into formic acid and hydroxylamine hydrochloride ; CIHC ; N-OH + 2H,0 = NH,OH.HCIl + HCOOH, 742 PERCUSSION CAPS Thus these two compounds and mercuric chloride are the products of the action of strong HCl on mercuric fulminate ; by precipitating the mercury by H,S and evaporating the solution, hydroxylamine hydrochloride may be crystallised, and this is one of the best methods for preparing this salt. Mercuric fulminate is formed when HgCl, is added to sodium nitromethane, CH,: NO-ONa, water being formed. This confirms the above constitution, but it must be added that the behaviour of the fulminate with halogens indicates the presence of a CN group. With Cl it yields HgCl,, CNCIl, and CCl,;NO, (chloropicrin), and with Br the reaction is similar, but dibromonitro-aceto-nitrile, Br.(NO,)C-CN, is an intermediate product. Again, NH; converts the fulminate into urea and guanidine, as though it contained an isocyanic-group (see Isocyanates). Cap composition.—The explosion of mercuric fulminate is so violent and rapid that it is necessary to moderate it for percussion-caps. For this purpose it is mixed with potassium nitrate or chlorate, the oxidising property of these salts possibly causing them to be preferred to any merely inactive substances, since they would tend to increase the temperature of the flash by burning the carbonic oxide into carbon dioxide, and would thus ensure the ignition of the cartridge. In the military caps, in this country, potassium chlorate is always mixed with the fulminate, and powdered glass is sometimes added to increase the sensibility of the mixture to explosion by percussion. Antimony sulphide is sometimes substituted for powdered glass, apparently for the purpose of lengthening the flash by taking advantage of the powerful oxidising action of potassium chlorate upon that compound (p. 57). Since the composition is very liable to explode under friction, it is made in small quantities at a time, and without contact with any hard substance. After a little of the composition has been introduced into the cap, it is made to adhere and waterproofed by a drop of solution of shellac in spirit of wine. If a thin train of mercuric fulminate be laid upon a plate, and covered, except a little at one end, with gunpowder, it will be found, on touching the fulminate with a hot wire, that its explosion scatters the gunpowder, but does not inflame it. On repeating the experiment with a mixture of 10 grains of the fulminate and 15 grains of potassium chlorate, made upon paper with a card, the explosion will be found to. inflame the gunpowder. By sprinkling a thin layer of the fulminate upon a glass plate, and firing it with a hot wire, the separated mercury may be made to coat the glass, so as to give it all the appearance of a looking-glass. Although the effect produced by the explosion of mercuric fulminate is very violent in its immediate neighbourhood, it is very slightly felt at a distance, and the sudden expansion of the gas will burst firearms, because it does not allow time for overcoming the inertia of the ball; but even if the barrel escape destruction, the projectile effect of the fulminate is found inferior to that of powder. It has been proved by experiment that the mean pressure exerted by the explosion of mercuric fulminate is very much lower than that produced by gun-cotton, and only three-fourths of that produced by nitroglycerin. Its great pressure is due to its instantaneous decomposition into CO, N, and Hg vapour within a space not sensibly greater than the volume of the fulminate itself, which volume being very small, on account of the high density of the fulminate, the escaping gases exert an enormous pressure at the moment of explosion. This detonating property of mercuric fulminate renders it exceedingly useful for effecting the detonation of gun-cotton and nitroglycerin. Berthelot finds that even such stable gases as acetylene, cyanogen, and nitric oxide are decomposed into their elements by the detonation of mercuric fulminate. CS, is similarly decomposed (p. 175). Silver fulminate, (CN):(OAg), (?), is prepared in a similar way to the mercury salt. 0-65 gram of silver is dissolved, by gently heating, in 5 c.c. of ordinary strong HNOs (sp. gr. 1-42) and 3-5 ¢.c. of water. As soon as the silver is dissolved, the lamp is removed, and 14 ¢.c. of alcohol (sp. gr. 0-87) are added. If the action does not start shortly, a very gentle heat may be applied until effervescence begins, when the fulminate will be deposited in fine needles, and may be further treated like the mercuric salt. In some cases a little red HNO; is necessary to start the action. It may also be obtained as a crystalline precipitate by warming solution of AgNO, with HNO, and alcohol until effervescence begins. FULMINATES 743 Silver fulminate is far more dangerous than mercuric fulminate, and, if stored dry, should be wrapped up, in small portions, in paper. Even if wet, it is not safe, in a glass bottle. When dry, it should be lifted with a slip of card. Silver fulminate crystallises in shining prisms, and is more soluble in boiling water (36 parts) than is mercuric fulminate ; it detonates sharply when pressed with a hard body, or when heated a little above 100°. When touched with a hot wire upon a piece of glass or thin metal, it gives a sharp report and shatjprs the plate, whilst mercuric fulminate emits a dull sound, and does not shatter unless closed in. Silver fulminate is used in toy crackers, such as the pull crackers, where it is mixed with powdered glass to increase the friction, and the throw-down crackers, where it is twisted up in thin paper with some fragments of quartz-pebble. It is occasionally mixed with mercuric fulminate in detonating tubes, to raise the note of the report. Warm ammonia dissolves silver fulminate, and deposits, on cooling, crystals of silver-ammonium fulminate, NH,O-CN:O-NCAg, which is even more violently explosive, and is dangerous while still moist. A similar compound is formed with mercuric fulminate. Potassium chloride, added to a hot solution of silver fulminate, removes only half the silver as precipitated chloride, and the solution deposits shining plates of silver-potassium fulminate, KO-CN-O-NCAg, which is very explosive. By the careful addition of HNO; the K may be exchanged for H, and the silver hydrogen fulminate, HO-CN-O-NCAg, obtained, which dissolves easily in boiling water and crystallises on cooling ; by boiling with silver oxide, it is converted into silver fulminate, or, with mercuric oxide, into silver-mercury fulminate. Zinc and copper fulminates may be obtained by decomposing moist mercuric fulminate with those metals ; they are soluble, crystalline, and explosive. : Sodium fulminate is obtained by the action of sodium amalgam on an aqueous solution of mercuric fulminate. On evaporating over lime and sulphuric acid, the sodium salt is deposited in prisms (with 2H,O), which explode when rubbed. A crystalline compound of single molecules of sodium fulminate and mercuric fulminate, and 4Aq, has been obtained. Fulminuric or isocyanuric acid, HO-NC(OC-NH),, is obtained as a potassium salt by boiling mercuric fulminate with potassium chloride. On adding silver nitrate, the sparingly soluble silver fulminurate crystallises out, and by decomposing this with H,§, and evaporating the filtrate, a solution of the acid is obtained ; it crystallises with difficulty, and is soluble in alcohol. XI. PHENOLS The phenols are hydroxy-benzenes, naphthalenes, &c., derived from aromatic hydrocarbons by substituting hydroxyl for the nucleal hydrogen atoms, eg. phenol, C,H;OH; orcinol, C,H,CH,(OH),; pyrogallol, C,H,(OH),; naphthol, C,,H,OH. If the hydroxyl is introduced into the methyl group instead of the phenyl group in the homologues of benzene (p. 566), an alcohol is produced; thus, CgH,-CH,(OH) is benzyl alcohol, whereas C,H,(OH)-CH, is methyl-phenol or cresol (cf. p. 584). Phenols are distinguished from alcohols in combining more readily with alkalies, which caused them originally to be mistaken for acids. The phenolic hydroxyl is more acidic in character than the alcoholic hydroxyl, C,H;,, &c., being more negative (acidic) than alcohol radicles ; it is less acid, however, than the carboxylic hydroxyl contained in the true acids. Thus sodium phenoxide, C,H,-ONa, is formed when phenol is dissolved in NaOH, but phenol does not dissolve in Na,CO;. Again, they do not yield aldehydes (or ketones) and acids when oxidised, being comparable in this respect with the tertiary alcohols ; and when attacked by HNO, and H,SO,, they yield substitution-products, whereas the alcohols yield esters; thus, phenol yields tri-nitrophenol or picric acid, C,H,(NO,),-0H, and phenol-sulphonic acid, C5H,(OH)-SO,-OH. The phenols have a great tendency to produce coloured products of oxidation, and ferric salts generally colour them intensely. 744 PHENOL The phenols are frequently products of the dry distillation of complex organic substances, e.g. coal. They are also obtained by fusing the sulphonic acids with alkalies ; thus benzenesulphonic acid yields phenol ; C,H;‘S0O,0K + KOH = C,H;-OH + K,803. The formation of phenols through the diazo-reaction has been already noticed (p. 716). Another general method sometimes employed is the distil- lation of aromatic hydroxy-acids either alone or with lime (see Pyrogallol). The halogen-substituted benzenes are not attacked easily by alkalies, but when they contain nitro-groups they more readily exchange Cl for OH, forming nitro- phenols ; thus CgH,(NO,)Cl yields CsH,(NO,)OH. The greater the number of nitro- groups the more readily this change occurs. The same remarks apply to the amido- and nitramido-benzenes. Monohydric Phenols. (1) Monohydroxybenzenes.—Phenol, or phenic acid, or carbolic acid or hydroxybenzene, CgH;-OH, is extracted from that portion of the heavy oil of coal-tar which boils between 150° and 200°. This is allowed to cool, when it deposits crystals of naphthalene, and is then well stirred with caustic soda of sp. gr. 1:34. On standing, two layers are formed, the upper consisting of the higher homologues of benzene, and the lower of an aqueous solution of sodium phenoxide. This is diluted with water, and exposed to air, when tarry oxidation-products separate, and the liquid is neutralised by successive additions of H,SO,, which first precipitates more tarry matters, then cresol, and other homo- logues of phenol, and finally phenol itself as a light oil. It is purified by fractional distillation, the portion distilling between 180° and 190° being collected and artificially cooled, to crystallise the phenol. Phenol is present in small quantity in urine, and in the trunk, leaves, and cones of the Scotch fir. It may be produced by the action of hydrogen peroxide on benzene ; C,H;-H + HO-OH = C,H;-OH + HOH. Benzene may also be directly oxidised to phenol by mixing it with aluminium chloride and passing oxygen gas. Benzene- sulphonic acid, when distilled with fused potash, yields phenol— C,H;-S0,-OH + KOH = C,H,-OH + KHSO,. Properties of phenol.—Phenol crystallises in needles, often several inches long, of not unpleasant peculiar odour. It fuses at 43° and boils at 183°. Fused phenol is slightly heavier than water (sp. gr. 1-084 at 0°). It dissolves in 15 parts of water at 20°, and easily in alcohol and ether. It becomes pink or brown when kept, from the presence of some impurity. When two molecules of phenol (198 parts) are heated with one molecule (18 parts) of water, and cooled to 4°, six-sided prisms of phenol aquate, (C,H,;-OH).Aq, are obtained, which fuse at 16°. With 10 per cent. (19-8 parts) water, it forms the “‘ liquefied phenol’? used in medicine. The commercial carbolic acid crystals generally consist of the aquate, and soon become liquid when the bottle is placed in warm water. It has a great tendency to remain superfused after cooling, solidifying suddenly on opening the bottle. The homologues of phenol, which accompany it in coal-tar, do not form crystalline aquates. Carbolic acid blisters the skin; it is poisonous, and arrests fermentation and putrefaction, so that it is largely used as an antiseptic. MacDougall’s disinfectant is a mixture of phenol with calcium sulphite. Calvert’s disinfecting powder consists of clay, with 12 or 15 per cent. of phenol. When phenol vapour is passed through a red-hot tube, it yields benzene, toluene, xylene, naphthalene, anthracene, and phenanthrene. The aqueous solution of phenol gives a purple-blue colour with ferric chloride. With ammonia and chloride of lime, it gives a blue colour. With the mixture of mercuric nitrate and nitrous acid obtained by dissolving mercury in cold nitric acid, it gives a yellow precipitate, which dissolves with a dark-red colour in nitric acid. CHLOROPHENOLS 745 Sulphuric acid (concentrated), to which 6 per cent. of potassium nitrite has been added, gives a brown colour, changing to green and blue, when gently heated with phenol. This is Liebermann’s general reaction for identifying phenols. Bromine water added to an aqueous solution of phenol produces a pale yellow precipitate of 2 : 4 : 6-tribromophenol, C,H,Br,:OH, m.-p. 92°, which redissolves until the bromine is in excess. This affords an excellent qualita- tive and quantitative test for phenol. If the precipitate be warmed with water and sodium amalgam, sodium phenoxide is produced, which gives the smell of phenol when heated with dilute sulphuric acid. By passing phenol vapour over heated zinc-dust, it is converted into benzene ; CsH;-OH + Zn = C,H, + ZnO. This is a general method for the conversion of phenols into the corresponding hydrocarbons. Phenol forms a crystalline compound with COs, which is stable only under pressure, and may be obtained by heating salicylic acid in a sealed tube at 260° (cf. p. 620). C,H,(OH)-CO,H = C.H;-OH,COp. Potassiuwm- and sodiwm-phenol, or phenolates, CgsH;-OK, CgH;-ONa, are soluble crystalline bodies obtained by heating phenol with hydroxide or carbonate of the alkali (see p. 709). See also Salicylic acid (p. 608). Phenol is not attacked by acids, as alcohol is, yielding esters, but corresponding phenyl compounds are obtained by indirect processes. When phenol is heated with PCI,, it yields chlorobenzene and phenyl orthophosphate ; the formation of chlorobenzene proves the existence of OH in phenol ; C,.H;-OH + PCl; = POC], + C.H;-Cl + HCl. The phenyl orthophosphate results from the action of more phenol on the POCI, ; POC]; + 3C,H;0H + PO(C,H;0); + 3HCl. Phenyl hydrosulphide, or thiophenol, or phenyl mercaptan, C,H;‘SH, is formed by the action of phosphoric sulphide on phenol— 8C,H,OH + P.S; = 2C,H;SH + 2(C,H;);P0, + 3H,8. It has an offensive odour, and boils at 169°. Its extra-radicle hydrogen may be exchanged for metals, as usual with mercaptans. With mercuric oxide, it yields mercuric thio- phenol, (CgH;S),Hg. When mixed with ammonia and exposed to air, phenyl hydro- sulphide is converted into diphenyl disulphide, a crystalline solid; 2CsH,SH + O = (CgH5)oSe + HO. Diphenyl sulphide, (CgHs5)oS, is obtained by distilling sodium benzenesulphonate with P,S;. It is an offensive liquid, boiling at about 292°. Nitric acid converts it into diphenylsulphone or sulphobenzide, (CgHs)28O2, which is also produced by the action of sulphuric anhydride on benzene; 2Cs,H;H + 280; = (CgHs)o80. + HpSO,. Chlorophenols, C,H,Cl-OH, and the corresponding bromine and iodine substitution- products, are obtained by the action of those elements on phenol. Nutrophenols, CsH,4(NOz)-OH, dinitrophenols, CgH3(NOz)2OH, and trinitrophenol, CgH:(NOz)3-OH, are produced when nitric acid acts on phenol. The last is known as picric acid (v.1.). By reducing nitrophenols with tin and HCl, the NO, group is converted into the NH, group, and amido-phenols are produced. ODinitro- and trinitrophenols admit of a partial conversion of the NO, groups, so that amido-nitrophenols are formed. The antipyretic phenacetine is a derivative of 1: 4-amido-phenol and has the formula C,H,(OC,H;)(NHCH,CO), p-acetamidophenetol. Closely related to the amidophenols is a group of substances characterised by their powerful effect in increasing the blood pressure ; 1/;900 mgm. of adrenaline is active. Amongst the members, adrenaline or-adrenine, HOS CH (OH).CH, NACH, the active principle of the supra-renal gland, is the best known, and is a catechol deri- vative ; the para OH is essential, but not the other. The corresponding ketone is HO less active. Similarly constituted are epinine, HOY \\CH,.CH,.NHCH,, a ees 746 PICRIC ACID synthetic product, p-hydroxy-phenylethylamine, HOS CHa CHa NE, one of the active principles of ergot, and hordenine, HO< > CHle CHa N(CH) obtained from barley ; they all have similar physiological properties. Phenylethylamine, ie \\cH,.CH.NE,, and other bodies similar to the above, but without OH, are amongst the products of digestion and of the putrefaction of proteins, so that these groups appear to be of great physiological importance. Picric acid or carbazotic acid, or trinitrophenol, CgH,(NO,)3°OH, is best prepared by dissolving phenol (1 part) in strong sulphuric acid (1 part) and adding the solution of phenolsulphonic acids thus obtained to strong nitric acid (3 parts) by degrees. When the violent action is over, the mixture is heated on the water-bath as long as much red gas is disengaged. On cooling, a crystalline mass of picric acid is obtained, which is purified by dissolving in boiling water, filtering, and crystallising. It is deposited in yellow plates or prisms, which are sparingly soluble in cold water, but more easily on heating, imparting a bright yellow colour to a large volume of water; alcohol dissolves it readily. Its solution has an intensely bitter taste (whence its name), and stains the skin and other organic matters yellow, which is turned to account in dyeing silk and wool. When heated, the crystals fuse at 122°, with partial sublimation, and explode slightly at a higher temperature, in consequence of the sudden formation of gas and evolution of heat by the action of the NO, upon the Cand H. This nitration of phenol into picric acid may be represented by the equation— C,H;-OH -++ 3(HO-NO,) = CsH(NO,),0H + 3HOH. Picric acid is one of the very few acids which forms sparingly soluble potassium salts ; a cold saturated aqueous solution of picric acid is even a better test for potassium than is tartaric acid, giving, especially on stirring, a yellow adherent crystalline preci- pitate of potassium picrate, CgH.(NO,);0K. This salt explodes violently when heated or struck, and has been used as anexplosive. Ammonium picrate is also a very explosive salt. Picric acid precipitates several of the alkaloids. An alcoholic solution of picric acid forms crystalline compounds with several hydrocarbons in alcoholic solution, particularly with benzene, naphthalene, and anthracene. Reducing-agents, such as glucose, in alkaline solutions, convert picric acid into picramic acid, CsH»(NOz)o(NH2)OH, which forms red salts. Gently heated with solution of chlorinated lime, picric acid yields chloropicrin, or nitrochloroform, C(NOg)Cl3, recognised by its pungent tear-provoking odour (p. 682). Picric acid is a very common product of the action of nitric acid upon organic substances ; indigo, silk, and many resins furnish it in considerable quantity, especially the fragrant red resin known as Botany Bay gum, obtained from one of the grass-trees of New South Wales, which is sometimes used for preparing picric acid. It is said that picric acid is used as a hop-substitute in beer ; its presence would be shown by the fast yellow colour imparted to a thread of white wool soaked in the warm liquid. The constitution of picric acid is expressed by the orientation [OH : (NO2)3 = 1:2:4: 6]; this follows from the fact that it can be obtained by oxidising symme- trical trinitrobenzene with potassium ferricyanide, a change which results in the sub- stitution of an OH for a hydrogen atom. A little consideration will show that this hydroxyl group can only take up a position between two nitro-groups if the trinitro- benzene is the symmetrical one (p. 565). Picramic acid, or 2-amido-3 : 4-dinitrophenol, CgH»(NOs)o(NH2)OH, is prepared by reducing ammonium picrate in alcoholic solution by passing hydrogen sulphide, evaporating to dryness, and decomposing the ammonium picramate with acetic acid ; CeHo(NOz)z-ONH, + 3H,S = CgHo(NOe)o(NH,)ONH, + 2H,O + 38. The picramic acid crystallises in red needles, which fuse at 165°. It is soluble in water and alcohol, forming red solutions, which become blood-red on adding an alkali. The change of the yellow colour of potassium picrate to the dark red of potassium picramate by tke CRESOLS—NAPHTHOLS 747 action of a reducing-agent in the presence of excess of potash, is employed in the exami- nation of urine for the detection and estimation of glucose, which easily converts the picrate into picramate when heated. The picramates of potassium and ammonium form ,dark-red crystals. ; Phenol-sulphonic, CsHs(OH)SO,OH, and disulphonic, Cg5H,(OH)(SO,0H)o, acids, are obtained by dissolving phenol in strong sulphuric acid, SO,OH-OH. Ortho- phenolsulphonic acid rapidly changes by migration of the OH group, into the para-acid when warmed. The antiseptic aseptol is a solution of phenolsulphonic acid. The sodium salt of di-iodo-(para)phenolsulphonic acid, C,H,I,0H-SO,OH, has lately’ been introduced under the name of sozoidol as an antiseptic ; it is said to be as effective as iodoform, and has no smell. Cresols, or methyl-phenols, or hydroxytoluenes, C,H,(CH,)OH, accom- pany phenol in coal-tar. The coal-tar kreosote is a mixture of phenol and cresol. The cresols may be prepared by dissolving the corresponding toluidines in sulphuric acid, adding potassium nitrate, and distilling by steam; C,H,(CH,)NH, + HNO, = C,.H,(CH,)OH + 2H,0 + N,. Orthocresol is solid, fuses at 31°, and boils at 188°. Metacresol is liquid, and boils at 201°. Paracresol is solid, fusing at 36°, and boiling at 198°; they are metameric with benzyl alcohol, C,H;-CH,-OH. Paracresol occurs in urine, and is a product of the putrefaction of albumin ; its dinitro-deriva- tive is a yellow dye, Victoria orange. Meta- and para-cresol give a blue colour with ferric chloride. The presence of the OH group in the cresols protects the methyl group from the easy oxidation which characterises the methyl group of the toluenes. But the sub- stitution of a radicle for the H of the OH group destroys the protective influence, and the methyl cresols Cg;H,(CH3)-OCH, are easily oxidised to methoxy-benzoic acids, CgH,(COOH)-OCH3. Creoline and lysol are sold as disinfectants ; they are solutions of crude cresol in soap and water. c Methylisopropylphenols.—Thymol Carvacrol (see p. 678). (2) Monohydroxynaphthalenes.—Naphthols, (C,)H,-OH, are prepared from naphthalenesulphonic acids or naphthylamines by the reactions described on pp. 744, 716. «a-Naphthol melts at 94° and boils at 280°; (3-Vaphthol melts at 122° and boils at 286°. The latter is the more soluble in water, and is used as an antiseptic.t The naphthols are true phenols, but they resemble the alcohols more nearly than the benzene phenols do. They give rise to a number of important dyestuffs, which are chiefly nitro-derivatives and diazo-derivatives. Thus, dinitro-a-naphthol, CyoH5(NOo).‘OH, is Martius’ yellow or naphthalene yellow, and the sodium salt of its sulphonic acid is naphthol yellow, or fast yellow. The photographic developer eikonogen is sodium amido- B-naphthol sulphonate, Cy)>H;(OH)(NH.2)(SO;Na). Naphtholsulphonic acids are very numerous and a large number has been prepared both for settling the constitution of naphthalenes and for use as dyestuff components (p. 718), for which purpose the most important are the | : 4-monosulphonic acid, C,oH,(OH)-SO3H (Neville and Winther’s acid) and the 2 : 3: 6- and 2: 6: 8-disulphonic acids, CjgH;(OH)(SO3H)., (R. and G. acids). Dihydric Phenols. Dihydroxybenzenes.—Pyrocatechol, 1 : 2-C,H,(OH)s, obtained by fusing potassium phenol-sulphonate with potash, C,H,(OH)$0,0K + KOH = 0,H,(OH), + K.SO,, is found among the products of distillation of catechu, an astringent body ex- tracted by boiling water from the inner bark wood of Acacia catechu and used intanning. Kino, asimilar extract from certain varieties of Pterocarpus, an Indian tree of the same botanical order, also furnishes it ; as do most vegetable extracts which contain tannin. The leaves of the Virginia creeper, a plant of the vine order, contain pyrocatechol. It is present in crude pyroligneous acid distilled from wood, and is said to be formed when cellulose, starch, 1 Betol, or B-naphthyl salicylate, CsH4(OH)COOC,,H., is used in medicine like phenyl salicylate (salol). 748 RESORCINOL or sugar is heated between 200° and 280°. Pyrocatechol crystallises.in prisms which fuse at 104° and boil at 245°, though it may be sublimed (below its fusing-point). It is very soluble in water, alcohol, and ether, It is a reducing-agent, precipitating Cu,O from alkaline cupric solutions on warming, and reducing silver nitrate in the cold. In presence of alkalies it absorbs oxygen from the air, becoming brown. With ferric chloride, it gives a green colour, changed to red by alkalies. Nitric acid oxidises it to oxalic acid. It has weak acid properties, and was formerly called oxyphenic acid. Guaiacol, or methylpyrocatechol, CsH4(OH)OCH3;, may be obtained by distilling guaiacum, a resinous exudation from the West Indian tree called lignum mite. The distillate is dissolved in ether, and mixed with alcoholic potash, which produces a crystalline mass of potassium guaiacol, which is washed with ether and decomposed by dilute sulphuric acid. It is also produced by heating to 180° a mixture of pyro- catechol, potassium methyl sulphate, and potash— CsH.(OH), + KCH,SO, + KOH = C,H,(OH)OCH; + K,SO, + HOH. Beech-wood kreosote also contains it. Guaiacol forms colourless crystals, m.-p. 28°, and b.-p. 203°. It mixes sparingly with water, but easily with alcohol. It gives an emerald-green colour with ferric chloride, and acts as a reducing-agent in alkaline solutions. When heated with hydriodic acid, it yields methyl iodide and pyrocatechol ; C,H,(OH)OCH, + HI = C,H,(OH), + CHsI. It has the properties of a weak acid. When potassium guaiacol is heated with methyl iodide, it yields veratrol or methyl guatacol; CgH,-OK-OCH, + CH3I = C,H,(OCH3). + KI. Veratrol is an aromatic liquid, which may also be obtained by heating with baryta the veratric (dimethyl-protocatechuic) acid, extracted from sabadilla seeds ; CsH;(OCHs)2‘CO.H + BaO = CgHy(OCH3)2 + BaCO3. Wood-tar kreosote contains phenol, cresol, phlorol, CgH3(CH3)2°OH, guaiacol, and creosol, CgH;(OCH;)(CH;)OH. This last is obtained from that portion of the tar which distils at 221°, by dissolving it in ether, and adding very strong KOH, which precipitates potassium-creosol, from which creosol is separated by H,SQ,. It is an aromatic liquid, which yields acetyl-creosol, CgHg(OCH3)CHg(OC.H30), when treated with acetyl chloride, and this, when oxidised by permanganate, becomes acetyl-vanillic acid, CgH3(OCH3)CO,H(OC,H30), from which vanillic acid (p. 621) may be obtained by treatment with NaOH. Resorcinol, 1: 3-C,H,(OH),, was named from resin, being obtained from several bodies of that class, and orcin, with which it is homologous. It is now prepared on a large scale for the manufacture of colours by the action of caustic alkalies on benzene-disulphonic acid. This acid is prepared by gradually adding benzene (4 parts) to fuming sulphuric acid, sp. gr. 2-244 (15 parts), gently heating for some hours, and finally at 275° ; CyH,g + 2H,8O, = Cy.Hy(SO2.0H). + 2H,0. The 1: 3-benzene-disulphonic acid forms a deliquescent crystalline mass on cooling. This is dissolved in a large quantity of water, neutralised with lime, and strained from the calcium sulphate formed by the excess of sulphuric acid. The solution of calcium benzene-disulphonate is decomposed by NasCO3, the precipitated CaCO filtered off, the solution evaporated to dryness, and the residue of sodium benzene-disulphonate fused with 2} times its weight of caustic soda, at 270°, for eight or nine hours ; CgHs(SO2'ONa), + 2NaOH = CyH,(OH). + 2803;Nag. The fused mass is dissolved in hot water, and boiled with HCI till all the SO, is expelled. The resorcinol is then extracted from the cooled aqueous solution by agitation with ether, and is obtained in crystals when the ether is distilled off. Resorcinol is obtained in considerable quantity by distilling eatract of Brazil- wood, a dye made by boiling the wood of Cesalpinia braziliensis with water, and evaporat- ing the solution. It was originally prepared by fusing with potash the gum-resin known as galbanum, obtained in Turkey and the East Indies as an exudation from the Galbanum officinale, an umbelliferous plant, Other gum-resins obtained from plantg ORCINOL 749 of the same order also yield resorcinol when fused with potash ; such as ammoniacum, assafotida, sagapenum, all more or less foetid-smelling medicinal bodies imported from the East. When these gum-resins are distilled alone, they yield wmbelliferone, CoHgQg, or .CgH,(CHO),CO, which is converted into resorcinol when fused with potash. Resorcinol crystallises in prisms or tables which fuse at 118°, and boil at 276°, but may be sublimed at a much lower temperature. It has a sweet taste, and is easily soluble in water, alcohol, and ether. Its solution gives a violet colour with ferric chloride. Exposed to air, it absorbs oxygen and becomes brown. Ammoniacal copper and silver solutions are reduced when heated with it. The most characteristic test for resorcinol consists in heat- ing it with phthalic anhydride (p. 628), dissolving in dilute sulphuric acid, and adding ammonia, when a splendid green fluorescence is produced, due to the formation of resorcin-phthalein, or fluorescein (q.v.). The resorcinol of commerce sometimes contains thioresorcinol, CgH,(SH)2, which may be obtained by reducing benzenedisulphonic chloride, CgsH4(SO2Cl)o, with tin and hydrochloric acid ; it melts at 179°. Styphnic acid, or trinitroresorcin, CeH(NO2)3(OH)., so named from its astringent taste (oripyvoc), is prepared from resorcinol just as picric acid is prepared from phenol, and by the action of nitric acid on those gum resins which yield resorcinol on fusion with potash. Styphnic acid forms yellow six-sided prisms or tables, sparingly soluble in cold water, but dissolving in alcohol and ether. It fuses at 175°, and explodes when strongly heated, though it sublimes when heated gradually. It is a dibasic acid, and forms salts which are more explosive than the picrates. Ferrous sulphate and lime-water give a green colour with styphnic acid, and a blood-red with picric acid. Dinitroso-resorcinol, CgH2(NO).(OH)2, produced by the action of nitrous acid on a solution of resorcinol, is a dyestuff known as fast green or solid green. Hydroquinone, or quinol, is the third (1:4) dihydroxybenzene ; it will be considered under quinone. Orcin, or orcinol, or 1:3: 5-dihydroxytoluene, C,H,CH,(OH)., is prepared from certain lichens, which are used by dyers for preparing the colours known as litmus, cudbear, and archil ; such as Lecanora tar- tarea, or rock-moss, Roccella tinctoria, or orchella weed, and others. The lichens are boiled with lime and water for some time, the solution filtered, evaporated to one-fourth, treated with CO, to precipitate the lime, and shaken with ether to extract the orcin. Some orcin appears to exist ready formed in the lichens, but the greater part of it is formed by the action of the lime and water upon certain acids, which may be extracted from the lichens by lime in the cold, and obtained as gelatinous precipitates by adding HCl. Thus, orsellinic acid, C,H,CH,(OH),CO,H, when boiled with lime, yields carbon dioxide and orcin, CsH;CH,(OH),. Erythric acid, Co9H2204o, yields orcin and erythrite (p. 591) ; evernic acid, Cy7Hy 607, from the lichen Evernia prunastri, yields orcin and everninic acid, CyHyo0x. Lecanoric acid, C,gH,,O7-H,O, when boiled with water, yields two molecules of orsellinic acid, CgH,Ox. Orcin is also produced by the action of fused potash on aloes, the juice of a plant of the Liliaceous order (dragon’s blood, obtained from the same order, yields phloro- glucol). Orcin may be prepared from toluene, CsH,'CH3, by converting it into (ortho)- chlorotoluenesulphonic acid, and fusing this with excess of potash— C,H,Cl(CH3)-SO0;H + 2KOH = KCl + KHSO, + CgH3CH;(OH)o. Orcin crystallises in colourless six-sided prisms (with 1H,O), melting at 58°, or when anhydrous at 107°, and boils at 289°. It tastes sweet and dissolves in water, alcohol, and ether ; ferric chloride colours it violet. It forms a crystalline compound with a molecule of ammonia, and when its solution in ammonia is exposed to air, it absorbs oxygen, becoming purple, and yielding with acetic acid a red colouring-matter, orcéin, C7H,O, + NH; + 30= 2H, O + C;H;NOs. This substance is the chief colouring-matter of the dyes prepared from lichens, by mixing 750 PYROGALLOL them with lime and urine (to furnish ammonia), and exposing them to the air for some weeks. The colour is pressed out, and made into cakes with chalk or plaster of Paris. Orcéin is sparingly soluble in water, but dissolves easily in alcohol and in alkaline liquids, yielding purple solutions which are reddened by acids, oreéin being preci- pitated. Trihydric Phenols. Trihydroxybenzenes.—Pyrogallol, 1:2:3-C,H,(OH),, formerly called pyrogallic acid, is a phenol obtained by heating gallic acid— CsH2(OH);-CO.H = CyH3(OH)3 + COs. To prepare it, gallic acid is heated with 24 parts of water in a digester (autoclave) at 210° to 220° for half an hour. The solution thus obtained is decolorised by animal charcoal and crystallised. Pyrogallol may be sublimed from nut-galls heated to about 215°, when the tannin is decomposed into pyrogallol and carbon dioxide ; Cy3H,07-CO,H + H,0 = 2CsH,(OH), +2CO,. It may be obtained synthetically by fusing chlorophenol- sulphonic acid (1: 2:3) with potash— CsH,Cl(OH)SO,H + 2KOH = C,H;(OH); + KCl + KHSO;. Pyrogallol crystallises in fine needles, which are felted together in light white tufts. It fuses at 132° and boils at 210°. It is very soluble in water (24 parts), alcohol, and ether. When its solution is mixed with an alkali, it at once absorbs oxygen from the air, becoming brown, and forming a carbonate, acetate, and other products, a little carbonic oxide being evolved. A mixture of potash and pyrogallol is employed to absorb oxygen in gas analysis. Pyrogallol is a strong reducing-agent, precipitating silver and mercury in the metallic state ; its action on silver-salts renders it useful in photography and in hair-dyeing. A pure ferrous salt gives no colour with pyrogallol, but a trace of ferric salt causes a blue coloration, while a pure ferric salt gives a red colour. When heated with phthalic anhydride, it yields pyrogallol phthalein, or gallein, CopH, )O7, which is used as a red dye. When chlorine is passed through a cooled solution of pyrogallol in acetic acid, trichloro-pyrogallol, CgCl,(OH)3, is obtained, and may be crystallised in needles, melting at 177°. Phloroglucol, 1:3: 5-CgsH;(OH)3;, was first obtained from a glucoside called phlorizin, existing in the bark of the apple-tree ; the glucol refers to its sweet taste. It is also made, like resorcinol, by fusing certain vegetable extracts and gum-resins with caustic potash. It is thus obtained from gamboge, the resinous juice of Gambogia gutta (Ceylon), from dragon’s blood, the resin of Dracena draco, from kino (p. 747), catechu, and from the yellow dye-wood, fustic. The residue of the preparation of extract of fustic with potash and a little water, dissolved in water, acidified with sulphuric acid, and shaken with ether, which extracts phloroglucol and protocatechuic acid : the ether is distilled off, and the aqueous solution of the residue mixed with lead acetate to precipitate the protocatechuic acid. The lead is precipitated by H,S, and the phloroglucol again extracted by ether. It may also be prepared by fusing resorcinol (1 part) with soda (6 parts) until the mass has a light chocolate colour, when it is treated as above, omitting the separation of protocatechuic acid. Phloroglucol is formed by fusing 1: 3 : 5-benzene-trisulphonic acid, CgH;(SO2°‘OH)s, with soda, or better by hydrolysing 1 : 3 : 5-triamido-benzene with HCl. It crystallises in prisms with 2Aq, which it loses at 100°. It fuses at 218°, and may be sublimed ; it dissolves easily in water, alcohol, and ether, and reduces alkaline cupric solution. Ferric chloride gives a violet colour. Its solution in hydrochloric acid stains wood violet-red, and is an excellent test for woody tissue. Alkaline solutions of phloroglucol are oxidised by air, and become brown. When dissolved in ammonia, it yields a crystalline base ; CsH,(OH),; + NH; = H,O + CgsH,NH,(OH)» (phloramine). Other phenols do not so readily exchange OH for NHp. When phloroglucol is dissolved in acetic acid and treated with potassium nitrite, at a low temperature, it yields, on addition of excess of potash and alcohol, green needles of a very explosive body, which is the potassium salt of tri-nitroso-phloro-glucol, INOSITE 751 C.(NO);(OK),. When this is gradually added to a mixture of nitric and sulphuric acids, it is converted into trinitro-phloroglucol, Cy(NO»)3(OH)3, which crystallises in yellow explosive prisms, and dyes wool and silk yellow like picric acid. It is a tribasic acid, and forms three series of coloured salts. In most of its reactions, phloroglucol behaves as symmetrical tri-hydroxybenzene ; but in the remainder it behaves as a triketone, yielding, for instance, a trioxime, CgH,(N-OH);, with hydroxylamine (p. 648). From this it seems probable that phloro- glucol exists in tautomeric forms (p. 735), namely, C(OH)-CH CO-CH, e econ and CHC * Sco. C(OH):CH CO-CH,” The first of these would represent a trihydroxybenzene (the enol form) containing a tertiary benzene ring, and the latter a triketone of hexamethylene, containing a secondary benzene ring. 1:2: 4-Trihydroxybenzene is called hydroxyhydroquinone. Inosite, CgH,20, + 2H,0. This compound was formerly included among the sugars under the name of flesh-sugar, but inasmuch as (1) it does not behave as a reducing agent (see Sugars), (2) it yields a hexanitrate, CsH,(ONO.),, when dissolved in strong HNOs, and (3) it is converted into benzene and tetriodophenol when heated at 170° with HI, it is now known to be a cyclohexane derivative, probably hexa- hydroxy-cyclohexane, CgH,(OH),. It is obtained from the juice of beef ; the chopped heart or lung of the ox is exhausted with water, the liquid pressed out, mixed with a little acetic acid, and heated to boiling. The liquid filtered from the coagulated albumin is mixed with lead acetate, filtered, and basic lead acetate added; this precipitates a lead compound of inosite, 2Cg,H20,.5PbO, which is to be suspended in water and decomposed by H.S, when the inosite passes into solution. The lead sulphide is filtered off, the solution evaporated on the water-bath, to a syrup, and mixed with ten volumes of alcohol and one of ether, when the inosite is precipitated. It forms prismatic crystals, which are sweet and soluble in 6 parts of water. It is but slightly soluble in weak alcohol, and insoluble in absolute alcohol and in ether. The crystals effloresce in air, and * become anhydrous dt 100°. Inosite is optically active, occurring in the usual modi- fications. It undergoes lactic fermentation and is oxidised by nitric acid to oxalic acid. Inosite may be identified by moistening it with dilute nitric acid, evaporating almost to dryness, and adding ammoniacal calcium chloride, which produces a rose colour. Inosite solution mixed with a drop of mercuric nitrate gives a yellow precipitate, which becomes red when heated. The proportion of inosite obtained from flesh is very small; many vegetables contain it more abundantly. The unripe French bean yields 0-75 per cent. of inosite ; walnut-leaves in August, 0-3 per cent. It is also present in the leaves of ash and vine ; grapes contain it, so that inosite is found in wine. Unripe peas, asparagus, and dandelions contain inosite. From these vegetables it may be extracted as from flesh. It has been found in urine in cases of Bright’s disease. Hexahydroxy-benzene, Cg(OH)g, has been obtained by a circuitous process. It is crystalline, sparingly soluble in cold water, alcohol, and ether; the solutions absorb oxygen, becoming violet, and reduce silver nitrate. It is converted into benzene by distillation with zinc-dust. Hexahydroxydiphenyl, CgH:(OH)3-CgH2(OH)s;, is the parent of the quinone coeru- lignone, O: CgH,(OCH3)2°‘CgH2(OCH3)2: 0, which is obtained during the refining of crude acetic acid from wood by K,Cr,0, ; it is soluble in ordinary solvents, but , crystallises from phenol in blue needles. It was formerly called cedriret in allusion to its interlaced crystals (cedria, pitch; rete, a net). Tin and HCI convert it into hydrocoerulignone, HO-CgH2(OCHs3)o°CgH2(OCH;)2-OH, which is colourless, and yields hexahydroxydiphenyl when boiled with HC]. Hexahydroxydiphenyl dissolves in potash with a blue colour. CH. XII. QUINONES Quinones are formed from aromatic hydrocarbons by the substitution of (O,)” for H,, and are therefore products of oxidation. 752 QUINONE Quinone, C,H,(0,)”, or benzoquinone, may be obtained by heating benzene with chromyl chloride, when HCl is evolved and a brown solid compound produced; this is decomposed by water with formation of quinone, which remains dissolved in the excess of benzene— (1) CgHg + 2Cr0,Cl, = 2HC1 + CgHy(Cr0sCl)p ; (2) CsH,(Cr0,Cl), + H,O = C.H,(0,)” + Cr0, + 2HCL. Many benzene derivatives also yield quinone when oxidised. It is best prepared by oxidising aniline with potassium dichromate and sulphuric acid. One part of aniline is dissolved in a mixture of 8 parts of sulphuric acid with 30 parts of water, and 34 parts of powdered potassium dichromate are slowly added to the cooled solution, which is then heated for some hours at about 35°. After cooling, the liquid is shaken with ether, which extracts the quinone, and leaves it in golden yellow crystals when evaporated. It is also obtained when quinic acid is oxidised with manganese dioxide and sulphuric acid ; C,H;(OH),CO,.H + O, = CgH,(O0).” + COg + 4H,0. Many plant-extracts yield quinone when thus treated. Quinone crystallises very easily in yellow prisms or plates, which sublime even in the cold, and fuse at 116°, emitting a characteristic odour, and subliming in long golden needles in the presence of steam. It is sparingly soluble in cold water, but dissolves in hot water, and crystallises on cooling ; alcohol and ether dissolve it. Its solution stains the skin brown. Quinone acts as an oxidising-agent, liberating iodine from hydriodic acid, and becom- ing converted into hydroquinone, or quinol, Cg,H,(OH)., which is ] : 4- dihydroxybenzene. In many reactions quinone behaves like a diketone; for instance, with hydroxylamine it yields both a monoxime, O:C,H,:N-OH, and a dioxime, HO-N : C,H, : N-OH (cf. p. 648). The formula “Oe See O: as Dero has therefore been proposed (by Fttig) for quinone. It has been pointed out, however, that if quinone contain true ketone groups, it should yield a secondary alcohol HOHE Doron when reduced, instead of, as is actually the case, the quasi-tertiary alcohol, hydroquinone, HOC? \c-on.t Moreover, when substituted quinones react with PCl;, each of the O atoms is exchanged for one Cl atom instead of two, as would be expected if the O were doubly linked to carbon. These considerations led Graebe to the ‘‘ peroxide ”’ formula, of 6-0= Se x for quinone. Fittig’s formula is, however, preferred. That the oxygen atoms in quinone occupy the 1 : 4-position is shown by its easy conversion into 1 : 4-dihydroxybenzene, and by the fact that its dioxime yields ] : 4-diamidobenzene when reduced. Quinonemonoxime appears to be identical with the compound obtained by the action of nitrous acid on phenol, nitroso-phenol, CgH,(OH)NO, also obtained by treating nitrosobenzene, CsH;NO, with NaOH. Hydroquinone is a constant product of the action of reducing-agents on quinone, and is best prepared by passing SO, through a warm saturated solution of quinone, when it is deposited in six-sided prisms, which fuse at 169° and sublime in mono- clinic tables, so that hydroquinone is dimorphous. It is moderately soluble in water, and easily in alcohol and ether. Hydroquinone is distinguished from other dihydroxy- benzenes (p. 747) by the action of oxidising-agents, such as FeCl,, which converts it 1 Against this argument it may be urged that a ketone may give rise to a tertiary alcohol by reduction, as, for example, in the formation of pinacone from acetone (p. 588), CHLORANIL 753 into fine green metallic prisms of green hydroquinone, or quinhydrone, CeH,02'CgH,(OH)>, also obtained by mixing aqueous solutions of quinone and hydroquinone. This is sparingly soluble in cold water, but dissolves in hot water to a brownish red solution, which deposits the splendid green crystals on cooling. It dissolves in alcohol and ether with a yellow colour. It is readily dissociated into quinone and hydroquinone. Hydro- quinone occurs among the products of distillation of the succinates, and has been produced from ethyl succinate by the following steps: Ethyl succinate, CoH,(CO2C2H5)o, acted on by sodium, yields ethyl succinyl-succinate, CO0C,H;,—CH—CO — CH, CH,—CO—CH—COO0C,H, ; when this is treated with bromine, hydrogen is abstracted, leaving ethyl quinol-dicar- boxylate, CgH4Oo(CO2‘CoHs)o. The acid obtained from this ethereal salt, quinol-dicar- boxylic acid, C5H,0.(CO,H)o, crystallises in needles, and yields a blue colour with ferric chloride. When distilled, it yields hydroquinone, CgH,(OH):, and 2CO,. As ethyl succinyl-succinate may also be obtained by the action of sodium on ethyl bromaceto- acetate, hydroquinone may be built up from acetic acid. It is used as a photographic developer. Tetrachloroquinone, or chloranil, CgCly(O2)”, is a frequent product of the action of chlorine or of a mixture of KC]O, and HCl upon aromatic compounds, such as phenol, aniline, salicin, and isatin. It may be prepared from quinone by the action of KCI1O3 and HCI, but more cheaply from phenol, by mixing it with potassium chlorate (4 parts) and adding it gradually to hydrochloric acid diluted with an equal volume of water. The mixture is gently heated, and more chlorate added, when a yellow mixture of trichloroquinone, CgHCl,(02)”, and tetrachloroquinone is precipitated. This is treated with sulphurous acid, which reduces the quinones to hydroquinones. The ¢etra- chlorohydroquinone, CgCl4(OH)s, is insoluble in water, whilst the trichlorohydroquinone, CsHCl;(OH)., dissolves. The former is then oxidised by strong nitric acid, which converts it into chloranil. This body, which is used in colour-making, is yellow, insoluble in water, and sparingly soluble in alcohol ; ether and benzene dissolve it, and deposit it in yellow crystals which may be sublimed. It is unattacked even by concentrated acids. Potash dissolves it with a purple colour, and yields purple crystals of potassium chloranilate ; C,Cl,O, + 4KOH = 2KCl + 2H,O + C,Cl,(OK),02. By dissolving the sparingly soluble potassium salt in hot water, and adding HCl, a red crystalline body is precipitated, which is chloranilic acid, CeClp(OH)202.Aq. Itis soluble in water, with a violet colour, but sulphuric or hydrochloric acid precipitates it from the aqueous solution. Bromanil, C,Br,(O2)”, has also been obtained from phenol. 0 NCI Quinone chlorimides, CgHZ and C,H, , are obtained by the action of el NCI chlorinated lime on 1 : 4-amidophenol and 1 : 4-diamidobenzene respectively. By reaction of quinonechlorimide with phenols, indophenols are obtained ; these are also formed by the oxidation of a mixture of phenol and a p-amidophenol. The typical indophenol is O : CsH, : N-C.H,-OH. Quinonechlorimide and a dialkyaniline react to form an indoaniline. These com- pounds are dyestuffs and are manufactured by oxidising a mixture of a paraphenylene- diamine and a phenol. Thus phenol blue, O: CgH, : N-CgH,'N(CH3)o, is made by oxidising a mixture of as-dimethylparaphenylenediamine and phenol. By hydrolysis with H,SO, it yields quinone and the original diamine. By substituting an aniline for the phenol in the foregoing reaction, an indamine is produced. Phenylene blue, NH: CeHy: N-C,H,-NH;, is the compound obtained when a mixture of paraphenylenediamine and aniline is oxidised. Naphthoquinones, C,oH¢(O2)”.—a-Naphthoquinone [0 : O = 1:4] is a true para- quinone, possessing the characteristic yellow colour, volatility, and pungent odour of these quinones, and being reduced to naphthohydroquinone, CyoHg(OH),. It is prepared by dissolving naphthalene (1 part), CjoHg, in glacial acetic acid (6 parts) and oxidising with chromic anhydride (3 parts), dissolved in glacial acetic acid (2 parts). The mixture is boiled, and distilled after adding more water, when the naphthoquinone passes over with the steam. _It is insoluble in water, sparingly soluble in cold aleohol, 48 754 ANTHRAQUINONE but dissolves in hot alcohol and in ether, crystallising in yellow tables, which fuse at 125°, and sublime below 100°. Alkalies dissolve it, and it is oxidised by strong nitric acid into phthalic acid, CsH,(CO2H)o. ; B-Naphthoquinone, [0:0 = 1: 2}, is an example of an ortho-quinone, possessing the red colour, the non-volatility and the lack of odour characteristic of these. It is obtained by oxidising 1 : 2-derivatives of naphthalene. pen. ; ; Anthraquinone, CoH Pete is prepared by dissolving anthra- co cene, C,,H, , in glacial acetic acid, and adding chromic anhydride to the hot solution ; on adding water, the anthraquinone is precipitated and may be purified by sublimation ; it has no quinone odour. It sublimes in yellow needles, which are sparingly soluble in alcohol and ether, but dissolve in hot benzene and in nitric acid. It fuses at 285° and boils at 382°. Potash does not dissolve it, but, when fused with KOH, it yields potassium benzoate. Sulphurous acid does not convert it into a hydroquinone, nor does hydriodic acid, but the latter reduces it to anthracene; as inter- mediate products of the reduction there are obtained, oxanthranol, foe \ fr. CoHaC Pots and anthranol, CoHaC | Dee Hence CH(OH) CH anthraquinone is more nearly a true diketone (diphenylenediketone) than is benzoquinone. Anthraquinone may be synthetically prepared by heating phthalyl dichloride with benzene and zinc-dust ; CoH. a C,H Z sae ae + ZnCl. H + CgHg + Zn = CoHy et tg. mCly + Hy. : *\co-c1 \co” This synthesis shows that the CO groups must be attached to one of the benzene rings in the ortho-position to each other. That this is the case also with the other benzene ring is seen from the fact that when bromanthraquinone, CgH3Br(CO),CgH4 (synthesised, as above, from bromophthalyl chloride, CsH,Br(COCl)s), is oxidised, the product is phthalic acid, not bromophthalic acid, showing that the brominated- ring has been removed, and that the CO groups must have been attached to the non- brominated-ring in the ortho-position. Anthraquinone is important chiefly. as the source of artificial alizarin. Alizarin, or 1 : 2-dihydroxyanthraquinone,’ C,H,(CO),.C,H.(OH)., may be prepared from anthraquinone by treating it with bromine, which converts it into dibromanthraquinone, C,H4(CO),.C,H,Br,, and when this is heated to about 180° with potash, it yields potassium alizarate, C,H ,(CO),C,H,(OK),; from the aqueous solution of this, hydrochloric acid precipitates alizarin. Alizarin, one of the chief vegetable dyes, was formerly obtained exclu- sively from madder, the root of Rubia tinctorum, imported from the South of France and the Levant. It does not occur ready formed in the plant, but is produced by the decomposition of ruberythric acid, C.,H,,0,4, which may be extracted from madder root by cold water, and crystallises in yellow prisms. When the root is allowed to ferment, or is treated with H,SO,, ‘the ruberythric acid is hydrolysed into alizarin and glucose, CopHegO14 + 2H20 = Cy4H,O4 + 2CgH20c. Alizarin is prepared on a large scale from anthraquinone by converting it into the sulphonic acid and fusing this with caustic soda. The anthraquinone is made by treating anthracene, in leaden tanks, with potassium dichromate and diluted sulphuric acid, the reaction being completed by boiling. The anthraquinone is dissolved in strong sulphuric acid and re-precipitated by water, * Anthracene derivatives are orientated similarly to those of naphthalene (p, 571). ALIZARIN 755 which retains the impurities in solution. After being washed and dried, it is heated for eight or ten hours at 160° with fuming sulphuric acid in an iron pot, being con- stantly stirred ; on diluting with water, any unaltered anthraquinone is precipitated, and anthraquinone mono- and di-sulphonic acids, CsH,(CO),CsH;(SO,H), and C,gH3(8O3;H)(CO).C,H,(SO;H), remain in solution. The mixed sulphonic acids are neutralised with lime, and the calcium salts are decomposed by sodium carbonate. The concentrated solution of the sodium salts is heated with caustic soda and a, little sodium chlorate, in a closed iron boiler, at about 180° for twenty-four hours, when a purple solution is obtained, containing the alizarate and anthrapurpurate of sodium. The sodium anthraquinone mono- sulphonate is first decomposed by the NaOH yielding sodoxyanthraquinone— CeH4(CO)sCgH3:80,Na + 2NaOH = CyHy(CO).CsH,(ONa) + 80,Na, + HO The sodoxyanthraquinone is then oxidised, by the oxygen from the chlorate, in presence of the excess of NaOH, into sodium alizarate— C,H,(CO).C.H3(ONa) + O + NaOH = C,H4(CO),CgH,(ONa), + H,O. The sodium anthraquinone disulphonate yields sodium anthrapurpurate— CgH,(SO3Na)(CO).CsH,(SO,Na) + 7NaOH = CsH;(ONa)(CO).CsH»(ONa), + 2Na,SO, + 4H,0. The solution is run into dilute sulphuric acid when a mixture of alizarin and anthra- purpurin is obtained as a yellow precipitate. Alizarin forms orange prisms (with 3H,O) very sparingly soluble in water, but easily soluble in alcohol and ether, and becomes red when dried. It fuses at about 290°, and may be sublimed. It dissolves in strong H,SO, with a deep-red colour, and is precipitated by water. It acts like a dibasic acid, dissolving in alkalies to purple solutions, which give purple- blue precipitates with salts of alkaline earths. The insolubility and the brilliant colours of the alizarates are of great value in dyeing and calico- printing. Alizarin gives red precipitates (madder lakes) with salts of Sn and Al, and a dark violet with salts of iron. That alizarin is an adjacent dihydroxyanthraquinone follows from the fact that it can be synthesised from phthalic anhydride and 1 : 2-dihydroxybenzene (pyrocatechol) in the presence of sulphuric acid at 150°. That the OH groups occupy the 1:2 (or 3:4 or 1’: 2’ or 3’: 4, all these being the same in value as 1 : 2) position follows from the fact that alizarin yields two mono-substitution products in which the sub- stituent is in the same ring as the OH groups; if the hydroxyl groups occupied the 2: 3-positions this would not be possible, since the positions 1 and 4, which would then be vacant, are of the same value. Anthrapurpurin, CgH3-OH-(CO)s°CgH2(OH)s, is formed as above mentioned in the preparation of alizarin, and may be obtained by oxidising alizarin with MnO, and H,SQ,. It resembles alizarin, but fuses at a higher temperature (330°), and is more soluble in water. The colours of its metallic salts are more brilliant than those given by alizarin, so that its presence in the artificial dye is advantageous. Purpurin or 1:2: 4-tri-hydroxy-anthraquinone, CgH,(CO),CgH(OH)3, is isomeric with the preceding, and is found accompanying alizarin in old madder root, and may be separated from it by boiling with alum, which dissolves only the purpurin. It may also be obtained by oxidising natural alizarin with MnO, and H,SQ,. Flavo-purpurin, CgsH,0H(CO).CgH2(OH)s, is sometimes formed in the manufacture of alizarin. It crystallises in golden needles soluble in alcohol. Petrahydroxy-anthraquinone, anthrachrysone, CeH(OH)o(CO)2CgH»(OH)s, or alizarine. bordeaux, is obtained by heating 1:3: 5-dihydroxybenzoic acid, CsH;(OH),-COOH, with H,SO,, which abstracts the elements of 2H,O from two molecules of the acid. Hexa-hydroxy-anthraquinone, CgH(OH),(CO),CsH(OH)3, rufigailic acid, or alizarin cyanine (see p. 621), is prepared by heating gallic acid with H,SO,, which removes the elements of 2H,O from two molecules of gallic acid, CsH,(OH),-COOH. It is used as a red dye. 756 ANTHRAQUINONE VAT DYESTUFFS All these anthracene derivatives yield that hydrocarbon when heated with zinc- dust. C.H,'CO Phenanthraquinone, | | , is prepared by oxidising phenanthrene (p. 573) C,H, -CO with chromic acid. It crystallises in orange-yellow needles, melts at 198°, and dissolves in hot alcohol. It is an ortho-quinone giving most of the reactions of a diketone. Coerulignone (p. 751) is a derivative of the quinone of diphenyl. . Vat Dyestuffs derived from Anthraquinone.—In order that the colour of a dyed fabric may he fast to washing, the colouring-matter must be insoluble ; on the other hand, it is essential that the dyestuff should be in solution in the dye-vat in order that the fibres may absorbit. One method of dyeing, known particularly as vat-dyeing, consists in taking advantage of the fact that the colouring-matter yields a soluble substance called a leuco-compound, when suspended in water and treated with a reducing- agent ; the goods to be dyed are saturated with the solution of the leuco- compound and then exposed to air in order to oxidise the leuco-compound to reproduce in the fibre the insoluble colouring-matter. Dyestuffs lending themselves to this treatment are called vat dyestuffs. Originally indigo and its analogues (p. 798) were the only known vat dyestuffs. The sul- phurised dyestuffs (p. 757), which may be regarded as of this class, were discovered in 1893, and since 1901 many vat dyestuffs have been prepared from anthraquinone and its derivatives. Generally, the anthraquinone derivative is fused with caustic alkali with or without an oxidising agent, and the insoluble dyestuff thus produced is treated with a reducing-agent (hydrosulphite) to obtain the leuco-compound. Indanthrene is a blue dyestuff made by fusing }-amino-anthraquinone with KOH and KNO, and reducing the insoluble dyestuff with sodium hydrosulphite. Its con- stitution appears to be N-dihydro-1 : 2:1’ : 2’-anthraquinonazine— Jor NH CO. CoH C,H, C,H, CpHy \co/ "Nw? Noo“ Flavanthrene is made by heating 3-amino-anthraquinone with KOH at 350°. It is a yellow dyestuff, yielding a blue vat by reduction, which dyes cotton blue, but the blue becomes yellow on exposure to air. The constitution is that shown. co Pe es SO Say Lt WAS Se Se co Flavanthrene. Benzanthrone. This compound is the product of condensation of anthraquinone with glycerin (compare Skraup’s method). A mixture of anthraquinone or anthranol, glycerin, and strong H,SO, is heated at 120°, and the product is crystallised from alcohol ; ANILINE DYES "187 pale yellow needles, m.-p. 170°. When heated with NaOH it yields blue and violet dyestuffs remarkable as being the only vat dyestuffs free from nitrogen. fs PE POS SF co Benzanthrone. Sulphurised Dyestuffs.—Black, brown, and blue dyestuffs, the con- stitution of which is still a matter of uncertainty, are made by heating with alkali sulphide at about 200° a large number of aromatic para-amino- (or nitro-) derivatives. They are precipitated from the dissolved melt by a current of air and must be brought into solution by sodium sulphide, which apparently reduces the dyestuff to a leuco-compound, before they can be used as a vat. So also the goods dyed in the vat must be exposed to the air to develop the colour. The original dyestuff, Vidal black, is made by heating p-amidophenol with Na,S and sulphur at about 160°. Immedial black is similarly prepared from dinitro-hydroxy- diphenylamine. Katigen blue, thiogen blue, and sulphur black are other important members of the class, but the whole subject is of little interest to the scientific chemist until a knowledge of the constitution of the dyestuffs has been ascertained. TRIPHENYLMETHANE DYESTUFFS These compounds include many of the colouring-matters commonly called the aniline dyes.+ Although they are amido- or hydroxyl derivatives, consideration of them has been postponed until now because they contain a benzene nucleus to which other groups are attached in a manner similar to that in which the oxygen atoms of quinone are linked to the benzene ring (quinonoid structure). When three amido-groups or three hydroxyl groups are introduced into triphenyl- methane, CH(C,H;)3 (p. 569), compounds are produced which are colourless, but readily become coloured when oxidised and treated with an acid. For example, triamido-triphenylmethane, CH(CgH,NHg)3, is a colourless substance ; when oxidised it becomes triamidotriphenyl carbinol, C(OH)(CgH,NH.)3, which is also a colourless substance, and yields colourless salts (with one equivalent of acid) when treated with cold acids, but coloured salts when treated with warm acids. The latter salts are dye- stuffs ; they are formed from the carbinol by loss of a molecule of water, and since the only oxygen in the carbinol is that of the alcoholic group, OH, it must be supposed that this group forms water with the hydrogen of the acid. This loss of the OH group entails the conversion of the ordinary benzene linking of one of the benzene rings into the quinonoid linking, the change being accompanied by a development of colour, Just as the conversion of the ordinary linking of hydroquinone (colourless) into the quinonoid linking of quinone, develops a colour, HO-C,H,-OH becoming O: C,H,: O. The following equation will make the change more clear : v v HCLNH,-C,H,-C(OH)(C.Hy-NH>). = CINH, : CeHy : C(CsHy-NH2), + H,0. Triamidotriphenylcarbinol hydro- Coloured salt ? chloride (colourless). (Pararosaniline chloride). The foregoing reactions are typical of the behaviour of every triphenylmethane dyestuff ; that_is to say, each may be obtained by oxidising a derivative of triphenyl- 1 It is here possible to call attention only to some typical ‘‘aniline dyes ’’; for information as to the chemical constitution of dyes of trivial names, the student must consult a work on dyestuffs. 2 A simpler view of the constitution of this salt is that it is that of an ethereal chloride, derived trom the carbinol by exchange of OH for Cl; (C,H, NH,);C°Cl. This view is not regarded as substantiated. 758 ROSANILINE SALTS methane and treating the product with a warm acid. The parent triphenylmethane derivative is called the leuco-base of the dyestuff ; the carbinol into which it is converted by oxidation is called the colour-base of the dyestuff ; whilst the coloured salt is the dyestuff itself. Thus, triamidotriphenylmethane is called leuco-pararosaniline ; triamidotriphenyl carbinol is pararosaniline base, whilst the coloured salt with the quinonoid linking is pararosaniline chloride. The converse changes are possible ; that is to say, by treating the dyestuff with a caustic alkali the colour-base is preci- pitated, and if this be treated by reducing-agents (nascent hydrogen) it yields the leuco-base. The triphenylmethane dyestuffs are classified into derivatives of: (1) Diamido-triphenylmethane, C,H,-CH(C,H,NH,),; the type of these is malachite green. (2) Triamidotriphenylmethane, CH(C,H,NH,),; the type of these is rosaniline (magenta). (3) Trihydroxytriphenylmethane, CH(C,H,:OH), ; the type of these is awrin. (4) Triphenylmethane carboxylic acid, CH(C,H;).(C,H,-CO,H) ; the type of these is eosin. Malachite green or tetramethyl-1 : 4-diamido-triphenylmethane chloride— CIN(CHs)o : CeHy : C(CeHs)[CeH4-N(CHa)z].- The leuco-base of this dyestuff is prepared by heating benzaldehyde with dimethy- aniline and zinc chloride (to act as a dehydrating agent)— CsH;-CHO + 2C.H;:N(CHg). = CeHs-CH[CgH4-N(CHs3)e 1, + Hp0. The leuco-base is oxidised by PbO, (when it yields the corresponding carbinol or colour-base, see above) in the presence of HCl (to produce the colour-salt). The dyestuff is then precipitated by zinc chloride and sold in the form of a double zinc- salt. Rosaniline salts constitute the bulk of the dyestuff known as magenia (fuchsine). They are formed by the action of acids on rosaniline-base, which is triamidotolyldiphenyl carbinol— NH2‘CgH3(CH3)-C(OH)(CeH4-NHo)o. The chloride, CINH, : C,H,(CH,) : C(C,H,-NH,),, nitrate and acetate are the most common salts on the market. They are prepared by heating aniline oil for red (p. 700), which should contain equi-molecular proportions of aniline, orthotoluidine and paratoluidine with an oxidising-agent (arsenic acid or nitrobenzene ! is generally used) ; CgH,(CHs)NH, /eeHs(CHs )-NH NH,-C,H.-CH, + + 80 = NH,-CpHy-C(OH)C C.H,-NH, C,H,:NH, The rosaniline base made in this way is converted into the chloride by adding hydrochloric acid, and this salt is precipitated by adding common salt. When recrystallised, rosaniline salts form bronze-green crystals which are sparingly soluble in cold water, but more readily in hot water, to a red solution. When the hot solution is mixed with ammonia and filtered quickly the rosaniline base crystallises from the filtrate in colourless plates which become red in air, from absorption of CO,. Reducing-agents bleach the red solution with formation of leucaniline, NH,-C,H,(CH;)-CH(C,H,-NH,),,? the leuco-base of rosaniline. Pararosaniline or triamidotriphenyl carbinol, C(OH)(C,H,NH,)s, is prepared by oxidising a mixture of paratoluidine ? (1 mol.) and aniline 1 This oxidising-agent is now more common than any other. When it is employed, HCl and iron filings form a part of the charge, so that the nitrobenzene is first reduced to aniline (which enters into the reactiod), and the ferric chloride formed by its reduction is the immediate oxidant. ® When diazotised (p. 715), and heated with alcohol, leucaniline yields metatolyldiphenyl-methane, C,H,(CH;)'CH(C.H,)3, (cf. p. 716), showing that leucaniline and therefore rosaniline must be a derivative of this hydrocarbon. 2 Its prefix appears to have been given to pararosaniline on account of the fact that paratoluidine is used in its manufacture. Since it has been recognised that paratoluidine is also necessary for rosaniline, the name has lost its significance. + 2H,0. EOSIN DYESTUFFS 759 (2 mols.) in the same way as is described for rosaniline. The salts are red dyestuffs, like the rosaniline salts. In both oxidations it may be supposed that the paratoluidine is oxidised to p-amido- benzaldehyde, which then condenses with the orthotoluidine and aniline (in the case of rosaniline) or with the aniline alone (in the case of pararosaniline). Many derivatives of pararosaniline and rosaniline, containing methyl, ethyl, and phenyl groups in place of the amido-hydrogen atoms, are prepared by heating para- rosaniline or rosaniline chloride with alkyl or phenyl halides ; these are also used as dyestuffs, the shade produced by them becoming more blue as successive alkyl or phenyl groups are introduced. Thus pentamethyl-pararosaniline is known as methyl violet, and triphenyl-rosaniline chloride as aniline blue. The combination of tetramethyl rosaniline, which is saturated with methyl groups, with methyl chloride or iodide, produces a green dyestuff known as iodine green. Aurin.—When pararosaniline base is diazotised (p. 715), the three NH, groups are converted into diazo-groups, and when the resulting compound is boiled with water it yields trihydroxytriphenyl carbinol, (CH ,-OH),C-OH (cf. p. 716). This compound is very unstable and loses a molecule of water, becoming aurin, O : C,H, : C(C,H,OH),, comparable in structure with pararosaniline chloride. It crystallises in green needles which dissolve in alkalies to a red solution, but are precipitated again by acids. Thus aurin behaves as an acid substance, as, indeed, is to be antici- pated from the presence of phenolic OH groups. It will be noticed that, whilst pararosaniline is a type of basic dyestuffs, tending to combine with acid mordants, aurin is a type of acid dyestuffs tending to combine with basic mordants. Rosolic acid bears the same relation to rosaniline as aurin bears to pararosaniline. Eosin.—Triphenylmethane-carboxylic acid (see above), or rather its hydroxy-derivative triphenyl-1-carbinol-2-carboxylic acid— (CgH5)o(CgH,-COOH)C-OH, gives rise to the dyestuffs of this class. Diphenylphthalide is the lactam (p. 709) of this alcohol acid ; it may also be regarded as derived from phthalic anhydride by substituting (C,H;).”” for O”, for it is prepared by the inter- action of phthalyl chloride and benzene in presence of AlCl,— cOocl C(CeHs)o OH +2GH.— GH YO + 2HC1 \cocl es co if Diphenylphthalide. By substituting phthalic anhydride for the chloride, a phenol for the benzene and a dehydrating agent for the AICI; in this reaction, the eosin dyestuffs are obtained. Thus, phenol-phthalein is obtained when phthalic anhydride is heated with two molecular proportions of phenol and ZnCl,— co C(CeH4:OH). Gu. So--ecor— on,0 No + H,0. \co”% ae” The mass is dissolved in an alkali and the phenolphthalein precipitated by an acid. Its alkali salts are pink in solution, and are decomposed by the feeblest acids (see p. 743), so that phenolphthalein is useful as an indicator in acidimetry. It can hardly be termed a dyestuff. It has been supposed that phenolphthalein may behave as dihydroryphthalein, C.H,(COC,H,OH),. As this does not import a quinonoid structure into its constitu- tion, it has also been suggested that the salts of phenolphthalein are from the pseudoform C,.H,0OH COOH -CeHa The ease with which the salts are decomposed by all C.H, :0 760 THE SUGARS acids seems to show, however, that they are derived from phenolic, not carboxylic groups. C[(CgH3:OH).0 } Fluorescein, C7 NO, is formed when phthalic anhydride is ‘ x co oe heated with resorcinol, 2 mols. H,O being liberated. It forms red crystals and dissolves in dilute alkalies, giving a solution which is red with a green fluorescence ; this is also noticeable on the dyed fabric, hence the dyestuff is frequently mixed with others for producing a fluorescent green. Eosin itself is a tetrabromo-derivative of fluorescein, and is made by brominating the latter in acetic solution. It dissolves in alkalies, giving a deep red solution which fluoresces green when diluted. XIII. CARBOHYDRATES It has been already indicated (p. 597) that this group of organic com- pounds is only a temporary one in chemical classification, and that it will be broken up so soon as the true constitution of the compounds which it now comprises is understood. Indeed, it is already on the eve of extinction, since several of the sugars, formerly the typical members of the group, have been shown to be either aldehyde-alcohols or ketone-alcohols. Originally, the compounds belonging to this class were such as contain hydrogen and oxygen in the proportion to form water, combined with six atoms, or some multiple of six atoms, of carbon. This is still true for a majority of the compounds of the class, but it is necessary now to describe several substances which do not fall in with the above definition, among the carbohydrates. The carbohydrates may be divided into two groups: (1) the Sugars, and (2) the Starches and Celluloses. The group of sugars contains compounds which are comparable in taste and other properties with the substance commonly called sugar. The molecular formule for the sugars may be said to be known in almost all cases, and it is found that whilst a number of them, such as glucose, CgH,.0g, correspond with the general formula C,(H.0),, others, such as cane-sugar, C,.H».0,,, correspond with the general formula C,(H20),-1. The molecular formule for the starches and celluloses are not known ; but the percentage composition of these compounds indicates that their molecular formula is (CgH,905)n. As may be expected, the compounds C,(H2O),-1 yield the compounds C,(H,0), when hydrolysed, and the compounds (CgH,)05), undergo a similar change. Sosy The above considerations have given rise to a classification of the carbohydrates into (1) saccharides or monoses, Cy(H_0), ; (2) disaccharides or saccharobioses, CygHo20x1 ; (3) trisaccharides or saccharotrioses, CygHg20 1g ; (4) polysaccharides, (CgH,905)n- THe SuGaRs These may be subdivided into glucoses (aldoses and ketoses), having the general formula C,(H,O),, disaccharides (formerly sucroses) or saccharo- bioses, having the formula C,,H,.0,,, and trisaccharides or saccharo-trioses, having the formula C,,H5.0,,.1_ The sugars of the second and third classes are converted into sugars of the first class by hydrolysis. The type of the sugars of the first class is grape-sugar, that of the second cane-sugar, whilst that of the third is raffinose. Since the sugars contain asymmetric carbon atoms, they give rise to a large number of optically active stereo-isomerides (p. 636). 1 According to one system of nomenclature the termination -ose is employed to designate sugars of the first. class, and the termination -on to indicate sugars of the second class. Thus C,H,,0, is hexose, whilst CisH 32011 is diheaon. GLUCOSES 761 The Glucoses.—These are named according to the number of carbon atoms which they contain—e.g. trioses, C;H,0, ; tetroses,C,H,O, ; pentoses, C5Hi,0;; hexoses, CgH,,0,; heptoses, C,H,,0,, &c. In constitution they are either aldehyde-alcohols or aldoses (containing the group -CH(OH)-CHO), or ketone-alcohols or ketoses (containing the group -CO-CH,OH), and accord- ingly behave as reducing-agents and yield hydrazones just as other com- pounds containing the aldehyde or the ketone group do. The glucoses must be regarded as the first oxidation-products of poly- hydric alcohols, the most important of which have been mentioned (p. 590). The aldoses would be formed by oxidation of the primary alcohol group, and the ketoses by oxidation of the secondary group. All the glucoses have asymmetric carbon atoms, and each exists in two stereoisomeric forms, the d- and the I- form, and in a third, externally compensated or racemic, inactive (d + 1) form ! (p. 636). Thus the simplest aldose would be glycollic aldehyde, CH,OH-CHO, from glycol ; glycerol yields both an aldose, glycerose (aldotriose), CH,OH-CHOH-CHO (p. 597) and a ketose, dihydroxyacetone (ketotriose), CH,OH-CO-CH,OH. (1) Tetroses.—Hrythrose, obtained by the oxidation of erythritol (p. 591) by the action of dilute nitric acid, is probably a mixture of the aldotetrose, CH,OH-[CHOH],-CHO, and the ketotetrose, CH,OH-CHOH:CO-CH,OH. A d- and an /- form are known. (2) Pentoses.—The aldopentoses, CH,OH-[CHOH],-CHO, are alone known at present. They are natural sugars, occurring in many plants. They resemble the aldohexoses (v.i.) in their general behaviour except that they are not fermented by yeast. Other characteristics are that they yield furfural (p. 599) or its homologues when distilled with dilute acids, and that they give a red colour with phloroglucinol and HCl. Eight optically active and four externally compensated aldopentoses are possible (p. 637). J-Arabinose, the chief member of the class, is prepared by boiling with dilute H,SO, gum arabic and other gums which yield little mucic acid when oxidised by HNO;. It crystallises in sweet prisms, melts at 160°, and is strongly dextro- rotatory.1 By reduction it yields the pentatomic alcohol arabitol, CH,OH-[CHOH],-CH,OH. Xylose (from wood-gum, straw, and jute) and ribose are isomerides of arabinose. Rhamnose (from quercitrin) and fucose (from sea-weed) are methyl arabinose, C;Hg(CH3)O;. (3) Hexoses, C,H,,0,.—These are the compounds which were origin- ally called glucoses. They are widely distributed in nature, but are mainly found in unripe fruit, the chief being dextrose, or grape-sugar, and levulose, or fruit-sugar ; they are produced by the hydrolysis of the disaccharides and polysaccharides, the change being effected both by enzymes and by dilute acids or alkalies. d-Glucose, d-mannose, d-galactose, and d-fructose are fermented by yeast, yielding alcohol. A few have been synthesised, and the constitution of nearly all has been settled (see below). (a) Aldohexoses, CH,OH-[CHOH],,CHO.—The substance commonly called glucose, grape-sugar or dextrose is d-glucose, there being also an l-glucose and a (d + 1)-glucose. It is the aldehyde of sorbitol (p. 592). d-Glucose is the crystallised sugar found in honey, raisins, and many other fruits; it is almost always accompanied by levulose, a keto-hexose, which is far more difficult to crystallise. Dextrose is also found in small quantity in several animal fluids, and in the liver, and in urine in cases of diabetes. Dextrose may be obtained from honey by mixing it with cold alcohol to dissolve the levulose, which forms about one-third of its weight, and 1 Much confusion is engendered by Fischer’s custom of naming the sugars d- and l- without reference to their actual rotation, but according to the way in which they are derivable from each other. 762 DEXTROSE leaves about an equal quantity of dextrose, which may be dissolved in boiling alcohol and crystallised. To extract it from fruits, they are crushed with water, strained, the liquid boiled to coagulate albumin, filtered, evapo- rated to a syrup, and set aside for some days, when crystals of dextrose are deposited. Fresh fruits contain chiefly levulose, which is gradually converted into dextrose. Dextrose is also a product of the hydrolysis of glucosides (q.v.), and di- and poly-saccharides (cane-sugar, starch, &c.). From cane-sugar it is best prepared by heating a mixture of 250 c.c. of alcohol -(sp. gr. 0-823) with 10 c.c. of strong HCl to 45° and adding 80 grams of finely powdered cane-sugar in small doses. When the sugar has entirely dissolved, the whole is set aside for a week and stirred to induce crystallisation. The crystals of dextrose are drained from the solution containing levulose and washed with alcohol. Commercial glucose or starch-sugar is made by heating starch with diluted sulphuric acid,! which first converts it into dextrin and finally into d-glucose, (CgH,905)n + nH,O = nOgHy.0g. Water containing about 1-5 per cent. of H,SO, is heated to boiling and a hot mixture of starch and water is allowed to flow gradually into it. The mixture is boiled for half an hour, neutralised with chalk, and concentrated by evaporation, when it deposits crystals of calcium sulphate. The clear syrup is drawn off and evaporated in a vacuum- pan till it is strong enough to crystallise, some glucose from a previous batch being added to promote crystallisation. The glucose thus obtained contains about 70 per cent. of d-glucose and also maltose, dextrin, and some calcium salts of organic acids ; it may be purified by washing with strong alcohol mixed with 3 per cent. of HCl, and afterwards with commercial absolute alcohol. When crystallised from an aqueous solution, dextrose forms six-sided scales (with 1H,O); these fuse at 86°, and become anhydrous at 110°; it crystallises from alcohol at 30° in small anhydrous needles, which melt at 146°. It is less sweet than cane-sugar, and can be directly fermented by yeast (p. 575). Glucose dissolves in 1-2 parts of cold water, in 50 parts of cold, and in 5 parts of boiling, alcohol (sp. gr. 0-837). When heated to 170°, it is converted into dextrosan (glucosan), C,H,,0;, a nearly tasteless substance, convertible into glucose by dilute acids. When boiled with caustic potash, glucose gives a dark brown solution, being ultimately con- verted into humus-like acids. In presence of alkalies, glucose acts as a strong reducing-agent. If a solution of glucose be mixed with CuSO,, and KOH be gradually added, the blue precipitate of cupric hydroxide produced at first dissolves in excess of potash to a fine blue solution ; if this be gently heated, a yellow precipitate of cuprous hydroxide is produced, which becomes red cuprous oxide when boiled ; a little metallic copper is precipitated at the same time, and the glucose is oxidised to a number of organic acids. Glucose precipitates metallic silver when warmed with ammonia-nitrate of silver, and metallic mercury from Hg(CN), mixed with KOH. Solution of glucose mixed with NaCl deposits crystals of 2CgH,.0,.NaCl.H,0, which is sometimes deposited from diaBv-.. ucine. Glucose is not so easily blackened by H,SO, as is sucrose, but forms an unstable compound with it. With alkaline earths dextrose combines to form compounds like CgH,,0,.CaO, which are precipitated by alcohol. Other reactions will be discussed under Constitution of the Glucoses (p. 765). Dextrose rotates the plane of polarisation to the right hand, but a solution which has been kept for some hours has only half the effect of a freshly made solution, a phenomenon known as bi-rotation, and probably due to the formation of hydrates. Glucose is used by brewers and distillers for making alcohol, and by confectioners ; dyers and calico-printers use it to reduce indigo. + Care should be taken that the sulphuric acid is free from arsenic, lest the latter pass into the glucose and thence into the beer brewed therefrom. LAVULOSE 763 d-Mannose is obtained, together with levulose, by the cautious oxidation of mannitol (p. 591), with platinum black or nitric acid. It may be prepared by boiling seminine, the reserve-cellulose of many seeds, with dilute H,SO, ; it is sometimes called seminose. Mannose has not been crystallised ; it is very soluble in water, and its solution is dextro- rotatory ; an J- and a (d + 1)- form are also known. d-Galactose is obtained, together with d-glucose, when milk-sugar and some varieties of gum arabic are boiled with dilute H,SO,. To prepare it, milk-sugar is boiled for six hours with four parts of water containing 5 per cent. of H,SQ,4. The solution is precipitated by baryta, filtered, evaporated to a syrup, and induced to crystallise by adding a few crystals of dextrose. The crystals are washed with alcohol of 80 per cent., and recrystallised from hot alcohol of 70 per cent. It crystallises in rhombic prisms, which are less sweet than cane-sugar, and melts at 166°. Itis not very soluble in cold water, and is insoluble in absolute alcohol. Galactose is also obtained by _ hydrolysing galactitol, CyH,,0,, a crystalline substance extracted by alcohol from yellow lupines. J- and (d + 1)-galactose are known. The guloses and taloses are artificial aldohexoses. Methylhexose or rhamnohexose, CgHi1(CH3)O.,, has also been prepared. (6) Ketohexoses, CH,OH-[CHOH],:CO-CH,OH.—d-Fructose is the most important of these. It is commonly known as fruit-sugar or levu- lose, and is prepared by heating cane-sugar with water and a very little sulphuric acid on a water-bath for half an hour, removing the acid by barium carbonate, and evaporating to a syrup. This syrup contains invert-sugar, a mixture of equal weights of dextrose and levulose, which mixture deposits crystals of dextrose when exposed to light. To obtain pure levulose, it is mixed with water, cooled in ice, and stirred with calcium hydroxide, which precipitates a sparingly soluble lime compound of levu- lose. This is suspended in water and decomposed by CO,; the filtrate from the calcium carbonate is then evaporated on a water-bath. The syrup is washed with cold alcohol and set aside in a cold place, when the levulose crystallises. Levulose is much sweeter than dextrose, rivalling cane-sugar in this respect. It does not ferment so readily as dextrose, so that when invert- sugar is mixed with yeast, the dextrose is the first to disappear. Also it reduces alkaline cupric solutions (p. 631) less readily. Lzevulose rotates the plane of polarisation of light to the left, whence its name, but a dextro- (1) and an inactive (d + 1) levulose also exist. It forms two crystalline compounds with lime, C,H,.0,-CaO-2Aq and C,H,,0,3CaO, dissolving respectively in 137 and 333 parts of cold water. When heated to 170°, levulose is converted into levulosan, CsH,,0;, which is dextro-rotatory. When heated with alkalies it is partly converted into d-glucose and d-mannose. (4) Heptoses, C7H,407, Octoses, CgH,0g, and Nonoses, CyHg09.—It has been found possible to produce a glucose containing x carbon atoms from one containing x-1 carbon atoms by treating the latter with hydrocyanic acid, whereby it is con- verted into a cyanohydrin (p. 595) just as any other aldehyde or ketone would be. This cyanohydrin is convertible into a carboxylic acid by hydrolysis; this may be reduced to a new sugar by sodium amalgam; thus, dextrose yields the cyanohydrin CH,OH-[CHOH],-CH(OH)-CN, which is converted into dextrose-carboxylic acid (gluco- heptonic acid), CH,OH-[CHOH];-CO.H, by hydrolysis, and when this acid is reduced it yields glucoheptose, CH,OH-[CHOH],-CHO. By these means each glucose may be made to yield a heptose, which, in its turn, may be converted into an octose and a nonose ; consequently the possible number of these sugars is very large. They have not been found in nature. . Synthesis of the Glucoses.—The key to the synthetical production of the glucoses was phenylhydrazine. Like other aldehydes and ketones the glucoses form hydrazones 764 SYNTHESIS OF SUGARS when heated with a solution of phenylhydrazine hydrochloride and sodium acetate (p. 720). Thus the aldohexoses form hydrazones CH,OH-: [CHOH],-CHOH-CH : N-NHC,H;, while the hydrazones from the ketohexoses have the form CH,OH-[CHOH],-C( : N-NHC,H;)-CH,OH. When an excess of phenylhydrazine is used, the hydrazones lose H, ‘on account of the tendency for CsH,NH-NH, to absorb H, and become CgH;NH, and NH; (p. 720). This converts the aldose hydrazone into a ketonic compound and the ketose hydrazone into an aldehydic compound— CH,OH:[CHOH],-CO-CH : N-NHC,H; CH,OH: [(CHOH],-C( : N-NHC,H;)-CHO. These immediately combine with a second molecule of phenylhydrazine to form osazones, both of which have the formula, . CH,OH: [CHOH};-C( : N-NHC,H;)-CH : N-NHC,H;. Thus the aldoses and ketoses yield the same osazones except in so far as these may differ stereochemically. The hydrazones are generally soluble in water, but the osazones are bright yellow, sparingly soluble, and easily crystallised. Thus their formation is often the best method of identifying a known sugar or of isolating a new one. For this latter purpose the osazone is dissolved in cold strong HCl; it is thus con- verted into the corresponding osone, a ketone-aldehyde ; CH,OH-[CHOH],:C( : N-NHC,H;):CH : N-NHC,H, + 2HCl + 2H,0 = CH,OH-[CHOH}];-CO-CHO (glucosone) + 2C,H;NH-NH,,HCl. The red liquid which is formed deposits phenylhydrazine hydrochloride ; it is filtered and neutralised with PbCO, ; the lead compound of the osone remains in solution ; it is precipitated by baryta and the precipitate-decomposed by H,SO,. To convert the solution of the osone, thus obtained, into a sugar, it is reduced by means of zinc and acetic acid ; CH,OH-[CHOH];:CO-CHO + 2H° = CH,OH:[CHOH},-CO-CH,OH. When dextrose is treated in this way it is converted into levulose. Formaldehyde is the first step in synthesising glucoses from their elements. Treated with lime-water, it is polymerised to a mixture of sugars, termed formose ; a similar mixture (methylenitan) is obtained from trioxymethylene (p. 593) in like manner. Two sugars, a- and /3-acrose, have been isolated from this mixture and also from the mass obtained by treating glycerose (p. 597) with alkalies. They are separated by taking advantage of the greater solubility of G-acrosazone, than of a-acrosazone, in ethyl acetate. The glucose recovered from a-acrosazone in the manner described above appears to be identical with (d + 1)-fructose, which by fermentation with yeast is converted into l-fructose, the d-constituent having been used by the yeast (see p. 637). This l-fructose is dextro-rotatory (see footnote, p. 761), and is not the levulose found in nature. When (d + 1)-levulose (from a-acrose) is reduced by sodium amalgam, it yields (d +1)-mannitol, CH,OH-[CHOH],-CH,OH, which may be oxidised to (d + /)- mannonic acid, CH,0H-[CHOH],CO,H. This can be resolved by crystallisation of its strychnine salt into J- and d-mannonic acids, which by reduction yield first /- and d-mannose and then /- and d-mannitol. By taking J- and d-mannose through the phenylhydrazine reactions they yield /- and d-fructose. When J- and d-mannonic acids are heated with quinoline they are converted into 1l- and d-gluconic acids, which are stereo-isomeric with them. By reduction, the gluconic acids yield /- and d-glucose (dextrose). Thus a number of hexoses has been synthesised. It will be observed that the monocarboxylic acids derived from the polyhydric alcohols are useful transition products in the syntheses, as they readily lend themselves to resolution by means of their salts with the alkaloids. Through these acids also it is possible to pass from the pentoses to the hexoses and vice versa. Thus l-arabinose combines with HCN as any other aldehyde does (p. 595), forming the cyanohydrin CH,OH-[CHOH],-CH(OH)-CN, which by hydrolysis CONSTITUTION OF THE GLUCOSES 765 yields i-mannonic acid, the CN becoming COOH as usual. Again, by oxidising d-gluconic acid with H,Oz, in presence of ferric acetate it yields d-arabinose ; or by treating d-glucose-oxime, CH,OH[CHOH],-CH : N(OH), with acetic anhydride and sodium acetate, it yields a pentacetyl derivative which becomes d-arabinose when treated with HCl. Constitution of the Glucoses.—The molecular weight of many of the sugars has been settled by Raoult’s method (p. 320). That the hexoses (the same arguments apply to the pentoses) are alcoholic aldehydes or ketones is shown by the following reactions : When heated with acetic anhydride and sodium acetate the hexoses yield pentacetyl- derivatives, CsH,0(OCH,CO);, showing that they contain 5 alcoholic hydroxyl groups (p. 590) and are pentahydric alcohols. Five out of the six atoms of oxygen are thus disposed of: that the sixth must be present either as an aldehyde or as a ketone group, is shown by the fact that these sugars give a number of the reactions which characterise aldehydes and ketones. In the aldohexoses this remaining oxygen atom must be present as an aldehyde group, for on oxidation these sugars yield acids containing the same number of carbon atoms, which would not be the case if the sugars were ketones (p. 648). Thus, the dextroses yield first gluconic acids, CH,OH:-[CHOH],-CO,H, and then, by further oxidation, saccharic acids, CO,.H:[CHOH}],-CO,H ; the mannoses yield mannonic acids and manno-saccharic acids, stereo-isomeric with the above acids ; whilst the galactoses yield galactonic and mucic acids, also stereo-isomerio with the preceding acids. Moreover, when reduced by sodium amalgam these sugars yield hexahydric alcohols; e.g. the mannoses yield mannitols, the dextroses sorbitol, and the galactoses dulcitol. This behaviour on reduction shows that the sugars are certainly open-chain compounds, for the above-named alcohols are all convertible into normal hexane by hydriodic acid. The rule already referred to as guiding us in the interpretation of chemical constitution, namely, that one carbon atom cannot hold more than one hydroxyl group, may be applied to these sugars, when it becomes evident that the five hydroxyl groups must be attached to five separate carbon atoms, forming one primary and four secondary alcohol groups ; the sixth carbon atom may constitute the aldehydic carbon. The ketonic character of the ketohexoses follows from the fact that when oxidised they yield two acids (p. 648). Thus, the levuloses yield trihydroxybutyric acid, CH,OH-[CHOH],‘CO,H, and glycollic acid, CH,OH-CO,H. By reduction, these sugars yield mannitol. The position of the ketone group in the open-chain repre- senting the levuloses may be said to be settled by the following facts. When levulose is treated with HCN it yields a cyano-hydrin which is almost certain to contain the group : C(OH)(CN) in place of the group : CO (p. 595); when this cyano-hydrin is hydrolysed it yields a corresponding carboxylic acid, which is equally certain to contain the group : C(OH)(COOH); when this acid is reduced by hydriodic acid, it yields methylbutylacetic acid, the structure of which shows that the carbonyl carbon of the original levulose must have had one carbon atom attached to it on the one hand and four carbon atoms attached to it on the other hand. The following equations will make this apparent : (1) CH,OH-[CHOH}],-CO-CH,OH + HCN = CH,OH-[CHOH}],-C(OH)(CN)-CH,OH (2) CH,OH-[CHOH],-C(OH)(CN)-CH,OH + 2HOH = CH, OH: [CHOH],-C(OH)(COOH)-CH,OH + NH, (3) CH,OH-[CHOH],-C(OH)(COOH)-CH,OH + 12HI = CH,-[CH,],-CH(COOH)-CH, + 61, + 6H,0. atlg CH,-[CH,];-CH(COOH)-CH; or on-coon is methylbutylacetic acid. CH; When dextrose is submitted to a similar series of reactions it yields normal heptylic acid, CH3:[CH,],-CH»-COOH, showing that the aldehyde group is at the end 4 of the open-chain, a position, indeed, which is the only possible one for the of group. H Reference must now be made to the stereoisomerism of compounds containing 766 STEREOISOMERISM OF THE GLUCOSES a number of asymmetric carbon atoms, as do these polyhydroxy-alcohols, aldehydes, ketones, and acids. It was shown at p. 637 that a compound containing two asymmetric carbon atoms can exist in four stereo-chemical modifications, when, as in the case of tartaric acid, each carbon atom has the same groups attached to it, that is, when the compound is of the type abeC—Cabc. Two of these modifications are optically active, one is inactive by internal compensation and one inactive by external compensation. In the case of a compound of the type abcC—Ca’b’c’ there can be no inactivity by internal compensation. A little reflection will show that, instead, there will be four optically active isomerides, one in which abe and a’b’c’ are both arranged to cause dextro-rotation, one in which they are both arranged to cause levo-rotation, and two in which they are oppositely arranged. In addition there will be two externally com- pensated, inactive forms. Now the pentahydric alcohols, CH,OH-C HOH-CHOH-C HOH-CH,OH, and the corresponding dicarboxylic acids, have two asymmetric carbon atoms (printed in heavy type) and are of the form abcC—Cabc. Hence, like tartaric acid, they occur in a d-form, an I-form, an externally compensated or d + J-form, and an internally compensated or i-form. There is, however, a fifth, viz. a second internally com- pensated form ; for although the central carbon atom is not asymmetric, being balanced on either side, it has an H and an OH attached to it, the positions of which may be reversed. The aldopentoses, CH,OH:¢ HOH-‘C HOH-CHOH-CHO, and the corresponding monocarboxylic acids, CH,OH[CHOH],COOH, have 3 asymmetric carbon atoms. Each of these should give rise to a + and a — form, and since the nature of the whole compound will depend on which carbon atoms have their attached groups in the -+ form and which have them in the — form, there should be as many aldopentoses as there are ways of writing + or — three times, e.g. + + +, —-— —, +—+,—- + — and so on. This number is eight, so that there are 8 optically active isomerides. As the aldopentoses are of the type abcC—Ca’b’c’, there are no internally compensated forms, but by combining pairs of the optically active forms, four racemic or externally compensated forms are possible. The hexahydric alcohols, CH,OH-C HOH-C HOH-C HOH-C HOH-CH,OH, and corresponding dicarboxylic acids, have four asymmetric carbon atoms, so that the number of optically active isomerides should be discoverable by finding the number of ways of writing + and — fourtimes. This will be found to be 16. But these alcohols are of the type abcC—Cabc, wherefore those forms in which the + and — are similarly arranged, but in opposite order, e.g. + — + —, — + — +, are identical, reducing the essentially different ways of writing + and — to 10, two of which represent internally compensated molecules, leaving 8 active isomerides. In addition there should be four racemic forms. Now the aldohexose formula, CH,0H-C HOH:C HOH-C HOH-C HOH-CHO, also contains four asymmetric carbon atoms, and is of the type abcC—Ca’b’c’, so that all 16 isomerides exist, none of which is internally compensated. Besides these there should be 8 racemic forms. At present 11 of the optically active forms are known, viz. d- and l-mannose, d- and 1- glucose, d- and J-gulose, d- and I-galactose, d-and J-idose, and d-talose. The ketohexoses, CH,OH-C HOH-C HOH-C HOH-CO-CH,OH, contain 3 asymmetric carbon atoms and are of the type abcC—Ca’b’c’ ; stereoisomerism among them, therefore, is similar to that among the aldopentoses. It has been found to be possible to orientate those carbon atoms which have a -- arrangement of groups and those which have a — arrangement in the glucoses, but for a description of the arguments employed, the student must be referred to the chemical dictionaries. ; The Disaccharides.—_The members of this class of sugars are characterised by being converted by hydrolysis into two molecules of glucoses (hence the synonym, saccharo-bioses).+ ' In one system of nomenclature, they are termed dipentons, dihexons, &c., according as the glucoses produced by the hydrolysis are pentoses or hexoses. Thus, arabinon, C,9H,,0, (from gum), is a dipenton, since it yields two molecules of arabinose by hydrolysis cane-sugar is a dihexon, since it yielda dextrose and levulose by hydrolysis. CANE-SUGAR 767 Cane-sugar or sucrose, C,,H».0,,, is found not only in the sugar- cane, but in many other plants, such as beetroot, sorghum, maize, barley, almonds, walnuts, hazel-nuts, coffee-beans, and madder root. It occurs also in the sap of the maple, lime, birch and sycamore, as well as in the juices of many fruits ; in these, it is generally accompanied by invert-sugar (v.1.). During the early period of vegetation, it appears that grape-sugar and fruit-sugar are formed, and that these become cane-sugar during the ripening. The green sugar-cane contains much dextrose and levulose, which are afterwards converted into sucrose. Honey contains cane-sugar and invert-sugar, in varying proportions, depending on the food of the bees. To extract sugar from plants, they should be cut up, dried at a tem- perature not exceeding 100°, and boiled repeatedly with alcohol of sp. gr. 0-87, which deposits the sugar in crystals, on cooling. On the large scale, sugar is manufactured by crushing the cane between rollers, when an acid juice is obtained, containing about 20 per cent. of sucrose; this is neutralised by lime, to prevent inversion of the sugar, and heated to coagulate the albumin. This is skimmed off the surface, and the syrup is evaporated till it is strong enough to crystallise. About half the sugar is thus obtained in brown crystals (moist sugar), the remainder being partly extracted as an inferior sugar (foots sugar) by another evaporation, and partly left as uncrystallisable sugar in the molasses or treacle. ‘To refine the raw sugar, it is dissolved in water, decolorised by filtering through a thick bed of animal charcoal, and evaporated at 60° C. (140° F.) in a copper vacuum-pan connected with an air-pump, since a higher temperature would invert the sugar. It may then be obtained in large crystals, sugar-candy, or, by stirring, in minute crystals which are drained in conical moulds, and washed with a saturated solution of sugar till they form white loaf-sugar. Sugar is extracted by a similar process from the juice of the white beetroot. The juice contains about 10 per cent. of sugar, about half of which is obtained in a crystallised state. A larger yield of crystallisable sugar has been obtained from cane and beet juice by the strontia process, which consists in precipitating the sugar from the boiling solution by adding strontium hydroxide; the precipitate, Cy.H»20.,(SrO)s, is washed with hot water, and afterwards suspended in boiling water and allowed to cool, when most of the strontia is deposited as hydroxide, and the remainder is precipitated from the solution by COg. Sometimes the potassium salts which are present in the molasses, and hinder crystalli- sation, are precipitated in the form of alum by adding aluminium sulphate. Properties of sucrose.—It crystallises in monoclinic prisms, which are insoluble in absolute alcohol, but dissolve to almost any extent in boiling water. 100 parts of saturated syrup at 20° contain 67 of sugar ; the solution of sugar is dextro-rotatory. When heated with dilute acids it is hydrolysed to a mixture of equal weights of dextrose (d-glucose) and levulose (d- fructose), C,.H,.0,, + H,O = CgHy,0, + CeH,.0.. This mixture is known as invert-sugar, since it is levo-rotatory (the levo-rotation of levulose being greater than the dextro-rotation of dextrose). It is prepared for the use of brewers (see foot-note, p. 762). Sucrose fuses at 160° C. (320° F.), and does not crystallise on cooling. If kept melted for some time, it is converted into a mixture of dextrose and levulosan; C,,H,,0,,; = C.H,.0, + C,H,,0;. If this be dissolved in water, and yeast added, the dextrose ferments, but the levulosan is unaltered. When further heated, but below 190° C. (374° F.), sucrose loses 2H,O and becomes brown, yielding caramelan, C,,H,,09, an amorphous, brittle, very deliquescent body, colour- less when pure, and not capable of reconversion into sugar. Commercial caramel, used for colouring liquids, is a mixture of this with other bodies formed at higher temperatures, and is usually made by heating starch- 768 PROPERTIES OF SUGAR sugar. It is bitter. Cane-sugar does not reduce Fehling’s solution unless boiled with it sufficiently long to effect the inversion of the sugar. When sugar is melted in a little water (barley-water was formerly used), it cools to a glassy mass (barley-sugar) enclosing a little water; this dissolves some of the sugar and deposits it in crystals, until in course of time the whole mass is opaque and crystalline. Heated with water at 160°, sucrose yields formic acid, carbon dioxide, and carbon. At 280° some pyrocatechin is produced. Dilute acids, even carbonic, convert sucrose into dextrose and levulose, slowly in the cold, and quickly on heating. Fused with potash, sucrose gives the potassium-salts of oxalic, formic, acetic and propionic acids, together with acetone. Sucrose acts as a reducing-agent ;- if ammonio-nitrate of silver is added to its solution, followed by sodium hydroxide, a mirror of silver is deposited on heating. The antiseptic properties of sucrose are well known: a strong syrup arrests fermenta- tion. Weak solution of sucrose, in contact with yeast, is first converted into dextrose and levulose, and then into alcohol and carbon dioxide (see p. 575). Sugar absorbs ammonia gas, forming Cj2H»,(NH4)O,,, which decomposes again on exposure to air. Sucrose behaves like a weak acid to strong bases. Sodium sucrate, CypyHNaQ,,, is precipitated when strong caustic soda is added to an alcoholic solution of sugar. Slaked lime is easily dissolved by solution of sugar; if equal molecules of sugar and lime be dissolved in cold water, and alcohol added, a precipitate of CaO.Cj,Ho.0u, is obtained, but if an excess of lime be employed, the precipitate is 2CaO.CjgHo.0,4. When the solution of either of these is boiled, it deposits 3CaO.Cj,.H»201,, which requires more than 100 parts of cold water and 200 parts of boiling water to dissolve it, but dissolves readily in solution of sugar. All these compounds are decomposed by COg. If strontium hydroxide be added to a boiling solution containing 15 per cent. of sucrose, the compound 2Sr0.C,.H2.0,, separates as a granular precipitate, and when 2-5 molecular weights of the hydroxide have been added, the precipitation of the sugar is nearly complete. If the precipitate be stirred with boiling water, it decomposes, on cooling, forming sugar and strontium hydroxide. Iron is much corroded by sugar, in the presence of air, the metal being dissolved as ferrous sucrate, CjpHooFe”’O,, (?), which, in contact with air and moisture, deposits ferric hydroxide, and is reconverted into sugar, which attacks # fresh portion of the iron. Lead is also attacked and dissolved by sugar solution, especially when heated. On boiling lead hydroxide with solution of sugar, it is dissolved, and, as the solution cools, it deposits diplumbic sucrate, CygH,gPb,0,,.Aq, as a white powder, which loses its waterat100°. The sugar may be completely precipitated in thisform. Triplumbic sucrate, CygH,gPb30,;, is precipitated when soda is added to a mixture of solutions of lead acetate and sugar ; it may be crystallised in needles from sugar solution. Many metallic oxides form compounds with sugar which are readily soluble in alkalies, so that the addition of sugar to solutions of copper and iron, for example, prevents their precipitation by alkalies. If solution of sucrose be mixed with cupric sulphate and potash gradually added, a blue precipitate of Cu(OH), is formed, which dissolves, when more potash is added, to a deep-blue liquid, which may be heated to boiling without change, but if long boiled or kept, deposits cuprous oxide or hydroxide as a red or yellow precipitate. When a solution containing sugar with one-fourth of its weight of common salt is allowed to evaporate spontaneously, it deposits deliquescent rhombic prisms of CypH2011.NaCl2Aq. Strong sulphuric acid converts dry sucrose into a brown mass, but if water be present, or if heat be applied, the mixture froths up and blackens, evolving CO, CO, and SO, gases. Dilute sulphuric and hydrochloric- acids, when boiled with sugar, convert it into a brown substance, partly soluble in alkalies, and containing about 63 per cent. of carbon (sugar contains 42). Formic acid (containing only 26 per cent. of carbon) is found in the solution. Strong nitric acid dissolves sucrose, and converts it, on heating, into oxalic and saccharic acids. When heated with dilute nitric acid, it yields, besides these, acetic, tartaric, hydrocyanic and carbonic acids, with evolution of N, NO and N,O;. CoH, 404(OH)g + 6NH; + 12H,0. Pyroxylin behaves like a nitrate when shaken with mercury and strong sulphuric acid, evolving the whole of its nitrogen as nitric oxide. The following proportions may be recommended for preparation of gun-cotton on a small scale: Dry 1000 grains of pure nitre (p. 363) at a very moderate heat, place it in a dry retort (Fig. 140), pour upon it 10 drachms (by measure) of strong sulphuric acid, and distil until 6 drachms of nitric acid have passed over into the receiver. Dry some pure cotton-wool, and weigh out 30 grains of it. Mix 24 measured drachms of the nitric acid with an equal volume of strong sulphuric acid in a small beaker. Allow the mixture to cool, immerse the cotton-wool in separate tufts, pressing it down with a glass rod, cover the beaker with a glass plate, and set it aside for fifteen minutes. Lift the cotton out with a glass rod, throw it into at least a pint of water, and wash it thoroughly in a stream of water till it no longer tastes acid or reddens blue litmus-paper. Dry the cotton by exposure to air or to a very moderate heat. 776 MANUFACTURE OF GUN-COTTON Gun-cotton is manufactured from the waste cuttings from spinning-machines (cotton-waste), which is first thoroughly cleansed. One part of nitric acid (sp. gr. 1-52) and 3 parts by weight (or 2-45 by volume) of sulphuric acid (sp. gr. 1-84) are placed in separate stoneware cisterns with taps, and allowed to run simultaneously, in slow streams, into another stoneware cistern furnished with a tap and an iron lid, through a second opening in which an iron stirrer is moved to mix the acids thoroughly. The mixture is set aside for several hours to become perfectly cool. A quantity of the mixed acids is drawn off into a deep stoneware pan standing in cold water, and provided with a perforated iron shelf, upon which the cotton may be drained. The well-dried cotton is immersed, a little at a time, in the acid, and stirred about in it for two or three minutes with an iron stirrer. It is then placed upon the perforated shelf, and the excess of acid squeezed out with the stirrer. Enough acid is drawn from the cistern to make good that which has been absorbed by the cotton, and more cotton is treated in the same way. Since a considerable rise of temperature is produced by the action of the nitric acid upon the cotton, it is necessary to keep the pan surrounded with cold water. A large proportion of the cotton is doubtless converted into gun-cotton in this preliminary immersion in the mixed acids ; but in order to convert the remainder, it is necessary to allow the cotton to remain in contact with the acid for a much longer period, so as to ensure its penetration into every part of the minute twisted tubes of the fibre. The skeins are next transferred to a jar with a well-fitting cover, in which they are pressed down and completely covered with the mixed acids, of which from 10 to 15 times the weight of the cotton will be required, according to the closeness with which the skeins are packed in the jar. The jar is placed in cold water, and the cotton allowed to remain in the acid for about twelve hours. The skeins are then removed, with the aid of an iron hook, to a centrifugal extractor, which is a cylinder made of iron gauze, through which the bulk of the acid is whirled out by the rapid rotation of the cylinder upon an axle. In order to wash away the remainder of the acid, the cotton is plunged, suddenly, to avoid rise of temperature, into a cascade of water, and is then drained in the centrifugal extractor, and again rinsed in much water, It is next reduced to pulp in a rag-engine such as is employed in paper- mills. The pulp is thoroughly washed by being well stirred by a poaching-engine for about forty-eight hours in a stream of warm water, so as to remove every trace of acid, which is assisted by rendering the water alkaline with a little lime or carbonate of soda or with ammonia. The pulp is then drained, moulded into discs or any other required form, condensed by hydraulic pressure until it has at least the same specific gravity as that of water, and dried upon heated plates. As it leaves the hydraulic press, the cotton contains about one-fifth of its weight of water, so that it may, if required, be cut up or bored without danger of explosion. When a mass of the gun-cotton wool is exploded in an unconfined state, the explosion is comparatively slow (though appearing to the eye almost instantaneous), since each particle is fired by the flame of that immediately adjoining it, the heated gas (or flame) escaping outwards, so that some time elapses before the interior of the mass is ignited. But when the gun-cotton is enclosed in a strong case, so that the flame from the portion first ignited is unable to escape outwards, and must spread into the interior of the mass, this is ignited simultaneously at a great number of points, and the decomposition occurs far more rapidly ; a given weight of cotton being thus consumed in a much shorter time, a far higher temperature is produced, and the ultimate products of the explosion are much less complex, as would be expected from the well-known simplifying effect of high temperatures upon chemical compounds. If a tuft of gun-cotton wool be placed at the bottom of a tall glass cylinder and inflamed by a heated wire, it will be seen that, immediately after the explosion, the gas within the cylinder is colourless, but soon becomes red, showing that NO was present among the products, and became converted into NO, by the oxygen of the air. The water formed by the combustion of the hydrogen converts the NO, into HNO, and HNO, (p. 204), and hence the acid character of the moisture deposited in the barrel of a fowling-piece in which gun-cotton cartridges are employed. A little ICN can be detected ameng the products of combustion of loose gun-cotton. Berthelot estimates the pressure produced by the detonation of gun-cotton, com- COLLODION 777 pressed to a density of 1-1, at 24,000 atmospheres, or about 160 tons per square inch, being only half the pressure assigned by him to the detonation of mercuric fulminate. If a piece of compressed gun-cotton be kindled with a hot wire, it burns rapidly away producing a large volume of flame, but without any explosive effect.1 In order that gun-cotton fired in this manner might be used for destructive purposes, it was found necessary to confine it in strong cases, so that the flame of the portion first ignited should be employed in raising the temperature of the rest to the exploding- point. The unconfined gun-cotton, however, can be made to explode or detonate with most destructive violence, by exploding in contact with it a detonating fuse, consisting of a little tube of quill or thin metal charged with a few grains of mercuric fulminate. Such detonation can be communicated along a row of pieces of compressed cotton placed at short distances from each other. This sympathetic explosion is by no means confined to gun-cotton but exists in the case of nitroglycerin, and even gunpowder. The modus operandi of the detonating fuse appears to consist in the influence of vibratory motion, and the nature of the motion necessarily depends upon the nature of the explosive. That it is not a result of the action of heat is proved by the circum- stance that wet gun-cotton may be exploded by a detonating fuse, so that torpedoes may be charged with a mixture of gun-cotton pulp and water, containing 15 per cent. of the latter, if a small charge of dry gun-cotton be placed in contact with the fuse. It has been found that the wet gun-cotton is more easily detonated when in a frozen state. The very destructive effect of the gun-cotton exploded in this way is, of course, due to the sudden manner in which the whole mass is resolved into gaseous products, When heat is the cause of the explosion, it must be comparatively slow, for gun-cotton transmits heat slowly, but the vibration caused by detonation is transmitted with the velocity of sound, and the explosion becomes rapid in proportion. Gun-cotton is more easily exploded than gunpowder ; the latter requires a tem- perature of at least 600° F. (316° C.), whilst gun-cotton may explode at 277° F. (136° C.), and must explode at 400° F. (204° C.). It is very difficult to explode gunpowder by percussion, even between a steel hammer and anvil ; but gun-cotton invariably detonates in this way, though the explosion is confined to the part under the hammer. The explosion of gun-cotton is approximately represented by the equation, C).H,40,(NO3)g= 5CO + 7CO, + 4H, + 3H,0 + 3Ne, and is attended by the evolution of 1071 heat- units per unit weight, but by no smoke, a most important advantage in mines, the atmosphere of which is sometimes rendered almost intolerable by the smoke of gun- powder used in blasting ; but death has been caused by the carbonic oxide generated. The absence of residue from the gun-cotton prevents the fouling of guns, and renders it unnecessary to sponge them after each discharge, for the amount of incombustible mineral matter present in the cotton is very small (from 1 to 2 per cent.), and is entirely scattered by the explosion. Nitrated cellulose is the main constituent of several modern sporting powders such as E. C. sporting powder, E. C. rifle powder, and Schultze’s powder. Soluble pyroxylin, or collodion cotton, is a mixture of cellulose nitrates lower than the hexanitrate—e.g. the penta-, tetra-, iri-, and di-nitrates. It is the product of the action upon cellulose of a mixture of HNO, (1 mol.) and H,SO, (1 mol.) slightly diluted with water (1? mols.). It differs from pyroxylin in being soluble in a mixture of ether with one-seventh of alcohol, yielding a viscous solution, which leaves the transparent collodion film when evaporated. It is much less rapidly combustible than pyroxylin. In order to prepare the soluble cotton for collodion, 3 measured ounces of ordinary HNO, (sp. gr. 1-429) are mixed with 2 ounces of water in a pint beaker. Nine measured ounces of strong H,SO, (sp. gr. 1-839) are added to this mixture, with continual stirring. A thermometer is placed in the mixture, which is allowed to cool to 140° F.; 100 1 Yoo much stress, however, should not be laid upon this as rendering gun-cotton magazines safer in case of fire than gunpowder magazines. The experiment with gunpowder mentioncd at p. 366 shows that if all the particles of an explosive be raised at once to near the inflaming-point, the first particle which inflames will cause the detonation of the remainder, Since the Inflaming-point of gun-cotton is low, the above condition would be easily fulfilled in a conflagration. 778 SALICIN grains of dry cotton-wool, in ten separate tufts, are immersed in the mixture for five minutes, the beaker being covered with a glass plate. The acid is then poured into another beaker, the cotton squeezed with a glass rod, and thrown into a large volume of water ; it is finally washed in a stream of water till it isno longer acid, and dried by exposure to air. Collodion balloons.—These balloons may be made in the following manner : Six grains of collodion cotton, prepared according to the above directions, are dissolved in a mixture of 1 drachm of alcohol (sp. gr. 0-835) and 2 drachms of ether (sp. gr. 0-725) in a corked test-tube. The solution is poured into a dry Florence flask, which is then turned about slowly, so that every part of its surface may be covered with the collodion, the excess of which is then allowed to drain back into the tube. Air is then blown into the flask through a long glass tube attached to the bellows as long as any smell of ether is perceptible. A penknife blade is carefully inserted between the flask and the neck of the balloon, which is thus detached from the glass all round; a small piece of glass tubing is introduced for an inch or two into the neck of the balloon, so that the latter may cling round it. Through this tube air is drawn out by the mouth, until one-half of the balloon has left the side of the flask and collapsed upon the other half ; by carefully twisting the tube, the whole of the balloon may be detached and drawn out through the neck of the flask, when it must be quickly untwisted, distended by blowing through the tube, tied with a piece of silk, and suspended in the air to dry. The average weight of such balloons is 2 grains. Celluloid, or artificial ivory, or xylonite, used for combs, billiard-balls, &c., is essentially compressed collodion-cotton mixed with camphor and zinc oxide. When collodion-cotton is kept for some time, especially if at all damp, it undergoes decomposition, filling the bottle with red fumes, and becoming converted into a gummy mass, which contains oxalic acid. Tunicin, CgHyoO;, or animal cellulose, is prepared from the outer covering or mantle of the molluscs belonging to the class T'unicata. The mantle is long boiled with hydro- chloric acid and potash, in succession, and the residue washed with water, alcohol, and ether. Tunicin is left as a translucent mass, so closely resembling cellulose in properties that it is believed by some chemists to be identical with it. XIV. GLUCOSIDES The compounds belonging to this class are capable of conversion into a sugar and some other compound by the action of acids, alkalies, and certain ferments, the change being generally the result of hydrolysis (p. 224). They are found in plants chiefly, and generally yield products of decomposi- tion belonging to the aromatic group. Some of them have been already noticed.! Salicin, C,H,,0,-0-C,H,CH,OH, is extracted from willow-bark (Salix) by boiling it in water, removing the colouring-matter and tannin from the solution by boiling with lead hydroxide, precipitating the excess of lead by H,S, and evaporating the filtered liquid, when the salicin crystallises in needles which may be recrystallised from alcohol. It forms bitter colour- less prisms (m.-p. 188°) soluble in about 30 parts of cold water, in less alcohol, but not in ether. It is readily distinguished by the bright red colour which it gives with strong sulphuric acid, which detects it when applied to the inner bark of the willow. With emulsin (p. 597) or saliva, its aqueous solution yields glucose and salicyl-alcohol or saligenin ; C,sH,s07 + H,O = CyH,.0, + CsH,(OH)-CH,-OH. The saligenin gives a blue colour with ferric chloride. Salicin is occasionally administered as a febrifuge, and is a common adulteration of quinine. 1 They will probably be shown to be ethereal alcoho derivatives, for several compounds, closely resembling glucosides in behaviour, have been synthesised by dissolving sugars in alcohols and saturating with hydrogen chloride. In this way, methyl alcohol and glucose have yielded methylglucoside, C,H,(OCH,)0,. GLUCOSIDES 779 When solution of salicin is boiled for some time with dilute sulphuric or hydro- chloric acid, it yields an amorphous precipitate of saliretin, a product of the decom- position of saligenin— 2C,H Og (saligenin) = H,O + C,4H,403 (saliretin). Sulphuric acid and potassium dichromate convert salicin into oil of spirza (p. 598). Fused with potash, it yields potassium salicylate. Dilute nitric acid converts salicin into helicin: O3H,gO7 + O = Cy3Hyg07 + H,O. This also is a glucoside, yielding glucose and oil of spireea, when hydrolysed by ferments or acids ; C,3;H,g0, + H,O = CgH120, + CrzH,O2. Strong nitric acid converts salicin into mnétrosalicylic acid, CsH3(OH)(NO,)CO,H. When acted on by chlorine, salicin yields substitution- products containing one, two or three atoms of chlorine, and these, when boiled with dilute acids, yield the corresponding chlorosaligenins. Populin, or benzoyl-salicin, C,3H,7(C7H;0)O, + 2H,0, is a sweet crystalline body existing, together with salicin, in the bark and leaves of the aspen (Populus tremula), a tree of the willow order, and may be extracted in the same way as salicin. When boiled with Ba(OH)p, it yields salicin and benzoic acid (which becomes barium benzoate) ; C,3H,7(C;H;0)0, + H,O = C,,;H,,07, + C7;H;0-OH. Boiled with dilute acids, it is converted into benzoic acid, saliretin and glucose. It is obtained artificially by fusing salicin with benzoic anhydride— Ci3Hig07 + (C7H;0)20 = CysHi7(C7H;0)0, + C,H;0-OH. Arbutin, Cj2H,.0,, is found in the leaves of the bear-berry (Arbutus uva ursi), an astringent plant of the Heath order, sometimes used medicinally, and in Pyrola umbellata, also a medicinal plant of the closely allied Winter-green order. It may be prepared like salicin, and crystallises in bitter needles from its aqueous solution. Emulsin or dilute acids decompose it into glucose and hydroquinone— Ci2Hig07, + H20 = CeHi20, + CeHy(OH)p. Phlorizin, Co;H1019 (pdowe, bark, and pila, root), is extracted by hot alcohol from the root-bark of the apple, pear, plum, and cherry tree. It crystallises from hot water in bitter needles with 2Aq. When boiled with dilute acids, it yields glucose and phloretin ; CygyHo4Oi9 + H,O = CyHy,0g + Cy5Hys0;. When exposed to air in the presence of ammonia, it is converted into a fine purple colouring-matter, phlorizein, Cay H39N2013 = (CoyHo,0,9 + 2NHz + 30). It melts at 108°. Glycyphyllin, Co,H240g, is a crystalline substance allied to phlorizin, extracted from the leaves of Smilax glycyphylla, an Australian plant -of the Sarsaparilla order. It is sparingly soluble in cold water, but dissolves in hot water and in alcohol. Its solution tastes like liquorice. It does not reduce alkaline copper solutions, and is not precipitated by normal lead acetate, though it is by the basic acetate. When boiled with dilute sulphuric acid, it yields phloretin and rhamnose (p. 761)— . C21H240,) + HyO = Ci5Hi4O5 + C5H(CH3)O5. Hesperidin, Co2Hog0y2, is contained in the fruit leaves, and stalks of the orange- tree and other members of the same family ; it is resolved by acids into glucose and hesperitin, CygH,40.. Aisculin, Cy;H 0g, is extracted by boiling water from the bark of the horse-chestnut (Aisculus hippocastanum), sometimes used as a febrifuge. The infusion of the bark is mixed with lead acetate, to precipitate the tannin and colouring-matter, filtered, the excess of lead precipitated by H,S, and the filtered solution evaporated, when esculin crystallises in colourless needles containing }Aq, sparingly soluble in cold water, but readily in hot water and in alcohol. The aqueous solution is slightly bitter, and has a strong blue fluorescence, destroyed by acids and restored by alkalies. EZmulsin and boiling dilute acids convert esculin into glucose and esculetin, a dihydroxycoumarin (p. 623)— CsHyg09 + HpO = CeHi20g + CyoHe Ou. Asculetin exists, in small quantity, in horse-chestnut bark. Paviin or fraxin,CygHygOro, accompanies esculin in horse-chestnut bark. It is more soluble in ether than is zsculin, and has a green fluorescence. Fraxin is obtained in larger quantity from the bark of the ash (Fraxinus -excelsior), which is also febrifugal. Trees of the genus Pavia, belonging to the same order as horse-chestnut (soap-worts), yield more paviin than zsculin, . 780 AMYGDALIN Amygdalin, C,,H,,NO,,, is extracted from bitter almonds, the kernels of the fruit of Amygdalus communis, of which one variety yields the sweet almond, containing no amygdalin. The almonds are pressed to extract the fixed oil (not the essential oil, but a glyceride), and the bitter- almond cake is boiled with alcohol, from which the amygdalin crystallises in pearly scales which dissolve in water, and crystallise from it in prisms with 3Aq. Amygdalin may also be extracted from the kernels of peaches and nectarines, both fruits of species of amygdalus. It is also present in the leaves and kernels of several varieties of cherry, and the bitter-almond oil formed from it confers the flavour upon cherry-brandy, noyau, ratafia, and maraschino. The production of glucose, hydrocyanic acid, and benzoic aldehyde, by the action of emulsin on solution of amygdalin, has been already noticed (p. 597). When long boiled with baryta, it yields ammonia and the barium salt of amygdalic acid, C.~H,,0,;. This acid is a glucoside, for when boiled with dilute acids it is converted into glucose and mandelic acid (p. 621)— CyoH25015 + 2H,0 = 2C,H,,0, + CsH,03. Daphnin, C,;Hyg09, isomeric with xsculin, is obtained from the bark of Daphne mezereum, used as a remedy for toothache. Dilute acids convert it into glucose and daphnetin, a dihydroxy-coumarin (p. 623) ; CysHyg0) + H2O = CgHy20g + CoHg Ou. Convolvulin, Cz;Hs5 90,6, and its homologue jalapin, Cz4H5gQ 5, are the purgative principles of certain of the Convolvulaceew, such as jalap and scammony. They are amorphous bodies, which yield glucose, and, respectively, convolvulinol, C3H2403, and jalapinol, CysH3903, when hydrolysed by acids or emulsin. Turpethin, isomeric with jalapin, is extracted from the roots of Convolvulus turpethum also used as a purgative. Helleborein, CygH440j5, is the narcotic poison from the root of black hellebore, a plant of the Buttercup order. It crystallises in needles, which dissolve easily in water, but sparingly in alcohol. Digitalin is the poisonous glucoside extracted from the leaves of the foxglove (Digitalis purpurea). It is amorphous, sparingly soluble in water, chloroform and ether, but dissolves in alcohol. Strong sulphuric and hydrochloric acids dissolve it with a yellow colour. Its formula is not known. It is the medicinally valuable principle of digitalis. Digitoxin is more poisonous, but uncertain and dangerous in its action. Digitonin is similar to saponin. Saponin, C3.H;,0j¢, is found in the soap-wort, in the root of the clove-pink, which belongs to the same natural order (Caryophyllacece), in quillaia bark, and in the fruit of the horse-chestnut. It may be extracted by boiling alcohol, which deposits it as an amorphous powder on cooling. It is soluble in water, and its solution lathers like soap. This leads to the use of decoctions containing it, such as that of the soap-nut of India, for cleansing delicate fabrics; also for making ‘‘ heading” for beverages. The dry powder of saponin causes sneezing. Coniferin, CygHo20,.2.Aq, crystallises from the gummy liquid found, in the spring, between the inner and outer barks of coniferous trees. In contact with water and emulsin, it yields glucose and coniferyl alcohol— CyeHo203 + H2O = CgHyeOg + Cio H 203. The latter is a crystalline body, soluble in ether, and smelling of vanilla. When distilled with potassium dichromate and sulphuric acid, it yields acetic aldehyde and vanillin ; C,oHi203 + O = C,H,O + CgH,0; (p. 599). Quercitrin, C2H5.0j, is the colouring-matter of quercitron bark, and is also found in horse-chestnut flowers, and in grape-vine, sumach and catechu. It may be extracted from quercitron bark by alcohol, the tannin precipitated by solution of gelatine, and the filtrate evaporated. Quercitrin forms yellow crystals, sparingly soluble in water. Dilute sulphuric acid converts it into rhamnose and quercetin ; C3gH3g02) + H,O = 2C5H9(CH3)05 + CosHigO0u. This last, also called flavin, is found in heather, in tea, and in the root bark of apple and other trees. It is a yellow crystalline body, which is sparingly soluble in water and more soluble in alcohol. It may be sublimed in yellow needles. Rutin, which occurs in rue and in capers, much resembles quercitrin. BITTER PRINCIPLES 781 Antiarin, C,4H2)0;.2Aq, is the principle of the Javanese arrow-poison, upasantiar, the juice of Antiaris toxicaria, a large tree of the Bread-fruit tribe. It may be crystallised from the alcoholic extract of upas, and is soluble in water and ether. With acids it behaves like a glucoside. Bitter Principles.—Picrotovin, C39H34013, is a narcotic poison contained in Cocculus indicus, the fruit of Anamirta paniculata, a tropical trailing shrub of the order Menispermacee. The fruit has been sometimes used as a hop-substitute by brewers. Picrotoxin may be extracted from the seeds by boiling with alcohol, from which it crystallises in needles ; it is sparingly soluble in water, and soluble in ether ; it is a mixture of picrotorinin, C,sHig0g, + HO, and picrotin, Cy,HgO7. Quassiin, Ca2H490,9, is another crystalline bitter principle, extracted by alcohol from quassia chips, the wood of Picrasma excelsa (bitterwood). This is also said to be used as a hop-substitute, and is not poisonous, except to flies. It is administered as a tonic. Water dissolves it sparingly, but acquires a bitter taste. Calumbin, Cy;Hy.0y, is a substance of the same kind, extracted from calumba root (Cocculus palmatus). Santonin, C,;H,03, is the bitter principle of the seeds of Artemisia santonica (worm- seed) and of Artemisia absinthium (wormwood) ; it may be extracted from absinthium by mixing it with lime and boiling with weak alcohol; the solution is evaporated and the residue boiled with acetic acid, which deposits colourless prisms of santonin, which become yellow when exposed to light. It is insoluble in water, but dissolves in alcohol and ether ; it is dissolved by alkalies, yielding santonates, e.g. sodium santonate, NaC,;H;90,, from which santonic acid, HC\;H,g0,, may be obtained by shaking with HCl and ether ; thus it appears to bea lactone. It contains a ketonic group. Santonin is moderately poisonous, and affects the perception of colours, rendering violet invisible ; it is contained in the liqueur known as créme d’absinthe, or Wermuth. Gentianin, C,4H,00;, is extracted by ether from the roots of the yellow gentian, used as a bitter and tonic. It forms yellow needles, sparingly soluble in water, but freely in alcohol and ether ; also soluble in alkalies, with a strong yellow colour. Elaterin (¢harnptoc, driving away, in allusion to its drastic quality), Cy>H2.,03, is the active principle of the drug elaterium, deposited from the juice of the squirting cucumber (Ecballium*elaterium). It is crystalline, insoluble in water, but soluble in alcohol and ether. It admits of sublimation. Kosine, Cz,H3g0,9, is the active principle of Kousso, an Abyssinian plant used as a vermifuge ; it crystallises in yellow needles, which are insoluble in water, but soluble in ether and alcohol. Aloin, CigH,,07, is a yellow crystalline bitter’substance extracted from aloes, the dried juice of various species of Aloe. It is non-glucosidal. Glycyrrhizic acid (formerly called glycyrrhizin), CyzHe,NOjg, is extracted from dried liquorice root (Glycyrrhiza glabra) by dilute acetic acid ; alcohol is added and the filtrate evaporated to a syrup. It is amorphous and has a sweet taste. Cantharidin, C,oHy2.04, is extracted from the Spanish fly and other insects. It is a bitter substance, melting at 218°, and subliming. It blisters the skin. Vegetable Colouring-Matters. — Notwithstanding the great variety and beauty of the tints exhibited by plants, comparatively few yield colour- ing-matters which are sufficiently permanent to be employed in the arts, the greater number of them fading rapidly as soon as the plant dies, since they are unable to resist the decomposing action of light, oxygen, and moisture, unless supported by the vital influence in the plant; some of them fade even during the life of the plant, as may be seen in some roses which are fully coloured only in those parts which have been screened from the light. Diligent research has disclosed the constitution of many of the vegetable colouring-matters, such as those of the madder and indigo plants ; these are considered under the classes of compounds to which they belong. Chlorophyll (from yAwpds, green; piAXov, a leaf) is the green colour- ing of the leaves and other parts of plants. Its function in photo-syn- thesis has already been referred to (p. 54) ; for its close chemical relation- ship with hemoglobin, the red colouring of the blood of animals see p. 793. Constitutionally it differs from haemoglobin in that the latter is composed of protein in union with a chromatogenic group, hematin, while chlorophyll 782 CHLOROPHYLL contains no group corresponding with protein, but is itself comparable with hematin. Both chlorophyll and hematin are metallic derivatives ; the former contains magnesium, the latter iron. The metals are not present as bases, but as integral parts of the complex molecules, probably exercising their subsidiary valencies, and uniting a number of pyrrol nuclei; thus —C C— —C Qe Os G Ng f ww aS ei gf a ae Mg: Fe? a ¢ a C —C Gu Sw on SwK a nd see Noe _% No Chlorophyll. Hemin (p. 793). Chlorophyll is an amorphous body, obtained by extracting the natural material under carefully regulated conditions. It consists of a tricarboxylic acid, chlorophyllin, C3,H.gN,Mg(COOH),, one carboxyl being free, one united to methyl and one to a simple unsaturated alcohol phytol, C,,.H,,0H, of which it contains an unvarying amount, 33 per cent. ; this has proved to be the case in chlorophyll from two hundred different kinds of plants. Hence, the formula of chlorophyll is CO,H Cy,HogNsMg | CO,Me | CO.CooFise A crystalline modification has been described; this contains ethyl instead of phytyl, and is a derivative produced during the extraction of chlorophyll by means of ethyl alcohol ; free phytol is eliminated simulta- neously. It is now known as ethyl chlorophyllide ; by using methyl alcohol, methyl! chlorophyllide is formed ; hence, chlorophyll is phytol chlorophyllide. A valuable résumé of recent work on chlorophyll occurs in the “hem. Soc. Ann. Reports, 1911. Saffron consists of the stigmas and tops of the styles of Crocus sativus ; dried and pressed into cakes they form the saffron of commerce, which has an agreeable odour. It is chiefly imported from Spain, and is often adulterated. It gives up to water and alcohol a yellow amorphous glucoside, termed polychroite. Annato is another yellow colouring-matter, which forms the pulp round the seeds of Bixa orellana, a West Indian shrub. It is used for colouring butter and cheese. The colouring principle is called bizin ; it is sparingly soluble in water, but dissolves in alcohol and in alkalies ; acids reprecipitate it without much change of colour. Turmeric is the root of an East Indian plant, the Curcwma longa, and is used in curry. It contains a crystalline yellow body, curcumin, Cy;Hs90., which may be extracted by boiling benzene. It is insoluble in water, but dissolves in alcohol. Alkalies dissolve it, forming red salts, from which acids precipitate it of a yellow colour. Paper dyed with turmeric is used as a delicate test for alkalies, which turn it brown. When acted on by boric acid and strong sulphuric acid, it is converted into rosocyanin, which crystallises in green needles dissolved by alcohol, with a red colour, which is changed to deep blue by alkalies. Turmeric-paper is used in testing for boric acid (p. 290). Weld is the Reseda luteola, a plant of the Mignonette order, the leaves of which give a yellow solution when boiled with water. The hot decoction, mixed with alum and chalk, gives a yellow precipitate, which is used in paper-staining. It contains a crystal- line yellow body, luteolin, Cjs;Hio0¢, sparingly soluble in water, but dissolved by alcohol and by alkalies. It sublimes in yellow needles. Fustic is a yellow dyestuff, of which there are two kinds. Old fustic is the wood of a tree of the Mulberry order (J/orus, or Maclura tinctoria), grown in the West Indies. Young fustic is the wood of Rhus cotinus, or Venice sumach, from Italy and the South VEGETABLE COLOURING-MATTERS 783 of France. When old fustic is boiled with water, the solution deposits yellow needles of morin, Cy3H,Og, soluble in alcohol. The mother-liquor of morin, when evaporated, yields maclurin or moritannic acid (p. 622). Gamboge is a yellow gum-resin, ‘originally obtained from Camboja in Asia, and is exuded by certain species of Guttifere. It contains about 30 per cent. of a yellow gum, soluble in water, and 70 per cent. of resin soluble in alcohol and alkalies, called gambodic acid. Purrée (piri), or Indian yellow, imported from India and China, and said to be the dried excrement of buffaloes fed on mango leaves, is a compound of magnesia, with euxanthin (or euxanthic acid) CyyH,g019. By extracting it with hydrochloric acid and alcohol, the euxanthin is obtained in yellow prisms, sparingly soluble in water, soluble in alcohol, ether, and alkalies. When heated, it yields a yellow crystalline sublimate of euxanthone, C,sHgO,. On fusion with potash, euxanthone yields hydro- quinone, and nitric acid converts it into trinitroresorcin, which opposes the idea that purrée is of animal origin. Safflower, which yields rouge, consists of the dried flowers of Carthamus tinctorius, cultivated in Egypt. It contains a yellow substance, which may be extracted by water, and a red colour, carthamin, Cy4H,,07, which may be dissolved out by sodium carbonate, and precipitated by acetic acid. Alcohol dissolves it to a red solution. It is used in dyeing, but soon fades when exposed to light. Carotin, C,gH240, is a red substance, found in small crystals in the cells of the carrot. It crystallises from alcohol in cubes having an agreeable odour. Santalin, C,5H,O;, is the colouring-matter of red sanders wood (Pterocarpus santa- linus), from which it may be extracted by alcohol, which deposits it in red crystals insoluble in water, but giving violet solutions with alkalies. Hematoxylin, C,.H,,0,4.3H,0, is extracted from logwood (Hematoxylon campechi- anum), which grows at Campeachy in the Bay of Honduras, by boiling the chips with water. It is deposited from the solution in yellow needles, which are soluble in water, alcohol, and ether. It resembles the phenols by dissolving in alkalies; the solution is purple and absorbs oxygen and forms a red colouring-matter, hematein, C,gHy.0,, sparingly soluble in cold water, which may also be obtained by oxidising hematoxylin, in ethereal solution, with nitric acid. Reducing-agents, such as sulphurous acid, convert it into hematoxylin. When fused with potash, hematoxylin yields pyrogallol. It contains five OH groups. Potassium chromate gives an intense black colour with infusion of logwood, which has been used as an ink, but is fugitive. Logwood boiled with distilled water gives a yellow solution, but with common water it gives a fine purple-red from the production of hematein by the oxidation of the hemotoxylin in presence of the calcium carbonate in the water. The solution of logwood is sometimes used as an indicator in alkali- metry. ae C,eH40;, is contained in Brazil wood (Cesalpinia brasiliensis); peach- wood (C.. echinata), and Sappan wood (C. sappan)—all dyewoods from the same botanical sub-order as logwood. Brazilin, when quite pure, forms colourless crystals, and yields colourless solutions in air-free water and alcohol ; but it soon becomes yellow (brazilein, C,,H,20,) by oxidation, and dissolves in alkalies with a fine red colour, which is bleached by reducing-agents. It contains four OH groups. Lac is a red dye extracted from the resinous exudation of certain tropical trees of the Fig tribe, punctured by an insect (Coccus). In its crude, natural state, encrusting the small branches, it is known as stick-lac, and has a deep red colour ; when broken off the branches and boiled with water containing sodium carbonate, it gives a red solution from which the colouring matter is precipitated as a lake by adding alum, and made into cubical cakes for the market. The resinous matter (about 68 per cent.) left undissolved by sodium carbonate is termed seed-lac ; this is melted, strained through a cloth, and allowed to solidify in thin layers, when it forms shell-lac, which is much used in the manufacture of sealing-wax and varnishes. The lacquer applied to brass is named after this resin, being an alcoholic solution of shell-lac, sandarach, and Venice turpentine. Indian ink is made by mixing lamp-black with a solution of 100 grains of lac and 20 grains of borax in 4 ounces of water. Carmine owes its_colour to carminic acid, Co2H»40,2, extracted by boiling water 784 PROTEINS—CLASSIFICATION from the cochineal insect, Coccus cacti, which is found upon a species of cactus in Mexico and Peru. Carmine-lake, which consists essentially of the aluminium salt of carminic acid, is precipitated by alum and potassium carbonate from the aqueous extract of the cochineal insect. The acid itself is a purple-red solid, casily soluble in water and alcohol, and sparingly in ether. It dissolves unchanged in strong sulphuric acid. XV. PROTEINS These embrace a large, well-characterised, though chemically ill-defined, group of substances of highly complex and unknown constitution derived directly or indirectly from living matter. Albumin (as white of egg), casein (from milk), globulin (from blood serum), gelatine (from bones) are familiar examples ; but proteins also exist in horn, silk and numerous other substances of various properties. Nearly all except the protamines and histones contain sulphur, and a few contain phosphorus. The limits of their composition approximate C 51-55 per cent., H 7 per cent., N 15-17 per cent., 8 0°4-2°5 per cent., O 20-30 per cent., the mean of which suggests the formula (CoqoH 39,N e801) where 7 is probably at least 3, as the molecular weights appear to exceed 15,000. Owing to the lack of precise knowledge there has been much confusion hitherto as to nomenclature and classification. In 1908 the Chemical and Physiological Societies of the principal countries agreed to adopt the follow- ing: (1) Protamines. These are amongst the more simply constituted proteins, usually occurring in combination with nucleic acids, &c., as conju- gated proteins (infra). They are strongly basic, absorb CO, from air, are the richest in N (25-30 per cent.), but contain neither 8 nor P. Their most abundant cleavage products are diamino acids. They are not coagu- lated by boiling. (2) Histones are basic, rich in N (17—20 per cent.), varied in properties. They yield a large number of amino acids on disintegration, and are precipitable by ammonia. (3) Albumins and (4) Globulins comprise the greater number of native proteins, and are the most characteristic groups ; they are coagulated when their solutions are heated. They contain sulphur, but usually not phosphorus. They are sometimes accompanied by carbo- hydrates as prosthetic groups (q.v.). They are distinguished chiefly by differences of solubility. The albumins are soluble in distilled water, but not the globulins. The former are salted out less readily than the latter. Egg-albumin, serum-albumin, serum-globulin, thyreoglobulin, fibrinogen, are typical examples. The last clots at low temperatures to form fibrin, the insoluble portion which can be whipped out of blood. (5) Glutelins, the alkali-soluble proteins of vegetable origin, are closely allied to the glo- bulins. (6) Gliadins, alcohol-soluble proteins found in the vegetable world. (7) Phospho-proteins, the vitellin-caseinogen group. (8) Sclero-proteins, including gelatin and keratin; several of them form hard and insoluble bodies. (9) Conjugated proteins. In these the protein molecule is united to a non-protein, “ prosthetic,’ group. According to the nature of the non- protein group they are sub-classified into (a) Nucleo-proteins, in which the various complex nucleic acids constitute the prosthetic group. They contain phosphorus, but not sulphur. These acids disintegrate into (i) phosphoric acid ; (ii) pyrimidin derivatives (monocyclic, p. 806) ; (iii) purin derivatives, closely related to the last, e.g. hypoxanthine, xanthine, guanine (bicyclic, p. 811); (iv) pentoses (p. 761); (v) levulinic acid (p. 649). (6) Chromo- proteins, eg. hemoglobin. (c) Gluco-proteins, containing carbohydrate groups, e.g. mucin. (10) Protein derivatives, (a) Metaproteins (acid-albumin, alkali-albumin, &c.); (6) Proteoses, complex cleavage products falling between the proteins proper and the peptones; (c) Peptones, products of the hydrolysis of proteins, which cannot be salted out from solution and PROTEINS 785 fail to give most of the protein colour-reactions, but they still give the biuret reaction; they are sufficiently complex to have molecular weights of 600 or so; (d) Polypeptides (q.v.). The chemistry of the subject has developed along three lines, the older arbitrary tests and processes, the study of degradation products, and attempts at synthesis. Along the first line, we find that proteins, e.g. egg-white, are neutral, but the neutrality is peculiar, for if acids or, in some cases, alkalies are added, the neutral reaction remains; many of them are in fact pseudo- acids and pseudo-bases. They are precipitated by heavy metals, FeCl,, FeA,, CuSO,, HgCl,, PbA,; also by most alkaloidal reagents (q.v.); and by strong nitric acid. With certain reagents they give rise to characteristic colours, and on the addition of saline substances to their solutions they are separated by “salting out” in a way peculiar to the given protein. (1) Some by NaCl, NaA, NaNO,, Na,SO,; (2) A greater number by CaCl,, CaSO,; MgSO, comes between (1) and (2); (3) ZnSO,, Am,SO, will precipi- tate nearly all. The chief means of studying the chemical nature of the natural proteins is afforded by the degradation products, i.e. the products obtained on breaking down a complex molecule into simpler entities. Hydrolysis by means of (a) superheated steam; (6) acids; (c) alkalies; (d) enzymes, is by far the most fruitful; fusion with alkalies and bio-chemical methods are also employed. Commonly, the first effect of hydrolysis is to reduce the protein molecule to the simpler though still complex peptones; these then break down to still simpler bodies such as tryptophane and the various amino acids, while these under more vigorous treatment yield NHg, CO,, &c. Amongst the better known and most frequent products are the following : Monamrxo ACIDS The more usual are dealt with at p. 708. Of the several methods for preparing the more complex, that of Fischer must suffice. The required alkyl-malonic acid, R.CH.(COOH)s, is brominated —~ R.CBr.(COOH),, and this on heating loses CO2, producing the a-brom-monocarboxylic acid, R.CHBr.COOH, which with NH, yields the a-amino acid, R.CH.NH,COOH. The amino acids are crystalline, soluble in water, nearly all are optically active, they have very high melting-points, as compared with the parent acids (cf. p. 642), and generally form intramolecular salts (cf. p. 709). a-acids are usual, t.e. with NH» on the C atom next to COOH. Glycine or glycocoll, a-amino-acetic acid, CH.NH,.COOH (p. 709). Alanine, a-amino-propionic acid, CH;.CHNH,.COOH (p. 712). Phenyl-alanine, «-amino-8-phenyl-propionic acid, C,H;CH,.CHNH,.COOH. Valine, a-amino-isovaleric acid, (CH,),CH.CHNH,.COOH. Leucine, a-amino-iso-caproic acid, (CH ,).CH.CH,.CHNH,.COOH (p. 712). Aspartic acid, amino-succinic acid, COOH.CH,.CHNH,.COOH (dibasic) (p. 713). ; Glutamic acid, a-aminoglutaric acid, COOH.CH,.CH,.CHNH,.COOH (dibasic) (p. 790). Hyproxy- AND THIO-AMINO ACIDS Serine, a-amino-@-hydroxy-propionic acid CH,.0H.CHNH,.COOH (p. 791). 50 786 PROTEINS Tyrosine, a-amino-p-oxyphenyl-propionic acid, HOC,H,.CH,.CHNH,.COOH (p. 713). Cysteine, a-amino-(-thio-lactic acid, CH,SH.CHNH,.COOH. Cystine, [—SCH,.CHNH,.COOH)},. Dramino Acips These are more basic than the last and precipitable by alkaloidal reagents. Ornithine, a-6-diamino-valeric acid, CH,NH,.(CH,),CHNH,.COOH. Lysine, a-e-diamino-caproic acid, CH,.NH,(CH2),CHNH,COOH. Arginine, a-amino-d-guanino-n-valeric acid, NH:C(NH,).NH.(CH,)3.CH(NH,) COOH. HETEROCYCLIC CoMPOUNDS The majority of these include the pyrrol group (p. 795) or this in conjugation with the benzene nucleus as the indene (p. 570) or indol (p. 796) group. Numerous other substances of physiological importance, no doubt of protein origin, depend on the same structure, e.g. skatol, indol, isatin, indigo. Proline, a-pyrrolidine-carboxylic acid, H,C——CH, H,C CH.COOH Ae NH Tryptophane, indol-amino-propionic acid, CH #* HC GO——C.CH,.CHNH,.COOH. be HC C Ne ANZ ¢ NH Histidine, imino-azolylalanine, N——-C—CH,.CHNH».COOH. | || HC CH ST NH As an instance of detailed consideration, an experiment by Fischer may be cited. 1000 g. casein was hydrolysed by 6 hours’ boiling with 3 1. HClone. The liquid was evaporated ™ vacuo, alcohol added, when, on saturating with HCl gas, crystals of glycocollic ester hydrochloride, CH,(NH,.HCl).COOC,H,, m.-p. 144°, separated. By repeating the alcohol and HCl treatment, other similarly constituted esters were obtained. The different fractions having been treated with alkali in the cold, the liberated esters were obtained on extraction with ether and evaporation. These impure esters were fractionated in a special apparatus designed for distilla- tion under very low (0-3 mm.) pressure ; Fig. 313. This form is in common use except the liquid air condenser, which serves to condense gaseous by- products which otherwise would spoil the vacuum. Liquids boil many (even 50°) degrees lower at such very low pressures-than they do at say 12 mm. pressure. Our precise knowledge of the subject has been greatly advanced in recent years by the synthetic work of Fischer and others; and truly remarkable ALBUMIN 781 achievements have been made, while some of the less complex products, e.g. tetrapeptides, arginine, histidine, &c., are identical with those obtained EH Recge ter EI ‘or E} | Condensed LICS Claisen flask surrounded Dewar aioe oy Ice - Fessed * Fic. 313. from natural sources ; but so far, no peptone as found in practice has been built up, although bodies of known constitution with molecular weights up to 1213 have been synthesised, and their properties found in general to simulate those possessed by substances of natural origin. The amino acids show a great tendency to form complexes of high molecular weight; for instance, glycocoll on bimolecular dehydration produces a diketo-piperazine (p. 807), and this on hydrolysis reopens the chain, forming glycyl-glycine, NH,CH,-CO-NH-CH,-COOH, the simplest polypeptide. This with chloracetyl chloride grows into : CH,Cl.CO.NH.CH,.CO.NH.CH,COOH, which by ammonia is converted into the tripeptide, diglycylglycine, NH,CH,.CO.NH.CH,.CO.NH.CH;.COOH ; and so on. An octadecapeptide (18—NH.CH,.CO—or similar groups) has been constructed. The peptones appear to be mixtures of polypeptides. Brief reference will now be made to some of the more important protein substances found in practice. Egg-Albumin, or white of egg, may be extracted from its aqueous solu- tion contained in the egg, by stirring it briskly to break up the membrane, adding a little acetic acid to neutralise the soda present in the white, filter- ing, placing for twelve hours on a dialyser (p. 281) to separate the sodium chloride and acetate, evaporating the contents of the dialyser below 50°, powdering the residue, and treating with ether to extract fatty matters. The albumin so prepared is an amorphous solid, of sp. gr. 131.1 It is levo-rotatory. When heated, it swells up, carbonises, and evolves offensive alkaline vapours, usually leaving a slight alkaline ash, containing a trace of calcium phosphate, which is very difficult to separate completely from the albuminoids, which is the former name for this kind of protein. In cold water, albumin slowly softens and dissolves, like gum ; if this solution be heated to 60° or somewhat higher, the albumin is converted into an insoluble form, becoming a white, soft solid, as in boiled eggs, if the albumin amounts to 12 per cent., and a flocculent precipitate if the solution be diluted. The coagulated albumin is not easily dissolved by acids or alkalies, and is more basic than the original albumin. Raw white of egg is inodorous, and does not blacken silver; but after boiling it smells of H,§, and blackens silver, showing that it suffers some decomposition during 1 It is stated that by adding a saturated solution of ammonium sulphate to egg albumin, filtering and evaporating the filtrate, crystals of albumin may be obtained. 788 PEPSIN—PEPTONES coagulation. When dried, coagulated albumin forms a translucent brittle mass, which becomes white and opaque in water. Soluble albumin, com- pletely dried below 50°, may afterwards be heated to 100°, without becoming insoluble. Alcohol precipitates albumin from its solution, and the soluble is con- verted into the insoluble form by digestion with strong alcohol. It is also precipitated by shaking with ether or turpentine. . Strong potash added to a solution of albumin precipitates a gelatinous compound of potash and albumin, which is soluble in boiling water, and gives, with metallic salts, precipitates containing albumin and metallic oxides. Acids coagulate the solution of potash-albumin. The mineral acids, except ortho- and pyro-phosphoric acids, precipitate a solution of egg-albumin, the precipitate being a compound of the acid with albumin, but the organic acids, except picric, do not, as a rule, precipitate it. Many of the compounds of albumin and acid have been proved to have a definite composition. Nitric acid has long been employed as a test for albumin (in urine, for example), since it forms a precipitate even in a very weak solution, but if the liquid be mixed with a very minute quantity of the acid, the flocculent precipitate formed at first disappears on shaking, and the clear acid liquid is not precipitated by boiling. The same thing is observed with sulphuric and hydrochloric acids. Picric acid is also commonly used in testing urine for traces of albumin. Strong nitric acid colours coagulated albumin yellow ; alkalies dissolve the yellow mass to an orange liquid, from which acids precipitate yellow flakes (xantho-proteic reaction). Albumin also gives a fine red colour with mercuric nitrate containing nitrous acid (Millon’s test ; prepared by dissolving mercury in twice its weight of nitric acid, in the cold, and adding twice its bulk of water). When boiled with moderately dilute sulphuric acid, or with potash solution, albumin yields leucine and tyrosine (p. 712). The putrefaction of the albuminoids gives rise to the ptomaines or toxines ; p, 701. Such poisonous products are also formed by the bacilli of diseases like diphtheria, and it is upon the introduction into the system of antidotes (antitoxines), derived from animals that have been able to survive the poisons, that the principle of inoculation depends. The gastric juice dissolves coagulated albumin digested with it at about 37°, and the solution is not precipitated by potassium ferrocyanide, nor coagulated by heating. In this condition it is said to have been peptonised, or converted into peptone (réxrw, to digest). The constituent of the gastric juice which effects this change is termed pepsin, and may be precipitated from the juice by alcohol. 1t resembles albumin in composition, but is much less putrescible. When dissolved in dilute hydrochloric acid, also present in the gastric juice, it yields a mixture which peptonises most albuminoids if digested at about 40°. The pepsin prepared from the stomach of the pig and other animals is sometimes administered medicinally to assist digestion. The action of pepsin and HCl on albuminoids is hydrolytic and occurs in several stages, the successive products between the original compound and peptone being a syntonin or acid-albumin and an albumose or propeptone. : Serum albumin forms nearly 8 per cent. of the serum of the blood, and is found in other liquid secretions. It may be prepared by precipitating the diluted serum with lead acetate, suspending the washed precipitate in water, and decomposing it with CO,; the filtered liquid is then evaporated below 50°. It appears to contain less sulphur than ovalbumin (egg albumin) in the ratio of 1-2: 1-6, but rather more oxygen (23-1: 22-4). In properties it very closely resembles ovalbumin, but it is not coagulated by ether, and gives precipitates with nitric and hydrochloric acids, which are more easily dissolved by excess than are these of egg albumin. It is more powerfully levo- rotatory than egg albumin. Vegetuble albumin is the substance which is precipitated by heat from the juices of plants, and from their infusions in cold water. It has not been obtained pure in BLOOD 789 - the soluble condition. It appears to contain less sulphur even than serum albumin contains, Globulin, or serum globulin, is very like albumin, but is insoluble in pure water ; it dissolves in a very weak solution of salt, and in very weak acids and alkalies. It dissolves in water saturated with oxygen, and is precipitated by carbon dioxide. This gas precipitates it in a granular form from the serum of blood ; saturation of the serum with salt also precipitates it. Crystallin is found in the aqueous humour and crystalline lens of the eye. Myosin (uijc, a muscle) separates from muscle plasma (the liquid contained in living muscle) after death, producing rigor mortis. Fibrin is the albuminoid which separates from the blood when this has been shed from the animal, causing the coagulation or clotting of the blood plasma. It appears to be formed from fibrinogen—a soluble protein existing in the plasma—by a ferment (thrombin derived from prothrombin) contained in the white blood corpuscles. Human blood yields about 0-25 per cent. of fibrin, which resembles myosin, but is not dissolved by solution of salt. It may be obtained from freshly drawn blood by whipping it with a bunch of twigs, when the fibrin adheres to them in threads which become “nearly white when washed, and may be freed from fat by alcohol and ether. If the blood be not stirred when freshly drawn, it forms a red clot, caused by the coagulation of the fibrin, and the entanglement in it of the red blood corpuscles ; if the clot be cut up and washed in a cloth, the corpuscles and blood serum may be washed away and the fibrin left. If 7 measures of blood be drawn into a vessel containing 1 measure of a cold saturated solution of Na,SO,, the fibrin will remain in solution, whilst the blood- globules will be deposited on standing. The clear yellow solution containing albumin, globulin, and fibrinogen is largely diluted with water, when fibrin is precipitated. Fibrin forms elastic strings which dry into a yellow horny mass. When fresh, it readily absorbs oxygen, and evolves CO, ; when moist, it decomposes H,Og, evolving O. It is insoluble in water, alcohol, solution of salt, and in cold very dilute HCl (0-1 per cent.), but this dissolves it at 60°. Solution of nitre at 40° also dissolves it. When heated for some time with water at 72°, it becomes insoluble in dilute acids and salts, but dissolves in alkalies. Fibrin is hardened and rendered non-putrescible when soaked in solution of tannin. Fibrinogen may be precipitated from blood plasma ‘by a solution of salt which is semi-saturated, and can in this way be separated from the serum globulin. Caseinogen (also called casein) is the characteristic albumin of milk. It is a phospho-protein, containing about 0-8 per cent. P. It yields much tyrosin and tryptophane. In the free state it is acidic in character and insoluble in water, but in milk it exists as a soluble calcium caseinogenate, from which it is separated as a curd when the base is neutralised either by adding an acid, or by the formation of an acid (lactic) by decomposition of milk-sugar caused by spontaneous fermentation. It is prepared by precipitating centrifugalised milk with acetic acid and washing the precipitate with water, alcohol and ether in succession, to remove soluble matters and fat; it is further purified by dissolving in weak sodium carbonate or ammonia, and precipitating it by acetic acid. Coagulated caseinogen is characterised by the facility with which it is dissolved by weak alkaline solutions, yielding a liquid upon the surface of which, when boiled, an insoluble pellicle forms, like that produced on the surface of boiled milk. Coagulated caseinogen may also be dissolved by acetic or oxalic acid; but sulphuric or hydrochloric acid reprecipitates it, these acids forming compounds with caseinogen which are insoluble in the acids, but soluble in water. If skimmed milk be carefully evaporated to dryness, and the fat extracted from the residue by ether, the caseinogen is left in the soluble form mixed with milk-sugar, and may be dissolved in water or in dilute alcohol. A distinctive property of caseinogen is its coagulation by rennet, the 780 GLUTEN—GELATINE mucous membrane of the stomach of the calf, a small quantity of which, or of its solution in brine, coagulates the caseinogen in a large quantity of milk ; caseinogen so coagulated is casein ; the coagulation does not appear to depend upon the formation of lactic acid, but upon a specific action of the rennet; the curd thus produced contains calcium and magnesium phosphates, and is not easily soluble in sodium carbonate. The caseinogen of milk is more readily coagulated by acids and by rennet when the milk is warmed ; hence milk which has undergone very slight fermentation is curdled when heated, but if fresh milk be heated to boiling, the decomposi- tion will be prevented. The caseinogen of milk is precipitated by some neutral salts, such as sodium chloride or magnesium sulphate, and even by an excess of sodium carbonate. Caseinogen shows no true coagulation by heat. ; Caseinogen combines with slaked lime to form a hard insoluble mass, so that a mixture of cheese with lime is sometimes used as a cement for earthenware. The curd of milk, washed and dried, is used by calico-printers, under the name of lactarine, for fixing colours. If it be dissolved in weak ammonia, mixed with one of the aniline dyes, printed on calico, and steamed, the colour is left as an insoluble compound with the caseinogen. By treating coagulated caseinogen with formaldehyde it becomes similar to horn, for which it is substituted in making combs and the like. Caseinogen or “ casein” hardened in various ways has many applications. Legumin, or vegetable casein, is found in peas, beans, and most leguminous seeds. It resembles caseinogen in that its solution forms a pellicle when heated, and in being coagulated by rennet. In composition it differs somewhat from casein, and shows the reactions of nucleo-albumins. When boiled with dilute sulphuric acid, legumin yields much less leucine than albumin and fibrin furnish, and very little tyrosine ; but it gives more aspartic acid and glutamic acid, C3H;(NH_2)(CO,H)s, homologous with aspartic acid. Gluten is the tough, sticky substance which is left when flour, especially wheaten, is made into dough, tied up in muslin, and kneaded in water as long as any starch passes through. It speedily putrefies when exposed to the air, and dries up to a brittle, horny mass at 100°. When fresh gluten is boiled with dilute alcohol, a portion is left undissolved and has been named vegetable fibrin, as it forms a tough elastic mass. It dissolves in very dilute HCl and in dilute alkalies, and is precipitated by acetic acid and by salts. When the alcoholic solution cools, it deposits white flakes of mucedin, and on adding water to the filtrate, gliadin is precipitated. These substances resemble legumin in composition, but contain twice as much sulphur. It has been asserted that gluten does not exist, as such in flour, but is produced from the proteins in the flour by the action of water, which may enable a ferment to effect the conversion. Gelatine.—This substance is so called from gelu, ice, because its solu- tion in hot water becomes a transparent jelly on cooling. It may be obtained by digesting bones in cold dilute hydrochloric acid, till the calcium phosphate and other salts are dissolved, leaving a residue of the same form as the bone, but of a soft, flexible character. This is termed osséin, and has the same composition as gelatine, into which it is converted by long boiling with water, especially under pressure, a solution being obtained which beeomes a jelly on cooling, and leaves a brittle, transparent mass (glue) when dried. Gelatine does not fuse when heated, but swells up and decom- poses, yielding very offensive alkaline vapours, containing ammonia and compound ammonias (methylamine, &c.), pyrrol and its derivatives, toluene, naphthalene, ammonium cyanide, water, &c. Dippel’s oil (p. 212), obtained by distilling bones, contains these products, together with others, in the formation of which the fat of the bones takes part, such as the cyanides of the fatty acid series (propionitrile, &c.), pyridine bases, phenol and aniline. ' The active principle (lab or chymosin) of the rennet may be obtained from rennet extract by saturat- ing it with salt, when the lab will rise to the surface. CHONDRIN—KERATIN 791 Gelatine softens and swells in cold water, but does not dissolve ; hot water dissolves it, and the solution gelatinises on cooling, even when it contains only 1 per cent. Continued boiling of the solution destroys the tendency to gelatinise. Gelatine is insoluble in alcohol, which precipitates it in white flakes from its aqueous solution. It is also precipitated by tannin, which combines with it to form an insoluble non-putrescible com- pound. Such compounds are produced in the formation of leather in the tanning of skins. Mercuric chloride also precipitates solution of gelatine. If gelatine solution be mixed with potassium dichromate, the jelly formed on cooling becomes insoluble on exposure to light, which is turned to account in photography ; the action probably consists in an oxidation of the gelatine. Acetic acid dissolves gelatine (liquid glue) ; alkalies also dissolve it. When boiled with strong alkalies or with diluted sulphuric acid for a long time, it yields leucine and glycocine (sugar of gelatine). Gelatine may also be obtained by the action of water at a high temperature on skin, sinews, and connective tissue. Jsinglass is very similar to gelatine and is prepared from the air-bladder of fish, especially of the sturgeon. It differs from gelatine in being liable to settle in flocks when stirred up with water; hence its application as a “ fining ’’ for beer, for which purpose it is made into an emulsion by treatment with sulphurous acid (cutting). Glue is made from the refuse and parings of hides, after being cleansed from hair and blood by steeping in lime-water, and exposed to the air for some days to convert the lime into carbonate, and prevent the injurious effect of its alkaline character upon the gelatine. They are then boiled with water till the solution gelatinises firmly on cooling, when it is run off into another vessel, kept warm to allow the impurities to settle down, after which it is allowed to set in shallow wooden coolers. The jelly is cut up into slices and dried upon nets hung up in a free current of air. Spring and autumn are usually selected for drying glue, since the summer temperature would liquefy it, and frost would, of course, split it and render it unfit for the market. Size is made in a similar manner, but finer skins are employed, and the drying is omitted, the size being used in the gelatinous state. The best size is made from parchment cuttings. Moist gelatine easily putrefies, becoming very offensive ; for this reason size is often treated with sulphurous acid. Chondrin (yévépoc, cartilage) is prepared by the action of water at a high temperature on the cartilages of the ribs and joints, and appears to be a mixture of gelatine and chondroitic acid compounds. The aqueous solution of chondrin is pre- cipitated by acetic acid, by alum, and by lead acetate, which do not precipitate gelatine. When boiled with dilute sulphuric acid, it yields leucine, but no glycocine. Boiled with hydrochloric acid, it gives a solution which reduces Fehling’s solution like glucose. Sericin, or silk-gelatine, CysH.;N;0g, is the so-called gum extracted from silk by boiling with water ; it resembles gelatine, but is precipitated by basic lead acetate, and, when boiled with sulphuric acid, yields leucine, tyrosine, and amidoglyceric acid (serin), CpH,(OH)(NH,)CO,H. (Cystine, C3;H,NO,8, found in some rare urinary calculi, appears to be a sulphur derivative of serin. Calculus cystine is not identical with protein-cystine, p. 786.) Keratin forms the chief part of horns, claws, nails, feathers, hair, and wool, and remains when these have been treated with all ordinary solvents. It is softened by long boiling with water, and is dissolved when heated with water under pressure. It swells up and gradually becomes soluble in strong alkalies and in acetic acid, especially on boiling. It contains more sulphur than do most of the proteins. Fibroin from silk, and spongin from sponge, are similar bodies. Chitin, CigHzoN20,2, is the chief constituent of the shells of lobsters, crabs, and beetles, and is left after exhausting them with water, alcohol, ether, acetic acid, and alkali. It is a white translucent substance, soluble in cold strong H,SO, to a solution which yields glucose when diluted ; the change appears to be a hydrolysis, 4H,O being absorbed to produce glucosamine, CgHiy(NH2)0;, (2 mols.) and acetic acid (3 mols.). 792 HAMOGLOBIN Mucin is the substance which gives the viscous character to bile, saliva, and some other animal secretions, and to the slime of the snail. To prepare it, snails are cut up, triturated with sand to a pulp, boiled with water, filtered while hot, and precipitated by excess of acetic acid; the precipitated mucin is washed with weak acetic acid as long as the washings are precipitated by tannic acid, indicating peptone. Dry mucin is unaffected even by hot water. Moist mucin swells up in 4 remarkable manner in water, but does not dissolve ; a little acid causes it to separate in flocks which do not easily dissolve in an excess of acid. Alkalies dissolve it and acids reprecipitate it. Mucin dissolves in a strong solution of salt, and is precipitated again by water. Alcohol coagulates mucin into flocks. Acid solutions of mucin are not precipitated by potassium ferrocyanide (unlike albumin). Boiling dilute acids dissolve mucin, converting it into a substance having the properties of glucose and another which resembles albumin. The composition of mucin varies with its origin. A number of allied bodies are known as mucoids. Nucleo-proteins are constituents of the cell-nucleus and spermatozoa. Sometimes they are salt-like in constitution, namely as protamine nucleate or histone nucleate, but at others their structure is not so simple. Some dissociate in the following manner : 7 nuclein——~ nucleic acid. -protein’ Nucleo ae NS protein ‘histone Thus the nucleins are intermediate between the nucleo-proteins and the simpler groups. The-disintegration of the nucleic acids is noticed at p. 784. Iron is contained in most if not all nucleo-proteins, and in this form appears to play an important rdle in metabolism. Hemoglobin is the colouring-matter which constitutes the major portion of red blood-corpuscles (94 per cent. in man, 86 per cent. in the dog). It is a chromoprotein, and is composed of a histone-like basic protein group called globin and a prosthetic group containing iron (about 0-43 per cent.) known as hematin, C,,H,,N,FeO;. The most remarkable property of hemoglobin is the way in which it absorbs and gives up gases; O,, N,, CO, CO., NO, H,8, HCN, &c. (g.v.). On this function the maintenance of animal life depends, for by it the oxygen necessary for generating the energy of life is taken up from the air in the lungs and carried to the sphere of action. When charged with oxygen the protein is oxyhemoglobin and has the much brighter colour characteristic of arterial blood. The combina- tion must be very loose as the gas can be removed by purely physical means, such as reduction of pressure or by the passage of an indifferent gas through the solution, so becoming reconverted into hemoglobin of duller or purplish colour. This change is attended with a difference in the action on trans- mitted light, for if white light be allowed to pass through the solution of oxyhemoglobin contained in a test-tube placed before the slit of a spectro- scope (p. 353), the green of the spectrum is seen to be crossed by two broad black bands, which are also seen when arterial blood is employed, whilst the solution of hemoglobin exhibits only one band in the middle of the green, which is seen when venous blood isemployed. This difference in the absorp- tion-spectrum is best shown by reducing the solution of oxyhemoglobin with a little ferrous sulphate, mixed with tartaric acid and ammonia in excess. Oxyhemogoblin, when shaken with carbon monoxide, parts with its oxygen and absorbs an equal volume of CO, its colour changing to purple ; the absorption-spectrum exhibits two dark bands, which are situated further from the sodium-line (D) and nearer to the blue of the spectrum than is the case with hemoglobin. This is turned to account in cases of poisoning BRAIN AND NERVE SUBSTANCE 793 by carbonic oxide. The compound of hemoglobin and CO may be obtained in bluish-red four-sided prisms. Further reference to this is made under carbon monoxide. The hemoglobins from different animals are not alike, but the hematin is always the same ; it is the protein group which varies. Most tests and experiments can be made on the blood freed from fibrin, and most of the records apply to experiments made on oxyhemoglobin and not to the oxygen-free compound. Hematin contains a hydroxyl group which is replaceable by chlorine producing hemin, C3,H3,CIN,FeO,. By the action of strong acids under certain conditions hematin yields a ferrous salt and a compound free from iron, hematoporphyrin, C,,H,,N,0;, which on reduction yields phyllo- porphyrin, a derivative of chlorophyll, the green colouring of plants. This is exceedingly interesting and significant, as it shows a chemical relationship between the green colouring of plants and the red colouring of animals, whose physiological functions are so vital, and in each case in relation to the absorption and elimination of the gases oxygen and carbon dioxide. See also chlorophyll, p. 781. The formation of hemin or hematin hydrochloride crystals, of a dark, violet-red colour, and metallic lustre, containing single molecules of hematin and HCl, is employed for the identification of blood-stains, the suspected matter being placed on a microscope slide, a little sodium chloride added, and glacial acetic acid allowed to run under the cover-glass ; on heating till bubbles appear, and cooling, the dark red hemin crystals become visible. Hzmatin is a magnetic substance, while oxyhemoglobin and carbonic oxide hemoglobin are diamagnetic. Brain and Nerve Substance.—The brain and nerves contain a peculiar phos- phorised fat which has been termed lecithin, and has the empirical formula C4y.H,,NPOg. It is a glycerol derivative, and its reactions show that it contains the group C,H; (glyceryl), and probably the radicles of palmitic and oleic acids, and a phosphorised group, N(CH3)3-C,H,(PO )Oe, closely related to neurine, N(CH3)3-C,H3;-OH (p. 701). A variation in the fatty acid radicles gives rise to lecithins of different formule, which appear to be constant constituents of the cell-material of organised bodies, both animal and vegetable, and hence necessitate a constant supply of phosphorus in the food of plants and animals. Lecithin may be prepared from the substance of the brain by exhausting it with ether, treating the residue with alcohol, and cooling the alcoholic solution in ice, when a mixture of lecithin and cerebrin is deposited. On treating this with ether, the lecithin is dissolved, and may be purified by evaporating the ether, redissolving in alcohol, adding an alcoholic solution of platinic chloride, and decomposing the platinum salt, (CygH,,NPO,HCl)o.PtCl,, with H.S ; on evaporating the filtrate, the lecithin is obtained as a fusible crystalline body, insoluble in water and sparingly soluble in cold alcohol and ether. It combines both with bases and acids. When boiled with acids or with potash or baryta, it yields neurine, phosphoglyceric acid, C;H;(OH)2.PO2(OH)s, palmitic, and oleic acids. Cerebrin, obtained from brain as above described, is a white powder which swells up like starch when boiled with water. It yields a substance re- sembling glucose when boiled with dilute acids. The formula of cerebrin, or cerebric acid, as it is sometimes called, appears to be C,;H3,NO3. It is also found in pus- globules. The so-called protagon appears to be a mixture of lecithin and cerebrin. Bile Constituents.— The chief colouring-matter of the bile is bilirubin, CigHigsN,03, which is accompanied by bilifuscin, CygHgoNoO4, and Ddiliprasin, CigHapN,Og. These may be extracted from gall-stones, in which they exist in com- bination with calcium. The powdered calculi are boiled with alcohol and ether to extract the cholesterol, and with dilute HCl to remove the lime. After washing and drying, the residue is boiled with chloroform, which extracts bilirubin and bilifuscin ; the chloroform is distilled off and the residue boiled with alcohol, which dissolves the 794 HETEROCYCLIC NUCLEI latter. ‘The original residue, undissolved by chloroform, contains biliprasin, which may be extracted by boiling with alcohol. Bilirubin crystallises from chloroform in dark-red prisms, insoluble in water and alcohol, but soluble in alkaline liquids, and imparting a yellow colour to a very large volume of solution. It appears to have acid properties. Its alkaline solutions absorb oxygen and become green, yielding a green precipitate of biliverdin, CygHigN2Oq, on addition of anacid. Bilifuscin and biliprasin are obtained as very dark green amorphous bodies, insoluble in water. The alkaline solutions of the biliary colouring-matters, when treated with nitric acid, yield successive tints of green, blue, violet, red, and yellow, which serve to indicate the presence of bile in other secretions. Glycocholic acid, Cy4H390,-NH-CH,CO.H, exists in bile as a sodium salt, together with the sodium salt of taurocholic acid, CoyH3y0,-NH-CH,CH,SO;H. To extract them, ox-gall is mixed with bone-black to a piste, which is dried on the steam-bath and digested with absolute alcohol, which dissolves the sodium salts together with cholesterol, and cholin. Ether is then added, to precipitate the sodium salts. These are dissolved in water, and decomposed by H,SO, dil., which precipitates the glyco- cholic acid, at first amorphous, but changing into colourless needles. It is sparingly soluble in water, but dissolves in alcohol, though not in ether. The alkali salts are very soluble and sweet. It is characterised by its behaviour with solution of sugar and strong H,SO,, which give a purple-red colour (Pettenkofer’s test for bile). It is an amido-acid, and yields chologlycholic acid, CygHygNO7, when treated with nitrous acid. When boiled with alkalies, glycocholic acid is hydrolysed into glycocine (amido-acetic acid) and cholic acid ; CogHy,NO, + H,O = CH,(NH2)-CO,H +C4H4,0;. Boiling with dilute HCl effects the same change, but converts the cholic acid into dyslysin, Co4H3g03, an amorphous precipitate, which becomes potassium cholate when boiled with alcoholic KOH. Taurocholic acid is not precipitated by normal lead acetate, which precipitates the glycocholic acid from ox-gall, and the filtrate gives a precipitate of lead taurocholate on adding basic lead acetate. When this is suspended in water and decomposed by HLS, a solution of the acid is obtained, which may be concentrated and mixed with ether, when the acid separates as a syrup which deposits needle-like crystals. Dog’s bile yields more taurocholic acid than that of the ox. Taurocholic acid dissolves readily in water and alcohol. It is decomposed, like glycocholic acid, by boiling with alkalies or acids, but it yields taurine, C,H,NSOsg, instead of glycocine ; CogH,,NSO, + H,O = CoH,NSO3 + CosH400s. XVI. HETEROCYCLIC COMPOUNDS Nearly all the.compounds hitherto considered have been hydrocarbons or derivatives thereof. There remains a class of substances having closed chain nuclei, composed not of carbon alone, as are the benzene and naphtha- lene nuclei, for example, but containing one or more atoms of N, O or S as member or members of the closed chain. Thus they are not strictly derivatives of hydrocarbons. In other respects they might have been considered under the preceding classes, for they are hydrides, alcohols, acids, &c., derived from these heterocyclic nuclei instead of from open-chain nuclei or from carbocyclic nuclei (like the benzene nucleus). A few compounds which are strictly within this class have already been described, such as succinic anhydride and the various lactones. These are, however, more of the nature of open-chain derivatives than are those that remain to be discussed. A number of the three- and four-membered heterocyclic compounds have also received passing notice—e.g ethylene oxide, trimethylene oxide, diazo-methane, &c. The five- and six-membered 1 rings of this kind, together with the conjugated nuclei corresponding with naphthalene, &c., will now receive attention. Five-membered Heterocyclic Compounds.—The prototypes of these 1 As in the case of the carbocyclic compounds, 7, 8, &c., membered rings are little known. FURFURANE—THIOPHEN 795 are furfurane, thiophen, and pyrrol, which possess constitutions expressed by the following formule : CH: CH CH : CH CH: CH = ’s. het ow CH : CH CH : CH H : CH Furfurane. Thiophen. Pyrrol. They resemble benzene in that they yield derivatives similar to those of that hydrocarbon, and show little disposition to form addition-products with the halogens. In fact, the arguments which lead to the closed-chain formula for benzene (p. 560) are equally applicable to these compounds. Eloquent of their constitution is their formation from y-diketones, such as acetonylacetone (p. 650); by dehydration this compound yields 1 : 4-dimethylfurfurane. CH,-CO-CH; CH: C(CHs)\ | — H,O = 7: CH,-CO-CH3 CH : C(CH;) With PS, it yields 1:4-dimethylthiophen, and with NH, 1:4di- methylpyrrol. Two classes of mono-substitution products are known from these compounds— the a-derivatives, which contain the substituent attached to a carbon atom adjacent to the O, S, or N, and the 3-derivatives, in which a hydrogen atom of one of the far carbon atoms has been displaced. A third class is possible in the case of pyrrol, for the H of the NH group can be substituted. The possible di-derivatives are more numerous than in the case of benzene; their orientation is expressed by numbering the near carbon atoms 1 and 4, and the far atoms 2 and 3 ; or by numbering the N, O, or S atom 1 and the C atoms 2, 3, 4, 5 successively. A reaction common to all three compounds is the blue colour produced by their reaction with isatin (q.v.) and strong H,SO,. Furfurane, C,H,O, together with several of its derivatives, is found in the first runnings of the distillation of wood-tar. It is made artificially by distilling pyromucic acid with lime. Pyromucic acid is itself obtained by the destructive distillation of mucic acid (p. 632), thus— CHOH-CHOH-COOH CH: NG | = |] f° + 3HOH + CO,. CHOH-CHOH-COOH CH : CH This indicates the constitution of pyromucic acid, and since this acid yields furfurane when distilled with lime it is probably furfurane-carboxylic acid (just as benzoic acid, which yields benzene on distillation with lime, is benzene-carboxylic acid). Thus the constitution of furfurane is settled. Furfurane is a colourless liquid, smelling like chloroform, insoluble in water and boiling at 32°. Its aldehyde (furfural) and carboxylic acid (pyromucic acid) have been already considered. Uvinic acid or pyrotritartaric acid, CyH(CH3),0-CO,H, found among the products of the destructive distillation of tartaric acid, is a-a,-dimethylfurfurane-/3-carboxylic acid; it is also produced together with uvitic acid (5:1: 3-methylphthalic acid) by heating pyrotartaric acid with baryta water. It melts at 135° and decomposes into CO, and dimethylfurfurane. Thiophen, C,H,S, its homologues and substitution-derivatives, are remarkable for their similarity to benzene, its homologues and derivatives respectively ; thus with a large number of benzene derivatives there are corresponding thiophen derivatives of approximately the same boiling-point. Thiophen and its homologues accompany benzene and its homologues in coal-tar, commercial benzene containing about 0-6 per cent. of thiophen. To separate it the benzene is shaken with about 10 per cent. of strong H,SO,, which extracts the thiophen as a sulphonic acid. Or the benzene may be heated with mercuric acetate, which forms a complex precipitate with the thiophen, decomposable by HCl into thiophen and HgCl,. : The thiophen passes over when the sulphonic acid is distilled with steam ; it is a colourless liquid (sp. gr. 1-06) which smells like benzene, boils at 84° and yields a 796 PYRROL blue colour when mixed with isatin and strong H,SO,; this reaction—due to the formation of indophenin, C,.H,NOS—serves to detect thiophen or its homologues in benzene. Several fatty compounds yield thiophen when heated with P,S; ; sodium succinate, for example— CH,:COONa. CH: ES | gives | )» CH,-COONa CH : CH Derivatives of selenophen, CzH,Se, are also known. Pyrrol, C,H,NH, is a secondary amine and therefore a feeble base. Its derivatives play a highly important part in bio-chemistry ; see Proteins, Chlorophyll, &c. It occurs in coal-tar and Dippel’s oil (¢.v.), from which it may be extracted by H,SO, and distilled over from the sulphates of the stronger bases ; it still contains nitriles of fatty acids and benzene hydrocarbons, and is separated from these by heating with solid KOH, which converts it into C,H,NK, decomposable into KOH and C,H,NH by water. It is a liquid of chloroform odour, sparingly soluble in water, boiling at 131°, of sp. gr. 0-97 and becoming brown in air. Hot dilute acids convert it into pyrrol-red, Ci2H,4N,0. Pyrrol imparts a fiery red colour to pine-wood moistened with HCl; hence its name. It readily polymerises, hydrogen chloride precipitating (C,H;N);HCl from its ethereal solution. 7 Succinimide yields pyrrol when distilled with zinc dust, and ammonium mucate yields it when distilled alone; it is also formed when a mixture of C,H, and NH, is passed through a red-hot tube. Pyrrol treated with 2NH,OH yields succinodialdoxime, (CH,-CH : N-OH),. There are 3 mono-substitution products from pyrrol, because the H in the NH group may be displaced, yielding n-derivatives, besides the c-derivatives. The n-alky] pyrrols are obtained from C,H,NK and alkyliodides. Lodopyrrol, CyI4NH, is an odourless substitute for iodoform. Several hydropyrrols and their derivatives are known; pyrroline is a-(-di- hydropyrrol, CysHgNH ; pyrrolidine is tetrahydropyrrol, or tertramethyleneimide, [CH,-CHy], : NH. Conjugated Nuclei from the Five-membered Heterocyclic Compounds.—These are believed to consist of one or two benzene nuclei conjugated with a furfurane, thiopen, or pyrrol nucleus, just as naphthalene consists of two, and anthracene of three benzene nuclei condensed together. They are probably represented by the following formule— CH CH CH fo es poy CHa CH(a) CH, CH(a) C,H, CH(a) Sgt ar Net Benzofurfurane. Benzothiophen. Benzopyrrol. CsH,——C,Hy C8 —O. i; C,——0, i, SF ee 8 NH Dibenzofurfurane. Dibenzothiophen. Dibenzopyrrol. Those derived from one benzene nucleus are formed by treating the corresponding chloro-styrolene with alkali, CoHa gives CoHaC fos where XH x XK = O, 8, or NH. Benzofurfurane or cowmarone is a product of the action of alcoholic KOH on coumarin (p. 623); it is found in coal-tar and boils at 177°. Coumarilic acid is its a-carboxylic acid. Benzothiophen melts at 31° and boils at 221°. Benzopyrrol or indol is the most important member of the group, as it is constitu- tionally the parent substance of indigo. It may be obtained by distilling reduced pn (q.v.) with zine dust, and by reducing o-nitro-cinnamic aldehyde with Zn and OH— CH-CHO CH Bea os + 7H = OK Oe + 3H,0. 2 INDOXYL 797 It crystallises in colour:ess prisms, m.-p. 52°, of disagreeable odour, and may be distilled in a vacuum or with steam. It is soluble in water and has weak basic properties, forming a sparingly soluble hydrochloride. A shaving of deal moistened with HCl and exposed to its vapour gives the pyrrol red colour. The hydrochloric solution is coloured red by potassium nitrite. Indol is produced by the action of the peculiar ferment of the pancreatic juice upon the albumin of blood or eggs, and the indican occasionally present in urine appears to be formed from it. Many derivatives of indol are known, but only the most important can receive notice here. The orientation of the substitution derivatives is expressed by the letters u, 3, n in the pyrrol ring (cf. formula above) and by the numbers 1, 2, 3, 4 in the benzene ring ; or by numbering the N atom 1 and the C atoms successively 2 and 3 in the pyrrol ring, and 4, 5, 6, 7 in the benzene ring. Py-l, 2, 3 and Bz-l, 2, 3, 4 are obvious variations. The alkylindols are obtained by heating phenylhydrazones of aldehydes or ketones with HCl or ZnCla, nucleal condensation occurring with evolution of NH3. Thus, {-methylindol or skatol is formed when propionic aldehyde phenylhydrazone is so treated— fen, CyH,NH-N : CH-CH,-CH, = CoHac FO + NH3. NH Skatol is also « product of the pancreatic fermentation of albumin, and is the chief constituent of the volatile portion of human excrement (cxardec, of dung). It crystallises from hot water in colourless plates, melts at 95°, boils at 265°, and has a fecal odour. Skatol is found among the products of the distillation of strychnine with lime, and in the wood of Celtis reticulosa, a plant of the Nettle-tree order. Indoxylic acid is /3-hydroryindol-a-carboxylic acid, and is obtained as its ethyl salt by heating ethyl o-phenylglycocinecarboxylate with sodium ethoxide— COOEt COOH). CeHy = CoH Pe COsEt + EtOH. NH— ’\NH-CH,CO,Et The free acid is obtained by heating the ethyl salt with fused NaOH, dissolving in water and precipitating by acid ; when heated with alkali and air it yields indigo. It is sold as indophor for cotton printing, since it is readily converted into indigo by oxidation on the fibre. Indoxyl is 3-hydroxyindol and is produced by heating indoxylic acid, which loses CO,, also by heating indigo with KOH in absence of air. It is an oily liquid, soluble in water to a yellow fluorescent solution. Tn alkaline solution it is easily oxidised to indigo, 2CgH;,ON + O2 = (CgH;ON). + 2H,0. The indoxyl derivatives are either from (-hydroxyindol or the pseudo-form—viz. C(O CO OH Now or LS Nom, respectively. The indogenides are deri- \ne 7% \wH” vatives of the latter form in which the =CH, group has condensed with a =CO group of an aldehyde or ketone to form a =C=C= nucleus. Indoxyl occurs in the form of potassium indoxyl-sulphonate in the urine (wrine- indican) of herbivora. eR - a-Methylindolin, CeH, CH-CH,, is a liquid boiling at 227°, obtained by reducing a-methylindol with Sn and HCl; by carrying the reduction further, with HI and P, o-propylaniline is produced. It will be seen that this compound is a methyl-derivative of dihydroindol, which does not exist; the oxygenated dihydro- indols, however, are known and are closely related to indigo. They are called indo- linones and are lactams of amidophenylacetic acid and its homologues (p. 714). They are also obtained by heating the phenylhydrazides (p. 720) of the acids with lime (see Oxindol). 798 INDIGO Oxindol, or a-indolinone, has been already noticed (p. 714); it is produced when acetylphenylhydrazide is heated with lime— Lo, CsH;NH-NH-COCH; = CoHaC f° + NHs3. NH It melts at 120° and is easily oxidised to dioxindol or (-hydroxyoxindol, which in its turn may be oxidised to isatin. co gx. Isatin CHA Noo, or CgHy C-OH, is prepared by oxidising indigo en Nav with nitric or chromic acid. It crystallises in orange-coloured prisms, m.-p. 201°, soluble in boiling water and alcohol. When heated, it sublimes with partial decompo- sition. It dissolves in KOH to a violet solution, and is precipitated again by acids. AgNO, added to the potash solution gives a carmine-red crystalline precipitate of silver isatin, CgH,AgNO,. Isatin forms crystalline compounds with NaHSO, (like the aldehydes and ketones). It yields aniline when distilled with strong KOH. With chlorine it yields chlorisatin and dichlorisatin, also formed when chlorine acts on indigo. When these are distilled with KOH, they yield mono- and di-chloraniline. Reducing agents convert isatin into hydro-isatin, or isatide, CygHygN20,, and then into dioxindol and oxindol. Isatin is also produced by treating o-nitrophenylpropiolic acid with alkali— © : COOH co Bak = GHC 00 +00, NO, NH Isatin condenses with indoxyl under action of alkalies to form the indogenide (v.s.) indirubin, an isomeride of eS ; co co CH, H v Sox ae pe = CoH. x Ses oe > NH + ne easy nn ea A Oe eye ei ee ee ae Tsatin. Indirubin. co Isatin reacts with PCl,; in benzene, yielding isatin chloride, OH peo the N formula for which supports the second formula given above for isatin. When this chloride is reduced it yields indigo-blue. Indigotin or indigo blue, C,,H,)N,0., is prepared from Indigofera tinctoria and cerulea, plants of the same natural order (Leguminose) as those furnishing the dye-woods described on p. 783, and like the colours obtained from those, it does not exist as such in the plant, but is a product of alteration of a nearly colourless substance termed indican. Woad (Isatis tinctoria), a crucifer, also yields indigo. Indican may be extracted from the leaves and twigs of the plant by digestion with cold alcohol, which leaves it, when evaporated, as a brown, bitter, syrupy liquid. It appears to be a glucoside of indoxyl and is hydro- lysed by fermentation or by boiling dilute acids into indoxyl and a glucose called indiglucin. The indoxy]l is rapidly oxidised by the air into indigotin, which forms a blue precipitate— CgHgON(CsHi105) + H,O = CyH,,0, + C,H,ON Indican, Indoxyl. CO COX co co POR aa a a Pe Nas poe + ae ao a aces Pugs posts +2H,0 Indoxyl. ae Indigotin. For the preparation of indigo on the large scale, the plants are cut just before they blossom, chopped up, covered with cold water, and allowed to ferment for twelve or fifteen hours, when the indican is hydrolysed as explained above. As soon as a blue scum appears upon the surface, a little lime is added, and the yellow liquid is INDIGO-WHITE 799 run into shallow vats and well beaten with sticks to promote the action of air, which oxidises the indoxyl. The indigo-blue is precipitated and collected, on calico strainers, to be pressed and cut up into cakes. As purchased, indigo-blue contains about half its weight of indigotin ; it may be purified by boiling, first, with acetic acid, which extracts a substance termed indigo-gluten, then with weak potash, to extract indigo- brown, and, lastly, for some time with alcohol, which removes indigo-red. Indigotin may be prepared from commercial indigo by boiling it with aniline, or heating it with melted paraffin; both solvents deposit the in- digotin in dichroic, rhombic crystals on cooling. From hot turpentine it crystallises in blue tables and from fused phthalic anhydride in needles. When commercial indigo is carefully heated, it is converted into a violet vapour, the sp. gr. of which settles the molecular formula for the compound. The vapour condenses in dark blue needles, with a coppery reflection. The best indigo-blue floats upon water. Indigotin is insoluble in water, alcohol, ether, and diluted acids and alkalies. Strong sulphuric acid and, more easily, fuming sulphuric acid, dissolve it, forming indigotin-monosulphonic acid, C,H (SO,-OH)N,O,, and indigotin-disulphonic or sulphindylic acid, C,,Hs(SO,-OH),N,O,. On adding water, a blue precipitate of the mono-acid is obtained, which is soluble in pure water and in alcohol. It is mono-basic, and its concentrated solution gives a purple precipitate of the potassium salt on addition of potassium acetate. The precipitate produced by K,CO, in the solution of indigo in H,SO, is known as indigo- carmine, and consists chiefly of potassium sulphindylate ; it is soluble in water. The sulphonic acids of indigo are bleached by zinc-dust, being converted into the correspond- ing acids of indigo-white, which become blue again when shaken with air. Sulphindylic or sulphindigotic acid is used in dyeing Saxony blue cloth. Indigo-white (leucindigo or hydrindigotin) is prepared by shaking powdered indigo with 2 parts of ferrous sulphate, 3 parts of slaked lime, and 200 parts of water, in a stoppered bottle placed in warm water, till the indigo has dissolved to a yellow liquid, when the calcium sulphate and ferroso-ferric hydroxide are allowed: to subside, and the clear solution drawn off into dilute hydrochloric acid in a vessel from which air has been expelled by CO,. ~ The hydrindigotin is precipitated in white flakes, which quickly become blue indigo when exposed to air. Other reducing-agents are sometimes substituted for ferrous sulphate in preparing the dyer’s indigo-vat. A mixture of indigo, madder, potassium carbonate, and lime, left to ferment, gives an alkaline solution of reduced indigo. Hydrosulphites (p. 173) and lime, or zinc-dust and alkali, are also employed for this purpose, and it has been suggested to apply electrolysis for the reduction. When linen and cotton are immersed in the indigo-vat and exposed to air, the indigo-white is oxidised to indigo-blue, which is precipitated upon the fabric. Hydrindigotin precipitated by acids from its alkaline solutions becomes crystalline after a time; it is soluble in alcohol and ether. It is probably of the same form as indigotin, but containing OH groups in place of the O atoms. When indigo is heated with dilute HNOg, it is oxidised into isatin, which gives a yellow solution, and sulphindylic acid is sometimes employed as a test for HNO;. By fusion with KOH it is converted, first into potas- sium anthranilate, and afterwards into aniline, which distils. Artificial Indigo.—The unremitting skill and labour which were concentrated during some twenty years on the attempt to make indigo from materials the cost of which would be comparable with that of cultivating the indigo plant were crowned with success. It may now be said that indigo is made from coal, wood and air, and that the cultivation of the plant is a doomed industry. 800 ARTIFICIAL INDIGO Naphthalene and ammonia from coal, acetic acid from wood and oxygen from air are the immediate raw materials for the manufacture ; sulphuric acid, chlorine, mercury and alkali are used as agents, but these may be recovered and returned to the process. ones The naphthalene is oxidised to phthalic anhydride, which is converted by NH, into phthalimide. When the latter compound is oxidised in alkaline solution by chlorine it yields anthranilic acid, which is then condensed with chloracetic acid to produce phenylglycocine-o-carboxylic acid. This acid is heated with alkali to transform it into indoxyl, which yields indigo when treated with air in alkaline solution. The operations are as follows: (1) The oxidation of the naphthalene is effected by atmospheric oxygen, not directly, but by heating the naphthalene in presence of mercury with sulphuric acid of 100 per cent. strength—most conveniently made by combining SO, with atmospheric oxygen by the catalytic method (p. 165), and dissolving the SO, in water. The mixture is distilled at 300°; phthalic anhydride passes over and CO, and SO, escape ; the latter is oxidised to sulphuric acid in the manner indicated and used again, thus conveying O from the air to the naphthalene. The mercury dissolves to sulphate and aids the reaction ; the sulphate remains in the retort and is used again. (2) The phthalic anhydride is treated with NH; under pressure when it becomes phthalimide. (3) The phthalimide is heated in a solution of alkali into which chlorine is passed (sodium hypochlorite). (4) The solution of alkali anthranilate thus obtained is boiled for some hours with mono-chloracetic acid and NagVO, in a vessel provided with a reflux condenser ; the solution is then acidified, whereupon crystals of phenylglycocine-carboxylic acid separate as the liquid cools. (5) This acid is heated with NaOH in a closed vessel at 200° until the orange colour no longer increases in intensity. (6) The fused mass, containing indoxyl, is quickly cooled, dissolved in water and air is passed through the solution to precipitate indigo ; if the precipitate is too crystalline it is dissolved in sulphuric acid and precipjtated by adding water. The following equations explain the chemistry of these processes : CH : CH PP (1) Colac | +90= CoH YP + 2CO, + 2H,0. CH : CH co CO co (2) CHC > + NH; = CHK NH + H,0O. VN //00Na (3) CH NH + NaOCl + 3Na0H = C,H, +NaCl+Na,CO3+H,0. aa NS co NH, COONa //S00Na (4) OC + CH,Cl-COOH + NagCO; = CoHaC NH, NH-CH,-COONa + NaCl + CO, + H,0. Os ge co AY (5) Coa + 2Na0H = Coa one + Na,CO; + 2H,0. NH-CH,COOH NH (6) The equation for the oxidation of indoxyl has been given above. It is probable that the process will shortly be simplified, for it has been found that the product obtained by heating anthranilic acid with a polyatomic alcohol or a carbo- hydrate and KOH yields indigo when treated with water and oxidised. Another promising method consists in heating phenylglycocine, made from aniline and monochloracetic acid, with sodamide. It is proposed to synthesise indigo from aniline by first heating it with CS, to produce thiocarbanilide (p. 707) ; the aqueous solution of this is to be heated with white lead and KCN, of which the former appropriates the S, while the latter introduces a cyanogen AZOLES . 801 group, the product being a hydrocyanocarbodiph.nylimide, which becomes a thioamide by treatment with (NH,).S. The thioamide is to be heated with strong H,SO, to produce the anilide of isatin, and this is to be reduced with (NH,))8 when it yields aniline and indigo : C,H;NH C,.H;NH C.H;NH co dos: » ; DOsNtt ; OH Ye: NC,Hs;. C,H;NH - CyH;N C.eH;N NH Thiocarbanilide. Cyanogen derivative. Thioamide. Isatin anilide. Other methods of synthesising indigo are now only of academic interest, either because the yield is too small or because the raw materials are too costly. From aniline it has been synthesised by heating the base with chloracetic acid to produce phenylglycocine, which yields indigo when heated with fused NaOH and afterwards treated with air. The fusion converts the phenylglycocine into indoxyl. From benzaldehyde the synthesis is by way of dissolving 1 : 2-nitrobenzaldehyde in acetone and adding NaOH, whereupon indigotin is precipitated. It is probable that the first action of the acetone and soda is to convert the 1 : 2-nitrobenzaldehyde into 1 : 2-nitrophenyl-hydroxy-ethyl-methyl ketone ; C,H,(NO,)-CHO + CH,-CO-CH, = CsH,(NO,)-CH(OH)-CH,-CO-CH,. This then breaks up into. indigotin, acetic acid, and water under further action of NaOH; 2[C,H4(NO,.)-CH(OH)-CH,-CO-CH3] = CygHioN20. + 2CH3;-CO,H + 2H,0. The ketone has been sold as its NaHSO, compound (p. 648), under the name indigo salt for printing on the fabric, which is then immersed in a bath of caustic soda. When cinnamic acid is treated with nitric acid, it is converted into nitrocinnamic acid. This combines directly, with two atoms of bromine, to form dibromo-nitro- phenyl-propionic acid, CgH,(NO.)-CHBr-CHBr-CO,H. When this is treated with caustic soda, two molecules of HBr are removed, producing the sodium salt of nitro- phenylpropiolic acid, CeH4(NO2)-C :C-CO,H. By heating this with an alkali and a reducing-agent, it is converted into indigotin. Closely connected with indigo is the sulphur analogue, thioindigotin, JO OO. CHC ; Dory ae Cots By condensing chloracetic and thiosalicylic acids in alkaline solution and heating the intermediate product, carborymethyl-o-thiobenzorc acid, COOH-C,H,:S:CH,:COOH, with gos. NaOH at 180°, CO, is lost and 2-hydrory-thionaphthen, CoH y for is produced, which on oxidation yields thioindigotin (thioindigo). Various dyes based on this have been obtained. Dibenzofurfurane (p. 796) is identical with diphenylene oxide and is obtained by distilling phenol with PbO. It melts at 81° and boils at 288°. Dibenzothiophen is diphenylene sulphide, obtained by heating phepyl sulphide m.-p. 97°, b.-p. 333°. Dibenzopyrrol is identical with carbazole (p. 701). Azoles.—Within the last few years a large class of compounds has been discovered, the members of which are regarded as derived from furfurane, thiophen and pyrrol by substitution of a trivalent N atom for a trivalent CH member of the ring, and are known as mono-, di-, or tri-azoles accordingly as 1, 2 or 3 of the CH members have been exchanged for N. : By one system, the azoles are distinguished by the prefixes furo-, thio, and pyrro- to indicate the parent ring, also by the numbers 2, 3, 4 or 5, or the letters a, a, b or b,, to show which of the four CH members has or have been exchanged. By another system they are classified as oxazoles, thiazoles, and pyrazoles, accordingly as they are allied to furfurane, thiophen and pyrrol respectively. Condensed azole nuclei, distin- guished by the prefix benzo, are also known (ef. furfurane, &c., p. 796). Generally speaking, the azoles are products of condensation of aldehydes or ketones with substitution-derivatives of NH, or NaH4, or H,NOH. 81 802 ANTIPYRINE CH: N Pyrazole or pyrro-2-azole, | /NEL is produced by combining acetylene CH : CH with diazomethane (p. 715), but better by distilling 3: 4: 5-pyrazole-tricarboxylic acid, made by condensing ethyl diazoacetate with ethyl acetylenedicarboxylate and saponifying. It is a feeble base, melts at 70° and boils at 187°. The substituted pyrazoles are nucleal condensation products from the hydrazones of -diketones. Thus benzoylacetone-hydrazone yields 1:3: 5-diphenylmethyl-2- pyrazole : C.H;'C:CH,-CO-CH; C.H,-C-CH : C-CHg - "| | | + m0. N—NHC,H; N— N-C.H; By reduction with Na in alcohol the pyrazoles yield dihydropyrazoles derived from CH2CHa. gas and called pyrazolines. H: N Pyrazolones are ketodihydropyrazoles, and are important as including the febri- CMe-NMe fuge antipyrine which is 1:2: 3-phenyldimethylpyrazolone, || NCH: pre- CH—CO pared by first heating ethyl aceto-acetate with phenylhydrazine to produce phenyl- methylpyrazolone, which is then heated with CH;I in CH,0H to introduce the second CH, group ; the alcohol is distilled and the antipyrine precipitated by NaOH. Anti- pyrine crystallises in white plates, melts at 114°, dissolves fairly easily in cold water and is a strong base ; its salicylate is sold as salipyrine and the homologue in which tolyl takes the place of phenyl, as tolypyrine. Another very complex pyrazolone derivative is the yellow dyestuff tartrazine. The tetrahydropyrazoles are called pyrazolidines, and the corresponding keto-deri- vatives are pyrazolidones, They are unimportant. F Fait The indazoles are benzopyrazoles from the isomeric forms CgH, ‘NH and hae CH C,H, Ny, and are so called by analogy with indol, the name given to benzo- Ne y g NH pyrrol. Indazole itself has the first form and is made by heating o-cinnamic-hydrazide. N : Ch The glyoxalines are pyrro-3-azoles, | jf obtained by condensing CH : CH a-diketones with NH;. Several of them, particularly lophin (triphenylglyowaline) phosphoresce when decomposed by caustic alkali. Lysidine, used as a remedy for gout because of the high solubility of its urate, is a methyldihydroglyoraline. CH: N K Isoxazole or furo-2-azole, and thiazole or thio-3-azole, he pon and : CH N : Cos PS respectively, yield a number of derivatives. The amidothiazoles, made CH: CH by condensing chloracetone with thiourea, behave like aniline and may be diazotised to produce thiazole dyestuffs. The true diazoles and triazoles of the pyrrol type have sometimes been miscalled triazoles and tetrazoles respectively, the prefix referring to the total number of N atoms. CH: N. Thus, pyrro-2 : 5-diazole, | poe has been called osotriazole. Its derivatives CH: N , are obtained by distilling the osazones of ortho-diketones, PYRIDINE BASES 803 The Pyrro-triazoles may be either | pe or | fe The former, N:N N: N 2:5: 4, is known as Zeérazole. The derivatives of thesescompounds as also those of the corresponding oxy- and thio-compounds are at present of theoretical interest only. Six-membered Heterocyclic Compounds.—The most important members of this class are the substances pyridine, quinoline and acridine. These may be regarded as analogous in constitution to benzene, naphthalene and anthracene respectively, containing, in each case, N in place of CH. This will be clear from the following formule : joy ae Nog "e Y ' i: a —N— , i | | | HC CH HC C CH HO O-=-O——c CH St Sr Ng ee Sal Pyridine. Duinline: Acridine. Their behaviour towards reagents indicates that they are closed chain compounds (cf. benzene, p. 560), and a study of their substitution products shows that the number of position isomerides which has been prepared is in accord with that prophesied from the above formule. An inspection of the formule shows that there should be three isomeric mono-sub- stituted pyridines, seven isomeric mono-substituted quinolines and five mono-sub- stituted acridines. The orientation is expressed similarly to that of the corresponding hydrocarbons, the N in pyridine and quinoline being 1. | By another system of orientation for pyridine, position 2 = a,6 = a’,3 = B,5 = /3’, and 4= y; for quinoline 2 = a, 3= 8, 4= y. Pyridine Bases.—The destructive distillation of bones yields ammonia and other bases, produced by the decomposition of the bone gelatine, or osséin, which forms about 30 per cent. of the bones, and contains about 18 per cent. of nitrogen. These bases form an homologous series, of which pyridine is the first member; many of them are also found in coal tar. They are liquids of disagreeable odour, and are tertiary monamines (p. 693). They may be extracted from the offensive oil known as Dippel’s animal oil, obtained by distilling bones, by shaking it with warm dilute H,SO,, which dissolves the bases as sulphates, and yields them up on adding alkali. They are separated by fractional distillation. Their solubility in water decreases with the increase of C atoms and is generally greater in cold water than in hot ; their boiling-points rise for each additional CH,, as follows: Pyridine . . CsH;N 115° Parvoline . . Cy HygN 188° Picoline.. . CgH,N 130° Coridine . . OoHy;N 211° Lutidine . . C,H,yN 142° Rubidine . . OyHy,N 230° Collidine . . CgHyN 179° Viridine . . OCpHyN 251° Pyridine bases are often present in commercial ammonia, and cause it to become pink when neutralised with hydrochloric acid. Like other tertiary amines the pyridines combine with alkyl iodides to form alkylpyridinium iodides, e.g. C;H;N-CH,I, and when these are heated they become alkyl - substituted pyridines, e.g. C;H,(CH3)N-HI, a behaviour similar to that of alkylanilines (p. 699). Pyridine is a colourless liquid which is soluble in water ; it forms a deliquescent hydrochloride, C;H;N-HCl, the solution of which is precipitated by HgCl, K,FeCyg, and PtCl,. By the action of sodium in alcohol, pyridine is hydrogenised to hexa- 804 QUINOLINES hydro-pyridine, C;H,,N, which is identical with piperidine (v.7.) and may be reconverted into pyridine by heating at 300° with H,SO,— CsH,,N + 3H,SO, = C;H,N + 380, + 6H,0. This conversion of pyridine into piperidine establishes the constitution of the former, that of the latter being known. Pyridine is obtained by heating amyl nitrate with P,O;, which removes the elements of water ; C;H,,NO; = 3H,0 + C;H;N. It is also formed when a mixture of hydrocyanic acid and acetylene is passed through a red- hot tube, HCN + 2C,H, = C;H;N. Like benzene, pyridine resists oxidation in high degree. Pyridine has been suggested as a remedy for asthma ; on the Continent it is used for denaturating alcohol. The alkylpyridines may be obtained by distilling the aldehyde-ammonias, either by themselves or with aldehydes or ketones. Thus acrolein-ammonia yields 3-methyl- pyridine (picoline), which is also obtained by heating glyceryl tribromide in a sealed tube at 250° with alcoholic NH; ; 2C,H;Br,; + NH, = 6HBr + C,H,N. The alkyl- pyridines are readily oxidised to pyridinecarboxylic acids (v. 7.). The hydroxy-pyridines behave in a manner which leaves it doubtful whether they are really phenolic or ketonic compounds (pyridones ; cf. phloroglucol, p. 751). Piperidine or hexahydropyridine, C;H,,N, obtained by reducing pyridine with Na and boiling alcohol, or electrolytically, may be regarded as pentamethyleneimide, for it is obtained by distilling the hydrochloride of pentamethylene diamine— CH,-CH,-NH, CH,-CH, OH, = CHC NE + NH. CH,-CH,-NH, CH,-CH, It is a secondary amine, boiling at 106°, smelling of pepper and NHz, soluble in water and forming crystalline salts (cf. Piperine). It combines with alkyl iodides to form alkyl- piperidinium iodides. Quinoline Bases.—These may be regarded as benzo-pyridines. They occur in bone oil and in coal-tar, and are products of the distillation of many alkaloids with KOH. They form an homologous series, quinoline being the lowest member :—Quinoline, C,5H,N ; lepidine, CysH,(CH,)N : cryptidine, Cy5H;(CH,).N. The quinoline bases are synthetically prepared (Skrawp’s method) by heating aniline or its homologues with glycerin, a dehydrating-agent (conc. H,SO,) and an oxidant (nitrobenzene) ; H H I #™® a CHLOE), HO OC) OCH OK a. a aes cH(OH) +0 = | | | + 4H,0, 2 (OH) HC OC.) OCH ee, H This synthesis shows that the N atom in quinoline must be attached to a benzene nucleus ; that it occurs in a pyridine ring is proved by the fact that when quinoline is oxidised with KMnO,, 5 : 6-pyridine dicarboxylic acid (quinolic acid), C;H3(CO.H).N, is formed (cf. the deduction drawn concerning the constitution of naphthalene from the oxidation of the hydrocarbon to phthalic acid). Quinoline is prepared by the action of H,SO, (50 parts) and nitro-benzene (12 parts) upon aniline (19 parts) and glycerin (60 parts). The mixture is cautiously heated at 130° in a flask with a reflux condenser, the lamp being removed when the reaction begins ; it is then again heated for three hours, and distilled with lime, when quinoline distils over together with aniline ; the latter is converted into phenol by the diazo- reaction (p. 716) and the mixture again distilled with alkali when quinoline passes over. It is a colourless liquid of tarry smell, of sp. gr. 1-09 and boiling-point 239°. It is sparingly soluble in water, and is a tertiary amine; it forms a sparingly soluble ISOQUINOLINE 805 chromate. It combines with alkyl iodides to form alkylquinoliniwm iodides which, when heated with potash, yield blue dyestuffs termed cyanines, used in orthochromatic photography. Quinoline derivatives are very numerous; a few only can be considered. 2-Methylquinoline or quinaldine, b.-p. 247°, is synthesised by boiling paraldehyde and aniline with HCl. By substituting other aldehydes for paraldehyde, the reaction becomes a general one for preparing alkylquinolines. 4-Methylquinoline or lepidine boils at 257°. Both occur in coal-tar and the CH, group in each shows a remarkable tendency to react with aldehydic and ketonic compounds. Quinaldine combines in this manner with phthalic anhydride, forming quinoline yellow, a dyestuff, (CgH,N)CH : (C,0.)CeHy. Carbostyril is 2-hydroxy-quinoline and is prepared by dehydrating o-amido-cinnamic CH : CH-:CO,H CH : CH acid, CoH = CoHac | + H,0, and by treating acetamido- NH, N_ : C(OH) benzaldehyde with NaOH. It melts at 199°. The tetrahydroquinolines, CgH,N, are produced by reducing the quinolines with nascent H. They behave like fatty amines, readily forming nitroso- and diazo-deri- vatives. That obtained by reducing carbostyril boils at 224° and yields with methyl iodide the compound kazrolin, CygH,)N-CHg, the hydroxy-derivative of which is kairine, CyH,(OH)N-CH; ; these two substances and thalline, CyHy(OCH;)NH, are used as substitutes for quinine. Isoquinolines yield 4: 5-pyridine-dicarboxylic acid when oxidised, showing that the N atom is in the 2-position of the naphthalene ring, H H FORT OX HC Cc CH ale 3 Ne \cF H H Isoquinoline accompanies the quinoline from coal-tar and is separated therefrom by fractionally crystallising the sulphates. It melts at 23° and boils at 240-5°. When a mixture of it with quinaldine is treated with benzotrichloride, quinoline red, a dye- stuff used in making orthochromatic photographic films, is obtained (cf. method of making malachite green, p. 758). Naphthoquinoline, Cy;HyN, and anthraquinoline, Cy,H,,N, are obtained by sub- stituting naphthylamine and amidoanthracene, respectively, for aniline in Skraup’s reaction (see above). When m- or p-phenylenediamine is the amine used, a phenan- throline, CygHgNo, is the product. These compounds are bases similar to quinoline and of complex constitution which cannot be discussed here. Alizarine blue is a dihydroxy- anthraquinoline obtained by applying Skraup’s reaction to m-amidoalizarine. C,H,-CH Phenanthridine, | || » bears the same relationship to phenanthrene (p. 573) CaHi:N that quinoline bears to naphthalene, and is obtained by heating benzylideneaniline, C,H;CH : NC,H;. It melts at 104°. Acridine Bases.—Acridine, C,;HgN, occurs in crude anthracene, from which it is extracted by dilute acids, yielding a fluorescent solution ; potassium dichromate precipitates it. It forms colourless needles, readily sublimes and has a very irritating vapour. It is a feebler base than pyridine and quinoline, but, like these, combines with alkyl iodides to form acridinium derivatives. The synthesis that establishes the constitution of acridine is from diphenylamine and formic acid by heating with ZnCl, ; formyldiphenylamine is first formed and then loses H,O: CH CoH, ig CHy = CoH | CyHy-+ H,0 PoP tage Se ee gee Qs 806 AZINES The dyestuff chrysaniline or phosphine, obtained as a by-product in making aniline, is meso-p-amidophenyl-2-amidoacridine. Acridine yellow and benzoflavine are also dyestuffs of this series. Azines.—Just as the azoles (p. 801) may be regarded as derived from the N-, O-, and S- five-membered heterocyclic rings, by substituting an N atom for a CH group, so the azines are derived by a similar substitution from the six-membered heterocyclic rings. They are either oxazines, thiazines, or diazines (also triazines and tetrazines) accordingly as they contain O and N, S and N, or N alone. They are further distin- guished by the prefixes ortho-, meta-, and para- accordingly as the O and N, S and N, or N and N are in the 1:2, 1: 3, or 1: 4 positions to each other respectively. Very few of these numerous compounds can be mentioned here. O Phenoxazine is a dibenzoparoxazine, ott OH produced by heating NH o-amidophenol with pyrocatechol ; it melts at 148°, and deserves notice only as the progenitor of the dyestuffs resorufine,1 O : CgH3 : [NO]: CsH30H, obtained by heating resorcinol with nitrosophenol and an oxidant to remove He, and gallo-cyanine, a more complex derivative made by heating gallic acid with nitrosodimethylaniline ; the former dyes red, the latter violet. To the dibenzoparathiazines belongs thio-diphenylamine, an '\ te the product of heating diphenylamine with sulphur. It melts at 180° - is the parent substance of the diphenylamine dyes; thus, by oxidising paraphenylenediamine in presence of H,S is obtained Lauth’s violet or thionine, N NH, CHC Doo : NH. The tetramethyl derivative of this thionine is methylene blue, N(CH3)o"CgHg : [NS] : CgH, : N(CH;).Cl, obtained by treating dimethylaniline hydrochloride with sodium nitrite and reducing the isonitroso-dimethylaniline (p. 699) with H,S ; the dimethyl-para-phenylenediamine, C.H4(NH2)-N(CH3)2, thus produced is then oxidised by FeCl, in presence of the excess of H,S ; the blue solution is next saturated with NaCl, and ZnCl, is added to precipitate the ZnCl, compound of the dyestuff, which forms bronze-green crystals, soluble in cold water, to a fine blue liquid, from which the colour is fixed on cotton with a tannin mordant. The production of methylene white, Cj.H;(CH3)4N,8, by the action of reducing-agents has led to the use of methylene blue for measuring the reducing power of different portions of the body. The formation of the blue is one of the most delicate tests for H,S in solution ; the liquid to be tested is mixed with excess of HCl, a little dimethyl-para-phenylene diamine sulphate added, followed by a drop of FeCl. CH : N—CH The simplest metadiazine is pyrimidine, |. |. a soluble base melting at CH: CH: a 21° and boiling at 124°. The pyrimidines are obtained by heating 3-diketones with amidines ; they are also products of the polymerisation of alkyl cyanides by sodium at 150°, and were originally called cyanalkines. Thus cyanmethine (CH3CN)g, from methylceyanide, is constitutionally dimethylamidopyrimidine ; it is a crystalline base having a bitter taste and soluble in water. Pyrimidine groupings appear to be present, in proteins (q.v.). Also note the connection with the purine group (p. 809). CH: N The benzometadiazines are derivatives of quinazoline, Os | » not N :CH itself known ; its a-methyl derivative is produced by treating o-amidobenzaldehyde with NH; ; it melts at 35° and boils at 238°, CH : N-CH The paradiazines are derived from pyrazine, | coll , obtained by distilling CH: N It will be noticed that these dyestuffs are represented as ee quinonoid linking (p. 757). INDULINES AND SAFRANINES 807 amidoacetaldehyde with HgCl, solution. It melts at 55° and boils at 115°, but sublimes at the ordinary temperature and smells of heliotrope. Hexahydropyrazine, CgHoNo, is called piperazine from its analogy to piperidine ; it is a remedy for gout. ; N: CH Quinoxaline is a benzoparadiazine, CoH , obtained by heating glyoxal N: CH CHO-CHO, with orthophenylenediamine ; m.-p. 27°; b.-p. 229°. Phenazine is a dibenzoparadiasine, CGH | OH obtained by condensing o-phenyl- N enediamine with pyrocatechol, 2H,O and H, being lost. It crystallises in yellow needles, melting at 171°. Several important dyestuffs belong to this class; thus the red fluorescent dyestuffs called ewrhodines are amido-derivatives of naphthophenazine, CeH4[N2]C,oH¢, while the eurhodoles are corresponding hydroxy-derivatives. Toluylene red is dimethyldiamidotoluphenazine, NH2C.H2(CH3)[No]CsH3N(CH3)o- The indulines and safranines are dyestuffs which may be regarded as derived from azoniums, i.e. the ammonium bases corresponding with the tertiary amines, the azines, such as C,H,: [N-NCH,Cl]: CgH,. The indulines are mostly blue dye- stuffs made by heating p-amido-azo-compounds with monamines and an acid, thus— N——_-, NH,C,H,N : NC,H; + H,N-C,H; = NH: CoH Pools + NH; + Ho: ‘N(CeHs) They are of three kinds; the benzindulines, having the above formula derived from phenazine ; the rosindulines, derived from naphthophenazine; and the naphthin- dulines, derived form naphthazine, C,pHg[No]CioHs. _ The safranines are diamido-derivatives of the azonium salts and may be classified like the indulines. Tolusafranine, NH 2CgH,(CH,): [N-N(C,H;)Cl]: CsH3NHe, the commercial red dyestuff called safranine, is made by oxidising a mixture of p-toluylene- diamine, o-toluidine and aniline. CH : CH y-Pyrone, CON. ze is a neutral substance obtained by heating comanic CH : CH acid, C;5H302'CO2H (cf. Comenic acid, p. 632). Dimethyl pyrone, CH=C(CH,) 00g : Yo, CH=C(CH;) orms salts and has ammonia-like properties, forming double salts with PtCl, &c. Its HCl salt is an oxzonium salt (q.v.), with the constitution, CH= C(CHs) A co (SBN 9 CH=C(CH3) Cl Just as trivalent N and divalent O are not basic, so pentavalent N and tetravalent O are basic. The basicity of tetravalent O was concluded by the work of Collie on this compound. Dehydracetic acid and coumarin are other pyrone derivatives (q.v.). jon a-pyrone, CH. fe is also known. CH—CO Uric AciD AND THE ALKALOIDS Uric Acid and its Derivatives—Although these are strictly heteronucleal compounds, they are more nearly related to open-chain compounds than are the substances just considered; however, their connection with the vegetable bases, originally all classed together as alkaloids, warrants their discussion at this place. Uric Acid, or lithic acid, C;H,N,O3, or C,(CO)3(NH)4.—Uric acid is generally prepared from the excrement of the boa-constrictor (serpent’s 808 URIC ACID urine from the Zoological Gardens), which consists chiefly of acid ammonium urate, H(NH,)C;H,N,0,; this is dissolved by boiling with dilute potash, which expels NH, and converts it into normal potassium urate, K,C;H,N,O,; by passing CO, through this, the sparingly soluble acid potassium urate, HKC;H,N,0,, is precipitated ; this is washed, dissolved in hot water, and decomposed by HCl, which precipitates the uric acid. Human urine also yields uric acid in small crystals when concentrated by evaporation, mixed hot with a little HCl, and set aside; the crystals are much tinged with urinary colouring-matter, and may be purified by dissolv- ing in potash and treating as above; healthy urine yields, at most, one thousandth, by weight, of the acid. : Guano, the partly decomposed excrement of sea-birds, contains much uric acid, which may be extracted from it by boiling it with a 5-per cent. solution of borax, and adding HCl to the filtered solution. Uric acid is a white crystalline powder, appearing under the microscope in peculiar modifications of the rhombic prism. It is very sparingly soluble in water, requiring 1800 parts of boiling water and 14,000 parts of cold water; and it is insoluble in alcohol and ether, but dissolves in glycerin and in alkaline liquids. When heated, it is carbonised and decomposed, emitting odours of NH; and HCN ; urea and cyanuric acid are also found among the products. Strong H,SO,, heated with uric acid, dissolves it without blackening, and, on cooling, deposits crystals con- taining 2H,SO,; water separates uric acid from them. Nitric acid dissolves uric acid easily when gently warmed, effervescing from escape of N, CO, and oxides of nitrogen. On evaporating the solution, the yellow residue becomes red when further heated. This residue is a mixture of several. oxidation-products of uric acid, and assumes fine purple colours when treated with NH3; or KOH (murexide test). Uric acid is a reducing-agent ; it precipitates cuprous oxide from alkaline cupric solutions, and reduces silver nitrate to the metallic state, if a little Na,CO3 is added. When uric acid is heated with strong hydriodic acid in a sealed tube to 160°-170°, it yields glycocine, CH,NH,-CO,H, and the products of decomposition of urea, viz. NH, and CO,. Conversely, if glycocine be heated with excess of urea to 230°, uric acid is formed— CH,NH,-COjH + 3CO(NHy). = C,(CO),(NH), + 3NH, + 2H,0. Urea is found among the products of distillation and oxidation of uric acid. The acid character of uric acid is feeble, and its salts are, for the most part, sparingly soluble ; it is dibasic. Acid sodium urate, HNaC;H,N,Oz, occurs in the gouty concretions termed chalk stones, and sometimes as a deposit from urine. The acid ammonium urate is the buff or pink deposit so often formed in urine on cooling ; it disappears on gently warming; the colour does not belong to the salt itself. Acid lithium urate, HLiU, is the most soluble urate, requiring 370 parts of cold and 40 parts of boiling water, whilst the sodium salt requires 1100 parts cold and 124 parts boiling, and the ammonium salt requires 1600 parts of cold water. Uric acid and urates are very common constituents of urinary calculi. They are also found in minute quantity in blood and some other animal fluids, and in the solid parts of some animals. There is no evidence that uric acid contains -COOH groups, or even ‘OH groups; it probably owes its acid character to the presence of : NH groups, which, as has been already explained (p. 704), impart acid properties to compounds containing them. When lead urate is heated with methyl iodide, dimethyl uric acid, containing two methyl groups in place of two H atoms, is obtained. This is also a dibasic acid, showing that it must still contain two NH groups, and when its lead salt is heated with methyl iodide, tetramethyluric acid is obtained. When these methyl uric acids are PURINE 809 decomposed, the N appears as methylamine ; hence each of the methyl groups is directly united to a nitrogen atom, in which case there must have been four NH groups in the original uric acid. The various decompositions of uric acid, described below, indicate that it contains three carbon atoms directly united, and that at least two of its NH groups must be attached directly to a CO group (for urea, CO(NH,),, is a product of its decomposition). These considerations have led to the structural formula for uric acid— H-CO-C: /NEOO-ONE, COC |_ poo NH—C-NH This formula represents uric acid as a diureide, a ureide being a com- pound which may be supposed to be formed by condensation of urea with a dibasic acid. Thus parabanic acid (v.i.) may be regarded as formed from urea and oxalic acid : /Nik ase pee co aR = CO + H,0. \w He COOH \w H le rs It will be seen that uric acid contains two urea residues, but the acid of which it is a diureide is not known. The view is supported, moreover, by the fact that most of its derivatives are of the ureide form. N : CH:C-NH Purine, OPN ly gon is obtained from uric acid by treating it’ with POCI, whereby it becomes trichloropurine, which yields successively diicodopurine and purine when treated with HI and Zn-dust. It melts at 216°, is very soluble in water and is both an acid and a base. The orientation of the nucleus common to uric . 1.6.5.7 | acid and purine will be understood from the scheme 2, | 8. 3—4.9 ° When uric acid is added by degrees to strong nitric acid, it dissolves with efferves- cence, caused by liberation of CO, and N, and the liquid becomes hot. On cooling, it DS deposits octahedral crystals of ulloxan, aa Be or mesoxalylurea, which NH-CO stains the skin pink, and gives an intense purple colour with ferrous sulphate and a trace of potash. The octahedral crystals contain 1Aq, but it may be crystallised in prisms with 4Aq. When alloxan is boiled with baryta-water, it deposits the barium salt of alloxanic acid; C303(NH),CO + H,O = NH,:CO-NH:[CO},-COOH. If the boiling be long continued, the products are urea and (the barium salt of) mesozxalic acid— NH,-CO-NH-[CO],-CO,H + 2HOH = CO(NH,). + C(OH)2(CO2H)». By hydrogenising alloxan by passing HS through its boiling solution, it is converted Pa into dialuric acid, or tartronyl-urea, OOK. fue: Dialuric acid crystal- NH-CO lises in needles which absorb oxygen when exposed to air, and are converted into alloxantin, CgH,N,O7, with loss of 2H,0. This body is also precipitated together with sulphur, when H,S is passed into a cold solution of alloxan, when the dialuric acid formed at first reacts with the excess of alloxan, and the alloxantin, being nearly insoluble in cold water, is removed from the further action of the H,8. Alloxantin is precipitated on mixing solutions of alloxan and dialuric acid, so that it is a diwreide formed from these two ureides by loss of one mol. H,O. When uric acid is dissolved in hot dilute nitric acid, alloxantin is the chief product, and its preparation may be combined with that of alloxan by treating the cooled mother- liquor from the alloxan with H,§, and boiling the precipitate with water, which extracts the alloxantin and deposits it, on cooling, in prisms containing 3Aq. It has an acid 810 URIC ACID DERIVATIVES reaction, and produces a fine violet precipitate with baryta-water, which is bleached by boiling, being converted into the alloxanate and dialurate. Ferric chloride and a trace of ammonia give a blue colour with alloxantin. It becomes red when exposed to air containing ammonia. On adding ammonium chloride to a hot saturated solution of alloxantin, it becomes first purple and then colourless, depositing a crystalline es. precipitate of uramil (murexan) or dialuramide, CO CHNH,, and leaving \wH-co” alloxan in solution. If an ammoniacal solution of uramil be mixed with an ammoniacal solution of alloxan, a purple solution is formed which deposits crystals, with a green metallic lustre, of murexide, or acid ammonium purpurate, NH4.C,H,N,0,.H,0, the constitution of which is uncertain, but the formula is the sum of one molecule of uramil, one of alloxan, and one of ammonia. Since alloxan and uramil are both produced when uric acid is evaporated with nitric acid, it is easy to account for the purple colour produced by treating the residue with ammonia. Murexide is also formed by heating alloxantin to 100° in a current of ammonia- gas, when water is eliminated, and by boiling uramil with water and HgO, when an atom of oxygen from the latter acts on 2 mol. of uramil, yielding murexide and water. Murexide is sparingly soluble in cold water, and insoluble in alcohol and ether. Potash dissolves it with a rich purple colour. Acids bleach it, apparently producing uramil. When alloxantin is heated with strong H,SO, at 100°, as long as SQ, is evolved, it is converted into barbituric acid, or malonyl-urea, which is also obtained synthetically by heating urea with malonic acid and phosphorus oxychloride— jor. 3CH,(CO-OH), + 3CO(NH,). + 2POCI;, = oOHER go + 2PO0(OH); + 6HCLI. CO-NH Barbituric acid is sparingly soluble in cold water. When boiled with alkalies, it yields malonic acid and urea. Amido-barbituric acid is identical with uramil, /NE-CO Re | » is the chief product of the more violent NH-CO oxidation of uric acid, and is prepared by gradually adding uric acid to 6 parts of HNO; (sp. gr. 1-3) at 70°, evaporating to dryness on the steam-bath, and re-crystallising from water. It forms prisms which are strongly acid, dissolve in alcohol, but not in ether. It is a dibasic acid ; its solution gives, with silver nitrate, a characteristic crystalline precipitate of CO: N,Ags(C,02).H,0. When boiled with dilute acids, parabanic acid yields urea and oxalic acid, and it may be synthesised from these substances in the presence of phosphorus oxychloride. Most oxidising-agents convert uric into parabanic acid. Oxaluric acid, NH,-CO-NH-CO-CO,H, is formed when parabanic acid is boiled with NH;, ammonium oxalurate crystallising in needles after cooling. If these be dissolved in hot water, HCl precipitates oxaluric acid as a crystalline powder. This acid has the same relation to parabanic acid as alloxanic acid has to alloxan— Alloxan . N,H,(CO),4 Parabanic acid . N,H,(CO); Alloxanic acid . N,H;(CO)3-CO.H Oxaluric acid . N,H;(CO),-CO.H A small quantity of ammonium oxalurate may be extracted from urine by animal charcoal ; after having served for the filtration of a large volume of urine, the charcoal is well washed with water, and boiled with alcohol, which leaves the oxalurate mixed with colouring-matter, when evaporated. Oxaluramide, N,H3(CO).-‘CO-NH,, is metameric with ammonium parabanate, CO-N2H(NH,)-C,0., and is obtained by heating that salt to 100°. Dimethyl-parabanic acid, CO-N,(CH3)2"C20s, or cholestrophane, is formed when silver parabanate is heated with methyl iodide. It is interesting from having been originally obtained by the oxidation of caffeine (see Caffeine). The principal immediate products of the oxidation of uric acid in solution have been seen to be alloxan, parabanic acid, and urea; but, when an alkaline solution of uric acd in potash is exposed to air, it slowly absorbs oxygen, and deposits crystals of the potassium salt of uroxanic acid, from which the acid may be precipitated by Parabanic acid, or oxalyl-urea, CO SYNTHESIS OF URIC ACID 811 HCl; C3HaN4O, + 2H,O + O = C3H,N,0,(CO,H),. When boiled with water, this acid is decomposed into single molecules of COz, urea, and glyoxylurea, foo ae , or allanturic acid. NH-CHOH When uric acid is boiled with PbO, and H,0, a precipitate of lead oxalate is formed, and the filtrate deposits crystals of allantoin, C,H,N,O3 and urea on evaporation ; 2C5H4N403 + O2 + 5H,0 = CyH_N,O0, + 2CON,H, + 2C,H,0,. Allantoin is found in the allantoic liquid of the cow. Iso-uric acid, having the same composition as uric acid, but more easily oxidised, is deposited on boiling alloxantin with solution of cyanamide— CyH4N,0, (alloxantin) + 2(CN-NH,) (cyanamide) = 20;H,N,Oz (iso-uric acid) + O. Some alloxan is formed at the same time by the oxidation of some of the alloxantin, which thus serves as the necessary reducing-agent. Uric acid has been synthesised by the following reactions : NH-C(CH. Action of urea on ethyl aceto-acetate yields methyl uracyl cog oN oi : NH-CO eae ON Action of HNO; on this yields nitrouracylcarboxylic acid CO CNOz. NH-CO——” NH-CH ‘ By heating with lime this yields nitrouracyl cog on Oz. NH-CO NH-CH By reduction this yields isobarbituric acid . é . cog oon NH-CO fs By oxidation this yields isodialuric acid . ; : Oe Joon, NH-CO— which yields uric acid when warmed with urea and H,SO,, Theoretically, the parent of uric acid is purine (p. 809), from which are also derived the bases— yp Ess NH:CO-C-NH._ co | CH, HN: © | CH,, \nH—G-N 7 \ya—-w 4 Xanthine. Guanine. NH-CO-C-NH N : C(NH,)-C-NH cH¢ | Don, cH |_ JOH. N——C-N N———_ C-N Hypoxanthine. Adenine. These, like uric acid, are products of degradation of the animal organism and are also present in some vegetable products, such as the juice of the beet-root. They are regular cleavage products of proteins, as also are several of the closely related pyrimidine derivatives ; see Proteins. They are all obtainable from uric acid through trichloro- purine (v. Purine, p. 809), which yields these four bases by different reactions. Guanine is converted into xanthine, and adenine into hypoxanthine, by HNO». Guanine, C;H;N;0, is extracted from guano (the excrement of sea-fowl) by boiling it with lime and water, and boiling the undissolved residue with NaOH, which dissolves the guanine and uric acid; these are precipitated by acetic acid, and the guanine dissolved out by hydrochloric acid, and precipitated by NH3. It is amorphous, insoluble in water and alcohol, and is at once a feeble di-acid base and dibasic acid. It gives the murexide reaction, and when oxidised by KClO3 and HCl, it yields CO,, parabanic acid and guanidine— C;H;N;0 + 30 + HO = CO, + CsH,N,03 + C(NH)(NHp)o. Guanine is found in the pancreas of the horse, in gouty deposits in pigs, in the excrement of spiders, and the scales of bleak. It is formed, together with xanthine and sarcine, _when yeast is allowed to decompose in water at 35°. 812 ALKALOIDS Xanthine, C;H,N,0., is prepared by the action of nitrous acid on guanine ; C;H;N;O + HNO, = C;H.N,O, + H,O + N,. It forms minute white crystals spar- ingly soluble in water, insoluble in alcohol, dissolved by alkalies, and reprecipitated by acids. It gives the murexide reaction. Its crystalline salts with acids are decom- posed by water. Its ammoniacal solution yields, with AgNOg, a gelatinous precipitate containing C;H,Ag,N,0,.H,O, which, when treated with CH,I, yields theo- bromine (q.v.). Xanthine occurs in certain rare urinary calculi, and, in small quantity, in urine, in the liver, pancreas, spleen and brain ; also in guano and yeast. Sarcine, or hypoxanthine, C;H,N,O, exists in extract of meat, amounting to about 0-6 per cent., and may be precipitated from the mother-liquor of the extraction of creatine (p. 711) by boiling with cupric acetate. The brown precipitate is dissolved in HNO, and precipitated by AgNO , which forms an insoluble compound from which the sarcine may be exttacted by decomposing with H,S and boiling with much water. It crystallises in minute needles, and is more soluble than xanthine, though it forms a less soluble hydrochloride. It is feebly basic and acid. Nitric acid oxidises it to xanthine. Sarcine is generally found together with xanthine, and occurs in many parts of the animal body, especially in marrow. Adenine, C;H;N;, found in the pancreas of the ox and in tea, crystallises in lustrous lamine (with 3H,O) and is soluble in water. Carnine, C7HgN403;, is also found in extract of meat, and much resembles xanthine and sarcine. Nitric acid or bromine-water oxidises it to sarcine. Alkaloids.—These possess particular interest for both the chemist and the physiologist on account of their peculiar chemical properties and their powerful action on the animal economy ; many of them are the active principles of vegetable drugs and are used in medicine either in the separate state, usually as “ alkaloidal salts,” or as galenical preparations of the crude drugs ; several of these preparations in the pharmacopeias are now “ standardised ”’ to contain a definite proportion of alkaloid. Few of the alkaloids have been prepared artificially. They all contain nitrogen, but rarely more than two atoms in the molecule, though there may be 20 or 30 atoms of carbon; they all contain oxygen except coniine, nicotine, sparteine, and piperidine, and these are further exceptional in being volatile, as also in being liquid. The term alkaloid in its wider sense embraces most “‘ alkali-like ’’ bodies, and so betaine, hordenine, and numerous others which are equally well classed in the amino or other groups are included. In the more restricted and generally, though not universally, accepted sense, only derivatives of pyridine, quinoline and similar heterocyclic nuclei, characterised by the undermentioned properties, are recognised, together with alkaloids of the purine group of which caffeine is the chief. Morphine and its analogues are exceptional in their constitution and many of their properties. With few exceptions they are colourless, crystalline solids, soluble in chloroform, many also in ether and alcohol, rarely in water except traces, optically active; the majority melt without decomposition, but very few are volatile. They all combine with acids forming salts just as ammonia does, B + HCl = BHCl1; most of the salts of the common acids are soluble in water, and give crystalline precipitates with PtCl,, AuCl,, &c.; also with the “ alkaloidal reagents,”’ of which the chief are (a) solution of iodine in potassium iodide; (b) potassio-mercuric iodide (Mayer's reagent) ; (c) potassio-bismuthic iodide (Thresh’s reagent) ; (d) picric acid ; (e) tannin ; (f) phosphomolybdic acid ; but a precipitate does not prove the presence of an alkaloid, as some other classes of bodies, e.g. the proteins, are also thrown down. Most alkaloids give very rich and intense ‘‘ colour reactions ”’ with certain special reagents, e.g. Frohde’s reagent. On oxidation they yield characteristic oxy- and acid-products. By acetyl or benzoyl chloride CAFFEINE 813 some are found to contain one or more OH groups; by Zeisel’s method, OCH, ; by hydrolysis some are resolved into basic and acid groups, ¢.g. atropine, cocaine, aconitine, piperine ; while on heating with zinc dust nearly all yield pyridine, quinoline or their homologues ; but morphine yields phenanthrene. . The Purine or Xanthine-alkaloids——The alkaloids, theobromine and caffeine, are methyl derivatives of xanthine : NH-CO-C-N(CH,) N(CH,):CO-C-N(CH,) cog Dor. cog Tl Dor. N(CH,)-C-N. N(CH,;)——C:N—— Theobromine, or 3 : 7-dimethylxanthine. Caffeine, or 1 : 3: 7-trimethylxanthine. Theobromine, C,H,N,Og, is extracted from the seeds of the cacao tree (Theobroma cacao), which grows in Demerara. These are known as cocoa-nibs, and are the raw material of cocoa and chocolate. The cocoa-beans contain 1 to 2 per cent. of theo- bromine, which may be extracted from them in the same way as caffeine (which it much resembles) from tea or coffee. When treated with KClO, and HCl, it yields methylalloxan and methyl-urea. When theobromine is dissolved in ammonia and boiled with silver nitrate, a white precipitate of silver theobromine, C,H,AgN,4Og, is obtained, and when this is heated with methyl iodide, it yields methyl-theobromine, or caffeine. Theobromine is similarly obtained from silver xanthine (p. 812). Theophylline, found in tea, is 1 : 3-dimethylxanthine ; m.-p. 264°. Caffeine or theine, C,H,,N,0,, is extracted from a plant of Cincho- naceous order, the coffee-tree (Caffea arabica), the seeds of which contain about 1-5 per cent. of caffeine. It is also found in the leaves; but those of the tea-plant (Thea) yield more of it, the proportion in the dried leaf varying from 2 to 4 per cent. To prepare caffeine, tea-dust is boiled with water to extract all the soluble matter, which amounts to about 30 per cent., and consists of tannin, caffeine, aromatic oil and other bodies. The decoction is filtered, mixed with excess of lead acetate, which precipitates the tannin, again filtered, the lead precipitated by H,S, and the filtrate from the lead sulphide evaporated to a small bulk, when the caffeine crystal- lises and may be purified by recrystallisation from alcohol. The waste tea-leaves which have been exhausted in the tea-pot yield a consider- able proportion of caffeine when treated in this way. Caffeine may be similarly extracted from ground unroasted coffee-beans. It may be sublimed from tea-leaves or coffee-beans by gently heating them in an evaporating-dish covered with a dial- glass ; one of the best processes for obtaining it is to precipitate decoction of tea with tribasic lead acetate, to evaporate the filtrate to dryness, on the steam-bath, at last, and cautiously to heat the dry residue in an evaporating-dish, when the caffeine sublimes on to the cover. Caffeine is contained in several plants which are used in various places for chewing or preparing drinks. Paraguay tea is made from the leaves of one of the Ilicacee, or Holly order, the Ilex paraguayensis, and is drunk, under the names of maté and congonha, in Paraguay, Brazil, Chili and Peru. The leaves contain caffeine. Another beverage containing caffeine is used by the Indians of Brazil and called Guarana, being prepared from the seeds of the Paullinia sorbilis, a tree of the order Sapindacec, to which the horse-chestnut belongs. The kola-nut, or seeds of Cola acuminata, used as food and medicine by the natives of West-Central Africa, contains about 2 per cent. of caffeine. Caffeine crystallises in fine silky needles (with | 1H,0). It becomes anhydrous at 100°, and then melts at 233°, and sublimes at 79° undecom- posed. It dissolves in 90 parts of cold water, yielding a bitterish solution, which is not alkaline. It is soluble in alcohol and ether, and more easily in benzene and chloroform. Caffeine is a very feeble base, its salts being decomposed by water. The hydrochloride, C;H,)N,0,.HCl.2Aq, crystallises from strong hydro- 14 ‘ CONIINE chloric acid in prisms, which leave pure caffeine at 100°. The sulphate, C,H, )N,0,-H,SO,, is obtained in needles by adding dilute sulphuric acid to a hot alcoholic solution of caffeine. The acetate is C,H,)N,0,(C,H,0,)o. Chlorine-water (or HCl + KCIO;) converts caffeine into amalic acid, or tetra- methyl alloxantin, C,(CH3)4N,O7.Aq. In the presence of air, water and ammonia, this yields murexoin, or tetramethyl murexide, Cy(CH3)4N;0¢(NH4), which crystal- lises from hot water in scarlet prisms with a golden lustre. The test for caffeine is based on this: dissolve it in strong HCl, add a crystal of potassium chlorate, and evaporate to dryness. A red residue is left, which becomes purple with ammonia, . and is bleached by potash. The final product of the action of chlorine-water on caffeine is cholestrophane (p. 810). When long boiled with baryta-water, caffeine is converted into epee C,H,.N,0, which is a stronger base than caffeine— CyHioN4O02 + Ba(OH). = C7H,2N,O + BaCO;. Pyridine-alkaloids.—The alkaloids piperine, coniine and nicotine, are simple derivatives of pyridine ; sparteine is a bridged derivative, atropine and cocaine contain a pyridine nucleus conjugated with a pyrrolidine group. Piperine, or piperidine piperate, CyyHyO.,CO-NC;Hjo, bears the same relationship O to piperic acid, cH OH OH : CH:CH : CH-CO,H, that acetamide bears to O acetic acid, the piperidine (p. 804) residue, -NC;Hjo, behaving like the ammonia residue, -NH,. It is a feeble base extracted by alcohol from white pepper, the ripe fruit of Piper nigrum (the unripe fruit is black pepper). It crystallises in prisms, m.-p. 128°, which are insoluble in water, but soluble in ether. The alcoholic solution tastes hot. When boiled with potash it yields piperidine and potassium piperate. It dissolves in H,SO,conc. with a red colour. Coniine, or 2-normal-propyl piperidine, C;Hg(C;H,)NH, is extracted from the seeds of hemlock (Coniwm maculatum) by crushing them and distilling with weak KOH. The distillate, which contains NH, and coniine, is neutralised with H,SO,, concentrated by evaporation, and mixed with alcohol to precipitate the (NH4),SOx4. On evaporating the filtrate and distilling with strong KOH, coniine distils with water, upon the surface of which it floats. It is dehydrated with dried K,CO,, and fractionated. Coniine has a strong odour like mice; sp. gr.o> 0-886, b.-p. 167° [a]p = + 18-3. It is sparingly soluble in cold water, giving an alkaline solution. It dissolves in alcohol, and ether. When exposed to air, it becomes brown, and evolves NH;. Oxidising- agents, such as nitric and chromic acids, convert it into butyric acid. When coniine is heated in a sealed tube with CH,I, it exchanges H for CH3, showing it to be a secondary monamine, NH(C,Hi,)”. The methylconiine, NCH;(C,H,,)”, sometimes occurs in hemlock. It combines with CH;I to form a crystalline coniine-methylium ‘iodide, N(CgHi¢)’(CHs3)2I, which yields a caustic base when decomposed by AgOH. Hemlock also contains another base, conhydrine, CgH,,NO, crystallising in plates. Coniine has been obtained artificially by the action of sodium on an alcoholic solution of allyl-pyridine, C;H4(C;H,)N, a liquid product of the action of paraldehyde upon picoline, C;H,(CH,)N. The base obtained in this way, however, is optically active ; when its tartrate is fractionally crystallised, it is split up into a levo-base and a dextro- base (cf. p. 637) ; the latter is coniine. Paraconiine, CgHy5,N, propyl tetrahydropyridine, is obtained by distilling the product of the action of alcoholic ammonia on butyric aldehyde— 2C;H,CHO + NH; = H,O + C,H,,NO (dibutyraldine) ; CgH,;NO = H,O + C,Hy,N (paraconiine). This base is very similar to coniine, and, like it, a powerful narcotic poison, but is optically inactive, and appears to be a tertiary monamine. Nicotine, C,)H,,N., is found chiefly as malate, in the seeds and leaves of tobacco, Nicotiana tabacum, a plant of the order Solanacew. Nicotine is extracted from tobacco leaves by digesting them with very dilute H,SO,, NICOTINE 815 evaporating to a small bulk, and distilling with excess of KOH. The distillate is shaken with ether, the ethereal layer is drawn off, the ether distilled, and the nicotine placed in contact with quick-lime to remove the water, and distilled in a current of hydrogen, since it is decomposed when distilled in air at the ordinary pressure. Nicotine is colourless when freshly prepared, but soon becomes brown in air. It smells strongly of tobacco, sp. gr. 1-011, b.-p. 247°, [a]so° = — 169-54°. It is soluble in water, alcohol, and ether ; its solution is alka- line. It is a di-acid base, but its salts do not crystallise well. When heated with ethyl iodide, it behaves as a tertiary amine, yielding nicotine- ethylium di-iodide, N.(C,>H,,)’’(C,H;).l5, which yields the corresponding caustic base when decomposed by AgOH. By oxidation with chromic acid, nicotine yields nicotinic acid (pyridine-3-carboxylic acid) C;H4(CO,H)N, which yields pyridine, when distilled with lime. Nicotine is a-pyridyl-n-methyltetrahydropyrrol, being obtainable by a somewhat complex series of reactions from the amide of nicotinic acid by introduction of a pyrrol group in place of the CONH, group. Virginia tobacco contains more nicotine than other varieties, the alkaloid amounting to nearly 7 per cent. of the weight of the leaf dried at 100°, whilst the Maryland and Havana varieties contain only 2 or 3 percent. Tobacco is remarkable for the very large amount of ash which it leaves CH,-CH, when burnt, amounting to about one-fifth of the weight of the CH,N dried leaf, and containing about one-third of K,COg, resulting \cH -CH, from the decomposition of the malate, citrate, and nitrate of potassium during the combustion. The latter salt is frequently LE CH. present in larger quantity than is found in most other leaves and HC N aids the combustion, for which purpose it is sometimes added ; \oH CHA but it is often present only in very small proportion and the Nicotine. burning quality of the tobacco is not impaired by its absence. Cigars are made directly from the moistened tobacco leaves which may or may not have undergone a fermentation ; but snuff, after being moistened, is subjected, in large heaps, to a fermentation extending over 18 or 20 months, when it becomes alkaline from the development of (NH4),CO, (by putrefaction of the vegetable albumin in the leaf) and of a minute quantity of free nicotine, which imparts the peculiar pun- gency to this form of tobacco. The aroma of the snuff appears to be due to the pro- _ duction of a peculiar volatile oil during the fermentation. The proportion of nicotine in snuff is only about 2 per cent., being one-third of that found in the unfermented tobacco ; and a great part of this exists in the snuff in combination with acetic acid, which is also a result of the fermentation. Sparteine, C,;H,No, is a narcotic alkaloid extracted from the common broom (Spartium scoparium) by digestion with weak sulphuric acid and decomposing the sulphate by distilling with potash. It is liquid, ee ay heavier than water, and boils at 311°. Itis spar- EB. a Seay cH”, cx ingly soluble in water, giving an alkaline solu- 2 -CH3. CH. oS as 7 F ‘ CH. 2 tion with a bitter taste. It smells rather like | ue aniline, and becomes brown when exposed to air. 2 CH, It acts as a di-acid base, and is a bi-tertiary 5, | ie amine. N Tropine-alkaloids.—Atropine, hyoscyamine, Sparteine hyoscine, and cocaine are derivatives of a base tropine which behaves as a 1-methyl-4-hydroxypiperidine wherein the 1- and 5-C atoms are linked by a -CH,-CH,- group. Atropine and hyoscyamine are isomeric forms of a salt of this base with tropic acid or a-phenylhydracrylic acid. CH, aN HC CH,-CH——CH, — ster, — NCH, CH-0-CO-CH(C,H;)-CH,OH. | CH,-CH—CH, ti dee Tropine. Atropine. 816 COCAINE Tropine, CgH,,NO, is a crystalline base melting at 62° and boiling at 263°, obtained by hydrolysis of atropine. Atropine and hyoscyamine, C,,H2;NO3, are physical isomerides associated in several plants of the order Solanacee, particularly in deadly nightshade (Atropa belladonna), thorn apple (Datura stramonium), and hyoscyamus (henbane). Both alkaloids have the characteristic (mydriatic) effect of dilating the pupil of the eye. The majority of the alkaloid exists as d-Hyoscyamine in the fresh plant, but during the process of extraction it becomes largely converted into the racemic Atropine unless proper precautions are taken. Atropine forms colourless prisms, fusing at 115°, sparingly soluble in cold water, and having a bitter burning taste, and a very poisonous action. Atropine is optically inactive and hyoscyamine levo-rotatory, [a]p = — 20-25°, but the levo-atropine obtained by resolving the inactive form is not identical with hyoscyamine. Hyoscy- amine forms snow-white minute silky needles, m.-p. 108-5°. Hyoscine or scopolamine, C,7H_,NO,4, from Hyoscyamus Scopola and some other Solanaceous plants, m.-p. 55°. Its hydrobromide is well crystallised and is used in medicine. These three alkaloids are easily characterised and tested for purity by the crystalline properties and melting- points of their respective aurichlorides. Homatropine, Cs;H,N(CH3).C,.H4.0.CO.CH(OH).C,H;, usually employed as its hydrobromide, is artificially prepared from tropine and mandelic acid. Its mydriatic action is less prolonged than that of atropine. Cocaine, C,7H.;NOy, is extracted from the leaves of Hrythroxylon coca, a Peruvian stimulant. It crystallises in prisms, melts at 98° and dissolves in alcohol. It is levo- rotatory and is a valuable local anesthetic, for which purpose the hydrochloride is more often employed. When hydrolysed, cocaine yields tropine carboxylic acid or ecgonine, benzoic acid, and methylalcohol. It is, therefore, a benzoate of methyl tropine carboxylate, and is closely associated with atropine. H,C—CH———CH.COOH H,C—_CH———_CH.C00.CH, | | | | N.CH, CH.OH N.CH, CH.O.CO.C,H; | H,C—CH———CH, H,C—CH. CH, Ecgonine. Cocaine. Truxilline and tropacocaine, also occurring in coca leaves, are likewise derivatives of ecgonine, and the latter obtained by their disintegration is benzoylated to benzoyl- ecgonine and this is methylated to cocaine ; this is a commercial process. Eucaine is a synthetic substitute for cocaine, having the advantage of feebler. toxicity, and shows close chemical relationships, but being monocyclic it is not an ecgonine derivative. From acetone and ammonia two compounds are producible : CHa, C——CH, OE on, 00.08 cH,’ | we BAe peas acetone NH co eae heat CH3, | | NH, BN Diacetonamine (acydic CH, we C—_—CH, Triacetonamine (pyridine derivative) The CO in the latter unites with HCN —- : C(OH)CN, which on hydrolysis and subsequent treatment with methyl iodide and benzoyl chloride yields eucaine A, (CH ;),C———-CH, 0.COC,H. fe I /9 LOCH | \co.ocH, (CH3),0-———CHy If the diacetonamine be treated with aldehyde instead of the third molecule of acetone, vinyl-diacetonamine is formed, which on continuing the process yields eucaine B ; they are merely the next lower homologues, MORPHINE 817 Opium Alkaloids—Opium (é7¢s, juice) is obtained from the unripe capsules of the opium-poppy, Papaver somniferum, cultivated in Turkey, Egypt, India and other Oriental countries. A few days after the poppy- flower has fallen, incisions are made in the unripe poppy-head, when a milky juice exudes. After twenty-four hours this becomes a soft solid mass of brown colour, and is scraped off and wrapped in leaves for the market. Opium contains about 25 per cent. of a gummy substance, 20 per cent. of ill-defined organic matters, a little caoutchouc, resin, oil and water, and variable proportions of a large number of alkaloids, of which morphine, codeine, narcotine, papaverine and narceine are the most abundant. Turkey opium which is used in medicine contains large quantities, 10 to 17 per cent., or more, of morphine and but little narcotine ; Indian and Chinese opiums, used for smoking, contain little morphine, 3 or 4 per cent., and much narcotine. Meconic acid (p. 632) is also a peculiar constituent (about 4 per cent.). Opium for use in medicine is standardised to contain 10 per cent. morphine. Tincture of Opium, or laudanum, containing 0-75 per cent. morphine, is made by extracting opium with dilute spirit, and subsequent standardisation. Morphine, or morphia, C,,H,)NO3, is extracted from opium by steeping it in warm water, which dissolves the meconate and sulphate of morphine, straining, and adding CaCl, which precipitates calcium meconate. The filtered solution is evaporated to a small bulk and set aside, when the hydro- chlorides of morphine, codeine and oxymorphine crystallise. These are dissolved in water, and the morphine precipitated by adding ammonia. It is recrystallised from alcohol in prisms (with 1H,O), which become anhy- drous at 120°. It is sparingly soluble in water, 1 in 1000, and nearly in- soluble in ether and chloroform, both of which dissolve most other alkaloids. Morphine is soluble in ethyl acetate (acetic ether) and in amyl alcohol, either of which may be employed to extract it from an aqueous solution. Even ether may be employed to extract morphine from an alkaline solution, if shaken with it immediately after adding the alkali, and before the morphine has precipitated. Morphine differs from most other alkaloids by being very soluble in potash and in lime water ; if a drop of weak potash be stirred with solution of a salt of morphine, the alkaloid is precipitated, but it is redissolved by a very little more potash. Ammonia does not easily redissolve it unless NH,Cl be present. Morphine behaves like a tertiary monamine ; it contains two OH groups and resembles, in some reactions, a phenol-alcohol. Its solutions are alkaline, and it com- bines with acids, like ammonia. It is easily oxidised. It yields phenanthrene on distillation with zinc dust, and not pyridine or quinoline as most alkaloids do. Its constitution is not yet settled. Morphine hydrochloride, Cy7HgNO3.HCl, is the chief form in which morphine is used in medicine. It crystallises in needles with 3Aq, and is easily soluble in water and alcohol. Morphine acetate, meconate and tartrate, all very soluble salts, are also used in medicine. Morphine and its salts act as powerful narcotic poisons ; they are easily identified by giving a blue colour with ferric chloride (purple in the case of meconate) and a golden yellow with strong nitric acid. Morphine acts, in many cases, as a reducing-agent ; it liberates iodine from iodic acid in solution ; it reduces potassium ferricyanide to ferrocyanide, and precipitates silver when boiled with silver nitrate. When distilled with potash, morphine yields methylamine. Morphine periodide, C,7H,yNOgI4, is obtained as a brown precipitate when solution of iodine in KI is added to morphine hydrochloride. Apomorphine, Cy7H,7NOz, is formed when morphine is heated with a large excess of strong HCl for some hours, at 150°; C,,HigNO; = C,,Hy,NO, + H,0. From the hydrochloride thus obtained, Na,CO; precipitates apomorphine as an amorphous powder, rapidly turning green in air, and then dissolving in ether with a purple colour, It is much more soluble in alcohol and ether than is morphine, and is a powerful emetic, even when injected under the skin. 52 818 NARCOTINE Codeine, codeia, or methyl morphine, Cy7Hyg(CH3)NO;, is obtained from opium by adding potash or soda to the ammoniacal filtrate from the morphine. It may be purified by crystallisation from ether. Codeine has been obtained from morphine by heating it with methyl iodide in alcoholic solution. Codeine melts at 150° and is soluble in water and ether, and very soluble (1 in 2) in alcohol or chloroform. It crystallises from ether in anhydrous octahedra, and from water in rhombic prisms, which contain Aq. The crystals fuse under water. It is a narcotic poison, though less powerful than morphine, and amounts in opium to only about 0-5 percent. It is strongly alkaline, gives no colour with ferric chloride, and does not reduce iodic acid like morphine. It is a tertiary monamine. When heated with caustic alkalies, it yields methylamine and triethylamine. Heated with strong HCl at 150°, it yields apomorphine and methyl] chloride. Other derivatives, prepared synthetically, are used in medicine; .e.g. Dionin, ethylmorphine hydrochloride, C,7Hj,(C,H;)NO3.HCl; Heroin, diacetylmorphine, C,7H,7(CH3.CO),NO; ; Peronine, benzylmorphine hydrochloride, C,H, 7(Cg,H;.CH,)NO3.HCl. ‘ Thebaine, C,7H,;(OCH;)2NO, is contained in opium in small proportion, 0-15 per cent. This alkaloid, similar to morphine instructure, is insoluble in water, but dissolvesin alcohol and ether, and crystallises in plates ; m.-p. 193°. It isinsoluble in alkalies. Its alcoholic solution is alkaline. Thebaine gives a blood-red solution with strong sulphuric acid. When heated with hydrochloric acid, it yields an isomeride, thebenine, which gives a blue colour with sulphuric acid. Thebaine is very poisonous, producing tetanic convulsions. Narcotine, C2,H,,NO,, is extracted by digesting with acetic acid the residue left after exhausting opium with water. The narcotine is dissolved and is precipitated on adding NH;. It crystallises from alcohol in prisms, which contain ‘Aq.; but like morphine, is almost insoluble in water ; it dissolves in ether, however, which extracts it from powdered opium, leaving the morphine. Narcotine is insoluble in potash, and melts at 176°. It is a very feeble base, not alkaline, dissolving in acids, but not forming well-defined salts. It has no narcotic effect, but resembles quinine in its action, hence it is more appropriately called anarcotine. When narcotine is long boiled with water it splits up intoa monocyclic amido-aldehydic base, co‘arnine, m.-p. 132°, soluble in water, and meconine, the lactone of meconinic (not meconic) acid or 5: 6-dimethoxyphthalide (phthalide being the lactone of 1: 2- go methylbenzoic acid, on yee Meconine also exists ready formed in opium CH, about 0-5 per cent.), is sparingly soluble in water and melts at 102°. Cotarnine hydro- chloride, also called stypticin, is employed in medicine. Cotarnine in forming salts with acids eliminates water and closes into an isoquinoline nucleus, an unusual reaction amongst alkaloids, also observed in its combination with meconine to reform dl-nar- cotine or gnoscopine, which on resolution with a-bromocamphorsulphonic acid yields the I-modification or ordinary narcotine. Meconine and cotarnine have both been synthesised and therefore narcotine also. Narcotine on oxidation yields opianic acid, 5 : 6-dimethoxyphthalaldehydic acid, (CH30)2.CgH,.CHO.COOH. The following equation explains the reactions referred to. OMe OMe Tae A gee CO CH,.0 CH.O Meconine panes OMe CHO << OMe CH or NHMe of \“ \xme nT nd) No < Pee a GH, CH, Cotarnine. Narcotine. QUININE 819 The chemistry of narcotine affords an instructive study to the student, and is of general interest on account of its close relationship to hydrastine, berberine, narceine, and other bodies of pharmacological importance. Narceine, C,3;H2,NOg, exists in opium, and may be produced from narcotine by heating with methyl iodide and then with potash ; the isoquinoline nucleus is broken, but the meconine group remains attached. It forms silky needles, sparingly soluble in water, m.-p. 170°. Papaverine, CooH2iNOq, occurs in opium, consists of dimethoxy-benzene joined through CH, to dimethoxyisoquinoline, constructed on the same model as narcotine. Crystalline needles, insoluble in water, m.-p. 147°, strongly narcotic. Hydrastine, C,,H,,NO,, m.-p. 132°, similar in structure to narcotine, occurs (1:5 per cent.) in the root of the golden seal, Hydrastis canadensis, together with (4 per cent.) berberine C,,H,,NO,, also related to narcotine. It is colourless and forms colourless salts. By acid oxidation hydrastine breaks up into opianic acid and hydrastinine, a body related to cotarnine. Berberine is more widely distributed, e.g. in barberry root, Berberis vulgaris, calumba root, &c. Berberine and its salts are yellow. M.-p. 145°, optically inactive. The nitrate is sparingly soluble. Cinchona alkaloids, of which the chief are quinine, quinidine, cincho- nine, and cinchonidine, exist in the barks of the trunks, branches and roots of various trees of the genus Cinchona. They grow on the slopes of the South American Andes, whence the name Peruvian bark, but it has for three or four decades been extensively cultivated in the East Indies, especially in Java, with most satisfactory results. The value is determined by the alkaloidal content (the mixture of total alkaloids is sold as quinetum) which may exceed 10 per cent. considerably, or more usually by the yield of quinine sulphate which may vary from 2 or 3 per cent. to 7 or 8 per cent. Fifty years ago quinine was very expensive owing to the great demands, particularly in time of war, and during an attempt at its artificial production Perkin discovered the first aniline dye. The quest for artificial quinine was followed enthusiastically for several years, but it was relinquished, except for scientific interest, when the cheapness of the cultivated drug destroyed all hope of financial remuneration. All these alkaloids are quinoline derivatives and yield quinoline when distilled with zinc dust, A large number of facts regarding the structure have been ascertained, but so far the whole constitution of none of them appears to have been settled finally. Quinic acid (p. 623) and quinotannic acid (p. 622) also exist in the bark in combination with the alkaloids. Quinine, C,,H,,N,0,, is prepared by boiling the bruised bark with diluted hydrochloric acid, and mixing the filtered solution with lime diffused through water, until it is alkaline. The precipitate, containing quinine, cinchonine and colouring-matter, is filtered off and boiled with alcohol, which dissolves both the alkaloids, leaving the excess of lime undissolved. A part of the alcohol is then recovered by distillation, and the solution neutralised with sulphuric acid, boiled with animal charcoal till decolorised, and filtered. On standing, quinine sulphate crystallises out, leaving the cinchonine sulphate in solution. The quinine sulphate is dissolved in water, and decomposed by ammonia (carefully avoiding excess in which quinine is soluble), which precipitates the quinine. : : Quinine crystallises in prisms containing 3Aq, which dissolve in 1900 parts of cold water and easily in alcohol, ether, and chloroform ; when anhydrous it melts at 117°. Its solutions are alkaline and bitter. ' Quinine is characterised by exhibiting a beautiful blue fluorescence when dissolved in dilute sulphuric acid, and by producing a fine green colour when its dilute acid solutions are mixed with a little chlorine- or 820 CINCHONINE bromine- or euchlorine-water (seezp. 119), and afterwards with ammonia. The green colour is due to the thalleioquin, formed by the reaction— CopHo4N202 + NH3 + 202 = CooHo7N30c. The constitution of quinine approximates the following, so also does that of cin- chonine, save that the OCH, group is missing. CH, : CH——-CH______ CH, / \ CH;0—-——. CH—CH,—CH,—N < % ‘ y — CH,—___CB____cH(OH) —__-Y Sy 2 \ p> Quinine is a di-acid base, but it sometimes forms salts in which it is monacid ; there are two hydrochlorides; Cz 9H24N20..2HCl is converted by water into Co9HesN20..HCl, which crystallises in needles of the formula 2(CopHosN202.HCl).3Aq. Normal quinine sulphate, CypH24N202.H,SO,.7Aq, is soluble in 10 parts of cold water, but the ordinary sulphate, (CopH24N20z)o-HpSO,.8Aq, requires 780 parts of cold water to dissolve it. This is the quinine salt generally used in medicine ; it forms very light silky needles, which dissolve easily in dilute sulphuric acid, forming the acid sulphate, Cop9H»4N202.(H2SO4)..7Aq, which is very soluble. Quinine is very slightly soluble in potash, and sparingly in ammonia, though it is more soluble in NH, than is any other cinchona alkaloid. If normal quinine sul. phate be dissolved in strong acetic acid, warmed, and an alcoholic solution of iodine added gradually, thin rectangular plates are deposited on cooling, having the formula (CopHo4NoOo)4.(H2SO,)3.(HI)o.14.6H,O. These crystals (herapathite, or artificial tour- maline) are bronze-green by reflection, but transmit light of a pale olive colour, which is perfectly polarised, like that transmitted by tourmaline, so that, if another plate be laid upon the first, no light is transmitted when their principal axes are at right angles. Quinidine, Cy9H4N.0o, is isomeric with quinine, and is extracted from a brown substance called quinotdine, or amorphous quinine, which is obtained from the mother- liquors of quinine sulphate and sold as a cheap substitute for quinine. It is also obtained in quantity from some of the inferior varieties of cinchona, such as Cinchona cordifolia, which yields the Carthagena bark. Quinidine forms larger prismatic crystals than quinine, and these contain only 2Aq. Its salts are more soluble than those of quinine, and they are strongly dextro-rotatory for polarised light, whilst those of quinine are levo-rotatory. Quinicine, also isomeric with quinine, is formed by heating quinine or quinidine with dilute sulphuric acid to 130°. It is resinous, but its salts crystallise. Its solutions are feebly dextro-rotatory. Cinchonine, CygH,.N20, remains as sulphate in the mother-liquor from quinine sulphate (v.s.), and may be precipitated by ammonia. It is almost insoluble in water, and sparingly soluble in alcohol. Ether scarcely dissolves it, and is used to distinguish it from quinine. It crystallises from hot alcohol in anhydrous prisms, which have an alkaline reaction. It melts at 225° and sublimes in hydrogen. The salts of cin- chonine are more soluble than those of quinine, and give a much more voluminous pre- cipitate with ammonia, which is insoluble in a large excess, and is not cleared up by shaking with ether, as is the case of quinine. Cinchonine sulphate, (CigH22N.0)2.H.SO,4.2Aq, fuses when heated, evolving an aromatic odour and becoming red. Solution of cinchonine sulphate is less strongly fluorescent than one of quinine sulphate. Cinchonine also differs from quinine in yielding solutions which are strongly dextro-rotatory. Cinchonidine is isomeric with cinchonine, but is strongly levo-rotatory. Cinchonicine, another isomeride, resembles quinicine in origin and properties. Emetine, (CisHa2NO2) 4.2, and Cephaeline, (Cj4HapNOo);,,2, are two similar alkaloids in ipecacuanha root. Emetineis colourless, amorphous, m.-p. 68°, strongly alkaline to litmus, becomes yellow on exposure to light, is insoluble in caustic alkali, forms crystalline salts. Cephacline is crystallisable, less soluble in ether, soluble in STRYCHNINE 821 caustic alkali, m.-p. 102°. They are both powerful emetics, the latter being twice as active as the former. , Strychnos Alkaloids.—Strychnine and brucine are obtained from nuz-vomica, the seeds of the tropical plant, Strychnos nux-vomica, from false angostura bark,' which is the bark of the same tree, and from I. gnatia amara, or St. Ignatius’ bean. Nux-vomica, or crow-fig, contains about 1 per cent. of strychnine and 1 per cent. of brucine. Strychnine, C,,H,,.N,0,, is extracted from the crushed seeds of nux- vomica by boiling them with very dilute HCl. The solution is mixed with milk of lime, and the precipitate filtered off and boiled with alcohol, which dissolves the strychnine and brucine, and deposits the strychnine first when evaporated. The mother-liquor is neutralised with HNO , when strychnine nitrate crystallises out, leaving brucine nitrate in solution. Both alkaloids are levo-rotatory. Strychnine crystallises in rhombic prisms, soluble in 7000 parts of water, and melting at 284°. It is insoluble in ether and in absolute alcohol, but dissolves in dilute-alcohol. It is very soluble in chloroform, which is the best agent for collecting it from aqueous solutions. Its intensely bitter taste is very remarkable, and may be imparted to one million parts of water (one grain in fourteen gallons). Its alcoholic solution is alkaline, and it is a monacid tertiary base, combining with methyl iodide to form strychnine- methylium iodide, C,,H,.O,N,‘CH;I, which yields the corresponding hydroxide base when decomposed by AgOH. But this ammonium base is not bitter, nor poisonous unless injected under the skin, when it induces paralysis. Strychnine is extremely poisonous, giving rise to tetanic convul- sions. Potash precipitates strychnine from its solution in acids, and an excess does not dissolve it ; the precipitate by ammonia dissolves in excess, but the strychnine crystallises out after a time. The smallest particle of strychnine may be identified by dissolving it in strong sulphuric acid and adding a minute fragment of potassium dichromate, which produces a fugitive blue-violet colour. It forms an insoluble ferrocyanide with K,Fe(CN), in acid solution, and may thus be separated from brucine. Strychnine is remarkably stable, persisting in a corpse many months after decomposition has set in. One of the N-atoms in strychnine is the tertiary ammonia nitrogen; the other pe COOH appears to be in the form of a lactam group (p. 709) QL which becomes — 5 yielding strychnic acid, when strychnine is heated with sodium ethoxide. When N(CH3)I the methylium iodide (see above) is treated with AgOH, the grouping ZCO \wH ZN (CA)s becomes Za 0 .e NH Brucine, C.3;H2gN20,, is precipitated by KOH from the solution of brucine nitrate obtained in the extraction of strychnine. It is more soluble in water and alcohol than strychnine is, and crystallises in prisms with 4Aq, melting at 178° when anhydrous. Like strychnine, it is nearly insoluble in ether. It is intensely bitter and strongly basic. HNO, dissolves it with a fine red colour, which becomes violet on adding stannous chloride. Both strychnine and brucine yield quinoline bases when distilled with KOH ; indicating their relationship with quinoline. The proportion of methyl alcohol obtainable from brucine by distilling it with MnO, and H,SO, shows that it ' True angostura bark is obtained from Galipea officinalis and @. cusparia, belonging to the order Rutacez. It is used as a febrifuge, 822 VERATRINE contains 2(0CH;); it may, therefore, be regarded as dimethoxy-strychnine. It is much less poisonous than strychnine. Aconitine, Cs3;Hz;NOj5, is extracted from the root of Aconitum napellus, a plant of the Ranunculaceous or Buttercup order, known as monk’s hood or blue rocket. It erystallises from alcohol in anhydrous plates, m.-p. 189°, and at slightly higher tempera- tures it evolves acetic acid ; it is dextro-rotatory, but forms well-defined salts, which are levo-rotatory. On hydrolysis it yields acetic acid and benzaconine, and this on further hydrolysis gives benzoic acid and aconine, CogHyNOy. Aconitine is one of the most poisonous alkaloids, and, as yet, no trustworthy chemical test for it is known, so that the toxicologist is obliged to place a little of the suspected substance on the tongue, when aconitine produces a numbing, tingling feeling, lasting for some time. The preparations sold as aconitine are often impure bases of very variable quality. Pseudaconitine, CzgH ygNO . + H,0, is also a highly poisonous alkaloid, m.-p. 201°, obtained from Aconitum ferox, an Indian plant of the same natural order. Heated with potash, it yields pseudaconine, C.,H4,NO,, and the potassium salt of veratric (or dimethyl protocatechuic) acid (p. 748). Veratrine, C;,H;,;NO,,, is extracted from the root of white hellebore (Veratrum album), and from the seeds of Veratrum sabadilla, plants of the natural order Colchicacez. The alkaloid is present in very minute quantity. It is extracted by digesting the root with alcohol containing a little tartaric acid, evaporating the alcohol from the filtered solution, dissolving the residue in water, liberating the alkaloid by caustic soda, and shaking with ether, which dissolves it. The ethereal layer leaves the alkaloid when evaporated. Veratrine is characterised by its power to cause violent sneezing when a particle of the powder is drawn into the nose. It dissolves in HCl, and the solution becomes red when gently heated. Strong H.SO, gives a yellow solution passing into carmine-red, and becoming purple with bromine-water. Cevadine, CzgH4gNOog, is another alkaloid which causes sneezing, and is extracted from Cevadilla seeds (Veratrum sabadilla). Veratralbine, CogsH4,;NO, ; jervine, CogH37NOq ; pseudojervine, CogH4gNO, ; and rubijervine, CogHs,NO5¢, are also extracted from the Veratrums. These plants are chiefly used for poisoning vermin. Colchicine, Co2H2;NOg, occurs in meadow saffron, Colchicum autumnale (belonging to the same order as the Veratrums) ; much used as a remedy in gout. It is a very feeble base, and is, in fact, the methyl ester of another alkaloidal principle, colchicein. It is soluble in water and alcohol, and does not crystallise. Physostigmine, or eserine, Cy;H»o,N3Oo, is obtained from the Calabar bean, the seed of a Papilionaceous plant. It is sparingly soluble in water, but dissolves in alcohol, is strongly alkaline, and very poisonous. It has the property of contracting the pupil of the eye. Cytisine, CyH,4N.0, is the poisonous alkaloid contained in the seeds of Cytisus laburnum, a Papilionaceous plant. Chelidonine, Cz>H,gNO;, has been extracted from celandine (Chelidonium majus), a plant of the Poppy order. Delphinine, CogH3,NOg, is the poisonous alkaloid contained in larkspur or stavesacre (Delphiniwm staphisagria), the seeds of which are used for destroying vermin (aconite belongs to the same order). : Pilocarpine, C,yH,gN.Oo, is extracted from Jaborandi leaves, Pzlocarpius pennati- folius, a plant of the Rue order. The base itself is not crystalline, but the hydrochloride and nitrate are crystalline salts, which are used in medicine. Jaborandine, CyyHgN20q, is another alkaloid obtained from the same source. INDEX Where several references to a subject are made, the pages where the more important information is to be found are given in heavy type. ABIETIC acid, 679 Absolute temperatures, 9 zero, 9, 316 Absorptiometer, 79 Absorption bands, 647 spectra, see Spectra Accidental properties, 1 Accumulator, 327 active mass for, 502 Acenaphthene, 572 Acetal, 595 Acetaldehyde, see Acetic aldehyde Acetamide, 702 Acetamido-benzaldehyde, 805 chloride, 703 phenetol, 745 Acetanilide, 698, 702 Acetates, see Acetic acid Acetic acid, 323, 578, 602, 603-606, 648 anhydrous, see Acetic anhydride glacial, 604 aldehyde, 594 anhydride, 606, 662 chloride, see Acetyl chloride esters, 666 ether, see Ethyl acetate peroxide, 606 series of acids, 600 Acetimido compounds, 703 Acetmethylamides, 695 Aceto-acetic acid, 649 Acetol, 649 Acetone, 323, 561, 578, 582, 588, 633, 648, 657, 659, 670, 801, 816 carboxylic acid, 649 diethylsulphone, 648 peroxide, 648 Aceto-nitrile, 604, 702, 734 Acetonylacetone, 650, 795 Acetophenone, 649 Aceturic acid, 710 Acetyl, 604 acetone, 650. bromide, 662 carbamides, 706 earbinol, 649 chloride, 604, 662 creosol, 748 dioxide, 606 glycocine, 710 hydride, 614 hydroxide, 614 iodide, 662 phenyl hydrazide, 720 sulphides, 606 urea, 706 vanillic acid, 748 Acetylation, 606 Acetylene, 5, 251, 257, 273, 274, 556, 657 Acetylene benzenes, 567 (and) chlorine, 107 chlorine substitution and addition pro- ducts, 557 ae into “Closed chain,” 557, 560 detected in coal-gas, 273 dicarboxylate, 612, 628, 802 dichloride, 557 formed from ethylene, 257 heat of formation, 255 hydrocarbons, 556-557 metal substituents, 557 naphthalene, 572 preparation of, 556 properties of, 253-255 series, 556 synthesis of, 251 tetrachloride, 659 Acetylides, 253, 254, 612, 684 Achro-dextrin, 771 Acid(s), 19, 51, 8-92, 101, 716 acetic series, 600-609, 628, 644 acetylene series, 612 albumin, 788 anhydrides, 51, 62, 88, 112, 606 anhydro, 91 aromatic series, 613-615, 628 avidity of, 344 basicity of, see Basicity benzoic series, 613 chlorides, 89, 198 classification of, 89 decomposition, 667 dibasic, 90, 623-631 egg, 164 fatty series, 600 separation of, 601 fluorides, 132 from polyhydric alcohols, 615-619 halogen compounds, 660-663 hydroxy, 615-623 monobasic, 90 diatomic, 616 nitriles, 733 nomenclature, 89 olefinic series, 609-612, 614, 623, 627 organic, 545, 599-683, 667 oxalic series, 623-627 oxides, see Acid anhydrides polybasic, 90, 632 polymethylene, 610 radicles, 88, 198, 605, 684, 693 residue, 198 salts, defined, 92 strength of, 344, 601 structure of, 89-92, 599 tetrabasic, 90 tribasic, 90 823 824 Acid value, 672 Acid- forming oxides, see Acid anhydrides Acidity of a base, 89 Aconine, 82 Aconitic acid, 633 Aconitine, 822 Acridine, 803, 805 yellow, 806 Acridinium derivatives, 805 Acrolein, 583, 590, 596, 598, 610 Acrosazone, 764 Acrose, 597, 764 Acrylic acid, 583, 610 aldehyde, see Acrolein series of acids, 609 Actinic rays, 105 Actinium, 401 “* Active mass,’’ 502 Acyclic compounds, 544 terpenes, 675 Addition products, see Organic chemistry Additive properties, 299 Adenine, 811, 812 Adeps lane, 674 Adipic acid, 627, 632 Adipocere, 608 Adjacent substitution-products, 564 Adjective dyes, see Dyes Adrenaline, 745 Adrenine, 745 Adsorption, 423, 424 Aischynite, 431 Atsculetin, 779 Atsculin, 779 Affinity, coefficients of, 341- under Chemical) measurement of, 341-345 predisposing, 345 residual, see Valency After-damp, 68, 249, 258 Agate, 280 Aich-metal, 510 Air, analysis of, by eudiometer, 26, 27 by nitric oxide, 49 by phosphorus, 50 aqueous vapour in, 72, 73 burnt in coal-gas, 264 composition of, 50, 51, 72 constants, 311 defined, 48 “* dephlogisticated,” 49 “ fire,”’ 49 “ fixed,” 48, 49, 63 history, 9 “inflammable,” 95 liquid, 54, 85, 97 material nature, 48 ‘* mephitic,”’ 48 * nitrous,’ 49 optically pure, 73 “ phlogisticated,”’ 49 pump, 355 Alabaster, 392 oriental, 45 Alanine, 712, 785 Albite, 367, 425 Albo carbon light, 571 Albumin of eggs, 416, 784, 787, 788 of milk, 789 of vegetables, 788 Albuminoid compounds, see Proteins Albumins, 784 Albumose, 788 Alearsin, 690 (see also INDEX Alcohol (ethyl), 251, 256, 317, 574-578, 559, 603 absolute, 576 acids, &c., see Hydroxy acids, &e. amines, 700 determination, 577 methylated, see Methylated spirit of crystallisation, 324, 577 oxidation by nitric acid, 616 radicles, see Alkyl structural formula determined, 543 synthesis of, 574 test for, 577 ultimate analysis, 540 Alcoholates, see Alkyloxides Alcoholic fermentation, 575 Alcohols, 544, 574-592, 661, 743 acetylene, 583 action of sulphuric acid on, 555, 650, 664 aromatic, 584 boiling-points of, 644 classification of, 574, 581 dihydric, 574, 586-588 distinguished, 581 general preparation of, 581 iso, 580 monohydric, 574-585 normal, 580 olefine, 583 of conjugated nuclei, 585 polyhydric, 590-592 primary, 580, 581 secondary, 580, 581, 647 tertiary, 580, 581 tetrahydric, 590 trihydric, 574, 588-590 unsaturated, 583 Aldehyde(s), 545, 581, 592-599, 615, 644, 720 acids, 619 alcohols, 760 ammonia, 594, 595 aromatic, 597 condensation, see Aldol chlorine compounds, 660 constitution of, 159, 592 resins, 594, 665 Aldol, 595 condensation, 595, 596, 615, 661 Aldoses, 760, 761 Aldoximes, 596-642 Algaroth, powder of, 479 Alicyclic, 572 compounds, 558 Aliphatic series, 544 Alizarates, see Alizarin Alizarin, 754 artificial, 754 blue, 805 bordeaux, 755 eyanine, 755 Alkali, caustic, 359 defined, 88 electrolytic production, 373 manufacture, 868-875 metals, group of, 358 mild, 359 waste, 370-371 Alkaline cupric solution, 630 earth metals, 385, 398 Alkaline (-inity), 19, 51, 88 Alkaloidal reagents, 812 Alkaloids, 640, 804, 807, 812-822 volatile, 812 Alkides, 684 INDEX Alkylanilines, 699 Alkyl benzenes, 566 cyanates, 739 cyanides, 733 cyanurates, 739 indols, 797 isocyanates, 739 radicles, 544, 605, 684 salts, 545 sulphates, 664 Alkylenes, 554 Alkyloxides, 582 Alkylpiperidinium iodides, 804 Alkylpyridines, 803, 804 Alkylpyridinium iodides, 803 Alkylquinolinium iodides, 805 Allantoin, 811 Allanturic acid, 811 Allene, 556 Allophanamide, 706 Allophanic acid, 706 Allotrope, 237 Allotropic modifications, 138, 150, 178, 179, 180, 213, 235, 284, 339, 436, 488 Allotropy, see Allotropic modifications Alloxan, 629, 809 Alloxanic acid, 809 Alloxantin, 809-811 Alloys, 7, 422, 459, 485 (see also the various metals) for bearings, 511 fusible, 474 lowering fusing-point of, 474 Allyl-alcohol, 588, 596 amine, 740 bromides, 659 chloride, 659 cyanamide, 740 guaiacol, 678 iodides, 586, 659, 740 isothiocyanate, 740 yridine, 814 sulphide, 586 thiocyanate, 740 thio-urea, 740 tribromide, 632 tricyanide, 632 Allylene, 556, 557, 567 Almond oil, bitter, see Benzaldehyde fixed, 597, 673, 780 Almonds, 780 Aloes, 781 Aloin, 781 Aludels, 125 Alumina, see Aluminium oxide Aluminates, 422, 424 Aluminium, 20, 96, 97, 284, 375, 412, 469, 420, 650 acetates, 605 alloys, 422 bronze, 422 carbide, 258 chloride, 425, 649, 744 ethide, 688 ethoxide, 578 extraction, 421 fluoride, see Kryolite group, review of, 431 hydroxide, 424 methide, 688 oxide, 421, 423, 424 crystallised, 467 phosphate(s), 426 potassium silicates, 283 | Aluminium, powdered, 456 resinate, 423 silicates, 283, 420, 425, 427 sulphates, 422 Alum(s), 41, 46, 299, 422, 429 ammonia, 424 basic, 423 burnt, 423 potash, 424 stone, 423 Alunite, 423 Amalgam(s), 414 ammonium, 187 electrical, 326 sodium, 187 Amalgamating battery plates, 15 Amalgamation of gold-ores, see Gold of silver-ores, see Silver Amalic acid, 814 Amber, 679 Amethyst, 280, 462 Amic acids, '702, '707 Amide(s), 189, 224, 693, '702 and amines, reactions of, 207 Amidines, 703, 806 Amido-acetic acid, 709, 785 acids, see Amino-acids alizarin, 805 anthracene, 805 azobenzenes, 718 compounds, 717, 718 azones, 721 barbituric acid, 810 benzenes (see also Aniline), 701 sulphonic acid, 699, 714 benzoic acids, 713 butyric acid, 709 caproic acid, 712 cinnamic acid, 623, 805 compounds, 694 dinitrophenol, see Picramic acid ethyl-sulphonic acid, 714 formic acid, 709 (see Carbonic acid) glutaric acid, 785 glyceric acid, 791 iso-caproic acid, 785 isovaleric acid, 712, 785 naphthalenes, see Naphthylamines nitrophenols, 745 phenols, 745, 753, 757 phenylacetic acid, 714, 797 amidoacridine, 806 glyoxylic acid, 714 propionic acid, 785 propionic acids, 712, 785 succinamic acid, 000 succinic acid, 713, 785 sulphonic acids, 714 thiazole, 802 toluenes, see Toluidines xylenes, see Xylidines Amidogen, 189 Amidoximes, 703 Amine(s), 189, 692 ef seq. derivatives, 684 distinction between, 694 Amino-acids, 693, 708-714, 785, 786 anthraquinone, 756 arseno-benzene compounds, 694 hydroxy-propionic acid, 785 oxyphenyl-propionic acid, 786 phenylarsinic acid, 691 © arsenoxides, 69] 825 826 Ammelide, 739 Ammeline, 739 Ammonia, 124, 182-189, 227, 241, 273, 289, 393, 440, 452 absorbed by charcoal, 241 absorption by ammonium nitrate, 380 action of chlorine on, 107 of iodine on, see Nitrogen iodides and cobalt salts (cobaltamines) 458 bases, see Amines combustion of, 185 by chlorine, 186 decomposed by spark, 186 derivatives, 545, 692-721 freezing machines, see Freezing gas, dried, 84, 183 heat of dissolution, 184 of formation, 183 of vaporisation, 81 liquefied, 32, 81, 82, 88, 331, 361 meter, 185 Nessler’s test for, 418 nitrification of, 42 oxidation of, 191 salts, see Ammonium soda process, 371, 373, 696 solution, solubility, 80, 184 sources of, 182, 183 Ammoniacal liquor, 183, 273, 380 Ammoniacum, 749 Ammonium, 380 acetate, 702 alum, 424 amalgam, 187 antimonates, 478 arsenite, 230 bases, 692, 693 bicarbonate, 372, 380, 381 borofluorides, 291 bromide, 382 carbamate, 380, 707, 740 carbonate(s), 82, 380, 381, 707 chloride, 44, 53, 183, 314, 345, 381. 405 dissociation, 314, 340 chloroplumbate, 505 cyanate, 737 cyanide, 726, 738 ‘formate, 702, 725 hydroxide, 184, 187 hypoiodite, 209 iodide, 209, 382 isocyanate, 704, 705, 737 isothiocyanate, 707 molybdate, 470 mucate, 796 nitrate, 196, 200, 211, 380 nitrite, 53, 191 oleate, 337, 612 oxalate, 625, 704, 707 oxamate, 707 parabanate, 810 persulphate, 362 phosphate, 218, 224 (microcosmic salt) 383 phosphomolybdate, 470 picrate, 746 platinichloride, 532 platinochloride, 532 purpurate, 810 quaternary compounds, 641, 693, 716 salts, 380. sesquicarbonate, 380 stannic chloride, 489 INDEX Ammonium succinate, 626 sulphate, 182, 183, 380 sulphides, 152, 382 sulphocyanide, 176 tartrates, 626 thiocarbamate, 708, 740 thiocyanate, 708, 738 urates, 808 vandates, 481 zine ferrocyanide, 728 ’ Amorphous condition, 333 phosphorus, see Phosphorus Ampére, 132 Amygdalic acid, 780 Amygdalin. 597, 725, 780 Amyl, 606 acetate, 668 alcohols, primary, 582, 607, 652, 679 secondary, 581 amine, 712 ethyl ether, 652 nitrite, 665, 715 sulphuric acid, 652 valerate, 668 Amylene, 555, 556 Amyl-ethyl ether, 652 Amyloid, 773. 775 Amylose, 770 Anesthetics, 200, 548, 656, 657, 816 Analysis, 14 gravimetric, 4 of gaseous hydrocarbons, 269 organic, 538-541 calculation of, 540, 541 qualitative, 4 quantitative, 4 theory of reactions in, 331 volumetric, 4 Ananas oil, 668 Anarcotine, 818 Anatase, 490 Ancaster stone, 391 Andrews, 84 Anethol, 655, 678 Angelic acid, 611, 649 Anglesite, 495, 504 Angostura bark, false, 821 Anhydrides, acid, 89, 606 bimolecular, 709 halogen compounds, 662 Anhydrite, 393 Anhydrosulphuric acid, 160 Anilides, 698 Anilido-acetic acid, 710 Aniline, 559, 697, 804 blue, 759 dyes, 757 empirical formula, 541 oil, 699 for blue, 700 red, 700 safranine, 700 salts, 698 substitution products, 698 sulphonic acid, 699 yellow, 718 Animal charcoal, 242 chemistry, 64, 131, 181, 182, 209, 235, 387, 585, 671 fats, 585 Animi resin, 679 Anions, 94, 327 Aniseed, essential oil of, 599, 655 Anisic acid, 620, 654 INDEX Anisic aldehyde, 599 Anisol, 654 Annatto, 782 Anode, 16 Anthracene, 569, 572, 621, 805 chlorine compounds, 572, 660 constitution of, 572 dihydride, 573 oil, 572 Anthrachrysone, 755 Anthracite, 271 Anthranil, 713 Anthranilic acid, 713, 800 Anthranol, 754 Anthrapurpurin (-ates), 755 Anthraquinoline, 805 Anthraquinone, 572, 754 sulphonic acids, 755 Antiarin, 781 Antichlore, 159, 171 Antifebrin, 702 Antimonates, 478 Antimonie acids, 477, 478 anhydride, 62 Antimonietted hydrogen, 477, 478 Antimonious acid, 477 anhydride, 477 Antimonites, 477 Antimony, 62, 474, 476-480, 497 alkides, 689 alloy, 476 amorphous, 477 ash, 477 black, 476 - butter of, 479 chlorides, 104, 479 chlorosulphide, 479 crocus of, 476 crude, 476 detection of, 478 flowers of, 477 glass of, 480 golden sulphuret, 480 grey ore of, 476 liver of, 480 oxides, 477-478, 631 oxychloride, 479 oxysulphide, 480 pentachloride, 479, 659 pentasulphide, 480 . potassio-tartrate, see Tartar emetic red ore, 480 regulus of, 476 star, 476 sulphate, 480 sulphides, 152, 154, 161, 172, 215, 476, 479 sulphuret (golden), 480 trichloride, 479 uses of, 476 vermilion, 172, 480 white ore, 477 Antimonyl, 477, 631 antimonate, 477 chloride, 479 Antipodes, 641 Antipyrin, 802 Antiseptics, 157 Antitoxines, 788 Anti-zymotics, 157 Ants, acid of, 602 Apatite, 209, 218, 394 Apocamphoric acid, 677 Apomorphine, 817 827 Apple oil, 668 Aqua fortis, 193 regia, 108, 199, 527 Aquamarine, 411 Arabic acid, 772 Arabin, 772, 773 Arabinose, 591, 761, 764, 772 Arabite, arabitol, 591, 761 Arachidic (butic) acid, 601 Aragonite, 388 Arbitrary properties, 1 Arbor Dianex, 414 Arbutin, 779 Archil, 749 Arctic sperm oil, 674 Argand lamp, 265 Argillaceous iron ores, 435 Arginine, 786, 787 Argol, 630, 637 Argon, 47, 49, 53, 298-295, 311 group, 2938, 302, 307 Argyrodite, 494 Aristotle, 296 Armstrong, 331, 332 benzene formula, 561 ** Aromatic,” 572 Aromatic acids, 613 alcohols, 584 aldehydes, 597 amines, 694 esters, 668 ethers, 654 hydrocarbons, 558 radicles, 566 series, 558 waters, 674 Arrhenius, 94, 326 Arrowroot, 771 Arsacetin, 691 Arsanilic acid, 691 Arsenates, 230, 232 Arsendimethyl, see Kakodyl Arsenetted hydrogen, see Hydrogen arsenide * Arsenic,” 225 Arsenic, 58, 96, 181, 225-234, 261, 408, 456, 500 acid, 231 amorphous, 226 anhydride, 202, 281 black, 226 bromides, 234 chlorides, 233 contamination by, 230 fluorides, 233 halides, 233 in beer, 230 in glucose, 230, 762 in sulphuric acid, 165, 230 iodides, 234 native, 225 oxides, 228 et seq. sulphides, 282, 233 tests for, 227 white, 202, 228 Arsenical alcohol, 690 iron, 225 nickel, 225 pyrites, 225, 228 soap, 230 Arsenides, 225 Arsenio-siderite, 232 sulphides, 225 Arsenious acid, 128 oxide, 228 828 Arsenious oxide, crystalline, 228 opaque, 228 solubility of, 229 vitreous, 228 sulphide, 232 Arsenites, 229, 230 Arsen-methyl dichloride, 690 oxide, 690 Arsenoxides, 691 Arsines, 226, 690 Arsinic acids, aromatic, 691 Arsonic acids, 691 Arsonium compounds, 691, 228 Aryl radicles, 566 Asbestos, 283, 402, 404 platinised, 160 Aseptol, 747 Asparagine, 713 Asparagus, 591 Aspartic acid, 713, 785, 790 Assafcetida, 749 Assay of gold by cupellation, 526 Asymmetric carbon atoms, 141, 636 substitution-products, 564 Atacamite, 514 Atmolysis, 77, 78 Atmosphere, 48 ; see Air Atom defined, 6 disintegration of, 296 modern view of, 327 Atomic heat, 298 theory, 6, 10, 296 volume, 304-306 weight, 6, 296-807 and specific heat, 297 determined, 297-801 standard for, 97 nit, 6, 137 Atomicity, 297 of gaseous molecules, 310, 311 Atoxyl, 691 Atropic acid, 615 Atropine, 704, 815, 816 Augite, 425 Aurantia, 699 Auric salts, see Gold Auricyanides, 732 Aurin, 758, 759 Aurosulphides, 528 Aurothiosulphuric acid, 528 Aurous salts, see Gold Autogenous soldering, 162 Auxochromes, 718 Available chlorine, 116 Avidity of acids, 344 Avogadro’s hypothesis, 9, 10, 96, 309 mathematical expression, 313, 314, 319 Axial-symmetrical configuration, 638 Azelaic acid, 627 Azines, 806 Azobenzene, 691-692, 717 Azo-compounds, 714-721, 717 dye-stuffs, 718, 721 Azoimide(s), 189, 719-721 Azoles, 801 Azonium compounds, 720, 807 Azote, 49 Azoxybenzene, 717 Azulmamide, 723 Azulmic acid, 722 Azulmin, 726 Azurite, 506 Azylines, 718 INDEX Bacon, Roasr, 296 Bacteria, 73, 42, 181 Baddelyite, 492 Baeyer, 642 Baking powders, 70 Balard, 121 Balloons, 21, 22, 96 Balmain’s luminous paint, 394 Balsams, 679 Barbier, 687 Barbituric acid, 810 Barff’s process for protecting iron, 454 Barilla, 368, 369 Barium, 18, 298, 385 carbonate, 885, 386 chlorate, 117, 386 chloride, 298, 886 chromate, 466 chromic oxalate, 625 cyanurate, 736 di-oxide, see Barium peroxide ethoxide, 578 hydroxide, 386 hypophosphite, 222 manganate, 463 methylsulphate, 664 nitrate, 386 oleate, 611, 612 oxide, 386 percarbonate, 143 platinocyanide, 356, 732 peroxide, 54, 141, 386, 422 salicylate, 620 sulphate, 160, 885 acid, 385 sulphide, 385 tannate, 622 tungstate, 471 Barlow and Pope, 299, 335 Barometer, 48, 414 Baryta, 386 water, 386 Barytes, 385 Baryto-calcite, 389 Basalt, 390, 425 Base, acidity of, 89 equivalent of, 89 Bases, 51, 62, 88, 94 Basic carbonates, 244 * oxides, 51, 62, 88, 112 oxygen, 137 properties, 88 salts, 93 slag, 446 Basicity of acids, 90, 221, 432, 600 Bassorin, 773 Bath stone, 390 Batteries, Leclanché, 382 Battery, galvanic, 15, 826 Baumé’s flux, 364 Bauxite, 88, 421, 423, 424, 428 Bay, oil of, 676 salt, 368 Bear, 470 Beckmann’s apparatus, 321 methods, 321, 323 Becquerel, 356 Beef suet, 673 Bees’ wax, 583, 609, 668, 674 Beetroot sugar refuse, &c., 579, 656, 695, 710 Beggiatoa alba, 145 Behenic acid, 612 Belladonna, 816 Bell-metal, 487, 510 _INDEX 829 Bell ‘process, 374 Bengal saltpetre, see Potassium nitrate Benzaconine, 822 Benzal chloride, 597, 613, 615, 660 Benzaldehyde, 584, 597, 614, 642, '780, 801 Benzaldoximes, 642 Benzamide, 703, 710 Benzamido-acetic acid, 710 Benzanthrone, 756 Benzene (8), 274, 321, 323, 335, 559, 614, 647, 745, 752 acetylene, 567 addition products, 559 adjacent, symmetrical and metrical, 564 azomethane, 717 bromo-, 562, 565, 566, 660 chlorides, 660 commercial, 566 constitution of, 560 derivatives, 564 dibromo-, 565 dihydro-, 568 disulphonic acid, 748, 749 formule discussed, 561 from acetylene, 557 hexahydride, 568 hexahydro-, 568 homologues of, 566 hydrocarbons, general preparation of, 567 isopropyl-, 567 Kekule’s formula, 561 objection to, 564 methylisopropyl-, 567 monobromo-, 562 of crystallisation, 324, 569 olefine, 567 orientation of, 563, 564, 565 ortho-, meta-, para-, 564, 566 : phenyl., 568 ring, substitution-products of, di, 563 mono, 562 tetra, 564 tri, 564 sulphonic acids, 652, 681, 703, 744, 750 tetrahydro-, 568 tetramethyl-, 567 trimethyl-, 567 Benzhydrol, 585 Benzidine, 701, 719, 720 dye-stuffs, 719 migration, 701, 720 Benzindulenes, 807 Benzine, 548 Benzoacetic anhydride, 614 Benzoates, 613 azoles, 801 flavine, 806 furfurane, 796 Benzoic acid, 322, 559, 597, 618, 642, 710 aldehyde, see Benzaldehyde anhydride, 614 chloride, see Benzoyl chloride ether, 668 peroxide, 614 series of acids, 613 sulphinide, 703 sulpho-imide, 703 sulphonamide, 703 Benzoin gum, 613, 679 | Benzole, see Benzene asym- Benzoline, 548 Benzomercuramide, 703 metadiazines, 806 nitrile, 642, 710, 734 paradiazine, 807 phenone, 585, 649 pyrazoles, 802 pyridines, 804 pyrrol, 796, 802 quinone, 752 thiophen, 796 trichloride, 660 Benzoyl, 614 acetone, 802 azoimide, 721 chloride, 614, 662 compounds, 614 ecogonine, 816 formic acid, 650 glycocoll, 709, 710 hydrazide, 721 hydride, 614 hydroxide, 614 salicin, 779 Benzyl, 614 alcohol, 584, 654 amines, 700, 734 benzene, 569 benzoate, 584, 668 chloride, 597, 660 cinnamate, 584, 668 cyanide, 734 ether, 654 hydride, 614 hydroxide, 614 morphine, 818 Benzylidene, see Benzal Benzylideneaniline, 805 Berberine, 819 Bergamot oil, 678 Berthelot, 671, 776 Berthollet, 4, 115, 117, 148, 721 Beryl, 411 Beryllium, 303, 411, 419, 650 chloride, 303, 412 ethide, 687 Berzelius, 94, 178, 186, 492 Bessemer converter, 446, 508 Bessemer process, 443, 446 Betaine, 695, 701, 710 Betol, 747 Biborate of soda, see Borax Bicarbonate of soda, see Sodium bicarbonate Bicarbonates, 244 Bichromates, 465 Bicyclic terpenes, 675 Bicycloheptane, 570 Bicyclopentane, 570 Biebrich scarlet, 719 Bile, 701 constituents of, 793, 794 Biliary calculi, 585 Bilifuscin, 793 Biliprasin, 793 Bilirubin, 793 Biliverdin, 794 Biochemistry, &c., 181 Bioses, see Disaccharides Biotite, 425 Bi-rotation, 640, 762 Bischofite, 405 Biscuit porcelain, 427 Bismarck brown, 718 Bismuth, 401, 474 830 INDEX Bismuth gallate, 621 glance, 475 hydroxide, 475 iodide, 475 nitrates, 475 ochre, 475 oxides, 475 oxycarbonate, 475 oxychloride, 475 sulphides, 475 telluride, 179 trichloride, 475 triethide, 689 trisnitrate, 475 Bismuthic acid, 475 anhydride, 475 Bismuthite, 475 Bisulphate of potash, see Potassium sul- phates Bisulphide of carbon, see Carbon disulphide Bisulphites, 159 Bisulphuret of carbon, see Carbon disul- phide Bitter almond oil, see Benzaldehyde principles, 781 Bittern, 121, 368 Bituminous coal, 271, 279 matter, 435, 438 Biuret, 705, 706 Bixin, 782 : Black ash, 370, 371, 373 band, 435, 438 dyes, 757 jack, 406 Joseph, 63 lead, 237; see Graphite manganese, 461 oxide, 472 sulphur, 145, 177 tin, 483 vitriol, 513 wash, 418 Blagden, 319 Blast-furnace, see Furnace Blasting gelatine, 670 powder, 670 with,gunpowder, 366 Bleach, electrolytic, 374 killed, see Antichlore Bleaching, 107, 114, 144, 157, 159, 375 by chloride of lime, 116 by chlorine, 107 by sulphurous acid, 157 powder, see Chlorinated lime presence of water in, 107 Blende, 406 Blistered steel, 449 Block tin, 484 Blood, 63, 355, 436, 784, 789 absorption spectrum of, 792 action of oxygen on, 792 coagulation of, 789 Bloom (iron), 444 Blow-holes, 446, 449 Blowpipe, and blowpipe flame, 267 hot blast, 268 oxyacetylene, 255 oxyhydrogen, 261, 268 reduction of metals by, 268 Blubber oils, 673 Blue bricks, 428 copper, 515 copperas, 513 dyes, 753, 754, 757, 759, 805, 807 — e Blue John, 131 metal, see Copper 14 Cran see Prussian blue stone, 513 Thénard’s, see Thénard’s blue Turnbull's, see Turnbull's blue verditer, 512 vitriol, 513 writing-paper, 426 Body, 1 Boghead cannel, 549 Boiled oil, 673 Boiler fluids, 44, 230 incrustations, 44, 230 Boiling-point, 323 defined, 32, 34 -points, 643 of alcohols, &c., 643, 644 of solutions, elevation of, 322 process (iron), 445 Bolivite, 476 Bonds, double, 350 triple, 350 Bone-ash, 210, 394 black, 242 charcoal, 210 . gelatine, 803 oil, 242 Bones as manure, 210 composition, 210 - destructive distillation, 183, 696, 790, 803 dissolved, 210 Boracic (boric) acid, see Boric acid Boracite, 290 Borates, 290 ' Borax, 288, 378, 487 (perborax), 379 vitrefied, 378 Boric acids, 288, 289, 379 anhydride, 288, 290, 397, 654 ether, 666 Borides, 291 Borneo camphor, 676 Borneols, 675, 676 Bornyl derivatives, 675, 676, 677 Borofluoric acid, 291 Borofluorides, 133, 291 Boroglyceride, 671 Boron, 235, 288-292 alkides, 688 amorphous, 290 carbide, 291, 378 crystallised, 290 diamond of, 290 ethide, 688 hydrides, 291 iodide, 291 methide, 688 nitride, 291 oxide, see Boric anhydride sulphides, 291 trichloride, 291 trifluoride, 291 Boronatrocalcite, 290, 378 Botany Bay gum, 746 Bottles, ceresin, 133 gutta-percha, 133 Boussingault, 51 Bower’s process for protecting iron, 454 Boyle, Robert, 296 Boyle’s fuming liquor, 382 law, 9, 74, 78, 79, 308, 313, 318, 319 proof of, 308 Brain, 701, 793 Brass, 510 malleable, 510 Brassidic acid, 612 Brassylic acid, 627 Brauner, 134 Braunite, 461, 462 Brazil wood, 748, 783 Brazilin, 783 Bricks, 426, 428 Brimstone, 60 ; see Sulphur Brin’s oxygen process, 54 Britannia metal, 476, 486 Brodie’s graphite, 237 Bromacetic acid, 623 Bromacetylurea, 706 Bromal, 661 Bromamines, 700 Bromanil, 753 Bromanilines, 698 Bromargyrite, 121, 521 Bromates, 124 Bromhydrins, 659 Bromic acid, 124 Bromides, 122, 124 Brominated lime, 124 Bromine, 121-125, 218, 256, 368, 745 hydrate, 122 oxy-acids, 124 water, 122 Bromobenzene, 562, 565, 566, 660 Bromocamphorsulphonic acid, 818 Bromoform, 121, 658 Bromosuccinic acid, 629 Bromous acid, 124 Bromum solidificatum, 122 Bronze, 487 annealing of, 452 coin, 487 manganese, 487 phosphor, 487 powder, 490 Bronzing, 511 Brookite, 490 Brown acid (sulphuric), 164 blaze, 411 coal, 271 dyes, 718 hematite, 435 Brownian movement, 333 Brucine, 821 Brucite, 88, 403 Brunswick green, 514 Building materials, 390 stones, 390 “* Bumping,” 340 Bunsen, 26, 79, 690 and Kirchhoff, 383 Burner, air-gas, 254 Argand, 265 Auer, 265 Bunsen’s, 254, 266 Drummond, 269 gauze, 267 regenerative, 265 smokeless, 254 Welsbach, 265 Burnett’s disinfecting fluid, 401 Butalanine, 712 Butanes, 547, 552, 657, 686 Butine, 557 Butter, 673 substitute, 673 Butyl alcohols, 582, 643 INDEX 831 Butyl amine, 696 carbinol, 582 chloral, 661 isothiocyanate, 74.1 Butylene, 556 isomers, 556 Butyric acids, 607, 616, 671, 673 aldehyde, 596, 814 ether, 668 fermentation, 607 Butyrin, 672, 673 Butyro-lactam, 709 Butyro-lactone, 618 Cacao nibs, 813 Cacodyl, see Kakodyl Cadaverine, 701 Cadet’s fuming liquor, 690 Cadinene, 676 Cadmia, 411 Cadmium, 300, 408, 411, 414, 419, 631 bromide, 300 sulphide, 154 tungstoborate, 471 Caen-stone, 391 Cesium, 358 and its compounds, 384 Caffeic acid, 623 Caffeidine, 814 Caffeine, 810, 812, 818 Caffeo-tannic acid, 622 Cailletet, 84 Cairngorm-stones, 280 Cajeput oil, 677 Calamine, 406, 409 electric, 406 Calcareous spar, 388 waters, 43 Calcination, 49 Calcite, 388 Calcium, 18, 53, 387-899, 492 acetate, 605 action on water, 18 aluminate, 391 arabates, 772, 773 arsenates, 232, 395 benzoate, 613 borate, 378 butyrate, 607 carbide, 36, 251, 895, 739 carbonate, 43, 45, 64,371, 372, 388, 389, 390 caseinogenate, 789 chlorate, 116 chloride, 325, 368, 393 chromate, 465 citrate, 633 cyanamide, 395, 739 ferrate, 454 fluoride, 131, 133, 210, 387, 394 formate, 593, 603 glyceroxide, 590 group, 307 hydride, 388 hydrosulphides, 176 hydroxide, 88, 253, 359, 373, 389, 390 hypochlorite, see Chlorinated lime hypophosphite, 222 hyposulphite, 171 iodate, 124 lactate, 607, 635 linolate, 613 malates, 629 meconate, 632 832 INDEX Calcium mesotartrate, 637 metal, 388 nitrate, 392 nitride, 53, 293, 388 nitrite, 392 oxalate, 624, 625 oxide, 3, 84, 88, 350, 387, 889, 440 oxychloride, 116, 394 peroxide, 392 phosphates, 209, 210, 218, 387, 394 phosphide, 217 platinate, 531 plumbate, 502 polysulphides, 155 pyrophosphate, 395 racemate, 637, 638 saccharate, 631 silicates, 387, 391, 395 silicide, 395 succinate, 626 sulphate, 43, 392, 404 sulphethylate, 586 sulphide, 370, 371, 394 sulphides (poly-), 155 superphosphate, 394 tartrates, 631, 637 thiocarbonate, 176 thiosulphate, 155 tungstate, 471 uranate, 472 Calc-spar, 388 Calculation, chemical, see General principles of formule, see Formula Calculi, 404 Caliche, 125, 379 Calico-printing, 369, 380, 481, 488, 650, 727, 790 Calomel, see Mercurous chloride Calorie, 32 Calorific intensity, 277 values, &c., 275, 277, 279 Calorimetric bomb, 276 Calorimetry, 32, 276, 347 Calumba root, 781 Calumbin, 781 Calx, 48, 49, 51 Calx chlorinata, 48, 49, 51; see Chlorinated lime Cameos, 280 Cameron, 401 Camphene, 674, 675 “Camphor, 315, 321, 325, 570, 674, 676, 677 artificial, 675, 677 oil of, 675, 676 synthetic, 677 Camphoric acid, 676, 677 Camphoronic acid, 677 Camphorsulphonic acids, 640, 641, 818 Canada balsam, 674 Canarin, 738 Candle, chemistry of, 262; see also Flame power, 265 Cane-sugar, 760, 762, 763, 767 Cannel, 279, 280 gas, 280 Cannizzaro, 10 Cantharidin, 781 Canton’s phosphorus, 394 Caoutchoue, 675, 679 artificial, 679 vulcanised, 680 Cap composition, 742 Capacity factor, 12, 327 Capillarity, 315 Capric ether, 668 Caprin, 673 Caproic acids, 607 aldehyde, 596 Caproin, 673 Caproyl alcohol, 583 Capryl alcohol, 583 aldehyde, 596 Caprylic acid, 607, 673 Caramel, 767 Caramelan, 767 Carats, 525 Carbamates, difference in behaviour with hypobromite and hypochlorite, 381 Carbamic acid and its compounds, 381, 707. 721 : Carbamide, see Urea Carbamines, 734, 735 Carbanilide, 707 Carbazole, 701, 801 Carbazotic acid, see Picric acid Carbides, 238, 244 Carbimide, 737 Carbinol, 578, 580, &c., 584 Carbocyclic nuclei, 794 Carbodiamine, 704 Carbodiimide, 738 Carbohydrates, 54, 760-778 Carbolic acid, see Phenol, 744 Carbon, 21, 54, 60, 76, 78, 285-280, 292, 357 allotropic modifications of, 235, 243 amorphous, 238, 243 calorific intensity, 278 value, 275 combustion of, see Combustion determination of, 269, 538 diamide-imide, 708 dioxide, 3, 4, 47, 48, 54, 68, 244, 257, 311, 372, 389, 456, 620; see also Carbon, 235-280 composition of, 235, 249 decomposed by carbon, 245 by electric sparks, 245 by metals, 245 by potassium or sodium, 245 determination, see Carbon, 269, 538 experiments with, 66-69 injurious effects of, 67 in respired air, 68 liquid, 71, 81, 82 respired by animals and vegetables 63 solid, 71, 82, 83 solubility, 70, '71, 80 sources, 63 synthesis of, 236 disulphide, 5, 174-176, 250, 251, 317, 606, 666, 692, 738 electrodes, 112, 244 halides, 250 heat of vaporisation of, 248 monosulphide, 176 monoxide, 4, 21, 238, 245, 260, 270, 274, 311, 360, 439, 444, 479, 602, 792 absorption of, in gaseous mixtures 514 : calorific value, 248 combustion of, 246-248 composition of, 249 formed in fires, 245 metallurgic uses, 246 poisonous properties, 249 preparation, 245-247 Carbon monoxide, properties of, 247 reduction by, 246 oxides, 244 oxychloride, 249 oxysulphide, 176 pure, preparation of, 244 specific heat, 243 suboxide, 249 sulphides, 174-176 telluride, 180 tetrabromide, 250 tetrachloride, 107, 250, 317 tetrafluoride, 250 Carbonado, 237 Carbonates, 235, 244 Carbonic acid, 602, 616 gas, see Carbon dioxide nitrile, 737 anhydride, see Carbon dioxide oxide, see Carbon monoxide Carbonising fermentation, see Coal, 271 Carbonyl chloride, 248, 249 Carbonylferrocyanides, 730 Carbonyls, iron, 456 metallic, 248 Carborundum, 285 Carbostyril, 805 Carbotriamine, 708 Carboxyhemoglobin, 249 Carboxyl, 599 Carboxylic (di) acids, 554 Carburetted hydrogen, 257 Carbyl sulphate, 555 Carbylamine reaction, 695 Carbylamines, 734 Carbyloxime, 741 Carey Lea, 521 Carius’ method, 539 Carmine, 783 lake, 784 Carminic acid, 783 Carnallite, 361, 368, 402, 405 Carnaiiba wax, 609, 674 Carnaiibic acid, 674 Carnelian, 280 Carnine, 812 Caro’s acid, 171, 698 Carotin, 783 Carré’s freezing apparatus, 80, 81 Carriers, 162, 165 Carthamin, 783 Cartilage, 791 Carvacrol, 678 Carvone, 678 Caryophyllene, 676 Cascade method, 84 Case-hardening, 450 Casein, 784, 786, 789 vegetable, 790 Caseinogen, 789 Cassel green, 463 yellow, 505 Cassia, oil of, 598 Cagsiterite, see Tin oxide Cast iron, see Iron steel, see Steel Castner’s process, 373, 374 Castor-oil, 673 : Catalysis, 143, 165-167, 333, 530 Catechu, 621, 750 Cathode, 16 rays, see Rays, cathode Cations, 94, 327 ; Cat’s eye, 280 $c INDEX 833 Caustic, 19 alkali, see Potassium and Sodium hydroxides lunar, 519 mitigated, 519 potash, 19; see Potassium hydroxide soda, 20; see Sodium hydroxide toughened, 519 Causticising, 373 Cavendish, 9, 25, 49, 95, 293 eudiometer, 25, 27 Cawk, 385 Cedriret, 751 Celestine, 387 Cell-galvanic, voltaic, 326, 329 Celluloid, 773, 778 Cellulose, 271, 624, 760, 770, 773 acetic esters, 774 action of nitric acid on, 774 animal, 778 converted into alcohol, 774 into sugar, 773 cotton, 773 nitrates, 773, 774-778 solvent for, 512 sulphuric esters, 773 xanthate, 773 Cement, hydraulic, 391 Portland, 391, 441 Roman, 391 Tust-joint, 150 Scott’s, 392 Sorel’s, 405 Cementation process, 448, 449 Cementite, 437, 441 Cephaeline, 820 Cerasin, 773 Cereals, 281 Cerebric acid, 793 Cerebrin, 793 Ceresin, 549 Ceria, 431 Cerite, 431 Cerium and compounds, 431, 482-438, 494 Cerotic acid, 609 Cerotin, 583 Ceruse, see White lead, 503 Cerussite, 495 Ceryl alcohol, 583 cerotate, 583, 609, 668 Cetin, 583, 674 Cetyl alcohol, 583 palmitate, 583, 668, 674 Cevadilla seeds, 822 Cevadine, 822 Ceylon moss, 773 Chalcedony, 280 Chalk, 64, 88, 388 in waters, see Water Chalkstones, 808 Chalybeate waters, 452 ; Chamber acid, crystals, process, see Sulphuric - acid Chamomile oil and flowers, 611 Chance’s sulphur recovery process, 371 Changes, chemical, physical, &c. 1, 3, 12 of state, 32, 348 phenomena of, 325 Charbon roux, 113 Charcoal, 194, 238 4) absorption of gases by, 54, 84, 240,2 action of steam on, of sulphuric acid on, 156 animal, 242 53 834 INDEX Charcoal as fuel, 273 ash, 240 burning, 239 coconut, 241 composition and variation in, 240 decolorising by, 242 deodorising by, 240 for gunpowder, 365 oxidised by nitric acid, 194 preparation of; 239 prepared at different temperatures, 240 » retort, 239 specific gravity, 241 suffocation, see Carbon di- and monoxide varieties, 238-242 wood, 238 Charles’ law, 9 Chelidonic acid, 632 Chelidonine, 822 Chemical affinity, 1, 341, 342 measurement of, 341 change, velocity of, 345 changes and physical phenomena, 296 combination, 1 influence of moisture on, see Water laws of, 5 compounds, 1 decomposition, 2 energy, 1, 12, 15, 326, 347 and measurement of, 341, 345 equivalent, 18, 19, 341 intensity, 341 properties, sce Properties Chemistry, 1 inorganic, origin of term, 538 of carbon compounds, 538; see Organic organic, origin of term, 538 Chill-casting, 442 Chimney, hot air, for lamps, 265 ventilation by, 69 China moss, 773 Chinese wax, 583 white, 409 Chinoline, see Quinoline Chitin, 791 Chloracetamides, 702 Chloracetic acids, 661 Chloracetyl chloride, 787 Chloral, 660 alcoholate, 661 hydrate, 315, 658, 661, 677 Chloralum, 389 Chloramines, 700 Chloranhydrides, 198 Chloranil, 753 Chloranilic acid, 753 Chloranilines, 698 Chloranthracenes, 572 Chlorate of potash, see Potassium Chlorates, 56 Chlorethers, 653 Chlorhydrins, 659 of glycol, &c., see Glycol, &c. Chlori¢ acid, 117 Chloridé of calcium tube, 538 of nitrogen, see Nitrogen Chlorides, 105, 112, 298 Chlorine, 21, 82, 101-121, 256, 298, 374 absolutely dry, 104 and acetylene, 255, 659 and hydrogen, 104 and oxygen, compounds of, 113 ‘f available,” 116 Chlorine, bleaching by, 107, 108 dioxide, 11 disinfecting properties, 108 electrolytic process, 103, 374 experiments with, {01-108 group of elements, 101-136 heptoxide, 120 hydrate, 82, 103, 341 monoxide, heat of formation, 114 oxides, 113 oxyacids, 113 peroxide, 119, 120 valency, 113 water, 103, 106 Chlorinated lime, 108, 114, 115, 369 soda, 114,115 _ Chlorinating agent, 479 Chloriodoform, 659 Chlorisatins, 107, 798 Chlorite, 120, 425 Chlorobenzenes, 660, 745 benzoic chloride, 663 chromic acid, 468 maleic acid, 663 chloride, 663 (tri)-methylchloroformate, 666 naphthalenes, 660 ; phenol sulphonic acid, 750 phenols, 745 propionic chloride, 662 Chloroform, 107, 323, 569, 599, 657, 812 of crystallisation, 324, 620 Chloroformoxime, 741 Chlorophosphamide, 224 Chlorophyll, 54, 781 Chlorophyllides, 782 Chlorophyllin, 782 Chloropicrin, 666, 682, 746 Chloroplatinates, 532 Chloroplatinites, 532 Chloroplumbiec acid, 505 Chloropropylene, 659 Chlorosaligenin, 779 Chlorosulphonic acid (809.C1.0H), 158 Chlorotoluenes, 660 Chlorous acid, 120 Chloroxalethyline, 704 Chlor-zinc-iodine, 774 Chocolate, 813 Choke-damp, 68 Cholesterol, 585, 671, 673, 794 acetate, 337, 585, 674 dibromide, 585 Cholestrophane, 810, 814 Cholic acid, 794 Cholin, 701, 794 Chologlycholic acid, 794 Chondrin, 791 Chondroitic acid, 791 Chromamines, 468 Chromates, 465 Chrome-alum, 467 iron-ore, 453, 465, 529 yellow, 466 Chromic acid, 466 anhydride, 465, 466, 467, 754 chromate, 467 hydroxide, 467 oxide, 465, 467 (per-) acid, 144, 465, 468 Chromites, 467 Chromium, 350, 465-470, 534 acetate, 468 ammonium salts, 353 INDEX Chromium chlorides, 468 compounds, preparation of, 465 cyanides, 730 dioxide, 465, 467 group reviewed, 473 metallic, 465 monoxide, 465 oxides, 465, 468 oxychloride, 468 sulphate, 467 sulphide, 468 Chromogens, 718 Chromophore, 718 Chromoproteins, 784 Chromyl] chloride, 467, 752 Chrysaniline, 806 Chrysean, 739 Chrysene, 573 Chrysoberyl, 411 Chrysoidine, 718 Cigars, 815 Cinchona alkaloids and bark, 623, 819 Cinchonicine, 820 Cinchonidine, 819-820 Cinchonine, 638, 819-820 Cinder (or coke), 272 (finery), 443 Cineol, 677 Cinnabar, 412, 418 Cinnamein, 668 Cinnamenc, 567, 615 Cinnamic acid, 567, 585, 598, 614, 801 aldehyde, 570. 585, 598 hydrazide, 802 Cinnamon oil, 598, 678 Cinnamy] alcohol, 584 cinnamate, 585, 668 Cisterns, incrustations in, 46 Cis-trans isomerism, 596, 638, 641 Citraconic acid, 627, 633 Citral, 676, 678 Citric acid and its compounds, 632 Citronella oil, 675, 675 Clarite, 233 Clark’s process, 46 Classes of organic compounds, see under Organic chemistry Classification of compounds, electrical, 327 of the elements, see Elements, and Periodic Classification Claus, benzene formula, 561 kiln, 371 Clay, 46, 283, 420, 426, 439, 440 Cornish (kaolin), 427 industries, 426 ironstones, 435 Clement, 125 Cleveite, 294 Clinkering, 427 Closed-chain hydrocarbons, sce carbons Clove oil, 676, 678 Coal, 271-280 ash of, 272 bituminous, 271 brown, 271 combustion of, 271 composition of, 271 distillation of, 273 dust explosions, 260 formation of, 271 gas, 257, 278, 456 constituents, 161, 176, 273, 559 enriching, 264, 274 Hydro- 835 Coal gas, explosions of, 259 sulphur in, 274 gases occluded in, 260 mines, explosions in, 258 firedamp of, see Firedamp storie, 272 spontaneous combustion of, 272 tar, 559, 566, 569, 570, 572, 795 bases, 559 distillation of, 559 dyes, sce Aniline kreosote, 747 varieties of, 271 Welsh, 272 Coarse metal, 507 Cobalt, 350, 456, 469 alums, 457 amine compounds, 458 arsenate, 225, 457 arsenides, 458 bloom, 225, 457 carbonyl, 458 chloride, 39 colour changes in solution, 324 cyanide, 458, 726 ferrocyanide, 728 glance, 225, 456 hydroxide, 457 nitrate, 457 nitrite, 457 oxides, 398, 456, 457 phosphate, 458 pyrites, 457 salts, 457-458 separated from nickel, 459 silicate, 458 sulphate, 457 sulphides, 457 tin-white, see Tin- white ultramarine, 458 vitriol, 457 yellow, 457 Cobalticyanides, 458, 727 Coca, 816 Cocaine, 815, 816 Cocculus indicus, 781 Cochineal, 784 Cocoa, 813 Cocoa-nut oil, 608, 678 Codeine, 818 - Cod-liver oil, 673 Co-efficient of absorption, 79 of affinity, 344 of expansion, 74 of pressure, 74 of solubility, 79 of velocity, 345 Coerulignone, 751 Coffee, 623, 813 Cognac oil, 673 Coke, 272 action of steam on, 275 composition of, 279 Colchicein, 822 Colchicine, 822 Coleothar, 161, 458 Cold-shortness, see Iron Colemanite, 378 Collidine, 803 Collie, 561, 807 Colligative properties, 299 Collodion, 777 balloons, 22, 778 cotton, 670, 777 836 INDEX Colloids, 233, 281, 282, 388, 419, 424, 526 Colophony, 674, 679 Colour, 39, 646 base, 758 changes in solutions, 324 Coloured fires, see Pyrotechny Colouring-matters, animal, 792, 793 vegetable, 781 Columbite, 481 Columbium, see Niobium Colza oil, 673 Comanic acid, 807 Combination, chemical, 1; see also Laws of, Combining proportions, 4-6 Combustible, 264 Combustion, 49, 51, 63, 88, 104, 119, 251-279, 364, 366 defined, 58, 349 furnace, 539 imperfect, 254 “ making a combustion,” 538 mechanics of, 270 of organic bodies, 588 perfect, 264 reciprocal, 104, 264 spontaneous, 272 supporter of, 264 temperature of, 63, 269 tube, 539 Comenic acid, 632 Common salt, see Sodium chloride Compensation, internal and external, 638, 639 Components, 338 Compo-pipe, 500 Composition, constancy of, 2, 3, 4 instances, 28, 112, 169, 269, 283 of compounds, 307, 352 tube, 500 Compound and mixture, 1, 2 defined, 1 ethers, 663 Compounds, electrical classification, 327 Compressibility, 316, 334 Concretes, 392 Condensation, see under Organic Chemistry products of acetone, 648 Condenser, Liebig’s, and others, 579, 587 Conductivity, 330 Condurrite, 225 Condy’s disinfecting fluid, 462, 463 Congo red, 719 Congonha, 813 Conhydrine, 814 Coniferin, 599, 621, 789 Coniferyl alcohol, 780 Conine, 812, 814 methylium iodide, 814 Conjugated nuclei, 568, 796, 814 proteins, 784 Conservation of energy, 341 of matter, see Mass Constantan, 459 Constituents (phase rule), 338 Constitution of compounds: (see also Composition) Barlow and Pope’s theory, 335 carbon dioxide, 235, 245 chlorinated lime, 116 hydrogen peroxide, 144 influence of, on heat of formation, 350 on magnetic properties, 350 nitrogen oxides, 204, 322 Constitution of compounds—continued organic, 546-547, 551-552, 558, 571, 588, 589, 592, 599, 602, 628, 658, 663, 680, 681, 741, 746, 804 potassium sulphate, 335 silicic acid, &c., 283 sulphur dioxide, 158 sulphuric acid, 158 sulphurous acid, 159 Tutton’s work on, 335 Werner’s theories, 332 Constitutive properties, 299 Contact process for sulphuric acid manu- facture, 160, 165-167 Continuity of state, 310 Converter, Bessemer’s, 446, 508 Convolvulin, 780 Convolvulinol, 780 Copaiba, 676 Copal, 679 Copper, 2, 505-515, 524 acetate, 605 aceto-arsenite, 605 acetylide, 253, 557 action of ammonia and air on, 512 of nitric acid on, 200 of sulphuric acid on, 156 alloys of, 510 for machine bearings, 511 with nickel, 459 ammonio-nitrate, 513 ammonio-sulphate, 513 arsenite, 231, 513 atomic weight, 28 blister, 507 blood of molluscs and, 506 carbonate (basic), 506, 510 chlorides, 254, 513, 514 (double), 514 chlorinating roasting, 508 cleaned, 510 coarse metal, 507 couple, 326 cyanides, 731 dead roasting, 506 dry, 508 effect of sea-water on, 510 electric conductivity of, 509 emerald green, 605 extraction by dry methods, 506 by Welsh process, 507 by wet method, 508 of, 147, 509; see also Metallurgy below ferrocyanide, 317, 728 furnaces employed, 507 fusing-point, 509 glance, 506 glycocoll, 710 hydrate, 512, 762, 774 hydride, 222, 512 impurities in, 509 in organic determinations, 539 iodide, 126, 514 kernel roasting, 514 Lake Superior, 505 matte, 506, 516 and slags, 507 metallurgy of, 506-509 native, 505 nitrate, 196, 512 (basic), 512 nitride, 512 ores, 505, 506 treatment of, for silver, 516 INDEX 837 Copper oxide(s), black (CuO), 2, 28, 56, 506, 511, 762 in organic analysis, 538 red (CugO), 398, 511 (CuQg), 512 oxychloride, 509, 514 peacock, 506 phosphide, 515 precipitate, 508 properties of, 509 pyrites, 147, 505, 508, 513 reduction by hydrogen, 28 refining blister copper, 508 electrolytically, 508 sand, 505 scale, 511 silicate, 511 suboxide, 398, 511 sulpharsenate, 233 sulphate, 39, 101, 155, 518 sulphide(s), 154, 514, 515 tartrate, 631 thiocyanate, 738 tinned, 510 tungstate, 470 uses of, 15, 509, 510 verdigris, 510, 605 vessels for cooking, 510 white metal, 507 ¢ xanthate, 176, 666 Copperas, see Ferrous sulphate blue, see Copper sulphate Copper-zine couple, 21 Coprolite, 209, 210, 218, 394 Coquimbite, 455 Coral, 388 Cordite, 670 Cornette, 526 Coronium, 293, 303 Corrosive sublimate, 416 Corundum, 88, 424 Cotarnine, 818, 819 Cotton, 773 (mineral cotton), 441 seed oil, 672, 673 soluble, 777 solvent for, 774 Coulomb, 327, 329 Coumaric acid, 623 Coumarilic acid, 796 Coumarin, 623, 796 Coumarone, 796 Courtois, 124, 125 * Co-volume,”’ 309 Crackers, detonating, 743 ‘** Cracking ” hydrocarbons, 263 Craigleith sandstone, 390 Cream of tartar, see Potassium bitartrate Creasote (kreosote), 748 Creatine, 711, 812 Creatinine, 711 Creoline, 747 Creosol, 748 Cresol, 662, '747 Cresotinic acids, 620 Critical constants, 35 density, 310 point, 309, 315, 316 pressure, 35, 84, 310 temperature, 35, 84, 310, 316 volume, 35, 310 Croceo-cobalt salts, 458 Crocus, 782 of antimony, 476 Crookes, 356, 399 Croton-chloral, see Butyl chloral oil, 611 Crotonic acids, 610 aldehyde, 557, 596 Crotononitrile, 740 Crotonylene, 557 Crow-fig, 821 Crucibles, plumbago, 449 Crum Brown, 566 Cryohydrates, 39, 841, 393 Cryohydric point, 341 Cryolite, see Kryolite Cryoscopic method, 820, 479, 643 Cryptidine, 804 Crystal carbonate, 372 structure, 300, 335; see also Crystallo- graphy Crystal(s), definition, 333 flowing, 337 from vitriol chambers, 162 “ liquid,” 333, 334, 887, 585 mixed, 299, 486 systems of symmetry, 336 Crystallin, 789 Crystalline condition, influence of, 32 Crystallisation, 40, 324, 384 Crystallography, 40, 299, 333, 336, 388 Crystalloids, 281 Cudbear, 749 Cumene, 567 Cumic, see Cuminic Cuminic acid, 614 aldehyde, 598 Cuminol, 598 Cummin, essential oil of, 611-614 Cupel-furnace, see Furnaces Cupellation, 497, 498, 526 Cupric acid, 512 Cuproso-propargyl alcohol, 584, Cuprous salts, 247, 716 Curcumin, 782 Curd of milk, 789 Curie, 399 Curve, atomic volume, 305 element density, 305 oxide density, 305 ratio, 305 solubility, 376 Cutch, 621 Cutting isinglass, 791 Cyamelide, 736 Cyanacetate of potassium, 625 Cyanalkines, 806 Cyanamide and derivatives, 707, 738, 739, 811 Cyanates, 723 Cyanethine, 734 Cyanic acid, 722-743, 736 Cyanide process in gold extraction, 5 24. Cyanides, 722 of hydrocarbon radicles, 694 Cyanines, 805 Cyanite, 425 Cyan-methine, 734, 806 Cyano-benzene, see Phenyl cyanide Cyanogen, 82, 440, 704, 721-748, 722 bromide, 121, 733 chloride, 733, 737, 739 compounds, 704, 721-748 derivatives, 600 group, 723 iodide, 126, 733, 738 838 INDEX Cyanogen, reactions of, 723 sulphide, 738 Cyanogenetic glucosides, 725 Cyanuramide, 739 Cyanuric acid and its salts, 705, 736 * chloride, 733 Cyclic compounds, 544 esters, 618 Cyclohexane, 559 Cycloparaffins, 558 Cymene, 675 Cymogene, 548 Cysteine, 786 Cystine, 786, 791 Cytisine, 822 Dautia roots, 772 Dalton, 4, 6, 9, 74, 78, 79, 81, 95, 296, 309, 313, 319 Dalton’s law, 9, 74, 809, 319 Dammar resin, 679 Daphnetin, 780 Daphnin, 780 Davy, 101, 108, 119, 125, 133, 284, 286, 360, 375 John, 705 lamp, 259 Deacon’s chlorine process, 103 process, 103 roasting, 506 Decane, 548 Decay, 64 Decolorising by charcoal, 242 Decomposition, 2, 64, 188 De Coppet, 320 Deflagrating spoon, 60 Deflagration, 364 Degradation products, 785, 811 pees of freedom (phase rule), 338 Dehydracetic acid, 667, 807 Dehydrating agent, 219 Pe auerenges 39 Delphinine, 822 Density, see also Specific gravity Guegalshea from Specific gravity, 31, 4 pase: and vapours, 11, 22, 187, 311, 312, 3 liquids and solids, 31 of elements, 305, 306 Deodorising by charcoal, 240 by chlorine, 108 Depression of the freezing-point, 320 Derbyshire spar, 131; see Fluor spar Dermatol, 621 Descloisite, 480 Desiccator, 169 Detinning iron, 490 Detonating gas, 16, 137 Detonators, 670, 741-743, 777 Devitrification, 398 Dewar, 84, 85, 87 vessels, 85 Dextrin, 762, 769, 771 Dextro-ethylidine lactic acid, 635 Dextro-rotatory, 634; see Optical Dextro-tartaric acid, see Tartaric acid Dextrosan, 762 Dextrose, 761, 762, 769 Dhil mastic, 501 Diabetes, 761 Diacetamide, 703 7 Diacetonamine, 816 Diacetyl, 650 Diacetyl oxide, see Acetic anhydride Diacetylene, 557 Diacetylmorphine, 818 Diad elements, see Valency Dialkylanilines, 699 Dialuramide, 810 Dialuric acid, 809 Dialyser, 281 Dialysis, 281, 320, 453 Diamides, 704 Diamido-azobenzene, 718 Diamidobenzenes, 683, 701, 753 Diamidonaphthalenes, 701 diphenyl, 701 Diamidotriphenylmethane, 758 Diamines, 693, 700 Diamino-acids, 786 caproic acid, 786 guanino-valeric acid, 786 valeric acid, 786 Diamond, 50, 235, 243, 261 artificial, 235 combustion of, 236 properties and constants, 243 Diaphragm process, 374 Diaspore, 424 Diastase, 576, 769, 772 Diathermic, 175 Diatomic, 310 Diatoms, 280 Diazines, 806 Diazo-acetamide, 715 acetic acid, 715 ester, 684 acids, 714 amidobenzene, 717, 718 compounds, 717 benzene, 715 butyrate, 716 chloride, 719 compounds, 721 hydroxide, 716 nitrate, 715 potassio oxide, 716 sulphonic acid, 718 -compounds, 714-721 dyestuffs, 719 ethane, 715 methane, 655, 715, 734, 794, 802 methanedisulphonate, 189 perbromides, 721 reactions, 207, 714 Diazoles, 802 Diazonium salts, 716 Diazotising, 716 Dibenzofurfurane, 796, 801 Dibenzoparadiazine, .807 Dibenzoparathiazines, 806 Dibenzoparoxazine, 806 Dibenzopyrrol, 796, 801 Dibenzothiophen, 796, 801 Dibenzoyl oxide, see Benzoic anhydride Dibenzyl, 569 Dibromo-nitro-aceto-nitrile, 742 phenyl-propionic acid, 801 propanes, 563 Dibutyraldine, 814 Dichloracetic acid, 661 Dichloracetone, 633 cyanhydrin, 633 Dichloracetonic acid, 633 Dichlorether, 653 Dichlorhydrin, 669 Dichloromethane, 550 INDEX 839 Dicinnamene, 568 Dicyanoacetonic acid, 633 Dicyanimide, 739 Didymium, 355 Dienes, 556, 568 Diethyl, see Butane amine, 696 glycol ether, 000 sulphide, 586 Diethylene-diamine, 700 Diethylnitrosamine, 696 Diethyloxamide, 704 Diethylphenylhydrazonium compounds, 720 Diffusion, 75-78 mathematical expression of, 309 of liquids, 316 Diformin, 672 Digallic acid, 622 Digitalin, 780 Digitonin, 780 Digitoxin, 780 Diglycerides, 672 ; see Glycerides Diglycollic acid and anhydride, 617, 618 Digivevieiyeine, 787 Dihydric alcohols, see Alcohols phenols, 747 Dihydroanthracene, 573 Dihydroanthraquinonazines, 756 Dihydropyrazoles, 802 Dihydropyrrols, 796 Dihydroxy-acetone, 761 anthraquinoline, 805 anthraquinone, 754, 755 azobenzenesulphonic acid, 719 benzaldehydes, 599 benzenes, 747, 749, 755 benzoic acid, 755 coumarin, 779, 780 mercurammonium hydroxide, 415 phthalein, 759 succinic acid, see Tartaric acid toluene, 749 Dihydroxyl, 145 Diiodopurine, 809 Dikakodyl, 690 Diketones, 649, 650, 684, 709, 754, 802, 806 Diketopiperazine, 787 Dimethoxyphthalide, 818 Dimethoxystrychnine, 822 Dimethyl, see Ethane amido-azobensulphonic acid, 718 yrimidine, 806 amine, 694, 695, 696 aniline, 699, 758 -arsenic acid, 690 arsine, 691 benzene, see Xylene carbamide, 706 diamidotolu-phenazine, 807 furfurane, 795 ketone, see Acetone oxamide, 704 oxide, see Methyl ether parabanic acid, 810 phenylenediamine, 806 protocatechuic acid, 748 pyridone, 137 pyrone, 137, 807 pyrrol, 795 thiophen, 795 urea, 739 uric acid, 808 xanthine, 813 Dimorphous, 282 Dinaphthyl, 572 Dinas fire bricks, 428 Dinitraniline, 699 Dinitric acid, 199 Dinitrobenzene, 683, 698 phenols, 745 Dinitro-soresorcinol, 749 Diolefine derivatives, 612, 675 Diolefines, 556 Dionin, 818 Dioximes, 642 Dioxindol, 798 Dipentene, 674-676 Diphenic acid, 573 Diphenyl, 568 acetylenes, 569 amine, 699, 805, 806 carbinol, 585 ethane, 569 ethylene, 569 puanldme, 708 ydrazine, 720 iodonium hydroxide, 660 ketone, see Benzophenone methane, 569 methylpyrazole, 802 oxide, 654 phthalide, 759 sulphides, 745 sulphobenzide, 745 sulphone, 745 -sulphurea, 707 urea, 707 Diphenylene diketone, 754 ketone, 574 oxide, 801 sulphide, 801 Dippel’s oil, 242, 790, 796, 803 Dipropargyl, 557 Dipyrotartracetone, 630 Disaccharides, 760, 766 Disacryl, 596 Disazo-dyestufts, 719 Discharge in calico printing, 729 Disdiazoamidobenzene, 717 Disinfectants, 744 Disinfecting by chloride of lime, 116 by chlorine, see Chlorine by ferric chloride, 455 by permanganates, 463 fluid, Burnett’s, 410 Condy’s, see Potassium permanga- nate Disintegration of rocks, 358, 390, 420 (theory) of elements, 293, 296, 356, 400, 401, 472 Dispersive power, 353 Displacement, collection of gas by, 49, 53 Dissociation, 188, 269, 314, 337, 344, 345 and evaporation, 347 degree of, 346 effect of pressure on, 301 electrolyte, see Ionisation of dissolved molecules, see Ionisation of sal-ammoniac, 188, 314 of steam, 269 pressure, 346 Dissolution, heat of, 80 Disthene, 425 Distillation, 29 destructive or dry, 238, 242, 262 fractional, 86, 549 under diminished pressure, 608, 787 | Distilled water, 29 840 INDEX Diterpene, see Terpenes Dithionio acid, 173 Ditolyls, 569 Diureides, 809 Divalent elements, see Valency Divi-divi, 621, 622 Divinyl, 556 Divisibility of matter, 6 Débereiner, 77, 53] Dodecane, 548 Dodecylic acid, 608 Dolomite, 390, 402, 403, 404 Dough, 770 Downeast shaft, 69 Dowson gas, 275 Dragon’s blood, 750 Driers, 501, 672, 673 Drummond light, 265, 269 Drying gases, 28 in vacuo, 169 oils, 612, 672 over oil of vitriol, 169 Dualistic theory, 94 Du Hamel, 375 Dulcite, dulcitol, 592 Dulong and Petit, 297, 298 Dumas, 51 method for vapour density, 312 Durene, 567 Dust, 73 explosions, 260; see Explosion Dutch liquid, 256, 479, 555 metal, 104 Dyeing, 717 Dyes, 355, 717, 754-760 adjective, 718 substantive, 717 Dyestuff component, 718 Dyestuffs, acid, 717, 718, 759 basic, 717, 718, 759 Dynamic isomerism, 735, 707 Dynamite, 670 Dyslysin, 794 Dysprosia, 431 Dysprosium, 433 i Earic®Xwake, see Porcelain and Pottery Earth’s crus, composition of, 7, 64 Earths, alkaline,“385-402 rare, 304, 482 Eau de Javellé, 115 Labarraque, 15 Ebonite, 680 Ebulliscopic method, 322, “44 Ecgonine, 816 c Effervescence, 70 Efflorescence, 39 Egg-shells, 388 Eggs, decomposition of, 151 preserving, 379 white, see Albumin of eggs yolk, 585, 701, 772 Eikonogen, 747 Ekasilicon, 303, 494 Elaidic acid, 612 Elaidin, 673 Elastine, 712 Elaterin, 781 Elaterium, 781 Elba iron ore, 436 Electricity, 15, 54, 14-17, 21, 36, 96, 138, 193, 245, 251, 139, 170, 451 Electric arc, 251, 252 172, 181, Electric furnace, 210, 237, 251, 284, 395, 396 sparks, 16 Electrical amalgam, 414 classification of compounds, 327 energy, 15 pressure, 17, 327 quantity, 17, 326 scattering, 519 tension, 17 Electrising, 139 Electro-chemical list, 329 equivalents, 329 chemistry, 12, 16, 326 gilding, 526, 732 magnet, 451 motive force, 327 negative elements, 16, 329 plating, 460, 517 positive elements, 16, 329 Electrodes, 14, Hlecore)yeiss 14, “138, 325, 327 def., 328, 369, 414 of carnallite, 402 of hydrochloric acid, 112 of hydrofluoric acid, 134 of hydrogen sulphide, 148 of organic substances, 5d, 555 of potassium carbonate, 249 hydroxide, 360 of salt, 374 of salts, 328 of sulphuric acid, 16, 328 of water, 14 Electrolytes, 14, 327 def. Electrolytic bleach, 374 cell, 14 dissociation, 327, 330 gas, 16 production of alkali and chlorine, 359, 361 Electron (alloy), 402 Electrons, 296, 327, 328, 356 Electrostatic concentration of ores, 406 Element, 1, 7 Elements, densities of, 304 ephemeral, 303, 357, 400, 401 groups of, 7 radio-active, 296 solid, 298 the, their properties, and theories relat- ing to, 296 transmutation, 296, 357 typical, 302, 304, 305 vapour densities, 31] Ellagic acid, 621, 622 | Ellagitannic acid, 622 “Timanation, 356 radium, see Niton thorium, 357 Embolite, 521 Emerald, 411 green, 605 Emery, 424 Emetics, 631 Emetine, 820 Empirical formule, 540, 541 Emulsin, 597, 778 Enantiomorphous, 638 Endothermic, 114, 141, 347 Energy, 137 general, 1, 12 see also Chemical heat, &c. Enol- form, 736 Enzymes, 333, 575, 672 Eosins, 628, 758, 759, 760 Eotvés, 316 Ephemeral elements, 295, 302 Epichlorhydrin, 669 Epinine, 745 Epsom salts, see Magnesium sulphate Equations, 4, 11, 12 Equilibrium, see Phase rule stage of reversible reaction, 343 Equisetum, 280 Equivalent defined, 13 electro-chemical, 329 Equivalents, chemical, 301, 328, 329 determination of, 297 of acids and bases, 89, 91 Erbia, 431 Erbium, 433 Ergot, 746, 769 Erucic acid, 612, 673 Erythrene, 556 Erythric acid, 749 Erythrin, 591 Erythrite, erythrol, 556, 590, 591, 761 Erythro-dextrin, 771 Erythrose, 761 Erythryl tetranitrate, 591 Eserine, 822 Essential oils, 664, 674 extraction of, 674 Esterification, law, 642 Esters, 317, 545, 662, 663-702 sulphuric, 664 Etching glass, 131, 183 Ethal, 583 Ethane, 547, 550 constitution of, 547 Ethene, 557, see Ethylene Ether (ethyl), 81, 254, 311, 583, 681 decomposition of, 254 of crystallisation, 653 preparation, 651 properties of, 652 Ethereal salts, 545, 663, see Esters Etherification, continuous, 651 theory of, 652 Ethers, 545, 606, 650-655 aromatic, 654 derivation from alcohols, 650 internal, 653 mixed, 650 perfuming and flavouring, 668 table of, 650 Ethine, 556 Ethionic acid, 555, 681 anhydride, 555 Ethiop’s mineral, 418 Ethoxides, 578 Ethyl, 684 acetamide, 702 acetate, 604, 666 aceto-acetate, 600, 649, 667, 802 acetylene, 557 dicarboxylate, 802 alcohol, see Alcohol aldehyde, see Aldehyde allophanate, 706 amines, 696 ammonium ethyl thiocarbamate, 741 arsenite, 666 benzoate, 668 borate, 666, 688 boric acid, 688 bromacetoacetate, 753 bromide, 656 INDEX 841 Ethyl butyrate, 668 caprate, 668 carbamate, 707 carbamine, 735 carbimide, 739 carbinol, 582 carbonate, 666 chloride, 656 cyanide, 734 diazo-acetate, 715, 802 diethylacetoacetate, 667 dimethyloxamate, 694 ether, 651-653 ethylacetoacetate, 667 fluoride, 656 formamide, 735 formate, 666, 702 glycol ethers, 653 hydride, see Ethane iodide, 575, 656, 685, 686 isocyanate, 739 isocyanide, 735 isothiocyanate, 740 malonate, 600, 669 morphine, 818 mustard oil, 740 naphthalenes, 572 nitrate, 665 nitrite, 665 nitrolic acid, 581 nitrosamine, 696 orthocarbonate, 666 oxalacetate, 669 oxalate, 669, 694, 704 oxalic acid, 669 oxamate, 704 oxamide, 704 palmitate, 668 pelargonate, 668 phenylhydrazine, 720 phosphates, 666 phosphines, 691, 692 phosphinic acids, 692 phosphites, 666 quinol dicarboxylate, 753 salicylate, 668 silicates, 666, 688 sodaceto-acetate, 667 sodethylaceto-acetate, 667 stearate, 668 succinyl succinate, 753 sulphates, 555, 664 sulphides, 586 sulphinic acid, 681 sulphites, 680, 681 sulphone, 586 sulphonic acid, 680, 681 sulphoxide, 586 sulphuric acid, 651, 652, 664 thiocarbimide, 740 thiocyanate, 740 ureas, 739 Ethylates, 578 Ethylene, 5, 123, 161, 251, 255, 262, 274, 479, 542, 555, 587, 656, 657 addition products, 555 alcohol, see Glycol bromide, 587, 626, 657, 700 chlorhydrin, 701 chloride, 555, 657 cyanide, 626 diamine, 700 glycol, see Glycol iodide, 657 842 INDEX Ethylene lactic acid, 617, 618 naphthalenes, 572 oxide, 653, 794 structure of, 542 succinic acid, 626 Ethylidene chloride, 657 cyanhydrin, 595 diethyl sulphone, 684 glycolsulphonic acid, 594 lactic acid, 617, 635 oxide, 653 succinic acid, 626 Eucaine, 816 Eucalyptol, 677 Eucalyptus oil, 676, 677 Euchlorine, 119 Eudiometer, 25, 26, 27, 261 Eugenol, 599, 678 Eupyrion matches, 120 Eurhodines, 807 Eurhodoles, 807 Europia, 431 Europium, 433 Eutectic, 486 composition, 486 mixture, 486, 497 point, 486 Euxanthic acid, 783 Euxanthine, 783 Euxanthone, 783 Euxenite, 431 Evaporation, 29, 156, 347 and dissociation, 347 influence of pressure on, 347 Even numbers, law of, see Law Evernic acid, 749 Everninic acid, 749 Evolution, 357, 399 Exalgin, 702 Exchange of atoms, 12 Exitéle, 477 Exothermic, 56, 347 Expansion coefficient, 9 Explosions, 24, 105 in coal-mines, 258, 260 influence of barometric pressure, 367 sympathetic, 777 Explosives, 87, 118, 119, 120, 140, 208, 209, 865, 415, 519, 591, 606, 669, 682, '741, 746, 773-777 (safety), 380 Extinguishing flame, 66, 67, 157 Fagorina, 444 Family, 302 Faraday, 81, 82, 83, 328, 329, 559 Farinose, 771 Fast green, 749 yellow, 747 Fats, 589, 640, 671-674 Fatty acid series, 600 Fehling’s test, 631 Felspar, 283, 358, 367, 420, 424, 427 Fenchene, 674, 675 Fenchone, 677 Fennel oil, 677 Fermentation, 64, 271, 761-770 acetous, see Acetic acid alcoholic, 575, 626 arrested, 157 viscous, 591, 773 Ferrates, 454 Ferric acetates, 604 acid, 454 Ferric ammonio-citrate, 633 benzoate, 614 carbonate, 454 chloride, 455 cyanide, 728 ferrocyanide, 724, 727 hydroxide, 453 iodide, 456 oxalate, 625 oxide, 56, 62, 161, 453 oxychloride, 455 phosphate, 455 pyrophosphate, 455 salts, succinate, 626 sulphate, 454, 455 (basic) 161, 454 thiocyanate, 737 Ferricum (i.e. Iron in ferric state), 401 Ferricyanides, 729 Ferrite, 351 Ferrocyanic acid, 722 Ferrocyanides, 722 Ferrocyanogen, 722, 727 Ferro-aluminium, 446 chrome, 465 chromium, 442 manganese, 442, 446, 461 pyrophosphate, 526 silicon, 442, 446 titanium, 446, 492 Ferrosoferric oxide, 21, 62, 453 ferrocyanide, 728 Ferrosum (7.e. Iron in ferrous state, 729) Ferrous ammonium sulphate, 455 arsenate, 455 bromide, 456 carbohate, 454 chloride, 455 cobalticyanide, 727 cyanides, 727 ferricyanide, 728, 729 ferrocyanide, 727 hydroxide, 453 iodide, 127, 861, 455 oxalate, 456, 625 oxide, 62, 453 phosphate, 455 pyrosulphate, 455 salts, 452 silicate, 443 sucrate, 768 sulphate, 96, 108, 151, 161, 324, 453, 454, 513 sulphide, 151, 154, 456 Ferrum redactum, 452, 454 Ferruretted chyazic acid, 722 Fibrin, blood, 784, 789 muscle, 789 vegetable, 790 Fibrinogen, 784, 789 Fibroin, 791 Finery cinder, see Cinder Fire-bricks, 428 -clay, 420 -damp, 257, 260 indicator, 261 Fires, blue flame in, see Carbon monoxide coloured, see Pyrotechny Fireworks, &c., see Pyrotechny Fischer, 761, 785, 786 Fish oils, 673, 674 shells, 388 Fittig, 752 INDEX 843 “ Fixed ” alkalies, 188 Fixing photographic prints, 172 Flags, Yorkshire, 390 Flake-white, 475 Flame, 18, 60, 61, 138, 259-269 analysis of, siphon, 263 behaviour with gauze, &c., 259 blowpipe, 267 candle, 262 cause of luminosity in, 261 effect of pressure on, 265 exggtion by gases, 23, 66, 67, 69, 7 mantle ” of, 264 oxidising and reducing, 268 structure of, 261 temperature of, 263 to illustrate nature of, 468 Flash-point, definition, 548 Flavanthrene, 756 Flavin, 780 Flavopurpurin, 755 Flesh, juice of, 711 sugar, 751 Flint, 28 and steel, 280 Floss-hole, 444 Flotation concentration of ores, 406 Flowers bleached, 157 Fluoboric acid, 291 Fluoplumbates, 288 Fluor spar calcium fluoride), 131, 133, 134, 286, 394, 439 Fluorene, 569 Fluorescein, 749, 760 Fluorescence, 356, 683, 749, 760, 779, 805, 819 Fluoric acid, 131, 286 Fluorides, 132 the storing of, 133 Fluorine, 21, 131, 188, 137 Fluorone, 574° Fluorsulphonic acid, 132 Fluostannates, 288 Flux, 131, 133, 394, 427, 451 Baumé’s, 364 Fog, 63, 73 Foot warmers, 605 Formal, 593 Formaldehyde, 128, 579, 598, 764 Formalin, 593 Formamides, 702 Formates, 248, 603 Formation, heat of, 129 Formazyl-derivatives, 721 Formic acid, 270, 579, 598, 600, 602, 805 aldehyde, see Formaldehyde esters, 666 ether, 666 thio-aldehyde, 596 Formins, 602, 672 Formonitrile, 603, 734 Formose, 593, 764 Formula, 11, 28 axial symmetrical, 638 calculation of, 196, 307, 540- constitutional, 543 empirical, 307 graphic, 543 : Polonia see Molecular and Organic plane symmetrical, 638 . rational (4.2. Structural, which see) structural, 205, 335, 548 Formyldiphenylamine, 805 Foundry iron, 442 Fowler’s solution, 230 Fractional distillation, see Distillation precipitation, 601 Frankland, 684 Franklinite, 453 Fraxin, 779 Free fatty acids, 672 -stone, 390 Freezing apparatus, 80, 81, 656 in red-hot crucibles, 156 mixtures, &c., 376, 393, 548 of water, 31 re of solutions, depression of, 320, 8 Fremy, 132 French chalk, 402 Friction-tubes, 480 Friedel and Craft’s reaction, 649 Fréhde’s reagent, 812 Frost, hoar, 33 Fructose, 763, 764 Fruit essences, 668 sugar, 761, 763 Fuchsine, 758 Fucose, 761 Fucosol, 599 Fuel, 61, 270 calorific intensity calculated, 277 value, 275, 279, 349 composition of, 279 gaseous, 273 loss of heat in use, 279 petroleum, 273 Fuller’s earth, 283, 421 Fulminates, 741-743 Fulminating gold, 732 platinum, 531 silver, 519 (compare 742) Fulminic acid, 741 Fulminuric acid, 743 Fumaric acid, 627, 629, 638 Fumaroid structure, 595, 633 Fumaryl dichloride, 663 Fumigation with sulphur dioxide, 153 Fumitory, 627 Furfural (furfurol), 599, 632, 793 Furfuramide, 599 Furfurane, 632, 795 Furfuryl alcohol, 599 Furnace(s), arc, 252 blast, 488, 496, 507 electric, 251 gas, 261 loss of heat in, 272 muffle, 500 ore, 506 regenerative, 279-446 resistance, 251, 279 reverberatory, 246, 484, 496, 498, 506, 507 roasting, 506 Siemens, 279 smelting, 438 Furo-azoles, 802 “ Furring ” in kettles, 44 Fusco-cobalt salts, 458 Fuse, electric, 515 percussion, 120 Fusel oil, 575, 582, 679 Fusible alloy, 474 . : Fusing-points, see Melting-point Fusion, 281 Fustic, 750, 782 844 GaDIningE, 701 Gadolinite, 431 Gadolinum, 433 Gahnite, 453 Galactonic acid, 765 Galactose, 592, 761, '768, 769 Galbanum, 748 Galena, 494 Galenical preparations, 812 Galileo, 48 Gall-nuts, 621-622 MQ -stones, 585 Gallein, 750 Gallic acid, 621, 750, 755 Gallium and compounds, 428-429 Gallocyanine, 806 Gallotannic acid, see Tannic acid Galvanic, see Electric Galvanised iron, 405 Gambodic acid, 783 Gamboge, 750, 783 Gangue, 406, 439, 440 Ganister, 445 Garlic, essential oil of, 586 Garnet, 425 Garnierite, 459 Gas, see also Coal gas and Gases burners, 265 composition of, 273 cylinder, 23 defined, 35, 48 Dowson, 275 explosions, 24-27 fires, 273 holder, 247 manufacture, 273 Mond, 275 producer, see Producer gas semi-water, 275 sylvestre, 63 water, see Water gas Gaseous constant, 309 Gases, 9, 307, 315; see also Gas absorption, 78, 240 adsorption of, 240 analysis of, 26 collecting over mercury, 108, 287 composition, determination of, 269 constitution of, 78 density, 66, 97 diffusion of, 75, 77, 309 heated, 353 “ideal,” 308, 310 illuminating, 249, 251, 255 inactive, 293 in waters, 41 laws of, 9, 307-315 of combination of, 9, 26 liquefaction, 80, 81 occlusion, 97, 240 by coal, 260 perfect and imperfect, 78 physical properties, 74-87, 98, 308 pressure of, see Pressure rare, 293 solidification, 80, 81 solubility of, 41, 71, 78 solution of, 240 weighing, 10, 11 Gasolene, see Petroleum spirit Gastric juice, 788 Gaultheria, oil of, 668 Gay-Lussac, 9, 125, 131, 164, 722 Gaylussite, 388 INDEX Gedge’s metal, 510 Geissler tube, 355 Gel, 333 Gelatin, 210, 333, 621, 622, 784, 790 Gelatine dynamite, 670 Gelose, 773 General principles, 296 Gentianin, 781 Geranial, 687 Geraniol, 678 German silver, 459 Germanium and its compounds, 303, 494, 688 Geysers, 281 Gibbs, 338 Gibson, 566 Gilding, 526 porcelain, see Porcelain Glass, 283, 286, 368, 369, 385, 895, 431, 439 Bohemian, 397 bottle, 397 coloured, green, 511 red, 512 composition of, 395-397 crown, 397 effect of radium on, 401 etched, 133 flint, 397 -gall, 397 irisation, 398 of antimony, 480 opal, 398 physical constitution, 397 plate, 397 potash, 397 silica, 396 silvered, see Silvering soda, 396 soluble, see Sodium silicate toughened, 398 window, 396 Glauber, 101, 108 Glauber’s salt, see Sodium sulphate, 376 Glauberite, 367, 376 Glaze for earthenware, 427 Glazier’s diamond, 237 Gliadins, 784, 790 Globin, 792 Globulin, 784, 789 Glover, 164 Glucinum, see Beryllium Glucoheptonic acid, 763 Glucoheptose, 763 Glucol, 750 Gluconic acids, 764 Glucoproteins, 784 Glucosamine, 791 Glucosan, 762 Glucosazone, 764 Glucose(s), 575, 576, 760, 761-766, 769 constitution of, 765 synthesis of, 763 Glucosides, 762, 778-784 Glucosone, 764 Glue, 790, 791 Glutamic aeid, 785, 790 Glutaric acid, 627 Glutelins, 784 Gluten, 770, 790 Glyceric acid, 619 aldehyde, 597 Glycerides, 589, 671 Glycerin, 589, 669 ; see also Glycerol, &c. and glycerol, distinction, 589 (note) INDEX 845 Glycerol, 575, 583, 588-590, 596, 602, 630, 654, 659, 804; see also Glycerin, &c. constitution, 589 esters of, 669 oxidation products, 590 synthesis, 589 Glycerophosphates, 671 Glycerose, 597, 761, 764 Glyceroxides, 590 Glyceryl, 588 arsenite, 671 borate, 671 chlorides, 659, 669 dinitrate, 671 esters, 669 ether, 654 phosphate, 671 phosphoric acid, 590, 671 salts of, 671 sulphuric acid, 671 tribromide, 659 trinitrate, 590, 669 Glycide, 709 alcohol, 590 Glycocholic acid, 794 Glycocine (glycocoll) (glycine), 709, 785, 787, 791, 794, 808 Glycocyamidine, 711 Glycocyamine, 711 Glycogen, 772 Glycol, 587 alcohol, 317 amide, 703 chlorhydrin, 588, 653, 714 dialdehyde, 588 empirical formula, 541 esters, 669 sodium, 588 Glycolide, 618 Glycollic acid, 588, 597, 616 aldehyde, 761 ester, 786 Glycols, 586-588, 593, 623 Glycolylurea, 706 Glycosine, 597 Glycovanillin, 599 Glycuronic acid, 619 Glycyl-glycine, 787 Glycyphillin, 779 Glycyrrhizic acid, 781 Glycyrrhizin, 781 Glyoxal, 588, 597, 807 Glyoxalic acid, 619 Glyoxalines, 802 Glyoxyl urea, 811 Glyoxylic acid, 597, 619 Gneiss, 425 Gnoscopine, 818 Gold, 269, 375, 428, 523-528 amalgam, 414 amalgamation process, 523 arsenide, 528 assay by cupellation, 526 association with copper and silver, 524 beater’s skin, 526 bronze, 471 carats, 525 chlorides, 527-528, 812 chlorination process, 524 coin, 525 colloidal, 526 crucible, 527 cyanide process, 524 eyanides, 527, 731, 732 i : , Gold dissolved, 199 electrolytic refining, 525 extracted from silver, 524 extraction, 414, 523-525 fineness, 525 free-milling ore, 523 fulminating, 528 hydroxide, 527 identified, 196 jeweller’s, 525 leaf, 526 occurrence, 523 ores, free-milling, 523 refractory, 523, 524 oxides, 527 physical properties of, 522, 526 pulp, 523 purple of Cassius, 526 reagent in analysis, 528 refining, 524, 525 refractory ore, 523 removal of mercury from, 524 salts of, 527 separated from silver, 169 slime, 523 sodium thiosulphate, 528 stamping, 523 standard, 525 sulphides, 528 tailings, 524 testing, 525, 526 thiosulphate, 528 thread, 527 Goniometer, 336 Goulard’s extract, 605 Graebe, 752 Graham, 77, 97, 309 Granite, 358, 390, 420 Granitic rocks, 358 Granulation, 95 - Granulose, 771 Grape-sugar, 760, 761 Graphite, 237, 243, 407, 437, 441 crucibles, 238 Graphitic acid, 237 Graphitised carbon, 244 Grasses, 280 Gravimetric reactions, &c., 4, 28 Green, arsenical, 270 borate of chromium, 467 Brunswick, 514 chrome, 467 colour of plants, see Chlorophyll dyes, 749, 758 fire, see Pyrotechny flame of barium, 385 of boracic acid, 289 of copper, 514 of thallium, 430 hydroquinone, 753 oil, 572 vitriol, see Ferrous sulphate Greenockite, 411 Grey antimony ore, 476 copper ore, 225, 506 iron, 441, 442 powder, 414 Grignard’s reaction, 684, 687 Grinder’s a en Grough saltpetre, Cisne I (Alkali metals), 358-384 review, 384 TI (Alkaline earths), 385-402 review, 398 846 Group IT (Magnesium group), 402-420 review, 419 III oe group), 420-433 w, 431 III and IV ( (Ci Si, B), 235-292 review, 292 IV (Tin group), 482-505 review, 505 V (Phosphorus group), 181-234 review, 234 (Antimony group), 474-482 review, 48: VI (Sulphur group), 137-180 review, 180 Chromium, 434 (Chromium group), 470-473 review, 473 VII (Halogen group), 101-136 review, 135 Manganese, 434 VIII (Platinum group), 529-537 review, 536 (Iron, cobalt, and nickel), 434-469 Argon, 293-295 Iron series (Fe, Co, Ni, Mn, Cr), 434- 469 review, 469 monovalent, 304 Rare earths, 431-433 Grove’s battery, 15, 236 Growth of plants, sce Vegetable chemistry Guaiacol, 748 Guaiacum, resin, 144 Guanidines and derivatives, 708, 711, 739 Guanine, 708, 784, 811, 812 Guano, 182, 218, 708, 808, 811 Guignet’s green, 467 Gulose, 763 Gum Arabic, 631, 761, 772 Bassora, 773 British, 771 resins, 679 Senegal, 772 sugar, 772 tragacanth, 773 Gums, 761, 772, 791 Gun-cotton, 670, 671, 775-777 compared with gunpowder, 777 composition, 775 explosion, 776, 777 manufacture, 775, 776 products of explosion of, 777 reconversion of, into cellulose, 775 Gun-metal, 487, 510 Gunpowder, 146, 240, 363, 865, 777 facing, 238 influence of size of grain, 366 mining, 365, 366 products of explosion, 366 smokeless, 365 temperature of combustion, 366 white, 119, 365 suthrie, 341 Gutta-percha, 680 Gutzeit’s arsenic test, 227 Gypsum, 392 Hapow, 730, 732 Hematein, 783 Hematin, 781, 792, 793 Hematite, 435, 451 Hematoporphyrin, 793 Hematoxylin, Tes Hemin, 793 INDEX Hemocyanin, 506 Hemoglobin, 63, 506, 781, 784, 792 Hair-dye, 520, 750 Halogen acid esters, 664 defined, 135 derivatives, 655-663 from acids, 660 from aldehydes, 660 of closed-chain hydrocarbons, 659 of open-chain hydrocarbons, 655 propylenes, 659 group, 101-136 general review, 135, 311 new element, 303 Halogens, determination in organic com- pounds, 539 Hammer-slag, 444 Hard metal, 487 water, 43 Hardness, degrees of, 45 permanent and temporary, 45 Hargreave’s soda process, 370 Hartshorn, spirit of, see Ammonia Hatchett’s brown, 728 Hauerite, 464 Hausmannite, 462 Heading, 780 Heat, 17, 30, 50, 58, 59 ; see also Temperature, Thermal, Thermo-, and Thermo. chemistry atomic, sce Atomic latent, see Latent mechanical equivalent, 309, 310, 341 molecular, see Molecular of combination, 325 of combustion, 347, 349 of decomposition, 347 of dilution, 325, 347 of dissolution, 80, 325, 347 of formation, 347, 349 of fusion, 325 of hydration, 325, 347 of ionisation, 325, 347 of neutralisation, 345, 347 of racemisation, 638 radiant, 85 relation to chemical attraction, 347, 348 specific, see Specific units, 32 “ Heating ” of hay-ricks, 271 Heavy lead ore, 502 spar, 385 Helianthin, 718 Helicin, 779 Heliotropine, 599 Helium, 47, 78, 87, 293-295, 357, 400, 401 Helleborein, 780 Hemimorphite, 406 Hemiterpene, 675 Hemlock, 814 Henbanc, 816 Henry’s law, 79, 110 Heptamethylene, 558 Heptane, 548 Heptoses, 761, 763 Heptylic acid, 607 Herapathite, 820 Heroin, 818 Hesperidin, 779 Hesperitin, 779 Heterocyclic compounds, 544, 786, 794-822 nuclei, 794 Heterogeneous systems, 338 Heveene, 679 Hexa-acetyl cellulose, 774 chlorethane, 659 decane, 553 diene, 557 hydric alcohol, 591 hydroanthraquinone, 755 hydrobenzene, 559 hydropyrazine, 807 hydropyridine, 804 hydroxyanthraquinone, 621 benzenes, 751 cyclohexane, 751 nitro-diphenylamine, 699 Hexane, 310 Hexonic acids, 619 Hexoses, 761 stereo-isomerism of, 766 Hexyl alcohols, 582 fermentation, 583 butyrate, 583 Hexylic acid, 607 Hide, 622 Hippurates, 711 Hippuric acid, 613, 709, 710 Histidine, 786, 787 Histones, 784, 792 nucleate, 792 Hofmann, 16, 559 method for vapour density, 312 Holmia, 431 Holmium, 433 Homatropine, 816 Homberg, 288 Homogeneous mixtures, 37 substances, 1 systems, 338, 343 Homolinolic acid, 613 Homologous series, 547, 642-645 Honey, 761, 767 Hop substitute, 746, 781 Hordenine, 746 Hornblénde, 425 Horn-lead, 504 quicksilver, 418 silver, 516, 520 Horse-chestnut bark, 779 Hot blast, 438 Hyacinth, 490 Hydantoin, 706 Hydracrylic acid, 618 Hydramines, 700, 701 Hydrargyllite, 424 Hydrargyrum, 412 cum creta, 414 Hydrastine, 819 Hydrastinine, 819 Hydrates, see also Various hydroxides Hydration of ions, 322 of solute, 322 Hydraulic cements and mortars, 39] main, Hydraziacetic acid, 715 Hydrazides, 720 Hydrazidines, 721 Hydrazido-acids, 721 Hydrazine, 189, 206, 719 hydrate, 189 identified, 720 sulphate, 189 Hydrazobenzene, 701, 717, 720 Hydrazoic acid, 189, 708 Hydrazones, 596, 648, 764 Hydrazonium compounds, 720 Hydrazotoluene, 720 INDEX 847 Hydrazulmin, 723 Hydrides, 97, 98, 227 Hydrindene, 570 Hydrindigotin, 799 Hydriodic acid, 127, 128, 315 Hydroanthraquinone, 755 Hydrobenzamide, 598 Hydrobenzoin, 588, 598 Hydrobromic acid, 123, 350 Shere ony: 5, 106, 251 et seg., 437, 450, boiling-points, 643, 644 chain, open, 557 closed, ring, or cyclic, 558 chief distinction between open and closed chain, 567 constitution of, 546-547 cracking, 263 derivatives, general, 574 from phenols, 745 haloid, derivatives of, 544 hydroaromatic, 568 metallic derivatives, 557 naphthenes, 548 nomenclature in paraffin series, 553 paraffin oils, see Paraffin residues, 544 ring systems, benzene, which see conjugate, 568, 569 saturated, 546-553 series, or classes, 546 acetylene, 556-558 benzene, 558-568 preparation of, 567 general formula for, 547 homologous, 547, 554 paraffin, 546-553 olefine, 554-556 terms applied to, 566 (note) substitution in, 547 synthesised, 716 unsaturated, 558, 655 with more than one benzene nucleus, 568 Hydrocellulose, 774 Hydrochloric acid, 82, 101, 108, 350, 370 electrolysis of, 112 from alkali works, 369 influence of light, 112 solubility, 80 yellow (¢tude), 109 Hydrocinnamic acid, 615 aldehyde, 570 Hydrocobalticyanic acid, 727 Hydrocoerulignone, 751 Hydrocyanic acid, 331, 597, 704, 723, 724, 780 cll acetylene, production from, 557 tests for, 725 Hydrocyanocarbodiphenylimide, 801 Hydroferricyanic acid, 729 Hydroferrocyanic acid, 722, 727 Hydrofluoboric acid, 291 Hydrofluoric acid, 131, 134, 284, 286 electrolysis of, 134 storage of, 133 Hydrofluosilicic acid, 287 Hydrogel, 333, 424 form, 282 Hydrogen, 21, 22, 28, 78, 95, 99, 142, 264, 309, 311, 342, 388, 436, 603 and chlorine, 104 antimonide, 478 arsenide, 226 848 Hydrogen bromide, see Hydrobromic acid calorific intensity calculated, 278 value, 275 chloride, see Hydrochloric acid combustion of, 98 diffusion, 76 dioxide, see Peroxide fluoride, see Hydrofluoric acid identified, 15 introduced into compounds, 129; see also Reduction iodide, see Hydriodic acid ions, 94 liquefaction of, 87, 97 mobile, 100 nascent, 99, 414 nitride, 189 peroxide, 57, 98, 137, 142, 704, 744 constitution, 144 tests for, 144 persulphide, 155 phosphides, 216, 221, 227, 253 preparation, 95 properties of, 96 pure, preparation of, 96 selenietted, 179 sulphide, 5, 47, 82, 123, 128, 148, 151, 158, 241, 253, 273 Hydrogenium, 98 Hydro-isatin, 798 Hydrolithe, 388 Hydrolysis, 36, 224, 345, 785 Hydrometer, 183 Hydronal, 331 Hydronaphthalenes, 572 Hydrone, 331 Hydrophenyl-ethylamine, 746 Hydrophthalic acids, 628 Hydroplatinocyanic acid, 732 Hydro-potassium tartrate, see Potassium Hydropyrrols, 796 Hydroquinolines, 805 Hydroquinone, 749, 752, 779 ; see also Quinone Hydroselenic acid, 179 Hydrosol form, 282, 333, 424 Hydrosulphides, organic, 585 Hydrosulphuric acid, see Hydrogen sulphide tests for, 153 use in analysis, 154 Hydrosulphurous acid, 173 Hydrotelluric acid, 180 Hydroterpenes, 676 Hydroxy-acetic acid, see Glycollic acid acids, 198, 587 aldehydes, 587, 595, 598 amines, 700 amino-acids, 785 azo-compounds, 719 benzaldehydes, 598, 599 benzenes, 719, 743 benzoic acids, 619-621 benzyl alcohol, 584 butyric acids, 618, 667 aldehyde, 595 caproic acid, 619, 712 choline, 701 cinnamic acids, 623 crotonic acids, 667 cyanogen compounds, 736 ethylamine, 700, 701 formaldehyde, 603 formic acid, 602, 616 indol, 797 INDEX Hydroxy-malonic acids, 629 methylbenzoic acid, 663 naphthalenes, 743, 747 oleic acid, 619 phenyl fatty acids, 623, 713 phenylarsinic acids, 691 propionic acid, 617, 618 pyridines, 804 pyrone, 632 quinoline, 805 succinnic acids, 629, 630 thionaphthen, 801 toluenes, 747 toluic acids, 620 tricarballylic acid, 632 Hydroxyl form, 736 groups, 89, 90, 198, 574, 584, 587, 592, 600, 616, 662, 745 and the carbon atom, 587 ions, 94 Hydroxylamates, 207 Hydroxylamine, 190, 206, 596, 642 hydrochloride, 206 Hydroxylaminomonosulphonic acid, 165 Hydroxylation, 270 Hygrometry, 72 Hygroscopy, 39 Hyoscine, 815, 816 Hyoscyamine, 815, 816 Hypnone, 649 Hypobromites, 124, 706 and hypochlorites, reaction with carba- mate, 381 Hypobromous acid, 124 Hypochlorites, 115, 658 Hypochlorous acid, 114 anhydride, 114 Hypoiodites, 129, 658 Hypoiodous acid, 129, 209 Hyponitrous acid, 206 Hypophosphorous acid and its salts, 216, 221 Hyposulphite of soda, see Sodium Thiosul- phate ener (dithionic) acid, see Dithionic aci Hyposulphurous acid, 171 Hypovanadates, 481 Hypoxanthine, 784, 811, 812 -Ic, 59 Ice, 81 Iceland spar, 388 Ignatia, 821 Illuminating value, 265 Imide group, 684 Imides, 693, 704 Imidiphenyl, 701 Imidocarbonic acid, 739 Imidogen, 704 Imidourea, 708 Imino-azolylalanine, 786 Immedial black, 757 Inactive gases, 293 Incandescence, 261 Incandescent mantles, 267, 493 Incorporating mill, 365 Incrustation on charcoal, 268 Incrustations in boilers, 44 Indamine, 753 Indanthrene, 756 Indazoles, 802 Indene, 569, 570, 786 Indian fire, 232 ink, ,783 INDEX 849 Indian yellow, 783 India-rubber, 679 Indican, 798 in urine, 797 Indicators, 94, 127, 718, 783 Indifferent oxides, 51 Indiglucin, 798 nee 377, 698, 755, 762, 796, 797, 798- artificial, 799 blue, 798, 799 brown, 799 carmine, 799 copper, 515 gluten, 799 manufacture of, 799 red, 799 reduced, 173, 799 salt, 801 synthesis, 800, 801 vat, preparation, 799 white, 799 Indigotin, 798-801 sulphonic acids, 799 Indirubin, 798 Indium and compounds, 303, 429-430 Indoaniline, 753 Indogenides, 797 Indol, 786, 796 Indolaminopropionic acid, 786 Indolinones, 797, 798 Indophenin, 796 Indophenols, 753 Indophor, 797 Indoxyl, 797, 798, 800, 801 Indoxylic acid, 797 Induction coil, 17, 25, 139 tube, 139 Inductive method, 296 Indulines, 718, 807 Industrial methylated spirit, 577 Inflammable (non-), rendering goods, 471 Ingenhousz, 54 Inks, 39, 133, 456, 622, 727, 783 marking, 520 stains removed, 625 Inorganic chemistry, 13 Inosite, 751 Insecticides, 231 Intensity factor(s), 12, 327, 342 Internal anhydrides, 624 Intramolecular anhydrides, 618 changes, 717, 718 condensation, 551 Intumescence, 378 Inulin, 770, 772 ~Inversion temperature, 85 Invert sugar, 575, 763, 76 Invertase, 575 Iodamines, 700 Iodates, 127 (note), 180 Iodic acids, 92, 127, 129, 180, 817 Todides, 129 Iodine, 124, 194, 209, 214, 361, 362, 368, 733, 812 bromides, 127, 180 chlorides, 127, 130 green, 759 oxides, 127, 129 oxyacids, 129 pentafluoride, 127, 180, 134 pentavalent, 660 scarlet, 418 test for, 127 Iodine, tincture of, 126 value, 671, 673 water, 126 Iodised starch, 127 Iodo-azoimide, 190 Todobenzene, 660 TIodoform, 658 Iodometry, 127 Iodonium compounds, 131, 660 Iodopyrrol, 796 Iodosobenzene, 660 Iodoxybenzene, 660 Ionic hypothesis, 94, 326 Ionisation, 94, 183, 327 degree of, 330 of gases, 399 Tonium, 401, 472 Ions, 94, 296, 326, 327 def. complex, 331 hydration of, 331 migration of, 327 Ipecacuanha, 820 Iridio-platinum alloy, 134 Iridium, 529-537 its properties and compounds, 536 ore, analysis of, 537 Iron, 62, 96, 408, 484-456, 458, 697, 782 acetate, 604 % action of acids on, 195, 452 of air on, 453 of nitric acid on, 452 of steam on, 453 on water, 21, 452 allotropic form, 436 alums, 455 and carbon, 437 and oxygen, 62 and steam, 341, 342 bar, 445, 448 Barff’s process for protecting, 454 basic open-hearth process, 446 Bessemer process, 446 basic, 447 black, 476 oxide of, 453 blow-holes in, 446, 449 Bower’s process for protecting, 454 carbide, 437, 724 carbon in, 237 carbonate, 454 carbonyls, 456 cast, 436, 440, 441, 443 wrought, and steel, distinction, 443 cementation, see Cementation chemical properties of, 451 chlorides, 455 cold-short, 445 decarburised, 443 dialysed, 453 direct extraction, 451 effect of process on composition, 447, 448 electric smelting, 451 refining, 451 extraction on small scale, 451 fagoting, 444 ferric state, 452 ferrous state, 452 fibrous structure, 445 foundry, 442 galvanised, 405 glance, 435 granulated, 324 grey, 441, 442 34 850 INDEX Iron group or series, 436-469 review of, 469 hydrated oxides, 453 ingot, 443, 445 iodide, 455 magnetic oxide, 453 malleable, 436, 442, 448, 445, 451 direct extraction from ore, 451 merchant bar, 445 metallurgy of, 422, 438-451 mottled, 441, 442 mould, 452, 774 Nos. 2 and 3 bar, 445 open-hearth process, 445 ores, 484-486, 451 calcining or roasting, see under Metallurgy of iron oxides, 43, 342, 453 passive state of, 452 perchloride of, see Ferric chloride peroxide, 453 phosphates, 455 phosphorus in, 445, 441 puddled, 443 puddling process, 443 pure, 436, 437 pyrites, 146, 161, 163, 166, 178, 271, 436, 456 pyrophorus, 248 red-short, 445 reduced, see Ferrum redactum refining, 443 regenerative firing, 445 rusting, 2, 452 sand, 436, 490 scurf, 428 Siemens Martin process, 445 smelting, 435 sulphate, see Ferric and Ferrous granulated, 324 sulphides, 456 sulphur in, 441 tannate, 452 tenacity, 436 Thomas process, 447 tincture of, 455 tinned, 485 detinning of, 490 tungstate, 471 welded, 445 white, 441, 442 wire-iron, 407 wrought, 443 Tronstones, 435 Isatic acid, 714 Isatide, 798 Isatin, 107, 714, 798 anilide, 801 chloride, 798 Isatoic anhydride, 714 Iserine, 490 Isethionic acid, 555, 681 chloride, 714 Isinglass, 791 Isobarbituric acid, 811 Iso-butane, 553 butyl alcohol, 582 butylene, 556 cholesterol, 585, 674 cyanates, 737, 739 cyanic acid and isocyanates, 737 cyanides, 734 cyanuric acid, 743 dialuric acid, 811 Iso-diazo salts, 716 Isomeric alcohols, 579 change, 736 dynamic change, 736 Isomerides; definition, 553 dynamic, 148 Isomerism, 138, 562, 579 dynamic, 735 position, 562 Isomers, 541 Isomorphism, 299, 513 Isomorphous compounds, 299 Isonitriles, 734 Isonitroso-derivatives, 699 Isoparaffins, 553 pentane, 553 phthalic acid, 628 propyl acetic acid, 607 alcohol, 580 benzaldehyde, 598 benzoic acid, 614 carbinol, 580 halides, 607 quinoline, 805, 818, 819 Isoprene, 675, 679 Tsosmotic solutions, 319 Iso-succinic acid, 626 uric acid, 811 Isotonic solutions, 319 Tsoxazole, 802 Isuret, 703 Itaconic acid, 628, 633 Ivory, artificial, 778 JABORANDINE, 822 Jalapin, 780 Jalapinol, 780 Jasper, 280 Jecoline, 673 Jervine, 822 Jet, 272 for burning gases, 23, 264 Jewellers’ rouge, 453 Joule, 85, 326, 329 Kamit, 362 Kairine, 805 Kairolin, 805 Kakodyl, 690 chlorides, 690 cyanide, 690 oxide, 690 sulphide, 690 Kakodylic acid, 690 Kali, 19 Kaolin, 420, 427 Kassner’s oxygen process, 502 Katigen blue, 757 Kauri resin, 679 Kekulé’s benzene theory, 560, 561 Kelp, 124 Kelvin-Joule effect, 85, 314 Keratin, 784, 791 Kermes, 480 mineral, 480 Kernel roasting, 514 Kerosene, see Paraffins Keten, 606 Ketodihydropyrazoles, 802 Keto-form, 736 Ketols, 649 Ketone-acids, 649 alcohols, 649, 760 INDEX 851 Ketone aldehydes, 649, 764 decomposition, 667 Melons pee 581, 588, 647-650, 667, 720, reactions of, 159, 648 Ketoses, 760-763 Ketoximes, 648 Kieselguhr, 670 Kieserite, 404, Kiln, 438 Kinetic energy, 308, 310 method of measuring affinity, 342, 345 _ theory of gases, 308 King’s yellow, 232 Kino, 747, 750 Kipp’s apparatus, 65 Kirchhoff, 380 Kish, 238 Kissingen, 121 Kjeldahl’s method, 539 Klaproth, 179 Kola nut, 813 Kolbe, 619 Kosine, 781 Koumiss, 769 Kousso, 781 Kreasote, 748 Kreatine, see Creatine Kresol, see Cresol, 747 Kreuznach, 121 Kryolite, 131, 367, 421 Krypton, 293-295 Kundt’s tube, 311 Kupfernickel, 225, 459 Kyanite, 425 Las, 790 Labile form, 736 Lac, 679, 783 Lacquer, 783 Lacquering, 511 Lactamide, 703 Lactams, 709 Lactarine, 790 Lactates, 618 Lactic acids, 595, 607, 617, 635, 662 fermentation, 607 Lactide, 617 Lactims, 714 Lactobiose, 769 Lactones, 618, 649, 794 Lactonitrile, 595 Lactose, 769 Lactyl chloride, 662-663 Levo-rotatory, 634; sce Optical Levulinic acid, 649, 784 Levulosan, 763, 767 Levulose, 761-763, 772 Lakes, alumina, 423, 783 Laminaria, 125 (note), 591 Lamp-black, 238 Lamp, safety, 260 without flame, 531 Lamps, electric incandescent, 471, 482, 530 Doébereiner’s, 77, 531 Landsberger’s apparatus, 323 method, 323 Lanolin, 674 Lanthana, 431 Lanthanum, 431 and compounds, 433 Lapis lazuli, 426 Lard, 673 Larderello, 289 Latent heat, 32 of fusion, 322, 642 of vaporisation, 323 Lathering, 608 Laudanum, 817 Laughing gas, 200 Laurel water, 725 Lauric acid, 608, 671 aldehyde, 596 Laurin, 672 Laurite, 536 Lauth’s violet, 806 Lava, 425 Lavender oil, 678 Lavoisier, 3, 11, 20, 49, 50, 54, 81, 88, 101, 235 Law, Neumann and Kopp’s, 298 of chemical combination, 5, 9 of conservation of mass, 3 of energy, 12 of constant proportions, 4 of electrolysis, 328 of esterification, 642 of even numbers, 541 of gaseous combination, 9, 26 diffusion, 77, 309 of multiple proportions, 4 of octaves, 301 of partial pressure, 79, 347 of reciprocal proportions, 5 periodic, see Periodic z third, 319 Lead, 401, 413, 474, 494-505 acetate, 502, 503, 605 basic, 503, 605 action of acids on, 500 of, on water, 46, 501 alkides,.689 antimonate (basic), 478, 497 argentiferous, 497 carbonate, 495, 503 basic, 500, 503 chlorides, 504-505 chlorosulphide, 505 chromates, 466 basic, 467 cistern, 46 corrosion of, 46, 500, 501 cupellation, 498 dioxide, 502 extraction from ore, 495-497 in laboratory, 499 ferricyanide, 728 . formate, 602 fume, 496 glass, 501 -glazed earthenware, 501 hard, 497 dross from, 497 hydroxide, 503 improving or calcining, 497 in cider, &c., 501 in water, 46 iodide, 505 malate, 629 metallurgy of, 495 molybdate, 470 nitrate, 196, 508 oleate, 589, 612 ores, 495, 502 oxalate, 501 oxides, 495, 501-503 in drying of oil, 501 in glazing earthenware, 501 in manufacture of glass, 501, 502 852 INDEX Lead oxides, puce, 502 oxychlorides, 504 Parkes’ desilvering process, 498 Pattinson’s desilvering process, 497 peroxide, 502, 672 persulphide of, 382 plaster, 589, 612 poisoning, 504 polysulphide, 505 propionates, 607 ~ pyrophorus, 501 selenide, 505 sesquioxide, 502 silicate, 496, 501 silver, extraction of, 497 slag, 496 composition of, 496 Spanish, 497 sucrates, 768 sugar of, see Acetate sulphate, 143, 165, 495, 504 sulphides, 143, 153, 382, 495, 504, 505 tartrate, 501 telluride, 179 test for, 46 tetracetate, 502 tetramethide, 689 tetrethide, 689 thiosulphate, 172 tribasic acetate, 605 triethide, 689 uses, 500, 530 vanadate, 481 vitriol, 504 Leather, 622 Le Bel, 636 Leblanc alkali process, 369-373 Lecanoric acid, 749 Lecithin, 671, 701, 793 Leclanché batteries, 382 Legumin, 790 Leguminous plants, 181, 182 Lemery, 288 volcano, 150 Lemons, essential oil of, 676 Lepidine, 804, 805 Lepidolite, 383, 384 Leucaniline, 758 Leucic acid, 619, 712 Leucindigo, 799 Leucine, 712, 785, 791 Leuco-base, 758 compounds, 756 Leuco-pararosaniline, 758 Levulose, 650 Leyden jar, 25, 27, 181 Lichens, colouring-matters from, 749 Liebermann’s reactions, 695, 745 Liebig, 705, 706 extract, 711 Light, influence, 54, 63, 105, 107, 108, 112, 117, 138, 140, 150, 153, 158, 171, 18], 249, 356, 402, 415, 472, 520, 521, 531 oil of coal-tar, 559, 570 standard of, 548 Lignite, 271 Ligroin, see Petroleum spirit Lime, 387; sce Calcium oxide air-slaked, 389 brominated, 124 burning, 64, 389 carbonate in waters, 45, 389 chloride of, see Chlorinated lime kilns, 389 Lime-light, 269, 493 mild, 388 quick, 389 slaked, see Calcium hydroxide stone, 64, 388, 389, 439, 440 superphosphate, 394 water, 390 Limited divisibility of matter, 6 Limiting volumes, 316, 334 Limonene, 638, 674, 676 Limonite, 88 Linalool, 676, 678 Linalyl acetate, 678 Linde’s machine, 85 Linolenic acid, 613, 673 Linolic acid, 612, 673 Linseed, mucilage from, 773 oil, 612, 613, 672, 673 drying of, 501 Liquation, 476, 484 Liquid waxes, 674 Liquids, 315 Liquor ammonie, see Ammonia chlori, 103 iodi, 126 sode chlorinatz, see Chlorinated soda Liquorice root, 781 Litharge, 499, 501, 672 Lithia, 383 mica, 383 Lithic acid, 807 Lithium and its salts, 53, 358, 383 nitride, 53, 293 urates, 808 Lithopone, 410 Litmus, 18, 749 Liver oils, 673 Loadstone, 62, 486 Loam, 421 Logwood, 157, 783 Looking glasses silvered, 414 Lophin, 802 Lothar Meyer, 301 Low temperature, production of, 82, 156 ; see also Freezing Lubricating oils (paraffin), 549 Lucifer matches, see Matches Luminosity of flames, &c., 59, 60, 258, 261, 266 effect of pressure on, 265 Lunar caustic, 519 Lunge, 165 Lupetidin, 144 Lutecium, 431, 433 Luteo-cobalt salts, 458 Luteolin, 782 Lutidine, 803 Luting for crucibles, 407 for iron joints, 150 Lycopodium, 260, 311, 420 Lye, 359, 589 Lysidine, 802 Lysine, 786 Lysol, 747 Macsripe, 63 MacDougall’s disinfectant, 744 Maclurin, 783 Madder, 489, 754 lakes, 755 Magenta, 758 bronze, 471 Magnalium, 402, 422 Magnesia, see Magnesium oxide INDEX 853 Magnesite, 402, 403 Mpenesiun, 53, 97, 132, 402, 419, 579, 687, action on water, 20 alkides, 687 alkyl compounds (Grignard),"687 ammonio-chloride, 405 phosphate, 404 ammonium arsenate, 404 borate, 290, 404 boride, 291 bromides, 121 carbonate, 43, 358, 402, 403 chloride, 45, 47, 361, 368, 404, 464 citrate, 633 ethide, 687 fluoride, 131 group, review of, 419 hydroxide, 403 limestone, 390, 402, 403, 404 methide, 687 methoxide, 579 nitride, 53, 293, 403 oxide, 402, 403 oxychloride, 103, 405 phosphates, 404 platinocyanide, 732 silicates, 283, 402, 404 silicide, 285 stearate, 609 sulphate, 43, 368, 402, 404, 410, 454 Magnetic, -ism, 58, 182, 291, 350, 356, 451, -459, 793 concentration of ores, 406 field, 452 = iron ore, 62, 436, 451 pyrites, 456 rotatory power, 640 Magnetite (Magnetic oxide of iron), 436 Magneto-chemistry, 350, 453 Magneto-fuse composition, 515 Magneton theory, 351 Magnus’ green salt, 532 Mahler’s bomb, 276 Malachite, 88, 506 green, 513, 758 Maleic acid, 627, 629, 638 anhydride, 627, 629, 638 Malenoid and fumaroid structure, 595, 638 Malic acid, 626, 629, 630, 639, 663, 713, 775 Malonic acid, 249, 624, 625, 629 ether, 669 Malony] urea, 810 Malt, 769 Maltose, 576, 769 Manchester brown, 718 Mandelic acid, 621, 650, 780, 816 Manganates, 462 “‘ Manganese,” 461 Manganese, 20, 351, 435, 437,441, 451, 461- 465, 469 black, 461 blende, 464 borate, 672 borides, 291, 351 bronze, 487 carbonate, 461 chlorides, 464 dichloride, 102 dioxide, 49, 55, 56, 101, 398, 461, 463, 672 464, hydrated, 462 dithionate, 173 ferrocyanide, 728 Manganese hydroxide, 462 iron, separated from, 464 nitrides, 351 oxalate, 625 oxides, 54, 461-462 peroxide, 461 recovery, 464 spar, 461 sulphate (manganic), 462 (manganous), 464 sulphides, 464 tetrachloride, 102 tungstate, 471 Manganic acid, 462 anhydrides, 462 Manganin, 459 Manganites, 463 Manganous acid, 463 Manna, 591 Australian, 770 trehala, 769 Mannitane, 592 Mannite (mannitol), 591, 763, 764 Mannonic acid, 591, 764 Mannose, 591, 761, 763, 764 Manny] hexanitrate, 591 Mantles for incandescent burners, 267, 493 Manures, 362, 379, 394, 441, 739, 380 Maquer, 721 Marble, 3, 64, 388, 390 Marcasite (iron pyrites), 456 Margaric acid, 608 Margarine, 673 Margraf, 131, 132 Marine animal oils, 673 Marking-ink, 520 Marl, 421 Marsh-gas, see Methane series, 546 Marsh’s test for arsenic, 227 Martensite, 437 Martius’ yellow, 747 Mascagnine, 182, 380 Mass, 1 action, 343 active, 343 conservation, law of, 3 Massicot, 501 Mastic, 679 Matches, 120, 214, 215, 222 safety, 215 without phosphorus, 120 Maté, 813 Matlockite, 504 Matte, 459 Matter, 1, 2, 6 conservation, 2, 3 Mayer’s reagent, 812 Mayow, 48, 49 Meadow-sweet, oil of, 598 Meconic acid, 817, 818 and meconates, 632, 817 Meconine, 818, 819 Meconinic acid, 818 Meerschaum, 402, 404 Melam, 739 Melamine, 739 Melaniline, 708 Melem, 739 Melezitose, 770 Melibiose, 770 Melissyl alcohol, 583 palmitate, 533, 668 Melitose, 770 854 INDEX Mellite, 633 Mellitic acid, 633 Mellone, 738, 739 Mellonides, 739 Melting-point, 32, 322, 339, 642 Menaccanite, 490 Mendeléeff, 8, 301, 303, 304, 423, 428, 494 periodic table, 8, 302 Mendipite, 504 Meniscus, 316 Menthene, 676 Menthol, 677, 678 Menthone, 678 Mercaptans, 585, 586, 648, 681 Mercaptides, 586 Mercaptol, 648 Mercerisation, 774 Mercuric acetamide, 702 chloride, 416, 489 and albumin, 416 cyanides, 722, 781 ethide, 687, 688 fulminate, 741 iodide, 127, 418 mercaptide, 586 methide, 687 nitrates, 196, 414, 415, 416 oleate, 612 oxide, 49, 412, 415 oxycyanide, 731 sulphate, 414, 416 sulphide, 412, 418 colloidal, 419 telluride, 179 thiocyanate, 737, 738 thiophenol, 745 Mercuroso-mercuric iodide, 418 Mercurous acetate, 604 chloride, 416, 417 cobalticyanide, 727 iodide, 127, 418 nitrate, 414, 415 oxide, 415, 418 sulphate, 414, 416 sulphide, 153 Mercury, 26, 27, 49, 311, 374, 412, 419, 490 alkides, 687 allyl-hydroxide, 659 iodide, 659 amalgams, 414 amido-chloride, 417 ammoniated oxide, 415 ammonium compounds, 415, 417 bichloride, see Mercuric chloride bronzing by, 511 chlorosulphide, 419 collection of gases over, see Gases diphenyl, 688 ethyl chloride, 688 hydroxide, 688 frozen, 83 fulminate, see Fulminates metallurgy of, 413 methyl chloride, 687 nitric oxide of, 415 oxides, 415 oxychlorides, 417 phenyl chloride, 688 ydroxide, 688 process, 374 protonitrate, see Mercurous nitrate stains removed from gold, 414 uses of, 294, 360, 414, 511, 516, 523 volatility of, 414 : Mercury, yellow oxide, 415 Mesaconic acid, 627 Mesity] oxide, 648 Mesitylene, 561, 567, 614, 648 Mesitylenic acid, 614 Meso-deri¥atives, 573 Mesotartaric acid, 630, 637-639 Mesothoria, 493 Mesoxalic acid, 629, 809 Mesoxalyl urea, 809 Metaboric acid, 289 Metachloral, 661 Metacinnamene (metastyrolene), 568 Metacresol, 747 Metacrolein, 596 Metadiazines, 806 Metaformaldehyde, 593 Metal(s), 16, 49, 51, 61, 62, 97, 858, 436, 456 action on water, 18-21 Aich, 510 alkides, 683-690 and metalloid derivatiyes of organic compounds, general, 649, 650, 669, 682, 683-692 instances, 584, 600, 702, 704, 782 bell, 487, 510 Britannia, 476, 486 definition of, 7 Gedges, 510 gun, 487, 510 hard,” 487 lowering fusing-point of, 474 Muntz, 510 noble, 21 speculum, 487, 510 type and stereotype, 474, 476 expanding of, in mould, 474 white, 507, 511 Metaldehyde, 595, 641 Metalepsis, 106, 129, 546, 655 Metallic anhydrides, 62 Metallography, 437, 486 Metamerides, 562, 643, 644 Metantimonic acid, 478 Metaphenylenediamine, see Phenylene- diamines Metaphosphates, 220 Metaphosphoric acid, 123, 210, 218, 219 Metaproteins, 784 Metarabin, 772 Metarsenic acid, 231 Metarsenious acid and its salts, 230 Metasilicic acid, 282 Metastable condition, 340 Meta-titanic acid, 491 ‘i Metavanadates, 481 Meteoric iron, see Iron Meteorites, 434 Methane, 5, 107, 257, 274, 349, 546, 550 constitution, 546 AEDST properties, and combinations, 0 heat of formation, 349 preparation of, 550 tetramethyl-, 553 thermo-chemistry of, 349 trimethyl-, 552 Methene, see Methylene Methoxybenzaldehyde, 599 benzoic acid, 620 groups, determination, 654, 813 Methyl, 197, 684 acetamide, 702 acetate, 579, 666 Methyl souplig acid, 610, 611 alcohol, 578, 593, 656 aldehyde, 593 amine, 694, 695 aniline, 699 anthranilate, 713 arsenic acid, 690 arsines, 690 benzenes, 566 benzoic acid, see Toluic acid bromide, 656 carbamides, 706 carbamine, 735 carbimide, 739 chloride, 107, 184, 655, 664, 696 coniine, 814 cyanate, see Isocyanate cyanide, 604, 702, 734 cyanurate, 739 dihydroglyoxaline, 802 dimethylacetylene, 557 divinyl, 675 ether, 650, 651 ethyl ketone, 647, 649 sulphide, 641 thetine, 641 urea, 739 fluoride, 656 formate, 664, 666 formic acid, 603 fumaric acid, 627 glycocines, 710 glycocyamidine, 711 glycocyamine, 71] glyoxal, 649 guaiacol, 748 anidine, 711 exose, 763 hydantoin, 712 hydrate, see Methy] alcohol hydrazine, 715 hydrindamine, 641 hydroxy-piperidine, 815 indol, 796, 797 indolin, 797 iodide, 656, 692 isocyanate, 695, 739 isocyanide, 735 isopropyl-benzene, see Cymenes maleic acid, 627 malonic acid, 626 methyl-salicylate, 668 morphine, 817 naphthalenes, 572 nitramine, 700 nitrite, 682 nonyl ketone, 649 orange, 718 oxalate, 579, 669 oxamide, 694 phenols, 747 phenylamine, 699 phenylketone, 649 phosphines, 692 phthalic acid, 795 propyl carbinol, 581 protocatechuic acid, 621 pyridines, 804 pyrocatechol, 599, 748 quinolines, 805 salicylate, 620, 654, 668 salicylic acid, 668 succinic acid, 627 sulphates, 664 “INDEX 855 Methyl] theobromine, 813 uracyl, 811 ureas, 739 violet, 759 Methylal, 593 Methylated ether, 652 spirit, 577 Methylene(s), 558, 568 dichloride, 107 iodide, 657 group, 593 malonic acid, 627 protocatechuic aldehyde, 599 succinic acid, 627-628 white, 806 Methylenitan, 764 Meyer, Lothar, 301 Victor, 318, 642 Mica, 283, 358, 420, 428 Microcosmic salt, 220, 888 Micro-organisms, 73 Middle oil of coal tar, 570, 744 Migration of groups, 100, 699, 701, 720, 786 of ions, 327 Mildew, 73 Milk, 2, 673, 769, 790 casein, 790 sugar, 631, 763, 769 Mill-cake, 365 Millon’s base, 415 test, 788 Millstone grit, 390 Mineral cotton, 441 een, 513 ermes, 480 kingdom, 64, 235 waters, 46, 52 yellow, 505 Mines, ventilated, 69 Minium, 502 Mirbane essence, 683 Mirrors, manufacture of, 517, 518, 533 Mispickel, 225 Mitchell, 83 Mitscherlich, 299, 559 Mixed glycerides, 672 Mixture defined, 2 Mobility, 100, 330 Modification, 138 Moiré metallique, 487 Moissan, 134 Moisture, influence of, 58, 104 Molasses, 767 Molecular “ aggregates,”’ 317 agitation, 334 architecture, 544; see Stereo-chemistry area, 316 atgraction, 334 formula, 540 determination of, 540, 541, 543 heat, 298, 310, 325 magnitude, 351 motion, intra-, 310 refraction, 245 rotatory power, 635 volume, 96, 305, 310, 316, 644 weight, 7, 297 determination of, 11, 312, 316, 317- 823 of a liquid, 312 of a non-volatile substance, 317 of a volatile substance, 316 Molecule, definition, 6 Molecules, 10 856 Molecules in motion, 334 structure of, see Theories velocity of, 75, 308 Molluscs, 506, 778 Molybdate of lead, 470 Molybdenite, 470 Molybdenum, 470 carbide, 470 chlorides, 470 disulphide, 470 glance, 470 metallic, 470 molydate, 470 Molybdic acid, 470 anhydride, 470 ochre, 470 oxide, 470 Molybdo-arsenates, 472 -phosphates, 472 -vanadates, 472 Molybdous oxide, 470 Monacetin, 672 Monad elements, 12 Monamides, 702 Monamines, 693, 695-708, 803 Monamino acids, 785 Monatomic elements, 420 Monazite, 431, 493 Mond gas, 275 Monel metal, 459 Monethy]l glycol ether, 653 Monkshood, 822 Monobasic acids, 90 Monobutyrin, 672 Monochloracetic acid, 710 Monochlorether, 653 Monochlorhydrin, 669 Monochlorobenzene, 559, 660 methane, 655 Monoclinic crystals, 336 Monocyclic terpenes, 675 Monoformin, 583, 602, 672 Monohydric alcohols, see Alcohols Monolaurin, 672 Monolein, 672 Monoses, 760 Monovalerin, 672. - Mordants, 423, 471, 488, 605, 612, 717, 718, 759 Morin, 783 Moritannic acid, 622, 783 Morphine and its salts, 701, 812, 817 Morpholine, 701 Morse cell, 318 Mortar for building, 391 Mosaic gold, 490 Mould, 73 Mountain-ash berries, 629 Mucedin, 790 Mucic acid, 681, 795 Mucilage, 772, 773 Mucin, 784, 792 Mucoids, 792 Muffle, see Furnace Multiple proportions, 4 Mundic (iron pyrites), 456 Muntz metal, 510 Murexan, 810 Murexide, 808, 810, 812 Murexoin, 814 Muriate of Fmmonia, see Ammonium chloride of morphia (Morphia hydro- chloride) Muriatic acid, 101 INDEX Muscarine, 701 Muscle plasma, 789 Muscovite, 425 Musk, artificial, 683 Muslin, non-inflammable, 380, 471 Muspratt, 369 Mustard oil, fixed, 612 test, 740 oils, 739, '740 Mutton suet, 673 Mycodermaceti, 604, 617 Mycose, 769 Mydatoxine, 701 Mydine, 701 Mydriatic alkaloids, 815, 816 Myosin, 789 Myrcene, 675, 676 Myricin, 583, 668 Myricyl alcohol, 583 Myristic aldehyde, 596 Myronic acid, 740 Myrosin, 740 Myrrh, 679 Naparaa, mineral, 548 Naphthalene, 569, 570, 628, 744, 800 chlorides, 571, 628, 660 chloro-substitution products, 660 constitution, 571 disulphonic acid, 681 heat of combustion, of, 276 molecular heat of fusion, 325 nitro-substitution products, 683 rings, 571 sulphonic acids, 681, 747 yellow, 747 Naphthalic acids, 629 Naphthalidine, 700 Naphthazine, 807 Naphthenes, 548 Naphthindulines, 807 Naphthohydroquinone, 753 Naphthoic acids, 615 Naphthol sulphonic acids, 747 Naphthols, 719, 747 yellow, 747 Naphthophenazine, 807 Naphthoquinolines, 805 Naphthoquinones, 753, 754 Naphthylamines and derivatives, 571, 700, 719, 747, 805 Naphthylene-diamines, 701 Naphthyl-phenyl-ketone, 649 salicylate, 747 Naples yellow, 478 Narcéine, 819 Narcotine, 818 Nascent condition, 99 Natrolite, 425 Natron, 372 Negative charge, 343 pole, 16 Neodymium, 431, and compounds, 488 Neon, 293-295 Neo-paraffins, 553 Neo-pentane, 553 Neroli oil, 713 Nerve substance, &c., 585, 793 Nessler’s test, 418 Nest sugar, 769 Neuridine, 701 Neurine, 701, 793 Neutralisation, 90 Newland’s law of octaves, 301 INDEX 857 Newton, 235 NH-group compared with O, 188, 686 Nicholson and Carlisle, 14 Nickel, 98, 350, 451, 458-461, 469, 472 ammonium sulphate, 460 arsenical, 225 arseniosulphide, 225 atomic weight, 461 blende, 459 carbonyl, 460 cobalticyanide, 727 coins, 459 copper alloy, 459 cyanide, 726 ferrocyanide, 728 finely divided, use in effecting organic combinations, 555, 557 glance, 225, 459 hydroxide, 460 metallurgy of, 459 ores, 459 Orford process, 459 oxides, 460 peroxide, 461 separation from cobalt, 459 steel, 459 sulphate, 460 sulphides, 460 Nicotine, 812, 814 ethylium dihydroxide, 815 Nicotinic acid, 815 Nightshade, 816 Nil album, 407 Niobates, 481 Niobium (Cb), 305, 481 Niton, 298-295, 302, 307, 357, 400, 401 Nitramines, 700 Nitranilines, 683, 698 Nitrate, 192 Nitrates, 42, 56, 196 as manure, 181, 379 effect of heat on, 196 formation in nature, 181 Nitration, 682 Nitre, see Potassium nitrate cubic, see Sodium nitrate -heaps, 363 pots, 163 Nitric acid, 15, 92, 129, 163, 192 action on hydrochloric acid, 199 on metals, 422 on organic bodies, 197, 669 on turpentine, 197 composition of, 196 formation from air, 190 from ammonia, 190 fuming, 193 preparation, 192 reduction, products of, 205 test of strength, 193 anhydride, 199 esters, 665 ether, 665 oxide, 49, 54, 63, 162, 200 peroxide, 203 Nitrides, 53, 182 Nitrification, 181, 363 Nitrifying organism, 363 Nitriles, 224, 693, 783 Nitrites, 42, 203 Nitro-benzaldehyde, 801 benzene, 197, 682, 697, 717, 804 benzoic acids, 614 cellulose, see Cellulose nitrates Nitro-chloroform, 682, 746 cinnamic acid, 801 aldehyde, 796 compounds, 681, 694 copper, 204 erythrite, 591 ethane, 681, 682 form, 682 glycerin, see Glyceryl tri-nitrate hydrochloric acid, 199 mannite, 59] metals, 204 methane, 682, 742 muriatic acid, 199 naphthalene, 571 naphthalenes, 683 naphthols, 747 paraffins, 581, 666, 682 derivatives, 684 phenols, 745 phenylamines, 698 phenyl-lactomethyl ketone (see p. 801) phenylpropiolic acid, 798, 801 prussides, 730 salicylic acid, 779 substitution, 197 products, 681 sulphites, 159 sulphonic acid, 162, 165, 199 sulphuric acid, 199 toluenes, 683 uracyl, 811 Nitrogen, 49, 51, 52, 54, 55, 58, 60, 47, 48, 84, 1238, 124, 181, 234, 294, 300, 311 ** active,” 181 as plant food, 181 bulbs, 539 ~ chloride, 107 ; see also Halides chlorophosphide, 224 determination, Dumas’ method, 539 Kjeldahl’s method, 539 Will and Varrentrap’s method, 539 group of elements, 234 halides, 208-209 liquefied, 84, 85 oxides, 5, 190, 204 peroxide, 63, 162, 208, 315, 322 preparation, 52 stereochemistry of, 641 sulphides, 208 tetroxide, 208, 315 trioxide, 162, 202, 322 Nitrogenised bodies identified, 242 Nitrolic acids, 581 Nitrometer, 142, 195, 665 Nitrosamines, 695 Nitrosobenzene, 698, 752 Nitrosomethylurethane, 715 Nitroso-phenol, 752 reaction, 695 Nitrosyl chloride, 199 sulphate, 199 Nitrous acid, 162 formed from ammonia, 190 anhydride, 202 esters, 665, 681 oxide, 63, 82, 200, 311, 401 thermo-chemistry of, 349 Nitroxyl, 204 compounds, 199 Nitryl chloride, 199 Nobel’s detonators, 670 Nonane, 548 Non-drying oils, 672 858 INDEX Non-inflammable fabrics, 471 Non-metals, 7, 16, 51, 58, 62 Nonoses, 763 Non-valent elements, 13, 298 Nony] alcohol, 578 methyl-ketone, 608 Nonylic acid, 608, 612 aldehyde, 612 Nordhausen oil of vitriol, 161 Normal salt defined, 92 Normandy’s still, 30 N.T.P., 9 Nucleal synthesis, 551, 555, 558 Nucleic acids, 784, 792 Nuclein, 792 Nucleoproteins, 784, 792 Nuggets, 523 Nutrition of plants, 209 Nux vomica, 821 Ocotvston of gases, 97, 400, 436 Ochres, 421, 435 Octadecapeptide, 787 Octane, 548 Octohydric alcohols, 770 Octoses, 763 Octyl acetate, 583 alcohol, 583 Octylic acid, 607 Cnanthic acid, 607 aldehyde, 596, 673 ether, 668 Oettel’s voltameter, 16 Oil of cress, 734 of gaultheria, 620 of meadow-sweet, 598 of mignonette root, 740 of mustard, 740 of nasturtium, 734 of rue, 608, 649 of spirea, 598 of vitriol, see Sulphuric acid of wine, 665 of winter-green, 620 wells, 548 Oils (see under their specific names) Br absorption, 543 essential or volatile, see essential oils fixed, see Fats I absorption, 543 Oleates, 612 Olefiant gas, see Ethylene Olefine acetylenes, 557 benzenes, 567 hydrocarbons, general preparation of, 554 Olefines, 554 structure of, 554 terpenes, 675, 676, 678 tri-, 557 Oleic acid, 608, 609-612 Olein, 608, 671, 672, 673 Oleo-resins, 679 Oligist iron ore, 435 Olive oil, 673 Olivine, 283, 404 Onnes, 87 Onyx, 280 Oolite limestone, 388 Oolitic iron ore, 436 Opal, 280 Open- and ¢losed-chain hydrocarbons, 557, 558 hearth process, 446 Opianic acid, 818 Opium, 680, 817 alkaloids, 817 Optical properties, 335, 6838-642, 645-647 Orange chrome, 461 III., 718 Oranges, essential oil of, 676 Orcéin, 749 Orchella weed, 749 Orcin, or orcinol, 668, 749 Ore concentration or dressing, 406, 483, 524 -furnace, see furnaces Orford process, 459 Organic acids, 545, 599-638, 667 acid radicles, 606 analysis, determination of, elements, 538-540 empirical formule, 540-541 molecular weight, see Mol’r weight formula, 540 of an acid, 540 of a base, 541 percentage composition, 540 structure, 541 : ultimate, 538, 540 bases, 528 chemistry, 13, 235, 292, 588 bonds or “‘ linkings,” 542, 557 double, situation determined, 543 ethylenic or double, 542, 554 chains, 542, 557 condensation, intramolecular, 551 or nucleal synthesis, 551, 555, 558 condensed nuclei, 568 constitution, see also under Con- stitution means of investigation, 545 of hydrocarbons, 546-547 isomerides and polymerides, defi- nition, 553 — nomenclature, 581 (note) iso, neo, normal, &¢., meaning of, 553 -diene, -triene, &c., 556 (note) nucleus (Carbon nucleus), 547 orientation of benzene and its de- rivatives, 563-566 radicles, 544, 548 reactions employed in, 545 Fittig’s, 567 Friedel and Craft’s, 567 Grignard’s, 552 : Perkin’s, 615 Sandemeyer’s, 716 Schotten Baumann, 662 Wurtz, 551, 555 saturated and unsaturated com- pounds, 542, 543 substitution and addition, 542 synthetic chemistry, 667 (natural), 668 compounds, absorption spectra, 646 action of nitric acid on, 197 boiling-points of, 578 classes of, 544-545 combustion of, 538 eyclic, 542, 544 divisions of, 544 gradation of properties, 548, 567, 578, 596, 601, 627, 643-647 melting-points of, 642 optical properties of, 645 INDEX 859 Organic compounds, refractive powers of, 646 rotatory polarisation of, 634 specific volumes, 644 structure of, 541 matter identified, 538 radicles, 605 Organo-mineral compounds, 683 Oriental alabaster, 45 amethyst, 424 Orientation of the benzene- -ring, 563-566 of giiee rings, 569, 571, 573, 795, 797, Ornithine, 786 Orpiment, red, 225, 232 yellow, 225, 232 Orsellinic acid, 691, 749 Orthite, 431 Ortho-, meta-, and para-compounds, 564 acetic acid, 667 acids, 91 antimonic acid, 478 arsenic acid, 231 boric acid, 92, 289, 290 carbonic acid, 91 eresol, 747 dibromobenzene, 564 formic ether, 658 phosphates, 91 phosphoric acid, 91 silicic acid, 91, 282, 283 stannic acid, 489 sulphuric acid, 91 toluidine, 699 Orthoclase, 425 Osazones, 764, 802 Osmamines, 535 Osmic acid, 529 (per) anhydride, 534 Osmiridium, 529 Osmium, 529-537, 584 its properties ‘and compounds, 535 ore, its analysis, 537 Osmosis, 317 Osmotic membrane, 317 pressure, 317, 319, 330 law of, 319 Osones, 764 Osotriazole, 802 Ossein, 790, 803 -ous, 59 Ovalbumin, 788 Oxalates, 625 Oxalethyline, 704 Oxalic acid, 246, 557, 583, 602, 624 aldehyde, 597 ether, 669 Oxalite, 625 Oxalonitrile, 734 Oxalovinic acid, see ethyl-oxalic acid, 669 Oxaluramide, 810 Oxaluric acid, 810 Oxalyl urea, 810 Oxamethane, 704 Oxamic acid, 707 Oxamide, 669, 704 Oxanthranol, 754 Oxazines, 806 Oxazoles, 801 Ox-gall, 714, 794 Oxidation, 58, 99 Oxide, definition of, 58 Oxides, 51, 58, 304, 306 basia, ‘61, 88, 112 Oxides, classification, 51 density of, 305, 306 different ‘reactions with hydrochloric acid, 112 neutral or indifferent, 51, 88 per-, 51, 88, 112 types of, 51 Oxidising agent, 99, 143, 158, 194, 375 flame, see Flame, 268 Oximes, 641, 648 Oximide, 707 Oxindol, 714, 798 Oxonium, 137, 180 salts, 807 Oxy-acetylene blowpipe, 255 Oxy-acids, gee also hydroxy-acids, 198 Oxycalcium light, 209 Oxycellulose, 774 Oxychlorides, 113 Oxygen, 2, 21, 24, 49, 50, 51, 54-63, 77, 100, 101, 114, 117, 118, 120, 129, 187, 180, 264, 361, 461, "499, "7150" absorption, 63, 672 by compounds, 63 active, 138 available, 101, 461, 463 basic, 807 carrier, 103 combustion in, 59 determined, 540 discovery of, 49 extracted from air, 54 liquefied, 84, 86 mixture, 57 nascent, 100, 115 occlusion of, 58, 518, 529 preparation, 54-57 pierre cheese. 58 sical, Oe en b3¢ test for free, 63, 200 tetravalent, 245, 352, 807 Oxyhemoglobin, 63, 792 Oxyhydrogen plowpipe, 268 Oxymorphine, 817 Oxynaphthylamine, 700 Oxyphenic acid, 748 Ozokerite, 549 Ozone, 14, 127, 137, 188-142, 212, 351 constitution, 141 test for, 139 Ozonic ether, 143 Ozonide-peroxide, 141 Ozonides, 141, 611, 673 Ozonisation by phosphorus, 139 Ozonised oxygen, 129 Ozonising apparatus, 139 Parn7(s), discolouring of, 153 luminous, 394 Paintings, effect of light and air on, 153 Palladium, 97, 529-537, 533 ammonium chloride, 533, 534 cyanide, 529, 533, 534 halides, 533 nitrates, 533 ore, analysis of, 537 oxides, oF spongy, mee of for mirrors, 533 Palm oil, 608, 673 Palmitic acid, a aldehyd Palmitin, 168° en 672, 673 860 INDEX Palmitolic acid, 613 Pandermite, 378 Papaverine, 819 Paper, 773, 774 action of nitric acid on, 774 conversion into glucose, 576 Para-azoxy-anisoil, 337 Parabanic acid, 809, 810 Parabin, 773 Para-compounds, 564 Paraconiine, 814 Paracresol, 747 Paracyanogen, 722 Paradiazines, 806 Paraffin, 547 derivation of term, 547 hydrocarbons, see Hydrocarbons oil, 548, 549 series, see Hydrocarbons wax, 143, 339, 549 Paraffins, cyclo-, 558 iso- or secondary, 553 neo- or tertiary, 553 normal, 553 production, forms and varieties, 548, Paraformaldehyde, 593 Paraguay tea, 813 Paralactic acid, 618 Paraldehyde, 595, 638, 641, 805, 814 Paramucic acid, 632 Paranthracene, 573 Pararosaniline, 757, 758, 759 Parchment paper, 169, 773 vegetable, 169 Paris green, 231 yellow, 505 Parkes’ process, 498 Partial pressures, law of, 79, 80 saturation, method of, 601 Parting of gold, 169 Parvoline, 803 © Passive state, 452 Pasteur, 637 Patent yellow, 505 Pattinson’s oxychloride, 504 process, 474, 497 Paviin, 779 Pea iron ore, 435 Pear flavouring, 668 Pearlash, 358 Pearl hardener, 393 Pearl-spar, 404 Pearl white, 475 Pearls, composition, 64 Peat-bog, 271 composition of, 271, 279 Pechiney process, see Weldon Pechiney Pelargonic acid, 608 ether, 668 Pellicle, 38 Penicillium, 637, 638 Pentad elements, 13 Pentamethylene, 558 constitution of, 553 diamine, 701, 804 imide, 804 Pentane(s), 547, 558 constitution of, 553 isomeric, 553 Pentathionic acid, 174 Pentosans, 772 Pentoses, 599, 761, 784 Pentylene, 556 ; see Amylene Pepper, 623 Peppermint, oil of, 678 Pepsin, 788 Peptones, 784, 785, 787, 788 peptonising, 788 Perborates, 290 Perborax, 379 Percarbonic acid, 249 Perchloracetic ether, 667 Perchlorates, 121 Perchlorethane, 659 Perchloric acid, 120 anhydride, 120 Perchlorinated ether, 653 Perchromic acid, 144, 465 Percussion cap composition, 480, 742 fuse, 119, 120 Perfume ethers, 664 Perfumes, extraction of, 674 Perhydrol, 142 Periclase, 403 Pericline, 425 Periodates, 130 Per-iodic acid, 92 Periodic classification, '7, 8, 89, 98, 135, 137, 294, 299, 300, 301-306, 432, 494, 683 law, 7, 8, 801, 335, 428 applications of, 303 tables, 8, 802, 432 Perkin, 30, 615, 623, 676, 679, 819 Perlite, 437 Permanent changes, 1 ink, 520 white, 385 Permanganates, 462, 463 Permanganic acid, 462, 463 anhydride, 462 Permeability, 334 Permeable membranes, 317 metals, 98 Permonosulphuric acid, 171 Permutites, 426 Peronine, 818 Perowskite, 490 Persulphocyanic acids, 737, 738 Persulphuric acid, 143, 170, 362 anhydride, 155, 170 Perthiocyanogen, 738 Peru, balsam of, 584, 668 Peruranates, 472 Peruvian bark, 819 Petalite, 383 Petrifying springs, 45 Petroleum, see also Paraffin spirits, varieties and properties, 548 Pettenkofer’s test for bile, 794 Pewter, 476, 486 solder for, 474, Pfeffer, 317, 318 Pharaoh’s serpent, 738 Phase rule, 138, 337 Phellandrene, 674, 676 Phenacetine, 745 Phenanthraquinone, 756 Phenanthrene, 569, 578, 756, 817 Phenanthridine, 805 Phenanthroline, 805 Phenazine, 807 Phene, 559 Phenetol, 655 Phenic acid, see Phenol, 744 Phenol, 620, 716, 744 acids, 619 INDEX 861. Phenol alcohols, 584 aldehydes, 598 blue, 753 properties of, 744 test for, 744, 745 Phenols, 545, 559, 570, 584, 748-751, 598 converted into hydrocarbons, 744, 745 monohydric, 744 Phenol-sulphonic acids, 743, 747 phthalein, 759 Phenomena, definition, 1 physical, 296 of liquids, 314, 316 of surfaces, 315 Phenoxazine, 806 Phenyl, 566 acetate, 668 acetic acid, 613, 734 acetonitrile, 734 acetylene, 568 acrolein, 598 acrylic acids, 614, 615 allyl alcohol, 585 amine, 697 aniline, 699 azoimides, 721 bromide, 660 carbamine, 658, 735 carbinol, 584 chloride, 660 chloroform, 660 cyanide, 710, 734, 735 dimethylpyrazolone, 802 ether, 654 ethyl amine, 746 ether, 654 isothiocyanate, 740 mustard oil, 740 ethylene, 567, 615 formic acid, 613 glycocine, 710, 800, 801 glycollic acid, 619, 621 glyoxylic acid, 650 hydracrylic acid, 815 hydrazine, 596, 648, 716, 719, 764, 802 hydrazones, 720 hydrosulphide, 745 hypophosphorous acid, 692 isocyanide, 735 keten, 606 mercaptan, 745 methane, 566 methyl ether, 654 pyrazolone, 802 olefinic acids, 614 orthophosphate, 745 . phenyl (diphenyl), 568 phosphine oxides, 692 phosphines, 692 phosphinic acid, 692 propiolic acid, 615 propionic acid, 615 salicylate, 668 sulphide, 801 sulphuric acid, 665 toluenes, 569 Phenylene blue, 753 brown, 718 diamines, 683, 701, 718, 753, 805, 807 Philosopher’s wool, 407 Phlobaphenes, 623 Phlogiston, 48 Phloramine, 750 Phosphoretted hydrogen, see Phloretin, 779 Phlorizein, 779 Phlorizin, 750, 779 Phloroglucol, 750 Phlorol, 748 Phorone, 648 Phosgene gas, 249 Phospham, 224 Phosphaniline, 692 Phosphates, 217 et seq. mineral, 209 Phosphenyl chlorides, 692 Phosphenylic acid, 692 Phosphenylous acid, 692 Phosphides, 214, 216 Phosphine (dye), 806 Phosphines, 691, 692; see also Hydrogen phosphide Phosphobenzene, 692 molybdate of ammonium, 470 . molybdic acid, 812 nitrile, 224 Phosphonium compounds, 217, 691, 692 Phosphoproteins, 784, 789 Phosphor-bronze, 487 Phosphorescence, 212, 221, 291, 355, 356, 394, 688 Hydrogen phosphide Phosphoric acid, monohydrated, 219 dihydrated, 220 trihydrated, 220 acid(s), 50, 217, 256 glacial, 218 acids (various) and their salts, 217-222 anhydride, or oxide, see Phosphorus pentoxide Phosphorised oil, 212 Phosphorite, 209, 218, 394 Phosphorous acid, 59 basicity of, 221 anhydride, or oxide, see Phosphorus trioxide Phosphorus, 50, 58, 123, 139, 181, 194, 201, 209-284, 261, 311, 441, 655 action of potash on, 216 of on metals, 214 allotropic varieties, 211, 213 amides, 224 amorphous, 213 and dry oxygen, 58 (note) bases, see Phosphines, 691 bromides, 123, 224 burnt under water, 120 chlorides, 198, 228, 311 cyanides, 738 ; estimation of, in organic compounds, 539 fluoride, 223 halides, 223 et seq. hydrides, 216 iodides, 128, 224 luminosity of, 212 match, 214 oxidation of, 212 oxides, 217-222 oxyfluoride, 132 pentabromide, 219 pentachloride, 592 pentoxide, 50, 59, 160, 219 red, 211, 213, 224 reduction of metals by, 214 salt, 383 sesquisulphide, 215 862 Phosphorus suboxide, 222 sulphides, 222, 745, 796 sulphochloride, 224 trichloride, 223, 317, 662, 738 trioxide, 59 vitreous, 21] yellow, 211 Phosphory] chloride, 223 Phosphurets, 214 Photochemical action, 106 Photochemistry, 12, 172, 174 Photographic plates, 521 printing, 172, 472 Photography, 12, 171, 625, 805 Photo-reduction, 522 Photo-salts, 521 Photo-sensitising agent, 512 Photosynthesis, 54, 63, 781 Phthalic acids, 567, 571, 628, 638 anhydride, 628, 749, 760, 800 Phthalide, 663 Phthalimide, 800 Phthalyl dichloride, 663, 754 Phycite, 591 Phylloporphyrin, 793 Physetolein, 673 Physical chemistry, 13, 296 properties, 1, 30 Physico-chemical properties, 307 Physics, 1, 30, 296 Physostigmine, 822 Phytol, 782 Phytosterol, 585, 671 Phytyl chlorophyllide, 782 Picnometer, 31 Picolines, 804, 814 Picramic acid, 746 Picric acid, 118, 571, 743, 745, 746, 788, 812 Picrotoxin, 781 Pictet, 84 Pig iron, 439, 442 phosphoric, 446 Pilocarpine, 822 Pimelic acid, 627 Pinacones, 588 Pine-apple flavouring, 668 Pine-needle oils, 676 Pinene, 570, 674, 675 Pinic acid, 675 Pink salt, 489 Pinonic acid, 675 Piperazine, 700, 807 Piperic acid, 599, 623, 814 Piperidine, 804, 812, 814 Piperine, 814 Piperonal, 599 Pitch-blende, 399, 472 Plane-symmetrical configuration, 638 Plants, see Vegetable Chemistry action of, on carbon dioxide, 54, 63 nutrition of, 209 Plaster of Paris, 392 Plate powder, 394 sulphate, 376 Platina muriate, 532 Platinammine derivatives, 532, 533 Platinates, 531 . Platinic acid, 531 Platinichlorides, 532 Platinicyanides, 732 Platinised asbestos, 166, 201 Platinite, 459 Platinochlorides, 532 INDEX Platinocyanides, 732 Platinoid (alloy), 459 pee 97, 191, 230, 261, 269, 326, 529- alloy, 134 ; ammonio-chloride, 529, 531 applications, 15, 165-167, 364, 511 arsenide, 230, 533 black, 531 | bronzing by, 511, 532 chlorides, 529, 581, 812 corroded, 531 cyanides, 732 fulminating, 531 group, review of, 536 hydroxide, 531 iodide, 533 occlusion of oxygen, 529, 581 ores, analysis, 537 treatment of, 529 oxides, 531 phosphide, 533 properties of, 529 silicide, 284 -silver chloride, 532 spongy, 529 stills, 132, 165, 527 substitute for, 459 sulphides, 533 wire (Wollaston), 530 Platodiammine chloride, 532 hydroxide, 532 Platosammine chloride, 533 oxide, 532 Pleonaste, 453 Plumbago, 237 Plumbates, 502 Plumbic anhydride, 502 Plumbite, 501 Polarimeter, 634 Polarisation, electrical, 15 of light, 634 Polarised light, 633 Pole, negative and positive, 15 Pollux, 384 Polonium, 401 Polyatomic, 310 Polychroite, 782 Polyhalite, 404 Polyhydroxy-monobasic acids, 619 Polymerides, definition, 553 Polymerism, 553 Polymethylenes, 558, 56] Polypeptides, 785, 787 Polyprene, 679 Polysaccharides, 760, 770 Polysilicic acids, 283 Pope, 335, 640 Poppy, 817 Populin, 779 Porcelain, 283, 426-428 Berlin ware, 427 biscuit ware, 427 glazing, 427 painting and gilding, 428 Porous cell, &c., 15, 317, 374 Porosity, 334 Porphyry, 390, 425 Porrett, 722 Portland cement, 391 stone, 390 Positive change,"343 Potash, 358, 359 -albite, 425 INDEX 863 Potash bulbs, 539 caustic, see Potassium hydroxide red prussiate, see Potassum ferricyanide Potassamide, 188 Rotem 18, 97, 153, 245, 858-367, 402, 99 action on water, 18° alizarate, 754 aluminium silicates, 283 anilide, 699 antimonates, 478 antimony oxalate, 625 antimony] tartrate, 631 arsenite, 230 aurate, 527 auricyanide, 732 aurocyanide, 731 azoimide, 721 azosulphonates, 715 barium ferrocyanide, 728 benzene diazotate, 716 beryllate, 412 bicarbonate, 359 bichromate, 53, 466 bismuthic iodide, 812 bisulphate, 143 bitartrate, 41, 680, 631 bromate, 124 bromide, 123, 361 calcium chromic oxalate, 625 ferrocyanide, 728 carbamate, 381 carbethylate, 666 carbon monoxide compound, 360 carbonate, 358, 696 carbonyl ferrocyanide, 730 carbovinate, 666 chlorate, 56, 117, 361, 362, 463 heat of decomposition, 118 chloride, 358-363, 861, 696 chlorochromate, 468 chromate, 466 chromic oxalate, 625 chromicyanide, 730 cobaltic nitrite, 457 cobalticyanide, 727 cobaltocyanide, 726 cyanacetate, 625 cyanate, 381, 726, 737 cyanide, 153, 440, 517, 705, 723, 724, 725 cyanurate, 737 dichromate, see Bichromate dimetantimonate, 478 ethyl carbonate, 666 sulphate, 586 ethyloxalate, 669 ferrate, 454 ferric ferrocyanide, 728 ferricyanide, 729, 817 ferrocyanide, 93, 705, 728, 727, 729 ferrous ferrocyanide, 724, 728 oxalate, 625 fluoride, 134, 362 fluorplumbate, 134 fluosilicate, 288 fluozirconate, 492 formate, 603, 726 fulminurate, 743 guaiacol, 748 hydrate, see Potassium hydroxide hydride, 361 hydrogen fluoride, 132 hydrosulphide, 153 Potassium hydroxide, 52, 88, 359 hypophosphite, 216 iodate, 362 iodide, 126, 361 isethionato, 714 isocyanate, 705, 737 isothiocyanate, 738 malates, 629 malonate, 625 manganate, 462 manganicyanide, 730 manganocyanide, 730 mercuric cyanide, 731 iodide, 812 metabisulphite, 159 metal, 360 metantimonate, 478 metastannate, 488 myronate, 740 nitrate, 37, 48, 49, 52, 181, 192, 196, 362-367, 815 nitrite, 53, 864 nitroprusside, 730 oleate, 608, 612 osmium compounds, 535 oxalates, 624, 625 oxides, 360, 361, 426 palmitate, 608 perchlorate, 56, 120, 121, 361 permanganate, 57, 102, 121, 463 perosmate, 535 persulphate, 143, 170, 362 phenol sulphonate, 747 phenoxide, 745 phenyl-sulphate, 665 picrate, 746 platinichloride, 533 platinicyanide, 732 platinochloride, 532 platinonitrite, 533 plumbate, 502 plumbite, 501 pyroantimonate, 478 pyrosulphate, 362 -pyrrol, 684 racemates, 637 saccharates, 631 silicofluoride, 284, 288 stannates, 488 succinate, 555 sulphates, 385, 358, 362, 740 sulphides, 170, 362, 671, 775 sulphindylate, 799 sulphocyanide, 737 tannate, 622 tartrates, 630 tartryl-antimonite, 631 test for, 361 thio-antimonates, 480 thio-antimonites, 480 thio-arsenite, 232 thiocarbonate, 176 thiocyanate, 737 titanate, 491 trichromate, 466 trithionate, 173 urates, 808 zincate, 409 Potato spirit, 582 starch, 770 Potential energy, 341 gradient, 330 Pottery, 426 Praseo-dymium, 431, and compounds, 433 864 INDEX Press cake, 365 Pressure coefficient, 9, 74 influence of, 33 of gases, 9, 137, 308, 318, 319 osmotic, 317, 319, 330 partial, law of, 347 Preston salts, 380 Priestley, 49, 63, 108 Primary amines, 693 Principles, 286 Producer, 246, 274, 445 -gas, 246, 274, 408, 446 Proline, 786 Promethean light, 120 Proof spirit, 577 Propadiene, 556 Propane, 547, 551, 558 (cyclo) constitution of, 547, 551 Propargy! alcohol, 583, 612 chloride, 659 Propenyl derivatives, 588, 669, 678 Propeptone, 788 Properties, various, 1, 4, 299, 307 Propine, 557 Propinyl alcohol, 583 Propiolic acid, 612 Propione, 648 Propionic acid, 606, 610 aldehyde, 596, 797 Propionitrile, 734, 735 Propyl acetylene, 679 alcohols, 582 amine, 696 benzoic acid, 614 carbinol, 582 hydride, 551 piperidine, 814 tetrahydro-pyridine, 814 Propylene, 556 glycol, 587 Prosthetic groups, 784, 792 Protagon, 793 Protamines, 784 nucleate, 792 Proteids, see Proteins Protein derivatives, 784 Proteins, 181, 746, 784-794, 806, 811 Proteoses, 784 Prothrombin, 789 Protocatechuic acid, 621, 750 aldehyde, 599 Protyle, 301 Proust, 4 Proustite, 225 Prout’s hypothesis, 301 Proximate organic analysis, see Organic analysis : Prussian blue, 455, 721, 724, '727 soluble, 728 green, 729 test, 725 Prussiate of potash, 723, 729 Prussic acid, 721 ; see Hydrocyanic acid Pseudaconine, 822 Pseudaconitine, 822 Pseudo-acids, 785 bases, 785 Pseudobutylene, 556 Pseudoform, 736 Pseudojervine, 822 Pseudonitrols, 581 Pseudosulphocyanogen, 738 Pseudourea, 706 Psilomelane, 461 Ptomaines, 701, 788 Ptyalin, 771 Puddled bars, 445 steel, 445 Puddling, 443 Pulp (ores), 407 Pulvis fulminans, 365 Pumice stone, 283, 421 Purbeck stone, 391 Purine and derivatives, 784, 806, 809, 811, 812, 813 Purple of Cassius, 526 Purpureo-cobalt salts, 458 Purpurin, 755 Purrée, 783 Putrefaction, 64, 182, 696, 746, 788 Putrescine, 701 Putty powder, 488 pv = RT, 309 Pyrazine, 806 Pyrazoles, 801, 802 Pyrazolidines, 802 Pyrazolidones, 802 Pyrazolines, 802 Pyrazolones, 802 Pyridine, 559, 662, 668, 790, 808, 812 a solvent for lithium salts, 383 alkaloids, 814 carboxylic acid, 815 dicarboxylic acid, 805 Pyridones, 804 Pyrimidin and derivatives, 784, 806, 811 Pyrites, arsenical, 225 burners, 163 capillary, 460 copper, 147 efflorescent, 161 Fahlun, 178 iron, see Iron magnetic, 456 oxidation in air, 161 radiated, 456 spent, 508 white, 161, 456 Pyroacetic spirit, 648 ; see Acetone Pyroantimonic acid, 478 Pyroarsenic acid, 231 Pyroboric acid, 289 Pyrocatechol, 599, 621, 747, 755 tannins, 622 Pyrocitric acids, 628 Pyrocomenic acid, 632 Pyrogallic acid, see Pyrogallol Pyrogallol, 52, 621, 622, 750 -phthalein, 750 tannins, 622 Pyroligneous acid, 238, 578, 603 ether, 578 Pyrolusite, 461 Pyrometer, 534 Pyromucic acid, 599, 632, 795 aldehyde, see Furfural Pyrone, 668, 807 Pyrophoric iron, 62 Pyrophorus, lead, see Lead Pyrophosphates, 220 Pyrophosphoric acid, 220 Pyroracemic acid, 649 aldehyde, 649 Pyrosulphites, 159 Pyrosulphuric acid, 160 Pyrosulphurous acid, 159 Pyrosulphuryl chloride, 250 Pyrotartaric acid, 627, 795 EE ae Pyrotechny, &c., 119, 150, 232, 386, 480 Pyrotritartaric acid, 795 Pyroxanthin, 579 Pyroxylic spirit, 578 Pyroxylin, 775 soluble, 777 Pyrro-azoles, 802 diazole, 802 triazole, 803 Pyrrol, 782, 786, 790, 795, 796 -red, 796 Pyrrolidine, 796 carboxylic acid, 786 Pyrroline, 796 Pyruvic acid, 618, 649, 669 QUADRIVALENT elements, see Valency Qualitative reactions, &c., 4 Quantitative reactions, &c., 4 Quartation of gold, 526 Quartz, 280, 282, 420, 440, 646 artificial, 283 Quassia, 781 Quassiin, 781 Quercetin, 780 Quercitannic acid, 622 Quercitrin, 761, 780 Quercitron, 780 Quicklime, see Calcium oxide Quicksilver, 412 Quillaia, 780 Quinaldine, 805 Quinazoline, 806 Quince oil, 668 Quinetum, 819 Quinhydrone, 753 Quinic acid, 623, 819 Quinicine, 820 Quinidine, 819, 820 Quinine, 819 amorphous, 820 sulphates, 820 Quinoidine, 820 Quinol, 749 ; see Quinone -dicarboxylic acid, 753 Quinolic acid, 804 Quinoline, 803, 804, 805, 812 bases, 804-822 cyanine, 805 red, 805 yellow, 805 Quinone and derivatives, 749, 752, 753 chlorimides, 753 Quinones, 751-760 Quinonoid structure, 757, 758 Quinotannic acid, 819 Quinoxaline, 807 Quinquivalent elements, see Valency RacematTeEs, 637 Racemic acid, 630, 687-640, 649 Racemisation, 638, 640, 676 Radiant matter, spectroscopy, 355 Radicles, 88, 197, 614 alcohol, 580 alkyl, 548 aralkyl, 566 aromatic, 566 aryl, 566 ; . organic, see Organic chemistry Radio-active equilibrium, 400 Radio-activity, 296, 356, 399-401, 472 Radiography; 356 © INDEX 865 Eee 294, 307, 356, 357, 399-401, 4 bromide, 399 chloride, 399 disintegration, 295, 400-401 emanation, see Niton metal, 400 oxide, 307 Raffinose, 760, 770 Rain, 41, 142 Raisins, 761 Ramsay, 49, 87, 293, 294, 295, 316, 320, 322, 357, 401 Rancidity, 672 Ransome’s artificial stone, 379 Raoult’s method, 320, 321, 322 Rape-oil, 612, 673 Rare earths, 304, 401, 431 gases, 293, 305-307 Raschig, 165 Ratio of densities, 305-307 Ratio of specific heats of gases, 311 Raw oil, 673 Rayleigh, 49, 53, 293 Rays (general), 356 a, 356, 400 B, 356, 400, 493 7, 356, 400, 493 6, 356 X, 237, 356, 732 cathode, 356 Reactions, complete, 342 reversible, 50, 128, 315, 342 Realgar, 225, 232 Réaumur’s porcelain, 398 Reciprocal combustion, 264 Rectified spirit, 577 Red antimony ore, 480 dyes, 719, 807 fire, see Pyrotechny lead, 49, 502 ochre, 435 paints, 419 precipitate, 415 prussiate of potash, see Potassium ferricyanide sanders-wood, 783 -shortness, 445 Redonda phosphate, 426 Reducing agent, 99, 143, 154, 158, 202, 422, 726 flame, see Flame, 268 Reduction, 99, 128 on charcoal, 268 Refining, electric, 451 Refraction equivalent, 646 of saltpetre, 363 Refractive index, 353 power, 646 Refrigerator, Carré’s, 80 Regenerative cooling, 85 firing, 445 heating, 279 Regulus of antimony, 476 Reichert value, 672, 673 Reimer’s reaction, 598, 599 Rennet, 789 Resenes, 679 Residual affinity, 332 Resin(s), 674, 679 alcohols, 679 esters, 679 Resinolic acids, 679 Resinols, 679 55 866 Resinotannols, 679 Resolution of stereoisomers, 637 Resorcin-phthalein, 749 yellow, 719 Resorcinol, 748 disazobenzene, 719. Resorufine, 806 Respiration, 54, 63, 68 Retene, 573 Reverberatory furnace, see Furnace Reversible reactions, 50, 128, 315, 342 Reverted phosphate, 359 Rhamno-hexose, 763 Rhamnose, 761, 780 Rhigolene, see Petroleum spirit Rhodium, 529-537 its properties and compounds, 534 ore, analysis of, 537 Rhombic crystals, 336 Ribose, 761 Rice, 770 Richards, 334, 567 Richter, J. B., 4 Ricinelaidic acid, 619 Ricinoleic acid, 619, 673 Rinmann’s green, 458 Roasting, chlorinating, 517 ores, 438 sulphides, 154 Robiquet, 722 Rocellic acid, 627 Rochelle salt, 631 Rock crystal, 280, 395, 646 moss, 749 oil, 548 salt, 367 Roebuck, 161 Roman cement, 391 Réntgen, 356, 732 Rosaniline, 569, 594, 758, 759 acetate, 758 nitrate, 758 salts, 758 Roscoclite, 480 Rose, otto of, 678 Roseo-cobalt salts, 458 Rosiclers, 522 Rosin, 674, 679 oil, 679 spirit, 679 Rosinates, 672 Rosindulenes, 807 Rosocyanin, 782 Rosolic acid, 759 Rotary kiln, 391 Rotation, optical, 634 ; see Optical Rotatory power, 634, 674 Rouge, 783 Rubber substitute, 673 Ruberythric acid, 754 Rubidine, 803 Rubidium, 121, 358, 388, 402 chloroplumbate, 505 Rubijervine, 822 Ruby, 424, 467 Rue, essential oil of, 649 Rufigallic acid, 621, 755 Ruhmkorff’s induction-coil, 17 Rupert’s drops, 398 Rust, 2, 452 and ammonia, 452 -joint cement, 150 Ruthenium, 529-537 its properties and compounds, 535 INDEX Ruthenium ore, analysis, 537 tetraoxide, 345 Rutherford, 48 Rutic, aldehyde, 596 Rutile, 490 Rutin, 780 SACCHARATES, see Sucrates, 768. Saccharic acid, 63] Saccharides, 760 Saccharin, 703 Saccharobioses, 760, 766 Saccharotrioses, 760 Safety lamp, 260 Davy’s, 259, 260 Stephenson’s, 259 Safflower, 783 Saffron, 782 bronze, 471 Safranines, 807 Sagapenum, 749. Saggers, 427 Sal-alembroth, 416 ammoniac, 182, 183, 881, 490; see Ammonium chloride -gemme, 367 Salicin, 584, 620, 778 Salicyl alcohol, 584, 778 aldehyde, 585 Salicylates, 620 Salicylic acid, 585, 619, 663, 745 aldehyde, 598 chloride, 663 Salicylide, 324, 620 Saligenin, 584, 598, 778 Salipyrine, 802 Saliretin, 779 Saliva, 771 Salol, 620, 668, 747 Sal prunelle, 364 volatile, 381 Salt cake, 109, 369 common, see Sodium chloride defined, 92 electrolysis of, 373 glazing, 428 ; of lemons, 625 of sorrel, 625 of tartar, 630 radicles, 135 table, see Sodium chloride, 375 Saltpetre, see Potassium nitrate and Sodium nitrate Chili, 367, 379 ‘ cubical, 379 flour, 364 impurities in, 364 made from sodium nitrate, 363 Peruvian, 379 prismatic, 362, 379 refining, 363 Salts, 51, 88, 92-94 acid, 92 basic, 93 changes of colour in solution, 324 classification of, 92, 93 constitution of, 92-94 | double, 92 electrolysis of, 328 fused, and electricity, 331: F normal, 92 Salvarsan, 691 Samaria, 431 Samarium and compounds, 433. Samarskite, 431 Sand, 280, 395 P Sandarach resin, 679, 783 Sandemeyer’s reaction, 716 Sandstone, 390 Craigleith, 390 Santalin, 783 Santonic acid, 781 Santonin, 781 Saponification of esters, 664 theory of, 608, 664, 671 value, 672, 674 Saponin, 780 Sappan wood, 783 Sapphire, 424 Sarcine, 812 Sarcolactic acid, 618, 635 Sarcosine, 710 Sassafras, 608 Satin spar, 388 Saturated compounds, 542, 543 solution, 37 vapours, 33 Sawdust, 624 Saxony blue, 799 Scale, boiler, 44 Scammony, 780 Scandia, 431 Scandium, 431, 433 Scheele, 49, 101, 131, 589, 721 731 Scheele’s green, 231, 513 Scheelite, 471 Schiff’s reagent, 594 Schlippe’s salt, 480 Schénbein, 138 Schotten-Baumann’s reaction, 662 Schultze’s powder,.777 Schwanhardt, 131 Schweitzer’s reagent, 774 Sclero-proteins, 784 Scopolamine, 816 Scorifying mould, 509 Scotch pebbles, 280 Scott’s cement, 392 Scurvy-grass, oil of, 74] Sea-water, 41, 45, 124 action on lead, 501 extraction of salts from, 368 weed, 124, 125, 773 ‘Sebacie acid, 611, 627 Secondary amines, 693 cells, 502 paraffins, 553 ‘Seeds, composition, 209 Seidlitz powders, 70, 631 ‘Beignette’s salt, 631 ‘Sel d’or, 528 ‘Selective absorption, 425 ‘Selenates of the alkalies, 299 ‘Selenic acid, 178, 527 Selenides, 178 ‘Selenietted hydrogen, 179 “Selenious acid, 178, 527 ‘Selenite, 392 Selenium, 178, 180, 233, 641 chlorides, 179 dioxide, 178 sulphides, 179 * Selenophen, 796 3s. . Self- burning gas, 267 -reduction, 476, 495. -oxidation, 120 Bellaite, 131 “Reltzer water, 64 INDEX 867 Semicarbazide, 721 Semicarbazones, 720 Semidine migration, 720 Semi-drying oils, 672 Seminine, 763 Seminose, 763 Semi-water gas, 275 Senarmontite, 477 Sensitising agent, 522 Separating funnel, 256 Sericin, 791 Serin, 785, 791 Serpent’s urine, 807 Serpentine, 283, 404 Serum albumin, 784, 788 globulin, 784, 789 ° Sesame oil, 673 Sesqui-terpenes, 676 Sewage, 42 Shaft, downcast and upcast, 69 Shale oils, 549 Shear steel, 449 Sheep-dipping composition ,230 Shell-lac, 679, 783 , Shells of fish, 791 Shields, 316 Shot, 500 Siberian red-lead ore, 466 Siderite, 232, 454. ' Siemen’s regenerative furnace, 279 Siemen-Martin process, 443, 445 Sienna, 421 Signal-light composition, 232 Silica, 3, 280, 379, 390, 394 glass, 396 vapour, 396 Silicates, 92, 280, 288, 287 Silicic acid, 91, 282, 283 anhydride, 210 ether, 666 similarity to stannic acid, 488 Silicium, see Silicon Silico-acetic acid, 285, 688 acetylene, 285 chloroform, 286 ethane, 286 fluorides, 133 nonane, 688 nonyl-alcohol, 688 chloride, 688 oxalic acid, 286 ropionic acid, 688 Silicon, 280-288, 284, 292, 437, 441, 490 alkides, 285, 688 amide, 285 amorphous, 284 borides, 285 carbide, 284 copper, 515 crystalline, 284 disulphide, 288 ethide, 688 ethoxides, 688 halides, 285 hexachloride, 286 hydride, 285 imide, 285 methide, 688 monosulphide, 288 nitride, 285 organic compounds of, 640 stereochemistry of, 640 tetrabromide, 286 tetrachloride, 286 868 INDEX Silicon tetrafluoride, 133, 286 tetraiodide, 286 Silicones, 285 Silk, artificial, 512 -gelatin, 791 Siloxicon, 285 Silver, 58, 97, 169, 269, 375, 413, 474, 495, 515-522, 524 acetamide, 702 acetate, 604 acetylide, 557 allotropic, 519 amalgam, 414 amalgamation process, 516 ammonio-nitrate, 520 arborescent, 516 arsenate, 522 arsenite, 522 auricyanide, 732 azoimide, 189 bichromate, 467 bromide, 300, 521 carbonate, 520 chloride, ammoniated, 83 chlorides, 83, 171, 516, 518, 520 chromates, 467 citrate, 519 coin, 517 colloidal, 419 crucibles, 519 cyanide, 517, 725, 781 cyanurate, 736 dead, 517 dendritic, 516 detected in lead, 499 extraction by amalgamation, 414, 516 electrolytically, 516 from copper ores, 516 from lead, 498 from ores, 516 ferricyanide, 728, 729 ferrocyanide, 728 fineness of, 517 fluoride, 133, 522 frosted, 517 fulminates, 742-743 fulminating, 519 fusing-point, 518 lycocoll, 710 he poniteite, 206. hyposulphite, 172 iodide, 521 isatin, 798 isocyanate, 706 meconates, 632 metaphosphate, 221 native, 516 * nitrate, 519 nitride, 519 nitrite, 520 nitroprusside, 730 occlusion of oxygen, 518 ore, red, 522 orthophosphate, 221, 522 oxalate, 625 oxides, 519 oxidised, 517 paracyanide, 731 periodate, 130 peroxide, 140 phosphate, 522 photo-salts, 521 plating, 517 properties of, 518 Silver, pure, preparation of, 518 pyrophosphate, 221 refining, 516 solder, 517 sprouting of, 518 standard, 517 sub-chloride, 520, 521 succinimide, 684, 704 sulphates, 169, 516, 522 sulphide, 153, 516 sulphite, 522 tartrate, 631 theobromine, 813 thiosulphate, 172 tree, 414 Silvering, 517, 518 dry process, 517 Sinamine, 740 Siphon eudiometer, 26 Sitosterol, 585, 671 Sitosteryl acetate, 585 Size, 791 Skatol, 797 Skraup’s method, 804, 805 Slag basic, 446 blast-furnace, 430, 440 iron-refinery, 443 lead-furnace, 496 wool, 44] Slaked lime, see Calcium hydroxide Slate, 283 Slip, 427 Slow port fire, 364 Smalt, 458 Smelling-salts, 380 Smelting, electric, 451 Smithsonite, 409 Smoke, 272 Smokeless gas burners, 266 powder, 366 Smut, 513 Snow, 30, 142 Snuff, 815 Soap, 43, 368, 369, 589, 608, 612, 671 arsenical, 230 glassmaker’s, 398 -making, kelp used in, 124 white curd, 609 Soda, 372 - action on hard waters, 46 ash, 371 caustic, see Sodium hydroxide of, 373 -crystals, 371, 372 -lime, 258 -lye, 373 manufacture, 369 washing, 372 -waste, 171 -water, 70 Sodamide, 188 Sodium, 18, 20, 61, 97, 245, 358, 367-380, 421, 523, 720 acetate, 40, 257, 605 acetylide, 557 action on water, 20 alizarate, 755 aluminate, 42] amalgam, 375, 414 in gold extraction, 523 eee hydrogen phosphate, 220, 83 racemate, 637 and oxygen, 61 INDEX Sodium anthrapurpurate, 755 antimonites of, 477 arsenates, 378 arsenite, 230 aurochloride, 528 aurosulphide, 528 aurothiosulphate, 528 azoimide, 189 bicarbonate, 372, 373 bichromate, 465, 466 bisulphate, see Sod. sulph. acid. bisulphite, see Sodium Hydrogen sulphite borates, 378 bromide, 123 carbonate, 38, 368-373 Castner-Kellner process, 373 chlorate, 380 cna 47, 101, 108, 341, 367-374, chromate, 465, 466 cyanurate, 736 ditungstate, 471 equivalent weight, 20 ethide, 686 ethoxide, 543, 578 extraction, 375 ferrite, 373 fluoride, 367, 376 formate, 602 fulminate, 742 glyceroxide, 590 glycol, 588 hydride, 375 hydrogen carbonate, 373 sulphate, see Sod. sulph.acid. sulphite, 376, 594, 648 hydroxide, 16, 20, 88, 96, 371, 373 hydroxysulphonates, 648 hypobromite, 124 hypochlorite, 115, 374 hypophosphite, 222 hyposulphite, see Thiosulphate iodate, 126, 193 iodide, 125, 126 line in spectrum, 354 manganate, 55, 462 metaborate, 378 metantimonate, 478 metaphosphate, 218, 383 metasilicate, 379 metastannate, 488 methoxide, 650 muriate, 101 nitrate, 125, 126, 181, 192, 363, 367, 379 nitrite, 379, 715, 730 nitromethane, 742 nitroprusside, 730 oleate, 612 oxalate, 624, 625 oxide, 61 palmitate, 608 perborate, 378 perchlorate, 379 perchromate, 468 periodate, 130 permanganate, 464 peroxide, 375, 379 phenoxides (phenols, phenolates), 619, 620, 743, 745 phenylhydrazine, 720 a phosphate, 377 (Hydrogen disodium phosphate) phosphite, 221 platinate, 531 869 Sodium platinochloride, 532 plumbite, 501 potassium alloy, 375 carbonate, 373 tartrate, 631 propionate, 607, 686 pyroborate, 378 pyrophosphate, 377 pyrosulphate, 376 salicylate, 620 sesquicarbonate, 373 silicates, 281, 367, 379 sodiolactate, 618 sodiosalicylate, 620 stannate, 488, 511 stannite, 488 stearate, 609 succinate, 796 sucrate, 768 sulphantimonate, 154 sulpharsenate, 154, 233 sulphate, 40, 101, 109, 852, 367-371, 373, 376, 397 acid, 109, 370, 376 sulphide(s), 371, 376, 757 sulphite, 376, 377 sulphostannate, 154 tetrathionate, 127, 172, 173 thioantimonate, 480 thiochromite, 468 thiocyanate, 738 thiophosphate, 223 thiosulphate, 40, 127, 154, 171, 377, 517, 521 tungstate, 471 uranate, 472 (per-), 472 urates, 808 urethane, 684, 707 zirconate, 492 Soffioni, 288 Soft soap, 612 water, 43 Soils, absorptive power of, 425 carbonic acid in, 64 phosphates in, 209 Sol, 333 Solanaceous alkaloids, 815, 816 Solder, 486 brazier’s, 511 silversmith’s, 517 Solid elements, 298 Solidifying point, 32 Solids, 333 Solubility, 38 curves, 363, 376 Soluble glass, 379 Solute, 38 hydration of, 324 Solution, 36-41, 313-317, 485; see also Dis- solution colloidal, 333 ; see also Colloid definition, 37 Solutions, freezing-points of, 320 isotonic, 319 nature of, 36 non-aqueous, 331 pseudo, 333 solid, 485 vapour pressure of, 322 Solvay’s process, 369 Solvent, 36, 38 “free,” 324 Sombrerite, 394 870 INDEX Soot, 272 Sorbic acid, 612 Sorbitol, 592, 761 Sorrel, salt of, 625 Sound, velocity of, 311 Sovereign, see Gold standard Sozoiodol, 747 Space interference, 642 Spanish fly, 781 Sparkling wines, 70 Sparteine, 812, 815° Spathic iron ore, 486, 454 Specific gravity of gases, 22, 31, 310; sce also Density distinguished from density, 31, 314 of liquids and solids, 31, 39, 656 gravities of the elements and their oxides, 304-307 heat, 32, 39, 81, 347; sce also Heat ratio of, 293 and atomic weight, 297, 301 (carbon), 243 properties, 1 refractive power, 646 rotatory power, 635 volume, 31, 34, 317, 644 Spectra of metals, 354, 429 Spectrogram, 355 Spectrograph, quartz, 354, 647 Spectroscope, 353, 646 Spectroscopy, 175, 358, 646 Spectrum, 353 absorption, 646, 792 analysis, 293, 294, 383; see Spectroscopy arc, 354 continuous, 353 flame, 354 é of a gas, 353, 354, 35 solar, 354, 355 spark, 355 Specular iron ore, 435, 453 Speculum metal, 487, 510 Speiss, £58, 459 Spelter, 61, 408 Spent oxide (spent pyrites), 508 Sperm oil, 674 Spermaceti, 583, 674 Sphene, 490 Spheroidal state, 156 Spiegeleisen, 461 Spinel, 424, 453 Spirit, methylated, 577 of hartshorn (Ammonia), 183 of salt (Hydrochloric acid), 101 of wine, 577 proof, 577 Spiritus rectificatus, 577 tenuior, 577 Spodumene, 383 Spongin, 791 Spring water, see Water Sprouting of silver, 518 Stable form, 736 Stahl, 48 Stalactites and stalagmites, 45 Standard gold, 525 oxygen as, 137 Stannates, 468 Stannic acid, 487, 488 ammonium chloride, 489 anhydride, 62 bromide, 490 chloride, 489 ethide, 689 Stannic oxide, 488 sulphide, 490 Stannonium compounds, 640 Stannous chloride, 489, 526, 719) ethide, 689 . hydroxychloride, 489 oxide, 488 sulphide, 490 Star antimony, 476 Starch, 576, 760, 762, '7'70 animal, 772 cellulose, 771 iodised, 127 soluble, 771 -sugar, 762 | varieties of, 770 Stas, 301, 510 Stassfurt, 121, 361, 367, 402 State of fine division, 21, 59, 62, 413 Static. method of measuring chemical energy, 342 Stavesacre, 822 Steam and iron, reaction between, 341, 342 and water, difference in kinetic energy, 348 boilers, to prevent incrustation in, 230 composition by volume, 27 decomposed by carbon, 249 by chlorine, 106 by electric sparks, 17 by heat, 18, 269 (note) dissociation of, 18, 269 distillation, 674 heat of formation of, 348 latent heat of, 32, 348 Stearic acid, 608, 609, 611 aldehyde, 596 Stearin, 609, 671, 672 candles, 609 Stearolic acid, 611, 613 Steatite, 402, 404 Steel, 436, 442 annealing, 450 Bessemer, 447 blistered, 449 case hardening, 450 cast, 449 crucible, 449 distinguished from iron, 448 hard, 443, 448 hardening, 450 influence of impurities, 448 manufacture, 448 mild, 443, 445, 448 definition of, 448 puddled, 445 shear, 449 tempering, 450 tool, 448 percentage of C., Mn., &c., 449 tungsten in, 451 Whitworth’s, 449 Stereochemistry, 335, 562, 595, 619, 628, 633-642, 760-770 Stereochromy, 379 Stereo-isomerides, see Stereochemistry Stereo-isomerism, see Stereochemistry Stereometry, 335, 352 Stereotype metal, 475 Steric hindrance, 642 Stibines, 689 Stibiopentamethyl, 689 Stibiotriethide, 689 Stibiotrimethide, 689 INDEX 871 Stibnite, 476 Stibonium compounds, 689 Stilbene, 569, 573 Still, 29 Stone, artificial, 379 coal, 272 decayed, 390 preservation of, 390 test of durability, 390 ware, 427 Storage cells, 503 Storax, 584, 585, 613, 615, 668 Stourbridge clay, 420 Strain theory, 642 Straits tin, 484 Stramonium, 816 Stream tin ore, 483 “Strength ” of acids, 344, 601 Strontia process for sugar-refining, 767, 768 Strontianite, 387 Strontium and its compounds, 18, 387 Structural formule, 205, 335 Structure of matter, 6, 350 Strutt, R. J., 181 Strychnic acid, 821 Strychnine, 637, 764, 797, 821 methylium iodide, 821 Strychnos alkaloids, 821 Stucco, 393 Stupp, 413 Styphnic acid, 749 Stypticin, 818 Styracin, 585, 668 Styrene, 567 Styrolene, 567 from acetylene, 557 (meta-), 568 Suberic acid, 627, 775 Suberone, 558 Sublimation, 33, 183 Substance, definition, 1 homogeneous, 1 Substantive dyes, 717 Substitution, 19, 20, 106, 197, 547 products, 547 rules concerning, 565 Succinamic acid, 707 Succinamide, 704 Succinic acid, 575, 624, 626, 630, 679, 753 electrolysis of, 626 anhydride, 626, 794 series of acids, 623-627 Succinimide, 704, 796 Succino-dialdoxime, 796 Succinyl dichloride, 663 Succussion, 165 Sucrates, 768 Sucrose(s), 760, 767 Sucrotetranitrate, 768 Suction-gas, 274 Sudbury ore, 459 Suet, 673 Sugar, 317, 318, 320, 767 animal fluids, &c., containing, 761 barley, 768 beetroot, 767 candy, 767 cane, 345, 635, 767 compounds of, see Sucrates extraction, 767 fruit, 761, 762, 763 extraction of, 762 invert, 345, 763 lime, 768 Sugar-loaf 767 ae 767 milk, 631, 763, 769 occurrence in nature, 767 of gelatine, 710 of lead, see Lead acctate of manna, 591 refining, 242 starch (glucose), 762 synthesis of, 764 unerystallisable, 767 Sugars, 760-770 constitution of, 649 isomerism among, 640 oxidation of, 619, 624, 631 synthesis of, 764 Suint, 359 Sulphanilic acid, 699 Sulpharsenates, 233 Sulphates, 145, 170 of the alkalies, 170, 299 Sulphethylates, see Ethylsulphates Sulphethylic acid, 555, 664 Sulphides, 145, 153, 730 action of air on, 154, formation of, 153 Sulphindigotic acid, 107, 140, 799 Sulphindylic acid, 799 Sulphinic acids, 68] Sulphites, 157, 159 Sulpho-, 666 ; see also Thio- Sulphobenzide, 745 carbonates, sce Thiocarbonates cyanic acid, 737 cyanides, 737 test, 725 phosphotriamide, 224 thiocarbonic acid, 666 urea, 707 vinic acid, see Sulphethylic acid Sulpholeic acid, 224 Sulphonal, 586, 648, 684 Sulphonamides, 703 Sulphones, 684 Sulphonic acids, 159, 585, 680 Sulphonium, 180, 586 Sulphur, 50, 60, 128, 145-177, 194, 311, 335, 339, 435, 441, 456 acids, 154 action of acids on, 150, 194 of alkalies on, 150 alcohols (thio-alcohols), 585, 680 allotropic states of, 150 amorphous or insoluble, 148 and dry oxygen, 58 (note) bases, 154, 176 black, 145, 177, 757 chlorides, 177, 251, 659, 673 colloidal, 150 dioxide, 5, 51, 60, 80, 123, 155, 163, 169, 310, 502 liquid, 82, 156, 331 distilled, 146 ductile, 148 electro-negative, 148 positive, 148 estimation of, in organic compounds, 539 extraction, 146-147 from soda-waste, 147, 371 flowers of, 146 fluorides, 177 for gunpowder, 365 group, 137-180 hexafluoride, 134 872 Sulphur, insoluble, 147 iodides, 127, 177 milk of, 147 octahedral, 149 oxides, 155 phase rule, 339 plastic, 148 precipitated, 147 prismatic, 149 properties, 147 recovered, 371 refining, 146 rhombic, 149 roll, 146 rough, 146 salts, 154 sesquioxide, 155, 160, 170 solubility, 148 soluble, 149 stereochemistry of, 641 sublimed, 146 superfused, 149 trioxide, 60, 147, 159 uses, 147 vapour density, 150 volcano, J50 Sulphurets, 145 Sulphuretted hydrogen, see Hydrogen sul- phide Sulphuric acid, 60, 108, 143, 161-170, 178, 348, 352, 527 action on metals, 23, 164, 169 on organic matters, 168 on sulphur, 169 anhydro-, 160 anhydrous, see Sulphuric anhydride Chamber process reactions, 165 composition of, 169 concentration, 164 diluted, turbidity of, 168 distillation of, 164 esters, 664 fuming, 160 glacial, 168 heat evolved in diluting, 168 hydrates, 168 manufacture by chamber process, 162 by contact process, 165 Nordhausen, 161 ortho-, 168 solidified, 168 specific gravity at various concen- trations, 167 (note) thermochemistry of, 350 anhydride, 155, 159, 166 ether, see Ether Sulphuring casks, 157 Sulphurised dyestuffs, 756, 757 Sulphurosyl chloride, 158, 159 Sulphurous acid, 50, 51, 156, 462 anhydride or oxide, see Sulphur dioxide Sulphuryl chloride, 158 Sumach, 621, 622 Supercooling, 32, 33 Superphosphate of lime, 394 Supersaturated solutions, 40, 423 Supra-renal gland, 745 Surface tension, 30, 97, 315, 316, 375 phenomena, 315 Swedish iron ore, 436 Sweet spirit of nitre, 665 Syenitic granite, 425 Sylvestrene, 674, 676 INDEX Sylvine, 361 Symbols, 7, 11 Symmetrical substitution-products, 564 Symmetry, 141 axes of, 336 elements of, 336 planes of, 336 systems of, 336 Synaptase (emulsin), 597 Synthesis, 10 of acids of the acetic series, 600, 602 of organic compounds, general, 632, 684, 686, 716, 723, 804 Syntonin, 788 Systems, components of, 338 heterogeneous, 338 homogeneous, 338, 343 variability of, 338 Systematic working, 370 “T'ABASHEER, 281 Tale, 283, 402, 404 Tallow, 673 Taloses, 763 Tamping-hole, 445 Tank liquor, 373 waste, 147, 171, 371 Tannates, 622 Tannic acid, 452, 621, 622, 812 Tannin, see Tannic acid Tanning, 622 Tantalates, 481 Tantalite, 481 Tantalum, 481, 482 Tar, 273, 440 Tartar, 630 -emetic, 476, 477, 681 salt of, 631 Tartaric acid, 626, 627, 629, 680, 687-640, 649, 663, 795 (meta-), 630 anhydride, 630 d- and 1- rotatory, 637 Tartralic acid, 630 Tartrates, 630 Tartrazine, 802 Tartronic acid, 629 Tartronyl urea, 809 Tartryl antimonious acid, 631 antimonites, 631 Taurine, 714, 794 Taurocarbamic acid, 714 Taurocholic acid, 794 Tautomerism, 735 instances of, 207, 667, 682, 751 Tea, 813 Teeth, artificial, 491 Telluretted hydrogen, 180 Telluric acid, 180 Tellurium, 179, 180 chlorides, 180 nitrate, 180 oxides, 179 Tellurous acid, 179 Temper, 450 Temperature, see also Heat absolute, 9 influence of, 32, 39, 54, 55, 59, 60, 61, 140, 166, 193, 257, 298, 316, 570, 642, 680, 683 Tempering, colours in, 450 Temporary changes, 1 Tennant, 115 Tennantite, 225 INDEX Terbia, 431 Terbium, 433 Terebic acid, 675 Terephthalic acid, 628 Terminology, 198 Terne plate, 485 Terpenes, 585, 674-676 Terpin hydrate, 678 Terpinene, 676 Terpineol, 677 Terra japonica, 621 Tertiary alcohols, 580 amines, 693, 803 benzene ring, 751 butyl alcohol, 580 paraffins, 553 Tetra-acetic acid, 668 Tetrachlorethane, 659 ether, 653 ethylene, 659 hydroquinone, 753 methane, see Carbon tetrachloride quinone, 753 Tetrad elements, 13 Tetrahedron, 636 Tetrahydric alcohols, 590 Tetrahydropyrazoles, 802 Tetrahydropyrrol, 796 Tetrahydroquinolines, 805 Tetrahydroxy-anthraquinone, 755 Tetrakisazo colours, 719 Tetraldehyde, 595 Tetramethyl-alloxantin, 814 -ammonium hydroxide, 696 iodide, 694, 696 arsonium hydroxide, 691 iodide, 691 benzene, 567 methane, 553 murexide, 814 pinacone, 588 stibonium hydroxide, 689 thionine, 806 uric acid, 808 Tetramethylene diamine, 701 Tetramethylenimide, 796 Tetramethylium compounds, 696, 716 Tetrapeptides, 787 Tetrathionic acid, 173 Tetratomic molecules, 312 Tetravalency, 640, 641 Tetrazines, 802, 806 Tetrazo-dyestufis, 719 Tetrazodiphenyl, 719 Tetrazole, 803 Tetrazones, 721 Tetrethyl ammonium hydroxide, 697 iodide, 697 Tetrethyl-phosphonium hydroxide, 692 iodide, 691 Tetrolic acid, 612 Tetroses, 761 Thalleioquin, 820 Thalline, 805 Thallium and compounds, 430-431 ethoxide, 578 Thebaine, 818 Thebenine, 818 Theine, see Caffeine Thénard, 131, 142 blue, 458 Thenardite, 376 Theobromine, 813 Theophylline, 813 873 Theories, &c., see also Laws atomic hypothesis, 6, 296 and molecular heats, 298 Avagadros’ hypothesis, 10 Bayer’s strain theory, 561 Boyle’s law, 9 chemical equivalents, 297 Dalton’s law, 9 disintegration hypothesis, 296, 358 dynamical, of a gas, 309 “ions ” or electrons, 94, 296, 326 isomerism, 636 isomorphism, 299 kinetic, 308 magneton, 351 of properties of atoms and molecules, 299, 300 on molecular constitution, 335, 351 on valency, 351 osmotic, 319 phlogistic, 48 Prout’s hypothesis, 301 stereoisomerism, 636 transmutation of elements, 296 Therm, 32 Thermal change accompanying change of state, 325; see also Heat, and Latent Heat accompanying dissolution, 325 Thermite, 422 Thermochemical data, 348 determination of, 349 application of, 350 Thermochemistry, 12, 275, 278, 325, 342, 345, 347 avidity of acids, determined, 345 calorific intensity, 277, 278 value of fuel, 275, 279 definition of, 12 of carbon, 248 Thermo-electric pile, 474, 476, 534 Thermos flasks, 85 Thetines, 641 Thiazines, 806 Thiazoles, 801, 802 Thilorier, 82 Thio-, 666, see also Sulpho- -acetic acid, 606 acids, 606 -alcohols, 585, 680 aldehydes, 598 amide, 801 amino acids, 785 anhydrides, 606 antimonates, 480 arsenates, 233 arsenites, 232 carbamic acid, 707 carbamide, 707, 708 carbanilide, 707, 800, 801 carbimides, 739 carbonates, 176, 774 chromites, 468 cyanates, 738 cyanic acid, 737 cyanogen compounds, 736 diphenylamine, 806 ethers, 585, 586 ethoxides, 586 formaldehyde, 740 indigotin, 801 peroxides, 606 phenol, 745 phosphates, 223 874 Thio phosphoryl chloride, 223 resorcinol, 749 salicylic acid, 801 -stannates, 490 sulphate, 154, 171 sulphuric acid, 171 urea, 739, 802 Thiogen blue, 757 Thionic acids, 173 Thionine, 806 Thionyl, 158 chloride, 158 Thiophene, 324, 559, 795 of crystallisation, 324 Thiosinamine, 740 Thomas process, 447 slag, 447 Thompson-Joule effect, 85 Thoria, 432, 493 radioactive, 493 X, 493 Thorianite, 493 Thorite, 493 Thorium, 399, 431, 493 compounds, 493 disintegration products, 493 emanation, 493; see Emanation Thresh’s reagent, 812 Thrombin, 789 Thuja oil, 677 Thulia, 431 Thulium, 433 Thyme, essential oil of, 678 Thymol, 678 Thyreoglobulin, 784 Tiglic acid, 611 Tilden, 679 Tiles, 428 Tin, 4, 62, 105, 322, 340, 411, 414, 488, 697 alkides, 640, 688 allotropes of, 485 alloys of, 486 amalgam, 414 binoxide, see Dioxide bisulphide, 490 black, 483 block, 484 chlorides of, 489 crystals, 489 dimethyl iodide, 689 dioxide, 483, 488 dropped, 484 foil, 484 grain, 484 prey, 484 exethide, 688 impurities, 487 metallurgy of, 484 methyl compounds, 640, 684, 688, 689 nitromuriate, 489 ores, 483 oxides, 4, 488 plate, 484 detinning of, 490 properties of, 484 pure, 487 purification of, 484 pyrites, 490 salts of, 489 sesquioxide, 489 spots, 487 stannate, 489 stereochemistry, 640 stone, 471, 483, 726 INDEX Tin straits, 484 sulphides, 490 tetrachloride, 489 tetramethide, 688 tetrethide, 689 -tree, 489 trimethyl-iodide, 689 Tincal, 288 Tinctura iodi, 126 Tinned iron, 485 detinning of, 489 Tinning copper, 485 Tinwhite cobalt, 225, 456 Titanic acids, 491, 492 anhydride, 490 iron ore, 490, 491, 529 oxides, 490, 492 Titanite, 490 Titanium, 436, 490, 491 alums, 491 chlorides, 491 fluorides, 491 nitrocyanide, 491 sulphate, 491 sulphide, 491 Titanofluoride, 491 Toast, 771 Tobacco, 814 Tolane, 569 Tolidine, 720 Tolu, balsam or oil of, 584 Toluene, 559, 566, 572, 597, 613 sulphonic acids, 703 Toluic acids, 566, 567, 613, 614 Toluidines, 683, 698, 699 ortho, meta, and para, 699 Tolusafranine, 807 Toluylene, 569 glycol, 588 reds, 807 Tolyl, 566 diphenylmethane, 758 Tolypyrine, 802 Tonka-bean, 623 Topaz, 131, 424 Torbane-hill mineral, 549 Torricelli, 48 Touch-paper, 364 -stone, 196 Touraco, 506 Tourmaline, 131, 290 artificial, 820 Tous-les-mois, 771 Toxines, 701, 788 Trans-, see Cis-trans Transition-point, 376 Transmutation of the elements, see Elements Trap-rock, 425 Treacle, 767 Tree-wax, see Waxes Trehalose, 769 Triacetamide, 702 Triacetonamine, 816 Triad elements, 12 Triallyl melamine, 740 Triamidoazobenzene, 719 benzene, 750 tolydiphenyl] carbinol, 758 triphenylmethane, 757, 758 carbinol, 758 Triamines, 693 . Triatomic, 310. Triazines, 806 Triazoacetic acid, 715 INDEX 875 Triazoles, 802 ‘Tribromanilines, 698 ‘Tribromhydrin, 659 "Tribromophenol, 745 ‘Tributyrin, 672 ‘Tricarballylic acid, 632, 677 ‘Tricarbon disulphide, 176 ‘Trichloracetic acid, 661 aldehyde, 660 aniline, 698 butyric aldehyde, 661 ethylidene glycol, 661 hydrin, 659 methyl chloroformate, 666 Trichlorobenzene, 660 hydroquinone, 753 methane, 657 nitromethane, 682 propane, 659 purine, 809 pyrogallol, 750 quinone, 753 Triclinic crystals, 336 Tridymite, 282 (note) Trienes, 566, 568 Triethylamine, 697 arsine, 228 phosphine, 691 stibine, 689 sulphonium compounds, 586 Triethylene diamine, 700 Triglycerides, 671; see Glycerides Trigonal crystals, 336 Trihydric alcohols, 588 phenols, 750 Trihydroxy-anthraquinone, 755 benzene, 750, 751 benzoic acids, 000 triphenyl-carbinol, 759 methane, 758 Tri-iodo-methane, 658 Triketones, 751 Trilaurin, 672 : Trimesic acid, 612, 614, 633 Trimethylamine, 656, 694, 695, 701, 710 arsine, 690 Trimethylene oxide, 654, 749 bromide, 659 Trimethylglycocoll, 710 Trimethylstibine, 689 tricarballylic acid, 677 vinyl ammonium hydroxide, 701 Trimorphous, 282 Trinitro-cellulose, 777 phenol, sce Picric acid phloroglucol, 751 resorcin, 749 Trinitrosophloroglucol, 750 Triolefinic derivatives, 613, 676 Triolein, 672 Trioses, 761 Trioximes, 751 Trioxymethylene, 593, 764 Tripalmitin, 672 Tripeptides, 787 Triphane, 383 Triphenylamine, 699 Triphenylcarbinol, 585 Triphenylglyoxaline, 802 Triphenylmethane, 324, 569, 585, 642, 757 carboxylic acid, 758, 759 dyestuffs, 757 rosaniline, 759 Triple phosphate, 404 Triple point (phase rule), 339 Tripoli, 282 (P Trisaccharides, 760, 770 Trisazo colours, 719 Tristearin, 672 Trisulphones, 596 Trithioaldehydes, 596 Trithionic acid, 173 Trivalent elements, 12 Trona, 373 Tropacocaine, 816 Tropeolin, 718 Tropic acid, 815 Tropine, 815, 816 Truxilline, 816. Tryptophane, 785, 786, 789 Tungstates, 471 Tungsten, 471 dioxide, 471 hexafluoride, 472 metal, 471 sulphides, 472 trioxide, 471 Tungstic acid, 471 hydrated, 471 anhydride, 471 chlorides, 472 oxide, 471 Tungsto-arsenates, 472 borates, 471 -phosphates, 472 -Silicates, 471 -vanadates, 472 Tunicin, 778 Turacine, 506 ‘ Turbith or turpeth mineral, 416 Turkey red oils, 673 Turmeric, 18, 782 action of boric acid on, 290 Turnbull’s blue, 728, 729 Turner’s yellow, 505 Turpentine, 140, 635, 674 action of nitric acid on, 197 in chlorine, 107 oil of, 672, 674, 675 Turpeth mineral, 416 Turpethin, 780 Turquoise, 426 Tutton, 299, 300, 335 Tuyére pipes, 438, 439, 443, 451 Type furniture alloy, 497 metal, 474, 476, 487, 500 Tyrosin, 712, 713, 786, 789 Tyrotoxicon, 716 Twyer pipes, 438, 496 ULTRAMARINE, 426 green, 426 yellow, 466 Ultramicroscope, 333 Umbelliferone, 749 Umber, 421 Undecylenic acid, 673 Unit of heat, 32 volume and weight, 1 Unsaturated compounds, 97 hydrocarbons, see Hydrocarbons vapours, 33 Upcast shaft, 69 Uramil, 810 Uranic salts, 472 Uranium, 294, 303, 356, 399, 401, 472, 728 carbide, 472 chlorides, 472 876 Uranium metal, 472, 473 oxides, 472 X, 472, 473 yellow, 472 Uranous salts, 472 Dranyl, 472 sulphate, 472, 808 Urates, 808 Urea, 124, 321, 381, 704-707, 737, 739 artificial formation, 705 derivatives of, 706, 707, 809 extraction from urine, 704 hydrochloride, 705 nitrate, 704, 705 oxalate, 705 Ureas, compound, 706 Ureides, 809 Urethane, 707 Uric acid, 807, 810, 811 action of nitric acid on, 809 Urine, 124, 613, 704, 710, 744, 747, 751, 761, 788, 797, 808, 812 indican, 797 Uroxanic acid, 810 Uvinic acid, 795 Uvitic acid, 649, 795 Vacuum-Pans, 767 vessel, 85 Valencies, auxiliary, 351 principal, 351 Valency, 12, 99, 299, 335, 351, 481, 684 Valentine, Basil, 108, 161 Valentinite, 477 Valerian root, 607 Valerianic acid, see Valeric acid Valeric acids, 607, 643 aldehyde, 596 Valine, 785 Vanadic acid, 481 anhydride, 481 Vanadinite, 480 Vanadites, 481 Vanadium, 351, 480 alums, 481 chlorides, 481 metal, 481 nitride, 481 oxide, 481 steel, 481 sulphide, 480 Vanadyl, 481 trichloride, 481 Van der Waal’s equation, 309, 319 _ Van Helmont, 48, 63 Van Marum, 138 Van’t Hoff, 636 Van’t Hoff’s law, 318, 319, 320, 322 Vanillic acid, 621, 748 Vanillin, 599, 621, 678, 780 Vaporisation, 32, 80 Vapour, defined, 35 densities, 10, 150, 311, 312, 346, 420 see also Density density determined, 11, 312 pressure of solutions, lowering of, 322 of water, 33-35 Variegated copper ore, 506 Varnishes, 679 Vaseline, see Paraffin Vat dyeing, 756 dyestuffs, anthraquinone, 756 indigo, 799 Vegetable black, 238 INDEX Vegetable butter, 673 chemistry, 43, 54, 64, 131, 181, 182, 235, 317, 358, 379, 387, 671 colouring-matters, 754, 781 fats, 585, 673 Velocities of molecules, 308 Velocity of chemical affinity, 345 Venetian red, 453 Venice turpentine, 674, 783 Ventilation, 69 Veratralbine, 822 Veratric acid, 748, 822 Veratrine, 822 Veratrol, 748 Verdigris, 510, 605 Verditer, 512 Vermilion, 419 Vesta matches, 120 Victor Meyer’s method for vapourdensity, 313 Victoria orange, 747 Vidal black, 757 Vinasses, 695 Vinegar, composition of, 604 manufacture, 603 Vinyl] alcohol, 583 compounds, 657, 701, 816 Vinylacetic acid, 610 Violet bronze, 471 Lauth’s, 806 Viridine, 803 Viscose, 316, 774 Viscosity, 316 Viscous fermentation, 773 Vitellin-caseinogen, 784 Vitriol, see Sulphuric acid black, 513 blue, 513 white, 410 Vivianite, 455 Volatile alkaloids, 812 oils, see Essential oils Volatilisation, 33, 188 Volcanic’ (various), 52, 109, 145, 155, 182, 380, 425 Volt, 327, 329 coulomb, 326 Volta, 15 Voltaic cell, 15 Voltameter, 15, 16 hydrogen, 329 silver, 329 water, 329 Volume, changes due to dissolution, 325 gram-molecular, 310 standard, 96 Volumetric reactions, &c., 4, 25 Vulcanised rubber, 680 Vulcanite, 680 Wap, 461 Walls, efflorescence on, 428 (note) Washburn, 332 Water, 14-47, 97, 98 action on metals, 46, 452 analysis, 14, 22 and steam, difference in kinetic energy, 348 and the phase rule, 338 chemical relations of, 36 concentration (of ores), 406 decomposed by electric sparks, 16 by electricity, 14-17 by electrolysis, 14 by heat, 18, 269 INDEX Water decomposed by metals, 1821, 422 by niton and radium, 401 by non-metals, 21 distilled, 29 electrolysis of, 14 ~gas, 21, 249, 274 gases in natural, 41 glass, 283, 379 hardness, 48, 393, 403 in chemical change and activity, 108, _ 140, 248, 332 in SEyeaseEte determinations, 321, 322, maximum density, 31 mineral (natural), 46, 47 natural supplies, 41 analysis of, 42, 47 of constitution, 39, 404 of crystallisation, 88, 324, 352 on energy of chemical reaction, 332 peculiarities, 36 purification, 42, 46 sea, 42, 47 softening, 46, 426 synthesis of, 25, 142 vapour, 33 Wavellite, 426 Waxes, 671, 674 Wedekind, 322, 350, 641 Weight, 1 Weiss, 351 Weld, 782 Welding, 255, 445 7 Weldon’s chlorine process, 103 manganese recovery process, 103, 464 Weldon-Pechiney process, 103 Welsbach incandescent light, &c., 267 Welsh coal, 272 process (copper smelting), 507 Wermuth, 781 Werner, 303, 332, 353 Wheatstone’s bridge, 330 White antimony ore, 477 arsenic, see Arsenious oxide lead, 153, 244, 503 ore, 495 poisonous effects, 504 metal, 507, 511 of egg, see Egg white precipitate, 417 fusible, 417 vitriol, see Zine sulphate Whitworth’s steel, 449 Willesden paper, 774 Willow-bark, 778 Windows, crystals on, 380 Winter-green oil, 620, 668 Wire-iron, 445 Witherite, 385 Woad, 798 Wohler, 705 Wolfram, 471 Wolframium, 471 ; Wollaston’s method of drawing platinum wire, 530 Wood as fuel, 273 charcoal, 238 combustion, 238 composition, 240 conversion into glucose, 576 distillation, 238, 648 gum, 773 kreasote, 748 naphtha, 578, 579 877 Wood spirit, 578 tar, 578, 748, 795 Wood’s fusible alloy, 474 Wool wax, 585, 674 Worm, 29 Worm-seed, 781 Wormwood, 781 Wort, 575 Wroblewski, 84 Wrought-iron, see Iron Wulfenite, 470 “X-Rays, see Rays X Xanthates, 176 Xanthic acid, 666 Xanthine, 784, 811, 812 alkaloids, 813 Xantho-cobalt salts, 458 proteic reaction, 788 Xanthogen persulphide, 666 Xanthosiderite, 232 Xenon, 293-295 Xylenes, 559, 567, 614 physical constants of, 567 Xylidines, 700 Xylonite, 778 Xylose, 761 Xylyl, 566 Yuast, 54, 64, 73, 575 Yellow cassel, 505 chrome, 466 dyes, 718, 719, 747, 805, 806 fire, see Pyrotechny Indian, 783 ochre, 435 orpiment, 225 Paris, 505 prussiate of potash, see Potassium ferrocyanide sheathing, 510 Turner’s, 505 ultramarine, 466 Yorkshire flags, 390 Ytterbia, 431 Ytterbium, 433 Yttralite, 431 Yttria earths, 431 Yttrium, 431, 433 Yttrotantalite, 431 ZAFFRRE, 458 Zeisel’s method, 654, 813 Zeolites, 425 Zine, 15, 20, 23, 61, 326, 405, 419, 498, 685 acetate, 605 alkides, 685 amalgam, 414 amalgamated, 414 amide, 409 arsenide, 226 arsenite, 230 boiling-point, 407 carbonate, 406, 409 chloride, 410, 655 copper deposited upon, 409 cyanide, 726 diamine, 409 distilled, 407 dust, 409 ethide (ethyl), 409, 640, 684, 685 ethoxide, 686 extraction, 407 ferrocyanide, 728 878 Zine furnace, 408 granulated, 95 hard, 408 hydrosulphite, 173 hydroxide, 409 impurities in, 408 lactates, 617, 618, 635 mercaptide, 686 metallurgy of, 407-408 methide (methyl), 604, 640, 684, 686 nitride, 409 ores, 406, 411 oxide, 62, 373, 406, 407, 409 oxychloride, 410 refining of, 408 removal of lead from, 408 silicate, 406 sulphate, 95, 410, 454 INDEX Zine sulphide, 154, 373, 410 orystals, 411 sulphite, 173, 377 volatility of, 407 white, 409 Zincates, 409 Zircon, 492 Zirconia, 492 Zirconides, 492 Zirconium, 105, 304, 357, 431, 492: amorphous, 492 carbide, 492 chlorides, 492 colloidal, 492 crystallised, 492 oxides, 333, 492 sulphate, 492 Zymase, 575 ABBREVIATIONS AND SYMBOLS ac, 572 -al, -ol, 596 anti-, syn-, 642 ar, 572 C, 320 cis-, 595 Cp Cv, 310 E.M.F., 327 meso-, 573 N.T.P., 9 peri-, 572 8, 31 Sol., 38 trans-, 595 ——, 11 a, B, ¥, 571, 573, 595, 609, 642, 80%: a-iron, 437 B-iron, 437 y-iron, 436 y (ratio of specific heats), 311 y (surface tension), 316 Ay B, 311 PRINTED BY BALLANTYNE AND COMPANY TAVISTOCK ST COVENT GARDEN LONDON ites eet es mre Toe ter oe pbaae ge a se ent ten ar : ore om OOo iar ISSO NT: to Pou) a + ih $0 He Th Samar ate 2 ; arena tS % RY Ths sort etree’ TILE Ok hae yy ee | a eel a ® SET OTN Te ee tty Nati) Le ks vt my Beha mh ot itt mit: ri