hS-\.\ Hbui fork HhU afoUcge of AgricuItutE At (JotneU ISLttivetBits 3tljata. 5J. 5. ICibtatg Cornell Unrverslty Ubrary QO 33.N62 EleiTientary manual of chemistry, abr. fro 3 1924 003 005 380 ™, Cornell University Library The original of tliis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924003005380 AN ELEMENTARY MANUAL OF CHEMISTRY. ABRIDGED FROM ELIOT AND STOKER'S MANUAL, WITH THE CO-OPERATION OF THE AUTHOU8. BY WM. RIPLEY NICHOLS, PROFESSOR OF GENERAL CHEMISTRY IN THE MASSACHUSETTS INSTITUTE OF TEOHSOLOQV. -. Revised Edition. NEW YORK • : • CINCINNATI ■ : • CHICAGO AMERICAN BOOK COMPANY Copyright, 1872, by C. W. Eliot, F. H. Stoeer and W. H. Nichols. Copyrigllt, 1877, by C. W. Eliot, P. H. Stoker & W. E. Nichols. Copyright, 1880, by C. W. Eliot, F. H. Stoker & W. K. Nichols. E. & s. E. M. c. IPrinteb bt Mililam Itiison new )?orli, HL S. a, EXTEACT FROM THE PEEFACE TO ELIOT AND STORER'S MANUAL OF INORGANIC CHEMISTRY. " In preparing this manual, it has been the authors' object to facilitate the teaching, of chemistry by the experimental and inductive method. . . . The authors believe that the study of a science of observation ought to develop and disci- pline the observing faiculties, and that such a study fails of its true end if it become a mere exercise of the memory. " The minute instructions, given in the descriptions of ex- periments and printed in the smaller type, are intended to enable the student to see, smell and touch for himself; these detailed descriptions are meant for laboratory use. In order to mark as clearly as possible the distinction between chemistry and chemical manipulation, the necessary instructions on the latter subject have been put in an Appendix. In cases in which it is impossible for every student to experiment for him- self, the authors hope that this manual will make it easy for the teacher, even if he be not a professional chemist, to ex- hibit to his class, in a familiar and inexpensive manner, experiments enough to supply ocular demonstration of the leading facts and generalizations of the science. . . . " There is little original in the book except its arrangement and method, in part, and its general tone. The authors have, of course, drawn largely from the invaluable compilations made by Gmelin, Otto and Watts, and they have also availed them- selves freely of the text-books of Stoeckhardt and Miller, and the writings of Hofmann.'' PREFACE TO THE ABRIDGMENT. This Abridgment, which is not simply an abridgment, is a shorter and easier, yet a more comprehensive manual than the original one. The larger manual covers only^ inorganic chem- istry ; the Abridgment includes the elements of what is gen- erally called organic chemistry. The chapter on Carbon in the original maimal has been subdivided and expanded, so as to comprehend the principal facts and theories of that part of chemistry which in most text-books is treated as a distinct branch under the name of organic chemistry. In this way the compounds of carbon are studied in their natural place and order, and the student htis a fairer view of the whole science than he is likely to get when the great majority of the carbon compounds are studied quite apart from carbon itself and from some of its longest-known compounds, and after all the other elements. In preparing the new chapters on the compounds of carbon, the authors have made free use of the works mentioned above, especially of the text-books of Stoeckhardt and MiUer ; they would also acknowledge indebtedness to Prof. Johnson's " How Crops Grow,'' from which several of the experiments have been taken. These experiments, as well as the others in these chap- ters, are such as have been found to stand the test of actual performance by students. vi PREFACE TO THE ALRIDGilENT. This manual is written in the interest of no particular theory ; the typical formulae have been employed in many cases in the chapters on carbon, as affording a convenient method of repre- senting the reactions in which the compounds take part. Teach- ers who desire to illustrate more fully the theory of the subject may refer to Cooke's Chemical Philosophy, from which some use- ful hints have been taken in preparing this Abridgment. Teachers who put the Abridgment into the hands of their pupils win find it useful to consult the larger manual for addi- tional facts and experiments and fuller explanations. March, 1872. PREFACE TO THE SECOND REVISED EDITION. Fkom time to time since the first issue of the book, corrections have been made of such errors as have come to the notice of the authors. The present edition has been thoroughly revised. The most important changes in the first revised edition were in Chap- ters IX and XI, and in §§ 27, 28, 36, 63, and 76 ; some new matter was also added. In the present edition, besides minoi corrections and additions. Chapter VI has been rewritten. The page numbers, however, as a rule, have not been altered, so that where the book is already in use there will be no difficulty in the way of the gradual introduction of this new edition. June, 1880. TABLE OF CONTENTS. PAGES Intro cluction. — Subject matter of chemistry. Chemical and physical changes. Analysis and synthesis. Elements. Fact and theory .... 1-4 Cliap* X, — Air> Atmosplieric pressure. Analysis of air. Oxygen and nitro- gen . . . 4-8 Chap. II. — Oxygen. Preparation and properties of oxygen. Oxygon supports combustion. Oxides. "Wide diffusion of oxygen. Oxidation . . . 9-11 Chap. III. — Nitrogen. Preparation and properties of nitrogen . , 11-13 Chap. IV. — "Water. Properties of water. The gramme. Specific gravity. Ice. Steam. AnalyFiis, electrolysis and synthesis of water. Atoms and mole- cules. Atomic weights. Distillation. Solution . . . . . 13 22 Chap. V. — Hydrogen. Preparation of hydrogen. Properties of hydro- gen. Lightness, diffusive power, inflammability of hydrogen. Hydrogen does not support combustion. Oxy-hydrogen blowpipe. Combustibles and supporters of combustion . . .... 23-30 Chap. VI. — Compounds of nitrogen vrith oxygen and hydro- gen. Nitrous oxide. Its composition and properties. Nitric oxide. Its preparation, properties, and composition. Nitrogen peroxide. Liquefaction of gases. Nitric anhydride. NitroiLS anhydride. Chemical compounds and me- chanical mixtures. Law of multiple proportions. Air a mixture. Nitric acid. Acid and alkaline reaction. Acids, bases and salts. Ammonia. Composition, source and preparation of ammonia. Preparation of ammonia water . . 30-49 Chap. VIT. — Chlorhydric acid. Properties, composition and prep- aration of chlorhydric acid. Chlorides. Quantivalence. Aqua regia. Practical applica!:ion of chemical equations . . 49-65 Chap. VITI. — Chlorin**. Preparation and properties of chlorine. Chlo- rine unites readily with hydrogen. Certain metals burn in chlorine. Chlo- rine both combustible and a supporter of combustion with reference to hydrogen. Chlorine as a bleachiug ag«nt and disinfectant Ox.\gen com- viii co^'TEyTS. pounds of chlorine. Bleaching-powder — Bromine. Occurrence and proper- ties of bromine. Bromhydric and bromic acids. — Iodine. Source and prop- erties of iodine. lodohydric and iodic acids. Nitrogen iodide. Tlie chlorine group. — Fluorine. Occurrence of fluorine, Fluorhydric acid. Etching glass . . . . . ... • 55-67 Chap. IX.— Ozone. An allotropic fonn of oxygen. Preparation of ozone. Ozone an oxidizing, bleaching, aitd disinfecting agent. Antozone clouds . 63-11 Chap. X. — Sulphur, selenium and tellurium. Source of sul- phur. Action of tiulphur when heated. Soft sulphur Crystallization of sulphur. Systems of crystallization. Snlphur unites with other elements. Prepa- ration, composition and properties of hydrogen sulphide. Sulphurous an- hydride. Preparation and properties. Sulphurous acid bleaches. Sulphuric acid. Oxidiang and reducing agents. Manu&cture of sulphuric acid. Prop- erties of sulphuric acid. Sulphates. Fuming sulphuric acid. Occurrence of selenium and tellurium. Sulphur, selenium and tellurium allied to oxygen . . ... 71-86 Chap. XT. — Combination by Tolume. Product volume. E«lation of combining weight to specific gravity. Molecular condition of the elementary 87-92 Chap. XII. — Phosphoius. Properties of phosphorus. Allotropic modi- fications of phosphorus. Compounds of phosphorus and hydrogen. Phosphorus and o:^gen. Phosphoi'ic anhydride. Phosphoric acid. Empirical and rational formulse. Typical formulae , . Chap. XIII. — Arsenic, antimouT and bismuth. Properties of arsenic. Hydrogen arsenide. Arpenious anhydride Poisonous character and uses of arsenions anhydride. Other compounds of arsenic. — Antimony occurs native. Properties and uses of antimony. Compounds of antimony with hydrogen, oxygen and with chlorine. — Properties of bismuth. The nitrogen group of elements . 102-108 Chap. XIV. — Carbon. Wide distribution and importance of carbon and its componnds. Allotropic modifications of carbon. Diamond. Graphite. Gas-carbon. Coke. Anthracite and bituminous coal Chartoal. Lamp- black. Charcoal a reducing agent. Charcoal absorbs gases. Charcoal a disinfecting agent. Charcoal decolorizes. Carbonic acid and carbonates. ?reparation and properties of carbonic acid. Solubility of carbonic acid. Carbonic acid produced in the processes of decay, fermentation and raspi- ration. Carbon protoxide. Properties. Carbon protoxide poisonous. Re- ducing power and inflammability of carbon protoxide. Combustion. Lumi- nosity of flames. All flames gaa-flames. Structure of flames. Blowpipe flames. Chimneys. Kindling temperature. Carbon and snlphur. Carbon bisnl- P^^*l« . . 109-135 Chap. XV. — Carbon (continued). Oi^nic chemistry. Compounds of carbon and nitrogen. Cyanogen and cyanhydric acid. Hydrocarbons. Methyl hydride or marsh-gas. Preparation. Chloroform. Manufiicture of illuminating gas. Composition of the gas. Marsh-gas scries. Petroleum. coy TEXTS. ix Alcohol . Yeast Fernientation. Fractional distillation . Fractional conlen- ftatiou . The alcohols L*reparatiou aud properties or ether The etheni. Mercaptans. Acetic acid. Preparation of vinegar. Chloral. Fatty acid series. Acetic and formic acids. Natural fats and oils. Manufacture of soap. Prepara- tion of glycerin. Nitroglycerin. Vegetable oils. Drying oils. Essential oils. Oil of cloves. Oil of turpentine. Camphor . .135-163 Cliaii* XVI. — Carbon (continued). Homologous series of hydrocarbons, Olefiant gas or ethylene. Preparation of Dutch liquid. Olefiant-gas series. Glycols. Definition of the term alcohol. Phenyl series. Distillation of coal- tar Benzol, ni^'ro-benzo) and aniline Constitution of aniline. Aniline colors. Preparation and properties of phenic or carbolic acid ; of picric acid. Naph- thalin and anthracene. Products of the destructive distillation of wood. Oil of bitter almonds. Relation of the oil of almonds to the phenyl series. Acetylene series . ... . . 163-175 Chap* XVII. — Carbon (continued). Organic compounds the direct pro- duct of the growth of animals and plants. Sugar. Manufacture of sugar. Properties of cane-sugar. Dextrose or grape-sugar. Levulose or fruit- sugar. Lactose or milk-sugar. Fermentation. Fermented and distilled liquors. Starch, occurrence and properties of. Dextrin. Gluten. Bread. Properties of cellulose or woody fibre. Vegetable parchment. Gun-cotton. Gum. Pectose. Balsams. Resins. Character and solubility of the resins. Gum-resins. Caoutchouc and gutta-percha. Fossil resins. Vegetable acids. Preparation and properties of oxalic acid. Malic acid. Source, preparation and uses of tartaric acid. Citric ncid Varieties and properties of tannic acid Gallic acid. Vegetable alkaloids. Opium. Strychnine. Organic coloring matters. Dyeing. Illustration of methods of dyeing Indigo. Indigo dyeing. Physio- logical chemistry. Complexity of the chemical substances concerned in the vital functions Properties of albumin. Fibrin. Casein. Milk, butter and cheese. Gelatin and glue. Decay of organic substances. Antiseptic and preservative agents .... • 176-204 Chap. XVIII — Silicon and boron. Abundance of silicon. Silicic an hydride or silica. Water-gla-ss. Silicates Various sorts of glass. Silica is attacked by fluorhydrie acid. Silicon fluoride and fluofiJicic acid AUotropic modifications of silicon. SiUcon in organic compounds. — Otcurrence of boron in nature. Boracic acid and boracic anhydride . . • • 204-208 Chap. XIX. — Sodium. Abundance of the element. Common salt or so- dium chloride. Manufacture of salt Solubility of common salt. Sodium sulphate. Glauber's salt. Manufccture of sodium carbonate. Reverberatory furnace. " Bicarbonate of soda."* The metal sodium. Sodium decomposes water. Sodium hydrate or caustic soda. Soap. Cleansing action of soap. Formation of salts. Borax. Other compound.s of sodium • • 209-210 Cliap. XX. — Potassium. Source of potassium compounds. Potash and pearlaah. Potassium carbonate. Potassium hydrate. Uses of caustic potash The metal potassium. Potassium decomposes water. Burns in carbonic acid. Potassium cyanide a reducing agent. Potassium ferro- and ferri-cyanide. Potas- sium nitrate formed in nature. Oxidizing power of potassium nitrate. Gun- powder. Potassium chlorate. Potassium tartrate ... . . 219-228 X CONTENTS. Ctiap. XXI. — Ammonium salts. The group of atoni'^, ammonium. Ammonia-water. Ammonium chloride, Ammoniunj sulphate. Ammonium ni- trate. Ammonium carbonates and sulphides. Isomorphism . ■ . 228-231 Chap. XXII. — Lithium, rubidium, caesium and thallium. Properties of lithium. Spectrum analysis. Occurrence and pi-operties of ru- bidium, csesium and thallium 231-234 Chap. XXIIT. — Silver. Ores of silver. Properties of the metal. The term metal. Silver nitrate. Silver chloride. Other silver salts. Photography.— The alkali group 234-241 Chap. XXIV. — Calcium, bariu-n, utrantium and lead. Calci- um. Calcium carbonate. Stalactites and stalagmites. Calcium oxide. Calcium hydrate, Air-slalied lime. Milk of lime. Mortar. Lime as a base. Calcium sul- phate. Gypsum and plaster of Paris. Hardness of water. Phosphates of calcium. Calcium chloride. Calcium hypochlorite. Oxygen from bleaching-powder.— Strontium and barium resemble calcium. Flame colored by salti of strontium and barium.— Ores of lead. The metal lead. Separation of lead and silver. Action of air and water on lead. Oxides of lead. Lead sulphide. Salts of lead . . . 241-250 Chap. XXV.— magnesium, zinc, and cadmium. Yarioua nat- ural coii)puuiid>t of magnesium. The metal. Oxide of magnesium. Bnlta of mag- nesium. — Ores of zinc. Properties of metallic zinc. The galvanic-current. The lead-tree. Electro-chemical relations of the elements. The terms negative and positive. Salts of zinc. — Cadmium . 251-257 Chap. XXVI. — Aluminum, chromium, mangranese, iron, co- balt and nickel. Abundance of aluminum. Properties of the metal. Alu- mina. Aluminum hydrate. Lakes. Mordants. Aluminum sulphate. Alums. A'liininuiu silicates. Eartlienware. — Ghiciiiuni — Indium. — Ores of r.hromium. CiiinmUiiii s'sqiiloxide. Chromium sulphate atid clnome alum. Chromic anhy- dride and chromic acid. — Compounds of manganese. Potassium permanganate. — Ores of iron. Extraction of iron from its ores. Cast-iron. The blast-furnace. Wrought-iron. Puddling. Steel. The Bessemer process Oxides and hydrates of iron. Ferrous and ferric salts. Ferrous sulphate or copperas. Method of re- ducing indigo. Iron silicate. Ferro- and ferri-cyanides. Prussian blue. Iron sulphides, — Cobalt and nickel. — The sesquioxide group. — Uranium . . 258-274 Chap. XXVII. — Copper and mercury. Occurrence of copper in na- ture. Ores of copper. Properties of copper. Alloys of copper. Oxides of copper. Copper sulphate. Copper acetates. — Ores of mercury. Properties of the metal. Oxides of mercury. Chlorides of mercury. Amalgams. Detection of mercury , 274-279 Chap. XXVIII. — Tin Ores of tin. Properties of the metal. Alloys of tin. Compounds of tin . . 27&-281 Chap. XXIX. — Gold and Platinum. Occurrence of gold in nature. Gold a noble metal. Alloys of gold. Salts of gold. — Occurrence of platinum. Uses of platinum. Platinum black, and platinum pponge. Platinum group . 281-285 Equivaleni weighis. Nomenclature, Quaiilivalence, Graphic symbols. Oxi- dation and reduction. Volumetric interpretation of symbols. Coincidence of atomic weight and unit-volume weight. Electrical relations of the atoms , , 28S-294 CONTENTS, xi Chap. XXX. — Atomic weights and clx^^Mficntinn or the eliments. AIj>liii- beiical liatiif \\w. elements. Groups of the elenitnis 295-296 Appendix. Glass-tubing. Cutting and cracking glass. Bending, drawing and closiae giass-tubes. Blowing bulbs. Lamps. The Bunsen burner. AYirc' gauze lamps. Blast-lamps. Bellows. Blowpipes. Caoutchouc tubing and stop- pers. CorKs and cork-cutters. Iron-stand, sand-bath and wire-gauze. Triangles. Pneumatic trough. Gas-holders Deflagrating-spoon . Platinum foil and wire. Filtering Folding filters. Drying gases. Water-bath. Self-regulating gas- generator. Gloss retorts. Flasks. Beakera. Test-tubes. Test-glasses. Pi- pettes. Measuring-glasses. Porcelain dishes and crucibles. Rings to support round-bottomed vessels. Crucibles. Iron retort. Tong^. Furnaces. Mortars, Spatulee. Thermometers. The metrical system of weights and measures. Table for the conversiou of grammes into grains, centimetres into inches and litres into quarts. Table for the conversion of degrees of the centigrade scale mto degrees of Fahrenheit's scale. Order-list of chemicals and apparatus i-xlr elementary Manual of Chemistry. INTEODUCTION. 1. The various objects which constitute external nature pre- sent to the observing eye an infinite variety of quality and circumstance. Some bodies are hard, others soft ; some are brittle, others tough or elastic. Some natural objects are en- dowed with life, — they grow ; others are lifeless, — they may be moved, but do not move themselves. Some bodies are in a state of incessant change ; whUe others are so immovable and unchangeable that they seem everlasting. In the midst of this infinite diversity of external objects, where lies the domain of Chemistry? What is the subject-matter of this science ? When air moves in wind, when water moves in tides or in the fall of rain or snow, the air and water remain air and water stUl ; their constitution is not changed by the motion, however frequent or however great. A bit of granite, thrown off from the ledge by frost, is stUl a bit of granite, and no new or altered thing. If a solid piece of iron be reduced to filings, each finest morsel is metallic iron stUl, of the same substance as the original piece, as will appear to the eye, if a morsel be sufficiently magnified under the microscope. The melted, fluid lead in the hot crucible, and the solid lead of the cold bullet cast from it, are the same in substance, only differing in respect 1 CHEMICAL CHAXOBS. [§2. to temperature. In all these cases, the changes are external and non-essential, not intimate and constitutional : they are called physical changes. 2. When iron is exposed to the weather, it becomes covered with a brownish, earthy coating, which bears no outward resem- blance to the original iron ; and, if exposed long enough, the metal completely disappears, being wholly changed- into this very different substance, rust. A piece of coal burns in the grate and soon vanishes, leaving nothing but a little ashes. Dead vegetable or animal matters, buried in the ground, soon putrefy, decay, and disappear. So, too, the fragment of granite which frost has broken from the ledge, exposed for centuries to the action of air and rain, becomes changed ; it " weathers," and after a time could no longer be recognized as granite. All these changes involve alterations in the intimate constitution of the bodies which undergo them : they are called chemical changes. Experiment 1. — Mix thoroughly 3 grammes (for Tables of the Metrical System of Weights and Measures, see Appendix) of coarsely- powdered sulphur with 8 grammes of copper-filings or fine turnings. rig. 1. Put the mixture into a tube of hard glass. No. 3, about 12 centimetres long, and closed at one end. (For the manipulation of tubing, see Appendix, §§ 1 - 4.) Hold the tube by the open end with the wooden nippers, as in Fig. 1, and heat the mixture over the gas-lamp (Appendix, § 5), until it suddenly glows vividly at the in- stant when the copper and sulphur combine. Before heat was applied, the mixture of the two substances was sunply mechanical, and the copper might have been cqjnpletely separated from the sulphur, by due care and patience ; biit, during the ignition, the copper and sulphur have united chemically, and there has been formed a substance, which, while containing both, has no external resemblance to either. In the new body the eye can detect neither copper nor sulphur. Processes by which the whole character and appearance of §3.] A.VALrSIS AND SYNTHESIS. the bodies concerned are changed, as m this experiment, so that essentially new bodies are formed from the old, are chemical processes. It is the function of the chemist, on the one hand, to investigate the action of each substance on every other, and to study the properties of the combinations resulting from this action ; and, on the other, to separate compound bodies into their simpler constituents : he further seeks the general laws by which the intimate combinations of matter are controlled. With these ends in view, he endeavors to pull to pieces, or, in technical language, to analyze, every natural substance on which he lays hands. Having thus found out the composition of the substance, he seeks to put it together again, or to recompose it out of its constituent parts. By one or both of these two pro- cesses, — analysis (unloosing) and synthesis (puttijig together), — the chemist studies all substances. 3. The first question which the chemist asks himself con- cerning every natural substance is, Of what is it composed i He then attempts to resolve the substance into simpler consti- tuents. If he succeeds in decomposing it, he obtains the answer to this first question ; if the body can not be decomposed by any known method of analysis, the substance must be regarded as being already at its simplest. Such simple bodies are called elements. Secondly, the chemist asks, How does this new sub- stance comport itself wlien brought into contact with other substances already familiar ? Between sixty and seventy sub- stances are at present admitted to be simple, primary substances, or elements ; other elementary substances may hereafter be (iis- covered, and substances which are now regarded as elements may hereafter be found to be compound ; so that the number of the substances considered as elements is subject to change. Of compound bodies, formed by the union of these elements with each other, we find a series, numbering many thousands, in the inorganic kingdom of nature, comprising all the diversified mineral constituents of the earth's crust; while another series, far more complex in composition, and almost innumerable in multitude, exists in the vegetable and animal world. The task of the chemist in thoroughly answering his second question 4 FACT AND THEORY. [§ 4. would clearly be endless, wore it not for the existence of general properties common to extensive groups of both elementary and compound bodies, and of general laws which chemical processes invariably obey. While, therefore, the chemist seeks the answers to the two fundamental questions above stated, he is at the same time in- quiring what relations exist between the properties of a body and its composition ; and he is also studying that natural and invariable sequence of chemical phenomena, which, when fully known, will constitute the perfect science of chemistry. 4. Generalizations from observed facts, so long as they are uncertain and incomplete, are called hypotheses and theories ; when tolerably complete and reasonably certain, they are called laws. The attention of the student should be constantly di- rected to the keen discrimination between facts and the spec- ulations founded upon those facts ; between the actual evidence of our trained senses brought intelligently to bear upon chemical phenomena, and the reasonings and abstract conclusions based upon this evidence ; between, in short, that which wc may kno^v and that which we may believe. CHAPTEE I. AIS. ,« We are everywhere surrounded by an atmosphere of in- visible gas, called air. In motion, it is wind, and we recognize its existence by its powerful effects ; but in the stillest places it exists as well. The presence of air in any bottle, flask or other hollow vessel which is empty, in the sense in which this word is ordinarily applied, can be shown very simply by attempting to put some other substance into the vessel, under such conditions that the air cannot pass out from it. If, for example, we wrap around the throat of a funnel with nari^ outlet, a strip of moistened cloth or paper,, so that the funnel shall fit V-] A TMOSPllKRIC PRESSURE. tightly into the neck of a bottle, and then fill the funnel with water, we shall observe that this water does not run into the bottle. The bottle which we have called empty is in reality filled with air, and it is this air which prevents the water from entering the bottle. If, now, the funnel be lifted slightly, so that the niouth'of the bottle shall no longer be completely closed by it, the air within tlie bottle will pass out, and the water in the funnel will instantly flow down. 6. We may actually pump the air out of the bottle by means ''of an apparatus known as the air-pump ; or we may remove a portion of the air by suction. Ezp. 2. — Fit to any small flask or bottle a perforated cork (for the manipvilation of corks, see Appendix, § 9), to which has been adapted a short piece of glass tubing. No. 7. Slip over the end of this glass tube a short piece of caoutchouc tubing. Suck part of the air out of the flask, and then nip the caoutchouc tube with thumb and finger, so that no air shall re-enter. Immerse the neck of the flask in a basin of water, and release the caoutchouc tube. Water will instantly rise into the flask to take the place of the air which has been sucked out. 7. The water, in this experiment, is forced into the flask by the pressure of the superincumbent atmosphere. Air has weight, a litre- of dry air, at the temperature of 0°, weighing 1.2932 gramme. It has been determined that the force with which the air is attracted to the earth is on an average equal to a weight of 1.033 kilogramme to the square centimetre of surface. That is to say, the ocean of air above us presses down upon every square centimetre of the earth's surface vnth a force equal to that which would be exerted by a bar of metal, or other substance, a centimetre square in section and long enough to weigh 1.033 kilogramme. If such a bar were constructed of iron, it would be 1.3 metre long ; if of water, — and a bar of this substance can readily be made by enclosing the water in a tube, — it would be 10.33 metres long. In addition to the qualities already mentioned, we find air to be tasteless and odorless ; it is also colorless when in small depths, but exhibits a blue tint when seen in large masses, as when in the absence of clouds we look at the sky or at a distant mountain. G AX A LYSIS OF AIR. [§ 8. 8. AVc will now proceed to study the chemical properties of air, first asking the question, Of what is air composed ? When a bar of iron is heated in the air, as at a blacksmith's forge, it • becomes covered with a coating, which flies off in scales when the iron is beaten upon the anvil. If a piece of wire or ribbon made of the metal magnesium be touched with a match, it will take fire and bum, and be entirely converted into white ashes. With the exception of gold, silver, platinum and a few other exceedingly rare metals, all the metals burn, or rust, when heated in the air. If no air be present, this rust or ashes wiU not be formed, however long or intensely the metal may be heated. But in what manner is the rust formed ? Is something driven out of the metal into the air, or does ■ something come oiit of the air and unite with the metal ? This question may be answered by experiment. If a weighed quantity of thi-foil be heated in a porcelain dish over the gas-lamp, the metal is gradually converted into white ashes. When all the metal has thus been changed, and the ashes have been allowed to cool, it will be found that the ashes are very sensibly heavier than the original metal. 9. It is possible that during the heating the metal may have lost something, but it is certain that it has gained more. We have, therefore, taken something out of the air, which, gaseous in the air, has become solid in the white ashes of the tin. It would be possible to recover from the tin-rust the some- thing thus taken from the atmosphere, and to compare it with common air, and so learn whether the matter which combined with the heated tin is air itself, or only a part of the air. The process, however, would be a circuitous one. From the rust of other common metals, as from that of mercury, for example, the absorbed gas can be very easily expelled. If metallic mercury be heated for a long time in the air, it will be en- tirely converted into a red substance known as " red oxide of mercury." Exp. 3. — Put into a tube of hard glass, No. 2, about 12 cm. long, 10 granmios of the red mercury oxide. Tubes of hard glass, for such § 9.] AXAI.VSIS OF AIR. 7 purposes, will be hereafter designated as " ignition-tubes." Attach to this ignition-tube, by means ol' a perforated cork or caoutchouc stop- per, a delivery-tube of glass, No. 8, Fig. a. of such shape and length that it shall reach beneath the inverted saucer in the pan of water, as re- presented in Fig. 2 ; the lower end of the ignition-tube should be about 4 c. ra. above the top of the lamp. The tube may be supported on the iron stand, and should be inclined < as represented in the figure. (For a description of the pneumatic trough, see Appendix, § 11.) Upon heating the ignition-tube, gas will begin to escape from the delivery-tube, and bubble up through the water. The first portion is simply the atmospheric air which filled the tubes at the beginning of the experiment, and which is expanded by heat. This air may be collected in a small bottle by itself, and thrown away. The volume of gas thus thrown away should not be much greater than that of the tubes. As the ignition-tube becomes hotter, gas will be freely given off from the mercury oxide contained in it, and should be collected in bottles of 100 to 150 c. c. capacity. It is necessary to avoid heating intensely any single small spot of the ignition-tube, lest the glass soften, and, yielding to the pressure from within, blow outward, and so spoil the tube and arrest the ex- periment. The gas-flame should be so placed and regulated as to heat 3 or 4 c. m. of the tube at once. As soon as the disengagement of gas slackens, lift the iron stand up, and take the deliverj'-tube out of the water, taking care that no water remains in the end of the tube. Then, and not till then, extin- guish the lamp. (See Appendix, § 11.) In the upper part of the ignition-tube, and sometimes in the delivery-tube also, metallic mer- cury will be found condensed in minute globules. The liquid metal is volatile at the temperature to which it has been subjected, and has distilled away from the hot part of the tube, and condensed upon the cooler part. If a lighted splinter of soft wood be introduced into a bottle of the gas jxist collected, it will bum with nmch greater brilliancy than in the air. If a candle which has just been extinguished be thrust, while the wick still glows, into another bottle of the gas, the glowing wick will burst into flame, and the candle will bum with extraordinary brightness. 8 COMPOSITION OF AIR. [§ 10. 10. It is very obvious, from these experiments, that the gas which enters into the composition of mercury-rust is not air itself ; but, since it came originally from the air, if it is not the whole of air, it must be a part of air. It has, indeed, been found to be a constant constituent of the air, and a chemical ele- ment of very various powers and great importance. It is called oxygen, and under this name, will form the subject of the next chapter. 11. If oxygen be not air itself, but only a constituent of air, it follows that air must have other constituents, or, at least, one other constituent. If mercury be heated for a long time in contact with a certam confined portion of air, it will abstract from this air all of the oxygen, and there will be left a gas differing from both oxygen and common air. It is unfit for the support of combustion and of animal life ; a candle is instantly extinguished by it, as if plunged in water; and small animals, thrust into the gas, die in a few seconds. The gas is, in reality, a second elementary substance, distinguished by marked chemical and physical peculiarities. It is called nitrogen, and under this name will be more completely studied in another chapter. If the experiment he so conducted that the bulk of the original air, and also that of the residual nitrogen, can be measured, it will be found that the latter gas occupies four-fifths as much space as the air did at the beginning of the experiment. Besides oxygen and nitrogen, minute quantities of two or three other gases are found in the air, either uniformly or occasionally ; hut the amount of these gases ia relatively very small, and they will not be considered at present. The air, then, is not an element, but is a complex substance ; and its two principal ingredients are the elementary bodies, oxy- gen and nitrogen, mixed in the proportion of foiir measures of nitrogen to one of oxygen. § 13. J OXYOEX. CHAPTEE II. OXYGEN. 12. Oxygen gas may be obtained, as has already been seen, by heating mercury oxide : it may, however, be prepared in a variety of ways ; among others, and very conveniently, by lieat- ing a mixture of p otassi um chlo rate and manganese binoxide, ■ — two chemical substances Whose constitution will be studied hereafter. Xizp. 4. — Mix intim.ately 5 grammes of potassium chlorate with 5 grammes of ""black oxide of manganese,'' which has been previously well dried. Place the mixture in a tube of hard glass, No. 1, 12 or 15 c. m. in length. Attach to this ignition-tube, hy means of a per- forated cork or caoutchouc stopper, a delivery-tube of glass. No. 7, as represented in Fig. 2, and described upon page 7. Heat the mixtme in the ignition-tube, and collect the gas which will be given off in bottles or jars of the capacity of about 250 c. c. The first 100 c. c. or so of gas shoidd be rejected, since it will be contaminated with the air originally contained in the apparatus. In performing this experiment, the following precautions should be observed. 1. Both the potassium chlorate and the manganese bin- oxide should be perfectly dry and pure ; that is, free from moisture, dust or particles of organic matter. 2. As soon as the oxygen begins to be dehvered, the heat beneath the ignition-tube should be dimin- ished, if need be, and so regulated that the evolution of gas shall be tranquil and uniform. 3. The xippermost portions of the mixture should be heated before the lower. 4. The ignition-tube should never be filled to more than one-third its total capacity, lest particles of solid matter be projected, into the delivery-tube, and the outlet for the gas be thus stopped. 5. The ignition-tube should always be inclined as represented Jh Fig. 2, and never placed upright in the flame. 13. Oxygen is a transparent and colorless gas, not to be dis- guished by its aspect from atmospheric air. Like air, it has neither taste nor smell. It i-, however, somewhat heavier than air. If the weight of a measure of air be taken as 1, 10 OXrOliN SUPPORTS COMBUSTIOX. [§ U. then the weight of the same measure of oxygen is found to be 1.1056. One of its most striking characteristics is its power of making things bum. This has been ah-eady illustrated in Exp. 3, § 9. If a piece of phosphorus the size of a small pea, having been well dried between pieces of blotting-paper, is placed in a deflagrating- spoon, touched with a hot wire or a lighted match, and then thrust into a jar of oxygen, it will bum with intense brilliancy, and with the formation of a dense white smoke. The following experiments will still further illustrate this property of oxygen : — Fig. 3. Exp. 5. — Place in a deflagrating-spoon (see Appendix, § 13) a bit of sulphur as large as a pea. Light the sulphur, and thrust it into a bottle of oxygen. It will burn with a beautiful blue flame, and much more brilliantly than in air. A suffocating gas is at the same time produced. Exp. 6. — Place a piece of charcoal — that of bark is best — in a deflagrating-spoon. Kindle the charcoal by holding it in the flame of a lamp, and then introduce it into a bottle of oxygen. It will burn vividly, throwing off brilliant sparks if bark-charcoal had been employed. In this experiment, as in the preceding, the products of the combustion are obviously gaseous, no solid substance being formed. Many substances commonly called incombustible because they do not burn readily in ordinary air, burn vigorously in oxygen. Of these, me- Flg. 4. tallic iron may be taken as an example. A watch-spring, which has been rendered flexible by igniting it and allowing it to cool slowly, is made into a spiral coil, and to the end is at- tached a bit of tinder or of twine soaked in sulphur. If the kindling-material be lighted, and the spiral then plunged into ajar of oxygen, the iron will bum brilliantly with scintillation. From time to time, glowing balls of molten matter fall off from the wire, and bury themselves in the layer of sand which should have been placed at the bottom of the bottle. 14. It is thus clearly proved that iron, when red-hot, com- bines with oxygen. It is the burnt or oxidized iron which falls in globules to the bottom of the bottle. The compounds which are formed by the union of oxygen with other elements are called oxides, The substances which have been heretofore' mentioned § 17.] OX J DAT/OX. 11 inider the more familiar name of rust, like iron-rust, tin-rust, mercury-rust, are called, in chemistry, oxides ; as iron oxide, tin oxide, mercury oxide. 15. The most important quality of oxygen is, that, with a single exception, it unites with all the other elements to form compounds which are sometimes solid, as in the case of iron, and sometimes gaseous, as in the case of sulphur (Exp. 5). Oxygen is the most widely diffused and the most abundant of all known substances. Not only does it constitute about one- fifth the volume of the air, but at least one-tliird of the solid crust of the globe is composed of it. It is the chief ingredient of water, as wUl appear in a subsequent chapter. Silica, in all its varieties of sand, flint, quartz, rock-crystal, etc., contains about half its weight of oxygen ; and the same is true of the various kinds of clay, and of chalk, limestone and marble. It enters largely into the composition of plants and animals, and is absolutely essential to the maintenance of animal and vege- table life. 16. The combination of oxygen with various substances is often accompanied by the development of light and heat, as in Exps. 5 and 6. All the ordinary phenomena of fire and light which we daily witness depend upon the union of the body "burned with the oxygen of the air. Indeed, the term combus- tion may, for all ordinary purpose's, be regarded sts synonymous with oxidation. CHAPTEE III. NITEOGEN. 17. The simplest method of preparing nitrogen is to bum out the oxygen from a confined portion of air, by phosphorus or by a jet of hydrogen. 12 PREPARATIOy OF XITHOGEX. [§18. Fig. 5. Exp. 7. — Into a small porcelain capsiile, supported on a piece of stout iron wire bent as represented in Fig. 5, put about a cubic centimetre of phosphorus, and set it on fire. Invert over the capsule a wide-mouthed bottle, of the capacity of a litre or more, and hold this bottle so that its mouth shall dip beneath , the surface of the water. During the first moments of the combustion, the heat developed thereby will cause the air within the bottle to expand to such an extent, that a few bubbles of the air will be expelled ; but, after several sec- onds, water will rise into the bottle to take the place of the oxygen, which has united with the phosphorus. The dense white cloud which fills the bottle at first is a compound of phosphorus and oxygen, which is soluble in water. It will, there- fore, soon be absorbed by the water in the pan, and will disappear ; so that at the close of the experiment nearly pure nitrogen will be left in the bottle. But, as the phosphorus ceases to burn before the last traces of oxygen are exhausted, the nitrogen obtained by this method is never absolutely pure. Remove the wire with the capsule, which may be readUy done by tipping the bottle to one side, taking care that the mouth does not come out of the water, and slip a glass plate under the mouth of the bottle ; invert the bottle so that it stands upright, and thrust a burn* ing splinter of wood or a lighted candle into the gas ; it will be in- stantly extinguished. . Nitrogen may also be prepared by passing a slow stream of air over bright copper-turnings heated to redness in a hard glass tuhe. The copjaer combines with the oxygen of the air, and retains it ; while the nitrogen escapes from the tube, and may be collected over water. 18. Nitrogen is a transparent, colorless, tasteless, odorless gas, not quite as heavy as air. In its chemical deportment towards other substances, it is remarkably unlike oxygen. Whilst oxygen is active and, as it were, aggressive, nitrogen, at least when in the condition in which it exists in air, is re- markably inert and indifferent as regards entering into combi- nation with other bodies. It is marked, rather by the absence of salient characteristics than by any active properties of its own. § 21. J PROPJiRTIES OF WATER. 13 As it extinguishes flames, so it destroys life. Animals can not live in an atmosphere of pure nitrogen. It is not poison- ous ; if it were, it could not be breathed in such large quanti- ties as it is in air. An animal immersed in it dies simply from want of oxygen. Nitrogen is widely diifused in nature. Besides occurring in the air, it is a constituent part of all animals and vege- tables, and of many of the products resulting from their de- composition. Notwithstanding the indisposition of nitrogen in the free state to enter into combination, a very large num- ber of interesting and important comipounds can be formed by resorting to indirect methods of eifecting its union with other elements. CHAPTEE IV. WATEE. 19. Another natural substance, quite as common as air, is water. Three-fourths of the earth's surface is covered with it. It is diffused through the atmosphere in the fonn of vapor, and qs a constituent of aU animal and vegetable substances and of many minerals. "We take up next this familiar substance, in order .that we may gain, through the study of it, a deeper insight into chemical principles, and enlarge our experience by making acquaintance with a new element. 20. At the ordinary temperature of the air, pure water is a • transparent liquid, devoid of taste or smell. In thin layers, it appears to be colorless ; but large masses of , it are distinctly blue, as seen in mid-ocean, in many deep lakes of pure water, and in masses of ice, such as icebergs and some glaciers, where it is possible to-look through the ice from below. 21. At 4°, the temperature at which it is densest, water is 773 times heavier than air at 0°. A cubic centimetre of water, at this temperature, weighed in a vacuum, is our unit of weight, 2 14 PROPERTIES OF WATER. [§ 22. — a gramme ; therefore, one litre of water, which measures 1,000 cubic centimetres, weighs a kilogramme. Pure water at 4°, the temperature of its greatest density, is taken as a standard to which the weights of equal bulks of other substances, liquid or solid, are referred. In other words, the specific gravity of water is taken as 1 ; and in terms of this unit the specific gravities of all other liquid and solid substances are expressed. The specific gravity of gold, for example, is 19.3 ; that is to say, the weights of equal bulks of water and of gold are to one another as 1 to 19.3. 22. When exposed to a certain degree of cold, water crystal- lizes with formation of ice, or snow, according to circumstances ; and, upon being heated sufficiently, it is transformed into an invisible gas, called steam. Both these changes, however, are purely physical : the chemical composition of the water is the same, whether it be liquid, solid or gaseous. The temperature at which ice melts is one of the fixed points of the centigrade thermometer, numbered 0°, and the temperature at which water boUs, under a pressure of 760 m. m. of mercury, is the other fixed point, numbered 100°. Water evaporates at all tempera- tures, and is therefore a constant ingredient of the atmosphere. Even ice slowly evaporates, at temperatures far below 0°, without first passing into the liquid condition. In crystallizing, that is to say, in assuming the solid form, water increases in volume. From this fact result many familiar phenomena, such as the floating of ioe, the upheaving and disin- tegrating action of frost, and the bursting of pipes and other hollow vessels, when water is frozen in them. Steam is a colorless, transparent gas, as invisible as atmos- pheric air, and considerably lighter than it. When steam es- capes into the air, it is partly condensed to the liquid state and there is formed a multitude of little globules precisely similar, to the minute drops of water which make up ordinary clouds and fogs. This steam-cloud is sometimes improperly spoken of as steam or vapor, an error against which the student should be on his guard. Similar fogs are formed whenever the atmosphere is §24.] AXALVSIS OF WAT£R. 15 cooled to a temperature so low that the aqueous vapor contained m it can no longer exist in the gaseous state. Water conducts heat very slowly ; it may even be boiled for many minutes at the top of a test-tube, while the lower end of the tube is held in the fingers without inconvenience. 23. Let us now pass to the analysis of water. Of what is water composed ? We can determine this point by methods similar to those which were adopted in the examination of air. At a low red heat water can be decomposed by several of the metals, such as iron, tin, zinc and magnesium. Iron is well adapted for this purpose. If water be boiled in a suitable flask, and the steam passed through an iron tube (a piece of iron gas-pipe answers very well) filled with ^bright iron-turnings, and heated red-hot, the steam is decomposed ; a gas escapes from the tube, and may be collected over water. On the application of a match, the gas will burn with a pale blue flame. This gas is one of the constituents of water, and is called hydrogen. If, after the tube has become cold, the iron-turnings be removed, they will be found to be covered with a black coating similar to that which forms on iron heated in the air. 24. There are certain metals which are capable of decomposing water without the application of heat. The metal sodium pos- sesses this power. Ezp. 8. — Make a small cylinder of wire-gauze, by rolling a piece of fine gauze, about 6 c. m. square, around a thick piece of No. 6 glass tubing. Twist fine wire around the cylhider, in order to pre- serve its form ; then slip the cylinder ofl^ the glass, and close one end of it by pressure with a stout pair of pincers. Within this cylinder of wire-gauze place a piece of metallic sodium as large as a pea, and then close the upper end of the cylinder by pressure with the pincer", as before. Attach the wire-gauze cage firmly ^iB- ^• to the end of a piece of stout iron wire and thrust it quickly into the water- pan, so that the cage will come di- rectly under the mouth of a small bottle of about lOQ c. c. capacity, which has been previously filled with water, and is liekl inverted in the pan (Fig. 6). 16 AXAirSJS OF WATER. [§25. As soon as the water comes in contact with the sodium, bubbles of gas will begin to escape from the wire-gauze cage, and, passing up through the water, will collect at the top of the inverted bottle. When the evolution of gaa has ceased, close the mouth of the bottle with a small plate of glass, turn the bottle mouth uppermost, remove the plate, and touch a lighted match to the gas. The gas will take fire with a sudden flash. The gas is hydrogen; the sodium' has united with the other constituent (or constituents) of the portion of water decomposed, and the new compound formed is dissolved by the water in the pan. 25. By these experiments it has been proved that one of the components of water is a gas called hydrogen. But, with the exception of the coating upon the iron alluded to in § 23, we have as yet nothing to indicate what other in- gredients the water may contain. Such evidence can, how- ever, be readily obtained by resorting to another method of analysis. If a galvanic current is caused to flow through water, the force by Fig, 7. which the constituents of the water are held together will be overcome, and the water will be resolved into the elements of which it is composed. On immers- ing the platinum poles of a galvanic battery in water, to which a little sulphuric acid has been added for the purpose of increasing its conducting power, minute bubbles of gas will immediately bo given ofl' from these poles, and will be seen rising through the liquid. If the apparatus be so arranged that we can collect the gas given off from each pole in a test-tube filled with water to which a little sul- phuric acid has been added, it will be foimd that twice as much gas has collected in the one tube as in the other. If the test-tube containing the larger volume of gas be now closed with the thumb, turned mouth uppermost, and the gas within touched with a lighted match, it will take fire and burn with the characteristic flame of hydrogen. It is, in fact, hydrogen. If the smaller volume of gas in the other tube be examined in the same way, it will not in- flame, although it gives intense brilliancy to the combustion of the match. If a splinter of wood, retaining but a single ignited spark, be I 26.] COMPOSITION OF WATER. 17 immersed in the gas, it instantly exhibits a vivid incandescence, and in a moment bursts into flame. This gas is oxygen. It is thus proved, that out of water may be unloosed two volumes of hydrogen, and one volume of oxygen. It remains to see whether we can produce water from a mixture of oxygen and hydrogen. If we introduce into a stout test-tube a mixture of two volumes of hydrogen and one volume of oxygen, on touching a lighted match to the mixed gas it instantly explodes with great violence, the hydrogen burning suddenly, so that for a moniept a flash of flame fills the whole interior of the tube. After the explosion, water will be found deposited as dew upon the inner walls of the tube. 26. "We have thus established the composition of water by anal- ysis, having resolved water into two gaseous constituents, hydrogen and oxygen ; we have also proved, by the converse or synthetical method, that hydrogen and oxygen are its only constituents, since we have reproduced water by effecting the chemical union of these two elementary materials mixed in due proportion. This proportion is fixed and invariable ; pure water is always made up of hydrogen and oxygen in the proportion of two vol- umes of the former for one of the latter. From the known spe- cific gravities of the two gases, as well as by direct experiment, the composition of water by weight has been found to be 1 part by weight of hydrogen to 8 parts by weight of oxygen. This pro- portion is also constant and it is in general true that, — Any yiveih chemical compound always contains the same elements combined ii/ the same proportions. This is the Law of Definite Proportions. There is one important point stiU to be considered. If the union of the elements be effected in an apparatus so arranged that the water, when formed, is kept at such a high temperature that it remains in the gaseous condition under which it is known as dry steam, we find that the two volumes of hydrogen and one volume of- oxygen which were mixed together have, by uniting chemically, become compacted into two volumes of steam. If equal volumes of hydrogen and oxygen be represented by equal squares, having the initials of the elements inscribed therein, the composition of water by volume, and the condensa- 9* 18 ATOMS AND MOLECULES. [§27 tion which occurs when the chemical union of the elements takes place, may be thus expressed to the eye : Each smallest possible or greatest conceivable vol- ■ 1 ume of steam will invaria- + H.O bly yield, on decomposition, •" its own volume of hydro- gen, and half its volume of oxygen. 27. It has been agreed among chemists to call by the name molecule the least quantity of a compound, or of an elementary substance which can exist by itself uncombined, or take part in any chemical process. The smallest conceivable portion of water (which by this definition is called the molecule) like any larger quantity of water, is made up of hydrogen and jjxygen, and if decomposed would yield twice as large a volume of hydrogen as of oxygen. The smaller masses of> matter which make up the molecules are called atoms. The term atom may be defined as the smallest quantity of an element which can be conceived to exist in combination. A molecule, as a rule, contains more than one atom, and may contain a great number ; these atoms may be all of one kind, in which case the molecule is that of a simple substance, or they may be of several kinds, as in the molecules of compound substances. There is good reason to believe that equal volumes of the elementary gases, oxygen and hydrogen (also nitrogen and chlo- rine to be studied hereafter) contain the same number of atoms. (See § 140.) If this be true there will be in the molecule of water twice as many atoms of hydrogen as of oxygen, because when any quantity of water whatever is decomposed, it yields twice as much hydrogen by volume as oxygen. The symbol HaO, which has been already used to indicate the volumetric composition of water (§ 26), may also be used to indicate the atomic composition ; the H^ will represent two atoms of hydrogen, the O an atom of oxygen, and the 'H..JO a molecule of water. 28. It must be distinctly borne in miud that as to the abso- § 30.] ATOMIC WMIQHTS. 19 lute size of the atoms, we know nothing ; the same thing is true with regard to their absolute weight. It is, however, not difficult to determine their relative weight. If we take the case of hydrogen and oxygen, any given bulk of oxygen weighs 16 times as much as the same bulk of hydrogen, and as there are the same number of atoms in equal bulks of these two gases, ' the single atom of oxygen must weigh 16 times as much as the single atom of hydrogen. The numbers 1 and 16 are called the atomic weights of hydrogen and oxygen, respectively, and it is possible, although not always by the same method, to determine the relative weights of the atoms of all the elements. The atomic weight is, in each case, referred to that of hydrogen, which is called 1 . If the atomic weights of hydrogen and oxygen be borne in mind, the symbol of water, HjO, will now remind us of the com- position of water hy weight, for as each molecule of water is made up of two atoms of hydrogen and one atom of oxygen, the proportion by weight in which these two elements are combined together will be as 2 to 16, or as 1 to 8. 29. Having thus succeeded in determining the constituents of air and water, we are naturally led to inquire whether it be not possible to resolve oxygen, nitrogen and hydrogen themselves into simpler forms of matter. To this question but one answer can be made, namely, that oxygen, nitrogen and hydrogen are incapable of decomposition by any means as yet at our disposal. We are, therefore, justified in regarding these gases as dmple bodies, or elements, in contradistinction to decomposable bodies, such as air and water. 30. The water which occurs in nature is never absolutely pure. In the form of ice, and as it faUs from the clouds as rain or snow, it is, indeed, tolerably free from foreign sub- stances ; but, after having once soaked into the ground, it be- comes charged with a variety of mineral and other substances, which, being soluble in water, are dissolved by, it as it trickles through the earth. Where the proportion of soluble matter contained in the water 20 DISTILLATION. [§ 31 is unusually large, and particularly if it possesses marked medi- cinal properties, the water is called mineral water, and the springs from which it issues are known as mineral springs. Sea-water may be regarded as a variety of mineral water. 31. For the conduct of chemical investigations, it is often necessary to purify natural water. This is done by a process called distillation. As a general rule, distilled water is employed in aU delicate chemical operations. Exp. 9. — In a retort of 500 c. c. capacity, put 200 or 300 e. e. of j.|g_ g. well-water. Thrust the neck of the retort into a half-litre receiver placed in a pan of cold water. Cover the re- ceiver with a cloth or with coarse paper, and upon this pour cold water from time to time, or pile upon it fragments of ice. Place the retort upon wire- gauze, on a ring of the iron lamp-stand, and adjust the distance of the retort from the lamp as described in Exp. 3, Fig. 2. Light the lamp beneath the retort, and bring the water to boiling. As fast as the water in the retort is converted into steam, this vapor will pass over into the cold receiver, and will there be con- densed again to the liquid condition. Continue to boil until about three-quarters of the water in the retort has evaporated. The earthy and saline ingredients of well-water are for the most part not volatile : very few of them are capable of accompanying the water as it goes oflf in vapor ; hence the greater part of the original impurity of the water will remain behind in the retort. Ezp. 9 a. — Place a few drops of the distilled water obtained in the preceding experiment upon a piece of platinum-foil (Appendix, § 14). Hold the foil with iron pincers above the gas-flame in such a manner that the liquid may slowly evaporate without boiling or spirting. After the water has disappeared, no residue will be found upon the foil. Take now the same number of drops of water from out the retort, and evaporate them upon the foil as before. A very decided residue of earthy matter wUl be left upon the foil. 32. In the operation of distillation, the substance to be distilled must in the first place be converted into the condition §33.] WATER DISSOLVES GASES. 21. of vapor ; this vapor must next be transferred to another vessel, and there, by refrigeration, be again condensed to the liquid state. As wiU appear from the foregoing experiment, the vaporization is effected in the retort or still, and the refrigera- tion in the condenser, In the experiment above given, the receiver acts at once as receiver and condenser ; but in many cases it is better to interpose a cooling-apparatus between the retort and the receiver. A convenient form of such apparatus, known as Liebig's condenser, is arranged so that the vapor to be condensed must pass into a long tube which is kept cool by being enclosed in a larger tube through which cold water is made to circulate. A figure representing, such a condenser will be found on page 146. 33. The mineral and other substances alluded to above are not the only impurities of natural water. It contains also oxygen and nitrogen in solution, as both of these gases, which are present in the air, are somewhat soluble in water. That water does actually contain dissolved gases may be shown by the following experiment. Ezp. 10. — By means of a sound perforated cork or oaoutchouc stopper, adapt to a flask of the capacity of 1 or 2 litres a gas-delivery tube. No. 6, long enough to reach to the water-pan in the usual way. Upon the outer end of the delivery-tube tie a short piece of caoutchouc tubing, to which a stopper made of a bit of glass rod, or a wooden plug, has been fitted. Fill the flask comisletely with ordinary well or river water ; fill also the delivery-tube with water, and close it by putting the stopper in the caoutchouc tube. Carefully place the cork of the delivery-tube in the neck of the flask in such manner that no air shall be entangled by the cork ; at the same moment remove the ])lug from the delivery-tube, and finally press the cork firmly into the flask. Both flask and tube will now be completely full of water. Place the dried flask upon a ring of the iron stand, and invert a bottle filled with water over the end of the delivery-tube. Now slowly bring the contents of the flask to boiling. As the water gradually becomes warm, numerqlis little bubbles of gas will be seen to separate from the liquid, and to collect upon the sides of the flask ; these subsequently coalesce to larger bubbles, which collect in the neck of the flask. As soon as the water actually 22 SOLUTION. [§ 34, boils, the steam will force this gas out of the flask, and it wUl collect in the inverted bottle at the end of the delivery-tube, the steam being meanwhile condensed as fast as it comes in contact with the cold water in the pan. By continuing to boil moderately during ten or fifteen minutes, nearly all the gas can be swept out from the flask by means of the escaping steam. The delivery-tube may then be lifted from the water-pan and the lamp extinguished. As to the exact character of the gases thus collected we shall learn something in a subsequent chapter. 34. As might be inferred from the foregoing, water has the property of dissolving many substances, solid, liquid and gas- eous. Sugar, for example, dissolves readily in water ; but sand is insoluble therein. A substance is said to be soluble in water when it is capable of being divided in and dispersed through the water so intimately and completely that its particles become invisible, and can no longer be separated by filtration ; the result of this coalescence, or the solution as it is termed, is a transparent liquid, as a general rule scarcely less mobile than the water itself. Of the various substances soluble in water, some dissolve in far larger proportion than others. With some liquids, as alcohol for example, water can be mixed in any proportion ; but of ether it dissolves but little, and of oil none. The proportion of any substance that can be dissolved in a given quantity of water is usually limited, and, under fixed conditions, is definite and peculiar for each substance. When a given quantity of water has dissolved as much of a substance as it is capable of dissolving at the temperature and pressure to which it happens to be. exposed, the solution is said to be saturated. Of nearly all solid substances, hot water dissolves a greater quantity than cold water : gases, however, are less soluble in hot than in cold water, as already illustrated by Exp. 10. §35.] UYDROGEX. 23 CHAPTEE V. ms. 9, HYSB06EIT. 35. The commonest method of preparing hydrogen is by treating zinc or iron with sulphuric or muriatic acid. Unless very large quantities of the gas are needed, this method is much more convenient than either of those heretofore mentioned. Exp. 11. — To a bottle 18 or 20 c. m. high, and of 500 or 600 c. c. capacity, the mouth of which has an internal diameter of 2.5 to 3 c. m., fit a caoutchouc stopper or a sound cork, furnished with a thistle-tube, Fig. 9, aud a gas 'delivery-tube, of No. 6 glass. Within the bottle put 15 or 20 grms. of granulated zinc, or small scraps of the sheet metal, and as much water as will fill about one- quarter of the bottle. Eeplace the cork in the bottle, taking care to press it in tightly, and gradually pour in com-, mon muriatic acid through the thistle-tube. The thistle-tube must reach nearly to the bottom of the bottle, so that its point may dip beneath the water ; and the muriatic acid must be added by small successive portions, — not more than a large thimbleful at a time. On the addition of the first portions of the acid, chemical action will ensue, the contents of the bottle will become warm, and gas wUl be seen to escape from the liquid. This gas is hydrogen. After all the air has been expelled from the bottle, the hydrogen may be collected over the water-pan, in inverted bottles tilled with water. The moment at which the hydrogen ceases to be contaminated with air can be deteraiined by collecting small portions of the escap- ing gas in wide-mouthed bottles of about 50 c. c. capacity, and testing its quality by moais of a lighted match. In doing this the small 24 CHEMICAL SYMBOLS. [§ 36. b) with a gas-holder containing hydrogen. The cock of the hydrogen gas-holdeir is first opened and the hydrogen is lighted at the point of the jet ; the cock of the oxygen gas-holder is then slowly opened vmtil the flame is reduced to a fine pencil. A constant and sufficient pressure should be maintained on the gas- holders. 28 UNION OF HYDROGEN AND OXYGEN. [§ 42. In the flame thus produced, a fine platinum wire will readily melt and fall into drops. The intense heat of the oxy-hydrogen flame is thus admirably illustrated, for platinum is an exoeedingly infusible metal, which can scarcely be softened in the hottest furnace. If a piece of chalk or iime, scraped to a fine point, be held in the flame of the oxy-hydrogen blow-pipe, it will quickly become white- hot, and evolve light of great brilliancy, almost comparable with that of the sun. On this principle is constructed the so-called Drnmmond or calcium light, often employed for night-signals and optical experi- ments. 42. No matter in what way hydrogen is burned, whether in the pure state or in combination with other materials, whether in pnre oxygen or in the air, the product of the combustion is always water. At the high temperature of the flame, this water must, of course, remain in the condition of a gas, but it can readily be brought to the liquid state by reducing the tem- perature. Esp. 15. — Over a jet of burning hydrogen, best obtained from a gas-holder, hold a dry, cold bottle. The glass soon becomes covered with a film of dew, as the water generated by the imion of hydrogen and oxygen condenses in di'oplets lipon the cold sides of the bottle. 43. If, instead of burning pure hydrogen as it flows into the air, the gas be first mixed with oxygen, and then ignited, a very diiferent result will be obtained. The hydrogen being ~now in contact with oxygen at all points, the entire mass of gas will bum with a violent explosion at. the instant when a light is touched to it. This may be illustrated by connecting a piece of glass tubing with Fig. 13. a gas-holder, or, better, a rubber bag, containing a mixture of 2 volumes of hydrogen and 1 vol- ume of oxygen. The end of the glass tube is dipped into a dish of soap-suds, and the gas allowed to flow until a I 45.] UNION OF ni'DROGEN AND OXYGMN. 29 mass of foam not too large Las formed on the- surface of the suds. If, after the removal of the gas-holder, the foam be touuhed with a long lighted stick, a violent explosion will occur. Care should be taken to throw away any remnant of the mixture of hydrogen and oxygen which may have been left in the gas-holder at the close of the experiment, and upon no accomit should fire ever be brought into its vicinity. The loud explosion is owing to the fact that the intense heat emitted at the moment of the combination of the two gases expands enormously the steam formed by their union. As the steam is immediately condensed, there results a partial vacuum, into which air rushes from all sides ; and it is the heavy and sudden undulations thus communicated to the air which oc- casion the noise. The outward and inward shocks follow one another so quickly that the ear cannot distinguish between them. 44. Mixtures of hydrogen and air produce less violent explo- sions than mixtures of hydrogen and oxygen, because of the inert nitrogen in the air, which acts as an elastic pad or cushion to break the force of the shock. Szp. 16. — Introduce 2 volumes of hydrogen and, 5 volumes of air into a strong round-bottomed bottle, such as is used for soda- water. Close the mouth of the bottle with a cork, and shake "vio- lently, in order that the gases shall be mixed. A small quantity of water should be left in the bottle to act as a stirrer. Grasp the bottle firmly in one hand, remove the cork with the other, and apply the open mouth of the bottle to a lighted candle. An explosion will im- mediately ensue. 45. Since air is everywhere about us, and since all ordinary combustions occur in it, it ha,s become customary to speak of it and of oxygen as supporters of combustion, in contradistinc- tion to the so-called combustibles, such as hydrogen. These terms are often convenient ; but that they have only a relative, and no absolute significance, may be shown experimentally, as follows : — 3* 30 coMPOuysa of nitboqen: [§46, Support a rather wide tube of thin glass — the neck of a broken re- Flg. 14. ■ tort, for example — in a vertical position, and connect the upper opening with a gas-holder containing hydrogen. Allow the gas to flow until the tube is filled ; then apply a lighted match to the mouth of the tube, and regulate the flow of gas so that the latter may continue to burn slowly at the lower edge of the tube. With a second gas-holder containing oxy- gen, comiect a piece of narrow glass tubing, drawn out to a fine point ; and, whUe the oxy- gen is flowing through this tube, pass it up into the larger tube filled with hydrogen. As the stream of oxygen passes through the burning hydrogen at the bottom of the vertical tube, it takes fire, and afterwards continues to bum in the atmosphere of hydrogen within the tube. CHAPTER VI. COMPOUNDS OF NITROGEN. 46. We have already learned that nitrogen is, "under ordinary conditions, a very inert substance, and indisposed to enter into chemical combination. Tliere are, however, many compounds of nitrogen which either exist in nature, or may be prepared by indirect methods, and the study of the compounds of nitro- gen and oxygen will bring t« view a new fact of great signifi- cance. The study of water showed us that in a chemical compound, the elementary constituents are combined in a certain definite proportion; we shall now learn that two chemical elements may combine in more than one definite proportion to form chemical compounds differing from each other ancl from the constituent elements. 47. Nitrous Oxide (^P). —The first compound of nitrogen and oxygen which we shall study may be readily obtained § 48.] PREPARATION OF NITROUS OXIDE. gi by gently heating a substance known as ammonium nitrato, of which we shall learn more hereafter. Exp. 17.— Into a dry flask of thin glass of about 300 c. c. capac- ity, introduce 10 or 15 grnis. of ammonium nitrate. From the flask placed upon the wire-gauze on the iron stand, carry a delivery-tube, No. 6, beneath the saucer in the water-pan ; but interrupt the tube at some convenient point to interpose, by means of a cork or caoutchouc stepper with two holes, a small bottle, which can be kept cool with water, as shown in the figure. Heat the flask . Fig. 15. moderately and cau- tiously, to avoid breaking it. The ammonium nitrate will melt, and little bubbles will soon begin to escape from the fused mass. The| heat must now be so controlled that the evolution of the gas shall not be tumultuous. The gas is to be collected in bottles of 300 to 400 c. c. capacity. ' If the process has been successfully conducted, there will be found an the cooled bottle through which the gas passes, a clear, colorless liquid, which on ex- amination will prove to be water, and nothing else. When one or two bottles of gas have been filled, and enough water for testing has condensed, the delivery-tube may be withdrawn from the water, and the lamp extinguished. The ammonium nitrate might be entirely resolved into water and the gas which now awaits examination ; but there is danger of breaking the flask. That the nitrate leaves no residue behind, when sufficiently heated, may be proved by heating a crystal of it on platinum foil over the gas-lamp. Exp. 18. — Insert a glowing splinter of wood into a bottle of the gas. It will re-inflame with almost as much energy as in oxygen. ^8. From the energy with which the glowing splinter bursts into flame, it may be inferred that oxygen is a constituent of the new gas which we have just prepared, and, indeed, repeated experiments have shown that it is composed of the elements 32 NITROGEN PROTOXIDE. [§48. nitrogen and oxygen ; and that, as in the case of water two volumes of hydrogen and one volume of oxygen are condensed into two volumes of dry steam, so two volumes of nitrogen and one volume of oxygen are here condensed into two volumes of this transparent gas. As the chemical for- mula or symbol of water is H^O so the formula of IT N + 1 N,0 this new gas is NjO, and . its volumetric composition may be represented by a diagram similar to that by which we conveyed to the eye the composition of water. The gas is called nitrogen protoxide or nitrous oxide. The equation which represents the chemical action by which it was produced may be thus writtea : NH.M-Oj = 2H,0 + 1T,0 Ammonium iiitrat«e. Nitrous oxide. From the above composition by volume, and from the known specific gravities of nitrogen and oxygen, the composition of nitrogen protoxide by weight is readily deduced. The specific gravity of nitrogen, referred to hydrogen, is 14 ; that of oxygen 16 ; since there are two volumes of nitrogen for each volume of oxygen, the two elements must, in any given weight of the gas, be combined in the proportion of 28 parts by weight of nitrogen to 16 of oxygen. The molecule of nitrogen protoxide, M'^O, must be composed, like any other quantity of the gas, of 28 parts by weight of nitrogen and 16 of oxygen j but, precisely as in the case of water, we conceive of the molecule as made up of two atoms of nitrogen and one atom of oxygen ; and we have already learned that if the atomic weight of hydrogen be represented by 1, that of oxygen must be 16. It follows, from the constitution of nitrogen protoxide, that, if 16 represents the smallest proportional weight of oxygen which exists in combination, 14 must be the corresponding smallest weight of nitrogen when thus united with oxygen. Nitrogen protoxide contains ^, or 36.36 per cent, of oxygen. §5C.j 33 49. Nitrous oxide, when pure, may be respired for a few minutes with impunity. When inhaled, it produces a lively intoxication, attended with a disposition to muscular exertion and violent laughter ; whence its trivial name of laughing gas. It may, however, be administered so as to cause complete insen- sibility to pain ; the effect lasts, however, for only a very short time. It is advantageously used as an anaesthetic in such sur- gical operations as can be performed in a few seconds. 50. Nitric Oxide (WO). — We now proceed to investigate another compound of nitrogen and oxygen which may be pre- pared from a chemical substance with wliich we shall soon be familiar, nitric acid. Exp. 19.— Place 15 or 20 F's- 16. grins, of copper turnings or filings in a bottle arranged precisely as for generating hy- drogen (see Experiment 11, § 35), and pour about 25 c. c. of dilute nitric acid made by adding to the common strong acid its own bulk of water. Brisk action will immediately occur. The generator be- comes filled with red fumes which gradually disappear, and when the gas disengaged is collected over water, it is found to be colorless. Collect three bottles, of 300 to 400 c. c. capacity of this gas, adding acid from time to time as may be necessary. Save the blue solution (copper nitrate) which remains in the generator for future use. Exp. 19a. — Dip a lighted candle into a bottle of the gas. The light is extinguished. Into the same bottle thrust a glowing splinter. It will not inflame. Exp 19b. — Lift a bottle of the gas from the water so that air may enter the bottle, and the gas may escape into the air. Red fumes, of very disagreeable smell, and very irritating when inhaled, are abun- dantly produced. Bring into contact with these fumes, a piece of mois- tened litmus-paper. It becomes red ; the significance of this action will appear later. 34 COMPOSITION OF NITUlV OXIDE. [§ 51,. Exp. 19c. — Thoroughly ignite a bit of sulphur in a deflagrating- spoon, and introduce it into a bottle of the gas. It will not bum. Into the same bottle thrust a piece of phosphorus as big as a pea, burn- ing actively. The combustion will be continued with great bril- liancy. 51. By the preceding experiments we learn that the new gas is transparent and colorless, and that it differs notably from all the otiier gases thus far studied in its relation to combustibles. Analysis shows that the gas consists of nitrogen and oxygen, one volume of each gas uniting to form two volumes of the compound gas. Its molecule will be represented by the for- mula NO ; and its elements are united by weight in the pro- portion of 14 parts of nitrogen to 16 of oxygen, because equal volumes of nitrogen and oxygen weigh respectively 14 and 16 times as much as the same volume of hydrogen. Its com- position may be represented by the accompanying diagram. <- — — 1 The gas is thus another ox- N 14 + O 16 NO 30 I ide of nitrogen ; it is gener- ally known as nitric oxide, but some regard the molecule as IfjOj and name the compound nitrogen binoxide. The action of the copper on the nitric acid in Exp. 19^ may be represented by the following equation : — 3Cu + SHNOj = 3CuNp„ -f 4Hp + 2NO. Copper. Nitric acid. Copper nitrate. Nitric cxide. When the same element unites with oxygen in more than one pro- portion, the compound containing a single atom of oxygen in the molecule is called the protoxide; when the molecule contains two atoms of oxygen, the compouhd is called the binosdde ; succeeding oxygen compounds would be the teroxide, guffdroxide, etc. The term peroxide may be applied to any compound containing more oxygen than the protoxide, although if there are several such oxides it is used conventionally, to denote a particular one. Sometimes the relative amount of oxygen is indicated by the terminations -oiis and ■ie ; in this case -ous implies less oxygen than -ic ; nitroMS oxide contains less oxygen than nitric oxide. These terminations are not § 52.] CONDENSATION OF NlTKOUilJS PEROXWE. 35 restricted in their use to oxygen compounds ; we shall, hereafter, meet such terms as ferrous chloride and ferric chloride, stannous sul- phide and stannic sulphide. 52. Nitrogen peroxide (IfO^).— The red fumes of Exp. I9b, Been when nitric oxide was brought into the air, were due to the chemical union of nitric oxide with oxygen ; a third oxide of liitrogen was formed, — ^nitrogen peroxide. The volumetric composition of nitrogen peroxide will be understood from the accompanying diagram. The molecule -will be represented by the formula NOj, and the composition of the substance by weight will be 14 parts of nitrogen and 32 of oxygen in every 46 parts by weight of nitrogen peroxide. N + NO, 53. Although at ordinary temperatures nitrogen peroxide is a gas, it can readily be condensed to a liquid. For this purpose, it is best prepared by heating a substance known as lead nitrate. Exp. 20. — Fill a perfectly dry ignition tube about one-third full of lead nitrale which has been finely powdered, and th/)ro^ighh/ dried. Connect the ignition tube' with a dry bottle, and finally with the water pan ; the arrangement is similar to that in Fig. 15, except that the flask is replaced by an ignition tube. The small bottle must be surrounded by a mixture of ice (or snow), and salt. Heat the ignition tube gently, and when the evolution of gas has once begun, care must be taken that the tube is not suffered to cool, so as to allow the water to suck back from the water pan. Red fumes will fill the delivery tubes, and will condense in the small bottle to a brownish-yellow liquid if the experiment is successful. A colorless gas will collect at the water pan-; it is oxygen, as may be shown by the insertion of a glowing splinter. The chemical action may be thus represented : — VbTSp, = PbO + O + 2NO,. Lead nitrate. Lead oxide. Nitrogen peroxide, 36 OXIDES OF NITROGEN. [§ 54. The experiment just performed is interesting, as showing the transformation of a substance which is usually a gas, into a liquid ; in this case, it was only necessary to lower the temperature. Many other gases may be liqueiied in the same manner, by being cooled to a low temperature ; and by the application at the same time of a very great pressure, it has been found possible to liquefy all known gases, even oxygen, nitrogen and hydrogen, which until recently were regarded as permanent or incondensable gases. 54. Other Oxides of Nitrogen. — A fourth oxide of nitrogen is an unstable, white, solid compound whose symbol is NjO^. It is called nitric anhydride, and is closely related to nitric acid. Nitric acid we have already used, and have learned that its sym- bol is HNOj . If the oxide NjO^ be treated with water the action which takes place may be represented by the equation : — H,0 + If A = H,0,NA = 2HNO,, Watfu'. Nitric anliydride. Nitric acid, which expresses the fact that, by the union of one molecule of water and one molecule of nitric anhydride, tliere are formed two molecules of nitric acid. On account of this reaction, nitric acid may be, and is sometimes regarded as a compound of nitric anhy- dride and water, and its formula may be written, Hp, NjOj. The origin and propriety of the term nitric anhydride now becomes apparent ; for this oxide of nitrogen, although it is obtained directly from nitric acid only with difficulty, may evi- dently be regarded as nitric acid deprived of water ; that is, rendered anhydrous. 55. There is still a fifth oxide of nitrogen the symbol of which is MTjOj. This compound may be formed as a brownish-red gas, similar to the IfOj and mixed with some of the latter gas, by heating together strong nitric acid and common starch. The compound is called nitrous anhydride. Exp. 21. — Into a flask of about 250 c. c. capacity, put 50 c. c. of strong nitric acid, and 5 grms. of starch. Warm the flask gently and as soon as the mixture begins to turn reddish-brown remove the lamp. The experiment should be performed where there is a good draft of air, as the red fumes are copiously evolved when the action once begins. § 57.1 ^-^ ^^ OF MULTIPLE PROPORTIONS. 37 56. The oxides of nitrogen, then, are — Nitrogen protoside, NjO ; Nitric oxide, NO ; Nitrous anhydride, N^Oj (from which we have nitroua acid, HNOj); Nitrogen pero^de, NOj ; Nitric anhydride, NjOj (from which we have nitric acid, HNO,). 57. These five bodies are all chemical compounds; they' are definite and constant in composition, and all differ essen- tially from their elementary constituents and from each other, as the experiments we have performed with several of them have demonstrated. It is, therefore, obvious that two of the elements are capable of combining in several proportions to form definite chemical compounds ; and what is here proved of two of the elements we shall hereafter find to be true of all, although not of every couple ; so that the series of oxides of nitrogen is but one illustration of a most comprehensive law. The difference between a mechanical mixture and a chemi- cal compound does not on this account become less marked. The possible mixtures of nitrogen with oxygen are innumer- able; the known combinations of these two elements are only five : two volumes of nitrogen combining chemically with either one, two, three, four or five volumes of oxygen, and with no other proportions whatsoever. As for volumes, so for weights : the proportional weight of "xygen in these oxides rises by definite leaps from the first member of the series to the last. This definite, . step-by-step mode of forming chemical com- pounds is one of the most characteristic, as it is one of the most general, facts of chemistry; it is the habitual mode in which the force called chemical ordinarily acts. The abstract results of observation and experiment may be expressed ia the following proposition, often called the Law of Multiple Pro- portions: If two bodies combine in more than one propor- 38 AIR A MIXTUR-tJ. [§ 58. tion, the ratios in which they combine in tlie second, third and subsequent compounds, are definite multiples of those in which they combine to fm'm the first. 58. Air a Mixture. — The distinction between a mechani- cal mixture and a chemical combination may be illustrated by the differences between common air -and the oxides of nitro- gen. Some of the considerations which go to show that air is simply a mechanical mixture of oxygen and nitrogen are as follows : — In the first place, while in the oxides of nitrogen the two elementary gases bear to each other some simple relation in re- spect to both volume and weight, in air they are mixed in the far from simple proportion of 20.96 measures of oxygen to 19.04 measures of nitrogen, or 23.18 parts by weight of oxygen to 76.82 parts of nitrogen; moreover, if 23.18 parts of oxygen are mixed with 76.82 of nitrogen, there is no development of either light, heat or electricity, such as usually attends the formation of a chemical compound ; and the physical charac- teristics of the mixture are such as should, according to calcu- lation, belong to a mere mixture of the gases. Again, if nitric oxide be brought into contact with air, suffo- cating red fumes of nitrogen peroxide are formed; but if the nitric oxide be brought into contact with nitrogen protoxide, no fumes are produced, although this gas contains as much oxygen as common air. These experiments go to show .that, while in nitrogen protoxide the oxygen is held in chemical com- bination, in air it is free. Further evidence that air is a mere mixture is afforded, by its behavior towards- water. All gases are soluble in water to a greater or less extent, each one dissolving in a certain fixed and definite proportion at any given temperature. If pure water be exposed to nitrogen protoxide, it will dissolve a certain amount of that gas, which may be recovered unchanged by boiling the water. "When water which has been exposed to the air is boUed, a gaseous mixture contaiiling oxygen and ni- trogen is given off (Exp. 10, § 33) ; but it has been found that § 59.] NITRIC ACID. 39 the gases are mixed in a different proportion from that in which they exist in the atmosphere. The water, in fact, dissolves out from the air a quantity of oxygen, just as if no nitrogen were present; at the same time it dissolves nitrogen to precisely the same extent that it would dissolve that gas if there were no oxygen in the air. 59. Nitric Acid (BJSO^. — In the preparation of the various oxides of nitrogen we have used either nitric acid or a compound which we have designated as a nitrate, as, for example, ammonium nitrate in Exp. 17, and lead nitrate in Exp. 20. We now pro- ceed to a study of those compounds, and, in the first place, of nitric acid itself. Two abundant sources of this material are found in nature and are familiar as articles of commerce. Salt- petre or nitre, a whitish saline crystallized substance, now mainly brought from India, is one of tliese sources ; a similar substance, known in commerce as " nitrate of soda," is collected on a desert tract in ChUi and Peru, and forms a valuable article of export from those countries. These two substances differ from each other only in this, — that the first contains potassium, the second the very similar element sodium, in either case combined with definite proportions of the elements nitrogen and oxygen. By the reaction of sulphuric acid (oil of vitriol) on either of these two substances, nitric acid is obtained. Exp. 22. — Into a tubulated glass-stoppered retort of 250 c. c. capacity^ put 40 grammes of powdered potassium nitrate, or, better, 34 grammes of powdered sodium nitrate, if it can be obtained, and through the tubulure pour 50 grammes of strong sulphuric acid, which has been weighed out in a bottle previously counterpoised upon the balance with shot or coarse sand. Imbed the bottom of the retort in sand contained in a small iron pan placed over the gas-lamp on a ring of the iron stand. Thrust the neck of the retort into a re- ceiver with two tubulures ; the retort-neck should fit the tubulure of the receiver with tolerable accuracy. The second tubulure of the receiver should be left open, or loosely covered with a bit of glass, in order to avoid the possibility of any pressure being created within the retort during the operation. Place the receiver in a pan of cold water, and cover it with cloth or bibulous paper, which must be kept 40 NITRIC ACID. [§60. wet during the distillation., (See Fig. 17.) Heat the sand-bath moderately (that the frothing which occurs may not become too violent) ; reddish vapors appear for a moment, then disappear, and a yellowish fuming liquid begins to condense in £he neck of the retort and to run down into the receiver. When all frothing has ceased and the mass in the retort is in a state of tran- quil fusion, while very little liquid passes over into the receiver, the lamp is to be put out. The very acid, corrosive and poisonous liquid in the receiver is nitric acid ; its faint color is not its own, but is due to the^presence of a compound of nitrogen and oxygen already described (NOa). Transfer the liquid to a glass-stoppered bottle, and keep it for future use. In all manipulations with nitric acid, it is desirable to avoid getting it upon the skiu, since it produces rather permanent yellow stains. As the retort cools, the residue solidifies into a white, saline mass, which must be dissolved out of the vessel by heating it with water after the apparatus has become thoroughly cold. It will be observed that the liquid sulphuric acid which was used has disappeared, al- though the saline residue is still intensely acid. 60. Nitric Acid is much used in the arts, and is prepared on the large scale from the same materials as here employed. The retorts are huge iron cylinders or kettles and the acid is collected in stoneware bottles. The pure acid is colorless and is about half as heavy again as water. It may be mixed with water in all proportions. Exp. 23. — To about 1 c. c. of the nitric acid obtained in the last experiment add 10 times its bulk of water. Notice the sour taste by touching a drop of this diluted acid to the tip of the tongue. Into the solution thrust a strip of litmus paper ; it will be turned red, showing that in spite of the amount of water added, the liquid is still strongly acid. Litmus is a blue coloring matter, prepared from various lichens. Unsized paper, colored with a solution of litmus in water, is a convenient test fo-r many acids, which, as a rule, change the color of the paper from blue to red. § 61.] ACIDS, BASES AND SALTS. 41 61. Acids, Bases and Salts — Nitric acid is an example of the class of bodies to which the term acid is generally applied. There is a class of bodies which act upon vegetable colors in just the opposite way from the acids, and will in fact neutralise their action in many cases. As an example of these substances, which are generally spoken of as bases, and which when soluble in water have what is called, an alkaline reaction, we may take caustic potash. Exp. 24. — Dissolve about one gramme of caustic potash in 20 c. c. of water. Notice the character of the solution by rubbing a little between the fingers, and by touching a small drop to the tip of the tongue. Into the liquid thrust the litmus paper, which was reddened by the nitric acid in Sxp. 23. It will be turned blue. The terms acid and base which we have used cannot be defined with exactness, because they are not applied by chemists with uniform precision to well-defined classes of substances. "We may say, however, in general terms, that the acids commonly possess a sour taste and act in a peculiar way upon vegetable colors (as nitric acid reddened the litmus paper in Exp. 23). The acids are usually compounds of hydrogen, oxygen and some one other chemical element, as, for example, nitric acid (HNO^) ; bases, likewise, are compounds of hydrogen, oxygen and some one other chemical element, as, for example, caustic potash (KHO) ; but while certain elements in uniting with hydrogen and oxygen form by preference acids, other elements form by preference bases. The so-caUed non-metallic elements, such as nitrogen, sulphur, etc., generally form acids: for example, nitric acid (HNO^) and sulphuric acid (H^SO^). The metallic elements, such as potas- sium, sodium, copper, etc., form bases ; thus caustic potash or potassium hydrate (KHO), sodium hydrate (WaHO) and copper hydrate (CuH^Oj), are bases. An important characteristic of the acids and bases is that they have the power, when one of either class is brought into contact with one of the other and opposite class, of forming new com- pounds possessing the characters of neither the acid or base from which the new compound, or salt as it is called has been formed. 42 ACIDS, BASMS AND SALTS. [§ 62, 62. The relations between acids and bases may be illustrated by the following experiment : — Sxp. 25. — To one-third of the nitric acid of Exp. 22, § 59, diluted with twice its bulk of water, add cautiously a rather dilute solution of caustic potash (potassium hydrate, KHO) until the mixture turns litmus-paper neither red nor blue. Evaporate the solution in a por- celain dish, taking care that the liquid does not actually boil, until a drop taken out on the end of a glass rod becomes nearly solid on cooling. Then remove the lamp, and allow the dish to become cold. The crystals which will separate from the liquid are potassium ni- trate, a compound which has already been used in the manufacture of nitric acid. The change that has taken place may be thus sym- bolized :— ■HN03 Jf KHO = KNO3 -f H.O. Nitrie acid. Caustic potash. Potassium nitrate. Water. The water in which the nitrie acid and caustic potash were dis- solved, together with that set free by the reaction, has for the most part been removed by evaporation. It might have been removed entirely if the evaporation had been carried further-. The potassium nitrate would then be obtained as a white crystalline substance, but not in well-defined crystals. When, as in the above experiment, an acid and a base are brought into contact, there is formed, besides water, a new com- pound. This compound is called a salt, the name being applied to it on account of the general resemblance which this class of compounds bear to common salt, — one of the earliest known and most familiar of saline bodies. 63. If we compare the formula of nitric acid (HNO,) with that of potassium nitrate (KNO3), we shall observe a striking resemblance between the two ; the two formulas are in fact identical, except that in the one case we have K, the symbol for potassium, where in the other we have H, the symbol for hydro- gen. Potassium nitrate is only one of a class of analogous com- pounds called nitrates ; the formula of each member of the class is that of one or more molecules of nitric acid, (HlfOj , HjNjOj, etc.,) except that the hydrogen is replaced by some metallic § 63.] ACIDS, BASES AND SALTS. 43 element. We have, indeed, already used several of these nitrates. Thus in Exp. 20, we used lead nitrate, the symbol of which is PbHjOg , and in Exp. 19, we prepared copper nitrate which re- mained in the solution, and the symbol of which is CulfsOj. As the nitrates correspond to nitric acid, so corresponding to every acid, there is a series of salts, the name common to all the series being derived from the name of the acid. Thus corres- ponding to sulphuric acid there are numerous sulphates, corres- - ponding to phosphoric acid there are phosphates, to oxalic acid oxalates, etc. As will be noticed in the cases above mentioned, the acid is designated by a term ending in ic, and the term ap- plied to the salts ends in ate ; if, however, the name given to the acid ends in ous, the name given to the salts ends in ite ; thus, corresponding to mitous acid we have a series of vMxites ; thus, nitrous acid, HNO^, potassium nitrite, KlfOj. Further use of the terms Acid and Base. — The term acid, besides being used as defined in § 61, is applied to certain bodies which are destitute of oxygen, like chlorhydric acid (HCl) ■ These- acids are those formed by the union of hydrogen with some mem- ber of the chlorine group (see page 65), and a few oth3rs. The salts corresponding to such acids are designated by terms ending in ide ; thus we have chlorides, bromides and fluorides from chlorhydric, bromhydric and fluorhydric acids respectively. The term base is sometimes used to denote certain compounds which contain no hydrogen. If potassium oxide (Kp), which may be formed by heating metallic potassium in dry air or oxy- gen gas, be treated with nitric acid, the following reaction will take place : — Kp + 2 HNO, = 2 KWO, + HP. The same "salt," potassium nitrate (KNO^), is produced as in Exp. 25, where potassium hydrate and nitric acid were brought together. On account of their taking part in such reactions as these, the anhydrous oxides of the metallic elements are often spoken of as bases. In some cases the oxide is more commonly employed than the hydrate, or base proper, in neutralizing acids and in forming salts. This is the case with oxide of lead. 44 NITBOOEN AND HTDBOOEN. [§64. Exp. 26. — Put the nitric acid which remains from Exp, 22, into an evaporating dish, dilute with twice its bulk of water, and add finely powdered litharge as long as it readily dissolves. Evaporate the solution carefully to dryness, using a very gentle heat. There remains a white saline substance which is lead nitrate such as was used in Exp. 20. Its formation is thus represented : — PbO + 2Hlf03 = PbN.Oj + Hp. Lead oxide. Lead uitrate. The term anhydride (or more definitely, acid anhydride) is commonly applied to an oxide of a non-metallic element, which in combination with the elements of water forms an acid, as was illustrated by nitric anhydride in § 54. To these anhydrides the term axid was formerly applied, as well as to the ■acids proper. To distinguish between the two sorts of compounds, the terms anhydrous and hydrated were employed ; thus, IfjOj was known as anhydrous nitric acid, and HNOj as hydrated nitric acid. NITROGEW AND HYDROGEN-. 64. Nitrogen and Hydrogen. — AVhile there are five com- pounds of nitrogen with oxygen, there is but one known com- pound of nitrogen and hydrogen. This is a gas, and may be readily prepared from ammonia-water, — the aqua ammonioe of the druggists. Pig 18. Fill a flask of 250 to, 500 c. c. capacity about half full of the strongest ammonia-water to be had at the druggist's. Close the flask by a cork provided with a fimnel- tube and an exit-tube ; carry the delivery-tube to the bottom of a tall bottle, having a capaci- ty of at least a litre, and filled with fragments of quick-lime. When the ammonia-water in the § 65.] PROPMRTIKS OF AMMONIA. 45 flask is gently boiled, the gas which passes off will be deprived of moisture by the quick-lime, and will issue dry from the bottle ; it may be collected over mercury, or by displacement, as shown* in the figure (Fig. 18). The gas is so extremely soluble in water, that it cannot be collected over the ordinary water-pan ; as it has little more than half the density of atmospheric air, it can be readily collected by displace- ment. When thus collected, the gas should be allowed to pass into the very loosely corked bottle, until a piece of turmeric paper, held at the mouth, is immediately turned brown ; the delivery-tube is then withdrawn, and the mouth of the bottle is tightly closed with a caoutchouc or glass stopper. If the gas be collected over mercury, the flask must be provided with a very long funnel-tube ; for the pressure to be overcome by the gas in forcing its way through even a few centimetres of mercury is quite considerable, and unless the funnel-tube were long enough to sustain a column of liquid exerting an equal pressure, the liquid in the flask would be forced out through this tube. The gas thus obtained is transparent and colorless, possesses an extraordinarily pungent odor which provokes tears, and has an acrid, alkaline taste. It will be found to be uninflammable, and is, of course, irrespirable. It turns red litmus to blue most ener- getically. One measure of water at 0° dissolves 1,049 measures of the gas. The ready solubility of ammonia-gas may be illustrated as fol- lows : Fill a stout glass tube — an ignition-tube, for example, — over mercury with the gas ; grasp the tube by the top, and, holding it up- right, dip its mouth into a vessel of water. The water will rush up the tube, if the gas be pure, with a force which might break the tube, if too thin. 65. The solution of ammonia if exposed to the air, or placed in a vacuum, or sunply boiled, loses all its gas. When the gas is cooled to 0° and subjected to a pressure of 4|- atmospheres, it is converted into a transparent mobUe liquid. The gas may also be liquefied at the ordinary pressure if cooled to — 40°. Liquid ammonia in passing into the gaseous state absorbs a large amount of heat from surrounding objects. In certain machines for the production of ice artificially, advantage is taken of this 46 AMMOMUM SALTS. [§GG. fact, the necessary cooling of the water being produced by the rapid evaporation of liquefied ammonia-gas, in contact with the vessel containing the water. 66. Analysis of dry ammonia-gas has shown that it is made up of nitrogen and hydrogen in the proportion of one volume of ni±rogen to three volumes of hydrogen, the four volumes of the elementary gases being condensed to two volumes in the compound. The formula of its molecule is NH,, and its com- position may be represented by the diagram, — H 1 ■ + H 1 N 14 = NH3 ir H 1 67. Ammonium Salts. — Since ammonia-water gives off the gas so easily when boiled or even when exposed to the air, it might seem, at first sight, that it was a case of simple physical solution ; there is, however, good reason for considering that each molecule of ammonia is in combination with a molecule of water, in the form of the compound If H^, H^O or NH^O. This compound may be supposed to be dissolved in the water present in excess of what is necessary to form the compound. When ammonia-water is mixed with nitric acid, a reaction occurs like that which takes place when nitric acid is mixed with a solution of caustic potash (Exp. 25, § 62) ; there is formed a salt called ammo- nium nitrate, resembling potassium nitrate ■ but, in order to bring out the resemblance, the eleinents of the compound of ammonia and water must be so arranged as to exhibit its analogy with caustic potash, whose formula is KHO. For that purpose, its formula must be written (ITH^^HO, so that the group of elements NH^ shall stand in the formula of ammonia-water where the element potassium stands in the formula of caustio § 68.] aouncjis of ammonia 47 potash. Tho reaction between ammonia-water and nitric acid may then be represented by the equation, — (NH,)HO + HNO3 = (NH,)N03 + H,0, Ainiiionia-watei'. Nitric atid. Airiiuonium uitrate. Water. just like — KHO + HNO3 = KNO, + H,0. If now the formula of ammonium nitrate, (NH<)N0„ bei compared with that of nitric acid, HNO3, it will appear that the group of atoms NH, replaces the atom H, just as the atom K did in the formula of potassium nitrate : for this reason it has been found convenient to give to this group of atoms a name bearing some resemblance to the names of metals ; and it has, therefore, been called ammoiuiuu. Ammonium is known only in its compounds ; many attempts have been made to obtain it in a free state, but hitherto in vain : as soon as the group of atoms escapes from combination, it is resolved into ammonia and hydrogen. The important compounds into which ammonium enters, commonly called the salts of ammoumm, will be studied hereafter in immediate connection with the analogous salts of sodium and potassium. 68. Ammonia exists in very minute quantity in the atmos- phere, and hence in rain-jvater, fog and dew. It is given off by putrefying animal and vegetable substances containing nitro- gen, and almost every process of slow oxidation in the presence of air and moisture is attended with the formation of ammonia or ammonium salts. The chief source, however, of ammonium compounds is the decomposition, either by putrefaction or by destructive distillation, of nitrogenous organic matter. The dis- tillation of bones and animal refuse, for the purpose of making bone-black, yields a large amount of ammoniacal liquor, which was formerly the principal source of ammonium compounds. The horns of deer used to be thus distilled ; whence the name " hartshorn." At present, the destructive distillation of coal in gas-works furnishes the great bulk of ammouium compounds used in the arts. 48 MAKING AMMONIA-WATER. [§69. 69. The solution of ammonia-gas in water is a reagent con- tinually required, as a test, in the laboratory, and much used in the arts. The solution is colorless, intensely alkaline, has a caustic taste, and, when concentrated, blisters the skin ; it is lighter than water, and so much the lighter in proportion to the amount of ammonia that it contains. The solution may be prepared from a mixture of ammoulum chloride and slaked lime. Exp. 27. — Mix 25 grms. of ammonium chloride, a substance generally sold under the name of sal ammoniac, with about the same Fig. 19. weight of cold, freshly-slaked lime. Introduce the mixture into a flask of 500 c. c. capacity, and place the flask on a sand- bath over the gas-lamp. Close the mouth of the flask with a good cork, provided with a de- livery-tube so bent as to con- nect conveniently, by means of a caoutchouc connector, with the first of the series of three-necked bottles (Woulfe-bottles) represented in Fig. 19. On heating the mix- ture, ammonia-geis will be disengaged, and will be absorbed by the water in the Woulfe-bottles. The first of this series of bottles is smaller than the rest, and is not filled so full of water as the others ; it should be kept cool by immer- sion in cold water ; the delivery-tube coming from the flask into this bottle must not dip into the water at all, so that it will be impossible for any water to suck back into the flask, should the gas suddenly cease to come oflF from the dry mixture. The construction of the apparatus will be easily understood from the figure ; the open tube which dips beneath the water in each bottle is a safety-tube, which by admitting air into any bottle in which a partial vacuum may hap- pen to be created by rapid absorption, prevents the contents of the succeeding bottle from flowing back into it. In order to show the action of the safety-tubes, the open tube in the first bottle may be closed for a moment with the fii:^er, and the bottle shaken very gently. "Water will be immediately forced back from the second bottle through the connecting-tube to fill the vacuum caused by the absorption of the § 70.] CHWRHYDRW ACID. -n animonia-gas ; but the moment the finger is removed from the safety- tube, air will enter through the latter to fill the vacumn, and the water in the connecting-tube will fall back into the second bottle. The aimnonia-gas can not avoid three separate contacts with water aa it passes through the apparatus, so that all the gas is sure to be ab- sorbed ; the contents of the first bottle will not be as pure as those of the succeeding. In this experiment the gas will be mostly absorbed in the first and second WouU'e-bottles. The reaction between the ammonium chloride and the slaked lime is represented by the following equation : — aNH^Cl -f CaHjO^ = 2NH, -\- CaClj, -|- 2HjO. Ammonium chloride. Slaked lime. Ammonia. Calcium cliloride. Water. Ammonium chloride is a compound which may be obtained by bringing together dry ammonia, NH,, and dry muriatic-acid gas, HCl. NH3 + HCl = NHjCl. It may obviously be regarded as a compound of the group called ammonium, NH, , with the element chlorine ; from this view is derived the name ammoninm chloride. Slaked lime is prepared by adding water to quick-lime, which is chemically the oxide of the metal calcium. CaO -f HjO = CaHjOj. J_ CHAPTER VII. CHLOEHYDEIC ACID. 70. Muriatic (sea-salt) acid, called in modem nomenclature chlorhydric acid, is a liquid which has been known for centu-"- ries, and is to-day an article of commerce, largely employed in the useful arts. The pure acid is a gas, as ammonia is ; the liquid muriatic acid of commerce is only an aqueous solution of 6 50 CHLORHYDRIC ACID. [§71. Fig. 80. this gas, and gives it up when heated, precisely as ammonia- water yields ammonia-gas. This operation may be conveniently performed in the apparatus shown in Fig. StT About 250 c. c. of the commer- cial acid is poured in- to the flask, which is then moderately heated ; the gas disengaged is charged with aqueous vapor, which needs to be removed before the gas is collected. For this purpose the deliv- ery-tube is carried to the bottom of a bottle filled with pieces of pumice- stone saturated with strong sulphuric acid : the moisture of the gas is greedily absorbed by the large surface of acid with which the gas comes into contact, as it is forced upward through the acid-soaked stone. The dry, colorless, transparent gas must be collected over mercury, for it is extremely soluble in water. The gas is strongly acid in taste and reaction on vegetable colors, provokes violent coughing and is wholly irrespirable. It is neither combustible, nor will it support combustion. The gas is somewhat heavier than air : it is very soluble in water, and may be condensed to a liquid, although with difficulty. The avidity of water for chlorhydric acid gas may be neatly shown by thrusting a bit of ice into a small cylinder of the dry gas standing over mercury : the ice instantly melts, and the gas as quickly disap- pears. 71. The composition of the gas has been determined, both by analysis and by synthesis ; and it has been found that one volume of hydrogen is combined with one volume of the ele- mentary gas chlorine (Cl) to form two volumes of chlorhydric acid. The molecule of chlorhydric acid will be represented by the formula HCl ; and, as the specific gravity of chlorine, that ■§72.] CULORHYDRIC ACID. 51 is, the weight of any volume compared with an equal volume of hydrogen, is 35.5, the following diagram represents the com- position of this important compound, both by volume and by weight : — H 1 + CI 35.5 HCl 36.5 72. The muriatic acid of commerce is made from the most abundant and cheapest of all the natural compounds of chlorine, — common salt, whose chemical name is sodium chloride, and whose formula is NaCl. This substance sup- plies the chlorine : the necessary hydrogen is obtained from common sulphuric acid (oil of vitriol), whose composition, as expressed in its formula H^SO,, we have already become familiar with. The reaction is somewhat various, according to the proportion of sulphuric acid employed ; it may be either of the reactions expressed in the following equations : — NaCl -f H„SO, Sodium cliloride. Sulplmric acid. 2 NaCl + HjSO, = HCl ClUorhydrio acid. = 2 HCl + HNaSOj Hydrogen Sodium sidpliate. + Na,SO,. Sodium sulphate. In the first of these reactions, only one-half of the hydrogen in each molecide of sulphuric acid is replaced by sodium ; in the second, both atoms of hydrogen are thus replaced. The first reaction requires more sulphuric acid, in proportion to the amount of the product than the second, but is accomplished with less wear of the apparatus, be- cause a more moderate heat suffices lor the first than for the second reaction. On the nianufactiuing scale, the salt and sulphuric acid are heated in large iron cylinders, and the evolved gas is absorbed by water con- tained in a series of stoneware Woulfe-bottles. The ordinary com- mercial acid contains from 30 to 40 per cent by weight of real acid. Exp. 28.— Place 30 gmis. of dry (or better, fused) coarsely powdered 52 PREPARATION OF CHLORHYDRIC ACID. [§ 73.- salt, in a flask of a litre capacity, provided with a delivery-tube which can be conveniently connected by a caoutchouc connector with a yj jjj_ series of small Woulfe-bottles, such as is represented in Fig. 21. Pour 50 grms. of strong sul- phuric acid upon the salt, and immediately cork the flask, place it upon a sand-bath on the iron- stand and connect the delivery- tube with the Woulfe-bottles. The tubes by which the gas en- ters the bottles should barely dip beneath the water contained in them, inasmuch as the solution of chlorbydrio acid is heavier than water : the bottles should not be more than half full, for the" water becomes hot, and increases considerably in bulk. As hot water holds less gas in solution than cold water, it is not amiss to place each three- necked bottle in a vessel of cold, water. The first Woulfe-bottle should contain but a small quantity of water, and the tube coming from the flask should not dip into this water. The contents of the flask must be very gradually and moderately heated, else a violent frothing is liable to occur, which would spoil the experiment. The acid will be purer in the second bottle than in the first, in the third than in the second, and so forth. 73. The uses of chlorhydric acid are very numerous : it is employed in making chlorine, potassium clilorate, and " chloride of lime " (bleaching powder) ; in preparing ammonium chloride' and tin chloride ; in the manufacture of gelatin ; for dissolving metals, either by itself or mixed with nitric acid ; and it is one of the most useful reagents in the chemical laboratory. 74. Chlorhydric acid, as has already been stated (§ 63), differs from the other acids with which we have become acquainted in that it contains no oxygen. As there are certain compounds called nitrates whose formulae may be derived from that of nitric acid by replacing the symbol of hydrogen in the acid by that of some metallic element ; so there is a series of compounds, the formulae of which may be derived from that of chlorhydric acid by putting the symbol of a metallic element in the place of the symbol of hydrogen in the acid. These compounds § 75.] QUAiVTl VALEXCE. 53 are called chlorides : thus sodium chloride^ comnion salt, is NaCl. Chlorides are i'omieil in some cases by treating the metal with chlor- hydaic acid, as in the formation of zinc chloride (ZnCl,), Exp. II, § 35 : in other cases they are formed by treating the oxide, or the hydrate, of the metal with chlorhydric acid, as may be seen in these ei^nations : — NaHO -f HCl = NaCl + H^O ; Sotliuni liytlrate. Sodium chloride. AgjO 4- 2 HCl = 2AgCl + HjO; Silver oxide. Silver chloride. CuO -|- 2 HCl = CuClj -f up. Copper oxide. Copper chloride. If the formula of silver chloride (AgCl) be compared with that of zinc chloride (ZnCl^), tliis difference will be observed between them, — that while the molecule of silver chloride may be regarded as a molecule of chlorhydric acid (HCl), in which the atom of hydrogen (H) is replaced by an atom of silver (Ag), the molecule of zinc chloride must be regarded as formed from two molecides of chlor- hydric acid (HjClj) by replacing two atoms of hydrogen (H^) by one atom of zinc (Zn). Now, there is a class of metals which, like silver, replace hydrogen 'atom for atom : these metals are said to be uni- valent. There is another class of metals which act like zinc in re- placing hydrogen : they are said to be bi-valent. The same dis- tinction is seen in the other compounds of these elements : thus, sulphuric acid being H^SO^, zinc sulphate is ZnSO^, and silver sulphate is AggSO,; nitric acid being HNOj, zinc nitrate is ZnN^Oj, and silver nitrate is AgNO,. It will appear hereafter that there are elements which are tri-valent, quadri-valent, etc. In gen- eral terms, the replacing-power of any element with respect to hydrogen is called its quantivalence ; this quantivalence of an element may be learned, not only from the number of hydrogen atoms which the atom of the element can replace, but also from the number of hydrogen atoms with which it can combine : thus, from the formular of chlorhydric acid, HCl, we learn that chlorine is here uni-valent, as the atom of chlorine combines with only a single atom of hydrogen. [See also page 288.] 75. Aqua Begia (Royal Water). — This name was given by the alchemists to a mixture of chlorhydric and nitric acids, because of its power to dissolve gold, the " king of metals." 54 AQUA REGIA.— NASCENT STATE. [§76. Exp. 29. — Place a few square centimetres of genuine gold-leaf at the bottom of a test-tube, and pour upon the gold a little strong chlorhydiic acid ; put some gold-leaf in a second test-tube, and pour upon it a few drops of nitric acid : neither acid attacks the gold, which remains undissolved. If the contents of the two test-tubes be mixed together in either tube, the gold-leaf will almost immediately dissolve. The efficacy of aqua regia as a solvent of gold depends upon the fact that the nitric and chlorhydiic acids mutually decom- pose each other. Chlorine is set free, and, as it issues from itf combination with hydrogen, acts on the gold much more ener- getically than it would in its ordinary condition. The chlorine in this case is said to be in the nascent state. There are numerous cases in which bodies, which do not unite under ordinary conditions, are capable of chemical combination at the instant when they are disengaged from other compounds ; and the phrase, " m the oiascent state," just used, is one of some convenience, although it must not be supposed to explain, or in any way to account for, the phenomena with reference to which it is employed. V 76. The practical importance of a knowledge of the atomic weights in calculating the proportional amounts of the different substances taking part in any 'case in a chemical action, baa already been explained in § 36, and may, at this point, be further illustrated as follows. In the manufacture of chlorhydric acid, for instance, suppose it were required to ascertain how much sulphuric^ acid would be necessary to decompose 100 kilos, of salt, bearing in mind that the result may be effected according to either of the two actions formulated on page 51. The molecular wt. of NaCl is 23 + 35.5 = 58.5 " " H,SO, is 2 -I- 32 -}- 4 X 16 = 98 " HNaSO, is 1 + 23 -f-.32 -f 64 = 120 " " " NsLJSO^ is 46-1-32-1-64 = 142 " " " HCl is 1 -f- 35.5 = 36.5 The weight of the sulphuric acid needed in tlie two cases is ascertained by solving the following proportions : — §77.] THE CHLORINE GROUP. 55 First ; reactioil ; Second reaction 58.5 Mol. wt. NaCl 117 Mol. wt. of 2NaCl 98 Mol. wt. H,SO. 100 : No. hilus. NaCl used. 98 = 100 X (= 167.52) No. kilos. H^SO, needed. X (= 83.76) The weight of chlorhydric acid gas produced in the two cases ■\vill he precisely the same : it is deduced from the propor- tions, — First ) reaction ) 58.5 : 36.5 = 100 : X (= 62.39) Mol. wt. Mol. wt. Kilos. Kilos. NaCl HCl NaCl used. HCl produced. Second ) reaction ) 117 Mol. tot. 2NaCl : 73 Mol. wt. 2HC1 = 100 : X {= 62.39) The weights of the residual sodium salts in the two cases may- he deduced as follows : — First reaction Second reaction 58.5 Mol. wt. NaCl 117 _ Mol. wt. 2NaCl : 120 = 100 Mol. wt. Kilos. HNaSO, NaCl used. : 142 Mol. wt. NajSO, = 100 X (= 205.13) Kilos, of HNaSO, X (= 121.37) Kilos, of Na^SO, produced. CHAPTEE VIIL CHIOBINE, BBOUIin;, IODINE AND FLUOBIirE. CHLOBINE (ol). 77. Chlorine is an abundant element and very widely dis- tributed in nature. It exists chiefly in combination with sodium as sodium chloride, which is "called rock-salt or searsalt, accordingly as it is found in beds in the earth, or dissolved in the -wjater of the ocean. Every litre of sea-water will yield about 56 PREPARATION OF CULORIXE. [§ 78. 5 litres of chlorine gas. Besides sodium cliloride, sea-water con- tains small quantities of the chlorides of several other metals j therfe are numerous minerals, 9:lso, which contain chlorine. 78. Chlorine can readily be prepared from cMorhydric acid by removiiig the hydrogfen of that acid by chemical means. Ezp. 30. — In a flask of about 500 c.c. capacity, furnished with a suitable delivery-tube, place 8 or 10 grms. of coai'sely-pDwdered manganese binoxide ; pour upon it 20 or 30 grms. of oouimon muriatic acid, and gently heat the mixture. Chlorine will soon be disengaged, and may be recognized by its peculiar color. Being very heavy, the gas may best be collected by displacement in dry bottles placed in the open air or in a case or box provided with an efficient draft. It may also be collected over warm water or brine in the water-pan. It can not be well collected over water at the ordinary temperature, since it is rather easily soluble therein ; though the difficulty may be obvi- ated in part by evolving the gas rapidly, or by passing the delivery- tube to the top of the bottle in which the gas is collected. It must, not be left standing over water, since it would soon be entirely ab- sorbed. In experimenting with chlorine, care must always be taken not to inhale it. The reaction which occurs in this experiment may be thus formu- lated : — MnO^ + 4HC1 = 2HjO + MnCl, -}- 2CL Manganese binoxide is a substance rich in oxygen, which, under certain conditions, it readily yields up to other elements. In the case before us, the oxygen of the manganese binoxide unites with the hydrogen of the chlorhydric acid to form water. The chlorine of the chlbrhydric acid unites in part with the manganese, to form man- ganese chloride, and is in part left free. 79. At the ordinary temperature, chlorine is a gas of yellow- . ish-green color, 2.5 times heavier than atmospheric air. Its specific gravity and atomic weight are 35.5. It is excessively irritating and suffocating, even when inhaled in exceedingly small quantities. Any attempt to breathe the undiluted gas would undoubtedly be fatal. 80. Chlorine is a powerful chemical agent. It combines with hydrogen with explosive violence when a mixture of the two gases is heated, or even exposed to sunlight. 81.] rnOPERTIES OF CHLORIXK. 57 Ezp. 31. — In a soda-water bottle, which, must be screened from strong light by wrapping it in a towel, unless direct and reflected sun- light be excluded from the room, mix equal volumes of chlorine and hydrogen, then remove the cork and hold the mouth of the bottle in the fiame of a lamp. A sharp explosion will ensue. A mixture of the two gases may be kept in the dark for any length of time without change : in diffused daylight, they usually unite only slowly and gradually ; but, in direct sun- light, the union is so instantaneous as to be attended with explosion. 81. Chlorine combines also very readily with many of the metals, the combination being in several instances attended with evolution of light. Exp. 32. — Fill a bottle of at least half a litre capacity with dry chlorine gas, by displace- I'ig- iS-S' ment. Gradually sift a gramme or two of very finely-powdered metallic antimony into the bottle. The metal will instantly take fire, and fall in a glowing state to the bot- tom of the bottle. This fire attends the formation of a compound of chlorine and antimony, a portion of which will be seen per- vading the bottle as a white smoke. It is necessary for the success -of this experiment, that the gas be thoroughly dried ; this is effected by heatmg the flask containing the manganese binoxide and chlorhydric acid gently, and passing the chlorine through a tube filled with chloride of calcium. (Ajipendix, § 16.) It is not amiss to inteqjose a small bottle between the flask and the drying-tube : this bottle may be kept cool by immersion in water, and will retain a considerable portion of the moisture carried forward by the gas. This experiment, and, indeed, all experiments with, chlorine, should be performed only in places where there is a current of air sufficiently 58 PROPERTIES OF CHLORINE. [§ g2. powerful to carry away from the operator the volatile products of the reaction, together with any chlorine which may escape from the bottle. As in the case of the union of sulphur with* copper (Exp, 1, § 2), so here it will be seen that burning, as commonly under- stood, is in no wise peculiar to the union of oxygen with the other elements. In the act of chemical combination, heat is always evolved, and, of course, light as well, if particles of solid matter be present, and become hot enough to be luminous. Since oxygen is very abundant, we are more accustomed to witness exhibitions of its chemical action than of that of any other element ; but we must not, therefore, lose sight of the fact that among the elements, there are several which possess chemi- cal power as great when brought into play, though not as fre- quently exhibited as that of oxygen. 82. A burning jet of hydrogen, on being introduced into a jar of chlorine, will continue to burn with a peculiar green light, the two gases uniting to form chlorhydric acid; and, by reversing the experiment, chlorine may just as well be burned in an atmosphere of hydrogen. Although chlorine is thus both combustible and a supporter of combustion, as far as hydrogen is concerned, it does not unite directly with cither oxygen or carbon. If a bit of paper, attached to a wire, be dipped in hot oil of turpen- Flg. 83. tine, and then quickly plunged into a bottle of chlo- rine, it will usually take fire spontaneously, and bum with evolution of dense black fumes. On account of the volatility and ready inflammability of oil of turpentine, it is best heated upon a water-bath (Ap- pendix, § 17), in a porcelain dish. Exp. 33. — Thrust a burning taper, or a bit of flaming wood or paper, into a bottle of chlorine gas ; the flame will become murky, and, after struggling for a moment, will go out. Much smoke is at the same time given off. The wax, wood, paper and turpentine of the fore- going experiments, and, indeed, most of the sub- stances ordinarily used as combustibles, contain hydrogen and carbon. § 83.] Pn.OPERTIES OF CHLORINE. 59 The hydrogen of these substances will bum in chlorine, that is, -will unite chemically with the chlorine to form chlorhydric acid ; but the carbon wiU not thus unite with chlorine. Hence it is that in the ex- periments in question the combustion is at the expense of the hydro- gen ; the hydrogen of the candle, turpentine and so forth, alone unites with chlorine ; while the carbon is set free as lamp-black or smoke. 83. Chlorine is a powerful bleaching agent, and, on this account, is of great importance in the arts. The chlorine to be used for this purpose must be moist : perfectly dry chlorine will not bleach. This may be illustrated by passing perfectly dry chlorine through a glass tube filled with bits of colored calico. The coloring matters will not be destroyed so long as they remain dry ; but if, after the dry chlorine has been allowed to act for a few minutes, a Uttle water be poured into the tube, so that its contents may be moistened, they will be bleached at once. Those coloring matters which are of vegetable or animal origin are, for the most part, complex compounds of carbon, hydrogen, nitrogen and oxygen. When moist chlorine is brought into contact with them, a somewhat complicated reaction occurs : a portion of their hydrogen is, no doubt, taken out by the chlorine ; but, at the same time, some of the water which is present is decomposed, and its oxygen assists the disorganization of the compound which is to be destroyed. As a rule, the coloring matters are far more easily oxidized than the cotton cloth ; hence they can readily be removed by the action of chlorine without injury to the cloth. But, if the action of the chlorine were to be continued after the coloring matter had been destroyed, the cloth itself would gradually be burned up. The bleaching properties of chlorine may be conveniently illus- trated by means of an aqueous solution of chlorine, ohlorine- •water, which may be prepared by connecting the flask in whicli the gas is generated with a series of Woulfe-bottles, as in the prepa- ration of chlorhydric acid. (Fig. 21, § 72.) Exp. 34. — Pour into a small bottle a quantity of chlonne-water, drop into it a small quantity of a solution of indigo, and stir the mixture with a glass rod. The blue color of the indigo will be imme- diately destroyed. In the same way, the color of litmus, cochineal, aniline-purple, or 60 CHLORINE AND OXYGEN. [§ 84. of flowers, calico, and the like, can be readily destroyed by immersion in chlorine-water. 84. Chlorine is also employed as a disinfectant. It destroys noxious effluvia, either by acting on them as on coloring matters, or by simply taking away hydrogen, as in the case of snlphuret- ted hydrogen, hereafter to be studied. 85. Oxides and Acids of Chlorine. — Five compounds of oxygen and chlorine are recognized by chemists, although they have not all been isolated. Pour of them combine with the elements of water to form acids. Of these compounds the most important is chloric acid (HCIO^) corresponding to nitric acid (HWO3), and giving rise to compounds called ctlorates. Potassium chlorate (KClOs), one of these compounds, was used in Exp. 4, § 12, as a source of oxygen. Under the in- fluence of heat, it is decomposed into oxygen and potassium chloride : KCIO3 = KCl + O3. One of the salts of hypochlorous acid (HCIO), namely, calcium hypochlorite, is of great importance in the arts, being an ingredient of " chloride of . lime," or bleaching- powder. This substance is used in very large quantities for bleaching purposes : its value depends upon the readiness with which it gives off chlorine under the influence of chemical agents. When it is treated with any acid, chlorine is disen- gaged. Exp. 35. — At the bottom of a large, tall beaker, or other wide- mouthed glass vessel, of the capacity of two or three litres, place a small bottle containing 15 or 20 grms. of bleaching-powder. Cover the beaker with a glass plate, or sheet of pasteboard, provided with a small hole at the centre : through this hole in the cover pass a thistle- tube down into the bottle of bleaching-powder, and pour upon it several small successive portions of snlphuric acid diluted with an eq^ual volume of water. Chlorine gas will immediately be set free from the bleaching-powder, and, falling over into the bottom of the large beaker, will gradually press out and displace the air therein contained, so that, after a short time, the beaker will be seen to be completely filled with the green gas. This is by far the easiest and most expeditious method of preparing chlorine. The heavy gas may § 88.] BROMIXE. Gl be ladled out of the jar with a dipper made of any small bottle, and poiired upon a solution of indigo to show its bleaching power. Z!zp. 36. — Soak a bit of printed calico in a half-litre of water, into which 10 or 15 grms. of bleaching-powder have been stirred. Observe that the color of the calico slowly undergoes change ; then transfer the cloth to another bottle filled with very dilute chlorhydric or sulphuric acid, and take note of the rapidity with which the color is discharged. If need be, again immerse the calico in the bleaching bath, and afterwards in the dilute acid. Finally, wash the whitened cloth thoroughly in water. BROMINE (sr). 86. Bromine is an element closely allied to chlorine. It is not found in the free state in nature but always in combination with some metallic element. Bromides occur in small quanti- ties in sea-water and in the water of many saline springs. One litre of sea-water will yield from 0.0143 to 0.1005 grm. of free bromine. Magnesium bromide is a constituent of the uncrystallizable residue, called bittern, which remains after the sodium chloride has been crystallized out from the natural brines : at several saline springs this bittern contains so large a proportion of the bromide, that bromine can be profitably extracted from it. Most of the bromine of commerce is thus obtained. 87. At the ordinary temperature, bromine is a liquid of dark brown-red color, about three times as heavy as water, and highly poisonous. Its odor is irritating and disagreeable, whence the name bromine, derived from a Greek word signifying a stench. It boils at about 60°, but is very volatile even at the ordinary temperature of the air. Ezp. 37. — By means of a small pipette, throw into a flask or bottle of .1 or 2 litres' capacity 3 or 4 drops of bromine. Cover the bottle loosely, and leave it standing. In a short time it will be filled with a red vapor, which is bromine gas. This vapor is very heavy, more than 5 times as heavy as air and 80 times heavier than hydrogen. 88. In its chemical behavior, as well as in many of its physi- cal propertias, bromine closely resembles chlorine. 62 IODINE. [§ 89. Its affinit}' for hydrogen, though weaker than that of chlorine, is still powerful. Like chlorine, it is an energetic bleaching and disin- fecting agent. If finely-powdered metallic antimony be thrown into bromine, violent chemical action takes place. The metal bums as in chlorine, antimony bromide being formed. 89. Bromhydric Acid (HBr). — Like chlorine, bromine forms with hydrogen a compound in which equal volumes of the two elements (tho bromine being in the state of vapor) are united * without condensation. Bromliydric acid is a colorless, irritating gas, readily soluble in water. Bromio acid ^HBrOj) is analogous to cMorie acid (HCIO,). The bromates resemble the corresponding chlorates. lODINR (l). / 90. In its chemical properties iodine bears a striking resem- blance to bromine, and to chlorine. Compounds of the element exist in sea-water and in many saline and mineral springs. The proportion of iodine in sea-water is exceedingly small, being even smaller than that of brpmine ; but iodine is obtained more readily than bromine ; for iodine is absorbed from sesrwater by various marine plants, which, during their growth, collect and concentrate the minute quantities of iodine which the searwater contains, to such an extent that it can be extracted from them ■ivith profit. 91. At the ordinary temperature, iodine is a soft, heavy, crystalline solid of bluish-black color and metallic lustre. Its specific gravity is 4.95. It evaporates rather freely at the or- dinary temperature of the air, and the more rapidly when it is in a moi^t condition. Its odor is peculiar, somewhat resembling that of chlorine, but weaker, and easily distinguished, from it. It is but slightly soluble in water, but dissolves readily in alco- hol. The atomic weight of iodine is 127. The vapor of iodine is of a magnificent purple color, whence the name iodine, derived from a Greek word signifying violet- colored. This vapor is very heavy, — indeed, the heaviest of § 93.] TESTS FOR IODINE AND CHLORINE. 63 all known gases ; it is nearly 9 times as heavy as air : its specific gravity referred to hydrogen is 127. Exp. 38. — Hold a dry test-tube in the gas-lamp by means of the wooden nippers, and warm it along its entire length, in ao far as this is practicable. Drop mto the hot tube a small fragment of iodine and observe the vapor as it rises in the tube. If only a small portion of the tube were heated, the vapor would be deposited as solid iodine upon the cold part of its walls. 92. Solid iodine is never met with in the amorphous, shape-- less state in which glass, resin, coal and inany other substances occur. No matter how obtained, its particles always exhibit a definite crystalline structure. If the iodine be melted, and then allowed to cool, or if it be converted into vapor and this vapor be subsequently condensed, crystals wiU be formed in either case. 93. A singular property of iodine is its power of forming a blue compound with starch. Hsp. 39. — Prepare a quantity of thin starch paste by boiling 30 c. c. of water in a porcelain dish, and stirring into it 0.5 grm. of starch which has previously been reduced to the consistency of cream by rubbiog it in a mortar with a few drops of water. Pom' 3 or 4 drops of the paste into 10 c. c. of water in a test-tube, and shake the mixture so that the paste may be equably diffused through the water, then add a drop of an aqueous solution of iodine, and observe the beautiful blue color which the solution assimies. If the solution be heated, the blue coloration will disappear, but it re- appears when the liquid is allowed to cool. Dip a strip of white paper in the starch-paste and suspend it, while still moist, in a large bottle, into the bottom of which two or three crystals of iodine have been thrown. As the vapor of iodine slowly diffuses through the air of the bottle, it will at last come in contact with the starch, and after some minutes the paper will be colored blue. This reaction furnishes a very delicate test for iodine. By its means it has been proved that iodine, though nowhere very abundant, is very widely distributed in nature. This reaction is also made the basis of a test for chlorine. Strips of paper are G4: COMPOUNDS OF lODIXE. [§ 94. smeared with starch-paste into which potassium iodide in solution has been stirred. The paper is dried and kept in stoppered bottles. When a strip of this paper is moistened andT exposed to clilorine gas, the chlorine attacks the potassium iodide, potassium chloride is formed, and iodine is set free. The iodine thus set free manifests itself by imparting the characteristic blue color to the starch: — KI + CI = KCl + L 94. As has been already stated, iodine, in its chemical be- havior, resembles chlorine and bromine, only its affinities are more feeble. It enters into combination with less energy than either of these elements, and is displaced by them from most of its combinations. Like them, it unites directly with the metals and with several other elements. It gradually corrodes organic tissues, and destroys coloring-matters, though but slowly. Iodine and certain of its compounds are mucji used in medicine and in photography., 95. lodohydric acid (hi) is a colorless acid gas of suffo- cating odor, very soluble in water. It is made up of equal volumes of hydrogen and iodine vapor. The proportions by weight are 1 part of hydrogen to 127 parts of iodine. The chemical effect of the small proportion of hydrogen contained in iodohydric acid is most remarkable. Only y^,, or less than 1 per cent of iodohydric acid is hydrogen ; yet this very small proportional quantity of hydrogen is competent to impart to the new compound properties possessed by neither the iodine nor the hydrogen : the acid bears no resemblance to either of its constituents. Iodic acid (HIO,) is analogous to chloric and bromic acids. The iodates correspond in composition and general character to the bromates and chlorates. 96. Nitrogen Iodide. — Nitrogen forms, with chlorine, bro- mine and iodine, a class of compounds which are very explosive. Nitrogen chloride is extremely dangerous, often exploding spon- taneously without apparent cause. Nitrogen iodide is much less explosive and may safely be prepared in very smaU quan- tities. § 97.] THK CHLORINE GROUP. 65 Ezp. 40. — Place 0.25 gmi. of finely-powdered iodine in a porce- lain capsule, pour upon it enough concentrated ammonia-water to somewhat more than cover the iodine and allow the mixture to stand during 15 or 20 minutes. Collect in several small filters (Appen- dix, § 15) the insoluble dark brown powder which will be fcund at the bottom of the liquid. Wash well with cold water and then remove the filters; together with their contents, from the funnels ; pin them upon bits of ^board, and allow them to drj' spontaneously. The powder is the nitrogen iodide. As soon as it has become thoroughly dry, it will explode upon being rubbed, even with a feather, or jarred, as by the shutting of a door, or by a blow upon the wall or table. 97. The Chlorine Group, — Chlorine, bromine and iodine constitute one of the most remarkable and best-defined natural groups of elements. "Whether we regard the uncombined ele- ments or their compounds, it is impossible not to be struck with the close analogies w^hich subsist between them. — • With hydrogen, all of these elements, uniib in the propor- tion of one volume to one volume, without condensation, to form acid compounds extremely soluble in water and pos- sessing thioughout analogous properties. Moreover, each of them forms a powerful acid containing three atoms of oxy- gen, besides divers other compounds of obvious likeness. With nitrogen they all form explosive compounds. Many similar analogies will be made manifest as we proceed to study the other elements and their compounds with this chlorine group. ■ There is a family resemblance between these three elements as regards their physical as well as their chemical charac- teristics ; but with all their properties, a distinct progression is observable from chlorine through bromine to iodine. At the ordinary temperature, chlorine is a gas, bromine a liquid and iodine a solid, though, at temperatures not widely apart, they are all known in the gaseous and liquid states. The specific gravity of bromine vapor is greater than that of chlo- rine, and that of iodine greater than that of bromine. Chlorine gas is yeUow, the vapor of bromine is reddish-brown, that of iodine violet. So with- all their other properties, — chlorine wiU 66 FLUORINE. [§ 98. be at one end of the scale, iodine at the other, while bromine invariably occupies the intermediate position. The properties- of the members of this group illustrate what seems to be a general principle ; namely, that among the mem- bers of a natural chemical group, chemical energy varies in the inverse direction of the atomic weights. Thus, the atomic weight of chlorine is 35.5, that of bromine 80 and that of iodine 137 ; while the chemical energy of these elements follows the opposite order. FLUORINE (p), 98. There is another substance, called fluorine, which is closely analogous to chlorine. It occurs tolerably abundantly in nature as calcium fluoride (CaPj), in the mineral known as fluor-spar. Small quantities of iiuorine are found also in several other minerals, in vegetable and animal substances, particularly in bones, and traces of it occur in sea-water and in various rocks and soils. Of late years a considerable mine of a fluorine min- eral called cryolite (fluoride of sodium and aluminum) has been worked in Greenland. 99. Fluorine can not be readily obtained in the free state and scarcely any thing is known of it in that condition. Of aU tlw elements, it appears to have the strongest tendency to enter into chemical combination. It is not only difficult to expel fluorine from the minerals in which it is found in nature ; but, on being set free from one compound, it immediately attacks whatever substance is nearest at hand, and so enters into a new combina- tion. Hence it is wellnigh impossible to collect it. Little or no doubt, however, is entertained as to the general nature of fluorine, since its compounds are closely analogous in many respects to the corresponding compounds of chlorine, bromine and iodine. It is to be remarked that fluorine is the only ele- ment known which forms no compound with oxygen. The symbol of flliorine is F. Its atomic weight is 1 9. ^ 100. Fluorhydric Acid (hf). — With hydrogen, fluorine forms, a powerful acid corresponding to chlorhydric acid and the § 100.] FLUORHYDRW ACID. 67 other hydrides of the chlorine group. It is a more energetic acid than either of these, but is specially cliaracterized by its corrosive action upon glass. It may be readily prepared by distilling powdered fluor-spar with strong sulphuric acid; the reaction being analogous to that which occurs when common salt" is treated with sulphuric acid : — CaFj + H,SO, = CaSO, + 2HP. Since the acid rapidly corrodes glass, the process must be con- ducted in metallic vessels. OrdinaiUy, retorts of lead or plati- num are employed, and the distillate is collected in receivers made of the same metals, and carefully cooled by means of ice. The acid thus prepared always contains a small amount of water which it is difficult to remove completely. The perfeftly dry acid, which may be niade by the distillation of dry hydrogen potassium fluoride is, like that prepared as above, a very volatile, fuming liquid ; it does not, however, act upon glass. This corrosive power, possessed by moist fluorhydric acid gas, as well as by its aqueous solution, is made use of for etch- ing glass. The graduations on the glass stems of thermometers and eudiometers may thus be made with great precision and ^.facility : the acid is largely employed also in ornamenting glass yith etched patterns. Exp. 41. — Warm a slip of glass, and rub it with beeswax so that it shall be everywhere covered with a thin, uniform layer of the wax. With a needle, or other pointed instrument, write a name, or trace any outline through the wax, so b§ to expose a portion of the glass. Lay the etching, face downward, upon a bowl or trough of sheet-lead, in which has been placed a teaspoonful of powdered fluor-spar and enough strong sulphuric acid to convert it into a thin paste. Cover the glass and the top of the dish with a sheet of paper and then gently heat the leaden vessel for a few moments, taking care not to melt the wax ; then set the dish aside in a warm place and leave it at rest during an hour or two. Finally, melt the wax and wipe it off the glass with a towel or bit of paper ; the glass will be found to he etched and corroded at the places where it was laid bare by the re- moval of the wax. 68 OZONE. [§ 101. CHAPTEE rX. OZOITE. I 101. Besides ordinary oxygen, such as is found in the air and has been prepared in Exps. 3 and 4, another kind or foim of this element is known to chemists. This new modification of oxygen has received a special name, and is called ozone. Several other elements, notably sulphur, phosphorus and carbon, occm-, as oxygen does, in very unlike states, or with very different attributes, while the fundamental chemical identity of the substance is preserved. The word allotropism is employed to express this capability of some of the elements : it is derived from Greek words signifying of a different habit or character. This word serves merely to bring into one category a considerable number of conspicuous facts, of whose essential nature we have no knowledge ; there is, of course, no virtue in the word itself to explain or accoimt for the phenomena to which it refers. 102. Ozone is an exceedingly energetic chemical agent wliich resembles chlorine in some respebts : it can therefore be advantageously studied in connection with the chlorine gi-oup. .It was long ago noticed that when an electrical machine was put in operation a peculiar, pungent odor was developed. More recently it has been observed that the same odor is mani- fested during the electrolysis of water (§ 26), and that this odor resembles that evolved by moistened phosphorus when exposed to the air. It has gradually been made out, that the odor in each of these cases is due to the presence of a peculiar modifica- tion of oxygen, called ozone from a Greek -word signifying to smell. 103. Ozone may be best prepared by certain electrical ma- chines devised for the purpose ; but the phosphorus method will usually be found most convenient. § 104.] PROPERTIES OF OZONE. C9 Ezp. 42. — In a clean bottle of 1 or 2 litres' capacity place a piece of phosphorus 2 or 3 c. m. long, the surface of which has been scraped clean (under water) with a knife ; pour water into the bottle until the phosphorus is half covered ; close the bottle with a loose stop- per, and set it aside in a place where the temperature is 20° or 30°. In the course of ten or fifteen minutes a column of fog will be seen to rise from that portion of the phosphorus which projects above the water : the original garlic odor of the phosphorus will soon be lost, and the peculiar odor of ozone will gradually pervade the bottle. After one or two hours, the bottle will be found to contain an abun- dance of ozone for purposes of illustration. The chemical changes which occur during this experiment are complicated ; it will be enough to say of them that the phosphorus unites with oxygen from the air in the bottle to form an o^de of phosphorus, that during this process of oxidation a portion of the oxygen in the bottle is changed into ozone, and that some of the ozone remains, even after several hours, diffused in the air of the bottle. It must be distinctly understood that only a very minuto quantity of ozone is obtained in the foregoing experiment ; but ozone is a substance possessing great chemical power, and but little of it is needed in order to exhibit its characteristic properties. 104. Ozone is an irritating, poisonous gas : air which is highly charged with it is irrespirable, and produces effects on the human subject similar to those produced by chlorine. Its odor, which has been compared to that of weak chlorine, is so powerful that it can be recognized in air containing only one- millionth part of the gas. Like chlorine, ozone bleaches and destroys vegetable, coloring matters, and is a powerful disin- fectant. Like clilorine, it instantly decomposes the iodides of the metals ; upon this property is based a ready method of testing for its presence. Exp. 43. — Into the bottle of ozonized air (Exp. 42), thrust a moistened slip of test-paper, saturated with starch and iodide of potassium, prepared as described in § 93 : the paper will instantly acquire a deep blue tint. 70 OXIDIZING POWER OF OZONE. [§ 106. As in the case where the test-paper is employed for detecting chlorine (§ 93), so here, the reaction depends upon the displacement of the chemically feeble iodine by the more powerful ozone : — 2KI + O = K,0 + 21. The ozone here acts as oxygen, in one sense : at all events, the potas- sium oxide formed is not to be distinguished from potassium oxide prepared with common oxygen ; but this in no wise contradicts the fact that ozone is an extraordinarily active and energetic variety of oxy- gen, inasmuch as common oxygen will not effect this decomposition. 105. The great difference between ordinary oxygen and the allo- tropic modification, ozone, is generally explained by supposing that while the molecules of oxygen and the molecules of ozone are both made up of oxygen atoms, the former contains two atoms in each mole- cule (see page 90), while the latter contains three atoms. This idea is strengthened by the fact that when oxygen is converted into ozone a condensation takes place, and when the ozone is reconverted into ordinary oxygen there is an expansion to the original bulk. Other observed facts lead to the same conclusion, and the action of ozone on potassium iodide would probably be more correctly expressed by this equation : , 2KI-1-O3 =KsO + 2lH-02. 106. The oxidizing power of ozone is intense. When moisture is present, it oxidizes aU. the metals excepting gold, platinum and the platinum metals : even silver is oxidized by it at the ordinary temperature, and becomes covered with a brown coating of an oxide of sUver. In like manner, most organic substances are quickly oxidized by ozone : when sub- stances such as saw-dust, garden-mould, powdered charcoal, milk or flesh, are thrown into a bottle of ozonized air, the odor of ozone instantly disappears. By virtue of this strong oxidizing power, ozone is of great importance as a disinfecting agent. It destroys instantly a multitude of offensive gases, such as arise from decaying animal and vegetable matter, and has been frequently recommended of lata as a substance well fitted for the purification of sick-rooms and hospital-wards. §109.J ANTOZONE CLOUDS. — SULPHTm. 71 107. A minute proportion of ozone seems to exist in norma] atmospheric air : it is especially abundant after a thunder-storm. It is seldom found in the air of thickly inhabited locali- ties. At temperatures above 100° ozone is converted into ordi- nary oxygen. 108. Antozone. During the oxidation of phosphorus in moist air, Exp. 42, it was no doubt noticed that the bottle became filled with white fumes. Also in Exp. V, § 17, during the rapid oxi- dation of phosphorus there was produced a white mist of considerable permanence, which remained long after the oxides of phosphorus, which were also formed, had been absorbed by the water. More- over, if electrized oxygen (or electrized air) be passed through a solution of potassium iodide, the ozone will be completely removed ; if, subsequently, the air or oxygen be allowed to bubble through water, the same peculiar mist will be formed. It was for a time sup- posed that this mist was caused by the presence of a thu'd modifica- tion of oxygen, called antozone, which was siipposed to be pro- duced simultaneously with ozone by electrical action, and by pro- cesses of oxidation. Later research has, however, disproved the existence of such a third modification, and although it is impossible at present to account for all the efi'ects which have been ascribed to antozone, in many cases they seem to be due to the presence of hydro- gen peroxide, an oxide of hydrogen having the symbol HgOg. CHAPTEE X. SnXFHTTB. SELENIUM AND TELLUSIUM. SULPHUR (s). 109. Sulphur occurs somewhat abundantly in nature both in the free state and in combination with other elements. Many ores of metals, for example, are sulphur compounds. It is a component of several abundant salts, such as the sulphates of calcium, barium and sodium, and occurs in small proportion in many animal and vegetable substances. Free sulphur is found 72 PROPERTIES OF SULPHUR. [§ HO. cliiefly in volcanic districts. Generally it occurs mixed with earthy matters, but it often forms distinct veins, and is some- times found in the shape of well-defined crystals of considerahle size. At the present time about nine-tenths of the sulphur of commerce comes from Sicily. Native sulphur is usually subjected to a rough purification at the place of its occurrence. This pm-iflcation is sometimes effected by distilling the volcanic earth in retorts or jars of earthenware ; or, if the earth be very rich in sulphur, it is simply heated in large kettles and the melted sulphur dipped off from above, while the earthy im- purities settle to the bottom of the kettle : sometimes the sulphur is piled up in heaps, or in kilns, and set on fire, a portion of the sulphur in bmning furnishing the heat by which the rest of the sulphur is melted : the melted sulphur flows out from the mass, and is collected in receivers. As the crude sulphur comes to us, it is in irregular lumps of a dirty light-yellow color, and is largely employed for manu- facturing pui-poses. It is purified by being distilled from iron retorts into large chambers constructed of masonry, in which it is deposited either in the form of a light powder, known as flowers of sulphur, or in the liquid state, according to the temperature of the chambers. 110. At the ordinary temperature of the air, sulphur is a brittle solid of a peculiar Ught-yeUow color. It has neither taste nor smell, excepting that when rubbed it exhales a faint and peculiar odor. Most of the odors which in every-day life are referred to sulphur are really the odors of various compounds of sulphur, and are not evolved by the element itself. The symbol of sulphur is S : its atomic weight is 32, being precisely twice as great as the atomic weight of oxygen. 111. Sulphur behaves in a very remarkable manner on being heated. AAHaen melted at the lowest possible temperature, 100° to 115°, it forms a limpid liquid of a light-yeUow color ; but, if this liquid be heated more strongly, it begins to become viscid and dark-colored at about 150°, and at 170° to 200° it is almost black, and at the same time so thick and tenacious that it can not be poured from the vessel which holds it, even if the vessel be inverted. At 330° to 340° it regains its fluidity in part, though the liquid is still dark-colored, and finally, at about § 113.] SOI^T SULPHUR. — CRYSTALLIZATION. 73 440'', it begins to boil, and is converted into an amber-colored vapor. The specific gravity of sulphur vapor, referred to hydro- gen, is 32. 112. If melted sulphur in the viscid state, or, better, that which has regained its mobility, be suddenly cooled, a semi-solid modification of sulphur, remarkably diiferent from the ordinary form, will be obtained. I^p. 44. — Place in a test-tube, of about 30 c. c. capacity, 15 to 20 grms. of coarsely-powdered sulphur ; melt the sulphur slowly over the gas-lamp, and contimie to heat it until it begins to boil, noting, meanwhile, the changes which the sulphur undergoes, — as described in § 111. Finally, pour the hot sulphur, in a fine stream, into a large dish full of cold water. There will be obtained a soft, elastic, reddish-brown mass, which can be kneaded and moulded like wax, and drawn out into threads like , caoutchotic. Fig. »4. This sofb sulphur can not be preserved for any great length of time ; it slowly hardens and changes into ordinary brittle yellow sulphur. 113. Sulphur may readily be obtained in the form of crystals. Exp. 45; — In a small beaker glass, or porcelain capsule, slowly heat 50 to 60 grnas. of sulphiir until it has entirely melted. Remove the vessel from the lamp, and allow it to cool slowly until about a quarter part of the sulphur has solidified ; then pour off into a basin of water that portion of the sulphur which is still liquid, breaking through, for this purpose, the crust at the top of the liquid, if any such have formed. The interior of the vessel will be found to be lined with transparent crystals. "Exp. 46. — In a test-tube, melt enough sulphur to fill one-quarter oi the tube ; place the tube in such a position that its contents may cool slowly and quietly, and then watch the formation of crystals as they shoot out from the comparatively cold walls of the tube towards the centre of the liquid. 7 74 SrST£MS OF CRYSTALLIZATION. [§ 114. Exp* 45 represents one general method of obtaining crystals. Crystals of many of the metals, lead and bismuth for example, can be obtained in a similar manner : it is only necessary to per- form the operation in a crucible of some refractory material, placed in a furnace. Exp. 46, besides illustrating the manner in which crystals form, teaches us something of the physical structure of solid bodies. The- solid mass of sulphur which is left in the test- tube, when it has become cold, is evidently nothing more than a compact bundle of interlaced crystals : it possesses what is called a crystalline structure. This crystalline structure is apt to render a body brittle : substances which possess it are liable to break " with the grain," or to split in certain direc- tions determined by the shape of the crystals, and called lines of cleavage ; a stick of roll-brimstone, for example, may be readily broken or cut across, but not so easily in the direction of its length. 114. Another easy way to crystallize sulphur is by the method of solution and evaporation,, such as was employed in the preparation of potassium nitrate (Exp. 25). Sulphur is not soluble in water, but it dissolves readily in a liquid com- pound of sulphur and carbon, known as carbon bisulphide, which, being readily volatUe, quickly escapes, on exposure to the air, and so deposits the sulphur. The crystals thus ob- tained differ in shape from those obtained by the method of fusion. Although thousands of crystal-forms occur in nature or have been produced by art, it has been found possible to refer these forms to six general classes called systems of crystallization. It is true of almost all chemical substances which can be obtained in crystals, that while the individual crystals may vary somewhat in form, all the forms in which the substance occurs are such as may be referred to one and the same system. In the case of sulphur, however, the crystals obtained by the method of fusion, and those obtained by the method of solution, must be referred to two entirely distinct systems. There are other substances besides sulphur which present this same phenomenon. Substances which are thus capable of assuming crystalline forms § IIG.] sirzrmDSS. 75 belonging to two different systems are said to be dimorphous (two- I'ormed). The two varieties of sulphur differ considerably in various physical properties. One variety niay, however, be converted into the other, and their chemical composition is identical. Each is sulphur, and nothing more. The amorphous " soft sulphur " obtained in Exp. 44 may be regarded as a third modification of sulphur. Crystals of sulphur of large size and great beauty occur in Na- ture, and are supposed to have been formed by sublimation, i. e., the sulphur has been converted into vapor,' and the vapor cooled very slowly. The method is hardly practicable in the laboratory, although crystals have been formed artificially in this way. 115. Sulphur unites energetically with most of- the other elements, such union being, in many cases, attended with evolution of light. Most of the metals, for example, combine with it directly, j ost as they do with oxygen. Fig. SS. This has already been illustrated in the case of copper by Exp. 1, § 2. The product of this reaction was copper sulphide ; and; in general, compounds of sulphur Avith the metallic ele- ments are called sulphides. Exp. 47. — Mix intimately 4 gnns. of flowers of sulphur and 1 gnns. of the finest iron filings. Place the mixture in an ignition- tube 10 to 12 c. m. long, and heat the lower end of the tube over the gas-lamp. In a short time the mass will begin to glow, as the sulphur and iron enter into chemical combination, and this ignition will, of itself, pass through the entire length of the tube, even if the lamp be withdrawn. The final product of the reaction is iron sulphide. 116. Sulphur unites readily with oxygen at a comparatively low temperature. "When heated in the air, it takes fire at about 250°, and bums with a peculiar blue light. The irritating, suf- focating gas, which is produced, will be shortly described under the name of sulphurous anhydride. The use of sulphur on ordinary matches depends on the low tern- 76 HYDROGEN SULPHIDE. [§ 117. perature at which it takes fire. Being ignited by the burning pkos- pjiorus, it burns until the less readily combustible wood is set on fire. ^117. Hydrogen sulphide (h,S) or sulphuretted hydrogen, as it is often called, is a colorless gas which smells like rotten eggs. It may be conveniently prepared by treating iron sulphide with dilute chlorhydric acid. Exp. 48. — In a gas-bottle, Fig. 26, put 10 or 12 grms. of iroi! sulphide (see Exp. 47) ; replace the cork in the bottle and, introduce rig. ae. the gas delivery-tube into another small bottle containing cold water, letting it dip 5 or 6 c. m. beneath the surface of the water. Through the thistle-tube, pour into the gas-bottle water enough to seal the lower extremity of this tube : then add, through the thistle-tube as be- fore, 2 or 3 teaspoonfuls of strong ehlorhydrie , acid, and observe -that bubbles of gas soon be- gin to pass through the water in the absorption bottle. J T^'^r WH Hydrogen sulphide is soluble in water to a J^ JaJiClMk nils considerable extent, and is consequently taken up by the water in the absorption bottle. The solution thus obtained, known as sulphuretted-hydrogen- water, is much employed as a reagent in chemical laboratories. When the disengagement of gas slackens, a new portion of chlor- hydric acid may be added through the thistle-tube, and this process continued until the water in the absorption bottle smells strongly of the gas. This experiment should be performed out of doors, or in a draught of air so arranged that those portions of the gas which escape solution shall be carried away from the operator. The reaction which takes place may be represented as follows < ^ FeS 4- 2HC1 =r PeCl, + H„S. 118. Hydrogen sulphide is readily inflammable. It burns with a blue flame, prodiicing water and sulphurous acid gas : — H,S + 30 = H,0 + SO,. Exp. 49. — To the delivery-tube of the gas-bottle employed in generating hydrogen sulphide, attach a drjang-tube containing § 120.] HYDROGKX SULPHIDE. 77 fragments of calcium chloride, and with the tube connect a piece of No.' 6 glass tubing drawn out to a fine point. FiK..87. When the apparatus is full of the gas, apply a match to the end of the tube. The gas will take fire, and burn with a blue flame. If a dry bot- tle be held over the flame, the walls will become coated with moisture which will have an acid reac- tion and will redden blue litmus paper. The jet of hydrogen sulphide should not be lighted until all the air is expelled from the apparatus, as this gas forms an explosive mix- ture with air. 119. Hydrogen sulphide is readily decomposed by heat, as may be shown by passing a current of the gas through a glass tube, heated for a portion of its length. The gas will be separ- ated into hydrogen and sulphur : the latter will be deposited on the cold portion of the tube. . Analysis has proved that the composition of hydrogen sul- phide, both by volume and by weight, may be expressed by the following diagram, in which the symbol S represents a unit volume of sulphur in the state of vapor. - H 1 + S 32 = H,S34 H 1 120. Hydrogen sulphide is very poisonotis : when respired in the pure state, it quickly proves fatal, and it is very deleterious, even though largely diluted with atmospheric air. It is there-j fore best, when experimenting with it, to operate where there isi a free circulation of air. The gas exists as a natural constituent of some mineral waters which are thence called sulphurous, such as the Virginia Sulphur Springs, and the mineral sgrings at Sharon, N. Y. It is also found in the air and water of foul sewers, and wherever animal matter is undergoing putrefaction. 7* 78 COMPOUNDS OF SULPHUR AND OXYGEN. [§ 121. 121. When moist hydrogen sulphide comes in contact with certain of the metals, it* is decomposed. Exp. 50. — Tlace a drop of sulphiiretted-hydrogen-water (Exp. 48) upon a bright piece of copper, lead or silver. The metal will quickly become black. The sulphur of the hydrogen sulphide unites with the metal, to form a sulphide of the metal, while the hydrogen escapes, or we may say that the metal replaces the hydrogen in the hydrogen sulphide. Cu + HjS = CuS + 2 H. 2 Ag -I- H^S = Ag,S + 2 H. From a solution of any compound of these metals, hydrogen , sulphide wiU throw down the sulphide of the metal. "Exp. 51. — Dissolve a small crystal of lead nitrate in a test-tube half full of water, and to this solution add a few drops of the sulphur- etted-hydrogen-water. Lead sulphide is thrown down as a black iprecipitate, and idtric acid is set free. PbNjO, -1- HjS = PbS + 2 HNO3. On account of this property of precipitating various metallic sulphides, hydrogen sulphide is much used in the chemical laboratory as a reagent. 122. Sulphur and Oxygen. — Of the compounds of sul- phur and oxygen the most important are sulphurous anhydride and sulphuric anhydride. 123. Sulphurous anhydride (SOj), commonly called sul- phurous acid (see § 63). — This is the only one of the various compounds of oxygen and sulphur which can be formed by the direct union of its constituents. It is produced whenever sul- phur is burned in air or in oxygen gas. Exp. 52. — Light a piece of sulphur in a deflagrating spoon, and suspend the latter in a half-litre bottle full of air. On examining the contents of the bottle, after the sulphur has ceased to bum, there will be found an irritat- ing, suiTocating gas having the peculiar odor which is famil- iar as that of a burning match. The bottle is now full of sulphurous anhydride, mixed with the nitrogen originally present in the air. § 125.] PROPERTIES OF SULPHUROUS ACID. 79 An easier method of preparing pure sulphurous acid is by depriving common sulphuric acid of part of its oxygen.* This can he effected by a variety of reducing or deoxidizing agents. For example, when concentrated sulphuric acid is heated with metallic copper, there is formed a sulphate of the metal, water and sulphurous acid : — Cu + 2 HjSO, = CuSO, + 2 H,0 + SO,. Certain other metals, such as mercury, for example, can be employed instead of copper, the reaction being precisely similar. 124. Sulphurous acid is a transparent and colorless gas. It is irrespirable and suffocating, and when mixed with air, even in small proportion, occasions violent coughing. It is not iuflam- mahle, but, on the contrary, it stops combustion. The flame of a taper is immediately extinguished on beiog immersed in sulphurous acid gas, just as it is by nitrogen. A useful application of this property of the gas is in extinguishing bundng chimneys. A handful of fragments of sulphur being thrown upon the hot coals in the grate, and the openings of the fireplace being closed in such man- ner that no air shall enter the chimney, excepting that which passes through the fire, the chimney will quickly become filled with an atmosphere of svdphurous acid mixed with nitrogen from the air em- ployed in burning the sulphur, and the burning soot upon the walls of the chimney will be immediately extinguished. It is, of course, essential that the chimney should then be closed at the top, so that air may be excluded and the chimney kept full of the fire-extinguishing atmosphere until its walls shall have cooled to below the kindling temperature of the soot. 125. Sulphurous anhydride can readily be obtained in the liquid state by passing the gas through a U-tube immersed in a freezing-mixture of ice and salt. On being exposed to the air at ordinary temperatures, this liquid evaporates with great rapidity, and consequently occasions very intense cold. * The substances now designated as anhydrides were formerly called acids, as stated in S 63. In the case of sulphurous, arsenious and carbonic anhydrides, the popular names sulphurous, arsenious and carbonic acids have such currency that they will be employed in this Manual where no ambiguity can arise from such use. 80 SULPHUROUS ACID BLEACHMS. [§ 126. If a quantity of the liquid be poured into water, the temperature of which is a few degrees above 0°, a portion will evaporate at once, another portion will dissolve in the water and a thiid portion of the heavy oily liquid will sink to tlie bottom of the vessel. If the por^ tion which has thus subsided be stirred with a glass rod, it will boil at once, and the temperature of the water will be so much reduced that a portion, or even the whole, of the water will be frozen. The volumetric composition of sulphurous anhydride is 1 volume of sulphur vapor and 2 volumes of oxygen condensed to 2 volumes of the compound gas. The gas is very readily soluble in water, and may be regarded as combining with a portion of the water to form sulphurous acid, the formula of which would be HjSOy The term " sulphurous acid " is, however, ordinarily used to denote the gas SO,. 1 26. An important property of sulphurous acid is its power of bleaching' vegetable colors. It , is extensively employed in bleaching articles of straw, wool, silk, etc., which would be injured by chlorine. The bleaching may be effected by immer- sion in the aqueous solution of sulphurous acid or by exposure to the fumes of burning sulphur. In the latter case the articles to be bleached must be moistened. The dry anhydride does not bleach. In most cases sulphurous acid does not destroy the coloring matters as chlorine does, but seems to combine with them to form colorless compounds. These colorless compounds can be broken up, with restoration of color, by exposing them to the action of various chemical agents capable of setting free sulphurous acid. Xizp. 53. — Bleach a red rose by hanging it in a bottle in which sulphur has been burned, or by holding it over burning sulphur. Im- merse the bleached rose in dilute sulphuric acid, dry and warm it, and observe that the color will re-appear. In the arts, the process of bleaching is usually conducted in large chambers, in which the slightly moistened articles are hung while sul- phur is burned below. The damp goods absorb the gas and gradually become \vhite. A practical illustration of the restoration of color by chemical agents is seen in the reproduction of the original yellow color of the wool when new flannel is washed. The alkali of the soap removes the sulphurous acid, and the color re-appears. § 129.] SULPHURIC ACID. 81 127. Sulphuric anhydride (SO,) may be prepared by the direct oxidation of sulphurous anhydride. If a mixtiue of sulphurous anhydride and oxygen be j)assed over heated, Tery finely divided j)latinum (platinum sponge), the two gases unite to form sulphuric anhydride, which .condenses in the cooled receiver. It is a white, waxlike soUd, crystallizing in silky fibres, resembling asbestos. If a bit of it be thrown into water, the water hisses as if a hot iron had been thrust into it ; and the sulphuric anhydride unites with a portion of the water with the evolution of great heat to form sulphuric acid. The solid anhydride has so great an attraction for water, that it can be preserved only in dry tubes sealed at the lamp. 128. Sulphuric acid (H^SOj is one of the most important products of chemical manufacture, and is made in enormous quantities. In the same way that the metal iron may be said to be the basis of all mechanical industries, sulphuric acid hes at the foundation of the chemical arts. By means of sulphuric acid, the chemist either directly or indirectly prepares almost every thing with which he has commonly to deal. 129. Sulphuric acid is made by oxidizing sulphurous acid. This oxidation cannot be effected directly in any economical manner ; it is necessary to use some o xi dizjn g agent. This term oxidizing agent is applied to a substance which habit- ually and readily imparts oxygen to other bodies with which it is brought in contact : on the other hand, a substance which habitually and readily takes oxygen out of other substances with which it is brought in contact is called a reducing agent.* Nitric acid, such as was prepared in Exp. 22, § 59, is a very powerful oxidizing agent, and sulphuric acid might be made by boiling sulphur for a long time in nitric acid. This method would, however, not be practicable on a lar^e scale. Nitric acid also oxidizes sulphurous acid. Exp. 54. — Chaise a bottle, of the capadty of a litre or more, with sulphurous acid by burning in it a bit of sulphur. Fasten a shaving, or, better, a tuft of gun-cotton, upon a glass rod or tube bent at one end in the form of a hook ; wet the shaving in concentrated nitric acid, and hang it in the bottle of sulphurous acid. Eed fumes of * The tenns oxidizing agent and reducing agent are often employed in a mncli wider sense than here implied. See page 290- 82 MANUFACTURE OF SULPHURIC ACID. [§ 130. nitrogen peroxide will immediately form about the nitric acid, and will gradually fill the hottle. The appearance of the red fumes (nitrogen peroxide) shows that there has been a loss of oxygen on the part of the nitric acid. The reaction may be thus written : — 2 HNO3 + BO, = H,SO, + 2 NO,. In this case sulphurous acid is an example of a reducing agent. Sul- phurous acid in the presence of much moisture can take oxygen from all the higher oxides (and acid.s) of nitrogen, as HNO,, NO,, and HNO„ and reduce them all to nitric oxide, NO. 130. The method employed in the actual preparation of sul- phuric acid upon the large scale depends upon the fact illus- trated in the last experiment. Fig. 29. Fig. 29 shows, in a rough and very general way, the manner in which the manufacture is conducted. The sulphurous acid is obtained by burning crude sulphur or, more commonly, a compound of sulphur and iron, known as iron pyrites, in properly-constructed furnaces. The gas, together with a large excess of atmospheric air, is then con- ducted into the first of a series of enormous chambers, into which jets of steam are constantly blowing : these chambers are constructed of sheet-lead, a metal on which cold sulphuric acid has little action. Nitrous fumes are supplied either by allowing nitric acid to fall in fine streams through the incoming current of sulphurous acid and air, or from the decomposition of sodium nitrate by means of sulphiirie acid, this decomposition taking place in an iron pot heated by the burning sulphur. In conformity with the principles above stated, the SO, in contact with the steam, reacts upon the nitrous fumes : there is formed sulphuric § 132.] FURMATION OF SULPHURIC ACID. 83 acid, which condenses upon the sides of the chamber and trickles down to the floor, and nitric oxide. But, as there is present in the chamber an excess of air, the NO immediately unites with a portion of the oxygen therein contained, and is converted into NO^. This NOj immediately reacts upon a new portion of SOj, and the process thus goes on through a whole series of leaden chambers, the very small portion of nitric acid at first taken being suificient to prepare a large quantity of sulphuric acid. In reality, the oxygen employed in converting the sulphurous into sulphuric acid all comes from the air, excepting'a very little at fii-st : the nitrous fumes serve only as a con- veyer of oxygen. The NO takes oxygen from the 'air and transfers it to the sulphurous acid, which is, by itself and unaided, incapable of combining with oxygen. It will, of course, be understood, that although we trace out these reactions as if they were consecutive, they are really, so far as we know, simultaneous. Theoretically, a single portion of nitric acid would be sufficient to effect the conversion of an unlimited amount of sulphurous into sul- phuric acid, but practically this power is qualified by a variety of cir- cumstances. It is found to be impossible, for example, to introduce new portions of air into the mixture of sulphurous acid and nitric oxide for an indefinite period ; for, at a certain point, these gases become so loaded down with nitrogen derived from the air already consumed, that they are as good as lost in it. In general, the flow of gases is so regulated that all the sulphurous acid shall be oxidized, and that nothing but nitric oxide and the waste nitrogen shall pass out of the last leaden chamber. 131. The acid obtained in the lead chambers as described above is very dilute. It is concentrated by evaporating it, first in leaden pans, and finally in large glass retorts or in platinum stills, until it has nearly the composition H^SO,. C The acid thus boiled down is the concentrated sulphuric acid, or oil of vitriol, of commerce ; its specific gravity is usually about 1.83, that of the absolutely pure acid being 1.842. Be- sides this slight excess of water, it contains also, in solution, a certain quantity of lead sulphate, and a variety of other impuri- ties. For most purposes, however, it will answer as well as the pure acid. Like the latter, it is a heavy, oily, colorless and odorless liquid, boiling at ahout 330°. i 132. At the ordinary temperature, sulphuric acid does not 84 PROPERTIES OF SULPHURIC ACID. [§ 133. vaporize, but, on the contrary, greedily absorbs water from the air, and so increases in bulk. In moist weather, its bulk may increase to the extent of a quarter or more, in the course of a single day, and, by longer exposure, a still larger quantity of water will be taken up ; the acid must always be kept, there- fore, in tightly-stoppered bottles. Sulphuric acid unites with liquid water, with great energy, much heat being evolved at the moment of combination : dur- ing the union a certain amount of condensation occurs, the mixture, when "cold, occupying less space than was previously occupied by the acid and the water. The water and acid may be mixed in all proportions, being mutually soluble one in thd other. In mixing wutet and sulphuric acid, the acid should always be poured into the water, in a fine stream, not the water into the acid, — the water being meanwhile stirred. In this way the heavy acid has an opportimity to mix with the water as it sinks down through it. If, by any accident, water were to fall upon sulphuric acid, it would float on top of it, and great heat would be developed at the point of contact of the two liqiuds : if the quantities of acid and water were large, sudden bursts of steam would be occasioned, and serious damage might arise from the scattering about of portions of the acid. Exp. 55. — Place in a beaker glass of about 250 c. c. capacity, 30 c. c. of water ; in accordance with the directions above given, pour into the water 120 gmis. of concentrated sidphuric acid, and stir the mixture with a narrow test-tube containing a teaspoonful of water. So much heat will be evolved during the union of the water and the acid that the water in the test-tube will boil. 133. Sulphuric acid is one of the most powerful acids known. "When diluted with a thousand times its bulk of water, it is still capable of reddening vblue litmus. It sets free most of the other acids from their salts, in the same way that we have seen it set free nitric acid from sodium nitrate in Exp. 22, § 59. It is intensely caustic and corrosive, and quickly chars and destroys most vegetable and animal sub- stances. Iixp. 56. — Into a test-glass pour a table-spoonful of sulphuric § 136.] SULPHATES. — FC'MIXG SULPHCRW ACID. 85 acid and immerse in it a splinter of wood. The wood will blacken as if charred by fire, and the acid will become dark-colored. Wood is composed of carbon, hydrogen and oxygen, and since sulphuric acid unites with compounds of hydrogen and oxygen, rather than with carbon, a portion of the latter is left free ; some carbonaceous matter is, however, dissolved by the acid and darkens it. The acid of commerce is often dark-colored from fragments of straw or other organic matter having accidentally fallen into it. 134. Sulphates. — If the hydrogen of sulphuric acid be replaced by various metals, a class of bodies is formed called sulphates : thus, Na^SO, is sodium sulphate ; CaSOt is calcium sulphate, etc. In the formation of the sulphates of those metals which replace hydrogen atom for atom (§ 74), it is not necessary that both atoms of hydrogen in the sulphuric acid, H^SO,, should be replaced. We may, for example, have a compound in which sodium replaces only one of the hydrogen atoms ; namely, HNaSO,, hydrogen sodium sulphate. Acids like sulphuric acid, which have two replaceable hy- drogen atoms, are called bi-basic. 135. Fuming Sulphuric Acid. — Sulphuric acid was for- merly made by distilling in earthen retorts the salt now known as ferrous sulphate, formerly called green vitriol. Hence the origin of the name oil of vitriol, which, in England and this country, has come to be applied solely to the common acid, H.SO^. The acid thus obtained is a dense" fuming liquid, which may be regarded as sulphuric anhydride dissolved in sulphuric acid. It is used principally for dissolving indigo, a certain quantity being still made for this purpose. There are other well-defined compounds of oxygen and sul- phur. They, are, however, of much less importance, and are of little interest in an elementary manual. SELENIUM (se) AND TELLURIUM (tb). l^i^^hese elements are rare, and of little or no industrial impor- tance ; but to the chemist they are exceedingly interesting on account of the close resemblance they bear to sulphur. The three elements sulphur, selenium and tellurium, constitute a group which is equally Missing Page Missing Page d 88 {_J/ PRODUCT-VOLUME. [§ 140. Lastly, still a third mode of combination by volume with condensation of four volumes to two occurs in the two following cases : — Nitrogen ^^ Hydrogen _ Ammonia nr ^ -i- ^' ^ NHj Ivol. "*" 3 vols. ~ 2 vols. '""^U "^ 3 17 Sulphur , Oxygen Sulphuric Anhy- S , Os SOj 1 vol. "^ 3 vols. ~ dride 2 vols. ' ""^ 32 "^ 48 80 In all these cases, the iinit-volume is, of course, the same for every element and compound ; what the absolute bulk of this unit-volume may be, is not an essential point, for the rela- tions remain the same, whatever the unit of measure. Three condensation-ratios are thus exhibited : first, ' a condensation of ; second, one of \ ; and third, one of ^. The space occu- pied by the compound molecule is, in each case, exactly twice the unit-volume. The examples just given, although including all the com- pounds which we have yet studied, are only very few compared with the vast number of gaseous compounds which have been investigated, and where the same thing has been found to hold true. Two volumes of a compound gas invariably result •irom the chemical combination of one volume of hydrogen with one volume of chlorine, of two volumes of hydrogen with one volume of oxygen, of three volumes of hydrogen with one vol- ume of nitrogen, and so on. This doubled volume is often called the normal or product-volume of a compound gas. If, in considering the compounds already mentioned in this chapter, we choose for our unit-volume the space occupied by the atom of hydrogen in the molecule of clilorhydric acid (i. e., in other words, the volume of the atom of hydrogen when not under condensation), we shall be led to very important theoret- ical results. For then our product volume will be in each case the space occupied by the molecule of the compound gas, and we shall be led to the conclusion that the space occupied by a single molecule of each of these gaseous compounds is the same. This is, indeed, believed to be true in the case of all gaseous molecules. In organic chemistry a great multitude of com- § 140. Till; ELEMENTARY QAHES. 89 pounds, many of them very complicated, have been investigated, and the same law has been found to hold good. The molecule of every compound in the gaseous state occupies a volume twice as large as that occupied by the atom of hydrogen. Since, then, the molecule of a compound gas or vapor occupies two of these unit volumes, and the specific gravity of a gas or vapor is the weight of one unit-volume of that gas or vapor as compared with the weight of the same volume of hydrogen, it is obvious that the specific gravity of the gas or vapor may be found from the molecular weight by dividing the latter by two. The specific yraoity of a compound gas or vapor is, therefore, one-half its molecular weight. 140. Molecular condition of elementary gases.— There are. certain physical laws in regard to compressibility and expansion which govern all gases, and which are best explained by the hypothesis,^ usually spoken of as the Iisl-w of Ampere, — that equal volumes of all gases, simple as well as compound, under like conditions of temperature ^nd pressure, contahi the same number of 'molecules. Staiting with this hypothesis, let us inquire what inferences we can draw with regard to the molecula? condition of the elementary gases when in the free state. Suppose, then, we take any volume of hydrogen, the volume occupied by 1000 molecules, for example : an equal volume of chlorine will contain the same number of molecules. If the two gases be mixed and exposed to diffused sunlight they will combine without condensation to form chlorhydiic acid. We shall then have two volumes of chlor- hydric acid. According to the assumption just made that equal vol- umes of all gases contain the same number of molecules, each of these two volumes will contain 1000 molecules of the acid and the two volumes will contain 2000 molecules. Each molecule of the acid contains one atom of hydrogen and one atom of chlorine, hence in the two volumes of chlorhj'dric acid we shall have 2000 atoms of hydro- gen and 2000 atoms of chlorine. These 2{K)0 atoms of hydrogen (or chlorine) came from the one volume of the gas which we supposed to contain 1000 molecules ; therefore, this volume contained at the same time 1000 molecules and 2000 atoms : hence each molecule must be made up of two atoms. It is clear that this train of reasoning is in- dependent of the particular numerical value assuined as the number of molecvdes in the two volumes of ehlorhydric acid. If, therefore. 90 MOLECULAR CONDITION OJP [§ 140. the molecule of ohlorhyclric acid is represented by the formula HCl, and the diagram, — + CI HCl there is good reason to assign to /ree hydrogen and /r«« chlorine the formulsB HH and ClCl, or (H^ and Cl^), and to represent the con- stitution of all uncombined gases by such diagrams as + HH CI + CI ClCl Upon these models the molecular formulss of most of the elements with which we have become acquainted might readily be written. It is only in a /ree state that the elementary gases and vapors are thiis conceived to exist as molecules ; when they enter into combination, it is by atoms rather than by molecules. An atom of hydrogen unites with an atom of chlorine : three atoms of hydrogen combine with one of nitrogen. We may study the molecular condition of the elementary gases from another point of view. If the Law of Anipdre be, as it is be- lieved to be, true of simple as well as of compound gases, it will be true that the vapor density (or the specific gravity of the sul)- stance in the state of gas) is one-half the molecular weight, and, vice versa, that the molecular weight is twice the vapor density. If, now, the specitic gravity of hydrogen be one, its molecular weight must be 2 X 1 = 2. If the molecule weigh 2 and the atom weigh 1, the unit of weight being the same in both cases, the molecule must contain 2 atoms. The same reasoning will hold in the case of the elementary gases, oxygen, chlorine, and nitrogen, also in the case of the elementary substances, bromine, iodine, sulphur, selenium, tellurium, sodium and potassium, which are not gases under ordinary atmospheric conditions, but which can be converted into gases at a higher temperature. As, for example, * § 140.J THE ELEMMNTAMY OASES. 9I Vapor Density. Molee. Weight. = V. D. X 2. Atomic Wt. ^O-tIH 16 32 16 2 CI 35.5 71 35.5 2 I 127 254 127 2 s 32 64 82 2 eta Of all the other elementary substances, four, namely, arsenio; phosphorus, mercury and cadmium, have been converted into vapor, and the specific gravity of their vapora determined. If we apply the same reasoning to them we find that the molecules of arsenic and phosphorus contain each four atoms, while the molecules of mercury and cadmium contain each a single atom only. It is probable that zinc should be classed with mercury and cadmium. Vapor Density. Molec. Wt. Atomic Wt. ^^-Zl As 150 300 75 4 P 62 124 31 4 Hg 100 200 200 1 Cd 56 IM 112 1 If this view of the molecular structure of free elementary gases and vapors be correct, perfect consistency would require that no equation should ever be written in such a mamier as to represent less than a single molecule of an element in a free state as either entering into or issuing from a chemical reaction. Thus, in- stead of 2 H + O — HjO, H + 3 H =N H,, HCl + Na = NaCl + H, it would be necessary to write 2 Hg + O^ = 2 H^O, Nj + 3 Hj = 2 NHs, 2 HCl + Na^ - 2 NaOl + Hj. We have not heretofore conformed to this theoretical rule, and do not propose to in the succeeding pages, and this for two reasons : first because many equations, representing chemical reactions, must be multiplied by two, in order to bring them into conformity with this hypothesis concerning molecular structure ; the equations are thiis rendered unduly complex ; — secondly, because, in undertaking to make chemical equations express the molecular constitution of ele- ments and compounds, as well as the equality of the atomic weights on each side of the sign of equality, there is imminent danger of tak- ing the student away from the sure ground of fact and experimental demonstration, into an uncertain region of hypotheses based only on definitions and analogies ; — thirdly, because we are ignorant of even 92 PBOSPHORUS. [§141. the probable molecular symbol of most of the elements. Of all the elementary substances recognized, we have reason to believe that eleven, when in the gaseous state, are made up of molecules contain- ing each two atoms, that two contain four atoms, and that three con- tain only a single atom to the molecule. Of the molecular structure of the remaining elements, numbering three-fourths of the whole, we^ at present, know nothing. 141. Volumetric interpretation of symbols. — This important matter forms the subject of § 51Y, page 291, but it should be studied as a part of the present chapter, as should also § 518, page 293, o CHAPTEE XII. FHOSFHOitirs (F). 142. Phosphorus occur.s somewhat abundantly and very widely diffused in nature. It is never found in the free state, but almost always in combination with oxygen and some one of the metals. The most a])undant of its compounds is calcium phosphate, which occurs as a native mineral and wliich also forms the mass of the mineral constituents of the bones of animals. The small amount of phosphorus present in the soil is collected by the growing plants ; the herbivorous animals in their turn consume the phosphorus which has been accumu- lated by the plants, and from the bones of animals chemists and manufacturers derive the phosphorvis of which they' stand in need. 143. Phosphorus, when perfectly pure, is a transparent, colorless, wax-like solid of 1.8 specific gravity, which, when freshly cut, emits an odor lite garlic, though under ordinary conditions this odor is overpowered by the odor of ozone, which, as has been previously stated (§ 103), is developed when phosphorus is exposed to the air. It unites with oxygen § 143.] lyFLAMMABlLITY OF PlWSPHOliCS. 93 readily, even at the ordinary temperature of the air, and with great energy at somewhat higher temperatures (above 60°) ; when in contact with air, it is all the while undergoing slow combustion. If the temperature of the slowly-burning phosphorus be slightly increased in any way, the mass wUl burst into flame and be rapidly consumed. On account of this extreme in- flammability, phosphorus must always be kept under water : it is best also to cut it under water, lest it become heated to the kindling-point by the warmth of the hand, or by friction against the knife ; for, when once on fire, it is exceedingly difficult to extinguish it, and in case it happens to burn upon the flesh, painful wounds are inflicted, which are very difficult to heal. On account of this easy inflammability by friction, phosphorus is extensively employed for making matches. The matter upon the end of an ordinary friction-match usually contains a little phosphorus, together with some substance capable of supplying oxygen, such as red-lead, black oxide of manganese, saltpetre or potassium chlorate. The phosphorus and the oxidizing agent are kneaded into a paste made of glue or gum, and the wooden match-sticks, the ends of which have previously been dipped in melted sidphur, are touched to the surface of the phoaphorized paste, so that the sulphured points shall receive a coating of it. The sulphur serves merely as a kindling material, which, as it were, passes along the fire from the phosphorus to the wood. By rubbing the dried, coated point of the match against a rough surface, heat enough is developed to bring about chemical action between the phosphorus and the oxygen of the other ingre- dient, combustion ensues, the sulphur becomes hot enough to take on oxygen from the air, and finally the wood is involved in the play of chemical force. Exp. 57. — Put a piece of phosphorus as big as a grain of wheat upon a piece of filter-paper, and sprinkle over it some lamp- black, or powdered bone-black. The phosphorus will melt after a time and will finally take fire. As stated above, phosphorus when exposed to the air is all the time undergoing slow combustion ; this action is attended by evolution of heat. Both the lampblack and the paper are bad conductors of heat, and serve to prevent the phosphorus 94 PROSPHOBESOENOE. — RED PHOSPHOEU^. [§ 144 from losing . that developed by the oxidation. Moreover, as will be explained more fully hereafter under carbon, the vapor of phosphorus which rises continually is absorbed by or dragged into the pores of the bone-black and brought into intimate contact with oxygen which is or has been^b^orbed from the air. Chemical action ensues between the phosphorus vapor and the oxygen gas, and as the heat which is generated is retained, the phosphorus ultimately takes fire. 144. At the ordinary temperature of the air, and stiU more at somewhat higher temperatures, phosphorus shines with a greenish-white light, as may be seen by placing the phosphorus in the dark; hence the name, phosphorus, from Greek words signifying light-bearing. This phosphorescence is seen when an ordinary friction-match is rubbed against any surface in a dark room. 145. In ^arm weather phosphorus is soft and somewhat flexi- ble, and may then be bent withont breaking. It melts at 44°, forming a viscid oily liquid, which boils at about 290° and is converted into colorless vapor Phosphorus can readily be dis- tilled in a retort filled with some inert gas, like hydrogen, nitro- gen or carbonic acid. When heated to about 230°, out of con- tact with the air, phosphorus is converted into an allotropic modification known as red phosphorus. Phosphorus is insoluble in water, but is somewhat solublo in ether, petroleum, benzol, oil of turpentine and other oils : it also dissolves abundantly in carbon bisulphide. If a solution of phosphorus in carbon bisulphide be poured upon a sheet of filter-paper, the carbon bisulphide will soon evaporate, leaving the phosphorus in a very finely divided state. The phosphorus begins immediately to oxidize, and, as the paper is a bad conductor of heat, it presently will burst into flame. The paper, however, is not com- pletely consumed, but a very considerable residue of carbon remains unburned. This depends upon the fact that the product of the com- bustion of the phosphorus, quickly covers the paper with a varnish which is not only incombustible in itself, but is quite impervious to air. l^' 146. E«d Phosphorus. — This remarkable allotropic modifi- cation of phosphorus is a body as unlike ordinary phosphorus § 147.] RED PHOSPHORUS. 95 in most respects as could well be conceived. It is of a scarlet- red color, has neither odor nor taste, is not poisonous so far as is known, is not phosphorescent, does not take fire at ordinary temperatures, is insoluble in bisulphide of carbon, and in general behaves altogether differently from the ordinary modification. It is easy, however, to convert one variety into the other. If ordinary phosphorus be heated to 230° out of contact of the air, the red variety is formed : if this be heated still further to 260°, it changes back into the ordinary variety. Szp. 58. — In a narrow glass tube, No. 6, about 30 c. m. long and closed at one end, place a quantity of red phosphorus as large as a small pea ; neat the phosphorus gently over the gas-lamp and note that a sublimate of a light-colored substance is quickly deposited upon the cold walls of the tube a short distance above the heated portion. This light-colored sublimate is ordinary phosphorus, as may be shown by cutting off the tube just below the sublimate, after the glass has been allowed to cool, and then scratching the coating with a piece of wire : the coating will take fire. The air in the narrow tube em- ployed is deprived of its oxygen by the combustion of a small portion of the phosphorus at the moment of its transformation from the red to the ordinary condition : the remaining phosphorus is thus enveloped in nitrogen, and so protected iiom further loss. Red phosphorus is employed, to a certain extent, as an adjunct to the so-called safety-matches. Such matches contain no phosphorus in themselves, and will not take fire readUy by friction upon an ordinary rough surface, though they burst into flame at once when rubbed upon a surface specially prepared with red phosphorus. The matter upon the tips of safety-matches is usually a mixture of potassium chlorate and antimony sulphide, made into a paste by means of glue : the sur- face upon which the match is to be rubbed is composed of red phos- phorus, black oxide of manganese "and glue. In favor of the use of red phosphorus for matches are the facts, that, unlike ordinary phos- phorus, it is not deleterious to the workmen who have to deal with it, and it is far less liable to be set on fire by accidental friction. 147. Phosphorus combines readily with many other elements besides oxygen. The ordinary modification of phosphorus com- bines violently with sulphur at temperatures near the melting- 96 UYUROOKN PHOSPHIDE. [§ 148. point of sulphur, the act of combination being attended with vivid combustion and loud explosion. With chlorine, bromine and iodine, ordinary phosphorus unites directly at the ordinary temperature of the air, the combination being rapid aud attended with inflammation. Phosphorus unites directly with most of the metals forming phosphides, 148. Compounds of Phosphorus and Hydxogen. — There are three compounds of phosphorus and hydrogek J of which, at ordinary temperatures, one is gaseous, HjP, one liquid, H^P, and one solid, HPj. The gaseous compound, lor rather the gaseous compound charged with the vapor of the liquid com- pound, is somewhat interesting, from the fact that it takes fire spontaneously, immediately on coming into contact with the air. Ezp. 59. — In a thin-bottomed flask of about 140 c. c. capacity, put 1 grm. of phosphorus and 115 c. c. of hydrate of sodium, obtained by dissolving 40 grms. of common caustic soda in 110 c. c. of water. Pour two or three drops of ether upon the liquid in the neck of the flask, then close the flask with a cork carrying a long delivery-tube of glass, No. 5. Place the flask over the gas-lamp, upon the wire-gauze ring of the iron stand, and immerse the end of the delivery-tube in the water-pan, then gently heat the flask. The ether is added to the contents of the flask, in order that the last traces of air may be expelled from the flask by the vapor which arises from this highly volatile liquid as soon as it is warmed. Fig. 30. ^g ^jjg soda-solution becomes hot, toiall bub- bles of gas will be seen to arise from the sur- face of the phosphorus, and in a short time large bubbles pf gas will escape from the deliv- ery-tube : each of these bubbles, as it comes in contact with the air at the surface of the water, will spontaneously burst into flame, and burn with a vivid light and § 149.] OXIDES OF PHOSPHORUS. 97 the formation of beautiful rir^s of white smoke, if the air be not dis- turbed by draughts. In burning, the hydrogen phosphide is con- verted into phosphoric acid, and of this product the white smoke is, of course, composed. 2 H,P + 8 O = 2 H,PO,. The atomic weight of phosphorus is 31 ; the specific gravity of its vapor has been found to be 62.1. In this respect phosphorus differs from the elements already studied where the combining weights and the unit-volume weights have been identical ; it follows that, if the molecule of hydrogen contains two atoms of hydrogen, the molecule of phosphorus will contain four atoms of phosphorus (p. 91). If we compare the formula of hydrogen phosphide, H^P (§ 148), with that of ammonia, H^N, we have the atom of phosphorus, which weighs 31, combining with the same quantity of hydrogen by weight as the atom of nitrogen ; but while from two volumes of ammonia-gas we may set free three volumes of hydrogen and one volume of nitrogen, from two volumes of hydrogen phosphide we have three vol- umes of hydrogen and only half a volume of phosphorus vapor. The composition of hydrogen phosphide may thus be represented by the accompanying diagram. U 149. Oxides of Phosphorus. — There are three oxides of phosphorus answering to the formulse P^O, P^O,, PjOj. Hypophosphorous Anhydride (PjO). — It is doubtful whether this oxide has been isolated. The corresponding acid, however, HjPO, (3 HjO, PjO = 2 HjPOj), is known, as are also the corre- sponding salts, the hypophosphites of certain metals : the hypo- phosphite of barium, for instance, is Ba 'H.^.fl^. Phosphorous Anhydride (PjOj) is formed by buniing phos- phorus with a limited supply of air. It is a white amorphous sub- stance, very soluble in water, and burning in the air to phosphoric; anhydride (PjOJ. The corresponding acid is H^POj (3 HjO, PjOj) and the corresponding salts are called phosphites. 9 H 1 H 1 • + 1/ , = PH, 34 H 1 , 98 OXIDES OF PHOSPHOliCS. [§ 150. i 150. Phosphoric Anhydride (PjOj. — This oxide of phos- phorus is the product of the rapid combustion of phosphorus in an excess of air or oxygen. Exp. 60. — Dry thorouglily a large porcelain plate, a small porce- laui capsule and a wide-mouthed bottle of two litres' capacity, by Fig. 31. warming them at a tire ; place the capsule upon the plate and put in the capsule a bit of dry phosphorus, of the weight of about half a gramme ; light the phosphorus and cover it at once with the inverted bottle. The phosphoric anhydride, formed by the combustion of the phosphorus, will be deposited as a white pow- der, like flakes of snow, upon the sides of the bottle, and much of it will fall down upon the plate below. The flocculent, amorphous, odorless powder, thus obtained, unites with water with remarkable facility : if it be left in the air for a few minutes, it deliquesces completely ; upon being thrown into water, it dissolves with a hissing noise and de- velopment of much heat. In order to preserve it, it must be placed in a dry tube, and the tube closed by sealing it in the [l^mp. ^ § 151. Phosphoric Acid. — By the union of phosphoric anhy- dride with water, there are formed three distinct acids : meta- phosphoric acid (HPO3), pyro-phosphorie acid (h^p^o,) and ordinary or tribasio phosphoric acid (h^po,).^ Corresponding to these three varieties of phosphoric acid, there are three series of phosphates, the metarphosphates, the pyro-phosphates and the ordinary phosphates. The number of possible phosphates is much increased from the fact that while meta-phosphoric acid (HPO,), like nitric acid, is monobasic, pyro-phosphoric acid (H^P^O,) is tetrabasic, i.e., has four replaceable atoms of hydrogen, and the ordinary phosphoric acid (H3PO,) is tribasio. (See § 134.) ^ 152. Empirical and Rational Formulae. — It has already been stated that when phosphoric anhydride is thrown into water, it jfnites ^ith" a portion of the water to form phosphoric acid. The § 152.] HMl'l RIVAL AND RATIONAL FORMl'L.E. 99 reaction may be thus symbolized : P2O5 -j- H^O = H^O, PjOj = HjPjO, = 2 HPOj (meta-phosphoric acid). If the anhydride be thrown into hot water, the reaction is PjO^ -\- 3 H^O = 3 H^O, P^Oj = HjPjOj ^ 2 HjPO, (ordinary phosphoric acid). We may rep- resent mfeta-phosphoric acid by the formula H^O, P^Oj or by HPO, ; we may represent ordinary phosphoric acid by 3 H^O, Vfi^ or by H5PO4 : in these cases we have two formulae to denote one and the same substance. If ordinary phosphoric acid were analyzed, it would be foimd to contain, for every three parts by weight of hydrogen, thirty-one parts of phosphorus and sixty-four (4 X 16) parts of oxy- gen. The resiilt of the analysis would be expressed most simply by the formula HjPO^. A formula which simply represents the number of atoms of each element in one molecule of any substance, as determined by analysis, is called an empirical formula. The truth of such a formula de- pends solely upon the correct performance of the analytical process, and upon the accuracy with which the atomic weights have been determined. Concerning such formulse, there is little room for dif- ference of opinion : they express all that we actually leaow of the elementary composition of any compound body. Chemists have, however, endeavored to contrive formulse which should express something more than the mere elementary composition by weight ; which shtSixld recall the materials from which the formulated sub- stance was made, and prophesy the products of its decomjjosition ; which should not only name and number the atoms of the sub- stance, but should also suggest such a grouping or arrangement of those atoms as- might serve to interpret its known reactions. Such fonnulse are called rational forinulEe. In the present ease 3 HjO, PjOj is a rational fommla of phosphoric acid. It recalls the fact that the acid can be made by causing phosphoric anhydride to unite with water. It is not altogether a matter of indifference whether phosphoric acid be written 3 HjO, P^Oj or HjPO, ; for in one case the weight of the molecule would be 196 and in the other 98. If it were possible to obtain this compound in the state of vapor, and the vapor could be weighed, the weight of the molecule could be found (§ 139) by multi- plying the vapor density by two. It is usual to regard the shorter Jormula as representing the molecule. The same difficulty occurs in the case of other compounds, nitric acid, for instance ; the molecule of nitric acid may be H^O, N„Oj = 126 or HNO^^ 63. In some 100 IJUALISTIC AND TYPICAL FORMUL.ii. [§ 153. reactions it is more convenient to employ one formula, and in other reactions the other formula. It is evident that there may be various rational formulae for the same substance : in fact, for acetic acid, a compound of carbon, oxygen and hydrogen to be described in a subseq^uent chapter, no fewer than nineteen formulis have been proposed. 153. All the acids (except those formed by "the union of hydrogen with members of the chlorine group) and the corresponding salts may be written in a manner similar to that employed in the case of phos- phoric acid SHjO, P^Oj: thus, — nitric acid, H^O, NjOj ; sodium nitrate, Na^O, NjO^ ; potassium sulphate, K^O, SO,. Such for- mulae are called dualistic, because they represent these bodies as of a dual nature, — as being made up of two oxides which were dis- tinct before they were brought together to form the compound, and will be distinct when separately extracted from it : in a dualistic for- mula these two distinct parts are conventionally represented as having some separate existence within the compound itself. The suppositiou is not unnatural : thus, for example, common plaster of Paris is a sub- stance containing the metal calcium and the elements sulphur and oxygen in the proportions by weight which are correctly expressed by the formula CaSO, ; but this substance may be made by methods which suggest another formula. If we put together quicklime, CaO, and sulphuric anhydride, SO3, in due proportions, under suitable conditions, plaster of Paris, or, as its chemical name is, calcium sul- phate, results : CaO -\- SO3 = CaO, SO3 ; or if we mix slaked lime, CaO, H^O, with sulphuric acid, H^O, SO3, in proper propor- tions, at a suitable temperature, we shall again obtain calcium sul- phate, and water will be eliminated : CaO, H^O -|- HjO, SO3 = CaO, SO3 + 2 H,0. 154. Another way of writing chemical formulce is in accordance with the doctrine of types. According to this doctrine, every pos- sible chemical con»bination may be imagined to be built upon the plan, or framed upon the type or model, of some one of three sub stances, chlorhydric acid (or free hydrogen), water and ammonia. These substances must be regarded as types only with reference to the supposed grouping of atoms in the compounds : the external properties of various substances referred to the same type may be totally different. Examples of compounds referred to the different types are : — § 154.] TYPICAL FORMULA. — RADICALS. 101 Type. Chlorhydric acid. H CI ! Type. Water. Hi» Type. Ammouia. H H J.N H ' Free Hydrogen. i! Sodium hydrate. Aniline. (CeH,) H H N Sodium chloride. Na ) CI \ Nitric acid. Methylamine. (CH3) ; H >N H Metliyl hydride.' (CH3) ) Alcohol. (CA) Aceiamide. (CftO) ) H >N It will be noticed in these examples ttat the hydrogen of the type may be replaced, not only by a single element, but also by a group of elements. Such groups of elementary atoms are called compound radicals, and, like the elementary atoms themselves, differ in their replacing power, some being wdvaient, some bvoalent, etc. The typical formula of some substances is written by regard- ing the substance as built upon the type of the double molecule of the typical compound : other substances are regarded as built upon a mixed type. The following examples will serve to illustrate a few of these cases : — Type. Sulphuric Calcium Lead acid. sulphate. nitrate. ^•!°. ^^■\o. 'So. 2 (NO,) Pb" Type. Urea. Type. Clvcerin. H.3) (CO)") i:l»- (C.H,)'" H. [n. H, H. ) Type. Sulphurous acid. H) ^ ) (SO,)" SO '2^0 H o, It is often convenient to mark the fact that an elementary atom or a radical is bivalent or trivalent by the use of the proper number of accents placed at the right hand of the symbol, as has been done in these examples. These t3rpical formulae will be found especially useful in the consid- 9* 102 AHSE^lC—Ui'DIiOUENARlSEMDE. [§155. eration of the compounds of carbon j it is, however, to be distinctly remembered that a rational fonniila is never to be regarded as the expression of an absolute truth, but only as a guide in classification, an aid to the memory and a help in instruction ; while the empirical formula expresses all that is actually known of the composition of any given body. CHAPTER Xm. AKSENIC, AKTIMONY AND BISMUTH. AE8ENIC (as). 155. In small quantity arsenic is very vpidely distributed in nature. It is sometimes found free in the metallic state, but generally in combination with oxygen or sulphur and some one of the metals, such as iron, cobalt, nickel and copper. 156. Arsenic is a brittle solid of a steel-gray color and metallic lustre. At a dull red heat it may be. converted into a vapor which has a peculiar garlic odor. Heated in the air or in oxygen, arsenic burns with a whitish Hame producing the white arsenic teroxide (arsenious anhydride). Arsenic com- bines readily with chlorine, bromine, iodine and sulphur ; it also unites by fusion with most metals, forming alloys, whicli the arsenic tends to make hard or brittle. lu the manufacture of shot, a little arsenic is added to the lead to facilitate the for- mation of regular globules. The symbol Of arsenic is As ; its atomic weight is 75. Like phosphorus, the specific gravity of its vapor is double its atomi weight, and conseqiiently its molecular symbol is As^. , 157. Hydrogen arsenide or ajseniuretted hydrogen (HjAs) is a colorless gas, having a fetid odor : even when very much diluted with air, it is intensely poisonous, and fatal results liave repeatedly followed its accidental inhalation. The gas may be prepared in an impure state mixed with hydrogen by introducing a solution of soiae compound of arsenic into a § 159.] IlYUROaES AliSESWM. — OXIDES OF ARSENIC. 103 generator in which hydrogen is being produced from zinc and a dQute acid. Hydrogen arsenide bums in the air with a whitish flame, forming water and a white smoke of arsenious anhydride ; but if a cold body, like a piece of porcelain, for example, be introduced into a jet of the burning gas, Wie hydrogen alone wiU bum, and the arsenic wiU be deposited in the metallic state upon the porcelain surface, forming a lustrous black spot. This effect is precisely similar to the deposition of soot on a cold body held in the flame ^'sr. 38. of a candle. The gas is also decomposed when caused to pass through tubes heated to dull redness, metallic arsenic being deposited as a brown or blackish mirror, whUe hydrogen gas escapes. These properties of hydro- gen arsenide are made use of in testing for the presence of arsenic in cases of suspected poisoning. 158. Compounds of Arsenic and Oxygen. — There are two weU-deiined oxides of arsenic, — arsenions anhydride (AbjOj) and arsenic anhydride (AsjOJ. 159. Arsenious anhydride (ASjO,) often called arsenious acid, ot white arsenic, is fornied 'vvheu metallic arsenic or arseni- cal ores are heated in the air. It ordinarily occurs in small octahedral crystals. When heated with free access of air, it volatilizes without change : if heated in contact with carbon, it gives up its oxygen, and metallic arsenic is liberated. Arsenious anhydride is somewhat soluble in water : it dissolves readily in hot chlorhydric acid ; but, when the sohition cools, most of the arsenious anhydride is deposited unchanged. Exp. 61. — Place a few particles of " arsenious acid " * in an open * The substances now designated as anhydrides were formerly called acids as stated in § 63. In the case of sulphurous, arsenious aud carbonic anhydrides, the popular names sulphurous, arsenious and carbonic acids have such currency that they will be employed in this Manual where no ambiguity can arise from such use. 104 ARSEXIOUS ACID. — ARliJiXITES. [§ 160. tube of hard glass (No. 5) about 10 c. m. long, and heat over the lamp, holding the tube in a sloping position : the white solid will be volatilized, but it will immediately be deposited again upon the cold part of the tube. By the aid of a lens, this deposit may be seen to be crystalline. viK. 33. Exp. 62. — Drop into the point of a drawn-oiTt tube of hard glass, No. 5, a morsel of arsenious acid, and above it place a splinter of charcoal (Fig. 33) ; heat the coal red-hot in the flame of the lamp, and then vola- tilize the arsenious acid. The acid will give its oxygen to the coal, and the airsenic will be deposited in a ring on the cold part of the tube, presenting a brilliant metallic appear- ance. Exp. 63. — Throw a particle of arsenious acid upon a piece of red-hot charcoal : the acid will be partly reduced, and the peculiar garlic odor of the vapor of metallic arsenic will be perceived. 160. Arsenious acid is a violent poison, all the more dan- gerous, because it has neither taste nor odor to warn the victim of its presence : two decigrammes of it will cause death. All the soluble salts of arsenious acid are likewise horribly poison- ous. The best antidote to the poison is a mixture of moist, freshly precipitated iron hydrate and caustic magnesia. Arsenious acid is largely used in the manufacture of a bril liant green pigment, a compound of arsenite and acetate of copper, commonly called Paris green ; it is applied as an oxidizing agent in the manufacture of glass ; it is consumed in considerable quan- tities for poisoning vermin, and for producing the arsenic acid which is used in the dyeing and printing of cloth ; it is used in very small doses as a remedy for asthma, and in so^ii^ skin diseases. 161. Arsenious anhydride is soluble in water. The solution is slightly acid, but it is doubtful whether a definite compound of the anhydride with the elements of water is formed ; if so, it would be properly designated as arsenious acid : there are compounds of various metals (called arsenites) which would imply an arsenious acid of the formula HjAsOj. Thus silver arsenite i.3 Ag3AsO,. § 165.] AXTiAioyr. 105 162. Arsenic anhydride (ASjOu) is prepared by heating arse- nic acid to dull redness. It forms a white amorphous mass, whioli by long exposure to water is gradually converted back into arsenic acid:" Arsenic acid (HjAsO,) is obtained by oxidizing arsenious anhydride with nitiic acid, aqua regia or other oxidizing agents. The corresponding salts of the metals are called arseniates. Arsenic acid and some of the arseniates are used in dyeing. 163. Sulphides of Arsenic. — Two sulphides of arsenic occur native, one (As^S^) is called realgar. It is iised in pyrotechny. The other (As^Sj) is called orpiment. It is also prepared artifi- cially, and is used somewhat as a pigment. ANTIMONY (sb). 164. Antimony, like arsenic, is found native : it also occurs alloyed with other metals, especially with arsenic, nickel and silver. There exist also a considerable number of minerals, which consist of, or contain, large proportions of the compounds of antimony with oxygen and sulphur. All the antimony of commerce is obtained from the mineral tersulphide, Sb^Sj. The symbol for antimony is Sb, from the Latin name of the sub- stance, Stibium. 165. Antimony is a brittle metal, having a bluish-white color, a brilliant lustre and a highly crystalline structure. The cakes of the commercial metal usually present upon their upper surfaces beautiful stellate or fern-like markings. Antimony melts at 450°, gives off vapors at a low red heat and takes fire at full redness, burning brilliantly with evolution of white fumes of the teroxide (Sb^Oj). The atomic weight of antimony is 120. Antimony enters into the composition of several very valu able alloys. Type metal is an alloy of lead and antimony, containing about 20 per cent of antimony. For stereotype plates -^to-^oi tin is usually added to this aUoy. The com- mon w^hite metallic alloys, such as Britannia metal, pevrter, etc., used for cheap teapots, spoons, forks and like utensils, are variously compounded of brass, tin, lead, bismuth and an- 106 COMPOUNDS 01'' AXTIMOXY. [§ 160. timony. The value of antimony in these alloys depends upon the hardness which it communicates to the compounds, without rendering them inconveniently brittle. (J 166. Hydrogen antimonide (H^Sb ?) is a colorless, inodorous gas which resembles hydrogen arsenide in being decomposed by heat ; it burus in the air with a whitish flame and gives off a smoke of antimony tero:side : when a bit of cold porcelain is held against a burning jet of the gas, a sooty spot of metallit antimony is deposited on the porcelain. These spots of metallic antmiony are distinguished from those of arsenic, obtained in a similar manner from hydrogen arsenide by difference in lustre, volatility and solubility in various chemical agents. 167. Antimony and Oxygen. — Antimony forms two well- defined oxides, — antimony teroxide (Sb^Oj) and antimonic anhydride (SbjO^). Antimony teroxide occurs as a native' miu- tr.d, and ia formed when metallic antimony is burned in the air. Antimoni*' anhydride is formed by heating antimonic acid. The acid may be obtained by oxidizing metallic antimony with nitric acid. A third oxide of antimony occurs native. Its formula is SbjO^ and it may be regarded as a compound of the other two oxides, — Sb^Oj, Sb^Oj = 2 Sb^O,. Q 168. Antimony and Chlorine. — Powdered antimony takes fire ^hen thrown into chlorine gas (Exp. 32, § 81) ; it also combines very energetically with bromine and iodine. "When very finely powdered, it is dissolved by boiling chlorhydric acid, with evolution of hydrogen ; if a little nitric acid be added to the chlorhydric, the metal dissolves easUy, to form a solution of antimony terchloride (SbCla). Antimony terchloride at the ordinary temperature is a trans- rig. 34. lucent yellowish substance of fatty consistency, whence its popular name, " butter of antimony." When thrown into water, it is decomposed into chlorhydric acid and antimony teroxide, which, however, remains united with a portion of the chloride, forming a white powder which contains antimony, chlorine and oxygen, but is somewhat variable in composition. Exp. 64. — In a flask of about 200 c. c. ca- pacity, heat gently 0.5 grm. of finely-powdered § 172.] BISMi'TB. 107 antimony with 30 c. c. of strong chlorhydric acid, to which 10 drops of nitric acid have been added. When complete solution has been effected, pour a little of the chloride into water, to demonstrate the decomposition just referred to. Evaporate the rest of the solution to the consistency of a thick sirup : it is the butter of antimony. 169. Antimony and Sulphur. — The native mineral known as gray antimony or antimony glance is antimony tersulphide (SbjSj). It is the source of the antimony of commerce. BISMUTH (bI). 170. The metal bismuth is found chieily in the metallic state, hut also occurs in combination %vith sulphur, oxygen and tel- lurium. It is prepared for the arts almost exclusively from native bismuth. It Is a tolerably hard, brittle metal, of a grayish-white color with a reddish tinge. When pure, it crys- tallizes more readily than any other metal ; by the method of fusion (§ 113) it may be obtained in most beautiful crystals, made highly iridescent by the thin film of oxide which forma on their surfaces while they are stiU hot. Bismuth promotes the fusibility of metals with which it is alloyed to an extraordinary extent. The most remarkable alloy of bismuth is that known as " fusible metal." When composed of 1 part of lead, 1 part of tin and 2 parts of bismuth, this aUoy melts at 93°. 75. The symbol of bismuth is Bi ; its atomic weight is 21.0. /y-^ 171. There is no compound of bismuth and hydrogen as yet known. There are three oxides corresponding to the oxides of antimony, — bis- muth teroxide (BijO,), bismuthic anhydride (BijOj) and the oxide BijOj which may be regarded as a compound uf the other two. Bis- muth terchloride (BiClj) resembles antimony terchloride. It is de- composed by water into chlorhydric acid, which dissolves a portion of the chloride, and a precipitate containing bismuth, chlorine and oxygen,' and called bismuth oxychloride (BiOCl). Vi 172. The Nitrogen Group of Elements. — The five elements, nitrogen, phosphorus, arsenic, antimony and bismuth, form a weU-marked natural group of elements. In the first place, the elements themselves exhibit a definite gradation of properties, 108 THE KITROGJiX GROUP. [§ 172. and, secondly, the analogy in composition and properties mani- fested by tlie similar compounds of the five elements is most striking and complete. Nitrogen is a gas, phosphorus a solid whose specific gravity varies from 1.8 to 2.2, arsenic has the specific gravity of 5.6, antimony of 6.7, while that of bismuth rises to 9.8. The me- tallic character is most decided in bismuth, is somejvliat less marked in antimony, is doubtful in arsenic and almost van- ishes in phosjihorus. The series of corresponding hydrides, oxides, chlorides and sulphides, which the elements of this group form, are very perfect : they prove the general chemical likeness of the five elements : — Hydrides. Oxides. Oxides. Oxides. Chlorides. Sulphides. NH, N,0, N,0, N,0, NC1,(?) P.S3 PH3 P.O„ Sb,0« p»o, PCI, As,S. AsH, AS.O3 BiA ASjO, ASCI3 Sb,S. SbH, Sb.O^ Sb,0, SbCl, Bi,S, Bi,0. BiA BiCl, PCI5 SbCL As,S, When the qualities of the corresponding compouuds which the members of the nitrogen group form with other elements are duly taken into account, it will be apparent that the relative chemical power of each element of the group may be inferred from its position in the series of elements : — N = 14, P = 31, As = 75, Sb = 122, Hi = 210. The chemical energy of these five elements, broadljconsidered, follows the opposite order of their atomic weights. § 175.] CARBON 109 CHAPTEE XIV, CABBOII (C).^ 173. Carbon is an extremely important and a very abundant element. All organic substances, all things which have life, contain it. In the mineral kingdom, the various forms of coal, graphite, petroleum, asphaltum, and all the different varieties of limestone, chalk and marble, contain it in large proportion. It is found also in the atmosphere and in the waters of the globe, and though existing therein in comparatively small proportion, it is an ingredient not less essential than either of their other constituents for the maintenance of the actual balance of organic nature. All vegetable life is directly dependent upon the pres- ence of the compound of carbon (carbonic acid) which exists in the atmosphere. 174. Three distinct allotropio modifications of carbon are distinguished, namely, 1. The diamond ; 2. Plumbago or graphite ; and 3. Ordinary charcoal or lamp-black ; of this last modification there are many sub-varieties. In each of its modifications, carbon is an infusible, non-volatile solid devoid of taste and smell. While the several modifications differ among themselves in color, hardness, lustre, specific grav- ity, behavior towards chemical agents, power of conducting heat and electricity and in various other respects, they all agree in this, that, on being strongly heated in presence of oxygen, they unite with it and form the same compound, an oxide of carbon (COj). 175. Diamond. — The diamond is pure or nearly pure carbon and occurs in nature in octahedral crystals. Its rarity and its high refractive power as regards light, together with the diffi- culty with which it is worked, make it the most precious of gems. It is the hardest known substance. The diamond has not as yet been produced artificially. The diamond is not attacked by the strongest acids or alka- 10 110 GnAPIIITK. — GAS-CARBOX. [§ 176. .lies, not even by fluorhydric acid ; nor is it acted upon by any of the non-metallic elements, with the exception of oxygen at high temperatures. At the ordinary temperature of the air, diamond undergoes no appreciable change. Out of contact with the air, or in an , atmosphere which has no chemical action upon it, it suffers no alteration at the highest furnace heat ; heated white-hot between the charcoal points of a power- ful galvanic battery, it softens and swells up, forming a black brittle mass like coke ; heated in oxygen gas, it bums to carbonic acid (coj. 1 76. Graphite or Plumbago, sometimes called " black-lead," is familiarly known as the material of common " lead pencils." It is -found as a mineral in nature in various localities. It occurs both in the form of crystals and in the amorphous, massive state. In both forms it is always opaque, of a black or lead-gray color and metallic lustre. Graphite is very friable ; when rubbed upon paper, it leaves a black shining mark, whence its use for pencils. Amorphous graphite is so soft and unctuous to the touch that it is often used as a lubricant for diminishing the friction of machinery : but in spite of this seeming softness, the particles of which the masses of graphite are composed are extremely hard ; they rapidly wear out the saws employed to cut these masses. In the air, at ordinary temperatures, graphite undergoes no change ; hence its use for covering iron articles to prevent their rusting. By virtue of its greasy, adhesive quality, it is easy to cover iron with a thin, lustrous layer or varnish of it ; the common stove-polishes, for example, are composed of pow- dered graphite. 177. Gas-Carbon. — An interesting sub-variety of carbon somewhat similar to graphite, and standing, as it were, between it and the ordinary modiiication of carbon, is obtained from the retorts in which common illuminating gas is manufactured. It is known as " gas-carbon," or " carbon of the gas-retorts," and results from the burning on of drops of tar •upon the in- terior walls of the retort, and the long-continued heating of the crust thus formed. § 178.] COKE. -ANTHRACITE AXD BITUMINOUS COAL. HI Gas-carbon is very hard, compact and dense ; it has a metallic lustre, and conducts electricity like a metal. On account of its high conducting power, it is employed in the manufacture of galvanic batteries and of pencils for the electric lamp. 178. Coke and Anthracite Coal are impure sub- varieties of carbon which, from the chemical point of view, may be classed either with graphite or charcoal, or better Ijetween the two. They are less like graphite, however, than gas-carbon is. Coke is the residue resulting from the destructive distillation of soft or bituminous coal. Exp. 65. — Put into a tube of ■* -^ ^^- ^^' haitl glass. No. 1, 12 or 15 c. m. in length, enough bituminous coal, in coarse powder, to fill one-third of the tube. Fit to this ignition-tube ' a large delivery-tube of glass. No. 4, and support the apparatus upon the iron stand, as shown in the figure. Heat the coal in the ignition-tube, and collect in bottles the gas which will be evolved. The gas will bvim with a yellow flame on the appli- cation of a match. This gas is, in the main, a mixture of several com- pounds of carbon and hydrogen ; for the present, it may be regarded as carburetted hydrogen. It is, in fact, ordinary illuminating gas. As soon as gas ceases to be given off from the coal, take the end of the delivery-tube out of the water, and when the ignition-tube has become cold, break it, and examine the cOke which it contains. The coke used for domestic purposes is obtained as an incidental product in the manufacture of illuminating gas. Bituminous coal is a substance of vegetable orgin, which ap- pe irs to have been formed from plants by a process of slow decay going on without access of air and under the influence of heat, mois- ture and great pressure. Like vegetable matter in general, it is composed of carbon and hydrogen, together with small proportions of oxygen and nitrogen, and a certain quantity of earthy and saline substances, commonly spoken of as inorganic matter. On being heated in the air, it bums away almost completely after a while, leav- ing nothing but the inorganic components as ashes. But when heated 112 CHARCOAL. — LAMP-BLACK. [§ 179. out of contact with the air, that is to say, when siibjecteil to destruc- tive distillation, as in Exp. 65, the volatile hydrogen is all driven off in combination with some carbon, either as gas or aa a tarry liquid; and the residue, or coke, contains only carbon contaminated with the inorganic matters originally present in the coal. In Europe, where anthracite is lacking, immense quantities of coke are prepared for metallurgical uses, the gas resulting from the decom- position of the coal being usually thrown away. Anthracite is supposed to have been formed, like bituminous coal, from the slow decay of vegetable matter, and then to have been subjected to some sort of natural distillation by which it has been de- prived of neaily all the hydrpgen, nitrogen and oxygen of the original wood. It is tlius a coke formed by natural agencies. 179. Both coke and anthracite are hard and lustrous. As compared with charcoal, they are rather difficult of combustion, Both anthracite and coke, the latter in spite of its porosity, conduct heat readily, as compared with charcoal ; hence one reason of the difficulty of kindling them. In building a char- coal fire, the heat evolved by the combustion of the kindling material is almost all retained by the portions of charcoal im- mediately in contact with the kindling agent, but in the case of coke or anthracite, a large proportion of this heat is conducted off and diffused throughout the heap of fuel, so that no portion of the fuel can at once become very hot. 180. Charcoal or Lamp-black is commonly taken as the representative of the third or amorphous modification of carbon. This kind of carbon can be obtained in a state of tolerable purity, either by heating in a close vessel sugar, starch or some other organic substance which contains no inorganic constituents, or by burning oil of turpentine in a quantity of air insufficient for its complete combustion. Charcoal can be obtained also by distilling wood in retorts in the same way fhat we have seen that coke can be procured from bituminous coal. (See Exp. 65.) ' /_ Xizp. 66. — Provide an ignition-tube and a delivery-tube similar to those employed in Exp. 65. Fill the iguition-tube with shavings or small fragments of wood, arrange the apparatus as before and light § 180.] PREPARATION OF CHARCOAL. 113 the gas-lamp. Collect in bottles the gas which is given off from the wood and test it as to its inflammability by applying a lighted match. After the flow of gas has ceased, remove the end of the delivery-tube from the water, plug it so that no air can enter the ignition-tube and lay the apparatus aside until it has become cpld. Finally, remove the cork from the ignition-tube and take out the charcoal which is contained in it. Heat a portion of this charcoal upon platinum foil and observe the mai\si«i in which it hums : it will illustrate the fact that solid substances which are incapable of evolv- ing volatile or gaseous matter do not bum with flame, -^ they merely glow. For use in the arts charcoal is sometimes prepared by distilling the wood in retorts, but more generally by burning the wood with little access of air. Logs of wood are piled up into a large mound or stack around a central aperture, which subsequently serves as a temporary chimney and also for the introduction of bnming substances for firing the heap. The finished heap is covered with chips, leaves, sods and a mixture of moistened earth and charcoal dust, a number of apertures being left open around the bottom of the heap for the admission of air and the escape of the products of dis- tillation and combustion. The heap is kindled at the cen- tre and burns dur- ^*s. 36. ing several weeks. When the process' is judged to be complete, all the openings are care- fully stopped in order to sufibcate the fire, and the heap is then left to itself until cold. The charcoal retains the form of the wood, — the shape of the knots and tlie annual rings of the wood being still perceptible in it, — but it occupies a much smaller volume than the wood : generally its bulk does not amount to more than three-fourths of that of the wood, and 10* lU LAMP-BLACK. [§ 181. its weight never exceeds one-fourth the weight of the wood. Sometimes kilns built of brick are used, instead of the rude heaps here described. Where charcoal is prepared by distilhng wood in retorts, the liquid products of distUIation, namely, tar and acetic acid (" pyroligneous acid "), are saved and utilized. 181. Lamp-black. — Upon the large scale, lamp-black is manufactured by heating 'organic matters, such as tar, resin or pine knots, which contain volatile ingredients very rich in. carbon, until vapors are disengaged, and then burning these vapors in a current of air insuificient for their complete com- bustion. The vapors consist of compounds of carbon and hydrogen, and the supply of air being insufficient to consume both hydrogen and carbon, a la,rge portion of the carbon of the combustible does not burn, but is deposited as a very fine powder precisely similar to that which constitutes the black portion of common smoke. Lanlp-black finds important ap- phcations in the arts as a pigment and as the chief ingredient of printers' ink. X!^. 67 . — Fill an ordinary spirit-lamp (Appendix, § 5) with oil of turpentme, light the wick and place over it an inverted wide- mouthed bottle of the capacity of a litre or more, one edge of the mouth of the bottle being propped up on a small block of wood, so that some air may enter the bottle. As the supply of air is insuffi- cient for the perfect combustion of the oil of turpentine, a quantity of lamp-black will separate and be deposited upon the sides of the bottle. Hydrogen kindles at a lower temperature than carbon, hence if the flame of a burning compound of carbon and hydrogen be cooled down below the temperature at which carbon takes fire, lamp-black wiU be formed, even if there be present an abundant supply of air. Ezp. 68. — Press down upon the flame of an oil-lamp or candle an iron spoon or a porcelain plate in such manner that the flame shall be almost, but not quite extinguished. The solid body not only ob- § 182.] CHARCOAL A REDUCl.VG AGENT. 115 structs the draught of air, and thereby interferes with the act of combustioii, but it also cools the flame by ^te- 37. actually conducting away part of its heat ; the temperature is thus reduced to below the kindling-point of carbon, and a quantity of lamp-black remains unconsumed and adher- ing to the spoon or plate. The deposit of lamp-black is, of course, comparable with the spots of arsenic and antimony, alluded to in §§ 157, 166, as being obtained upon porce- lain, as products of the incomplete combus- tion of the hydrogen compounds of these elements. 182. In aU its varieties, charcoal is a very important chemi- cal agent, chiefly because of the readiness and energy with which it combines with oxygen at high temperatures. It might almost be said that the art of metalltirgy, as it now exists, is based upon the affinity of carbon for oxygen. Exp. 69. — Mix two an,d a half grammes of copper oxide with a quarter of a gramme of powdered, charcoal ; place a portion of the mixture in an ignition-tube made of No. 3 glass, and heat it strongly in the gas-lamp. The charcoal will unite with the oxygen of the copper oxide, and the compound thus formed will escape in the form of gas, while metallic copper will remain in the tube. This experiment is analogous to Exp. 62, where arsenious acid was reduced by means of charcoal. Both experiments are typical of the manner in which hot charcoal acts upon metallic oxides. At a white heat it removes oxygen from its combinations with some elements which hold it with great force, such as the oxides of sodium and potassium, phosphoric acid and water. If a current of steam be passed over red-hot charcoal, the steam is decomposed ; the hydrogen is set free, and the oxygen of the steam combines with a portion of the carbon to form carbon protoxide (CO), an inflammable gas. The reaction which occurs may be formulated as follows : C -\- H^O = CO + 2 H. The deoxidizing power of charcoal, thus illustrated, is exhibited oidy at high temperatures. At- the ordinary tem- perature of the air, the chemical energy of charcoal is exceed- 116 PROPERTIES OF CHARCOAL. [^ 183. ingly feeble. Charcoal is, in fact, one of the most durable of substances. Specimens of it have been found at Pompeii and upon Egyptian mummies, to all appearance as fresh as if just prepared : the action of the air continued through centuries has exerted no appreciable iniluence upon it. Fence-posts which are sunk for a certain distance into the ground are often charred on the outside, and thus rendered more durable. 183. A physical property of charcoal, which is of great practical importance, is its power of absorbing and con- densing within its pores a great variety of gases and vapors. Freshly-burned charcoal exposed to damp air, in a cellar for instance, wiU gain 10 or 12 per cent in weight in the course of a single day. Exp. 70. — Take from the fire a piece of charcoal which has been heated to full redness for some time ; thrust it under water so that it may be suddenly cooled, and observe that it sinks in the water and that few or no bubbles of gas escape from its pores. Take another piece of charcoal which has long been exposed to the air and has not recently been heated, attach to it a quantity of sheet- lead sufficient to sink it in water,'and immerse the whole in a large beaker-glass two-thirds full of hot water. The mobile water will im- mediately enter the pores of the charcoal, and a portion of the air which had previously been absorbed by these pores wiU be driven out, and can be seen escaping in bubbles through the water, chiefly from the broken ends of the coal. To the presence of air and aqueous vapor, which lias been thus absorbed, is to be attributed the snapping and crackling of old charcoal when it is thrown upon a hot fire. Different gases are absorbed by charcoal in very different propor- tions : thus a cubic centimetre of dry, compact charcoal, such as that from boxwood, will absorb as much as 90 c. c. of ammonia-gas in the course of 24 hours ; while in the same time it will absorb only 35 c. c. of carboidc acid and only 2 c. o. of hydrogen. 184. Charcoal is much employed as a disinfecting agent. It is capable of removing many offensive odors from the air. 5 lOO.J l^IWl^MKTIES OF CHARCOAL. 117 such, for example, as the fetid products given off during the putrefaction of animal and vegetable substances. Animal mat- ter in an advanced stage of putrefaction loses all offensive odor when covered with a layer of charcoal, and the flesh of a dead animal buried beneath a thin layer of charcoal will gradually waste away and be consumed without exhaUng any unpleasant smell. E2p. 71. — Place a small quantity of powdered charcoal in a bottle containing hydrogen sulphide gas, and shake the bottle. The odor of the hydrogen sulphide will quickly disappear. In the same way, an aqueous solution of hydrogen sulphide (Exp. 48) can be de- odorized by filtering it through a layer of charcoal. In all these cases, the use of charcoal as a disinfectant depends not merely upon its mechanical ability to absorb offensive gases, but also and mainly upon the fact that the absorbed gases are chemically destroyed within the pores of the coal by the oxygen which is sucked into these spaces from the air. The purifying action depends upon oxidation, upon the burning up of the offensive gases. The charcoal is in no sense an antiseptic or preservative agent proper to prevent decay ; on the contrary, it actually hastens the destruction of putres- cible organic matters. Under ordinary circumstances, the pores of charcoal contain more or less oxygen which has been absorbed from the air, and any new gas which is dragged in is forced into intimate contact with this oxygen If the new gas is one on which oxygen can act, it is destroyed ; and as fresh portions of the gas. are absorbed by the charcoal, additional quantities of oxygen are also absorbed, so that the action may go on for a long time. A great merit of charcoal as a disinfectant is, that it constantly draws in to destruction the offensive matters around it ; pans of charcoal placed about a room, — the wards of a hospital, for example, — the air of which is offensive, soon remove the unpleasant smell. 185. Charcoal not only destroys odors, but it removes colors as well, and for this purpose it has long been employed in the purification of sugar and of many chemical and pharmaceu- tical preparations.- Almost any coloring matter can be re- moved from a solution by filtering the liquid through a layer of charcoal. , 1" 118 CHARCOAL DECOLORIZES. [§186 Fig. 38. Exp. 72. — Provide four small bottles of the capacity of 100 or 200 c. c, and. place in each of them a table-spoonful of bone-black (§ 186) ; into the first bot- tle pour a quantity of the blue compound of iodine I and starch obtained in III Exp. 39 ; into the second, a decoction of cochineal ; into the third, a dilute solution of soluble indigo blue ; into the fourth a solution of blue litmus, of logwood, or indeed ot almost any other vegetable coloring matter ; enough of the solution being taken in each instance to nearly fill the bottle. Cork the bottles and shake them violently, then pour the contents of each upon a filter (see Ap- pendix, § 15) , and observe that the filtrate is in each instance color- less, or nearly so. In case the first portions of the filtrate happen to come through colored, they may be poured back upon the filter and allowed to again pass through the coal. In the purification of brown sugar, the coloring matters are removed in a manner similar to the foregoing, the colored sirup being filtered through layers of bone-black. Besides coloring matters, charcoal can absorb many other substances : sulphate of quinine, for example, is removed from its solutions, to a very considerable extent, by charcoal, and the same remark applies, with perhaps still more force, to strych- nine. The bitter principle of the hop, " lupulin," may be entirely removed from ale by filtering the latter through bone-black. In all these cases where coloring matters, and the like, are removed from solutions, the action of the coal appears to depend in the main directly upon the physical property of adhesion; the subsequent oxidizing action being here far less clearly marked than in the instances previously studied (§ 184) where gases are acted upon. Much of the absorbed color or other matter will usually be found attached to the surfaces of the coal, undecomposed and unaltered. 186. As obtained from different sources, charcoal exhibits very different degrees of decolorizing^ povv^er ; but of the varie- § 188.] CARBONIC ANHYDRIDE. 119 ties commonly met with and to be procured in commerce, bone- black is the most efficient. Bone-black is prepared for the use of sugar-refiners, by subjecting bones to destructive distillation in large iron cylinders and carefully cooling the charcoal out of contact with the air. As dry bones contain about 66 per cent of mineral matter, the charcoal thus obtained is left in an exceedingly porous condition, distributed over and among the particles of the mineral matter. CV' 187. Compounds of Carbon and Oxygen. — There are two of these compounds, — Carbonic anhydride (COj) and carbon protoxide (co). 188. Carbonic anhydride, commonly called carbonic acid (COj), is always formed when carbon or any of its compounds is burned in an excess of air or of oxygen gas, or in contact with substances, gaseous, liquid or solid, which are rich in oxygen, and yield it readily to other bodies. Exp. 73. — Place a Uve coal (charcoal) upon a deflagrating spoon, and thrust it into a bottle full of air, or, better, oxygen gas : when the coal has ceased to glow, pour into the bottle some lime-water, — a solution of common slaked lime in water, — and shake the bottle. The liquid will become milky and turbid, and, when left at rest, will deposit a white powder (calcium carbonate). The presence of carbonic acid can readily be detected by means of lime-water, since this insolu- ble precipitate of calcium carbonate is formed when the two sub- stances are brought together. From the formulae of the class of bodies known as carbonates (sodium carbonate = Na^COj), we should infer the existence of a carbonic acid of the formula H^COj. Carbonic anhydride does dissolve in water, and the solution has a slightly acid reaction : it is, however, doubtful if a definite compound is formed. The term car- bonic acid has, however, been so long applied to the oxide of carbon, COj , and the tenn has such a foothold in onr language and literature, that it will be used in this chapter in its popiilar sense. Ezp 74. — As was just now said, carbonic acid may be produced also by heating carbon in contact with solid bodies which contain oxygen, such, for example, as the red oxide of mercury. Mix 11 grms. of red oxide of mercury with 0.33 grm. of charcoal ; place the 120 CARBONIC A CID. — CA UBOXA TES. [§ 189. mixture in an ignition-tube arranged as in Figure 35 ; heat the tube and collect over water the gas which is evolved. Test the product with lime-water, as in Exp. 73. The reaction between the charcoal and the mercury oxide may be written as follows : — 2 HgO + C = COj + 2 Hg. The metallic mercury set free condenses in droplets upon the cold upper portions of the ignition-tube. Here, again, as in Exps. 62 and 69, the metallic oxide is reduced by the charcoal. 189. Carbonic acid may readily be obtained from certain compounds called carbonates, several of which are abundant minerals. Common chalk, marble and limestone, for example, are composed of calcium carbonate; and carbonic acid can readily be obtained by strongly heating them, or by subjecting them to the action of strong acids. Exp. 75. — In a gas-bottle of 500 or 600 c. c. capacity, arranged precisely as for generating hydrogen (see Exp. 11, § 35), place 10 or 12 Fig. 39. grms. of chalk or marble in small lumps ; cover the chalk with water, and poiu' in through the thistle-tube con- centrated chlorhydric acid, by small portions, in such quantity as shall insure a continuous and equable evo- lution of gas. Collect sev- eral bottles of the gas over water, then replace the an- terior portion of the deliv- ery-tube with a straight tube and collect one or two bottles of the gas by displacement ; -carbonic acid gas is half as heavy again as air. The reaction between the calcium carbonate and the chlorhydric acid may be thus formulated : CaCOj -4- 2 HCl = CaClj + H,0 -f CO,. 190. At the ordinary atmospheric temperature and pressure, carbonic acid is a transparent, colorless gas, of a slightly acid smell and taste. It is incombustible, being already the product of .the complete combustion of carbon, and is, moreover, inca- § 192.] PROPERTIES OF CARBOLIC AVID. 121 pable of supporting the combustion of most other bodies : it is also incapable of supporting animal life. Exp. 76. — Thrust into a bottle of the gas, obtained in Exp. 75, a lighted candle, or, better, a large flame of alcohol burning upon a tuft of cotton ; in either case the flame will be instantly extinguished. 191. The specific gravity of carbonic acid is 22 ; being thus 1.53 times heavier tlian air, it can be poured from one vessel to another almost as readily as if it were water. Exp. 77. — • From a large bottle or other vessel full of the gas, pour a quantity of car- bonic acid upon the flame of a lamp or can- dle ; that is to say, hold the mouth of the open bottle of carbonic acid obliquely over the candle flame, so that the gas shall fall like water upon it . the flame will immedi- ately be extinguished. Carbonic acid can be obtained in the liquid state by subjecting the gas to pressure. It can also be obtained in a solid snow-like state by exposing the liquid to cold. 192. Carbonic acid gas is soluble in water to a considerable extent. One measure of water at the ordinary temperature and pressure, will dissolve one measure of carbonic acid gas, but its solubility increases if the pressure be increased. Exp. 78. — Into a long-necked flask or phial filled with carbonic acid, pour a quantity of water, close the bottle with the finger and shake it; immerse the mouth of the bottle in water, and remove the finger ; vvater will rush into the bottle to supply the place of the gas which has been dissolved. Again place the finger upim the mouth of the bottle, shake the bottle as before and subsequently open it beneath the surface of the water ; a fresh portion of water will flow into the bottle to supply the new vacuum ; in this way, by repeated agitation with water, all of the carbonic acid in the bottle can be absorbed. When subjected to increased pressure, carbonic acid gas dis- solves in water much more abundantly than at the ordinary pressure of the air. Water thus surcharged with carbonic acid has an agreeable, acid, pungent taste, and effervesces briskly 11 122 PRODUCTION OF CARBONIC ACID. [§ I93. when the compression is suddenly removed, as when the liquid is allowed to flow out into the air ; such carbonic acid water flows from the earth in many localities as at , Selters or Seltz in Ger- tnany (Seltzer water) and at Saratoga, N. Y. It is also prepared artificiallj', in large quantities, and sold as a beverage under the meaningless name of soda-water. The efiervescent qualities of fermented liquors, such as cider, champagne and beer, are, in like manner, dependent upon the presence of compressed carbonic acid gas. 193. Carbonic acid is produced, not only in the actual com- bustion of all substances which contain carbon, but also during the decay and putrefaction of all animal and vegetable sub- stances. During fermentation it is evolved in large quantities, and it is continually given off during the respiration of ani- mals. Ezp. 79. — Dissolve 10 grms. of honey or molasses in 100 c. c, of water ; fill a large test-tube with the mixture and add to it a few drops of bakers' or brewers' yeast ; close the open mouth of the test- tube with the thumb, and invert it in a small saucer or porcelain capsule filled with the diluted sirup. Place the saucer and tube, with their contents, in a warm place, having a temperature of about 20° or 30°, and leave them there during 24 hours. In a short time fer- mentation sets in, and the sugar of the sirup is gradually converted into alcohol and carbonic acid. C,H^O, = 2 C,H,0 + 2 CO,. Sugar. Alcohol. The carbonic acid thus formed rises in minute bubbles, causing a gentle effervescence in the liquid, and collects in the upper part of the tube, while the alcohol remains dissolved in the liquid. Bzp. 80. — Provide two test-glasses or small bottles; place in each 15 or 20 c. c, of lime-water ; through a glass tube, blow into the lime-water of one of the bottles air coming from the lungs. By means of bellows, to the nozzle of which a gas-dehvery tube has been attached, force through the lime-water of the second bottle a quantity of fresh air. The clear liquid of the first bottle will quickly become turbid through deposition of calcium carbonate, while the lime-water of the second bottle will remain clear for a long while. A 194. Carbonic acid is an exceedingly weak acid ; it faife to § 196.] CARBON PROTOXIDE. 123 neutralize (§61) completely the causticity of li}'^drates, such as those of the alkaline luetals ; the normal carbonate of sodium, for example, is decidedly alkaline in its reaction and properties. Al- most all the carbonates are readily decomposed by acids, — even by very weak acids, — with an effervescence caused by the escape of carbonic acid : many, among them calcium carbonate, are decomposed by heat. Carbonic acid is bibasic (§ 134) like sulphuric acid ; thus there exist a sodium carbonate, Na^COj, and a hydrogen sodium carbonate, HNaCOj ("bicarbonate of soda"). 195. Carbon Protoxide (CO), called also carbonic oxide, may be prepared by passing carbonic acid over hot charcoal (C -l" CO2 = 2 CO) or by beating the oxides of almost any of the metals with an excess of charcoal. The gas is, however, contaminated with some carbonic acid. It may be prepared pure as follows : — Exp. 81. — In a flask of about 250 c. c. capacity, provided with a delivery-tube and with a safety-tube (Fig. 41), heat gently a mixture of 5 gmis. of finely-powdered potassium ferrocyanide (yellow prus- siate of potash) and 40 or 50 grms. of strong sulphuric acid. Collect the gas over water and test it as to its inflammability. Thrust also a lighted splinter into the gas and observe that it will be extinguished. The reactions which occur between the chemicals employed will be explained in a subsequent section (see § 387). 196. Carbon protoxide is a transparent, colorless gas, hav- ing little, if any, odor ; it may be liquefied, but with great diffi- culty. The gas is somewhat lighter than air, its specific gravity being 14, while that of air is 14.5. It is but little soluble in water, and may be collected over water without much loss. It extinguishes combustion just as hydrogen does, and destroys animal life. Unlike hydrogen and nitrogen, however, it is a true poison. It destroys life, not negatively by mere suffoca- tion or exclusion of oxygen, but by direct noxious action. It is the presence of this gas which occasions the peculiar sensation of oppression and headache which is experienced in rooms into which the products of combustion have escaped from fires of charcoal or anthracite. Carbon protoxide is very much more 124 CARLOS PROTOXIDE. — COMBUSTION. [§ 197. poisonous than carbonic acid. Much of the ill repute which attaches to carbonic acid really belongs to carbon protoxide, for since both these gases are produced by burning charcoal, many persons are liable to confound them ; but carbonic acid is, com- paratively speaking, almost innocuous. 197. Carbon protoxide plays a very important part in many metallurgical operations on account of the power which it pos- sesses at high temperatures of taking away oxygen from many compounds containing that element. Much of the reducing action which is, commonly speaking, attributed directly to car- bon, is really effected in practice through the mediation of the protoxide. * 193. Carbon protoxide burns readily in the air, the sole Fig. 41. product of the burning be- ing carbonic acid. The forms an explosive mixture with air or oxy- gen. Exp. 82. — To the ap- paratus employed in Exp. 81 , provided air has not been allowed to enter by the cooling down of the mixture, attach a piece of glass tubing drawn out at the end (bat not to a very fine point) and bent in such a naanner that a stream of gas may be delivered upwards from the point. Li"ht the gaa as it flows out of the tube, and hold over the pale-blue flame a clean, dry bottle. No moisture is deposited. That carbonic acid has been produced may be proved by pouring a little lime-water into the bottle and shaking it about in the gas therein contained. 199. Combustion. — Now that we have become acquainted with carbon, hydrogen and oxygen, and with some of the more important compounds formed by the union of these elements, the subject of combustion can be more fully discussed than has been possible hitherto. Tlie materials employed as com- §201.] COMBUSTIOX. — CHARACTER OF FLAMES. 125 bustibles are, as a general rule, compounds of carbon and hy- drogen ; there are some exceptions to this rule, as when the metal magnesium is burned for light, or the heating of a sul- phuretted ore is eifected by the combustion of its own sulphur. 200. In almost aU cases artificial light results from the in- . candescence of particles of solid matter, or of dense vapors. When the heat, which is an invariable accompaniment of chemi- cal combination, can play directly upon such solid or semi-solid particles with force enough to ignite them, an exhibition of light will accompany the chemical change. The hydrogen flame af- fords no light, or as good as none, because in it nothing but a highly attenuated gas is heated. But when a solid body, such as the platinum wire or the piece of lime of § 41, is placed in this non- luminous hydrogen flame, intense light is radiated from the heated solid. Ezp. 83. — Sprinkle fine iron filings into the flame of an alcohol lamp, or into the non-luminous flame of the gas-lamp, ami observe the light given off by the particles of metal as they become incandescent while passing through the flame. Or rub together two pieces of char- coal above a non-luminous flame, ui such manner that charcoal pow- der shaU fall into the flame. 201. In ordinary luminous flames, such as those of candles, lamps and illuminating gas, the ignited substance is carbon, or rather a vapor or fog of certain carbon compounds contain- ing more or less hydrogen. Ordinary illuminating gas may be decomposed by passing it through a tube heated red-hot ; the carbon will separate, in a finely- divided state, while hydrogen will escape from the tube : or, by put- ting a cold body into a luminous gas-flame, the carbon is deposited as soot (see Exp. 68, § 181). This breaking up of the compounds of carbon and hydrogen under the influence of heat takes place when the gas is burned in the air, and if the supply of air furnished be insuflicient to convert all the carbon and hydrogen to carbonic acid and water, the particles of carbon which escape nnconsumed will cause the flame to be smoky. If the supply of air be excessive, the combustion will be complete, and no light will be afforded by the flame. 126 GAS-FLAMES. — LAMPS AND CAKDLES. [§ 202. Fig. 4,%. If we unscrew the tube of a common Bunsen lamp (Appendix, § 5) and light the gas as it issues from the slit (or holes) in the lower part of the burner, we shall have a luminous and perhaps even smoky flame. When, however, the tube is in its place, the gas be- comes mixed with air which enters by the holes at the base of the lamp, and when the mixture is lighted, the gas isf in intimate contact with air enough to burn it at once, and completely. A luminous flame may also be produced by simply closing the holes at the base of the lamp, with the fingers or by means of a metallic tube, as represented in Fig. 42. If across the top of the chimney of a lighted Argand gas-burner, which is burning with a low flame, we slip a strip of sheet-iron, and •thus obstruct the flow of air, the flame will increase in size, becoming more and more luminous, and finally will actually smoke. The amount Fig- 43. of gas supplied has remained the same ; the difference in the amount of light is owing to the decrease of the supply of air. The murky flame, such as was obtained just before actual smoking began, in which the largest number of particles of carbon or heavy carbonaceous va^ por are heated, •although none of them are heated very hot, yields the largest amount of light that can be obtained from a given burner ' with a given sample of gas. Such a flame, how- ever, does not furnish the light most agreeable to the eyes. 202. The flames of ordinary lamps and candles are, strictly speaking, gas-fiames. Exp. 84. — Construct a lamp as follows : To a wide-mouthed bottle of the capacity of about 50 c. c. fit a cork loosely ; bore a hole in the cofk and place therein a short piece of glass-tubing. No. 3, open at both ends ; through this glass-tube draw a piece of lamp- wicking, or any loose twine, long enough to reach to the bottom of the bottle. It is essential, either that the cork should fit the bottle loosely, or that there should be a hole in the cork, in order that the § 202.] STRUCTURE OF FLAMES. 127 pressure of the external air may act upon the surface of the alcohol, — to this end a very small glass-tube may be inserted in the cork at some distance from the tube which carries the wicii. Fill the bottle nearly full of alcohol, and, after a few minutes, touch a lighted match to the top of the wick. The fluid alcohol is drawn up out of the bottle by force of capillary attraction exercised by the pores of the vegetable fibre of which the wick is composed. When heat is applied to the alcohol at the top of the wick, some of it is converted into vapor ; this vapor then takes fire, and, in burning, furnishes heat for the vaporization pi' new portions of the alcohol. From the top of the wick there is constantly arising a column of gas or vapor, and upon the exterior of this conical column chemical combination is all the while going on between its constituents and the oxygen of the air. The dark central portion of the alcohol flame is nothing but gas or vapor. Exp. 85. — Thrust the phosphorus end of an ordinary friction- match directly into the middle of the flame of the alcohol-lamp of Exp. 84. The combustible matter upon the end of the match will not take fire in the atmosphere of carbonaceous gases, of which the centre of the flame consists ; the wood of the match-stick, of course, takes fire at the poiat where it is in contact with the outer edge of the flame. The portion of the match in the centre of the flame becomes so strongly heated during its sojourn within the circle of fire, that it is ready to inflame as soon as it comes in contact with the air ; it is therefore somewhat difficult to withdraw the match from the flame without its talcing fire. Ezp. 86. — Hold a thin wire (best of platinum, though iron will answer "well enough) or a splinter of wood across the flame of the alcohol-lamp, as shown in Fig. 44. The wire will ^is- **• be heated to redness, and the wood will bum, only at the outer edges of the flame where the gas and air meet ; in the interior of the flame, the wire will remain dark and the wood unbumed, for there is no combus- tion there, and comparatively little heat. If the wire be successively placed at diff'ereiit heights in the flame the size and shape of the internal cone of gas can easily be made out ; it wiU appear, moreover, that the hottest part of the flame is just above the top of the interior cone of gas. As a rule, when glass- tubing, or the like, is to be heated in a flame, it should never be placed below this point of the greatest heat. 128 STRUCTURE OF FLAMES. [§ 203. When a candle is lighted for the first time, the cotton of which the wick is composed takes fire, and is at once consumed for the most part, but, in burning, the cotton gives off considerable heat, and some of the wax or tallow of which the candle is composed is thereby melted and converted into oil. The liquid oil ascends the wick by virtue of capillary attraction, and is converted into vapor or gas by the heat of the cotton still burning at thd stump of the wick ; this gas then bums precisely like the alcohol vapor in Exp. 84, and by the heat thus disengaged new portions of wax or tallow are continu- ally melted. There is always a little cup of oil at the top of the rod of wax or tallow of which the candle consists, and the apparatus is as truly an oil-lamp as if the oil were held in a vessel of glass or metal. If the flame of the candle, when the snuff has become long, be blown out, a current of vapor continues to ascend from the hot wick and this vapor may be ignited some distance above the wick. After the flame has been extinguished, the wick retains heat enough for a few moments to distil off a quantity of gas, although there is not heat enough generated to inflame this gas. To the gas or vapor thus evolved is to be referred the disagreeable odor which is observed when a candle is blown out. Ezp. 87. — Press down a piece of "white letter-paper, for an instant, upon the flame of a candle until it almost touches the wick, then quickly remove the paper before it takes fire, and observe that Fig. 45. its vipper surface is charred in the manner shown in Fig. 45. There will be obtained, in fact, burned into the paper, a diagram of the part of the flame where combustion is taking place. It is thus seen to be ring- shaped in section, and to enclose a space where no combustion is going on. 203. All flames, which are rendered luminous by incandes- cent carbonaceous particles, have the same general structure. This structure is best studied in the flame of a candle. In the candle-flame four portions or divisions of the flame can be distinguished (Fig. 46). First, there is the small blue cup-shaped portion of the flame (a h) at the base of the wick ; here a part of the combustible gases coming from the wick are burned completely, as the oxygen of the air has free access to this part of the flame. The heat thus produced converts into vapor the oil which the wick draws up § 204.] PniA-CIPLE OF TflM BLOWPIPE. 129 from the candle. This carbonaceous vapor rises and Ibrnis the second part of the flame, the non-luminous cone (c). Here no combustion can take place : the oxygen of the air, it is true, tends to pass, by dif- fusion, into the interior of the flame ; but, as fast as it Fig. 46. approaches, it meets carbon and hydrogen in the outer portion of the flame, and enters into combination with these elements : the nitrogen of the air, however, dif- fuses freely into the interior of the flame, and is found, mixed with the combustible gases of the cg,ndle and with some carbonic acid and steam, in the space (c). The third portion of the flame is the luminous zone (d). Here the combustion is incomplete ; the gaseous com- f pounds of carbon and hydrogen are broken up by heat into their constituent elements. The carbonaceous par- ticles are intensely ignited, and bum to carbon pro- toxide by taking oxygen from the air, and also from the carbonic acid and steam which diffuse inwards from the outermost portion of the flame. The fourth portion of the flame is the thin, scarcely perceptible, non-luminous mantle (/e/) which surrounds the entire flame. Here the carbon protoxide and liydrogen burn to carbonic acid and steam, and, as has already been seen, a part of these gases diff'use inwards and are decomposed, furnishing oxygen for the partial combustion of the carbon in the luminous portion of the flame. 204. The principle of the oxy-hydrogen blowpipe, as well as of the ordinary blast lamps in which air and illuminating gas are used instead of oxygen and hydrogen, is the throwing of oxygen into the combustible gas so that the combustion is in- tense and concentrated. On the same principle depends the use of the mouth-blowpipe. ' (For a description of the mouth-blowpipe, see Appendix, § 7.) Exp. 88. — To use the mouth-blowpipe, place the open end of the tube between the lips, or, if the pipe is provided with a mouth- piece, pre.ss the trumpet-shaped mouth-piece against the lips ; fill the mouth with air till the cheeks are widely distended, and insert the tip in the flame of a candle or of a lamp with a flat wick ; close the com- munication between the lungs and the hiouth, and force a current, of air through' the tube by squeezing the air in the mouth with the muscles of tlie cheeks, breathing, in the mean time, regularly and quietly 130 OXIDIZING AND REDVCIXG FLAME. [§ 205^. through the nostrils. The knack of blowing a steady stream for sev- eral minutes at a time is readily acquired by a little practice. It is possible with the blowpipe to produce either an ozidizing or a reducing flame. When the jet of the blowpipe is inserted into the lamp or gas-fianie, as shown in Fig. 47, and a strong blast is Fis. 47. forced through the tube, a blue cone of flame {a b) is ^ produced, beyond and out- ^ side of which stretches a more or less colored outer cone {a c). The point of greatest heat in this flame is at the point of the inner blue cone ; oxidation takes place most rapidly at, or just beyond the point (c) of the flame, pro- vided that the temperature at this point is high enough for the special substance to be heated. To obtain a good reducing flame, it is necessary to place the tip of the blowpipe, not within, but just outside of the flame, and to blow somewhat gently over rather than through the middle of the flame Fig. 48. (Fig. 48). In this manner, .7^~^ . the flame is less altered in '"^ its general character than in the former case, the chief p£irt consisting of a large, luminous cone, containing a quantity of free carbon in a state of intense ignition and just in the condition for tak- ing up oxygen. This flame is, therefore, reducing in its effect. The substance which is Jo be reduced by exposure to this flame should be completely covered up by the luminous cone, so that contact with the air may be entirely avoided. 205. Instead of forcing the air (or oxygen) into the burning fuel, the supply of air may be furnished by means of chimneys. Chimneys, whether of lamps or furnaces, are simply devices for bringing an abundance of air, and therefore of oxygen, into the fire ; that in so doing they, at the same time, carry off the waste prdducts of combustion is an incidental advantage. § 205.] EXPERIMENTS ON COMBUSTION. 131 Fig. 49. Exp. 89. — Light a piece of a candle 8 or 10 c. m. long, and stand it upon a smooth table ; over the candle place a rather tall, narrow lamp-chimney of glass, the bottom of the chimney being made to rest upon the table, and observe that the candle- flame will soon be extinguished. No fresh air can enter the chinmey from below to maintain the chemical action, and the small quantity of air which can creep down the chimney from above is alto- gether insufficient to meet the require- ments of the case. Exp. 90. — Eelight the candle of Exp. 89, and again place over it the lamp-chimney ; but instead of allow- ing the chimney to rest closely upon the surface of the table, prop it up on two narrow strips of wood, so the air can have free en- trance into the chimney from below. The candle will now continue to bum freely, for the heavy, cold air outside will continually press into the lower part of the chimney, and push out the warm, light products of combustion, and the candle-flame will all the while be supplied with fresh air. The direction of the current of air may be shown by placing a piece of burning " touch-paper " at the foot of the chinmey. Touch- paper is made by soaking ordinary brown paper in a strong solution of potassium nitrate, and then drying it. On being lighted, the paper bums without flame, while emitting clouds of smoke. Exp. 91. — Eepeat Exp. 90, and when the candle is burning quietly, cover the top of the chimney tightly with a piece of tin or sheet-iron, or with a strip of window-glass ; the candle will soon cease to burn precisely as if the chimney were closed at the bottom, for, the escape of the hot products of combustion being prevented, no air can pass into the chimney to reach the candle-flame. It is by inducing the current of fresh air (Exp. 90), or draught, as it is ordinarily termed, that chimneys are specially useful. Through the chimney the hot air from the lamp flows straight forward and rapidly, and, of course, a correspondingly direct and rapid current of fresh air presses in to supply its place. Owing to this power of rapidly supplying air, chimneys are employed upon lamps burning petroleum and other highly carbonized oils which are liable to smoke. Exp. 92. — It is not absolutely necessary that the fresh air 132 KiyDLiya-TEMPEllATCRE. [§ 206. Fig. 50. should flow into a chimney from below. Divide the upper part of the chimney of Exp. 89 into two channels, by hanging in it a strip of sheet-iron or tin, as a partition at the centre of the chimney (see Pig. 00). Place the chimney thus divided over a burning candle, and observe that the candle will continue to bum as if in a strong draught of air, although no air can enter the chimney from below. Hold a piece of burning touch-paper at the top of the divided chimney ; the smoke will be drawn down into the chinmey on one side • of the partition, and thrown out again upon the other, as indicated by the arrows in Fig. 50. It appears from this, as well as from the tremulous motion of the flame, that a current of cold air presses down upon one side of the division wall and sup- plies the required oxygen. 206. Kindling-Temperature. — In order that any combusti- ble substance shall burn, or, in other words, in order that brisk chemical action shall occur between the combustible and the oxygen of the air, it must first be heated to a certain tempera- ture, and then kept at that heat. The temperature at which any substance takes fire is known as the kindling-temperature of that substance. Exp. 93. — Place a small bit of phosphorus and another of sul- phur, not in contact with the first, upon a fragment of porcelain 6 or 8 c. m. across, and heat them slowly over the gas-lamp ; the phos- phorus will soon take fire at a temperature of 68°-70°, but the sulphur will not inflame until the temperature of the porcelain support has . risen to about 250°, as can be ascertained by the thermometer. As was just now said, the degree of heat necessary to start any fire must be kept up continually, or the fire will go out. When- ever burning bodies are cooled below the kindling-temperature, they are extinguished, — the chemical action which occasioned the appearance of heat and light ceases. If we pile up upon an iron grate, thick in metal, and supported in such manner that air may enter beneath it, several pieces of red-hot § 207.] KINDLING-TEMPERATURE. I33 charcoal, the charcoal will go on burning until nearly all of it has been consumed, for the heat generated by the combustion of the por- tions first bui-ned keeps up the temperature necessary to kindle the subsequent portions. If, however, we scatter about upon a cold grate' several small pieces of red-hot charcoal, taking care that no two pieces of the coal shall come in contact, or be placed so as to heat one another, each of the pieces of charcoal will soon cease to burn ; for the metallic grate is so good a conductor of heat that it removes heat from the isolated pieces of charcoal more rapidly than these can pro- duce it : the temperature of the charcoal is, consequently, soon re- duced to below the kindling-point. 207. Precisely as coals can be extinguished by placing them upon cold metal, so flames may be put out. Exp. 94. — Upon a ring of the iron-stand place a sheet of clean wire-gauze about 10 c. m. square ; lower the ring so that the gauze shall be pressed down upon the flame of a lamp or candle almost to the wick, as shown in Fig. 51. No flame will be seen above the gauze, but instead of flame a cloud of smoke. ^'s- Si- The gauze is a mere open sieve ; there is nothing about it which can prevent the gas, which was just now burning with flame above the wick of the candle, from passing through. Indeed, it may be seen from the smoke that the particles of carbon which, in the original undisturbed flame, were becoming incandescent, and so affording light, do now actually come through the gauze. The explanation of the phenomenon is simply that the metallic sieve conducts away so much heat that the temperature of the candle- flame is reduced to below the kindling-point. That this is really so, is proved by the fact, that after the gauze has become sufficiently heated by long-continued contact with the flame below, — after it has attained the kindling-point of the candle-gas, — it will no longer extinguish the flame. In like manner, a candle-flame may be cooled to such an extent that it will go out by placing over it a small coil of cold copper wire, while, if the wire be previously heated, the flame will continue to biuii. If the smoke and unbumed gas which has passed through the cold wire-gauze be touched with a lighted match, and so brought to the kindling-temperature, it ^vill burst into flame. ]2 134 SAFETY-LAMPS. [^ 207. The power of wire-gauze to prevent the passage of flame has been usefully applied in several ways, notably for the prevention of explo- sions in those coal-mines which are liable to accumulations of marsh- gas (§ 215). For this purpose safety-lamps are constructed by enclos- ing an ordinary oil-lamp completely in wire-gauze, so that the flame within the gauze can not kindle any combustible or explosive gas into which it may be carried. In case such a lamp be carried into a , place fdled with explosive gas, the latter will, of course, pass into the lamp through the meshes of the gauze, and burn within the cage. This combustion gives warning of the presence of the dangerous gas, and indicates to the workman that he should withdraw from the locality : the gas can then be expelled by appropriate methods of ventilation. Exp. 95. — Beneath a sheet of wire-gauze resting on a ring of the lamp-stand, place an unlighted Buuseu's burner, at such a distance that the gauze shall be 3 or 4 c. m. above the top of the lamp ; turn on the gas and light it above the wire- gauze : it will continue to burn on top of the gauze for an indefinite period, for the gauze will, in this case, always be kept cool by the cold gas which is continu- ally passing through it. Carefully and gradually lift the ring which carries the gauze, and determine how far it is possible to lift the gauze above the gas-jet with- out extinguishing the flame. An efiect somewhat similar to that produced by wire-ganze is often seen in ordinary fires. When a mass of red-hot anthracite, charcoal or coke is burning freely upon a grate in the open air, there is always a blue flame of carbon protoxide burning above the coal. This gas results from the reduction of carbonic acid by means of hot carbon. Air enters at the bottom of the grate and combines with the hot coal which it finds there to fonu carbonic acid, COj. This carbonic acid, as it rises through the hot coal in the middle of the fire, is deprived by the heated carbon of half its oxygen : COj + C = 2 CO. The carbon protoxide being combustible, will at once take fire on coming in contact with the air, provided the temperature at the summit of the fire be equal to the kindling-temperature of this gas. But if the temperature of the fire is in any way reduced below this point, as, for example, by throwing on too large a quantity of cold fuel, which is, of course, equivalent to covering the fire with a sheet of wire- gauze, then the carbon protoxide will be extinguished, and, escaping into the chimney, will produce no useful efl'ect. § 209.] CARBON BISULPHIDE. I35 208. Carbon and Sulphur. — Carbon bisulphide (csj is interesting from its correspondence to carbonic anhydride, COj, and forms another instance of the analogy between the com- pounds of oxygen and sulphur. Carbon bisulphide is prepared by passing the vapor of sulphur over red-hot charcoal. It is a colorless, strongly-refracting liquid which boils at about 54° and evaporates rapklly at the ordinary temperature of the air. It possesses an ethereal odor when purified, but the common bisul- phide has a peculiar and very disagreeable smell. It is very inflammable and burns with a blue flame, the product of the combustion being carbonic and sulphurous anhydrides. It is used as a solvent of phosphorus and sulphur, and is employed in the cold process of vulcanizing caoutchouc. Exp. 96. — Into a small beaker or watch-glass put two teaspoon- iiils of carbon bisulphide. Set the glass upon a wet piece of wood, and by means of a glass tube direct a current of air from the lungs, or from a pair of bellows, across the surface of the liquid. The volatile carbon ' bisulphide rapidly evaporates, and in so doing pro- duces such an amount of cold, that the glass will be frozen to the wood. This experiment should be performed where there is a good draught of air, and out of the neighborhood of any lighted lamp. CHAPTER XV. CAEBON (continued). 209. Carbon unites -with hydrogen, oxygen or nitrogen, or with two of these elements, or with aU three of them, in the most varied proportions. A great number of different com- pounds are thus formed, some of them being extremely com- plex. Since many of these more complex compounds of carbon occur ready formed in animals and plants, or are produced by the transformation of substances derived from these sources, they are usually classed together and studied under the head of "Organic Chemistry." 136 CYASOGEN.— CYAKHYDRIC ACID. [§210. •There is no sufficient reason, chemically speaking, for making this division : chemical compounds, whether derived from the animal, vegetable or mineral kingdotns, are governed by the same laws : it is, moreover, impossible to draw any sharp line of demarcation between organic and inorganic chemistry ; still, on account of the vast number of the carbon compounds, the mere names of which would fill a volume, this arrangement has the merit of convenience. In this and the two following chapters a few of the more important of these so- called organic bodies will be considered. Other elements besides those already mentioned, such as sulphur and phosphorus, enter into the conipositi(ni of these bodies. Many of the complex substances which exist in the bodies of animals, such as albumin and the matter which forms the substance of the hair, contain sulphur as an essential ingredient. Moreover, the numerous organic acids form salts of the various metals, and many of these salts exist ready formed in nature. ) 210. Carboa and Nitrogen.— Prominent among the componuds of carbon and nitrogen is cyanogen (CN), which is an important compound radi;;al, and which also exists in the free state. 211. Cyanogen (CN or Cy). — Carbon and nitrogen do not unite directly, but when a current of nitrogen is passed over red-hot charcoal which has been previously soaked in a solution of potassium carbonate, there is formed potassium cyanide, a compound containing the radical cyanogen. K.CO, -H 4 C -I- 2 N = 2 KCN + 3 CO. Free Cyanogen is best prepared by heating mercuric cyanide ; thu3, — HgCy-j = Hg -I- 2 Cy. It is a colorless, poisonous gas of suffocating odor and ready inflammability. Its molecule contains two atoms of the radical and is written (CN)2. /y 212. Cyanhydric Acid (HCN). — Cyanhydric acid, which may be prepared by passing hydrogen sulphide over mercury cyan- ide (Hg (CN)j + H,S = HgS -|- 2 HCN), is a combustible and volatile liquid : it possesses the odor of bitter almonds and is intensely poisonous. In aqueous solution it is known as prussic acid. Several of the cyanides are important bodies, and will be mentioned under the head of the different metallic elements. § 214.J HYDROCARBONS.— M£TUrL HYDRIDE. 137 They correspond in composition to the chlorides, the univalent radical (§ 154) CN occupying the place of CI ; thus potassium cyanide is KCN ; zinc cyanide is Zn(CN)ij. Exp. 97. — To a very minute quantity of solid potassium cyanide, add a few drops of strong sulphuric acid. The effervescence which taJses place is due to the escape of cyanhydric acid, which may he recognized by its peculiar odor. The reaction is similar to that which takes place when common salt is treated with sulphiiric acid in the production of chloi'hydric acid. It may be expressed as follows : 2 KCN + H,SO, = K^SO, + 2 HCN. The cyanates correspond to cyanic acid (HCyO). Thus, potas- sium cyanate is KCj O. 213. Compounds of Carbon and Hydrogen or Hydrocarbons are very numerous. We first consider one of the most famUiar of them, marsh-gas. 214. Methyl Hydride or Marsh-Gas (CH,). — In hot sum- mer weather bubbles of gas are often seen rising to the sur- face of stagnant pools : if a pole be thrust into the mud at the bottom of the pool, a considerable amount of the gas wiU rise and may be collected by holding an inverted bottle full of water over the ascending bubbles. The gas thus collected contains a certain amotmt of carbonic acid (which may be removed by putting some milk of lime into the bottle, and shaking it for a short time), together with a little nitrogen : the greater part, however, consists of a colorless gaseous com- pound of carbon and hydrogen. This gas is a product of the putrefaction of vegetable matter under water, where the sup- ply of air is insufficient to oxidize the whole of the organic matter to carbonic acid and water ; hence the name marsh- gas. The formula of marsh-gas is CH,, and it may be regarded as a compound of hydrogen (H) with a group of atoms (CH^) called methyl. This group of atoms (CHj) hke the group (NH,) which has been designated as ammonium (§ 67), and like cyanogen (§ 211), takes part in chemical transformations, as if it were a simple elementary atom. The chemical name of marsh-gas is methyl hydride, or methane. 12* 138 METHYL UVDRIDIS OR MARSH-GAS. [§ 215. 215. Methyl hydride forms a very considerable portion of ordinary illuminating gas made by distilling coal; from some varieties of bituminous coal, it is disengaged at the ordinary temperature, and forms the " fire-damp " of coal-mines ; like hydrogen, it forms an explosive mixture -with air, and the ex- plosion of this mixture in badly-ventilated mines is often the cause of frightful loss of life. The gas may be prepared arti- ficially as follows : — "Exp. 98. — Mix together two grms. of crystallized sodium acetate, 4 grms. of caustic soda and 8 grms. of slaked lime. Heat the mix- ture gently upon an iron plate, until all the water of crystallization of the acetate has been expelled, and the mass has become dry and friable. Charge an ignition-tube 20 c. m. long with the dry powder, Fig. 53. heat it above the gas-lamp, and collect the gas at the water-pan. Mnrsh-gas is evolved from the mix- ture, at a temperature below red- ness, and a residvie of sodium car- bonate is left in the ignition-tube. The purpose of the lime is to ren- der the mass porous and infusible, or nearly infusible, so that the tube may be heated equably. The re- action may be represented as follows : — NaCjHjOj -f NaHO = CH^ -f Na^COs. Dry sodium Sodium Marsh- Sodium "" acetate. hydrate. gas. carhonate. 216. Marsh-gas is transparent, colorless and little more than half as heavy as air. Next to hydrogen it is the lightest known substance, its specific gravity being only 8. It takes fire readily when touched with a lighted match, and burns with a bluish- yeUow flame. 217. That marsh-gas really contains hydrogen and carbon may be readily proved by bringing into play, under appropriate conditions, the strong affinity of chlorine for hydrogen. Exp. 99. — Fill a tall bottle of at least one litre capacity with warm water, invert it over the water-pan, and pass marsh-gas into it, until a little more than one-third of the water is displaced ; cover §219.] CHLOROFORM. -ILLUMINATING GAS. 139 the bottle with a thick towel, to exclude the light, and then fill the rest of the bottle with chlorine. Cork the bottle tightly, and shake it vigorously, in order to niix the gases together, keeping the bottle always covered with the towel. Finally, open the bottle and apply a light to the mixture. Ignition takes place, chlorhydric acid is pro- duced, while the sides and mouth of the bottle become coated with solid carbon in the form of lamp-black. The presence of the acid may be proved by the smell, by its reaction with moistened blue litmus-paper, and by the white fumes which are generated when a rod moistened with ammonia-water is brought in contact with the escaping acid gas. 218. Chloroform (CHCl,). — When chlorine is allowed to act slowly on marsh-gas, there is formed, besides carbon quadrichloride (CCIJ, a compound having the formula CHCI3 and called chloro- form. Chlororomi (CHCI3) may be regarded as marsh-gas, in which three atoms of hydrogen have been replaced by three atoms of chlorine. It is manufactured in practice by distilling dilute alcohol with " chloride of lime." Water and chloroform come off together, but do not mix in the receiver : the chloroform, being the heavier, sinks to the bottom, and may be withdrawn and purified. Chloro- form is a colorless, volatile liquid, the vapor of which when inhaled causes temporary insensibility to pain, and on this account it is used in surgical operations. 219. Illuminating Gas. — The principle involved in the manufacture of Ulumiijating gas has already been illustrated in Exps, 65 and 66. Illuminating gas is ordinarily prepared by distilling bituminous coal ; other substances made up wholly or in part of compounds of hydrogen and carbon, such as wood, oU, resin, petroleum and even bones, are sometimes used. Fig, 54 shows in a general way the processes involved in the manu- facture and purification of coal-gas. The coal is introduced into the retorts, C, which are cylindrical 01 semi-cylindrical tubes of clay or iron, arranged in sets of three or five, or even more, and heated by a coke fire burning on the grate- bars, A. All the products of the distillation, except the coke which remains in the retort, are volatile at the high temperature employed, and pass up the vertical pipe, T. The relative proportions of these products, and to a certain extent their character, depend on the quality of coal employed, and on the temperature at which the dis- 140 MANUFACTURE OF COAL-GAS. [§ 219. te- 10 >-»>!!■/ -'- 1-^ \ it-- 3 I I 1 W- L- !- ^ < % O, an atom of hydrogen being replaced by a hypothetical oxygenated radical, C^HjO, called acetyl. This radical has not been isolated : its chloride, however, is known. If • this hypothetical radical acetyl, CjHjO, be compared with ethyl, C^Hj , it will appear that two atoms of hydrogen in the latter are rep- resented by one atom of oxygen in the former. By the similar device from may be derived the hypothetical radical of Methyl CH, Formyl CHO Formic acid CHjO, Propyl C,Hj Propionyl C3H5O Propionic acid C^HjO, Butyl C,H, Butyryl C,HjO Butyric acid C^HjO, Amyl C5H11 Valeryl C5H5O Valeric acid C^Jii, Etc. Etc. Etc. \ Acetic acid is thus one member of a series of acids ; they are called the fatty acids, and several members of the series are of very great industrial importance. 238. Acetic acid is one of the products of the distillation § 239.] ACETIC ACID —FORMIC ACID. 153 of wood (§ 282), and, thus obtained, it is known in the, crude state as pyroligneous acid. The pure acid is obtained by acting on some acetate, as sodium acetate, with sulphuric acid, and then distilling the mixture. At the ordinary temperature, acetic acid is a volatile liquid possessing a pungent odor, but at 17° it becomes a transparent solid ; hence the name glacial acetic acid applied to the strongest acid. »,— Exp. 107.— To the acid liquid of Exp. 106, or to 40 or 50 c. c. ' of common vinegar, add powdered chalk (calcium carbonate) as long aa the addition causes effervescence. Calcium acetate is formed and remains dissolved in the liquid. Filter the solution, and evaporate the filtrate to diyiiess at a gentle heat. The solid residue is an im- pure calcium acetate. Place a portion of this calcium acetate in a small test-tube, and heat gently with a few drops of strong sulphuric acid. Acetic acid will be set free, and may be recognized by its pecu- liar odor. If ordinary vinegar be used in this experiment, it will be better to decolorize tbe solution of calcium acetate by mixing it with powdered bone black before filtering (see Exp. 72, § 185). TSThe acetates are important bodies, and many of them are used in the arts and in medicine. Aluminum acetate is used in dyeing (§ 451) ; lead acetate is familiar under the name of sugar of lead, ; copper acetate is known as vexfyris ; ethyl acetate is acetic effier. 239. Formic acid (CHjOj), another member of the fatty acid series, is secreted by ants, and was first obtained by dis- tilling the bodies of these insects : it bears the same relation to methyl alcohol (CH,0) that acetic acid does to ordinary (ethyl) alcohol, and may be prepared by the oxidation .of methyl alco- hol. Formic acid is interesting because one of its salts, potas- sium formate, may be readily prepared from what are usually classed as inorganic substances. y y If moist caustic potash be exposed to carbon protoxide at a tem- 'perature of 100°, the gas is slowly absorbed, and potassium for- mate is produced : from potassium formate thus made the acid itself may be indirectly obtained. Hi° + CO = (^^^^JO Potassium hydrate. Carbon protoxide. Potassium formate. L64 NATURAL FATS AND OILS. [§ 240. Formic acid is one of a vast numtier of compounds whifih formerly were supposed to be produced only through the agency of Hving organisms, but which now can be made in the labora- tory from inorganic substances. This synthetical construction of so-caUed organic substances has contributed to obscure the distinction formerly drawn between organic and inorganic chem- istry./}' 240. One of the salts of formic acid will serve as an excellent illustration of the value of rational funnulce (§ 152). The formula of methyl formate (C^H^Oj) is the same as that of acetic acid, and the empirical formulse afford no means of distiaguishing be- tween these two substances ; if, however, methyl formate be written VcH \ \ ^ ^^^ acetic acid, as before, ^ °tt ( ® ^'^^^^ formulEB represent to the mind two distinct bodies. As the properties of the two substances are very different, we naturally seek to account for such different manifestations of the same elements in the same pro- portions by imagining some difference in the arrangement of the atoms within the molecule ; and, although we cannot know what this arrangement is, we can recall by the rational formiilse some of the reactions which occur in the formation or the decomposition of the substances in question. Bodies which like acetic acid and methyl formate have the same ultimate composition are called isomeric. Other acids of the fatty acid series will be brought to our notice by the study of a very important natural group of organic compounds, that of the fats and oils. 241. Natural Fats and Oils, — The various fats and non- volatile oils obtained from both the animal and the vegetable kingdom are in the main mixtures of three well-defined bodies, two of which, stearin and palmitin, are solid at the ordinary temperature, while the third, olein, is liquid. Ezp. 108. — Expose a test-liibe full of olive-oil to cold by sur- rounding it with a mixture of salt and pounded ice. A portion of the oil solidifies, while another portion remains liquid. The solid portion is mainly palmitin, the liquid, olein. Olive oil consists essentially of olein and palmitin ; beef-tal- low is mainly stearin ; lard is made up of olein and palmitin ; § 243.J MANUFACTURE OF SOAP. 155 butter is olein, palmitin, together with several other peculiar fats, to which its taste and odor are due. 7 — '■ (_J The chemical constitution of these bodies may be best represented by the use of typical fonnulse. Stearin is a salt of stearic acid, and may be regarded as buUt upon the type of three molecules of water : its formula may be derived from that of stearic acid by substituting for three atoms of hydrogen in three molecules of the acid one atom of the trivalent radical glyceryl (CjHj), thus : — Type, Stearic acid. Stearin. (Three molecules.) (One molecule.) H J ' H3 j » (C3H5) S ' Stearin is glyceryl stearate ; similarly palmitin is glyceryl palmitate, and olein is glyceryl oleate. Oleic acid does not belong to tha same series with stearic and palmitic acids ; hut, from the association in nature of the oleates and the stearates, it is con- veniently intioduced iu this connection. 242. The various fats and oiLs are insoluble in water ; they are, however, readily dissolved by certain liquids, such as ether, benzol, oil of turpentine, etc. Ii2p. 109. — FiU a small bottle half full of water, and pour in a few drops of olive-oU. The oil remains on the top of the water, and is not dissolved by agitating the mixture. £!zp. 110. — Into a small bottle put two teaspoonfuls of concen- trated ether, and add one quarter as much olive-oil. Cork the bottle tightly, and shake it : the oil is readily dissolved by the ether, /j >■ 243. Mamifaoture of Soap. — Very gi'eat industrial impor- tance attaches to many of the natural fats and oils on account of their use in the manufacture of soaps and " stearine " candles ; in both of these industries, a hydrate of glyceryl, glycerin, *TT ( ^»i i^ ^ secondary product. The manufacture of soap may be illustrated by the following experiment : — Ezp. 111. — Dissolve 15 grms. of solid caustic soda in 120 c. c. of water. When the suspended impurities have settled to the bottom of the solution, pour off one half of the clear liquor into a deep iron 158 MANUt'ACTURM OF SOAP. [§ 244. or porcelain dish of at least 500 c. c. capacity (see Appendix, § 21), add an equal bulk of water, and 50 grms. pf beef tallow. Bring tbe mixture to boiling and boil it steadily for tlu'ee quarters of an hour, supplying from time to time the water lost by evaporation ; then add the, remainder of the solution of caustic soda, and continue to boil steadily for an hour or more, allowing the liquid to become somewhat more concentrated towards the end of that time ; then add 20 grms. of fine salt, boil for a minute or two, and allow the liquid to cool. A part of the mass becomes solid, and rises to the top ; it is hard soap. The chemical action is thus explained : when tallow (glyceryl steaiate and oleate) is boiled with sodium hydrate, theie is formed so- dium stearate (and oleate) and glyceryl hydrate. When common salt is added, the soap (sodium stearate and oleate), being insoluble in the saline liquid, separates as a solid. The liquid remaining contains in solution the excess of sodium hydrate employed, as well as the salt and the glycerin. Soap may be made more quickly by using castor-oil instead of beef- tallow. Mix 100 c. c. of castor-oil and 100 c. c. of caustic soda solution prepared as above, and boil for 30 minutes. Then add 150 c. c. of water, bring to a boil, and add 20 grms. of salt. The soap rises to the top and may be removed when cold. Castor-oil is mainly glyceryl ricinoleate ; the chemical change is similar to that just described. Ezp. 112. — Heat some of the soap of Exp. Ill with soft water. A nearly clear solution will be obtained if the decomposition of the tallow or oil was complete. Add dilute chlorhydric acid imtil the solution is decidedly acid. The liquid will become turbid, and on standing, will become covered with a layer of a fatty substance which is a mixture of stearic and oleic acids (or mainly ricinoleic acid if castor-oil was used). The sodium chloride formed will be held in solution by the liquid; Other bases besides caustic soda may be used to effect the decomposition of oils or fats. If caustic potash be used, a soft soap is formed ; if slaked lime be employed, there is formed a lime soap, calcium stearate, etc., insoluble in water ; if lead oxide be used, there results an insoluble lead soap used in medi- cine under the name of lead plaster or diachylon. ii]r244. In Exp. Ill, one of the products of the reaction, gly- cerin, remained dissolved in the solution of sodium chloride and hydrate. This substance may be prepared as follows : — § 245.]^ GLY€KR]^•. — NITRO-GLYCEm^'. 157 Exp. 113. — Into a deep porcelain dish put 50 gnns. of litharge and 75 c. c. water. Into this mixture stir 50 grnis. of olive oil, and boil the mixture steadily for 50 or 60 minutes with constant stirring, and occasional addition of water to replace that lost by evaporation. The oil is gradually decomijosed ; an insoluble lead soap (lead plaster) is formed, and the color of the mass in the dish becomes lighter. When the oil seems to be entirely decomposed, pour off the liquid portion through a filter, add 50 c. c. of water to the lead plaster, boil for five minutes, and pass this liquid also through the filter. The glycerin is dissolved by the water, and with it passes through the filter. Evaporate the filtered liquid to dryness at a gen- tle heat: the glycerin will remain as a sirupy, non-volatile liquid, having a sweet taste. As the amount of glycerin obtained will be very smsill, it is well to transfer the solution when nearly evaporated to a watch-glass, and to finish the evaporation on a water-bath. .,> Glycerin, when pure, is a colorless, sweet-tasting, sirupy liquid, which mixes with water in all proportions. When heated in the air, it is slightly volatile, but cannot be distilled without decomposition, and the formation of vapors of acrolein very irritating to the eyes. This same substance is formed when fat burns, and is the cause of the peculiar odor given off from the smouldering wick of a tallow candle. Glycerin is used some-vshat in medicine, mainly for external applications : its use depends upon the fact that it is but slightly volatile, and does not dry up or undergo change when exposed to the air. 245. Nitro-Glycerin is an oily liquid heavier than water which is formed when glycerin is allowed to flow gradually into a cooled mixture of nitric acid and oil of vitriol. It is a highly explosive compound, being decomposed either by direct application of heat, or by percussion. It is used for blasting purposes instead of gun- powder, but is very dangerous to transport : the danger in using it can be very much lessened by making the nitro-glycerin im- mediately before use at the quarry or other locality where it is to be employed, or by impregnating wdth it some porous materiaL Dynamite, for instance, is infusorial earth thus impregnated. The formula of nitro-glycerin is ^'^ '^ | O3, while that of gly- 158 SAPONIFICATION. [§ 246. cerin is ' » »^ [ O, ; that is, three atoms of hydrogen have given place to three atoms of the radical nitryl (NO^) : nitro-glycerin may be regarded as glyceryl nitrate. 246. As has been stated, glycerin is also a product of the manufacture of what are known as stearine candles. These candles are not, properly speaking, stearin, but are made of the solid fatty acids ; namely, stearic and palmitic. Any process by which stearin (and, of course, palmitin and olein) is decomposed, so that the fatty acid or glycerin, or both bodies, are set free, is termed saponificatiou, even in cases where no soap results from the reaction. By treating the fat with sulphuric acid, it may be decomposed . with formation of the fatty acids and glycerin, and the two pro- ducts can be readily separated from each other. The decomposi- tion may also be effected by the use of superheated steam, and in the manufacture of candles these two methods are employed to a very large extent, although the fatty acids are sometimes obtained by first fonning a lime soap and then decomposing it with acid, as the soda soap was decomposed in Exp. 112. The fatty acids are cooled and submitted to preastire, which separates the oleic acid : the solid acids are thenjnoulded into proper forms. Candles are also manufactured from spermaceti, paraffin and wax. Spermaceti is a solid fat obtained by cold and pressure from the oil of the sperm whale ; when saponified, it yields palmitic acid and etbal (O16H34O). Paraffin is at ordinary temperatures a white solid having a pearly lustre. It is generally regarded as a mixture of several mem- bers of the marsh-gas series of hydrocarbons (Cn Hsn+s), which, indeed, are sometimes designated as the paraffin series or the paraffins. It occurs in petroleum, and when the petroleimi is distilled, it comes off in abundance at the latter part of the distillation. It is separated from the accompanying liquid hydrocarbons by cold and pressure. Paraffin also occurs in smaller quantity among the products of the distillation of bituminous coal and wood. Beeswax is mainly a salt of palmitic acid, melissyl palmitate, together with a free acid, cerotic acid. Chinese wax, produced by an insect belonging to the same genus as the cochineal insect, yields on saponification two bodies, carotin and cerotic acid : it is cerotyl cerotate. § 249.1 VEGETABLE OILS. 159 247. Artificial Fats. — While by the various processes of saponi- fication it is possible to obtain from the natural fats (with the ele- ments of water) both glycerin and a fatty acid, it has also been found possible to reproduce the fats by bringing the fatty acids and glycerin together under appropriate conditions : in this case water is elimi- nated precisely as water was set free in the formation of potassium nitrate from caustic potash and nitric acid (Exp. 25, § 62). Glycerin. Stearic acid. Stearin. Water. (C« J „. + 3 ^,SO,. Carbon Potassium Iron Ammonium protoxide. sulphate. sulphate. sulphate. This reaction has already been taken advantage of in the prepara- tion of carbon protoxide (Exp. 81, § 195). 388. Potassium Ferricyanide (K^eCyJ. —When a current of clilorine gas is passed through a solution of ferrocyanide of §391.] POTASSIUM NITRATK 225 potassium the following reaction takes place : — K^reCy, -(- CI =i= KjPeCy, + KCl. The compound K^PeCyj, potassium ferricy- anide, may be obtained in beautiful deep-red crystals by evap- orating the solution. This compound is known in commerce as " red prussiate of potash." Potassium ferricyanide is a salt of ferri - cyanhydrio acid (H^eCy,), a compound of hydrogen with the hypothetical triva- leut radical, PeCy, or Fdcy. The ferro- and ferri-cyanides of potassium afford valuable means of identifying iron in its com. pounds, as will be seen in § 477. 389. Potassium sulphate (KjSO<) diifers from sodium sul- phate in crystallizing as an anhydrous salt. The salt enters into the composition of many of the double sulphates which are called alums, from the name of the commonest member of the class, the aluminum and potassium sulphate. 390. Hydrogen Potassium Sulphate (hkSO,). — This salt, commonly called the " bisulphate," is formed on a large scale as a residuary product, whenever nitric acid is manufactured from potassium nitrate. When ignited, sulphuric acid is given off and potassium sulphate remains : — 2 (HKSOJ = KjSO, -|- H,SO,. ,; 391. Potassium Nitrate (KNOj. — This valuable salt, com- monly called saltpetre, or nitre, is very widely diffused in nature. In many localities, it is found in caverns or caves in calcareous formations, but the chief commercial source of the salt is the soil of tropical regions, especially of districts in Arabia, Persia, and India, where the nitrate is found as an efflorescence upon the sur- face of the ground, or in the upper portion of the soil itself. The saltpetre is extracted by treating the earth with water, and ob- tained in an impure state by evaporating the solution. The crude product is purified by successive recrystallizations. This natural production of nitrates appears to result mainly from the putrefaction of vegetable and animal matters, in presence of the air and of alkaline or earthy bases capable of fixing the nitric acid as soon as formed. The well-waters of towns, contaminated by neigh- boring sewers or cesspools, nearly always contain nitrates. Nitrates are seldom wholly wanting in a fertile soil, or in spring or river water. 226 OXIDIZma POWEB OF POTASSIVM NITRATE. [§392. The process oi,nUrificiMon seems to be brought about by: an organised ferment which Jives in vegetable mould. We have seen that the yeast plant accomplishes the conversion of sugar into alcohol (§ 225) j some- thing.similar is supposed to take -place in nitrification, -y 392. Potassium nitrate is white, inodorous and anhydrous, and has a cooling, bitter taste. When pure, it is permanent in the air, — a fact of great importance, inasmuch as the chief use of this salt is in the manufacture of gunpowder. Were it hygroscopic, like sodium, nitrate, it would not be applicable to this use. It is very soluble in water, especially in hot water ; it melts below a red heat to a colorless liquid without loss of substanoBj but at a red heat it gives off oxygen, and suffers decomposition. Its most marked chemical characteristic is its oxidizing power. Xizp. 184. — Mix 5 grms. of powdered saltpetre with 1 gmi. of dry, powdered charcoal ; place the mixture on a piece of porcelain lig. 7JJ, and ignite it with a hot wire. When the deflagration is over, a white solid will be found upon the porcelain. Dissolve this solid in a few drops of water ; the solution v^ill be alkaline to test-paper ; iidd a few drops of a dilute acid ; a brisk effervescence marks the escape of carbonic acid. The nitrate has oxidized the carbon to carbonic acid, part of which escaped with the nitrogeji during the deflagration, while part entered into com^bination with the potassium : — 4 KNO, -f S C = 2 K^COj + 3 CO, -[- 4 N. Gunpowder is an intimate mechanical mixture of soft-wood char- coal, sulphur and potassium nitrate, in the proportions of 70 or 80 per cent of the nitrate to 10 or' 12 per cent of each of the other ingredients. When gunpowder burns in a closed space, the reaction that takes place is quite complex ; speaking in general terms, how- ever, we may say that the oxygen of the nitrate combines with the carbon to form carbonic acid and carbonic oxide, while the sulphur is retained by the potassium, and nitrogen is left free. A very large pror. portion of gas, as compared with the bulk of the solid powder, is thus evolved when powder is burned. Moreover gunpowder bums rapidly and with great evolution of heat, so that the volume of gas, large at § 39^.] POTASSIUM CHLORATE AN OXIDIZING AGENT. 227 any temperature,' is enormously expanded at the moment of its forma- tion ; henee it'iappens that the gas set free may be capable of occu- pying a thousand or fifteen hundred times as much space as the powder which generated it. An enormous pressure is thus engen- dered at the spot where the powder burns, and to this pressure some part of the matter which confines the powder must yield. In the case of fire-arms it is the ball which yields to the pressure : in blast- ing it is the solid rock itself that is torn apart. 393. Fotassinm chlorate (KClOg) is a white, crystallized salt much used in medicine, in calico-printing, in pyrotechny, in the match-manufacture and in the chemical laboratory, on account of its large oxygen contents. It is an oxidizing agent of the most vigorous description. At a red heat it is resolved into potassium chloride and oxygen (Exp. 4) : — KCIO, = KCl -t- 3 O. Potassium chlorate is so prompt an oxidizing agent that mix- tures of it with combustible bodies often detonate violently when struck of heated. These combustions are attended with great danger unless very small quantities be used. "Exp. 185. — Provide a bit of ordinary phosphorus, as large as a pin's head ; add enough finely powdered potassium chlorate to cover the phosphorus ; fold the mixture tightly in a small piece of writing- paper ; place the parcel, upon an anvil and strike it sharply with a hammer. The mixture will explode with violence. Strong acids like sulphuric, nitric and chlorhydric acids, de- compose potassium chlorate with evolution of oxides of chlorine, or of chlorine and oxygen. The decomposition is often at- tended with decrepitation, and sometimes with a ilashing light ; combustibles, like sulphur, phosphorus, sugar and resin, are in- flamed by the gases evolved. Ezp. 186. — Pour into a conical test-glass 25-30 c. c. of water, and throw into the water some scraps of phosphorus, weighing to- gether not more than 0.3 grm., and 3-4 grms. of crystals of potassium chlorate. By means of a thistle-tube bring 5 or 6 c. c. of strong sulphuric acid into immediate contact with the chlorate at the bottom of the glass. Then withdraw the thistle-tube. In a moment the 228 AMMOXIUM SALTS. [§ 394. phosphoiua is kindled, and bums -with vivid flashes of light beneath the water. An evolution of chlorine accompanies the reaction. Esp. 187. — Rub 4 or 5 grms. of clean potassium chlorate, free from dust, to a fine powder in a porcelain mortar. In powdering potassium chlorate, care must be taken that the mortar and pestle are perfectly clean, and the salt is free from organic matter, and violent percussion and heavy pressure upon the contents of the mortar must be wholly avoided. Place the powdered chlorate on a piece of paper, add an equal bulk of dry, powdered sugar to the pile, afld with the fingers and a piece of card, mix the two materials thoroughly together. Mixtures of potassium chlorate and organic matter are liable to ex- plode, if strongly rubbed or but lightly struck. Wrap the mixture in a paper cylinder, and place the cylinder on a brick in a strong draught of air ; let fall upon the mixture a drop of sulphuric acid fiom the end of a glass rod ; a very vivid combustion will ensue, with the violet-colored flame characteristic of potassium. 394. Potassium tartrate (KjC^H^O^) is a very soluble crys- talline salt ; the hydrogen potassium tartrate (hKCy Exp. 204, is an exhibition of this same relation. Metallic copper maybe thrown down from a solution of one of its salts by the jtntroduction of metallic iron or zinc ; a. little metallic mercury put into a solution of silver nitrate will cause the formation of a silver-tree. In these cases the metal which goes into solution is said to be electro-posjtive to the metal which is precipitated, and the latter is electro-negative U> the former. - -J' 444. Salts of Zinc. — Zinc oxide (ZnO) is formed when jnetallic zinc is burned in the air, and may also be prepared by igniting the carbonate. Under the name of - zinc white, it is somewhat largely employed as a white paint. It dis- solves readily in acids. Zinc chloride (ZnCI^) is a white, soluble, deliquescent siibstance, formed by dissolving, zinc in chlorhydric acid. .It is used for preserving timber, also in soldering to cleanse the surface of the metal. Zinc sulphate (ZnSO,), or rather the hydrated compound (ZuSO, -1- 7 HjO), known as white vitriol^ is used to a certain extent in medicine, and also in the arts. // CADHTOM (Cd). 445. Cadmium is a eomparativel3f rare metal, found associated with zinc in nature ; it is remarkably similar to zinc in its chemical relations. It is a bluish-white lustrous metal, tarnishing somewhat when exposed to the air. It melts and volatilizes at temperatures below redness. Heated in the air, it takes fire and burns to a brown oxide. Cadmium sulphide is of a bright yellow color, and has been Tised as a pigment. • See in thlB connection some additional statements on page 293. 23 » 258 I'ROPMRTIES OF ALUMINUM. [§ 446. CHAPTER XXVI. AIT7MINirM, OLirCINUM, CHBOUIUH, HANGANXBE, XBOK, COSALT AKD NICKEL. ALUMINUM (a1.) 446. Alnminnm is perhaps the most ahundant element upon the earth's surface, next to oxygen and silicon. It is the most ahundant of all the metals, as much as a twelfth of the solid crust of the globe being composed of it. It occurs in enormous quantities in combination with oxygen and sili- con, in most rocks and soils. It is contained in clay, marl and slate, as well as in feldspar, mica and many other common minerals. Although the compounds of almninnm are so abundant, no cheap method of obtaining the metal itself has yet been de- vised. For this reason it cannot be applied to many uses for which it is otherwise well suited. It is generally prepared by heating metallic sodium either with chloride or fluoride of alu- minum, or with a double chloride or fluoride of aluminum and sodium. 447. Aluminnin is a bluish-white metal, of remarkable light- ness. Its specific gravity, 2.56, is about the same as that of porcelain, and only about a quarter of that of mlver. The metal is malleable, ductile and tenacious, and may be beaten into thin sheets, hke gold and silver, and drawn into fine wire. It is remarkably sonorous : a bar of it suspended by a wire rings with a clear musical note on being struck. Alumi- num-bronze, an alloy of 90 parts copper and 10 parts alumi- num, is exceedingly hard, very malleable, as tenacious as steel, of a beautiful golden color, and .,SO,. Put two or three drops of ■ the moist aluminum hydrate into another test-tube and cover them with ammonia- water ; no clear solution wlU be obtained, for aluminum hydrate is but slightly soluble in ammonia-water. Put two or three drops of the moist aluminum hydrate into still another test-tube, and cover them with a solution of sodium hydrate ; the precipitate will dissolve immediately ; sodium aluminate is formed, and this salt is easUy soluble. Xizp. 206. — Take another portion of the clear solution of alumi- num sulphate prepared in Exp. 205, and add to it, drop by drop, a dilute solution of caustic soda. A precipitate will soon fall, as in Exp. 205, and if no excess of sodium hydrate were added, this pre- cipitate would remain undissolved, but on adding more of the soda solution the precipitate dissolves at once, with formation of sodium aluminate (NajAl^O,). 449. Almninnm hydrate combines readily with many organic coloring-matters, forming compounds insoluble in water. Exp. 207.— Take a small quantity of the solution of cochineal prepared in Exp. 154, add to it an equal bulk of a solution of alu- minum sulphate (or of common alum), and then add to the mixture ammonia-water, as in Exp. 205. A colored precipitate, consisting of aluminum hydrate and of the coloring matter of the cochineal, will be thrown down ; it is the substance called carmine-lake. Similar precipitates may be prepared by substituting almost any other organic coloring matter for the cochineal of this experiment. Precipitates thus formed by the union of a metallic hydrate and a coloring matter are classed as lakes. 2G0 USE OF MORDANTS IN DYEING. [§ 45O. V 450. Mordants. — The fibre of cotton, when impregnated with alumina, can be made to retain colors which the cotton itself has no power to hold, Exp. 156, § 339: hence the use of aluminum salts as mordants in dyeing. In fact, mere im- mersion in a solution of a salt of aluminum suffices to make a great difference in the amount of coloring matter taken up by cotton. An acetate of aluminum is much employed in dyeing, because when exposed to the air on the cloth it is partly decom- posed, a certain amount of acetic acid is set free and volatilized, leaving the fibres impregnated with aluminum hydrate or oxide. Ezp. 208. — Prepare an acetate of aluminum as follows : — Dis- solve' 6 grms. of sugar of lead (lead acetate) in 8 c. c. of Lot water ; also dissolve 8 grms. of common aluiii in 12 c. c. of hot water ; mix the two solutions and filter off the insoluble lead sulphate which, is formed. In the solution thus prepared, soak a piece of cotton cloth, and then hang it up in a moist and warm atmosphere for several day.s. Treat this cloth, as well as a piece of ordinary cotton of the same size, with a solution of logwood as described in Exps. 156, 157, and observe the difference in the amount of color imparted to the fabric. Other oxides or hydrates besides the aluminum hydrate are used as mordants. An acetate of iron made by dissolving scraps of iron in the crude pyroligneous acid obtained by the destructive distillation of wood (§ 238) is much used by dyers ; salts of tin, of chromium and of other elements are employed to a greater or less extent. 451 . Aluminnm sulphate (ai, 3 (SO,)) is prepared by treat- ing hot roasted clay, which is an aluminum silicate, with sul- phuric acid. The mixture of aluminum sulphate and silica obtained is called alnm-cake, and from it the aluminum sul- phate can be obtained by treating with water, which dissolves the aluminum sulphate and leaves the silica behind. Aluminum sulphate is employed as the source oi the various compounds of /I aluminum used in dyeing and calico-printing. 452. Alums. — Potassium alum is an aluminum potassium r sulphate crystallizing in sharply defined crystals. Its composi- tion is represented by the formula Al^Kj 4 (SO,) -j- 24 H,0. It is known as common alum, although of late years ammonium §456.] CLAY, EARTHESrVi'ARE, AND PORCELAIN. 2c)l alum has to a considerable extent taken its place. The formula of ammonium alum is Alj (NH,\ 4 (SO,) + 24 HjO. 453. Aluminiuii Silicates. — Of all the aluminum com- pounds the sihcates are by sfar the most important. Glay in aU its varieties is a hydrated aluminum silicate, usually mixed with an excess of sUica, besides other impurities derived from the rocks from whose decotnposition the olay itself has been formed. Clay is remarkable on account of its plasticity when moist, of the facility with which it is converted into stone-like masses .when strongly heated, and of its infusibility when pure. Earthenware, bricks, and ordinary pottery are made from common clay, by mixing the clay with water enough to form a plastic paste, which is then moulded into any desired form, dried and intensely ignited. The red color of certain varieties of ware is due to the iron oxide they contain. Porcelain is made from a very pure clay (kaolin). The glaze on articles of pottery is made by coating them with an easily fusible substance, such as a mixture of litharge and clay, or in the case of porcelain finely ground feldspar, and subjecting them thus coated to high heat. Ordinary stone-ware is glazed by throwing common salt into the kiln. The salt volatilizes and coming in contact with the heated ware it is decomposed, and a fusible silicate results which renders the articles impervious to moisture. GLTJcnrnM (g1) and indium (in). 454. Glucinum is a rather rare metal, found, together with alumi- num, in the emerald, in beryl and in a few other minerals. It closely resembles aluminum in its chemical and physical properties. The atomic weight of glucinum is 14 ; its symbol is Gl. 455. Indium is a rare metal, found associated with zinc in certain ores, and was discovered by means of spectrum analysis. It is a soft white metal. Its atomic weight is 113.4 ; its symbol In. CHBOMIUM (C!r). 456. The chief ore of chromium is a compound of iron, chromium, and oxygen {TeCx^O^ called chrome iron-ore. The compounds of chromium are somewhat extensively employed in the arts. 262, SALTS OF CHROMIUM.— MAyUAKKSK. [§457. 457. Chromium sesquioxide {CxjQ^ prepared by igniting the hydrate. (Cr^HjO,), is a green powder somewhat used as, a pigment. The hydrate may be obtained by adding ammonia- water to a solution of a salt of chromium. It forms a bulky green precipitate. 458. Chromium sulphate (Cr^ 3 (30,)) is sometimes prepared in the pure state ; generally, however, it is prepared in combina- tion with potassium (or ammonium) , sulphate forming chrome alum, a beautiful violet crystalline salt. The formiila of ordi- nary chrome alum is Cr^K, 4 (SOJ -f- 24 H^O. "Exp. 209. — Dissolve 15 grms. of powdered potassium Lichro- mate in 100 c. c. of warm water ; cool the solution, and then add to it 25 grms. of concentrated sulphuric acid ; cool the liquor again, and pour it into a porcelain dish, surrounded with cold water ; slowly stir into the mixture 6 grms. of alcohol, and set the whole aside. In the course of 24 hours, the bottom of the dish will become covered with well-defined, octahedral crystals of chrome almn. In this experiment the chromic acid which is set free by the sulphuric acid gives up a part of its oxygen to the alcohol, and is converted into chromium sulphate, which unites with the potassium sulphate to form chroaie alum : the alcohol is oxidized in part to aldehyde (§235) (the peculiar odor of which is distinctly perceived) and partly to acetic acid. 459. Chromic anhydride (CrOj) may be obtaiaed by treating potassium bichromate with sulphuric acid. The chromic anhy- dride separates in red crystals, which dissolve in water with formation of chromic acid (H^CrOj. Several of the chromates find application in the arts, as the normal potassium chromate (KjCrOj, the potassium bichromate (K^CrjO, = KjCrO^CrOj) and the lead chromates. MANGANESE (lin). "^ 460. Manganese is a grayish-white, hard, brittle metal, the principal ore of which is the binoxide (MnOj, which has al- ready been employed in the generation of oxygen (Ezp. 4, § 12) and of chlorine (Exp. 30, § 78). The residue in the latter case consisted of manganese chloridOi which may be §461.] POTASSIUM PKllMASGAyATIi OXIDIZFS. -203 obtained in pink crystds (MnClj -)- 4 H^O) by filtering tlic liquid left in tlie flask and evaporating the solution until it crystallizes. / There are several oxides of manganese besides the binoxide. ^j 461. Manganic anhydride (MnOj and manganic acid (HjMnOj have never been obtained in a free state. Seven;! of the manganates, however, are well-known bodies. Potassium manganate (K^MnO^) may be made by fuaijig together man- ganese binoxide, caustic potash, and potiissium chlorate. The manganate is soluble in water, the solution being of a green color. When this green solution is boiled potassium perman- ganate (KjMiijOj) is foriived, which gives a dark purple colored solution. The manganates and permanganates readily give up oxygen and lose their color ; even a piece of wood or paper thrown into the green or red solution of a manganate, or per- manganate, will quickly abstract oxygen from the solution and destroy its color. Potassium permanganate is largely employed for disinfecting putrid water, as well as animal or vegetable matters in a condition of putrefaction. The oxidizing acticn of potassium permanganate may be shown by the following experiment. Ezp. 210. — In a beaker or flask dissolve 0.25 grm. of crystallized oxalic acid in 50 c. c. of water, add 5 c. c. strong sulphuric acid, and warm the solution to about ^60°. Then add a solution of potassium permanganate drop by drop, and observe that the color is at first inunediately destroyed. Continue to add the permanganate until it is no longer decolorized. The reaction that has taken place may be thus represented : — K^iijOs + 5 C^H^O, -I- 3 H,SO, = 2 MnSO, -f K,S04 -f 8 H^O + 10 CO^. The oxalic acid (C^HjO,) is entirely converted into water and car- bonic acid : the potassium permanganate gives up its oxygen and is converted into a mixture of manganese and potassium sulphates. On this property of potassium permanganate are based methods for the quantitative estimation of readily oxidizable substances such as oxalic acid or the ferrous salts. 2G4 • ORES OF iHOy. [§ 4G2. IRON (pe). 462. Although iron is one of the most widely diffused and most abundant of the metals, it is rarely found native in the metallic state. Meteors, however, faU upon the earth from outer space, which consist mainly of metallic iron, contaminated with several other elements in small proportions. Minerals contain- ing iron occur in great numbers ; and there are indeed few natural substances in which iron, is not present. It is found in the ashes of most plants, and in the blood of animals. The natural compounds of iron which are available as ores of the metal are chiefly. oxides and carbonates. From the richer iron-ores a very excellent iron can be ob- tained by simply heating the broken ore with charcoal in an open forge fire, urged by a blast. The ore is deoxidized by the carbon of the fuel, and the reduced iron is agglomerated into a pasty lump called a " bloom," while the earthy impurities con- tained in the ore combine with a portion of the oxide of iron to form a fusible glass or slag. This process is not economical in the chemical sense, for much iron is lost in the slag, and much fuel is burnt to waste in an open fire, but when well conducted it yields an admirable quality of iron, and is easily practised by people possessing but little mechanical skUl and no chemical knowledge ; it is undoubtedly the oldest method of extracting iron from its ores. 463. In the extraction of iron from its common ores, the metal is usually" obtained, not pure, but in a carburetted fusi- ble state, known as cast-iron or pig-iron. The main features of the process are, first, a previous calcination or roasting to expel water, carbonic acid, sulphur and other volatile ingredients of the ore ; secondly, the reduction of the oxide of iron to the metallic state by ignition with carbon ; thirdly, the separation of the earthy impurities of the ore by fusion with other matters into a crude glass or slag; and lastly, the carbonizing and melt- ing of the reduced iron. The preliminary calcination is not always essential, but with many ores, especially the carbon- ates and hydrates, it is very desirable ; not unfrequcntly all the § 463.] THE BLAST-FURNACE. 265 Fig. 75. drying necessary is effected in the upper part of the blast-fur- nace itself, within which the three last steps of the process always take place. The blast-furnace for iron consists essentially of a double cone, built of firerbrick and masonry, and -is about 50 feet in height, and from 15 to 18 feet in width at its broadest part. An idea of its con- struction may be obtained from Fig. 75. The furnace is closed at the bottom, the air necessary for the support of the combustion being sup- plied by a powerful blast blown through pipes called tuyiws (pro- nounced tweers). At the high tem- perature produced the carbon of the fuel removes the oxygen from the iron- ore, and the metallic iron is set free. The reduction of the oxide of iron, however, is not alone sufficient to secure the metal ; iron-ores almost always contain earthy admixtures, consisting chiefly of silica, clay and calcium carbonate, and these sub- stances are so intimately mixed with the reduced metal, that it is essential to melt them before fhe iron can separate by virtue of its greater spe- cific gravity. This is brought about by converting these impurities into fusible double silicates by the addition of some proper substance which is called a, flux. With ores in which the earthy admixture is chiefly cal- careous, the flux nmst be clay or some siliceous material, but in the more frequent case of ores containing clay or silica the flux will be; limestone or quicklime. In either case a fusible double silicate of aluminum and calcium is the essential constituent of the slag. The blast furnace is charged at the top with alternate layers of the fuel, (which may either be charcoal, anthracite or coke) the ore and the flux, which is generally lime ; and air is constantly supplied in immense quantities at the bottom of the furnace. The blast coming in contact with a great excess of incandescent carbon, there is formed immediately ciirbou protoxide, and this gas, together with 2.3 266 CAST- AND WROUGHT-IRON. [§ 464. the unaltered nitrogen ascends the shaft. The layers of solid mate- rial thrown in at the top of the furnace gradually sink down, and as soon as a stratum of ore has descended sufficiently to be heated by the hot mixture of nitrogen and carbon protoxide it becomes reduced to spongy metallic iron, which, mixed with the flux and the earthy impurities of the ore, settles down to hotter parts of the fur- nace, where it enters into a fusible combination with carbon, while the flux and earthy impurities melt together to a liquid slag. The liquid carburetted iron settles to the very bottom of the furnace, whence it is drawn out, at intervals, through a tapping-hok which is stopped with sand when not in use. The viscous slag flows out over a dam, so placed as to retain the iron, but to allow the escape of the slag which floats on the iron, as fast as it accumulates in sufiicient quantity. As fresh portions of the ore, fuel and flux are continually supplied, and the iron is withdrawn from time to time, the process goes on without interruption sometimes for several years. The gases which issue from the mouth of the blast-furnace are charged with an enormous heating power, for besides being them- selves intensely hot they contain, even after having effected the reduction, a large proportion of combustible gases, such as carbon protoxide, carburetted hydrogen and hydrogen. They are, there- fore, collected at the top of the furnace by a sort of conical hood, con- ducted off through a pipe, and burned in suitable furnaces, the heat produced being utilized in raising the temperature of the blast of air forced into the furnace through the tuyk-es. Cast-iron contains from 2 to 6 per cent of carbon ; in white iron, which is hard and brittle, and of crystalline texture, the carbon seems to be mainly in combination with the iron ; while in gray iron, which is slightly malleable and of granular texture, the carbon exists chiefly as graphite mechanically disseminated through the iron. Cast-iron also contains a small amount of silicon and not imfrequently manga- nese ; it is, moreover, usually contaminated with minute quantities of sulphur and phosphorus. 464. The production of malleable or "wrought "-iron from cast-iron consists essentially in burning out the carbon, silicon, sulphur and phosphorus which cast-iron contains. Thi? oxida- tion of the impurities of cast-iron is effected by a process known as puddling. The operation consists in melting the iron in a reverberatory furnace and stirring it so that the air will come in contact with it. § 466.] REVERUERA TOR Y FURNACE. —STEEL. 2G7 Fig. 76 represents a reverberatory furnace, such as is used in puddling. The principle of this furnace has already heen explained in § 370. In puddling it is customary to add to the charge of pig-iron a quantity of iron scale or other oxide of iron. The oxidation of the silicon, carbon, phosphorus, and other impurities is effected partly by the air but chiefly by the oxide added to the charge. When the cast-iron is so far decarbonized as to be pasty in the fire, it is gathered into lumps on the end of an iron bar and carried from the furnace to a hammer or squeezer which expresses the liquid slag and welds into a coherent mass the tenacious iron. The wrought-iron thus produced has a gray color, is malleable and may be welded at a red heat. It still con- tains from 0.05 to 0.25 per cent of carbon. 465. Steel. — Intermediate in composition between cast- and wrought-iron as far as the amount of carbon is concerned is the invaluable substance, — steel. It may be made from wroTight-iroH by heating bars of iron to redness for a week or more in contact with powdered charcoal in close boxes from which air is carefully excluded. Though the iron is not fused, nor the carbon vaporized, yet the carbon gradually penetrates the iron and alters its original properties ; when the bars are withdrawn from the chests in which they were packed, the metal has become fine-grained in fracture, more brittle and more fusible, and contains from I to 2 per cent of carbon. This process of preparing steel is called the " cementation " process ; it is a curious instance of chemical action between solid materials which are apparently in a state of rest. •*- 4GC. A new and very rapid method of preparing cast-steel 2G8 Tllli LESSICMKR PROCESS. [§ 4G7. directly from cast-iron is that known as the Besssmer process, From two to six tons of cast-iron, previously melted in a suitable furnace, are poured into a large covered crucible, called the con- verter, which is made of the most refractory materials, and swung on pivots in such a manner that it can be tipped up and emptied by means of an hydraulic press. Through uumerouM apertures in the bottom of the crucible^ a blast of air is forced up into the molten metal ; the combustion of the carbon ani silicon of the iron, as well as of a portion of the iron itseli, causes an intense heat, which keeps the mass fluid in spite of its rapid approach to the condition of malleable iron. Towards the end of the operation a sufficient quantity of spiegeleisen is introduced into the crucible. This spiegeleisen is a peculiar aUoy of iron, manganese and carbon : the manganese removes some of the oxygen previously combined with iron and some sulphui' ; the carbon converts the whole mass into steel, and the melted steel is immediately cast into ingots. The symbolof iron is Pe (\j>.t\xi,ferrum) ; its atomic weight is 56. 467. Oxides and Hydrates of Iron. — The best known of the compounds of iron and oxygen are the protoxide (PeO), or fer- rous oxide, as it is often called ; the sesquioxide (PejOs), often called ferric oxide ; and the magnetic oxide (Pe304). 468. Iron protoxide or ferrous oxide (PeO) may be ob- tained by igniting ferrous oxalate in close vessels ; it absorbs oxygen so rapidly that it takes fire when brought in contact with the air. Ferrous hydrate (PeHjOj), obtained by adding caustic alkali to a solution of a ferrous salt, is a white precipitate which rapidly changes on exposure to the air by taking on oxygen. 469. IrQU sesquioxide or ferric oxide (Fefi^); called also red oxide of iron, occurs abundantly in nature as hematite, specular iron and red ochre. It is valuable as an ore of iron. It is also prepared artificially, and is much used as a pigment. A fine variety, known as rouge, is used for polishing glass and jewelry. By heating ferric oxide in a current of hydrogen, or other reducing gas, metallic iron is readily obtained. This oxide § 472.] 0X1 DKS OF IRON. 269 of iron is called sesquioxide because it contains once and a half as many atoms of oxygen as of iron (sesqui, Latin, one and a half). Ferric hydrate (Fe^HjO,) may be prepared by adding an excess of ammonia-water to the solution of almost any ferric salt. Ezp. 211. — Cover a teaspoonful of fine iron filings or small tacks wdth 8 or 10 c. c. of dilute sulphuric acid in a small bottle ; when the evolution of hydrogen slaokeiLS, dilute with an equal bulk of water and filter into a small flask. To the liquid add a few drops of strong nitric acid, and heat it to boiling. The liquor will soon be colored dark-brown by the nitrous fumes resulting from the decom- position of the nitric acid, which are for a short time held dissolved by the liquid ; but this deep coloration soon passes away, and there is left only the yellowish-red color of the ferric sulphate which has been formed. Add to the solution ammonia-water, until the odor of the latter persists after agitation, and collect upon a filter the flocculent red precipitate of ferric hydrate. / 470. There are several ferric hydrates vrhich occur in nature and differ somewhat in composition from this the normal hy- drate. Yellow ochre is a variety of ferric hydrate. The readi- ness with which ferric oxide gives up oxygen to reducing agents is shared by the hydrate as well. The iron nails em- ployed in the construction of ships, bridges, fences, or shoes, actually corrode, " eat up " or " burn out " the organic matter in contact with them, by absorbing oxygen from the air and transferring it to the carbon compound with which they are in contact. The rotting of canvas by iron rust, or of a fishing- line by the rtj«ty hook, are familiar instances of corruption by rust. Ferric hydrate readily absorbs sulphuretted hydrogen with formation of an iron sulphide ; it is much used on this account in the purification of coal-gas. V 471. The magnetic oxide of iron (FejOj occurs native. It is the richest of the ores of iron, and when pure contains about 72 per cent of iron. 472. Ferrous and Ferric Salts. — There are, generally speak- 270 FlCItliOUS AND FERRIC SALTS. [§ 473. iiig, two series of iron salts, in one of which the atom Fe is bivalent, and in the other of which the douhle atom (PeJ is sexivalent. Thus there are two chlorides, — ferrous chloride, PeClj, and ferric chloride, (Fej)Cl, ; similarly there are two nitrates,: two sulphates, etc. CI \ 473. Ferrous Sulphate (PeSO,). — A hydrate of this com- pound, of composition PeSO^ -f- 7 H^O, usually called copperas or green, vitriol, is the most common of all the compounds of iron. It may readily be prepared by dissolving metallic iron or ferrous sulphide in dilute sulphuric acid. On the large scale it is commonly prepared by roasting iron pyrites (FeSj) at a gentle heat. When perfectly pure, the crystals of ferrous sulphate aro compact, transparent and of a bluish-green color ; but in dry air they effloresce and become covered with a white incrusta- tion, the color of which subsequently changes to rusty brown through absorption of oxygen. The common commercial arti- cle is of a grass-green color, and. is contaminated with more or less ferric sulphate. When heated, the crystals first lose their water of crystallization, and on further application of heat the salt is decomposed, sulphurous and sulphuric anhy- drides are given off, while ferric oxide remains. Upon this fact depends the preparation of filming sulphuric acid (§ 135). '^ [l 474. Ferric sulphate (Pe^ 3 SO,) is interesting, chiefly from its analogy with aluminum sulphate. Like the aluminum salt, it combines with the sulphates of the alkali-metals, to form well- defined alums. 475. When exposed to the air, or to oxidizing agents, the ferrous salts have a great tendency to absorb oxygen. Ezp. 212. — Pour a solution of copperas into an open capsule, and leave it exposed to the air for a day or two ; the solution will gradually become yellow as the oxidation proceeds, and after a while a rusty precipitate of ferric oxide, or of highly basic ferric sulphate, will fall. Exp. 213. — Dip a small piece of cotton cloth in the solution of nutgalls prepared in Exp. 151, and allow it to become dry; then dip § 476.] USK OF FJiRROUS SULPIIATK JN DYKIXG. 271 it ill the solution of copperas aiiil hang it up in damp air. Black, in- soluble iron tannate will be so finuly precipitated in and upon the fibres of the cloth, that it cannot be washed away. This experiment illustrates one general method of dyeing, by means of which blacks and grays of various shades may be applied to cloth or leather, though in practice other astringent aye-stuffs, such as cate- chu, cutch or gambler, are coinmonly employed in place of niitgalls. Ferrous sulphate is lai^ely employed in dyeing, sometimes directly, as in the foregoing experiment, but often as the source of other com- pounds of iron, which are employed as mordants ; ferrous acetate, for example, obtained by decomposing ferrous sulphate with calcium ace- tate, is a compound much used by dyers. It should be remarked, however, that fe^ous acetate is sometimes made directly by dissolv- ing scraps of iron in vinegar or pyroligneous acid (§ 238). Ferrous sulphate is also used in dyeing with indigo. Its use depends upon the fact, that, when a solution of copperas is treated with calcium hy- drate, a feiTous hydrate is precipitated ; this ferrous hydrate has such a tendency to absorb oxygen, that a mixture of copperas and slaked- lime forms a powerful reducing mixture. Ezp. 214. — Dissolve 1 grm. of copperas (iron sulphate) in 100 c. c. of water in a bottle of 200 c. c capacit}'. Into the solution stir a mixture of 1 grm. of finely powdered indigo and 1.5 grms. of freshly slaked lime ; fill up the bottle with water and cork it. Shake the bottle occasionally, and, after eight or ten hours, pour off, or remove with a pipette (Appendix, § 20), a portion of the clear and nearly colorless liquid without disturbing the precipitate in the bottom of the bottle. Expose this liquid to the air in a shallow dish ; it con- tains white indigo in solution, but the oxygen of the air rapidly causes the formation of blue indigo insoluble in the liquid, as was seen in Exps. 159, 160, § 342, where a different reducing agent was employed. 476. Silicates of Iron. — Several native silicates of iron ' are known, but none of them are of special interest. The green tinge of ordinary glass is due to the presence of a fer- rous silicate, and by increasing the proportion of the ferrous salt, a deep bottle-green color may be imparted to the glass. This color may be destroyed by introducing into the glass dur- ing the manufacture manganese binoxide, or some other ox- idizing agent. The ferrous silicate is thus converted into ferric silicate which has little coloring power. Vf^ I'RL'SSIAX BLUE.— SULPHIDES Of IROX. [§ 477. f 477. Cyanides of Iron. — There is a ferrous cyanide (Fe(CN)j), known as a yellowish-red precipitate, which takes up oxygen and becomes blue when exposed to the air, and a ferric cyanide {Fe^{C'l!f)^ has been obtained in solution. But by far the best known of the cyanides of iron are certain double compounds, which constitute the familiar pigments, known, collectively, as Prussian blue. Common Prussian blue (Pe,C,jN„ -(- 18 HjO), may be regarded as a compound of fer- Tous and ferric cyanides, 3 Pe(CN)j,2 (Pe/CN)^) -|- 18 H^O; it may be prepared as follows : — Exp. 215. — Add to an exceedingly dilute solution of almost any ferric salt, such, for example, as the ferric sulphate of Exp. 211, a drop of potassium ferrocyanide (§387). A beautiful blue precipitate will form, and will remain suspended in the liquor for a long while. Another variety of Prussian blue, known as Twrtbull'sblue, may be obtained by mixing a solution of potassium ferricyanide (§ 388) with a solution of copperas or other ferrous salt. Since potassium ferrocyanide will give no blue coloration with ferrous salts, and since the ferricyanide yields no blue with ferric salts, it is evident that the two solutions may be used as tests by which to detect the presence of ferrous and ferric salts, respectively, in any solution. Exp. 216. — Soak a piece of cotton cloth in a solution of ferric, sidphate (Exp. 211), and then immerse it in an acidulated solution of potassium ferrocyanide. Prussian blue will be precipitated upon the cloth, and will remain firmly attached to it. Prussian blue is largely employed in dyeing and calico printing in a variety of ways. 478. Iron protosulphide (PeS) is a substance of great value to the chemist as the cheapest source of the important reagent, sulphuretted hydrogen (§121). The sulphide may be pre- pared by igniting pyrites in a covered crucible, by rubbing roU brimstone against a white hot iron bar, or by fusing to- gether sulphur and iron turnings (Exp. 47, § US). Ezp. 217. — Dissolve a small crystal of ferrous sulphate (cop- peras) in water, and add to the liquid a drop or two of ammonium sulphydrate ( § 401). Black iron sulphide will be thrown down. The finely divided protosulphide thus obtained in the wet way, dis- § 481.] COBALT AAD yiVKEL. 273 solves much more quickly in acids than the compact sulphide obtained by the way of fusion ; in contact with acids it evolves gas so tuniultu- ously that it would be inconvenient as a source of hydrogen sulphide. The black earth between the stones of the pavements of cities, and at the bottom of drains and cesspools, owes its color to iron proto- sulphide formed by the putrefaction of sulphuretted compounds in contact with ferric oxide contained in the earth. \^ 479. Iron bisnlpMde (FeSj occurs abundantly in nature as the well-known mineral iron pyrites. When the pyrites is roasted at a high temperature, sulphurous anhydride is formed, and ferric oxide left, as in the manufacture of sulphuric acid. "When the temperature of the burning pyrites is kept low, the product is principally ferrous sulphate, and a large amount of copperas is thus obtained by roasting pyrites and then treating with water. Under certain conditions pyrites oxidizes in the air at the ordinary temperature ; the spontaneous combustion of many kinds of coal is due to the oxidation of iron pyrites dis- seminated through the combustible. COBALT (co) AND NICKEL (Ni). 480. Cobalt and nickel are two metals remarkably similar to each other in both physical and chtmical properties. They occur together in nature, generally in combination with sulphur and arsenic. They have the same atomic weight (58.8) and nearly the jsame specific gravity (8.2 to 8.9). Nickel is somewhat used as an ingredient of certain alloys, of which German silver, composed of copper, zinc and nickel, is the most familiar. Like iron, cobalt and nickel form protoxides (CoO and NiO) and corresponding proto-salts ; like iron, they form sesquioxides (COjO, and NijOj) and corresponding per-salts. Unlike iron, however, the protoxides are more stable compounds than the sesquioxides. To designate the two series of salts, the terms cobaltous and cobaltic, niclcelous and nichelic are sometimes employed. 481. The Sesquioxide Group. — The most striking char- acteristic of the metals which have been grouped together in this chapter is the property which they possess of forming sesquioxides and a corresponding series of salts ; most of them 274 COPPER. [§ 482. form protoxides as well^ and if we arrange the metals in the order of their atomic weights, Gl = 14, Al = 27.4, Cr = 52.5, Mn = 55, Fe = 56, Ni = 58.8, Co = 58.8, the sesquioxides of the metals at the head of the list are the most stable of the sesquioxides, and the protoxides of nickel and cohalt are the most stahle of the protoxides, while with manganese and iron both forms of oxide are well represented. Glucinum and aluminum have no protoxides at all, and the protoxide of chromium is very unstable. 482. Uranium (Ur) (at. wt. = 120). — With the members of this group may be classed the rare metal uranium, the sesquioxide of which is used to give a beautiful yellowish-green color to glass, and also the following elements, which are more or less nearly related to alumi- num and iron : — Yttrium, Yt ; Erbium, Er ; Cerium, Oe ; Lanthanum La ; Didymium, Di ; Gallium, Ga. CHAPTEE XXVII. COFFER AND UERCUBT. COPPER (cu). 483. Though by no means one of the most abundant metals, copper is nevertheless very widely diffused in nature, and is largely employed by man. Traces of it exist in almost every soil, whence it is taken up by plants, in which it may almost always be detected by refined testing. Traces of it have repeatedly been found also in the various animal organs and secretions. Besides occurring in the native state, copper is found in a great variety of combinations ; the most common of its ores, however, is the sulphide, or rather a compound of cop- per sulphide and iron sulphide in varying proportions, known as copper pyrites. The carbonates and oxides of copper are also valuable as ores. § 487.] tOMPOUNUS Ai\D ALLOYS OF COPPER. 275 484. Copper is a ratlior hard metal, of a well-known red color ; it is very tenacious, ductile and malleable. At the or- dinary temperature the metal is not altered in dry or moist air, unless finely divided. When heated in the air it becomes covered with a coating of a black oxide. Metallic copper is not very readily acted upon by acids, excepting those rich in oxygen. Except when finely divided it is scarcely acted upon by even concentrated chlorhydrio acid ; in hot sulphuric acid it dissolves as copper sulphate, sulphurous anhydride being given off; in nitric acid somewhat diluted, it dissolves readily as copper nitrate, and nitric oxide escapes (Exp. 19, § 60). 485. Several of the compounds of copper with other metals are of great importance in the arts. Brass and the yellow- metal used for sheathing ships are alloys of zinc and copper; bronze, gun-metal and bell-metal are alloys of tin and copper, and various compositions are produced by mixing these alloys with brass ; copper is also an essential ingredient of all the common coins, implements and ornaments of gold and silver. 486. Cnproas and Cnpric Salts. — There are two series of copper salts, in one of which the atom Cu is bivalent, while in the other the double atom CUj is bivalent. Thus, cupric chloride is CuCl, ; cuprous chloride is Cu^Cl^. As a rule the cupric salts are the more common and the more stable of the two series. 487. Oxides of Copper. — There are two oxides of copper.^ Copper suboxide, cuprous oxide or red oxide of copper (CujO) occurs in nature as " ruhy copper." It may be prepared artifi- cially in various ways, as, for example, by the action of certain reducing agents on alkaline solutions of cupric salts (Exp, 135, § 298). Cuprous oxide is used to give a ruby-red color to glass. Copper oxide, cupric oxide or black oxide of copper (CuO) may be prepared by heating the metal in a current of air, or by igniting the carbonate, hydrate or nitrate. Ezp. 218. — Bind a bright copper coin with wire, in such man- ner that a strip of wire 8 or 10 c. m. long shall be left projecting from the coin ; tlirii! the symhol of the compound is written HjO. The proportion of hydrogen to oxygen is in hoth cases the same ; and, in general, it is; evident that the relative proportion in which any two or more elements exist in a chemical compound is a m^itter of fact determined by analysis : it is something which no theoretical conceptions of ours can change. The atomic weights, however, or the values which we assign to the symhola of the elements, must be fixed by what we hold to be true with regard to the number of atoms in the molecule of the compound. It is a better knowledge of the molecular constitution of bodies than was accessible to their predecessors that has led the chemists of the present day to employ new atomic weights in the case of a considerable num- ber of the elements. The more common elements whose atomic weights are double the equivalent weights formerly assigned to them are as follows : — Aluminum, Iron, Platinum, Barium, Lead, Selenium, Cadmium, Magnesium, Silicon, Calcium, Manganese, Strontium-, Carbon, Mercury, Sulphur, Chromium, Nickel, Tin, Cobalt, Oxygen, Uranium, Copper, Palladium, Zinc. In passing, then, from the formulas of the older system to the cor- responding formulee of the new, if the atomic weight of any element is double the old equivalent weight, it becomes necessary, in writing the symbol of any molecule containing this element, either to taie half as many atoms of the element in question or to take twice as many atoms of the other elements in the molecule unless they also have had their combining weights doubled. Thus the symbol of the stannic chloride was formerly written Su Cl^ ; now, since the atomic weight of tin is 118 whUe the old equivalent weight was 59, the sym- bol must be written Sn CI4, in order to express the same relative proportion of chlorine and tin. 514. Nomenclature. — In connection with the adoption of the atomic weights now in use, although not logically dependent upon it, there have occurred certain changes of nomenclature, especially in regard to the salts of the ordinary acids. The term acid itself is not used in the same sense as formerly. Now (see pages 41 - 43) we are inclined to restrict the term acid to bodies containing hydrogen which 288 NOMENCLATURE. [§ 616 can be replaced by a metallic element ; it was formerly applied also to bodies which in this book have been called anhydrides. Thus SO, was called sulphuric acid (or anhydrous sulphuric acid), and HjSO, was regarded as a compound of SO3 and water, and written H,0, SO,. In like manner the sulphates were regarded as com- pounds of SO, with the oxides of the metallic elements, and were named, in; accordance with this idea, sulphate of soda, sulphate of lime, etc., instead of sulphate of sodium, sulphate of calcium, etc. There is at the present time, however, no uniformity of nomenclature. Some chemists say sulphate of sodium, some say sodium sulphate, others fey sodic sulphate ; while the old term sulphate of soda con- tends with them and with the still older term, Glauber's salt, for a place in the language of commerce, of literature, and of ordinary life. As a rule, when there are two series of salts derived from the same element, it is usual to distinguish between the two by the use of the terminations -ous and -ic, as, for example, ferroits sulphate and fernc sulphate. In the designation of the so-called binary compounds (i. e. com- pounds of two elements only) there is the same diversity of practice ; thus the names soda, oxide of sodium, sodium oxide, and sodic oxide are all applied to the same compound of oxygen and sodium. Where there are two oxides of the same element (or chlorides, sulphides, etc.), the terminations -ous and -ic are sometimes employed ; more gener- ally, however, prefixes, either Latin or Greek, are used : thus, when the molecule of an oxide contains only one atom of oxygen it is called ihf: p-otoxide or monoxide; when there are two atoms of oxygen in the molecule, it is- called the hinoxide or di-oxide ; succeeding compounds would te the teroxide or trioxide, quadroxide or tetroxide, etc. (see page 37). 515. Quantivalence. — In addition to the statements of § 74, it may be remarked that the atom of the same element does not always possess the same quantivalence. Thus, while the quantivalence of hydrogen is always taken as 1, and that of oxygen as 2, the quantivalence of sulphur is sometimes 6, sometimes 4, and sometimes 2, that of nitrogen is sometimes 5 and sometimes 3. As a rule, when an element varies in quantivalence, the various degrees of quantivalence possible to the same atom are either all odd or all even. We do not know to what the observed difference in the combining power of the different atoms is due. In order, however, to represent it to the eye, it is usual to attach to the symbol of the atom of an element as many dashes as will indicate the quantivalence. If com- § 515.] qUA^TIVALENCE. 289 bination takes place between elementary atoms of two kinds, the total quantimlence oi each element must be the same. If this be ex- pressed graphically, the number of dashes attached to each symbol, or, as is often said, the number of bonds must be the same. Thus, in H — CI we have represented the union of 2 univalent atoms ; in H — O — H the union of one bivalent with two univalent atoms. If a compound is made up of atoms of more than two kinds, it is still possible to write the symbol graphically, so as to represent each atom as united to other atoms by all the bonds attached to it to indicate its quantivalence. Thus, H2SO4 and AgNOs may be written H-O — S— O — H Ag — O — N In these symbols the atoms are represented, H and Ag as univalent, O as bivalent, N as quinquivalent, and S as sexivalent. No mol- ecule can exist, by this theory, in which the atoms must be repre- sented with bonds unconnected with other atoms : thus there cimld be no such molecule as HO, for if written graphically, H — O — , it is seen that the oxygen is " unsatisfied." Such a group of atoms is called a compound radical, and the number of bonds unsatisfied is the quantivalence of the radical. Thus HO — is a univalent rad- ical, while H — O — H, H — O — O — H (hydrogen peroxide), H — O — Ca — O — H (calcium hydrate) are satisfied or "satu- rated" molecules. This shows how it is possible for the single atom of copper to be bivalent ( — Ou — ) and for the group of two atoms to form a bivalent combination ■ — (Ou — Cu) — . This grouping of the atoms together is not an arbitrary matter of the na- ture of a "dissected map.'' In the arrangement of the atoms it is not simply a question of so linking the atoms together that the con- ditions implied by the quantivalence of the atoms shall be satisfied ; such formulae attempt also to represent in some sense the structure oj the molecule, at least so far as to indicate the relations which we be- lieve to exist among the various atoms which compose it ; this is, however, a matter not sufficiently elementary in its character to be considered in this place. Undue stress is laid upon this matter of quantivalence by many chemists ; but the theory expresses, although in a rather crude way, relations which actually exist, and although it 290 OXIDATION AMD MEDUVTION. [§ 516. may, and probably will, be diaplaoed by some other theory which will explain the sanie facts in a more satisfactory manner, it has been, and is, of great value. To the beginner it is chiefly valuable for the aid afforded in writing formulae and equations. The graphical formulae and equations written in accordance with this theory, are useful, chiefly because they can be made to represent more facts and more suppositions than can be expressed in ordinary formulae and etjuations. The term atomicity is applied to the highest degree of quantiva- lence which the same atom may possess ; and the atoms are desig- nated as monads, dyads, triads, tetrads, pentads, hexads and heptads, according as the atomicity is one, two, three, four, five, six, or seven. These terms, monad, dyad, etc., are sometimes used, however, to denote the more common degiee of quantivalence, rather than the highest which the atom is capable of exhibiting. Thus the atomicity of lead is four ; its prevailing quantivalence is two ; lead would thus, according to the fii-st plan, be spoken of as a tetrad, according to the second as a dyad. 516. Oxidation and Heduction.^The terms oxidation and reduc- tion are used in a much wider sense than is implied in § 129 on page 81, although the simplest use is as there indicated. As an example of another use of the terms we may take the case of the two chlorides of tin. If by some chemical process the stann to bubble through a few centi- metres' depth of the liquid acid, or it may be forced to pass through the interstices of a column of bro- ken pumice-stone which has been previously soaked in the acid. The latter method is the most effectual, because it secures a more thorough contact of the gas with the hygro- scopic acid than is possible during =4]^ the rapid bubbling of the light gas jj through a shallow lay^r of the dense liquid. The column of fragments of pumice-stone may be held in a 27 39= xxvi APPEXDIX. U-tube, arranged like that shown in Fig. XXVIII ; but the vertical cylinder shown in the same figure is better adapted for this use, be- cause the acid, as it becomes dilute from absoi-ption of m.oisture, grad- ually trickles' from the pumice-stone, and is apt to collect in such quan- tity at the bottom of the U-tube as to completely close the tube. In preparing the upright cylinder for use, the portion below the contrac- tion is not tilled with puniioe-stone ; it receives the drippings from the pumice-stone column. The gas to be dried enters by the lower lateral opening, and goes out at the top of the cylinder. Though especially adapted to the column of acid-soaked pumice-stone, this cylinder may very well be used with either ol the other drying agents, calcium, chloride or quicklime. Either of the forms of drying-tube represented in Fig. XXVIII may be employed with these latter substances ; in charging the horizontal tubes, bits of loose cotton-wool should first be placed against the exit- tube to prevent any particles of the calcium chloride, or quicklime, from entering that tube ; pieces of the. perfectly dry solid are then introduced in such a way that the tube may be compactly filled with fragments which leave room for the gas to pass very deviously between them, but offer no direct channels through which the gas could find straight and quick passage. Quick- lime must be charged much more loosely than calcium chloride, because of its great expansion when moistened. Fused calcium chloride is not so well adapted for drying gases as the^ unfused sub- stance. It is not at all necessary that the fragments of calcium chloride, or quicklime, should be of imiform size. When the tube is nearly full, a plug of loose cotton should be inserted before putting in the cork. A calcium chloride tube, once filled, will often serve for many experiments ; whenever out of use, its outlets should be covered with paper caps ; or, better, caoutchouc connectors may be slipped upon»the exit-tubes, and bits of glass rod thrust into these connectors. The moisture of the air is thus kept from the calcimn chloride. The dimensions of drying-tubes are of course very va- rious ; the bulb-tube shown in Fig. XXVIII is seldom used with a greater length than 25 c. m. ; when this form of tube is employed the gas should invariably enter by the end without a cork, where the small size of the tube permits direct connection with a common gas- Jeli very-tube by means of a caoutchouc connector ; the other hori- zontal tube, shown in the figure, may be of any length, but whenever a great extent of drying surface is necessary, U-tubes have the advan- tage pf compactness, for many can lie hung upon one short frame ; the upright pylinder may be from 25 c. m. to 40 c. ni. in height. APPENDIX. xxvii The choice between one or other of the three drying substances is determined in each special case by the chemical relations of the gas to be dried ; thus ammonia-gas, which is absorbed by sulphuric acid and by calciimi chloride, must be dried by passing it over quick- lime, while sulphurous acid gas, which would combine with quick- lime, must be dried by contact with sulphuric acid. 17. 'Water-bath. — It is often necessary to evaporate solutions at a moderate temperature which can permanently be kept below a certain known limit ; thus, when an aqueous solution is to be quietly evaporated without spirting or jumping, the temperature of the solu- tion must never be suffered to rise above the boil- fm. xxix. ing-point of water, nor even quite to reach this poiirt. This quiet evaporation is best effected by ihe use of a water-bath, — a copper cup whose top is made of concentric rings of different di- ameters to adapt it to dishes of various sizes (Fig. XXIX). This cup, two-thirds full of water, is supported on the iron-stand over the lamp, and the dish containing the solution to be evaporated is placed on that one of the several rings which will permit the greater part of the dish to sink into the copper cup. The steam rising from the water im- pinges upon the bottom of the dish, and brings the liquid within it to a temperature which insures the evaporation of the water, but will not cause any actual ebullition. The water in the copper cup must never be allowed to boil away. Wherever a constant supply of steam is at hand, as in buildings wanned by steam, the copper cup above described may be converted into a steam-bath by attaching it to a steam-pipe by means of a small tube provided with a stop-cock. A cheap but serviceable water-bath may be made from a quart milk-can, oil-can, tea-canister, or any similarly shaped tin vessel, by inserting the stem of a "glass funnel into the neck of the can through a well-fitting cork. In this funnel the dish containing the liquor to be evaporated rests. The can contains the water, which is to be kept just boiling. On account of the shape of the funnel, dishes of various sizes can be used with the same apparatus. , When a gradual and equable heat higher than can be obtained upon the water-bath is required, a sand-bath will sometimes be found useful. A cheap and convenient sand-bath may be' made by beating a disk of thin sheet-iron, about four inches in diameter, into the form of a saucer or shallow pan, and placing within it a quantity of dry APPESDIX. Pig. XXX. sand. The dish or flask to be heated is embedded in the sand, and the apparatus placed upon a ring of the iron -stand over a gas-lamp. ig. Self-regulating Gas-geUerator. — An apparatus which is always ready to deliver a constant stream of hydrogen, and yet does not generate the gas, except when it is immediately wanted for use, is a great conveliienee in an active laboratory or on a lecture-table. The same remark applies to the two gases, hydrogen sulphide and carbonic acid, which are likewise vised in considerable quantities, and which can be conveniently generated in precisely the same form of apparatus which is advantageous for hydrogen-. Such a generator may be made of divers dimen- sions. The following directions, with the accompanying figure (Fig. XXX), will enable the student to construct an ap- paratus of convenient size. Procure a glass cylinder 20 or 25 c. m. in diam- eter and 30 or 35 c. m. high ; ribbed candy-jars are sometimes to be had of about this size ; procure also a stout tubu- lated belLglass 10 or 12 c. m. wide and 5 or 7 c. in. shorter than the cylinder. Get a basket of sheet-lead 7.5 c. m. deep and 2.5 c. m. narrower than the bell-glass, and bore a number of small holes in the sides and bottom of this basket. Oast a circular plate of lead 7 m. m. thick and of a diameter 4 c. ni. larger than that of the glass cylinder ; on what is intended for its under side sykler three equidistant leaden strips, or a continuous ring of lead, to keep the plate in proper position as a cover for the cylin- der. Fit tightly to each end of a good brass gas-cock a piece of brass tube 8 c. m. long, 1.5 to 2 c. ni. wide, and stout' in metal. Perforate the centre of the leaden plate, so that one of these tuhes will snugly pass through the orifice, and secure it by solder, leaving 5 c. m. of the tnbe projecting below the plate. Attach to the lower end of this tube a stout hook on which to hang the leaden basket. By means of a sound cork and common sealing-wax, or a cement made of oil mixed ■with red and white lead, fasten this tube into the tubulure of the bell-glass air-tight, and so firmly that the joint will bear a weight of several pounds. Hang the basket by means of copper wire within the bell 5 e. m. ahove the bottom of the latter. To the tuhe which extends above the stop-cock attach by a good cork the neck of a tubulated receiver of 1(X) or 150 c. c. capacity, the interior of which has been loosely stuffed with cotton. Into the second tubulure of the receiver fit tightly the delivery-tube carrying a caoutchouc connector ; into this connector can be fitted a tube adapted to convey the gas in any desired direction. This apparatus is charged by placing the zinc, iron sulphide or marble, as the Ciise may be, in the basket, hanging the basket in the bell, and tlsen putting the bell-glass full of air into its place and closing the stop-cock; the cylinder is then filled with dilute acid to wthin 4 c. m. of the top. On opening the cock, the w^eiglit of the acid expels the air from the bell, the acid comes in con- tact with the solid in the basket, and a steady supply of gas is gener- ated until either the acid is saturated or the solid dissolved : if the cock be closed, the gas accumulates in the bell, and pushes the acid below the basket, so that all action Ceases. In cold weather the ap- paratus must be kept in- a warm place. For generating hydrogen, sulphuric acid diluted with four or five parts of water is used ; for hydrogen sulphide, sulphuric acid is diluted with fourteen parts of water ; for carbonic acid, chlorhydric acid diluted with two or three- jJaTts of water is to be preferred. 19. Glass Retorts, Flasks, Beakexs, Test-tubes, Teet- glasses and Bottles. — All glass vessels which are meant for use in heating liquids must have uniformly thin bottoms. Tubulated re- torts are much more generally useful than those without a tubulure ; as retorts are expensive in comparison with flasks, they are less used than formerly. The neck of a flask should have such a form that it can be tightly closed by a cork, and the lip must be strengthened to resist the force used in pressing in the cork, either by a rim of glass added on the outside, or better by causing the rim itself to flare outward. The actual edge of the rim must never be sharp or rough, but always smooth and rounded by partial fusion. Beakers are thin flat-bottomed tumblers with a slightly flaring rim. They are to be bought in sets or nests which sometimes include a large range of sizes. The small sizes are very useful vessels ; the large are so fragile as to be almost worthless. Up to the capacity of about a litre, beakers are to be recommended for heating liquids whenever it is an object to have the whole interior of the vessel readily accessible. Test-tubes are little cylinders of thin glass, with round, thin bot- XXX APPENDIX. tonis, and lips slightly flared. Their length may be from 12 c. m. to 18 c. m., and their diameter 1 c. ni. to 2 c. m. ; they should never have Fig. XXXI. a diameter SO large that the open end cannot be closed by the ball of the thumb. To hold the tubes upright a wooden rack is necessary ; besides the row of holes to receive a dozen test-tuhes bottom down, the rack should have a row of pegs on which the test-tubes may be inverted when not in use ; iii this position the water in which they are rinsed drains off, and dust cannot be deposited within the tubes. Test-tubes are much used for heating small quantities of liquid over the gas- or spirit-lamp ; they may generally be held by the upper end in the fingers without inconvenience, but if a liquid is to be boiled long in a test-tube, the tube must be held in wooden nippers (see Fig. 1), or in a strip of thick folded paper, nipped round the tube and grasped between the thumb and forefinger just outside the tube. The wooden nippers, above mentioned, are made of two bits of wood about a foot long hinged to- gether at the back, and at once connected and kept apart by a sliding steel or brass spring, somewhat like those used on certain pruning- shears and some kinds of steel nippers. When a liquid is boiling actively in a test-tube, it sometimes happens that portions of the hot liquid are projected out of the tube with some force ; the operator should always be careful not to direct a tube, which he is thus using, either towards himself or towards any other person in his neighbor- hood. Test-tubes are cleaned by the aid of cylindrical brushes, made of bristles caught between twisted wires, like those used for cleaning lamp-chimneys : they should have a round end of bristles. An excellent holder (see Pig. 35), devised by Professor Caldwell, is made of flexible copper or brass wire, 1-J m.m. thick. This wire is twisted about a cork which serves as a handle, or, being perforated, the cork may be slipped on to the rod of a ring-stand. By opening the coils at the ends more or less, it can be adapted to any test-tube or ignition tube, and the tube can be supported at any angle. Two precautions are invariably to be observed in heating test-tubes ; first, the outside of the tube must be wiped perfectly dry ; secondly, the tube must be moved in and out of the flame for a minute or two when first heated. It should be rolled to and fro also to a slight extent between the thumb and forefinger, in order that each side of it A PPEXDIX. XXxi may be equally exposed to the flame. A drop of water on the out- side of the tube keeps one spot cooler than the rest. The tube breaks, because its parts, being unequally heated, expand unequally, and tear apart. In heating glass and porcelain vessels of whatever form, the tem- perature nuist not be raised too rapidly. When a large flask or beaker containing a cold liquid is first warmed over a lamp, moisture almost invariably condenses upon the bottom of the vessel : tliis moisture should be wiped oft' with a cloth. Stout conical glasses with strong stems and feet are convenient for many uses not involving the application of heat. They are called test-glasses, and may be had of various shapes and sizes. It is obvious that cheap wine- or beer-glasses and common jelly-tumblers would answer the purposes which these test-glasses serve. For the collection of gases at the pneumatic trough, and for many other purposes, ordinary green glass " packing-bottles " may take the place of more expensive apparatus. The smaller sizes may be con- veniently used instead of beakers and test-glasses, but the bottles can- not be used for the heating of liquids. 20. Pipettes. — • Pipettes are tubes drawn to a point and some- times furnished with a bulb or a cylindrical enlargement. They are chiefly used to suck small quantities of fluid out of a j.^^ xxxn vessel without disturbing the bulk of the liquid. Fig. xxxn represents three forms of pipette ; the form with the lower end bent upwards is used to introduce liquids into a bell or bottle of gas standing over mercury. Pipettes graduated into cubic centimetres, or holding a certain number of cubic centimetres when filled to a mark on the stem, are often convenient. Measuring-glasses, divided into cubic centimetres, are made in the cylindrical form and also in the flaring shape common in druggists' mea-suring-glasses ; the cylindrical form, is to be preferred. Such a glass of 250 c. c, or better of 500 c. c. capacity, is a very use'ul implement : flasks holding I litre, 500 c. c, or 250 c. c, when filled to a mark on the neck, are also conve- nient. 21. Porcelain Dishes and Crucibles. — Open dishes, which will bear heat without cracking, arc necessary implements in the laboratory for conducting the evaporation of liquids. The best evap- orating-dishes are those made of Berlin porcelain, glazed both inside xxxii APPEyOlX. and out, anJ provided with a little lip projecting beyond the riro. The dishes made of Meissen porcelain are not glazed on the outside, and are not so durable as those of Berlin manufacture ; but they are much cheaper, and with proper caie last a long time. The siriall Berlin dishes will, generally bear an evaporation to dryness on the wiie-gauze over the open flaine of the gas-lamp ; the Meissen dishes ' do not so well endure this severe treatment. Evaporating-dishes are made of all diameters from 3 c. m. to 45 c. m. ; they should be ordered by specifying the diameter desired. The large sizes are expensive, and not very durable ; they should never be used except on a sand-bath. Dishes of German earthenware are as good as porce- lain for many uses, and are much to be recommended in place of the Fig XXXIII large sizes of porcelain dishes. Deep porcelain dishes provided with handles (called casseroles) are very useful in heating liquids which have a tendency to froth (see Ezps. Ill and 113), and may be obtained of various sizes. Very thin, highly glazed porcelain crucibles with glazed covers are made both at Berlin and at Meissen, near Dresden ; they are indispensable implements to the chemist. In general, the Meissen crucibles are thinner than the Berlin, but the Berlin crucibles are somewhat less liable to crack ; both kinds are glazed inside and out, except on the outside of the bottom. Crucibles should be ordered by specifying the diameters of the sizes desired ; they are to be had of nearly a dozen diflferent sizes, with diameters varying from 2 c. m. to 9 c. m. The smallest and largest sizes are little used ; for most purposes the best sizes are those between 3 c. m. and 5 c. m. in diameter. As the covers are much less liable to be broken than the crucibles, it is advantageous to buy more crucibles than covers, when- ever it is possible so to do. Porcelain crucibles are supported over the lamp on an iron- wire triangle ; they must always be gra *• i 1 cj 3 1