(itoxmll ^Ettibersits iLitratg. THE GIFT OF LONGMANS, GREEN & CO., lH-d^2.ru^.,l.3.'6.f..... Cornell University Library arV10354 The fundamental principles of chemistry 3 1924 031 234 564 olin.anx 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/cu31924031234564 CHEMISTRY PRACTICALLY TAUGHT NEW EDITION OF WATTS'S DICTIONARY OF CHEMISTRY. WATTS'S DICTIONARY OF CHEMISTRY. REVISED AND ENTIRELY RE-WRITTEN BY H. FORSTEB, MORLEY, M.A. D.Sc. FELLOW OF, AND LATELY ASSISTANT-PROFESSOR OF CHEMISTRY IN, UNIVERSITY COLLEGE, LONDON \ AND M. M. PATTI80N MTJIR, M.A. F.R.S.E. ELLOW AND PRELECTOR IN CHEMISTRY, OF GONVILLE AND CAIUS COLLEGE, CAMBRIDGE, ASSISTED BY EMINENT CONTRIBUTORS. To be published in 4 vols. 8vo. Vol. I. royal 8vo. price 42J. LIST OF CONTRIBUTORS TO VOL. I. W. OsTWALD, Ph.D. Professor of Physical Chemistrj^, Landwirthschaftliches In^ti- tut, Leipzig. R. T. Plimpton, Ph.D. Assistant-Professor of Chemistry at University Coll. London. William ^ Ramsay, Ph.D. Professor of Chemistry, University College, London. Thos. Stevenson, M.D. Lecturer at Guy's Hospital. C. S. O'Slillivan, Esq, F.R.S. Consulting Chemist, Burton-on- Trent. J.J. Thomson, M.A. /.R.S. Professor of Experimental Physics in the University of Cambridge. T. E. Thorpe, Ph.D. F.R.S. Professor of Chemistry, Royal School of Mines, South R. Warington, Esq. F.R.S. [Kensington. Chemistry in the Finsbury Technical ' C. J. Wilkinson, Esq. F.LC. Consulting College. I Chemist, University College, London. C. F. Cross, B.Sc. Consulting Chemist. William Dittmar, Ph.D. F.R.S. Professor of Chemistry, Anderson's Coll. Glasgow. A. G. Green, F.I.C. Research Chemist at Atlas Works, Hackney Wick. W. D. Halliburton, M.D. B.Sc. Assistant- Professor of Physiology at University College, London. J.J. Hood, Esq. D.Sc. F. R. Japp, M.A. Ph.D. F.R.S. Assistant- Professor for Research, Science Schools, South Kensington. E. Ray Lankester, F.R.S. Professor of Zoologyat University College, London. Lothar Meyer, Ph.D. Professor of Chem- istry in the University of Tubingen. Raphael Meldola, h'.R.S. Professor of The great advances in Chemistry made within recent years have rendered it almost imperative that a new edition of Watts's Dictionary should be prepared. Not only has an immense number of descriptive facts been added to Chemistry in the quarter of a century which has elapsed since the publication of the first edition began, but the whole aspect of the science, and its relations to other branches of natural knowledge, have greatly changed in that time. The changes have been so great and far-reaching that a new edition of a Chemical Dictionary which saw the light twenty-five years ago must needs be a new book. The new edition will occupy four volumes, of about 750 images each. To state the chief facts of the science, and to give an account of the generalisations, hypotheses, and theories — which are so all-important in Chemistry— in the allotted space, becomes possible only by putting every statement in the fewest words compatible with clearness and accuracy, and excluding all matters which do not belong to the domain of pure Chemistry. The present edition takes no cognisance of Technical Chemistry (this subject will be dealt with in a companion volume under the editorship of Professor Thorpe) ; Analytical Chemistry is treated in one general article, which is to be regarded rather as a guide to the principles of analysis than as a detailed description of particular methods. No articles on Physics will be found in this edition, but the applications of physical methods to chemical questions will be fully discussed. Importance has been put upon making clear the analogies and connexions between chemical facts, as well as cataloguing the facts themselves. Considerable space is devoted to accounts and discussions of important theories, but mere speculation has always been avoided. Attention has been paid to stating the physical constants which are of special chemical importance of each body mentioned in the book. The references to original memoirs are full and, it is hoped, accurate. The Editors have endeavoured to arrange the matter dealt with as clearly and methodi- cally as they can. It is hoped and expected that any chemist consulting the book will be able to find what he wants quickly and without much trouble. The Editors have obtained the help of many chemists —English, American, and foreign — of acknowledged repute. London : LONGMANS, GREEN, & CO. THE FUNDAMENTAL PRINCIPLES OF CHEMISTRY PRACTICALLY TAUGHT, BY A NEW METHOD ROBERT GALLOWAY, M.R.LA, F.C.S. HONORARY MEMBER OF THE CHEMICAL SOCIETY OF THE LEHIGH UNIVERSITY, U.S AUTHOR OF 'education, SCIENTIFIC AND TECHNICAL, OR HOW THE INDUCTIVE SCIENCES ARE TAUGHT, AND HOW THEY OUGHT TO BE TAUGHT ' ' A TREATISE ON FUEL, SCIENTIFIC AND practical' ETC. LONDON LONGMANS, GREEN, AND CO. AND NEW YORK : 15 EAST iS" STREET 1888 Q A II rights 7'eserved vi Fundamental Principles of Chemistry tary substances given in the usual text-books, involving a repetition of details as profitless to the general student as it is tedious and uninteresting.' The plan of this book is, I am confident, more in harmony with the laws of thought than the chemical text-books that are in use in schools, and for teaching junior students generally. Many of these books afe little more than mere compilations of unclassified facts ; hence the reason is not cultivated, and consequently the science is not attained ; for unless the first is reached, the second is not gained. As the student cannot be properly instructed in chemistry without having previously acquired a knowledge of the physical properties of matter and the physical forces, I have com- menced with a course of physics suitable for the course of pure chemistry given in the after part of the work. In the teaching of this portion of the work the exercises, illustrations, &c., have been selected to bear on the after course, and on chemical operations generally ; thus, in explaining porosity, filtration is illustrated and taught practically ; the collecting and storing of gases under impenetrability ; the determination of boiling- points, fractional distillation, &c., under heat ; the action of charcoal and dyeing under adhesion, &c. ; so that when the purely chemical portion of the work is reached the student will not be perplexed and impeded when, in describing chemical operations and chemical properties, reference has to be made to physical properties and physical forces, as he has already become practically acquainted with them. The principles, both in the course on chemical physics and on pure chemistry, are taught by experimental and arithmeti- cal exercises and examination questions ; the questions, both on physics and chemistry, which I have not framed myself, have been taken mainly from the examination papers of the London University, the Royal University of Ireland, and Owens College, Manchester ; and they and the exercises have been selected so as to impart a wide and sound knowledge of the different subjects dealt with : answers to many of the exercises are given at the end of the work. The language of the science and the mode of expressing chemical changes are taught in a series of progressive exercises, which will give the student a Preface vii complete mastery over it. It being all-essential that the student should at an early period of his studies become acquainted with the language, this is essentially necessary, for without a know- ledge of it he would be unable to think and reason about the science, because language is the atmosphere in which thought lives. It is for this reason the student is directed to pass over portions of Chapters VI., IX., XI., XII., XIII., until he has reached and studied Chapter XIV., as he has then completed the study of the language, and he is thus enabled to study more intelligently the more advanced portions of these chapters. This book is complete on all the subjects it treats upon ; but should its sale justify it, a second volum#will be published giving the advanced portions of the science which have not been dealt with in this. I am greatly indebted to two friends and former students, Mr. James Roberts, LL.B., Barrister-at-Law, and Mr. Thomas Bayley, consulting chemist, in kindly assisting me in eliminating errors. ROBERT GALLOWAY. LoiSTDON : February 1888 Missing Page Missing Page X Fundamental Principles of Chemistry CHAPTER V. Density— Specific Gravity. PAGE Absolute Density — Specific Gravity — Difference between Density and Specific Gravity — Specific Gravity of Liquids — Exercises-- Specific Gravity of Solids — Exercises — Tables of Specific Gravi- ties, their Use — Exercises — The Hydrometer, its Use — Specific Gravity of Mixtures — Exercises — Experimental Exercises — Weight and Specific Gravity of Gases — Exercises — Specific Gravity of Vapours —Exercises — Questions . . . .123 CHAPTER VI. Sublimation — Solution — Precipitation. SubHmation — Experiments — Simple^ Solution — Experiments— Crys- tallisation — Experiments— Questions — Chemical Solution — Ex- periments — Precipitation 154 CHAPTER Vn. Adhesion — Capillary Action. Adhesion — Capillary Action — Experiments — Adhesive Action of Charcoal — Experiments — Dyeing — Experiments — Questions . 163 CHAPTER Vni. Elements and Compounds — Chemical Affinity. Chemical Affinity — All Substances either Elementary or Compound — Distinction between Elementary and Compound Substances — Classification of the Elements — Exercises — Elements can Com- bine Together — Experiments — Characters of Chemical Attraction The Differences between a Mixture of Substances and a Chemical Compound — Changes which attend Chemical Combination — Experiments — The Different Elements do not Unite with equal Facility — Experiments — Temperature at which Combination takes place — Experiments — Suspension of Chemical Action by Depression of Temperature — Experiments — The Terms Em- ployed in Ordinary Language to Express the Chemical Union of Substances — Experiments — Development of Heat by Chemical Action — Experiments — Influence of Pressure on the Heat and Light of Combustion — Experiments — Questions . . .170 Contents xi CHAPTER IX. The Different Classes of Compound Substances. PAGE Combination of a Compoiind with an Additional Quantity of one of its Elements — Experiments — Combination of a Compound with another Element — Basic Oxides and Acid Oxides — Hydroxides — The Action of Bases and Acids on Test-Papers — Combination of Compound Substances — Salts — Experiments — The Solid State less favourable to Chemical Action than the Fluid State — Experiments — Relative Intensity of Affinity — Experiment — Questions^The Physical and Chemical Properties of the more commonly occurring Elements — Their Extraction from their Compounds — Questions 205. CHAPTER X. General Laws of Chemical Comkination. Laws of Combination — Law of Definite Proportions — Exercises — Law of Equivalent Proportions — Law of Multiple Proportions — Atomic Constitution of Matter — Gay-Lussac's Law of Volumes— Experiments — Exercise — Atoms and Molecules — Avogadro's Law — Table of the Molecular Weights and Volumes of the Gaseous and Vaporisable Elements^The Volume-Weights of Elements and Compounds — Exercises — Atomicity — Graphic Notation -r Classification of the Elements according to their Atomicity — Exercises — Questions ...... 227 CHAPTER XI. Nomenclature and Notation — Basic Substances. Chemical Nomenclature and Notation — Exercises — Basic Substances — Table of the more commonly occurring Bases — Basic Sulphides — Exercises — Questions — The Methods adopted for Preparing the Bases — Table showing, the Solubility of the Bases in Water and the Alkalies — Exercises — Questions . . . . ,261 CHAPTER XII. Acids and Acid Anhydrides. Characteristics of an Acid — Acids either monobasic or polybasic — A List of Acids and Acid Anhydrides— Nomenclature of the Anhydrides and Acids — Graphic Notation of these Substances — Questions — ^The Methods for preparing the Acids and Anhy- drides, with a Description of their Properties — Exercises — Action of Acids upon Salts — Exercises — Questions . . . ' . 280 xii Fundamental Principles of Chemistry CHAPTER XIII. Salts — Their Formation and Properties. PAGE Salts — Their Classification — Acid and Normal Salts — General FormuljE of Salts — Exercises — Basic and Double Salts — Solu- bility of Salts — Supersaturated Solutions — Water of Crystallisa- tion — Cryohydrates — Saline Water— Freezing Mixtures — Iso- morphism — Exercises — Questions — Table of the Solubility of Salts — Action of Metals upon Salts — Experiments — Action of Salts upon each other — Experiments — General Properties of the Salts — Tests for the Acid-radicals — Experiments — Illustrations of the Methods adopted for distinguishing and separating Sub- stances from each other — Exercises — Outline of Volumetric Methods — Exercises — Questions ...... 300 CHAPTER XIV. On the Moue of Expressing Chemical Changes — Exercises— Appendix .... 338 CHAPTER XV. Combination of Similar Atoms— Determination of Atomic Weights. Combination of Similar Atoms — The Nascent State — AUotropy — Determination of the Atomic Weights of the Elements — Physi- cal and Chemical Relations of Atomic Weights— Questions . 346 Answers to the Exercises 357 Errata. line 29, fo; 216, Page 145, line z^, for (P-/) = _Z^ read {V - p) ^'^- 4 — I H - ■""^ )i 30, yir 644 ?-fa(^ 643. „ 31, for 670 read 673. ,, ^6, for 721 read 724. ,, 26, _/»r 700 r«ffifl? 703. ,, 2"], for 661 read 664. 760 THE FUNDAMENTAL PRINCIPLES OF CHEMISTRY. CHAPTER I. MATTER — STATE OF AGGREGATION OF BODIES — PHYSICAL PROPERTIES OF BODIES — EXPERIMENTS — MOLECULAR FORCES — COLLECTING AND STORING GASES— FITTING UP CHEMICAL APPARATUS — QUESTIONS. I. Those who take up this book with the intention of studying it, will, no doubt, have heard the word matter em- ployed in conversation, and they will also have without doubt met with it in some of the books they have read ; and most probably they themselves will have used it both in conversation and in writing ; they must therefore have attached some meaning to this important word, for it is a very important word, especially for what it signifies in Natural Science. I wish those studying this book to reflect for a few moments before going further as to the meaning they attached to it when they or others employed it. Like many other words it is employed both in ordinary and scientific language. The following are a few of its meanings in ordinary language, and they are given in order to impress on the young student, that whilst a word has many different significations in ordinary language, it has one, and only one, in the particular department of science in which it is employed as a scientific term ; hence one word cannot be substituted for another in scientific, as it frequently can in ordinary, language to convey the same idea ; just as, for instance, if we speak of any tool, say a spade, hammer, &c., we cannot substitute any other word for the word spade or hammer, B 2 Fundamental Principles of Chemistry as no other word would convey to other minds the particular tool we meant. The student will, we hope, gather from these marks the imperative necessity of learning, in order to become acquainted with a science, the exact and precise meaning of every scientific word and phrase employed. 2. The following are a few of the meanings of the word ' matter' as given in dictionaries : — I. The contents of any speech or writing; the thing said ; the mean- ing ; sense. (2) Good sense ; substance, as opposed to empty verbosity or frivolous jesting. 'To speak all mirth and no matter.' (3) Subject; thing treated ; that about which we write or speak. (4) Affair ; business ; event; course of things; as 'Mattershave succeeded well thus far'; 'Observe how matters stand ' ; ' Thus the matter rests at present ' ; ' Thus the matter ended.' (5) In logic that which forms the subject of any mental operation, as distinguished from the form. (6) Body ; substance extended ; anything perceptible by any of the senses ; that of which the whole sensible universe is composed. 3. The last meaning is the only one in which it is used in Natural Science, or, in other words, when its meaning is confined to the Material World. For when employed in Natural Science it includes, but is restricted to, everything which possesses weight and occupies space ; these are termed the essential properties of matter, since they suffice to define it. 4. A young child knows from observation that all matter is not of the same kind, but that there are many different kinds; there are, for example, gold, silver, iron, copper, sulphur, common salt, chalk, and a very large number of other kinds of matter. Now each of these different kinds of matter is termed a substance or body ; and each substance exists in one or other of the three states of aggregation in which matter can exist, viz. the solid, the liquid, and the gaseous state ; some substances exist naturally in only one of these states, as, for example, gold, silvfer, or iron in the solid state ; but most of them, and perhaps all of them, can be made to pass into one or both of the other states in which they do not naturally exist, by the application of heat, cold (diminution of heat), or pressure ; or by a com- bination of pressure and one of the other two agents, as we shall learn further on. Water, for example, exists naturally in all the three states ; in all climates it exists in the liquid state ; and in all climates it exists in the gaseous or vaporous state in the air ; and in the Arctic regions, and in temperate climates Law of Gravitation 3 in winter, it exists in the solid state as ice and snow. Some of the water in the gaseous state in the air passes, or becomes converted, into one of the other two states of aggregation, owing to a diminution of temperature in the atmosphere; it then appears in the form of dew, or comes down to the earth in the form of rain — the liquid state, or of hail or snow — the solid state. 5. It has already been stated that all substances, whether existing in the solid, the liquid, or the gaseous state, occupy a certain space ; the amount of space a substance occupies is termed its volume. 6. Every particle of matter attracts every other particle of matter, whether the matter exists in the solid, the liquid, or the gaseous state, not only in the world we dwell in, but through- out the entire universe ; this attraction is called the Law of Gravitation. This force or attraction operates at the greatest conceivable distances, and is common, as we have stated, to the three forms of matter, and as each particle attracts, the mass containing the greatest number of particles must consequently exert the greatest attractive force ; hence it is that all bodies, with the exception of the celestial ones, when at some distance from the earth's surface and unsupported, fall or descend to it. One of the effects of this attraction is the downward pres- sure which substances exert on whatever supports or prevents them from falling to the earth ; this pressure is termed their ■weight. 7. The word ' particle ' which has been employed has several different meanings in ordinary language, but it is only necessary to give the one which corresponds with its scientific meaning, viz. 'a minute part or portion of matter, the aggre- gation of which parts constitutes the whole mass ; ' this cor- responds with its scientific meaning, for the smallest portion of matter which is mechanically divisible is termed a particle. But it is believed by scientific men that there are more minute portions of matter than particles ; these minute portions are indivisible ; the largest of these mechanically indivisible portions are termed molecules ; the molecules are chemically divisible; the still smaller portions, which are both mechanically and chemically indivisible, are termed atoms. 4 Fundamental Principles of Chemistry 8. Before going further we must inform the student that the terms particle and molecule have been used indiscrimin- ately, and in some scientific works at the present time the word particle is sometimes used in place of the word molecule ; but in this work the two words have separate and distinct meanings; particle being employed to signify the smallest portion of matter that is mechanically divisible ; molecule the smallest 'portion which can exist in the free slate, and which is mechanically in- divisible but chemically divisible. 9. It will be evident to the student from what has been stated that the minutest particle is an aggregation of molecules, as a mass of matter is an aggregation of particles. Science cannot at present inform us how many molecules are required to form the minutest particle ; but, to form an idea of the size of molecules, Sir William Thompson gives this illustration. Imagine a drop of rain, or a glass sphere the size of a pea, magnified to the size of the earth, the molecules in it being in- creased in the same proportion ; the magnified structure would be coarser-grained than a heap of small shot, but probably less coarse-grained than a heap of cricket-balls. The number of molecules of gas in a cubic centimetre (0-06103 cubic inch) of air is calculated at twenty-one trillions. Molecules and atoms are treated of in a subsequent chapter. 10. We will here cite a few examples to show to what an almost incredible extent matter admits of being subdivided ; and the minuteness of some organised bodies. 1. ' WoUaston succeeded in obtaining threads of platinum of a diameter not exceeding 3pn^,)„„ of an inch. The method which he employed for preparing them consisted in drawing a silver wire with a platinum core, and dissolving the shell of silver in nitric acid. In this way threads can be ob- tained so fine that they are actually invisible to direct view ; their existence can only be detected by the aid of certain special optical phenomena. In the art of beating gold, leaves are obtained whose thickness cannot exceed 55^55 of an inch. A square inch of this leaf would weigh less than the jjjljg of an ounce, and as a square whose side is jL of an inch is visible to the naked eye, it follows that this square inch of leaf contains more than 60,000 visible parts.' 2. ' According to Biot, the thread by which a spider lets itself down is composed of more than 6,000 single threads. But more surprising than all is the microcosm of organised nature in the infusoria. Of these creatures, which for the most part we can see only by the aid of the microscope, there exist many species so small that millions piled on each other would not equal a single grain of sand, and thousands might swim at once through the Divisibility of Matter 5 eye of the finest needle. The coats-of-mail and shells of these animalcules exist in such prodigious quantities on our earth that, according to Ehrenberg's investigations, pretty extensive strata of rocks, as, for instance, the smooth slate near Belin, in Bohemia, consist almost entirely of them. By microscopic measurements, one cubic inch of this slate contains about 41,000 millions of these animals. Since a cubic inch of this slate weighs 220 grains, 187 millions of these shells must go to a grain, each of which would consequently weigh about the j|ymillionth part of a grain. Conceive further that each of these animalcules, as microscopic investiga- tions have proved, has its limbs, entrails, etc. , the possibility vanishes of our forming the most remote conception of the dimensions of these organic forms. 3. 'The two following examples show that when substances evade the perception of our sight and touch, our olfactory nerves frequently detect the presence of matter in the atmosphere, of which no chemical analysis could afford us the slightest intimation. 4. ' It is well known that a grain of musk will continue for years to supply the air, which is continually being renewed around it, with a suffi- cient number of particles to communicate to it its odour ; and papers laid near musk may be conveyed to the East Indies and back without losing the smell. The mind cannot form an idea of the number of f articles which must volatilise from the musk every second, in order to render the scent perceptible in all directions ; and not only of their number, but also of their minuteness. In like manner a single drop of oil of lavender evapo- rated in a spoon over a lamp, fills a large room with its fragrance for a length of time. ' 11. These and numerous other examples, which might be given, would, if there were no opposing facts, lead us to believe that matter can be infinitely divided ; but our present interpre- tation of chemical phenomena leads us to assume that there is a limit, as we have previously stated, and shall more fully ex- plain further on, to the division of matter. 12. When particles cohere together then, as has been stated, a mass of matter is formed ; and the more numerous the particles cohering, the larger, of course, the volume of the mass ; a piece of lump sugar, for example, is an aggregation of a number of particles of that substance. In some substances the particles are, as it were, indiscriminately united ; in other substances they are arranged in a crystalline form, as seen in sugar, alum, epsom salts, &c. 13. The particles cohere together in different solid sub- stances with very different degrees of attractive force ; some solids, for instance, are very easily pulverised, that is their particles are very easily separated ; other solids, on the contrary, resist pulverisation by ordinary means. The particles of the substances employed as building materials, as stone, iron, &c., 6 Fundamental Principles of 'Chemistry are united very firmly together ; hence the great strength of these substances ; and this is the case with all solids whose particles are, like the solids named, firmly bound together. We may here state, what has already been implied, that each particle of a pulverised body possesses the same properties or qualities as the entire mass did before pulverisation. 14. In some cases if the parts of the same substance which have been divided are brought into very intimate contact they will unite ; thus on pressing together two clean, smooth, and freshly cut surfaces of lead, they cohere, and a force of some pounds is required to separate them. In the same way, two perfectly polished plates of glass cohere, sometimes so com- pletely that they may be cut and worked as a single piece. This has not unfrequently happened in plate-glass manu- factories. No doubt two pieces of all substances might be made to cohere, as lead does, if they could be brought into sufficiently intimate contact. When it is desired to unite two pieces of a metal like iron, which cannot be made to unite by simply pressing them together, the cohesion between the particles of each piece is first weakened by heating them ; the consequence is they become quite soft, and can be readily bent ; when they are pressed or hammered together in this state they cohere and form one piece ; this operation is termed ■welding. 15. However compact a substance in the solid state may appear, its molecules are not in actual contact, there are spaces or pores, as the spaces are termed, between the molecules. The Florentine Academicians in 166 1 proved the existence of pores between the molecules of so compact a solid as gold ; they proved this by filling a thiri globe of gold with water, and after hermetically sealing its orifice subjected the globe to pressure ; the result was, that the water was forced through the pores of the gold, and appeared in the form of dew, on the outer surface of the globe. In the building of the Britannia bridge it was also found that the water used in the enormous hydrostatic presses employed to raise the tube, was freely forced through the pores of the thick iron cylinders of the press. ' I ' No decisive proof of the porosity of vitreous bodies, such as glass, seems yet to have been obtained. That they form almost a solitary class of excep- ■Experiments on Porosity 7 16. There are two kinds of pores, viz., sensible pores and physical pores ; the sensible pores are apparent to the eye, either alone or aided by the microscope. Filtration is an application or utilisation of the porosity of certain substances, as paper, woven fabrics, stones, &c. ; the sensible pores of these substances are sufficiently large to allow liquids to pass through them, but small enough to arrest the passage of solid particles which may be suspended in the liquid. 17. The physical pores are not apparent to the sight, and are the spaces or intervals between the molecules. 18. The space between the molecules can be diminished to a greater or less extent, in other words the molecules can be forced nearer to each other by the action of external pressure. This property is called compressibility, and is both a conse- quence and a proof of their porosity. Experiments on Porosity. 1. Immerse a piece of chalk in water, air-bubbles will at once begin to ascend to the surface of the liquid, in consequence of the water displacing the air in the pores of the chalk. 2. Pour some water on a piece of marble ; the water will rest on the surface, it will not enter into the pores, unless great pressure is used and for a sufficient length of time. Yet chalk and marble are formed of the same constituents ; they differ only in their physical properties ; and this difference is chiefly, if not entirely, due to the cohesiveness being less between the particles of the chalk than between the particles of the marble, and therefore the greater porosity of the former than of the latter substance. 19. Different liquids possess different degrees of facility for penetrating the pores of solid bodies ; for instance, if pohshed marble is wetted with water very little, if any, enters its pores, while oil, on the contrary, is rapidly absorbed by it ; and a bag of cambric or gauze, whose pores are visible to the eye, holds mercury securely, until sufficient pressure is applied to force out the liquid. 20. As filtration is in constant use in chemical laboratories, and as it is also a utilisation of the porosity of substances, we will now describe the operation, and illustrate it with experi- ments. Filtration is employed for separating liquids from tions to an otherwise general rule seems highly, improbable. It is most likely that vitreous bodies have not yet been proved to be porous only because we have not yet discovered the proper mode of testing them for this property. 8 Fundamental Principles of Chemistry solids, and usually is accomplished by passing the mixture of solid and liquid matter through filtering paper (a paper made for the purpose) of proper size and shape, supported in a funnel. The pores of the paper permit the fluid, and the solids dissolved in it, to pass, whilst the undissolved solid matter being unable to pass through the pores, remains behind on the filter. Sometimes, however, the undissolved solid matter is in such a finely divided state that the filter does not at first intercept all the solid particles, some portion passing through the pores of the filter ; in such cases the imperfectly filtered portion must be returned to the filter until it becomes perfectly bright and clear. 21. If any coloured solid dissolves in the liquid the liquid, even when perfectly filtered, will not be colourless, but coloured. 22. To prepare a filter, cut the filtering paper in circular form, and fold it so as to form a half-circle, and then again fold it at right angles to the first fold (fig. i) ; the paper ought to fall wholly within the funnel (fig. 2). The paper, when placed within the funnel, must be mois- FlG. I. tened with water, and then the liquid to be' filtered must be gradually poured on. The funnel is supported in one of the rings of the retort-stand (fig. 2). 23. The liquid which passes through the filter is called the filtrate. When the solid particles are very heavy, the superna- tant liquid can be separated from the solid, without passing it through a filter. This is accomplished by simply inclining the COHBSIOM 9 vessel, so as to allow the fluid to pass away unattended by the ' undissolved solid '; this is called decantation; or the fluid may be removed by a syphon. Experiments on Filtration. 3. Mix some powdered chalk with water ; then pass the mixture through a filter ; if the filtrate comes through turbid at Srst (not clear), return it to the filter as often as is necessary to obtain it perfectly clear and bright. 4. Mix some soil with water ; a portion of the soil will dissolve in the water, and a portion will remain undissolved ; subsequently filter the solu- tion ; the filtrate will most probably be coloured, on account of some of the coloured components of the soil having dissolved in the water. 24. We have yet to mention a remarkable class of illustra- tions proving the porosity of solid bodies. Not only can gases pass through unglazed pottery, but hydrogen, the lightest of known gases, can pass through platinum and iron when they are red-hot ; but we must reserve any further remarks on the passage of gases through metallic and non-metallic septa until we treat on the motion of gases in Part II. 25. The cohesive attraction between the molecules of sub- stanfces varies not only in different substances, that is in sub- stances of unlike constituents, but also, as shown by Expt. 2, in some substances composed of- the same constituents ; and an alteration in the molecular attraction can in some solids be produced by artificial means, the difference in the mechani- cal properties of tempered and untempered steel, for example, is owing to the difference in the molecular attractions produced by the tempering. 26. It is owing to a natural difference in the molecular attraction in some solids, and to the alteration which can be effected in the molecular arrangement in others by the action of physical agents, that solids vary, or can be made to vary, in the properties of hardness, tenacity, ductility, and malleability. Silver, gold, and platinum, which are the most ductile and malleable of the metals, can be drawn out into the form of wire, or beaten out in the form of thin leaves to an almost in- conceivable extent without any rupture or breach of continuity between the molecules taking place. Platinum, which is the most ductile of metals, has been drawn out into wire so fine that it was only o'oooo3 of an inch in diameter ; and gold, lo Fundamental Principles of Chemistry which is the most malleable of metals, has been beaten into leaves so fine that they were only about jj^^th of an inch thick. 27. Ductility and malleability are not the same property or quality ; for the same metals are not always both ductile and malleable, or do not at least possess these properties in an equal degree. Iron possesses ductility in a much greater degree than it possesses malleability ; for it admits of being drawn into extremely fine wire, though it cannot be beaten into extremely thin plates. Tin and lead, on the other hand, are highly malleable ; they can be beaten into extremely thin leaves ; but they are not ductile, since they cannot be drawn into fine wire. 28. A property the very opposite of malleability and duc- tility is brittleness ; the molecules of brittle substances do not, as in malleable and ductile solids, admit of any very con- siderable displacement without losing their cohesiveness ; in other words a brittle substance cannot be nmch altered in form without breaking. 29. We must now explain the meaning of the word properties we have been employing. By the term properties, as applied to bodies, we understand the different ways in which bodies present themselves to our senses, and we distinguish general from specific properties. The former are shared by all bodies, and among the most important are impenetrability, extension, divisibility, porosity, compressibility, elasticity, mobility, and inertia. 30. Specific properties are such as are observed in certain bodies only, or in certain states of these bodies ; such are solidity, fluidity, tenacity, ductility, malleability, hardness, trans- parency, colour, &'c. 31. We have so far, in speaking of the cohesion of the molecules of bodies, confined and limited our descriptions and illustrations to solid bodies ; we have now to notice how far this attraction between the molecules of the same substances operates in bodies that are liquid, and in bodies thait are gaseous at ordinary temperatures. 32. As regards the particles of liquids, they have, as com- pared with those of solids, no fixed position, on account of the less cohesive attraction between them ; hence they glide or pass over each other with the greatest ease, being displaced by Cohesion i i the slightest force ; liquid bodies on this account are capable of assuming the shape of any vessel in which they are placed. But there is nevertheless a greater or less cohesion between the molecules of liquids, which causes them to be more or less viscous. But the cohesive power between the molecules of liquids is more strikingly shown in the rounded form assumed by detached drops ; this is very beautifully exemplified in rain- drops as they fall through the air, and in drops of dew ; in these small masses, water, as is seen, assumes the spheroidal shape. 33. The difference in the form assumed by large and small masses of liquids is thus explained — in large masses the force of gravity overcomes the cohesive force ; hence liquids acted upon by the former force have no specia.1 shape ; they take that of the vessel in which they are contained ; and the free surface of the liquid is a horizontal plane perpendicular to the force of gravity. But in smaller masses cohesion overcomes the force of gravity, and therefore in minute masses liquids assume the spherical or globular form. Experunents Illustrating the Tendency of Liquids in Small Masses to Assume the Spherical Form. 5. Introduce by means of a pipette (fig. 3) a drop of oil into the middle of some alcohol which has been diluted with water to precisely the same specific gravity as the oil ; the two liquids will not mix with or dissolve each other, but the oil will remain suspended in the diluted alcohol in the form of a perfectly spherical mass. 6. Pour into a narrow-necked bottle a saturated solution of zinc sulphate, add a few drops of carbon disulphide, coloured by some iodine dissolved, which will float on the surface of the zinc solution.. Then carefully add some distilled water so as to make it rest on the surface of the zinc solution and not mix with it ; the carbon disulphide will, if these conditions have been obtained, collect in the form of a flattened spheroid, presenting the appearance of blown coloured glass, and will be larger than the neck of the bottle if a sufficient quantity of the carbon compound has been employed. 34. The Florentine Academicians made the ex- periment which has already been described (par. 15) not for ascertaining whether solids were or were not porous ; but whether liquids were or were not com- pressible; the liquid they operated upon, as already stated, was water. As the globe was completely filled with 12 Fundamental Principles of Chemistry water, any pressure on it they expected would, by altering its shape and diminishing its capacity, either compress the liquid, if it were compressible, or, if it were incompressible, would burst the globe. Neither of these expected results occurred ; but, contrary to the expectations of the experimenters, the ex- periment proved that gold was porous. 35. The Academicians inferred, from the results of the experiment, that water was not compressible, and this opinion was accepted as correct for some time afterwards ; but later re- searches have proved that all liquids are compressible, but only to a slight degree as compared with either solids or gases. Thus, for a pressure equal to that of the atmosphere — 15 lbs. per square inch— mercury experiences a compression of o'ooooog part of its original volume, water a compression of 0-00005, and ether a compression of 0-000133. The compressibihty of Hquids is, however, greater the higher their temperature ; thus that of ether at 14 °C. is one-fourth greater than its compressibility at 0° C. The apparatus employed for measuring the compres- sibility of liquid is named the piezometer, the term being derived from two Greek words, one signifying ' I compress,' and the other 'measure.' 36. As liquids are compressible their molecules, as in the case of solids, are not in actual contact, but are separated by spaces termed pores. The pores in liquids are not so obvious as they are in many solids, but it is none the less certain that they exist in liquids as in solids ; this is proved not only from their being compressible ; but also from the fact that two liquids that can mix together will, when added together, ■ often occupy a less volume than the two occupied before being mixed. Experiment on the Porosity of Liquids. 7. Half-fill with water a glass bottle, in shape like the specific gravity bottle (fig. 47), and fitted with a ground stopper, then pour some alcohol carefully down the inside of the vessel, so as not to mix the two liquids. The bottle should be so filled that a few drops of alcohol are pushed out when the stopper is inserted ; this must be done in such a careful manner that no air-bubbles enter the bottle. Raise the bottle between the thumb and fingers, press the forefinger firmly on the stopper, and then invert the bottle several times so as to mix the two liquids together. When they are thoroughly mixed, it will be seen, on placing the bottle on the table, that Elasticity, Ductility, and Malleability 13 the volume of the mixed liquids is less than they occupied before they were mixed, hence proving their porosity. The same phenomenon may be ob- served in mixing many other liquids. If the water is coloured red with a solution of aniline-red (magenta), it will be seen whether the alcohol has been successfully introduced into the bottle. 37. When the external compressing force is removed, liquids always regain exactly their original volume. Bodies which re- cover their original form perfectly on the removal of the external pressure are said to be perfectly elastic under compression ; if they only partially recover their original shape, their elasticity is said to be imperfect, and they remain distorted permanently. All liquids and gases are perfectly elastic, but no solid is perfectly elastic, this property being always confined in sohds within certain limits. Imperfect elasticity gives rise to the re- markable properties of ductility and malleability in some solids, properties we have already noticed. 38. The elasticity we have been speaking about is called the elasticity of compression. Two other kinds of elasticity are recognised, viz., the elasticity of extension, and the elasticity of torsion. Liquids and gases possess only the elasticity of compression ; the other two kinds are possessed by soUd bodies only. The student is referred for further informa- tion on these two latter kinds of elasticity to works on natural philosophy. 39. There is no cohesive attraction between the particles of gaseous bodies ; they actually repel each other, and to such an extent does this repulsion extend, that the particles of a gas not confined in a close vessel, or subjected to some external pressure, would disperse in all directions, owing to their mutual repulsion ; they, therefore, exert a pressure in an outward direction upon the sides of the vessels which contain them ; and the pressure is greater or less according as the elasticity of the gas is increased or diminished. 40. Owing to the absence of any cohesive attraction be- tween their particles, gases are much more compressible than either solids or liquids ; by sufficient pressure they may be made to occupy ten, twenty, or even some hundred, times less space than they occupy under ordinary circumstances. There is, however, a limit beyond which, when the pressure is in- creased, they are converted into the liquid state. 14 Fundamental Principles of Chemistry 41. In regard to their greater compressibility, gases dififer in a marked manner from liquids ; and they differ also from liquids, in that all gases follow the same law of compressibility, whereas every liquid, like every solid, has a degree of compres- sibility peculiar to itself, that distinguishes it from every other liquid. In Chapter III. this subject will be fully considered ; at present we will simply state the law of compressibility that gases follow in general terms : the volume of a gas varies in- versely as the pressure to which it is exposed ; consequently by doubling the pressure we halve the volume, by trebling it we reduce it to one-third ; but the elasticity is increased directly as the pressure ; by doubling the pressure we double the elasticity. 42. Their high compressibility is a proof of their great porosity ; for it is the pores, and not the molecules, that are made smaller by compression. Water, for instance, when converted into steam at the ordinary atmospheric pressure, and at the ordinary temperature of boiling water, expands 1,700 times, so that a cubic inch of water gives about a cubic foot of steam ; the number of molecules has not of course increased in the conversion of the water into steam, nor have we any reason to suppose any increase in their size ; the greater space occupied by the steam appears to be due solely to the spaces between the molecules being much greater in the gaseous than in the liquid state. 43. The distinguishing characters of the three states of aggregation in which matter can exist are briefly : — Solid bodies. — Definite shape. Definite volume. Liquid bodies. — Indefinite shape. Definite volume. Gaseous bodies. — Indefinite shape. Indefinite volume. Experiments lllustrati?ig the Expansibility, the Compressibility, and the Porosity of Gases. 8. A glass retort is partly filled with water and inverted, as shown in fig. 4. By sucking at the aperture a the water rises at b, and sinks at c ; the air in the bulb of the retort above c expanding. But by firmly closing the lips round the aperture a and strongly blowing into the beak of the retort the water will sink in the beak and rise in the bulb ; the air in the bulb above c being compressed. 9. A cork, which must fit tightly into the mouth of a round white Expansibility, etc., of Gases 15 medicine bottle, is pierced with a round file, or cork -borer, and one end of a glass tube is fitted tightly into the hole, and the other end of the tube is fitted tightly into another pierced cork ; this latter cork is inserted into the mouth of a calf s bladder which has been filled with water ; the neck of the bladder is tied tightly round the cork. The other cork is then fitted tightly into the mouth of the bottle ; when this is done, the bottle is placed in a vertical position (fig. 5). If the bladder be now strongly pressed with the hand, some of the water will pass into the bottle ; owing to the compression of the air in the bottle, when the pressure is removed from the bladder, the air within Fig. 4. Fig. s. the bottle expands again to its original volume, driving the water back into the bladder. 10. Plunge a round-bottomed flask of a pint or a quart size, with its mouth upwards, into some boiling water ; the water must not be allowed to enter the flask ; keep it in the water until it is well heated ; on removing it out of the water, introduce a few firagments of iodine into it, and im- mediately close its mouth with a cork. The iodine will be vaporised ; the vapour, which is of a beautiful violet colour, will fill the flask, proving that the air is highly porous, for the iodine vapour diffuses in the flask, although it is already filled with air. The flask is warmed, not only to volatilize the iodine, but also to prevent it from being immediately con- densed in the upper part of the flask, which would occur if that portion of the flask were cold. 44. The attraction between the molecules of the same kind of matter is due to a force which has been called the force of cohesion or the cohesive force. Unlike the attraction of gra- vitation, which tends to draw together dissimilar, as well as similar, kinds of matter, and in the mass, and ' which operates through distances so vast that the mind is lost in the attempt to estimate and explore them,' the cohesive force is exerted only through distances so minute as to be inappreciable to our unaided senses, and between molecules of the same kind of matter ; it is one of the molecular forces — that is, one of the forces which act only between molecules at exceedingly minute distances. 1 6 Fundamental Principles of Chemistry 45. Reacting against this and the other molecular forces — these we shall notice further on — is the repulsive power of heat ; and upon the relative intensity of these two opposing forces — cohesion and repulsion — depends the solid, fluid, or gaseous condition of matter. When the cohesive force prevails, bodies exist in the solid state ; when the repulsive power is in the ascendant, matter, as we have learned, assumes the gaseous form ; and when the two forces are balanced, the liquid state is the result. 46. We must here explain the meaning of the term ' force ': ' When a body is at rest it has no innate power of changing its state of rest ; when it is in motion it has no innate power of changing its state of uniform motion in a straight line. This property of matter is termed its inertia. Any cause which sets a body in motion, or which changes the magnitude or direction of its velocity if in motion, is z. force. Gravity , friction, elas- ticity of springs or gases, electrical or magnetic, attraction or repulsion, etc., sxe. forces. All changes observed in the motion of bodies can be referred to the action of one or more forces.' 47. Before treating at greater length on the repulsive power of heat, it is desirable to notice another general property of matter, viz. impenetrability. Impenetrability is that property of matter which prevents two substances from occupying the same space at the same time ; we cannot, for instance, cause one particle or mass of matter to occupy the place of another particle or mass without moving or displacing it, and the oppo- sition met with in displacing it is termed its resistance. The most cursory observation is sufficient to inform anyone that solid and liquid bodies possess this property ; but it is not so readily apparent that gaseous bodies possess this property ; because matter in the gaseous state can be displaced without sensible effort, and the gases most commonly met with are colourless, and therefore not evident to the sight. 48. The impenetrability of the air is easily shown by in- serting a tumbler, mouth downwards, into a vessel containing water ; the water will not enter the tumbler, except the small quantity due to the compression of the air, on account of the tumbler being already filled with air. The diving-bell is an ex- ceedingly interesting application of this property ; the bell may Impenetrability 17 be said to be a large tumbler, which is inserted mouth down- wards in water ; the diver is perfectly safe in the bell, owing to the impenetrability of the air ; the only disagreeable feeling he experiences, as the bell descends in the water, is due to the compression of the air. Experiments Illustrating the Impenetrability of Gaseous Bodies. 11. Bend a glass -tube in the form of a syphon (fig. 28) ; fix tightly by means of thin wire or silk cord on the end of one limb of the tube an india- rubber blowing ball ; introduce the other limb of the tube into an inverted beaker ; then squeeze the ball as tightly as possible and place the beaker, mouth downwards, into a vessel containing water ; the water will not enter the beaker, except the small quantity due to the compression of the air, on account of that vessel being filled with air. Remove the pressure from the ball ; then, owing to the partial vacuum in the ball, some of the air in the beaker will pass into it through the tube ; as the air passes out of the beaker, water will ascend into it and occupy the space the air had occupied. When all the air, or the volume sufficient to fill the ball, has passed out of the beaker, again squeeze the ball, when the air will ascend through the water into the beaker, and displace the volume of water which had entered it when the air was withdrawn. 49. The difficulty of pouring a liquid into a vessel having only one small hole arises from the impenetra- bility of the air, as the liquid can run into the vessel only as the air makes its escape. The following experiment illustrates that fact : — 12. Fit up an ordinary wide-mouthed bottle with funnel tube and bent tube as shown in fig. 6, immerse the outer leg of the tube in a glass containing water ; then pour into the funnel water in small quantities at a time, and it will be seen that, as the water descends into the bottle, the air makes its escape through the tube, as is proved by the ascent of the bubbles of air in the water in the glass. Fig. 6. 50. It not unfrequently happens that students, when first commencing the study of practical chemistry, find, to their sur- prise, that in performing a filtration the liquid does not pass through the filter ; this is due in many cases to the leg of the funnel fitting air-tight into the mouth of the vessel into which the funnel dips : hence as the air cannot escape from the vessel, the liquid cannot enter. The following experiment is given to impress this fact on the student's mind : — 13. Fit the leg of a funnel air-tight into the neck of a bottle by means of a perforated cork (fig. 7) ; then place a filter in the funnel and filter ; 1 8 Fundamental Principles of Chemistry only a small quantity of the liquid will enter the bottle, owing to the im- penetrability of the air. The small quantity of the liquid which enters is due to the compression of the air by the liquid in the funnel. 51. As impenetrability and displacement are being constantly applied by the chemist in collecting and storing gases, this is the most appropriate place in the book for explaining to the student the apparatus, &c., employed for collecting gaseous bodies. 52. All my readers will have noticed the vessels — gas-holders — employed at gas-works for holding the gas ; these vessels may be likened to a tumbler placed with its mouth '"" ' downwards in a vessel containing water; at the first start the holder is filled with water ; then as the gas passes into it the water is displaced, and this is continued until the holder is full of gas, and the gas being lighter than water the holder rises in the air : when the gas is being drawn off into the street-mains the water re-enters the holder, and it again sinks into the outer vessel. 53. AH gases are collected in the laboratory by displacing some liquid or gaseous body ; when the gas to be collected is much heavier or lighter than air, it is frequently collected by displacing the air in the vessel in which it has to be collected. When the gas to be collected is heavier than air, the delivery tube from the vessel in which the gas is generated must pass down to the bottom of the collecting vessel, a piece of paper or a glass plate partially covering the mouth of it, during the time it is being filled with the gas ; when it is filled, the delivery tube must be removed, and the mouth of the bottle closed as speedily as possible with the stopper. When the gas is lighter than air, the extremity of the delivery tube must pass upwards instead of downwards, and the vessel in which the gas has to be collected must be inverted over the extremity of the tube, the latter passing up to the bottom of the vessel. The collecting vessels employed in both these cases are wide- mouthed glass stoppered bottles of about a quart size. 54. By the other methods for collecting gases, the vessels in which they have to be received are first filled either with Collecting Gases 19 water or mercury. Everyone is aware that if a vessel, say a glass jar, open only at one end, be immersed in a vessel con- taining water, with its open end upwards, yet covered with water, the air with which it was filled will escape, and it will become filled with water. If it be now inverted (open end downwards), it may be raised until the water contained in the outer vessel (the one in which it is immersed) only just covers the open end or mouth, yet so long as this keeps covered it will remain filled with water. If a delivery tube from which the gas is issuing be placed underneath the open end of the jar, when in this position, the gas will, of course, ascend and dis- place an equal bulk of the water, and in this way the jar becomes filled with the gas. Gases are thus collected over water ; the vessel containing the water is called a pneumatic trough, which, for teaching purposes, is usually made of japanned tin ; it varies in capacity from one to six gallons, in length from 10 to 16 inches,, in width from 6 to i inches, and in height from 6 to i inches; but it may be made of any siz( It is provided with a shelf, fixed aboi three inches below the edge. Hole are bored in the shelf at short dis tances, in order to allow the gas to pas into gas jars standing on the shelf with their open ends over the aperture (fig. 8). When a jar has to be filled with gas, it is first filled with water in that part of the trough not covered with the shelf ; it is then placed on the shelf in an inverted position, over one of the holes ; the operator then directs the point of the gas delivery tube (which is bent a little upwards) whence the gas is to issue into or underneath the hole in the shelf. The water in the trough must always stand an inch or so above the shelf 55. Besides the pneumatic trough with its glass jars, it is desirable to have vessels of larger capacity, in which consider- able quantities of gas can be collected, and from which it can be drawn off at pleasure. Such vessels are called gas-holders Fig. 8. 20 Fundamental Principles of Chemistry or gasometers, and are constructed of japanned tin, or of copper. The figure (fig. 9) represents one of the most con-, venient ; a is a metalhc drum or cylinder closed in all direc- tions ; B is an open vessel communicatirig with a by a small tube c, which terminates in the roof of the cylinder, and a large one, D, which descends to nearly the bottom ; e is simply a pillar to support the funnel ; f is a tube placed at an angle with the cylinder, and provided with a nut which screws into its mouth, and fits it air-tight ; g is a stop-cock, projecting laterally from the top of the cylinder. In the figure the gas- holder is represented in the condition in which it would ordinarily be called empty — in other words, full of air. As a preliminary step to filling it with gas, water is poured into b. It descends by the tube d, and partly by c, whilst the air escapes by c and g When the water runs out at G, the cylinder is full, and all the stop-cocks are then shut. The nut of the oblique tube f, is then un- screwed, and the beak of the retort, or exit tube of the flask, from which the Fic. 9. Fig. gas is issuing, is inserted through r, and pushed in until its end is fairly within the cylinder. The gas, rising vertically, accumu- lates in A, whilst the water it displaces flows out at f, past the neck of the retort or tube of the flask. When the water is all expelled, the retort or flask is withdrawn, and f closed again with the nut. A glass tube or gauge, h, communicating at each end with the cylinder, and in which the water stands at the same level as in a, allows the amount of gas in the latter to be readily observed. The gas is drawn off" either by c or by G. If a jar is to be filled, water is poured into b, and the jar full of water is placed, mouth downwards, over c. c and d are then opened, and the water, which descends by d, expels the gas Gas Jars 2 1 "by c. If a bladder (fig. 10) has to be filled, or a current of gas is wished, as for the lime-light, or the oxyhydrogen blow-pipe, the tube to convey it is attached to the end of g. b is kept full of water, and when d and g are opened, the gas rushes out by the latter. The stopcocks at d and g admit of the current being very nicely regulated. 56. In collecting gas over water, the extremity of the delivery tube ought not to be immersed in the liquid as soon as heat is applied to evolve the gas, because the air in the gas vessel become expanded by the he t, and therefore a portion of it escapes ;- if after this escape of air, and before the gas begins to be evolved, the intensity of the heat becomes in the least diminished, the air within the vessel contracts, the cold water rushes up the delivery tube (we are supposing that the delivery tube has been placed in water) into the gas-generat- ing vessel, causing it to break, The gas ought to have been freely issuing from the exit of the delivery tube for ia few seconds before immersing it in water, and before collecting any of the gas sufficient should be allowed to escape to ensure the expul- sion of all the common air. When the gas ceases to be evolved, the exit tube ought to be removed out of the water instantly, in order to prevent the water rushing up through the tube into the generating vessel. 57. Gas jars or receivers are of various kinds. Plain jars should be from twelve to sixteen inches in length, two and a half or three inches in diameter, and of such thickness as to withstand the general liabilities of use (about one-eighth or one-tenth of an inch), and ground at the edges, so as, when moistened or greased, to be closed accurately by a flat glass plate. Stoppered jars have an aperture above, fitted air-tight with a ground-glass' stopper, and resemble stoppered bottles without bottoms. They are transferred from the pneumatic trough to the lecture table, upon a common dinner plate con- taining, water, in order to prevent the air having access to the gas contained in the jar. When substances have to be burned in gases, they are introduced through the mouth of the jar to the gaseous atmosphere within by means of a deflagrating spoon (fig. 11), which consists of an iron cup about the size of a shil- ling, to which is attached a long handle of iron wire passing 22 Fundamental Principles of Chemistry through the jar. Fig. II. a stuffing-box, which serves to cover the mouth of A cork or piece of flat metal may be substituted for it ; if a cork be employed it must not be fixed firmly into the mouth of the jar, because gas, when heated, expands, and the cork must, therefore, be sufficiently loose to allow for the necessary quantity of the expanded gas to escape, otherwise the glass vessel will most probably be shattered. 58. We shall give here a few directions as to the fitting up of apparatus and its uses. Corks, glass tubing, rubber tubing are required in fitting up apparatus ; we shall therefore begin by informing the student how these three articles are moulded, so as to render them equally serviceable in all cases. 59. Corks are constantly required in the laboratory, not only as stoppers for bottles, jars, &c., but for many other purposes, especially for connecting wide apertures with narrow ones. As they are used for rendering vessels air- as well as water-tight, they must be free from pores. A good cork is inestimable in a laboratory, a bad cork is a constant source of trouble. In fitting them into the mouths and apertures of vessels, they should be softened, either by pressure under the fingeis, or by rolling them under the foot (in the latter case in a piece of paper, so as to protect them from dirt), taking care to preserve their conical form. If too large, they may be reduced to the proper size, either by the aid of the rasp or knife ; but it is better to select them of the proper size in the first instance, rather than have recourse to these expedients. In fitting a cork into a glass vessel, the latter should be held firmly, close to the aperture, and, for the sake of security, covered with a piece of cloth. They require, for connecting wide apertures with narrow ones, to be perforated ; this is done by piercing them in the proper place (the middle, if only one tube has to be fitted in) with a rat-tail file, taking care to make Fitting up Apparatus 23 the bore straight, and especially eqiial. It is. necessar)', in order to make an equal bore, to introduce the file alternately, at each end of the cork ; the hole can, of course, be made of any size by filing, and employing larger files 'as the size of the aperture increases. 60. After having selected a piece of hard glass tube of the proper bore and thickness, the next thing, if it does not require bending, will be to cut it into the required lengths. For this purpose, a mark is made round the tube, at the proper place, with the edge of a three-cornered file ; the tube is then held in the hand as you would a stick you were about to break ; a slight and sudden pressure is then exerted at the mark, which causes the tube to break evenly in two. The depth of the mark made with the file must vary with the thickness and diameter of the tube, and in filing very small or thin tubes, the manipulator must not press too much on the file, otherwise the tube wiU be broken. When a tube has to be introduced into a cork, it is necessary to round its sharp edges before doing so, else the cork will be so cut and torn that it will be rendered perfectly useless. To effect this, the tube must be heated in the flame of a gas or spirit lamp ; it must be healed gradually, so as to prevent its cracking, by holding it near the flame at first, and by degrees introducing it. As soon as the edge becomes faintly red-hot, the thing is accomplished, and the tube ought then to be removed from the flame, otherwise the opening at the extremity might contract, which, to say the least, is better avoided. If the heat of the lamp be not sufficient to round the edges it must be rounded in the blow-pipe flam.e. A hot tube must not be laid on any cold surface, and it must be allowed to cool before inserting it into a cork. The perforation in the cork must, if anything, be a trifle smaller than the diameter of the tube which has to be inserted, in order that the connection may be perfectly air-tight. The best plan of fitting the tube into the cork is to screw the tube, holding both it and the cork firmly, the first close to the extremity which has to be inserted ; the tube may be greased very slightly at the part to be introduced. 61. Gas jets are sometimes required in the combustion of gases ; they are made in the follpwing way : — a hard glass tube of the proper diameter and thickness is heated in a spirit or 24 FUNDAMENTAI. PRINCIPLES OF CHEMISTRY gas lamp, at such a distance from one extremity that there is sufficient left as a handle for the manipulator, and also suffi- ciently remote from the part to be heated that it does not become insupportably hot. The part to be heated is to be brought, not into the flame, but into the current of hot air, which passes off in the same direction from it, and the tube is to be turned, so as to become heated all round, and also moved a little to the right and left, that the temperature of the neigh- bouring parts may be raised. After a few seconds, when the glass has become hot, it should be brought towards the point of the flame, and ultimately into it, being turned round all the time, and also moved laterally, though not to the same extent as before. When sufficiently soft it is drawn out into a capillary,. as shown in fig. 13. The two ends are then separated at abouf Fig. 13. the centre of the portion drawn out. The elongated extremity of the end to be used is filed down until the orifice is of sufficient size ; it is then rounded at the edges in the flame of the lamp. 62. The flame of a gas lamp, using a fish-tail burner, is sufficient for bending ordinary glass tubing without the aid of the blowpipe. The tube must be heated about an inch in length uniformly ; it must be supported by the hands on each side of the part to be heated ; it must be gradually introduced into the flame, in the way described in the preceding paragraph, and turned round continually during the process of heating, as there stated. Both fends must be turned alike, and in such a way that the heated part, when soft, shall retain its cylindrical shape, being neither twisted, nor bent, nor elongated, nor thrust up. When the glass has become sufficiently soft, remove it from the flame, and gently bend it to the desired shape. The bend ought not to become flat at the convex portion, or in folds at the concave ; to avoid these imperfections, the glass ought not to be made too soft, it ought to be heated uniformly to the length of about an inch, and the bend ought to be made very round. The side of the tube last exposed to the flame will be slightly hotter, and therefore softer, than that which is Gas Apparatus 25 opposite to it. This hotter side should form the concave side of the bent tube. 63. Vulcanised india-rubber tubes are employed for joining glass tubes; they can now be purchased of any size, and there- fore the chemist has no need to make them. In connecting glass tubes by means of the rubber tubing, the ends of the glass tubes should not be brought quite close together inside the rubber connector, but should be left a very slight distance apart, in order to allow of a certain degree of flexibility. If the vulcanised india-rubber tubing does not fit the glass tube air-tight, it must be tied on with some silk cord. 64. The manipulator having carefully attended to the pre- cedmg instructions, will experience very little difficulty in fitting up the different apparatus now to be described. 65. Apparatus for generating gases, heat not being re- quired. — A bottle, with two or three separate openings, called a Woulfe's Bottle, is a very convenient vessel for generating gases when heat is not required. It need only have two open- ings ; one for the funnel tube, which serves for the introduction of liquid, and which must pass down nearly to the bottom of the vessel, being covered by the liquid in the vessel to the ex- tent, at least, of half an inch ; the other, for the conveying of the gas to the receiver ; this is called the delivery tube ; it need only project into the bottle a trifle beyond the cork. The de- livery tubes are of various shapes. If the bottle is provided with three openings, the middle one can be closed with a plain cork, and be used for introducing any solid substance into the bottle. Wide-mouthed bottles may be used in the place of Woulfe's bottles ; the only objection to them is the difficulty of making them air-tight, as large corks, free from pores, can seldom be obtained. If any of the corks be porous, it will be advisable, after the cork has been fitted into the apparatus, to paint the top of the cork with a solution of sealing-wax in spirit of wine. But if the tube does not fit the perforation in the cork perfectly air-tight, a paste, made with linseed meal and water, or better still, with lime-water, ought to be used for stopping the leakage. Gases should not be generated too rapidly ; if an acid be employed for disengaging the gas, it ought to be added by degrees, commencing with a little, and 26 Fundamental Principles of Chemistry when the gas begins to be disengaged slowly, to add a little more, &c. The delivery tubes are, as we have said, of various shapes; fig. 14 represents aWoulfe's bottle fitted up in the way just described, the delivery tube being made of the shape re- quired for collecting the gas at the pneumatic trough, or in the gasholder. The other (fig. 15) is fitted up for collecting the gas by displacement, or for passing it through a solution. Sometimes it is necessary to wash the gas, which is done in the following way ; a wide-mouthed bottle, capable of holding about half a pint, is fitted with two tubes, as shown in fig. 16, one of which, a, should be about half an inch in diameter, straight, and of sufficient length to reach nearly to the bottom of the bottle, the water in which ought to cover the tube to the depth of half an inch ; the other (the delivery tube) should only c p 6 ^ 1 J a 11 ^\ s 1 hIH 1 1 1 Fig. 14. Fig. 15. Fig. 16. just pass through the cork, and be bent according to the mode of collecting the gas. The delivery tube of the vessel, in which the gas is generated, is made to pass down the tube a, and project a httle beyond it in the bottle ; the gas will then rise up through the liquid and pass off by the delivery tube b of the washing-bottle. 66. Apparatus used in the disengagement of gases, heat being required. — Flasks, test-tubes, and retorts are the ordin- ary kinds of apparatus used for this purpose. Figures 16 and 17 represent the first two, with their different fittings and con- nections. The first are used in preference to retorts on account of their cheapness, and the second are the most convenient when only a small quantity of gas is required. The materials used in the production of a gas ought only to occupy, at the Gas Lamps 27 most, one third of the space in the generating vessel, whether heat be employed or not. When the materials for the produc- tion of the gas consist of a hquid and a powder, the liquid Fig. 17. Fig. 18. ought to be put into the vessel first, and after the powder has been added, they ought to be well mixed by shaking the vessel before heat is applied. 67. Heat has to be employed in a great many chemical operations ; gas is the most convenient and economical fuel; it requires to be mixed with a certain quantity of air in the tube of the lamp before being burnt, so as to prevent the de- posit of any soot on the vessels. A cheap and most convenient lamp is that called Bunsen's gas-burner ; it consists (fig. 19) of a brass tube, a, b ; these tubes are made of different dia- meters ; air enters by holes at c, the amount being regulated by Fig. 19. Fig. ; Fig. 21. means of a small slide, which closes them wholly or partially as may be required. The gas enters at d; when a more diffuse flame is required an iron rose (fig. 20) is screwed on to the top, the rim of which is perforated with a number of small holes. When gas cannot be obtained, wood naphtha or methyhted spirit is 28 Fundamental Principles- of Chemistry the fuel usually employed ; where a great amount of heat is not required it is burnt in the lamp (fig. -21). When the lamp is finished with, the cap ought to be placed over the wick in order to prevent the loss of the liquid by evapora- tion. The cap ought not to be used as an extinguisher, because the air in the cap be- comes, if it is so used, so rarefied that it is afterwards difficult to remove it, but the flame ought to be blown out before the cap is replaced. The heat ought to be apphed gradually for two reasons : (i) in order to pre- vent the breaking of the vessel, which is almost sure to be the case if the heat be ap- plied suddenly ; (2) to prevent a tumultuous disengagement of the gas ; when the evolu- tion of the gas diminishes in rapidity, the heat ought then to be increased. A retort or flask is supported on one of the rings of a retort-stand (fig. 22) ; a test-tube is held over the lamp by the fingers. Fig. 22 Examination Questions. 14. Define the meaning of the word ' matter ' as applied to the material world. 15. Describe the operation called 'welding.' 16. Define the meaning of the terms ' particle ' and ' molecule.' 17. What precautions are necessary in getting out of an omnibus in mo- tion, so as to avoid falling to the ground ? assign a reason for what you state. 18. State the difference between specific and general properties. 19. What properties are bodies said to possess when they admit of being bent without breaking, and retain the form they have been made to assume ? 20. Define the meaning of the term inertia as it has been employed in the text. 21. What are the external signs by which the existence of matter in its various forms is made evident to our senses ? 22. Give a sketch of the apparatus you would employ, and in its proper position, if you had to collect agaS lighter than air ; also the apparatus for a gas heavier than air ; each of the gases being collected by displacing the air in the receiving vessel. 23. When the term ' hard ' is applied to solid bodies, what does it signify ? 24. What is meant by the terms ' soft ' and ' brittle ' when applied to solid bodies? 25. What is meant by the term ' elasticity ' wh?n applied to bodies ? 29 CHAPTER II. MOLECULAR ATTRACTION— GENERAL EFFECTS OF HEAT — MAXIMUM DENSITY OF WATER — HYPOTHESIS AS TO THE NATURE OF HEAT — DIFFERENCE BETWEEN HEAT AND TEMPERATURE— MEASURE- MENT OF TEMPERATURES — EXERCISES — SPECIFIC HEAT, AND THE METHODS FOR I'JS DETERMINATION — EXERCISES — LATENT HEAT — QUESTIONS — DYNAMICAL THEORY OF HEAT — QUESTIONS. 68. The molecules of all substances are under the influence, as has been previously stated, of two contrary forces ; one of which tends to bring them together, the other tends to separate them from each other. According to the manner in which the molecular attraction— the attractive force — operates, it is designated by the terms cohesion, adhesion, or chemical affinity ; cohesion has already been explained ; adhesion and affinity will be explained subsequently ; the opposing force has here to be considered. 69. The repulsive force exerted between the molecules of substances is developed by the action of heat ; hence one of the effects of heat upon bodies is to cause them to expand, in other words, to increase in volume ; and also to change the state of aggregation of solids and liquids — that is, it causes solids to pass into the liquid state, and liquids to pass into the gaseous state. When a solid body, for example, is exposed to the in- fluence of heat, it expands according to three dimensions, viz, I. In length, called its linear expansion. 2. In surface, called its superficial expansion. 3. In volume or bulk, called its (Tw^zW expansion : and when the solid is perfectly homogeneous, it expands uniformly throughout its entire volume. The in- crease of surface is twice, the increase of volume is thrice, the increase of the linear expansion ; and one of these expansions, it rtiay be observed, never takes place without the other. That solids increase in volume by increase in temperature is easily shown : an iron or brass ball, which just goes through a ring when cold, will not fall through it when heated ; but if left on the ring will, on cooling, fall through it. This experiment not only proves that solids expand on being heated, but it likewise 30 Fundamental Principles of Chemistry proves that they contract on cooling. There is a very common and useful application of the expansion and contraction of solids in the hooping of the wheels of carts, carriages, &c. ; the hoop or band of iron is purposely made less than the wheel itself, so that it cannot go on when cold ; but when it is heated it expands sufficiently to be placed on the wheel, and when in its proper position cold water is poured upon it, which causes it instantly to contract and bind the wheel tightly together. 70. Solids dilate pretty regularly, at temperatures between the freezing and boiling points of water ; consequently, equal increments of heat correspond with equal increments of volume. At higher temperatures, the expansion proceeds at a greater rate than the successive additions of heat. The degree of ex- pansibility varies, of course, in different substances. 71. One or two solid bodies are known which, at least within certain limits of temperature, form exceptions to the general rule of expansion by heat, for they contract as the temperature is raised up to a certain degree of temperature. An alloy consisting of 2 parts bismuth, i part tin, and i part lead expands when heated from 0° to 44° C. ; when still further heated, it contracts, so that at 56° its density is the same as it was at 0°, and at 69° still greater ; beyond this temperature, expansion again takes place ; at 87'5° the alloy has once more the same density as at 0°, and at 94° the same as at 44°. 72. Liquids, like solids and gases, expand when they are heated and contract when they are. cooled ; they expand. pro- portionately much more rapidly than solids ; they differ also in expansibility to a much greater extent, the most volatile being generally the most expansible. . The rate of dilatation of liquids is not generally uniform, like that of solids and gases, it increases with increase of temperature ; and as the liquid approaclies solidification on the one hand, and the point of vaporisation on the other, other irregularities in its contraction and expansion take place. 73. Water is a most remarkable exception to the law of expansion by heat and contraction by cold ; it contracts on cooling like other liquids until it reaches the temperature of 4° C. (39"2° F.) ; at this temperature it attains its greatest density, for on further cooling it begins to expand, and just Expansion and Contraction 31 before it begins to freeze, its volume at that temperature and that at 9° C. are equal : if then the temperature of water either rises above or sinks below 4° C. the water expands. On freezing the expansion is so great and sudden that the force exerted is enormous ; thick iron shells, filled with water and their fuse- holes securely plugged, when they have been exposed to the severe cold of a Canadian winter night, have been found split open in the morning. In our comparatively mild winters we are made aware of this great expansive force in the bursting of water-pipes and breaking of vessels by the freezing of the water they contain ; the expansion is nearly ^ the volume of the water. The student must, however, note the distinction between the expansion on freezing, and the expansion as the water cools from 4° C. to the point it begins to freeze ; it is this latter expansion that is anomalous, for no other substances besides water expand on solidifying. 74. The freezing of water in the joints and crevices of rocks acts as a disintegrator- and pulveriser even of the hardest of them, thus facilitating the chemical action of the carbon dioxide in the air in converting rocks into fruitful soil. This anomalous expansion makes water perform other important functions in the economy of Nature ; were it not for its ex- pansion after a certain temperature is reached, lakes and rivers would become solid masses of ice in winter, which the summer heat would not be sufficient to melt, and all aquatic life in these waters would necessarily perish. This is prevented, owing to the cooling taking place at the surface ; the surface water becoming heavier than that underneath sinks and is re- placed by less dense water; this replacement of the surface water by that underneath continues until the whole mass acquires a temperature of 4° C. ; when this temperature has been reached the surface water ceases to sink, owing to its becoming of less density than the water underneath ; and the lighter water on the top protects that underneath from a further reduction of temperature owing to its bad heat-conducting power ; and when it solidifies by further cooling, the ice formed remains on the surface, because its density is less than that of the water underneath. When the surface is frozen, the tempera- 32 Fundamental Principles of Chemistry ture of the deep water remains at 4° C. ; aquatic animals are thus kept in a temperature high enough for their existence. 75. Several methods have been devised for determining the maximum density of water ; the one we describe is that devised by Hope ; it consists of a deep glass tube-shaped vessel (for lecture experiments it is frequently made of tin as it renders it less costly) having two lateral openings, one near the top and the other near the bottom ; a thermometer is placed in each of these openings (fig. 23). The tube is filled with water, and its middle is surrounded with a freezing mixture. ' The fol- lowing phenomena will then be observed. 76. ' The lower thermo- meter descends steadily to 4° C, and there remains sta- tionary. The upper thermo- meter at first undergoes very little change, but when the lower one has reached the fixed temperature, the upper one begins to fall, reaches the temperature of zero, and, finally, the water at the surface freezes, if the action of the frigorific mixture continues for a sufficiently long time. These facts admit of a very simple explanation. ' As the water in the middle portion of the tube grows colder, its density increases, and it sinks to the bottom. This process goes on till all the water in the lower part of the vessel has attained the temperature of 4°. But when all the water from the centre to the bottom has attained this temperature, any further cooling of the water in the centre fails to produce motion until needles of ice are formed. These being specifically lighter than water rise to the surface, and thus produce a circulation which causes the water near the surface to freeze, while that near the bottom remains at the temperature of 4°' (Deschanel). 77. Salts dissolved in water lower its point of maximum density, common salt (sodium chloride) especially ; in sea-water, Fig. 23. Expansion of Liquids and Gases 33 which contains an abundance of common salt, the maximum density occurs at i3"68° C. (25-38° F.), atemperature below its freezing-point. 78; The only body in the liquid state whose variation of volume through a considerable range of the thermometric scaje is found to be exactly proportional to its change of temperature, is mercury. 79. From what has been stated with regard to the expan- sion of solids by heat the student will at once see that the increase of expansion of any liquid, in a vessel, is not its real or absolute expansion, but only its apparent expansion ; in order to arrive at the absolute expansion of a liquid, the changes in the capacity of the vessel at the same temperature which contains the liquid must be determined ; the apparent expansion of a liquid is therefore equal to its absolute expansion for the same interval of temperature diminished by the corresponding expan^ sion of the containing vessel. 80. In the expansions of liquids, the cubical expansion is alone considered. 81. All gases, on account of the absence of any cohesive- ness between their particles, expand alike, the pressure being the same for equal additions of heat ; the rate of expansion being equal and uniform at all degrees of temperature ; they expand rather more than one-third their volume on being raised from the temperature at which ice melts to that at which water boils at the ordinary atmospheric pressure. The expansion of gases is more fully treated of in Chap. III. 82. The two prevailing opinions with regard to the nature of heat, are the theory of emission, and the theory of undulation. 83. According to the first theory, heat is a subtle imponder- able fluid, which surrounds the molecules of bodies and which can pass from one body to another. According to the other theory, which is the one now generally accepted, the heat of a substance is caused by the oscillatory motions both of the particles of bodies, and of a very subtle medium which is con- sidered to pervade all space, and which is capable of trans- mitting a vibratory motion with great velocity. 'A rapid vibratory motion of this ether produces heat, just as sound is produced by a vibratory motion of atmospheric air, and the D 34 Fundamental Principles of Chemistry transference of heat from one body to another is effected by the intervention of this ether.' Heat, according to this view, is not a substance, but a condition of matter, and a condition which can be transferred from one body to another ; it is, in short, looked upon as 2. form of motion. 84. The general effects of heat we have already noticed ; here we will make one remark before going further into the subject : — whenever, as in the case of heat, we have to speak of any agent whose nature is unknown, the expressions and allusions we employ in regard to it must necessarily possess a degree of vagueness ; and to those students who require exact definitions, they must appear unsatisfactory. This vagueness is further increased if different views have prevailed at different times as to the nature of the agent, because the terms which have been employed under one theory are frequently retained when other and totally different views prevail. These few general observations on the terms employed we have thought it necessary to make, in order to show the student that the terms which may appear vague and unsatisfactory to him are equally so to all who study the subject. 85. The term heat we apply to the agent ; the term temperature we apply to that portion of heat in a body which we can perceive by the senses. The temperature of a body can be increased or diminished. If two bodies of different temperatures are brought together, the one containing the most sensible heat — in other words, having the highest temperature — will lose heat, which the body with the lower temperature will absorb. This imparting of heat by the one body, and the receiving of it by the other, will only cease when they have both arrived at the same temperature. If, therefore, we bring the hand, or any other part of our body, in contact with a substance having a higher temperature, heat is imparted by that substance to the hand, and we experience the sensation we term heat. If, on the contrary, the hand is warmer than the substance, it imparts some of its heat to the substance, and we then experience the sensation we term cold. The student will observe, from these illustrations, that heat and cold are merely relative terms. 86. Our sense of touch cannot be employed to ascertain Thermoscopic Agents 35 the correct temperature of substances ; for that will only tell us whether the substance has a higher or a lower temperature at the time than that part of our body which comes in contact with it. The same body might even be made to be feel both hot and cold at the same moment, if we made one hand hotter and the other colder than the body, before we brought them in contact with it. For the same reason, we pronounce a cave cold in summer, hot in winter, although the temperature of the cave may have remained the same. To measure the correct tempe- rature of bodies, we have recourse to the physical action of heat on bodies. These actions are of various kinds. Expansions and contractions have been adopted, as being the easiest to observe. But heat also produces electrical phenomena in bodies, on which very delicate methods of observing temperatures have been based. 87. Instruments termed thermometers (from dcpfibc, hot, ficTpov, a measure) are employed to measure temperatures up to about 600° F. Instruments termed pyrometers (from wvp, fire), are employed to measure temperatures higher than 600° F. 88. Although bodies in each of the three states of aggrega- tion expand on being heated and contract on cooling, they are not equally suitable for thermoscopic agents. Solids, as a rule, are not suitable, as their expansion is comparatively slight ; their increase, therefore, in volume for an increase of temperature cannot be easily or accurately observed. Air is much more delicate in its indications of temperature than liquids, and its expansion being uniform at all degrees of tem- perature (par. 81) would render it the best thermometric agent, were it not that a difference in atmospheric pressure, indepen- dent altogether of temperature, causes ah alteration in its volume. Elaborate and special contrivances, consequently, are required to render it a reliable thermoscopic agent ; its use is therefore limited; it is chiefly used in ascertaining the specific gravities of volatile substances, and other delicate experiments. Liquids, as a rule, are best suited for measuring changes of temperature, and the liquids used for this purpose are mercury and alcohol. 89. Mercury is the best thermoscopic agent for general purposes, for it has the widest range between its solidifying 36 Fundamental Principles of Chemistry and boiling-point of any liquid ; it also more nearly resembles gases in uniformity of expansion for equal increments of heat, at ordinary temperatures, than any other liquid (par. 78). It is likewise easily purified; it is also a very good conductor of heat, and therefore becomes almost immediately of the same temperature as the substance it comes in contact with ; and, owing to its calorific capacity being very small, the heat it ab- stracts from the heated body it is in contact with causes such a slight change in the temperature of the heated body, that this slight lowering of temperature may be generally neglected, and, owing to its small calorific capacity, it is rapidly heated and cooled. 90. Alcohol is employed to measure very low temperatures, as it does not solidify at the greatest known cold. 91. We must refer the student to the general works on chemistry and physics for descriptions of the differential thermo- meter, the thermo-electric multiplier, the self-registering ther- mometer, the air-thermometer, the pyrometer, — in fact, all the varieties of heat-measurers but the mercurial thermometer, which all my readers will have seen, at least in its most inac- curate form, viz. that used for common purposes^ and which is provided with a boxwood scale. 92. We shall not enter into the minutiae for constructing a mercurial thermometer ; but we will very briefly state the essentials and the mode for testing its accuracy, as it is a very important and indispensable instrument in most physical and chemical researches. The first essential in the manufacture is to select a capillary glass tube of uniform bore throughout its entire length, so that equal lengths of the tube will contain equal volumes of mercury. To ascertain this, a small drop of mercury is introduced into the tube, sufficient to fill about one inch of the tube. The mercury is gradually moved from one end of the tube to the other, and its length is measured in each suc- cessive position. The length, of course, should be the same in every part of the tube ; if it be not, the tube must be rejected. Having selected the tube, the next thing to be done is to blow a bulb upon one end of it. The ordinary shape of the bulb is spheri- cal, but an elongated tubular-shaped bulb is more convenient in most chemical investigations, and as it exposes a much larger sur- Mercurial Thermometer 37 lace for the conduction of heat, in proportion to its capacity, it is consequently more sensitive. The thickness of the glass is an important po;nt ; if too thin it is liable to be altered in shape by the pressure of the atmosphere, and thus the graduation would be rendered inaccurate ; and if it be too thick, it will render the instrument insensitive. The instrument is now ready to be filled with mercury, if the interior of the tube is thoroughly clean and dry. ' The following is the most perfect mode of filling the thermometer with mercury : — A sufficient length of the tube, a b, is marked off to form the stem of the thermometer, and a second bulb, rather larger than the first is roughly blown at b. When the bulb is half-cooled, the open end of the tube is held in pure and well-boiled mercury, which gradually rises into the first bulb. By inverting the position of the tube, and alternately heating and cooling the lower bulb (a). Fig. 24, sufficient mercury may be made to pass from b into a, almost to fill a, a little remaining over in b. The whole tube is now held by the handle, shown in fig. 24, over a charcoal fire or a series of powerful gas-burners, so as to be strongly and uniformly heated throughout its whole length. The mercury boils easily and its vapour drives out every trace of air or moisture. When this is thoroughly accomplished, and the mercury yet boiling, the open end of the tube, which must not be very hot, is thrust against a piece of sealing-wax, and then at once withdrawn from the heat. As the tube cools, a httle wax is drawn in, and, in time becoming solid, prevents the en- trance of any air. When quite cool, the mercury perfectly fills the whole of the lower bulb and tube. Let the tube be now inclined, and the lower bulb raised to a temperature rather higher than the thermometer is intended ever to indicate. A part of the mercury is thus expelled, and as the column begins to retreat again on cooling, the tube is to be melted and her- metically sealed just below the bulb b, which is then drawn off. The perfection of the vacuum thus produced within part of the 38 Fundamental Principles of Chemistry tube may be known by the mercury running freely up and down, especially if the tube be not very fine. This process is more simply but less perfectly performed by some makers, who omit the second bulb, and place the mercury in a little funnel of glass or paper affixed to the open end of the tube.' At the time of sealing the tube, it contains, or at least should only contain, mercury and vapour of mercury, all trace of air and moisture having been expelled by boiling the mercury in the tube. 93. The thermometer has, of course, to be graduated, that is, provided with a scale to which variations of temperature can be referred ; and in order to be able to compare one ther- mometer with another, it is necessary, in the graduation of thermometers, to select two standard temperatures as fixed points ; the temperatures which have been universally chosen, are those of melting ice and boiling water. The thermometer ought not to be graduated immediately after it is sealed, as the bulb contracts, and does not attain its fixed dimensions until some months after the sealing ; consequently, if the fixed points were determined before the bulb arrived at its fixed capacity, the graduations on the scale would fndicate a tempera- ture higher than the true one from a quarter to half a degree. 94. Owing to a frequent rise in the melting-point after graduation, which is generally supposed to be due to atmo- spheric pressure, the question whether the boiling-point or the freezing-point ought first to be determined is a matter not settled. Most scientific men consider that the freezing-point ought to be determined first; others, on the contrary, think that the boiling-point ought to be taken before the freezing- point ; whichever plan be adopted, a considerably long interval ought to elapse between the taking of the two points. 95. To determine the freezing-point the thermometer is placed upright in a vessel containing snow or finely pounded ice, and which has a hole at the bottom to let the water drain away as the ice melts. The whole of the mercury, both in the tube and in the bulb, must be surrounded with ice, and must be left in it for half an hour ; the ice may then be removed just sufficiently to allow a mark to be made at the top of the mercurial column ; this mark of course represents the point on the scale at which ice melts ; the instrument is now removed. Graduation op the Thermometer 39 96. ' The boiling-point is ascertained by placing the ther- mometer vertically in a cylindrical metal vessel, so that the bulb shall be close above the surface of distilled water in rapid ebullition, the whole of the mercurial column being likewise raised to the same temperature as the bulb by the rising vapour. The water having been thoroughly boiled for a length of time, and the mercury standing quite stationary, a mark is made at the top of the mercurial column, and this must be done while the boiling continues uninterruptedly. As the boiling-point of water depends entirely on the pressure of the air at the time, the pressure, by means of the barometer must be determined. If it stand at 760 millimetres (or 30 English inches), the tem- perature of boiling water is exactly 100° C. (212° F.). If not, the temperature must be calculated, allowing a change of + i°C. for every divergence of pressure equal to + 267 milli- metres (or 171° F. for every inch of pressure).' 97. The two fixed points having been marked on the tube, the distance between them is divided into equal parts, termed degrees. The degrees are designated by a small cipher placed a little above on the right of the number which marks the tem- perature ; and, to indicate temperatures below zero, the minus sign is placed before the figures thus :— 15 '^signifies 15° belowzero. In accurate thermometers, the scale is marked on the glass itself, which is accomplished by covering the glass with a thin coating of beeswax, then marking the divisions and numbers with a steel point, and subsequently exposing the thermometer for a short time to the action of hydrofluoric acid gas : where the wax has been removed by the steel point the glass is etched by the gas. 98. There are unfortunately three different thermometric scales, viz., the Centigrade, or Celsius (the latter the name of the person who invented the scale), the Fahrenheit scale (this scale originated with an instrument-maker at Dantzic), and the Rdaumur scale. The Centigrade scale is adopted on the Con- tinent, especially in France, and it is the one most generally employed in scientific investigations. The Fahrenheit scale is universally employed in England for ordinary purposes, and frequently in purely scientific investigations ; it is also employed in America and Holland. The Reaumur scale is employed in Russia and Germany. 40 Fundamental Principles of Chemistry 99. The freezing-point is made the zero-point, both in the Centigrade and Reaumur scale ; but on the Fahrenheit scale the zero-point is placed at the 32nd division below the freezing- point, so that on this scale the freezing-point is 32°- The reason for fixing the zero of the scale at 32° below the freezing- point was, that at the time it was believed to be the natural zero of temperature, or the greatest possible degree of cold. Much lowei: temperatures, natural and artificial, have since been ob- served, and it is very improbable that the absolute zero can be reached.' 100. The distance between the freezing and boiling points is divided in the Centigrade scale into 100 degrees, so that o°C. represents the one point, and 100° C. the other ; the dis- tance between the two pofnts on the Reaumur scale is divided into 80 degrees, so that o°R. represents the one point, and 80° R. the other. The distance between the two fixed points is divided on the Fahrenheit scale into 180 degrees, so that 32° F. repre- sents the one, and 212° F. the other point. The length of a degree having been thus ascertained by dividing the distance between the two points, the tube is graduated in degrees of the same length below the freezing-point, and above the boiling- point, as far as may he desired. 101. ' A scale divided upon the principles already described evidently depends for accuracy on the supposition that equal \increments of heat produce an equal amount of expansion. With •^ue precautions, a pound of water at 32° F. mixed with a pound 1 ' Reckoning from o° C. upwards, we find that every degree added to the temperature of a gas produces an augmentation of elastic force equal to -^^ of that which the gas possesses at 0°, and hence that, by imparting 273", we double the elastic force. Supposing the same law to hold good when we reckon from o° downwards — that for every degree of temperature withdrawn from the gas we diminish its elastic force, or the motion which produces it, by 5^ of what it possesses at 0°, it is manifest that at a temperature of 273° C. below 0°, we should cease to have any elastic force whatever. The motion to which this elastic force is due must then vanish, and we reach what is called the absolute zero of teTnperature. ' No doubt, practically any gas deviates from the above law of contraction before it sinks so low, and it would become solid before reaching —273° C. , or the absolute zero. This is considerably below any temperature which we have as yet been able to obtain.' — Heat considered as a Mode of Motion, by Dr. Tyndall. Thermometric Scale 41 of water at 2 1 2° F. should yield a mixture in which the ther- mometer should stand at 122°, the exact mean. Yet it is not true that even in the same substance equal increments of heat, at (f«^r(f«/ temperatures, produce an equal amount of expansion ; for example, the expansion of mercury for the 10 degrees be- tween 30° and 40° is less than its expansion for the 10 degrees between 200° and 210°. In the mercurial thermometer, for temperatures between freezing and boiling water, it may never- theless be assumed, without sensible error, that equal increments of heat raise the thermometer through an equal number of degrees. The increase in the capacity of the glass bulb, espe- cially if the thermometer be made of crown glass, almost ex- actly compensates for the increasing rate of the expansion of mercury, though for temperatures above this point the com- pensation is not so exact. The general result is, that for all bodies, in proportion as the temperature rises the expansion increases ; the distance between the particles augments with the heat, and consequently their mutual cohesion is more readily overcome. The total expansion of mercury, for example, for three progressive intervalsjof 180" F., according to Regnault, is the following :— between 32° and 212° it is i part in 5S'o8 ; between 212" and 392° it is i in 54"6i ; and between 392° and 572°, I in 54-01. 102. 'The temperature of 572° F., as measured by an air- thermometer, if measured by the expansion of mercury in an ordi- nary thermometer, ^srould be indicated as 586°, because the appa- rent dilatation of the mercury increases as the temperature rises.' 103. The mercurial thermometer cannot be employed for temperatures below— 33° F., as mercury solidifies at — 4o°F.; and it cannot be employed with accuracy for temperatures above 580° F. ; for although its boiling-point under the ordinary atmospheric pressure is above 650° F., owing to its being in vacuo in the thermometer-tube its point of ebullition is consider- ably lowered. 104. ' The whole thermometric scale is to be regarded as purely arbitrary, and may be compared to a chain, extending indefinitely both upwards and downwards. We select some point on the chain, and begin to count the degrees from that. We fix the length of our degrees by selecting a second point, 42 Fundamental Principles of Chemistry at a convenient distance above the first, and dividing the in- tervening length into an arbitrary number of equal parts. Thus all is arbitrary ; and there is no peculiar virtue in the two points which have been chosen, other than that they can be easily determined with accuracy, and include between them the range of temperature with which we are usually most concerned.' 105. When a thermometer is introduced into melting ice, the level of the mercury in the tube should stand exactly at the point of the scale which indicates this temperature ; and when it is suspended in the steam of boiling water, the level of the mercury should stand, at the standard pressure, exactly at the point of the scale which indicates the temperature of boihng water. To ascertain whether the value of the degrees is uni- form throughout the entire length of the tube, a little column of mercury must be detached from the rest of the metal, the tube must then be inclined so as to make the small column pass from one part of the tube to another part, and we must ascertain by measurement whether it occupies the same length in the tube in each position. To ascertain whether the air has been perfectly expelled before sealing the tube, the instrument must be inverted, so that the bulb is uppermost; if the mercury descends with ease quite to the end of the tube, we may be satisfied that air is absent in that part of the instrument. But there may be some in the bulb — to ascertain this, we must ob- serve whether the bubble which is in the bulb during the time it is inverted entirely disappears when we restore the instru- ment to its proper position ; if it does, the thermometer is perfect as regards the entire absence of air. 106. ' Sometimes a thermometer, when inverted, does not allow the mercury to descend, and inexperienced persons are liable to imagine that air must necessarily be present ; but the effect alluded to is frequently caused by the adhesion between the mercury and the glass ; if, however, we warm the bulb, so as to cause the mercury to ascend in the tube, and then invert the instrument, the metal should descend ; and if no moderate tapping or swinging will make it do so, we may safely conclude that air forms the impediment.' 107. As it is frequently necessary to translate the figures on the Centigrade scale into those of Fahrenheit, and vice Specific Heat 43 versoi, tables are constructed by which the degrees on the one scale can be converted into those of the other at a glance. But it is necessary to know how to convert the one into the other by calculation, which is easily accompUshed; 100° C. = 180° F., or 5° C. = 9° F. ; hence, 1° F. =f° C. + 32 : the 32 is added because the zero of Fahrenheit is 32 Fahrenheit degrees below the zero of the Centigrade. The conversion is easily effected by the use of the following formulae : — Fahrenheit to Centigrade . . |(F.°-32) = C.° Centigrade to Fahrenheit . . |C.°+32=F.° Reaumur to Fahrenheit . . . |R.°+32=F.° Fahrenheit to Reaumur . . . |(F.°-32) = R.° Exercises on the conversion of one thermometric degree into another of a different scale. 26. Reduce 60° F. to the degrees of C. and R. ; 60° of R. to F." ; 50° C. to F.° ; 20° F. to C.°; -2-2° F. to C.°; -2° C. to F.°; -5-8° F. to C.°;S°C. toF.°;-24°C. to F.° ; -36° C. to F." 108. If equal quantities of the same liquid, at different tem- peratures, are mixed together, the temperature of the mixture will be the mean of the two; thus, if one pound of waterat 60° is mixed with the same quantity at 212°, the temperature of the mixed mass will be 136°. But if equal weights of different Xio^x&s, are mixed together, the temperature of the mixture will not be the mean of the two ; thus, if one pound of mercury at 40° is mixed with the same quantity of water at 156°, the temperature of the mixture will be i52'3°. Therefore, whilst the tempera- ture of the water has only been depressed 37°, enough heat has been evolved to raise the temperature of the mercury ii2'3°. If we substitute volumes for weights, we find that water requires double the quantity of heat that an equal volume of mercury requires, to raise it to a certain number of degrees; thus, if two glass vessels, one containing water, and the other an equal volume oi mercury, be immersed at the same time in a hot water bath, it will be found that the mercury becomes heated to the temperature of the water in the bath, in half the time that the water in the glass vessel requires to gain that tem- perature ; and if the vessels containing the mercury and water be removed from the bath, after the two liquids have arrived at 44 Fundamental Principles of Chemistry the same temperature, the mercury, it will be found, will cool twice as rapidly as the water. To take another example ; if one pound of iron filings at 68° be placed in one pound of water at 32°, the temperature of the mixture will be 36° ; con- sequently, the quantity of heat, the loss of which lowers the temperature of the iron 32", increases the temperature of the water only 4°. It is evident, from these examples, that equal weights and equal volumes of different substances require the addition of different quantities of heat to produce the same alteration in their temperature ; hence, different bodies at the same temperature, and whose volumes or weights are equal, contain unequal quantities of heat. 109. From what has just been stated, the student will clearly see that the thermometer only measures the temperature of bodies, and not the amount of heat they contain ; for dif- ferent bodies, at the same temperature, and whose volumes or weights are equal, contain unequal quantities of heat. Unequal quantities, by volume or weight, of the same body, may also indicate the same temperature, though the larger quantity must necessarily contain more heat than the lesser quantity ; for in- stance, the water in a wineglass will have the same temperature as the water in a cistern, if filled from the same source. In one condition only the thermometer becomes a direct measure of the amount of heat, and that is in the case of the same weight of the same substance. Thus if we take the one pound of water, it is true that, if a given amount of heat will raise its temperature 1°, twice the amount will raise its temperature 2"; here, then, we have a unit for measuring the amounts of heat. 110. The absolute quantity of heat which a body gains or loses cannot be measured ; but we can ascertain how much one body gains or loses compared with another, either by the process of mixing described in the examples we have given, or by other methods we shall presently describe ; we ascertain by these methods the relative quantities of heat which equal volumes or weights of different substances require, to raise them to a given temperature. Thus we have already noticed, that if one pound of mercury at 40° F. is mixed with one pound of water at 156° F., the mixed mass will have a temperature of 15 2 '3° F. Consequently the same weight of water requires, Specific Heat 45 according to these numbers, rather more than thirty times as much heat as mercury requires to produce the same elevation of temperature ; as mercury requires a less amount of heat than water to raise it a given number of degrees, it is said to have a less capacity for heat than water. The capacities for heat of all solid and liquid bodies are expressed in numbers in relation to that of water ; these numbers • are termed the specific heats of bodies. III. Quantity of heat must, like all other quantities, be measured in the terms of some unit ; pure water is taken as the standard substance in measuring quantities of heat ; but several different units of heat, and units of mass, are employed. In England, for practical purposes, the unit 7nass is one pound avoirdupois of water, and the unit of heat is one degree Fahrenheit, or Centigrade ; but the temperature of the water from which the standard is taken varies ; some adopt, as the thermal unit, the quantity of heat required to raise i lb. of water one degree F. between 55° and 60° ; others adopt as the thermal unit the quantity of heat necessary to raise that quantity of water from 0° to 1° C. Whichever of the two thermometric scales is employed, the unit of heat is termed the pound-degree. In France and in all countries, for scientific purposes, the unit of mass employed is either one kilogramme, or one gramme, of water ; and the unit of heat one degree Centigrade, and from 0° to 1° C. ; when the gramme is employed it is termed the gramme degree. We thus learn, that by the term specific heat, or calorific or thermal capacity of a substance, is meant the quantity of heat which is required for raising its temperature through one degree, compared with the quantity of heat which an equal weight of water would require to be raised through the same degree. Thus, if we take five vessels, containing respectively one pound of water, one pound of sulphur, one pound of iron, one pound of silver, one pound of mercury, and expose them all to such a source of heat that equal amounts must enter each vessel during the same time — if, now, we observe the thermo- meters which have been placed in these vessels, we shall find, when the temperature of. the water has risen one degree, and consequently, when one unit of heat has entered each vessel, that the temperatures of the other substances have increased 46 Fundamental Principles of Chemistry by the number of degrees given in the second column of the following table. By the principle just established, it follows that, if one unit of heat will raise the temperature of one pound of mercury 30°, it will only require one-thirtieth as much, or o'o33 of a unit of heat, to raise the temperature of the same weight one degree. In like manner, the fractional parts of a unit of heat required to raise the temperatures of one pound of each of the other substances one degree can be easily calculated, and are given in the third column of the table ; these fractional parts are termed the specific heats of the substances : — Unit of heat Temperature (Specific heat) Water . . . .10° i-ooo Sulphur . Iron , Silver . Mercury 4-9 0-203 8-8 0-114 17-5 0-057 30-0 0-033 Water, then, at the same temperature, contains 4-9 times as much heat as the same weight of sulphur, 8-8 times as much as the same weight of iron, 17-5 times as much as the same weight of silver, and 30 times as much as the same weight of mercury ; and, in like manner, we should find that at the same temperature, and for equal weights, water contains more heat than any solid or other liquid known. Hence the specific heat of solid or liquid substances is always expressed by fractions. 112. ' Three methods have been employed for determining the specific heat of solids and liquids — the method of the melt- ing of ice, the method of mixtures and that of cooling. In the latter, the specific heat of a body is determined by the time it takes to cool through a certain temperature. Before describing these methods, it is important to explain how we measure the quantity of heat absorbed by a body of which the mass and the specific heat are given, when the temperature is elevated a certain number of degrees.' 113. Measure of the sensible heat absorbed or lost by a body when raised or lowered from one temperature to another. Let the unit of heat be that amount of heat which would raise the temperature of a pound of water from 0° to i" C. If H be the specific heat of any substance, it follows from the definition of specific heat we have given, that H will represent the quantity of heat required to raise the temperature of a pound Specific Heat 47 weight of such substance 1° ; 2 H the quantity required to raise it 2° ; and so on. 114. If the temperature of a pound weight of a substance, whose specific heat is H, be raised through any number of degrees, say D, the amount of heat required will be measured by H X D. A body whose specific heat is H, weighing W pounds will therefore require a quantity of heat W x H x D to raise it through D degrees of temperature. This is usually expressed thus : Q = W H D. Example : — How much heat is required to raise the tempera- ture of 167 pounds of iron from 25° to 35", the specific heat of iron being o'ii4? Here the number of degrees through which the body is to be raised is 10°, since 35° —25° = 10° ; 167 must therefore be multiplied by o-ii4and by 10. The result is : Q = WHD= 167 X 0-114 X 10= 190-38^ of heat. 115. The above formula will also give the quantity (or degrees) of heat given out by a body of weight W, and specific heat H, in cooling down through D degrees of temperature. To illustrate it we will give the previous example shghtly altered : — How much heat is given out on the temperature of 167 lbs. of iron being reduced from 45° to 35°? Here the number of degrees the metal is reduced in temperature is 10° (since 45°— 35°= 10°); 167 must therefore be multiplied by 0-114 and by 10. The result is : — Q = WHD= 167 X 0-114 X 10 = 190-38° of heat. 116. Method of the fusion of ice. — Black employed a block of ice in which a cavity' was formed, and which was provided with a cover of ice, as a calorimeter. The substance whose specific heat had to be determined was heated to a certain temperature, and then placed in the cavity, and covered with the ice-cover. When the body had become cooled to zero, the cavity was opened, and both the substance and the cavity were wiped perfectly dry with a cloth which had been previously 48 Fundamental Principles of Chemistry weighed. The cloth was subsequently weighed ; the increase in weight gave, of course, the quantity of ice which had been converted into water ; and from the weight of ice melted was calculated the specific heat of the body. Lavoisier and Laplace substituted a more complicated apparatus for the block of ice employed by Black, on account of the diiificulty of obtaining ice in sufficiently large blocks. This apparatus is termed the ice calorimeter ; the results obtained by it are in- accurate. Recently Bunsen has devised a calorimeter founded on the same principle, ' but in the use of which the sources of error are eliminated, and the physical constants determined with a degree of precision seldom before attained in researches of this kind.' 117. Method of Mixtures. — If a hot body be immersed in a cold liquid, after a short time both will be at the same temperature, the liquid gaining the same quantity of heat as the other body loses. This enables us to find the specific heat of a body in the following way : The body is weighed, and then raised to a knowri temperature, by keeping it, for instance, in a current of steam for some time ; it is then immersed in cold water, the weight and temperature of which are known. Let :— W=weight of the body. K/=weight of water. H= specific heat of the body. The specific heat of water is unity. D= difference of the temperature of the body before and after the experiment. ^= difference of the temperatures of the water. By par. 114, the quantity of heat lost by the body is WHD. And the quantity of heat gained by the water is wd. Therefore— WHD=z«/rf ; and H=-^ Example : — If 5 oz of gold at a temperature of 67° C. are immersed in 6 oz. of water at 29°, the temperature of the mix- ture becomes 30° ; what is the specific heat of gold ? Specific Heat 49 Here, D=67°-3o°=37° ; and (/=3o°-29°=i W=5 ;andw=6 We have — Sp. ht. of Gold=H=,^=_^=o-o3243. WD 5x37 ^ ^^ Exercises on Specific Heat. 27. Taking the specific heat of iron as 0-114, ^ovi much sensible heat would be absorbed by 10 lbs. of iron raised from 0° to 20° C. ? z8. How much heat would be disengaged, if 15 lbs. of copper were cooled down from 100° to 5° C. , its specific heat being 0'096 ? 29. If 3 lbs. of mercury, at 30° C. , are mixed with 3 lbs. of water, at 10° C. , and the temperature of the mixture is found to be 10 639° C. , what is the specific heat of the mercury ? 30. If 0-685 ^- of sulphur, at 60° C. , is immersed in 4-573 lbs. of water, at 12° C. and the temperature of the mixture is 13-42°, what is the specific heat of the sulphur ? 31. If4lb5. of zinc at a temperature of 97" C. , be immersed in 11 lbs. of water at 5°, and the resulting temperature of the mixture be 8°, what is the specific heat of zinc ? 32. If 13 lbs. of platinum at 50° be immersed in 6 lbs. of water at 36', and the resulting temperature of the mixture be 37°, what is the specific heat of platinum ? 118. It is obvious that the vessel which holds the cooling water must change its temperature with that of the water, so that the heat lost by the substance which is cooled not only raises the temperature of the water, but also the temperature of the material of which the vessel is composed to the same degree. In accurate experiments the amount of heat required for this purpose must be estimated and allowed for. The amount is easily estimated if we know the weight of the vessel and the specific heat of the substance of which it is made. The vessel is usually a small cylinder of silver or brass, with thin polished sides, so that these data can be readily obtained. If w' be the weight of the vessel and h! its specific heat, then the vessel, being raised through d degrees, will absorb a quantity of heat w' h' d. Now if v be the weight of warer which would absorb as much heat as the vessel does, then z/=?e/ H, hence the heat lost by the body is absorbed by the water and the vessel, that is by a quantity of water w, and by an equivalent to a quantity of water v. Thus, instead of w in E 50 Fundamental Principles of Chemistry the preceding formula, we write w-\-v ; the formula then be- comes — • ^_ {w-\-ii) d . V is said to be the reduced value in water of the vessel. Example :— Three lbs. of silver at a temperature of 84° are immersed in 5f lbs, of water contained in a glass vessel whose weight is i^lb., both being at 10° ; the mixture becomes of a temperature of 12". Calculate the specific heat of silver, that of glass being '198? Here w'=\\= 1-25, ,^'=-198 ; therefore, v = w' ^'=1-25 X -198 =-2475 ; and w=sf=575, d=i2 — io=2 ; D=84— i2,W=3 hence : ■^_(v + w) '/_ (-2475 + 575) X 2 - 5'9975 x ^ — -prr WD 3x72 3x72 119. In accurate experiments, it is necessary also to allow for the heat absorbed by the glass and mercury of the thermo- meter ; and if, as is usually the case, the substance is enclosed in a glass tube in a small basket of wirework, it is also neces- sary to pay regard to the weight and specific heat of these envelopes in the calculation. This method of determining the specific heat of solids and liquids admits of great accuracy, but its practical application requires many precautions, owing to the numerous sources of error. Exercises on Specific Heat. 33. A piece of iron weighing 20 grammes at the temperature of 98° C. is dropped into a glass vessel weighing 12 grammes, and containing 150 grammes of water at io° C. The temperature of the water is thus raised I0'29C. Required the specific'Beat of the iron, knowing that the specific heat of the glass is 0'I9768. 34. Calculate the specific heat of oil of turpentine from the following data : — 42'57 grammes of the oil at 337 were mixed with 470'3 grammes of water at 12 •23". The temperature of the mixture was found to be 15-57°. 120. When we wish to determine the specific heat of a liquid or of a body which liquefies at a temperature little higher than that of the surrounding air, we are obliged to have recourse to the inverse method, which consists in cooling the body in a Specific Heat 51 freezing mixture, and determining the depression of temperature which is produced by its immersion in the calorimeter. 121. The specific heat of a body is not a constant quantity ; it increases with the temperature ; a greater amount of heat is therefore required to raise a body one degree at a high, than at a low, temperature. Examples : — The specific heat of water at 180° C. is i'o364 ; the mean specific heat of silver, between 0° and 100°, is 0*0557 : while between 0° and 200° it is o"o6ii. The student will now understand the reason why, in the de- finition of the unit of heat, a particular temperature, and not 1° at any temperature, was named. 122. The specific heat of a body is greater in the liquid than in the solid state : thus the specific heat of water is i,that of ice is 0-504 ; liquid bromine, ciii, solid bromine, o"o8i; melted tin, '0637, solid tin, •05632. Knowing these facts, we might infer what is really the case, — that the increase of specific heat with the temperature is greatest as solid bodies approach the melting-point ; and that the specific heat of solids dimi- nishes with the increase in their density, or molecular aggrega- tion. Examples : — Solid copper, when annealed, has a specific heat equal to '09501 ; but by hammering, its density is in- creased, and consequently its specific heat is diminished. The specificheat of copper which has been hammered is '0936. The density of tin and lead is not increased by mechanical pressure ; their specific heats are not, therefore, diminished by pressure. The specific heat of a substance is not the same in its different allotropic modifications ; in these cases, also, the specific heat diminishes as the density of the substance increases. Ex- ample : — Specific gravity Specific heat Wood charcoal . . 0-300 0-2415 Graphite . . 2-300 0-2027 Diamond . ■ 3 500 0-1469 123. The specific heat of liquids, with the exception of water, increases with the temperature much more rapidly than that of sohds. 124. Mercury, on account of its small specific heat, is rapidly heated and cooled. This property, as well as some of its other properties which have been already explained, renders 52 Fundamental Principles of Chemistry it well adapted for a thermometric agent. Water, on the other hand, from its great specific heat, requires a long time in being heated or cooled. For the 'same weight and temperature, it absorbs or gives out far more heat than any other known liquid or solid, and is only exceeded by that of hydrogen. The ocean becomes, from this property of water, the great storehouse of heat; and we can at once see the important part water plays as the great regulator of climates, on account of this property. Comparing equal weights, the specific heat of water being i, that of atmospheric air is 0-25 ; hence ilb. of water, in losing 1° of heat, would raise the temperature of i lb. of air 4°, or 4 lbs. of air i" ; but, owing to its much less density, i lb. cf air fills about 770 times the space of i lb. of water ; consequently, 4 lbs. of air fill 3,080 times the space ; therefore, water, by parting with i" of heat to the air, increases with that heat the temperature of 3,080 times its own bulk of air 1°. A large quantity of heat becomes stored up in the ocean in summer, which is slowly re- stored to the air in winter. ' Hence one cause of the absence of extremes in an island climate. In various parts of the Continent fruits grow which our summers cannot ripen ; but in these same parts our evergreens are unknown ; for they can- not live through the winters. The winter of Iceland is, as a general rule, milder than that of Lombardy.' 125. Specific heat of gases. — The specific heat of gases is re- ferred either to that of water or air. Gases, according as they are allowed to expand, or they are not allowed to expand, being kept at a constant volume, on being heated, have a different capacity for heat ; the former is called the specific heat under constant pressure, the latter the specific heat under constant volume ; under the former condition the specific heat is greater than under the latter condition, by the amount of heat consumed in the expansion. 126. The specific heat of air, and of gases not readily liquefiable, does not increase with a rise of temperature, at all events between the temperatures of —30° and 200° C. It has also been ascertained that, for pressures ranging between one and twelve atmospheres, the specific heat of equal weights of air, and of gases not readily liquefiable, is uniformly the same, and is independent of the density ; consequently, the specific Expansion and Contraction of Matter 53 heat of a given volume of gas increases directly as its density is increased. 127. All solid, liquid, and gaseous bodies, we have learned, expand vi\\&n they are heated and contract when they are cooled ; and the rate and degree of expansion of each substance are always the same, no matter how often it may be heated, if its tempe- rature be the same at the commencement of each experiment, and the same amount of heat be added. For example, — if a substance at the temperature of 40° F. be heated up to 100° R, it will always expand to the same bulk when raised from 40° to 100° F., and it will always contract to the same bulk when cooled down again to 40° F. ' 128. The same amount of heat affects matter in its three states very unequally. It produces the greatest expansion in gases, and the least in solids, because there is no cohesiveness between the particles of matter in the gaseous state ; the heat has, therefore, no opposing force to overcome ; and as the co- hesive force is less in liquids than in solids, a less amount of heat is neutralised in overcoming this opposing force, and, therefore, for the same amount of heat, a greater expansion takes place in liquids than in solids. 129. All gases, on account of the absence of any cohesive- ness between their particles, expand alike,''' the pressure being the same, for equal additions of heat; and contract alike for equal subtractions of heat ; but the different liquids and solids expand and contract unequally, for equal additions and subtractions of heat. 130. Having stated that all gases expand and contract alike on account of the absence of any cohesiveness between their particles, the following law, known as the law of Charles, that all gases measured under constant pressure, expand equally for equal increments of heat, might even be inferred ; one volume of any 1 ' Lead is an exception to the rule ; it is so soft that its particles shde over each other in the act of expansion, and do not return to their original position. For example, a. leaden pipe used for conveying steam permanently lengthens some inches in a short time ; and the leaden flooring of a sink which often receives hot water, becomes, in the course of time, thrown up into ridges and puckers.' — Graham. '' All that is stated with respect to gases applies also to vapours at some distance above their points of condensation. 54 Fundamental Principles of Chemistry gas at o° C. expands to i'366s at ioo° C, so that the coefficient of expansion of gases is o'oo3665 or nearly -^^^^ for an increase from o° to 1° C. 131. We have learned that when substances are submitted to the action of heat, their temperature is raised, and they in- crease in volume. These are the first effects of heat on all substances, and they are the only ones produced on gases. But if the application of heat to solids and liquids be continued after these changes have commenced, a temperature is reached at which the solids and liquids change their state. The temperature at which each solid changes its state is constant and peculiar to itself, and this is called its melting-point, or point of fusion. Ebul- lition, like fusion, /(7r a given pressure commences at a certain teftiperature, which varies in different liquids, but which, for equal pressures, is always the same in the same liquid ; but this is not the case with evaporation, which takes place even with the same liquid at very different temperatures. 132. For the conversion of a sohd into a liquid, and a liquid into a gas, a large amount of heat must be communicated to the solid, and to the liquid, to cause them to change their state ; and this heat is not indicated in the substance by the thermo- meter ; thus, if equal weights of water at o" C, and water at 79° C, be mixed together, the temperature of the mixture will be the mean of the two temperatures, viz. 39*5° ; but if i lb. of pounded ice at 0° is mixed with i lb. of water at 79°, the ice will be melted, but the temperature of the 2 lbs. of water will only be 0° ; 79° of heat have, therefore, disappeared or become latent in melting the i lb. of frozen water. This absorbed heat is not lost or destroyed, for if the 2 lbs. of water be frozen that heat, and the latent heat of the water employed, will be evolved. The heat required to melt unit mass of ice without change of temperature is called the heat of liquefaction of ice or the latent heat of water, and amounts, as we have learned, to 79 thermal units of the Centigrade scale ; an amount of heat that would raise 79 lbs. of water one degree Centigrade. 133. Black, in 1757, was the first to clearly establish that in order to convert water at the boiling temperature into steam of the same temperature a large quantity of heat must be com- municated to it. ' He and many of his followers supposed Latent Heat 55 heat to be a substance which when it makes a thing hot is sensible, but which when it is not perceived by the hand or the thermometer still exists in the body in a latent or concealed state. Black supposed that the difference between boiling water and steam is, that the steam contains a great deal more caloric than the hot water, so that it may be considered a com- pound of water and caloric ; but, since this additional caloric produces no effect on the temperature, but lurks concealed in the steam ready to appear when it is condensed, he called this part of the heat latent heat.' 134. This view of the theory of heat, as has been previously explained, is not now accepted ; and the late Professor Clerk Maxwell, in his work 'Theory of Heat,' which we quoted the last extract from, says, ' and, as I think Sir Isaac Newton's opinion that heat consists in the internal motion of the particles of bodies much the most probable, I choose to use the expres- sion, "heat is generated," an expression Cavendish first employed.' 135. 'We shall not now be in danger of any error if we use latent heat as an expression meaning neither more nor less than this : 136. ' Definition. — Latent heat is the quantity of heat which must be communicated to a body in a given state in order to con- vert it into another state without changing its temperature. 137. ' We here recognise the fact that heat when applied to a body may act in two ways : by changing its state, or by raising its temperature ; and that, in certain cases, it may act by changing the state without increasing the temperature. 138. ' The most important cases in which heat is thus em- ployed are — '(i) The conversion of sohds into liquids. This is called melting or fusion. In the reverse process of freezing or solid!, fication heat must be allowed to escape from the body to an equal amount. ' (2) The conversion of liquids (or solids) into the gaseous state. This is called evaporation, and its reverse condensa- tion. ' (3) When a gas expands, in order to maintain the tem- perature constant, heat must be communicated to it, and this. 56 Fundamental Principles of Chem/stry when properly defined, may be called the latent heat of ex- pansion. ' (4) There are many chemical changes during which heat is generated or disappears. 139. ' In all these cases the quantity of heat which enters or leaves the body may be measured, and in order to express the result of this measurement in a convenient form, we may call it the latent heat required for a given change in the substance. 140. ' We must carefully remember that all we know about heat is what occurs when it passes from one body to another, and that we must not assume that after heat has entered a substance it exists in the form of heat within that substance. That we have no right to make such an assumption will be abundantly shown by the demonstration that heat may be transformed into and may be produced from something which is not heat' 141. The facility with which solids liquefy is proportional to the quantity of heat required for their liquefaction. Example : Ice cannot be liquefied until it has received as much heat as would raise its own weight of water 142-65° F. ; therefore ice liquefies very slowly, because the latent heat of water is consider- able ; whilst phosphorus and lead are liquefied by as much heat as would raise their own weight of water 9° F. ; therefore, they melt rapidly, because the heat required for their liquefaction is small. 142. Solids when heated up to their melting-point invariably liquefy ; they cannot be heated beyond this point and remain solid. But liquids, under particular circumstances, may be cooled down delow their freezing-point, or point of solidifica- tion, that is below the point at which, when in the solid state, the same substances melt. Example : Ice invariably melts or liquefies at 32° F. (0° C), but water can, under certain circumstances, be cooled down to 5° F. and not freeze. This retardation of solidification can be effected by slow cooling, and protection from all agitation ; but if it be the least agitated a portion of it is instantly converted into ice, and the tempera- ture immediately rises to 32° F., by reason of the portion which becomes solid disengaging its latent heat, which becomes sensible, and keeps a portion of the water, at least for a time, in the liquid state. The heat disengaged would raise as much Latent Heat 57 water as is equal in weight to the ice itself 142-65° ; it would raise, therefore, 14:^ times this quantity of water through 10° F. • 143. ' This test of the quantity of latent heat of water was applied with complete success, experimentally, by Dr. Thom- son, who showed that when water, cooled without congelation to 22° R, was suddenly agitated, a portion was congealed, which bore the proportion of 10 parts in 142-65 of the entire mass. He found, likewise, that the same result was obtained when the water was cooled to any other temperature below 32° without congelation. Thus, when water cooled to the temperature of 27° without congelation was agitated, it was found that the 28-5 part of the whole mass was congealed. In this case the whole mass was raised through 5° ; and since the heat deve- loped by the frozen portion would be sufficient to raise 28J times this portion through five degrees, it follows that the frozen portion must be the 28-5 part of the whole mass.' Examination Questions. 35. What is meant by the linear and what by the cubical expansion of a solid, and how are the two related ? 36. What do you mean by the maximum density of water ? 37. What is meant by the apparent, and what by the real expansion of a liquid ? Is the expansion of the mercury in a thermometer its apparent or real expansion ? 38. Explain how it is that the summer on an island is not so hot, and the winter not so cold, as on a continent in the same latitude. 39. Explain, as fully as you can, the reasons why mercury is usually chosen for thermometers, in preference to other liquids. 40. Explain and exemplify the terms specific heat and Icitent heat. 41. It has been laid down that water attains its maximum density at 4° C. ; explain precisely what this means, and describe an experiment by which you could prove it. 42. Distinguish between heat and temperature. 43. What experiment would you arrange in order to ascertain whether a pound of mercury absorbs as much heat as a pound of water when heated from 40' F. to 80° F. ? 44. Describe the filling and closing of a mercurial thermometer. It is sometimes found that when a mercurial thermometer is placed in melting ice, the temperature indicated is not zero, but a fraction of a degree above zero : how is this explained ? 45. Are the rails of a railway of the same length in winter and summer ? 46. In newspapers it is frequently stated during the winter season there has been during the night so many degrees of frost ; what do you under- stand by the expression ? 47. How do you know that the temperature at which water freezes is constant ? Water, when quite still, may be cooled some degrees below 58 Fundamental Principles of Chemistry 32° F, , and yet not freeze ; but on shaking it a portion freezes, and the temperature of the remainder rises to 32°. Explain the rise of temperature, and why a portion still remains liquid. 48. Why does not the entire mass of ice and snow instantly melt when the temperature reaches 32" or above ; and would the effect be beneficial or otherwise if they did instantly melt ? 49. Why should a glass vessel be more liable to crack when hot water is poured into it, if it be of uneven than if it were of even thickness ? 50. I wish to dry a solid substance at a particular temperature ; for this purpose I place it in a closed oven-shaped vessel, called an air-bath ; the vessel has a small opening on one side at the bottom, to admit small volumes of fresh air into the chamber, and a tube at the top to carry off the healed moist air ; it has also another opening at the top in which a ther- mometer is fixed, the bulb of which descends into the chamber. I place a Eunsen's gas-burner underneath the vessel, and so regulate the flame that when the air in the chamber has reached the temperature I desire it remains stationary, although I continue to heat the vessel with the gas flame. Account for the temperature remaining stationary after it has reached a given point. 51. How does water act as an extinguisher of fire ? 52. Why do some solids melt more rapidly than others ? 53. Define the meaning oi a. unit of heat, and explain the different kinds of unit in common use. 54. Why is the boiling-point of water more variable than its freezing- point ? ' 144. It has been at all times needful for the chemical student to be acquainted with the general properties of heat ; but it is more than ever essential for the student at the pre- sent time to be acquainted with heat phenomena, as Thermo- chemistry is becoming such an important branch of physical chemistry. On this account we shall explain a little further at length the present theory, called the mechanical or dynamical theory of heat.^ 145. According to this theory heat and motion are conver- tible one into the other. The first experiment devised which really proved the immateriality of heat was one by Sir H. Davy. He caused two pieces of ice to be rubbed against each other in vacuo, at a temperature of 0° C. ; the heat developed at the surfaces of contact melted the ice. Now ice has only half the capacity for heat that water has ; and we are further aware that it requires a large amount of heat to convert ice into water of the same temperature ; the heat that was required for the liquefaction for the ice, could not, therefore, come from the ice ^ The rest of the chapter m-ust be passed over until Chaps. III. and IV, have been completely studied. '^ ' Dynamics ' is derived from a Greek word signifying foi'ce. Dynamical Theory of Heat 59 itself ; hence Davy drew the conclusion that, ' the immediate cause of the phenomena of heat is motion, and the laws of its communication are precisely the same as the laws of motion.' Friction is a source from which, we all know, heat can be pro- cured : we rub our hands together to impart more warmth to them ; savages obtain fire by rubbing pieces of wood together ; the axles of wheels — railway-carriage wheels, for example — be- come heated by friction, and to prevent the reconversion of the motive force into heat, from which it was obtained, the axles are greased from time to time to prevent the friction. The total quantity of heat in the universe, according to the older view, never varied in quantity ; it could not be generated, nor could it be destroyed ; according to the present theory, heat can be generated by the conversion of motion into it ; a rifle- bullet, for example, when it strikes a target is instantly heated, the destruction of the motion producing heat. Another ex- ample of the conversion of motion into heat is illustrated in the stoppage of a railway train by means of the brake ; motion in this case is also transformed into heat ; indeed sparks may be seen flying out from the brake-wheel on a dark night. Heat, on the other hand, can be converted into motion, as is shown by the powerful mechanical effects produced by steam. The important principle of the present theory is this : — ' In all cases where mechanical effect is produced by heat, a quantity of heat is used up, proportional to the mechanical effect produced ; and con- versely, the same quantity of heat can be again generated by the expenditure of just so much mechanical effect.^ 146. It has been fully established that the quantity of heat generated by the same amount of force is fixed and invariable- ' The quantity of heat necessary to raise one pound of water one degree Fahrenheit in temperature, it has been proved, is equal to that generated by a pound weight, falling from a height of 772 feet against the earth. Conversely, the amount of heat necessary to raise a pound of water one degree in temperature, would, if all applied mechanically, be competent to raise a pound weight 772 feet high, or it would raise 772 lbs. one foot high. The term " foot-pound " has been introduced to express in a convenient way the lifting of one pound to the height of a foot. Thus, the quantity of heat necessary to raise the tempera- 6o Fundamental Principles of Chemistry ture of a pound of water one degree Fahrenheit being taken as a standard, 772 foot-pounds constitute what is called the inechantcal equivalent of heat. If the degree be Centigradcs 1,390 foot-pounds constitute the equivalent.' 147. From what has already been explained about the dynamical theory of heat, the student will no doubt have inferred that according to this theory the heat that is required, and which becomes insensible, for the conversion of a solid into a liquid, or a liquid into a gas, is not supposed to exist as heat in the liquid or the gas, but that it has become transformed into another force ; for as not a molecule of matter is, or can be, destroyed, so no force can be annihilated, but one force can be converted into another force. We must attempt to explain briefly the views that are held in accordance with this theory of heat, both on the sensible heat present in substances, and on what is technically termed the latent heat of liquids and gases. 148. At the outset we must define what is meant by the term energy ; this term is employed to denote capacity or powier of doing work, and work is done when resistance is overcome. There are two kinds of energy, viz. energy in action and energy in store ; the first is called energy of motion or kinetic ' energy, and the second is termed potential energy ; and they are con- vertible one into the other. There are various forms of energy, and they are divided into two classes, viz. visible energy, and molecular energy. Heat, as has been already stated, is one of the forms of energy ; and, in accordance with the dynamical theory, it is believed when a substance is heated, the heat communicated performs two different kinds of work ; a portion is transformed into a peculiar motion of the molecules of the body heated ; we apply to heat in this form the term tempera- ture, for it is perceptible to our senses and can be measured by thermometers. The more the vibrations of the molecules increase in intensity, the hotter, as we express it, the body becomes. An- other portion of the heat is expended in producing energy of expansion — in other words, in acting in antagonism to the cohesive force by causing the molecules to recede further from each other by weakening or superseding that force. The heat 1 Kinetic is derived from a Greelt word signifying motion. Dynamical Theory of Heat 6i which performs this work is what Black called latent heat, because it is not sensible ; it only becomes sensible when the cohesive force, either by cooling or other agency, again comes into play. 149. The molecules of matter in each of the three states in which matter can exist are, it is supposed, in a continual state of motion ; in solids the movement of the molecules is confined to a very small region of space. In fluids the path of the molecules is not confined within a limited region, as in the case of soUds, but may penetrate to any part of the space occupied by the fluid. In gases the molecules have very great freedom of motion, and they are supposed to move forward in straight Unes till they impinge against each other, or against the sides of the vessel containing the gas ; their course then is changed, and they start on a new path. These encounters also alter, and produce an inequality in, their velocity. ' This constant impact of the molecules produces the expansive tendency or elasticity which is peculiar to the gaseous state. The total quantity of heat in the gas is majje up of the progressive motion of the molecules, together with the vibratory and other motions of the constituent atoms ; but the progressive motion alone, which is the cause of the expansive tendency, determines the tempera- ture. Now, the outward pressure exerted by the gas against the containing envelope arises, according to our hypothesis, from the impact to a great number of gaseous molecules against the sides of the vessel. But at any given temperature — that is, with any given velocity — the number of such impacts taking place in a given time, must vary inversely as the volume of the given quantity of gas ; hence the pressure varies inversely as the volume or directly as the density, which is Boyle's law. 150. ' When the volume of a gas is constant, the pressure resulting from the impact of the molecules is proportional to the sum of the masses of all the molecules multiplied into the squares of their velocities — in other words, to the so-called vts viva or living force of the progressive motion. 151. ' If, for example, the velocity be doubled, each mole- cule will strike the sides of the vessel with a twofold force, and its number of impacts in a given time will also be doubled ; hence the total pressure will be quadrupled. 62 Fundamental Principles of Chemistry 152. ' Now we know when a given quantity of any gas is maintained at a constant volume, it tends to expand by -j^g^ of its bulk at zero for each degree Centigrade. Hence the pres- sure or elastic force increases proportionally to the temperature reckoned from —273° C. ; that is to say, to the absolute temperature. Consequently, the absolute temperature is propor- tional to the vis viva of the progressive motion.^ We may notice in conclusion that the expansion of air is attended with a diminution of temperature ; and its compression with an increase of temperature ; in fact, a compression or expansion amounting to o'oo366 of the volume which the air would occupy at zero, alters its temperature by o'4i° C. The cooling of the air by expansion, and the development of heat by its compres- sion, is thus explained on the dynamical theory of heat. Work is done in the expanding ; consequently a portion of the heat of temperature is expended in producing the energy of expansion ; hence the diminution of the temperature of the expanded gas. On the other hand, on compression there is a diminution of the expansive force, and to this diminution is due the develop- ment of heat. At times a cloud is formed in the receiver of the air-pump, when the air is being pumped out of it, because the rarefied air becomes chilled ; consequently some of the aqueous vapour it contained is condensed and forms the cloud ; if the air, during its presence, be readmitted, as the air necessarily becomes heated, ' the cloud melts away, and the perfect transparency of the air is restored.' Examination Questions. 55. Define what is meant by the mechanical equivalent of heat ; state what it is in foot-pounds. 56. In exhausting the receiver of an air-pump a cloud sometimes appears in the receiver ; explain the cause of this. 57. Explain the difference between the specific heat of air at constant pressure, and its specific heat at constant volume. Which of them is greater, and why ? 58. What is meant by saying that the specific heat of water is 30 times as great as that of mercury ? 63 CHAPTER III. WEIGHT — THE BALANCE — WEIGHTS AND MEASURES — EXERCISES WEIGHT AND PRESSURE OF THE AIR — DENSITY OF THE AIR AT DIFFERENT HEIGHTS — THE AIR-PUMP — EXPERIMENTS — FILTER- PUMP — PHYSICAL PROPERTIES OF GASES — EXPERIMENTS — EXER- CISES — QUESTIONS. 153. The particles of different bodies are, as we have already stated, attracted to each other, and this attraction is all-per- vading, for it operates throughout space, and is termed gravita- tion. Now as each particle attracts, the mass containing the greatest number of particles possesses, in consequence, the greatest attractive force; thus, according to the law of Newton, the attractive force of bodies is to each other directly as their masses, and inversely as the square of their distances ; therefore, if the mass of one body be two, three, four, or five times greater than that of another, its gravity or attractive force is also two, three, four, or five times greater ; and with a distance of two, three, four, or five times greater, the force of gravity will be four, nine, sixteen, or twenty-five times less. 154. Owing to this attractive force, the earth attracts all terrestrial objects towards itself, and is itself attracted by them ; but as their masses are so extremely small in comparison with the earth's mass, their motion only is apparent to us; hence the earth's attraction, or terrestrial gravitation as it is generally termed, tends to cause all bodies to fall to its surface. One of the effects of this attraction is the downward pressure which substances exert on whatever supports or prevents them from falling to the earth, and this pressure is termed their weight, ox more precisely their absolute weight ; and this is one of the subjects we have to consider in the present chapter. 155. Mass, or the quantity of matter in a substance, is estimated in terms of some standard : the British unit of mass is the standard pound (avoirdupois) ; and the balance, or weighing-machine, is used for the comparison of masses. There are other kinds or relations of weight; these we shall treat of by-and-by. 64 Fundamental Principles of Chemistry 156. The determining of the weight of substances is being constantly carried on in every-day life, and ' scales ' is the name usually given to the smaller weighing-machines in common use. 157. The weighing-machine used in experimental science is called a balance (fig. 25); it has to be not only extremely accurate, as also the weights employed, but must also be so delicate that it will readily indicate o'oo2 of a grain when carrying a load of 1,000 grains ; for, as the late Dr. Miller re- marked, the foundation of all accuracy in experimental science consists in the possibility of determining with exactness the quantity or mass, and the size or bulk, of those substances which are submitted to examination. The late Baron Liebig made the following observations in his ' Letters on Chemistry ' in reference to this instrument. 'The great distinction between the manner of proceeding in chemistry and natural philosophy is, that one weighs, the other measures. The natural philo- sopher has applied his measures to nature for many centuries, but only for fifty years have we attempted to advance our philosophy by weighing. 158. ' For the great discoveries of Lavoisier, he was in- debted to the " balance," that incomparable instrument which gives permanence to every observation, dispels all ambiguity, establishes truth, detects error, or shows us that we are in the true path. 159. 'The balance, once adopted as a means of investi- gating nature, put an end to the reign of Aristotle in physics. The explanation of natural phenomena by mere fanciful specu- lations, gave place to a true natural philosophy.' 160. It would be out of place in a work like this to enter upon the mechanism of the balance, but it will not be out of place to give the student a few hints as to the using of a deli- cate chemical balance. It is always placed in a glass case (fig. 25), in order to protect it from air-currents, dust, and moisture; as air-currents affect the weighing, no substance whilst hot must be weighed, because heat causes air-currents. An mdex-needle or pointer is fixed to the beam, and oscillates with it in front of the graduated arc a, and when the beam is suspended and at Weighing 65 Fig. 25. rest, no weight of any kind being in the scale-pans, the index should point to the zero of the scale. When the correct weight is being nearly approached, the balance-case should be closed ; and as the beam of a delicate balance oscil- lates for a long time, it is usual to weigh, in order to save time, whilst it is oscillating, adjusting the weights until the movements of the pointer on each side of the zero of the scale are equal ; results even more accurate, are ob- tained in this way, than if the beam was at rest during the time of weighing, because whilst oscillating, we are certain that no resistance is offered through the beam ' stick- ing.' The same pan for the weights should always be used ; the two arms of the beam should be of equal length, otherwise unequal weights would be required to produce equilibrium. The error occasioned by inequality of the arms of the balance may be eliminated by the method of double weighing, which consists in weighing the substance first in one pan and then in the other ; the weights will not be the same in the two weigh- ings, the geometric mean is, therefbre, the correct weight, and is found by multiplying the true apparent weights together, and taking their square root ; but if the true apparent weights be nearly equal, their common arithmetic mean is quite close enough to the truth. ' The balance will only give accurate comparisons of mass when the weighing is performed in vacuo, unless the body weighed happens to have the same density as the standard weights. The reason is that if the body and the weights are of unequal volume, they will displace different amounts of air, and hence lose weight unequally. It is, how- ever, easy to make the requisite correction.' When the weigh- ing is completed, the weights must always be removed from the scale-pan and replaced in the weight-box. F 66 Fundamental Principles of Chemistry 161. ' The standard of weight used in this country is an arbitrary quantity called the avoirdupois pound, which is sub- divided into 7,000 grains. It was enacted in 1855, " that the platinum weight deposited in the Exchequer shall be denomi- nated the imperial standard pound avoirdupois, and that the tttW^ of it shall be a grain, while 5,760 such grains shall denote one pound troy." 162. ' The two systems of weights — troy and avoirdupois — have no common integer except the grain. Although the names, pound, ounce, are common to both systems, they de- note different quantities in each.. The English troy pound is subdivided into 12 ounces, and each ounce is equal to 480 grains. These are the weights generally employed ; but for philosophical purposes ambiguity is most easily avoided by employing the grain as integer, and the laboratory should be provided with good sets of weights, from 1,000 grains downwards : the grain should be subdivided into tenths, hun- dredths, and thousandths.' Troy Weight. Pound, lb. I Ounce, oz. = 12 I Pennyweight dwts. = 240 = = 20 = I = . Grain. ?'■• 5760 480 24 Avoirdupois Weight. Pound, I , Ounces. Drachms. = 16 = 256 = 1 .= 16 = I = Grains. 7000 437 -S 27-34 163. ' The system of weights is connected with the measures of capacity in use in this country, through the medium of the imperial gallon ; which is defined by an Act of Parliament of the year 1824 to be a measure containing 10 lbs. avoirdupois of distilled water weighed in air at a temperature of 62° F., the barometer standing at 30 inches. The gallon of distilled water, therefore, contains 70,000 grains. 164. ' These measures of capacity are related to those of length by the determination that a gallon contains 277-276 cubic inches. A cubic inch of distilled water weighs, in air at 62° F., with the barometer at 30 inches, 252-456 grains; in Weights and Measures 67 vacuo it weighs 252722 grains. The standard of length is the yard measure, and is subdivided into 36 inches. The standard yard is defined by an Act of Parhament passed in 1855, where- by it is enacted that the straight line or distance between the centres of two gold plugs in the bronze bar deposited in the office of the Exchequer shall be the genuine standard yard at 62° F., and if lost it shall be replaced by means of its copies.' — Miller. 165. The French or metrical system of weights and measures is connected together in a more philosophical man- ner than the English one ; it is the one that is almost uni- versally adopted abroad by scientific men, and is now largely employed by scientific men in England. It is a decimal systemi founded upon the metre, which is ^j^^^th part of a quadrant of the meridian : this constitutes the unit of the system. 166. The French mfetre is equal to 39"37o7 English inches. The tnetre is, in France, the integer of the measure of length, and from it all measures of surface, capacity, and weight are derived. The integer of the measure of capacity is the litre, which is the cubic decimfetre, and is equal to 35*275 fluid ounces, or i'763 imperial pints. The integer of the measure of weight is the^/-«w»2«,= i5"43 English grains. It is exactly equal to the weight of a cubic ceutimetre of water, weighed m vacuo at its maximum density (39"2° F.). The cubic centimetre is employed by French chemists in all measurements of gases, in place of our cubic inch. It is equal to 0-06103 of a cubic inch. The weight of the cubic centimetre of water is to the cubic inch of water as i5'432 to 252-468; hence there are 16-34 cubic centimetres to an English cubic inch. 167. This rule is sufficiently correct for practical purposes. It is to be observed, however, that the French take the weight of the cubic centimetre of water at 39-2° F. in vacuo. The English take the weight of the cubic inch (252-458) grains at 62° F. in air. Assuming the specific gravity of water at 32° to be 1-000,000, the specific gravity at 39-2° is to the specific gravity at 62° as 1-000,099 to 0-999,000. 168. ' The French measures increase and decrease in de- cimal proportions. For the increase, a prefix is used derived from the Greek deca, hecto, kilo, and myria ; the integer. 68 Fundamental Principles of Chemistry whether mfetre, litre, or gramme, being multiplied by lo, loo, i,ooo, and 10,000 respectively. To indicate the decrease, the prefixes deci, centi, and milli, derived from the Latin, are em- ployed. In this case the integer is supposed to be divided by 10, 100, or 1,000. 169. ' Various plans have been devised for converting the French weights and measures into their English equivalents. The following tables will be found useful for this purpose : — Measures op Length. In English inches In English inches Millimetre • = -03937 Decametre = 393-70790 Centimetre • = -39371 Hectomkre = 3937-07900 Decimetre • = 3-93708 Kilometre . - 3937079000 Metre • = 39-37079 Myriomhre = 393707-90000 I inch= 2*539954 centimetres. 1 foot = 3 '0479449 decimetres. I yard = 0-9I43835 tahxt. I mile = I ■6093149 kilometre. Measures of Volume, or Capacity in Cubic Inches. Millilitre, or cubic centimetre . . . = O*o6l03 Centilitre, or 10 cubic centimetres . . = 0'6i027 Decilitre, or 100 cubic centimetres . . . = 6"I027I Litre, or cubic decimetre, or 1000 cubic centi- metres = 61-02705 Decalitre, or centistere . . . . = 610-27052 Hectolitre, or decistere .....= 6102-70515 Kilolitre, or stere, or cubic metre. . . = 61027-05152 Myriolitre, or decastere . . . . = 610270-51519 I cubic inch I cubic foot I gallon = 16-386176 cubic centimetres. = 28-315312 cubic decimetres, or litres, = 4-543358 litres. Measures of Weight. In English grains Milligramme . = 0-01543 Centigramme . = 0-15432 Decigramme . = 1-54323 Gramme . . = 15-43235 In English grains Decagramme = 154-32349 Hectogramme = 1543-23488 Kilogramme = 15432-34880 Myriogramme = 1 54323 -48800 I gram I troyoz. 0-064799 gram. 31-103496 grams. lib. avois. = 0-453593 kilogr. I cwt. . = 50-802377 kilogrs. Weights and Measures 69 Measures of Surface. In English square feet In English square yards = 9 square feet In English poles = 272-25 square feet in English roods = 10,890 square fee. In English acres = 43,560 square feet Centiare or square ) mfctre . . , Are or 100 square 1 infetres . . ' Hectare or 10,000 1 square metres . J 10-764299 1076-429934 107642-993418 I '196033 119-603326 11960*332602 0*0395383 3*9538290 395 '3828959 0-0009885 0*0988457 9*8845724 0-0002471 0-0247114 2-4711431 1 square inch = 6 '45 13669 square centimetres. 1 square foot = 9 '2899683 square decimetres. I square yard = 083609715 square metre, or centiare. I acre =0 '40467 1 02 hectare. 170. ' With respect to the equivalents of English and French weights and measures, some slight differences will be found among English writers. These arise from the calculations being based on the employment of a larger or smaller number of decimal figures.' JExercises on the Conversion of French into English Measures, and vice versa. 59. Convert five centimetres into the corresponding length in English inches. 60. What is the corresponding French weight to one English grain ? 61. Convert twelve cubic centimetres into English inches. 62. What is the corresponding French volume to three cubic inches ? 63. Convert three kilogrammes into the corresponding English avoirdupois weight. 64. Convert one English inch into the corresponding French measure. 65. i determine the amount of silver in a silver-lead ore, I obtain 0'020 grains of silver from 400 grains of the ore ; for commercial purposes the silver contained in any given ore is estimated in ounces, pennyweights, and grains ; one ton of the ore being, in all cases, taken as the standard of unity. How many ounces, pennyweights, and grains of silver were contained in a ton of this ore ? 66. The late Baron Liebig, in his work The Natural Laws of Husbandry, states that an average wheat crop yields from a hectare of land 2,000 kilogrammes of grain and 5,000 kilogrammes of straw ; and arye crop from the same area 1,600 kilogrammes of grain and 3,800 kilo- grammes of straw ; convert these foreign weights and measures into their English equivalents. 171. All bodies in each of the three states of aggregation, possess weight, and dissimilar bodies have almost invariably a different weight for equal volumes. A child knows that solids ;o Fundamental Principles of Chemistry and liquids possess weight, but it is not so readily realised that gases possess weight, and that they differ in weight for equal volumes ; in other words, all gases have not the same weight ; some are heavier, some are lighter than others ; in brief, gases differ in weight like solids and liquids. The ascension of a balloon in the air is a very instructive illustration that gaseous substances differ in weight ; for its ascension is due to its being filled with a gas lighter than atmospheric air. Experiments on the Weight of Gases. 67. Fill a small balloon of goldbeater's skin, or a soap-bubble, ' with dry hydrogen gas, or coal-gas ; after the balloon is filled allow it to ascend in the air ; hydrogen being much lighter in weight than coal-gas, the balloon will be much more buoyant if filled with it, than if filled with coal-gas. 68. Prepare some carbon dioxide and let the exit tube of the apparatus dip into a dry glass vessel (fig. 26) ; the tube ought to reach to the bottom of the vessel. As soon as the vessel is filled with the gas, which is ascertained by a candle being extinguished when introduced just below the edge of it, pour the gas as you would a liquid into another vessel of exactly equal size and shape. Prove that the gas has been really transferred from the one vessel to the other by introducing a lighted candle first into the vessel originally containing it (in which the candle ought now to burn), and then into the one which ought now, if the experiment has been properly performed, to contain it, and in which the candle ought not now to burn. If great care be observed in the experiment, it may be transferred from one vessel to the other three or four times. This ex- periment shows the great density of the gas : it also shows the incapability of the gas to support the combustion of a candle. 69. Fill a wide and deep glass jar half-full of carbon dioxide, the upper half being filled with atmospheric air ; fill a collodion balloon with hydrogen and air in such proportions that the balloon will just sink in air ; when so prepared, let the balloon sink into the jar ; as soon as it reaches the uppermost layer of the oxide of carbon it will rebound as if it had touched a solid body ; it will finally float quietly upon it, and it is curious to see the balloon suspended midway in the jar, apparently resting upon ' For making soap-bubbles the following is the best method for making the soap solution : put into a quart bottle some of the best white Castile soap (or, still better, pure palm-oil soap). Cut the soap (about four ounces) into thin shavings, then fill up the bottle with distilled water or rain water, shake the mix- ture very well ; repeat the shaking until a saturated solution of soap is obtained. If on standing the soap is not all dissolved, pour off the liquid, and add more water to the soap which remains undissolved, shaking as before. Then add to two volumes of the soap solution one volume of pure, concentrated glycerine. Fig. 26. The Barometer 71 nothing. This experiment is an exceedingly interesting and instructive one if well performed. 172. The barometer is an instrument that proves that the air possesses weight, for it is the pressure of the atmosphere on the surface of the mercury in the cistern (fig. 27) that sustains or makes the mercury in the tube stand about 30 inches above the level of that in the cistern, for if, instead of having the upper end of the tube herme- tically sealed, it were closed by means of a stopcock, and that it was opened when the mercury was stand- ing in the tube, the mercury would instantly sink in the tube to the same level as that in the cistern ; proving that it was the pressure of the air upon the mercury in the cistern that supported the mercury column. 173. The barometer illustrated in fig. 27 is called the cistern barometer ; there are other forms of the mercurial barometer, but they all depend on the same ^"^' °'' principle, viz. the pressure of the air on the mercury. There are barometers, as the aneroid, without any liquid ; but they likewise depend on the pressure of the air. 174. The space above the column of mercury must be entirely free from air and moisture, for if present, they would exercise a pressure on the mercury in the tube which would counteract, to a greater or less extent according to their amount, the pressure of the air on the mercury in the cistern, and thus render the barometer more or less inaccurate. It is therefore necessary in the construction of a barometer, in order to have it accurate, to have not only the mercury pure and free from air, but the tube must also be free from air and moisture ; to obtain this result, a small quantity of pure mercury is placed in the tube and boiled for some time. It is then allowed to cool, and a further quantity previously warmed, added, which is boiled, and so on, until the tube is quite full ; in this manner the moisture and the air which adhere to the sides of the tube pass off with the mercurial vapour. 175. That portion of the upper part of the tube which is unfilled with mercury is the nearest approach, to a perfect vacuum which can be procured by art, for on lowering the tube 72 Fundamental Principles of Chemistry deep enough into the cistern of mercury, the whole tube will become completely filled with the mercury ; and on elevating the tube in the cistern the mercury again sinks in the tube. The vacuum thus obtained is termed the Torricellian vacuum, from its being first observed in 1663 by Torricelli, a pupil of Galileo. Although this is the most perfect vacuum that can be obtained, it is, nevertheless, not a perfect one, as the apparently empty space of the tube contains a minute quantity of mercurial vapour. 176. It need scarcely be remarked that all other liquids would, like mercury, be supported in a tube by the pressure of the air, the height of the column varying with the weight of the liquid ; water, for example, being 13^ times lighter than mercury, the height of a column of that liquid would be \'^\ times greater than that of mercury : the column of water would therefore measure about 34 feet ; in other words, when any other liquid than mercury is used, the height of the barometric column will be inversely as the specific gravity ; the specific gravity of mercury at 60 F. is 13 "568, the specific gravity of water being taken at I'ooo ; the height of a column of water corresponding to a column of 30 inches of mercury at 60° F. would therefore stand — 30 X -3-2 — , or 407-04 inches or 33'92 feet high. I'OOO 177. From these facts we learn that the pressure of the atmosphere is capable of supporting a column of mercury about 30 inches in height, and a column of water about 34 feet in height ; or, fb state it conversely, the pressure of a column of mercury of 30 inches, and a column of water of 34 feet, in height is equal to the pressure of the atmosphere. 178. As the pressure of the atmosphere supports a column of mercury whose base is a square inch 30 inches in height ; and as a cubic inch of mercury weighs, in round numbers, half a pound, 30 cubic inches of the metal will weigh 15 lbs. ; it, therefore, follows that the pressure of the atmosphere on each square inch of surface is equal to 15 lbs., and this pressure of 15 lbs. on the square inch is called the pressure of one atmo- sphere. If the elastic force of a gas or vapour, say that of steam The Barometer ;?3 in a boiler, were equal to a pressure of 60 lbs. on the square inch, then its pressure would be equal to that of four atmo- spheres, and it would be so stated. 179. Mercury being the densest of all liquids, it stands at the least height ; it is therefore chosen in preference to any other liquid in constructing barometers. 180. Having stated in general terms how the barometer is constructed, and the principle in its construction for measuring the pressure or weight of the atmosphere, we must now de- scribe it a little more fully, as it is an important instrument in the chemical laboratory, for at the moment the.phernist weighs Or measures a gas he must take the pressure of^the atmosphere by means of this instrument ; and he likewise requires to know the atmospheric pressure when he has to make very accurate weighings of light bodies, in order that the weight of air they displace may be allowed for. 181. As the height of the mercurial column varies, so does the quantity of mercury in the cistern vary ; for example, if the column stands high, there must necessarily be less mercury in the cistern than when the column stands comparatively low ; consequently, the true variation in the length of the column is not obtained by noticing the top of the mercury only, since the base of the column also varies, and therefore a correction has to be made for the amount of variation ; but this correction is not needed in most of the best forms of the instrument now made for scientific purposes ; as the whole scale is made movable, and, therefore, allows of adjustment as the level in the cistern fluctuates, consequently, the numbers marked on the scale always express the real distance from the level of the mercury in the cistern. 182. There are other corrections that require to be made which we must notice : the first we will allude to arises from the capillary action between the glass and mercury ; this will be noticed in the chapter (VII.) which treats of adhesion ; the next correction to be noticed is that for temperature. Mercury ex- pands with increase of temperature, and contracts with de- crease of temperature, hence its density changes, and inversely with its expansion, and therefore the height of the column will be inversely proportional to the specific gravity. To ascer- 74 Fundamental Principles of Chemistry tain the temperature of a barometer a thermometer is always attached to it. All readings have, therefore, to be reduced to a determinate temperature ; the temperature which has been adopted is that of melting ice, at which temperature the specific gravity of mercury is 13 '6. Tables have been drawn up for making the necessary correction at different temperatures. 183. Many more examples might be given to prove that the air possesses weight ; but we will notice first the instru- ments already illustrated, and which depend for their action on the pressure of the air. The action of the pipette (Exper. 5) depends upon atmospheric pressure ; the lower end of the in- strument is dipped into a liquid, and suction is applied by the mouth or other means to the upper end ; the withdrawing of the air diminishes the pressure within ; the liquid is therefore pressed upwards by the excess of the external over the internal pressure ; it rises in the pipette, and on closing air-tight the upper opening with the finger the liquid cannot flow back even when the instrument is raised out of the liquid, provided the lower aperture is not too large ; but if it is so large that the air and liquid have sufficient space to pass each other, then the latter cannot, of course, be retained in the pipette. 184. The syphon is another in- strument of frequent use in the chemical laboratory. It is a bent glass tube open at both ends, and is generally shaped somewhat in the form of a U> and it is usually so bent that the legs are of un- equal length. It is used for trans- ferring a liquid from one vessel to another. It may be filled by invert- ing it, and so inclining it that the orifice of the shorter leg is higher than the other ; the liquid is poured in until the longer leg is filled ; its orifice is then closed with the finger, and more liquid is then added until the other leg is full ; having closed both orifices with the fingers insert the shorter leg into the liquid which has to be removed, then Pressure of the Air 75 withdraw the fingers and the liquid will flow out of the longer leg. It is frequently made to work by inserting one leg in the liquid and sucking at the other end. It is by the combined action of the pressure of the air and the weight of the liquid that the instrument acts. The pressure of the column of liquid in the immersed portion is exactly counterbalanced by the pressure of the water in the vessel ; and the pressure of the air is equally exerted on the liquid in the two legs ; in the leg im- mersed the pressure is transmitted by the liquid in which it is inserted ; in the other the pressure acts directly on the aperture. For the syphon to act, the length of the column of liquid in the leg immersed from the surface of the liquid in the vessel to the highest point in the bend of the syphon must be less than the length of the column in the other leg ; otherwise, the pressure of the air being equal on both columns of liquid, and these being of equal length, there could be no flow from the outer limb. If therefore the two legs are of equal length, one leg must be immersed in such a manner that the column of the liquid in the two limbs is of unequal length. 185. There is, of course, a limit to the action of the syphon, for in order to convey the liquid the bend of the syphon must not be at a greater height above the level of the liquid than that of a column of the liquid which the pressure of the atmo- sphere will support. We have learned already that it will support a column of water 34 feet in height, and a column of mercury 30 inches in height ; therefore, the shorter limb should be rather less in length, if water has to be conveyed, than 34 feet from the level of the water to the bend, and rather less than 30 inches if mercury has to be conveyed ; for the height to which a liquid can be raised by a syphon depends on its specific gravity. 186. Another form of the syphon is represented in fig. 29. It is filled by dipping the end a into the liquid, and closing the Fig. 29. 76 Fundamental Principles of Chemistry end h with the finger. The syphon is then filled by sucking at c. When both branches, adzxA bd, are full, the finger is withdrawn, and the hquid runs out at b. When syphoning acids the end b ought to be provided with a stopcock, so that the finger need not be employed. 187. The gas jar filled with water or mercury, and standing on the shelf of the pneumatic trough, (par. 54, fig. 8) is another example of the pressure of the air ; so also is the gasometer (fig. 9) when it is filled with water, and the stopcocks C and D are closed, and the nut of the tube F is opened ; no water flows from F, owing to the pressure of the air. 188. A simple contrivance sometimes adopted by chemists for washing solid sub- stances on filters without having to give fre- quent attention to the washing, is founded on the same principle. A bottle is filled with water, and its mouth being closed air-tight by the finger is inverted into the filter so that its mouth dips about an inch into it, as shown in fig. 30. As long as the mouth remains covered with the liquid no water escapes from it, but whenever so much of the liquid has passed through the filter as to make the sur- face sink lower than the mouth of the bottle, the air ascends in the latter, and the water flows out until the mouth again becomes covered with the liquid, and this intermittent flow of water out of the bottle goes on until all the water has flowed out of it. 189. The action of the boy's toy called a sucker is due to atmospheric pressure. And flies and some other animals are able by the same action as that of the sucker to sustain their bodies in opposition to the force of gravity. 190. It is thought that all throughout infinite space there is no such thing as a vacuum ; all space is believed to be everywhere filled with matter of one form of aggregation or another ; in other words there is no such thing as an empty sface in nature. 191. On the earth and within the limits of the earth's atmo- Physical Properties of the Air jj sphere, all space, that is not filled with matter in the solid or liquid state, is filled with atmospheric air, with a few trifling exceptions, as, for instance, the accumulations of one of the constituents — carbon dioxide, of the air in some valleys, and the accumulation of gases, other than air, in some chemical manufacturing processes, as, for example, the accumulation of carbon dioxide in the fermenting vessels in breweries ; but in the general sense the statement is true, that on the earth all space, that is not filled with sohd or liquid matter, is filled with air. We have, therefore, next to consider some of the physical properties of the air. 192. The air is a mixture of several gases, viz., oxygen, nitrogen, carbon dioxide, ammonia, and a form of oxygen called ozone ; and it always contains a varying proportion ot aqueous vapour : there is also present in it finely divided solid particles of different substances which it is not necessary in this part of the work to specially name. 193. The atmosphere has, it is believed, a definite limit ; from observations made as to the length of time during which twilight is visible in the zenith, it is considered that it reaches in a state of sensible density to a height of from forty to forty-five miles above the earth's surface. ' Meteorites, however, ignite at an elevation of about 200 miles, proving the presence of a medium, which, though of too great tenuity to reflect light, still possesses density, and offers resistance to the passage of bodies through it. It is probable that even this height does not denote the upper limit of the atmosphere.' 194. The density of the air is not the same throughout its entire height, for, owing to its elasticity, its density diminishes as its distance from the earth increases, the lower strata having a much greater density than the higher strata, because each layer bears the pressure of the layers above it, but not of those underneath ; therefore, the pressure must decrease on each ascending layer ; the lowest layer will bear the pressure of all the rest ; the one next above the lowest will bear the pressure of all but the layer underneath it ; and the third lowest layer will bear the pressure of all but the two layers underneath it ; and so on with the succeeding higher layers. 195. As the pressure on each ascending layer decreases so 78 Fundamental Principles of Chemistry the density must decrease, because the density of a gas is directly as the pressure, and inversely as the volume. The air decreases in density in the following progression : at an elevation of 3*4 miles it is \ the density of the air at the sea-level ; at 6-8 miles it is ;|^ ; at io'2 miles \; at i3'6 miles -^■^\ and at 17 miles ^ of that density. The bulk of equal weights of air at these suc- cessive heights increases in geometrical progression, the volume being doubled for each step in the ascent ; while the density, and the corresponding height of the barometer, decrease in the same geometric ratio, being at each successive elevation exactly half what they were in the preceding one ; for all practical purposes it is sufficient to take it, that the barometer falls one- tenth of an inch for every 95 feet of height in this country in summer, and for heights not exceeding 3,000 feet. The baro- meter can be, and is, employed to measure the heights of moun- tains, and other altitudes. 196. Not only does the pressure of the atmosphere decrease as we ascend from the level of the sea, but at the sea-level the mean pressure of the atmosphere varies with the latitude. At the equator, the mean level of the barometer is 29-84 inches ; it increases with the latitude up to 40° N. where it amounts to 30-04 inches ; and at higher latitudes it again decreases. 197. But in addition to these changes of atmospheric pres- sure with change of altitude or place, the pressure at the same place undergoes continual variations. ' It is observed that the course of the barometer is generally in the opposite direction to that of the thermometer ; that is, that when the temperature rises the barometer falls, and vice versa ; which indicates that the barometric variations at any given place are produced by the expansion or contraction of the air, and therefore by its change in density. If the temperature were the same through- out the whole extent of the atmosphere, no currents would be produced, and, at the same height, the atmospheric pressure would be everywhere the same. But when any portion of the atmosphere becomes warmer than the neighbouring parts, its specific gravity is diminished, and it rises and passes away through the upper regions of the atmosphere, whence it follows that the pressure is diminished, and the barometer falls. If any portion of the atmosphere retains its temperature, while AiR-PuMP "jg the neighbouring parts become cooler, the same effect is pro- duced ; for in this case, too, the density of the iirst-mentioned portion is less than that of the others. Hence, also, it usually happens that an extraordinary fall of the barometer at one place is counterbalanced by an extraordinary rise at another place. With reference to the daily variations, they appear to result from the expansions and contractions which are periodically produced in the atmosphere by the heat of the sun during the rotation of the earth.' — Ganot. 198. Before commencing to describe the physical properties of air, taking air as the type of gaseous bodies in general, we must describe how air can be removed from a confined space, a vacuum being produced j this is effected by means of an instru- ment called the air-pump, which was invented by Otto von Guerick in 1650, a few years after the invention of the barometer. 199. There are various forms of this instrument, but the principle is the same in every form of it. It is identical in principle with the water pump ; and the principle of its construction can be very t easily explained and illustrated : — A metallic cylinder * (fig. 31), accurately bored, is fitted with a piston which is covered with a flap or valve of oiled silk which opens upwards ; when the piston is forced down, the air in the outer cylinder will, owing to the compression, escape into the atmosphere through the valve ; on raising the piston no air will be able to re-enter the cylinder, and owing to the pressure of the atmosphere on its upper surface, a resistance will be experienced in raising it. If the cylinder has a valve at the bottom, opening in the same direc- tion as that in the piston, as shown in the figure, this valve will on thrusting down the piston be closed by the elasticity of the air in the cylinder, while the upper valve will be opened ; on raising the piston the effect is reversed — the valve in the bottom of the cylinder will be opened by the pressure of the air under it, and the air will, of course, pass through it. 200. The air-pump, of which a perspective view is given in fig. 32, and a section in fig. 33, is an apparatus consisting usually b Fig. 31. So FUXDAMENTAL PRINCIPLES OF CHEMISTRY of two exhausting syringes, B B' (fig. 33), mounted so as to be worked by a single winch and handle, as represented at D, and communicating by a common pipe, T, with a glass vessel, R, in which may be placed the objects of experiment. The vessel R, called a receiver, has an edge, S, ground smooth, resting upon a plate, also ground smooth, and kept in air-tight connection with it by being smeared with lard. A stopcock C is provided in the pipe T, by which the communications between the receiver R and the syringes can be made and broken at pleasure. Another stopcock is provided elsewhere, by which a communication can be made at pleasure between the interior of the receiver R and the external air. To indicate the extent to which the rarefaction is carried from time to time by the operation of the syringes, a mercurial gauge, H G M, is provided, constructed in all respects similar to a barometer. The atmo- Air-pump 8i sphere presses on the surface of the mercury in the cistern M, while the column of mercury in the tube HG is pressed upon by the rarefied air in R. The height of the column, therefore, sustained in the tube, indicates the difference between the pressure of the external air and the air in the receiver. ' When a gauge of the form represented in fig. 33 is used, it is necessary that it should have the height of about 30 inches, since when a high degree of rarefaction has been effected, a column of mercury will be sustained in the tube HG very little less than in the common barometer. In small pumps, where this height would be inconvenient, a syphon-gauge, such as that Fig. 33- Fig. 34, represented in fig. 34 is used. This gauge is screwed on to a pipe communicating with the receiver. Mercury fills the leg A B, which is closed at the top A, and partially fills the leg S. When the atmosphere communicates freely with the tube D C, the surface of the mercury in S, being pressed by its full force, sustains all the mercury which the tube B A can contain, and this tube consequently remains completely filled ; but when the pipe D C S is put in communication with the exhausted receiver, the surface of the mercury in S being acted upon only by the pressure of the rarefied air in the receiver, the weight of the higher column in B A will predominate, and the mercury will fall in it, until the difference, of the- levels in the two G 82 Fundamental Principles of Chemistry legs shall be equal to the pressure of the rarefied air in the receiver.' ' 201. All the air in the receiver cannot be removed, for when the air has become so rarefied that its elastic force is not sufficient to raise the valve V, the degree of exhaustion attainable has been reached. It is easy to explain the rate at which the air is drawn from the receiver. If we suppose that the volume of the re- ceiver and the pipe together is nine times that of the cylinder, then when the air is diffused through the receiver, the pipe, and the cylinder, that in the cylinder is -^th of the whole. Thus by the up-and-down stroke of the piston we can remove ^^th of the air originally in the receiver and the pipe ; and there- fore we leave y^ths. At every succeeding stroke, -i^th of what remained after the preceding stroke will be expelled, and in the same way i%ths will remain. 202. The air-pump is an important instrument in the chernist's laboratory ; and it is also in frequent requisition in other branches of science. 203. Some experiments illustrating the pressure of the atmo- sphere will now be described, which could not be explained satisfactorily until the air-pump had been described.' In these experiments it will be seen that the pressure of the air is per- ceptible only when it acts in one direction ; in other words, when there is a vacuum on the opposite side of the body to that on which the air presses.^ Experiments Illustrating the Pressure of the Air. 70. On one of the open ends of a strong glass cylinder, a piece of bladder is to be tied so tightly as to be quit^ air-tight ; the edge of the other open end of the cylinder, which must be ground and well greased, is then placed on the plate.of the air-punrip and pressed, so as to make the con- tact air-tight ; the pump is then worked to exhaust the air in the cylinder ; the bladder becomes first depressed, and finally bursts, accompanied by a. loud report caused by the sudden entrance of the air. The exhaustion must be rapid, for if the rarefaction of the air in the cylinder is slow, the bladder distends without bursting, the air passing through its pores. 71. Substitute for the bladder a thin piece of india-rubber ; it will be forced, in consequence of its elasticity, into the interior of the vessel. If the top of the cylinder were of thin glass it would be broken. ' Lardner's Handbook of Natural Philosophy. 2 A much simpler and less expensive air-pump than the one described is suflScient for educational purposes. Physical Properties of the Air 83 204. The experiment with the cylinder covered at one end with bladder shows why the pressure of the atmosphere on our bodies, which on a man of. middle size is equal to about 16 tons, does not in the least inconvenience us ; for as the air in the cylinder counterbalanced the pressure of the external air, and thus prevented the bladder from being burst by the external pressure until the internal air was pumped out. in like manner the air and liquids in the bodies of animals produce a pressure outwards equal to the pressure of the external air . inwards ; the external and internal pressure being equal, no part of the body is, consequently, crushed. 205. The following experiment with the apparatus called the Magdeburg hemispheres shows very strikingly the force of the pressure of the air : — ■ 72. The apparatus consists of two hollow brass hemispheres with evenly ground edges, which admit of being brought into air-tight contact when smeared with lard; one of the hemispheres is provided with a stopcock, ahd its end terminates in a screw by which it can be screwed on the plate of the air-pump, and on the other hemisphere there is a handle. When the hemispheres are joined together, and as long as they remain filled with air, they can be easily separated, as the external pressure of the atmosphere is counterbalanced by the elastic force of the air in the ap- paratus. When screwed on to the plate of the air-pump for the purpose of pumping out the air, the stopcock is opened ; and when a sufficient exhaustion has been effected, it is closed, and the apparatus is unscrewed from the pump-plate ; it will now require a powerful force to separate them ; and as this is the case in. whatever position they are held, it fol- lows that the pressure of the air is trahsrnitted in all directions. The section of the hemispheres employed by the inventor of the apparatus, Otto von Guericke, measured 113 square inches, and they were held together, by a force equal to about three-fourths of a ton. 206. We have pointed out in par. 172 a means of proving that it is pressure of the atmosphere that supports the column of mercury in the barometer tube ; another and most complete demonstration is shown by placing the instrument under the receiver of the air-pump and exhausting; the column sinks as the pressure diminishes ; and when the air is readmitted into the receiver, the column recovers its original height. 73. Place a flask, about half-full of water under the receiver, the mouth of the flask being closed by a cork through which passes a glass tube, which dips into the liquid ; when the air in the receiver becomes sufficiently rarefied, the elastic force of the air in the flask causes a jet of water to issue from the tube. 74. Introduce a piece of coke into a vessel of water, and then place the vessel under the receiver ; on first exhausting the air an evolution of G 2 84 Fundamental Principles of Chemistry innumerable bubbles of air from the coke takes place, and as the exhaus- tion proceeds the water appears to boil, owing to the evolution, and the coke rises to the surface, being buoyed up in the water by the adhering bubbles of rarefied air ; but on gently readmitting the air into the re- ceiver, the coke will sink to the bottom of the vessel like a piece of lead. 207- Liquids evaporate more readily in a vacuum than they do in air, and they also boil at lower temperatures ; the air- pump is frequently used for these purposes in the laboratory : and sugar solutions are boiled in sugar-refineries in a vacuum- pan, as the sugar sustains less injury when its solutions are boiled at low temperatures. Substances liable to ferment and putrefy may be kept in vacuo for a long time without undergo- ing any change, owing to the oxygen of the air, which causes them to change, being removed ; and it is the exclusion of the air that causes food in the hermetically sealed tins to re- main in a good condition for a length of time ; but if all the air has not been expelled at the time the tin is sealed, the food will be found in an unsavoury state when the tin is opened. 208. As we proceed we shall have to bring under the notice of the student some other effects produced by increasing and by decreasing the ordinary pressure of the atmosphere ; at pre- sent we shall simply draw attention to the fact that the pres- sure of the air will force fluids, even mercury, through porous bodies like wood, if the pressure on the opposite side is removed. 209. Another form of air-pump has been devised by Sprengel ; it depends on the principle of converting the space to be exhausted into a Torricellian vacuum. The idea and construction of the apparatus are thus described by the inventor. 210. If an aperture be made in the top of a barometer- tube the mercury sinks and draws in air; if the experiment be so arranged as to allow air to enter along with the mercury, ' and that the supply of air is limited while that of mercury is unlimited, the air will be carried away and a vacuum produced. The following is the simplest form of the apparatus in which this action is realised. In fig. 35 c d\% a glass tube longer than a barometer, open at both ends, and connected by means Spsengel's Air-pump 85 of india-rubber tubing with a funnel A, filled with mercury and supported by a stand. Mercury is allowed to fall in this tube at a rate regulated by a clamp at c ; the lower end of the tube cdfiX.s in the flask B, which has a spout at the side a little higher than the lower end oi cd; the upper part has a branch at X to which a receiver R can be tightly fixed. When the clamp at c is opened, the first portion of mercury which runs out closes the tube and prevents air from entering below. As the mer- cury is allowed to run down, the exhaustion begins, and the whole length of the tube from .x to ^ is filled with cylmders of air and mercury having a downward motion. Air and mercury escape through the spout, of the bulb B which is above the basin H, where the mercury is collected. It is poured , back from time to time into the funnel A, to be repassed through the tube until the exhaustion is complete. As this point is approached the enclosed air between the mercury cylinders is seen to diminish, until the lower part of c d forms a con- tinuous column of mercury F'g. 35. about 30 inches high. Towards this stage of the process a clicking noise is heard hke that of a water-hammer when shaken ; the operation is completed when the column of mercury en- closes no air, and a drop of mercury falls on the top of the column without enclosing the slightest air-bubble. The height of the column then represents the height of the column of 86 Fundamental Ps/NtrPLES of Chemistry mercury in the barometer ; in other words, it is a barometer whose Torricellian vacuum is the receiver R. This apparatus has been used with great success in experiments in which a very complete exhaustion was required. 211. We have now to consider more fully than has yet been done in the previous part of the work, the physical properties of gaseous bodies. The first property to be noticed is their ex- pansibility, tension, or elastic force, as this property is indifferently termed. 212. Owing to the almost, if not complete, absence of any attraction between their molecules, they necessarily would be continually tending to occupy a larger space, unless their ex- tension was checked by some boundary, or by some counter- acting force, which was equal to their own force of expansion. 213. Liquids exert a pressure on the sides of the vessels containing them ; but gases exert a pressure in all directions upon the surfaces by which they are bounded, and the pressure is equal in all directions. If the resisting medium offer an equal resistance on all sides, the gas, by virtue of this eccentric expansibility will assume a spherical form. Soap-bubbles, and the small bubbles which rise in water, have invariably a globular figure, and show the eccentric expansibility of atmospheric air. 214. If a vessel containing a gas does not enlarge with it, or if the elastic force of the gas exceeds the cohesive force of, the solid material in which it is enclosed, then a disruption of the solid takes place, and some of the gas escapes. But if the vessel is subjected to an external pressure, which is equal to the internal pressure, then the vessel suffers no disruption, how- ever weak its sides may be, as we have shown is the case with regard to the human body. Experiments on the Expansion and the Compression of Gases. 75. Place a lilaader fitted with a stopcock, which is closed, the bladder being half-full of air, under the receiver of the air-pump ; pump the air out of the receiver, and immediately the bladder will distend, and on readmitting the air into the receiver it will immediately collapse to its original bulk. 76. Press the rod of the piston of the pneumatic syringe, an appa- ratus which consists of a stout glass tube closed at one end, and provided with a tight-fitting solid piston ; it will of course move down the tube, the effect being, that the air is compressed into a smaller volume ; when The Physical Properties of Gases 87 the force is removed, the piston is pushed upwards by the elastic force of the air to its original position, the air regaining its original volume. 77. To one of the necks of a two-necked Woulfe's bottle containing some water, as represented in fig. 36, a bladder filled with air is tied tightly on ; in the other neck a glass tube is fitted air-tight by means of a perforated cork, the, lower end , reaching almost to the bottom of the vessel. On compressing the bladder, the water, owing to the compression of the air, will ascend in the tube. 215. We have noticed the great difference there is between matter in the gaseous state and in its two other states of aggre- gation, as regards its compressibility, and we have explained and shown by experiment that the air is capable not only of compression, but that with its compression its density and elastic force increase. The law that expresses the com- pressibility of gaseous matter was discovered by the Hon. Robert Boyle in England in 1660, and by Mariotte in France in 1668 ; the law tears the names of both philo- sophers. It may be expressed as follows : (i) The elastic force of a gas is directly as the pressure, and inversely as the volume. (2) The density of a gas is also directly as the pressure, and inversely as the volume. (3) And the volume of a gas, as before noticed, is inversely as the pressure. 216. It may be proved by the following simple experiment: A syphon-shaped tube (fig. 37) of uniform bore is employed; the longer leg is open at the top, the end of the shorter one is either hermetically sealed, or it is furnished with a stopcock as shown in the figure. , The stopcock being opened, a quantity of mercury is poured into the open end. The surfaces of the mercury, Aa, will, of course, stand at the same level in both legs. The two columns of air, A C and a D, sustain a pressure equal to the weight of a column of air continued from A and a Qo Fig. 36. Fig. 37. 88 Fundamental Principles of Chemistry to the top of the atmosphere. If we now close the stopcock, D, the effect of the weight of the whole atmosphere above that point is cut off, so that the surface, a, can sustain no pressure arising from the weight of the atmosphere. Still the level of the mercury remains the same, because the elasticity of the column of air, a D, is precisely equal to the weight of the whole column before this small length was cut ofiF. The sur- face, A, is still pressed by the whole atmospheric column, and thus we see that these two different properties of the atmo- sphere,' its elasticity and its weight, exactly counterbalance each other. 217. ' We have learned that the atmospheric pressure, under ordinary circumstances, is equal to 15 lbs. on the square inch, or to a column of mercury 30 inches high. It is evident therefore, that the atmospheric pressure acting on A is the same as would be produced by a column of mercury, 30 inches high, resting on the surface of A. So, also, the force with which the air confined in « D presses by its elasticity on the surface, a, is also equal to a column of mercury 30 inches high. The pressure of the atmosphere acting on the surface. A, is transmitted by the mercury to the surface a, and balances the elastic force of the isolated column, a D. 218. ' If we now pour an additional quantity of mercury into the open end of the tube at C, an increased pressure, arising from the weight of the metal, will be transmitted to the surface, a, and will prevail over the elasticity of the confined air ; the surface, a, will therefore rise towards D, compressing the air into a smaller space. On continuing to pour in mercury, until the surface, a, rises to b, or half-way between a and D — that is, until the confined air is compressed into exactly half its former limits — it will be found, on drawing a horizontal line from the surface b to the opposite b' in the longer limb, that the column of mercury, b' B, measures 30 inches, the weight of which is equal to the atmospheric pressure. The force with which the surface, b, is pressed upwards towards D, is therefore equal to two atmospheres, or double the force with which a was pressed upwards towards D. Hence it appears that the elasticity of the confined column of air, b D, is double its former elasticity 1 This applies not only to air but to all gaseous bodies. Tbe PnysicAL Properties of Gases 89 when filling the space a D ; so that when the air is compressed i into half its volume, its elasticity is doubled. If we again pour mercury into the tube at C, until the air enclosed in the shorter limb be reduced to a third of its bulk, as at c D, the com- pressing force will be equal to three times the atmospheric pressure. The height of the compressing column of mercury •would reach to C, namely 60 inches above the level, e. If we still add mercury, until the column rise to the height of 90 inches above its level in the short limb, the elastic force of the confined air would be four times greater than at first, and it would be compressed to the bulk of one-fourth its original volume. The experiment proves that the tension or elastic force of gases varies in exactly the same proportion as their density. 219. 'As in a state of rest the tension everywhere exactly -balances the pressure, the two terms are frequently interchange- able, although it is usual to estimate pressure as so many pounds on a square inch, and to measure the tension by the height of the column of mercury which it is capable of sustaining. Either of these measures, however, can always be easily reduced to the other.' ' 220. When a gas in a confined space is heated, its tension increases by ■^\^ its value at 0° C. for every degree Centigrade through which its temperature is raised. This is part of Charles's law and may be thus expressed : — The tension of a constant volume of gas varies directly as the absolute tempera- ture. 221. — The rate of expansion of gases at increased tempera- tures has been stated in general terms. We must now enter more fully into the subject. It was there stated that the rate of expansion of all' gases is equal and uniform at all degrees of heat. Although this is sufficiently accurate for all chemical requirements, the coefficient of expansion is not rigidly uniform for all gases. ^ A volume of any gas at the melting-point of ice ' Tomlinson's Pneumatics. ^ The mare readily condensable gases display irregularities, especially near their points of solidification and liquefaction. Regnault and Magnus have published independent and elaborate investigations on the expansion various gases undergo by the application of heat. According to their experiments the coefficient of expansion is not rigidly uniform for all gases, the expansion being go Fundamental Principles of CHEMisfEV increases in bulk, the pressure remaining constant during the operation, to i '3665 volumes when raised to the temperature of boiling water. As on the Centigrade scale the interval between the melting-point of ice and the boiling-point of water is, as we have learned, divided into 100 degrees, it follows that any gas which measured one volume at the melting-point of ice would increase 0-003665 in bulk, for each degree it increased in temperature. 222. As the interval, between the melting-point of ice and the boiling-point of water on the Fahrenheit scale, is divided into 180 degrees ; it results that, for each degree F. that the gas increases in temperature, it must increase in bulk -^^. Knowing the coefficient of expansion, we can compute the volume a gas would occupy at some other temperature than that at which it was measured ; we will explain how these calculations are made, and give a few exercises for the student to work out. 223. To calculate the volume of a gas from a lower to a higher temperature on the Centigrade scale, we multiply the number by 0-003665, which is the amount we have learned one volume of any gas expands for each degree C, and to the product thus obtained we add i for the volume unit; we then multiply the number thus obtained, by the number of volume-units the gas measured at the lower temperature ; this will give us the volume the gas we have measured would occupy at the higher temperature. Suppose, for the sake of illustration, we wanted the greatest for those which are the most readily condensable ; whilst the least readily condensable exhibit scarcely any appreciable difference. The following table contains a summary of Regnault and Magnus's experi- mental results. Expansion of Gases by Heat. 1000 parts, at yp F., become At 212° F. Regnault Magnus Hydrogen . . . . Carbon monoxide . Atmospheric air . Nitrogen . . Hydrochloric acid Carbon dioxide Protoxide of nitrogen Cyanogen . . Sulphurous acid 1366 "13 1366-88 1367 '06 1366-82 1368-12 1370-99 i37i"95 1387-67 1 390 '28 1365 "659 1366-508 1369-087 1385-618 Correction of Gases for Temperature 91 to know what volume a gas measured at 0° C. would occupy at 30° C, we multiply o'oo3665 by 30 and add one forthe volume- unit, which gives i '01099 j we then multiply the number we have obtained by the number of volume-units the gas measured at the lower temperature ; this will give us the volume the gas we have measured would occupy at the higher temperature. In our example the lower temperature is 0° C, and the higher temperature is 30° C, and suppose the gas measured 20 cubic inches at 0° C. we should have- to multiply i*oio99 by 20 ; the product would be the volume the 20 cubic inches the gas measured at 0° C, would occupy at 30° C. ; thus, — r '01099 >^ 20 =20 '2 1 98, the number of cubic inches the gas would measure at 30° C. The following would be the general formula for calculating the volume of a gas from a lower to a higher temperature, according to the Centigrade scale, v denoting the known volume, Vi the unknown volume, and / the temperature : — ?/) =» X (i + -003665 X i), 224. To reduce the volume of a gas from a higher to a lower temperature on the Centigrade scale, the number of volume-units the gas measures at the higher temperature must be divided by the number obtained by multiplying o'oo3665 by -the thermo- metric degree at which the gas is measured, and adding to the product I for the volume-unit; the quotient will be the volume the gas will occupy at the lower temperature. As an example, we will reverse our former illustration. What volume will 20-2198 cubic inches of gas at 30° C, occupy at 0° C? 20-2198 , . . , -Z =20 cubic mches. 1+0-003665 X30 The following is a general formula for reducing the volume of a gas from a higher to a lower temperature, according to the Centigrade scale : — V ?'.== — I + -003665 y.t. 225. The volume of a gas from a lower to a higher tempera'^ ture on the Fahrenheit scale may be calculated thus : 491 volumes pf a gas increase one volume for every increase in degree on 92 Fundamental Principles of Chemistry the F. scale ; therefore 491 volumes at 32° F. would measure 509 volumes at 50° F., because there is a difference of 18° between 32° and 50° ; therefore if we wished, for example, to know what volume 20 cubic inches of gas at 32° F. would measure at 50° F., we make the following proportion sum ; — 491 : 509.: 20 : 20733. The general formula would be (^1 denoting the temperature of the unknown volume) : — J, _ z^X49i+(A-/) ' 491 If, instead of calculating the volume of a gas from a lower to a higher temperature, we were by this plan to reduce the volume from a higher to a lower temperature, the calculation would be as follows, reversing our former illustration, viz., What volume will 20733 cubic inches of gas, at 50° F., occupy at 32° F. ? 509 : 491 :: 20733 • ■»=2o cubic inches. The general formula would be : — _ 2^X491 49i + (^— /i) V, Exercises on the computation of the volume of gases at different temperatures. 78. A gas measures 20 cubic inches at 50° F. What would it measure at 60 ' F.? 79. A gas measures 15 cubic inches at 90° F. What would it measure at 60^" f: V 80. A gas measures 7-3 cubic inches at 180° F. What would it measure at 60° F. ? 81. A gas measures 100-3 cubic inches at 40° F. Whatwould it measure at 60° F. ? 82. A gas measures 107 cubic inches at 320° F. What would it measure at 80' F. V 83. A gas measures 15 cubic inches at 0° C. What would it measure at 60^ C. ? 84. A gas measures 40- 1 cubic inches at 100° C. What would it measure at 0° C. ■'. 85. A gas measures 3-5 cubic inches at 0° C. What would it measure at 80" C. ? 86. What would a decilitre of gas at 0° C. measure at 80° C. ? 87. What would 7 cubic centimetres at 24 • C. measure at 0° C. ? 88. A room of 2000 cubic feet capacity, is heated from 60° to 80° F. VeNTILA TIQN 93 How much air is expelled from the room, using Regnault's coefficient of expansion, viz. jij of the bulk at 32° for each degree of Fahrenheit's thermometer ? 226. As hot air is lighter than cold air, air as it becomes heated rises and accumulates in the upper part of a room. This is easily demonstrated by partially opening the door of a warm room, and holding a lighted candle near the top; if the window be not open, the flame will be forced in the outward direction by the current of heated air which is escaping from the room. Midway down, the flame will not be affected either inwards or outwards, it will be stationary ; while near the floor it will be blown into the room by reason of the cold air enter- , ing at the bottom. 227. By the respiration of human beings and other animals, ; and by the burning of substances for the production of heat and light, the oxygen of the air is being constantly removed,; and is replaced by carbon dioxide, which is emitted from both these sources ; and this gas is inimical to animal life, and is in- capable of supporting combustion. The air of a room where people are assembled requires to be constantly renewed,, whether combustible substances are being burnt or not. The quantity of carbon dioxide evolved by the lungs and skin ot one person ' amounts to about 07 cubic foot per hour. In order that it may be breathed again without inconvenience, this should be distributed through at least 140 cubic feet of fresh air, or a space measuring 5-2 feet each way '; hence the neces- sity for a constant supply of fresh air by ventilation even when no gas, candles, &c., are burnt, but when combustibles are burnt, the necessity is increased enormously. The contaminated air proceeding from both sources — respiration and combustion — being of higher temperature tKanthe surrounding air ascends, colder air which is fresh, taking its place ; it requires, therefore, only proper ventilation of rooms for this contaminated air to be carried away. 228. The ventilation of rooms, the student will see from what has been stated, is an important art, and is dependent on the currents produced in air by diff'erences of temperature. The draught of a fire is simply caused by the ascent of the heated air in the chimney, and the ascent is quickened by 94 Fundamental Principles of Chemistry reason of the chimney keeping the heated air together ; and the longer the chimney the more powerful the draught ; this is the reason why factory chimneys are made of such a length ; it is not, as many suppose, for solely carrying the smoke high up in the air. As tall chimneys quicken the draught, chimneys of short length have only a moderate draught ; hence the chimneys of cottages, and the upper rooms of houses are more liable to smoke than those that are longer, as the draught is proportioned to the length of the chimney. If the section of the chimney is larger than is necessary to allow an exit for the products of combustion, descending as well as ascending currents are produced in it, which causes it to smoke. In open fireplaces, a large quantity of the colder air of the room enters the chimney above the fire, and mixes with air heated by the fire ; this mixture ascends more slowly than if hot air alone had entered the chimney. By excluding a portion of the cold air by placing a plate of metal or even a piece of paper across the opening, the fire begins to burn more quickly, by reason of the draught being increased, owing to the exclusion of the cold air. In close fireplaces, as those of steam-engines, when the furnace door is shut, no air can enter the chimney but directly through the fire ; a powerful draught is consequently produced. ' Rumford was the first to attempt rational improvements in chimneys. He reduced the opening of the chimney and the depth of the fireplace, and added polished plates inclined at an angle which serve both to guide the air to the fire, and to reflect heat into the room.' An open fireplace, however im- proved, will always be an imperfect and costly mode of heating ; it is estimated that only 13 per cent, of the total heat is made available ; but although an imperfect and costly mode of heat- ing, it ensures ^(701^ ventilation. The fresh air to supply that carried up the chimney is usually supplied through the crevices of the doors and windows ; if no fresh air were admitted into the room, there would be produced a downward current of aii in the chimney, and as a consequence the chimney would smoke. Exercise on Ventilation. 89. A chimney, 4 feet in length, is filled with air of the average tem- perature of 104° F., the outer air being 44-5° F. What height would be the column of the outer air, which the air in the chimney would balance ? Liquefaction and Solidification of Gases 95 And what would be the ascensional force of air in the chimney owing to the difference in weight of equal columns of the inner and outer air ? 229. In par. 4 it is stated that matter in one state of aggre- gation can be made to pass into one or both of the other two states of aggregation, by the application of heat, cold, or pressure, or by a combination of pressure and one of the other two agents. All known gaseous bodies have now been, lique- fied ; some are easily liquefied, either by pressure or cold ; others require intense pressure combined with extreme cold ; and some have been solidified. 230. Faraday, who was one of the earliest to liquefy gases, adopted a very simple method for liquefying the gases that are most readily liquefied ; a substance, containing the gas to be liquefied as a constituent, he placed in one of the limbs of a strong narrow bent tube (fig. 38), the open end of which was then sealed up. The gas was disengaged from the substance containing it by heating that end of the tube, and immersing the other limb in cold water ; the gas accumulating in the tube became liquefied by its own pressure. With less easily liquefied gases he had to employ cold with the pressure. But with this appa- ratus he was unable to liquefy many gases : , - 'Tin • Fig, 38. these have since yielded to more intense pres- sures and more extreme cold than he was able to employ ; for the liquefaction of hydrogen and oxygen, for example, it requires for the liquefaction of the former a pressure of 450 , atmospheres, coupled with a temperature of —140° C. ; and for the latter 22-5 atmospheres, and a temperature of — 136° C. 231. When the pressure is removed the liquefied gas vola- tilises, and its volatilisation is, of course, attended with a great . diminution of heat, so much so that in some cases a portion of the liquefied gas is solidified ; in this way the gas, carbon dioxide, was long ago obtained in the solid state ; and very recently oxygen had also been solidified by like means. 232. From what has been stated about the liquefaction of gases, the student will no doubt generalise that some bodies that are gaseous in our climate would assume the liquid state in the Arctic regions ; just as some bodies that are in the liquid state in our climate would there be in the solid state, and he g6 Fundamental Principles of Chemistry will have generalised correctly ; he may also, probably, further' generalise, and the generalisation will be correct, that some bodies that exist in the liquid state in our climate become gaseous in tropical countries. The vapourisation of liquids will form the subject-matter of the next chapter. Examination Questions. 90. Explain the distinction between mass and weight. 91. E.\plain the principle of the syphon, and state the limitation of its action. 92. Describe the barometer, and explain how it may be used for de- termining the difference of the altitudes of two stations. 93. A body when placed successively in the two pans of a balance, weighs in one pan 63 grammes, and in the other 65 ; calculate its true weight. 94. Give your reasons for preferring an air thermometer as the best means for measuring temperature. 95. Suppose you wish to verify the accuracy of a Centigrade thermo- meter at its freezing and boiling points, desrribe in detail how you would proceed to do so ; which point would you commence with first ? Give a reason for your reply. 96. If ice at the freezing-point is dissolved in ten times its weight of water at 20° C, what will be the temperature of the mixture? 97. A small cube of wood is placed floating in a glass of water, the glass is then placed under the receiver of an air-pump, which is then partially exhausted : will the wood rise or sink ? Explain clearly your answer. 98. State the law of dilatation of gases for changes of temperature. 99. 40 cubic centimetres of atmospheric air are enclosed in a tube over mercury, the height of the mercury in the tube above the level in the trough outside being 50 cubic centimetres. The tube is depressed, until the mercury in the tube above the level in the trough is equal to 30 centimetres. What is now the volume of air ? The temperature ( 1 5° C. ), and the height of the barometer (76 centimetres), have not changed during the observations. 100. It is found that a kilogramme of water at 100° C., mixed with a kilogramme of snow without loss of heat, gives 2 kilogrannnes of water at the temperature of 10' C. Show how to find from this the latent heat of water. loi. As gravity acts on all substances with the same intensity, why do bodies fall through the air with unequal velocities ? 102. A certain quantity of air at atmospheric pressure has a volume of 2 cubic feet, the temperature being 55° F. What does the volume of air become when the pressure is increased by ^, th6 temperature meanwhile remaining the same ? 103. Can you assign any reason why two chimneys should not com- municate ? 104. If only 13 per cent, of the total heat yielded by coal is obtained by burning it in an open fireplace, what becomes of the rest of the heat ? 105. Explain scientifically why a chimney ought to be at least of " certain height. 106. State precisely, and illustrate by numerical example, the laws which give us the relations between the temperature, the pressure, and the volume of a given gas. Evaporation gy 107. 500 cubic centimetres of oxygen are measured when the tem- perature is 20° C. ; the temperature is subsequently raised to 40° C. , the pressure meanwhile remaining invariable. What is the volume of oxygen at the latter temperature ? (The coefficient of expansion of oxygen is 3000/* ■ 108. Air is allowed to expand to double its original volume ; how much must its temperature be raised that its pressure may remain un- changed ? 109. Let the volume of a gas be 5 litres at the pressure of 290 milli- metres of mercury, and at 10° C. What will be its volume at the pressure of 350 millimetres and at 72° C. ? Use the coefficient o-oo366s. CHAPTER IV. EVAPORATION — EBULLITION — DISTILLATION — TENSION OF VAPOURS — CORRECTION OF GASES FOR PRESSURE — EXERCISES — CORRECTION OF GASES FOR TEMPERATURE, PRESSURE, AND TENSION OF AQUEOUS VAPOUR — EXERCISES — QUESTIONS. 233. Solid and fluid bodies, in the, gaseous state, are called vapours, and their conversion into this state is called evapora- tion, or vaporisation. Vapours, of which- steam is the most familiar to us, are light; expansible, and generally colourless gases, resembling air, and other gaseous bodies ; but vapours are more readily condensed by a change of a temperature than bodies which are gaseous under the ordinary conditions both of temperature and pressure. 234. Vapours, when they are separated from the liquids which have yielded them, obey the same laws as gases ; but if the liquid is present, hcci not only expands the vapour, but also increases its volume by the addition of a new, quantity of vapour. Example : Steam, when heated by itself, apart from the liquid which produced it, does not possess a greater elasticity than an 'equal bulk of air confined and heated to the same de- gree, and may be heated to the .temperature at which .the con- taining vessel becomes red-hot, without acquiring great elastic force.; but if water be present, then more and more steam continues to rise, adding its elastic force to that of the vapour previously existing, so that the pressure becomes excessive. H 98 Fundamental Principles of Chemistry 235. The passage from the liquid state to the state of vapour is distinguished from the passage of the solid state to the liquid state by the important fact that, whilst the liquefaction of each solid is produced at one temperature, the vaporisation of each fluid occurs at a variety of temperatures. 236. When a liquid vaporises, with or without the applica- tion of heat, and the elastic force of the vapour is not equal to the pressure of the atmosphere, the process is called evapora- tion, and the liquid is said to evaporate. 237. When a liquid vaporises, with or without the applica- tion of heat, and the elastic force of its vapour is equal to the pressure of the atmosphere, the vapour produces a bubbling or boiling, and the liquid is said to boil ; and the temperature at which this takes place is called the boiling-point of the liquid. In evaporation, the vapour is formed only from the surface liquid ; in boiling, the vapour is formed from the whole mass of the liquid. 238. It will be evident, from what has been stated, that if the pressure of the atmosphere be diminished, either artificially or by ascending to greater heights in the air, as the tops of lofty mountains, liquids will, on account of the diminished pressure boil at lower temperatures ; ' and if the pressure be increased, either artificially, or by descending into mines, hquids will, on account of the increased pressure, boil at higher tem- peratures : in other words, the boiling-point of liquids varies with the pressure. Nevertheless, the temperature at which each liquid boils is quite constant under the same circumstances, and the boiling-point often becomes a physical character of great importance in distinguishing liquids which much resemble each other ; as different liquids, under the same circumstances, boil at very different temperatures. Ether, for example, boils at 94°-8° F., whilst mercury boils, under the same circumstances, at 662° F. 239. The following very simple and beautiful experiment proves that, with the diminution of pressure, liquids boil at ^ We have already noticed that the heights of mountains can be measured by means of the barometer ; they can also be measured by ascertaining, by means of a very delicate thermometer, at what temperature water boils. A difference of about 1° F. is occasioned by an ascent of about 535 feet. Ebullition gg lower temperatures. A little water is made to boil in a flask until all the air is expelled, and the steam issues from the neck. A tightly fitting cork is then inserted, and the lamp at the same moment withdrawn. By plunging the flask into cold water the boiling is renewed, because a partial vacuum is produced by the cold water condensing the steam in the flask. The boiling ceases on plunging the flask into hot water, because the steam ceases to be condensed, and its pressure stops the boiling. 240. In aPapin's digester, which is a tight and strong kettle with a safety valve, water may be raised to 300° F., or 400° F., without boiling, but the instant that the great pressure is removed, the boiling commences with great violence. 241. There are other circumstances besides pressure which influence the temperature at which liquids boil. The presence of air in a solution has been found to assist the evolution of vapour. Water deprived of air may be raised many degrees above its boiling-point, and it will then be suddenly converted into steam with explosive violence. ' The nature of the vessel, or rather the state of its surface, also exercises an influence on the boiling-point, and this to a much greater extent than was formerly supposed. It has long been noticed that in a metallic vessel water boils, under the same circumstances of pressure, at a temperature one or two degrees below that at which ebullition takes place in glass ; but it has been shown that, by particular management, a much greater difference can be observed. If two similar glass flasks be taken, the one coated on the inside with a film of shellac, and the other completely cleansed by hot sulphuric acid, water heated over a lamp in the first will boil at 211° F., whilst in the second it will often rise to 221° F., or even higher. A momentary burst of vapour then ensues and the thermometer sinks a few degrees; after which it rises again. In this state, the introduction of a few metallic filings, or angular fragments of any kind, occasions a lively disengage- ment of vapour, while the temperature sinks to 212" F., and then remains stationary. These remarkable effects must be attributed to an attraction between the surface of the vessel and the liquid. The solution of solids in a liquid, on account of the adhesion between them, also causes the liquid to boil at a higher temperature. loo Fundamental Principles of Chemistry 242. An opinion formerly prevailed that not only bodies which are vapours at a moderate temperature, but even sub- stances, as the earths and some of the metals, which cannot be volatilised in the fire, emit vapours at all temperatures, even the lowest. This has been shown by Faraday to be an erro- neous opinion. He has proved that there is a temperature below which volatilisation ceases — a temperature which varies for different substances. For mercury, the limit is about 40° F., for sulphuric acid the limit is much higher, since the acid undergoes no sensible evaporation at ordinary atmospheric temperatures. The cohesive force between the particles of a liquid is greater probably than the repellant power between the particles at the temperature at which the liquid ceases to evaporate, and it is this which puts a stop to the evaporation. 243. Some solid bodies, such as camphor and arsenic, pass at once into vapour without being hquefied ; but most solids become liquids before they are converted into vapour. Even ice and snow can evaporate without first liquefying. It is owing to this evaporation that patches of snow and tufts of ice are observed gradually to disappear even during the con- tinuance of a severe frost. 244. On the application of heat to a liquid, the temperature of the hquid continues to increase until the - boiling-point is reached ; but the moment ebullition commences, the tempera- ture of the liquid remains stationary, however intense the heat appHed may be, and however long continued. This fact is of importance in domestic economy, particularly in cookery, and attention to it would save much fuel. Soups, &c., made to boil in a gentle way, by the application of a moderate heat, are just as hot as when they are made to boil on a strong fire with the greatest violence. 245. Although liquids are converted into vapours at and below the ordinary temperature of the air, they nevertheless require for this conversion a large amount of heat, which becomes latent in the vapour. If, for instance, a few drops of ether be allowed to fall on the hand, the ether evaporates, and a sensation of cold is experienced, because the ether requires for its vaporisation a large amount of heat, which it obtains from the hand, hence the cold. Water may even be frozen by Latent Heat ioi the rapid absorption of heat occasioned by its own evaporation. The porous water-jars which are used in warm countries to keep liquids cool owe their efficacy to the latent heat of vapours. 246. The sensible heat of vapours is the same as that of the liquids from which they are produced, therefore a vapour produced from a liquid which has the temperature of 60° F. will also have that temperature ; but if the liquid had a tempera- ture of 212° F., the vapour would also have a temperature of 212° F. 247. Equal weights of different liquids require very dif- ferent amounts of heat to convert them into vapour. But a much larger quantity of heat is necessary to convert fluids into vapours than solids into fluids. As an example, observe the quantity of heat necessary to convert ice into water, and water into steam : i lb. of ice at 32° F. requires for its conversion into I lb. of water at 32° F., i42'65° F. of heat; in other words there is as much heat absorbed in the liquefaction of i lb. of ice as would raise 142 '65 lbs. of water through 1° F. ; but i lb. of water at 212° F. requires for its conversion into i lb. of steam at 212° F., 966 '6° F. ; so that 966-6° F. of heat have become latent in converting water into the vaporous state ; the latent heat of steam is therefore 966-6° F. ; consequently, the conver- sion of I lb. of steam at 212" F. into water at 212° F. would evolve as much heat as would raise 966-6 lbs. of water 1° F. If the heat necessary for the vaporous state is abstracted, the vapour is converted into the liquid state. The well-known process of distillation is an application of this principle. 248. Equal bulks of different liquids produce very different volumes of vapour. Water furnishes, bulk for bulk, a much larger amount than any other liquid, a cubic inch of water at 212° F. expanding to nearly a cubic foot of steam at 212°, or to state it accurately, to 1,696 times its volume. The following table shows the volume of vapour which is furnished by a cubic inch of four different liquids, at their respective boiling-points. Equal volumes of different vapours, taken at the boiling- points of their respective liquids, consequently possess very different weights, as is shown by the last column of the table :— I02 Fundamental Principles of Chemistry 1 cubic inch of each liquid at 60-* F., yields in ihe case of Cubic inches of vapour at its boiling-point Boiling-point "V. Weight in grains of 100 cubic inches of each vapour at its boiling-point Water Alcohol . Ether Oil of Turpentine 1,696 528 298 193 212 173 95 314 14-93 40-49 64-71 117-71 249. Before proceeding farther with respect to the elastic force of vapours, it is necessary to describe the mode of de- termining the boiUng-point of Uquids, and their distillation, as these are operations in frequent use in chemical laboratories. The size of the vessel in both operations is determined by the quantity of liquid at the command of the operator. 250. We have already noticed that the temperature at which each liquid boils is quite constant under the same circum- stances. We have also learned that other circumstances besides pressure influence the temperature at which liquids boil; but these circumstances do not affect the temperature of the vapour of the boiling liquid ; this at once adjusts itself to the pressure of the atmosphere, and is always constant for the same liquid under the same pressure. In determining, therefore, the boiling-point of a liquid we do not allow the bulb of the thermometer to dip into the liquid, but we bring it almost into immediate contact, so that it may be completely surrounded by the vapour. 251. As the boihng-point of any body of definite composi- tion, and perfectly pure, is stationary during the entire time it is kept boiling, whilst the boihng-point of a mixture ot substances keeps constantly increasing as the more volatile substances evaporate, the boiling-point becomes the most important physical character for determining the identity and purity of a volatile liquid. 252. When we have only a small quantity of liquid to operate upon we may employ a test-tube fitted with a cork ; the cork must be pierced with two holes, in one of which is inserted the thermometer, and in the other the exit-tube. If we have a large quantity of liquid at our command, we may employ a tubulated retort ; the tubulure is fitted with a cork pierced with one hole, in which the thermometer is inserted. Determination of Boiling-Points 103 If we do not wish to lose any of the Hquid, we condense the vapour by connecting the exit-tube from the test-tube, or the beak of the retort, with a Liebig's condenser (see fig. 40). The liquid is allowed to boil until the greater part of it has distilled over : we note the pressure of the barometer, and we also note the temperature during the whole time. 253. The temperature indicated by the thermometer is less than that of the true boiling-point, if only part of the stem of the thermometer is exposed to the vapour of the liquid. For a thermometer to indicate the true temperature of vapour or any other medium, it is necessary to immerse both the bulb and stem in the medium whose temperature is to be measured; for if the stem of the thermometer is exposed to a lower tem- perature than the bulb, the whole of the mercury will not be fully expanded, and the thermometer will indicate too low a temperature : this difference between the indicated and the true temperature becomes impor- tant when the temperature of the medium greatly exceeds that of the air. 254. We can adopt one of two methods for obtaining the exact temperature at which a liquid boils : we may either have, by a simple contrivance, the stem of the ther- mometer immersed in the vapour of the boiling liquid ; or we may by calculation make the necessary correction. We will describe both methods : — I. The following simple appa- ratus for the exact determination of boiling-points has been devised by Berthelot. It consists of a long- necked glass flask (fig. 39), having a capacity of 100-200 c.c. The neck is enclosed in a wide glass tube, closed with two perfo- rated corks, and passes through the lower cork ; and the tube of a thermometer passes through both ; its bulb and stem are ^^ I Fig. 39. I04 Fundamental Principles of Chemistry thus immersed in the vapour of the boiling liquid. The lower cork is also traversed by a bent tube, which serves to carry off the vapour to a condenser, and thus prevent any excess of pressure in the apparatus. Due attention must be paid, in taking the observations, to the barometric pressure at the time. 2. For making the correction by calculation it is necessary to know the mean temperature of the exterior portion of the column of mercury exposed to the air, compared with that part below the cork A, surrounded by the vapour; for this purpose we fix to the stem of the first a second thermometer, in such a way that its reservoir is about the middle of the column of mercury which is above the distillatory apparatus. If we represent by T° the temperature indicated by the thermometer in the vapour, by t° the mean temperature, and by TV* the number of degrees which the exterior mercury column measures ; lastly by 2, the coeifficient of the apparent expansion of mercury in glass (o:=o'oooi54 for i°C), the quantity to be added to T° for obtaining the true boiling- point becomes N. {T-t) S. As an example, suppose we have found i7i'3° C. = J" for the boiling-point of the liquid, with a thermometer having 25 degrees above zero in the distillatory apparatus ; in this case, i7i'3° — 25, or i46'3°=iV. If the exterior thermometer indi- cates 43°=/ for the mean temperature of this portion of the column of mercury, 171-3 — 43°, or i28-3=( J"— /). The cor- rection becomes then — i46'3° X 128-3 xo-oooi54=2-9", and we find that the true boiling-point of the hquid under the observed barometric pressure is i7i-3''-f 2-9°=i74-2. 255- The operation by which a liquid is converted into vapour ; and the vapour is re-converted into the liquid state, is termed distillation. In this form of distillation, which we shall term ordinary distillation, there is no alteration in the constitu- tion of the substances which distil over ; but there is a form of distillation, which is termed destructive distillation, in which the DlS TILLA TION I O 5 original substance is destroyed, and gaseous and liquid bodies are generated from the destruction, and they distil over ; the manufacture of coal-gas is a familiar example of destructive distillation. We shall at present explain only ordinary distilla- tion. 256. We can by means of ordinary distillation separate liquids of different volatilities ; and we can separate liquids from the solid bodies which may be dissolved in them. The chemist in most of his operations, has to employ pure water, he has therefore to distil the well or river water to free the water from the solid substances these waters always contain ; the pure water thus obtained generally goes by the name ' distilled water.' When fresh water is not to be had on board ship, or in the neighbourhood of the sea, the sea-water is distilled to obtain this necessary liquid. 257- The still, as the apparatus is termed which is used on the large scale, consists of three parts, viz. the body which holds the liquid to be distilled (the body is placed over a furnace) : from the body proceeds a tube for the vapour to escape by, this tube terminates in a spiral pipe of tube called the worm ; the worm is in a kind of cistern which is being constantly supplied with cold water during the distillation. The vapour is condensed in the worm, owing to the worm being always kept cold during the operation by the cold water which surrounds it externally. The cold water is conducted to the bottom of the refrigerator, as the cistern containing the worm is called, thus displacing the heated water, which, on account of its less specific gravity, rises to the upper part of the re- frigerator, and flows off. 258. The arrangement of the distillatory apparatus employed in chemical laboratories varies with the kind of liquid to be distilled ; a moderate or a very high temperature, for example, may be required for the conversion of the Hquid into vapour as the range of temperature at which different liquids boil and are converted into vapour is very extensive ; in like manner the temperature at which the vapours of different liquids are condensed varies exceedingly : some are condensed at such a moderate temperature that no special condenser is required ; on the other hand some require an exceedingly low temperature to 106 Fundamental Principles of Chemistry effect their condensation. In such a work as this, it would be out of place to describe all the various modifications of the apparatus required for the distillation of different liquids ; we shall therefore describe the most usual form of the distillatory apparatus. 259. A retort or flask is employed to hold the liquid to be distilled ; a stoppered retort (A) is the holder shown in fig. 40- The condenser employed is called, after the name of the inventor, Liebig's condenser ip) ; it consists of an outer metallic or glass tube ; into this is fitted, by means of perforated corks, a glass tube, c, about 30 inches in length ; into this tube Fig. 40. the neck of the retort is fitted. Into the space between outer and inner tubes of the condenser a constant stream of cold water flows from the vessel d ; the heated water running out through the tube e. The condensed vapour passes into the receiver/. When the liquid has been placed in the retort, and the apparatus is all arranged, and the space between the two tubes in the condenser has been filled with cold water, heat is gradually applied to the retort by means of a gas-burner, as shown in the figure. 260. By a single distillation, carried on in this manner, a liquid can be perfectly separated from one or many non-vola- tile substances ; but two or more volatile liquids cannot be separated by a single distillation, owing to liquids evaporating Fractional Distillation 107 below their boiling-points ; the two liquids pass over together but in different proportions, the more volatile passing over in the largest proportion in the first portion, and the less volatile in the last portions, of the distillate ; and of course the greater the difference in the boihng-points of the liquids the more perfect the separation effected. But in order to obtain a perfect separation more distillations than one have to be made, and portions of the distillate have to be collected separately, the receiver being changed at every increase of 5° C, as the boiling-point of a mixture of liquids is not stationary, as the temperature keeps gradually increasing. And to facilitate the separation, a modification of the distilling vessel has to be made ; this kind of distilla- tion is called yrflfiT/wi^fl/ distillation, which we will briefly describe. 261. The mode for facilitating the sepa- ration of different liquids consists in causing the less volatile of the liquids to condense in the upper part of the distilling appa- ratus, and flow back into the flask containing the liquid. The best mode yet devised for effecting this condensation is to insert into the mouth of the flask, by means of a per- forated cork, a vertical tube represented in fig. 41, having several bulbs blown upon it, and a side tube to assist in conveying back the condensed liquid into the flask. In the mouth of the vertical tube a thermometer is inserted ; its bulb is passed down into the uppermost bulb on the tube. To effect the separation of different liquids, even with this modification, the receiver must be changed at every 5° C. And each fraction thus obtained must be submitted to another fractionation until each fraction has a constant, or almost con- stant, boihng-point. 262. Wanklyn has shown that we cannot, even by fractional distillation, laborious as the operation is in many cases, sepa- rate different liquids, if the vapour-tensions and vapour-densities are proportional to one another, for in such cases the mixture distils over unchanged. Fig. 41. io8 Fundamental Principles of Chemistry 263. Methods for dispensing with frequent and costly dis- tillations were employed in the arts long before any similar method was invented for laboratory operations. One of the most ingenious and effective methods is that adopted in Coffey's still, but it would carry us beyond the scope of this work to describe it. 264. In concluding our observations on distillation we may observe that the operation called sublimation is closely allied to distillation, for they have both the same object, and they require the same means ; for both consist of the conversion of a body into vapour ; the difference consists in the state the vapour assumes when condensed ; if it assumes the solid state, the operation is called sublimation, an operation which will be more fully explained farther on. 265. The earth and the atmosphere, it may be noticed in passing, form a kind of distilling apparatus ; from the dry land, as well as from the sea and the other waters of the earth, water in the form of vapour rises unceasingly, and on reaching air rarer and colder than that on the surface of the earth, it condenses into drops, which descend to the earth in the form of rain if uncongealed, or in the form of snow or hail if in the congealed state. For these phenomena to go on, evapora- tion must be unceasingly gomg on from the surface of the earth. 266. We now return to the consideration of the physical properties of bodies in the vaporous state. 267. The heat absorbed in vaporisation decreases as the temperature of the vaporising liquid increases. For instance, a given weight of water at 212° F. requires less heat for its vaporisation than the same quantity at 100° F. requires ; there- fore the quantity of heat which is rendered latent by the con- version of a liquid into vapour varies with the temperature at which the evaporation takes place, the quantity of heat which becomes latent increasing as the temperature decreases. Watt concluded from his experiments on steam that liquids require for their conversion into vapour the same total quantity of heat at all temperatures, and as the quantity that remained sensible increased, the quantity that became latent decreased in the same proportion. ' For instance : — ■Latent and Sensible Heat of Steam 109 A certain weight of steam at 212° F., j 1 80° of sensible heat, condensed at 32° F., gives out | 950° of latent heat. Amounting together to . . . .1130° The same weight of steam at 250°, 1 ^„ of sensible heat. condensed at 32°, gives out J But only 912° of latent heat. Still amounting together to . . .II 30° The same weight of steam at 100°, 1 ,„, , •! 1 1^ 1 condensed at 32°, gives out | 68' of sensible heat. But now as much as ... . 1062° of latent heat. Making together, as before . . . 1130°'' 268. If liquids required for their conversion into vapour the same total quantity of heat, there would be no economy in distilling at one temperature rather than another. 269. Regnault has submitted the subject to a rigorous ex- amination, and his results show that the total amount of heat at all temperatures is not the same, but increases by a constant difference equal to 0-305 for each degree C. He found that the latent heat of steam at o°C. is 606-5 j so that the formula for calculating the total quantity of heat in steam at different temperatures becomes — A.=6o6-5 +0-305/, in which X represents the sum of the latent and sensible heat, while 606-5 is the latent heat of the vapour at 0°, and /the given temperature. 270. The elastic force of a vapour varies with the conditions under which the vapour is formed ; if the vapour is produced below the boiling-point of the'liquid, its elastic force is not equal to the pressure of the atmosphere ; if the vapour is produced at the boiling-point of the liquid, its elastic force is equal to the pressure of the atmosphere ; if the vapour is produced above the normal boiling-point of the liquid, its elastic force exceeds the normal pressure of the atmosphere. Steam of greater teasion than the atmospheric pressure is called high pressure steam. The tension of steam increases very rapidly ; at the temperature of 250-52° F. it is equal to two atmospheres 1 Miller's Chemical Physics, and edition. no Fundamental Principles of Chemistry (twice the pressure of the atmosphere) ; at 5io'62° F. it is equal to 50 atmospheres. 271. We have now to consider how the tension of vapour at different temperatures has been determined. 272. For measuring the elastic force of the vapour of water below zero, Gay Lussac made use of two barometer tubes filled with mercury, the open ends dipping under mercury in the same basin (fig. 42.) One of the tubes. A, which is straight and perfectly freed from air and moisture, by boiling the mercury in the tube, serves to measure the pressure of the atmosphere. The outer tube is bent, so that a part of it can be sur- rounded with a freezing mixture, as represented in the figure. If we now introduce a few drops of water above the mercurial column in the tube, B C, we observe that the level of the mercury in this tube is lower than in the tube, A, by a quantity which varies with the temperature of the freezing mixture. Fig. 42. -10' — 20' -30' C. , the depression is in millimetres 4-60 1-96 0-84 0-36 These depressions, which are necessarily due to the tension of the vapour in the tube, B C, show that at very low tempera- tures there is still aqueous vapour in the air. 273. Only a portion of the vapour in the tube, B C, is ex- posed to the freezing mixture ; but it is an established principle of hygrometry, that when the temperatures of two vessels com- municating with each other are unequal, the tension of the vapour is the same in both, and is always that^ which corresponds to the lowest temperature. 274. Dalton measured the elastic force of the vapour of water from 32° F. to 212" F. by means of the following appa- Elastic Force of Vapour III paratus. Two barometer-tubes, A and B (fig. 43), are put into the same basin of mercury, which is placed upon a furnace. The barometer, B, is completely freed from air and moisture ; in other words, it is a perfect baro- meter ; the barometer, A, contains a small amount of water above its mercury column. These two baro- meters are enclosed in a tall glass cylinder filled with, water, and a thermometer, T, dips into the water in the centre of the cylinder, which gives the temperature of the liquid. In heating gradually the basin con- taining the mercury, and conse- quently the water in the glass cylinder, the water in the tube con- tinues to vaporise, and as the ten- sion of the aqueous vapour aug- ments, the mercury in A falls lower and lower. The depression which is produced in A, below the level in B, for each degree the temperature is increased, is noted upon the scale, E. The apparatus of Dalton can be used so long as the elastic force of the vapour does not exceed the pressure of the atmosphere, When the tension is equal to the atmospheric pressure, the surface of the mercury column will be depressed to the level of the mercury in the basin, and the experiment is at an end. 275. Regnault employed' a form of apparatus which has the advantage of indicating all pressures and temperatures, whether above or below the boiling-point. ' His process consists in boiling water in a vessel under a known pressure, and ascertaining the temperature at which it boils. This method depends upon the principle that when the water boils, the steam it produces will have a pressure precisely equal to. that to which the water itself is submitted. 276. ' The apparatus consists of a copper boiler (fig. 44),, closed so as to be steam-tight, filled to about a third of its Fig, 43. 112 Fundamental Principles of Chemistry capacity with water, and placed upon a charcoal furnace. The tubes of four thermometers, whose bulbs descend to different depths in it, pass steam-tight through collars in the top. Two of these bulbs are immersed in the upper, and two others in the lower strata of the liquid. The boiler, C, is connected by a tube, A B, with a large glass globe, M, having a capacity of about five gallons, which is filled with air. The tube, A B, is surrounded by a larger tube, D, which is kept filled with cold water, flowing from a cistern, E, and discharged into another, Fig. 44. A'. From the upper part of the globe, M, two tubes proceed, one of which communicates with an air-gauge, O, and the other, H, is terminated in a connecting pillar H', which may be attached at pleasure, either to the plate of an air-pump, or to that of a condenser, so that the air in M can be made to have any degree of pressure, either above or below that of the atmosphere. The globe, M, is immersed in a reservoir of water at the temperature of the surrounding air. Elastic Force of Vapour 113 277- ' If it be desired to measure the pressure of the vapour of water corresponding to temperatures below the boiling-point, the connector H' is attached to the plate of an air-pump, and the air in M is gradually rarefied, so as to assume a series of decreasing pressures below that of the atmosphere. The thermometer in C shows the temperatures corresponding to these pressures severally, and the gauge O shows the corre- sponding pressures. 278. ' If it be desired to ascertain the pressures correspond- ing to temperatures above the boiling-point, the connector H' is attached to a condenser or a force-pump, by means of which the air in M, and in the boiler C, is submitted to a series of increasing pressures above that of the atmosphere. The cor- responding temperatures, as before, at which the water boils in C. are indicated by the thermometers.' 279. These researches have resulted in the construction of tables which make known the elastic force of the vapour of water at different temperatures. The following tables give the degree of tension for the various temperatures at which analyses are likely to be made. The tension of the vapour of water is expressed by the height of a column of mercury counterbalancing it. The first table gives the elastic force in inches of mercury for Fahrenheit's thermometer ; the second gives the elastic force in millimetres of mercury for the Centigrade thermometer. Table I. — Eloitic Force of Aqueous Vapour in Inches of Mercury, for Fahrenheit's Thermometer. ' Temp. Fah. Force. Inches of Mercury Temp. Fah. Force. Inches of Mercury Temp. , Fah. Force. Inches of Mercury 0° 0-051 14 0-092 28 0-159 I 0-053 tS 0-095 29 0-165 2 0-056 16 . 0-099 30 0-172 3 0-058 17 0-103 31 0-179 4 0-060 18 0-107 32 0-186 5 0-063 19 0-II2 33 0-193 6 0-066 20 O-II6 34 0-200 7 0-069 21 1 0-I2I 35 0-208 8 0-071 22 0-126 36 0-216 9 0-074 23 O-I3I 37 0-224 10 0-078 24 0-136 38 0-233 II 0-081 25 0-142 39 0-242 12 0-084 . 26 0-147 40 0-251 13 0-088 27 0-153 41 0-260 I 114 Fundamental Principles of Chemistry Temp. Fah. Force. Inches of Temp. Fah. Force. Inches of Temp. Fah. Force. Inches of Mercury. Mercury. Mercury. 42 0-270 70 0-723 98 1-764 43 0-280 71 0-748 99 1-819 44 0-291 72 0-773 100 1-874 45 0-302 73 0-799 lOI 1-931 46 -0-313 74 0-826 102 1-990 47 0-324 75 0-854 103 2-050 48 0-336 76 0-882 104 2-112 49 0-349 77 0-911 105 2-176 SO 0-361 78 0-942 106 2-241 51 0-375 79 0-973 107 2-307 52 0-389 80 1-005 108 2-376 S3 0-402 8r 1-036 109 2-447 54 Q-417 82 1-072 110 2-519 55 0-432 83 I -106 111 2-593 56 0-447 84 1-142 112 2-669 57 0463 85 1-179 113 2-747 58 0-480 86 I-2I7 114 2-826 59 0-497 87 1-256 "5 2-908 60 0-514 88 1-296 116 2992 61 0-532 89 1-337 117 3-078 62 0-551 90 1-380 118 3-166 63 0-570 91 1-423 119 3-257 64 0-590 92 1-468 120 3-349 65 0-611 93 1-514 121 3-444 66 0-632 94 1-562 122 3-542 67 0-654 95 1610 123 3-641 68 0-676 96 1-660 124 3-743 69 0-699 97 1-712 Table I I.— Elastic Fo! 'ce of Aqu 'ous Vapour in Millimeti 'es of Mercury for Centigrade Thermometer. Force of the Force of the Force of the Temp. Aqueous Temp. Aqueous Temp. Aqueous Cent. Vapour in Cent. Vapour in Cent. Vapour in Milhmetres. Millimetres. Millimetres. 0° 4-525 14° 11-882 28° 28-148 1 4-867 15 12-677 29 29-832 2 5-231 16 13-519 30 31 -602 3 5-619 17 14-409 31 33-464 4 6-032 18 15-351 32 35-419 5 6-471 19 16-345 33 37-473 6 6-939 20 17-396 34 39-630 7 7-436 21 18-505 35 41-893 8 7-964 22 19-675 36 44-268 9 8-525 23 20-909 37 46-758 10 9-126 24 22-211 38 49368 II 9-751 ^1 23-582 39 52-103 12 10-421 26 25-026 40 54-969 13 11-130 27 26-547 Elastic Force of Vapour 115 280. The tension of the vapour of other liquids could be determined by the methods which have been given for deter- mining the tension of aqueous vapour. 281. Vapours occupy a much larger volume than the liquids from which they are produced, and equal volumes of different liquids generate very different volumes of vapour. At the same temperature the elastic force of the va- pours of different liquids is different, — the more volatile the hquid' the greater the tension of its vapour. This is easily proved for elasticities below that of atmo- spheric air, by filling a number of barometer tubes (fig. 45) with mer- cury, and inverting them in a bath of the same metal. One of the tubes, A, is used as a baro- metef to measure the pressure of the external air ; into B is introduced, by means of a pipette, a few drops of water ; into C, a few drops of alcohol ; and into D, a few drops of ether ; the different liquids will ascend to the top of the mercury and then evaporate. The elastic force of each vapour will depress the column of mercury, but the amount of depression will vary with the hquid ; the vapour of water will cause the least depression, and therefore its elastic force is least ; alcohol the next ; and ether the greatest. The elastic force of the vapours counteracts the pressure of the atmosphere to the extent of the depression they cause in the mercurial column ; consequently, it is easy to find the pressure each of these vapours exercises, say, upon every square inch; for, if the I 2 Fig. 45. ii6 Fundamental Principles of Chemistry atmosphere at the time supports a column of mercury 30 inches in length, its pressure is equal to 15 lbs. on every square inch ; if the vapour of water dejjresses the mercurial column one inch, its pressure must be equal to ^V of 15 lbs. ; if the alcohol de- presses the mercury 2 inches, and the ether depresses it 20, the pressure they exercise is found in the same way. It has been proved that the elasticity of the vapour emitted from each liquid increases as the temperature rises, until, at the boiling-point of each liquid, the elasticity of the vapour is equal to the pressure of the atmosphere.' 282. Dalton considered that all vapours have the same elasticity at an equal number of degrees above or below their boiling-points ; other experimenters have not found this to be perfectly correct, although for short distances above or below the boiling-point it is very nearly true, except in the case of mercury. 283. The quantity of vapour that can be formed from any liquid depend"! upon the space and the temperature ; the same quantity of vapour will pass into the space if it be filled with gaseous matter or with other vapours, or if it be perfectly empty ; the only difference being that it requires a longer time to pass into the space which contains other gaseous or vaporous bodies than it would do if the space were empty. ' Different gases and vapours offer no resistance to each other's elasticity ; thus, the particles of watery vapour in the air are not subjected to the pressure of the atmosphere, but only influenced by the pressure of the particles of the same kind ; and hence, at 32", when the elasticity of the vapour is only o"2oo inch, it retains perfectly its elastic constitution, though diffused through an atmosphere the elasticity of which may equal thirty inches.' 284. The mixture of a gas and vapour obeys the two following laws ; these laws were discovered by Dalton, and are known under the name of the ' Laws of Dalton ' : — 1. The amount of vapour which will saturate a given space at a given temperature, and its tension, are the same, whether the space be completely empty or filled with gas. 2. The elastic force of a mixture of gas and vapour is equal to the sum of the tensions which each would have separately. ' E is a graduated scale for measuring the depressions. Gas Analysis 117 285. Some of the aqueous vapour in the air is deposited, we have before noticed, in the form of dew, rain, hail, or snow when the temperature becomes lowered ; ' and everyone must have observed, that when a vessel containing cold water is brought into a warm room, moisture becomes deposited on its outer surface owing to the air surrounding the vessel becoming cooled by the water. The temperature at which the deposition takes place is called the dew-point ; instruments which are employed to measure the amount or degree of moisture in the air, are termed hygrometers. The degree of moisture does not depend on the absolute quantity of aqueous vapour in the air, but on the greater or less distance of the air from its point of saturation. When the air is cold, it may be moist with very little vapour, and, on the contrary, when it is warm, very dry, even with a large quantity of vapour ; but we must refer the student for further information on this subject to works on Natural Philo- sophy. 286. We will close this chapter with instructions for cor- recting the volume of gases for the tension of aqueous vapour, and with some exercises on the subject ; but it is necessary first to describe the apparatus employed to hold gases for analysis : and the correction of gases for pressure. 287. In gas analysis, the gases are collected and measured \tl graduated tubes over mercury ; in Bunsen's method of gas analysis, two gas tubes are employed, one is called the absorp- tion tube (fig. 46), and the other is called the eudiometer (fig. 47). In this latter tube the combustible gases are exploded ; there is therefore fused into the closed end of the tube, as shown in the figure, two platinum wires for the purpose of conducting the electric spark. The tubes are first filled with mercury, the mouth of the tube is then closed air-tight with the thumb and 1 The condensation ot some of the aqueous vapour in the atmosphere in the form of dew takes place most copiously, as no doubt all my readers will have noticed, during a, calm, clear night succeeding a hot day. This is due to the earth's surface substances, especially the vegetation, radiating heat, which is not re- radiated except on cloudy nights, the temperature on the earth's surface is therefore lowered, and consequently some of the aqueous vapour in the stratum of air in contact with the surface is deposited on account of this reduction in temperature ; just as moisture is deposited on a glass containing cold water when brought into a warm room. ii8 Fundamental Principles of Chemistry 1 Fig. 46. Fig. 47. inverted, mouth downwards, in the trough containing mercurj'. The gaseous substance to be analysed is then conveyed into the tube, and it displaces, of course, an equal volume of mercury in the tube. At each stage of the analysis, four observa- tions have to be made : ist, the height of the mercury in the gas tube ; 2nd, the height of mercury in the trough as measured on the scale of the gas tube ; 3rd, the temperature ; and 4th, the atmospheric pressure. 288. At the moment a gas is weighed or measured, it is necessary to observe the height of the barometer, as this gives the pressure to which the gas is then sub- jected, provided the liquid over which the gas is collected stands on the same level both in and outside the vessel con- taining the gas. If, however, the liquid stands higher inside than outside the gas- vessel, the gas will be subjected to a pressure less than that of the atmosphere at the time, by the amount necessary to support the column of liquid above its outer level. If the liquid stands lower in the gas vessel than outside, the gas is under greater pressure than that of the atmosphere by the amount of pressure which a column of the liquid, equal to the difference in its height, without and within the gas-vessel exercises. In this latter case, the perfect level of the liquid within and without the vessel may readily be restored by raising the gas-vessel. If the fluid stands higher within than outside the vessel, which is generally the case, it is rarely possible in practice to bring it to the same level. A correction has therefore to be made for this inequality of level, which is accomplished in the following way : — Suppose the gas to have been collected over mercury ; in order to allow for the dilatation occasioned by the inequality of level, the difference of the two heights must be accurately measured, and the measurement so obtained must be subtracted from the height of the mercurial column in the barometer at the time. A similar correction is required if the gas be standing Correction of Gases for Pressure, &c. iig over water, but it is smaller in amount, — a column of water, 13-6 in height, being equivalent to one inch of mercury. When this correction has been made, a simple calculation enables one to discover the volume any gas would measure at the standard pressure. Example. — What volume would a gas, standing over mercury, measure at the standard pressure, which measures 60 cubic inches, the barometer at the time standing at 2875, the level of the mercury in the gas-vessel being i -5 inch higher than that outside 1 By Mariotte's law, the bulk of a gas is inversely as the pressure to which it is subjected. Therefore, — Standard Observed Observed True pressure pressure volume volume 30 ' I 287S-i-5o = ( 27-25 :: 60 : 54-5 Exercises on the Correction of Gases for Pressure. 1 10. What volume would a gas, standing over mercury, measure at the standard pressure, which measures 19 cubic inches, the barometer at the time standing at 29-05, the level of the mercury in the gas- vessel being 0-5 inch higher than that outside ? 111. What volume would a gas, standing over mercury, measure at the standard pressure, which measures 20 cubic inches, the barometer at the time standing at 28-05, the level of the mercury in the gas- vessel being I -o inch higher than that outside ? 112. What volume would a gas, standing over mercury, measure at the standard pressure, which measures 15 cubic inches, the barometer at the time standing at 31, the level of the mercury in the gas-vessel being 0-2 inch higher than that outside ? 289. Correction of gases for the tension of aqueous vapour. — We learn from Table I., that the elastic force of the vapour of water at 80° F. would depress the mercurial column one inch ; or its tension is one-thirtieth of the usual tension of the air ; therefore if a gas perfectly dry were saturated with aqueous vapour at 80° F., the vapour would increase the tension of the gas, if it were confined, by one-thirtieth ; or if the gas were allowed to expand, the vapour would increase its bulk by one- thirtieth. A gas containing aqueous vapour must therefore occupy more space than if it were perfectly dry, by reason of the pressure which the vapour exercises oa the confining fluid. It is, therefore, necessary to take care, in measuring gases, that they are either perfectly dry, or thoroughly saturated with 120 Fundamental Principles of Chemistry aqueous vapour. To find the actual pressure upon a gas saturated with vapour, we must subtract from the apparent pressure the amount neutralised by the tension of aqueous va- pour. Example : — Suppose a gas saturated with aqueous vapour measured loo cubic inches, the temperature being 50° F., and the atmospheric pressure at the time 29"36i inches; how much space would the gas occupy in the dry state, and at 30 inches pressure? The tension of aqueous vapour at 50° F. is 0-361 (Table I.), therefore the gas is not under the apparent pressure of 29'36i, but under the actual pressure of 29'36i — o'36i = 29-0 inches; therefore, — Standard Observed Observed True pressure pressure volume volume 30 : ( 29-361 —0-361 = \ \ 29-0 / :.- 100 : 96-6 290. We have to attend to the following points in the measuring of gases : — i. We must determine as accurately as possible the height of the water or mercury in the vessel con- taining the gas, above that outside ; and the difference must be subtracted from the height of the barometric column at the time. 2. If moist, we must correct for the tension of aqueous vapour. 3. These two corrections being made, and having observed the height of the barometer, we have to sub- tract from the apparent pressure, the height of the liquid in the gas-vessel and the tension of the vapour, to get the actual pressure to which the gas is subjected at the moment it is measured. 4. We must correct the gas for temperature.' As the volumes of gases can be compared only if measured at the same temperature, under the same pressure, and in the same hygroscopic state; the temperature is generally reduced to 60° F.,^ the hygroscopic state of the gases to o, and the pressure to 30 inches.' 291. If it is desired to find the weight of a gas which has been measured, it is necessary to ascertain the weight corre- sponding to the volume found, before the proportional amount ■ It does not matter in what order the corrections are made. * This, as we have before stated, is the English standard ; the continental oneiso°C. = 32''F. ' The standard pressure adopted on the Continent is 760 millimetres = 29 -922 inches. Exercises on the Correction of Gases 121 of the gas in 100 parts by weight of the analysed substance can be calculated. But as the exact weight of a certain definite volume of the various gases has been determined very accu- rately, the calculation is a simple rule-of-three question, after the gas we have measured has been corrected, if moist, for the tension of the aqueous vapour, and brought to the standard of comparison as regards the temperature and pressure. Exercises on the Correction of Gases for Temperature, Pressure, and Tension of Aqueous Vapour. 1 13. If a voluire of dry air at (xp F., and under a pressureof 30 inches, measures 80 cubic inches, what will it measure if saturated with water ? 1 14. What is'the total quantity of heat in steam at 100° C. ? 115. A gas (moist) measured 15 cubic inches, the temperature was 80° F., the pressure was 29-5 inches, and the height of the column of mercury in the vessel containing the gas above that outside was 0'25 ; what volume would the dry gas measure at the English standard for tem- perature and pressure ? 116. A gas (moist) measured 25 cubic inches, the temperature was 45° F., the pressure was 29-0 inches, and the height of the column of mercury in the vessel containing the gas above that outside was o-6 ; what volume would the dry gas measure at the English standard for tem- perature and pressure ? 117- A gas measured over water 15 cubic inches, the temperature was 50° F. , the pressure was 29-5 inches, and the height of the column of water above that in the trough was 6 '8 inches : what would be the measure of the dry gas at the standard (English) pressure and temperature ? 118. A gas measured over water 12 cubic inches, the temperature was 70° F., the pressure was 30 inches, and the height of the column of water above that in the trough was 10 '2 inches ; what volume would the dry gas measure at the English standard for temperature and pressure ? 119. A gas (moist) measured 114 millimetres, the temperature was 16° C, the pressure was 76''4 millimetres, and the height of the column of mercury, above that in the trough, was 72- 1 millimetres. Correct the volume for temperature, pressure, and tension of aqueous vapour, giving the corrected volume at o" C, and i metre pressure. 120. A gas (moist) measured io7'9 millimetres, the temperature was I4'3° C, the pressure was 766-8 millimetres, and the height of the column of mercury, above that in the trough, was 59 '8 millimetres. Correct the volume for temperature, pressure, and tension of aqueous vapour, giving' the corrected volume at o" C. , and i metre pressure. 121. A gas (moist) measured 96^8 millimetres, the temperature was 13° C, the pressure was 772 'I millimetres, and the height of the column of mercury, above that in the trough, was 69-6 millimetres. Correct the volume for temperature, pressure, and tension of aqueous vapour, giving the corrected volume at o" C. , and I metre pressure. Examination Questions. 122. Do liquids evaporate at a fixed temperature ? 123. How does the boiling-point vary (i) with the pressure, (2) with 122 Fundamental Principles of Chemistry the nature of the vessel, (3) with the substance dissolved in the liquid, (4) with the nature of the liquid ? 1 24. Of four barometer-tubes standing in the same cistern of mercury, one has the ordinary Torricellian vacuum, while the other three have, re- spectively, a little water, a little alcohol, and a little ether, in their Tor- ricellian chambers. Will these additions (all of small weight) cause any perceptible change in the lengths of the various columns ? Give a reason for your reply. 125. Water is boiled in two tubes, the depth of the water in the one being 6 inches, and in the other 24 inches. I find that at f temperature when bubbles of steam rise from the bottom of one tube, they do not rise from that of the other. Explain this. 126. Why are air-balloons not completely filled with gas before they are allowed to ascend ? What would be the effect if they were completely filled ? At what point do they cease to ascend ? 127. An open vessel containing water is sometimes placed on the top of a stove, when the latter is employed for heating a room. Can you assign any reason for this somewhat peculiar custom ? 128. What would be the effect of heat and cold on a liquid which can pass into the other two states of aggregation ? Answer the question fully. 129. A glass flask, filled with boiling water and steam, is corked, and immediately removed from the source of heat. It will presently cease boiling. If now cold water be poured over that part of the flask filled with steam, the water will commence to boil again. Give a full explana- tion of this, and a complete enunciation of the law made use of in your explanation. 130. £xplain the difference between destructive and non-destructive distillation. 131. What is meant by the dew-point ; and is it a fixed or a changeable point? 132. Explain fully the distinction between a thermometer and a baro- meter. 133. Why does a person feel more uncomfortable in a hot-house, the atmosphere of which is saturated with aqueous vapour, than in a hot-house of the same temperature in which the quantity of vapcur in the air is less? 134. If you were to force two cubic feet of gas into a space which, under the normal condition of atmospheric pressure, would only hold one cubic foot of gas, what would be the increase in the tension ; and what would be the increase if three cubic feet were forced in : and how would the tension correspond with the pressure ? 135. If a vessel filled with air is fitted air-tight with a stopcock at the foot of a high mountain, what will take place when the stopcock is opened on the summit of the mountain ? And if the flask is closed air-tight on the top, and the stopcock is opened on reaching the foot of the mountain, what will occur ? 1 36. In tropical islands and coasts the wind blows from the sea during the day ; this is appropriately called the sea-breeze ; but during the night the wind blows from the land to the sea, producing what is termed the la>id-breeze. How do you account for these opposite phenomena ? 137. Why is the boiling-point of water more variable than its freezing- point ? 138. How do you account for air, that has come down from a snow- clad mountain, being of medium temperature ? Density 123 139. What are the fixed points from which a thermometer is graduated ? State why they have been selected. What degree on the Fahrenheit scale corresponds with - 7° Cent. ; and what degree on the Cent, scale with 70° F. ? 140. What occasions the «'«^'«^ noticed in liquids before they begin to boil ? 141. How do you account for. sea-fogs ? " 142. Why do some liquids on exposure to the air increase in volume ? 143. If a closed vessel filled with steam at 2iz°F. at the ordinary atmospheric pressure be raised to 300°, will the presence or absence of water, as well as steam, within the vessel affect the expansive force ? 144. Give the true definition of the boiling-point of a liquid. 145. Define what is meant by specific heat ; and give the specific heat of three or four familiar substances. Exercise. — Given two vessels of equal size, one filled with water at io° C. ; the other with mercury at 10° C. ; find out how much heat each liquid must receive before it begins to boil, the weight of the water being 2 lbs., the specific heat of mercury -033, and its boiling-point 350" C. 146. Why does a standing leap fall short of a running one ? 147. If I wished to evaporate a liquid spontaneously, whether would it be more advisable, in order that it should evaporate as speedily as possible, to place it in a vessel which causes the depth to be greater than the surface ; or in a vessel in which the surface of the liquid is greater than its depth ? 148. How is deposition of dew affected by the presence or absence of clouds in the sky ? 149. What is the theory of fractional distillation ? How is the pro- cess carried out ? ' CHAPTER V. ABSOLUTE DENSITY — SPECIFIC GRAVITY — DIFFERENCE BETWEEN DENSITY AND SPECIFIC GRAVITY — SPECIFIC GRAVITY OF LIQUIDS — EXERCISES — SPECIFIC GRAVITY OF SOLIDS — EXERCISES — TABLES OF SPECIFIC GRAVITIES, THEIR USE— EXERCISES — THE HYDRO- METER, ITS USE — SPECIFIC GRAVITY OF MIXTURES — EXERCISES — EXPERIMENTAL EXERCISES — WEIGHT AND SPECIFIC GRAVITY OF GASES — EXERCISES— SPECIFIC GRAVITY OF VAPOURS — EXERCISES — ■ QUESTIONS. 292. In Chapter III. the meaning of the word mass was ex- plained ; it meant, it was stated, the quantity of matter in a sub- stance, and that it was estimated in the terms of some standard. We have now another term, absolute density, t,o explain before we can enter satisfactorily upon the subject-matter of the present chapter. We have constantly, in every-day life, 1 The student must now return to Chapter II. and complete the study ot it, commencing at par. 144. 124 Fundamental Principles of Chemistry to notice and speak of one substance being lighter than another. Now we do not mean, by that expression, that one ounce, or one pound, of the one substance weighs less than an ounce or a pound of the other substance ; but we mean, that the Hghter of the two substances we are alluding to, weighs less for an equal volume or bulk than the other substance ; one cubic inch of cork, for example, weighs less than a cubic inch of iron. We say, in like manner, that, of the two liquids — water and mercury — water is the lighter of the two, because we know by experience that, if we were to weigh equal volumes of the two liquids, mercury would prove the heavier of the two bodies ; then, that is the more dense which in equal volume com.a.ms the greater mass. Different bodies have, therefore, as we daily notice, different densities ; and the sim- plest way of determining the density of a substance is to find the mass of a known volume of it by weighing it, and to divide the mass obtained by the volume ; we thus obtain the quantity of matter in unit-volume of any substance, and this is defined as the absolute density of that substance. If, then, we denote the mass by M, the volume by V, and the density of the body by D, we have 293. Having explained what is meant by the term absolute density, we have now to explain what is meant by the relative density, or, as it is generally termed, the specific gravity, of a substance ; these two terms are apphed to the ratio between the masses of equal volumes of a given body and of some standard substance ; and this forms the subject-matter of the present chapter. 294. Density means, then, comparative mass, and specific gravity comparative weight. These expressions, although really relating to distinct things, are often used indifferently in chemical writings, and without practical inconvenience, since mass and weight are directly proportional to each other. 295- To arrive at the relative weights of equal volumes of different substances, it is necessary to fix upon one as the standard of comparison : distilled water has been selected as Calculation of Specific Gravities 125 the standard for solid and liquid bodies, its density being reckoned as 1000 or i. The specific gravity of substances heavier than water is consequently represented by a higher number, and those which are lighted: by a lower number than 1000 or I. 296. The specific gravity of the metal platinum is stated to be 2i"5 ; by this is meant that ior equal volumes platinum is 2i'5 times heavier than water. Thus, one cubic foot of water, at the temperature of 60° F., weighs 1,000 ounces ; therefore as platinum, bulk for bulk, is 21-5 times heavier than water, one cubic foot of platinum, at 60° F., will weigh 21,500 ounces. Again, comparing equal volumes, turpentine is lighter than water in the proportion of 792 to 1,000; therefore, as one cubic foot of water, at the temperature of 60° F., weighs 1,000 ounces, a cubic foot of turpentine at that temperature will weigh 792 ounces. 297. In order to calculate the specific gravity of a body it is sufficient to determine its weight and the weight of an equal volume of water, and then divide the weight of the body by the weight of water; the quotient is the specific gravity of the body, as compared with that of water taken as unity. The formula for specific gravity is, therefore, w W representing the weight of the body, w the weight of an equal volume of water, and S the specific gravity of the substance. 298. It is desirable at the outset to inform the student that the experiment is generally made in this country at a tempera- ture of 60° F., and the standard barometric pressure for gases and vapours is 30 inches ; in almost all other countries the French standards of pressure and temperature are employed ; viz., 760 milUmetres, or 29-922 inches for the pressure ; and 4° C, or 39°-2 F., for temperature, for at that temperature water attains, as we have already learned, the point of maximum density. 299. Bottles (fig. 48) are made for the express purpose of determining the sp. gr. of liquids ; they are made to hold 1,000, 500, 250, &c., grains or grammes of distilled water. A weight 126 Fundamental Principles of Chemistry is usually sold with them, which counterpoises the bottle full of distilled water, and upon which is marked the quantity of dis- ^^ tilled water the bottle holds. All that ij is required in estimating the sp. gr. of 11^1 ^ any other fluid is to fill the bottle with t completely ; to close the bottle with I he stopper in such a way that no bub- )les of air are left in it ; then, after viping it perfectly dry, to ascertain its veight, by observing how much heavier I )r lighter it is than the weight of water \ he bottle is capable of holding, and idding or subtracting accordingly; and ^_, ;he result, divided by the weight of "~^ T water the bottle is capable of holding, will be the sp. gr. 300. A bottle capable of holding 500 grains of distilled water will hold 922-5 grains of sulphuric acid; the latter weight divided by the former will give the sp. gr. of the acid, water be- ing taken as i ; thus, "^ =1-845 sp. gr. of the acid : again, the same bottle, or one of like size, will hold only 396 grains of turpentine, therefore ■g||-g^=o-7g2 sp. gr. of the turpentine. 301. As the volume of liquids expands with increase of temperature, the quantity of ponderable matter in a given volume becomes thereby proportionably diminished ; it is therefore requisite, in determining the sp. gr. of substances, to conduct all the experiments at one uniform standard of temperature. For the same reason, the bottle should never come in contact with the naked hand during the experiment ; it should be protected by a cloth during the wiping and drying of it and its transfer to the balance. Exercises on the Calculation' of the Specific Gravity of Liquids. 150. If a bottle, capable of holding 300 grains of distilled water, holds 260 of some other liquid, what is the sp. gr. of that liquid ? 151. If a bottle, capable of holding 360 grains of distilled water, holds 320 grains of some other liquid, what is the sp. gr. of that liquid ? 152. If a bottle, capable of holding 400 grains of distilled water, holds 470 grains of some other liquid, what is the sp. gr. of that liquid ? 153. If a bottle, capable of holding 700 grains of distilled water, holds 600 grains of some other liquid, what is the sp. gr. of that liquid ? Weight from Volume and Specific Gravity 127 302. The weight of any substance may be calculated if the volume and specific gravity be known. The weight of the volume- unit, be it a gallon, a cubic inch, a cubic foot, &c., as the case may be, must first be determined, and this is arrived at by multiplying the weight of the same volume-unit of water by the specific gravity of the substance. The product is the weight of the volume-unit of the substance. Thus, if we represent the weight of the volume-unit of water by w, and the specific gravity of the substance by S, and the weight of the volume- unit of the substance by W ; then W=Sxze/. Example : i. Required the weight in pounds of twenty gallons of sulphuric acid, the sp. gr. of which is i '85. Now, the weight of a gallon of water, which is in this case the volume-unit, is 70,000 grains, or ten pounds avoirdupois ; therefore — 10 lbs. X i'85 = i8'5 lbs. weight of i gallon of sulphuric acid. i8'5 lbs. X 20 = 37o'o lbs. weight of 20 gallons. 2. Required the weight in pounds of a dry block of fir con- taining 50 cubic feet, the sp. gr. of the wood being 0-47. Now the weight of a cubic foot of water, which is in this case the volume-unit, is 62 '5 lbs.; therefore, 62-5 lbs. xo-47=29,375 lbs. .weight of i cubic foot of fir. 29,37s lbs. X 50=146875 lbs. weight of 50 cubic feet of fir. Exercises on the Calculation of the Weight of Liquids from their Volume and Specific Gravity. 154. Required the weight in pounds of a gallon of linseed oil, its sp. gr. being 0-953. 155. Required the weight in pounds of a gallon of turpentine, its' sp. gr. being o 792. 1 56. Required the weight of a gallon of the water of the Dead Sea, its sp. gr. being IT72. 157. Required the weight of a gallon of vinegar, its sp. gr. being I -063. 158. Required the weight of 1 cubic inch of mercury, the sp. gr. of which is I3'S9 ; a cubic inch of water weighing 252-458 grains. 303. When a solid is immersed in water or any other liquid, it displaces a quantity of the fluid equal to its own bulk 128 Fundamental Principles of Chemistry (as no two bodies can occupy the same space at the same time) ; the weight of the displaced water being determined, as well as that of the solid, the sp. gr. of the solid is the quotient obtained by dividing the latter weight by the former. 304. The specific gravity of solids in the form of powder or small fragments is determined by weighing them in air and then introducing the weighed particles into a sp. gr. bottle filled with water ; a quantity of water overflows, equal in bulk to the solid particles introduced ; the bottle containing the substance weighs, therefore, less than the bottle filled with water and the substance when they are weighed separately, the difference being the weight of the volume of water expelled by the solid. Thus, if we weigh 200 grains of sand and then in- troduce it into a sp. gr. bottle holding 500 grains of water, if no water were expelled, the water and sand together would weigh 700 grains; but instead of that it only weighs 624 grains, the difference, 76, being the weight of the water expelled, there- fore 7%"= r.''63, the sp. gr. of the sand. 305. Great care must be taken to prevent air being ad- mitted when the solid is added to the water in the bottle, and if any should be introduced every bubble must be expelled before weighing, if we would. obtain accurate results. Exercises on the Calculation of the Specific Gravity of Solids. ■ 159. If 100 grains of a solid be introduced into a bottle holding 500 grains of water, and if after the introduction of the solid the bottle weighs 560 grains, what is the sp. gr, of the solid ? 160. If 160 grains of a solid be introduced into a bottle holding 400 grains of water, and if after the introduction the bottle weighs 500 grains, what is the sp. gr. of the solid ? 161. If 300 grains of a solid be introduced into a bottle holding 700 grains of water, and if after the introduction the bottle weighs 850 grains, what is the sp. gr. of the solid ? 306. When the substance whose sp. gr. has to be deter- mined is soluble in water, it is necessary to employ some other liquid in which it is insoluble ; alcohol, naphtha, turpentine, oil, &c., are the liquids generally employed when water cannot be used. The sp. gr. of the solid in reference to the fluid em- ployed is first determined; then the sp. gr. (if it is not known) of the fluid in reference to water; the two numbers thus obtained, Methods of determining Specific Gravities 129^ multiplied together, give the sp. gr. of the solid as referred to water. For, let W represent the weight of the substance in air, and n the weight of an equal volume of naphtha or other liquid in which the sohd is insoluble, s the sp. gr. of the substance in reference to naphtha, and s" the sp. gr, of the naphtha in reference to water, then , W and n S" z=It w w Example : 50 gr. of a solid is introduced into a bottle hold- ing 396 gr. of turpentine ; the bottle weighs, after the introduc- tion of the solid, 4.21 grs. n. 25 the sp. gr. of the substance in reference to the turpentine. A bottle holding 500 grs. of distilled water holds 396 grs. of the turpentine. /' =1=396 _„. w 500 the sp. gr. of the turpentine in reference to water. s' xi-"=S=2-oxo79=i-s8 the sp. gr. of the solid, taking water as the standard. Exercises on the Calculation of the Specific Gravity of Solids which are soluble in Water. 162. If 200 grains of a solid be introduced into a bottle holding 400 grains of alcohol, the sp. gr. of which is 0'87o, and the bottle weighs," after the solid is introduced, 570 grains, what is the sp. gr. of the solid, taking water as the standard of comparison ? 163. If 300 grains of a solid be introduced into a bottle holding 700 grains of turpentine, the sp. gr. of which is 0790, and the bottle weighs, after the introduction of the solid, 870 grains, what is the sp. gr. of the solid, taking water as the standard of comparison ? 307. We have noticed one of the effects of the immersion of solids in liquids, viz., the displacement of so much of the K 130 Fundamental Principles of Chemistry liquid as is equal in volume to the solid immersed ; and if we can collect and weigh the volume of the liquid displaced, and we have weighed the solid previous to its immersion, their weights are of course the relative weights of equal volumes of the solid and liquid. We have now to consider another of the effects attending the immersion of solids in liquids. It is this; 308. The solid will he pressed uptvards with a force equal to the weight of the liquid it displaces. For when a solid is wholly immersed in a liquid, the lateral pressures a and b are equal, and contrary to each other, and therefore neutralise each other; but the vertical pressures on the faces d and c are unequal, the upiuard pressure being greater than the downward ; therefore the solid, as a consequence, has a tendency to move upwards. Thus suppose that a cube is immersed in a vessel of water (fig. 49), and that four of its sides are arranged verti- cally. These four sides, presenting the same surface to the Hquid, and being immersed to the same depth, experience equal pressures, and as the sides are opposite to each other, two and two, the lateral pressures must be contrary as well as equal ; hence they are neutralised, or in equilibrium. With regard, however, to the pressures which act vertically on the horizontal sides d and ir, it is evident that the downward pressure on d is equal to that of the weight of a column of water having the side d for its base, and d n for its height : and that the up- ward pressure on c is equal to that of the weight of a column of water having the side c for its base and c n for its height. The cube, therefore, tends to rise under the pressure of a force equal to the difference of these pressures, which is equal, evi- dently, to the weight of a column of water having the same base and the same height as the cube; consequently, this pres- sure is equivalent to the weight of water displaced by the body immersed. 309. If the weight of the solid be equal to that of the mass of fluid which it has displaced; in other words, if its density or Fig. 49. Methods of determining Specific Gravities 131 specific gravity be equal to that of the fluid, it will remain sus- pended in the liquid wherever it may be placed. If the solid has a greater density than the liquid, it will sink, because the pressure of its weight is greater than the upward pressure of the liquid. If the solid has a less density than the liquid, the upward pressure of the latter will exceed the weight of the solid ; the solid will therefore be forced up to the surface of the liquid with a force equal to the difference between the weights of equal volumes of the solid and the liquid. It is usual to express these effects by stating that a solid which is plunged beneath the surface of a liquid loses as much of its weight as is equal to that of the liquid displaced. 310. This principle, which constitutes the foundation of the theory relating to immersed and floating bodies, is known by the name of the principle of Archimedes. 311. The sp. gr. of solids in the mass is determined by suspending them by means of a horsehair from the hook under one of the scale- pans; the mass is then weighed in air, the operator having previously taken care to remove any dust or loosely adhering par- ticles. A vessel of pure water at 60° F. is arranged in such a manner that the solid, still suspended from the scale-pan, can be immersed as nearly as possible in the centre of the vessel (fig. 50), and covered by at least half an inch of water (if air- bubbles should adhere to the solid when immersed in the water, they must be re- ^ moved by means of a feather) ; it is now — .,,=»^ to be weighed,- and the weight will be less ^■°- s°- than in air ; subtract the weight in water from the weight in air, and the remainder will be the weight lost on immersion, or, in other words, the weight of an equal volume of water ; divide the weight in air by the weight lost on immersion, the quotient will be the sp. gr. of the solid. Exercises on the Calculation of the Specific Gravity of Solids. • ■ 164. Required the sp. gr. of a solid which weighs 36 grains in air and 26 in water. 133 Fundamental Principles of Chemistry 165. A body which weighs 100 grains in air, weighs 75 grains in water ; calculate its sp. gr. 1 66. A body weighs 150 grains in air, and 80 in water, what is its sp. gr. ? 167. A piece of metal weighs S'2I grains in air, and 4-13 grains in water ; what is the sp. gr. of the metal ? 168. A piece of silver weighs 200 grains in air, and 180 grains in water ; required its sp. gr. 312. The above method must be modified for a soHd lighter than water ; the solid is first weighed in air, it is then connected with a piece of lead or other metal heavy enough to sink it, the weight of the metal and the weight it loses on immersion being known. From the weight lost by the two bodies united, deduct the weight lost by the metal, and the re- mainder will be the weight of the volume of the fluid displaced by the lighter body. Divide the weight of the light body by the weight of the water it displaces, and the quotient will be its sp. gr. A piece of white wax weighed . 50 grs. , copper „ ■ 388 „ Weight of the two substances . = 438 grs. Lost on immersion by the two =■ 95 '8 „ „ copper = 44-2 „ „ „ wax = _^r6 „ .•. the specific gravity of the white wax is — ■ c W 50 , w 51 '6 Exercises on the Calculation of the Specific Gravity of Solids Lighter than Water. 169. Determine the sp. gr. of ash wood ' from the following data : Weight of wood in air 25-35 grs. , , , , a copper sinker . . . . 1 1 'OO , , ,, , wood and sinker under water . . . 5-10 ,, „ „ copper 977 ' Air-bubbles are sometimes very difficult of removal, especially from porous substances like wood and cork. A simple plan of removing them consists in heating the water to ebullition, and introducing the body, which has been weighed in the air, into the still boiling liquid, which is then allowed to cool to the standard temperature, when the second weighing is made. In cases where the liquid and substance cannot be heated, it is necessary to employ an air-pump ; this is especially necessary when the body is of small bulk. Specific Gravities Applied 133 170. A piece of wood which weighs 15 lbs. in air has attached to it a piece of copper which weighs 18 lbs. in air, and 16 lbs. in water ; the weight of the united mass in water is 6 lbs. ; required the sp. gr. of the wood. 171. A piece of cork weighs 96 grains in air ; it is attached to a piece of metal which weighs 86-5 grains in air, and 75-6 grains in water; the united mass weighs 48 grains in water ; required the sp. gr, of the cork. 172. A piece of metal weighing 36 lbs. in air, and 32 lbs. in water, is attached to a piece of wood, the weight of which in air is 30 lbs. ; the weight of the combined solids in water is 12 lbs. ; required tne sp. gr. of the wood. 313. Use of tables of specific gravities. — Tables of specific gravities possess numerous applications. The sp. gr. of a body is often the most distinctive of its physical characters. The mineral iron pyrites, for instance, is in colour almost exactly like gold ; but it is at once distinguished from the precious metal by the difference in sp. gr., an equal bulk of gold being nearly four times as heavy. By means of tables of specific gravities the weight of a body may be calculated when the volume is known, and also the volume when the weight is kijown. ' Since the weight of a cubic foot of water is 1,000 ounces,' it follows that if the sp. gr. of water be expressed by 1,000, the numbers which express the specific gravities of all other liquids and solids will also express the number of ounces contained in a cubic foot of each. Thus the sp. gr. of gold being i9"36o, it follows that a cubic foot of gold will weigh 19,360 ounces. 314. ' By the tables of specific gravities the volume of any proposed weight of a body can be readily calculated, for it is only necessary to divide the number expressing the weight in ounces by the number representing the sp. gr., omitting the decimal point ; the quotient will express the number of cubic feet in the volume. Thus, for example, if it be desired to ascertain the bulk of a ton weight of gold, it is only necessary to reduce the ton weight to ounces, and to divide the' number of ounces by 19,360, and the quotient will be the number of cubic feet in the ton weight ' (Lalrdner). From what has been stated, the student knows that, to find the volume of a substance, 1 A cubic foot of water, at 62° F., weighs 997'i37 ounces ; but for all prac- tical purposes a cubic foot may be taken to weigh 1,000 ounces. An imperial gallon of water weighs 10 lbs., and the volume of a gallon of water is 277 '274 cubic inches. 134 Fundamental Principles of Chemistry the weight of the whole mass of the substance must be divided by the weight of one volume-unit of that substance ; the method for finding the weight of a volume-unit of a substance has already been given. Exercises for computing the Weight from the Volume and the Volume from the Weight of Substances. 173. What will be the weight of a block of limestone containing 12 cubic feet; l cubic foot of water weighing 62-5 lbs., the sp. gr. of the stone being 2 '64 ? 1 74. How many cubic feet are there in a block of coal weighing I cwt. , its sp. gr. being i "232 ? 175. The sp. gr. of bar iron is 7788 ; required the weight of a cubic foot. 176. The sp. gr. of flint glass is 3 '329 ; required the weight of a cubic foot. 177. The sp. gr. of oak is 0-845 ! required the weight of a cubic foot. 178. The sp. gr. of cork is 0-240 ; required the weight of a cubic foot. 179. The sp. gr. of ice is 0-930 ; required the weight of a cubic foot. 180. The sp. gr. of silver is 10-474; required the weight of a cubic inch. 181. A solid weighs 49 grs. in air, and 42 grs. in water ; required the weight of a cubic foot of the substance. • 182. A block of marble, of which the sp. gr. is 2-4, weighs 5 cwt. ; find its volume, the weight of a cubic foot of water being 62-5 lbs. 315. The sp. gr. of a liquid may also be determined by the following method : — Take a piece of glass, or some other solid heavier than and insoluble in water, determine by the method described at par. 311 the weight of the volume of water at 60° F. the solid displaces ; let this weight be represented by w. Then determine by the same method the weight of the volume the solid displaces of the liquid whose sp. gr. we wish to find ; let this weight be represented by w'. Divide the loss of weight in the hquid by the loss of weight in water, the quotient will be the sp. gr. of the liquid. w' ' w ' The specific gravity of the liquid may also be found by multiplying the difference in weight of the solid in air and in the liquid by the specific gravity of the solid, and dividing the product by the absolute weight of the solid ; the result will be the specific gravity of the liquid. For the first of these quantities, namely the difference in weight of the solid in air and in the liquid, is the weight of the volume of the liquid, which is equal to the volume of the solid ; and the second of these quantities is the weight of a volume equal to the volume of the solid. Methods of determining Specific Gravities 135 \ ^ An Indirect Method for determining the Specific Gravity of Substances. 183. A solid whose weight in air is 60 grs. weighs 40 grs. in water and 30 grs. in sulphuric acid ; required the sp. gr. of the acid. 184. A glass ball, weighing 10 grs., loses 3'64 grs. in water, and 2 '88 grs. in alcohol. What is the sp. gr. of the alcohol ? 185. If a piece of metal weigh in air 300 grs. more than in water and 252 grs. more than in spirit, what is the sp. gr. of the spirit ? l85. A body weighs 252 grs. in air, 36 in water, and 63 in spirit ; what is the sp. gr. of the body and of the spftit ? 187. A piece of copper (sp. gr. 8-85) weighs 446-3 grs. in a liquid and 490 grs. out of it ; required the sp. gr. of the liquid. 188. A piece of gold (sp. gr. I9'36) weighs 140 grs. in a liquid and 1597 grs. in air ; what is the sp. gr. of the liquid ? 316. For commercial purposes the sp. gr. of liquids is determined by means of an instru- ment called the hydrometer ; this instrument is not so. accurate as the sp. gr. bottle, but it is preferable to it on account of its simplicity ar -' the rapidity with which the experiment can 1 made with it, and at the same time it is suf ciently accurate for all commercial purposes. 317. ' The hydrometer (fig. 51) in general u e consists of a floating vessel of thin metal glass, having a weight beneath to maintain it an upright position, and a stem above bearii a divided scale. The use of the instrument very simple. The liquid to be tried is put in the glass jar represented in the figure, and tl instrument floated in it. It is obvious th t the denser the liquid the higher will the hydr meter float, because a smaller displacement t fluid will counterbalance its weight. For tl same reason in a liquid of less density, it sin deeper. The hydrometer comes to rest almc t immediately, and then the mai-k on the ste may be read off. The graduation of the ste is very commorily arbitrary, two or three different scales being unfortunately in use. These May be - Fig. 51. sometimes reduced, however, to the true numbers expressing 136 Fundamental Principles of Chemistry the sp. gr. by the aid of tables of comparison drawn up for the purpose.' ' 318. The sp. gr. of a tnixture of two liquids can be found, if the sp. gr. of each of the liquids comprising the mixture be known, and if the proportions by volume in which the two liquids have been mixed together be known, and assuming that no alteration in volume occurs on mixing the two liquids : — Multiply the volume of each of the liquids by its sp. gr. ; add the two products together, the sum will be the weight of the mixture ; then add the volumes of the liquids together, and the sum will be the volume of the mixture \ then divide the weight of the mixture by its volume, and the quotient will be the specific gravity of the mixture. To express this process in an algebraic form, let s' represent the sp. gr. of one of the liquids and v' its volume, and let s" represent the sp. gr. of the other hquid and r/' its volume, and let 6' represent the sp. gr. of the mixture, Fits volume, and JFits weight, then — ^_ W _ v' s' + v' s" F v' + v" 319. In like manner, the sp. gr. of a mixture (whether of liquids or solids) can be found, if the sp. gr. of each of the two substances composing the mixture be known, and also the proportion by weight in which they are mixed, assuming as before that no contraction takes place ; for, find the volume of each of the two substances by dividing its weight by its sp. gr., add the two volumes thus found together, and tfie sum will be the volume of the mixture ; add also the weight of each of the two substances together, and the sum will be the weight of the mixture ; divide this weight by the volume as previously found, and the quotient will be the sp. gr. of the mixture. Thus, let w' represent the weight of one of the solids, and w" the weight of the other solid, then — w' + w"-=W, the weight of the mixture. — + -77-=7;-=V, the volume of the mixture. s' s a ' Fownes' Elements of Chemistry. Methods of determining Specific Gravities 137 Therefore, dividing the first of these expressions by the second, 7£/ , w^'= yithe specific gravity sought. ^ 7^ 320. To find the weight of each of two substances when com- bined in one mass. — The weight of each of two substances when combined in a mass, can be found, if the weight of the mixture be known, and also the specific gravity both of the mixture and of each of its components. Let S represent the specific gravity of the mixture and W its weight, and / and s" the specific gravity of the two components : then, (.r'-j")S the weight of one of the substances in the mixture ; and W — w'=w'', weight of the other substance. Exercises for finding the weight of each of two substances when combined in one mass. 189. If the specific gravities of gold and silver are I9"35, I0'5I re-: spectively, find the sp. gr. of a mixture consisting of seven parts by weight of gold, and six of silver. 190. An alloy of gold and silver weighs lo grs. in air, 9-37 grs. in water ; what are the proportions of gold and silver ? 191. An alloy of copper and silver weighs 37 grs. in the air, and loses 3 '66 grs. when weighed in water. What are the proportions of silver and copper ? The sp. gr. of copper = 8-85. 192. British standard gold contains 11 parts by weight of pure gold, and I part of copper ; required its sp. gr. 193. A mixed mass of gold and quartz (the sp. gr. of the quartz being 2 ■6) weighs 20 lbs. , its sp. gr. is 8 '5 ; how much gold does it contain ? 194. A fluid of sp. gr. 1'I2 is mixed with three times its bulk of another fluid having sp. gr. . of 1 7. Supposing the fluids do not act chemically on one another, and there is no contraction, what will be the sp. gr. of the mixture ? 321. We have now to describe the methods pursued in determining the sp. gr. of gases ; but before doing so we will gave a few easy experimental exercises which the student will find no difficulty in performing. Experimental Exercises. 195. Determine the sp. gr, of a sample of olive oil, by means of the sp. gr. bottle. 138 Fundamental Principles of Chemistry 196. Determine the sp. gr. of a sample of hydrochloric acid by means of the hydrometer. 197. Determine the sp. gr. of marble both in powder and in lump. 198. Determine the sp. gr. of bees'-wax. 322. The determination of the sp. gr. of gases is very simple in theory, but is an exceedingly delicate operation to perform. Air at 6c° F., and the barometer standing at 30 inches, is the English standard of comparison ; but the standard of temperature and pressure adopted on the Con- tinent and in England for scientific purposes, is 0° C. for the terhperature, and 760 millimetres for the pressure. 323. Before describing the operation itself, we will describe (i) How to find the weight of any gas or vapour, its sp. gr. being known. To accomplish this we have simply to multiply the weight of an equal volume of air by the specific weight of the gas or vapour ; the product will be the weight of the volume, at the standard temperature and pressure of the gas or vapour. Example : What is the weight of 100 cubic inches of hydrogen, its sp. gr. being -0694 ? 30-935 X •o694=;2'i47 grains weight of 100 cubic inches of H. (2) How to find the volume of a given weight of any gas or vapour. The weight of some volume (say a cubic inch) of the gas or vapour must first be ascertained by the preceding rule ; then the given weight must be divided by the weight of the cubic inch ; the quotient will be the volume in cubic inches of the given weight of the gas, at the standard temperature and pressure. Example : What is the volume of 2'i47 grains of hydrogen, its sp. gr. being o'o694 ? ^' =100 cubic inches. •02147 Exercises for finding the weight of a given volume of a gas or vapour from its specific gravity. 199. What is the weight of a cubic inch of oxygen, its sp. gr. being 1-1057 1. 200. What is the weight of a cubic inch of nitrogen, its sp. gr. being 0-9713? 201. What is the weight of a cubic inch of carbon dioxide, its sp. gr. being I -529 ? Buoyancy of the Am 139 202. What is the weight of a cubic inch of gaseous ammonia (NHJ, its sp. gr. being 0-59? 203. What is the volume of 54 grains of chlorine, its sp. gr. being 2-44? 204. What is the volume of 45 grains of carbon monoxide, its sp. gr. being 0-967 ? 324. It is necessary, in order that the student may fully understand Regnault's method for the determination of the density of gases, to direct his attention in the first instance to the buoyancy of the air. The general fact, that air, like liquids, buoys up all bodies immersed in it, may be illus- trated by means of the appa- ratus represented in fig. 52. It consists of a closed globe, suspended to one arm of a delicate balance, equipoised by a weight suspended to the other. The two are in equi- librium in the air, but only because the globe, being larger than the weight, is buoyed up by a greater force. If, now, the apparatus is placed upon the plate of an air-pump and covered with a glass bell, we shall find, on removing the air, that the globe will preponderate, as is shown in the figure. By re- rnoving the air we increase the apparent weight both of the globe and of the counterpoise by just the weight of the air displaced by each ; but as the globe is much the largest, we increase its weight more than that of the smaller brass counterpoise, and hence the result. If we allow the air to re-enter the bell, it will buoy up the globe, as before, so much more than the counterpoise as to restore the equilibrium. 325. An important consequence of the principle just illus- trated is evident. The balance does not give us the true rela- tive weight, W, of a body, but a slightly different weight de- pending on the weight of air displaced by the body, compared with the weight of air displaced by . the brass or platinun\ Fig. 52. 140 Fundamental Principles of Chemistry weights used in weighing. As the volume of these weights is generally less than that of the body, the weight indicated by the balance is almost always too small ; but when the volume of the weights is greater than that of the body, the weight in- dicated by the balance is too large. When the two volumes are equal, the balance will indicate the same weight in air as in a vacuum. It is easy to ascertain the correction which it is necessary to add or to subtract from the weight of a body in air in order to obtain its true weight.' 326. It must be remembered that the brass and platinum weights which are used in delicate determinations of weight are only standard when in a vacuum. Let us, then, represent the various values as follows : — W'=Weight of the body in air as estimated by standard weights ; and also the weight of the standard weights them- selves in a vacuum. V'= Volume of the standard weights in cubic centimetres. V=r Volume of the body in cubic centimetres, «/=Weight of one cubic centimetre of air at the time of the weighing. W=Weight of the body in a vacuum — which we wish to find. We can now easily deduce the following values : — V'w = Buoyancy of air on the weights. Vw = Buoyancy of air on the body. ' 'The weight of the displaced portion of air may be easily ascertained if the specific gravity of the body be known ; for, from the observed weight of the body, we can calculate directly the weight of an equal bulk of water, and -g-fYth of this weight will give the weight of a corresponding bulk of air at mean tem- perature and pressure. This weight must be added to that actually found ; at the same time, a similar and opposite correction will be required for the metallic weights used in the experiment, because they will also appear to be lighter than they really are ; and an amount of weight greater than the true one will be re- quired to effect the counterpoise. If, therefore, the weights have the same specific gravity as the body counterpoised, the two corrections will neutralise each other ; but if, as in weighing gases, there is a great difference between them, the correction will be one of importance. The true weight sought will be thus obtained : — Add to the weight of the body in air, the weight of the hulk of air which it has displaced, and deduct from this the weight of the bulk of air diS' placed by the weights employed.' — Miller. Weight of a Body in Am 141 W' — V'7« = Actual weight of standard weights in air. W — Yw = Actual weight of body in air. Since these weights just balanced each other, we have — W - Yw = W — Yhu ; W = W + a/ (V — V'). 327. The correction w (V— V') which must be made to the weight determined by a balance in air in order to obtain the weight in a vacuum, is evidently additive when the volume of the body is greater than that of the weights, and subtractive when these conditions are reversed. When the volumes are equal, the correction becomes o. 328. In all ordinary cases of weighing, the correction is so small that it may be neglected without sensible error ; but it becomes of the greatest importance in determining the weight of a gas. In such cases, we have to determine the weight of a large glass globe, when completely vacuous, and when filled with gas ; and it not unfrequently happens that the buoya;ncy of the air is greater than the weight of the gas itself, and it is always a considerable part of it. If the buoyancy of the air is the same when the globe is weighed in its vacuous condition and when filled with gas, it would not affect the weight of the gas, which would be obtained by subtracting the first weight from the last. But, unfortunately, the buoyancy is constantly changing ; and it is, therefore, necessary to determine the amount carefully at each weighing, and reduce the weights of the globe in the two conditions to what they would be if the experiments had been made in a vacuum. 329. When the temperature is 0° C, and the barometer stands at 760 mm. and when the air contains neither vapour of water nor carbon dioxide, w is equal to o'ooi293 grams. Were the atmosphere always in this condition, nothing would be easier than to calculate the actual weight of a body from the weight found by weighing in this normal atmosphere. But this is far from being the case ; for the temperature, the pressure, and the composition of the atmosphere are changing at eachmoment, and the value of w varies with all these atmospheric changes. 330. It is frequently possible to conduct the process of weighing in such a way that the correction for the buoyancy of the atmosphere, always somewhat uncertain, may be avoided. For example, in weighing a gas, instead of equipoising the glass 142 Fundamental Principles of Chemistry globe, when empty, by means of ordinary weights, we may equipoise it by means of a second globe, hermetically closed and having the same volume as the first, in the manner repre- sented in fig. 53. It is evident that in this case, whatever may be the buoyancy of the atmosphere, it will equally affect both globes, and we shall only have to consider the buoyancy of the air on the small weights necessary to restore the equilibrium after the globe is filled with the gas to be weighed ; but this is so small that it may always be neglected.' 331. The most accurate method of determining the specific gravity of a gas is due to Regnault ; it consists in determining with the apparatus, fig. 53, the weight of the given gas which a large balloon will contain at 0° C. and 760mm. and then dividing this weight by that of an equal volume of air pre- viously determined in the same way. The balloonin which the gas is weighed is counterpoised, not entirely by weights, but chiefly, as we have already stated, by another balloon of the same kind of glass and of the same bulk. To do this, it is necessary to de- termine the volume of air displaced by the balloon in which the gas is to be Fig. 53. weighed, and which we will call A. It is to be filled with water and then weighed in water of the same temperature. The apparent weight of the balloon in water is so small that this may be effected on the balance to be used for the densities. The balloon is now to be removed, and weighed, after wiping, but still filled with water, on a strong balance capable of indi- J Cooke's Chemical Physics. Densities of Gases 143 eating one decigramme. The difference in the two weighings is equal to the weight of water displaced by the external volume of the balloon. Another balloon, B, fig. 53, of nearly the same capacity as A, but, preferably, a little smaller than that of the first and its stopcock, and made of the same kind of glass, is taken, and has connected to it a brass mounting, terminating in a hook, to enable it to be suspended from the balance-pan. If the united weight of the water displaced by the balloon, B, and its mounting, is less by n grammes than the weight of the water displaced by the balloon A, we must attach to B a glass tube closed at each end, and having an exterior bulk = n cent. cub. of water,' 332. The engraving, fig. 53, shows the method of suspend- ing the balloons beneath the scale-pans of the ba- lance, in a chamber closed with glass doors to prevent currents of air. The ba- lance, although large, is of great delicacy; for when charged with one kilo- gramme in each pan, it permits, with certainty, an appreciation of half a milli- gramme. The balloons em- ployed have a capacity of about 10 htres. 333. The balloon A has a stopcock attached to it, which allows it to be connected either with a three-way tube communi- cating with the gas-holder, or with the air-pump. ■*!^! Fig. 54. The air having been removed as com- pletely as , possible, the gas is allowed to enter ; but, as a small amount of air still remains, the operation is to be re- peated twice. Previous to the third time of filling the globe, it is, after as complete exhaustion as possible, to be placed in 1 Because i cent. cub. of water weighs i gramme. 144 Fundamental Principles of Chemistry a case, a b, fig. 54, and covered with melting ice ; the cock being opened, the globe is allowed to fill with gas, and when full, a momentary communication is made with the atmo- sphere to equalise the pressure ; the cock, c, is closed, the globe removed, wiped with a damp cloth to prevent electrical excitation, which might cause serious errors in the weighing, and suspended on the balance. It is not weighed until two hours have elapsed, so as to permit the temperature to become the same as that of the balance-case, and thus obviate currents of air, and also that its surface may be covered with the normal amount of humidity. After careful weighing the balloon is placed anew in the case, a b, fig. 54, sur- rounded with ice, and the gas removed by the pump. 334. It is necessary now to ascertain both the atmospheric pressure and the elastic force of the gas remaining in the balloon. For this purpose, an instrument called a barometric manometer is made use of. It consists of two tubes, A B and C D, fig. 55, attached to a sup- port, which is secured perpendicularly to a wall. The tube, A B, is a barometer of 20 mm. interior diameter ; the metal in the tube having been carefully boiled, it is inverted in a cistern of dry mercury. This cistern is a box divided into two parts, the smaller of which serves for the cistern of the barometer. Into the second compartment is plunged the tube,' C D, which has the same diameter as A B. C D is capable, by means of a leaden tube, a b, of being placed m communication with the balloon. 335. When it is intended to ascertain the atmospheric pressure by means of this instru- ment, mercury is poured into the cistern until it rises above the level of the division, m n. The double-pointed screw V is then adjusted, until its lower end just touches the surface of the mercury. If now we measure. Fig. 55. Specific Gravity of Gases 145 by means of a catbetonaeter, the difference of level between the surface of the mercury in the barometer and the upper point of the screw, and add to this the length of the screw previously ascertained, we have the height of a column of mercury exactly balancing the atmospheric pressure. The tube, C D, of the manometric apparatus, is, as we have said, to be placed in com- munication with the air-pump and the balloon, by means of the three way tube and the leaden pipe a b. The gas having been removed, the cock communicating with the air-pump is closedi and the difference of level between the two columns of mercury in the tubes, A B and C D, is measured by a cathetometer. This difference is the measure of the elastic force of the gas remaining in the balloon. A thermometer, T, indicates the temperature at the time of the experiment. 336. The division, m n, in the cistern is necessary, in order to prevent air reaching the barometer, in consequence of the great oscillations in the level of the mercury, during experi- ments. The balloon, thus again exhausted, and having the elasticity of its residual gas known, is to be closed, removed, wiped, and weighed as before. 337. The difference, P— /, between the two weighings, repre- sents the weight of the gas, which at 0° C. = 32° F. fills the balloon under a pressure equal to the barometric pressure, H, observed at the moment of closing the cock, diminished by the elastic force, h, of the gas remaining in the balloon after making the exhaustion. The weight of the gas at 0° C, and under the normal pressure of 760 mm. (29'922 inches), is obtained by the formula '— /-r, ,\ 760 338. Bunsen's method. — The specific gravities of various gases are represented by the weights which equal volumes of these gases possess. As the volume occupied by a given weight of any gas is dependent upon the variations of the force of gravity accompanying change of geographical latitude, or eleva- tion above the sea's level, all gases, of which the absolute volumes are required, must be reduced to the same latitude and elevation above the sea, and to the same barometric pressure and temperature. 1 Greville Williams's Handbook of Chemical Manipulations. L 146 Fundamental Principles of Chemistry 339. According to the most accurate experiments, for which we are indebted to the classical labours of Regnault, one gramme of atmospheric air at the level of the sea, in the 45th degree of latitude, at 0° C., and under a pressure of 760 mm. of mercury, occupies a volume of 773"526 cubic centimetres In the latitude 52° 36' — as, for instance, in Berlin, — a gramme of dry air at 0° C, and under a pressure of 760 mm., occupies exactly 773 cubic centimetres. 340. The accuracy of gasometric determinations is seldom so great that the differences resulting from the variation of gravitation extend beyond the limits of the possible observa- FlG. 56. tional errors. Hence, excepting in normal determinations, where the greatest accuracy is required, the volume of one gramme of dry air at 0° C, and 760 mm. pressure of mercury, may be represented in our latitudes by 773 cubic centimetres ; and the specific gravity of a gas may be defined to be the weight in grammes of gas which, under the same conditions, occupies a space of 773 cubic centimetres. 341. In cases in which a normal determination is not required, a common light flask, g, fig. 56, is employed for measuring the volume of gas of which the specific gravity is t'o be estimated. 342. The volume of the flask should be about 200 or 300 cubic centimetres, and the neck, a, thickened before the gas blow-pipe, must be drawn out so as to have an aperture of the thickness of a straw, into which a glass stopper is ground air- Specific Gravity of Gases i/[y tight by means of emery and turpentine. Through this neck, which is furnished with an etched scale in millimetres, mercury is poured, by means of a funnel reaching to the bottom of the flask, until the whole is filled. As soon as this is accomplished, the flask is transferred, with its mouth downwards, into the mercury trough, AA, and gas is allowed to enter, until the level of mercury in the neck of the flask stands a few millimetres higher than that in the trough. In order to secure the absence of all gaseous impurities, this gas is evolved from as small a vessel as possible, and allowed to enter the flask through a narrow delivery tube, and in the moist state. The gas is dried in the flask itself by a smair piece of fused chloride of calcium, /;, which had previously been made to crystallise on the side of the flask by bringing it in contact with a single drop of water, and alternately heating and cooling the glass. This small piece of chloride of calcium serves also to free the mercury and the sides of the flask from its adhering moisture. In order to be able to close the flask at any time without warming it with the hand, the little lever, cf, is employed. On the lower end, 7^ of this lever the stopper is so fastened in a cork that it passes into the neck of the flask without closing it, and the lever is held in its right place by a wedge, d, pushed under the finger-plate, c. As soon as the apparatus has attained the constant temperature, /, at the barometric pressure, P, the volume, V, of the gas, and the height, /, of the column of mercury rising above the level of the metal in the trough, are observed with the cathetometer- telescope. If the observed volume of gas in cubic centi- metres, reduced from a table of capacity, be represented by V,, this volume, at 0° C, and 760 mm. pressure, becomes, in cubic centimetres, — ^ 760 (i-f 0-00366 t) 343. It is now only necessary to determine the weight, G^, of this volume, V^. This is obtained in the following manner :— The wedge, d, is taken away ; the flask is thereby closed, and by withdrawing the pin, e, it can then be removed, together with the lever, c f, from the trough. After having been most carefully freed from all adhering matters, and having attained L 2 148 FUXDAMENTAI. PRINCIPLES OF CHEMISTRY the temperature, /,. of the balance, by the pressure Z',, the flask can be weighed. Let G represent the weight in grammes thus found. The glass stopper is now removed, and replaced by a caoutchouc tube, con- nected with a drying tube. b, fig. 57. The apparatus thus arranged is placed under the receiver of an air-pump, and' the air so often withdrawn and ad- mitted until all the gas has been replaced by dry air. If this weight amounts to G, grammes, the weight, G2, of the volume of gas, Vj, measured in the flask, is equal to — Fit;. 57- G2 = G-Gi + 773 X 760 X (i -f 0-00366 /,) 344. From this value, Gj, the specific gravity is obtained by the help of the following formula : — ^ G, S=773 V, Exercises for Calculating by Exact Methods the Weight and Specific Gravity of Gases. 205. Calculate the weight of one litre of dry air at 0° C. and 760 mm. from the following determination by Regnault : — Globe full of air, atid surrounded by ice. Height of barometer at the time of closing the stopcock 76i'i9mm. Weight added to globe to equipoise it in balance. I -487 gram. Globe exhausted of air, and surrounded by ice. Tension of air remaining in globe, as indicated by the manometer at the moment of closing the stopcock 843 mm. \\'eight required for equipoise .... I4'I4I gram. ' The unequal specific gravity of the glass and mercury on the one hand, and the metal weights on the other, is not considered in this calculation , as the inaccuracy thus introduced is inconsiderable, in comparison with the observational errors. ' From Bunsen's Gasometry, translated by .Sir H. Roscoe. Specific Gravity of Gases 149 206. Calculate the weight of one litre of hydrogen at o° C. and 760 mm. from the following determinations of Regnault : — Globe fall of gas, and sttrrounded by ice. Height of barometer at the time of closing the stopcock 756'i6 mm. Weight added to globe to equipoise it in balance. 13 '301 gram. Globe exhausted of gas, and surrounded by ice. Tension of gas remaining in globe, as indicated by the manometer at the moment of closing the stopcock ...... 3-40 mm. Weight required for equipoise .... I4'I785 gr. 207. Calculate the weight of one litre of carbon dioxide at 0° C. and 760 mm. from the following determinations by Regnault ; — Globe full of gas, and surrounded by ice. Height of barometer at the time of closing the stopcock ....... 763 '04 mm. Weight added to globe to equipoise it in balance. 0'6335 gr. Globe exhausted of gas, and sttrrounded by ice. Tension of gas remaining in globe, as indicated by the manometer at the moment of closing the stopcock . . . . . • i '57 nim. Weight required for equipoise .... 20'2li gram. 208. The following observations were made in determining the vapour density of gaseous bromide of methyl by Bunsen's method. From these data calculate the specific gravity of the gas. Volume of gas ...... 42'i9 c.c. Temperature of room . . . . . i6'8"C. Height of barometer. ..... 746 -4 mm. Height of the column of mercury above that in the trough . . . . . . .24-3 mm. Weight of flask and gas 7 -9465 gram. Weight of flask and air 7 '8397 ,, Temperature in balance-case . . . . 6-2" C. Height of barometer at the time of weighing . 742-1 mm. 209. The following observations were made in determining the density of a gaseous mixture by Bunsen's method. Calculate the density from these data. Volume of gas ..... . 211-23 c.c. Temperature of room .... . 6-2" C. Height of barometer .... . 760-9 mm. Height of the column of mercury above that in trough 19-4 m m. Weight of flask and gas . • 54 '62 1 3 gram Weight of flask and air . • 54-4838 ,. Temperature in balance-case . • 7-9° C. Height of barometer at the time of weighing . 760-9 mm. ISO Fundamental Principles of Chemistry 210. The following observations were made in determining the density of a gas by Bunsen's method. Calculate from these data the density of the gas. Volume of gas ...... 2I0'2 c.c. Temperature of room ..... 197° C. Height of barometer . . . . . 748 'o mm. Height of the column of mercury above that in the trough ....... 17 -2 mm. Weight of flask filled with gas .... S3'59i gram. Weight of flask filled with air .... 53-5775 >> Temperature in balance-case .... 20 '5° C. Height of barometer at the time of weighing . 748 mm. Examination Questions. 211. What is meant by specific weight ? 212. Explain why a body weighs more in air than in water. 213. Explain precisely what is meant when it is said that gold is heavier than iron. 214. Explain the use of a table of specific gravities in calculating the weight of assigned volumes of the various kinds of substances ; state the principles of the calculation. 215. Explain the method of determining the specific gravity — 1. Of a solid heavier than water ; in a state of powder, and also in the mass. 2. Of a solid lighter than water. 3. Of a solid soluble in water. And state the precautions required to .obtain accurate results. 216. Heiro, a king of Syracuse, gave a goldsmith a certain weight of gold to make into a crown. When the king received the crown, he found it weighed exactly the same weight as the gold which he had given to the goldsmith ; but he suspected that part of the gold had been replaced by an inferior metal ; Archimedes discovered this to be the case, and he iiscertained the exact amount of the inferior metal in the crown ; state how he could ascertain the amount. 345. Sp. gr. of vapours. — AVe shall limit our description to the means for determining the density or sp. gr. of vapours to the method invented by Victor and Carl Meyer ; the two oldest methods Dumas' and Gay Lussac's are now no longer employed ; and we refer those of our readers who wish to become acquainted with Hofmann's method to vol. iii. of Roscoe and Schorlemmer's Treatise on Chemistry. 346. V. and C. Meyer's process is suitable for very wide ranges of temperature : it has also the merit of requiring very little substance ; it takes but little time, and does not require either the exact temperature of the bath or the volume of the vapour flask to be known. The only observation which is Specific Gravity op Vapours 151 required is the volume of the vapour in the form of its equal volume of air, measured at the temperature of the air. 347- The apparatus is shown in fig. 58. It consists of the boiling-flask c, in which is placed the cylindrical glass vessel b, having a capacity of about 100 c.c, with a height of 200 mm. to which is fused a tube 600 mm. long, and 6mm. diameter, and terminating above in a thimble-shaped en- largement, which is closed by a caoutchouc stopper, d. A lateral tube, a, of not more than I mm. internal diameter, and 140 mm. long, is so bent as to carry the air expelled by the vapour into the graduated tube, e, which stands in the water contained in the pneumatic trough,/ Before com- mencing the operation, a little recently ignited asbestos is placed at the bottom of b, to prevent its fracture when the tube con- taining the substance to be operated upon is dropped in. In the bulb of the flask c is placed the fluid or substance by the vapour of which the vessel b is to be heated.' The experiment is commenced by heating, by means of the vapour in the flask c, the vessel b, containing as yet only the asbestos, the tube being closed by the stopper d; and the gas delivery tube must dip into the water in the trough, but must not yet be placed beneath the graduated tube. -As soon as the temperature becomes constant, and when, therefore, no further evolution of air is observed, the stopper d is quickly removed, and a weighed quantity of the substance (such in amount that its vapour does'not occupy more than half the volume of the vessel b) is introduced into that vessel, and the cork quickly replaced ; in the act of replacing it a few bubbles of 1 If it be necessary to work at a temperature above 310° C. the heating tube is replaced by a bath of mohen lead. Fig. s8. 152 Fundamental Principles of Chemistry ail will escape by the lateral tube a ; they must not, however, be allowed to enter the graduated tube e ; after they have escaped, the delivery tube must be placed beneath the graduated one, which has been previously filled with water. The substance at once evaporates, and in fifteen seconds displaces its own volume of air, which collects in the tube e. As soon as no further bubbles of air are emitted, the operation is finished, and the caoutchouc stopper is instantly removed, to prevent the water in /from rushing back into the tube d. The lower extremity of the graduated tube is then to be closed with the thumb and transferred into a cylinder of cold water. When a sufficient time has elapsed for the air in the tube to attain the same temperature as the water, the water inside and outside the tube are brought to the same level ; the temperature of the water and the height of the barometer are then accurately taken, and the volume of air in the tube is instantly read off. ' These ob- servations yield sufficient data for the calculation : — S^weight of substance. ;'=temperature of the water. B=barometric pressure reduced to o°. 7«'=tension of vapour of water. V:=volume of air. ' The vapour density is calculated by the formula : S X 760 (1+0-003665/) (B — z&)Vxoooi293 or by collecting the constants : S(i +0-003665/) X 587780 ,1 (B-W)V ■ Example : 1008 grammes of the vapour of a substance taken at a temperature of 16 -5° C, when the barometer stands at 707-5 mm., occupy 22 cc. ; calculate its vapour density. The barometric pressure of 707-5 mm. at 16-5" C. is equi- valent to 705-503 mm. at 0° C. This correction is made from tables constructed for the purpose.^ ' The student will seethat the number 587,780 is obtained by dividing 760 by -001293. 2 Owing to the expansion of the mercury and glass tube, which has already been explained, the same pressure will be indicated by different readings on the Specific Gravity of Vapouss 153 We find from the table that the vapour density of water at 16-5° C. is 13-964 mm. We have therefore the following data : S:= "looS t= 16-5 3 = 705-503 V= 22 W=: 13-964 substituting these values in the above formula, we obtain for the density required : • 1008 X 760 X (i + -003665 X i6-5 )_ 1008 X 760 X 1-06042 (7°S'5°3—i3'964) X 22 X -001293 691-539x22 x -001293 = 4-i3- Exercises for finding the Density of a Vapour by Meyer's Process. 217. From the following data determine the vapour density of the organic substance operated on : 5 = 0-0855 grammes, /=l6°C., 6=717-8 mm., w = 22 cc. Barometric correction from Bunsen's tables, 1-971. 218. From the following data determine the vapour density of the organic substance operated on : S = 0-0905 grammes, ^= 17° C, 6 = 714-8 mm., z;= 13-6 cc. Barometric correction 2-08. Examination Questions. 219. Would a lump of cork and a lump of lead, which each weigh I lb. in the air, have an equal weight in vacuo ? 220. If the mercurial barometer stands at 29 inches, and the density of the mercury compared with that of water be 13-57, find what would be the height of a water-.barometer. 221. Define exactly what is meant by the specific gravity of a body, and what by its density, and state precisely what is the difference between them. 222. A substance, of which the sp. gr. is 6, weighs 180 grs. in air, and 155 grs. in a liquid ; calculate the sp. gr. of this liquid. 223. A Prussian dollar, made of an alloy of silver and copper, has the sp. gr. 10-05. Determine the amount of silver and copper in it, thesp. gr. of silver being 10-5, that of copper 8-7. 224. What does a barometer measure ? At the bottom of a mine a mercurial barometer stands at 77 -4 centimetres ; what would be the height of an oil barometer at the same place, the sp. gr. of mercury being 13-596, and that of oil 09 ? 225. Describe the process of determining the sp. gr. of a liquid by scale at different temperatures. Hence they are always reduced to the reading at zero temperature. To avoid the trouble of calculating, tables have been constructed so that the correction can be immediately ascertained. In the example and exercises the corrections are given. 1 54 Fundamental Principles of Chemistry weighing a solid in it. A piece of glass rod weighs 35 gram, in air, and 21 gram, in water. ^Vhat is its weight in alcohol of sp. gr. 0-9 ? 226. Why, in fixing the boiling-point of a mercurial thermometer, must the thermometer not dip into the liquid ? 227. Explain why a body weighs less in water than in air. If a piece of metal weigh hi vacuo 300 grs. more than in water, and 252- grs. more than in spirit, what is the sp. gr. of the spirit ? 228. Two similar vessels are filled, one with water and the other with mercury, and are placed over two precisely similar lamps : which would you expect to boil first, and why ? 229. Assuming the sp. gr. of mercury to be 13 '6, and the mercurial barometer to stand at 29 inches, at what height would an oil barometer stand, the sp. gr. of the oil being 0-845 ' 230. Why is it easier to raise a bucket filled with water from a well whilst it is in the water, than when it is in the air ? 231. On the launching of our ironclads, certain facts with regard to them are generally given in the newspapers at the time ; for instance, at the time the author was writing this part of the book, the twin-screw armour-plated battle-ship ' Sans Pareil ' was launched ; it was stated in the newspapers : ' Length, 340 ft. ; breadth, 70 ft. ; depth, 37 ft. 6 in. ; displacement in tons, 10,470.' What is meant by displacement? 232. How would you find the sp. gr. of a piece of sugar ? 233. If the sp. gr. of iron be 7 -2, what would a cubic foot weigh ? And how much less would the cubic foot weigh if it were immersed in water ? CHAPTER VI. SUBLIMATION — EXPERIMENTS — SIMPLE SOLUTION— EXPERIMENTS — CRYSTALLISATION — EXPERIMENTS — QUESTIONS — CHEMICAL SOLU - TION — EXPERIMENTS — PRECIPITATION. 348. In the conversion of a solid into vapour, if on the condensation of the vapour, it assumes the solid state, the operation is called, as has been already stated, sublimation. The apparatus used for subliming substances is generally extremely simple, and is less various than that employed in distillation. 349. We will now give a few practical exercises on the sub- liming of substances. Exercises on Sublimation. 234. The apparatus to be employed consists of an evaporating basin, having a beaker inverted over it ; the two vessels are joined with paper pasted round ; by this arrangement the student will be able to see the subliming as it goes on. The dish ought to be seated in a small sand bath, which is heated by a gas lamp. Dissolving op Solids in Liquids 155 235. Place some iodine in the dish, then join a beaker with it as fle- scribed, and seat the dish in the sand-bath. 236. Perform the same experiment substituting indigo for the iodine. 237. Perform the same experiment substituting mercury biniodide for the iodine. 238. Perform the same experiment substituting naphthaline for the iodine. 350. Many solid bodies, when placed in contact with a liquid, disappear by dissolving \n the liquid. Example : A lump of sugar placed in water dissolves. The solid is said to be soluble in the liquid in which it dissolves, insoluble in that in which it does not dissolve. Ex. : Sugar is soluble in water but insoluble in cold absolute alcohol. The liquid in which the solid dissolves is called the solvent or menstruum. The more minutely any substance is powdered, the more its solution is facilitated. Solid substances are generally reduced to powder in mortars. 351. Solutions are of two kinds, simple and chemical. A simple or mechanical solution is the mere dissolving of a solid in a liquid, no chemical change occurring in either ; on the removal, therefore, of the liquid by evaporation, the solid is obtained in its original condition. Common salt dissolved in water affords an illustration of a simple solution. In a chemical solution, the solid- and fluid combine together, forming an entirely new substance, from which the original solid and fluid can no longer be extracted by mere mechanical operations. Chalk dissolved in hydrochloric acid affords an example of a chemical solution. 352. The solvent, in a simple solution, cannot dissolve un- limited quantities of the substance to be dissolved ; it can only dissolve certain fixed quantities of the solid, the amount vary- ing with the kind of solid, and the amount of any particular solid varying with the solvent. When the solution contains as great a quantity of the solid matter as it is capable of dissolving, it is said to be saturated. A solution is known to be saturated when fresh solid matter of the same sort, on being put into it, remains undissolved. But as fluids dissolve generally larger quantities of a sub- stance, the higher their temperature, the term saturated, as ap- plied to simple solutions, is only relative, and refers invariably to a certain temperature. From the tendency of heat to 1 56 Fundamental Principles of Churiistry diminish the force of cohesion, it naturally results that the solubility of most bodies is increased by heat ; thus, 100 parts of water, at 60° F., dissolve 11 of potassium sulphate, and at 212 dissolve 25. At 60° F., 32 parts of dry magnesium sulphate are dissolved by roc of water, but 74 at 212"^. This, however, is not always the case ; some bodies, as common salt, are equally soluble in water at all temperatures, whilst in other cases the solubility is greater at particular tempera- lures than either above or below them. Of this peculiarity, sodium sulphate and nitrate are examples. Thus, 100 parts of water dissolve of dry sodium sulphate, at 32°, 5'02 ; at 52", io'22 ; at 76°, 28 ; at 93°, 53 ; at 122", 47 ; and at 212°, 42 ; the solubility increasing up to 93, and from thence diminish- ing. 100 parts of water dissolve of sodium nitrate, at 21°, 63 j at 32", 80; at 50", 23 ; at 60°, 55 ; and at 246°, 218 parts. Here the peculiarity is of the opposite kind to what occurs with sodium sulphate ; the solubility diminishing up to 50, and from thence progressively increasing. The liquids employed as solvents in simple solutions are water, alcohol, ether, oils, &c. The most importantsolventis water ; the others are only resorted to when the substance to be dissolved is insoluble in that liquid. 353. Some substances are rendered more soluble in water if the water contains in solution some particular substance ; thus lime is much more soluble in solutions of sugar than in pure water. 354. When a substance dissolves in more than one solvent, as iodine in water, alcohol, carbon disulphide, &c., it does not dissolve in the same quantities in e^z^a/ volumes of the different solvents. When a substance dissolves only in small quantity in a solvent it is said to be sparingly soluble in that liquid ; i part of iodine, for example, requires 7,000 parts of water to dis- solve it at ordinary temperatures. In some cases one solvent will remove a substance from its solution in another solvent in which it is less readily soluble. For this to take place the two liquids must be incapable of mixing together ; see Expt. 246. In some cases a portion of the substance dissolved in a liquid is precipitated from that solvent, on the addition of another liquid in which it is less soluble ; for this to occur the two liquids must mix together ; Expt. 247 illustrates this fact. In Simple Solutions 157 some cases the solution of the same substance in different solvents is not of the same colour ; the solution of iodine in water, in alcohol, and in carbon disulphide (Expts. 242, 243, and 244) are striking examples of this. 355- The process of solution is conducted either in evapo- rating dishes, flasks, or test-tubes. The latter are generally employed when the quantity of the solid operated upon is small. Exercises on Simple or Mechanical Solutions. 239. Make a saturated solution of potassium nitrate (saltpetre) in cold water, by triturating (rubbing) in a mortar an excess, say l,ooo grains, of this powdered salt, vi'ith 2,000 grains of water ; after the liquid has become saturated, pour 1,000 grains of the clear solution into a flask ; heat the solution in the flask until it boils, but in such a way that the temperature of the solution increases slowly ; add from time to tiime (that is to say, as fast as the salt dissolves) weighed quantities (twenty grains at a time) of the nitrate, until the solutionis saturated at the boiling-point. 240. Make a saturated solution of potassium chlorate in cold water, in the way previously described, employing 400 grains of the salt'for 2,000 of the water. Take 1,000 grains of the clear saturated solution, and apply heat until it boils, in the way previously described, adding during the time the solution is being heated, weighed quantities of the salt, twenty grains at a time, until the solution is saturated at the boiling-point. 241. Make a saturated solution of common salt (sodium chloride) in cold vfater; emjiloy 1,000 grains of salt for every 2,000 grains of water. Take 1,000 grains of the clear saturated solution, and heat it until it boils, adding during the time the solution is being heated ten grains of the salt ; this ought not to dissolve, as common salt isalmost equally soluble at all temperatures. 242. Add a little iodine to about half a pint of cold water and shake them well together. 243. Add iodine to about an ounce of alcohol as long as it continues to dissolve. 244. Add a very liitle iodine to about an ounce of carbon disulphide. ' 245. Observe the different colours of these three solutions of iodine. 246. Add to the aqueous solution of iodine obtained in Experiment 242, a little carbon disulphide, and shake the two liquids together, and then allow the liquid to stand ; the carbon disulphide will fall to the bottom, and it will be readily apparent that it has removed all the iodine from its solution in water. 247. Add some water to the alcoholic solution of iodine obtained in Experiment 244 ; sorne of the iodine will be precipitated from the solution in the form of a brown powder. 248. Make a saturated solution of lime in cold water ; employ five grains of quicklime for 2,000 grains of water. Take 1,000 grains of the clear saturated solution and boil it, which will cause the liquid to become turbid, as lime is less soluble in hot than cold water. ■ ^ By dissolving a large quantity of iodine in carbon disulphide, a solution is obtained which is perfectly opaque to rays of light, though it allows heat rays to pasS' freely. iS8 Fundamental Principles of Chemistry 356. When a saturated solution of a substance, which is more soluble in a hot than a cold liquid, is made at the boil- ing-point, the proportion which has been dissolved by reason of the temperature separates from the solution when it becomes cold. Thus, if 151 parts of magnesium sulphate be dissolved in 100 parts of boiling water, and allowed to cool to 60", a quantity of the salt in a crystalline form will be obtained, weighing 86 parts, for at 60° the 100 of water can only dissolve 65 parts of the salt, and the difference between that and the 151, which had been dissolved by the boiling water, must separate from the solution in the solid state. If the body be like common salt, equally soluble in water at all temperatures, the above process cannot be applied, and a quantity of the liquid must be evaporated, an operation now to be explained. 357. Evaporation is an operation which has frequently to be performed for the purpose of obtaining a more concentrated solution of the dissolved body ; this is effected by volatilising a portion of the solvent. Thus, if we have a weak solution of magnesium sulphate, and we required it in a more con- centrated state, we should evaporate so much of the water as would render the solution of the necessary degree of con- centration. 358. Evaporation is also had recourse to for the purpose of obtaining a solid back from its solution ; this is effected of course by vaporising the solvent. Thus, if we desired to obtain sodium chloride from a solution of this salt in water, we should evaporate the water, and thus obtain the salt in the solid state. If the evaporation be conducted slowly, the solid matter will frequently, on being deposited, assume a crystalline form. The operation is then termed crystallisation. 359- When a liquid evaporates at common temperature, it is said to undergo spontaneous evaporation. 360. We can frequently separate two or more solid bodies from one another by taking advantage of the different degrees of solubility which different substances possess. Example : Commercial potassium nitrate (saltpetre) always contains variable quantities of potassium chloride and sodium chloride, and from these substances it must be entirely free when used in the manufacture of gunpowder. Now, 100 parts Simple Solutions 159 of water at 70° F. dissolve the same quantity (35 parts) of each of these salts ;' but 100 parts of water at 212° F. dissolve 240 parts of potassium nitrate, 35 parts of sodium chloride, and 55 of potassium chloride. Suppose we had some saltpetre containing, for every 240 parts of that salt, 30 parts of sodium chloride, and the like quantity of potassium chloride; if we were to dissolve it in the proportion of 300 parts of the salt to 100 of boiling water, and let this solution become cold, about 200 parts of the potassium nitrate would crystallise out, whilst the whole amount of the other two salts wpuld remain in solution. These 200 parts of potassium nitrate would be perfectly pure, with the exception of the small quantity of mother-liquor,' with which they would be moistened ; to free the crystals from this impurity they may be washed with a small quantity of cold water, or better with a saturated solution of pure potassium nitrate.'^ If the mother-liquor, which would contain nearly equal quantities of each of the three salts, were evaporated at 212°, 84 parts of water out of eyery 100 could be evaporated, without any of the potassium nitrate being de- posited, whereas the expulsion of so much water would cause 25 parts of sodium chloride, and 22 of potassium chloride, to separate. If the clear solution (that is, free from the chlorides which have crystallised out), when it has reached this degree of concentration, were drawn off into another vessel and allowed to cool, a further crop of crystals of potassium nitrate, nearly pure, would be obtained ; they might easily be rendered perfectly pure by washing them in the way just stated. Exercises on Crystallisation. 249. Allow the boiling saturated solutions obtained in Experiments 239, 240, to become cold ; as these solutions cool, the salt they contain will begin to crystallise out, and when ' the solutions have become quite cold all the salt dissolved by warming the solution will in both cases crystal- lise out. 250. Dissolve some cupric nitrate in water, then evaporate the solution until it reaches the crystallising point, then place it aside to cool ; when it has ceased to deposit crystals, pour the liquid from them, and then dry them between blotting-|)aper, and afterwards place them in a bottle. Evaporate the solution again, and so obtain a further crop of crystals. 1 The liquor from which the crystals have separated. 2 After water has been saturated with one substance, although it cannot dissolve a further quantity of that one, it can still dissolve other substances. i6o Fundamental Principles of Chemistry To ascertain whert a solution has reached the crystaUising point, that is to say, when a hot solution has reached such a degree of concentra- don that it will deposit crystals when cold, transfer a drop of it by a rod upon a cold glass plate, and observe whether it deposits crystals as it cools ; if it does, then the evaporation must be discontinued, but if not, it must go on until such a result is obtained. 251. ' Let equal parts of potassium nitrate and sodium sulphate be mixed and dissolved in five parts of water, and the solution divided be- tween two similar dishes ; on a crystal of potassium nitrate being laid in one dish, and a crystal of sodium sulphate being laid in the other, a crystallisation of pure potassium nitrate will occur in the former, whilst nothing but sodium sulphate will crystallise in the latter dish. ' A little crystal of the same kind of salt which it is intended to crystalline, is often introduced into the solution about to crystallise, in order to serve as a nucleus round which the new crystals may gather ; and in a solution con- taining many salts, the nature of the salt which shall crystallise may be determined by the nature of the little crystal introduced. Examination Questions. 252. If powdered chalk is added to water, and the mixture is shaken, the liquid will appear milky ; whereas if common salt is added to water, it will disappear, and the liquid will be as clear and bright as it was before the salt was added. How do you account for the difference in these two cases ? 253. I boil the solution of a substance ; on being boiled it becomes turbid ; how do you account for the turbidity ? 254. How would you prove that a liquid contained any solid substance dissolved in it ? 255. I add some solid substance to a liquid ; on the first addition of the solid it dissolves, on the after-additions it ceases to dissolve, but on boiling the mixture the solid all dissolves ; how do you account for this ? 361. The Student must pass over the rest of this chapter for the present ; he will be directed when to return to it. 362. A chemical solution may be accelerated by elevation of temperature, and this is indeed usually the case, since heat generally promotes the chemical action of bodies upon each other. But the quantity of the dissolved body remains always the same in proportion to a given quantity of the solvent, whatever may be the difference of temperature — the combining proportions of substances being invariable, and altogether independent of the gradations of temperature. The liquids which produce chemical solutions are, in most cases, either acids or alkalies. Exercises on Chemical Solution. 256. Dissolve some chalk in dilute (one part of strong acid to two of water) hydrochloric acid. Precipitation i6i 257. Dissolve some magnesia in dilute hydrochloric acid. 258. Dissolve some iron filings in dilute sulphuric acid, one part of strong acid and three of water. 259. Mix equal parts of common salt, calcium carbonate (chalk), and sand together. The first is soluble in water, the second is insoluble in water, but soluble in hydrochloric acid ; the last is insoluble both in water and acids. Take a few grains of the mixture, and separate the three -substances from each other by dissolving out the salt by means of water, — then the chalk, by means of dilute hydrochloric acid, so that finally no other substance but the sand remains undissolved. ' 363. When a substance in solution is added to another in solution, and a substance is formed by the union of one or more of the constituents of the two substances, which is insoluble in the liquid in which the two substances were dissolved, the operation is called precipitation, the insoluble substance is called th.& precipitate, and the substance which is added to the other substance is called the reagent or precipitant. The pre- cipitate generally falls to the bottom of the liquid, with different degrees of readiness, owing to its being specifically heavier than the liquid ; but in some cases, owing to its being specifically lighter than the liquid, it floats on the surface of the liquid ; in each case, however, it is called the precipitate. 364. Precipitates are classified, according to their appear- ances, into crystalline, pulverulent, flocculent, curdy, and gelatinous. The terms turbid and turbidity are applied when the precipitate is so small that it cannot be distinguished, except by impairing the transparency of the fluid. 365. Precipitation is an operation which is constantly practised in the preparation of substances in the chemical manufactory as well as in the laboratory. We also resort to it in the laboratory, for the purpose of detecting and separating substances from one another. Thus, if we had a solution which might contain some compound of baryta and lime, — to ascertain whether baryta was present, and if it was, to separate it from the solution, before ascertaining whether lime was likewise present, we might add a soluble chromate ; if baryta was present, the chromic acid would combine with it, and as barium chromate is insoluble in water, it would precipitate, whilst cal- cium chromate, being soluble, would remain in solution. If we ^ The student, when he has completed the study of this chapter, must pass on to par. 478, Chap. XI. , and complete the study of that chapter. M 1 62 Fundamental Prisciples of Chemistry were now to add to the clear filtered solution some soluble oxalate — calcium oxalate, being insoluble in water, would precipi- tate. If the chromate produced no precipitate, there could be no baryta ; if the oxalate produced no precipitate after having separated the baryta, if present, lime must be absent. 366. The separation of '^"^' ^'' precipitates from the liquid is, with a few exceptions, much assisted by the application of heat and agitation. The operation is conducted in test-tubes, if used as an analytical process ; at the lecture table it must be performed in flasks, if heat has to be applied ; if not, in vessels of the description illustrated in fig. 59. 367. The student has already been made acquainted with filtration ; and that by the aid of filtration we can separate a substance insoluble in a liquid from other substances that are soluble in the hquid ; but the mere filtration does not com- pletely separate a precipitate from the soluble substances, inasmuch as it remains moist- ened with .the liquid in which they are dissolved ; in most chemical operations it has to be completely freed from these substances ; this is effected by washing the precipitate with distilled water. It is usually washed by means of a wash- bottle ; the usual arrangement of the bottle is that shown in fig. 60, but there are other forms of it ; one we have given (fig. 30, par. 188) ; the one shown here consists, as seen by the figure, of a flask in which are fitted, by means of a perforated cork, two bent tubes; the operator blows Fic. 60. Adhesion 163 through the blow-tube a ; this forces a fine strong jet of water through the other, b, which is directed on the precipitate. If hot water can be used the precipitate is sooner washed free from the extraneous matter than if cold water were used ; sometimes other liquids, as alcohol, ether, &c., have to be used in place of water. CHAPTER VII. ADHESION — CAPILLARY ACTION— EXPERIMENTS — ADHESIVE ACTION OF CHARCOAL — EXPERIMENTS — DYEING — EXPERIMENTS — QUESTIONS. 368. The cohesive force we have considered ; we have now to become acquainted with a series of phenomena, which are considered to be due to another molecular force, viz. that of adhesion. 369. This force may be, and most probably is, merely a modification of the cohesive force ; and as the phenomena produced by the operation of these two forces are so similar in some cases, scientific authorities differ as to which of the two forces the adhering is due ; this difference of opinion arises in the case of the adhering of pieces of the same substance, as the adhering of two pieces of lead or two pieces of glass ; some authorities consider the action due to the cohesive force, other authorities consider it due to the adhesive force. 370. Whatever difference of opinion there may be as to which of these two forces is to be attributed the adhering of pieces of the sa7ne substance, there is no difference of opinion as to the adhering of unlike substances, as, for example, the writing with chalk, charcoal, plumbago, &c. The adherence of unlike substances is always attributed to the adhesive force. 371. The principal cause of the resistance to motion which is termed friction is due to the adhesive attraction exerted between solids. The action of cements is due to adhesion : and that adhesion is exerted between different kinds of matter with varying degrees of force is seen in the variety of cements required for the variety of materials that have to be united ; glue, for example, will join pieces of wood together, but is valueless for joining stone or brickwork together. 164 Fundamental Principles of Chemistry 372. The action of the adhesive force is not confined to solids, but is exerted, as will be shown, between solids and liquids, solids and gases, between liquids, and the adhesion of gases to liquids. 373. When a piece of glass or wood is dipped into water or oil, the solid when withdrawn comes out wetted, owing to the adhesive attraction between the solid and the liquid ; but if the solid is dipped into mercury on its withdrawal no mercury will be adhering to it, owing to the cohesive force in this case exceeding the adhesive one. The simple solution of solids in liquids is due to the adhesive force ; in these cases the adhesion overcomes the cohesion existing between the particles of the solid ; hence, by weakening the cohesion between the particles of a solid, by powdering it or other means, its solution is hastened. 374. From the facts just stated we learn that a solid body is moistened by a liquid if the cohesion of the liquid is less than the adhesion betweeti it and the solid ; but if the cohesion is greater than the adhesion, the solid will not be moistened by the liquid. 375. The adhesion of some, and the non-adhesion of other liquids to solids give rise to some important effects due to capillary attraction, so called because they are best seen and studied in tubes the bore of which is not greater than the diameter of a hair ; the Latin word for hair being capillus. 376. The surface of a liquid in equilibrium is a horizontal plane, but in contact with solids capillarity causes it to be more or less curved ; being concave if the liquid adheres to (wets) the solid, convex if it does not. Fig. 61 repre- sents two glass tubes of different diameters inserted in a liquid which wets the sides of ^ , the glass. By the aid of the figure we learn Fig. 61. . , ° two facts : ist, that the liquid is curved, and that the curve is concave, which is called the concave meniscus ; 2nd, that the liquid stands higher in the narrower tube. Fig. 62 represents the insertion of two glass tubes of differ- ent diameters in mercury ; the glass is not moistened by the Capillary Action 165 liquid metal ; the mercury, in consequence of the non-adhesion, is depressed at the sides of the glass, and below the level of the exterior mercury, and the curve is convex, which is called the convex meniscus; and the depression, it will be observed, is the greater in the narrower tube. 377. The following law of diameters has been arrived at — Capillary elevations and de- ^^°' ^^" pressions, when all other circumstances are the same, are in- versely proportional to the diameters of the tubes. 378. The elevation of the column of liquid in tubes of equal diameter varies with the nature of the liquid, the variation depending partly on the difference of cohesion between the particles of the liquid, partly upon the difference of adhesion between the liquid and the glass. In consequence of the decrease of both these forces by heat, the height of the column diminishes as the temperature rises. Experiments on Capillary Attraction and Depression. 260. Insert several glass tubes open at both ends, and of different bores, in a vessel of water ; and observe whether the height at which the water stands and its curvature corresponds with what has been stated in the text. 261. Insert tubes of similar sized bores in alcohol and note the results. 262. Insert tubes of similar sized bores in mercury and note the different effects. 379- Both the elevation, and the depression of liquids in tubes above and below that of the liquids surrounding the tubes, appears at first sight to be opposed to the law of gravita- tion ; but these facts are really no contravention of that force ; as we have learned that, although the molecules of gases repel each other, the atmosphere, nevertheless, cannot indefinitely expand ; it ceases to expand when its elastic force and the attraction of gravitation are balanced ; in like manner, the adhesion between a liquid and a solid causes the liquid to ascend in a tube to a height above the liquid surrounding the tube, and were the adhesive force unrestrained the liquid might ascend in the tube to any height ; but the height is limited by the action of gravity, the pressure of the atmosphere, and the 1 66 Fundamental Principles of Chemistry cohesion existing between the particles of the liquid. The influence that the pressure of the air exercises is illustrated by placing in water a capillary glass tube shorter in length than the height a column of water would ascend to if the tube were of proper length ; the water will ascend to the top of the tube, but will not overflow, and the curvature of the liquid which was concave becomes convex when it reaches the top. 380. In the case of capillary depression, the liquid sinks as much below the original level as will bring the depressed column of liquid into equilibrium with the capillary repul- sion. 381. In noticing the corrections that require to be made for reading accurately the barometric height, we stated that the capillary action between the glass and mercury was one, and that we should notice it in this chapter on adhesion. The capillary depression, we now know, will vary with the diameter of the tube ; in tubes of large bore the depression is inappreci- able ; large-bore tubes are therefore always employed in con- structing important standard barometers. In tubes of small bore the depression is sufiSciently great to render it necessary to make a correction ; the following table will therefore be found useful, as it shows the difference in depression in tubes of different diameters. Diameter of Tube. Depression. Diameter of Tube. Depression. Hundredths of an Hundredths of an Hundredths of an Hundredths of an Inch Inch Inch Inch S . 17 26 . 4-0 10 14 28 3-5 12 II 30 3'i 14 9 32 2-8 16 8 34 2-5 ;8 7 36 2-2 20 6 38 1-9 22 5-2 40 17 24 4-5 382. In reading off" the level of mercury in a barometer, or in a eudiometer, the height of the metal should be taken from the convexity of the curve ; but in estimating the volume of a liquid which wets the surface of the glass the determination should always be made from the bottom of the curve. 383. If in place of the tubes we employ two glass plates, .Capillary Action 167 and so place them in water, or other adhesive fluid, that one end of each touches the other, their sides being at a small distance asunder, the highest point of the liquid will be where the plates are nearest together. If the plates are immersed in mercury, a corresponding depression is produced. 384. Everyone is familiar with capillary attraction in a variety of forms : — the ascent of oil, or melted tallow or wax, in the wicks of lamps and candles ; the absorption of liquids by sponge, blotting-paper, &c. ; the swelUng of wood in damp weather ; the dampness in the basement storey of houses ; and the filtering of liquids through any poroUs vessel that may contain them, will immediately recur to the student as familiar examples of capillarity. There is one example which at first appears rather perplexing : water will pass through gauze, but mercury will not, unless the gauze is wetted with water, then the mercury passes through ; the reason is this, the cohesion existing between the particles of the mercury preponderates over the adhesion of the gauze for the mercury, but this is overcome when the gauze is wetted, and of course the passage of the mercury through the pores is aided by gravity. 385. Immense force can be developed by capillary action : large blocks of stone, for example, can be split by the insertion of wedges of porous wood, which are then saturated with water ; the absorption causes the wood to expand, and by the expan- sion the rock is split. Considerable weights may be raised in the following manner : let one end of a rope be fixed at a point, and the other end to a weight vertically below the point ; the rope is then stretched tight, and afterwards wetted '; the wetting causes the rope to swell, the swelling shortens its length, and owing to the shortening the weight is raised. 386. The adhesion of a solid body for other solid bodies is sometimes so extremely powerful that it can remove them from their solutions in water and other liquids. This is notably the case with charcoal ; charcoal is obtained from both vege- table and animal substances ; animal charcoal is more powerful than vegetable charcoal, and it is usually prepared from bones by exposing them to a high temperature in closed vessels ; by thus excluding them from the air during the time they are heated the gelatinous tissue of the bone becomes carbonised or 1 68 Fundamental Principles of Chemistry charred. Charcoal removes a variety of colouring matters from their solutions ; it is used for this purpose in sugar refineries, for removing the colouring matters from the solutions of brown sugar. It also removes bitter and poisonous vegetable sub- stances from their solutions, and also many of the oxides of the metals ; and it is also employed on the domestic scale for purifying water. If any of my students should be cultivators of hyacinths, they will find, if they grow them in water, that the water will be prevented from becoming foul if they suspend a piece of wood charcoal in it, so that there will be no occasion for changing the water during the growing and flowering of the plant. 387. Since adhesion is a surface action, it is evident that increase of extent of surface will materially increase the adhesive effect ; hence the minute subdivision of charcoal, and of other substances which have similar adhesive action, greatly inten- sifies their adhesive power. Experiments on the Adhesive Action of Animal Charcoal. 263. To an infusion ' of litmus add some animal charcoal, warm the solution to about 100° F., and then pass the liquid through a filter ; observe the decrease in colour of the filtrate. 264. Warm an infusion of red cabbage with animal charcoal, and then pass the liquid through a filter, and observe the colour of the filtrate. 265. Warm an infusion of hops with some charcoal, then filter and test by the taste whether any of the bitter substance has been removed by the charcoal. 266. Warm some porter with charcoal and then filter ; notice not only the colour of the filtrate, but also whether the liquid has lost any of its bitterness. 267. Dissolve some browii sugar in water, observe the colour of the solution, then add to it some animal charcoal, mix thoroughly, then heat the solution to about 180° F. , and keep it at that temperature for about ten minutes, then filter and note the decolourisation of the liquid. 388. Many other substances in a finely divided state remove colouring matters from their solutions, and thus decolourise a coloured solution, besides charcoal, the decolourising power of each substance varying with the kind of colouring substance ; but animal charcoal removes a larger number of colouring matters, and more effectually, than any other decolouriser. ' When hot water is poured on a substance, the solution is termed an infusion : e.g. tea, the liquid, is an infusion. Dyeing t6g 389. Dyeing and calico-printing depend not only on the adhesive attraction between the material — be it cotton, wool, or silk — and the' colouring substance (the dye), but the adhesive attraction between the two must be so powerful that the dye is rendered insoluble in water. In a large number of cases the adhesive attraction is so slight between the material-^especially cotton — and the dye, that water will remove the dye from the cloth ; substances in such cases have to be employed which adhere to both— the material and the dye— and render the dye irremovable from the cloth by water ; these substances are termed mordants, from the French ' mordre,' to bite — from an idea which the old dyers had that these substances (5/2" or <7^ewi/ a passage into the fibres of the cloth, giving access to the dye. Although this theory of their action is now discarded, the term is still retained. When the dye will adhere to the material in an insoluble state, without the aid of a mordant, it is termed a substantive colour, when it requires the aid of a mordant to render it insoluble, it is termed an adjective colour. The sub- stances which act as mordants are almost entirely confined to the metallic oxides ; and of these, alumina, and the oxides of tin and iron, have the most general application. 390. It may be as well to observe that the animal fabrics silk and wool — will absorb and retain colouring matters with much greater facility than the vegetable fabrics — cotton and linen. Experiments exhibiting the adhesive Attraction of Colouring Matters for Silk and Cotton. 268. Immerse a skein of silk in a solution of indigo in sulphuric acid ; observe whether the liquid becomes decolourised, and on the removal of the silk wash it well in water, and it will be found that it retains the colour. 269. Immerse a piece of cotton in the indigo solution ; it will be found that this fabric will have no decolourising effect on the solution, and on washing it in water it will be found that all the colouring matter is removed from it. 270. Immerse a piece of cotton in a solution of cochineal or of log- wood ; after soaking it for some time, remove it and wash it in water ; it will be found that all the dye is removed from it by the water. 271. Mordant the cotton by boiling it in a solution of acetate of alumina, then soak it in the cochineal or logwood solution ; on removing it and washing it in water, it will be found that the red dye cannot be removed from it by water. 1 70 Fundamental Principles of Chemistry Examination Questions. 272. Four cistern-barometers, the diameters of the tuljes of which are ^, \, % and A inch respectively, are placed side by side. Will their readings be all alike ? Give reasons for your answer. 273. A platinum dish containing ether is set in a small pool of water under the receiver of an air-pump, which is then worked ; the ether boils, the water freezes, and the ice is full of bubbles : explain these facts. 274. When a bottle of soda-water is opened, the temperature of the liquid falls : explain the reason. 275. Two similar silver vessels containing, one an ounce of water, and the other an ounce of oil, both at 60° C. , are taken into a cold room ; which will cool the quicker ? If one falls to 59° in three minutes, and the other takes 1 1 minutes to fall to 59', what is the ratio of the two specific heats ? CHAPTER VIII. CHEMICAL AFFINITY — ALL SUBSTANCES EITHER ELEMENTARY OR COM- POUND—DISTINCTION BETWEEN ELEMENTARY AND COMPOUND SUBSTANCES — CLASSIFICATION OF THE ELEMENTS —EXERCISES — ELEMENTS CAN COMBINE TOGETHER— EXPERIMENTS — CHARACTERS OF CHEMICAL ATTRACTION— THE DIFFERENCES BETWEEN A MIX- TURE OF SUBSTANCES AND A CHEMICAL COMPOUND— CHANGES WHICH ATTEND CHEMICAL COMBINATION —EXPERIMENTS— THE DIFFERENT ELEMENTS DO NOT UNITE WITH EQUAL FACILITY^ EXPERIMENTS — TEMPERATURE AT WHICH COMBINATION TAKES PLACE — EXPERIMENTS— SUSPENSION OF CHEMICAL ACTION BY DE- PRESSION OF TEMPERATURE— EXPERIMENTS — THE TERMS EM- PLOYED IN ORDINARY LANGUAGE TO EXPRESS THE CHEMICAL UNION OF SUBSTANCES— EXPERIMENTS— DEVELOPMENT OF HEAT ' BY CHEMICAL ACTION— EXPERIMENTS — INFLUENCE OF PRESSURE ON THE HEAT AND LIGHT OF COMBUSTION — EXPERIMENTS — QUESTIONS. 391. We have now to become acquainted with the other molecular force, viz. chemical affinity or chemical attraction., and the changes produced on matter by the action of this force. We shall, as we proceed, find that it differs essentially from the Other two molecular forces. Substances when they are united together, either by the cohesive or adhesive force, undergo, we have seen, not the least change in their properties by the union ; whereas when substances are united together by the chemical force they lose, as we shall learn, their individual properties, the substances produced by the union being endowed with totally new ones. We will commence as before with what the Simple and Compound Substances 171 student knows, and will lead him gradually on into the domain of chemical science which is yet unknown to him. 392. We are all of us aware that the planet on which we dwell is not built up of any one substance — as sulphur, iron, silver, gold, &c.— but that it is made up of a variety of sub- stances. Most of us, if not all of us, know that from some substances we can extract others ; far example, we extract, by a chemical process termed smelting, the metals from their ores, we extract iron from iron ores, copper from copper ores, &c. The first question which naturally arises in the mind is this, In what respect do the ores differ in constitution or composition from the metals ? We will commence answering the question by directing the attention of the student to the difference between a letter and a word : letters, as we all know, are the simplest signs employed in language, and words are generally composed of two or more letters. Now metals belong to that class of substances which are terminated elements, or simple sub- stances, because we cannot resolve them into other substances. Ores, on the other hand, belong to the only other class of sub- stances ; these substances are termed compound bodies because we can resolve them into other substances, as they are formed ox produced \yj tht chemical union of two or more elements. 393. All material substances, then, whether ««/;««/, vegetable, or mineral, are simple or compound. The elements composing a chemical compound are united together by the chemical force ; and when so united the compound possesses properties totally different from those the elements possess when disunited. We have a good familiar example of this in the difference in the properties of metals and their ores. This is' the groundwork of the science of chemistry. 394. As the elements are what may be termed the letters, and compounds the words, of matter, it is as necessary to become acquainted, on first commencing the study of chemistry, with the names and symbols — for the names are seldom written at full length — of the more commonly occurring elements as it is to become acquainted with the letters of the alphabet before attempting to become acquainted with printed words, or to attempt to read from print. 395. About seventy elementary substances have up to the 1/2 Fundamental Principles of Chemistry present time been discovered ; but some of them are so rare that it is not necessary for the beginner even to become acquainted with their names. They are usually divided into two great classes, metals and non-metals ; the latter were formerly termed metalloids. This classification, which was adopted when a few elements only were known, has now become to some extent arbitrary, and therefore the same boundary-line is not adopted by all chemists ; some basing the division on the physical pro- perties, others on the chemical properties of the elements. 396. Some of the elements are very abundant and are widely distributed ; oxygen, for example, is a constituent of water and of many of the solid substances composing the earth, and is one of the two gases constituting the air that exists in the elementary or uncombined state ; it forms nearly half the total weight of the earth. Some of the elements are very irregularly distributed, having been met with only in limited areas ; and some even in the small areas are present only in minute quantities. Others are widely distributed, although occurring only in small quantities. A few of them exist in their free or uncombined state in nature ; but they, as well as the others, exist also in a state of combination, being chemically united with one or more of the other elements. 397- The names of the elements are seldom written, as already stated, at full length, but are generally indicated by the first letter of their Latin names, a second being employed when more than one element begins with the same letter. When a single letter is employed, as the symbol of an element, it is always printed as a capital ; but when two are employed, the initial letter only is a capital. These symbols or abbreviations are taken from the Latin names of the elements, that they may be universally understood. The student must commit to memory the names and symbols of the elements in the table on opposite page. 398. A few of the elements have a popular as well as a scientific name. Brimstone, for example, is the common or popular name for sulphur ; quicksilver for mercury ; whilst for carbon there are several, these varying according to the state and preparation of this element : it is met with in nature in two different crystalline forms ; diamond is one of the forms, and Simple and Compound- Substances 173 this much admired ' brilliant ' is carbon in its purest state ; graphite or black-lead, used in the manufacture of pencils, is the other form.' It is obtained artificially from several of its compounds, and, according to its source and mode of extrac- tion, it passes under the name of lamplack, bone or ivory black, soot, charcoal, Src. Table of the more commonly occurring Elements with their Symbols. Names of the Elements Sym- bols 1 Names of the Elements Sym- bols NON-METALS. ' METALS {continued.) oJygef": 'gaseous at chiZ: : p-t- H Calcium Chromium Ca Cr N Cobalt .... Co F Copper (Cuprum) . Cu CI Gold (Aurum) Au Bromine fluid . Br Iron (Ferrum) Fe Iodine . , I Lead (Plumbum) . Pb Carbon C Lithium 2 Li Boron Solid at the B Magnesium . Mg Silicon • common Si Manganese . Mn Phosphorus temperature. P Mercury (Hydrargyrum) . Hg Sulphur ' S Nickel .... Ni Arsenic .... As Platinum Pt Potassium (Kalium). K METALS Silver (Argentura) . Ag Aluminium . Al Sodium (Natrium) . Na Antimony (Stibium) Sb Strontium Sr Barium .... Ba Tin (Stannum) Sn Bismuth Bi Zinc .... Zn Cadmium Cd 399. Mercury is the only metal that is liquid at common temperatures ; all the other metals are solid bodies. Fluorine is stated in the table to be gaseous at common temperatures, but it is the element that is the most difficult to obtain in its free or uncombined state ; it is still doubtful whether it has yet been obtained in its elementary state ; and therefore it is still uncertain what its physical state would be if it were obtained uncombined with any other element. We have already noticed 1 This name was given to this form'of carbon when it was considered, from its appearance, that it was a lead substance. 2 Lithium is a rare element, but as some of its compounds are extensively used in medicine, we have thought it desirable to introduce it into the table. 174 Fundamental Principles of Chemistry that all the gaseous elements have been liquefied ; and one of them, oxygen, has been solidified. 400. The most obvious differences between metals and non-metals are physical. The metals in the mass, but not in a finely divided state, reflect light powerfully, which gives them that peculiar appearance termed ' metallic lustre.' Metals are also good conductors of heat and electricity. These three pro- perties are never found associated in the non-metals. A differ- ence in the chemical properties of the compounds the metals and non-metals form with oxygen is noticed in par. 468. Exercises on Chemical Nomenclature and Notation. 276. Write out the symbols for bromine, boron, barium, and bis- muth. 277. What elements do the following symbols denote, — C, Cu, Cd, Cr, Ca, CI, and Co ? 278. What elements do the following symbols denote, — H, Hg, O, N, Pb, Au, Na, Sn, Fe, K, and Ag ? 279. Do the following symbols denote compound bodies ; if so, what are the elements composing these different compounds — Na, CI, Agl, KBr, andHCl? 401. Compound substances, we have stated, are formed or produced by the chemical union of two or more elements ; the elements must, therefore, be capable of chemically uniting together. That two elenients are capable of uniting together and forming a compound substance the following experiments are given as proofs : — Experime?its on the Comhination of Two Elements. 280. Place a piece of phosphorus, about half the size of a pea, in the deflagrating spoon (having previously dried it by pressing it gently between folds of blotting paper), ' (fig- 11); hold the spoon in the flame of a lamp until the phosphorus takes fire, introduce it then into ajar (fig. 12) filled with oxygen.- The light produced by the combination of these two ele- ments is so intense that the eye can scarcely bear it. The compound pro- ' The experimenter must dry the phosphorus as expeditiously as possible, and avoid friction, as phosphorus takes fire readily and causes very severe burns ; he must also obey the instructions as to the size of the pieces of phos- phorus to be used in the experiments. 2 Oxygen is most conveniently prepared from potassium chlorate (KCIO3). For this purpose, powdered potassium chlorate is intimately mixed with one- fifth of its weight of manganese dioxide (MnOj), and then introduced into a flask, or large test-tube, with a bent tube, as shown in figs. 17 and 18. The ilask, or test-tube, may be heated by a gas or spirit lamp — at first moderately. COMBINAT.ON OF TwO ELEMENTS 1 75 duced, appears at first under the form of white smoke, which gradually collects into flakes, falls to the bottom of the vessel, and is dissolved in the water. The white compound is called phosphorus pentoxide (P2O5). 281.. Dry a piece similar in size and in the same way ; cut it into small fragments, and introduce them tmignited, by means of the spoon, into a bottle filled with chlorine.' The phosphorus will instantly take fire, burning with a yellowish-green flame. The compound produced is called phosphorus trichloride (PCI,). 282. Place a few fragments of phosphorus (dried) upon a plate, and throw upon them a small quantity of iodine ; the two elements will instantly combine, and form a red solid called phosphorus tri-iodide (PI3), The combination is attended with evolution of heat and light. 2S3. Place a piece of roll sulphur about the size of a pea in the cup of the spoon, hold the cup in the flame of a lamp or candle until the sulphur takes fire, and then introduce it into a wide-mouthed bottle or jar filled with oxygen. The sulphur will instantly burst into a brilliant purple flame and rapidly disappear. The two elements form by their union a gaseous compound called sulphur dioxide (SO2), which is very soluble in water, and has an intensely suffocating odour. 284. Introduce, by means of the spoon, a piece of red-hot charcoal into a jar filled with oxygen ; the charcoal enters into a vivid state of com- bustion. The compound produced by the union of these two non-metals is a gaseous compound called carbon dioxide (CO.^). ^ 285. Coil a thin iron wire round a thin stick so as to bring it into a corkscrew shape, and then draw it off. Tip one end of the wire with sulphur, by immersing it in melted sulphur, the other end being fixed into a cork which fits the mouth of the gas jar. The sulphur having been ignited, the spiral wire must be immediately inserted into a jar filled with oxygen, and the cork is in this case not closely pressed into the mouth of the jar. The sulphur wilh burst into full flame ; the iron, thus becoming heated strongly, is capable of entering into combination with the oxygen ; a brilliant light accompanies the union, and the compound produced, an oxide of iron, falls down in brilliant sparks. 286. Put a little powdered antimony into a small fine muslin bag, and shake the bag over a bottle filled with chlorine, in such a manner that the small particles of metal coming through the muslin may fall into the bottle ; they will take fire and burn brilliantly, a compound of chlorine as the gas, on the first application of heat, comes off very abundantly and rapidly ; the heat is gradually increased as the evolution of gas decreases. The gas may be collected over water in the pneumatic trough. 1 Chlorine is prepared in the following way : — One part of finely-powdered manganese dioxide (Mn02) is placed in a capacious flask, and four parts of hydrogen chloride (hydrochloric acid, HCl) are added ; the flask is fitted with a tube bent at right angles — the shorter limb is fitted into the neck of the bottle by means of a perforated cork, and the longer one is conducted to the bottom of a dry, wide-mouthed, stoppered bottle. The flask is gently warmed, and as soon as the gas begins to be evolved, the heat is removed until it commences to be slowly evolved, when it is again applied. The gas being much heavier than air collects in the bottle by displacing the air ; as soon as the bottle is filled, which is easily seen by the colour, it is removed, and another substituted ; the full bottls is immediately stoppered, the stopper being first slightly greased. 176 Fundamental Principles of Chemistry and antimony being produced. The experiment may be varied by sub- stituting powdered arsenic for the antimony. In both cases the experi- menter must be very careful not to inhale any of the vapour, and the apparatus, as soon as the experiment is completed, ought to be removed from the room. If copper or gold leaf be introduced into chlorine, the non-metal and metal combine, and the combination is attended, as in the two preceding cases, with evolution of heat and light. 402. It is not intended that the teacher should explain how the different elements employed in the preceding lesson are obtained from their compounds ; to do so would be to derange entirely the plan of the work. The object of the lesson is not to teach the learner how the different elements are obtained from their compounds, but what is much simpler, viz. that two elements can combine together. The self-instructed student is requested to prepare the different gases without attempting to understand the mode by which they are obtained from their different compounds. The methods for extracting the elements from their compounds form the subject of a future lesson. 403. The student need not trouble himself to remember the names of the compounds formed in the different experiments, or their symbols ; as chemical notation and nomenclature are taught in a series of systematic lessons farther on. 404. The collection and transference of the gases, the ves- sels in which they are collected, as well as the vessels in which they are generated, are described at the end of Chapter I. 405. It may be stated in general terms, that all chemical ex- periments are either experiments oi combination or experiments of decomposition, or they area combination of the two ; the student ought therefore to remember that, however complex any chemical experiment he witnesses may appear, it must either be an ex- periment of combination, which is termed a synthetical experi- ment, or an experiment of decomposition, which is termed an analytical experiment, or it must be both a synthetical and an analytical experiment. No chemical compound is composed of all or a majority of the elements ; a large proportion are only made up of some two, three, or four. The elementary sub- stances composing a compound are called its constituents or com- ponents. 406. — The last course of experiments was given to teach the Conditions Necessary for Combination 177 learner the important fact that two elements can combine together, and that a compound substance is produced by their union. One of the experiments must be repeated before we attempt to extract any further information from them ; suppose we repeat the eighth, which was the most brilliant. 287. Burn a piece of phosphorus in ^ jar of oxygen, in the way de- scribed in Experiment 280. 407. Chemical attraction differs from the attractions of cohesion and adhesion in a great many important particulars. When substances combine by means of chemical attraction, they lose their individual properties so long as they remain united — the compound produced by the union possessing properties perfectly distinct from those of its constituents. If we contrast the properties of the compound we have just formed by the combination of phosphorus and oxygen, with the properties of its constituents, we shall see that this is the case. First of all, the compound we have just formed is a solid body, and there- fore oxygen, which, in its uncombined state, is a gas, has become transformed into a solid by its union with phosphorus. Then again, the compound is very soluble in water, and there- fore differs from phosphorus, which is entirely insoluble in that liquid, and from its other constituent, oxygen, which is only very slightly soluble ; and it possesses other properties which neither of its constituents possesses. 408. Although, in all the experimental exercises, the student's attention will be drawn to the fact that substances lose their individual properties when they combine together, and that the compound formed assumes properties peculiar to itself, yet it may be as well, whilst we are alluding solely to this particular effect of chemical combination, to adduce a few more examples. Let us take, as our first example, the compound body water. One would not suppose, from its appearance, that it is a compound body — much less that it is composed of two gases, oxygen and hydrogen. One of them, hydrogen, is one of the most inflammable substances in nature, and yet water cannot be set on fire ; oxygen, on the other hand, enables bodies to burn with great brilliancy, whilst water extin- guishes combustion-. The pungent substance ammonia is com- N 178 Fundamental Principles of Chemistry posed of the two gases, hydrogen and nitrogen, both destitute of odour. The constituents of sugar are carbon, hydrogen, and oxygen. The first of these bodies is a solid, which has never in its elementary state been dissolved in any liquid ; the other two components of sugar are colourless gases, — yet the com- pound produced by their union is a white, solid substance, which is very soluble in water and has a sweet taste. The com- pound resulting from the union of the two solid substances carbon and sulphur, is a volatile, colourless liquid, so volatile that it even evaporates in stoppered bottles, unless covered with a layer of wafer.' Hydrogen chloride (muriatic acid) when applied to vegetable substances that are blue in colour, changes the colour to red; if ammonia be applied to the substance thus reddened the blue colour is restored ; ammonia has, as stated above, a pungent odour ; and these two substances are gaseous bodies ; when they are brought together they chemically unite, the compound produced by the union being a white solid substance, which does not change or alter colours, and is destitute of odour. As' the properties of the two substances are, by the union, destroyed so long as they remain united, they are said to have neutralised each other. The leading circum- stance which characterises chemical combination is, as these examples sufficiently illustrate, the loss of properties experienced by the combining substances, the compounds produced being endowed with entirely new ones. 409. But chemical affinity differs from the attractions of cohesion and adhesion in another respect ; affinity causes sub stances to unite in certain definite proportions by weight, whereas substances cohere or adhere in any proportions. The full con- sideration of this peculiarity of chemical affinity forms the sub- ject of a future lesson. 410. From what has already been stated, the learner will be able to understand the difference between a mere mixture of substances and a chemical compound ; in a mere mixture of sub- stances the different ingredients composing the mixture do not lose their individual properties, but retain them unaltered and unimpaired, and they can be mixed together in any proportions ' Carbon disulphide being heavier, and not miscible with water, this lattei- hquid floats upon its surface. Conditions Necessary for Combination 179 by weight. But when substances chemically combine, they lose their individual properties, and the compound produced is endowed with entirely new properties ; and when substances chemically unite, they can only do so in certain definite pro- portions by weight. Ex. : ist. Gunpowder is a mere mechanical mixture of charcoal (carbon), sulphur, and potassium nitrate (saltpetre) ; but when heat is applied to the mixture these substances disappear, for they enter into chemical union, and most of the compounds produced by the substances are gases . 2nd. If sand, lime, and potash are merely mixed together, the three substances each retain their properties unaltered and unimpaired ; but when they are chemically combined we have the substance produced known as glass. 3rd. ' If we mix together iron and sulphur in the finest powder, in the proportions in which we know they will chemically combine to form iron pyrites or ferric disulphide, namely, 47 parts of iron and 53 of sulphur, they will remain a mere mixture, each with its physical properties unaltered. Owing to the presence of iron the powder will have magnetic properties, and when placed in water the iron will rust, and remove oxygen from a vessel of air. If a magnet be drawn over the powder the iron will be removed and the sulphur remain. When the sulphur and iron are, however, chemically united in the proportions above mentioned, as in iron pyrites, they will be found to have lost their characteristic physical and chemical properties. The compound has no magnetic properties ; it is not, like sulphur, rendered electric by slight friction, and in the state of fine powder it does not remove oxygen when placed in a jar of air over water. A magnet drawn over this powder produces no effect upon it : the iron is not separated from the sulphur ; we have, in fact, an entire change of properties, and the new pro- perties acquired are retained so long as the two elements are chemically combined. By the aid of the chemical force the two elements may be separated and obtained in their elemen- tary state. The iron and sulphur will then be found to have re-acquired all the properties, physical and chemical, which they had lost as the result of their combination.' 411. We have inquired as to the cause of substances chemically uniting ; we have now to inquire whether any out- i8o Fundamental Principles of Chemistry ward manifestations or plienomenaa/Z^W chemical combination . This has already been partly answered in the affirmative, when we stated, and proved by example, that substances, when they chemically combine, lose their individual properties, the com- pound produced being endowed with entirely new ones. And we observed that the combination of phosphorus and oxygen was attended with very marked phenomena ? We saw that it was attended with an intense development of light, and we also discovered that it was attended with a great development of heat. Chemical combination is generally attended with the liberation of heat, and frequently with the evolution of light. Chemical combination is also frequently attended with change of colour. 412. A change of colour frequently attends chemical com- bination. Thus, when mercury and sulphur combine, the beautiful scarlet-coloured substance called vermilion is pro- duced. Silver and sulphur form by their union a black- coloured substance. The beautiful blue-coloured pigment called ultramarine is composed of three colourless bodies — silica (sand), alumina, and soda — besides which it contains small traces of iron and sulphur, neither of which is blue. This is one of the many natural compounds which the chemist has prepared artificially, and it furnishes a striking proof of the advantages which have resulted to commerce and the arts from the study of chemistry ; ' for the artificial ultramarine is even more beautiful than the natural, whilst for the price of a single ounce of the latter we may obtain many pounds of the former.' — {Liebig.) In addition to these examples showing that chemical combination is frequently attended with change of colour, we will add the following experimental illustrations. Experiments showing that chemical combination is sometimes attended mith a change of colour and also of form. 288. Dissolve some lead nitrate and also some potassium iodide in water ; add some of the potassium iodide solution to the lead solution ; when the two solutions are mixed together, the iodine and lead will unite, and form a solid compound (lead iodide), which is insoluble in water, and of a brilliant j'«//oje/ colour. 289. Dissolve some corrosive sublimate (mercuric chloride) in water ; add to this solution the remainder of the potassium iodide solution ; when the two solutions are mixed together, the iodine and mercury will unite and form a solid compound (mercuric iodide), which is insoluble in water, and of a most brilliaut scarlet colour. Conditions Necessary for Combination i8i 290. Dissolve some ferrous sulphate in water, and add to the solution some ammonium sulphide ; the sulphur and iron will unite and form a solid compound (ferrous sulphide), which is insoluble in water, and of a black colour. 291. Dissolve some zinc sulphate in water, and add to the solution so me ammonium sulphide ; the sulphur and zinc will unite and form a solid compound (zinc sulphide), which is insoluble in water, and of a white colour. 413. The' preceding experiments are likewise examples of precipitation, which is a change of for7n ; the compounds that were formed, as the learner saw, were insoluble in the liquid in which their constituents were dissolved ; they therefore fell or were precipitated to the bottom of the vessel. Chemical combination is, therefore, sometimes attended with a change of form ; the last experiments were examples of this in one direction ; the following experiments are examples of it in other forms.' Ftirihei' experiments showing that chemical combination is sometimes attended with a change of form. 292. Place some fragments of marble or chalk in a deep glass vessel, add some water, and finally some hydrochloric acid ; effervescence will be produced on the addition of the acid ; effervescence is caused by a gas in its passage through a liquid ; the gas (carbon dioxide) in this instance is liberated from the marble by the hydrochloric acid. When the evolution of gas is instantaneous and for a moment, we call it not effervescence but an explosion ; as, for instance, when we apply heat to gunpowder, and convert it into gaseous substances. 293. Take two precipitating vessels of equal size, moisten the sides^ of one with a few drops of ammonia, the sides of the other with a few drops of hydrochloric acid ; ammonia and hydrochloric acid are gaseous bodies, and they escape from their aqueous solutions when exposed to the air ; the atmosphere of the jars becomes therefore filled with these gaseous bodies. The mouths or openings of the two vessels are then to be brought together, and the two gaseous bodies will combine, and the compound produced by their union will be a white solid body, which will appear like smoke, owing to its finely divided state. By this experiment we learn that gases may produce by their union solids. 414. It has already been stated, and it will be proved experimentally hereafter, that the elements of water are two 1 Refer back to par. 363, and read over that par. and pars. 364-366 on precipitation. ' i82 Fundamental Phinciples of Chemistry gases, consequently gases sometimes produce by their union liquids. 415. Therefore the changes of form or state that attend chemical combination are exceedingly various ; the combination of gases may give rise to liquids or solids ; solids sometimes become liquids, and liquids solids. And we have seen by the experiments that several familiar chemical phenomena, such as detonation, effervescence, and precipitation are owing to these changes. 416. The next question, I think, any learner would ask about chemical combination would be this, — Can every element unite with every other element ? Every element has been made to unite with the greater number of the elements, but never with all ; but the student is not to conclude from this that every element cannot unite with every other element. All we are entitled to say is, that it has not as yet been accomplished. Oxygen, for example, has been united with every element but fluorine, and we conclude from analogy that it would unite with this element if they were brought together under the proper, conditions. 417. But although every element may be capable of uniting with every other element, they do not all unite with equal facility, nor do they all unite by direct methods, as the student will learn from the following experiments. Experiments shoiving thai the elemetits do not all unite with equal facility, and also that they do not all unite by direct combination. 294. Introduce into a jar filled ^^■ith nitrogen gas ' a small piece of ignited phosphorus, by means of the deflagrating spoon ; the phosphorus will cease to burn in the nitrogen ; it will on its introduction into the gas be immediately extinguished, because a union of the two elements cannot be effected under these conditions. 295. Introduce into a. jar filled with nitrogen a fragment of ignited sulphur, by means of the deflagrating spoon ; the sulphur, like the phos- phorus, will cease to burn in the nitrogen, because the union of the two elements, sulphur and nitrogen, cannot be effected under these conditions. 296. If a piece of burning charcoal in a cage of thin copper wire is introduced, when in a vivid state of combustion, into a jar of chlorine, the ' Nitrogen is most easily prepared by inverting a glass jar in water and burning phosphorus in the confined air contained in the jar. The phosphorus and o.xygen combine together, and produce phosphorus pentoxide (PjOs), which is dissolved by the water, whilst the nitrogen remains behind almost pure. Conditions Necessary for Combination 183 charcoal will cease to burn, but the copper will take fire, showing the great affinity of the chlorine for the copper, and its indifference for car- bon. 297. Place a piece of phosphorus in a small porcelain crucible or small saucer, floating in water contained in a soup plate. Kindle the phosphorus, and when fully burning, cover it completely with a jar filled with hydrogen ' as with an extinguisher. The hydrogen will be inflamed at the mouth of the jar, but the phosphorus and it will cease to burn when the jar rests in water. If the manipulator is not much accustomed to chemical manipula. tions he had better not perform this experiment, as it requires to be care- fully performed in order to avoid an explosion. 418. The Student must not conclude from these experi- ments that the elements which were brought together will no unite ; they were only given to teach him that all the elements do not unite with the same facility, and that they cannot all be made to unite directly. Nitrogen, for example, has only been inade to combine directly with a few elements. 419. The combination of phosphorus with oxygen, and phosphorus with chlorine, will now be contrasted, and the student must observe the different circumstances which mark the combination of phosphorus with these two elements. Experiments showing that the temperature at which combination takes place varies with different substances. 298. Introduce a piece of ignited phosphorus into a jar of oxygen, in the way directed in Experiment 280. 299. Introduce a piece of unignited phosphorus into a jar of chlorine, in the way directed in Experiment 281. 420. These two experiments have been contrasted for the sake of teaching the student the important fact that the tem- ' Hydrogen may be prepared by acting on zinc or iron with dilute sulphuric acid, one part by measure of the acid and eight parts by measure of water. The apparatus employed may be a Woulfe's bottle (fig. 14) ; clippings of the metal having been introduced into the bottle, sufficient of the dilute acid is poured in through the funnel-tube until the metal is covered to the depth of an inch or so with it ; at all events, enough acid should be added to produce a brisk but not violent effervescence, and as the end of the funnel-tube is covered with liquid, the gas evolved can only escape through the other tube. The gas must not be collected until the whole of the air in the different parts of the apparatus has been expelled, as a mixture of this gas and air or oxygen is dangerously explosive. To guard against this, as much of the newly-formed hydrogen ought to be allowed to escape uncollected as would fill the gas ap- paratus two or three times ; after this it may be collected with perfect safety. When the gas begins to be slowly evolved, the addition of a little more acid through the funnel-tube causes it to be evolved again as briskly as at the 184 Fundamental Principles of Chemistry perature at which combination takes place varies with the dif- ferent substances. In order to effect the combination of the oxygen with the phosphorus, the phosphorus had to be intro- duced into the oxygen in an ignited state ; whereas the chlorine and phosphorus combined at the ordinary temperature of the air. The student may ask, Would not the phosphorus com- bine with the oxygen, without the aid of heat ? Not to form the compound produced when the phosphorus burns in oxygen gas, unless it be kept in contact with the air for some time. The reason of this is fully explained in paragraph 462 ; but in order to give the learner a convincing proof that a certain tem - perature is requisite for the combination of substances, and that the temperature varies with the different substances, the following experiment must be made : — 300. Place in a beaker, or other convenient glass vessel, a piece of phosphorus, and half-fill the vessel with water. Fill a bladder, which is fitted with a stopcock and bent tube (fig. 10), with oxygen, and direct a stream of gas upon the phosphorus. When the two elements come in contact, the phosphorus will not burst into flame ; increase the temperature of the water ten degrees, and then direct the stream of oxygen upon the phosphorus. Continue to increase the temperature of the water ten degrees, after each occasion the oxygen has been directed upon the phosphorus, until the phosphorus bursts into flame, when the two elements are brought into contact. When this takes place, the temperature of the water will be about 145° F. 421. ,We will give a few more examples and experiments to prove that the temperatures at which bodies enter into rapid combustion is very various. Ex. : Chlorine, we have seen, com- bines with phosphorus (Expts. 281 and 299), with antimony, and arsenic (Expt 286), at the ordinary temperature of the atmosphere, the combination being attended with evolution of light ; but at the temperature of— 106° it does not enter into combination with these substances. Phosphuretted hydrogen bursts into flame when it comes into contact with the air at the ordinary temperature. Carbon disulphide ignites when touched with a warm glass rod. If a jet of coal gas be made to impinge on a bar of iron only visibly red, the gas will not ignite : it will only be ignited by the metal when it is bright red. Sulphur enters into combination with the oxygen of the air at about 500°, hydrogen enters into combination with it below 600° ; carbon enters into combination with it at about 1000°, and zinc Conditions Necessary for Combination 185 enters into combination at about 1900°. But it must be observed that the temperature at which combination takes place depends greatly upon the state of division of the substance if it be a solid body ; thus iron, lead, and many other substances which will only combine with the oxygen of the air with vivid com- bustion at very high temperatures when in masses, will when in a state of fine powder combine with the oxygen of the air with vivid combustion at the ordinary temperature of the atmosphere. Paradoxical as it may appear, iron and lead when in a state of fine division ignite at lower temperatures than gunpowder, as the following experiment illustrates. Experiment showing that Iron ignites at a lower temperature than Gunpoivder. 301. Place some spirit of wine upon a dinner plate, ignite it, then allow a little gunpowder to fall through the flame. Perform the same experiment, but substitute for the gunpowder iron in powder. 422. A certain temperature, then, is requisite for the com- bination of substances ; and after combination has commejQced, the heat necessary for its continuance is produced by the combina- tion ; for we have already seen that heat is evolved when two substances combine together. 423. As a certain temperature is necessary for the combi- nation of substances, it follows that if the heat evolved by sub- stances in the act of combining be conducted away, the combination must cease for ivant of the necessary amount of heat. The following experiments are given to teach the student this fact. He must remember what has been stated, that metals are good conductors of heat. Experiments showing that cot?ibination ceases when the heat evolved is conducted away. 302. Form a small metallic spiral (fig. 63), by twisting a piece of copper wire around a pencil ; if it be placed cold over the flame of a wax candle, the flame is extinguished, because the heat evolved by the combining substances is conducted away by the metal, and therefore the combination ceases for want of the necessary amount of heat. The experiment must be repeated, first heating the spiral // to redness in the flame of a spirit lamp, and then placing it over // the flame. Under the circbmstances, the flame is not extinguished. Fig. 5,_ 424. Inflammable vapour cannot, for the same reason, pass through wire gauze in an ignited state, because the metal i86 Fundamental Principles of Chemistry conducts away a large portion of heat, and thus reduces the temperature below the point at which combination can take place between the elements of the vapour and the oxygen of the air ; the flame ceases therefore as the vapour passes through the orifices. 3Q3. Lay a piece of camphor on some iron wire gauze, and kindle it. The camphor will burn on the surface with a smoky flame, whilst a portion of the melted mass will pass through the gauze. The melted camphor, in its passage from the upper to the under surface of the gauze, will be de- prived by the metal of so much heat that, when it comes in contact with the air at the under surface, they will be unable, from the low temperature of the vapour, to enter into a state of combination. 304. Place a piece of wire gauze over a jet from which coal gas is issuing ; apply a light to the upper surface of the wire, when the gas will instantly take fire. The metallic gauze may be raised an inch or two above the jet from which the gas is issuing ; the gas above the gauze will continue to burn, whilst that below will remain unignited. 425. Sir H. Davy beautifully applied this impenetrability of metallic gauze to ignited vapour, in the construction of a lamp for coal mines, which invention may be truly regarded as ' one of the happiest efforts . of his genius.' A gas composed of carbon and hydrogen, called by chemists methane, and by miners fire- damp, often issues in considerable quantities from the fissures in the coal-beds, and gradually mingles with the atmosphere of the mine. This gas not only burns in air, but they likewise form, when mingled together in certain proportions, a most explosive mixture, which on ignition detonates with terrific violence. Davy attempted the task of finding some plan whereby the miner could carry a light into the explosive atmosphere without causing it Fig. 64. ^^ ignite, and thus prevent those terrible ex- plosions which were the dread and destruction of the miner. Davy accomplished this apparently impossible task by simply screwing on to the top of a common oil-lamp a cylinder of wire gauze (fig. 64), of about 1,500 orifices in the square inch. The lamp, with this addition, can be carried safely into the most exp losive atmospheres ; for although the cylinder becomes filled with flame, from the ignition of the ex- plosive atmosphere within the cage, yet the explosive atmo- Conditions Necessary for Combination 187 sphere without cannot become ignited, by reason of the heat- conducting power of the metallic gauze. The fire-damp may even burn within the cage with such energy as to heat the wire to dull redness, yet, even then, the flame is not communicated to the external atmosphere, as methane requires a high tem- perature before its elements can separate and enter into com- bination with the oxygen of the air ; ' and hence, most fortu- nately for humanity, it is one to which the cooling orifices may be most -successfully appHed." 426. We have learned, then, the important fact that a certain temperature is necessary for the combination of sub- stances, and that after the combination has commenced the heat necessary for its continuance is produced by the union of the substances, and that if this heat be conducted away the combination ceases for want of the necessary degree of heat. We have now to show that in some cases, although they are comparatively few, the teinperature produced by the union is not as high as that at which the combination takes place, and conse- quently the combination, after it has commenced, cannot con tinue unless the temperature is increased by external heat, because the temperature produced by the combination is lower than that required for the combination. Experiment showing that the heat evolved by the chemical union is sometimes lower than that required for the union. 305. Generate some ammonia gas ; pass it througli an iron tube heated to redness by a gas furnace ; apply a light to the end of the tube from which the gas is issuing, it will burn readily ; subsequently turn off the gas of the apparatus by which the iron tube is heated, and as the iron tube cools, the ammonia gas will cease to burn, for the reason just stated. 427. For the same cause the air cannot, to use a popular expression, be set on fire ; that is, the oxygen and nitrogen of the air cannot be made to unite chemically in any consider- able quantity. The temperature at which nitrogen and oxygen combine is a very high one, being about 5400° F. Now the temperature produced by ordinary oil, gas, and candle flames and by an ordinary fire, is below that ; consequently none of ' Recently it has been shown by one of the Inspectors of Mines, Mr. Gallo- way, that a violent external explosion destroys the action of the safety-lamp , and forces the flame to pass through the gauze. 1 88 Fundamental Pkinciplf.s of Chemistry these sources of heat are sufficient to raise the temperature of the air to the point required for the combination of the oxygen and nitrogen. But the temperature of the oxyhydrogen flame IS, as we shall presently learn, far beyond that required for their combination, and they enter into union whenever a flash of lightning passes thi ough the air, and yet only an inconsiderable amount of the two gases unites under these circumstances, because the heat produced by their union is below that required for their combination ; therefore the combination of nitrogen and oxygen cannot be propagated from particle to particle ; hence the union will not extend beyond the particles of these elements which are in close proximity to the oxyhydrogen flame, or in the path of the lightning. 428. We will resume the experiments and remarks on the combinations of substances by burning some iron wire in oxygen gas ; the wire must be tipped with sulphur. Before the experiment is made, we must inform the student why the iron has to be tipped with sulphur, as several facts will claim his attention after the experiment. We proved in our last lesson, as the student will remember, that substances require a certain temperature for their combination, and that the degree of heat varies with the substances. That iron must re- quire a high temperature for its combination with oxygen, the student must be aware, from his own experience : he will have seen carbon burn in the atmosphere, he will have seen sulphur burn in the atmosphere, and he will have seen phosphorus burn in the atmosphere, when lighted ; but he will not have seen iron burn in the atmosphere, with the exception of the sparks at a smith's forge. It is evident, then, that iron must require to be heated intensely in order to make it unite with oxygen ; the heat required is so great that, although a gas or spirit lamp might give the necessary degree of heat, yet by the time the iron had been removed from the flame and placed in the oxygen gas it would have become too cold ; we therefore tip it with a substance which combines with oxygen at a much lower tem- perature. The substance we have selected for this purpose, as the most convenient in every respect, is sulphur. We ignite the sulphur, and then plunge it into the oxygen gas ; the sulphur and the oxygen combine and the heat liberated by their com- Conditions Necessary for Combination 189 bination is sufficient to cause the iron and oxygen to combine. A similar plan is adopted for kindling coal fires ; for coals, like all other substances, require to be heated to a certain degree before they will burn. This is accomplished, as all know, by the use of the more readily combustible paper and wood. Experiments showing how the heat necessary for combination to commence is sometimes generated. 306. Coil a thin iron wire round a stick so as to bring it into a cork- screw shape, and then draw it off. Tip one end of the wire with sulphur, by immersing it in melted brimstone, the other end being fixed into a cork which fits the mouth of the gas jar. The sulphur having been ignited, the spiral wire must be immediately inserted into a jar filled with oxygen gas, and the cork is pressed into the mouth of the jar. The suIjDhur will burst into full flame ; the iron, thus becoming heated strongly, is capable of enter- ing into combination with the oxygen ; a brilliant light accompanies the union, and the compound produced, an oxide of iron, falls down in bril- liant sparks. This experiment is an illustration of the statement made in a preceding page, that the combination of iron with oxygen is sometimes attended with an evolution of both light and heat. 307. We will now make the same experiment, with the exception that instead of plunging the wire into oxygen gas, after the sulphur is ignited, we will allow it to remain in the air, to see if the iron wire will burn in the air : you see that after all the sulphur has entered into combination with the oxygen of the air the combustion ceases, no union taking place between the iron and the oxygen of the air. 429. Atmospheric air is merely a mixture of the gas oxygen, in which the iron burned in Expt. 306, and nitrogen ; then why will not the iron burn as well in air as in oxygen gas ? Because the nitrogen, which does not enter into combination with the iron (307), or contribute in anyway to the combination, absorbs some of the heat evolved by the combination of the sulphur and oxygen, and thus reduces the temperature below the point at which combination will take place between the iron and oxygen. This gaseous body nitrogen acts with respect to the burning of iron in the air in the same way that the metallic spiral acted in Expt. 302, and the wire gauze in Expt. 303. An example of the same kind the student will frequently have seen ; he will have seen, for instance, that when glowing coals were placed on considerable masses of metal the combus- tion was extinguished, simply because the metal conducted away the necessary degree of heat which was required for their combustion. 430. By the non-combustion of iron in atmospheric air and I go Fundamental Principles of Chemistry its combustion in pure oxygen, we learn why substances that will burn in air as well as oxygen, burn more vividly in oxygen than in air. The indentation made in the plate by the oxide of iron produced in Expt. 306 shows that great heat is generated by the combination of iron and oxygen. 431. By the generality of persons, an evolution of heat and light is regarded as a sign of destruction ; they suppose that, as matter disappears by burning, it is therefore destroyed. This prevailing opinion is owing to the substances, which are produced by the combustions ordinarily witnessed, being gaseous and invisible. Had charcoal, like zinc, phosphorus, and iron, produced a solid substance in burning, this erroneous idea could never have arisen. Instead of these agents, heat and light, being indicative of destruction, they are, as we saw by the experiments, signs that two or more substances are in the act of combining. ' But the learner may say. Are not coal, tallow, and similar combustible substances destroyed by burn- ing ? The reply to this question will be conveyed most intel- ligibly by first selecting some one substance. For example, the elements of tallow — carbon and hydrogen — separate from each other at high temperatures when in contact with air ; they each unite with the oxygen of the atmosphere, the carbon forming with that element carbon dioxide, and the hydrogen forming with it water. The particular combination, therefore, of the carbon and hydrogen which formed the tallow, is destroyed by the burning, but not the elements themselves, for matter is indestructible. Coal, peat, tallow, wax, gas, and all kinds of combustibles (coke and charcoal excepted), whether for heat or illumination, consist essentially of carbon and hydrogen ; the two latter kinds of fuel consisting of carbon only. Atmo- spheric air is a mere mixture of oxygen and nitrogen.' When, therefore, a compound of carbon and hydrogen is burnt in the atmosphere, the burning is due to the decomposition of the compound into its elements, and the combination of each of the elements with oxygen. The decomposition is caused by the oxygen having a greater afifinity for the hydrogen than this latter element has for carbon at a high temperature ; the two 1 It contains small quantities of other gaseous substances, which need not be regarded in questions on combustion. Conditions Necessary for Combination 191 former, consequently, unite and form water, whilst another portion of oxygen unites with the liberated carbon and forms with it carbon dioxide. The nitrogen having no affinity, under the circumstances, for either the carbon or the hydrogen, plays no part in the chemical action, its only office being to dilute the oxygen and thus to moderate the combustion, rendering it slower and less brilliant than it would be if the air were com- posed of oxygen only ; for the phenomena and the results are the same whether a substance be burnt in air or pure oxygen, the only difference being in the intensity of the combustion. 432. We employ in ordinary language several terms to ex- press the combination of substances. If it be attended with evolution of heat and light, we call it burning or combustion ; for example, when a piece of sulphur, or of carbon, is set on fire, we say it burns, because heat and light are evolved ; we likewise say it consumes, because it gradually decreases in bulk and at last disappears entirely. When it is a combination of a metal with the oxygen of the air, and the combination is not attended with evolution of light, we say the metal rusts, or we say it corrodes. 433. A few experiments must now be made, and the student must regard these experiments as illustrations of the facts and principles which have been explained. Experiments illustrating the facts and principles which have been explained. 308. Introduce a piece of ignited phosphorus into a jar of oxygen in the way described in Experiment 280. 309. Introduce a piece of unignited phosphorus into a jar of chlorine in the way described in Experiment 281. 310. Add some phosphorus and iodine together in the way described in Experiment 282. 311. Introduce a piece of ignited phosphorus into ajar of nitrogen in the way described in Experiment 294. 312. Introduce some burning sulphur into a jar of oxygen in the way described in Experiment 283. 313. Take a fragment of sulphur and melt it in the cup of the spoon ; as soon as it is liquid, and before it takes fire, introduce it into a bottle filled with chlorine gas. It will immediately take fire, and burn rapidly, a compound called chloride of sulphur being formed. 314. Introduce some burning sulphur into a jar of nitrogen in the way described in Experiment 295. 315. Burn some iron wire in ajar of oxygen in the way described in Experiment 306. 192 Fundamental Principles of Chemistry 316. Make a small ball of turnings of zinc, and enclose in it a small fragment of phosphorus. Place the ball in the cup of the spoon, and set fire to the phosphorus by means of a lamp, and then introduce the spoon as quickly as possible into a jar of oxygen. The zinc will enter into com- bustion and burn with a beautiful white light. 317. Introduce some ignited charcoal into ajar of oxygen in the way described in Experiment 284. 434. We have learned that for a substance to burn in air or oxygen a certain temperature must be reached ; this point is termed the temperature of ignition ; and the temperature at which the ignition takes place varies widely with different sub- stances. The development of heat by chemical action will be dealt with in Part II. of this book ; but we must here briefly notice the subject. We have learned that chemical combi- nation is attended with a development of heat, and frequently with an evolution of light As heat is evolved in the combina- tion of bodies, so heat is required to decompose them ; and it has been found that the separation of any two substances is attended with the absorption of a quantity of heat equal to that which is evolved in their combination. Experiment has likewise proved that the amount of heat which each element emits when entering into combination is definite and has a specific relation to the combining number of each substance. Thus i lb. of hydrogen when burned in oxygen always emits heat enough to melt 315 '2 lbs. of ice ; 31 lbs. of phosphorus, when burnt — phosphorus pentoxide being formed — yields heat sufficient to melt 1,576 tons of ice; and 12 lbs. of carbon, when converted into carbon dioxide, emits heat sufficient to melt 700 lbs. of ice. But the amount of heat emitted cannot, in the majority of cases at least, be the actual quantities due to the chemical action ; because as each change of state, and even each change in the state of aggregation, is attended with an evolution or absorption of heat, it follows that if the combination is attended with a change of state, or even with a change in the state of aggregation, there must be an addition to, or subtraction from, the amount of heat developed by the chemical action ; for ex- ample, matter cannot pass from the solid to the fluid, or from the fluid to the gaseous state, without an absorption of heat ; on the other hand, matter cannot pass from the gaseous to the fluid, or from the fluid to the solid state, without an evolution of Emjss/on of Light and Heat 193 heat. If matter only changes its state of aggregation, the change is generally attended with an evolution or absorption of heat ; if the bulk of the body be diminished, for instance, heat will be evolved ; if, on the other hand, it be increased, heat will be absorbed. The heat evolved will, in some cases, exceed that due to combination, and in some cases be less than that due to combination. 435' That different substances evolve very different quantities of heat may be further illustrated by the tempera- ture of different flames : — Sulphur flame . 3308° F. Sulphide of carbon flame ..... 3983° Coal-gas flame ....... 4262° Carbonic oxide flame ...... SS07'6' Hydrogen flame (in air) 5898° Oxyhydrogen flame ...... 14542° 436. The heat produced by the combination of hydrogen and oxygen is the most intense that can be obtained by chemical action ; it is only surpassed by the heat of the electric arc, or by the concentration of the rays of the sun through a powerful lens or mirror. 437. It is a well-known fact that solid substances emit light when heated beyond a certain degree, the intensity of the light depending upon the degree of heat to which the substances are exposed. A lump of iron or hme, for instance, becomes red-hot when heated to a certain temperature, and the higher the temperature the whiter or more intense the light becomes. Substances are said to be incandescent or ignited ' when they are heated to such a degree that they emit light. 438. All substances which do not undergo any chemical change when ignited — lime and porcelain are examples of such substances — do not themselves supply the heat necessary for their incandescence, but require to be supplied with it ; the incandescence of such substances consequently ceases when they are removed from the source of heat. But there are other substances — carbon, for example — which, after they have been • The fire which accompanies the process of combustion appears either as glow or incandescence (white heat), when the burning body does not, before combustion, pass into the gaseous state — or asjlame, whenthe burning body is previously converted into gas or vapour. O 194 Fundamental Principles of Chemistry once ignited, continue incandescent after they are removed from the source of heat which first caused their ignition ; because the ignition enabled them to entfer into chemical com- bination with some other substance — oxygen of the air, for instance — and the union furnished sufficient heat to render the solid, whether it be the compound formed, as in the case of phos- phorus and oxygen, or the uncombined portion, as in the case of carbon, incandescent. 439. Gases develop little light, even on intense ignition. It is a well-known fact, that common air may be heated to such an extent that it will inflame pieces of wood, and yet itself remain invisible. A good illustration of this is afforded by the air which issues from the chimney-glass of an argand burner, which is suflSciently hot to ignite pieces of paper, and even to make a thin piece of wire red-hot. Upon the fact, that all bodies evolve light when heated to a high degree, depends the possibility of obtaining artificial illumination. And as gaseous bodies evolve in burning so small an amount of light as scarcely to be visible, it is evident that a solid body must be present in all materials used for illumination ; therefore, when the sub- stances which combine and the substance which isfortned are gases, little or no light is evolved ; for light to be produced, either one of the combining substances or the compound formed must be solid at the temperature at ivhich the combination takes place. 440. The light and heat emitted by burning bodies bear no proportion to each other ; for the heat is due solely to the energy of the chemical action, without respect to the state of the combining matter. Experiments on the Evolution of Light. 318. Generate some hydrogen gas as directed in the note, page 183. Fit a narrow glass tube into a perforated cork, the latter fitting air-tight into the neck of the bottle ; the tube should be made of hard infusible glass, and the end, which is not fixed into the cork, should be drawn out into a fine open point. A light must be applied to the orifice as soon as the operator considers that all the common air has been expelled from the bottle, but not before ; on account of the violent explosion which ensues when hydro- gen, mixed with oxygen or common air, is inflamed, the utmost care and precaution are always necessary in inflaming this gas. To prevent any accident arising from the bursting of the vessel, it is advisable to wrap the vessel in a towel before applying the light. When a light is applied to the orifice, the hydrogen takes fire, and burns with a pale, bluish-coloured. Emission of Light and Heat 195 flame, which is scarcely visible in the daytime, but is intensely hot. The burning of the hydrogen is caused by its combining with the oxygen of the atmosphere, forming with it water : this is readily proved, for if a dry glass vessel be held over the burning gas, it becomes covered with drops of water. If a glass tube, about three feet long, an inch and a half wide, and open at both ends, be held over the flame, strange musical sounds will be produced, the sharpness varying with the depression or elevation of the tube. This phenomenon is produced by a series of small explosions, which succeed each other so rapidly that they produce a continuous sound. The explosive nature of a mixture of hydrogen and oxygen is better exhibited by filling a soda-water bottle two-thirds full of hydrogen and one-third full of oxygen, and then inflaming the gases by applying a light to the mouth of the bottle ; the explosion is less violent if atmospheric air be used instead of pure oxygen. ' If air be employed, five-sixths of it are required for one- sixth of hydrogen ; but whether atmospheric air or oxygen be used, it is requisite, before exploding the mixture, to wrap the bottle in a towel. 319. Hydrogen is the lightest body in nature, being fourteen and a half times lighter than air, and sixteen times lighter than oxygen. This pro- perty is pleasingly demonstrated by filling a small balloon of gold-beaters' skin with the gas, and allowing it to ascend in the lecture-room. The hydrogen ought not to pass direct from the generating vessel into the bal- loon ; before entering the balloon it ought to be made to traverse a tube filled loosely with fragments of quicklime, which will absorb any sulphuric acid that may have been carried up by the gas, as well as arrest the moisture which accompanies the gas. 320. Fill a soda-water bottle with equal volumes of chlorine and hydro- gen, and inflame the mixture by applying alight to the mouth of the bottle, — the explosion is more feeble than with oxygen and hydrogen, and the light is faint. The compound produced is hydrochloric acid. The acid nature of the compound may be demonstrated by applying a piece of blue litmus paper to the bottle. 441. The hydrogen flame, the student will observe, develops little light, although there is a great evolution of heat ; indeed, the flame of a mixture of oxygen and hydrogen produces the most intense heat that can be obtained by chemical action. 442. That a solid is necessary for the evolution of light, is beautifully exemplified in the following way : — The combus- tion of a mixture of oxygen and hydrogen produces the most intense heat that can be obtained by chemical action, yet the light produced by the combination of the two gases is so small as scarcely to be visible. If we place in this almost invisible flame a substance like lime, which will not melt, or undergo 1 The student will see that the difference between combustion and explosion consists simply in the difference in the rapidity of the combination ; in combus- tion the two substances combine together by degrees, but in explosions they are both intimately intermingled, and therefore can be made to combine instanta- neously. 196 Fundamental Principles of Chemistry any chemical change, a light so brightly luminous will be pro- duced as to rival in intensity the noon-day sun. This light is caused by the solid becoming luminous from being intensely heated. 321. Exhibit the oxyhydrogen limelight,' so as to prove to the student that a solid is necessary for the evolution of light. 443. The luminosity of the ordinary hydrogen ilame is also greatly increased if a platinum wire coated with a little film of lime, which is obtained by burning upon the wire paper which has been immersed in a solution of calcium chloride, be intro- duced into the flame. 444. Paper soaked in solution of calcium chloride and burnt in the flame of a spirit lamp, leaves a white network of ashes, which, when held in the feeblest alcohol flame, emits a brilliant light. 445. This method of introducing the solid matter which is to evolve the light, into the burning matter from which the heat proceeds, is one which is never employed for ordinary illumina- tion. The principle upon which all practical methods of illu- mination proceeding from chemical action are founded is, that the heat-producing material and the incandescent solid both exist in the substances employed for illumination, and that the burning of the former sets free the latter, yielding at the same time by combustion the necessary degree of heat to render it luminous. 446. All substances employed as illuminating materials are compounds of carbon and hydrogen, and the flame produced by their combustion contains solid particles of carbon, which can be proved by a very simple experiment. 322. Introduce a cold body, such as a plate of metal, or a piece of glass, or even a piece of card, into a luminous flame ; it speedily becomes 1 The burning of a mixture of oxygen and hydrogen requires great care. The gases ought to be contained in separate holders, and mixed only at the jet ; or if they are contained in the same vessel, the tube which conveys them to the jet must be filled with small iron rods, so that in case the flame were to recede, it would be cooled by the rods below the point at which combination takes place between the two gases, so that by no possibility could the flame reach the gaseous mixture in the gas-holder ; for a mixture of the two gases, when ignited, explodes with terrific violence. Nature of Flame 197 blackened from the deposition of carbon. Intercept the flame by means of the card, far down near the wick ; then higher up, about the middle of the flame, and then at the top. The deposit of carbon near the wick will be very slight ; the deposit will be considerable in the middle of the flame, and only very slight at the top. 447- We learn, by this simple experiment, not only that carbon is present in the flame, but that it is not present in equal amount in different parts of the flame ; the quantity is small in the area of the faintly illuminated halo just around the wick ; it is also small towards the summit of the flame ; it is present in the largest quantity about the middle of the flame, in that portion from which the maximum of light is given forth. We have now to explain how the free carbon comes to be present in the flame. Tallow, oil, gas, and all other substances employed as illuminating materials, consist essentially of carbon and hydrogen, as previously stated. During the burning, both the elementary bodies combine with the oxygen of the air, but not at the same time ; the hydrogen, having a greater affinity for the oxygen than it has for the carbon, instantly combines with the former element. The carbon is consequently liberated in the form of minute solid particles (soot), which become incandescent, from the intense heat evolved by the combustion of the hydrogen ; the incandescent carbon, when it reaches the edge of the flame, likewise combines with oxygen, its place being immediately occupied by another particle of liberated carbon.' If there is not a sufiScient supply of air to consume all the hberated carbon, the unconsumed portion will pass off in the form of smoke. 448. The flame of a candle is a good illustration of the principles just stated. The heat generated by the flame melts the tallow, which is conveyed by the capillarity of the wick to the sphere of combustion. The flame itself consists of three parts ; the first, or outer part of the flame, is of a pale blue colour, so faint as scarcely to be visible, because no separation of carbon occurs, the hydrogen and carbon burning simulta- neously, as the air is in excess ; it is the hottest though the least luminous part of the flame. The air has not free access to the next or luminous part of the flame ; the consequence is, that the oxygen is almost entirely consumed in combining with the hydrogen, whilst almost the whole- of the carbon is liberated 198 Fundamental Principles of Chemistry in minute solid particles, which become intensely heated, and give out a bright light. The interior part surrounding the wick consists of black, inflammable vapour, which, from having no access to the external air, is incapable of entering into combi- nation. The presence of this inflammable vapour may be easily shown by holding obliquely in the flame a glass tube, open at both ends, the lower end of the tube being placed in the centre of the flame, and the upper end reaching beyond its edge. A large quantity of the inflammable vapour will pass up the tube, and may be ignited at the upper end. The cup shape of the candle at the base of the flame, and the tapering form which the flame assumes, are both due to the ascending current of air caused by the combustion of the candle. The flame melts the inner part of the wax or tallow, but the exterior does not melt, on account of the cooling influence of the current ; hence the formation of the beautiful cup in candles. 323. In describing the different parts of the flame of a candle, we have drawn attention to the fact, that if the illuminating material be burned in such a manner that its carbon and hydrogen are consumed at the same moment, the largest possible amount of heat is procured, but the amount of light evolved is not greater than that obtained from the burning of pure hydrogen ; this is due to the immediate combustion of the carbon, and there- fore the absence of any solid matter in the flame, which is necessary, as we have previously stated, for the evolu- tion of light. That illuminating materials derive their light from the separation of their carbon, and that if they be so burnt that this separation does not take place, owing to the carbon being burnt simultaneously with the hydrogen with which it was united, little or no light will be produced, is very simply and very conclusively demon- strated in the following way. Place over a gas jet a '°' ^' chimney, or hollow cylinder, covered over at the top with wire gauze, as shown in fig. 65 ; when the gas — i.e. coal-gas — is turned on, it ascends within the chimney, and mixes with atmospheric air before passing through the gauze. On lighting it above the wire gauze, if the air and gas have been so proportioned that its carbon and hydrogen are con- sumed at the same time, it will burn with a pale blue flame of no more illuminating power than that of pure hydrogen. ' 449. When the burning body does not exist as a gas natu- rally, or does not pass into the state of gas at the temperature at which it combines with the other body — oxygen in the air, for ' Bunsen's burner (fig. 19) can be employed in place of this lamp for illustrating the principle stated. Nature of Flame 199 instance— the fire which accompanies the combustion appears as glow, for it is necessary for the production of flame that the burning body should exist naturally in the state of gas, or be converted into gas at or below the temperature at which com- bination takes place, otherwise no flame results. Well-burned charcoal, and also iron, burns with a steady glow, unattended with flame, as these two elements do not volatilise at the tem- perature at which their combination takes place. Sulphur, phosphorus, zinc, &c., burn with flame, because they either exist naturally in the form of gas, or they pass into the gaseous state at the temperature at which they enter into combina- tion. Flame is, in fact, produced whenever, by a sufficiently elevated temperature, a continuous supply of vapour or gas is made to combine with oxygen or some other gaseous substance with which it comes in contact. Flame, then, is produced when two vaporous or gaseous substances enter into combina- tion, and the combination is attended with evolution of light and heat ; and as combination can only take place at the point of contact, it is the boundary line of the two gases ; hence the flame is hollow ; that it is hollow may be easily shown by holding a wooden match for a few seconds across the middle of the flame of a spirit-lamp with a large wick ; the match will become charred at the edge of the flame, but the intermediate portion will remain uninjured. 450. We have learned, for light to be produced a solid body must be present ; but a few remarks have yet to be made on the production of heat by chemical combination. We learned in Chapter II., that, according to the dynamical theory of heat, motion and heat are convertible one into the other ; and that the molecules of matter in each of the three states in which matter can exist are, it is supposed, in a constant state of motion ; therefore, the molecules of two different bodies must, we are led to suppose, rush together for their atoms to enter into chemical union, and this energy becomes converted by their union into heat. 451. A considerable diminution of temperature occurs in the vessel from which air escapes into a vacuum. Hence, as the gaseous products of combustion increase in volume on the atmosphere becoming rarefied, the temperature of the flame 200 Fundamental Principles of Chemistry must be diminished to some extent by rarefying the medium in which it burns ; but this diminution of the temperature may be nearly or quite neutralised by the smaller amount of refrigera- tion caused by the rarefied atmosphere. In order to eluci- date this point, Dr. E. Frankland made the following experi- ments. ' A spiral of platinum wire was ignited to visible redness in a flame of hydrogen ; then, on rarefying the air round the flame and wire, no appreciable alteration of the temperature of the platinum spiral could be noticed. A similar experiment was tried with an alcohol flame, and with the same result. A spiral of platinum wire placed under the receiver of an air-pump, was ignited to visible redness by a voltaic current ; on exhausting the receiver, the glow of the platinum gradually increased nearly to whiteness. On readmitting the air, it again diminished to dull redness, showing that the refrigerating effect of rarefied air is much less than of air at ordinary pressure. Thus, whilst the temperature produced within a given flame is lowered by rarefaction, the escape of heat from its exterior is hindered by the same process, the result apparently being that the actual temperature of the flame undergoes but little alteration. This confirms Sir H. Davy's conclusion, that rarefaction and com- pression, -within certain limits at least, do not exert any consider- able influence upon the heat of flame! 452. It has also been proved by Dr. Frankland ' that the brightness of ordinary flames increases and diminishes with the pressure of the atmosphere. There is a uniform diminution in the light of the flame with the rarefaction of the air from atmo- spheric pressure down to a pressure of 14 inches of mercury ; below 14 inches the luminosity diminishes at a less rapid rate. Between the limits of pressure above mentioned the amount of diminution is expressed by the following law : — Of 100 units of light, emitted by a gas-flame burning in air at a pressure of 30 inches of mercury, 5-1 units are extinguished by each reduction of I tnercurial itich of atmospheric pressure. A quantity of coal- gas which in London would yield a light equal to 100 candles, would, if burnt in Munich, give an illuminating effect equal to little more than 91 candles : whilst if used to light the city of Mexico, its luminosity would be reduced to 61-5 candles. These numbers are independent of the change of volume by Heat and Light of Combustion 201 reduced pressure. If equal volumes of the same sample of coal-gas were consumed in London and Mexico, the illuminating effects would be as 100 : 46-2, the temperature being the same in both cases. This diminution of light in rarefied air is not caused, we have seen (par. 451), by a reduction in temperature ; neither is it due to imperfect combustion, for the flames which smoke at ordinary pressures become smokeless in rarefied air, and undergo more complete combustion ; ' and Dr. Frankland found by experiment that the gases evolved from a candle- flame, burning under a pressure of only 8 mercurial inches, have the same composition as those from a flame burning under the ordinary pressure. 453- With increased pressure, on the contrary, the separation of carbon is increased ; candles, for example, evolve much smoke when burnt under a pressure of two atmospheres ; and even a small alcohol flame, which burns with a pure blue light at ordinary pressures, becomes highly luminous in air four times compressed ; and Dr. Frankland remarks, it can scarcely be doubted that at a pressure of five or six atmospheres the luminosity of the alcohol flame would be equal to that of sperm oil burning at atmospheric pressure. 454- That the quantity of free carbon in the flame de- creases with the rarefaction of the air is proved by the fact that flames become smokeless in rarefied air which smoke at the ordinary pressure, and that it is to this diminution of carbon in the .flame that the decrease in light is due. The decrease in carbon must be caused by a greater interpenetration of air into the flame. ' But it may be asked,' remarks Dr. Frankland, ' what conditions are there in the combustion of flame in rare- fied air, that favour the admission of a larger proportion than usual of air to the interior of the flame ? ' In reply, it may be stated that there are two conditions, in such combustion, both of which directly tend to produce this result. The first of these conditions, and the one to which Dr. Frankland con- ceives nearly the whole of the effect is due, is the greater mobility of rarefied gaseous bodies, which must produce a more rapid admixture of the flame-gases and external air than would otherwise take place. The second condition is the gradual, though slow increase in the volume of the flame as 202 Fundamental Principles of Chemistry the atmospheric pressure decreases, thus causing the flame to present a gradually increasing surface of contact with the exterior air. 455- We have already stated that the term combustion is employed to express chemical combination when attended with an evolution of light as well as heat. It is not unusual in chemical books to call one of the combining substances the combustible hoAy, and the other combining substance the incom- bustible body, or the supporter of combustion ;\h.\is, in the combina- tion of phosphorus with oxygen the phosphorus would be called the combustible body, and the oxygen the supporter of combus- tion . We have to prove that these terms are inappropriate, and for this purpose we will commence with the followingexperiment. Experi}?ients proving the incorrectness of calling some substances combustible, and others supporters of combustion. 324. Place a piece of sulphur in a long test-tube or flask of hard glass ; heat the vessel by means of a lamp until the sulphur melts, and the vessel has become fillecl with its vapour. Introduce a narrow strip of tinfoil into the sulphur atmosphere ; the metal will instantly inflame, a compound of tin and sulphur being formed. The experiment may be varied by employ- ing, instead of the tinfoil, a narrow strip of sheet lead, the combination being attended with evolution of heat and light. If very thin iron and copper wires be twisted into a coil and introduced into an atmosphere of sulphur, they will likewise combine with that metalloid, the combination being attended with evolution of heat and light. 456. The burning of sulphur in oxygen gas, or of tinfoil in sulphur vapour, proves the incorrectness of calling some sub- stances combustible, and others supporters of combustion ; for in the first of these experiments we should have to call the sulphur the combustible substance, whilst in the latter it would be the supporter of combustion. The fact is, that combustion, like all other examples of chemical combination, is really a re- ciprocal phenomenon, each body, in popular phraseology, burn- ing, or, in chemical language, combining with the other body ; and the heat and light are derived from the combination. Oxygen is as capable, for example, of being burnt in an atmo- sphere of hydrogen or coal-gas|as these substances are in one of, or containing, oxygen. If our atmosphere, for instance, had consisted of coal-gas, we might then have burnt oxygen, just as we now burn coal-gas, for the purposes of light and heat. The experiment of burning the oxygen of atmospheric air in Affinity and Cohesion 203 an atmosphere of coal-gas may be performed in the following manner : — 325. Fill a bell-jar, that is fitted with a stopcock, with atmospheric air, press it down in water, and open the jet. Bring over the jet a small bottle of coal-gas. Just when the mouth of the bottle is in contact with the jet, apply a light. Immediately depress the bottle so as to bring the jet into the middle of the bottle. Blow out the flame at the mouth of the bottle. The atmospheric air will continue to burn at the jet amid the atmosphere of coal-gas. 457. But the learner will find it stated in many chemical works that this or that substance is not a supporter of com- bustion. He will find it stated in such works that hydrogen is a combustible substance, but not a supporter of combustion ; and in proof of the last assertion, the fact that a lighted taper is extinguished when immersed in an atmosphere of hydrogen or coal-gas is adduced. Now, it would be quite as correct to say that oxygen is not a supporter of combustion, because carbon dioxide cannot be made to burn in an atmosphere of that gas. If one element, B, has already combined with another element, A, in the largest quantity it is capable of uniting with it, the resulting compound cannot, of course, unite with a still further quantity of the element, A. Hence paraffin cannot burn in hydrogen, or carbon dioxide in oxygen ; the first, paraffin, being a compound of carbon and hydrogen, cannot unite with 2t, further quantity of the latter element ; for the same reason, carbon dioxide, being a compound of carbon and oxygen, cannot unite with z. further quantity of the latter element. To say that an element is not a supporter of combustion is to say that it cannot enter into chemical combination with any other substance, which is incorrect, as every element can combine, either directly or indirectly, with some of the other elements, if not with all. 458. The difference in colour different substances impart to a flame will be described in the second part. 459. We will now briefly summarise some of the leading differences between the action of the chemical force and that of cohesion. Like cohesion it acts only at immeasurably small distances ; but it differs from that force by causing dissimilar substances to unite, and they can unite only in certain definite and invariable proportions by weight : physical changes also attend its action, chemical compounds having totally different 204 Fundamental Principles of Chemistry physical properties to those of their constituents. Chemical combination is also attended with an evolution of heat, some- times amounting, we have seen, to vivid combustion ; and chemical decomposition is attended with an absorption of heat. The formation and resolution of chemical compounds are also attended with changes in the electrical state of their elements. The following exercises must now be answered by the student either viva voce or in writing. Examination Questions. 326. What is the difiFerence between a mere mixture of substances and a chemical compound ? 327. What is the burning of phosphorus, of carbon, of sulphur, of hydrogen in the air due to ? 328. State some of the changes which characterise the chemical union of bodies. 329. Name some of the elements which combine at the ordinary tem- perature of the atmosphere, and name some which require a higher tem- perature for their combination. 330. Name some of the terms employed in ordinary language to express the combination of substances. 331. State some of the conditions necessary for the combination of phosphorus and oxygen, of phosphorus and chlorine, and the phenomena which accompany the combinations, and the properties of the compounds produced. 332. State the effects which intense heat has upon solid and gaseous bodies, and give examples. 333. Explain the points of difference and agreement between the forces of cohesion and affinity. 334. Name some of the conditions necessary for the combination of antimony and chlorine, and of sulphur and oxygen, and the phenomena which accompany the combinations, and the properties of the compounds produced. 335. Why do substances burn more vividly in pure oxygen than they do in atmospheric air ? 336. What is steam ? Is it an element or a compound ; and can it unite with oxygen ? 337. Upon what facts depends the possibility of artificial illumination ? 338. What is necessary for the production of flame ? 339. Do all the elements unite with equal facility ? Support your opinion by examples. 340. Of what elements are all materials employed for illumination com- posed, and what changes do they undergo when burned in the air ? 341. Explain the ilame of a candle. 342. Explain very fully the principles on which Davy's Safety Lamp is constructed. 343. Do the light and heat emitted by burning bodies bear any pro- portion to each other ? Confirm the opinion expressed by examples. 344. Supposing a space to be filled with pure coal-gas, would the gas explode on the introduction of a lighted candle ? What are the conditions Formation of Compounds 205 necessary to an explosion of the gas, and what are the chemical products of the explosion ? 345- Two substances are brought together ; by what phenomena would you know whether chemical action takes place between them ? 346. You now know what compound is formed when phosphorus is burned in air or oxygen ; and also what compound is formed when hydro- gen is burned in either of these gaseous substances. What compound or compounds would you infer would be formed when phosphuretted hydro- gen (PHj) was burned in air or oxygen ? 347- What are the conditions necessary for light to be produced in chemical combination ? 348. Explain why coal-gas burns quietly when it issues from a gas- burner ; whilst a mixture of air and coal-gas explodes on being lighted ? 349. To what are effervescence and explosion due ; and state the dif- ference between the two ? 350. When a compound of carbon and hydrogen is burnt in a deficient supply of air, what is the result ? 351. A cold plate held above the flame of a candle is bedewed with moisture, and if held in the flame it is covered with soot : explain these facts. 352. State what you know about the point of ignition. 353- Describe Meyer's new method for the determination of vapour densities. 354. By what characteristics are chemical phenomena distinguished from physical phenomena ? CHAPTER IX. COMBINATION OF A COMPOUND WITH AN ADDITIONAL QUANTITY OF ONE OF ITS ELEMENTS — EXPERIMENTS — COMBINATION OF A COM- POUND WITH ANOTHER ELEMENT — BASIC OXIDES AND ACID OXIDES — HYDROXIDES — THE ACTION OF BASES AND ACIDS ON TEST-PAPERS — COMBINATION OF COMPOUND SUBSTANCES — SALTS — EXPERIMENTS — THE SOLID STATE LESS FAVOURABLE TO CHEMICAL ACTION THAN THE FLUID STATE — EXPERIMENTS — RELATIVE IN- TENSITY OF AFFINITY— EXPERIMENT— QUESTIONS — THE PHYSICAL AND CHEMICAL PROPERTIES OF THE MORE COMMONLY OCCURRING ELEMENTS — THEIR EXTRACTION FROM THEIR COMPOUNDS — QUESTIONS. 460. We have now to inform and demonstrate to the learner that more than one compound can be formed, in many cases, by the union of the same elements ; this will at once be rendered easily intelligible to him if we make use of our former comparison ; there are different words composed of the same letters ; there are, for instance, two different words both com- posed of the letters T and O, viz. to and too ; the same with 2o6 Fundamental Principles of Chemistry the letters B and E, viz. be and bee ; and other examples will at once recur to the student. In like manner, for example, there are two compounds of carbon and oxygen, viz. carbon monoxide, the symbol for which is CO, and carbon dioxide, which, for the present, we will represent by the symbol COO ; this latter compound, it will be seen from the symbol, contains double the quantity of oxygen the former contains. Experiments on the combination of a compound with additional quantity of one of its elements. 355. Place in a test-tube some crystals of oxalic acid, add to them some strong sulphuric acid, and then warm the tube in the flame of a lamp. As soon as effervescence commences, apply a piece of lighted paper, or a splinter of wood, to the mouth of the tube, until the evolved gas takes fire : it burns with a blue flame. The gas is the compound carbon'monoxide (CO) we have already alluded to ; the heat and light are occasioned by its com- bining with some of the oxygen of the air, and forming with it carbon dioxide (COO). 461. When a compound contains more proportions than one of one or more of its elements, instead of repeating the symbol in order to indicate the number of proportions, chemists attach a figure to the syrnbol of the element, or elements, to in- dicate the number of proportions. The use of the figures in connection with the symbols can be rendered more intelligible perhaps, if we employ our former illustration j the words ' to ' and ' too ' differ in their orthography, inasmuch as the latter word has one of the letters repeated. From habit we look upon this way of repeating a letter as the only rational one, yet it might be rendered equally intelligible if, instead of repeating the letter, we were to place the figure 2 after it in the following manner, Xa^. This method chemists employ : thus, for in- stance, instead of representing carbon dioxide by the symbol COO, they represent it thus— COj. We shall hereafter adopt this method for indicating the different proportions of an ele- ment or elements in a compound when they are present in more proportions than one. 356. Put into a Woulfe's bottle or flask a few small pieces of metallic copper (copper turnings), and add to the metal, by means of the fiannel- tube, equal parts of nitric acid and water ; effervescence, without the application of heat, will instantly ensue. On the first evolution of the gas the bottle will be filled with reddish fumes ; when they have nearly passed away, the gas may be collected by dipping the exit tube under the mouth Formation of more Compounds than one 207 of a gas jar or wide-mouthed bottle, which is filled with water, and stand- ing inverted on the shelf of the pneumatic trough. This gas is a com- pound of nitrogen and oxygen, and is called nitrogen dioxide (NO). 357. Pass rapidly-into a jar half full of this nitrogen dioxide (the vessel containing it being inverted on the shelf of the pneumatic trough) a quantity of oxygen ; as soon as the two gases are brought together, the jar will be instantly filled with an orange-red gas, which is very soluble in water ; this liquid will therefore rapidly ascend in the vessel by dissolving the new- formed gas. The oxygen and nitrogen dioxide unite together, and the compound produced is this orange-coloured substance named nitrogen tetroxide (NOj). This experiment furnishes a striking example of the dif- ference between a mere mixture of substances and a chemical combination. If the oxygen and nitrogen dioxide had merely mixed, and not chemically united, these two colourless gases, in whatever proportions they were mixed, wonld never have become coloured ; neither would the mere iiiixture of two gases insoluble in water render both of them soluble in that liquid. 358. The experiment may be made in the following manner : — Fill a large jar with nitrogen dioxide, remove it from the pneumatic trough, and expose it with its mouth upwards to the air ; the compound will instantly combine with some of the oxygen of the air, and ,become converted into nitrogen tetroxide ; immediately on the formation of this latter compound place the jar, with its mouth downwards, in the water in the trough ; the water will ascend as in the previous experiment. 462. These experiments prove that some compounds have the power of uniting with another quantity of one of their con- stituents ; thus carbon monoxide can combine with another quantity of oxygen, which converts it into another compound, viz. carbon dioxide : in hke manner, carbon dioxide can unite with another quantity of carbon and by that union becomes converted into carbon monoxide. This interesting chemical action we frequently witness. The blue flame which is fre- quently seen on the surface of coal fires, and which is seen issuing froni lime-kilns and iron furnaces, is occasioned by the carbon monoxide combining with some of the oxygen of the air, carbon dioxide being formed, as in Experiment 355. The combination is produced in our fires in the following way ; the air being in excess at the bottom of the grate, the oxygen unites with, the carbon in its highest quantity, forming carbon dioxide ; as this gas ascends up through the red-hot fuel it gives up one-half its oxygen to another portion of carbon ; the carbon dioxide is thus reduced to carbon monoxide ; and carbon monoxide is also formed by the union of another portion of carbon with the oxygen given up by the dioxide. When the carbon monoxide reaches the surface of the fire it combines with some of the oxygen of the air, and becomes converted 2o8 Fundamental Principles op Chemistry into the dioxide, and the blue flame is the effect of the com- bination. 463. Nitrogen dioxide cannot combine with oxygen if this element be already in a state of chemical combination ; it can only appropriate it when it is uncombined ; in other words, when it is in a pure state or is one of a mere mixture of gases. As it can abstract oxygen from the atmosphere, we conclude, from this and other facts, that the atmosphere is not a chemical compound, but a mere mixture of oxygen and nitrogen.' 464. But some compounds can either combine with another proportion of one of their constituents or with some other element. Example : Carbon monoxide can take up an addi- tional quantity of oxygen, which converts it into carbon di - oxide ; likewise if carbon monoxide and chlorine be mixed together, they combine, a compound called carbon oxychlo- ride being formed. Sulphur dioxide (SO2) (the compound produced by burning sulphur in oxygen) can combine, under certain circumstances, with another proportion of oxygen, which converts it into another compound, named sulphur tri- oxide (SO3) ; sulphur dioxide can also take, in the place of this additional proportion of oxygen, a quantity of chlorine, another compound being formed. 465. There are some elements which can combine both at ordinary and higher temperatures ; different compounds being produced at the different temperatures : when this is the case, the lower combination is attended with little or no evolu- tion of light, and the amount of heat developed is less than that produced by the higher combination. Example : Potas- sium combines at common temperatures with oxygen, forming potassium monoxide (KjO) ; but when heated it burns with flame, and combines with four times as much oxygen. When ■ One of the most convincing proofs that the air is a mixture of these gases is the manner in which the air behaves with water. If the air were a compound, the oxygen and nitrogen would be dissolved by the water in the same propor- tions as they exist in air, which is not the case. If, on the contrary, air is only a simple mixture of these two gases, and as they are not equally soluble in water, the composition of the dissolved gases in the water will be different from that of the air, which is the case. Another proof is, that if oxygen and nitrogen are mixed in the proportion constituting the air, we obtain a gaseous mixture identical with our atmosphere. Basic and Acid Oxides 209 phosphorus is exposed to the air, it always appears to emit a whitish smoke, which in the darlc is luminous. This effect is due to a slow combination of the phosphorus with the oxygen of the air, forming with it phosphorus trioxide (P2O3) ; if phosphorus be heated, it bursts, as we have seen, into a bril- liant flame, phosphorus pentoxide (P2O5) being produced, which contains two-thirds more oxygen than phosphorus trioxide. 466. Having shown, by a number of examples and experi- ments, that many elements can combine in more proportions than one, it might be expected that the theory by which chemists attempt to explain these and like facts would be stated ; but we think it better to here teach the student the fact that many elements can combine in more proportions than one, giving rise to as many different compounds, and explain the theory in the next chapter. 467- We have compared in this chapter simple substances or elements to letters, and compound substances to words. This illustration may be carried still further ; there are, as we all know, words having different functions, as noun, verb, &c., and we have now to learn that different chemical compounds possess different functions. 468. The student will not have failed to notice in the examples and experiments that have been given, that the com- pounds formed by the union of oxygen with other elements were called oxides ; this is the general term for such compounds. Now many of the oxides of the metals have what are termed basic properties ; they are therefore termed basic oxides. The oxides of the non-metals have properties the very opposite of those possessed by the basic oxides ; these last are termed acid oxides. Here is the proper place for pointing out to the student a chemical distinction between a non-metal and a metal ; the oxides of the non-metals never possess basic properties. 469. The oxides forming each of these classes combine with water, forming compounds, the general term for which is hydroxides. The compounds formed by the union of the basic oxides with water are also termed bases. There is a very common example of the conversion of a basic oxide into a hydroxide, which all my readers must have witnessed ; it is the slaking of p 2IO Fundamental Principles of Chemistry lime. Lime (CaO) is a basic oxide, and by adding water to it there results the formation of the hydroxide (CaHoOj), in ordinary language called slaked lime. The combination of the water (HjO) and the lime being attended with a great develop- ment of heat, a quantity of the water that has not combined is expelled in the form of steam. The compounds formed by the union of the acid oxides, or as they are also termed acid-forming oxides, with water are termed acids. Bases turn paper stained with turmeric brown in colour, and they turn red litmus paper b/ue. Acids do not affect the colour of turmeric paper, but they redden blue litmus paper.' Acids possess, as we know from the taste of vinegar (acetic acid), a sour taste. Bases and acids possess also the property of uniting with each other, a new class of compounds being formed, which are noticed in the next paragraph. 470. In ordinary language we call some substances salts ; thus we speak of Epsom salts, common or table salt, saltpetre, and Glauber's salt ; these are salts, but there are many more known salts than these, for all the compounds formed by the union of acids and bases are termed salts ; and when the salt formed does not change the colour oi blue or ^i?^ litmus paper, the acid and base composing it are said to have neutralised each other. 471. There is another class of compound substances ; these compounds have neither acid nor basic properties, nor have they the composition of salts ; we distinguish them by the term indifferent bodies. The student will have learned from what has been stated that compound substances can unite with each other. Experiments on the combination of two compound substances. 359. Take two flasks ; place in one of them one ounce of a solution of ammonia, and in the other an equal quantity of hydrochloric acid ; fit a narrow straight tube to each of the flasks, by means of a perforated cork ; place them upon retort-stands, and adjust two bottles or flasks in such a way that the tubes may ascend into them; then boil the liquid in both vessels 1 The turmeric paper and blue and red litmus paper are called test papers ; they can be bought at a trifling cost at any operative chemist's. There are other test papers besides these, but these are sufficient for ordinary purposes. The teacher ought to show his class the action of acids and bases on these test papers. Formation of Salts 211 for a few minutes. Ammonia and hydrochloric acid are gaseous bodies, and lighter than atmospheric air; consequently when their solutions are boiled they escape and collect in the bottles ; if the mouths of the two vessels be brought together after they are filled with the gaseous compounds, the gases will combine and form a solid substance, a salt called ammonium chloride. 360. Add some dilute sulphuric acid to a dilute solution of ammonia, in such quantity that the solution', after the addition, has no action on blue or red litmus paper, which proves that the acid and base have united and formed a salt that has no action on test papers ; the acid and base have therefore neutralised each other. ' 472. Salts are capable of uniting with each other, thus forming more complex compounds. 473- ^^ ■will giv6 ^ few more experimental exercises, some of them illustrating what has already been stated, but in a some- what different manner. 474- The more opposite substances are in properties the greater is their tendency to unite together ; for example, acids and bases always unite when brought together, and acids dissolve the metals forming with them salts. Experiments illustrating the action of Adds on Metals. 361. Add some nitric acid to some copper filings ; the copper will be dissolved, the acid and the metal combining together ; the solution of the compound, a copper salt, will be of a beautiful bUie colour. 362. Add some dilute sulphuric acid to some iron filings ; the iron wil. be dissolved, the acid and the metal combining together, and forming an iron salt. 475- These experiments are also examples that the com- pound formed by the union of two or more substances possesses properties perfectly different from those of its constituents. If, for example, the blue liquid which has been produced by the action of nitric acid on the copper were evaporated to dryness, we should obtain this blue crystalline substance ^ ; or, if we evaporated the solution we have obtained by acting on iron with sulphuric acid, we should obtain this green-coloured salt. Now what relation or resemblance is there between the copper and the nitric acid and this blue crystalline solid ; or between ' What are termed standard solutions of sulphuric acid and ammonia can be purchased at the operative chemist's ; on adding a given measure of each of the solutions together, the acid and the base will exactly neutralise each other. 2 Specimens of cupric nitrate and ferrous sulphate ought to be on the lecture table. p 2 212 Fundamental Principles of Chemistry this green crystalline solid and the sulphuric acid and iron ? We learn from these examples that there is no resemblance between the properties of a compound and those of its con- stituents. The properties of a compound cannot he predicted either from a knowledge of the properties of its constituents, or from miy other source. 476. As chemical affinity is a molecular force it acts only at insensible distances. For substances to combine, it is neces- sary, therefore, that they should be in intimate contact, or separated only by immeasurably small distances. On this account the solid state is less favourable to chemical action than the fluid state ; for in the solid state the particles of un- like bodies cannot be brought into that close proximity which is essential for the development of their mutual affinities. The following exercises are given to teach the student the fact that solid bodies can rarely be made to combine by merely mixing them together, but if they are brought into a state of solution, combination will at once take place if the substances are capable of entering into combination. Experiment illustrating that the solid state is less fai'our able to chemical action than the fluid state. 363. Mix together in a mortar some tartaric acid and sodimn carbonate, each in the stale of dry powder. No chemical action will take place as long as they remain in the solid state, no matter how long they are mixed together. After being well mixed, dissolve the powder in water and instantly chemical action takes place (proved by the effervescence) because in solution the substances are brought into more intimate contact. 477- Another peculiarity of the chemical force is that it is exerted between different kinds of matter with different degrees of force. Nitric acid, for instance, will oxidise and combine with most of the metals ; it oxidises and unites, for instance, with silver, mercury, copper, lead, and iron, but it unites with these metals with very different degrees of intensity: with silver the combination is less powerful than with mercury; with mercury less powerful than with copper ; with copper less powerful than with lead ; and with lead less powerful than with iron. Experiment on the relative intensity of affinity. 364, place a piece of metallic iron in a solution of cupric nitrate (about a quarter of an ounce of the copper salt in half a pint of water) ; the nitric PROPERTIES OF SOiMB OF THE ELEMENTS 213 acid will leave the copper, and combine with the iron, forming with it ferrous nitrate ; the metallic copper set free will be precipitated on the portion of the metallic iron which remains uncombined. Examination Questions. 365. Explain what is meant by chemical action, and give some illustra- tive examples. 366. What part does air take in the process of combustion ? 367. If sulphur were heated in a vacuum, would it burn, or would it undergo any change ? 368. When an element is consumed is there any gain or loss in weight ? 369. Would any difference in the intensity of the light be obtained by supplying heated air to a gas-flame in place of cold air ? 370. Why should the breath appear visible in cold weather and not at other times? From its appearing visible, what element or compound would you infer is one of the substances in the respired air ? 371. Two powders are given you: one is a mechanical mixture, the other a chemical combination of sulphur and iron. In what respects would the two powders differ, and how could you prove that the mechani- cal mixture was not a chemical compound ? 372. Give some proof that the air is a mixture, and not a chemical compound. 373. Describe the properties of an acid. 374. Can more compounds than one be formed out of the same ele- ments ? 375. Why will not carbon dioxide burn in air ? 375. Describe the properties of a base. 377. What causes the blue flame which is frequently seen on the sur- face of coal-fires ? 378. When are acids and bases said to have neutralised each other ? 379. Why will not water burn in air ? 380. Are the substances produced on burning a given weight of coal, equal, lighter, or heavier in weight than the coal itself? ' 478. In giving a brief description of the properties of the more commonly occurring elements, and the method for ex- tracting them from their compounds, we will treat the two divisions — non-metals and metals — apart ; and we will com- mence with the first division. 479. Hydrogen. — This element is met with in nature in the free state in small quantities— it is one of a mixture of gases in certain volcanic emanations ; it is given off from some of the oil-wells ; it has also been found occluded in meteoric iron ; and it is evolved during fermentation, and in the decay and decomposition of organic substances. But it occurs almost entirely in a state of combination ; water is one of its most 1 The rest of the chapter must te passed over for the present ; the student will be directed when to return to it. 214 Fundamental Principles of Chemistry important compounds, and it is a constituent of nearly all animal and vegetable substances. It can be obtained, as has been shown (Experiment 400), by electrolysing water; this is one of the best methods for obtaining it in a pure state. We have learned that Na and K set it free from H2O at ordinary temperatures: Li, Ba, Sr, and Ca likewise set it free from H2O under the same conditions. Several of the other metals set it free at higher temperatures, the H2O being passed over them in the state of steam, an anhydrous oxide of the metal being formed. Examples : Mg, Zn, Cd (monoxides of these metals being formed), and Fe, in the latter case a complex oxide, ferrosoferric oxide, Fe304, is formed. It is usually obtained by the action of H2SO4 or HCl on Zn, or on Fe (see note page 183), but there are numerous other metals, the alkaline, and alkaline earth, metals, also Al, Cd, &c., which displace the H in these acids. Zn, we have learned, can displace the H in KHO, or NaHO ; and Al sets free H from solutions of the alkalies, with probably the formation of a similar Al com - pound to that of the Zn one. With regard to its properties we have learned that it is the lightest body in nature. It "com- bines with O at ordinary temperatures if the two elements are brought together in the nascent state ; and they combine to- gether at the ordinary temperature when not in the nascent state by the action of the metal Pt, which by condensing them brings them sufficiently in contact for chemical union to take place ; this is called surface action, a kind of action the student has not yet been made acquainted with as regards gaseous com- binations. Under no other conditions, as far as is known, does chemical union take place between H and O at ordinary tem- peratures; but at higher temperatures, we have learned, combin- ation invariably takes place between them, and we have become acquainted with the phenomena which accompany the union. 480. Oxygen. — We are already aware that this element is present in the free state in the air ; and we have also learned that it is the element which exists in the largest quantity, and is the most extensively diffused, in our planet. We have learned how to extract it from several of its compounds in Chapter XIV. ; and also in note page 1 74, the method usually adopted for obtaining it for lecture purposes ; but we will give Properties of some of the Elements 215 here two others, as we can by these methods obtain it from the atmosphere, (i) If air is passed over BaO when heated to a low red heat, it combines with O, forming BaOa; at a bright red heat the latter compound is decomposed into BaO and O ; this is an example that the temperature required for combina- tion and that required for decomposition are not in some cases far apart. (2) If sodium or potassium manganate, Na2Mn04, is heated in a current of steam it parts with some of its oxygen, NaHO, and MngOa being formed ; after the O has been evolved the current of steam is discontinued and air is passed over it ; the manganate is again formed. By this and the pre- ceding process it will be seen O and N can be alternately ob- tained from the air. We learn from these two processes that O can be abstracted from the air and then given up over and over again by the same portion of substance. It has been combined, as we have learned, with all the elements but F; we have learned also that its combinations at high temperatures are not only attended with an evolution of heat but also of light; and that it is the gaseous body in the air that causes our fuel and light-producing substances to burn ; it also causes metals to rust, and dead animal and vegetable matter to decay, by oxidising them. The respiration in animals is analogous to the burning of fuel ; the oxygen inspired oxidises the worn- out animal matter, converting its carbon into CO2 and its hydrogen into HjO, which are expired ; and the oxidation of these elements in the body, as their oxidation in the fire- place, is attended with an evolution of heat. 481. There is an allotropic modification of oxygen called ozone ; it is one of the most powerful oxidising agents known, more powerful than ordinary oxygen ; hence it oxidises bodies at ordinary temperatures, which only enter into union with ordi- nary oxygen at high temperatures. It is a colourless gas, with a peculiar odour, which has been compared to that of very dilute chlorine. Its molecular formula is O3, three volumes of ordinary oxygen being condensed to two volumes in its formation. It is present in very minute quantities in the air, but it is only in the air of the country, and especially in that over the sea, that it is most constantly met with : in the air of towns it is almost always absent, owing to the quantity of 2i6 Fundamental Pj^inciples of Chemistry oxidisable matter in the atmosphere. The usual method em- ployed for detecting it in the air is by exposing paper moistened with a mixture of starch and KI; it sets free the" I, which turns the starch blue ; the following is its action upon KI : 2KI + 03 + H20=2KOH + l2 + 02. This test requires to be employed with care as there are fre- quently present in the atmosphere other substances which colour the paper blue. Ordinary oxygen can be converted into ozone, but as yet only very small quantities have been so transformed. Ozone can be obtained in small quantities by one of the three following methods: ' (i) It is evolved at the positive pole in the electrolysis of acidulated water. (2) It is obtained by the slow oxidation of phosphorus in the air. (3) It is formed by the discharge from an electrical machine through air or through oxygen.' It is not only converted into ordinary oxygen by heat, but even at ordinary temperatures it gradually changes into oxygen. 482. Chlorine. Bromine. Iodine. Fluorine. — These ele- ments belong to one group. As it is as yet uncertain whether F has been obtained in the free state, we shall confine our remarks to the other three ; not one of the three has been met with in nature in the free state. We are already acquainted with some of their physical, as well as their chemical, properties ; we know that under ordinary conditions CI is a greenish-yellow coloured gas, Br is a dark brown coloured liquid, and I is a solid of a blackish-grey colour and having a kind of metallic lustre. Common salt (NaCl) is the best known and most widely distributed compound of CI. It may be obtained direct from NaCl as described in note, page 175; but it is more generally obtained by first obtaining HCl from NaCl (Ex. 644) then CI from HCl (Ex. 670). I exists in combination with NaK, or Mg in small quantities in sea- water ; it is also present in certain seaweeds, from the ash of which it is commercially extracted ; it is also found along with Chili saltpetre (NaNOs,) ; from the mother liquor of this salt it is also commercially extracted. The usual method adopted on the manufacturing scale is that given in Ex. 721. Br is present in small quantities in sea- water as a bromide : also in some sea-weeds from the ash of which it Properties of some of the Elements 217 is extracted by the same process as that adopted for the ex- traction of I. It is also present in the potash-beds of Stassfiirth, also in certain mineral springs in America in quantities sufficient to make its extraction commercially profitable. 483. Sulphur. — This element is met with in large quantities in the free state in volcanic districts ; but in a state of combi- nation it occurs in much larger quantities, and is much more widely distributed. The two most extensive classes of sulphur compounds are the sulphides and the sulphates ; the common ores of Cu, Pb, and Zn are sulphides, and there is a sulphur ore of iron, iron pyrites, FeS2, which is extensively employed for converting, by roasting the ore, the S into SO2 for the manufacture of sulphuric acid. The principal natural sulphates are those of Ca, Ba, Mg, Na, and Fe. Various sulphur com- pounds exist in the vegetable and animal world. Although it exists in large quantities in the free state in some countries, FeS2 is submitted to destructive distillation for the purpose of obtaining it, thus — 3FeS2 = Fe3S4-FS2. It is also obtained in the purification of coal-gas. It occurs in , three forms in commerce, viz., roll sulphur or brimstone, flowers of sulphur, and milk of sulphur. The latter is obtained by decomposing a polysulphide of calcium with HCl ; in this form it is in a very finely divided state, is of a white colour, and is used as a medicine. This element exists in several allotropic modifications. 484. Phosphorus. — This element does not exist in the free state of nature : it is very widely distributed, especially in com- bination with O and Ga, as calcium phosphate. This salt forms the chief inorganic constituent of the bones of animals, and it is from bones that P is obtained. The bones being freed from the organic matter and in the form of ash are treated with sufficient sulphuric acid to form an acid phosphate : Ca3(P04)2 + 2H2SO4 = CaH4(P04)2 + 2CaS04. The solution of the acid phosphate is poured ofi" from the insolu- ble CaS04 ; the solution is evaporated to a syrupy consistence ; it is then mixed with a sufficient amount of charcoal, evapo- rated to dryness, and afterwards gradually heated to full redness 2i8 Fundamental Principles of Chemistry in an appropriate vessel : two-thirds of the phosphorus distils over, and is condensed by the water contained in the receiving vessel. The operation may be regarded as consisting of two stages: — ist, the conversion of the acid phosphate into calcium metaphosphate ; 2nd, the setting free of the phosphorus : — (i). CaH^ (P04)2 = Ca2P03 + 2H2O. (2). 3(Ca2P03) + loC = P4 + Ca3 (P04)2 + loCO. We have learned that P unites with O at ordinary as well as high temperatures ; but there is an allotropic modification of the element called red phosphorus from its colour, which does not combine with O at a temperature lower than 240° C. It is produced when ordinary phosphorus is heated, in an atmosphere of CO2 or H, to a temperature of 240" C. for some time. 485. Nitrogen. — This is one of the two gaseous elements in the free state in the atmosphere, and it forms four-fifths of the bulk of the air ; it also occurs in combination in ammonia, nitric acid, and other bodies, and is a constituent of many animal and vegetable substances. We have learned how it may be obtained from the air ; it may also be obtained by heating a concentrated solution of ammonium nitrate. This element is distinguished by its inactive properties; it combines directly with but few of the elements, and it is difficult, we have learned, to make it combine even with these few ; but it combines indirectly with a large number of the elements. 486. Arsenic. — The substance which popularly is called arsenic is not the element, as we have before stated, but AS2O3 ; the element is of a steel-grey colour. It is widely dis- tributed in nature; it occurs both in the free state and in combination with various metals. It is obtained by heating arsenical pyrites (Fe2S2As); the As is expelled and the S and Fe remain combined ; it is also obtained by heating AS2O3 with carbon. A small quantity of it is added to the lead in the manufacture of shot, as it causes that metal to assume more readily the spherical form and it also renders it harder. 487. Carbon. — This element is met with, as before pointed out, in three different modifications, viz., as the diamond, as graphite (black-lead), and in the form of charcoal, lamp-black, bone or ivory black, soot, &c. If we can consider some of the Properties of some of the Elements 219- elements more important than the rest, carbon is a most impor - tant one : all organic substances, whether animal or vegetable, are compounds of carbon ; hence organic chemistry, or that de- partment of chemistry treating of organic substances, has been defined as the chemistry of carbon compounds Although all organic substances contain carbon, all carbon compounds cannot be classed as organic substances. From what has been stated, the student will not be surprised on being told that the com- pounds of this element exceed those of any of the others both in number and variety. It only combines directly with a few of the elements. When any organic substance is heated in. the absence, or in a deficiency, of air a portion of the carbon remains behind in its amorphous form. In all its three forms it is infusible at all temperatures ; and it is insoluble in any of the ordinary solvents ; the only solvent of it at present known is fused iron. With the halogens and with nitrogen it does- not unite directly; its compounds with these elements can only be obtained by indirect methods. It does not combine directly with hydrogen, oxygen, or sulphur below 100° C. ; but at high temperatures its affinity for the two latter elements is very great ; it is on this account extensively employed in the extraction of metals from their ores, being, as it is termed, one of the most powerful reducing agents known. 488. Boron. — This element is not' met with in nature in the free state ; and it is only met within combination with oxygen, either as free boracic acid, or that acid in combination with bases forming the salts called borates. It has been obtained in two allotropic states, the amorphous and crystalline. It was until recently the only non-metallic element of which no hydrogen compound had been obtained, but recently this com- pound has been formed. 489. Silicon. — This element is not met with in nature in the free state; it is always met with in combination with oxygen,, either in the state of silicic anhydride— as quartz, flint, &c. — or as silicic acid in combination with bases forming the exten- sive and important class of minerals termed silicates. It has been obtained both in the amorphous and crystalline state. It is the chief constituent, next to oxygen, of the solid earth. 490. Metals.- -The elements belonging to this class vary 220 Fundamental Principles of Chemistry very much both in their physical and chemical properties ; as examples we may notice the difference in their densities; K,Na, and Li are lighter, as we have learned, than water, whilst Pt is twenty-one times heavier than an equal bulk of that liquid ; again, Au, Pt, and some of the rarer metals do not unite directly with O, whilst all the other metals do unite with it directly at ordinary or higher temperatures ; K, Na, Sr, and Ba have such an affinity for it that they enter into union with it at common temperatures ; and some of the metals, lead and iron for example,"which in their massive state are unacted upon by air or pure oxygen unless moisture is present, when, in a very finely divided state, they come in contact with air in- stantly unite with oxygen, the combination being attended with ignition. Alloys are the intimate mechanical mixtures pro- duced by melting metals together. Those alloys which con- tain mercury are called amalgams. Alloys and amalgams can only be produced from metals. 491. Potassium. Sodium. Lithium. — K and Na are obtained by placing a mixture of their dry carbonates and charcoal in an appropriate iron vessel and applying a strong heat : the metals distil over : — KjCOj-f 2C=K2-|-3CO. These metals can also be obtained by the action of Fe on their hydrates at a strong white heat : — 4NaH0 + 3Fe= 2K2 + Fe304 + 2H2. Very recently another method has been invented for obtain- ing them from their hydrates, which is said to be so great an improvement that they can now be manufactured at as many pence a pound as formerly it cost shillings to obtain them. This method consists in heating their hydrates with carbide of iron (FeC2), but in practice, instead of carbide of iron, an inti- mate mixture of Fe, in a very finely divided state, and pitch is used. Lithium cannot be obtained by the processes we have described for extracting the two previous metals ; as yet it has only been obtained by the electrolysis of some of its salts. Owing to the great affinities of K and Na for O and CI, they are employed for obtaining various non-metals and metals from their oxides and chlorides. Properties of some of the Elements 221 492. Barium. Strontium. Calcium. Magnesium. — These metals can be obtained either by the electrolysis of some of their salts, or by decomposing their chlorides with Na. The first three have no useful application ; but Mg is now manu- factured on a large scale ; it is met with in commerce in the form of wire or ribbon. ' It may be ignited at the flame of a candle, and burns with an intensely brilliant white light, very rich in chemically active rays, a property which has led to its use in photography. Besides its application in photo- graphy, its light has been used in signalling ; it has been seen at sea at a distance of 28 miles.' 493. Aluminium. Chromium. — The first of these metals is obtained by passing the vapour of its chloride over heated K or Na. The preparation of the chloride from the mineral bauxite, a hydrate of alumina and ferric oxide, is somewhat com- plicated, and to describe it would occupy more space than we can afford. Al is used in the manufacture of various physical instruments ; it is also employed in the manufacture of its alloy with copper, which possesses the appearance of standard gold. If it could be obtained at a cheaper rate, it would have still more extensive applications, owing to its lightness, tenacity, un- alterability in the air, &c. Chromium is obtained by heating its chloride with Zn in a crucible, and using a mixture of KCl and NaCl as a flux. The hardness of steel is greatly increased by the addition of 0*5 to 0-75 per cent, of this metal. 494. Zinc. Cadmium. — The first of these metals is extracted both from its carbonate and its sulphide ; the former ore is roasted to drive off the CO 2 and HjO present; the latter is roasted to expel the S in the form of SO2 ; in both cases the ZnO is left in the state of oxide by the roasting. The ZnO is mixed with powdered coal, the mixture is placed in an appro- priate furnace and heat applied ; the carbon of the coal removes the O ; the metal being volatile at a bright red heat distils over and is collected in appropriate receivers. Its most impor- tant uses are generally known. The latter metal is associated with Zn in its ores, and being more volatile than Zn distils over first, but, becoming in part oxidised, the distillate is mixed with small coal and distilled at a low temperature. It has no commercial importance. 222 Fundamental Principles of Chemistry 495. Iron.- — This metal, whose uses are so numerous, is, on that account, universally known, but, curious to say, the pure metal is not an article of commerce; very few indeed have seen it in a state of chemical purity ; all the different varieties of iron met with in commerce contain carbon and some other foreign substances. All the substances associated with it exercise, no doubt, some influence on the character of the metal; but it may be said in general terms that it is chiefly to the amount and state of the carbon it contains that commercial iron in its different forms owes its characters ; and to the varying amount and state of the carbon is due the several varieties of the metal known as pig or cast iron, wrought or malleable iron, and steel. It would be almost impossible to give, even in several pages, a very brief description of the methods adopted for the extraction of the metal from its various ores ; we can therefore only glance at one or two points in the few lines we can devote to the subject. There are several varieties of pig iron; some contain more combined than uncom- bined carbon, in other kinds it is just the reverse. Pig iron contains a larger total of carbon than any other variety ; steel contains the next largest quantity of C ; and wrought iron contains the least. The metal is extracted from the native oxides and carbonates by first roasting the ores, and then smelt- ing them in a furnace along with coal and hmestone ; the latter being employed to form a fusible mass with the gangue of the ore; this fusible mass is termed the slag. 496. Manganese. — This metal has no commercial import- ance ; it may be obtained by subjecting a mixture of an oxide of the metal and charcoal to a strong heat in a crucible. 497. Cobalt, Nickel. — The first of these metals is not used in the metallic state in the arts ; the latter is largely used in the form of rolled plates for nickel-plating ; it is also one of the metals employed in the manufacture of the alloy known as Ger- man silver; and in some countries an alloy of nickel and copper is used as the material for the coinage in place of copper coinage. The two metals always occur associated together in nature, the one being in excess in some minerals, the other in other minerals ; they are both constantly met with in metallic meteo- rites, and the student will probably have noticed that they Properties of some of the Elements 223 have nearly the same atomic weight. Ni is prepared from the mineral NiAs and from an arsenical cobalt' mineral called cobalt-speiss by removing the cobalt by a series of processes, and then reducing with charcoal. 498. Copper. — This metal can be very easily obtained from its carbonates, for they are reduced directly by heating with char- coal ; but the ores of copper most generally smelted are sulphur ores; thechiefone is a double sulphide ofCuandFe(Cu2S.Fe2S3) called copper pyrites ; it requires about six different processes to remove the sulphur and iron from the copper ; the smelting of this ore is therefore a very complex process. The iron pyrites now burnt for the production of sulphuric acid con- tains on an average three per cent, of copper, which all remains in the burnt ore ; it is extracted from the burnt mass by roast- ing it with NaCl ; the Cu is converted into a chloride, which dissolves out on treating the roasted mass with water, and is precipitated in the metallic state by placing scrap iron in the aqueous solution. This metal, which is one of those longest known to man, is employed for a great variety of purposes in the arts : it is very tenacious, ductile, and malleable. Brass is an alloy of copper and zinc : and bell-metal and gun- metal are alloys of copper and tin. 499. Lead. — This is one of the well-known metals; its most abundant ore is the sulphide, galena, PbS ; and from this ore the metal is most generally extracted. The process most generally employed for extracting the metal from galena is by converting one-half the ore into sulphate by roasting; the whole quantity is then mixed together and the temperature raised, when the following reaction takes place. PbS04 4- PbS = 2Pb + 2SO2 The metal can be worked very easily, and as it resists the action of air and moisture, it is employed for many purposes. Various alloys of the metal are used in the arts ; type-metal is an alloy of lead, tin, and antimony ; plumber's solder is an alloy of lead and tin. Galena almost invariably contains some silver as well as lead ; the quantity is very variable, but even if it does not exceed three or four ounces in the ton of metal it is profitable to extract it, and the quality of the lead is improved 224 Fundamental Principles of Chemistry by the removal. The process most generally employed is called Pattinson's process, from the name of the inventor. This process is founded on the fact that an alloy of lead and silver is more fusible than pure lead. The metal obtained on the reduction of the ore is melted in a large vessel, and then allowed to cool slowly; the portion which first crystallises is nearly pure lead; this is removed by a perforated ladle ; the re- melting both of the richer and poorer lead is continued until the largest quantity of the metal is all but free from silver, whilst the silver has increased in the richer portion to, say, 300 ounces of silver to the ton. This rich mass is placed in a cupel or shallow dish made of bone-earth (calcium phosphate), and again re-melted and exposed to a current of air, which oxidises the lead ; the lead oxide thus formed melts and a portion flows off, whilst the rest is absorbed by the bone-earth ; and the silver is left in the metallic state, and almost chemically pure ; this process is called cupellation. 500. Silver. — This metal occurs in the metallic state, but it is in a state of combination that it occurs in the largest quantity. It is extracted from its ores by three different processes : ' either it is alloyed with lead and then the lead removed by oxidation, a process we have already described, or it is amalga- mated with mercury and this removed by distillation ; or, lastly, it is brought into solution as a salt and the metal pre- cipitated by means of copper. The practical adoption of one or other of these processes depends upon the nature of the ore, the position of the mine, and the price of labour, fuel, &c.' 501. ' Pure silver is very little employed in the arts, as it is too soft to resist wear. In order to increase its hardness and tenacity, it is alloyed with a small proportion of copper, an addition which does not affect its colour, and in this form it is employed for plate, ornaments, coinage, &c. Standard silver is an alloy of silver and copper of a given composition fixed by law, and this standard varies in different countries. ■?; In England the standard contains 92-5 percent, of silver.' 502. Bismuth. — This is not an abundant metal ; it occurs in the metallic state disseminated through various rocks, from which it is separated by simple fusion ; it is found also associated with nickel and cobalt, and from these ores it is also Properties of some of the Elements 225 extracted. It is employed in the manufacture of fusible metals. 503. Antimony. — This metal is always extracted from antimo- nious sulphide, SbjSa ; this ore is first roasted, antimonious oxide and sulphurous anhydride being produced ; the oxide is then reduced by carbon. It is only employed as a con- stituent of some alloys ; it imparts to the alloy the property of expanding on solidification. The crude antimony of commerce is merely the sesquisulphide ore freed from the greater part of its earthy impurities. 504. Tin. — Independent of its value as a metal, tin is in- teresting to the inhabitants of Great Britain, as ' these isles became first known to the civilised nations of the ancient world by the commercial quest for tin, whether carried on by the direct voyages of the Phoenicians or Carthaginians (a ques- tion still in dispute), or by the overland route through Gaul, with the aid of its great rivers, to Massalia and other Greek colonies on the Mediterranean, which is fully described by Diodorus Siculus and Strabo. From the former source, Herodotus, in the fifth century B.C., may have derived his information about the islands in the extreme west of Europe, called Cassiterides, whence, he says, tin is brought to us.' ' Tin is never met with in the metallic state ; it is met with only in combination with oxygen, as SnOs, called tin-stone. After the tin-stone has been freed from its earthy and metallic im- purities, it is mixed with charcoal and reduced in a furnace. It is employed in coating other metals to prevent them from rusting, and it is a constituent of several alloys. 505. Mercury. — This metal occurs in its uncombined or native state, but it is chiefly met with in a state of combination ; its most abundant ore is cinnabar, mercuric sulphide. It may be obtained from this ore either by burning off the sulphur and distilling the mercury ; or by heating the ore with some sub- stance which forms a non-volatile compound with sulphur, and distilling off the liberated mercury. It is used in silvering mirrors, and extracting gold and silver by the amalgamation process ; it is of great use in physical and chemical laboratories ' Smith and Groves's Historical Atlas of Ancient Geography ; Biblical and Classical. 226 Fundamental Principles of Chemistry The alloys of the various metals with mercury are termed amalgams. 506. Gold. — This metal always occurs in its native state, and is always alloyed with silver, and sometimes with other metals. If it does not contain more than 10 per cent, of Ag it may be separated from that metal by melting the alloy in a clay crucible glazed inside with borax, and passing a current of CI through the molten mass. The Ag is converted into chloride, which is prevented from volatilising by a layer of fused borax ; if Zn, Sb, Bi, and Sn are present, they are also converted into chlorides, which are volatilised. The metal thus purified contains from 99-1 to 997 per cent, of Au. Its uses need not be stated, as they are so generally known. 507- Platinum. — This metal always occurs in its native state ; it is mixed with palladium and other rare metals ; these metals, in fact, are rarely found excepting associated with Pt. It is found only in comparatively few places, the largest amount being met with in Russia. On account of its extreme infusi- bility, its mode of extraction is complicated and peculiar. Owing to its being little acted upon by most chemical agents, and its high fusing-point, it is extensively employed in the manufacture of vessels for chemical purposes. Examination Questions. 381. Calculate the weight and volume of oxygen, at the standard tem- perature and pressure, obtainable from 100 grams, of manganese dioxide, a. by heat (Exercise 700). b. by sulphuric acid (Exercise 661). How would you extract silver from argentiferous galena ? 382. If 100 grams, of steam is decomposed by passing it over red-hot iron, what will be the increase in weight of the iron, and what the volume in litres of the gas obtained measured at 0° C and 760 mm. ? 383. From what you have learned as to the constitution of ozone, what is your inference, if any, as regards the constitution of allotropic bodies in general ? 384. A splinter of a colourless body is given to you ; how would you prove by a chemical test that it was diamond and not a piece of glass ? 385. What are the materials you would require for making chlorine, and what quantities must be used in order to obtain 1,000 grams, of this gas? 386. Give the meaning of the terms gangije and slag. 387. What volume of air at 0° C. and 760 millimetres pressure is needed for the combustion of one gramme of hydrogen ? What would be the volume of the product at 300° C. ? Laws of Combination 227 388. What are alloys, and what are amalgams ? 389. Describe as fully as possible the means of obtaining hydrogen from water ? 390. What are the sources of iodine ; and how is it extracted from its compounds ? Describe some of its physical and chemical properties, and state its vapour-density. 391. What is meant by saying certain substances are reducing agents? 392. Name the characteristic element in organic compounds. 393. For what purpose is the metal antimony employed ? 394. Name the metals which, on being set free from their ores or com- pounds, are obtained by volatilising them. ' CHAPTER X. LAWS OF COMBINATION — LAW OF DEFINITE PROPORTIONS — EXERCISES — LAW OF EQUIVALENT PROPORTIONS — LAW OF MULTIPLE PRO- PORTIONS — ATOMIC CONSTITUTION OF MATTER — GAY-LUSSAC's LAW OF VOLUMES — EXPERIMENTS — EXERCISE — ATOMS AND MOLECULES — AVOGADRO'S LAW — TABLE OF THE MOLECULAR WEIGHTS AND VOLUMES OF THE GASEOUS AND VAPORISABLE ELEMENTS— THE VOLUME-WEIGHTS OF ELEMENTS AND COMPOUNDS— EXERCISES — ATOMICITY — GRAPHIC NOTATION — CLASSIFICATION OF THE ELE- MENTS ACCORDING TO THEIR ATOMICITY— EXERCISES — QUESTIONS. 508. A chemical compound is distinguished from a mere mixture of substances, or from a simple adhesion of different substances, not only by its possessing properties entirely different from those of its constituents, but by the still more reriiarkable characteristic that it is always composed not only of the same el ements, but they are always united in unvarying proportions by weight. We have to remember, then, that bodies always oxyca- \)m&\r\ fixed ^nd, invariable proportions by weight, and this law, it may be observed, is the basis of chemistry. No circumstances whatever can alter the proportional quantities of the constituents of a compound. Thus common kitchen or table salt — whether obtained from the salt-beds in Poland or from those in Cheshire, wherever found or however prepared, whether by the agency of man or by the operations of nature — is always made up of the two elementary bodies, chlorine and sodium, and in the invariable proportion of 23 parts by weight of sodium to ^ The student imist now pass on to far. 6oi, Chap. XI. ^ and complete the study of that chapter, Q 2 228 Fundamental Principles of Chemistry 35 '5 parts by weight of chlorine. Substances can, under certain circumstances, assume different forms or states ; for instance, calcium carbonate exists both crystallised (marble) and uncrystallised (chalk) ; water can assume the solid, the liquid, and the gaseous states. Under all forms and states, however, the chemical composition remains the same. Water — whether in the solid state, as hail and snow ; or in the liquid state, as rain or dew ; or in the gaseous state, as steam, — is always made up of the two elementary bodies, hydrogen and oxygen, and always in the proportion of one part by weight of the former element to eight of the latter. 509. From these and similar facts we deduce the law, that substances always combine in fixed and invariable proportions by weight, which is not interfered with when two or more substances are brought together in proportions different from those in which they will unite. If they combine they do so in the very same proportions they would have done had they been brought together in their natural proportions, the only difference being that a portion — constituting the excess, of one or more of the substances — remains uncombined. Oxygen and zinc combine in the proportion of 8 parts by weight of the former to 32 parts by weight of the latter element ; 40 parts by weight of the com- pound, — zinc oxide— being formed. Let us suppose that they are brought together in the proportion of 8 of oxygen to 36 of zinc ; the combining proportion of the two elements neverthe- less would be the same, 8 parts of oxygen combining with 32 parts of zinc, 40 parts of oxide of zinc being formed, and 4 parts of zinc remaining uncombined. To take another assumed case :— Suppose they were brought together in the proportion of g of oxygen to 32 of zinc, nevertheless 8 parts of oxygen, as before, would combine with 32 parts of zinc, 40 parts of oxide of zinc being formed and i part of oxygen remaining uncombined. Water and lime combine in the proportion of g parts by weight of the former compound, to 28 parts by weight of the latter, 37 parts by weight of hydrate of lime being formed. Suppose that we added 1 1 parts of water to 28 of lime, the consequence would be that two parts of water would remain uncombined, 37 parts of hydrate of lime being produced ; or that we added to every g parts of water 31 parts of lime, 37 parts of hydrate of Law of Definite Proportions 229 lime would still be formed, whilst 3 parts of lime would remain uncombined. 510. This constancy of composition in chemical com- pounds, not only as regards their elements, but also as regards the weight of these elements, will be better understood, perhaps, if we select a few more examples, and arrange them in a dif- ferent manner. Water contains Hydrochloric acid contains in 100 pts. in 100 pis. Oxygen 88 -89 Chlorine 97-26 Hydrogen niix8 = 88-88 Hydrogen 274 x 35-5 = 97-27 Hydrosulphuric Acid contains Hydriodic Acid contains in 100 pts. in 100 pts. Sulphur 94-12 Iodine 99-22 Hydrogen 5-88x16 = 94-08 Hydrogen 0-78x127-99-06 100-00 100-00 511. It is evident from these examples that the different constituents of a chemical compound are present in different proportions by weight. Thus, in water, there is 8 times more, by weight, of oxygen than of hydrogen ; for if we multiply the quantity of hydrogen contained in that compound by 8, the product will be the number representing the quantity of oxygen present in that liquid. In the same way, there is 16 times more by weight of sulphur than of hydrogen in hydrosulphuric acid ; for if we multiply the quantity of hydrogen in 100 parts of that compound by 16, it will give us the number representing the quantity of sulphur the compound contains in 100 parts; and • so with respect to the other two examples. 512. We may therefore express these facts in the following simple form. To one part by weight of hydrogen there is found — In Water In Hydrochloric Acid 8 parts of oxygen. 35-5 parts of chlorine. In Hydrosulphuric Acid In Hydriodic Acid 16 parts of sulphur. 127-1 parts of iodine. Every 9 parts of water, then, are invariably composed of 8 parts of oxygen, and i of hydrogen ; every 36- 5 parts of hydrochloric acid are composed of 35-5 parts of chlorine, and I part of hydrogen &c. 513. Chemical compounds are therefore always constant and 230 Fundamental Principles of Chemistry definite in cojnposition, not only as regards their components or elements, but likewise as regards the quantity by weight of these elements. This is the first of the three great laws of chemical combination. Exercises on the proportions by weight in which substances combine. 395. How much water would be produced from 28 lbs. of oxygen and 5 lbs. of hydrogen, and would either of the elements be in excess ? 396. How much hydrochloric acid would be produced from 5 lbs. of hydrogen and 178 lbs. of chlorine, and would either of the elements be in excess ? 397. How much hydriodic acid would be produced from 7 lbs. of hydrogen and 1,000 lbs. of iodine, and would either of the elements be in excess ? 398. How much hydrosulphuric acid would be produced from 6 lbs. oi hydrogen and 80 lbs. of sulphur, and would either of the elements be in excess ? 514. The student became acquainted in the last chapter with two modes by which chemical compounds can be formed, (i) By direct combination of elements or compounds with each other ; (2) By the displacement or substitution of one element, orcompound substance, for another, see Experiment 363.' We must now give a few more examples of this latter method of forming chemical compounds, in order that the student may comprehend what is meant by equivalent proportions. 515. It has been shown that nitric acid dissolves some of the metals; it dissolves most of them. The chemical action is this: the metal removes from one portion of the acid sufficient oxygen to form with it a basic oxide; another portion of the acid oxide combines with this basic oxide, a salt being the result of the union; the acid oxidises and unites, for instance, with silver, mercury, copper, lead, and iron ; but it unites with these metals with very different degrees of intensity. With silver the combination is less intense than with mercury ; with mercury less intense than with copper ; with copper less intense than with lead ; and with lead less intense than with iron. If, therefore 1 This experiment not only illustrates the fact that the solid state is less favourable to chemical action than the fluid state ; but it also illustrates the fact that one compound substance can displace another from its combination ; thus tartaric acid displaces the acid oxide, carbon dioxide, in the salt sodium car- bonate ; the carbon dioxide on being set free resumes its natural gaseous con- dition, and in bubbling up through the water causes the effervescence ; by this displacement the original salt is, of course, destroyed, and a new one, sodium tartrate, is produced. Equivalent Proportions 231 mercury were added to the compound produced by the combi- nation of the acid with silver, the mercury would displace and take the place of the silver ; if copper were added to the compound produced by the combination of the nitric acid and mercury, the copper would, displace and take the place of the mercury ; if lead were added to the compound produced by the combination of the nitric acid and copper the lead would displace and take the place of the copper ; iron were added to the compound produced by the combination of nitric acid and lead, the iron would displace and take the place of the lead ; therefore any metal in the list can dis- place all the metals which precede it, and can be displaced by each of the metals which follow it. 516. Mercury replaces silver in the proportion, by weight, of 100 parts of mercury for every 108 parts of silver ; copper replaces mercury and silver in the proportion of 317 parts of copper for every 100 parts of mercury, or 108 parts of silver; lead replaces copper, mercury, or silver in the proportion of 1037 parts of lead for every 317 parts of copper, or 100 parts of rnercury, or 108 parts of silver ; iron replaces lead, copper, mercury, or silver, in the proportion of 28 parts of iron for every 1037 parts of lead, or every 317 parts of copper, or every 100 parts of mercury, or every 108 parts of silver. We will illustrate the proportions in which substances replace and are replaced by a few more examples : — Sixteen parts of sul- phur, we have learned, combine with i part of hydrogen and form 17 parts of hydrosulphuric acid ; if we were to replace the sulphur in hydrosulphuric acid by iodine we should require i27'i parts of iodine for every 16 of sulphur, and the compound, after the sulphur had been replaced by the iodine, would not be hydrosulphuric acid; it would be hydriodic acid: if we were to replace the sulphur in hydrosulphuric acid, or the iodine in hy- driodic acid, by chlorine we should require 35 "5 parts of chlorine to replace every 16 parts of sulphur, or every 127-1 parts of iodine. From these examples it will be seen that whether a substance. A, combines with another substance, B, by direct combination, or by replacing some other substance with which B is united, it (A) always combines with B m the same propor- tions by weight in whichever way the combination takes place : thus, chlorine always unites with hydrogen in the proportion 232 Fundamental Principles of Chemistry by weight of 35-5 parts of chlorine to every i part of hydrogen, whether the chlorine unites with the hydrogen by direct com- bination, or by displacing some substance with which the hydro- gen was united. 517- From these and like facts the second of the laws of chemical combination, and which is called the Law of Equivalent Proportions has been deduced, viz., that when one element or compound takes the place of another element or com- pound, th^ replacement takesplace in different but definite amounts. 518. The third law is called the Law of Multiple Propor- tions; it has been deduced from innumerable facts the chemist has discovered ; he has found, as we have learned, that some substances combine in more proportions than one, forming to- tally distinct compounds ; and that the higher proportions are multiples of the lowest combining proportion of the substance : but before we can enter more fully with advantage to the student on this subject, it is desirable he should be made acquainted with certain theories. 519. It was by the aid of the balance that chemists dis- covered that substances unite in certain definite proportions by weight ; and by the aid of the balance they have determined the proportions by weight of the different substances that unite ; and the proportions by weight in which they replace each other, in other words their equivalent proportions. Scientific facts are truths, and are consequently unalterable ; bnt the explanations or interpretations scientific men give of those facts are at the best only guesses at truth. Different theories may, and often are, devised by different scientific men to explain the same series of facts ; and even the theory which is most gene- rally accepted is liable to change with the progress of the science, as we shall learn from the theory we have now to explain. 520. The cause of elements and compounds always uniting in unvarying proportions by weight is unknown to us ; all that we know from chemical investigations is that it is a principle impressed on matter by the Creator ; and we further see how important it is ; for if substances did not unite in unalter- able proportions by weight there would be no stability in the composition or properties of natural and manufactured chemical substances ; what at one time might be a food, might at another Atomic Theory 233 time be a poison. Although we do not know why substances always unite together in unvarying proportions by weight, a beautiful theory was invented by the late Dr. Dalton to account for the fact ; it is known as Dalton's Atomic Theory, and although purely speculative, has exerted an important influence in aiding the progress of chemical science. The ancient philosophers had conceived; before it had been discovered that " the elements unite in certain fixed and definite proportions by weight, that rnatter was made up of small indivisible particles they termed atoms. Dalton adopted this view of the constitu- tion of matter, but he conceived that the atoms of the different elements differed in weight, which the ancients had not con- ceived, for they had no knowledge of elementary substances ; fire, earth, air, and water they regarded as the elements. It will be seen that, if Dalton's theory be admitted, the difficulty of explaining why the elements should always combine, and replace each other, in certain definite proportions by weight is removed ; for according to this view, it is one or more atoms of one element combining with one or more atoms of another element : for atoms, unlike molecules, are chemically, as well as mechanically, indivisible. The absolute weight of the atoms cannot of course be determined, because they cannot be isolated or got into a separate state ; the atomic weights are therefore relative, not absolute weights. 521. Hydrogen being the lightest substance that is known, its combining proportion by weight is less, as we have seen, than that of the other elements ; Dalton, therefore, assigned as the weight of its atom the least whole number, viz. one ; and as at the time he propounded his Atomic Theory there was only one compound of hydrogen and oxygen known, viz. water ; and as water is composed of these two elements in the propor- tion, as we have already shown, of one part by weight of hydro- gen to eight parts by weight of oxygen, Dalton considered that in the formation of water one atom of each of the elements unite together ; therefore, if the atom of hydrogen be taken to weigh one, the atom of oxygen, according to this interpretation, must weigh eight. ^)2Z. But Dalton in framing his system of Atomic Weights neglected to observe, or at all events to take into account, the 234 Fundamental Principles of Chemistry proportions by volume in which gaseous substances combine. This oversight is not surprising if we notice the few elements that are naturally gaseous, and the comparatively few that can be rendered gaseous ; and it had been by weighing that the discovery had been made that substances unite and replace each other in certain definite proportions by weight. About the time Dalton was constructing his Atomic Theory, Humboldt and Gay Lussac observed that oxygen and hydrogen unite by volume, to form water, in the proportion of i volume of the former to 2 volumes of the latter element ; therefore, if Dalton's hypothesis were correct, the hydrogen atom must occupy double the volume the oxygen atoiji occupies. Now, if this were the case, we should expect a difference in their dilatation and com- pression when subjected to the same variations of temperature and pressure ; but it has been proved by experiment that there is no difference in this respect between the two gases ; they expand and contract alike, the pressure being the same for equal additions or subtractions of heat, and they also experi- ence the same change in volume for equal pressures. This uniformity in expansion and contraction extends to all gases and also to vapours, at some distance above their points of conden- sation. This uniformity of gases in their relations to heat and pressure led scientific men some years ago to believe that in the same volume all gases contain the same number of ponderable atoms set at equal distances, and whose natural repulsion is expressed by the same law. 523. But this generalisation — that equal volumes of gases under the same conditions of pressure and temperature contain an equal number of atoms — is true only within certain limits. In the sense which is now attached by chemists to the word atom the proposition is true only for a certain number of the gaseous and vaporisable elements : hydrogen, oxygen, nitrogen, chlorine, bromine, for example ; but it is not correct as regards phospho- rus, arsenic, mercury, &c., as we shall learn as we proceed, for they do not contain in equal volumes the same number of atoms as hydrogen, oxygen, chlorine, &c. Neither is it correct, as we shall learn, as regards compound gases ; although they are subject to the same laws of expansion as the simple gases. What is ac- cepted is that equal volumes of gases contain the same number of molecules, and that a molecule of each substance occupies two Combination by Volume ■^■h'ii volumes if one atom of hydrogen occupies one volume. Equal volumes, however, of hydrogen and oxygen contain the same number of atoms ; and as one volume of oxygen is sixteen times heavier than one volume of hydrogen, and as equal volumes of the two gases contain the same number of atoms ; it follows that the atom of oxygen must be sixteen times heavier than the atom of hydrogen, and not eight times, as Dalton thought ; and therefore, the correct formula for water will not be HO, but must be HjO, as two volumes of hydrogen unite with one volume of oxygen to form one molecule of water which occupies two volumes. 524. Although in everyday life we all see liquids measured as well as solids weighed, yet I have, and I believe other chemical teachers have likewise, found that students less readily comprehend volume-relations than they do those relating to weight ; we will therefore, before going further into the subject, give a few experimental exercises, showing the volumetric pro- portions in which the elements hydrogen, chlorine, oxygen, and nitrogen combine to form the compounds hydrochloric acid, water, and ammonia ; and the proportion by volume in which hydrogen combines with the non-volatile ele- ment carbon to form the gaseous compound methane, as the student will then learn by observation the principles of volume-combina- tion. Experiments illustrating the volumetric consti- tution and condensation ratios of gaseous compounds. 399. The following experiment proves that hydro- chloric acid can be formed by the direct union of its elements, hydrogen and chlorine ; and that they unite in equal volumes, and that the volume the hydro- chloric acid occupies is the mm of the volume of its constituents, there being no condensation. 'Two stoppered glass vessels of exactly equal capa- city (fig. 56) are united by a tube, which is closed by a stopcock. After closing the stopcock, one of these is filled with chlorine and the other with hydrogen, arid the stoppers are replaced. On opening the stopcock in the dark, diffusion will cause the gases to mix, an action which will be more rapid if the part of the apparatus containing the chlorine be placed uppermost. If the apparatus be now exposed to the diffused light of a well-lighted room, but not to direct sunlight — otherwise an explosion will occur — the colour of the Fig. 66. 236 Fundamental Principles of Chemistry diluted chlorine, at first visible, will rapidly disappear. The reaction may be completed by exposure to sunlight for a few minutes, there being no longer any danger of explosion. If one of the stoppers be now removed under mercury, there will be no rise of mercury in the vessel, showing that no coniraction\i3s occurred during combination, and also that no free chlorine ' remains. If water, coloured blue with litmus, be poured on the surface of the mercury, and the apparatus be raised until its orifice is above the mer- cury, but under the water, the latter will rush in, completely filling the double vessel (a proof that no free hydrogen remains) ; whilst the blue tint turns to red, owing to the action of the acid. Equal volumes of hydrogen and chlorine therefore combine without change of volume to form hydro- chloric acid gas.' 525. The two next experiments prove to us that the elements of water, hydrogen and oxygen, unite by volume to form that compound in the proportion of two volumes of H to one volume of O, and that the steam produced occupies only two volumes ; condensation therefore of three volumes into two takes place on the union of these gases to form water. 400. Let the terminal wires of a Smee's battery, consisting of at least six pairs of plates, be placed, by means of the conductors A B, in communication with the platinum plates P P. The tubes are filled with n water, which is rendered a better conductor by the addi- y tion of some sulphuric acid, and inverted in the vessel E, ■ filled with the same fluid over the platinum plates P P. I Immediately connection is made with the battery the Jll platinum plates will become covered with bubbles of gas, s|te F which, being evolved, will rise in the tubes in unequal -^B ' proportions, rather more than twice as much gas being g|(WH collected in a given time in one tube than in the other. ijj The smaller volume is oxygen, the larger volume is hy- /^*S^^^g drogen ; the former is always evolved at the surface of •zy'VsT^i^ the positive pole of the battery, and the hydrogen atways (^'l^~y~^ ^t the negative pole. As these gases are evolved from \,„,^^^:^^ thfi decomposed water their volumes ought to be to each other as two to one : the reason why they are not pre- '°' '■ cisely in this proportion is to be found in the partial solubility of oxygen in water ; and hence, on this account, the volume obtained is rather below the true quantity. Dr. Hofmann substituted for this apparatus (fig. 67) the one shown in fig. 68. It consists of a three-branched tube ; the longer one terminates in a globe a, which acts as a reservoir; the other two limbs, /; and f, are fitted at their upper ends with glass stopcocks ; at the lower ends platinum plates are inserted, and the terminal wires of the battery are connected with these plates by means of the binding screws d and e. The stopcocks are opened when the apparatus has to be charged with water acidulated with sulphuric acid ; the water is poured into the globe-tube until the limbs b and c are ' If any free chlorine were present, it would immediately combine with some of the mercury, a solid compound being formed ; there would therefore be a diminution in the volume of the gas, and consequently the mercury would rise in the vessel. Combination by Volume full ; the stopcocks are then closed. The hydrogen and oxygen set free by the decomposition of the water by the electric current collect in the two limbs, and by means of the stopcocks we can subject the two gases to chemical tests, and prove that they are oxygen and hydrogen. 526. The decomposition of water by voltaic electricity, whichever of the two apparatuses is employed, only shows us that in the formation of water two volumes of hydrogen are united' to one volume of oxygen ; but it does not show us whether when these two gases unite together in these volume-proportions, any condensa- tion takes place ; in other words, what number of volumes the gaseous water produced occupies ; to prove this the next experiment has to be made : 401. The closed limb of the U-shaped eudio- meter, fig. 69, is filled with mercury, and it must be observed that this closed limb is fitted, at a point near its sealed extremity, with two platinum wires, a a, welded to the glass, and separated at their inner ends by a distance of only two millimetres, while their outer ends are formed into loops for the attachment of the battery wires. Into the sealed limb, after it has been filled with mercury, a mixture of hydrogen and oxygen, in the propor- tions in which they form water, is introduced into it through a, tube passed down the open limb. The quantity of the mixed gases admitted should be from 25 to 30 centimetres. The mercury dis- placed by the gas should be run out at the tap b. The mixed gases must be, of course, in the pro- portion by volume of 2 of H to I of O ; this mixture, in the correct proportions, is most easily obtained by decomposing water by a bat- tery, and collecting the two gases in a single vessel ; the mixed gases are then introduced as directed into the (J "tube. On causing the two gases to combine, it is necessary, in order to ascertain whether any con- traction of volume takes place, to keep the water formed in the vaporous state ; to effect this we have to surround the sealed limb with a vapour, which in its liquid state has a boiling-point con- siderably above that of water ; amylic alcohol is the liquid employed for this purpose, it boils at a temperature of 132° C, To be able to surround Fig. 68. Fig. 69. 238 Fundamental Principles oe Chemistry Ihe limb with the vapour, we have to enclose it in a high glass cylinder d (fig. 70), the lower mouth of which is fastened around it by means of a perforated cork, whilst its upper mouth (likewise closed by a cork) rises about five centimetres above the sealed extremity. The glass tube e is con- nected with a tube from the flask con- taining the amylic alcohol ; the vapour of the alcohol, after protracted ebullition of the liquid, passes into the annular space and raises the temperature of the gases in the sealed limb to 132° ; this increase of temperature causes them to expand. The mercury must be kept at a ttniform level in both limbs, either by adding or withdrawing a portion of the metal, the latter by the stopcock b. When the gaseous mixture ceases to expand, the height is marked by slipping a caout- • chouc ring over the outer glass cylinder ; a little more mercury, say an inch, is then poured into the outer limb of the U -tube, which is then tightly closed by a cork. A spark is now passed from the induction coil [this part of the apparatus is not shown in the fig.] by the wires — and -I- . After the explo- sion the cork is removed from the open limb, and the mercury levelled in the two limbs, when the volume of steam will be found to be just two-thirds of the volume of the gaseous mixture be- fore the explosion, if the experiment has been correctly made. On cooling down, the steam condenses, and the mercury, with the exception of the small space the water occupies, entirely fills the closed limb of the IJ-tube. To prevent the alcohol vapour from escaping into the atmosphere, the lower extremity of the glass cylinder is con- nected, by means of the glass tube g, with the condenser h ; the worm of the condenser being surrounded with cold water. The tube conveying the alcohol vapour into the glass cyhndei is jacketed with caoutchouc to prevent loss of heat. 527- By the next experiment we learn the proportions by volume in which nitrogen and hydrogen combine to form the gaseous compound ammonia (.NHj), and the amount of con- densation that takes place on their union. The compound is best prepared by mixing one part of ammonium chloride in powder with two parts of slaked lime, and heating the mixed mass in a flask to which a bent tube is connected, and with Fig. 70. Combination by Volume 239 that a drying tube containing unslaked lime ; to the other end of the drying tube a bent tube is attached, to convey the gaseous compound into the eudiometer. 402. 100 cubic centimetres of ammonia are passed into a eudiometer tube (fig. 47). Electric sparks, furnished by an induction coil, are passed through the gas by means of the platinum wires as long as any increase in the volume of the gaseous mixture takes place, as the ammonia is decom- posed by the electric spark. After allowing the gases to cool, the volume is measured, and it is found that the gaseous mixture just measures double the volume the gaseous ammonia measured. We have learned, then, that two volumes of ammonia furnish, on decomposition, four volumes of its constituents ; but we have yet to learn what is the volume-proportion of the two gases. We add for this purpose to the 200 c.c. of the mixed gases 100 c.c. of oxygen. We then explode by the electric spark, and only the hydrogen under these conditions unites with the oxygen ; after allowing time for the gases to return to the temperature of the air, we observe the volume, and we find that it only measures 75 '^■'^- > there has, therefore, been a contraction of 225 c.c. ; two-thirds of this, viz. 150 c.c, represents the amount of hydrogen in the 200 c. c. of the mixed gases ; consequently, there was present 50 c. c. of nitrogen in the 200 c. c. The two gases, there- fore, combine to form ammonia in the proportion of three volumes of hydrogen to one of nitrogen ; and on their union there is a condensation to two volumes. 528. By the next experiment we shall learn the volume- proportion of one of the constituents of the compound methane, or marsh-gas as it is frequently called, because it is produced in the decomposition of vegetable matter under water, and is given off when the mud at the bottom of stagnant pools is stirred : it also constitutes the 'fire-damp' of coal mines. Methane, CH4, is a compound, as shown by the symbol, of carbon (one of the elements which has never been volatilised, although this and many of its other compounds are gaseous bodies), and of hydrogen. This hydrogen compound differs from the three preceding ones, viz., HCl, HjO, ' and H3N, that whereas both constituents of these are gaseous, in this fourth one the hydrogen is united with a body which is not only solid at common temperatures, but incapable of volatilisa- tion by any, the intensest, means at our present command. Hence, while the first three compounds illustrated, with an admirable symmetry, and in an unbroken ascending scale, the laws of combination and progressive condensation, by volume as well as by weight, the fourth exemphfies volume-combination and condensation only so far as its gaseous ingredient is con- cerned ; our positive knowledge, as to its solid constituent 240 FUNDAMENTAI. PRINCIPLES OF CHEMISTRY extending only to the weight-x^'ixo, and any views we may entertain as to the volume-xdiio of this element being of necessity speculative. It is indeed, maintained by many chemists, and not without some show of reason, that analogy affords a fair basis for such speculation ; but not until carbon shall have been actually volatilised, and its vapour actually weighed, shall we be entitled to rank marsh-gas, with respect to its volumetric con- stitution, on the same certain footing as experiment already assigns to hydrochloric acid, water, and ammonia.' 403. To prepare marsh gas, mix very intimately one part of sodium acetate with four parts of soda lime ; both chemicals can be obtained of the operative chemist. Place the mixture in a flask of glass (or better of copper or iron), arranged for gas-disengagement ; then heat the flask to the point at which the gas begins to be evolved. It is ei^ht times heavier than hydrogen ; hence, taking the unit-volume of hydrogen as one, two volumes of the gas weigh sixteen. The experiment for ascertaining how much hydrogen is present in two volumes of the gas is performed in the (J -tube, fig. 70 ; it is decomposed by causing a spark current of the induction coil to traverse the wires in the tube. The decomposition proceeds rapidly at first, but afterwards more slowly, so that a considerable time is required to bring the operation to a close. The volume of hydrogen, when the experiment is complete, ought to be double the volume of the marsh-gas operated upon, but on allowing the mercury to run out at the tap till it has become level in the two limbs of the tube it will not be found, even in the most successful experiment, to be quite double the volume, owing to a minute portion of the methane escaping decomposition. The experiment teaches us that there are four volumes of hydrogen in two volumes of methane, and two volumes of this carbon compound weigh sixteen, and as four volumes of hydrogen weigh four, the amount of carbon by weight in two volumes is, of course, twelve. 529. We will give one exercise, and in this one the student will have to explain each step in the experiment after the teacher has made it ; and he must further state the proportions by volume in which the two elements combine, and what con- densation, if any, takes place on their union. 404. The gaseous compound selected is one of the oxides of nitrogen ; from the effects it produces when respired in small quantities it is known under the name of laughing gas. It is prepared by heating, gently at first, ammonium nitrate, previously dried in a flask to which a delivery tube is attached, and collecting the gas over mercury or warm water. 100 c.c. of the gas are collected in the eudiometer tube, fig. 47; 150 c.c. of hydrogen are then added, and the mixture is exploded by the electric spark. After the gaseous substance which remains has cooled down to the surrounding temperature, it is found to measure 150 c.c. ; loocc. has therefore disappeared. We are unable as yet to deduce the composition of the oxide of nitrogen gas ; and the student must state the Law of Volumes 241 reason why we cannot. We have, on this account, to add oxygen and ex plode again — say we add 50 c. c. of oxygen. After the explosion and the gas has cooled down, there remains only 125 c.c. ; 75 c.c. have therefore disappeared. How many c.c. of oxygen, and how many c.c. of nitrogen combined to form 100 c.c. of the compound gas ? 530. Having made the student acquainted with the fact that substances combine in certain definite proportions by weight, and that if they are brought together in proportions different to those in which they will unite they nevertheless combine together in their natural proportions, the only difference being that the excess quantity of one or more of the substances remains uncombined, he will of course infer that this must extend to volume-combinations — that is to say, if we bring two gases together in volume-proportions different from those in which they will combine, they will nevertheless unite in their natural proportions, the excess volume of the one remaining uncombined ; thus if we brought hydrogen and chlorine together in the proportion of one volume of the former ele- ment to two volumes of the latter element, and made them combine, one volume of H would combine with one volume of CI, one volume of the latter element remaining uncombined. 531. We have learned that the weight of a compound is the sum of the weight of its constituents, there has been no addi- tion or diminution of weight ; and we have also learned that the volume of a gaseous compound is not always the sum of the volume of its constituents, for that only occurs when gases com- bine in e^z^fl/ volumes; when they combine in unequal volumes, the compound always occupies a less volume, never a larger one, than the sum of the volume of its constituents. 532. From the facts demonstrated by the experiments on the volumetric combination of gases, and from similar facts, the following conclusions have been drawn. 1. There is a sijnple relation between the volume of gases which combine. 2. There is a simple relation between the sum of the combine ing gases and the volume of the gas resulting from the combi- nation. This law is termed, from its discoverer, Gay-Lussac's laiv of volumes. 533- We have now to direct the student's attention to R 242 FUMDAMENTAL PRINCIPLES OF CHEMISTRY molecules and atoms. We have already stated that a molecule i s the smallest mass of matter that is mechanically indivisible, but chemically divisible ; an atom is the smallest mass, for it is both chemically as well as tnechanically indivisible ; there are therefore, the student must remember, no half-atoms. No smaller mass of matter than an atom can exist, and it only exists in a chemical compound, not in afree state ; a molecule being the smallest mass that exists in the free state. 534- ^'s have learned that the same variations of tempera- ture and pressure produce in all gases the same changes in volume ; from this Avogadro in 1811 deduced the law that equal volutnes of all gases at the same temperature and pressure contain an equal number of molecules ; this law is now one of the chief foundations of modern chemistry. 535- Molecules, as well as atoms, are invisible. We gave, in par. 9, Sir W. Thomson's illustration of the size of a molecule. Although a molecule of any substance is invisible, we can ascertain the relative weight of a molecule of any gaseous or vapori sable substance, as we shall show presently ; and we can chemically divide it, by decomposing it into its constitutents. 536. That the molecule of a compound, although mechani- cally indivisible, is a larger mass of matter than the portions of matter of the different elements of which it is composed will be obvious to all my student-readers ; these smaller portions of matter we term atoms. The word atom is derived from two Greek words signifying a particle of matter so minute as to admit of no division. 537. That the molecules of compounds composed of dissi- tnilar elements are formed out of a combination of the atoms of the elements composing them is self-evident ; but the question naturally arises. Are the atoms of the elements them- selves in the free state united, or do they exist singly ; in other words, is a mass of any element an agglomeration of the mole- cules of that element or of its atoms ? In answering this question, we will commence by informing the student that it is only of recent date that chemists have called the smallest mass of an element in the free state a molecule. It was formerly termed an atom, as well as the smallest mass which is chemically indivisible. It was also formerly considered that Molecules and Atoms 243 only dissimilar elements could unite together ; now, it is ad- mitted that the atoms of the same element can chemically unite with each other ; and that the homogeneous atoms, in some cases, are united by a stronger affinity than are the heteroge- neous atoms of some compounds. ' For example, the molecule of nitrogen is a much more stable compound of the two atoms of the element than the compounds of nitrogen with oxygen, or with hydrogen or chlorine.' We shall adduce chemical evidence in proof that the atoms of the elements are, as a rule, united together in the free state in the last chapter ; but here we will call the attention of the student to the fact that the mole- cules of the same substance, whether composed of dissimilar or similar elements, never exercise chemical action upon one another. 538. It is now believed, as has been implied, that the ele- ments are, as a rule, united in pairs ; thus the molecule of hydro- gen is composed of two atoms of that element ; it is therefore symbolically represented thus, HH or Hg, whilst the atom is represented by only one H : these symbols not only signify the molecule and atom, but they also represent the weight of the molecule and atom of the element, the molecular weight being double the atomic weight ; and we take, as we have already learned, the hydrogen atom as the unit of the atomic weights of the elements. 539. The molecule bf hydrogen, of oxygen, of chlorine, of nitrogen, and of some of the other elements, as is shown in the following table, is composed of two atoms of the element ; the symbols of their molecules are therefore represented as follows. HH or Hj, 00 or O2, ClCl or Clj, NN or N.^, and of course the molecule of these elements occupies double the volume the atom occupies. And the specific gravity of their molecules is double the sp. gr. of their atoms ; when the molecular weight of the element is twice that of its atomic weight, the molecule is diatomic, that is composed of two atoms ; and in a notation devised by Dr. Hofmann one volume of the element is repre- sented by a square, and the molecule by a double square, as shown in the following table. 540. The number of atoms in a molecule of an elementary body can be found by dividing the molecular weight, as deduced 244 FUNDAIilENrAL PRINCIPLES OF ChEMISTPY 9 E ^ ^ ^^^ bill ffi y pq K u K _ O " O m CO N t3 U ■an {/I tn « ^1 ^£^^^^0HHESE[^ dK Em II 8w o \0 iJ~t K U P3 -' O N T3 bo o S 3 Di 3 o rt O a, % Oh cU bo 1) > c ^H OJ ■a 2 'a ■■3 o. W u « O ID &. o rt o. 3 > g ^ O 3 > 3 (J •vj u S o o, rt > O tn CX -^ .y Volume of Atoms and Molecules 245 from the vapour density by the atomic weight. The student will see from the table, and he can, as we have just described, also ascertain it for himself by a simple division sum, that the number of atoms in the molecules of the different gaseous and vaporis- able elements are not the same in all cases ; the molecular weights of the vapours of mercury, of cadmium, and of zinc are the same as their atomic weights ; their molecules are therefore inonatomic ; their atoms consequently occupy double the volume the atom of hydrogen occupies ; their atoms as well as their molecules are represented, therefore, according to Hofmann's notation by a double square, and the symbols for their mole- cules are the same as for their atoms. An atom of phosphorus and an atom of arsenic, on the other hand, occupy only half the. volume that an atom of hydrogen occupies ; their molecules are tetraatomic, and are represented symbolically thus :— PPPP or P4, AsAsAsAs or AS4 ; and the atomic volumes of these elements are represented by triangles in Hofmann's notation. Chemists are unable at present to explain why these five ele- ments differ from the other gaseous and vaporisable elements in their atomic volumes ; we shall find, however, as we proceed, that their volatile compounds follow the same law as regards their densities as other volatile compounds. 541. The specific gravities and atomic weights of the gaseous and vaporisable elements, whose molecules are diatomic, are the same. They all contain in the same volume, under like conditions of temperature and pressure, the same number of atoms ; and therefore their combining volumes are equal ; that is to say, when any two of these elements combine together in equal atomic proportions they combine together in equal volumes : the formation of hydro- chloric acid is an example of this. When they combine in the proportions of two atoms of one element to one atom of the other, they combine in the same proportions by volume : the formation of water is an example of this. When they combine in the proportion of three atoms of one element to one of the other, they combine in the same volume-pro- portions. We have seen experimentally that the formation of ammonia by the direct combination of its elements is an illustration of this, &c. 246 Fundamental Principles of Chemistry 542. The numbers expressing the specific gravities of the elements whose molecules are monotomic are half those which express their atomic weights ; and their combining volumes are, of course, double those of the diatomic elements. The numbers expressing the sp. gr. of phosphorus and arsenic are double those which express their atomic weights, and their combining volumes are only half those of the diatomic elements in the gaseous state. 543. The temperature at which the vapour density is taken affects the atomic structure of sulphur, and perhaps that of some of the other elements which are solid at ordinary tem- peratures ; this element, sulphur, is hexatomic at 524° C; this atomic structure breaks up into three diatomic molecules at 860° C. 544. We have now to modify some of our previous state- ments ; for we have learned that the atom and the molecule of zinc, of mercury, and of cadmium are the same in weight and volume ; therefore, if we term the least indivisible particle of these elements in its free state a molecule, in these cases then a molecule is not chemically divisible. We have also learned that equal volumes of the gaseous elements, measured at the same temperature and pressure, do not in all cases contain an equal number of atoms ; but, as far as we know at present, equal volumes contain an equal number ot molecules, if we call the indivisible particles of the three elements, we have just named, molecules. 545. The molecules of all compound bodies in the gaseous state occupy, with very few exceptions,' two volumes, in other words twice the volume an atom of hydrogen occupies, no matter what may be the number of atoms or volumes which enter into the compound. 546. We must now direct the student's attention to the standard units of measurement of gases and vaporisable sub- stances whether elementary or compound. The standard most 1 Many of the exceptions have been satisfactorily accounted for, inasmuch as the compounds that were supposed to be exceptions were found to decompose, when heated, into two simpler compounds, and a molecule of each of these two compounds occupied two volumes. So that at the temperature at which their density was taken, the experimenter was operating on two molecules and not Hydrogen Litre-Weight or Crith 247 generally adopted in scientific treatises is that proposed by Dr. Hofmann ; we cannot therefore do better than quote his own description of it : — 547- Dr. Hofmann selected i cubic decimetre (i litre) of hydrogen at 0° C, and at a pressure of 760 milimetres of mercury, as the unit of volume, and the weight of this measure of pure hydrogen as the unit of weight ' The actual weight of this cube of hydrogen, at the stan- dard temperature and pressure mentioned, is o'o896 gramme, a figure which I earnestly beg you to inscribe, as with a sharp graving-tool, upon your memory. There is probably no figure in chemical science more important than this one to be borne in mind, and to be kept ever in readiness for use in calculation at a moment's notice. For this litre- weight of hydrogen, = 0-0896 gramme (I purposely repeat it), is the standard multiple, or coefficient, by means of which the weight of I litre of any other gas, simple or compound, is computed. Again, therefore, I say — Do not let slip this figure — 0-0896 gramme. So important, indeed, is this stan- dard weight-unit that some name — the simpler and briefer the better — is needed to denote it. For this purpose I venture to suggest the term crith, derived from the Greek word Kpi^i), signifying a barleycorn, and figuratively employed to imply a small weight. The weight of i litre of hydrogen being called I crith, the volume-weight of other gases, referred to hydrogen as a standard, may be expressed in terms of this unit. 548. ' For example, the relative volume-weight of chlorine being 35 "5, that of oxygen 16, that of nitrogen 14, the actual weight of I litre of each of these elementary gases, at 0° C, and o-76m. pressure, may be called respectively 35-5 criths, 16 criths, and 14 criths. 549. 'So, again, with reference to the compound gases, the relative volume-weight of each is equal to half the weight of its product-volume. Hydrochloric acid (HCl), for example, consists of I vol. of hydrogen + i vol. of chlorine = 2 volumes or by weight i -h3S'S =36'S units ; whence it follows that the relative volume-weight of hydrochloric acid gas is ?— 5. = 18-25 units, which last figure, therefore expresses the number of criths 248 Fundamental Principles of Chemistry which I litre of hydrochloric acid gas weighs at 0° C. tem- perature and 0-7601. pressure ; and the crith being (as I trust you already bear in mind) 0-0896 gramme, we have 18-25 x 0-0896 = 1-6352 as the actual weight in grammes of one litre of h ydrochloric acid gas. 550. ' So, once more, as the product- volume of water-gas (H2O), taken at the above temperature and pressure, con- tains two vols, of hydrogen -f i vol. of oxygen, and therefore t8 weighs 2 -I- 16= 18 units, the single volume of water-gas weighs — = 9 units ; or substituting, as before, the concrete for the abstract value, i litre of water-gas weighs 9 criths, that is to say, 9 X 0-0896 gramme=o-8o64 gramme. 551. ' In like manner the product-volume of sulphuretted hydrogen (HjS) = 2 litres of hydrogen, weighing 2 criths + i litre of sulphur-gas, weighing 32 criths, together 2 -1-32=. 34 criths, which divided by 2 gives 5ir = 17 criths =17 x 0-0896 2 gramme= 1-5232 gramme=the weight of i litre of sulphuretted hydrogen at standard temperature and pressure. 552. ' And so, lastly, of ammonia (H3N ) : it contains in 2 litres 3 litres of hydrogen, weighing 3 criths, and i litre of nitrogen, weighing 14 criths ; its total product volume- weight is therefore 3-1-14=17 criths, and its single volume or litre- weight is consequently —= 8-5 criths= 8-5 x 0-0896 gramme =0-7616 gramme. 553. ' Thus, by aid of the hydrogen litre-weight or crith= 0-0896 gramme, employed as a common multiple, the actual or concrete weight of one litre of any gas, simple or compound, at standard temperature and pressure, may be deduced from the mere abstract figure expressing its volume-weight relatively to hydrogen. 554- ' From this knowledge, the weight of one litre of any gas, simple or compound, at any other than standard tempera- ture or pressure, or under any variation both of standard tem- perature and pressure, may be deduced by the application of the formulae devised by physicists to express the laws of ex- pansion and contraction for gases under varying conditions of temperature and pressure. Value of this Standard 249 555- ' This fact is of great value, as enabling us to include in common and comparable forms of expression the gas volume- weights of bodies that are not, as well as of those that are, gases at 0° C. Bodies which are liquid, or even solid, under this standard physical condition, have only to be weighed at the temperature, however elevated, at which they do assume the gaseous form, and from the weight of one litre under this physical condition the weight which one litre would assume at the standard tem- perature, could it remain gaseous thereunder, is deducible by computation.' 556. Formerly the densities of gases and vapours were always referred to air as unity, and this standard is not abandoned, but hydrogen is also now adopted as a standard ; the student has therefore to be taught how to ascertain the sp. gr. of a gas on the air standard from its sp- gr. on the hydrogen standard, and vice versa. We have learned that the weight of a litre of any gas or vapour is identical with its sp. gr., hydrogen being taken as unity : knowing this number it is easy to calculate the sp. gr. of the gas, air being taken as unity. For as the sp. gr. of hydrogen is o'o693, air = i, it is only necessary to multiply the sp. gr. of the gas by 0*0693. Examples : — The sp. gr of oxygen compared with air is r6 x 0-0693 = i'io88. The sp. gr. of hydrochloric acid is 18-25 ^ o'o693 = 1-264725. To compare the densities of gases, air having been taken as the unitj with their densities hydrogen being the standard, we have simply to multiply the density by the air standard by 14-44, ^ir being 14-44 times heavier than hydrogen, to ascertain the density, hydrogen = i. Thus to reverse the former examples : if we multiply the density I -1088 of oxygen, taking air as unity, by 14-44 we obtain 16 as the density, hydrogen =1 : and if we multiply 1-264725, the sp. gr. of HCl, air = i, by i4'44, we get almost the identical number 18-25, which is the sp. gr. of HCl, H = i. 557. As equal volumes of all gases contain, according to Avogadro's law, equal numbers of molecules, their molecular weights are double their specific gravities, the specific gravity of an atom of hydrogen being taken as unity : the molecular weight of hydrogen, for example, is double the weight of the sp. gr. of its atom, as shown in the table. To find the molecular weight of a gas whose sp. gr. has been referred to that of 250 Fundamental Principles of Chemistry air as unity, we must multiply its sp. gr. by 28'88, and not by i4'44, as the latter number only gives us half the molecular weight, as shown in the hydrochloric acid example. 558. We must now notice the unit volume adopted by Dr, Williamson, and that adopted by Professor Wanklyn. 559. The absolute volume Dr. Williamson adopts is, in round numbers, 11 '2 litres, 'which is the bulk of one gramme of hydrogen, of sixteen grammes of oxygen, of fourteen grammes of nitrogen, &c., at the normal temperature and pressure : in fact the bulk of that quantity of any one of those gases which weigh as many grammes as there are units in the number ex- pressing its atomic weight.' 560. It is desirable, for many practical purposes, to adopt in this country an English measure for the unit volume of gases. Professor Wanklyn adopts one cubic foot as the unit, because the English system of weights and measures admits then of being decimalised just as well as the French system. 561. A cubic foot of water weighs 1,000 ounces : and that is the weight of six and a quarter gallons of water. A litre of water weighs, as we have learned, 1,000 grammes ; and a cubic decimetre = one litre of hydrogen at 0° C., and at a pressure of 760 millimetres, weighs o'oSge gramme : one cubic foot of hydrogen weighs, of course, at the same temperature and pres- sure 0-0896 ounces. According to Wanklyn's system, a cubic foot corresponds to a litre, a fluid ounce to a cubic centimetre, and an ounce to a gramme. Exercises on volume-weights atid volume-combinations. 405. What is the weight of 200 cubic inches of o-xygen ? ' 406. How many cubic inches will 100 grains of nitrogen occupy? 407. How many cubic centimetres will 1 00 grammes of chlorine occupy ? 408. What is the weight of 100 cubic centimetres of bromine vapour?. 409. A certain volume of oxygen weighs 100 grammes ; what is that volume ? And what would be the weight of the same volume of nitrogen ? 410. If a mixture of 50 cubic centimetres of hydrogen and 20 cubic centimetres of oxygen at the temperature of 132° C. is exploded, what will be the volume of gas left at that temperature ? And what will it consist of? ' In these and all other exercises involving the volumes of gases and vapours, if no particular temperature and pressure is stated, the student must iinderstand that it is the standard temperature, o° C. , and the standard pressure, 760 millimetres, which is intended. Multiple Proportions 251 411. I wish to burn l,ooo cubic centimetres of hydrogen in oxygen ; how much by weight and vohime of oxygen would be required ? 412. What volume of iodine vapour would be required to unite with one cubic inch of hydrogen to form hydriodic acid (HI) ? And what volume would the HI occupy ? 413. What volume of sulphur vapour would be required to unite with two cubic centimetres of hydrogen to form hydrosulphuric acid (H^S) ? And what would be the volume of the H^S produced ? 414. What volume of phosphorus vapour would be required to unite with three cubic centimetres of hydrogen to form phosphuretted hydrogen (H3P) ? And what would be the volume of the H,P produced? 415. What is the specific gravity of nitrogen taking air as unity? 416. The sp. gr. of iodine vapour is 87884, air= i ; what is its sp. gr., H= I? 417. When the atomic and molecular weight of an element are equal, how many atoms are there in a molecule ? 418. If the sp. gr. of N be 0-97, and that of H be 0-069, fi°^•3 13 d pN J-" U,A ^■y H.H .y^ C (3 g C C cncfi S<1 W 12; J 5.< ° a 3 c ■ o "I o o g «j _ 3 „ " ■ d ~-'-.3 " O T^ 4J 55 rrt o s'H^ ° 3 ° S F! .3 o ° S _,.S.3 c-3 fl.3 S g S. § =i 3 a .3 C ° sS?aS-3«.gd^.2 << 3 sot" O -rt 3 )-< M n 3 3 § O o 5 u u B oj V d J o'S orS o a o '3 g S g o a S "B ^ 'C •^ .iS '(- ^ 3 266 Fundamental Principles of Chemistry in the table, are really alike ; the only difference being that in the latter case the formula of the hydroxyl is placed in a bracket, and the number of molecules is indicated by a figure after the bracket. It is immaterial which plan the student follows. 588. The bases, both anhydrous and hydrated, are usually divided into the four following orders, viz., alkalies, alkaline earths, earths, and the oxides of the heavy metals. 589. The Arabians introduced the term alkali vaio chemistry; they discovered a substance possessing certain properties in the ashes of plants called kali, and to this substance they gave the name alkali by prefixing the Arabic definite article Al to the word kali. The alkalies given in the table are potash, soda, lithia, and ammonia ; there are some other alkalies besides these, but they are the oxides of some of the rare metals, and therefore they are not given in the list, 590. Potash and soda were, when first discovered, con- founded together ; the ammonium base resembling them very much in properties was likewise termed an alkali. The ammonium alkali being volatile was called the volatile alkali ; and potash and soda not being volatile were called the fixed alkalies. The ammonium base was also termed the animal alkali, being derived from animal matter ; whilst soda was the mineral alkali, being derived from rock salk, or the ocean ; and potash received the name of the vegetable alkali, from its only known source at that time being the ashes of plants growing upon land. 591. The alkaUes are very much more soluble in water than the next class of bases ; but they vary in solubility, lithia and its carbonate being more insoluble in water than the other three alkalies and their carbonates. The great solubility of the alkalies in water in comparison with the other bases is one of their distinctions ; they restore the blue colour of reddened litmus ; they turn the yellow of turmeric brown ; and they neutralise the strongest acids. The metals of the alkalies are termed alkaline metals, and NH4, as it has the same functions as a metal, is called the compound metal ; it is as yet a hypothetical compound, for it has not been isolated. 592. Baryta, strontia, lime, and magnesia are termed alkaline earths : they are far less soluble in water than the Basic Bodies 267 alkalies ; magnesia indeed being only very slightly soluble in water. They react faintly alkaline, that is to say they react on reddened litmus paper, and on the colour of turmeric like the alkalies, but more faintly ; and they neutralise acids. They are distinguished from the alkalies by their carbonates being insoluble in water. Their metals are called the metals of the alkaline earths. 593. The only oxide we have given in the list belonging to the order of earths is alumina ; the other oxides belonging to this order are the oxides of some of the rare metals ; they do not, therefore, come within the scope of this work. The other earths, as well as alumina, are insoluble in water, and have therefore no action on reddened litmus or on the colour of turmeric. 594. The remaining basic oxides in the list are sometimes termed the oxides of the heavy metals ; many of them are coloured, and are easily fusible or volatile ; they may be said to be insoluble in water, although some of them exhibit a certain degree of solubility in that liquid, alkaline reaction, and metallic taste. Their afiSnity for acids is in some cases greater, in others less, than that of the earths. A few of them, as the auric and platinic oxides, have almost equal claims to be classed as acids, as they combine with strong bases. 595. The heaviest metals of this class of oxides are calle d noble metals, as mercury, silver, gold, platinum, and some o f the rare metals. As regards the term heavy applied to metals , we may observe, it was universally believed at the commence - ment of the present century that every metal must possess a comparatively high sp. gr. — that is, must be considerably heavier than water. But on the discovery of potassium and sodium this view was found to be incorrect, as they are lighter than water. And lithium, which was isolated later, is the lightest known solid. 596. We requested the student to commit to memory the names and formulae of the anhydrous and hydrated bases, not only for the reason that they are a most important class of compounds, and are therefore being constantly met with and alluded to in chemical writings ; but also because they are the types of the composition of the basic sulphides, selenides, and 268 Fundamental Principles of Chemistry tellurides. As selenium and tellurium belong to the class of rare elements, we will not further allude to their combinations with the metals ; we shall confine our remarks to the sul- phides. The sulphides correspond in composition to the oxides, sulphur in its diatomic state occupying in the sulphides the place of the oxygen in the oxides ; but it must be observed that some oxides are known to which no corresponding sul- phides have, as yet, been obtained, and there are some sul- phides known to which no corresponding oxides have been obtained ; but these exceptions do not apply to the list of oxides we have given ; for every given oxide in the list there is a corresponding sulphide ; the student knowing, therefore, the formula for potassium oxide (KjO) can at once write out the formula for potassium sulphide (K2S). The soluble basic sulphides have an alkaline reaction. The sulphides of the alkaline, and alkaline-earth, metals are soluble in water, but calcium and magnesium sulphides are only sparingly soluble in that liquid. 597- There are also sulphur compounds corresponding to the hydrated bases ; these compounds have been termed sulph- hydrates, thiohydrates, hydrosulphides, or hydric sulphides. We shall employ the term hydrosulphide ; therefore, as we name KHO potassium hydrate, we name KHS potassium hydro- sulphide; and as the hydrated bases are sometimes represented as compounds of the metallic oxides and water, so these hydrosulphides are sometimes represented as compounds of the metallic sulphides and hydrogen sulphide (sulphuretted hydrogen), H2S. According to this view potassium hydrosul- phide is represented thus : K2S,H2S. The alkaline, and alkaline earth, metals are the only metals that form these hydro- sulphides, and these hydrosulphides are all soluble in water. Exercises on the Nomenclature and Notation of the Sulphides. 441. Name the following sulphides : (NHj)2S, BaS, Fe^Sj, SnS^, PbS, CaH^S^. 442. Give the formulae of the following sulphides : Magnesium sulphide, Ammonium hydrosulphide, Cupric sulphide, Platinic sulphide, Barium hydrosulphide, Auric sulphide. 598. We can also, from knowing the formulae of the basic oxides, construct the formula of the compounds of the metals FORMULM OF THE ChLORWES, &C. 269 with the monatomic elements, chlorine, bromine, iodine, and fluorine. With the monatomic metals these monatomic non- metals unite atom for atom : thus, the formula for potassium chloride is KCl. With diatomic metals they unite, of course, in the proportion of two atoms to one atom of the metal : therefore, the general formula, say of the chlorides, taking the letter M to stand for any diatomic metal, is MCI2 The general formula for the compounds formed with tetrad metals is MCI4 And the simplest general formula with triad metals is MCI3 and this is the way auric chloride is formulated ; and some chemical writers also formulate ferric chloride, chromic chloride, and aluminium chloride in the same way ; but it is more usual to formulate them thus : Fe2Cl6Cr2,Cl5Al2Cl6 ; because the latter formulae correspond to two volumes of their vapour, whilst the former formulae correspond only to one ; and formulae are now chosen which correspond to two volumes of vapour, if purely chemical considerations are not opposed. Exercises on the Notation and Nomenclature of the Chlorides, Iodides, Bromides, and Fluorides. 443. Name the following compounds : Nal, MgBr.,, SnCl^, Al^Fj. 444. Give the formulae of the following compounds : Ferrous iodide, Nickelous chloride, Platinic chloride, Chromic fluoride. 599. The following are the members of the third class of bases : Ammonia. ...... H5N Phosphuretted hydrogen .... HjP The hydrogen in these bodies can be replaced in part or altogether by metals or compound electro-positive radicals. Example : KHjN (potassic dihydric nitride), K3N (potassic nitride), Cu"3P2 (cupric phosphide). 600. Ammonia combines with acids : but phosphuretted 270 Fundamental Psinciples of Chemistry hydrogen, on account of its weak basic character, has b.6en combined with only two, hydrobromic and hydriodic, acids. There are two other hydrogen compounds which have a close affinity with the two we have just described ; these are arse- nuretted hydrogen (HjAs), and antimonuretted hydrogen (HjSb) ; these two hydrogen compounds have not been com- bined with acids, but when the hydrogen has beep replaced by compound radicals they behave with acids like the similar ■compounds of nitrogen and phosphorus. Nitrine is the new name for ammonia, phosphine for phosphuretted hydrogen, arsine for arsenuretted hydrogen, and stibine for antimonuretted hydrogen. Examination Questions. 445. What are the characteristics of a basic body ? 446. Why is the formula of aluminium chloride notated AljClj and not AICI3 1. 447. Why have the bases that are insoluble, unlike those that are soluble, in water no action on paper stained with turmeric or with reddened litmus ? ' 601. By means of the following table the student will learn not only the bases that are soluble in water ; but which of the bases, insoluble in that liquid, are soluble or insoluble in the fixed alkalies, and in the volatile one. This table is given as we have now to make the student acquainted with methods for obtaining the anhydrous and hydrated bases ; and from the experiments and descriptions he will also become acquainted to some extent with the individual properties of the different bases. 602. The bases which are soluble in water, and not volatile, can be obtained in their anhydrous state in two ways : — i. By burning the metals in dry air or oxygen gas. 2. By decomposing those of their salts the acids of which are volatilised by heat. Nitrates and carbonates are the salts particularly employed for this purpose. KgO and Na^O are prepared by the first method ; LijO, BaO, and SrO are prepared by igniting their nitrates ; CaO and MgO are prepared on a large scale by igniting their carbonates. All my readers must have seen limestone, CaCOa, converted into lime (quicklime) CaO by burning the CaCoj in a lime-kiln. 603. These bases can be obtained in the hydrated states by 1 The rest of the chapter must be passed over for the present ; directions will be given when the student is to study tlie remaining portion. 2/1 Table showing the Solubility or Insolubility of the Basic Oxides and their Hydrates in Water, and the Alkalies. Soluble in water. Names Potassium hydrate (white) Sodium hydrate (white) FORMUL-E KHO NaHO Names Barium hydrate (white) . Strontium hydrate (white) Calcium hydrate (white) FORMUI.-^ BaHaO, SrHaO» CaHaO, The following are insoluble in water : lead, silver , and magnesittm oxides are to a certain extent exceptions, as they dissolve slightly in water. ■ Soliible in avinioriia and the fixed alkalies. Zinc hydrate (white) Insoluble in ammonia and the fixed alkalies.^ Ferric hydrate (reddish brown) Bismuthous hydrate (white) . FeaH^Oa BisOs.HaO Mercurous oxide (black) ) forms no hydrate . ) Mercuric oxide (yellow and ) red) forms no hydrate . f Insoluble in ammonia, soluble in the fixed alkalies. Aluminium hydrate (white) . Stannous hydrate (white) Stannic hydrate (white)_ . Antimonious oxide (white) . Al.HoO, SnHaOa SnH^O^ Sb.Oa Chromic hydrate (bluish \ green). (This oxide is in- I soluble in boiling solutions f of the fixed alkalies') . . J Plumbic hydrate (white). \ (This hydrate is only very [ slightly soluble in the fixed j al^lies) . . . . / ZnHaOa Hg,0 HgO Cr„H„0„ PbH^Oa Soluble in aiuTnonia, insoluble in the fixed alkalies. The presence of ajnm-oniacal salts prevents some of them, front being completely precipitated by the fixed alkalies. Cobaltous hydrate (pale red) . Nickelous hydrate (green) . Argentic oxide (brown) forms 1 no hydrate . . . I Cadmium hydrate (white) . C0H3O3 NiH^Oa Ag,0 CdH^Oa Cupric hydrate (whitish * green). (If the fixed alka- lies are added to cold solu- tions of copper salts, the hydrate is precipitated ; if added to boiling solutions, the anhydrous oxide is pre- cipitated . . .' CuH,0, Insoluble in ammonia and the fixed alkalies, but in the presence of salts of am^nonia the •volatile alkali cannot precipitate them, and the fixed alkalies only do so in part. Magnesium hydrate (white) . Manganese hydrate (white), \ speedily becoming brown by absorbing oxygen from |- the air, and becoming con- verted into a higher oxide ; MgH.O, MnO.HO Ferrous hydrate is of a white \ colour, which, on exposure to the air, finally becomes > red, owing to its being con- verted into ferric hydrate . ] FeH^Oa ' Ammonia does not precipitate from mercurous and mercuric salts the oxides either in the anhydrous or hydrated state, but mercurammonium ja/^j ;_ the fixed alkalies 1 ikewise precipitate these mercurammonium salts, if salts of ammonia are present, but i n the absence of ammonium salts they precipitate the oxides in the anhydrous state. 2/2 Fundamental Principles of Chemistry treating their anhydrides with water : we all know that calcium hydrate, slaked lime, is obtained in this way on a very large scale ; and the union of the two compounds, we also know, is attended with a great evolution of heat. KHO and NaHO are prepared on the large scale by dissolving their carbonates in water, and adding to the solution slaked lime ; the lime removes the CO2 by combining with it, forming insoluble carbonate of lime ; the KHO or NaHO, as the case may be, remains in solution. BaH202 is prepared on a large scale by heating BaCOs in earthenware retorts and passing superheated steam over it ; the following decomposition takes place — BaCOg + H2O = BaHjOa + CO3. MgHaOj can be obtained by adding to a magnesium salt a solution of caustic potash or soda, as shown in the table. 604. The bases soluble, and most of those insoluble, in water, on being set free from their salts in aqueous solutions, combine with one or more molecules of water, the hydrated base being of course formed. 605. The term caustic, when applied to potash and soda, as caustic potash, &c., signifies the hydrates of these bases ; but the term caustic is only applied to baryta, strontia, lime, and magnesia in their anhydrous state. 606. We will direct the student's attention to the fact that anhydrous potash, soda, baryta, and strontia cannot be obtained from their hydrates by heat, as water cannot be expelled from them by simple ignition ; we shall have to call his attention to this fact again presently. 607. The bases insoluble in water can be obtained in their anhydrous state by several methods : — i. Many of the metals of these oxides unite with oxygen at high temperatures ; when the metals are easily volatile they burn with a bright flame in the air or in oxygen. A few metals, such as gold and platinum, cannot be made to unite directly with oxygen eve n at the highest temperatures. The oxides of such metals can, however, be prepared by indirect means. Chlorine attacks all metals, and if the chlorides of these metals, which are not directly oxidisable, be decomposed by an alkali, their oxides are formed, thus : — 2AuCl + 2KOH=Au20 + 2KCI + HjO. Formation op the Basic Bodies 273 2. By decomposing those of their salts the acids of which are volatile, by heat. 3. They are not unfrequently prepared by expelling water from their hydrates by heat. 608. Most of these oxides, as shown in the table, form hydrates ; and they are always obtained in their hydrated state by decomposing some one of their soluble salts when in a state of solution by an alkali or an alkaline earth; an alkali is preferred in the generality of cases to the latter. In the table their solubility or insolubiUty in the fixed alkalies and ammonia is shown. Now if a salt is decomposed by an alkali — volatile or fixed — in which the oxide set free from the salt is soluble, none of the liberated oxide will be dissolved if just sufficient alkali is added to combine with all the acid radical of the salt ; if less of the alkali is added than is sufficient to combine with the whole quantity of the acid radical, then 2^ portion of the salt will remain undecomposed ; but if a larger quantity of the alkali is. added than is necessary to «>;«&«« with the acid radical, then some of the insoluble oxide will be dissolved in the excess quantity of the alkali, and if a sufficient excess is added, the whole of the insoluble base will be dissolved in the excess quantity. 609. Some of the hydrates possess a diiferent colour to what the same oxides do when anhydrous. 610. We have now to consider the third class of bases, especially ammonia or nitrine ; and with nitrine we shall connect ammonium, ammonia (NH4HO), and hydroxalamine (NH3HO). 611. NH4 has not yet been obtained in the free state, but it exists as the basic radical in ammonium salts. It is a monad, and it is thought that if it could be obtained in the free state, it would possess metallic lustre, and the other characteristics of a metal, for it forms an amalgam — an unstable one — with mer- cury, which hasa metallic lustre like all other amalgams. One method of preparing this amalgam is by pouring into a slightly warmed solution of NH4CI an amalgam of potassium or sodium; KCl or NaCl is formed and the ammonium amalgam, which rapidly decomposes into Hg, NH3, and H. If I were teaching a class of students they might very naturally say to me that the 274 Fundamental Principles of Chemistry formation of the ammonium amalgam was satisfactory, as far as it goes, to prove that the radical NH4 exists in the ammonium salts ; but why, as stated by chemists, this radical, if it exists in the ammonium salts, has not been obtained in the free state, like the simple metals to. which it corresponds in functions, would be a very fair question for any student I was teaching directly to ask me. It is a still more pertinent question to ask by those who are only taught by me through the pages of this book, and I feel bound to answer it. In decomposing any ammonium salt by a metal, the NH4,when set free, decom- poses at the moment of liberation into NH3 and H ; pos- sibly hereafter by conducting the decomposition at a lower temperature, or under greater pressure, or under both these conditions, than has yet been done, it may be obtained in the free state. The anhydrous oxide (NH4)20, and the hydrated oxide (NH4HO) have neither of them been obtained in their free state. When a solution of ammonia, which is considered to be a solution of NH4HO, is exposed to the air, NH3 escapes from it, even at common temperatures, and still more rapidly at higher temperatures ; also, when an ammonium salt in solution is decomposed by another base, NH3 is set free and not (NH4)20, thus, (NH4)2S04 + 2KHO=NH3 -h K2SO4 + 2H2O. As NH3 escapes, like HCl, from an aqueous solution at common temperatures, an aqueous solution of ammonia was long con- sidered to be, like a solution of hydrochloric acid gas in water, merely a mechanical solution of NH3, no chemical union taking place between the NH3 and HjO ; especially as the odour and other properties of the solution are the same as those possessed by the gas NH3. But this view is no longer held ; it is now considered that the ammonia solution is a solution of NH4HO. Amongst other reasons for this view, all the four atoms of H in ammonium have been replaced by compound radicals having the same functions as H. Ammonia occurs in small quantities in the air, and it is present in rain water and in fertile soils ; it is formed during the decay of animal and vegetable substances containing nitrogen ; and some organic substances containing nitrogen when boiled in a solution of Formation of the Basic Bodies 275 caustic potash are decomposed, the nitrogen being converted into NH3. We have learned that it is evolved on decomposing ammonium salts by other bases ; and that when it is passed into water, it is dissolved and converted into NH4HO. Hydroxylamine, or Oxyammoniutn, NH3O ; this substance is a base, and combines, like NH3, directly with acids forming crystallisable salts. It is formed by the direct union of H with NO ; it is very volatile, and is easily decomposed, and can be obtained only in solution. Its salts are decomposed by KHO, with evolution of N and formation of NH3. 612. Phosphine. Arsme.— Three compounds of P and H have been formed, but we shall only notice the one having the composition PHg, and we only notice this on account of its basic character. It is a colourless gas, having an odour resem- bling that of garlic ; it is very poisonous ; it is combustible both in air and oxygen. It unites directly with HCl,HBr, and HI, forming compounds analogous to the haloid salts of ammonium, phosphonic bromide, PH4,Br, for example. It can be prepared by several different methods ; one of the easiest is to treat calcium phosphide with water : — Ca3P2 + 6H20=2PH3 + sCaHjOj. Arsine is a colourless gas, and is one of the most poisonous substances known. When exposed to a low red heat, without access of air, it is decomposed into H and As. It has not been combined with acids, but when the hydrogen is replaced by compound radicals, these compounds are basic. It is pro- duced in all cases when nascent hydrogen and arsenic are brought together, especially in acid liquids ; see exercise 717. This conversion of the As in its compounds into AsHj is em- ployed for detecting minute traces of As ; it is called Marsh's test. 613. On account of the basic hydrates being formed by the action of ^water on the anhydrous bases, it was long held by chemists in all countries that they were therefore compounds of water and the metaUic oxides ; but as far back as 1834, the late Mr. John J. Griffin, the well-known manufacturer of scien- tific apparatus, made the following statement with regard to these compounds in a book he published in that year. ' Every 276 Fundamental Principles of Chemistry chemist but myself assumes the hydrates of metallic pro- toxides to consist of metallic protoxides combined with water. They make this assumption even in cases where the hydrates have been exposed, under common atmospheric pressure, to a red heat, without suffering decomposition, or giving off a particle of steam. But my opinion is that the hydrates of the metallic protoxides contain neither protoxides nor water, but are con- stituted of one atom each of metal, oxygen, and hydrogen. This is the ultimate constitution. What the. proximate consti- tution is, I cannot tell. It may be KH + 0, or KO + H, or K + HO ; we have no means of determining which. I rest upon the ultimate constitution.' Some years after Mr. Griffin had published his views, the late eminent French chemist M. Gerhardt published similar views, and employed the same line of argument as Mr. Griffin had done. 614. We will now give a summary of the action which bases exert on salts. 615. When a salt is brought into contact with an addi- tional quantity of the same base which it already contains, no reaction ensues, unless the acid of the salt can forma salt more basic than the original one. If potash be added to a solution of potassium sulphate, and the liquid evaporated, the original sulphate crystallises out unchanged. In other cases, combi- nation ensues : thus, potash added to a solution of potassium disulphate produces the neutral sulphate. 616. If the base added to a saline solution is different from that existing in the salt, the original salt is frequently decom- posed, and a new one formed ; and the decomposition is determined by circumstances analogous to those which cause the reaction of acids on salts. I St. Generally speaking, a soluble salt, in a state of solution, is decomposed, when the reacting base can form an insoluble salt with the acid of the salt. If baryta be added to a solution of potas- sium sulphate, barium sulphate is precipitated, and caustic potash remains in the liquid. Baryta also decomposes potassium carbon- ate in a dilute solution, and barium carbonate is precipitated. ' ^ We have learnt in par. 603 that caustic potash and soda are manufactured from their carbonates by removing the COo by means of slaked lime, the CO3 forming with the lime an insoluble salt. The Action of Acids and Bases on Salts 277 The state of concentration of the liquids exerts great influ- ence over these decompositions ; for, if barium carbonate is boiled with a concentrated solution of caustic potash, a consi- derable quantity of carbon dioxide is abstracted from it, and potassium carbonate is formed. If the base of the original salt is insoluble it is precipitated, as well as the insoluble salt which has been formed by the union of the base which was added with the acid in the salt employed. 2nd. A soluble salt containing an insoluble base is decom- posed on adding to its solution a soluble base. The soluble base decomposes the salt by taking away the acid oxide from the insoluble base ; the latter — viz., the insoluble base — being set free will consequently precipitate, on account of its insolubility in the liquid. The bases, when set free in this manner, combine, with one or two exceptions, with water ; this compound of the base and water is termed the hydrate of the base, whatever base it may be. a. Some of the insoluble bases are soluble in solutions of the soluble bases, as shown in the table, and we here add a few examples : — Oxide of zinc is soluble in solutions of the iixed alkalies and ammonia ; ferric oxide is insoluble in the fixed alkalies and ammonia ; alumina is insoluble in ammonia, but soluble in the fixed alkalies ; cupric oxide is insoluble in the fixed alkalies, but soluble in ammonia ; magnesia is insoluble in ammonia and the fixed alkalies, but the volatile alkali cannot . precipitate it from its solutions when salts of ammonia are present, and the fixed alkalies can only do so partly when these salts are present. b. It has already been stated that if, to a solution of any of the soluble salts of the insoluble bases, a soluble base is added, the soluble base will take away the acid from the insoluble base ; the latter (viz., the insoluble base) being set free, will consequently precipitate, on account of its insolubility in the liquid. If a soluble salt of an insoluble base is decomposed by a soluble base, which dissolves that insoluble base, the insoluble base will be completely precipitated if the soluble base is added only in sufficient quantity to take away the acid oxide from the insoluble base ; but if more of the soluble base is added than is necessary to remove the acid oxide from the insoluble base, then in the excess of the soluble base the insoluble base dis- 2/8 Fundamental Principles of Chemistry solves ; as an example, add to a solution of zinc sulphate ammonia, drop by drop, until a precipitate is formed ; if the addition of ammonia is continued after the formation of the precipitate, the precipitate will finally dissolve in the free, that is, in the excess of ammonia. 3rd. An insoluble metallic oxide sometimes decomposes a sail formed by a base equally insoluble. Thus, oxide of silver de- composes nitrate of copper in solution, precipitating oxide of copper ; the decomposition is determined, in this case, only by the preponderating affinity of oxide of silver for nitric acid. 4th. When the base of a salt is volatile, it is generally expelled by a more fixed base, particularly when assisted by heat. Experimental Exercises on the Preparation of the Anhydrous and Hydrated Bases. 448. The experiments ought to be made by each of the students ; and whenever it is not otherwise stated, they ought to conduct the operations in test-tubes. When want of room, or other causes, prevents the student from performing the experiments for themselves, the teacher ought to per- form them. Dissolve the solid substances in water, ' in the proportion of one part by weight of solid to ten parts by weight of water ; and dilute the acids and ammonia '' in the proportion of one of acid or ammonia to four of water, and use these dilute solutions always, unless expressly directed to use the concentrated. Caustic soda and caustic potash can be used in- discriminately ; and they may be used as obtained from the operative chemist's. 449. Mix quicklime and solid ammonium chloride together, and intro- duce the powder into a flask and apply heat ; nitrine will be evolved and calcium chloride formed. This experiment exemplifies the rule stated at par. 616 — 4th. 450. Dissolve one part of potassium carbonate in about ten parts of water. Boil the solution, and then add to it slaked lime (which has been made into a thin paste with water) until the clear solution no longer effervesces on the addition of hydrochloric acid in excess. The lime re- moves CO2, forming with it calcium carbonate, which, on account of its insolubility, precipitates ; K^O is set free, and instantly combines with water, forming caustic potash, which dissolves in the water. This experi- ment may be made in a flask; and exemplifies the rule stated at par. 616— 1st. 451. Add to a solution of sodium sulphate a solution of barium hydrate; barium sulphate will be formed, which, owing to its insolubility, will pre- cipitate, whilst the NajO, on being set free, will combine with water and form the hydrate which will dissolve in the liquid. This experiment exem- plifies the rule stated at par. 616 — 1st. • Distilled water ought to be employed ; but if that cannot be obtained, rain water must be used. ' The word ammonia used here and in the exercises means the solution of NH4HO, and not nitrine. Preparation of the Bases 2^9 452. Add ammonia to a solution of ferric chloride ; a precipitate (Fe^HijOi,) will be formed, which will remain undissolved on the further addition of the alkali. This experiment exemplifies the rule stated at par. 616 — 2nd. 453. Ignite bismuthous nitrate or carbonate in a porcelain crucible, the acid radical will be expelled, and Bi^O, will be left. 454. Add ammonia to a solution of aluminium sulphate (common alum can be employed) ; a precipitate (AljEtjOj) will be formed, which will not be dissolved on the further addition of ammonia (par. 6l6 — 2nd.) 455. To a solution of chromic chloride add a cold solution of caustic soda, until the precipitate which first appears is redissolved, then boil the solution until the hydrate once more precipitates. 456. Ignite some dry nickelous hydrate in ^ porcelain crucible, water will be expelled, and nickelous anhydride left. Observe the difference in colour between the anhydride and the hydrate. 457. To a solution of alum add caustic soda, until the precipitate which first forms is redissolved, then add hydrochloric acid until the solution manifests an acid reaction, and finally ammonia in excess. 458. Add caustic soda to a solution of ferrous sulphate. Boil another portion of the solution of the iron salt with a few drops of nitric acid until it becomes peroxidised, which will be indicated by the solution becoming yellow ; when this is attained, add caustic soda in excess. Observe the difference in colour between the two precipitates. 459. Take three portions of a solution of cupric sulphate ; to one add ammonia until the precipitate, which is first formed, redissolves ; to the second portion add caustic soda in the cold. Boil the third, and add to it caustic soda. 460. Ignite cobaltous hydrate or cobaltous carbonate out of contact with the air ; in either case CoO will be left ; but if either of them is heated in contact with air, CojO^ will be formed. These examples are given to show the student that not in all cases is the anhydride obtained if the hydrate or the carbonate is heated in contact with air (par. 6i6 — 2nd). To a solution of magnesium sulphate add ammonia, which will precipitate a portion of the magnesia as hydrate. To a solution of the same salt add ammonium chloride and then ammonia : in this case the ammonia will not produce a precipitate, as the oxides which are insoluble in ammonia, and yet not precipitated by it in the presence of ammoniacal salts, form with these salts double soluble salts, from which combinations the ammonia cannot precipi- tate them (par. 6i6- and, a).. 46 1. Mixtogethera solution of a ferric salt and a solution of al umin ium sulphate (common alum can be employed), add caustic soda in excess to the mixed solution ; FeaHjOs will be precipitated ; boil and filter. To the filtrate add hydrochloric acid in excess, and lastly ammonia, to precipitate the alumina ; this illustrates one of the modes of separating the insoluble bases from each other, and detecting the different bases. 462. Ignite cobaltous nitrate in a porcelain crucible ; Co^Oj and not CoO will be left. This experiment is given to show the student that not in all cases is the anhydrous protoxide of the metal left on the ignition of nitrates. 463. Dissolve some ammonium sulphate in water, place it in a stoppered retort, then pour into the retort some solution of caustic soda or potash ; after the addition of the alkali and the retort being connected with the con- denser and the receiver in its place, heat is to be applied by means of a gas- lamp or other heat source, and three-fourths of the liquid 'distilled over. 28o Fundamental Principles of Chemistry The distillate will be found to contain, from the smell, ammonia ; and it will of course turn red litmus paper blut, and turn turmeric paper brown. This experiment exemplifies the rule stated at par. 6i6 — 4th. Examination Questions. 464. Give as many methods as you can for obtaining cupric oxide in the anhydrous state. 465. If you add to a soluble salt, the base of which is insoluble in water, a base which forms, with the acid oxide of the salt, a salt insoluble in water, what will be the result ? 466. If you are directed to add to a salt a base in excess, or not in excess; what is meant ? Illustrate your answer by showing, by means of chemical equations, the chemical changes that would take place on adding, and not adding, ammonia in excess to a solution of aluminium sulphate. 467. If I burn one ton of limestone, how much quicklime ought I to obtain ? 468. If I had to decompose I cwt. of NH4CI with CaH^O^, how much of the latter substance must I employ, and how much NHj would be set free? 469. I wish to prepare 10 lbs. of BaO by igniting Ba(N03)2. How much of the nitrate must I employ ? ' CHAPTER XII. CHARACTERISTICS OF AN ACID — ACIDS EITHER MONOBASIC OR POLY- BASIC— A LIST OF ACIDS AND ACID ANHYDRIDES — NOMENCLATURE OF THE ANHYDRIDES AND ACIDS — GRAPHIC NOTATION OF THESE SUBSTANCES — QUESTIONS — THE METHODS FOR PREPARING THE ACIDS AND ANHYDRIDES, WITH A DESCRIPTION OF THEIR PRO- PERTIES—EXERCISES — ACTION OF ACIDS UPON SALTS — EXERCISES — QUESTIONS. 617. Some of the substances belonging to the class of bodies termed acids were known at a very early period ; and the word acid, which is equivalent in ordinary language to sour, indicates one of the properties of the soluble acids, for they have a sour taste. Lavoisier, after he discovered oxygen, found by experiment that several acids contained this newly discovered substance ; he concluded, in consequence, that oxygen was a constituent of all acids, and that it was the acidify- ing principle. According to this view an acid is an oxidised body having a sour taste, reddens blue organic colouring matters — litmus for example — and neutralises alkalies. But ' The student must now pass on to far. 639, Chap, XII. , and complete the study of that chapter. Definition of an Acid Body 281 this definition was shown, some time afterwards, to be too limited, as a large class of bodies became known which possess all the properties of acids, and do not contain oxygen as a constituent. Moreover, there are some bodies which, from their insolubility in water, have no sour taste or action on vegetable colours, yet from their behaviour with bases are regarded as acids ; and some bodies admitted to be acids are even unable to neutralise completely the alkaline re- action of the alkalies. 618. In accordance with the most recent views, an acid may be defined as a compound containing one or more atoms of hydrogen, which become displaced by a metal when the latter is presented to the compound in the form of a basic hydrate ; the compound produced by the metallic substitution is termed a salt. The hydrogen capable of being so displaced may be conveniently termed displaceable hydrogen. 619. Examples of the substitution of a metal for the hydro- gen in acids : ist Example : Substitution of potassium for the hydrogen in hydrochloric acid : HCl -f KHO = KCl -f H2O Hydrochloric Potassium Potassium Water, acid. hydrate. chloride. 2nd Example : Substitution of potassium for the hydrogen in nitric acid : + H2O HN03 + KHO = KNO3 Nitric acid. Potassium nitrate. 3rd Example : Substitution of one atom of potassium for one of the atoms of hydrogen in sulphuric acid : H2SO4 + KHO = KHSO4 + H2O Sulphuric Hydric acid. potassium sulphate. 4th Example : Substitution of two atoms of potassium for the two atoms of hydrogen in sulphuric acid : H2SO4 -)- 2KHO = K2SO4 -t- 2H2O. 620. The student must not conclude that the hydrogen in 282 Fundamental Principles of Chemistry acids can only be displaced by a metal when the latter is pre- sented to the acid in the form of hydrate, for it can also take place when the metal is in the form of a basic anhydride, and it can take place in many cases when the metal is in the metallic state. 621. Examples of the substitution of a metal for the dis- placeable hydrogen, when the metal is in the form of a basic anhydride : Na^O + 2HCI = 2NaCl + HjO 622. Examples of the substitution of a metal for the dis- placeable hydrogen in acids when the metal is in the metallic state : Zn" + H2SO4 = Zn"S04 + Hj. 623. Acids containing one atom of displaceable hydrogen are said to be monobasic ; those containing two atoms of dis- placeable hydrogen are said to be dibasic ; those containing three such atoms are said to be tribasic, &c. Acids of greater basicity than unity are frequently termed polybasic acids. 624. When it became admitted that there were acids that contained no oxygen, they were divided into two groups, viz., oxygen acids and hydrogen acids ; but according to the de- finition just given all distinction is abolished ; but as it will be convenient hereafter to distinguish the acids formerly termed hydrogen acids from those which were termed oxygen acids, we will term the first set acids containing non-oxygenated radicals, and the second set we will term acids containing oxygenated radicals. 625. In the list of oxygen acids, a list of the corresponding acid anhydrides is given. The word anhydride signifies destitute of water, and is applied here to the oxygen compound which remains after the removal of the displaceable hydrogen in com- bination with sufficient oxygen to form water. Examples : (i) 2HNO3 - H2O = N2O5 (2) H,S04 - H2O = SO3 (3) 2H3PO4 - 3H2O = P2O5. 626. The name of the oxygen acids is generally formed by adding ic as the terminal to the name, or to an abbreviation of it, of the element united with the oxygen. And when the same Acids and Acid Anhydrides 283 element forms two acids with oxygen, the one containing the least oxygen terminates in ous, and the other in ic. 627. We have given both the old and new names of the acids containing non-oxygenated radicals ; but we have not given the new and more systematic names of the oxygen acids, as those given are almost universally employed by chemists at the present time. The names in italics are the oldest of the names given, and they are the common names ; and one of them, sulphuretted hydrogen, is still very frequently used in chemical writings. The CN in the formula for hydrogen cyanide represents the composition of the compound radical cyanogen, which can be obtained in its isolated state, and is analogous in its chemical relations to the non-metallic elements, especially chlorine ; thus we learn that some compound radi- cals resemble the non-metals in their chemical relations, whilst others, like ammonium, resemble the metals. CN is scarcely ever employed as the symbol of cyanogen, Cy being employed in place of it. 628. The names and symbols of the following acids, and their anhydrides, must now be committed to memory. List of the more commonly occurring Acids. Acids containing non-oxygenated radicals. Nenv Names. Old Names. Hydrogen chloride. Hydrochloric acid {muriatic acid) . . HCl. Hydrogen bromide. Hydrobromic acid HBr. Hydrogen iodide. Hydriodic acid HI. Hydrogen fluoride. Hydrofluoric acid ..... HF. Hydrogen cyanide. Hydrocyanic acid [p-ussic acid) HCN = HCy . Hydrogen sulphide. Hydrosulphuric acid (sulphuretted hydrogen) HjS . Acids containing oxygenated acid radicals. Nitric acid {aquafortis) HNO3 Chloric acid HCIO3 Sulphurous acid HjSOs ' SuVphxaic 3.ciA {oil of z/itriol) H2SOJ Carbonic acid H^COj' Oxalic acid HjCsO, Chromic acid HjCrO,' Arsenious acid H3ASO, 1 Sulphurous, carbonic, chromic, and arsenious acids have not yet been obtained ; they are supposed to exist in solution, but suffer decomposition when their solutions are evaporated. Sulphurous acid has, however, been recently 284 Fundamental Principles of Chemistry Arsenic acid Tribasic phosphoric acid or orthophosphoric acid . Boric acid or boracic acid ..... Silicic acid ....... Acid anhydrides or acid radicals. Nitric anhydride, nitrogen pentoxide . Chloric anhydride (not yet obtained) Sulphurous anhydride, sulphur dioxide Sulphuric anhydride, sulphur trioxide . Carbonic anhydride, carbon dioxide Oxalic anhydride (not yet obtained) Chromic anhydride, chromium trioxide Arsenous anhydride, arsenic trioxide . . Arsenic anhydride, arsenic pentoxide . Phosphoric anhydride, phosphorous pentoxide Boric or boracic anhydride, boron trioxide . Silicic anhydride (silica) . . HjASO^ H3PO, H3BO3 H^SiO, N,0, so; SO3 CO2 CrO, AS2O3 As,03 PP= B2O3 SiO, 629. The anhydrides or, as they are also termed, acid-forming oxides., were formerly regarded as the acids, and the bodies we now term acids were considered to be compounds of water and these acids : carbonic anhydride is even yet best known under its old name carbonic acid. The oxygen acids are now frequently repre- sented as compounds of the univalent radical hydroxy!, HO, and an oxygenated radical peculiar to each individual acid. Exs. : nitric acidN02(H0), sulphurous acid S0(H0)2, sulphuric acid S02(HO)2, phosphoric acid P0(H0)3 &c. When there are two or three different varieties of an acid, as in the case of phos- phoric and silicic acids, the common one is termed the ortho- acid ; ortho-phosphoric acid means the trihydric phosphate, ortho-silicic acid means the tetrahydric silicate. The different salts of the ortho-acids are also distinguished by the prefix ortho-, as ortho-phosphates, ortho-silicates. 630. Some of the acids, such as sulphurous, carbonic, and chromic acids, are so readily split up, as we have already stated, into their anhydrides and water that they cannot be isolated from their solutions, as they immediately decompose into these sub- stances.^ Other acids, on the contrary, cannot be decomposed obtained in combination with water in the form of cubical crystals on cool- ing a solution of it to 0° C. ; the compound thus obtained has the formula H2SO3, 14H2O. 1 This compound is the white arsenic of the shops. 2 Sulphurous acid in combination with water of crystallisation, we have pointed out in the note on page 283, has recently been obtained. Acids and Acid Anhydrides 285 into their anhydrides and water ; the anhydrides in these cases are obtained from their salts. Some anhydrides, such as chloric and oxalic, are so unstable that they have not been obtained. 631- In some cases there are more than two acids in a series ; the sulphur oxygen acid series for example ; when only two more were known belonging to the series besides those ending in ous and ic, the prefixes hypo and hyper, derived from two Greek words signifying under a.nd above, were, and are to some extent still, employed ; thus the acid H2S2O3 was named hypo- sulphurous acid, because it contained a less quantity of oxygen than sulphurous acid for an equal quantity of sulphur ; in like manner the acid H2S2O5 was named hypo-sulphuric acid. These names are now being replaced by others ; thus, the first is now named thiosulphuric acid, and the other is called dithionic acid ; thio and thion being derived from a Greek word signifying sulphur. The salt, sodium thiosulphite, is largely employed in the arts, and its old name, hyposulphite of soda, is still its commercial name. 632. We have shown by examples in par. 625 the decom- position of the oxygen acids into their anhydrides. In the decomposition of the monobasic and bibasic acids there can only be one stage in the decomposition, as is there shown ; in the case of the monobasic acids we see that two molecules of the acid are required in the decomposition ; and in the case of bibasic acids only one molecule of the acid is required. In the decomposition of tribasic acids there can be three stages : — ist, in which two atoms of acid are required, and one third of the hydrogen in the form of water is removed, a tetra- basic acid remaining. 2nd, in which one atom of the acid is required, and two-thirds of the hydrogen is removed in the form of water, a monobasic acid remaining. 3rd, in which two atoms of acid are required, all the hydrogen being removed in the form of water, the acid anhydride remaining. Examples : — (i) 2H3PO4 — H2O = H4P2O7 Trihydric . Tetrahydric phosphate phosphate. (Pyrophosphoric acid.) (2) H3PO4 — H,0 = HPO3 Monohydric phosphate. (Metaphosphoric acid.) H^O = H^SiOs Dihydric silicate. (Metasilicic acid.) 2H2O = SiOa Silicic anhydride. 286 Fundamental Principles of Chemistry (3) 2H3P04 - 3H2O = P2O5 Phosphoric anhydride. The Student will see that there can be two stages in the decomposition of a tetrabasic acid — ist, in which one-half "Ay^ hydrogen is removed in the form of water, a bibasic acid remain- ing ; 2nd, in which the whole of the hydrogen is removed, the acid anhydride remaining. Examples : — (l) H4Si04 (2) H4Si04 633. Some chemists have abandoned the term anhydride ; in place of this name, they call this class of bodies ' acid-forming oxides.' When they are so termed, the second name given in the list of these bodies is adopted, as nitrogen pentoxide in place of nitric anhydride, &c. 634. All acid anhydrides are more or less quickly converted into the corresponding acids by the action of water or of hydrates. In the dry state, or when dissolved in ether or other liquids which do not change them into acids, they are without action on litmus and other vegetable colours. 635. The attention of the student was directed in the last chapter to the fact that sulphur combines with the metals, and that some of these sulphur compounds are basic. We have now to point out to him that some of these metallic sulphides, and also some non-metallic sulphides, possess the character of acids. 636. The following are all the sulphur compounds possess- ing acid characters that it is necessary to bring under the notice of the student. Thiocarbonic acid or sulphocarbonic acid, H2CS3, and the sulphur compound, CS2, corresponding to carbon dioxide is called carbon disulphide, but it is better known in commerce by its old- name bisulphide of carbon. Arsenic trisulphide, AS2S3 ; arsenic pentasulphide, AsjSs j antimony tri- sulphide, SbjSj ; antimony pentasulphide, Sb.2S,, ; stannous sulphide, SnS ; stannic sulphide, SnSj ; auric sulphide, AujSs ; Acids and Acid Anhydrides 287 platiriic sulphide, PtSj. We shall refer to these sulphides in the next chapter. 637. The anhydrides of the polybasic acids combine with nitrine, forming a peculiar class of acids. Examples : — sulphamic acid, NH3SO3 ; carbamic acid, NH3CO2 ; Oxamic acid, NH3C2O3, &c. 638. We have now to direct the student's attention to the varying atomicity of some of the elements composing these compounds, and first with regard to sulphur. In the table of the elements we represented it as a dyad, and it acts as a dyad in H2S ; as a tetrad in sulphurous acid and its anhydride ; as a hexad in sulphuric acid and its anhydride. These five sulphur compounds may, therefore, be graphically represented thus :— O II (i) H-S— H. (2) 0=S=0. (3) H— O— S^O— H. O O II II (4) 0=S=0 (5) H— O— S— O— H. II o Nitrogen in nitric acid and its anhydride, phosphorus in phosphoric acid and its anhydride, and arsenic in arsenic acid and its anhydride, are pentads. We show by two examples the mode of formulating graphically the compounds of the pentad elements when they contain the dyad element oxygen ; we have already given an example of the mode of formulating them when they only contain monad elements : — o II II II (i) P— O— P (2) H— O— P— O— H II II I o I H Examination Questions. 470. Define the terms base and acid. 471. What is the valency of carbon in carbon monoxide (CO), and nitrogen in nitrogen monoxide (NjO) 1 472. Explain what is meant by the terms monobasic, dibasic, and tri- basic acids, and give examples of each class. 288 Fundamental Principles of Chemistry 473- Give the graphic formulae of arsenous acid, and its anhydride. 474. Give the new names of hyposulphurous and hyposulphuric acids, and their formulse. 475. Give the graphic formula of boracic acid. 476. What is the new name for hyposulphite of soda ? and give its formula.' 639. We will now describe methods for obtaining the acids and acid-forming oxides, and also some of their properties. 640. Hydrogen chloride. Hydrogen bromide. Hydrogen iodide. Hydrogen fluoride. — The first three of these acids are gases, and they are soluble in water ; the fourth is a liquid. Only HCl of these four acids is met with in nature, and it is met with in small quantities only, in certain volcanic gases. HCl is obtained by the action of H2SO4 on NaCl (Ex. 643) and HF by the action of H2SO4 on CaF^. But H2SO4 cannot be usefully employed for the preparation of HBr and HI from their corresponding salts, for on their formation a portion is decomposed by some of the H2SO4 : — H2SO4 + 2HBr=Br2 + 2H2O + SO2. They can be obtained by heating one of their alkaline salts with H3PO4, and they can also be prepared by acting on their phosphides with water. They are very easily prepared in solution by suspending Br or I, as the case may be, and passing H2S through the water, as both Br and I decompose HjS by removing the H and combining with it. HCl in solution is manufactured on a very extensive scale, as the for- mation of Na2S04 from NaCl is the first step in obtaining sodium carbonate and caustic soda from that salt : HCl is employed industrially, but it is more extensively used for the production of CI (Ex. 673), the CI being required in the manu- facture of the well-known bleaching powder, chloride of lime- CI decomposes both HI and HBr by removing the H and combining with it. HI in solution is rapidly decomposed by contact with air, the O removing the H. 641. Hydrocyanic acid. — This acid is a volatile liquid ; it has a strong stupefying odour ; it is present in laurel water, and in the water distilled from the kernels of many stone fruits, such ' The rest of the chapter must ie passed over for the present: the student will ie directed when to return to it. Formation of the Acid Bodies 289 as the plum, the peach, the apricot, &c. Although a valuable medicine in small doses, in larger doses it is one of the most powerful poisons known. It can be prepared from mercuric cyanide (HgCy ) by adding to an aqueous solution of this salt H2SO4 diluted with water, and Fe in the state of filings ; on shaking the mixture and then distilling, HCy distils over : — HgCy2 + Fe + H2S04=2HCy+FeS04 + Hg. Chlorine easily decomposes it. Its compound radical CN is a colourless gas resembling the acid in oddur. C and N do not unite together when heated alone, but they readily unite when K is present ; thus, by passing pure N or air over an ignited mixture of carbon and K2CO3, KCy is formed. 642. Hydrogen sulphide. — This compound is a colourless gas having the odour of rotten eggs : if inhaled it has a poisonous action. It is evolved along with other gases from volcanoes, and is present in sulphur waters, as those of Harrogate. It is generally prepared by acting on metallic sulphides, as FeS, with H2SO4 ; there must be sufificient water present to dissolve the metallic sulphate formed, otherwise the H2SO4 will have little or no action on the sulphide. It burns in air or O with a bluish flame, if sufficient O is present H2O and SO2 are formed, but if there is an insufficient quantity only H2O is formed, S being deposited. It is soluble in HjO, from which it is expelled on boiling the liquid. It is in frequent use in the chemical laboratory for precipitating metals from their solutions as sulphides. 643. Nitric acid. — This is one of the acids that is manu- factured on a large scale ; it was formerly obtained from potas- sium nitrate, saltpetre or nitre, as it is commercially called, by acting upon it with H2SO4 ; but since the discovery of sodium nitrate, or Chili saltpetre, as it is frequently called, in large deposits in the province of Tarapaca on the Peruvian coast, it has been substituted for the nitre, as it is cheaper and yields a larger proportion of HNO3. The acid is a colourless liquid fuming strongly in the air, and absorbs moisture from the air with the greatest avidity. It is powerfully corrosive, cauterising the skin and staining it yellow. The acid of commerce con- tains about 30 per cent, of water, and boils at 120-5° C It is u 290 FuyOAMEMTAL PRINCIPLES OF CHEMISTRY a powerful oxidising agent, and its action upon metals is of a somewhat complicated character, varying not only with different metals, but also, for the same metal, with the strength of the acid employed and the temperature at which the reaction takes place. Nitrates of the metals are formed, but at the same time another portion of the nitric acid is reduced to some lower oxide of nitrogen. All the metals in common use are oxidised by HNO3 with the exception of Au and Pt, but they are not all dissolved ; Sn and Sb are left by the acid in the state of insoluble oxides. We are dwelling on this action of HNO3 on the metals, because the action of this acid on the metals does not conform with the statement previously made that a metal can displace the hydrogen in the hydroxyl of the acid ; in all cases the NO2 is partially or completely broken up and the metallic oxide formed is then converted into the nitrate by the action of some of the undecomposed HNO3. Examples : — (i) Ag20+2HN03=2AgN03 + H20. (2) CuO + 2HN03=Cu2N03 + H20. We will now give three examples of the breaking up of the NO2, or rather, as it should be said, of its deoxidation : — (i) When Ag is dissolved in the cold in an excess of HNO3, nitrous acid (HNO2) is formed : — Ag2 + 3HN03=2 AgN03 + HNO^ + HjO. When copper and other metals are acted upon by the acid of moderate concentration NO is evolved : — 3Cu + 8HN03=3(Cu2N03) + 2NO + 4H2O. With a very concentrated acid NOo is evolved : — Cu + 4HN03=Cu2N03 + 2N02 + 2H20. And when the decomposition occurs at a high temperature free N is usually disengaged in considerable quantities : — SCu + i2HN03=5(Cu2N03) + N2 + 6H20. When Zn or Sn is acted upon by a very concentrated acid, not only is the NOj completely deoxidised, but NH3 is one of the products formed : — 4Zn + 9HN03=4(Zn2N03) + NH3 + 3H2O. Formation of the Acid Bodies 291 644. Nitric anhydride. — This is a white crystalline solid ; it boils with decomposition at about 45° C. It can be prepared by acting on anhydrous HNO3 with P20a : — 2HN03 + P20,,=N205 + 2HP03. It can also be prepared by passing CI over dry silver nitrate. Two reactions occur in its preparation by this method ; ist, a volatile liquid called nitroxyl chloride, NO2CI, is formed ; 2nd, this compound reacts on the excess of AgNOs with the forma- tion of N2O5. (i) AgN03 + Cl2=N02Cl + AgCH-0. (2) N02Cl + AgN03=N20g+AgCl. 645. Aqua regia. — We must notice here the mixture of HCl and HNO3, to which the alchemists gave the name aqua regia from its power of dissolving gold, the king of metals. It is employed for dissolving Au and Ft, and also ores and other bodies. The solvent power of the mixture depends on the fact that, on heating the mixture, CI is evolved, thus : — HNO3 + 3HC1= NOCl + CI2 + 2H2O. Nitroxyl chloride. 646. Chloric acid. — This acid is a syrupy liquid of a yellow- ish colour ; it is easily decomposed, yielding up its oxygen, hence it is a powerful oxidising agent. Organic bodies, as wool or paper, decompose it at once, also sulphur and phosphorus. It is prepared by acting on Ba2C103 with dilute H2SO4 ; the reagents must be added in exact atomic proportions, as no excess of either must remain. 647. Sulphurous anhydride. — This compound is a colourless gas, which condenses to a mobile liquid when exposed to pressure or cold. Its suffocating odour is well known, as it is the compound always formed when sulphur is burnt in air or oxygen. It may be prepared not only by burning sulphur ; but also by heating S and H2SO4 together ; also by acting on Cu Hg, or Ag with concentrated H2SO4 ; it is made on a large scale, for the preparation of the sulphites, bv heating carbon and H2SO4 together :— u 2 292 Fundamental Principles of Chemistry (1) S + 2H2S04 = 3S02+2HA (2) CU + 2H2S04 = CUS04 + S02+2H20. (3) C + 2H2S04 = 2S02 + C02+2H20. 648. Sulphurous acid. — This acid is formed by passing SO2 into H2O ; the solution has a strong acid reaction, and smells and tastes like the gas. Until recently the acid had not been isolated, owing to its so readily splitting-up into SO2 and H2O ; but it has recently been obtained on cooling its solution to 0° C. It crystallises out at that temperature, the formula of the crystals being H2SO3 + 14H2O. Both SO2 and the solution of H2SO3 exert a bleaching action on vegetable colours. The acid is employed in bleaching wool and silk. 649. Sulphuric acid. — This acid is manufactured on an enormous scale, on account of its many and important indus- trial applications ; the late Baron Liebig after describing some of the most important of them in his work 'Familiar Letters on Chemistry,' goes on to say : ' After these remarks you will per- ceive that it is no exaggeration to say, we may judge with great accuracy of the commercial prosperity of a country from the amount of sulphuric acid it consumes.' It is made on the large scale by conveying into large chambers made of lead dioxide or trioxide of nitrogen, steam, and SO2 ; the following reaction takes place : — S02-(-N02-f-H20=H2S04 + NO. The NO is converted into NO2 by uniting with some of the oxygen of the air in the chamber ; the NO2 thus re-formed is again reduced to NO, owing to its yielding up one-half its oxygen to a fresh quantity of SO2, and the NO is again con- verted into NO2. This oxidation and deoxidation of these two oxides of nitrogen ought to go on indefinitely ; therefore, having once started a chamber with a sufiScient amount of the oxide of nitrogen, no further amount ought to be required ; but in practice there is a considerable loss of the oxide, which has constantly to be replaced. Formerly the SO 2 was always made by burning sulphur, but now, except when the acid is required pure, it is obtained by roasting iron pyrites, FeS2. The concentrated acid is a colourless oily liquid. The acid has a strong attraction for water, it withdraws it from the air, and Formation of the Acid Bodies 293 chemists employ it for drying those gases on which it has no action, by passing them through it. So powerful is its attrac- tion for water than when an organic substance, as wood, is dipped into it, it abstracts oxygen and hydrogen from the substance in the proportion to form water ; the organic substance becomes by this abstraction brown or black (charred), and the acid itself becomes brown. When it is diluted with water great heat is evolved. It is one of the strongest acids ; it expels nearly every other acid from its salts. Although the metals displace the hydrogen, a sulphate of the metal being formed, we have become aware that the concentrated acid when hot is decom- posed by some of the metals. Au and Pt are unacted upon even by the boiling acid ; if its vapour is passed over red-hot platinum it is decomposed into SO2, O, and H2O. It has been proposed to employ this process for making oxygen on the large scale. Nascent hydrogen reduces the concentrated, but not the dilute, acid to HgS. The acid boils at 620° F. and maybe distilled without decomposition. 650. There is another sulphuric acid, viz. disulphuric or pyrosulphuric acid, H2S2O7 (also called fuming sulphuric acid and Nordhausen sulphuric acid) ; it is obtained by heating a basic ferric sulphate in clay retorts. 651. Sulphuric anhydride. — This compound is a white crystalline solid ; it melts at 15° C. and boils at 46°- It is com- monly prepared from Nordhausen sulphuric acid, by gently heating the acid in a retort ; the anhydride volatilises and con- denses in the cooled receiver in white silky crystals of needle- like form. It is especially characterised by its strong attraction for water. 652. Orthophosphoric acid. — This acid is a solid, but as it deliquesces on exposure to the air, becoming a syrupy liquid, it is usually seen in that state. It is one of the strongest of the inorganic acids : it expels H2SO4 from its salts at high tem- peratures, as it is less volatile than that acid. It can be pre- pared by oxidising P with HNO3, or by dropping PCI5 in small quantities at a time into H2O ; but it is prepared on the large scale by acting on bone-earth with sulphuric acid. 653. Phosphoric anhydride. — When P is burned in excess of dry air or oxygen this compound is formed ; it is a light 294 Fundamental Principles of Chemistry snow-white powder; it readily attracts moisture from the air, becoming converted by its union with that liquid into phos- phoric acid. Its attraction for water is so great that when thrown into that liquid it hisses like red-hot iron. 654. Chromic anhydride and acid. — The anhydride is pre- pared by adding to i volume of a cold saturated solution of potassium dichromate li volumes of concentrated H2SO4 ; on the addition of the acid the mixture becomes strongly heated, on cooling the anhydride crystallises out in long red needles ; the crystals are dried by placing them on a porous tile. It is a powerful oxidising agent, as it readily yields up half its oxygen, being converted into chromic oxide. It is readily soluble in water, and it is supposed to be converted by the solution into the acid ; the acid, as previously stated, is un- known in the free state. 655- Arsenious anhydride and acid. — The anhydride is pre- pared on a large scale by roasting various minerals containing As. When first prepared it forms a colourless vitreous mass, which becomes after a time white and opaque ; it volatilises at 380° F. It is employed in the manufacture of arsenical pigments, and in the manufacture of glass. The acid is pro- bably contained in an aqueous solution of the anhydride, but it has not yet been obtained in the free state. 656. Arsenic acid. — This acid is obtained by treating AS2O3 with HNO3; on evaporating the solution hydrated crystals of the acid are deposited. It is, as we already know, a tribasic acid hke H3PO4 ; like that acid it parts with, at dif- ferent temperatures, hydrogen and oxygen in the proportion to ■ form water, forming pyrarsenic acid, H4AS2O7, metarsenic acid, HAsOj, and finally, at a low red heat, the anhydride, AS2O5. The acid in solution gives up its oxygen to many substances even at ordinary temperatures. Nascent hydrogen reduces it, as well as arsenious acid, in acid liquids, to ASH3. In con- sequence of the readiness with which it parts with oxygen, it is largely employed in the arts. 657. Arsenic anhydride. — As does not, like P, become converted into its highest oxide, AS2O5, on being burnt in air or oxygen, because at the temperature of the combustion of arsenic AsjOj is decomposed into AsjOg and oxygen. This Formation op the Acid Bodies 295 anhydride is formed, as we have seen, on heating the acid to low redness ; it is a white amorphous substance. 658. Boracicacid.—'Y\A\ei% of steam which escape through the fissures in the ground in the volcanic districts of Tuscany contain traces of this acid ; the steam is made to pass through large basin-shaped vessels containing water, and the acid is left in the water. After the water has become charged with a con- siderable quantity of the acid it is evaporated to the crystallis- ing point ; the acid crystallises out in colourless lustrous tab- lets. The aqueous solution of the acid possesses both a faint acid and alkaline reaction ; it reddens blue litmus paper, and yet it turns yellow turmeric paper brown. It has not yet been solved how the acid comes to be present in the jets of steam ; the most probable explanation appears to be, that it is pro- duced by the action of the steam on boron nitride, as ammo- nium compounds are always present along with the acid in the steam. Boracic acid is a solid; it volatilises very slowly on intense ignition; it differs from most, if not all, other solid bodies, as it volatilises with the steam when its aqueous solution is boiled. 659. Boracic anhydride. — This compound is prepared by heating the acid to redness ; it is a colourless, transparent^ vitreous solid. 660. Silicic anhydride. — This is the only oxide of silicon known ; it is very abundant in nature ; quartz or rock crystal is crystallised silica. 'The minerals agate, chalcedony, opal, jasper, flint consist of amorphous silica mixed to some extent with the crystalline modification. Some of these, e,g. opal, are of attractive colours and are used as jewels. Ordinary sand consists of particles of silica, which when united together by some. cementing substance constitute the different varieties of sandstone J It is a non-volatile solid, insoluble in water ; the only acid that acts upon it is HF. 661. Silicic acid. — This acid may be obtained in a gelati- nous state by decomposing an alkaline silicate with HCl, or by passing CO2 through the solution. It is difficult to obtain a silicic acid in the dry state of definite constitution, as, like other weak polybasic acids, it parts with water easily, finally becoming converted into the anhydride. 662. Carbonic anhydride. — This compound is always formed 296 Fundamental Principles of Chemistry when any of the forms of carbon or any compound of carbon is burnt either in an excess of oxygen or air. It is a colourless and, of course, incombustible gas, and Js widely distributed in nature, both in the free state and in combination. It is a con- stituent of the air, the average proportion being about o'o3 per cent. ; it is evolved in considerable quantities from the fissures of the earth in many places, chiefly in the neighbourhood of active or extinct volcanoes ; all spring waters contain it It exists in combination with lime, forming the abundant rock limestone, with magnesia, with lime and magnesia, with baryta, strontia, soda, oxide of iron, &c. It is expelled from the carbonates on the addition of stronger acids. It is formed on the oxidation of the worn-out tissues in the living body, and is given off from the lungs during respiration ; it is also formed in the processesof decay, putrefaction, and fermentation ; hence, every moment a large quantity of this gas is being poured into the atmosphere from a variety of sources. It can neither support combustion nor respiration ; and it is injurious to animal life even when largely diluted with air. It would soon accumulate in the atmosphere to an extent injurious to life were it not that it is as constantly being removed from the air as it is being added to it. It is absorbed by the leaves of plants, in the presence and with the aid of sunlight, is there decomposed, the carbon being retained, as it is required for the building up of their tissues, whilst the oxygen is returned to the atmosphere. When it is passed over carbon it is, as we have learned, reduced to the lower oxide CO. It can be liquefied and solidified ; it is of great density, and it is soluble in water : at ordinary tem- peratures and pressure water dissolves about its own volume of the gas. It contains its own volume of O, for there is pro- duced on burning carbon in O a volume of CO2 equal to the volume of O consumed. When brought into contact with lime water it produces a white precipitate, CaCoj ; this test distin- guishes it from nitrogen, which like it neither burns nor supports respiration. 663. Carbonic acid. — This acid has not been isolated, but it is believed to be formed when CO2 is passed into water, for CO2 does not redden blue litmus paper, whilst the solution does redden that test paper. Formation of the Acid Bodies 297 664. Oxalic add. — The potassium salt of this acid occurs in various kinds of sorrel and other plants ; calcium oxalate occurs in some lichens ; oxalates occur also in many other plants. The acid is not now obtained from plants, but is artificially prepared on a large scale. At one time it was obtained by acting on starch (CgHmOs) with nitric acid ; but it is now obtained from some form of cellulose, generally sawdust. Cellulose is similar in composition to starch. The sawdust is mixed with KHO and some NaHO, and the mixture is heated until it fuses ; the cellulose is oxidised, hydrogen is evolved, and a large part of the carbon is converted into oxalic acid which unites with the alkaline metals. The fused mass is treated with water, the solution is neutralised with HCl, and to the solution one of CaCla is added; CaC203 precipitates. , This insoluble salt is afterwards suspended in water, and H2SO4 added, which removes the Ca; the acid is thus set free in solu- tion, and is obtained in the crystalhne state on evaporating the liquid. ' Of theoretical interest is the fact that oxalic acid can be obtained from CO^ by reduction. If dry CO2 is conveyed over potassium amalgam, a brisk reaction takes place, and potassium oxalate is formed. The mercury of the potassium amalgam undergoes no change, but serves simply as a diluent. 2C02 + K2=K2C204.' We have already noticed its conversion by concentrated H2SO4 into CO2 and CO. It is classed as an organic acid. Miscellaneous Exercises. 477. It is stated in par. 643 that a larger amount of nitric acid can be obtained from a given weight of sodium nitrate than from the same weight of potassium nitrate ; show how this comes to pass. 478. Does boracic acid possess any peculiar properties ? 479. If I had to analyse an alloy consisting of tin, lead, and zinc, and I treated it with nitric acid, what would take place ? 480. If I were to burn carbon in 100 c.c. so as to convert the whole of the oxygen into COj ; how much carbon would be required, and what volume of COj would be produced ? 481. I treat an alloy of gold and silver with sulphuric acid ; state the action the acid would have on the alloy. 482. Define the terms artiad and perissad, and give examples. 483. How can HBr and'HI be easily prepared in solution ? Illustrate your answer by chemical equations. 484. If I treat an alloy of silver and platinum with nitric acid, what would be the action of the acid on the alloy ? 298 Fundamental Principles of Chemistry 485. If I burn 100 c.c. of HjS in oxygen gas, what volume will the steam and the SO, produced occupy ? 486. Why are organic substances blackened when dipped into strong sulphuric acid ? 665. We will now give a summary of the action of acids upon salts. 666. If the acid which is added to the salt is the same as that contained in the salt, and it is a polybasic one, and the salt contains no replaceable atoms of hydrogen, the salt will combine with a further quantity of the acid, forming with it an acid salt. Examples : — If sulphuric acid be added to di- potassium sulphate, hydric potassium sulphate will be formed ; and if a current of CO2 be passed into an aqueous solution of dipotassium carbonate, hydric potassium carbonate will be formed. 667- If the base of the salt does not combine with a greater quantity of acid, the salt often dissolves in the acid added, especially if the latter be mixed with a large quantity of water. Thus potassium nitrate dissolves in a dilute solution of nitric acid ; but if the liquid be evaporated, the nitrate crystallises out unchanged. 668. If the acid added differs from that existing in the salt decomposition will ensue under several circumstances. I St. Decomposition will ensue when the salt, being soluble in water, and being dissolved in that liquid, the reacting add can form an insoluble compound with its base. 2nd. An acid can decompose a salt which is in a state of solution, if the acid of the salt is either completely insoluble, or only sparingly soluble in water. 3rd. A salt can always be decomposed by an acid less volatile than that which it contains. 669. The state of concentration of an acid and the tem- perature exert a powerful influence over these reactions. If a solution of sulphuretted hydrogen be poured into a dilute solu- tion of antimony chloride, a precipitate of antimony sulphide is formed. But if antimony sulphide be heated with a con- centrated solution of hydrochloric acid, antimony chloride is formed and sulphuretted hydrogen disengaged. 670. When the acid of a salt, and that employed to react on Action of Acws on Salts 299 it, are both gaseous, and at the same time but slightly soluble in water, and when, moreover, their affinities for the bases are nearly equal, the acid which is present in excess will expel the other. Thus, by passing a current of CO2 for some time through the solution of an alkaline sulphide, the latter is entirely converted into a carbonate, and sulphuretted hydrogen driven off. Reciprocally, by passing sulphuretted hydrogen for some time through a solution of an alkaline carbonate, it is entirely con- verted into a sulphide. 671. The vapour of water at a high temperature expels CO2 from alkaline carbonates, when the latter are heated in platinum tubes in a current of steam, and hydrates are formed. Reciprocally, the alkaline hydrates, heated to the same tem- perature in a current of CO2, are converted into carbonate. 672. These facts (670, 671) exhibit the mfluence of mass, the influence of which on chemical affinity will be noticed at greater length in Part II. Experiments of the Action of Acids on Salts. 487. Mix twenty or thirty grains of precipitated calcium carbonate with three or four ounces of water. Pass CO.^ through the mixture until a clear solution is obtained. This experiment exemplifies the rule stated at par. 666. 488. Add to a solution of barium chloride sulphuric acid ; barium sul- phate will be precipitated, and hydrochloric acid will go into solution. This experiment exemplifies the rule stated at par. 668 — 1st. 489. Add to calcium carbonate, suspended in water, nitric acid ; COj will be evolved, and calcium nitrate will be formed, which, being soluble, will dissolve in the water. This experiment exemplifies the rule stated at par. 668— 3rd. 490. To a hot concentrated solution of sodium biborate add dilute sul- phuric acid in excess ; as the solution cools, boracic acid will crystallise out. This experiment exemplifies the rule stated at par. 668— 2nd. 491. Add some dilute nitric acid (say, add to one measure of the com- mercial acid two of water) to an aqueous solution of cupric nitrate, then pass sulphuretted hydrogen through the solution ; collect the cupric sul- phide formed on a filter, then transfer it to a dish, and add nitric acid and boil ; the cupric sulphide will be decomposed and cupric nitrate will be formed. This exemplifies the statement made in par 669. Examination Questions. 49. You have learned how HCl is prepared from NaCl, and how HNO3 is obtained from the alkaline nitrates ; state what rule or rules the preparation of these acids exemplifies. 493. If you were to add sulphuric acid to a sulphite and apply heat, 300 Fundamental Principles of Chemistry would any chemical change take place ? If your answer is in the affirma- tive, illustrate it by a chemical equation. 494. Describe a method for the preparation of hydrosulphuric acid, and state the conditions necessary for its formation. 495. We have learned that ?IBr and HI can be prepared from their salts by acting on the latter with phosphoric acid ; what rule is exemplified in preparing these acids by this method ? 496. Which, if any, of the following acids would set free sulphuric acid from potassium sulphate at a high temperature : — hydrochloric acid, phos- phoric acid, nitric acid, and carbonic acid ; and assign reasons for your answer. ' CHAPTER XIII. SALTS — THEIR CLASSIFICATION — ACID AND NORMAL SALTS — GENERAL FORMULAE OF SALTS — EXERCISES — BASIC AND DOUBLE SALTS — SOLUBILITY OF SALTS — SUPERSATURATED SOLUTIONS — WATER" OF CRYSTALLISATION — CRYOHYDRATES — SALINE WATER — FREEZING MIXTURES— ISOMORPHISM — EXERCISES- QUESTIONS — TABLE OF THE SOLUBILITY OF, SALTS — ACTION OF METALS UPON SALTS- EXPERI- MENTS — ACTION OF SALTS UPON EACH OTHER — EXPERIMENTS — GENERAL PROPERTIES OF THE SALTS — TESTS FOR THE ACID- RADICALS — EXPERIMENTS — ILLUSTRATIONS OF THE METHODS ADOPTED FOR DISTINGUISHING AND SEPARATING SUBSTANCES FROM EACH OTHER — EXERCISES — OUTLINE OF VOLUMETRIC METHODS — EXERCISES — QUESTIONS. 673. We have now to become acquainted with the third class of characteristic substances, viz. salts. Certain substances were called salts long before chemistry had at all reached the position of an exact science, or even had become a science ; the following, for example, are popular names for substances belonging to this class of bodies : common, kitchen, or table salt, for sodium chloride (NaCl) ; saltpetre, for potassium nitrate (KNO3) ; Epsom salts, for magnesium sulphate (MgS04) ; Grlauber's salt, for sodium sulphate (NaS04) &c. These substances are admitted by chemists at the present time to belong to that numerous class of substances they term salts. It is difficult to give a short and precise definition of a salt ; we will therefore commence with describing one very general mode for forming them ; viz., by replacing the hydrogen in acids either wholly or partly by a metal ; this method for their 1 The student, having completed the study of this chapter, must pass on to par. TL'i. Classification and Formation of Salts 301 ibrmation we had to describe briefly in giving a definition of acids. 674- When the displaceable hydrogen of an acid is replaced either wholly or partly by a metal, the compound produced s called, as has been stated, a salt. It will at once be evident to the student that monobasic acids, as they contain only one atom of replaceable hydrogen in one molecule of the acid, will form but one class of salts ; the metal, according as it is a monad, a dyad, a triad, &c., will take the place of the hydrogen in one, two, three, &c., molecules of the acid. 675- Diabasic acids form two classes of salts with monad metals ; in one class only half, in the other class the whole, of the hydrogen is replaced by the metal ; in this latter case there may be two different metals. Ex.: Na (NH4) SO4. Dyad and triad metals form only one class of salts with dibasic acids ; a dyad replaces the whole of the hydrogen in one molecule of the acid ; two atoms of a triad replace the whole of the hydrogen in three molecules. 676. Tribasic acids contain three atoms of hydrogen which are replaceable by metals. Monad metals can form three classes of salts with this class of acids, viz., one in which one- third, the second in which two-thirds, and the third in which the whole, of the hydrogen is replaced by a metal. When two-thirds or the whole of the hydrogen is replaced by a metal there may be two or three different metals. Ex. : Na (NH4)HP04. In the case of dibasic metals one-third of the hydrogen may remain in the salt, or it may be replaced by a monad metal, Exs. : CaHP04, CaKP04. The whole of the hydrogen can be replaced by a dyad metal ; in that case three atoms of the dyad replace the whole of the hydrogen in two molecules of the acid. One atom of a triad metal replaces the three atoms of the hydrogen in one molecule of the acid. 677. A salt which contains displaceable hydrogen is called an add salt ; a salt which contams no displaceable hydrogen is called a normal or neutral salt.^ 678. An add salt is one in which the displaceable hydrogen of the add is only partially exchanged for a metal or cotnpound radical like ammonium, that plays the part of a metal. 1 The term normal ought only to be employed, and the term neutral only of those salts which have no action on vegetable colours. 302 Fundamental Principles of Chemistry 679. A normal salt is one in tvhich the displaceable hydrogen of the acid is all exchanged for an equivalent amount of a metal or compound radical resembling in properties a metal. 680. Having explained very fully the different varieties of salts that can be formed by the monobasic, bibasic, and tribasic acids, we need not enter upon the different classes formed by the quadrobasic acids, as the student will, or certainly ought to be able to, make them out for himself ; but, in order to remove all reasonable difficulty, their general formulse are given in the following table. 681. The nomenclature of salts is yet in a somewhat tran- sitional state ; and as, in the naming of the oxides, some chemists, as we pointed out, do not alter the name of the metal, whilst others add the termination ic to it, the same difference occurs in the naming of salts ; thus, some chemists name, for example, KNO3 and ZnS04, potassium nitrate and zinc sulphate, others name them potassic nitrate and zincic sulphate. We shall adopt, in the main, the first plan ; but instead of writing the word hydrogen in full when that element is a constituent of a salt, we shall employ in its place, as is generally done, the word hydric. By the examples given in the following table, the student will see that we employ no prefix to express the quantity of the metal in a salt when the hydrogen of the acid is entirely replaced, not by different metals, but by one only : for instance, we do not designate Na2S04 as disodium, but simply sodium sulphate : in like manner, we do not designate Q,z.^{?0^)lue, as is also the chloride having the following formula, CoCl2.2H20 ; whilst C0CI2.6H2O Vi pink} 696. The late Professor Guthrie discovered that all salts, even those which are termed anhydrous, which are soluble in water form definite solid compounds with that liquid. The crystals of salts which are anhydrous at temperatures above o°C., as NaCl and NH4CI, on crystallising out of an aqueous solution below this temperature contain water of crystallisation ; thus a concentrated solution of common salt deposits at 7° crystals having the composition NaCl2H20 ; and at — 23 crys- tals having the composition NaClio.sHjO. The hydrated salts formed below the freezing-point of water are termed cryo- hydrates; and each cryohydrate has a constant composition, and has a definite freezing and melting-point. Under certain conditions we learn, from Guthrie's discovery, that all salts are hydrated ; therefore, when we speak of an anhydrous salt, we mean a salt that is anhydrous at temperatures above 0° C. ' A dilute solution of this salt may be used as a sympathetic ink. When so employed it remains invisible when cold ; but when the paper is placed before the fire it becomes blue and visible, and again fades in the cold, owing to its abstracting moisture from the air. Double Salts 311 697. When two salts which do not chemically unite are dissolved in water, the quantity of each which is dissolved is, as a rule, less than if they were dissolved separately ; hence if to a concentrated solution of one salt another were added and the mixture shaken, some of the latter would dissolve, whilst a portion of the other salt would separate- out of the solution. But some salts chemically unite with each other and form double salts ; double salts are common between two diiiferent haloid salts ; for instance, between the haloid salts of the less oxidisable metals and the haloid salts of the alkaline metals. Exs. : Potassium platinochloride : 2 KCl,PtCl4 ; potassio-mercuric iodide, 2KI,Hgl2. The sulphates of the sesquioxides of the metals in many cases unite with the sul- phates of the protoxides. Exs. : Potassium alum, K2S04,Al2 3S04:24H20; ammonium alum (NH4)2 SO4, AI2 3SO4.24H2O ; iron alum, K2S04, Fe23S04.24H20, &c. Magnesium sulphate, zinc sulphate, and several sulphates of that class, contain seven molecules of water, their general formula being MSO4. 7H2O, but one of these molecules is more strongly attached to the sulphate than are the other six, and it possesses quite different functions, as we shall show. If we expose crystals of one of these magnesium sulphates to a temperature of 100° C. six molecules are expelled, and with this loss the crystalline structure of the sulphate is destroyed ; but it requires a temperature of about 210° C. to expel the seventh molecule, and this seventh molecule is not water of crystallisation, for the crystalline structure was de- stroyed by the expulsion of the six molecules ; and, further, this seventh molecule can be replaced by some non-isomorphous anhydrous sulphate, as potassium sulphate. Ex. : If magnesium sulphate, or some other sulphate of that class, and K2SO4, be separately dissolved in equal molecular proportions, and the solutions mixed whilst hot, and allowed to crystallise, a double salt having the formula MgS04, K2SO46H2O is deposited, which has the same crystalline form as the magnesium sulphate, but differing in its constitution, in that the seventh atom of water in the magnesium sulphate has been displaced by potassium sulphate ; water that can thus be replaced by a salt has been termed constitutional or saline water. 698. The atomicity theory, which we have already described, the student will see does not explain why water chemically 312 Fundamental Princjples of Chemistry unites with salts, or why some salts can unite together and form double salts ; for in most of these cases the union is effected between two saturated compounds ; the force which causes the union we are unacquainted with. Such compounds have been called molecular compounds, i.e. compounds produced by the chemical union of molecules. This expression, it has been properly observed, explains nothing ; it simply states that the molecules of saturated compounds are capable of uniting with one another to produce new compounds. 699. The mechanical solution of salts in water is attended, as we have shown, by an absorption of heat, which is due mainly, if not entirely, to the liquefaction of the solid ; hence artificial cold is produced by the solution of salts. Most of us are aware that if common salt and ice, or better still snow, are mixed together, intense cold is produced ; but a still more intense cold — a cold sufficient to freeze mercury^ — is produced by mixing in certain proportions crystallised calcium chloride and snow. On the principle of the liquefaction of solids the action o{ freezing mixtures depends ; for instance, water contain- ing common salt in solution freezes at a much lower tempera- ture than pure water, hence snow melts on salt being added to it. Guthrie's discovery enables us to understand more clearly the action of freezing mixtures, and the degree of cold to be attained by them. He found that the /«««^-point of that cryohydrate which is formed at the lowest temperature is the limit to the degree of cold attainable with a given freezing mixture, since any further abstraction of heat from the mixture occasions, not depression of temperature, but separation of the cryohydrate. 700. We have learned that some salts effloresce ; some others, on the contrary, have so great a tendency to combine with water, that on exposure to the air they abstract moisture from it, and become moist, or deliquesce. Calcium chloride is an exceedingly deliquescent salt ; hence chemists employ it for drying air and other gases. 701. When substances pass from the liquid, or gaseous, into the solid state, the solids generally assume definite geo- metrical forms ; to such forms the term crystal is applied ; it is derived from a Greek word signifying ice — a name given by the Crystallisation 313 ancients to prisms of quartz or rock-crystal, which, from their transparency and hardness, were regarded as formed of in- tensely consolidated water. 702. 'Some crystals are very simple in their forms, and .present solids remarkable for their symmetry ; while others are exceedingly complex, being bounded by more than a hundred different surfaces.' Solids which do not crystallise are termed amorphous, i.e. without form. 703. We shall not enter upon the different crystalline forms ; the student will find them described in the general works on chemistry ; but I would recommend those who are commencing the study of crystallography to obtain ' Jordan's Elementary Crystallography,' in which is given a series of Nets for the construction of models illustrative of the simple crystal- line forms. 704. Crystallisation is an important chemical process ; by means of it two or more salts that are present in the same solu- tion can be separated, and each obtained in their pure state : especially, if they are present in varying quantities in the liquid, are of unequal solubility, and of different crystalline forms ; and the forms of crystals are a most valuable means of identifying substances. Crystallisation from aqueous solutions may be effected, either iDy cooling a hot solution of a strength suffi- cient to deposit crystals when cold, or to evaporate a weak solution until it has arrived at that degree of concentration for the first crop of crystals of the most insoluble salt to be deposited. Whether crystals or an amorphous powder are deposited by cooling a hot solution, or by evaporating the solution, a quantity- of the salt which first deposits will remain in solution, as it will have a certain degree of solubility in the cold. When the crystallisation ceases, the solution, which is technically called the mother liquor, is again evapo- rated until it reaches the crystallising point ; and this is repeated until the whole of the salts have crystallised out. If a salt, as common salt, is present which is almost equally soluble at all temperatures, portions of it will separate out as the evaporation proceeds, and only a very slight quantity will be deposited as the solution cools. When there are two or more salts in solution the first crops of crystals are never perfectly pure ; to 314 Fundamental Principles of Chemistry obtain them pure, they have to be redissolved in distilled wate r and recrystallised, sometimes three or four times. For the successful performance of the operation, considerable attention to minute detail is required, which can only be acquired by experience. When substances have the same crystalline form, crystallisation is not effectual for their separation, unless their difference in solubility is very great. 705. Many substances, both elementary and compound, crystallise in two or more forms belonging to different crystal- line systems ; such substances are said to be dimorphous^ triptorphous, or, gen^xsWy, polymorphous. 706. Some compounds which are analogous in chemical constitution, and are similar in crystalline form, are capable of replacing, each other in the same crystals in indefinite propor- tions, when a mixed solution of these substances are submitted to the process of crystallisation ; and there can also be ob- tained crystals consisting of alternate layers of different salts, if they have nearly the same degree of solubility in water. For example, if a crystal of potash alum (K2S04,Al2,3S04. 12H2O) be placed in a solution of ammonia alum (NH4) 2SO4, AI23SO4. 1 2H2O), the crystal augments in size owing to the depo - position on it of layers of the latter salt. If the crystalline mass be now transferred to a solution of iron alum (K2S04,Fe23S04. 12H2O) layers of this salt will be deposited on the crystal ; if it then be transferred to a solution of chrome alum (K2SO4, Cr23S04.i2H20) layers of this salt will be deposited on it; and if it be now transferred to a solution of potash alum, layers of this salt will be deposited ; the deposition of layers of the different alums could thus be continued again in succession. Substances which can thus replace each other in the same crystals in indefinite proportions are said to be isomorphous, a word which is derived from two Greek ones, one signifying equal, the other /^^/«. 707. From the preceding example we learn that the sulphates of aluminium, chromium, and iron in the ferric state, are isomorphous ; also that the sulphates of potassium and ammonium are isomorphous. Isomorphous salts can never be separated by crystallisation, unless their difference in solubility is very great. Example : Copper sulphate and ferrous sulphate Isomorphism 315 are isomorphous, and as they do not differ greatly in solubility they cannot be separated when present in the same solution by crystallisation; however frequently the substance is recrystallised the crystals always contain, throughout their whole mass, iron as well as copper. But if the iron is converted from the ferrous into the ferric state pure crystals of copper sulphate can then be obtained. 708. The same intermixture of isomorphous substances which takes place in artificial salts is found to occur in minerals, and affords a luminous explanation of the great variety, both in kind and proportion, of substances which may coexist in a mineral species, without its external character being thereby essentially affected. 709- Isomorphism frequently affords valuable aid in deter- mining the atomic weights of the elements ; for example, we only know one oxide of aluminium, which is coinposed of 18-3 parts by weight of the metal, and 16 of oxygen ; is it a monoxide, a dioxide, a sesquioxide, &c., for upon the constitution of the oxide depends the atomic weight of the metal ? As the aluminium oxide is isomorphous with sesquioxide of iron, it is also regarded as a sesquioxide ; the atomic weight of the metal is therefore 2 7 •4. Farther on we shall describe the method for determining the rational formula for compounds containing isomorphous constituents. 710. Nitrine unites, as has already been stated, with acids, and the salts formed are the same in character as those which are formed when ammonic hydrate unites with acids. Example : NH3 + HCl = NH4CI Ammonium chloride. 2NH3 + H2SO4 = (NH4)2S04 Ammonium sulphate. 711. Phosphine unites directly with hydriodic and hydro- bromic acids when they are presented to it in the nascent state, forming compounds isomorphous with the corresponding salts in the nitrogen series : — PH3 + HI = PHJ Phosphonium iodide. PH3 + HBr = PH4Br Phosphonium bromide. 3l6 FUXDAMENTAL PuiXCfPLES OF CHEMISTRY 712. We noticed in the chapter on basic bodies that the hydrogen in ammonium can be replaced by metals ; there are consequently ammonium salts which contain a metal in place of some or all of the atoms of hydrogen in ammonium ; in some cases the metal replaces the hydrogen in a single ammonium molecule ; in other cases the metal, on its replacing its equiva- lent amount of hydrogen, causes tivo molecules of ammonium to coalesce mto one molecule. Examples : — Dimercuric am- monium chloride, NHg,Cl ; Mercuric diammonium chloride, N^HgHgCla. Exercises on the Notation of Salts. 563. Potassium aluminium sul- phate. 564. Cupric diammonium sul- phate. 565. Sodium auric chloride. 566. Tribasic mercuric sulphate. 567. Platinic diammonium chloride. 568. Potassium' ferric sulphate. 569. Mercuric ammonium chloride. Examination Questions. 570. What is meant by the term 'isomorphism ' ? 571. What is meant by saying that a salt is efflorescent ? and what by saying that a salt is deliquescent ? 572. I dissolve a substance, say a salt, in water ; I add to the solution another liquid, say alcohol, which will mix with the solution ; after adding the liquid some of the solid dissolved in the water is precipitated ; what do you infer from that ? 573. Explain what is meant by neutralisation, and what by saturation. 574. What is the difference between saline or constitutional water, and water of crystallisation ? 575. I have some commercial potassium nitrate (saltpetre) containing potassium and sodium chlorides, which I wish to purify. In every 6,000 lbs. of the saltpetre these substances are present in the following proportions : Potassium chloride .... 360 lbs. Sodium chloride ..... 840 ,, Potassium nitrate .... 4,800 ,, 6,000 1,200 lbs. of water, at a temperature of 212°F., is capable of dissolving the following quantities of these substances ; and the same quantity of water at 65° F. is capable of holding in solution the following quantities : At a temp, of At a temp, of 212= F. 6s° F. Potassium chloride . . 684 lbs. 396 lbs. Sodium chloride . . . 324 ,, 318 ,, Potassium nitrate . . . 4,800 ,, 348 ,, I treat the 6,000 lbs. of saltpetre with 1,200 lbs. of boiling water. What takes place ? I allow the clear boiling solution to cool down to 65° F. What occurs ? and what finally remains in solution, and in what amounts ? Solubility of Salts 317 _ 576- I dissolve a substance in water ; I add to the solution another liquid which will not mix with it, and being heavier than water sinks to the bottom. I shake the two fluids together, and then allow them to separate ; when they have separated, I find the liquid has dissolved out of the water all the solid substance. What do you infer from that ? 577. What is the difference between saline and crystalline water? Illustrate the difference in the formula of magnesium sulphate, and explain the part the former plays when this salt crystalhses from the same solution with potassium sulphate. 578. What are cryohydrate salts ? and what are anhydrous salts ? 579- Does the atomicity theory explain why water chemically unites with salts ? and why two salts unite together to form double salts ? 580. On what does the action of freezing mixtures depend ? ' 713. We have now to bring under the notice of the student, (i) the action of metals on salts ; (2) the action of salts upon each other ; (3) the properties of each class of salts. For the student intelligently to understand much that will be stated, and which he will be called upon to perform and explain, the following table showing the solubility of different normal salts is required. 714. To ascertain the solubility of any salt by the table, find the name of the base in the upright column,and that of the acid in the line at the top ; the number placed at the point where the two rows meet shows whether the salt formed by their com- bination is soluble or otherwise. Thus, if it is wished to find the solubility of a sulphide, hydrosulphuric acid is the acid under which it will be found ; in like manner hydriodic acid is the acid for the iodides, hydrochloric acid the acid for chlorides, and hydrobromic acid the acid for bromides. The figures indicate the liquids which dissolve the substances. 'Thus, figure I means that it is soluble in water ; 2, that it is insoluble in water, but soluble in hydrochloric or nitric acid ; and 3, that it is insoluble in water and acids ; 1-2 signifies a substance dif- ficultly soluble in water, but soluble in hydrochloric or nitric acid ; 1-3, a body difficultly soluble in water, and of which the solubility is not increased by the addition of the acids ; and 2-3, a substance insoluble in water, and difficultly soluble in hydrochloric acid and in nitric acid. The deportment of a sub- stance with hydrochloric acid differs materially from that which it exhibits with nitric acid in the following cases : — • 1 The student must pass over the rest of the chapter for the present ; he will be directed when to return to it. 318 Fundamental Principles of Chemistry ounqd]ns ro r "^^ 7r\"r\ i ^3^ ^'■' °^ °"^ molecule of zinc. 1 ^1 zinc chloride. 757- The above decomposition would be expressed by the following mode of expressing chemical changes now universally adopted ; it will be well therefore for the student to adopt it, although at the first outset he may find the previous one renders him more certain as to the accuracy of his results. 2HCI + Zn" = Zn"Cl2 + H2 Substances added. Substances fanned or set free. Ex. 5. — Solution of ferric sulphate. . Ferric chloride. Solution of barium chloride. And ■ . ? 208 wt. of one molecule of J Fe"'a — — — p. f 32s wt. of one molecule ferric sulphate. IsSO*^'^^^^^ ^^^^ a n -j of ferric chloride. 624 wt. of three molecules f Ba" >.^^ ^ t> c;n / 5°7 wt. of three molecules of barium chloride. 3 1 CI. ^ 3Basu»-( of barium sulphate Fe^sSO, + BaCl^ = FejCl^ + sBaSO^ Substances added. Substances formed or set free. Ex. 6. — Solution of aluminium Aluminium hydrate, chloride. Hydric ammonium sulphide. And ? the left hancL^and those of the new substances resulting from the change on the right ; tM number of atoms of each element on one side should be equal to the number of atoms of each element on the other side. Exercises on Chemical Changes 341 268 wt._ of one molecule of aluminium, chloride. 108 wt, of six molecules of water. 306 wt. of six mole- cules of hydric am- 6 monium sulphide. Al H O J ^57 ^*'" <^^oii6 molecule - " " I of aluminium hydrate 6H,S f 204 wt. of six molecules 1 of hydrogen sulphide '6NH,C1 [321 wt. of six molecules I of ammonium chloride K\C\ + 6H,0 + eNHJ-IS = Al^HjOs + 6H ^S + 6NH,CI • Exercises on the mode of expressing chemical changes. Substances added. Substances formed or set free. 634- Sol. of potassium iodide. Sol. of silver nitrate. Silver iodide. « And ? 6S'i. Potassium chloride. Sodium chloride. Boiling sol. of sodium nitrate. And ? 636. Hydrochloric acid. Iron. Ferrous chloride. And ? 6S7- Sol. of hydric disodium phos- Sodium chloride. phate. Sol. of calcium chloride. And ? 6s8. Sol. of sodium carbonate. Sodium nitrate. Sol. of strontium nitrate. And ? 639- 640. Sol. of cupric sulphate. Hydrostilphuric acid. Sol. of potassium chloride. Cupric sulphide. And ? Plumbic chloride. Plumbic nitrate. And ..-.. ? 641. Boiling sol. of potassium hydrate. Zinc. Potassium zinc oxide (KjZnOj). And ? 642. Hydrochloric acid. Sol. of sodium hydrate. Sodium chloride. And ? 643- Sulphuric acid. Sodium chloride. Sodium sulphate. And ? 644. Sol. of sodium chloride. Silver chloride. Sol. of silver nitrate. And ? 645- Sulphuric acid. Potassium nitrate. Potassium sulphate. And ? 646. Sol. of hydrosulphuric acid. Iodine. Hydriodic acid. And ? 647. Ammonium sulphide. Sol. of zinc sulphate. Zinc sulphide. And ? ' When the word solution is employed, as in Examples 3, 5, and 6, it is in- troduced for the purpose of informing the student that the chemical change takes place when the substances are dissolved in water ; but water must not on this account be introduced as one of the substances added ; it must only be introduced when it takes part in the chemical change, as in Example 6. 2 When the student can give correctly the weights of the substances added, and the weights of the substances set free and produced, he n-".y discontinue giving them. 342 Fundamental Principles of Chemistry Substances added. 648. Sol. of potassium chromate. Sol. of barium chloride. 649. Sol. of sodium hydrate. Sol. of manganous chloride. 650. Sol. of ammonium carbonate. Sol. of calcium nitrate. 651. Hydrosulphuric acid. Sol. of plumbic nitrate. 652. Sol. of sodium sulphate. Sol. of barium chloride. 653. Sol. of oxalic acid. Sol. of barium nitrate. 654. Ammonium sulphide. Sol. of cobaltous nitrate. 655. Hydrochloric acid. Sol. of mercurous nitrate. 656. Hydrosulphuric acid. Sol. of mercuric chloride. Substances formed or set free. Barium chromate. And ? Manganous hydrate. And ? Calcium carbonate. And ? Plumbic sulphide. And ? Barium sulphate. And ? Barium oxalate. And ? Cobaltous sulphide. And ? Mercurous chloride. And ? Mercuric sulphide. And ? 657. When potassium chlorate in the solid state is ignited, it is decom- posed into oxygen and potassium chloride. How many atoms of oxygen will be liberated from one molecule of the salt ? 658. When ammonium nitrate in the solid state is heated, it is decom - posed into nitrogen monoxide (laughing gas, Nj,0) and some other substance. What is the other substance, and how many molecules of each will be formed from one molecule of the salt ? 659. We know the substances that are formed on heating NH4NO3 ; what substances will be formed on igniting ammonium nitrite, NH4NO2 ; and how many molecules of the substances formed will be produced from one molecule of the salt ? Substances added. 660. Hydrochloric acid. Ferric oxide. 661. Sol. of cupric chloride. Sol. of potassium iodide. 662. Sol. of hydric disodium arsenite. Sol. of cupric sulphate. 663. Sol. of sodium hydrate. Sol. of chromic chloride. 664. Sulphuric acid. Manganese dioxide. 665. Antimonious chloride. Water. 666. Sol. of ferric sulphate. Sulphurous acid. 667. Sol. of sodium hydrate. Sol. of aluminium sulphate. 668. Sol. of hydric disodium phosphate. Sol. of barium nitrate. Substances formed or set free. Ferric chloride. And ? Cuprous iodide (CuJ.^). And ? Hydric cupric. arsenite. And ? Chromic hydrate. And ? Manganous sulphate. And ? Oxychloride of antimony (SbCl3,Sb,03). And ? Ferrous sulphate. And ? Aluminium hydrate. And ? Hydric barium phosphate. And ? Exercises on Chemical Changes 343 Substance^ added. 669. Sol. of hydric disodium phosphate. Sol. of argentic nitrate. 670. Sol. of hydric disodium phosphate. Sol. of cupric sulphate. 671. Hydrosulphuric acid. Sol. of ferric sulphate. 672. Arsenous acid. Sulphuric acid. Zinc. 673. Hydrochloric acid. Manganic dioxide. 674. Sol. of hydric disodium phosphate. Sol. of ammonia. Sol. of magnesium sulphate. 675. Sol. of cupric nitrate. Sol. of ferrous sulphate. Sol. of potassium iodide. 676. Sol. of aluminium sulphate. Sol. of ammonium carbonate. 677. Sol. of chromic chloride. Sulphide of ammonium. 678. Sol. of ferric chloride. Sol. of ammonium carbonate. Substances formed or set free. Triargentic phosphate. And ? Hydric cupric phosphate. And ? Ferrous sulphate. And ? Arsine. And ? Manganous chloride. And .? Ammonium magnesium phate. And ? phos- Cuprous iodide. Ferric sulphate. And ? Aluminium hydrate. And ? Chromic hydrate. And ? Ferric hydrate. And ? 679. When potassium bichromate and sulphuric acid are heated together, chromic sulphate and other substances are formed. What are the other substances ? 680. Chlorine converts solutions of ferrous salts into ferric salts ; show the changes which take place when chlorine is added to a solution of ferrous sulphate. Substances added. 681. Sol. of ferrous chloride. Sol. of potassium bichromate. Hydrochloric acid. 682. Manganic dioxide. Sodium chloride. Sulphuric acid. 683. Sol. of potassium hydrate. Potassium nitrate. Zinc. 684. Boiling sol. of potassium hydrate. Sol. arsenious acid. Zinc. 685. Antimonious sulphide. Hydrochloric acid. 686. Sulphurous acid. Sol. of iodine. 687. Sol. sodium thiosulphate(Na2S203). Sol. of iodine. 688. Sol. of oxalic acid. Manganese dioxide. Sulphuric acid. Substances formed or set free. Ferric chloride. And . ? Manganous sulphate. And ? Potassium zinc oxide. And ? Potassium zinc oxide. And ? Antimonious chloride. And ? Sulphuric acid. And ? Sodium tetrathionate (NajSjOu). And ? Manganous sulphate. And ? 344 Fundamental Principles of Chemistry Substances added. Substances forTned' or set free, 689. Cuprous oxide (Cu.^O). Ferrous chloride. Sol. of ferric chloride. And ? Hydrochloric acid. 690. Ferrous sulphate. Ferric sulphate. Sol. of potassium permanganate And ? (K„Mn.,0„). Sulphuric acid. 691. Sol. of potassium chlorate. Ferric chloride. Ferrous chloride. And ? Hydrochloric acid. 692. Sol. of potassium iodide. _ Manganous sulphate. Manganese dioxide. And ? Sulphuric acid. 693. Arsenious zincide (AsjZnj). Zinc sulphate. Sulphuric acid. And ? 694. Name two acids, either of which, on being added to zinc, would yield hydrogen, and show the reactions by means of equations. 695. Give as many methods as you can, from the preceding exercises in this chapter, for the preparation of oxygen. 696. When ammonium nitrate is heated, what are the products of decomposition ? 697. Name one or more substances which reduce ferric salts to the state of ferrous salts. 698. Explain the following chemical reactions by means of symbols : a. The decomposition of steam by zinc. b. The decomposition of water by potassium. c. The formation of hydrochloric acid and sodium sulphate from common salt and sulphuric acid. d. The action of chlorine on sulphuretted hydrogen. e. The formation of sulphuretted hydrogen from ferrous sulphide and sulphuric acid. 699. What substance would you add to common salt and sulphuric acid if you wished to obtain chlorine. 700. What substance would you employ if you wished to precipitate by copper sulphate the whole of the iodine from potassium iodide in the form of cuprous iodide ? 701. How would you prepare chlorine ? 702. When a small quantity of water is added to pentachloride of phosphorus, oxytrichloride of phosphorus (POCI3) and some other substance are formed. When an excess of water is added to the pentachloride, phos- phoric acid and some other substance are formed. Express each reaction by an equation. 703. When manganese dioxide is strongly heated, it is decomposed ; a complex oxide of manganese, MnjOj, is produced. What other substance is formed or set free ? 704. When silicic anhydride, calcic fluoride, and sulphuric acid are heated together, calcium sulphate and some other substances are formed. What are the other substances, and how many molecules of each are formed ? 705. If sulphurous anhydride be transmitted through water in which finely divided manganese dioxide is suspended, manganous hyposulphate (manganous dithionate), Mn"S^05, is formed if the liquid be kept cool. ' Express the reaction by an equation. ExExcis£s ON Chemical Changes 345 _ 706. Silicon tetrafluoricle is decomposed by water into hydrofiuosilicic acid, HjSiFj, and some other substance. What is the other substance, and how many molecules of each are formed? 707. If manganous sulphide is digested in a solution of ammonium sul- phate, ammonium trithionate (NHj)2S30j„ and other substances are formed. What are the other substances, and show by an equation how many mole- cules of each are produced ? 708. If chlorine be transmitted through a weak and cold solution of potassium hydrate, potassium hypochlorite (KCIO) and other substances are formed. Express the reaction by an equation. 709. If chlorine be transmitted through a hot or concentrated solution of potassium hydrate, potassium chlorate and other substances are formed. Express the reaction by an equation. 710. If a current of hydrogen sulphide be transmitted through a solution of sulphurous acid, pentathionic acid (HjSsOj) and other substances are formed. Express the reaction by an equation. 711. When calcium hydrate and an excess of sulphur are boiled to- gether in water, pentasulphide of calcium and other substances are formed. Express the reaction by an equation. 712. When phosphorus is boiled with barium hydrate in water, barium hj^ophosphite (Ba2PIl20.2) and another substance are formed. What is the other substance ? 713- When a solution of ammonia is added to a solution of mercuric chloride, dichloride of dimercurammonium (Hg"2H4N2Cl2) and another sub- stance are formed. Express the reaction by an equation. 714. If phosphine is passed through a solution of silver nitrate, phos- phoric acid and other substances are formed. Express the- reaction by an equation. 715- Can you name any method for the production of ammonia from nitric acid ? 716. What is the action of chlorine on a dilute solution of potash ? 717. What is the composition of arsine ? and state as many methods as you can for its preparation. 718. Name one or more methods for the preparation of hydrogen sul- phide. 719. What is the action of ammonia on mercuric chloride ? 720. Give the action of potassium permanganate on a solution of a ferrous salt in the presence of sulphuric or hydrochloric acid. 721. Give a method for the preparation of potassium chlorate. 722. How would you prepare phosphine ? 723. Sodium thiosulphate is used as an antichlore for removing the lasl; traces of chlorine from substances bleached by that agent. Show by an equation how it acts as an antichlore. 724. When an iodide or a bromide is treated with MnOj and HjSOj, the iodine or bromine is set free. Express the reaction by an equation. 725. How would you prepare barium sulphate from a soluble barium salt ? 726. Are you- acquainted with any method for the preparation of an oxychloride ? ' Appendix. Laurent, in his 'Chemical Method,' recommends that when substitu- tional reactions are represented in the form of an equation, the second 1 The student must now return to Chap. VI. and complete the study of it, commencing at par. 362. 346 FVXDAMENTAL PRINCIPLES OF CHEAflSTRY member of the equation should be written underneath the first. This is a very good plan in many cases, for we at once perceive, when the equation is written in this manner, that to each term of the superior member there is a corresponding term in the inferior one, as shown in the following examples : 1st. — Action of chlorine upon / CI CI + HH = hydrogen. . . \H Cl + HCl. 2nd. —Chlorine upon potas- / CI CI + K H O + KHO = sium hydrate . . \K C1 + KC10 + HHO. 3rd.— Chlorine upon potas- / 3 CI CI + 2 KHO + KHO + 3 KHO = sium hydrate . . 1_3KC1 + 2KC1 hKClO, +3 HHO. 4th.— Action of chlorine and TS CI Cl + S HHO + HHO +11 = iodine on water . \ S H CI + 5 HCl + H I Oj + HIO3. 5th. — Sulphuric acid upon di- ] H.^SO., + W[vO„ = oxide of manganese . 'i Mn^SO., + H.;0 + O. 6th. — Sulphuric acid upon fH.iSO,, + K2C03 = potassium carbonate . \ K^SOj + COj + H.^0. In the fifth reaction, peroxide of hydrogen ought to be formed ; but this body, not being capable of existing in . the presence of binoxide of manganese, undergoes decomposition, and sets free its oxygen, whence the interference with the symmetry of the reaction. In the sixth reaction, the symmetry is destroyed, because HjCOj being, under ordinary circumstances, incapable of existing, becomes decomposed immediately into H._,0 and COj. CHAPTER XV. COMBINATION OF SIMILAR ATOMS— THE NASCENT STATE — ALLOTROPY — DETERMINATION OF THE ATOMIC WEIGHTS OF THE ELEMENTS — PHYSICAL AND CHEMICAL RELATIONS OF ATOMIC WEIGHTS — QUESTIONS. 758- We have now to lay before the student the chemical evidence which goes to prove that the atoms of most of the elements in the free state are united and not separated. The evidence in support of this we will arrange in three classes. 759- i-f^ Class. — In a great many of the chemical combina- tions, in which an element is one of the combining bodies, an even number of atoms of the element is required. The atoms of the element appear, therefore, to be associated in binary groups.' Examples : — I. When chlorine acts upon potash, potassium hypo- ' The ferissad elements are considered only to unite in pairs ; but the artiad elements may unite in groups of two, three, or more. Combination of Similar Atoms ^47 chlorite or potassium chlorate is formed. The following is the reaction when potassium hypochlorite is produced : 2KHO + Cl2=KC10 + KCl + H20. Potassium hypochlorite. When potassium chlorate is formed the following reaction takes place : 6KH0 + 3Cl2=sKCl + KCIO3 + 3H2O. 2. When sulphur is fused at a gentle heat with an alkaline hydrate, or boiled with an aqueous solution of the alkali, two compounds, dipotassium pentasulphide and potassium hypo- sulphite, are formed : 6KHO-|-6S2=K2S203 + 2X385 + 3HA 760. When metallic sulphides oxidise in the air, both elements enter into combination with oxygen ; thus, NiS + 200=NiS04 761. In organic acids the whole or part of the hydrogen in the acid radical can be replaced by the halogen elements, especially by chlorine, and there does not exist a single organic compound upon which we can effect any reaction by employing an uneven number of atoms of chlorine. In every case it is CI2, or a multiple thereof, which determines the reaction ; the compound may contain an uneven number of atoms. The following are examples of this statement : — HC2H3O2 + Cl2=HC2H2C102 + HC1.1 Acetic acid Monochloracetic acid HC2H3O2 + 3Cl2 = HC2Cl302 + 3HCI. Trichloracetic acid 2nd Class. — There are a great number of decompositions which cannot be explained in any satisfactory manner unless we admit that the atoms of the same elements are capable of entering into combination with each other. 762. When a solution of potassium dichromate is poured into a strong acid solution of barium peroxide (Ba02) in ' The hydrogen in the acid radical is not replaceable by metals, but is re- placeable by the halogen elements, as exemplified by the action of chlorine on acetic acid. 348 Fundamental Principles of Chemistry hydrochloric or nitric acid, a violent effervescence takes place, due to the escape of oxygen. Apart these solutions are perfectly stable, but when brought together they are both decomposed ; oxygen is liberated from both compounds, the metals becoming converted into chlorides ; thus — loHCl + K^CrOi. Cr03 + Ba02=Cr2Cl6 +2KCl+BaCl2 + SH2O + 2OO. The late Sir B. Brodie regarded the oxygen itself in this experiment as the true reducing agent ; he believed that the chromic acid is decomposed by the oxygen of the peroxide of hydrogen, according to the same law of decomposition, and for the very same reason as it would be by hydrogen itself if a piece of zinc were thrown into the solution, the reason being the polarity of the particles induced by chemical change. 763. Before passing on to the 2nd example in the 2nd class, it is desirable to inform the student that the reason assigned for the chemical union of the atoms of the same ele- ment is the same as that assigned for the union of the atoms of different elements, and of the molecular atoms of compound substances ; it is this, that at the moment oi chemical change a chemical difference exists between the substances, whether elementary or compound, that are set free and combine, which is expressed by the terms positive and negative ; therefore, when chemical combination takes place between the atoms of the same or unlike substances, a chemical difference exists between the atoms as they are to one another in 2i positive and negative relation. 2. Cuprous hydride, CuH, in contact with strong hydro- chloric acid, is decomposed along with the acid, cuprous chloride, CuCl, being formed, and hydrogen evolved ; thus — + - +- CuH -)- HCl=CuCl -h 2HH. This is perfectly analogous to the following decomposition : — + - + - CujO + HCl=Cu2Cl2 + H20. Hydrochloric acid scarcely acts upon copper ; the combina- tion of hydrogen with copper, far from favouring the action of Combination of Similar Atoms 349 the acid upon the metal, ought, according to the idea that the atoms of the same element do not unite but remain free, to add a new obstacle to it. Hydrochloric acid also dissolves an alloy of copper and zinc, although on the copper itself it has little action. The hydride of copper is itself, in its chemical relations, an alloy ; the action of the acid corisequently is the same upon the compound of copper and hydrogen as upon the compound of copper and zinc, and the explanation of these facts involves similar phenomena. Thus — + - + - +- 2HCl + ZnCu + 2ClH=ZnCl2 + CuCl2 + 2HH. The oxides of gold, silver, and mercury, on being placed in a solution of hydrogen dioxide (H2O2), decompose and are decomposed by that body, although apart the metallic oxides and the dioxide are perfectly stable ; the metallic oxides lose the whole of their oxygen, whilst the dioxide loses one-half a molecule of oxygen, a molecule of the metal and water being formed. Example : — + - + — + AgaO + H200= Ag2 + 00 + H2O. 764. yd Class. — As a chemical compound possesses pro- perties perfectly different from those of its constituents, it follows that, if two or more atoms of the same element are capable of entering into combination, the homogeneous com - pound ' and the elementary atoms in their free state will be dis- tinguished by a difference in their properties. That the element s do not possess under all circumstances the same physical and chemical properties, but that the same element differs as much in properties under, different conditions as some heterogeneous compounds differ from their constituents, is evidenced by the allotropic modifications of some of the elements,^ and by the nascent, compared with the ordinary, state of the elements. ^ We shall call compounds consisting of a combination of the atoms of the same element, homogeneous compounds, to distinguish them from compounds composed of unlike elements : the latter class of compounds, composed of unlike elements, we shall call lieterogeneous compounds, 2 ' There appear to be four different conditions in which solid bodies may- exist. They may be — ist. Crystalline, as diamond, garnet, felspars. 2nd. Vitreous, or glassy, as glass itself, transparent arsenious acid, and barley sugar. 350 Fundamental Principles of Chemistry i. The affinities of the elements in their nascent state ' are much more powerful than in the ordinary state of the elements ; nitrogen, for instance, cannot, except with very great difficulty, be made to unite directly with any element, but requires for its combination that one or both the elements should be in the nascent state. In order to effect the combination of chlorine and hydrogen, oxygen and hydrogen, independently of any agent, such as heat, it is necessary to bring them together in their nascent state. To effect the union of a solid with a gas- eous body, it is necessary, in a number of cases, to bring them together in their nascent state ; thus, no chemical combination ■will take place if a stream of hydrogen be passed into sulphur. If, however, the two elements are set free from other combina- tions at the same moment and in presence of one another, they combine together and form hydrosulphuric acid. This is also the case with hydrogen and the following substances : — phosphorus, carbon, arsenic, antimony, &c. We cannot well explain why the affinities of the elements should be so much greater at the moment they are set free from their (heteroge- neous) combinations than they are afterwards, unless we admit that the atoms of the same elements are capable of entering into combination. If we admit the existence of molecular atoms, then there is no difficulty in accounting for the great disparity in the affinities of the elements in the two states ; for in the nascent state the atoms of the element are uncombined, in the ordinary state they are united ; consequently when two •elements are set free from other combinations at the same moment and in presence of each other, the two elements enter into combination, because the unlike atoms have a greater affinity for each other than the like atoms have ; or, as it would be expressed on Brodie's theory, the unlike atoms are in a greater positive and negative relation. 2. Phosphorus, sulphur, carbon, and silicon are very strik- ing examples of the allotropic modifications or conditions of 3rd. Amorphous, ox AitilMMs of crystalline form altogether, as tinder, chalk, or clay. 4th. Organised, or arranged in masses, consisting of cells, fibres, or membranes, like the tissues of animals or \egetables, as hair, muscle, skin, wood, bark, leaves, Sec.'— Miller. ' The moment elements are set free from their combinations they are said to be in their nascent state. Allotropy 351 matter. Phosphorus can be obtained in the crystalline, vitreous, and amorphous state. In its ordinary state, it is a soft, semi- transparent, colourless, waxy-looking solid, which fumes in the air, emitting white vapours of an alliaceous odour. Its specific gravity is i'83. It fuses at iii's° F. It is very inflammable ; it takes fire in the open air a few degrees above its fusing point. The crystalline form is equally inflammable with the vitreous. Amorphous phosphorus is red. In this state it is insoluble in a great many hquids in which the crystalline and waxy forms dissolve. The density of red phosphorus is 2-14. It has no smell ; and it may be heated in the open air, -without change, until the temperature reaches 500° F. : at this heat it melts, and bursts into flame. One form of sulphur has a density of 2-05 and melts at 239° F. ; another form of the element has a density of 1 '98, and melts at 248° F. ; and a third form has a density of i'9S7. These three varieties of sulphur are also distinguished from each other by a difference- in some of their other properties. The student has only to contrast the pro- perties of the diamond, graphite (the black-lead of pencils), and ordinary charcoal, to see that the properties of carbon are as various as the conditions in which it can exist. Silicon can be obtained in two distinct modifications, viz. the amorphous and the crystalline modification ; and its properties in the two diff"erent states differ remarkably. 765. Allotropy is as yet unexplainable ; it is probably due to the molecules of the different modifications containing a different number of atoms, as we have seen is the case with ozone, the allotropic modification of oxygen. 766. We shall conclude this, the last chapter of this volume with a description of some of the methods adopted for deter- mining the numerical values of the atoms of the elementary bodies. 767. According to Dalton's atomic theory the atoms of the same element are all of equal size and weight ; and the atoms of one element differ from those of the other elements in weight and in chemical properties ; and as hydrogen is the lightest substance in nature, and the proportion in which it enters into combination is less than that of any other element, Dalton chose it as the unit in his scale of atomic weights, and 352 FUXDAMRNTAL PRINCIPLES OF CHEMISTRY it is accepted as the unit wherever chemistr)' is studied. Dalton also assumed that the most stable compound of two elements must be binary, i.e. composed of one atom of each of the elements. Now, as the most stable combination of oxygen and hydrogen is water, and as in that compound the two ele- ments are united in the proportion by weight of one part of H to eight of O, Dalton assumed the atomic weight of oxygen to be eight ; the formula of the compound consequently became HO. Chemists at the present time regard the atomic weight of oxygen as double that number, viz. i6 ; and they have doubled the atomic weights of several of the other elements ; for the atomic weights are now arrived at from more considerations than guided Dalton in fixing his scale of atomic weights. The considerations which guide chemists at the present time in arriving at the atomic weights of bodies ' are often some- what complicated, based partly on the law of gaseous volumes, partly on, the experimental results upon the specific heat of the bodies under investigation, partly on the isomorphism or similarity in crystalline form of bodies of analogous constitution ; and the principle of analogy frequently enables us to determine satisfactorily the molecules and atomic weights of bodies with which we are comparatively but little acquainted.' 768. We will commence the examination of the foundation on which our present system of atomic weights and our nota- tion rest, with the four typical compounds we employed to illustrate the volume-proportions in which gaseous and vapour- isable substances unite ; the compounds are HCl, H^O, H3N, and H4C. The first question it would be natural forthe student to ask would be this, — Why are the formulse for water, nitrine, and methane not as simple as the one for hydrochloric acid ? If these three compounds were written thus, HO, HN, and HC, then the atomic weight of oxygen would have to be reduced to 8, the atomic weight of nitrogen to 4"67, and the atomic weight of carbon to 3. In placing before the student the considerations which guide chemists in fixing the atomic weights of bodies, we will first direct his attention to the chemical action of some simple and compound radicals on these four typical compounds. 769. When sodium, for example, acts upon hydrochloric acid, the whole of the H in the compound and never a portion Determination of the Atomic Weights 353 of it, is always expelled ; a compound is therefore neve r formed containing both hydrogen, sodium, and chlorine, but it always consists solely of sodium and chlorine. If, on the other hand, we act on water with sodium, a compound consisting of sodium, oxygen, and half the hydrogen the water contained, is obtained ; the other half of the hydrogen having been expelled by the sodium, the latter taking its place. If the NaHO is heated with a further quantity of Na, the other half of the H is expelled by the Na, the compound NagO being formed . One half the hydrogen in water can, therefore, unlike the H in HCI, be displaced by Na. Now, if water had the same atomic con- stitution as HCI, sodium ought to expel the whole of the H, as it does in that compound, and never in part, because if it ex- pelled a part, the atom of H must divide, which is contrary to the fundamental notion of atoms, namely that they are in- divisible. 770. In nitrine the hydrogen is replaceable by thirds, and not, as in water, by half the amount. In methane we can dis- place the hydrogen by other radicals by one-fourth, or two- fourths, or three-fourths, or four-fourths. 771- By these reactions we find, — that the hydrogen in hydrochloric acid is not divisible ; that in water it is divisible into two equal parts ; in nitrine into three parts, and not into two parts as in water, nor into four parts as in methane ; in methane it is divisible into four parts, and not into three parts as in nitrine. The student will therefore see that these reac- tions afford strong evidence for the belief that a molecule of hydrochloric acid contains one atom of H ; that a molecule of water contains two atoms of hydrogen ; that a molecule of nitrine contains three atoms of that element ; and that a mole- cule of methane contains four atoms of it. 772. We further find by chemical reactions that when water is the agent or resultant of a reaction it must contain two atoms or some multiple of two atoms, of hydrogen ; in like manner when nitrine is the agent or resultant it cannot be expressed with less than three atoms of that element ; and when methane is the agent or resultant it cannot be expressed with less than four atoms of it. 773. We have learned in studying the duality of the ele- A A 354 FUXDAMENTAL PRINCIPLES OF CHEMISTRY mentary molecules that 35-5 parts by weight of chlorine can replace one part of hydrogen ; it is therefore accepted, from this and other evidence, that 35-5 is the relative weight of an atom of chlorine. One unit weight of hydrogen is never replaced by 8 of oxygen ; oxygen always replaces hydrogen in the proportion of 16 parts to 2 of hydrogen ; the relative weight of an atom of oxygen is taken to be 16. Nitrogen replaces hydrogen in the proportion of 14 of nitrogen to 3 of the latter element, 14 is therefore accepted as the relative atomic weight of nitrogen. It has been shown that 12 parts of carbon replace 4 parts ot hydrogen in 3 molecules of nitrine in the formation of an organic compound called guanidine. These are a very few examples of the aid derived from the valency of the atoms in determining the atomic weights of the elements. 774. When the specific gravity of hydrogen is taken as unity the specific gravities, as we have already learned, of most of the elementary gases and vapours are expressed by numbers identical with those that have been selected to express their atomic weights. We have also learned, 'that the molecules of compounds which are gaseous or volatile without decomposi- tion occupy two volumes, if an atom of hydrogen occupies one volume. The result of this is that the molecular weights of volatile compounds are accurately given by their densities. And if we refer these densities to that of hydrogen taken as unity, we have only to multiply the numbers obtained by 2 to find the weight of the molecules compared with that of an atom of hydrogen=i. This is a general rule. 775. ' The atomic weigh ts of a certain number of non-metals and metals may be calculated from the molecular weights. Thus the atomic weights of phosphorus, arsenic, antimony, silicon, tin, mercury, and lead may be calculated from the mole- cular weights of their volatile compounds. For example — 776. ' The molecular weight of chloride of silicon (obtained by doubling its vapour-density) is 170, and analysis shows tha 170 parts of chloride of silicon contain 142=4 x 35-5 of chlo- rine and 28 of silicon. The vapour-density and analysis of chloride of silicon assign, therefore, to this body the formula SiCl4, and to silicon the atomic weight 28, for we have reason Determination of the Atomic Weights 355 for the belief that the molecule of chloride of silicon, only con- tains a single atom of silicon. 777. ' This example shows the use which may be made of the law of Avogadro in the determination of molecular weights and in settling atomic weights.' 778. Analogy is also, as we have stated, a guide in deter- mining the atomic weights of the elements ; because when compounds are analogous, as the selenium and tellurium com- pounds with those of sulphur, they are assigned similar formulse; therefore, for example, if we assign the formula H2S to sulphur- etted hydrogen, the formula for selenuretted hydrogen must be HgSe, and for telluretted hydrogen HaTe ; hence, from these hydrogen compounds we can determine the atomic weights of Se and Te. 779- Isomorphism is also of assistance in determining, as we have seen in the case of alumina, the molecule of a compound and the atomic weights of its constituents : for, if the compo- sition of one substance is known, the composition of another substance, isomorphous with it, can be inferred, and the atomic weight of its constituents determined. The student must, however, bear in mind that substances having, the same cry- stalline form are not isomorphous, unless they are able to re- place each other in the same crystal. 780. The specific heats of the elementary bodies in the solid state, if equal weights of the elements are employed, differ very considerably ; but if, instead of employing equal weights, quantities in proportion to their atomic weights are employed, the specific heats of the elements, with some slight exceptions, are equal. So that an atom of any simple substance, whether its atomic weight is small, as that of lithium, or large, like those of bismuth and lead, has the same capacity for heat, and requires the same quantity of heat to raise its temperature, as an atom of any other element ; this quantity is called its atomic heat, and can be arrived at by multiplying the atomic weight of the ele- ment by its specific heat. Conversely, the chemist is guided in fixing the atomic weight of an element by the number he ob- tains by dividing the mean atomic heat (6'4) of solid elemen- tary bodies by the specific heat of the element in the sohd state. This important law was discovered by Dulong and Petit. We 3S6 Fundamental Principles of Chemistry have very briefly explained this law ; but we shall explain it more fully in the second volume of this work, and also the periodic law, first discovered by Newlands. 781. We will summarise what has been set forth in the words of the late Professor Wurtz: — (i) The present system of atomic weights is founded on the law of volumes, and is in harmony with the hypothesis of Avogadro. (2) It is in harmony with the law of isomorphism; (3) And it is in harmony with the law of Dulong and Petit. Examination Questions. 727. What multipliers must be used to transform the atomic weights of the toUowing elements into their respective molecular weights : oxygen, sulphur, zinc, phosphorus, mercury, ozone, arsenic, cadmium, and hydrogen ? 728. What products are formed on burning cyanogen in oxygen ; and how much oxygen is required for the combustion of one cubic inch of cyanogen ? What would be the volume of the resultant gases at the initial temperature and pressure ? 729. What facts and considerations can you adduce in support of the theory of duality of certain elementary molecules ? ANSWERS TO THE EXERCISES. Witk one or two exceptions answers are not given to the experimental exer- cises, as the experiments explain themselves. The questions are classed as exercises. The contractions — as par, for paragraph — are all sufficiently intelligible. CHAPTER I. Ex. 14, par. 3. Ex. 15, par. 14. Ex. 16, par. 8. Ex. 1 7. Persons in an omnibus participate in its motion ; on alighting when the vehicle is moving, advance slowly for a short distance in the direction it is going, and do not attempt either to stand still, or move in an opposite direction ; par. 46. Ex. 18, pars. 29, 30. Ex. 19. Bodies which admit of being bent without breaking, and which retain the form they have been made to assume, are said to be ductile and pliable. Ex. 20, par. 46. Ex. 21. The physical properties are the external signs ; all our senses are not equally made use of; in our decisions we are generally guided by the evidence of sight and touch. Ex. 23. Bodies are said to be hard which resist a considerable external force, either by pressure or impact : of two bodies, that is said to be the harder which causes the disruption of the other. Ex. 24. Bodies are called soft which can be made to change their form on the application of a trifling force, no disruption of their parts taking place : for ' brittle ' see par. 28. Ex. 25, pars. 37, 38. CHAPTER n. Ex. 26, 15-5; 12-4; 167; i22;-6-6;— 19;— 28-4;— 2i;-4i ;— — II -2;— 32-8. Ex. 27, 22-8. Ex. 28, 136-8. Ex. 29, 0-033. Ex. 30, 0-2035. Ex. 31, 0-0927. Ex. 32, 0-0355. Ex. 33, 0-0252. Ex. 34, 2-035. Ex. 35, par. 69. Ex. 36, par. 73. Ex. 37, par. 79, Ex. 38, par. 124. Ex. 39, pars. 89, 124. Ex. 40. Equal weights and equal volumes of dissimilar substances require diflerent amounts of heat to produce the same alteration in their temperature. Of two substances the one that requires the lesser amount to 3S8 Fundamental Principles of Chemistry raise its temperature a given number of degrees is said to have the lesser capacity for heat ; and the quantity of heat which a substance requires to raise its temperature from o° C. to i° C. compared with the quantity re- quired to raise an equal weight of water through the same interval, is called its specific heat ; pars. io8, i lo. For 1 atent heat, see par. 136. Ex. 41, pars. 73, 75. Ex. 42, par. 85. Ex. 43, par. 108. Ex. 44, pars. 92, 93. Ex. 45. No ; they vary in length, becoming shorter in winter and longer in summer. In laying down a line of railway this change of length has to be taken into account, space being left between the rails to allow of their expansion. Ex. 46. The degrees from and below the freezing-point. Ex. 47, pars. 142, 143. Ex. 48. On account of the heat (i42'65° F.) that has to be absorbed, and becomes latent in order to liquefy it ; if ice and snow were speedily to liquefy, as they would, if the latent heat were only one or two degrees, sudden and destructive floods would be formed ; conversely the oceans in non-tropical climates would speedily be frozen. Ex. 49. Owing to the unequal expansion of the different thicknesses. Ex. 50. The vessel being exposed to a. constant source of heat, the quantity it receives is always the same in the same time, but its temperature does not increase indefinitely, for what it loses increases with the excess of the temperature over that of the surrounding medium; consequently a point is reached, in accordance with Newton's law of cooling, at which the quantity of heat emitted is equal to that absorbed, and the temperature then remains stationary. Ex. 51. By requiring such a large amount of heat (966'6° F.) for its conversion into steam. Ex. 52, par. 141. Ex. 53, par. III. Ex. 54. Because the temperature at which liquids boil varies with the pressure to which they are subjected. Ex. 55, pars. 145, 146. Ex. 56, par. 152. Ex. 57, par. 152. Ex. 58, par. III. CHAPTER III. Ex. 59, 1-9685. Ex. 60, 0-0648 gram. Ex. 61, 0-73236. Ex. 62, 49-156 c.c. Ex. 63, 61bs. 90Z. I3drms. Ex.64, 2-54 centimetres. Ex. 65, i oz. idwt. l-6gr. Ex. 66, 2-5 acres 11 yards; 2,000 kilos. =4,409 lbs. ; 5,000 kilos. - 11,023 lbs. ; 1,600 kilos. =3,527 lbs. ; 3,800 kilos. =8,377 lbs. Ex. 78, 20-3935.' Ex. 79, 14-1791- Ex. 80, 5-9273. Ex. 81, 104-3265. Ex. 82, 7-4. Ex. 83, 18-2985. Ex. 84, 29-345. Ex. 85, 4-5265. Ex. 86, 1-293. Ex. 87, 6-416. Ex. 88, 77 cubic feet expelled. Ex. 89. The weight of 4 feet of air at 104° F. is equal to the weight of 3-58 feet at 44-5°F. ; henceacolumn of air fourfeet in the chimney would balance a column 3-58 feet outside. Therefore the ascensional force will be 0-42 of the weight of a cubic foot of air on each square foot of the cross-section of the chimney. Ex. 90, par. 155. Ex. 91, pars. 184, 185. Ex. 92, pars. 172, 173, 195. Ex. 93, true weight = 63 -992 grms. 1 The formulae in pars. 223, 224, and 225 are for calculating the volume to and from 0° C. or 32° F. Answers to the Exercises 359 Ex. 94. Up to 260° C. air and mercurial thermometers agree, but above that point mercury expands relatively more than air ; the air thermometer is above this temperature regarded as the standard instrument : see also par. 88. Ex. 95, pars. 105, 106. Ex. 96. The latent heat of water is between 79° C. and 80° C. ; we have taken it at 79° C. ; at this temperature the 1 1 lbs. of water will have consequently a temperature of 11° C. Ex. 97, Expt. 74. Ex. 98, pars. 221, &c. Ex. 99, 22-6 c.c. Ex. 100. The latent heat of water in this question is taken as 80° C. Ex. loi. Bodies fall to the ground in consequence of the earth's attraction on each of their molecules ; therefore, all bodies, whatever their size, ought to fall with equal rapidity, and they do fall with equal rapidity in a vacuum, but not, as we all know, in air, owing to the unequal resist- ance air opposes to their descent. Ex. 102. One cubic foot, 1 563 -43 cubic inches. Ex. 103. Because descending as well as ascending currents of smoke and air would take place. Ex. 104. The air which passes up the chimney carries off the rest. Ex. 105. The draught of a chimney is proportional to its height ; hence chimneys of a shorter height are much more liable to smoke than chimneys of greater height. Ex. 106. The volume of a gas is inversely as the pressure ; the volume being decreased one-half if the pressure be doubled. Heat, on the other hand, we have learned, expands gases ; see also par. 221. Ex. 107, 534-16 c.c. Ex. 108, 273° C. Ex. 109, 5-051 litres, CHAPTER IV. Ex. 110, l8-o8 cub. inches. Ex. in, 18-03 cub. inches. Ex. 112, 15-49 cub. inches. Ex. 113; 81-395 cub. inches. Ex. 114, 637° C. Ex. 115, 13-598 cub. inches. Ex. 116, 24-113 cub. inches. Ex. 117, 14-6 cub. inches. Ex. 118, 11-195 cub. inches. Ex. 119, 72-77 mm. Ex. 120, 71-24 mm. Ex. 121, "63-88 mm. Ex. 122, par. 235. Ex. 123, pars. 237, 238, 241, 248. Ex. 124, par. 281. Ex. 125. On account of the greater pressure. . Ex. 126. If they were filled, they would, on ascending, tend to burst, owing to the gas expanding by reason of the pressure of the atmosphere diminishing, pars. 194, 195. They cease to ascend, and can only take a horizontal direction when the buoyancy becomes equal to the weight of the balloon. Ex. 127. Moisture is always present in air, and the quantity varies greatly ; warm air can take up more than cold air, par. 285. And if a confined portion of air be heated, and no additional moisture be added, we experience in such an atmosphere unpleasant sensations, owing to the rapidity with which evaporation takes jjlace; hence the skin feels dry; and it is to remedy this that a plate containing water is frequently placed on the top of stoves. Ex. 128. In one case it would be converted into the gaseous state, and in the other case it would be solidified. Ex. 129, par. 239. Ex. 130, par. 255. Ex. 131. The dew-point is a name used to denote the lowest tempera- 360 Fundamental Principles of Chemistry ture to which the air can be cooled down without depositing some of its moisture. Ex. 132. Consult the paragraphs describing these instruments, and note particularly the difference in their construction. Ex. 133. Because in the one saturated with moisture perspiration from the skin is impeded. Ex. 134, pars. 215-218. Ex. 135. Some of the air will rush out of the vessel on the top of the mountain ; at the foot some of the external air will rush into the vessel. Ex. 136. The surface of the earth and the air over it is much warmer than the surface of the sea and the air over it, during the day ; the hot air over the island consequently ascends, and the cooler air, the j«ffl-breeze, sets in from the sea. Conversely, during the night the sea gives out some of the heat it absorbed during the day, whilst the surface of the earth, from the absence of the sun, becomes comparatively cold. This reverse change in the temperature of the air over the land and sea produces the /a«(^-breeze. Ex. 137, pars. 235-238. Ex. 138. Because the air becomes more compressed, and therefore its sensible heat is diffused through less bulk. Ex. 139, pars. 94, 1 04. Ex. 140. The bubbles of vapour first formed condense on passing up through the colder layers of water ; and the formation and condensation of the bubble occasion the singing. Ex. 141. They are due to a current of moist air of a higher temperature than the surface of the sea ; the cooling causes a condensation of some of the moisture, which appears in the form of fog or thick mist. Ex. 142. Because they absorb moisture from the air ; sulphuric acid is a liquid which absorbs a large quantity. Ex. 143, par. 234. Ex. 144. It is that temperature at which the tension of its vapour exactly balances the pressure of the atmosphere. Ex. 145, par. III. Ex. 146. Because the motion of the body is not added to the muscular effort, as it is when a run is made before leaping. Ex. 147, par. 237. Ex. 148. On cloudy nights little or no dew is deposited, because the heat radiated from the earth is radiated back by the clouds, and therefore the reduction of temperature necessary for the deposition of dew does not take place ; but on cloudless nights the heat emitted is not returned, hence dew is deposited. Ex. 149, pars. 260, 261. CHAPTER V. Ex. 150. 0-86'. Ex. 151. 0-8'. Ex. 152. 1-175. Ex. 153. 0-857. Ex. 154. 9-53 lbs. Ex. 155. 7-92 lbs. Ex. 156. ii-72lbs. Ex. 157. io-63lbs. Ex. 158. 3430-9 grains. Ex. 159. 2-5. Ex. 160. 2-6'. Ex. 161. 2-0.. Ex. 162. 5-8. Ex. 163. 1-823. Ex. 164. 3-6. Ex. 165. 4-0. Ex. 166. 2-143 Ex. 167. 4-824. Ex. 168. lo-o. Ex. 169. 0-844. Ex. 170. 0-6. Ex. 171. 0-777. Ex. 172. 0-6. . Ex. 173. 1980 lbs. Ex. 174. I -45 cub. ft. -, Ex. 175. 486-3 lbs. Ex. 176. 208-llbs. Ex. 177. 52-8 lbs. Answers to the Exercises 361 Ex. 178. 15 lbs. Ex. 179. 58-2 lbs. Ex.180. 2644-2 grains. Ex. 181. 437-5 lbs. Ex. 182. 373' cub. feet; Ex. 183. 1-5. Ex. 184. 0-79. Ex. 185. -084. Ex. 186. I -16' .sp. gr. of the body; 0-875 sp- gr- of the spirit. Ex. 187. 0-789. Ex. 188. 2-388. Ex. 189. 13-94. Ex. 190. The alloy consists of 7-29 parts of gold, and 2-71 of silver. Ex. 191. The alloy consists of 29-19 parts of silver, and 7-81 parts of copper. Ex. 192. 17-608. Ex. 193. 16-04. Ex. 194. 1-555. Ex. 199. 0-3420. Ex. 200. 0-3004. Ex. 201. 0-4729. Ex. 202. 0-1825. Ex. 203. 71 -54 cub. inches. Ex. 204. 150-43 cub. inches. Ex. 205. 12-776 gram. Ex. 206. 0-886 gram. Ex. 207. 19-54 gram. Ex. 208. 3-25. Ex. 209. 1-547. Ex. 210. 1-07. Ex. 211, pars. 292-294. Ex. 212, pars. 307, 308. Ex. 213, par. 292. Ex. 214, par. 313. Ex. 215. (l)par. 304; (2) par. 312; (3) par. 306. ^ Ex. 216, par. 320. Ex. 217. 4-22. Ex. 218. 5-83. Ex. 219. No ; cork, being of greater bulk, is buoyed up in the air by greater force, and hence weighs less in air ; par. 324. Ex. 220. 32 ft. 9-5 inches, par. 176. Ex. 221, par. 294. Ex. 222. 0-8333. Ex. 223. 105 pts. by wt. of silver to 29 pts. by wt. of copper. Ex. 224, par. 180 ; oil barometer 11-692 metres. Ex. 225, par. 309 ; 22-4 grms. in alcohol. Ex. 226, par, 250. Ex. 227, par. 308; 0-84sp.gr. of the spirit. Ex. 228, par. 108. Ex. 229. 38 ft. 10-73 inches. Ex. 330. Because it is buoyed up with greater force by the water. Ex. 231. The weight of water displaced, and the quantity displaced, is equal in weight to the ship itself. Ex. 232. As it is soluble in water, its sp. gr. must be determined in some liquid in which it is insoluble. Ex. 233. Weight of a cub. ft. 450 lbs. ; weight immersed in water 387 -5 lbs. CHAPTER VI. Ex. 252. The chalk is insoluble, and the salt is soluble in water. Ex. 253. The turbidity is due to the substance being less soluble in hot than in cold water. Ex. 254. By evaporating the solution in an evaporating dish to dryness, and then examining whether any solid remains. Ex. 255. When it ceases to dissolve it is a proof that the liquid is satu- rated, and by the solid dissolving in the boiling liquid it shows that it is more soluble in the hot than in the cold liquid. CHAPTER VII. Ex. 272, par. 381. Ex. 273. By diminishing the atmospheric pressure the normal boiling- point of the ether is lowered, and it abstracts from the water the heat necessary for its ebullition, which causes the latter liquid to freeze. Ex. 274. It is due to the gas expanding on removing the pressure. Ex. 275. The ratio is as 0-27 to i. B B 362 Fundamental Principles of Chemistry CHAPTER VIII. Ex. 326, par. 410. Ex. 327. The burning is due to their combining with some of the oxygen of the air. Ex. 328, pars. 411, 412, 415. Ex. 329. Expts. 280, 283-285 ; and 281, 282, 286. Ex. 330, par. 432. Ex. 331, par. 420. Ex. 332, par. 439; Ex. 333, pars. 407-409- Ex. 334, Expts. 286, 283. Ex. 335, pars. 429, 430. Ex. 336. Steam is water in the gaseous state, and its two elements, H and O, have entered into the highest state of combination. Ex. 337, par. 445. Ex. 338, par. 449. Ex. 339, par. 417. Ex. 340, par. 446. Ex. 341, par. 448. Ex. 342, par. 425. Ex. 343, par. 440. Ex. 344. No ; it must be mixed with air or oxygen. The products of the. explosion are carbon dioxide and water, and if the air has been em- ployed there is likewise nitrogen. Ex. 345, par. 459. Ex. 346. Phosphoric anhydride (P-^Os) and water (H^O). Ex. 347, par. 439. Ex. 348. When burnt as it issues from the burner its elements only enter into union with the oxygen of the air at the point of contact, and therefore only in small quantities at a time ; but when the air and gas are mixed the combination is instantaneous throughout the entire mass ; and the great heat developed instantaneously causes a great and sudden ex- pansion of the gaseous products. To this and the after-contraction the explosion is due. Ex. 349. Expt. 292. Ex. 350. According to the quantity of air, either the whole or part of the carbon will be set free in the form of soot. Ex. 351, Expt. 322. Ex. 352, par. 434. Ex. 353, pars. 345-347- Ex. 354, pars. 391, 407, 411, 459. CHAPTER IX. Ex. 366, par. 431. Ex.367. It would simply volatilise. Ex. 368. A gain in weight. Ex. 369. Yes ; the intensity would be increased. Ex. 370. On account of the aqueous vapour it contains. Ex. 371, par. 410. Ex. 372, par. 463. Ex. 373, pars. 468, 469. Ex. 375. Because the carbon cannot combine with a further quantity of oxygen. Ex. 376, pars. 468, 469. Ex. 377, par. 462. Ex. 378, par. 470. Ex. 379. Because the hydrogen cannot combine with a further quantity of oxygen. Ex. 380. Heavier by the amount of oxygen they have combined with. Ex. 381, a 12-36 grams." 8-55 litres; b 18-39 grams. 12-75 litres.' Silver is extracted from argentiferous galena by the process described in par. 499. ' The number of the Exercises ought to be a. 703 ; i. 664. Answers to the Exercises 363 Ex. 382. The amount of iron oxidised would be 233-33 grams. ; and the increase in weight would be 322-21 grms., and the volume of hydrogen gas set free would be 124 litres ; for the formula of the oxide formed see par. 479. Ex. 383. If we take ozone as the type of allotropic bodies in general, then we might infer that allotropy is due to the molecules of the different modifications of an element containing a different number of atoms. Ex. 384. If the substance was exposed to heat and it took fire and burnt, it would prove it was diamond and not glass. Ex. 385. It is most conveniently prepared by acting on MnO^ with HCl ; this is the way it is prepared on the manufacturing scale : 1225-3 grams, of MnOa, and 2056-3 grams, of HCl. Ex. 386. The earthy substances in ores are termed the gangue. Slag is the fusible mass that is formed by the fusion of the gangue with the substances added, which are called the_/?«x ; par. 495. Ex. 387. 38-44 vols, of air; 2-0995 vols, of steam, 63-9 vols, of nitro- gen in the air employed. Ex. 388, par. 490. Ex. 389, par. 479. Ex. 390, par. 482. Ex. 391. A reducing agent is a substance which removes oxygen from other substances, metals for instance, with which it is united, owing to its greater affinity for the oxygen. The reduction of metallic oxides on the manufacturing scale is also termed smelting. Ex. 392, par. 487. Ex. 393, par. 503. Ex. 394, pars. 491, 494, 505. CHAPTER X. Ex. 395. 31-5 lbs. of HjO, and I -5 lbs. of H in excess. Ex. 396. 182-5 lbs. of HCl, and 0-5 lb. of CI in excess. Ex. 397. 896 lbs. of HI, and III lbs. of I in excess. Ex. 398. 85 lbs. of H.^S, and I lb of H in excess. Ex. 404. On account of not knowing the condensation that has taken place in the union of the O and N, we have therefore to ascertain how much H remains uncombined after the first explosion. We ascertain this by adding O and again exploding. There is a reduction in volume 'on this second explosion of 75 c.c. , owing to the condensation of the water formed ; there- fore 50 c. c. of H remained uncombined after the first explosion ; conse- quently 100 c.c. of the oxide of nitrogen gas consisted of 100 c.c. of N and 50 c. c. of O. Ex. 405. 68-41 grains. Ex. 406. 327-65 cub. inches. Ex.407. 31-44 litres. Ex.408. 0-716 gram. Ex. 409. 69-92 litres; and 87-84 grams. Ex. 410. 40 c.c. of aqueous vapour, and 10 c.c. of H. Ex. 411. 500-07149 grams. Ex. 412. One cubic inch ; two cubic inches. Ex. 413. One c.c. ; two c.c. Ex. 414. 0-5 c.c. ; 2 c.c. Ex. 415. 0-9688. Ex. 416. 126-53. Ex. 417. One. Ex. 418. 0-588; Ex. 419. 169-87. Ex. 420. Four. Ex. 421. 1,176. Ex. 422. Two. Ex. 423. 9-39. Ex. 424. 23-01 of O ; and 76-99 of N. Ex. 425. 5,301. Ex. 426. 106-5 ; three ; AuClj. Ex. 427. 127 ; Aul. Ex. 428. 24 ; AI.P3. Ex. 429. 106-5 ; BCl,. Ex. 430. 142-0; SnClj. Ex. 432. Na = 23, Ag=io8, Mg=i2. Ex. 433. Ca = 20, B = 3-66, Sn = 29-5. 364 Fundamental Principles of Chemistry Ex. 434. Fe" = 28, Fe"'= 18-66. Ex. 435, pars. 392, 576, 577, 520. Ex. 436, par. 391. Ex. 437, par. 541. Ex. 438, par. 557. CHAPTER XI. Ex. 445, par. 584. Ex. 446, par. 598. Ex. 447, pat. 593. Ex. 465, par. 616— 1st. Ex. 466. Taking the limestone as pure, it would yield 14027 lbs. Ex. 467. 154-9 lbs. of CaH.O.. ; and 3J-6 1bs. ofNHj. Ex. 468. 13 lbs. CHAPTER XII. Ex. 476. On account of the smaller atomic weight of sodium. Ex. 477, par. 658. Ex. 478, par. 643. Ex. 479. -053 grams, of C. ; 100 c.c. ofCO„. Ex. 480. The acid acts upon the silver, converting it into sulphate, but it does not act upon the gold, par. 649. It is employed in separating gold and silver on the manufacturing scale. Concentrated acid has to be em- ployed, and the alloy must not contain more than 25 per cent, of gold ; if i t contains more it must be further alloyed with a sufficient amount of silver. Ex. 481, par. 573. Ex. 482, par. 640. Ex. 483, par. 643. Ex. 484. 100 c.c. of each of the products. Ex. 485, par. 649. Ex. 491, par. 668 — 3rd. Ex. 493, par. 642. Ex. 494, par. 668 — 3rd. Ex. 495. Phosphoric acid, because it is less volatile than sulphuric acid. CHAPTER XHI. Ex. 620. The hardness of waters is due to the presence of salts of lime and magnesia ; their carbonates are insoluble in water, but they are dis- solved in water containing CO^, and on adding lime to water of this kind the carbonates are precipitated ; see par. 742. Ex. 621, par. 733. Ex. 622, 36-5. Ex. 623, pars. 720-722. Ex. 624, pars. 735, 739. Ex. 625. o-i6. Ex. 626, par. 744. Ex. 627, pars. 740, 738. Ex. 628. 49. Ex. 629, par. 746. Ex. 630. A silicate will be formed, par. 668 — 3rd ; on adding HCl the silicate will be decomposed, a chloride being formed, and a varying quantity of silicic acid will be precipitated, par. 668 — 2nd. Ex. 631. 5-6. Ex. 632. 0-84 gram. Ex. 633. 32-66. Spottiswoode &^ Co. Printers^ New-street Square, London.