UNIVERSITY OF CALIFORNIA 
 
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THE 
 
 ELEMENTS OF CHEMISTRY 
 
 BY 
 
 PAUL C. FREEB, M.D., PH.D. (MUNICH) 
 
 UNIVERSITY OF MICHIGAN 
 
 Boston 
 
 ALLYN AND BACON 
 
 1895 
 

 COPYRIGHT, 1895, 
 r PAUL C. FREER. 
 
 PETEBS & SON 
 BOSTON. 
 
PREFACE. 
 
 IN undertaking an ELEMENTARY CHEMISTRY, I was 
 actuated by a growing conviction that the methods of 
 teaching beginners now very generally in vogue do 
 not make prominent what is essential in the science. 
 In the following pages I have endeavored thoroughly to 
 familiarize the pupil with the general aspects of chemi- 
 cal changes, using only a few of the most important 
 elements and compounds for the purposes of illustra- 
 tion ; the work is quantitative, both in the text and 
 laboratory appendix. Chemistry is growing to be more 
 of an exact science every day, and in it quantitative 
 work can no more be neglected than it can in the study 
 of physics. The atomic theory is not introduced until 
 the pupil has sufficient chemical experience to compre- 
 hend its meaning and advantages, and until he thor- 
 oughly understands that theories are based on facts, not 
 facts on theories. The theory of valence I have only 
 briefly touched upon, as it is not necessary for an under- 
 standing of Elementary Chemistry. Its dogmatic appli- 
 cation may be productive of more harm than good. 
 
 Chemical Equations I have avoided as much as possi- 
 ble, because I wished to give them only the relative 
 importance which belongs to them. The too frequent 
 use of these equations may lead to the view that all 
 
 iii 
 
iv ELEMENTS OF CHEMISTRY. 
 
 reactions which can be so formulated must in reality 
 take place. 
 
 The domain of so-called physical chemistry is con- 
 stantly growing, and can no longer be ignored in works 
 of this kind. For this reason I have introduced some 
 of the simple general facts which have been universally 
 adopted in this branch of the science, notably under the 
 head of electrolysis and double decomposition. 
 
 The laboratory experiments are largely quantitative in 
 their nature. Experience has shown me that none of 
 them are too difficult for beginners. It has been too 
 much the custom to seek easy experiments, without 
 considering whether such experiments would teach 
 general principles and, above all, would emphasize 
 quantitative relations. In the study of an exact science, 
 the latter are, however, the most important. 
 
 I have endeavored to simplify the apparatus as much 
 as possible, and am sure that the outfit required suc- 
 cessfully to follow this book will not be too expensive. 
 Certain kinds of good apparatus every chemical labora- 
 tory must have in order to do successful work; and in 
 all cases where cheap and inefficient things are used, 
 the result is a sacrifice of science in the interests of 
 economy. A good balance, a barometer, two gasom- 
 eters for the storing of larger quantities of gases, 
 and a combustion furnace are the most expensive pieces 
 required. Whatever is used should be of the best 
 quality, for exact results can only be obtained by exact 
 methods. A chemical experiment, when correctly per- 
 formed, is as certain to have an unvarying result as is 
 one in physics. 
 
 The figures in the Appendix have all been made from 
 
PREFACE. V 
 
 photographs which were taken from apparatus in actual 
 use, so that, if they are used as models, no difficulty 
 will be found in the laboratory work. 
 
 I wish to take this opportunity of thanking Mr. Geo. 
 O. Higley for his assistance in compiling the laboratory 
 appendix, and Mr. Geo. A. Bacon for his careful read- 
 ing of the manuscript copy. 
 
 PAUL C. FREER. 
 ANN ARBOR, September, 1895. 
 
TABLE OF CONTENTS. 
 
 PAGE 
 
 CHAPTER I. Changes in Matter 1-8 
 
 Aims of Modern Chemistry. Phlogiston Theory. Lavoisier's Experi- 
 ments. Law of the Conservation of Matter. Importance of Correct 
 Observation. 
 
 CHAPTER II. Chemical Nomenclature 9-12 
 
 Chemical Elements. Chemical Compounds. 
 
 III. Water 13-18 
 
 Physical Properties of Water. Solutions. Water of Crystallization. 
 Efflorescence and Deliquescence. Anhydrous and Hydrated Crystals. 
 Impurities in Water. Distillation. 
 
 HAPTER IV. Water (Continued) 19-28 
 
 Action of Sodium and Potassium on Water. Decomposition of Water 
 by the Electric Current. Formation of Water from Hydrogen and Oxygen. 
 Relation of Hydrogen to Oxygen by Weight. Summary. 
 
 CHAPTER V. Products of the Action of Sodium and 
 
 Potassium on Water 29-31 
 
 Caustic Soda and Caustic Potash. 
 
 CHAPTER VI. Changes of Energy -which take place in 
 the Formation of Water, Potassium Hydroxide, and 
 Potassium Oxide 32-37 
 
 Energy. Conservation of Energy. Changes of Energy in the Forma- 
 tion of other Compounds. Kindling Temperature. 
 
 CHAPTER VII. Hydrogen Chloride, Preparation and 
 
 Properties 33-44 
 
 Decomposition by Sodium; by the Electric Current. Difference be- 
 tween the Structure of Hydrogen Chloride and Water. Formation of 
 Hydrogen Chloride from its Constituent Elements. Summary. Resem- 
 blances between Hydrogen Chloride and Water. 
 
 vii 
 
Vlil CONTENTS. 
 
 PAGE 
 
 CHAPTER VIII. The Action of Metals on Hydrochloric 
 Acid. The Neutralization of Hydrochloric Acid by 
 Bases 45-52 
 
 Changes of Energy. -.Action of Hydrochloric Acid on the Oxides and 
 Hydroxides of the Metals. Neutralization of Hydrochloric Acid by Bases. 
 Changes of Energy. Summary. 
 
 CHAPTER IX. The Oxides of Sulphur 53-65 
 
 Acids and Salts in General. Formation of Sulphur Dioxide and Tri- 
 oxide. Laws of Definite and Multiple Proportions. Formation of Sul- 
 phuric Acid. The Anhydrides of Acids. The Action of Metals on Diluted 
 Sulphuric Acid. The Neutralization of Sulphuric Acid by Bases. Com- 
 parison of the Structure of Sulphuric Acid with that of Water and of 
 Hydrochloric Acid. Relationship between the Amounts of Base necessary 
 to form the Primary and Secondary Sulphates. Summary. 
 
 HAPTER X. The Atmosphere. Physical Properties 
 of the Atmosphere. The Barometer. Boyle's Law 
 and Charles's Law 66-71 
 
 The Weight of the Atmosphere. Calculation of Gas-volumes to Stan- 
 dard Conditions. 
 
 CHAPTER XI. The Atmosphere (Continued}. Combus- 
 tion in Oxygen and in Air . . .72-80 
 
 Isolation of Nitrogen from the Atmosphere. Combustion in Oxygen 
 and Changes of Energy. Slow Oxidation. Production of a Flame. Re- 
 versible Phenomena of Gaseous Combustion. General Nature of the Phe- 
 nomena of Combustion. Enduring Nature of Chemical Energy. Breathing 
 Analogous to Combustion. 
 
 CHAPTER XII. The Atmosphere (Continued}. Composi- 
 tion of the Atmosphere 81-87 
 
 Estimation of the Relative Amounts of Oxygen and Nitrogen in the 
 Atmosphere. Other Substances Present in the Atmosphere. Summary of 
 Chapters on the Atmosphere. 
 
 CHAPTER XIII. The Compound of Hydrogen and Ni- 
 trogen. (Ammonia.) 88-97 
 
 Preparation and Properties. Decomposition of Ammonia by means of 
 Magnesium. Isolation of Nitrogen in Ammonia. Parallelism between 
 Ammonia, Hydrogen, Chloride, and Water. The Volumetric Composition 
 of Ammonia. Changes of Energy attending the Decomposition and Forma- 
 tion of Ammonia. Decomposition of Water and Ammonia by Chlorine ; by 
 Oxygen. Summary. 
 
CONTENTS. ix 
 
 PAGE 
 
 CHAPTER XIV. The Compounds of Ammonia -with 
 
 Acids 98-105 
 
 Resemblances between Potassium Chloride and Ammonium Chloride. 
 Liberation of Ammonia from Ammonium Chloride and Changes of En- 
 ergy. Chemical Character of a Solution of Ammonia in Water. Differ- 
 ence between Ammonium and Potassium Salts. Summary. 
 
 CHAPTER XV. The Theory which Seeks to Explain the 
 
 Laws of Definite and Multiple Proportions . . . 106-122 
 
 The Definite Composition of Chemical Compounds. The Equivalent 
 Weights of the Metals. The Atomic Theory. Difficulty of determining 
 the Number of Atoms combined in a Molecule. Practical Advantages of 
 the Atomic Theory. The Formation of Compounds from the Equivalent 
 Weights of the Elements. Summary. 
 
 CHAPTER XVI. Modern Theory of the Nature of Gases. 
 Relation between Specific Gravities of Gases and 
 
 their Molecular Weights 123-128 
 
 Kinetic Gas Theory. Summary. 
 
 CHAPTER XVII. Determination of Atomic Weights by 
 
 the Use of the Specific Gravities of Gases . . . 129-138 
 
 The Molecules of Hydrogen consist of Two Atoms. The Molecular 
 Weight of Hydrogen can be taken as the Standard for measuring other 
 Molecular Weights. Determination of the Maximum Atomic Weights of 
 the Elements. Determination of the Number of Atoms united in Mole- 
 cules by considering the Combining Volumes of Gases. Summary. 
 
 CHAPTER XVIII. The Expression of Chemical Changes 
 
 by Formulae and Equations 139-148 
 
 Composition of the Molecules of Sulphur Dioxide and Trioxide. Rela- 
 tive Atomic Weights of Sodium and Potassium. Neutralization of Hydro- 
 chloric Acid. Neutralization of Sulphuric Acid, and Formation of Ammo- 
 nium Chloride in Terms of the Atomic Theory. Summary. 
 
 CHAPTER XIX. Carbon 149-152 
 
 Various Modifications of Carbon; Diamond; Graphite. Decompo- 
 sition of Animal and Vegetable Substances. Formation of Coke ; Charcoal ; 
 Lamp-black. 
 
 CHAPTER XX. Carbon Dioxide 153-162 
 
 Formula for one Molecule of Carbon Dioxide. Preparation and Prop- 
 erties of Carbon Dioxide. Formation of Carbonates. The Primary and 
 Secondary Carbonates of Potassium and of Sodium. Calcium Carbonate, 
 Magnesium Carbonate, and Carbonate of Iron. Formation of the Soluble 
 Primary Carbonate of Calcium from the Insoluble Secondary. Summary. 
 
X CONTENTS. 
 
 PAGE 
 
 CHAPTER XXI. Carbon Monoxide and Methane. (Hy- 
 
 drogen Carbide) 163-171 
 
 Preparation and Properties of Carbon Monoxide. Reduction. Me- 
 thane. Occurrence. Formation. Preparation and Properties. Deter- 
 mination of Chemical Formula of Methane. Summary. 
 
 CHAPTER XXII. Substitution of Hydrogen in Methane 
 
 by Chlorine 172-184 
 
 Substitution of Hydrogen in Metals. Difference between the Action 
 of Chlorine and of the Metals. Methyl Chloride. Methylene Chloride. 
 Methin Chloride. Atomic Weights of Carbon and Chlorine. Valence. 
 Summary. 
 
 CHAPTER XXIII. The Formation of Salts by Double 
 
 Decomposition 185-194 
 
 Formation of Salts by Substitution and Neutralization. Salt Forma- 
 tion by Action of an Acid on a Salt. Double Decomposition between Two 
 Salts. Causes of Double Decomposition. Electrolysis. Formation of 
 Insoluble Substances. Neutralization of Bases by Acids. Summary. 
 
 CHAPTER XXIY. Chemical Nature of Some Other Ele- 
 ments and Compounds related to Those which have 
 been studied 194-205 
 
 Elements of Chlorine, Oxygen and Nitrogen Families. Hydrogen Com- 
 pounds of Chlorine and of Oxygen Family. Hydrogen Sulphide, Prepara- 
 tion and Properties. Formation of Sulphides. Hydrogen Compounds of 
 Elements of the Nitrogen Family. 
 
 LABORATORY APPENDIX . 206-284 
 
ELEMENTS OF CHEMISTRY. 
 
 CHAPTER I. 
 
 CHANGES IN MATTER. 
 
 Change in Matter. All matter is subject to change. 
 In some cases, for example when a piece of wood is 
 burning or when water is flowing, the change is per- 
 ceptible ; in other cases it takes place too slowly to be 
 observed. Instances of the latter kind may be found 
 in the wearing away of a rocky mountain along the bed 
 of a stream, or in the gradual decomposition of crystal- 
 line rocks into other and different materials through 
 the influence of the weather. 
 
 Classification of Changes. It is customary to classify 
 those alterations which are superficial and transitory 
 under the head of physics, and those which involve a 
 change in the essential properties of substance under 
 the head of chemistry. A sharp line, however, cannot 
 be drawn. There is a considerable field lying along 
 the border between the two subjects which is claimed 
 by both. Operations so simple as the dissolving of 
 salt in water, probably involve a chemical change as 
 well as a physical one. 
 
 1 
 
2 ELEMENTS OF CHEMISTRY. 
 
 Observation of Changes. From the earliest times, the 
 instability of his surroundings attracted the attention 
 of man, and he speculated as to the causes of the 
 changes going on around him; yet, until the last two 
 hundred years, theories regarding chemical phenomena 
 were not based on scientific observation. The essential 
 difference between the methods of thought preceding 
 the eighteenth century and those of modern times is, 
 that, during the earlier period, theories concerning struc- 
 tural changes in matter were not subjected to proof by 
 experiment. During the later period, theories have 
 been made only to explain facts determined by the 
 most laborious investigations. In consequence of the 
 perverted system of former times, little progress was 
 made toward rationally explaining the composition of 
 even the simplest forms of matter. During the first 
 sixteen centuries of the Christian era, the growth of 
 chemical science was hopelessly retarded, first, by the 
 theory that all substances were composed of four prin- 
 ciples, earth, water, fire, air ; and second, by a purely 
 mercenary aim, the hope of transforming baser metals 
 into gold. 
 
 Superficial and Fundamental Differences in Matter. Cop- 
 per and zinc when melted together form a mass (brass) 
 similar to gold in appearance, and the earlier workers 
 in chemical lines supposed this alloy to be a some- 
 what modified gold. Copper when heated with arsenic 
 assumes a white color, and the resulting substance was 
 believed to be a metal which differed but little from 
 silver. Thus, merely superficial qualities, such as color, 
 were regarded as essential, while really fundamental 
 differences between various forms of matter were un- 
 
CHANGES IN MATTER. 3 
 
 observed. We now know that although brass has the 
 color of gold, it nevertheless is entirely different from 
 that metal, for it corrodes when heated, or when brought 
 in contact with acids, while gold does not. Copper and 
 zinc, the constituents of brass, can by the proper means 
 be separated from the alloy; while from gold, no matter 
 what changes the metal may undergo, nothing but gold 
 has ever been obtained. A given volume of gold has 
 an entirely different weight from the same volume of 
 brass. It has a different melting point ; jn fact, in all 
 the properties which we now recognize as essential, the 
 two substances are distinct. 
 
 Aims of Modern Chemistry. It is one of the aims of 
 modern chemistry to distinguish accurately between the 
 various forms of matter, and to discover what changes 
 involve an alteration in the nature of a substance. 
 
 The advance from superficial to scientific methods of 
 chemical thought was not brought about abruptly, neither 
 did the idea that experimentation should always be re- 
 sorted to, as proof of a theory, immediately find adoption. 
 
 The Phlogiston Theory. At the beginning of the eigh- 
 teenth century, a chemist (Stahl) constructed a theory 
 which apparently furnished a uniform and consistent 
 explanation of a common chemical phenomenon, cqm- 
 bustion. According to this theory, any substance capa- 
 ble of burning contained an element, or principle, which 
 was called phlogiston.* This principle was supposed 
 
 * At one time phlogiston was considered as a material substance ; at 
 another, as merely a principle devoid of weight. Again, it was identical 
 with the element at present called hydrogen; at another time it was 
 supposed to have negative weight (i.e., to he repelled by the earth). It 
 was also looked upon as the principle of fire. This confusion of ideas is 
 
4 ELEMENTS OF CHEMISTRY. 
 
 to pass off while the body was burning, the remainder 
 being " dephlogisticated." Charcoal, for example, burns 
 readily and leaves a small quantity of ash. During the 
 last century this ash was considered a chemical element 
 which, when united with a large amount of phlogiston, 
 formed charcoal. If iron-rust is heated with charcoal, 
 the latter substance disappears, while iron is produced, 
 mixed of course with the ash. The iron-rust was there- 
 fore supposed to take up the phlogiston from the char- 
 coal, hence iron was phlogisticated iron-rust. Although 
 this theory was false, nevertheless it led to a great ad- 
 vance in the science of chemistry, because it indicated 
 a direction in which new work could be conducted. 
 During the eighty years following its establishment, 
 greater progress was made than during the preceding 
 fifteen centuries, while at the same time chemistry as 
 an independent science began to be followed for its own 
 sake. Still, investigators of the " phlogiston " period 
 had not entirely outgrown the superficial methods of 
 thought belonging to their predecessors. Although a 
 marked advance had been made, they were still un- 
 able, in many cases, to distinguish with sufficient clear- 
 ness essential from non-essential phenomena. Thus, for 
 example, it was supposed that iron in burning or rust- 
 ing gave off " phlogiston," and yet the rust weighs 
 more than the iron. True, the ash of the charcoal 
 weighs much less than the charcoal itself; but if a thor- 
 ough investigation of the combustion of that substance 
 were undertaken, the weight of the ash, plus that of 
 the gaseous products, would be found to exceed that 
 
 sure to come where a false theory is called upon to explain a large class 
 of phenomena. Perhaps the nearest approach to " phlogiston " in mod- 
 ern scientific language is to be found in " energy." 
 
CIIANGES IN 
 
 of the original charcoal. This essential relation, be- 
 tween the weight of a burning body and that of the 
 bodies produced by burning, was generally ignored dur- 
 ing the phlogiston period. It is, however, of such fun- 
 damental importance that, when the facts were finally 
 recognized, the theory which overlooked them was of 
 necessity abandoned.* The new one which took its 
 place, being founded solely on experimental evidence, 
 caused a much greater acceleration in the already rapid 
 pace at which chemistry was advancing. In order to 
 understand clearly the reasons for such a radical change 
 of views, it will be necessary to detail one or two 
 important experiments. 
 
 Lavoisier's Experiments. A French chemist, Lavoisier, 
 carefully weighed a piece of tin, placed it in a flask, 
 hermetically sealed the latter, and then accurately de- 
 termined the weight of the whole. He afterward kept 
 the flask heated during a period of some weeks, and 
 observed that the tin had changed into a white powder. 
 At the same time the flask had neither gained nor lost 
 in weight, and consequently no phlogiston could have 
 passed off. On opening the vessel, air rushed in (a par- 
 tial vacuum having been created), and the total weight 
 was greater than it had been after sealing. Further- 
 more, the white powder weighed more than the original 
 tin. Lavoisier, therefore, came to the conclusion that 
 the tin, when heated, took up one of the constituents of 
 the enclosed air ; that the diminution in volume of the 
 air was connected with the increase in weight of the tin ; 
 
 * A theory as to the cause of any natural phenomenon must of neces- 
 sity be abandoned as soon as any fact is discovered which contradicts 
 that theory. 
 
6 ELEMENTS OF CHEMISTRY. 
 
 and that the metal did not give off phlogiston when 
 heated. He felt sure that the tin took up a constituent 
 of the atmosphere, but he could not at that time give 
 any absolute proof of his theory, because that portion of 
 the air which is absorbed by burning substances had 
 not as yet been isolated. By a strange coincidence, 
 the chemical theory which was destined to overthrow 
 that of phlogiston was finally established by an ardent 
 adherent of the phlogistic school, Joseph Priestley, who 
 was the first to isolate this unknown constituent of the 
 air. Priestley demonstrated that red precipitate,* when 
 heated, yielded mercury and gave off a new gas, which 
 he called dephlogisticated air,t but which Lavoisier at 
 once recognized as that part of the atmosphere which 
 had acted on the tin. The alteration in the metal was 
 analogous to combustion, and it was Priestley's new gas 
 which united with substances when they burned. Hav- 
 ing come to this conclusion, Lavoisier, by repeating 
 Priestley's experiment with red precipitate (taking the 
 precaution to weigh carefully first the substance, and 
 then the resulting gas and mercury produced), further 
 succeeded in discovering a fundamental law of natural 
 science which reads as follows : 
 
 Law of the Conservation of Matter. During chemical 
 changes the amounts of matter entering into such changes 
 remain constant, and the total amount of matter con- 
 tained in the universe never varies. From this it fol- 
 lows that when the oxide of mercury (red precipitate) 
 is decomposed, the sum of the weights of the resulting 
 
 * Oxide of mercury. 
 
 f Called dephlogisticated air because substances burned in it more 
 readily than in common air. Dephlogisticated air could contain but 
 little phlogiston, since it was capable of taking up phlogiston so readily. 
 
CHANGES IN MATTER. 7 
 
 oxygen * and mercury are exactly equal to the weight 
 of the original substance. The tin which Lavoisier 
 heated in a flask gained in weight, but this gain was 
 exactly balanced by the loss in weight of the air en- 
 dosed in the vessel. If a candle were burned in a 
 scaled glass globe, the candle would apparently disap- 
 pear, yet the weight of the globe would remain unal- 
 tered. The chemical compounds at first present in the 
 candle, together with a given quantity of oxygen, would 
 have rearranged themselves into other and less complex 
 compounds, differing in character from either the air or 
 the candle, but the total amount of matter would have 
 remained the same. 
 
 Importance of Correct Observation. The length of time 
 which it took to come to the conclusion that matter is 
 constant in quantity, and the obstinacy displayed by 
 the adherents of phlogiston, should emphasize for us the 
 importance of careful observation, as well as of a con- 
 scientious weighing of all the facts in regard to a given 
 chemical change, before we venture to construct any 
 definite theories regarding it. 
 
 Importance of a Knowledge of Facts. In undertaking the 
 study of any science, it is absolutely essential to become 
 acquainted with well-established facts before undertak- 
 ing to understand any of the theories which have been 
 brought forward to explain the existence of these facts. 
 We must also remember that facts remain as they 
 are, no matter what theories we may advance for their 
 explanation. Almost invariably, however, exactly the 
 reverse of this course has been adopted. As a result, 
 
 * The name given to the gas first isolated by Priestley. 
 
8 ELEMENTS OF CHEMISTRY. 
 
 students acquire the opinion that chemical science is a 
 mere collection of visionary theories, which experimen- 
 tation may or may not bear out. This is not the case. 
 When, for example, we speak of atoms, we have at least 
 as exact experimental evidence of their existence as the 
 physicist has of the waves which he discusses in the 
 undulatory theory of light. Because of the danger of 
 confusing really existing things with those which are 
 imaginary, it will be the aim of this book to discuss 
 chiefly facts, leaving the theoretical deductions to be 
 made from them for a larger work. 
 
CHEMICAL NOMENCLATURE. 
 
 CHAPTER II. 
 
 CHEMICAL NOMENCLATURE. 
 
 THE language of every science is peculiar to itself ; 
 advances are recorded by alterations, and history is 
 preserved by the use of old expressions. In order to 
 express one's self properly and intelligently, a knowl- 
 edge of accepted nomenclature is necessary. An ex- 
 tended acquaintance in this line can come only after 
 considerable experience, still it is not out of place to 
 become familiar with a few terms in chemistry even 
 prior to any advance in the study. 
 
 Chemical Elements. Toward the end of the last cen- 
 tury, the idea*became firmly established that those sub- 
 stances which cannot be decomposed into two or more 
 simpler ones, having entirely different properties, are to 
 be considered as chemical elements. This term, how- 
 ever, must not be understood as meaning substances 
 which may not at some future time be broken down. 
 Indeed, past experience indicates that such decomposi- 
 tions will be brought about in substances now classed 
 as elements. An example of such an experience is 
 found in the history of the substance known as caustic 
 potash,* which was formerly supposed to be non-decom- 
 posable, and was called an element. Afterwards it was 
 decomposed into a metal (potassium) and two different 
 
 * Potassium hydroxide. 
 
10 ELEMENTS OF CHEMISTRY. 
 
 gases, oxygen and hydrogen. These three substances 
 are now considered elements ; but subsequent experi- 
 ment may possibly prove these, or any other so-called 
 elements, to be compounds, as was done in the case of 
 caustic potash. 
 
 Number of Elements. We are at present acquainted 
 with about seventy different kinds of matter which 
 have not been decomposed into two or more simpler 
 forms.* Five of these are gases at ordinary temper- 
 atures and pressures, two are liquids,! and the re- 
 mainder are solids. These substances are our present 
 chemical elements. 
 
 Classification of the Elements. Elements can be roughly 
 divided into two great classes ; namely, metals and not- 
 metals. The most pronounced metals are malleable 
 and ductile, are good conductors of electricity, and 
 have a so-called metallic lustre. $ The most charac- 
 teristic not-metals, whether gaseous, liquid, or solid, 
 are neither malleable nor ductile, do not conduct elec- 
 tricity (or at least are poorer conductors than the 
 metals), are frequently transparent (oxygen, nitrogen, 
 sulphur crystals) or translucent (bromine, iodine in 
 thin sections), and they have no metallic lustre. It 
 is a matter of experience that the most pronounced 
 metals easily form stable compounds with the not- 
 
 * A table of elements will be found at the end of the book. 
 
 t A third element, called rubidium, is liquid at about blood heat, and 
 possibly a fourth very rare element, caesium, may be liquid when it is 
 pure. 
 
 J An appearance like that of the most familiar polished metals, such 
 as silver, gold, brass, etc., is termed a metallic lustre. Substances with 
 metallic lustre are not transparent or translucent except in the very thin- 
 nest plates. . 
 
CHEMICAL NOMENCLATURE. 11 
 
 metals, but no absolute prediction as to the behavior 
 of two elements toward each other can be made, even 
 if it is known that one is a metal and the other a 
 not-metal. 
 
 Nomenclature of Compounds. Compounds containing 
 but two elements are called binary ones. In the no- 
 menclature of such compounds, the termination of the 
 name of one element is, as a rule, changed to -ide^ the 
 name of the other remaining unaltered. 
 
 EXAMPLES : The compound of iron and oxygen is called 
 iron oxide or oxide of iron. 
 
 The compound of hydrogen and sulphur is called hydrogen 
 sulphide or sulphide of hydrogen. 
 
 The compound of chlorine and sodium is called sodium 
 chloride or chloride of sodium. 
 
 The compound of phosphorus and oxygen is called phosphorus 
 oxide or oxide of phosphorus. 
 
 The same element may, however, enter into combina- 
 tion with a series of others. In such an event, it is 
 customary to form for the series a class-name taken 
 from that of the element which all of the members 
 have in common, the termination being altered to -ide. 
 
 EXAMPLES : Oxides are compounds of oxygen with other 
 elements. Sulphides are compounds of sulphur with other ele- 
 ments. Chlorides are compounds of chlorine with other elements. 
 Phosphides are compounds of phosphorus with other elements. 
 
 In naming such a series of compounds, it is in- 
 variably the name of the not-metallic element, or of 
 the element acting like a not-metal,* which suffers a 
 change. 
 
 * Arsenic, for example, is an element which frequently acts like a not- 
 metal. 
 
 xiara 
 
12 ELEMENTS OF CHEMISTRY. 
 
 EXAMPLES : Sodium, potassium, and iron are metals ; chlo- 
 rine is a not-metal. The terms sodium chloride, potassium 
 chloride, iron chloride, are, therefore, in use, while the expres- 
 sions chlorine sodide, potasside, or ironide are inadmissible 
 although logically just as correct as the others. 
 
 Where the binary compound is formed of two not- 
 metals or two metals, then, of course, convention must 
 settle the rules. 
 
 EXAMPLES : We speak of an oxide of sulphur, a sulphide of 
 phosphorus, a chloride of iodine ; yet even in such cases it is the 
 name of the most pronounced not-metal which is altered. 
 
 Popular Names. It must be remembered that not a 
 few chemical compounds retain the names which were 
 in use before the chemical theories of the present cen- 
 tury were adopted, and that some have since that time 
 been given special designations. 
 
 EXAMPLES : Oxide of hydrogen is called water ; a nitride of 
 hydrogen is called ammonia; a phosphide of hydrogen is called 
 phosphine. 
 
 Chemical Elements and Chemical Compounds. In chemi- 
 cal work we have two conditions in which the elements 
 are encountered. The first is that of the elements in 
 "their separate and individual state, the second that of 
 the elements united in compounds. A compound dif- 
 fers radically in behavior and properties from the ele- 
 ments of which it is composed. A chemical compound 
 is not a mechanical mixture (as sand and salt would 
 be) ; for the mixture has properties which are the 
 mean between those of fits constituent parts, while the 
 compound has 110 res|eml)limce to its components. 
 
WATER. 13 
 
 CHAPTER III. 
 
 WATER. 
 
 The Physical Properties of Water. In taking up the sub- 
 ject of chemistry, it is best to study thoroughly a few 
 chemical bodies and the changes which they undergo. 
 We can in this way become familiar with chemical 
 phenomena without introducing theories which are apt 
 to give the impression that chemistry is a visionary and 
 unreal science. Of all known bodies, water is the one 
 which naturally suggests itself for first consideration. 
 
 Method of Study. In studying this substance we ex- 
 amine first its physical characteristics, and secondly its 
 chemical characteristics. 
 
 Physical Properties of Water. Water is a liquid substance, 
 transparent and nearly colorless when pure, though in very thick 
 masses it apparently has a deep blue color. When heated, it 
 expands ; when cooled, it contracts, excepting in the interval ^>f 
 temperatures between 4 and 0, * * where exactly the reverse 
 takes place. At pure water changes to ice, and the ice, fol- 
 lowing the usual law, continues to contract as the temperature is , 
 lowered. At 100 f water boils, and then changes to a vapor, J 
 which expands regularly when further heated. 
 
 * Throughout the book temperatures are indicated by the Centigrade 
 thermometer. 
 
 1 The superior numbers in the text refer to the numbers of the labor- 
 atory notes in the Appendix. 
 
 t At the standard pressure of one atmosphere at the level of the sea. 
 This standard is equal to a pressure of 760 millimetres of the mercury 
 barometer. The pupil can become acquainted with the structure and 
 uses of the barometer and the thermometer, from Note 1 of the Appendix. 
 
 J A vapor always exists in the presence of the liquid from which it is 
 
14 ELEMENTS OF CHEMISTRY. 
 
 Solutions. Water has the power to dissolve a large 
 variety of other substances which are then said to be 
 in solution. Solutions are homogeneous mixtures of 
 two or more substances, at least one of which must be 
 a liquid.* 
 
 Solutions of Liquids in Liquids. When all the substances 
 are liquid, then the following special cases must be dis- 
 tinguished: The solution may take place in any pro- 
 portion if the liquids are perfectly miscible (alcohol and 
 water), or the liquids may only partially mix (ether 
 and water). In either case it is not proper to speak of 
 one liquid as dissolving another, for the alcohol has just 
 as much to do with dissolving the water as the latter 
 has with dissolving the alcohol. Where one liquic^ only 
 partially mixes with a second, it is also true that the 
 latter will take up an equal proportion of the former. 
 Not infrequently two liquids, when brought in contact, 
 will not mix at all (oil and water). 
 
 Solution of Solids in Liquids. When a solid dissolves in 
 a liquid, the latter can take up only a certain quantity 
 called a maximum, which is constant for constant tem- 
 peratures. In the case of any given solid, this maxi- 
 mum of weight which can be dissolved in a liquid 
 
 under fixed conditions, is called its solubility,! and the 
 
 
 
 formed. When the temperature is high enough to vaporize the liquid 
 completely, and to keep it vaporized, we use the term gas instead of 
 vapor. 
 
 * Two or more gases can also form homogeneous mixtures; indeed, 
 all gases are perfectly miscible ; yet such mixtures, being formed as they 
 are without change in the total volume or in the total heat, can scarcely 
 be compared with ordinary solutions. 
 
 t The solubility of a solid is expressed either in percentage by weight 
 of solid which is dissolved in 100 parts of solvent, or in percentage by 
 weight which is dissolved in 100 parts of solution. 
 
WATER. 15 
 
 solution is said to be " saturated " ; i.e., it nas taxen up 
 of the solid all that it can. 
 
 As a rule, the solubility of a solid is increased by increase of 
 temperature. A solution which is saturated at a given tempera- 
 ture will, therefore, be unsaturated at a point above this, and, 
 as a consequence, will take up more of the solid. On the other 
 hand, when a saturated solution cools, a separation must occur, 
 as the solubility of the solid diminishes.* 
 
 In an unsaturated solution, when the freezing point 
 is reached, the water t will separate in the form of pure 
 ice until the unfrozen solution becomes saturated ; then 
 the solvent and the dissolved solid will separate simul- 
 taneously, sometimes in definite relations by weight. 
 The solid mixtures which are formed in this way will 
 have definite compositions, and, for that reason, have 
 sometimes been considered as chemical compounds, and 
 have received the special name of cryohydrates. 2 
 
 Water of Crystallization. Not infrequently substances 
 separate in the form of crystals from solutions in water, t 
 These crystals often contain a definite quantity of water 
 for a definite weight of solid. The form of the crystal, 
 as well as the relative amount of water, never varies 
 for the same substance under the same conditions. 
 The water which is so combined to form a solid crystal 
 is called water of crystallization. Compounds formed 
 
 * Generally the solid separates in a definite geometric form, with 
 plane faces which have a uniform angle with each other. The process 
 is then called crystallization, and the solid so formed is a crystal. 
 
 t Provided the solvent is water. The phenomena are the same with 
 any other liquid, provided it be capable of freezing within the limits of 
 the experiment. In the case of a liquid like alcohol, which does not 
 freeze, the cooling of course goes on until the solution is saturated, then 
 separation begins. 
 
 | The same is true of a number of other solvents. 
 
16 ELEMENTS OF CHEMISTRY. 
 
 between a substance and its water of crystallization can 
 be easily broken down. Sometimes the water passes 
 off even at ordinary temperatures, and the substance 
 crumbles to a powder (soda crystals) ; sometimes the 
 temperature must be raised to the boiling point of 
 watery or even above this, in order to produce the 
 same result (alum crystals). A number of cases are 
 known in which a portion of the water cannot be 
 driven off, even if the temperature is increased far be- 
 yond the boiling point ; but a careful investigation of 
 these exceptions proves that water is no longer present 
 as such, but has been broken down to enter into an 
 entirely new class of compounds. True water of crys- 
 tallization is always easily expelled. 3 
 
 Efflorescence and Deliquescence. Substances which lose 
 a part of their water of crystallization at ordinary tem- 
 peratures are efflorescent (soda crystals, copper sulphate 
 crystals). On the other hand, bodies are known which 
 greedily absorb moisture when they are brought in con- 
 tact with it, sometimes attracting enough liquid to 
 dissolve them. Such bodies are deliquescent. 4 " 
 
 Anhydrous and Hydrated Crystals. It must always be 
 remembered that crystals need not necessarily contain 
 water of crystallization (diamond, chromate of potas- 
 sium, nitrate of silver, and saltpetre) ; indeed, by far 
 the greater part do not. Substances which contain no 
 water of crystallization are said to be anhydrous ; those 
 with it, Jiydrated. 
 
 Solutions of Gases in Liquids. There is as great a va- 
 riation in the solubility of gases as there is in that of 
 
solids and liquids, some being very readily dis'solved 
 (ammonia, hydrochloric acid) ; some less readily (chlo- 
 rine) ; others with great difficulty (hydrogen). With 
 one or two exceptions, the solubility of gases diminishes 
 as the temperature of the solvent increases. An in- 
 crease of the pressure to which a gas is subjected brings 
 with it a corresponding increase in the solubility of the 
 gas. When the pressure is removed, the dissolved gas 
 passes off until the normal solubility at the temperature 
 and pressure of the atmosphere is reached.* The solu- 
 bility of a gas varies directly as the pressure. 5 
 
 Impurities in Water. Distillation. The impurities found 
 in water are either mechanically suspended or dissolved. 
 The suspended impurities can be removed by filtration,! 
 the dissolved ones, in certain cases, by distillation. Dis- 
 tillation consists in heating the solvent to its boiling 
 point in an apparatus suitably arranged for collecting 
 and condensing the vapors in a separate vessel. Where 
 the substances dissolved are solid, they are in most 
 cases $ removed by this process. Liquid substances 
 dissolved in water can be removed by distillation only 
 when the boiling point of the liquid is much above or 
 below that of water ; for, unless this be the case, a por- 
 tion of one liquid will always vaporize with the other. 
 Even where there is a considerable interval between the 
 boiling points, the operation of distilling must be re- 
 
 * The effervescing of soda-water is an illustration of this phenomenon. 
 The gas, carbon dioxide, is forced to dissolve in the water by great pres- 
 sure. When the pressure is removed, the carbon dioxide must escape. 
 
 t By passing the water through a porous substance ; for instance, espe- 
 cially prepared blotting-paper or unglazed porcelain. 
 
 \ Certain solid substances vaporize with the water. uch substances 
 cannot, of course, be removed by ordinary distillation. 
 
18 ELEMENTS OF CUEMISTltT. 
 
 peated several times, the lower and higher boiling por- 
 tions being collected, separated, and then again distilled 
 from separate vessels. This operation is called fractional 
 distillation. , 6 
 
 Natural Waters. Natural waters are all more or less 
 impure. Rain-water or melted snow is nearest to abso- 
 lute purity, but even this contains solid and gaseous 
 substances collected in. passing through the atmosphere. 
 When rain-water soaks through the soil, it takes up a 
 certain portion of the solid substances with which it 
 comes in contact. If poisonous substances in the soil 
 or organisms Deleterious to life are taken up, the water 
 will be unfit for drinking purposes ; and this is some- 
 times the case in well -or spring water. Where certain 
 constituents of the soil are of an extremely soluble 
 nature, like common salt, Epsom salt, etc., they are of 
 course taken up by the water which filters through. 
 Where such a water escapes from the soil, it produces 
 mineral springs. Naturally the impurities dissolved in 
 well or spring water vary with the nature of the soil 
 through which the rain-water forming the well or spring 
 has trickled. 
 
WATEE. 19 
 
 CHAPTER IV. 
 
 WATER (Continued-}. 
 
 THE first inquiry into the chemical nature of water 
 should have for its object the definite solution of the 
 question whether water is a chemical element or a com- 
 pound,* and in order to find an answer we must resort 
 to experiment.! At the same time, it will be possible, 
 by the study of a few facts, to get a clearer conception 
 of what is actually meant by a chemical element. 
 
 Action of Sodium and Potassium in Water. If a piece 
 of the metal sodium is placed in contact with water, an 
 instantaneous change takes place ; the sodium becomes 
 hot, it melts, and the globule of metal will move rap- 
 idly round on the surface of the water. t If the water 
 is thickened with starch paste so that this movement 
 cannot take place, the heat developed will finally pro- 
 
 * See page 8. 
 
 t In former times water was regarded as an element. One reason for 
 this was that water is so common, and it appears to be generated during 
 so many chemical processes (for instance, the combustion or distillation 
 of wood). The chief means for decomposing substances which the older 
 chemists had at their disposal was the action of fire. Certainly no 
 temperature which they could produce would destroy water, and this 
 was another reason for supposing it to be an element. We should our- 
 selves be compelled to regard water as an element were we not able to 
 decompose it into two different substances. 
 
 \ The specific gravity of sodium is less than that of water; .that is, a 
 given bulk of water would weigh more than the same bulk of sodium. 
 The sodium, therefore, floats on water. 
 
20 ELEMENTS OF CHEMISTRY. 
 
 duce a flame which is caused by the burning of a gas 
 which is passing off. That such a gas is really liberated 
 is easily proved by placing the piece of sodium in a wire 
 net, and inverting over this a tube closed at one end, and 
 filled completely with water. The gas will rise in bub- 
 bles, and, if the original quantity of the sodium was 
 sufficient, will entirely fill the tube. If the latter is 
 now removed, mouth downward, and held over a flame, 
 the gas will take fire, and burn up completely when 
 the tube is inverted. Essentially similar phenomena 
 will be observed if the metal potassium * is substituted 
 for sodium, except that the change is much more vio- 
 lent. The gas bursts into flame even when the water 
 has not been previously thickened with starch paste. 
 The color of the flame with sodium is yellow, with po- 
 tassium bluish-violet; and to a superficial observer it 
 might appear that the gas given off by potassium and 
 water is different from that produced by sodium and 
 water. That this is not the case, however, can be 
 shown by comparing the flame of the gas collected in 
 a test-tube from sodium with that collected from potas- 
 sium. In both cases the flame will be nearly color- 
 less. 7 
 
 The yellow and the violet colors are due to something derived 
 from the potassium and the sodium. The explanation is that 
 small particles of the metals are carried up into the flame, and, 
 being heated to incandescence, give off the colored light peculiar 
 to each. 
 
 * Potassium is a metal very much like sodium in appearance and 
 character. Its specific gravity is less than that of water, therefore it 
 floats. Both sodium and potassium are soft> can he easily cut with a 
 knife, and the freshly cut surfaces possess a brilliant metallic lustre, 
 which almost instantly disappears on exposure to the air. Because they 
 are so easily altered hy exposure to the air, they must be preserved under 
 petroleum. 
 
WATER. 21 
 
 Nature of the Action of Sodium and Potassium on Water. 
 Is the gas which is developed in this process due to a 
 breaking down of the water, or does it come from the 
 potassium and the sodium? Either view seems plaus- 
 ible ; and, indeed, had the two metals in question been 
 known in the last century,* the latter interpretation 
 of the change would undoubtedly have been the one 
 adopted. Sodium and potassium would have been re- 
 garded as compound substances, and it would have been 
 supposed that they gave up a gas (phlogiston) when 
 brought into contact with water. The substances, 
 therefore, which remained behind, dissolved in the 
 water (caustic soda and caustic potash), would have 
 been classed as elements. Such an explanation is en- 
 tirely incorrect, however, for the gas does not- come 
 from the potassium or the sodium. It results from 
 the breaking down of water into two parts, one of 
 which passes off as a gas, while the other unites with 
 the potassium or sodium to form a new compound body, 
 which dissolves in the water. That this is really the 
 case is shown by the following experiments : 
 
 Decomposition of Water by the Electric Current. If 
 water t is placed in a cup, into the bottom of which 
 two pieces of platinum foil are placed in such a man- 
 ner that they can be connected with the two poles of 
 an electric battery, and an electric current is passed 
 through the water, bubbles of gas will appear at both 
 pieces of foil. If a tube, closed at one end and filled 
 
 * Sodium was discovered in 1807 by Davy ; potassium, in 1808, by the 
 same investigator. 
 
 t Rendered slightly acid by means of sulphuric acid ; pure water does 
 not conduct electricity. 
 
22 ELEMENTS OF CHEMISTRY. 
 
 with water, is inverted over each piece of foil, the gases 
 can easily be collected. It will then be found that the 
 water in one tube is expelled more rapidly than in the 
 other. If the tubes selected are of the same size, one 
 will be exactly filled with gas at the moment when the 
 other is only one-half full. 8 It is evident, then, that 
 water decomposes into two gases, one of which separates 
 at the positive, the other at the negative pole ; and it is 
 also true that there is about twice as much of one gas 
 as of the other. If the tube containing the greater 
 quantity * is removed, and brought in contact with a 
 flame, the gas will be found to burn with a flame iden- 
 fcieal in appearance with the one observed during the 
 combustion of the gas produced from sodium and po- 
 tassium. It is probable, therefore, that the gas lib- 
 erated when experimenting with those metals had its 
 origin in the water with which they were brought in 
 eontact, and that it did not come from the metals 
 themselves. f 
 
 The proof that the gas which is formed by the action 
 of sodium or potassium on water does not come from 
 the metal, but that it has its origin in the water which 
 is decomposed, has also been obtained by other methods. 
 These, however, would involve more difficult experi- 
 mentation than is possible for beginners. It has been 
 
 * Experimentation will show that this has been collected at the 
 negative pole of the battery. It is, therefore, the electro-positive con- 
 stituent. 
 
 f The proof that the gases obtained by the action of sodium or potas- 
 sium on water, and the gas collecting at the negative pole when water 
 is decomposed by the electric current, are really identical has not been 
 shown by the experiments which have been given. The only point 
 made use of is that they both burn with a similar flame. Something 
 more than this is necessary before we can really be satisfied as to their 
 identity. This proof is found in the fact that the gas from both sources, 
 when burned, forms the same substance; namely, water (see page 27). 
 
WATER. 23 
 
 shown that the sum of the weights 01 the sodium used 
 and of the water decomposed is equal to the sum of 
 the weights of the gas produced and of the compound 
 of sodium which remains dissolved. If all excess of 
 water is removed by heat, then the sodium compound 
 remaining weighs more than did the sodium originally 
 used. The sodium, therefore, could not have given off 
 the gas, for in that event it would have diminished in 
 weight. 
 
 That the volume of one of the gases into which water 
 is broken down is exactly twice as great as that of the 
 other gas cannot be proved from the decomposition of 
 water by the electric current, since the method employed 
 is not sufficiently accurate. A more careful and ex- 
 tended study of the composition of water by other 
 means is necessary to show that the ratio of the two 
 gases by volume is exactly 2:1. 
 
 Sodium and Potassium are Elements ; Water is a Compound. 
 A number of observations similar to the ones just given, 
 and involving the action of sodium and potassium on 
 other substances which are chemically like water, have 
 brought us to the conclusion that sodium and potassium 
 are not decomposable. In all cases of experiment, when 
 a theory that these metals are decomposed into simpler 
 substances might seem plausible, closer analysis will 
 show that it is not sodium or potassium that is broken 
 down, but the other substances with which these metals 
 are brought in contact. Sodium and potassium are, 
 therefore, elements, and water is a compound. Having 
 settled this, the next step is to discover what and how 
 many dissimilar substances can be produced by the sep- 
 aration of the water into its constituent parts. 
 
24 ELEMENTS OF CHEMISTRY. 
 
 Hydrogen and Oxygen. We have seen that when an 
 electric current is passed through water, a gas separates 
 both at the positive and at the negative pole (see 
 page 22). The accumulation at the latter is twice as 
 great as that at the former, and the question at once 
 arises : are the gases identical, or do they differ from 
 each other? To all appearances they are alike, both 
 are colorless, neither possesses an odor; yet a distinc- 
 tion will at once become apparent if a lighted taper is 
 applied to each in turn. The one which has been col- 
 lected at the negative pole burns with a flame identical 
 in appearance with that shown by the gas obtained from 
 the action of sodium or potassium on water. Indeed, 
 as we have seen, it is in reality the same substance. 
 This gas is termed hydrogen.* The gas collected at the 
 positive pole does not burn, but it causes a taper placed 
 in it to burn much more energetically than it would in 
 the air. Even if the taper has but a feeble spark, it 
 will burst into flame. This gas is called oxygen. 9 
 
 Formation of Water from Hydrogen and Oxygen. It has 
 been shown that hydrogen and oxygen can be obtained 
 from water ; can water also be produced from these sub- 
 stances? Because if it can, then these two elements 
 alone make up the compound, water. The following 
 experiment will demonstrate this fact: - 
 
 A tube, sealed at one end, is filled with mercury, then 
 
 * Neither of the methods which have heen discussed are expedient 
 for the preparation of the considerable quantities of hydrogen necessary 
 for ordinary laboratory purposes. To accomplish this end another way 
 is necessary, which is described in Experiment 9, Appendix. Both oxy- 
 gen and hydrogen are called elements; for no experiments have been 
 discovered by means of which these forms of matter can be separated 
 into two or more different substances as, for example, has been done in 
 the case of water. 
 
WATER. 25 
 
 closed at the other end by the thumb, and inverted over 
 a trough filled with the same liquid. Perfectly pure 
 hydrogen is then run into the tube until the latter is 
 filled for about five centimetres.* Oxygen is added so 
 that its bulk is approximately two centimetres, and the 
 tube is firmly closed. The tube used in this experi- 
 ment has two short platinum wires fused through its 
 sides near the closed tip. These are connected with 
 the two short poles of an induction coil, and a spark is 
 allowed to pass through the mixture of gases. A bright 
 flash is seen, a slight explosion is heard, and the mercury 
 rises in the tube. A portion of the gas will remain, and 
 this will be found to have the properties of hydrogen. 
 All the oxygen with a part of the hydrogen has been 
 used to form water. If the tube is carefully marked 
 in cubic centimetres, so that the volumes of the gases 
 which were introduced can be accurately measured, it 
 can easily be proved that the contraction in total volume 
 is such that exactly two volumes of hydrogen have united 
 with one of oxygen to form water. 10 t 
 
 A mixture of hydrogen and oxygen remains without 
 change indefinitely under ordinary conditions, union 
 only taking place if a lighted taper is brought in contact 
 with the gases, or if an electric spark is passed through 
 the mixture. An explosion which may be violent will 
 then result, provided the proportions in which the gases 
 taken are nearly two parts by volume of hydrogen to 
 one of oxygen. 
 
 * For the preparation of pure hydrogen, see Experiment 9, Appendix. 
 
 t Of course the amount of water which can be formed in a small glass 
 tube is too little for identification as such. In order to prove that water 
 is really the product of the action of hydrogen on oxygen, a large quantity 
 of hydrogen must be burned in oxygen. In order to be able to furnish 
 this proof, the pupils should perform the experiment given in Note 12 of 
 the Laboratory Appendix. 
 
26 ELEMENTS OF CHEMISTRY. 
 
 Relation between the Volumes of Hydrogen and Oxygen, 
 and of the Water Produced. If exactly two volumes 
 of hydrogen and one of oxygen are exploded in the 
 apparatus described in the preceding paragraph,* the 
 mercury will completely fill the tube, because the vol- 
 ume of liquid water which is formed is inconsiderable, 
 compared with the volume of the gases from which it 
 has been produced. But if the tube which contained 
 the hydrogen and oxygen is kept heated by a steam- 
 jacket, so that its temperature is that of the boiling 
 point of water, then the water vapor produced will 
 not only occupy a visible portion, but this volume will 
 be exactly two-thirds of that taken up by the gases 
 before explosion. 11 The facts which have been dis- 
 covered are, therefore, as follows : Hydrogen and oxy- 
 gen unite chemically to form a new substance, which is 
 water. This substance is produced by the interaetion 
 of exactly two volumes of hydrogen and one of oxygen. 
 The volume of the vapor of this compound is exactly 
 two-thirds of the sum of the volumes of the original 
 gases from which it is formed. If more than two vol- 
 umes of hydrogen to one of oxygen have been mixed 
 before the explosion, then some hydrogen will remain 
 unaltered ; if more than one-half as much oxygen as 
 hydrogen by volume was present, then some oxygen 
 will be found in the tube after the explosion. No 
 matter in what proportions hydrogen and oxygen are 
 mixed, they will unite to produce water only in the 
 proportion, two of hydrogen to one of oxygen. 
 
 Relation of Hydrogen to Oxygen by Weight. Obviously 
 a given volume of hydrogen must always have the same 
 
 * For an exact description of this apparatus, see Note 10, Laboratory 
 Appendix. 
 
WATER. 27 
 
 no matter where it is found, provided the condi- 
 tions of temperature and barometric pressure remain 
 identical,* and the same must also be true of a given 
 volume of oxygen. Hence, it follows from the above 
 experiments that water is always produced by the inter- 
 action of hydrogen and oxygen in a certain definite ratio 
 by weight. This ratio can be discovered by weighing a 
 glass globe which has been emptied by means of an air- 
 pump, weighing the same after filling it with pure 
 hydrogen, then removing the hydrogen, filling the globe 
 with oxygen, and again weighing. Comparing the re- 
 sults, we shall have the relation existing between the 
 weight of a given volume of hydrogen, and that of 
 the same volume of oxygen. This relation has been 
 found to be as one to sixteen ; or,t in other words, if the 
 specific gravity of hydrogen is placed at unity, the spe- 
 cific gravity of oxygen is sixteen. But we have learned 
 that two volumes of hydrogen unite with one of oxygen 
 to form water; hence, the relationship by weight be- 
 tween the hydrogen and oxygen which form water is as 
 two to sixteen, or one to eight. $ 
 
 One fact still remains to be shown, for we have not 
 yet definitely proved that the product of the explosion 
 between hydrogen and oxygen really is water. The 
 quantity of the latter substance obtainable by the 
 method we have employed is so small that it could 
 not practically be identified. However, all doubts on 
 this subject can be removed by arranging a hydrogen 
 
 * See pages 67, 68, 69. 
 
 f I.e., if the volume of the globe was.such as to hold exactly one gram 
 of hydrogen under the conditions of the experiment, then the oxygen 
 would weigh sixteen grams. The same ratio would be preserved, no 
 matter what was the weight of the original volume of hydrogen. 
 
 | Throughout this book proportions are given by weight unless vol- 
 ume is expressly stated. 
 
28 ELEMENTS OF CHEMISTRY. 
 
 apparatus which will deliver pure, dry hydrogen through 
 a jet,* lighting the gas, and then plunging the jet into 
 a jar filled with oxygen. It will continue to burn more 
 energetically than in the air, and drops of water pro- 
 duced by the combustion will soon collect on the sides 
 of the vessel. 12 Experiment has shown that, no matter 
 what the origin of the hydrogen may be, it always pro- 
 duces water whenever it is burned in oxygen. 
 
 Summary. The facts which we have now learned in 
 regard to the chemical nature of water can be summed 
 up as follows : 
 
 1. When sodium or potassium are brought in contact 
 with water, a gas, hydrogen, is given off from the water. 
 
 2. Considerable heat is developed during the process, 
 the sodium melting, and, if kept stationary, even setting 
 fire to the hydrogen, while the gas passing from the 
 potassium takes fire even if the metal is moving. 
 
 3. Water can be decomposed by the electric current, 
 hydrogen and a second gas, oxygen, being produced by 
 the process. 
 
 4. The ratio by volume between these gases when 
 they are formed from water is as two volumes of 
 hydrogen to one of oxygen. 
 
 5. Water can be produced from hydrogen and oxy- 
 gen by exploding a mixture of the two gases. 
 
 6. Water is the result of the union of exactly two 
 volumes of hydrogen and one volume of oxygen. 
 
 7. Water is formed by the union of two parts by 
 weight of hydrogen with every sixteen of oxygen.f 
 
 8. Hydrogen being selected as the standard, the specific 
 gravity of oxygen is sixteen. 
 
 * See Experiment 9, Appendix. f In exact numbers, 2 : 15.88. 
 
PRODUCTS OF ACTION OF SODIUM, ETC. 29 
 
 CHAPTER V. 
 
 THE PRODUCTS OF THE ACTION OF SODIUM 
 AND POTASSIUM ON WATER. 
 
 Caustic Soda and Caustic Potash. When sodium or po- 
 tassium is brought in contact with water, we have seen 
 that both metals dissolve, while, at the same time, heat 
 is given off. We have further learned that the hydro- 
 gen wjiich is produced is a constituent of the water. 
 What becomes of the sodium or potassium? Appar- 
 ently they have disappeared, and the water feel% soapy. 
 If the liquid in which the metals were dissolved is 
 evaporated, there will remain, in each case, a white, 
 semizsolid deliquescent * mass, which will readily harden 
 when heated to about 150* c^tigrade. Owing to the 
 fact that these substances win burn the skin and mu- 
 cous membrane, and that they contain hither sodium or 
 potassium, they are called caustic soda and potash, 
 respectively. 13 
 
 Electrolysis of Caustic Soda or Caustic Potash. Put one 
 of these solids into a small platinum dish, mix with it 
 a little water, f and connect the mass with the negative 
 pole of a powerful battery, while the dish is joined to 
 the positive. The liquid will become warm, bubbles of 
 gas will escape, and globules of a metallic substance will 
 appear at the top of the wire. These can be scraped 
 
 * See page 16. t Not enough to dissolve. 
 
SO ELEMENTS OF 
 
 off. They corrode, and even may take fire in moist air. 
 They decompose water, yielding hydrogen. In short, 
 they possess all of the properties belonging to sodium 
 or potassium. We have thus proved that when sodium 
 or potassium dissolves in water, there remains in solu- 
 tion a compound which, on electrolysis, yields sodium 
 or potassium in a manner exactly parallel to the forma- 
 tion of hydrogen from water. 
 
 (In the following paragraphs, the nature of caustic potash 
 alone will be considered, the pupil bearing in mind that what 
 applies to that substance is equally true of caustic soda.) 
 
 Chemical Structure of Caustic Potash. If caustic potash 
 is heated with potassium,* hydrogen will soon pass off. 
 If the hydrogen developed by dissolving a weighed 
 quantity of potassium in water were measured, and 
 the resulting volume were compared with that obtained 
 from heating the same weight of potassium with caustic 
 potash, the two quantities would be found to be iden- 
 tical. 14 The action of potassium on water can, there- 
 fore, be divided into twflfetages, first, one-half of the 
 hydrogen contained in the water is expelled, t leaving 
 caustic potash (potassium hydroxide) ; and then the 
 second half can be removed in the manner mentioned 
 above, leaving oxide- of potassium.^- 
 
 * In a silver dish or glass tube ; hot caustic potash attacks a platinum 
 vessel, while the clumsiness and weight of an iron one are objectionable. 
 
 f Provided enough potassium is used to change the entire amount of 
 any given quantity of water into potassium hydroxide. 
 
 J That the oxide of potassium must remain will be seen by a little 
 reflection ; for water, as has been proven, is composed of hydrogen and 
 oxygen. The hydrogen in the above experiment has been expelled by 
 potassium ; but as no oxygen has passed off, that element must have 
 remained behind in combination with the potassium. That the oxide 
 of potassium is really formed in this way can be proveiexperimentally by 
 burning a little piece of potassium in oxygen. The oxide so produced is 
 identical with that formed by the complete action of potassium on water. 
 
PRODUCTS OF ACTION OF SODIUM, ETC. 3l 
 
 Formulation of the Action of Potassium on Water. In 
 forming- water, two volumes of hydrogen unite with one 
 volume of oxygen. The preceding experiments also 
 show that the hydrogen in water can be divided into 
 two parts. These two facts can be made clearer if 
 we represent the two halves of hydrogen obtained from 
 water each by H, and the oxygen formed by the same 
 means by O. The structure of water will then be 
 represented by the combination HOH ; and designating 
 the potassium which acts upon water by a letter K, the 
 two stages of the reaction could be represented as fol- 
 lows : 
 
 HOH + K = H + KOH. 
 KOH + K = H + KOK.* 
 
 The potassium in potassium oxide is therefore com- 
 posed of two halves, just as much as is the hydrogen in 
 water, so that caustic potash (potassium hydroxide) is 
 simply water in which potassium has taken the place 
 of one-half the hydrogen, while rotassium oxide is water 
 in which potassium has replaced all of the hydrogen. 
 Such substitutions are by no means uncommon in chem- 
 ical reactions, and the changes studied above will serve 
 as an example for all others. 
 
 The conclusion at which we have arrived, using po- 
 tassium, would have been equally apparent had we 
 employed sodium. 
 
 * In these equations the quantity of water represented by HOH is 
 such that it is entirely decomposed by the amount of potassium repre- 
 sented by K. The letter K is used to designate potassium, because it is 
 the first letter of the Latin name (Kaliurri) of that element. 
 
82 ELEMENTS OF CHEMISTRY. 
 
 CHAPTER VI. 
 
 CHANGES OF ENERGY 
 
 Which take place in the Formation of Water, Potassium 
 Hydroxide, and Potassium Oxide. 
 
 Work and Energy. Potential Energy. When a sub- 
 stance, either by reason of its position or of its motion, 
 is capable of performing work, it is said to possess 
 energy. When energy is applied to overcoming resist- 
 ance, we say work is done. The energy possessed by a 
 body may be divided into two classes, energy of posi- 
 tion (potential energy), and energy of motion (kinetic 
 energy). A stone at the top of a hill possesses poten- 
 tial energy ; for, by reason of its position, it is capable 
 of performing work when the force holding it in place 
 is removed. The worK which it can do is measured by 
 the mass of the stone multiplied by the distance through 
 which it acts (L = MS). 
 
 Kinetic Energy. The capacity for. work which a body 
 in motion possesses by reason of that motion is called 
 its kinetic energy; and the measujje of this is one-half 
 the mass of the body multiplied by the square of its 
 
 ., /Mv 2 
 velocity ( - 
 
 . 
 * 
 
 Conversion of Potential into Kinetic Energy. Conservation 
 of Energy. If a portion of the potential energy pos- 
 
 * For the derivation of this formula, consult any elementary text-book 
 on physics. 
 
CHANGES OF ENERGY. 33 
 
 sessed by a body is converted into kinetic energy by its 
 assuming motion, then the snm of the capacity for work 
 still remaining, and of the kinetic energy already pro- 
 duced, is equal to the potential energy originally con- 
 tained in the body. This sum is also equal to the 
 kinetic energy which would be produced if its entire 
 potential energy had been used for the performance of 
 work* The sum of the potential and of the kinetic 
 energy is, therefore, constant. (Principle of the con- 
 servation of energy.) 
 
 If the - phenomena attendant upon the burning of 
 hydrogen in oxygen are recalled, it will be remembered 
 that heat is evolved during the process. If this heat 
 were properly applied (as, for instance, in changing 
 water into steam with which to move an engine), it 
 would be capable of performing work.* Hydrogen and 
 oxygen, when in contact, possess a form of energy 
 (chemical energy) which is akin to potential energy. 
 The only distinction between these is that in the latter 
 the capacity for work can be resolved into two factors, 
 the weight of the acting body and the distance through 
 which it acts, while in the former the distances 
 through which the action takes place, and the weights 
 of the particles into which we suppose all bodies di- 
 vided, are so small that chemical energy cannot be 
 resolved into two factors. The amount of chemical 
 energy can, however, be measured by the amount of 
 work which given weights of the interacting bodies are 
 
 * This tendency which certain elements have to unite with each other 
 to form compounds is termed "chemical affinity," or " chemism." The 
 nature of the force acting between the elements we cannot explain ; hut 
 it is by reason of this mutual attraction that they can perform work, just 
 as tlve stone which possesses potential energy can perform work owing 
 to the attraction of gravitation. 
 
34 ELEMENTS OP CUEMIST&Y. 
 
 capable of performing. When hydrogen and oxygen 
 unite to form water, their chemical energy is converted 
 into kinetic energy, and is manifested in the form of 
 heat which is susceptible of measurement. 
 
 i 
 
 The Energy required to Decompose a Body is equal to 
 that given off in its Formation. A stone when elevated 
 above the ground possesses potential energy. When 
 the force sustaining this stone is removed, it falls, and 
 in so doing changes its potential energy into kinetic 
 energy. To raise it to its original position after it has 
 fallen, we must add exactly as much energy as was 
 given off during the fall. In the formation and decom- 
 position of water we are confronted by a parallel case ; 
 for exactly as much kinetic energy must be used in de- 
 composing a given quantity of water into its constituent 
 elements, oxygen and hydrogen, as was given off in the 
 formation of the same weight of liquid. We accom- 
 lished the decomposition by the electric current, and 
 the quantity of electricity used could perform exactly 
 as much work as could the heat .given off in forming 
 the water which was decomposed. This conclusion can 
 be summed up as follows : - 
 
 The kinetic energy given off in the formation of a 
 given weight of water is equal to the kinetic energy 
 necessary for its decomposition ; or, as the electricity 
 used in the breaking down can be converted into heat,* 
 
 * In the case of water it is not practically possible to decompose the 
 compound hy heat alone, the temperature at which the decomposition 
 takes place being too high. In order to effect the decomposition we 
 must resort to the electric current. Heat can, however, be used to break 
 down many other compounds ; and in such cases it is, of course, possible 
 to measure the heat of decomposition. 
 
CHANGES OF ENERGY. 35 
 
 we say the heat of formation of a given weight of water 
 is equal to the heat of decomposition. 
 
 Energy Changes in forming Sodium and Potassium Hy- 
 droxide. When potassium or sodium is placed in contact 
 with water, there is a manifest evolution of heat, for 
 the metals are melted as they float on the surface. In 
 this case, however, the relationship in the energy is not 
 so easily understood as it is in the case of the formation 
 of water, because a portion of the hydrogen is given off 
 from the water, while potassium or sodium takes its 
 place. To form potassium hydroxide, energy must first 
 Be added to the water in order to decompose that sub- 
 stance, and so expel one-half of the hydrogen. It is 
 only after this, that potassium can take its place ; but 
 as it is manifest that heat is given off during the com- 
 plete change, potassium hydroxide must have a greater 
 heat of formation than has the water which has been 
 decomposed by the metal. When potassium hydroxide 
 has once been formed, it is in the same condition as the 
 stone which has fallen to the ground ; i.e., energy must 
 be added to bring it back to its original condition. It 
 follows that if it were practically possible to change 
 potassium hydroxide back into water and potassium 
 by means of hydrogen, the hydrogen, in order to effect 
 this change, would have to be assisted by an amount 
 of kinetic energy equal to that given off during the 
 decomposition of an equivalent quantity of water 
 by potassium. 
 
 If we designate a given quantity of hydrogen by X , an amount 
 of oxygen exactly necessary to change all of this hydrogen to 
 water by F, and a quantity of potassium just sufficient to decom- 
 
36 ELEMENTS OF CHEMISTRY. 
 
 pose the water so formed by Z, the compounds produced being 
 XY (water), YZ (potassium hydroxide) then : 
 
 I. II. 
 
 X + Y = XY. 
 
 Hydrogen 4- Oxygen = Water. 
 
 XY+Z = |YZ + |. 
 
 Water + Potassium = Potassium hydroxide + Hydrogen.* 
 
 In each case the substances under I., in being converted into 
 those under II., would give off heat ; they consequently possess 
 energy, for, when brought in contact, they are capable of per- 
 forming work. 
 
 Energy Changes in the Formation of other Compounds. 
 Substances which mutually possess chemical energy are 
 capable of entering into chemical reactions when they 
 are brought in contact, and the bodies produced by 
 these reactions manifestly possess less energy than the 
 uncombined constituents. Thus the chemical changes 
 which take place are accompanied by an evolution of 
 heat. It is, however, necessary in many cases to give 
 an impulse to the substances which we intend to have 
 enter into combination. For example, we saw that 
 hydrogen and oxygen could be mixed without suffer- 
 ing any change, the chemical union of the two gases 
 taking place only by contact with a flame or an elec- 
 tric spark. This condition can be compared to that of a 
 stone at the brow of a hill, since an impulse may have 
 to be given it before it begins to roll toward the bottom. 
 
 V 
 
 * In these equations the terms XY and T^YZ mean hydrogen and oxy- 
 gen joined to form water, and oxygen, potassium, and one-half as much 
 hydrogen united to form potassium hydroxide. The same letters sepa- 
 rated by the sign -f- mean that the substances represented are mixed 
 together, but that they have not as yet reacted to form new bodies. The 
 quantities of matter to the left and to the right of the sign of equality 
 are equal. 
 
CHANGES OF ENERGY. 37 
 
 Kindling Temperatures. The great majority of bodies 
 capable of uniting with oxygen, and of evolving light 
 and heat during the change, must, as is the case with 
 hydrogen, first be heated to a certain degree before the 
 union begins to take place. The temperature at which 
 combination with oxygen begins, is constant for a given 
 substance, and is called the kindling temperature of that 
 substance, while the subsequent reaction is called com- 
 bustion. A little reflection will show that the kindling 
 temperature of different bodies may vary greatly ; for it 
 is a matter of daily experience that coal has a very high 
 kindling temperature, while phosphorus * can be ignited 
 by the heat produced by friction. 15 
 
 * On match-heads. 
 
38 ELEMENTS OF CHEMISTRY 
 
 CHAPTER VII. 
 
 HYDROGEN CHLORIDE. 
 
 Common Salt. One of the chemical substances most 
 widely distributed is common salt. It is fourtd dis- 
 solved in sea-water, in the water of rivers, springs, and 
 lakes, in mineral deposits often very extensive in mass, 
 and in animal and vegetable tissues. 
 
 Preparation of Hydrogen Chloride. If salt is mixed 
 with sulphuric acid,* there is evolved a gas with a 
 most penetrating and acid odor. This gas is called 
 hydrogen chloride. 16 
 
 Properties of Hydrogen Chloride. Hydrogen chloride is a color- 
 less gas at ordinary temperatures. It is changed to a liquid at 
 under a pressure of twenty-six atmospheres-! It is extremely 
 soluble in water, one cubic centimetre of the latter absorbing 452 
 cubic centimetres of the former at ordinary temperatures. The 
 solution has a specific gravity of 1.20, and contains 42 per cent 
 of hydrogen chloride. " Muriatic " or " hydrochloric " acid is 
 simply this solution more or less diluted with water. Usually it 
 is of a yellow color, owing to impurities ; but when chemically 
 pure, it is colorless. The gas, or the concentrated solution, appears 
 to smoke (fume) when exposed to the air, a phenomenon due to 
 the condensation of the moisture present in the atmosphere which 
 
 * See page 56. 
 
 t The question of changing a gas to a liquid is merely one of temper- 
 ature and pressure. For example, steam (gaseous water) is changed to 
 a liquid (water) at 100, and at the pressure of one atmosphere. 
 
HYDROGEN CULOUIDE. 39 
 
 forms a solution of hydrogen chloride. When dissolving in water, 
 hydrogen chloride causes a considerable rise in the temperature. 
 A volume of hydrogen chloride is considerably heavier than the 
 same volume of air, its specific gravity being 1.23 (air =1). In 
 order to obtain the pure gas, it must be collected by displacing 
 dry air from a flask placed mouth upward, x or by expelling mer- 
 cury from a tube filled with the latter, and inverted over a trough 
 containing the same substance. Hydrogen chloride cannot be 
 collected over water, owing to its solubility in that liquid. 17 
 
 The Decomposition of Hydrogen Chloride by Sodium. In 
 studying the chemistry of hydrogen chloride, the first 
 question to be settled is whether the gas is a compound 
 or an element. The methods which suggest themselves 
 are, naturally, the same as those employed for the de- 
 composition of water. In this case, however, the sodium 
 or potassium cannot be treated in exactly the same 
 way as in the investigation of the chemical structure of 
 water, because when pieces of these metals are brought 
 in contact with dry hydrogen chloride, they soon be- 
 come coated with the solid products of the reaction * 
 which ensues, and are by this means protected from 
 further change. We can avoid this interference by dis- 
 solving sodium or potassium in mercury, f and then 
 substituting this solution for the pure metals. The 
 changes brought about will not be altered by this varia- 
 tion in the conditions, and we have the advantage of 
 avoiding the protective coating. 
 
 If a current of hydrogen chloride is passed through a 
 bottle containing sodium amalgam, the gas which is col- 
 
 * In the case of water the sodium or potassium hydroxide is dissolved 
 as fast as it is formed, and the metals are, therefore, not protected. 
 
 f The solutions produced by dissolving metals in mercury are called 
 amalgams. The solution of sodium would thus he called sodium 
 amalgam. 
 
40 ELEMENTS OF CHEMISTRY. 
 
 lected after the passage is no longer hydrogen chloride. 
 It is but slightly soluble in water, it has no odor, and it 
 burns in the air with a colorless flame in short, it is 
 hydrogen. We have already seen that this gas is not 
 contained in the sodium ; the only possible conclusion, 
 therefore, is that hydrogen chloride is a compound, and 
 that it contains hydrogen. 18 
 
 Decomposition of Hydrochloric Acid by the Electric Current.* 
 What are the other constituents of hydrogen chloride ? 
 The answer to this question can be found by decom- 
 posing hydrochloric acid by the electric current exactly 
 as was done with water; and investigation has shown 
 that a concentrated solution of hydrochloric acid in a 
 saturated t solution of common salt is the best sub- 
 stance to be employed in order to study this change. 
 If two pencils of gas carbon t (connected with the poles 
 of an electric battery) are placed in such a solution, 
 bubbles will appear first at the negative pole, and later 
 at the positive one. If two tubes filled with the liquid 
 undergoing decomposition are inverted over the two 
 pieces of carbon, the gases produced can be collected 
 separately ; and if the tubes are of the same size, it will 
 be seen that equal volumes of the two gases are collected 
 in them during equal intervals of time. The gas forming 
 at the negative pole is easily shown to be hydrogen. 
 That at the positive pole has a peculiar and most irri- 
 
 * The solution of hydrogen chloride in water is termed hydrochloric 
 acid. 
 
 t See page 14. 
 
 \ The hard pieces of carbon used in producing the arc electric lights. 
 
 The reason why the gas does not appear immediately at the positive 
 pole is hecause it is to a certain extent soluble in the liquid undergoing 
 decomposition. Only after the latter has taken up as much of this gas 
 as it will, does the excess escape. 
 
* 
 
 HYDROGEN CFjLOmBE. W \ 
 
 tating odor ; it bleaches moist vegetable dyes which are 
 brought in contact with it, and, owing to its greenish- 
 yellow color, is called chlorine. Hydrogen chloride can, 
 therefore, be decomposed into two elements, hydrogen 
 and chlorine. 19 
 
 Difference between the Structure of Hydrogen Chloride and 
 of Water. There is a marked difference in one respect 
 between the behavior of water and of hydrogen chloride 
 toward metals. When enough sodium or potassium acts 
 on the former to insure complete decomposition, the 
 metal liberates but one-half of the hydrogen, while in 
 the case of the latter it separates the entire quantity. 
 This same distinction is shown by the relative volumes 
 of the gases which are produced by electrolysis ; for 
 water is decomposed into two volumes of hydrogen and 
 one of oxygen, while hydrogen chloride, under similar 
 conditions, yields equal amounts of hydrogen and of 
 chlorine. The hydrogen of hydrogen chloride is not, 
 therefore, separable as two distinct and equal portions 
 like that of water. If, then, we express the structure 
 of water by the formula HOH (see page 31), we can 
 express that of hydrogen chloride by H Cl. 
 
 Formation of Hydrogen Chloride from its Constituent Ele- 
 ments. In order to complete all of the data necessary 
 for a knowledge of its structure, it only remains to 
 prove that hydrogen chloride can be produced from hy- 
 drogen and chlorine. This, however, is not so easily 
 accomplished as is the formation of water from hydro- 
 gen and oxygen, because of the practical difficulty that 
 chlorine cannot be collected over mercury (see page 24), 
 as it readily attacks that metal. But hydrogen and 
 
42 ELEMENTS OF CHEMISTRY. 
 
 chlorine in equal volumes (produced by the decomposi- 
 tion of hydrogen chloride by the electric current) may 
 be passed through a tube with a glass stopcock at each 
 end until all of the air is expelled.* If the stop- 
 cocks are then closed, and the tube is left in diffused 
 daylight, the hydrogen and chlorine will gradually 
 unite, and the gas which is produced will have exactly 
 the properties which characterize hydrogen chloride. 
 If care is taken not to lose any of the product of the 
 reaction, we can easily prove that the volume of gas 
 left in the tube after the union has taken place is 
 exactly equal to the sum of the volumes of hydrogen and 
 chlorine with which it was filled in the beginning. 
 Hydrogen chloride, therefore, is produced by the union 
 of equal volumes of hydrogen and chlorine. 
 
 The volumes of hydrogen and chlorine which combine to form 
 hydrogen chloride are equal, no matter how the acid is produced, 
 and, therefore, hydrochloric acid is formed by the union of defi- 
 nitely related masses of its constituent elements. As a given 
 volume of hydrogen always has a constant weight when meas- 
 ured under the same conditions, and as this is necessarily also 
 true of a given volume of chlorine, it follows that hydrochloric 
 acid is produced by the interaction of definitely related weights 
 of hydrogen and chlorine. As the volumes of these two gases 
 when they enter into combination are equal, it must be true that 
 the relative weights in which they combine are to each other in 
 the same ratio as their specific gravities; that is, as 1 to 35.45 
 (see page 27). 
 
 Summary. From the preceding experiments we have 
 learned the following facts : 
 
 * This experiment must be performed in a dark room, A mixture 
 of equal volumes of hydrogen and chlorine unite with a sharp explosion 
 if they are exposed to the sunlight, or even to the rays of an arc electric 
 light, or to those of a burning piece of magnesium. 
 
HYDROGEN CHLORIDE. 43 
 
 1. Hydrogen chloride is decomposable into hydrogen 
 and chlorine by means of the electric current. 
 
 2. Hydrogen chloride is produced from hydrogen 
 and chlorine. 
 
 3. Equal volumes of hydrogen and chlorine unite to 
 form .hydrogen chloride, and the gas so formed occupies 
 a space equal to the sum of the volumes of hydrogen 
 and chlorine from which it is produced ; or, one volume 
 of hydrogen and one volume of chlorine form two 
 volumes of hydrogen chloride. 
 
 4. The ratio by weight in which hydrogen and chlo- 
 rine unite is as 1:35.45. 
 
 5. Hydrogen chloride possesses less chemical energy 
 than does a mixture of hydrogen and chlorine ; for if 
 the latter mixture is brought into the sunlight, the two 
 gases will unite with a sharp explosion, heat and light 
 being given off at the same time. 
 
 6. Hydrogen and chlorine possess more chemical 
 energy than does hydrogen chloride. The latter sub- 
 stance is extremely stable, but can be broken down by 
 the electric current, or, in other words, by the addition 
 of energy (see page 34). 
 
 Resemblances between Hydrogen Chloride and Water. All 
 the above changes are exactly parallel to the similar 
 ones which we observed while studying water ; and if 
 we measure the heat given off in the formation of a 
 given weight of hydrogen chloride, and the heat-equiv- 
 alent of the electricity necessary to decompose the same, 
 the two will be found equal. The heat of decomposition 
 of hydrogen chloride is, therefore, equal to the heat of 
 its formation (see page 34). When hydrogen chloride 
 is dissolved in water, considerable heat is evolved. 
 
44 ELEMENTS OF CHEMISTRY. 
 
 Therefore, the solution requires more energy for its 
 decomposition than does the dry gas. In consequence 
 of this fact, the solution is of necessity more stable. 
 That this is the case can be shown by the follow- 
 ing experiments : - 
 
 If a mixture of hydrogen chloride and oxygen is passed 
 through a heated tube,* chlorine is developed, while water is 
 formed by the union of the hydrogen of the chloride with the free 
 oxygen which has been added. On the other hand, a solution of 
 chlorine in water, when placed in direct sunlight, forms hydro- 
 chloric acid, and gives off oxygen. 21 In the first case, then, the 
 hydrogen chloride and oxygen possess more energy than water 
 and chlorine. In the second case, however, the water being de- 
 composed by the chlorine, this relationship is exactly reversed. 
 Water is, therefore, more stable than is dry hydrogen chloride, 
 while, on the other hand, hydrochloric acid in solution is more 
 stable than water. The bleaching action of moist chlorine 
 (see page 41) can, in most cases, be referred to the effect of 
 oxygen which is liberated from water, the oxygen being chemi- 
 cally more active in the instant of its separation from its com- 
 pound than it is at other times. 22 
 
 * The tube had better contain porous bodies, such as pumice stone. 
 
THE ACTION OF METALS. 45 
 
 CHAPTER VIII. 
 
 > 
 
 THE ACTION OF METALS 
 
 On Hydrochloric Acid. The Neutralization of Hydrochloric 
 Acid by Bases. 
 
 WE have seen that when sodium acts on hydrogen 
 chloride a change is produced similar to the one which 
 we studied when considering the formation of sodium 
 hydroxide from water, with the difference that, in the 
 former case, if enough of the metal is added, the hydro- 
 gen is all separated, while sodium chloride remains. It 
 is a matter of experience, however, that more metals 
 will spontaneously react with hydrochloric acid than 
 will decompose water. 
 
 Action of Metals on Hydrochloric Acid. Pieces of zinc 
 or of iron,* when placed in a solution of hydrochloric 
 icid, are instantly attacked; hydrogen is liberated, 
 while the metals dissolve. If, after the reaction 
 is completed, the excess of acid is evaporated, there 
 will remain behind solid, salt-like bodies, which are 
 chlorides of zinc and of iron respectively. 23 The paral- 
 lelism between these changes and those taking place 
 between sodium or potassium and water becomes clear 
 if we use formulae similar to those already employed 
 
 * The metals are practically not acted upon by water at ordinary 
 temperatures. The solution of hydrogen chloride in water is hydro- 
 chloric acid. 
 
Just as 
 
 46 ELEMENTS OF CHEMISTRY. 
 
 (on page 31). Representing by H the one part* of 
 hydrogen which is combined with the 35.45 parts of 
 chlorine t in hydrochloric acid, and the corresponding 
 chlorine by Cl, we have 
 
 H + Cl = H Cl. 
 
 Hydrogen + Chlorine = Hydrochloric acid, and 
 
 H Cl + K = K Cl + H. 
 
 Hydrochloric acid + Potassium = Potassium chloride + Hydrogen. 
 
 HOH + K = KOH + H. 
 
 Water + Potassium = Potassium hydroxide + Hydrogen. 
 
 If we use zinc in place of potassium, representing 
 by zn the quantity of zinc which will decompose the 
 above weight of hydrochloric acid (i.e., which contains 
 one part of hydrogen combined with 35.45 parts of 
 chlorine), then $ - 
 
 zn + HCl = znCl + H. i 
 
 Zinc + Hydrochloric acid = Zinc chloride + Hydrogen, 
 
 or, in general, using the term Me to represent any metal 
 which is acted on by hydrochloric acid 
 
 Me + H Cl = Me Cl + ti. 
 
 In reacting with hydrochloric acid, the metals, while 
 liberating hydrogen, form the corresponding chlorides. 
 The chlorides can, therefore, be looked upon as hydro- 
 
 * In this book wherever proportions are indicated they are always 
 understood to be by weight, unless volume is expressly stated. 
 
 t Hydrogen, as we have seen, combines with chlorine in the ratio of 
 1 : 35.45. If we select 35.45 as the weight of chlorine in the above exam- 
 ples, we have numbers which may be called combining weights, for they 
 represent the ratio by weight in which hydrogen and chlorine unite. It 
 is obviously of advantage, in this and other cases, to select the weight 
 numbers which are determined for us by nature. 
 
 J The symbol zn is used to designate the amount of zinc which will 
 unite with as much chlorine as will the quantity of potassium repre- 
 sented by the symbol K. 
 
THE ACTION OF METALS. 47 
 
 chloric acid, in which the hydrogen has been replaced 
 by other metals. 
 
 Changes of Energy taking place during the Decomposition 
 of Hydrochloric Acid by Metals. Heat is developed during 
 the decomposition of hydrochloric acid by metals so 
 that the energy changes during these reactions are par- 
 allel to those encountered when sodium and potassium 
 are brought in contact with water. The heat given off in 
 the formation of the metallic chlorides must, therefore, 
 exceed that required for the decomposition of hydro- 
 chloric acid. Were it possible to convert the chloride 
 back to the metal and hydrochloric acid by means of 
 hydrogen, exactly as much energy would have to be 
 added to assist this reaction as was given off in the 
 formation of the chloride from the metal and hydro- 
 chloric acid. 
 
 In the change which is represented by the equation 
 H Cl + Me = Me Cl + H, 
 
 the substances to the right of the sign of equality possess less 
 energy than do those to the left. They are in the state of a stone 
 which has fallen to the ground, for energy must be added to 
 bring them back to their original condition. The reactions men- 
 tioned above take place spontaneously, because chemical energy 
 can be transformed into kinetic (see page 35). 
 
 Action of Hydrochloric Acid on the Oxides of the Metals. 
 The chlorides of the metals can be formed in another 
 and much more general way than by the direct substi- 
 tution of hydrogen : 
 
 EXAMPLE : If. the oxide of potassium is brought in contact 
 with hydrochloric acid, an energetic reaction at once results, 
 
48 ELEMENTS OF CHEMISTRY. 
 
 much heat is developed, and, when the excess of liquid is evapo- 
 rated, potassium chloride will remain. The oxide of potassium with 
 hydrochloric acid produces potassium chloride and water. 
 
 If we use the same formula for oxide of potassium that w r e 
 used on page 31, and the one for hydrochloric acid which we 
 employed on page 46, then the change can be represented as 
 
 follows : 
 
 K + HC1 KC1 H* 
 
 O +0 
 
 K + H Cl K Cl H 
 
 What is true of potassium oxide is true of most of 
 the oxides of other metals as well, the chlorides being 
 formed by the action of these oxides on hydrochloric 
 acid. 24 
 
 Action of the Hydroxides of the Metals on Hydrochloric 
 Acid. If we compare potassium hydroxide with potas- 
 sium oxide, we shall see that the former can be looked 
 upon as water in which all of the hydrogen has been 
 replaced by potassium, while the latter is water in 
 which but one-half of the hydrogen has suffered the 
 same substitution (see page 31). It seems reasonable 
 to suppose, therefore, that potassium hydroxide, being of 
 a nature similar to potassium oxide, will react similarly 
 with hydrochloric acid, and, indeed, this is the fact. 
 
 Potassium hydroxide with hydrochloric acid also produces po- 
 tassium chloride and water. This change becomes apparent if 
 
 * In order to secure additional clearness, the formula for potassium 
 oxide is written in a vertical line. This obviously makes no difference. 
 It thus becomes plain that the hydrogen of the hydrochloric acid unites 
 with the oxygen of potassium oxide to form water. The quantity of hy- 
 drochloric acid represented by H Cl is supposed to be exactly sufficient 
 to form potassium chloride with one-half of the potassium represented 
 by KOK. We must, therefore, use twice this quantity to express the 
 complete reaction. It is also clear that in our equation the hydrogen of 
 the water formed is divisible into two halves (see page 31). 
 
THE ACTION OF METALS. 49 
 
 we employ formulae similar to those already used in previous 
 
 cases : 
 
 KOH + H Cl = K Cl + HOH.* 
 
 What is true of potassium hydroxide is also true of 
 most hydroxides of other metals, so that these hydrox- 
 ides, when brought in contact with hydrochloric acid, 
 produce the corresponding chlorides and water. The 
 oxides and hydroxides of metals which react in the 
 above manner with hydrochloric acid are termed bases. 25 
 
 Neutralization of Hydrochloric Acid by Bases. The 
 changes outlined above always take place between defi- 
 nitely related quantities of the bases and of hydrochloric 
 acid. 
 
 This fact can readily be made apparent by experiment, but 
 we must first procure some means of discovering with certainty 
 the presence of a base when it is dissolved in water. This means 
 is furnished by the use of methyl orange, a substance prepared in 
 recent years by a complicated chemical process from one of the 
 constituents of coal-tar. A solution of methyl orange in water is 
 of an orange color when a soluble base is present, but turns to 
 deep red on contact with an acid.t 26 
 
 If a weighed quantity of potassium hydroxide is dis- 
 solved in water, a very little methyl orange added, and 
 then hydrochloric acid is carefully run into the solution 
 drop by drop, a point will finally be reached at which 
 
 * The quantity of hydrochloric acid here selected and represented by 
 H Cl is supposed to be exactly enough to form potassium chloride with 
 the potassium present in the hydroxide used. Experience teaches us 
 that the amount of hydrogen in the acid will be exactly enough to form 
 water with the oxygen and hydrogen present in potassium hydroxide. 
 
 t Substances which turn the red solution of methyl orange to orange 
 yellow are called alkaline. The orange solution is said to be of an 
 " alkaline reaction," and the substance (in this case methyl orange) 
 which shows that the alkali is present is termed an "indicator." Sub- 
 stances which have the opposite effect are said to be of an " acid 
 reaction." 
 
50 ELEMENTS OF CHEMISTRY. 
 
 the orange yellow of the " indicator " changes to red. 
 A trace of potassium hydroxide would now restore the 
 original color, which, again, a trace of acid would alter 
 to red. At this point the liquid is said to be neutral. 
 If the excess of water is evaporated from this solution, 
 nothing but potassium chloride remains ; for all the 
 caustic potash and all the hydrochloric acid have re- 
 acted with each other to form the salt. 
 
 We have supposed that we started with a definite quantity of 
 potassium hydroxide. Let us suppose also that the solution 
 of hydrochloric acid is so prepared that we know exactly the 
 amount of that substance in a, cubic centimetre of liquid. It is 
 then obvious that, by measuring the number of cubic centimetres 
 which it takes to neutralize the base, we can ascertain the total 
 amount of acid which is used for such neutralization. Repeated 
 experiments will show that, with a fixed quantity of potassium 
 hydroxide, the amount of acid necessary for neutralization is also 
 fixed, no matter what circumstances may surround the experi- 
 ments. What is true of potassium hydroxide is true of all other 
 bases, so that 
 
 A fixed quantity of hydrochloric acid is always neu- 
 tralized by an unvarying quantity of a given base, but 
 the amounts which will neutralize this quantity are 
 never alike with different bases. 27 
 
 FOR EXAMPLE : One part of hydrochloric acid is always 
 exactly neutralized by 
 
 1.535 parts of potassium hydroxide, 
 1.096 parts of sodium hydroxide, 
 1.014 parts of calcium hydroxide, 
 0.791 parts of magnesium hydroxide, 
 1.360 parts of zinc hydroxide, etc. 
 
 We shall subsequently see that what is true of hy- 
 drochloric acid is true of all other acids as well ; i.e., 
 
THE ACTION OF METALS. 51 
 
 the salts are formed by the interaction of quantities of 
 acids and bases which bear a definite relationship to each 
 other by weight. These facts are not unexpected if 
 we consider that every one of the chemical compounds 
 heretofore encountered is formed by the union of defi- 
 nitely related masses of the elements. 
 
 Energy Changes during the Neutralization of Bases by 
 Hydrochloric Acid. During the neutralization of bases 
 by hydrochloric acid, heat is given off, so that the chlo- 
 ride and the water which are formed possess less energy 
 than do the hydroxide and the acid. The substances 
 to the right of the sign of equality in the following 
 equation, therefore (as in the previous cases which have 
 been cited), possess less energy than those to the left; 
 for work must be done (energy added) to bring them 
 back to their original condition : - 
 
 Me OH + H 01 = Me Cl + HOH. 
 
 Base (metallic hydroxide) + Hydrochloric acid = Metallic chloride + Water. 
 
 Summary. The facts which have been brought for- 
 ward in the last chapter can be summed up as 
 follows : - 
 
 1. Hydrochloric acid attacks many metals, hydrogen 
 being liberated, and the chloride remaining. 
 
 2. Heat is given off daring the changes, consequently 
 the chlorides possess less energy than the metals and 
 the acid. 
 
 3. Hydrochloric acid unites with the oxides of met- 
 als (bases) to produce the chlorides and water. This 
 change is termed the neutralization of the base by the 
 acid. 
 
 4. Hydrochloric acid reacts with the hydroxides of 
 
52 ELEMENTS OF CHEMISTRY. 
 
 metals .(bases) to produce the chlorides and water. 
 This is also termed neutralization. 
 
 5. The replacement (substitution) of the hydrogen 
 in the acid takes place in such a way that a fixed quan- 
 tity of a given metal always takes the place of a fixed 
 quantity of hydrogen. There is a definite relationship, 
 therefore, between the mass of the metal dissolved, the 
 mass of hydrogen evolved, and the mass of chlorine 
 found united to the metal in the chloride. This rela- 
 tionship is constant for any one metal, but is different 
 for any two metals. 
 
 6. The neutralization of the acid always takes place 
 in such a way that there is a definite ratio between the 
 mass of the base neutralized and the mass of the acid 
 used for neutralization. The chloride produced also 
 contains the same proportion of metal to chlorine as it 
 would contain were it formed by dissolving the metal 
 in the acid. 
 
 7. Heat is given off during the processes of neutrali- 
 zation, consequently the chloride and the water which 
 are formed possess less energy than the base and the 
 acid before neutralization. 
 
THE OXIDES OF SULPHUR. 53 
 
 CHAPTER IX. . 
 
 THE OXIDES OF SULPHUR. 
 
 The Chief Oxides of Sulphur, and the Acids derived from these 
 Oxides. The Laws of Definite and Multiple Proportions. The 
 Neutralization of Sulphuric Acid by 
 
 Acids and Salts in General. The processes of neutrali- 
 zation with which we became familiar during the study 
 of hydrochloric acid are of fundamental importance in 
 chemistry, because there is a vast number of other acids 
 which, like hydrochloric, react with bases. Hydrogen 
 chloride contains only two elements, but most acids are 
 formed from three or even more. In any event, one of 
 these elements must be hydrogen, which is replaceable 
 by other metals. The term salt is applied to substances 
 produced either by direct substitution of the acid hydro- 
 gen by metals, or by neutralization of bases ; and a given 
 salt has the same composition, no matter what the man- 
 ner of its formation may be. 
 
 Undoubtedly the most important of acids is sulphuric 
 acid ; and, in order to understand the nature of this sub- 
 stance, it is necessary to inquire into the manner of its 
 formation. This we can most successfully do by first 
 studying the product formed by burning sulphur in 
 oxygen. 
 
 Formation of Sulphur Dioxide. If sulphur is ignited, it 
 burns with a blue flame, the sulphur disappears, and a 
 gas takes its place. If the combustion is performed in 
 
54 ELEMENTS OF CHEMISTRY. 
 
 a jar of pure oxygen with a sufficient quantity of sul- 
 phur, nothing but this gas (sulphur dioxide) will re- 
 main, and the volume of sulphur dioxide produced is the 
 same as the volume of oxygen entering into its formation.* 
 
 Formation of Sulphur Trioxide from Sulphur Dioxide. A 
 large amount of heat is given off when sulphur burns, 
 so that the sulphur dioxide which is produced by this 
 process obviously possesses much less energy than do 
 the oxygen and sulphur from which it is formed. Sul- 
 phur dioxide is, however, capable of still further union 
 with oxygen if placed under proper conditions, and the 
 product of this union is a solid called sulphur trioxide? 
 
 The quantities of oxygen which are united with a fixed 
 amount of sulphur in the above two oxides are to each other in 
 the ratio of 2 to 3 ; for in sulphur dioxide one part by weight of 
 sulphur is united to one of oxygen, while in sulphur trioxide one 
 part of sulphur is combined with one and one-half parts of 
 oxygen.* 
 
 These facts can be summed up as follows : 
 
 1. Each of the oxides of sulphur is produced by the 
 union of definitely related weights of sulphur and of 
 oxygen. 
 
 2. The weight of oxygen which is united to a fixed 
 amount of sulphur in sulphur dioxide is in simple ratio 
 ,to the weight of oxygen which is united to the same 
 fixed quantity of sulphur in sulphur trioxide. 
 
 The statement made in the first of the above clauses 
 is equally true, as we have seen, if rt is applied to any 
 one of the chemical compounds which we have studied ; 
 
 * Sulphur dioxide, when wanted for laboratory use, is not prepared 
 by the burning of sulphur. The method which is employed, and the 
 means of converting sulphur dioxide into sulphur trioxide, are given in 
 the Laboratory Appendix, experiments 28 and 29. 
 
THE OXIDES OF SULPHUR. 55 
 
 that in the second will be found to apply to every series 
 of compounds in which each member is produced by the 
 union of the same two elements. Facts so general in 
 their application as these can be summed up in the form 
 of laws, so that as the basis of chemical science we have 
 the result of extended investigation in the following : - 
 
 1. Law of Definite Proportions. Every chemical com- 
 pound contains its constituent elements in an unvarying 
 ratio by weight, no matter under what circumstances the 
 compound may be formed. 
 
 2. Law of Multiple Proportions. If two elements (A 
 and B) unite in more than one proportion, the parts of 
 B which enter into combination with a fixed quantity of 
 A will, in the series so produced, be in simple ratio to 
 each other. 
 
 EXAMPLES OF LAW 1. 
 
 One part of hydrogen always unites with 8 parts of 
 oxygen to produce water. 
 
 One part of hydrogen always unites with 35.5 parts 
 of chlorine to produce hydrogen chloride. 
 
 One part of hydrogen always unites with 39 parts 
 of potassium and 16 parts of oxygen to produce potas- 
 sium hydroxide; 
 
 EXAMPLES OF LAW 2. 
 
 Sulphur and oxygen produce two compounds. In 
 one of these one part of sulphur unites with one part of 
 oxygen to' produce sulphur dioxide ; in the other, one 
 part of sulphur unites with one and one-half parts 
 of oxygen to produce sulphur trioxide. Proportions 
 of oxygen, 2: 3. ^ THl^ 
 
 HJIIViaSXTT] 
 
 -** *. . /I 
 
56 ELEMENTS OF CHEMISTRY. 
 
 Iron and sulphur produce two compounds. In one 
 of these one part of iron unites with 1.143 parts of 
 sulphur ; in the other, one part of iron unites with 2.286 
 parts of sulphur. Proportions of sulphur, 1:2. 
 
 Nitrogen and oxygen produce five compounds. In 
 this series one part of nitrogen is united with .569, 
 1.138, 1.707, 2.276, and 2.845 parts of oxygen. Pro- 
 portions, 1:2:3:4:5. 
 
 Properties of Sulphur Trioxide. Sulphur trioxide is a colorless 
 liquid at ordinary temperatures. Below 15 it changes to a solid. 
 It boils at 46, and forms a colorless vapor having a specific grav- 
 ity of 2.76. (Air = 1.) 
 
 Formation of Sulphuric Acid from Sulphur Trioxide. Sul- 
 phur trioxide dissolves in water with a hissing noise, 
 resembling that attending the immersion of a red-hot 
 iron; much heat is developed, and if the excess of 
 liquid is evaporated there remains an oil-like fluid 
 which is termed sulphuric acid. 30 Sulphuric acid is, 
 therefore, formed by the union of water with sulphur 
 trioxide (which is termed an anhydride). 
 
 The Anhydrides of Acids. The anhydrides of acids 
 constitute a class of bodies which has many representa- 
 tives. They are oxides of not-metals which on addi- 
 tion of water unite with that substance to produce the 
 corresponding acids. 
 
 EXAMPLES : Sulphuric anhydride (sulphuric trioxide) by the 
 addition of water produces sulphuric acid. 
 
 Phosphoric anhydride (produced by burning phosphorus in 
 oxygen) by the addition of water produces phosphoric acid. 
 
 Nitric anhydride (a compound of nitrogen and oxygen) by 
 the addition of water produces nitric acid. 
 
THE OXIDES OF SULPHUR. 57 
 
 Properties of Sulphuric Acid. Sulphuric acid is a colorless 
 liquid which on superficial examination appears like an oil. 
 When pure it has a specific gravity of 1.88 (water = 1) ; at it 
 crystallizes in large prisms which melt at 10.5. It boils at 338; 
 but before that point is reached the acid begins to decompose 
 into sulphur trioxide and water, or, in other words, in a direction 
 which is the reverse of that of its formation. This separation is 
 complete at a temperature somewhat above the boiling-point of 
 the acid. Sulphuric acid has a strong inclination to take up water. 
 During the process of solution a great amount of heat is devel- 
 oped; the diluted acid,* therefore, possesses much less energy 
 than does the pure, and, as a consequence, it is less readily decom- 
 posed. Concentrated sulphuric acid violently attacks the skin 
 and mucous membrane, so that it is a poison. 31 
 
 Action of Metals on Diluted Sulphuric Acid. It is obvi- 
 ous that sulphuric acid must contain hydrogen, for 
 it is produced by the union of sulphur trioxide with 
 water. That this hydrogen can be replaced by other 
 metals is proven by the following experiments : - 
 
 When diluted sulphuric acid is brought in contact 
 with pieces of zinc, a gas is developed which can easily 
 be identified as hydrogen. If the excess of liquid is 
 evaporated (after as much zinc has been added as the 
 acid will dissolve), a solid crystalline substance (zinc 
 sulphate) will remain. Similar phenomena are observed 
 when iron or magnesium is added to dilute sulphuric 
 acid. With the former iron sulphate is formed, while 
 with the latter magnesium sulphate is produced. So- 
 dium or potassium also reacts with diluted sulphuric 
 acid with the greatest violence, hydrogen being evolved, 
 while sodium or potassium sulphate remains after evap- 
 
 * Dilute slowly by adding sulphuric acid to an excess of water, not by 
 adding water to sulphuric acid; otherwise, the heat produced may be 
 great enough to cause the water to boil, and in this way drops of hot acid 
 may be scattered about. 
 
58 ELEMENTS OF CHEMISTRY. 
 
 oration. Zinc sulphate, iron sulphate, magnesium sul- 
 phate, sodium sulphate, and potassium sulphate are 
 salts ; for, as we have seen, they are produced by re- 
 placing the hydrogen of sulphuric acid by other metals. 32 
 
 Neutralization of Sulphuric Acid by Bases. The phe- 
 nomena which have just been detailed are parallel to 
 those which we observed while studying hydrochloric 
 acid (see page 46 and following) ; and in order to make 
 this parallelism more apparent, the processes attending 
 the neutralization of sulphuric acid should next be con- 
 sidered. 
 
 The oxides of zinc, iron (ferrous oxide), or magne- 
 ium, are insoluble in water ; but they readily dissolve 
 in djluted sulphuric acid. If in each case enough of 
 the oxide is added to the acid so that a portion will 
 remain undissolved (even after standing for some 
 time), and if then this excess is removed by nitration, 
 sulphates, identical with those obtained by ,the action 
 of diluted sulphuric acid on the corresponding metals, 
 will be deposited as crystalline solids upon evaporating 
 the excess 'of the liquid. In the same way sodium 
 oxide will produce sodium sulphate, and potassium 
 oxide, potassium sulphate. Sulphuric acid is, therefore, 
 neutralized by these oxides to form the corresponding 
 salts and water, and similar processes can also be ob- 
 served upon the solution in sulphuric acid of a very 
 large number of the oxides of other metals. 33 
 
 Difference between the Neutralization of Sulphuric Acid 
 and of Hydrochloric Acid. So far we have observed no 
 distinction between the action of sulphuric acid and 
 hydrochloric acid during the process of neutralization. 
 
THE OXIDES OF SULPHUR. 59 
 
 That there is a marked difference, however, will become 
 apparent as soon as we study the neutralization of sul- 
 phuric acid by means of sodium or potassium hydroxide. 
 We weigh off sodium hydroxide and sulphuric acid in 
 such proportions, that for one part of the former we 
 have 2.45 parts of the latter, and then, after dissolving 
 the sodium hydroxide in water and diluting the sul- 
 phuric acid with the same, bring the two solutions in 
 contact. All the sulphuric acid and all the sodium 
 hydroxide will enter into the reaction, and a salt will 
 be produced. This salt can be isolated by evaporating 
 the excess of liquid. It differs from those we have 
 previously encountered in the fact that, in spite of its 
 being formed by the action of an acid on a base, it still 
 contains replaceable hydrogen.* This salt, therefore, 
 has resulted from replacing by sodium only a portion 
 of the available hydrogen of sulphuric acid. That this 
 is a fact can readily be shown by dissolving the salt in 
 water, adding a second quantity of sodium hydroxide 
 equal to the first, and again evaporating the excess of 
 liquid. There will remain a sodium sulphate, which 
 no longer contains replaceable hydrogen ; and this sub- 
 stance differs radically in properties from the one which 
 was isolated in the first instance. The salts which are 
 produced by replacing only one-half the hydrogen of 
 sulphuric acid by metals are termed primary or acid ; 
 those formed by replacing all the hydrogen, secondary 
 or neutral sulphates. 3 * 
 
 Comparison of the Structure of Sulphuric Acid and of 
 Water. In its structure sulphuric acid can be com- 
 pared to water; for its hydrogen is divisible into two 
 
 * I.e., hydrogen which can be replaced by other metals to form a salt. 
 
60 ELEMENTS OF CHEMISTRY. 
 
 halves by means of metals, just as the hydrogen of 
 water is. This parallelism will be made clear if we 
 consider the following two formulae (X representing 
 what is united with hydrogen to form sulphuric 
 acid) : - 
 
 H - O - H and H - X - H 
 
 Water. Sulphuric acid. 
 
 The substitution of hydrogen by sodium in these two 
 substances can be expressed as follows : 
 
 1. Na * + HOH = Na OH + H. 
 
 Sodium + Water = Sodium hydroxide + Hydrogen. 
 
 Na OH + Na = Na ONa + H. 
 
 Sodium hydroxide + Sodium = Sodium oxide + Hydrogen. 
 
 2. Na + HXH = Na XH + H. 
 
 Sodium + Sulphuric acid = Primary sodium sulphate + Hydrogen. 
 
 Na XH + Na = Na X Na + H. 
 
 Primary sodium sulphate + Sodium = Secondary sodium sulphate + Hydrogen. 
 
 Comparison of the Structure of Hydrochloric Acid with that 
 of Sulphuric Acid. When sodium hydroxide is brought 
 in contact with twice as much hydrochloric acid as it is 
 capable of neutralizing, one-half the available hydro- 
 gen will be replaced by the sodium ; but this hydrogen 
 will be the constituent part of only one-half the hydro- 
 chloric acid, while the other half will remain unchanged. 
 With sulphuric acid, on the other hand, if the same 
 quantitative relationship between the base and the acid 
 is retained,! one-half the hydrogen will also be replaced ; 
 but, at the same time, all the sulphuric acid will have 
 
 * The quantity of sodium represented by the symbol Na is, as in pre- 
 vious instances, supposed to be exactly enough to substitute one part by 
 weight of hydrogen. 
 
 f I.e., if one-half as much sodium hydroxide as is necessary for com- 
 plete neutralization of the sulphuric acid is added. 
 
THE OXIDES OF SULPHUR. 61 
 
 entered into the reaction and so have produced the 
 primary sulphate of sodium. An acid like hydrochloric 
 acid is termed a monobasic acid ; an acid like sulphuric 
 acid is termed a dibasic acid. What is true of hydro- 
 chloric acid and of sulphuric acid is equally true of all 
 monobasic and diabasic acids. 
 
 The Sulphates are formed by the Interaction of Definitely 
 Related Weights of Bases and of Sulphuric Acid. The 
 method by which we can ascertain that an unvarying 
 amount of a given base is always necessary to neutral- 
 ize completely a fixed quantity of sulphuric acid is iden- 
 tical with that employed in the study of hydrochloric 
 acid (see page 49). A little methyl orange (page 
 49) is added to dilute sulphuric acid, and then potas- 
 sium hydroxide or sodium hydroxide solution is added 
 until the color just changes from deep red to orange 
 yellow. At this point the sulphuric acid will be com- 
 pletely neutralized, and the secondary sulphate will be 
 formed. If we start with a definite quantity of the 
 base, and if the solution of sulphuric acid is so pre- 
 pared that we know exactly the amount of that sub- 
 stance in a cubic centimetre of the liquid, it is obvious 
 that, by measuring 'the number of cubic centimetres 
 which it takes to neutralize the base, we can ascertain 
 the total amount of the acid used for such neutrali- 
 zation. If this method is carefully followed out, a 
 series of experiments will develop the following 
 law. 35 
 
 A fixed quantity of sulphuric acid is always com- 
 pletely neutralized by an unvarying quantity of a given 
 base, but in no two different bases are the amounts which 
 will neutralize this quantity of acid alike. 
 
62 ELEMENTS OF CHEMISTRY. 
 
 EXAMPLES : One part by weight of sulphuric acid is always 
 completely neutralized by 
 
 1.143 parts by weight of potassium hydroxide, 
 0.817 parts by weight of sodium hydroxide, 
 0.755 parts by weight of calcium hydroxide, 
 0.595 parts by weight of magnesium hydroxide, 
 1.013 parts by w r eight of zinc hydroxide, etc. 
 
 If we compare the above table with the similar one 
 on page 50, in which the quantities of the same hy- 
 droxides necessary to neutralize one part of hydrochlo- 
 ric acid are given, there will be brought to light the 
 remarkable fact that the amounts of the hydroxides are 
 in the same ratio. This fact will become apparent if 
 we multiply all of the numbers in the first table by 
 86.5, and all of those in the second by 49 ; * for 
 
 56 parts of potassium hydroxide, 
 40 parts of sodium hydroxide, 
 39 parts of calcium hydroxide, 
 29.5 parts of magnesium hydroxide, 
 49.65 parts of zinc hydroxide, 
 
 are completely neutralized either by 36.5 parts of hydro- 
 chloric acid, or by 49 parts of sulphuric acid. If simi- 
 lar investigations are conducted with any other acid, 
 the above parts of the hydroxides are also the quanti- 
 ties which are necessary to neutralize that particular 
 amount of any acid which contains one part of hydro- 
 gen ; and from this it follows that the reverse must also 
 be true. We could, therefore, construct a table of 
 acids with numbers so selected that each would repre- 
 
 * The reason for selecting 36.5 and 49 as the numbers with which to 
 multiply the quantities is that 36.5 and 49 are the parts by weight of 
 hydrochloric acid and of sulphuric acid which contain one part by weight 
 of hydrogen. 
 
THE OXIDES OF SULPHUR. 68 
 
 sent a weight of acid containing one part of hydrogen, 
 and then any one of those quantities would exactly 
 neutralize any one of the amounts given in the above 
 table of hydroxides. It is, of course, understood that 
 all these weights are to be measured by the same unit. 
 The relative weights of bases and acids so ascertained 
 are termed their equivalent weights. 
 
 Relationship between the Amounts of Base Necessary to 
 form the Primary and Secondary Sulphates. It has been 
 shown that the hydrogen of sulphuric acid is, like that 
 of water, divisible into two equal parts by the action 
 of sodium or potassium hydroxide. We should there- 
 fore select, as a basis for consideration, not the equiva- 
 lent weight of sulphuric acid, but twice that amount, 
 or, in other words, that part by weight of sulphuric 
 acid which contains two parts of hydrogen. If we do 
 this, we find that 98 parts of sulphuric acid react with 
 
 56 parts of potassium hydroxide and 
 40 parts of sodium hydroxide 
 
 to form the primary sulphates of these metals, and with 
 
 112 parts of potassium hydroxide and 
 80 parts of sodium, hydroxide 
 
 to form the secondary sulphates. 
 
 These quantities of potassium and of sodium hy- 
 droxide are, however, in the simple ratio of 1:2; so 
 that the law of multiple proportions (page 55) applies 
 to the more complicated processes of neutralization as 
 well as to the comparatively simple ones of the union 
 of the same two elements with each other to form more 
 than one compound. 
 
64 ELEMENTS OF CHEMISTRY. 
 
 Summary. 
 
 1. Sulphur, in burning, unites with oxygen to form 
 sulphur dioxide. 
 
 2. Sulphur dioxide can further take up oxygen, 
 under proper conditions, to form sulphur trioxide. 
 
 3. The parts of oxygen which are united with a 
 fixed quantity of sulphur in these oxides are to each 
 other as 2 : 3. 
 
 4. Sulphur trioxide unites with water to produce 
 sulphuric acid. A large amount of heat is given off 
 during this change, and the same is true if the acid 
 is diluted with water. Diluted sulphuric acid, conse- 
 quentjy, is more difficult to decompose than concen- 
 trated. 
 
 5. Diluted sulphuric acid when in contact with cer- 
 tain metals liberates hydrogen while the corresponding 
 sulphates are formed. The hydrogen of the acid is 
 replaced by the metals. 
 
 6. Diluted sulphuric acid reacts with the oxides or 
 hydroxides of metals (bases) to form sulphates and 
 water. 
 
 7. Sulphuric acid can form two sulphates each of 
 sodium and of potassium. These sulphates differ as 
 follows : In one class (primary or acid sulphates), only 
 one-half the hydrogen contained in the sulphuric acid 
 from which the salts are formed is replaced by the 
 metal. In the other class (secondary or neutral sul- 
 phates), all the hydrogen is replaced by the metal. 
 Sulphuric acid is* a dibasic acid. 
 
 8. Hydrochloric acid differs from sulphuric acid ; for 
 when brought in contact with sodium or potassium 
 hydroxide it forms but one kind of chloride, i.e., the 
 chloride produced by replacing all of the hydrogen of 
 
THE OXIDE*k OF SULPHUR. 65 
 
 the hydrochloric acid which is neutralized. If an 
 excess of hydrochloric acid is present, this excess re- 
 mains unaffected by the base. Hydrochloric acid is a 
 monobasic acid. 
 
 9. The sulphates are formed by the interaction of 
 definitely related amounts of base and acid. 
 
 10. The ratio between the weights of various bases, 
 which are so related in quantity that they will exactly 
 neutralize a given weight of one acid, is also the ratio 
 by weight in which these same bases will exactly neu- 
 tralize a fixed amount of any other acid. 
 
66 ELEMENTS OF CHEMISTRY. 
 
 CHAPTER X. 
 
 THE ATMOSPHERE. 
 
 Physical Properties of the Atmosphere. The Barometer. Boyle's 
 and Charles's Laws. 
 
 IN the previous portions of this book mention has 
 been made of the fact that substances which burn in 
 oxygen will do the same thing, with somewhat dimin- 
 ished intensity, in the air. As by far the greater num- 
 ber of combustions take place in the latter medium, 
 and as it plays such an important part in the most fre- 
 quently recurring chemical phenomena, it is advisable 
 to become acquainted with the composition and prop- 
 erties of the atmosphere at an early period in the 
 study of chemistry. This is the more necessary be- 
 cause one of its constituents (nitrogen) is an element 
 with some of whose compounds we must soon become 
 familiar. 
 
 The Weight of the Atmosphere. The colorless, gaseous 
 envelope which surrounds the earth is termed its atmos- 
 phere. The atmosphere, being a material substance, 
 possesses weight, and by reason of this weight it exerts 
 a pressure on all things beneath its surface. That this 
 is the case can readily be shown by the following experi- 
 ments : 
 
 A piece of sheet rubber is tied over one end of a 
 glass cylinder, while the other end, ground so as to fit 
 
THE 
 
 air-tight over the plate of an air-pump, is"p!aced over 
 the opening which connects with the pump. The sheet 
 of rubber will be pressed inward as soon as part of the 
 air in the cylinder is exhausted. Two hollow hemi- 
 spheres, which lit air-tight along their edges, are held 
 firmly together when the air within them is rarefied. 
 The above phenomena are not observed until the air is 
 exhausted ; but this is due to the fact that the atmos- 
 phere, being perfectly elastic, presses equally in all 
 directions. It can, therefore, make its pressure mani- 
 fest only when a difference is established. 
 
 The Barometer. If a tube is entirely filled with liquid, and 
 the lower end is then opened under the same fluid while the 
 upper end remains closed, the liquid will not drop from the tube, 
 but will remain in equilibrium at a certain height. This is owing 
 to the pressure exerted by the surrounding atmosphere upon the 
 surface of the fluid in the exterior vessel. The height of the 
 column which can be so maintained is inversely proportional to 
 the specific gravity of the liquid employed. It. varies with the at- 
 mospheric pressure, and is therefore used to measure it. If a 
 tube is longer than this column, then a space containing no air 
 will remain above the liquid in it. This space is termed a Torri- 
 cellian vacuum. An instrument called the barometer is con- 
 structed on the above plan, the fluid in use being mercury ; and 
 the distance from the upper level of the meniscus of the mercury 
 in the tube to the upper level of that in the container underneath 
 is termed the height of the barometer. The mean height of the 
 barometer at the level of the sea is 760 millimetres, and this is 
 taken as the standard for all measurements. The pressure exerted 
 by a column of mercury 760 millimetres high on a square centi- 
 metre is 1.033 kilograms. The standard pressure of the atmos- 
 phere upon the same surface is, therefore, equal to the same 
 quantity. If this pressure is diminished, the mercury will fall ; 
 if it is increased, it will rise. If, therefore, the barometer is taken 
 from the sea level to a point above the same, a diminution in the 
 height of the column corresponding to a diminution in the weight 
 
68 ELEMENTS OF CHEMISTRY. 
 
 of the atmosphere above it will be observed. The barometric 
 height at any place is frequently changing because the atmosphere 
 is not at rest, and is subject to variations in density, owing to 
 differences in temperature. When any portion of the atmosphere 
 is warmed, its density diminishes ; the warm air will rise, its 
 pressure will diminish, and, as a consequence, the barometer will 
 fall. The same result is brought about if the temperature re- 
 mains constant while that of contiguous portions of the atmos- 
 phere is lessened. 36 
 
 Relation of the Volume of a Gas to Pressure. If a given 
 volume of air (V) is subjected to a certain pressure 
 (P), the volume will be diminished as the pressure is 
 increased. If the second volume produced by this 
 increased pressure is termed V and the second pressure 
 P', then the relation 
 
 V: V: : P' : P 
 
 will be realized. The same is true of all other gases 
 which, like the atmosphere, are at a temperature far 
 above the point at which they become liquid. This 
 fact can be summed up in the following law : 37 
 
 Boyle's Law. If the temperature remains constant, the 
 volume of a given quantity of gas varies inversely as 
 the pressure to which it is subjected. 
 
 EXAMPLES: 
 
 Let P = the pressure of one atmosphere, 
 Let P ' = the pressure of two atmospheres, 
 Y = 10 cubic centimetres, 
 
 VP 10 
 then, V = -p7 = -o- = 5 cubic centimetres. If P' = 3 atmospheres, 
 
 then V = 3^ cubic centimetres, and so on. 
 
 If P is equal to the pressure of one atmosphere, it is equal to 
 the pressure exerted by 760 mm. of the barometer. If h repre- 
 sents the height in millimetres of the observed barometric pres- 
 
THE ATMOSPHERE. 69 
 
 sure, and V the volume of a gas at 760 mm. pressure, and V t 
 that volume at the observed pressure, then, V : V t : : h : 760, 
 from which it follows that 
 
 Vt = ^ ' (Equation 1.) 
 
 Application of Boyle's Law in the Calculation of Gas 
 Volumes. To find the volume which any gas occupies 
 at other than the standard barometric pressure, we must 
 multiply its volume at the standard pressure by 760, and 
 divide by the observed height of the barometer. 
 
 From equation 1 it follows that 
 
 Vo== ~7^ (Equation 2.) 
 
 To find the volume of any gas at standard barometric 
 pressure, we must multiply the observed volume by the 
 observed barometric pressure in millimetres, and divide 
 by 760. 
 
 Law of Charles and Gay Lussac. All gases when not 
 too near the point at which they liquefy, expand very 
 nearly 573 * of their volume for each increase of 1 cen- 
 tigrade in temperature. This fraction is called the 
 co-efficient of expansion of gases, and is independent 
 of the pressure to which the gas is subjected. 
 
 EXAMPLES : A litre of gas at will be 1 + ^ at 1, 1 + 373 
 at 2, ten litres would be 10 + ^ at 1, and so on, so that 
 
 3. Vt = V + V t 
 
 4. Vt = V (l + t) 
 
 Vt 
 
 5. V = 
 
 1 -f at 
 
 where V = the volume of any gas at 0, V t the volume of the gas 
 at the temperature t, and = j| 7 . 
 
 * Inexact numbers .QQ367. 
 
70 ELEMENTS OF CHEMISTRY. 
 
 To calculate the volume which a gas would occupy 
 at (the standard temperature), we must divide the 
 observed volume by 1 + t. 
 
 When a gas is at ordinary temperature and pressure, and we 
 wish to ascertain its volume at standard barometric pressure (7 GO 
 millimetres) and temperature 0, corrections must be made both 
 for temperature and pressure. This can be done in one operation 
 by combining equations 2 and 5, which gives 
 
 6. Vo= 
 
 760(1 + at) 
 
 If a gas is introduced into the Torricellian vacuum so that a 
 part of the mercury is expelled from the tube, this gas is obviously 
 under atmospheric pressure, minus the height of the mercury still 
 in the tube. If this latter quantity is w, then equation 6 becomes 
 
 y 
 
 " 
 
 760(1 + at) 
 
 Standard Conditions for the Measurement of Gas Volumes. 
 A gas at temperature and pressure 760 millimetres 
 is said to be under standard conditions ; and all com- 
 parisons between the volumes of different gases pre- 
 suppose that these volumes are under those conditions, 
 unless the contrary is expressly stated. 
 
 Vapor Pressure and Correction for the same. Gases which are 
 undergoing observation may contain water. If this is the case, a 
 further correction must be made for the pressure of the vapor of 
 water, since it is obvious that this vapor exerts a pressure which 
 increases with the temperature exactly as does that of the gas 
 which is to be measured. This amount, in millimetres, must 
 therefore be deducted from the observed barometric height, so that 
 equation 7 becomes 
 
 y t(h -w-*) 
 760(1 + at) 
 
 where <*> represents the vapor pressure in millimetres at the tem- 
 perature of observation. What is true of water vapor is true of 
 
THE ATMOSPHERE. 71 
 
 the vapors of other liquids as well, with the distinction that at the 
 same temperature the vapors of different liquids exert different 
 pressures.* As a matter of fact, water vapor and, at high tem- 
 peratures, the vapor of mercury, are the only ones to be consid- 
 ered in elementary work. 88 
 
 * A table giving the tension of water vapor at different temperatures 
 can always be found in the larger manuals of chemistry, or in small vol- 
 umes of "tables" for chemists. One of the latter should always be 
 easily accessible. 
 
72 ELEMENTS OF CHEMISTRY. 
 
 CHAPTER XI. 
 
 THE ATMOSPHERE (Continued). 
 Combustion in Oxygen and in Air. 
 
 Isolation of Nitrogen from the Atmosphere. Heat to red- 
 ness a long tube containing a quantity of fine copper 
 shavings. Pass air through this tube, and collect the 
 gas that emerges in a tube closed at one end, filled 
 with water and inverted in a water trough. This gas 
 will be found to differ in properties from the air which 
 originally contained it. It is colorless and odorless. 
 A burning pine splinter placed in it is instantly extin- 
 guished. At the same time, unlike hydrogen, it does 
 not itself burn. This gas is an element and is termed 
 nitrogen. 
 
 Properties of Nitrogen. Nitrogen has a specific gravity (air || 1) 
 of .97209. At a pressure of 35 atmospheres and at temperature 
 of 146.3 it becomes liquid. This liquid boils at 193 and 
 solidifies at 203. Chemically, nitrogen in a free state is a re- 
 markably indifferent substance, uniting with other elements only 
 under the greatest provocation. Owing to this indifference, it will 
 neither burn nor support combustion, and animals are suffocated 
 when placed in it. 
 
 The Atmosphere contains Nitrogen and Oxygen. The hot 
 copper over which the air was passed is completely 
 changed, and at the same time it has gained in weight. 
 The same alteration in the copper can be brought about 
 
THE ATMOSPHERE. 73 
 
 by heating it in pure oxygen. Hence, we conclude that 
 in the above experiment it has been oxidized by the 
 air to form copper oxide. The atmosphere, therefore, 
 contains nitrogen and oxygen. 39 
 
 Combustion in Oxygen. Oxygen is a supporter of com- 
 bustion. This means that many substances, if they are 
 heated in the gas to points above their kindling temper- 
 atures, will unite with it energetically, evolving heat 
 and light (see page 36). 40 
 
 EXAMPLES : A small piece of phosphorus, if ignited in the air 
 and placed in a jar of oxygen, will burn with dazzling brilliancy, 
 the product of the combustion being an oxide of phosphorus 
 (phosphorus pentoxide). 
 
 Sulphur, ignited in the air, will burn energetically in oxygen, 
 producing an oxide of sulphur (sulphur dioxide ; see page 53). A 
 piece of charcoal heated to redness will burn brightly in oxygen, 
 the resulting compound being an oxide of carbon (carbon dioxide). 
 
 In the same way many other elements, sodium, potassium, 
 magnesium, will burn in oxygen with the greatest energy, while 
 in each case the corresponding oxide is produced ; and even sub- 
 stances which under ordinary circumstances are considered as 
 being non-combustible (for example, a steel watch-spring) can be 
 ignited in oxygen. 
 
 Changes of Energy during Combustion. The cause un- 
 derlying all these phenomena is the same, and is iden- 
 tical with the one discussed when we studied the 
 formation of water during the combustion of hydrogen 
 in oxygen. The substances which burn all possess 
 chemical energy when in the presence of oxygen. This 
 chemical energy is converted into kinetic energy (light 
 and heat) during the combustion, so that the resulting 
 bodies possess less energy than do the substances from 
 which they are produced. Obviously, therefore, as 
 
74 ELEMENTS OF CHEMISTRY. 
 
 mucn energy would have to be added to decompose 
 these substances as is given off in their formation, 
 provided equal quantities of matter are considered in 
 each case (see page 34). 
 
 Slow Oxidation. Oxidation may take place so slowly 
 that the heat given off during any given time is too 
 small to be observed by the senses, and can be measured 
 only by apparatus specially constructed for the purpose. 
 The total amount of kinetic energy manifested during 
 such a change is, however, the same as it would be 
 were the same amount of the same substance burned 
 rapidly, provided that the oxides produced are identical. 
 The amount of energy employed to decompose a given 
 quantity of these oxides is unvarying, no matter whether 
 they have been produced rapidly or slowly. A parallel 
 condition is found in that of a weight which has been 
 lowered from a height. It obviously requires a certain 
 expenditure of energy to bring this weight back to its 
 original position, and this expenditure is entirely inde- 
 pendent of the circumstances attending the fall. We 
 have already seen that the heat given off during the 
 formation of a chemical compound is equivalent to the 
 amount of energy necessary for its decomposition (see 
 page 34). 
 
 Incandescence during Combustion. Production of a Flame. 
 The phenomena of combustion are, therefore, caused 
 by the union of certain substances with oxygen, the 
 change taking place in so short an interval of time that 
 the heat caused by the reaction is not conducted away 
 with sufficient rapidity, and raises the temperature to a 
 point at which the burning body becomes incandescent. 
 
THE ATMOSPHERE. 75 
 
 When the ignited substance is a gas, or when in burn- 
 ing it either gives off a gas or is converted into a gas, 
 a flame is produced, as in the case of the burning of 
 phosphorus or sulphur. On the other hand, when no 
 vapor is present, the burning substance simply glows, 
 as is seen during the combustion of carbon. A flame 
 is, therefore, developed by an incandescent gas. 
 
 The Phenomena of Gaseous Combustion are Reversible. 
 Where a gas is capable of uniting with oxygen with 
 sufficient energy to produce a flame, it is a matter of 
 indifference which of the two gases forms the entering, 
 and which the surrounding medium, since the phenom- 
 ena of combustion are caused solely by the chemical 
 union of the two. The terms "combustible" and "a 
 supporter of combustion," as applied to gases, are used 
 simply because it is more usual to see gases burning in 
 oxygen or air than it is to see oxygen or air burning in 
 other gases. 41 
 
 EXAMPLES : Hydrogen burns quite readily in oxygen with a 
 very hot flame, and, vice versa, oxygen will burn in hydrogen 
 with an equally hot flame. In both instances water is produced. 
 Sulphur will burn in oxygen, and, on the other hand, oxygen will 
 burn in the vapor of sulphur, the same oxide of sulphur being 
 formed in each case. 
 
 Union with Oxygen is not Necessary to cause Incandescence. 
 Any two elements which are capable of directly uniting, 
 give off heat during such union ; and this heat may be 
 sufficient to cause both substances to become incan- 
 descent. 
 
 EXAMPLES : Hydrogen, when heated to its kindling tempera- 
 ture, will readily burn in an atmosphere of chlorine, the product 
 
76 ELEMENTS OF CHEMISTRY. 
 
 being hydrogen chloride ; and, of course, chlorine will also burn 
 in hydrogen. 
 
 Phosphorus is capable of burning in chlorine to form a chloride 
 of phosphorus, just as it will burn in oxygen to form an oxide. 
 
 Iron filings, when mixed with finely divided sulphur, will 
 unite with the latter with the greatest energy, if sufficient heat is 
 applied to melt the sulphur, and thereby cause an intimate contact 
 between the two elements. The mixture becomes brightly incan- 
 descent, and sulphide of iron is formed as a product of the re- 
 action. f5 *. 
 
 General Nature of the Phenomena of Combustion. The 
 phenomena of combustion in oxygen are therefore 
 merely special cases of chemical reactions which are 
 very general in their character. The fact that enough 
 heat is given off during these changes to cause the 
 reacting elements to glow is incidental, and not essen- 
 tial to the character of the phenomena as a whole. The 
 essential feature is that elements which are capable of 
 direct union possess chemical energy, and this chemical 
 energy is converted into kinetic energy when such 
 union takes place. We have two conditions in which 
 the elements can be encountered : 
 
 1. Those in which they are chemically separate ; 
 
 2. Those in which they are chemically combined; 
 and if the union of the elements can be brought 
 about without the addition of external energy, then 
 those substances under the second head possess less 
 chemical energy than do those under the first. 
 
 Enduring Nature of Chemical Energy. Chemical energy 
 is a most enduring form of energy. A piece of coal 
 or of sulphur may remain buried in the earth for years 
 without the least loss of the power which these sub- 
 stances are capable of yielding when burned. Chem- 
 
THE ATMOSPHERE. 77 
 
 ical energy is also the most concentrated form of energy. 
 The amount of heat given off by the combustion of one 
 gram of hydrogen would be capable of raising 14,000 
 kilograms through the distance of one metre if this 
 heat could be completely converted into mechanical 
 work. At the present time no other form of energy 
 combines so great convenience and permanence in 
 transportation as does chemical. Steamboats crossing 
 the ocean take along their stock of chemical energy in 
 the form of coal, which, by the heat given off in its com- 
 bustion, furnishes the power to propel the vessel. In 
 former geologic periods the flourishing vegetation stored 
 up this force by making use of the radiating energy of 
 the sun ; this vegetation was destroyed, buried by the 
 debris of succeeding catastrophes, and is now, in the 
 form of coal, finding its uses in the daily avocations of 
 men.* 
 
 Chemical Energy is also possessed by Chemical Compounds. 
 The separate elements which are capable of chemical 
 union are not the only forms of matter which possess 
 chemical energy. Many chemical compounds also unite, 
 with the evolution of heat and even of light, to produce 
 new compounds possessing less chemical energy than 
 did those from which they were formed. We have 
 studied examples of such changes in the neutralization 
 of acids by bases, and in the union of salts with their 
 water of crystallization. Tn short, the tendency of 
 substances which possess chemical energy is so to inter- 
 act with each other as to transform the whole or a part 
 of that chemical energy into kinetic energy, or, in other 
 
 * This paragraph is in part taken from Ostwald, Lehrbuch der Allge- 
 meinen Chemie, 2 ] , 53. 
 
78 ELEMENTS OF CHEMISTRY. 
 
 words, to pass from a state of higher energy to one of a 
 lower. Those changes attendant on combustion of oxy- 
 gen are, therefore, only specific cases of what in reality 
 is most general in chemistry. They have assumed such 
 great relative importance only because of the general 
 distribution of the element oxygen, and because of its 
 essential bearing upon life. From a scientific point of 
 view, any one of the parallel chemical reactions in 
 which the union of elements is attended with the evo- 
 lution of light and of heat is as important in illustrat- 
 ing a general law as is the union of elements with 
 oxygen. 43 
 
 Combustion in Air. Substances which burn in oxygen 
 will also burn in the air, but with diminished intensity, 
 owing to the fact that the oxygen is diluted by the in- 
 different gas, nitrogen. If the combustion takes place 
 in a closed space, it will continue until all, or nearly all, 
 the oxygen is used up, and then, provided the products 
 of combustion are solid, nothing but nitrogen will 
 remain. 
 
 EXAMPLES : A piece of phosphorus ignited and placed in a 
 closed jar of air will continue to burn until the oxygen is ex- 
 hausted. The oxide of phosphorus produced in this way is 
 identical with the one formed in oxygen. The gas which remains 
 has all of the properties of nitrogen ; it will neither burn nor sup- 
 port combustion. 
 
 A burning candle placed in a closed air-space will gradually 
 be extinguished after using up the available oxygen. The gases 
 which remain consist of nitrogen, carbon dioxide, and some 
 oxygen.* 
 
 * All the oxygen is not used by the burning candle,,or by an animal 
 placed in a closed air-space. The extinction of the flame and asphyx- 
 iation take place while a considerable quantity of oxygen is still 
 uncombined. 
 
THE ATMOSPHERE. 79 
 
 This mixture will neither burn nor support the combustion of a 
 candle. 44 
 
 An animal placed in a closed air-space will become unconscious 
 and finally die. The oxygen inhaled by the lungs is in part ab- 
 sorbed by the blood, and is used in the body for purposes of oxi- 
 dization. As the tissues of the body consist mostly of compounds 
 of the element carbon with hydrogen, nitrogen, sulphur, etc., the 
 products of this oxidization are in large part carbon dioxide and 
 water vapor. The air exhaled from the lungs contains less oxy- 
 gen and more carbon dioxide than does that which is inhaled. 
 All the oxygen taken in, however, is not consumed in the produc- 
 tion of these two gases ; for there are other constituents of the 
 body (sulphur, phosphorus) which are also oxidized and separated 
 by different channels, while a portion of the oxygen is returned 
 to the air unchanged. As the oxygen of the air becomes used up 
 by a breathing animal, and is in part replaced by carbon dioxide, 
 the closed air-space becomes unfit for the support of animal life 
 long before all of the oxygen is consumed. This takes place the 
 more rapidly because, in addition to the substances mentioned, 
 there are other gases of a poisonous nature exhaled from the 
 lungs. 
 
 The Process of Breathing is Analogous to Combustion. 
 The process of breathing can, therefore, be compared 
 to 'combustion. The animal and the surrounding oxy- 
 gen possess chemical energy which is converted into 
 kinetic energy by respiration and its consequences. 
 This kinetic energy is manifested as heat, so that the 
 body preserves a temperature above that of the sur- 
 rounding atmosphere, while the substances produced 
 possess much less chemical energy than did those which 
 were originally present. 
 
 The Total Heat given off in Combustion in Air is the 
 same as that given off in Combustion in Oxygen. A num- 
 ber of other examples of combustion in air could be 
 mentioned; but, as they do not differ in principle from 
 
80 ELEMENTS OF CHEMISTRY. 
 
 combustion in oxygen, it is not necessary to enumerate 
 them. The total amount of heat given off during the 
 combustion of a given weight of a substance is the same, 
 whether it is burned in air or in oxygen. This fact is 
 obvious when we consider that it will take exactly as 
 much energy to decompose the body which is formed 
 as has been given off in its production. The amount 
 necessary for this decomposition is manifestly independ- 
 ent of the circumstances surrounding the formation. 
 
THE ATMOSPHERE. 81 
 
 CHAPTER XII. 
 
 THE ATMOSPHERE (Continued). 
 Composition of the Atmosphere. 
 
 WE have learned that the atmosphere contains 
 oxygen and nitrogen, but we have not ascertained the 
 relative proportion of the two gases, nor have we de- 
 cided whether they are chemically combined or present 
 merely as a mechanical mixture. 
 
 Estimation of the Relative Amounts of Oxygen and Ni- 
 trogen in the Atmosphere. A rough means of estimating 
 the amount of oxygen and nitrogen in the atmosphere 
 is found in the following experiment : 
 
 A glass tube sealed at one end is divided into five equal parts 
 by means of five rubber rings slipped over the outside. This is 
 inverted over a cylinder of water so that the level of the liquid 
 within and without is at the first ring, and the tube is then 
 firmly clamped in this position. A piece of phosphorus is fixed 
 on the end of a long, sharp-pointed wire, and then the wire is 
 bent so that the phosphorus can be thrust up into the tube. 
 Slow oxidization of the phosphorus will set in, and the oxide of 
 phosphorus produced will be dissolved by the water, which will 
 rise in the tube so as to take the place of the oxygen absorbed. 
 The reaction is complete after some days ; and then it will be dis- 
 covered, after the tube has been lowered so that the level of the 
 liquid without and within is again the same, that four-fifths of 
 the air have remained unabsorbed. Approximately, therefore, by 
 
82 ELEMENTS OF CHEMISTRY. 
 
 bulk one-fifth of the atmosphere consists of oxygen, and four-fifths 
 of nitrogen. 45 
 
 More accurate results can be obtained by the use of the eudi- 
 ometer tube (described on page 24, and in Experiment 10 of the 
 Appendix). This is filled with so much mercury, that, when it is 
 inverted over the mercury trough, about fifteen cubic centimetres 
 of air will remain enclosed. This volume is recalculated to 
 standard conditions by noting the temperature, barometric pres- 
 sure, and height of the column of mercury above the trough 
 (see page 68 and following). About seven cubic centimetres of 
 pure hydrogen are now added ; and the volume of this gas is also, 
 after making the necessary observations, recalculated to standard 
 conditions. The mixture is now exploded by means of an electric 
 spark. The contraction in volume which results is due to the for- 
 mation of water from the union of hydrogen and oxygen; and 
 as two volumes of hydrogen combine with one of oxygen to 
 produce water, it follows that one-third of the total diminution 
 in volume must represent the amount of oxygen which was ori- 
 ginally present. 46 
 
 Relative Volume of Oxygen and Nitrogen in the Atmosphere. 
 Careful investigations by this means have shown that 
 the volume of oxygen in ordinary out-door air varies 
 from 20.3 to 21.5 volumes in 100.* This variation 
 is sufficient to show us that in all probability the at- 
 mosphere is not a chemical compound; for, as we have 
 seen, true chemical compounds are characterized by an 
 unchanging composition (see page 55). This proba- 
 bility is transformed to a certainty by the following 
 experiment : 
 
 Proofs that the Atmosphere is not a Chemical Compound. 
 A given volume of water will dissolve quite a little 
 more oxygen than nitrogen, so that if we collect the 
 
 * I.e., in 100 cubic centimetres of air there are 20.3 to 21.5 cubic 
 centimetres of oxygen. 
 
THE ATMOSPHERE. 83 
 
 gas which passes off from water which has been ex- 
 posed to the air under pressure, it will contain a greater 
 proportion of oxygen than it did before. Using the 
 air which has thus been altered in composition, this 
 operation can be repeated with a similar result until 
 nearly pure oxygen is finally obtained. 
 
 As a final proof it may be mentioned that oxygen 
 and nitrogen, mixed in the proper proportions, form air 
 without alteration either in the total volume of the 
 two gases or of the temperature, provided they were 
 under like conditions before being brought in contact. 
 The atmosphere is, therefore, a mechanical mixture of 
 oxygen and nitrogen, containing in round numbers one 
 part by volume of the former to four parts of the 
 latter. 
 
 Other Substances Present in the Atmosphere. In addi- 
 tion to the two fundamental gases, other substances 
 are present in the air in small quantities. These may 
 be of two kinds, gaseous and solid. The chief gas- 
 eous impurities are water vapor, carbon dioxide (see 
 page 154), and compounds of ammonium (see page 
 99). The solid substances are present as dust. 
 
 Water Vapor in the Atmosphere. The quantity of water vapor 
 present depends upon the temperature, season of the year, and 
 locality ; but it is seldom of sufficient amount to cause the atmos- 
 phere to be completely saturated. The evaporation of oceans, 
 lakes, and rivers, furnishes a never-ending supply of water, which 
 is increased by hot weather, and is generally greater by day than 
 by night. If the atmosphere is nearly saturated with moisture, 
 any diminution in the temperature will cause a fall of rain or the 
 formation of dew. Very little evaporation can take place while 
 such a condition prevails. Drops of water collect upon a cold 
 surface because the air in the immediate neighborhood is cooled 
 
84 ELEMENTS OF CHEMISTRY. 
 
 below the point at which it is saturated with vapor. The tem- 
 perature at which these drops collect is called the dew-point ; and 
 as the maximum amount of water vapor which can be contained in 
 a given volume of the atmosphere at any definite temperature is 
 known, the discovery of the dew-point affords a ready means of 
 ascertaining the amount of moisture really present in the air. 
 The ratio between the tension of water vapor (see page 70), 
 which would be found were the air fully saturated at the prevail- 
 ing temperature, and that tension which really exists, is called 
 the relative humidity. 47 
 
 Water in the atmosphere is absolutely essential to plant life. 
 The liquid falls upon the soil as rain, and is absorbed by the 
 radicles of plants. Afterwards it circulates through the entire 
 system of the plant, taking part in various physiological changes, 
 and finally evaporating from the leaves. The amount of moisture 
 which passes from large areas covered by vegetation is enormous, 
 so that wooded districts cause an equitable distribution of rain. 
 
 Carbon Dioxide in the Atmosphere. Carbon dioxide is invari- 
 ably found in the air, and is as important to living organisms as 
 oxygen itself. It is constantly added to the atmosphere by burn- 
 ing fuel, from volcanic craters and fissures, from the breathing 
 of animals, and from decomposing organic matter. If no means 
 were provided for the removal of carbon dioxide from the atmos- 
 phere, the increase would soon destroy all living organisms de- 
 pendent upon respiration. Fortunately plants growing in the 
 sunlight absorb carbon dioxide from the air, using for this ab- 
 sorption a green coloring-matter which is contained in the leaves, 
 and which can eliminate oxygen from, and add hydrogen to, car- 
 bon dioxide. By this means a substance is produced which can 
 form all the innumerable compounds of carbon, hydrogen, and 
 oxygen occurring in the vegetable kingdom. 48 
 
 The Quantity of Carbon Dioxide in the Atmosphere. The 
 quantity of carbon dioxide in a given volume of air 
 varies slightly ; but, normally, it is about three parts in 
 ten thousand. It seems that the proportion of carbon 
 dioxide is greater at night than in the daytime, and in 
 
THE ATMOSPHERE. 85 
 
 summer than in winter. The amount of carbon dioxide 
 in crowded rooms is increased by the breathing of peo- 
 ple within the closed air-space, yet this does not often 
 take place to such an extent that the oppressive feeling 
 caused by such an atmosphere can be ascribed entirely 
 to this increase. The unpleasant effect is due in part 
 to exhalations of organic matter which passes off from 
 the lungs. 
 
 The presence of oarbon dioxide in the atmosphere can be 
 proved at any time by exposing some clear lime-water to the 
 action of the air. If carbon dioxide is present, a white crust of 
 the carbonate of calcium will be found upon the surface in a 
 short time. 
 
 Ammonia in the Atmosphere. Another impurity present in 
 the atmosphere is ammonia, which is found combined with acids, 
 as ammonium carbonate, nitrate, or nitrite. These substances are 
 washed into the soil by rains, and are then taken up by plants to 
 form essential portions of their tissues which contain nitrogen. 
 The amount of ammonium compounds in the atmosphere is very 
 small, not more than forty parts by weight in one million parts of 
 air. 
 
 The solid particles of dust floating in the air may be 
 such substances as common salt (sodium chloride), or 
 they may consist of micro-organisms, which not infre- 
 quently are capable of inaugurating disease. 
 
 Summary of the Chapters on the Atmosphere. 
 
 1. The atmosphere is composed of oxygen and nitro- 
 gen, with small quantities of other substances. (Carbon 
 dioxide, water vapor, ammonium salts, solid particles.) 
 
 2. Nitrogen is chemically an indifferent gas, and 
 does not support combustion. 
 
 3. Oxygen is a supporter of combustion ; i.e., many 
 substances will burn in the gas, producing oxides. 
 
86 ELEMENTS OF CHEMISTRY. 
 
 4. Substances which burn possess chemical energy 
 when in the presence of oxygen. This chemical energy 
 is converted into kinetic energy during the combustion. 
 
 5. The substances produced by the union possess less 
 chemical energy than do those from which they are 
 formed. 
 
 6. Oxidation may be slow or rapid. The amount 
 of chemical energy converted into kinetic energy is, 
 however, the same in either case, provided the amounts 
 of the substances used are the same and the products 
 of combustion are identical. 
 
 7. In rapid combustion the temperature is raised to 
 a point at which the reacting body becomes incan- 
 descent. If the burning substance is a gas, or gives 
 off a gas, then a flame is produced. It is a matter of 
 indifference which gas is entering, and which forms the 
 surrounding medium, the combustion taking place just 
 the same in either case. 
 
 8. The phenomena of combustion in oxygen are only 
 special cases of chemical reactions which are general in 
 their character; similar changes, therefore, take place 
 when bodies unite with substances other than oxygen. 
 
 9. We have two conditions in which the elements 
 are encountered, those in which they are chemically 
 separate, and those in which they are chemically com- 
 bined. The separate elements are not the only forms 
 of matter which possess chemical energy. Chemical 
 compounds can also unite, with the evolution of light 
 and heat. 
 
 10. Substances which burn in oxygen will also burn 
 in air with diminished brilliancy. The process of breath- 
 ing can be compared to combustion. 
 
 11. The total amount of heat given off during the 
 
THE ATMOSPHERE. 87 
 
 combustion of a given weight of a body Is the same 
 whether it is burned in air or in oxygen. 
 
 12. The oxygen in the atmosphere varies from 20.3 
 to 21.5 volumes in 100. The air is a mixture of oxy- 
 gen and nitrogen, and not a chemical compound. 
 
 13. The air contains water vapor in varying amounts, 
 carbon dioxide in about three parts in ten thousand, 
 
 and very small quantities of ammonium compounds and 
 of solid substances. 
 
88 ELEMENTS OF CHEMISTRY. 
 
 CHAPTER XIII. 
 
 THE COMPOUND OF HYDROGEN AND NITROGEN. 
 (AMMONIA.) 
 
 THE not-metallic elements which have been discussed 
 (oxygen and chlorine) unite with hydrogen to form 
 water and hydrogen chloride respectively. Naturally, 
 then, in studying nitrogen we ask if it also will combine 
 with hydrogen, and if it does, what the nature of the 
 resulting compound is. 
 
 Direct Union of Nitrogen and Hydrogen Difficult. The 
 chemically indifferent nature of nitrogen becomes appar- 
 ent when we make the attempt to bring about its union 
 with hydrogen. If an electric spark is passed through 
 a mixture of hydrogen and nitrogen no explosion takes 
 place, and even if the operation is continued for some 
 time the elements will be found to have united only in 
 the smallest quantity. The direct union of the elements, 
 therefore, affords us no practical method for the prepara- 
 tion of the hydrogen compound of nitrogen, but we can 
 easily obtain it by other means. 
 
 The Preparation of Pure Ammonia. Concentrated commercial 
 ammonia water is placed in a flask, so arranged that any gases 
 evolved can be passed through a tube containing pieces of quick- 
 lime, to a vessel containing mercury, in which is placed a glass 
 tube, closed at one end, filled with the same liquid, and in- 
 
COMPOUND OF HYDROGEN AND NITROGEN. 89 
 
 verted.* The quick-lime is introduced for the purpose of drying 
 the gas which passes off as soon as the flask is gently warmed. 
 This gas can be collected above the mercury in the inverted 
 tube.f 49 
 
 Properties of Ammonia. The gas isolated in this way is termed 
 ammonia. It has a specific gravity, air = 1, of .589 ; and, being 
 relatively lighter than air, it can be collected by passing it 
 through a long tube extending up to the bottom of an empty jar 
 held mouth downward. This method is convenient if absolutely 
 pure ammonia is not required. Ammonia becomes liquid at a 
 temperature of 40 under a pressure of one atmosphere. One 
 cubic centimetre of water is capable of dissolving 813 cubic cen- 
 timetres of ammonia, and it is owing to its extreme solubility in 
 water that we are compelled to collect the gas over mercury. 
 
 Commercial ammonia is simply a solution of ammonia gas in 
 water; we have learned (page 16) that gases are less soluble the 
 higher the temperature of the liquid in which they are dissolved. 
 Ammonia gas is, therefore, evolved when ammonia water is 
 heated, and the above experiment for the isolation of ammonia 
 is based upon this fact. 60 
 
 Decomposition of Ammonia. The first question which 
 we must decide in regard to ammonia is whether the 
 gas is an element or a compound. A method of de- 
 composition suggests itself similar to those employed in 
 the study of water and of hydrogen chloride ; i.e., to see 
 whether ammonia is decomposed by sodium or potas- 
 sium. These experiments are not so easily carried out 
 in this case as they were with the substances previously 
 studied, for if sodium or potassium is placed in pure 
 
 * Arrangement as iu the collecting of gases in the eudiometer tube 
 (see page 24, and Experiment 10 of Laboratory Appendix). 
 
 1 If the generated gas is allowed to escape freely for a little wbile 
 before an attempt is made to collect it, the air will all have been expelled 
 from tbo apparatus so that the pure product will be obtained. If this 
 precaution is not taken, the inverted tube will, of course, be partly filled 
 with air. 
 
90 ELEMENTS OF CHEMISTRY. 
 
 ammonia gas at ordinary temperatures no appreciable 
 change takes place. A different result is obtained when 
 the metals are heated ; but as hot potassium and sodium 
 are dangerous to handle, we must look for some other 
 metal which, while decomposing ammonia as readily as 
 the two just mentioned, will be easily handled and safe 
 for experimentation. Such a metal is found in mag- 
 nesium. 
 
 Magnesium is a metal with a bright white lustre. When 
 exposed to the air it gradually oxidizes. Unlike sodium or potas- 
 sium, it does not attack cold water, liberating hydrogen. Mag- 
 nesium is generally brought into the market in the form of a 
 narrow ribbon, or as wire ; the powdered metal is also used to a 
 considerable extent. When ignited in the air, magnesium burns 
 with a brilliant white flame. It should be prevented from tarnish- 
 ing by being kept in a well-stopped bottle. 
 
 Decomposition of Ammonia by Means of Magnesium. A tube 
 of so-called infusible gas, partly filled with pieces of magnesium 
 ribbon, is connected at one end with an apparatus which will 
 generate dry ammonia (Experiment 49), and at the other end 
 with a vessel of water in which is inverted a small bottle filled 
 with water. All air is first expelled from the apparatus by means 
 of a slow current of ammonia; and then, without interrupting the 
 current, the magnesium is gently heated by means of an ordinary 
 burner. The metal soon becomes coated with a grayish powdery 
 crust, while the gas which passes on is collected in the inverted 
 flask over water. When all the liquid has been expelled from the 
 inverted bottle, the latter should be removed, and a lighted taper 
 applied to its mouth. The gas which has been collected burns 
 with a colorless flame, and has the properties which we have 
 learned to associate with hydrogen.* 8l 
 
 * Ammonia extinguishes a lighted taper, but does not take fire; hy- 
 drogen extinguishes a lighted taper which is plunged into it, but itself 
 takes fire at the point of contact with oxygen. Another distinction be- 
 tween the gas which is here collected and the ammonia from which it is 
 generated is, that ammonia is very soluble in water, while this gas is not. 
 
COMPOUND OF HYDROGEN AND NITROGEN. 91 
 
 The Hydrogen which is liberated comes from the Ammonia. 
 We have already seen (page 23) that hydrogen is not 
 formed from the metals which act upon water or hydro- 
 chloric acid, but that it owes its origin to a decomposi- 
 tion of those compounds, hy means of which the metals 
 take the place of (substitute) the hydrogen. It seems, 
 therefore, scarcely necessary to advance similar proofs 
 that the hydrogen generated by the action of magnesium 
 on ammonia does not come from the magnesium, but 
 does come from the ammonia. Ammonia, therefore, 
 contains hydrogen, which is liberated from it by the 
 action of magnesium, just as the same gas is generated 
 by the action of metals on hydrogen chloride or water. 
 It now remains to be ascertained with what element the 
 hydrogen in ammonia is united. 
 
 Isolation of the Nitrogen in Ammonia. For this purpose a 
 bottle is filled with a concentrated solution of common salt, and 
 inverted over a vessel containing the same fluid. This bottle is 
 then completely filled with chlorine generated as described in Ex- 
 periment 21 of the Appendix. It is then tightly closed with the 
 thumb, and transferred to a vessel containing concentrated ammo- 
 nia solution, in which it is placed mouth downward. A change 
 immediately sets in, dense white fumes fill the flask, the color of 
 the chlorine disappears, and at the same time the liquid rises in 
 the bottle. When the reaction is entirely at an end, the bottle is 
 again closed with the thumb, and transferred to a vessel contain- 
 ing diluted hydrochloric acid, in which it is opened and allowed 
 to stand for some time. It can now be removed with its mouth 
 closed, then placed upright and opened. The gas which remains 
 is colorless and odorless. A lighted taper placed in it is extin- 
 guished ; in short, it is nitrogen.* 52 
 
 * The chlorine completely decomposes a portion of the excessive am- 
 monia, forming hydrogen chloride with the hydrogen, and leaving nitro- 
 gen. The action of this not-metal on ammonia is, therefore, the reverse 
 of the action of the metal (magnesium). 
 
92 ELEMENTS OF CHEMISTRY. 
 
 Parallelism between Ammonia, Hydrogen Chloride, and 
 Water. The foregoing experiments have clearly demon- 
 strated that a metal (magnesium) removes the nitrogen 
 from ammonia and liberates hydrogen, while a not- 
 metal (chlorine) removes hydrogen and liberates nitro- 
 gen. Ammonia, therefore, is a compound of nitrogen 
 and hydrogen ; and its behavior, so far as we have stud- 
 ied it, has been exactly parallel to hydrogen chloride 
 and water. 
 
 Relative Volumes of Hydrogen and Nitrogen in Ammonia. 
 The next step in our investigation must be to ascertain 
 the relative volumes of hydrogen and of nitrogen in 
 ammonia. This is not so simple an operation as it was 
 with hydrochloric acid or with water. 
 
 In order to discover the proportion of nitrogen in a given vol- 
 ume of ammonia, we resort to a modification of the experiment 
 which was based upon its decomposition by chlorine (see page 91, 
 and Experiment 52 of the Laboratory Appendix). In place of 
 the bottle we can substitute a long glass tube, closed at one end, 
 and divided into three equal parts by means of rubber rings. This 
 tube is carefully rilled with pure chlorine by the same means that 
 were used in the previous experiment. Then, by successive im- 
 mersions of the open end in concentrated ammonia solution and 
 in diluted hydrochloric acid, the isolation of nitrogen can be 
 effected as before.* The tube should now be transferred to a deep 
 cylinder of pure water, and lowered therein to the point where 
 the liquid without and within occupies the same level ; f it 
 
 * As we shall see in the next chapter, hydrochloric acid is capable of 
 uniting with ammonia to form a new compound (ammonium chloride). 
 This acid is, therefore, removed by the surplus of ammonia solution from 
 the nitrogen which is left. Afterward the flask is placed in diluted hy- 
 drochloric acid to absorb any excess of ammonia remaining with the gas 
 which has been separated. Diluted sulphuric acid would accomplish the 
 same result. 
 
 t The tube must be plunged far enough into the water so that the 
 level of the liquid without and within is the same, because by this 
 
COMPOUND OF HYDROGEN AND NITROGEN. 93 
 
 will then be seen that the nitrogen which has been isolated occu-' 
 pies exactly one-third of the total volume of chlorine with which 
 we started. 53 The logical interpretation of this result is as 
 follows : 
 
 We have seen that chlorine unites with an equal volume of hy- 
 drogen to form hydrogen chloride (see page 42). In the above 
 experiment, the hydrogen which combined with chlorine came 
 from the ammonia ; and as the volume of the chlorine was equal 
 to the capacity of the tube, the volume of hydrogen which was 
 contained in the decomposed ammonia must also have been equal 
 to the capacity of the tube. The nitrogen must have come from 
 that portion of the ammonia which gave up its hydrogen ; and as 
 the volume of nitrogen remaining is equal to one-third the total 
 volume of chlorine, it follows that this quantity of nitrogen must 
 have been combined with a volume of hydrogen equal to that of 
 the chlorine which filled the tube. This tube was divided into 
 three equal parts in the beginning, and of these three parts one is 
 left as nitrogen, so that 
 
 One volume of nitrogen combines with three volumes 
 of hydrogen to form ammonia. 
 
 Total Volume of Hydrogen and Nitrogen produced by the 
 Decomposition of Ammonia. A final proof of the volu- 
 metric composition of ammonia is easily obtained by the 
 following experiment : - 
 
 About 25 cubic centimetres of ammonia gas are enclosed in the 
 eudiometer tube (see page 24), the volume being accurately 
 measured and recalculated to the standard conditions. Electric 
 sparks are now passed through from a battery with an induction 
 coil. These sparks effect the decomposition of the ammonia into 
 nitrogen and hydrogen ; and as this goes on the volume of the gas 
 will increase until it reaches 50 cubic centimetres (recalculated), 
 at which point it becomes stationary. If the mouth of the eudi- 
 ometer is now closed with the thumb, the tube inverted, and a 
 
 means we place the remaining nitrogen under atmospheric pressure, as 
 was the chlorine with which we started. 
 
94 ELEMENTS OF CHEMISTRY. 
 
 lighted taper applied, the gas will burn. This shows that hydro- 
 gen has been liberated, the nitrogen being left uncombined.* 54 
 
 We have already seen that in ammonia three volumes of hy- 
 drogen are united with one volume of nitrogen, but we have not 
 seen what volume of ammonia is produced by the union of three 
 volumes of hydrogen with one of nitrogen. The experiment 
 which we are now considering furnishes this evidence, for the 50 
 cubic centimetres of hydrogen and nitrogen which we have ob- 
 tained by the decomposition of 25 cubic centimetres of ammonia 
 in the eudiometer tube must contain 
 
 3 X 12.5 cubic centimetres of hydrogen = 37.5 cubic centimetres. 
 
 12.5 cubic centimetres of nitrogen = 12.5 cubic centimetres. 
 
 The total = 50 cubic centimetres. 
 
 These 50 cubic centimetres of the mixed gases are, however, 
 obtained by the breaking down of 
 
 2 x 12.5 cubic centimetres of ammonia = 25 cubic centimetres. 
 
 If we reduce all the above figures to simple numbers by dividing 
 by 12.5 we have as a result 
 
 Two cubic centimetres of ammonia produce three 
 cubic centimetres of hydrogen and one cubic centi- 
 metre of nitrogen ; or, in general terms, two volumes 
 of ammonia are decomposed to form three volumes of 
 hydrogen and one volume of nitrogen. Of course the 
 reverse, that two volumes of ammonia are formed from 
 three volumes of hydrogen and one of nitrogen, must 
 also be true. 
 
 Comparison of the Volumetric Composition of Hydrogen Chlo- 
 ride, Water, and Ammonia. If what we have just learned 
 be compared with the results obtained with hydrogen 
 
 * Nitrogen does not combine with mercury under the above circum- 
 stances, as might be supposed from the action of ammonia on magne- 
 sium. This can easily be shown by enclosing some nitrogen in the eudi- 
 ometer tube and passing electric sparks through the gas, according to 
 the method shown above. The volume of gas will not be altered by this 
 means. 
 
COMPOUND OF IIYDUOGEN AND NITROGEN. 95 
 
 chloride and water, we shall discover the following 
 remarkable regularity : - 
 
 One volume of hydrogen combines with one volume 
 of chlorine to form two volumes of hydrogen chloride. 
 
 Two volumes of hydrogen combine with one volume 
 of oxygen to form two volumes of water vapor. 
 
 Three volumes of hydrogen combine with one volume 
 of nitrogen to form two volumes of ammonia. 
 
 Definite Composition of Ammonia. As a result of our 
 investigations with ammonia, we have seen that this 
 substance, like all of the chemical compounds which we 
 have encountered, has a definite composition. (See page 
 55.) The specific gravity of nitrogen is 14 if hydro- 
 gen = 1 ; or, in other words, if a volume of nitrogen 
 weighs 14 grams, the same volume of hydrogen weighs 
 one gram. Three volumes of hydrogen (the amount 
 necessary to form ammonia with one volume of nitro- 
 gen) would, therefore, weigh three grams, so that 
 
 Fourteen parts by weight of nitrogen combine with 
 three parts by weight of hydrogen to form seventeen 
 parts by weight of amomnia. 
 
 Changes of Energy attending the Decomposition and For- 
 mation of Ammonia. In order to decompose ammonia 
 into hydrogen and nitrogen, it was necessary for us to 
 add energy. But it is evident, from the ease with 
 which this decomposition was accomplished by means 
 of the electric spark, that the amount of energy re- 
 quired for a quantity of ammonia containing a given 
 weight of hydrogen is not as great as in the case of an 
 equivalent amount of hydrogen chloride or water. In 
 chemical language, ammonia is less stable than the lat- 
 
96 ELEMENTS OF CHEMISTRY. 
 
 ter two substances. Although it is not practically pos- 
 sible to cause nitrogen and hydrogen to unite directly, 
 these elements must possess chemical energy when in 
 contact; for the compound which they form cannot 
 afterward be decomposed without the addition of 
 energy. 
 
 Decomposition of Ammonia and of Water by Chlorine. 
 Reviewing the experience gained in the study of the 
 three hydrogen compounds investigated,* we find that 
 chlorine will easily decompose ammonia, forming hy- 
 drogen chloride and nitrogen, and that the same ele- 
 ment decomposes water quite slowly, and in the sunlight 
 producing hydrochloric acid and oxygen. This shows 
 us that chlorine and ammonia, and chlorine and water, 
 when in contact, possess chemical energy, which is con- 
 verted into kinetic energy by the change into hydro- 
 chloric acid and nitrogen, and into hydrochloric acid 
 and oxygen. The tendency in these reactions, as in 
 the previous ones which we have studied, is toward a 
 state of more stable equilibrium ; the chlorine and water, 
 or the chlorine and ammonia, having more chemical 
 energy than the resulting substances. In these cases, 
 therefore, as in the others, energy is degraded. (See 
 pages 76 and 77.) 
 
 Decomposition of Ammonia by Oxygen. Ammonia is 
 also decomposed by oxygen under the proper condi- 
 tions. A mixture of ammonia gas and oxygen will 
 combine with a weak explosion when ignited. Water 
 and nitrogen are formed by this reaction. It follows 
 
 * Hydrogen chloride, water, and ammonia. 
 
COMPOUND OF 11YDHOGEN AND NITROGEN. 97 
 
 that ammonia and oxygen possess more chemical energy 
 than water and nitrogen. 50 
 
 Summary. 
 
 1. It is not practically possible to cause the free 
 elements, nitrogen and hydrogen, to unite. 
 
 2. Ammonia is decomposed by hot potassium, sodium, 
 or magnesium, while hydrogen is liberated. The hy- 
 drogen which is liberated comes from the ammonia. 
 
 3. Chlorine easily decomposes ammonia, liberating 
 nitrogen and forming hydrochloric acid. 
 
 4. Ammonia is a compound of hydrogen and nitrogen. 
 
 5. Three volumes of hydrogen unite with one vol- 
 ume of nitrogen to produce two volumes of ammonia. 
 
 6. In comparing chlorine, oxygen, and nitrogen, we 
 find that the volumes^ of hydrogen which unite with 
 one volume of these elements to form their respective 
 hydrogen compounds are as 1 : 2 : 3. 
 
 7. Ammonia has a definite composition by weight. 
 Three parts by weight of hydrogen unite with fourteen 
 parts by weight of nitrogen to produce seventeen parts 
 by weight of ammonia. 
 
 8. It takes energy to decompose ammonia, hence 
 energy must be given off in its formation. 
 
 9. Chlorine decomposes water to form hydrochloric 
 acid and oxygen, and it also decomposes ammonia to 
 form hydrogen chloride and nitrogen. 
 
98 ELEMENTS OF CHEMISTRY. 
 
 CHAPTER XIV. 
 
 THE COMPOUNDS OF AMMONIA WITH ACIDS. 
 
 The Union of Ammonia with Hydrogen Chloride. If 
 ammonia gas is brought in contact with hydrogen chlo- 
 ride, a change immediately sets in, heat is given off, and 
 dense white clouds of a solid substance are produced^ 
 which soon collects on the sides of the vessel in which 
 the reaction has taken place. If exactly equal volumes 
 of ammonia and hydrochloric acid are taken, neither of 
 these substances will remain after the two gases are 
 brought in contact. This fact can easily be proved by 
 the following experiment:- 
 
 Two glass tubes of equal size, with one end of each narrowed 
 down, are connected at the narrow ends by means of a short 
 piece of rubber tubing closed at the centre by a pinch-cock. The 
 two glass tubes are filled with mercury and placed mouth down- 
 ward, side by side, in a mercury trough. Fill one of them with 
 pure ammonia, the other with pure hydrogen chloride. When this 
 has been done, remove the pinch-cock so that a free communica- 
 tion is established between the two. As the union of the two 
 gases takes place, the mercury will rise in the tubes until, pro- 
 vided no air has been admitted, it fills both vessels completely, 
 with the exception of the small space occupied by the solid 
 produced during the reaction. The ammonia and hydrochloric 
 acid have, therefore, without a remainder of either, united to 
 form a solid substance. The bulk of this solid, as compared to 
 that of the original gases, is so small that it can be neglected. 65 
 
THE COMPOUNDS OF AMMONIA WITH ACIDS. 99 
 
 Ammonium Chloride. The solid substance produced 
 by the union of ammonia and hydrogen chloride has 
 the appearance of salt, and in properties and structure 
 can be compared with potassium chloride. We have 
 learned that in ammonia there are three volumes of 
 hydrogen united with one volume of nitrogen, and 
 that in hydrochloric acid there is one volume of hy- 
 drogen to every volume of chlorine. If, then, we 
 cause equal volumes of ammonia and hydrogen chlo- 
 ride to unite, we shall have a solid substance which 
 for every volume of nitrogen contains four volumes of 
 hydrogen and one of chlorine. This solid is termed 
 ammonium chloride. 
 
 Resemblance between Potassium Chloride and Ammonium 
 Chloride. We can separate potassium chloride into two 
 substances, potassium and chlorine. If we remove 
 the chlorine from ammonium chloride, we have as a 
 remainder a compound of one volume of nitrogen with 
 four of hydrogen.* This grouping of the two elements, 
 nitrogen and hydrogen, therefore, in the formation of 
 ammonium chloride, plays the same role as potassium 
 does in forming potassium chloride. For potassium 
 chloride and ammonium chloride closely resemble each 
 other; and, as the chlorine is the same in both, the re- 
 mainder, potassium and ammonium, must have a simi- 
 lar effect in determining the character of chemical 
 compounds in which they occur. The difference be- 
 tween potassium and ammonium is that the former 
 has not been found to be decomposable into two or 
 
 * This compound is probably capable of only a very brief separate 
 existence under peculiar circumstances. It very soon breaks down into 
 ammonia and hydrogen. It is stable when united with chlorine in 
 ammonium chloride. 
 
100 ELEMENTS OF CHEMISTRY. 
 
 more elements, while the latter has. In chemical lan- 
 guage, ammonium is termed a radicle which can play 
 the part of an element. Such radicles are quite fre- 
 quent in chemistry, and they display the character of 
 very different chemical elements. 
 
 If we represent the one volume of nitrogen in a given amount 
 of ammonia by the letter N, and the three volumes of hydrogen 
 by H 3 , we can construct for ammonia a formula, NH 3 , which ex- 
 presses this relationship. If we represent the volume of hydro- 
 chloric acid which will unite with the above quantity of ammonia 
 to form ammonium chloride by H Cl, then we can represent the 
 change which takes place when ammonia and hydrogen chloride 
 are brought in contact as follows : 
 
 NH 3 + H Cl = NH 4 Cl. 
 
 Now, if we represent the quantity of potassium which will 
 unite with the amount of chlorine in the above volume of H Cl 
 by the letter K (from the word kalium, meaning potassium), then 
 the formula for this weight of potassium chloride will be K Cl, 
 and the relationship between potassium and ammonium chloride 
 is made clear as follows : 
 
 K Cl (NH 4 ) Cl 
 
 Potassium chloride Ammonium chloride. 
 
 Liberation of Ammonia from Ammonium Chloride. If 
 potassium hydroxide (see page 31) is intimately mixed 
 with ammonium chloride, a change takes place ; potas- 
 sium chloride is formed, and ammonia passes off. Dur- 
 ing this reaction, water also is produced, as will he 
 evident from the following : - 
 
 Potassium hydroxide (caustic potash), we have seen, may be 
 regarded as water in which one-half of the hydrogen has been 
 replaced by the metal potassium. (Page 31.) Ammonium chlo- 
 ride contains, for every volume of nitrogen, four volumes of 
 hydrogen and one of chlorine. .When ammonium chloride and 
 potassium, hydroxide are brought together, ammonia (which con- 
 
THE COMPOUNDS OF AMMONIA WITH ACIDS. 101 
 
 tains one volume of nitrogen to three of hydrogen) passes off. 
 One volume of the hydrogen in ammonium chloride has, there- 
 fore, been left behind. In forming potassium chloride, however, 
 the potassium parted with oxygen and one-half as much hydro- 
 gen as is necessary to form water. The other half, therefore, was 
 supplied by the ammonium chloride. The change will become 
 more apparent if we once more use formulae which represent the 
 combining volumes, for then 
 
 NH 4 Cl + KOII = NH 3 4- HOH + K CL* 
 
 Changes of Energy taking place during the Decomposi- 
 tion of Ammonium Chloride, During the above change, 
 heat is evolved, so that the substances at the right of 
 the sign of equality possess less chemical energy than 
 do those at the left. Chemical energy has been trans- 
 formed into kinetic energy in passing from the ammo- 
 nium chloride and potassium hydroxide to ammonia, 
 water, and potassium chloride. f It is partly for this 
 reason that the change takes place spontaneously ; yet 
 another factor also ' comes into play, namely, the vola- 
 tility of ammonia. It is a matter of repeated experi- 
 ence that decompositions like the above are apt to be 
 complete if a volatile substance can be formed. The 
 reason for this fact cannot be entered into here, for its 
 comprehension requires a somewhat extended knowl- 
 
 * In this equation N represents one volume of nitrogen, H 4 four 
 volumes of hydrogen, Cl one volume of chlorine, O one volume of 
 oxygen, and K the amount of potassium which will replace one volume 
 of hydrogen in a quantity of water containing one volume of oxygen. 
 This may he clearer if we substitute the term cubic centimetre for 
 volumes, thus 
 
 N represents one cubic centimetre of nitrogen, etc. 
 
 t Ammonium chloride is decomposed not only by potassium hy- 
 droxide ; but a number of other hydroxides, such as sodium hydroxide, 
 calcium hydroxide, etc., will accomplish the same end. Of course with 
 sodium hydroxide, sodium chloride, and with calcium hydroxide, cal- 
 cium chloride would be formed. 
 
102 ELEMENTS OF CHEMISTRY. 
 
 edge of chemical phenomena. It is, however, not out 
 of place to call attention to another case Avhere the 
 volatility of a compound formed during a chemical 
 reaction determines the completeness of that reaction. 
 We saw that sodium chloride and sulphuric acid pro- 
 duced sodium sulphate and hydrogen chloride. In this 
 case hydrogen chloride was the volatile substance. If, 
 in either of the reactions just referred to, enough water 
 is added to dissolve completely all the ammonia or all 
 the hydrogen chloride which passes off, then, under 
 ordinary circumstances, complete decompositions will 
 not result. Neither ammonia nor hydrogen chloride 
 would then be more volatile than the water in which 
 they are dissolved. 
 
 The decomposition of ammonium chloride by bases is a favor- 
 ite method of preparing ammonia gas for laboratory use. As a 
 general rule, moist calcium hydroxide (slaked lime) is employed 
 for this purpose. 56 
 
 Combination of Ammonia with Acids in General. Ammo- 
 nia combines with other acids as well as with hydrogen 
 chloride, and in each case the ammonium salt of the 
 corresponding acid is produced. The examples which 
 are of importance to us in this work are as follows : 
 
 Ammonia in contact with nitric acid produces ammonium 
 nitrate. 
 
 Ammonia in contact with nitrous acid produces ammonium 
 nitrite. 
 
 Ammonia in contact with carbonic acid produces ammonium 
 carbonate. 
 
 These three ammonium compounds occur in small amounts in 
 the atmosphere and also in the soil. 
 
 If a given quantity of sulphuric acid is brought into contact 
 with one-half as much ammonia as can possibly be taken up by 
 
THE COMPOUNDS OF AMMONIA WITH ACIDS. 103 
 
 this acid, the primary (acid) sulphate of ammonium is formed. 
 This primary sulphate is able to take up a second quantity of 
 ammonia, equal to the first, so as to produce the secondary (neu- 
 tral) ammonium sulphate. There are, therefore, two sulphates of 
 ammonium, just as there are two sulphates of potassium. (See 
 page 59.) Indeed, all the ammonium compounds greatly resemble 
 those of potassium. When brought in contact with soluble 
 bases, like potassium, sodium, or calcium hydroxide, all ammonium 
 salts liberate ammonia exactly as is the case with ammonium 
 chloride. 57 
 
 Changes of Energy in forming Ammonium Compounds. 
 The combination of ammonia with acids to form ammo- 
 nium compounds is attended with the evolution of 
 heat. The ammonium salts produced, therefore, pos- 
 sess less chemical energy than do the separate ammonia 
 and acids. 
 
 Chemical Character of a Solution of Ammonia in Water. 
 The solution of ammonia in water acts very much like 
 a solution of potassium hydroxide. It can neutralize 
 acids to form ammonium salts, just as the latter neutral- 
 izes acids to form potassium salts. (See pages 48, 58.) 
 For this reason it has been supposed that the solution 
 of ammonia in water is really ammonium hydroxide ; 
 but as all direct proof on this subject is in the contrary 
 direction, we must conclude that ammonium hydroxide 
 does not exist. Further, a belief in ammonium hydrox- 
 ide is not necessary in order to understand why ammo- 
 nia solution neutralizes acids, since it is obvious that 
 ammonia gas, when dissolved in water, should be just 
 as capable of union with acids to form ammonium salts 
 as it is in the pure state. 
 
 Difference between Ammonium and Potassium Salts. One 
 characteristic sharply distinguishes the ammonium com- 
 
104 ELEMENTS OF C1IEMISTRY. 
 
 pounds rom those of potassium ; they are all decom- 
 posed by heat, while the ammonia passes off as such if 
 the acid with which it was combined is not volatile. 
 If the acid with which the ammonia is combined is 
 volatile, the ammonia is vaporized with the acid, so 
 that the vapor contains ammonium salts. On the other 
 hand, potassium does not vaporize except at high tem- 
 peratures ; so that, under usual conditions, potassium 
 salts are not volatile. 
 
 S miim ar y . 
 
 1. A volume of ammonia is capable of uniting with 
 an equal volume of hydrogen chloride to form a salt- 
 like body (ammonium chloride). 
 
 2. In ammonium chloride there is combined one 
 volume of nitrogen with four of hydrogen and one of 
 chlorine. 
 
 3. The group of substances composed of one volume 
 of nitrogen and four of hydrogen is termed ammonium, 
 and its compounds resemble those of potassium. 
 
 4. Ammonium chloride is decomposed by potassium 
 hydroxide to form potassium chloride, ammonia, and 
 water. Other pronounced bases, such as sodium hy- 
 droxide or calcium hydroxide (slaked lime), can also 
 liberate ammonia from ammonium chloride. 
 
 5. Heat is evolved during these changes. Therefore 
 the chlorides, the ammonia, and the water which are 
 produced possess less chemical energy than the am- 
 monium chloride and the base, which acted on each 
 other. 
 
 6. Ammonia combines with other acids as well as 
 with hydrogen chloride. With the acids it forms am- 
 monium salts, which resemble those of potassium. 
 
THE COMPOUNDS OF AMMONIA WITH ACIDS. 105 
 
 There is a primary and secondary sulphate of am- 
 monium. 
 
 7. The solution of ammonia in water acts like a base 
 (potassium hydroxide), since it is capable of neutraliz- 
 ing acids to form ammonium salts. 
 
 8. By heat, ammonium compounds are decomposed 
 into ammonia and the corresponding acid. If the 
 ammonium salt was that of a volatile acid, the vapors 
 of ammonia and of the acid combine as soon as they 
 become cooler, once more forming ammonium salts. 
 
106 ELEMENTS OF CHEMISTRY. 
 
 CHAPTER XV. 
 
 THE THEORY WHICH SEEKS TO EXPLAIN THE 
 
 LAWS OF DEFINITE AND MULTIPLE 
 
 PROPORTIONS. 
 
 The Definite Composition of Chemical Compounds. All 
 the chemical compounds which we have encountered 
 are formed, as we have seen, by the union of definitely 
 related masses of matter. While the number of these 
 compounds has not been great, it has been enough to 
 show us that this definite relationship is not the result 
 of mere chance. The idea of chance is, indeed, entirely 
 eliminated if we extend our view so as to draw upon 
 the experience of others as well as our own. We shall 
 find that all the numberless true chemical compounds 
 with which we are surrounded have this in common, 
 - that they are formed by the interaction of definitely 
 related quantities of the elements. So general has this 
 observation been, that a definite and unalterable com- 
 position is regarded as an essential characteristic of a 
 chemical compound. 
 
 Meaning of the Term " Definite Composition." What is 
 understood, by definite composition has already been 
 explained in the preceding chapters ; yet a repeti- 
 tion of a few examples taken from those already 
 studied will develop this meaning with greater clear- 
 ness. 
 
DEFINITE AND MULTIPLE PROPORTIONS. 107 
 
 One volume of hydrogen unites with an equal volume of chlo- 
 rine to produce hydrogen chloride. If more of either gas than is 
 necessary for this relationship is present before union, then this 
 excess will remain uncombined afterward. Hydrogen chloride 
 is, therefore, formed by the interaction of definitely related vol- 
 umes of hydrogen and chlorine. A given volume of hydrogen 
 must always have the same weight if it is under the same condi- 
 tions, so must a given volume of chlorine. The ratio between the 
 weights of equal volumes of hydrogen and chlorine is as 1 : 35.5. 
 Hence one part by weight of hydrogen unites with 35.5 parts by 
 weight of chlorine to form 36.5 parts by weight of hydrogen chlo- 
 ride. The composition by weight of hydrogen chloride is, there- 
 fore, a definite one, and so is the relationship between the weights 
 of its constituent parts, hydrogen and chlorine. 
 
 Similar considerations have shown us that the ratio between 
 the volumes of hydrogen and oxygen, and hydrogen and nitrogen, 
 which are united in watdr and ammonia respectively, is a definite 
 one (2 : 1 in water and 3 : 1 in ammonia). The ratio between the 
 weights of equal volumes of hydrogen and oxygen is as 1 : 16, and 
 between those of equal volumes of hydrogen and nitrogen as 1 : 14. 
 Therefore the relationship between the weights of hydrogen and 
 oxygen in water is a definite one ; i.e., 2:16 (2 volumes of hydro- 
 gen, 1 volume of oxygen), or in simpler numbers, 1 : 8. Similarly, 
 the relationship between the weights of hydrogen and nitrogen 
 in ammonia is as 3 : 14 (3 volumes hydrogen to 1 volume nitro- 
 gen) or 1 : 4.67. 
 
 Definite Relationship between the Weights of Chemically 
 Interacting Compounds. That a definite relationship also 
 exists between the weights of chemically interacting 
 bodies is shown by the following examples which we 
 have encountered: 
 
 Sodium attacks water to form sodium hydroxide. Suppose 
 we take 18 grams of water; i.e., the amount of water which is 
 produced by the union of two grams of hydrogen with 16 of 
 oxygen. This quantity of water will be completely converted 
 into sodium hydroxide when exactly one-half the hydrogen (one 
 
108 ELEMENTS OF CHEMISTRY. 
 
 gram) has been expelled by the sodium. If less sodium is used, 
 then some water will remain unaffected; if more sodium, then 
 some sodium will remain unchanged. Sodium hydroxide, then, 
 has a definite composition ; it contains for every 23 parts of 
 sodium, 16 of oxygen and one of hydrogen. It can be shown 
 in the same way that 39 grams of potassium always replace one 
 gram of hydrogen in water, so that potassium hydroxide contains 
 for every 39 parts by weight of potassium, 16 of oxygen and one 
 of hydrogen. 
 
 When metals are acted on by dilute acids, a similar definite 
 relationship exists between the weight of metal dissolved, the 
 amount of hydrogen evolved, and the composition of the salt pro- 
 duced. Thus hydrogen chloride, as we have seen, contains 35.5 
 parts of chlorine to one part of hydrogen. If 36.5 grams of 
 hydrogen chloride are acted upon by enough sodium to replace 
 all the hydrogen, then 23 grams of sodium will be necessary for 
 this decomposition. The sodium chloride which is produced, 
 therefore, contains 23 parts of sodium to every 35.5 parts of 
 chlorine. If potassium is used to act upon the above quantity 
 of hydrogen chloride, 39 parts of potassium replace one part of 
 hydrogen to produce potassium chloride, which salt has 39 parts 
 of potassium to 35.5 parts of chlorine. Parallel results can be ob- 
 tained with other metals which are attacked by dilute acids. The 
 following table embodies the results developed by a study of the 
 action of a few of the metals on diluted acids and on water : 
 
 One part of hydrogen is replaced by 23 parts of sodium in its 
 action on water. 
 
 One part of hydrogen is replaced by 39 parts of potassium in 
 its action on water. 
 
 The resulting compounds have the following composition: 
 
 Sodium hydroxide contains 23 parts of sodium to 16 of oxygen 
 and 1 of hydrogen. 
 
 Potassium hydroxide contains 39 parts of potassium to 16 of 
 oxygen and 1 of hydrogen. 
 
 One part of hydrogen is replaced by 23 parts of sodium in its 
 action on hydrogen chloride. 
 
 One part of hydrogen is replaced by 39 parts of potassium in 
 its action on hydrogen chloride. 
 
DEFINITE AND MULTIPLE PROPORTIONS. 109 
 
 One part of hydrogen is replaced by 32.6 parts of zinc in its 
 action on hydrogen chloride. 
 
 One part of hydrogen is replaced by 12.1 parts of magnesium in 
 its action on hydrogen chloride. 
 
 One part of hydrogen is replaced by 28 parts of iron in its action 
 on hydrogen chloride. 
 
 The resulting compounds have the following composition : 
 
 Sodium chloride contains 23 parts of sodium to 35.5 parts of 
 chlorine. 
 
 Potassium chloride contains 39 parts of potassiam to 35.5 parts 
 of chlorine. 
 
 Zinc chloride contains 32.6 parts of zinc to 35.5 parts of 
 chlorine. 
 
 Magnesium chloride contains 12.1 parts of magnesium to 35.5 
 parts of chlorine. 
 
 Iron chloride contains 28 parts of iron to 35.5 parts of chlorine. 
 
 One part of hydrogen is replaced by 23 parts of sodium in its 
 action on sulphuric acid. 
 
 One part of hydrogen is replaced by 39 parts of potassium in its 
 action on sulphuric acid. 
 
 One part of hydrogen is replaced by 32.6 parts of zinc in its 
 action on sulphuric acid. 
 
 One part of hydrogen is replaced by 12.1 parts of magnesium in 
 its action on sulphuric acid. 
 
 One part of hydrogen is replaced by 28 parts of iron in its action 
 on sulphuric acid. 
 
 The resulting compounds have the following composition : 
 
 Sodium sulphate contains 23 parts of sodium to 16 of sulphur 
 and 32 of oxygen. 
 
 Potassium sulphate contains 39 parts of potassium to 16 of 
 sulphur and 32 of oxygen. 
 
 Zinc sulphate contains 32.6 parts of zinc to 16 of sulphur and 
 32 of oxygen. 
 
 Magnesium sulphate contains 12.1 parts of magnesium to 16 
 of sulphur and 32 of oxygen. 
 
 Iron sulphate contains 28 parts of iron to 16 of sulphur and 32 
 of oxygen. x 
 
110 ELEMENTS OF CHEMISTRY. 
 
 The Equivalent Weights of the Metals. It will be no- 
 ticed, on examining the above table, that the weight of 
 any given one of the metals which replaces one part of 
 hydrogen in the acids is the same, no matter whether we 
 use hydrochloric or sulphuric acid. The same is true 
 whatever acid we employ. For example, 23 parts of 
 sodium always replace one part of hydrogen in any 
 acid. The relative weights of the metals which are 
 given above are termed their equivalent weights, since 
 they are equivalent in combining power to one part 
 of hydrogen. . These equivalent weights can be easily 
 determined by experiment. We have but to weigh a 
 small quantity of the metal whose equivalent weight we 
 wish to determine, dissolve this in an acid, and carefully 
 collect and measure the hydrogen evolved. Knowing 
 the weight of one cubic centimetre of hydrogen,* we 
 can readily discover the volume occupied by one gram, 
 and, knowing the weight of the metal dissolved and the 
 number of cubic centimetres of hydrogen evolved, we 
 can calculate the quantity of metal necessary to give us 
 one gram of hydrogen. 58 The salts mentioned in the 
 above table can also be produced by neutralizing the 
 corresponding acids with the corresponding hydroxides 
 of the metals ; but their composition by weight remains 
 unaltered, no matter what has been their method of 
 formation. 
 
 An Explanation of the Existence of Fixed Relationship by 
 Weight in Chemical Compounds is found in the Atomic 
 Theory. As the fixed relationship existing between 
 the masses of the combining elements in chemical 
 compounds is not the result of mere chance, it follows 
 
 * One cubic centimetre of hydrogen weighs .00009001 gram. 
 
DEFINITE AND MULTIPLE PROPORTIONS. Ill 
 
 that some reason may be found for this regularity. 
 Why should chemical compounds always show an un- 
 varying composition by weight? Why should not 
 water, for example, at one time contain, for every one 
 part of hydrogen, seven of oxygen, and at another time 
 nine ? The scientific world has sought for an explana- 
 tion of these conditions, and has produced a theory 
 which satisfactorily accounts for all the phenomena en- 
 countered. This theory is known as the atomic theory. 
 
 The Atomic Theory. Let us suppose that all of the 
 elements are composed of extremely small particles 
 which we will term atoms. Let us further suppose 
 that the weight of an atom of a given element is equal 
 to that of each other atom of the same element, but 
 differs from that of an atom of any other element. 
 The atoms of different elements unite to form the 
 smallest individual group of the compound. Atoms 
 of the same kind unite to produce the smallest indi- 
 vidual group of an element. These groups we term 
 molecules, and the agglomeration of molecules forms 
 tangible matter. To make the results of a theory such 
 as this more apparent, we can use an illustration in 
 which certain visible portions of matter will serve as 
 atoms. Let us take two kinds of shot, one kind lead, 
 the other copper, the lead shot each to weigh one gram, 
 the copper shot five grams. If,, now, one of the lead is 
 fastened to one of the copper, the resulting combination 
 will contain one part of lead to five of copper. Next, 
 let us continue this process of uniting one lead shot 
 with one copper shot until we have a large number to- 
 gether, say six hundred grams. It is obvious that, if we 
 separate all the copper from all the lead, we shall have 
 
112 ELEMENTS OF CHEMISTRY. 
 
 five hundred grams of the former to one hundred grams 
 of the latter. In other words, this large mass of com- 
 bined lead and copper will have the same relationship 
 by weight between the constituent elements as is found 
 in the individual shot. Furthermore, if the above con- 
 ditions have been carefully adhered to, it will not be 
 possible to have any other relationship between the 
 copper and lead than that of five to one, no matter 
 how many shot we take. Obviously it is not neces- 
 sary to know how many shot we have in a given mass 
 in order to ascertain the relative weights of the par- 
 ticles of lead and of copper. We need but to separate 
 and weigh all the lead and all the copper to know that 
 the proportion of each is as one to five. While this 
 last separation will tell us what the proportional parts 
 by weight of the constituent metals in each of the com- 
 bined particles are, it will not tell us how many indi- 
 vidual shot are united in each of these unless we know 
 the weight of each. If some one, for example, had sub- 
 stituted lead shot weighing half a gram each for those 
 originally used, and had attached two lead shot to one 
 of copper, the results on separating the lead from the 
 copper would remain the same, five parts of copper to 
 one of lead. In such case we could not ascertain the 
 number of lead shot without counting them. 
 
 Difficulty of Determining the Number of Atoms combined 
 in a Molecule. It is in this latter condition that chem- 
 istry finds itself. It can take large masses of matter, 
 separate these into their constituent elements, and weigh 
 the latter. It can show that so many parts by weight of 
 one element combine with so many parts by weight of 
 another. It can, therefore, determine that the small- 
 
DEFINITE AND MULTIPLE PROPORTIONS. 113 
 
 est particles of the compound (the molecules) contain 
 so many parts of one element to so many parts of an- 
 other ; but without some special means of counting, it 
 cannot determine the number of atoms of any of the 
 elements which go to make up those smallest particles. 
 A direct count, as in the case of the shot, is out of the 
 question, for we can neither see nor weigh the individ- 
 ual atoms. For example, we have abundant proof in 
 the preceding work that one part of hydrogen combines 
 with eight parts of oxygen to form nine parts of water. 
 We have the theory that hydrogen and oxygen are 
 formed of atoms, that one or more atoms of hydrogen 
 unite with one or more atoms of oxygen to form the 
 smallest particle (the molecule) of water. We can say 
 that this molecule contains one part of hydrogen to 
 eight of oxygen, but we cannot, with the knowledge 
 which we now possess, determine how many atoms of 
 hydrogen and how many atoms of oxygen there are in 
 this molecule. As a consequence, we cannot, using the 
 knowledge we have so fa? obtained, ascertain the rela- 
 tive weights of these atoms in this case. We merely 
 know that there is eight times as much oxygen as 
 hydrogen. We may, at the very outset, abandon the 
 hope of determining the absolute weights of the atoms; 
 for, unlike the shot which we used as an illustration, 
 they are too small to be weighed directly. What is 
 true of water is also true of hydrogen chloride, of am- 
 monia, of caustic soda, and of every other compound 
 which we have studied and found to be of definite 
 composition by weight. We can determine the num- 
 ber of parts by weight of each element which enters 
 into these compounds. We can suppose that the cause 
 of this definite relationship is to be found in the fact 
 
114 ELEMENTS OF CHEMISTRY. 
 
 that these elements are composed of atoms, each hav- 
 ing a definite mass. We assume that the combination 
 of these atoms produces molecules of a fixed composi- 
 tion which belongs also to the tangible quantities of the 
 compounds produced by heaping together these mole- 
 cules, but further than this we cannot go. 
 
 Practical Advantages of the Atomic Theory as we have 
 so far developed it. The atomic theory, as we have so 
 far developed it, has, therefore, no particular practical 
 bearing on our understanding of chemistry. It affords 
 an explanation of the law of definite proportions (see 
 page 55) ; but without it we can just as well go on 
 studying chemical reactions and chemical energy, and 
 determine the relative parts by weight in which the ele- 
 ments combine. If, however, we can find some method 
 of ascertaining the number of atoms combined in the 
 individual molecules of a large number of chemical 
 compounds, we can ascertain the relative weights of 
 the individual atoms. By "this means, possibly, we 
 can make clear relationships existing between com- 
 pounds which would otherwise be concealed. In that 
 case the atomic theory would be of the greatest prac- 
 tical importance. 
 
 Thoroughly scientific means of ascertaining the num- 
 ber of atoms united in the individual molecules of many 
 compounds really have been established, and one of the 
 methods, the most important, we will examine in the 
 next chapter. Before we take up this part of the discus- 
 sion, however, we must examine two other chemical laws 
 which, while not absolutely essential in establishing the 
 atomic theory, are, nevertheless^ of great importance in 
 furnishing proof that is based upon correct reasoning. 
 
DEFINITE AND MULTIPLE PROPORTIONS. 115 
 
 The Law of Multiple Proportions. The first of these 
 laws is known as the law of multiple proportions. The 
 illustrations of this law which we have studied were 
 found during the discussions of the oxides of sulphur 
 and of sulphuric acid. (See Chapter IX.) We there 
 saw that sulphur is capable of forming two oxides, sul- 
 phur dioxide and sulphur trioxide, and the parts of 
 oxygen which unite with one part of sulphur in these 
 two compounds are to each other as 1: 1.5. If we 
 multiply hy two, so as to produce whole numbers, we 
 have 
 
 Two parts of sulphur are united with two parts of 
 oxygen in sulphur dioxide. 
 
 Two parts of sulphur are united with three parts of 
 oxygen in sulphur trioxide." 
 
 This individual case is but an example of what gen- 
 eral experience in chemistry has taught us. Many 
 elements, like sulphur and oxygen, combine with each 
 other in more than one proportion, forming more than 
 one compound. In every instance where one element 
 (A) unites with a second element (B) in more than 
 one proportion, in the series of compounds so produced 
 the proportional parts of B, which combine with a given 
 quantity of A, are to each other in a simple ratio such 
 as 1 : 2, or 2 : 3, or 3 : 4. What is true of compounds 
 composed of two elements is also true of those contain- 
 ing three or more. 
 
 Relation of the Law of Multiple Proportions to the Atomic 
 Theory. This law of multiple proportions can readily 
 be explained by the atomic theory, as will be evident if 
 we once more resort to our illustration with the lead 
 and the copper shot. We have a number of lead shot 
 
116 ELEMENTS OF CHEMISTRY. 
 
 each weighing one gram, and a number of copper shot 
 each weighing five grams. If we fasten one lead shot 
 to one of copper, we shall have produced a mass con- 
 taining one part of lead to five of copper. Now let us 
 take a second lead shot and attach it to two of copper. 
 It is obvious that the resulting body will have one part 
 of lead to ten of copper, and if we compare the two 
 combinations, we see that the weight of the copper 
 united to one part of lead in the first, is to the weight 
 of copper united to one part of lead in the second, as 
 1:2. The same must be true if we take any number of 
 individuals of the first combination and compare them 
 with any number of the second. The proportion be- 
 tween the weights of the lead and copper in the first 
 will always be as 1 : 5, and in the second as 1 : 10 ; and 
 the relation between the weight of copper united with 
 one part of lead in the two will always be as 1 : 2. 
 
 We can explain the law of multiple proportions in 
 the same way if we use the atomic theory outlined on 
 page 110. We have two oxides of sulphur. In the 
 first we have two parts of sulphur to two of oxygen, 
 and in the second two parts of sulphur to three of 
 oxygen. Let us suppose now that the smallest par- 
 ticles (the molecules) of the first oxide are each formed 
 of one atom of sulphur united to two atoms of oxygen, 
 each molecule containing equal parts by weight of sul- 
 phur and oxygen. One atom of oxygen would then 
 weigh half as much as an atom of sulphur. Since any 
 large mass of this sulphur oxide would be formed of 
 these molecules, it would follow that, if we separated 
 all the sulphur from all the oxygen in this large mass, 
 we should obtain equal weights of sulphur and of oxy- 
 gen. Next, let us return to the molecule and add to 
 
DEFINITE AND MULTIPLE PEOPORTIONS. 117 
 
 it one atom of oxygen. This second molecule would 
 then contain two parts of sulphur to three of oxygen, 
 and, obviously, a tangible mass made up of these mole- 
 cules would also be separable into two parts of sulphur 
 and three of oxygen. The relationship existing between 
 the amounts of oxygen united to a given weight of 
 sulphur in the two oxides of sulphur (sulphur dioxide 
 and sulphur trioxide) is therefore explained by the 
 atomic theory. If this explanation applies to the two 
 compounds which we have discussed, it must also 
 necessarily apply to any other series of compounds 
 which, like the two oxides of sulphur, are formed of 
 two or more elements according to the law of multiple 
 proportions. 
 
 The Law of Multiple Proportions cannot help us to deter- 
 mine the Relative Weights of the Atoms. We cannot, how- 
 ever, see and weigh the molecules directly ; they are too 
 small. We can only determine the proportional parts 
 in which the elements unite in tangible masses of the 
 compounds. It follows from this that we cannot, by 
 ascertaining these proportional parts alone, absolutely 
 fix the relative weights of the atoms themselves ; we 
 can only say that they must be so united in the mole- 
 cules of the compounds that the weight of all the 
 atoms of one element in one molecule must be to the 
 weight of all the atoms of the second element in that 
 molecule as the weight of one element is to the weight 
 of the other in the large quantity of the compound 
 with which we come in contact. That this is so will 
 be seen by the following: 
 
 We supposed that one atom of sulphur was united to two 
 atoms of oxygen in the molecules of the first oxide of sulphur, 
 
118 ELEMENTS OF CHEMISTRY. 
 
 and that one atom of sulphur was united to three of oxygen in 
 those of the second. Let us now change this hypothesis to read 
 that one atom of sulphur is joined to four of oxygen in one mole- 
 cule of sulphur. dioxide, and to six in one of sulphur trioxide, one 
 atom of oxygen having just one-fourth of the weight of one atom 
 of sulphur. The latter view of the case would agree with the ex- 
 perimental results exactly as well as the former ; for if the mole- 
 cules of the oxides of sulphur were constructed in this way, sulphur 
 dioxide would have two parts of sulphur united to two of oxygen, 
 and sulphur trioxide two of sulphur joined to three of oxygen. 
 These facts are unalterable, and any hypothesis which we choose 
 to adopt must agree with them. 
 
 We must therefore come to the conclusion that, while the re- 
 lations existijig between the proportional parts in which oxygen 
 and sulphur unite are explainable by the atomic hypothesis, the 
 determination of these proportional parts alone cannot possibly 
 help us to ascertain the relative weights of the atoms themselves. 
 The atomic theory, therefore, in the form which we at present 
 have it in this work, has no particular bearing on the systematic 
 study of chemistry. This conclusion we have already reached in 
 the law of definite proportions. 
 
 The Equivalent Weights of Elements. One other series of 
 facts in support of the atomic theory is found by comparing a 
 number of the compounds, each of which contains the same 
 element united to others, which latter are however different in 
 each one of the series. This comparison has already been insti- 
 tuted in the table which was. constructed at the beginning of this 
 chapter (pages 108 and 109). 
 
 On consulting this table we find that 
 
 23 parts of sodium, 
 
 39 parts of potassium, 
 
 32.6 parts of zinc, ] are united with 
 
 12.1 parts of magnesium, 
 
 28 parts of iron, 
 
 16 parts of oxygen and 1 of hydrogen in the hydroxides of the 
 above metals, and with 35.5 parts of chlorine in the chlorides of 
 the above metals. 
 
DEFINITE AND MULTIPLE .I*UOPOKTIONS. 119 
 
 Furthermore, as we have seen, 8 parts of oxygen' are united 
 with one part of hydrogen in water. This table shows us that 
 2 times 8 parts of oxygen are combined with 23 parts of sodium 
 in sodium hydroxide, and with 39 parts of potassium in potassium 
 hydroxide. Also on page 109 we saw that 4 times 8 parts of 
 oxygen are found together with 23 of sodium and 39 of potas- 
 sium in potassium sulphate. 
 
 The examples which have been cited have been con- 
 fined to the few elements encountered during the prog- 
 ress of this work, but we should have arrived at similar 
 results had we used any other ones for our basis of 
 study. If, therefore, we define as the equivalent weight 
 of an element that part of this element which will com- 
 bine with one part of hydrogen, or which will replace 
 one part of hydrogen in a chemical compound (see 
 page 110), we shall arrive at the following rule : 
 
 All true chemical compounds are produced by the 
 union of the equivalent weights, or of simple multiples or 
 sub-multiples of the equivalent weights, of the elements. 
 
 The Formation of Compounds from the Equivalent Weights 
 of the Elements is in accordance with the Atomic Theory. 
 The equivalent weight of an element is, therefore, a 
 constant which accompanies it throughout its combina- 
 tions with other elements. It remains while apparently 
 all of the other characteristics of the element (i.e., color, 
 malleability, ductility, etc.) have been lost in the for- 
 mation of a compound differing in all its properties 
 from the elements of which it is composed. 
 
 This result is entirely in accordance with the atomic theory ; 
 for, if the elements are formed of atoms, these atoms must always 
 retain the same relative weights, no matter how varied are the 
 compounds formed by them. If an atom of sodium weighs 
 
120 ELEMENTS OF CHEMISTEY. 
 
 23 times as much as an atom of hydrogen, and if one molecule 
 of water is acted on by sodium in such a way that an atom of 
 sodium replaces one of hydrogen, then 23 parts of sodium will 
 take the place of one part of hydrogen, no matter how large a 
 quantity of water or of sodium is taken. Furthermore, if one 
 atom of potassium weighs 39, one atom of zinc 32.6, one of 
 iron 28, times as much as one of hydrogen, then potassium, zinc, 
 or iron, must retain these relative weights, no matter in what 
 compound they are encountered. 
 
 The Relative Weights of the Atoms are Simple Multiples 
 or Sub-multiples of the Equivalent Weights. At first 
 glance it would seem that the equivalent weights 
 might be considered as the relative weights of the 
 atoms themselves, but a little reflection will show us 
 that such a conclusion would be arbitrary and without 
 warrant. In the above paragraph, for example, we have 
 assumed that one atom of sodium replaces one atom 
 of hydrogen in water. If this were true, the relative 
 weights of the atoms of hydrogen and of sodium would 
 be the same as the equivalent weights; namely, 1 and 
 23. With equal right we might suppose, however, 
 that two atoms of hydrogen are replaced by one of 
 sodium, in which case the relative weights of the 
 atoms of hydrogen and sodium would be 1 and 46, 
 and the same considerations would show us that the 
 relative atomic weights of iron and hydrogen might be 
 1 and 28, or 1 and 56, etc. The equivalent weights 
 of the various elements may possibly represent the rela- 
 tive weights of the atoms themselves, but they may 
 also be some simple multiple or sub-multiple of those 
 atomic weights. While the fact that all true chemical 
 compounds are produced by the union of the equiva- 
 lent weights, or of simple multiples or sub-multiples of 
 the equivalent weights of the elements, is an added 
 
DEFINITE AND MULTIPLE PROPORTIONS. 121 
 
 support to the atomic theory, the determination of 
 these equivalent weights does not, without further ex- 
 perimental aid, help us to decide upon the true relative 
 weights of the atoms themselves. 
 
 After a consideration of all the arguments which have 
 been advanced, the question naturally presents itself: 
 Are no experimental means at our disposal which will 
 enable us to determine the relative weights of the 
 atoms? Must the atomic theory always be to us sim- 
 ply an explanation of the reason why certain regulari- 
 ties in the composition of chemical compounds are 
 encountered, without having any practical bearing in 
 ascertaining the number of atoms which are combined 
 in the chemical compounds, or the relative weights of 
 the atoms themselves? An attempt to answer these 
 questions involves a more minute consideration of the 
 laws underlying the combining volumes of gases, and 
 is, therefore, reserved for a separate chapter. 
 
 Summary. 
 
 1. All chemical compounds are formed by the union 
 of definitely related masses of matter. 
 
 2. A definite relationship also exists between the 
 weights of chemically interacting bodies. 
 
 3. The quantity of any metal which is capable of 
 liberating one part of hydrogen from acids is termed the 
 equivalent weight of that metal. A given weight of a 
 metal when acted upon by certain dilute acids always 
 liberates the same quantity of hydrogen. 
 
 4. The salts formed by the substitution of hydrogen 
 in acids have a definite composition by weight. This 
 composition is constant, no matter what is the method 
 of their formation. 
 
122 ELEMENTS OF CHEMISTRY. 
 
 5. The fixed relationship existing between the com- 
 bining weights of the elements is explainable by means 
 of the atomic theory. 
 
 6. The atomic theory supposes that all the elements 
 are made up of extremely small particles termed atoms. 
 The weight of an atom of a given element is equal to 
 that of each other atom of the same element, but differs 
 from that of an atom of any other element. 
 
 7. The atoms of different elements unite to form the 
 smallest individual group of a compound. This group 
 is termed a molecule. 
 
 8. While the fact that a given chemical compound 
 always has a definite composition is explainable by 
 means of the atomic hypothesis, the discovery of the 
 relative weights of the different elements which form 
 that compound cannot determine for us the relative 
 weights of the atoms themselves. 
 
 9. Chemical compounds are produced by the union 
 of the equivalent, or of simple multiples or sub-multi- 
 ples of the equivalent, weights of the elements. 
 
MODERN THEORY OF NATURE OF GASES. 123 
 
 CHAPTER XVI. 
 
 MODERN THEORY OF THE NATURE OF GASES. 
 
 The Relation between Specific Gravities of Gases and their 
 Molecular Weights. 
 
 A CONSIDERATION of the relative parts by weight in 
 which the atoms unite cannot provide us with a satis- 
 factory means of determining the relative weights of 
 the atoms themselves. But a combination of the com- 
 bining weights with the combining volumes and with 
 the specific gravities of the gaseous elements and com- 
 pounds furnishes us with a means of deciding what 
 multiples or sub-multiples of those combining weights 
 we must regard as representing .the true relative weights 
 of the atoms. In order to comprehend how this com- 
 bination of the three constants (combining weights, 
 combining volumes, and specific gravities of gaseous 
 elements and compounds) has led to the desired result, 
 we must first understand the prevailing belief as to the 
 physical nature of a gas. This prevailing belief is in 
 accordance with the atomic theory. 
 
 The Kinetic Gas Theory. A gas is at the present 
 time regarded as a form of matter, the individual 
 particles of which (molecules) are so far separated 
 that each is capable of motion independently of the 
 others. 
 
124 ELEMENTS OF CHEMISTRY. 
 
 That the particles of a gas must be comparatively far apart is 
 proven by the fact that they occupy a space many hundred times 
 greater than that of the liquids from which they are formed by 
 heating. These particles are at such a distance from each other 
 that they are not subject to those mutual influences (cohesion, 
 etc.) which are present in liquids and solids. They are, therefore, 
 acted upon only by the attraction which all masses exert on each 
 other at a distance (gravitation). As a consequence, the individ- 
 ual molecules attract each other only in a very slight degree. 
 Accordingly, the small particles of which a gas is composed are 
 continually in motion, and, following the ordinary laws of me- 
 chanics, move in right lines until they collide with some other 
 molecule of their own kind, or with the walls of the enclosing 
 vessel, when, being perfectly elastic, they rebound. The pres- 
 sure exerted by a gas is, therefore, due to the continual impacts 
 given by its molecules upon the sides of the retainer. This pres- 
 sure must consequently increase with the number of molecules 
 and with the mass and velocity of each molecule. The energy 
 possessed by a moving body is measured by its mass multiplied 
 by the square of its velocity and divided by two ( ). Therefore, 
 
 if we multiply the mass of each individual molecule in a given 
 volume of the gas by one-half the square of its velocity, we shall 
 obtain the energy of motion possessed by that molecule ; and the 
 sum of all these products will, obviously, be a quantity propor- 
 tional to the pressure of the gas. In discussing the atmosphere, 
 we learned that gases expand yfj of their volume for each rise 
 of one degree in temperature (law of Gay Lussac, see page 69). 
 However, if the volume of the gas be kept constant while the 
 temperature is raised, then the increase of the pressure of the gas 
 is found to be proportional to the increase in the temperature (the 
 latter being calculated from 273). In this velume of gas the 
 mass remains constant, so that it follows that the temperature is 
 proportional to the square of the velocity of the molecules. 
 
 Let us suppose that we have two equal spaces, each filled with 
 a different gas, under the same temperature and pressure. From 
 what has been said ab^ve, the sum of the kinetic energy pos- 
 sessed by the particles in one of the gases will be equal to the 
 sum in the other. We will assume that in these equal gas volumes 
 
MODERN THEORY OF THE NATURE OF GASES. 125 
 
 there are equal numbers of molecules (hypothesis of Avogadro). It 
 will follow that the kinetic energy (-5*) belonging to each indi- 
 vidual particle in either of the gases averages the same. If 
 both gas volumes are brought into communication, they will mix 
 without suffering either a change in temperature or pressure, pro- 
 vided always that they exert no chemical action on each other. 
 In the mixture so produced, therefore, there is also on the average 
 the same amount of kinetic energy belonging to each individual 
 molecule. 
 
 In Equal Volumes of Gases, under like Conditions, there are 
 Equal Numbers of Molecules. Assuming that in equal vol- 
 umes of gases, under the same temperature and pressure, 
 there are equal numbers of molecules, if we take into 
 consideration only the simple laws of mechanics, we 
 can understand why two gases can be mixed without 
 a change in temperature or total volume. We can also 
 find a reason for like changes in volume caused by like 
 changes in temperature (law of Gay Lussac), and for 
 the fact that all gases expand alike and are altered alike 
 in volume by like changes in pressure (law of Boyle, 
 see page 68). 
 
 The matter assumes an entirely different aspect, however, if 
 we do not assume that in equal volumes of gases there are equal 
 numbers of particles under like conditions of temperature and 
 pressure. For example, suppose that one of the above gas volumes 
 contains twice as many molecules as the other. Then, since the 
 pressure exerted by both gases is alike, and the sum of the kinetic 
 energy of all the particles in the one must be equal to that sum 
 in the other, each of these particles will possess only one-half the 
 kinetic energy which belongs to a particle* of the other gas. It 
 would then be difficult to understand how the equality of temper- 
 ature and pressure could be preserved after the two gases are 
 mixed. For we should have in this mixture particles possessing 
 twice as much kinetic energy as others, and we could see no 
 
126 ELEMENTS OF CHEMISTRY. 
 
 reason why, owing to frequent collisions, these should not impart 
 some of their energy to those with which they come in contact. 
 If this were to occur, however, we could scarcely maintain the 
 former equality of temperature and pressure, since both of these 
 are proportional to the kinetic energy possessed by the molecules. 
 Avogadro's hypothesis, that in equal volumes of gases there are 
 equal numbers of molecules, is, therefore, the only one in accord- 
 ance with the laws of mechanics. With the establishment of this 
 hypothesis we have a method of determining the relative weights 
 of the molecules of gaseous substances. 
 
 The weight of a given volume of gas is obviously the 
 sum of the weights of the molecules of which it is com- 
 posed. If, now, we weigh equal volumes of a series of 
 different gases, all under the same conditions as to the 
 temperature and pressure, the weights so obtained will 
 have the same relationship to each other as do the 
 weights of the individual molecules, because in equal 
 volumes of gases there are equal numbers of the latter. 
 
 Relation between the Molecular Weights and Specific Gravities of 
 Gases. Let us suppose that we have equal volumes of two gases, 
 the molecules of which weigh x and y respectively. If the num- 
 ber of molecules in the first volume is n, then the number in 
 the second will also be n, and 
 
 nx : ny : : x : y 
 
 but nx and ny represent the weights of the two gases * (w and w'), 
 so that 
 
 w : w ' : : x : y. 
 
 The weights of equal volumes of various gases, when compared 
 with the weight of an equal volume of some other gas taken as 
 a standard, represent the specific gravities of those gases. From 
 what has gone before, we can establish the following rule : 
 
 * If all of the molecules of a given.gas volume are of the same kind, 
 then the sum of the weights of the individual molecules can he repre- 
 sented as a product, where n represents the number of molecules. 
 
Ill + litres 
 
 MODERN THEORY OF THE NATURE OF GASES. 127 
 
 The molecular weights (the relative weights of the 
 individual molecules) of gases are to each other as the 
 specific gravities of those gases. 
 
 Standard for Specific Gravities of Gases. It is generally cus- 
 tomary to compare all specific gravities of gases with that of air 
 as unity ; i.e., to weigh gas volumes which are equal to that occu- 
 pied by one gram of air. For our purpose, however, it will be 
 better to use hydrogen as a standard, and to understand by the 
 term specific gravity of a gas, the relative weights of volumes 
 equal to the space occupied by the unit weight of hydrogen. 
 
 EXAMPLES : One gram of hydrogen occupies 11 
 at and 760mm. pressure. 
 
 11.111 + litresof oxygen weigh 16 grams, 
 
 11.111 + litres of chlorine weigh 35.5 grams, 
 
 11.111 + litres of nitrogen weigh 14 grams, 
 
 11.111 + litres of hydrogen chloride weigh 18.25 grams, 
 
 11.111 + litres of water weigh 9 grams, 
 
 11.111 + litres of ammonia weigh 8.5 grams, 
 
 and the specific gravities are as follows : 
 
 Hydrogen = 1. 
 
 Oxygen = 16. 
 
 Chlorine = 35.5. 
 
 Nitrogen = 14. 
 Hydrogen chloride = 18.25. 
 
 Water = 9. 
 
 Ammonia = 8.5. 
 
 These specific gravities, as we have seen, bear the 
 same relationship to each other as do the molecular 
 weights of the respective gases. We need then but to 
 decide upon the molecular weight of one of them in order 
 to have given to us the relative molecular weights of all of 
 the others. Such a decision has been reached, and the 
 reasons which have led to it will be outlined in. the 
 next chapter. 
 
128 ELEMENTS OF CHEMISTRY. 
 
 Summary. 
 
 1. The individual particles (molecules) of a gas are 
 so far separated that each is capable of motion inde- 
 pendently of the others. 
 
 2. The pressure exerted by a gas is due to the im- 
 pacts of its molecules upon the sides of the container. 
 
 3. The sum of the kinetic energy of all the mole- 
 cules is proportional to the gas pressure. 
 
 4. In equal volumes of gases, under the same con- 
 Editions of temperature and pressure, there are equal 
 J numbers of molecules. 
 
 \ 5. The weights of equal volumes of gases are to each 
 other as the molecular weights. 
 
 6. The molecular weights are to each other as the 
 specific gravities. 
 
 7. The specific gravities of gases are usually ascer- 
 tained with air as a unity. In our chemical work it is 
 better to select hydrogen as the standard. 
 
 8. If we decide upon the molecular weight of one 
 gas, we can, by determining their specific gravities, dis- 
 cover the molecular weights of other gases. 
 
DETERMINATION OF ATOMIC WEIGHTS. 129 
 
 CHAPTER XVII. 
 
 THE DETERMINATION OF ATOMIC WEIGHTS BY 
 USE OF THE SPECIFIC GRAVITIES OF GASES. 
 
 IN the preceding chapter we learned that, because 
 equal volumes of gases contain equal numbers of mole- 
 cules, the relative weights of equal volumes of gases must 
 bear the same relationship to each other as the molec- 
 ular weights. The determination of various molecular 
 weights, therefore, becomes a comparatively easy mat- 
 ter, provided we can determine the molecular weight of 
 some one element which we can select as a standard, 
 and with which we can compare the other gaseous sub- 
 stances. In order to do this we must examine more 
 closely into the lessons taught us by the study of the 
 combining volumes of elementary gases. 
 
 The Molecules of Hydrogen consist of Two Atoms. One 
 
 volume of hydrogen unites with one volume of chlorine 
 to produce two volumes of hydrogen chloride. Let us 
 now suppose that we have a volume of hydrogen which 
 contains one hundred molecules. From what we have 
 learned, it follows that an equal volume of chlorine also 
 contains one hundred molecules. These gas volumes 
 we will represent by squares, as follows : 
 
 1 volume hydrogen. 1 volume chlorine. 
 
130 
 
 ELEMENTS OF CHEMISTRY. 
 
 The above volumes of hydrogen and chlorine are capa- 
 ble of uniting to form a quantity of hydrogen chloride 
 equal to twice the volume of hydrogen : - 
 
 1 VOL. 
 HYDROGEN 
 
 + 
 
 1 VOL. 
 CHLORINE 
 
 = 
 
 
 2 volumes of hydrogen chloride. 
 
 Now, each volume of hydrogen chloride must contain as 
 many molecules as an equal volume of hydrogen or of 
 chlorine; i.e., 100 molecules, so that 
 
 100 MOLS. 
 
 
 100 MOLS. 
 
 
 100 MOLS. 
 
 
 100 MOLS. 
 
 OF 
 
 HYDROGEN 
 
 + 
 
 OF 
 
 CHLORINE 
 
 
 HYDROGEN 
 CHLORIDE 
 
 + 
 
 HYDROGEN 
 CHLORIDE 
 
 It follows from this, however, that 100 molecules of 
 hydrogen must have taken part in the formation of 200 
 molecules of hydrogen chloride, so that each molecule 
 of hydrogen must have been divided into two parts. The 
 molecule of hydrogen thus contains at least two atoms. 
 The same of necessity must be true also of chlorine, for 
 the 100 molecules of chlorine have also taken part in 
 the formation of 200 molecules of hydrogen chloride. 
 What is true of the above gas volumes is obviously 
 true of any other equal volumes of hydrogen and chlo- 
 rine, for in equal volumes there are equal numbers of 
 molecules. The above reasoning does not exclude a 
 theory that a molecule of hydrogen may contain more 
 than two atoms ; but such a view has no great proba- 
 bility, because in the formation of the various hydrogen 
 compounds we encounter no instance in which one 
 volume of hydrogen enters into the production of more 
 than two volumes of the compound gas. 
 
DETERMINATION OF ATOMIC WEIGHTS. 131 
 
 EXAMPLES : Two volumes of hydrogen and one of oxygen 
 produce two volumes of water vapor. 
 
 Three volumes of hydrogen and one of nitrogen produce two 
 volumes of ammonia. 
 
 The Molecular Weight of Hydrogen can be taken as the 
 Standard for Measuring other Molecular Weights. It seems 
 reasonably certain, therefore, that one molecule of hy- 
 drogen is formed of two atoms. Its molecular weight, 
 then, is twice its atomic weight. We have no accurate 
 means of determining the absolute weights of the atoms, 
 but for our purposes this is not necessary. The relative 
 weights answer all purposes ; and we need only select 
 the weight of an atom of some one element as a stand- 
 ard, and measure all others by this.* Hydrogen is, 
 relatively, the lightest of known elements. 
 
 It is convenient, therefore, to fix upon the weight 
 of an atom of hydrogen as unity, and to say that other 
 atoms weigh 16, 14, 35.5, etc., times as much as one 
 atom of hydrogen. If the atom of hydrogen weighs 
 
 1, then the molecule of hydrogen weighs 2. 
 
 \ 
 
 Determination of the Molecular Weights of Gases. We 
 are now in a position to determine the relative molecu- 
 lar weights of other gaseous elements and compounds ; 
 for we need but select a volume of hydrogen which 
 weighs two grams, and then weigh off volumes of the 
 other gases equal to that volume of hydrogen. Their 
 relative weights will represent the relative weights of 
 the molecules. 
 
 * The object of measuring anything is simply to determine its relation 
 to other things. We fix upon some arbitrary standard (a foot, a metre,, 
 an inch) as a unit, and measure all other lengths by this. The same is 
 true of weights the unit of weight (a grain, a gram, a kilogram) is one 
 of arbitrary selection. 
 
132 
 
 ELEMENTS OF CHEMISTRY. 
 
 If n represents the number of molecules in 2 grams of hydrogen, 
 then - will be the weight of each individual molecule. If x, y, z 
 represent the weights of volumes of other gases equal to that of 
 2 grams hydrogen, then -, ^, -, will be the relative weights of 
 the individual molecules of each of those gases, since n remains 
 the same ; and 2 : x : y : z : : - : - : V- : - '-. Hence, if 2 represents the 
 weight of one molecule of hydrogen, the relative weights of the 
 other molecules are represented by x, y, and z ; i.e., by their specific 
 gravities. Obviously the same result will be obtained if we begin, 
 not with two grams of hydrogen, but with two units of any other 
 standard of weight, so that we can establish the following rule : 
 
 If hydrogen is placed at 2, the specific gravities of all 
 other gases (which are measured by these two parts of hy- 
 drogen) are the same numbers as their molecular weights. 
 This rule is illustrated by the following table : - 
 
 Hydrogen = 2. 
 
 GAS. 
 
 SPECIFIC 
 GRAVITY. 
 
 MOLECULAR 
 WEIGHT. 
 
 Chlorine 
 
 71. 
 
 71. 
 
 Oxv^en 
 
 32. 
 
 32. 
 
 Nitrogen 
 
 28. 
 
 28. 
 
 Hydrogen chloride . . . 
 Water (gas) 
 Ammonia 
 
 36.5 
 18. 
 17. 
 
 36.5 
 
 18. 
 17. 
 
 
 
 
 Determination of the Maximum Atomic Weights of 
 the Elements. By means of these results we obtain a 
 method for determining the maximum numbers which 
 can represent the relative weights of the atoms of chlo- 
 rine, oxygen, and nitrogen. This conclusion is evident 
 if we analyze the figures a little more closely. 
 
 - The weight of a molecule of water is 18 if the molecule of 
 hydrogen is 2. Our previous work has shown us that in 18 parts 
 of water there are 16 of oxygen and two of hydrogen. Hence 
 
DETERMINATION OF ATOMIC WEIGHTS. 133 
 
 one molecule of water contains 16 parts of oxygen and two of 
 hydrogen. Obviously, then, one atom of oxygen cannot weigh 
 more than 16 times as much as one atom of hydrogen ; for, if its 
 relative weight were supposed to be greater than this, one mole- 
 cule of water would contain a fraction of one atom of oxygen. 
 We cannot with equal certainty state that an atom of oxygen may 
 not have a relative weight of less than 16, for it is easily conceiv- 
 able that a molecule of water may contain more than one atom of 
 oxygen. Such a supposition, however, would be entirely without 
 experimental backing. We have never encountered any one of 
 the numerous compounds of oxygen (which we can obtain as 
 gases, and the molecular weights of which we consequently know) 
 in which we have less than 16 parts of oxygen in each molecule. 
 If, therefore, we place the weight of one atom of hydrogen at 
 unity (one-half the molecular weight), we have every reason to sup- 
 pose that one atom of oxygen weighs 16 times as much as that unit. 
 In one molecule of water we therefore have two ato?ns of hydrogen 
 and one of oxygen. 
 
 The relative weight of a molecule of hydrogen chloride is 36.5. 
 This molecule contains one part of hydrogen and 35.5 of chlorine. 
 The maximum atomic weight of chlorine is, therefore, 35.5 ; and 
 as we have never encountered less than this quantity of chlorine 
 united with one part of hydrogen or its equivalent in any gasifi- 
 able chlorine compound, we must conclude that 35.5 is the mini- 
 mum. One atom of chlorine, therefore, weighs 35.5 times as 
 much as an atom of hydrogen, and in one molecule of hydro- 
 gen chloride we have one atom of hydrogen and one atom of 
 chlorine. 
 
 The relative weight of a molecule of ammonia is 17 ; this mole- 
 cule contains three parts of hydrogen to 14 of nitrogen. The 
 maximum atomic weight of nitrogen is, therefore, 14, and for 
 reasons similar to those given with oxygen and chlorine, its mini- 
 mum is also 14. One molecule of ammonia, then, contains three 
 atoms of hydrogen and one atom of nitrogen. 
 
 The above table now shows us that the relative mo- 
 lecular weights of the elements, chlorine, oxygen, and 
 nitrogen, represent numbers which are twice as large as 
 the relative atomic weights of those elements as deter- 
 
134 ELEMENTS OF CHEMISTRY. 
 
 mined from their hydrogen compounds. Therefore, the 
 molecules of these elementary gases contain at least two 
 atoms. We can now construct the following table : * 
 
 The weight of an atom of hydrogen is placed = 1. 
 
 ELEMENTS. 
 
 ATOMIC WEIGHT. 
 
 MOLECULAR WEIGHT. 
 
 Hydrogen . . . 
 Chlorine .... 
 
 1. 
 35.5 
 
 2. 
 71. 
 
 Oxygen .... 
 Nitrogen .... 
 
 16. 
 14. 
 
 32. 
 
 28. 
 
 Chemical notation can be very much simplified if we 
 represent the atoms of each of the elements, with the 
 atomic weights of which we are acquainted, by means 
 of certain symbols. The system universally adopted is 
 one which uses the first letter of the English, Latin, or 
 Latinized name of the element in question ; i.e., H rep- 
 resents one atom of hydrogen, O one atom of oxygen, 
 etc.t The structure of the molecules of the elements 
 is then expressed by writing after the symbol a sub- 
 script number, representing the number of atoms in the 
 molecule ; e.g., H 2 represents one molecule of hydrogen, 
 O 2 one molecule of oxygen, N 2 one molecule of nitro- 
 gen. The molecules of compounds are represented by 
 writing the symbols of the elements entering into their 
 formation side by side, with the subscript numbers rep- 
 
 * The relative weights of the atoms of the different elements, measured 
 hy some standard atomic weight (in this case by hydrogen = 1), are for 
 purposes of simplicity termed the atomic weights. This expression will 
 he used in the future. For the same reason the relative molecular weights 
 are termed molecular weights. 
 
 t In some cases the first letter of the Latin name is used ; e.g., K for 
 Kalium (Latin for Potassium), Na for Natrium (Sodium). Where sev- 
 eral elements have the same initial a second letter may he added; C = 
 Carbon; Cl = Chlorine; Cu = Copper; Ca Calcium. 
 
DETERMINATION OF ATOMIC WE IG PITS. 185 
 
 resenting the number of atoms entering into their for- 
 mation after the respective symbols; i.e., H 2 O represents 
 one molecule of water containing two atoms of hydro- 
 gen and one of oxygen ; H Cl, one molecule of hydrogen 
 chloride containing one atom of hydrogen and one of 
 chlorine. NH 3 , one molecule of ammonia containing 
 one atom of nitrogen and three of hydrogen. As these 
 symbols represent the uniting atoms, they must of ne- 
 cessity also stand for the atomic weights. For exam- 
 ple, the combination H 2 O means, not only that two 
 atoms of hydrogen with one atom of oxygen form one 
 molecule of water, but it also represents the fact that 
 two parts of hydrogen are united with 16 of oxygen to 
 produce 18 of water. 
 
 Determination of the Number of Atoms united in Mole- 
 cules by considering the Combining Volumes of Gases. We 
 arrive at the same conclusions regarding the number of 
 atoms uniting to form the molecules of the gaseous 
 compounds which we have studied, if we take into con- 
 sideration the combining volumes of the elementary 
 gases without regard to their specific gravities. This 
 will be clear from the following reasoning : 
 
 Composition of Hydrogen Chloride. We learned (page 41) that 
 hydrogen chloride is produced by the union of equal volumes of 
 hydrogen and of chlorine. From the principles of the kinetic 
 gas theory, this must mean that equal numbers of molecules of 
 hydrogen and chlorine react to form hydrogen chloride; i.e., one 
 molecule of hydrogen with one molecule of chlorine. We have 
 also learned that the volume of hydrogen chlorine which results is 
 twice as great as the initial volume of hydrogen, so that there 
 must be formed twice as many molecules of hydrogen chloride as 
 there were either of hydrogen or of chlorine. One molecule of 
 hydrogen, which contains two atoms, with one molecule of chlo- 
 
136 
 
 ELEMENTS OF CHEMISTRY. 
 
 rine, which contains two atoms, therefore, produces two molecules 
 of hydrogen chloride, which contain each one atom of hydrogen 
 and one of chlorine. This result can be expressed by chemical 
 notation as follows : 
 
 H 2 + C1 2 
 
 1 mol. of hydrogen + 1 mol. of chlorine 
 
 HC1 + HC1. 
 
 2 molecules of hydrogen chloride. 
 
 Now let us suppose that the volume of hydrogen which we se- 
 lected weighs two grams. From the preceding tables, we know 
 that an equal volume of chlorine must weigh 71 grams. The two 
 grams of hydrogen uniting with 71 grams of chlorine produce 73 
 grams of hydrogen chloride, which 73 grams occupy twice the 
 volume taken by two grams of hydrogen, and, consequently, a 
 volume of hydrogen chloride equal to that of two grams of hydro- 
 gen would weigh 36.5 grams. The specific gravity of hydrogen 
 chloride (hydrogen = 2) is therefore 36.5. Hence the molecular 
 weight of hydrogen chloride is also 36.5, a conclusion which we 
 reached by direct comparison in the first portion of this chapter. 
 
 Composition of One Molecule of Water. We learned that water 
 is produced by the union of two volumes of hydrogen and one of 
 oxygen, hence, in its formation, two molecules of hydrogen react 
 with one molecule of oxygen. The volume of water vapor which 
 results is equal to that of the hydrogen with which we started ; i.e., 
 it is two volumes, and hence represents two molecules. One 
 molecule of oxygen with two molecules of hydrogen, therefore, 
 produces two molecules of water. This result can be expressed 
 as follows : 
 
 H 2 + H 2 +0 2 =H,0 + H 2 0. 
 
 1 mol. of hydrogen + 1 mol. of hydrogen + 1 mol. of oxygen = 2 mols. of water. 
 
 2 grams hydrogen + 2 grams hydrogen + 32 grams oxygen = 18 grams water + 18 grams water. 
 
DETERMINATION OF ATOMIC WEIGHTS. 137 
 
 If, now, one of these volumes of hydrogen weighs 2 grams, 
 then the same volume of oxygen, as we have seen, weighs 32 
 grams, and 4 grams of hydrogen with 32 grains of oxygen pro- 
 duce 36 grams of water vapor. This quantity, however, occupies 
 twice the volume taken by 2 grams of hydrogen. Hence the 
 weight of a volume of water vapor equal to that of 2 grains of 
 hydrogen is 18 grams. The specific gravity of w r ater vapor (hy- 
 drogen = 2) is consequently 18, and the relative weight of a 
 molecule of water is also 18. 
 
 Composition of One Molecule of Ammonia. Three volumes of 
 hydrogen and one of nitrogen unite to form two volumes of 
 ammonia. (See page 94.) Three molecules of hydrogen, there- 
 fore, react with one molecule of nitrogen to form two molecules 
 of the compound. As one molecule of nitrogen is capable of 
 forming two molecules of ammonia, it must follow that each 
 nitrogen molecule is divisible into at least two parts, so that each 
 must contain at least two atoms of the element. As each hydro- 
 gen molecule also contains two atoms, the formation of ammonia 
 can be represented as follows : 
 
 H 2 + H 2 + H 2 + N 2 = NH 3 
 
 3 mols. hydrogen +1 mol. nitrogen = 2 mols. of ammonia. 
 
 j o 
 
 a! 
 
 4 o 
 p o 
 
 ~ % 
 
 If one volume of hydrogen weighs two grams, an equal volume 
 of nitrogen \veighs 28 grams. Therefore 6 grams of hydrogen 
 with 28 grams of nitrogen produce 34 grams of ammonia. This 
 quantity of ammonia occupies twice the volume of two grams of 
 hydrogen, hence the weight of a volume of ammonia equal to that 
 of two grams of hydrogen is 17. The specific gravity of ammo- 
 nia (hydrogen = 2) is therefore 17, and its molecular weight is 
 also 17. 
 
 Summary. 
 
 1. Each molecule of hydrogen consists of at least 
 two atoms. 
 
138 ELEMENTS OF CHEMISTRY. 
 
 2. The weight of a molecule of hydrogen is twice 
 the weight of one atom. The weight of a molecule of 
 hydrogen is the standard for measuring other molecular 
 weights. 
 
 3. If hydrogen as 2 is made the standard for measur- 
 ing the specific gravity of gases, then the specific gravity 
 of any gas is the same as its molecular weight. 
 
 4. The determination of the specific gravities, and 
 hence of the molecular weights of gaseous compounds, 
 gives us a means of ascertaining the maximum numbers 
 to be assigned to the relative weights of the atoms of 
 the elements. The minimum numbers for these relative 
 atomic weights are fixed by reasoning that, because we 
 find no gaseous compounds which have less than these 
 minimum quantities of the elements in one molecule, 
 therefore no smaller quantities need be considered. 
 
 5. The molecules of the elements, chlorine, oxygen, 
 and nitrogen, consist of at least two atoms. 
 
 .6. One atom of each of the different elements can be 
 represented by an appropriate symbol. The molecules 
 formed by the union of these atoms can be represented 
 by joining together the symbols, with subscript numbers 
 after each. These numbers indicate the number of 
 atoms of each element which enters into a molecule 
 of the compound. 
 
 7. The number of atoms united in the molecule of 
 gaseous compounds can be ascertained by a proper con- 
 sideration of the combining volumes of the gaseous 
 elements. 
 
THE EXPRESSION OF CHEMICAL CHANGES. 139 
 
 CHAPTER XVIII. 
 
 THE EXPRESSION OF CHEMICAL CHANGES BY 
 FORMULAE AND EQUATIONS. 
 
 THE various considerations advanced in the preceding 
 chapter have shown us that the proper interpretation 
 of the relationships between the combining volumes 
 of gases, and the volumes of the compounds produced 
 by such combinations, determines the molecular weights 
 of those compounds. Knowing the molecular weights, 
 and also the relative parts by weight in which the ele- 
 ments unite, we can, therefore, form a conclusion as to 
 the number of atoms in each molecule, and as to the 
 relative atomic weights. These results, so far as we 
 have gone, can be summed up in the following table : 
 
 
 S3 
 
 
 
 
 < 03 
 
 
 
 
 J H 
 
 
 
 FORMULAE. 
 
 ij 53 
 
 O o 
 
 COMPOSITION 
 
 ATOMIC WEIGHTS, 
 
 
 3 3 
 
 BY WEIGHT. 
 
 H = 1. 
 
 
 a* 
 
 
 
 Hydrogen chloride, HC1 
 
 3G.5 
 
 1 part H, 35.5 Cl 
 
 Chlorine, 35.5 
 
 Water, H 2 O 
 
 18. 
 
 2 parts H, 16 O 
 
 Oxygen, 16. 
 
 Ammonia, H 3 N 
 
 17. 
 
 3 parts H, 14 N 
 
 Nitrogen, 14. 
 
 Composition of the Molecules of Sulphur Dioxide and Sul- 
 phur Trioxide. In our previous work we have repeatedly 
 had occasion to mention two other gasifiable compounds 
 (sulphur dioxide and sulphur trioxide). With our 
 
140 ELEMENTS OF CHEMISTRY. 
 
 present knowledge we are in a position to determine 
 the number of atoms of sulphur and of oxygen which 
 are combined in these two substances. 
 
 Sulphur Dioxide. Sulphur dioxide is produced by burning sul- 
 phur in oxygen ; and if care is taken to determine the relationship 
 between the volume of oxygen used in the combustion, and the 
 volume of sulphur dioxide produced, we shall arrive at the follow- 
 ing results : 
 
 When sulphur and oxygen unite to produce sulphur dioxide, 
 the volume of sulphur dioxide formed is the same as the volume 
 of oxygen with w r hich we started. (See page 54.) 
 
 As the volume of oxygen and sulphur dioxide are equal, it fol- 
 lows the sulphur dioxide must contain exactly as many molecules 
 as did the oxygen. Let us suppose that a volume of oxygen con- 
 tains one hundred molecules. Then the sulphur dioxide which 
 would be produced by burning sulphur in this same volume would 
 also contain one hundred molecules. It follows from this that 
 one molecule of sulphur dioxide contains one molecule of oxygen. 
 But as we have seen that one molecule of oxygen contains two 
 atoms, it follows that one molecule of sulphur dioxide has two 
 atoms of oxygen. We have decided that the atomic weight of 
 oxygen is 16, provided that of hydrogen be considered as one. 
 Therefore two atoms of oxygen, measured in the hydrogen stand- 
 ard, would weigh 32. Since sulphur dioxide has equal parts of 
 sulphur and of oxygen, we can say, in terms of the atomic theory, 
 that 32 parts of sulphur are joined to 32 parts of oxygen in sulphur 
 dioxide. Xow, it can be decided that 32 represents the weight of 
 one atom of sulphur, hydrogen representing unity ; for in no com- 
 pound of sulphur which is a gas, and the molecular weight of 
 which we consequently know, do we find less than 32 parts by 
 weight of sulphur in one molecule. The specific gravity of sul- 
 phur dioxide (hydrogen = 2) is 64. In 64 parts of sulphur diox- 
 ide there are 32 parts of sulphur and 32 of oxygen. It follows 
 from this that the atomic weight of sulphur cannot be more than 
 32, for otherwise we should have to accept the existence of a frac- 
 tion of an atom of sulphur in one molecule of sulphur dioxide. 
 Therefore, the composition of sulphur dioxide is such that one 
 atom of sulphur is joined to two atoms of oxygen in each mole- 
 
THE EXPRESSION OF CHEMICAL CHANGES. 141 
 
 cule. This result can be expressed by the following formula (in 
 which S represents one atom of sulphur) SO2- 
 
 Sulphur Trioxide. When sulphur dioxide is changed into sul- 
 phur trioxide, it adds oxygen in such quantity that the resulting 
 compound contains for every one part of sulphur, 1.5 parts by 
 weight of oxygen. Therefore (the 32 parts by weight of sulphur 
 in 64 of sulphur dioxide remaining unchanged), sulphur trioxide 
 contains 32 parts of sulphur to 48 of oxygen (1 : 1.5). Now, 32 
 represents the relative weight of a sulphur atom, measured in the 
 hydrogen standard, and 48 = (3 x 16) represents the relative weight 
 of three oxygen atoms. Hence a molecule of sulphur trioxide 
 contains, for every atom of sulphur, three atoms of oxygen. The 
 specific gravity of sulphur trioxide in the form of a gas is 80 
 (hydrogen = 2), so that its molecular weight is also 80 (H 2 = 2). 
 In 80 parts of sulphur trioxide there are 32 parts of sulphur and 
 48 parts of oxygen. A molecule of sulphur trioxide is therefore 
 represented by the formula SO 3 . 
 
 Formation of Sulphuric Acid from Sulphur Trioxide and Water. 
 Sulphur trioxide unites with water to produce sulphuric acid. 
 (See page 56.) This change is of such a nature that 80 parts 
 of sulphur trioxide take up 18 parts of water to produce 98 parts 
 of pure sulphuric acid. Eighty represents the relative weight of 
 one molecule of sulphur trioxide, and 18 that of one molecule of 
 water. This change can therefore- be represented as follows : 
 
 H 2 O + SO 3 H 2 S() 4 * 
 
 Sulphuric acid, therefore, contains, for every two atoms of hydro- 
 gen, one of sulphur, and four of oxygen. 
 
 Relative Atomic Weights of Sodium and Potassium. In 
 order to complete our understanding of the chemical 
 changes discussed in the preceding chapters, it is 'neces- 
 sary to determine the relative weights of the atoms of 
 potassium and sodium. This. is not easily accomplished 
 
 * In the member at the right of the sign of equality we have simply 
 added the two terms at the left. The masses of matter on both sides are 
 therefore equal. 
 
142 ELEMENTS OF CHEMISTRY. 
 
 for gasifiable compounds of the elements in question are 
 not to be obtained by simple means. However, sufficient 
 data are at hand to warrant our forming a conclusion. 
 
 An element known as iodine exists which is, in all of its chem- 
 ical aspects, similar to chlorine. Iodine forms a hydrogen com- 
 pound, hydrogen iodide, \vhich is a gas like hydrogen chloride. 
 Reasoning similar to that advanced under hydrogen chloride has 
 led us to the conclusion that one molecule of hydrogen iodide 
 contains one atom of hydrogen and one atom of iodine. The mo- 
 lecular weight of hydrogen iodide (H 2 = 2) is 127.5. This quan- 
 tity of hydrogen iodide contains one part of hydrogen and 12G.5 
 parts of iodine. Therefore, the relative weight of one atom of 
 iodine is 126.5, hydrogen being one. IS T ow, potassium reacts with 
 hydrogen iodide just as it does with hydrogen chloride, replacing 
 the hydrogen and producing potassium iodide. Potassium iodide, 
 when changed to a gas by great heat, has a specific gravity (hy- 
 drogen = 2) of 165.5, hence its molecular weight (H 2 = 2) is also 
 165.5. In 165.5 parts of potassium iodide there are 126.5 of 
 iodine (the proportional part representing one atom of iodine) and 
 39 parts of potassium. In the absence of any evidence to the 
 contrary, 39 may, therefore, be regarded as the relative weight of 
 one atom of potassium. 
 
 Action of Potassium and Sodium on Water in Terms of the 
 Atomic Theory. When potassium acts upon water, one-half the 
 hydrogen in the water attacked is replaced by potassium. An 
 analysis of the product (potassium hydroxide) shows us that 39 
 parts of the metal take the place of one part of hydrogen. If 39 
 and one represent the atomic weights of potassium and of hydro- 
 gen respectively, then one atom of potassium replaces one atom of 
 hydrogen in eacn molecule of water. This change can be repre- 
 sented as follows : 
 
 K + HOH KOH 4- H. 
 
 1 atom of potassium * + 1 mol. of water = 1 mol. of potassium hydroxide + 1 atom of hydrogen. 
 
 Potassium hydroxide, therefore, can be considered as water, in 
 each molecule of which one atom of hydrogen has been replaced 
 
 * K represents one atom of potassium, atomic weight 39. This sym- 
 bol is taken from the Latin Kalium. 
 
THE EXPEESSION OF CHEMICAL CHANGES. 143 
 
 by one atom of potassium. From the great similarity between 
 potassium hydroxide and sodium hydroxide, it may be presumed 
 that they are alike in their constitution. The latter then may be 
 regarded as water, in each molecule of which one atom of sodium 
 has taken the place of one atom of hydrogen. As 23 parts of 
 sodium replace one part of hydrogen, it may also be presumed that 
 the. atomic weight of sodium is 23 if that of hydrogen is one. 
 The action of sodium on water can, therefore, be represented as 
 
 follows : * 
 
 Xa 4- HOH = Na OH + H. 
 
 Neutralization of Hydrochloric Acid in Terms of the Atomic 
 Theory. When sodium hydroxide acts on hydrochloric acid the 
 latter is neutralized (see page 48), and the resulting salt (sodium 
 chloride) contains 23 parts of sodium for every 35.5 parts of chlo- 
 rine. These parts also represent the relative atomic weights of 
 sodium and chlorine, so that sodium chloride is produced by the 
 union of equal numbers of sodium and chlorine atoms, and its 
 formula is represented by Na Cl. The neutralization of sodium 
 hydroxide by hydrogen chloride can now be written in terms of 
 the atomic theory as follows : 
 
 Na OH + H Cl = Na Cl + HOH. 
 
 Adding the atomic weights of the members to the left of the sign 
 of equality, and doing the same with those on the right, we have 
 
 Sodium, atomic weight, 23 Sodium, atomic weight, 23 
 
 Oxygen, atomic weight, 16 Chlorine, atomic weight, 35.5 
 
 Hydrogen, atomic weight, 1 Sodium chloride, total, 58.5 
 
 Sodium hydroxide, total, 40 
 
 Chlorine, atomic weight, 35.5 Oxygen, atomic weight, 16 
 Hydrogen, atomic weight, 1 Hydrogen, two atoms, 2 
 Hydrochloric acid, total, 36.5 Water, total, 18 
 
 40 + 36.5 = 58.5 + 18. 
 
 According to this equation, therefore, 40 parts of sodium hydrox- 
 ide will exactly neutralize 36.5 parts of hydrochloric acid, produ- 
 cing 58.5 parts of sodium chloride and 18 parts of water. This 
 
 * The symbol Na represents one atom of sodium, atomic weight 23. 
 This symbol is taken from the Latin Natrium. 
 
144 ELEMENTS OF CHEMISTRY. 
 
 theoretical result is exactly in accordance with what we actually 
 found in the experiments on neutralization (see page 62). No 
 other conclusion is admissible, since the atomic theory to have 
 any stability must of necessity coincide with known facts. 
 
 Neutralization of Sulphuric Acid by Sodium and Potassium Hy- 
 droxide in Terms of the Atomic Theory. In neutralizing sulphuric 
 acid with potassium hydroxide or sodium hydroxide, we learned 
 that two salts of each metal could be produced. These salts were 
 designated as being primary and secondary. In the primary salt, 
 one-half the hydrogen of the combining sulphuric acid is replaced 
 by the metal (sodium or potassium). In the secondary salt, all the 
 hydrogen is so replaced. In terms of the atomic theory, we can 
 express these facts as follows : 
 
 1 ( Na OH 4- Ho SO 4 = ISTa HSO 4 + H 2 O. 
 
 I Na OH 4- Na HSO 4 = Na 2 SO 4 + H 2 O. 
 
 2 fKOH + H 2 S0 4 =KHS0 4 + H 2 0. 
 
 I KOH 4- KHSO 4 = K 2 SO 4 + H 2 O. 
 
 Adding the members to the right and those to the left of the sign 
 of equality as we did before, we have 
 
 Sodium, atomic weight, 23 Sodium, atomic weight, 23 
 
 Oxygen, atomic weight, 16 Sulphur, atomic weight, 32 
 
 Hydrogen, atomic weight, 1 4 atoms of oxygen, 64 
 
 Sodium hydroxide, total, 40 Hydrogen, atomic weight, 1 
 
 Primary sod. sulphate, total, 120 
 
 Sulphur, atomic weight, 32 
 
 4 atoms of oxygen, 64 Oxygen, atomic weight, 1 6 
 
 2 atoms of hydrogen, 2 2 atoms of hydrogen, 2 
 
 Sulphuric acid, total, 98 Water, total, 18 
 
 and 40 4- 98 = 120 4- 18. 
 
 In forming the secondary sulphate of sodium, we would, therefore, 
 
 have 
 
 Sodium hydroxide, 80 parts by weight, 
 Sulphuric acid, 98 parts by weight, 
 Secondary sodium sulphate, 142 parts by weight, 
 Two molecules of water, 36 parts by weight, 
 
 and 
 
 80 4- 98 = 142 + 36. 
 
THE EXPRESSION OF CHEMICAL CHANGES. 145 
 
 So that 40 and 80 parts of sodium hydroxide are capable of 
 reacting with 98 parts of sulphuric acid to produce 120 and 142 
 parts of the primary and the secondary sulphate of sodium re- 
 spectively. These results are in accordance with those which we 
 found experimentally on page 63. With potassium hydroxide 
 and sulphuric acid we have 
 
 Potassium, atomic weight, 39 Potassium, atomic weight, 39 
 
 Oxygen, atomic weight, 16 Sulphur, atomic weight, 32 
 
 Hydrogen, atomic weight, 1 4 atoms of oxygen, 64 
 
 Potassium hydroxide, total, 56 Hydrogen, atomic weight, 1 
 
 Potass, pr. sulphate, total, 136 
 Sulphur, atomic weight, 32 
 
 4 atoms oxygen, 64 Oxygen, atomic weight, 16 
 
 2 atoms of hydrogen. 2 2 atoms of hydrogen, 2 
 
 Sulphuric acid, total, "98 Water, total, 18 
 
 56 + 98 = 136 -f 18. 
 
 In forming the secondary sulphate of potassium we should, there- 
 fore, have 
 
 Potassium hydroxide, 112 parts, 
 
 Sulphuric acid, 98 parts, 
 
 Secondary potassium sulphate, 174 parts, 
 
 Two molecules of water, 36 parts, 
 
 112 + 98 = 174 + 36. 
 
 So that 56 and 112 parts of potassium hydroxide are capable of 
 reacting with 98 parts of sulphuric acid to produce 136 and 174 
 parts of the primary and secondary sulphate of potassium respec- 
 tively. These results are in accordance with those which we 
 found experimentally on page 63. 
 
 Formation of Ammonium Chloride in Terms of the Atomic 
 Theory. The only remaining compound which was discussed at 
 length in the preceding work is ammonium chloride. This sub- 
 stance is produced by the union of equal volumes of ammonia and 
 hydrogen chloride, therefore it is formed from equal numbers of 
 molecules of ammonia and hydrogen chloride. In other words, 
 one molecule of ammonia with one molecule of hydrogen chloride 
 forms one molecule of ammonium chloride. Under proper condi- 
 
146 
 
 ELEMENTS OF CHEMISTRY. 
 
 tions ammonium chloride can be vaporized without change. Its 
 specific gravity (hydrogen = 2) is then 53.5, so that its molecular 
 weight is also 53.5. In this 5.35 parts of ammonium chloride 
 there are 14 of nitrogen, 4 of hydrogen, and 35.5 of chlorine. 
 The composition of one molecule of ammonium chloride can, 
 therefore, be represented by the formula NH 4 Cl, and its forma- 
 tion from ammonia and hydrogen chloride as follows : 
 
 NH 3 + H Cl = NH 4 Cl. 
 
 The group of elements NH 4 , composed of one atom of nitrogen 
 and four of hydrogen, is the one which under the name of am- 
 monium can take the place of one atom of potassium or sodium 
 in chemical compounds. (See page 99.) 
 
 Table of Atomic Weights and Formulae of Compounds 
 already studied. The atomic weights of the elements 
 which we have encountered, the formulae of the com- 
 pounds, and the reactions leading to their formation, 
 are summed up in the following table : 
 
 HYDROGEN ATOMIC WEIGHT = 1. 
 
 ELEMENTS. 
 
 SYMBOLS. 
 
 ATOMIC 
 WEIGHTS. 
 
 COMPOUNDS. 
 
 FORMULA. 
 
 COMPOSITION BY 
 WEIGHT. 
 
 Chlorine 
 
 Cl 
 
 35.5 
 
 Hydrogen chloride 
 
 HC1 
 
 1 of hydrogen, 35.5 of 
 
 
 
 
 
 
 chlorine. 
 
 Oxygen 
 
 
 
 16 
 
 Water 
 
 H 2 
 
 2 of hydrogen, 16 of 
 
 
 
 
 
 
 oxygen. 
 
 Nitrogen 
 
 N 
 
 14 
 
 Ammonia 
 
 H 3 N 
 
 3 of hydrogen, 14 of ni- 
 
 
 
 
 
 
 trogen. 
 
 Sodium 
 
 Na 
 
 23 
 
 Sodium hydroxide 
 
 NaOH 
 
 23 of sodium, 16 of oxy- 
 
 
 
 
 
 
 gen, 1 of hydrogen. 
 
 Potassium 
 
 K 
 
 39 
 
 Potassium 
 
 KOH 
 
 39 of potassium, 16 of 
 
 
 
 
 
 
 oxygen, 1 of hydro- 
 
 
 
 
 
 
 gen. 
 
 
 
 
 1 Sulphur dioxide 
 
 S0 2 
 
 32 of sulphur, 32 of oxy- 
 
 
 
 
 
 
 gen. 
 
 
 
 
 Sulphur trioxide 
 
 S0 3 
 
 32 of sulphur, 48 of oxy- 
 
 Sulphur 
 
 S 
 
 32 
 
 
 
 gen. 
 
 
 
 
 Sulphuric acid 
 
 H 2 S0 4 
 
 32 of sulphur, 64 of oxy- 
 
 
 
 
 
 
 gen, 2 of hydrogen. 
 
 
 
 
 Ammonium chloride 
 
 NH 4 C1 
 
 14 of nitrogen, 35.5 of 
 
 
 
 
 
 
 chlorine, 4 of hydro- 
 
 
 
 
 
 
 gen. 
 
THE EXPRESSION OF CHEMICAL CHANGES. 147 
 REACTIONS. 
 
 Na + HOH = Na OH + H. . 
 
 Action of sodium on water, 1 atom of sodium replacing 1 atom hydrogen. 
 
 K + HOH = KOH + H. 
 
 Action of potassium on water, 1 atom of potassium replacing 1 atom hydrogen. 
 
 Na OH + H 2 SO 4 = Na HSO 4 + H 2 O. 
 
 Action of sodium hydroxide on sulphuric acid, 1 atom of sodium replacing 1 atom hydrogen. 
 
 2 Na OH + H 2 SO 4 = Na 2 SO 4 + 2 H 2 O. 
 
 Action of sodium hydroxide on sulphuric acid, 2 atoms of sodium replacing 2 atoms hydrogen. 
 
 KOH + H 2 SO 4 KHSO 4 + H 2 O. 
 
 Action of potassium hydroxide on sulphuric acid, 1 atom of potassium replacing 1 atom hydrogen. 
 
 2 KOH + H 2 SO 4 = K 2 SO 4 + 2H 2 O. 
 
 Action of potassium hydroxide on sulphuric acid, 2 atoms of potassium replacing 2 atoms hydrogen. 
 
 NH 3 + H Cl = NH 4 Cl. 
 
 Action of ammonia on hydrogen chloride, forming ammonium chloride. 
 
 Meaning and Uses of Chemical Equations. The changes 
 taking place during chemical reactions can, as we have 
 seen, be expressed in the form of equations. To the 
 left of the sign of equality are those substances which 
 are about to react with each other, to the right are the 
 new and more stable bodies which result from those 
 reactions. The same elements appear in both. These 
 equations represent what takes place between the small- 
 est particles of the substances taking part in the chemi- 
 cal changes. As what is true of these smallest particles 
 must also be true of the large masses which are com- 
 posed of them, it follows that these equations also 
 represent the changes which take place in visible por- 
 tions of matter. As the symbols of the various ele- 
 ments represent the relative atomic weights of these 
 elements, the equations must represent both the relative 
 weights of the substances which are reacting, and the 
 relative weights of the masses handled. In practice 
 there is frequently present an excess of one or the 
 other of the substances undergoing chemical change ; 
 but as such an excess does not enter into the chemical 
 formation of the compound produced, it need not be 
 
ft 
 
 148 ELEMENTS OF CHEMISTRY. 
 
 considered in the notation. One serious defect is evi- 
 dent in equations such as we have considered, they 
 do not take cognizance of the changes of energy during 
 chemical reactions. They simply concern themselves 
 with the reacting masses. Nevertheless, they give us 
 a short and convenient way of illustrating one of the 
 main features of the various chemical changes, and 
 involve a considerable saving in time. Two things 
 must be borne in mind ; first, chemical notation and 
 chemical equations are not absolutely essential to an 
 understanding of chemical change ; secondly, chemical 
 equations must be used to express only those reactions 
 which have actually been studied. They are merely 
 brief and convenient ways of expressing knowledge 
 already acquired by experiment. The careful study of 
 all the phenomena attending a chemical change must 
 be carried out before the results of such a study can 
 properly be brought in the form of a chemical equation. 
 
 Summary. 
 
 The changes taking place during chemical reactions 
 can be expressed in the form of equations. These equa- 
 tions do not consider either the excess of one or the other 
 of the reacting bodies, or the changes of energy which 
 take place during reactions. They do, however, express 
 the masses of the bodies undergoing chemical change, 
 and these masses must be in accordance with facts which 
 have been experimentally proven. The reactions which 
 have been encountered in this book are given, in the 
 form of equations, on pages 143, 144, and 147. 
 
 Having discussed the atomic theory, the next step in 
 the work is to consider the chemistry of another ele- 
 ment, and of its compounds. 
 
CAEBON. 149 
 
 CHAPTER XIX. 
 
 CARBON. 
 
 CAEBON is one of the most important chemical ele- 
 ments. In nature it occurs uncombined in three modi- 
 fications, two of which (diamond and graphite) are of 
 crystalline structure, while the third is not crystalline 
 (coal, charcoal, lamp-black, etc.). 
 
 Various Modifications of Carbon. That all these forms 
 are really modifications of the same element is proved 
 by the fact that they all yield the same substance (car- 
 bon dioxide) when they are burned in oxygen. By 
 proper means, not-crystalline carbon can be regained 
 from carbon dioxide, no matter whether it has been 
 formed by the combustion of diamond, graphite, or 
 coal. 
 
 Diamond. The diamond is an extremely hard sub- 
 stance, very often transparent, with a great power of 
 refracting light, and brilliant lustre when polished. 
 Not-transparent black diamond is also found.* When 
 heated in the air to a bright white heat, diamond burns, 
 forming carbon dioxide, and leaving only a slight trace 
 of ash. The diamond may be classed among the rare 
 minerals. 
 
 * Diamonds were originally imported into Europe from the East Indies. 
 From this portion of the,world and from Borneo came the only specimens 
 known until the year 1727, when large diamond fields were discovered in 
 Brazil. In 1867 the diamond fields of South Africa were opened. 
 
150 ELEMENTS OF CHEMISTRY. 
 
 Graphite. Graphite (also called plumbago or black 
 lead) is the second crystalline form of carbon. Some- 
 times graphite is found in a pure state, as in some parts 
 of Ceylon, where beds of from twenty to thirty feet in 
 thickness occur. Sometimes it is very impure, being 
 mixed with so much foreign material that it is entirely 
 unfit for use. Graphite may be artificially prepared by 
 the crystallization of carbon from melted iron. It then 
 can be separated in the form of small, delicate scales 
 when the iron is dissolved away by acids. Graphite is 
 used in the manufacture of lead pencils, in making infu- 
 sible crucibles, and as a lubricator. It is adapted to the 
 latter purpose because it is soft and scaly. It is grayish- 
 black in color, and has almost a metallic lustre. When 
 burned in the air it forms carbon dioxide, and leaves an 
 ash which varies in quantity according to the amount 
 of impurity originally present. 
 
 Decomposition of Animal and Vegetable Substances. The 
 compounds formed in animal and vegetable organisms, 
 and classed under the general head of organic sub- 
 
 ^. ^ . 
 
 stances, are produced by the union of very few ele- 
 ments, namely, carbon, hydrogen, oxygen, nitrogen, 
 sulphur, and phosphorus, although occasionally other 
 elements are found. When exposed to the action of 
 moisture and of the air, organic substances are com- 
 pletely decomposed, changing for the most part into 
 gaseous products (carbon dioxide, ammonium com- 
 pounds, etc.). Vegetable fibres when protected by a 
 layer of water or of earth, so that an insufficient supply 
 of oxygen is present, decompose very slowly, certain 
 constituents, especially oxygen and hydrogen, pass off 
 in other combinations, and the vegetable matter be- 
 
CARBON. 151 
 
 comes changed, first into peat, and then into bituminous 
 (soft) coal. At the same time the percentage of car- 
 bon increases. Peat, brown coal, bituminous coal, and 
 anthracite coal are successive steps in the process of 
 vegetable decomposition. When the anthracite stage is 
 reached, the changes have become so complete that a 
 black, shiny, homogeneous mass remains, and the origi- 
 nal vegetable structure has entirely disappeared, or be- 
 come so indistinct that special means must be taken for 
 its detection. The pressure to 'which the dead organic 
 structures are subjected has a material influence on the 
 rapidity with which a peat formation is changed to 
 anthracite. In districts of Russia where there has not 
 been great pressure, a brown coal (lignite), scarcely to 
 be distinguished from peat, is found in places where the 
 age of the deposit would lead one to expect anthracite. 59 * 
 
 Formation of Coke. Changes similar to those produced 
 in the transformation of vegetable matter into coal can 
 be brought about by heating the same class of sub- 
 stances in retorts, if the air is excluded. By means 
 of this process, certain portions pass off as gases and 
 liquids,! while* a not-crystalline variety of carbon is 
 
 * The following table illustrates the increase in the percentage of car- 
 bon during the change from wood to anthracite coal. This table takes 
 into consideration only the combustible materials, and not the ash : 
 Wood contains 50 pei cent of carbon, 6 per cent of hydrogen, and 44 per cent 
 
 of oxygen and nitrogen. 
 Peat contains 60 per cent of carbon, 5.7 per cent of hydrogen, and 34.3 per cent 
 
 of oxygen and nitrogen. 
 Bituminous coal contains 87 per cent of carbon, 5.6 per cent of hydrogen, 
 
 and 7.4 per cent of oxygen and nitrogen. 
 Anthracite contains 94 per cent of carbon, 3.4 per cent of hydrogen, and 2.6 
 
 per cent of oxygen and nitrogen. 
 
 t Gaseous products, Illuminating gas, ammonia, sulphuretted hy- 
 drogen, etc. 
 
 Liquid products, Water, benzene, toluene, carbolic acid, etc. 
 Solid products, Naphthaline, anthracene, etc. 
 
152 ELEMENTS OF CHEMISTRY. 
 
 left behind as a black shiny mass termed coke. The 
 commercial production of coke is generally brought 
 about by heating bituminous coal. 
 
 Charcoal. Wood charcoal is produced by the imper- 
 fect combustion of wood, animal charcoal, by a similar 
 treatment of animal refuse. All forms of charcoal have 
 a remarkably pronounced tendency to absorb coloring 
 matters from solutions. 60 
 
 Lamp-black. The purest form of not^crystalline car- 
 bon is lamp-black. This results when carbon and hy- 
 drogen compounds are burned in an imperfect supply 
 of oxygen. The lamp-black of commerce is obtained by 
 burning resinous pine wood, tar, or some kinds of bi- 
 tuminous (soft) coal. The substance is collected on 
 coarse cloths hung over the burning wood, which is 
 placed in suitable chambers. Lamp-black is used in 
 the manufacture of India ink and printers' ink. 
 
CARBON DIOXIDE. 153 
 
 CHAPTER XX. 
 
 CARBON DIOXIDE 
 
 CARBON is capable of forming two oxides which are 
 distinguished by the terms carbon monoxide and carbon 
 dioxide. Of these the latter is the easier to produce 
 and study. A consideration of the former will be post- 
 poned to a subsequent chapter. 
 
 Formation of Carbon Dioxide and the Formula for one 
 Molecule of Carbon Dioxide. When carbon is burned in 
 the air or in oxygen, it unites with the oxygen to pro- 
 duce a colorless gas which is an oxide of carbon. If 
 the combustion takes place in a closed space, so that 
 the volume of gas present at the beginning of the opera- 
 tion and at the end can be carefully measured, it will 
 be seen that no change in the total volume has oc- 
 curred. 61 All of the oxygen has been consumed, and 
 carbon dioxide has taken its place. A similar result, 
 it will be remembered, was encountered in studying 
 the formation of sulphur dioxide (see page 54). We 
 are, therefore, justified in drawing similar conclusions 
 as to the structure of the carbon dioxide molecules. 
 We can assume that as there is no change in the total 
 volume of gas, and no change in the total number of 
 molecules, then n molecules of oxygen, as a consequence, 
 produce n molecules of carbon dioxide, and (if n = 1) 
 one molecule of oxygen enters into the formation of one 
 
154 ELEMENTS OF CHEMISTRY. 
 
 molecule of carbon dioxide. Since one molecule of 
 oxygen contains two atoms, it must follow that one 
 molecule of carbon dioxide also contains two atoms of 
 oxygen. The specific gravity of carbon dioxide (hy- 
 drogen = 2) is 44. Its molecular weight (H 2 = 2) is 
 also 44. In 44 parts of carbon dioxide there are 32 of 
 oxygen and 12 of carbon. Therefore, 12 represents the 
 maximum atomic weight of carbon, provided that of 
 hydrogen is one. That 12 is also the minimum atomic 
 weight is probable from the fact that no gasifiabLe car- 
 bon compound contains less than 12 parts of carbon 
 (measured in the hydrogen standard) in one molecule. 
 The 12 parts of carbon in the molecule of carbon diox- 
 ide, therefore, represent one atom of carbon, and the 
 32 parts of oxygen represent two atoms of oxygen, and 
 the formula for carbon dioxide is CO 2 . This formula, 
 is, therefore, parallel to that for sulphur dioxide : 
 
 C0 2 S0 2 
 
 Carbon dioxide, Sulphur dioxide. 
 
 Preparation of Carbon Dioxide. If an iron tube in which are 
 placed pieces of charcoal be heated in a furnace, and pure oxygen 
 be then passed over the hot carbon, the carbon dioxide which is 
 formed can be collected in bottles. This gas has a higher spe- 
 cific gravity than the atmosphere, and consequently will flow down- 
 ward, just as a liquid would. 62 
 
 Properties of Carbon Dioxide. Carbon dioxide is a colorless gas 
 with a specific gravity (air= 1) of 1.529 or (H 2 = 2) of 44. The 
 latter number is a}so its molecular weight. Because carbon diox- 
 ide has such a high specific gravity, it can be poured downward 
 from any vessel containing it. For this reason it collects at the 
 bottoms of wells or mines into which the gas is escaping. Carbon 
 dioxide does not burn in oxygen, neither does it give up any por- 
 tion of its oxygen readily enough to support combustion. Cold 
 and pressure combined can condense it to a liquid which boils at 
 
CARBON DIOXIDE. 155 
 
 78.2. Its vapor tension (see page 70) at is 36 atmospheres, 
 its critical temperature * is 39.9, and its vapor pressure at this 
 point is 73 atmospheres. When carbon dioxide is rapidly evapo- 
 rated in a vacuum, its temperature sinks to 97, and it then 
 changes to a snow-like solid. Any considerable increase in the 
 quantity of carbon dioxide normally present in the air (3 parts in 
 10,000, see page 84) causes a marked feeling of discomfort to 
 those breathing it, and a proportion of approximately 10 per cent 
 will cause death. The reason for this is that the pressure of car- 
 bon dioxide in the inhaled air is equal to that of the carbon diox- 
 ide passing off from the lungs. When this condition is reached, 
 no elimination of carbon dioxide can take place, the normal pro- 
 cesses of life are interfered with, and the animal dies. Plants, 
 when placed in the sunlight, are, on the other hand, capable of ab- 
 sorbing carbon dioxide, changing it into new compounds of car- 
 bon (which form a portion of their tissues), and eliminating a 
 portion of the oxygen. One cubic centimetre of water can dis- 
 solve about its own volume of carbon dioxide at ordinary tem- 
 peratures. 
 
 Formation of Carbonates from Carbon Dioxide and Bases. If 
 carbon dioxide is passed into a solution of potassium hydroxide, 
 complete absorption takes place. If this operation is continued 
 until the base has taken up all the gas which it possibly can, and 
 if the excess of water used for solution is then evaporated, there 
 remains a salt-like body which differs entirely from potassium 
 hydroxide. If a little of this salt is placed in a test-tube, and 
 some solution of hydrochloric acid is added, a violent evolution of 
 gas will take place. This gas will neither burn nor support com- 
 bustion, and in all its properties is identical with carbon dioxide. 
 We find, therefore, that carbon dioxide can unite directly with 
 potassium hydroxide to produce a new body. By carefully meas- 
 uring the quantity of carbon dioxide obtained from a given weight 
 of this body by adding hydrochloric acid, we learn that exactly 
 44 parts of carbon dioxide (representing one molecule) have united 
 with 56 parts of potassium hydroxide (represented by the formula 
 
 * I.e., the temperature above which no pressure can convert it to a 
 liquid. 
 
156 ELEMENTS OF CHEMISTRY. 
 
 KOH, see page 142). The reaction which takes place can be rep- 
 resented as follows : 
 
 KOH + C0 2 = KHC0 3 
 
 potassium hj'droxide + carbon dioxide = The product of addition. 
 56 parts -f 44 parts = 100 parts. 
 
 If, now, two grams of this salt are placed in a test-tube of infu- 
 sible glass, and then gently heated to below red heat, a gas will pass 
 off which can be shown to have the properties of carbon dioxide. 
 At the same time water is formed, as can be seen by the drops of 
 that liquid collected on the sides of the tube in which the salt is 
 heated. After no more carbon dioxide passes off, the water can be 
 removed by placing the tube in an air-bath heated to about 150. 
 After cooling, the two grams of the salt will be found to have lost 
 .62 grams of carbon dioxide and water, while 1.38 grams of a sec- 
 ond salt-like body will remain. This body, on addition of hydro- 
 chloric acid, will give off a gas, which is carbon dioxide. In this 
 respect it resembles the first salt which was formed. The change 
 taking place on heating can therefore be represented as follows : 
 
 KHCO 3 = KjCOs + H 2 O + CO 2 
 
 2.00 parts = 1.38 parts of the second salt + .18 parts of water + .44 parts of carbon dioxide.ea 
 
 The Primary and Secondary Carbonates of Potassium are 
 Salts of an Acid, H 2 C0 3 . The two salt-like bodies pro- 
 duced, first by the addition of carbon dioxide to potas- 
 sium hydroxide, and second by heating the substance so 
 formed, can be considered as derived from an acid to 
 which we assign a formula, H 2 CO 3 . This acid does 
 not in reality exist. Whenever any attempts have been 
 made to isolate it as a chemical individual, it has at 
 once broken down into water and carbon dioxide. The 
 salts produced by substituting metals for the hydrogen 
 of this acid are, however, as we have seen, permanent. 
 This acid is termed carbonic acid, and the salts derived 
 from it by substituting metals for the hydrogen are 
 called carbonates. The two bodies just examined are, 
 therefore, primary and secondary potassium carbonates. 
 The former is produced by replacing one-half of the 
 
CARBON DIOXIDE. 157 
 
 hydrogen in a given quantity of carbonic acid by the 
 metal potassium, and the latter by replacing all of the 
 hydrogen in the same way. The learner will recall in 
 the discussion of a similar case the primary and second- 
 ary sulphates (see pages 60 and 61), and the formation 
 of the two carbonates of potassium can be compared to 
 the neutralization of sulphuric acid by potassium hy- 
 droxide. This relationship will be made clearer if we 
 compare the formulae assigned to the sulphates of 
 potassium with those just given for the carbonates: 
 
 KHSO 4 , primary sulphate of potassium. 
 K 2 SO 4 , secondary sulphate of potassium. 
 KHCO 3 , primary carbonate of potassium. 
 K 2 CO 3 , secondary carbonate of potassium. 
 
 Difference between the Primary and Secondary Salts of 
 Potassium. The primary potassium salts are those in 
 which one part of hydrogen in the acids has been re- 
 placed by 39 parts of potassium, and the secondary salts 
 are those in which two parts of hydrogen have been 
 replaced by 78 (2x39) parts of potassium. The pri- 
 mary sulphate of potassium is converted into the second- 
 ary sulphate (page 59) by the addition of potassium 
 hydroxide. If the relationship between the carbonates 
 and the sulphates is to hold good, it must therefore fol- 
 low that the primary carbonates can be converted into the 
 secondary by similar means. That this is the case can 
 easily be shown by dissolving one gram of the primary 
 carbonate in a little water, and then adding .56 grams * 
 
 * This quantity, in centigrams, represents the sum of the atomic 
 weights of potassium, oxygen, and hydrogen, which go to form potassium 
 hydroxide (see page 145). 
 
 potassium, atomic weight, 39 
 
 oxygen, atomic weight, 16 
 
 hydrogen, atomic weight, _^ 
 
 Total, 56 
 
158 ELEMENTS OF CHEMISTRY. 
 
 of potassium hydroxide.* On evaporating the excess of 
 water from the solution, a salt will remain, which, on 
 addition of hydrochloric acid, gives off carbon dioxide, 
 but which does not evolve that gas on heating. In 
 short, it has all of the properties of the secondary car- 
 bonate. 
 
 The above change can, therefore, be represented in chemical 
 formulae as follows : 
 
 KOH + KHCO 3 K 2 CO 8 +H 2 O 
 
 Potassium hydroxide + Primary potassium carbonate = Secondary potassium carbonate + Water. 
 56 parts + 100 parts 133 parts + 18.parts. 
 
 The primary carbonate of potassium can, therefore, 
 be converted into the secondary by the addition of 
 potassium hydroxide, just as the primary sulphate is 
 converted into the secondary by the same means. 64 
 
 Occurrence of the Carbonate of Potassium. The secondary car- 
 bonate of potassium occurs as one of the constituents of the ashes 
 of land plants, from which it can be extracted by means of water. 
 As this operation was usually performed in iron pots or kettles, 
 the name potash was given to potassium carbonate; and since 
 potassium hydroxide is prepared from the latter, the term caustic 
 potash was brought into use to designate the hydroxide. 
 
 Formation of the Primary and Secondary Carbonates of Sodium. 
 The sodium carbonates are chemically closely related to those of 
 potassium. If, then, in the above reactions, we had made use of 
 sodium hydroxide, instead of potassium hydroxide, the result would 
 have been identical ; except that the primary and secondary car- 
 bonates of sodium would have taken the place of those of potas- 
 sium. The chemical formulae of these two substances would 
 therefore be Na IICO 3 and Na 2 CO 3 , and they would be produced 
 as follows : 
 
 * This should be in the form of a solution where one cubic centimetre 
 contains .05(5 grams of potassium hydroxide. The solution can be meas- 
 ured in a burette (see page 49, and Experiment 27 of the Appendix). 
 
C A UK ON DIOXIDE. 159 
 
 NaOH* + CO 2 = NaHCO 3 . 
 
 Sodium hydroxide + Carbon dioxide = Primary sodium Carbonate. 
 40 parts + 44 parts = 84 parts. 
 
 Na HCO 3 + Na OH Na CO 3 + H 2 0. 
 
 Primary sodium carbonate + Sodium hydroxide = Secondary sodium carbonate + Water. 
 &i parts + 40 parts = 124 parts + 18 parts. 
 
 Sodium carbonate is commercially more important than potas- 
 sium carbonate, as it is used extensively in the arts, and in the 
 preparation of soap and of glass. 
 
 Occurrences of Calcium Carbonate, Magnesium Carbonate, and 
 Carbonate of Iron. The carbonates of several other metals are 
 extensive and valuable mineral constituents of the earth's crust. 
 The carbonate of calcium occurs in a massive, not-crystalline form, 
 as limestone, in blocks formed of minute, not-separable crystals, as 
 marble, and in well-formed, often transparent crystals, as calcite, 
 peculiarly developed forms of which are termed Iceland spar. 
 The shells of mollusks, and the protective coating of many infuso- 
 ria, consist largely of calcium carbonate. 
 
 Magnesium carbonate, as the mineral magnesite, occurs in ex- 
 tensive deposits. Magnesium and calcium carbonates (dolomite) 
 is the chief mineral in a range of mountains in the Alps. The 
 carbonate of iron is valuable as an ore. 
 
 Preparation of Carbon Dioxide by the Action of Acids on 
 Carbonates. All of the carbonates are more or less 
 readily decomposed by acids. The result in each case 
 is the production of the salt of the acid which is used 
 with the metal contained in the carbonate. At the 
 same time carbon dioxide and water are formed. We 
 found this to be the case in studying potassium carbon- 
 ate, and an examination of other carbonates will show 
 the same result. For example, calcium carbonate with 
 
 * NaOH represents: 
 
 One atom of sodium, atomic weight, 23 
 
 One atom of oxygen, atomic weight, 16 
 
 One atom of hydrogen, atomic weight, 1 
 
 Total, 40 
 
 (See page 143.) 
 
160 ELEMENTS OF CHEMISTRY 
 
 hydrochloric acid, forms calcium chloride, carbon diox- 
 ide, and water. 
 
 Calcium carbonate, in the form of marble, can be easily han- 
 dled in the laboratory. It is so readily attacked by hydrochloric 
 acid that the reaction just given is the one universally employed 
 in preparing carbon dioxide for laboratory use. 65 
 
 Most Carbonates are Insoluble in Water. Formation of 
 the Soluble Primary Carbonate of Calcium from the Insoluble 
 Secondary. The carbonates "of most metals do not dis- 
 solve in water. In our present work we may consider 
 that only the carbonates of potassium and of sodium are 
 soluble. As an illustration we can show that if carbon 
 dioxide is passed into a solution of calcium hydroxide 
 (lime-water), the insoluble carbonate of calcium separates 
 as a white powder. If, however, gas is added after 
 the separation of the calcium carbonate is completed, 
 the latter substance will gradually dissolve in the ex- 
 cess of carbon dioxide solution, because the primary 
 carbonate of calcium (which is soluble in water) is pro- 
 duced by this means. When the solution so formed is 
 boiled, carbon dioxide passes off, and the insoluble sec- 
 ondary carbonate of calcium is again produced. This 
 happens because primary calcium carbonate is less stable 
 than primary potassium carbonate, and hence it decom- 
 poses at a lower temperature. This change is parallel 
 to the decomposition of primary potassium carbonate 
 by heat, which we studied at the beginning of this 
 chapter. 66 
 
 Occurrence of the Primary Calcium Carbonate in Spring and River 
 Water. Owing to the action of carbon dioxide on the carbonate 
 of calcium, which, in the form of mineral deposits, constitutes a 
 large portion of the beds of springs and rivers, part of the lime- 
 stone is dissolved as primary calcium carbonate. Water, which 
 
CARBON DIOXIDE. 161 
 
 contains this substance in solution, will, when boiled, deposit sec- 
 ondary calcium carbonate on the walls of the kettle. This phe- 
 nomenon is always observed where hard water is boiled. In 
 addition to the primary calcium carbonate, calcium sulphate, 
 which is also slightly soluble in water, is generally found in 
 spring and river water. This substance is not separated by boil- 
 ing. Waters which contain either primary calcium carbonate, or 
 calcium sulphate, or both, are termed hard waters. Those which 
 have only primary calcium carbonate are temporary hard waters, 
 for this constituent can be removed by boiling; those which 
 contain calcium sulphate are permanent hard waters. 
 
 Summary. 
 
 1. When carbon is burned in the air, carbon dioxide 
 is produced. 
 
 2. Carbon dioxide, in each molecule, contains one 
 atom of carbon and two of oxygen. Its formula is 
 C0 2 . 
 
 3. Carbon dioxide is absorbed by potassium hydrox- 
 ide. When a solution of potassium hydroxide is com- 
 pletely saturated by carbon dioxide, it contains primary 
 potassium carbonate, the formula of which is KHCO 3 . 
 
 4. When the primary carbonate of potassium is 
 heated, or when potassium hydroxide is added to it, it 
 is changed into the secondary carbonate of potassium, 
 the formula of which is K 2 CO 3 . There is also a pri- 
 mary and a secondary carbonate of sodium to which 
 respectively the formulae Na HCO 3 and Na 2 CO 3 can be 
 assigned. 
 
 5. The carbonates of a number of other metals (cal- 
 cium, magnesium, iron) form extensive mineral de- 
 posits. These carbonates are insoluble in water, while 
 those of potassium and sodium are soluble. The car- 
 bonates, on addition of acids, liberate carbon dioxide. 
 
162 ELEMENTS OF CHEMISTRY. 
 
 6. The primary carbonates are all soluble in water. 
 The above insoluble minerals are, therefore, partly 
 brought into solution by the combined action of water 
 and the dissolved carbon dioxide. 
 
 7. When the water containing them is boiled, these 
 primary carbonates are decomposed, and the insoluble 
 secondary carbonates are deposited. From primary 
 calcium carbonate in temporary hard water, a deposit 
 of secondary calcium carbonate is produced. 
 
CARBON MONOXIDE AND METHANE. 163 
 
 CHAPTER 
 
 CARBON MONOXIDE AND METHANE 
 (HYDROGEN CARBIDE). 
 
 THE second oxide of carbon is carbon monoxide. 
 This gas is easily produced by taking away a portion of 
 the oxygen from carbon dioxide. 
 
 Preparation and Properties of Carbon Monoxide. If carbon diox- 
 ide is passed through an iron tube containing pieces of charcoal 
 heated to redness, and then into bottles rilled with water and in- 
 verted over a vessel filled with the same liquid, the gas collected 
 will differ from carbon dioxide. It will not be absorbed by the 
 potassium hydroxide as carbon dioxide is ; it will burn in the air 
 when a lighted taper is applied to the mouth of the jar containing 
 it ; and it is scarcely soluble in water. This new gas is termed 
 carbon monoxide. It is intensely poisonous. Its specific gravity 
 (hydrogen = 2) is 28, its molecular weight (H 2 = 2) is also 28. 
 In 28 parts there are 12 of carbon and 16 of oxygen. These 
 numbers, as we have seen, represent the relative atomic weights 
 of carbon and oxygen respectively, so that one molecule of carbon 
 monoxide contains one atom of carbon and one of oxygen. Its 
 structure can therefore be represented by the formula CO. 67 
 
 Reduction. The process of taking away oxygen from 
 carbon dioxide to form carbon monoxide is the reverse 
 of the oxidation by which carbon monoxide is converted 
 into carbon dioxide. Such a process, in chemical lan- 
 guage, is termed reduction. 
 
 Change in Energy when Carbon Monoxide burns to form 
 Carbon Dioxide. When carbon monoxide burns, a large 
 
164 ELEMENTS OF CHEMISTRY. 
 
 amount of heat is given off. The carbon dioxide pro- 
 duced, therefore, possesses less chemical energy than 
 the monoxide. We can determine the total amount of 
 heat evolved in burning a given weight of carbon. We 
 can also ascertain the total heat produced when carbon 
 monoxide, containing the same weight of carbon, is con- 
 verted into carbon dioxide. The difference between 
 these two quantities must necessarily give us the heat 
 given off in forming the equivalent amount of carbon 
 monoxide.* By this means it has been ascertained 
 that carbon, in being partially oxidized to carbon mon- 
 oxide, gives off kinetic energy, and that the resulting 
 gas contains less chemical energy than did its original 
 constituents, carbon and oxygen. Furthermore, carbon 
 monoxide, in burning to carbon dioxide, again gives off 
 energy. The energy changes attending the formation 
 of carbon dioxide can, therefore, be considered as 
 taking place in two stages ; but the total amount of 
 kinetic energy evolved when a given weight of carbon 
 burns to carbon dioxide is the same as if the same 
 amount were first changed to carbon monoxide and then 
 to carbon dioxide. The total kinetic energy manifested 
 during a chemical change is, therefore, independent of 
 the intermediary bodies which may be formed. This is 
 exactly the case with a weight which is allowed to fall 
 from a certain height to the ground. The total energy 
 given off is obviously the same, no matter whether it Jbe 
 allowed to descend without interruptions, or whether it 
 be stopped at intervals.. It will obviously require the 
 same amount of energy to bring it back to its original 
 position, no matter what were the circumstances attend- 
 ing its fall. 
 
 * I.e., the amount of carbon monoxide containing the above given 
 weight of carbon. 
 
CARBON MONOXIDE AND METHANE. 165 
 
 Far more important than carbon monoxide, for the 
 purposes of our present work, is the hydrogen com- 
 pound of carbon which is known as methane, or hydro- 
 gen carbide. 
 
 Methane; Natural Occurrence and Formation. Hydrogen and 
 carbon cannot be brought to unite directly except with the great- 
 est difficulty, and then only irl the smallest quantity. In this re- 
 spect carbon resembles nitrogen (see page 88). It is not difficult, 
 however, to produce methane from other compounds which con- 
 tain both carbon and hydrogen. For example, it is constantly 
 formed at the bottom of swamps and stagnant pools where vege- 
 table matter (largely made up of the two elements in question) 
 is decaying under the influence of micro-organisms, and where 
 the amount of" oxygen required for a complete decomposition is 
 not accessible. The methane produced by these processes of 
 decay passes off in the form of bubbles, the number of which can 
 be increased by stirring the bottom of the pool with a stick. It 
 is owing to the above origin that methane is frequently termed 
 " marsh gas." Natural marsh gas is contaminated with carbon 
 dioxide and nitrogen. The " natural gas," which escapes freely 
 from borings in many localities, consists largely of methane, 
 which probably found its origin in the decomposition of vegetable 
 matter buried in past geologic eras. The remains of this now 
 constitute bituminous and anthracite coal. Owing to similar 
 reasons, methane frequently occurs in coal-mines. 
 
 Preparation of Methane for Laboratory Purposes. In preparing 
 methane for laboratory purposes, we have to make use of a corn- 
 pound known as sodium acetate, with the exact constitution of 
 which we need not at present be acquainted. It is sufficient for 
 our purposes to know that it is formed of carbon, hydrogen, oxy- 
 gen, and sodium, and that, when heated in the presence of a mix- 
 ture of sodium hydroxide and calcium oxide, it separates, in the 
 form of methane, a portion of the carbon and all of the hydrogen 
 which it contains. 68 
 
 Properties of Methane. Methane is a gas, colorless, odorless, 
 and tasteless. If a jar of it is collected over water, and a lighted 
 
166 ELEMENTS OF CHEMISTRY. 
 
 taper is applied to the jar, which has been removed -from the 
 water and held mouth downward, we shall find that the gas burns 
 with a nearly non-luminous flame. This flame greatly resembles 
 that of hydrogen, but, nevertheless, can be distinguished from it 
 because the hydrogen flame is entirely non-luminous. The spe- 
 cific gravity of methane is less than that of air. This can easily 
 be shown by filling two cylinders with methane, and holding one 
 mouth upward and the other mouth downward for a few seconds. 
 The former will no longer contain a combustible gas, for its 
 methane will have risen into the air. The latter will have re- 
 tained all its methane, and if a lighted taper is applied, will show 
 the characteristic flame of that substance. Methane is nearly 
 insoluble in water. 69 
 
 Determination of the Chemical Formula of Methane. In 
 determining the chemical formula of methane, we can- 
 not have so easy a task as we did when engaged in 
 similar studies with hydrogen chloride, water, or am- 
 monia. Both constituents entering into the formation 
 of each of the latter compounds are gases, and for that 
 reason a study of the uniting gas volumes together 
 with the fundamental theory that in equal volumes of 
 gases there are equal numbers of molecules, directly 
 led us to the structure of those three substances, and 
 thence to the formulae, HC1, H 2 O, and NH 3 . In 
 methane, however, one of the constituent elements 
 (carbon) is a solid under any conditions which we can 
 command. Therefore, any view which may be held as 
 to the relative volume of that element entering into the 
 formation of the gas cannot be based upon direct meas- 
 urement. It must be established both by reasoning 
 from our experience with the other hydrogen com- 
 pounds (hydrochloric acid, water, and ammonia), and 
 by noting chemical changes to which we can subject 
 methane. 
 
CARBON MONOXIDE AND METHANE. 167 
 
 Previous experience has shown us that we have three 
 kinds of gaseous hydrogen compounds of the not-metals 
 which, we may say, belong to three distinct types. The 
 first of these, hydrogen chloride, is produced by the 
 union of ^one volume of hydrogen with one volume of 
 chlorine, the second by the union of two volumes of 
 hydrogen with one volume of oxygen, and the third 
 by the union of three volumes of hydrogen with one 
 volume of nitrogen. In each of these cases one volume 
 of the not-metal is united with one or more volumes of 
 hydrogen. If methane is a compound which is at all 
 parallel, it seems reasonable to suppose that it contains 
 one volume of carbon united with one or more volumes 
 o hydrogen. This volume of hydrogen is consequently 
 to be ascertained by chemical changes to which we can 
 subject methane. 
 
 Volumetric Composition of Methane by Explosion with 
 Oxygen. When methane burns in oxygen it produces 
 carbon dioxide and water. This fact gives us a means 
 of ascertaining the volume of hydrogen which is con- 
 tained in one volume of methane. 
 
 Introduce about ten cubic centimetres of methane into a eudi- 
 ometer tube over mercury, and then admit omewhat more than 
 twice this volume of pure oxygen. Heat the eudiometer to the 
 temperature of boiling water by means of a steam-jacket (see page 
 26, and Experiment 11 of Appendix), and explode the gas mixture 
 by an electric spark, exactly as was done in the study of the com- 
 bining volumes of oxygen and hydrogen. If all due precautions 
 have been taken, it will be found that no change in the total volume 
 takes place when methane and oxygen are converted into carbon 
 dioxide and water. There are consequently as many molecules 
 of carbon dioxide and water produced as there were molecules of 
 methane and oxygen before the explosion. If, now, the whole 
 apparatus is allowed to cool, the water vapor will be changed to a 
 
168 ELEMENTS OF CIIEMISTItY. 
 
 liquid, so that its volume can be neglected in the subsequent cal- 
 culation. As the water condenses, the mercury will rise, owing to 
 the contraction of the total gas volume, and, when its position is 
 constant, there will have been exactly twenty cubic centimetres 
 diminution. These twenty cubic centimetres must therefore 
 represent the volume of water vapor which was formed from ten 
 cubic centimetres of methane.* If a very small piece of caustic 
 potash is now introduced at the bottom of the tube, it will rise to 
 the top of the mercury, and absorb the carbon dioxide which was 
 produced by the explosion, so that a further contraction will take 
 place. This latter will be exactly ten cubic centimetres, which is 
 equal to the volume of methane originally present. The gas 
 which finally remains is oxygen, and represents the excess of that 
 substance which was added. The results of the above measure- 
 ments can be tabulated as follows : 
 
 1. Volume of methane =10 cubic centimetres. 
 
 2. Volume of gases at 100 before and after the explosion, 
 unaltered. 
 
 3. Contraction, owing to condensation of water vapor, 20 cubic 
 centimetres. 
 
 4. Contraction, owing to the absorption of carbon dioxide, 
 10 cubic centimetres. 
 
 Volume of methane = 10 cubic centimetres. 
 Volume of water vapor = 20 cubic centimetres. 
 Volume of carbon dioxide =10 cubic centimetres. 
 As a final result, therefore, we find the following 
 
 * Of course the above description presupposes that all the volumes 
 mentioned have been calculated to and 760 mm. pressure. In actual 
 practice the height of the barometer, the temperature, the height of the 
 column of mercury in the eudiometer tube, and the volume of gas in the 
 cube, must be noted at the following stages of the experiment: 1. After 
 admitting the methane. 2. After admitting the oxygen. 3. After ex- 
 ploding the gas mixture (this volume is at 100). 4. After allowing the 
 products of the explosion to cool. In this instance the tension of water 
 vapor must be taken into account, as at this point the water pi-oduced by 
 the explosion is present as such. 5. After introducing the piece of 
 caustic potash. The calculation for the tension of water vapor here dis- 
 appears, for the caustic potash will absorb the water which is present. 
 See pages 68, 69, and 70. 
 
CARBON MONOXIDE AND METHANE. 169 
 
 Results of the Explosion of Methane with Oxygen. One 
 
 volume of methane, when exploded with oxygen, produces 
 one volume of carbon dioxide and two volumes of water 
 vapor. As in equal volumes of gases there are equal 
 numbers of molecules, this result means that one mole- 
 cule of methane produces one molecule of carbon dioxide 
 and two molecules of water. Now we have decided that 
 two molecules of water must contain four atoms of 
 hydrogen; and since these four atoms of hydrogen 
 have been furnished by one molecule of methane, it 
 must follow that 
 
 One molecule of methane contains four atoms of hy- 
 drogen. 
 
 We have also come to the conclusion that one mole- 
 cule of carbon dioxide contains one atom of carbon (see 
 page 154); and, since this one atom of carbon must 
 have been furnished by one molecule of methane, it 
 follows that 
 
 One molecule of methane contains one atom of carbon. 
 
 Combining these two results we find that: 
 
 One molecule of methane is composed of one atom 
 of carbon and four atoms of hydrogen. Therefore its 
 formula is represented by CH 4 . 70 
 
 Formula of Methane from a Consideration of its Specific 
 Gravity. This conclusion as to the formula of methane 
 is borne out by its specific gravity, which is 16 (hydro- 
 gen = 2). The molecular weight of methane (H 2 = 2) 
 is consequently 16 ; and in 16 parts of methane we find, 
 on analysis, twelve of carbon and four of hydrogen. 
 In working with carbon dioxide we decided that 12 
 represented the relative weight of one atom of carbon 
 measured by the standard of one atom of hydrogen. 
 
170 ELEMENTS OF CHEMISTRY. 
 
 For the same reason 4 represents four times the weight 
 of one atom of hydrogen ; so that, judging from the 
 specific gravity of methane, its structure is such as 
 would be produced by the union of one atom of carbon 
 with four of hydrogen ; thus its formula is CH 4 . 
 
 Summary. 
 
 1. Carbon monoxide can be produced by the reduc- 
 tion of carbon dioxide. 
 
 2. When carbon monoxide burns, carbon dioxide is 
 produced, heat is given off. Therefore carbon dioxide 
 possesses less chemical energy that carbon monoxide. 
 
 3. The energy changes attending the formation of 
 carbon dioxide can be considered as taking place in 
 two stages, the first corresponding to the formation of 
 carbon monoxide, and the second to the conversion 
 of carbon monoxide into carbon dioxide. 
 
 4. The total kinetic energy manifested during the 
 conversion of a given weight of carbon into carbon 
 dioxide is independent of any intermediary formation 
 of carbon monoxide. 
 
 5. The hydrogen compound of carbon, which is 
 termed methane, is produced in nature by the decom- 
 position of vegetable matter protected from the direct 
 action of the air. 
 
 6. The chemical formula of methane cannot be 
 directly determined from combining gas volumes, first, 
 because carbon is not a gas, and second, because the ele- 
 ments carbon and hydrogen do not easily unite directly. 
 
 7. The formula of methane can be ascertained by 
 exploding the gas with oxygen and then measuring the 
 volume of water vapor and of carbon dioxide which is 
 produced by this means. 
 
CAB 13 ON MONOXIDE AND METHANE. 171 
 
 8. One volume of methane, under these circum- 
 stances, produces one volume of carbon dioxide and 
 two volumes of water vapor. Hence, one molecule of 
 methane produces one molecule of carbon dioxide and 
 two molecules of water. 
 
 9. One molecule of carbon dioxide contains one 
 atom of carbon, and two molecules of water contain 
 four atoms of hydrogen. Hence, methane contains one 
 atom of carbon to every four atoms of hydrogen. 
 
 10. Methane contains one atom of carbon and four 
 atoms of hydrogen in each molecule, for its specific 
 gravity (hydrogen = 2) is 16. Hence its molecular 
 weight is 16. Such a molecular weight is equal to 
 the sum of the atomic weights of one atom of carbon 
 (12), and four atoms of hydrogen (4). Therefore the 
 formula for one molecule of methane is CH 4 . 
 
172 ELEMENTS OF CHEMISTRY. 
 
 CHAPTER XXII. 
 
 SUBSTITUTION OF HYDROGEN IN METHANE 
 BY CHLORINE. 
 
 Substitution of Hydrogen by Metals. We have learned 
 in discussing the hydrogen compounds which preceded 
 methane, that certain metals could replace a portion, 
 or all, of the hydrogen in those compounds. This 
 process, which was general with all but methane, we 
 termed substitution. We also learned that the same 
 kind of substitution takes place when metals act on 
 acids. Therefore salts were considered as being the 
 acids in which a portion, or all, of the hydrogen had 
 been replaced by other metals. If we have carefully 
 observed all the phenomena attending the substitution 
 of hydrogen in hydrogen chloride, water, and ammonia 
 by metals, we shall have noticed that the ease with 
 which the hydrogen is so replaced, and the number of 
 metals capable of entering into such substitutions, di- 
 minishes as we pass from hydrogen chloride to water, 
 and from water to ammonia. Finally, in methane we 
 have a hydrogen compound which, under ordinary cir- 
 cumstances, is entirely indifferent to metals. Sodium, 
 for example, can be left in contact with pure, dry 
 methane for any length of time without suffering the 
 slightest alteration. 
 
 Difference between the Action of Chlorine and of the 
 Metals. On the other hand, we have a radically differ- 
 
SUBSTITUTION OF HYDROGEN IN METHANE. 173 
 
 ent behavior toward chlorine. Chlorine, of course, has 
 no effect on hydrogen chloride ; but when we dissolved 
 chlorine in water, and exposed the solution to the sun- 
 light, we saw that hydrochloric acid was formed and 
 oxygen was liberated (see page 44), while with am- 
 monia and chlorine we produced hydrogen chloride and 
 nitrogen (see page 92). In each instance, then, chlorine 
 liberated the not-metal which was present in the hydro- 
 gen compound, while it itself appropriated the hydrogen. 
 Obviously these reactions could not be compared with 
 substitution. It is now in order to study the action of 
 chlorine on methane. 
 
 Action of Chlorine on Methane. Two glass jars of equal size are 
 taken, one filled with chlorine, the other with methane. A glass 
 cover is placed on each so that no gas can escape. ^ The mouths 
 are then brought together, the glass coverings are removed, and 
 the chlorine and methane are intimately mixed by inverting the 
 jars once or twice, while their mouths are held tightly to- 
 gether.* 
 
 If, now, a lighted taper is applied to one of the vessels, the mix- 
 ture of gases will burn, dense fumes of hydrogen chloride will be 
 given off, while carbon will separate from the methane in the 
 form of soot. Under the circumstances which have been out- 
 lined, methane acts toward chlorine just as water and ammonia 
 do, carbon is separated, while the chlorine appropriates the hy- 
 drogen to form hydrogen chloride. An entirely different result, 
 however, is obtained if chlorine and methane are allowed to act 
 upon each other gradually. 71 
 
 For this purpose the apparatus can be used which 
 was employed to demonstrate that equal volumes of 
 ammonia and hydrogen chloride unite to form ammo- 
 nium chloride (see Experiment 55 of the Appendix). 
 
 * This operation must be conducted in a dimly lighted room, and not 
 in the sunlight. 
 
174 ELEMENTS OF CHEMISTRY. 
 
 One of the two equal tubes is carefully filled with pure chlorine, 
 the other with methane, and the tips are sealed. The apparatus 
 is placed in strong daylight, and the two gases are allowed to 
 mingle slowly. After some days the color of the chlorine will 
 entirely disappear. If, now, one of the tips is broken off under a 
 solution of blue litmus, the liquid will rise in the apparatus until 
 exactly one-half is filled, while the litmus will turn from blue 
 to red, showing that an acid is present. This acid can easily 
 be shown to be hydrochloric acid.* If the upper tip of the tube 
 is now broken off, and the whole lowered into the litmus solution 
 so as to produce a slight pressure, the escaping gas can be ignited. 
 It will burn with a greenish flame entirely different from that 
 of pure methane. This flame is characteristic of burning com- 
 pounds of carbon, hydrogen, and chlorine. The explanation of 
 the above experiment is simple. The volume of methane .reacted 
 with an equal volume of chlorine to produce one volume of the 
 new chlorinated gas. The hydrogen chloride which was formed 
 at the same time, and which is readily soluble in water, was 
 absorbed by the litmus solution. It is, therefore, evident that 
 one volume of methane with one volume of chlorine produced one 
 volume of the new gas and one volume of hydrogen chloride. 
 Therefore, one molecule of methane with one molecule of chlo- 
 rine formed one molecule of hydrogen chloride and one molecule 
 of chlorinated methane. As one molecule of chlorine contains 
 two atoms of that element, the change can be represented as 
 follows : 72 
 
 CH 4 + C1C1 = CH 3 C1 + HC1. 
 
 One mol. of methane 4- Onemol. of chlorine = One mol. of new gas + Oneniol. of hydrogen chloride. 
 
 The First Product of the Action of Chlorine on Methane 
 is Methyl Chloride. The new gas which is produced is 
 called methyl chloride. It is methane in each molecule 
 of which one atom of hydrogen has been replaced (sub- 
 stituted) by one atom of chlorine. It is evident, there- 
 fore, that if chlorine is allowed to act slowly on methane, 
 
 * By adding a solution of silver nitrate to the litmus solution, the in- 
 soluble chloride of silver will be produced, thus indicating the presence 
 of hydrochloric acid. 
 
SUBSTITUTION OF HYDROGEN IN METHANE. 1 
 
 substitution takes place, and that the chTo'niie'^vrmch is 
 introduced takes the place of the hydrogen which has 
 been expelled. 
 
 Chlorination of Methyl Chloride. The operation of substitution 
 can be carried still farther if, when the hydrogen chloride has 
 been removed by means of the litmus solution, one arm of the tube 
 containing methyl chloride (after the action of chlorine on meth- 
 ane) is not opened. Close the stopcock separating the two halves 
 of the apparatus, and drain off the water contained in the lower 
 half. Fill this again with chlorine and seal it, allowing the gases 
 to mix as in the first instance. The phenomena previously observed 
 will be repeated ; i.e., the color of the chlorine will disappear, and, 
 when the tube is opened under a litmus solution, it will be found 
 that one volume of hydrogen chloride and one volume of a chlo- 
 rinated methhl chloride will have been formed. From this it fol- 
 lows that one molecule (volume) methyl chloride with one molecule 
 (volume) of chlorine produces one molecule (volume) of hydrogen 
 chloride and one molecule (volume) of chlorinated methane. This 
 second change can be represented as follows : 73 
 
 CH 3 C1 + C1C1 = CH 2 C1 2 + HC1. 
 
 1 mol. methyl chloride +1 mol. chlorine = 1 mol. new gas + 1 mol. hydrogen chloride. 
 
 The Second Product of the Action of. Chlorine on Methane 
 is Methylen Chloride. The second chlorinated gas which 
 is produced is called methylen chloride. It is methane 
 in each molecule of which two atoms of hydrogen have 
 been replaced (substituted) by two atoms of chlorine. 
 
 Chlorination of Methylen Chloride. Methylen chloride is also 
 capable of reacting with chlorine, but in this instance we cannot 
 easily measure the gas volume produced. The reason is that the 
 third substitution product of methane is a liquid at ordinary tem- 
 peratures, so that on opening the tube under water, the latter will 
 rush in and entirely fill the apparatus, except the very small space 
 occupied by the substitution product. We will soon see, however, 
 that by a careful study of the specific gravity of the vapor of the 
 liquid formed, we can ascertain that this substitution has pro- 
 ceeded like the others, and that 
 
176 ELEMENTS OF CHEMISTRY. 
 
 One molecule of methylen chloride, with one molecule of chlo- 
 rine, has produced one molecule of the new substitution product, 
 together with one molecule of hydrogen chloride. This change 
 can be represented as follows : 74 
 
 CH 2 C1 2 + C1C1 = CHC1 3 + HC1. 
 
 1 mol. methylen chloride + 1 mol. chlorine = 1 mol. of the new product + 1 mol. hydrogen chloride 
 
 The Third Product of the Action of Chlorine on Methane 
 is Methin Chloride, and the Fourth, Carbon Tetrachloride. 
 The third substitution product of methane is methin 
 chloride, commonly known as chloroform. If chloro- 
 form is subjected to the continued action of chlorine, 
 the last remaining hydrogen atom in each molecule 
 will be substituted, and we shall finally have a methane 
 in which all the hydrogen has been replaced by chlo- 
 rine. This last methane is called carbon tetrachloride. 
 It is a liquid at ordinary temperatures, but can easily 
 be converted into a gas. 
 
 Specific Gravities and Boiling-Points of Methane and its 
 Substitution Products. It is most instructive to compare 
 the specific gravities of methane and of its chlorine 
 substitution products, when all five substances have 
 been heated to a temperature sufficient to convert them 
 into gases. That this is easily accomplished will be 
 seen from a table giving their boiling-points. 
 
 Methane boils at .... ...."- 164. 
 
 Methyl chloride boils at .... - 23 .7. 
 
 Methylen chloride boils at . . . . + 40. 
 
 Methin chloride (chloroform) boils at + 61. 
 Carbon tetrachloride boils at . . . + 76. 
 
 Since all these compounds are gases at temperatures 
 below the boiling-point of water (100) their specific 
 gravities as vapors can easily be ascertained. These 
 specific gravities are given in the following table : 
 
SUBSTITUTION OF HYDROGEN IN METHANE. 177 
 
 Specific gravities of methane and its substitution products as gases. 
 Hydrogen = 2 
 
 Methane, specific gravity 16, molecular weight 16, contains 12 
 parts of carbon and 4 of hydrogen. 
 
 Methyl chloride, specific gravity 50.5, molecular weight 50.5, con- 
 tains 12 parts of carbon, 3 of hydrogen, and 35.5 of chlorine. 
 
 Methylen chloride, specific gravity 85, molecular weight 85, con- 
 tains 12 parts of carbon, 2 of hydrogen, and 71 of chlorine. 
 
 Methin chloride, specific gravity 119.5, molecular weight 119.5, 
 contains 12 parts of carbon, 1 of hydrogen, and 106.5 of 
 chlorine. 
 
 Carbon tetrachloride, specific gravity 154, molecular weight 154, 
 contains 12 parts of carbon and 142 parts of chlorine. 
 
 Atomic Weights of Carbon and Chlorine as ascertained 
 from the Specific Gravities of Methane and the Chlorinated 
 Methanes. The figures in this table furnish additional 
 proof that the weight of an atom of carbon is twelve 
 times that of an atom of hydrogen, since we have here 
 five compounds, each containing 12 parts of carbon 
 in every molecule. The atomic weight of carbon 
 cannot, therefore, be more than 12. That it is not 
 less than this number is rendered more probable the 
 more gaseous compounds of carbon are investigated, 
 since each will be shown to contain not less than 12 
 parts of that element in every molecule. Furthermore, 
 it is evident that the relative atomic weight of chlorine 
 cannot be a multiple of 35.5, because we have one of 
 the above compounds (methyl chloride) which contains 
 but 35.5 parts of chlorine in each molecule. It follows 
 from this that methylen chloride, methin chloride, and 
 carbon tetrachloride contain, in each molecule, two, 
 three, and four atoms of chlorine respectively. Rea- 
 soning from the specific gravities of methane and of 
 the chlorinated methanes, when those substances are 
 
178 ELEMENTS OF CHEMISTRY. 
 
 converted into gases, we must come to the conclusion 
 that their molecules have the formulae CH 4 , CH 3 Cl, 
 CH 2 C1 2 , CH C1 3 , and C C1 4 . 
 
 In Substituting Hydrogen by Chlorine, the Essential 
 Character of Methane is not changed. In substituting 
 hydrogen by chlorine in methane, the essential char- 
 acter of the latter is preserved. All the chlorinated 
 compounds contain one atom of carbon in each mole- 
 cule. The hydrogen has been substituted while the 
 carbon has remained. It seems reasonable to suppose, 
 therefore, that in a molecule of methane, it is the 
 carbon atoms which hold the four hydrogen atoms in 
 chemical union with it. In producing the chlorine sub- 
 stitution products, the substituting chlorine atoms have 
 taken the place of the hydrogen atoms which are sub- 
 stituted. We can express this conclusion in the fol- 
 lowing way: - 
 
 The Number of Atoms with which one Atom of Carbon 
 can combine in one Molecule is never more than Four. One 
 atom of carbon is capable of uniting with four atoms 
 of hydrogen, with three atoms of hydrogen and one of 
 chlorine, with two atoms of hydrogen and two of chlo- 
 rine, with one atom of hydrogen and three of chlorine, 
 and, finally, with four chlorine atoms. In short, one 
 atom of carbon can combine with four atoms of hydro- 
 gen, or with any other four atoms which are in com- 
 bining power equivalent to hydrogen. The number 
 of single atoms with which one atom of carbon can 
 combine in one molecule is never more than four. 
 
 Valence. Applying what we have learned with car- 
 bon to the hydrogen compounds of other elements, we 
 
SUBSTITUTION OF HYDROGEN IN METHANE. 179 
 
 draw the following conclusions : One atom of hydro- 
 gen combines with three of nitrogen to form am- 
 monia; two atoms of hydrogen combine with one of 
 oxygen to form water; and one atom of hydrogen 
 combines with one of chlorine to form hydrogen chlo- 
 ride. We see, then, that the individual atoms of 
 the four elements, carbon, nitrogen, oxygen, and chlo- 
 rine, unite each with a different number of hydrogen 
 atoms, or, to use another term, they have a different 
 value toward hydrogen. This we call a difference in 
 valence; and we say chlorine has a valence of one 
 toward hydrogen, oxygen of two, nitrogen of three, 
 and carbon of four. 
 
 This distinction can be expressed in chemical formu- 
 lae by writing the symbol for each atom in one mole- 
 cule separately, grouping those of the hydrogen atoms 
 round the atom of the not-metal, which is supposed to 
 join the different atoms in the molecule. Thus we 
 
 H H H 
 
 HC1 HOH HtfH HCH HCH HOC! 
 
 H H Cl Cl 
 
 Hydrogen chloride. Water. Ammonia. Methane. Methyl chloride. Methylen chloride, etc. 
 
 Valence of Carbon, Nitrogen, Oxygen, or Chlorine may not 
 be the same toward all Elements. We must not suppose 
 that each atom of chlorine, oxygen, nitrogen, or carbon 
 can combine with as many atoms of every other element 
 as with those of hydrogen or of chlorine. That this is 
 not the case is shown by the fact that, so far as we 
 know, one atom of carbon can combine with no more 
 than two atoms of oxygen, provided no other elements 
 are present. What has been said in regard to valence, 
 therefore, must be confined exclusively to chlorine and 
 hydrogen compounds, 
 
180 
 
 ELEMENTS OF CHEMISTRY. 
 
 For further illustration, the formulae and composition 
 of all the gaseous or gasifiable compounds which we 
 have encountered, are given in the following table : 
 
 FORMULA. 
 
 COMPOSITION BY WEIGHT. 
 
 Hydrogen chloride 
 
 HC1 
 
 One part of hydrogen to 35.5 of chlorine. 
 
 Water 
 
 H 2 
 
 Two parts of hydrogen to 16 of oxygen. 
 
 Ammonia 
 
 H 3 N 
 
 Three parts of hydrogen to 14 of nitrogen. 
 
 Methane 
 
 H 4 C 
 
 Four parts of hydrogen to 12 of carbon. 
 
 Methyl chloride 
 
 H 3 C1C 
 
 Three parts of hydrogen to 12 of carbon, 35.5 
 of chlorine. 
 
 Methylene chloride 
 
 H 2 C1 2 C 
 
 Two parts of hydrogen to 12 of carbon, 71 of 
 
 
 
 chlorine. 
 
 Methin chloride 
 
 HC1 3 C 
 
 One part of hydrogen to 12 of carbon, 106.5 
 
 
 
 of chlorine. 
 
 Carbon tetrachloride 
 
 C1 4 C 
 
 Twelve parts of carbon, 142.0 of chlorine. 
 
 Sulphur dioxide 
 
 S0 2 
 
 Thirty-two parts of sulphur to 32 of oxygen. 
 
 Sulphur trioxide 
 
 S0 3 
 
 Thirty-two parts of sulphur to 48 of oxygen. 
 
 Carbon monoxide 
 
 CO 
 
 Twelve parts of carbon to 16 of oxygen. 
 
 Carbon dioxide 
 
 C0 2 
 
 Twelve parts of carbon to 32 of oxygen. 
 
 From this table it is apparent that in one molecule of carbon 
 monoxide or carbon dioxide we have twelve parts of carbon, just 
 as we have in methane and in the chlorinated methanes. There- 
 fore, by these oxides also, the maximum atomic weight of carbon 
 is fixed at twelve. Furthermore, we see that the least quantity oi 
 oxygen occurring in any of the above compounds is 16, and that 
 in all the oxides mentioned we have either 16 parts of oxygen, 
 or some multiple of 16. In the same way the maximum atomic 
 weight of sulphur is fixed at 32, because we havo 32 parts ot sul- 
 phur in one molecule of sulphur dioxide and oi sulphur trioxide. 
 
 It has been demonstrated that the number of oxygen 
 atoms with which one carbon atom can unite in either 
 carbon monoxide or carbon dioxide is different from the 
 number of hydrogen atoms with which one carbon atom 
 can unite in methane. If we compare carbon dioxide 
 and methane, we see that two hydrogen atoms have 
 exactly the same combining power as one oxygen atom. 
 This difference is not confined to the compounds of 
 
SUBSTITUTION OF HYDROGEN IN METHANE. 181 
 
 carbon alone. With all elements one oxygen atom is 
 equal in combining power to two hydrogen atoms. 
 
 The Burning of Methane is a Process of Substituting Hy- 
 drogen by Oxygen. The burning of methane, forming 
 water and carbon dioxide, ,is analogous to the substitu- 
 tion of hydrogen by chlorine. In this case, however, 
 two atoms of oxygen take the place of four atoms of 
 hydrogen, while in substituting with chlorine, one atom 
 of chlorine takes the place of one atom of hydrogen. 
 This comparison is made more evident by the follow- 
 f ormulse : 
 
 CH 4 + 20 2 = C0 2 + 2H 2 0. 
 
 1 mol. of methane + 2 mols. of oxygen = 1 mol. of carbon dioxide + 2 mol. of water. 
 
 CH 4 + 4C1 2 = CC1 4 + 4HC1. 
 
 1 mol. of methane 4 mols. of chlorine = 1 mol. carbon tetrachloride 4 mols. hydrogen chloride. 
 
 The action of chlorine on hydrogen compounds is, 
 therefore, analogous to the processes attending the 
 combustion of the same substances in oxygen. In 
 the first case the chlorides 'may be produced, and in 
 the second the oxides. In either case heat is evolved 
 during the process, and the resulting compounds pos- 
 sess less chemical energy than the ones used for the 
 substitution.* 
 
 the Valence of an Element toward Hydrogen is Constant, 
 while it may be Variable toward Oxygen. Finally, the 
 above table shows us that the number of oxygen atoms 
 
 * In some cases of the action of chlorine or of oxygen on hydrogen 
 compounds, substitution does not take place, but the not-metal is liber- 
 ated. This is the case with the action of chlorine or ol oxygen on ammo- 
 nia. When chlorine reacts wit>h ammonia, hydrogen chloride and nitro- 
 gen are produced. When oxygen reacts with ammonia, water is formed, 
 and nitrogen is liberated. The two processes are therefore analogous. 
 
182 ELEMENTS OF CHEMISTRY. 
 
 with which one atom of a given element can unite may 
 vary, while experience has shown us that this is not 
 the case with the hydrogen compounds. The valence of 
 an element toward hydrogen seems to be constant, while 
 toivard oxygen it assumes different values, according to 
 circumstances. * 
 
 We have encountered one exception to the above 
 rule. In ammonia one atom of nitrogen unites with 
 thre.e atoms of hydrogen in each molecule ; but, as we 
 have seen (pag^e 98), ammonia can add hydrogen chlo- 
 ride to form ammonium chloride. We have demon- 
 strated that in ammonium chloride there are, one atom 
 of nitrogen, four of hydrogen, and one of chlorine in 
 each molecule. It seems possible, therefore, for one 
 nitrogen atom to increase the number of hydrogen 
 atoms with which it is united to four, provided there 
 is some not-metallic element or group of elements 
 (such as chlorine) taken into the combination at the 
 same time. Toward hydrogen alone, nitrogen seems to 
 have an invariable valence of three, in compounds con- 
 taining but one atom of nitrogen in each molecule. 
 Chemically, it is said that ammonia is unsaturated be- 
 cause it can add to itself certain acid compounds in 
 order to produce ammonium salts. In ammonium chlo- 
 ride we have one atom of nitrogen joined to four atoms 
 of hydrogen and one of chlorine ; the valence of nitro- 
 gen in this compound is consequently five. 
 
 Summary. 
 
 1. When chlorine acts on most hydrogen compounds 
 of the not-metals, hydrogen chloride is produced, and 
 the not-metal contained in the particular compound in 
 question is liberated. 
 
SUBSTITUTION OF HYDROGEN IN METHANE. 183 
 
 2. If an excess of chlorine acts violently on methane 
 (i.e., when a mixture of methane and chlorine is 
 ignited), carbon is liberated, and hydrogen chloride 
 is produced. 
 
 3. If chlorine acts slowly upon methane, substitution 
 takes place in such a way that one atom of chlorine 
 always takes the place of one atom of hydrogen. At 
 the same time one molecule of hydrogen chloride is 
 formed. 
 
 4. The four hydrogen atoms in one molecule of 
 methane can be successively substituted by chlorine, 
 producing substances having the chemical formulse 
 CH 3 C1, CH 2 C1 2 , CH C1 3 , and C C1 4 . 
 
 5. The specific gravities of methane and of its sub- 
 stitution products, when the latter are heated to a tem- 
 perature high enough to convert them into gases, confirm 
 the formulae given under 4. 
 
 6. The atomic weights of carbon and of chlorine, 
 determined by the specific gravities of gaseous methane 
 and its substitution products, are 12 and 35.5 respec- 
 tively. 
 
 7. The number of single atoms with which one atom 
 of carbon can combine in any one molecule is never 
 greater than 4. 
 
 8. One atom of chlorine, oxygen, nitrogen, or carbon 
 can unite with different numbers of atoms of hydrogen. 
 This is termed a difference in valence. Chlorine has a 
 valence of one toward hydrogen, oxygen of two, nitro- 
 gen of three, and carbon of four. 
 
 9. The number of oxygen atoms with which one 
 atom of these elements can unite is different from the 
 number of hydrogen atoms. This difference is such 
 that one oxygen atom can take the place of two hydro- 
 
184 ELEMENTS OF CHEMISTRY. 
 
 gen atoms, and is shown in the table comparing the 
 formulse of the gaseous compounds discussed in this 
 work. 
 
 10. The number of oxygen atoms with which one 
 atom of the above elements can unite may vary. This 
 is shown by the existence of two oxides of sulphur, 
 sulphur dioxide and sulphur trioxide, and of the two 
 oxides of carbon, cabron monoxide and carbon dioxide. 
 
THE FORMATION OF SALTS. 185 
 
 CHAPTER XXIII. 
 
 THE FORMATION OF SALTS BY DOUBLE 
 DECOMPOSITION. 
 
 Formation of Salts by Substitution and Neutralization. 
 Thus far in considering the formation of salts we have 
 found two methods available for the purpose, one by 
 the action of metals on acids (see page 45 and 57), the 
 other by neutralization of acids by bases (see pages 48 
 and 58). In both cases the salt is formed by a process 
 of substitution in which the metal, either alone or in 
 combination with oxygen, takes the place of the hydro- 
 gen in the acid. The salt is therefore the acid in which 
 the whole, or a part, of the hydrogen has been replaced 
 by some other metal. The acids, therefore, may be 
 considered as salts of the metal hydrogen. Thus, sul- 
 phuric acid is hydrogen sulphate, hydrochloric acid is 
 hydrogen chloride, and nitric acid is hydrogen nitrate ; 
 while the salts of these acids are termed sulphates, 
 chlorides, and nitrates. The parallelism can be made 
 clearer by comparing the following formulae : 
 
 H 2 SO 4 . Na 2 SO 4 . 
 
 Hydrogen sulphate (sulphuric acid). Sodium sulphate. 
 
 H Cl. Na Cl. 
 
 Hydrogen chloride (hydrochloric acid). Sodium chloride. 
 
 HNO 3 . NaNO 3 . 
 
 Hydrogen nitrate (nitric acid). Sodium nitrate. 
 
186 ELEMENTS OF CHEMISTRY. 
 
 Salt Formation by Action of an Acid on a Salt. There 
 are, however, other means of salt formation of as great 
 importance chemically as those just mentioned which 
 do not involve the action of an acid on a base. 
 
 If sodium chloride is brought in contact with an excess of con- 
 centrated sulphuric acid, a gas passes off, which from its proper- 
 ties can easily be recognized as hydrogen chloride (see page 38 
 and Experiment 16, Appendix). After the reaction is completed, 
 if the remainder is dissolved in water and the solution evapo- 
 rated, crystals of a salt, which differs from sodium chloride, will 
 separate. This salt does not liberate hydrogen chloride when sul- 
 phuric acid is added to it. It melts when heated, and finally gives 
 off dense fumes of sulphuric acid. It then again solidifies, to melt 
 once more at a bright white heat. In short, it has all of the prop- 
 erties belonging to primary sodium sulphate (see Experiment 34, 
 Appendix). From sodium chloride and hydrogen sulphate we have 
 therefore produced sodium sulphate and hydrogen chloride. This 
 change can be made plain by the following chemical formulae : 
 
 Na Cl + HHSO 4 = H Cl + Na HSO 4 . 
 
 A reaction of this kind is termed a double decompo- 
 sition, since both the sulphuric acid and the sodium 
 chloride have been altered in such a way that sodium 
 and hydrogen have exchanged places. Hydrogen chlo- 
 ride is a gas, and, as a consequence, passes off, so that 
 at the end of the experiment nothing remains but pri- 
 mary sodium sulphate, together with the excess of sul- 
 phuric acid which has been used. In such a reaction 
 the action of sodium chloride is analogous to that of 
 sodium hydroxide on sulphuric acid ; in one case so- 
 dium chloride and sulphuric acid produce sodium sul- 
 phate and hydrogen chloride ; in the other, sodium 
 hydroxide and sulphuric acid form sodium sulphate 
 and hydrogen oxide (water). It follows from this that 
 the neutralization of an acid by a base is also a reaction 
 involving a double decomposition. 
 
THE FORMATION OF SALTS. 187 
 
 Double Decompositions between Two Salts. The reactions 
 which have been cited involve the action of a salt or a 
 base on an acid. We can, however, have other double 
 decompositions, in which two salts change each other 
 so as to produce two new salts, in which case the 
 metals exchange places. If, for example, a solution 
 of barium chloride is brought in contact with one of 
 sodium sulphate, a double decomposition takes place, 
 while the insoluble barium sulphate is separated. This 
 change can be expressed as follows : 
 
 Barium chloride+ Sodium sulphate = Barium sulphate + Sodium chloride. 
 
 soluble soluble insoluble soluble. 
 
 The separation of an insoluble substance from a solu- 
 tion by double decomposition is termed precipitation. 
 Processes similar to the above are of such frequent 
 occurrence in chemical work as to warrant the estab- 
 lishment of the following arbitrary rule: 75 
 
 Double decompositions occur whenever a volatile or an 
 insoluble substance can be produced. 
 
 EXAMPLES: 
 
 1. Calcium chloride + Potassium carbonate = Calcium carbonate + Potassium chloride. 
 
 soluble soluble insoluble soluble. 
 
 2. Barium chloride + Sodium carbonate= Barium carbonate + Sodium chloride. 
 
 soluble soluble insoluble soluble. 
 
 3. Sodium chloride 4- Silver nitrate = Silver chloride + Sodium nitrate. 
 
 soluble soluble insoluble soluble. 
 
 4. Magnesium sulphate + Barium chloride = Barium sulphate + Magnesium chloride. 
 
 soluble soluble insoluble soluble. 
 
 In the above changes, the result is such that two 
 soluble salts so react that they completely decompose 
 each other in order to produce two new salts, one of 
 which is insoluble in the medium in which the re- 
 
188 ELEMENTS OF CHEMISTRY. 
 
 action takes place. Of course, if any substance is added 
 to the solvent which will prevent the formation of 
 an insoluble substance, then precipitation cannot take 
 place. For example, the carbonates are decomposed 
 by acids, with the liberation of carbon dioxide and 
 water. It follows that reactions 1 and 2 cannot take 
 place if an acid be present, as the carbonate of calcium 
 which should be formed would be decomposed by this 
 acid. If, however, in reaction 2 the acid were sulphuric 
 acid, then a precipitation of the insoluble barium sul- 
 phate would take place, instead of that of the equally 
 insoluble barium carbonate. 76 
 
 Causes of Double Decomposition. Electrolysis. The rea- 
 son why such double decompositions take place is prob- 
 ably to be found in the following explanation : - 
 
 If the two poles of a battery are placed in a salt solution, the 
 salt will be decomposed by the electric current which is conducted 
 from one pole to the other. Of these two poles, one is positive 
 and the other negative. The current passes from the negative to 
 the positive pole. Substances which, like salts, are decomposed 
 by an electric current are termed electrolytes. The terminals 
 from which the current enters or leaves the solution are called 
 the electrodes. The positive electrode is the anode, and the nega- 
 tive one the kathode. The portions into which the electrolyte 
 separates are termed the ions. The ion which passes off at the 
 positive pole (itself negative) is the anion, that passing off at the 
 negative pole (itself positive) is termed the kation. For example, 
 hydrochloric acid is separated by means of an electric current into 
 its ions, hydrogen and chlorine. The kation is hydrogen, the 
 anion is chlorine ; and, if proper means are taken to collect the 
 gases, pure hydrogen can be obtained from the negative pole and 
 chlorine from the positive, as was done in the experiments with 
 hydrochloric acid in Experiment 19, Appendix. In the same way 
 a solution of sodium chloride is separated into sodium (the ka- 
 tion) and chlorine (the anion). A solution of potassium chloride 
 
THE FOEMATION OF SALTS. 189 
 
 will separate into potassium (the kation) and chlorine (the anion), 
 or a solution of potassium sulphate (chemical formula K SO 4 ) into 
 potassium (kation) and the group SO 4 (anion).* Only such solu- 
 tions as contain substances capable of separation into their ions 
 have the power of conducting electricity. Hence it seems proba- 
 ble that salts 'separate, at least partially, when they are dissolved, 
 even if no electric current is passed through them. This supposi- 
 tion is borne out by a number of other experimental facts of too 
 complex an order to be mentioned here. 
 
 A solution of sodium chloride contains the ions rep- 
 resented by the symbols Na and Cl, one of potassium 
 chloride, K and Cl, one of potassium sulphate, 2 K and 
 SO 4 , and so on. We cannot, however, demonstrate the 
 presence of the uncombined ions in such a solution 
 (i.e., we cannot prove the presence of free chlorine and 
 free sodium in a solution of sodium chloride) so long 
 as these elements are not collected at electrodes by 
 the action of an electric current. 
 
 It can be supposed, for example, that, when sodium chloride 
 separates into Na and Cl, the individual atoms do not remain 
 permanently isolated, but that they frequently recombine. Each 
 atom of chlorine, however, does not unite with the same atom of 
 sodium with which it was originally joined, but with another, 
 and again separates and rejoins others in the throng of atoms 
 which it may encounter. 
 
 Change in the Conditions if an Insoluble Substance can be 
 formed. According to this theory, if a solution of sodium 
 chloride is mixed with one of potassium sulphate, we 
 shall have present the ions of Na -j- Cl and 2 K -f SO 4 . 
 Such a mixture is obviously practically identical with 
 one of potassium chloride and sodium sulphate, for the 
 
 * Of course, the potassium or sodium, being in the presence of water, 
 will react again with that liquid. The metals themselves can only be 
 separated by electrolyzing the fused salts, when the water is present. 
 
190 ELEMENTS OF CHEMISTRY. 
 
 latter contains ions K + Cl and 2 Na + SO 4 . The result 
 would then be the same as if on mixing potassium chlo- 
 ride with sodium sulphate we were to have partial 
 double decomposition forming sodium chloride and po- 
 tassium sulphate, both of which are soluble in water. 
 An entirely different effect is obtained if one of the 
 salts produced is insoluble. For example, silver nitrate 
 in solution with sodium chloride undergoes double de- 
 composition, forming the insoluble silver chloride and 
 the soluble sodium nitrate. Now, in a solution of silver 
 nitrate we have the ions Ag* and NO 3 (the chemical 
 formula of silver nitrate is Ag NO 3 ), and in a solution 
 of sodium chloride we have the ions Na and Cl. The 
 chemical structure of such a solution could be repre- 
 sented by the formula 
 
 Na + Cl + Ag + N0 3 . 
 
 kation anion kation anion. 
 
 The kation Ag is capable of uniting with the anion 
 Cl, when it comes in contact with it, and the resulting 
 compound (Ag Cl, silver chloride) is insoluble. It is, 
 therefore, precipitated, and separates from the solution. 
 A second kation Ag can come in contact with a second 
 anion Gl, and so on until all of the silver and chlorine 
 present are separated as silver chloride. The solution 
 will then contain only the ions Na and NO 3 t, which, 
 after the solvent is evaporated, will leave sodium ni- 
 trate. What is true of the above reaction must be 
 true in every case where salts in solution are brought 
 
 * The chemical symbol for one atom of silver is Ag, from the latin ar- 
 gentum (silver). 
 
 t Of course if more sodium chloride than is necessary to form silver 
 chloride with all of the silver in solution is present, then that excess 
 remains after the double decomposition, and vice versa. 
 
THE FORMATION OF SALTS. 191 
 
 in contact, when one of the products of the union of the 
 ions is insoluble. If one of the constituents is volatile, 
 it is just as surely removed from the solution as if it 
 were insoluble. From the above considerations it fol- 
 lows that complete double decomposition must take 
 place whenever insoluble or a volatile substance can 
 be produced. 
 
 Electrolysis of Water and of Hydrochloric Acid. The 
 
 process of electrolysis has been repeatedly used during 
 the progress of this work. Thus water acidulated with 
 sulphuric acid was decomposed into hydrogen and oxy- 
 gen by the electric current (see page 21). Pure water 
 is not a conductor of electricity, and consequently is 
 not subject 'to electrolysis. But when sulphuric acid 
 is dissolved in water the mixture becomes a conductor, 
 and if an electric current is passed through it, the 
 kation H 2 separates at the negative pole, and the anion 
 SO 4 at the positive. But SO 4 is not capable of exist- 
 ence as such ; it breaks down into sulphur trioxide 
 (SO 8 , see page 56) and oxygen, which passes off. The 
 sulphur trioxide, being the anhydride of sulphuric acid, 
 dissolves in water to form sulphuric acid, so that no 
 loss of the latter substance takes place. The only 
 compound which is decomposed is therefore water. 
 
 This change may be represented as follows by chemical 
 symbols : 
 
 H 2 SO 4 = H. 2 + SO 4 . 
 
 Sulphuric acid = kation + anion. 
 
 SO 4 = SO 3 + O. 
 
 The anion = sulphur trioxide + oxygen. 
 S0 3 +H 2 = H 2 S0 4 . 
 
 Sulphur trioxide + water = sulphuric acid. 
 
 The substances passing off are hydrogen and oxygen. 
 
192 ELEMENTS OF CHEMISTRY. 
 
 A concentrated solution of hydrochloric acid is de- 
 composed into hydrogen and chlorine by the electric 
 current (see page 40). In this case the kations of hy- 
 drogen separate at the negative pole and the anions of 
 chlorine at the positive. 
 
 Neutralization of Bases by Acids. To illustrate the 
 neutralization of bases by acids, let us take the neutral- 
 ization of hydrochloric acid by sodium hydroxide. This 
 change can be represented by the chemical formulae 
 
 HC1 + NaOH = NaCl + HOH. 
 
 Hydrochloric acid + Sodium hydroxide = Sodium chloride + Water. 
 
 In solution, hydrochloric acid exists as the ions H -f Cl, 
 and sodium hydroxide as the ions Na +OH. When 
 these are brought in contact the ions would be I'- 
 ll + Cl + Na + OH. 
 
 Now, the only substance which is present in excess, and 
 which, while being capable of formation from the above 
 constituents, would not have a tendency toward ioniza- 
 tion, is water. Water, therefore, would be produced by 
 the interaction of these ions, while the ions Na -f- Cl 
 alone would be left. The same result is obtained when 
 other acids and bases are brought in contact; so that 
 one of the chief reasons for the fact that acids and bases 
 neutralize each other is found in the formation of water. 
 Of course the neutralization would be the more rapid 
 and complete the more readily ionization took place on 
 solution. 
 
 The process of electrolysis has been a most impor- 
 tant one in the history of chemistry. By means of an 
 electric current, Davy first succeeded in decomposing 
 
THE FORMATION OF SALTS. 193 
 
 caustic potash (potassium hydroxide) and caustic soda 
 (sodium hydroxide), and in isolating the metals potas- 
 sium and sodium. Before that time caustic potash and 
 caustic soda were considered elements. 
 
 Summary. 
 
 1. Acids are salts of the metal hydrogen, and salts 
 are acids in which the hydrogen has been replaced by 
 other metals. 
 
 2. Salts of some acids can be formed by the action of 
 those acids upon the salt of some other acid ; for exam- 
 ple, by the action of sulphuric acid on sodium chloride 
 we can produce sodium sulphate. 
 
 3. Such reactions are termed double decompositions, 
 for in them the metal of the salt and the hydrogen of 
 the acid acting upon it exchange places. 
 
 4. The neutralization of a base by an acid is also a 
 double composition. 
 
 5. Double decomposition can also take place between 
 two salts. In such a case the metals in the two salts 
 exchange places. Complete double decompositions 
 occur if a volatile or an insoluble substance is formed 
 during the reaction. 
 
 6. Salt solutions are decomposed (electrolyzed) by 
 the electric current. The salt separates into two ions, 
 
 the kation (metallic constituent) and the anion (not- 
 metallic constituent). Only such solutions as contain 
 substances separable by electrolysis conduct electricity. 
 
 7. Salts, when dissolved, separate into their ions, 
 at least in part. The presence of these ions cannot 
 be demonstrated by ordinary means. They can, how- 
 ever, be collected at the electrodes by the action of the 
 electric current. 
 
194 ELEMENTS OF CHEMISTRY. 
 
 8. When, on mixing two salts, a new insoluble salt 
 can be produced, then a precipitate of such salt is 
 formed. The remaining two ions stay in the solution 
 and form the second new salt on evaporation of the 
 solvent. The case is the same if one of the substances 
 produced is volatile. 
 
 9. In electrolyzing water acidulated with sulphuric 
 acid, the acid is decomposed into its ions, hydrogen and 
 a group of elements represented by the formula SO 4 . 
 The latter separates at the positive pole, and breaks 
 down into sulphur trioxide (SO 3 ) and oxygen. The 
 elements which pass off are, therefore, hydrogen and 
 oxygen. The sulphur trioxide remains, and, with the 
 water which is present, regenerates sulphuric acid. 
 
 10. The process of neutralization is explained by 
 the decomposition of the acid and the base into their 
 ions. Two of these ions must always be hydrogen and 
 hydroxyl (H and OH), and these unite to form water. 
 There would then remain in solution only the metallic 
 and notnnetallic ions which were originally present as 
 constituents of the base and acid respectively. These 
 ions, when the solvent is evaporated, unite to form the 
 salt. * 
 
CHEMICAL NATUEE OF OTHER ELEMENTS. 195 
 
 CHAPTER XXIV. 
 
 THE CHEMICAL NATURE OF SOME OTHER ELE- 
 MENTS AND COMPOUNDS RELATED TO THOSE 
 WHICH HAVE BEEN STUDIED. 
 
 Chemical Elements are Separable into Groups and Fami- 
 lies. The chemical elements are not individuals each 
 with distinct characteristics which do not recur in the 
 natural history of the others. They are members of 
 certain groups or families, the representatives of which 
 are all more or less related to each other, both chemi- 
 cally and physically. To trace out these relations in 
 their entirety would involve too great extension of the 
 limits of an elementary work. We can call attention 
 only to a few individuals which are closely related to 
 the elements which we have studied. 
 
 Elements of the Chlorine Family. Chlorine is very 
 closely connected, chemically, with three other elements, 
 fluorine, bromine, and iodine. These substances, like 
 chlorine, are always found in nature in combination 
 with metals, as fluorides, bromides, and iodides. The 
 bromides and iodides of potassium and sodium are 
 generally found in conjunction with the chlorides of 
 the same metals, but they are present in lesser quantity 
 on the earth's surface. In sea-water there are large 
 amounts of sodium chloride and small amounts of 
 sodium bromide and iodide. All the elements of the 
 
196 
 
 ELEMENTS OF CHEMISTRY. 
 
 chlorine family, with the exception of fluorine, can be 
 isolated from their salts by the same means. 
 
 Of these four elements, fluorine has the smallest 
 atomic weight, chlorine the next higher, bromine the 
 next, and iodine the greatest. In the following table 
 these elements are given in the order of their increasing 
 atomic weights, while the physical properties, which 
 vary regularly in the order given, are placed opposite 
 each individual : 
 
 
 
 03 
 
 
 h 
 
 
 
 
 
 
 U H 
 
 '-' ^ W 
 
 
 O pJ 
 
 O oj 
 
 gw 
 
 ^ U3 Q 
 
 
 Sg 
 
 O - 1 
 
 s" 
 
 USUAL CONDITION. 
 
 2 
 
 35 
 
 pS 
 
 5 a o 
 
 
 H 
 
 ^ 
 
 
 iJ ^ 
 
 
 
 ^0 
 
 a ^02 
 
 
 
 *5" 
 
 
 
 
 * 
 
 
 ^oS 
 
 Fluorine 
 
 19. 
 
 1.364 
 
 Slightly yellow gas 
 
 Yellow 
 
 
 
 
 
 
 
 Chlorine 
 
 35.5 
 
 2.46 
 
 Yellowish-green gas 
 
 Yellow 
 
 35 
 
 102 
 
 
 Bromine 
 
 80. 
 
 5.54 
 
 Dark-brown liquid 
 
 Brown 
 
 63 
 
 7.3 
 
 
 Iodine 
 
 127.6 
 
 8.84 
 
 Crystalline black solid 
 
 Violet 
 
 200 
 
 114 
 
 4.94 
 
 As is seen from the above, the specific gravities, both 
 of the gaseous and solid substances, increase with in- 
 creasing atomic weight, the color deepens, and finally 
 (with iodine) becomes black. The boiling and melting 
 points also increase with increasing atomic weight. 
 
 Elements of the Oxygen Family. Oxygen and sulphur 
 also belong to a family which contains four elements. 
 In order to show the similarity to the chlorine family 
 in the changes brought about by the increase in atomic 
 weight, a table containing the principal physical proper- 
 ties of these elements is given on opposite page. 
 
 Elements of the Nitrogen Family. In the family of 
 which nitrogen is a member, we have five individuals, 
 
CHEMICAL NATURE OF OTHER ELEMENTS. 197 
 
 
 
 O tx CH 
 
 
 
 
 
 & J! 
 
 wn 
 
 
 W 
 
 g| 
 
 ff 
 
 USUAL CONDITION. 
 
 tf o 
 % 
 
 3 g 
 o 
 
 ELTIX 
 J OINT. 
 
 &S3 
 w^ 
 
 
 
 coOg 
 
 
 
 
 w" 
 
 ^ 
 
 UJ oS 
 
 Oxygen 
 
 16. 
 
 1.105 
 
 Colorless gas 
 
 Colorless 
 
 182 
 
 
 
 
 
 Sulphur 
 
 32. 
 
 2.2 
 
 Yellow solid 
 
 Brown 
 
 440 
 
 114 
 
 2.045 
 
 Selenium 
 
 78. 
 
 5.7 
 
 Dark-brown, almost 
 
 Brown 
 
 665 
 
 217 
 
 4.5 
 
 
 
 
 black solid 
 
 
 
 
 
 Tellurium 
 
 125. 
 
 9. 
 
 Metallic appearing solid 
 
 Orange 
 
 
 500 
 
 6.25 
 
 nitrogen, phosphorus, arsenic, antimony, and bis- 
 muth. Of these, the element with the smallest atomic 
 weight (nitrogen) is completely a not-metal, while that 
 with the highest (bismuth) is a metal, physically and 
 chemically. In this family, therefore, we have the same 
 change in properties, with increasing atomic weight, as 
 was observed in the families of which chlorine and oxy 
 gen are representatives. This fact will be plainer by 
 consulting the table : 
 
 
 TOMIC 
 EIGHT. 
 
 ECIFIC 
 AVITT 
 
 GASES. 
 
 USUAL CON- 
 DITION. 
 
 to 
 
 
 
 O co 
 
 S5 
 
 O 
 
 2 ^ 
 
 H ^ 
 
 iff 
 
 w ^W 
 
 
 *t 
 
 &G% 
 
 
 ^ 
 
 & 
 
 s<? 
 
 02O ta 
 O 
 
 Nitrogen 
 
 14 
 
 .972 
 
 Colorless gas 
 
 Colorless 
 
 -193 
 
 -203" 
 
 
 
 Phosphorus 
 
 31 
 
 4.16 
 
 Yellow solid 
 
 Colorless 
 
 290 
 
 440 
 
 1.83 
 
 Arsenic 
 
 75 
 
 10.3 
 
 Steel-gray solid 
 
 Lemon 
 
 450* 
 
 
 
 5.76 
 
 
 
 
 
 yellow 
 
 
 
 
 Antimony 
 
 120 
 
 9.78 1 
 
 Silver white solid 
 
 
 
 About 1200 
 
 425 
 
 6.7 
 
 Bismuth 
 
 208.9 
 
 10.1 
 
 Reddish metallic 
 
 
 
 1400 (?) 
 
 270 
 
 9.93 
 
 
 
 
 solid 
 
 
 
 
 
 * Arsenic vaporizes without previously melting. 
 
 t The specific gravity of antimony vapor is less than that of arsenic. 
 This is because arsenic, when a gas, has molecules formed of four atoms, 
 while antimony, as a gas, has molecules formed of two or less. The 
 molecules of gaseous bismuth consist, in part, of but one atom, hence its 
 low specific gravity. 
 
198 ELEMENTS OF CHEMISTRY. 
 
 In all these families which have been mentioned, the 
 increase in atomic weight, as we pass from member to 
 member, brings with it an increase in specific gravity 
 both as a vapor and as a solid. There is also a gradual 
 change from a not-metallic to a metallic element, or, 
 at least in the chlorine family, to an element which 
 is more like a metal than the original member. 
 
 Comparison of the Three Families. As a rule then, in 
 these three families, the specific gravities of the ele- 
 ments, both when taken as gases and as solids, increase 
 as the atomic weight increases, and at the same time 
 the melting-points become higher. The elements with 
 the lowest atomic weights are not metallic, while those 
 with the highest are either metallic in appearance (tel- 
 lurium and arsenic, antimony and bismuth), or at least 
 approach the metallic character (iodine). In chemical 
 character we find the same close family relationship. 
 
 Chemical Resemblances in the Hydrogen Compounds. 
 Our attention, in the preceding portions of this work, 
 has mainly been directed to a consideration of com- 
 pounds of the elements with hydrogen. Therefore, in 
 calling attention to the chemical resemblances of the 
 members of the three families under discussion, we 
 shall use the hydrogen compounds as a basis. 
 
 Hydrogen Compounds of the Chlorine Family. Fluorine, 
 chlorine, bromine, and iodine are capable of producing 
 one hydrogen compound each ; and this, like hydrogen 
 chloride, is a gas at ordinary temperatures.* These 
 hydrogen compounds are all readily soluble in water, 
 
 * Hydrogen fluoride boils at 19, and is, therefore, a gas at summer 
 heat, but a liquid at winter temperature. 
 
CHEMICAL NATURE OF OTHER ELEMENTS. 199 
 
 and their solutions are acids, capable of neutralizing 
 bases to form salts. These substances are termed hy- 
 drofluoric, hydrochloric, hydrobromic, and hydroiodic 
 acids. The salts derived from the acids by replacing 
 the hydrogen by other metals are the fluorides, chlo- 
 rides, bromides, and iodides. These hydrogen com- 
 pounds are all formed on the same structural plan ; i.e., 
 by the union of equal volumes of hydrogen and of the 
 not-metallic element (fluorine, chlorine, bromine, or 
 iodine), so that their smallest particles contain one 
 atom of hydrogen and one atom of fluorine,* chlorine, 
 bromine, or iodine. The chemical formulae of these 
 substances are, therefore 
 
 HF, the chemical symbol for one atom of fluorine being F. 
 H Cl, the chemical symbol for one atom of chlorine being Cl. 
 H Br, the chemical symbol for one atom of bromine being Br. 
 HI, the chemical symbol for one atom of iodine being I. 
 
 The stability of these hydrogen compounds diminishes 
 as the atomic weight of the not-metallic element in- 
 creases. As a consequence, hydrogen iodide is much 
 more readily decomposed than hydrogen bromide, and 
 hydrogen bromide more readily than hydrogen chloride. 
 Hydrogen fluoride has not been separated into its ele- 
 ments by heat alone. Hydrogen chloride is decom- 
 posed only at a high white heat, while hydrogen iodide 
 can be broken down by a red-hot wire placed in the gas. 
 The relative stability of the last three of these compounds 
 is readily shown by the following experiments : - 
 
 If a few drops of a solution of chlorine in water are added to a 
 solution of hydriodic acid, iodine will at once separate and hydro- 
 
 * The specific gravity of hydrogen fluoride, as a gas, shows that this 
 suhstance has a molecule composed of two atoms of hydrogen and two of 
 fluorine. Its formula, therefore, heing H 2 F 2 . 
 
200 ELEMENTS OF CHEMISTRY. 
 
 chloric acid be formed. Chlorine, therefore, expells iodine from 
 its hydrogen compound, to form the more stable hydrochloric 
 acid. In the same way bromine is replaced by chlorine, when 
 the latter element is brought in contact with hydrobromic acid ; 
 and lastly, iodine is expelled from hydroiodic acid by bromine. 77 
 
 Hydrogen Compounds of Elements of the Oxygen Family. 
 The elements of the family of which oxygen is a mem- 
 ber all form hydrogen compounds which, with the ex- 
 ception of hydrogen oxide (water), are colorless gases 
 at ordinary temperatures. These hydrogen compounds 
 are all of the same structural plan, for their molecules 
 are formed of two atoms of hydrogen and one atom of 
 the not^metallic element. This will be seen from the 
 following chemical formulae : 
 
 H 2 O, water. 
 
 H 2 S, hydrogen sulphide. 
 
 H 2 Se, hydrogen selenide (the chemical symbol for one atom 
 
 of selenium is Se). 
 H 2 Te, hydrogen telluride (the chemical symbol for one atom 
 
 of tellurium is Te). 
 
 In regard to their relative stability, these hydrogen 
 compounds follow the same rule as in the case of 
 chlorine, bromine, and iodine ; the higher the atomic 
 weight of the element forming them is, the more easily 
 are they decomposed. Thus, water is broken down 
 into hydrogen and oxygen only at a high white heat, 
 while hydrogen telluride is so unstable that it decom- 
 poses in part, even at ordinary temperatures. The 
 compounds hydrogen sulphide and hydrogen selenide 
 lie between these two extremes. 
 
 Hydrogen Sulphide, Preparation and Properties. Next 
 to water, the most important hydrogen compound of 
 
CHEMICAL NATURE OF OTHER ELEMENTS. 201 
 
 the elements of the oxygen family is hydrogen sulphide. 
 This substance is so frequently used as a laboratory 
 reagent that a brief description of its properties and 
 its reactions is necessary. 
 
 The preparation of hydrogen sulphide involves the 
 same principle as that of hydrogen chloride. The sul- 
 phide of a metal is treated with an acid, just as sodium 
 chloride is brought in contact with sulphuric acid, in 
 order to liberate hydrogen chloride ; for example : - 
 
 Sulphide of iron (ferrous sulphide) with hydrochloric acid 
 forms chloride of iron (ferrous chloride) and hydrogen sulphide. 
 
 Sulphide of zinc with sulphuric acid forms zinc sulphate and 
 hydrogen sulphide. 
 
 All metallic sulphides, however, are not decomposed 
 by acids, there being a considerable number which are 
 not acted upon. In the laboratory preparation of hy- 
 drogen sulphide, it is advisable to decompose ferrous 
 sulphide with dilute sulphuric acid, producing ferrous 
 sulphate and hydrogen sulphide. 78 In chemical nota- 
 tion this reaction can be expressed as follows : - 
 
 FeS + H 2 SO 4 = FeSO 4 + H 2 S. 
 
 Ferrous sulphide + Sulphuric acid = Ferrous sulphate + Hydrogen sulphide. 
 
 This reaction, therefore, involves a double decomposition, and 
 is entirely analogous to the neutralization of a base by an acid, as 
 the following reaction will demonstrate : 
 
 FeO + H 2 S0 4 = FeS0 4 +H 2 O. 
 
 Ferrous oxide (a base) + Sulphuric acid = Ferrous sulphate + Water. 
 
 Properties of Hydrogen Sulphide. Under ordinary conditions, 
 hydrogen sulphide is a gas with a most disagreeable odor. When 
 inhaled, even in comparatively small quantities, it is poisonous. 
 It is soluble in water in considerable quantity (one cubic centi- 
 metre of water dissolves three of hydrogen sulphide at 18) ; and 
 its solution, when allowed to stand exposed to the air, gradually 
 
202 ELEMENTS OF CHEMISTRY. 
 
 deposits sulphur, owing to the fact that it is oxidized. This 
 change can chemically be repeated as follows : 
 
 H 2 S + O == H 2 + S. 
 
 Hydrogen sulphide + Oxygen = Water + Sulphur. 
 
 It naturally follows from the above that hydrogen sulphide 
 burns in the air just as does methane. When methane burns, it 
 forms carbon dioxide and water ; when hydrogen sulphide burns 
 in an excess of oxygen, it forms sulphur dioxide and water. 
 
 Formation of Insoluble Sulphides by Double Decomposi- 
 tion between Hydrogen Sulphide and the Salts of Metals. 
 Most sulphides of the metals are not soluble in water ; 
 and, as has been mentioned above, a considerable num- 
 ber are not decomposed by dilute acids. Consequently, 
 in many cases, the insoluble sulphides are precipitated 
 from solutions of metallic salts by the addition of hy- 
 drogen sulphide. 79 For example : 
 
 Copper sulphate 4- Hydrogen Sulphide = Copper sulphide -*- Sulphuric acid. 
 
 Soluble soluble insoluble soluble. 
 
 Lead acetate -(-Hydrogen sulphide = Lead sulphide + Acetic acid. 
 
 Soluble soluble insoluble soluble. 
 
 Some Sulphides Insoluble in Water are Soluble in Dilute 
 Acids. The sulphides of certain metals, although they 
 are insoluble in water, are decomposed by dilute acids, 
 and hence are soluble in the latter. This is the case 
 with ferrous sulphide or zinc sulphide which were men- 
 tioned above. Under these circumstances, it is obvious 
 that no precipitate, or at least very little precipitate, of 
 the sulphide is produced by hydrogen sulphide ; for, 
 as the action of hydrogen sulphide in producing the 
 sulphide of the metal liberates an acid, it follows that 
 the latter would reverse the reaction as soon as it is 
 formed, In other words, it would attack the sulphide, 
 
CHEMICAL NATURE OF OTHER ELEMENTS. 203 
 
 and reproduce the original salt of the metal together 
 with hydrogen sulphide. For example : 
 
 Zinc sulphate + Hydrogen sulphide = Zinc sulphide + Sulphuric acid. 
 
 Soluble soluble insoluble soluble. 
 
 After a certain quantity of sulphuric acid has been 
 formed, the latter attacks the zinc sulphide in order to 
 reproduce zinc sulphate and hydrogen sulphide. If care 
 is taken to neutralize the acid as fast as it is formed, 
 the precipitation is complete. The neutralization can 
 be accomplished by adding the sulphide of an alkali 
 metal instead of hydrogen sulphide, thus : 
 
 Zinc sulphate + Potassium sulphide = Zinc sulphide -f Potassium sulphate. 
 
 Soluble soluble insoluble soluble. 
 
 In this case no free sulphuric acid is formed, and 
 hence no solution of the zinc sulphide takes place. 80 
 The chemical importance of hydrogen sulphide is 
 mainly found in its use as a means of separating cer- 
 tain groups of metals from each other when they are 
 found in solution as salts. If hydrogen sulphide is 
 added to the acid solution of the salts of a number 
 of metals, some of which form sulphides insoluble in 
 dilute acids, while others produce soluble sulphides, 
 it is obvious that the metals of the first class can be 
 completely separated by the addition of the hydrogen 
 sulphide, while those of the second remain dissolved. 
 After the hydrogen sulphide has separated all that it 
 will, the precipitate can be filtered off, and then the 
 soluble sulphides can be separated by the neutrali- 
 zation of the acid by a base. By this means a com- 
 plete separation of the two classes of metals can be 
 
204 ELEMENTS OF CHEMISTRY. 
 
 effected, and such separations are the basis of the 
 branch of chemistry termed analytical chemistry? 1 
 
 The Hydrogen Compounds of the Elements of the Nitro- 
 gen Family. The elements of the nitrogen family, with 
 the exception of bismuth, are capable of forming hy- 
 drogen compounds which are constructed on the same 
 plan as ammonia; i.e., for one atom of the charac- 
 terizing element in each molecule of the hydrogen 
 compound, we have three atoms of hydrogen : 
 
 Ammonia (hydrogen nitride), chemical formula, NH 3 . 
 Phosphine (hydrogen phosphide), chemical formula, PH 3 .* 
 Arsine (hydrogen arsenide), chemical formula, AsII 3 . 
 Stibine (hydrogen antomonide), chemical formula, SbH 3 . 
 
 Like the hydrogen compounds in the other families, 
 those in this diminish in stability as the atomic weight 
 of the element entering into their formation increases. 
 Ammonia is quite stable, while arsine and stibine are 
 both very easily decomposed into their constituent ele- 
 ments by heating. 
 
 Lastly, in the carbon family, we also have five ele- 
 ments, carbon, silicon, germanium, tin, and lead. We 
 have here the same changes with increasing atomic 
 weight. Carbon is a not-metal ; lead, with the highest 
 atomic weight, is a metal. Only carbon and silicon are 
 capable of forming compounds with hydrogen, and the 
 hydrogen compound of silicon, while much less stable 
 than methane, is formed according to the same plan : 
 
 Methane, chemical formula, CH 4 . 
 Silicon hydride, chemical formula, Si H 4 . 
 
 * The chemical symbols for one atom of phosphorus, arsenic, and 
 antimony are P, As, and Sb respectively. The symbol Sb for antimony 
 is derived from the Latin stibium. 
 
CHEMICAL NATURE OF OTHER ELEMENTS. 205 
 
 The few relationships which have been mentioned 
 will serve to show what is meant by the statement that 
 " the elements are divided into certain groups or fami- 
 lies." What is true of the few elements studied is also 
 true of every other element with which we are ac- 
 quainted. Each one of these is a member of a family 
 with several representatives which are closely related 
 chemically and physically. In larger works on chemis- 
 try, where the characteristics of all of the elements are 
 considered, the grouping by families forms the basis for 
 the systematic arrangement of such works. 
 
APPENDIX. 
 
 PRECAUTIONS TO BE TAKEN WHILE WORKING IN THE 
 LABORATORY. 
 
 BEFORE entering upon laboratory work the pupil should read 
 and remember the following cautions : 
 
 Burns, stains, and Jire. Yellow phosphorus should never be 
 handled except with a pair of tongs or pincers. When exposed 
 to the air in a warm room it may take fire spontaneously. If 
 touched by the hand it will take fire. The burns so produced 
 are extremely painful, and may become dangerous by reason of 
 phosphorus poisoning. Sodium and potassium are kept under 
 naphtha. Pieces larger than beans should never be placed in 
 water ; and in any event, a very small piece should first be tested. 
 Sodium which has not a clear and bright surface when cut, 
 should be rejected. In all cases the outer coating of oxide should 
 be cut away before placing the metal in water. Burns are best 
 treated by covering the spot with a solution of cocaine in sweet 
 oil, and then with an emulsion of lime-water, glycerine, and sweet 
 oil. Nitric acid stains the skin yellow. Where concentrated, it 
 will cause an ulcer to form. Bromine stains the skin brown, and 
 unless instantly removed it will cause a painful ulcer. Iodine 
 stains the skin dark violet ; nitrate of silver, black. Of course 
 every precaution should be taken to keep the above substances 
 from touching the hands or face ; but, in case of accident, washing 
 with clean water will be best in the case of nitric acid and bro- 
 mine. A solution of sodium hyposulphite followed by water will 
 remove iodine. Concentrated sulphuric acid will attack the skin ; 
 not so rapidly, however, as nitric acid. In case of an accident 
 this can often be removed by washing with water or sodium car- 
 bonate solution before serious results have followed. Hot sul- 
 phuric acid will instantly produce the most painful burns. Any 
 
 207 
 
208 ELEMENTS OF CHEMISTRY. 
 
 test-tube in which sulphuric acid or anything else is being heated, 
 should be held by a test-tube holder with its mouth pointing away 
 from the manipulator or from any one standing near. Ether or car- 
 bon bisulphide must not be used within six feet of a burning Bun- 
 sen burner. These liquids take fire with the greatest readiness. 
 Matches should be kept in a tin box, which is never to be placed 
 in the drawer of the desk, but should always be kept outside. 
 
 Inhalation of fumes and gases. Chemical experiments which 
 will develop poisonous or irritating gases should always be per- 
 formed under a hood with a good draught.* Chlorine and bromine 
 attack the mucous membrane of the eyes, throat, and nose. 
 Continued inhalation will give rise to bronchial inflammation. 
 Chlorine or bromine will also cause nausea. If, by accident, the 
 pupil should take an excessive quantity of chlorine into the lungs, 
 the quickest remedy is probably the inhalation of the fumes of 
 alcohol. The gaseous oxides of nitrogen are poisonous, causing 
 violent headache and nausea. Phosphine, arsine, and stibine are 
 very poisonous. Ammonia is quite irritating. Work in which 
 these substances are generated or used must be done under the 
 hood. Sulphuric acid should not be heated to above 150 unless 
 the apparatus is under the hood. The acid will break down, 
 partly into water and sulphur trioxide ; the vapors of the latter 
 are irritating to the lungs. Liquids containing hydrochloric acid 
 or nitric acid should be evaporated under the hood. Sulphuretted 
 hydrogen is poisonous and disagreeable ; continued inhalation of 
 even small quantities will cause headache, and may have serious 
 results. It is, therefore, imperatively necessary, unless a room 
 is especially provided in which to generate this gas, that all work 
 with hydrogen sulphide should be performed under the hood. 
 Sulphur dioxide is extremely irritating ; work with this gas must 
 always be done under the hood. 
 
 Explosions Most accidents result from carelessness ; there- 
 fore, the invariable rule by which the student should govern him- 
 self in the laboratory is, " Never be careless ; for carelessness may 
 
 * So urgent is this rule that pupils should be forbidden even to heat 
 test-tubes or small evaporating dishes with reagents which will give off 
 fumes of hydrochloric acid, nitric acid, hydrogen sulphide, bromine, 
 chlorine, nitric oxide, etc., unless they do so under the hood. A good 
 hood is as necessary as a good burner. 
 
APPENDIX. 209 
 
 result in permanent disfigurement or loss of sight." Hydrogen 
 and oxygen, hydrogen and air, hydrogen and chlorine, gaseous 
 hydrocarbons and oxygen, phosphine and oxygen, or phosphine 
 and air, as well as the other not very stable hydrogen compounds 
 of the riot-metals, mixed with oxygen or air, will cause violent 
 explosions when ignited. In generating these gases, extreme 
 care must be taken not to bring a flame near the exit-tube of the 
 apparatus until the pupil is sure that a brisk current of the gener- 
 ated gas has traversed the apparatus for sufficient length of time 
 to expel all air. No definite time rule can be established, be- 
 cause this will vary with the size of the apparatus ; but, when 
 using the ordinary generating flasks of from 300 to 500 cc., the 
 pupil should wait at least seven to ten minutes. Chlorate of 
 potassium, permanganate of potassium, and similar powerful oxidi- 
 zers must not be rubbed in a mortar when in contact with sub- 
 stances which are readily oxidized (sugar, starch, sulphide of 
 antimony, sulphur, phosphorus, etc.). Care must be taken to 
 have all drying trains or other apparatus for washing gases in 
 such a condition that a current of gas can pass through freely ; 
 otherwise, when a gas is being generated, the pressure caused by 
 a stoppage may give rise to a dangerous explosion. Safety-tubes 
 must always be open ; otherwise they are no longer safety-tubes, 
 for their being stopped may cause an explosion. The openings 
 by which gases escape from the generating apparatus must be 
 sufficiently large to allow a free current of gas to flow. 
 
 In a well-conducted laboratory, desks and apparatus must 
 always be kept as clean as possible, and reagent bottles returned to 
 their proper places as soon as the occasion requiring their use is 
 over. Bunsen burners can be cleaned by unscrewing the outer 
 tube, and brushing the nipple with a dry, stiff, test-tube brush. 
 
LABORATORY EXPERIMENTS. 
 
 Carefully read the laboratory precautions on preceding pages. 
 
 THE following experiments are to be conducted in the 
 laboratory in connection with the work on the text. The 
 pupil must carefully follow all the directions, and answer 
 all questions, putting his observations and answers in a 
 note-book. Some of the experiments can be performed 
 only by the teacher. These are marked " Teacher's 
 experiments.'' Their description is to be given in the 
 pupil's note-book exactly as if they had 'been performed 
 by the pupil himself. 
 
 1. The Thermometer 
 
 The thermometer in general scientific use is the centi- 
 grade ; the one in popular use in the United States is the 
 Fahrenheit. The usual thermometer measures the tem- 
 perature by means of the expansion of mercury when the 
 temperature is increased, or the contraction when it is di- 
 minished. It consists of a capillary tube, one end of which 
 terminates in a bulb. This bulb and a portion of the 
 capillary tube are filled with mercury. The upper part of 
 the tube is either a vacuum, or is filled with nitrogen, and its 
 tip closed by fusing the glass. The bulb is first placed in 
 melting ice, and the position of the mercury column is 
 marked as (in the centigrade thermometer). The ther- 
 mometer is then transferred to water which is boiling under 
 a pressure of one atmosphere, and the point at which the 
 
 211 
 
212 
 
 ELEMENTS OF CHEMISTEY. 
 
 upper end of the mercury column stands is marked 100. 
 The interval is divided into 100 equal parts, called degrees. 
 In the Fahrenheit thermometer the melting-point of ice is 
 marked 32, and the boiling-point of water, 212. The divis- 
 ions in each thermometer are carried some distance below 
 0, and these are designated by the minus sign. The dia- 
 gram, Fig. 1, shows the difference between the centigrade 
 and Fahrenheit thermometers. 
 
 FAHREHHEIJ. 
 
 BOIL/NCPOINJ 
 OF mifR 
 
 
 
 too 
 
 \ * 
 
 ^/2 
 
 MELTIHt, 
 P01HT 
 
 1 
 
 1 
 
 OF ICE 
 
 
 32" 
 
 17% 
 
 
 0" 
 
 Fig. 1. 
 
 The fundamental difference between the thermometers is 
 that 
 
 100 Centigrade = 180 Fahrenheit, 
 or 5 = 9 " 
 
 The temperature centigrade in terms of Fahrenheit is 
 therefore given by the following calculation : 
 
 t Centigrade = (f + 32) Fahrenheit, 
 where t represents the observed temperature. 
 
LABOEATOEY EXPEEIMENTS. 213 
 
 On the other hand, t Fahrenheit 32 = f 1 Centigrade. 
 For temperatures below Fahrenheit, the formula for 
 change to centigrade is 
 
 I ( t Fahrenheit + 32) = t Centigrade, 
 and I ( t Centigrade) 32 = t Fahrenheit, 
 and if f t = 32, then the temperature is at Fahren- 
 heit. 
 
 In all scientific work the metric system is employed 
 exclusively. If the pupil is not already familiar with this 
 system, he should thoroughly familiarize himself with it 
 before beginning work. The metric system and the centi- 
 grade thermometer are used in this book. For a description 
 of a barometer and its use, see Experiment 36. 
 
 2. Solution. 
 
 a. In a test-tube make a saturated solution of common 
 salt (sodium chloride) in boiling water * by adding more salt 
 than the water will dissolve. Allow the undissolved por- 
 tion to settle, and pour off the hot, clear, supernatant liquid 
 into a second test-tube, setting the latter aside to cool. 
 (Why cool ?) Make a careful examination with the aid of 
 a small magnifier of the crystals which have formed. 
 
 Repeat, using blue vitriol (copper sulphate) instead of 
 sodium chloride. 
 
 Repeat with potassium chlorate. Use the same amount 
 of water in each of these experiments, and note the differ- 
 ence in the quantities of the three substances which are 
 deposited on cooling. - 
 
 Repeat the above with a small piece of marble ; pour off 
 the water, and evaporate the remainder to dryness in a 
 small porcelain dish over a flame, or, better, on a water 
 bath. (Why use a water bath ?) Note if any residue 
 is formed. Is marble soluble in water ? 
 
 * Distilled water should be used in all chemical work. 
 
214 ELEMENTS OF CHEMISTRY. 
 
 6. Heat Changes During Solution. 
 
 Take 10 c.c. of distilled water in a test-tube or small 
 beaker, and ascertain the temperature. Add 5 grams of 
 sodium chloride, and stir with the thermometer until solu- 
 tion is effected. Again note the temperature. 
 
 Eepeat with copper sulphate and with potassium nitrate 
 (saltpetre). (Use a clean beaker and fresh water in each 
 case.) 
 
 (The lowering of temperature on solution of salts is caused by the 
 absorption of heat, which is used to produce the fluid condition from 
 the solid.) 
 
 3. Water of Crystallization. 
 
 a. Carefully dry some crystals of common salt (sodium 
 chloride) by pressing them between filter paper, then place 
 the crystals in a test-tube, and heat in the Bunsen flame. 
 
 Eepeat with (b) crystals of sodium sulphate (Glauber's 
 salt), (c) white vitriol (zinc sulphate), (d) copper sulphate. 
 What is the difference between the behavior of these sub- 
 stances and that of common salt ? 
 
 Determination of the water of crystallization. 
 
 Put about 2 gins, of copper sulphate crystals in a 
 weighed and clean porcelain crucible, and heat for one hour 
 at 225 in an air bath. Cool in a desiccator and weigh. 
 Heat again and weigh, continuing the operation until the 
 weight is constant. What is the change in appearance of 
 crystals ? In weight ? 
 
 Eepeat the same experiment with a second sample of 
 copper sulphate crystals, and then ascertain the per cent 
 of loss in weight which the crystals have suffered in each 
 experiment. Is the result the same in both cases ? * 
 
 * In performing experiments like the above, care must be taken to 
 have good, clean chemicals. The copper sulphate crystals must be fresh 
 and must not have lost any of their lustre, otherwise no constant results 
 can be obtained. 
 
LABORATORY EXPERIMENTS. 215 
 
 4. a. Efflorescence. 
 
 Expose to the air for twenty-four hours some crystals of 
 sodium carbonate on a dry watch-glass. Do the same with 
 some crystals of sodium sulphate. With some crystals 
 of copper sulphate. Note the result in each case. 
 
 b. Deliquescence. 
 
 Expose to the air, as in the above experiments, some 
 pieces of calcium chloride. Some caustic potash. Some 
 caustic soda. Note the result in each case. 
 
 c. Heat changes during solution of anhydrous substances capable of 
 uniting with water of crystallization. 
 
 Repeat the experiments under 2 &, using 10 cc. of dis- 
 tilled water, and dissolving in this (a) 5 grams of fused 
 calcium chloride, (b) Eepeat with 5 grams of copper 
 sulphate which has been dried at 200. Note changes of 
 temperature in each case. Compare with the results ob- 
 tained by dissolving copper sulphate containing water of 
 crystallization. 
 
 5. Solution of Gases in Liquids. 
 
 a. Under the bell jar of an air-pump, place a beaker of or- 
 dinary water and exhaust the air. (Teacher's experiment.) 
 
 b. Take a beaker half full of water, place it on a wire 
 netting covering the ring of a retort stand, and heat gently. 
 Note that bubbles of gas pass off before the water comes 
 to a boil. 
 
 The following law governs the solution of gases in liquids. 
 The quantity of a given gas which can be dissolved by 
 a fixed quantity of a liquid varies directly as the pressure 
 on that gas. This form of solution is termed the absorp- 
 tion of a gas by a liquid. Where chemical union takes 
 place between the gas and the solvent, the above law does 
 not hold good. When the pressure is removed, the gas 
 escapes until the solution is saturated at ordinary pressure. 
 
216 
 
 ELEMENTS OF CHEMISTRY. 
 
 Example : One cubic centimetre of water dissolves 1.05 
 cubic centimetres of carbon dioxide at one atmosphere 
 pressure, and 3.15 cubic centimetres at three atmospheres. 
 Ordinary soda-water contains carbon dioxide dissolved 
 under pressure. When the pressure is removed, the gas 
 escapes ; i.e., the liquid effervesces. 
 
 6. Filtration and Distillation. 
 
 The proper arrangement of a filter in a funnel is shown 
 by Fig. 2. The filter paper (unsized paper) is circular and 
 is folded twice, so as to form a quad- 
 rant. This is opened so that one 
 thickness of paper is on one side, and 
 three on the other. The paper is now 
 pressed snugly into the funnel, moist- 
 ened with water, and brought evenly 
 into place by sucking on the stem. 
 A filter should never reach above the 
 edges of the funnel. Take some pow- 
 dered chalk, suspend it in 20 cc. of 
 water, and pour this on the filter. 
 Note if the liquid passing through is 
 clear. (That which passes through is 
 termed the filtrate, that which remains 
 on the filter the precipitate.) 
 Fig. 3 represents the ordinary distilling apparatus, com- 
 posed of a flask, Z>, with the thermometer, T, condenser, (7, 
 and receiver, ft. The liquid in the flask is boiled, the vapor 
 is condensed by a current of cold water, which is admitted 
 between the outer jacket and the inner tube of the con- 
 denser at the lower opening, and which escapes into a 
 basin at the upper opening. 
 
 Distillation. 
 
 a. Place in the distilling-flask, which should be of 100 
 to 200 c.c. capacity, a solution of 2 grams of copper sul- 
 
 Fig. 2. 
 
LAB OR A TOR Y EXPERIMENTS. 
 
 217 
 
 phate in 50 c.c. of water. Replace the stopper with the 
 thermometer, and heat until about one-half of the solution 
 has passed over into the receiver. Note the boiling-point 
 of the liquid in the flask. Evaporate the contents of the 
 receiver to dryness, and do the same with the contents of 
 the distilling-flask. 
 
 (The contents of the receiver, after distillation, is termed 
 the distillate.) 
 
 1). Distil 90 c.c. of ordinary water until about 10 c.c. 
 remain, then add 50 c.c. more, without emptying the distil- 
 ling-flask, and repeat this operation four times. Now put 
 the contents of the distilling-flask into an evaporating-dish, 
 
 Fig. 3. 
 
 and evaporate to dryness on a water-bath. Put the distillate 
 into an evaporating-dish, and also evaporate on a water- 
 bath. What is the difference between the two waters 
 which you have evaporated ? What class of substances 
 can be separated from water by distillation ? 
 
 7. Action of Sodium and Potassium on Water. 
 a. Take a clean piece of sodium as large as a pea, care- 
 fully remove the naphtha with a piece of filter paper, and 
 
218 
 
 ELEMENTS OF CHEMISTRY. 
 
 throw the sodium into a basin of water. Repeat with a 
 piece of potassium. Compare the action of potassium 
 with that of sodium. Be careful to stand aside at least 
 eight feet while the action is going on. 
 
 b. Collecting the gases generated by the action of sodium on water. 
 Fig. 4 shows a vessel, preferably of glass or of sheet 
 iron, with a capacity of at least one litre. Nearly fill this 
 
 vessel with water, and invert 
 over it a small test-tube filled 
 with water. Now wrap in wire 
 gauze a clean piece of sodium 
 as large as a pea, and with a 
 pair of forceps quickly place it 
 under the mouth of the test- 
 tube, or use an inverted wire- 
 gauze spoon, as shown in the 
 cut.* When the tube is full 
 of gas, place the thumb over 
 its mouth, then light a splinter 
 of wood, remove the thumb, 
 and quickly apply the flame to 
 the mouth of the tube. Taste 
 a drop of the water left in the trough. Insert the fingers 
 into the trough, and note the feel of the water. 
 
 8. The Electrolysis of "Water. 
 
 The apparatus (Fig. 5) consists of a shallow glass vessel 
 with a wide mouth, closed by a water-tight rubber stopper. 
 Through the stopper pass two stout platinum wires about 
 two or three centimetres apart, and extending several cen- 
 
 * Care should be taken to test the sodium to be used in any of these 
 experiments by placing a small piece on water, and then standing aside ; 
 for unless the metal is clean there is great danger of an explosion. 
 Scraps of sodium which have been kept in the laboratory for some time 
 should never be used. The brown rind must always be carefully removed 
 from the sodium before using. 
 
 Fig. 4. 
 
LA B OEA TOE Y EXPERIMENTS. 
 
 219 
 
 timetres above and below the stopper. To the lower ends 
 of the platinum wires connect two or more cells of a bichro- 
 mate battery by means of insulated copper wires. Fill the 
 glass vessel with distilled water, 
 also fill two tubes * with the same 
 liquid, and invert them in the ves- 
 sel so that their mouths are over the 
 wires ; adjust the tubes in a ver- 
 tical position by means of clamps, 
 and turn on the current. Is there 
 any action ? (See page 191.) Now 
 add concentrated sulphuric acid to 
 the water, drop by drop, until there 
 is a satisfactory development of gas 
 at each pole. What gas collects at 
 the negative pole ? What gas col- 
 lects at the positive pole ? 
 
 When 10 to 15 c.c. of gas has 
 collected at the kathode,t raise the 
 carbon and zinc plates from the 
 battery jar, allow the apparatus to 
 stand for five minutes, and then 
 carefully read off the volumes of 
 the two gases which have collected. 
 Now with the thumb close the tube 
 over the negative electrode, remove 
 it from the basin, invert it, and 
 instantly apply a lighted taper to 
 
 Fig. 5. 
 
 * The tubes should be divided into cubic centimetres. 
 
 f The negative pole of the battery is the one connected with the zinc, 
 the positive pole is the one connected with the carbon in the cell. The 
 positive pole is termed the anode, the negative pole the kathode, and 
 the liquid which is decomposed is the electrolyte. The two platinum 
 wires are termed the electrodes. 
 
220 
 
 ELEMENTS OF CHEMISTRY. 
 
 its mouth. Remove the tube over the positive pole in the 
 same way, and insert into it a glowing pine splinter. What 
 is the difference between the two gases ? Did you obtain 
 exactly twice as much of one gas as of the other ? If this 
 relationship is not exactly correct, what is the reason for 
 the discrepancy ? 
 
 9. Preparation of Hydrogen and Oxygen for Laboratory Use. 
 
 a. The preparation and collecting of hydrogen. 
 It has been found that hydrogen is liberated by the action 
 of certain substances termed acids (see pages 45 and 57) on 
 certain metals. For example, zinc when covered by dilute 
 sulphuric acid generates hydrogen, while at the same time 
 the zinc is dissolved by the acid, and enters into the forma- 
 tion of a substance termed zinc sulphate. At the present 
 time the means by which it is done does not interest us so 
 much as the study of the properties of the hy- 
 f /{ A drogen which we can obtain. 
 
 The apparatus for the preparation of hydro- 
 gen is shown by Fig. 6. It consists of a heavy 
 walled flask, into which is fitted a rubber stopper 
 with two holes. Into one of these a so-called 
 safety-tube is fitted (the curved tube with the 
 
 Fig. 6. 
 
LABORATORY EXPERIMENTS. 221 
 
 funnel top and bulb in the middle; see figure), and into 
 the other is inserted a glass tube bent at a right angle, and 
 reaching just to the bottom of the stopper. When all is 
 ready, place 15 grams of zinc in the flask, insert the stop- 
 per, and pour dilute sulphuric acid through the safety- 
 tube, adding more acid from time to time as occasion 
 requires.* To purify the hydrogen generated by zinc 
 and sulphuric acid, pass it through a wash-bottle f con- 
 taining a solution of two grams of caustic potash in 10 
 grams of water, and through a second one with concen- 
 trated sulphuric acid. 
 
 b. Experiments with hydrogen. 
 
 Fill two or three test-tubes or cylinders with the gas, 
 over water, as shown in the figure. Remove one of these 
 from the water, mouth downward, and quickly insert a 
 lighted taper. Connect an ordinary clay pipe (coated with 
 paraffine on the outside) with the hydrogen generator, and 
 bring the mouth of the pipe into some strong soap-suds, to 
 which has been added a little glycerine or gum arabic. 
 Note if the soap-bubbles rise in the air. Is hydrogen 
 very soluble in water ? How would you discover whether 
 a gas is very soluble in water ? 
 
 c. The preparation and collecting of oxygen for laboratory use. 
 
 In preparing large quantities of oxygen for laboratory 
 
 * Dilute sulphuric acid is prepared by adding one part of commercial 
 acid to six parts of water. In diluting sulphuric acid, pour the acid into 
 the water slowly, but do not pour the water into the acid. Cool the 
 acid by placing the flask in which it is diluted under the hydrant 
 before using. 
 
 t A wash-bottle consists of an ordinary wide-mouthed bottle, fitted 
 with a stopper having two holes. Into one hole of the stopper is inserted 
 a tube, bent at a -right angle, and reaching to the bottom of the flask. 
 Into the other is fitted a glass tube bent at a right angle, and reaching 
 just to the bottom of the stopper. The gas enters through the former 
 tube, and passes out through the latter. When a liquid is placed in the 
 bottle the gas must bubble through this liquid, and is washed by it. 
 (See Fig. 6.) 
 
222 
 
 ELEMENTS OF CHEMISTRY. 
 
 use, it is not expedient to decompose water by the electric 
 current. There is a salt-like body (chlorate of potassium) 
 which, when heated to a sufficiently high temperature, 
 gives off oxygen. 
 
 The apparatus for the preparation of oxygen in large 
 quantities, shown in Fig. 7, consists of a flask of 200 c.c. 
 capacity, fitted with a stopper in which is placed a glass 
 tube bent at two right angles. This tube is 
 put into the flask just to the bottom of the 
 stopper, and its other end is connected with a 
 safety-bottle. This safety-bottle must always be 
 interposed between the water- 
 trough in which the gas is col- 
 lected, and the generating-flask, 
 in cases where the latter is 
 heated to a high temperature. 
 By this means, if the water 
 should suck back, it 
 is collected in the 
 empty safety-bottle, 
 and a dangerous ex- 
 plosion is avoided. 
 The arrangement of 
 the safety -bottle is 
 shown in the cut. 
 The oxygen passes 
 from the delivery tube of the safety-bottle, and is collected 
 over water just as hydrogen is. 
 
 In the generating-flask place 15 grams of chlorate of 
 potassium, connect the apparatus, invert several test-tubes 
 in the water-trough, and then heat the chlorate of potas- 
 sium until gas passes off with moderate rapidity, and until 
 all of the air has been expelled from the apparatus and 
 safety-bottle. Now collect the gas in the test-tubes. Ke- 
 
 Fig. 7. 
 
LABORATORY EXPERIMENTS. 
 
 223 
 
 move one of the tubes, and insert in it a glowing pine 
 splinter. Repeat with a second tube, using a small piece 
 of charcoal heated to redness and placed on the end of an 
 iron wire tightly wrapped around it. Repeat the same 
 experiment with the soap-bubbles which was made with 
 hydrogen. Which gas is more soluble in water, hydrogen 
 or oxygen ? 
 
 10. Explosion of a Mixture of Hydrogen and Oxygen in the Eudiom- 
 eter Tube, Fig. 8. (Teacher's Experiment.) 
 The apparatus in which this explosion is performed is 
 termed a eudiometer tube. 
 This instrument is a glass 
 tube, A, closed at one end, 
 and graduated in cubic cen- 
 timetres. It has two plati- 
 num wires inserted near the 
 closed tip, (7, in such a man- 
 ner that an electric spark 
 can pass from one to the 
 other. This tube is filled 
 with mercury, and inverted 
 over a mercury trough, I. 
 In order to prove the volu- 
 metric composition of water, 
 slant the tube to one side, 
 and admit about 10 c.c. of 
 hydrogen prepared and puri- 
 fied as in 9 a. Bring the 
 tube to a vertical position, 
 and make careful readings 
 of the f ollowing : 
 
 1. Volume of gas. 
 
 2. Temperature. 
 
 3. Height of barometer. Fig. 8. 
 
224 ELEMENTS OF CHEMISTRY. 
 
 4. Height of the column of mercury in the tube (in 
 millimetres). 
 
 Place the readings in your note-book. Now again slant 
 your tube, and admit about 7 c.c. of oxygen from the 
 teacher's gasometer, or from the apparatus which was 
 prepared for the generation of oxygen.* 
 
 Be careful to run in the oxygen very slowly through a 
 tube drawn down to a small opening, otherwise too much 
 will be admitted by a sudden burst from the generator. 
 Now once more bring the eudiometer tube to a vertical 
 position, and note : 
 
 1. Volume of gas. 
 
 2. Temperature. 
 
 3. Height of barometer. 
 
 4. Height of the column of mercury in the tube. 
 
 Clamp the tube tightly in position, with its open end 
 pressed down against a leather washer in the bottom of the 
 mercury trough. Now pass a spark from an induction coil 
 or Leyden jar through the gases by connecting the two 
 poles with the platinum wires in the eudiometer.f After 
 the explosion raise the eudiometer slightly from the 
 washer, and allow the apparatus to stand twenty minutes 
 while cooling. Now note : 
 
 1. Volume of gas. 
 
 2. Temperature. 
 
 3. Height of the barometer. 
 
 4. Height of the column of mercury in the tube. 
 
 * Oxygen from a gasometer is pretty sure to contain nitrogen. It is 
 therefore better to prepare fresh oxygen from potassium chlorate. Be 
 sure that the gas has run through the generating-apparatus for a suffi- 
 cient length of time to expel all air, before collecting in the eudiometer 
 tube. - 
 
 t Not infrequently the eudiometers come to the laboratory with the 
 ends of the wires so near together that the spark will not be large 
 enough to ignite the gases; if such is the case, force the ends apart care- 
 fully with a long glass rod. 
 
L Alton ATOR r EXPERIMENTS. 
 
 225 
 
 Recalculate all the above observations so that the gas 
 volume in each is reduced to and 760 mm. of the 
 barometer.* 
 
 If 10 c.c. (corrected) of hydrogen and 7 c.c. of oxygen 
 were admitted to the eudiometer, then 10 c.c. of hydrogen 
 will unite with 5 c.c. of oxygen to form water (2 volumes 
 of hydrogen to 1 of oxygen), and 2 c.c. of oxygen will 
 remain unaltered. The residual gas may 
 be tested for oxygen in the usual manner. 
 It is well to repeat the experiment, this 
 time employing an excess of hydrogen. 
 
 11. Proof that Two Volumes of Hydrogen with 
 One of Oxygen form Two Volumes of "Water 
 Vapor. Fig. 9. (Teacher's Experiment.) 
 
 The apparatus consists, essentially, of 
 a eudiometer surrounded by a glass jacket 
 joined to the eudiometer by means 
 of a tightly fitting triple bored 
 stopper. The three holes in the 
 stopper are for the following pur- 
 poses : The one in the mid- 
 dle is for the eudiometer 
 tube; the second (a), for 
 the admission of steam by 
 means of a glass tube bent 
 with a right angle ; and the 
 third for the exit of the con- 
 densed water by means of a 
 similarly bent glass tube. Fig Q 
 
 * For the formulae necessary to recalculate gases to standard condi- 
 tions, and for the reasons for such formulae, see pages 68, 69, and 70. The 
 experiments numbered 36, 37, and 38 can, if desired by the teacher, be 
 performed in this place before the pupil does the work of recalculating 
 the gas volumes noted in his observations of the above experiment. 
 
226 ELEMENTS OF CHEMISTRY. 
 
 Fill the eudiometer with perfectly clean, dry mercury, 
 carefully removing every bubble of air,* and invert it in a 
 cylinder of mercury about 30 centimetres in depth. Now 
 raise the eudiometer until its mouth is just below the sur- 
 face of the mercury in the trough, and admit about 15 c.c. 
 of the mixture of hydrogen and oxygen obtained from the 
 electrolysis of water, f Now pass a jet of steam into the 
 
 jacket until the apparatus 
 is heated to 100 C, and 
 note the volume of the gas 
 as well as the height of the 
 column of mercury in the 
 eudiometer tube above that 
 in the trough. Lower the 
 eudiometer tube and jacket 
 so that the open end is well 
 under the mercury, wrap a 
 towel round the top of the 
 mercury trough, and ex- 
 plode the gases as in the 
 
 Fig. 10. . . 
 
 previous experiment. Now 
 
 adjust the tube so that the height of the column of mer- 
 cury in it is the same as it was before, and make a second 
 reading of the volume of gas, taking care that the tem- 
 
 * Remove bubbles of air by nearly filling the tube with mercury, 
 closing the open end with the thumb, and slowly passing a large bubble 
 of air back and forth through the entire length of the tube. 
 
 t A simple apparatus for generating this mixture of oxygen and 
 hydrogen is shown by Fig. 10. This consists of a wide-mouthed bottle 
 of 100 c.c. capacity, closed with a single bored rubber stopper. In this 
 stopper are inserted two stout platinum wires, hammered flat at the 
 ends, and in the opening is placed a glass tube of one or two millimetres 
 internal diameter, bent as in the figure, and reaching just to the lower 
 edge of the stopper. Almost fill the bottle with dilute sulphuric acid, 
 insert the stopper, connect with the battery, wait for some minutes until 
 the gas has passed off, and then collect in the eudiometer. 
 
LA B OR A TOR Y EX L 'MR U1EN TS. 
 
 227 
 
 perature is still at 100 C. What is the ratio between 
 the volumes of gas before and after explosion ? Allow 
 the tube to cool, and observe the remaining volume 
 of gas. 
 
 12. Burning of Hydrogen* in Oxygen, and Formation of "Water by 
 this Means. (Teacher's Experiment.) Fig. 11. 
 
 The apparatus consists of a vessel constricted in the 
 middle, and is fitted with a glass stopcock delivery-tube. 
 A wide globe funnel with a long stem is placed in the 
 upper opening of this vessel. The zinc is 
 placed in the middle globe, and dilute sul- 
 phuric acid is added from above until the 
 apparatus is filled to about the middle of 
 the funnel. On opening the stopcock, the 
 
 Fig. 11. 
 
 acid ascends to the metal. On closing it, the generated 
 hydrogen once more expels the acid from the central globe. 
 In this way the metal can be indefinitely kept out of 
 
 * The hydrogen needed must be available in a current which is easily 
 regulated. For this purpose it is best prepared in a so-called Kipp's gas- 
 generator. A description of this generator is given above, and it is 
 shown at the extreme right of the cut. 
 
228 ELEMENTS OF CHEMISTRY. 
 
 contact with the acid, and need only be acted on by it 
 when the stopcock is opened.* 
 
 A regular current of hydrogen such as is necessary to 
 maintain a small flame, cannot be obtained if the gas is 
 purified by passing through wash-bottles. For this reason 
 so called U-tubes (shown in the centre figure) must be 
 substituted. The contents of these purifying tubes, count- 
 ing from the generator, are 
 
 1. Pieces of brick moistened with a solution of potas- 
 sium permanganate. 
 
 2. Coarse pieces of solid caustic potash. 
 
 3. Granular (anhydrous) calcium chloride. 
 
 The exit tube of No. 3 terminates in a platinum tip of a 
 diameter not more than one millimetre, made from a roll 
 of platinum foil, and fused into the open end of the glass 
 tube. The wash-bottle at the extreme left contains con- 
 centrated sulphuric acid to dry the oxygen which is passed 
 in from left to right. Both the hydrogen and oxygen which 
 are to be admitted into the vertical cylinder are therefore 
 perfectly dry and pure. 
 
 Manipulation: Remove the platinum tipped tube from 
 the vertical cylinder, and start the hydrogen generator. 
 After waiting at least ten minutes, when all the air has 
 been expelled from the train and apparatus, ignite the hy- 
 drogen at the tip, and regulate the current so that a flame 
 of not more than one centimetre in length is obtained. In 
 the meantime expel all the air from the vertical cylinder 
 by a steady stream of oxygen from the teacher's gasometer. 
 Now pass the jet of burning hydrogen upward through the 
 central opening in the stopper, so that it is just above the 
 place where the oxygen enters. What collects on the sides 
 of the cylinder ? Taste the liquid which soon passes off 
 through the exit tube at the upper end.f 
 
 * If necessary the hydrogen can be generated as described in experi- 
 ment 9 a. 
 
 t See foot-note on page 25. 
 
LABORATORY EXPERIMENTS. 229 
 
 13. Examination of the Substance "which remains in the Water 
 after it has been acted upon by Sodium. 
 
 Cut a piece of sodium as in 7a, and throw it into a small 
 evaporating-dish containing 150 c.c. of water. Stand aside 
 until the action is over, and until all the sodium has dis- 
 appeared. Now add a second piece, and wait as before. 
 Continue the operation until four pieces have been added. 
 Evaporate the solution as far as possible on a water-bath, 
 transfer the small quantity of liquid which is left to a 
 small porcelain crucible, and dry in an air-bath at 150. 
 Note the appearance of what is left'. Has it any resem- 
 blance to sodium ? Is it soluble in water ? Make a very 
 dilute solution of a portion of it, and taste a drop. Com- 
 pare this taste with that of a very dilute solution of 
 caustic soda which you obtain from the side-table. Com- 
 pare the feel of the solution with that of a solution of 
 caustic soda. 
 
 14. Decomposition of the Caustic Soda obtained by the Action of 
 Sodium on "Water. Proof that This Substance contains Hydrogen. 
 
 a. A mixture of sodium and caustic soda when 
 heated will develop hydrogen, thereby furnishing 
 absolute proof that only a portion of the hydrogen 
 is expelled from water when it is acted on by 
 sodium ; but this experiment probably can be per- 
 formed successfully only by the teacher. Dry 
 some caustic soda completely by fusing it in an 
 iron crucible over a Bunsen flame. Allow to cool, 
 powder the caustic soda, and place about three 
 grams in a test-tube of so-called infusible glass. 
 Add one-half gram of clean sodium, and fit into 
 the test-tube a single-bored rubber stopper which is 
 provided with a glass tube drawn out to a point, so 
 as to make a burner (Fig. 12). Now gently heat 
 the sodium (holding the test-tube by a holder) 
 until the metal is melted. Gradually increase the Fig, 12. 
 
230 ELEMENTS OF CHEMISTRY. 
 
 temperature, and light the hydrogen at the tip of the 
 burner. This is a conclusive proof that caustic soda 
 contains hydrogen. It has been shown, therefore, that 
 water is first changed by the action of sodium so that a 
 part of the hydrogen is set free, leaving caustic soda ; 
 and then sodium, acting on caustic soda, sets free the 
 remainder. The hydrogen in water is therefore divisible 
 into two parts. The experiments which prove that these 
 are two equal parts are too difficult to perform here; it 
 is sufficient to know that .1 gram of sodium, acting on 
 water, sets free 48.22 c.c. of hydrogen; and when the 
 caustic soda formed from this amount of sodium is care- 
 fully dried and heated with sodium, a second 48.22 c.c. 
 of hydrogen are liberated. The hydrogen in water is 
 therefore divisible into two equal parts. 
 
 15. Inauguration of Chemical Action by Heat. Kindling 
 Temperature. 
 
 (Perform these experiments under the hood.) 
 
 Place five drops of carbon bisulphide in a dry test-tube, 
 and warm with the hand until the tube is filled with the 
 vapors of the liquid, then insert in the mouth of the test- 
 tube a glass rod which has previously been warmed in the 
 flame of a Bunsen burner. 
 
 Cut a piece of phosphorus half the size of a pea (phos- 
 phorus must always be cut under water, and handled with 
 forceps), dry it quickly by pressing it between sheets of 
 filter paper, transfer it to a deflagrating spoon, and bring 
 it gradually toward the flame. Repeat with red phos- 
 phorus. Sulphur. Carbon. 
 
 What is the cause of the explosion in a eudiometer tube 
 when the electric spark is passed from one platinum wire 
 to the other, as in Experiment 10 ? 
 
 16. Preparation of Hydrogen Chloride. 
 
 Arrange an apparatus as shown in Fig. 13. The gen- 
 
LABOR A TOE Y EXPERIMENTS. 
 
 231 
 
 erating-flask should have a capacity of about 500 cubic 
 centimetres. The wash-bottle contains concentrated sul- 
 phuric acid. 
 
 Place in the generating-flask 25 grams of sodium chloride, 
 pour upon it 50 c.c. of dilute sulphuric acid (2 volumes of 
 concentrated sulphuric acid to 
 1 volume of water), and heat 
 gently. Collect four small jars 
 of the gas by displacement of 
 air,* covering them with a glass 
 plate as soon as filled. Collect 
 the remainder of the gas in a 
 small beaker of water. 
 
 17. Properties of Hydrogen 
 Chloride. 
 
 Invert one jar of gas in a 
 vessel of water. Taste' a drop 
 of the solution. Blow the 
 breath across the mouth of 
 a second jar. Insert into an 
 other jar a burning splinter. 
 
 Fig. 13. 
 
 18. a. Preparation of Sodium Amalgam. (Under the Hood.) 
 To prepare sodium amalgam place 500 grams of clean, 
 dry mercury in a large clay crucible, and cover with a 
 piece of sheet iron. Cut 5 grams of clean sodium into 
 pieces the size of a hickory nut, and place them in the cru- 
 cible. 4Fo start the reaction, heat a few grams of mercury 
 in a test-tube, slightly raise the cover of the crucible, pour 
 in the mercury, and instantly withdraw the hand. A reac- 
 
 * Gases which are specifically heavier than air may be collected by 
 passing the delivery tube, through which the gas is flowing, to the bottom 
 of the jar; gases specifically lighter than air are collected in an inverted 
 jar by passing the delivery tube to the top of the jar. (See Fig. 31.) 
 
232 
 
 ELEMENTS OF CHEMISTRY. 
 
 tion, accompanied by a flash of light, will occur. Stand 
 aside, so as not to inhale the fumes of the mercury. When 
 the reaction is finished, stir the amalgam with an iron wire, 
 allow it to cool, and place it in a stoppered, wide-mouthed 
 bottle. 
 
 b. Decomposition of hydrogen chloride by sodium. Fig. 14. 
 
 Take a glass tube 30 cm. in length and 15 mm. in diam- 
 eter, sealed at one end. Divide this tube by means of two 
 a rubber rings slipped over it. One rubber ring is 
 placed at a distance from the sealed end repre- 
 sented by 10 c.c. of the capacity of the tube,* and 
 the other is placed half-way between this ring 
 
 and the open end of the 
 tube. Have ready a 
 small glass test-tube, c, 
 of 10 c.c. capacity, com- 
 pletely filled with so- 
 dium amalgam. Now 
 completely fill the large 
 tube with hydrogen chlo- 
 ride, displacing the air, 
 as shown in the cut. The 
 hydrogen chloride must 
 be dried by passing it 
 through a wash-bottle 
 containing sulphuric acid. When the tube is filled, pour 
 in the sodium amalgam, quickly cover the mouth of the 
 tube with the thumb, and bring every part of the gas in 
 contact with the amalgam by repeatedly inverting the tube. 
 
 * This 10 c.c. of the tube is to be filled with sodium amalgam ; hence 
 the volume of hydrogen chloride which will be left, after introducing 
 the sodium amalgam, will be represented by the interval between the 
 ring at 10 c.c. and the remainder of the tube. 
 
 Fig. 14. 
 
LAB OR A TOE Y EX PER IMENTS. 
 
 233 
 
 Finally, place the open end of the tube in a deep cylinder, 
 under water, and remove the thumb. Lower the tube in 
 the water so that the level within and without is the same 
 (shown by b in the figure). What is the relation between 
 the volume of gas remaining and that which was originally 
 present ? Now place the thumb over the mouth of the 
 tube, take it from the water, invert it, remove the thumb, 
 and instantly apply a lighted taper. The pupil can con- 
 vince himself that mercury alone has no action on hydro- 
 gen chloride, by repeating the above experiment, using 
 10 c.c. of pure mercury instead of sodium amalgam. 
 What decomposes 'the hydrogen chloride ? 
 
 19. Decomposition of Hydrochloric Acid by Means of the Electric 
 Current. Fig. 15. Hood! 
 
 The apparatus consists of a letter-U- 
 shaped tube, which is connected at the 
 centre of the curve with an upright fun- 
 nel tube, serving for the introduction of 
 the liquid. The two arms terminate in 
 glass stopcocks. The electrodes must be 
 made of the carbon which is used in arc 
 electric lights, because platinum is attacked 
 during the electrolysis of hydrochloric acid. 
 These carbon poles must extend well up 
 into the tubes, and must be protected, ex- 
 cept at the tips, by a glass tube slipped 
 over them, and made water-tight by pour- 
 ing in melted paraffine between the carbon 
 and the tube. This apparatus is designed 
 for teachers' use. 
 
 A simple apparatus for pupils can be 
 made similar to that shown by Fig. 5, 
 the platinum wires being replaced by two 
 cylinders of carbon, which are connected Fig. 15, 
 
234 
 
 ELEMENTS OF CHEMISTRY. 
 
 with the battery by copper wires. Fill either apparatus 
 with a saturated solution of commou salt to which has been 
 added one-tenth of its volume of a saturated solution of 
 hydrogen chloride in water. When the current is turned 
 on, a gas will be evolved at the negative pole. When the 
 tube over this electrode is full of gas, remove it, and test 
 for hydrogen. The gas at the positive electrode will not 
 be apparent for some time, because it is soluble, to a cer- 
 tain extent, in the liquid. After a time it, too, will appear. 
 What is its color ? Odor ? Apply a lighted taper to the 
 mouth of the tube in which this gas is collected. Pill a 
 second tube, and place in it a small prece of .moist red 
 calico. If the electric current is allowed to run long 
 enough, equal volumes of the two gases will be evolved 
 in equal lengths of time. Compare this result with that 
 obtained when water is electrolyzed. What does this ex- 
 periment and the preceding one teach you in regard to the 
 composition of hydrogen chloride by volume ? 
 
 20. Formation of Hydrogen Chloride from Hydrogen and Chlorine. 
 Volumetric Composition of Hydrogen Chlorine. Fig. 16. Teach- 
 er's Experiment. 
 
 The apparatus consists of two tubes, each 
 about 15 cm. in length. These two tubes are 
 connected by a stopcock, which is so arranged 
 that either one of the tubes can be made to 
 communicate with the outside air, while, by 
 turning it through 45, the two tubes can be 
 made to communicate exclusively with each 
 other, the opening to the outside being closed. 
 This kind of stopcock is termed a three-way 
 stopcock; its arrangement is shown by Fig. 
 17. The two tubes are drawn out into nar- 
 row openings at the two outer extremities, 
 and are so selected as to be of equal volume. 
 
 Fig. 18. 
 
LABORATORY EXPERIMENTS. 235 
 
 Manipulation. Connect the three-way stopcock at A 
 with an apparatus furnishing dry chlorine. This is done 
 by the apparatus described in Experiment 21&. Turn the 
 stopcock so that the chlorine will pass 
 through one of the tubes, and allow the 
 gas to enter until all air is expelled. 
 Now seal the tip of the tube in a Bunsen 
 name, and turn the stopcock so that the 
 chlorine tube is closed and the second 
 tube is open to the atmosphere. Fill 
 this tube with dry hydrogen (prepared 
 as in Experiment 9&), and when all air 
 is expelled, seal this tip also in the 
 Bunsen flame. Now turn the stopcock 
 so that the two tubes will communicate with each other 
 while they are both shut to the outside air. Allow tne 
 apparatus to stand in the daylight for twenty-four hours. 
 Has the color of the chlorine disappeared ? Scratch one of 
 the tips with a file, bring it into a vessel containing dry 
 mercury, and break the tip with a pair of pincers. Does 
 the mercury rise in the tube ? What does this teach regard- 
 ing the volume of gas remaining after the experiment, as 
 compared with that before ? Hydrogen chloride, as we 
 have learned, is extremely soluble in water, while hydrogen 
 and chlorine are not. Remembering this, we can easily 
 ascertain whether the hydrogen and chlorine have all been 
 used to form hydrogen chloride, by pressing a piece of 
 rubber over the broken tip of the apparatus, and transfer- 
 ring it to a vessel of water. 
 
 If hydrogen chloride has been formed, and if all the 
 hydrogen and all the chlorine have united, the water will 
 rush in and completely fill the apparatus.* Is this the 
 
 * Of course, if care has not been taken^o expel all the air from the 
 tubes, this air will remain after the experiment, and the result will be 
 inaccurate. 
 
236 
 
 ELEMENTS OF CHEMISTRY. 
 
 case ? What does the experiment teach as regards the 
 relative volumes of hydrogen and chlorine which unite to 
 form hydrogen chloride ? As regards the relation between 
 the volumes of hydrogen and chlorine used, and the volume 
 of hydrogen chloride produced ? Compare these results 
 with those obtained in Experiments 10 and 11. 
 
 21. a. Preparation of Chlorine by the Action of Oxygen on 
 Hydrogen Chloride. Fig. 18. 
 
 It is not expedient to prepare chlorine for laboratory use 
 by the electrolysis of hydrochloric acid. Chlorine can be 
 prepared by decomposing hydrogen chloride by oxygen, 
 the oxygen uniting with the hydrogen of the hydrogen 
 chloride, while the chlorine is set free. This change takes 
 place only at a high temperature. Prepare an apparatus, A, 
 
 Fig. 18. 
 
 for generating hydrogen chloride as described in Experi- 
 ment 16, with this difference, that the wash-bottle, 7?, is 
 fitted with a triple-bored rubber stopper. The wash-bottle 
 contains sulphuric acid in order to dry the gases. The 
 three holes are for the following purposes : 
 
 1. For the admission of hydrogen chloride. 
 
 2. For the admission of oxygen. 
 
 3. For the exit of the mixed gases into an iron tube, E, 
 which is placed in a gas furnace (shown in the cut) so 
 that it can be heated to redness. 
 
LABORATORY EXPERIMENTS. 237 
 
 By this means a mixture of dry oxygen and hydrogen 
 chloride is obtained and passed through the heated tube. 
 The bubbles of hydrogen chloride and of oxygen passing 
 through the wash-bottle should be of equal number in the 
 same interval "of time. The ends of the iron tube are 
 fitted with cork stoppers, into which pass the entrance and 
 exit tubes for the gases. The joints are made secure by 
 a coating of plaster of Paris. Between the iron tube and 
 the water-trough beyond is placed a safety bottle, C, such 
 as is described in Experiment 9c. When the apparatus is 
 ready, the tube is heated to redness in the furnace, and the 
 mixture of hydrogen chloride and oxygen is passed through. 
 Finally pass the gases under a tube, D, inverted in a 
 beaker of water. rfoes the odor of chlorine become appar- 
 ent ? Test the water for chlorine by placing in it a small 
 piece of red calico. Is it bleached ? 
 
 This experiment shows us that although we can obtain 
 chlorine by the action of oxy gen on hydrogen chloride, the 
 method is not practical for laboratory use. However, we 
 need not use gaseous oxygen for this purpose; for it is 
 known that many compounds which contain oxygen give 
 off that oxygen readily under certain circumstances, and 
 that such oxygen, when it is just in the act of being 
 liberated from chemical compounds, readily decomposes 
 hydrogen chloride, setting free chlorine, and forming water. 
 Such an oxygen-containing compound is black oxide of 
 manganese. 
 
 b. Preparation of chlorine from black oxide of manganese 
 and hydrochloric acid. (Experiment under Hood.) 
 
 Arrange an apparatus as shown by Fig. 13, Experiment 
 16. In the flask place 50 grams of black oxide of man- 
 ganese, and pour over it through the safety-tube enough of 
 a concentrated solution of hydrogen chloride in water to 
 cover the oxide. In the wash-bottle put sulphuric acid, 
 
238 ELEMENTS OF CHEMISTRY. 
 
 and collect the gas which passes off by displacement of air, 
 as you did hydrogen chloride. Color of gas ? Place in 
 one of the jars a piece of dry colored calico. Place in a 
 second jar a piece of moist colored calico. Odor of gas ? 
 (Do not inhale more than a very small quantity of 
 chlorine. Pan the air above the cylinder of chlorine 
 with the hand, and get the odor of the gas while you are 
 at some distance.) Invert one of the jars in a basin of 
 water. Is chlorine soluble in water ? As soluble as hydro- 
 gen chloride ? Pass chlorine into a beaker of water until 
 you have a saturated solution. Color and odor of solution ? 
 Does it bleach colored calico ? 
 
 22. Decomposition of "Water by Chlorine in the Sunlight. Fig. 19. 
 Take a tube 40 cm. long, bent as shown in the figure, 
 and closed at the upper end of the long arm. Completely 
 fill this tube with solution of chlorine in water, invert it as 
 shown in the figure, pour off about 20 c.c. of the solution, 
 and clamp the tube in an upright position. Cover the open 
 end with a test-tube, and leave it in the sun- 
 light for some days. When about 20 c.c. 
 of gas has been collected, close the open end 
 of the tube with the thumb, invert it so that 
 the gas ascends to the bend, then once more 
 bring it to an upright position, allowing the 
 gas to pass into the small arm. Now remove 
 the thumb, and quickly bring a glowing pine 
 splinter into the tube. Taste the liquid re- 
 maining in the tube. In this case, what action 
 has the chlorine on the water ? Why does 
 Fj 1g chlorine bleach moist colored calico and not 
 
 dry calico ? 
 23. Action of Hydrochloric Acid on Metals. 
 
 a. In a test-tube place a little sodium amalgam, and pour 
 over it some hydrochloric acid. Apply a lighted taper to 
 
LABORATORY EXPERIMENTS. 239 
 
 the gas which passes off, or, better, arrange the test-tube as 
 shown by Fig. 12, and light at the tip. After the action 
 has ceased, pour off the liquid from the mercury, and evapo- 
 rate to crystallization on a water-bath. Examine the crys- 
 tals under a magnifying-glass. In what experiment have 
 you seen similar crystals ? What substance is formed ? 
 
 b. In a test-tube place some mercury, and pour on it 
 hydrochloric acid. Is there any action ? In the above 
 experiment, what acted on the hydrochloric acid ? 
 
 c. Repeat a, using a few pieces of granulated zinc 
 instead of sodium amalgam. If necessary, filter the 
 solution which is formed, and evaporate. 
 
 d. Repeat a with iron filings. 
 
 e. Repeat a with a piece of magnesium wire. 
 
 24. Action of Hydrochloric Acid on the Oxides of Metals. 
 
 a. In a test-tube place a small piece of quicklime (cal- 
 cium oxide). Pour on it dilute hydrochloric acid. Evap- 
 orate the solution, and examine as in 22a. 
 
 b. Repeat, using zinc oxide. 
 
 c. Repeat, using oxide of iron. 
 
 d. Repeat, using magnesium oxide. In the last three 
 cases determine whether water alone has any solvent 
 action. 
 
 25. Action of Hydrochloric Acid on the Hydroxides of Metals. 
 
 a. In a test-tube place a small piece of caustic soda 
 (sodium hydroxide), dissolve it in water, and place a drop, 
 taken out with a glass rod, on a piece of paper dyed with 
 red litmus. Now add dilute hydrochloric acid to the liquid 
 in the test-tube until a drop turns a strip of paper dyed 
 with blue litmus to red.* Now evaporate as in 22a, and 
 examine the crystals. 
 
 * Acids turn blue litmus (a vegetable dye) to red ; alkalies, like 
 caustic soda, turn red litmus to blue. 
 
240 ELEMENTS OF CHEMISTRY. 
 
 b. In a test-tube place a small piece of quicklime (cal- 
 cium oxide), and add a few drops of water. Wait a few 
 minutes. Pour on 10 c.c. of water, shake well, and filter. 
 Take a drop of the filtrate, and put on a piece of red lit- 
 mus paper. Now add hydrochloric acid, and proceed as 
 in a. 
 
 c. Obtain some magnesium hydroxide, and add hydro- 
 chloric acid until solution is effected. Evaporate as in a. 
 
 d. Repeat, using zinc hydroxide. 
 
 e. Repeat, using hydroxide of iron. 
 
 26. Use of Indicators. 
 
 Solutions which contain alkalies (sodium hydroxide, po- 
 tassium hydroxide, calcium hydroxide) are termed alkaline. 
 The reverse of an alkaline solution is an acid solution. 
 We are acquainted with a number of colored substances 
 which assume colors varying with the solution, whether it 
 be alkaline or acid. Such substances are termed indica- 
 tors. Litmus (Experiment 25), as we have seen, is blue in 
 the presence of alkalies, and red in the presence of acids. 
 It is obvious that, with the aid of litmus, we can tell 
 whether a solution is acid or alkaline ; but there are cer- 
 tain objections to this vegetable dye. These objections are 
 that it is changed in color not only by the alkaline hydrox- 
 ides, but by a number of salts as well. For this reason 
 litmus has largely been superseded by a number of other 
 indicators, the most convenient of which is a dye made 
 from coal-tar, and called methyl orange. 
 
 Dissolve one-half a gram of methyl orange in 25 c.c. of 
 water. To a little of this solution in a test-tube add two 
 or three drops of hydrochloric acid. To this acid solution 
 add a dilute solution of caustic soda until the color changes. 
 At the point where the color changes, the solution is said 
 to be neutral ; i.e., there is neither hydrochloric acid nor 
 
LAB OR A TOR Y EXPERIMENTS. 
 
 241 
 
 sodium hydroxide present, for the acid has neutralized the 
 hydroxide to form sodium chloride and water. Repeat, 
 using potassium hydroxide. Repeat, using a solution of 
 calcium hydroxide. 
 
 27. 
 
 Neutralization of Known Quantities of an Acid by 
 vice versa. 
 
 , ana 
 
 Liquids are most accurately 
 measured by means of burettes. 
 (Fig. 20.) A burette is a glass 
 tube graduated into T T c.c., open 
 above, closed below either with 
 a rubber tube closed with a 
 pinchcock and terminating in 
 a glass tip drawn to a point, 
 or with a glass stopcock. By 
 opening the stopcock, liquid 
 runs out, and its amount can 
 be accurately measured by the 
 graduation above. 
 
 a. To make a solution of alkalies. 
 
 1. Dissolve 4 grams of sodium 
 hydroxide, weighed as accurately 
 as possible, in 500 c.c. of distilled 
 water. Place the solution in a 
 tightly stoppered bottle, and 
 keep for future use. 
 
 2. Make and bottle a solution of the same quantity of 
 potassium hydroxide in the same amount of water. 
 
 &. Solution of hydrochloric acid. 
 
 Measure accurately 5 c.c. of hydrochloric acid (1 part of 
 pure concentrated hydrochloric acid to 1 part of water), 
 and dilute to 250 c.c. Preserve this solution for future 
 use in a stoppered bottle. 
 
 Fig. 20. 
 
242 ELEMENTS OF CHEMISTRY. 
 
 Have two burettes ; fill one with solution a 1, the sec- 
 ond with solution b, and cover the open ends by slipping 
 over them two inverted test-tubes. Clamp the burettes in 
 an upright position, as shown in the cut. 
 
 In a clean beaker place 10 c.c. of solution b, add a few 
 drops of a solution of methyl orange (Experiment 26), and, 
 after noting accurately the quantity of solution in the 
 burette containing solution a 1, add this, drop by drop, to 
 the acid in the beaker, at the same time stirring with a 
 glass rod. Stop adding solution a 1, at the point where 
 the color of the methyl orange just changes permanently, 
 and note the number of cubic centimetres of the alkali 
 which have been used. What amount of sodium hydrox- 
 ide, in grams, does this represent ? Repeat with a second 
 10 c.c. of acid, and note whether the two results agree. If 
 they do, pour out the alkali solution from the burette, 
 wash the instrument carefully with distilled water, dry it, 
 and fill with solution a 2. Take 10 c.c. of the acid solu- 
 tion, and proceed as before. What amount in grams of 
 potassium hydroxide was used to neutralize 10 c.c. of the 
 acid ? Is this amount the same as the quantity of sodium 
 hydroxide used to neutralize the same quantity of acid ? 
 If it is not, what is the ratio between the amounts of 
 sodium hydroxide and potassium hydroxide which are 
 used to neutralize the same quantity of acid ? 
 
 c. Preparation of a solution containing a known quantity of 
 hydrochloric acid. 
 
 Into a distilling-flask, arranged as in Fig. 3, place 15 
 grams of sodium chloride ; add a cold mixture of 40 grams 
 of sulphuric acid and 80 grams of water. Arrange the 
 condenser so that it terminates in an ordinary pair of wash- 
 bottles (shown by Fig. 6), each containing about 10 c.c. of 
 water. Place the thermometer tightly in the distilling- 
 
LABORATORY- EXPERIMENTS. 243 
 
 flask, and distil until one-half of the liquid has passed 
 over. Allow it to cool, add another 80 grams of water to 
 the distilling-flask, and distil again. All the hydrochloric 
 acid will now have passed over with the distillate. Take 
 the contents of the wash-bottles, carefully wash them into 
 a graduated cylinder, and dilute to 500 c.c. Fifteen grams 
 of sodium chloride produce 9.18 grams of hydrochloric acid, 
 therefore the 500 c.c. of solution contain 9.18 grams of 
 hydrochloric acid. Take 10 c.c. of this solution, and neu- 
 tralize with solution a 1. With solution a 2. How much 
 by weight of sodium hydroxide is neutralized by 1 gram of 
 hydrochloric acid ? How much of potassium hydroxide ? 
 What is the ratio between the amounts of sodium hydrox- 
 ide and of potassium hydroxide which will neutralize 1 
 gram of hydrochloric acid? Compare this result with 
 those obtained in this Experiment, b. The quantities of 
 sodium hydroxide and of potassium hydroxide which will 
 exactly neutralize the same amount of hydrochloric acid 
 are said to be equivalent. 
 
 28. a. Burning of Sulphur in Oxygen and the Product formed. 
 
 Fill a 32-oz. wide-mouthed bottle with oxygen. Place 
 about .5 grams of sulphur in a deflagrating-spoon passed 
 through a piece of sheet tin large enough to cover the 
 mouth of the bottle. Ignite the sulphur in the flame of a 
 burner, and lower it into the bottle. When combustion is 
 completed, remove the spoon, cover the jar with a glass 
 plate, and allow it to stand for a few minutes. Color of 
 gas ? Lower a burning pine splinter into the jar. Moisten 
 a piece of blue litmus paper, attach it to the glass cover, 
 and allow it to stand in the bottle. Changes of color ? 
 Test the odor of the gas as you did with chlorine. (Ex- 
 periment 21&.) The product of this combustion is termed 
 sulphur dioxide, 
 
244 ELEMENTS OF CHEMISTRY. 
 
 b. Preparation of sulphur dioxide for laboratory use. 
 
 It is not expedient to prepare sulphur dioxide for labora- 
 tory use by the above method. In order to obtain sulphur 
 dioxide in large quantities/ advantage is taken of the fol- 
 lowing fact : 
 
 Sulphuric acid is composed of hydrogen, sulphur, and 
 oxygen. When it is heated with certain metals it gives 
 up a portion of this oxygen, much in the same way as 
 black oxide of manganese gives up its oxygen to hydro- 
 chloric acid (see Experiment 21&). What is left of the 
 sulphuric acid after it has lost a portion of its oxygen 
 then breaks down into sulphur dioxide and water, the 
 sulphur dioxide being a gas. The best metal to use for 
 this purpose is copper. 
 
 Arrange an apparatus as in Experiment 16, Fig. 13. In 
 the generating-flask place 25 grams of copper shavings, and 
 add 100 c.c. of concentrated sulphuric acid through the 
 safety-tube. Connect all parts of the apparatus (the wash- 
 bottle should contain concentrated sulphuric acid), and heat 
 by means of a Bunsen burner until gas begins to come off. 
 At this point lower the flame until you obtain a regular 
 and slow evolution of gas. Collect the evolved gas by dis- 
 placement of air in four small jars, which you cover with 
 glass plates as soon as filled, and pass the excess of gas into 
 a beaker of water. Odor of gas ? Compare with odor of gas 
 obtained from burning sulphur. Invert one of the jars in a 
 vessel of water. Is the gas very soluble in water ? Lower 
 a lighted splinter into another jar. Pour into one of the 
 jars a little blue litmus solution, and allow it to stand for 
 a short time. Obtain a red rose, dip it in water, and sus- 
 pend it in a jar of sulphur dioxide for some time. A solu- 
 tion of sulphur dioxide is easily changed back to sulphuric 
 acid by means of oxygen. To a few drops of sulphur 
 dioxide solution, in a test-tube, add, drop by drop, a solu- 
 
LAB OEA TOR Y EXPERIMENTS. 
 
 245 
 
 tion of chlorine in water until the odor of sulphur dioxide 
 disappears. What is the means by which chlorine is able 
 to add oxygen to sulphur dioxide ? 
 
 29. Changing of Sulphur Dioxide to Sulphur Trioxide by Means of 
 
 Oxygen. 
 
 Arrange an apparatus as shown in Fig. 21. 
 The generating-flask is the same as in Ex- 
 periment 28 ; but the wash-bottle contains a 
 triple-bored rubber stopper, arranged as in 
 Experiment 21, Fig. 18. Into one of the 
 holes of the wash-bottle pass a tube 
 connected with the sulphur dioxide 
 generator; into the second pass a 
 
 tube from the oxygen gasometer. By this means a mixture 
 of sulphur dioxide and oxygen is obtained in the wash-bot- 
 tle. This mixture passes from the third tube into a second 
 wash-bottle and then into a tube of infusible glass, in the 
 middle of which is blown a bulb, into which is stuffed, with 
 a glass rod, a little platinized asbestos.* The farther end 
 of this bulb tube is connected with a small distilling-flask, 
 
 * Platinized asbestos is asbestos coated with a very fine deposit of 
 platinum. It has been found that many chemical reactions between 
 gases take place much more readily if they are passed over heated, finely 
 divided platinum, such as is deposited on platinized asbestos. The rea- 
 son for this is that the platinum condenses the gases on its surface, and 
 gives them a more intimate contact. Platinized asbestos is furnished by 
 dealers in chemicals. 
 
246 ELEMENTS OF CHEMISTRY. 
 
 by which is surrounded by snow or ice, and the exit tube of 
 which dips under mercury.* The mercury constitutes a 
 valve for the escape of gases, while at the same time it pre- 
 vents moisture from getting back into the apparatus. When 
 all is ready, pass the mixture of sulphur dioxide and oxygen 
 slowly through the bulb tube, and heat the platinized as- 
 bestos by a Bunsen burner. The sulphur trioxide which 
 is formed is condensed in the small receiving-flask. After 
 the apparatus has been running about half an hour, stop 
 the inflow of gases, and remove the receiving-flask. Is sul- 
 phur trioxide a solid or a liquid? If a solid, warm the flask 
 slightly with the hand. Does the sulphur trioxide melt ? 
 
 30. Formation of Sulphuric Acid from Sulphur Trioxide and "Water. 
 Surround a receiver containing sulphur trioxide with 
 cold water, and carefully add water, drop by drop, until all 
 is liquid. Dilute a few drops of this liquid with a good 
 deal of water in a test-tube. Taste a drop. Add a few 
 drops to a solution of methyl orange. Place a drop on 
 a strip of blue litmus paper. Take a few drops of sul- 
 phuric acid from your reagent bottle, dilute as above, and 
 repeat these tests. Evaporate any excess of water in 
 the sulphur trioxide by placing the solution in a small 
 evaporating-dish on a water-bath. Compare the appear- 
 ance of the remainder after evaporation with ordinary 
 sulphuric acid, and preserve it until the next experiment 
 is finished. 
 
 31. Dehydrating Action of Sulphuric Acid. 
 
 a. Put a little sugar in a test-tube, and pour on it just 
 enough concentrated sulphuric acid to cover. Set it aside 
 in the test-tube rack. Put some concentrated sulphuric 
 acid in a test-tube, place in it a small piece of wood, and 
 allow it to stand. The effect on the wood and on the 
 
 * The shape and relative size of the distilling-flask is shown by a in 
 the figure. 
 
LABORATOR 
 
 sugar is due to the fact that sulphuric*acM*Tras a great 
 tendency to take up water. Sugar and the greater portion 
 of the wood contain hydrogen and oxygen in exactly the 
 proportions necessary to form water. When acted on by 
 sulphuric acid a reaction takes place, and the water is 
 absorbed by the acid. Eepeat the above, using the sul- 
 phuric acid formed by the action of water on sulphur 
 trioxide. 
 
 b. Changes of temperature when sulphuric acid is diluted. 
 
 Kepeat Experiment 4c, gradually adding concentrated 
 sulphuric acid to water, and stirring it with the thermom- 
 eter. Note changes in temperature. Place some concen- 
 trated sulphuric acid in a test-tube, and surround with a 
 mixture of snow and salt. Does the acid freeze ? Weigh 
 a small stoppered flask, then add 10 c.c. of sulphuric acid, 
 and again . weigh ; pour out the acid, and wash well with 
 water. Now place 10 c.c. of water in the flask, and weigh. 
 What is the specific gravity of the acid ? 
 
 32. Action of Dilute Sulphuric Acid on Metals. 
 Repeat Experiment 23&, #, c, d, and e, using dilute sul- 
 phuric acid instead of hydrochloric acid (1 part concen- 
 trated acid to 20 parts of water). What substances are 
 formed ? What gas passes off ? 
 
 33. Action of Sulphuric Acid on the Oxides of the Metals. 
 Eepeat Experiment 24a, b, c, d, using dilute sulphuric 
 acid instead of hydrochloric acid. What substances are 
 formed ? 
 
 34. Neutralization of Sulphuric Acid by Potassium Hydroxide and 
 Sodium Hydroxide. 
 
 Use burettes, as in Exp. 27, Pig. 20. Measure accu- 
 rately 10 c.c. of sulphuric acid (containing 1 volume of 
 pure, concentrated sulphuric acid, specific gravity 1.84, to 
 
248 ELEMENTS OF CHEMISTRY. 
 
 6 volumes of water*), and dilute this to 500 c.c. Put it 
 in a stoppered bottle, and preserve it. 
 
 a. Place 50 c.e. of this solution in a beaker, add a few 
 drops of methyl orange solution (Experiment 26), and run 
 in from a burette a solution of sodium hydroxide prepared 
 exactly as in Experiment 27a, 1. After about 30 c.c. have 
 been added, begin to add your alkali cautiously, drop by 
 drop, until the solution becomes neutral. Evaporate the 
 solution on a water-bath until crystals separate. Examine 
 these carefully under a magnifying-glass. Dry some of 
 the crystals with filter paper, place them in a test-tube, 
 and heat cautiously. Compare the result with that ob- 
 tained in Experiment 3b. Finally heat the crystals to the 
 full heat of a Bunsen burner, and test the water which 
 has collected on the upper part of the test-tube with blue 
 litmus paper. 
 
 b. Eepeat a, using a solution of potassium hydroxide 
 prepared as in Experiment 27a, 2. 
 
 Are the quantities of sodium hydroxide and potassium 
 hydroxide necessary to neutralize the same quantity of 
 acid equal? If not, what is the ratio between the two? 
 Is this ratio the same as that obtained in Experiment 27 
 in neutralizing hydrochloric acid ? 
 
 c. Repeat a, placing in the beaker 100 c.c. of the acid, 
 and adding just as much sodium hydroxide as was found 
 necessary to completely neutralize 50 c.c. Evaporate the 
 solution on the water-bath, examine the crystals, and heat 
 as in a. Test the moisture which collects on the sides of 
 the test-tube with blue litmus paper. Is it acid ? What 
 is the difference between the salt formed in this experi- 
 ment and the one in a ? If you had used the same 
 amount of sulphuric acid in each case, what would be the 
 
 * A large quantity of this acid can be prepared by the teacher, and 
 kept for use. 
 
LABORATOB Y EXPERIMENTS. 
 
 249 
 
 ratio between the amount of sodium hydroxide used iri a 
 and in c. 
 
 d. Repeat c, with a solution of potassium hydroxide 
 prepared as in Experiment 27 'a, 2. 
 
 35. Comparison of the Results obtained with Sulphuric Acid and 
 Those with Hydrochloric Acid. 
 
 If the sulphuric acid which you used was accurately pre- 
 pared, 10 c.c. contained .0511 gram of sulphuric acid. 
 How much sodium hydroxide by weight was necessary to 
 neutralize completely one gram of sulphuric acid ? How 
 much potassium hydroxide ? How much sodium hydroxide 
 reacted with one gram of sulphuric acid in c ? In. d ? 
 What is the ratio between the quantities of sodium hydrox- 
 ide and potassium hydroxide necessary to neutralize one 
 gram of sulphuric acid ? Is this ratio the same as that 
 between the sodium hydroxide and potassium hydroxide 
 
 BASE. 
 
 HYDROCHLORIC 
 ACID. 
 
 SULPHURIC 
 ACID. 
 
 WEIGHT OF HYDROXIDE 
 IN THE SOLUTION WHICH 
 
 WAS USED. 
 
 
 1O c.c. 
 
 2O c.c. 
 
 lOc.c. 
 
 2O c.c. 
 
 for 1O c.c. 
 of Sulphu- 
 ric Acid. 
 
 for 1O c.c. 
 of Hydro- 
 chloric 
 Acid. 
 
 
 c.c. 
 
 c.c. 
 
 c.c. 
 
 c.c. 
 
 grams. 
 
 grams. 
 
 Sodium 
 hydroxide. 
 
 
 
 
 
 
 
 Potassium 
 hydroxide. 
 
 
 
 
 
 
 
 
 WEIGHT OF HYDROXIDE NECESSA 
 HYDROCHLORIC ACID. 
 
 RY TO NEUTRALIZE ONE GRAM OF 
 SULPHURIC ACID. 
 
 Sodium 
 hydroxide. 
 
 Potassium > 
 hydroxide. 
 
 
 
 Ratio, 
 
 sodium hydroxide : 
 potassium hydroxide : 1 : x. 
 
 Ratio, 
 
 sodium hydroxide : 
 potassium hydroxide : 1 : x. 
 
250 
 
 ELEMENTS OF CHEMISTRY. 
 
 necessary to neutralize one gram of hydrochlo- 
 ric acid ? Concordant results can be obtained 
 in the above experiments only by the most 
 careful work. Each determination should be 
 made at least twice, so as to insure accuracy. 
 The table on preceding page will be found ex- 
 pedient in tabulating results. 
 
 Fig. 22. 
 
 36. Construction of a Barometer. 
 
 a. Seal one end of a glass tube one metre 
 in length and about one cm. in internal diam- 
 eter. Nearly fill this tube with dry mercury, 
 close with the thumb, and remove small air- 
 bubbles by passing a larger bubble to and fro 
 in the tube. Now entirely fill the tube, again 
 close, and invert in a vessel of mercury. 
 Clamp the tube in an upright position, and 
 measure with a metre-stick the distance be- 
 tween the level of the mercury in the lower 
 vessel and the level in the tube. 
 
 1). The barometer shown by Fig. 22 is con- 
 structed on the following principle. The tube 
 is curved so that the shorter arm, a, takes the 
 place of the lower vessel described above, the 
 mercury being held in place, with its lower 
 level at a, by the pressure of the atmosphere. 
 The tube is filled with mercury, carefully 
 heated until all small air-bubbles are expelled, 
 and then inverted. At the upper level of the 
 mercury, and extending 150 mm. above and 
 below it, is placed a portion of a metre scale, 
 the point of which is given by a movable 
 mark at a. The scale has attached to it a 
 sliding vernier, b, so that the level of the 
 
LABORATORY EXPERIMENTS, 251 
 
 mercury can be read to ^ of a millimetre. As the height 
 of the barometer varies, so must the level of the mercury 
 above and below vary. However, as the measurement 
 must always begin at the same point, provision is made 
 for adjusting the level of the lower mark so that it cor- 
 responds to the lower level of the mercury. When the 
 vernier is placed at the upper level, the corresponding mark 
 on the scale gives the total height of the barometer, c rep- 
 resents a thermometer attached to the instrument. 
 
 c. As water is specifically much lighter than mercury, 
 it must be true that the atmosphere can support a higher 
 column of water than of mercury. In order to prove this, 
 cover the mercury vessel in this Experiment, a, with about 
 an inch of water, and then carefully raise the barometer 
 tube until its mouth is just above the level of the mercury, 
 but below the level of the water. The mercury flows out, 
 the water takes its place, and completely fills the tube. 
 
 37. Proof That a Given Volume of Gas varies Inversely as the 
 Pressure on It. 
 
 The apparatus is arranged as in Fig. 23, 1. It consists 
 of a tube about one and one-third metres in length and 20 
 cm. internal diameter. It is open at both ends, and curved 
 so as to form a short arm of about 30 cm. in length. The 
 short arm is closed with a rubber stopper, single-bored, into 
 which is fitted an absolutely tight glass stopcock. The 
 tube is fastened to a board, on which are marks indicating 
 distance, in inches or centimetres. 
 
 Manipulation : Open the glass stopcock, and carefully 
 pour in clean, dry mercury through the long arm, until the 
 level in both arms stands at (Fig. 23, 1). Now close the 
 stopcock. Note the volume of confined air, which obvi- 
 ously is under a pressure of one atmosphere. Note also 
 the height of the barometer. Again pour mercury into the 
 long arm, until the differ ence in the level of the mercury is 
 
252 
 
 ELEMENTS OF CHEMISTRY. 
 
 equal to one-half the observed barometric height (Fig. 
 23, 2). The confined air is now subjected to a pressure of 
 one and one-half atmospheres. What is the ratio between 
 the present volume and the original volume of air ? Again 
 add mercury until the gas is subjected to a pressure of two 
 atmospheres (Fig. 23, 3). What is now the volume of 
 gas ? What is the ratio between this and the original vol- 
 
 Fig. 23. 
 
 ume ? Of course, if a sufficiently long tube is taken, this 
 experiment can be extended so as to include 3 or 4 atmos- 
 pheres, and it can be repeated with other gases (hydrochlo- 
 ric acid, sulphur dioxide, oxygen, and hydrogen). Other 
 gases can be filled in by attaching the gas generator to the 
 open stopcock, while at the same time enough mercury 
 
LA B OR A TOR Y EXPERIMEN TS. 
 
 253 
 
 Fig. 24. 
 
 is placed in the tube to bring both sides to 0. The gas 
 will then be forced in, will bubble out, and through the 
 mercury, and expel the air. 
 
 38. Influence of Vapor Pressure on the Volume of Gas 
 enclosed in a Barometric Tube. 
 
 a. Arrange a barometer as in Experiment 36 a, 
 marking the height of the mercury column with 
 a rubber ring. Slip under the open mouth of 
 the barometer tube the end of a curved pipette 
 (Fig. 24) filled with water, the upper end of 
 which you have closed with the finger. Remove 
 , . the finger, and blow in- 
 
 to the upper end of the 
 pipette, so as to force 
 about 10 drops of water 
 into the barometer. 
 What is the level of 
 the mercury after introducing the 
 water ? Note the temperature, and 
 measure in millimetres the differ- 
 ence between the original height of 
 mercury and the present. Warm 
 the tube at its upper end, where 
 the water is, by holding the hand 
 round it for a few minutes. Warm 
 it in a cloth dipped in hot water. 
 Note change in the height of the 
 barometer in each case. 
 
 b. Repeat &, using alcohol in- 
 stead of water. 
 c. Kepeat a, using ether instead of alcohol. 
 Fig. 25 represents four barometer tubes. Tube a is an 
 ordinary barometer ; tube b contains water vapor ; tube c, 
 alcohol ; and tube d, ether. 
 
 Fig. 25. 
 
254 ELEMENTS OF CHEMISTRY. 
 
 d. Expansion of gases by heat. 
 
 Repeat Experiment 36a, with the difference that in fill- 
 ing the barometer tube you allow 5 c.c. of air to remain. 
 Mark the height of mercury in the tube by a rubber ring. 
 Now warm the enclosed gas with the hand. With a cloth 
 dipped in hot water. To perform this experiment accu- 
 rately, so as to ascertain the degree of expansion with each 
 degree of temperature, is too elaborate for this work. The 
 pupil must remember, arbitrarily, that gases expand ^1^ for 
 each degree of increase in temperature. Using the for- 
 mula on page 70, ascertain what the volume of 25 c.u of 
 air would be at 760 mm. pressure, if this air is measured 
 at 743 mm. What is the volume of 25 c.c. of air at and 
 760 mm. if the air is measured at 22 and 760 mm. ? 
 Twenty-five c.c. of air, containing water vapor, and en- 
 closed in a tube over mercury, are under the following 
 conditions : 
 
 Temperature = 30. 
 
 Barometer = 725 mm. 
 
 Height of mercury column = 425 mm. 
 
 What is the volume of the dry gas at and 760 mm. ? 
 
 e. Fill a glass tube of 100 c.c. capacity, graduated in half 
 c.c., one-fourth full of mercury, and invert it in a cylinder 
 of mercury about 30 c.m. in depth. Lower the tube so that 
 the level of the mercury without and within is the same. 
 Under what pressure is the enclosed volume of gas ? Note 
 accurately the enclosed volume of gas and the height of 
 the barometer. Eaise the tube a few centimetres, clamp 
 it in this position, and allow it to stand for five minutes. 
 Again read the volume of gas, and measure carefully the 
 height of the column of mercury in the tube above that in 
 the cylinder. 
 
 Repeat, raising the tube still higher. 
 
LABORATORY EXPERIMENTS. 
 
 255 
 
 If v = the first volume, 
 
 v l = the second volume, 
 B = barometric height, 
 h = height of column of mercury in tube, 
 show that v : v 1 : : B h : B. 
 
 39. Preparation of Nitrogen from the Atmosphere. Fig. 26. 
 The apparatus consists of a tube of infusible glass, with 
 a bulb blown in the middle. This bulb is filled with copper 
 filings. At the right this tube is connected by means of a 
 capillary glass tube with a large bottle fitted with a double- 
 bored stopper, into one hole of which a siphon is tightly 
 
 Fig. 26. 
 
 fitted. The siphon should be fitted with a rubber tube and 
 pinchcock, so as to regulate the flow. The end of the hard 
 glass tube farthest from the siphon is connected with two 
 wash-bottles, both of which contain strong sodium hydrox- 
 ide solution. These wash-bottles are to remove carbon 
 dioxide from the air, which is to be drawn through the 
 tube containing the copper. When all connections are 
 made air-tight, heat the copper filings with a Bunsen 
 
256 ELEMENTS OF CHEMISTRY. 
 
 burner, and after a few minutes start the aspirator slowly. 
 Air will now be drawn into the apparatus through the 
 wash-bottles and over the copper filings. That which re- 
 mains will be collected in the large bottle. Change of 
 color will occur in copper. Why ? After the bottle is 
 one-half full of gas, tightly close the siphon, disconnect 
 the apparatus, raise the double-bored stopper, and insert 
 a burning pine splinter. Note the difference of the be- 
 havior of the gas as compared with ordinary air. 
 
 Pass a current of air over heated copper filings until all 
 original copper color has disappeared. Connect the tube 
 containing this altered copper with a hydrogen generator, 
 delivering pure dry hydrogen (Experiment 12, Fig. 11), and 
 after the gas has passed over for at least five minutes, gen- 
 tly heat the altered copper by means of a Bunsen burner. 
 What is the change in appearance. What collects in the 
 farther end of the tube ? What chemical change has taken 
 place ? 
 
 40. Combustion in Oxygen. 
 
 Prepare an 'oxygen generator as in Experiment 9c. Col- 
 lect the gas, over water, in five wide-mouthed 32-oz. bottles. 
 Prepare a deflagrating-spoon by slipping the wire handle 
 through a hole in the centre of a piece of sheet tin, larger 
 than the mouths of the. bottles (Fig. 27). Kemove one of 
 the bottles from the water by placing a glass plate over the 
 mouth, holding it in position, and raising plate and bottle 
 from the water. Place the bottle upright, and insert a 
 glowing pine splinter. Into a second bottle lower a defla- 
 grating-spoon on which is a small piece of ignited sulphur. 
 Repeat with a piece of phosphorus the size of a pea. 
 Test the water remaining in the jars with blue litmus 
 paper. Repeat, using a small piece of carbon heated to 
 redness. 
 
 Heat in a Bunsen flame a 4-inch piece of steel watch- 
 
LABORATORY EXPERIMENTS. 
 
 257 
 
 spring, and straighten it. Slip one 
 end of the spring through the sheet-tin 
 cover used with the deflagrating-spoon. 
 and fasten with a cork. Wrap a 
 bit of cotton round the other end, 
 and dip it into a little molten 
 sulphur. Eemove a jar of oxy- 
 gen from the water, light the sul- 
 phur, and when it is burning 
 plunge the watch-spring into the 
 oxygen. 
 
 What is the difference be- 
 tween the above combus- 
 tions and combustions in 
 the air ? Why ? 
 
 41. Keversing the Phenomena 
 of Combustion. Burning 
 of Oxygen in Hydrogen. 
 
 Fig. 27. 
 
 The apparatus necessary to demonstrate the combustion 
 of oxygen in hydrogen is shown by Fig. 28. C is the neck 
 ^ of an ordinary retort. Into the narrow 
 
 * * end of this is fitted a single-bored rub- 
 ber stopper, which connects at A with 
 a generator furnishing a brisk current of dry 
 hydrogen, generated as in Experiment 9a. 
 Allow the current of hydrogen to pass for some 
 time, until all air is expelled ; then light the 
 hydrogen at the wide end of C. Have ready a 
 burner, B, with a platinum tip 
 (described in Experiment 12), 
 through which a slow stream of 
 oxygen is passing from the gas- 
 ometer. The oxygen is dried 
 Fig. 28. by means of a small tube, filled 
 
258 ELEMENTS OF CHEMISTRY. 
 
 with anhydrous calcium chloride. (Wash-bottles can- 
 not be used, because the bubbling of the gas through the 
 liquid will cause the flame to flicker.) Thrust the burner, 
 through which oxygen is passing, up into the tube C. As 
 it passes through the burning hydrogen at the mouth, the 
 oxygen will be ignited, and will continue to burn in C. 
 What is the cause of the flame ? 
 
 42. Heating of Iron Filings and Sulphur. Incandescence during 
 
 Union. 
 
 Thoroughly mix in a mortar 7 grams of fine iron filings 
 and 4 grams of flowers of sulphur. Place the mixture in 
 a large test-tube, and hold it in the flame so that it is 
 strongly heated at one point. When the mass begins to 
 glow, remove the tube from the flame. What resemblance 
 is there between this change and those encountered in 
 ordinary combustion ? What is produced ? 
 
 43. a. Combustion of Phosphorus in Chlorine. 
 (Experiment under Hood.) 
 
 Place a piece of phosphorus as large as a pea in a defla- 
 grating-spoon, fitted with a piece of sheet tin as described 
 in Experiment 40. Ignite the phosphorus, and lower it 
 into a jar of dry chlorine. Compare this combustion with 
 that of phosphorus in oxygen. What is the product in 
 each case ? Is there an evolution of light and heat ? 
 
 b. Heat changes during the neutralization of acids by bases. 
 Repeat Experiment 4c, using in the beaker 10 c.c. of 
 sodium hydroxide solution, containing 5 grams of sodium 
 hydroxide to 10 c.c. of water. Gradually add hydrochloric 
 acid (one part concentrated hydrochloric acid to one part 
 of water), stirring with the thermometer. Note change in 
 temperature. Repeat, adding sulphuric acid (one part 
 sulphuric acid to five parts of water). 
 
LAB OR A TOR Y EXPERIMENTS. 
 
 259 
 
 44. Burning of Phosphorus and of a Candle in a Closed Air Space, 
 
 and testing, the Air which remains. Fig. 19. 
 
 G. Prepare a float made of a flat cork, on which, is fas- 
 tened a porcelain crucible cover. Place this cork in a pneu- 
 matic trough, with a piece of phosphorus the size of a bean 
 on the cover, and light the phosphorus with a hot wire. 
 Invert a be]J jar of three litres capacity over the float, 
 and slightly raise the stopper at the top, so as to let out 
 the air, which expands greatly owing to the heat given off 
 by the burning phosphorus. If this precaution is omitted, 
 the air will be forced out at the bottom of the jar in large 
 bubbles, and the disturbance may tip over the phosphorus 
 float. After the violent combus- 
 tion is over, insert the stopper of 
 the bell jar, and allow to cool. To 
 test the remaining gas, add enough 
 water to the pneumatic trough to 
 make the level within and without 
 the bell jar alike, and then intro- 
 duce a lighted taper. 
 
 I. Repeat, attaching a piece of 
 candle to a cork float, lighting the 
 candle, and bringing it under the 
 
 bell jar. When the light is extinguished, test the gas 
 as before. Compare this with the action of air 011 copper. 
 What is the distinction between combustion in air and in 
 oxygen ? Does the candle use up all of the oxygen before 
 it is extinguished ? What becomes of the phosphorus ? 
 Test the water in the apparatus with blue litmus. 
 
 45. Determination of the "Volumetric Composition of the Atmosphere. 
 
 Fig. 30. 
 
 Take a long glass tube, closed at one end, and divide it 
 into five equal parts by means of rubber rings. Invert 
 this over a long cylinder filled with water, so that the level 
 
 Fig. 29. 
 
200 
 
 ELEMENTS OF CHEMISTRY. 
 
 without and within is at the first ring, and then clamp the 
 tube in place. Fix a piece of phosphorus the size of a 
 bean on a long copper wire, bend the wire as shown- in the 
 cut, thrust the phosphorus up into the tube, and set the 
 apparatus aside for two days. Then sink the tube so that 
 the level of the water without and within is the same. 
 What is the ratio between the volirme of gft,s remaining 
 and the volume of gas originally present ? By noting the 
 height of the barometer before and after the experiment, 
 ^ and then applying the necessary cor- 
 
 rections, quite accurate results can 
 be obtained, if a carefully graduated 
 tube is substituted for the crudely 
 divided one indicated. 
 
 The figures (No. 30) show a tube 
 such as is described. In one (V) the 
 phosphorus has just been thrust into 
 the enclosed air space ; in the other 
 (a) the same tube has been al- 
 lowed to stand two days, and 
 then has been adjusted so that 
 the level without and within is 
 the same. 
 
 46. Accurate Determination of the Vol- 
 umetric Composition of the Atmos- 
 phere by Means of the Eudiometer 
 Tube. Teacher's Experiment. 
 
 Fig. 30. 
 
 In order to measure accu- 
 rately the relative amounts of 
 
 oxygen and nitrogen in the atmosphere, the eudiometer is 
 employed (Fig. 8, Experiment 10). The instrument should 
 have a capacity of 100 c.c., should be partially filled with 
 mercury, and inverted over the mercury trough so that 
 about 25 c.c. of air will remain enclosed. About 14 c.c. of 
 
LABOEAT011Y EXPERIMENTS. 261 
 
 dry hydrogen are now run in, by slanting the tube and pla- 
 cing under its mouth the delivery tube of a hydrogen ap- 
 paratus which is generating pure, dry hydrogen. Take all 
 the precautions mentioned in Experiment 10, and ignite the 
 mixture of gases with an electric spark. Be sure to read 
 accurately the volume of air and the volume of hydrogen 
 before the explosion, and also to measure the height of the 
 column of mercury at each step, as indicated in Experiment 
 10. After the explosion, allow it to stand for ten minutes, 
 and then read the volume of remaining gas, and reduce to 
 standard conditions exactly as was done before. Note the 
 diminution in volume. The hydrogen will have united 
 with the oxygen to form water, therefore one-third of the 
 diminution in volume must have been due to oxygen. 
 Why ? What is the volumetric composition of the atmos- 
 phere as given by the above experiment ? 
 
 47. Determination of the Dew Point. 
 
 Suspend a thermometer over a beaker of water so that 
 the bulb is immersed in the liquid. Note the temperature. 
 Gradually add small pieces of ice to the water, and stir the 
 liquid until a point is reached when moisture begins to col- 
 lect on the outside of the beaker. Note the temperature. 
 
 48. Proof that Carbon Dioxide occurs in the Atmosphere. 
 
 a. Make a solution of calcium hydroxide (lime-water) 
 as in Experiment 256. Place this in a beaker, and expose 
 it to the air for some time. What is observed ? Explain. 
 
 b. Arrange an apparatus as in Experiment 39, Fig. 26, 
 substituting an empty bottle in place of the tube contain- 
 ing copper shavings. Fit this bottle with a double-bored 
 rubber stopper, so arranged that air can be sucked into 
 this empty bottle through two wash-bottles containing 
 sodium hydroxide. When all connections are made, open 
 the siphon, and draw air slowlv. through the apparatus. 
 
262 
 
 ELEMENTS OF CHEMISTRY 
 
 Remove the empty bottle, pour quickly into it some clear 
 lime-water, and tightly stopper. Does the lime-water 
 change ? What alteration was produced in the air by 
 sucking it through the caustic soda solution ? After the 
 lime-water has stood for some time in the empty bottle, 
 open the bottle, introduce into it a small piece of glowing 
 charcoal, and stopper again. Now observe the lime-water.* 
 Take a little clear lime-water in a test-tube, and blow a 
 current of air through it by means of a glass tube. Wha-t 
 change do you observe ? 
 
 49. Preparation of Ammonia Gas from a Solution of Ammonia in 
 Water. Fig. 31. (Experiment under Hood.) 
 
 In a generating-flask, a, of 500 c.c. capacity place 200 c.c. 
 of strong ammonia water (aqua ammonia fortior). Connect 
 the delivery tube with a so-called drying-tower, b, which 
 
 is a cylinder with a tu- 
 bulated opening below, 
 and with a single-bored 
 stopper and delivery 
 tube above. The 
 drying-tower contains 
 pieces of quicklime. 
 When the apparatus 
 is ready, heat the gas 
 gently, and collect sev- 
 eral cylinders of it by 
 upward displacement 
 of the air, c. Finally, 
 collect the remaining 
 gas in a beaker of 
 water. Cover the jars 
 with glass plates as 
 fast as they are filled. 
 
 Fig. 31. 
 
 * Charcoal, in burning, produces carbon dioxide. 
 
LAB OR A TOR Y EXPERIMENTS. 
 
 263 
 
 50. Experiments with Ammonia. 
 
 a. Place one jar, mouth downward, in a vessel of water. 
 Is ammonia very soluble in water ? Introduce a lighted 
 splinter into the second jar. Test the odor of ammonia as 
 you did that of chlorine. Test the solution of ammonia 
 in water by means of a piece of red litmus paper. After- 
 wards expose this litmus paper to the air for a short time. 
 
 b. Bring together, mouth to mouth, a jar of ammonia 
 and an equal-sized jar of oxygen. Tightly hold the two 
 in position, and invert them several times. Finally apply 
 a lighted splinter to the mouth of each jar. 
 
 51. Decomposition of Ammonia by Metals. Fig. 32. 
 Arrange an apparatus for the preparation of dry ammo- 
 nia, as in Experiment 49. Connect the delivery-tube with 
 a tube of infusible glass, as in Experiment 39. Fill the 
 bulb of this tube with shavings of magnesium; connect 
 the farther end with a safety-bottle, and from the latter 
 run a delivery-tube to a vessel of water. Invert a test- 
 tube full of water in the vessel, and have 
 it ready for collecting the gas evolved. When 
 all is ready, heat the ammonia water in the 
 generating-flask very gently, so as to secure a 
 
 Fig. 32. 
 
264 ELEMENTS OF CIIEMISTliY. 
 
 very slow evolution of gas. When all air lias been 
 expelled from the apparatus, heat the bulb containing 
 magnesium to a low red heat, and collect the evolved 
 gas in the inverted test-tube. Remove the test-tube, 
 closing its mouth with the thumb, and instantly apply 
 a lighted taper. What change in the appearance of 
 the magnesium ? Expel all ammonia from the bulb- 
 tube by means of a current of air, and add water to 
 
 the contents of the bulb. What odor do you note ? 
 
 52. Decomposition of Ammonia by Chlorine. 
 
 Prepare a saturated solution of common salt, invert 
 over it a 32-oz. bottle filled with the same liquid, and 
 then replace this liquid by chlorine. Next, cover the 
 Fig. chlorine bottle with a glass plate, and transfer it, 
 33 ' mouth downward, to a vessel containing ammonia 
 water. Does the color of the chlorine disappear ? Does the 
 gas diminish in volume ? When no further change takes 
 place, again cover the bottle with a glass plate, transfer, 
 mouth downward, to another vessel containing dilute sul- 
 phuric acid (1 part sulphuric acid to 20 of water), and allow 
 it to stand a few minutes. Then cover again, invert the 
 bottle, and introduce a burning pine splinter. Has the odor 
 of the chlorine disappeared ? What is the gas remaining ? 
 
 53. Determination of the Volumes of Hydrogen and Nitrogen in a 
 Known Volume of Ammonia Gas. Fig. 33. 
 
 Take a tube one-half metre in length and 15 cm. in 
 diameter, closed at one end. Divide this tube into three 
 equal parts by two rubber rings. Fill it with a saturated 
 solution of common salt, and invert it over a vessel con- 
 taining the same liquid. Now expel the salt solution by 
 means of chlorine. When the tube is entirely filled with 
 chlorine, close the mouth with the thumb, and transfer, 
 
LABORATORY EXPERIMENTS. 265 
 
 mouth dowmvard, to a vessel containing a solution of am- 
 monia in water. When action has ceased transfer again, 
 keeping the mouth tightly closed with the thumb, to a cyl- 
 inder one-half metre in depth, which is filled with a dilute 
 solution of sulphuric acid (1 part of sulphuric acid to 20 
 of water). Adjust the tube so that the level of the liquid 
 without and within is the same. At what point does it now 
 stand ? Test the gas which remains as in Experiment 52. 
 The tube was divided into three equal parts, and filled 
 with chlorine. When the chlorine acted on the ammonia 
 dissolved in water, it decomposed an equivalent quantity 
 of ammonia, and set free a corresponding amount of 
 nitrogen. This nitrogen occupies one-third the volume of 
 the chlorine used; but the chlorine has united with the 
 hydrogen which was originally combined with this one- 
 third volume of nitrogen. As chlorine unites with hydro- 
 gen, volume for volume, to form hydrogen chloride (see 
 Experiment 20), it follows that the three volumes of 
 chlorine, indicated by the three divisions of the tube, must 
 have united with three volumes of hydrogen; hence, 1 
 volume of nitrogen was united with 3 volumes of hydrogen 
 in ammonia. The hydrochloric acid which was formed 
 was removed from the tube by the ammonia water, and 
 any ammonia which may have entered the tube has been 
 removed by the dilute sulphuric acid, so that finally 
 nothing but pure nitrogen is left. 
 
 54. Decomposition of Ammonia by the Electric Spark. Teacher's 
 Experiment. 
 
 Fill a eudiometer tube with clean, dry mercury, and 
 invert it in a mercury trough. Introduce 15 c.c. of dry 
 ammonia gas prepared as in Experiment 49. Note accu- 
 rately : 
 
 1. Volume of gas. 
 
 2. Height of barometer. 
 
266 ELEMENTS OF CHEMISTRY. 
 
 3. Temperature. 
 
 4. Height of column of mercury in tube. 
 
 Connect the two platinum wires with an induction coil, and 
 allow electric sparks to pass through the ammonia until no 
 further increase in volume is observed ; then disconnect 
 the coil, allow to stand for five minutes, and note : 
 
 1. Volume of gas. 
 
 2. Height of barometer. 
 
 3. Temperature. 
 
 4. Height of column of mercury in tube. 
 
 Reduce the gas volume to standard conditions of tempera- 
 ture and pressure. What is the relation between the first 
 volume and the second ? Combining what you learned 
 in Experiments 53 and 54, what volumes of nitrogen and 
 hydrogen unite to form ammonia ? What volume of 
 ammonia is produced from these volumes of hydrogen 
 and nitrogen ? Compare the results with the ones obtained 
 in determining the volumetric composition of water and 
 of hydrogen chloride. In the formation of hydrogen chlo- 
 ride, 1 volume of hydrogen -f 1 volume of chlorine = 2 
 volumes of hydrogen chloride. In the formation of water, 
 2 volumes of hydrogen -j- 1 volume of oxygen = 2 vol- 
 umes of water vapor. What is the case with ammonia, 
 as shown by Experiment 54 ? 
 
 55. Action of Ammonia on Hydrogen Chloride. 
 A cheap apparatus, which will demonstrate that equal 
 volumes of hydrogen chloride and ammonia unite to pro- 
 duce a solid, is described in the text, page 98. This exper- 
 iment can, however, be performed more accurately and 
 neatly by using the apparatus described in Experiment 20, 
 Figs. 16 and 17.* 
 
 * The glass stopcock must have a very large bore, otherwise the ammo- 
 nium chloride will fill it, and prevent communication between the tubes. 
 
LABORATORY EXPERIMENTS. 267 
 
 Manipulation exactly as in the demonstration that hy- 
 drogen chloride is formed of equal volumes of hydrogen 
 and chlorine. Through the three-way stopcock (Fig. 17) 
 pass a current of dry ammonia (Experiment 49, Fig. 31), 
 having turned the stopcock so that the gas passes^ in 
 through one of the tubes, and out at the narrow tip. Allow 
 the current to pass until you are sure that all the air is 
 expelled (five to ten minutes). Now close this arm with 
 the stopcock, and seal the tip in the flame of the Bunsen 
 burner. Next, fill the second arm in the same way with 
 dry hydrogen chloride (Experiment 16, Fig. 13), and, after 
 sealing the tip, turn the stopcock so that the two tubes 
 communicate. Allow the apparatus to stand for twenty- 
 four hours, and then, after scratching one of the tips with 
 a file, dip it under dry mercury, and break the tip. 
 
 56. Preparation of Ammonium Chloride. The Decomposition of 
 Ammonium Chloride by Slaked Lime. 
 
 a. In a beaker place 25 c.c. of ammonia solution. Take 
 out a drop, and place it on a strip of red litmus paper. 
 Allow the litmus paper to stand in the air for some min- 
 utes, and then examine. To the solution of ammonia add, 
 gradually, a solution of hydrochloric acid until neutral 
 toward litmus. Kow evaporate the solution to dry ness in 
 a porcelain dish on a water-bath. What is the appearance 
 of the remainder ? Heat a little on a piece of platinum 
 foil in the Bunsen burner. What is the effect ? 
 
 b. In a porcelain e vapor at ing-dish place about 10 grams 
 of quicklime, and gradually, a few drops at a time, add 
 water. Keep on adding until the lime is of the consist- 
 ency of very thick paste. Now arrange an apparatus as 
 shown in Fig. 31, Experiment 49 ; place the slaked lime 
 in the generating-flask, and add to it 10 grams of your 
 ammonium chloride, which you have powdered in a mortar. 
 
268 ELEMENTS OF CHEMISTRY. 
 
 Connect all parts of the apparatus, and heat the generating- 
 flask very gently. Collect the gas which passes off by dis- 
 placement of air, as was done in Experiment 50. What 
 gas has been collected ? Identify it by its action on a 
 piece of moist red litmus paper, and by its solubility in 
 water. Over the mouth of one of the tubes of gas hold a 
 glass rod, on the tip of which is a drop of a concentrated 
 solution of hydrochloric acid in water. What is the 
 effect ? 
 
 57. Formation of the Ammonium Salts of Various Acids. The 
 
 Decomposition of these Salts by Bases. 
 
 a. In a beaker place 5 c.c. of a diluted solution of nitric 
 acid (1 : 5), and then add ammonia solution until neutral 
 toward litmus. What is the change in temperature ? 
 Evaporate to dry ness on a water-bath. Heat a little of 
 the salt thus produced on a piece of platinum foil in the 
 Bunsen burner. To some of the salt in a test-tube add a 
 concentrated solution of potassium hydroxide (one part 
 caustic potash to one of water). Odor of gas passing off ? 
 In the mouth of this test-tube suspend a moist strip of red 
 litmus paper, so that it does not touch at the sides. Over the 
 mouth of this test-tube hold a glass rod, on the tip of which 
 is a drop of a concentrated solution of hydrochloric acid. 
 
 b. Repeat, using diluted sulphuric acid (1 : 5) instead 
 of nitric acid. 
 
 c. Repeat a and b, using sodium hydroxide instead of 
 potassium hydroxide. 
 
 58. The Determination of the Volumes of Hydrogen produced by 
 
 the dissolving of Known "Weights of Metals in Acids. (Repeat 
 Each of the Following Experiments until the Two Results in 
 Each Case exactly agree.) 
 
 a. Arrange an apparatus as shown in Fig. 34. It con- 
 sists of a glass beaker, a, into which is placed a small 
 
L A E OR A TOE Y EXPERIMENTS. 
 
 269 
 
 Fig. 34. 
 
 funnel, c, the stem of which is cut off. Ac- 
 
 curately weigh off about .1 gram of pure 
 
 zinc, place it under the inverted funnel, and 
 
 nearly fill the beaker with distilled water. 
 
 Now fill a gas-measuring tube, b (which has 
 
 a capacity of 200 c.c., and which is graduated 
 
 in i c.c.), with diluted hydrochloric acid, in- 
 
 vert the tube in the beaker, and fix it 
 
 in position, so that its mouth is over the 
 
 opening of the funnel. Owing to its 
 
 greater specific gravity, the hydrochloric 
 
 acid will descend into the water, and will 
 
 come in contact with the zinc. All of 
 
 the hydrogen which passes off must 
 
 necessarily collect in the gas-measuring 
 
 tube. When all of the zinc has disap- 
 
 peared, tightly close the tube with the thumb, and transfer 
 
 it to a deep cylinder of pure water ; clamp so that the level 
 
 without and within is the same. Note temperature and 
 
 barometer, and recalculate the gas-volume to standard con- 
 
 ditions. What weight of hydrogen, in grams, does this 
 
 volume represent ? From the data at hand ascertain the 
 
 quantity of zinc which would be necessary to liberate one 
 
 gram of hydrogen. 
 
 b. Repeat a, using dilute sulphuric acid (1 : 10) instead 
 of hydrochloric acid. 
 
 c. Repeat a and Z>, using about .1 gram of pure iron 
 (piano wire). 
 
 d. If desired, a and b can be repeated, using a piece 
 of magnesium ribbon which has been carefully cleaned. 
 In this case a gas-measuring vessel of at least 300 cubic 
 centimetres capacity must be selected. What are the 
 equivalent weights of iron and zinc as slipway by. the exper- 
 
 iments? ' 
 
 
 
270 ELEMENTS OF CHEMISTRY. 
 
 59. Alteration in "Wood by Heating. 
 
 In a test-tube of so-called infusible glass, place a piece of 
 fresh pine wood, and bring it into the flame of the Bunsen 
 burner. Gradually increase the heat. Alteration in the 
 appearance of the wood ? Odor ? Apply a lighted taper 
 to the mouth of the tube. 
 
 60. a. The Absorption of Coloring Matter by Charcoal. 
 
 1. In a test-tube place a little indigo, add to this a few 
 drops of concentrated sulphuric acid, warm slightly, and 
 then dilute with water, and filter. Pour the blue solution 
 into a 300 c.c. flask in which you have placed 10 grams of 
 fresh animal charcoal.* Warm the solution, and shake 
 vigorously for a short time; then filter off the charcoal. 
 What is the color of the filtrate ? 
 
 2. Repeat, using a solution of blue litmus. 
 
 3. Repeat, using a solution of logwood. 
 
 b. Absorption of gases by charcoal. 
 
 Arrange an apparatus for the preparation of ammonia as 
 in Experiment 49, Fig. 31. Collect a test-tube full of the 
 gas over dry mercury, and leave the test-tube clamped in 
 position, so that its mouth dips under the mercury. Now 
 heat a small piece of wood-charcoal for an instant in the 
 flame of the Bunsen burner, f After allowing any portion 
 which may be glowing to become extinguished, slip it 
 quickly under the mercury, so that it will rise in the test- 
 tube. When no further absorption takes place, prepare a 
 second, piece of charcoal as above, and bring it into the 
 tube. What is true of ammonia gas is true of a large 
 number of other gases which, like ammonia, are easily 
 condensed to liquids (sulphur dioxide, hydrogen sulphide, 
 etc.). 
 
 * Animal charcoal is to be obtained from any dealer in chemicals. 
 t Hold the charcoal by a pair of pincers or a pair of tongs. 
 
LABORATORY EXPERIMENTS. 
 
 271 
 
 61. Burning of Charcoal in a Closed Space of Oxygen. 
 
 Prepare a glass tube 30 cm. in length and 10 cm. inter- 
 nal diameter, sealed at one end, and bent as shown in 
 Fig. 35. Slip into the tube a piece of wood-charcoal the 
 size of a pea, fill the tube with mercury, and invert it in a 
 small vessel, b, of the same liquid, 
 clamping it in position as shown in 
 the cut. Now admit dry oxy- 
 gen into the tube until the mer- 
 cury is expelled as far as 
 the bend, and mark the 
 position of the liquid by 
 means of a strip of 
 paper. Now gently 
 heat the charcoal with 
 the Bunsen burner un- 
 til combustion begins, 
 then remove the flame, 
 and allow the charcoal to stand until combustion is complete, 
 and the apparatus has cooled to its former temperature. Is 
 there any change in the volume of the gas ? 
 
 Fig. 35. 
 
 62. Formation of Carbon Dioxide by passing Oxygen over Hot 
 Charcoal. 
 
 Arrange the apparatus used in Experiment 21, Fig. 18, 
 with the difference that in place of the hydrochloric acid 
 generator (A), you have an apparatus delivering dry oxygen. 
 Fill the iron tube with about 15 grams of charcoal in 
 pieces the size of a pea, connect all parts of the apparatus, 
 and collect the gas which passes off by displacement of air 
 in several cylinders placed mouth upward. Cover each 
 cylinder, after the air is expelled, with a glass plate. Into 
 one of the cylinders introduce a burning taper. iDto an- 
 other pour a few drops of a filtered solution of slaked lime 
 
272 
 
 ELEMENTS OF CHEMISTRY. 
 
 [Experiment 25&] (formation of calcium carbonate). In- 
 vert a cylinder in a vessel containing a solution of caustic 
 potash. In one of caustic soda. 
 
 63. Formation of the Primary and Secondary Carbonates of Potas- 
 sium and Sodium. 
 
 For these experiments, arrange an apparatus for generat- 
 ing carbon dioxide as described in Experiment 65. 
 
 a. Prepare a solution of 10 grams of potassium hydrox- 
 ide in 50 grams of water, place this solution in a small 
 beaker, attach a funnel small enough to pass inside this 
 beaker to the exit tube of an apparatus generating carbon 
 dioxide, and then dip the funnel into the beaker so that its 
 edge is just below the surface of the liquid (Fig. 36). 
 Now pass a brisk current of carbon dioxide into the solu- 
 tion of caustic potash until a drop, taken out and placed 
 on a piece of red litmus paper, is neutral. Now evapo- 
 rate gently to dryness in a porcelain dish on a water-bath. 
 
 What is the appearance of the 
 '* remainder? Is it like caustic 
 
 potash ? Place a little of the re- 
 mainder in a test-tube, and add to it a 
 few drops of diluted hydrochloric acid, 
 and then in the mouth of the tube hold 
 a glass rod, on the tip of which you 
 have a drop of clear solution of slaked 
 lime. Compare this behavior with that 
 of caustic potash under the same con- 
 ditions. Heat some of the remainder 
 in a test-tube, and hold over the mouth 
 a glass rod, on the tip of which is a 
 drop of a clear solution of slaked lime. 
 
 b. Purify 5 grams of the primary carbonate of potas- 
 ium (prepared by the above experiment), by dissolving it 
 
 Fig. 36. 
 
LABORATORY EXPERIMENTS. 273 
 
 in cold distilled water, evaporating the solution at a gentle 
 heat to crystallization, and then drying the crystals between 
 pieces of filter paper. Finally, powder the crystals, and 
 place them in a desiccator over concentrated sulphuric acid 
 for twenty-four hours. Take a gas-measuring tube (of 100 
 c.c. capacity, and graduated to .1 c.c.), fill it with dry 
 mercury, and invert it over a trough of the same liquid. 
 Now carefully weigh off .2 grams of your pure primary 
 carbonate of potassium, wrap it in a piece of filter paper 
 so as to form a package small enough to slip up into the 
 mercury tube, and then bring it under the mouth so that 
 it will rise to the top. From a curved pipette (Fig. 24) 
 introduce a few drops of diluted hydrochloric acid into the 
 tube. What is the effect ? When the gas no longer in- 
 creases in volume, introduce another drop of the acid, and 
 see if it has any further effect. Carefully continue this 
 operation until no further evolution of gas and increase in 
 volume are observed. Now allow the tube to stand for some 
 minutes, and then measure the gas volume, taking account 
 of the temperature, barometer, and height of the column 
 of mercury in the gas-measuring tube. Reduce the gas 
 volume to standard conditions of temperature and pressure. 
 What weight of carbon dioxide is liberated by one gram 
 of potassium primary carbonate ? * 
 
 c. Carefully weigh off 2 grams of pure, dry primary 
 carbonate of potassium, and place it in a deep porcelain 
 crucible or test-tube of infusible glass. Weigh the whole, 
 and then heat, gently at first, and finally to a red heat 
 for fifteen minutes. Allow it to cool, and again weigh. 
 What is the loss in weight ? What is the weight of the 
 remainder ? Continue the above operation until no fur- 
 ther change in weight takes place. What volume of carbon 
 dioxide would this loss i-n weight represent ? Compare 
 
 * One cubic centimetre of carbon dioxide weighs .001986 gram. 
 
274 ELEMENTS OF CHEMISTRY. 
 
 this volume with that given off by 2 grams of primary 
 potassium carbonate when treated with acids (&). Weigh 
 carefully .138 gram of pure, dry secondary potassium car- 
 bonate, and with this repeat b. Compare the volume of 
 carbon dioxide given off with that formed in b. From the 
 data thus obtained, calculate the weight of primary potas- 
 sium carbonate which would contain one molecular weight 
 of carbon dioxide. Calculate the amount of potassium 
 hydroxide combined with one molecular weight of carbon 
 dioxide. 
 
 64. Prepare a solution of potassium hydroxide as indi- 
 cated in Experiment 27 'a. Now weigh off 1 gram of pri- 
 mary potassium carbonate, dissolve in 25 c.c. of water, place 
 in a beaker, and carefully add to it from the burette an 
 amount of potassium hydroxide solution representing .56 
 gram of solid potassium hydroxide. Evaporate the solu- 
 tion so formed to dryness, and heat a little of the remainder 
 in a test-tube. Does it give off carbon dioxide ? To a 
 little in a test-tube add a few drops of a dilute solution of 
 hydrochloric acid. Hold a glass rod, on the tip of which 
 is a drop of a clear solution of slaked lime, over the mouth 
 of the tube, after adding acid. Is the product of the 
 action of potassium hydroxide on primary potassium car- 
 bonate primary or secondary potassium carbonate ? 
 
 65. Preparation of Carbon Dioxide for Laboratory Use. 
 
 The apparatus is the same as that represented by 
 Fig. 13. 
 
 In the generating-flask place about 25 grams of clean 
 marble * in pieces the* size of a hickory-nut. Connect all 
 parts of the apparatus (have some pure water in the wash- 
 ing-bottle), and then pour diluted hydrochloric acid (one 
 
 * Completely fill the flask with water before dropping in the pieces 
 of marble, and after all is added pour off the water. If this precaution 
 is not taken, the pieces of marble may crack the flask as they are dropped. 
 
LABORATORY EXPERIMENTS. 275 
 
 part concentrated acid to five of water) in through the 
 safety tube. Collect the gas which is evolved in a cylin- 
 der, which is placed mouth upward. Place a burning 
 candle in a cylinder of air, and then pour into it carbon 
 dioxide from a second cylinder, just as one would pour 
 water. Into a cylinder of carbon dioxide place a little 
 blue litmus solution, cover the cylinder with a glass plate, 
 and shake. Invert a test-tube full of carbon dioxide over 
 a solution of potassium hydroxide. 
 
 66. Formation of the Secondary and Primary Carbonates of Calcium. 
 In a beaker place 15 c.c. of a clear solution of slaked 
 lime. Into this solution pass carbon dioxide from the 
 generator. Continue to pass in carbon dioxide until the 
 white precipitate, which is at first produced, disappears. 
 When the solution is clear, discontinue the carbon dioxide, 
 and then warm the water in the beaker to boiling. 
 
 67. Preparation of Carbon Monoxide. 
 
 Arrange a carbon dioxide apparatus as in Experiment 66. 
 Connect the delivery tube with an iron tube which you can 
 heat in a furnace, as in Experiment 21, Fig. 18. Introduce 
 a safety-bottle, c, after the iron tube; put in the tube 15 
 grams of charcoal in pieces the size of a pea, connect all 
 parts of the apparatus, heat the iron tube to redness, and 
 then pass a slow current of carbon dioxide over the char- 
 coal. Collect the evolved gas in cylinder over a dilute 
 solution of potassium hydroxide (1 : 20). When the quan- 
 tity is sufficient, remove one of the cylinders, place it 
 mouth upward, and introduce a lighted taper. After com- 
 bustion is over, pour a little of a clear solution of slaked 
 lime into the cylinder, cover with a glass plate, and shake. 
 Is the gas which you have obtained by the action of carbon 
 dioxide on charcoal soluble in potassium hydroxide ? How 
 does it differ from carbon dioxide ? 
 
276 
 
 ELEMENTS OF CHEMISTRY. 
 
 68. Preparation of Methane. (Hydrogen Carbide.) 
 The apparatus is shown by Fig. 37. The tube a is of 
 so-called infusible glass, sealed at one end, and stoppered 
 with a single-bored rubber stopper, which is connected 
 with a safety bottle and delivery tube. Prepare an inti- 
 mate mixture in a mortar, of 10 grams of sodium acetate 
 (which has previously been dried by heating to fusion in 
 an open dish), and 10 grams of a mixture of sodium hydrox- 
 
 Fig. 37. 
 
 ide and calcium oxide (so-called soda-lime),* and then half 
 fill your tube with this mixture. Place the tube on its 
 side, and pound it lightly on the table until you have 
 formed a canal for the free passage of the gas.f Now 
 connect all parts of the apparatus, and wrap a piece of 
 wire gauze around the tube, to prevent its cracking when 
 
 * Soda-lime can be purchased of dealers in chemicals. 
 
 t One must be absolutely certain that there is no packing of the mix- 
 ture in the tube. Any portion of the tube which may be closed gas-tight 
 will cause a dangerous explosion, by preventing the escape of gas. 
 
LABORATORY EXPERIMENTS. 277 
 
 heated. Then heat gently with a Bunsen burner, begin- 
 ning at the closed portion of the tube, until there is a regu- 
 lar evolution of gas. Wait until all air is expelled from 
 the apparatus, and then collect in cylinders or test-tubes, 
 over water. 
 
 69. Properties of Methane 
 
 Remove one of the cylinders from the water, invert it, 
 and instantly apply a lighted taper to the mouth. Remove 
 a second cylinder, place it mouth upward, allow it to stand 
 for a few seconds, and then apply a lighted taper. What 
 is the effect ? Is methane specifically heavier or lighter 
 than air ? Remove a third cylinder, light the gas while 
 it is held mouth downward ; now invert the cylinder. 
 Into a cylinder in which you have burned methane pour 
 a few drops of a clear solution of slaked lime, cover the 
 cylinder with a glass plate, and shake. 
 
 70. The Volumetric Composition of Methane. Teacher's Experiment. 
 The apparatus is given by Fig. 9, Experiment 11. Fill 
 the graduated eudiometer tube with clean, dry mercury, 
 and invert it in the deep cylinder as described in Experi- 
 ment 11. Now introduce about 10 to 15 c.c. of pure, dry 
 methane (prepared as in Experiment 68) into the tube, 
 pass steam, into the jacket until the temperature is con- 
 stant, and then carefully measure the gas-volume after 
 taking the usual observations. (What are they ?) Now 
 pass in approximately 25 c.c. of dry oxygen, allow to 
 remain for a minute, and again measure. Then lower the 
 tube into the mercury cylinder as far as it will go, wrap 
 a towel around the mouth of the cylinder, so as to prevent 
 spattering, and explode with a spark from an induction 
 coil (Experiment 10).* Bring the eudiometer tube back 
 
 * Be sure that the steam-jacket is thoroughly heated during the 
 entire experiment. 
 
278 ELEMENTS OF CHEMISTRY. 
 
 into position, so that the height of the column of mercury 
 is the same as it was before the explosion, and note if 
 there was any change in the volume of gas. Now allow 
 to cool until the entire apparatus is at the temperature of 
 the surrounding air; then introduce a drop of water into 
 the eudiometer,* and measure the volume as before, this 
 time taking the tension of water vapor into account during 
 your calculations. Next, cut a small piece of potassium 
 hydroxide, take it by a pair of pincers, and slip it under 
 the eudiometer tube, so that it will rise to the upper level 
 of the mercury. Allow to stand until no further contrac- 
 tion in volume takes place, and then again measure the 
 gas-volume. (This time neglect the pressure of water 
 vapor.) The volume of contraction on cooling corresponds 
 to the volume of what product of the explosion ? The 
 volume of contraction after adding potassium hydroxide ? 
 From the data you have obtained, calculate the composi- 
 tion of methane by volume. 
 
 71. The Action of Chlorine on Methane. 
 
 Take two jars of the same size, with ground tops ; fill 
 one with chlorine (Experiment 21&), and the other with 
 methane over water (Experiment 68). Cover each jar with 
 a glass plate, bring them together, mouth to mouth, then 
 remove the plates which separate them, hold "tightly in 
 position, and invert several times. When the gases have 
 completely mixed, apply a lighted taper to the mouth of 
 each. Result ? 
 
 72. The Gradual Action of Chlorine on Methane. 
 
 a. The apparatus is that described in Experiment 20, 
 Figs. 16 and 17, and the manipulation is the same, except- 
 
 * This drop of water is introduced so as to be certain that the gases 
 to be measured are completely saturated with moisture. 
 
LABORATORY EXPERIMENTS. 279 
 
 ing that one of the arms of the double tube is filled with 
 methane instead of hydrogen. The apparatus must stand 
 for at least twenty-four hours in daylight or sunlight before 
 the reaction is completed and the color of chlorine has 
 entirely disappeared. After this time bring one of the 
 arms of the tube into a solution of blue litmus, and, after 
 scratching with a file, break the tip. Change in the color 
 of litmus ? What portion of the apparatus becomes filled 
 with the litmus solution ? After allowing to stand for 
 a few minutes, remove the tube from the liquid, turn the 
 stopcock so that this fluid can drain off, then bring the 
 opened end of the tube into a deep cylinder of mercury 
 (described in Experiment 11, Fig. 9), and press down until 
 the liquid rises to the stopcock. Turn the stopcock as 
 it was before, and then break off the second tube which 
 extends upward, quickly apply a lighted taper to its mouth, 
 and force out the remaining gas by pressing the apparatus 
 down into the mercury. Color of flame ? To the solution 
 of blue litmus add a few drops of a solution of silver 
 nitrate. Result ? What insoluble substance separates ? 
 
 73. The Action of Chlorine on Methyl Chloride. 
 
 Repeat Experiment 72, with the difference that after 
 you have opened the tube under litmus solution you allow 
 the liquid to drain off, and then, after drying, once more 
 fill it with chlorine, and seal the tip, while the branch con- 
 taining methyl chloride is carefully kept closed. After 
 establishing communication between the two arms of the 
 tube, allow to stand in the daylight, and then follow 
 directions as in Experiment 72. Compare the two results. 
 
 74. The Action of Chlorine on Methylene Chloride. 
 
 Repeat Experiment 73, using the apparatus in which 
 you have produced methylene chloride ; i.e., which contains 
 
280 ELEMENTS OF CHEMISTRY. 
 
 methane which has twice been acted on by chlorine. After 
 the chlorine has acted on the methylene chloride for twenty- 
 four hours, open the tube, as before, under a solution of lit- 
 mus, and note the result. How does this differ from the 
 two preceding cases ? Odor of product which is formed ? 
 
 75. The Formation of Salts by Double Decomposition. 
 
 a. To a solution of barium chloride in a test-tube add 
 a few drops of a diluted solution of sulphuric acid. What 
 is formed ? Does the precipitate dissolve on boiling ? 
 Does it dissolve in an excess of sulphuric acid? 
 
 I). Repeat a, using a solution of potassium sulphate 
 instead of one of sulphuric acid. 
 
 c. Repeat b, using a solution of magnesium sulphate. 
 
 76. Precipitation of Salts by Double Decomposition. 
 
 a. To a solution of calcium chloride add a few drops of a 
 solution of potassium carbonate. What is formed ? Does 
 the precipitate dissolve on boiling ? Filter the precipitate 
 after boiling, and to the substance on the filter paper add 
 a few drops of hydrochloric acid. Does the precipitate 
 dissolve ? See if the precipitate will dissolve in nitric acid. 
 In sulphuric acid. What gas passes off in each case ? 
 
 b. Repeat , using a solution of barium chloride instead 
 of one of calcium chloride. 
 
 c. To a solution of sodium chloride add a few drops of 
 a solution of silver nitrate. What is formed ? Does the 
 precipitate dissolve on boiling ? Does it dissolve in hydro- 
 chloric acid ? In nitric acid ? To the precipitate add a 
 slight excess of a solution of ammonia in water. Does it 
 dissolve ? 
 
 d. Repeat c, using solution of hydrochloric acid instead 
 of sodium chloride. 
 
 e. To a solution of magnesium sulphate add a few drops 
 
LABORATORY EXPERIMENTS. 281 
 
 of a solution of barium chloride, and repeat directions in 
 Experiment 75a. Compare the result with that obtained 
 in 75a. 
 
 77. The Action of Chlorine on Hydrobromic Acid, Hydriodic Acid, 
 
 Sodium Bromide, and Sodium Iodide. 
 
 a. Obtain a solution of hydrobromic acid from the side- 
 table, place a little in a test-tube, add to it three or four 
 drops of carbon bisulphide, and then add a little of a 
 solution of chlorine in water. Close the mouth of the 
 tube with the thumb, and shake. Change of color in the 
 carbon bisulphide ? * What change takes place ? 
 
 b. Repeat a, using a solution of hydriodic acid. (Take 
 care not to add more than a little chlorine water, other- 
 wise the color of the separated iodine may be destroyed.) 
 Color of a solution of iodine in carbon bisulphide ? 
 
 c. Repeat b, using a solution of bromine in water instead 
 of one of cholorine. 
 
 d. Repeat a, b, and c, using solutions of potassium bro- 
 mide and iodide instead of hydrobromic acid and hydro- 
 iodic acid. 
 
 78. The Preparation of Hydrogen Sulphide. (All Experiments with 
 
 Hydrogen Sulphide must be performed under the Hood.) 
 
 The apparatus is the same as that used for the prepara- 
 tion of hydrogen chloride (Experiment 16, Fig. 13). Into 
 the gas-generating flask place 10 grams of fused ferrous 
 sulphide (precautions in this case as in Experiment 65) 
 about the size of a bean, connect all parts of the apparatus, 
 and add diluted sulphuric acid (1 : 5) through the safety 
 tube. The wash-bottle should contain pure water. Collect 
 
 * Carbon bisulphide dissolves bromine and iodine so readily that it 
 will extract them from their solutions in water. Their color is there- 
 fore rendered more apparent by being concentrated in the fow drops of 
 carbon bisulphide. 
 
282 ELEMENTS OF CHEMISTRY. 
 
 the gas in jars by displacement of air, taking care during 
 the operation to partly cover each jar with a glass plate, so 
 as to just leave room for the delivery-tube of the apparatus. 
 Completely cover the jars with glass plates as fast as they 
 are filled. Remove the cover of one of the jars, and apply 
 a lighted taper. What separates on the sides of the jar ? 
 Why ? Is the result different if you mix hydrogen sul- 
 phide with oxygen, and then ignite ? (Perform this latter 
 experiment in a test-tube, and wrap a towel around it 
 before approaching the flame.) Odor of hydrogen sul- 
 phide? (Precautions as in testing the odor of chlorine.) 
 Solubility of hydrogen sulphide in water ? 
 
 79. The Action of Hydrogen Sulphide on the Salts of Metals. For- 
 mation of Sulphides which do not dissolve in Dilute Acids.* 
 
 a. In a test-tube prepare a solution of copper sulphate 
 in water, add two or three drops of hydrochloric acid, and 
 then pass hydrogen sulphide into the solution. Color of 
 precipitate ? Filter the precipitate, wash it with warm 
 water, dry it 011 its filter, and then bring it into a second 
 test-tube. Is it soluble in cold hydrochloric acid ? In 
 hot hydrochloric acid ? In nitric acid ? In a mixture of 
 one part nitric acid to three parts hydrochloric acid ? 
 
 b. Repeat a, substituting a solution of lead acetate for 
 copper sulphate, and in this case acidify with two drops 
 of nitric acid instead of hydrochloric acid. 
 
 c. Repeat a, using a solution of the oxide of arsenic in 
 an excess of hydrochloric acid. 
 
 d. Repeat a, using a solution of silver nitrate, acidified 
 with a few drops of nitric acid. 
 
 * In working with hydrogen sulphide, pass the gas into the solutions 
 through a tuhe with a very small bore (a so-called capillary tube). By 
 this means excessive waste of the gas by reason of a too rapid cur- 
 rent is avoided, and the danger of poisonous effects is reduced to a 
 minimum. 
 
LABORATORY EXPERIMENTS. 283 
 
 80. Formation of Sulphides which dissolve in Dilute Acids. 
 
 a. Repeat 79a, using a solution of zinc sulphate which 
 you have not acidified. Filter whatever precipitate you 
 may have, and test the clear filtrate with a strip of blue 
 litmus paper. Is it acid ? To the clear filtrate add a few 
 drops of a solution of potassium sulphide.* Does zinc 
 sulphide separate from this filtrate ? To zinc sulphide 
 add a few drops of hydrochloric acid. Odor of gas pass- 
 ing off on acidifying? Compare the result with that 
 obtained by adding hydrochloric acid to calcium carbonate 
 (Experiment 76). 
 
 To a solution of zinc sulphate which has been acidified 
 with a few drops of sulphuric acid add hydrogen sulphide. 
 Is there any precipitate ? To this solution add potassium 
 sulphide. Result ? 
 
 b. Repeat a, using a solution of ferrous sulphate (green 
 vitriol). 
 
 81. The Separation of Two Metals by using Hydrogen Sulphide. 
 
 In a test-tube place a little of a solution of zinc sulphate, 
 and add to it the same quantity of a solution of copper 
 sulphate. Acidify with three or four drops of dilute 
 sulphuric acid, and then pass in hydrogen sulphide. Con- 
 tinue to pass in the gas until its odor remains in the solu- 
 tion after standing for some time. Now filter off the 
 copper sulphide which is formed, and to the filtrate add 
 a solution of potassium sulphide. Result ? 
 
 * In order to prepare potassium sulphide, dissolve 5 grams of potas- 
 sium hydroxide in 50 c.c. of water, take one-half of the solution, and 
 pass in hydrogen sulphide until no more gas will dissolve. Now pour 
 into this the other half of the solution. 
 
284 
 
 ELEMENTS OF CHEMISTRY. 
 
 The Principal Elements, with Their Atomic "Weights. 
 
 NAME OF 
 ELEMENT. 
 
 CHEMICAL 
 SYMBOL. 
 
 USUAL CONDITION. 
 
 ATOMIC 
 WEIGHT. 
 
 SPECIFIC 
 
 GRAVITY. 
 
 Aluminium 
 
 Al. 
 
 White, metallic solid 
 
 27. 
 
 2.56 
 
 Antimony 
 
 Sb. 
 
 Crystalline, metallic solid 
 
 120. 
 
 6.7 
 
 Arsenic 
 
 As. 
 
 Gray, crystalline solid 
 
 75. 
 
 5.7 
 
 Barium 
 
 Ba. 
 
 Reddish metal, attacked by water 
 
 137.5 
 
 3.7 
 
 Bismuth 
 
 Bi. 
 
 Reddish crystalline metal 
 
 208.9 
 
 9.7 
 
 Boron 
 
 B. 
 
 Grayish-black powder 
 
 11. 
 
 2.68 
 
 Bromine 
 
 Br. 
 
 Dark brown liquid 
 
 80. 
 
 3.2* 
 
 Calcium 
 
 Ca. 
 
 Reddish metal. Attacks water 
 
 40. 
 
 1.57 
 
 Carbon 
 
 C. 
 
 Solid, appears in 3 forms : dia- 
 
 
 
 
 
 mond, graphite, and charcoal 
 
 12. 
 
 2.2 
 
 Chlorine 
 
 Cl. 
 
 Greenish-yellow gas 
 
 35.5 
 
 2.45 f 
 
 Chromium 
 
 Cr. 
 
 Grayish metallic powder 
 
 52.1 
 
 6.8 
 
 Copper 
 
 Cu. 
 
 Red metal 
 
 63.6 
 
 8.8 
 
 Gold 
 
 Au. 
 
 Yellow metal 
 
 197.3 
 
 19.3 
 
 Hydrogen 
 
 H. 
 
 Colorless gas 
 
 1. 
 
 .069 1 
 
 Iodine 
 
 I. 
 
 Black, crystalline solid 
 
 127. 
 
 4.95 
 
 Iron 
 
 Fe. 
 
 Grayish metal 
 
 56. 
 
 7.8 
 
 Lead 
 
 Pb. 
 
 Gray, soft metal 
 
 207. 
 
 11.44 
 
 Magnesium 
 
 Mg. 
 
 White metal 
 
 24.3 
 
 1.74 
 
 Manganese 
 
 Mn. 
 
 Grayish-white metal 
 
 55. 
 
 8. 
 
 Mercury 
 
 Hg. 
 
 White, liquid metal 
 
 200. 
 
 13.6 
 
 Nitrogen 
 
 N. 
 
 Colorless gas 
 
 14. 
 
 .972 1 
 
 \ Oxygen 
 
 0. 
 
 Colorless gas 
 
 16. 
 
 1.105 f 
 
 Phosphorus 
 
 P. 
 
 In 2 forms : a yellow solid and a 
 red powder 
 
 31. 
 
 1.83 to 2.1 
 
 Potassium 
 
 K. 
 
 Grayish metallic solid. Attacks 
 
 
 
 
 
 water 
 
 39. 
 
 .865 
 
 Silicon 
 
 Si. 
 
 Black solid in small, lustrous 
 
 
 
 
 
 crystals 
 
 28.4 
 
 2.5 
 
 Silver 
 
 Ag. 
 
 White, metallic solid 
 
 108. 
 
 10.5 
 
 Sodium 
 
 Na. 
 
 White, metallic solid. Attacks 
 
 23. 
 
 .972 
 
 
 
 water 
 
 
 
 Sulphur 
 
 S. 
 
 Yellow solid 
 
 32. 
 
 2.045 
 
 Tin 
 
 Sn. 
 
 White metal 
 
 119. 
 
 7.3 
 
 Zinc 
 
 Zn. 
 
 Grayish-white metal 
 
 65.3 
 
 7.15 
 
 * Specific gravity as liquids. 
 
 t Specific gravity as gases ; air = 1. 
 
SCIENCE. * 51 
 
 Descriptive Inorganic General Chemistry 
 
 A text-book for colleges, by Professor PAUL C. FREER, University of 
 Michigan. Revised Edition. 8vo, cloth, 559 pages. Price, $3.00. 
 
 IT aims to give a systematic course of Chemistry by stating 
 certain initial principles, and connecting logically all the 
 resultant phenomena. In this way the science of Chemistry 
 appears, not as a series of disconnected facts, but as a harmo- 
 nious and consistent whole. 
 
 The relationship of members of the same family of elements 
 is made conspicuous, and resemblances between the different 
 families are pointed out. The connection between reactions is 
 dwelt upon, and where possible they are referred to certain prin- 
 ciples which result from the nature of the component elements. 
 
 The frequent use of tables and of comparative summaries lessens 
 the work of memorizing, and affords facilities for rapid reference 
 to the usual constants, such as specific gravity, melting and boil- 
 ing points, etc. These tables clearly show the relationship be- 
 tween the various elements and compounds, as well as the data 
 which are necessary to emphasize this relationship. They also 
 exhibit the structural connection between existing compounds. 
 
 Some descriptive portions of the work, which especially refer 
 to technical subjects, have been revised by men who are actively 
 engaged in those branches. In the Laboratory Appendix will 
 be found a list of experiments, with descriptive matter, which 
 materially aid in the comprehension of the text. 
 
 Professor Walter S. Haines, Rtish Medical College, Chicago. : The work is 
 worthy of the highest praise. The typography is excellent, the arrange- 
 ment of the subjects admirable, the explanations full and clear, and facts 
 and theories are brought down to the latest date. All things considered, 
 I regard it as the best work on inorganic chemistry for somewhat advanced 
 general students of the science with which I am acquainted. 
 
 Professor J. H. Long, Northwestern University, Evanston, III.: I have 
 looked it over very carefully, as at first sight I was much pleased with both 
 style and arrangement. Subsequent examination confirms the first opinion 
 that we have here an excellent and a very useful text-book. It is a book 
 which students can read with profit, as it is clear, systematic, and modern. 
 
48 SCIENCE. 
 
 The Elements of Physics 
 
 By Professor HENRY S. CARHART, University of Michigan, and H. N. 
 CHUTE, Ann Arbor High School. i2mo, cloth, 392 pages. Price, $1.20. 
 
 THIS is the freshest, clearest, and most practical manual on 
 the subject. Facts have been presented before theories. 
 
 The experiments are simple, requiring inexpensive apparatus, 
 and are such as will be easily understood and remembered. 
 
 Every experiment, definition, and statement is the result of 
 practical experience in teaching classes of various grades. 
 
 The illustrations are numerous, and for the most part new, 
 many having been photographed from the actual apparatus set 
 up for the purpose. 
 
 Simple problems have been freely introduced, in the belief 
 that in this way a pupil best grasps the application of a principle. 
 
 The basis of the whole book is the introductory statement 
 that physics is the science of matter and energy, and that noth- 
 ing can be learned of the physical world save by observation and 
 experience, or by mathematical deductions from data so obtained. 
 The authors do not believe that immature students can profitably 
 be set to rediscover the laws of Nature at the beginning of their 
 study of physics, but that they must first have a clearly defined idea 
 of what they are doing, an outfit of principles and data to guide 
 them, and a good degree of skill in conducting an investigation. 
 
 William H. Runyon, Armour Institute, Chicago : Carhart and Chute's text- 
 book in Physics has been used in the Scientific Academy of Armour 
 Institute during the past year, and will be retained next year. It has 
 been found concise and scientific. We believe it to be the best book on 
 the market for elementary work in the class-room. 
 
 Professor M. A. Brannon, University of North Dakota, Grand Forks: I 
 am glad to express the opinion, based on the use of this work in Elemen- 
 tary Physics last year, at Fort Wayne, Ind., that it is the most logical and 
 clear presentation of the subject with which I am acquainted. The prob- 
 lems associated with the discussion of Physical phenomena, laws, and ex- 
 periments serve the dual purpose of leading the scholar to reason, and 
 put into practice the previous clearly and concisely stated principles of 
 Elementary Physics. It is a book that will greatly elevate the standard 
 of scholarship wherever 
 
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