GIFT OF PROF. W.B. RISING LECT UBE-NOTES ON THEORETICAL CHEMISTRY. BY FERDINAND G. WIECHMANN, PH.D., \N Instructor in Chemical Physics and Chemical Philosophy, School of Mines, Columbia College. FIRST EDITION. FIRST THOUSAND. NEW YORK : JOHN WILEY & SONS, 53 EAST TENTH STREET. 1893. COPYRIGHT, 1898, BY FERDINAND G. WIECHMANN. ROBERT DRUMMOND, Electrotyper, 444 & 446 Pearl Street, New York. SO parents, 11 (SraitttttJr. 237367 PEEFACE. THE study of theoretical chemistry has not, in general, met with that recognition and appreciation which is warranted by the interest and importance attaching to this branch of chemical science. Seeking for an explanation, it appears that to many this study presents considerable difficulty, on account of the num- ber and variety of themes frequently exhibiting no organic connection to which the attention of the student is invited. The difficulty is inherent in the nature of the subject, for as yet there is no philosophy of chemistry, and work in this domain, of necessity resolves itself into a study of the material from which such a philosophy may, at some future time, be constructed. May these pages be of service to those who are entering upon a study of these subjects. It has been the intention of the writer to offer a general view over the wide domain of chemical theory, to exhibit, as clearly as might be, the correlation of the many lines of re- search along which investigations of the questions of theoret- ical chemistry are at present conducted, and, last but not least, to point out the practical bearing of its teachings on iii IV PREFACE. problems to be constantly met with in the application of chemical knowledge. As indicated by its title, this treatise does not pretend to offer an exhaustive discussion of the subjects considered; volumes have been written on most of the topics to which here but a scant chapter or two has been devoted. Indeed, it is one of the aims of this book to incite to a thorough study of this literature, a literature so constantly increasing in scope and in importance. With this object in view, a list of works on theoretical chemistry is placed at the end of this volume. This list is believed to be sufficiently comprehensive to meet the require- ments of most students. To facilitate the study of the sub- ject from an historical point of view, the titles given are arranged in chronological order. The periodicals enumerated, barring some few exceptions, of course devote but a part of their space to papers of the character here considered, yet reference to them has been deemed expedient, because frequently important researches are first recorded in their columns. Considerable prominence has been given in these pages to stoichiometry the arithmetic of chemistry and examples are freely introduced in illustration of the different principles discussed. A thorough working familiarity with these principles of stoichiometry is essential, and should be acquired by the solv- ing of numerous problems ; however, insertion of such prob- lems seemed superfluous, in view of the fact that several excel- lent collections of this kind have been but recently published. In making acknowledgment of his obligations, the writer would state that he has considered it his duty, no less than his pleasure, to consult all sources of information available. No attempt has been made to cite and to give credit for individual articles referred to in the journal literature; how- ever, the periodicals in which they appear are naimd. PREFACE. V All books consulted, are marked by asterisks in the bib- liography appended, but special mention must be made of the writer's indebtedness to the standard works of Kopp, Ostwald, and Muir. F. G. WlECHMAXX. SCHOOL OF MIXES, COLUMBIA COLLEGE. TABLE OF CONTENTS. CHAPTER I. INTRODUCTORY. PAGE Introductory 1 Origin and Meaning of the Term Chemistry 2 Aims of Chemistry and of Chemical Philosophy 3 Definitions 5 Stoichiometry 5 CHAPTER II. SPECIFIC GRAVITY. Definition of Specific Gravity 7 Standards of Specific Gravity 7 Relations between Specific Gravity, Mass, and Volume 8 Determination of the Specific Gravity of Solids 9 I. By the Balance : a. The solid is insoluble in, and heavier than water 9 b. The solid is insoluble in, and lighter than water 10 II. By the Specific Gravity Flask : a. The solid is insoluble in water 10 b. The solid is soluble in water 11 Determination of the Specific Gravity of Liquids : I. By the Specific Gravity Flask 11 II. By Weighing a Solid Insoluble in Water and in the Liquid, in Air, Water, and the Liquid 12 vii Vlll CONTENTS. PAGE III. By the Method of Balanced Liquid Columns 12 IV. By Areometers 13 Areometers with Arbitrary Scales , . . . 14 True value of Baume degrees 14 Relation between Specific Gravity, Degrees Baume, and Degrees Brix 15 Specific Gravity of Gases and Vapors 17 Determination of the Specific Gravity of Gases 19 I. Weighing Equal Volumes of the Standard selected and of the Gas the Specific Gravity of which is to be determined. 19 a. By collecting in a vessel over mercury. (Bunseu.). , . . 19 b. By displacement 19 c. By counterbalanced globes. (Regnault.) 19 II. Effusion Method. (Buuseu.) 19 Determination of the Specific Gravity of Vapors 20 I. Weighing a Known Volume of the Vapor taken at an Ascertained Temperature and Pressure 20 Methods of (a) Dumas 20 (b) Deville 20 (c) Troost 20 II. Direct Measurement of the Volume of Vapor produced by the Evaporation, in a Closed Space, of a Known Weight of the Substance 20 Methods of (a) Hofmanu 20, 24 (b) Gay-Lussac 20 III. The Indirect Measurement of the Volume of Vapor pro- duced by the Evaporation, in a Closed Space, of a Known Weight of the Substance, accomplished, by measuring the Volume of a Liquid or of some Gas, displaced by the Vapor 20 Method of Victor Meyer 20, 26 CHAPTER III. CHEMICAL NOMENCLATURE AND NOTATION. Earliest Times 29 Notation of the Alchemists ... 29 Nomenclature in the Seventeenth Century. 31 CONTENTS. IX Bergman's System 31 Black's List of Synonyms 33 French Systems of Nomenclature 34 Symbols of Hassenfratz and Adet 37 Other Systems Proposed 38 System of the Present 41 Names and Symbols of the Elements 42 Names of Compounds 42 American Spelling and Pronunciation of Chemical Terms 45 CHAPTER IV. ATOMS ATOMIC MASS VALENCE. Introductory , 52 Laws of Chemical Combination 52 Atomic Mass 53 Standards of Atomic Muss 54 Table of Atomic Masses 55 Determination of Atomic Mass 57 Direct Determination 57 Indirect Determination 59 Aids in Determining Atomic Mass 59 Vapor Density 59 Atomic Heat 61 Isomorphism 63 Valence 63 Standard of Valence 64 Manner of Designating Valence 65 Variable Valence 65 Determination of Valence.. . 66 CHAPTER V. CHEMICAL FORMULA. Introductory 69 Determination of Empirical Formulae 69 Determination of Molecular Formulae 71 X CONTENTS. PAGE Determination of Molecular Mass 72 Method of Chemical Analysis 72 Method of Vapor-Density Determination 72 Methods based on Properties of Substances when in Solution. . 73 Method A. Osmotic Pressure 73 Method B. Lowering of the Vapor-pressure 74 Method C. Elevation of the Boiling-point 75 Method D. Depression of the Freezing-point 75 CHAPTER VI. THE STRUCTURE OF MOLECULES. Introductory 78 Molecular Volume 79 Molecular Refraction 81 Magnetic Rotation of the Plane of Polarized Light 84 Isomerism 84 Stereochemistry 85 CHAPTER VII. CHEMICAL EQUATIONS AND CALCULATIONS. Definitions 89 Oxidizing Agents 91 Reducing Agents 92 Laws of Chemical Interchange 92 The Writing of Chemical Equations 93 The Analytical Method 93 The Method of Negative Bonds 96 The Algebraic Method 97 Calculations of Chemical Problems 99 Calculation of the Molecular Mass of a Substance 99 Calculation of the Amount of any Constituent in a Compound. 100 Calculation of the Amount of a Compound which can be pro- duced from a given Amount of any of its Constituents 100 Calculation of the Percentage Composition of a Compound from its Formula. . . 101 CONTENTS. XI PAGE Calculation of the Chemical Formula of a Compound from its Percentage Composition 101 a. Calculation of the empirical formula 101 b. Calculation of the molecular formula 101 c. Calculation of the formulae of minerals 101 Methods of Indirect Analysis 107 I. The Residue Method 107 II. The Substitution Method 108 III. The*Method based on Numerical Differences between Mo- lecular Masses. 108 a. The components of the mixture have one constituent in common 108 b. The components of the mixture have more than one con- stituent in common. . Ill CHAPTER VIII. VOLUME AND WEIGHT RELATIONS OP GASES. Volume Relations of Gases 115 Law of Volumes 119 Relations between Mass and Volume in Gases 124 Analysis of Gases 128 Introductory 128 Proximate Analysis 128 Method of Explosions 130 CHAPTER IX. THE PERIODIC LAW. Introductory 133 The Periodic Law 134 Newlands' Table 134 Mendeleeff's Table 136 Lothar Meyer's Table 137 Atomic Analogues 139 Mendeleeff's Predictions 139 Importance of the Periodic Law 139 CONTENTS. Graphic Curves 139 Periodicity of the Properties of Elements and Compounds 141 CHAPTER X. SOLUTIONS. * Definition 143 Solutions of : Gases in Gases 143 Gases in Liquids 144 Gases in Solids. 145 Liquids in Gases 145 Liquids in Liquids 145 Liquids in Solids 147 Solids in Gases 147 Solids in Liquids 147 Solids in Solids 149 Dilute Solutions 149 Osmotic Pressure 150 Measurement of Osmotic Pressure , 151 Diffusion... . 153 CHAPTER XI. ENERGY CHEMICAL AFFINITY. Introductory 155 Measurement of Force 155 The Gravity Unit of Force 156 The Absolute Unit of Force 156 Relation between Gravity Units and Absolute Units 156 Measurement of Energy 157 The Gravity Unit of Work 157 The Absolute Unit of Work 157 The Law of the Conservation of Energy 157 Chemical Affinity 158 Hypotheses regarding the Nature of Chemical Affinity 159 CONTENTS. Xlll PAGE Measurement of Chemical Affinity 161 Laplace 161 Morveau , Gay-Lussac, etc 161 Weuzel 161 Lavoisier 161 Tables of Affinity 162 Geoffrey 162 Bergman 163 Kirwan 163 Berthollet 163 Guldberg and Waage 164 Clausius and Maxwell 164 Electrical Methods. . . 165 CHAPTER XII. THERMAL RELATIONS THERMO CHEMISTRY. Introductory 167 Temperature 167 Heat Units 168 Mechanical Equivalent of Heat 168 Latent Heat 169 Specific Heat 169 Determination of Specific Heat 169 I. The Method of the Ice Calorimeter 170 II. The Method of Mixtures 171 III. The Time Method 172 Combustion 173 Calorific Power 173 Calorific Intensity 174 Thermo-chemistry 178 Methods employed in Thermo-chemistry 178 Laws of Thermo-chemistry 179 Exothermous and Endothermous Compounds 181 The Language of Thermo-chemistry 181 Energy-equations ,,.,,,.,.,.,.,,., 183 XIV CONTENTS. CHAPTER XIII. PHOTO-CHEMISTRY. PAGE Introductory 187 Chemical Union 187 Chemical Decomposition 187 Physical Changes 189 Mode of Action 190 Measurement of the Chemical Activity of Light 191 CHAPTER XIV. ELECTRO-CHEMISTRY. Introductory 192 Electrolysis 193 The Ion Theory 193 Electrolytic Dissociation 194 Electrical Units 196 Quantitative Relations 199 BIBLIOGRAPHY. Periodicals 203 Books . 204 LECTURE-NOTES ON THEORETICAL CHEMISTRY. CHAPTER I. INTRODUCTORY. KNOWLEDGE consists in an intelligent perception and understanding of facts and ideas. Science is systematized knowledge. A science which has been established solely by the process of reasoning, which deduces theories from ideas, which does not base on experience, is termed a deductive science; the pure mathematics will serve as an illustration of this type. A science which rests on observation and experience, which owes its existence to the inference of theories and the evolu- tion of laws from observed facts, is an inductive science; chemistry is a representative science of this character. The aims pursued by the devotees of chemistry have at various times been so very different, that chemistry, in the sense in which the term is now understood, is a science of comparatively recent origin. The very beginning of chemical history can be traced back to the remote past. However, until the fourth century no attempt was made to collate the chemical facts then known, or to employ them for the attainment of any definite purpose. 1 2 LECTURE-NOTES OK 'THEORETICAL CHEMISTRY. The era beginning with the fourth century and extending to the first quarter of the sixteenth century may be denoted as the age of alchemy. From that time on, and to the middle of the seventeenth century, chemistry was made to serve the interests of medicine, and this period is designated as the age of medical chemistry or iatro-chemistry. It was with the ter- mination of this era that chemistry entered upon the pursuit of independent and well-defined aims. Origin and Meaning of the Term Chemistry. The origin of the word chemistry is involved in some doubt. The first one to record this expression was, it seems, Julius Maternus Firmicus, who lived about 340 A.D. This author wrote a treatise on astronomy entitled " Mathe- sis." Among other matters there is in this work a reference to the influence exercised on the inclinations of mortal man by the relative position which the moon and a planet may chance to hold at the hour of his birth. In this instance the word " Alchemise," or, as some manuscripts have it, " Chemiae," is used for the first time in a sense similar to that in which the expression chemical knowledge is used at the present time. This author, however, gives no explanation or definition of the term, apparently assuming the word " Chemia" to be well known. The true meaning of the word chemistry has also been a matter of considerable doubt. Two appellations, " Chemia" and "Chymia," have been in use for a long time, and these terms admit of diiferent interpretations as to their origin. Of these two expressions the term " Chemia" is the older, " Chymia" being of a more recent date. It is most probable that the first attempt to collate chemical facts and to apply them to the solving of any one task, was made in Egypt. It is also likely that the art which was the result of this attempt, was named from the country where it originated. According to Plutarch, about 100 A.D., the original name INTRODUCTORY. 3 of Egypt was Xrjuia, Chemia. This name was given to it on account of the black color of its soil. The black of the eye, the pupil, as the symbol of the dark and mysterious, was also denoted by the same term. It seems, therefore, most proba- ble that the word chemistry originally meant Egyptian knowl- edge, and later on, it was frequently termed the secret, or the black art. Zosimus, about 400 A.D., used the term XWi** to indicate the whole of the secret art which was said to have been imparted to man by superior beings, and in which the art of making gold and silver was included. In later times the expression " Chymia" was assigned to all knowledge of this description, and the use of this term has led to an attempt to account in a different way for the name of this science. It is said to have been derived from the Greek word ^ujwo's", a fluid or sap, and it was inferred that thereby the art to work with solutions was indicated. This word has the same root as the Greek word ^eo?, to pour out, to make fluid, to melt; yet for various reasons the above infer- ence concerning the origin of the word chemistry, seems un- tenable. Aims of Chemistry and of Chemical Philosophy. The aim of chemistry is the study of matter the constitution of matter, its properties and its transformations. This indicates at once the wide range and scope of this branch of knowledge. In order to facilitate the work and to permit of a compre- hensive view over the whole field, a division of the subject into various sections has been made, as, for instance, into general chemistry, applied chemistry, analytical chemistry. But whatever the classification into groups or sections, the task of chemical philosophy is to generalize all information gained in the study and in the laboratory, to seek out the relation between chemical phenomena and their causes, to trace the laws which govern these phenomena, and ultimately, by the comparison and co-ordination of numerous data secured by 4 LECTtJRE-KOTES OK THEORETICAL CHEMISTRY. observation and experiment, to deduce and establish the fundamental principles of chemical science. Chemistry, as a philosophical system, is as yet in the period of evolution, and probably is still far from the form in which it will ultimately rest. Newly-discovered facts call for explanation ; new hypotheses are constantly appearing; new theories displace the old. As, however, in the development of all sciences, so in chemistry, no advance can ever displace a truth once discovered and established, although the form in which it is expressed, may have to be greatly modified or extended. It is important to assign their proper value to inferences and conclusions which may be drawn from observations, and care should be taken to employ correctly the terms hypothesis, theory, and law. An hypothesis is a supposition provisionally adopted to account for and to explain certain facts; it is a tentative con- jecture concerning the nature and cause of phenomena. A theory represents the logical deductions ' that can be drawn from a working hypothesis; it is an exposition of general principles, and is intended to exhibit the relations existing between the parts of a systematic whole. The crucial test as to the value and validity of any hypoth- esis or theory rests of course in its concordance with the facts ascertained by experiment and observation. The discovery and establishment of any fact or facts which may not be in harmony with a given hypothesis or theory, of course forces the abandonment, or at least the modifi- cation, of the latter, and calls for the formulation of some theory which shall take due account of such newly-ascertained facts. A law may be defined as a mode or order of sequence. A law must not only embrace all known facts and phenomena to which it refers, but it must also be able to account for all. phenomena of like character which may ever be discovered INTRODUCTORY. 5 In fact, a law must, to a certain extent, be capable of predict- ing the existence of such phenomena. Definitions. There are a few terms used in chemical science which are also frequently employed in general language. As a clear conception of the precise meaning assigned in science to these terms is essential, the following definitions may not be superfluous: Matter. That which has extension, which occupies space; which is perceptible by the senses; which constitutes the universe. Mass. Any portion of matter appreciable by the senses. Also, the amount (quantity) of matter in a substance. Molecule. The smallest particle into which matter can be divided without destroying its identity. Atom. The smallest quantity of matter that can enter into chemical combination. Weight. The amount of attraction between two masses; in a restricted sense, the amount of attraction of the earth on a substance. ' Volume. The amount of space occupied by a substance. Motion. Change of position. Rest. Permanence of position. Work. The overcoming of resistance. Energy. The power of doing work; the cause of all change experienced by matter. Force. Included in above definition of energy; in a more restricted sense, any cause which tends to produce, change, or destroy motion. Stoichiometry. The term stoichiometry is derived from the Greek o-roz^ezov, elementary substance, and /^erpov, measure. It treats of the quantitative relations of chemical substances. The idea that salts contain acid and alkali in definite pro- portions, seems to have been held at a very early date; at least, certain passages in the writings of Geber, an alchemist of the eighth century, are quoted in support of this view. 6 LECTURE-NOTES ON" THEORETICAL CHEMISTRY. Definite evidence of it is certainly found in the writings of Van Helmont, 1640, and in 1699 Homberg made an investi- gation in order to ascertain the quantities of different acids which would combine with a stated amount of alkali. The outlines of stoichiometrical teachings, to the extent to which they had been developed up to that time, were pub- lished by a German, Carl Friedrich Wenzel, in 1777.* The term stoichiometry was introduced by another Ger- man chemist, Jeremias Benjamin Richter, most of whose writings treat of the application of mathematics to chemistry. In 1792-94 this author published a work of three volumes relating to stoichiometry. \ The growth of this branch of chemistry was by no means rapid. The law of combination in definite proportions was first enunciated by Proust in 1801, with reference to oxides. The law of multiple proportions was discovered by Dalton. Dalton's views, which he had conceived as early as 1804, were published only in 1807 in Thomson's "System of Chemistry." In the year following, Dalton issued his own work, " New System of Chemical Philosophy/' in which his views and teachings were fully stated. Active among the workers who advanced theoretical chem- istry in the latter part of the eighteenth, and in the earlier part of this century, were Lavoisier, Gay-Lussac, Von Hum- boldt, Berzelius, and Avogadro. At the present time, chemistry is rapidly approaching the condition of an exact science, and in consequence, the study of stoichiometry is one of growing importance; even now it would seem, that the day is not far distant when chemistry shall become firmly established on a mathematical basis. * Vorlesungeii iiber die chemische Verwandtscbaft der Kftrper. f Stochiometrie oder Messkunst chymischer Elemente. SPECIFIC GRAVITY. CHAPTER II. SPECIFIC GRAVITY. Definition of Specific Gravity. The specific gravity of a substance is the ratio of its mass to the mass of an equal volume of some other substance taken as unity. Standards of Specific Gravity. The choice of standards of specific gravity has been an arbitrary one. . For solid and for liquid substances the standard now universally adopted, is pure water at its greatest density, that is, at 4 C. The standard selected for gases and vapors is either hy- drogen, air, or oxygen, perfectly dry and at a temperature of C. and under a pressure of 760 mm. of mercury; these con- ditions of temperature and pressure are termed the standard conditions. The specific gravity of any substance, A, is found by divid- ing the mass of one volume of A by the mass of one volume of the substance selected as the standard. Let W = mass of one volume of A ; W mass of one volume of standard. Then Sp. Gr. of A = ^. Specific gravity, or, as it is frequently termed, relative mass, is entirely independent of the system of weights in which the masses of substance and standard are expressed. Special attention should be paid to the distinction between the terms mass and weight. Mass, is the amount of matter in a substance, and is an invariable quantity ; weight, expresses the 8 LECTURE-NOTES ON THEORETICAL CHEMISTRY. force with which the substance is attracted by the earth, and varies according to the place where it is measured. Relations between Specific Gravity, Mass, and Volume. In the metric system the relation between the unit of mass and that of volume is an intimate one. One cubic centimetre of pure water at 4 C. has a mass of one gramme. Therefore, in all specific-gravity determinations of solids and liquids, where the values are expressed in the metric system, W of the preceding formula may be replaced by V, signifying the volume of the water displaced. Let W.= mass of one volume of A', V = mass of one volume of standard. Then the formula becomes : Sp. Gr. = -^. From this are deduced the values of W and of V\ W= V-x Sp. Gr.; Sp. Gr: In the formula, W- Vx Sp. Gr. Sp. Gr. stands for the specific gravity referred to water. If the Sp. Gr. is referred to hydrogen, as in the case of gases, this value must be reduced to the water standard before using it in the formula. The Sp. Gr. of hydrogen referred to water is 0.0000896; the reduction is therefore easily effected by simply multiply- ing by this value. The formula then reads : W= VX Sp. Gr. X 0.0000896. SPEC I F I C G K A V IT Y . The weight of one cubic decimetre or litre of hydrogen gas at the standard temperature and pressure is 0.089578 gramme, or, for all practical purposes, 0.0896 gramme. In order to simplify calculation, Prof, von Hofmann pro- posed that this value be introduced into chemistry as a unit of weight. It is termed the crith. The crith is therefore denned, as the weight of one cubic decimetre (litre) of hydro- gen gas at the standard temperature and pressure, and is equal to 0.0896 gramme. Let We =. the weight of a gas in criths; Wg = the weight of a gas in grammes; V the volume of this gas in litres. Then We = V x Sp. Gr. and Wg = We X 0.0896. To ascertain the specific gravity of solids, liquids, and gases, numerous methods have been devised to meet the various conditions under which the determinations may be presented; but the principle underlying these devious methods, is of course always the same. The following examples will illus- trate some of the more commonly occurring problems. Determination of the Specific Gravity of Solids. I. By the Balance. This method is based on the principle of Archimedes : a body immersed in a liquid loses in weight, an amount equal to the weight of the liquid displaced. a. The solid is insoluble in, and heavier than, water. EXAMPLE : Weight of solid in air = 10.000 " " "water = 8.000 Weight of water displaced by the solid is: 10.000 8.000 2.000 Sp. Gr, = = 5.0. 10 LECTURE-NOTES ON THEORETICAL CHEMISTRY. 1. The solid is insoluble in, and lighter than, water. As the solid is lighter than water, there must be attached to it a piece of some other substance which is heavy enough to immerse the combination. The substance thus attached is called a sinker. EXAMPLE : Weight of solid in air =25.350 " sinker in air = 11.000 " " solid and sinker in water = 5.100 Specific gravity of sinker 9.000 Weight of solid in air = 25.350 " " sinker in air.. .. = 11.000 " solid + sinker in air = 36.350 Specific gravity of sinker = 9.000 Weight of sinker in air = 11.000 Volume of sinker = y = 1.222 This expresses also the loss in weight the sinker would sustain if immersed alone in water. Weight of solid -f sinker in air =36.350 " " " " "water = 5.100 Loss of weight of solid + sinker in water = 31.250 " " " " sinker in water = 1.222 " " " " solid in water = 30.028 /^O. oOU r\ S P- GI> - = 30.028 = ' 844 - II. By the Specific-gravity Flask (Pyknometer). a. The solid is insoluble in water, This method is especially indicated in cases where the solid is in a fine state of division ; for instance, in the case of a powder. EXAMPLE : Weight of solid in air = 10.000 " " pyknometer =. 5.035 " " " + water =40.535 " " " -f solid and water* =46.755 * This fills the space in the fl^sk not occupied by the solid. SPECIFIC GRAVITY. 11 Weight of pyknometer + water =40.535 " " " = 5.035 " " water... .. =35.500 Weight of pyknometer -{- solid -f- water = 46.755 " " ..= 5.035 " solid + water 41.720 " solid . . . = 10.000 " " water in space not occupied by the solid = 31.730 The solid therefore occupies a space of 35.50 less 31.72 = 3.78 c. b. The solid is soluble in water. ' Some liquid must be used in which the solid is not soluble; alcohol, naphtha, turpentine, or oil are usually employed. The specific gravity of the liquid used, with reference to water, and the specific gravity of the solid with reference to the liquid used, must be ascertained. A multiplication of these two values represents the specific gravity of the solid with reference to water. EXAMPLE : Weight of solid in air .......................... = 400.CO " " "turpentine ................... =182.50 " "an equal volume of turpentine ....... = 217.50 400 Sp. Gr. of solid referred to turpentine = J~ . . . = 1.84 Sp. Gr. of turpentine referred to water .......... = 0.87 Sp. Gr. of solid referred to water = 1.84 X 0.87.. = 1.60 Determination of the Specific Gravity of Liquids. I. By the Specific-gravity Flask (Pyknometer). EXAMPLE : Weight of pyknometer .......... .............. = 5.000 -|- water .................. =20.000 + liquid .................. = 17.000 LECTURE-NOTES ON THEORETICAL CHEMISTRY. "Weight of pyknometer -f water =20.000 " . . = 5.000 water = 15.000 Weight of pyknometer -f liquid = 17.000 " " = 5.000 "liquid = 12.000 Sp. Gr. of liquid = ^? = 0.80 10. 00 II. By Weighing a Solid Insoluble in Water and in the Liquid, in : Air, Water, and the Liquid. EXAMPLE : Weight of solid in air = 12.000 " " ''water - 7.000 " " "liquid = 8.000 Weight of solid in air = 12.000 " " "water = 7.000 " " water displaced = 5.000 Weight of solid in air = 12.000 " " "liquid = 8.000 " liquid displaced = 4.000 Sp. Gr. of liquid = j^. . . = 0.80 o.U III. By the Method of Balanced Liquid Columns. This method depends on the principle of the equilibrium of liquids in connected vessels. Two vertical glass tubes are connected at their upper ends with each other, and with the chamber of an air-syringe. The lower end of one of these tubes dips into water; that of the other tube dips into the liquid, the specific gravity of which is to be ascertained. The air is partially exhausted from the upper part of the two tubes, and in consequence, the water and the liquid rise. Closing the stop-cock which connects the tubes with the air-syringe, the liquids will remain standing at a certain height in their respective tubes, the two columns being in equilibrium. The SPECIFIC GRAVITY. 13 specific gravity of the liquid is found, by dividing the height of the column of water by the height of the column of liquid. EXAMPLE : Height of column of water =80 cm. " " " "liquid =60 cm. QA Sp. Gr. of liquid = ^ = 1.333 IV. By Areometers. This is an indirect method of ascer- taining the specific gravity of fluids. The instruments em- ployed for the purpose are made of glass or of metal. They consist of a bulb or float filled with air, a stem placed above this float and bearing a scale, and a smaller bulb, the counter- poise, placed beneath the float and weighted with mercury or shot, so as to keep the instrument in an upright position when placed in a fluid. A body immersed in a liquid floats, when it has displaced an amount of the liquid equal in weight to its own weight. It is therefore evident, that an areometer will sink more deeply in a liquid of less density, than it will in a liquid of greater density. Areometers are provided with scales which either indicate specific-gravity values, or else bear an arbitrary graduation. In instruments graduated to show specific-gravity values, the spaces between successive degrees are unequal. These areometers are constructed on the principle, that equal differences of specific gravities are indicated by quan- tities proportional to the differences of the reciprocals of the specific gravities. On areometers graduated according to an arbitrary scale, the divisions are usually equal. Different kinds of areo- meters with arbitrary scales are employed in the arts and in- dustries. To determine the specific gravity of a liquid by means of an areometer, due attention being paid to the temperature of the liquid, the instrument is placed in the liquid, and that 14 LECTURE-NOTES ON" THEORETICAL CHEMISTRY. degree of the scale which is in contact with the surface of the liquid, is noted. If the areometer is graduated according to specific-gravity values, the figure thus indicated denotes the specific gravity of the liquid. If the graduation on the instrument is accord- ing to some arbitrary scale, conversion into the corresponding specific-gravity value must be made by calculation, or else is determined by aid of tables prepared for the purpose. AREOMETERS WITH ARBITRARY SCALES. Among the numerous areometers provided with arbitrary scales, those devised by Antoine Baume in 1768, and bearing his name, are probably used more extensively than any other kind. Although Baume described very accurately the manner in which he obtained the scales for his two instruments the one for liquids heavier, the other for liquids lighter, than water yet, in the course of time, the makers of these in- struments deviated from his directions, and in consequence there resulted great confusion as to the actual relation between the values of the so-called Baume degrees and specific gravity. True Value of Baume Degrees. In a paper delivered by C. F. Chandler before the National Academy of Sciences in 1881, there are given no less than twenty-three different scales for liquids heavier than water and eleven different scales for liquids lighter than water, no two of which are identical, and not one of which was made in exact accordance with the original directions of Baume. ID order to ascertain the true value of these degrees in terms of specific gravity, the original French directions were secured, Baume's experi- ments were most carefully repeated, and the following table, by C. F. Chandler and the author, gives, as the result of these investigations, the true values of Baume's degrees for liquids heavier than water, calculated by the formulae : _ PXjl. p _ n n ~P-l' ~- n-d' SPECIFIC GRAVITY. 15 In which P = the specific gravity ; d = the Baume de- gree; n - the modulus.* = 1. and 15 = 1.1118988, by the modulus 149.04969. [Temperature 10 R. = 12.5 C. = 54.5 R] Baum6 Degrees. Specific Gravity. Baume Degrees. Specific Gravity. Baum6 Degrees. Specific Gravity. 1.00000 26 1.21129 52 1.53580 1 1.00675 27 1.22122 53 1.55179 2 1.01360 28 1.23131 54 .56812 3 1.02054 29 1.24156 55 .58479 4 1.02757 30 25199 56 .60182 5 1.03471 31 .26260 57 .61923 6 1.04194 32 .27338 58 .63701 7 1.04927 33 .28436 i 59 1.65519 8 1.05671 34 .29552 60 1.67378 9 1.06426 35 .30688 61 1.69279 10 1.07191 36 .31844 62 .71223 11 1.07968 37 1.33021 63 .73213 12 1.08755 38 1.34218 64 .75250 13 1.09555 39 1.35438 65 .77335 14 1 . 10366 40 1 36680 66 .79470 15 1.11189 41 1.37945 67 .81657 16 1.12025 42 1.39234 68 .83899 17 1 . 12873 43 1.40547 69 1.86196 18 1.13735 44 1.41885 70 1.88551 19 1.14609 45 1.43248 71 1.90967 20 1 . 15497 46 1.44638 72 1.93446 21 1.16399 47 1.46056 73 1.95989 22 1.17316 48 1.47501 74 1.98601 23 1.18246 49 1.48975 75 2.01283 24 1.19192 50 1 . 50479 76 2.04038 25 1.20153 51 1.52014 Relation between Specific Gravity, Degrees Baume, and Degrees Brix. An areometer which is most extensively used in the sugar industry to gauge the density of saccharine solu- tions, is known as the saccharometer of Balling or Brix. * That part of an areometer which is immersed when the instrument floats in water. 16 LECTURE-XOTES OX THEORETICAL CHEMISTRY. This instrument bears a scale of 100 degrees, and its read- ings indicate the percentage of sucrose in aqueous solutions. Comparison between specific-gravity values, degrees Baume, and degrees Brix, can be made by means of the following for- mulae, due to von Lorenz.* The temperature at which these relations obtain, is 17.5 C. SPECIFIC GRAVITY AXD DEGREES BRIX. Let d = specific gravity, s degrees Brix. For the range of : 35 Brix., ..< 29375 100s 35 70 Brix., ..d = 70 100 Brix.. ..d = 35163 - 100s 42067 + 92s 42908 - 100s DEGREES BRIX AXD SPECIFIC GRAVITY. For the range of: 49908^ 42067 1.350881.55785.. . .s = WOd -f- 92 SPECIFIC GRAVITY AXD DEGREES BAUME. Let d = specific gravity, n = degrees Baume. 146.78 d = 146.78 - n * Oesterreichisch-Ungariscbe Zeitschrift fiir Zuckeriudustrie uud Landwirthscbaft, 1891, Vol. XX. p. 571. SPECIFIC GRAVITY. 17 DEGREES BAUME AXD SPECIFIC GRAVITY. n = 146.78^-^* DEGREES BRIX AXD DEGREES BAUME. Let s = degrees Brix, n = degrees Baume. For the range of: 10 -4- 20P7 0.00 19.60 Baume s = 19.60 38.12 Baume 38.12 52.56 Baume 1195 n 433 -f 814.5ft, 488 - n 1342 -f 457.2/i 306.3 - n DEGREES BAUME AND DEGREES BRIX. For the range of : 35 Brix., ..w = An extensive table, exhibiting the corresponding values of specific gravity, degrees Brix, and degrees Baume for pure sugar solutions from to 100 per cent, at 17.5 C., has been calculated by Mategczek and Scheibler,* and the data of this table agree very closely with the results obtained by calcula- tion with the formulae of von Lorenz. Specific Gravity of Gases and Vapors. In making determinations of the specific gravity of gases and vapors, great attention must be paid to the conditions of temperature and pressure obtaining at the time, for, * Loc. cit. ; also, Wiechmami, Sugar Analysis. 18 LECTURE-tfOTES ON THEORETICAL CHEMISTRY. according to the Law of Charles, the volume of a gas varies directly as the temperature, and, according to the Law of Mariotte,* the volume of a gas varies inversely as the pressure. The standard of specific gravity of gases and vapors gen- erally adopted is pure, dry hydrogen, or pure, dry air, at the temperature of C. and under the pressure of 760 mm. of mercury. Specific-gravity values determined in terms of one of these standards, can readily be expressed in terms of the other. One litre of hydrogen under the standard conditions weighs 0.0896 gramme. One litre of air under the standard conditions weighs 1.293 grammes. The specific gravity of hydrogen referred to air as standard is, therefore, and the specific gravity of air referred to hydrogen as stand ard, is equal to, 1 9QQ - = 14.43. 0.0896 Hence, if the specific gravity of a gas or vapor be given in terms of hydrogen as standard, this value multiplied by 0.0693 will express its specific gravity with reference to air as standard. If the specific gravity is referred to air as standard, the value given multiplied by 14.43 will express the specific gravity on the hydrogen basis. The principal methods employed in the determination of the specific gravity of gases and vapors are the following. * Also known as the Law of Boyle. SPECIFIC GRAVITY. 19 Determination of the Specific Gravity of Gases. I. Weighing Equal Volumes of the Standard selected and of the Gas the Specific Gravity of which is to be determined. a. By collecting in a vessel over mercury. (Bunsen.) b. By displacement. The gas the specific gravity of which is sought, is passed into a vessel of known volume, and displaces an inert gas which this vessel contains. The temperature is kept con- stant throughout the experiment. c. By counterbalanced globes. (Regnault.) These methods require the following data : P = the weight of the empty vessel, in air. P' = the weight of the vessel filled with the gas, in air. V = the capacity of the vessel in cubic centimetres. v = the volume of the residual air in cubic centimetres. H = height of barometer ) [ at which P' is found. t = the temperature ) H 9 = height of barometer \ m I at the time of sealing or closing T = the temperature of V , , , , , f the vessel. the bath ) k = the coefficient of cubical expansion of the material of the vessel. 0.00367 the coefficient of expansion of a gas at constant pressure. The specific gravity referred to hydrogen, is calculated by the formula: 0.0012933. (F-tQ.jy s r (1 + 0.00367 T). 760 ~F 1+0.00367. yi H' X 0.00008958 V 1+0.00367. J760. (1+0.00367 T)' II. Effusion Method. (Bunsen.) This method is based on the principle that the specific gravity of gases varies directly as the square of the time of effusion of equal volumes.* * Sometimes expressed in this form : The rates of effusion are in- versely as the square roots of the specific gravities of the gases. 20 LECTURE-NOTES ON THEORETICAL CHEMISTRY. Equal volumes of the standard gas, and of the gas the specific gravity of which is to be determined, are allowed to escape through a very small aperture from the vessel in which they are contained, and the time required by each to do this, is noted. EXAMPLE : One volume of air effuses ID 180 seconds. One volume of gas the specific gravity of which is sought, effuses in 120 seconds. ISO' 2 : ISO 2 ::l: xi 32400 : 14400 : : 1 : a?; * = 0.44. Hence, 8p. Gr. of the gas referred to air is 0.44. Determination of the Specific Gravity of Vapors. The specific gravity of a vapor is usually determined by: I. The Weighing of a Known Volume of the Vapor taken at an Ascertained Temperature and Pressure. Methods of (a) Dumas, (5) Deville, (c) Troost. II. The Direct Measurement of the Volume of Vapor pro- duced by the Evaporation in a Closed Space of a Known Weight of the Substance. Methods of (a) Hofmann, (b) Gay-Lussac. III. The Indirect Measurement of the Volume of Vapor produced by the Evaporation in a Closed Space of a Known Weight of the Substance, accomplished by measuring the Volume of a Liquid or of some Gas displaced by the Vapor. Method of Victor Meyer. I. Dumas' Method. To calculate the specific gravity of a vapor by Dumas' method, it is necessary to ascertain the weight of a known volume of this vapor at a known temper- ature and under a known pressure, and to divide this value SPECIFIC GRAVITY. 21 by the weight of the same volume of air, or hydrogen, at the same temperature and under the same pressure. A glass vessel filled with dry air or hydrogen is weighed. Then the substance, the specific gravity of whose vapor is to be determined, is introduced and vaporized. When the ves- sel is filled completely and exclusively with this vapor, the neck of the vessel is sealed and the vessel is reweighed. The formula by which the density of a vapor determined by Dumas' method, and referred to air as unity, is calcu- lated, is the following: o -, # + c a Specific gravity = - . In which: a = the weight of the vessel; b = the apparent weight of the vessel and the vapor; c = the weight of the air displaced by the vessel; W= the weight of an equal volume of air at the same pressure and temperature. The increased volume of the vessel at the higher temperature must of course be taken into account. Before illustrating the application of this formula by an example, the manner of calculating some of the values used in this formula should be explained. Suppose it were required to ascertain the weight ( TF) of dry air at a temperature t and at a pressure H, contained in a glass vessel whose capacity is V at C. 1 c. c. dry air at a pressure of 76 cm. and at a temperature of C. weighs 0.001293 gramme. The weight of a given volume of any gas varies directly as the pressure and inversely as the temperature. The weight of V cubic centimetres of dry air at any tem- perature and at any pressure other than C. and 76 cm., respectively, would be calculated by the formula: 22 LECTURE-NOTES ON THEORETICAL CHEMISTRY. If the change in temperature is great, the capacity of the glass vessel is altered, and allowance for this must be made. If the coefficient of expansion of the vessel is represented by Jc, then the preceding formula is changed to : W = 0.001293 - g ^~- t V(\ + tk). Should the weight of dry hydrogen be required instead of dry air, as here calculated, the value 0.0000896, the weight of 1 c. c. dry hydrogen at C. and at 76 cm., must be sub- stituted for the value 0.001293 in above formula. If the calculation is to be made by logarithms, the for- mula can be cast into the following form : For air : log. W= 7.6670 + log. H+ ar. co. log. (273 + t) -flog. F+log. (l + aO-20. For hydrogen : log. W= 6.5077 + log. H + ar. co. log. (273 + t) + log. F+ log. (! + *&) -20. The constant in above formula, for air, viz., 7.6670, is thus obtained : The formula previously given contains the constant quanti- 273 ties 0.001293 -^. /b To abbreviate the calculation, the value for this expression has been figured as follows : log. 0.001293 = .111599 3 log. 273 2.436163 ar. co. log. 76 = 8.119186 - 10 .666948 3 3.666948 + 10.000000 7.666948 (- 10.) which can be contracted to 7,6670 ( 10.) SPECIFIC GRAVITY. 23 The value for hydrogen, 6.5077, is obtained in the same manner. The following will illustrate the calculation of a vapor density determination by Dumas' method: EXAMPLE: Calculate from the following data the specific gravity of camphor vapor referred to air as standard: "Weight of glass vessel a =50.134 grs. Height of barometer. . . H = 74.2 cm. Temperature t 13.5 C. "Weight of vessel aud vapor b =50.842 grs. Height of barometer H' = 74.2 cm. Temperature t' = 244 C. Volume . ... V - 295 c. c. Coefficient of expansion of glass k = 0.000025. As previously stated, specific gravity = * C ~ a . Calculation of c : Constant log. 7.6670 10. H= 74.2 log. 1.8704 273 -f t = 286.5 ar. co. log. 7.5428 - 10. V= 295 log. 2.4698 1.5500 c = 0.3548 Calculation of W: Constant log. 7.6670 10. H' = 74.2 log. 1.8704 273 + t' = 517 ar. co. log. 7.2865 - 10. V= 295 log. 2.4698 (1 + 244 X 0.000025) = 1.0061 log. 0.0025 L2962 b= 50.842 c= 0.3548 b+c= 51.1968 a = 50.1340 (6-fc-a)= .T0628 Wlog. = 9.2962 (b -f c - a) log. = 10.0265 0.7303 Number log. 0.7303 = 5.374 Hence, specific gravity sought = 5.374 24 LECTURE-NOTES ON THEORETICAL CHEMISTRY. II. Hofmann's Method. This method is particularly ap- plicable in dealing with substances of comparatively low boil- ing point. It bases on the observation of the volume and the tension of vapor produced from a weighed amount of sub- stance. The apparatus consists of a graduated glass tube,, which is first filled with mercury and then inverted over a mercury trough. The mercury on falling to its proper level, leaves a vacuous space in the upper part of the tube. This tube is jacketed by another tube of glass, so made that steam, or the vapor of some liquii boiling at a higher temperature than water, can be kept playing about the enclosed tube. A small quantity of the substance the vapor density of which is to be determined, is weighed off, passed up through the mercury and is thus introduced into the space above. There it vaporizes, and, in consequence of its tension, de- presses the mercury column. This depression of the mercury as well as the barometric pressure and the temperature obtaining at the time are noted, and these values, together with the weight of the substance taken, furnish all the data necessary for the calcu- lation. Referred to hydrogen as standard, the specific gravity of the vapor can be calculated by the formula : - w. 760. (1 + 0.00367 y) P ' v . 0.00008958 . (H - h) . (1 + kT) ' where w = weight of substance taken, and hence weight of vapor formed; v = observed volume of vapor expressed in cubic cen- timetres ; H reduced height of barometer at time of experi- ment ; SPECIFIC GRAVITY. 25 h = reduced height of mercury in tube above that in trough; T temperature of vapor; lc coefficient of cubical expansion of glass. Or, calculation can be effected by the formula: Sp. Gr. = --, where IF' represents the weight of an equal volume of air, under conditions identical with those under which the volume of the vapor was determined. EXAMPLE : Calculate from the following data the specific gravity of chloroform vapor referred to air as standard : Weight of substance, and hence i w = Q 2500 gr. Weight of vapor ) * ' Volume of vapor V = 110 cc. Height of barometer H = 75.62 cm. Reduced height of mercury in tube above that in trough h = 32.25 cm. Temperature of vapor T = 100 C. Solving by means of logarithms, the value of IF' is found by the formula: log. FF= 7.6670 -f log. (Hh) + ar. co. log. (273 + t) -f log. V + log. (1 + 1 0.000025) - 20. Constant log. 7.6670 10. H-h = 43.37 log. 1.6372 273 -f t = 373 ar. co. log. 7.4283 - 10. F= 110 log. 2.0414 (1 + 100 X .000025) log. 0.0008 8.7747 - 10. w = 0.2500 log. 9.3979 - 10. 0.6232 Number log. 0.6232 = 4.20 Hence, specific gravity of vapor sought = 4.20. 26 LECTURE-XOTES ON THEORETICAL CHEMISTRY. III. Victor Meyer's Method. This method, which is equally well adapted for vapor-density determinations of substances with a high, as for those with a low, boiling-point, is the method now generally employed. A weighed amount of substance is vaporized in a vesse_ which contains air. The vapor displaces an equal volume of air, and this ex- pelled volume of air is measured. The apparatus consists of a jacketed glass cylinder of about 100 cubic centimetres capacity which opens into a nar- row glass tube that is provided with a well-fitting glass stop- per. A little below this stopper, a short branch-tube is attached, which leads into a water-trough and which termi- nates under a graduated glass vessel, an eudiometer, filled with water. To make a determination with this apparatus, the jacket surrounding the glass cylinder is filled with a liquid of known boiling-point. The liquid selected for this purpose of course has a boiling-point higher than that of the substance the vapor density of which is to be ascertained. A small amount of the substance to be examined is weighed out, placed into a small stoppered tube or bulb, and is intro- duced into the jacketed cylinder, where it is vaporized. The vapor produced expels an equal volume of air; this, in turn, displaces some of the water in the eudiometer, being itself thus confined and measured. The calculation is simple. The specific gravity of the vapor is equal to the weight of the vapor (the weight of the substance used), divided by the weight of an equal volume of air, i.e., by the weight of the air expelled. Expressed in a formula, taking air as standard, it would be : _ . .. 0.0012937 v.(H-p) SPECIFIC GRAVITY. 27 and, taking hydrogen as standard, _ w. (I 4- 0.00367 T) . 760 bp< ~ 0.00008958 . v . (H - p)' in which formulae, w = weight of substance taken; v = the observed volume of displaced gas in cubic centi- metres; H = reduced height of barometer at time of experiment ; p = tension of aqueous vapor at the temperature of the measuring vessel. T = temperature of the water in the collecting trough. Calculation of determinations made by Victor Meyer's method, can of course also be effected by logarithms. The value sought, specific gravity referred to air as standard, can be calculated by the formula: log. Sp. Gr. = log. w log. w', where w = weight of vapor, to' = weight of displaced air, and where the value of log. w' is found by the expression, log. w' 7.6670 - log. (H - p) -f ar. co. log. (273 + t) + log. V- 20. Or, the specific gravity can also be calculated by use of the following expression: log. Sp. Gr. = 2.3330 + ar. co. log. (H - p) 4- log. (273 -f- t) + ar. co. log. F+ log. W 20. The value 2.3330 is obtained by subtracting the constant 7,0670 from 10,0000, 28 LECTUKE-KOTES ON THEORETICAL CHEMISTBY. EXAMPLE Calculate from the following data the specific gravity of carbon disulphide referred to air us standard: w= 0.0495 gr. *> = 16.4 c. c. H= 71.78 c. m. P = 1.40. T= 16.5 C. Log. Sp. Gr. = 2.3330 + ar. co. log. (Hp) -f- log. (273 -f t) -\- ar. co. log. v -f- log. w 20. 23330 (// - p) ar. co. log 8.1525 - 10 (273 + log..., 2.4617 ar. co. log. v 8.7852 10 log.w 2.6946 0.4270 Number log. 0.4270 = 2.673. Hence, specific gravity of vapor = 2.673. CHEMICAL NOMENCLATURE AND NOTATION. 29 CHAPTER III. CHEMICAL NOMENCLATURE AND NOTATION. THE development of the language of chemistry, condi- tioned as it has been by the evolution of the science, presents an interesting subject for study. Earliest Times. The oldest chemical terms were either very general, or else suggestive of the origin of the substances to which they were applied. Since the earliest times, the term " sal " has been used for everything having a salty taste; since the eighth century the kind or origin of the substance was indicated by an addi- tional word ; for instance, " sal maris." In Gebers writings there is no attempt at any system in the naming of chemical bodies; whether or not he was familiar with the use of any of the symbols for the metals which were used by the alchemists in later times, is very doubtful. They are certainly to be found in his works, but as these consist almost exclusively of Latin translations made in the sixteenth century, it is an open question whether they appeared in the original, or were inserted by the translators. Notation of the Alchemists. With the thirteenth century the alchemists commenced to use certain symbols quite freely. The seven metals, gold, silver, mercury, copper, iron, tin, lead, were known by the following names and symbols : Gold = Sol O Silver = Luna 3 Mercury = Mercurius 9 Copper = Venus 9 Iron = Mars ^^ zinc ' ni / cke ? 1 ' etc., eWorld, etc. j etc " chlond ' etc ' < VM ?' terminations in -ic, supra). arsenetted hydrogen arsin antimonetted hydrogen stibin phosphoretted hydrogen phosphin sulfuretted hydrogen, etc. . . hydrogen sulfid, etc. beryllium glucinum niobium columbium glycerin glycerol hydroquinone (and hydrochi- non) quinol pyrocatechin catechol resorcin, etc resorcinol, etc. mannite mannitol dulcite, etc dulcitol, etc. benzol benzene toluol, etc toluene, etc. thein caffein furfurol furfuraldehyde fucusol fucusaldehyde CHEMICAL NOMENCLATURE AND NOTATION. 51 For Use anisol methyl phenate phenetol ethyl phenate anethol methyl allylphenol alkylogens alkyl haloids titer (n.) strength or standard titer (v.) titrate monovalent univalent divalent, etc bivalent, etc. quantivalence valence Fate, fat, far, mete, met, pine, pin, marine, note, n6t, move, tube, tub, rule, my, y = i. ' Primary accent; " secondary accent. N.B. The accent follows the vowel of the syllable upon which the stress falls, but does not indicate the division of the word into syllables. 52 LECTURE-NOTES ON THEORETICAL CHEMISTRY. CHAPTER IV. ATOMS, ATOMIC MASS, VALENCE. Introductory. Lavoisier was the first to recognize the fact that the elements combine in definite mass-proportions. Proust, another French chemist, was the first to prove that the elements combine in a small number of definite fixed pro- portions, but he did not succeed in giving a correct explana- tion of chemical combination. John Dalton's investigations led him, independently of the work of others, to the discovery of the law of combination in multiple proportions. Laws of Chemical Combination. The two important laws of chemical combination can be thus stated: LAW or DEFINITE PROPORTIONS: Chemical combination always takes place between definite masses (weights) of sub- stances. LAW OF MULTIPLE PROPORTIONS: If two elements com- bine in different proportions, the relative amounts of the one which combine with a fixed amount of the other are simple multiples of each other. In order to explain these facts, Dalton advanced his famous Atomic Theory. Two hypotheses concerning the constitution of all ele- mentary forms of matter present themselves for considera- tion. Matter is either infinitely divisible, or it is not infinitely divisible. Concerning the former hypothesis this, from its very nature, is incapable of direct proof or demonstration, and must always remain solely a subject for speculation. ATOMS, ATOMIC MASS, VALENCE. 53 Acceptance of the second hypothesis involv-es of necessity the assumption of the existence of ultimate, indivisible par- ticles of matter. Such particles are termed atoms, from the Greek aro/fos, signifying indivisible. Dalton conceived the idea that there might be some con- nection between the laws of fixed and multiple proportions, and the hypothesis that matter consists of indivisible par- ticles, atoms. Atomic Mass. One universal property of matter is mass (weight). As atoms are assumed to be the ultimate ^articles of matter, atoms must be possessed of mass (weight). As the different fundamental forms of matter, the so-called elements, differ from one another in their mass, it is only reasonable to suppose that the very atoms of the elements differ from one another in this respect. It is assumed whenever chemical combination occurs be- tween two elements, that the union takes place between the atoms of these elements. In case an equal number of atoms of two elements, A and B, are allowed to enter into chemical combination, a new substance will be formed as the result of such union, and, providing that said elements combine with each other atom for atom, no trace will be left of either of the constituents A and B. If the mass of an atom of .4 is 1, and the mass of an atom of B is 15, then, as A and B are supposed to combine atom for atom, the resulting compound would contain A and B in the proportion of one part by weight of A to fifteen parts by weight of B. If therefore, on analysis, a compound is found to contain one part by weight of one element to, say, fifteen parts by weight of another, the inference might be drawn that the masses of the atoms of these elements bear to each other the ratio of 1 : 15, an inference which does not necessarily follow. Assuming matter to consist of atoms, and assuming chem- 54 LECTURE-NOTES ON THEORETICAL CHEMISTRY. ical action to take place between atoms, it is evident why chemical action always takes place between definite amounts by weight, and there is thus gained a feasible explanation of the law of combination in definite proportions. Furthermore, it follows, as atoms are indivisible, that if elements combine with one another in more than one propor- tion, the proportions in which they combine must necessarily be a very simple one ; for instance, as 1 : 1, as 1 : 2, as 1 : 3, and so on. This would fully explain the law of combination in multi- ple proportions. Standards of Atomic Mass. The atom is the smallest mass of an element which can enter into chemical combination. The atomic mass of an element is the relative mass of an atom of that element, referred to the mass of an atom of some other element taken as unity. The selection of an element as standard of atomic mass presents considerable difficulty. Hydrogen was selected by Dalton as his standard, and it is the unit of atomic masses still generally used, because hydro- gen enters into chemical combinations in smaller proportion by weight than any other element. Berzelius adopted oxygen as standard, calling 100. As the atomic masses of many elements can be determined directly with reference to oxygen, some eminent chemists have lately again urged the adoption of oxygen as the standard, making = 16. This would assign to hydrogen an atomic mass of from 1.003 (Ostwald) to 1.007 (Clarke), according to some of the most recent and exact investigations. The atomic mass values in the first column, with = 16, are taken from a table revised by F. W. Clarke, October, 1891; the values in the second column, with H 1, are taken from A. Rossing, Einf iihrung in das Studium der theoretischen Chemie, 1890. ATOMS, ATOMIC MASS, VALENCE. Table of Atomic Masses. 55 Name. Symbol. Atomic Mass, = 16. Atomic Mass, H = l. Aluminum Al 27 2704 Antimony Sb 120. 119.6 Arseuic As 75. 74.9 Barium .... Ba 187 1369 Bismuth Bi 208.9 207.3 Boron B 11 109 Bromine Br 79.95 79.75 Cadmium Cd 112. 111.7 C&sium Cs 132 9 132 7 Calcium . ... ... Ca 40 39 91 Carbon C 12. 11.97 Cerium Ce 140 2 139 9 Chlorine Cl 3545 35.37 Chromium Cr 52 1 524 Cobalt . ... Co 59 58 6 Columbium Cb 94 93 7 Copper . Cu 63 6 63 18 Erbium Er 166 3 166. Fluorine F 19. 19 1 Gadolinium Gd 156 1 Gallium Ga 69 699 Germanium Ge 72.3 723 Glucinum Gl 9 9 08 Gold Au 1973 196 7 Hydrogen H 1.007 1 Indium In 113.7 113.6 Iodine I 126 85 126 54 Iridium Ir 193.1 192 5 Iron Fe 56. 55.88 Lanthanum La 1382 138 Lead .... Pb 206 95 2064 Lithium Li 7.02 701 jVIafiruesium . . .... Mg 24 3 24 30 jManganese Mn 55. 54 8 jMercurv Hg 200 199 8 Molybdenum Mo 96 959 Xeodymium Nd 140.5 Nickel Ni 58 7 58 6 ^Nitro r en . N 1403 14 01 Os 190.8 191 Oxvtren O 16 15 96 Palladium . . ... Pd 106 6 106 2 LECTURE-NOTES OK THEORETICAL CHEMISTRY. TABLE OF ATOMIC MASSES. Continued. Name. Symbol. Atomic Mass, O ^ 16. Atomic Mass, H = 1. Phosphorus P 81. 30.96 Platinum Pt 195. 194.3 Potassium K 39.11 39.03 Praseodymium Pr 143.5 Rhodium Rh 103. 104.1 Rubidium . Rb 85.5 85.2 Ruthenium ... Ru 101.6 103.5 Samarium Sm 150. 150. Scandium Sc 44. 43.97 Selenium . . Se 79. 79.0 Silicon Si 28.4 28.3 Silver Aff 107 92 107.66 Sodium . Na 23.05 23.0 Strontium Sr -. 87.6 87.3 Sulphur S 32.06 31.98 Tantalum Ta 182 6 182. Tellurium Te 125 125. Terbium Tb 160. Thallium Tl 204 18 203.7 Thorium .... Th 2326 232.0 Thulium ... Tu 170.7 Tin Sn 119 1188 Titanium . . Ti 48 480 Tungsten .... W 184. 183.6 Uranium u 239.6 239.0 Vanadium v 51 4 51 1 Ytterbium Yb 173 172 6 Yttrium Yt 89 1 88 9 Zinc Zu 65 3 65 1 Zirconium . . Zr 90 6 90.4 It is evident that in many instances the values given in these two tables are based on different sets of data. If it be desired to learn the atomic mass of any element determined with reference to =16, on the basis of H = 1, it will only be necessary to fix on the ratio of to H, and then a simple calculation by proportion will yield the desired result. This ratio has been most carefully determined by several observers; following are some of the results obtained, ATOMS, ATOMIC MASS, VALENCE. H. O. Dumas 1 Erdmann, Marchand 1 Cooke, Richards (with Rayleigh's corrections) . 1 Keiser 1 Regnault, Rayleigh, Crafts 1 15.96 15.96 15.869 15.949 15.91 15.884 Rayleigh 1 Determination of Atomic Mass. The determination of the atomic masses of the elements is based on a chemical analysis of their compounds. It is, however, impossible to ascertain the atomic mass of an element solely from the results of an analysis of its com- pounds, for atoms cannot be isolated and then be weighed. If atoms of different elements were to combine with each other in only one proportion, a determination of the relative masses in which these elements are present in compounds, would permit of an inference as to the relative masses of the atoms. But elements frequently combine with each other in more than one proportion, and therefore, besides ascertaining the relative amounts by weight in which the different elements are present, it is absolutely necessary that the number of atoms constituting a molecule be known. Direct Determination. In order to determine the atomic mass of an element, the first step to be taken, is the analysis of all of the compounds of the element with hydrogen, assum- ing hydrogen to be adopted as the unit of atomic mass, and a comparison of the values found, in order to ascertain the smallest amount by weight of that element which exists in combination with hydrogen. A few problems will illustrate the method pursued. EXAMPLES. a. Required, the atomic mass of chlorine. The compound of chlorine with hydrogen is hydrochloric acid. This compound, subjected to most careful analysis, shows that in every 100 58 LECTURE-NOTES ON THEORETICAL CHEMISTRY. parts by weight of hydrochloric, acid there are contained 2.74 parts by weight of hydrogen and 97.26 parts by weight of chlorine. Making the proportion: 2.74: 97.26:: 1 : x, x = 35.5. This means that, in this compound, the amount of chlorine which combines with unit mass, i.e., with one atom of hydrogen, has a mass 35.5 times as great as that of the hydrogen, and as no compound of hydrogen and chlorine is known which contains less of chlorine by weight than this amount, 35.5 is considered the smallest amount of this element which will enter into chemical combination with hydrogen. b. Required, the atomic mass of oxygen. Oxygen forms two compounds with hydrogen: water and hydrogen peroxide. 100 parts by weight of water consist of 11.112 parts of hydrogen and 88.888 parts of oxygen. 11.112 : 88.888 ::!:*, x = 8.0. This means that, in this compound, 8 parts by weight of oxygen unite with 1 part by weight of hydrogen. 100 parts of hydrogen peroxide consist of 5.882 parts of hydrogen and 94.118 parts of oxygen. 5.882 : 94.118 :: 1 : x, x = 16.0. This means that, in this compound, 16 parts by weight of oxygen unite with 1 part by weight of hydrogen, and as no other compounds of oxygen with hydrogen are known, besides these two here considered, i.e., water and hydrogen peroxide, it appears, that 8 parts by weight of oxygen, is the smallest amount of this element which enters into chemi- cal combination with 1 part by weight of hydrogen. The number which expresses the smallest weight of an element which will combine with or replace the unit weight of hydrogen, is called the chemical equivalent of that element. The atomic mass must be identical with, or must be a multiple of, this value. ATOMS, ATOMIC MASS, VALENCE. 59 Indirect Determination. In cases where the element, the atomic mass of which is sought, does not form a compound with hydrogen, if that be the unit to which the atomic masses are referred, the atomic mass of the element is determined indirectly, that is, with reference to some other element, the atomic mass of which has been directly determined. The atomic masses of many, if not of most, of the elements have been determined in this manner. EXAMPLE : 100 parts of sodium chloride consist of 60.68 parts of chlorine aud 39.32 parts of sodium. As 35.5 parts of chlorine combine with 1 part of hydrogen, the amount of sodium which combines with 35.5 parts of chlorine represents the atomic mass of the sodium. 60.68 : 39.32 :: 35.5 : x t x = 23. Therefore the atomic mass of sodium is 23, of course, on the supposi- tion that the molecule of sodium chloride consists of only one atom of chlorine and one atom of sodium. When the relative mass of an element in combination with one atom of hydrogen has been thus determined, directly or indirectly, there remain to be ascertained the number of hy- drogen atoms in the compound; the mass of the other con- stituent, combined with these hydrogen atoms, represents the total atomic mass of that element. Aids in Determining Atomic Mass: Vapor Density. When the compounds analyzed can be vaporized without decompo- sition, a determination of the vapor density affords the means of determining their molecular mass. The weights of equal volumes of gases bear to one another the same ratio as the atomic masses of those elements.* Thus, 1 litre of hydrogen weighs 0.0896 gramme. 1 " " nitrogen " 1.2544 grammes. 1 " " oxygen " 1.4336 " * Excepting mercury, cadmium, zinc, phosphorus, and arsenic 60 LECTURE-NOT KS OX THEORETICAL CHEMISTRY. The ratio of the atomic masses of these elements is practically the same as that shown by the figures, viz., 1 : 14 : 16. According to the hypothesis of Avogadro, "equal volumes of all gases, under the same conditions of temperature and pressure, contain the same number of molecules." As before stated, the weights of equal volumes of gases are readily determined; these weights bear the same relation to each other as do the masses of the molecules of these substances; hence it follows, that the molecular mass of all substances is directly proportional to the specific gravity of these substances in the state of a perfect gas. Under the standard conditions of temperature and pressure, one litre of hydrogen weighs 0.0896 gramme, and one litre of hydrochloric acid gas weighs 1.6352 grammes. The weight 16352 of a molecule of hydrochloric acid must therefore be * = o y o 18.25 times as great as that of a molecule of hydrogen. 18.25 parts by weight of hydrochloric acid gas consist of 0.5 of hydrogen combined with 17.75 of chlorine. Therefore 36.5, that is, 18.25 X 2, contains unit weight of hydrogen, and hence is the smallest number that can be adopted as the molecular mass of hydrochloric acid. As seen above, the molecule of hydrochloric acid is 18.25 times as heavy as that of hydrogen; therefore, if the atom of hydrogen is 1, the molecular mass of hydrogen must be 36.50 9 18.25 : The atom of hydrogen is the unit of the atomic masses, and the molecule of hydrogen, consisting of two atoms, has been adopted as the standard for the specific gravity of gases. Hence, the molecular mass of any substance is equal to twice its specific gravity in the state of gas. To return to two of the examples previously given, those referring to hydrochloric acid and to water. As the molecular mass of every substance is the sum of its ATOMS, ATOMIC MASS, VALENCE. 61 atomic masses, the values obtained by analysis the combin- ing masses must, when added together, result in either the molecular mass, or in a number of which the molecular mass is a multiple. Analysis has shown, that for every 1 part by weight of hydrogen in hydrochloric acid there are 35.5 parts by weight of chlorine. Hence 1 -f 35.5 = 36.5 is the molecular mass of hydrochloric acid, or if not, then the molecular mass of hydrochloric acid must be some multiple of this value. The vapor density of hydrochloric acid is found to be 18.25. As the molecular mass of a substance is equal to twice its vapor density, 18.25 X 2 = 36.5 must be the molec- ular mass of hydrochloric acid, as previously stated. But this is also the value found by analysis; therefore hydrochloric acid must consist of one atom of hydrogen and one atom of chlorine, and the atomic mass of chlorine must therefore be 36.5 - 1.0 = 35.5. Now, turning to the other example. Analysis of water shows that 1 part by weight of hydrogen combines with 8 parts by weight of oxygen. 1 -j- 8 = 9 ; therefore 9 must be the molecular mass of water, or else the molecular mass of water must be some multiple of this value. The vapor density of water is = 9. The molecular mass of water is therefore equal to 9 X 2 = 18. The combining masses of hydrogen and of oxygen in water were, by analysis, found to be respectively 1 and 8. But the molecular mass was found to be twice this value, that is, 18. and therefore a molecule of water must contain twice as much of each constituent, that is to say, 2 of hydrogen and 16 of oxygen, and the atomic mass of oxygen is therefore 16.* Atomic Heat. When the vapor density of an element cannot be obtained, then, in order to fix upon its atomic mass, recourse is often had to the fact discovered by Dulong and Petit in 1819, that the specific heat of an element is inversely proportional to its atomic mass. * Assuming the molecule of water to consist of three atoms. 62 LECTURE-NOTES ON THEORETICAL CHEMISTRY. Specific heat is the ratio of the amount of heat required to raise a given weight of a body one degree in temperature, compared to the amount of heat required to raise the same weight of water to the same extent. The product of the specific heat by the atomic mass is approximately a constant; it is called the atomic heat. Its average value is 6.4, and the atomic mass of an element may therefore be approximately obtained by dividing the specific heat of the element, in the solid state, into 6. 4. EXAMPLE: 100 parts of chloride of silver consist of 75.26 parts of silver and 24.74 parts of chlorine. As 35.5 parts of chlorine combine with 1 part of hydrogen, the amount of silver which combines with 35.5 parts of chlorine must be the atomic mass of silver. 24.74 : 75.26 :: 35.5 : as x = 108. Hence the atomic mass of Ag = 108. To confirm, or to dispose of, the assumption that this value represents the mass of one atom of Ag, the constant 6.4 is divided by the specific heat of silver. The specific heat of silver has been ascertained to be 0.057. 6.400 : 0.057 = 112. This value 112 is near enough to 108 to show that this represents the mass of one atom, and not of several atoms of silver To a limited extent the principle here referred to can also be extended to chemical compounds, for the specific heat of elements is practically the same when they are in a state of combination, as when they are in a free state. The molecular mass of a compound, multiplied by its specific heat, is equal to as many times 6.4 as there are atoms in the molecule. The specific heat of sodium chloride, for instance, is 0.214. Its molecular mass, on the assumption that it consists of one ATOMS, ATOMIC MASS, VALENCE. 63 atom of sodium and one atom of chlorine, is 23.0 -f- 35.5 = 58.5. 58.5 X 0.214 = 12.52; 12.52 -f- 6.4 = about 2, thus confirming the view above assumed in regard to the constitution of the molecule of sodium chloride. Isomorphism. This property was at one time regarded as a valuable aid in the determination of the atomic mass of ele- ments. Mitscherlich believed, that isomorphism, which he defined as identity of crystalline form, was due only to the number and the arrangement of the atoms in a molecule, and that it was entirely independent of the chemical nature of these atoms. He taught, that an equal number of atoms united in the same manner, gives the same crystalline form. This statement, if it were borne out by the facts, would furnish a valuable guide in atomic-mass determinations. For, two compounds being isoinorphous, it could be assumed that they contained the same number of atoms in their molecules. Then, knowing the atomic masses of the elements in the molecule of one of these substances, the atomic mass of one element in the other substance could be easily calculated. However, it can readily be shown that this method does not give reliable results, at least not, if the broad meaning assigned by Mitscherlich to the term isomorphism, be retained. Valence. It has been established by experiment that some elements will enter into chemical combination in but one proportion, while other elements will readily enter into com- bination in more than one proportion. To account for these facts, the hypothesis has been advanced, that this power of forming combinations is inherent in the atoms. This property is usually designated as the valence, the valency, atomicity, quantivalence, or the atomic value of the 64 LECTURE-KOTES OK THEORETICAL CHEMISTRY. atoms, and the valence of an element is generally expressed by the number of hydrogen atoms, or their chemical equiv- alent, which one atom of that element can combine with, or replace. Thus : 1 atom of Cl combines with 1 atom of H. 1 " " " 2 atoms of H. 1 R, Si a . CHEMICAL EQUATIONS AND CALCULATIONS. 107 Multiplying through by 2, and dividing by the valences II and IV respectively, there is obtained : 1X2 2x2 II IV Tf IV 1 : 1 and the mineralogical formula of pyroxene is therefore: RO, Si0 2 . Methods of Indirect Analysis. The quantitative determination of certain constituents in substances, is sometimes effected by methods of indirect an- alysis. As an illustration of these methods, the following types will be considered: The residue method, the substitution method, and the method which is based on numerical differences between molecular masses. I. The Residue Method. The substance is chemically acted upon by a reagent which is added in known quantity, but in excess. This excess is determined, and the amount of the substance sought is calculated from the data thus obtained. EXAMPLE. Calculate the amount of CO 2 in a sample of impureCaCOs from the following data: 0.305 gramme CaCO 3 were dissolved in 35 c. c. of normal HNO 3 . The HNO 3 which remained uncombined was neu- tralized by a solution of normal NaOH, of which 30.0 c. c. were used. Total HNO 3 = 35.0 c. c. HNO 3 neutralized by NaOH = 30.0 c. c. HNO 3 neutralized by CaCO 3 = 5.0 c. c. 1 c. c. normal HNO 3 = 0.063 HNO 3 . 5c.c. " " = 0.315HNO,. 2 HN0 3 + CaC0 3 = Ca(NO 8 ) a + CO 2 -f H 3 O. 2HN0 3 : CO 2 :: 0.315: x 126 : 44 : : 315 : x x = 0.110 gramme CO 2 . 0.305 : 0.110 :: 100 :a> 108 LECTURE-NOTES ON THEORETICAL CHEMISTRY. II. The Substitution Method. The substance to be deter- mined is replaced by an equivalent amount of some other substance, which is directly determined, and from this the value sought is then calculated. EXAMPLE. Determine the strength of a solution of chlorine from the following data: A solution of potassium iodide was added in excess to 100 c. c. of the chlorine solution. A standard solution of Na 2 S 2 O 3 was used to deter- mine the iodine which was set free, and 50 c. c. of the Na a S 2 O 3 (sodium thiosulphate) solution were used. 1 c. c. Na 9 S a Oa' solution ............... , ____ = 0.01268 I. 50c. c.Na 2 S 2 3 " .................... = 0.634001. Hence 0.6340 gramme iodine was liberated. Atomic mass of I ......................... = 126.8 " " Cl .......................... = 35.5 I : Cl : : 0.6340 : x 126.8 : 35.5 : : 0.6340 : x x = 0.1775. Hence 0.1775 gramme of chlorine is contained in 100 c. c. of the chlorine solution, and 1 c. c. of the solution contains 0.001775 gramme of chlorine. III. The Method based on Numerical Differences between Molecular Masses. Two divisions of this method must be recognized : A. The components of the mixture have one constituent in common. B. The components of the mixture have more than one constituent in common. A. In a mixture of two salts which have one constituent in common and which differ in their molecular masses, the com- mon constituent and the combined weight of the two salts are determined, and from these data the amounts of the other constituents are calculated. CHEMICAL EQUATIONS AKD CALCULATIOKS. 109 EXAMPLE 1. Mixed Silver Salts. Given, the weight of a precipitate, consisting of the mixed chloride and bromide of silver, and the weight of the silver therein contained. Required, to calculate the proportions of chlorine and bromine in the sample. If the common constituent be calculated to its combination with the element or group having the lowest atomic or molecular mass, the figure obtained will fall short of the given amount of the mixed salts, by an amount proportional to the excess of the higher combining mass over the lesser. AgBr -j- AgCl = 0.75 ; Cl atomic mass = 35.5 ; Ag therefrom =0.50; Br " " =80. Calculating all the Ag to its equivalent of AgCl : Ag : AgCl : : 0.50 : x 108 : 143.5 : : 0.50 : x 71.75 = 108-c 0.6643 = x. Then, 0.7500 less 0.6643 0.0857 excess due to Br. Br - Cl : Br : : .0857 : x 44.5 :80 : : .0857 : x 6.8560 = 44.5z 0.1540 = x. Hence, the Br = 0.1540. 0.7500 is the total amount of the mixed silver salts. Ag = 0.5000 Br --= 0.1540 Ag -|- Br = 0.6540 0.7500 less 0.6540 Cl = 0.0960 Hence, Ag present = 0.5000 Br " = 0.1540 Cl " -= 0.0960 110 LECTURE-NOTES ON THEORETICAL CHEMISTRY. The results may be thus verified : Br : AgBr : : 0.154 : X 80 : 188 : : 0.154 : x 28.952 = 80z 0.3619 = x. .% AgBr = 0.3619. Cl : AgCl : : .096 : x 35.5 : 143.5 : : .096 : x 13.776 = 35. 5x 0.3881 = x. .-. AgCl = 0.3881. Hence, AgBr = 0.3619 AgCl = 0.3881 Total AgCl -f AgBr = 0.7500 EXAMPLE 2. Mixed Sulphates. Given, the weight of a precipitate con- sisting of the mixed sulphates of potassium and sodium, 0.371 gramme. SO 3 present therein, 0.200 gramme. Required, the amount of Na 2 O and the amount of K 2 O in the sample. Calculating all the SO 3 to its equivalent of Na 2 SO 4 : S0 3 : Na a S0 4 : : 0.200 : x 80 : 142 : : 0.2 : x 28.4 = 80* 0.355 = x. that is, all of the SO 3 present would be equivalent to 0.355 Na a SO 4 . Subtracting tiiis from the total of the mixed sulphates : 0.371 - 0.355 = 0.016, which amount is due to the higher atomic mass of the potassium. Hence, K 2 O - Na 2 O : K 2 O : : .016 : x 32 :94 :: .016 :x 1.504 = 32z 0.047 = x. CHEMICAL EQUATIONS AND CALCULATIONS. Ill Hence, the KO 2 present is equal to 0.047, and: 0.371 0.247 Na a O present = 0.124 To check the results obtained: K 2 : K 2 SO 4 : : 0.047 : x 94 : 174 : : 0.047 : x 8.178 = 94z 0.087 = x. That is, K 2 SO 4 =0.087. Na 2 O :Na 2 SO 4 : : 0.124 : x 62 : 142 : : 0.124 : * 17.608 = 62z 0.284 = x. That is, Na 2 S0 4 = 0.284. K 2 SO 4 = 0.087 Na 2 S0 4 = 0.284 Total mixed sulphates = 0.371 B. In a mixture of two salts which have more than one constituent in common, the amounts of these common con- stituents are determined and then calculated to their respec- tive combinations. This class of problems can be readily solved by arithmetic, but perhaps even more conveniently by algebraic methods, as the following will show : EXAMPLE. Iu a sample of commercial bicarbonate of soda there are present : Sodium oxide = 32.00 per cent. Carbon dioxide =45.00 " 112 LECTURE-XOTES OK THEORETICAL CHEMISTRY. Calculate the amount of sodium monocarbonate and of sodium bicar- bonate in the sample. Sodium monocarbonate Na 2 CO 3 = Na 2 O -[- CO a . Sodium bicarbonate 2NaHCO 3 = Na 2 O -j- 2CO 2 -f H 2 O. The first step to be taken is to calculate all theNa 2 O to its equivalent in CO 2 : Na 2 O : CO 2 : : :32.0 : x 62 : 44 : : 32.0 : * x = 22.7096CO,. This amount of CO 2 would be required to transform all of the Na 2 O into Na 2 CO 3 (monocarbouate), but as the main portion of the sodium oxide is present in the form of NaHCO 3 (bicarbonate), there is needed this amount of CO 2 , 22.7096 per cent, and as much more as is necessary to form the bicarbonate. As 2NaHCO 3 = Na 2 O -f 2CO 2 -f H 2 O, the difference between the total CO 2 in the sample, and the above amount, 22.7096 per cent, must be multiplied by 2, and this product calculated to sodium bicarbonate. Thus : Total CO 2 in sample, 45.0000 per cent, less 22. 7096 22.2904 per cent. 22.2904 X 2 = 44.5808 C0 2 : NaHC0 3 : : 44.6 : x 44 : 84 : : 44.5808 : * x = 85.108 per cent. Hence, NaHCO 3 = 85.1100 Total CO 2 = 45.0000 a combined in the form of bicarbonate = 44.5808 CO 2 = 0.4192 which must be calculated as present in the form of monocarbonate. CO 2 : Na 2 C0 3 : : 0.4192 : x 44 : 106 : : 0.4192 : x x - 1.01. CHEMICAL EQUATIONS A2?D CALCULATIONS. 113 Hence, Na 2 CO 3 = 1.01 per cent, and the sample therefore contains: NaHCO 3 =85.11 per cent, Na,CO 3 = 1.01 ' To prove the correctness of the results thus obtained, a check calcuia tion is easily made. Thus : Na,CO, : CO 2 : : 1.01 : x 106 : 44 : : 1.01 : x x = 0.41. NaHCO, : CO 2 : : 85.11 : x 84 : 44 : : 85.11 : x x = 44.59 ; that is, CO 2 in form of Na 2 CO 3 = 0.41 CO 2 " " NaHCO 3 = 44.59 Total = 45.00 which corresponds to the amount as found by analysis. The same problem can be solved by algebra in the following manner: CO 2 = 45.00 per cent, Na a O = 32.00 " Let x percentage of Na 2 CO 3 ; y - Then, r(\ ro = 45 Na 2 C0 3 ' 2NaHC(V Substitute the molecular masses in their proper places, and solve for y. y = 85.11 114 LECTURE-tfOTES ON THEORETICAL CHEMISTRY.- Hence, NaHCO 3 = 85.11 percent. 85.11 :*: : 2NaHCO 8 : Na 3 O 85.11 :x :: 168 : 62 * = 31.41 per cent Na 2 O present as NaHCO Total Na a O in sample = 32.00 Na 2 O present as NaHCO 3 = 31.41 Na 2 O " " Na 2 CO 3 = 0.59 Na 2 O : Na 2 CO 3 : : 0.59 : x 62 : 106 : : 0.59 \x x = 1.01 per cent. Hence, the sample contains: NaHCO 3 =85.11 per cent a a C0 3 = 1.01 VOLUME AKD WEIGHT RELATIONS OF GASES. 1 15 CHAPTER VIII. VOLUME AND WEIGHT RELATIONS OF GASES. Volume Relations of Gases. The ratio of weights of equal volumes of elements, in the form of gas, is the same as the ratio of their atomic masses. Exceptions to this are the ele- ments zinc, mercury, cadmium, phosphorus, and arsenic, which will be considered later. Thus : One litre of : weighs : Atomic Mass. Hydrogen 0.0896 gramme 1 Oxygen 1.4295 grammes 16 Nitrogen 1.2555 " 14 From these figures it appears that, weighing equal volumes, oxygen weighs about sixteen times as much, and nitrogen about fourteen times as much, as hydrogen. Strictly speaking, 1.4295 is only 15.9 times 0.0896, and 1.2555 is a trifle over 14 times 0.0896, but the unavoidable errors of experiment will account for these differences. One litre of hydrogen weighs 0.0896 gramme. This value is termed a crith, and therefore one litre of hydrogen is said to weigh one crith. As oxygen weighs sixteen times as much as hydrogen, one litre of oxygen is said to weigh 16 criths, one litre of nitrogen weighs 14 criths, and so on. The following table, prepared by the writer, may prove convenient for reference in calculations concerning gases. 116 LECTURE-KOTES OK THEORETICAL CHEMISTRY. 2-8.23! **!~.2S i-iCDO^CDOSO^aO^^O5^O ^ 05 CO -H GO J> O ^t< CO t- O - Oi " 1O CO GO Oi "^ O5 OO GO 00 CO O CD {>-^'^t | T- 1 t~- O-"JOS^J>COOi r-J o ^' GO* ^ CD' os GO o "<^COGOGOI>COO5COC50O1OCDJ>GO-^O530CO'<^OCOO <00 i-HOi ^COt>T-i QOCOOO OOOOO1COOOOO a--i 1 ^ 6 6 S 1 o o fe 5 f i c c ^ o o 8 E g 8 s -o -c b x 1 s -31! 8 S g g II o S 8Sf s inch cubic |i| a c S S 3 3 "3 O O O = C QO 1! SgJ 2|l 2 c :Ce 140.0? I . Au 197.0 Hg 200.0 Te 203.6 Pb 207.0 Bi 210.0 ;; Er 1780? La 180.0? Ta 182.0 W 184.0 pV Ir Os 197'. 4 198.0 199.2 d e f g Th 235.0 ::::::: .. U 240.0 NOTE. " The quautivalence of the elements on the different hori- zontal lines is usually as follows : Line a, Monads. Line d, Tetrads. Line g, Monads (or " b, Dyads. " e, Triads (or Pentads). Heptads)." " c, Triads. " f, Dyads (or Hexads). ?_F. G. W. 136 LECTURE-NOTES ON THEORETICAL CHEMISTRY. Mendel6efFs Table* which shows the distribution of the elements in periods, shows two small periods, each containing seven elements, and five, so-called, large periods. The elements at the commencement of each series are base- forming, those at the end of the series are acid-forming elements. This is especially marked in the two short periods. The transition from base to acid forming elements is gradual, the intermediate members forming oxides, which are neither pronouncedly basic nor acid. There is a striking contrast in the chemical properties between the last member of any given series and the first member of the series next following. Mendeleeff's Table. The Atomic Weights of the Elements. DISTRIBUTION OF THE ELEMENTS IN PERIODS. Groups. Higher Salt- forming Oxides. Typical or 1st Small Period. Large Periods. 1st. 2d. 3d. 4th. 5th. I.. II.. III.. IV.. V.. VI.. VII.. VIII R 2 no R 2 3 R0 2 R 2 & R0 3 R 2 7 ( Li = 7 Be = 9 B =11 C =12 N =14 =16 F =19 K 39 Ca 40 Sc 44 Ti 48 V 51 Or 52 Mu 55 Fe 56 Co 58.5 Ni 59 Ou 63 Zn 65 Ga 70 Ge 72 As 75 Se 79 Br 80 Rb 85 Sr 87 Y 89 Zr 90 Nb 94 Mo 96 Cs 133 Ba 137 La 138 Ce 140 | Ybl73 Ta 182 W 184 Tli 232 Ur 240 Ru 103 RU104 Pdl06 Agl08 Cd 112 In 113 Sn 118 Sb 120 Te 125 I 127 Os 191 Ir 193 Pt 196 Au 198 Hg200 Tl 204 Pb 206 Bi 208 \" , I.. II.. III.. IV.. V.. VI.. I. VII.. ( ...... R 2 OJ RO R 2 3 R0 2 R a 6 R0 3 R 2 7 H = i Na =23 Mg = 24 Al = 27 Si =28 P =31 S =32 01= 35.5 IJdSmal? Period. * The Principles of Chemistry, by D. Mendeleeff. Translated from the Russian (Fifth Edition) by George Kamensky and A. J. Greenaway. London and New York, 1891. THE PERIODIC LAW. 137 Lothar Meyers Table* shows the symbols of the elements written in the order of their atomic masses, but in horizontal rows. Hydrogen being accepted as the unit of atomic mass, the first line is commenced by Li = 7.01, then comes Be = 9.08, and so on. Writing is continued in the same horizontal line until an element is reached, which resembles lithium in its chemical properties. The symbol of this element, Na = 23.0 is placed under that of Li, and thus forms the beginning of the second line, which line ends with Cl = 35.37. K = 39.03 begins the third line, and the writing is continued in this manner, until the symbols of all of the elements have been noted in the order of their atomic masses. If on the tabular scheme thus produced, horizontal lines be drawn under each line of symbols, and if vertical lines be drawn after each symbol, it will be seen, that the elements are divided into horizontal and into vertical rows. The former are termed series or periods, the latter, groups. The groups contain elements closely allied in their properties; for instance, Group I. consists of : Li, Xa, K, Kb, Cs. In the first two series, each of which consists of seven members, the two elements which fall into the same group, closely resemble each other; thus, for instance, Li and Na, C and Si, Fe and 01. The gaps which appear in all of these tables where they are indicated by dots will probably some day be filled by elements as yet undiscovered. * Outlines of Theoretical Chemistry, by Lothar Meyer. Translated by P. Phillips Bedson and W. Carleton Williams. London and New York, 1892. 138 LECTURE-NOTES ON THEORETICAL CHEMISTRY. Lothar Meyer's Table. Natural System of the Elements. HYDROGEN H = 1. I. n. III. IV. Li 7.01 Na 23.0 K 39.03 Cu 63.18 Rb 85.2 Ag 107.66 Cs 132.7 Be 9.08 Mg 24.3 Ca 39.91 Zn 65.10 Sr 87.3 Cd 111.7 Ba 136.9 B 10.9 Al 27.04 Sc 43.97 Ga 69.9 Y 88.9 In 113.6 La 138 Yb 172 6 C 11.97 Si 28.3 Ti 48.0 Ge 72.3 Zr 90.4 Sn 118.8 Ce 139.9 i Au 196.7 Hg 199.8 Tl 203.7 Pb 206.4 Th 232.0 V. VI. VII. VIII. N 14 01 O 15 96 F 19 06 P 30 96 S 31 98 Cl 35 37 V 51.1 As 74.9 Xb 93 7 Cr 52.45 Sc 78.87 Mo 95 9 Mu 54.8 Br 79.76 Fe 55.88 Ru 101 4 Sb 119 6 Te 125 I 126 54 Ta 182 W 183 6 Os 191 Bi 207 3 U 239.6 VI tl. Co 58.6 Ni 50.6 Rh 102.7 Pd 106.35 Ir 192.3 Pt 194.3 ::::::::: THE PERIODIC LAW. 139 Atomic Analogues. Mendeleeff pointed out, that in many instances the value of any given property of an element is approximately the average of the values of the same property of the two elements which immediately adjoin it, either in the same series, or in the same group. Thus, glancing at Lothar Meyer's table, it will be seen that the atomic mass of S = 31.98 is approximately the mean of the atomic mass of P = 30.96 and 01 = 35.37 which adjoin it on the right and left, and that it is also the average of the atomic mass of = 15.96 and of Or = 52.45 which are placed immediately above and below it in the scheme. Four elements thus related, are termed atomic analogues. Similar groups of analogues can be traced with reference to other properties of the elements. Mendel6eff's Predictions. Mendeleeff, from such considera- tions, predicted the existence and the properties of elements which were to fill the gaps existing between boron and yttrium, aluminium and indium, and, silicon and tin, respectively. These elements received from him the provisional names of eka-boron, eka-aluminium, and eka-silicon. Gallium, discovered in 1875, proved to be the element whose existence and properties Mendeleeff had predicted as eka-aluminium; scandium, discovered in 1879, met the re- quirements claimed for eka-boron, and germanium, discovered in 1886, proved to have the atomic mass and the properties predicted for eka-silicon. Importance of the Periodic Law. A study of the elements when arranged in such systems according to the periodic law. has resulted not only in the prediction of the existence and the properties of elements as yet undiscovered, but has proved of value also in leading to the correction of several erroneous atomic mass values of some of the elements of tellurium, of caesium, and of indium, among others. Graphic Curved. Perhaps the best way of clearly bringing out the fact that the properties of the elements are periodic 140 LECTURE-NOTES ON THEORETICAL CHEMISTRY. functions of their atomic masses, is to present these relations graphically, by means of curves. Such curves are of value in affording an immediate and comprehensive view over a great number of data, in illus- trating the co-ordination of different phenomena, and also in serving as a ready means for controlling the correctness of conclusions and inferences drawn from experiments. As was first shown by Lothar Meyer, the atomic volumes afford an excellent illustration of periodic variation. The term specific volume expresses the volume occupied by the unit mass of a substance; this value multiplied by the atomic mass of an element, gives as the product a value termed, the atomic volume. In the following cut the symbols of the elements are recorded on the horizontal line at distances from zero pro- portional to their atomic masses, and the atomic volumes are marked on the scale of the vertical line, according to their respective numerical value. The curves which result on combining the consecutive points are irregular, but bear a certain resemblance to each other. Taking the curve as a whole, it will be found to con- sist of two kinds of curves, or periods, as they are called. The first two are short, and the others are long periods. It will be seen, that the first element of each period is an alkali metal, and thus in general, similar positions in the dif- ferent periods are held by elements similar in their chemical properties. THE PERIODIC LAW. 141 142 LECTURE-KOTES OK THEORETICAL CHEMISTRY. Periodicity of the Properties of Elements and Compounds. Many of the chemical and physical properties of the elements are periodic, and the same holds true of the properties of their compounds. Thus, the periodicity of valence, of the specific gravity in the solid state as shown by a comparison of the atomic vol- umes, of the electro-chemical properties, of the melting-point, of the magnetic power, of the refractive power, of the con- ductivity for heat and electricity, of the toxic properties of the metals, etc., have all been carefully studied. The period- icity of the molecular volume of the oxides, as well as the acid and the basic properties of these compounds, must also be mentioned. A tracing out of these different relations is most interest- ing, and although the periodic law cannot as yet give a logical explanation of all these phenomena, still it stands unques- tioned, that it is one of the most far-reaching, if it be not, the most important law of chemistry. SOLUTIONS. 143 CHAPTER X. SOLUTIONS. Definition. Mixtures which are perfectly homogeneous, chemically as well as physically, and from which the com- ponents cannot be separated by mechanical means, are termed solutions. Sometimes they are also referred to as "physical mixtures," and this term is understood as embracing homo- geneous gaseous mixtures, solutions, alloys, etc. . The state of aggregation of substances determines to a great extent their ability to form solutions, and perhaps the best way to point out the relations obtaining, will be to consider briefly the behavior of substances towards each other when in the gaseous, the liquid, and the solid condition. Gases in Gases. Gaseous mixtures afford the best oppor- tunity for studying tjie behavior of solutions, because the existing conditions are most simple. If the gases are so chosen, that no chemical action takes place between them, the ability to form solutions is unre- stricted ; this means, that they can intermingle and mix with one another in all proportions. In such a mixture, each gas will retain to the fullest extent its original properties, and will exhibit the same in the same manner, as if it alone were present. Thus, the pressure exerted by any gaseous mixture is equal to the sum of the pressures exerted by its individual com- ponents. That is to say, each gas, uninfluenced by the presence of the other gases, exercises the same pressure which it would exercise if it alone filled the entire space, a fact 144 LECTtJRE-HOTES OK THEORETICAL CHEMISTRY. already recognized by Dalton in 1802. This pressure is termed the partial pressure of the gas. The power of a gaseous mixture to absorb light and to re- fract light, has likewise been shown to be in accordance with the law of addition, in virtue of which, any given property of a gaseous mixture is equal to the sum of that property of its components. The reason why the laws governing solutions of gases in gases, are simple and easy of discernment, is found in the fact, that in the gaseous state the individual particles of matter are at a considerable mean distance from each other, a dis- tance sufficiently great to prevent the mutual action of the particles induced by close proximity. Gases in Liquids. With hardly an exception, all gases are soluble in all liquids, but the amount of different gases which liquids can dissolve, varies within very wide limits, and is de- pendent upon the nature of both the liquid and the gas concerned. The amount of a gas dissolved by a liquid is generally expressed in terms of volume, and not in parts by weight. " Coefficient of absorption " is the term used by Bunsen to denote the volume of a gas under standard conditions of temperature and pressure, absorbed by the unit volume of a given liquid under normal pressure. Ostwald uses the expression " solubility of a gas," to denote the ratio of the volume of gas absorbed to the volume of the absorbing liquid, at any specified temperature and pressure. Solutions of gases in liquids are divided into two groups: (a) Those solutions from which the dissolved gas can be removed easily by decreasing the pressure or by increasing the temperature; and (b) those solutions which refuse to yield up all of the dissolved gas when subjected to the indicated changes in pressure and temperature; but in such instances a chemical change has most likely taken place, thus leaving the matter no longer a problem of simple solution. SOLUTIONS. 145 Solutions of gases in liquids, belonging to the first of these two groups, act in obedience to the law of Henry, which holds, that: the quantity of a gas dissolved by a certain amount of a liquid, is proportional to the pressure of the gas. Bearing in mind the fact that the volume of a gas is in- versely as the pressure to which it is subjected, Henry's law can also be thus stated: A given amount of a liquid will always dissolve the same volume of a gas, irrespective of the pressure. When a gaseous mixture is dissolved by a liquid, the quan- tity of each gas dissolved is proportional to its partial pressure; that is to say, in absorbing a gaseous mixture, the liquid ab- sorbs each constituent of this mixture as if it alone were present, and exerted its own independent pressure. Gases in Solids. A well-known instance of a gas dissolved in solids (metals), is furnished by the absorption of hydrogen by palladium, iron, platinum, potassium, and sodium. At a red heat, palladium will absorb about 935 times, platinum about 3.8 times, its own volume of hydrogen gas. Hydrogen has also been found absorbed " occluded," as it is termed, in certain meteorites. The meteorite of Lenarto, for instance, when heated in vacuo yielded more than 2.5 times its own volume of this gas. Liquids in Gases. The tendency of liquids to pass into the gaseous condition, to evaporate, is closely allied to the facility with which liquids mingle with gases and form gaseous mix- tures. Dalton stated as the law obtaining in these cases: the vapor pressure of a liquid in a gas is the same as in a vacuum. The accuracy of this has been questioned by Regnault and others, but recently, careful observations made on the behavior of water and ether, in vacuo and in air, showed the differences to be very slight as a rule, not exceeding one per cent. Liquids in Liquids. In studying the solution of liquids in liquids, a division into three groups is generally made. 146 LECTURE-NOTES ON THEORETICAL CHEMISTRY. GROUP I. embraces those liquids which readily mix with each other in all proportions; water and alcohol, for instance, will serve as an illustration of this type. But the solubility of liquids is materially affected by the temperature; and certain liquids for example, water and ani- line, which at the ordinary temperature will dissolve one another but very slightly will, if heated up to nearly 170, mix together in all proportions. Likewise, phenol and water become miscible in all proportions when a temperature of 80 is reached. Generally speaking, the properties of mixtures of liquids are not additive, as was found to be the case in gaseous mix- tures. This means, that any given property of a mixture of liquids is not necessarily equal-to the sum of that property of its constituents. Thus, the volume of a mixture of two or more liquids is not necessarily equal to the sum of the volumes of the com- ponent liquids: in most instances it is smaller, than this sum. A satisfactory explanation of this has not yet been advanced ; for, although changes of temperature frequently occur on the mutual solution of liquids, such changes may consist in an increase or in a decrease of temperature, and no definite con- nection between changes in temperature and changes in the volume of the mixtures has yet been traced. GROUP II. consists of liquids which dissolve each other, but only in restricted proportions. An example of this type is afforded by water and ether. If a mixture of these two liquids is made, then, when separation into layers is brought about, the water solution will contain 10$ of ether, and the layer of ether will be found to hold 3$ of water. GROUP III. is reserved for those liquids which exercise practically no solvent action on each other. There are even at present very few liquids which can be placed in this SOLUTIONS. 147 group, and it seems likely, that improved methods of analysis, i.e., the power of determining very minute quantities of cer- tain substances, would transfer to the second group all liquids now classed in this division. Liquids in Solids. An instance of the solution of a liquid in solids is afforded by the mixture of mercury with the solid metals. Mixtures of this kind are termed amalgams. Amalgams may be solids they even frequently occur in the crystalline condition; or they may be liquids, in which case they contain a considerable excess of mercury. As a rule, amalgams are unstable, and some can be decom- posed by subjecting them merely to high pressure. The formation of amalgams is attended in some instances by the evolution, in others by the absorption, of heat. As to whether amalgams should be considered as chemical com- pounds or as physical mixtures, the preponderance of evidence seems to favor the latter view, although the existence of definite compounds of mercury with some metals is unques- tioned. Solids in Gases. Ostwald considers it justifiable to speak of the solution of solids in gases, " inasmuch as certain solids can be evaporated without going through the liquid condi- tion." * As yet the law of these phenomena has not been deter- mined by experiment, but Ostwald presumes that Dalton's law will be found to hold good also for solutions of solids in gases. Solids in Liquids. The solution of solids in liquids is the most common, as well as the most important instance of solu- tions to be considered. A solid soluble in a liquid will dissolve if it be merely left in contact with the solvent, but solution will in most cases be * Ostwald, W., Solutions, 1891 ; translated by M. M. Pattison Muir. 148 LECTURE-KOTES OK THEORETICAL CHEMISTRY. materially hastened if solid and solvent are well stirred or shaken together. When a solvent refuses to absorb any more of a solid, the solution is said to be saturated with respect to that solid. In other words, a solution is saturated, when at any given tem- perature the solvent has absorbed the maximum amount of a solid which it can normally hold in solution at that tempera- ture. Under certain conditions however, solutions can be made to contain more than the quantity above referred to, and in that case they are said to be supersaturated; but such super- saturated solutions can be formed by all soluble bodies, and this condition must not be considered as exceptional. The fundamental law governing the behavior of solids go- ing into solution in liquids, is analogous to that which is valid for vapor-pressures. The influence which pressure exerts on the solubility of substances has been much studied. Moller and Sorby demonstrated that a change of pressure affects the solubility independently of a change of tempera- ture. Recent investigations have shown, that although an increase of pressure generally conditions an increase of solu- bility, yet, at very high pressures a decrease of solubility is induced. The manner in which changes in temperature influence solubility was already examined into by Gay-Lussac in the first quarter of this century, and since that time this prob- lem has occupied the attention of several investigators. As a rule, solubility increases with increasing temperature, and usually the solubility increases faster than the tempera- ture increases. However, there are substances for instance, some of the salts of calcium the solubility of which is less at higher than at lower temperatures. When a solid is dissolved in a liquid, generally speaking, a diminution of volume occurs. The amount of this diminution SOLUTIONS. 149 is determined by the ratio between the solvent and the solid dissolved; for a given amount of solid, the contraction is the greater, the greater the amount of solvent employed. Solids in Solids. Mixtures resulting from the permanent union of two or more metals which are solids at the ordinary temperature and pressure, are termed alloys. Alloys are usually prepared by the aid of heat, but some alloys, of certain soft metals, can be made by pressure alone, and without elevation of temperature. Whether alloys are true chemical compounds, or whether they are to be regarded as solutions of metals in each other, has long been a mooted question. Definite compounds of metals in definite proportions by weight, undoubtedly do exist. It is, however, difficult to isolate these compounds, as they seem to dissolve in all pro- portions in the melted metals; and, as a rule, it appears that alloys are mixtures of definite compounds with an excess of one or more metals. This view seems to be borne out by the fact that alloys pre- serve, more or less, some characteristics of their constituents. Solutions of solids in solids do not, however, necessarily ex- hibit an additive character in their properties. The melting- points are usually lowered, the average density is increased. In certain alloys the conducting power for electricity is pro- portional to the relative volume of the components; in other alloys this is not the case. In many instances the volume of an alloy is less than the sum of the volumes of its components; in other instances the reverse is true. Dilute Solutions. A condition analogous to that obtaining in the gaseous state, can be produced by causing a substance gaseous, liquid, or solid to enter into contact with a liquid solvent, with which solvent said substance will form a homo- geneous mixture, arranging the conditions so that the solvent will be present in considerable excess. Such a solution is termed dilute. It is evident that in such 150 LECTURE-NOTES ON THEORETICAL CHEMISTRY. a solution the particles of the dissolved substance will be widely separated from one another, and the behavior of sub- stances when in a state of dilute solution, closely resembles the behavior of gaseous mixtures. When two solutions of the same substance, but of different concentrations, are placed in contact, the two solutions will mingle with each other, and their movement will continue until the composition of the entire solution is homogeneous. If this intermingling of the solutions is interfered with by the insertion of a membrane or of some other partition which will permit the passage of the solvent but not of the dissolved substance, then the latter will exert a pressure on the ob- structing partition. This pressure is spoken of as the osmotic pressure, and is undoubtedly produced by the dissolved sub- stance, for the" solvent can pass freely through the partition, and moreover, an increase in the amount of the dissolved substance is accompanied by a proportionate increase of press- ure on the partition. This power of movement is inherent in the particles of the dissolved substance, and it is merely ren- dered apparent by its action on the partition. The phenomena which are caused by the action of this force in the particles of dissolved substances are termed osmotic or pressure phenomena; the movements alluded to are spoken of as the phenomena of diffusion. Osmose and diffusion play a very important part in nature. Osmotic Pressure. The conditions which are of special importance in studying the gaseous condition are the volume, the temperature, and the tension under which gases exist. In dilute solutions, the first two conditions are determined by the volume and the temperature of the solvent, whereas, corresponding to the tension of gases, solutions exhibit the so-called osmotic pressure. As enunciated by Van't Hoff, this osmotic pressure is in- dependent of the nature of the solvent, and, in dilute solutions, SOLUTIONS. 151 is subject to the laws obeyed by gases the laws of Boyle, Charles, and Avogadro. Thus, for instance, for constant volume, osmotic pressure is proportional to absolute temperature, and, for all gases and vapors which dissolve in a solvent in amounts proportionate to their pressure, the osmotic pressure is equal to the cor- responding gas-pressure. A careful consideration of most copious experimental data has led to the conclusion, that the osmotic pressure of a sub- stance in solution is equivalent to the gaseous pressure which would be observed, provided the solvent were removed and the dissolved substance, in the gaseous condition, were made to occupy the identical space. This fact is of great practical importance, because, as already explained in the chapter on the determination of molecular mass, it permits the molecular mass determination of substances, the vapor density of which cannot be ascer- tained. This peculiar relation between osmotic pressure and mo- lecular mass, obtained in a purely empirical manner, called for an explanatory hypothesis. Such an hypothesis was advanced by Van't Hoff, and it is practically an enlargement of Avogadro's Law, namely: Solutions of identical osmotic pressure, termed isosmotic or isotonic solutions, contain at a given temperature, in equal volume, the identical number of molecules of dissolved sub- stance ; moreover, this number of molecules is the same as would be contained in the identical volume of a perfect gas, at the same temperature and pressure. Measurement of Osmotic Pressure. Several methods have been devised for the direct measurement of osmotic pressure. Thus, Pfeffer placed a clay cell filled with a sugar solution, to which a little sulphate of copper had been added, into a dilute solution of ferrocyanide of potassium. This resulted in the deposition of a thin membrane of ferrocyanide of 152 LECTURE-KOTES ON THEORETICAL CHEMISTRY. copper in the interior of the cell, a deposit which possesses the peculiarity of permitting water to pass through it, but which prevents the passage of many substances soluble in water, cane-sugar for instance. The sugar molecules are thus prevented from escaping, and if cell and contents are placed into a vessel with water, the latter, in obedience to the laws of diffusion, will permeate the membrane of ferrocyanide of copper, and, entering the cell, will increase the volume of the sugar solution. If the cell be provided with a mercury manometer, the osmotic pressure can be directly ascertained, or if, instead of having this at- tachment, a tube is inserted in the cell, the sugar solution will rise in this tube, and the height to which the solution will rise above the level of the liquid in the cell will serve as a measure of the intensity of the osmotic pressure of the solution. From Pfeffer's determinations many most interesting data were obtained. Thus, for instance, he found that the osmotic pressure is dependent to a very great extent on the nature of the dissolved substance; solutions of different substances of equal concentration produced very different, and some of them, very great pressures. For instance, a 1^ per cent solution of potassium nitrate produced a pressure of over three atmos- pheres. But in most cases, it is a matter of extreme difficulty to meiisare osmotic pressures directly, and various methods have been devised to obtain the result desired, in an indirect man- ner. All of these latter methods base upon a measurement of the amount of work which must be done in order to effect a separation of the solvent and the substance dissolved. For the osmotic pressure is a direct measure of this work, and therefore, if the latter be known, the former can be readily ascertained. Among the principal methods resorted to to effect this sepa- SOLUTIONS. 15o ration of the solvent and of the substance dissolved, crystalli- zation, evaporation, and selective solubility are perhaps most frequently employed. As each of these methods can be used in two ways, i.e., as either the solvent can be removed from the dissolved substance, or as the reverse can be effected, this practically opens up six distinct ways of indirectly determin- ing osmotic pressure. Diffusion. As has been previously stated, the power of movement is inherent in the particles of a dissolved substance. In virtue of this property when two liquids of unequal con- centration are placed in contact, they will mix with each other until a perfectly homogeiieous solution is produced. This process is termed diffusion, and is a manifestation of osmotic pressure. Graham, about the middle of this century, was the first to thoroughly investigate this matter, and in 1855 Fick ad- vanced the theory that, " the quantity of a salt which diffuses through a given area is proportional to the difference between the concentrations of two areas infinitely near one another." The truth of this statement was demonstrated by an inves- tigation made by H. F. Weber twenty-four years later. Graham, in his investigations, found that there is a very marked difference in the speed with which the particles of different substances move through water. To those substances which diffuse relatively fast and which generally occur in the crystalline form, he gave the name crystalloids, while those substances which diffuse slowly, and which usually are amor- phous, were by him termed colloids. Colloidal substances permit the passage of crystalloids, but are usually impervious to other colloids. By inserting a membrane of some colloid between pure water on the one hand and a mixture of colloids and crystal- loids on the other, a more or less perfect separation of the colloids and the crystalloids can be effected, because the latter will readily pass through the membrane and the colloids 154 LECTURE-KOTES ON THEORETICAL CHEMISTRY. will not. The process of effecting a separation in this manner is termed dialysis parchment-paper is usually the substance used as a membrane. Even the brief outline sketch given in these pages of the laws of solutions and of the relations obtaining among them, will indicate the great importance which attaches to this department of theoretical chemistry ; it is undoubtedly along these lines that great advances will be made in the near future. ENERGY CHEMICAL AFFINITY. 155 CHAPTER XL ENERGY CHEMICAL AFFINITY. Introductory. Associated with matter is energy, and, like matter, energy is indestructible. Energy is the cause of all changes, of all transformations in the universe, and is perhaps best defined as : the capacity of doing work, of overcoming resistance. Every particle of matter in space is in a determinate posi- tion with reference to other particles of matter. Continuous change of position is termed motion, and all energy is re- garded as primarily due to the motion of matter. Varying with the kind of motion, energy appears in various forms, as : heat, light, sound, as electrical, or as chemical energy. These forms of energy are to a great extent mutually con- vertible, and convertible without loss. Manifestations of energy are frequently referred to as forces, and as all energy is regarded as due to the motion of matter, force may be defined as : any cause that tends to pro- duce, change, or destroy motion. As energy is the cause of all change, many phenomena in nature are conventionally ascribed to the action of certain forces. Thus, the falling of bodies towards the surface of the earth is ascribed to the force of gravity; the combustion of a fuel, to the force of chemical affinity. Measurement of Force. In order to compare the magnitude of forces, it is necessary to effect their measurement, and in order that this may be done, some standard of measure, some unit of force must be adopted. 156 LECTURE-NOTES ON THEORETICAL CHEMISTRY. Forces are equal when they can produce the same accelera- tion on the same mass or on equal masses, and therefore a force may be measured by comparing it with the gravity of some known mass of matter. THE GRAVITY UNIT OF FORCE is the gravity of any unit of mass, which unit of mass may of course be selected at pleasure. The attraction exerted by the earth upon a given mass is variable; it varies according to the position of the mass on the earth's surface with the latitude. Thus, at the sea-level, one gramme is drawn towards the earth with a velocity of : 978.1 centimetres per second, if at the equator, 980.6 " " " , " " latitude 45, 983.1 " , " " the pole. The gravity unit of force is hence a variable value. THE ABSOLUTE UNIT OF FORCE is another unit by which force is measured. This unit represents the force that, acting during the unit of time on the unit of mass produces the unit of velocity. Different absolute units of force can be constructed, based on different units of time, length and mass. In science, the absolute or kinetic unit of force now almost universally adopted, is based, on the centimetre as the unit of length, on the gramme as the unit of mass, and on the second as the unit of time. This system of measurement is called the centimetre-gramme-second system, and is usually desig- nated as the 0. G. S. system. The absolute unit of force in the C. G. S. system, is called the dyne. The dyne is the force that, acting on a mass of one gramme for one second produces a velocity of one centi- metre per second. RELATION BETWEEN GRAVITY UNITS AND ABSOLUTE UNITS. Gravity units are easily transformed into absolute units. It has already been stated, that in latitude 45, one gramme is drawn to the earth with a velocity of 980.6 centi- ENERGY CHEMICAL AFFINITY. 157 metres per second. A dyne has been defined as imparting a Telocity of one centimetre per second to a mass of one gramme, therefore, the weight of one gramme is equal to 980.6 dynes in latitude 45, at the sea-level. Measurement of Energy. Energy is measured by the work which it can accomplish. The units selected for such measure- ment are : a. The gravity unit. b. The absolute unit. THE GRAVITY UNIT OF WORK. The gravity-unit usually adopted, is the kilogramme-metre. It represents the work done in raising one kilogramme vertically through the height of one metre. THE ABSOLUTE UNIT OF WORK. The absolute unit of work and in consequence, of energy, adopted in science, is the erg. The erg represents the work done in moving a body, free to move, one centimetre against a force of one dyne. Thus, the work done in lifting one gramme one centimetre vertically against the force of gravity, in latitude 45, is equal to 980.6 ergs, for one gramme = 980.6 dynes in latitude 45. And again, in raising a body weighing 20 dynes vertically through a height of 50 centimetres 20 X 50, i.e. 1,000 ergs of work are done. The amount of kinetic energy possessed by matter depends upon the mass of this matter and upon its velocity. If, m denotes the mass. " v " " velocity with which m is moving, then.: Kinetic Energy %mv*. The answer obtained, is of course in terms of the erg. The Law of the Conservation of Energy states, that the sum of all the various energies in the universe is a constant quantity. The proof that matter is indestructible, can easily be given by quantitative chemical experiments, but the principle of the conservation of energy does not admit of such direct demon- 158 LECTURE-NOTES ON THEORETICAL CHEMISTRY. stration. The truth of this law can however be readily proven by indirect evidence. For, if a law is true, then the prediction of certain results under certain conditions, must be possible, and in the case of this law of the conservation of energy, all tests ever made in this manner, have affirmed its correctness. Thus, for instance, Joule furnished the experimental demonstration of the law according to which work can be transformed into heat, prac- tically a proof of the law of the conservation of energy. Chemical Affinity. Introductory. The one manifestation of energy which is of the greatest importance in chemistry, is the force of chemical affinity. Attraction is one of the universal attributes of matter, but according to the conditions under which it is ex- ercised, for instance, whether at measurable or at inappreciable distances, whether between similar or between dissimilar par- ticles or masses of matter, its action is designated by various terms. Thus, gravitation or gravity is the name applied to attrac- tion when exerted at measurable distances; the particles or masses of matter between which it is exercised, may be similar or dissimilar. Attraction at inappreciable distances, when exerted between dissimilar particles is termed adhesion, between similar par- ticles, cohesion. An important point to be noted in this connection is, that the exercise of these various forms of attraction entails no change in the properties of the matter acted upon. When the various forms of matter come to be studied from the chemical point of view, it is found, that matter is endowed with a property, in virtue of which, two or more dissimilar particles when brought into intimate contact, can give rise to other forms of matter, the properties of which can be, and generally are, entirely different from their own. ENERGY CHEMICAL AFFINITY. 159 For instance, when sodium, a metal, is, under proper con- ditions, brought into contact with chlorine, a poisonous gas, sodium chloride is formed, a white salt, which not only is non-poisonous, but which is actually essential to the animal economy. Again, when hydrochloric acid in aqueous solution, is allowed to act on calcium carbonate, a solid, there is formed, carbon dioxide, a gas, and chloride of calcium, a salt, both substances with properties entirely different from the proper- ties of the substances through the inter-action of which they were formed. This peculiar property of matter has been designated by various terms, viz. : affinity, chemical affinity, heterogeneous affinity, chemical attraction, chemical action, molecular gravi- tation, elective gravitation, and chemism. By exercise of chemical affinity, the physical, physiological and chemical properties of substances, either, or all, can be greatly influenced and affected. Chemical affinity can be modified by mechanical action, for instance, by pressure, agitation, or percussion. It can also be modified by the influence of light, by heat and by cold. Heat usually promotes, while cold exerts a retarding influence on chemical action. Hypotheses regarding the Nature of Chemical Affinity. Although nothing positive is known, even at the present day, concerning the nature of chemical affinity, yet a number of hypotheses concerning this subject have been advanced from time to time, and a brief review of these, in the order of their sequence, is not without interest. The Greek philosophers sought to explain the difference of be- havior between different substances, by assuming the existence of likes and dislikes, inherent in the various forms of matter. Under influence of the teachings of Galileo, these views of chemical affinity were abandoned, and chemical affinity came to be regarded as due to the actual bringing into use of little 160 LECTURE-NOTES OK THEORETICAL CHEMISTRY. hooks, points and projections, with which the ultimate parti- cles of matter were conceived as endowed. The next important change of view in regard to the nature of chemical affinity, was due to Sir Isaac Newton. He ascribed chemical affinity to the attractive action of small particles, but held, that the cause of chemical actions differed from that of general gravitation in several ways, principally, with respect to the influence that distance exercised on the result. Bergman, Berthollet and others, deemed chemical affinity and gravitation to be forces of the same character, and claimed, that the seeming difference in their action must be ascribed solely to the difference in conditions under which these forces are exhibited. Sir Humphry Davy, as early as 1807, expressed the belief, that the primary cause of electrical and chemical effects might be the same force. Electrical phenomena resulted, when this force was exerted between masses of matter, whereas chemical phenomena appeared, when this force was exercised between the smallest particles of substances. A complete revolution in the ideas entertained with regard to the nature of chemical affinity, was introduced by Berzelius. Berzelius carefully studied the chemical effects produced by the electric current, and concluded electricity to be the pri- mary cause of activity in all Nature. He conceived each atom as bearing a charge of electricity both positive and negative; one of these charges predominated, and the dominant charge determined the electrical character of the atom. He regarded every compound as formed of two parts, one of which bore a charge of positive, the other of negative electricity. The work of Joule and Mayer about the middle of this century, demonstrated the relationship between chemical affinity and various forms of energy, such as heat, electricity, etc. The mutual transmutability of these forces was shown, and thus the necessity of any further theorizing as to the nature of chemical affinity no longer existed. EXERGY CHEMICAL AFFINITY. 1G1 In other words, chemical affinity is now generally regarded as one of the manifestations of energy, and it seems certain that it can, at least partially, be transformed into heat, light and electricity. Measurement of Chemical Affinity. Attempts to measure chemical affinity have been numerous and varied. Laplace studied the action of acids upon compounds decom- posable by acids, and expressed the view, that the intensity of the action of an acid was directly proportionate to its specific gravity. Morveau, Gay-Lussac and others, believing, that adhesion must be regarded as the first stage of chemical affinity, by means of weights determined the force necessary to separate disks of uniform size, from various liquids. These disks were constructed of different materials, for instance, of metal, of glass, etc. Wenzel, who commenced his investigations of the laws of chemical affinity in 1777, believed that the times required for the solution of metals in weak acids, afforded a means of meas- uring the strength of chemical affinity. The fact, that different amounts of heat are required to effect the decomposition of different compounds, led Lavoisier and others to attempt a measurement of chemical affinity on this basis. For instance, it was noticed that FeS., is decom- posed by a temperature of 816 C. and that sulphur volatilizes at 447 C.; the difference between these two values, was pro- nounced to be the numerical expression of the affinity between iron and sulphur. This idea, advanced thus early in the history of chemical theory, may be regarded as the foreshadowing of a hypothesis concerning the nature of chemical affinity, which was brought forward at a much later date. This hypothesis holds, that chemical affinity consists in an attraction between the atoms, and that this attraction is dependent on variations in the potential energies of the atoms. The thermal changes which accompany chemical reactions, 162 LECTURE-NOTES Otf THEORETICAL CHEMISTRY. have been regarded as indicative of the transformation of potential energy into kinetic energy, and attempts have been made to measure this transformation of energy by thermal methods. But thermal measurements, although they serve to throw some light on certain phases of the question, cannot lead to an understanding of the nature of chemical affinity, because the values yielded by the present methods of thermo- chemistry, express but the ultimate outcome of several chemi- cal changes, the sum or the difference between the heats of decomposition and the heats of formation of the factors involved. Moreover, a portion only of chemical energy is transformed into heat, while other portions may appear in different forms. Von Helmholtz designates the former por- tion as bound, the latter, as free energy. The theory, that the force acting between two different kinds of matter is analogous to the force acting between two masses of matter, had, in its day, a number of eminent men among its adherents. Reactions occurring between com- pounds, involving both decompositions and combinations, were ascribed to the action of two opposite forces, in which the stronger chemical affinity gained the victory. This view found expression in the so-called "Tables of Affinity." In these, substances were arranged in the order of their supposed affinity for one another. The earliest of these tables, of which the following is a specimen, were published by H. Geoffroy in 1718. Table of Attraction. SULPHURIC ACID. POTASH. Baryta , Sulphuric acid Strontia Nitric acid Potash Muriatic acid Soda Acetic acid Lime Carbonic acid Ammonia Magnesia ENERGY CHEMICAL AFFINITY. 163 Bergman, in recognition of the fact, that chemical reactions vary according to the conditions under which they take place, in his tables of affinity, stated the behavior of each substance, when in aqueous solution, "in the wet way," and when at the temperature of fusion, "in the dry way." The following for instance, is the table he formulated for potash. POTASH. Wet Way. Dry Way. Sulphuric acid Phosphoric acid Nitric " Boric " Hydrochloric " Arsenic " Phosphoric " Sulphuric " Arsenic " Nitric " Acetic " etc. Hydrochloric " etc. Kirwan sought a solution of the problem in the different percentage amounts of the constituents of salts, i.e. of acids and bases. He formulated two general laws based on his observations. " The quantity of any base required to saturate a given quantity of any acid is directly as the affinities." And, "The quantity of any acid required to saturate any given quantity of a base, is inversely as the affinities." Bethollet, whose views on chemical affinity have already been referred to, was the first to emphasize the important influence which is exercised by the quantity of the various factors taking part in any chemical reaction. Whether a certain metathesis takes place or not, depends not only on the so-called affinity, which the different factors may have for one another, but also on the relative amounts in which these factors are present. To elucidate this particular aspect of the question, was the aim of the researches of two Norwegian scientists Guldberg and Waage, who enunciated a mathematical law with respect to the influence of mass. They claimed, that the amount of a chemical change is 164 LECTURE-KOTES OK THEORETICAL CHEMISTRY. proportional to the products of the active masses of the bodies concerned, and the coefficients of affinity of the reac- tion, of course presupposing elimination of secondary actions. The term " coefficient of affinity " is best explained in their own words.* " In a simple decomposition of the form AB -\- C AC-}- B, the formation of AC is chiefly brought about by the attraction between A and C; but there are also attrac- tions between the other substances, and ihe force which causes the formation of AC is the resultant of all these attractions. This force may be regarded as constant for a definite temper- ature; we represent its amount by k, which we call the coeffi- cient of affinity for the reaction in question. In the same way, in the double decomposition, AB -f- CD = AC -f- BD, the force which causes the formation of the new substances, is a function of all the attractions between the bodies A, B, C, D, AB, CD, AC, and BD, and the resultant force, k, is the coefficient of affinity for the reaction." Among other investigators whose labors have been directed to studying the influence of mass in chemical reactions, there should be mentioned H. Rose, Bunsen, Debus, Gladstone, and Ostwald. The theory of Guldberg and Waage, which later on was formulated as a law by Van't Hoif, is practically identical with the views of Williamson and Pfaundler. L. Pfaundler, in 1867, was the first who applied hypotheses resting on a mathematical basis, to the views concerning the states of ag- gregation of matter, which had been advanced by Bernoulli, Joule and others. Later on this theory was developed principally by Clausius and Maxwell, who assumed that substances consist of mole- cules, which are in continuous motion. It is claimed, that in the gaseous state, the velocity of the motion is directly pro- portional to the temperature, and inversely proportional to the * From M. M. P. Muir : A Treatise on the Principles of Chemistry. ENERGY CHEMICAL AFFINITY. 165 square root of the molecular mass. There is supposed to be an oscillatory motion within the molecules, which in its in- tensity, stands in a definite relation to the motion of the mole- cules themselves. These views lend themselves readily to an explanation of partial reactions, of reversible reactions, and so forth. The study and the measurement of chemical affinity by electrical methods has engaged the attention of many of the most eminent investigators, among them, of Faraday, Sir W. Thomson, Von Helmholtz and Ostwald. The view is held, that in all solutions capable of conducting an electric current, the ions do not owe their existence to the action of the electric current, but that they exist as such, before the passage of the electrical current. The electric conductivity of solutions is thus made to serve as a means for ascertaining the condition of the substances which are dissolved, for the number of dissociated molecules, i.e. the ions, determine, and are therefore a measure of, the quantity of electricity passing through a solution. The term "conductivity" represents the quantity of electricity which is conveyed in unit time by unit electromotive force. The conductivity possessed by a solution which contains the molecular mass in grammes, of the electrolyte, is termed the molecular conductivity. This molecular conductivity in- creases with the temperature, and with the degree of dilution. The conductivity of equivalent quantities, is called equiva- lent conductivity. As all equivalent ions transport the same quantity of electricity, and as the amount of electricity transported in a given time and by a given electromotive force, is directly proportionate to the number of moving ions and to the speed with which they move, to quote the words of Ostwald, "the equivalent conductivity is thus a direct measure of the velocity of migration of the ions." As first enunciated by KohJrausch, the molecular conduc- 166 LECTURE-NOTES ON THEORETICAL CHEMISTRY. tivity of an electrolyte is equal to the sum of the velocities of migration of the ions, or if : m = molecular conductivity, a = velocity of migration of anion, c = velocity of migration of cathion, x = the amount of the electrolyte dissociated into ions, then, m= x(a -\-c) As can be shown by experiment, it is only on attaining infinite dilution, that the dissociation of an electrolyte into its ions becomes complete, and then : m GO = a -f c From these equations, m= x(a + c) m oo = a -\- c by division, there is found, m Ju m co This formula expresses the fact that, " the degree of dis- sociation of a dissolved electrolyte at any state of dilution is equal to the ratio of the molecular conductivity at this state, to the molecular conductivity at infinite dilution," and this value x, is made to serve as a measure of the chemical affinity of substances. THERMAL RELATIONSTHERMOCHEMISTRY. 167 CHAPTER XII. THERMAL RELATIONS-THERMOCHEMISTRY. Introductory. According to the theory of undulation, now generally accepted, heat is caused by the oscillatory motion of molecules. It is a form of energy, and is supposed to be transmitted through the intervention of an imponderable medium termed ether, which is assumed to completely pervade all space, that between molecules included. Temperature. The term temperature is given to that por- tion of heat, which can be perceived by the senses. Variations in temperature are appreciable to the sense of touch; the extremes of the sensations experienced, are termed heat and cold. The sense of touch furnishes, however, only a relative indication of the temperature of a body, that is to say, through this sense of touch it can only be determined whether a substance is more warm or less warm than some other substance. To ascertain the temperature of a body, resort is had to the physical action of heat on substances. As a rule, the expan- sion of substances caused by heat is measured and the value found is expressed in terms of some arbitrary unit. Temperatures from about 40 to about -f- 340 C. are usually registered by means of thermometers. The medium selected for use in thermometers is generally mercury, because this metal expands quite uniformly throughout the range indicated. Very high temperatures are measured by various devices. Sometimes they are determined by measuring the expansion of gases; rings made of different metals and alloys, 168 LECTURE-NOTES ON THEORETICAL CHEMISTRY. or cones constructed of fire-clay, the fusing points of which are known, are frequently made use of for the purpose. Although temperature must not be confounded with quan- tity of heat, yet temperature can be made to serve as a basis for the measurement of heat quantity, because it always requires the same amount of heat to raise the temperature of a given amount of a substance from one determined point to another. Heat Units. In. order to measure amounts of heat, some thermal unit has to be selected in terms of which the values found, can be expressed. The unit of heat adopted, is the amount of heat necessary to raise a unit mass of pure water through one degree of a thermometer-scale. Different values are in use, varying with the units of weight and with the thermometer-scale employed. The unit of heat now generally accepted, is the amount of heat required to raise the temperature of 1 kilogramme of pure water from to 1 C. For some purposes, the amount of heat required to raise the temperature of 1 gramme of water from to 1 C. is adopted as unit. In these pages the term kilogramme-calorie (k. c.) will be used to denote the former, and the term gramme-calorie (g. c.) to designate the latter value. The temperature of the water chosen as the standard tem- perature, is sometimes 4 C., sometimes, some other tempera- ture more convenient for the purposes of the work undertaken, but, whatever the value taken, according to this method, a quantity of heat is measured by the quantity of water at a selected temperature which that quantity of heat would raise one degree in temperature. Mechanical Equivalent of Heat. The mechanical equivalent of heat is 423.99 kilogramme-metres. This means, that the energy, in form of heat, which is required to raise the temper- ature of one kilogramme of water from to 1 C. can perform work equivalent to raising the weight of 1 kilogramme through a height of 423.99 metres. THERMAL RELATIONS THERMOCHEMISTRY. 169 Latent Heat. When matter is caused to pass from the solid to the liquid state, or, from the liquid to the gaseous state, a certain amount of heat is absorbed, which is not indi- cated by the thermometer. This heat is called latent heat, and it may be defined as: The amount of heat required to effect a change of state of a body without affecting its tem- perature. The latent heat of liquefaction is the amount of heat necessary to convert a substance from the solid into the liquid state, without sensibly affecting the thermometer. Thus, the latent heat of water is between 79 and 80, i.e., it will require between 79 and 80 heat-units to convert 1 kilogramme of ice at C. into water at C. In reversing the process, i.e. con- verting the water again into ice, the above-mentioned number of heat-units are again set free. The latent heat of vaporization is the amount of heat necessary to convert a substance from the liquid to the gase- ous state, without sensibly affecting the thermometer. Thus, the latent heat of steam is 537. This means, that 1 kilo- gramme of water at 100 C. absorbs 537 heat-units in its transformation into steam exhibiting a temperature of 100 C. In condensing steam into water, all of the heat-units previ- ously absorbed are again yielded. Specific Heat. The specific heat of a body, previously re- ferred to in connection with the determination of atomic masses, is the ratio of the amount of heat required to raise a given weight of a body one degree in temperature, compared to the amount of heat required to raise the same weight of water, one degree in temperature. Determination of Specific Heat. In the determination of specific heat values, three methods are principally used. These are : 1. The method of the ice calorimeter. 2. The method of mixtures. 3. The time method. 170 LECTURE-NOTES Otf THEORETICAL CHEMISTRY. 1. THE METHOD OF THE ICE CALORIMETER. In this method, a known weight or the substance is heated to a cer- tain temperature. This temperature is noted, and then the substance is surrounded by dry ice at C., and allowed to remain in contact with this ice until the temperature of the substance has fallen to C. The amount of water formed by the partial melting of the ice is weighed, and the calcula- tion is based on the latent heat of liquefaction of ice. Of course proper precautions must be taken in all such experiments, to avoid as much as possible loss of heat by ra- diation, conduction, etc., so that all the heat lost by the sub- stance may be considered to have been absorbed by the ice. In these experiments the data required, are : 1 . Weight of the substance. 2. Initial temperature of the substance. 3. Weight of the water formed. The substance will have lost : (1) X (2) X specific heat The water will have gained : (3) X 79.25* Since, according to the conditions of the experiment, all that has been gained in heat by the one substance has been lost by the other, these two quantities must be equal to each other, and as a result, we have an algebraic equation in which the specific heat sought is the only unknown quantity. EXAMPLE: Weight of a mass of nickel ............... 145.9 gms. luitial temperature of tbe nickel ........... 500 C. Weight of water formed .................. 100 gms. The nickel has therefore yielded in heat-units 0.1459 X 500 X specific heat of Ni., and the ice has absorbed, in heat-units: 0.100x79.25. Therefore, 0.1459 X 500 X specific heat of Ni = 0.100 X 79.25 7 Q95 Specific heat of nickel = ~^i = 0.10863. Accepting this as the latent heat of water. THERMAL RELATIONS THERMOCHEMISTRY. 171 2. THE METHOD OF MIXTURES. A known weight of the body whose specific heat is to be determined, is mixed with a known weight of water or of some other substance, the spe- cific heat of which is known. The temperatures of the two components are noted at the moment of mixture, and the temperature of the mixture is taken after thermal equilibrium has been established, that is, when both components have attained the same temperature. The necessary data are : 1. \Veight of the substance, the specific heat of which is to be determined. 2. Temperature of this substance before mixture. 3. Weight of the substance, the specific heat of which is known. 4. Specific heat of this substance. 5. Temperature of this substance before mixture. 6. Temperature of the mixture. The difference between (6) and (5) gives the change in temperature of the substance whose specific heat is known; the difference between (G) and (2) is the change experienced by the substance experimented on. Having obtained these values, the rest of the calculation is made as in the preceding instance. This method is used principally to determine the specific heat of liquids, but it can also be employed to determine the specific heat of solids, as shown in the following example. EXAMPLE : Weight of a piece of zinc 2 kilogrammes. Initial temperature of the zinc 150 C. Weight of water used 3 kilogrammes. Specific heat of water 1. Initial temperature of the water 10 C. Final temperature of the mixture 18.4 C. The zinc has lost : 2 X (150-18.4) X specific heat of Zn. 172 LECTURE-NOTES ON THEORETICAL CHEMISTRY. The water has gained : 3 X (18.4-10) X 1. Therefore, 25 2 Specific heat of zinc = - = 0.0957. The ice calorimeter may evidently be regarded as a special application of the method of mixtures. 3. THE TIME METHOD. In this method, sometimes termed, the method of cooling, a known weight of the substance, the specific heat of which is to be determined, is heated to a cer- tain temperature, and then allowed to cool. The time which it needs to cool down to a certain temperature, compared with the time required, under identical conditions, by a known weight of water, or some other substance of known specific heat, to cool to the same extent, is made the basis of the cal- culation; the times for identical weights being proportional to the specific heats. The data required, are: 1. Weight of the substance a, the specific heat of which is to be determined. 2. Time in which this substance a, cools a stated number of degrees. 3. Weight of the substance b, the specific heat of which is known. 4. Specific heat of this substance b. 5. Time in which this substance b, cools to the same extent as a. In making determinations by this method, equal volumes of the substances are taken, which differ in weight by amounts proportional to their respective specific gravities. The method of calculation used in this method, is best illustrated by a problem. THERMAL RELATIONS THERMOCHEMISTRY. 173 EXAMPLE : Determine the specific heat of turpentine. Weight of turpentine ....................... = 1.3 kilogrammes. Time in which 1.3 kilogrammes of turpen- tine will cool from 25 to 5 C ............ 22 minutes, 9 seconds. Weight of water ........................... = 1.5 kilogrammes. Specific heat of water ...................... =1.0. Time in which 1.5 kilogrammes of water will cool from 25 to 5 C ..................... =60 minutes. 1.5 : 60 : : 1.3 : That is to say, y = 52 minutes. This is the time required for 1.3 kilo- grammes of water to cool from 25 to 5 C. Hence : Time for cooling of 1.3 kilogrammes of water : Time for cooling 1.3 kilogrammes of turpentine : : Sp. lit. of water : Sp. ht. of turpentine. 52 : 22.15 : : 1 : x x = 0.426 Therefore, the specific heat of turpentine = 0.426. Of course, if in place of water, any other substance is used, the specific heat of which is known, the corresponding values for this substance must be used in place of those given for water in the above example. This method is the least accurate of the three here de- scribed, but is convenient of application in certain instances. The specific heat of gases may be determined either under constant pressure, or under constant volume. The tables of these data usually bring the former values, unless the contrary is specified. Combustion. In the process of combustion, the energy which is liberated in the formation of the products of com- bustion, appears principally as heat. In instances of the perfect combustion of the ordinary fuels, these products are carbon dioxide and water. CALORIFIC POWER. The calorific power of a substance is the amount of heat, i.e. the number of heat-units, evolved by 174 LECTURE-NOTES OK" THEORETICAL CHEMISTRY. the combustion of one unit-weight of the substance. The gramme or the kilogramme is usually the unit weight selected. CALORIFIC INTENSITY. The calorific intensity is the max- imum theoretical temperature to which the products of com- bustion are raised. The calorific power of a substance is a constant value. It is immaterial whether the combustion proceeds rapidly or slowly, whether it is completed at once, or is achieved in several stages. Calorific intensity however, is a value dependent, to a certain extent, on the conditions under which the combustion is effected. Let: C. J. represent the calorific intensity, C. P. represent the calorific power, 8, S', 8", represent the specific heats of the products of combustion of one unit weight of the substance, m, m', m", represent the amounts by weight of the products of combustion of one unit weight of the substance. Then: In this formula there are reckoned as the products of com- bustion, not only the carbon dioxide and the water produced, but also the nitrogen of the atmosphere if the combustion takes place in air, and the mineral matter, the ash of the fuel, if it contains any, for heat is used in raising the temperature of these bodies. If water is produced in any process of combustion, atten- tion must be paid to the state, liquid or gaseous, in which it is obtained. The calorific power of 1 kilogramme of hydrogen burned THERMAL RELATIONS THERMOCHEMISTRY. 175 in oxygen is 34,462 kilogramme-calories. This value includes the latent heat given out on the condensation of the water- vapor to the liquid state, that is, during its change from steam at 100 0. to water at 100 C. In ordinary combustions, the water remains in the gaseous state, therefore, if the calorific intensity of hydrogen is to be calculated from its calorific power, there must be deducted from the value above given, the latent heat of vaporization of the water formed. EXAMPLES. Calculation of Calorific Power. The symbol of methyl alcohol is CH 3 OH. It is required to calculate its calorific power. The first step is the calculation of the percentage composition of the substance named. C = 12 12 * 10 = 37.50 per cent. o2 H.= 4 4 -^ =12.50 " 1 \x inn O = 16 32 32 100.00 As the calorific power of combustibles is usually given for 1 kilo- gramme of the substance, the composition of methyl alcohol i? expressed in parts per thousand, and is, C= 375 H= 125 O = 500 1000 It is customary to assume all of the oxygen present in a combustible to be combined with hydrogen, and the first calculation made, is to KG LECTURE-NOTES OK THEORETICAL CHEMISTRY. ascertain how much of the hydrogen present is thus in combination with the oxygen in the form of water.* O :2H :: 500 : x 16 : 2 : : 500 : x x = 62.50 Total amount of H present ..................... = 125.0 H in combination with O ...................... = 62.5 H available as fuel ............................ = 62.5 The calorific power of 1000 grammes of carbon = 8080 heat-units, (k. c.) Calorific power of 1000 grammes of hydrogen = 34,462 heat-units, (k. c.) Therefore, the carbon present, 375 grammes, yield : = 3030 heat-units, k. c. and the hydrogen present, available as fuel, 62.5 grammes, yield : 34,462X62.5 - = 2154 heat-units, k. c. 1000 3030 2154 Total, 5184 heat-units, k. c. There must now be determined the total amount of water produced 2H : H 2 O : : 125 : x 2 : 18 :: 125 : x y = 1125 This means, that 1125 grammes of H 2 O are formed. * If there is not enough hydrogen to satisfy all of the oxygen, then a certain amount of the carbon is assumed to exist in combination with the oxygen, and only the balance of the carbon present is calculated as available for thermic effect. THERMAL RELATIONS THERMOCHEMISTRY. 17? 1000 grammes of water absorb 537 heat units in passing into the gaseous condition, 1125 grammes absorb 604 beat units, (k. c.) for : 1000 : 1125 :: 537 : x x = 604 Heat-units produced, (total) .......... ........ 5184 k. c. Heat-units absorbed ............... .......... 604 ' ' Calorific power of CH S OH ................ = 4580 k. c. Calculation of Calorific Intensity. Calculate the calorific intensity of ethyl alcohol, burned in oxygen. The calorific power of ethyl alcohol (1 kilogramme) .................... = 6850 kilogramme-calories. Specific heat of steam ......... ......... = 0.475 Specific heat of carbon dioxide .......... = 0.2164 The combustion of ethyl alcohol takes place according to the equation : C 2 H 6 -f 30, = 2C0 2 + 3H a O On the combustion of 1 kilogramme of C a H 6 OH, there are formed : C a H 6 OH:2C0 2 :: 1 : * 46 : 88 :: 1 :x x = 1.913 kgs. CO,. And: C 2 H 5 OH : 3H 2 :: 1 : x 46 : 54 : : 1 : x x= 1.227 kgs. H 2 O The calorific intensity is calculated by application of the formula previously given : P T _ ~ 1.913 X .2164 + 1.227 X -475 6850 _ 6850 ~ :4l39-f.5828 ~ .9967 and the calorific intensity, of ethyl alcohol = 6872 C. 178 LECTURE-NOTES OK THEORETICAL CHEMISTRY. Thermochemistry. Of all the forms in which energy is manifested, there is perhaps none of greater importance, and of more frequent occurrence, than that denoted as chemical energy. But not- withstanding this fact, unfortunately, no means are known whereby energy, appearing in this form, can be directly meas- ured. Chemical energy is however readily transformed into heat, and thermochemistry has for its object the measurement of chemical energy in thermal units ; the amount of heat liber- ated or absorbed in chemical processes, serving as a measure of the changes taking place in the chemical energy of the system or systems, involved in a given operation. Methods Employed in Thermochemistry. The apparatus used to make thermochemical determinations of course varies considerably, according to the nature of the determination to be made. Measurements which are to be made on substances in aqueous solutions, are conducted in a vessel termed a calo- rimeter ; these calorimeters are generally made of glass or of platinum. If of metal, the sides of the calorimeter are made as thin as possible. Its capacity generally ranges from about five hun- dred to one thousand cubic centimetres ; its shape is usually cylindrical. This cylinder is provided with a very accurate thermometer, graduated in fiftieths of a degree. This allows readings to be made accurately to yj-j- of a degree, and, when read by a telescope, permits estimations up to -^^ of a degree. Insulation of this cylinder is made as perfect as possible, in order to prevent loss of heat by radiation. The experiments made, are completed in as short a time as possible ; the actual rise in temperature of the water is never allowed to exceed a few degrees, and great care is taken to distribute the heat generated uniformly through the water, by means of mechanical stirrers, which are kept constantly in motion during the progress of the experiment. THERMAL RELATIONS THERMOCHEMISTRY. 179 Of course, the weight of all parts of the apparatus, as well as that of the water, must be very carefully ascertained. Furthermore, allowance must he made for the specific heat of the metal, of which the apparatus is constructed. If, for instance, the vessel is made of platinum, which has a specific heat of 0.032, and if it has a weight of 180.0 grammes, then : 180.0 X 0.032 = 5.760, which amount must be added to the weight of the water con- tained in the calorimeter, for this weight of platinum is equiv- alent to, i.e., has the same calorific value, as 5.760 grammes of water. Lavoisier was probably the first one to'study thermo-chem- ical phenomena from a theoretical point of view ; he recog- nized the principle, that, in the formation of a compound from its elements, the same amount of heat is set free as is required to decompose this compound. In 1840, G. H. Hess announced the important law of constant heat-summation, viz. : " the initial and final stages alone determine the develop- ment of heat in chemical processes." Laws of Thermochemistry. The following are the three fundamental laws of thermochemistry as formulated by Ber- thelot : I. The amount of heat set free in any chemical reaction is a measure of the total work, both chemical and physical, ac- complished in the reaction. II. Whenever a system of bodies undergoes physical or chemical changes capable of bringing it to a new state, with- out producing any mechanical effect exterior to the system, the amount of heat set free or absorbed in these changes, depends only on the initial and final states of the system, and is independent of the nature or order of the intermediate states. III. Every chemical change which is effected in a system 180 LECTURE-^OTES 0^ THEORETICAL CHEMISTRY. without the aid of outside energy, tends to the production of that body or system of bodies, the formation of which, evolves the maximum heat. These principles permit the determination of thermal val- ues of reactions, which cannot be directly measured. In 1853, Julius Thomsen first applied the results of the mechanical theory of heat, to thermo-chemistry. The principal work thus far done in thermochemistry, has resulted in the accumulation of a very great number of obser- vations concerning the heat of formation of substances.* In making these determinations on the heat of formation of compounds, the molecules of the elements have been chosen as the starting point. However, as for the most part the mole- cules of elements are combinations of atoms, and as in the formation of molecules from these atoms chemical energy must have come into play, the problem of ascertaining the heat of formation of compounds is not a simple one. For, before the molecules of compounds can be formed, the atoms which make up the molecules of the elements engaged in the reaction, must be separated from one another. This requires energy, and therefore the heat of formation of a com- pound merely expresses the difference in energy (heat), between the amount required to separate the atoms of the elementary molecules, and the amount of energy (heat) evolved or absorbed in the formation of the new compound. If the latter value is greater than the former, and this is generally the case, the heat of formation of a compound is a plus (-J-) value; if the energy (heat), evolved on the forma- tion of a compound is less than the energy required to separate the atoms of the original molecules, then the heat of forma- tion of that compound is a minus ( ) value. * For tables of these data see the " Annuaire," published by the Bu- reau des Longitudes in Paris. Also, Ostwald : Outlines of General Chemistry; and, Muir and Wil- son : The Outlines of Thermal Chemistry. THERMAL RELATIONS THERMOCHEMISTRY. 181 Exothermous and Endothermous Compounds. Those sub- stances whose formation is attended by the evolution of energy (heat), are called exothermoiis compounds, while those sub- stances whose formation is attended by an absorption of energy (heat), are called endothermous compounds. The latter as a rule, are very unstable substances, for the tendency of all matter is to assume that state of equilibrium, which, is most stable under existing conditions, and as already stated, in every chemical reaction, the tendency is to form those products whose formation gives rise to the evolution of the greatest quantity of heat. The Language of Thermochemistry. The ordinary chem- ical formulas and equations express relations by mass, that is to say, in addition to showing the substance or substances concerned in a reaction, and the substance or substances produced, they show the amounts of the different factors in- volved. Thus, the equation. Na + 01 = NaCl not only expresses the fact, that the element sodium combines with the element chlorine to form the compound sodium chloride, but it also shows, that this reaction takes place between 23 parts by weight of sodium and 35.5 parts by weight of chlorine, and that 23 + 35.5 = 58.5 parts by weight of sodium chloride are produced. If, in addition to this, it be desired to indicate the amount of energy involved in a chemical reaction, for instance, in the reaction above given, the equation must be extended, so as to show the amount of heat involved, for chemical energy, it will be remembered, is here to be measured in thermal units. By experiment it has been found, that the formation of from Na and Ci is accompanied by the evolution of 182 LECTURE-NOTES ON THEORETICAL CHEMISTRY. 97600 gramme-calories, and in order to indicate this fact, the equation above given, viz. : Na + 01 = NaCl must be written as follows : Na + Cl = NaCl + 97,600 g. c. This shows, that 23.0 grammes of Na and 35.5 grammes of Cl, together contain the same amount of energy as 58.5 grammes of NaCl plus 97,600 g. c. This equation can be variously transformed. Thus for instance : (1) NaCl = Na + Cl - 97,600 g. c. which means, that in order to decompose NaCl into its con- stituents, 97,600 gramme-calories must be furnished. Or, again : (2) Na.-f Cl - NaCl = 97,600 g. c. This shows, that 97,600 gramme-calories is the difference in energy between Na plus Cl and NaCl. To furnish another illustration of thermochemical expres- sion: H + I = HI - 6100 g. c. This shows, that the formation of hydro-iodic acid from iodine (solid), and from hydrogen, is attended by an absorp- tion of heat, equivalent to 6100 gramme-calories. By transforming above equation algebraically : HI = H + I -f 6100 g. c. From this it will be seen, that a breaking up of HI into its constituents II and I, is accompanied by an evolution of 6100 gramme-calories. THERMAL RELATIONS THERMOCHEMISTRY. 183 Most of the data expressing the energy of chemical reac- tions, have been obtained at, or are referred to, a normal tem- perature of 18 C. The mass-amounts of the substances involved in these reactions always correspond to the atomic or the molecular masses of the substances, expressed in grammes. The thermal unit employed is either the gramme- calorie as here used, or a value 1000 times as great, and termed the kilogramme-calorie. The condition in which the substances exist, i.e. whether in the solid, the liquid, or the gaseous state, exercises an im- portant bearing on the amount of energy associated with the same. Very frequently the reactions studied, take place in large quantities of water. This, within certain limits, does not affect the thermal relations, and the symbol Aq (aqua) is used to indicate water when it thus exists as a passive factor in a reaction. Energy-equations. The examples thus far given, illustrate the heat of formation of an exothermous and of an endother- mous compound. Very often however, it is not possible to measure the thermo-chemical values of a given reaction directly, and in these instances, use is made of the funda- mental principle, that the initial and final stages alone, deter- mine the amount of heat of a chemical reaction. All that is required, is to execute and to measure any two reactions in which the initial and the final substances take part, and to devise a series of equations by means of which all intermediate reactions can be eliminated. As already stated, the heat of formation of a compound is merely the difference between the chemical energy of the compound formed, and that of the elements which form it. Na -f Cl = NaCl + 97,600 g. c., signifies that the heat of formation of sodium chloride is 97,600 gramme-calories, as before stated. Therefore, 97,600 g. c, is the loss of energy experienced by 184 LECTURE-NOTES ON THEORETICAL CHEMISTRY. the sodium and the chlorine in forming the compound sodium chloride. The absolute magnitudes of the quantities of energy in- volved, are unknown. If the energy of the elements be taken as zero, and the quantities of energy be figured therefrom, then, if: Na and Cl = 0, the equation: Na + Cl = NaCl + 97,600 g. c. can be written : -f = NaCl + 97,600 g. c. and this corresponds to: - 97,600 g. c. = NaCl. From this it follows, that in energy-equations, the heats of formation of compounds with their signs changed, can be sub- stituted for the formulae of these compounds, and this princi- ple is frequently used in thermochemical calculations. The following selected examples will illustrate the solving of thermochemical problems. EXAMPLE I Calculate the heat of formation of carbon monoxide. The data obtained by experiment, are : C + 2O = CO 2 + 97,OOOg. c. (A) CO -f O = CO 2 -f 68,000 g. c. (B) Subtracting B from A : C -f 2O - CO - O = 29,000 g. c. Hence : = CO-i-29 > OOOg. c. The heat of formation of CO is therefore 29,000 g. c. EXAMPLE II. Determine the heat of formation of hydrobromic acid, from the following data ; THERMAL RELATIONS THERMOCHEMISTRY. 185 A. (KBr -f Aq) + iC! 2 = (KC1 + Aq) + UBr-+Aq) 11, 478 g. c. B. ^H 2 -f iCl a + Aq = (HC1 -f Aq) 39,315 g. c. C. (KOH-f "Aq) + (HCl + Aq) = (KC1 + Aq) 13,750 g. c. D.(KOH + Aq) + (HBr4-Aq) = (KBr + Aq) 13,750 g. c. E. ^Br 2 4- Aq = ($Br s -f Aq) 539 g. c. F. HBr -f Aq = (HBr -f Aq) 19,940 g. c. From A : 1. (KC1 -|- Aq) = 11,478 -f (KBr + Aq) - (|Br a -f Aq). From E : (iBr, 4- Aq) = 539. Hence : 2. (KC1 4- Aq) = 10,939 + (KBr + Aq). From C: (KC1 + Aq) = 13,750 + (KOH + Aq) + (HC1 + Aq). (HC1 4- Aq) = 39,315. Hence : 3. (KC1 -|- Aq) = 53,065 4- (KOH + Aq). Placing the second members of equations No. 2 and No. 3 equal to each other : 10,939 4- (KBr 4- Aq) = 53,065 + (KOH 4- Aq). 4. (KBr 4- Aq) = 42,126 + (KOH + Aq). From D : 5. (KBr 4- Aq) = 13,750 -f (KOH -f Aq) 4- (HBr + Aq). Placing the second members of equations No. 4 and No. 5 equal to each other : 42,126 _j_ (KOH 4- Aq) = 13,750 + (KOH + Aq) 4 (HBr + Aq). 186 LECTURE-NOTES ON THEORETICAL CHEMISTRY. Hence : 6. (HBr + Aq) = 28,376. In F. the heat of solution of HBr is given = 19,940. Hence : H + Br = HBr = 28,376 - 19,940, and the heat of formation of HBr is therefore equal to 8436 gramme calories. PHOTO-CHEMISTRY. 187 CHAPTER XIII. PHOTO-CHEMISTRY. Introductory. Light, one form taken by the radiant energy emanating from the sun, is a powerful agent in effecting chemical changes. It can induce chemical union between substances, it can cause the decomposition of chemical compounds, and, in cer^ tain instances it can produce important alterations in the physical, as well as in the chemical, properties of the matter subjected to its influence. Chemical Union. A mixture of hydrogen and chlorine, if kept in the dark, will remain practically unchanged. On exposure to diffused light chemical combination will grad- ually ensue, but, if a mixture of these gases be exposed to direct sunlight their union is accomplished instantaneously and with great violence ; an explosion usually accompanying the reaction. Chemical Decomposition. Chlorine gas can be kept un- changed in aque'ous solution for a long time, provided it be carefully guarded from the light. Exposed to its influence the water is partially decomposed, hydrochloric acid is formed and oxygen liberated. Potassium iodide is decomposed by sunlight, iodine being set free. Concentrated nitric acid suffers partial decomposi- tion if acted on by light ; some of the oxides of nitrogen are formed, and these impart a yellow or brown coloration to the otherwise colorless acid. Many organic coloring matters fade and bleach, because 188 LECTURE-NOTES ON THEORETICAL CHEMISTRY. light promotes the affinity of the atmospheric oxygen for two of their principal constituents, carbon and hydrogen. Most silver salts are blackened by the action of light, and it is on this action of light upon some of the silver salts, that the art of photography is based. A plate of glass, or of some other transparent material, is coated with iodide of silver, one of the silver compounds most sensitive to light. The plate thus prepared is placed in a camera, and the image of the object which is to be photographed is allowed to fall upon it. The plate is then immersed in a solution of ferrous sulphate or of some other reducing agent, and thereby the iodide of silver, which has been acted upon by the light, is more or less blackened and the picture is thus developed. In order to fix the picture and avoid any further action of the light on the plate, the iodide of silver which remains is removed by washing with a solution of potassium cyanide, or of sodium thiosulphate, commonly termed, sodium hypo- sulphite. The plate thus prepared constitutes the negative. On this of course, those parts of the image which in the object pictured were brightest, appear most dark, for from them came the greatest amount of light, and this light affected the iodide of silver directly in proportion to its intensity. To print pictures from a negative, the latter is placed on a surface, generally paper, coated with chloride of silver, and then light is allowed to fall upon it. The rays of light of course pass most readily through the undarkened portions of the negative, and thus produce in the film of chloride of silver a darkening, a distribution of light and shade, which is exactly the reverse of that existing on the negative. The picture thus formed the positive is then fixed, made per- manent, by the use of proper reagents, and the photograph is finished. But most important of all, must be counted the transfor- mation of radiant energy into chemical energy, through the agency of plants. Plants absorb carbon dioxide from the air, PHOTO-CHEMISTRY. 189 and under the influence of sunlight this compound is decom- posed into carbon and oxygen; the former is stored in the plant, the latter is returned to the atmosphere. That green plants, in sunlight, will purify air containing carbon dioxide, was noticed by Priestley as early as 1772. The full importance of this process in the economy of Nature was however pointed out only by Justus von Liebig, almost seventy years later. Physical Changes. Among the most frequently cited phe- nomena of this description is the transformation of the com- mon, colorless variety of phosphorus into its red amorphous modification; this change of outward form and color is more- over accompanied by very great alterations in the chemical properties of the substance. The influence which light exercises on the crystallization of inverted sucrose solutions, has been made the subject of study by the author. Three solutions of invert-sugar were prepared from chemically pure sucrose; the first contained 90.9$, the second 80.6$ and the third 58.0$ of invert-sugar. These solutions were placed into twenty-four glass flasks and these were divided into four groups A, B, C, D, of six flasks each. Each of these groups contained the following samples : 90.9$ invert-sugar. Sol. : slightly acid 90.9" " " " neutralized 80.6" " " " slightly acid 80.6" " " " neutralized 58.0" " " " slightly acid 58.0" " " " neutralized. Group A. was exposed to direct sunlight, group B. to diffused daylight, group C. to the rays of an electric arc-light, group D. was kept in darkness. As a full account of the interesting relations brought out in this investigation would here not be in place, mention 190 LECTURE-NOTES OK THEORETICAL CHEMISTRY. shall only be made of the fact, that crystallization by which is meant transformation of the entire fluid contents of the flasks into the solid state, was effected in five of the flasks exposed to direct sunlight, before a single one of the other series attained to this condition. The series exposed to diffused dayfcght was the next to experience this transformation,, and this, while the solutions which were kept in darkness, for the greater part still retained their fluidity. Mode of Action. The chemical action of light depends upon its absorption this has been proved by experiment. As a substance does not absorb all wave-lengths of light alike, the chemical effects which the different color-rays exercise on a body are not identical. It has been determined that the chemical effect of light is dependent upon the color of the light and upon the nature of the body on which it acts. The short wave-lengths of light, the violet rays, are gener- ally held to be the most powerful in inducing chemical changes. However, in the work performed in plants the decomposition of carbon dioxide into its constituents, the red and the yellow rays are the principal agents, and in fact, all rays of light are capable of producing chemical effects. An hypothesis advanced to explain the chemical action of light holds, that the vibrations of the luminiferous ether excite in the substance acted upon, corresponding vibrations, that is to say, vibrations of the same period as those of the ether. The molecules which thus receive this supply of energy, are thrown into commotion, and the atoms, constituting these molecules, will tend to assume different positions. If this disturbance results in the production of more stable molecular systems, for instance, in the decomposition of a compound into its constituents, some of the radiant energy absorbed may be used for this purpose and remain in the system as bound energy. PHOTO-CHEMISTRY. 191 Measurement of the Chemical Activity of Light. Attempts to effect such measurement, have been made in various ways. Senebier prepared a number of papers coated with argentic chloride, upon which light of a known intensity was allowed to act for a certain time. The amount of blackening which these papers experienced, depended of course upon the inten- sity of the light acting upon them, and upon the time of their exposure. In this manner, a sort of scale was obtained, which was of value for comparative measurements. Bunsen and Roscoe perfected a method, originally indicated by Draper, in which the formation of hydrogen chloride by the action of light, is made the basis of operations. Hydrogen and chlorine gases, in the proportion of their chemical equiv- alents are introduced into a thin glass bulb, the lower half of which is blackened, and in which water has been placed. This bulb is in connection with a measuring tube, which terminates in another vessel, also containing water. The light falling upon the mixture of hydrogen and chlo- rine, causes their chemical union, forming hydrochloric acid gas, and this is at once absorbed by the water. The consequent diminution in volume causes the water in the measuring tube to move towards the bulb wherein the hydrochloric acid was formed. The amount of water thus moved, is ascertained from the scale on the tube, and this affords a measure of the activity of the light, which has in- duced the chemical union of the hydrogen and the chlorine. 192 LECTTRE-XOTES OX THEORETICAL CHEMISTRY. CHAPTER XIV. ELECTRO-CHEMISTRY. Introductory. The proof that chemical energy can be transformed into electrical energy, is easily given. Pun? zinc and pure platinum are not attacked by dilute sulphuric acid, whether these metals are immersed singly, or together, only provided, that they do not come into contact with each other. The instant however, that contact is estab- lished between them, either by placing them together, or by connecting them by some piece of metal, the zinc will be attacked by the sulphuric acid and will commence to dissolve, while bubbles of a g^s will appear on the surface of the plati- num. The connecting wire will at the same time be found to have become endowed with certain properties which it did not possess before it served to connect the pieces of metal, and which properties it loses, the instant that its connection with one or both of the metals is broken, or. when one of the latter is removed from the liquid. This clearly demonstrates the fact, that the energy set free by action of the sulphuric acid on the zinc, has become trans- formed into a form of energy which is capable of passing from the place of its liberation, and is capable of doing work else- where in its course, in the so-called electrical circuit, which then becomes the seat of the electrical current. The existence of this electric current can be shown to be due entirely and only to the chemical action between the acid and the metal: the amonnt of electricity generated, stands in ELECTRO-CHEMISTRY. 193 direct relation to the amounts of chemicals, zinc and sul- phuric acid, involved in the process. Electrical energy must be regarded as the product of two factors, quantity and tension. This latter is also termed electro-motive force, or potential. The electro-motive force in its more general sense, is the force which tends to move the electricity from one point of the circuit to another; its more specific meaning will be defined later. The electro motive force, in establishing and maintaining an electrical current, has to overcome a certain amount of f rictional resistance ; the work which the electro-motive force does in overcoming this frictional resistance, appears as heat. Electrolysis. If the electric current is made to pass through a certain class of conductors, solutions of acids, salts, etc., cer- tain chemical changes take place in the system, simultaneous with the passing of this current, and the energy which these chemical changes represent, forms the remaining part of the work done by the electro-motive force in establishing and maintaining the electrical circuit. Chemical decomposition brought about by a current of electricity is termed, electrolysis. The substance decomposed, is called an electrolyte, and the constituents produced, are known as ions. The poles are called electrodes. The metals of salts, metallic radicals, and the hydrogen of acids, are always liberated at the negative electrode (cathode), which is that electrode in connection with the metal most strongly attacked by the acid ; these ions are termed positive ions, or cathions. The acid radicals, oxy- gen, chlorine, bromine, iodine, the group hydroxyl, etc., are set free at the positive electrode (anode), and are termed negative ions, or anions. Only certain classes of compounds are capable of serving as electrolytes. The Ion Theory. From certain phenomena it appears probable, that it is not the electric current which effects the 194 LECTURE-NOTES ON THEORETICAL CHEMISTRY. decomposition of compounds into ions, but that these ions pre-exist in all solutions which can serve to conduct an electric current. This view was first suggested by Williamson (1851) and independently by Clausius, six years later. Clausius assumed, that the presence of only a very few free ions in a solution was necessary in order to make such a solution a conductor of electricity. The atoms of the base and the acid, constituting the salt in solution, were not supposed to be firmly united to one another, but were, in virtue of molecular encounters, supposed to readily enter into new combinations. Thus, molecule I, formed of one atom of base B and one atom of acid radical A, and molecule II, also formed of one atom of the same base B and the same acid radical A, would both be readily decom- posed, and give rise to the formation of two new molecules of the same compound. One of these newly-formed molecules would consist of base B, of the original molecule I in combi- nation with acid radical A of original molecule II, and the other newly-formed molecule would consist of base B of the original molecule II combined with the acid radical A, of original molecule I. While these exchanges were going on, the electricity was supposed to make use of some of these momentarily free atoms for its transportation to the electrodes. Electrolytic Dissociation. However, in 1887, this theory, which failed to account for many phenomena, was replaced by Arrhenius by a theory which is now known as, the theory of electrolytic dissociation. This investigator reached the conclusion, that in electrolytic solutions, for instance in aqueous solutions of strong acids and bases, these substances are either wholly, or at least in great part, dissociated, that is to say, that their constituents are present in the form of free ions. In dilute solutions the dis- sociation of a substance into free ions, is most perfect. For ELECTRO-CHEMISTRY. 195 the laws governing this dissociation are the same as those which control gaseous dissociation, and the dissociation of gases increases with a decrease of pressure. But in solution, we have the osmotic pressure analogous to gaseous pressure, and the osmotic pressure of a solution is decreased as the concentration of the solution is lessened, therefore, dilution decreases the osmotic pressure and correspondingly encourages dissociation into ions. Attention must be called to the fact, that an ion of an element does not correspond to a free atom of that element. For instance, if a solution of sodium chloride were used as an electrolyte, the ions would of course consist of sodium and of chlorine. But the sodium ions and the chlorine ions, as long as they exist as ions, that is to say, as long as they are charged with electricity, do not behave like the ordinary free atoms of sodium and of chlorine. The sodium ion, for instance, will not decompose water, while, as is well known, sodium not electrically charged will do this most energetically; likewise, the ion chlorine behaves diiferently from an ordinary free atom of chlorine. But when the charges of electricity which the ions bear, have been discharged at the respective electrodes, the elements resume their customary properties and functions. Ions may be either atoms of elements, or groups of atoms. The anions carry negative, the cathions bear positive elec- tricity. These ions of course move towards opposite elec- trodes; those charged with positive electricity move towards the negative electrode, and those charged with negative elec- tricity travel to the positive electrode, and there discharge their electricity. Thus, in decomposing a solution of sulphate of copper, the copper atoms, after giving up their charge of electricity, are precipitated as metallic copper, while the S0 4 radical decomposes the water in which the reaction takes place, forming sulphuric acid and liberating oxygen gas. An interesting point to be mentioned in this connection is the fact, that chemical reactions for certain substances can be 196 LECTURE -NOTES ON THEORETICAL CHEMISTRY. * obtained only, when the substances tested for, can appear, on electrolysis, as free ions, and not, when these substances occur as constituents of complex ions. Thus, for instance, chlorine is generally tested for by nitrate of silver. But while this test is a very satisfactory one for free chlorine, for chlorine when existing in the form of hydrochloric acid and in the form of numerous metallic chlorides, it will not answer for the detection of chlorine when in the form of potassium chlorate. Careful examina- tion shows, that this test for chlorine can be obtained only in such of its compounds, which, when subjected to electrolysis, yield the chlorine as a free ion. The tendency of the ions of an electrolyzed solution to recombine chemically, gives rise to an electro-motive force, which is called the electro-motive force of polarization, and which has been regarded as offering a means to measure the chemical affinity of the ions. Electrical Units. Whenever an electric current is estab- lished in a closed circuit, and performs work at different points of its path, any and all chemical changes which are induced, will be found to be the exact chemical equivalents of each other. These quantitative relations were first enun- ciated by Faraday, and are expressed in his laws. Before however passing on to a consideration of these relations, the system of units employed for the measurement of electrical energy requires mention. In the centimetre-gramme-second system, generally referred to as the C. G. S. system of units, the centimetre is adopted as the unit of length, the gramme as the unit of mass, and the second as the unit of time. From these fundamental units there are derived the C. G. S., or as they are sometimes called, the " absolute" units of velocity, acceleration, force, work, energy, and, heat ; they are as follows : ELECTRO-CHEMISTRY. 197 UNIT OF VELOCITY: the velocity of oiie centimetre per second. UNIT OF ACCELERATION: an acceleration of one centi- met^e-per-second per second. UXIT OF FORCE: that force which acting for one second on a mass of one gramme, imparts to it a velocity of one centimetre per second. It is named the Dyne. UXIT OF WORK: the work done in moving a body one centimetre against the force of one Dyne. It is named the Erg. UXIT OF EXERGY : the Erg as above defined, for the energy of a system is measured by the work it can accomplish. UXIT OF HEAT: the amount of heat required to raise the temperature of one gramme-mass of water from to 1 C. It is termed the gramme-calorie. Two systems of electrical units are derived from these fun- damental units : the electro-static, and the electro-magnetic units. The practical units employed in the measurement of electrical quantities follow; they are derived from the electro- magnetic units. The Ohm = unit of resistance. (10 9 C. G. S. units of resistance.) It is the resistance offered by a column of mercury 106.28 c.m. long and 1 sq. mm. in section at C. The Volt = unit of electromotive force. (10 8 C. G. S. units of electro-motive force.) The electro-motive force of a Daniell cell is 1.079 volts. The Coulomb = unit of quantity. (10- 1 C. G. S. units of quantity.) It is the quantity of electricity which in one second flows through the section of a conductor between the ends of which there is an electro- motive force of 1 Volt, and the resistance of which is 1 Ohm. 198 LECTURE-NOTES ON THEOEETICAL CHEMISTRY. The Ampere = unit of current-strength. (1CT 1 C. G. S. units of current.) It is the current produced by 1 Volt through 1 Ohm, i. e., 1 Coulomb per second, is 1 Ampere. The Watt = unit of power, i.e., the rate of doing work. (10 7 C. G. S. units of power.) It is the power conveyed by a current of 1 Ampere in 1 second through a difference of potential of 1 Volt. The Farad = unit of capacity. (10- 9 C. G. S. units of capacity.) It is the capacity of a condenser that will be raised to a potential of one Volt by a charge of one Coulomb. (As a condenser of this capacity is too large to be con- structed, the Micro-farad = 0.000001 Farad is adopted as the working unit of electrical capacity. ) The Joule = unit of work or heat. (10 7 C. G. S. units of work. ) It is the mechanical equivalent of the heat generated per second by a current of 1 Ampere flowing through a resistance of 1 Ohm, i. e. the heat generated by 1 Watt. To indicate quantities a million times as great as those here given, the word mega- is prefixed to the term; in order to denote quantities a million times as small, the prefix micro- is employed; while quantities one thousand times as small are designated by the prefix milli-. The system of index notation, as used above in expressing values in the C. G. S. system, has been adopted for the sake of convenience and in order to economize space. Only the significant figures of a quantity are written down, the ciphers are indicated by an index written above. Thus: 100 = 10 X 10 = 10 3 1000 = 10 X 10 X 10 = 10 3 10000 = 10 X 10 X 10 X 10 = 10* and thus 90,000 can be written : as 9 X 10 4 ELECTRO-CHEMISTRY. 199 Decimals have negative indices. Thus 0.000128 is ex- pressed by: 128 X 10~ f as it is equal to 128 X .000001. Quantitative Relations. The following formulae express some of the relations existing between electrical units. Let,, C denote Ampere, E " Volt, R " Ohm, W " Watt, H " Heat-work, Q " Quantity of electricity, t " time, Then, C = ^ (Ohm's Law.) E= Cx R W= CxE F* W- ~ R TT= C*R H^ C'Rt (Joule's Law.) ff= QE Q=Ct The amount of the ion set free in a given time, at an electrode, is dependent upon the strength of the current, and is directly proportional to it. This is one of Faraday's elec- trolytic laws. One Coulomb of electricity, in passing through water, liberates an amount of hydrogen which has been variously stated to be * : * S. P. Thompson : Elementary Lessons in Electricity and Magnet- ism. 1892. 200 LECTURE-NOTES ON THEORETICAL CHEMISTRY. 0.000010352 gramme, Lord Rayleigh 0.000010354 " Kohlrausch 0.000010415 " Mascart This quantity is termed the electro-chemical equivalent of hydrogen. The electro-chemical equivalent of any element is obtained by dividing the atomic mass of the element by its valence, and then multiplying the resulting quotient by 0.000010352. Thus, the electro - chemical equivalents, (expressed in gramme per Coulomb), of a few of the elements are as follows : Silver ................ -^- 8 X .000010352 = 0.0011180 c compounds } Tf X 00010352 = - 0003293 fn'cuprous compounds } ^ X -000010352 = 0.0006584 /"* ** Q Zinc ................. ~|^- X .000010352 = 0.0003379 Oxygen .............. ^ X .000010352 = 0.0000828 The actual weight in grammes of any ion liberated by electrolysis is obtained by the formula : w = zct, where, w = weight in grammes, z the electro-chemical equivalent of the ion, c = strength of current in Amperes, t = time in seconds during which the current flows. This principle has been practically applied by Edison in measuring the quantities of electricity supplied to stations from central electric plants. A solution of cupric sulphate is electrolyzed between two copper electrodes. The anode will be dissolved by the current, while the equivalent amount ELECTRO-CHEMISTRY. 201 of copper will be deposited on the cathode. Therefore, if one of these electrodes is weighed before and after the pas- sage of the electric current, the quantity of electricity which has passed can be readily calculated. If a metal which has been deposited by an electric current is made to undergo combustion, or is dissolved in acid, its potential energy will be given up in the form of heat, and the equivalent amount of work can be easily calculated, provided, that the mechanical equivalent of heat has been ascertained. As stated by Thompson : " The electro-motive force of any chemical reaction is equal to the product of the electro-chem- ical equivalent of the separated ion into its heat of combi- nation, expressed in dynamical units." Embodying this in a formula, and exemplifying by a problem * : e = zHJ where, z absolute electro-chemical equivalent, in grammes, of the ion. f H number of heat-units evolved by 1.0 gramme of the substance on entering into the combination considered. J = Joule's equivalent. Example : Find the electro-motive force of hydrogen tend- ing to unite with oxygen. For hydrogen, z = 0.00010352, H = 34,000 gramme-calories, J = 42 X 10 6 .00010352 X 34,000 X 42 X 10 6 = 1.47 X 10 s absolute units of electro-motive force. As 10 8 absolute units of electro- motive force are equivalent to one Volt, the value found corresponds to 1.47 Volts. * S. P. Thompson, loc. cit. p. 389. f The absolute electro-chemical equivalents are ten times as great as the values previously given for the electro-chemical equivalents, for the. Coulomb is 0.1 of the C, G. S. unit of quantity. Bibliography PERIODICALS are arranged in alphabetical order, book-titles in chronological sequence. 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LADENBURG, A, Ueber die Entwickelungsgeschichte der Chemie in den letzten 100 Jahren. 2d Edition. Braun- schweig. 1887, * MEYER, L. Modern Theories of Chemistry. Translated from the 5th German edition by Bedson, P. P., and Williams, W. C. London and New York. 1887. *Mura, M. M. P., and CARNEGIE, D, Practical Chemistry. A Course of Laboratory Work. Cambridge. 1887. REYNOLDS, J. E. Experimental Chemistry for Junior Stu- dents, 4th Edition. London, BIBLIOGRAPHY. 211 1887. *Tn>Y, C. M. Handbook of modern Chemistry, inorganic and organic. 2d Edition. London. 1887. WISLICENUS, J. Ueber die raumliche Anordnung der Atome in organischen Molekiilen, etc. Leipzig. 1887. * WOODWARD, C. J. Arithmetical Chemistry or Arithmetical Exercises for Chemical Students. 2d Edition. London and Birmingham. 1888. FUHRMANN, A. Naturwissenschaftliche Anwendungen der Differential rechnuug. Berlin. 1888. * GALLOWAY, R. The Fundamental Principles of Chemistry practically taught, by a new method. London and New York. 1888. GRIMAUX, E. Lavoisier, 1743-94, d'apres sa correspondence, ses mss. et d'autres documents inedits. Paris. 1888. *HAGEMANN, G. A. Die chemischen Krafte. Translated from the Danish by Knudsen, P. Berlin. 1888. LE CHATELIER. Recherches Experimentales et The"oriques sur les Equilibres Chimiques. Paris. 1888. LEHMANN, O. Molekular Physik. Leipzig. 1888. * MEYER, VON, E. Geschichte der Chemie. Leipzig. 1888. * THOMSON, J. J. Applications of Dynamics to Physics and Chemistry. London. 1888. * WATTS, H. Dictionary of Chemistry. Ed. by Morley, H. F., and Muir, M. M. P. London. 1889. BERTHELOT, M. Introduction a 1'etude de la chimie des anciens et du moyen age. Paris. 1889. MEYER, J. L., und SEUBERT, K. Das natiirliche System der Elemente nach den zuverlassigsten Atomgewichtswerthen. Leipzig. 1889. *MuiB, M. M. P. Treatise on the principles of chemistry. 2d Edition. Cambridge. 1889. OSTWALD, W. Editor-in-chief. Die Klassiker der Exakten Wissenschaften. Leipzig. 1889. OSTWALD, W. Ueber die AffimtatsgrossenorganischerSauren und ihre Beziehungeu zur Zusammensetzung und Consti- tution derselben. Leipzig. 1889. * PUPIN, M. Der Osmotische Druck und seine Beziehung zur freien Energie. Berlin. 212 BIBLIOGRAPHY. 1889. WALD, F. Die Energie und ihre Entwerthung. Leipzig. 1889. * WEITZ, M. Geschichte der Chemie in synch ronistischer Dar- stellung. Berlin. 1890. * AUWERS, K. Die Entwickhmg der Stereochemie. Theoret- ische und Experimentelle Studien. Heidelberg. 1890. *DITTMAR, W. Chemical Arithmetic. Part I. A collection of Tables, mathematical, chemical and physical, for the use of chemists and others. Glasgow. 1890. *EARL, A. G. The Elements of Laboratory Work. A Course on Natural Science. London and New York. 1890. FUHRMANN, A. Naturwissenschaftliche Anwendungen der Integralrechnung. Berlin. 1890. * HAGEMANN, G. A. Die chemische Energie. Translated from the Danish by Knudsen, P. Berlin. 1890. *HIORNS, A. H. Mixed Metals or Metallic Alloys. 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Edin- burgh. 1891. * GLUCKSMANN, C. Kritische Studien im Bereiche der Funda- mentalanschauungen der theoretischen Chemie. I Theil : Ueber die Quantivalenz. Leipzig und Wien. BIBLIOGRAPHY. 213 1891. * JAHN, H. Die Grundsatze der Thermochemie und ihre Be- deutung fiir die theoretische Chemie. 2d Edition. Wien. 1891. * MENDELEEFF, D. The Principles of Chemistry. Translated by Kamensky, G. Edited by Greenaway, A. J. London and New York. 1891. * MEYER, VON, E. A History of Chemistry from Earliest Times to the present day, being also an introduction to the Study of the Science. Translated by M'Gowan, G. London and New York. 1891-93. *OSTWALD, "W. Lehrbuch der allgemeinen Chemie. 2d Edition. (1st Edition, 1885.) Leipzig. 1891. *OSTWALD, W. Solutions. Translated by Muir, M. M. P. London. 1891. * SCOTT, A. An Introduction to Chemical Theory. London and Edinburgh. 1891. * THORPE, T. E., and TATE, W. A Series of Chemical Prob- lems. New Edition. London. 1891. *VAN'T HOFF, J. H. Chemistry in Space. Translated and edited by Marsh, J. E., from "Dix Annees dans 1'histoire d'une Theorie." Oxford. 1892. *DAMMER, O. Handbuch der Anorganischen Chemie. Band 1. Allgemeiner Theil, von Nernst, W. 1892. * DOBBIN, L., and WALKER, J. Chemical Theory for Beginners. London and New York. 1892. KRUSS, G. Specielle Methoden der Analyse. Anleitung zur Anwendung physikalischer Methoden in der Chemie. Hamburg und Leipzig. 1892. * MEYER, L. Outlines of Theoretical Chemistry. Translated from the German by Bedson, P. P., and Williams, W. C. London. 1892. * MEYERHOFFER, W. Stereochemie. Nach J. H. Van't HoflTs, "Dix Annees dans Thistoire d'une theorie." Unter Mit- wirkung des Verfassers neu bearbeitet. Leipzig und Wien. 1892. *OSTWALD, W. Ueber die Farbe der lonen. Leipzig. 1892. *REMSEN, J. The Principles of Theoretical Chemistry, with special reference to the constitution of chemical compounds. 4th Edition. Philadelphia. 1892. * TAYLOR, R. L. The Student's Chemistry : being Outlines of Inorganic Chemistry and Chemical Philosophy. London, 214 BIBLIOGRAPHY. 1892. * WHITELEY, R. L. Chemical Calculations. With Explanatory Notes, Problems, and Answers. London. 1892. WILDE, H. On the origin of elementary substances and on some new relations of their atomic weights. Berlin. 1892. * WINDISCH, K. Die Bestimmung des Moleculargewichts in theoretischer und praktischer Beziehung. Berlin. 1893. ' ADRIANCE, J. S. Laboratory Calculations and Specific Gravity Tables. 2d Edition. New York. 1893. BERTHELOT, M. Traite pratique de calorime*trie chimique. Paris. 1893. DUHEM, P. Introduction a la mecanique chimique. Gand. 1893. HANTZSCH, A. Grundriss der Stereochemie. Breslau. 1893. MEYER, L. Grundziige der Theoretischen Chemie. 2d Edi- tion. Leipzig. 1893. NERNST, W. Theoretische Chemie vom Standpunkte der Avogadro'schen Regel und der Thermodynamik. Stuttgart. 1893. VAN LAAR, J. J. Die Thermodynamik in der Chemie. Leipzig. INDEX OF SUBJECTS. PAGE Absolute unit of force 156 Absolute unit of work 157 Absorption, coefficient of 144 Adhesion 158 Affinity, chemical 158 Affinity, coefficient of 164 Affinity, tables of 162 Agents, oxidizing 91 Aids in determining atomic mass 59 Aims of chemical philosophy 3 Aims of chemistry 3 Alchemists, notation of 29 Alchemy, age of 2 Algebraic method of writing chemical equations 97 Alloys 149 American system of spelling and pronunciation of chemical terms. 45 Analogues, atomic 139 Analysis of gases 128 Analysis, proximate 128 Analytical method of writing chemical equations 93 Anious 193 Anode 193 Areometers 13 Atom, definition 5 Atomic analogues. . . 139 Atomic heat 61 Atomic mass 53 Atomic mass, aids in determining 59 Atomic mass, determination of 57 Atomic mass, standards of 54 Atomic masses, table of 55 Atomic volumes, diagram of 141 215 216 ItfDE^X OF SUBJECTS. PAGE Avogadro, law of , 119 Baume areometers 14 Bauine degrees, true values of 15 Bergman's system .- 32 Berzelius on chemical symbols and nomenclature 40 Bibliography 202 Black's list of synonyms 33 Boiling-point, elevation of v 75 Boyle, law of , 18 Calorific intensity 174 Calorific power 173 Calhions 193 Cathode 193 Charles, law of 18 Chemical activity of light, measurement of 191 Chemical affinity 158 Chemical affinity, measurement of 161 Chemical affinity, nature of 159 Chemical calculations 89 Chemical decomposition, induced by light 187 Chemical equations 89, 90 Chemical equivalent 58 Chemical formulae 69, 89 Chemical philosophy, aims of 3 Chemical problems, calculation of 99 Chemical terms, oldest 29 Chemical union, induced by light 187 Chemism 159 Chemistry, aims of 3 Chemistry, origin and meaning of the term 2 Coefficient of absorption 144 Coefficient of affinity 164 Cohesion 1 58 Colloids 153 Combustion 173 Conductivity, equivalent 165 Conductivity, molecular. . , 165 Conservation of energy 157 Constituents of compounds, calculation of 100 Constitutional formulae 89 Crith, value of . 115 INDEX OF SUBJECTS. 217 PAGE Crystalloids 153 Curves, graphic . v 139 Dalton's symbols 39 Deductive sciences, definition 1 Depression of the freezing-point method 75 Determination of atomic mass 57 Determination of valence 66 Difference Method 108 Diffusion 150, 152 Dilute solutions 149 Dissociation, electrolytic.. 194 Dumas' Method 20 Dyne, the 156 Effusion method 19 Equations, energy , 183 Equivalent, chemical 58 Equivalent conductivity 165 Equivalent, electro-chemical 200 Electrical energy 193 Electrical units 196, 197, 198 Electrical units: quantitative relations 199 Electro-chemical equivalent * 200 Electro-chemistry 192 Electrodes 193 Electrolysis 193 Electrolyte 193 Electrolytic dissociation 194 Elevation of boiling-point method 75 Eudothermous compounds 181 Energy.. 5, 155 Energy, bound 162 Energy, conservation of 157 Energy, electrical 193 Energy-equations 183 Energy, free 162 Energ3 r , kinetic 157 Energy, measurement of 157 Empirical f ormulse 69, 89 Equations, chemical 89, 90, 93 Erg, the 157 Exothermous compounds 181 218 INDEX OF SUBJECTS. PAGE Explosions, method of 130 Force 155 Force, absolute unit of 156 Force, definition 5 Force, gravity unit of 156 Force, measurement of 155 Formulae, chemical 69, 89 Formulae, constitutional 89 Formulae, empirical 69, 89 Formula from percentage composition 101 Formulae, mineralogical 101 Formulae, molecular 71, 89 Formula, weight and volume 127 Freezing-point, depression of 75 French system of nomenclature 34 Gases, analysis of 128 Gases, determination of specific gravity ' . 20 Gases in gases, solution of 143 Gases in liquids, solution of 144 Gases in solids, solution of 145 Gases, table of 116 Gases, volume relations of 115 Geoffrey's symbols 31 Germanic system of nomenclature 39 Gramme-calorie 168 Graphic curves 139 Gravitation 158 Gravity unit of force 156 Gravity unit of work 157 Hassenfratz and Adet's symbols 37 Heat, latent 1 69 Heat, mechanical equivalent of 168 Heat, specific 1 69 Heat units 168 Henry's law 145 Hofmann's, von, method 24 Hydrogen, occluded 145 Hypothesis, definition 4 latro-chemistry, age of 2 Ice calorimeter method 170 Index notation, system of . . . , , , 198 INDEX OF SUBJECTS. 219 PAGE Indirect analysis, methods of 107 Inductive sciences, definition 1 Interchange, chemical, laws of 92 Invert-sugar solutions, action of light on, 189 Ion theory, the 193 Isomerism 84 Isomorphism 63 Kilogramme-calorie 168 Kinetic energy 157 Knowledge, definition 1 Laplace 161 Latent heat 169 Law of Avogadro 119 Law of Boyle or Muriotte 18 Law of Charles 18 Laws of chemical combination 52 Laws of chemical interchange 92 Law of definite proportions 52 Law of Henry 145 Law of multiple proportions 52 Law, periodic, the 133, 134 Law of volumes 119 Light, action on invert-sugar solutions 189 Light, chemical decomposition induced by 187 Light, chemical union induced by 187 Light, mode of action , 190 Light, physical changes induced by 189 Liquids in gases, solution of 145 Liquids in liquids, solution of 145 Liquids in solids, solution of 147 Lowering of vapor- pressure method 74 Magnetic rotation of polarized light 84 Manner of designating valence 65 Mariotte, law of 18 Mass, definition 5 Mass and volume in gases, relation between 124 Matter, definition 5 Maximum valence 68 Measurement of chemical affinity 161 Measurement of chemical activity of light 191 Measurement of energy , 157 220 I&DEX OF SUBJECTS. PAGE Measurement of force 155 Mecbauical equivalent of heat 168 Meudeleeffs predictions 139 Mendeleeff's table of atomic masses 136 Method of explosions 130 Methods of indirect analysis 107 Meyer, Lothar, table of atomic masses 138 Meyer's, V., method 26 Mineralogical formulae.. 101 Minimum valence 68 Mixtures, method of 171 Molecular conductivity 165 Molecular formulae 71, 89 Molecular mass, calculation of 99 Molecular mass, determination of 72 Molecular refraction 81 Molecular refraction-equivalent - 83 Molecular volume 79 Molecule, definition 5 Molecules, structure of 78 Motion, definition 5 Negative bond method of writing chemical equations 96 Newlands' table of atomic masses 135 Nomenclature in the seventeenth century 31 Nomenclature, French system of 34 Notation of the alchemists. . . 29 Occluded hydrogen 145 Osmose 150 Osmotic pressure 73, 150 Osmotic pressure, measurement of 151 Oxidizing agents 91 Percentage composition from formula 101 Periodic law, the 133, 134 Periodicity of properties of elements 142 Photo-chemistry 187 Photography 188 Physical changes induced by light , . . 189 Polarized light, magnetic rotation of 84 Predictions, Mendeleeff's 139 Present system of symbols and nomenclature 41 Pressure, osmotic. ... 73, 150 IXDEX OF SUBJECTS. 221 PAGE Properties of elements, etc. , periodicity of 142 Proximate analysis 128 Reducing agents 92 Refraction-equivalent, molecular 83 Refraction, molecular 81 Refractive power, specific 83 Relation between mass and volume in gases 124 Relations between specific gravity, degrees Bauine and Brix 15 Relations between specific gravity, mass and volume 8 Residue method 107 Rest, definition. > 5 Science, definition 1 Solids in gases, solution of 147 Solids in liquids, solution of 147 Solids in solids, solution of 149 Solutions 143 Solutions, dilute 149 Solution of gases in gases ; 143 Solution of gases in liquids 144 Solution of gases in solids 145 Solution of liquids in gases 145 Solution of liquids in liquids 145 Solution of liquids in solids 147 Solution of solids in gases 147 Solution of solids in liquids 147 Solution of solids in solids 149 Specific gravity, definition 7 Specific gravity of gases and vapors 17 Specific gravity of gases, determination of 19 Specific gravity of liquids 11 Specific gravity of solids 9 Specific gravity of vapors 20 Specific gravity, standards of 7 Specific heat 62, 169 Specific heat, determination of 169 Specific refractive power 82 Standards of atomic mass 54 Standards of specific gravity 7 Standard of valence 64 Stereo- chemistry 85, 86 Stoichiometry 5 222 INDEX OF SUBJECTS. PAGE Structure of molecules 78 Substitution method 108 Symbols of Hassenf ratz and Adet 37 Tables of affinity 162 Tables of atomic masses 55 Mendeleeff's 136 Meyer, Lothar 138 Newlands' 135 Table of gases, Wiechmann's 116 Temperature 167 Theory, definition 4 Thermal relations 167 Thermo-chemistry, language of 178, 181 Thermo-chemistry, laws of 179 Time method 172 Units, electrical 196 Valence 63 Valence, determination of *. 66 Valence, manner of designating 65 Valence, maximum 68 Valence, minimum 68 Valence, standard of 64 Valence, variable 65 Vapor-density, determination of 72 Vapors, specific gravity, determination of 20 Vapor-pressure, lowering of 74 Volumes, atomic, diagram of . . , 141 Volume, definition 5 Volumes, law of 119 Volume, molecular 79 Volume relations of gases 115 Von Hofmann's system of nomenclature 44 Weight and volume formula 127 Weight, definition ,. 5 Wiechmann's table of gases ,.r 116 Work, absolute unit of .-. 157 Work, definition 5 Work, gravity unit of 157 INDEX OF NAMES CITED. PAGE Adet 37 Arago 86 An henius 194 Avogadro 6 Baume 32 Bedson 137 Bergman 160, 163 Bernoulli 164 Bertbelot 179 Berthollet 35, 160, 163 Berzelius 6, 54, 160 Biot 86,88 Black 33,39 Bolton 46 Bottomley 97 Briihl 83 Bunseu 144,164, 191 Chandler, C. F 14 Clarke 54 Clausius 119, 164, 194 Cooke 133 Dalton 6, 52, 53, 54, 144, 145 Davy 39,160 Debus 164 Dobereiner 133 Draper 191 Dumas 133 Edison 200 Faraday 84, 165, 196 Fick 153 Fourcroy 35 Galileo 159 Gay-Lussac 6, 119,148, 161 223 224 INDEX OF NAMES CITED. PAGE Geber 29 Geoffroy 162 Gernez , 88 Gladstone 134, 164 Gmeliii 183 Graham 153 Greenaway 136 Guldberg 163, 164 Hart 46 Hasseu fratz 37 Helmholtz, vcm 162, 165 Hofmaiiu, vou 44 Homberg 6 Howe 46 Humboldt, von 6, 119 Johnson 96 Joule 160, 164 Kainensky 136 Kirwau 163 Kohlrausch . 165, 200 Kopp 79 Kremer 133 Landolt , 83 Lavoisier 6, 35, 52, 161 Le Bel 86, 88 Liebig, von 189 Lorentz 82 Lorenz 82 Lorenz, von 16 Macquer 32 Mascart 200 Maxwell 164 Mayer 160 Mendeleeff 134, 136, 139 Meyer, L 135, 137 Mitscherlich 63 MOller 148 Morveau, de 34, 161 Muir 147, 164, 180 Newlands , 134 Newton.. . 160 INDEX OF NAMES CITED. 225 PAGE Norton 46 Olding 133 Ostwald 54, 144, 147, 164, 165 Perkins 84 Pettenkofer 133 Pfaundler 164 Pfeffer 151 Priestley 189 Proust 6, 52 Quesneville 41 Rayleigh, Lord 200 Regnault 145 Remseu 66 Reusch 86 Richter, J. B 6 Rose, H 164 Roscoe 191 Schwanert 97 Seuebier 191 Sorby 148 Button 131 Thompson, S. P 198, 201 Thoinseu, J 180 Thomson, Sir W 165 Thomson 6, 39 Van Helmont 6 Van'tHoff 86, 87, 88, 150, 151, 164 Von Helmholtz 162, 165 Von Hof mann 44 Von Humboldt 6, 119 Von Liebig 189 Von Lorenz 16 Waage 163, 164 Weber 153 Wenzel 6, 161 Wiechmann 14, 17, 116, 189 Williams , 137 Williamson 164, 194 Wilson 180 Wislicenus 85 Wurtz.. 66 14 DAY USE RETURN TO DESK FROM WHICH BORROWED LOAN DEPT. This book is due on the last date stamped below, or on the date to which renewed. Renewed books are subject to immediate recall. LD 21A-50m-8,'57 (C8481slO)476B General Library University of California Berkeley IA 237367