GIFT OF W B. RISING- Y'V 2 * T PRINCIPLES CHEMICAL PHILOSOPHY, JOSIAH P. COOKE, JR., AXD XDXBJLL06T ILLET.LD THIRD EDITION, BEVI5ED AND COBEECTED, BOSTON: JOHX ALLYX. PUBLISHER, LATE SEVER, FRANCIS, A CO. 1874. Entered according to Act of Congress, in the year 1871, by JOS1AH P. COOKE, JR., in the Clerk's Office of the District Court of the District of Massachusetts. CAMBRIDGE : PRE88WOBK BY JOHN WILSON AND SON. PREFACE TO THE SECOND EDITION. THE object of the author in this book is to present the phi- losophy of chemistry in such a form that it can be made with profit the subject of college recitations, and furnish the teacher with the means of testing the student's faithfulness and ability. With this view the subject has been developed in a logical order, and the principles of the science are taught indepen- dently of the experimental evidence on which they rest. It is assumed that the student has already been made familiar with this evidence, and with the more elementary facts which the philosophy of the science attempts to interpret. At most of our American colleges this instruction is given in a course of experimental lectures ; but for less mature students a course of manipulation in the laboratory will be found a far more effi- cient mode of teaching, and some preliminary training of this kind ought to be made one of the requisites for admission to our higher institutions of learning. 1 The author has found by long experience that a recitation on mere facts, or descriptions of apparatus and experiments, is to the great mass of college undergraduates all but worthless, while the study of the phi- losophy of chemistry may be made highly profitable both for instruction and discipline. It must never be forgotten, how- ever, that chemistry is peculiarly an experimental science, and that the chief value of its culture in a college course depends on the facilities which it affords for cultivating the power of observation, and for teaching the methods of experimental in- l For such a course of practical study the student can desire no better guide than the excellent work of Professors Eliot and Storer, recently published, " A Manual of Inorganic Chemistry, arranged to facilitate the Experimental Demonstration of the Facts and Principles of the Science." By C. W. Eliot and F. H. Storer. New York, 1868. 237516 iv PREFACE. vestigation. It is not to be expected or desired that many of our college graduates should become professional chemists, but it is all important that every man of culture should understand or at least appreciate the methods and the inductive logic of physical science. The elementary facts of chemistry can be efficiently taught only by leading the student to observe for himself the phenomena in which they appear, and the attempt to learn them memoriter from a text-book will not only fail in its immediate object, but miss the chief end of scientific study. The author, therefore, would most earnestly deprecate the use of this book except as supplementary to some course of labora- tory or lecture-room instruction. It is only after the student has become, in some limited measure at least, familiar with chemical phenomena, that he is prepared to study the science in a systematic way ; but all who have this preparation will acquire most rapidly a general knowledge of the whole field when the subject is presented in a condensed and deductive form. The author has had especially in view this class of stu- dents, and has endeavored to meet their wants. Part I. of the book contains a statement of the general laws and theories of chemistry, an explanation of its nomenclature and mode of symbolical notation, together with so much of the principles of molecular physics as are constantly applied in chemical investigations. It might be figuratively called a grammar of the science. It is intended to be studied inde- pendently in consecutive lessons, and is adapted for class-room recitations, which should be accompanied, however, by such experiments or further explanations as the teacher may find necessary to render the subject intelligible. Part II. of the book presents the scheme of the chemical elements. It should only be studied in connection with exper- imental lectures or laboratory work, and will be found chiefly usefnl for systematizing and reviewing the facts and phenomena observed in the lecture-room or laboratory. It is in fact a note- book intended to aid the student in gaining the greatest benefit from a course of systematic lectures, enabling him to insure the accuracy of his knowledge, and giving the teacher the means of testing the student's acquirements. The value of problems as means of culture and tests of at- tainment can hardly be overestimated, and they have therefore PREFACE. V been made a chief feature in this book. Since those which are here given are chiefly intended as guides to the student, the answers have always been added ; and where the method was not obvious, the chief steps in the solution have been given as well. Every teacher will be able to multiply problems after these models to suit his own requirements. The questions, which accompany the problems, form another essential feature in the plan of instruction here presented. They are intended not only to direct the student's attention to the most important points, but also to stimulate thought by sug- gesting inferences to which the principles stated legitimately lead. These questions, moreover, will indicate to the teacher the manner, in which it is intended that the book should be studied. Care should be taken not to overstrain the memory, but to dis- tribute the necessary burthen through many lessons. Thus, for the first seven chapters, the student should not be expected to reproduce the symbols and reactions, nor even to call the names of the substances represented, except those of the sub- stances with which he is familiar. It will be sufficient for the time if he understands the principles which the symbols illustrate, and the relations of the parts of the reactions, al- though as yet these conventional signs may have for him no more definite meaning than the paradigms of a grammar. As he advances through chapters VIII. and IX., he should be expected to familiarize himself with the names of the com- pounds, and should begin to reproduce the symbols. "When reciting on chapter X. he should be called upon to give not only the names of all the symbols, but also the symbols corre- sponding to all the names, and so on for the rest of the book. In reviewing the book a full knowledge of the names and sym- bols will be of course expected from the first. The questions and problems appended to each chapter will give the student a clear idea of what, in any case will be required* The author has been in the habit of writing out, for his own class, similar problems on separate cards, together with the names, symbols, reactions or other data< which may in any case be given. These cards are distributed at the beginning of each recitation, and the student is not called upon to recite until he has placed his work upon the blackboard. This plan obviates many prac- tical difficulties, and has been found to work with great success. vi PEEFACE. ' In arranging the chapters of Part I. the only aim has been to present the several subjects in a logical sequence, and in other respects the order adapted is not always the most philo- sophical; but the teacher can of course vary the order at pleasure. So also in regard to Part II., the teacher may pre- fer to take up the elements in his lectures in a different order from that in which they are there classified, but then the sev- eral sections may be studied in any order he would be likely to adopt with equal advantage. The philosophy of chemistry has been developed in this book according to the " modern theories " ; and the author would acknowledge his obligations to the recent works of Frankland, Kekule, Miller, Naquet, Roscoe, Watts, William- son, and Wurtz, all of which he has freely consulted. Care- ful attention has been given to the chemical notation ; and a method has been devised of writing rational symbols which, while it fully exhibits the relations of the parts of the mole- cule, condenses the formula, and saves space and labor in printing. The nomenclature adopted accords with what the author regards as the best English usage. Innovations would hardly be justified in an elementary work, but every one must regret that the usage is not more uniform and consistent with the modern chemical philosophy. In the chapter on this sub- ject, the old names are given with the new. Lastly, the me- tric system of weights and measures, and the centigrade saale of the thermometer, are used throughout the book. In reviewing the work for a new edition, the chapter on the Electrical Relations of the Atoms has been rewritten, and the facts presented in the light of a new theory, which it is hoped will bring them into more intelligible relations. Important additions have also been made to the chapters on Stochiometry and Chemical Equivalency, and a new chapter has been added which treats of a number of interesting but highly complex compounds that were not included in the general plan of the book, and may be more advantageously studied in an appen- dix. Moreover, throughout the book the text has been altered wherever corrections have been made necessary by the recent progress of the science. CAMBRIDGE, September 1, 1871. CONTENTS. PAET I. CHAPTER I. INTRODUCTION 1 II. FUNDAMENTAL CHBMICAL RELATIONS ... 7 III. MOLECULES 11 IV. ATOMS . 24 V. CHEMICAL NOTATION 33 VI. STOCHIOMETRY 41 VII. CHEMICAL EQUIVALENCY 54 VIII. CHEMICAL TYPES 62 IX. BASES, ACIDS, AND SALTS 80 X. CHEMICAL NOMENCLATURE 100 XI. SOLUTION AND DIFFUSION 107 XII. THERMAL RELATIONS OP THE ATOMS .... 114 XIII. MOLECULAR WEIGHT AND CONSTITUTION . . .126 XIV. CRYSTALLINE FORMS 137 XV. ELECTRICAL RELATIONS OF THE ATOMS . . .155 XVI. RELATIONS OF THE ATOMS TO LIGHT . . .174 XVII. CHEMICAL CLASSIFICATION . . . .191 viii CONTENTS. PART II. CHAPTER PAGB XVIII. THE PERISSAD ELEMENTS 201 DIVISION I. Hydrogen 201 " II. Fluorine. Chlorine. Bromine. Iodine 207 '* III. Sodium. Potassium . . . . .213 " IV. Silver * 220 " V. Thallium . . 222 VI. Gold , 222 " VII. Boron 228 " VIII. Nitrogen. Phosphorus. Arsenic. Anti- mony. Bismuth 233 " IX. Vanadium 291 " X. Uranium 293 " XI. Columbiura. Tantalum 296 XIX. THE ARTIAD ELEMENTS . . . . . . . 300 DIVISION I. Oxygen . 300 " II. Sulphur. Selenium. Tellurium . . 308 " III. Molybdenum. Tungsten . . . .321 " IV. Copper. Mercury 328 " V. Calcium. Strontium. Barium. Lead . 340 " VI., VII. Magnesium. Zinc. Indium. Cadmium 354 " VIII., IX. Glucinum. Yttrium. Erbium. Ceri- um. Lanthanum. Didymium . . . 363 " X. Nickel. Cobalt 365 " XL Manganese. Iron 373 " XII. Chromium 398 " XHI. Aluminum 408 " XIV. to XVI. The Platinum Metals. Ruthenium. Osmium. Rhodium. Iridium. Palladium 418 " XVII. to XIX. Titanium. Tin. Zirconium . . 430 " XX. Silicon 444 " XXI. Carbon. Carbon and Oxygen, or Sulphur. Carbon and Nitrogen. Carbon and Hydro- gen. Alcohols and their Derivatives . . 458 XX. APPENDIX. Complex Amines and Amides, Chlorals, Mellitic Acid, Quinones, Electrical Measurements . 534 TABLE I. French Measures, " II. Elementary Atoms. " III. Specific Gravity of Gases and Vapors. LOGARITHMS AND ANTILOGARITHMS FIRST PRINCIPLES OP CHEMICAL PHILOSOPHY. PAKT I. CHAPTER I. INTRODUCTION. 1. Definitions. The volume of a body is the space it fills, expressed in terms of an assumed unit of volume. The weight of a body, as the word is used in chemistry and generally m common life, is the amount of material which the body con- tains compared with that in some other body assumed as the unit of weight. The specific gravity/ of a body is the ratio of its weight to that of an equal volume of some substance which has been selected as the standard. Solids and liquids are al- ways compared with water at its greatest density, which is at 4 centigrade, and hence the numbers which stand for their specific gravities express how many times heavier they are than an equal volume of water at this temperature. Gases, however, are most conveniently compared with the lightest of all known forms of matter, namely, hydrogen, and in this book the number which indicates the specific gravity of a gas ex- presses how many times heavier it is than an equal volume of hydrogen, compared under the same conditions of temperature and pressure. 2. Volume and Weight. All experimental science rests upon accurate measurements of these fundamental elements, and it is therefore very important that there should be a gen- eral agreement among scientific men in regard to them. This 1 has been secured by the almost universal adoption of the French system of measures and weights in all scientific inves- tigations. The details of this system are given in Table I., and they require no further explanation. Its great advan- tage over our ordinary English system is not only in its deci- mal subdivision, but also in the simple relation which exists between the units of measure and of weight. Since the unit of weight is the weight of the unit volume of water, and since the specific gravity of solids and liquids is always referred to water, as the standard, it is always true in this system that W= VX Sp. Gr. [1] If the volume is given in cubic centimetres, the weight ob- tained is in grammes ; but if the volume is given in cubic deci- metres or litres, the weight is found in kilogrammes. In this formula, Sp. Gr. stands for the specific gravity referred to water. If the specific gravity is referred to hydrogen, as in the case of gases, the value must be reduced to the water- standard before using it in the formula. The reduction is easily made, by multiplying by 0.0000896, a fraction which is simply the specific gravity of hydrogen itself referred to water. Using Sp. Gr. to represent the specific gravity of a gas referred to hydrogen, the formula becomes W= V X Sp. Gr. X 0.0000896, [2] and may then be used in all calculations connected with the weight and volume of aeriform bodies. In such calculations, in order to avoid the long decimal fractions which the use of the gramme entails, Hofmann has proposed to introduce into chemistry a new unit of weight which he calls the crith. This unit is the weight of one cubic decimetre or litre of hydrogen gas at the standard temperature and pressure, and is equal to 0.0896 grammes. If now we estimate the weight of all gases in criths, and let W represent this weight, while W represents the weight in grammes, and V the volume in litres, we shall also have W = V X Sp. Gr. and W = W X 0.0896, [3] and all problems of this kind will then be reduced to their simplest terms. INTRODUCTION. 3 The specific gravity of gases is also frequently referred to dry air, which for many reasons is a convenient standard. The weight of one litre of air under standard conditions is 1.293187 grammes. Hence, representing specific gravity re- ferred to air by Sp. (B>r. we have Sp. Gr. : Sp. (Sr. = 1.2932 : 0.0896, or Sp. Gr. = Sp.<>r. X 14.42, and Sp. <&r. Sp. Gr. X 0.06929. 3. Chemistry and Physics. Among material phenomena we may distinguish two classes. First, those which are mani- fested without a loss of identity in the substances involved. Secondly, those which are attended by a change of one or more of the materials employed into new substances. The science of chemistry deals with the last class of phenomena, that of physics with the first, and hence the terms chemical and physical phenomena. An illustration will make this dis- tinction plain. When a bar of iron is drawn out into wire, is rolled out into thin leaves, is reduced by mechanical means to powder, is forged into various shapes, is melted and cast into moulds, is magnetized, or is made the medium of an electric current, since the metal does not in any case lose its identity, the phenomena are all physical. When, on the other hand, the iron bar rusts in the air, is burnt at the blacksmith's forge, or is dissolved in dilute sulphuric acid, the iron is converted into a new substance, iron rust, iron cinders, or green vitriol, and the phenomena are chemical. The distinction between these two departments of human knowledge is not, however, so strongly marked as the definition would seem to imply. In fact they coalesce at many points, and a knowledge of the elements of physics is an essential preliminary to the successful study of chemistry. In the following pages it will be assumed that the student is acquainted with the most elementary princi- ples of this science, and references will be made to the sections of the author's work on Chemical Physics. The same rela- tion which physics bears to chemistry on the one side, chemis- try bears to physiology and the natural-history sciences on the other. 4 INTRODUCTION. Questions and Problems. 1. Reduce by Table I. at the end of the book, 30 Inches to fractions of a metre. Ans. 0.7619 metre. 76 Centimetres to inches. Ans. 29.92 inches. 36 Kilometres to miles. Ans. 22.38 miles. 10 Metres to feet and inches. Ans. 32 ft. 9.7 inches. 1 Cubic metre to quarts. Ans. 880.66 quarts. 1 Cubic foot to litres. Ans. 28.31 litres. 1 Pint to cubic centimetres. Ans. 567.8 cTmT, 3 1 Litre to cubic inches. Ans. 61,027 cubic inches. 1 Pound Avoirdupois to grammes. Ans. 453.6 grammes. 1 Kilogramme to ounces avoirdupois. Ans. 35.27 ounces. 1 Ounce to grammes. Ans. 28.35 grammes. 2. If the globe were a perfect sphere what would be the circum- ference and what the diameter in kilometres ? Ans. Circumference 40,000 kilometres) Diameter 12,732.4 " 3. The length of the metre was determined by measuring the dis- tance between Dunkirk (in France), Latitude 51 2' 9" and For- mentera (one of the Balearic Islands), Latitude 38 39' 56", both on the same meridian. This distance was found by triangulation to be equal to 730,430 toises. What is the length of a metre in terms of this old French unit of measure ? What, also, was the length measured in English miles ? No account is to be taken of the ellip- ticity of the earth. Ans. The metre, 0.5314 toise. The length was 854 miles. 4. The Sp. Gr. of iron is 7.84. What is the weight of 10 c.~m. 3 of the metal in grammes ? What is also the weight in kilogrammes of a sphere of iron whose diameter equals one decimetre ? Ans. 78.4 grammes and 4.105 kilogrammes. 5. What is the weight in grammes of 50 c. in. 3 of oil of vitriol, when the Sp. Gr. of the liquid is 1.8? Ans. 90 grammes. 6. The Sp. Gr. of alcohol being 0.8, what volume in litres would weigh 7.2 kilogrammes? Ans. 9 litres. 7. Assuming that the earth is spherical, and its mean Sp. Gr. 5.67, what would be its weight, using as the unit of weight a kilometre cube of water at its greatest density ? Ans. 6,130,000,000,000. 8. Determine the Sp. Gr. of absolute alcohol from the following data: weight of empty bottle 4.326; weight of same filled with water 19.654 ; weight of same filled with alcohol 16.741. Ans. 0.8095. INTRODUCTION. 5 9. Determine the Sp. Gr. of lead from the following data : weight of bottle filled with water 19.654; weight of lead shot 15.456 ; weight of bottle filled in part with the shot and the rest with water 33.766. Ans. 11.5. 10. Determine the Sp. Gr. of iron from : weight of iron in air 3.92 , weight under water 3.42. Ans. 7.84. 11. Determine Sp. Gr. of wood from : weight of wood in air 25.35 ; weight of sinker under water 9.77 ; weight of wood with sinker under water 5.10 grammes. Ans. 0.8445. 12. How much volume must a hollow sphere of copper have, weighing one kilogramme, which will just float in water ? What must be the volume of the copper ? Sp. Gr. of copper 8.8. Ans. One cubic dicemetre and 113.6 c. m. 3 13. How much volume must a hollow cylinder of iron have, which weighs 10 kilogrammes and sinks one half in water, and what must * be the volume of the metal ? Ans. 20 and 1.276 cubic decimetres. 14. What is the weight in grammes (under standard conditions) of 128 c.~m. 3 of oxygen gas (Sp. Gr. = 16) ? Ans. 0.1834 grammes. 15. How many litres of carbonic anhydride gas (Sp. Gr. = 22) would weigh (under normal conditions) 4.480 kilogrammes? Ans. 2274 litres. 16. Solve the last two problems by [3], and show in what respect the method differs from that indicated by [2]. 1 7. What is the weight in criths (under standard conditions) of one litre of nitrogen gas (Sp. Gr. = 14), of one litre of chlorine gas (Sp. Gr. = 35.5), of one litre of marsh gas (Sp. Gr. = 8), and of one litre of ammonia gas (Sp. Gr. = 8.5) ? Ans. 14, 35.5, 8, and 8.5 criths respectively. 18. What is the weight in grammes of one litre of each of the same gases under the same conditions ? Ans. 1.254, 3.180, 0.7165, and 0.7617 respectively. 19. The weight of one litre of hydrochloric acid gas is 1.642 grammes ; of carbonic oxide gas 1.2500 grammes; of cyanogen gas / 2.335 grammes, and of hydrogen gas 0.0896 grammes. What is the specific gravity of each of these gases referred to air ? Ans. 1.270, 0.9665, 1.806, and 0.0693 respectively. 20. What is the volume (under standard conditions) of 12.54 grammes of nitrogen gas, when specific gravity referred to air is 0.9703? Ans. 10 litres. 6 INTRODUCTION. 21. What is the weight of one litre of air in criths? Ans. 14.42. 22. What would be the ascensional force of one thousand litres of hydrogen, under normal conditions ? Ans. The ascensional force is the difference between the weight of the hydrogen and that of the air displaced. Hence in the present example, the ascensional force would be 14,420 1000 = 13420 criths, or 1,201 grammes. 23. What is the value of a crith in grains, English weight. Ans. 1.382 grains. CHAPTER II. FUNDAMENTAL CHEMICAL RELATIONS. 4. Compounds and Elements. With sixty^three exceptions, all known substances, by various chemical processes, may be decomposed, and hence are called chemical compounds; while the sixty-three substances which have as yet never been resolved into simpler parts are called chemical elements. There is some reason for believing that many, if not all, of these elementary substances may hereafter be decomposed, and hence they can only be considered chemical elements provis- ionally ; but, however this may be, all known materials may still be regarded as formed by the union of the particles of one or more of these sixty-three substances. A list of the chemical elements is given in Table II. The names of the more abun- dant, or otherwise more important elements are printed in Ro- man letters. The others are very rare substances^ and are practically unimportant. Of these elementary substances more than three fourths possess metallic properties, and among them are all the useful metals, including the liquid metal mercury. The rest present every variety of physical character. Oxygen, hydrogen, and nitrogen are permanent gases. Chlorine, and probably fluorine, though gases under ordinary conditions, may by pressure and cold be condensed to liquids. Bromine is a very volatile liquid ; and among the solids we have every gra- dation between the highly volatile iodine, or the easily fusible phosphorus, on the one hand, and carbon, which has never even been melted, on the other. We find, also, among the ele- ments every difference as regards density. Hydrogen gas is the lightest, and the metal platinum the heaviest substance known. Several of the elementary substances occur in a free state in nature, for example, oxygen and nitrogen in the at- mosphere, carbon in the coal beds, sulphur in the neighborhood of active volcanoes, iron in meteoric stones, while arsenic, an- 8 FUNDAMENTAL CHEMICAL RELATIONS. timony, bismuth, copper, gold, silver, mercury, and platinum, with a few other rare associates, are sometimes found In a more or less pure state in metallic veins. Gold and platinum are usually found in a free condition, though as a rule slightly alloyed with their associated metals ; but all the other elements are generally found in combination, and the greater number appear in nature only in this condition. From such compounds the elements may be extracted by various chemical processes, which will appear as we proceed. Among these elements the useful metals are the tools of civilization, carbon is our uni- versal fuel, while sulphur, phosphorus, arsenic, chlorine, bro- mine, and iodine have found important applications in the arts, and are therefore articles of commerce ; but the greater number of the elements are only to be seen in the chemist's laboratory, and are solely objects of chemical investigation. The elements are distributed in nature in very unequal proportions. At least one half of the solid crust of the globe, eight ninths of the water on its surface, and one fifth of the atmosphere which surrounds it, consist of the one element, oxygen. Moreover, the other elements are usually found in combination with oxygen, so that oxygen may be regarded as the cement by which these elementary parts of the world are held together. Next in abundance is silicon, which, after oxygen, is the chief constituent of the rocks, and makes up about one fourth of the earth's crust. Silicon is always found combined with oxygen, and more than one half of the oxygen of the globe is in com- bination with this element. Hence, the compound of the two, which we call silica or quartz, must make up more than one half of our solid globe, at least as far as its composition is known. After silicon in the order of abundance would follow the elements aluminum, calcium, magnesium, potassium, so- dium, iron, carbon, sulphur, hydrogen, chlorine, nitrogen, which, without attempting to discriminate between them, make up altogether very nearly the other fourth of the earth's mass ; for the remaining fifty elements including all the useful metals except iron do not constitute altogether more than one one-hundredth. Of the sixty-three known elements, then, thirteen alone make up at least -^j of the whole known mass of the earth. 5. Analysis and Synthesis. The composition of a chemical FUNDAMENTAL CHEMICAL RELATIONS. 9 compound may be made evident in two ways. First, by break- ing up the compound into its constituent parts ; secondly, by reuniting these parts and reproducing the original substance. The first of these methods of proof is called analysis, the sec- ond, synthesis. The study of the processes by ^vhich the com- position of a body may be discovered, and the relative amounts of its various constituents determined, forms an important branch of practical chemistry, which is known as Chemical Analysis, and this is subdivided into Qualitative and Quantita- tive Analysis, according to the object we have in view. Syn- thesis is chiefly used to prove the results of analysis. 6. Law of Definite Proportions. Numberless analyses have proved that any given chemical compound always contains the same elements combined in the same proportions. Thus, when we analyze water, sugar, and salt, we always obtain the result given below ; and this result is invariable, saving small errors of observation, from whatever source these materials may be drawn. The composition is given in per cents, as is usual in such cases. Water (Dumas). Salt. Sugar (Peligot). Hydrogen, 11.112 Sodium, 39.32 Carbon, 42.06 Oxygen, 88.888 Chlorine, 60.68 Hydrogen, 6.50 Oxygen, 51.44 100. 100. 100. Chemists have not yet succeeded in making sugar by com- bining its elements, but the synthesis both of water and salt is easily effected, and illustrates still more forcibly the same law. Thus we may mix together hydrogen and oxygen gas in any proportion, but when, by passing an electric spark through the mixture, we cause the elements to combine, then the gases unite in the exact proportion indicated above, and any excess of one or the other which may be present is left over. The law of definite proportions gives to chemistry a mathematical basis ; for, since the analyses of all compounds have been made and tabulated in a way that will be soon explained, it is always possible, when the weight of a compound is given, to calculate the weights of its constituents, and, when the weight of one of its elements is known, to calculate the weights of all the other elements present. 10 FUNDAMENTAL CHEMICAL RELATIONS. 7. Mixture and Chemical Compound. The law of definite proportions gives a simple criterion for distinguishing between a mixture and a true chemical compound. In the first the ele- ments may be mixed in any proportion, but in the true com- pound they are always combined /in definite proportions. Thus we may mix together copper-filings and sulphur in any propor- tion, but as soon as we apply heat, and cause the elements to combine, then the copper combines with one half of its own weight of sulphur, and the excess of either element above these proportions is discarded. Again, in a mixture however homogeneous, we can generally, by mechanical means alone, distinguish the ingredients. Thus, in the mixture just referred to, a microscope would show the grains of sulphur and metallic copper, with all their characteristic appearances ; and by means of carbonic sulphide we can easily dissolve out all the sulphur from the mixture ; but after the chemical union has taken place, the characteristic properties of the elements are merged in those of the compound, and no such simple mechanical sep- aration is possible. But although these distinctions are gener- ally sufficient, nevertheless we find in some alloys, in solutions, and in a few other classes of compounds, less intimate condi- tions of chemical union where these criterions fail. 8. Law of Multiple Proportions. It is generally the case that the same elements unite in more than one proportion, form- ing two or more different compounds. Now we always find that the proportions of the elements in such compounds are simple multiples of each other. This law is best illustrated by the compounds of nitrogen and oxygen, which are five in number, and have the names indicated in the table below. In order to make evident the law, we give, not the percentage composition as above, but the amount of oxygen, which is in each case combined with one and three fourths parts of nitro- gen. COMPOUNDS OF NITROGEN WITH OXYGEN. Nitrogen. Oxygen. Nitrogen. Oxygen. By -weight. By weight. By volume. By volume. Nitrous Oxide, 1.75 1 2 1 Nitric Oxide, 1.75 2 2 2 Nitrous Anhydride, 1.75 3 2 3 Nitric Peroxide, 1.75 4 2 4 Nitric Anhydride, 1.75 5 2 5 CHAPTER III. MOLECULES. 9. Molecules. In order to bring the facts of chemistry into relation with each other, and unite them in an harmonious sys- tem, the following theory, first proposed by the English chemist, Dalton, and known as the Atomic Theory, is generally accepted by chemists. This theory assumes, in the first place, that every body, whatever its substance may be, is formed by the aggre- gation of minute particles of the same kind, which cannot be further subdivided without destroying the identity of the sub- stance. Thus a lump of sugar is an aggregate of minute particles of sugar. If the sugar is burnt, these particles will be further subdivided ; but the sugar will be thus changed into new substances. In like manner, a drop of water is an aggre- gate of minute particles of water. By passing a current of electricity through the drop, these particles will be subdivided, but then we shall have no longer water, but the two elemen- tary gases, oxygen and hydrogen. The smallest particles of any substance which can exist by themselves, we call molecules. 10. Physical Properties of Matter. The physical qualities of a body depend solely on the relations of its molecules. The physicist has therefore no occasion to continue the subdivision beyond the molecule, which is his unit. Solid. In a solid the molecules firmly cohere, and the force which binds them together has been called cohesion. On the form and size of the molecules, and also on the mode of aggregation, is supposed to depend the crystalline form of each substance, which is one of the most important and character- istic properties of matter, and one to which we shall have occasion hereafter to refer. On certain relations of the mole- cules, which we do not fully understand, depend undoubtedly elasticity, tenacity, ductility or malleability, hardness, transpar- ency, diathermancy, and the allied qualities of solid bodies. 12 MOLECULES. Liquid. In the liquid condition of matter the molecules have more freedom of motion than in the solid, but still the motion is circumscribed within the liquid mass. Moreover, a certain cohesion still exists between the molecules, and on this depends the form of the rain-drop. The various phenomena of capillary action also are effects of the cohesion of the liquid molecules modified by their adhesion to the surfaces of solids, and the solvent power of liquids is a still further effect of the same mutual action. Connected also with this freedom of molecular motion is the property of liquids of transmitting pressure in all directions, and the well-known principles of hydrostatics to which it leads; but this property belongs to the third condition of matter as well. Gas. In the aeriform condition of matter, the motion of ihe molecules is only circumscribed by the walls of the con- taining vessel, or by some force acting on the mass from with- out. The molecules of a gas are constantly beating against the walls which confine them, and were they not thus restrained would fly off into space. The molecules of the atmosphere are restrained by the force of gravitation, and, as they fly up- wards like a ball thrown into the air, they are at last brought to rest, and fall back again to the earth. Hence gases always exert pressure against any surface with which they are in con- tact, and we measure the pressure, or, as we frequently call it, the tension of the gas, by the height to which it will raise a column of mercury. Chem. Phys. (158). The instrument used for this purpose is called a barometer. The height of the mercury column which represents the pressure or tension of a gas is always represented by H. In our latitude, at the surface of the sea, the atmosphere in its normal conditions will raise a column of mercury 76 c. m. high. Hence If = 76, and to this standard we always refer in comparing together the volumes of different gases. 11. Mariotte's Law. The most characteristic feature of the aeriform condition is the great change of volume which gases undergo, under varying pressure, and the special law of compressibility which they obey. If we represent by If and H' two conditions of pressure to which the same body of gas is at different times exposed, then the law is expressed by the formula V: V' H':H. [4] MOLECULES. 13 Moreover, since the specific gravity of a given mass of gas must be the greater the less its volume, it is also true that Sp. Gr. : Sp. Gr 1 . = H: H>, [5] and lastly, since the weight of a given volume of gas is obvi- ously proportional to its specific gravity, we also have W : W = H: H 1 , [6] in which W and W represent the weight of an equal volume of the same gas under the two pressures H and H'. 12. Heat a Manifestation of Molecular Motion. The effects of what we call heat are supposed to be merely mani- festations of the motion of the molecules of bodies. The greater the moving power of the molecule, the more forcibly it strikes against our nerves of feeling, and hence the more in- tense is the sensation of heat produced ; and to the condition of matter which produces this sensation we give the name of temperature. The greater the moving power of the molecules, the higher the temperature ; the less the moving power, the lower the temperature. Moreover, since by the very defini- tion all molecules at the same temperature are in the condition to produce the same sensation of heat, we must assume further, that, whatever their size or weight, they must all have, at the same temperature, the same moving power. The light mole- cule of hydrogen must move much faster than the heavy mole- cule of carbonic anhydride in order to produce the same effect. If now we represent the mass of any molecule by m, and by V its velocity at any given temperature, then the moving power will be represented by m F 2 , Chem. Phys. (42), and this will have the same value for every molecule at the same tempera- ture. With a few exceptions, all bodies expand with an in- creasing temperature, and in the case of mercury the change of volume is so nearly proportional to the change of tempera- ture that we may use the varying volume of a confined mass of this liquid as a measure of temperature. This is the sim- ple theory of the common mercurial thermometer, and in this book we shall refer all temperatures to the degrees of the cen- tigrade scale. These degrees are purely arbitrary ; but to each one corresponds a definite value of ^m F 2 , although we have not as yet been able to connect our arbitrary with our theoretical measure. 14: MOLECULES. When we increase the temperature of a body, we must of course increase the moving power of all the molecules, each by the same amount, and the sum of the moving powers which they thus acquire is the legitimate measure of the amount of heat which the body receives. Hence, while \m V 2 represents the temperature of a body, 2 m V 2 represents the whole amount of heat which it contains. Practically, however, we measure quantity of heat by an arbitrary standard, and we shall use in this book as our unit the amount of heat required to raise the temperature of a kilogramme of pure water from to 1 centigrade. This we call the Unit of Neat, and it has been found, by careful experiments, that this unit of heat represents an amount of moving power which is adequate to raise a weight of 423 kilogrammes one metre, or to do any other equivalent amount of work. 13. .Expansion by Heat. The amount of expansion which bodies undergo when heated has been carefully measured for many different substances, and the results are tabulated in all works on physics. Chem. Phys. Table XV. In each case is given the coefficient of expansion, which is the small fraction of its volume which a body increases when heated one centi- grade degree. If, now, K represents this fraction, V the initial volume, V the new volume, t the initial temperature, and f the new temperature, then, if we assume that the expansion is proportional to the temperature, we easily deduce the formula, Chem. Phys. (239), V' = V(l + K(t' t)). [7] This formula serves to calculate the change of volume both of solids and gases, which expand, nearly at least, proportion- ally to the temperature. The same, however, is not true of liquids, whose rate of expansion frequently increases, with the temperature, very rapidly ; and for such bodies we are obliged to use the following formula, which is of the general form in which every algebraic function may be developed, and is much less simple : V F(l + At + Bt* + Ct* + $c.). [8] In this formula, V represents the required volume at some temperature, t, and F", the volume at 0, which is assumed to V k^owu ; while A, B, G, &c., are numerical constants, which MOLECULES. 15 have been determined by experiment in the case of most liquids. Chem. Phys. (255). Both solids and liquids expand with irresistible force, and we have, therefore, only this one effect to consider in regard to the action of heat upon them. It is different, however, with gases. By enclosing a gas in a tight vessel, we can raise its temperature without changing its volume, except so far as the vessel itself becomes enlarged by the heat. The effect of the heat is, then, to increase the tension or pressure of. the gas. Hence, in the case of a gas, we may have two distinct effects ; first, an increase of volume, when the pressure is constant ; secondly, an increase of tension, when the volume is constant. The increased volume may always be calculated from the in- itial volume and difference of temperature, by means of the formula, V = F(l + 0.00366 (tf 0), [9] which differs from that just given only in that the numerical value has been substituted for K, this being the same for all gases. On the other hand, the increased tension may always be calculated from the initial tension, by means of the corre- sponding formula, H 1 = H(l + 0.00366 (tf 0), [10] in which ffaud H 1 stand for the heights of the mercury col- umns which measure the initial and final tension respectively. The last formula is easily deduced from the first, on the prin- ciples of Mariotte's law, stated above. Chem. Phys. (261) and [201]. Variations of temperature produce such important changes in the volume and specific gravity of all bodies, and especially of gases, that it becomes frequently essential, before compar- ing together different observations, to reduce them all to some standard temperature. Most scientific men use, as this stand- ard temperature, centigrade, and scientific measures are generally adjusted to this standard ; but 60 Fahrenheit, corre- sponding to 15.5 centigrade, is often a more convenient stand- ard, because it is nearer the mean temperature of the air, and is, therefore, not unfrequently employed. 14. Change of State. Many substances are capable of ex- 16 MOLECULES. isting in all the three conditions of matter. Now, we find that whenever a solid changes to a liquid, or a liquid to a gas, heat is absorbed ; and conversely, whenever a gas is liquefied, or a liquid becomes a solid, heat is evolved ; although, as a general rule, this change of state is accompanied by no change of tem- perature. Thus, one kilogramme of ice, in melting, absorbs 79 units of heat, although the temperature remains at dur- ing the change ; and when, by boiling, a kilogramme of water is converted into steam, under the normal pressure of the air, no less than 537 units of heat disappear, although the tem- perature both of the steam and of the water is constant at 100 during the whole period. On the other hand, when the steam is condensed or the water frozen, absolutely the same amount of heat is set free as was before absorbed. The heat thus ab- sorbed or set free is generally called the latent heat of the liquid or gas, and in the case of many substances the amount has been carefully measured. Chem. Phys. (277) and (299). Ac- cording to the theory we are studying, these effects are the direct results of the molecular condition of matter. The change of state must be accompanied by a change in the relative position of the molecules, or in their distance from each other ; and this change, in its turn, must be attended with a destruction or pro- duction of the moving power on which the effects of heat de- pend. Chem. Phys. (215 bis.). 15. Sources of Heat. The sun is the original source of almost all the heat we enjoy on the earth, for the effect of the earth's internal heat, at its surface, is at best very small, and all our artificial sources of heat have drawn their supply either directly or indirectly from the great central luminary. According to our theory the effect of the sun's rays is a simple result of the transfer of molecular motion from the sun to the earth, either by some unknown influence exerted from a distance, or else by an actual transfer of motion through the material particles of the ether, which is assumed to fill the in- tervening space. The great source of all artificial heat is com- bustion in its many forms, and this, as we shall hereafter see, is merely a clashing together of material molecules, and is neces- sarily attended with a great development of that moving power to which we refer all thermal effects. 16. Specific Heat. The amount of heat required to raise MOLECULES. 17 to the same extent the temperature of equal weights of differ- ent substances is by no means the same. The quantity is capa- ble in any case of exact measurement, and is called the specific heat of the substance. The amount of heat required to raise the temperature of one kilogramme of water one centigrade degree has been assumed as the unit, and we express the specific heat of other substances in terms of this measure. Moreover, since with the exception of hydrogen the specific heat of water is greater than that of any substance known, the specific heat of all other bodies must be expressed by fractional numbers. In every case, unless otherwise stated, the numbers indicate what fraction of a unit of heat would be required to raise the temperature of one kilogramme of the substance from to 1 centigrade. Chem. Phys. (232). 17. Molecular Condition of Gases. The aeriform state is by far the simplest condition of matter, and there are two peculiarities in its properties which lead to important conclu- sions in regard to its molecular conditions. These character- istics are as follows : First, All true gases obey the same law of compressibility. Secondly, Equal volumes of all true gases expand equally on the same increase of temperature. Chem. Phys. (262). Now, according to the mechanical theory of heat ( 10) these peculiar relations of the aeriform condition of matter are best explained on the assumption that Equal volumes of all gases contain the same number of molecules; and since, moreover, this theoretical deduction harmonizes with almost all the facts of chemistry, it has been universally adopted as a fundamental principle of the science. This peculiar molecular condition, however, is only found in the gas, for it is only in this state that the molecules are sufficiently separated from each other to be freed from the mutual action of those molecular forces which give rise to far more com- plicated relations in both liquid and solid bodies. Moreover, with our ordinary gases (in the degree of condensation in which they exist under the pressure of the atmosphere), the molecules are not yet sufficiently far apart to be wholly freed from the effects of their mutual action, and hence the theo- retical condition is not absolutely fulfilled ; and in vapors, where the molecules are still closer together, the variation from the theory is quite large. In proportion as the gas ex- 2 18 MOLECULES. pands, the theoretical condition is approached, and, when in a state of great expansion, equal volumes of all gases would undoubtedly contain exactly the same number of molecules. It is only then that we reach the condition of what we have called above the true gas, and this is our criterion of its state, that it obeys absolutely the law of Mariotte. A very important corollary follows at once from the principle we have just de- duced. The molecular weight of all substances is directly propor- tioned to their specific gravities in the state of gas. We have adopted in this book hydrogen gas as our unit of specific gravity for aeriform substances, and were we also to take the molecule of hydrogen as our unit of molecular weight, then the number which expresses the specific gravity of a gas would express also its molecular weight. But for reasons which will appear hereafter, we have selected the half hydrogen molecule as our unit, and hence the molecular weight of any substance in terms of this unit is always twice its specific gravity in the state of gas. In Table III. we have given, according to the most accurate experimental data, the Sp. Gr. (referred to hydrogen) of all the best known gases and vapors, and in a parallel column we have also given the Half-molecular Weights of the same substances determined by chemical analysis, in a manner which will be hereafter described. It will be seen that the numbers in the second column are almost precisely the same as those in the first, and the slight differences which will be noticed, either arise from the fact that the vapors, under the conditions in which alone their Sp. Gr. can be accurately determined, are not true gases, that is, do not exactly obey Mariotte's law ; or in other cases, where the differences are more considerable, may be referred to a partial decomposition of the substance itself in the process of the experiment. In solving the problems of this book, and generally in most chemical problems, the Half-molecular weight may be taken as the true Sp. Gr. The logarithms of these values given in the last column of the table will be found useful in this connection. Although only given to four places of decimals, they exceed in accuracy the experimental data. The values in the column of 0p. (J$. referred to air, are given, as a rule, to one decimal place beyond the limit of error. MOLECULES. 19 Questions and Problems. 1. Are the qualities of a molecule of any substance, the same as those which distinguish the substance itself? 2. What is the distinction between cohesion and adhesion ? 3. When the barometer stands at 76 c. m., with what weight in grammes is the air pressing against each square centimetre of sur- face? Sp. Gr. of mercury 13.596. Ans. 1033. 4. To what difference of pressure does a difference of one centi- metre in the barometric column correspond ? Ans. 13.596 grammes. 5. When a mercury barometer stands at 76 c. m*. how high would a water barometer stand ? Also, how high would barometers stand filled with alcohol or sulphuric acid, disregarding in each case the tension of the vapor? Sp. Gr. of alcohol 0.81 ; Sp. Gr. of sulphuric acid 1.85. Ans. 1033; 1275 and 558.2 c. m. 6. A volume of hydrogen gas was found to be 200 c. m. 3 The height of the barometer observed at the same time, was 74 c. m. What would have been the volume if observed when the barometer stood at 76 c. m. Ans. 194.7 cTm: 3 7. A volume of nitrogen standing in a bell-glass over a mercury pneumatic trough measured 250 cTm". 8 The barometer at the time stood at 75.4 c. m., and the level of the mercury in the bell wa? found by measurement to be 6.5 above the surface of the mercury in the trough. Required to reduce the volume to standard pressure. Ans. The pressure of the air on the surface of the mercury in the trough (measured at 75.4 c. m.) was balanced first by the column of mercury in the bell, and secondly by the tension of the confined gas. Hence the pressure to which the gas was exposed was equal to 75.4 6.5 = 68.9 c. m. and we have 76 : 68.9 = 250 : x = 226.7 cTnT: 8 8. What would be the answer to the same problem, had the trough been filled with water ? Ans. The water column in the bell exerts a pressure which is as much less than the pressure of the mercury column in the previous problem, as the Sp. Gr. of water is less than the Sp. Gr. of mercury. Hence we have 13.6 : 1 = 6.5 : 0.48, also 75.4 0.48 = 74.92, and 76 : 74,92 = 250 : x = 246.4 cTm: 8 9. A closed vessel, which displaces one litre of air, is poised on a balance with weights, whose volume is inconsiderable when com- pared with that of the vessel. The balance is in equilibrium when 20 MOLECULES. the barometer stands at 76 c. m. If the barometer falls to 71 c. m. how much weight must be added to restore the equilibrium ? Ans. 85 milligrammes. 10. Given the weight of one litre of dry air under the normal conditions as 14.42 criths, what will be the weight of one litre of dry air at the normal temperature, but under a pressure of 72 c. m. ? Ans. 13.67 criths. 11. A volume of gas measures 500 c. m. 3 at 15 what will be its volume at 288. 2 ? In this and the next three problems the pressure is assumed to be constant. Ans. 1000 cHS: 3 12. To what Jemperature must an open vessel be heated before one quarter of the air which it contains at is driven out ? Ans. 9P.07. 13. An open vessel is heated to 819.6. What portion of the air which the vessel contained at remains in it at this temperature ? Ans. ^. 14. A closed glass vessel, which at 13 was filled with air having a tension of 76 c. m. is heated to 559.4. Determine the tension of the heated air. Ans. 3 atmospheres. 15. Reduce the following volumes of gas measured at the tem- peratures and pressure annexed to and 76 c. m. 1. 140 cTm. 3 H=57c. m. t = 136.6 Ans. 70 cTni. 3 2. 320 cTW #=95c. m. t= 91.l Ans. 300 cTm. 3 3. 480 .c~m; 3 H=38c. m. *= 68.3 Ans. 192 cTm. 3 16. What is the weight of dry air contained in a glass globe of 40 cTTS: 3 capacity at the temperature 546.4 and under a pressure of 71.25 c. m. Ans. 0.2583 grammes. General Solution. In order to make the solution general we will represent the capacity of the globe, the temperature and the height of the barometer by V, t and H respectively. We can also easily find from Table III. that one cubic centimetre of dry air at 0, and when the barometer stands at 76 c. m., weighs 14.42 criths or 0.001292 grammes. To find what one cubic centimetre would weigh when the barometer stands at H centimetres, we make use of proportion [6], whence we derive w = 0.001292 . 5, the weight of one cubic centimetre at and under a pressure of H centimetres. To find what one cubic centimetre would weigh MOLECULES. 21 under the same pressure but at t, it must be remembered that one cubic centimetre at becomes (1 -f- t 0.00366) cubic centimetres at t [7] ; therefore at t and at H centimetres of the barometer (1 -f- t 0.00366) 67W weigh 0.00129 . 3 grammes. By equating these two terms we obtain whence . (1 + * 0.00366)':= 0.00129 . 5 76 1 0.00129 - ' 1 -{-t 0.00366 * 76* the weight of one cubic centimetre at t and under a pressure of H centimetres. The weight of Y cubic centimetres (w) is evidently Thus far in this solution we have neglected the cha'nge in capacity of the glass globe due to the change of temperature. This causes no sensible error when the change of temperature is small, but when the change of temperature is quite large the change of ca- pacity of the globe must be considered. If the capacity is Y c. m. 3 at it becomes at t V (1 -f- t 0.00003). (See Chem. Phys. 241 - 244.) Introducing this value for Y into the above equa- tions we obtain = 0.00129 V (1 + t 0.00003) . . . [10 J] 1 7. Required a general method for determining the gtj. (g>r. of a vapor. Solution. The specific gravity of a vapor has been denned as its weight compared with the weight of the same volume of hydrogen gas under the same conditions of temperature and pressure, but practically it is most convenient to determine the m. (!$. with reference to air, and subsequently to reduce the result to the hydrogen standard. To find, then, the Sp. (J$r. of a vapor, we must ascertain the weight of a known volume, Y, at a known temperature, t, and under a known pressure, H, and divide this by the weight of the same volume of air at the same temperature, and under the same pressure. The method may best be explained by an example. Suppose, then, that we wish to ascertain the j;n ({$. of alcohol vapor. We take a light glass globe having a capacity of from 400 to 500 cTliT. 3 , and draw the neck out in the flame of a blast lamp, so as to leave only a fine opening, as shown in the figure at a. The first 22 MOLECULES. step is now to ascertain the weight of the glass globe when com- pletely exhausted of air. As this cannot readily be done directly, we weigh the globe full of air, and then subtract the weight of the air, ascertained by calculation from the capacity of the globe, and from the temperature and pressure of the air, by means of equation (10 a). Call the weight of the globe and air W, and the weight of the air 10, then W w is the weight of the globe exhausted of air. The second step is to ascertain the weight of the globe filled with alcohol vapor at a known temperature, and under a known pressure. For this purpose we introduce into the globe a few grammes of pure alcohol, and mount it on the support represented in the accompanying figure. By loosening the screw, r, we next sink the balloon beneath the oil contained in the iron vessel, V, and secure it in this position. We now slowly raise the temperature of the oil to between 300 and 400, which we observe by means of the thermometer, T. The alcohol changes to vapor, and drives out the air, which, with the excess of vapor, escapes at a. When the bath has attained the requisite temperature, we close the opening a, by suddenly melting the end of the tube at a with a mouth blowpipe, and as nearly as possible at the same moment observe the tempera- ture of the bath and the height of the barometer. We have now the globe filled with alcohol vapor at a known temperature, and under a known pressure. Since it is hermetically sealed, its weight cannot change, and we can therefore allow it to cool, clean it, and weigh it at our leisure. This will give us the weight of the globe filled with alcohol vapor at a known temperature, Z', and under a known pressure, H'. Call this weight W. The weight of the vapor is W' W -f- w. The third step is to ascertain the weight of the same volume of air at the same temperature and under the same pressure. This can easily be found by calculation from equa- tion (10 &). The last step is to find the capacity of the globe, which, although we have supposed it known, is not actually ascertained experimentally until the end of the process. For this purpose we break off the tip of the tube (a), under mercury, which, if the ex- periment has been carefully conducted, rushes in and fills the globe completely. We then empty this mercury into a carefully gradu- ated glass cylinder, and read off the volume. We find then the MOLECULES. 23 Gp. (!5t. by dividing the weight of the vapor by the weight of the au-. The formulas for the calculation are then Weight of the globe and air, W. " air, w = 0.001292 V . L- 1 + t 0.00366 76 " " globe exhausted of air, W w. " " ** filled with vapor at a temperature t' and under a pressure H', W'. " " vapor, W' W -f w. " " air at t' and under a pressure H', = 0.001292 V (1 -f t 0.00003) . W W + w 0.001292 V (1+ t' 0.00003) . ^^ . ' 1. Ascertain the Qy f ^^. of alcohol vapor from the following data : Weight of glass globe, W 50.804 grammes. Height of barometer, H 74.75 centimetres. Temperature, t 18 Weight of globe and vapor, W 50.824 grammes. Height of barometer, H' 74.76 centimetres. Temperature, t' 167 Volume, V 35 1.5 cubic centimetres. Ans. 1.575. 2. Ascertain the Pm (H). of camphor vapor from the following data : Weight of glass globe, W 50.134 grammes. Height of barometer, H 74.2 centimetres. Temperature, t 13.5 Weight of globe and vapor, W' 50.842 grammes. Height of barometer, H' 74.2 centimetres. Temperature, {' 244 Volume, V 295 cubic centimetres. Ans. 5.371. CHAPTER IV. ATOMS. 18. Definition. The atomic theory assumes that so long as the identity of a substance is preserved its molecules remain undivided ; but when, by some chemical change, its identity is lost, and new substances are formed, the theory supposes that the molecules themselves are broken up into still smaller particles, which it calls atoms. Indeed it regards this division of the molecules as the very essence of a chemical change. The word atom is derived from a, privative, and re/mo (I cut), and recalls a famous controversy in regard to the infinite divisibility of matter, which for many centuries divided the philosophers of the world. But chemistry does not deal with this metaphysical question. It asserts nothing in regard to the possible divisibility of matter ; but its modern theories claim that, practically, this division cannot be carried beyond a certain extent, and that we then reach particles which cannot be fur- ther divided by any chemical process now known. These are the chemical atoms, and the atom is simply the unit of the chemist, just as the molecule is the unit of the physicist, or the stars the units of the astronomer. The molecule is a group of atoms, and is a unit in the microcosm, of which it is a part, in the same sense that the solar system is a unit in the great stel- lar universe. The molecule has been defined as the smallest particle of any substance which can exist by itself, and the atom may be now defined as the smallest mass of an element that exists in any molecule. When a molecule breaks up, it is not supposed that the atoms fall apart like grains of sand ; but simply that they arrange themselves in new groups, and thus give rise to the formation of new substances. Indeed, as a rule, the atoms cannot exist in a free state, and with few exceptions every molecule consists of at least two atoms. This is thought to be true, even of the chemical elements. The difference between the molecules of ATOMS. 25 an elementary substance and those of a compound, according to the theory, is merely this, that while the first are formed by the union of atoms of the same kind, the last comprise atoms of different kinds. The molecules of oxygen gas are atomic aggregates as well as those of water, only the molecules of oxygen consist of oxygen atoms alone, while the molecules of water contain both oxygen and hydrogen atoms. Such at least is the constitution of most elementary substances. Nevertheless, in the case of mercury, zinc, cadmium, and some other me- tallic elements, the facts compel us to believe that the molecule consists of but one atom, or, in other words, that in these cases the molecule and the atom are the same. 19. Atomic Weights. There must be evidently as many kinds of atoms as there are elementary substances ; and, since these substances always unite in definite proportions, it must be also true that the elementary atoms have definite weights. This once assumed, the law of multiple proportions, as well as that of definite proportions, becomes an essential part of our atomic theory ; for, since the atoms are by definition indivis- ible, the elements can only combine atom by atom, and must therefore unite either in the proportion of the atomic weights or in some simple multiples of this proportion. We have dis- covered no means of measuring even approximately the ab- solute weight of an atom ; but, after we have determined, from considerations hereafter to be discussed, what must be the num- ber of atoms of each kind in one molecule of any substance, we can easily calculate their relative weight from the results of analysis. A few examples will make the method plain. 1. The analysis of water, given on page 6, proves that in 100 parts it contains 11.112 [farts of hydrogen and 88.888 parts of oxygen. Every molecule of water, then, must contain these two elements in just these proportions. Now we have good reason for believing that each molecule of water is a group of three atoms, two of hydrogen and one of oxygen. Then, since (11.112) : 88.888 = 1 : 16, it follows that the oxygen atom must weigh 16 times as much as the hydrogen atom ; and, if we make the hydrogen atom the uni.t of our atom- ic weight, then the weight of the oxygen atom, estimated in these units, must be 16. 2. The analysis of hydrochloric acid gas proves that it con- given in Table II. These numbers are the mm of chemical science, and the basis of almost all the numerical calculations which the chemist has to make. The elements of a compound body are always united either in the proportions, by weight, expressed by the^e numbers, or else in some simple multiples of these proportions ; and whenever, by the breaking up of a complex compound, or by the mutual action of different substances on each other, the elements rearrange themselves, and new compounds are formed, the same numerical propor- tions are always preserved. The atomic weights evidently rest on two distinct kinds of data ; Jirst, on the results of chemical analysis, which are facts of observation, and in regard to which the only question can be as to their greater or less accuracy ; secondly, on our conclu- sions in regard to the number of atoms in each molecule of the substance analyzed. This conclusion again is based chiefly on two classes of facts, whose bearing on the subject we must briefly consider. L In the first place we carefully compare together all the compounds of the element we are studying, with the view of discovering the smallest weight of it which enters into the com- position of any known molecule ; for this must evidently be the atomic weight of the element. An example will make the course of reasoning intelligible. In the following table we have a list of a number of the most important compounds containing hydrogen, all of which either are gases, or can easily be changed into vapor by heat, ATOMS. 27 so that their specific gravities in the state of gas can be readily determined. From these specific gravities we learn the weights of the molecules (compare 17) which are given in the second column of the table. In the third column we have given the weight of hydrogen contained in the molecules, referred, of course, to the same unit as the weight of the molecules themselves : Weight of Molecule referred to Weight of Hydrogen Compounds of Hydrogen. Hydrogen Atom. in the Molecule. Hydrochloric Acid 36.5 1 Hydrobromic Acid 81.0 1 Hydriodic Acid 128.0 1 Hydrocyanic Acid 27.0 1 Hydrogen Gas 2,0 2 Water 18.0 2 Sulphuretted Hydrogen 34.0 2 Seleniuretted Hydrogen 81.5 2 Formic Acid 46.0 2 Ammonia 1 7.0 3 Phosphuretted Hydrogen 34.0 3 Arseniuretted Hydrogen 78.0 3 Acetic Acid 60.0 4 Olefiant Gas 28.0 4 Marsh Gas 16.0 4 Alcohol 46.0 6 Ether 74.0 10 Assuming now, as has been assumed in this table, that a molecule of hydrogen gas weighs 2, it appears that the smallest mass of hydrogen which the molecule of any known substance contains, weighs jtist one half as much, or 1. We infer, therefore, that this mass of hydrogen cannot be divided by any chemical means, or, in other words, that it is the hydro- gen atom. The molecule of hydrogen gas contains then two hydrogen atoms, and this atom is the unit to which we refer all molecular and atomic weights. If now, in like manner, we bring into comparison all the volatile compounds of oxygen, we shall find that the smallest mass of oxygen which exists in the molecule of any known substance weighs 16, the atom of hydrogen weighing 1, and hence we infer that this mass of oxygen is the oxygen atom. Moreover it will appear that a molecule of oxygen gas weighs 28 ATOMS. 32, and hence it follows that each molecule of oxygen gas, like the molecule of hydrogen, is formed by the union of two atoms. A similar comparison would show that, while the molecule of nitrogen gas weighs 28, the atom weighs 14, so that here again the molecule consists of two atoms. This method of investiga- tion can be extended to a large number of the chemical ele- ments, and the conclusions to which it leads are evidently le- gitimate, and cannot be set aside, until it can be shown that some substance exists whose molecule contains a smaller mass of any element than that hitherto assumed as the atomic weight, or, in other words, until the old atom has been divided. 2. The second class of facts on which we rely for determin- ing the number of atoms in a given molecule is based on the specific heat of the elements (compare 16). It would appear tHal'tlie specific heat is the same for all atoms, and, if this is true, we might expect that equal amounts of heat would raise to the same extent the temperatures of such quantities of the various elementary substances as contain the same number of atoms, provided, of course, that these atomic aggregates are compared under the same conditions. Now we can determine accurately the number of units of heat required to raise the temperature of equal weights of the elementary substances one degree, and the results, which we call the specific heat of the elements, are given in works on physics. Chem. Phys. (232). Evidently, if our principle is true, these values must be pro- portional in every case to the number of atoms of each element contained in the equal weights compared. Representing then by S and S' the specific heat of two elementary substances, by m and m) the weights of the corresponding atoms, and by unity the equal weights compared, we shall have, in any case, S:S'= i:i, OTmS=m'S', [11] m m 9 L . J that is, The product of the atomic weight of an elementary sub- stance by its specific heat is always a constant quantity. Taking now the atomic weights obtained by the method first given, and the specific heats of the elements as they have been determined by experimenting on these substances in the solid state, we find that, with only three exceptions, our inference is ATOMS. 29 correct ; and this principle not only frequently enables us to fix the atomic weight of an element, when the first method fails, but it also serves to corroborate the general accuracy of our results. It is true, owing undoubtedly to many causes which influence the thermal conditions of a solid body, that this prod- uct is not absolutely constant. It varies between 5.7 and 6.9, the most probable value being very nearly 6.34. But the variation is riot important, so far as the determination of the atomic weights is concerned. This determination, as we have seen, rests chiefly on the results of analysis. The question al- ways is only between two or three possible hypotheses, and as between these the specific heat will decide. For example, an analysis of chloride of silver proves that each molecule contains for one atom, or 35.5 parts of chlorine, 108 parts of silver. Now, 108 parts of silver may represent one7two, three, or four atoms, or it may be that this quantity only represents a fraction of an atom. To determine, we divide 6.34 by 0.057, the specific heat of silver. The result is 111, which, though not the exact atomic weight, is near enough to show that 108 is the weight of one atom, and not of two or three. The exceptions to this rule referred to above are carbon, boron, and silicon. But the specific heat of these elements varies so very greatly with the differences of physical condition the so-called allotropic modifications which these elements present, Chem. Phys. (234), that the exceptions are not regarded as invalidat- ing the general principle. The law simply fails in these cases, and we can see why it fails. This important law, whose bearing on our subject we have briefly considered, was first discovered by Dulong and Petit, and was subsequently verified by the very careful experiments of Regnault. More recently it has been found, by Voestyn and others, that its application extends, in some cases at least, to chemical compounds ; for it would seem that the atoms retain, even when in combination, their peculiar relationsTto heat, so that the product of the specific heat of a substance by its molec- ular weight is equal to as many times 6.3 as there are atoms in the molecule. Thus the specific heat of common salt, multiplied by its molecular weight, gives 0.214 X 58.5 = 12.52, which is very nearly equal to 6.3 X 2 ; while in the case of corrosive sublimate the corresponding product, 0.069 X 271 = 18.70, is 30 ATOMS. nearly equal to 6.3 X 3, results which are in accordance with our views in regard to the number of atoms in the mole- cules of these substances. We have here, then, an obvious method by which we might determine the number of atoms in the molecule of any solid, and which would be of the very greatest value in investigating the atomic weights, could we rely on the general application of our law. We do not expect mathematical exactness. We know very well that the specific heat of solid bodies varies very greatly with the temperature, as well as from other phys- ical causes, and that it is impossible to compare them under precisely the same conditions, as would be required in order to secure accuracy. But, unfortunately, the discrepancies are so great, and we are so ignorant of their cause, that as yet we have not been able to place much reliance on the specific heat as a means of determining the number of atoms in the mole- cules of a compound. 3. Lastly, assuming that both of the means we have consid- ered fail to give satisfactory evidence in regard to the number of atoms in the molecule of a given substance (which we may have analyzed for the purpose of determining some atomic weight), we may frequently, nevertheless, reach a satisfactory, or at least a probable conclusion, byjcomparing the substance we are investigating with some closely allied substance whos.e constitution is known. Thus, if the molecule of sodic chlo- ride (common salt) contains two atoms, it is probable that the molecules of sodic iodide, as well as those of potassic chloride and potassic iodide, contain the same number ; for all these compounds not only have the same crystalline form and the same chemical relations, but also they are composed of closely allied chemical elements. Nevertheless it is true, in very many cases, that our conclusion in regard to the number of atoms which a molecule may contain is more or less hypo- thetical, and hence liable to error and subject to change. This uncertainty, moreover, must extend to the atomic weights of the elements, so far as they rest on such hypothetical conclu- sions. If we change the hypothesis in any case, we shall obtain a different atomic weight; but then the new weight will be ATOMS. 31 some simple multiple of the old, and will not alter the impor- tant relations to which we first referred. These fundamental relations are independent of all hypothesis, and rest on well- established laws. The atomic weights are the numerical constants of chem- istry, and in determining their value it is necessary to take that care which their importance demands. The essential part of the investigation is the accurate analysis of some compound of the element whose atomic weight is sought. The compound selected for the purpose must fulfil several conditions. It must be one which can be prepared in a condition of absolute purity. It must be one the proportions of whose constituents can be determined with the greatest accuracy by the known methods of analytical chemistry. It must contain a second element whose atomic weight is well established. Finally, it should be a compound whose molecular condition is known, and it is best that this should be as simple as possible. When they are once thus accurately determined, the atomic weights become essen- tial data in all quantitative analytical investigations. Questions and Problems. 1. Does the integrity of a substance reside in its molecules or in its atoms ? 2. We find by analysis that in 100 parts of potassic chloride there are 52.42 parts of potassium and 47.58 parts of chlorine. Moreover, we know from previous experiments that the atomic weight of chlorine is 35.5, and we have reason to believe that every molecule of the compound consists of two atoms, one of potassium and one of chlorine. What is the atomic weight of potassium ? Ans. 39.1. 3. We find by analysis that in 100 parts of phosphoric anhydride there are 43.66 parts of phosphorus and 56.34 parts of oxygen. Moreover, we know that the atomic weight of oxygen is 16 ; and we have reason to believe that every molecule of the compound consists of seven atoms, 2 of phosphorus and 5 of oxygen. What is the atomic weight of phosphorus ? Ans. 31. 4. In Table III. the student will find the molecular weights of the following oxygen compounds; and we give below, following the name, the weight of oxygen (estimated like the molecular weight in hydrogen atoms) which each contains. From these data it is 32 ATOMS. required to determine the atomic weight of oxygen. Oxygen Gas, 32 ; Water, 16 ; Sulphurous Anhydride, 32, Sulphuric Anhydride, 48; Phosphoric Oxychloride, 16; Carbonic Oxide, 16; Carbonic Anhydride, 32 ; Osmic Anhydride, 64 ; Nitrous Oxide, 16 ; Nitric Oxide, 16 ; and Nitric Peroxide, 32. Ans. 16. 5. We give below the weight of chlorine in one molecule of several of its most characteristic volatile compounds. It is required to deduce the atomic weight of chlorine on the principle of the last problem. Chlorine gas, 71; Phosphorous Chloride, 106.5; Phos- phoric Oxychloride, 106.5; Arsenious Chloride, 106.5; Phosgene Gas, 71 ; Stannic Chloride, 142 ; Stanno-triethylic Chloride, 35.5 ; and Hydrochloric Acid, 35.5. Ans. 35.5. 6. Review the steps of the reasoning by which the atomic weights have been deduced in the last two problems, and show that the " molecular weight " and " the weight of the element in one molecule * are actual and independent experimental data. 7. Analysis shows that in 1 00 parts of mercuric chloride there are 73.80 parts of mercury and 26.20 parts of chlorine. The specific heat of mercury is 0.032. What is the probable atomic weight of mercury, that of chlorine being 35.5 V Also, how many atoms of each element does one molecule of the compound contain ? Ans. Atomic weight of mercury, 200. Each molecule consists of one atom of mercury and two of chlorine. 8. Analysis shows that in 1 00 parts of ferric oxide there are 70 parts of iron and 30 parts of oxygen. The specific heat of iron is 0.114. What is the probable atomic weight of iron, that of oxygen being 16? and also, how many atoms of each element does one molecule of the oxide contain ? Ans. Atomic weight of iron, 56. One molecule of ferric oxide contains 2 atoms of iron and 3 of oxygen. 9. The molecular weight of silicic chloride is 1 70, and its specific heat, 0.1907. How many atoms does one molecule of the compound probably contain ? Ans. 5. 10. The molecular weight of mercuric iodide is 454, and its specific heat, 0.042. How many atoms does one molecule of the compound probably contain ? Ans. 3. CHAPTER V. CHEMICAL NOTATION. 20. Chemical Symbols. The atomic theory has found ex- pression in chemistry in a remarkable system of notation, which has been of the greatest value in the study of the science. In this system, the initial letter of the Latin name of an element is used as the symbol of that element, and represents in every case one atom. Thus stands for one atom of Oxygen, N for one atom of Nitrogen, H for one atom of Hydrogen. When several names have the same initial, we add for the sake of dis- tinction a second letter. Thus O stands for one atom of Car- bon, Cl for one atom of Chlorine, Ca for one atom of Calcium, Cu for one atom of Cuprum (copper), Or for one atom of Chromium, Co for one atom of Cobalt, Cd for one atom of Cadmium, Cs for one atom of Caesium, and Ce for one atom of Cerium. The symbols of all the elements are given in Table II. Several atoms of the same elq^kt are generally indicated by adding figures, but distinguisKiqg them from alge- braic exponents by placing them below the letters. Thus Sn 2 stands for two atoms of Stannum (tin), S 3 for three atoms of Sulphur, and I 5 for five atoms of Iodine. Sometimes, how- ever, in order to indicate certain relations, we repeat the symbol with or without a dash between them, thus H-H represents a group of two atoms of Hydrogen, Se=Se a group of two atoms of Selenium. We can now easily express the constitution of the molecule of any substance by simply grouping together the symbols of the atoms of which the molecule consists. This group is generally called the symbol of the substance, and stands in every case for one molecule. Thus NaCl is the sym- bol of common salt, and represents one molecule of salt. ff 2 is the symbol of water, and represents, as before, one molecule. So in like manner H%N stands for one molecule of ammonia gas, H 4 C for one molecule of marsh gas, KNO^ for one mole- cule of saltpetre, H 2 SO^ for one molecule of sulphuric acid, 3 34 CHEMICAL NOTATION. O 2 N 4 2 for one molecule of acetic acid, H-H for one molecule of hydrogen gas. We do not, however, always write the symbols in a linear form, but group the letters in such a way as will best indicate the relations we are studying. When several molecules of the same substance take part in a chemical change, we represent the fact by writing a numerical coefficient before the molecular symbol. A figure so placed always multiplies the whole symbol. Thus &H-N0 3 stands for four molecules of nitric acid, 3C 2 JH 6 for three molecules of alcohol, 600 for six molecules of oxygen gas. When clearness requires it, we enclose the symbol of the molecule in parentheses, thus, 4(// 3 ^), or (ff s =N) 4 . The precise mean- ing of the dashes will hereafter appear. They are used, like punctuation marks, to point off the parts of a molecular sym- bol, between which we wish to distinguish. 21. Chemical Reactions. These chemical symbols give at once a simple means of representing all chemical changes. As these changes almost invariably result from the reaction of one substance on another, they are called Chemical Reactions. Such reactions must necessarily take place between molecules, arid simply consist in the breaking up of the molecules and the rear- rangement of the atoms in new groups. In every chemical re- action we must distinguish between the substances which are involved in the change and those which are produced by it. The first will be termed the factors and the last the products of the reaction. As matter is indestructible, it follows that The sum of the weights of the products of any reaction must always be equal to the sum of the weights of the factors, and, further, that The number of atoms of each element in the products must be the same as the number of atoms of the same kind in the factors. This statement seems at first sight to be contradicted by experience, since wood and many other combustibles are consumed by burning. In all such cases, however, the apparent annihilation of the substance arises from the fact that the prod- ucts of the change are invisible gases ; and, when these are col- lected, their weight is found to be equal, not only to that of the substance, but also, in addition, to the weight of the oxygen from the air consumed in the process. As the products and factors of every chemical change must be equal, it follows that A chemical reaction may always be represented in an equation CHEMICAL NOTATION. 35 by writing the symbols of the factors in the first member and those of the products in the second. Thus, the following equa- tion expresses the reaction of dilute sulphuric acid on zinc, by which hydrogen gas is commonly prepared. The products are a solution of zinc sulphate and hydrogen gas. Zn + (ff 2 S0 4 + Aq) = (ZnSO t + Aq) + HHH. [12] The initial letters of the Latin word Aqua are here used simply to indicate that the substances enclosed with it in pa- rentheses are in solution. The symbol Zn is printed in " full- faced " type to indicate that the metal is used in the reac- tion in its well-known solid condition ; while the symbol of the molecule of hydrogen is printed in skeleton type to indi- cate the condition of gas. This usage will be followed through- out the book; but, generally, when it is not important to indicate the condition of the materials involved in the reaction, ordinary type will be used. The molecule of hydrogen gas consists of two atoms, as our reaction indicates, and this is the smallest quantity of hydrogen which can either enter into or be formed by a chemical change. The molecule of zinc is known to consist of only one atom. When the molecular constitution of an element is not known, we simply write the atomic symbol in the reaction. Among chemical reactions we may distinguish at least three classes. First, Analytical Reactions, in which a complex mole- cule is broken up into simpler ones. Thus, when sodic bisul- phate is heated, it breaks up into sodic sulphate and sulphuric anhydride, SO S . [13] So, also, by fermentation grape sugar or glucose breaks up into alcohol and carbonic anhydride, <7 6 # 12 6 = 2 C 2 ff 6 + 2 C0 2 . [14] Secondly, Synthetical Reactions, in which two molecules unite to form a more complex group. Thus baryta burns in an atmosphere of sulphuric anhydride, and forms baric sulphate, [15] 36 CHEMICAL NOTATION. In like manner ammonia enters into direct union with hydro- chloric acid to form ammonic chloride, HJT + HCl = HJTCl [16] Thirdly, Metathetical Reactions, in which the atoms of one molecultT change place with the dissimilar atoms of another, one atom of one molecule replacing one, two, three, or more atoms of the other, as the case may be. Thus, when we add a solution of common salt to a solution of argentic nitrate, we ob- tain a white precipitate l of argentic chloride, while sodic nitrate remains in solution. The result is obtained by a simple in- terchange between an atom of silver and an atom of sodium, as the following reaction shows : (Na Cl+ AgNO, + Ag) = (NaNO, + Aq) + AgCl. [17] In the next example, one atom of barium changes place with two atoms of hydrogen. Baric chloride and sulphuric acid yield hydrochloric acid and insoluble baric sulphate, which 'is precipitated from the solution in water as the reaction in- dicates, (Sa C1 2 + ff 2 S0 4 + Ag) = (ZHCI + Aq) + BaSO 4 . [18] Of the three classes of chemical reactions the last is by far the most common, and many chemical changes which were for- merly supposed to be examples of simple analysis or synthesis are now known to be the results of metathesis. In very many cases, however, a chemical reaction cannot be explained in either of these ways alone, but seems to consist in a primary union of two or more molecules and a subsequent splitting up of this large group. Indeed, this is the best way of conceiving of all metathetical reactions, for we do not suppose that in any case there is an actual transfer of atoms from one molecule to the other. The word metathesis is merely used to indicate the result of the process, not the manner in which the change takes place, and the same is true of the words analysis and synthesis. 1 The separation of a solid or sometimes of a liquid substance in a fluid menstruum, as the result of a chemical reaction, is called precipitation, and the material which separates, a precipitate ; and this, too, even when the ma- terial, being lighter than the fluid, rises instead of falls. CHEMICAL NOTATION. 37 The common method of preparing carbonic anhydride is to pour a solution of hydrochloric acid on small lumps of marble (calcic carbonate), CaC0 3 + (2ffCl + Ag) = ( Ca CO, H, C1 2 + [19] Aq) = (OaCl 2 + H.,0 -f Aq) + We may suppose that the molecules of the two substances are, in the first place, drawn together by the force which manifests itself in the phenomena of adhesion, 1 but that, as they approach, a mutual attraction between their respective atoms comes into play, which, the moment the molecules come into collision, causes the atoms to arrange themselves in new groups. The groups which then result are determined by many causes whose action can seldom be fully traced ; but there are two conditions which, when the substances are in solution, have a very important influence on the result. These conditions may be thus stated : 1. Whenever a compound can be formed, which is insoluble in the menstruum present, this compound always separates as a precipitate. 2. Whenever a gas can be formed, or any substance which is volatile at the temperature at which the experiment is made, this volatile product is set free. The reactions 17 and 18 of this section are examples of the first, while the reactions 12 and 19 are examples of the second of these conditions. The facts just stated illustrate an important truth, which must be carefully borne in mind in the study of chemistry. A chemical equation differs essen- tially from an algebraic expression. Any inference which can be legitimately drawn from an algebraic equation must, in some sense, be true. It is not so, however, with chemical sym- bols. These are simply expressions of observed facts, and, although important inferences may sometimes be drawn from the mere form of the expression, yet they are of no value whatever unless confirmed by experiment. Moreover, the facts 1 We find it convenient to distinguish between the force which holds to- gether different molecules and that which unites the atoms of the molecules. To the last we give the name of chemical affinity, while we call the first co- hesion or adhesion, according as it is exerted between molecules of the same kind or those of a different kind. 38 CHEMICAL NOTATION. which are expressed in this peculiar system of notation are as purely materials for the memory as if they were described in common language. 22. Compound Radicals. In many chemical reactions the elementary atoms change places, not with other elementary atoms, but with groups of atoms, which appear to sustain rela- tions to the compounds they leave or enter similar to those of the elements themselves. Thus, if we add to a solution of ar- gentic nitrate a solution of ammonic chloride, we get the reac- tion expressed by the equation AgNO, + NH{ 01 = NH.-NO, + Ag CL [20] Here the group NH has taken the place of Ag. So, also, in the reaction of hydrochloric acid on common alcohol, the group 2 # 5 in the molecule of alcohol changes places with the atom of hydrogen in the molecule of hydrochloric acid, C 2 ff 5 -0-H+ HCl = H-0-H+ C 2 ff 5 -CL [21] Alcohol. Ethylic Chloride. We write the symbols in this peculiar way in order to make it evident to the eye that such a substitution has taken place. Lastly, in the reaction of chloroform on ammonia, the group Cffof the first changes places with the three atoms of hydro- gen of ammonia gas, OH-- C1 3 + H,N = ZHCl + GffiN. [22] Chloroform. Hydrocyanic Acid. Such groups as these are called compound radicals. Like the atoms themselves, they cannot, as a rule, exist in a free state ; but aggregates of these radicals may exist, which sus- tain the same relation to the radicals that elementary substances hold to the atoms. Thus, as we have a gas chlorine consisting of molecules, represented by Cl- Cl, so there is a gas cyanogen consisting of molecules, represented by CN-CN , where CWis a compound radical called cyanogen. Again, the important radicals CO, S0 2 , and PC1 3 , are also the molecules of well- known gases. These radical substances correspond to the ele- mentary substances previously mentioned, in which the mole- cule is a single atom. But with few exceptions the radical substances have never CHEMICAL NOTATION. 39 been isolated, and the radicals are only known as groups of atoms which pass and repass in a number of chemical reac- tions. Indeed, in the same compound we may frequently assume several radicals. The possible radicals of a chemi- cal symbol correspond in fact almost precisely to the possi- ble factors of an algebraic formula, and in writing the sym- bol we take out the one or the other, as the chemical change we are studying requires. A number of these radicals have received names, and among those recognized in mineral com- pounds a few of the most important are Hydroxyl HO Sulphuryl S0 t Hydrosulpkuryl HS Carbonyl CO Ammonium II^N Phosphoryl PO Amidogen H 2 N Nitrosyl NO Cyanogen CN Nitryl N0 a . The radicals recognized in organic compounds are very numerous, and will be tabulated hereafter. Questions and Problems. 1. For what do the following symbols stand ? jRT; Ca,; 2. For what do the following symbols stand ? 07; S 3 -, 0-0-, H,N; ff.SO^ 3C. 2 ff G 0. 3. For what do the following symbols stand ? 0; H,-, Se-Se-, NaCl; H.O ; 3KN0 3 . 4. Analyze the following reaction. Show that the same number of atoms are represented on each side of the equation, and state the class to which it belongs. Fe + (ZffCl + A(f) = (Fed, + Aq) + HI-HI. Hydrochloric Acid Ferrous Chloride. 5. Analyze the following reaction. Show in what the equality consists, and state the class to which the reaction belongs. Ammonic Nitrate. Water. Nitrous Oxide. 6. Analyze the following reaction. Show in what the equality consists, and state the class to which the reaction belongs. r+ o--o co. Carbon. Oxyten. Carbonic Ar.hydr'.lc. 40 CHEMICAL NOTATION. 7. Analyze the following reaction. Show in what the equality consists, and state the class to which the reaction belongs. 2ff-0-ff+ Na-Na = 2Na-0-H + H-H. Water. Sodium. Sodic Hydrate. 8. The following reaction may be so written as to indicate that the products are formed by a metathesis between two similar mole- cules. It is required to show that this is possible. + N-JT. Ammonia gas. Hydrogen gas. Nitrogen gas. 9. Write the reactions [17] and [18] so as to indicate the manner in which the metathesis is supposed to take place. 10. State the conditions which determine the metathesis in the various reactions given in this chapter so far as these conditions are indicated. 11. Write the reactions [21] and [22] so as to indicate the mariner in which the metathesis is supposed to take place. 12. Analyze the following reaction. Show what determines the metathesis and also what is meant by a compound radical. (Pb=(N0 3 ) 2 Plumbic Nitrate. Ammonic Chloride. Pbl 2 + (2Nff 4 -N0 3 + Aq) Plumbic Chloride. Ammonic Nitrate. 13. Compare with [22] the following reaction and point out the two radicals, which, as we may assume, hydrocyanic acid contains. (Ag-NO, + H-CN+ Aq) = Ag-CIV + (H-NO S + Aq) Argentic Nitrate. Hydrocyanic Acid. Argentic Cyanide. Nitric Acid. 14. When sulphuric anhydride (S0 3 ) is added to water (H. 2 O) a violent action ensues and sulphuric acid is formed. The reaction may be written in two ways, and it is required to explain the different views of the process, which the following equations express. ff 2 0+ SO s = ff 2 SO, or 2H-0-H + S0,= = Iff Of SO, + H f 0. 15. State the distinction between a chemical element and an elementary substance. Give also the distinction between a com- pound radical and a radical substance. 16. Give the names of the following radicals. HO-, HS; NH; NH^ S0 2 ; CO-, PO-, N0 2 . CHAPTER VI. STOCHIOMETRY. 23. Stochiometry. The chemical symbols enable us not only to represent chemical changes, but also to calculate ex- actly the amounts of the substances required in any given pro- cess as well as the amounts of the products which it will yield. Each symbol stands for a definite weight of the element it rep- resents, that is, for the weight of an atom ; but, as only the rela- tive values of these weights are known, they are best expressed as so many parts. Thus H stands for 1 part by weight of hydrogen, the unit of our system. In like manner stands for 16 parts by weight of oxygen, N for 14 parts by weight of nitrogen, G for 12 parts by weight of carbon, C 5 for 60 parts by weight of carbon, and so on for all the symbols in Table IL The weight of the molecule of any substance must evidently be the sum of the weights of its atoms, and is easily found, when the symbol is given, by simply adding together the weights which the atomic symbols represent. Thus Jf 2 stands for 2 + 1 6 = 18 parts of water, H^Nkr 34-14 = 17 parts of ammonia gas, and <7 2 Z^0 2 f r 24 -|- 4 -f- 32 = SO parts of acetic acid. 1 Having then given the symbol of a substance, it is very easy to calculate its percentage composition. Thus, as in 60 parts of acetic acid there are 24 parts of carbon, in 100 parts of the acid there must be 40 parts of carbon, and so for each of the other elements. The result appears below ; and in the same way the percentage composition both of alcohol and ether has been calculated from the accompanying symbol. 1 In this book " the molecular weight of a substance " will always mean the sum of the atomic weights of the atoms composing one molecule, and we shall use the phrase, " the molecular weight of a symbol ," or " the total atomic weight of a symbol," to denote the sum of the atomic weights of all the molecules which the symbol represents. 42 STOCHIOMETRY. Acetic Acid Alcohol Ether C t H t O z . C 2 H 6 0. Ck-HioO. Carbon 40.00 52.18 64.86 Hydrogen 6.67 13.04 13.52 Oxygen 53.33 34.78 21.62 100.00 100.00 100.00 The rule, easily deduced, is this : As the weight of the mole- cule is to the weight of each element, so is one hundred parts to the percentage required. On the other hand, having given the percentage composition, it is easy to calculate the number of atoms of each element in the molecule of the substance. This problem is evidently the reverse of the last, but it does not, like that, always admit of a definite solution ; for, while there is but one percentage compo- sition corresponding to a given symbol, there may be an infinite number of symbols corresponding to a given percentage com- position. For example, the percentage composition of acetic acid corresponds not only to the formula C. 2 H0. 2 , given above, but also to any multiple of that formula, as can easily be seen by calculating the percentage composition of CH 2 0, C 3 ff 6 Sy (7 4 /7 8 4 , &c. They will all necessarily give the same result, and, before we can determine the absolute number of atoms of each element present, we must have given another condition, namely, the sum of the weights of the atoms, or, in other words, the molecular weight of the substance. When this is known, the problem can at once be definitely solved. Suppose we have given the percentage composition of alco- hol, as above, and also the further fact that its molecular weight is 46. We can then at once make the proportion 100 : 52.18 = 46 : x = 24 the weight of the atoms of carbon, 100 : 13.04 = 46 : x = 6 " " " " " " hydrogen, 100 : 34.78 = 46 :z= 16 " " " " " "oxygen. Then it follows that f | = 2 the number of atoms of carbon in one molecule, % = 6 " " u " " hydrogen in one molecule, ^| = 1 " " " " " oxygen in one molecule. It is evident from this example, that, in order to determine STOCHIOMETRY. 43 exactly the symbol of a compound, we must know its molecular weight. When the substance is a gas, or is capable of being changed into vapor, we can easily determine its molecular weight by the principle on page 18 . The molecular weight is simply twice its specific gravity referred to hydrogen. For all the problems given in this book, which deal only with the com- mon gases and vapors, the molecular weight can be at once taken from Table III. If we are dealing with a new substance, we must determine its specific gravity experimentally by one of the methods which will hereafter be described. When, on account of the fixed nature of the substance, the last mo'de of investigation is impossible, we can still frequently determine with great probability the molecular weight, by study- ing the chemical reactions into which the substance enters, and connecting, by careful quantitative experiments, the molecular weight sought with that of some substance whose molecular weight is known. The methods used in such cases will be in- dicated hereafter ; but even when all such means fail, we can nevertheless always find which of all possible symbols ex- presses the composition of the substance we are studying in the simplest terms, in other words, with the fewest number of atoms in the molecule. Suppose the substance to be cane sugar, which cannot be volatilized without decomposition, and of which no reaction is known which gives any definite clew to its mole- cular weight. Peligot's analysis, cited on page 9, shows that it contains, in 100 parts, 42.06 parts of carbon, 6.50 parts of hydrogen, and 51.44 parts of oxygen. Assume for the mo- ment that the molecular weight is equal to 100 then = 3.50 the number of atoms of carbon. JJ2 6.50 " " " hydrogen. 51 : g 4 = 3.22 " oxygen. This would be the number of atoms of each element if the sum of the atomic weight, that is, the molecular weight, of sugar, were equal to 100. As, from the very definition, frac- tional atoms cannot exist, these numbers are impossible, but any other possible number of atoms must be either a multiple or a submultiple of the numbers found ; and we can easily dis- 44 STOCHIOMETRT. cover the fewest number of whole atoms possible, by seeking for the three smallest whole numbers which stand to each other in the relation of 3.50 : 6.50 : 3.22, a proportion which is very nearly satisfied by 12 : 22 : 11. Hence, the simplest possible symbol is O^H^O^ and this has been adopted by chemists as the symbol of cane sugar, although, from anything we as yet know, the symbol may be a multiple of this. If now, taking this symbol as our starting-point, we calculate the percentage composition which would exactly correspond to it, we obtain the following results, which we have arranged in a tabular form, so that the student may compare the theoretical compo- sition with the numbers Peligot obtained by actual analysis. Composition of Cane Sugar, Peligot's Analysis. Theoretical. Carbon 42.06 42.11 Hydrogen 6.50 6.43 Oxygen 51.44 51.46 100.00 100.00 The difference between the two is now seen to be within the probable errors of analysis, and this example illustrates the method of arranging analytical results generally adopted by chemists. From the above discussion we can easily deduce a simple arithmetical rule for finding the symbol of a compound when its percentage composition is known. But this rule may be best expressed in an algebraic formula, which will show to the eye at once the relation of the quantities involved in the calcula- tion, and enable us to extend our method to the solution of many classes of problems which we might not otherwise foresee. Let us then represent By M the weight of any chemical compound in grammes. 44 m the molecular weight of the compound in hydrogen atoms. " W the weight of any constituent of that compound, whether element or compound radical, in grammes. " w the total atomic weight of element or radical in one molecule. STOCHIOMETRY. 45 = proportion by weight of the constituent in the compound, Then w m and ^- = weight of constituent in M grammes of compound, or 771 W=M-. [23] Any three of these quantities being given, the fourth can, of course, be found. Thus we may solve four classes of problems. 1. We may find the weight of any constituent in a given weight of a compound, when we know the molecular weight of the compound and the total atomic weight of the constituent in one molecule. Problem. It is required to find the weight of sulphuric anhydride S0 3 in 4 grammes of plumbic sulphate PbO, S0 3 . Here, w = 32 -f 3 X 16 = 80, m = 207 + 16 + 80 = 303, and M= 4. Ans. 1.056 grammes. 2. We can find the weight of a compound which can be produced from, or corresponds to, a given weight of one of its constituents, when the same quantities are known as above. Problem. How many grammes of crystallized green vitriol, FeS0 4 . 7ff 2 0, can be made from 5 grammes of iron? Here, w = 56, m = 278, W= 5. ' Ans. 24.821. 3. We can find the molecular weight of a compound when we have given the weight of one constituent in a given weight of the compound, and the total atomic weight of that constitu- ent in the molecule. Problem. In 7.5 grammes of ethylic iodide, there are 6.106 grammes of iodine ; the total atomic weight of iodine in one molecule is 127. What is the molecular weight of ethylic iodide? Ans. 156. 4. We can find the total atomic weight of one constituent of a molecule when the molecular weight is given, and also the weight of the constituent in a known weight of the compound. 46 STOCHIOMETRY. Problem. The molecular weight of acetic acid is 60, the per cent of carbon in the compound 40. What is the total atomic weight of carbon iii one molecule ? Ans. 24. Whence number of carbon atoms in one molecule, 2. The last problem is essentially the same as that of finding the symbol of a compound when its percentage composition is given, while the first corresponds to the reverse problem of deducing the percentage composition from the symbol. By a slight change the formula can be much better adapted to this class of cases. For this purpose we may put M = 1 00, since we are solely dealing with per cents, and also put w = na, a standing for the atomic weight of any element, and n for the number of atoms of that element in one molecule of the compound we are studying. We then have 100 a [24] L J The first of these forms is adapted for calculating the per cent of each element of a compound when the molecular weight, the number of atoms of each element in one molecule, and the several atomic weights, are known ; and it is evident that all these data are given by the chemical symbol of the compound. The second of these forms enables us to calculate the number of atoms of each element present in one molecule of a com- pound when the percentage composition, the molecular weight, and the several atomic weights, are known, and illustrates the principle before developed, that the molecular weight is an essential element of the problem. 24. Stochiometrical Problems. The principles of the pre- vious section apply not only to single molecular formulas, but obviously may also be extended to the equations which repre- sent chemical changes. Since the molecular symbols which are equated in these expressions represent known relative weights, it must be true in every case that we can calculate the weight of either of the factors or products of the chemical change it represents, provided only that the weight of some one is known. If we represent by w and m the total atomic weight of any two symbols entering into the chemical equations, and by W and M the weight in grammes of the factors or products STOCHIOMETRY. 47 which these symbols represent, then the simple algebraic formulae of the last section will apply to all stochiometrical problems of this kind, as well as to those before indicated. These formulae, however, are merely the algebraic expression of the familiar rule of three, and all stochiometrical problem < are solved more easily by this simple arithmetical rule. Usin^ the word symbol to express the sum of the atomic weights it represents, we may state the rule as applied to chemical prob- lems in the following words, which should be committed to memory. Express the reaction in the form of an equation ; make then the proportion, As the symbol of the substance given is to the sym- bol of the substance required, so is the weight of the substance given to x, the weight of the substance required ; reduce the symbols to numbers, and calculate the value of x. This rule applies equally well to all problems, like those of the last section, in which the elements or radicals of the same molecular symbol are alone involved ; only in such cases there is of course no equation to be written. A few examples will illustrate the application of the rule. Problem 1. We have given 10 kilogrammes of common salt, and it is required to calculate how much hydrochloric acid gas can be obtained from it by treating with sulphuric acid. The reaction is expressed by the equation (2Na 01 + ff 2 S0 4 + Aq) = (Na 2 S0 4 + Aq) + 2IH@/, whence we deduce the following proportion, 117 73 2NaCl.: 2ffCl= 10 : x = Ans. 6.239 kilogrammes. Problem 2. It is required to calculate how much sulphuric acid and nitre must be used to make 250 grammes of the strongest nitric acid. The reaction is expressed by the equation KNO, + ff, S0 4 = K, ffS0 4 + HNOfr whence we get the proportions 63 98 JffN0 3 : HzSO = 250 : x = Ans. 1. 388.9 grammes sulphuric acid. fiS 101.1 s : KN0 3 = 250:x = Ans. 2. 401.2 grammes nitre. 48 STOCHIOMETRY. The student should also solve by the same rule the problems given in the last section. 25. Gay-Lussac's Law. This eminent French chemist was the first to state clearly the important truth, that, when gases or vapors react on each other, the volumes both of the factors and of the products of the reaction always bear to each other some very simple numerical ratio. This truth is generally known as the law of Gay-Lussac, but, since the principle is a direct con- sequence of the atomic theory, it is best studied in that relation. It is, as we have seen, a fundamental postulate of the theory that equal volumes of all substances, when in the aeriform condition, contain the same number of molecules. Hence it follows, that the volumes of all single molecules are the same, and, if we take this common volume as our unit of measure, it follows, further, that the total molecular volume represented by any symbol is always equal to the number of molecules. We are thus led to a most important fact, which gives an additional meaning to our chemical symbols, for it appears that Every chemical equation, when properly written, represents not only the relative weights, but also the relative volumes of its factors and products, when in the state of gas. This principle is illustrated by the following equations : + Carbonic Anhydride. Aqueous Vapor Nitric Oxide Gas. Hydrogen Gaa. Ammonia Gas. Aqueous Vapor. The squares which here serve to indicate equal volumes, and to impress on the mind the meaning of the symbols, are evidently unnecessary and will not be used hereafter. The important rule of the last section may be expressed by the following proportion nm:n'm':= W: W' = W:W Here m and m' represent the molecular weights of any two substances, n and n' the number of molecules of these sub* STOCHIOMETRY. 49 stances, which take part in a chemical reaction whether as factors or products, while n m and n' m y represent what in the statement of our rule we have called the symbols of the sub- stances, and the equation expresses the fact that the sum of the atomic weights indicated by the symbols is proportional to the weights of the substances involved in the chemical reac- tion, whether these weights are estimated in grammes or in criths (2). Now by (17) m' = 2 Sp. Gr. and by [3] W = V X Sp. Gr. Making these substitutions we may reduce the above propor- tion to the following form n m : n' = W : V and this gives us another stochiometrical rule, by which we can calculate the volume of a gas or vapor involved in a chemical reaction, when the weight of some other factor or product is known, or inversely, when the volume is given calculate the weight. Express the reaction in an equation ; make then the propor- tion, As one half of the symbol of the first substance is to the number of molecules of the second, so is the weight in criths of the first to the volume in litres of the second ; reduce the symbol to numbers, and calculate the value, of the unknown quantity. This rule has the same general application as the first, and a few examples will illustrate the use of it. Problem 1. How much chlorate of potash must be used to obtain one litre of oxygen gas ? The reaction is expressed by the equation whence we get the proportion 122.6 (2K C10 3 ) : 3 = x : 1 . x = 40.9 criths, 40.9 X 0.0896 = Ans. 3.664 grammes. Problem 2. How many litres of oxygen gas can be obtained from 500 grammes of chlorate of potash ? The reaction is the same as before, but in this case the grammes must first be reduced to criths. The proportion will then be written 4 50 STOCHIOMETRY. KC10: 3 = : x = Ans. 136.G litres. In applying the rules of this chapter to the solving of stochiometrical problems, the student should carefully bear in mind, first, that the rule of (24) applies to all those cases in which the weight of one substance is to be calculated from the weight of another ; secondly, that when volume is to be deduced from volume the answer can be found by mere inspection of the equation according to the principles stated in (25), and thirdly, that the rule of page 49 applies only to those problems in which volume is to be calculated from weight, or the reverse. In using this last rule it must be remembered that the " first substance " is always the one whose weight is given or sought, while the " second substance " is always the one whose volume is given or sought. Moreover, the student will notice that the volume of any aeriform factor or product may also be found by dividing its weight in grammes, calculated by the rule of (24), by the known weight of one litre of the gas or vapor, found from Table III. by [3]. Questions and Problems. 1. What is the molecular weight of plumbic sulphate, Pb=0 2 =SO z ? Of calcic phosphate, Ccr 3 10 6 l(PO) 2 ? Of ammonia alum, (NH t \, [4J a ]|0 8 |(S0 a ) 4 . 24# 2 0? Ans. 303, 310, and 906.8. 2. What are the molecular weights of the symbols 3C 2 ff 4 2 -, 5(FeS0 4 . 7ff 2 0) and 7K 2 =OfCO? Ans. 180, 1390, and 967.4. 3. Are the total atomic weights of the two members of the follow- ing reaction equal ? * Fe + (H 2 S0 4 + Ag) = (FeSOt + Aq) + H-H. Ans. The total weight of each member of the equation is 154. 4. Calculate the percentage composition of ammonic chloride, NH^CL Ans. Nitrogen, 26.17; Hydrogen, 7.48; Chlorine, 66.35. 5. Calculate the percentage composition of nitrobenzole, C^H^NO.^ Ans. Carbon, 58.53; Hydrogen, 4.07 ; Nitrogen, 11.39 ; Oxygen, 26.01. STOCHIOMETRY. 51 6. Given the percentage composition of chloroform as follows : Carbon, 10.04; Hydrogen, 0.83; Chlorine, 89.13. Required the symbol, knowing that the Sp. Gr. of chloroform vapor equals 59.75. Ans. 7. Given the percentage composition of stanno-diethylic bromide as follows: Tin, 35.13; Carbon, 14.29; Hydrogen, 2.97; Bromine, 47.61. Required the symbols, knowing that the Sp. Gr. of the vapor equals 168. Ans. Sn C 4 H lo Br 2 . 8. Given the percentage composition of ethylene chloride as fol- lows : Carbon, 24.24 ; Hydrogen, 4.04 ; Chlorine, 71.72. Required the symbol, knowing that the Sp. *Gr. of the vapor equals 49.5. Ans. 9. Given the percentage composition of cream of tartar as fol- lows: Potassium, 20.79; Hydrogen, 2.66; Carbon, 25.52; Oxygen, 51.03. Required the simplest symbol possible. Ans. KH^C t O y 10. Given the percentage composition of crystallized ferrous sul- phate as follows: Iron, 20.15; Sulphur, 11.51; Oxygen, 23.02; Water, 45.32. Required the simplest symbol possible. Ans. Estimating the number of molecules of water (T^O), as if water were a fourth element with an atomic weight of 18, we get FeSO,. 7H 2 0. 11. The percentage composition of morphia according to Liebig's analysis is Carbon, 71.35 ; Hydrogen, 6.69 ; Nitrogen, 4.99 ; Oxy- gen (by loss), 16.97. What is the symbol of this alkaloid, and how closely does this symbol agree with the results of analysis ? Ans. The symbol C 17 /7 19 A T 3 wouM require 71.58 Carbon, 6.66 Hydrogen, 4.91 Nitrogen, and 16.85 Oxygen. 12. It is required to find the weight of phosphorus in 155 kilos. of calcic phosphate (Ca 3 P 2 ^ 8 )' Ans< 31 kilos. 13. It is required to find the weight of sulphuric anhydride (S0 3 } in 284 kilos, of sodic sulphate, Na 2 S0 4 . Ans. 160 kilos. 14. How many grammes of plumbic sulphate, (PbSO^ can be made from 2.667 grammes of sulphuric anhydride (50 3 ) Ans. 10.1 grammes. 15. How many grammes crystallized cupric sulphate (Cw50 4 . 677 2 0) will yield 317 grammes of copper ? Ans. 1337 grammes. 16. Required the total molecular weight of crystallized sodic phosphate, knowing that 71.6 parts of the salt contain 9.2 parts of sodium, and that the total atomic weight of sodium in one mole- cule of the compound is 46. Ans. 358. 52 STOCHIOMETRY. 17. The molecular weight of potassic nitrate is 101.1, and 2.359 grammes of the salt contain 1.120 grammes of oxygen. What is the total atomic weight of oxygen, and also the number of oxygen atoms in one molecule ? Ans. Total atomic weight 48. No. of oxygen atoms 3. 18. How much nitric acid (HNO^ is required to dissolve 3.804 grammes of copper (CV) and how much cupric nitrate (CuN^O^ and how much nitric oxide (NO) will be formed in the process V The reaction is expressed by the equation Ans. 10.08 grammes of nitric acid; 11.244 grammes of cupric nitrate and 1.20 grammes of nitric oxide. 19. How much common salt (NaCl) must be added to a solution containing 30 grammes of argentic nitrate (AgNO s ) in order to throw down the whole of the silver, and how much argentic chloride (AgCF) will be thus precipitated ? (AgNO, + NaCl + Aq) = AgCI + (NaNO, + Aq). Ans. 10.32 grammes of salt and 25.32 grammes argentic chloride. 20. How many litres of ammonia gas (SSTllj) and how many of chlorine gas (^1-^oJl are required to make one litre of nitrogen gas S^SS" ? How many litres of hydrochloric acid gas (HK2J1) are also formed ? 2S3HI 3 + 3(oJl-(oJl = 6H3(J1 -|- S9XS3 1 . Ans. 2 litres of ammonia gas ; 3 litres of chlorine gas, and 6 litres of hydrochloric acid gas. 21. How many litres of hydrochloric acid gas (IHOl) and how many of oxygen gas (=) can be obtained from one litre of aqueous vapor (IILzdD), and how many litres of chlorine gas must be used in the process ? 4- Ans. 2 litres of hydrochloric acid gas, litre of oxygen gas, and 1 litre of chlorine gas. . 22. How many litres of oxygen gas ((o>()) are required to burn completely (i. e. to combine with) one litre of alcohol vapor ((Bailie), and how many litres of carbonic anhydride (OCDa) and how many of aqueous vapor (m 2 (o)) are formed by the process ? The chemical reaction which takes place when alcohol burns is expressed by the equation STOCHIOMETRY. 53 3= = Ans. 3 litres of oxygen gas ; 2 litres of carbonic anhydride, and 3 litres of aqueous vapor. 23. How many litres of oxygen gas are required to burn one litre of arseniuretted hydrogen (IH 3l ^s)> and how many litres of arsenious acid vapor (ys\s 3 ) and how many of aqueous vapor are formed in the process V 4IH 3 As -f 9 (acetic acid) and C 2 H 2 4 (oxalic acid) arc saturated mole- cules, what is the atomicity of the radicals HO (hydroxyl) ; C 2 /7 6 (ethyl) ; C 3 # 4 (ethylene) ; C,H,0 (aldehyde) ; CO (carbonyl) ; C 2 // 3 <9 (acetyl) and C 2 <9 2 (oxilyl). CHAPTER VIII. CHEMICAL TYPES. 29. Types of Chemical Compounds. There are three modes or forms of atomic grouping, to which so large a num- ber of substances may be referred, that they are regarded as molecular types, or patterns, according to which the atoms of a molecule are grouped together. These types may be repre- sented by the general formulae : IT iin i ii i R -R R,R--R or R-R-R [33] i i i in i i in i R, R, R-R or R, R--R-R. It will be noticed, that in the first of these types a single uni- valent atom or radical 1 is united to another single univalent atom, that in the second a bivalent atom binds together two univalent atoms or their equivalents, and that in the third a trivalent atom binds together three univalent atoms, or their equivalents. The dashes are used to separate what has been called the central, the dominant, or the typical atom from those which it thus unites into one molecular whole, and serve at the same time to point out the parts of the symbol to which its affinities are directed. Commas are used to separate the subordinate atoms so united. It will be further noticed, that in each case the quantivalence of the dominant atom is equal to the sum of the quantivalences of the subordinate atoms, or radicals, on either side; and the peculiarity in each case consists solely in the relations of the parts of the molecule which we thus attempt to indicate by the symbol. The three compounds, hydrochloric acid, water, and ammonia, ii ii ii iiini H- Cl, H, H-- 0, H, H, H=-N, 1 Here, as elsewhere through the book, we use the symbol R for any univalent, R for any bivalent, and R for any trivalent atom or radical. More- over, to avoid unnecessary repetition, we shall for the future conform to the general usage, and speak of the atoms of a radical as well as of those of an element, and use the word " atom " as applying to both, although the usage frequently involves an obvious solecism. CHEMICAL TYPES. 63 are generally taken as representatives of these types, and sub- stances are described as belonging to the type of hydrochlo- ric acid, to the type of water, or to the type of ammonia, as the case may be. These substances, however, are regarded as types in no other sense than that their molecules present the same mode of grouping which is indicated above by the more general symbols. Substances belonging to the same type may have widely different properties. To the type of water be- long the strongest alkalies and the most corrosive acids known. In what, then, it may be asked, does the type outwardly con- sist, or in what is it manifested ? for the grouping of the atoms can only be a matter of inference. The answer is, that the type of the molecules of a substance is manifested solely by its chemical reactions. Substances belonging to the same type are simply those whose reactions may be classed together ac- cording to some one general plan. Thus water, alcohol, and acetic acid are classed in the same type, because, when submit- ted to the action of the same or similar reagents, they undergo a like transformation, which seems to point to a similarity of atomic grouping. # H-0 -f PCI, = PCl.O + H-Cl + H-Cl Water. Phosphoric Chloride. Hydrochloric Acid. H, O. 2 H 5 =0 + PCI. = PC1 3 + H-Cl + C. 2 H 6 -Cl [34] Alcohol. Phosphoric Oxy-chloride. Ethylic Chloride. H, C,H.O-0 + PCI, = PC1 3 + H-Cl + C^O-Cl. Acetic Acid. Acetylic Chloride. On studying these reactions, it will be seen that both the man- ner in which the three compounds break up, and the probable constitution of the products formed, point to the conclusion, that, in each, one bivalent atom holds together two univalent atoms or radicals. It will be found, in the first place, that in all three cases the reaction consists primarily in the substitution of two atoms of chlorine for one of oxygen in the original molecule. It will appear, in the next place, that as soon as this dominant atom, which holds together the parts of the molecule, is taken away, each of the three molecules splits up into two others of a similar type ; and lastly, it is evident from the third example that one of the oxygen atoms of acetic acid stands in a very different relation to the molecule from the other. All this 64 CHEMICAL TYPES. points to the inference just made. At least, these and a vast number of similar reactions are best explained on this hypoth- esis, and herein its only value lies and its probability rests. In section 27 we have already given the symbols of a number of chemical compounds so printed that they can be at once re- ferred to one or the other of the three types here alluded to, and it will not, therefore, be necessary to multiply examples in this place. 30. Condensed Types. In the same way that a bivalent atom may bind together two univaleut atoms or their equiva- lents, so, also, it may serve to bind- together two molecules, and, in like manner, a trivalent atom may bind together three mole- cules into a more complex molecular group ; and thus are formed what are called condensed types. We may represent i n i a double molecule of the type of water thus, RfR^R^ but it must be borne in mind that such a symbol stands for two molecules, since, by the very definition, two molecules of the same kind cannot chemically combine. We can, however, solder them, as it were, into one molecular whole by substituting i n for the two univalent atoms R. 2 a single bivalent atom R, when we obtain a mode of molecular grouping represented by i n n T) _ T> _ 7~> r*o en R 2 -R. 2 =R, [35] which may be called the type of water doubly condensed. The constitution of common sulphuric acid is best represented after this type by the symbol, n R 2 =0 2 =S0 2 . [36] n The soldering atom is here the bivalent radical S0 2 . In like manner, by using a trivalent atom, we can solder together three molecules of the same water-type, as in the general symbol, i n in which represents the type of water trebly condensed. In the same way we may derive the symbol, i i in CHEMICAL .TYPES. 65 which represents the type of ammonia doubly condensed. The substance urea, one of the most important of the animal secre- tions, is best represented by a symbol after this last type, H ff^N^CO [39] where the soldering atom is the bivalent radical carbonyl. Chemists have also been led to admit the existence of what are called mixed types, which are formed by the union of mole- cules of different types soldered together by a single multiva- lent atom or radical as before. Thus, the molecules of sul- phurous acid may be regarded as formed of a molecule of water soldered to a molecule of hydrogen by an atom of sulphury 1, S0 2 -, thus, H-O-Haud H-H, united by S0 2 give So, also, the composition of a complex organic compound called sulphamide, or sulphamic acid, is most simply expressed when regarded as formed by the union of water and ammonia soldered together by the same radical sulphuryl ; thus, from in n m n n H, H-N-H, and H-O-HvfQ have H, H=N-S0. 2 -0-H. [41] Lastly, if we bind together on the same principle molecules of the type of hydrochloric acid, we shall simply reproduce the types of water and of ammonia, thus showing that all the types are only condensed forms of the simplest. We must not, therefore, attach to the idea of a chemical type any deeper sig- nificance than that indicated above. It is simply a conven- ient ^mode of classifying certain groups of chemical reactions, and a help in representing them to the mind; and we may regard the same substance as formed on one type or on the other, as will best help us to explain the reactions we are study- ing. Moreover, it is frequently convenient to assume other types besides those here specially mentioned. 31. Substitution. When cotton- wool is dipped in strong nitric acid (rendered still more active by being mixed with twice its volume of concentrated sulphuric acid), and after- wards washed and dried, it is rendered highly explosive, and, 5 66 CHEMICAL TYPES. although no important change has taken place in its outward aspect, it is found on analysis to have lost a certain amount of hydrogen and to have gained from the nitric acid an equivalent amount of nitric peroxide NO Z in its place. becomes Cotton. Gun-Cotton. Under the same conditions glycerine undergoes a like change, and is converted into the explosive nitro-glycerine, becomes Glycerine. Nitro-glycerine. So, also, the hydrocarbon naphtha, called benzole, is changed into mtro-benzole, C & H Q becomes C 6 (H 5 ^0 2 ). Benzole. Nitro-benzole. The last compound is not explosive, and the explosive nature of the first two is in a measure an accidental quality, and is evidently owing to the fact that into an already complex struc- ture there have been introduced, in place of the indivisible atoms of hydrogen, the atoms of a highly unstable radical rich in oxy- gen. The point of chief interest for our chemical theory is that this substitution does not alter, at least essentially, the outward aspect of the original compound. Every one knows how closely gun-cotton resembles cotton-wool. In like manner nitro-glycer- ine is an oily liquid like glycerine, and nitro-benzole, although darker in color, is a highly aromatic volatile fluid like benzole itself. Products like these are called substitution products, and they certainly suggest the idea that each chemical compound has a certain definite structure, which may be preserved even when the materials of which it is built are in part at least changed. If in the place of firm iron girders we insert weak wooden beams, a building, while retaining all its outward as- pects, may be rendered wholly insecure, and so the explosive nature of the products we have been considering is not at all incompatible with a close resemblance, in outward aspects and internal structure, to the compounds from which they were derived. The idea that each body has a definite atomic structure is CHEMICAL TYPES. 67 even more forcibly suggested by another class of substitution products first studied by Dumas, in which atoms of chlorine, bromine, or iodine have taken the place of the hydrogen atoms of the original compound. Thus, if we act upon acetic acid with chlorine gas, we may obtain three successive products, as shown in the following table, although only the first and the last have been fully investigated. Acetic acid C 2 F 4 O a or (C z H 3 6)-^-H Chloracetic acid C 2 (H 3 CI)0 Z " (C Z H Z CIO)-0-H Dichloracetic acid C t (H t ClJO, (C 2 HC1 2 0)-0 -H Trichloracetic acid C 2 (HC1 3 )0 3 (C,C7,0)-0-// We cannot, however, replace the fourth atom of hydrogen by chlorine ; and this fact seems to prove that there is a real difference between this atom of hydrogen and the other three, and gives an additional ground for the distinction we make when we write the symbol of acetic acid after the type of water, as in the second column. The three atoms of hydrogen in the radical placed on the left-hand side of the dominant atom may all be replaced by chlorine, but the single atom of hydrogen placed on the right cannot. These products all resemble acetic acid in that they form with the alkalies crystalline salts, when the fourth atom of hydrogen is replaced by an atom of sodium or potassium, as the case may be. It was the study of these and similar substitution products which first led to the conception of chemical types, and the word as first used was intended to convey the idea of a definite structure, although perhaps as yet unknown ; but as the theory was extended more and more, and to widely different chemical compounds, it was found that the first definite conception could not be maintained, and the idea gradually assumed the shape we have given it in the last section. Still, the facts from which the original conception was drawn remain, and they point no less clearly now than they did before to the existence of a def- inite structure in all chemical compounds as the legitimate ob- ject of chemical investigation. 68 CHEMICAL TYPES. 32. Isomorphism. Closely associated with the facts of the last section, which find their chief manifestation in substances of organic origin, are the phenomena of isomorphism, which are equally conspicuous among artificial salts and native rain- Fig. i. erals. There seems to be an intimate connection between chemical composition and crystalline form, and two substances which under a like form have an anal- .ogous composition are said to be isomor- phous. Thus the following minerals all crystallize in rhombohedrons (Fig. 1,) which have very nearly the same inter- facial angles, and, as the symbols show, they have an analogous composition. They are therefore isomorphous. n n n Calcite or calcic carbonate ii ii ii Magnesite or magnesic carbonate Mg=O z =CO n n n Chalybdite or ferrous Fe= O a = C n n n Diallogite or manganous " Mn-O^CO n ii n Smithsonite or zincic Zn=O z =CO The most cursory examination of these symbols will show that they differ from each other only in the fact that one me- tallic atom has been replaced by another. It is not, however, every metallic atom which can thus be put in without altering the form. This is a peculiarity that is confined to certain groups of elements, which for this reason are called groups of isomorphous elements. Moreover, as a rule, there is a close re- semblance between the members of any one of these groups in all their other chemical relations. These facts, like those of the last section, tend to show that the molecules of every substance have a determinate structure, which admits of a limited substi- tution of parts without undergoing essential change, but which is either destroyed or takes a new shape when in place of one of its constituents we force in an unconformable element. A well-known class of artificial salts, called the alums, affords even a more striking illustration of the principles of isomorphism than the simpler example we have chosen ; but all the bearings CHEMICAL TYPES. 69 of the subject cannot be understood without a knowledge of crystallography, and we must therefore refer for further details to works on mineralogy. 33. Rational Symbols. Chemical formulae, like those of the last few sections, which endeavor, by grouping together the elementary symbols, to illustrate certain classes of reactions, and to illustrate the manner in which a complex molecule may break up, are called rational symbols, and are to be distinguished from the simpler symbols used earlier in the book, which ex- press only the relative proportions in which the elements are combined, and which, since they are simply expressions of the results of analysis on a concerted plan, are called empirical symbols. Whether these rational symbols can be regarded in any sense as indicating the actual grouping of the material atoms is very doubtful, although facts like those stated above would seem to indicate that such may be the case, at least to a limited extent. It is difficult, for example, to resist the con- clusion that in alcohol and its congeners the atoms C 2 ff s are grouped together in some sense apart from the rest of the molecule ; but then we have no evidence of this grouping apart from the reactions of these compounds, and, until greater cer- tainty is reached, it is not best to attach a significance to our symbols beyond the truths they are known to illustrate. It is objected to the use of rational symbols that they bias the' judgment on the side of some theory, of which they are more or less the exponents. But when they are used in the sense stated above, this objection has no force, for the reactions they prefigure are no less facts than the definite proportions they conventionally represent, and we employ one mode of grouping the symbols or another, as will best indicate the reactions we are studying. Moreover, as science advances, we have every reason to believe that we shall gain more and more knowledge of the actual relations between the parts of a material molecule, and as has already been intimated, there can hardly be a doubt that in some cases our rational symbols do express even now actual knowledge of this sort, however crude and partial it may be. Our present typical symbols are indeed the ex- pressions of partial generalizations, which, however imperfect, have an element of truth. Hence it is that they have pointed out new lines of investigation, have led to new discoveries, and 70 CHEMICAL TYPES. have been of the greatest value to science. They will doubt- less soon be superseded by other rational symbols, expressing other partial generalizations, to serve the same purpose in their turn and be likewise forgotten. We must not, however, de- spise these temporary expedients of science. They are not only useful, but necessary, and cannot mislead the student if he re- members that all such aids are merely the scaffoldings around the science, on which the builders work. It is from this point of view alone that we are to look at the whole idea of chemi- cal atoms, which lies at the basis of our modern chemical philosophy. That this idea is actually realized in the concrete form which it takes in some minds, can hardly be believed. The true chemical idea of the atom is more nearly represented by the corresponding Latin word individuum. The atom is the chemical individual, the unit, in which the mind seeks to repose for the time the individuality of that as yet undivided substance we call an element. 34. Graphic Symbols. A more graphic method of repre- senting the relations between the atoms of a molecule than that of our ordinary rational symbols has been contrived by Kekule, and has a similar value in aiding the conceptions, and thus facilitating the study of chemistry. In describing this system we shall speak of the possibilities of combination of any polyad atom with monad atoms as so many centres of at- traction or points of attachment, and, also, as so many affinities. Kekule represents a monad atom, with its single centre, thus, Q, while the symbols (T"7), (. . .), (. . . .}, & c ., represent polyad atoms of different atomicities. When the several affini- ties are satisfied, the points are exchanged for lines pointing in the direction of the attached atoms. Thus, the symbol represents a dyad atom with its two affinities satisfied by two ii monad atoms, as, for example, in a molecule of water H-Q-H. In like manner the symbol (|^ ( {"T )( ^TT > T"o repre- v ii sents a molecule of nitric anhydride N t O and the symbol !! ii a mo ^ ecu ^ e f sulphuric anhydride S0 3 . Mole- cules like these, in which all the affinities are satisfied, are said to CHEMICAL TYPES. 71 v be saturated or closed, while the atomic group NO.^ represented by > ^ ^N has one point of attraction still open, and, therefore, acts as a inonad radical. So, also, the molecular group S0. 2 represented by > |^-| p _ >., acts as a dyad radi- cal. These graphic symbols enable us to illustrate several impor- tant principles which could not readily be understood without their aid. First. In the examples given in this section thus far, the quanti valence of a group of atoms of the same element is equal to the sum of the quanti valences of all the atoms of the V II group. Thus, in the molecule N 2 5 , the group of two pentad atoms presents ten affinities, and is saturated by the group of five dyad atoms, which presents the same number of affinities in return. So, also, in the molecule SO& a group of three dyad atoms just saturates the single hexad atom S. Such, how- ever, is not necessarily the case, for it frequently happens that the similar atoms of such groups are united among them- selves, and that a portion of the affinities (necessarily always an even number) are thus satisfied. For example, although C is a tetrad atom, the hydrocarbons, (7 2 /^, C 2 ff 4 , and C 2 ff^ are all saturated molecules, as is shown by the following graphic symbols, and it is evident that in the first the two carbon atoms have been united by two, in the second by four, and in the third by six, of their eight affinities, while a corresponding number of points to which hydrogen atoms might otherwise have been at- tached are thus closed. In like manner we have a well-known series of hydrocar- bons, whose symbols are CH, c^iifo c s iT S i C^H^ CsHift CQJET U , &c., the molecule of each one differing from that of the last by the group CH. 2 . In all these compounds the carbon atoms are 72 CHEMICAL TYPES. united among themselves at the smallest possible number of points, as is shown, in a single case, by the following graphic symbol, and by constructing the graphic symbols of the other members of the series, it will be easily seen that the number of affinities thus closed is in every case equal to 2 n 2, while the number remaining open is 4 n (2 n 2) = 2 n -\- 2, where n stands for the number of carbon atoms in the molecule. Hence, while the groups just mentioned form saturated molecules, the atomic groups Off, Methyl. Ethyl. Propyl. act as univalent radicals. Ci i i u &c., Butyl. Amyl. The graphic symbol of ethyl is , and in a similar way the graphic symbols of In like manner the other radicals may be easily constructed, may be also constructed the graphic symbols of the following important compound radicals, which form a series parallel to the first, and are all evidently dyads : Ethylene. Propylene. Butylene. 5 ff w &c. Amylene. Here again the graphic symbols enable us to explain a remark- able fact. These last atomic groups act not only as compound radicals, but also form the molecules of definite hydrocarbons (the first in the series being the well-known olefiant gas), and the difference in these two conditions may be represented to the eye, in the case of amylene, for example, as below : GGJ CiXD (DO) QXL> Radical C S H 10 . Hydrocarbon C r ,H 10 . The molecule in the first case is open, and presents two points of attraction, while in the second case it is closed. CHEMICAL TYPES. 73 The members of the two classes of hydrocarbon radicals mentioned above are the characteristic constituents of an im- portant class of compounds called alcohols, and hence they are usually called alcohol radicals. If, in these atomic groups, we substitute oxygen for a portion of the hydrogen, one atom of oxygen always taking the place of two atoms of hydrogen, we obtain still other series of radicals, which are the characteristic constituents of several important organic acids, and belong to the class of acid radicals, which will be defined in the next chapter. Among the most important of the radicals thus de- rived are those of the followin series : OHO C 2 H 3 -C S H 5 C 4 H 7 G 5 N g O Formyl. Acetyl. Propionyl. Butyryl. Valeryl. and the student should construct the graphic symbol of each. The compounds of carbon have been selected to illustrate the apparent change of atomicity which frequently accompa- nies the grouping together of similar atoms, because this ele- ment is peculiarly susceptible of such a mode of combination, and in fact the almost infinite variety of its compounds may be traced to this circumstance. The same phenomenon, however, is presented, although to a less marked degree, by other ele- ments. Thus arises the remarkable fact that a group of two atoms of a bivalent element has not unfrequently only the same quantivalence as a single atom. For example, there are two compounds of mercury and chlorine Hg=Gl z represented graphi- cally by S=y^ an( ^ D^Jfe] = C%a represented by ^\r^\- So also we have Cu=0 and [(7w 2 ] = (9. We also frequently meet with another illustration of the same principle in an important class of tetrad elements whose atoms readily pair together, forming an atomic group which is sexivalent. Thus are formed the well-known compounds When these same elements enter into combination by single atoms, they are almost invariably bivalent, and thus we have, in several cases, two very distinct classes of compounds, the one formed with the single and the other with the double atom of the element ; for example, 74 CHEMICAL TYPES. Fe-Cl 2 and FeWl Q Fe-0 and It will be noticed that although in the compounds of the second class the quantivalence of the single atoms is twice as great as it is in the first, yet their atom-fixing power is only increased by one half, and hence the name of ses^m'-oxides or sesgw'-chlorides, &c., which is frequently applied to them. In order to distinguish the groups of similar atoms whose affinities are all open, from those groups where the affinities are in part closed by the union of the atoms among themselves, we may, as above, enclose the symbols of the last in brackets ; and this rule will generally be followed. In most cases, however, the relations of the parts of the symbol are sufficiently evident without this aid. Secondly. The graphic symbols illustrate another important theoretical principle, which, although almost self-evident, might be overlooked if not dwelt upon specially ; namely, that on the multivalence of one or more of its atoms depends the integrity of every complex molecule. According to our pres- ent theories, no molecule can exist as an integral unit unless its parts are all bound together by such atomic clamps. More- over, the whole virtue of a compound radical consists in the circumstance that it is an incomplete structure of the same sort, and its quantivalence is in every case equal to the number of univalent atoms (or their equivalents) which are required to complete it, or which it may be regarded as having lost. Hence the law of Wurtz finds a perfect expression in this sys- tem of graphic notation. Thirdly. The graphic symbols illustrate most forcibly the relations of the parts of a complex molecule. Thus, for ex- ample, the symbols of alcohol and acetic acid given below show r } p) that in these compounds the dominant atom of oxygen acts as a bond uniting a complex radical to a single monad atom. They also show how it is possible that three of the atoms of hydrogen in acetic acid may stand in a very different relation to the mole- cule from the fourth (31). Again they show that the molecule of acetic acid differs from that of alcohol in the CHEMICAL TYPES. 75 fact that one dyad atom has taken the place of two monad atoms; and, lastly, they give form to the idea of chemical types, so far as it has any real significance. When the com- position of a compound is represented in this way, all the accidental or arbitrary divisions of our ordinary notation dis- appear, and only those are preserved which are fundamental. We gain thus more accurate conceptions of molecular struc- ture. We understand better the relations of the various com- pound radicals (compare 28), and, above all, we thus realize the full meaning of the fundamental tenet of our new philoso- phy, which holds that each chemical molecule is a completed structure bound together in all its parts by a system of mutual attractions. There is another system of graphic symbols, frequently used in works on modern chemistry, which has some advantages over the one just described. In this system the atoms are represented by small circles circumscribing the ordinary sym- bol, and the atomicity is indicated by dashes radiating from these circles. A few examples will sufficiently illustrate the application of this method. ll I II -- ---- ---- Water II I H-O-H @ @ @ Alcohol. Acetic Acid. C Z H 3 -0-H. C 2 H 3 0.0-H. It is obvious, however, that the circles here used are not es- sential, and if we omit them, and only use dashes between the dominant atoms, and also, for convenience in printing, bring the whole expression into a linear form, using commas to separate disconnected atoms, and such other signs as may be necessary to avoid ambiguity, we have at once the ordinary system of nota- tion adopted in this book. The graphic symbols last described are merely an expansion of this system. Nevertheless, the prac- tice of developing the ordinary symbols into either of the more graphic forms will tend to impress the full meaning of the symbols on the mind of the student, and will thus greatly aid him in acquiring a clear conception of the theory of modern chemistry. 76 CHEMICAL TYPES. We may, however, extend the use of dashes so as to indicate the relations of all the parts of a complex molecule by our or- dinary notation. Thus we may write the symbol of alcohol or that of acetic acid and these expanded symbols may frequently be used to ad- vantage in place of the graphic forms. When thus developed, the symbol indicates the quantivalence of each of the atoms of the molecule, and in every case, if the symbol is correctly written, the number of dashes will be one half of the total quantivalence of all the atoms which are thus grouped together, for each dash evidently represents two affinities. The remarks at the close of the last section apply, of course, still more forcibly to such bold and material conceptions as these graphic symbols appear to represent, and when we re- call the hooked atoms of an elder philosophy, we cannot but smile to think how closely our modern science has reproduced what we once considered as strange and grotesque fancies. But, absurd as such conceptions certainly would be, if we supposed them realized in the concrete forms which our diagrams em- body, yet, when regarded as aids to the attainment of general truths, which in their essence are still incomprehensible, even these crude and mechanical ideals have the very greatest value, and cannot well be dispensed with in the study of science. Questions and Problems. 1. To what types may the following symbols be referred, and what is the quantivalence of the different compound radicals here distin- guished ? Study with the same view the symbols already given in the previous chapter. fr(0 7 ff*0) izole. Oil of Bitter Almonds. Ethylene. Gly collie Acid. H-0-(C 7 H.O) SfC Phenic Acid. Benzoic Acid. Glycol. Oxalic Acid. Aniline. Benzamide. / Q TJ \ \-ftT TT Ethylene diamine. CHEMICAL TYPES. 77 ZT, H-N-( C 2 H 2 OyO-H H, H-N-( C 2 2 )- 0-H Glycocol. Oxamic Acid. ff, ( C 7 H 5 0}=N-( C 2 H 2 0)- 0-H H, H-N-( C 2 0,)- 0-( G,H 6 ) Hippuric Acid. Oxamethane. 2. Analyze the following reactions, and show that by comparing the reactions in each group, the typical structure of the various compounds may be inferred. d-d + H-H = HCl + HCl Chlorine gas. Hydrogen gas. Hydrochloric Acid. Hydrochloric Acid. Cl-Cl . + (C 7 H 5 0)-H = (C 7 H 5 0)-Cl + HCl Oil of Bitter Almonds. Benzoyl Chloride. H-Cl + K-O-H = KGl + H-O-H Potassic Hydrate. Potassic Chloride. Water. H-Cl + (C.H^-O-H = (C. 2 H 5 )-Cl + H-O-H Alcohol. Ethylic Chloride. H,H=S + PWl, = PiCkS + HCl + HCl Sulphohydric Acid. Phosphoric Chloride. H, ( C 2 H 3 Oy-S + Pi Gl t = Pi Cl S + ( C*H 0)- Cl + HCl Thiacetic Acid. Acetyl Chloride. KfOfHi + (CO), H~=N = KfOf(CO} + H, Potassic Hydrate. Cyanic Acid. Potessic Carhonate. Ammonia. N= K 2 =0. 2 =(CO)+H, H, Cyanic Ether. Ethylamine. 3. What would be the symbols of cyanic acid and cyanic ether (see last problem), on the supposition that they contain the radical cyan- ogen, and are formed after the water type ? Is the following reaction compatible with that last given ? K-0-H+ (C<,H,)-0-(CN) = (C 2 H 5 )-0-H+ K-( Cyanetholine. Alcohol. Potassic Cyanate. and if not, what conclusion must you draw in regard to the two compounds cyanic ether and cyanetholine ? 4. What bearing have the phenomena of substitution on the doc- trine of chemical types ? Does the circumstance that the proper- 1 This product in the actual process is decomposed by the excess of potash into potassic carbonate and ammonia. 78 CHEMICAL TYPES. ties of the substitution products are frequently quite different from those of the original substance invalidate the doctrine ? 5. How does the action of chlorine on acetic acid indicate that this compound is fashioned after a determinate type ? On what particular fact does this evidence chiefly rest V 6. What bearing have the phenomena of isomorphism on the doc- trine of types ? Enforce the argument by some familiar illustra- tion. 7. The radical allyl C 3 H 5 is univalent in oil of garlic (C 3 #" 5 ) 2 =S, and in allylic alcohol (C 3 H 5 )-0-H, but trivalent in glycerine (C*H^=OfH y Moreover, this radical when set free doubles, forming a volatile hydrocarbon oil, which has the composition (C 3 PI^(C 3 H^), and which combines directly with bromine, the resulting product hav- ing the symbol (C 3 H^-(C z H^Br^. Represent these symbols by the graphic method, and thus explain the different relations of the radical. 8. Represent the symbols of phenic acid and benzoic acid by the second graphic method, and explain why the radical phenyl (C 6 f/ 5 ) and benzoyl (C 7 7J 5 0) are only univalent. 9. Why is it that the addition of the atoms CH 2 does not change the atomicity of a radical ? 10. What is the quantivalence of Al in the symbol \_Al- Al~]iCl 6 ! Is there any difference in the quantivalence of Fe in the two com- pounds Fe=O z =CO and [Fe-Fe]i0J(S0 2 ) 8 ? Answer the questions by the aid of graphic symbols. 11. Is there any difference in the quantivalence of nitrogen in potassic nitrite K-O-NO and potassic nitrate K-O-NO^ 12. Represent by graphic symbols the difference between cyanic ether and cyanetholine (see problems 2 and 3 above). 13. The symbol \Hg^\Cl t represents a single molecule, while Na z Cl 2 represents two molecules, and would be more properly writ- ten 2NaCl. What is the difference in the two cases ? 14. Represent by the graphic method the symbols of potassic car- bonate K 2 ]I(#0) 6 Calcic Hydrate. Ferrous Hydrate. Chromic Hydrate. Ammonia. Closely allied to these metallic hydrates is a very remarkable compound, formed by dissolving ammonia gas, JV7/3, in water. Although the product resembles, in many of its physical relations, a simple solution of gas in water, yet the compound in all its chemical relations acts like a metallic hydrate, NH, + R 2 = Ammonia Gas. Water. Ammonic Hydrate. which has led chemists to write its symbol after the type of water, and to assume the existence of a univalent compound i radical NH, to which has been given the name of ammonium. Metallic Oxides or Basic Anhydrides. Closely allied to the metallic hydrates, in the relation we are now considering, are many of the simple compounds of the metals with oxygen which are called in general metallic oxides. Such compounds as Ca-0 Ba-0 Pb=0 Fe-0 Gu-0 Aa. 2 =0 Calcic Oxide. Baric Oxide. Plumbic Oxide. Ferrous Oxide. Cupric Oxide. Argentic Oxide. may be regarded as formed from one or more molecules of water, by replacing all the atoms of hydrogen with those of some metal ; and these oxides as well as the hydrates before mentioned are frequently classed together under the common title of bases. although it would be best to confine this term to the metallic BASES, ACIDS, AND SALTS. 83 hydrates alone, and to distinguish the basic oxides as basic anhydrides. (37) Salts. The atoms of hydrogen still remaining in a metallic hydrate may be replaced with the atoms of a well-defined class of non-metallic elements and compound radicals ; and, for a reason which will soon appear, the replacing atoms are called acid or negative radicals. 1 From this replacement results a new class of compounds we call salts. Thus, K-O-H gives K-O-Cl, also K-0-N0 2 and K-0-(C 2 ff 3 0) Potassic Hydrate. Potassic Hypochlorite. Potassic Nitrate. Potassic Acetate. Ca-OfK 2 gives Ca-0.rS0. 2 Ca=OfCO Ca=0,=(C 2 ff 3 0) 2 Calcic Hydrate. Calcic Sulphate. Calcic Carbonate. Calcic Acetate. ' 36. Acids. Opposed in chemical properties to the so- called bases is another very important class of compounds called acids. They derive their name from the fact that they are generally soluble in water and have a sharp or sour taste, although there are many exceptions to the rule. Like the bases, they all contain hydrogen ; but this hydrogen can no longer be replaced by non-metallic elements or negative radi- cals, but only by metallic elements and positive radicals, and it is herein that the chief distinction lies. Moreover, the opposi- tion of these two classes of compounds also appears in the fact that, while in bases the replaceable hydrogen atoms are united to a metallic atom or positive radical, which for this reason we frequently call a basic radical, in the acids, on the other hand, 1 The word radical, as used in chemistry, stands for any atom or group of atoms, which is, for the moment, regarded as the principal constituent of the molecules of a given compound, and which does not lose its integrity in the ordinary chemical reactions to which the substance is liable. The distinc- tion between basic and acid radicals (or positive and negative radicals as they are more frequently called) will become clear as we advance. It is sufficient for the present to state that, although these terms imply an opposition of rela- tions rather than a difference of qualities, yet, as a general rule, the metallic atoms are basic radicals, while the non-metallic atoms are acid radicals. Moreover it may be added, that among compound radicals those consisting of carbon and hydrogen alone are usually basic, and those containing also oxy- gen usually acid ; and, further, that of the two most important radicals con- taining nitrogen, ammonium (Nff t ) is strongly basic, and cyanogen ( CN) as decidedly acid. In this book, with few exceptions,. the basic radicals are always placed on the left-hand, and the acid radicals on the right-hand side, of the molecular symbols. 84 BASES, ACIDS, AND SALTS. these same hydrogen atoms are united as a rule to a non- metallic atom or negative radical, frequently, also, called as above an acid radical. In most cases there is a vinculum which unites the two parts of the molecule ; and both in acids and in bases this vinculum consists usually of one or more oxygen atoms, although in a large class of acids the hydrogen atoms are united directly to the radical without any such con- nection. The acids of this class have by far the simplest constitution ; and we will give examples of these first, adding in each case a reaction to illustrate the acid relations of the compound. In studying these reactions, it must be borne in mind that the evidence of acidity is in each case to be found in the fact that one or more of the hydrogen atoms of the com- pound may be replaced by positive radicals or metallic atoms. This replacement may be obtained in one of four ways, by acting on the acid, either with the metal itself, or with a metallic oxide, or with a metallic base, or with a metallic salt. (2HCI + Aq) + NaNa = (2 Na Cl + Aq) + HI-HI Hydrochloric Acid. Sodium. Sodic Chloride. (2HCl + Aq) + ZnO = (ZnCl 2 + R 2 + Aq) Zincic Oxide. Zincic Chloride. [47] (HBr + K-O-H -\- Aq) = (KBr + Hydrobromic Acid. Potassic Hydrate. Potessic Bromide. (JSI+ Ag-0-N0 2 + Aq) = Agl + (ff- Hydriodic Acid. Argentic Nitrate. Argentic Iodide. Nitric Acid We will next give examples of more complex acids, in which the two parts of the molecule are united by a vinculum of oxy- gen atoms. (H-0-(C Z H S 0) 4- Na-0-H4- Aq) = (Na-0-( C 2 H 3 0) -4-H 2 04-Aq) Acetic Acid. Sodic Hydrate. Sodic Acetate. 4- C u = (Cu=OfSO a -f- H,0 -f Aq) Sulphuric Acid. Cupric Oxide. Cupric Sulphate. (H 3 =0,=PO -f SK-O-H -f Aq) = (K^O^PO + 3H,0 -f Aq) Phosphoric Acid. Potassic Hydrate. Potassic Phosphate. Such acids as these are called oxygen acids. Like the hydrates, they may be regarded as compounds of hydroxyl, but with negative instead of positive radicals, thus : BASES, ACIDS, AND SALTS. 85 ffO-N0 2 Nitric Acid. Sulphuric Acid. Phosphoric Acid. This mode of writing the symbols is not only frequently con- venient, but has been of real value by bringing out unex- pected and important relations. It does not, however, indicate any fundamental difference of opinion in regard to the consti- tution of these hydrates, and this at once appears when the symbols are put into the graphic form. When an acid, like acetic acid, contains but one atom of hy- drogen, which is replaceable by a metallic atom or a positive radical, it is called monobasic ; when, like sulphuric acid, it con- tains two such hydrogen atoms, it is called dibasic ; when, like phosphoric acid, it contains three, it is tribasic, &c. Moreover, one evidence of this difference of basicity is found in the fact that whereas a monobasic acid can only form one salt with a univalent radical, a dibasic acid can form two, and a tribasic three. Thus, while we have only one sodic nitrate, there are two sodic sulphates and three sodic phosphates. Na-0-N0. 2 Sodic Nitrate. Acid Sodic Phosphate. H,Na-0.rS0 2 Acid Sodic Sulphate. Neutral Sodic Phosphate. Neutral Sodie Sulphate. Basic Sodic Phosphate. There is, however, but one calcic sulphate, for, since the cal- cium atoms are bivalent, a single one is sufficient to replace both of the hydrogen atoms in the acid. 37. Acid Anhydrides. Besides the acids properly so called, all of which contain hydrogen, there is another class of com- pounds which bear the same relation to the true acids which the metallic oxides bear to the true bases. To avoid confusion, com- pounds of this class have been distinguished as anhydrides^ and they may be regarded as one or more molecules of water in which all the hydrogen has been replaced by negative or acid radicals. As among the most important of these we may enumerate Sulphuric Anhydride S0. 2 =0 or S0 3 , Nitric Anhy- 1 More precisely acid anhydrides, but as the basic anhydrides are usually called simply metallic oxides, the qualifying term is seldom added. 86 BASES, ACIDS, AND SALTS. dride (N0 2 ) 2 =0 or N Z 0# Carbonic Anhydride 00=0 or C0 2 , i Phosphoric Anhydride (P0 2 ) 2 = or P 2 5 , and Silicic Anhy- IV dride /Si=0 2 . Most of the anhydrides unite directly with water to form acids, and several of the acids, when heated, give off water and are resolved into anhydrides. [Compare 44 and 45.] H 2 + S0 3 = 3ff 2 + P 2 5 = [49] fffOfSi = SiO a + 2ff 2 Silicic Acid. Silicic Anhydride. = R 2 3 + 3ff 2 Boric Acid. Boric Anhydride. Moreover in many cases these anhydrides will combine di- rectly with the metallic oxides to form salts ; and the reac- tions are best indicated by a rational formula, which represents the oxide and anhydride as radicals in the resulting compound. Thus, baric oxide burns in the vapor of sulphuric anhydride, yielding baric sulphate ; and lime also unites directly with the same anhydride, although with less energy, forming calcic sul- phate. BaO + S0 3 = BaO, S0 3 and CaO + S0 3 = CaO, S0 3 We are thus led to the old formulae of the dualistic system, according to which the metallic oxides were the only true bases, the anhydrides were the only true acids, and the two w r ere regarded as paired in all true salts. But, although in its modern theories our science has fortunately left the ruts to which the dualistic ideas for so long limited its progress, yet it must be remembered, that, according to our present definitions, these dualistic formulae are perfectly legitimate, and still give the simplest exposition of a large number of important facts. 38. Salts. The definition of the term "salt" has been clearly implied in the definitions of "base" and "acid" already given. It is any acid in which one or more atoms of hydrogen have been replaced with metallic atoms or basic radicals ; it is any base in which the hydrogen atoms have been more or less re- placed by non-metallic atoms or acid radicals ; or it may be the BASES, ACIDS, AND SALTS. 87 product of the direct union of a metallic oxide and an anhy- dride. A neutral salt is, properly speaking, one in which all the hydrogen atoms, whether of base or acid, have been re- placed as just stated. A basic salt is one in which one or more of the hydrogen atoms of the base remain undisturbed, and therefore still capable of replacement by acid radicals. An acid salt is one in which one or more of the hydrogen atoms of the acid remain undisturbed, and therefore capable of replace- ment by basic radicals. But, besides the basic and acid salts, which come under these definitions, there are also others which can be most simply de- fined as consisting of several atoms of the metallic oxide to one of anhydride, or of several atoms of anhydride to one of the metallic oxide. As an example of acid salts of the second class we have, be- sides the two sodic sulphates mentioned on page 85, also a third, which may be written Na 2 0,2S0 3 . This is easily ob- tained by simply heating the acid sulphate. = Na. 2 0, 2S0 3 + I$1M [50] Acid Sodic Sulphate. Sodic Bisulphate. Water. If heated to a still higher temperature, one atom of the anhy- dride is set free, and the salt falls back into the neutral sul- phate. S0 3 + Bisulphate. Neutral Sulphate. Anhydride. This reaction justifies the dualistic form given to the symbol; but other relations of the bisulphate may be better expressed by the following typical formula, Sodic Bisulphate. Neutral Sulphate. Anhydride. in which a group of two atoms of SO& soldered together by one atom of oxygen, acts as a bivalent radical. As an example of a basic salt of the second class we have, in addition to the two plumbic acetates of the normal type, Pb- Of( CA 0) 2 and Pb= Of( C 2 ff s 0), H Neutral Plumbic Acetate. Basic Plumbic Acetate. 88 BASES, ACIDS, AND SALTS. a third salt containing three times as much lead, (Pb-0-Pb-0-Pb) = 2 =(C 2 ff 3 0) 2 , [51] Triplumbic Acetate. in which a group of three atoms of lead, soldered together by two atoms of oxygen, acts as a bivalent radical. It is evident that, theoretically, any number of multivalent radicals might be united in this way, and also that the complex radical thus formed will have a quantivalence easily determined by esti- mating the number ( f bonds which remain unsatisfied ; but, practically, the grouping cannot be carried to a very great ex- tent, for the stability of the radical diminishes with its com- plexity, and a condition is soon reached when it can no longer sustain, if we may so express it, its own weight. Moreover, while some radicals, like the atoms of lead, copper, mercury, and iron, are prone to group themselves in this way, the larger number show but little tendency to this mode of union. The symbols of these acetates may also be written on the dualistic type, which represents them as compounds of plumbic oxide, Pb 0, and acetic anhydride, (7 4 // 6 3 . We have, then, PbO, 4 ff,0 3 and 3PbO, C 4 ff0 3 [52] Neutral Plumbic Acetate. Triplumbic Acetate. and we may thus best illustrate the important fact that the second compound is prepared by combining with the first an additional quantity of plumbic oxide. It will appear on reviewing the symbols of the acids, base?, and salts given in this section, that, in by far the greater num- ber, the two parts of the molecule are held together by one or more atoms of oxygen, which act as a vinculum. Such com- pounds are called oxygen salts, using the word salt, as is fre- quently done, to stand for acids and bases, as well as for the true metallic salts; and in fact they all belong to the same type of chemical compounds. Since oxygen plays so impor- tant a part in terrestrial nature, we might well 'expect that these oxygen compounds would hold a very conspicuous place in our chemical science, and such is indeed the fact. Dur- ing the dualistic period the study of chemistry was almost wholly confined to the oxygen^ compounds, and, even no\v, they occupy by far the largest share of a che:ni>t's attention. BASES, ACIDS, AND SALTS. 89 There is, however, another element, namely, sulphur, which is capable of filling the place occupied by oxygen in many of its compounds, and thus may be formed a distinct class of bodies which are called sulphur salts. These compounds are not nearly so numerous as the oxygen salts, and have not been so well studied, so that a few examples will be sufficient to illustrate their general composition, and the relations which they bear to the corresponding oxygen compounds. Oxygen Salts. Sulphur Salts. H-O-H H-S-H Water or Hydric Acid. Sulphohydric Acid. K-O-H K-S-H Potassic Hydrate. Potassic Sulphohydrate. KrO.rCO KfSfCS Potassic Carbonate. Potassic Sulphocarbonate. 39. Test-Papers. The soluble bases and acids, when dis- solved in water, cause a striking change of color in certain vegetable dyes, and these characteristic reactions give to the chemist a ready means of distinguishing between these two important classes of compounds. The two dyes chiefly used for this purpose are turmeric and litmus, and strips of paper colored with the dyes are employed in testing. Turmeric paper, which is naturally yellow, is turned brownish red by bases, while litmus paper, which is naturally blue, is turned red by acids, and in both cases the natural color is restored by a compound of the opposite class. If to a solution of a strong base, like sodic hydrate, we add slowly and carefully a solution of a strong acid, like sulphuric, we shall at last reach a condition in which the solution affects neither test-paper, and it is then said to be neutral. On evap- orating this solution we obtain a neutral salt, like sodic sulphate, and the presence in the solution of the slightest excess of acid or base beyond the amount required to form this salt would have been made evident by the test-papers. Tn such cases, we may therefore use these test-papers to distinguish between acid, basic, and neutral salts, but only with great caution ; for we find that when, as in acid-carbonate of soda, a strong base is asso- ciated with a weak acid, the reaction is still basic, although 90 BASES, ACIDS, AND SALTS. the acid may be greatly in excess, and, on the other hand, when, as in cupric sulphate, a weak base has been associated with a strong acid, the reaction may be strongly acid even in the basic salts. The explanation of these apparent anomalies is to be found in the fact that these colored reagents are all salts themselves, and the reactions examples of metathesis. The coloring matter of these dyes is an acid which varies its tint according as the hydrogen atoms have or have not been replaced ; and when, for any reason, the acid or base of the salt examined is not in a condition to determine the necessary me- tathesis, the characteristic change of color does not take place. Unfortunately, the facts just stated have led to great confu- sion in the use of the words "acid" and "basic" as applied to salts, since these terms sometimes have reference solely to the number of atoms of hydrogen, in the acid or base, which have not been replaced in the formation of the salt, and at other times refer to the reactions of the salt on the colored reagents just described. A confusion of this sort must have been noticed in the names of the three phosphates of soda on page 85. The so called neutral phosphate is theoretically an acid salt, and the basic phosphate a neutral salt, but the salts give with test- papers the reactions which their names indicate. The theo- retical is the only legitimate use, and the one we shall adhere to in this book, except in regard to names of compounds which cannot be arbitrarily changed. 40. Alcohols, Fat Acids, Ethers. The hydrocarbon radicals mentioned in 34 yield a very large number of compounds after the type of water, which are closely allied to the hy- drates and anhydrides, both acid and basic, just described. Jf one of the hydrogen atoms in the molecule of \iater is replaced by either of the univalent basic radicals, methyl, ethyl, propyl, &c., we obtain a class of compounds, called alcohols, of which our common alcohol is the most important. On the other hand, if the atom of hydrogen is replaced by one of the uni- valent acid radicals, formyl, acetyl, propionyl, &c., we obtain an important class of acid compounds, of which acetic acid (vine- gar) is the best known, but which also includes a large number of fatty substances closely related to our ordinary fats. Hence the name Fat Acids, by which this class of compounds is gen- erally designated. BASES, ACIDS, AND SALTS. 91 Basic Hydrates or Alcohols. Methylic Alcohol (wood spirits) CH^O-H. Ethylic Alcohol (common alcohol) C 2 ff 5 -0~H. Propylic Alcohol C 3 H 7 -Q-H. Butylic Alcohol C 4 H,-0-ff. Amylic Alcohol (fusel oil) C.H^-O-H. (With six others already known.) Acid Hydrates, Fat Acids. Formic Acid H-O-CHO. Acetic Acid H-0-Q&O. Propionic Acid H~ - C 3 H 5 0. Butyric Acid E- 0- C 4 E 7 0. Valerianic Acid H- 0- G & ff 9 0. (With fifteen others already known.) If now we replace both of the hydrogen atoms of water by the same basic radicals mentioned above, we obtain a class of compounds called ethers, which correspond to the metallic oxides or basic anhydrides; and if we replace the two hydro- gen atoms by the corresponding acid radicals, we obtain a similar series of acid anhydrides. Lastly, if we replace one of the hydrogen atoms by a basic radical, and the other by an acid radical, we get a class of compounds also called ethers (but distinguished as compound ethers), which correspond to the salts. Examples of Anhydrides. 1. Simple Ethers. Methylic Ether CE 3 ~0-CE 3 or (CH 3 } 2 =0. Ethylic Ether (common ether) C 2 H 5 -Q-C 2 H 5 or (O 2 H 5 ) 2 =0. 2. Mixed Ethers. Methyl-ethyl Ether CH S -0- O 2 H 5 . Ethy 1-amyl Ether C 2 E 5 - - C 5 H U . 3. Compound Ethers. Acetic Ether C. 2 E 5 - 0- C,R. 0. Butyric-methyl Ether CE 3 -Q-C 4 E 7 0. 4. Acid Anhydrides. Acetic Anhydride C. 2 H^ 0~0~ CM* or ( C*E 3 0).,= 0. Valerianic Anhydride C 5 H0-0-C 5 H,0 or (C 5 H,0)iO. 92 BASES, ACIDS, AND SALTS. The positive radicals, of which the alcohols consist, hold an intermediate position between the strong basic radicals on the one hand, and the strong acid radicals on the other, and the same is true of the alcohols themselves, which hold a middle place between the strong basic and the strong acid hydrates. This is indicated by the following reactions ; in what way it is left to the student to inquire. H-H 2 CH 3 ~0-H+ HfOfSOi 41. Glycols. The class of hydrates described in the last sec- tion belong to the simple type of water. But we have also a class of analogous compounds belonging to the type of water doubly condensed. If in the double molecule of water (H.f 2 =H 2 ) we replace one of the pairs of hydrogen atoms by either of the bivalent positive radicals, ethylene, propylene, butylene, &c., we obtain a series of compounds closely resembling the alco- hols, called glycols, and by substituting the related negative radicals we obtain two series of acid hydrates, which stand in the same relation to the glycols that the fat acids bear to the alcohols. These relations are shown in the following scheme, which, however, includes only the five first members of each of these three series of compounds. It should be noticed in this connection that each of the bivalent positive radicals yields two related negative radicals, while the univalent positive radi- cals of the last section yield only one such negative radical ; and moreover that the acids in the first series, although dia- tomic, are only monobasic, while those in the second series are both diatomic and dibasic (43). Ethylic Glycol. Glycolic Acid. Oxalic Acid. Propylic Glycol. Lactic Acid. Malonic Acid. H 2 =0 2 =C 4 fI 4 2 Butylic Glycol. Oxybutyric Acid. Succinic Acid. Amylic Glycol. Valerolactic Acid. Pyrotartaric Acid. efftfOfH, HfOfC,H w O Hf0 2 =C 6 ff s Hexyl Glycol. Leucic Acid. Adipic Acid. BASES, ACIDS, AND SALTS. 93 Corresponding to these basic and acid hydrates we have also been able to obtain in several cases the basic and acid anhydrides, besides a very large number of compound ethers. 42. Glycerines and Sugars. In the alcohols one hydrogen atom from the original typical molecule (typical hydrogen] re- mains undisturbed. In the glycols there are two such hydro- gen atoms, and hence these compounds are frequently called diatomic alcohols. Our common glycerine is a triatomic alco- hol, and may be regarded as formed from a molecule of water trebly condensed (H^O^H Z ), by replacing one of the groups of hydrogen atoms with the trivalent radical glyceryl (C 3 H 5 ). It is probable that a large number of triatomic alcohols or glycer- ines may hereafter be obtained, but only two are now known. Propylic Glycerine (common glycerine) Amylic Glycerine From the glycerines we may derive acids, anhydrides, and compound ethers, bearing to each other the same relations as those derived from the alcohols of a lower order, but only a few of the possible compounds which our theory would foresee are yet known. The natural fats are compounds of glycerine with the fat acids, and it is probable that our common sugars are likewise derived from alcohols of a still higher order of atomicity. 43. Atomicity and Basicity of an Acid. By the atom- icity of a compound is meant the number of hydrogen atoms which it retains from the original typical molecule still unre- placed, and the use of this term with reference to the basic hydrates has been already abundantly illustrated in this chap- ter. In the case of the acids a distinction must be made be- tween atomicity and basicity, which is frequently important. The formula of every acid may be written on the type of one or more atoms of hydrochloric acid, as H n 7? n , in which H n stands for^the replaceable atoms of hydrogen, and Jt* for all the rest of the atoms of the molecule, which may be regarded as forming a radical with an atomicity equal to the number of replaceable i n in hydrogen atoms. The symbols H-NO S HfSO fffPO* are 94 BASES, ACIDS, AND SALTS. written on this principle. In each case the acid is said to have the atomicity of the radical. The basicity of the acid, on the other hand, depends, not on the total number of replace- able hydrogen atoms, but on the number which may be replaced by metallic atoms or basic radicals. As a general rule, it is true that the basicity is the same as the atomicity, but this is not always the case. Thus lactic acid is diatomic but monobasic, and the same is true of the other acids homol- ogous with it (page 92). ff, H=(C 3 ff 4 3 ) Na,H=(C 8 HA) Na, (C 7 ff 5 Lactic Acid. Sodic Lactate. Sodic Benzolactate K, C 2 ff/( 3 H 4 3 ) C Z H 6 , C,H^( C 3 ff 4 3 ) Potassic Ethyl-lactate. Diethylic-lactate. Only one atom of hydrogen can be replaced by a metallic radical, but a second may be replaced by either a negative or an alcoholic radical, as in the last three symbols, and in desig- nating the atoms, thus differently related to the molecular struc- ture, it is usual to call the first basic and the other alcoholic hydrogen. We might, in like manner, distinguish between the atomicity and the acidity of a base, but this distinction has not been found as yet to be of practical importance. 44. Water of Crystallization. Among the most striking char- acteristics of the class of compounds we call salts is their sol- ubility in water and their tendency on separating from it, in consequence of either the evaporation or the cooling of the fluid, to assume definite crystalline forms. These crys- tals, as a general rule, are complex crystalline aggregates of molecules of the salt and molecules of water. The water is held in combination by a comparatively feeble force, and may be generally driven off by exposing the salt to the temperature of 100 C., when the crystals fall to powder. Sometimes it'es- capes at the ordinary temperature of the air, when the crystals, as before, fall to powder and are said to effloresce. It thus evi- dently appears that the water, although an essential part of the crystalline structure, is not inherent in the chemical molecule, and hence the name Water of Crystallization. The presence of BASES, ACIDS, AND SALTS. 95 water of crystallization in a salt is expressed by writing after the symbol of the salt, and separated from it by a period, the number of molecules of water with which each salt molecule is associated. Thus we have FeSOJHtO Crystallized Ferrous Sulphate or Green Vitriol. Crystallized Sodic Carbonate or Sal Soda. The same salt, when crystallized, at different temperatures not unfrequently combines with different amounts of water of crystallization, the less amounts corresponding to the higher temperatures. Thus manganous sulphate may be crystallized with three different amounts of water of crystallization. We have MnSO.7H 2 when crystallized below 6 C. MnSO^H^O " u between 7 and 20. MnSO^AH^O " " between 20 and 30. The crystalline forms of these three compounds are entirely different from each other ; and this fact again corroborates the view that the molecules of water, while a part of the crystalline structure, are not a part of the chemical type of the salt. It will be well to distinguish the molecular aggregate, which the symbols of this section represent, from the simpler chemical molecules by a special term, and we propose to call them crys- talline molecules. While, however, there is little room for difference of opinion in regard to the relations in which the molecules of water stand to the structure of most crystals, there are cases where the condition is apparently far less simple, and where we find the water so firmly bound to the salt itself that it seems to form a part of its atomic structure. Questions and Problems. 1. Analyze reactions [42]. Show what is meant by a metallic hydrate, and define the term alkali. Write the similar reactions which may be obtained with lithium, caesium, and rubidium. Name in each case the class of compounds to which the factors and pro- ducts belong. Also represent these reactions by graphic symbols. 2. Analyze reactions [43]. State the distinction between an alkaline earth and an alkali, and write the similar reactions which may be obtained with barium and strontium. Name in each case 96 BASES, ACIDS, AND SALTS. the class of compounds to which the factors and products belong. Also represent the reactions by graphic symbols. 3. Analyze reactions [44] and [45], and write the similar reac- tions which may be obtained with either of the metals, calcium, strontium, barium, and magnesium. What theory of the constitution of the metallic hydrates do these reactions suggest V 4. In what respects do the hydrates Ca= 2 = // 2 and Mg= 2 =H 2 differ from K-O-H and Na-O-H ? 5. Analyze reactions [46], and show that the principal products must be regarded as hydrates. Name the class of compounds to which the other products and factors belong. 6. State the third theory which is held in regard to the constitu- tion of the hydrates, and write the symbols of the different hydrates according to this view. Also bring these symbols into comparison with those of the same compounds written after the other two plans, and show by means of graphic symbols how far these forms are arbi- trary, and how far they represent fundamental differences. 7. In what sense may the solution of ammonia gas in water be regarded as an hydrate ? Write reactions [46], using ammonic hy- drate instead of the hydrates of sodium, potassium, and barium. 8. In what relation do the metallic oxides stand to the hydrates ? Define the term base. 9. Define the term salt, and illustrate your definition by examples. 10. Define the term acid. How does an acid differ from a me- tallic hydrate ? Is an acid necessarily an hydrate ? What two classes of acids may be distinguished ? 11. What is the distinction between an acid and a basic radical. How are they related to the two hydrogen atoms of water ? As- suming that there is no difference between these two atoms in the original molecule of water, does not the replacement of one of the atoms by a radical of either class alter the relations of the second ? Is there not an analogy between these phenomena and those of magnetism ? 12. Analyze reactions [47 et seq.], and point out the evidence of acidity in each case. 13. Analyze the following reactions. K-O-H + HF = KF Ca-0.fH 2 + HfOfCO = Ca=0.fCO + 2H,0 Cu-0 2 =E 2 + 2H-0-NO, = Cu-0 BASES, ACIDS, AND SALTS. 97 Na Cl + Ef 0./SO, =. E, Na- Of SO, + HI^l ZNaCl + H 2 =0 2 =S0 2 = Na 2 =0 2 =S0 2 + 211101. Point out the different acids and bases. In what does the evidence of their acidity or basicity appear either in these or in reactions pre- viously given ? Show in each case how the replacement of the hy- drogen atoms is obtained, and illustrate the difference between the hydrogen atoms of an acid and those of a base. What two classes of acids may be distinguished ? 14. Regarding the hydrates as compounds of hydroxyl, how can you define the acids and bases of this class ? 15. Represent the composition of nitric, sulphuric, and phosphoric acid by graphic symbols, and show that the two modes of writing their symbols embody essentially the same idea. 16. Hydrochloric acid, acetic acid, nitric acid, hydriodic acid, hy- drobromic acid, sulphuric acid, carbonic acid, and phosphoric acid have what basicity ? Point out, in the various reactions given in this chapter, the evidence in each case, and write the symbols of the possible sodic salts of the different acids. 17. What class of compounds do the symbols S0 3 , ^V 2 5 , P 2 5 , COy and Si0 2 represent ? By a comparison of symbols show how these compounds may be regarded as formed from water, and how they are related to the corresponding acids. To what class of com- pounds do they stand in direct antithesis ? 18. Define the terms basic and acid hydrate ; basic and acid an- hydride, and compare reactions [49] with [44 and 45]. 19. Analyze the reaction, BaO -J- S0 3 = BaO, S0 y What reason may be urged for writing the symbol of baric sulphate in this way V What was the theory of the dualistic system in regard to such compounds ? Represent the symbol by the graphic method, and seek to determine whether the dualistic form is compat- ible with the theory of molecular unity. 20. The following symbols represent compounds of what class ? H-O-H; HfOfPOiFerOfEti 2H-(HO); (P0,) 2 =0; K-0-H-, Ca-0 2 =ff 2 -, C 2 H 5 -0-H;2Na-0-H; C 5 # 9 2 = 98 BASES, ACIDS, AND SALTS. Give in each case the name of the compound so far as you are able to infer it from examples previously given, and show how the sym- bol is related to that of water. 21. Point out the acid basic and neutral salts among the com- pounds represented by the following symbols : ^' ff,K-0 2 =(C 2 2 ) (Hg-0-Hg-0-Hg)-OfS0. 2 Na 2 =0 2 =CO K 2 =0 2 =(C 2 2 ) #2, Cu= Of-Si Cu=0 2 =(N0 2 ), H Bi=-0.f(N0 2 \H 2 H 2 , K~=OfAs K 2 =0 2 =(S0 2 -0-S0 2 ). What two classes of basic salts may be distinguished ? Convert the symbols into the dualistic form. 22. Analyze reactions [49 and 50], and show how far they justify the dualistic form given to the symbols. Represent the same reac- tions in the graphic form. 23. What class of compounds do the following symbols represent ? Ag^SfAs Ag-S-SbS Ca-S./H^ Write the symbols of the corresponding oxygen compounds. 24. Explain the theory of the colored test papers, and the use of the terms acid and basic in connection with them. To what confu- sion does the double meaning of these terms sometimes lead ? 25. The members of the series of alcohols stand in what relation to each other ? Does the same relation exist between the members of the series of fat acids, glycols, &c. ? Find a general symbol, which will represent the composition of each of these classes of com- pounds. 26. In what relations do the alcohols stand to the fat acids, and the glycols to the acids derived from them ? 27. Select examples from each of the classes of compounds de- scribed in sections 40, 41, and 42, and bring the symbols into com- parison with those of some simple hydrate or anhydride with which they exactly correspond. 28. We are acquainted with a class of compounds known as con- densed glycols, one of which has the following symbol : 4 - 0- C 2 H,- 0- C 2 H 4 ) - OfH 2 . BASES, ACIDS, AND SALTS. 99 To what class of salts does this correspond ? 29. Judging from the following symbols of a few of the salts of tartaric acid, what conclusion should you reach in regard to the atomicity and basicity of this acid ? 30. What is the atomicity and basicity of the different acids whose symbols have been given in this chapter ? Does the basi- city of the different hydrocarbon acids ( 40 to 43) appear to have any connection with the number of oxygen atoms in the rad- ical? 31. How do you explain the state of combination of the water which enters into the composition of most crystalline salts ? Show by an example how this mode of combination is represented sym- bolically. What facts may be adduced in support of the opinion that the molecules of water are not a part of the chemical type of the salt. NOTE. Should the teacher think it best to introduce in this connection definitions of the several compounds formed after the type of ammonia gas, he will find them given in sections 166 to 171 of Part II. ; and, if he finds it necessary, he should dwell more at length on the acids and salts of the type of hydrochloric acid than has been thought necessary in this chapter. CHAPTER X. 1 CHEMICAL NOMENCLATURE. 45. Origin of Nomenclature. Previous to the year 1787 the names given to chemical compounds were not conformed to any general rules ; and many of these old names, such as oil of vitriol, calomel, corrosive sublimate, red precipitate, saltpetre, sal-soda, borax, cream of tartar, Glauber's and Epsom salts, are still retained in ^common use. As chemical science advanced, and the number of known substances increased, it became important to adopt a scientific nomenclature, and the system which came into use was due almost entirely to Lavoisier, who reported to the French Academy on the subject, in behalf of a committee, in the year named above. In the Lavoisierian nomenclature the name of a substance was made to indicate its composition ; and at the time of its adoption, and for fifty years after, it was probably the most perfect nomenclature which any science ever enjoyed. It was based, however, on the dualistic theory, of which Lavoisier was the father ; and, when at last the science outgrew this theory, the old names lost much of their significance and appropriateness. Within the last few years the English chemists have attempted to modify the old nomenclature so as to better adapt the names to our modern ideas. Unfortunately the result, like most attempts to mend a worn-out garment, is far from satisfactory, although it is prob- ably the best which under the circumstances could be attained. The new nomenclature has not the simplicity or unity of the old, and its rules cannot be made intelligible until the student is more or less acquainted with the modern chemical theories. Fortunately, however, the admirable system of chemical sym- bols supplies the defects of the nomenclature, and for many 1 In studying this chapter, the student is expected to remember the names corresponding to the different symbols, and also the symbols corresponding to the names. CHEMICAL, NO^ENCLATij^fc: \\1 ^ \ 101 purposes may be used in its place. We have, therefore, devel- oped this system first, but have also used, meanwhile, the corre- sponding scientific narnes< so that the student might become familiar with the nomenclature, and gather its rules as he advanced. A brief summary of these rules is all that will be necessary here. 46. Names of Elements. The names of the elements are not conformed to any fixed rules. Those which were known before 1787, such as sulphur, phosphorus, arsenic, antimony, iron, gold, and the other useful metals, retain their old names. Several of the more recently discovered elements have been named in allusion to some prominent property or some circum- stance connected with their history : as oxygen, from 6vs yewdta (acid-generator) ; hydrogen, from vdvp yewda (water- generator) ; chlorine, from ^Xopdf (green) ; iodine, from lady: (violet) ; bromine, from /fyw/zos (fetid odor). The names of the newly discovered metals have a common termination, urn, as potassium, sodium, platinum ; and the names of several of the newly discovered metalloids end in ine, as chlorine, bromine, iodine, fluorine. Equally arbitrary names have been given to the compound radicals ; but, with a few exceptions, they all terminate in yl or ene, as ethyl, acetyl, hydroxyl, and ethylene, acetylene, &c. 47. Names of Binary Compounds! The simple compounds of the elements with oxygen are called oxides, and the specific names of the different oxides are formed by'placing before the word "oxide" the name of the element, but changing the termi- nation into ic or ous, to indicate different degrees of oxidation, and using the Latin name of the element in preference to the English, both for the sake of euphony and in order to secure more general agreement among different languages. When the same element unites with oxygen in more than two pro- portions, the Greek numeral prefixes, di, tri, tetra, penta, &c., are added to the word " oxide," in order to indicate the addi- tional degrees. Formerly these compounds were called ox- ides of the different elements, the degrees of oxidation being indicated solely by the prefixes ; and, as the old names are still in very general use, they are also given in the following ex- amples : 1 Compounds of two elements. 102 * i IUM1 AgO NO FeO New Names. is Argentic Oxide " Nitrous Oxide " Nitric Oxide " Nitric Dioxide " Ferrous Oxide . " Ferric Oxide or u u u u a NOMENCLATURE. Old Names. Oxide of Silver Protoxide of Nitrogen Deutoxide of Nitrogen Peroxide of Nitrogen Protoxide of Iron Sesquioxide of Iron. An exception to the above rules is sometimes made in the case of those oxides which, when combined with the elements of water, form acids. As has been already stated, page 85, such compounds are called anhydrides, but the degrees of oxi- dation are distinguished as before, thus : S0 3 C0 2 New Names. Sulphurous Anhydride Sulphuric Anhydride Nitrous Anhydride Nitric Anhydride Phosphorous Anhydride Phosphoric Anhydride Carbonic Anhydride Silicic Anhydride Old Names. or Sulphurous Acid " Sulphuric Acid " Nitrous Acid " Nitric Acid " Phosphorous Acid " Phosphoric Acid " Carbonic Acid " Silicic Acid. The names in common use, even among chemists, of the earths, the alkaline earths, and the alkaline oxides, make another important exception to the general rules given above, thus : AI Z 3 Aluminic Oxide is commonly called Alumina BaO Baric Oxide " " " Baryta SrO Strontic Oxide " " " Strontia CaO Calcic Oxide " " " Lime MgO Magnesic Oxide " " " Magnesia K Z Potassic Oxide " " " Potassa Na z O Sodic Oxide " " " Soda. As this last class of oxides stands in the same relation to the bases in which the previous class stands to the acids, they have also been called by some chemists anhydrides. The names of the binary compounds of the other elements are formed like those of the oxides. CHEMICAL NOMENCLATIVE. 103 Compounds of Chlorine are called Chlorides " Bromine " u Bromides " Iodine " u Iodides " Fluorine " u Fluorides " Sulphur " Nitrogen " " Phosphorus " " Arsenic " u M M Sulphides "Nitrides PhospluWes Arsenides " Antimony " " Carbon " M u Antimonides CarbomWes. Moreover, the specific names of the several compounds also follow the analogy of the oxides, thus : Old Names. Protochloride of Tin Perchloride of Tin Subsulphide of Iron Protosulphide of Iron Sesquisulphide of Iron Bisulphide of Iron Fluoride of Calcium. Here, again, must be noticed several exceptions to the gen- eral rule. Several simple compounds of the elements with hy- drogen, of which the hydrogen is easily replaced with a metal or positive radical, are called acids, and retain the specific names of the old nomenclature, thus : New Names. Sn C/ 2 is Stannous Chloride or SnCl " Stannic Chloride a Fe^ Diferrous Sulphide u FeS Ferrous Sulphide " Fe S " Ferric Sulphide u FeS* " Ferric Disulphide u CaFl 2 Calcic Fluoride a or HCl HBr " HI HFl H n S " Hydric Chloride is called Hydric Bromide " " Hydric Iodide " " Hydric Fluoride " " Hydric Sulphide " Hydrochloric Acid Hydrobromic Acid Hydriodic Acid Hydrofluoric Acid Hydrosulphuric Acid. The last compound is frequently called also sulphuretted hydrogen, and several other hydrogen compounds are named after the same analogy, while others again are always called by their well-known trivial names, thus : H 3 Sb H 3 As H,P Antimoniuretted Hydrogen Arseniuretted Hydrogen Phospnuretted Hydrogen Ammonia Gas Marsh Gas or Light Carburetted Hydrogen Olefiant Gas or, as a radical, Ethvlene. 104 CHEMICAL NOMENCLATURE. 48. Ternary Compounds. Of the old class of ternary compounds, it is only those which are formed after the type of water for which the rules of the nomenclature need at present be explained. 49. Bases. These we call simply hydrates, and for the specific name we take the name of the positive radical, chang- ing the termination into ic or ous, and using such prefixes as circumstances may require, thus : New Names. Old Names. K-O-H is Potassic Hydrate or Hydrate of Potassa Ca=OfH z " Calcic Hydrate " Hydrate of Lime Fe*O f H 9 " Ferrous Hydrate j Hydrate of .Protox- ( ide of Iron. Fe*OfH % Ferric Hydrate j Hydrate of Sesquiox- ( ide of Iron. ZctO^Hi Zirconic Hydrate or Hydrate of Zircoriia. 50. Acids. The inorganic acids all take their specific names from the name of the most characteristic element of the nega- tive radical, which is modified by terminations and prefixes as before, only the last are usually taken from the Greek rather than the Latin. Here the old and the new names coincide. H-0-N0 2 is called Nitric Acid H 2 =0 Z =SO Z " " Sulphuric Acid " Sulphurous Acid HfOf(S-0-S) " " Hyposulphurous Acid The specific names of the organic acids are, as a rule, arbitrary, like tartaric acid, citric acid, malic acid, gallic acid, uric acid, and the like. 51. Salts. The name of a salt is formed from the name of the acid from which the salt is derived, preceded by the names of the basic radicals. When the name of the acid ends in ic the termination is changed into ate, when in ous into ite. Moreover, the terminations ous and ic are retained in connec- tion with the name of the basic radical, and such prefixes are used as may be necessary for distinction, thus : Ferric Sulphate Pehate f CHEMICAL NOMENCLATURE. 105 New Names. Old Names. Ca-OfCO is Calcic Carbonate or ( Carbon ate of ( Lime Ca=0,=(S-0-S) Calcic Hyposulphite Hyposulphite ( of Lime Ba=0. 2 =SO " Baric Sulphite Sul P hite of ( Baryta Fe-0,=S0 2 Ferrous Sulphate Protosulphate of Iron P ^), Mg=Or=PO " Ammonio-magnesic Phosphate H, (NHJ, Na-=0/PO " Hydro-ammonio-sodic Phosphate. H, NarO^PO Hydro-disodic Phosphate. #4, Ca vi 6 vi (PC>) 2 Tetrahydro-calcic Diphosphate. NafOfB 4 5 Disodic Tetraborate (Borax). NOTE. The rules of the nomenclature given above conform to what the author regards as the best present use among chemists. There is, however, an important departure from the more general use, which must not be overlooked. Several English authors, who think that the adjectives derived from the Latin names of the ele- ments, with terminations in ic and ous, are not in harmony with English idioms, use such terms as Gold Chloride, Silver Nitrate, and Iron Sulphate, instead of Auric Chloride, Argentic Nitrate, and Ferrous Sulphate. This usage, however, appears to the writer open to equally just criticism, besides abridging greatly the capabilities of the nomenclature, which is full of similar incongruities. Nor does he sympathize with the same class of writers in rejecting the word " anhydride " as a part of the name of a substance, on the ground that it does not express its constitution, but only a mode of its deri- vation ; for a similar objection might be urged with, equal force against the terms " acid " and "hydrate." Moreover, he has thought it best, in a work designed chiefly for instruction, not only to intro- duce no novelties, but also to represent the actual usage, so far as possible, in all its phases. He would, however, offer the following suggestions as guides to the student in selecting for his own use a more uniform and consistent system, hoping that before long some agreement will be reached among chemists, by which greater uni- formity may be secured. He would recommend, 106 CHEMICAL NOMENCLATURE. First, that the terminations ic, ous, ate, and tie, with the modify- ing Greek and Latin prefixes, should be used so far as possible to distinguish the quantivalence of the chief multivalent radical of the compound. Secondly, that the Greek numeral prefixes should be used when necessary to indicate the number of atoms of any radical which each molecule of such compound contains. Thirdly, that in forming the name of a compound it should be the great object to indicate its composition, and that the use of such terms as acid, basic, or anhydride as parts of the name should be avoided, except when it is desired to make conspicuous the peculiar chemical relations which they express. By referring to the list of sulphates on page 319, and to the list of sulphites on page 315, the student will find good examples of the application of these principles. He will notice that salts in which the quantivalence of sulphur is six are called sulphates, while those in which it is four are called sulphites, and those in which it is two hyposulphites v Again, on page 230 he will find the proper applica- tion of the term anhydrde explained, the term acid and basic hav- ing been already defined on page 82. Questions and Problems. 1. Give the names of the compounds represented by the follow- ing symbols: a. KCl; K 2 0-, K 2 S; KfOfSO; K 2 =0 2 =S0 2 -, KfOf(S-O-S); b. FeO-, Fe=0 2 =ff 2 ; Fe=0 2 =CO; Fe=0.fC 2 2 ; [Fe 2 yO s ; jy0JJ5r 6 ; [#. 2 ]i0J(JF0,) C.-H-CI-, H-F-, H-O-NO^ H-0-NO-, fffOfSO^ 2. Write the symbols of the following compounds : a. Calcic Sulphide ; Calcic Sulphite ; Calcic Hyposulphite ; Cal- cic Sulphate; Calcic Hydrate; Calcic Sulphohydrate ; Calcic Car- bonate ; Calcic Sulphocarbonate ; Calcic Silicate. b. Water ; Potassic Hydrate ; Nitric Acid ; Potassic Nitrate ; Nitric Anhydride ; Potassic Oxide. c. Magnesic Oxide ; Magnesic Hydrate ; Magnesic Nitrate ; Magnesic Carbonate ; Magnesic Phosphate ; Ammonio-magnesic Phosphate. N. B. Examples like the above should be greatly multiplied by the teacher, pains being taken to group together the names and symbols in the way best calculated to exhibit their relations and to assist the memory. CHAPTER XI. SOLUTION AND DIFFUSION. 52. Solution. The solvent power of water is one of the most familiar facts of common experience, and all liquids pos- sess the same power to a greater or less degree, but they differ very widely from each other in the manifestation of their solvent power, which for each liquid is usually limited to a certain class of solids. Thus mercury is the appropriate rol- vent of metals, alcoliol of resins, ether of fats, and water of salts and of similar compounds of its own type. Water is by far the most universal solvent known, and for this reason, as well as on account of its very wide diffusion in nature, it becomes the medium of most chemical changes. The phenomena of aqueous solution form therefore a very important subject of chemical inquiry, and these alone will be considered in this connection. The solvent power of water, even on bodies of its own type, differs very greatly. Some solids, like potassic carbonate, or calcic chloride, liquefy in the atmosphere by absorbing the moisture it contains. Such salts are said to deliquesce, and are rendered liquid by a very small proportion of water. Other salts, like calcic sulphate, require for solution several hundred times their weight of water, and others again, like baric sul- phate, are practically insoluble. As a general rule the solvent power of water increases with the temperature ; but here, again, we observe the greatest dif- ferences between different substances. While the solubility of some salts increases very rapidly with the temperature, that of others increases not at all, or only very slightly ; and there are a few which are actually more soluble in cold water than in hot. The solubility of each substance is absolutely definite for a given temperature, and we can determine by experiment the exact amount which 100 parts of water will in any case dissolve. The results of such experiments are best represented to the eye by means of a curve drawn as in the accompanying figure on the principles of analytical geometry. 108 SOLUTION AND DIFFUSION. Fig. 2. The figures on the horizontal line indicate degrees of tempera- ture, and those on the vertical line parts of salt soluble in 100 parts of water. To find the solubility of any salt, for a stated temperature, the curve being given, we have only to follow up the vertical line corresponding to the temperature until it reaches the curve, and then, at the end of the horizontal line which intersects the curve at the same point, we find the num- ber of parts required. These curves also show in each case the law which the change of solubility obeys. When a liquid has dissolved all of a solid that it is capable of holding at the temperature, it is said to be saturated ; but when saturated with one solid the liquid will still exert a solvent power over others ; indeed, in some cases the solvent power is thereby increased. When several salts are dissolved together in water, a definite amount of metathesis seems always to take place, and the different positive radicals are divided between the several acids in proportions which depend on the relative strength of their affinities, and on the quantities of each pres- ent. If in this way either an insoluble or a volatile product is formed, the solid or the gas at once falls out of the solution, and, the equilibrium being thus destroyed, a new metathesis takes place, and this goes on so long as any of these products can be formed. Here, then, we find a simple explanation of the two important laws already stated on page 37. SOLUTION AND DIFFUSION. 109 53. Solution of Gases. Most liquids, but especially water and alcohol, exert on gases a greater or less solvent power, which is marked by differences of manifestation similar to those we have already studied in the case of solids, although the peculiar physical conditions of the gas somewhat modify the result. Under the same conditions, the volume of gas dis- solved is always the same ; but it varies with the pressure of the gas on the surface of the liquid, with the temperature, and with the peculiar nature of the gas and the absorbing liquid. The quantity 1 of gas dissolved by one cubic centimetre of a liquid on which it exerts a pressure of 76 c. m. is called the coefficient of absorption. This coefficient, in almost every in- stance, diminishes with the temperature ; but, as in the case of solids, each substance obeys a law of its own, which must be determined by experiment. The observed values for se'veral of the best known gases, when absorbed by water and alcohol, are given in the Chemical Physics, Table VII. With these data we can easily calculate the quantity of any of these gases which a given volume of water or alcohol will absorb, assuming that the gas exerts on the liquid a pressure of 76 c. m. Moreover, since the quantity of a gas absorbed by a liquid varies directly as the pressure which the gas exerts upon it, we can easily calculate from the first result the quantity absorbed at any given pressure. Again, it is a direct consequence of the last' principle that at a fixed temperature a given mass of liquid will dissolve the same volume of gas, whatever may be the pressure. Lastly, if a mass of liquid is exposed to an atmosphere of mixed gases, it will absorb of each the same quantity as if this gas was alone present and exerting on the liquid the same partial pressure which falls to its share in the atmosphere. The amount dissolved of each gas is easily calculated when the partial pressure and the coefficient of absorption are known. It is thus that water absorbs the oxygen and nitrogen gases of our terrestrial atmosphere ; and the fact that these two gases are found dissolved in the ocean in very different proportions from those present in the atmosphere is a conclusive proof that the air is a mixture, and not, as was formerly supposed, a chem- ical compound. 1 By quantity of gas is here meant the volume in cubic centimetres meas- ured under the standard conditions of temperature and pressure. 110 SOLUTION AND DIFFUSION. 54. Solution and Chemical Change. There seems at first sight to be a wide difference between solution and chemical change ; for, while in the first the solid body becomes diffused through the liquid menstruum without losing its chemical identity or destroying that of the liquid, there is in the second a complete identification of the combining substances in the resulting compound. The same wide difference appears also between mechanical and chemical solution, which are sometimes confounded by students, because, unfortunately, the same term has been applied to both. When salt or sugar is dissolved in water, the differences between salt and solvent are preserved ; but when chalk is dissolved in hydrochloric acid, or copper in nitric acid, there is^ a complete identification of the differences in the resulting compound; and the only ground for calling such chemical changes solution is the fact that the solution of the resulting salt in the water, used as the medium of the chemical change, is frequently an essential condition of the process. But if, instead of comparing extreme cases, we study the whole range of chemical phenomena, we shall find that the distinction is by no means so clearly marked. In many cases what seems to be a simple solution can be shown to be a mixed effect at least of solution and chemical combination ; and be- tween this condition of things, where the evidence of chemical combination is unmistakable, and a simple solution, like that of sugar in water, we have every degree of gradation. To such an extent is this true, that the facts seem to justify the opinion that solution is in every case a chemical combination of the substances dissolved with the solvent, and that it differs from other examples of chemical change only in the weakness of the combining force. The metallic alloys afford another striking illustration of the same principle. They are originally solutions of one metal in another ; but in many cases the result is greatly modified by the chemical affinities of the metals and their tendency to form definite^ chemical compounds. 55. Liquid Diffusion. Closely connected with the phe- nomena of solution are those of liquid diffusion. These phe- nomena may be studied in their simplest form, by placing an open vial filled with a solution of some salt in a much larger SOLUTION AND DIFFUSION. Ill jar of pure water, as shown in Fig. 3, and so carefully arranging the details of the experiment that the surfaces of the two liquids may be brought in contact without mixing them me- chanically. It will then be found that the salt molecules will slowly escape from the vial and spread throughout the whole volume of the water. The rate of the diffusion in- creases with the temperature equally for all substances, and the whole phe- nomenon is probably caused by that same molecular motion to which we refer the effects of heat. At best, how- ever, the diffusion is very slow, as we should expect, considering the limited freedom of motion which the liquid molecules possess. It is found, also, that the rate of diffusion differs very greatly for the different soluble salts ; but these may be divided into groups of equidiffusive substances, and the rates of diffusion of the several groups bear to each other simple numerical ratios. If a mixture of salts be placed in the vial, it is found that the presence of one salt affects to some degree the diffusion of the other ; but if the difference of rate is considerable, a partial separation may be effected, and even weak chemical compounds may be thus decomposed. 56. Crystalloids and Colloids. There is a very great differ- ence of diffusive power between the ordinary crystalline salts (including most of the common acids and bases) and such sub- stances as gum, caramel, gelatine, and albumen, which are incapable of crystallizing, and which give insipid viscid solu- tions, readily forming into jelly ; hence the name colloids, from KoXXrj, glue. The last class is distinguished by a remarkable sluggishness and indisposition to diffusion ; as is illustrated by the fact that sugar, one of the least diffusible of the crystalloids, diffuses seven times more rapidly than albumen, and fourteen times more rapidly than caramel. Our theories would lead us to believe that this great difference of diffusive power is caused by the fact that the molecules of colloids are far more complex atomic aggregates than those of crystalloids, and therefore are heavier and move more slowly. Moreover, the diffusive power 112 SOLUTION AND DIFFUSION. is only one of many characters which point to a great molecu- lar difference between these two classes of substances. 57. Dialysis. The difference of diffusive power between the two classes of compounds distinguished in the last section is still further increased when the aqueous solution is separated from the pure water by some colloidal membrane, and upon this fact Professor Graham of London, to whom we owe our whole knowledge of this subject, has based a simple method of sepa- rating crystalloids from colloids, which he calls dialysis. A shallow tray is prepared by stretching parchment paper (which is itself an insoluble colloid) over one side of a gutta- percha hoop, and holding it in place by a somewhat larger hoop of the same material. The solution to be dialysed is poured into this tray, which is then floated on pure water whose volume should be eight or ten times greater than that of the solution. Under these conditions the crystalloids will diffuse through the porous septum into the water, leaving the colloids on the tray, and in the course of two or three days a more or less complete separation of these two classes of substances will have taken place. In this way arsenious acids and similar crystalloids may be separated from the colloidal materials, with which, in cases of poisoning, they are frequently found mixed in the stomach ; and by an application of the same method alumina, ferric oxide, chromic oxide, stannic, metastannic, titanic, molybdic, tungstic, and silicic acids have all been obtained dissolved in water in a colloidal condition. All these substances usually exist in a crystalline condition. The colloidal condition appears to be an abnormal state, and in almost all such substances there is a tendency towards the crystalloid form. 58. Diffusion of Gases. Gases diffuse much more rapidly than liquids, as we should naturally expect from the greater freedom of motion which their molecules possess. Moreover, if the theory of the molecular condition of gases is correct, we ought to be able to calculate the relative rates of diffusion of different gases from their respective molecular weights. If it is true, as stated on page 13, that at any given temperature %m V^ ^m' V* then it follows that V\ V = \J$m' : v/ m = y/Sp. Gr'. : y/Sp. Gr. I SOLUTION AND DIFFUSION. 113 Hence, if two masses of gas are in contact, the molecules of either gas must move into the space filled by the other with velocities which are inversely proportional to the square roots of the respective specific gravities. If one gas is hydrogen ( Sp. Gr. = 1), and the other oxygen (Sp. Gr. 16), the molecules of hydrogen must move past the section separating the two masses four times as rapidly as those of oxygen ; and, since all gas molecules occupy the same volume, it follows further that four volumes of hydrogen must enter the space filled by the oxygen, while one volume of oxygen is passing in the opposite direction Numerous experiments have fully confirmed this theoretical deduction, and the close agreement between theory and experiment furnishes important evidence in favor of the theory itself. Such experiments can be made, moreover, with great accuracy, since the molecular motion is not arrested by various porous septa, which may be used to separate the two masses of gas, and which entirely prevent the passage of gas currents that might otherwise vitiate the results. CHAPTER XII. RELATION OF THE ATOMS TO HEAT. 59. The Atmosphere. The earth is surrounded by an ocean of aeriform matter called the atmosphere, and many of the most important chemical changes which we witness in nature are caused by the reaction of this atmosphere on the substances which it surrounds and bathes. The great mass of the atmos- phere consists of the two elementary gases, oxygen and nitro- gen, mixed together in the proportions indicated in the follow- ing table : Air Composition Composition contains. By Volume. By Weight. Oxygen, 20.96 23.185 Nitrogen, 79.04 76.815 100. 100. That the air is a mixture, and not a chemical compound, is proved by the action of solvents upon it ( 53) ; but, neverthe- less, the analyses of air collected in different countries, and at different heights in the atmosphere, show a remarkable con- stancy in its composition. Besides these two gases, which make up over 93 per cent of its whole mass, the air always contains variable quantities of aqueous vapor, carbonic anhydride, and ammonia, and sometimes also traces of various other gases and vapors. 60. Burning. Of the two chief constituents of the atmos- phere, nitrogen gas is a very inert substance, and serves chiefly to restrain its more energetic associate. Oxygen gas, on the other hand, is endowed with highly active affinities, and tends to enter into combination with other elementary substances, and with many compounds which are not already saturated with this all-pervading element. Many of these substances, such as phosphorus, sulphur, petroleum, coal, and wood, have such a strong affinity for oxygen, that, under certain conditions, they will absorb it from the atmosphere, and combine with it COMBUSTION. 115 under the evolution of heat and light. These substances are said to be combustible, and the process of combination is called combustion. Moreover, all burning with which we are familiar in common life consists in the union of the burning body with the oxygen of the air. The chemical process in these cases may be expressed, like any other chemical reaction, in the form of an equation. Burning of Hydrogen Gas. Hydrogen Gas. Aqueous Vapor. 2 HHS -f - = 2 HL. I * Burning of Carbon {Charcoal'). Carbon. Carbonic Anhydride. C + = = @ 2 . [54] Burning of Benzole. Benzole. 15= = 12@ 2 + 6SI 2 . [55] Burning of Alcohol. Alcohol. 3- = 2@ 2 + 3H3 2 . [56] Burning of Sulphur. Sulphurous Anhydride. 2= = 2^ 2 . [57] Burning of Phosphorus. Phosphoric Anhydride. + 5= = 2P,O. [58] Burning of Magnesium. Magnesic Oxide. 2 Mg + = 2 MgO. [59] The four substances, hydrogen gas, charcoal, benzole, and alcohol, may be regarded as types of our ordinary combustibles ; and, as the first four reactions show, the products of their com- bustion are aeriform. Moreover, these products are wholly devoid of any sensible qualities, and hence the apparent annihi- 116 COMBUSTION. lation of the burning substance, and the reason that for so long a period the nature of the process remained undiscovered. That these qualities of the products of ordinary combustion are not ne- cessary conditions of the process, but remarkable adaptations in the properties of those combustibles which are our artificial sources of light and heat, is shown by the fact, that, in the last two reactions, the products of the combustion are solids, while in [57] the product is a noxious suffocating gas. A careful inspection of the reactions will also teach the student several other important facts in regard to the processes here represented. It will be seen that, in the burning of hydrogen gas, two volumes of hydrogen gas and one volume of oxygen gas combine to form two volumes of aqueous vapor. It will further be noticed, that, in the burning of carbon and of sulphur, a given volume of oxygen gas yields in each case its own volume of the aeriform product. The carbon in the one case, and the sulphur in the other, are absorbed, as it were, by the gas, without any increase of volume. Further, if the ex- periments are made, which these reactions represent, it will appear that, in all those cases where the combustible is repre- sented as a gas, the combustion is accompanied by flame, while in the case of carbon, which is a fixed solid, there is no proper flame. Hence we learn that flame is burning gas, and that only those substances burn with flame. which are either gases themselves, or which, at a high temperature, become vola- tilized, or generate combustible vapors. Still other important facts connected with the process of combustion will be learned by solving the following problems according to the rules al- ready given ( 24 and 25). Problem. How many cubic centimetres of hydrogen gas, and how many of oxygen gas, are required to form one cubic centimetre of liquid water? 1 Ans. 1,240cm 8 of hydrogen gas, and 620 ~(Tm of oxygen gas. Problem. How many cubic metres of air are required to burn 448 kilogrammes of coal, assuming that the coal is pure carbon ? Ans. 833.333 m 8 of oxygen gas, or 3,975.83 m 8 of atmospheric air. 1 Here, as in all other problems throughout the book, it is understood, unless otherwise expressly stated, that the measurements and weights are all taken at the standard temperature and pressure. (Compare 10 and 13.) COMBUSTION. 117 Problem. How many cubic metres of carbonic anhydride are formed by the burning of 1,000 kilogrammes of coal, as- suming, as before, that the coal is pure carbon ? Ans. 1,860. Problem. How many litres of carbonic anhydride, and how many of aqueous vapor, would be formed by burning one litre of benzole vapor ? Ans. Simple inspection of the equa- tion shows that 6 litres of the first and 3 litres of the second would be formed. Problem. How many litres of carbonic anhydride, and how many of aqueous vapor, would be formed by burning one litre of liquid alcohol (C 2 tf 6 0) ? Sp. Gr. of liquid at = 0.815. Ans. One litre of alcohol weighs 815 grammes or 9,097 criths, and, since the Sp. Gr. of alcohol vapor is 23, this quantity of liquid would yield 395.6 litres of vapor. Hence there would be formed 2 X 395.6 = 791,2 litres of carbonic anhydride, and 3 X 395.6= 1,186.8 litres of aqueous vapor. 61. Heat of Combustion. The reactions of the last section represent only the chemical changes in the processes of burning. The physical effects which accompany the chemical changes our equations do not indicate, but it is these remarkable mani- festations of power which chiefly arrest the student's attention, and on this power the importance of the processes of combus- tion as sources of heat and light wholly depends. The immediate cause of the power developed in the process of combustion is to be found in the clashing of material atoms. Urged by that immensely powerful attractive force we call chemical affinity, the molecules of oxygen in the surrounding atmosphere rush, from all directions, and with an incalculable velocity, upon the burning body. The molecules of oxygen thus acquire an enormous moving power ; and when, at the moment of chemical union, the onward motion is arrested, this moving power is distributed among the surrounding mole- cules, and is manifested in the phenomena of heat and light. 1 (Compare 12.) 1 According to our best knowledge, the phenomena of light are merely another manifestation of the same molecular motion which causes the phe- nomena of heat. When we speak of the amount of heat produced, we refer always to the total amount of molecular motion; although, even in the most brilliant illumination, the amount of mechanical power manifested as light appears to be inconsiderable as compared with that which takes the form of heat. 118 COMBUSTION. The quantity of heat evolved during combustion varies very greatly with the nature of the combustible employed, but it is always constant for the same combustible if burnt under the same conditions, and is exactly proportional to the weight of combustible consumed. We give in the following table the amount of heat evolved by one kilogramme of several of the most common combustibles when they are burnt in oxygen gas in their ordinary physical state. The numbers represent what is called the calorific power of the combustible. With the exception of the two last, which are only approximate values, they are the results of very accurate experiments made by Favre and Silbermann. Calorific Power of CombustibUs. Units. Units. Hydrogen, 34,462 Sulphur, 2,221 Marsh Gas, , 13,063 Wood Charcoal, 8,080 defiant Gas, 11,858 Carbonic Oxide, 2,400 Ether, 9,027 Dry Wood (about), 3,654 Alcohol, 7,184 Bituminous Coal, " 7,500 The calorific power of our ordinary hydrocarbon fuels may be calculated approximately when their composition is known. Most of these combustibles contain more or less oxygen, and it is found, as might be expected, that the amount of heat developed by the perfect combustion of the fuel is equal to that which would be produced by the perfect combus- tion of all the carbon, and of so much of the hydrogen as is in excess of that required to form water with the oxygen present. The rest of the hydrogen may be regarded, so far as relates to the present problem, as in combination with oxy- gen in the state of water ; and in estimating the available heat produced, we must deduct the amount of heat required to con- vert, not only this water into steam, but also any hygroscopic water which may be present. Moreover, if we use in our cal- culation the value of the calorific power of hydrogen given in the table above, we must also deduct the amount of heat re- quired to convert into vapor all the water formed in the process of burning, because, in the experiments by which this value was obtained, the aqueous vapor formed was subsequently con- densed to water and gave out its latent heat. Problem. Given the average composition of air-dried wood as in the table, to find the calorific power. Carbon, 400 Hydrogen, 48 Oxygen, 328 Nitrogen and Ash, 24 Hygroscopic Water, 200 1000 COMBUSTION. 119 From the results of analysis we easily deduce Quantity of H in combination with 41 " " available as fuel 7 Quantity of water formed by burn- ing 48 parts hydrogen Hygroscopic Water 200 Total quantity of water evaporated 632 Units of Heat. 400 grammes of carbon yield 3,232 7 " " hydrogen " 241 ^473 Deduct amount of heat required to convert 632 grammes pf water into vapor. (See 14.) 339 Calorific power of air-dried wood 3,134 From the mechanical equivalent of heat given on page 14, and from the data of the above table, we can easily calculate the mechanical power developed in ordinary combustion, and the student will be surprised to find how great this power is. The burning of one kilogramme of charcoal produces an amount of heat which is equivalent to 8,080 X 423 = 3,41 7,840 kilogramme metres ; that is, the moving power which is de- veloped by the clashing of the atoms during the combustion of this small amount of coal is equal to that which would be produced by the fall of a mass of rock weighing 8,080 kilo- grammes over a precipice 423 metres high, and, could this power be all utilized, it would be adequate to raise the same weight to the same height, or to do any other equivalent amount of work. The steam-engine is a machine for apply- ing this very power to produce mechanical results ; but, unfor- tunately, in the best engines we do not utilize much more than 2\j of the power of the fuel ; and to find a more economical means of converting heat into mechanical effect is one of the great problems of the present a?e. 62. Calorific Intensity. The calorific intensity of fuel is to be carefully distinguished from its calorific power. By calorific power is meant, as we have seen, the total quantity of heat developed by the combustion of a given amount of fuel. By calorific intensify, we mean the maximum temperature de- veloped in the process of combustion. Provided the products are the same, the total amount of heat produced in any case is 120 COMBUSTION. not materially influenced by the rapidity of the process ; but it is evident that the temperature pf the burning fuel will de- pend, other things being equal, on the rapidity with which the heat is developed as compared with the rapidity with which it is dissipated through surrounding objects ; and, when the com- bination with oxygen is very slow, the heat may be dissipated as fast as it is generated, and then the temperature of the burning body will not rise above that of the surrounding at- mosphere, as is the case in many of the processes of slow com- bustion. Assuming, however, that all the heat is retained by the products of combustion, we can calculate the maximum tem- perature which can in any case be produced, provided the calorific power of the fuel and the specific heat of the products of combustion are known. The calorific intensity is simply the temperature to which the heat generated by the burning of each portion of the fuel can raise the products of its own combustion. Assume that the quantity burnt is one kilo- gramme, that the calorific power or number of units of heat produced is (7, that the weights of the various products of com- bustion are W, W, W", &c., and that the specific heats of these products are S, &, S", &c. Then WS + W'S' + W"S" -|-&c., represents the amount of heat required to raise the tem- perature of the whole mass of the products one centigrade de- gree ( 16), and the maximum temperature, to which these products can be raised in the process of combustion, must be - Problem. Find the calorific' intensity of charcoal burnt in pure oxygen, and also in air under constant atmospheric pressure. Solution. By [54] we easily find that each kilogramme of carbon yields, by burning, 3.67 kilogrammes of carbonic anhy- dride, which is the sole product of its combustion when burnt in pure oxygen. The specific heat of carbonic anhydride (Chem. Phys. 235) is 0.2164. The calorific power of charcoal is 8,080. By substituting these values in [60] we get T = 10,174. When the charcoal burns in air, the 3.67 kilogrammes of carbonic anhydride formed by the combustion are mixed with a COMBUSTION. 121 large mass of inert nitrogen, which must bo regarded as one of the products of the combustion. The weight of this nitrogen is easily calculated from the known composition of air by weight ( 59) and from the amount of oxygen consumed in the process. 23.2 : 76.8 = 2.67 : x ; or x = 2.67 X 3.31 = 8.84. We have now, besides the values given above, W = 8.84 and S,' the specific heat of nitrogen, equal to 0.244. Whence T 2,738. Problem. Find the calorific intensity of hydrogen gas burnt in oxygen and burnt in air. Solution. One kilogramme of hydrogen yields 9 kilogrammes of aqueous vapor. The specific heat of aqueous vapor is 0.4805. The calorific power of hydrogen is not so great when the gas is burnt under ordinary conditions as that given in the table on page 118 ; for in the experiments of Favre and Silbermann the vapor formed by the combustion was subsequently condensed to water, and gave out its latent heat, while in a burning flame of hydrogen no such condensation takes place. Hence C = 34,462 (537 X 9) 29,629. We also have W= 9 and S= 0. 480. Whence T= 6,853. When hydrogen is burnt in air, the nitrogen, mixed with the aqueous vapor, weighs 26.49 kilogrammes and S 1 is the same as in the previous problem. Whence T = 2,746. It appears then from these problems, that, although the calorific power of hydrogen is much greater than that of car- bon, its calorific intensity is less. But it must be remembered that the conditions assumed in these problems are never real- ized in practice, for the heat generated by the combustion is never wholly retained . in the products. The process of com- bustion requires a certain time, and during this time a portion of the heat escapes. Moreover, more air passes through the combustible than is required for perfect combustion, and many of the data which enter into the calculation are uncertain. The results, therefore, can only be regarded as approximate. The theoretical conditions are most nearly realized in a gas flame, and especially in that form of burner known as the Bunsen lamp. The temperature of the flame of this lamp, when carefully regulated, is very nearly that which the theory would assign. 122 COMBUSTION. 63. Point of Ignition. In order that a combustible body should take fire, and continue burning in the atmosphere, it must be heated to a certain temperature, and maintained at this temperature. This temperature is called the point of igni- tion ; and although it cannot always be accurately measured, and is undoubtedly more or less variable under different con- ditions, yet, nevertheless, it is tolerably constant for each sub- stance. For different substances it differs very greatly. Thus phosphorus takes fire below the boiling point of water, sulphur at 260, wood at a low red heat, anthracite coal only at a full red heat, while iron requires the highest temperature of a forge. If a burning body is cooled below its point of ignition, it goes out; and our ordinary combustibles continue burning in the air only because the heat evolved by the burning main- tains the temperature above the required point. If the tem- perature of the combustible is not maintained sufficiently high, either because the chemical union is too slow, or because the calorific power is too small, then the combustible will not con- tinue to burn in the air of itself, although it may burn most readily if its temperature is sustained by artificial means. Hence many of the metals which will not burn in the air burn readily in the flame of a blowpipe, and an iron watch- spring burns like a match in an atmosphere of pure oxygen. The calorific intensity of all combustibles, when burnt in the atmosphere, is, as we have seen, greatly reduced by the pres- ence of nitrogen ; and hence it is that, although the burning watch-spring is maintained above the point of ignition in pure oxygen, it soon falls below this temperature, and goes out when ignited in the air. Thus it is that the nitrogen of our atmosphere exerts a most important influence on the action of the fire element ; and it can easily be seen that, were it 'not for these provisions in the constitution of nature, by which the active energies of oxygen are kept within certain limits, no combustible material could exist on the surface of the earth. 64. Calorific Power derived from the Sun. The great mass of the crust of our globe consists of saturated oxygen com- pounds, or, in other words, of burnt materials ; and the total amount of combustible materials which exists on its surface is, comparatively, very small. That which exists naturally consists almost entirely of carbon and its compounds, such as coal, COMBUSTION. 123 naphtha, and wood ; and all these substances are the results of vegetable growth, either of the present age or of earlier geo- logical epochs. Moreover, whatever subsequent changes the material may have undergone, it was all originally prepared by the plant from the carbonic acid and water of our atmos- phere ; for, in the economy of nature, these products of com- bustion have been made the food of the vegetable world. The sun's rays, acting on the green leaves of the plant, exert a mys- terious power, which decomposes carbonic anhydride, and per- haps also water ; and, as the result of this process, oxygen is returned to the atmosphere, while carbon and hydrogen are stored up in the growing tissues of the plant. The sun thus undoes the work of combustion, and parts the atoms which the chemical affinities had drawn together. In doing this, the sun exerts an enormous power ; and the work which it thus ac- complishes is the precise measure of the calorific power of the combustible material, which it then prepares. When we wind up the weight of a clock, we exert a certain power which reap- pears in its subsequent motions ; and so, when the sun's rays part these atoms, the great power it exerts is again called into action, when in the process of combustion the atoms reunite. Moreover, what is true of calorific power is true of all mani- festations of power on the surface of the earth. Every form of motion is sustained by the running down of some weight which the sun has wound up ; and, according to the best theory we can form, the sun's power itself is sustained by the gradual falling of the whole mass of the solar system towards its com- mon centre. However varying in its manifestation, all power in its essence is the same, and the total amount of power in the universe is constant. 65. Heat of Chemical Combinations. The heat of combus- tion is only a striking manifestation of a very general principle, which holds true in all chemical changes. It would appear that whenever, in a chemical reaction, atoms or molecules are drawn together by their mutual affinities, a certain amount of moving power is developed, which takes the form of heat ; and whenever, on the other hand, these same atonas or molecules are drawn apart by the action of some superior force, the same amount of moving power is expended, and heat disappears. Every chemical reaction is a mixed effect of such combina- 124 COMBUSTION. 9 tions and decompositions, and it is simply a complex problem in the mechanical theory of heat to determine what must be in any case the * thermal effect. The numerous facts with which we are acquainted in regard to the heat of chemical combination generally agree with the mechanical theory ; and, where the facts do not appear to conform to it, the discrepancy probably arises from our ignorance of the nature of the chem- ical change in question. It would be incompatible with our design to discuss these facts in this book. It must be sufficient to state a few general results, which may be summed up in the following propositions : First. The heat absorbed in the decomposition of a com- pound is equal to the heat evolved in its formation, provided the initial and the final states are the same. Second. The heat evolved in a series of successive chemical changes is equal to the sum of the quantities which would be evolved in each separately, provided the bodies are finally brought into identical conditions. Third. The difference between the quantities of heat evolved in two series of changes starting from two different states, but ending in the same final state, is equal to that which is evolved or absorbed in passing from one initial condition to the other. For example, if a body m evolves a certain amount of heat in uniting with n to form m n, and if the body m n is decom- posed by a third body p, so that m p is formed, the quantity of heat evolved in this last reaction is less than that which would be evolved in the direct union of m and p by the amount evolved in the formation of m n. All these propositions, however, are but special cases under a more general principle which is at the basis of the whole mechanical theory of heat, and which may be enunciated as follows: Whenever a system of bodies undergoes chemical or physical changes, and passes into another condition, what- ever may have been the nature or succession of the changes, the quantity of heat evolved or absorbed depends solely on the initial and final conditions of the system, provided no mechan- ical effect has been produced on bodies outside. COMBUSTION. 125 Questions and Problems. 1. How many times more space does the carbonic anhydride formed by burning charcoal (Sp. Gr. = 2) occupy than the char- coal burnt ? Ans. One cubic centimetre or two grammes of charcoal yields 3.720 litres. Hence the gas occupies 3,720 times the volume of the charcoal. 2. How many litres of oxygen gas are required to burn one litre of alcohol vapor, and how many litres of aqueous vapor, and how many of carbonic anhydride, will be formed in the process ? Ans. 3 litres of oxygen, 3 litres of aqueous vapor, 2 litres of car- bonic anhydride. 3. Given the symbol of alcohol C Z H Q to find its calorific power. Ans. 6,572 units, or 7,200 units, assuming that the steam formed was condensed. 4. The composition of dried peat is as follows : Carbon, 625.4 ; Hydrogen, 68.1 ; Oxygen, 292.4 ; Nitrogen, 14.1. Find the calor- ific power. Ans. 5,521 units. 5. Find the calorific intensity of marsh gas burnt in oxygen. CJJ 4 + 20=0 = CO, + 2H. 2 Calorific power of marsh gas, 13,063. Specific heat of steam, 0.4805 ; of CO,, 0.2164. Ans. 7,793. 6. Find the calorific intensity of olefiant gas burnt in oxygen. C 2 ff 4 + 3OO = 200 2 + 2R 2 Calorific power of C 2 fiT 4 11,858. Specific heat of steam and car- bonic anhydride as in last problem. Ans. 9,136. 7. Find the calorific intensity of marsh gas and olefiant gas burnt in air. Besides the data already given, we have also specific heat of nitrogen 0.244. Ans. 2,662, and 2,916. CHAPTER XIII. MOLECULAR WEIGHT AND CONSTITUTION. 66. Determination of Molecular Weights. It has already been stated that the molecular weight of a substance is an essential element in fixing its symbol and in judging of its chemical relations, but until now the student has not possessed the knowledge necessary in order to understand the methods by which this important constant is determined. Whenever the substance is a gas, or is capable of being vola- tilized without decomposition at a manageable temperature, we always ascertain the molecular weight from the specific gravity on the principle already several times enforced ( 17). The problem then resolves itself into finding the specific gravity of the substance in the state of gas. The methods used in such cases are described on page 21, and more in detail in the au- thor's work on Chemical Physics (330 et seq.), and in the same book tables are given which very greatly facilitate the calcula- tion of the results. The specific gravity of the gas or vapor having been found by either of these methods, and referred to hydrogen gas as the unit, the molecular weight of the substance is simply twice the number thus determined. But in applying this important principle, on which our modern chemical philoso- phy so greatly rests, two precautions are essential. It is only true that equal volumes of all substances contain the same number of molecules when they are in the condition of true gases. Now, while some substances, like alcohol, assume this condition at temperatures only a few degrees above their boiling point, at least nearly enough for all practical pur- poses, others, like acetic acid, only attain it at temperatures one or two hundred degrees above their boiling point, and others still, like sulphur, only at the very highest temperatures at which we have been able to experiment. For this reason, the specific gravity of sulphur vapor was for a long time an anomalous fact in the science, and it was not until St. Clair Deville, by MOLECULAR WEIGHT AND CONSTITUTION. 127 using a porcelain globe, succeeded in determining its specific gravity at a very high temperature, that its value was found to correspond with the probable molecular weight, and it is pos- sible that a similar anomaly which still exists in the case of phosphorus and arsenic may be due to the same cause. The chemist, however, can always have a sure criterion of the condition of any vapor whose specific gravity he is deter- mining by repeating his experiment at a somewhat higher tem- perature. If the second result does not agree with the first, it is a proof that the vapor is not yet in a proper condition, and that the temperature employed in the experiment was too low. A series of determinations of the specific gravity of the vapor of acetic acid made by Cahours furnish an excellent illustra- tion of the importance of the precaution we are discussing, and will also point out another important relation of this whole sub- ject. This acid when in the most concentrated state boils at 120, and the specific gravity of its vapor referred to hydrogen at the same temperature and pressure was found to have the following values at the temperatures annexed : At 125 45.90 At 170 35.30 At 240 30.16 " 130 44.82 " 180 35.19 " 270 30.14 " 140 41.96 " 190 34.33 " 310 30.10 " 150 39.37 " 200 32.44 " 320 30.07 " 160 37.59 " 220 30.77 336 30.07 It will be noticed that, as the temperature increases, the specific gravity diminishes, at first very rapidly, afterwards more slowly, and does not become constant until the tempera- ture has risen 200 above the boiling point, when we have the true specific gravity of acetic acid m the state of gas. This gives for the molecular weight of acetic acid 60 very nearly, which corresponds to the received formula, C. 2 ff 4 2 . The slight difference between the theoretical and the observed results may be in part due to errors of observation, but is most prob- ably to be referred to the same cause which determines even in the permanent gases, when under the atmospheric pressure, a variation from Mariotte's law. We do not expect> moreover, to find from the specific gravity the exact molecular weight. The precise value is determined by the results of analysis, which are, as a rule, far more accurate, and the specific gravity is 128 MOLECULAR WEIGHT AND CONSTITUTION. only used to decide which of several possible multiples must he the true value. (Compare carefully 23.) 67. Disassociation. But, besides taking care that the tem- perature is sufficiently high to bring the substance we are studying into the condition of a true gas, we must look out that the compound is not decomposed in the process. It is now well known that at very high temperatures the disassociation of the elements of a compound body is a constant result, and it is probable that in some cases the same effect is produced at the much lower temperatures which are employed in the determi- nation of vapor densities. The specific gravity of the vapor of ammonic chloride, instead of being 26.75, as we should ex- pect from the undoubted .weight of its molecule, NffCl, is only about one half of this amount ; and the reason probably is, that, when heated, the molecule breaks into two, and in conse- quence the volume of the vapor doubles. It is very difficult, however, to obtain any further evidence that such a change has taken place ; for, as soon as the tempera- ture falls, the molecules recombine in assuming the solid condi- tion, and all the phenomena attending the change of state are precisely the same as those observed in any other volatile body. Indeed, although many very ingenious experiments have been made with a view of settling the question, it is still uncertain, not only in this, but also in several other cases, whether disassociation has taken place or not. The question is of great importance to the theory of chemistry. If disasso- ciation does not take place, the cases referred to are exceptions to the law of equal molecular volumes, and specific gravity can no longer be regarded, as now, the sole measure of molecular weight. If, however, it can be proved that such a change does take place, then the unity of our present theory is preserved, and the chemist has only to guard against this cause of error in his experiments. 68. Indirect Determination of Molecular Weight. Al- though our modern chemical theories rest in great measure on the molecular weight of a few typical compounds determined, MOLECULAR WEIGHT AND CONSTITUTION. 129 at least approximately, by their specific gravities, yet it is only in a comparatively few cases that we are able to refer the molecular weight of a substance directly to this fundamental measure. Most substances are so fixed, or so easily decom- posed by heat, that it is impossible to determine the specific gravity of their vapor, even when such a condition is possible. In these cases, however, we endeavor to refer the molec- ular weight indirectly to the fundamental measure, by estab- lishing a relation of chemical equivalency between the sub- stance whose molecular weight is sought and some closely allied volatile substance whose molecular weight has been pre- viously determined in the manner described above. A few ex- amples will make the application of this principle intelligible. It is required to determine the molecular weight of nitric acid. A careful study of the numerous nitrates leads to the conclusion that this acid, like hydrochloric acid, ffCl, con- tains but one atom of replaceable hydrogen. For example, we find but one potassic nitrate and one sodic nitrate, whereas we should expect to find several, if the acid were polybasic. Hence we conclude that one molecule of argentic nitrate, like one molecule of argentic chloride, AgCl, contains but one atom of silver. Next, we analyze argentic nitrate, and find that 100 parts of the salt contain 63.53 parts of silver. We know the atomic weight of silver, 1 08, and evidently this must bear the same relation to the molecular weight of argentic nitrate that 63.53 bears to 100. But 63.53 : 100 = 108 : #=170, which is the molecular weight of argentic nitrate, and, since the molecule of nitric acid differs from that of argen tic nitrate only in containing an atom of hydrogen in place of the atom of silver, its own weight must be 170 108 -f- 1 = 63. It is required to determine the molecular weight of sul- phuric acid. A comparison of the different sulphates shows that sulphuric acid is dibasic. We find two sulphates of potas- sium and sodium, an acid sulphate and a neutral sulphate, and hence we conclude that this acid contains two replaceable atoms of hydrogen, and hence that one molecule of neutral potassic sulphate contains two atoms of potassium. In ana- lyzing potassic sulphate it appears that 100 parts of the salt contain 44.83 parts of potassium,, and evidently this weight 9 130 MOLECULAR WEIGHT AND CONSTITUTION. bears the same relation to 100 that the weight of two atoms of potassium bears to the weight of the molecule of potassic sul- phate. Thus we have, 44.83 : 100 = 78 : x = 174 ; the M. W. of Potassic Sulphate, and 174 78 -f 2 = 98 ; the M. W. of Sulphuric Acid. By a similar course of reasoning we may deduce from the results of analysis, and from the general chemical rela- tions, the molecular weight of any other acid or base. If there is any question in regard to the basicity of the acid or the acidity of the base, there will be the same question as to the molecular weight ; but we cannot be led far into error, for the true weight will be some simple multiple or submultiple of the one assumed, and the progress of science will sooner or later correct our mistake. From the molecular weight of any acid we easily deduce the molecular weights of all its salts. When the substance is not distinctively an acid or a base, but is capable of entering into combination with other bodies, we can frequently discover its molecular weight by determining experimentally how much of this substance is equivalent to a known weight of some allied but volatile substance whose molecular weight is known. Thus ammonia gas, whose molec- ular weight is one of the best-established data of chemistry, enters into direct union with a compound of platinic chloride and hydrochloric acid (Pt Cl ti H 2 ) to form a definite crystalline salt whose composition is exactly known. PtCl G H 2 + 2NJJ 3 = PtCk(NHt) f [61] Now a very large number of substances allied to ammonia form with this same platinum salt equally definite products, so that by simply determining the weight of platinum in these compounds, which is very easily done, their molecular weights may at once be referred to the molecular weight of ammonia. Lastly, if other means fail, we may sometimes discover the molecular weight of a compound by carefully studying the reac- tions by which it is formed or decomposed, and inferring the weight of the compound from that of its factors or products. We seek to express the reaction in the simplest possible way, and give that value to the molecular weight which best satisfies the MOLECULAR WEIGHT AND CONSTITUTION. 131 chemical equation. Evidently, however, such results are less trustworthy than those obtained by either of the other methods. 69. Constitution of Molecules. It is a favorite theory with some chemists that no molecule can exist in a free condition with any of its affinities unsatisfied, but those who hold this view are compelled to admit that two points of attraction in the same atom may, in certain cases, neutralize each other. Hence, they would distinguish between a dyad atom like that of oxygen ( ), with its affinities open, and a dyad atom like that of mercury (~ -), with its affinities closed through their own mutual attraction. The first could not exist in a free condition, while the last could. In like manner any atom, having an even number of points of attraction, can exist in a free state because all its affinities may be satisfied within itself; but an atom hav- ing an uneven number of points cannot, for at least one of its affinities must be open as is shown by the symbol (^ ). As thus interpreted it must be admitted that the theory explains many facts. For example, among the univalent elements, chlorine, bro- mine and iodine are all known to have molecules consisting of two atoms. So, also, the molecule of cyanogen gas consists of two atoms of the radical ON, and the same is true of ethyl, propyl, &c., at least if the hydrocarbons so named have really the constitution first assigned to them. Passing next to the dyads, we find that, while oxygen, sulphur, selenium and tellurium have molecules consisting of two atoms, the metals mercury and cadmium, and the radicals ethylene, propylene, &c. (O 2 ff 4 and CgZQ, have molecules which coincide with their atoms. Of the well-defined triad elements none are volatile, but the two triad radicals which have been obtained in a free state' allyl 1 (C s ff 5 ) and kakodyl ((Cff 3 ) 2 As) both have double atomic molecules. In like manner none of the tetrad elements are volatile, and the only tetrad radicals known in a free state have single atomic molecules. Of the pentad elements nitrogen has a molecule of two atoms, while phosphorus and arsenic have molecules of four 1 See page 78, Problem 7. 132 MOLECULAR WEIGHT AND CONSTITUTION. atoms. No compound radicals of this order are known in a free state. Lastly, the only hexad radical known in a free state, benzine, C 6 ff 6 , has a molecule which coincides with its atom. Thus it appears that in general the theory is sustained by the facts. Nevertheless, there are several well-marked exceptions in i to it. Thus the well-known compounds NO and N0 2 have molecules which act as radicals of uneven atomicities and yet contain but one complex atom. We must be careful, therefore, not to give too much weight to this hypothesis, but still it may be useful in co-ordinating facts. It leads at once to three gen- eral principles which will be found to be almost universally true. The first is that the sum of the atomicities of the atoms of every molecule is an even number. The second is that the atomicity of any radical is an odd or even number according as the sum of the atomicities of its elementary atoms is odd or even. The third is that the quantivalence of elementary atoms must be, as stated on page 59, either even or odd. They are artiads or perissads, and the two characters can never be mani- fested by the same elements. It has also been a question among chemists whether molec- ular combination was possible ; in other words, whether it is possible for molecules of different kinds to combine chemically, each preserving its integrity in the compound. Some of the advocates of the unitary theory, in the reaction against the dualistic system, have been inclined to doubt the possibility of such compounds, and have attempted to represent the symbols of all compounds in a single molecular group ; but any ante- cedent improbability, on theoretical grounds, is far more than outweighed by the evidence of a large number of compounds whose constitution is most simply explained on the hypothesis of molecular combination. For example, in the crystalline salts it is impossible to doubt that the water exists as such, not as a part of the salt molecule, but combined with it as a whole. So, also, there are a number of double salts whose constitution is most simply explained on a similar hypothesis, and, in the pres- ent state of the science, it seems unnecessary to complicate their symbols by forcing them into the unitary mould. It is a MOLECULAR WEIGHT AND CONSTITUTION. 133 characteristic of such molecular compounds as are here assumed, that the force which holds together the molecules is much feebler than that which binds together the atoms in the molecule. When the molecular attraction is very strong, it is probable that in almost all cases the different molecules coalesce into one ; and between the extreme limits we find compounds in which it is difficult to determine whether true molecular combination ex- ists or not. Such coalescing of distinct molecules seems always, however, to be attended with a greater development of heat, and, in general, with a more marked manifestation of physical ener- gies, than usually attends either molecular aggregation or atomic metathesis. In the notation of this book molecular combination is indi- cated by writing together the symbols of the different molecules thus united, but separating these symbols by periods. Thus the symbols ^KCLPtCl^ and 3NaF.SbF 3 represent compounds of this class. 70. Isomerism, Allotropism, Polymorphism. We should infer from the doctrine of chemical types that the same atoms might be grouped together in different ways, so as to form different molecules which in their aggregation would present essentially distinct qualities. Hence, we should expect to find distinct substances having the same composition ; and in fact our science, organic chemistry especially, is rich in examples of this kind. Such substances are said to be isomeric. and the phenomenon is called isomerism. There are different phases of isomerism, which it will be well to distinguish, not so much on account of any essential differences in the phenomena as in order to make ourselves better acquainted with its manifesta- tions. In the first place, we have examples of isomeric bodies having the same centesimal composition, but showing no rela- tion to each other in their properties or in their chemical reactions. Sometimes we have assigned to them the same formula, but in other cases the symbol of one is a simple multiple of that of the other. Thus aldehyde and oxide of ethylene have both the symbol C 2 Jf 4 ; cane sugar and gum arabic, the common formula O^H.^ n ; lactic acid, the formula C 3 ffiO 3 i and glucose, C 6 //i 2 6 . These compounds bear no resemblance to each other, and have no relations in common 134 MOLECULAR WEIGHT AND CONSTITUTION. save the single fact that their centesimal composition is the same. In the second place, we have numerous examples of isomeric compounds, which, with the same centesimal composition, have also the same molecular weight, and whose molecules, therefore, consist of the same number of -atoms, but where a fundamental difference in the grouping of the atoms may be inferred from the nature and products of the chemical reactions, by which such isomeric compounds are formed or decomposed. Thus, for ex- ample, ethylic formiate (C 2 ff 5 )-0-(CffO) has exactly the same composition and molecular weight as methylic acetate (CH^y- 0~( O^ff 3 0). The same is true of cyanic ether and cyanetholine, whose symbols have already been given (page 77) in connec- tion with the reactions, which indicate their molecular constitu- tion, and another still more remarkable case will be found in Part II. of this work [164] and [165]. In the third place, we have several groups of isomeric com- pounds, especially among the hydrocarbons, which have the same general properties and the same percentage composition, but which differ from each other in their molecular weights ; so that the symbol of one is a multiple of that of the rest. The hydrocarbons ethylene C 2 ff^ propylene C & ff G ^ butylene C 4 ff^ form a group of this kind. Compounds of this class are fre- quently called polymeric, and sometimes the heavier com- pounds may be regarded as condensed forms of the lighter. Lastly, we may distinguish still a fourth class of isomeric compounds which have the same general properties, the same symbol, and the same general system of reactions, but which differ in a few marked qualities, physical or chemical, and which preserve these characteristics to a greater or less extent in their compounds. The two forms of toluic acid, C 8 H S 0^ be- long to this class, and such compounds are isomeric in the fullest sense of the word. In all the above examples the differences between the iso- meric compounds are sufficiently great to lead chemists to assign to each a distinct name. When, however, the differ- ences are not sufficiently great to justify a distinct name, the two bodies are said to be different allotropic states of the same substance. Thus there are two varieties of tartaric acid ; the first of which deviates the plane of polarization of a ray of light MOLECULAR WEIGHT AND CONSTITUTION. 135 to the left, while the second deviates it to the right ; but since in almost every other respect these two bodies are identical, we do not speak of them as different substances, but merely as different allotropic states of tartaric acid. There are also three other varieties of tartaric acid, but these differ so greatly from the normal acid in crystalline form, in solubility, and also in other relations, that they may fairly be regarded as distinct substances. Again, there are many substances where the difference of state or aUotropism is associated with difference of crystalline form ; and when this difference of form is fundamental, the substance is said to be dimorphous or trimorphous, as the case may be, and the phenomenon is called polymorphism. Thus common calcic carbonate crystallizes in two fundamentally dis- tinct forms, corresponding to the two mineralogical species, calcite and aragonite. Such difference of form, however, is invariably accompanied by a marked difference of properties, so that polymorphism is merely one of the indications of allo- tropism. Differences of condition similar to those we have described manifest themselves even more markedly among elementary substances ; and indeed the word allotropism was first applied to phenomena of this last class. Thus there are two allotropic states of phosphorus, which differ so much from each other that no one would suspect from their external characters that there was any identity between them, and to these two states corre- spond two fundamentally different crystalline forms. In some cases the differences between the allotropic states of the same element are far greater than any which are seen between the most unlike isomeric compounds. No substances could be better defined by well-marked and utterly distinct qualities than diamond, plumbago, and charcoal, and yet they are all three allotropic modifications of the one elemental substance we call carbon ; and such phenomena as these give us strong grounds for believing that our present elements may have a composite structure. 136 MOLECULAR WEIGHTS AND CONSTITUTION. Questions and Problems. 1. What are the molecular weights of alcohol and camphor as de- duced from the results of the jtj. (B>t. determinations given on page 23? Ans. 45.5 and 155, which, although not closely agreeing with the theoretical numbers, enables us to decide that the symbols of these compounds are C 2 H 6 and C lo H l6 as the simplest interpretation of the analyses would indicate. 2. At the temperature of 470 the gm. (J$r. of the vapor of sul- phuric acid is approximately 1.697. How does this result agree with the generally received symbol of this compound, and how do you explain the discrepancy ? 3. A study of the different tartrates has led to the conclusion already expressed that tartaric acid, although tetratomic, is dibasic. It also appears that one hundred parts of neutral argentic tartrate yield when ignited 55.39 parts of metallic silver. Required the molecular weight of tartaric acid. Ans. 1 76. 4. An hundred parts of baric oxide, BaO, (whose composition is assumed to be known) yield when treated with sulphuric acid 152.3 parts of baric sulphate. Further it is assumed, as the result of care- ful study, that sulphuric acid is dibasic, and the metal barium a biva- lent radical. Required the molecular weight of sulphuric acid. Ans. 98. 5. The well-known base aniline gives with platinic chloride a definite crystalline product, one hundred parts of which yield on ignition 32.99 parts of platinum. Required the molecular weight cf aniline. How does this result agree with the gp. (gr. of aniline vapor, which has been found by observation to be 3.210. ? Ans. 93 ; which corresponds to gjj. (g>r. of 3.223. 6. The base triethylamine gives in like manner a platinum salt, one hundred parts of which yield on ignition 32.13 parts of plati- num. Required the molecular weight. Ans. 101. 7. Compare together the symbols of the compounds of the va- rious alcohol radicals on pages 90 to 93 and point out the exam- ples of isomerism. CHAPTER XIV. CRYSTALLINE FORMS. 71. Relations to Chemistry. Almost every substance affects a definite polyhedral form, although it may manifest this tendency only under favorable conditions. Such forms are called crystals, arid the process of crystalline growth, or de- velopment, is called crystallization. The one essential condi- tion of crystallization is a certain freedom of motion, and crys- tals, more or less perfect, are usually formed whenever a molten liquid " sets," or a solid is deposited from a condition of solution or of vapor ; and in each case the slower the process the larger and the more perfect are the crystals. The crystalline condi- tion is, in fact, the normal state of solid matter. It is true that there are a few substances which, like glue, are only known in the colloid state; but in most of the so-called colloid sub- stances this state is abnormal, and there is a constant tendency to crystallization. Moreover, its peculiar crystalline form is one of the most characteristic, and apparently one of the most es- sential, properties of a substance, and is therefore of great value in determining its chemical affinities. The study of the geomet- rical relations of these forms is, however, in itself a separate science, and in this connection we can only dwell on the few elementary principles of the subject on which our system of chemical classification in part rests. 72. Definitions. In the forms of crystals the idea of sym- metry is the great controlling principle. Each substance fol- lows a certain law of symmetry, which seems to be inherent, and a part of its very nature ; and. when, from any cause, the character of the symmetry changes, the substance loses its identity, and, even if its chemical composition remains the same, it becomes, to all intents and purposes, a different sub- stance. In every crystal the symmetry points to a few direc- tions, to which not only the position of the planes, but also the physical properties of the body, are closely related. Certain of 138 CRYSTALLINE FORMS. Fig. 4. these directions, more or less arbitrarily chosen, are called the axes of the crystals, and a crystalline form may be defined as a group of similar planes symmetrically disposed around these axes. As is evident from this definition a crystalline form, like a geometrical form, is a pure abstraction, and this conception is carefully to be kept distinct from the idea of a crystal, which implies not only a cer- tain form, but also a certain structure. Moreover, in by far the larger number of cases the same crystal is bounded by several forms. Thus, in Fig. 4, which represents a crystal of common quartz, the planes of the prism and the planes of the pyramid are distinct crystalline forms. 73. Systems of Crystals. A careful study of the forms of crystals has shown that these forms may be classified under six crystalline systems, each of which is distinguished by a peculiar plan of symmetry. These divisions, it is true, are in a meas- ure arbitrary ; for here, as elsewhere in nature, no sharp dividing lines are found ; but nevertheless the distinctions on which the classification rests are clearly marked. We can only give in this book a very imperfect idea of these several plans of sym- metry by representing with figures a few of the more charac- teristic forms of each. 74. First or Isometric System. 1 The three most frequently occurring forms of this system are the regular octahedron, the Fig. 5. Fig. 6. Fig. 7. rhombic dodecahedron and the cube, Figs. 5, 6, and 7. These and all the other forms of the system may be regarded as 1 Called also monometric. CRYSTALLINE FORMS. 139 grouped around three equal and similar axes at right angles to each other, and hence the name isometric (equal dimensions). They present the same symmetry on all sides, and the appear- ance of the form is identical, whichever axis is placed in a ver- tical position. In this system no variation in the relative posi- tions or lengths of the axes is possible, for this would change the plan of symmetry on which the system is based. 75. Second or Tetragonal System}- The plan of symmetry in this system is best illustrated by the square octahedron, Fig. 8. Of this form the basal section, Fig. 9, is a square, and to Fig. 9. Fig. 8. this fact the name of the system refers. The vertical section, on the other hand, is a rhomb, Fig 10. Here, as in the first system, the forms may all be referred to three rectangular axes, but only two have the same length ; the third may be either longer or shorter than the others. The last is the dominant axis of the form, and hence we always place it in a vertical position and call it the vertical axis. The length of the verti- cal axis bears a constant ratio to that of the lateral axes in all crystals of the same substance, but this ratio differs very greatly for different substances, and is therefore an important crystal- lographic character. The familiar square prism is another very characteristic form of this system. r. 11. Fig. 12. Moreover, the planes both of the prism and of the octahedron may have different positions with reference to the lateral axes, as is shown by the two basal sections, Figs. 11 and 12; - Called also dimetric. 140 CRYSTALLINE FORMS. and this leads us to distinguish two square prisms and two square octahedrons, one of which is said to be the inverse of the other. 76. Third or Hexagonal System. In the last system the planes were arranged by fours around one dominant axis, while in this system they are arranged by sixes. The most character- istic forms of this system are the hexagonal pyramid, Fig. 13, and the hexagonal prism, Fig. 14. The basal section through either of these forms is a regular hexagon, Fig. 15, and, besides Fig. 13. Fig. 14. Fig. 15. the dominant or vertical axis, we also distinguish as lateral axes the three diagonals of this hexagonal section. These lateral axes stand at right angles to the vertical axis, but between themselves they subtend angles of 60 Here, as before, the ratio of the length of the vertical axis to the common length of the lateral axes has a constant value on crystals of the same substance, but differs very greatly with different substances, the vertical axis being sometimes longer and sometimes shorter Fig. 17. Fig. 16. than the other three. The rhombohedron, Fig. 16, and the scalenohedron, Fig. 17, are also forms of this system, and occur CRYSTALLINE FORMS. 141 even more frequently than the more typical forms first men- tioned. Lastly, a difference of position in the planes of the prism or pyramid with reference to the lateral axes gives rise in this system to the same distinction between the direct and the inverse forms as in the last. 77. Fourth or Orthorhombic System. 1 The most character- istic forms of this system are the rhombic octahedron, Fig. 18, and the right rhombic prism, from which the system takes its name. The three principal sections of the octahedron, repre- sented by Figs. 19, 20, and 21, and also the basal section of the Fig. 18. Fig. 19. Fig. 20. prism, are all rhombs, whose relations to the form are indicated by the lettering of the figures. We easily distinguish here three axes at right angles to each other, but of unequal lengths, and in regard to the ratios of these lengths, the remarks of the last two sections are strictly applicable. 78. Fifth or Monodinic System. The forms classed together under this system may be referred to three unequal axes, one of which stands at right angles to the plane of the other two, while they are inclined to each other at an angle, which, though con- stant on crystals of the same substance, varies very greatly with different substances, as vary also the relative dimensions of the axes themselves. Fig. 22 represents an octahedron of this system, and Figs. 23 and 24 represent two sections made through the edges FF and DD' of this form. A section through the edges G O would be similar to Fig. 23, and these three sections give a clear idea of the relative positions of the axes. The section, Fig. 24, containing the two oblique axes, l Called also trimetric. 142 CRYSTALLINE FORMS. is called the plane of symmetry, and the faces on all monoclinic crystals are disposed symmetrically solely with reference to this plane. In a word, the symmetry is bilateral, and corresponds Fig. 22. Fig. 23. Fig. 24. to the type with which we are so familiar in the structure of the human body. This plan of symmetry is well illustrated by Figs. 25, 26, and 27, which represent the commonly occurring forms of gypsum, augite, and felspar, three of the most com- mon minerals. These figures, however, do not, like those of the previous sections, represent simple crystalline forms. The crys- tals here represented are in each case bounded by several forms, and indeed in this system such compound forms are alone pos- sible, for no simple monoclinic form can of itself enclose space. Fig. 25. Fig. 26. Fig. 27. 79. Sixth or Triclinic System. This system is distinguished by an almost complete want of symmetry. Only opposite planes Fig. 28. are similar, and two such planes constitute a complete crystalline form. Hence on every crystal there must be at least three simple forms. We may refer the planes of any crystal to three unequal axes all oblique to each other, but the position we assign to them is quite ar- bitrary, and they have therefore little value as crystallographic elements. Fig. 28 represents a crystal of sulphate of copper, one of the very few subtances which crystallize in this system. CRYSTALLINE FORMS. 143 80. Modifications on Crystals. When several crystalline forms appear on the same crystal, some one is usually more prominent or dominant than the rest, and gives to the crystal its general aspect, the planes of the secondary forms only ap- pearing on its edges or solid angles, which are then said to be modified or replaced. Thus, in Figs. 29, 30, and 31, the solid angles of a cube are replaced (or truncated) by the faces of an octahedron ; in Fig. 32 the edges of the cube are replaced by the faces of the dodecahedron ; in Fig. 33 the edges of the octahedron are modified in the same way ; and in Fig. 34 the solid angles of a dodecahedron are replaced by the faces of an Fig. 29. Fig. 30. Fig. 31. octahedron. These are all forms of the isometric system, and the relations of the simple forms to each other, which deter- mine in every case the position of the secondary planes, will be readily seen on comparing together the figures already given on page 138. These figures, like all crystallographic drawings, are geometrical projections, and represent the planes in the same relative position towards the crystalline axes which they have on the crystal itself. Moreover, since in all figures of crystals of this system the axes are drawn in absolutely the same position on the plane of the paper, the same face has also the same position throughout. As a general rule, all the similar parts of a crystal are simultaneously and similarly modified. This important law, 144 CRYSTALLINE FORMS. which is a simple inference from the principles already stated, is illustrated by the figures just gn r en, and also by Figs. Fig. 35. Fig. 36. Fig. 37. Fig. 38. 35 to 50. By carefully studying these figures, as well as Figs. 25 to 28 on page 142, the student will be able to refer each of Fig. 39. T?J Af\ Fig. 41. Fig. 40. the compound crystals here represented to one or the other of the systems of symmetry already described, and from this and Fig. 42. _ Fig. 43. Fig. 44. similar practice he will learn, better than from any descrip- tions, how clearly the modifications on a crystal point out its crystallographic relations. CRYSTALLINE FORMS. 145 81. Hemihedral Forms. To the law governing the modi- fications of crystals just stated, there is one important excep- Vig. 45. Fig. 46. Fig. 47. Fig. 48. tion. It not unfrequently happens that half the similar parts of a crystal are modified independently of the* other half. Thus Fig. 49. Fig. 50. in Fig. 51 only one half of the solid angles of the cube are truncated. The modifying form in this case is the tetrahedron, Fig. 52. Fig. 53, also a simple form of the isometric system. When all the solid angles of the cube are truncated, the modifying form, as has been shown, is the octahedron, and the relation which the tetrahedron bears to the octahedron is shown by Fig. 52. The rhombohedron, Fig. 54, stands in a similar re- lation to the hexagonal pyramid, Fig. 55. From these figures- 146 CRYSTALLINE FORMS. it is evident that while the octahedron and the hexagonal pyra- mid have all the planes which perfect symmetry requires, the Fig. 55. tetrahedron and the rhombohedron have only half the number, and in crystallography all forms which bear a similar relation to the forms of perfect symmetry are said to be ^e/m'hedral, while the forms of perfect symmetry are distinguished as kolo- hedral. The hemihedral forms are quite numerous in all the systems, but with the exception of the tetrahedron, rhombohe- dron, and scalenohedron (Fig. 17), they seldom appear except as modifying planes on the edges or solid angles of the more perfect forms. As a general rule, they are easily recognized, but not unfrequently they give to a crystal the aspect of a dif- ferent system from that to which it really belongs, and may lead to false inferences ; but these can, in most cases, be cor- rected by a careful study of the interfacial angles. 82. Identity of Crystalline Form. As has already been stated, every substance is marked by certain peculiarities of outward form, which are among its most essential qualities, and we must next learn in what these peculiarities consist. As a general rule, the same substance crystallizes in the same form, but under unusual circumstances it frequently appears in other forms of the same system. Thus fluorspar is usually found crystallized in cubes, but in large collections crystals of this mineral may be seen in almost all the holohedral forms of the isometric system, including their numerous combinations. In like manner common salt usually crystallizes in cubes, but out of a solution containing urea it frequently crystallizes in octa- hedrons. Moreover, the same principle holds true in regard to substances crystallizing in other systems, most of whose forms never appear except in combination. Thus the mineral CRYSTALLINE FORMS. 147 quartz generally shows the simple combination represented in Fig. 4 ; but more than one hundred other forms, all, however, belonging to the same system, have been observed on crystals of this well-known substance. So also the crystals of gypsum, augite, and felspar, in most cases present the forms already figured on page 142, although other forms are common, which, however, in each case all belong to the same crystalline system. We never find the same substance in the forms of different sys- tems except in those cases of polymorphism already described, page 135, where the differences in other properties are so great that the bodies can no longer be regarded as the same substance. Among substances crystallizing in the isometric system the crystalline form is not so distinctive a character as it is in other cases. In this system the relative dimensions are invariable, and the octahedron, the dodecahedron, and the cube, more or less modified by different replacements, are the constantly re- curring forms. Even here, however, specific differences may at times be found in the fact that some substances affect hemi- hedral forms on modification, while others do not. In all the other systems the dimensions of the crystal (the relative lengths of its axes and the values of the interaxial angles) distinguish each substance from every other. But here, also, the general statement must be somewhat modified. We frequently find on the crystals of the same substance several forms having different axial dimensions. Thus, on the crystal represented by Fig. 56, belonging to the tetragonal system, there are three different octahedrons, and three cor- responding values of the vertical axis. But if, beginning with the planes of the octahedron 0, we determine the ratio which its vertical axis bears to the Flg ' 56 ' common length of the two lateral axes, and call this value a, we shall find that the cor- responding values for the two other octahe- drons are 2a and a respectively. More- over, if we extend our study we shall also find that this example illustrates a general principle, and that the crystalline forms of a given substance include not only those of identical axial dimensions, but also those whose dimensions tear to each other some simple ratio. 148 CRYSTALLINE FORMS. This most important law gives to the science of crystallog- raphy a mathematical basis, and enables us to apply the exhaus- tive methods of analytical geometry in discussing the various re- lations of the subject. Among the actual forms of a given sub- stance we fix on some one as the fundamental form, and, taking the values of its axial dimensions as our standards, we are able to express the position of the planes of all the possible forms by means of very simple symbols, and also to express by mathe- matical formulae the relations of the interfacial angles to the same fundamental elements of the crystal; so that the one may readily be calculated from the other. It may seem at first sight that the crystallographic distinction between different substances, insisted on above, is greatly ob- scured by the important limitations just made. But it is not so, at least to any great extent. The selection of the funda- mental form of a given substance is not arbitrary, although it is based on considerations which it lies beyond the scope of this book to discuss. Moreover, an error in this choice is not fun- damental, since the true conception of the form of a substance includes not only the fundamental form, but all those which are related to it. This conception, though not readily embodied in ordinary language, is easily expressed by a general mathemat- ical formula, and is as tangible to one familiar with the subject as the general statement first made. But however obscure, to those who are not familiar with mathematical conceptions, may be the distinction between the forms of different substances in the same system, the difference between the different systems is clear and definite, and it is with this broad distinction that we have chiefly to deal in our chemical classification. 83. Irregularities of Crystals. It must not be supposed that natural crystals have the same perfection of form and regularity of outline which our figures might seem to indicate. In addition to being more or less bruised or broken from acci- dental causes, crystals are rarely terminated on all sides, one or more of the faces being obliterated where the crystal is im- planted on the rock, or where it is merged in other crystals. But by far the most remarkable phase which the irregularities of crystals present is that shown by Figs. 57 to 67. By com- paring together the figures which have been here grouped to- CRYSTALLINE FORMS. 149 gether on the page, and which represent in each case different phases of the same crystalline form, it will be seen that the variations from the normal type are caused by the undue de- Fjg. 58. rig. 57. velopment of certain planes at the expense of their neighbors, or by an abnormal growth of the crystal in some one direction. Fig. 61. Fig- 60. Such forms as these, however, although great departures from the ideal geometrical types, are in perfect harmony with Fig. 62. Fig. 63. the principles of crystallography. The axis of a crystal is not a definite line, but a definite direction ; and the face of a crystal 150 CRYSTALLINE FORMS. is not a plane of definite size, but simply an extension in two definite directions. These directions are the only fundamental elements of a crystalline form, and they are preserved under Fig. 64. Fig. 66. all conditions, as is proved by the constancy of the interfacial angles, and of the modifications, on crystals of the same sub- stance, however irregular may have been the development. 84. Twin Crystals. Every crystal appears to grow by the slow accretion of material around some nucleus, which is usually a molecule or a group of molecules of the same substance, and which we may call the crystalline molecule or germ. Now we must suppose that these molecules have the same differences on different sides which we see in the fully developed crystal, and which, for the want of a better term, we may call polarity. As a general rule, in the aggregation of the molecules a perfect parallelism of all the similar parts is preserved. But, if molec- ular polarity at all resembles magnetic polarity, it may well be that two crystalline molecules might become attached to each other in a reversed position, or in some other definite position determined by the action of the polar forces. Assume now that each of these crystalline molecules " germinates," and the result would be such twin crystals as we actually find in nature. The result is usually the same as if a crystal of the normal form were cut in two by a plane having a definite position towards the crystalline axes, and one part turned half round on the other ; and twins of this kind are therefore called hemitropes. Figs. 68 to 71. At other times the germinal molecules seem to have become attached with their dominant axes at right angles to each other, and then there result twins such as are represented in Figs. 72 and 73 ; and many other modes of twin- CRYSTALLINE FORMS. 151 ning are possible. Some substances are much more prone to the formation of twin crystals than others, and the same sub- stance generally affects the same mode of twinning, which may Fig. 71. Fig. 68. Fig. Fig. 69. thus become an important specific character. The plane which separates the two members of a twin crystal, called the plane Fig. 72. Fig. 73. of twinning, has always a definite position, and is in every case parallel either to an actual or to a possible face on both of the two forms. Twin crystals always preserve the same symmetry of group- ing, and the values of the interfacial angles between the two forms are constant on crystals of the same substance, so that they might sometimes be mistaken for simple crystals by un- practised observers. There is, however, a simple criterion by which they can be generally distinguished. Simple crystals never have re-entering angles, and, whenever these occur, the faces which subtend them must belong to two individuals. The same principle which leads to the formation of twin crystals may determine the grouping of several germinal molecules, and lead to the formation of far more complex com- 152 CRYSTALLINE FORMS. binations. Frequently, as it would seem, a large number of molecules arrange themselves in a line with their principal axes parallel and their dissimilar ends together, and hence re- sult linear groups of crystals alternating in position, but so fused into each other as to leave no evidence of the composite char- acter except the re-entering angles, and frequently these are marked only by the striations on the surface of the resulting faces. Such a structure is peculiar to certain minerals, and the resulting striation frequently serves as an important means of distinction. The orthoclase and the klinoclase felspars are distinguished in this way. 85. Crystalline Structure. The crystalline form of a body is only one of the manifestations of its crystalline structure. This also appears in various physical properties, which are fre- quently of great value in fixing the crystallographic relations of a substance, and such is especially the case when, on ac- count of the imperfection of the crystals, the crystalline form is obscure. Of these physical qualities one of the most impor- tant is cleavage. As a general rule, crystallized bodies may be split more or less readily in certain definite directions, called planes of cleav- age, which are always parallel either to an actual or to a pos- sible face on the crystals of the substance, and are thus inti- mately associated with its crystalline structure. At times the cleavage is very easily obtained, when it is said to be eminent, as in the case of mica or gypsum, which can readily be split into exceedingly thin leaves, while in other cases it can only be effected by using some sharp tool and applying considerable mechanical force. With a few unimportant exceptions the cleavage planes have the same position on all specimens of the same substance. Thus specimens of fluor-spar may be readily cleaved parallel to the faces of an octahedron, Fig. 5, those of galena parallel to the faces of a cube, Fig. 7, those of blende parallel to the faces of a dodecahedron, Fig. 6, and those of calc-spar parallel to the faces of a rhombohedron, Fig. 16. In these cases, and in many others, the cleavage is a more distinc- tive character than the external form, and can be more fre- quently observed, and we generally regard the form produced by the union of the several planes of cleavage as the funda- mental form of the substance. Again, we always find that cleavage is obtained with equal CRYSTALLINE FORMS. 153 ease or difficulty parallel to similar faces, and with unequal ease or difficulty parallel to dissimilar faces. Moreover, the dissimilar cleavage faces thus obtained may generally be dis- tinguished from each other by differences of lustre, striation, and other physical character ; and such distinctions are fre- quently a great help in studying the crystallographic relations of a substance. Similar differences on the natural faces of crystals are also equally valuable guides. But, of all the modes of investigating the crystalline structure of a body, none can compare in efficiency with the use of polar- ized light. It is impossible to explain the theory of this beau- tiful application of the principles of optics without extending this chapter to a length wholly incompatible with the design of this book. It must suffice to say, that if we examine with a polarizing microscope a thin slice of any transparent crystal of the second or third system, cut perpendicular to the dominant axis, we see a series of colored rings, intersected by a black cross, and it is evident that ^the circular form of the rings answers to the perfect symmetry which exists in these systems around the vertical axis. If, however, we examine in a similar way a slice from a crystal of one of the last three systems, cut in a definite direction, which depends on the molecular structure, and must be found by trial, we see a series of oval rings with two distinct centres, indicating that the symmetry is of a dif- ferent type. Moreover, the distribution of the colors around the two centres corresponds in each case to the peculiarities of the molecular structure, and enables us to decide to which of the three systems the crystal belongs. The use of polarized light has revealed remarkable differ- ences of structure in different crystals of the same substance, connected with the hemihedral modifications described above. The Figures 74 and 76 represent crystals of two varieties of tartaric acid, which only differ from each other in the position of two hemihedral planes, and are so related that when placed before a mirror the image of one will be the exact representa- tion of the other. The intermediate Figure, 75, represents the same crystal without these modifications. Since the solid angles are all similar, we should expect to find them all modi- fied simultaneously ; but, while on crystals of common tartaric acid only the two front angles (as the figure is drawn) are re- placed, a variety of this acid has been discovered having simi- 154 CRYSTALLINE FORMS. lar crystals, whose back angles only are modified. Now, it is found that a solution of the common acid rotates the plane of polarization of a beam of light to the right, while a similar so- Fig. 74. Fig. 75. Fig. 76. lution of this remarkable variety rotates the plane of polariza- tion to the left. This difference of crystalline structure, more- over, is associated with certain small differences in the chemi- cal qualities of the two bodies ; but the difference is so slight that we cannot but regard them as essentially the same sub- stance, and the polarized light thus reveals to us the beginnings of a difference of structure, which, when more developed, mani- fests itself in the phenomena of isomerism. It is a remarkable fact, worthy of notice in this connection, that these two varieties of tartaric acid chemically combine with each other, forming a new substance called racemic acid. Questions. 1. By what peculiar mode of symmetry may each of the six crys- talline systems be distinguished ? How may crystals belonging to the 1st system be recognized V How may crystals of the 2d, 3d, and 4th systems be distinguished by studying the distribution of the similar planes around their terminations or dominant axes ? By what peculiar distribution of similar planes may the crystals of the 5th and 6th systems be distinguished from all others ? State the system to which each of the crystals, represented by the various figures of this chapter, belongs, and give the reason of your answer in every case. 2. We find in the mineral kingdom two different octahedral forms of titanic acid belonging to the tetragonal system. In one of these forms the ratio of the unequal axes is 1 : 0.6442, in the other it is 1 : 1.7723. Can these forms belong to the same mineral substance ? CHAPTER XV. ELECTRICAL RELATIONS OF THE ATOMS. 86. General Principles. If in a vessel of dilute sulphuric acid (one part of acid to twenty of water) we suspend a plate of zinc and a plate of platinum, opposite to each other, and not in contact, WSTimT'tnat no chemical action whatever takes place, provided the Fig, 77. zinc and the acid are perfectly pure. As soon, however, as the two plates arejinited by a copper wire, as represented in Fig. 77, chem- ical action immediately ensues, and the follow- ing phenomena may be observed. Firsj. Bubbles of hydrogen gas are evolved from the surface of the platinum plate. Secondly: The zinc plate slowly dissolves, the zinc combining with the radical of the acid to form zincic sulphate, which is soluble in water. Lastly : A peculiar mode of atomic motion called electricity is transmitted through the copper wire, as may be made evident by appropriate means. If the connection be- tween the plates is broken by dividing the conducting wire, the chemical action instantly stops, and the current of elec- tricity ceases to flow ; but, as soon as the connection is renewed, these phenomena again appear. Similar effects may be produced by other combinations than the one just mentioned, provided only certain conditions are realized. In the first place, the two plates must consist of materials which are unequally affected by the liquid contained in the vessel, or cell; and the greater the difference in this respect, within manageable limits, the better. In the second place, the materials, both of plates and connector, must be con- ductors of electricity ; and, lastly, the liquid must contain some substance for one of whose radicals the material of one of the plates has sufficient affinity to determine its decomposition un- der the conditions present. Such a combination is called a 156 ELECTRICAL RELATIONS OF THE ATOMS. Voltaic Cell The mode of action of this instrument, which since its first discovery has been a subject of controversy, is very obscure, but the following theory gives an intelligible ex- planation of the general phenomena, and may serve a useful purpose until greater certainty can be attained. Polarity. The phenomena of magnetism have made us familiar with a condition of matter we call polarity, in which bodies manifest a mode of energy known as polar force. The characteristics of polar force are as follows : 1. The energy is chiefly concentrated at opposite points of the polarized body called its poles. 2. The poles differ in kind in so far that, while unlike poles attract, like poles repel each other, and while unlike poles neutralize, like poles enhance each the other's effect. 3. With every pole is always associated its op- posite, either on the same or a neighboring body, and in every polar system the sum * of the polar energies of one kind is exactly equal to that of those of the opposite kind. 4. A polarized body induces a similar state in ail neighboring bodies susceptible of this condition, a pole of a given kind determining nearest to itself a pole of the opposite kind. 5. Induction is attended with no loss of energy in the inducing body, whose condition is frequently exalted by the reaction of the induced polarity. 6. Polarity appears of different kinds as well as in different degrees ; the phenomena of magnetic, electrical, and chemical polarity, though similar in their general features, differing widely in their modes of man- ifestation. 7. Substances differ from each other, not only in their susceptibility to polarity of any given kind, but also in their power of retaining it. 2 The study of this class of phenomena has shown that the energy man- ifested by polarized bodies is always the effect of an attraction or repul- sion between poles, and that whenever they appear to act on a neutral body the last is always first polarized by induction. Thus the nails attracted by a magnet or the straws attracted by an electrified stick of sealing-wax are all in a polar condition. A horseshoe magnet, with its keeper attached, affords a familiar illustration of these principles, which will aid us in explaining the more obscure phenomena of the Voltaic cell. The horseshoe magnet was originally polarized by induction, and since it is made of hardened steel retains its magnetism. The soft-iron keeper while in contact with the magnet is as truly polarized as the steel. It has a north pole in contact with the south pole, and a south pole in contact with the north pole of the magnet. But the moment it is with- drawn, all its polarity disappears. Again, while the magnetic circuit, as we call it, is closed, the keeper, by reacting on the source of power, greatly enhances the energy of the magnet, which will lift a much greater weight suspended from the keeper than it can when the two poles act separately. Fig. 77 a. Lastly, if we break a steel magnet, each of the parts will be found to be magnetized with Lf. poles relatively situated as is 1 shown in Fig. 77 a, and since - this relation" of parts is pre- 1 There may be several poles on the same mass of matter, and the polarity may be very irregularly distributed. Such is frequently the condition of the lode-stone or of a steel bar irregularly magnetized. 2 For example, the metals iron, nickel, and cobalt, with a few of their com- pounds, are the only substances susceptible of magnetic polarity to a high degree. Again, a hardened steel bar retains the polar condition more or less permanently as in the common magnet, but soft iron loses its magnetic virtue the moment the inducing cause ceases to act. ELECTRICAL RELATIONS OF THE ATOMS. 157 served, however far we may carry the subdivision, we are led to the conclu- sion that the polarity is a Fi 77 6 molecules of which it con- gists, and picture to our- selves as the condition of a magnetized bar that which is rudely represented in Fig. 77 6. Theory of Chemical Polarity. As the molecules of iron may be mag- netically polarized, we infer that the molecules of all substances are sus- ceptible of different polar states, and we conceive that chejjusjnJLJ.S ft manifestation of a molecular condition, which we may distinguish as chemical polarity. It must be remembered, however, that we do not un- derstand the cause of the differences in the various modes of polar energy; and in saying that the molecules of matter may be^chemically polarized, we mean merely that they are susceptible of a condition whose general features have been indicated above. Our theory further assumes that with some molecules the polarity is inherent and therefore permanent, while with others it can only be .induced by extraneous causes. These last, however, may become polarized by induction to as high or even a higher degree than the first, but the condition, like that of an electro- magnet, is transient, varying with the inducing eause. Again, as every analogy would lead us to believe, our theory further assumes that different substances are susceptible of chemical polarity (whether it be inherent or assumed) to very different degrees,, and that the susceptibility varies un- der different conditions. Lastly, our theory supposes that the chemical activity of a substance depends on the degree of polarity inherent in its molecules, and it refers the well-known active qualities of acids and alkalies to the fact that their peculiar constitution renders their molecules strongly polarized, while the inert qualities of most of the elementary substances is explained by the neutral condition which their homogeneous structures would naturally produce in their molecules. Thus, for exam- ple, we suppose that every molecule of sulphuric acid, H^SO^ or of hy- drochloric acid, H-Cl, or of sodtc hydrate, H-NaO, is naturally polarized, while on the other hand the molecules of zinc, Zn, of magnesium, Mg, of hydrogen, H~H, and of oxygen, 0=0, are all normally neutral. As soon, however, as we place zinc in contact with dilute sulphuric acid, the metallic molecules become polarized by induction to the degree of which they are susceptible under the influence of this acid. A powerful attraction is thus developed and a familiar chemical change is the result. If magnesium is treated in a similar way, the action is more energetic, because, as we suppose, the molecules of this metal are susceptible of u higher degree of polarity, and the force developed is therefore proportion- ally stronger. On the other hand, with metallic copper there is no action under the same conditions, because the molecules of the metal do not ac- quire a sufficient degree of polarity to determine chemical change. While, however, the molecular structure appears to be the most impor- tant, it is evidently by no means the only cause which determines chemical polarity. The highly active qualities of the alkaline metals and of the chlorine group of elementary substances indicate that their molecules, although apparently homogeneous in structure, must be permanently polarized. Moreover, the fact that a high degree of energy is developed in many of the elementary substances, as in oxygen gas, by a simple ele- vation of temperature, and the general principle that heat hastens chem- 1 This term is synonymous with the old term chemical affinity, to which it is on many accounts to be preferred. 158 ELECTRICAL RELATIONS OF THE ATOMS. ical changes,. seem to indicate that the polar condition may be frequently produced . by this agent alone. So also the process of photography is most simply explained by the theory that the sun's rays excite a similar condition in the silver compouncis on the surface of the sensitive plate, and the effect of continuous electrical discharges in converting oxygen gas into that peculiar active modification of this substance called ozone, may be regarded as a direct result of their polarizing power. Theory of Electricity. The study of the phenomena of optics has led physicists to the conclusion that there exists throughout space, filling not only the interplanetary but also the intermolecular spaces, a highly atten- uated but at the same time wonderfully elastic medium which is called the ether (92)X Again, the phenomena of heat indicate that the molec- ular forces have an energy which is adequate to cope with this very great elasticity ; and we can conceive that they condense around these molecules greater or less quantities of this ether, thus giving to each a distinct at- mosphere, but one which merges into that unrversally diffused medium in which molecule and planet alike float. Now our theory supposes that electrical phenomena are caused by disturbances in the composition of these ethereal atmospheres. The electrical ether, 1 as we assume, consists of two separable materials, which, adopting names long used in science, we will call positive and -negative or vitreous and resinous electricities. In all the terrestrial region of the solar system at least these electricities are blended in certain definite proportions, like the constituents of the earth's atmosphere, but by various causes they may become separated and more or less isolated either on the same or on different molecules. Whenever this takes place, the two electricities tend to flow together until the nor- mal condition is restored in accordance with the law of diffusion ; but the force of diffusion in these molecular atmospheres is vastly greater and the process vastly more rapid than it is in the terrestrial atmosphere, be- cause the elasticity of the ether so greatly exceeds that of the air. This being granted, our theory further supposes that every process of electrical excitement causes a separation of the constituents of the ether, and that an electrified body is one on whose molecules one or the other of the two electricities is to a greater or less degree isolated ; and again, that the fa- miliar phenomena of attraction and repulsion between electrified bodies are the effects of pressure caused by the diffusive force ; and lastly, that an electrical current consists in an actual transfer of the ethereal material between the molecules of the conductor. We have not space, however, to follow out the theory into its mechanical details, and we must content ourselves with applying it to the explanation of the phenomena of the Voltaic cell. Theory of Voltaic Cell. In studying chemical reactions we have thus far overlooked the molecular atmospheres ; but it is evident that, if the above theory is correct, they must enter as important factors into every chemical change. This theory assumes that 'the condition of the atmosphere is intimately connected with that of the molecule, although in what way it does not attempt to explain. When the molecule is polar- ized, the two electricities are more or less fully separated and isolated around the molecular poles ; and if the polarity is inherent this condition is permanent. If, however, the polar state is induced, the neutral condi- tion is restored as soon as the inducing force ceases to act. Let us study now frcm this new point of view the familiar reaction of sulphuric acid on zinc referred to above. Zii + (H z SOt -f- Aq) = (ZnSOt + Ag) + SMS. 1 As it is not important for our present purpose to inquire whether the elec- trical ether is identical or only is mingled with the luminiferous ether, this question is here left in abeyance. ELECTRICAL RELATIONS OF THE ATOMS. 159 The molecule H A SO^ is inherently polarized and induces at once a similar condition in the normally neutral molecule ^Zn. At the poles of each of these molecules we have therefore free electricity. When now Zn replaces 7/ 2 in H 2 S0 4 it takes with it into its new combination only free positive electricity, leaving behind the corresponding negative electricity on the adja-ent molecule of zinc. Meanwhile the hydrogen atoms thus liberated bring with them to form the molecule H-H only positive elec- tricity. We have thus set free on opposite molecules at the same time equivalent quantities of the two electricities, and the equilibrium being thus disturbed, an interchange at once takes place between them, by which the normal condition of their atmospheres is restored. In order to make this point clearer, we have endeavored to illustrate the reaction in the following diagram : HfSOi Zn Zn ' Factors M || ^| IP ^ir ^IIP 7 ^ JP" H-H Zn^SOi Zn Products if Til Jill This diagram, however, indicates very imperfectly the conception we have formed of the process, and there are certain quantitative relations between the parts which must not be overlooked, although they can be as yet but very imperfectly understood. We should naturally infer that the quantity of ethereal atmosphere would be determined in every case by the mass of the molecule, but the quantities of free electricities separated from this 'atmosphere under different conditions seem to depend on the atomicities of the radicals of which the molecule consists. At least, the facts indicate that the amount offree electricity which any group of atoms takes out of the, molecule from which it is parted is exactly meas- ured by the number of atomic bonds thus broken. Hence in our diagram the amount of positive electricity which H^ takes from H^SO^ is a defr- nite quantity and exactly equal to that 'which Zn carries in to take its place. Moreover, this last quantity came originally, not from one, but from two zinc molecules, and the chemical metathesis between H z and Jn was accompanied by an interchange of electricities between the zinc molecules, by which all the free positive electricity passed to the one which entered into combination, and all the free negative electricity to the one left behind ; and further, as already stated, this free negative elec- tricity is equivalent to the free positive electricity on the hydrogen mole- cule formea at the same time. If, as in the usual form of the reaction we have been studying, the acid sufficiently diluted is poured upon clippings of sheet zinc, it is found that, although the mass of the metal is polarized throughout, the polarity is very irregularly distributed. A multitude of negative polar points are formed upon the surface, from which bubbles of hydrogen gas are evolved, and around these are spaces positively polarized* WfieTe the metal enters into solution. According to our theory, when the molecules of metal re- place the atoms of hydrogen they take with them positive electrical charges, leaving behind equivalent negative charges, and these are trans- 'initted from molecule to molecule of the metal, until they reach one of the negative polar points above mentioned. It is there that the inter- change takes place with the positive charges on the molecules of hydro- gen gas as rapidily as these are formed. The polar points just referred to appear to be determined by variations of texture or bits of impurity 160 ELECTRICAL RELATIONS OF THE ATOMS. in the metal, and this is the reason that the_en.eral polarity of the mass is so irregularly distributed. If the metal is absolutely pure and uni- form in texture, or if the surface of the common sheet zinc is previously amalgamated, there is no local action, and the zinc will not dissolve unless we fasten to the metal a piece of some material less readily acted on by the acid, which must be also a conductor of electricity. But when this is done, the whole mass becomes polarized uniformly throughout, after the pattern represented in Fig. 77 b. Of this system the surface of the zinc forms the positive pole, and the surface of 'the second material the nega- tive pole. Chemical action ensues as before, and while zinc dissolves at the positive pole, hydrogen gas is evolved from the negative pole. We are now prepared to understand the conditions in the Voltaic cell represented in Fig. 77. Here we have a plate of zinc and a plate of pla- tinum, united by a metallic wire and dipping together into the acid liquid, with their surfaces opposed to each other and not touching. Here, also, the two plates with the conductor form one uniformly polarized system, of which the surface of the zinc is the positive and the surface of the pla- tinum the negative pole. The polarity of this arrangement is induced by the action of the acid, whose molecules are inherently polarized. Moreover, under these conditions the mass oTacicT oe- Fig- 78. tween the plates forms also a uniformly polarized system, the molecules arranging themselves in polar lines as represented in Fig 78. We may compare the combination thus formed to a magnetic circuit, consisting of a horseshoe magnet and its armature, or rather of a bar magnet with a horseshoe armature. The inherently polarized liquid corresponds to the permanent magnet, the system of metallic plates to the armature with its'induced polarity. Now just as in the magnetic cir- cuit we have a strong attractive force" at the surfaces where the armature touches the magnet, so in the Voltaic circuit we have a powerful^ force exerted at each of the corresponding surfaces. A mutmu attraction is exerted between the hydrogen end of the acid molecule and the platinum surface on one side, and the sulphion end x of the same molecules and the zinc surface on the other side. These forces are adequate to decom- pose the acid. The sulphion atoms enter into union with the zinc to form zincic sulphate, which dissolves in the acid liquid, while the hy- drogen atoms combine with each other to form molecules of hydrogen gas, which collects in bubbles that rise along the surface of the platinum plate. Meanwhile, every molecule of zinc which enters into solution leaves behind 'a charge of negative electricity, and every molecule of hy- drogen gas carries to the surface of the platinum plate a charge of posi- tive electricity, and these opposite charges flow together through the con- ductor, forming what we call an electrical current, which tends to restore the electrical equilibrium that the chemical action destroys. Electrical Current. According to our theory an electrical current con- sists in the last analysis in the transfer of the ethereal medium between neighboring molecules, the one giving up a quantity of positive electricity SffdTeceiving an equivalent portion of negative electricity in its stead. This transfer is supposed to take place at the surface of contact between the molec- ular atmospheres by a process similar to diffusion (58), and implies an oscillation of the molecules by which each is brought alternately in near proximity to its neighbors on either side. The oscillatory motion is maintained by the alternate attractions and repulsions, which the varying phases of the molecules necessarily determine, and is a most important l For the sake of simplicity we have represented in the figures molecules of H-Cl instead of SfSO^ but the theory applies equally to both. ELECTRICAL RELATIONS OF THE ATOMS. 161 element of the electrical current. It can easily be imitated by suspending with silk threads small metallic balls between two brass knobs connected with the conductors of an electrical machine, so that they hang near but at equally small distances from each other on the same line. The continu- ous oscillation of these balls, while the machine is in action, illustrates what we conceive to be the mode of motion in the molecules of a conductor. If the above explanation is correct, it is obvious that an electrical cur- rent in a solid conductor has two distinct elements : first, an oscillatory motion of the molecules; secondly, a mutual transfer of the two modifica- tions of the electrical ether from molecule to molecule, along the lirfes'TrYrlt- ing the opposite poles of the polar system, which every current implies. But in the acid liquid, which not only originates the current but, also forms a part of the circuit, the relations are somewhat different. There the transfer of the two electricities is attended with a decomposition of the acid molecules, and the opposed atoms, each bearing' its charge of elec- tricity, actually travel from one plate to the other. Thus we have the singular phenomenon produced of two coexisting atomic currents through- out the mass of the liquid, a stream of sulphion atoms constantly setting towards the zinc plate, and a stream of hydrogen atoms flowing in v the opposite direction in the same space towards the platinum plate. The result is produced by a constant metathesis along the whole line of mole- cules between the two plates, so that for every atom of sulphion which enters into union with the zinc a double atom or molecule of hydrogen is set free at the face of the platinum plate. As our theory shows, the opposite currents of atoms in the liquid and the opposite currents of electricity in the solid conductor are mutually dependent. Hence, if the connection is broken so that the motion can no longer be transmitted through the conductor, the motion in the liquid itself ceases ; and if by any means the motion through the conductor is checked the motion of the atoms in the liquid is reduced to the same ex- tent. The two currents, which, as we have seen, are continuous through- out the whole circuit, take the names of the two kinds of electricity which they respectively carry ; that flowing into the conducting wire from the platinum, or inactive plate, being called the positive current, and that from the zinc, or active plate, the negative current. Reasoning from cer-. tain mechanical phenomena, the physicists originally concluded that the electrical current flowed in but one direction, that is, through the con- ducting wire from the platinum plate to the zinc, and from the zinc plate through the liqiiid back again to the platinum ; and now, when the direc- tion of the current is spoken of, it is this direction, that of the positive current, which is always meant. 87. Electrical Conducting Power or Resistance. Different materials transmit the electric current with very different de- grees of facility ; for while in some this peculiar form of molO ular motion is easily maintained, in others the molecules yield to it only with difficulty, and many substances seem not to be susceptible of it. The conducting powers of different metallic wires have been very carefully studied, and some of the most trustworthy results are collected in the following table. Silver is the best conductor known, and, assuming that a silver wire of definite size and 100 centimetres long is taken as the standard, the number opposite the name of each metal is the length in centimetres of a wire made of this metal, arid of the same siz.e 11 162 ELECTRICAL RELATIONS OF THE ATOMS. as the first, which will oppose the same resistance to the trans- mission of the current. The second column gives the relative resistances of wires of the same materials when of equal size and of equal lengths. The relative or specific resistances of two such wires must evidently be inversely proportional to their conducting powers, and thus the "numbers of the second column are easily calculated from those of the first. For the results collated in this table we are indebted to the careful investiga- tions of Professor Matthiessen. Pure Metals. Conducting Power. Specific Resistance. Silver (hard drawn) At 0. At 100. 100.00 71.56 At 0. At 100. 1.000 1.397 Copper (hard drawn) 99.95 70.27 1.0005 1.423 Gold (hard drawn) 77.96 55.90 1.283 1.788 Zinc 29.02 20.67 3.445 4.838 Cadmium 23.72 16.77 4.216 5.964 Cobalt 17.22 5.808 Iron (hard drai m) 16.81 5.948 Nickel 13.11 7.628 Tin 12.36 8.67 8.091 11.53 Thallium 9.16 10.92 Lead 8.32 5.86 12.02 17.06 Arsenic 4.76 3.33 21.01 30.03 Antimony 4.62 3.26 21.65 30.68 Bismuth 1.245 0.878 80.34 113.9 Commercial . Metals. C.P. Sp. R. (P. Commercial Metals. C. P. Sp. R. GO. Copper 77.43 1.291 18.8 Iron 14.44 6.924 20.4 Sodium 37.43 2.672 21.7 Palladium 12.64 7.911 17.2 Aluminum 33.76 2.962 19.5 Platinum 10.53 9.497 20.7 Magnesium 25.47 3.926 17.0 Strontium 6.71 14.90 20.5 Calcium 22.14 4.516 16.8 Mercury 1.63 61.35 22.8 Potassium 20.85 4.795 20.4 Tellurium 0.00077 129,800 19.6 Lithium 19.00 .5.262 20.0 Red Phosphorus 0.00000123 81,300,00024.0 If, next, we compare wires of the same material, but of dif- ferent sizes, we find that the resistance increases as the length, and diminishes as the area, of the section. Moreover, if we adopt some absolute standard of resistance, like that selected by the English physicists, we can easily express the resistance of any given conductor in terms of this unit. It must be remem- bered, however, in making such comparisons, that the resist- ance varies with the temperature, and also that the conducting power of the same metal is materially influenced both by its physical condition and by the presence of impurities. ELECTRICAL RELATIONS OF THE ATOMS. 163 88. Ohm's Law. The first effect of the chemical forces in the cell of an electrical combination is to marshal the dissimilar atoms of the active liquid between the plates into lines, which at once begin to move in parallel columns, but in opposite di- rections (Fig. 78). MoreoverTeach one of these lines of moving atoms is continued by a corresponding line of oscillating atoms in the conducting wire, and thus is formed a continuous circuit returning upon itself. The union of all the lines of force in the two opposite coexisting streams constitutes in any case the electrical current, and the different parts of this continuous chain are so related that the total amount of motion is always the same at every point on the circuit, and no more lines of moving atoms form in the liquid between the plates than can be continued through the oscillating atoms of the solid conductors. If we adopt this theory, it is obvious that the strength of any electrical current must depend, first, on the number of con- tinuous lines of force, and secondly, on the strength of the polarity transmitted through each of these channels. Of these two elements, the first is determined solely by the total resist- ance which the various parts of the circuit oppose to the elec- trical motion, and the greater this resistance the less will be the number of the lines of force. The second element is de- termined by the value of the resultants of all the polar forces acting in any combination, which draw the dissimilar atoms towards the opposite plates, a value which depends solely on the chemical relations of the materials of the plates to that of the active liquid, and is what is called the electromotive force of the combination, a quantity we will represent by E. It appears, then, from the above analysis, that an electrical current is a continuous chain, which is sustained in a regulated and equable motion in all its parts by the chemical activity in the cell, and that the strength of this current at any point of the chain must be directly proportional to the electromotive force, and inversely proportional to the sum of the resistances through- out the circuit. If, then, we represent the resistance in the con- ducting wire by r, the resistance of the liquid between the plates of the cell by 7?, 1 and also the strength of the current by <7, we shall have, in every case, [62] The resistance of any circuit may be conveniently divided into two parts, 164 ELECTKICAL RELATIONS OF THE ATOMS. The quantities (7, J?, r, and E may all be accurately measured, and stand in each case for a certain number of arbitrary units, whose relations will hereafter be stated. 89. Electromotive Force and Strength of Current. It would seem at first sight as if the strength of an electric current might be increased by simply enlarging the size of the plates in the combination employed, and obviously the number of possible lines of moving atoms which could be marshalled in the liquid between the plates would thus be increased ; but, as has been stated, the parts of the circuit are so intimately connected that no greater number of lines of atoms can form between the plates than can be continued through the whole circuit, and practically there may be formed between the smallest plates a vastly greater number of atomic lines than can be continued through any con- ductor, however good its quality or however ample its size. Hence it is, that by increasing the size of the plates we mul- tiply the lines of force only in so far as we thereby lessen the resistance in the liquid part of the circuit. We thus simply lessen the value of R in Ohm's formula [62] ; but if this value is already small as compared with r, that is, if the resistance in the cell is small compared with that in the conductor, no mate" rial gain in the power of the current, or in the value of (7, will result. On the other hand, if the exterior resistance, r, is small, or nearly nothing, as when the plates are connected by a thick metallic conductor, then the value of C will increase in very nearly the same proportion as the size of the plates is enlarged, and the value of JR, in consequence, diminished. Under these conditions, the number of lines of moving atoms is greatly mul- tiplied, and we obtain a current of very great volume, but only flowing with the limited force which the single cell is capable of maintaining. Such a current has but little power of over- coming obstacles ; and if we attempt to condense it by using a smaller conductor, we reduce, as has been said, the chemical action which keeps the whole in motion, and thus lessen the volume of the flow. This is generally expressed by saying first, the resistance of the conducting wire, and secondly, the resistance of the liquid portion of the circuit between the two plates of the cell. The resistance 01 the solid conductor may be readily estimated on the principles stated in the last section, and the resistance of liquid may be measured in a similar way. The last depends, 1. On the conducting power of the liquid ; 2. On the length of the liquid circuit, which is determined by the distance apart of the plates ; 8. On the area of the section of the liquid conductor, which is determined by the size of the plates; and, 4. On the temperature. ELECTRICAL RELATIONS OF THE ATOMS. 165 that the current has large quantity, but small intensity, or more properly, electromotive power. It must now be obvious from the theory, that we cannot in- crease effectively the intensity of a current (its power of over- coming obstacles) without in some way increasing the chemical activity, or, in other words, the electro-motive force of the com- bination employed, and Ohm's formula leads to the same result. If the value of r in our formula is very large as compared with R, we cannot increase it still farther without lessening the total value, <7, unless at the same time we increase the value of E. Now, this electro-motive force may be, to a certain ex- tent, increased by using a more active combination ; but the limit in this direction is soon reached, and the construction of the cell which has been found practically to be the most effi- cient will be described below. We can, however, increase the effective electro-motive force to almost any extent by using a number of cells, and coupling them together in the manner represented by Fig. 79, the plati- num plate of the first cell being united by a large metallic con- nector to the zinc plate of the second, and so on through the line, until finally the external conductor establishes a connec- tion between the platinum plate of the last cell and the zinc plate of the first. Such a combination as this is called a Gal- vanic or Voltaic * battery, and the current which flows through such a combination has a vastly greater power of overcoming resistance than that of any single cell, however large. The increased effect obtained with such a combination will be easily understood, when it is remembered that each of the innumerable closed chains of Fig. 79. moving molecules now ex- tends through the whole combination, and that all its parts move in the same close mutual dependence as be- fore. But whereas with a single cell the motion throughout any single chain of molecules is sustained by the chemical energy at only one point, it is here reinforced at several points; 1 From the names of Galvani and Volta, two Italian physicists, who first investigated this class of phenomena. 166 ELECTEICAL RELATIONS OF THE ATOMS. and the polar energy at any point of the circuit is the effect of the induction of the acid molecules between each pair of plates concurring with that produced by the similar molecules between every other pair. The electro-motive power is then increased in proportion to the number of cells; and the effect on the cur- rent would be increased in the same proportion, were it not for the fact that the current must keep in motion a greater mass of liquid, and hence the resistance is increased at the same time. The value of this resistance, however, is easily estimated, since it is directly proportional to the distance through which the cur- rent has to flow in the liquid ; and hence, if the liquid is the same in all the cells, and the plates are at the same distance apart in each, the liquid resistance will be n times as great in a combination of n cells as it is in one. Moreover, since the effec- tive electro-motive force is n times as great also, while the ex- ternal resistance remains unchanged, the strength of the current from such a combination will still be expressed by formula [62] slightly modified. This formula shows at once, that, when the exterior resist- ance is very small, or nothing, very little or no gain will result from increasing the number of cells, for the ratio of nE to nR is the same as that of E to R ; and, under such conditions, in order to increase the strength of the current, we must increase the surface of the plates. If, on the contrary, the exterior re- sistance is very large, the formula shows that great gain will result from increasing the number of the cells, and that little or no advantage will accrue from enlarging the surface of the plates. Moreover, the formula enables us in any case to de- termine what proportion the number of cells should bear to the size of the plates in order to obtain the full effect of any battery in doing a given work; and in the numerous applications of electricity in the arts we find abundant illustrations of the principles it involves. The methods used in finding the values of the quantities represented in the formula lie beyond the scope of this work, and for such information the student is re- ferred to works on Physics. 90. Constructions of Cells. It is found practically that the ELECTRICAL RELATIONS OF THE ATOMS. 167 simple combination of plates and acid first described must be slightly modified in order to obtain the best results. In the first place, both the zinc and sulphuric acid of com- merce contain impurities, which give rise to what is called local action, and cause the zinc to dissolve in the acid when the battery is not in action. Fortunately, however, it has been found that such local action can be wholly prevented by care- fully amalgamating the surface of the zinc and filtering the acidulated water. The mercury on the surface of the zinc plates acts as a sol- vent, and gives a certain freedom of motion to the particles of the metal. These, by the action of the polar forces, are brought to the surface of the plate, while the impurities are forced back towards the interior, so that the plate constantly exposes a surface of pure zinc to the action of the acid. By filtering we remove the particles of plumbic sulphate which remain floating in the sulphuric acid for a long time after it has been diluted with water, and which, when deposited on the surface of the zinc, become points of local action, even when the plates have been carefully amalgamated. In the second place, the continued action of the simple com- bination first described develops conditions which soon greatly impair, and at last wholly destroy, its efficiency. The hydrogen gas, which by the action of the current is evolved at the platinum plate, adheres strongly to its surface, and with its powerful affinities draws back the lines of atoms moving towards the zinc plate, and thus diminishes the effec- tive electro-motive force. Moreover, after the battery has been working for some time, the water becomes charged with zincic sulphate ; and then the zinc, following the course of the hydro- gen, is also deposited on the surface of the platinum, which after a while becomes, to all intents and purposes, a second zinc plate, and then, of course, the electric current ceases. Both of these difficulties, however, have also been sur- mounted by a very simple means discovered by Mr. Grove, of London. The Grove cell, Fig. 80, consists of a circular plate of zinc well amalgamated on its surface, and immersed in a glass jar containing dilute sulphuric acid. Within the zinc cylinder is placed' a cylindrical vessel of much smaller diameter, made of porous earthenware, and filled with the strongest nitric acid, 168 ELECTRICAL RELATIONS OF THE ATOMS. and in this hangs the plate of platinum, Fig. 81. The walls of Fig. 81. the porous cell allow both the hydrogen and the zinc atoms to pass freely on their way to the platinum plate ; but the moment they reach the nitric acid they are at once oxidized, and thus the surface of the platinum is kept clean, and the cell in condi- tion to exert its maximum electro-motive power. In this com- bination we may substitute for the plate of platinum a plate of dense coke, such as forms in the interior of the gas retorts, which is very much cheaper, and enables us to construct large cells at a moderate cost. The use of gas coke was first sug- gested by Professor Bunsen of Heidelberg, and the cell so constructed generally bears his name. The Bunsen cell, such as is represented in Fig. 82, is exceedingly well adapted for use Fig. 82. in the laboratory. These cells are usually made of nearly a ELECTRICAL RELATIONS OF THE ATOMS. 169 uniform size, the zinc cylinders being about 8 c. m. in diameter by 22 c. m. high, and they are frequently referred to as a rough standard of electrical power. They may be united so as to produce effects either of intensity or of quantity. The inten- sity effects are obtained in the manner already described (see Fig. 79), and the quantity effects are obtained with equal readi- ness ; since by attaching the zinc of several cells to the same metallic conductor, and the corresponding coke plates to a similar conductor, we have the equivalent of one cell with large plates. Many other forms of battery, differing in more or less important details from those here described, and adapted to special applications of electricity, are used in the arts, and are fully described in the larger works on physics. 91. Electrolysis. As our theory indicates, the electrical current has the remarkable power of imparting to the unlike atoms of almost all compound bodies motion in opposite direc- tions, like that in the battery cell itself, and this, too, at what- ever point in the circuit they may be introduced. The galvanic battery thus becomes a most potent agent in producing chemi- cal decompositions, and it is in consequence of this fact that the theory of the instrument fills such an important place in the phi- losophy of chemistry. If we break the metallic conductor at any point of a closed circuit, the two ends, which in chemical experiments we usually arm with platinum plates, 1 are called poles. The end con- nected with the platinum or coke plate, from which the positive current is assumed to flow, is called the positive pole, and the end connected with the zinc plate, from which the negative current flows, is called the negative pole. Let us assume that Fig. 83 represents the two platinum poles dipping in a solution of hydrochloric acid in water, which thus becomes a part of the circuit. The Fi s- 83< moment the circuit is thus closed, the /Tand Cl atoms begin to travel in opposite direc- tions, just as in the battery cell below. The hydrogen atoms move with the positive cur- rent towards the negative pole, and hydro- gen gas is disengaged from the surface of 1 We use platinum plates because this metal does not readily enter into combination with the ordinary chemical agents. 170 ELECTRICAL RELATIONS OF THE ATOMS. the negative plate, while the chlorine atoms move with the negative current towards the positive pole, and chlorine gas is evolved from the surface of the positive plate. More- over, it will be noticed that each kind of atoms moves in the same direction on the closed circuit, that is, follows the course of the same current, both in the battery cell below and in the decomposing cell above ; and wherever we break the circuit, and at as many places as we may break it, the same phenomena may be produced, provided only that our battery has sufficient power to overcome the resistance thus introduced. If next we dip the poles in water, the atoms of the water will be set moving, as shown in Fig. 84; hy- c drogen gas escaping as before from the neg- Iative pole, and oxygen gas from the positive. We find, however, that pure water opposes a very great resistance to the motion of the _ current ; and, unless the current has great intensity, the effects obtained are inconsider- able. But if we mix with the water a little sulphuric acid, the decomposition at once becomes very rapid ; but then it is the atoms of the sulphuric acid, and not those of the water, which are set in motion. The molecule H 2 SO divides into ff 2 and SOi ; the hydrogen atoms moving in the usual direction, and the atoms of S0 4 in the opposite direction. As soon, however, as the last are set free at the positive pole, they come in contact with water, which they immediately decompose, 1 2ff 2 0+2S0 4 =2ff 2 S0 4 + 0=0, and the oxygen gas thus generated escapes from the face of the platinum plate. Thus the result is the same as if water were directly decomposed, but the actual process is quite different. So also in many other cases of electrolysis, as these decom- positions by the electrical current are called, the process is complicated by the reaction of the water, which is the usual medium employed in the experiments. Thus, if we interpose between the poles a solution of common salt, Na Cl, the chlorine atoms move towards the positive pole, and chlorine gas is there evolved as in the first example. The sodium atoms move also, but in the opposite direction. As soon, however, as they are set free at the negative pole, they decompose the water present; hydrogen gas is formed, which escapes in bubbles from the ELECTRICAL RELATIONS OF THE ATOMS. 171 platinum plate, while sodic hydrate (caustic soda) remains in solution, a-0 H-H. ^ | c \ so * B 8 s * I We add but one other example, which illustrates a very important application of these principles in the arts. We as- sume, in Fig. 85, that the positive pole is armed with a plate of copper, ^ Flgl and that to the negative pole has been fastened a mould of some medallion c \ so * B 8 s * I \ we wish to copy, the surface of which, at least, is a good conductor. We assume further that both copper plate and mould are sus- pended in a solution of sulphate of copper, Gu=S0 4 . In this case the atoms of the compound are set in motion as before. Those of copper accumulate on the surface of the mould ; and at last the coating will attain such thickness that it can be re- moved, furnishing an exact copy of the original medallion. Meanwhile the atoms of S0 have found at the positive pole a mass of copper, with whose atoms they have combined ; and thus fresh sulphate of copper has been formed, and the solution replenished. The process has in effect consisted in a transfer of metal from the copper plate to the medallion ; and, by using appropriate solvents, silver and gold can be transferred and deposited in the same way. In all these processes of electrolysis, one remarkable fact has been observed, which has a very important bearing on the theory of the battery. If in any given circuit we introduce a number of decomposing cells, containing acidulated water, we find that in a given time exactly the same amount of gas is evolved in each ; thus proving, what we have thus far assumed, that the moving power is absolutely the same at all points on the circuit. Moreover, the amount of gas which is evolved from such a decomposing cell in the unit of time is an ac- curate measure of the strength of the current actually flowing in any circuit, and this mode of measuring the quantity of an electrical current is constantly used. We should infer from the facts already stated, and the prin- ciple has been confirmed by the most careful experiments, that the chemical changes which may take place at different points 172 ELECTRICAL RELATIONS OF THE ATOMS. of the same closed circuit are always the exact equivalents of each other. If, for example, we have a series of Grove's cells, arranged as in Fig. 79, and interpose in the external circuit two decomposing cells, as in Figs. 84 and 85, we shall find (provided there is no local action) that the weight of zinc dis- solved in each of the five Grove's cells is the exact chemical equivalent, (26) not only of the weight of hydrogen gas evolved from the first decomposing cell, but also of the weight of me- tallic copper deposited on the mould in the second. For every 63.4 grammes of copper deposited, 2 grammes of hydrogen are evolved, and 65.2 grammes of zinc are dissolved in each cell of the battery. If there is also local action in the cells, the chemical change thus induced is added to the normal effect of the battery-current. This important principle (discovered by Faraday) is in entire harmony with the theory of electricity developed in this chap- ter. In the single Voltaic cell, Fig. 77, there is but one source of free electricity, which all flows through the same conductor, In a Voltaic battery, Fig. 79, there are as many sources of free electricity as there are separate cells ; but only the free elec- tricity received on the end plates flows through the longer con- ductor, 1 for that received on the intermediate plates becomes neutralized in the shorter conductors 1 uniting the cells. In either case, if a liquid forms a part of the principal conductor, as in Fig. 83, then the molecules of the liquid decomposed by the current become an additional source of electricity, and the currents flowing from the two ends of the battery are neutral- ized by the charges of electricity, which the atoms liberated from the electrolyte 2 bring with them to either electrode. 2 Thus, in Fig. 83, the positive electricity flowing from the inactive plate of the battery is neutralized by the negative electricity, which the chlorine atoms yield, and the negative electricity from the active plate of the battery by the positive electricity, which the hydrogen atoms yield. Now, since, according to our theory, the strength of a current is necessarily the same at all points of a 1 It will be noticed that each of the five conductors in Fig. 79 sustains the same relations to the battery as a whole. 2 The liquid submitted to electrolysis is frequently called an electrolyte^ and the inactive poles dipping into the liquid are also called electrode*. ELECTRICAL RELATIONS OF THE ATOMS. 173 continuous circuit, however extended, and since the amount of electricity set free in the decomposing cell, as in the battery cells, must be proportional to the number of atomic bonds broken (86), it is evident that it would require, for example, twice as many hydrogen as copper atoms, liberated on the face of an electrode in a given time, to supply the same current, and this is equivalent to the principle stated above. The examples which have been given are sufficient to illus- trate the remarkable power which the electric current possesses of setting in motion the atoms of compound bodies. Innumer- able experiments have shown that, in reference to their rela- tions to the current, the atoms, both simple and compound, may be divided into two great classes : first, those whicn travel on the line of the circuit in the direction of the positive current and follow hi the lead of the hydrogen atoms ; and, secondly, those which follow the lead of the chlorine atoms, and move in the opposite direction with the negative current. The first class of atoms, or radicals, we call positive ; and the second class, negative. The opposition in qualities of the chemical atoms, which the study of these electrical phenomena has revealed, is, in many cases at least, relative, and not absolute. For, while there are some atoms which always manifest the same character, there are others which appear in some associations positive, and in other associations negative. To such an extent is this true, that the electrical relations of the atoms are best shown by grouping the elements in series, which may be so arranged that each member of the series shall be electro-positive when in combination with those elements which follow it, and electro- negative when combined with those which precede it. NOTE. Questions and problems bearing on this chapter will be found in the Appendix, page 567. CHAPTEE XVI. RELATIONS OF THE ATOMS TO LIGHT. 92. Light a Mode of Atomic Motion. It has already been intimated ( 61, note), that the phenomena of vision are the effects of an atomic motion transmitted from some luminous body to the eye through continuous lines of material particles, and such lines we call rays of light. This motion may origi- nate with the atoms of various substances ; but in order to explain its transmission, we are obliged to assume the existence of a medium filling all space, of extreme tenuity, and yet having an elasticity sufficiently great to transmit the luminous pulsations with the incredible velocity of 186,000 miles in a second of time. This medium we call the ether, but of its existence we have no definite knowledge except that obtained through the phenomena of light themselves, and these require assumptions in regard to the constitution of the ethereal medium which are not realized even approximately in the ordinary forms of matter ; for while the assumed medium must be vastly less dense than hydrogen, its elasticity must surpass that of steel. According to the undulatory theory, motion is transmitted from particle to particle along the line of each luminous wave very much in the same way that it passes along the line of ivory balls in the well-known experiment of mechanics. The ethereal atoms are thus thrown into waves, and the order of the phenomena is similar to that with which all are familiar in the grosser forms of wave motion. But in this connection we have no occasion to dwell on the mechanical conditions attending the transmission of the motion. The motion itself may be best conceived as an oscillation of each ether particle in a plane perpendicular to the direction of the ray, not RELATIONS OF THE ATOMS TO LIGHT. 175 necessarily, however, in a straight line ; for the orbit of the oscillating molecule may be either a straight line, an ellipse, or a circle, as the case may be. Such oscillations may evidently differ both as regards their amplitude and their duration, and on these fundamental elements depend two important differences in the effect of the motion on the organs of vision, viz. intensity and quality, or brilliancy and color. If our theory is correct, it is obvious that the intensity of the luminous impression must depend upon the force of the atomic blows which are transmitted to the optic nerves, and it is also evident that this force must be proportional to the square of the velocity of the oscillating atoms, or what amounts to the same thing, to the square of the amplitude of the oscillation ; assuming, of course, that the oscillations are isochronous. The connection of color with the time of oscillation is not so obvious, and why it is that the waves of ether beating with greater or less rapidity on the retina should produce such sensations as those of violet, blue, yellow, or red, the physiologist is wholly unable to explain. We have, however, an analogous phenomenon in sound, for musical notes are simply the effects of waves of air beating in a similar way on the auditory nerves ; and, as is well known, the greater the frequency of the beats, or, in other words, the more rapid the oscillations of the aerial molecules, the higher is the pitch of the note. Red color corresponds to low, and violet to high notes of music, and, the gradations of color between these extremes, passing through various shades of orange, yellow, green, blue, and indigo, correspond to the well-known gradations of musical pitch. From well-established data -we are able to calculate the rapidity of the oscillations which produce the different sensa- tions of color, and also to estimate the corresponding lengths of the ether waves, and the following table contains the results. It must be understood, however, that these numbers merely correspond to a few shades of color definitely marked on the solar spectrum by certain dark lines hereafter to be men- tioned ; and that equally definite values may be assigned to the infinite number of intermediate shades which intervene between these arbitrary subdivisions of the chromatic scale. 176 RELATIONS OF THE ATOMS TO LIGHT. Number of waves or oscilla- Length of waves in frac- Color. tions in one second. tions of a millimetre. Red 477 million million. 650 millionths. Orange 506 " 609 Yellow 535 " " 576 " Green 577 " " 536 " Blue 622 " 498 " Indigo 658 " u 470 " Violet 699 " " 442 " 93. Natural Colors. It follows, as a necessary consequence of the fundamental laws of mechanics, that an oscillating mole- cule can only transmit to its neighbor motion which is isochronous with its own. Hence a single ray of light can only produce a def- inite effect of color, and this quality of the ray will be preserved however far the motion may travel. A beam of light is simply a bundle of rays, and if the motion is isochronous in all its parts, that is, if the beam consists only of rays of .one shade of color, such a beam will produce the simplest chromatic sensa- tion possible, that of a pure color. If, however, the beam contains rays of different colors, we shall have a more complex effect, and the infinite variety of natural tints are thus produced. When, lastly, the beam contains rays of all the colors mingled in due proportion, we receive an impression in which no single color predominates, and this we call white light. The colors of natural objects, whether inherent or imparted by various dyes, are simply effects upon the retina produced by the beam after it has been reflected from the surface or trans- mitted through the mass of the body, and the peculiar chromatic effects are due to the unequal proportions in which the dif- ferent colored rays are thus absorbed. The color reflected, and that absorbed or transmitted, are always complementary to each other, and if mingled they would reproduce white. It is obvious, moreover, that no beam of light, however modified by reflection or transmission, could produce the sensation of a given color, if it did not contain from the first the correspond- ing colored rays. Hence it is that the colors of objects only appear naturally by daylight, and when illuminated by a monochromatic light, all colors blend in that of this one pure tint. 94. Chromatic Spectra and Spectroscopes. When a beam of light is passed through a glass prism placed as shown in Fig. RELATIONS OF THE ATOMS TO LIGHT. 177 Fig. 86. 86, it is not only refracted,iha,t is, bent from its original rectilinear course, but the colored rays of which the beam consists, being bent unequally, are separated to a greater or less extent, and fall- ing on a screen produce an elongated image colored with a suc- cession of blending tints, which we call the spectrum. The red rays, which are bent the least, are said to be the least refran- gible, while the violet rays are the most refrangible, and inter- mediate between these we have, in the order of refrangibility, the various tints of orange, yellow, green, blue, and indigo. Thus a prism gives an easy means of analyzing a beam of light, and of discovering the character of the rays by which a given chromatic effect is produced. Such observations are very greatly facilitated by a class of instruments called spectro- scopes, and Figs. 87 and 90 will illustrate the principles of their construction. In the very powerful instrument first represented, the beam of light is passed in succession through nine prisms (each having an angle of 45), and the extreme rays are thus widely separated, while the beam itself is bent around nearly a whole circumference. The only other essential parts of the instru- ment are the collimator A and the telescope B. The light first enters the collimator through a narrow slit, and having passed through the prisms is received by the telescope. The tele- scope is adjusted as it would be for viewing distant objects, 178 RELATIONS OF THE ATOMS TO LIGHT. and a lens at the end of the collimator serves to render the rays diverging from the slit parallel, so that when the two Fig. 87. tubes are in line, one sees through the telescope a mag- nified image of the slit, just as if the slit were at a great Fig. 88. distance. In like manner when the telescopes are placed as in Fig. 88, and when the light before reaching the telescope RELATIONS OF THE ATOMS TO LIGHT. 179 HH mi' ' m |Ora-|Yel-| Green. i Blue. I Inge. I low. I I I passes through the whole series of prisms, we still see a single definite image whenever the slit is illuminated by a pure monochromatic light. Moreover, this image has a definite position in the field of view, which, when the instrument is similarly adjusted, depends solely on the refrangibility of the light. Thus, if we place in front of the slit a sodium flame, which emits a pure yellow light, we see a single yellow image of this longitudinal opening, as in Fig. 89, Na. If we use a lithium flame, we see a similar image, 1 but colored red, and at some distance from the first, to the left, if the parts of our in- strument are disposed as in Fig. 88. If we use a thalium flame, we in like manner see a single image, but colored green, and falling considerably to the right of both of the other two. If now we illuminate the slit by the three flames simultaneously, we see all three images at once in the same relative position as before. So also if we examine the i The second image shown in Fig. 89, Li ia not ordinarily seen. 180 RELATIONS OF THE ATOMS TO LIGHT. flame of a metal, which emits rays of several definite degrees of refrangibility, we see an equal number of definite images of the slit. If, next, we illuminate the slit with sunlight, which contains rays of all degrees of refrangibility, we see an infinite number of images of the slit spread out along the field of view, and these, overlapping each other, form that continuous band of blending colors which we call the solar spectrum. If, lastly, we examine with our instrument the light reflected from a colored surface, or transmitted through a colored medium, we also see a band of blending colors, but at the same time we observe that certain portions of the normal solar spectrum are either wholly wanting or greatly obscured. With a spectroscope of many prisms like the one represented by Fig. 87, we can only see a small portion of the spectrum at once. By moving the telescope, which, fastened to a metallic arm, revolves around the axis of the instrument, different portions of the spectrum may be brought into the field of view ; while a vernier, attached to the same arm and moving over a graduated arc, enables us to fix the position of the spectrum lines, as the images of the slit are usually called. The other mechanical details shown in the figure are required in order to adjus) the various parts of the instrument, and especially in order to bring the prisms to what is termed the angle of minimum deviation. But an instrument of this magnitude and power is not required for the ordinary applications of the spectroscope in chemistry. For this purpose a small instru- ment consisting of a collimator, a single prism, and a telescope, all in a fixed position, are amply sufficient. In the field of such a spectroscope the whole spectrum may be seen at once ; and the position of the spectrum lines is very easily determined by means of a photographic scale placed at one side, and seen by light reflected into the telescope from the face of the prism. The various parts of the instrument, as arranged for ob- servation, are shown in Fig. 90. A is the collimator, P the prism, and B the telescope. The tube C carries the photo- graphic scale, and has at the end nearest to the prism a lens of such focal length that the image both of the slit and the scale may be seen through the telescope at the same time, the one appearing projected upon the other. The screw e serves to adjust the width of the slit. Moreover, one half of the RELATIONS OF THE ATOMS TO LIGHT. 181 Tig. 90. length of the slit is covered by a small glass prism so arranged that it reflects into the collimator tube the rays from a lamp placed on one side. Thus the two halves of the slit may be illuminated independently by light from different sources, and the two spectra, which are then seen superimposed upon each other (see Fig. 91), exactly compared. The various screws, which appear in Fig. 90, are used for adjusting the different parts of the instrument. 95. Spectrum Analysis. The atoms of the different chem- ical elements, when rendered luminous under certain definite conditions, always * emit light whose color is more or less characteristic, and which, when analyzed with the spectroscope, exhibit spectra similar to those which are represented in Fig. 89, so far as is possible without the aid of color. Sometimes we see only a single line in a definite position, as in the case of Na, Li, and Th, already referred to. At other times there are several such lines ; and, still more frequently, to these lines (or definite images of the slit) there are super- added more or less extended portions of a continuous spectrum. Moreover, not only is the general aspect of each spectrum exceedingly characteristic, but also the occurrence of its peculiar lines is, so far as we know, an absolute proof of the 182 RELATIONS OF THE ATOMS TO LIGHT. presence of a given element, and these lines may be readily recognized by their position, even when the character of the spectrum is otherwise obscure. It is evident then that we have here a principle which admits of most important ap- plications in chemical analysis, and it only remains to con- sider under what conditions the elementary atoms emit their characteristic light. First. All bodies when intensely heated are rendered lumi- nous, and, other things being equal, the higher the temperature the more intense is the light. The brilliancy of the light emitted at the same temperature by different bodies varies very greatly, the densest bodies being, as a general rule, the most intensely luminous. Secondly. Solid and liquid bodies, if opaque, emit when ignited white light, or at least light which shows with the spec- troscope a continuous spectrum more or less extended. At a red heat the light from such bodies consists chiefly of red rays, but as the temperature rises first to a white and then to a blue heat, the more refrangible rays become more abundant and finally predominate. Thirdly. The elementary substances give out their pecu- liar and characteristic light only in the state of gas or vapor. Hence, when we examine with a spectroscope a source of light, we may infer that a continuous spectrum indicates the presence of solid or liquid bodies, while a discontinuous spectrum, with definite lines or images of the slit, indicates the presence of gases and vapors ; and in the last case we can, as has been seen, infer from the position of the lines the nature of the luminous atoms. It would seem, however, from recent investigations, that under certain conditions even a gas may show a continu- ous spectrum, and there are other seeming exceptions which admonish us that the general principles just stated should be applied with caution. Fourthly. At the very high temperatures at which alone gases or vapors become luminous, compound bodies, as a rule, appear to be decomposed, and the elementary atoms disasso- ciated. Hence the observations with the spectroscope have been almost entirely confined to the spectra of the elementary substances, and our knowledge of the spectra of compound sub- stances is exceedingly limited. In some few cases where the RELATIONS OF THE ATOMS TO LIGHT. 183 spectrum of a compound has been obtained, it has been noticed that, as the temperature rises, this spectrum is suddenly re- solved into the separate spectra of the elements of which the compound consists. Fifthly. At a high temperature the metallic atoms of a compound body are far more luminous than those of the other elementary atoms with which they are associated. Hence, when the vapor of a metallic compound is rendered luminous, the light emitted is so exclusively that of the metallic atoms, disassociated by the heat, that when examined with the spec- troscope the spectrum of the metal is alone seen ; and this is the probable explanation of the fact that the sa)ts of the same metal, when treated as will be described in the next para- graph, all show, as a general rule, the same spectrum as the metal itself. Lastly. The substance, on which we wish to experiment, may be rendered luminous in several ways. If the substance is a volatile metallic salt, the simplest method is to expose a bead of the substance (supported on a loop of platinum wire) to the flame of a Bunsen's burner (Fig. 90), which by itself burns with a nearly non-luminous flame. The flame soon be- comes filled with the disassociated atoms of the metal and shines with their peculiar light. In order to study the spectra of the less volatile metals like aluminum, iron, or nickel, we use two needles of the metal, and pass between the points, when about one fourth of an inch apart, the electric discharges of a powerful Ruhmkorff coil, condensed by a large Leyden jar. The metal is volatilized by the heat of the electric current, and the space between the points becomes filled with the intensely ignited vapor, which then shines with its characteristic light." 1 In a similar way we can experiment on the permanent gases and lighter vapors, enclosing them in a glass tube with plati- num electrodes, and before sealing the tube reducing the ten- sion with an air pump, when the discharge will pass through a length of several inches of the attenuated gas. The light then emitted comes from the atoms or molecules of the gas, and where the electric current is condensed as in the capillary por- 1 An electric spark is in every case merely a line of material particles ren- dered luminous by the current. 184 RELATIONS OF THE ATOMS TO LIGHT. tion of the tubes constructed for this purpose, the light is suf- ficiently intense to be analyzed with the spectroscope. The three different modes of experimenting just described do not by any means always give the same spectrum when ap- plied to the same chemical element. It constantly happens that as the temperature rises new lines appear, which are usu- ally those corresponding to the more refrangible rays, and at the very high temperatures generated by the electric discharge many of the spectra change their whole aspect. The ill-defined broad bands or luminous spaces which are so conspicuous at a low temperature (see Fig. 89), disappear, and are replaced by a greater or less number of definite spectrum lines. Gen- erally, however, the characteristic lines which mark the ele- ment at the lower temperature are seen also at the higher ; but sometimes there is a sudden and complete change of the whole spectrum. The cause of these differences is not understood, but it has been thought by some investigators that the normal spectra of the elementary atoms consist of bright bands alone, and that the more or less continuous spectra, which are also seen at the lower temperatures, are to be referred to the im- perfect disassociation of the atoms, whose mutual attractions or partial combinations produce a state of aggregation ap- proaching the condition which determines the continuous spec- tra of liquid or solid bodies. 96. Delicacy of the Method. Having now stated the general principles of spectrum analysis, and the conditions under which these principles may be applied, it need only be added that the method is one of extreme delicacy. It enables us to detect wonderfully minute quantities of many of the metallic elements, and has already led to the discovery of four elements of this class which had eluded all methods of investi- gation previously employed. The names of these elements, Rubidium, Caesium, Thallium and Indium, all refer to the color of their most characteristic spectrum bands. 1 97. Solar and Stellar Chemistry. When a beam of sun- light is examined with a powerful spectroscope, the solar spectrum is seen to be crossed by an almost countless number of dark lines distributed with no apparent regularity, and dif- 1 The different bands of the same element' are usually distinguished by Greek letters, following the order of relative brilliancy. RELATIONS OF THE ATOMS TO LIGHT. 185 fering very greatly in relative strength or intensity. These lines were first accurately described by the German optician Fraunhofer, and have since been known as the Fraunhofer lines. A few of the most prominent of these lines are shown in Fig. 89, with the letters of the alphabet by which they are designated. These lines, like the bright lines of the elements, correspond in every case to a definite degree of refrangibility, and therefore have a fixed position on the scale of the spectro- scope. Moreover, what is very remarkable, the bright and the dark lines have in several cases absolutely the same position. It is easy to construct the spectroscope so that the two halves of the slit may be illuminated from different sources. If then we admit a beam of sunlight through one half, and the light of a sodium flame through the other half, we shall have the two spectra super-imposed in the same field, as in Fig. 91, Fig. 91. and it will be seen that the two parts of the sodium band, which appears as a double line under a high power, coincide absolutely in position with the double dark line D in the solar spectrum. But a still more striking coincidence has been observed in the case of iron, for the eighty well-marked bright lines in the spectrum of this metal correspond absolutely both in position and in strength with eighty of the dark lines of the solar spectrum. Now, the chances that such coinci- dences are the result of accident, are not one in one billion billion ; and we are therefore compelled to believe that the two phenomena must be connected. A simple experiment shows what the relation probably is. If we place before the spectroscope a sodium flame, we see, of course, the familiar double line. If now we place behind 186 RELATIONS OF THE ATOMS TO LIGHT. the sodium flame a candle flame, so that the candle also shines into the slit, but only through the sodium flame, we shall see the same bright lines projected upon the continuous spectrum of the candle. If, however, we put in place of the candle an electric light, we shall find that while the continuous spectrum is now far more brilliant than before, the sodium lines appear black. The explanation of this singular phenomenon is to be found in a principle, now well established both theoretically and experimentally, that a mass of luminous vapor, while other- wise transparent, powerfully absorbs rays of the same refrangi- bility which it emits itself. Hence, in our experiment, the very small portion of the spectrum covered by the sodium line is illuminated by the sodium flame alone, while all the rest of the spectrum is illuminated from the source behind, and the effect is merely one of contrast, the sodium lines appearing light or dark according as they are brighter or darker than the contiguous portions of the spectrum. In a similar way the bright lines of a few other elements have been inverted, and these experiments would lead us to infer that the Fraunhofer lines themselves are formed by a brilliant photosphere shining through a mass of less luminous gas. In other words, it would appear that the sun's luminous orb is surrounded by an immense atmosphere which intercepts a portion of his rays, and that we see as dark lines what would probably appear as bright bands, could we examine the light from the atmosphere alone. If then our generalization is safe, the dark and the bright lines are the same phenomena seen under a different aspect, and the one as well as the other may be used to identify the different chemical elements. Hence, then, there must be both iron and sodium in the sun's atmosphere, and for the same reason we conclude that our luminary must contain Hydrogen, Calcium, Magnesium, Nickel, Chromium, Barium, Copper, and Zinc, while there is equally good evidence that Gold, Silver, Mer- cury, Cadmium, Tin, Lead, Antimony, Arsenic, Strontium, and Lithium are not present, at least in large quantities. It is, moreover, worthy of notice that the lines neither of oxygen, nitrogen, nor indeed of any of that class of bodies formerly called metalloids, have been recognized in the solar spectrum ; but then the spectra of these elements, so abundant on the RELATIONS OF THE ATOMS TO LIGHT. 187 earth's surface, are so much feebler than those of the metals, that it is doubtful whether the negative evidence of the spec- troscope is trustworthy in these cases. The elements thus recognized in the sun only account for a small portion of the dark lines, and the scheme of the chemical elements is apparently so incomplete on the earth, at least so far as we know it (103), that we should not be surprised to find a multitude of new forms of elementary matter at the cen- tre of the solar system. But, on the other hand, the meteorites have brought to us no new elements, and their evidence, there- fore, as far as it goes, is adverse to the assumption that there exists in the sun's atmosphere such a great number of unknown elements as the dark lines would indicate, and this obvious ex- planation of their vast number cannot be regarded as probable. If next we turn the spectroscope on some of the brighter fixed stars, we shall see continuous spectra like the solar spectrum, of greater or less extent, and covered by dark lines. A careful comparison of these lines would seem to indicate that the stars differ very greatly from each other, although in general they are bodies similar to our sun ; and if our theory is correct, we have been able to detect the presence of sodium, magnesium, hydrogen, calcium, iron, bismuth, tellurium, antimony, and mercury in Aldebaran, and other elements in other stars. The most remarkable result of stellar chemistry remains yet to be noticed. On examining the nebulas with the spectro- scope, it has been found that while some of them show a con- tinuous spectrum, there are a number of these remarkable bodies which exhibit the phenomena of bright lines. This would lead us to the conclusion that the last are really, as the nebular theory assumes, masses of incandescent gas, while the first are not true nebula, but simply clusters of very distant stars. An examination of the comets has confirmed the pre- vious conclusion that they also are mere masses of gas, but, singularly enough, the light from the coma of one of those bodies gave a continuous spectrum, due probably to reflected sunlight. 98. Absorption Spectra. When a luminous flame is viewed with a spectroscope through a solution of any salt of the metal Erbium, the otherwise continuous spectrum of the flame 188 RELATIONS OF THE ATOMS TO LIGHT. is seen to be interrupted by several broad bands, which have a definite position, and are a valuable means of recognizing the presence of this very rare element. This absorption spectrum, as it is called, is simply the reverse, the " negative " of the luminous spectrum of the same element. In like manner the salts of Didymium give an equally characteristic, although very different, absorption spectrum, which is in fact the only sure test we possess for this remark- able elementary substance ; and as the bands may under some conditions be seen with reflected, as well as with transmitted light, we may apply the test even to opaque solids. Also, the same absorption bands are obtained either when the light is transmitted through a liquid solution, or through a solid crystal of any salt of the metal ; and, moreover, the incandescent vapor of the metal shows bright bands corresponding to the dark bands in position. These facts would seem to show that the characteristic spectrum bands of an element may be, at least to some extent, independent both of the state of aggregation, and of the condition of combination of the elementary atoms. Many substances besides the compounds of the elements just noticed, give characteristic absorption spectra which have been found to be useful chemical tests, especially in the case of blood, and certain other bodies of organic origin. The most remarkable phenomena of this class are the absorption spectra which are seen when a luminous flame is viewed with a spectroscope through various colored vapors, such as those of nitric per-oxide, bromine, and iodine. The dark bands are then very numerous, and in some cases may be resolved into well-defined lines. Indeed, the absorption bands are a class of phenomena closely allied to the Fraunhofer lines, many of which are known to result from the absorption by the earth's atmosphere of solar rays of certain degrees of refrangibility : and all these facts, with many others, prove that gases and vapors may exert their peculiar power of elective absorption at the ordinary temperature, as well as when incandescent. As a general rule, however, the absorption bands are not, like the bright lines of the metallic spectra or their representatives among the dark lines of the solar spectrum, definite images of the slit, but they are darker portions of the spectrum more or less regularly shaded, and correspond to the broad bands or RELATIONS OF THE ATOMS TO LIGHT. 189 luminous spaces in the spectra of the metallic vapors when not intensely heated. In each case the effect results from the blending of a greater or less number of images of the slit, differing in relative position and intensity. 99. Theory of Exchanges. The facts of the two last sections are all illustrations of a general principle already referred to in connection with the reversal of the sodium spectrum. This principle is known as the " Theory of Ex- changes," and has been stated as follows : " The relation between the power of emission, and power of absorption for each kind of rays (light or heat) is the same for all bodies at the same temperature." . . . . " Let R denote the intensity of radiation of a particle for a given description of light at a given temperature, and let A denote the proportion of rays of this description incident on the particle which it absorbs ; then R-7-A has the same value for all bodies at the same temperature, that is to say, this quotient is a function of the temperature only." The law of exchanges finds its widest application in the phenomena of radiant heat, and so far as experiments have been made, it appears to be true in its greatest generality. In applying it to explain the reversal of the spectra of colored flames, we have only to deal with a single body in its relations to rays of different qualities. If the principle is true, the absorbing power of such a body at a given temperature must bear a fixed ratio to its power of emission for each kind of ray. If, for example, it has a great power of emitting certain rays of red light, it has a proportionally great power of absorbing the same rays. If, again, it has a feeble power of emitting violet rays of definite quality, its power of absorbing such rays is proportionally feeble, and bears the same ratio to the power of emission as before ; and, lastly, it has no power of absorption over such rays as it does not itself emit. More- over, it would follow that, although the relation of the absorb- ing to the radiating power might vary very greatly, so that,, as the temperature falls, the last may become inconsiderable as compared with the first, or even vanish, no essential change in the character of the elective absorption would be thus in- duced. Hence, we should expect that bodies would absorb when cold rays of the same quality which they emit when hot,. 190 RELATIONS OF THE ATOMS TO LIGHT and also that opaque solids when heated would emit white light. We have seen that the general order of the phenomena is that which the law of exchanges would predict, and here, for the present, our knowledge stops. We have as yet been able to form no satisfactory theory in regard to the relations of the molecular structure of bodies to the medium through which the waves of light or heat are transmitted. It is, however, worthy of notice that Euler, one of the earliest and ablest investigators of undulatory motion, predicted the discovery of the law of exchanges, in assuming as a fundamental principle of the undulatory theory that a body can only absorb oscillations isochronous with those of which it is itself susceptible. 100. General Conclusions. The facts that have been stated in this chapter are sufficient to show, that, although yet in its infancy, spectrum analysis promises to be one of the most powerful instruments of investigation ever applied in physical science. It seems to be the key which will in time open to our view the molecular structure of matter ; and even now the results actually obtained suggest speculations in regard to the ultimate constitution of matter, of the most interesting character. The several monochromatic rays which the atoms of the elements emit, must receive their peculiar character from some motion in the atoms themselves which is isochronous with the motion they impart. Is it not then in this motion that the individuality of the element resides, and may not all matter be alike in its ultimate essence? Such speculations, however wild, are not wholly unprofitable, if only they stimulate investigation and thus lead to further dis- coveries. CHAPTER XVII. CHEMICAL CLASSIFICATION. 101. General Principles. The glimpses that we have been able to gain of the order in the constitution of matter give us grounds for believing that there is a unity of plan pervading the whole scheme, and encourage a confident expectation that hereafter, when our knowledge becomes more complete, chem- ists may attain to at least such a partial conception of this plan as will enable them to classify their compounds under some natural system ; and in imagination we may even look forward to the time when science will be able to express all the possibilities of this scheme with a few general formulae, which will enable the chemist to predict with absolute cer- tainty the qualities and relations of any given combination of materials or conditions. But although to a very slight extent the idea has been realized for a small class of the compounds of carbon, yet as a whole this grand conception is as yet but a dream. The more advanced student will find that in limited portions of some few fields of investigation a fragmentary clas- sification is possible, as in mineralogy ; but, when he attempts to comprehend the whole domain, he becomes painfully aware of the immense deficiencies of his knowledge ; he is confused by the numerous chains of relationship, which he follows, with no result, to sudden breaks, and soon becomes convinced that all such efforts must be fruitless until more of the missing links are supplied. The best that can now be done in an elementary treatise on chemistry is to group together the elements, or, rather, the elementary atoms, in such families as will best show their natural affinities ; and then to study, under the head of each element, the more important and characteristic of its com- pounds. However little value such a classification may have in its scientific aspect, it will bring together, to a greater or less extent, the allied facts of the science, and thus will help the mind to retain them in the memory. 192 CHEMICAL CLASSIFICATION. In classifying the elementary atoms, the three most impor- tant characters to be observed are the Prevailing Quantivalence, the Electrical Affinities, and the Crystalline Relations. The first of these characters serves more particularly to classify the elements in groups, the second to determine their position in the groups, and the last to control the indications of the other two. The crystalline relations of the atoms can only be deter- mined by comparing the crystalline forms of allied compounds, and involve the principles of isomorphism already discussed. Moreover, in order to reach the most satisfactory scheme of classification, we must take into consideration other properties of these compounds besides the crystalline form; which, al- though they may not be so precisely formulated, are frequently important aids in forming correct opinions as to the relations of the atoms. It will also be evident, from what has previously been stated, that more trustworthy inferences as to these rela- tions may frequently be drawn from the crystalline form and properties of allied compounds than from those of the element- ary substances themselves ; for, in addition to the fact that so many of these substances crystallize in the isometric system, whose dimensions admit of no variation, it is also true that, in our ignorance of the molecular constitution of most of them, we often have more certainty, in the case of compounds, that our comparisons are made under identical molecular conditions. 102. Metallic and Non-Metallic Elements. In all works on chemistry since the time of Lavoisier, the elementary sub- stances have been divided into two great classes, the metals and the non-metals ; and the distinction is undoubtedly funda- mental, although too much importance has been frequently attached to the accident of a brilliant lustre. The character- istic qualities of a metal, with which every one is more or less familiar, are the so-called metallic lustre, that peculiar adapt- ability of molecular structure known as malleability or ductility, and the power of conducting electricity or heat. These qualities are found united and in their perfection only in the true metals, although one or even two of them are well developed in several elementary substances which, on account of their chemical qualities, are now almost invariably classed with the non- metals, as, for example, in selenium, -tellurium, arsenic, CHEMICAL CLASSIFICATION. 193 antimony, boron, and silicon. Besides the properties above named, many persons also associate with the idea of a metal a high specific gravity ; but this property, though common to most of the useful metals, is by no means universal ; and, among the metals with which the chemist is familiar, we find the lightest, as well as the heaviest, of solids. The non-metallic elements, as the name denotes, are distinguished by the absence of metal- lic qualities ; but the one class merges into the other. The presence or absence of metallic qualities in the ele- mentary substances is for some unknown reason intimately associated with the electrical relations of their atoms, those of the metals being electro-positive, while those of the non- metals are electro-negative, with reference, in each case, to the atoms of the opposite class. In the classification given in Table II. we have associated together in the same family both the metals and the non-metals having the same quantivalence, believing that such an arrangement not only best exhibits the relations of the atoms, but also that in a course of elementary instruction it presents the facts of chemistry in the most logical order. 103. Scheme of Classification. The classification of the elementary atoms which has been adopted in this book is shown in Table II. In the first place the atoms are divided into two large families, the Perissads and the Artiads (27). Secondly, these families are subdivided into groups (separated by bars in the table) of closely allied elements. The atoms of any one of these groups are isomorphous ; and they are arranged in the order of their weights, which is found to correspond also, in almost every case, to their electrical relations. Each group forms a very limited chemical series ; and not only the weights and the electrical relations of the atoms, but also many of the physical qualities of the elementary substances, vary regularly as we pass from one end of the series to the other. The order of the variation, however, is not always the same ; for while in some cases the lightest atoms of a series are the most electro- negative, in other cases they are the most electro-positive. Thirdly, in arranging the groups of allied atoms we have followed the prevailing quantivalence of the group, and those groups whose elementary atoms exhibit in general the lowest 194 CHEMICAL CLASSIFICATION. quantivalence are, as a rule, placed first in order; but with our present limited knowledge there must be some uncertainty in regard to the details of such an arrangement, and the prin- ciple has sometimes been violated so as to bring together those groups of atoms which are most allied in their chemical rela- tions. The remarks already made in regard to the general scheme of chemical classification apply with almost equal force to the partial system here attempted. The very attempt makes evi- dent the fragmentary character of our knowledge, even in re- gard to the exceedingly limited portion of the subject with which we are dealing. The idea of classification by series was first developed in the study of organic chemistry, where the principle is much more conspicuous than among inorganic com- pounds. Thus, as has been shown (40), we are acquainted with twenty acids resembling acetic acid, which form a series begirining with formic acid and ending with' melissic acid. Each member of this series differs in composition from the preceding member by Cff& or by some multiple of this symbol ; and the properties of the compounds vary regularly between the extreme limits, according to well-established laws. Moreover, many other similar, although more limited, series of compounds are known, and the principle realized in these organic series seems to be the true idea of all chemical classification. But, in attempt- ing to apply it to the chemical elements, we find only two or three groups of atoms where the series is of sufficient extent to make the relations of the members evident. In most cases it would seem as if we only knew one or two members of a series, and this apparent ignorance not only throws doubt on the general application of our principle, but also renders uncertain the details of our scheme, even assuming that the principle of the classi- fication is correct. Hence, also, great differences of opinion may be reasonably entertained in regard to the position which the different atoms ought to occupy in such a scheme. Another very important cause of uncertainty in any scheme of classifying the elements arises from the double relationships which many of them manifest. Thus iron, which we have associated with manganese and aluminum, is in some of its relations closely allied to magnesium and zinc. Many other elements resemble iron in having a similar two-fold character, CHEMICAL CLASSIFICATION. 195 and different authors may reasonably assign to such elements different places in their systems of classification, according as they chiefly view them from one or the other aspect. Hence arises a degree of uncertainty which affects our whole system, and cannot be avoided in the present state of the science. Indeed, no classification in independent groups can satisfy the complex relations of the elements. These relations cannot be represented by a simple system of parallel series, but only by a web of crossing lines, in which the same element may be represented as a member of two or more series at once, and as affiliating in different directions with very different classes of elements. In the present fragmentary state of our knowledge, such a classification as we have just indicated is not attainable. The scheme adopted in this book only indi- cates in each case a single line of relationship ; but we have always endeavored to place each element in that relation which is the most characteristic ; and, however imperfect such a scheme may be, it will nevertheless assist study by bringing before the student's mind the facts of the science in a syste- matic and natural order. 104. Relations of the Atomic Weights. If the principle of classification which we have adopted is correct, and the ele- ments actually belong to series like those of the compounds of organic chemistry, we should naturally expect that the atomic weights would conform to the same serial law ; and it is a re- markable fact that the differences between the atomic weights of the elements of the same group are in most cases very nearly multiples of 16. The value of this common difference varies between 15 and 17, and we must admit in some cases the simplest fractional multiples ; but the mean value is^ very nearly 16, and the frequent occurrence of this difference is very striking. This numerical relation is not absolutely exact, but here, as in the periods of the planets, in the distribution of leaves on the stem of a plant, and in other similar natural phenomena, there is a marked tendency towards a certain nu- merical result, which is fully realized, however, only in com- paratively few cases. Other numerical relations which have been noticed between the atomic weights are probably only phases of the same law of distribution in series. Thus the atomic weight of sodium is 196 CHEMICAL CLASSIFICATION. very nearly the mean between that of lithium and potassium ; and the atomic weights of chlorine, bromine, and iodine, of glu- cinum, yttrium and erbium, of calcium, strontium, and barium, of oxygen, sulphur, and selenium, are similarly related. Again, there are several pairs of allied elements, between whose atomic weights there is very nearly the same difference. Thus the difference between the atomic weights of indium and cad- mium is very nearly the same as that between the atomic weights of magnesium and zinc, and the difference between the atomic weights of niobium and tantalum the same as that be- tween the atomic weights of molybdenum and tungsten. A careful study of the atomic weights will also reveal many other approximate relations of the same sort ; but although the study of these relations is highly interesting, and may lead here- after to valuable results, yet no great importance can be at- tached to them in the present state of the science. PART II. INTRODUCTION. HAVING developed in Part I. the fundamental principles of chemical science, we shall next give, in Part II., a brief sum- mary of the more important elements and compounds, exhib- iting their constitution and relations by means of formulae and reactions, and adding a number of questions and problems, which will serve to direct the attention of the student to the more important facts and principles, or to those which, being only implied in the context, might be otherwise overlooked, and which will also give him the means of testing the thor- oughness and accuracy of his knowledge. The answers to the problems have been calculated with the four-place logarithms, which will be found at the end of the volume. Used in con- nection with the table of antilogarithms which accompanies them, the logarithms give results which are accurate to the fourth significant figure, and this degree of accuracy exceeds in almost every case that of the experimental data given in the problems. With certain exceptions referred to below, the answers to the questions are either stated or implied in the immediate context, or in the sections and formulae to which reference is made. The references to sections are enclosed in parentheses, and those to formulae in brackets. Direct ques- tions on the facts stated in the summary are seldom given, and obviously would be superfluous ; but the student should make himself thoroughly acquainted with the subject-matter of each section before he attempts to answer the questions or solve the problems which follow. In studying the book, however, he should aim to acquire a knowledge of the general principles and mutual relations which are exhibited, rather than to com- mit to memory the isolated facts. He must never forget that he is dealing, not with abstractions, but with real things and actual phenomena, and that chemical formulae are merely ex- 200 INTRODUCTION. pressions of definite facts ascertained by experiment. More- over, he must discriminate with the greatest care between the facts directly stated or expressed by the reactions, and the in- ferences drawn from them, and he should be required to state clearly the successive steps in every process of inductive rea- soning. As was stated in the preface, this portion of the book is only intended as an auxiliary to lecture-room or laboratory instruction, and the closer the lessons can be connected with the experimental illustrations the better. The elements are studied in the following chapters in the order in which they are arranged in Table II., and in connec- tion with each element we describe, or at least mention, the more important compounds which it forms with the elements preceding it in our classification. At least this is the general rule, but, so far as regards the compounds, we do not follow this order invariably, departing from it whenever it may be necessary to illustrate the relations of the element we may be studying. Thus we describe with each element its chief oxy- gen and sulphur compounds from the first. No attempt has been made to embrace the whole field, but the aim has been to illustrate fully the principles of chemical philosophy, and to give a clear idea of that phase of the scheme of nature which has been revealed by the study of chemistry. As stated in the Preface, the " Questions and Problems " are an essential feature in the plan of the work, and serve to supplement as well as to illustrate the text. The student will find that the knowledge which he gains inferentially, while seeking the answers to the questions or solving the problems, is peculiarly valuable, and the acquisition has something of the zest of new discovery. As he advances, he will meet with questions which he cannot fully answer without consulting more extended works, and which are intended to direct his study beyond the limits of this book. He may consult in such cases Watts's Dictionary of Chemistry, Miller's Elements of Chemistry, Percy's Metallurgy, and Dana's System of Mineralogy. CHAPTER XVIII. THE PERISSAD ELEMENTS. Division I. 105. HYDROGEN. H 1. Monad. The .lightest atom, and the standard of quantivalence. Very widely diffused in nature. Forms one ninth of water, and is a constituent of almost all vegetable and animal substances as well as of many minerals. The essential constituent of all acids and bases, from which it is readily displaced by other atoms. 106. Hydrogen Gas. H-H. The lightest substance known in nature. Sp. Gr. = 1, the standard of comparison. Seldom found in a free state in nature. Best prepared by the action of zinc or iron on dilute sulphuric acid. Zll + (J2JS04 + Aq) = (ZnSOt + Aq) + HI-SI. [64] Very combustible. Has the greatest calorific power of any substance known. Aqueous vapor sole product of its com- bustion. 2m-in + = 2m 2 . [65] 107. Hydric Oxide (Water}. H.,0. The universally dif- fused liquid of the globe. The life-blood of nature, and the chief constituent of organized beings. Below a crystalline solid (hexagonal system, Figs. 14 and 16). Sp. Gr. = 0.918. Under the ordinary pressure of the air it boils at 100, but exists in the atmosphere in the state of vapor, at all temper- atures. For maximum tension of vapor at different temper- atures see Chem. Phys. (284 and 312). Water is an almost universal solvent and the medium of most chemical changes. Its molecular structure is regarded as the type of a very large class of chemical compounds. Its composition may be determined, First, by electrolysis (91 and [65] reversed). 9* 202 HYDROGEN. [ 108. Secondly, by passing a mixture of steam and chlorine gas through a red-hot tube. 2IH 2 (Q> + 2O1-O1 = 45HO1 -f =. [66] Thirdly, by exploding in an eudiometer-tube a mixture of oxy- gen and hydrogen gas [65]. Fourthly, by passing hydrogen gas over heated cupric oxide. CuO + SHU = Cu + HI,. [67] Water combines with anhydrides to form acids, as t , r681 or P 2 5 + 3H 2 = 2fff OfPO. It combines with metallic oxides to form hydrates, bases, or alkalies, as CaO-\-H 2 0=Ca=0 2 =H 2 . [63] It combines with many salts as water of crystallization, as Fe=S0 4 . 7H 2 Cryst. Ferrous Sulphate. 108. Hydroxyl. HO. An important compound radical, which may be regarded as a factor (28) in the molecules of many chemical compounds, and for this reason it is sometimes convenient to write its symbol Ho (22). The oxygen bases may be considered as compounds of hydroxyl with electro-posi- tive atoms or radicals, and the oxygen acids as compounds of the same with electro-negative atoms or radicals. Thus we may write the symbols of the following compounds as shown below : Na-Ho, fe [70] Sodic Hydrate Baric Hydrate Ferric Hydrate Na-O-H Ba-OfH, or u Nitric Acid Sulphuric Acid Phosphoric Acid H-0-NO Z u a 109. Hydric Peroxide (Oxygenated Water). Jf 2 2 orffo-ffo. 109.] QUESTIONS AND PROBLEMS. 203 Best regarded as the "radical substance" (22 and 69) corresponding to hydroxyl. In its most concentrated form it is a colorless liquid of the consistency of syrup, and having a de- cided odor resembling chlorine. Soluble in water in all pro- portions. Prepared by action of carbonic acid on baric peroxide. BaO 2 + (ff 2 C0 3 + Aq) = BaCO* + (ff 2 O 2 + Aq). [71] Carbonic anhydride is passed through water in which Ba 0% is suspended and the solution of Jf 2 2 subsequently evaporated in vacuo. Decomposed by fine metallic powders, and also spon- taneously at temperatures higher than 22, into water and oxy- gen gas. (2ff 2 2 + Aq) = (2ff 2 + Aq) + (SXD. [72] It liberates iodine from its compounds. 2KI+ (Ho-Ho + Aq) = I-I + (ZK-Ho + Aq). [73] It generally acts as an oxidizing agent. PfoS+ (ff 2 2 + Aq) = ?k$0 4 + (4ff 2 + Aq). [74] It sometimes, however, acts as a reducing agent. [75] Questions and Problems. 1 1. What distinction can be drawn between a chemical element and an elementary substance, it being understood that the word ele- ment is used in a restricted sense, as applying only to the ultimate atoms into which matter may be resolved ? Illustrate the distinction by the case of hydrogen. (69 ; 18 and 22.) 2. What is the essential characteristic of an acid and of a base ? (35 and 36.) 3. What is the ground for the belief that each molecule of hydro- gen gas consists of two atoms ? (19.) 1 It is assumed in all the problems of this book that the temperature is C., and the pressure 76 c. m., unless otherwise stated. The following abbreviations will be used: c. m., centimetre; c~m7 8 , cubic centimetre; d. m. 3 , cubic decimetre; kilo., kilogrammes, &c. (See Table I.) 204 QUESTIONS AND PROBLEMS. 4. The litre and the crith, the molecular weight of hydrogen and its molecular volume, sustain what relation to each other ? State the reason for the rule on page 49. (2 and 25.) 5. How many grammes of zinc and how many of sulphuric acid will yield one litre of hydrogen gas ? Ans. 2.92 grammes of zinc, and 4.39 grammes of sulphuric acid. 6. If 45 grammes of zinc are used in reaction [64], how many cubic centimetres of sulphuric acid must be used also, and how many grammes of zincic sulphate, and how many litres of hydrogen gas, will be formed in the process (Sp. Gr. of H Z SO = 1.843) ? Ans. 36.7 cTm. 3 of sulphuric acid, 111.3 grammes of zincic sul- phate, and 15.4 litres of hydrogen. 7. What volume of water should be mixed with the sulphuric acid in the last problem, assuming that the reaction takes pkce at 20, and that 100 parts of water at that temperature will dissolve 53 parts of zincic sulphate ? Ans. 209.9 cmn 3 , or enough to dissolve all the zinc salt formed. 8. What weight of iron must be used to generate sufficient hydro- gen to raise in the atmosphere by its buoyancy a total weight of 121 grammes (Sp. Gr. of air 14.5 nearly) ? Ans. 100 litres of hydrogen gas will be required, and this can be made from 250.9 grammes of iron. 9. Assuming that the principle of (1 7) is correct, why does it fol- low from reaction [65] that the molecule of oxygen gas must contain at least two atoms V 10. What is the volume of 4.480 grammes of hydrogen at 273.2 [9]? Ans. 100 litres. 11. What is the volume of 4.480 grammes of hydrogen at and under a pressure of 38 c. m. [4] ? Ans. 100 litres. 12. A block of ice weighs 36.72 kilos. What is its volume [1] ? Ans. 40 cLln: 3 13. An iceberg is floating in sea water (Sp. Gr. = 1.028). What proportion of its bulk is submerged? Ans. 0.8932. 14. One kilogramme of steam at 100 will melt how many kilos, of ice ? Ans. The steam by condensing and cooling would give out 637 units of heat, which is adequate to melt 637-f-79 = 8 + kilogrammes of ice. (14 and 16.) 15. What is the weight of one litre of confined steam at the tem- perature of 144 ? Tension of steam at 144 equals 4 atmospheres. Ans. Weight of litre of steam at and 76 c. m. would be theo- retically 9 criths. Hence weight at 144 and 4 X 76 c. m. is, by [6] and [10], 23.58 criths or 2.113 grammes. QUESTIONS AND PROBLEMS. 205 16. What is the weight of one litre of superheated steam under normal pressure, and at 546.4 ? Ans. 0.2688 grammes. 1 7. Water is forced into a glass globe containing dry air, at the temperature of 100 C. and under the normal pressure, as long as it continues to evaporate. What will be the tension of the moist air ? Ans. Water or any other liquid evaporates into a confined space until- the vapor attains its maximum tension for the existing temperature, even when the space is filled with another gas ; and the tension of the mixture of gas and vapor is equal to the sum of the tension which each would exert separately. Chem. Phys. (312). The maximum tension of aqueous vapor at 100 is 76 c. m., and hence the tension of the nioist air in the globe must be 152 c. m. 18. A volume of hydrogen gas standing in a bell-glass over a pneumatic trough, and consequently saturated with moisture, meas- ures 100 cTm: 3 . The temperature is 22. 3 and pressure on the gas 76 c. m. What would be the volume under the same conditions if the air were perfectly dry ? Ans. The maximum tension of aqueous vapor at given temper- ature is 2 c. m. Hence if vapor were removed, the tension of the gas would become 74 c. m., provided the volume re- mained constant. But the exterior pressure being 76 c. m., the volume must accommodate itself to this condition, and hence by [4] would be reduced to 97.36 c. m. 19. What is the Sp. Gr. of aqueous vapor? What is meant by the term Sp. Gr. as applied to a vapor, and under what conditions is it assumed to be taken ? (1 and 17.) Ans. 9. 20. In Table III. the weight of one litre of aqueous vapor under the standard conditions of temperature and pressure is given as 9 criths. AVhy is this value a fiction ? and why is an impossible value given in the table ? Chem. Phys. (329). 21. In the experiment indicated by reaction [66] the oxygen gas was collected in a bell-glass over water. It measured 1,101 c. m. 3 at the temperature 22.3 and under a pressure of 76 c. m. What was the volume of chlorine gas used, measured under the normal conditions ? The tension of aqueous vapor at 22.3 is 2 c. m. Ans. 2 litres. 22. How much copper will be reduced in the formation of nine grammes of water, and what volume of hydrogen gas will be used in the reaction ? Ans. 31.7 grammes of copper and 11.16 litres of hydrogen. 23. It has been found by exact experiments that for every nine 206 QUESTIONS AND PROBLEMS. grammes of water formed by reaction [6 7] the cupric oxide lost in weight eight grammes. What is the percentage composition of water? Ans. 11.112 of hydrogen and 88.888 of oxygen. 24. Given percentage composition of water and the Sp. Gr. of aqueous vapor, and assuming that the molecule of water contains only one oxygen atom, how can you deduce the atomic weight of oxygen ? (23.) 25. Assuming that all the heat of combustion is utilized, how many litres of hydrogen must be burnt to convert into free steam one kilogramme of boiling water, and how does the volume of steam generated compare with the volume of gas burnt ? Ans. 176.8 litres of hydrogen gas and 1,240 litres of steam, when reduced to standard conditions. (14 and 17.) (61.) 26. Assuming that all the heat of combustion is retained in the aqueous vapor formed from the burnt hydrogen, how will the vol- ume of the expanded vapor compare with that of the gas consumed ? Ans. By problem on page 121 it appears that the temperature of the vapor would be, under the conditions assumed, 6,853. Hence the volume would be 26.08 times as great as that of the gas [9]. 27. Assuming that the whole volume of gas resulting from the electrolysis of water is retained in the space previously occupied by the water, what would be its tension? Ans. 1,860 atmospheres. 28. What is the relation of an anhydride to an acid, or of a me- tallic oxide to a hydrate ? (37 and 47.) 29. What objections may be raised to the method of writing the symbols of acids and bases used in [70] ? 30. What is the distinction between a compound radical and a radical substance ? 31. Why does reaction [73] sustain the view that hydric perox- ide contains the radical hydroxyl? Do not reactions [72], [74], and [75] point to another view of its constitution? 32. Analyze reaction [75], and show that it is in harmony with the modern theory of the constitution of the oxygen moleculel 113.] FLUORINE. CHLORINE. 207 Division H. 110. FLUORINE. ^=19. Quantivalence usually one, but its atomicity is probably of higher order. A chief constit- uent of fluor-spar, CaF^ and of cryolite, Na^Al^F-^. Found also, but in small quantities, in Apatite, Tourmaline, Mica, and a few other minerals. Also in the bones of animals, especially in the teeth. The elementary substance F-F is undoubtedly a gas, but it has not with certainty been isolated. 111. Hydrofluoric Acid. HF. The anhydrous acid is at 15 a colorless mobile liquid, extremely volatile, boiling at 19.5, densely fuming in the air, and attracting greedily water from the atmosphere. It is exceedingly corrosive, and a highly dan- gerous substance, The dilute acid is obtained by distilKng a mixture of powdered fluor-spar and sulphuric acid in a plati- num or lead retort. CaF 2 + (H.SO, + Aq) = CaSO 4 + 2H3I? + ^q. [76] Cryolite may be used advantageously instead of fluor-spar. This acid is distinguished for its power of dissolving silica, with which it forms volatile products. Hence it is much used in chemical analysis for decomposing siliceous minerals, and in the arts for etching glass. 112. CHLORINE. 01= 35.5. Quantivalence usually one, but atomicity probably of a higher order. Very widely dis- tributed in nature, chiefly in combination with sodium, forming common salt. 113. Chlorine Gas. Cl-Cl. Yellowish-green gas, which may be liquefied by pressure, but has never been frozen. Sol- uble in water, with which it forms at a crystalline hydrate. Highly corrosive, and enters into direct union with most of the elementary substances. Discharges vegetable colors and de- stroys noxious effluvias, and hence much used in the arts as a bleaching and disinfecting agent. Best prepared by gently heating in a glass flask a mixture of hydrochloric acid and man- ganic dioxide. Aq) = (MnCl 2 + 2H.O + Aq) + 01-!. [77] Chlorine gas is a very important chemical reagent. It not 208 CHLORINE. [ 114. only converts many simple chlorides into perchlorides, but, with the intervention of water or of some other oxygen compound, it also acts as an oxidizing agent, and to this effect its bleaching power is probably in great measure owing. (Sn C1 2 + C1 2 + Aq) = (Sn C1 4 + Aq). [78] 3 Co-(HO) 2 + ( Cl- Cl + Aq) = [Co 2 ]!(HO) 6 (CoCl 2 + Aq). [79] Chlorine has also a remarkable power of replacing hydrogen in many of its compounds. (31) 114. Hydrochloric Acid. H~Gl. A colorless gas which may be liquefied by cold and pressure, but has not been frozen. Exceedingly soluble in water, which at 4 absorbs its own weight or about 480 times its volume of the gas. This solu- tion is very much used in the laboratory as a reagent, and an impure solution called muriatic acid is manufactured on a large scale for the uses of the arts. From the Sp. Gr. of the liquid acid we can determine very closely the quantity of gas held in solution, by means of tables in which the results of careful ex- perimental determinations have been tabulated. The following extracts from a table of Dr. Ure's give all the data required for calculating the problems in this book. Sp. Gr. 15 C. Per Cent. HCl. Sp. Gr. 15 C. Per Cent. HCl. Sp. Gr. 15 C. Per Cent. HCl. Sp. Gr. 15 C. Per Cent. HCl. 1.200^ 1.1893 40.777 38.330 1.1410 1.1308 28.544 26.505 1.0899 1.0798 18.349 16.310 1 .0397 1.0298 8.155 6.116 1.1802 36.292 1.1206 24.466 1.0697 14.271 1.0200 4.078 1.1701 34.252 1.1102 22.426 1.0597 12.233 1.0100 2.039 1.1599 32.213 1.1000 20.388 1.0497 10.194 1.0060 1.124 Muriatic acid is prepared by heating common salt with sul- phuric acid in large iron retorts, and conducting the gas formed into large glass vessels containing water. 2Na a + H 2 S0 4 = Na 2 SOt + 2 SIOI. [80] When we make pure hydrochloric acid in the laboratory, we only use half as much salt. The gas is then given off at a much lower temperature, and glass retorts may be employed. [81] 116.] CHLORINE. 209 Hydrochloric acid may also be obtained by directly uniting hydrogen and chlorine gas. + i-oi = 2nm [82] By electrolyzing the aqueous solution, the last reaction is re- versed and the acid is decomposed. It may also be readily decomposed by metallic sodium. 2mOl + Na-IVa = 2NaCl + HI-HI. [83] Liquid hydrochloric acid dissolves most of the metals and the metallic oxides, and its uses in practical chemistry are illus- trated by the following reactions. See also [77]. Sll + (2ffCl + Aq) = (SnCl 2 + Aq) + HI-HI. [84] ZnO + (2HCI + Aq) = (ZnCl 2 + H 2 + Aq). [85] [Al,]0 3 + (GffCl + Ag)= ([Al 2 -]Cl 6 +3H 2 + Aq). [86] 115. Compounds of Chlorine and Oxygen. All of them unstable and most of them explosive. In regard to their mo- lecular constitution different views are entertained. Hypochlorous Anhydride C1 2 Cl-0-d, Hypochlorous Acid HCIO H-O-Cl, Chlorous Acid HC10 2 ff-0-O-Cl, Chlorous Anhydride C1 2 3 Cl- 0-0- 0- Cl, Chloric Acid HC10 3 H-0-O-O-Cl, Chloric Peroxide C1 2 4 Cl-0-O-O-O-Cl, Perchloric Acid HC10 4 H-0-O-O-O-CL 116. Potassic Chlorate. The most important salt of any of the chlorine oxygen acids. Obtained by passing a stream of chlorine gas through a warm solution of caustic potash. Aq) + 3Cl-Cl = (KC10 3 + 5KCI +3ff 2 + Aq). [87] Potassic chlorate, being much the less soluble, is readily freed from the potassic chloride by two or three crystallizations. It is decomposed by heat alone into potassic chloride and oxygen gas. = 2KCI + 3 (SXD. [88], 210 BROMINE. IODINE. [117. Much used for making oxygen gas, and also in fireworks and the preparation of detonating powder. 117. BROMINE. Br = 80. Quantivalence usually one, but atomicity probably of a higher perissad order. Associated with chlorine in minute quantities in saline waters and certain silver ores. The elementary substance (Br-Br} is a very volatile deep-red liquid. &p. Gr. = 3.187. Boils at 63. Freezes at 7. 3. Prepared from the bittern of certain salt springs, by treating with chlorine and dissolving out the liberated bromine with ether. 118. IODINE. 1= 127. Quantivalence and atomicity same as with bromine. Associated with chlorine in still smaller quantities than bromine. The elementary substance is obtained from the ashes of certain seaweeds. Crystalline solid ; Sp. Gr. = 4.95. Melts at 107. Boils at 175, forming a dense violet vapor. Very slightly soluble in water, but is readily dissolved by alcohol, ether, and carbonic sulphide. Imparts to starch paste a deep blue color. The three elements, chlorine, bromine, and iodine, form a well-defined natural group, and a careful comparison will show that the properties both of the elementary substances and of their compounds conform closely to the law of progression which marks a chemical series. These elements are all highly electro- negative bodies, but as we descend in the series we find that this character becomes less marked, and hence their chemical energy, as manifested by the strength of their affinity for ele- ments of the opposite class, such as hydrogen and the electro- positive metals, diminishes as the atomic weight increases ; and this law, as will appear, obtains with few exceptions in all the chemical series. Moreover, it will also be found, as might indeed be anticipated, that elements so closely related as these are almost invariably found associated in nature. 119. Characteristic Reactions. The soluble chlorides, bro- mides, and iodides all give, with a solution of argentic nitrate, precipitates insoluble in water and acids. The iodide of silver may be distinguished from both the chloride and the bromide of the same metal by its yellow color and insolubility in aqua ammonia, in which the last two readily dissolve. Bromine and iodine may both be expelled from their salts by chlorine gas, when the first may be recognized by the red color which it im- 119.] QUESTIONS AND PROBLEMS. 211 parts to ether or chloroform, and the last by the exceedingly characteristic blue color which it gives to starch paste. Flu- orine is easily discovered because its compounds, when heated in a glass tube with potassic bisulphate, yield hydrofluoric acid which etches the glass. This element, although closely allied to the other three, differs so greatly in some of its chemical re- lations that it is doubtful whether it belongs to the same chem- ical series. Questions and Problems. 1. It appears that 10 grammes of pure fluor-spar yields 17.436 grammes of calcic sulphate [76]. Assuming that the atomic weight of calcium is 40, that of S0 96, and also that the symbol of fluor- spar is CaF v what is the atomic weight of fluorine ? Ans. 19. 2. How much fluor-spar and how much sulphuric acid must be used to generate sufficient hydrofluoric acid to neutralize 53 granules of sodic carbonate ? Ttc Ans. 39 grammes of fluor-spar and 49 of sulphuric acid. 3. How much liquid hydrochloric acid, Sp. Gr. 1.1893, and how much MnO v will yield one litre of chlorine gas ? Ans. 3.897 grammes of MnO^ and 17.06 grammes of hydrochloric acid. 4. Fifty-nine grammes of metallic tin were dissolved in hydro- chloric acid [84], and into this solution chlorine gas was passed until all the tin was converted into perchloride. How many litres of hy drogen gas were evolved in the first process, and how many of chlo- rine gas absorbed in the second ? Ans. 11.16 litres of each. 5. Analyze reactions [66 and 79], and show in what way the chlorine gas acts as an oxidizing agent. 6. Five grammes of liquid hydrochloric acid are ynixed with a solution of argentic nitrate, the last being in excess. The precipi- tated argentic chloride was collected, washed, dried, and weighed. The weight was 3.206 grammes. Required the per cent of HCl in the solution. Ans. 16.31. 7. One volume of common muriatic acid, Sp. Gr. 1.2, contains how many volumes of HCl gas ? Ans. 1 c. m. 3 , or 1.200 grammes, contains 0.489 grammes of HCl, or 315.8 cTlin 3 measured at 15 [9]. 8. In order to make one litre of common muriatic acid of Sp. Gr. 212 QUESTIONS AND PROBLEMS. 1.16, how much salt and how much sulphuric acid must be used, and how much water must be placed in the condenser ? [81] Ans. 598.9 grammes of salt, 1003. grammes of sulphuric acid, and 786.3 grammes of water. 9. On what does the economy of the process [80] over [81] de- pend? 10. The reaction [82] is said to prove that both hydrogen and chlorine gas have molecules consisting of two atoms. On what pos- tulates does the proof rest ? (1 7) (1 9.) 11. One litre of hydrochloric acid gas will yield by [83] how many litres of hydrogen gas ? Ans. ^ of a litre. 12. Point out the differences between the reactions [84, 85, 86, and 87], and the relations on which the differences depend. 13. Show that the compounds of chlorine and oxygen may be re- garded as compounds of chlorine and hydroxyl, less a certain number of molecules of water. What atomicity would it then be necessary to assign to chlorine ? vii vn Ans. For one case, (HO)^Cl 3H Z = (T0)-C7J 0,0,0. 14. It has been found by very careful experiments that 100 parts of potassic chlorate yield by [88] 60.85 parts of potassic chloride; and further, jthat 100 parts of potassic chloride give by precipitation 192.4 parts of argentic chloride. Assuming that the symbols of these compounds are those given above, what must be the atomic weights of chlorine, potassium, and silver ? It is also assumed, as found by previous experiments, that the atomic weight of oxygen is 16, and that 100 parts of silver combine with 32.87 of chlorine. Ans. Cl = 35.5, K = 39.1, Ag = 108. 15. The chlorine gas evolved from 1.740 grammes of Mn0 2 is passed into a solution of potassic iodide. How much iodine will be thus set free? Ans. 5.081 grammes. 16. Bromine and iodine form both with hydrogen and oxygen compounds simHar to those of chlorine. Compare together the sev- eral compounds and point out the resemblances and differences in their properties. (See Miller's Chemistry.) 123.] SODIUM. 213 Division HI. 120. SODIUM. Na = 23. Monad. Combined with chlorine it forms common salt, a substance which is very widely distributed throughout nature. It also enters into the composition of a few other minerals as an essential constituent, and several of its salts find important applications both in the arts and in common life. 121. Metallic Sodium. Na-Na. Soft, white metal with brilliant lustre, but rapidly tarnishing in the air. Sp. Gr. = 0.97. Fuses at 90, and boils at a red heat. When heated in the air, it burns with intensely yellow flame. Decomposes water at the lowest temperatures. Prepared by distilling in an iron retort a mixture of sodic carbonate and charcoal. + 2 C = STa-SSa + 3 CD. [89] Used in the extraction of aluminum, and in the chemist's labora- tory as a powerful reducing agent, 122. Sodic Chloride (Common Salt). NaCl White crys- talline salt (Isometric, Fig. 7). Sp. Gr. = 2.078. Melts at red heat. Volatilizes at white heat. Soluble in about three times its weight of water. Obtained from salt-beds and by the evaporation of saline waters. An essential article of food. The source of almost all the sodium salts. Used for preserving meat. 123. Sodic Carbonate (Sal Soda). Na. 2 C 3 . The crystal- lized salt contains in addition I0ff 2 0, but effloresces in dry air. White soluble salt, having an alkaline reaction. Formerly pre- pared by the lixiviation of the ashes of certain marine plants called barilla. Now almost universally made from common salt by Leblanc's process. This consists, First, in treating common salt with sulphuric acid, which converts sodic chloride into sodic sulphate. 2Na Cfl + H,SO, = Na 2 SO, + 2 SK9L [90] Secondly, in melting on the hearth of a reverberatory furnace the sodic sulphate with chalk and fine coal. 5Na. 2 S0 4 + 20 C = 5Na 2 S + 20 @(S>. [91] , ICaO 4- 2WD~ T921 214 SODIUM. [ 124. Thirdly, by lixiviating the non-volatile product of the last re- action (called black-ball) with water, which dissolves only the sodic caroonate. Used in washing, in the manufacture of glass and soap, and in the preparation of other sodium salts. Also an important reagent in the laboratory. Precipitates from so- lution of their salts most of the metals, generally as carbonates. (CaCL 2 +Na 2 C0 3 + Aq)=CaCO 3 +(2NaCl+Aq). [93] When fused in large excess with insoluble silicates or sulphates, it decomposes them. Sodic silicate or sulphate is formed, which is soluble in water, and metallic carbonates, soluble in acids. BaC0 3 + Na^SO, + (x 1) Na 2 GO B . [94] 124. Acid Sodic Carbonate (Bicarbonate of Soda). The crystallized neutral carbonate, when exposed to an at- mosphere of carbonic anhydride, absorbs the gas and is converted into this product (a white powder). -f @ 2 = 2ff,Na=C0 3 + 9ff 2 0. [95] Used, under the name of saleratus, for raising bread, and in the preparation of various effervescing powders. (ff,Na=C0 3 + &K=C 4 ff 4 6 + Aq) = Cream of Tartar. Q + JT 2 -f Aq) + @ 2 . [96] Rochelle Salts. 125. Sodic Hydrate (Caustic Soda). Na-O-H. Amor- phous white solid, having very strong attraction for water, in which it dissolves in all proportions, evolving considerable heat. Solution powerfully alkaline and strongly caustic. Prepared by adding milk of lime to a solution of sodic carbonate. (Na 2 =C0 3 + Ca-(HO), + Aq) = Ca=CO 3 + (2Na-HO + Aq). [97] To obtain the solid, the solution must be decanted from the in- soluble chalk ( Ca C0 3 ) and evaporated to dryness. The solu- tion itself is a very valuable reagent in the laboratory, and a crude solution (lye) is used in the arts for making soap. 130.] POTASSIUM. 215 Caustic soda will completely neutralize the strongest acids. On evaporating the neutral solution, we obtain the sodic salt of the acid used. (NaO-H+ H0-N0 2 + Aq) = NaO-N0 2 + ff 2 + Aq). [98] (2NaO-ff4- (HO) 2 =C 2 2 -f Ag) = Oxalic Acid. ((NaO)fC 2 2 + 2H 2 + Aq). [99] Sodic salts of weak acids have an alkaline reaction. 126. Oxides of Sodium. Sodic Oxide, Na^O. Sodic Per- oxide, Naf( 0-0). 127. Sodic Nitrate (Chili Saltpetre or Cubic Nitre). Na-N0 z . A natural product found incrusting the soil in the desert of Atacama. Crystallizes in rhombohedrons resembling cubes. Much used for making nitric acid. 128. POTASSIUM. K= 39.1. Monad. An impor- tant constituent of felspar and mica, two very widely distrib- uted siliceous minerals. A constituent also of all fertile soils which are formed in part by the disintegration of rocks con- taining these minerals. By the action of atmospheric agents on the soil, soluble potassium salts are formed which are ab- sorbed by the growing plants, whose ashes are the chief source of the potassium salts of commerce. But these salts are now also obtained from the salt-beds of Stassfurt in Germany. 129. Metallic Potassium. K-K. Resembles sodium, but has a bluish tinge of color ; Sp. Gr. = 0.865. Brittle at 0. Soft at 15. Melts at 55. Sublimes in green vapors at a low red heat. Burns when heated in the air, and takes fire spon- taneously on water. Prepared by distilling in an iron retort the intimate mixture of potassic carbonate and charcoal obtained by charring crude tartar. Reaction same as [89], substituting K for Na. More powerful reducing agent than sodium ; hence obtained with greater difficulty. More expensive, and less used on that account. 130. Potassic Carbonate. K 2 CO S . White deliquescent salt, with strong alkaline reaction. The crude salt (Pot-ashes of commerce) is obtained by lixiviating wood-ashes and evap- orating the lixivium. Purified by dissolving in a small quantity of boiling water, and crystallizing out the impurities. Largely 216 POTASSIUM. [ 131. consumed in the arts for manufacturing glass and soap, and for preparing other compounds of potassium. 131. Acid Potassic Carbonate (Bicarbonate of Potash). H,K=CO & . White crystalline salt, prepared by passing C0. 2 through a strong solution of the neutral carbonate. Reaction like [95], substituting ^Tfor Na. 132. Potassic Hydrate (Caustic Potash). ff,K=0. White amorphous solid, prepared like caustic soda [97], which it closely resembles, but is more deliquescent and more strongly alkaline. Forms with fats " soft soaps," while soda forms " hard soaps." Like caustic soda, an important reagent in the labor- atory. Precipitates from solutions of their salts most of the metals, generally as hydrates, but sometimes as oxides. In some cases the precipitate is soluble in an excess of the reagent. (Ca-SO, + 2K-(HO) + Aq) = Ca=(HO) 2 + (KfSOt + Aq). [100] - Aq) = +(R 2 + 2K-N0 3 + Aq). [101] ([A1 2 ~\ a, + QK-(HO) + Aq) = [ AlJi(HO) a + (*KCl + Aq). [102] [ AIJi(HO) 6 + (SK-HO + Aq) = + SH.,0 + Aq). [103] Potassic Aluminate. 133. Oxides of Potassium. Potassic Oxide, K^O. Po- tassic Dioxide, Kf(O-O). Potassic Tetroxide, Kf(O-O-O-O). 134. Potassic Chloride (Sylvine). KCl. Isornorphous with Na Cl Found associated with Carnallite (KGl . MyCl 2 . QH. 2 0) in the mines of Stassfurt. 135. Potassic Nitrate (Nitre). KN0 3 . White crystalline .salt. Dimorphous. Usual form of crystals orthorhombic prisms, but under certain conditions crystallizes in rhombohedra like NaN0 3 (Hexagonal). Melts at 339 without decomposition. Is decomposed at a red heat, giving off a mixture of oxygen and nitrogen gas. Deflagrates on glowing coals. Nitre is a natural product, and is chiefly used in the manufacture of gunpowder. It is also employed in curing meat, and the fused salt (sal pru- nelle) is a useful medicine 138.] QUESTIONS AND PKOBLEMS. 217 136. Characteristic Reactions. Salts of potassium are dis- tinguished from those of sodium by giving a precipitate with an excess of tartaric acid and with acid platinic chloride. (KCl + H,H=C 4 ff 4 6 + Aq) = Tartaric Acid. H,K=C 4 H 4 6 + (HCl + Aq). [104] Acid Potassic Tartrate. (2KCI + PtCflA + Aq) = PtCl 6 K 2 + (2HCH + Aq). [105] 137. Lithium, Rubidium, and Ccesium are found in very minute quantities in certain mineral waters, in lepidolite mica, and in a few other rare minerals. They are always associated with potassium and sodium, to which they are closely allied in all their chemical relations. They form with sodium and po- tassium a series of electro-positive elements quite as well marked as the series of electro-negative elements of the previous group ; and, following the same law, the most electro-positive elements are the lowest in the series and have the highest atomic weights. Hence, therefore, the chemical energy of the elements of this group, as manifested by the strength of their affinities for ele- ments of the opposite class, like those of the chlorine group, increases as we descend in the series. 138. Characteristic Reactions. The compounds of each of the five " alkaline metals " impart a peculiar color to the flame of the Bunsen lamp. These colored flames, when examined with the spectroscope, exhibit characteristic bands, by which the elements may be distinguished, and both rubidium and cae- sium were discovered by this means. (Chapter XVI.) Questions and Problems. 1. What is the Sp. Gr. of sodium vapor V Ans. 23. 2. What is the weight of one litre of sodium vapor at 1,093, but under the normal pressure ? [9] and (1). Ans. Weight of hydrogen gas under the conditions named is 1 of a crith. Hence, weight of sodium vapor is 4.6 criths or 0.4121 of a gramme. 3. In the preparation of sodium [89] what weight of metal ought to be obtained from 20 kilos, of sodic carbonate, and how many litres 10 218 QUESTIONS AND PROBLEMS. of carbonic oxide gas should be formed for every gramme of sodium obtained ? Ans. 8.680 kilos, of sodium and 1.456 litres of carbonic oxide. 4. One cubic decimetre of rock-salt contains how many cubic decimetres of metallic sodium, and how many litres of chlorine gas ? Ans. 0.8422 d. m. 3 of sodium and 896.5 litres of chlorine. 5. To what extent is the solubility of common salt influenced by the temperature ? (Fig. 2, page 108.) 6. Given the specific heat of common salt (0.214), and the atomic weights of its elements (sodium and chlorine), to find its symbol. 7. How much carbonate of soda can be made from 500 kilo- grammes of common salt ? How much sulphuric acid ? How much coal and how much chalk are required in the process, according to the theory? Ans. 453 kilos, of NaC0 3 , 418.8 kilos, of H 2 SO^ 205 kilos, of C, and 598.2 of CaCO s . 8. What relation ought the price of crystallized carbonate of soda to bear to that of the dry salt, if the intrinsic value is alone consid- ered? Ans. Price of dry salt 2.7 of crystallized. 9. In order to convert ten kilogrammes of crystallized sodic car- bonate into acid carbonate, what volume of C0 2 will be absorbed ? Ans. 780.3 litres. 10. What is the difference between the two sodic carbonates, and what is the reason for the name acid carbonate ? (36). 11. What volume of C0 2 can be obtained from 3.72 grammes of acid sodic carbonate ? [96]. Ans. 1 litre. 12. The symbol of sodic hydrate may be written Na-O-H, or Na-Ho, or (NaO)-H, and to what three possible views of its consti- tution do these symbols correspond? [70] (235). Why should the radicals HO or NaO be monads, and what advantage would be gained by writing the symbol in one way or the other? (22) and (28). 13. Why does calcic hydrate, a comparatively weak base, decom- pose sodic carbonate ? (21) (52). 14. A solution of caustic soda was exactly neutralized by 0.630 of a gramme of crystallized oxalic acid (//0 2 =C 2 2 . 2// 2 0). What weight of sodium does it contain ? Ans. 0.230 of a gramme. 15. In what different ways may you write the symbol of potassic nitrate ? Illustrate by diagrams like those of (34). State what rules must be followed in grouping the atoms. (22, 28, 34. and 69.) Ans. K-NO V KO-NO Z , or K-O-NO Z . QUESTIONS AND PROBLEMS. 219 16. What conclusions may be drawn in regard to the distribution of the soluble salts of sodium and potassium based on the nature of the plants from which they are obtained ? 1 7. On what relations of solubility does the process of purifying potassic carbonate depend ? 18. If in a chemical process potassic or sodic carbonates may be used indifferently, what relation ought their prices to bear to each other in order that they may be used with equal profit ? Ans. 138 : 106. 19. Analyze equations [100, 101, 102, 103], and show that the various symbols are written in conformity to the rules referred to above, No. 15. 20. If a saturated solution of nitre is made at 38, and subse- quently cooled to 10, what proportion of the salt will crystallize out ? (Fig. 2.) Ans. Two thirds. 21. The difference between the two kinds of soap corresponds to what difference of properties between sodic and potassic carbonate ? Ans. The one effloresces and the other deliquesces in the air. 22. Draw diagrams illustrating the constitution of the different potassic oxides. (34.) 23. Why would not the salts of sodium be precipitated by the same reagents used in [104 and 105] ? Apply the same principle to the interpretation of the other reactions of this section. 220 SILVEK. [ 139. Division IV. 139. SILVER. Ag= 108. Monad. Found in small quantities in nature, chiefly in the metallic state, or in com- bination with chlorine, sulphur, arsenic, or antimony. 140. Metallic Silver. Ag-Agt Sp. Gr. 10.474 Fuses at about 1,000. The principal ores are Native Silver Ag-Ag, Horn Silver AgCl, Silver Glance Ag.,S, Light-red Silver Ore (Proustite) (AgS) ? =As, Dark-red Silver Ore (Pyrargyrite) (AgS)^Sb. These ores are found chiefly in mineral veins either by them- selves or associated with ores of lead and copper, with which they are frequently smelted, and the silver subsequently .sepa- rated from the regulus thus obtained. Silver does not oxidize when heated in contact with the air, and for this reason is readily separated from lead in the process of cupellation. xAg 2 . yPb -f ^yO~- == xAg-Ag -f yPb 0. [106] The cupel furnace is so arranged that the melted litharge (PbO) runs off as fast as formed, and leaves the silver pure. Melted silver can dissolve about twenty-two times its volume of oxy- gen gas ; but the gas is given off, in great measure, when the metal solidifies. 141. Argentic Nitrate. AgN0 3 . The most important sol- uble salt of silver. Obtained by dissolving silver in dilute ni- tric acid. 3Ag-Ag + (SffNO, + Aq) = (6AgN0 3 + 4ff 2 + Aq) + 23SST. [107] White crystalline solid which melts at 219. Fused salt is called lunar caustic, and is much used in surgery as a cautery. Argentic nitrate, although not changed by the light when pure, is readily decomposed when in contact with organic matter, and the black stain of metallic silver thus formed cannot be removed by washing. Hence its application for making hair dyes and 143.}- SILVER. 221 indelible ink. It is also used in large quantities in the art of photography. 142. Argentic Chloride. AgCL White crystalline solid (Fig. 7). Melts at about 260, and on cooling forms a horny sectile mass, whence the mineralogical name, horn silver. Pre- pared by adding to a solution of argentic nitrate any soluble chloride. (AffN0 8 + NaCl + Aq) = AgCl + (NaNO, + Aq). [108] We thus obtain a white curdy precipitate, which is insoluble in water and acids, but soluble in ammonia, in potassic cyanide, and in sodic hyposulphite. Owing to a partial reduction, the white powder blackens in the light, especially in the presence of organic matter and an excess of argentic nitrate. On this property is based the ordinary process of photographic printing. In contact with dilute acids, argentic chloride is very readily reduced by metallic zinc. 2Ag Gl -f Zn, = Zn C1 2 + Ag 2 . [109] It may also be reduced by hydrogen or hydrocarbon gas passed over the chloride in a heated tube. [110] In the process of electro-plating, argentic chloride, dissolved in an aqueous solution of potassic cyanide, is decomposed by the electric current. (91). 143. Argentic Bromide^ AgBr, and Argentic Iodide, Agl, resemble argentic chloride, and are formed in a similar way. The last, however, has a yellow color, and is insoluble in am- monia. In presence of an excess of argentic nitrate, and after exposure to light, they are at once reduced to the metallic state by solution of ferrous sulphate. Before exposure the reduction takes place very slowly, and on this reaction is based the art of photography. The steps of the process are : 1. Spreading over a glass plate a film of collodion, holding in solution a mix- ture of metallic bromides and iodides ; 2. Immersing the coated plate in a solution of argentic nitrate until a mixture of argen- tic bromide and iodide is formed in the film ; 3. Exposing the plate to light in the camera, where the image formed by a lens falls upon it ; 4. Developing the latent image by a solution of 222 THALLIUM. GOLD. [ 144 ferrous sulphate ; 5. Dissolving out the undecomposed silver salt by a solution of sodic hyposulphite. 144. Argentic Oxide. Ag 2 0. Argentic Peroxide. Ag 2 2 . The first is very slightly soluble in water, and the solution has an alkaline reaction. 145. Characteristic Tests. Most silver compounds may be reduced to pure silver before the blow-pipe; and whenever they are brought into solution the silver can be recognized and the amount very accurately determined by the reaction just given. [108]. Silver is remarkable for forming anhydrous salts ; and whenever we wish to determine the molecular weight of an acid, it is generally best to analyze its silver salt. (68). Division V. 146. THALLIUM. Tl = 204. Usual quantivalence one, but atomicity probably three. A very rare element, found in some varieties of pyrites. Its oxide, T1 2 0, is soluble in water, and absorbs carbonic anhydride from the air. v Its vapor imparts a green color to the flame of a Bunsen lamp, and shows a single green band in the spectroscope. Division VT* 147. GOLD. Au = 197. Triad. Probable molecular symbol of metal, Au=Au. Almost always found in the native state, or only slightly alloyed with other metals. The only well-defined native compounds are those with Tellurium. Very sparingly but very widely disseminated through many of the crystalline rocks and in the alluvium resulting from their disintegration. In the gold-bearing rocks the metal is frequently found accumulated to a greater or less extent in veins of quartz (auriferous quartz). It is also constantly associated in minute quantities with other metallic ores, especially with those of sil- ver, and in some localities the veins of iron and copper pyrites yield large amounts of the precious metal. It is extracted either by simple washing or by bringing the finely pulverized ore in contact with metallic mercury, which has a great affinity for gold and picks out the minute particles from the mass of 147.] GOLD. 223 refuse. The process is very simple, and the cost of the product depends, to a great extent, on the very large amount of material which must be handled; for gold ores do not on the average contain but a few ounces of metal to the ton. From the re- sulting amalgam the mercury is recovered by distillation, and the residual metal may then be melted and cast into bars. The gold thus obtained, however, is more or less alloyed, chiefly with silver, and is refined before being used for coinage. This is best accomplished by dissolving the metal in aqua-regia, evaporating to dryness to remove the excess of nitric acid, dis- solving in a large volume of water, and precipitating the gold with ferrous sulphate. Lastly, the precipitate is collected and melted under borax. If the proportion of alloy is very large, it is best removed by boiling the metal with nitric or sulphuric acid. When nitric acid is used for parting gold from silver, the separation is not complete when the amount of gold is more than one fourth of the weight of the alloy ; and since in most cases the alloy must be first reduced to this proportion, the process is called quartation. When sulphuric acid is used, the amount -of gold must not exceed one fifth. Gold has been called the king of metals ; for it not only pos- sesses the qualities distinguishing a metal in their highest per- fection, but also, under all ordinary conditions, preserves its brilliant lustre unimpaired. With the exception of platinum, iridium, and osmium, gold is the densest solid known ; Sp. Gr. 19.34. It may be drawn into wire of such fineness that three kilometres only weigh a single gramme, and may be beaten into leaves not more than one ten-thousandth of a millimetre thick. Gold has a familiar yellow color, but thin leaves trans- mit a green light. It has been found that an exceedingly thin film of gold attached to the surface of a glass plate, and heated to a temperature not exceeding 315, loses its metallic lustre and appears ruby-red by transmitted light ; and finely divided gold, when suspended in water or melted into glass, imparts to the medium the same beautiful color. Gold is nearly as soft as lead, and pieces of pure gold may be welded together without heat by pressure or concussion, as in dentistry. In order to increase its hardness it is alloyed with copper. The standard gold of both the United States and the French coinage contains one tenth copper, that of the English one twelfth of the same 224 GOLD. [ 147. alloy. Gold melts at about 1,100. It is only slightly volatile at the highest furnace heat ; but before the compound blow-pipe it is dispersed in purple vapor. It is an excellent conductor of heat and electricity, but is inferior in this respect both to silver and copper. Gold is not dissolved by any of the common acids, and is not attacked by the fused caustic alkalies. It enters, however, into direct union both with chlorine and bromine, and is readily dis- solved by any liquid mixture which liberates chlorine. The usual solvent is a mixture of four parts of hydrochloric acid with one of nitric acid, called, on account of its power of dissolving gold, aqua-regia. Au*Au + (2ffN0 3 + QHCl + Aq) = (2AuCl 3 -\- 4ff 2 + Aq) + 2S5T. [111] When gold is dissolved in aqua-regia, if hydrochloric acid is used in excess, the solution, evaporated at a gentle heat, yields yellow needle-shaped crystals, which appear to be a molecular compound of AuCl 3 with HCL If, however, the evaporation is pushed still further, but at a temperature not exceeding 120, a red crystalline mass is obtained, which is essentially Auric Chloride, An Cl& although it is difficult to expel the last traces of HGl without still further decomposing the salt. If this pro- duct is heated above 160 it loses two atoms of chlorine, and there is left a pale-yellow, sparingly soluble powder, which is Aurous Chloride, Au Cl, and at 200 this last is also decom- posed and reduced to metallic gold. Auric chloride is deli- quescent, and yields an orange-colored solution easily distin- guished from the solution of Au C1 3 . HCl, which is yellow. It also forms yellow crystalline salts with the alkaline chlorides, similar in constitution to the compounds with HCL Their for- mulas are Au Cl s . KCl .5ff 2 0, and Au C1 8 .NaCl.^ff, 0. In like manner it unites with ammonic chloride and with the chlo- rides of most of the organic bases, forming crystallizable salts, which are often employed to determine the molecular weight of these alkaloids. Auric chloride is a very unstable compound, and is readily reduced to the metallic state. Solutions of fer- rous sulphate, of antimonious chloride, of oxalic acid, and of sulphurous acid, all precipitate the gold in a finely-divided state. Phosphorous and hypophosphorous acid and solutions 147.] GOLD. 225 of their salts produce the same effect, as do also phosphorus it- self and many of the metals. The brown gold powder thus ob- tained is much used for gilding porcelain. A solution of stan- nous chloride mixed with stannic chloride produces in neutral solution of auric chloride a beautiful purple precipitate called Purple of Cassius, which is much used for coloring glass and porcelain. The compound contains both gold and tin combined with oxygen, but its chemical constitution is still in question. Metallic tin gives a similar precipitate. There appear to be two iodides of gold, Auland Aul& but only one bromide, AuBr& has been described. There are also two oxides, Au 2 3 and Au 2 0. The first acts as an acid, the second as a very feeble basic anhydride. The following reactions illustrate the forma- tion and relations of these compounds. (AuCl 3 + GK- (KfOfAu + 3KCI -\-3ff 2 + Aq). [112] u + 3ff-0-O 2 ff 3 + Aq) = (%K-0-C 2 H 3 -}- Aq). [113] u = Au 2 3 + 3ff 2 0. [114] To obtain these reactions, the solution o?AuCl 3 should be boiled after the addition of K-0-ffa.ud. then acidified with acetic acid. The precipitate thus obtained has, when dried, the composition of Au 2 3 . The compound Au 2 is obtained as an insoluble vi- olet powder by digesting Au Cl with a solution of caustic alkali. (2AuCl + 2Na-0-H-\- Aq) = Au 2 0+(2NaCl+ff 2 + Aq). [115] It does not enter into direct combination with acids, but there is an hyposulphite of gold and sodium which plays an impor- tant part in photography, and appears to have the formula Au,Na=0. 2 =(S-0-S). Singularly, however, gold is not precipi- tated from the solution of this salt by the ordinary reagents. There are two sulphides of gold, Au^ and Au 2 S. The first is precipitated by ff 2 S from a cold solution and the last from a boiling solution of AuCl 3 by the same reagent. They both dissolve in alkaline sulphides and form sulphur salts. Thus u + Aq) + 3ff 2 S. [116] 10* o 226 QUESTIONS AND PEOBLEMS. [148. 148. Characteristic Reactions. With the exception just noticed, gold, when in solution, can be distinguished by the fact that it is precipitated by ferrous sulphate, provided the solution, though -acid, does not contain an excess of nitric acid. (2AuCl s + QFe=0 2 =S0. 2 + Ag) = [117] The formation of purple of Cassius, and the easy reduction of all the compounds to the metallic state by simple ignition, are other indications by which the presence of gold may be readily recognized. The reduced gold, even when in fine powder, ac- quires its peculiar lustre if rubbed against a hard surface, as in the process of burnishing. Besides the important uses of gold for coinage and for articles of ornament or luxury, the metal is peculiarly well adapted, both by its softness and its power of resisting corrosive agents, for its applications in dentistry. It is also largely employed in the various methods of gilding, which consists either in directly applying thin gold-leaf to the surface to be covered, or, when the surface is metallic, by de- positing upon it a thin film of gold with the aid of galvanism or by the simple action of chemical affinity. Questions and Problems. 1. Given the percentage composition of Proustite. Silver, 65.45; Sulphur, 19.39; Arsenic, 15.16. Required the symbol. Ans. Ag 3 S 3 As. 2 How much greater is the per cent of silver in Proustite than in Pyrargyrite ? Ans. 5.68 per cent. 3. Draw diagrams illustrating the molecular constitution of the different silver ores. 4. Analyze reaction [107], and point out the difference between it and the class of reactions of which [64] is the type. 5. If a given mass of argentiferous lead contains three fourths of one per cent of silver, how many kilogrammes of litharge will be made in the process of cupellation to each kilogramme of silver ex- tracted, and how many cubic metres of oxygen gas will be absorbed by the process ? Ans. 142.5 kilos, of litharge, and 7.134 in? of oxygen. QUESTIONS AND PROBLEMS. 227 6. One gramme of silver treated as indicated by [107] and [108] yielded 1.328 grammes of argentic chloride. What is the atomic weight of silver ? The atomic weight of chlorine is assumed to be known, 35.5, and also the specific heat of argentic chloride, 0.091. Ans. 108. 7. One gramme of argentic chloride reduced by hydrogen [110] yielded 0.7526 of a gramme of silver. What is the atomic weight of silver ? The same values are assumed as in the last problem. Ans. 108.- 8. One gramme of argentic oxalate yields when heated 0.7105 of a gramme of silver. We have reason to believe that oxalic acid is bibasic. What is its molecular weight ? (68). Ans. 90. 9. Write the reactions of sulphurous acid and of oxalic acid on solution of auric chloride, assuming that sulphuric acid in one case, and CO Z in the other, are a part of the products. 10. What evidence do you find of the quantivalence of gold in the above sections ? 11. Does gold act as an acid or a basic radical ? 12. What is the chief chemical characteristic of gold? 13. There has been a question about the cause of the color which purple of Cassius imparts to glass and porcelain glaze. Do the facts stated aboye explain this phenomenon ? 228 BORON. [ 149. Division VII. 149. BORON. B = 11. Triad. Very sparingly distrib- uted. Always found in combination with oxygen. In boric acid and in various borates, including the minerals Datholite and Danburite, boron is the electro-negative element, while in Axi- nite and Tourmaline, and in many artificial salts, it acts the part of a basic radical. The elementary substance (B=Bt) may be obtained both in an amorphous and a crystalline form. The first is obtained by decomposing boric anhydride with sodium. B 2 3 + 3Na-Na = 3Na 2 + B~=B. [118] It is an infusible dark-brown powder, which soils the fingers and dissolves slightly in water. At about 300 it takes fire in the air and burns into B 2 3 , and it is also oxidized when heated with sulphuric acid or with the alkaline nitrates, sulphates, car- bonates, or hydrates. It decomposes nitric acid even when slightly concentrated and cold. [119] [120] Boron is one of the very few elements which unite directly with nitrogen. B=-B -f AW 2B~=N. [121] If amorphous boron is heated intensely in a closed crucible, it becomes much denser, and is then less easily oxidized. It dis- solves in melted aluminum, and when the molten metal sets, the boron crystallizes in quadratic octohedrons (75) more or less highly modified. These crystals are nearly as hard as the dia- mond, have an adamantine lustre, and Sp. Gr. = 2.68. They may also be obtained directly from boric anhydride, which is decomposed by aluminum. [^ 2 ] + B 2 3 = [^] 3 + B-=B. [122] The crystals thus prepared are sometimes nearly colorless, but more frequently they have a yellow or red color, and some- times the color is so deep that they appear black. They are 150.] BORON. probably never wholly pure, and it is worthy of remark that they sometimes, if not always, contain a considerable quantity of carbon. They resist the action of all acids, and even of fused nitre, but are oxidized when fused with acid potassic sulphate. It appears, from recent investigations, that the so-called graphi- toidal boron, which is formed with the crystals just mentioned, is a compound of aluminum and boron. 150. Boric Acid. HfO^B. A product of volcanic action. Found in some natural waters, and has been detected in the waters of the ocean. It is collected in large quantities, but in an impure condition, from the hot vapors of the "fumerolles " in the Maremma of Tuscany. The pure acid is best prepared from borax by the reaction + 2ffCl + 5ff 2 + Ag) = (2NaCl+Aq). [123] The hydrochloric acid should be mixed with a hot saturated so- lution of borax, which as it cools deposits boric acid in white nacreous crystalline scales. Boric acid is sparingly soluble in cold water, but dissolves in three times its weight of boiling water. It is also soluble in alcohol, and imparts to the flame of burning alcohol a peculiar green tint, which exhibits in the spectroscope five well-marked green bands. The solution both in water and in alcohol cannot be evaporated without loss, as the vapor always takes with it an appreciable amount of the acid. The solution evaporated on turmeric paper changes the color to brown, like an alkali, but it affects litmus paper like other weak acids. At the temperature of 100 it loses one atom of water. HfOfB = H-O-BO + 2T 2 0. [124] The compound H^OfB is called orthoboric acid. The pro- duct H-O-BO is frequently described as the first anhydride of this acid, and is called metaboric acid. If this is heated to a still higher temperature two molecules unite, while at the same time they lose another atom of water, forming the second and last anhydride, boric anhydride. ZH-O-BO = B. 2 3 + H 2 0. [125] At a red heat B 2 3 fuses to a viscid glass, which remains clear 230 BORON. [ 151. as it cools, but soon becomes opaque and crumbles if exposed to the air. It also forms fusible compounds with the metallic oxides. Hence the use of boric acid and the borates as fluxes. 151. Borates. It is evident from the principles of (38) that, besides orthoboric acid, many others are theoretically pos- sible. Thus: Boric Acid HOB Diboric Acid L Triboric Acid H 6 l 5 ^(B- 0-B- 0-B), Tetraboric Acid ff 6 W^(B-0-B-0-B-0-B), Polyboric Acid H n +2 O n + 2 (B n O n ^ These may be regarded as formed by the coalescing of sev- eral molecules of orthoboric acid, and the elimination from this condensed molecule of a sufficient number of molecules of water to set free the number of oxygen atoms required to cement to- gether the atoms of boron in the resulting radical. By .elimi- nating additional molecules of water, we may obtain from either of the above acids a series of anhydrides (distinguished as the first, second, &c., anhydrides), and the number of possible an- hydrides in any case is equal to the number of pairs of hydro- gen atoms which the acid contains. It must be understood that all these possible forms are not real compounds. Indeed, only the three already mentioned have been actually prepared ; but there are several borates whose constitution is best explained when we regard them as salts of acids derived from orthoboric acid in the way just indicated. The most important of these is common borax, which may be regarded as the sodium salt of the second anhydride. of tetraboric acid. 152. Borax, Na 2 =0 2 =(B=0 2 =B-0~B=0 2 =B) .I0ff 2 0, was orig- inally brought from a salt lake in Thibet, and was called Tincal. It also occurs in large crystals in the mud of Borax Lake, in California, and it has been found in solution in many mineral springs, and even in minute quantities in the ocean. Is man- ufactured in large quantities from the crude boric acid of the Tuscan lagoons. White crystalline salt, which when heated gives up its water of crystallization. At a red heat melts to a transparent glass, which has the property of dissolving almost 153.] BORON. 231 all the metallic oxides. Many of them impart to the glass characteristic colors ; and these reactions, which are readily ob- tained with a small bead of borax supported by a loop of plat- inum wire, are useful blow-pipe tests. It is also used for solder- ing metals, for making enamels, for fixing colors on porcelain, and as a flux in various metallurgical processes. The ordinary crystals contain as above IOR 2 0, and belong to the monoclinic system ; but the salt can be crystallized with only 5If 2 in oc- tahedrons belonging to the isometric system. 153. Boric Chloride, BC1 3 , can be obtained by passing chlo- rine gas over an intimate mixture of B 2 3 and carbon, heated to a red heat in a porcelain retort. B. 2 3 -f 3G + 3Cl-Cl= 3OO + 2BO1 3 . [126] It is a very volatile liquid (Sp. Gr. 1.35 at 7), boiling at 17, and yielding a dense vapor whose Sp. Gr., as found by experi- ment, is 56.85 ; chiefly interesting as establishing the quanti- valence of boron. It is at once decomposed by water. BCl, + 3ff 2 = ff 3 -=0 3 -=B + 3HCI. [127] 154. Boric Bromide, BBr& prepared like the chloride, is a volatile liquid (Sp. Gr. 2.69), boiling at 90, and giving a vapor whose Sp. Gr. has been found by experiment equal to 126.8. Decomposed by water like the chloride. 155. Boric Fluoride, BF& is best prepared by intensely heating a mixture of B 2 3 and fluor-spar. 2B, 3 + 3 GaF 2 = Ca 3 W 6 W 2 + 2BF 3 . [128] A colorless gas, whose Sp. Gr. has been found by experiment equal to 34.2. This gas is eagerly absorbed by water, which dissolves seven hundred times its volume and forms a corrosive acid liquid called borofluoric acid, whose constitution is not well understood. If its composition is that usually assigned to it, its formation will be expressed by the reaction 2BF 3 + 3ff 2 = B 2 3 . GffF. [129] The same compound may be also prepared by dissolving B. 2 3 in HF -|- Aq, and then concentrating the solution. If borofluoric acid is largely diluted with water, one fourth 232 QUESTIONS AND PROBLEMS. [ 156.' of the boron separates in the form of boric acid, and there is left in solution what has been called hydrofluoboric acid. Aq). [130] Hydrofluoboric acid forms salts with basic radicals, and the compound with potassium may be formed by the action of boric acid on a dilute solution of potassic fluoride. (SKF + 2fff 2(KF. F 3 ) + (6K-0-H+ Aq). [131] 156. Characteristic Reactions. The peculiar green color which boric acid imparts to an alcohol or blow-pipe flame is the best indication of its presence, and this test is made still more decisive by analyzing the colored light with the spectroscope. The acid, however, must first be set free before the reaction can be obtained. In many of its relations boron resembles carbon. Questions and Problems. 1. Write the reaction of sulphuric acid on solution of borax. 2. What test can be applied to determine when an excess of sul- phuric acid has been added ? 3. Define an ortho acid, regarding orthoboric acid as a type of the class. 4. Make a table showing the relations of the various possible de- rivatives of boric acid. 5. The empirical symbol of boracite is Mg 3 O l5 B y What is its ra- tional symbol, and what is its relation to the ortho-borates ? 6. Boric sulphide, B t S# may be prepared by passing over a mix- ture of carbon and boric anhydride the vapor of carbonic sulphide, CS V The products are 2B 2 S S and SCO. Write the reaction. 7. Boric sulphide is readily decomposed by water, giving boric acid and sulphuretted hydrogen. Write the reaction. 8. In reaction [126] what double affinities are called into play? 9. In what respect do you find reaction [131] remarkable ? 10. What evidence do you find of the prevailing quanti valence of boron ? Are there any facts which would indicate that boron is a pentad ? 158.] NITROGEN. 233 Division Vlll. 157. NITROGEN. N= 14. Pentad, but as frequently trivalent or univalent. Chief constituent of the atmosphere ; but to this and the materials of organized beings it is almost exclusively confined. It is the characteristic ingredient of ani- mal tissues, which are composed mainly of the four elements carbon, hydrogen, oxygen, and nitrogen. Vegetable tissues, on the other hand, consist chiefly of only the first three of these elements ; but nitrogen is never entirely absent from plants, and is an essential ingredient of many important vegetable products, as, for example, of the albuminoid compounds and of the vege- table alkaloids. Nitrogen is marked by weak affinities, and hence its compounds are usually unstable, as is illustrated by the well-known tendency of animal substance to decay. 158. Nitrogen Gas, N=N, constitutes four fifths of the vol- ume of the atmosphere, and can be obtained in a pure condi- tion, First, by slowly or rapidly burning phosphorus in a con- fined volume of air. Secondly, by passing air over ignited copper-turnings, which combine with the oxygen. Thirdly, by passing chlorine gas through a solution of ammonia, (8ff s N+ Aq) + 3 Cl- Cl = (GfftNCl + Ag) + NiN. [132] Fourthly, by heating ammonic nitrite or a mixture of potassic nitrite and ammonic chloride, (HJf) -0-NO = 2ff, + mN. [133] K-O-NO + (HJST) Cl = KGl + 2R 2 + mff. [134] Nitrogen gas has never been condensed to a liquid condition. According to Regnault, one litre of nitrogen gas, under standard conditions, weighs 1.256167 grammes. It is remarkable for its inertness, and one of its chief offices in the atmosphere is to moderate the action of its violent associate. The only element- ary substances with which it directly combines are boron and titanium. Nevertheless, nitrogen has a great capacity for com- bination, and is distinguished by the large number and varied 234 NITROGEN. [ 159. nature of Its compounds ; but these can only be formed by in- direct methods. Oxides of Nitrogen. Nitrous Oxide N 2 0, Nitric Oxide NO, m Nitrous Anhydride N 2 0& Nitrous Acid H-O-NO, Nitric Peroxide N0 2 , v Nitric Anhydride N^O* Nitric Acid H-0-NO*. 159. Nitric Acid. HNO& When electrical discharges are passed through air which is in contact with caustic or carbo- nated alkalies, or when organic matter decays in the atmosphere under the same conditions, a partial union of the elements of the atmosphere takes place, and nitrates of potassium, sodium, or calcium are the usual result. From either of these native ni- trates, or nitres, the acid may be obtained. It is usually pre- pared by distillation from a mixture of sodic nitrate (127) and sulphuric acid. Na-0-N0 2 +ff 2 =0 2 =S0 2 = ff,Na=0 2 =S0 2 +H-0-N0 2 . [135] One molecule of sulphuric acid is adequate to decompose two molecules of nitre ; but the temperature required is then much higher, and the nitric acid is in part decomposed. The strong- est acid thus prepared is a colorless, fuming liquid, boiling at 86 and freezing at 49. Its Sp. Gr. = 1.552 at 20. It is un- stable, and is partially decomposed when exposed to the light. 4H-0-NO, = 2H 2 + 4N0 2 + 0-0. [136] The remaining acid is thus diluted, while the nitric peroxide colors it yellow. A similar decomposition takes place during the distillation of the acid. This decomposition continues until the hydrate 2HNO S . 3ff 2 is formed, which is far more stable and distils unchanged at 123. This is the common strong nitric acid of commerce, but it is not a definite compound, the composition varying with the pressure under which the acid distils. A still weaker acid is much used in the arts under the name of aqua-fortis. The strength of the acid may be deter- mined from its specific gravity by means of tables prepared for the purpose. 159.] NITROGEN. 235 Sp. Gr. Per Cent. HNO 3 Sp. Gr. Per Cent. HNO 3 Sp. Gr. Per Cent HNO S 1.500 92.98 1.395 64.17 1.228 36.28 1.470 82.71 1.343 51.50 1.165 26.95 1.435 73.10 1.289 45.62 1.105 17.62 Nitric acid is one of the most corrosive agents known. With a very few exceptions, it oxidizes all the elementary substances, converting them into oxides, acids, or nitrates, as the case may be. In these reactions, as a general rule, nitric oxide is evolved; but the products vary to a certain extent with the conditions of the experiments, and examples will be found under the differ- ent elements, and also in [107], [142], [151], and [156], illus- trating the different phases which the reaction may assume. Ni- tric acid corrodes all organic tissues, oxidizing them, and forming various products, among which the most common are water, carbonic acid, and oxalic acid. When more dilute, it stains the skin, wool, silk, and other albuminoid bodies of a bright yellow color. Very strong nitric acid, when mixed with strong sul- phuric acid, acts on some organic compounds in a very remark- able way. It removes one or more atoms of hydrogen, and sub- stitutes an equal number of atoms of the radical N0 2 in their place. (31). e + H- 0-N0 2 = 6 ff 5 (N0 2 ) + H 2 0. [137] Benzol. Nitro-Benzol. With the various bases it forms a large class of important salts. When the radical is univalent, these salts have the general i symbol R-0~N0 2 . When the radical is bivalent, the general IT IT formula becomes R=0.f(NO^)<^ or R=OfN 2 0^. Salts of these types are, in the ordinary use of the term, the normal or ortho- nitrates ; but, theoretically, nitrogen is capable of fixing five univalent radicals, and hence some chemists regard the assumed compound T 5 =0 5 ^Nas orthonitric acid, and salts of that type as orthonitrates. By eliminating from this orthoacid first one and then two molecules of water, we obtain the following anhydrides, the last of which is the ordinary acid. Orthonitric Acid H^O^N, or H~0-N0. 2 . 2ff 2 0, Metanitric JfyOfNO, or H-0-N0 2 . ff 2 0, Dimetanitric " H- 236 NITROGEN. [161. Salts are known whose symbols may be written on all these types, but they may also be written on the ordinary type as well. Thus or Dihydro-bismuthic Orthonitrate. Basic bismuthic Nitrate. [138] or (Mg-0-Mg-0-MgyOf(NOJ) f Magnesic Metanitrate. Trimagnesic Nitrate. Such distinctions are of no practical importance, but they are of value in pointing out the many-sided relations of our subject Under no condition does potassic hydrate form more than one salt with nitric acid, and the important theoretical bearing of this fact is evident. 160. Nitric Anhydride, N 2 5 , may be obtained by passing dry chlorine gas over dried argentic nitrate heated to 95. 4AgN0 3 + 2 01- Cl AgCl + 2N 2 5 + 0-0. [139] It is a white solid, crystallizing in prisms of the fourth system, melting at 29.5, and boiling at 45. Very unstable, undergoing spontaneous decomposition in a sealed glass tube. By the ac- tion of water it forms nitric acid. H 2 = 2HN0 3 . [140] 161. Nitrous Anhydride. N 2 3 . Best prepared by the action of dilute nitric acid (Sp. Gr. 1.25) on starch. Is also formed in the following reactions : [141] N 2 3 + 3Jf 2 0. [142] 4S9" + = = 2N 2 S . [143] In each case brownish-red fumes are formed, which, at a low temperature, become condensed into a very volatile blue liquid, boiling at about 0. With a small quantity of water it yields nitrous acid, H-O-NO, but a large quantity at once decom- poses it. [144] If the red vapor is passed into a solution of potassic hydrate, 162.] NITROGEN. 237 we obtain potassic nitrite, and in a similar way other nitrites may be made. (2KOff+ Aq) + N 2 S = (2K-0-NO + ff 2 0+Aq). [145] According to the theory of the last section, ordinary nitrous acid is the first anhydride of an assumed acid, H^OfN. This would be called orthonitrous acid, and the ordinary acid would then be metanitrous acid. The compound Pb z lO & lN 2 , accord- ing to this view, is plumbic orthonitrite, but it may be also re- garded as a triplumbic nitrite of the ordinary type (Pb-0~Pb- 0-Pb)=0 2 =(NO) 2 . 162. Nitric Peroxide, N0 2 , is best prepared by mixing two volumes of nitric oxide with one of oxygen gas, both absolutely dry. [146] The two gases when mixed immediately combine, yielding a deep brownish-red vapor, which, if passed into perfectly dry tubes cooled by a freezing mixture, is condensed to a crystalline solid. This solid melts at 9 to an orange-colored liquid, which boils at 22, but when once melted it does not freeze even at 20. The substance is decomposed by water with the greatest readiness. A mere trace of water is sufficient to prevent the formation of the crystals, occasioning instead the production of a green liquid, which appears to be a solution of nitrous anhydride in nitric acid. N0 2 + H 2 = 2HN0 3 + N 2 S . [1 47] If a larger amount of water is present, we obtain nitric oxide in place of nitrous anhydride, and the equation becomes 3N0 2 + H 2 == 2HNO S + NO. [148] In a similar way, when acted on by metallic hydrates and basic anhydrides, it yields a mixture of nitrate and nitrite. Thus" 2K-0-H+ 2N0 2 = K-O-NO + K-O-NO, + H 2 0. [149] Nitric peroxide may also be obtained by distilling plumbic nitrate, 0=0. [150] 238 NITROGEN. [163. Owing to the presence of a little moisture, we first obtain the green liquid mentioned above, but towards the end of the pro- cess the anhydrous peroxide comes over and may be crystallized. Nitric peroxide appears also to be formed in the reaction of nitric acid on tin, ff w 1Q Sn 5 5 + 5ff 2 0+ 20N0 2 ; [151] but in this, as in other reactions of nitric acid on the metals, the main product is more or less mixed with other oxides of nitrogen. 163. Nitric Oxide, NO, is best prepared by the action of dilute nitric acid (Sp. Gr. about 1.2) on copper-turnings. (3Gu(NO s ) 2 + H,0 + Aq) + 2NO. [152] The reaction appears to consist, first, in a metathesis of the metal with the hydrogen of the acid, and secondly, in the re- duction of a further portion of the acid by the hydrogen thus liberated. In order to obtain a pure product it is important that the acid should be in excess. Nitric oxide may also be obtained perfectly pure by heating together a mixture of fer- rous chloride, nitre, and hydrochloric acid. (QFeCl 2 + ZKNOz + SHCl + Aq) = 2NO. [153] A mixture of ferrous sulphate, nitre, and dilute sulphuric acid (Sp. Gr. 1.18) may also be used. Nitric oxide is a colorless permanent gas (Sp. Gr. = 15), but slightly soluble in water (one volume of water dissolves one twentieth of a volume of NO). It extinguishes a burning candle, but both phosphorus and charcoal, if burning vigorously, continue to burn, and with great intensity, when plunged into the gas. It is the most stable of the oxides of nitrogen, and is not decomposed by a red heat. It is neither an acid nor a basic anhydride, but it is marked by its avidity for oxygen, with which it forms the brownish-red fumes either of N0 2 or of N Z 0& ac- cording to the proportions present. [143] and [146]. It dis- solves freely in a solution of ferrous sulphate, forming a deep reddish-brown liquid, from which the gas may be expelled by 165.] NITROGEN. 239 heat. A similar product may be obtained with other ferrous salts, and this reaction may be used as a test for nitric acid. 1 64. Nitrous Oxide, N 2 0, is best prepared by gently heating ammonic nitrate in a glass flask or retort, NH; 0-N0 2 = 2ff 2 + N 2 0. [154] It may also be obtained by exposing nitric oxide gas to the action of moistened iron-filings, which absorb one half of the oxygen. NO __ o-O = 2N 2 0. [155] It is also evolved when zinc dissolves in dilute nitric acid, or, more surely, when a mixture of equal parts of nitric and sul- phuric acids, diluted with eight or ten parts of water, is used for dissolving the metal. Zn + (WffN0 3 + Aq) = (Zn(N0 3 ) 2 + 5ff 2 + Aq) + N 2 0. [156] Nitrous oxide is a colorless gas (Sp. Gr. 22), which, by pres- sure and cold, may be condensed to a colorless liquid, boiling at 88 and freezing by its own evaporation at about 101. It is less stable than nitric oxide. It is decomposed by heat, and all combustibles burn in it with nearly the same readiness and brilliancy as in pure oxygen gas. When pure, it can be in- haled without danger, and is much used as an anaesthetic agent. With some patients it produces at first a transient intoxication, attended at times with uncontrollable laughter. Hence the pop- ular name of laughing-gas. It manifests no tendency to unite with more oxygen. It is soluble in water to a limited extent, and to a much greater degree in alcohol. At one volume of water dissolves 1.3 volumes, and one volume of alcohol 4.18 volumes, of this gas. 165. Oxychlorides of Nitrogen. If in reaction [111] no gold or other metal is present to unite with the chlorine evolved by the aqua-regia, this element combines with the nitric oxide set free at the same time, and besides chlorine gas we obtain, as products of the reaction, two compounds which we may call ni- trous oxychloride and nitric oxydichloride respectively. Aq) + NOCl + Cl-Cl [157] 240 NITROGEN [166. or (2HNO S + GffCl + Aq) = (4Hi + Aq) + 2NOC1 2 + Cl-d [158] During the early stages of the decomposition of aqua-regia the second of the two reactions prevails, and the product is nearly pure NO Ol z '> Dut as tne process advances this becomes more and more mixed with NO 01 At the ordinary temperature both substances are gases, NO Cl having an orange, and NO C1 2 a deep lemon-yellow color ; but by cold they may be readily condensed to liquids, which have a red color and resemble each other in odor and aspect. They have neither acid nor basic relations, but are readily decomposed by chemical agents into nitric oxide and chlorine ; and by mixing together these two gases the same or similar compounds may be reproduced. By the action of dry hydrochloric acid on anhydrous nitric perox- ide, still a third compound is formed, which has the symbol N0% Cl, and resembles the other two. The last compound may also be obtained by mixing phosphoric oxytrichloride with plumbic nitrate. 3Pb=Of(N0 2 ) 2 +2POCl 3 =Pl> s W) 2 + 2fff0 2 =S0 2 = 2Ca-0 2 =S0 2 -f When dried, ff 4 ,CaWi=(PO) 2 = Ca= 2 =(P0 2 ) 2 3Ca=0 2 =(P0 2 ) 2 + C 10 = Ca s W^(PO 181. Common Phosphorus, P 4 , when perfectly pure, is a 182.] PHOSPHORUS. 251 colorless, transparent solid, but ordinarily it has a yellowish tint, and is only translucent. At low temperatures it is brittle, but at 20 it is soft like wax. It melts at 45, and boils at 290. Sp. Gr. of solid 1.83. Insoluble in water, slightly soluble in alcohol and ether, still more soluble in both the fixed and vola- tile oils, and very soluble in sulphide of carbon or chloride of sulphur. Phosphorus is by far the most combustible of the chemical elements. It takes fire below the boiling point of water, and slowly combines with the oxygen of the air at the ordinary temperature. If in not too small quantity, the heat evolved by its slow combustion soon raises the temperature to the point of ignition, and it is therefore always preserved under water or alcohol. The product of the rapid combustion is phosphoric anhydride ; that of the slow combustion in moist air chiefly phosphorous acid. Exposed to the air in the dark, phosphorus emits a greenish light, and hence its name, from (j>a>s (f>opbs ; but this phosphorescence, though always accompany- ing the slow combustion, does not appear to be necessarily con- nected with it. Sticks of phosphorus, when kept under water, become covered after some time with a white crust, which con- sists of a mass of microscopic crystals ; and in the course of many years these crystals may acquire considerable size. The form of the crystals is the regular dodecahedron of the first sys- tem (Fig. 6), and crystals of the same form are obtained by slowly evaporating the solution of phosphorus in sulphide of carbon. 182. Red Phosphorus. Exposed to the direct sunlight under water, phosphorus becomes covered with a red coating, and the same red modification is formed in great abundance when ordinary phosphorus is heated for several hours to a temperature below 235 and 250 in an atmosphere of carbonic anhydride, or some other inert gas. Red phosphorus is insol- uble in carbonic sulphide, and is thus easily separated from the portion which has not been changed. Iodine facilitates the con- version, and if a solution of phosphorus in sulphide of carbon, containing a little iodine, is sealed up in a glass flask and heated for some time to only 100, red phosphorus is slowly precipi- tated. As usually obtained, red phosphorus is an amorphous powder ; but it has been crystallized, and it appears that the crystals are rhombohedrons belonging to the third system. 252 PHOSPHORUS. [ 183. Hence phosphorus is dimorphous, and in this respect resembles arsenic and antimony. The Sp. Gr. of red phosphorus is about 2.1. It undergoes no change in dry air, and may even be heated to 250 without taking fire ; but at a slightly higher temperature it changes back to common phosphorus and in- flames. The specific heat of red phosphorus is 0.1700, while that of the ordinary variety is 0.1387 ; and hence, as we should anticipate, this reverse change is attended with the evolution of heat. Moreover, the calorific power of common phosphorus is to that of red phosphorus in the proportion of 1.15 to 1. In general, red phosphorus is less active, chemically, than common phosphorus, and is not, like the latter, poisonous. Both varie- ties are largely used in the manufacture of friction-matches. The red variety is not used in making the match itself, but only in the preparation of the surface on which it is rubbed. 183. Phosphorus and Oxygen. The following compounds of phosphorus with oxygen, or with both oxygen and hydrogen, have been observed : Phosphorous Anhydride P^O^ Phosphoric Anhydride P^.0^ Hypophosphorous Acid H-Q-(P^O,H), Phosphorous Acid ff 2 =Of(P=0,H), Orthophosphoric Acid Ify0 3 =(P=0), Metaphosphoric Acid H~0-(P^ 2 ) , Pyrophosphoric Acid HfOf(P=OfP), Sodium salt of Hexabasic Acid Na 6 W 6 l(P= 2 =P-= 0/P-- 2 =P), Sodium salt of Dodecabasic Acid Na^ 0^ *n. (P IQ 19 ) . The relations of these compounds will be best understood by taking as our first starting-point an assumed compound, JI 5 i0 5 ^P, in which the atoms of phosphorus are united to hy- droxyl by all their five affinities. Ortho 1 and metaphosphoric acids are now simply the successive anhydrides of this pent- atomic acid. Starting next from the double molecule of our assumed compound, the following anhydrides are possible : ff^O^P,, 3d. 1st. J7 8 viii0 8 viii(p-0-P), 4th. 2d. H 6 W^(P=OfP), 5th. 1 The assumed pentatomic acid is by some called orthophosphoric. 186.] PHOSPHORUS. 253 Of these possible compounds the second and fourth are identical with ortho and meta-phosphoric acids, of which the symbols rep- resent two molecules, while the third and the fifth are the pyro- phosphoric acid and phosphoric anhydride of the above list. The first anhydride of this series has not yet been observed. In like manner we may take three, four, or more molecules of the first compound, and deduce from each of these condensed molecules another series of anhydrides ; but of the infinite num- ber of compounds thus possible, only the salts of the hexabasic and dodecabasic acid mentioned above are known. This scheme, however, does not include hypophosphorous and phosphorous acids, which have an anomalous constitution. They may be regarded as orthophosphoric acids in which atoms of hydroxyl (two in the first case and one in the second) have been replaced with atoms of hydrogen. The molecules of both acids contain three atoms of hydrogen, but the first is only monobasic and tf ' second dibasic ; and this fact illustrates an important principle. In ail the so-called oxygen salts, only those atoms of hydrogen are replaceable by metallic atoms, which are united to the neg- ative radical by a vinculum consisting of an equal number of oxygen atoms. The hydrogen and oxygen atoms thus paired are equivalent to so many atoms of the radical hydroxyl [70]. Phosphorous anhydride is the only one of this class of com- pounds in which the phosphorus atoms are not quinquivalent. 184. Phosphoric Anhydride is readily prepared by burning phosphorus in dry air. It is an amorphous white powder, hav- ing an intense affinity for water, and is sometimes used as an hygroscopic agent. It hisses when dropped into water, and gives a solution of 185. Metaphosphoric Acid. This compound is obtained as a vitreous solid (glacial phosphoric acid) by heating orthophos- phoric acid to redness. Its solution coagulates albumen, and one molecule of the acid saturates only one molecule of sodic hydrate. By boiling the solution the acid loses its power of coagulating albumen, and acquires greater capacity of satura- tion, having changed into 186. Orthophosphoric Acid. This is much the most im- portant of these compounds. It is readily prepared by boiling phosphorus in not too strong nitric acid, and evaporating the liquid product to the consistency of syrup. The ordinary phos- 254 PHOSPHORUS. [ 187. phates are all salts of this acid, and one molecule of acid is ca- pable of saturating three molecules of base. Many of the phos- phates are thus constituted, and these are, theoretically (38), the neutral salts ; but evidently we may also have for each base two acid salts. Thus in the case of soda we have ff,Na 2 =-0 8 -=PO, H*Na=- 8 =-PO ; so in the case of lime we have H 2 , Ca 2 l 6 I(PO) 2 , ff 4 , GalO,l(PO) Here, as in many other cases, a diatomic metal serves to solder together two molecules of the acid. 187. Common Sodic Phosphate, ff,Na 2 =0 3 =PO . 12^0, is by far the most important of the salts which phosphoric acid forms with the bases previously studied. It is, moreover, the chief soluble salt of the acid, and is much used in the laboratory as a reagent. It is also highly interesting, theoretically, be- cause it illustrates by its reactions the relations we have just been considering. A solution of the salt is neutral to test-paper, but when mixed with a solution of argentic nitrate, also per- fectly neutral, we obtain a yellow precipitate of argentic phos- phate, Ag^O^PO, and at the same time the solution becomes acid. Heat now the salt to 120, and it will be found that it loses twelve molecules of water ; "but when the dried mass is dissolved in water, and the solution evaporated, we obtain crystals of the same form (rhombic prisms, Fig. 45) and composition as before, and which give again the same reaction. But heat the same salt to a red heat, and we have a wholly different result. The salt has lost thirteen molecules of water ; the residue is less soluble than before. On evaporation we obtain crystals of a different form and composition (Na 4 P 2 7 . KX/ZjO), and the solution, after precipitation with argentic nitrate, although pre- viously alkaline, becomes neutral. Moreover, the precipitate, instead of being yellow, is white, and has the composition 188. Microcosmic Salt. H,NH*Na=-OfPO . H 2 0. If we mix together hot saturated solutions of common sodic phosphate and sal ammoniac, we obtain the following reaction : H 2 + Aq) = . 4ff 2 + (NaCl + Aq). [180] 189.] PHOSPHORUS. 255 As the solution cools, the microcosmic salt crystallizes out, leav- ing sodic chloride in solution. This salt, when ignited, loses both its water and its ammonia, and the sodic metaphosphate, which remains, fuses into a colorless glass at a red heat. This glass acts very much like borax, and is used in the same way as a blow-pipe flux. 189. Phosphorus and Hydrogen. When phosphorus is boiled with strong potash or soda lye, or with milk of lime, a gas is evolved, called phosphuretted hydrogen, which on com- ing in contact with the air inflames spontaneously. This gas consists almost entirely of the compound ff 3 P ; and when soda is used, the reaction by which it is formed is as follows : Aq) = [181] This crude product, however, is not pure ff 3 P ; for when it is passed through a tube cooled by a freezing mixture it deposits a small amount of a very volatile yellow liquid, which has been found to be a second compound of phosphorus and hydrogen, HPft and has the property of inflaming spontaneously to a high degree. Moreover, the gas thus treated loses its power of self- lighting, and this quality in the crude product is evidently due to a small admixture of the liquid substance. When exposed to the direct sunlight, the liquid compound gives off H S P, and deposits a yellow solid, which is a third compound of phospho- rus and hydrogen, H Z P. 5ff 4 P 2 = HJ> + 6# 3 P. [182] This same solid compound is deposited on the sides of the ves- sel when the crude product first mentioned is exposed to the sunlight, and in this case, also, the gas loses its self-lighting power. There are, then, three distinct compounds of hydrogen and phosphorus. But of these the first is by far the most impor- tant, and the other two are chiefly interesting as explaining the singular phenomena just noticed. The compound H Z P is the analogue of ammonia gas, and differs from it in composition only in containing in the place of nitrogen the next lower element of the same chemical series. But the differences in properties 256 PHOSPHORUS. [190. are so great that to superficial observation it would seem as if there were no similarity between the two compounds. Thus phosphuretted hydrogen is insoluble in water, except to a very slight degree, and does not unite with any of the common acids. A more careful study, however, discovers very marked resem- blances, for it appears that H 3 P does unite with HBr and HI to form the compounds (HP)Br and (H 4 P)I, which resemble and (H 4 N)I. Moreover, the atoms of hydrogen in may be replaced by methyl, CH%, ethyl, C 2 H 5 , and other radicals yielding compounds similar to the tertiary amines, which we call the phosphines ; and it further appears that the phos- phines have a strong basic character, combining with all the ordinary acids to form a class of salts corresponding to those of the compound ammonias, and yielding also, by reactions similar to [177] and [178], compounds analogous to the hydrates of the ammonium radicals. There are, however, even here, dif- ferences to be noted, quite important, because they point to a tendency in the series which develops into a marked character in the next element, arsenic. The compounds trimethylphos- phine, (Cff 3 ) 3 P, and triethylphosphine, (C 2 ff 5 ) 3 P, not only combine with acids, but they also unite as diatomic radicals either with two atoms of chlorine, bromine, or iodine, or with one atom of sulphur or of oxygen. Thus are formed the crys- talline compounds ( 2 ff 5 ) s P- C1 2 , ( 2 ff 5 ) 3 P- 0, ( 2 ff 5 ) 3 P-S. Lastly, a compound has been described corresponding to liquid phosphuretted hydrogen, and having the symbol (Cff s ) 2 P, which, like the former, is both liquid and spontane- ously inflammable. It has, moreover, the properties of a feeble basic radical, and in the chemical series finds its analogue on one side in the radical amidogen, and on the other in the re- markable compound kakodyl (198). 190. Phosphorus and Chlorine. Phosphorus combines with chlorine in two proportions. When the phosphorus is in excess, phosphorous chloride, P07 3 , is formed, which is a fuming, colorless liquid. When, on the other hand, the chlorine is in excess, we obtain phosphoric chloride, PCI& a white crystalline solid. Both compounds are decomposed by water, and when the water is in large excess the reactions are as follows : 192.] ARSENIC. 257 PC/ 3 + (3ff 2 0+Aq) = (H/0./PffO + 3IfCl + Aq). [183] PC1 5 + (ff 2 + Aq) = (H^O^PO + 5HCl + Aq). [184] If in the last reaction water is not present in sufficient quantity, we obtain quite a different result. PC1 5 + ff 2 = PC1 3 + ZffCl. [185] The first of the three reactions is important, because it gives an easy method of preparing phosphorous acid, and the last has a special interest because it illustrates a valuable application of phosphoric chloride. This reagent gives us the means of re- placing an atom of oxygen with two atoms of chlorine, and (as is illustrated not only by [185], but also by [34]) this simple change frequently gives a clew to the molecular constitution of a chemical compound. The compound PC1 3 is called phos- phoric oxychloride, and there is also a phosphoric sulphochlo- ride, PC1 3 S. Both are fuming, colorless liquids. The last, when heated with a solution of caustic soda, gives the following remarkable reaction : (PG1 3 S + [186] 191. ARSENIC. As = 75. Trivalent or quinquivalent. One of the less abundant elements, but in minute quantities quite widely distributed. Found native, and in combination both with sulphur and with many of the metals. The most abundant of the native compounds is Mispickel, FeS 2 . FeAs r # and by simply heating this mineral in a closed vessel the ele- mentary substance is easily obtained. 2Fe 2 As 2 S 2 = 4FeS+Ast. [187] It is also prepared by subliming a mixture of arsenious anhy- dride and charcoal. 2As 2 3 + 3 O = As 4 + 3 CO? [188] 192. "Metallic Arsenic" As 4 , has a bright, steel-gray lustre, and conducts electricity with readiness. It is, therefore, fre- quently classed among the metals, and hence the trivial name. Q 258 ARSENIC. [193. On the other hand, it is very brittle, and closely allied in all its chemical relations to the class of elements with which it is here grouped. Arsenic, like phosphorus, is dimorphous, and may readily be crystallized both in octahedrons of the first system, and in rhombohedrons of the third. Corresponding to these two forms are two allotropic modifications, distinguished also by differences of density and of other physical qualities, although these differences are not so marked as those between the two states of phosphorus. In its ordinary condition, arsenic, when heated out of contact with the air, begins to volatilize at about 130 without previously melting, and it cannot be brought into the liquid condition except under pressure. The Sp. Gr. of the solid is 5.75, and that of the vapor referred to air 10.6. Heated in contact with the air, it burns with a pale blue flame, and the product of the combustion is arsenious anhydride, As 2 3 . It cannot, however, maintain its own combustion, and goes out unless the temperature is kept above the point of ignition by external means. At the ordinary temperature it rapidly tar- nishes in the air, and, when in large bulk, the oxidation is some- times sufficiently rapid to ignite the mass. Serious accidents have originated from this cause. The burning of arsenic is attended with a peculiar odor resembling garlic, which is very characteristic. It is insoluble in water or any of the ordinary solvents. 193. Arsenic and Oxygen. Arsenious Anhydride. As 2 3 . The white powder which is formed by the burning of arsenic is the most important and the best known of the compounds of this element. It is obtained in very large quantities as a sec- ondary product in the roasting of many metallic ores. Like ar- senic itself, this compound is dimorphous, and may be obtained crystallized both in octahedrons of the first system and in rhom- bic prisms of the fourth. Moreover, when freshly sublimed, it appears as a vitreous solid, and in this third state it is three times more soluble in water than in the crystalline condition. Common white arsenic is only sparingly soluble in water, but by continuous boiling with water this crystalline condition is changed into the vitreous (or colloidal) modification, and a much larger amount enters into solution. This change, however, is not permanent, and after long standing the excess before dis- solved is all deposited in octahedral crystals. When digested 194.] ARSENIC. 259 with the mineral acids, or with aqna ammonia, white arsenic dissolves still more readily than in water, but on standing, the larger part of the As 2 3 is deposited from these solutions in oc- tahedral crystals as before, and by evaporation the whole may be thus recovered, indicating that no stable compound had been formed. 194. Arsenites. Arsenidus acid, ff 3 =0 3 =As, is only known in solution; and indeed there is no evidence that As 2 3 forms with water a definite hydrate. There are, however, several well-defined arsenites. Potassic Arsenite (Fowler's Solution) HK= 3 =As, Cupric Arsenite (Scheele's Green) JI,Cu=0 3 =As, Argentic Arsenite (Brilliant Yellow) Ag 3 =O^As. The first is obtained by adding to a solution of caustic potash an excess of As 2 3 , and the last two are precipitated when a solution of the first is added to the solution of a silver or copper salt. Arsenious anhydride is a most violent mineral poison. It is also a powerful antiseptic, and is much used in packing hides and for preserving anatomical preparations. 195. Arsenic Acid, JT/0 3 =AsO, is readily obtained by treat- ing As 2 3 with nitric acid. As 2 3 + 2#- 0-N0 2 + 2ff 2 = 2ff 3 -=0 3 zAs + N 2 3 . [189] On evaporating the resulting solution under regulated condi- tions of temperature, definite hydrates, all white solids, may be obtained corresponding to the three conditions of phosphoric acid. But they differ from the latter in that when dissolved in water they all yield solutions having the same properties and containing the same tribasic acid. From this acid a large num- ber of arseniates may be prepared. The following,, all of which may be obtained in well-defined crystals, are isomorphous with the corresponding phosphates : .ff 2 0, H^ 3 =-As 0. These salts may be all rendered anhydrous by heat, and from the acid salts products may be thus obtained corresponding in 260 ARSENIC. f196. composition to the meta and pyro-phosphates ; but when dis- solved they reunite with water and become tribasic. Hence aqueous solutions of all these arseniates give, with argentic ni- trate, the same precipitate, Ag 3 =0 & =AsO. This precipitate has a brick -red color, and enables us to distinguish an arseniate from an arsenite. It is not formed, however, if an excess of ammonia or a free acid is present. On adding a solution of magnesic sulphate containing an excess of ammonia to a solu- tion of an arseniate, a precipitate is obtained, (H 4 N),Mg=0 3 = AsO . 6^0, which very closely resembles the corresponding precipitate obtained with a phosphate under the same conditions. 196. Arsenic Anhydride, As 2 5 , is obtained as a white amorphous solid when arsenic acid is heated nearly to redness. At a higher temperature it fuses and is decomposed into As 2 3 and 0=0. 197. Arsenic and Hydrogen. There are two compounds, a solid, HAs z , and a gas, H 3 As. The gas is formed whenever hydrogen, in its nascent condition, comes in contact with a com- pound of arsenic, and its formation gives us one of the most delicate means of detecting the presence of arsenic in cases of poisoning. Thus, when arsenious acid is introduced into an apparatus evolving hydrogen, we have the reaction ff s =-0 3 =-As + SU-ff= 3ff 2 + H 3 As. [191] As thus obtained, however, the gas is more or less mixed with hydrogen. It may be obtained pure by the following re- action : Sn 3 As 2 + (KffCl+ Aq) = (3Sn O1 2 + Aq) + 231^8. [192] It is a colorless gas (Sp. Gr. 33.9), which may be condensed to a liquid boiling at 30. It has a repulsive odor, and is exceed- ingly poisonous. It burns in the air, forming As 2 3 and H 2 0. In the interior of the flame the combustion is imperfect, and hence the flame deposits on a cold surface, which is pressed upon it, a brilliant mirror of metallic arsenic. The gas is de- composed when passed through a red-hot glass tube, and a sim- ilar mirror is formed on the inner surface in front of the heated portion. By careful experimenting these mirrors may be ob- tained with hydrogen gas, which contains only a mere trace of 198.] ARSENIC. 261 arsenic. When arseniuretted hydrogen is passed into a solu- tion of argentic nitrate, we obtain the following remarkable reaction : H 3 As + SAg-O-NO, SJf-0-N0 2 + ff 3 =-0 3 -=AsO. [193] 198. Compounds with the Alcohol Radicals. Arsenic forms compounds analogous to the amines, phosphines, and their de- rivatives. The compounds trimethyl-arsine, (CH 3 ) 3 As, and tri- ethyl-arsine, ( C 2 H 5 ) 3 As, do not, however, like the corresponding phosphines, combine directly with HCl and the similar acids, but they do unite very readily with two atoms of chlorine, bro- mine, or iodine, or with one atom of oxygen or sulphur, forming such compounds as (CH^As-Cl^ (C 2 ff 5 ) B As=r 2 , (Cff 3 ) 3 As=0, (O 2 H,} 3 As-S. They also unite with the iodides and bromides of the alcohol radicals, forming such compounds as (Cff 3 ) 4 As-I or (CvH^As-Br, and from these may be derived basic compounds analogous to ammonic hydrate, like (CH^As-0-H or (C 2 H 5 ),As-0-H. But by far the most important of this class of compounds are those which may be regarded as derived from a remarkable radical substance, (Cff 3 ) 2 As-(CH 3 ) 2 As, called kakodyl, which is formed when a mixture of arsenious anhydride and potassic acetate is submitted to distillation in a closed retort A crude complex product is thus obtained, from which the radical sub- stance may be subsequently separated. Pure kakodyl is a spontaneously inflammable, exceedingly fetid, fuming liquid, resembling in many respects the corresponding compound of phosphorus. It enters into direct combination with several of the elements, and is one of the best defined of the radical sub- stances. Representing the group of atoms (Cff 3 ) 2 As by Kd, the symbols of a few of the more characteristic compounds will be as follows : 262 ARSENIC. [198. Kakodyl Ed-Ed, Kakodylous Oxide Kd z O, Kakodylic Oxide Kd 2 0^ Kakodylic Acid H- 0-KdO, Kakodylic Anhydride ? Kd 2 & , Kakodylous Sulphide Kd^S, Kakodylic Sulphide Kd& Sulpho-kakodylic Acid H-S~KdS, Sulpho-kakodylic Anhydride Kd 2 S 8l Kakodylous Chloride, Bromide, or Iodide KdCl,KdBr, or Kdl, Kakodylic Chloride, Bromide, or Iodide Kd Cl 3 ,Kdr 3 , or Kdl* The mutual relations of the different compounds studied in this section are illustrated by the following scheme, which includes all the known compounds of arsenic with methyl (Me = Cff 3 ) and chlorine : Type H 3 N. Type CtH^N. Cl,Me,Me -As, Cl, Cl,Me,Me,Me ~=As, Cl, Cl,Me^As, Cl, Cl, Cl,Me,MelAs, Gl, Cl, CteAs, Cl,Cl, Cl, Cl,MelAs. By direct union with C7 2 , the compounds of the first column may be changed into the compounds of the second column on the next lower line, and the compounds of the second column, when heated, break up into MeCl, and the corresponding com- pound of the first column on the same line. Moreover, the first compound of the first column unites directly with MeCl to form the first compound of the second column. Besides the compounds mentioned above, this scheme includes another class of compounds, which may be regarded as formed from the rad- ical (Cff^As (corresponding to HN), not yet isolated. Such are (Cff s )As=I 2 , (Cff 3 )As=0, They are called arsenmonomethyl iodide, oxide, &c., and the last, arsenmonomethylic acid. It is evident that the atomicity of the radical is not the same in all the compounds. 203.] ARSENIC. 263 199. Compounds with Chlorine, Bromine, and Iodine. These elements unite directly with arsenic, but only in one proportion forming AsCl& AsJSr s , and AsI 3 . The first is a liquid, the last two are volatile solids at the ordinary tempera- ture of the air. They are all decomposed by water. 2AsBr s + 3ff 2 = As 2 3 -f ZHBr. [194] 200. Compounds with Sulphur. Arsenic and sulphur may be melted together in all proportions. They also form several distinct compounds. The most important are 201. Realgar, As 2 S 2l a brilliant red solid, much used as a pigment, and found in nature well crystallized. 202. Orpiment, As 2 S 3 , a brilliant yellow solid, also used as a paint. Formed whenever arsenic is precipitated from its solu- tions by H 2 S. Also found crystallized in nature. Soluble in ammonia and caustic alkalies, and precipitated from such solu- tions by acids. 203. Arsenic Sulphide. As 2 S 5 . Only known in combination. The last two compounds are " sulphur anhydrides," and form with the sulphur bases a very large and important class of sul- phur salts, many of which are native compounds and important metallic ores. The following reactions will illustrate the forma- tion of compounds of this class : As 2 S 3 + (1K-0-H+ Aq) = fAs + H 2 + Aq), [195] (ff,Na 2 -=S 3 =-As + 3ff 2 + Aq). [196] Sulpho-arsenites. Proustite, Hexagonal Ag^S^As, Tennantite, Isometric [Cu^lS^lAs^ . FeS, Sartorite, Orthorhombic Pb=S 2 =As z S^ Dufrenoysite, Orthorhombic Sulpho-arsem'ates. Enargite, Orthorhombic 264 ANTIMONY. [204. These symbols should be compared with those of the corre- sponding compounds of antimony, in connection with which their mutual relations will be explained. 204. Characteristic Reactions. The importance of proving the presence or absence of arsenic in cases of suspected poison- ing has led to a most careful study of the characteristic reac- tions of this element, and hence our knowledge on these points is unusually accurate and full. The most striking of these re- actions have already been given. Further details or descrip- tions of methods by which arsenic, even when in minute quan- tities, may be detected and distinguished from antimony lie beyond the scope of the present work. 205. ANTIMONY. Sb = 122. Trivalent or quinquiva- lent. This element is less abundantly distributed than arsenic, although found in similar associations. The most abundant na- tive compound is the gray sulphide (Antimony Glance), Sb. 2 S 3 , which occurs not only in a pure state, but also in combination with other metallic sulphides. Antimony is sometimes, although rarely, found in the metallic state, and likewise in combination with oxygen. 206. Metallic Antimony, Sb?, is most readily extracted from the native sulphide by smelting the ore with metallic iron. Sb 2 S 3 -f 3Fe = 3FeS + Sb* [197] It is also extracted by first roasting the ore, 2Sb. 2 S 3 + 90=0 = 2Sb 2 3 -f QS0 21 [198] and then melting with charcoal and sodic carbonate. The last converts into oxide the small portion of the sulphide which es- caped oxidation in the roasting process, fOO = Sb 2 3 + 3Na 2 S + 3 C0 2 , [199] and the charcoal reduces the oxide to metallic antimony, Sb 2 3 + 30 = Sb, + 3 00. [200] By oxidizing the crude metal with nitric acid, and again re- ducing with charcoal, the antimony may be obtained in a pure condition. 206.] ANTIMONY. 265 Antimony is closely allied to arsenic, but possesses the prop- erties of a metal to a still higher degree. It has a bright me- tallic lustre, which it preserves in the air. It has a high Sp. Gr. (6.7), and conducts heat and electricity with facility. Its conducting power, however, is inferior to that of the perfect metals, and, moreover, it is very brittle and may be readily re- duced to powder. It has also a highly crystalline structure, and like arsenic it may be obtained crystallized both in rhom- bohedrons of the third system, and in octahedrons of the first. The first is the common form, and lumps of the metal may some- times be cleaved parallel to the rhombohedral planes, which are always more or less evident on the fractured surface. Antimony melts at 430, and it volatilizes, but only very slowly, at a full red heat. The melted metal, when heated in the air, slowly ox- idizes, and before the blow-pipe it burns, the product of the oxidation being in either case Sb 2 3 . Antimony is only very slightly acted on by pure hydrochloric acid, even when concen- trated and boiling ; but on the addition of a very small amount of nitric acid the metal dissolves easily, forming a solution of Sb 2 + (GHCl + 6HN0 3 + Aq} = (2SbCl 3 + QIf 2 + Aq) -f 6N0 2 . [201] With the aid of heat it dissolves in strong sulphuric acid. Sb 2 + Sff 2 S0 4 = Sb 2 W 6 l(S0 2 ) 3 + 3S0 2 + QH 2 0. [202] Nitric acid, when in excess, converts the metal into a white powder insoluble in the acid (chiefly Sb 2 4 ). If, however, the nitric acid contains a little hydrochloric acid, the product is metantimonic acid. 2H-0-Sb0 2 + H 2 + N 2 3 + 2NO. [203] Lastly, antimony dissolves readily in a mixture of tartaric and nitric acids, which is one of the best solvents of the metal. Metallic antimony is chiefly used in the arts to alloy with other metals, to which it imparts a greater hardness and durability. Type-metal is an alloy of four parts of lead and one of antimony. This alloy expands in " setting," and therefore takes a sharp 12 266 ANTIMONY. [207. impression of the mould in which it is cast ; and this property, as well as the hardness, renders type-metal peculiarly suitable to the important use to which it is applied. Britannia metal, an alloy of brass, antimony, tin, and lead, much used as the base of plated silver-ware, also owes its hardness and durability to the antimony it contains. 207. Antimony and Chlorine. Antimonious Chloride. SbCl 3 . A solution of this compound is readily obtained either by [201] or by dissolving the native sulphide in hydrochloric acid. On evaporating the excess of acid, and distilling the resi- due, the chloride is obtained as a white crystalline solid. It is deliquescent, very volatile, and melts so readily (72) that it was formerly known as butter of antimony. The Sp. Gr. of its vapor, as found by experiment, is 1 12.7. Antimonious chlo- ride may also be obtained by distilling antimony or antimonious sulphide with mercuric chloride, and al^o by distilling a mixture of antimonious sulphate wiih common salt. [204] Sb 2 S 3 + Sffg C1 2 = 3HgS + 2 ^bOl 3 . [205] = 3Na 2 =0 2 =S0 2 + 2SbCl 3 . [206] Antimonious chloride is decomposed by water, forming an insoluble oxychloride and hydrochloric acid. Hence the solu- tion obtained by [201] becomes turbid when diluted with water. The presence of tartaric acid in sufficient quantity prevents the decomposition, and a solution of this acid dissolves the oxychlo- ride when formed. By long-continued washing the oxychloride may be converted into antimonious oxide. (SbCl, + ff 2 + Aq) = SbOCl + (2HCI + Aq). [207] 2SbOCl+ (H 2 + Aq) = &k 2 3 + (2ffCl + Aq). [208] Antimonious chloride combines with the chlorides of the metals of the alkalies and of the alkaline earths, and forms sol- uble crystalline salts. Hence it may be mixed with concen- trated solutions of these chlorides, as also with strong hydro- chloric acid, without undergoing decomposition. The following are the symbols of a few of these double chlorides, which are best regarded as molecular compounds : 209.] ANTIMONY. 267 1 JJ210, 1 3KCl.SbCl 3 , 2KCl.SbCl 9 , . SbCl 3 . 208. Antimonic Chloride, Sb Cl& may be formed by passing chlorine gas over Sb C1 3 , or by acting on the metal with an ex- cess of the same reagent. It is a volatile, fuming liquid, which readily parts with two fifths of its chlorine, and is therefore sometimes used, like PC1 5 , as a chloridizing agent. It is at once decomposed by water. With only a small quantity it forms an oxychloride (compare [185]). ff 2 o + Sb C1 5 = 2HCI + Sb C1 3 0. [209] With an excess of water, either ortho-antimonic acid or pyro- antimonic acid results. SbCl s + 4# 2 = HfOfSbO + 5HCI, [210] or 2SbCl 5 + 7ff 2 = H 4 W^Sb 2 B + WHCL [211] The presence of tartaric acid prevents these reactions. By the action of H 2 S on Sb C1 5 a sulpho-chloride may be formed. Sb C1 5 + H 2 S = Sb C1 3 S + 2HCL [212] A bromide of antimony, SbBr 3 , and an iodide, Sbl& are readily formed by the direct action of these elements on the metal, but no penta-bromide or iodide has yet been obtained. They are both fusible and volatile solids, and when acted on by water are converted into SbBrO and SblO. The correspond- ing fluoride dissolves in water without decomposition, and forms with the alkaline fluorides a number of double salts. ZNaF. SbF 3 , 2(ff 4 N)F. SbF^ KF . SbF 3 . 209. Antimony and Oxygen. Antimonious Oxide. Sh 2 3 . This compound, already mentioned as a product of the direct oxidation of antimony, may, like As 2 0& be obtained crystallized both in octahedrons of the first system or in rhombic prisms of the fourth, and on this difference of form depends the distinc- 1 These symbols are thus written to show the relations of the compounds. To be strictly accurate they should be doubled. 268 ANTIMONY. [209. tion between the two minerals Senarmontite and Valentinite, both of which consist of this same substance. The oxide is most readily prepared artificially by pouring a solution of Sb C1 3 [201] into a boiling solution of sodic carbonate. fCO + 2SbCl s + Aq) = Sfo 2 O 3 + (ZNaCl + Aq) + 3* [213] Antimonious oxide acts both as a basic and as an acid anhy- dride, although the first is by far its most marked character. It is but very slightly soluble in water. When the solution of SbCl 3 -is poured into a cold solution of sodic carbonate, we have the reaction, (BNofOfCO + 2SbCl 3 + H 2 + Aq) = 2H O fcfoO + (QNaCl + Aq) + 3 2 , [214] and the product may be regarded as metantimonious acid, for it dissolves in caustic alkalies and forms definite, although very unstable, salts. On the other hand, the oxide dissolves in fum- ing sulphuric and fuming nitric, as well as in hydrochloric acids, forming crystalline salts, in which the antimony plays the part of a basic radical. The most important salt of this class is that formed by dis- solving Sb 2 3 in a solution of acid potassic tartrate (cream of tartar). This compound is very much used in medicine as an emetic, and hence the trivial name tartar emetic. Tartaric acid is tetratomic, but only bibasic (43), and we have the following series of compounds : Tartaric Acid H 2 , Hf 4 i( C 4 ff 2 <9 2 ), Neutral Potassic Tartrate K 2 , HfOf( C 4 ff 2 2 ), Acid Potassic Tartrate K,H, H 2 =0^( O 4 H 2 6> 2 ), Tartar Emetic (crystallized) K,SIO , " after heating to 200 It will be noticed that in forming tartar emetic the radical SbO of the compound ff-O-SbO takes the place of one atom of basic hydrogen, which still remains unreplaced in cream of tartar. On heating the crystallized salt to 100 it gives up its 210.] ANTIMONY. 269 water of crystallization. At 200 it gives off an additional atom of water, formed at the expense of the oxygen in the rad- ical just named and of the two atoms of hydrogen distinguished as negative in the acid; and it will be seen that, in the anhydrous salt thus obtained, one atom of antimony takes the place of three typical atoms of hydrogen in tartaric acid. Compounds similar to tartar emetic may be made in a similar way with the oxides of arsenic, bismuth, and uranium. Their symbols differ from that of tartar emetic only in having the radicals As 0, As 2 , BiO, or UO, in place of SbO, and they undergo a similar de- composition when heated. Compounds of the same class may also be obtained with other anhydrides than those of the group of elements we are now studying (as Fe^0 z Cr 2 B , B 2 3 , &c.), and when it is further added that the potassium in these com- pounds may be replaced by other univalent radicals, or even by bivalent radicals soldering together two molecules of the ordi- nary type, it will be seen that a very large number of such salts are possible. Lastly, the fact that a compound has been prepared in which two of the typical atoms of hydrogen are replaced by the positive radical ethyl, while the other two are replaced by the negative radical acetyl, and the additional fact that no salt can be obtained in which all the four atoms are re- placed by a well-defined positive radical, give a strong presump- tion in favor of the formula of the tartrates adopted above. Antimonious oxide, when heated out of contact with the air, volatilizes unchanged, but under the same conditions in the air it burns like tinder, forming a higher oxide, Sb 2 4 , which is fixed, even at a high red heat. By ignition with charcoal or hydrogen, all the oxides are readily reduced to the metallic state. 210. Antimonic Acid. The reactions l^,ve already been given [203], [210], [211] by which the three conditions of this acid may be prepared. They are Metantimonic Acid H- 0~Sb 0* Orthoantimonic Acid ff s =0 3 =SbO, Pyroantimonic Acid Pyroantimonic acid may also be prepared by acidifying the solution of acid potassic pyroantimoniate mentioned below, Aq) = SbtOt + (2KCI + Aq), [215] 270 ANTIMONY. [211. but when this precipitate is dried, it loses water and changes into metantimonic acid, HfOfSbtOi 2ff-0-Sb0 2 + H Z 0. [216] The existence of orthoantimonic acid has not been as yet well established, but the other two are well known, and many of their salts have been investigated. The most interesting of these salts is obtained by fusing antimonic anhydride with an excess of potassic hydrate, and extracting the fused mass with water. An alkaline solution is obtained, containing a salt whose composition is expressed by the symbol H^K^O^ =Sb 2 3 . Thi$ solution produces a precipitate in solutions of salts of so- dium, and is sometimes used as a reagent in testing for this element. The sodic salt thus precipitated has the composition HvNa. of nitric oxide referred to air is 1.038. How does this compare with the theoretical number ? 30. When sodium is heated in a confined quantity of NO, the volume of the gas is reduced to one half, and the residue is found to be pure nitrogen. Assuming that the Sp. Gr. is known, show that this fact proves that the symbol we have assigned to the com- pound must be correct. 81. Analyze reaction [154], and show in what it differs from [133]. 32. What weight and what volume of nitrous oxide can be ob- tained from 240 grammes of ammonic nitrate ? Ans. 132 grammes, or 66.9 litres. 282 QUESTIONS AND PEOBLEMS. 33. One litre of nitric oxide gas will yield by [155] what volume of nitrous oxide ? Ans. \ litre. 34. Analyze reaction [156], and represent the two stages by sep- arate equations. 35. What evidence is given that nitrous oxide is less stable than nitric oxide ? 36. When sodium is heated in nitrous oxide no change of volume results, and the residue is pure nitrogen. The Sp. Gr. of nitrous oxide is 22. Deduce from these facts the symbol of the compound. 37. What volume of gas would a litre of nitrous oxide yield when decomposed by heat ? Ans. \\ litres. 38. What is the quantivalence of nitrogen in nitrous oxide, and what in nitric oxide ? 39. What are the relations of the oxychlorides of nitrogen to the oxides ? 40. What strong reason may be adduced for doubling the formula of nitric oxydichloride ? Would not the same principle require us to double the symbols of two of the oxides ? and what argument can you urge in favor of the symbols adopted in this book ? 41. What is the specific gravity of ammonia gas referred to air, and referred to hydrogen ? Ans. 0.591, and 8.5. 42. What would be the volume of 3.0464 grammes of ammonia gas at 273.2 and 38 c. m. ? Ans. 16 litres. 43. What weight of ammonia would be obtained from one litre of NO by reaction [160] ? Ans. 0.7614 grammes. 44. Ammonia gas may also be formed by the action of metallic zinc (when in contact with platinum or iron) on a mixture of a nitrate with a solution of potash. Write the reaction [161]. 45. In order to determine the amount of nitric acid present in a specimen of crude soda nitre, 1.000 gramme was treated as in the last reaction. The ammonia evolved was conducted into a solution of hydrochloric acid, and subsequently precipitated with platinic chloride. This precipitate weighed 2.101 7 grammes. What was the per cent of pure soda nitre ? Ans. 80%. 46. In order to obtain 10 litres of ammonia gas, how many grammes of sal ammoniac must be taken ? Ans. 23.96. 47. What volume of nitrogen would be formed by burning one litre of ammonia ? Write the reaction. Ans. ^ litre. 48. When an organic substance is heated with soda lime (a mix- QUESTIONS AND PROBLEMS. ture of caustic soda and lime), all the nitrogen present is evolved as ammonia, which may be collected in hydrochloric acid and com- bined with platinic chloride as above. In a given determination the weight of the precipitate thus obtained was 2.232 grammes. What was the weight of nitrogen in the compound ? Ans. 0.140 grammes. 49. Deduce from the results of the eudiometric experiments de- scribed on page 241 the symbol of ammonia gas. Must we know the specific gravity in order to fix the formula definitely ? 50. Show that the result of the experiment with chlorine gas confirms the formula just deduced. 51. Write the symbols of the different amines according to the plan of (29). 52. The amides may be derived from the corresponding acids through what replacement ? 53. After what two types may the symbols of the amides be written ? 54. Write the symbols of oxamic and succinamic acids after the water type. 55. Explain the meaning of the terms basic and alcoholic, as applied to the atoms of hydrogen. 56. Write the symbols of the two lactamides after the ammonia type. 57. How may the imide and nitrile compounds be regarded as constituted on the type of ammonia ? 58. The nitriles (170) may be regarded as cyanides of what radicals ? 59. Why should you anticipate that the imide compounds would have an acid, and the nitrile compounds a basic character? 60. Write the reactions which take place when acetic, benzoic, lactic, and oxalic acids combine with ammonia. 61. Write the reactions corresponding to [174 and 175], using the sodium instead of the ammonium salts. 62. What proof do you have that ammonium is a univalent rad- ical? 63. What per cent of NH 3 does the platinum salt contain ? 64. When aqua ammonia is added to a solution of ferric chloride, (Fe)Clv ferric hydrate, (Pe^Ho^, is precipitated. Write the re- action. 284 QUESTIONS AND PEOBLEMS. 65. Write two reactions in which aqua ammonia acts like a solu- tion of caustic soda, and two others in which it does not. 66. Write the reaction which takes place when a mixture of am- monic chloride with calcic carbonate is sublimed. 67. Write the reaction by which the sublimed carbonate when exposed to the air changes to the acid carbonate. 68. When a solution of ammonic chloride is boiled with a solution of caustic soda, ammonia gas is evolved. Write the reaction. 69. Write the symbols of the compounds formed by the union of the amines described in (167), both with hydrochloric acid and with water. 70. Write the symbol of the ammonium base which contains the radicals phenyl, C T 6 , amyl, C 6 H W ethyl, C 2 # 6 , and methyl, CH y 71. Show what different compounds may be formed by the dehy- dration of the acetate, lactate, and oxalate of ammonia. Phosphorus. 72. The Sp. Gr. of phosphorus vapor has been observed to be 63.8, and according to Deville no material change is effected by a temperature of 1,040. Moreover, the specific gravities of the va- pors of the following compounds have been determined, and also the per cent of phosphorus which they contain. c Per cent of Phosphorus. Phosphuretted Hydrogen, 17.1 91.18 Phosphorous Chloride, 68.4 22.55 Phosphoric Oxychloride, 76.6 20.19 Given these results of observation, show how the atomic weight of phosphorus and the molecular constitution of the elementary sub- stance may be determined. 73. The atomic weight of phosphorus, now received, was found by burning a known weight of red phosphorus in perfectly dry air, and weighing the phosphoric anhydride thus formed. Assuming that one gramme of phosphorus yields 2.2903 grammes of phosphoric anhydride, what must be the atomic weight of phosphorus? How far does this experiment modify the conclusion reached in the last, problem ? 74. How much phosphorus can be obtained from 9.3 kilos, of pure calcic phosphate by [179] ? Ans. 1.24 kilos. 75. Can you discover any connection between the difference of specific heat of the two varieties of phosphorus, and the difference QUESTIONS AND PROBLEMS 285 of calorific power ? Does the first difference wholly explain the last? 76. Show that ortho- and meta-phosphoric acid may be derived from the assumed pentatomic acid by successive dehydration, and make a table which shall exhibit the different possible derivatives of this compound. 77. Taking orthophosphoric acid as the starting-point, in place of the assumed pentatomic acid, show how the different varieties of phosphoric acid may be deduced. 78. What is the basicity of phosphorous and hypophosphorous acid's ? and what is the quantivalence of phosphorus in these com- pounds ? 79. When either phosphorous or hypophosphorous acids are heat- ed, they break up into orthophosphoric acid and PH y Write the reaction in each case. 80. Compare together the nitrates and phosphates of the univa- lent and bivalent metallic radicals. 81. Write the reaction of a solution of argentic nitrate on a solution of common sodic phosphate, and show why, after precipita- tion, the solution must be acid. 82. Write the reaction which takes place when common sodic phosphate is heated to redness. 83. Write the reaction of a solution of argentic nitrate on a solu- tion of sodic pyrophosphate. If the first salt is used in excess, why must the solution after the precipitation be neutral ? 84. Pyrophosphoric acid may be prepared by first adding plum- bic acetate to a solution of sodic pyrophosphate, when plumbic pyrophosphate is precipitated, and then decomposing this precipi- tate suspended in water with H 2 S. The solution thus obtained evaporated in vacuo gives crystals of the compound. Write the reactions. Why may not the solution be evaporated by heat in the usual way ? 85. Write the reaction which takes place when PH 3 burns. 86. Write the symbols of Trimethyl-phosphine ; Tetramethyl- phosphonium Hydrate ; Trimethyl-amyl-phosphonium Iodide. 87. Write the symbols of the platinum and gold salts of tetra- ethyl-phosphonium. (136) (147). 88. Write the symbols of Triethyl-phosphine Oxide and Triethyl- phosphine Iodide. How does the last differ from Triethyl-phospho- nium Iodide ? 286 QUESTIONS AND PROBLEMS. 89. Explain the use of PCl & as a reagent, and give illustrations of its peculiar action. 90. Can you devise a method by which the reaction [183] may be applied in the preparation of phosphorous acid ? 91. Does the reaction [186] throw any light on the constitution of phosphoric acid ? 92. What different degrees of quanti valence does phosphorus manifest in the compounds described above ? Point out the ex- amples of each condition. 93. Make a summary of the resemblances and differences be- tween the compounds of nitrogen and those of phosphorus. Arsenic. 94. Represent by graphic symbols the constitution of Mispickel, and show how it is possible that the double atom of sulphur should replace the double atom of arsenic. 95. What should be theoretically the specific gravity of arsenic vapor referred to air ? Ans. 10.4. 96. Compare together the formulas of nitrous and arsenious acids, and point out their relations to each other. Is phosphorous acid allied to the other two ? 97. Write the reactions by which cupric and argentic arsenites are formed. 98. Write the symbols of the three hydrates of arsenic acid, and give their names, following the analogy of phosphoric acid. 99. If the arseniates [190] are heated until all the water is expelled, what will be the symbols of the compounds left ? 100. Write the reaction of argentic nitrate on a solution of either of the compounds. [190.] 101. Write the reaction of a solution of magnesic sulphate and ammonia on a solution of either of the compounds. [190.] 102. State the differences between phosphoric and arsenic acids. 103. Write the reaction which takes place when H 3 As burns, both with a sufficient and with a limited supply of oxygen. 104. How may the reactions described in (197) be used to detect the presence of arsenic in a suspected liquid ? 105. How could you discover the presence of the arsenic acid formed by reaction [193] ? QUESTIONS AND PROBLEMS. 287 106. State the resemblances and differences between the amines, the phosphines, and the arsines. 107. Is the quanti valence of arsenic the same in all the com- pounds of kakodyl ? 108. In what respects does kakodyl resemble, and in what does it differ from, the corresponding compound of phosphorus ? 109. Does the relation of arsenic to chlorine differ materially from the relation of phosphorus to the same element '? 110. Write the reaction of H Z S on a solution of As 2 3 in dilute hydrochloric acid. 111. Analyze the reactions [195] and [196], and give the names of the products which are formed. 112. What would be the chemical names of the minerals Prous- tite and Enargite, and what are the corresponding oxygen com- pounds ? Define the class of compounds to which these minerals belong. Antimony. 113. Why is the molecular weight of antimony doubtful? 114. Theoretically, what weight of metallic antimony should be obtained from 1,020 kilos, of antimony glance ? Ans. 732 kilos. 115. The most common impurities of commercial antimony are arsenic, iron, copper, and lead. Why should the process described (206) tend to remove these substances ? 116. Write the reaction when antimony burns. 117. Write the reaction of nitric acid on antimony, assuming that the products are Sb a 4 and NO. 118. Write the reaction of hydrochloric acid on Sb^S s . What will prevent the resulting solution from becoming turbid when mixed with water ? 119. What should be theoretically the Sp. Gr. of SbClJ 120. Why is it probable that the double chlorides (207) are molecular compounds ? 121. When SbCl 3 is mixed with strong HCl -f- Aq, what com- pound would analogy lead us to suppose is formed in the solution ? 122. Write the reaction of chlorine gas (in excess) on antimony and on Sb C7 8 . 123. Write the reaction of water on SbBr 3 and SW 8 . 288 QUESTIONS AND PROBLEMS. 124. Write the reactions when Sb z 3 dissolves in HCl-\-Aq and H Z SO. [202.] 125. Write the reaction when Sb 2 3 dissolves in cream of tartar. 126. Write the reaction when tartar emetic is heated to 200. 127. Write the symbols of the compounds formed by dissolving As z O z , Asfiv or Bispfr in cream of tartar. 128. Write the symbols of the compounds of the same class derived from Fe z O# CV 2 3 , and B Z 0^ assuming that the radicals Fe z O z , O 2 2 , and BO replace the SbO of tartar emetic. 129. Write the reaction when to a solution of tartar emetic is added a solution of calcic chloride, knowing that the corresponding lime compound, being insoluble, is precipitated. Calcium, it must be remembered, takes the place of two atoms of potassium. 130. Write the symbol of diaceto-diethylic tartrate. 131. State the grounds for the distinction between the three sets of hydrogen atoms which tartaric acid contains. By what names do you distinguish the different sets of atoms, and what other ex- amples have been studied in which a similar distinction has been made ? 132. What is the name of the compound H 2 ,K 2 =OfSb 2 3 ? Write the reaction of a solution of this reagent upon a solution ofNaCl. 133. On boiling its solution, the acid potassic pyroantimoniate changes into a metantimoniate which does not precipitate soda. Write the reaction. 134. Write the reaction off(HCl-{-Aq) on Zn s Sb y assuming that the product is H a Sb. 135. Write the symbols of the ethyl and amyl compounds of antimony, following the analogy of the methyl compounds whose symbols are given. 136. Write the reaction of triethyl-stibine on hydrochloric acid. 137. Represent by graphic symbols the constitution of Zn a Sb t and Zn z Sb z , and give the symbols of other compounds formed after the same type. 138. Write the reaction when antimonious oxide and sulphur are melted together. 139. Write the reaction when H 2 S is passed through a solution of tartar emetic. 140. Analyze reactions [221], [222], and [223], and name the classes of compounds to which the several products belong. QUESTIONS AND PROBLEMS. 289 141. Show by symbols the relations of the assumed sulphur acids to which the several sulphantimonites are referred. 142. Explain the distinction between a chemical compound and a molecular aggregate. What different orders of combination do the facts and the atomic theory require of us to assume in such a mineral as Tetrahedrite ? 143. How are the phenomena of isomorphous substitution in the mineral kingdom to be explained in harmony with the atomic theory ? 144. Write the reaction of H^S on a solution of SbCl & . 145. Write the reaction of hydrochloric acid on the precipitate obtained by the last reaction. Bismuth. 146. Represent by graphic symbols the constitution of Bismuth Glance, and Tetradymite. 147. Compare the qualities of metallic bismuth with those of the other elementary substances belonging to the same series, consider- ing especially the crystalline form and the specific gravity. 148. Write the reaction of nitric acid on bismuth, and compare* this reaction with that of nitric acid on antimony. 149. Write the reaction of aqua-regia on bismuth. 150. Compare the compounds of the alcohol radicals with the different members of the nitrogen series of elements, and present the subject in a written form. 151. Write the different reactions by which BiCl a may be formed* 152. Write the reaction of water on BiCl# and the reaction when a solution of bismuthous nitrate is poured inta a solution of common salt. 153. Why does the presence of a large amount of HNCl prevent a solution of BiCl 3 from becoming turbid when mixed with water? 154. Compare BiCl 3 with the corresponding chlorides of the same series. What inference do you draw from the fact that the com* pound Bid^ has not been obtained ? Have any other facts been mentioned pointing to the same conclusion ? What is the evidence that bismuth is ever quinquivalent ? 155. Write the reaction when bismuth burns> or is more slowly oxidized. 156. Write the reaction when bismuthous nitrate is heated to a 13 8, 290 QUESTIONS AND PROBLEMS. low red heat. Why in this process is it important to avoid a higher temperature ? 157. Write the reaction when a solution of bismuthous nitrate (in dilute nitric acid) is poured into a solution of potassic hydrate. 158. Write the reactions when bismuthous oxide dissolves in hydrochloric, nitric, or sulphuric acid. 159. Compare the oxides and hydrates of the elements of the nitrogen series, and, by tabulating their symbols, show that their molecular constitution is analogous. Trace also the variation in their properties as you descend in the series. 160. Write the reaction of water on bismuthous nitrate, assum- ing that the basic salt whose symbol is given above, together with free nitric acid, are the resulting products. 161. If Bi 2 S s and Sb z S s are precipitated together, how may the two be separated ? 162. Write the reaction when Bi 2 S 3 is roasted in a current of air. 163. To which of the three classes of salts, distinguished on page 273, must the several sulpho-bismuthites be referred V 164. Compare the sulpho-salts of bismuth, antimony, and arsenic, and point out their mutual relations. Division IX. 225. VANADIUM. F== 51.21. Trivalent and quinqui- valent. A very rare element, discovered in 1830 in the iron ores of Taberg in Sweden. It has since been found associated with the iron and uranium ores of other localities, and more recently it has been found in considerable quantities in certain remarkable metalliferous sandstone beds occurring in the county of Cheshire in England. Vanadium is also the essential con- stituent of a few very rare minerals. Of these the most impor- tant is Vanadinite, which is a vanadate of lead, and so closely resembles the native phosphate and arseniate of the same metal as to leave no doubt that all three have a similar molecular con- stitution, and hence that vanadium is a perissad element like phosphorus and arsenic. Thus we have the following minerals, which are all isomorphous with each other : Apatite (Oz 5 F)i*<9 9 ix(P<9) 3 , Pyromorphite (Pb & 01} i* 9 225.] VANADIUM. 291 Mimetine Vanadinite (P& 5 Ol) *0^( V0) z . The study of the other compounds of vanadium leads to the same conclusion, and shows that the same character already no- ticed in Bismuth and Antimony is developed in this element to a still higher degree. The lowest oxide of vanadium, VO, is a powerful univalent or trivalent radical, and combines with chlo- rine or replaces hydrogen like an elementary substance, and almost all of the compounds of the element, formerly known, and which can be directly prepared from the native vanadates, are compounds of this radical, now called vanadyl, but which was for a long time mistaken for the element itself. We have, for example, ( VO) (7/ 3 , a yellow fuming volatile liquid boiling at 126 7 with Sp. Gr. = 1.84 and Sp. Gr. = 88.2, also ( VO) (7/ 2 in brilliant green tubular crystals, next ( VO) Cl, a light brown powder, and lastly, ( V0) 2 Ol, a brownish yellow powder resembling mosaic gold. The true chlorides of vana- dium can only be prepared from the metal or its nitride, and the air must be carefully excluded during the process. The following have been recently described by Roscoe: VCI& a bright apple green, solid in hexagonal plates, with a micacious lustre ; F07 3 , in brilliant tubular crystals with color of peach blossoms ; and VC1 4 , a dark reddish-brown volatile liquid, boil- ing at 154, with Sp. Gr. at 0= 1.858 and Sp. Gr. = 93.3. Roscoe was unable to obtain the pentad compound. The oxides of vanadium are, first, V 2 2 or VO-VO, ob- tained as a gray metallic powder when the vapor of VO Cl s mixed with hydrogen is passed over red-hot carbon. It dis- solves in dilute acids with the evolution of hydrogen, and can- not be deprived of its oxygen except with the greatest difficulty. Secondly, F 2 3 , obtained as a black powder when V 2 5 is re- duced by hydrogen at a red heat. It is insoluble in acids. Thirdly, F 2 4 , obtained in the form of blue shining crystals by allowing V 2 3 to absorb oxygen from the air. Fourthly, V 2 5 , vanadic anhydride, a brownish-red crystalline solid, fusible at a red heat, and sparingly soluble in water. The solution has a yellow color, and is strongly acid ; but no definite hydrate has been described. Vanadic anhydride dissolves in concentrated sulphuric acid when boiling, giving a dark red solution. If this is diluted with fifty times its volume of water, and heated with metallic zinc, it rapidly changes color, passing through all 292 VANADIUM. [225. shades of blue and green until it attains a permanent lavender tint. To each of these shades corresponds a certain degree of oxidation of the dissolved vanadium, thus bright blue to V 2 0^ green to V Z 0^ and lavender to V 2 2 -, and by using less active reducing agents the change may be arrested at any desired point. The lavender solution absorbs oxygen with such avidity as " to bleach indigo and other vegetable coloring matters as quickly as chlorine, and far more powerfully than any other known agent." From vanadic anhydride we derive the vanadates, of which there appear to be three classes corresponding to the phosphates. 1. Metavanadates as in NH^OV0 2 or PfcOf ( F0 2 ) 2 . Dechenite. 2. Pyro vanadates as in NafOf F 2 <9 3 or PbfOf( Descloizite. 3. Orthovanadates as in NafOfVO . Uff 2 0or Ca^0 Of these salts the metavanadates are the most and the ortho- vanadates the least stable, the reverse of what is true in the case of the phosphates. There are two nitrides of vanadium, VN and VN Z . The first is a black powder obtained by acting on ( VO) C1 3 with dry Nff B . Its composition has been determined by analysis, and it is interesting not only as fixing the atomic weight of the metal, but also as the starting-point from which the true chlorides of vanadium, and the metal itself, have been reached. Metallic vanadium has been obtained by reducing VC1 2 W1 'th hydrogen. It is a light whitish-gray powder, which under the microscope appears as a brilliant crystalline metallic mass with a silver-white lustre. This metallic powder has a Sp. Gr. ==. 5.5, and is not magnetic. It does not volatilize or fuse when heated to redness in an atmosphere of hydrogen. It does not tarnish in the air or decompose water at the ordinary tempera- tures, but when thrown into a flame it burns with brilliant scin- tillations. It does not dissolve in hydrochloric acid hot or cold, and only slowly in hot sulphuric acid, but nitric acid of all strengths attacks it with violence. It is not acted upon by solutions of the caustic alkalies, but when fused with sodic hydrate hydrogen gas is evolved and a vanadate formed. It unites directly with chlorine gas to form F(7/ 4 , and with nitro- gen gas to form VN, and it is capable of absorbing as much as 226.] URANIUM. 293 1.3 per cent of hydrogen gas. It attacks all glass and porce- lain in which it is heated, a compound of silicon and the metal being formed. It yields also an alloy with platinum, and for these reasons, as well as on account of its very great avidity (when heated) for both oxygen and nitrogen, it has been one of the most difficult of all the elements to isolate. Division X. 226. URANIUM. U= 120. One of ^he rarer elements. Always found in nature combined with oxygen, chiefly in Pitchblende, which is essentially the compound ^0 4 , and in a rare mineral called Uranite.' Of the last there are two vari- eties: the first is a phosphate of uranium and calcium, and the second a phosphate of uranium and copper. or \ In many of its chemical characteristics, uranium very closely resembles vanadium. Like the last element, it forms an oxide, UO, which acts as a univalent radical, replacing hydrogen and combining directly with chlorine; and all the most important stable and characteristic compounds of uranium may be re- garded as compounds of this radical. Moreover, U 2 2 , like V 2 2 , cannot be decomposed by the ordinary reducing agents, and was formerly mistaken for the metal itself. Uranyl acts both as a basic and as an acid radical. Of the uranyl com- pounds, the most important, besides the native phosphates al- ready mentioned, are Uranyl Chloride, ( UO) Cl, Uranyl Fluor- ide, ( UO)F, Uranyi Hydrate, (UO}~0-H (a yellow powder), Uranyl Nitrate, (t70)-0-N0 2 .Sff 2 (a beautiful yellow salt, crystallizing in long striated prisms), and Uranyl-potassic Sul- phate, K,((70)=0 2 =S0 2 .ff 2 0; and to these may be added a number of remarkable double salts, which may be formed by the union both of the chloride and the fluoride of uranyl with the chlorides or fluorides of the metals, of the alkalies, or earths. [ndeed, these double salts are a characteristic feature of ura- lium, and one which becomes still more marked in the next lenient, Columbium. 294 URANIUM. [226. If to a solution of a uranyl salt we add ammonia, or the so- lution of any other alkali or earth, we obtain a yellow precipi- tate. This is not, however, as might have been expected, the hydrate of uranyl, but a compound of the radical with the alkali, in which uranyl acts as an acid radical. The constitution of these compounds is not well understood, but they are probably mixtures of uranyl hydrate with a compound of the form R-O-(UO). The so-called yellow uranium oxide of commerce is a hydrate thus prepared, retaining about two per cent of am- monia. All these uranyl compounds have a yellow color, and the yellow oxide is used to communicate a beautiful and pecu- liar yellow to glaSfe. Glass thus colored, and the transparent uranyl salts, are to a high degree fluorescent. Judging from the uranyl compounds alone, we should con- clude that uranium was a perissad closely allied to vanadium and the nitrogen group of elements ; but there are other com- pounds of uranium which do not readily conform to this theory. Thus we have a chloride, UCl^ and a series of uranous salts (all having a green color), in which one atom of the metal ap- pears to combine with two atoms of chlorine, or to replace two atoms of hydrogen. These would seem, on the other hand, to indicate that uranium was an artiad element allied to iron ; and the important fact that the native oxide, U 3 4 , is isomorphous with the magnetic oxide of iron sustains this view. Uranium thus appears to stand between the nitrogen group of elements of the perissad family and the iron group of the artiad family. It belongs in a measure to both, and its compounds may be in- terpreted according to the one or the other plan of molecular grouping. In classing it with the perissads we merely follow what appear to be its normal relations ; but others may reason- ably entertain a different view, and further investigation is re- quired to determine its quantivalence. Uranium thus illustrates very forcibly the remarks already made on chemical classifi- cation. (103.) Of metallic uranium but little is known. It has been ob^ tained by decomposing the chloride UC1 2 with potassium, and appears to be a steel-white metal (Sp. Gr. = 18.4), which is slightly malleable, and not readily oxidized by atmospheric agents. If heated, however, it burns in the air, and dissolves in dilute acids with the evolution of hydrogen. The compounds 226.] QUESTIONS AND PROBLEMS. 295 of uranium have found but few applications in the arts. The " yellow oxide " is used, as already stated, for coloring glass, and the so-called black oxide (7 4 5 ), obtained by igniting the nitrate, is employed as a black pigment in painting on porcelain. The nitrate, which is the most common soluble salt, has been thought to have some valuable qualities in photography. Questions and Problems. 1. State the grounds on which the conclusion in regard to the atomicity of vanadium is based, and represent by . graphic symbol the constitution of Vanadinite. 2. How does the Sp. Gr. of the vapor of vanadic oxytrichloride compare with the theoretical value ? 3. It has been shown by careful analysis that the above chloride contains 61.276 per cent of chlorine. What is the atomic weight of vanadyl, and what that of vanadium? Ans. 67.29, and 51.29. 4. In order to determine the atomic weight of vanadium from vanadic anhydride, Roscoe reduced VzO & by hydrogen to vanadic oxide, F 2 3 . Four experiments gave the following results : Weight of F 2 O 5 used. Weight of F 2 O 3 obtained. 1st, 7.7397 grammes, 6.3827 grammes. 2d, 6 5819 " 5.4296 " 3d, 5.1895 " 4.2819 " 4th, 5.0450 4.1614 " Deduce the atomic weight of vanadium. 5. Berzelius assigned to Yanadic Anhydride the symbol F0 3 , and to Vanadyl Chloride the symbol VCl y On this hypothesis he found for the atomic weight of vanadium, by the method of the last prob- lem, the value 137 (when = 16), which would be reduced to 134.74 by the more accurate determinations of Roscoe. State the reasons for believing that the true atomic weight of the element is 51.21, and that the compounds have the symbols assigned to them above. Show how far these conclusions have been proved, and point out the cause of the former error. 6. State the grounds for classing uranium with vanadium, as well as the reasons which might be urged for associating it with iron, and write the rational symbols of the uranium compounds on the as- sumption that this element is an artiad. 296 COLUMBIUM. 227.] Division XL 227. COLUMBIUM (Niobium). Cb = 94. - Pentad. This element forms the acid radical of Pyrochlore, Columbite, Samarskite, Euxenite, Aeschynite, Fergusonite, and a few other rare minerals. They are all compounds of columbic anhydride, Cb 2 0& with various metallic oxides, among which those of cerium, yttrium, and their associated elements are especially to be distinguished. The columbium, however, is almost invariably replaced to a greater or less extent by tan- talum. Columbite, the most abundant of these minerals, has the symbol [Fe,Mn~\ = 2 =([ Cb, Ta~\ 2 ) 2 . It has a black color, a submetallic lustre, and a specific gravity from 5.4 to 6.5, in- creasing as the proportion of tantalum increases. When finely powdered it is easily decomposed by fusion with potassic bisul- phate, and on subsequently boiling the fused mass with water a white insoluble residue is obtained, which consists chiefly of Cb 2 5 , and from this the different compounds of columbium may be prepared. Of these the most characteristic are the following : 228. Columbic Anhydride. Cb 2 5 . A white powder, which becomes crystalline when heated, and is afterwards insoluble in all acids. It has a Sp. Gr. between 4.37 and 4.53. Before ignition, and when in condition of hydrate (Columbic Acid?), it dissolves in strong sulphuric and in hydrofluoric acids. After boiling with strong hydrochloric acid, in which it is nearly in- soluble, the product dissolves in water, and the solution treated with zinc turns blue and finally deposits a blue-colored oxide. When a large excess of hydrochloric acid is present, the solu- tion deposits a brown oxide under the same conditions ; but the constitution of neither of these compounds is as yet known. It has been stated that oxides having the composition Cb 2 2 and Cb 2 4 have also been obtained. Columbic acid forms salts called columbates, and, besides the native compounds mentioned above, we are acquainted with several potassic columbates, three of which have been obtained in well-defined crystals, but they have a very complex constitution. 229. Columbic Chloride. CbCl 5 . A yellow crystalline solid, melting at 194, and boiling at 241. It has been found 232.] TANTALUM. 297 by analysis to contain 65.28 per cent of chlorine, and the Qp. (J$. of its vapor, by experiment, is 9.6. 230. ColumUc Oxychloride. Cb C1 3 A white solid, crys- tallizing in silky tufts, which volatilizes in the air, without pre- viously melting, at 400. It contains, according to analysis, 48.9 per cent of chlorine, and the 0p. (>r. of its vapor has been found to be 7.9. Moreover, it has been recently proved that it contains oxygen. Both chlorides, when treated with water, yield columbic acid. 231. Columbic Oxy fluoride. CbOF 8 . This compound is probably formed when columbic acid is dissolved in hydrofluoric acid, but it has not yet been isolated in a pure condition. The solution, however, forms definite crystalline salts with several metallic fluorides, and these are among the most important com- pounds of columbium. The salt 2KF . CbOF 3 .ff 2 is very readily obtained in nacreous scales, and being far more soluble than the compound of tantalum formed under the same condi- tions, 2KF. TaF 5 , it gives us the only useful means yet dis- covered of separating this element from columbium. A salt has also been formed, having the composition 2KF . CbF 5 , and isomorphous with the compound of tantalum just mentioned. It is interesting as pointing to a fluoride of columbium, CbF &1 which is not otherwise known. The metal columbium has not with certainty been obtained. The black powder described as such by Rose is said to be the oxide Cb. 2 2 . An infusion of gall-nuts gives with acid solutions containing columbium a deep orange-red precipitate ; and by this reaction columbium may be distinguished from tantalum, which, under the same conditions, gives a bright brown precipitate. 232. TANTALUM. 7^ = 182. This element, associated with columbium in the native columbates named above, is the chief constituent of Tantalite, Yttrotantalite, and of a few other minerals equally rare. Tantalite is isomorphous with colum- bite, has the same composition, save only that the acid radical is wholly tantalum, and differs chiefly in having a higher Sp. Gr., which varies from 7 to 8. Although tantalum is so closely allied to columbium, yet its compounds differ from those of this last element in several important respects. There appears to be no tendency to form oxychlorides or oxyfluorides, at least 13* 298 QUESTIONS AND PROBLEMS. [232. no such compounds are known. . The chloride is Ta C7 5 , a pale yellow solid, melting at 211, boiling at 242, and having a vapor density = 12.8. It contains by analysis 48.75 of chlo- rine, and is decomposed by water, yielding tantalic acid. The fluoride, is in like manner, Taffy. It forms double salts with the metallic fluoride, the most important of which is the potassic fluotantalate, 2KF '. TaF 5 , mentioned above. Tantalic anhy- dride, Ta 2 5 , is a white powder, insoluble in acids. It closely resembles colurnbic anhydride, and is prepared in a similar way from the native tantalates, but it has a higher density (Sp. Gr. = 7.6 to 8), arid forms with the alkalies a larger number of crystallized salts. There is a hydrate (Tautalic Acid?), and also probably several lower oxides of the element. A solution of 1aCl 5 in strong sulphuric acid, when diluted with water and reduced with zinc becomes colored blue, but yields no brown oxide as in the case of columbium. By reducing sodio-tantalic fluoride with sodium, a black powder is obtained which has been supposed to be metallic tantalum. Questions and Problems. 1. Calculate the percentage composition of columbite, on the as- sumption that the basic radical is wholly iron and the acid radical wholly columbium. Ans. 21.17 FeO and 78.83 C\0 y 2. Explain the meaning of the symbol of columbite in (227). 3. How far do the theoretical 0. (Jfa. of columbic chloride and oxychloride compare with the experimental results ? 4. The mean of twenty analyses of the potassio-columbic oxyfluor- ide, 2KF. CbOF s . H Z O, gave the following results: From 100 parts of the salt there were obtained by the process of analysis adopted 5.87 parts of water, 44.36 of columbic anhydride, 57.82 of potassic sulphate, and 31. 72 of fluorine. Assuming that the symbol of colum- bic anhydride is C6 2 5 , and estimating the per cent of oxygen by the loss, deduce the percentage composition of the compound and its symbol. Ans. Columbium, 31.12; Potassium, 25.92; Oxygen, 5.37; Flu- orine, 31.72; Water, 5.87. 5. What would be the atomic weight of columbium if deduced from the result of the above analyses? Ans. 93.9. 6. Previous to the recent investigations of Marignac, the symbol QUESTIONS AND PROBLEMS. 299 of columbic acid was usually written CbO a when = 8, or Cb 2 O s when = 16. What proofs have been given of the correctness of the symbol adopted in this book ? What was the probable cause of the error made by the earlier investigators ? 7. By what general method may tantalum be separated from co- lumbium ? How can you tell when the separation is complete ? 8. What compounds of tantalum and columbium are isomorphous ? What bearing does this fact have on the symbol of tantalic anhy- dride ? Does the vapor density of tantalic chloride agree with the symbol which has been adopted ? Why is there a necessary connec- tion between the symbol of the chloride and that of the anhydride ? 9. How may tantalite be distinguished from columbite ? 10. State the resemblances and the differences between the two members of this group of elements. CHAPTER XIX. THE AETIAD ELEMENTS. Division I. 233. OXYGEN. 0=16. Dyad. The most abundant, and the most widely diffused of the elements. Forms one fifth of the atmosphere, eight ninths of water, more than three fourths of organized beings, and one half of the solid crust of the globe. 234. Oxygen Gas. 0=0. Exists in a free state in the at- mosphere, but mixed with nitrogen gas. May be extracted from the air by either of the following double reactions. Me- tallic mercury or baric oxide is first heated in the air, and then the products of the first reaction raised to a much higher tem- perature. 2. 2ffO = 2ff =. 2. 2Ba0= Generally obtained from commercial or natural products, rich in oxygen, by one of the reactions given below. The materials must in each case be heated to a definite temperature, and the last two reactions require a full red heat. 2KC10 3 = 2KCI + 3 =.! [229] -f 8^0 + 3=. [230] 2Mn0 2 + 2ff 2 S0 4 = 2MnS0 4 -f 2ff 2 + =. [231] 3Mn 2 = Mn 3 + =. [232] t = 2ff 2 + 2S0 2 + =. [233] Also by electrolysis of water and by [66]. Oxygen gas is a chief product of vegetable life. Under the influence of the 1 This reaction is greatly facilitated by mixing the potassic chlorate with cupric oxide or manganic dioxide, which, however, undergo in the process no apparent change. 235.] OXYGEN. 301 sun's rays the plants decompose the carbonic acid of their food, fixing the carbon and liberating the oxygen. Oxygen gas man- ifests intense affinities, but these are only called into play under regulated conditions. (Review Chapter XII. on Combustion.) When an elementary substance unites with oxygen it is said to be oxidized, and when the compound is decomposed the oxide is said to be reduced. 235. Oxygen Compounds. The most important classes of oxides are illustrated by the following symbols and examples: i ii 1. R 2 or R,R as in H 2 K 2 Ag 2 s 2. R 2 2 " R,(R-0)*0 " H 2 2 K 2 2 Ag 2 0^ 3. RO R-0 FeO CaO PbO, 4. R 2 " (R-R)--O Cu 2 Hg z O Pb 2 0, 5. R0 2 (R-0)-~0 Mn0 2 Ba0 2 Pb0 2 , m v in m 7. R0 2 J?i<9 2 Sn0 2 Si0 2 C0 21 IV IV IV II & IV II IV 9. R " R=0~[R~\=0 fi Fe Cr Co v v v v v v 1 1 . R<> il \R ~R) 1 4 V 2 4 Sb 2 4 -Bi 2 0^ VI VI 12. R0 3 RW 3 " S0 3 Se0 3 Mo0 3 . As a rule, the oxides of the forms 1 and 3 act as anhydride bases (47), and are called protoxides. On the other hand, the oxides of the forms 6, 7, 10, and 12 generally act as anhydride acids. The oxides of the form 8 are called sesquioxide. They usually act as basic, but sometimes as acid anhydrides, and at other times like the hyperoxides mentioned below. The oxides of the forms 9 and 11 are very indifferent bodies, and those of the first class are sometimes called saline oxides. The oxides of the forms 2 and 5 are called di or hyper-oxides. They act as powerful oxidizing agents, readily giving up one half of the oxygen they contain [74] [77]. The oxides of the form 4 are called suboxides. They sometimes act as anhydride bases, but in most cases when acted on by acids they change into protox- 302 OXYGEN. [236. ides, either giving up one half of the metal or taking up as much again oxygen as they contain. The relation of the oxides to the acids, bases, and salts has been already explained. (Review Chapters IX. and X.) Besides the above classes of oxides, all of which comprise actual compounds, there are others, most of which are only known as compound radicals. With many of these radicals the student is already familiar, such as S0 2 , SO, NO Z , NO, PO, in all of which the oxygen atoms only satisfy a part of the affini- ties of the multivalent atoms, with which they are grouped, and the quantivalence of the radical is easily found by Wurz's rule. (28.) The chemists have also been led to assume a very differ- ent type of oxygen radicals, in which the affinities of the oxygen atoms predominate, and, moreover, it is frequently convenient, in expressing the composition of complex compounds, to indicate these radicals by a single symbol. The following examples illustrate the most important classes of these radicals : Radicals. Symbols. Examples. RO (R-6) Ro Ho Ko (NJB^o. R0 2 (0-R-O) Ro Oao Zno Feo. VI VI VI It will be noticed that the number of oxygen atoms in all these cases corresponds to the quantivalence of the metallic ele- ment with which they are united, and that the quantivalence of the radical is the same as that of its characteristic element. Hydroxyl, Ho, is the type of this class of radicals, and names may be given to them all formed after the same analogy as Potassoxyl, Zincoxyl, but such names are rarely used. The relations of this type of radicals to the three great classes of chemical compounds has been already in part illustrated (108), and will be still further developed in the present chapter. 236. Ozone. (0-0) = 0. The* best opinion that can at pres- ent be formed in regard to the constitution of this remarkable substance is expressed by the rational symbol here given. Ozone is formed under a great variety of conditions, as, 1. During the passage of electric sparks through air or oxygen. 2. During the electrolysis of water. 3. During the slow com- 23G.] OXYGEN. 303 bustion of phosphorus in moist air. 4. During the slow com- bustion of alcohol, ether,' and volatile oils. 5. By decomposing potassic permanganate with sulphuric acid, and by several other similar reactions. Ozone as thus obtained, however, is very largely diluted with air or oxygen gas, and we have not yet succeeded in preparing it in a pure condition. It differs from ordinary oxygen gas, 1. In having a peculiar odor, with which we are familiar, as a concomitant of electrical action. 2. In acting as a powerful oxidizing agent at the ordinary temper- ature of the air. It corrodes cork, india-rubber, and other or- ganic materials. It bleaches indigo. It even oxidizes silver, and displaces iodine from its metallic compounds. If a slip of paper moistened with starch and potassic iodide is inserted in a jar containing the smallest trace of ozone, it is immediately colored blue, owing to the liberation of the iodine (119). In like manner, paper wet with a solution of manganous sulphate is turned brown by ozone, owing to the oxidation of the man- ganese, and paper stained with plumbic sulphide is bleached by the same agent, because the black sulphide is changed to the white sulphate. 3. In the fact that its Sp. Gr. is 24 instead of 16. The formation of ozone in a confined mass of oxygen gas is attended with a reduction of volume ; and since the ozone thus formed may be absorbed by oil of turpentine, we have thus the means of determining its specific gravity, and the results, if cor- rect, prove that the molecule of ozone consists of three oxygen atoms. Again, during most cases of oxidation by ozone, the volume of the ozonized oxygen does not change, and this fact is consistent with the theory of its constitution which our molecular formula expresses, as is illustrated by the following reaction : Ag-Ag + 2(OO) = = Ag 2 2 + 20=0. [234] li has been shown, however, that oil of turpentine absorbs the molecule of ozone as a whole, and is, therefore, an exception to the general rule. The metal in the above reaction is raised to the condition of peroxide, and it is probable that several of the oxides and oxygen acids contain one or more atoms of oxy- gen in the same condition as in ozone. Such compounds have been called ozonides, and among them are classed the peroxides of silver, lead, and manganese, the sesquioxides of nickel and 304 OXYGEN. [237. cobalt, as also chromic, manganic, and permanganic acids, with their various salts. Ozone appears to be constantly present in the atmosphere, and important effects have been attributed to its influence. It has been thought to be the active agent in all processes of slow combustion and decay, and to play an impor- tant part in the economy of nature. At a temperature of 300 ozone is instantly changed into common oxygen gas, and at a temperature no higher than boiling water, it slowly returns to the same condition. + 237. Antozone. (0-0) = 0. Whenever ozone is prepared, there appears to be formed at the same time a second modifica- tion of oxygen gas, which presents such a singular antithesis to ozone as to lead us to believe that it is in fact the same sub- stance, only oppositely polarized. Hence we have called it an- tozone, and assigned to it the symbol at the head of this section, although our theory is not based on any conclusive experiments, and our knowledge of the substance is still very imperfect. It may be obtained in several ways, 1. When dry electrified air is passed through a solution of pyrogallic acid or potassic iodide, the ozone is absorbed and the air is left charged with antozone. 2. When baric peroxide is dropped into sulphuric acid, the oxy- gen evolved is more or less charged with the same agent. 3. When phosphorus is burnt in dry air, a small amount of oxygen is always left unconsumed, and this appears to be in th condi- tion of antozone. Indeed, it has been supposed that, in all sim- ilar processes of oxidation, both ozone and antozone are formed ; but that, while the oxygen atoms of the first enter into combi- nation with the burning body, those of the last do not, owing to their polar condition. Antozone has an odor like ozone, but much more repulsive. It does not displace iodine or color the iodized paper. It does not oxidize silver or the solution of manganous sulphate, but, on the contrary, removes from the paper prepared with the man- ganous salt the brown stain which ozone had made. On all ozonides it acts as a reducing agent. [236.] There is, how- ever, another class of substances which it oxidizes, and ^jnong these the most important is water, with which it forms hydric peroxide. 0+ 0-0. [235] 237.] QUESTIONS AND PROBLEMS. 305 In many processes of ozonizing air, the antozone unites with and thus condenses the vapor present, although, in most cases at least, the union appears to be rather mechanical than chemi- cal. The reaction is consequently attended with the formation of mists or clouds, which is one of the most striking properties of antozone. The smoke of gunpowder, tobacco, and smoulder- ing wood has been thought to be an antozone cloud, and the clouding of gas jars in many chemical experiments has been referred to the same cause. Opposed to the ozonides we have a class of antozonides, among which have been classed, besides the peroxide of hydrogen, the peroxides of barium, strontium, sodium, and potassium, and reactions may be obtained between these two classes of compounds which are very interesting. They mutually decompose each other, with the evolution of oxygen gas, thus : (Pb-0)-d + ff J ffo=0 = PbO-\-ff 2 + 0-0. [236] Compare also [75]. Antozone is more unstable than ozone, and changes back to oxygen gas at a still less elevation of tem- perature. Questions and Problems. 1. Wbat is the reason for writing the symbol of oxygen gas O=0? (17) and (19.) 2. What is the difference between the condition of oxygen gas in the atmosphere, and that of the same gas in a pure condition con- tained in a bell-glass standing over a pneumatic trough ? 3. Were the nitrogen gas of the atmosphere removed, would the physical condition of the oxygen gas be changed ? 4. If by either of the methods [228] oxygen gas is obtained di- rectly from the atmosphere, how many litres of air would be required to yield one litre of oxygen gas at same temperature and press- ure? (59.) Ans. 4.77 litres of air. 5. How much potassic chlorate must be used to yield 100 litres of oxygen gas at 30 and 38 c. m. pressure? Ans. 165 grs. 6. What weight of potassic dichromate [230] must be used to yield a litre of oxygen gas, Sp. Gr. = 96 ? Ans. 52.77 grs. 7. If 32.05 grammes jof potassic chlorate are decomposed in a 306 QUESTIONS AND PROBLEMS. closed vacuous vessel of 1,010 cTmT 8 capacity, what will be the tension of the gas in the vessel at 273 ? Ans. 131.6 c. m. 8. What weight of oxygen gas is required to fill a globe of 10 litres' capacity at 27. 3 and 38 c. m. pressure? Ans. 6.515 gram. 9. From a given weight of Mn0 2 how much more oxygen gas can be obtained by reaction [231] than by [232] ? Ans. \ more. 10. A volume of air measuring 100 c. niT 8 is mixed with 50 c. m. 8 of hydrogen gas and exploded. What volume of gas is left, assum- ing that the volumes are all measured under standard conditions, and that all the water formed is condensed ? (59.) Ans. 87.12 cTm: 8 . 11. In an experiment like the last, with the same initial volume of air and hydrogen, the volume of the residual gas measured 89.41 c. m. 8 What is the composition of the air ? It is assumed that the volumes are measured under a constant pressure of 76 c. m., and at a temperature at which the tension of aqueous vapor equals 2 c. m. Ans. 20.96 oxygen, 79.04 nitrogen. 12. Analyze reaction [230], and show from which of the factors the oxygen is derived. 13. Represent reaction [232] by graphic symbols. 14. What volume of chlorine gas is required to decompose one litre of aqueous vapor ? Ans. 1 litre. 15. If one gramme of water is decomposed by galvanism in a closed glass globe containing 1.86 litres of air under normal condi- tions, what will be the tension of the resulting gas mixture, leaving out of the account the tension of the aqueous vapor which may be present? Ans. 152 c. m. 16. Represent by graphic symbols the constitution of the various classes of oxides and oxygen radicals. 17. In the symbols of acids, hydrates, and salts (35) written on the water type, to what do the oxygen radicals correspond ? 18. Explain the change of color which takes place when paper moistened with a solution of starch and potassic iodide is exposed to the action of ozone. 1 9. Explain the method of finding the Sp. Gr. of ozone. 20. Can you devise a method of finding the Sp. Gr. of ozone based on the principle of (58) ? 21. Explain the reasons for writing the symbol of ozone (#-#)=#. QUESTIONS AND PROBLEMS. 307 22. How would you write the symbols of argentic peroxide and plumbic peroxide, on the same principle ? 23. Why is it essential in preparing antozone that the electrified air should be dry ? 24. In what different ways may the symbol of hydric peroxide be written, and what theories of its composition do the symbols suggest? By what reactions are these theories sustained ? 308 SULPHUR. [ 238. Division U. 238. SULPHUR. S = 32. Usually bivalent when in combination with metals or positive radicals, but in other asso- ciations frequently quadrivalent and sexivalent. Widely and abundantly distributed in nature, chiefly in combination, form- ing various metallic sulphides and sulphates. The most abun- dant of these are iron pyrites, FeS* and gypsum, CaSO^ . 2ff 2 0. Found also native in volcanic districts. It is, moreover, an es- sential, although a very subordinate, ingredient of the animal tissues. Sulphur is very closely allied to oxygen, and, corre- sponding to each metallic oxide, there is usually a sulphide of the same form ; and, substituting the symbol of sulphur for that of oxygen, the table of oxides on page 301 will serve equally well as a classification of the sulphides. Moreover, we have found it convenient to assume a number of sulphur radicals cor- responding in all respects to the oxygen radicals, and we repre- sent them by separate symbols formed in a similar way. Thus, Jfi, Pbs, Cutf, Sbtf stand for the radicals HS, PbS 2 , Cu 2 S^ Sb 2 S 6 respectively. The greater part of the sulphur of commerce comes from the mines of Sicily, where it is either melted or distilled from the volcanic earth. A small quantity is obtained by roasting or distilling iron pyrites. Common sulphur is a very brittle, yel- low solid, melting at 114, and boiling at 440, when it forms a dense red vapor. It is insoluble in water, and nearly so in alcohol, ether, and chloroform, but readily soluble in carbonic bisulphide, benzole, and oil of turpentine, the solvent power of the last two liquids being greatly increased by heat. Sulphur assumes a great variety of allotropic modifications, which are manifested by differences of crystalline form, specific gravity, solubility, and color. At the ordinary temperature it crystal- lizes in octahedrons of the orthorhombic system, Sp. Gr. 2.05, and above 105 in oblique prisms of the monoclinic systems, Sp. Gr. 1.98. Moreover, the one crystalline condition passes into the other at the temperature at which it is normally formed. If heated to 230, melted sulphur becomes darker colored, thick, and pasty, and if suddenly cooled the mass remains plastic for 239.] SULPHUR. 309 some time. At 100 this plastic material suddenly changes back to brittle sulphur, with evolution of heat, and the same change soon follows, although more slowly, at the ordinary temperature. If sulphur is heated to 230, and suddenly cooled several times in succession, it is in part converted into a peculiar dark-colored variety, wholly insoluble in all solvents, and easily separated by carbonic sulphide from the unchanged portion. Moreover, ordinary flowers of sulphur (formed by condensing the vapor of sulphur in cold brick chambers) consist in part of a yellow powder, insoluble in carbonic sulphide, which appears to be still another condition of sulphur, and several other modifications, including a black and a red variety, have been described as distinct allotropic states. Some chemists have thought to find among these various modifications a difference of polar condition similar to that observed in the modifications of oxygen. Sul- phur appears, even in the state of vapor, to present differences of condition. Just above its boiling point the Sp. Gr. of sul- phur vapor is 96, which corresponds to the molecular formula S^S 3 ', and not until the temperature reaches 1,000 does the Sp. Gr. become 32, corresponding to the formula S=S, like that of oxygen gas. Sulphur has strong affinities for the metals, many of which burn in its vapor with great brilliancy. It has also a strong affinity for oxygen. It is very combustible, taking fire at a low temperature, and forming by burning S0 2 . It is chiefly used for making sulphuric acid, and vulcanizing india- rubber; but it has many subordinate applications both in the arts and in medicine. The so-called milk of sulphur, used in pharmacy, is obtained by dissolving flowers of sulphur in alka- line liquids, and subsequently precipitating with acid. 239. Hydric Sulphide, Sulphohydric Acid, Sulphuretted Hydrogen, ff. 2 S. A colorless gas, which by pressure and cold may be condensed to a limpid, colorless liquid (Sp. Gr. = 0.9), boiling at 62, and freezing at 86. Is soluble in water and alcohol, one measure of water at dissolving 4.37 meas- ures, and one volume of alcohol dissolving 17.9 measures, of the gas at the same temperature. Has a repulsive odor, and is a constant product of decaying animal tissues. Generally obtained by the reaction FeS + (H 2 S0 4 + Aq) = (FeSO, + Aq) + H,S; [237] 310 SULPHUE. [239. but as the ferrous sulphide commonly used contains more or less metallic iron, the gas thus prepared is mixed with hydrogen. It is obtained in a purer condition from Sb 2 S 3 + (QHCl + Aq) = (2SbCl 3 -f- Aq) + 3ff 2 S. [238] Hydric sulphide is very combustible, and burns with a pale blue flame. = 2ff 2 + 2S0 2 . [239] The solution of the gas exposed to the air soon becomes turbid, owing to the oxidation of the hydrogen and consequent sepa- ration of sulphur. Aq) + = = (2ff 2 + Aq) + S=S. [240] If the action is assisted by porous solids, the oxidation is more complete. (H 2 S + Aq) + 2= = (HfOfSOs + Aq). [241] The substance is also decomposed by chlorine, bromine, or iodine. (2H 2 S + 27-7+ Aq) = (4777+ Aq) + &&. [242] On this last reaction is based a simple process of determining volumetrically the amount of H 2 S in a given solution. The compound may be analyzed by heating metallic tin in a confined volume of the gas. SI^ + Sn SnS + SHS. [243] Although the sulphur is removed by the tin, the volume of the gas does not change. Hydric sulphide is not unfrequently formed in nature from calcic sulphate, which in contact with decaying animal or vegetable matter loses its oxygen, when the carbonic acid of the atmosphere, acting on the resulting calcic sulphide, sets free the compound in question. It is thus that the soluble sulphides in many mineral springs probably originate. Hydric sulphide is one of the most important chemical re- agents, and is used to convert into sulphides various metallic hydrates and other salts. 239.] SULPHUR. 311 1. Action on alkaline hydrates. (K-0-JI+ H 2 S + Aq) = (K-S-ff+ ff 2 + Aq). [244] (K-S-JI+ K-0-H+ Aq) = (K 2 S+ff 2 + Aq). [245] Thus may also be formed Na-Hs, Na?S, Nfffffs, (38.) 2. Action on salts of the more electro-negative metals. (CdSO, + H 2 S + Aq) = CdS + (& 2 S0 4 + Aq). [246] So also may be precipitated from acid solutions of their salts As 2 S 3 , Sb 2 S 3 , Sb 2 S 5 , SnS, SnS PtS 2 , Au 4 S 4 , Yellow. Red. Orange. Brown. Yellow. Brown. Black. all of which are soluble in alkaline sulphides, and CdS, CuS, Bit/8* Ag 2 S, HgS, [Eg AS, PbS, Yellow. Black. Black. Black. Black. Black. Black. all of which are insoluble in alkaline sulphides. 3. Action on salts of the more electro-positive metals. The following sulphides, although not precipitated from acid solu- tions, are precipitated when sufficient ammonia is added to neu- tralize all the acids present, or when an alkaline sulphide is used in place of H 2 S. ZnS, MnS, FeS, NiS, OoS. TVhite. Pink. Black. Black. Black. At the same time aluminum and chromium are also precipitated as hydrates. The remaining common metals, viz. : Ha, Sr, Ca, Mg, K, and Na, forming sulphides soluble in water, are not pre- cipitated by H 2 S under any conditions. Thus ff 2 S serves to divide the metallic radicals into groups, and on these relations the ordinary methods of qualitative analysis are based. 4. Action as reducing agent. Ck + ZffCl + Aq) + S. [247] (K z [ Cr z ~] 7 + SffCl d> Green. + 2KCI +7ff 2 + Aq) + S [248] Q . [249] Pentathlonlo Acid. 312 SULPHUR. [240. 240. Hydric Persulphide, H^S^ analogous to H^O^ can be obtained by gradually adding to hydrochloric acid sodic bisul- phide. It is a yellow, oily liquid, and very unstable. 241. Alkaline Sulphides and Sulphohydrates. Solutions of the simple sulphides and sulphohydrates are best formed as above. These solutions readily dissolve sulphur, and various persulphides are thus formed. The following six sulphides of potassium are known : K 2 S, K 2 S 2 , K 2 S& K Z S^ K 2 S 5 , and K Z S 7 . Other modes of preparing similar compounds are illustrated by the following reactions : [250] Ignited in gas current. 125+ (6JT- 0-ff+ Aq) = Boiled in solution. ^^ + ^ Q + ^ Q + ^ ^^ Fentasulphide. Hyposulphite. . [252] Melted together at a high temperature. SS + 3K 2 =0 2 =00 = 2K 2 S 3 + K 2 S 2 0, + 3 CO* or 125+ 3K 2 =0 2 =CO = 2K 2 S 5 + K 2 S 2 S + 3(70 2 . Melted together at a lower temperature. The products of the last two reactions are not constant, but various persulphides are formed, depending on the temperature and the conditions of the process. The resulting mixture is a yellow solid called liver of sulphur. When treated with acids, the various sulphides react as follows : (K-Hs + HCl + Aq) = (KCl + Aq) + 3SA [254] (K 2 S + 2HCI + Aq) = (2KCI + Aq) + SJA [255] (K 2 S 3 + 2HCI + Aq) = (2 KCl + Aq) + S 2 + IHA [256] 3 + SffCl + Jy) = S0 2 + JET,0 + Aq) + 9S + 2HI 2 ^. [257] Solutions of the alkaline sulphides or sulphohydrates absorb oxygen from the air, and are thus changed into persulphides and hyposulphites. (SNff 4 -S-ff+ Aq) + 5= = Colorless solution. 243.] SULPHUR. 313 Sulphur and hydric sulphide react on the alkaline earths in nearly the same ways as on the alkalies. Ca + H,S = CaS + ff 2 0. [259] Ignited in gas current. CaS0 4 + ff-ff= CaS + H 2 0. [260] Ignited in gas current. CaS 0^ + 4(7= CaS + CO. [261] Ignited together. 2 CaS + HfO z =H z = Ca=S 2 =ff 2 + Ca-OfH^ [262] Mixed with water. (Ca=O 2 =H 2 + 2ff 2 S+Aq) = Pa^ng^Sthroughmilkoflime. ^ Ca=S 2 =ff 2 + 2ff 2 0-}-Aq). [263] By boiling sulphur with milk of lime, a mixture of calcic hy- posulphite with various calcic persulphides is obtained, among which may be distinguished CaS 2 and CaS 6 . By melting to- gether sulphur and calcic hydrate or carbonate, there results a mixture of calcic sulphide and calcic sulphate. If pulverized charcoal is also added, the product is chiefly calcic sulphide. 242. Compounds of Sulphur and Oxygen. The following are known : Sulphurous Anhydride SO& 9 Sulphurous Acid HfO z =SO, Hyposulphurous Acid Hf 2 =(S- 0-S), Sulphuric Anhydride 3 , Sulphuric Acid ff 2 =OfS0 2 , Nordhausen Acid Hf 2 =(S0 2 - 0-S0 2 ), Dithionic Acid H z = 2 =(S0 2 -S0 2 ), Trithionic Acid Sf Tetrathionic Acid Hf Pentathionic Acid Jf 2 = 2 =(S0 2 -S-S-S~S0 2 ). 243. Sulphurous Anhydride. S0 2 . Colorless gas, having a familiar suffocating odor. It is easily condensed to a colorless liquid, boiling at 10 and freezing at 76 ; 0|). <&r. = 1.49. Natural product of volcanic action, and abundantly evolved dur- ing the roasting of copper pyrites and other sulphurous ores. May be prepared by either of the following reactions : 14 314 SULPHUR. [244. [264] Burning. 2H 2 S0 4 + ffff = HgSOt + 2^0 + ^ 2 . [265] 2Jf 2 S0 4 -f O= 2^ 2 -|- O a -f2IH 2 (o). [266] S=S + Jtfw 2 = JfnS + ^2. [267] May be decomposed by the reactions 2S0 2 + ff-ff= ff 2 + S-S. [268] SO, + 3ff-ff=: 2ff 2 + ff 2 S. [269] The first reaction is obtained by passing a mixture of the two gases through a red-hot tube ; the second, by adding to the so- lution containing S0 2 & small amount of hydrochloric acid with a few pieces of zinc. The ^/S may be detected by a strip of paper moistened with a solution of acetate of lead, and the reac- tion gives us the means of discovering small quantities of SO Z . Sulphurous anhydride is a powerful reducing agent. Thus 5S0 2 + 4# 2 + Aq) = (I-I+ 5H 2 S0 4 + Aq). [270] (As 2 5 + 2S0 2 + 2# 2 + Aq) = (As 2 3 + 2ff 2 S0 4 + Aq). [271] [272] (2S0 2 + 2# 2 6> + Aq) + = == (2ff 2 S0 4 + Aq). [273] Pb0 2 + ^ 2 = PtoS0 4 . [274] It is also a powerful disinfecting and antiseptic agent, and is much used for retarding fermentation and putrefaction. It also bleaches some of the more fugitive colors, but the effect is fre- quently transient, and the reaction not well understood. 244. Sulphites. At water absorbs 68.8 times its bulk of SO& and three crystalline hydrates have been described, one of which has the composition S0 2 . If 2 0, and has been regarded as sulphurous acid, but this opinion may be questioned. The aque- ous solution acts in all .its mechanical relations like the simple 246.] SULPHUR. 315 solution of a gas. Nevertheless, in its chemical relations it acts like an acid, and yields, with many of the metallic oxides, hy- drates, or carbonates, a numerous class of salts called the sul- phites. The following examples will illustrate their general composition : Hydro-sodic Sulphite HJfa = Of SO . 4ff 2 0, Disodic Sulphite No? Of SO . 7ff 2 0, Calcic Sulphite Oa = Of SO. The sulphites are generally best prepared by transmitting a stream of S0 2 through water in which the metallic oxide, hy- drate, or carbonate is suspended. The alkaline salts are the only sulphites which are freely soluble in wa^r. The sulphites of barium, strontium, and calcium dissolve to some extent in water charged with SO^ and in this respect the sulphites re- semble the carbonates. Argentic sulphite, which may be read- ily obtained by precipitation, undergoes a remarkable reaction when boiled with water. AffOfSO + (H 2 + Aq) = Ag-Ag + (ff 2 =0 2 =SO 2 + Aq). [275] 245. Hyposulphites. Hyposulphurous acid has never been isolated ; but several hyposulphites may be obtained by passing a stream of SO Z through solutions of the corresponding sul- phides, or digesting a solution of the sulphite on powdered sulphur. S + (Na 2 =0 2 =SO + Aq) = (NafOf(S-0'S) + Aq. [276] Calcic hyposulphite is formed spontaneously in large quanti- ties, both in the refuse lime taken from the purifiers of the gas- works, and in the refuse after the lixiviation of the black-ball at the alkali works, and from this source sodic hyposulphite is now obtained. It is the only hyposulphite of practical value, and is not only used in photography, but also for removing the. last traces of chlorine from the bleached pulp used in paper- making, and in the treatment of silver ores. 246. Sulphuric Anhydride. S0 3 . Soft, white, silky-looking crystalline solid, melting at 25, and volatilizing at 35. May be obtained either by distillation from the Nordhausen acid or 316 SULPHUR. [247. from sodic disulphate, or else by passing a mixture of S0 2 and 0=0 through a heated tube filled with platinum sponge. [277] = Na 2 =O 2 =S0 2 + ^ 3 . [278] [279] It unites with many metallic oxides to form sulphates, and baryta burns in its vapor. BaO + ^3 = BaO,SO 3 . [280] It has an intense affinity for water, and the heat developed by the union is so giat that the solid hisses like red-hot iron when dropped into the liquid. The product is common sulphuric acid. 247. Sulphurylic Chloride. 2 C7 2 . May be formed by the direct union of S0 2 and Gl~Cl under the influence of the sunlight, also by the reaction H 2 SO, + 2P01 5 = S0 2 G1 2 + 2PCI S + 2HCL [281] The product is a liquid boiling at 80 ; Sp. Gr. 1.68. Slowly decomposed by water. S0 2 C1 2 + 2ff 2 = ff 2 S0 4 + 2HCL [282] There have also been described the allied compounds H-0-S0 2 Cl and S0 2 I 2 ' The relations of these compounds to sulphuric acid will be made more evident by writing the symbols thus : HofSO* ffo,Cl=S0 2 , ClfS0 2 , I 2 =S0 2 . 248. Sulphuric Acid. ff 2 =0 2 =S0 2 or ffofSO* The follow- ing reactions are interesting as illustrating the constitution of this important acid, although of no practical value as methods of making it : Ho-Ho + S0 2 JJOfS0 2 , [283] S0 3 = H 2 0,SO S . [284] 2ff 2 = 2 =SO + - = 2ff 2 = OfSO,. [285] S-S + H-0-N0 2 = 2H 2 -0 2 =S0 2 + 4NO. [286] 248.] SULPHUR. 317 For the uses of the arts the acid is made in enormous quanti- ties by burning sulphur in large brick ovens, and conveying the S0 2 thus formed, together with steam and nitric acid fumes, generated simultaneously [135], into large chambers lined with sheet lead. 1. S0 2 + 2HNO Z = ff 2 S0 4 + 2NO? [287] 2. 3N0 2 + ff 2 = 2HN0 3 + NO. [288] 3. 2NO +0=0 = 2 NO? [289] These reactions may be repeated indefinitely, and it is evi- dent that the same quantity of nitric acid would serve to con- vert an infinite amount of S0 2 into H 2 SO^ were it not for the loss occasioned by the constant draft of air through the cham- bers. The reaction consists essentially in a transfer of oxygen from the air to the S0%, the nitrogen compounds acting as the mediator, and the draft yields the requisite supply of oxygen gas. When the amount of aqueous vapor is insufficient, there forms in the chambers a white crystalline compound of some- what uncertain composition, but to which has been assigned the symbol (N0 2 )f(S0 2 -0-S0 2 ). When mixed with water, this compound breaks up into sulphuric acid and nitrous anhydride, so that the formation of the acid may also be represented by the following equations, which are thought by some chemists to rep- resent the process more accurately than those given above : 1. S0 2 + 2ffoN0 2 = ffo 2 S0 2 + 2N0 2 . [290] 2. 4]V0 2 + 4S0 2 + 0-0 = 2(N0 2 ) 2 =(S0 2 -0-S0 2 ). [291] 3. (N0 2 ) 2 =(S0 2 - -S0 2 ) + 2ff 2 = 2ffo 2 S0 2 + N 2 3 . [292] 4. 3N 2 3 +ff 2 0=z 2ffoN0 2 + 4NO. [293] 5. 2NO + 0-0 = 2N0 2 . [294] In manufacturing sulphuric acid iron pyrites is now frequently used instead of sulphur. This ore, burnt in kilns adapted to the purpose, yields a plentiful supply of S0 2 , which is converted into sulphuric acid in lead chambers as before. The acid drawn from the chambers is very dilute, and for most uses must be 318 SULPHUR. [248. concentrated by evaporation, which is begun in leaden pans, but completed in retorts of glass or platinum. The strongest acid thus obtained corresponds to the symbol H 2 SO^. It is an oily liquid (oil of vitriol), Sp. Gr. = 1.842, boiling at 327, and crystallizing at a low temperature. If during the evaporation the temperature is limited to 205 C., an acid is obtained of the composition ff 2 S0 4 . ff 2 0, and Sp. Gr. 1.78, which crystallizes at 9, and by limiting the temperature to 100, still a second definite hydrate may be obtained, ff 2 S0 4 . 2ff 2 0, which has Sp. Gr. = 1.62. Oil of vitriol may be mixed with water in any proportion, and the hydration of the acid is accompanied by a condensation of volume and a great evolution of heat, the max- imum of condensation and the maximum of heat being attained when the proportions are such as to form the second hydrate. A definite Sp. Gr. corresponds to each degree of dilution, and tables have been prepared by which, when the specific gravity is known, the strength of the acid may be determined. The short table which follows gives all the data required for the problems in this book : Per Cent of H 2 S0 4 . Sp. Gr. at 15^. Per Cent of SOy Per Cent of H 2 SO V Sp. Gr. at 15. Per Cent of SOy 100 1.8426 81.63 50 1.3980 40.81 95 1.8376 77.55 45 1.3510 36.73 90 1.8220 73.47 40 1.3060 32.65 85 1.7860 69.38 35 1.2640 28.57 80 1.7340 65.30 30 1.2230 24.49 75 1.6750 61.22 25 1.1820 20.40 70 1.6150 57.14 20 1.1440 16.32 65 1.5570 53.05 15 1.1060 12.24 60 1.5010 48.98 10 1.0680 8.16 55 1.4480 44.89 5 1.0320 4.08 In consequence chiefly of its strong attraction for water, sul- phuric acid disorganizes and blackens both animal and vegeta- ble tissues. It is also used as a hygroscopic agent, and, under limited conditions, for the dehydration of various chemical com- pounds. Its action on different chemical agents has been al- ready repeatedly illustrated. (See [64], [231], [65].) It forms several classes of salts, as is illustrated by the following examples : 251.] SELENIUM. TELLURIUM. 319 Hydro-sodic Sulphate ffo,Nao=S0 2 , Disodic Sulphate Nao 2 =S0 2 and with Sodic Disulphate Naof(SO Cupric Sulphate Cuo =S0 2 . Ferrous Sulphate Feo =S0 2 . 1H 2 0, Potassio-ferrous Disulphate Feo=(SO=0 2 =SO)--Ko z Aluminic Sulphate Alr. of S0 t referred to air? Ans. 2.234. 29. How much mercury is required to make one litre of 50 2 ? Ans. 8.96 grammes. 30. Leaving out of view the value of the mercury used, as it may be easily recovered, by which of the two reactions [265] or [266] may SO Z be most profitably prepared ? 31. How much Mn0 2 would be required to yield by reaction [267] sufficient $0 2 to neutralize 1.29 grammes of sodic carbonate? Ans. 1.059 grammes. 32. Point out the volumetric relations in reaction [268]. 33. Are the conditions under which the reaction [269] is obtained in any way peculiar ? 34. Compare reactions [271] and [272], and inquire whether a method of volumetric analysis based upon them might not be devised. 35. Represent by graphic symbols the sulphites whose symbols are given in (244). 36. The refuse lime of the gas and alkali works contains calcic disulphide, CaS z . In what way would this be changed by exposure to the air into calcic hyposulphite, and how from this product could sodic hyposulphite be prepared ? 37. Write the reaction of hydrochloric acid on sodic hyposulphite, knowing that hyposulphurous acid, when liberated, breaks up into sulphurous anhydride and sulphur. 38. The specific gravity of the vapor of sulphuric anhydride has been found by experiment to be 39.9. How does this agree with the theoretical value ? Compare the densities of 0=0, SO^ and S0 3 as regards the relative degree of condensation in each. 39. What are the relations of the compounds S0 2 C7 2 , SO Z CIHO, S0 8 , and H Z SO^ to each other? 40. Analyze the two sets of reactions [287 et seq."] and [290 et seqJ], and show from whence the oxygen required to oxidize the sulphur- ous acid is derived, and what part the oxides of nitrogen play in the process. 326 QUESTIONS AND PROBLEMS. 41. In the process of making oxygen gas from sulphuric acid, from whence is the oxygen in the first instance derived ? Might not the same quantity of acid be made to yield an indefinite supply of gas ? 42. It appears by experiment that the Sp. Gr. of H Z SO^ vapor is 24.42. How does this agree with theory, and how do you explain the discrepancy ? 43. It has been found by exact experiments that 100 parts of lead yield 146.45 parts of plumbic sulphate. What is the molecular weight of sulphuric acid ? What assumption does your calculation involve (68) ? Why do you regard this result as more trustworthy than that of the last problem ? Ans. 98.16. 44. How do the symbols of the hydrates of sulphuric acid compare with those of the crystalline salts of this acid ? 45. Write the symbols of sulphuric acid and its two hydrates, rep- resenting them as compounds of SO^ with hydroxyl. Point out the distinction between the ortho and meta acids, and show that a simi- lar distinction may be made among the salts. 4.6. How many litres of sulphuric acid, Sp. Gr. = 1.615, can be made from 1,000 kilos, of pyrites, assuming that all the sulphur in the mineral is burnt ? Ans. 1444.4 litres. 47. How much sulphuric acid by weight, Sp. Gr. = 1.501, will be required, 1st. To neutralize 53 grammes of sodic carbonate? 2d. To dissolve 32.6 grammes of zinc '? 3d. To precipitate completely 2.08 grammes of baric chloride ? Ans. 81.666 grammes, 81.666 grammes, 1.633 grammes. 48. Represent the constitution of the various sulphates by graphic symbols. 49. In what does the symbol of dizincic sulphate differ from that of a sulphite ? 50. If the specific gravity and molecular weight of a solid sub- stance be given, how can you find the molecular volume of the substance in the solid condition ? 51. How does the molecular volume of sulphur compare with that of selenium, 1st. In the solid condition ? 2d. In the crystalline con- dition ? 52. What is true of the molecular volumes of all substances in the state of gas ? 53. Compare the molecular volumes of tellurium and bismuth. QUESTIONS AND PROBLEMS. 327 54. What are the analogies, and what are the chief points of dif- ference between sulphur, selenium, and tellurium ? 55. Write the reaction of hydric selenide on a solution of plumbic acetate, also of potassic selenate on a solution of baric chloride ? 56. Write the reaction when Molybdenite is roasted in the air. 57. Write the reaction of H Z S on a solution of molybdic acid in hydrochloric acid. 58. What is the relative proportion of tungstic anhydride in the two varieties of Wolfram ? Ans. 76.47 to 76.38 %. 59. Write the reaction of hydrochloric acid on Scheelite. 60. In what respects does tungsten resemble molybdenum ? 61. What is the atomicity of tungsten and molybdenum, and what is the prevailing quantivalence in each case ? 328 COPPER. [254. Division IV. 254. COPPER. Ou = 63.5. Dyad. One of the most abundant metals, and known from great antiquity. Of its ores, by far the most important is Copper Pyrites, Fe=S z -Cu, which is found to a greater or less extent in almost all countries. This mineral resembles iron pyrites, but is distinguished from it by greater softness and a ruddier tint. The smelting of the ore is a complex process, and consists in an alternating series of roastings and meltings, during which the iron passes into the slags, while the copper accumulates in the successive "mattes," as they are called, until at last a nearly pure sub-sulphide is obtained. This is now heated in a current of air until the metal is partially oxidized, and then the mass is melted, when the following reaction results : 2 Ou + Cu^S = 4Cu + S0 2 . [295] The crude metal thus obtained must, however, be subsequently refined. To this end it is first kept melted in the air for many hours, until all the impurities are oxidized ; and then the oxides of copper, formed at the same time, are reduced by submitting the mass to the action of carbonaceous gases, which are gener- ated by thrusting a stick of green wood under the molten metal. 255. Metallic Copper. Cu. Found native crystallized in forms of the isometric system. Has a brilliant lustre, and a familiar reddish color. Has great hardness and tenacity. Is very ductile and malleable, and one of the best conductors of heat and electricity. Sp. Gr. 8.8. Fuses at about 780. Vol- atilizes only at a very high temperature. Its vapor burns with a beautiful green flame, which shows in the spectroscope char- acteristic bands. Under ordinary conditions copper undergoes no change in the atmosphere, but if heated to redness in the air it is rapidly oxidized. In presence of acids or solutions of chlo- rides, like sea-water, copper absorbs oxygen from the air at the ordinary temperature, and is more or less rapidly corroded. A similar effect is also produced by aqua ammonia and solutions of ammonia salts. Out of contact with the air, dilute hydro- chloric or sulphuric acids have but little action upon metallic 257.] COPPER. 329 copper. If boiled with strong hydrochloric acid, it very slowly dissolves with the evolution of hydrogen gas. Under the same conditions sulphuric acid, if not too dilute, is decomposed by it, cupric sulphate is formed, sulphurous acid is evolved, and the reaction is similar to [265]. "Nitric acid is the best solvent, but, singularly, the strongest acid has no action on the metal. When diluted with water, however, the action is very violent; cupric nitrate is formed, and a gas is evolved which is generally NO ; but when the acid is very dilute this product is more or less mixed with N 2 0. 256. Cupric Oxides. \_Cu z ~\0 and OuO. Both of which act as basic anhydrides, although the salts of the second are by far the most stable and important compounds. [ Cu^\ has a red color, and when melted into glass imparts to it a beautiful ruby or purple color. It is the Red Oxide of Copper of mineralogy, and is found massive and beautifully crystallized in various forms of the isometric system, also in splendid capillary tufts (Chalcotrichite). CuO is black, but imparts to glass a green color. It is found sparingly in nature, rarely crystallized {Black Oxide of Copper, or Melaconite). May be prepared by roasting copper or igniting the nitrate. Is very easily reduced by hydrogen 67] or carbonaceous materials, and is much used as an oxidizing agent in the process of organic analysis. The following reactions illustrate some of the relations of these oxides and their hydrates: When cold, (Cu=0 2 =SOs + lK-O-H-\- Aq) = CuO 2 H 2 + (KfOfSOt+Ag). [296] Byboiling, (Ou = 0?ff a +Ag) = CuO+(ff a O+Ag). [297] By boiling with grape sugar, 2 =S0. 2 + 1K-0-H 0+Aq) = [Cu 2 ]O + (2KfOfSO s + 2ff 2 + Aq). [298] Bed. An orange-yellow hydrate, 4[(7w 2 ]O. /ZjO, is precipitated on first warming the liquid, but this is rendered anhydrous 'by boiling. 257< Cupric Sulphate (Blue Vitriol). Cu=OfS0 2 . 5ff 2 0. The most important soluble salt of copper. Although when pure 330 COPPER. [ 258. it always crystallizes with five molecules of water, as above, yet it is capable of forming isomorphous mixtures with ferrous sul- phate, Fe = 2 =S0 2 . 1H 2 0. When in this mixture the copper ia in excess, the crystals take 5ff 2 and the form of cupric sul- phate (Fig. 28). If, however, the iron is in excess, they take 1H 2 and the form of ferrous sulphate, similar to Fig. 26. The anhydrous salt is white, but becomes blue on uniting with water, for which it has a very strong affinity. Of the five molecules of water with which the crystalline salt is united, one is held much more firmly than the other four, and may be replaced by a molecule of an alkaline sulphate. This gives a reason for writing the symbol of the salt thus, Ho 2 ,Cuo^SO . 4H 2 0. In like manner the symbols of several so-called basic salts may be written thus, Ho,(Cu0 2 ff) 3 iSO, Ho z ,(CuO z H}^S (Brochantite), Ho,(Cu0 2 ff) 5 lS.2ff 2 0, in which the group Cu0 2 H acts as a monad radical. From solutions of cupric sulphate the copper is readily precipitated by Zn or Fe. Zn + (CuSO, + Aq) = Cll + (ZnS0 4 + Aq). [299] 258. Carbonates. Malachite, ( Ou 2 ff) 2 = CO. Same com- pound may be obtained by mixing hot solutions of cupric sul- phate and sodic carbonate. Azurite, Cuo&Ho 2 C 2 or Ho,Cuo = C-Cuo-C=Cuo,Ho. Mysorin, Cuo 2 =C. The normal carbonate is not known. 259. Nitrates. Cuo=(N0 2 ) 2 . QJT 2 when crystallized be- low 60, and Cuo=(N0 2 ) 2 .3ff 2 when crystallized above 60, a deliquescent blue salt. A green basic nitrate has the symbol 260. Cupric Phosphate, Cuo s l(PO) 2 , is obtained on adding a solution of sodic phosphate to a solution of cupric sulphate. 261. Cupric Silicate. Dioptase, Ho,(Cu0 2 H)=SiO. 262. Sulphides:- Copper Glance [Cu^S, Covelline (Indigo Copper) CuS, Copper Pyrites Fe=S 2 =Cu, Erubescite Fe =$=([ CkJ -S-[ CfcJ), Tetrahedrite [ OuJ^S 6 1 Sb 2 . ZnS. 2G7.] COPPER. 331 When H 2 S is passed through the solution of a copper salt, a black precipitate falls having the composition Cu^S^IIo^ which rapidly oxidizes in the air. 263. Fluohydrate of Copper. (CuOH)-Fl. Chlorides. Cuprous Chloride, [<7w 2 ] 01%. White compound, insoluble in water, crystallizes in tetrahedrons. Cupric Chloride, CuCl 2 . 2ff 2 0, crystallizes in green needles, very soluble in both water and alcohol. Cupric Oxichloride, ( Cu 4 3 )= C1 2 . ^H z 0, is much used as a paint (Brunswick green), and the mineral Atac- amite is the same compound, with only one, or at most two, mole- cules of J? 2 0. 264. Cupric Hydride. CuJT 2 . A brown powder, which gives, with hydrochloric acid, the following remarkable reaction : CuJH a +(2ffOl + Ag) = (OuOl a +Aq) -\-2ff-ff. [300] 265. Ammoniated Compounds. When a solution of ammo- nia or of ammonia carbonate is added to a solution of a salt of copper, the light-green precipitate first produced readily dis- solves in an excess of the reagent, producing a deep-blue solu- tion ; and this striking coloration is one of the most characteristic tests of the presence of copper. The effects are caused by the formation of certain remarkable compounds, in which a portion of the hydrogen of the ammonia appears to have been replaced by copper. The following are a few examples: , . ff,0. 266. Characteristic Reactions. The presence of copper in a solution may be readily detected, not only by ammonia as in- dicated above, but also by the action of polished iron (a needle, for example), which, in a feebly acid solution, soon becomes covered with a red metallic coating. Copper ores, when mixed with fluxes, are readily reduced on charcoal before the blow- pipe, and this is one of the best means of recognizing such compounds. 267. Uses. Besides the numerous uses of the metal itself, copper is employed in the arts still more extensively when alloyed with other metals. The varieties of brass and yellow metal are alloys of copper and zinc in different proportions, 332 MERCUEY. [ 268. while bronze, bell-metal, gun-metal, and speculum-metal are all essentially alloys of copper and tin. Several of the compounds of copper are much used as paints. 268. MERCURY. Ify = 200. Dyad. This element is not widely disseminated, but its ores are abundant in a few lo- calities, of which the most noted are Idria in Austria, Almaden in Spain, New Almaden in California, and Huancavelica in Peru. The ores at all these localities consist chiefly of Cinnabar, HgS, but they frequently contain a small quantity of the metal in the native state. They are easily smelted, the sulphur of the ore serving as fuel. The assorted ores are arranged in layers in kilns of peculiar construction, and the mass kindled with brush- wood. As the sulphur burns away, the mercury is volatilized, and the products thus formed are passed through earthen pipes ("aludels") or brick chambers, which condense the mercury vapor, while the S0 2 gas escapes into the atmosphere. ffgS+ 0*0 = ffff+SO* [301] In the Palatinate, mercury is obtained from cinnabar by mixing the ore with slaked lime and distilling in iron retorts. 4ffgS + 4 CaO = 3 CaS + CaS0 4 -f Hg. [302] 269. Metallic Mercury. Hg. The only metal liquid at or- dinary temperatures. Freezes at 40. Boils at 350 and evaporates, but only with exceeding slowness at the ordinary temperature. Sp. Gr. of liquid, 13.596. Sp. Gr. of vapor by experiment, 100.7. Has a brilliant metallic lustre, silver-white color. In solid condition is malleable, crystallizes in octahedrons, Sp. Gr. 14.4. In contact with the air pure mercury undergoes no change at the ordinary temperature, but if boiled in the at- mosphere, it is slowly converted into HgO. Hydrochloric acid is without action on the metal, and the same is true of dilute sulphuric acid. Strong sulphuric acid, however, is decomposed by it [265]. The best solvent is nitric acid, which yields dif- ferent products according to the proportions of metal, acid, and water used. Chlorine, Bromine, Iodine, and Sulphur all enter into direct union with mercury. By simple trituration the liquid metal admits of being mechanically mixed in a state of minute subdivision with chalk and with saccharine or oleaginous sub- 272.] MERCURY. 333 stances, and many important pharmaceutical preparations are made in this way, blue-pills, mercurial ointments, etc. 270. Oxides of Mercury. Mercurous Oxide, [_Hg 2 ~\0. Black powder, very unstable. Decomposed by exposure to light or to a very gentle heat. \_Hg 2 ~\ = Hg -f- Hg. Mercuric oxide, Hg 0. Red crystalline scales or yellow powder, according to mode of preparation. Stable compound, but decomposed at red heat into mercury and oxygen [228]. No corresponding hydrates are known, but both oxides form stable salts. 271. Nitrates. Mercurous nitrate is obtained by dissolving metallic mercury in an excess of nitric acid diluted with four or five times its bulk of water. Mercuric nitrate is best obtained by dissolving mercuric oxide in an excess of nitric acid. These, like other salts of mercury, tend to form basic compounds. Mercurous Nitrate Dimercurous Nitrate Trimercurous Dinitrate Mercuric Nitrate Hg - OfN 2 4 . 2ff 2 0, Dimercuric Nitrate (Hg - -Hg) = 2 =JV 2 4 . 2ff 2 0, Trimercuric Nitrate (Hg-Q-Hg-0 -Hg) = 2 =N 2 4 .IT 2 0. A solution of mercurous nitrate with caustic soda gives a black precipitate of mercurous oxide. 2Na-0-ff+ Aq) = Iffg*] + (2Na-0-N0 2 + ff 2 + Aq). [303J A solution of mercuric nitrate with caustic soda gives a yel- low precipitate of mercuric oxide. Aq). [304] Mercurous nitrate, if heated, is converted into the red crys-^ talline variety of mercuric oxide. = 2 =N 2 Oi = 2ffffO + 2N0 2 . [305] 272. Sulphates. When mercury is gently heated with an ex- cess of strong sulphuric acid, Mercurous Sulphate, 334 MERCURY. [ 273. is formed; but if the heat be increased, and the evaporation carried to dry ness, the first product is changed into Mercuric Sulphate, ffg = 2 =S0 2 , which is a white crystalline powder r readily dissolving in a solution of common salt, but decomposed by pure water into a soluble acid and an insoluble basic salt. The last is known as turpeth-mineraL It has a yellow color, and its composition is expressed by the symbol, Mercurous sulphate is also prepared for the manufacture of calomel by triturating together mercuric sulphate with a quan- tity of mercury equal to that which it already contains. 273. Sulphides. Mercurous Sulphide, [Hg^\S, obtained as a black precipitate on passing ff 2 S gas through the solution of a mercurous salt. Very unstable, like the corresponding ox- ide. Mercuric Sulphide (Vermilion, Cinnabar), HgS, is pre- cipitated by the same reagent from the solution of a mercuric salt. This precipitate is also black, but when sublimed the sub- stance acquires the peculiar vermilion tint. Vermilion is usually prepared by rubbing together mercury and sulphur, and sub- liming the black product. Crystals are frequently thus obtained identical in form with those of natural cinnabar (76). 274. Chlorides. Mercurous Chloride, \_Hg%~\ C1 2 , may be obtained either as a white powder or in crystals (75), 1st. By subliming a mixture of mercuric chloride and mercury, Hg C1 2 + Hg = \Hg^ C1 2 . [306] 2d. By subliming a mixture of mercurous sulphate and com- mon salt, = Na 2 S0 4 + [Zfo] C1 2 . [307] 3d. By precipitation from a solution of mercurous nitrate, ([ffffdNtO, + 2NaCl + Ag) = C^,] C1 2 + (2NaN0 3 + Aq). [308] Calomel is insoluble in water, alcohol, and ether. The Sp. Gr. of its vapor is only one half of that which the theory would require, an anomaly which is explained as an effect of disas- 276.] MERCURY. 335 sociation. Sublimes below a red heat without melting. When triturated with a solution of soda or potash, it" is turned black, owing to the formation of (ffy 2 ) 0, and when heated with alka- line chlorides it is converted into HgCl z . In the presence of or- ganic matter, acids, and air, this last change may take place, to some extent at least, at a temperature of 38 or 40. Calomel is an invaluable medicine. It was first prepared by rubbing together in a mortar Hg -f- Hg C1 2 , but this product, although having all the medicinal properties of the white sublimate, had a brilliant black color, whence the name, from Ka\bs p.t\as. 275. Mercuric Chloride (Corrosive Sublimate). ffgCl 2 . Crystalline (77) white solid, melting at 265, boiling at 293, and yielding a vapor whose Sp. Gr. (141.5) conforms very nearly to the theory. Soluble in water, alcohol, and ether. Forms salts with the alkaline chlorides as %Na Cl . Hg C1 2 . May be prepared by subliming a mixture of mercuric sulphate and common salt, but adding a small amount of Mn0 2 to the mix- ture to prevent the formation of calomel. Also found when mercury is burnt in chlorine gas. Coagulates albumen, and forms with it, as well as with other albuminoid substances, sta- ble compounds insoluble in water. Acts as a violent poison. Used for preserving from decay wood, dried plants, and other objects of natural history, and this effect appears to be due in part to its peculiar action on albuminoid compounds. It is also a valuable reagent, and is used to prepare other anhydrous chlorides. Mercury forms, like copper, a large number of oxichlorides. It also combines with the other members of the chlorine group of elements. Among these compounds the most interesting is the iodide, Hgl^ which affects two different crystalline forms dis- tinguished also by striking differences of color. As obtained by precipitation (Hg (74 + 2KI+ Aq) = HgI 2 + (2 KCl + Aq), [309] it appears as a crystalline red powder (75). This when heated changes its crystalline condition (77) and becomes yellow, but the yellow variety is changed back to the red by mere friction. 276. Ammoniated Compounds. The compounds of mer- 336 MEECUKY. [277. cury, when acted on by ammonia or its salts, yield a large num- ber of complex products. Among these the most remarkable is a powerful base called Mercuramine, which is formed by the action of aqua ammonia upon yellow precipitated oxide of mer- cury. There is a difference of opinion in regard to the arrange- ment of the atoms in this compound, but the most probable symbol is (Hg,(HgOH),H^N)-Q-H. ff 2 0. The hydrate ab- sorbs O0 2 from the air, and forms definite salts with all the common acids. This compound is unstable, but when heated, two molecules of the hydrate give up three molecules of water, and there is left a dark brown product permanent in the air, whose symbol may be represented after the type \_H^N^ Z 0. The following are the symbols of a few only of the many mer- curial compounds of this class : formed by the action of ammonia gas on pre- cipitated calomel. black compound, formed from calomel by action of aqua ammonia. = C^ "White Precipitate," formed by adding to aqua ammonia a soluti Clto "Soluble White Precipitate. 277. Characteristic Reactions and Uses. The salts of mer- cury, whether soluble or insoluble, are all reduced to the metal- lic state by a solution of stannous chloride. Any of the salts heated in a closed tube with sodic carbonate give a sublimate of minute globules of mercury. From solutions of its salts mer- cury is deposited as a gray film on metallic copper, and if short lengths of copper wire thus coated and carefully dried be heated in a closed tube, the sublimate is obtained as before. The chief consumption of metallic mercury is in the treat- ment of gold ores. It is also used for silvering mirrors, for making various philosophical instruments, and for other pur- poses in the arts. Large quantities are consumed in prepar- ing its various compounds, and these are among the most im- portant articles of the materia medica. QUESTIONS AND PROBLEMS. 337 Questions and Problems. 1. Write the reaction of boiling sulphuric acid on copper. 2. Write the reaction of nitric acid on copper, 1st, assuming that NO is the aeriform product ; 2d, that it is N Z 0. 3. Write the reaction which takes place when cupric nitrate is decomposed by heat. 4. Why does not concentrated nitric acid act on copper ? 5. Represent the constitution of the hydrate 4[Cw ]0 . H Z in the typical form. How may it be regarded as related to the normal hydrate [CwJ=flb, ? Ans. It equals 4[Cw 2 >#o a 3# 2 0. 6. How may anhydrous cupric sulphate be used to detect the presence of moisture ? 7. In what other way may the symbols of the different basic sul- phates be written ? Ans. The symbol of Brochantite may be written (Cu-O-Cu-0- Cu-0-Cu)=0 2 =S0 2 . BH 2 0, and the others in a similar way. 8. How may the symbols of the basic sulphates be derived from the hydrates ? Ans. Disregarding the water of crystallization, we may regard Bro- chantite as formed from the condensed hydrate 4Cu=0 2 =H z by first eliminating 3H Z O and then replacing the remaining H 2 by SO y 9. If the symbol of Brochantite is written as in the text, to what order of sulphates does it belong ? Ans. Orthosulphates. 10. Show by graphic symbols that the radical Cu Z H must be a monad. 11. Represent by graphic symbols the composition of Malachite and Azurite. 12. Both Malachite and Azurite may be regarded as formed by the molecular union of cupric hydrate and cupric carbonate. Write the symbols on this theory. 13. Malachite is how related to cupric hydrate? Ans. It may be regarded as the hydrate doubly condensed with two of the hydrogen atoms replaced by CO thus, Cu,=OfCO,tf 3 or Cu-O^CO . Cu-OfH$. Symbol of Azurite in the same way becomes Cu,W^(CO\,H 3 or 2Cu=0 2 =CO. Cu=OfH f 14. To what order of carbonates does Mysorin belong? 15 V 338 QUESTIONS AND PKOBLEMS. 15. In what other ways may the symbol of the cupric nitrates be written ? Ans. Cu=Of(NO a \ and Cu=0=NO^H y or Cu=Of(NO^,H . Cu* 16. Write the symbol of dioptase in the same typical form. Ans. H z ,Cu=OfSL 1 7. To what order of silicates may dioptase be referred ? Ans. Orthosilicates. 18. Write the reaction of solution of sodic phosphate on solution of cupric sulphate. 19. Represent the constitution of the various sulphides of copper by graphic symbols. 20. In what relation does the fluohydrate of copper stand to the hydrate and fluoride of the same metal ? Ans. It holds an intermediate position, as shown by the symbols Cu=Ho z , Cu=Ho,Fl, CuFl z . 21. Regarding the molecule of water in the common variety of Atacamite as water of constitution, how may the formula of this mineral be simplified ? Ans. It may be halved and written (Cu-0-Cu)=Ho,CL 22. How is Atacamite related to cupric hydrate ? Ans. 2Cu=Ho 2 = (Cu-0-Cu)=Ho 2 -\- H 2 0, then replacing one atom of Ho in basic hydrate by CL 23. What do you find that is remarkable in the reaction of cupric hydride on hydrochloric acid ? Compare it with reaction [236], and consider whether it indicates a difference of condition in hydrogen similar to that in oxygen. 24. Write the symbols of the ammonia compounds of copper in the vertical form. 25. What evidence can you find that a portion of the nitrogen atoms in two of the compounds stand in a different relation to the molecule from the others ? Ans. If the nitrogen atoms were all typical, we should expect the basic radicals to fix more than the equivalent of two univa- lent acid radicals. 26. Write the symbols of the hydrates which correspond to the different basic nitrates of mercury, and show how such basic hy- drates may be derived from the assumed normal hydrates. 27. How is it possible that salts should exist corresponding to hy- drates that cannot be isolated ? QUESTIONS AND PKOBLEMS. 339 28. Show how turpeth-mineral may be derived from an assumed normal hydrate. 29. How would you seek to determine whether the black product obtained by grinding together Hg -j- S is a mixture or a compound ? 30. By experiment it appears that the specific gravity of calomel vapor is 118.5. What should it be theoretically? Into what is it probably decomposed when heated ? Ans. 235.5 ; Hg and HgCl^. 31. In administering calomel as medicine, what associations with other drugs should be avoided ? 32. How may calomel be distinguished from corrosive sublimate ? 33. What is the theoretical Sp. Gr. of HgCl y and why should you anticipate so great a difference between it and the experimental re- sult? Ans. 135.5. In such a dense vapor the deviation from Mariotte's law would probably be large. 34. Write the reaction which takes place when a mixture of mer- curic sulphate and common salt are sublimed. 35. In cases of poisoning by corrosive sublimate, why should milk or the white of eggs be useful as temporary antidotes until the stomach can be emptied by an emetic or otherwise ? 36. Write the symbols of the chloride, nitrate, sulphate, and car- bonate of mercuramine. 37. Write the symbol of the oxide of mercuramine described above. 38. Represent the different ammoniated compounds of mercury by vertical symbols, and point out the type of each. 340 CALCIUM. 278.] Division V. 278. CALCIUM. Oa 40. Dyad. One of the most abundant and important constituents of the crust of the globe. The elementary substance is a soft, malleable metal, with a reddish tinge of color. Readily tarnishes in the air, and burns when heated, forming lime. Decomposes water at all temper- atures, forming calcic hydrate. The metal is obtained with difficulty either by the electroly- sis of the melted chloride or by decomposing the iodide with sodium. 279. Calcic Carbonate. Co, = 0. 2 = CO or Cao = CO. The chief lime mineral. Remarkable for the great variety of its crystal- line forms. Dimorphous (Hexagonal and Orthorhombic). The hexagonal forms (Figs. 14, 16, 17, 40, 41, and 42) belong to the mineral species Calcite. The orthorhombic forms (74) to the species Aragonite. Sp. Gr. of Calcite 2.72, of Aragonite 2.94. The last is also distinguished from the first by superior hardness, and falling to powder when heated. The crystalline varieties of calcite are readily recognized by a very striking rhombohedral cleavage. Limestones, Oolite, Chalk, Marble, Travertine, Tufa, Calcareous Marl, are names of varieties of rocks, which consist chiefly or wholly of one or the other of these two minerals, generally of calcite. Many of these rocks make excellent building stones. All the varieties of calcic carbonate dissolve with effervescence in dilute nitric and other acids, and may thus be distinguished from the siliceous miner- als which they sometimes outwardly resemble. Calcic carbonate, although nearly insoluble in pure water, is readily dissolved by water charged with C0 2 . Thus it is held in solution by the water of lime districts, and to a greater or less extent by most spring water. Such water, when strongly charged, deposits calcic car- bonate on exposure to the air, and thus are formed stalactites, tufa, and travertine. It also forms deposits in boilers, and de- composes the soap used in washing. (Hard water.) Calcic carbonate may be readily formed artificially by the reaction 282.] CALCIUM. 341 (OaCl 2 + (Nff,) 2 =C0 3 + Aq) = Ca-C0 3 + (2(Nff 4 ) Cl + Ag). [311] Singularly, however, if the products of the reaction are boiled together, the reverse change takes place ; calcic chloride is formed, which dissolves, while ammonic carbonate is carried away with the steam. 280. Calcic Oxide ( Quick-lime). Ca 0. Obtained by burn- ing limestone in kilns. Ca CO 3 = CaO + @ 2 . [312] Amorphous white solid. Very infusible, and emitting an intense white light when ignited (Drummond Light). Has strong af- finity for water, and the chemical union is attended with the evolution of much heat (slaking). Exposed to the air, it grad- ually absorbs both water and carbonic anhydride (air slaking). 281. Calcic Hydrate. Ca=Ho 2 . A light dry powder. Sol- uble in about 425 parts of cold water (lime-water). With a smaller quantity of water it forms a sort of emulsion called milk of lime, and with still less water it gives a somewhat plastic paste, which, mixed with sand, is ordinary mortar. Hydraulic cements,, which harden under water, are made from limestones containing from fifteen to thirty-five per cent of finely divided silica or clay ; also by intimately mixing with chalk a due proportion of clay under regulated conditions, and subsequently burning. Calcic hydrate acts on the skin like a caustic alkali, and is used by the tanners for removing hair from hides. It has a strong affinity for CO* and hence is used for rendering soda and potash caustic [97]. It is also em- ployed for purifying coal-gas, and in many other processes of the arts. It is largely used as a manure. Whitewash is milk of lime mixed with a little glue. 282. Chloride of Lime or Bleaching Powder, CaOCl 2 , is formed by passing chlorine gas into leaden chambers containing slaked lime, which absorbs the gas very rapidly. Ca + Cl- Cl=(Ca- 0)- C1 2 . [313] Very much used in the arts for bleaching cotton goods. The cloth having been well washed and digested in a weak solution 342 CALCIUM. [283. of chloride of lime, is passed into very dilute sulphuric acid, which liberates the chlorine in the fibre of the cloth. May also be used in the laboratory r,s a source of chlorine gas. (CaOCl z + Jf 2 S0 4 + Aq) = t + ff 2 -t- Aq) + 01-01. [314] 283. Calcic Peroxide. (Ca-0)=0. Formed by adding to lime-water, but is a very unstable compound. 284. Calcic Sulphate. Ca = 2 = S0 2 . Second in importance of the lime minerals. It occurs in nature both in an anhydrous and hydrous form. The anhydrous mineral is called Anhydrite, the hydrous mineral is Gypsum. Anhydrite crystallizes in the orthorhombic system (77), and has Sp. Gr. = 2.9. Gypsum (CaS0 4 . 2ff 2 0) crystallizes in the monoclinic system (Fig. 25), has Sp. Gr. = 2.3, and is softer than the first. Calcic sulphate is soluble in about 400 parts of water, and, like several of the lime salts, is much less soluble in hot water than in cold ; and when water holding gypsum in solution is heated to a high tem- perature in steam-boilers, the whole is deposited in an insoluble condition (CaS0 4 . \H^G). It is a very common impurity of spring waters, and is another cause of their hardness, and of the crusts which they sometimes form on the inner surface of boilers. It is found in considerable quantity in the water of salt springs, and of the ocean. When these waters are evap- orated it is deposited before the common salt. Hence in nature we find that beds of rock-salt are usually associated with anhy- drite and gypsum. The last is by far the most abundant min- eral, forming in some places extensive rock deposits of great thickness. It is, moreover, found in beautifully transparent crystals (Selenite), which can be easily split into very thin plates, and it also forms the ornamental stone called alabaster. When heated, gypsum readily gives up its water of crystalliza- tion, and when not overburnt the dry product, if reduced to powder and made into a paste, again unites with water and sets into a hard mass. This reunion, however, will not take place if the gypsum has been heated above 300 ; and anhydrite is then formed. The calcined gypsum, called Plaster of Paris, is used in immense quantities for making casts, and in various forms of stucco-work. Ground gypsum is also a valuable ma- nure, and finds other applications in the arts. 288.] CALCIUM. 343 285. Calcic Phosphate. Cao 3 (PO) 2 . The chief earthy con- stituent of the bones of animals. The animal obtains it from the plants, and the plant draws its supply from the soil. The .grains of the cereals are especially rich in this bone-making material, and as the supply in the soil is usually limited, these plants, when cultivated year after year, soon exhaust it. Hence it is all important for the agriculturist to restore to his land the phosphates as fast as they are removed by the crops, and ground bones, guano, phosphorite, and other forms of calcic phosphate, are used for this purpose. The mineral Apatite is a crystal- line variety (Fig. 14) of this same material, but contains also about eight per cent of calcic fluoride mixed with more or less calcic chloride. Its symbol may be written (Ca 5 F)ixO Q ix(PO) s . 286. Calcic Silicate (Tabular Spar), Cao=SiO, is a not un- common mineral. Formed on the surface of the grains of sand when mortar hardens ; and the valuable qualities of hydraulic cements are probably due to a still more complete union of the same kind. An artificial stgne of great strength may be made by first mixing together solutions of calcic chloride and sodic silicate, and then incorporating with the half-fluid mass a large proportion of sand. 287. Calcic Fluoride (Fluor- Spar). CaF 2 . An abundant mineral and the most important compound of fluorine. It is found both massive arid crystallized in the forms of the isomet- ric system, generally in cubes. Has octohedral cleavage. The pure material is colorless, but the native crystals are frequently beautifully colored, and are among the most splendid specimens of our mineral cabinets. Exposed to the light, they frequently exhibit a remarkable fluorescence, and many varieties of the mineral phosphoresce when heated. Although not very fusible by itself, fluor-spar forms a very fusible slag with gypsum and other earthy minerals frequently associated with lead ores. This property renders it a valuable flux in the process of smelt- ing such ores, and hence the name fluor. In small quantities it is almost invariably associated with calcic phosphate, not only in the mineral kingdom, but also in the bones and teeth of animals. 288. Calcic Chloride. CaCl 2 . A deliquescent salt, readily obtained by dissolving calcic carbonate in hydrochloric acid. Also a secondary product in the preparation of ammonia [162]. 344 STRONTIUM. BARIUM. [289. OaO0 3 + (2HOI + Aq) = (CaCl 2 -\-ff 2 + Aq) + C0 2 . [315] A useful reagent, and also employed, on account of its hygro- scopic qualities, for drying gases. 289. Calcic Nitrate. Cao=(N0 2 ) 2 . Also a very soluble deliquescent salt, which is formed in the soil, in cellars, in lime caverns, and wherever organic matter decays in contact with calcareous materials. Chiefly important as a source of saltpetre. 290. STRONTIUM, Sr=87.6, and BARIUM, Ba = l37. Dyads. The compounds of these elements are closely allied to the corresponding compounds of calcium, and the differences are only those which we should expect between members of the same chemical series. They are, however, far less abundantly distributed in nature. The most important native compounds are Strontic Carbonate, Strontianite, SrC0 3 , Sp. Gr. 3.70. Baric Carbonate, Witherite, BaCO s , Sp. Gr. 4.32. These are isomorphous with Aragonite. No hexagonal forms corresponding to calcite are known. In like manner we have Strontic Sulphate, Celestine, SrSO# Sp. Gr. 3.95. Baric Sulphate, Heavy Spar, BaSO^ Sp. Gr. 4=AS. These are isomorphous with anhydrite. No hydrous minerals corresponding to gypsum are known. Strontic sulphate is much less soluble in water than calcic sulphate, and baric sulphate is practically insoluble. Moreover, the solubility of these salts is not increased by the presence of weak acids. Hence a solution of calcic sulphate will give a precipitate in solutions containing either strontium or barium, and a solution of strontic sulphate only in the last. The sulphates are both easily prepared artifi- cially from solutions of corresponding chlorides by precipitation with sulphuric acid. 291. The Strontic and Baric Nitrates and the Strontic and Baric Chlorides are all soluble salts, but less soluble than the corresponding salts of calcium, the barium compounds being in each case the less soluble of the two. They are easily prepared by dissolving the native carbonates in dilute nitric or hydro- 295.] STRONTIUM. BARIUM. 345 chloric acids. Baric nitrate is precipitated from its aqueous solution by strong nitric or hydrochloric acid in consequence of its sparing solubility in these reagents. They may also be pre- pared from the native sulphates, as is illustrated by the follow- ing reactions : SrS0 4 + 4(7= SrS+ 4. [316] (SrS + ZHCl + Aq) = (SrOl 2 + Aq) + SL^. An intimate mixture of the powdered sulphate with some car- bonaceous material is first intensely heated in a crucible. The resulting product is then exhausted with water, and the solution treated with hydrochloric or nitric acid as required. 292. Strontic and Baric Hydrates may also be prepared from the solution of the sulphides, obtained as above, by the reaction (BaS + H,0 + Aq) = CuS+(Ba=ffo 2 +Aq). [317] The relative solubility of the hydrates follows the inverse order of that of the other salts, baric hydrate being much the most sol- uble and dissolving in twenty parts of water. 293. Strontic and Baric Oxides may be readily obtained by igniting the nitrates. They slake when mixed with water, like quick-lime. 294. Strontic and Baric Peroxides are prepared by heating the oxides in an atmosphere of oxygen gas. They are more stable than calcic peroxide, and baric peroxide is an important reagent. 295. Characteristic Reactions. Calcium, strontium, and barium are all precipitated from their solutions by alkaline car- bonates and by oxalic acid. They may be distinguished from each other by the relative solubility of their sulphates, 1 and by the colors of their flames, which show characteristic bands with the spectroscope. The compounds of strontium impart to a colorless flame a brilliant crimson color, and those of barium a 1 Calcic sulphate gives an instantaneous precipitate in solutions of barium salts, while in those of strontium the precipitate only forms after a perceptible interval of time. 15* 346 LEAD. [296. yellowish green. Hence they are much used by makers of fire- works. The soluble salts of barium are important reagents in the laboratory, and both the native and the artificial sulphate furnish an important white paint. 296. LEAD. Pb = 207. Bivalent or quadrivalent. One of the more abundant metallic elements, found chiefly in mineral veins. Principal ore is Galena, PbS. There is also a native Plumbic Carbonate called Cerusite (PbC0 3 , Sp. Gr. 6.48), isomorphous with Aragonite, and a native Plumbic Sulphate called Anglesite (PbSO# Sp. Gr. 6.30), isomorphous with an- hydrite. 297. Metallic Lead. Pb?Sp. Gr. 11.36. Melting-point, 325. So soft that it can be moulded by pressure. Obtained, 1st. By alternately roasting and melting the galena in a rever- beratory furnace. Roasting stage, 30=0 = PbS ZPbO 2^(fi> or 20=0 = PbS + PbS0 4 -, Melting stage, PbS + 2PbO = 3Pb + ^ 2 , or PbS+ PbSO* = 2d. By smelting the galena with scrap-iron in a blast-furnace, PbS + Fe = FeS + Pb. [320] Practically, nowever, both processes are far more complex than the reactions would indicate. The ore is in all cases mixed with gangue, which can only be melted with the aid of some flux, and the slags thus formed contain a large amount of metal and must be smelted again. Lead dissolves readily in dilute nitric acid, but is not acted on, or only very slightly, by either hydrochloric or sulphuric acids, unless concentrated and boiling. Employed in number- less ways in the arts, both pure and alloyed, with other metals. Type-metal, britannia-metal, and solder are among the most im- portant of its alloys. 298. Plumbic Oxide. PbO. Obtained by heating tead in a current of air, when, if the heat is not too great, a yellow pow- der is obtained called Massicot. At a heat a little below red- 302.] LEAD. 347 ness the oxide melts and crystallizes on cooling in yellowish red scales called Litharge. Largely used in the arts for mak- ing flint-glass, for glazing earthenware, and for preparing vari- ous paints and lead salts. 299. Plumbic Peroxide. Pb0 2 . A dark-brown powder, very useful in the laboratory as an oxidizing agent. The bright red powder called Minium, obtained by still further roasting massicot at a low red heat, is a mixture of Pb0 2 and PbO. There is also a suboxide, Pb 2 0. 300. Plumbic Hydrate. The normal hydrate, Pb=Ho^ has never been obtained, but we can readily form Diplumbic Hydrate (Pb-0-Pb)=ffo 2 , Triplumbic Hydrate (Pb-0-Pb-0-Pb)-Hb^ by the following reactions : 2Pb=(N0 3 ) 2 + (\K-Ho + Aq) = (Pb-0-Pb)-Ho 2 + (K-NOs + ff 2 + Aq). [321] ((Pb 3 2 )-(C 2 ff 3 2 ) 2 (Pb 3 2 )-ffo 2 -f (2(NHt)-(C 2 Hs0 2 ) + Aq). [322] A plumbic hydrate is formed by the simultaneous action of air and water on lead, which is slightly soluble ; and as all lead salts are poisonous, and even in minute quantities, if the dose is often repeated, may be injurious to health, it is not safe to use, for drinking, water which has been kept in cisterns lined with lead or drawn through lead pipes. The presence of nitrites, nitrates, or chlorides greatly increases the corrosive action of water on lead, while carbonates and sulphates exert a preser- vative influence. 301. Plumbic Nitrate. Pb=(NO s ) 2 . Obtained by dissolving litharge or lead in dilute nitric acid.. Soluble in water, but in- soluble in strong nitric acid. PbO+ (2ff-N0 3 + Aq) = (Pb=(N0 3 ) 2 +ff 2 0+Aq). [323] (SH-N0 3 + Aq) = (3Pb-(N0 3 ) 2 + H. 2 + Aq) + 23BST. [324] 302. Plumbic Acetate (Suyar of Lead). 848 LEAD. [303. Sff 2 0. The most important soluble salt of lead, easily ob- tained by dissolving PbO in acetic acid. Lead has a great tendency to form basic salts (38). Hence a solution of the neutral acetate will dissolve a large additional quantity of litharge. 2PbO + (Pb=(C 2 ff 3 2 ) 2 -}- Aq) = ' ((Pb-0-Pb-0-Pb)=(C 2 ff 3 2 ),+ Aq). [325] If O0 2 is now passed through this solution, the excess of PbO is precipitated as carbonate. Fresh portions of Pb may then be dissolved and the process repeated. The plumbic carbonate, which is obtained by this and other analogous methods, is very much used as a white paint under the name of white lead. The products of the different processes have not, however, the same composition, but are mixtures of the carbonate and hydrate in varying proportions. 303. Plumbic Sulphate, PbS0 4 , is obtained as a white pre- cipitate on adding sulphuric acid or a soluble sulphate to a solu- tion of a salt of lead. It is practically insoluble in pure water and dilute sulphuric acid. 304. Plumbic Phosphate is found in nature in the mineral Pyromorphite, which is isomorphous with apatite and has an analogous constitution (Pb & Cl) i* Q ix(PO) B . The mineral Mim- etine is the corresponding isomorphous arseuiate. A melted globule of plumbic phosphate assumes on cooling a peculiar radiated crystalline structure, which is very characteristic. 305. Plumbic Chloride, PbCl 2 , may be obtained as a white crystalline powder by the reactions PbO + (2HOI + Aq) = PbCl 2 -\-(ff 2 + Aq).> [326] (Pb(N0 3 ) 2 + 2HOI + Aq) = PbOl 2 + (2HN0 3 + Aq). [327] It is only very slightly soluble in cold water, but in boiling water dissolves quite readily. 306. Plumbates. Caustic alkalies dissolve Pb very freely, forming salts in which the lead plays the part of a negative radical. Hence the precipitate formed in reaction [321] dis- solves /in an excess of the reagent, and a solution of Pb in lime-water is used as a hair-dye. 307.J REACTIONS AND PROBLEMS. 349 307. Characteristic Reactions. The lead compounds, in many of their reactions, are closely allied to the compounds of the first three elements of this group. For example, the sol- uble salts give precipitates with the alkaline carbonates and with oxalic acid. But in other reactions there are marked dif- ferences. Thus, 1. A strip of metallic zinc placed in a solution of plumbic acetate precipitates all the lead. Zn, + (Pb-(0 2 ff 3 2 ) 2 + Aq) = Pb + (Zn=(C 2 ff 3 2 ) 2 + Aq). [328] 2. Sulphuretted hydrogen gas passed through either an acid or an alkaline solution of a salt of lead gives a black precipitate of plumbic sulphide. (Pb-Cl 2 + H 2 S + Aq) = PbS + (2ffOl + Aq). [329] When the solution is acidified with hydrochloric acid, the pre- cipitate is first red, owing to the formation of (Pb-S-Pb)=Cl 2 , but this is soon converted into the black sulphide. 3. Heated on charcoal before the blow-pipe, with reducing fluxes, the compounds of lead yield a soft, malleable bead of metal, and the charcoal immediately around the bead is at the same time coated with an incrustation of oxide which is orange-colored while hot, but becomes lemon-yellow when cold. By these reactions lead is easily distinguished from calcium, strontium, and barium. Indeed, the distinction is so marked, that, al- though the resemblances are very striking, it may be doubted whether lead belongs to the same chemical series. Reactions and Problems. 1. Calcite and Aragonite are both not unfrequently found in acic- ular crystals. How may they be distinguished ? 2. Compare the molecular volumes of Calcite and Aragonite. 3. By igniting 100 parts of pure calcic carbonate, Dumas obtained exactly 56 parts of lime. What is the atomic weight of calcium? Ans. 40. 4. What assumptions are made in the last problem ? (19.) 350 REACTIONS AND PROBLEMS. 5. How much Ca can be obtained from 1 00 kilogrammes of pure limestone ? How much Ca=Ho z will this amount yield ? Ans. 56 kilos, and 74 kilos. 6. How much limestone must be burnt to yield 560 kilos, of quick- lime ? How many cubic metres of C0 2 would be set free in the process? Ans. 1,000 kilos, and 223.1 m". 3 7. In one cubic metre of limestone assumed to be pure calcic car- bonate, Sp. Gr. 2.72, how many cubic metres of CO Z are condensed ? Ans. 607.1 m: 8 8. What is the cause of the incrustation of boilers by calcic car- bonate ? 9. Lime-water is used to purify hard water. Explain the reaction. 10. A bed of limestone, Sp. Gr. = 2.75, and 100 metres thick, would make a bed of anthracite coal of what thickness ? Assume that the Sp. Gr. of anthracite is 1.8, and that it contains 90 per cent of carbon. Ans. 20.37 metres. 11. In order to precipitate lime as completely as possible with ammonic carbonate, it is important to avoid an excess of ammonia salts, and to warm the liquid, but not to boil it. Give the reasons for these precautions. Also analyze reactions [311 and the reverse], and state the principle under which they may be brought. 12. One cubic decimetre of quick-lime, Sp. Gr. 3.18, will absorb how many cubic decimetres of water ? How many units of heat will be evolved by the change of state which the water undergoes ? Ans. 1.022 d^i: 8 13. In burning quick-lime it is found that the process succeeds best in damp weather, and is facilitated by injecting steam into the kiln. Why should you infer that this would be the case ? (58.) 14. Give an explanation of the hardening and adhesion of mortars and cements. 15. When milk of lime is spread over walls in the process of white- washing, what compound is formed on the surface ? 16. How many cubic metres of C0 2 can be absorbed by a quan- tity of milk of lime, containing 112 kilos, of lime (CaO) ? 1 7. When lime-water is shaken up with CO Z it is rendered turbid. How do you explain the reaction, and to what application of lime- water in the laboratory does it point? 18. In order to render 100 kilos, of sal soda caustic how much quick-lime must be used? [97.] Ans. 52.83 kilos. 19. How many litres of chlorine gas would be absorbed by 100 1 REACTIONS AND PROBLEMS. 351 kilos, of lime (CaO) first reduced to hydrate, and how much MnO t must be used to yield the requisite amount ? , Ans. in part, 39.85 litres of chlorine. 20. Bleaching salts have been regarded as a mixture of calcic chloride with calcic hypochlorite. How would you write the symbol on this theory ? 21. Represent by graphic symbols CaCO & CaO v CaOCl 2 . 22. The percentage composition of gypsum is calcium, 23.26 ; sul- phur, 18.61 ; oxygen, 37.21 ; water, 20.92. Calculate the symbol. 23. Is the incrustation of steam-boilers by insoluble calcic sulphate due to the same cause as the incrustation of salt-pans by gypsum? Explain the difference. . 24. If the calcium contained in one cubic decimetre of anhydrite could be replaced by H v what would be the volume of the product formed ? . 25. If a concentrated solution of sodic sulphate is mixed with a .concentrated solution of calcic chloride, the whole mass becomes solid. Write the reaction, and explain what becomes of the water of solution. Ans. (Na 2 SOt -f CaCl, -f 2// 2 0) = 2NaCl -f CaSO^ . 2H^O. 26. How could you detect the presence of sulphuric acid and lime in a solution of gypsum? Write the reactions 27. Represent the constitution of apatite by a graphic symbol. 28. How may you regard apatite as derived from calcic hydrate ? What important part does fluorine play in the compound ? Does not the presence of such a univalent element in this compound fur- ,nish an argument in favor of the diatomicity of calcium ? 29. How much hydrochloric acid, Sp. Gr. 1.1, will be required to dissolve 50 grammes of chalk, and how many litres of O g could be thus obtained ? Ans. 179 grammes of acid and 11.16 litres of C0 y 30. By what single reaction could you change a solution of calcic nitrate into a solution of nitre ? 31. What evidence do you find in this section that calcium is bivalent ? 32. Compare the molecular volumes of the native carbonates of strontium, barium, and lead with those of Aragonite and Calcite. ' 33. Write the reactions by which strontic and baric sulphates may be prepared from the corresponding nitrates or chlorides. 34. Analyze the reactions by which the chlorides and nitrates of 352 EEACTIONS AND PROBLEMS. etrontium and barium may be prepared from the corresponding sul- phates, and show why such a circuitous method is necessary. 35. Compare the molecular volume of the sulphates of this group with that of the corresponding carbonates. 36. How may solutions of calcic and strontic sulphates be used to detect barium and strontium, even if mixed together in the same solution ? 37. Knowing that sulphuric acid if in excess will completely pre- cipitate barium and strontium, how can you detect the presence of lime in a solution containing all three ? 38. On what does the use of the salts of barium as tests for sul- phuric acid depend ? 39. To how much S0 3 do 0.932 grammes of baric sulphate cor- respond ? Ans. 0.320 grammes. 40. A quantity of Witherite weighing 0.591 grammes was dissolved in hydrochloric acid and precipitated with sulphuric acid. The pre- cipitate when washed, dried, and ignited weighed 0.699 grammes. What per cent of barium does the mineral contain ? Ans. 69.37 per cent. 41. Baric and strontic carbonates are not, like calcic carbonates, easily decomposed when heated in the air, but readily give off CO Z if heated in an atmosphere of hydrogen. How do you explain these facts ? and do they confirm or otherwise your answer to question 13 ? 42. What is the percentage of lead in the three minerals Angle- site, Cerusite,and Galena? Ans. 68.32, 77.54, 86.62. 43. Analyze reactions [318 - 320] and state the general theory of the smelting process, including the removal of the gangue and the reduction of the ore. 44. Explain the peculiar action of lead with acid solvents. Why must the nitric acid be diluted, and to what extent ? 45. How many kilos, of litharge can be obtained from 37.1 kilos, of lead, and what volume of oxygen gas would be absorbed in the process? Ans. 39.96 kilos, and 2 in. 8 46. Represent the plumbic oxides and hydrates by graphic sym- bols, and show how the basic hydrates are related to the assumed normal hydrate. 47. The action of nitric acid on lead depends on the degree of concentration and on the temperature. Write the reaction assuming that N Z is formed. 48. How many kilos, of crystallized sugar of lead can be made from 6.69 kilos, of litharge? Ans. 11.37 kilos. REACTIONS AND PKOBLEMS. 353 49. How much litharge will a solution containing 11.37 kilos, of sugar of lead dissolve, assuming that triplumbic acetate is the product formed ? Ans. 13.17 kilos. PbO. 50. Write the reaction of CO Z on a solution of basic acetate of lead. 51. How may the basic acetates be regarded as derived from the normal hydrates ? 52. Write the reaction of dilute sulphuric acid on a solution of plumbic nitrate. 53. Represent the constitution of pyromorphite and mimetene by graphic symbols. 54. What is the derivation of the name pyromorphite ? 55. Will the whole of the lead be precipitated from its solution in acetic acid by an excess of HCl -j- Aqf 56. By what reagent may you precipitate the whole of the lead from a solution of one of its salts ? 57. Why should a solution of PbO in lime-water blacken the hair or any other organic material containing sulphur ? 58. How could you detect the presence of lead in water ? 59. From a solution containing all the members of this group, how could you separate the whole of the lead ? 60. The solubility of the corn-pounds of the elements of this group diminishes, as a general rule, in proportion as the atomic weight of the metallic radical increases. Does this fact conform to the law which generally obtains in chemical series in regard to the chemical energy of the different members ? 354 MAGNESIUM, [308. Divisions VI. and VII. 308. MAGNESIUM. Mg = 24 Dyad, One of the most widely distributed elements, although not so abundant as Calcium, with which it is usually associated* In some of its relations it is very closely allied to calcium,, but also differs from it in many important respects. 309. Metallic Magnesium, Mg, is readily obtained by decom- posing the anhydrous chloride with metallic sodium, also by electrolysis. It is a silver-white metal, melting at a red heat, and volatilizing at a high temperature in an atmosphere of hy- drogen. It is malleable and ductile, is susceptible of a high polish, and does not tarnish in dry air. Heated in the air it takes fire and burns with great splendor [59J, and it is now much used as a source of pure white light when great bril- liancy is required. Boiling water acts upon the metal quite rapidly, but it decomposes cold water only very slowly. 310. Magnetic Oxide (Calcined Magnesia) , MgO, is obtained when the metal is burnt in air. It can also be obtained by cal- cining the carbonate or the nitrate. It is a bulky white powder, wholly infusible, and emitting a bright white light when heated before the blow-pipe. Intensely heated, it appears to volatilize unchanged. When mixed with water it slowly unites with it to form a hydrate. The oxide obtained by calcining the nitrate is much denser than that made from the carbonate, and possesses remarkable hydraulic qualities. When mixed with water, it soon sets forming a hard compact mass resembling marble. If the oxide is heated to a very high temperature, it loses its power of uniting with water, and dissolves only slowly even in the strong- est acids. Crystallized MgO (Figs. 5 to 7), Periclase, has been found in small grains imbedded in a limestone rock ejected from Vesuvius, but otherwise it does not occur uncombined in nature. 311. Magnetic Hydrate, Mg=OfH^ is found native, crystal- lized in large hexagonal plates (76), Brucite. It can be read- ily formed artificially as above, also by adding caustic potassa, soda, or baryta to the solution of any of its salts. It is but very slightly soluble in water, yet sufficiently to give a distinct alkaline reaction (39). It absorbs O0 2 slowly from the air, but much more slowly than calcic hydrate. 313.] MAGNESIUM. 355 312. Magnetic Carbonate. Mg=0 2 =CO. Sp. Gr. 3.056. The mineral Magnesite, isomorphous with Calcite. Insoluble in pure water, but in carbonic acid water more soluble than calcic carbonate. This solution is much used as a medicine (liquid magnesia). If exposed to the air, the magnesic car- bonate slowly separates in crystalline flakes, containing three atoms of water. Anhydrous magnesic carbonate is not readily obtained artificially. The precipitate obtained on adding to a boiling solution of a magnesia salt sodic carbonate is a mixture of magnesic carbonate and magnesic hydrate in variable pro- portions (Magnesia Alba). The product, however, appears to be rather a mixture of several definite compounds of these two salts ; and a crystalline mineral is known called Hydromagnesite, which has the formula H^Mgf> l2 G^ . 2ff 2 or Hof(C*MgofC*MgofC) . 2ff 2 0. Magnesic carbonate is found united with calcic carbonate in the mineral Dolomite (Sp. Gr. 2.9). This is by far the most abundant native compound of magnesium, and forms in many localities extensive beds of rocks. It occurs in large and well- defined crystals which are isomorphous with calcite and magne- site (Fig, 16). The mineral is somewhat variable in its com- position, and may either be regarded as an isomorphous mixture of these two substances, or else as a definite compound mixed with an excess of one or the other of its constituents. MaC0 3 +CaC0 3 or Mgo-(G-0 2 =G)-Cao. When calcined at not too high a temperature, the magnesic car- bonate is alone decomposed, and a product obtained which forms an excellent hydraulic cement. From the calcined mass the magnesia can be dissolved out by carbonic acid water and freed from the lime. In this way pure magnesic carbonate is pre- pared. 313. Magnesic Sulphate (Epsom Salt). MaS0 4 . 7ff 2 0. The most important soluble salt of magnesia. Obtained from the bittern of sea-water, or by treating the native carbonates or Dolomite with sulphuric acid. It is a very common ingredient of mineral waters, like those of Epsom, and is formed when water saturated with gypsum filters through Dolomitic rocks. 356 MAGNESIUM. [314. The salt, with seven molecules of water, is dimorphous, crystal- lizing both in orthorhombic forms isomorphous with ZnS0 4 . 7HO, and in monoclinic forms isomorphous with FeSO^ . 1 HO. It may also be obtained crystallized with 1, 2, 3, .... 12 mole- cules of water under regulated conditions, chiefly of temperature. The compound MgS0 4 . JT 2 (Kieserite) is found in the Stass- furt salt-beds. Epsom salt is reduced to the same composition when heated to 150, but the last molecule of water is retained even at 200, and this leads us to believe that it forms a part of the molecule of the salt, whose formula would then be writ- ten, Mgo=SO=Hop This opinion is confirmed by finding that this molecule of water may be replaced by the molecule of an alkaline sulphate, forming a double salt, which crystallizes with 6ff 2 in tKe same form as magnesic sulphate with 7H 2 0. The symbol of the potash salt is Mgo=(SO=0 2 =OS)=Ko 2 . Epsom salt dissolves in about three times its weight of cold water. It is a valuable medicine, but, like all the soluble salts of magnesium, it has a bitter, disgusting taste. 314. Magnesic Silicates. The well-known minerals, Ser- pentine, Talc (Soap-Stone), and Chrysolite (Olivine), are es- sentially magnesic silicates ; and in many other native silicates, including the Hornblendes, Augites, Chlorites, and some vari- eties of Mica, magnesium is one of the principal basic radicals. 315. Magnesic Chloride. MgOl 2 . Found dissolved in sea- water, and the cause of its bitter taste. Obtained by dissolving magnesic carbonate in hydrochloric acid, and evaporating in an atmosphere of hydrochloric acid gas. If evaporated in the air, the salt is partially decomposed. Very fusible. Used for making magnesium. Forms double salts with alkaline chlorides (134). 316. Characteristic ^Reactions. Magnesium, although closely related to calcium, is distinguished from the alkaline earths by the great solubility of its sulphate, also by its ten- dency to form soluble double salts with ammonium, in conse- quence of which no precipitate is formed in solutions of its salts either by ammonia or ammonic carbonate, when sufficient excess of some ammonia salt is present. The ammonic magnesian phosphate, however, (NH^) 2 ,Mg^O & lP 2 2 . l2ff 2 O is insoluble, and is formed whenever sodic phosphate is added to an am- moniacal solution of a magnesium salt. This reaction furnishes the most delicate test for magnesium salts. 320.] ZINC. 357 317. ZINC. Zn == 65.2. Dyad. One of the more abun- dant metallic elements. The principal ores are Red oxide of Zinc 1 ZnO Hexagonal, Blende ZnS Isometric, Smithsonite Zno = CO Hexagonal, Calamine Zno^Si . 2H 2 Trimetric. The ores are reduced by first roasting or calcining until the metal is in the condition of an oxide, and then distilling with a mixture of coal in earthen retorts or muffles. 318. Metallic Zinc. Zn. Sp. Gr. 6.8 to 7.2. Fuses at 500. Boils at a red heat. The polished surface has a bright lustre, with a bluish tint, but soon tarnishes in moist air. Has a crystalline structure, but, although brittle both at a high and a low temperature, it may readily be rolled out into sheets at a temperature of about 140. Sheet-zinc is nearly as cheap as sheet-iron ; and since it does not rust, or at most only very su- perficially, it is preferable for many purposes. Iron, however, is a much stronger metal, and is frequently coated with zinc to protect it from rusting. It is then said to be galvanized. Zinc readily dissolves in dilute acids with the evolution of hydrogen, and is much used in the laboratory, together with dilute sul- phuric acid, for making this gas. The metal is first granulated by pouring it, when melted, into water. When boiled with a solution of caustic soda or potash, it also dissolves with evolution of hydrogen. Zn + (2Ko-ff+ Aq) = (KofZn -f Aq) + SHS. [330] It is used as the electro-positive metal in the galvanic battery. 319. Zincic Oxide, ZnO, which is made in large quantities by burning zinc vapor at the mouth of the reduction furnaces, is a very light white powder, much used, when mixed with oil, as a white paint. A denser oxide is obtained by calcining zincic nitrate. 320. Zincic Hydrate, Zn=Ho^ is formed by the reaction (ZnSO, + ^K-Ho + Aq) = Zn-Ho 2 + (K^SO^-\- Aq), [331] but is soluble in an excess of reagent. 1 The color is due to the presence of a small amount of manganese. 358 ZINC. [321. 321. Zincic Carbonate, ZnC0 3 , is isomorphous with magne- site and calcite. When prepared by precipitation, a mixture of hydrate and carbonate is formed, as in (312). 322. Zincic Sulphate (White Vitriol). ZnS0 4 .7ff 2 0.Very soluble salt, isomorphous with Epsom salt, which it closely re- sembles in most of its chemical relations, forming similar double salts. Preparation as in [64]. Used in pharmacy. 323. Zincic Chloride. ZnCl 2 . A solution of zinc in hydro- chloric acid can be concentrated by evaporation without decom- position. All the water is not driven off until the temperature reaches 250. The result is a thick syrup, which forms, on cooling, a white, deliquescent solid, melting at 100, called by the alchemists Butter of Zinc. It has an intense affinity for water, and by its aid the elements of water may frequently be removed from a chemical compound without producing any further change. Thus, alcohol may be converted by it into ether or ethelyne. According to the proportions used, we have or 2C 2 H Q 0IT 2 = 2C 2 ff 5 0. [332] Ethylene. Ether. For the same reason it acts as a cautery on the skin. It is also used in solution as an antiseptic and disinfecting agent. 324. Zinc and the Alcohol Eadicals. Zinc Methide, Zn=(Cff s ) 2 ; ZmcEthide,w=(Q^) 2 ; Zinc Amylide,^=((7 5 J7 n ) 2 . Observed 0p. (S>r. of vapor, 3.29, 4.26, and 6.95 respectively. Obtained both by heating zinc with the iodides of methyl, ethyl, or amyl in sealed tubes, and by the action of zinc on the mer- cury compounds of the same radicals. They are all three colorless, transparent, strongly refracting, and mobile liquids. They are also volatile, boiling at the temperatures of 46, 118, and 220 respectively. They are, likewise, highly inflammable, and the first two take fire spontaneously in the air. As these compounds do not, as a whole, combine with any of the ele- ments, their molecules are evidently saturated, and they are interesting as fixing beyond all doubt the atomic relations of zinc. Moreover, they are useful reagents in many processes of organic chemistry. 325. Characteristic Reactions. Zinc, like magnesium, forms soluble double salts with ammonia, but it is easily distin- guished by the fact that its sulphide is insoluble, not only in 326.] INDIUM. CADMIUM. 359 solutions of the fixed alkalies, but also in those of ammonia and its salts. Hence it is precipitated from all alkaline solutions by sulphuretted hydrogen. The sulphide thus obtained is a white precipitate, soluble in dilute mineral acids, but insoluble in acetic acid. 326. INDIUM. In = 72. Sp. Gr. 7.42. CADMIUM. Od= 112. Sp. Gr. 8.69. Dyads. Two rare metallic ele- ments associated with zinc. Indium only in exceedingly mi- nute quantities, and at very few localities. Cadmium far more generally, and -in much larger amounts. Indium is less vola- tile, and cadmium more volatile, than zinc, and hence in distill- ing zinc from its ores the cadmium is found in the " zinc dust" which is collected in the early stage of the process, while the indium comes over later with the great mass of the zinc, with which it remains alloyed. With sufficient differences to mark their individuality, these metals resemble zinc in almost every particular. They form similar oxides and hydrates, similar sol- uble salts with hydrochloric, nitric, and sulphuric acids, similar soluble compounds with ammonia salts, similar light-colored sul- phides insoluble in alkaline solutions and acetic acid. Cadmi- um differs from the others in this respect, that its hydrate is insoluble in caustic soda or potash, its basic carbonate insoluble in excess of ammonic carbonate, and its yellow sulphide insolu- ble in dilute mineral acids. This sulphide is found in nature, and the mineral is called Greenockite. Zinc precipitates cad- mium from solutions of its salts, and both zinc and cadmium precipitate indium. Indium and cadmium are more fusible than zinc, and form very fusible alloys. Indium melts at 176, cad- mium at 242, and an alloy of cadmium with lead, tin, and bis- muth has been made which melts at 60. Cadmium boils at 860, and the Sp. Gr. of its vapor has been found by obser- vation to be 56.85. Indium and cadmium burn when heated before the blow-pipe, the first yielding a yellow, and the last a brown oxide, very unlike the white oxide of zinc. Although go closely allied to magnesium and zinc, these associated ele- ments probably belong to a different although parallel series, and the relation between the atomic weights of the four ele- ments is in harmony with this view. All these four metals show very characteristic bands with the spectroscope, and in- dium was first discovered by the well-marked indigo-blue band, from which it takes its name. 360 QUESTIONS AND PROBLEMS. Questions and Problems. 1. Write the reaction of sodium on magnesic chloride. 2. When water is decomposed by magnesium, what are the prod- ucts ? Write the reaction. [43.] 3. How do you account for the intense brilliancy of the light emitted by burning magnesium? (95.) 4. Write the reaction of water on calcined magnesia. [45.] 5. Write the reaction of solution of caustic soda on solution of magnesic chloride. Ans. (MgCl z + 2NaHo -f Aq) = MgHo^ -f (2NaCl -J- Aq.) 6. Represent the composition of hydromagnesite by graphic symbols. 7. Represent, graphically, the compound radicals Mgo, Cao, Zno, and show their relations to hydroxyl. 8. Represent) graphically, the composition of Dolomite. t 9. What do you understand by the term isomorphous mixture ? 10. Explain the theory of the preparation of magnesic carbonate from Dolomite. 11. The symbol of magnesic sulphate may be written MgSO, or Mg=O z =SO^ or Mgo=SO z . What different ideas do these forms suggest V 12. Write the reaction of sulphuric acid on the two constituents of dolomite, and show how pure Epsom salt may be thus prepared. 13. Write the reaction of a solution of gypsum on magnesic carbonate. 14. Represent by graphic symbols MgSO^ . H Z 0. 15. Represent by graphic symbols the composition of potassic magnesic sulphate, and explain the relations of the crystallized salt to Epsom salt. 16. Write the reaction of hydrochloric acid on magnesic carbonate. 17. Explain the decomposition which results when a solution of magnesic chloride is evaporated in the air, and why an atmosphere of II Cl should prevent the change. 18. What is the difference between the relations of baric and magnesic carbonate to calcic carbonate ? Ans. The first is related to Aragonite, the second to Calcite. 19. What is the difference between the reactions of sodic carbon- QUESTIONS AND PROBLEMS. 361 ate on solutions of calcic and magnesic salts, and on what does the difference depend ? Write the reactions in the two cases. 20. What is the difference between the reaction of ammonic car- bonate on the same solutions ? 21. Write the reaction of sodic phosphate on a solution of mag- nesic and ammonic chloride. Ans. (MgCli + NH 3 + HJTofOfPO + Aq) = (NHJ,MgK> 3 ;PO . 6H 2 -f (2NaCl + Aq.) 22. Write the reactions when zinc blende and smithsonite are calcined. Ans. ZnC0 3 = ZnO -j- CO,, and 2ZnS -f 3(o)=(o) = 2ZnO 23. Write the reaction when zincic oxide is reduced. Ans. ZiiO + C = Sn 24. Write the reactions of dilute sulphuric, hydrochloric, and acetic acids on zinc. 25. What part does zinc play in reaction [330] ? 26. In what different ways may the symbol of zincic hydrate be written? Ans. Zn=0= 2 H 2 , Zn=Ho 2 , Zno=H 2 . 27. When zincic hydrate dissolves in caustic soda, what is formed ? 28. Write the reaction of sodic carbonate upon a solution of zincic sulphate, assuming that three molecules of zincic hydrate are formed to every two molecules of zincic carbonate. Ans. (5ZnSO, -f- 5Na,CO s -f SH,0 + Aq) = 2ZnC0 3 -f 3ZiiHo 2 -f (5Na 2 SO, -f- Aq) + 3@ 2 . 29. In what different ways may the symbol of zincic sulphate be written, both the anhydrous salt and the salt with one molecule of water ? Represent graphically. 30. Write the symbol of potassic zincic sulphate. What is the crystalline form of this double salt, and with how many molecules of water does it crystallize ? 31. Write the reaction of ammonic sulphide on a solution of zincic sulphate. Ans. (ZnSO, + (NH,\S -f Aq) = 32. Write the reaction of sulphuretted hydrogen on a solution of zincic acetate. 33. Would zincic sulphide be precipitated from a solution of zincic chloride containing an excess of hydrochloric acid ? What is the difference between this case and that of 32 ? (21.) 16 362 QUESTIONS AND PROBLEMS. Cadmium. 34. Write the reaction of dilute sulphuric acid on cadmium. 35. Write the reaction of sodic hydrate on solution of cadmic sulphate. 36. Write the reaction of zinc on solution of indium chloride. 37. Write the reaction of sulphuretted hydrogen on solution of cadmic chloride. 38.' By what reactions may cadmium be separated from zinc ? Ans. By metallic zinc, by aminonic carbonate, and by sulphuret- ted hydrogen. 39. What is the electrical order of magnesium, zinc, indium, and cadmium ? 40. Assuming that the atomic weight of cadmium is 112, what in- ference may be drawn from the Sp. Gr. of its vapor in regard to the constitution of its molecule ? Does the conclusion have any bearing on the other dyad elements ? 328.] GLUCINUM. YTTRIUM. ERBIUM. 363 Divisions VIII. and IX. 327. GLUCINUM. Gl = 9.3. Dyad. A metallic ele- ment, found only in the Beryl, Glo z l(Si 6 O b )lAl^ the Chryso- beryl, Glo=Al 2 2 , and a few other rare minerals. The metal is very light, Sp. Gr. 2.1, is malleable, has a bright white lustre, does not alter in the air even when heated, and does not decom- pose aqueous vapor at a red heat. It resembles aluminum, as do also its oxide, hydrate, and chloride the corresponding com- pounds of the same metal. The hydrate differs, however, from that of aluminum in several important respects. Although sol- uble in caustic alkalies, it is again precipitated on boiling the diluted solution. It dissolves in solutions of carbonate of am- monia, with which it forms a crystalline salt. It yields with sulphuric acid a well-crystallized sulphate, GIS0 4 . 4/^0, which forms with potassic sulphate a double salt, K^GU(SO^) Z . 2^0, wholly different from alum. Lastly, it absorbs O0 2 from the air. The salts of this metal have an acid reaction and a sweet taste, whence the name from y\vP- a (color). The only important native compounds are Chromite (Chrome Iron) Isometric .Fe,[O 2 ]vm0 4 , Crocoite Monoclinic Pb=0 2 =Cr0 2 . The first is the ore from which all the chrome pigments used in the arts are indirectly prepared. It has an iron-black color, and has been found in abundance at a few localities, associated with serpentine. The second, although a very rare mineral, is well known on account of its brilliant red color, and in it the element chromium was first discovered (by Vauquelin in 1797). 343. Metallic Chromium may be prepared by reducing Cr. 2 3 with carbon at a very high temperature, and still more readily by reducing Or. 2 Cl 6 with zinc, magnesium, or the alkaline metals. On account of its very great infusibility, it has never been ob- tained in compact masses, and its qualities are therefore imper- fectly known. The whitish-gray porous mass, formed when the oxide is reduced by carbon, has a Sp. Gr. of 5.9. It is, like cast-iron, a combination of the metal with carbon, and consists of grains, which are as hard- as corundum. The crystalline powder, obtained by reducing the chloride with zinc, has a Sp. Gr. of 6.81, and is undoubtedly a purer condition of the metal. When in fine powder, chromium takes fire below redness ; but in its more compact forms it resists oxidizing agents as well as aluminum, and acts towards the different mineral acids in a similar way. 344. Chromous Compounds. This class includes all those compounds of chromium in which the element is bivalent ; but, since its atoms in this condition have still four strong affinities unsatisfied, the compounds of this order are all very unstable. The most important is CrCl^ which is obtained by heating Cr 2 Cl e to redness in a current of dry hydrogen. The white powder thus formed gives a blue solution with water, which, however, rapidly absorbs oxygen, and becomes green when ex- 345.] CHROMIUM. 399 posed to the air. Chromous hydrate, which falls as a dark brown precipitate on adding caustic potash to the blue solution, even decomposes water with evolution of hydrogen. The most stable of the chromous salts is K 2 ,CnOf[SO,'] 2 . 6// 2 0, which forms beautiful blue crystals isomorphous with the corresponding fer- rous salt. 345. Chromic Compounds. In these compounds the ele- ment is quadrivalent, but they all contain the sexivalent radical [ (7rJ. The commercial chromic oxide is a brilliant green pow- der, which is very much used in the arts, not only as a common paint (chrome green), but also as a vitritiable pigment, since it imparts a beautiful green color to glass and to the glazing of porcelain ware. It may be prepared from the chromates in a great variety of ways, as is illustrated by the. following re- actions : 4[HgJ=O/CrO a = 2[CrJO 8 + SHIg + 5=. [345] (NH 4 )/0./Cr 2 5 = [CrJOs + 4IU 2 + SMST. [346] 4Oii a ,oi a = 2[Cr 2 ]io 3 + 4K9i + =. [347] K 2 0/Cr.Os + 01-01 = [CrJiO. + 2KC1 + 2(o)=CD. [348] The first two reactions are obtained by simply igniting the solid chromates. The third, by passing the vapor of chloro-chromic anhydride through a red-hot porcelain tube, and the last, by passing chlorine gas over ignited potassic dichromate. By the third reaction the oxide may be obtained in definite rhombohe- dral crystals (Sp* Gr. 5.21), which have the form and hardness of specular iron, and even the amorphous commercial oxide is so hard that, when finely levigated, it may be used like rouge for polishing glass. In this hard condition the oxide is almost insoluble in acids. There is, however, a less dense condition of the oxide (obtained by cautiously heating the hydrate), which dissolves freely in all the mineral acids. It has a darker color, and, like ferric oxide, changes suddenly with incandescence into the insoluble modification, if heated above a definite point. At the highest temperatures chromic oxide does not lose oxygen, and cannot be reduced by hydrogen. It may be melted by the heat of a forge fire, and the molten oxide forms, on cooling, a very hard dark-green crystalline solid. 400 CHROMIUM. [345. There are a number of chromic hydrates corresponding to the ferric hydrates ; but the different compounds cannot be isolated as readily, and their symbols have not been as accurately deter- mined. When sodic or potassic hydrate is added to the solu- tion of a chromic salt, the chromic hydrate first precipitated is dissolved by an excess of the reagent, but the precipitate reap- pears on boiling the liquid. These precipitates retain a portion of the alkali, which modifies the qualities of the hydrate, and this circumstance renders the investigation of these compounds very difficult. The only way to procure a pure hydrate is to precipitate with ammonia from boiling solutions. The light- blue precipitate thus obtained retains from one to seven mole- cules of water, according to the conditions under which it is dried. * The soluble chromic salts affect, as a rule at least, two modi- fications. In one state they have a violet color, and crystallize more or less readily, while in the other they have a green color, and are uncrystallizable. Thus we have, besides an anhydrous chromic sulphate, which is red and insoluble, the two following hydrous salts : Violet Sulphate (soluble and cryst.) [Cr^W^SO.^ . 15ff 2 0, Green (soluble but uncryst.) [OJ 1 0^(S0 2 ) 8 . 5R 2 0. The second is obtained by heating the crystals of the first to 100. But the water thus driven off cannot be wholly water of crystallization, for on simply boiling a solution of the violet compound the same change of color and crystalline character takes place. There is evidently an essential alteration in the molecular structure of the compound, but further than this we have as yet no knowledge. The best known of the chromic salts is chrome alum, which is easily prepared from commercial potassic bichromate by the reaction. BS0 2 + Ag) = H,0 + Aq). [349] This salt, like the other alums, crystallizes with 24^0 in octa- hedrons having a dark purple (nearly black) color, but which, when sufficiently thin, transmit a beautiful ruby red tint. Care 348.J CHROMIUM. 401 must be taken in reducing the chromate that the temperature of the solution does not rise too high, for above 70 or 80 the change above described takes place, and the salt loses its power of crystallizing. By keeping, however, the green solution thus formed for several weeks, it gradually recovers its violet color, and then will yield the normal crystals. 346. The Chromic Oxalates form two interesting series of double salts. Those of the first class have a dark-blue, and those of the second class a ruby-red color. Thus we have Blue Salt K*\_ O 2 ] u 0^( O 2 2 ) 6 . Gff 2 0, Red Salt 7T 2 ,[ O 2 ] #8 viii ( an(i are generally distinguished by a red color. 367. Platinous Hydrates, Pt=Ho 2 , which is obtained as a black powder by digesting platinous chloride with a solution of caustic potash, dissolves both in alkalies and acids, but the compounds thus formed are very unstable. Platinous nitrite and sulphite, however, form crystallizable double salts with several of the more basic radicals. Platinic Hydrate, Pt^Ho^ prepared indi- rectly from platinic chloride, is also soluble both in acids and alkalies. The compounds thus formed are all unstable, those in which the element acts as an acid radical being the more definite. Platinic sulphate and platinic nitrate, although they 428 QUESTIONS AND PKOBLEMS. [367 have not been crystallized, are easily obtained in solution, the sulphate by evaporating a solution of the chloride with sul- phuric acid, the nitrate by decomposing the sulphate with baric nitrate. Lastly, by cautiously heating the hydrates we can obtain the corresponding oxides, but if the temperature exceeds a limited degree they are at once completely reduced. By acting on different platinum salts with ammonia, a re- markable class of compounds have been obtained, which are best regarded as salts of platinum bases, and as formed by the coalescing of two or more molecules of H$N soldered together by atoms of Pt= or Pfc, although they probably contain in some cases more complex platinum radicals. Similar compounds have also been formed with palladium and iridium; but, although highly interesting subjects of study on account of their manifold types and complex constitution, this new class of ammonia bases illustrate no principles not already fully discussed, and for a description of them we must refer to more extended works. Questions and Problems. 1. Calculate the percentage composition of platinum ore, elimi- nating from the results given in (359) the quantity of iridosmine and sand with which the ore is mixed. 2. Explain the old method of working platinum ores, and illustrate the various steps in the process by reactions. To what extent are the associated metals precipitated by ammonic chloride ? 3. Point out the relationship between the platinum metals and iron. Compare also these elements with each other, and consider especially the characteristics distinguishing the three groups into which they have been divided in Table II. 4. By what characters are the platinum metals as a class chiefly marked ? Make a table which will bring into comparison the dif- ferent double chlorides of these elements. 5. Explain, on the principle of dialysis, the transmission of hydro- gen gas through the walls of a heated palladium or platinum tube. 6. Regarding the hydrogen condensed by platinum as chemically combined with the metal, cannot you find in this circumstance an explanation of the enhanced energy of the gas when in this condi- tion. Consider the polarization of the negative platinum plate in a voltaic cell as an illustration of the same principle. QUESTIONS AND PROBLEMS. 429 7. Show in what way the platinic salts may be used to determine the molecular weight of an organic base, and give an illustration of the principle. 8. Write the reactions by which platinic sulphate and nitrate may be prepared. 9. Write the reaction of a solution of platinic chloride on a solu- tion of potassic nitrate. Platinic nitrate is one of the products. 10. Write the reaction of sodic carbonate on a solution of platinic sulphate, assuming that the chief product is platinic hydrate. 11. Write the reactions by which platinous hydrate may be pre- pared. 12. When platinous chloride dissolves in hydrochloric acid in con- tact with the air, what is the reaction ? 13. Make a scheme illustrating the constitution or relations of the more important compounds of the platinum bases. 14. Explain a method of separating the platinum metals from each other. 430 TITANIUM. [ 368. Divisions XVII. to XIX. 368. TITANIUM. Ti = 50. Tetrad. No compounds corresponding to a lower degree of quantivalence are with cer- tainty known. A comparatively rare element, but not unfre- quently associated with iron. The most abundant native com- pound is Menaccanite or Titaniferous Iron, whose symbol has already been given among the iron ores. This mineral, how- ever, is in most cases an isomorphous mixture of ( Ti~Fe) 3 and Fe%0s, sometimes containing also magnesium and manga- nese, and thus arise the numerous varieties which have been distinguished. The other important compounds are Rutile, Brookite, and Octahedrite (2d or 4th System) Ti 2 , Perofskite (Rhombohedral) Ca = Of Ti 0, Sphene (Monoclinic) (Ca-0-Ti)zOSi. Titanium is also associated with columbium, tantalum, cerium, yttrium, and zirconium in a number of rare minerals. 369. Metallic Titanium has never been obtained as a mas- sive metal, and its properties are very imperfectly known. As formed by decomposing the potassio-titanic fluoride with potas- sium it is a dark-green powder, showing under the microscope the color and lustre of iron. In this condition it is very com- bustible, readily dissolves in hydrochloric acid, and even decom- poses water at the boiling-point. 370. Titanic Chloride, Ti Cl, is obtained by passing chlorine gas through an intimate mixture of titanic oxide and carbon in- tensely heated. It is a heavy, colorless liquid, boiling at 135, and yielding a vapor whose Sp. Gr. = 98.65. Exposed to the air it absorbs moisture, and gradually solidifies, forming a crys- talline hydrate which readily dissolves in water. From this solution, if sufficiently dilute, almost the whole of the titanium is precipitated as a hydrate on boiling, and the same is true of the solution formed by dissolving the native oxides (after fusion with an alkaline carbonate) in hydrochloric acid. 371. Titanous Chloride, Ti 2 Cl 6 , is formed bypassing a mix- ture of WiOl 4 and HI-HI through a red-hot porcelain tube. The compound is thus obtained in dark violet scales, which readily 376.] TITANIUM. 431 dissolve in water forming a violet solution, but in contact with the air this solution gradually loses its color and deposits titanic hydrate. The same color is produced by boiling with tin a so- lution of titanic oxide in hydrochloric acid, and this reaction is the best test for titanium. The solution of titanous chloride is a very powerful reducing agent, which indicates that the radical [ 7Y 2 ]1 is not a stable condition of the element. 372. Titanic Bromide, and Iodide, TiBr and TiI 4 , are fusi- ble and volatile crystalline solids. 373. Titanic Fluoride, TiF, is a fuming, colorless liquid, obtained by distilling a mixture of fluor-spar and titanic oxide with sulphuric acid. This compound is resolved by water into soluble hydro-titanic fluoride and insoluble titanic oxyfluoride. 374. Hydro-titanic Fluoride, TiF 4 . ZHF, is the acid of a large class of salts which are easily made from the solution pro- duced as just stated. The ammonium and potassium salts, which are the most important, both crystallize in white anhy- drous scales. 375. Titanic Hydrates. A large number of these hydrates have been distinguished, and they affect two very different mod- ifications. Those obtained by precipitation with ammonia read- ily dissolve in acids, and when heated are converted into the anhydride with vivid incandescence. Those obtained by boil- ing dilute solutions of the chloride or sulphate are insoluble in all acids except strong sulphuric. They give off water more readily than the others, and the dehydration is not attended by the same incandescence. The composition of these hydrates depends on the temperature at which they are dried, and they may be regarded as derived from the normal hydrate by the method repeatedly illustrated and expressed by the general equation nTiffo 4 mff 2 = (O m Ti^Ho^ n .^, [353] The two modifications have been obtained in the same degrees of hydration, and, so far as known, they are isomeric. Moreover, by dialysis a pure aqueous solution of "titanic hydrate has been procured, which gelatinizes when concentrated, and evidently" contains the compound in a colloidal condition. 376. Titanic Oxide, TiO^, is chiefly interesting from the fact that it affects three different modifications, which are rep- resented in nature by the minerals Rutile, Brookite, and Octa- 432 TITANIUM. [ 377. hedrite. These three isomeric bodies differ from each other in crystalline form, in density, and in hardness. Rutile, the most abundant, has the greatest hardness and density. Its crystals are tetragonal and isomorphous with those of Sn 2 . Brookite, which stands next in hardness and density, affects forms of the orthorhombic system, which are approximately isomorphous with those of Mn0 2 . Lastly, Octahedrite is softer and less dense than either of the others, and its crystals, although tetragonal, differ essentially from those of Rutile. (Problem 2, page 144.) The same differences have been observed in crystals obtained artificially by decomposing TiF or TiGl with steam, and it is found that the nature of the product depends on the temperature at which the reaction takes place, the hardest and most dense crystals being formed at the highest temperature. In its densest condition titanic oxide has a red color, and is insoluble in all acids ; but the white anhydride, obtained by ig- niting titanic hydrate, is converted into a sulphate when heated with strong sulphuric acid, and may then be dissolved in water. The native oxides, also, may be rendered soluble by fusion with alkaline carbonates or bisulphates. It melts before the com- pound blow-pipe. 377. Titanous Oxide, Ti 2 3 , is obtained as a black powder when a stream of hydrogen is passed over ignited Ti0 2 . It dissolves in sulphuric acid, forming a violet solution, from which the alkalies precipitate a brown hydrate. A similar reduction takes place, and the same violet color is produced, when Ti0 2 is dissolved in fused borax or microcosmic salt, and the bead heated before the blow-pipe on charcoal in contact with a small globule of tin. 378. Titanic Sulphide, TiS 2 , is formed in large, brass-yellow, lustrous scales when a mixture of IH^ and I SPil 4 is passed through a glass tube heated to incipient redness. It is decom- posed by water, and cannot, therefore, be obtained by precipi- tation. 379. Nitrides. Titanium has a marked affinity for nitro- gen, and combines with it in several proportions. When dry ammonia gas is passed over TiCl 4 it is rapidly absorbed with great elevation of temperature, and the resulting brown-red powder has the symbol (H^N^Tiy^Cl^ This compound, heated in a stream of ammonia gas, yields a copper-colored substance, 381.] TIN. 433 which is the nitride Ti z N^ and this, when further heated in a current of hydrogen, is converted into a second nitride (Ti^N^) having a golden-yellow color and metallic lustre. A third vio- let-colored nitride has the symbol TiN 2 . Lastly, the very hard copper-colored cubic crystals sometimes found adhering to the slags of iron-furnaces, and formerly mistaken for metallic tita- nium, have the composition expressed by the symbol 7Y 5 (7A^. 380. TIN. Sn = llS. Bivalent and Quadrivalent. The last is the most stable condition. The only valuable ore of tin is the oxide Sn0 2 , called in mineralogy Cassiterite or Tin Stone, and this is found at but few localities, chiefly in Corn- wall, Malacca, Bolivia, Australia, Bohemia, and Saxony. This element is also an essential constituent of Tin Pyrites \_Zn,Fe~\, [ Cu^SfSn, and is associated with columbium, titanium, zir- conium, &c., in a few rare minerals, but its range in nature, so far as known, is very limited. The metal is obtained by reducing the native oxide with coal ; but, although in theory so simple, this process is in practice quite complicated. The ore requires, previous to smelting, a pro- longed mechanical treatment, and in the furnace a large amount of metal passes into the slags, which therefore have to be worked over. 381. Metallic Tin has a familiar white color and bright lustre. It has a crystalline structure, and the breaking of the crystals against each other, when a bar of the metal is bent, produces the peculiar sound known as the cry of tin. By slowly cooling the fused metal distinct crystals can be obtained, which belong to the tetragonal system. The tenacity of tin is feeble, but it can readily be rolled and beaten into thin leaves, which are well known under the name of tin-foil. Sp. Gr. = 7.3. .Melts at 222. Boils at a white heat. Inferior conductor of heat or electricity. Tin does not tarnish in a moist atmosphere which is free- from sulphur, but when melted in the air it slowly oxidizes, and at a red heat decomposes steam. Hydrochloric acid dissolves the metal rapidly, the products being stannous chloride and hy- dro^en gas. It also dissolves slowly when boiled with dilute O O J sulphuric acid, yielding stannous sulphate and liberating hydro- gen as before. When the sulphuric acid is concentrated, S0 2 is evolved and stannous sulphate formed only so long as the tia 19 SB 434 TIN. [382. is in excess. If the acid is in excess, sulphur separates and the product is stannic sulphate. Very strong nitric acid does not act on the metal, but when somewhat diluted it converts the tin into a white hydrate, insoluble in an excess of the acid. Aqua-regia, if not too concentrated, dissolves tin as stannic chloride, and the alkaline hydrates and nitrates also act upon it at a high temperature. Tin unites directly with most of the non-metallic elements, and forms alloys with many of the metals. The alloys with copper have already been mentioned. Pewter and plumber's solder are alloys of tin and lead. Britannia metal, an alloy of brass, tin, lead, and bismuth, and the silvering of mirrors an amalgam of tin and mercury. On account of its beautiful lustre and power of resisting atmospheric agents, tin is much used for coating other metals. The common tin ware is made of sheet- iron thus protected. 382. Stannous Chloride. Sn O1 2 . The anhydrous com- pound (butter of tin) obtained by heating mercuric chloride with an excess of tin, or by heating the metal in hydrochloric acid gas, is a fusible white solid with a fatty lustre, soluble in water and alcohol. The hydrous salt (tin salts), formed by crystallizing the solution of tin in hydrochloric acid, has the symbol SnCl 2 . 2ZT 2 0. The pure crystals dissolve perfectly in a small amount of water, free from air, but a large amount of water produces a partial decomposition. (2SnCl 2 + 3ff 2 + Aq) = Sn 2 OCi 2 . 2H 2 O + (2ffCl + Aq). [354] So, also, when the solution is exposed to the air. (GSnCl 2 + H 2 + Aq) + = = 2(Sn 2 OCI 2 . 2H 2 0) + (2SnOl, + Aq). [355] The oxychloride, which is milk white and insoluble (even in dilute acids), renders the solution in both cases turbid. Free hydrochloric acid, tartaric acid, and sal ammoniac prevent the decomposition. Owing to the unsatisfied affinities of the tin radical, stannous chloride is a powerful reducing agent (277), and is much used for this purpose both in the laboratory and the dye-house. It also acts as a mordant. Lastly, it forms salts with several of the metallic chlorides. 383.] TIN. f 435 Potassio-stannous Chloride SnCl 2 . 2KCI . (1, 2, or 3ff 2 0), Bario-stannous Chloride Sn C1 2 . Ba C1 2 . 4ff 2 0. 383. Stannic Chloride, Sn C1 4 , may be made either by dis- tilling a mixture of tin and mercuric chloride, the last being in excess, or by heating tin in chlorine gas. It is a colorless, fum- ing liquid, boiling at 115, and yielding a vapor whose Sp. Gr. = 132.7. The liquid, exposed to the air, eagerly absorbs moist- ure, and changes into a crystalline solid. When mixed with water intense heat is evolved, and a solution formed which yields on evaporation rhombohedral crystals of SnOl 4 . 5ff 2 0. These crystals, dried in vacua, lose 3ff 2 0, and there is reason to be- lieve that the remaining 2ff 2 are a part of the molecule of the salt. If we regard the atoms of chlorine as trivalent, we can easily see that such an atomic group would be possible, for we might then have the univalent radical (H- Cl= Cl) = Hd re- placing Ho, and the symbol of the dried salt would be written Sn^Ho 2 ,ffcl 2 . The same principle may be applied in other cases where the violence of the action indicates that a chemical union has taken place between an anhydrous chloride and water. Such bodies, however, may also be regarded as chlorhydrines (349), to which molecules of HCl are united in place of water of crystallization. Thus the symbol of the hydrous chloride we have been discussing might be written Sn^Cl 2 ,Ho 2 . 2ITCL Although stannic chloride forms a clear solution with a small amount of water, copious dilution determines the precipitation of the greater part of the tin as an insoluble stannic hydrate. Heat favors this decomposition, and, on the other hand, the pres- ence of a large excess of hydrochloric acid prevents it. Stan- nic chloride unites with a considerable number of bodies both organic and inorganic, and forms double salts with several of the metallic chlorides. Ammonio-stannic chloride, Sn C7 4 . 1NHCl (pink salts of the dyers) is isomorphous with the cor- responding compound of platinum. An impure solution of stannic chloride, made by dissolving tin in aqua-regia, is also extensively used in dyeing for brightening and fixing certain red colors. There are two bromides and iodides of tin corresponding to the chlorides. There is also a stannous fluoride, and although stannic fluoride has not been isolated, a large number of double 436 TIN. [384. stannic fluorides or fluostannates are known, which are isomor- phous with the corresponding compounds of titanium and silicon. 384. Stannous Hydrate. The precipitate which falls on adding an alkaline carbonate to a solution of stannous chloride is said to have the composition JBof(iSlnfO). It is soluble in both alkalies and acids. Boiled with water or a weak solution of potash it is rendered anhydrous, but if boiled with a concen- trated solution of this alkali it yields potassic stanriate and me- tallic tin. The moist hydrate absorbs oxygen from the air, and acts, like the chloride, as a reducing agent. The only impor- tant oxygen salt corresponding to this hydrate is stannous sulphate. 385. Stannic Hydrate, like titanic hydrate, affects both a soluble and an insoluble modification. The hydrate precipitated when ammonia is added to a solution of stannic chloride dis' solves readily both in acids and alkalies, while that obtained by boiling the same solution greatly diluted, or by acting on tin with nitric acid, is insoluble in acids, and dissolves less readily than the first in alkalies. The composition of these bodies varies with the temperature at which they are dried, and they are usually distinguished as stannic and meta-stannic hydrates. Like the corresponding compounds of titanium, they may be regarded as derived from a normal hydrate of either class by the elimination of successive molecules of water. The salts ob- tained by dissolving stannic hydrate in oxygen acids are unim- portant. The sulphate is the most stable, but this is completely decomposed, and the tin precipitated as meta-stannic hydrate when the aqueous solution is diluted and boiled. The atoms Sn= form much more stable compounds when they act as acid radicals. The alkaline stannates crystallize readily, and both potassic and sodic stannates, (K or Na) 2 =OfSnO . 4// 2 0, are commercial products much used as mordants. Their efficacy depends on the fact that ammonic chloride and all acids, even the C0 2 of the atmosphere, decomposes these salts when in so- lution, and the stannic hydrate thus precipitated in the fibre of the cloth binds the coloring matter. The compounds obtained by dissolving meta-stannic hydrate in alkaline solvents cannot be crystallized, but are precipitated on adding to the solution caustic potash. The potassium salt thus obtained, dried at 126, has the composition K 2 = OfSn & 9 . 387.] TIN. 437 It was formerly supposed that the peculiar qualities of the meta-stannic hydrates and the meta-stannates were due to the atomic grouping here represented, but this opinion has not been sustained by recent investigations. The water represented as water of crystallization cannot be removed without decomposing the salt, and is evidently water of constitution ; so that we have good reason for writing the symbol H^K^x. 0^(8^0^) after the type of the normal stannates, and we may regard it as an ex- ample of the soluble colloidal hydrates, to which we have before referred (337). This view harmonizes with the facts that on boiling an aqueous solution of this compound meta-stannic hy- drate is precipitated, and that by dialysis a solution both of meta-stannic and stannic hydrates in pure water may be ob- tained. The two classes of compounds are probably isomeric, but differ in the degree of molecular condensation. 386. Oxides. Stannous Oxide, SnO, may be obtained in various ways, and its color differs according to the mode of preparation. It has a strong affinity for oxygen, and if set on fire when dry burns to stannic oxide. Stannic oxide has been crystallized artificially, not only in the forms of Tin-stone isomorphous with Rutile, but also in forms isomorphous with Brookite. As obtained by igniting the hy- drate, or by burning metallic tin, it is an amorphous white pow- der. It offers even greater resistance to the action of chemical agents than Ti0. 2 . It is not attacked by acids even when con- centrated. It is not dissolved by fusion with alkaline carbon- ates, but is rendered soluble by fusion with caustic alkalies. It is al.-o taken up when fused with acid potassic sulphate, but separates completely when the fused mass is dissolved in water. Moreover, like titanic oxide it is very hard and infusible, but unlike that it is reduced to the metallic state when ignited in a stream of hydrogen gas. Besides SnO and SnO 2 an intermediate oxide, Sn 2 s , has been distinguished, but it does not form definite salts. Dissolved in hydrochloric acid it gives with auric chloride the beautiful purple precipitate known as Purple of Cassius (147). 387. Sulphides. The dark -brown precipitate which falls when ff. 2 S is passed through an acid solution of a stannous salt is SnS, and the dull yellow precipitate which forms under the same circumstances in a solution of a stannic salt is a hydrate 438 TIN. [388. of SnS 2 . The last of these dissolves readily m solutions of al- kaline sulphides, and forms with them definite salts. It is also soluble in the fixed alkaline hydrates, and in either case is pre- cipitated unchanged when the alkali is neutralized with an acid. Stannous sulphide, on the other hand, does not form salts with the alkaline sulphides, and does not dissolve in solutions of these compounds, unless, like the common yellow ammonic sulphide, they contain an excess of sulphur, when it is converted into SnSft and as such is precipitated on neutralizing the alkali. It does, however, dissolve in the fixed alkaline hydrates, but when an excess of acid is added to the solution a yellow pre- cipitate of SnS 2 falls, containing only one half of the tin present. The beautiful yellow flaky material known as mosaic gold, and used in painting to imitate bronze, consists of anhydrous stannic sulphide, and is obtained by subliming a mixture of tin, sulphur, sal-ammoniac, and mercury. There is also a sesqui- sulphide, Sn 2 S 3 . 388. Compounds with the Alcohol Radicals. These com- pounds are very numerous and highly important, theoretically, because they establish beyond all doubt the atomic relations of tin. Compounds have been obtained containing methyl, ethyl, and amyl, either singly or associated together. Three com- pounds are known containing only tin and ethyl. Putting Et = (C 2 ff 5 ) we have All three are colorless oily liquids. The last is the most stable, boiling at 181, and yielding a vapor whose Sp. Gr. = 116. The others cannot be volatilized without decomposition, and unite directly with oxygen, chlorine, bromine, and iodine. The first, especially, like other stannous compounds, acts as a redu- cing agent, absorbing oxygen from the air, and precipitating sil- ver from a solution of the nitrate. This is the only stannous compound known among this class of bodies. In all the others the tin atoms exert their maximum atom-fixing power, and they may be regarded either as compounds of the radicals (SnEt 2 )= or (SnEt^)-, or else as formed from stannic ethide by replacing either one or more of the atoms of ethyl by other radicals. The following are a few examples : 391.] ZIRCONIUM. 439 Stanno-diethylic Bromide Stanno-diethy lie Oxide (SnJEt. 2 )=0, Stanno-diethy lie Acetate (SnM 2 )= 2 =( O 2 ff s 0)% Stanno-diethylic Sulphate (SnEt^)=OiS0 2l Stanno-triethylic Chloride (SnM 3 )- Cl, Stanno-triethylic Hydrate (SnEt s yO-H, Stanno-triethylic Oxide (SnEt s ) 2 =0, Stanno-triethylic Carbonate (SnEt^O^GO. v The methyl and amyl compounds are formed after the same analogy, and also others which contain both methyl and ethyl. These compounds are either liquids or crystalline solids. The chlorides, bromides, and iodides are, as a rule, volatile and spar- ingly soluble in water. The oxides and oxygen salts, on the other hand, generally dissolve freely in water, and are more easily decomposed by heat. The vapor densities of several of these compounds are given in Table III., and this list might be greatly extended. 389. ZIRCONIUM. Zr = 89.6. Tetrad. Found only in Zircon, Eudialyte, and a few other very rare minerals. The elementary substance closely resembles silicon. It may be ob- tained by similar reactions in three corresponding states, amor- phous, crystalline, and graphitoidal. Amorphous zirconium is a very combustible black powder. The crystals, Sp. Gr. 4.15, resemble antimony in color, lustre, and brittleness, and burn only at a very high temperature. The graphitoidal variety forms very light steel-gray scales. Zirconium is very infusible, is but slightly attacked by the ordinary acids, but hydrofluoric acid, and in some conditions aqua-regia, dissolve it rapidly. 390. Zirconic Chloride, ZrCl A , is a white volatile solid (Sp. Gr. = 117.6), which dissolves easily and with evolution of heat in water. This solution, or the solution of the hydrate in hy- drochloric acid, yields on evaporation a large mass of white silky needles, which, when heated, lose water and hydrochloric acid, leaving an oxychloride, Zr 9 O 4 Ol^ 391. Zirconic Fluoride, ZrF# is likewise a volatile white solid, and forms a crystalline hydrate, ZrF . Sff 2 0, which is decomposed by heat, leaving pure ZrO f Zirconic fluoride unites with many other metallic fluorides, forming salts which are isomorphous with the corresponding compounds of silicon, 440 ZIRCONIUM. [392. titanium, and tin. The following symbols illustrate the known types : Cadmio-zirconic Fluoride ZrF . 2CdF 2 . 6# 2 0, Tripotassio-zirconic Fluoride ZrF . 3KF, Dipotassio-zirconic Fluoride ZrF 4 . 21fF, Potassio-zirconic Fluoride ZrF . KF . ff 2 0, Sodio-zirconic Fluoride 2ZrF 4 . 5NaF. 392. Zirconic Hydrate, precipitated from the chloride by ammonia, and dried at 17, has the symbol Zr^ffo 4 . Dried at a higher temperature, (ZrO)=ffe 2 ' It i a yellowish, translu- cent, gummy mass, having a conchoidal fracture. The hydrate precipitated and washed cold dissolves easily in acids, and, very slightly, even in water; but when precipitated from hot solu- tions, or washed with hot water, it dissolves only in concen- trated acids. Zirconic hydrate acts both as a base and an acid. There are several zirconic sulphates. The normal salt can be crystallized, and the formation of a basic sulphate, which is precipitated when a neutral solution of zirconia in sulphuric acid is boiled with potassic sulphate, is one of the most charac- teristic reactions of zirconium. The salts of zirconium have an astringent taste, and the solutions redden turmeric paper. The precipitated hydrate is insoluble in caustic alkalies, but when precipitated by a fixed alkaline carbonate, or, better, by a bicarbonate, it dissolves in an excess of the reagent. The alka- line zirconates can be obtained by fusion, and several definite crystalline zirconates of the more basic radicals have been studied. 393. Zirconic Oxide (Zirconia), Zr0 2 , is obtained by heat- ing the hydrate. Prepared at the lowest possible temperature it forms a white tasteless powder soluble in acids ; but when heated to incipient redness it glows brightly, becomes denser and much harder, and is then insoluble in any acid excepting hydrofluoric and strong sulphuric. Zirconia has been crystal- lized artificially in the same form as Tin-stone and Rutile. The mineral zircon is usually regarded as a silicate of zirco- nium, Zr^OfSi, but the symbol may also be written {j8r'J9Fj*0* and this view harmonizes with the fact that the crystalline form is almost identical with that of ZrO^ SnO^ and fVOj. More- 394.J QUESTIONS AND PROBLEMS. 441 over, several isomorphous varieties of this mineral are known (Malacone, Oerstedite, &c.) in which the proportions of Zr and Si are quite variable. They are more or less hydrous, and for the most part comparatively soft, but, like pure Zr 2 , they be- come, when heated, exceedingly hard as well as more dense. 394. THORIUM. Th = 115.7. The mineral Thorite, or Orangeite, is essentially a hydrous silicate of this exceedingly rare metallic element, which has also been found, but only as a subordinate constituent, in Euxenite, Pyrochlore, Monazite, Gadolinite, and Orthite. When Thorite is decomposed by hy- drochloric acid a solution of thoric chloride, Th Cl, is obtained, from which the caustic alkalies precipitate a hydrate insoluble in an excess of the reagent. A similar precipitate is obtained with the alkaline carbonates, but this readily dissolves when an excess is added to the solution. In the same solution a precip- itate is obtained with oxalic acid, potassic sulphate, and potassic ferro-cyanide. As the above reactions indicate, Thorium is allied in many of its properties to the metals of the glucinum and cerium groups, but in other respects it resembles more nearly zirco- nium, with which it is here associated. The anhydrous oxide Th0 2 is a white powder, which glows when heated, becomes more dense, and after ignition is insoluble in any acid except concentrated sulphuric. It has a high specific gravity, and by fusion with borax has been obtained in tetragonal crystals (Fig. 37) resembling those of Tin-stone, Sn0 2 , and Rutile, Ti0 2 . The anhydrous chloride is volatile, and the hydrated chloride forms a radiate crystalline mass like Zr C7 4 . The chloride may be reduced by sodium, and the metal may be thus obtained as a gray lustrous powder which readily burns in the air. Questions and Problems. Titanium. 1. Compare by means of graphic symbols the composition of Pe- rofskite and Menaccanite. Can they be regarded as similarly con- stituted ? 2. Write the reaction by which titanic chloride is made. 3. According to the experiments of Isidore Pierre, 0.8215 gramme 19* 442 QUESTIONS AND PROBLEMS. of TiCl 4 yield 2.45176 grammes of AgCL Calculate the atomic weight of titanium, and state clearly the course of reasoning by which the result is reached. Ans. 50.34. 4. Write the reaction which takes place when a dilute aqueous solution of TiCl is boiled. 5. Write the reactions which take place when a solution of titanif- erous iron in hydrochloric acid is boiled with tin, and explain the use of this reaction as a test for titanium. 6. Write the reaction by which TiF+ is prepared, and also show how it is decomposed by water. 7. Represent the constitution of hydro-titanic fluoride by a graphic symbol, assuming that F is trivalent. 8. Represent in a tabular form the possible titanic hydrates. 9. Do the hydrates of any of the preceding elements present phe- nomena similar to those of titanic hydrate ? 10. Write the reaction by which TiS^ is prepared, and also the reactions by which crystals of TiO z may be obtained. 11. Compare the specific gravities and hardness of the native ti- tanic oxides. What would these differences indicate in regard to the molecular constitution of these minerals ? 12. Represent by graphic symbols the constitution of the nitrides of titanium. 13. Point out the analogies between titanium and the platinum metals. Is titanium in any way related to iron ? Tin. 14. Write the reactions of hydrochloric, nitric, and sulphuric acids on metallic tin. 15. Write the reaction of stannous chloride on solution of HgCl r 16. Write the reaction by which anhydrous SnCl z is prepared. 17. Analyze reactions [354] and [355], and explain the use of tin salts as a mordant. 18. Write the reactions by which anhydrous SnCl^ is prepared. 19. Represent the constitution of hydrous stannic chloride by graphic symbols, and apply the same principle to the interpretation of other similar compounds. 20. Write the reaction when a dilute aqueous solution of stannic chloride is boiled, and explain the use of this solution as a mordant. 21. Write the reaction which takes place when stannous hydrate is boiled with a concentrated solution of potassic hydrate. QUESTIONS AND PROBLEMS. 443 22. Make a table exhibiting the possible stannic hydrates, and explain the difference between the two classes of these compounds. 23. Write the reaction which takes place when a dilute aqueous solution of stannic sulphate is boiled. 24. Write the reaction which takes place when a solution of sodic stannate is boiled with ammonic chloride. 25. Represent the constitution of meta-stannic hydrate by graphic symbols, and explain the two opinions which have been entertained in regard to it, showing how far they are sustained by facts. 26 . Write the reaction of H Z S on a solution of stannous or stannic chloride. 27. Write the reaction which takes place when SnS is dissolved in yellow ammonic sulphide, and that which follows on neutralizing the alkaline solvent with an acid. Write also the reactions when an alkaline hydrate is used as the solvent. 28. Point out the analogies and the differences between tin and titanium. By what simple reaction may the two elements be sepa- rated when in solution ? 29. How is tin related to the platinum metals? 30. According to the experiments of Dumas, 100 parts of tin, when oxidized by nitric acid, yield 127.105 parts of Sn0 2 . What is the atomic weight of the element, assuming that the oxide has the constitution represented by the symbol ? Ans. 118.06. 31. On what facts do the conclusions in regard to the atomicity of tin and the constitution of its several compounds rest ? 32. Show that the atomic weight of tin, deduced from the percent- age composition and vapor densities of its compounds with the alco- hol radicals, agrees with the value given above. Show, also, that these compounds fully illustrate the atomic relations of the elements. 33. State the reasons for classing zirconium and thorium with tin and titanium. 34. Point out the resemblances between zirconium and silicon, and give the reasons for classing zircon with tin-stone and rutile. 444 SILICON. [395. Division XX. 395. SILICON. Si = 28. Tetrad. Most abundant of the elements after oxygen, forming, as is estimated, about one fourth of the rocky crust of the globe. Always found in nature united to oxygen either as quartz, Si0 2 , or associated with more basic radicals in the various native silicates, many of whose symbols have already been given (333) (352). The elementary substance may be obtained in three different condi- tions, amorphous, graphitoidal, and crystalline. 1. By decomposing SiF 4 . 2AjPwith potassium or sodium, or by heating the same metals in a current of the vapor of SiClto silicon is obtained as a dull-brown powder, which soils the fingers, and readily dissolves in hydrofluoric acid or a warm solution of caustic potash, although insoluble in water and the common acids. When ignited it burns brilliantly, but the grains soon become coated with a varnish of melted silicon, which pro- tects them from the further action of the air. 2. The brown powder just described, when intensely heated in a closed crucible, becomes very much denser and darker in color, and afterwards is insoluble in hydrofluoric acid, and does not burn even in the oxyhydrogen flame. It does dissolve, however, in a mixture of hydrofluoric and nitric acids, or in fused potassic carbonate, and it deflagrates if intensely heated with nitre. \ 3. At the highest temperature of a wind-furnace silicon melts, and may be cast into bars which have a crystalline struc- ture, a sub-metallic lustre, and a dark steel-gray color. More- over, by reducing silicon in contact with melted aluminum or zinc the molten metal dissolves the silicon, and afterwards, on cooling, deposits it in definite crystals. These crystals have a reddish lustre and the form of diamond, which they almost rival in hardness. 396. Silicic Anhydride or Silica. Si0 2 . By far the most abundant of all mineral substances. The mineralogists distin- guish two principal modifications, Quartz and Opal. Quartz crystallizes in the hexagonal system (Figs. 64 to 67), has a Sp. Gr. 2.5 to 2.8, is so hard that it cannot be cut with a file, and even in powder is but slightly acted on by hot solutions of caus- 397.] SILICON. 445 tic alkalies. Opal is amorphous or colloidal, has a Sp. Gr. 1.0 to 2.3, is easily abraded with a file, and dissolves in alkaline so- lutions. Each of these mineral species exhibits numerous va- rieties, determined by differences of structure or admixtures of different bodies. Among those of quartz may be mentioned common quartz, milky quartz, smoky quartz, amethyst, chal- cedony, carnelian, agate, onyx, flint, hornstone, jasper, sand- stone, and sand. Among those of opal we have precious opal, common opal, jasper opal, wood opal, siliceous sinter, float-stone, and tripoli. These two conditions of Si 0%, however, are some- times found alternating on the same specimen, and the chalce- donic varieties of quartz have frequently the appearance of opal, through which state they probably passed in the process of for- mation. The opals are more or less hydrous, but the water present is usually regarded as unessential. Both in its crystalline and in its amorphous condition silica is insoluble in water and in all acids excepting hydrofluoric acid, which is its appropriate solvent. The heat of the oxyhy- drogen flame is required for its fusion, but at this temperature it melts to a transparent glass, and may be drawn out into fine flexible elastic threads, the fused silica affecting the amorphous condition. When added in powder to melted sodic or potassic carbonate it causes violent effervescence, and if the silica is pure the product is a colorless glass. Unless the silica is in great excess the alkaline silicates thus obtained are soluble in water, and are generally known as soluble or water glass. They yield alkaline solutions, which are very much used in the arts, 1. As a cement for hardening and preserving stone; 2. In pre- paring walls for fresco-painting ; 3. For mixing with soap ; and 4. In preparing mordanted calico for dyeing. The same solu- tions can be also made by digesting flints in strong solutions of the caustic alkalies at a high temperature under pressure. 397. Silicic Hydrates. If to a solution of an alkaline sili- cate in water hydrochloric acid be added gradually, a gelatinous precipitate of silicic hydrate is formed, which, in its initial con- dition, probably has the composition Ho^Si ; but in drying it passes through every degree of hydration, and the various hy- drates which have been obtained in this and in other ways may be represented by the general formula nHo.Si mR 2 = Ho^_^(O m Si n ). [356] 446 SILICON. [398. They are all, however, very unstable bodies, some losing water at low temperatures, and others very hygroscopic, so that it is difficult to obtain definite compounds. If, instead of making the experiment as just directed, a dilute solution of an alkaline silicate be poured into a considerable ex- cess of hydrochloric acid, no precipitate is formed. The whole of the hydrate remains in solution mixed with the alkaline chlo- rides and free hydrochloric acid. These crystalloid substances, however, can readily be separated by dialysis from the colloid hydrate, and a pure solution of silicic hydrate may be thus ob- tained containing as much as five per cent of Si 2 . Moreover, by boiling in a flask the solution may be concentrated, until the quantity of silica reaches fourteen per cent. This solution is limpid, colorless, tasteless, and has a feebly acid reaction, which a very small quantity of K~Ho is sufficient to neutralize. Evidently, then, silicic hydrate has both a soluble and an in- soluble modification, but the last is by far the most stable con- dition. The concentrated solution, formed as above, in a few days completely gelatinizes. Moreover, even in a closed vessel this jelly gradually shrinks, spontaneously squeezing out the greater part of the water, until at last it becomes a hard mass resembling opal. When, however, the solution is quite dilute, it can be kept indefinitely without gelatinizing, and most spring and river waters hold an appreciable amount of silicic hydrate thus dissolved. The power of dissolving silica, which natural waters possess, is greatly enhanced by the presence of alkaline carbonates ; and when the action of the alkaline liquid is aided by a high temperature, as in the case of hot springs, large quantities of silica are frequently dissolved, and such solutions have undoubtedly exerted an important agency in the geolog- ical history of the earth. Whenever a solution of silicic hydrate is evaporated to dryness, the whole of the silica is rendered in- soluble and cannot afterwards be dissolved either in water or common acids. 398. Silicates. Although it is impossible to isolate the numberless intermediate silicic hydrates comprehended in [356], yet we find in nature numerous mineral silicates formed after the same types, and which may be regarded as derived from the hydrates by replacing the hydrogen atoms with various basic radicals. These silicates, like silica itself, affect both the crys- talline and the colloidal condition. 398.] SILICON. ' 447 The crystalline silicates are represented by numerous well- defined mineral species, and by the rocks which are simply ag- gregates of such minerals. They have been formed in many ways; for example, 1. By deposition from solution; 2. By the action of heated water or vapor on igneous and sedimentary rocks ; 3. By the slow cooling of molten siliceous material. The colloidal silicates are represented by the obsidians, the pitch-stones, and other volcanic rocks, which have probably al- ways been formed by the sudden cooling of melted lavas. To the last class belong also the various artificial silicates we call glass, and the slags obtained in many metallurgical processes. Thus crown-glass is a silicate of sodium or potassium with cal- cium, flint-glass a silicate of either of these alkaline radicals with lead, and the slags silicates of calcium, magnesium, aluminum, and iron in various combinations. Since many of the basic hy- drates and anhydrides may be melted with silica in almost every proportion, we do not find in the colloidal silicates the same definite composition as in the crystalline minerals, but they are probably in all cases mixtures of definite compounds. Most of the silicates are fusible, and their fusibility is in- creased by mixture with eacb other. As a rule, those which contain the most fusible oxides melt the most readily, and the more readily in proportion as the base is in excess. Only the alkaline silicates above referred to are soluble in water. Most of the hydrous silicates, and many which are anhydrous but contain an excess of base, are decomposed by acids; 1 but the anhydrous, normal, or acid silicates are, as a rule, unaffected by any acid, except hydrofluoric, although they can be rendered soluble by fusion with an alkaline carbonate. When the fused mass is treated with HCl -\- Aq, evaporated to dryness, and again digested with the same acid, the silica remains as a gritty insoluble powder, and can at once be recognized. The pres- ence of silica in a mineral can generally also be discovered by fusing a small fragment before the blow-pipe with microcosmic salt. This decomposes the mineral, but does not dissolve the silica, which is left floating in the clear bead. 1 Soluble compounds of the basic radicals are thus formed, while the silica separates either as a gelatinous hydrate, or as a loose, anhydrous powder. Sometimes, however, the silica also dissolves, and generally it is taken up to a limited extent. In every case the silica becomes anhydrous, and completely insoluble if the solution is evaporated to dryness at the boiling-point of water. 448 SILICON. [399. 399. Constitution of Native Silicates. The symbols of many of the native silicates have already been given, and those of others will be discovered by solving the problems which fol- low this division. Moreover, the principles on which these sym- bols are written have been fully developed. There is still, however, an uncertainty in regard to the constitution of some of these minerals, and it is not always possible to deduce from the results of analysis a probable rational formula, even when these results are known to be essentially accurate. This uncer- tainty arises from several causes : 1. We have no sure crite- rion of the purity of the mineral, since we are not able, as in the case of artificial products, to eliminate admixtures by re- peated crystallizations ; 2. The methods commonly used to de- termine the molecular weight of compounds (66) entirely fail in the case of these silicates, and this important element for fix- ing the symbol is therefore wanting 1 (23). Moreover, when the molecule is condensed (that is, contains several atoms of silicon) unavoidable inaccuracies in the processes may vitiate conclusions based on analysis alone ; 3. The constant replace- ment of one radical by another (214) renders the composition of most silicates very complex, and we are frequently at a loss to determine the part which a given radical may play in the compound. This is especially true of hydrogen, for we have no certain means of deciding whether the atoms of this element in a hydrous silicate are a part of the molecule itself, or only connected with it in the water of crystallization. 400. Symbols of Native Silicates. The composition of most native silicates may be so varied by replacements, without any essential change in external qualities, that such a mineral spe- cies cannot be distinguished as a compound of definite radicals, but merely as conforming to a certain general formula, and the only specific character is the atomic ratio between the several composite radicals of which the mineral may be supposed to consist (214). Thus the composition of common Garnet may in general be represented by the formula n vi iv 1 We have reason to hope that a more accurate knowledge of the laws which govern the molecular volume of compounds in the solid condition may here- after supply this deficiency. 400.] SILICON. 449 n v* but It may be either Ca, Mg, Fe, Mn, or Or, and [#J either [ Alt], [Fe]to or [ O 2 ], and garnets have been analyzed in which these several radicals are mixed together in every conceivable way consistent with the general formula, to which they all con- form. This formula, however, is merely the expression of a defi- nite ratio between the atomicities of the several classes of radicals taken as a whole, and in the last analysis this ratio is itself the specif c character. Hence the great importance of the atomic ratio in mineralogy, and we have already seen how easily it can be calculated when the symbol of the mineral is given (Probs. 58 and 95, pages 394 and 397). On the other hand, from the ratio we can as easily construct the general formula of the mineral. Thus in the case of garnet the ratio between the dyad, hexad, and tetrad radicals is 6 : 6 : 12, or 1 : 1 : 2, which is evidently expressed in its simplest terms by the symbol above. In works on mineralogy the atomic ratio is given for each of the native silicates, and in any case this ratio is easily deduced from the results of analysis by simply extending the method for finding the symbol of a body whose molecular weight is un- known (page 43). Having obtained the several quotients which represent the relative number of atoms on the supposition that the molecular weight is 100, we next multiply each of these quotients by the quantivalence of the respective radicals. Last- ly, we add together these products f6r each class of replacing radicals, and compare the several sums thus obtained. For ex- ample, an actual analysis of the Bohemian Garnet (Pyrope) gave the following results: Si 19.30 or Si0 3 41.35 [Jt/ 2 ] 11.92 A1 2 5 22.35 Fe 7.73 FeO 9.94 Mn 2.01 MnO 2.59 Mg 9.00 MgO 15.00 Ca 3.77 " CaO 5.29 Or 3.19 CrO 4.17 0' 43.77 100.69 100.69 Dividing now each per cent by the atomic weight of the radical, and multiplying by its quantivalence, we obtain the following numbers : cc 450 SILICON. [ 400 2.76 1.31 Si IAI;_ Fe Mn Ca Cr (19.30 -J- 28 ) X 4 = 2.76 | (11.92 -r- 54.8) X 6 = 1.31 ( 7.73 -7- 56 ) X 2 = 0.27 ( 2.01 -T- 55 ) X 2 = 0.07 ( 9.00 -r- 24 ) X 2 = 0.75 ( 3.77 _^_ 40 ) x 2 = 0.19 ( 3.19 -*- 52.2) X 2 = 0.12 1.40 whence we deduce the ratio, 1.40 : 1.31 : 2.76 or 1:1:2 nearly. This ratio, although not exact, is as near the theory as we can expect, considering the material and methods used, and is as near as we usually obtain. There is an uncertainty in the results of all calculations of this kind, which arises from the fact that we have no sure guide in selecting the radicals to be grouped together. Although it is true in general tkat replacements are limited to radicals of the same atomicity, yet most mineralogists admit that radicals of the form [./yi ma 7 replace 37?=, and some go so far as to reckon a part of the Si among the basic radicals. Hence our results are to a certain extent arbitrary, and in many cases give no satisfactory information as to the constitution of the mineral analyzed; but by deducing the atomic ratio according to the rule just given, we in all instances reduce the results, as it were, to the simplest terms, and bring them into a form in which they can be most conveniently compared with each other. It is usual in works on mineralogy to present the results of analysis on the old dualistic plan, as if the mineral were formed by the union of various basic anhydrides with silicon. Starting with such data it is not, however, necessary to calculate the per cent of each radical in the assumed anhydrides before applying the above rule, because obviously by dividing the per cent of each anhydride by its molecular weight we shall obtain the same quotients as before. For example, in the analysis garnet cited above, where the data are given in both forms, we have Si : So 2 = 19.30 : 41.35 or 19.30 -f- 28 == 41.35 -f- 60, and so for each of the other values. In the symbols of the silicates as formerly written on the du- 402.] SILICON. 451 alistic theory, the atoms of oxygen were necessarily apportioned among the different radicals in proportion to their quantivalence, although this fundamental distinction between them was itself overlooked. Thus the general symbol of garnet would be writ- ten, dualistically, and it is evident that the number of oxygen atoms is in each case a measure of the relative atomicities of the radicals with which they are associated. Hence the atomic ratio might also be found by comparing together the quantities of oxygen which the several assumed oxides contain, and this is the manner in which the calculation has generally been made hitherto. Hence, also, the atomic ratio has been called the oxygen ratio, and was long used in mineralogy before its true meaning was understood. But although the old method gives the same results as the new, it is not in harmony with our modern theories, and is practically less simple. Moreover, the principle is far more general than the old method would imply, and may be used with all classes of compounds as well as with those in which the radicals are cemented together by oxygen. Furthermore, it is sometimes useful to compare the atomic ratios of the complex radicals which may be assumed to exist in different minerals, and inter- esting relations may frequently be discovered in this way which the old method would entirely overlook. This has already ap- peared in solving the problems under aluminum, and requires no further illustration. 401. Silicic Sulphide. SiS. 2 . When the vapor of OS 2 is passed over a mixture of silica and carbon intensely ignited, this compound is deposited in the colder part of the tube in "long, white, silky, flexible, asbestiform needles." It can be volatilized in a current of dry gas ; but in contact with moist air, or when heated in aqueous vapor, it rapidly decomposes, the products being IH^ and amorphous silica, the latter of which retains the form of the sulphide. It undergoes a similar de- composition in contact with liquid water, but the silica formed dissolves completely, and the solution, when concentrated, yields the same singular vitreous hydrate, resembling opal, described above. 402. Silicic Fluoride, SiF^ is a colorless gas (Sp. Gr. = 52) 452 SILICON. [ 403. which can only be reduced to the liquid state by great pressure and cold. It is easily prepared by the reaction -f [357] When brought in contact with the air it is at once decomposed by aqueous vapor and forms dense fumes. Passed into water it is absorbed in large quantities, and the products are silicic hydrate and hydro-silicic fluoride. Aq). [358] The same solution can also be obtained by dissolving silica in hydrofluoric acid. It forms, when saturated, a very sour, fum- ing liquid, which evaporates at 40 in a platinum vessel without leaving any residue. Hence a very simple way of testing the purity of silica. The solution of hydro-silicic fluoride acts as a strong acid. It dissolves iron or zinc with the evolution of hydrogen, and decomposes many metallic oxides, hydrates, and carbonates, forming definite salts. It is therefore frequently called silico- fluoric acid (H^SiF^ and its salts are named silico-fluorides. The potassium salt, KfSiF 6 , and the barium salt, &a*SiF& are both sparingly soluble in water, and may, therefore, be readily obtained by precipitation. Moreover, since the corresponding sodium and strontium salts are much more soluble, this reagent may be used to distinguish potassium from sodium, but more especially barium from strontium. Several of the silico-fluor- ides may be readily crystallized. Ammonic silico-fluoride (NH^^SiF^ . xff 2 0, Cupric silico-fluoride Cu s SiF 6 . 7ff z O, Manganous silico-fluoride Mn=SiF 6 . 1H 2 0. 403. Silicic Chloride, SiCl 4 , is formed by passing a current of chlorine gas through an intimate mixture of silica and car- bon heated intensely in a porcelain tube. SiO 2 -+ C 2 + 2O1-O1 = 2O + Si]* [359] It is a colorless, volatile liquid (Sp. Gr. 1.52), boiling at 50, 406.] SILICON. 453 and is decomposed by water into hydrochloric acid and silicic hydrate. 0J). (6r. of vapor 5.94. It is also slowly decomposed by R,S. HCl [360] The new product is a colorless liquid, boiling at 96, and yield- ing a vapor whose 0jj. (6>r. = 5.78. When the vapor of SiCl^ is passed through a white-hot por- celain tube it undergoes a partial oxidation, and is in part con- verted into an oxychloride, t + = Si 2 OCl 6 + K91, [361] the oxygen required coming from the glazing of the tube. This compound is also a colorless fuming liquid, resembling the chlo- ride. It boils at 138, and has 0p. (r. = 10.05. 404. Silicic Bromide, SiBr, may be formed in a similar way, and closely resembles the chloride x but is less volatile, boiling at 153, and crystallizing at from 12 to 15. Sp. t. of vapor 12.05. The compound SiCl^I, 0p. (0>r. = 7.25, is also known. 405. Silicic Iodide, SiI 4 , is a colorless crystalline solid, melt- ing at 120.5, and boiling at about 290. Sp. (g)r. of vapor 19.12. It crystallizes in regular octahedrons, and is obtained by passing iodine vapor in a stream of C0 2 over ignited silicon. 406. Silicic Hydride. Siff 4 . One of the silicic ethers (409), when heated with sodium, furnishes this remarkable compound in a pure condition. iSI^ [362] The sodium induces the chemical change by its mere presence. The composition of silicic hydride has been determined by the following reaction : (2K-0-H+ ff 2 + Ag) = (KfOfSiO + Aq) + 4SI-SL [363] It is a colorless gas, which inflames at a very low temperature (under some conditions spontaneously), and yields when burnt silicic anhydride and water. 454 SILICON. [407. 407. Silicic Hydrochloride, SiHCl & , is a colorless inflamma- ble liquid, obtained by passing HGl over ignited silicon. It has 0n. (6>r. = 4.64, and may be regarded as the chloride of the radical (Siff) = Cl& corresponding to chloroform (CH) = Cl& among the compounds of carbon. The corresponding bromine and iodine compounds are also known. When mixed with water these substances are decomposed, and a voluminous white powder is formed which has been called leukon. 2SiffOl s + 3H 2 = (SiOH)fO + QffOl. [364] Leukon dissolves in the alkaline hydrates or carbonates, yield- ing an alkaline silicate and evolving hydrogen. It also decom- poses water, and acts in general as a reducing agent. 408. Silicic Ethide, Si( <7 2 # 5 ) 4 , and Silicic Methide, Si( CH 3 ) 4 are two colorless volatile liquids, prepared by heating SiOl 4 with zinc ethide and zinc methide in sealed tubes. They boil respectively at 30 and 153, and their vapors have a 0p. (S>r of 3.08 and" 5. 13. Also another compound has been described whose symbol may be written 0=Si^( C 2 ff s )& 409. Silicates of .the Organic Radicals or Silicic Ethers. A large number of these compounds have been prepared, con- taining the radicals methyl, ethyl, and amyl, either singly or associated in different combinations. They are all colorless volatile liquids, highly combustible, and having for the most part an ethereal odor. We give in the following table the symbols, the boiling-points, and the vapor-densities of several of the most interesting ethers, and of the chlorhydrines (349) derived from them. Sp. Gr. of Liquid. Boiling-point. Vapor-density. Obs. Calc. 1.059 1.195 1.259 1.144 0.968 121 -122 98 -103 82 -86 201-202.5 165 -166 5.38 5.58 5.66 5.66 9.19 7.32 5.26 5.42 5.57 5.73 8.93 7.27 409.] SILICON. 455 Sp. Gr. of Liquid. 1.048 1.44 1.291 1.020 1.004 0.981 0.915 0.913 Boiling-point. 134 157 137 104 190 143 -146 155 -157 245 -250 280 - 285 Vapor-density. Obs. 7.05 6.76 6.38 12.02 6.18 Calc. 5.68 6.81 6.54 6.22 11.86 7.69 6.23 6.72 10.12 11.57 The following equations illustrate some of the reactions by which these compounds have been prepared : 4C 2 ff 5 -0-ff+ SiClt = (C 2 H 5 )/0/Si + 1HCL [365] SiCl, = (C&)OfSCL [366] SiCl, = ^(C^fOfSiClf [367] 3(C 2 H 5 )-0-ff+ (C Z H 5 }-0-H+ Si 2 OCl 6 = [368] SffCL [369] +6 HCl [370] In general, these reactions may be obtained by simply heat- ing together the several factors, enclosed if necessary in sealed tubes. The process is usually complicated by accessory changes, and a mixed product results, which must be purified by repeated fractional distillation. 456 QUESTIONS AND PROBLEMS. Questions and Problems. 1. Compare the properties of silicon in its different conditions with those of boron. 2. Make a table illustrating the relations of the possible hydrates of silicon. 3. Required the general formula of the following mineral species whose atomic ratios are given in the table : Anorthite Sarcolite Epidote Vesuvianite Leucite Beryl lolite Oligoclase Natrolite Analcime Harmotome Stilbite VI H Formula required. iii,Si- a 6 . 5/7,0 The number of atoms of oxygen, which form the vinculum in each of the above formulas, is always necessarily equal to the total atom- icity of all the' basic radicals, and as many atoms of oxygen are asso- ciated with the acid radical as are required to complete the molecule. The last evidently serve to bind together the atoms of silicon when they are in excess over the number required to neutralize the base (151). The precise form we give to the symbols is in great meas- ure arbitrary, and must be determined from many circumstances, which do not influence the results of analysis ; and the great advan- tage of expressing these results in the form of an atomic ratio is found in the fact that they are thus reduced to the simplest terms, and ex- hibited independently of all hypothesis, leaving each student to con- struct the formulae according to his own theoretical conceptions. QUESTIONS AND PROBLEMS. 457 4. Represent the constitution of Anorthite, Sarcolite, and Beryl by graphic symbols. 5. In the following table the percentage composition of a number of native silicates is given on the usual plan, as if they were composed of basic anhydrides and silica. It is required in each case to deduce the atomic ratio and construct the formula. Na 2 K a O Li z O FeO CaO MgO A1 2 S Fe 2 3 SiO z H 2 O Ratio. Wollastonite 48.3 51.7 1:2 Pyroxene 8.0 24.9 13.4 53.7 1:2 Spodumene 6.4 29.4 64.2 1:2 Petal! te 1.2 3.3 17.8 77.7 1:4 Forsterite 57.14 42.86 1:1 Iron-Garnet 17.3 12.4 33.1 37.2 1:1:2 Zoisite 37.3 22.8 39.9 1:2:3 Ilvaite 31.5 12.3 23.4 32.8 3:2:5 Sarcolite 4.1 33.4 22.8 39.7 1:1:2 Andesine 6.53 1.08 5.77 1.08 24.28 1.58 59.60 1:3:8 Analcime 14.1 23.3 54.4 8.2 1:3:8:2 Heulandite 9.2 16.9 59.1 14.8 1 : 3 : 12 : 5 6. It was formerly supposed that the symbol of silica was corresponding to that of boric acid, JB 2 3 , when Si = 21 and O = 16. What facts can you adduce in support of the symbol adopted in this book? 7. Deduce the atomic weight of silicon from the data of (409) ac- cording to the principle of (19). It is assumed that the percentage composition of the various compounds has been accurately determined by analysis. 8. Point out the analogies between the properties of silicic fluoride and chloride, and those of the corresponding compounds of boron. 9. Compare the chemical qualities of silicon with those of the elements immediately preceding it in our classification. To which element is it more closely allied ? 10. Compare the chemical qualities of silicon with those of carbon, and illustrate by examples the analogies between those elements. 11. Point out the examples of chlorhydrines in the table of (409). 1 2. Describe and illustrate by reactions the methods by which the silicic ethers and chlorhydrines are prepared. 20 458 CAKBON. [ 410. Division XXL 410. CARBON. G= 12. Tetrad. One of the most widely diffused, and one of the most important elements in the scheme of terrestrial nature. United to the three aeriform ele- ments, oxygen, hydrogen, and nitrogen, it forms the chief solid substratum of all organized structures. Combined with oxygen it forms the carbonic anhydride of the atmosphere, which is the food of the whole vegetable world. In a nearly pure condition, or combined with hydrogen, it is found in the strata, forming those deposits of coal and petroleum which are such great stores of light, heat, and motive power (64). Lastly, it is an essential constituent of the limestones and Dolomites, which constitute an important part of the rocky crust of the globe (279) (312). The elementary substance is found in nature in three very dif- ferent conditions, namely, coal, graphite, and diamond. 411. Coal. All organized tissues, and many other carbo- naceous materials, when heated without free access of air, are charred ; that is, the volatile ingredients are driven off, and more or less of the carbon is left behind in an uncombined condition. Common charcoal, animal charcoal, lamp-black, ivory -black, &c. are all artificial products of this kind, and mineral coal is the charred remains of the rank vegetation of an early geological epoch. Since carbon is, under all circumstances, infusible and non-volatile, coal frequently retains the structure of the organic tissue from which it was derived, and this element may therefore be regarded as the skeleton of all organic forms, which in the process of growth gather around this solid nucleus the elements of air and water. The great porosity of many kinds of coal, which results from its organic structure, renders it a powerful absorbent both of aeriform and liquid materials, and hence the use of wood-charcoal as a disinfecting, and of bone-black as a decolorizing, agent. The ready combustibility of coal is, how- ever, the most characteristic and important, as it is the most familiar, quality of this variety of carbon, which is peculiarly adapted for its all-important uses as fuel, not only on account of its high calorific power, but also because it retains its solid con- dition at the highest furnace heat, and because the product of its combustion is an invisible innocuous gas, the appropriate 413.] CARBON. 459 food of the plant. In its more porous conditions coal is a non- conductor of heat and electricity, has a low specific gravity and a high specific heat, both varying, however, in different varieties between quite wide limits. 412. Graphite has usually a foliated structure, and is found occasionally in small six-sided tables belonging to the third sys- tem, but it is also met with in compact amorphous masses. From its frequent association with crystalline minerals, evidently the products of aqueous action, we naturally infer that it must have been formed in a similar way ; but the nature of the process is not understood. Graphite is very soft, leaving a black shining streak on paper, and has a Sp. Gr. = 1.209. It is practically incombustible, although it burns slowly in an oxyhydrogen flame. It has a metallic lustre, and, since it also conducts electricity nearly as well as the metals, it has been called metallic carbon. The carbon which separates from some varieties of cast-iron when the molten metal slowly cools is in the condition of graph- ite, and the cavities in iron slags are sometimes lined with crys- talline plates of the same material. Moreover, when coal is intensely heated in a close vessel, it acquires the characteristic lustre and conducting power of the same mineral, and a similar product is formed in the iron retorts in which illuminating gas is manufactured. Ordinary coke also sometimes approaches the same condition, but all these materials are very hard, and thus differ from true graphite. Graphite may be obtained in a state of minute sub-division by heating with strong sulphuric acid the coarsely pulverized mineral, previously mixed with one fourteenth of its weight of potassic chlorate, and, after washing with water and drying, igniting the residue. If this process is many times repeated the graphite is converted into a yellow crystalline product which has been called graphitic acid, and which has been regarded as a peculiar compound of the graphitoidal condition of carbon. Analysis gives the symbol O u ff 4 5 . 413. Diamond. This well-known gem is also a crystalline condition of carbon. It affects the forms of the monometric system, and may be cleaved in directions which are parallel to the faces of the regular octahedron. Its peculiar brilliancy is due to a very high refractive and dispersive power united to a strong lustre called adamantine. The effect is greatly increased 460 CARBON. [413. by the lapidary, who cuts numerous facets on the gem, which reflect and disperse the light in various directions. Diamond is the hardest substance known, and can therefore only be cut with its own powder. Opaque stones called "black diamonds," which are otherwise valueless, are pounded up and used for this purpose. On account of its great hardness the diamond is also used for cutting glass, and the convex faces of the crystals en- able them to bear the necessary pressure without breaking. The diamond burns at a high temperature much more readily than graphite, and in an atmosphere of pure oxygen sustains its own combustion, yielding C0 2 like all other forms of carbon. It is a poor conductor of electricity, but when intensely heated in the voltaic arc it suddenly acquires this power, becomes spe- cifically lighter, and is converted into a kind of coke. The dia- mond has never been made artificially, and we have no knowl- edge as to its origin. It is found in alluvial soil at only a few localities, chiefly in India, Borneo, and Brazil. It will tnus be seen that carbon presents the most remarkable example of allotropism which has been observed in nature, and the essential differences between the three states appear chiefly in the form, density, and capacity for heat, which we sum up in the table below : Crystalline Form. Sp. Gr. Sp. Heat. Wood Charcoal Amorphous 0.300 0.2415 Graphite Hexagonal 2.300 0.2027 Diamond Isometric 3.500 0.1469 In all these forms carbon is chemically the same, and yields the same product ( O0 2 ) when burnt. It is not only non-vola- tile and infusible, but does not even soften in the hottest fire ; although in the experiments of Despretz, with a voltaic battery of intense energy, it appears to have undergone incipient fusion, and to have been partially volatilized. Lastly, although com- bustible at a high temperature, yet under ordinary conditions carbon effectually resists, and for an indefinite period, the action of all atmospheric agents, and its uses for fuel on the one hand, and for printing-ink on the other, are remarkable illustrations of the singular twofold aspects of this element hi the economy of nature. 414] CARBON AND OXYGEN. 461 CARBON AND OXYGEN, OR SULPHUR. 414. Carbonic Anhydride. O0 2 . With this aeriform pro- duct of ordinary combustion the student must have already be- come familiar. Although a gas under ordinary conditions, it can be condensed by pressure and cold to a colorless limpid liquid, which freezes by its own evaporation to a light flocculent solid, outwardly resembling snow, a condition in which it is used to produce a great degree of cold. As a gas it is distinguished by the absence of all those qualities which affect the senses, and hence, although playing such an important part in nature, it es- caped notice until the year 1757, when it was first discovered by Dr. Black. It is not only a product of the combustion of all carbonaceous materials, and of the slow oxidation of organic tissues called decay, but it is also one of the chief products of respiration, and of the other processes of animal life. Carbonic anhydride is likewise formed during fermentation, and is the cause of the effervescence in all fermented liquids. It is a pro- duct of volcanic action, and is copiously evolved from the earth in many localities, especially in volcanic districts. As it is much heavier than the air, 0p. (S)r. = 1.529, it not unfrequently col- lects in wells, mines, and caverns, and it is the choke-damp which has occasioned so many serious accidents ; for, although not, properly speaking, poisonous, the free secretion of carbonic an- hydride from the body is an essential condition of life, and this is arrested as soon as the amount in the atmosphere exceeds a few per cent. Hence also the necessity of ventilating crowded apartments. Although an immense flood of carbonic anhydride is being constantly poured into the atmosphere from the various sources just enumerated, yet in the beautiful balance of creation the plant restores the equilibrium which these causes tend to dis- turb. This product of animal life, of decay, and of combustion is the food of the vegetable world, and, as has been stated (64), the sun's rays acting on the leaves of the plant undo the work of destruction, and while the plant fixes the carbon in its tissues, the oxygen is restored to the atmosphere. While the plant is an apparatus of reduction, the animal is an apparatus of com- bustion, in which the carbon it receives with its food is burnt in each act of life, and every breath carries back carbonic an- 462 CARBON AND OXYGEN. [415. hydride to the atmosphere, ready to be reabsorbed by the plant, and repass through the phases of organic life. Water dissolves very nearly its own volume of carbonic anhydride gas (53), and this important agent is as universally diffused through the waters of the globe as it is through the atmosphere, and sustains the same intimate relations to the plants and animals which inhabit the water as it does to those which live in the air. Moreover, in this condition of solution carbonic anhydride is a very active and important agent in the mineral kingdom, exerting a powerful solvent action on many minerals which would be otherwise unaffected by water, and thus causing extensive geological changes. (279), (312), and Prob. 67, page 394. Although the solution of O0 2 in water acts in all respects like a simple solution (54), yet there are reasons for regarding it as a solution of carbonic acid, and writing its symbol thus, (H 2 =0 2 -O0 -f- Aq). It has an acid reaction (39), and dissolves iron with the evolution of hydrogen gas (335). Moreover, it neutralizes many basic hydrates, and such reactions are most simply regarded as examples of direct metathesis, thus : (Ca=0 2 =ff 2 + HfOfCO + Aq) = Ca=0 2 =CO + (2H 2 + Aq). [371] Carbonic acid is a weak dibasic acid, and forms two distinct classes of salts, the most important of which have already been described (123), (124), &c., and, as may be inferred from what has been said, carbon is next to silicon the most abundant acid radical in the mineral kingdom. The quantity of O0 2 formed by the burning of a known weight of carbon can be collected and weighed with the greatest accuracy, and it was thus that the atomic weight of carbon was determined. Dumas found in a series of very accurate experi- ments that 100 parts of pure carbon yield exactly 366.66 + parts of C0 2 . 415. Carbonic Oxide, CO, is, like C0 2 , a colorless gas, but contains in the same volume only one half as much oxygen, and its molecules not being saturated, act as powerful dyad radicals (69). The gas is devoid of odor or taste, is very poisonous, is but slightly soluble in water, and has never been condensed to the liquid state. When ignited it burns with a blue flame, and 415.] CARBON AND OXYGEN. 463 when in contact with heated metallic oxides it acts as a power- ful -reducing agent, in each case eagerly absorbing more oxygen without changing its volume. It is formed abundantly in all furnaces and grates whenever the first product of combustion, always O0. 2 , subsequently passes through a mass of ignited car- bonaceous combustible, and it plays an important part in many metallurgical processes, not unfrequently occasioning a great loss of heat by escaping combustion. It is also formed when steam is passed over ignited coal, and it is a chief ingredient in the so-called water gas. Carbonic oxide may be obtained in a pure condition by a number of chemical reactions, of which the following is the most available : Potassic Ferrocyanide. Fe=OfSO a + 2KfOfSO a + 3(Nff 4 ) 2 =0 2 =S0 2 -f- 6(9. [S72] So, also, when oxalic acid is dehydrated, best by heating the crystals with concentrated sulphuric acid, it breaks up into C0 2 and CO, which are evolved in equal volumes, and the CO may be isolated by passing the gas through a solution of caustic alkali which absorbs the C0 2 . [373] In theoretical chemistry CO is chiefly interesting as an im- portant acid radical, and when acting in this capacity it is usu- ally known as carbonyl. It is the acid radical not only in the normal carbonates, but also in almost all of the organic acids. The following beautiful synthetical reaction, obtained by simply heating carbonic oxide gas with potassic hydrate, illustrates the relations of this radical to an important class of organic acids. K-0-H + CO = K-O-(CO-H). [374] Potassic Formate. Under the influence of direct sunlight, carbonic oxide combines directly with chlorine, forming CO=C1 2 , called phosgene gas. This compound is at once decomposed both by water and am- monia (Nffz), and in each of the resulting reactions the radical CO evidently retains its integrity. CO- C1 2 + H 2 = 2ffCl + CO,. . [375] CO - Cl, + ff s N = H,,H.fN f CO + 2NH 4 Cl. [376] Urea. 464 CARBON AND OXYGEN. [416. 41 6. Oxalic Acid. Hf 2 = C 2 2 . 2ff 2 0. The anhydride of this acid, C 2 3 , has never been obtained, and the acid itself forms the first term of an important series of compounds, all of which contain hydrogen. Strictly, therefore, it cannot be classed with the simple compounds of carbon and oxygen, but neverthe- less it is best studied in this connection. The calcic and potassic salts of oxalic acid are found in the juices of many plants, and when organic bodies are oxidized by nitric acid or similar agents, this acid is one of the most com- mon products. It is made in the arts by the action of nitric acid on sugar or starch, and also by heating sawdust with caustic potash. Oxalic acid easily crystallizes in prisms which have the com- position indicated above. These crystals lose their water of crystallization at 100, and at 160 the body itself is broken up, the products being carbonic anhydride and formic acid ; but the greater part of the last is still further decomposed into water and carbonic oxide, and a portion of the oxalic acid al- ways sublimes unchanged. C 2 ff 2 0, = Cff 2 2 + C0 2 and Cff 2 2 = H 2 + CO. [377] When, however, the acid is heated with glycerine, the reaction is arrested at the first stage, and yields the equivalent quantity of formic acid. Oxalic acid is both diatomic and dibasic. Thus we have Normal Potassic Oxalate X 2 =0 2 =C 2 2 . H. 2 0, Acid Potassic Oxalate ( Salt of Sorrel) . H,K~- 2 = C 2 2 . H 2 0, Super-acid Potassic Oxalate ff,K=OfC 2 2 . JffOfC 2 2 . 2H 2 0. The last is usually regarded as a molecular compound. With the exception of the alkaline salts, the oxalates are, as a rule, insoluble or difficultly soluble in water, and on the great insolu- bility of calcic oxalate several important analytical processes depend. Calcic oxalate, when heated, is converted into calcic car- bonate. Ca*OfC 2 2 = Ca-OfGO + CO. [378] When, however, the acid itself is heated with an excess of lime, we obtain a somewhat different result. -ff. [379] 416.] CARBON AND OXYGEN. 465 Oxidizing agents convert oxalic acid into C0 2 (Prob. 18, page 391) by removing the typical hydrogen. HfOfCiOt +0 = ff z O + 2C0 2 . [380] Substances having a strong attraction for water transform the acid into <70 2 and CO [373]. Argentic oxalate, when heated, is resolved with explosion into metallic silver and OO Z . AfffOfCiO, = Aff-Aff + 2 (70, [381] On the other hand, when an amalgam of pota?sium is heated in an atmosphere of (70 2 , the gas is absorbed and potassic ox- alate results. K-K + 2C0 2 = Kf 2 = C 2 2 . [382] These reactions all justify the rational symbol assigned to ox- alic acid, and by writing the symbol as in the mar- gin the relation of the atoms is made more evident. H-0-&0 We thus see that dry oxalic acid may be regarded H-O-frO as formed by the union of two atoms of the com- pound radical (ffo-CO); held together by one affinity of each of the carbon radicals, which, when not thus satisfied, may join the radical to any other group of atoms that is in the condition to hold it. This radical is called oxatyl, and dry oxalic acid is evidently the corresponding radical substance. Oxatyl, as is evident, is not only univalent, but also monobasic, and therefore must transform any group of atoms to which it is united into an acid. Moreover, the basicity of such an acid will be meas- ured by the number of atoms of oxatyl which it contains. Now nearly all the so-called organic acids may be regarded as com- pounds of oxatyl with the different hydrocarbon radicals. Those containing one atom of oxatyl are monobasic, those con- taining two atoms are dibasic, those containing three are triba- sic. Oxatyl, however, must itself be regarded as a compound of carbouyl with hydroxl, and thus we arrive at this important general principle. The basicity of an organic acid is determined by the number of atoms of Ho which it contains associated with carbonyl. 1 Moreover, it now appears why the basicity may be 1 This theory of the constitution of organic acid, which has been recently advanced and abundantly illustrated by Professor Frankland, of London, is-one 20* DD 466 CABBON AND NITROGEN. [417. less than the atomicity; for the last is measured by the total number of Ho atoms present, however united to the nucleus of the compound (43). But while the hydrogen of all the Ho atoms in a compound may be displaced by very positive met- als, or compound radicals of either class, we can only displace by double decomposition with bases the hydrogen of those atoms which are associated with carbonyl. The explanation of this important principle seems to be that, while a strong positive metal, such as sodium, will, like a pow- erful magnetic pole, increase the attraction of the point of affin- ity to which it is opposed, and thus give to it an energy it would not otherwise possess, yet in the ordinary metathetical reactions the atoms of hydrogen cannot be displaced unless they are in a polar condition, such as is determined by their associ- ation with carbonyl. 417. Carbonic Sulphide. CS 2 . Charcoal burns in an at- mosphere of sulphur vapor with almost as much energy as in oxygen, forming a colorless gas, which at the ordinary temper- ature of the air condenses to a very volatile liquid, distinguished for its very great refractive and dispersive power, and much used in the arts as a solvent of phosphorus, sulphur, and caout- chouc. The compound CS has never been obtained in a free state, but the following reactions indicate that it exists as an acid radical in certain sulphur salts (38). K^S + CS, = KfSf CS. [383] (Pb=0 2 =(N0 2 ) 2 + ZfSfCS + Aq) = (2K-0-N0 2 + Aq). [384] = PbS+ (H 2 =S 2 =CS+Aq). [385] CARBON AND NITROGEN. 418. Cyanogen. CN. Although carbon will not combine directly with nitrogen, yet when heated in an atmosphere of this gas, and in the presence of a strong alkaline base, the two elements unite with the alkaline metals, and the resulting pro- of the most important contributions recently made to Chemistry, and the au- thor would here acknowledge his great indebtedness to the papers of this emi- nent chemist in the preparation of the present division of this work. 419.] CARBON AND NITROGEN. 467 duct contains the compound radical GN, with which the stu- dent is already familiar, under the name of cyanogen. KfOfCO-\-C+N*N= 2K-CN+ SCO. [386] Like carbouyl, cyanogen is a very strong negative or acid radical, and, if we accept the theory of Frankland, we need admit no other acid radical than these two " in investigating the whole range of organic compounds." * In many of its chemical relations cyanogen closely resembles the elements of the chlorine group, forming many compounds which are analogous to the corre- sponding chlorides, bromides, and iodides, but in other respects it differs widely from these elements, both on account of its compound nature, and the singularly complex relations of the two elements of which it consists. Its univalent condition is an obvious result of the atomicities of its two constituents. 419. Cyanogen Gas, CN-CN or Cy-Cy, bears the same re- lation to the radical GN that chlorine gas bears to the element chlorine (69), (113). It is easily made by heating mercuric cyanide. [387] At the same time a brown non-volatile product is formed which is called paracyanogen. This body is isomeric with the gas, but probably represents a more condensed molecular condition, and is converted wholly into cyanogen when heated in an inert atmosphere. Cyanogen has been condensed to a liquid, boiling at 20.7, and freezing below 34, which is its melting-point. The gas is colorless, has a suffocating odor, and is poisonous. It burns with a beautiful flame, which recalls the color of peach-blossoms, and the products of its combustion are C0 2 and W^N". It dis- solves in water, but not so freely as in alcohol. The aqueous so- lution, moreover, is not permanent, for the cyanogen slowly unites with the elements of water, changing into ammonic oxalate. CN- CN + 4ff 2 = (NH^f Of C 2 0* [388] 1 There is, however, a class of somewhat obscure acids, formed by the action of H 2 =0 3 =S0 2 on various organic substances, in which the radical (Ho-S0 z )- appears to play the same part as the radical oxatyl in the compounds just no- ticed. Such bodies were formerly said to be copulated er conjugated, and these terms, though latterly discarded, were not wholly inappropriate. 468 CAKBON AND NITROGEN. [420. On the other hand, when ammonic oxalate is heated the action is reversed, and these facts show how easily carbonyl and cyan- ogen are convertible. Cyanogen unites directly with potassium, forming K-CN. 420. Hydrocyanic Acid. H-CN. The anhydrous acid (a combustible and very volatile liquid) is most readily obtained by passing H. 2 S over Hg Gy 2 , but a solution of the acid in water (the prussic acid of pharmacy) may be made by distilling po- tassic cyanide or ferro-cyanide with dilute sulphuric acid. Hydrocyanic acid has the peculiar odor of bitter almonds, and is intensely poisonous. It is a very unstable body, and both the hydrous and the anhydrous acid undergo spontaneous decomposition, which is greatly accelerated by the action of the light. When diluted with water, and mixed with a mineral acid, it is more permanent, but it is so volatile that even the very dilute acid used in pharmacy rapidly loses strength when exposed to the air. By absorption of the elements of water both ammonic oxalate and ammonic formate are slowly formed in the aqueous acid. The first by a reaction similar to [388], and the second thus, H- GN + 2H 2 = Nff 4 - 0-( OO-ff). [389] Ammonic Formate. When the vapor of ammonic formate is passed through a red- hot tube, the last reaction is reversed. In like manner, when hydrocyanic acid is mixed with hydrochloric acid (both concen- trated), we have H- GN + HGl + 2ff 2 = H-0-( OO-ff ) + Nff< Gl. [390] Formic Acid. 421. Cyanides. Hydrocyanic acid reddens litmus feebly, and potassic cyanide has an alkaline reaction (39). It however freely dissolves Hg 0, forming Hg Gy& and in a similar way (or more readily by metathesis from potassic cyanide) a large num- ber of metallic cyanides may be obtained. The alkaline cyan- ides are very soluble in water, and several of the cyanides of the heavier metals, like Hg Cy^ dissolve to a limited extent. Most of them, however, are insoluble in pure water, but with few exceptions they all dissolve freely in solutions of the alka- line cyanides, with which they form double salts, and solutions of Ag Gy and Au Gy in (KCy + Aq) are very much used in 422.] CARBON AND NITROGEN. 469 the process of electroplating. The double cyanides are a still more definite and numerous class of salts than the simple cyan- ides. Among them we may cite as examples Ag Cy . KCy and Zn Cy 2 . 2 KCy. All these cyanides contain cyanogen as such, and, with few exceptions, when heated with dilute hydrochloric acid, they yield HCy, and, if soluble, are violent poisons. There is, how- ever, another class of compounds formed by combining with the alkaline cyanides the cyanides of iron, cobalt, chromium, pla- tinum, and a few of the rarer metals, which do not evolve HCy under the influence of hydrochloric acid, and have not the same deadly character. Moreover, the metals which they con- tain cannot be displaced by the usual metathetical methods. Hence we have come to the conclusion that these bodies are not simple cyanides of the metals, but contain far more complex radicals, of which the metals just mentioned form a part. The most important of these compounds are described in the next two sections. 422. Ferrocyanides. R^(FeC 6 N & } or RfCfy. Potassic ferrocyanide (yellow prussiate of potash), KfCfy, is an impor- tant commercial product, manufactured on a large scale by fus- ing nitrogenized animal matter with potassic carbonate and iron- filings, lixiviating the resulting mass with water, and crystalliz- ing. The salt forms large yellow, square, tabular crystals, is very much used in dyeing, and is the primary source of all the cyanogen compounds. It may also be made from KCy or HCy by the following reactions : FeS + SK-CN K^FeC^) + K^S. [391] . [392] Prussian Blue. -ffo + Ag) = 2lFe,JHo s + (SKfCfy + Aq). [393] When fused, the ferrocyanide is partially decomposed, yield- ing potassic cyanide, which is made in great quantities .in this = \K- GN + Fe Q +N-N. [394] 470 CARBON AND NITROGEN. [423. way. By previously mixing the ferrocyanide with potassic carbonate a larger product is obtained, but less pure, as potassic cyanate is formed at the same time. e + COr [395] From the solution of the potassium salt various ferrocyanides are easily prepared by simple metathesis, and several of them have striking and characteristic colors. Thus, when the solu- tion is mixed with hydrochloric acid and ether, hydro-ferrocy- anic acid is precipitated. Ofy + HCl = Hf Cfy + KCL [396] c salt we obtain Pr C7 6 + ZK^Cfy + Aq) = With a ferric salt we obtain Prussian blue (ferric ferrocy- anide). (12JTCT + Aq). [397] Hence the origin of the name cyanogen (KVUVOS With a ferrous salt the precipitate is white or nearly so, but becomes blue in contact with the air. (Fe-Cl, + KfCfy + Aq) = K 2 ,Fe=Cfy + (2KCI + Aq). [398] 30-0 = ^Fe^Cfy s + SKfCfy + 2Fe 2 & . Blue With cupric salts we have a red precipitate. Cu z =Cfy + (2K 2 =OfS0 2 + Aq). [399] The soluble ferrocyanides, as a rule, crystallize readily, and the crystals usually contain several molecules of water, thus: Na^Cfy . 12H Z 0, Na,K^Cfy . 6H 2 0, Ba=Cfy . K v Ba=Cfy. 8fi t d, Zn=Cfy . 3H Z 0, 423. Ferricyanides. By passing Cl- Cl through a solution of K^Cfy a compound is formed, K^\_Cfy 2 ~], containing the hexad radical (Cfy-Cfy)l, which sustains the same relation to [424. CARBON AND NITROGEN. 471 Ofy that Tfe bears to [ 7Y 2 ]I. On evaporating the solution we obtain the salt in deep-red crystals, which are an article of commerce under the name of red prussiate of potash. + Aq). [400] Other ferricyanides may be obtained from the potassium salts by metathesis. With a solution of potassic ferricyanide ferrous salts give a deep-blue precipitate called Turnbull's blue. + (SJTCT + Aq). [401] Ferric salts, on the other hand, give no precipitate, and it will be noticed that, while these salts give. a blue precipitate with the ferrocyanides, the ferrous salts give a blue precipitate only with the ferricyanides. Hence, a simple means of distin- guishing the two classes of salt. 424. Other Compounds of Cyanogen. Chlorine forms with cyanogen three polymeric compounds. Cy-Cl (Sp. Gr. 30.7), (%) = .f^ ( S P- Gr ' 6L5 )> In like manner there are three polymeric oxygen acids. ff-O-Qy, Cyanic Acid. Dicyanic Acid. Cyanuric Acid. The tendency to polymerism (70), here manifested, is a re- markable feature of the cyanogen compounds, and gives rise to products of great complexity, most of which, however, have been but little studied. Their condensed molecules are evidently held together by complex radicals formed by the coalescing of several atoms of cyanogen, and it is evident that the atomicity of such radicals must be equal to the number of elementary atoms of any one kind, nitrogen or carbon, of which they consist. On the same principle the constitution of the ferro- and ferri-cyan- ides, as. well as that of paracyanogen, may be explained. 472 CARBON AND NITROGEN. [425. 425. Cyanates. Cyanic acid, referred to above, forms an important class of salts which have a great theoretical interest on account of the remarkable transformations of which many of them are susceptible. Potassic cyanate is readily prepared by dropping litharge into the fused cyanide, or ferrocyanide, so long as the oxide is reduced. KCy + PbO = K-0-Cy + Pb. [402] In order to crystallize the salt the fused mass should be ex- hausted with alcohol of 80%, since on evaporating an aqueous solution the salt is slowly decomposed. The same change takes place rapidly when the salt is heated with potassic hydrate. K-0-GN+K-O-H+HtO^KfOfCO + NB* [403] When potassic cyanate is mixed in solution with ammonic sulphate a metathesis takes place, but the resulting ammonic cyanate is at once transformed into a remarkable compound- ammonia or amine (167) called urea, NHi 0-GN H^HfNf CO, [404] and by this reaction the synthesis of this complex organic pro- duct was first obtained. The most interesting of the cyanates are the compounds called cyanic ethers, in which methyl, ethyl, &c. are the basic radicals. They are easily obtained, K- 0- Gy + K, G,Hf 2 =S0 2 = K 2 = Of SO, + O 2 ff 5 - 0- Cy, [405] Distilled together. and the investigation of the many wonderful transformations of which they are susceptible was one of the most important steps in the progress of organic chemistry. As cyanic acid when heated with an excess of potash yields ammonia, so these cyanic ethers yield various amines. H-0-CN+ 2K-0-ff= KfOfCO [406] - 0-GN+ 2K- 0-ff= K 2 = 2 = GO + H,H, C 2 H^N. Ethylamine. The following reactions are equally instructive : O 2 H 5 - 0-CN+2K-0- C 2 ff 5 = Kf Of CO+(O, ffJfN. [407] Triethvlamine. 427.] CARBON AND HYDROGEN. 473 C0 2 . [408] ff-0-C 2 ff 3 = Acetic Acid. Ethylacetamide. 2 ,(C 2 ff 5 )/N 2 =CO + (70^ T409] Diethylcarbamide. The above reactions will appear more simple if the symbols of the cyanic ethers are written after the ammonia type thus, OfffytGO'^ and that this is their true constitution is rendered probable by the fact that a body has recently been discovered called cyanetholine, which appears to be a true cyanic ether. It is made by the reaction Na-0-C z H 5 + CyCl = NaCl + C 2 ff 5 -0-Cy; [410] and when acted upon by potash it yields, not ethylamine, but common alcohol. (Prob. 3, page 77.) 426. Sulpho-cyanates. By fusing potassic cyanide with sulphur we obtain the sulphur salt corresponding to potassic cyanate, or K~S~ Cy, and from this, as from the cyanate, a large number of compounds may be derived. Potassic sulpho-cyan- ate, although without action on the ferrous compounds, strikes a deep-red color in a solution which contains the least trace of a ferric salt, and for this reason is a very useful reagent. CARBON AND HYDROGEN. 427. "Organic Chemistry." It has already been stated that organized beings consist of materials composed chiefly of carbon, hydrogen, oxygen, and nitrogen ; but few as are the chemical elements concerned in the processes of organic life, nevertheless the number of compounds which have been discovered in the tissues of animals and plants, or formed by their chemical met- amorphosis, is exceedingly great. Such compounds are called Organic Compounds, and in works on chemistry they are usually studied together under the separate head of Organic Chemistry. While the molecules of mineral compounds consist for the most part of only a few atoms, those of organic compounds fre- quently contain a very large number, and the diversity in or- ganic chemistry is obtained, not by multiplying the number of elements, but by varying the molecular grouping. It was for- 474 CARBON AND HYDROGEN. [428. merly supposed that the great complexity thus produced was sustained by what was called the vital principle ; but although the cause which determines the growth of organized beings is still a perfect mystery, we now know that the materials of which they consist are subject to the same laws as mineral matter, and the complexity may be traced to a peculiar quality of carbon already described. 1 The atoms of carbon are prone to combine among themselves, and the same tendency which appears in several of the elements to a limited extent is developed in the case of carbon to a very high degree. Carbon is the skeleton of an organic compound in a peculiar sense. Its atoms, locked together like so many vertebrae, form the framework to which the other elements are fastened, and thus a complex molecular structure is rendered in a wonderful measure compact and stable. Organic chemistry is simply the chemistry of the compounds of carbon, and has no distinctive character except that which the peculiar qualities of this singular element give. More- over, although in a compendium of the science it may be con- venient, or even necessary, to distinguish between mineral and organic chemistry on account of the great preponderance and importance of the compounds of carbon ; yet in a work on Chem- ical Philosophy, where the object is not to enumerate facts, there seems to be no good reason for departing, in the case of this single element, from the general scheme, or treating it more fully than is required to illustrate the new and important principles which it presents to our notice. Indeed, in an ele- mentary work no other course is possible, since a mere list of the known compounds of carbon would fill a large volume. 428. Hydrocarbons. If we conceive that the carbon atoms of the successive molecules are held together by the smallest possible number of bonds, then, as shown in (34), the symbols of the possible hydrocarbon compounds of this class would be expressed by the general symbol j7 M ^ +2 , and each number of the series would differ from the preceding by CH 2 . Again, if we conceive that the skeleton of carbon atoms, instead of pre- senting at either end an open affinity as in Fig. a, forms a closed chain as in Fig. b, the hydrocarbon atoms of this second class would be expressed by C n H^ and form another series with a constant difference as before of Cff 2 . Lastly, if we start with l The student should very carefully review (34) in this connection. 428.] CARBON AND HYDROGEN. 475 a nucleus of carbon atoms grouped together as in Fig. c, form- Fig, a. Fig. b. Fig. c. ' # s (7 = (7 = ff 10 or &( CH^H, and with a little ingenuity the student will readily discover in any case the number of such commutations possible, only he must carefully distinguish between a mere arbitrary change in the relative position of the atoms and a fundamental difference of arrangement. The last alone implies a difference of quali- ties in the substance which the formulae represent, and indicates the possibility of isomeric modifications. Review in this con- nection (70). It must not be supposed that all the hydrocarbons which our theory prefigures are actually possible, that is, represent com- pounds which either have been or may be isolated ; for as yet the theory has taken into account but one condition, namely, the atom-fixing power of carbon, and many causes may intervene to render unstable the compounds which are, from this one point of view, theoretically possible. As the number of carbon atoms increases, a condition is soon reached, when, if we may so ex- press it, the molecule cannot sustain its own weight, and in all cases the atoms must be so grouped as to preserve certain polar relations between its several parts. As yet, however, we do not understand the laws which determine molecular stability, and cannot, therefore, foresee the result in a given case, so that we are unable to control our algebraic method. Still, with all this uncertainty the theory has its value, and not only serves for the time to classify our facts, but gives us one of those glimpses of the order of creation which are the greatest privi- lege that the student of nature enjoys. But with all the limitations which the conditions of stability impose, the number of possible hydrocarbons must be very large, and the compounds actually known can form but a very small portion of those which may hereafter be isolated. The series of homologues given on page 477 include the greater part as well 428.] CARBON AXD HYDROGEN. 477 as the most important of the known compounds of this class. Of other series a few members here and there have been recog- nized, but in regard to most of these our knowledge is imperfect and uncertain. Many hydrocarbons are found in a free state in nature, but mixed together in the petroleums, and in those combustible gases like the fire-damps of coal-mines which are evolved from the earth in many localities. Others are found among the products of the dry distillation of coal, wood, or other organic tissues, and in either case the individual compounds are isolated by various processes of fractional distillation. Others, again, have been obtained by various chemical reactions, and of these a few of the more characteristic are given below : Marsh Gas Series. Acetylt C n H tn + Z. B. P. ( Methylic Hydride CH t Acetylene Ethylic Hydride C Z H Q Allylene Propylic Hydride C Z H S Crotonylene Butylic Hydride C t H w o.o Valerylene Amy lie Hydride C 5 H IZ 30.2 Allyl? Hexylic Hydride C G H lt 61.3 Heptylic Hydride CjH w 90.4: Octylic Hydride C 8 H 19 119.5 Nonylic Hydride C Q H 20 150.8 Olefiant Gas Series. Es sen QA. B. P. Ethylene <7 2 JFT 4 Propylene C 3 H 9 17.8 Oil of Turpentine Butylene C t H 8 -f35.0 Amylene CB^IO 56.0 Hexylene C 6 H 13 39.0 Heptylene C,H lt 55.0 Octylene ^8-^ia 95.0 pi Nonylene 9-^18 125.0 fi> em Decatylene ^10-^20 174.9 C* Endecatylene C^Hy^ 195.8 n Dodecatylene ^12^21 216.2 Benzol Tridecatylene ^13^26 235 Toluol Cetene C lG If 3a Xylol Cerotene (parafflne) C 21 H M 270 Cumol Melene Qo^eso 375 Cymol n"2-6 C 7 H 8 B. P. 111 129 148 175 Several of the terms in the above series are represented by at least two isomeric compounds. Thus we find in the Penn- sylvania petroleums, mixed with the last six members of the marsh gas series, five other hydrocarbons, C^o to C B ff^ iden- 478 CARBON AND HYDROGEN. [429. tical in composition, but having boiling-points uniformly eight degrees higher. The common difference between these boiling- points (which have been determined with great accuracy) is very nearly 30, and it is probable that a similar constancy would appear in all series of truly homologous compounds, and the discrepancies noticeable in several members of the series as above exhibited are probably to be referred to the fact that bodies are here included which do not belong to the same type. 429. Marsh Gas Series. C n H^ + ^ Molecules having this composition must necessarily be closed and saturated. Hence the hydrocarbons of this class are indifferent bodies, but they readily yield substitution compounds containing chlorine and bromine. Thus, when we act on marsh gas ( Cff 4 ) with chlo- rine, hydrochloric acid is formed, and we obtain either CH 3 Cl, CHCI& (7(7/4, or (7, the products of the reaction varying with the conditions of the experiment and the proportions of the fac- tors. Marsh gas may be obtained perfectly pure from zinc methide (324), which is decomposed by water, as shown by the following reaction : 2ff 2 = Zn-OfH^ + 2Off 4 . [411] By a similar reaction ethylic and amylic hydrides can be ob- tained from zinc ethide and zinc amylide. The first member of the series has long been known as a product of the decomposition of vegetable tissue under water, and hence the trivial name Marsh Gas. It is the chief constit- uent of the fire-damp of coal-mines, and of common illuminating gas obtained by the dry distillation of coal. It is most conven- iently prepared by heating potassic acetate with a large excess of potassic hydrate mixed with quicklime. K-0-C 2 H & + K- 0-ff= KfOfCO + OJH. [412] - It can also be obtained by either of the following reactions, but they have only a theoretical interest. [413] CffCl 3 + Bff-ff= 3HCI + Cff 4 . [414] 4Cn = 4CuS + OH3 4 . [415] 430.] CARBON AND HYDROGEN. 479 The first two reactions are obtained by reducing carbonic chlo- ride or chloroform with nascent hydrogen, the last by passing JI 2 S gas mixed with CS 2 vapor over ignited copper. Marsh gas has no sensible qualities, and has never been lique- fied. Like the other members of the series it is highly combus- tible, and burns with a luminous flame. Marsh gas and its homologues may be regarded as hydrides of radicals having the general form C^/^i+u and we are al- ready acquainted with many compounds in which these atomic groups manifest a marked individuality. Ethylic iodide is easily prepared, and by acting on this compound with zinc we obtain a hydrocarbon which may be regarded as the corresponding radical substance. 2C 2 ff a -I+ Zn == Znl, + C 2 ff 5 -C 2 ff 5 . [416] In like manner similar products may be obtained with several of the homologous compounds, and by using iodides of two radi- cals simultaneously the so-called double or mixed radicals may be produced. Zn = Znl* + CH Z -C,H 5 . [417] These hydrocarbons, however, are all isomeric, if not identical, with the normal terms of the marsh gas series. 430. Olefiant Gas Series. C n H^ Molecules of this type are not necessarily closed, but are capable of fixing two addi- tional monad atoms, and of acting as dyad radicals. The first member of the series was discovered by an association of Dutch chemists in 1795, who, noticing its characteristic property of combining directly with chlorine, called it Olefiant (oil making) Gas, because the product of this union is a thick flowing liquid. This product, long known as the Oil of the Dutch chemists, is ethyleue chloride, C 2 HC1 2 . Ethylene bromide and ethylene iodide may be formed in a similar way, and the tendency to form compounds of this type distinguishes this class of hydro- carbons, which are called, for this reason, olefines. Moreover, the hydrogen atoms of the bivalent radical may all be replaced by chlorine or bromine, and the resulting compound still retain the same typical character. This is shown by the following reactions : + Br-Br = ( Cf^-Br^ [418] 480 CARBON AND HYDROGEN. [431. (C 2 fft)=Br 2 + K-0-H= C 2 ff 3 Br + KBr + H Z 0, [419] C 2 ff 3 Br + Br-Br = ( C 2 ff B Br)=Br [420] (O 2 ff 3 Br)=Br 2 + K-0-H= C 2 ff 2 Br 2 + KBr + ff 2 0, [421] which may be repeated with the successive products, until at last we obtain 2 Br 4 and ( O 2 Br 4 )=Br 2 as the final results. Olefiant gas is most readily obtained by heating alcohol with several times its volume of strong sulphuric acid. The reaction is somewhat complicated, but the result is a dehydration of the alcohol, and the same effect may be produced with zincic chloride (323). O 2 ff 6 ff 2 = O 2 ff 4 . [422] Like marsh gas this aeriform hydrocarbon has no sensible qualities save a slight odor, due probably to a trace of ether. It has, however, been liquefied, and is slightly soluble in water. Containing twice as much carbon in the same volume, it burns with a more luminous flame than the lighter gas, and the illumi- nating power of coal-gas is due in no inconsiderable measure to its presence. Olefiant gas combines directly, not only with chlorine, bromine, &c., but also with the hydrogen acids. 2 H, + ffl= C 2 HJ. [423] Moreover, it unites with hypochlorous acid, forming a chlor- hydrine. o, Cl. [424] These reactions of olefiant gas illustrate in general the chemi- cal relations of this series of hydrocarbons ; but it is probable that several of those included in the list on page 477, although isomeric with terms of the series, are really formed after a dif- ferent type. A large number of them are only known as con- stituents of petroleum or products of dry distillation, and have not been prepared by any intelligible process. 431. Acetylene Series. C n ff 2n _ 2 , Acetylene. This gas is formed by the direct union of its elements, when the current from a powerful voltaic battery passes between carbon poles in an atmosphere of hydrogen. It may also be obtained by the action of water on potassic carbide. = 2K-0-H+ O 2 ff 2 . [425] 433.] CARBON AND HYDROGEN. 481 It is not unfrequently a product of the incomplete combustion of bodies containing carbon and hydrogen, and it may also be prepared in other ways. Acetylene acts as a dyad or tetrad radical, combining with nascent hydrogen to form C 2 Jf 4 (ethy- lene), with bromine to form G. 2 H 2 Br. 2 or C> 2 H. 2 Br^ and with hy- drobromic acid to form O 2 H B Br or O 2 ff 4 Br 2 . It is not yet de- termined whether these bodies are identical with the isomeric compounds of the defiant gas series. When the gas is passed through a solution of cuprous chloride in ammonia, a highly explosive compound is formed as a red precipitate, which has the composition (C. 2 H\_Cii^\)fO, and acts as a basic anhydride. The other hydrocarbons of the series have similar chemical re- lations, but have not been thoroughly studied. 432. Allyl. When allylic iodide is digested with sodium and distilled, we obtain a hydrocarbon which has the composi- tion Na-Na + 2(C 3 ff 5 )-I= 2Na~I + C 3 ff 5 -O 3 ff 5 . [426] This product, moreover, unites directly with one or two mole- cules either of Br-Br or ff-I, and in general its chemical rela- tions are those of a homologue of acetylene. But, as the above reaction indicates, it may also be regarded as the radical sub- stance (22) corresponding to allyl, and this view is sustained by the fact that there is an isomeric hydrocarbon having similar chemical relations, but different physical qualities, which is. more probably the fifth member of the acetylene series. 433. Essential Oik. C n H% n _^ Oil of Turpentine and many other essential oils have a composition represented by the sym- bol 6i ^ 6 , and there are a few others which, although also iso- meric, must be represented by a multiple of this symbol ; but no other members of the series are known. Oil of turpentine combines l^)th with the hydrogen acids and with water, forming compounds in which ( O w ff l6 ) acts either as a dyad or a tetrad radical, and others in which the double molecule acts as a hexad. radical. Thus we have Exposed to the air oil of turpentine absorbs oxygen, yieldipg a resinous product, and the same is true to a greater or less de- gree of the other essential oils. They all appear to have simi- 21 EE 482 CARBON AND HYDROGEN. [434. lar chemical relations, and are singularly susceptible of allo- tropic conditions ; but on what the differences between these isomeric bodies depend we are as yet ignorant. 434. Phenyl Series. C n ff 2n _ & . The hydrocarbons of this class are found in coal-tar and Rangoon petroleum, and are iso- lated by fractional distillation. Benzol, or benzine, is very much used in the arts, but the commercial product is more or less mixed with the associated hydrocarbons. When pure, benzol becomes solid at a low temperature, melting only at 5.5. Benzol may be obtained artificially by heating benzoic or phthalic acid with an excess of lime. CaO=: Benzoic Acid. Benzol. [427] O s ff,0 4 + 2CaO = 20aOO B + C 6 ff 6 . Phthalic Acid. Benzol. Benzol, when treated with chlorine or bromine, yields a num- ber of substitution products. By the action of nitric acid we obtain (31) Nitro-benzol Dinitro-benzol and when acted on by reducing agents (as zinc and hydrochloric acid, sulphuretted hydrogen, &c.), nitro-benzol is converted into aniline (167), and thus becomes the source of the aniline dyes. 6 fT 5 (N0 2 ) + 3ff 2 S = C & H & (NH,) + 2ff 2 + S 3 . [428] The other hydrocarbons of this series may be regarded as containing the same group of carbon atoms as benzol, and as derived from it by replacing one or more of its hydrogen atoms with the radicals methyl, ethyl, or amyl. It is evident that by replacing several atoms of hydrogen with methyl we -should ob- tain a body of the same composition as by replacing a single atom with a radical richer in carbon, and we have abundant evidence that compounds thus obtained, though isomeric, are not identical. The radical C Q H 6 , called Phenyl, appears to be the nucleus of all the hydrocarbons of this series. By acting on boiling benzol with bromine, we obtain the bromide of this radical, + Br-Br = C,H 5 -Br + H-Br, [429] 435.] CARBON AND HYDROGEN. 483 and when this product is treated with sodium a hydrocarbon is formed which is regarded as the corresponding radical substance. 2 O 6 ff 6 -Br + Na-Na = C 6 H 6 -C 6 ff & + 2NaBr. [430] Benzol is then phenylic hydride, and its homologues are hy- drides of more complex radicals, which may be designated as methyl-phenyl, dimethyl-phenyl, &c. Besides the hydrocarbons included in the five series just described we know also a few others. Of these the best studied are phenylene, (7 c /4 and cinnamene, C s ff 8 , corresponding to the symbol O n ff 2n _ 8 , and napthaline, C lo ff 8 , corresponding to C n ff 2n _i 2 . They all com- bine with chlorine and bromine, and have in general the chem- ical relations of artiad radicals. The last of these especially yields with these elements, besides the direct compounds, a very large number of substitution products, and the careful investiga- tion of these bodies by Laurent was an important step in the progress of chemistry (31). 435. Hydrocarbon .Radicals. It is evident from the prin- ciples developed in (22) and (28), and still further illustrated in (34), that, by eliminating successive atoms of hydrogen, each of the possible hydrocarbons of the scheme exhibited above may yield a series of compound radicals, and that the atomicity of such radicals is equal in any case to the number of hydrogen atoms thus lost. Such of these radicals as contain an even number of hydro- gen atoms are necessarily artiads, and isomeric with either ac- tual or possible hydrocarbons. Moreover, it follows from (428) that we may have several artiad radicals isomeric with each of the more complex compounds. Thus we may have two radicals ((7 2 ^)= and (C 2 ff 2 )= isomeric with acetylene, and the same is true of each of the homologues of this hydrocarbon. Indeed, parallel to each series of hydrocarbons, except the first, we may have one or more series of artiad radicals isomeric, term by term, with the normal compounds, and the number of possible isomers in any case is the same as the number of the series in the order of isologues (428). It is, however, an open question whether such hydrocarbons as ethylene or acetylene are essen- tially different from the radicals of the same composition (69), and we do not distinguish the radicals by separate names. The hydrocarbon radicals which contain an odd number of hydrogen atoms are necessarily perissads, and cannot, without 484 CARBON AND HYDROGEN. [43G. reduplication, exist in a free state [416], [417], and [426]. Nevertheless, the radicals homologous with methyl and phenyl play such an important part in numberless chemical reactions, and preserve their integrity through so many changes, that, al- though only known in combination, their individuality is as well marked as that of the elements themselves. Hence it is with reason that they have received distinctive names. With most of these the student is already familiar, but to those previously noticed we may here add Vinyl, C 2 H 3 -, Glyceryl, C s fff (the trivalent condition of allyl), and the radical of chloroform, CN=, which are all important perissads. 436 Oxygenated Radicals. Unless associated with some very powerful basic radical, like the alkaline metals, the simple hydrocarbons always form basic or positive radicals (40). To every such radical, however, corresponds an acid or negative radical having the same atomicity, which is generated by re- placing a portion of the hydrogen with oxygen (34). Thus : Methyl Cff 3 yields Formyl OHO or CO-H, Ethyl C 2 ff 5 " Acetyl C 2 ff 3 C0-Cff s , Propyl C 3 ff 7 Propionyl O 3 ff 5 C0-C. 2 ff 5 , Butyl C 4 ff 9 " Butyryl O^H 7 CO-C 3 JT 7 , Amyl C 5 ff n Valeryl O 5 H Q t Allyl 3 ff 5 Acryl C 3 ff 3 Ethylene C 2 X yields Glycolyl CO-C H z and Carbonyl (C0) 3 Propylene C a H 6 " Lactyl CO-C 2 H, " Malonyl (CO)=C H Acetylene C 4 # 8 " Acetonyl CO-C 3 H Q Succinyl If the theory of (41 6) is correct, it is evident that the virtue of these oxygenated radicals depends entirely on the number of atoms of carbonyl which are generated in the hydrocarbon radical, and we find that only those atoms of hydrogen can be replaced which are so related to the molecule that the atoms of carbonyl thus formed may have an open bond, and by the addition of Ho be converted into oxatyl. Hence the number of oxygen atoms which can thus be introduced into the radical can never exceed its atomicity, and the basicity of the acids, formed by the union of the resulting negative radicals with ffo, is equal to the number of oxygen atoms which any such nega- tive radical contains. 438.] MONATOMIC COMPOUNDS. MARSH GAS SERIES. 485 ALCOHOLS AND THEIR DERIVATIVES. 437. Definition. The name of alcohol is applied to a class of bodies which resemble common vinic alcohol chiefly in that under like conditions they are susceptible of similar reactions. They are produced in a variety of processes, especially by fer- mentation ; but the reactions cannot usually be traced. They may be regarded as hydrates of the hydrocarbon radicals (40), or as formed from the hydrocarbons themselves by replacing one or more atoms of hydrogen with hydroxyl, and their atom- icity (43) depends on the number of atoms of Ho thus intro- duced into the molecule. Hence we have monatomic, diatomic, triatomic alcohols, &c., and these are still further subdivided according to the class of hydrocarbons from which they are de- rived. Moreover, each alcohol is one of a group of compounds which may be derived from each other by simple reactions, not affecting the arrangement of the atoms in the carbon skeleton that may be regarded as the nucleus of the group. The com- pounds thus related have frequently little in common, and in more extended works would be classed under their appropriate heads. Our only object is to exhibit a few of the general prin- ciples and wonderful relations which the study of organic chem- istry has revealed, and this will best be gained by associating with each class of alcohols those of their derivatives which have the same atomicity. MONATOMIC COMPOUNDS. 1. MARSH GAS SERIES. 438. Alcohols. This very important class of compounds may be regarded as derived from the normal hydrocarbons of the marsh gas series by replacing a single atom of hydrogen with Ho, and consequently they are hydrates of the radicals of the methyl series (40). Of these bodies the following are known : Boiling-point. Methylic Alcohol CH*0-H 66.5 Ethylic Alcohol C z ff 5 -0-ff 78.4 Propylic Alcohol C s ff 7 -0-H 96 Butylic Alcohol C 4 ff 9 -0-ff 109 486 ALCOHOLS AND THEIR DERIVATIVES. [438. Melting-point. Boiling-point. Amylic Alcohol C 6 H U ~0-H 20 132 Hexylic Alcohol C G ff 13 - 0-h. Heptylic Alcohol C 7 H 16 -0-ff Octylic Alcohol C & H lf O-H 178 Cetylic Alcohol C^H^O-H 50 Cerotic Alcohol C^H^O-H 79 Melissic Alcohol C^H^O-H 85 The lower members of the series are liquids, the higher solids, and the boiling-point increases about 19 for every addition of CH^ The following reactions illustrate the production of methylic alcohol from marsh gas : 4 + Ol-Ol = HGl + CfffCl, [431] fCl + Ag-0-C 2 ff 3 = AgCl + Cff 3 -0-C 2 ff 3 0, [432] -H; [433] and the same method applied to the homologues of marsh gas yields other members of the alcohol series. We may also start with olefiant gas, and having combined this with HGl we may convert the C%H 5 Ql thus formed into common alcohol by the same series of reactions as before, or we may reach the same result by combining olefiant gas with sul- phuric acid and distilling the product with water. 4 = H, C 2 H 5 = 2 =S0 2 . [434] ff,C 2 ff 5 =0 2 =S0 2 + H-0-H= H 2 =0 2 =S0 2 + O 2 ff 5 -0-ff. [435] Propylic alcohol may be obtained from O 3 ff 6 by similar re- actions, but these processes applied to the other members of the olefiant series either give no results or yield compounds which, although resembling the true alcohols, and isomeric with them, manifest in their reactions an essential difference of molecular structure. These bodies have been called pseudo-alcohols. By means of the following reactions we may ascend from one member of the alcohol series to the next higher : fSO t + ff 2 0. [436] 439.] MONATOMIC COMPOUNDS. MARSH GAS SERIES. 487 K, C. 2 Hf 2 =S0 2 + K-CN= Kf 2 =S0 2 + C 2 & 5 - GN. [437] . [438] 2C 3 ff f O-ff+ H 2 + 2N-2T. [439] Common alcohol is always obtained in the arts by the fer- mentation of grape sugar (480), and other compounds of the series are not unfrequently formed in small amounts during the same process. The typical hydrogen of the alcohols may be replaced by sodium or potassium. 2H- 0- C 2 H 6 + K-K = 2K- 0- C 2 ff 5 + H-H. [440] An alcohol in which the oxygen has been replaced by sul- phur may be obtained by the following reaction : + K-S-H= Kf OfS0 2 + C 2 H & -S-H. [441] This sulphur alcohol is called mercaptan, and a corresponding selenium alcohol is also known. By the action of oxidizing agents the alcohols are converted first into aldehydes and then into acids, C 2 ff 5 -ffo + = Alcohol. Aldehyde. [442] C 2 ff 3 0-ff+ = C,ff s O-Ho; Aldehyde. Acetic Acid. but only in a few cases can the process be arrested at the first stage. 439. Fat Acids. The acids formed by the oxidation of the monatomic alcohols belong to a remarkable series of organic compounds, of which more members are now known than of any other. These acids may be regarded as hydrates of the oxygenated radicals of the methyl series (40), (436), or as formed from the hydrocarbons homologous with marsh gas by replacing one atom of hydrogen with oxatyl (416). The fol- lowing are known : 488 ALCOHOLS AND THEIR DERIVATIVES. [439. Melting- Boiling- poiut. point. Formic Acid H-O-CHO or Ho-(CO-Hy +1 100 Acetic Acid H-0-C 2 H 3 Ho-(CO-CH 8 -) -J-17 117 Propionic Acid H-0-C 3 H,0 " Ho^CO-C^H,) 141 Butyric Acid H-0-Cfl.O " Ho-(CO-C 3 H 7 ) 20 161 Valeric Acid H-0-C & H 9 " Ho-(CO-C t H 9 ~) 175 Caproic Acid H-0-C,H U " Ho-(CO-C^H n ) +5 198 (Enanthylic Acid H-0-C\H 13 " Ho-(CO-C 6 H l3 ) 212 Caprylic Acid H-0-C B H ra O Ho-(CO-C,H l& ) 14 236 Pelargonic Acid H-O-C^O Ho-(CO-C z H^) 18 260 Capric Acid H-0-C 10 H 19 Ho-(CO-C 9 H l9 ) 27 Laurie Acid H-0-C^H^O " Ho-(CO-C u H 23 ) 44 Myristic Acid H-0-C u H a O Ho-(CO-C u H a ) 54 Palmitic Acid H-0-C 16 H 31 " Ho-(CO-C^fI 3l ) 62 Margaric Acid H-0-C^H^O Ho-(CO-C u H u ) 60 Stearic Acid H-0-C l6 H^p " Ho-(CO-C^H 35 ) 69 Arachidic Acid H-O-C^O " IIo-(CO-CM 75 Behenic Acid H-0-C^H^O Ho-(CO-C 2l H i3 ) 76 Cerotic Acid H-O-Cffff^O " Ho^CO-C^H^) 78 Melissic Acid H-0-C^H^O " Ho-(CO-C^H 5g ) 88 Formic acid is found in nettles, and is secreted by ants. Va- leric acid is found in the valerian root, pelargonic acid in the essential oil of the Pelargonium roseum, and cerotic acid in beeswax. Chinese wax is cerylic cerotate, spermaceti cetylic palmitate, and the natural fats are mixtures of salts of various acids of the group, in which glyceryl, C 3 H 5 , is the basic radical. Several of these acids may be procured by the oxidation of al- buminous compounds. Propionic and butyric acids are pro- duced in some kinds of fermentation, and acetic acid is made in the arts in large quantities from the products of the dry distil- lation of wood and other similar substances. The formation of the fat acids by the oxidation of the corre- sponding alcohol is illustrated by the reactions already given [442]. They may also be formed from the cyanides of the alcohol radicals, and the method is interesting as indicating their molecular constitution. 1 The student will not fail to notice that all dashes used in connection with the hydrocarbon radicals must refer exclusively to the carbon atoms, since the hydrogen atoms, being united to the carbon skeleton by their only bond, can present no open affinity. 439.] MONATOMIC COMPOUNDS. MARSH GAS SERIES. 489 H-CN + HOI + 2H,0 = NH, Ol + (H- CO) -Ho. [443] 2 H 6 - CN+ HGl + 2H 2 = NH 4 - Gl + ( O 2 H 5 - GO) -Ho. So also C 2 H 6 -ON+ K-Ho + H 2 = (C 2 H 5 -OO)-Ko + NH 3 . [444] On the other hand, when the aramonic salts of these acids are heated with P 2 5 they are converted back into the cyanides of the radicals of the methyl series, ( OH,- GO}-(NH,)o + 2P 2 5 = OH 3 - ON+ H- 0-PO* [445] and from the cyanide thus obtained the corresponding alcohol may be produced by [438], and in this way [442] is reversed. The acid may also be converted into the alcohol by another remarkable series of reactions, of which the following series is an example : (OH s -00)-Ko + (H-GO)-Ko = Potassic Acetate. Potassic Formate. (CH 3 -OO)-H + Ko z -G0. [446] Acetic Aldehyde. Potassic Carbonate. (CH 8 -00)-H+ H-H = 2 H 5 -0-ff. [447] The potassic salt of the acid is first distilled with potassic for- mate, and the aldehyde thus obtained transformed into alcohol by nascent hydrogen. Starting now with ethylic alcohol, we can convert it into ethylic cyanide by [436] and [437], and then by [438] or [444] we can produce propionic acid. Thus we are able to pass from one fat acid to the next as from one alcohol to the next, and since formic acid can be made directly from its elements [374] the synthesis of this whole class of or- ganic compounds is, theoretically at least, possible. All these reactions seem to indicate that the fat acids contain the radicals of the methyl series united to oxatyl, and this view is rendered more probable by the fact that sodic acetate may be formed by the direct combination of O0 2 with sodic methide. ( OH s )-Na + 00 2 =( Off,- CO) -Nao. [448] Again, it appears that, when the acids of this series are acted upon by nascent oxygen in the process of electrolysis, O0 3 is 21* 490 ALCOHOLS AND THEIR DERIVATIVES. [440. formed, and the radical assumed to have been previously united to the oxatyl is thus set free. 2(0ff 3 -00)-ffo + 0= Cff B -CH B + ff 2 + 2G0 2 . [449] If this theory of the constitution of the fat acids is correct, it is obvious that if we could replace the radical hydrogen of for- mic acid with the radicals methyl, ethyl, &c., we should obtain the successive members of the series. The direct substitution has not been accomplished, but with acetic ether an analogous series of reactions has been obtained. 2C,ff 5 -0-(CO-Cff 3 ) + Na-Na = 2 C,H 5 -0-( GO-CH^Na) + H-H. [450] G z H & -0-(GO-CH 2 Na) -f Cff 3 I = C,H,-0-(GO-G,H 5 ) + NaL [451] G 2 ff 5 -0-(GO-G 3 ff 7 ) + NaL [452] 440. Formic Acid, on account of its peculiar constitution as the first member of the series, presents some special reactions which are highly instructive. Thus, when heated with strong sulphuric acid, (H- GO) -Ho = ff 2 + GO. [453] So also when acted on by chlorine gas, (H-GO)-Ho + Gl-Gl = 2HGI + GO? [454] It even acts as a reducing agent, (H-GO) -ffo + ffgO = ffg + ff 2 + G0 2 . [455] 441. Acetic Acid, the acidifying principle of vinegar, is the best known of all the lower members of this series of com- pounds, and the student has already become familiar with it in many reactions. The remarkable substitution products which it yields with chlorine have already been described (31), and the manner in which it breaks up when acted on by PG1 5 has also been illustrated (29). By this last reaction a chloride of the assumed oxygenated radical (acetyl) is obtained. 443.] MONATOMIC COMPOUNDS. MARSH GAS SERIES. 491 442. Isomers of the Fat Acids. It is obvious that with the higher members of the acetic acid series one or more isomeric modifications are possible, depending upon the different ways in which the atoms of the hydrocarbon radical may be grouped (428). Such differences of structure have been actually real- ized by means of reactions similar to [450 et seq.~], using, how- ever, as the starting-point, the products obtained by replacing two or all three of the hydrogen atoms of the acid radical in ethylic acetate with sodium. C 2 ff 6 -0-(GO-CHNa 2 ) + 2Cff 3 I= 2NaI-\-C 2 ff 5 -0-(CO-Off=(Cff 3 ) 2 ). [456] C 2 ff 5 -0-(CO-CNa 3 ) ZNaI+C 2 H 5 -0-(CO-0-(CH 3 ) 3 ). [457] By acting on these ethylic salts with K-Ho, the corresponding potassic salts are readily obtained, from which the acids them- selves may be easily set free. Now the first of these products is isomeric, but not identical, with butyric acid (boiling at 152 instead of 161), and the second sustains a similar relation to valeric acid. By exhibit- ing the symbols graphically, the difference of structure will be made evident, and it will appear that, although reactions like [451] yield the normal acids of the series, reactions similar to the last must necessarily give the so-called iso-acids. It can also be discovered how many isomers are possible in any case. 443. Ethers. These compounds are the anhydrous oxides of the alcohol radicals (40), and our common ether, (C^H^^O, may be taken as the type of the class. It is prepared by the action of sulphuric acid on alcohol, and the process may be di- vided into two stages : C 2 ff 5 -0-ff+ ff 2 =0 2 =S0 2 = ff,C 2 H 5 =0 2 =S0 2 + JSg. "458] 2 =S0 2 +C 2 R 5 -0-ff=- The alcohol and sulphuric acid, mixed in equivalent proportions, are heated in a retort, when the water and ether distil over to- gether, and if the loss is supplied by fresh alcohol (flowing glowly into the retort through a tube adapted to the tqbulature) the same quantity of sulphuric acid will convert an unlimited quan- tity of alcohol into ether. 492 ALCOHOLS AND THEIR DERIVATIVES. [444. Ether may be reconverted into alcohol by reversing the above reaction, thus : ( CJff t )f + 2ff 2 = 2 =S0 2 = 2ff, C 2 ff 6 = 2 =S0 2 + IH 2 (D. [459] H, 2 ff 5 = 2 =S0 2 + H- 0-11= Hf 2 =S0 2 + @ 2 IH 5 -CcHll. By using in the second stage of " etherification " an alcohol containing a different radical, mixed ethers as they are termed may in some cases be obtained. H,C 5 ff n =0 2 =S0 2 +C 2 ff 5 -0-ff= Hf0 2 =S0 2 + C 2 ff 5 ,C 5 ffifO. [460] Other bodies of this class have been formed, thus : 2 Cff 3 -0-ff+ Na-Na = 2 CH 3 0-Na + H-H. [461] CHz-O-Na + C 2 H 5 I= Nal + Cff 3 -0-C 2 ff 5 . 444. Compound Ethers. We include under this head the numberless salts of the hydrocarbon radicals usually distin- guished as different kinds of ether. These bodies are, for the most part, volatile, and have an agreeable odor which resembles that of fresji fruit, and several of them are used by the confec- tioners as essences. They are produced by reactions similar to those employed in the preparation of metallic salts. C 2 ff 5 -Cl + Ag-0-O 2 ff 3 = AgCl + C 2 ff 5 -0-O 2 ff 3 0. [462] Argentic Acetate. Acetic Ether. . [463] Butyrylic Chloride. Butyric Ether. n = OfS0 2 + K- 0- 2 H 3 = Potassic Acetate. . [464] Amylic Acetate. H-0~C 2 ff 3 = C 2 ff 5 -0-C 2 ff 3 + H,0. [465] In reactions like the last, when a weak acid is unable by it- self to produce the decomposition of the alcohol, the presence of a strong mineral acid will sometimes determine the forma- tion of the ether. The reaction is then best expressed as if in two stages. 446.] MONATOMIC COMPOUNDS. MARSH GAS SERIES. 493 fOfSOt = H,C 2 ff 5 =0 2 =S0 2 + H,0. + H-0-G 7 H 5 = [466] Benzole Acid. H 2 =0 2 =S0 2 +C 2 ff 5 -0-C 7 ff 5 0. Benzole Ether. HGl = G^-Gl 4- ff 2 0. [467] 0,ff,-Gl + H-O-GHO = HGl + C 4 H 9 -0-OffO. When acted on by strong alkaline bases the compound ethers yield a metallic salt and an alcohol. C 2 ff 5 -0-C 2 ff 3 + K-0-ff=K-0-C 2 H 3 0+C 2 ff 6 -0-r. [468] Since the ethers are quite insoluble in water, such reactions are best obtained in alcoholic solutions, and this kiud of decomposi- tion is frequently called saponification. At a high temperature the ethers may be saponified by water alone. 445. Anhydrides. The simple and mixed ethers are anhy- drides, but the name is usually confined to the oxides of the acid radicals. Acetic anhydride may be^obtained by the fol- lowing reaction, K- 0- G 2 H 3 + C 2 ff 3 0- Gl = KOI + ( G 2 ff s 0) 2 = 0, [469] and propionic, butyric, and valerianic anhydrides may all be prepared in a similar way. Formic anhydride, however, has not as yet been formed. In contact with water these anhy- drides dissolve only slowly, in measure, as they are converted into the corresponding acids. 446. Haloid Ethers. The term haloid means resembling common salt, and is applied to those compounds which, like sal^ are formed after the simple type of HGl, and includes the cyanides, chlorides, bromides, &c., of the hydrocarbon radicals. These ether-like bodies are formed in a great variety of re- actions. HGl = O 2 ff & -Cl + H 2 0. [470] ll -0-H+ PC1 3 = HfOfPOH+ 3 O 5 ff n -OL [471] ff 3 ^PO+5C 2 ff 5 -I+ H,0. {472] CH, + Gl- Gl = Cff 3 - Gl + H- Gl [473] 494 ALCOHOLS AND THEIR DERIVATIVES. [ 447* When acted on by an alcoholic solution of potash, all the haloid ethers, except the cyanides, are converted into alcohols. C 5 ff lf Cl + K- 0-ff= KCl + CJfftfO-H. [474] The reaction of the cyanides has already been given [444]. The haloid ethers are allied to the hydrogen acids, and like these combine with ammonia, and by the action of potash on the salts thus formed various amines may be obtained. NH, [475] -0-H= Ethylamine. Ethylic iodide, heated in a sealed tube with water, is con- verted into common ether. [476] Me thy lie chloride, when acted on by chlorine, yields the fol- lowing substitution products, and it will be noticed that the boiling-point increases in proportion as the atoms of hydrogen are replaced. B. P. B. P. B. P. B p. CHj-Cl 21, Cff 2 Cl 2 31, CffOl s 60.8, GC1 4 78. The compound CffOl 3 is called chloroform, and is an anaes- thetic agent made in large quantities by heating alcohol or wood spirit (methylic alcohol) with a solution of chloride of lime (282). When boiled with an alcoholic solution of potash, chlo- roform is converted into potassic formiate, and chlorine gas, under the influence of sunlight, changes it into carbonic chloride. -0-ff= 3KCl+K-0-(CO-ff)+2ff 2 0. [477] Bromoform, CHBr& and lodoform, OHI& are also known. 447. Aldehydes. These bodies, already mentioned as the products of the imperfect oxidation of the alcohols [442], may also be obtained by distilling a mixture of potassic formate with the potassic salt of the acid corresponding to the aldehyde re- quired. K-O-(OO-H) + K-0-(GO-CH,} = [478] Acetic Aldehyde. 448.] MONATOMIC COMPOUNDS. MARSH GAS SERIES. 495 The aldehydes are distinguished by a strong affinity for oxy- gen. They not only absorb oxygen gas from the air, but they reduce argentic oxide, and when heated with alkaline hydrates they evolve hydrogen, passing in each case into the correspond- ing acid. H-O-(CO-CHi). [479]- Aldehyde. Acetic Acid. ff-(00-0ff s ) + Acr. 2 = ff-0-(CO-Off 3 ) + Ag-Ag. [480] ff-(OO-Cff 3 ) + K-0-ff= K-0-(GO-CH 3 ) + H-H. [481] By nascent hydrogen (water and sodium amalgam) the alde- hydes are converted back into alcohol. H-( G0-0ff 3 ) + ff-ff O 2 fl s -0-ff. [482] Most of them yield crystalline compounds with ammonia. H-( GO-Off,) + Nff 3 = NHf( 00-0ff 3 ). [483] So also by dissolving potassium in aldehyde we obtain the reaction 2ff-(GO-Off 3 ) + K-K= 2K-(OO-Off 3 ) + H-H. [484] The aldehydes are named after the corresponding acids. The first is formic aldehyde ff-(OO-ff), and the seven succeed- ing terms of the same series have been obtained. Of acetic aldehydes there are three polymeric modifications. The nor- mal compound is a very volatile liquid, boiling at 21 and hav- ing a strong suffocating odor. 448. Ketones. This name is applied to a class of com- pounds outwardly resembling the alcohols and having a pleas- ant ethereal odor. They are isomeric with the aldehydes, but differ from them widely in their chemical relations, for they are comparatively inactive bodies, and show no tendency to unite with oxygen. They are most readily obtained by distilling the potassic or calcic salts of the monatomic acids. Oa=0,=(00-0ff 3 )i=:0a=0f00+(0ff s )f00. [485] Calcic Acetate. Acetone. Ca*Of(CO-C 9 ff 8 ) t = Ga-OfGO + (G 2 ff 5 \fGO. [486] Calcic Propionate. Propione. 496 ALCOHOLS AND THEIE DERIVATIVES. [449. It will be noticed that the two ketoues thus obtained differ by 2 GHz, although the initial acids only differ by CH. 2 ; but by dis- tilling an intimate mixture of the two salts we can obtain the intermediate term of the series, namely, Gff 3 ,0 2 IT 5 = GO. Ketones can also be obtained by acting on acetyl chloride or its homologues with zinc methide or ethide. 2(Off 3 -GO)-Cl + Zn=(GH 3 ) 2 =ZnOl 2 +2(Gff 3 ) 2 =00. [487] Moreover, they have been formed by the action of carbonic oxide on sodic ethide and the homologous compounds. 2Na-G 2 ff 5 + CO = Na-Na -f (O^fOO. [488] 449. Pseudo-Alcohols. By the action of nascent hydrogen the ketones are converted into compounds isomeric, but not identical with the alcohols. ( Gff 3 ) 2 = 00 + H-H= ( GH 3 )f GH-Ho. [489] The bodies of this class are also called secondary alcohols, and are distinguished by the prefix iso. Their relations to the normal alcohols are illustrated by the following symbols : (OH 3 -Off 2 )-iro, (Cff 3 -GO)-ff, (GH,-GO}-Ho, Ethylic Alcohol. Aldehyde. Acetic Acid. Propylic Alcohol. Aldehyde. Propionic Acid. ( OH 3 )f GH-Ho, ( Gff 3 ) 2 = GO. Isopropylic Alcohol. Acetone. As common alcohol passes by oxidation first into aldehyde and then into acetic acid so normal propylic alcohol, when oxidized, yields similar products. But under the same con- ditions the isopropylic alcohol gives acetone, which, although isomeric with propionic aldehyde, cannot be converted by fur- ther oxidation into propionic acid, and it is evident that such a change would not be possible without a complete remodelling of the molecule. The difference between these isomeric alco- hols, indicated by their reactions, is still further manifested in their boiling-points, since while the normal alcohol boils at 96, the pseudo-alcohol boils at 87. Besides the isopropylic two other pseudo-alcohols have been obtained which probably be- long to the same class. 451.] MONATOMIC COMPOUNDS. VINYL SERIES. 497 Isoamylic Alcohol ( CH 3 , O 3 fff CH)-Ho, Isohexylic Alcohol ( CH^ C t Hf CH)-Ho. Lastly a pseudo-alcohol has been discovered, isomeric with butylic alcohol, which appears to be constituted after still a third type, and to be the first of a class of tertiary alcohols. Pseudo-butylic Alcohol ( C7/ 3 ) 3 = C-Ho. If we represent by H any univalent hydrocarbon-radical, the general symbols of the three classes of alcohols we have dis- tinguished would be as follows : HfC-ffo. Primary Alcohol. Secondary Alcohol. Tertiary Alcohol. 2. VINYL SERIES. 450. Vinylic Alcohol Acetylene like ethylene dissolves in sulphuric acid, and when the product is distilled with water we obtain the hydrate of the radical vinyl or vinylic alcohol. Jf 2 =0 2 =S0 2 + C 2 ff 2 = [490] ff,C 2 ff 3 =0 2 =S0 2 ff-0-ff=ff 2 =0 2 =S0 2 This alcohol is isomeric both with acetic aldehyde and the oxide of ethylene. > C 2 ff 4 =0. Vinylic Alcohol. Acetic Aldehyde. Ethylenic Oxide. No acid has been obtained from it by the action of oxidizing agents. 451. Allylic Alcohol. The second term of the vinyl series may be formed from glycerine by the following reactions. -I. [491] Allylic Iodide. AfffOfC,0, = 2A 9 I+ (0 8 ff s )fOfO a O f [492] Argentic Oxalatc. Allylic Oxalate. 0, + 2 ff s N= ,ff 5 -0-ff. [493], Oxamide. Allylic AlcohoL RF 498 ALCOHOLS AND THEIR DERIVATIVES. [452. When dehydrated by phosphoric anhydride (184) this alcohol gives allylene the second member of the acetylene series. (C&)-0-ff H 2 = C s ff 4 . [494] Oil of garlic is the sulphide of allyl ( C 3 ff 5 ) 2 =S and oil of mustard the sulphocyanate C & H 6 ~S-CN. When acted on by oxidizing agents, allylic alcohol yields both an aldehyde and an acid, and the following symbols indi- cate the relations and probable constitution of the three bodies. o, (Cff 2 =CH-CO)-H, Allylic Alcohol. Acrolein (Aldehyde). Acrylic Acid. 452. Acrolein is formed abundantly during the dry distil- lation of fats or similar glycerides (474), and the pungent odor of its vapor, so intensely irritating to the eyes, is familiar to every one. It may be best procured by the action of dehy- drating agents, such as phosphoric anhydride or sulphuric acid, on glycerine, from which it differs by 2H 2 0. ot 2ff 2 = (CSfCff-CO)-ff. [495] Glycerine. Acrolein. 453. Acrylic or Oleic Series of Acids. Acrylic acid is the first member of a large and important series of acids, which are associated with the acids of the acetic series in the natural fats and oils. Only those members of the series are included in the following list which we have reason to believe are con- stituted like acrylic acid. Of the constitution of the other fat acids of this class we have as yet no knowledge. Acrylic Acid C 3 ff 4 2 or Ho-(CO CH-C JT 2 ), CrotonicAcid C 4 ff 6 2 " Ho-(00-CH=C 2 H^ Angelic Acid C 5 ff 8 2 ffo-(CO-Cff*CJ%), Pyroterbic Acid <7 6 # 10 2 Ho-( CO- CH- C 4 ff 8 ), Oleic Acid <7 18 #34 2 m-(CO-Cff*C u ff n ). These acids are closely allied to those of the acetic series. Acrylic acid under the influence of nascent hydrogen changes into propionic acid, and when acted on by bromine it yields a simple derivative of the same compound. 454.] MONATOMIG COMPOUNDS. VINYL SERIES. 499 Ho-(GO-GH-GH,} [496] = ffo-(CO-C 2 ff s Br 2 ). Moreover, when heated with caustic potash all the acids of the above list break up into two acids of the acetic series, one of which is always acetic acid itself. Ho-(GO-GH-GH 2 ) + 2K-0-ff= + Ko-(GO-H) + H-H. [497] Ho-(GO-GH-G 2 H,) + 2K-0-ff= Ko-(GO-GH B ) + Ko-(CO-Off 3 ) + H-H. [498] 2K-0-H = -GHz) + Ko-(CO-0 2 ff 5 ) + H-H. [499] 2K-0-ff= -f Ko-(CO-O 3 ff 7 ) + H-H. [500] Ko-(GO-C^H^ + H-H. [501] Salt of Palmitic Acid. The alkali appears to act on the defines (430), assumed to exist in the radicals of these compounds, and replaces them with HK thus forming acetic acid in every case, while at the same time it converts the olefine itself into another acid of the acetic series. 454. Secondary Acids. Acids isomeric with those of the acrylic series have been obtained by means of reactions which indicate the structure of the resulting molecules, and a com- parison of the reactions of these artificial products with those of the normal acids shows that the rational symbols we have assigned to the latter must be essentially correct. The sym- bol of oxalic ether may be written Et-0-(GO-GO)-0-Et, and there are good reasons for writing the symbols of the zinc compounds of the monad radicals (324) thus, (^wH)'Hi indicating, as is undoubtedly the case, that the group (Znft)- acts as a monad radical. When now a body of this class acts on oxalic ether, the following reaction takes place : Et-0-(GO-GO)-0-Et + 2(^nH)-E = Et-0-(GO-G^)-0-(ZnW) -{- Et-O-(ZnW). [502] 500 ALCOHOLS AND THEIR DERIVATIVES. [455. If next water is added, the product of the last reaction undergoes a still further change, -H, [503] and the whole effect, as will be seen, is to replace one atom of oxygen in the radical of oxalic acid with two atoms of a radical of the methyl series. Lastly, if we subject one of these acids, thus synthetically obtained, to a dehydrating agent (PO1 3 or P 2 5 ), the result is an isomer of the acrylic series. Et-0-(CO-C^-0-H H 2 = &-0-(CO-Cfcto). [504] Here R stands for a dyad radical of the olefiant series, and the symbols of the compounds which have been obtained in this way are given below. By comparing these with the symbols of the normal isomers, the difference of structure will be evident. Secondary Acids. Normal Acids. Methyl-acrylic Acid H-0-(CO-C(CH^CH Z ) H-0-(CO-CH=C 2 HJ Methyl-crotonic " H-0-(CO-C(CH^C t H^ H-0-(CO-CH=CJQ Ethyl-crotonic " JJ-0-( CO- C( N 2 C 8 Oo Mesoxalic Acid. TT ( TT ***) n % Alloxanic Acid. Alloxan. CO ) Ho-C 2 ff,0 C 2 H,0[N 2 Acetic Acid. jj \ Acetyl Urea. CO ) CO Glycollic Acid. TT -o 3 ) J Glycoluric Acid. Hydantoin. 486.] Acids. ffo 2 =C 3 ff 2 2 Malonic Acid. DIUREIDES. Monureides. 541 Monureides. CO Barbituric Acid. CO) Tartronic Acid. H-(CO-CO)-Ho Glyoxalic Acid. Dialuric Acid. CO ff-(CO-CO) Allanturic Acid. 486. Diureides. These may be regarded as formed by the union of a monureide with an additional molecule of urea, the combination involving as before the elimination of one or two molecules of water. The following are a few examples : CO ) ffo-C 2 H 2 V- CO Glycoluric Acid. CO H-C 2 2 N CO ) C CO H 2 = H-C 2 2 AUanturic Acid. CO ffo-C 3 H0 2 H, Dialuric Acid Urea. Allan toin. CO J ff 2 ) Urea. Barbituric Acid. Xan thine. ") o( N C a ff,0 p ffj Hypoxanthine. 542 URIC ACID. [487. It must not be inferred that the equations either of this or of the last section represent actual processes by which the various urides have been prepared. They merely indicate the most probable theory in regard to the constitution and chemical re- lations of these bodies which we have been able to form. The substances themselves are either products of the animal organism, or else have been prepared from such products by different chem- ical processes, and our only knowledge in regard to their mo- lecular structure has been derived from a study of their prop- erties, and of the chemical changes in which they are formed or broken up. For the evidence on which the rational sym- bols here given are based we refer the student to the memoirs of Baeyer, in the Annalen der Chemie und Pharmacie, contain- ing the results of his very extended investigations of this class of compounds. 1 487. Uric Acid is not only the most important of the ureides, but it is the source from which almost all the rest have been derived. It is a constant product of the animal organism, re- sulting from the imperfect oxidation of the nitrogenized tissues. With the reptiles, birds, and insects it forms (in combination with ammonia) the chief part, and in some cases nearly the whole, of their solid excrements ; but in mammalia the oxidation proceeds further in the body and the product voided is princi- pally urea. Nevertheless, uric acid is always present in human urine, and in certain abnormal states of the system the amount becomes increased to an injurious extent, giving rise to sedi- ment, gravel, or calculi. In some forms of gout all the fluids of the body become saturated with it, and in combination with soda it is deposited in the joints, forming what are familiarly known as chalk stones. Uric acid, when pure, forms a white crystalline powder, which under the microscope exhibits definite and character- istic crystalline forms ; but the crude acid is more or less tinted by the coloring matter of the urinary secretion, from which it is prepared. When heated, it decomposes without melting, yielding a sublimate of cyanuric acid, ammonic cyanate (or urea), and ammonic carbonate, leaving a carbonaceous residue 1 See, also, an article in Silliman's Journal, vol. 96, page 289, by Dr. W. Gibbs, in which rational symbols for these bodies are theoretically deduced from either the known or assumed polymeric forms of cyanic acid. 487.] URIC ACID. 543 behind. It is almost insoluble in water and the dilute mineral acids; but it dissolves readily in alkaline solutions, since it forms with the alkaline radicals more or less soluble salts. It also forms salts with several of the more basic metallic rad- icals, which may either replace one or two of its typical hydro- gen atoms. We have, therefore, in several cases both an acid and a basic salt of the same radical. But while we can only replace two of the hydrogen atoms with metallic radicals we can replace three with ethyl. The rational formula of uric acid has alre^iy been given. It is based chiefly on the following considerations. When the acid is treated with a mixture of hydrochloric acid and potas- sic chlorate (a strong oxidizing acid), it is converted wholly into a mixture of alloxan and urea, N& C 5 3 +0 + H 2 = N 2 ff 2 C 4 0, + N 2 H, CO. [559] Uric Acid. Alloxan. Urea. Now the first effect of the oxidation would be naturally to re- move the hydrogen atoms from the hydrocarbon radical we have assumed to exist in uric acid, changing it into the hypo- thetical compound N 4 ff 2 C 5 3 , and then this, by absorbing two molecules of water, gives at once alloxan and urea. CO) CO) jV 2 -f-// 2 >^V 2 . [560] "2 ' ""a' ""a t v J Uric Acid. Hypothetical Intermediate. Alloxan. Urea. Further, when alloxan is boiled with an alkaline solution it yields urea and the mesoxalate of the alkaline radical. Lastly, mesoxalic acid is a crystalline solid resembling oxalic acid, and like it is dibasic. As its composition is well determined there can be no question that it contains the radical C 3 3 , and is the third term of a series of which carbonic acid and oxalic acid are the other three. AlOcT \J \J JLlOf C/2 C/2 -tlOf ^3 ^/3* Carbonic Acid. Oxalic Acid. Mesoxalic Acid. This completes the chain of evidence, but the student will not fail to see that it has a weak point. The view of the constitution of uric acid here adopted is further supported by a reaction observed by Strecker, who found that, when treated with hydriodic acid, one molecule of uric acid breaks up into one molecule of glycocoll (L 544 UEIC ACID. [ 487. , three molecules of ammonia and three of carbonic di- oxide. Now if uric acid contains, as we have assumed, the tartronyl radical, it must have the graphic symbol given below, leaving the parts in brackets undeveloped (473), and by com- paring this with the symbols of tartronic acid and glycocoll on either side, it can readily be seen that the products are pre- cisely such as might be expected from the action of the reagent used, assuming of course that our theory is correct. OHO OH,0 OH Ho-G-C-C-Ho (NBfrQ-G&(Ni<$ (NH 2 )-C-C-H. Ho Ho Ho Tartronic Acid. Uric Acid. GlycocolL Uric acid is remarkable for the facility with which it is al- tered by oxidizing agents, and for the great number of definite and crystallizable compounds obtained, either in this manner or by treating the immediate products of oxidation with various reagents. The following list includes all the more important derivations : Derivatives Br of Uric Acid, Hydantoin, Hydurilic Acid, Leucoturic Acid, Mesoxalic Acid, Murexide, Mycomelic Acid, Oxaluric Acid, Paraban, Pseudo-uric Acid, Srryphnic Acid, Thionuric Acid, Uramil, Urinilic Acid, Uroxanic Acid, Violantin, Violuric Acid, Xanthine, Allantoin, Allanturic Acid, Allituric Acid, Alloxan, Alloxanic Acid, Alloxantin, Barbituric Acid, Bromo-barbituric > Acid, > Dibromo-barbituric ) Acid, J Dibarbituric Acid, Dialuric Acid, Dilituric Acid, Glycoluric Acid, Glycoluril, Hydantoic Acid, It must not be supposed that the term acid, used in connection with so many of these compounds, implies that they all have the constitution of true organic acids, that is, contain one or more atoms of oxatyl. That there are among them true acid 487.] UBIC ACID. 545 amides (168) has already been shown, but in most cases the apparent acid reaction arises from the power, which many amides possess, of exchanging one or more of their atoms of typical hydrogen for the basic radicals of metallic hydrates, and this relation undoubtedly shows that the molecules of these bodies are in a polar condition not unlike, although less marked, than that of the true acid molecules of the water type. For the various processes by which the uric acid derivatives have been prepared we must refer the student to Watt's Dic- tionary of Chemistry, from which, with some alterations, the above table has been taken. But in spite of the apparent com- plexity of the results, the chemical changes involved in the production of these bodies may be referred to a few types. We may have : First. The breaking up of a diureide into a monureide and urea. co\ ao ) ) C,Hf> } N < + H * = ^ t N * +^ 2 f N * t 561 ] 77 1 fii} ^2 ) **4 ' Hydantoin. Urea. Glycoluril. By boiling a solution of glycoluril with acids, and the reaction [560] given, above is an example of a similar change. Secondly. The formation of a biureide from a ureide. 2tf 2 K 2 4 4 = N 4 ff 4 8 7 . [562] Alloxan. Alloxantin. By the action ofhydric sulphide or nascent hydrogen on a solution of alloxan. Thirdly. A modification of the more complex radical of the ureide, without altering its relations to the compound. CO) CO ) C 8 \-&2 + = C 2 2 V- N 2 + 00, [563] # 2 ) H,\ Alloxan. Paraban. By gently warming alloxan with nitric acid. .O & + + ff 2 = N 4 ff 6 4 s + 00 2 . Uric Acid. Allantoin. By boiling uric acid with water and plumbic dioxide., 4 3 2 ,, 4 0*+H, 0. [564] Allantoin. Glycoluril. ~ By the action of sodium amalgam on a solution of allantoin. CO) 00) C 2 H 2 BrO y# a = HBr + O 2 ff 2 f- N 2 [565] ) ff 9 ) Bromacetyl Urea. Hydantoin, By the action of ammonia. 546 ALLANTOIN AND MUREXIDE. [488. CO) CO) = C S H(NO,) 0, [ N 2 [566] Barbituric Acid. Nitrobarbituric or Dilituric Acid. By the action of nitric acid. CO) CO) C 3 3 kJ5 + ff 2 = ffo-C 3 3 [.JK [567] HI) ff 3 ) Alioxan. Alloxanic Acid. Fourthly. A breaking up of the ureide into ammonia and the hydrate of its principal radical. CO) C 3 3 ^N- 2 + 3ff 2 0=C0 2 + IfofC 3 3 + 2NIf 3 [568] IT \ Mesoxalic Acid. ^2 ) Alioxan. CO) C 3 ff 2 2 [N' 2 + 3ff 2 = C0 2 + ffo 2 =C 3 ff 2 0, + 2NIT 3 [569] 77" V MalonicAcid. ^2 ) Barbituric Acid. By heating with solutions of caustic alkalies. It will, of course, be understood that in the actual processes two or more of such reactions as have been here illustrated may concur or may succeed each other. Indeed, it has been found very difficult to isolate them. 488. Allantoin and Murexide are the only bodies among the uric acid derivatives which have any other interest than that which is connected with their chemical composition, and the only special interest attaching to allantoin arises from the isolated fact that it appears to be an essential constituent of the allantoic liquid. Murexide, however, is a most brilliant purple pigment, and before it was superseded by the aniline colors was manufactured on a large scale. It can be readily prepared by adding ammonia to the solution of alloxan and alloxantin, which is obtained by dissolving uric acid in dilute nitric acid under regulated conditions, and the production of a purple color under such circumstances is a delicate test for uric acid. Murexide crystallizes in brilliant garnet-colored prisms, which appear gold-green by reflected light. It gives with wa- ter a rich purple solution, but is insoluble in alcohol or ether. It appears to be the ammonium salt of a very complex amide, which has been called purpuric acid ; but although the ammo- nium radical may be readily replaced by various metals the 489.] GUANINE AND GUANIDINE. 547 amide itself has not been isolated, and our knowledge in regard to these beautiful compounds is as yet too limited to enable us to assign to them any probable rational symbols. Similar pro- ducts are obtained by the action of potassic cyanides on picric acid (457), and these isopurpurates, as they are called, are isomeric with the corresponding uric acid derivatives. 489. Gkianine and Guanidine. The first of these com- pounds resembles uric acid, and is found associated with it in some kinds of guano, but it forms an amorphous instead of a crystalline powder, and has basic rather than acid relations. Ultimate analysis gives the empirical symbol Jf 5 N 5 O 5 0, and it may be regarded as derived from xanthine by replacing the radical HO by H 2 N, a view of its constitution which is sus- tained by the fact that when treated with nitrous acid it yields that well-known diureide, [570] Guanine. Xanthine. An equally interesting reaction is obtained by digesting guanine with a mixture of hydrochloric acid and potassic chlorate, when it breaks up into paraban and a remarkable amine called guanidine. Guanme ' H 5 N, + H 2 N, 3 3 + 00 2 . [571] Guanidine. Faraban. There are also formed at the same time, although in smaller quantities, xanthine, oxaluric acid, and urea. Guanidine is a crystalline solid having a strong basic reac- tion, absorbing C0 2 from the air, and forming with acids crys- talline salts, which, like H 5 N 3 O . ffCl, contain for every mole- cule of a monobasic acid one molecule of the amine. It can be formed synthetically by heating iodide of cyanogen with an alcoholic solution of ammonia in a closed tube, and this reac- tion leaves no doubt in regard to its molecular structure. HI. [572] Guanidine has also been obtained by heating with the same solution, and under similar conditions, chlorpicrin, a product of the action of chlorine on picric acid. Chlorpicru, ff^ Q . ffCl + 2ffCl + HN0 3 . [573] 548 GLYCOCYAMIN AND GLYCOCYAMIDINE. [ 490. The interpretation of this reaction is aided by the fact that when the same chlorpicrin is distilled with alcohol and sodium it yields an ether which is a true ortho-carbonate, thus : ( G 2 ff 5 )/ Of G + 3Na Gl + NaN0 2 . [574] The same ether, heated with aqua ammonia in a closed tube, gives guanidine. jgfc 4 i 4 i G + 3 Nff 3 = Et- OH + HN= G-(NH Z \. [575] There are also known a number of well-marked amine bases, which may be regarded as derived from guanidine by replacing one, two, or three atoms of its typical hydrogen by hydrocar- bon radicals. 490. Glycocyamin and Glycocyamidine, Greatine and Grea- tinine. By passing chloride of cyanogen and ammonia gas simultaneously into anhydrous ether, the ammonic chloride which is formed separates out, while there remains in solution one of the simplest and at the same time most remarkable compounds of the amide group. CN-Ol + 2Nff s NfffCN + NH A Gl. [576J Cyanamide. Now we can directly unite the cyanamide thus formed with glycocoll, and the product is called glycocyamine, which when acted upon by dry HGl yields an allied base called glycocyami- dine. The constitution of these bodies can be inferred with great certainty from the simple synthetical process by which the first is formed, interpreted by reactions [572] and [576]. It will be noticed that the factors in these two reactions are nearly the same, and the difference in the products depends on slight variations of conditions. Indeed, guanidine may be ob- tained by the action of NH 8 on the chloride as well as on the iodide of cyanogen, only it is not then the chief product, for the reaction tends to take the form of [576] rather than of [572]. An analysis of these reactions will show that the dif- ference in the results depends on the circumstance that, while in [576] the two atoms in the cyanogen radical remain united by the three original bonds, in [572] one of these bonds is let Joose, forming points of attachment to which the two radicals jfiTand NH 2 join themselves. Now the union of glycocoll with cyanamide probably depends on a similar change, so that in 490.] CREATINE AND CREATININE. 549 the resulting glycocyamine the two atoms in the original cya- nogen radical remain joined by two bonds, while the two parts of the glycocoll molecule, NH 2 and HO~O 2 H 2 0, unite to the points of attachment which the breaking of the third bond fur- nishes. The subsequent production of glycocyamide is simply an example of the change from a monad to a dyad radical by the elimination of HO with which we are so familiar (485). The interest attaching to the above compounds arises from the fact that there is found in muscular juice a crystalline base called creatine (supposed to have important physiological rela- tions), which is the first homologue of glycocyamine, and which yields, when treated with acids, a second base, creatinine, that is the first homologue of glycocyamide. Thus we have the following triamides: C ) O } jr}*! Ho-0 2 H 2 olN, C 2 H 2 IN, Guanidine. Glycocyamine. Glycocyamidine. C \ C Ho-C 2 H 2 ( N C 2 H 2 , N OH, p Vs OH 3 ^ Creatine. Creatinine. Both creatine and creatinine have been found not only in mus- cular flesh, but also in the urine, in the blood, and in other ani- mal fluids ; but it is difficult to determine to what relative extent they exist in the living body, since, while strong acids convert creatine into creatinine, alkaline reagents change crea- tine back to creatinine, and these changes may take place in the processes of extraction. These bases unite directly with acids, forming well-crystallized salts, and one molecule of base neutralizes in each case one molecule of a monobasic acid. Creatine has been formed synthetically by a process which plainly indicates its molecular constitution ; for as glycocya- mine results from the union of cyanarnide with glycocoll, so creatine is the product of the union of cyanamide with methyl- glycocoll, a compound usually called sarcosine, and the reac- tions below, which show that sarcosine is really methyl-glyco- coll, complete the evidence. 1st. Synthesis of glycocoll. Ho-( ry7 2 0)- C 1 + &ff 3 = Ho-( C,ff 2 0)-N=ff 2 + HCl. [577] Chloracetic Acid. Glycocoll. L J 550 CAFFEINE AND THEOBROMINE. [492. 2d. Synthesis of sarcosine. Ho-(C 2 ff 2 0)~Cl + Ji( CH 9 )& = Methylamine. Ho-( GA 0)-N-( GH,\H -f HOI. [578] 491. Caffeine and Theobromine. These well-known or- ganic bases which are regarded as the active agents in tea and coffee on the one hand, and in the cacao-bean on the other, are closely allied to the class of compounds we have been studying. They are probably the methyl substitution products of a sim- pler amide not yet discovered. That caffeine is methyl-theo- bromine there is no doubt, for theobromine can be converted into caffeine by a simple process of substitution. It is also probable that theobromine itself contains methyl, for when caffeine is oxidized by chlorine and water it yields well-known dimethyl products. Moreover, these products are the methyl- ated forms of two well-known uric acid derivatives, viz. allo- xanthine and paraban, indicating that caffeine and theobromine are allied to the diureides. Now it appears from their empiri- cal symbols that theobromine differs from xanthine by just (<7# 2 ) 2 , thus: Xanthine. Theobromine. Caffeine. But theobromine can not be simply dimethyl-xanthine, for this last compound has been made, and although isomeric with theo- bromine is not the same substance. When caffeine is treated with baric hydrate there is formed during the first stage of the process a new base called caffeidine, but this is subsequently decomposed, and the ultimate products of the reaction are, be- sides carbonic dioxide and ammonia, formic acid, methylamine, and sarcosine. Creatine similarly treated yields, besides car- bonic dioxide and ammonia, only sarcosine, and these reactions indicate that the unknown amide, of which caffeine is a methyl- ated substitution product, is allied to creatine, probably con- taining like this the glycol radical. 492. Vegetable Alkaloids. The active principles of many medicinal or poisonous plants are cry stall izable bodies, which closely resemble in their general properties and chemical re- lations the complex amines or basic amides we have been study- ing. Several of them, like quinine and morphine, are well- known articles of the materia medica, and are perhaps the 492.] VEGETABLE ALKALOIDS. 551 most valuable medicinal agents which we possess. As a gen- eral rule they are soluble in water, have a strong, bitter taste, and form well-marked crystalline salts with acids. Hence the name of vegetable alkaloids. The number of these bodies now known is exceedingly large. The dried juice of the poppy, which we call opium, alone contains not less than eight distinct bases. Two of the alkaloids, conine and nicotine, from the hemlock and tobacco plant respectively, are volatile oily liquids, and they do not contain oxygen. The great body, however, of the alkaloids are oxygenated compounds, and can- not be distilled without decomposition. These two classes of alkaloids correspond to the volatile amines on the one hand, and the non-volatile ammonium bases on the other ; but no safe conclusion in regard to their constitution can be drawn from this seeming analogy, for not only are the facts we have been studying sufficient to show that the class of amines or alkaline amides includes many non-volatile oxygenated bases, but all the natural alkaloids combine directly with acids in forming salts. Moreover, in several cases we are able to substitute hydrocarbon radicals for one or more of the hydrogen atoms of the alkaloid, and obtain bodies which, like the ammonium bases, eliminate water when they combine with acids. Among the most important of the vegetable alkaloids may be mentioned morphine, narcotine, and codeine from opium; quinine and cinchonine from cinchona bark ; strychnine and brucine from nux-vomica and other strychnos plants ; aconi- tine from the monkshood ; atropine from belladonna and stra- monium ; veratrine from the white hellebore. All these sub- stances have been carefully studied, and their general properties and chemical relations are accurately known. Their empirical formulae show that with few exceptions they must be very complex bodies, but beyond this very little has been made out in regard to their chemical constitution. In several cases the number of replaceable atoms of hydrogen have been deter- mined, and in others the natural alkaloid has been proved to be a methylated substitution product of a simpler base, but in no case has the molecular structure been fully developed. The great difficulty encountered in investigating the constitution of these bodies arises from the fact that we know of no reagent by which we can replace nitrogen by monad radicals, and thus 552 AMINE-AMIDES, OR ALKAMIDES. [493. break up the alkaloid into the several atomic groups of which it consists, without decomposing the radicals also. The student should study in this connection the important investigation of Matthiessen l on morphine and codeine, and that of Schiff 2 on conine, the first alkaloid which has been produced synthetically. 493. Amine-Amides, or Alkamides. It must have been noticed that with the complex compounds we have been re- cently studying, the clear distinction between amines and amides previously drawn (167, 168) is almost wholly obscured. The effect of introducing several radicals, both acid and basic, into the same ammonia group, cannot be traced to any general principle. The resulting molecule has sometimes basic and sometimes acid relations. Hence it is that we have been obliged to class with the amides so many substances having well-marked alkaline properties, and for this reason many chemists distinguish a third class of compounds under the am- monia type, to which they give the name of arnine-amides or alkamides (alkaline amides). An alkamide is frequently de- fined as a compound of the ammonia type, in which the hydro- gen atoms are in part replaced by basic and in part by acid radicals; but we prefer to give to the term the simple meaning which the derivation indicates, for urea, which contains only an acid radical, is one of the best-defined bodies of the cla^s, at least if we accept the view of its constitution usually taken. The distinction has not been before made in this book, because the study of the alkamides cannot well be separated from that of the true amides to which they are so closely related ; and since several of the more important of these compounds have already been described, further examples are unnecessary. 1 Proceedings of the Royal Society of London, XVII. 455 ; also, Ann. Chem. und Pharm., VII. Supplementband, 170. a Berichte der Deutschen chem., Gesellschaft, Jahrgang, HI. 946. 494.] ALCOHOLS AND THEIR DERIVATIVES. 553 Alcohols and their Derivatives. 494. Chlorals. The white solid which is the ultimate re- sult of the action of chlorine gas on absolute alcohol is a com- pound of alcohol with one of its chlorinated derivates called chloral. When the crude product of this reaction is treated with strong sulphuric acid the chloral separates out, and may be decanted and purified by repeated distillation over lime. It is a thin colorless oil, having a pungent odor and astringent taste, boiling at 986, with Sp. Gr. 1.49 and Sp. Gr. = 74.04. It readily dissolves in water, yielding a neutral solution which does riot precipitate nitrate of silver, but in so dissolving it enters into combination, and if the amount of water is small the union is attended with a marked elevation of temperature. If the amount taken is about one eighth of the weight of the chloral the whole mass solidifies, and the white translucent solid thus formed is the familiar preparation which is now so highly valued as an anesthetic agent. Chloral Hydrate has a strong, pungent, ethereal odor, volatilizes gradually in the air, and dis- tils without decomposition when heated. It melts at 50 to 51, boils at 97 to 99, has Sp. Gr. = 1.61 and Sp. Gr. = 39.84, showing that chloral and water are disassociated at 100. This substance was discovered by Liebig in 1832, but it is only re- cently that its valuable medicinal qualities have been appreci- ated or its chemical relations fully understood. Chloral is a chlor-aldehyde, and has the same structure as acetic aldehyde, but contains Cl$ in place of the fl 3 in the methyl radical. CfffCO-ff CClfCOIL Acetic Aldehyde. Acetic Chloral. Its constitution is shown by the following reactions : 1st. Acetic aldehyde when acted on by chlorine gas, under regu- lated conditions, is converted into chloral. 2d. Chloral when acted on by nascent hydrogen chapges back to aldehyde. 3d. Chloral combines with NH& forming a compound correspond- ing to aldehyde ammonia. 4th. Oxidizing agents convert chlo- ral into chloracetic acid (31) and [479]. When chloral or its hydrate is treated with a solution of a caustic alkali it yields chloroform, together with a formiate 24 554 CHLORALS. [ 494. of the alkaline metal, and the value of the hydrate as an anesthetic agent seems to depend on the fact that a similar re- action takes place in the blood. (OOl s )-OOH+(K-OyH=K-0-(00-ff) + CClfff. [579] Chloral. Potassic Formate. Chloroform. When chloral is heated with nitric acid there is formed, be- sides chloracetic acid, which is the direct product of the oxida- tion due to this reagent, also a small amount of a substance called chlorpicrin. The last is the product of a metathesis be- tween the radicals of the acid and the chloral, thus : (OO1 3 )-00-H + (ff-O)-NO, = choral. H-(>(CO : H) + CCls(N0 2 ). [580] Formic Acid. Chlorpicrin. It will be noticed that while in this reaction the radical OO1 3 changes place with HO, in the previous reaction it changed place with KO, and this fact is a most striking illustration of the theory of chemical polarity. Chlorpicrin is an oily liquid, usually obtained by the action of chlorine on picric acid, and may be regardad as chloroform in which the remaining hydro- gen atom has been replaced by N0 2 . Chloral combines not only with water and with ethylic al- cohol, but also with other alcohols of the same family, with urea, and with several amides. These products are generally regarded as molecular compounds, but it is more probable that they have the constitution represented in the scheme below : ( OH 3 - Off)- ( O Clf Off)- 0. Acetic Aldehyde. Chloral. Chloral Hydrate. (OOl 3 -OH)-Eto,Ho. Chloral Hydro-ethylate. ( Cff 3 - Off)-Mo 2 ( COlf OH )=Eto 2 . Acetal. Chloral Diethylate. As here represented, the Compounds, with water and alcohol, are intermediate terms between chloral and another substitution product, which bears the same relation to acetal l that chloral 1 Acetal is a well-known product of the oxidation of ethvlic alcohol. It contains the radical ethylidene, and differs both in Sp. Gr. and boiling-point from an isomeric compound containing ethylene, which has also been isolated. 495.] MELLITIC ACID. 555 bears to acetic aldehyde. These formulae are supported by the fact that, while aldehyde chloral and chloral hydrate are all converted by PO1 5 into ethylidene chloride (31) (464), the compound of chloral with alcohol yields, under the same condi- tions, a substance represented by the symbol ( OC1 3 - CH)=Eto^ Cl, and not the normal products of the action of PC1 5 on chloral and alcohol separately, as we should expect if they were pres- ent as such in the compound in question. It has been stated above that acetic chloral may be formed from acetic aldehyde by the direct action of chlorine gas un- der regulated conditions. It is simply necessary that there should be present with the aldehyde lumps of marble to absorb the HCl, which is formed by the reaction ; for HGl converts acetic aldehyde into crotonic aldehyde, and this product is then, the only point of attack for the chlorine gas. Thus it is that when chlorine acts on acetic aldehyde without any check, the final product is not acetic chloral, but a new chloral derived from crotonic aldehyde (453). ( Off,- V& Off- CO)-H ( C01 3 - Off= Cff- 00)- ff. Crotonic Aldehyde. Crotonic Chloral. Crotonic chloral resembles outwardly acetic chloral, and forms a similar compound with water. It is the only other chloral which has thus far been isolated ; but an insoluble iso- meric modification of common chloral is known whose relations are not yet understood. 495. Mellitic Acid. This compound has long been known as a constituent of the mineral mellite or honeystone, which is mellitate of aluminum, \_Al^\O 6 0^ . $ff 2 0, and is found in reddish-yellow octahedral crystals in the brown coal at several localities ; but it is only recently that its remarkable chemical relations have been discovered. It has been shown by Bayer that this acid is hexabasic and belongs to the phenyl group. It may be regarded as derived from benzol, C 6 ff G , by replacing all the six atoms of hydrogen with oxatyl. Benzoic acid, it will be remembered, is benzol with one of the hydrogen atoms replaced by oxatyl, and Bayer has not only been able to iden- tify three of the four intermediate acids which are theoretically possible, but he has also shown that each of the three is capa- ble of two isomeric modifications. Thus we have : 556 MELLITIC ACID. [ 495. Normal Series. Benzol. Benzole Acid. Terephthalic Acid. Trimellitic Acid. Pyromellitic Acid. Isomsric Series. Isophthalic Acid. Trimesic Acid. Prehnitic Acid. 2d Isomeric Series. Phthalic Acid. Hemimellitic Acid. Mellophanic Acid. C 6 H 3 =( CO-Ho~) y C 6 H a =C C0-Ho\. Mellitic Acid. C 6 vi The isomeric modifications probably result from a variation of the order in which the hydrogen and oxatyl atoms are attached to the carbon atoms of the primary nucleus (428, Fig. c.) and (456). One of the compounds included in the above scheme has certain other remarkable chemical relations which point with great certainty to its molecular constitution. Phthalic acid is not only a derivation of benzol, but also of naphthaline; for this well-known hydrocarbon (434), when heated with strong oxidizing agents, yields a mixture of phthalic and oxalic acids. Assuming it proved that phthalic acid has the benzol nucleus, the best theory we can form in regard to this reaction gives to the molecule of naphthaline the singular constitution represented below ; and it can be seen by comparing the three graphic symbols placed side by side that the reaction is thus fully explained. H H H H <>, H\G ^ A .H A A .H C N tf \ C G CO C ,C / C <7 A$* p' *Q H / c' % o * ^ H * C ' ^ G' H H H H H Oxalic Acid. Naphthaline. Jf Phthalic Acid. If this theory is correct, it follows that in phthalic acid the two oxatyl groups are united to adjacent carbon atoms of the nucleus, and that its constitution is so far determined. Again, it will be noticed that these adjacent carbon atoms are united by a double bond, and that in the closed chain, of which they are a part, the links are joined by double and single bonds al- ternating. Now it is evident that if either of these double bonds could be exchanged for a single one, the nucleus would 4i)j.] MELLITIG ACID. 557 be able to attach to itself two additional hydrogen atoms, six in all, and that if, besides, we could break the chain between the two adjacent atoms above referred to, the nucleus could hold yet two more, and we should then have suberic acid (470). Now all these transformations appear to be possible, for we have been able to prepare the following series of bodies : Phthalic Acid, O 6 fff( COffo) 2 . Hydro-phthalic Acid, C 6 Hf( COffo) 2 . Tetrahydro-phthalic Acid, C^H^GO-So) f Hexahydro-phthalic Acid, C<&H IQ =( C0-Ho) 2 . Suberic Acid, O 6 ff 12 =( GOHu) 2 . We are also acquainted with still another derivative of benzol called tartro-phthalic acid, which differs from hexahydro-phtha- lic acid only in that there is associated with each oxatyl group, and attached to the same carbon atom, HO in place of H. Tartro, hexahydro, and tetrahydro-phthalic acids are related by a peculiar kind of homology to tartaric succinic and maleic acids respectively, which will be evident on bringing together their graphic symbols. The theory that in all these acids ex- cept suberic the two oxatyl groups are joined to adjacent car- bon atoms is sustained by other considerations than the one we have given here, but for these we must refer the student to the original memoirs. The graphic symbol of naphthaline being so symmetrical, it would seem impossible to determine on which side the division of the nucleus takes place in the reaction represented above j but there are conditions in which even this can be traced. We have written below the symbol of naphthaline so as to indicate in a measure its bilateral structure, and on the same line we have given the symbols of two of its well-marked substitution products, which are very numerous : Naphthaline. Dichlordioxynaphthaliue. Pentachlornaphthaline. Now the first of these derivatives when oxidized gives phthalic acid like naphthaline itself, while under the same conditions the second gives tetrachlorphthalic acid. Evidently, then, in the first case the substitution is confined to one side of the naphtha- line molecule, and the division which accompanies the oxida- tion takes place on the same side ; while in the second case not 558 MELLITIC ACID. [495. only all the hydrogen atoms on one side are replaced, but also one on the other, and the division takes place on the side of the single chlorine atom ; for were the nucleus divided on the other side we should have not tetrachlorphthalic but monochlorphthalic acid. These reactions, moreover, furnish very strong evidence in favor of the theory of the structure of the naphthaline mole- cule stated above. Since, as we obtain a body having the structure of phthalic acid on whichever side we divide the molecule, it is evident that the two sides must have the same structure, so that if we are not mistaken in regard to the struc- ture of phthalic acid there can remain but little doubt in regard to that of naphthaline. Now phthalic acid, when heated with an excess of lime, yields benzol, and benzol, when oxi- dized under certain conditions, yields benzbic and phthalic acid, reactions which may be almost said to prove that this acid contains the benzol or phenyl nucleus. The simple rela- tions of phthalic to benzoic acid are evident. If, with Kekule, we number the carbon atoms of the phenyl nucleus from 1 to 6, and assume that in phthalic acid the two oxatyl radicals are united to the first and second atoms of the nucleus, then it is evident that, without altering the general structure, two modifications of it may be obtained by changing the position of the oxatyl radical, which can also be attached either to the first and third or to the first and fourth atoms of the closed chain. Now there is good reason for believing that such is the position of the radicals in isophthalic and tere- phthalic acids respectively, but for the evidence we must refer to the original papers. 1 1 Ann. Chem. und Pharm., VII. Supplementband, 1; also CXLIX. 27; also Jour. Chem. Soc. of London, Vol. IX. 372. 496.] QUINONE. 559 Quinone Group. 496. Quinone. The artificial production of alizarine, the coloring principle of madder, is not only one of the most re- markable achievements of modern chemistry, but is also a direct corroboration of the validity of the mode of reasoning which the new philosophy of the science has introduced. Ali- zarine was actually constructed by following out the indications of a theory of its molecular structure, to which a study of its reactions and those of allied compounds had led. In order to make clear the course of the investigation we must go back to the discovery of quinone in 1838. This body was obtained by the oxidation of quinic acid, a vegetable acid found in cin- chona bark, where it is combined with cinchonine and quinine. Quinone is a volatile solid, crystallizing by sublimation in shining yellow needles, which have the composition indicated by the empirical symbol C^H^O^ When heated with a mix- ture of hydrochloric acid and potassic chlorate it is rapidly converted into tetrachlorquinone, C Q Gl^O^ a compound which is identical with chloranil, a product of the action of the same agents on carbolic acid, aniline, and other well-known bodies of the phenyl group. But although these reactions indicated a close relationship with the class of compounds formed around the carbon nucleus, represented in Fig. c., page 457, the first satisfactory theory in regard to the molecular structure of quinone was that advanced by Graebe in 1868. 1 He concluded, as the result of a very extended investigation of the whole class of allied compounds, first, that the molecule of quinone contains the phenyl nucleus ; secondly, that the two atoms of oxygen in this molecule are united together by a common bond, thus forming a dyad radi- , cal which aids in binding together two adja- ,, O s cent carbon atoms of the phenyl nucleus, thus : H-C C~0 so that, according to his view, quinone may jj-Q be regarded as derived from benzol by re- * C placing two neighboring hydrogen atoms in its molecules by the radical =[ 2 ] H 1 Untersuchungen iiber die Chinongruppe, Ann. der Chem. und Pharm., CXLVI. 5GO QUINONE. [ 496. The above conclusions are based chiefly on the following facts. In support of the first we have a large number of re- actions besides those mentioned above, whose concurrent testi- mony leaves no doubt that the benzol and the quinone group of compounds are formed around the same carbon nucleus, so that if we accept Kekule's 1 theory in regard to the first, we must extend it also to the last. In support of the second, we have the fact that when by reactions, which are well under- stood, the oxygen of the quinone molecule is replaced by hy- droxyl or chlorine, the two atoms are exchanged for only two atoms of 'these monad radicals, and not for four, as would be the case if the oxygen atoms were united to the carbon nucleus by all four of their bonds. Thus, when quinone is acted on by hydriodic acid it yields hydroquinone, whose symbol is O 6 fffffo 2 , and oxidizing agents change this body back to qui- none. Again, when tetrachlorquinone, C$C1 4 2 , is acted on by phosphoric chloride the products are C 6 C1 6 and free chlorine gas. It is impossible, however, in a few words, to do justice to the arguments which Graebe advances in support of his theory, which will be found clearly stated in the paper already re- ferred to. In studying the derivatives of quinone Graebe recognized certain general characteristics, which he attributed to their supposed molecular structure. Of these, the most striking, after the two just illustrated, is the fact that two of the monad atoms, H or Cl, associated with the oxygen radical, =[ 2 ], in the molecular group may be readily replaced by Ho, H^N, or JFTSO& the product being an acid, an amide, or a sulpho-acid. This well-marked character of the quinone group of compounds Graebe attributes to the influence of the atomic group [<7 2 2 ] on the rest of the molecule, which, as he supposes, throws the neighboring atoms into a polar condition, similar to that pro- duced by CO in the organic acids and aldehydes. The three characteristics of the quinone group we have signalized are better illustrated by the chlorine derivatives of quinone than by quinone itself. Take, for example, tetrachlorquinone or 1 Kekul6 originated the theory in regard to the molecular structure of the radical phenyl which has been presented in this book. For the evidence on. which it is based we must refer to Kekule"'s well-known work on Organic Chemistry, as it is too extended to be given here ; also, Ann. Chem. und Pharm., CXXXVII. 129. 497.] NAPHTHO-QUINONE. 561 chloranil, mentioned above, which has the following chemical relations : 1. Reducing agents readily convert chloranil into tetrachlor- hydroquinone, C 6 ClfHo 2 , a compound which oxidizing agents as readily change back to chloranil, and whose atoms of hydro- gen may be replaced by metals or organic radicals, giving such bodies as C 6 OlfKo^ C^ClfEto^ O 6 Cl 4 =Aco 2 . 2. When acted on by phosphoric chloride, chloranil yields O & C1 6 and free chlorine, as stated above. 3. If chloranil is dissolved in a solution of potassic hydrate, a metathesis takes place between C1 2 in the first and Ko 2 in the last, in conformity with the third characteristic we have de- scribed, and if the proportions are rightly regulated there crys- tallize out from the solution red needles of potassic chloranil- ate, Kof C 6 (7/ 2 =[ 2 ]. From a solution of this salt hydrochloric or sulphuric acids precipitate chloranilic acid, /& 2 = (7 6 (74 = [ 2 ] in similarly colored crystals. Trichlorquinone, C & CI S H0. 2 , yields also similar derivatives, which for the most part contain C 6 Cl B H'm place of (7 6 07 4 , but when treated with potassic hydrate it yields chloranilic acid, the same product which is obtained from tetrachlorquinone, showing that the single remaining hydrogen atom is one of the two replaced in the reaction. 497. Naphtho-quinone. Graebe's next step, in the course of investigation we are following, was to recognize in the com- pound we have called dichlordioxynaphthaline (495) a body having the same general structure as quinone. In a paper published in 1869, 1 he showed that this body, which he calls dichlornaphtho-quinone, 2 has the same general characteristics as tetra- or tri-chlorquinone. Thus it appears, 1st. That dichlornaphtho-quinone, when acted on by reducing agents, yields dichlorhydronaphtho-quinone, Moreover, in this compound, as in tetrachlorhydro-quinone, ffo 2 may be replaced by Aco z . 2d. That dichlornaphtho-quinone yields with phosphoric chlo- ride the compound C w ff s Cl s , by which it is evident that, as in 1 Ann. der Chem. und Pharm., CXLIX. 2 The German name for quinone is chinon, ano\ the names of the different quinone derivatives are formed from this root. 24* jj 562 ANTHRAQUINONE AND ALIZAEINE. [498. the case of tetrachlorquinone, the group [ 2 ] is replaced by (7/ 2 , although at the same time a further replacement of the hydrogen atoms of the original naphthaline molecule is effected so that no free chlorine is evolved. 3d. That when dichlornaphtho-quinone is dissolved in a solu- tion of potassic hydrate there are formed cherry-red needles of the potassic salt, of an acid corresponding to chloranilic acid, and from this salt, by the action of hydrochloric acid, the acid itself is readily obtained, as a yellow precipitate having the composition expressed by the symbol Ho-C^H^Cl^O^]. It will be noticed that in the reactions by which the so-called chloroxynaphthalic acid is formed only one atom of chlorine is replaced by hydroxyl, and not two, as in the case of chloranilic acid. The acid is a coloring matter, dyeing wool a scarlet or orange color, but has no affinity for alumina mordants. The above facts certainly justified the theory of Graebe in regard to the constitution of these derivatives of naphtha- line, and since his paper was published naphthoquinone itself, (7 10 ^ = [0 2 ], has been obtained. Thus the word "quinone" has become the name of a class of compounds, and indicates the peculiar molecular structure we have described. Dichlornaphtho-quinone and chloroxynaphthalic acid were discovered by Laurent, 1836-40, and the great similarity, as indicated by ultimate analysis, between the last and alizarine was noticed soon after. Indeed, chloroxynaphthalic acid was for some time regarded as chlorinated alizarine, and this opin- ion was apparently confirmed by the fact that both these sub- stances yield phthalic acid by decomposition with nitric acid. But about six years since Martius and Griess succeeded in replacing the single atom of chlorine in chloroxynaphthalic acid with hydrogen, and a coloring matter was obtained having the formula C 10 # 6 3 , which is identical with that assigned to alizarine by Strecker. This body, however, did not prove to be alizarine, although it was supposed at the time to be iso- meric with it. 498. Anthraquinone and Alizarine. Graebe, now associ- ated with Liebermann, beginning the investigation of alizarine at the point we left it in the last section, naturally inferred, from the resemblance to chloroxynaphthalic acid, that the col- oring matter of madder might be a similar acid, though derived 498.] ANTHRAQUINONE AND ALIZARINE. 563 from a different quinone, and, in order to obtain some clew to the hydrocarbon to which it is related, these chemists fc sought as a first step to reduce natural alizarine by heating it with powdered zinc, adopting a method first suggested by Bayer for reducing similar compounds. The result was a solid body, which was soon recognized as identical with anthracene, a hy- drocarbon (Cnff lo ) associated with naphthaline in coal-tar, and it was of course at once inferred that alizarine was the quinone acid of this well-known hydrocarbon, thus : O l4 ff w O l4 ff 8 2 ffofC^O,-]. Anthracene. Anthraquinone. Anthraquinonic Acid or Alizarine. The formula of alizarine thus deduced, although differing from that of Strecker, agreed with that of Schunk, who had made a most extended investigation of the constituents of madder. Before, however, this theory of the constitution of alizarine could be established, it was essential to reverse the process of reduction and produce alizarine from anthracene, and the first step was to obtain the anthraquinone. Here again Graebe was aided by the previous investigations of Laurent, who long before had obtained an oxygenated derivative of anthracene, which he called, in accordance with a peculiar nomenclature of his own, anthracenuse. The substance had been re-examined by Ander- son, who gave it the symbol C U H^O^ and in it Graebe and Lie- bermann at once recognized the required quinone. It only now remained to replace two atoms of the hydrogen in this body by hydroxyl, in order to settle the question whether aliza- rine is the quinone acid of anthracene or not. The method was obvious. Anthraquiuone was heated with bromine, which, replacing two of its hydrogen atoms, yielded the compound <7 14 /^flr 2 =[0 2 ], and this heated to 180 with a solution of po- tassic hydrate gave an intense blue solution, from which hydro- chloric acid precipitated a yellow crystalline powder identical in every respect with the alizarine obtained from madder. This was the first instance of the artificial production of a vegetable coloring matter, and we have dwelt at more length than usual on the history of this beautiful discovery, because it affords an admirable illustration of the methods of modern chemistry. 1 Before the discovery could be applied in the arts 1 In preparing this section we have been aided by an interesting paper of W. H. Perkins (Journal of Chem. Soc. of London, for 1870, page 133), in which specimens of prints made with artificial alizarine are given. 564 CONSTITUTION OF ANTHRACENE. [500. it was of course essential that the synthetical process should be modified so as to adapt it to a manufacturing scale, and this has been in a great measure accomplished by substituting for bromine sulphuric acid, which when heated with anthraquinone converts it into a sulpho acid, (HSO Z )^C U H^\_0^ and this, like the corresponding bromine compound, yields alizarine when heated with potassic hydrate. 499. Purpurine. There is associated with alizarine in madder a second coloring material called purpurine, but as it is not absorbed by mordanted calicoes it has little commercial value. Like alizarine, it is reduced to anthracene by zinc powder, and the result of its ultimate analysis agrees very well with the symbol HofC u H 5 =[0.>~]. but we have no further proof -of its correctness. A third coloring principle has also been distinguished, called pseudopurpurine, whose analysis gave results corresponding to the symbol Ho^C u Hf\_0^\. It is probable that all three of these coloring materials occur in the madder-root as glucosides. 500. Constitution of Anthracene. We have now distin- guished three quinones, viz. benzoquinone, naphthoquinone, and anthraquinone. Graebe and Liebermann have shown in their recent paper 1 that the last has the chief characteristics we have distinguished in the other two, and that it gives simi- lar derivatives. It only remains to add a few works in regard to its molecular constitution. In the paper just referred to Graebe and Liebermann advance the theory that the anthracene molecule has a structure which may be represented thus : HG EG V ffO HO C C <> / * N HO G HG HG. HG HG Anthracene. and hence that anthracene bears the same relation to naphtha- line that naphthaline bears to benzol (428) and (495). This theory is not only rendered probable by the similar chemical relations of those three hydrocarbons which we have been l Ann. der Chem. und Pharm., VII. Supplementband, 1870, 312. 500.] CONSTITUTION OF ANTHRACENE. 565 studying, but it also furnishes a satisfactory explanation of two synthetical processes by which anthracene has been produced. 1. When benzylchloride, C G ff 5 - Cff 2 - Ol, is heated with water in a closed tube to 180, anthracene is one of the chief pro- ducts. If we suppose that the production of the hydrocarbon results from the coalescing of two molecules of the chloride, the reaction may be indicated thus : HC HO-H.GI HO* ' '? HC^ HO "HO' This synthesis was observed by Berthelot, who also obtained anthracene under similar conditions from toluol and also from a mixture of benzol and ethylene. Both processes admit pf a similar simple explanation based on the above formula. In the last case the chief product is styrol, which probably pre- cedes the formation of anthracene. The three hydrocarbons, benzol, naphthaline, and anthra- cene, form a well-defined series, whose successive members differ from each other, not, as in the alcohol family, by CH% but 566 CHRYSENE AND PYKENE. [501. by C 4 ff 2 , and to this corresponds a difference of about 140 in the boiling-points. 6 ff 6 Diff. C in ff a Diff. O u ff 1Q . B. P. 80 136 216 144 360 Apart from similar differences which the gradations in the series necessarily determine, these bodies strikingly resemble each other both in their physical and chemical qualities. The last point has been illustrated in this chapter so far as regards the formation of the quinone derivatives, and the impression produced by the facts here presented would be strengthened by a further study of the subject. All this of course indicates a similarity in the molecular structure of these bodies, and the cumulative evidence in favor of the theory here adopted is therefore much greater than that which can be obtained in re- gard to either of the substances separately. 501. Ghrysene and Pyrene. Since the identification of anthraquinone it has been discovered that two other hydrocar- bons associated with naphthaline and anthracene, among the least volatile of the products of the distillation of coal-tar, were capable of yielding derivatives belonging to the class of quinones. The names chrysene and pyrene were given by Laurent to impure products, and it is only very recently that these bodies have been isolated and their composition accu- rately determined. 1 Chrysene, C 18 ff 12 , makes evidently the fourth term of the naphthaline series, differing from anthracene by C 4 ff 2 , and its molecule may be CH-CH regarded as formed from that of * anthracene by the addition of x , another phenyl nucleus, thus: f C= O^ Pyrene, O 16 ff m although not be- C&0 OCff longing to the same series, appears QJJ * C- Q* V^ to be similarly constituted, and * ' W/ may be regarded as phenylene- naphthaline ( C lQ H 6 y( C 6 ff 4 ). Chryso-quinone, C W H 1 J[0 2 '], has the chief characteristics of a true quinone, but in pyrene-qui- none, (7 16 Z^[ 2 ], the characters are less strongly marked. 1 Graebe und Liebermann, Ann. Chem. und Pharm., CLVIIL, 285 and 299. June, 1871. 502.] ELECTRICAL RELATIONS OF THE ATOMS. 567 Electrical Measurements. 502. Fundamental Laws. The following formulae express the most important properties of electrical currents : (1.) G=F. (2-) tf=- (3-)Q = Ct. (4.) W *=&&.(&.) W=QE. The first defines strength of current as a magnitude propor- tional to the force which it exerts on a magnetic pole under constant conditions. These conditions are the strength of pole, w, the length' of the conductor, L, assumed, as in the com- mon form of galvanometer, to be bent in a circle around the pole, and the radius of this circle, K. The unit of force is that force which imparts to one gramme of matter the velocity of one metre in one second, and the unit pole that pole which at a distance of one metre repels a similar and equal pole with the unit force. The second is Ohm's formula (88), and expresses the prin- ciple, which can be readily demonstrated experimentally, that the strength of current, as defined by (l),is directly propor- tional to the electromotive force of the given circuit, and in- versely proportional to the resistance of the circuit. It also involves the still further truth that in different parts of the same circuit, where the strength of current is necessarily the same (88), the difference of tension or potential l between any two points is always proportional to the resistance between these points. The third expresses a truth first verified experimentally by 1 The influence of the electromotive force extends throughout the circuit, causing at every cross section of the conductor what we may call an electrical pressure, which regulates the flow of the electrical current. This pressure is greatest at the surface of the active plate where the power originates, and diminishes as we proceed round the circuit in either direction. At some intermediate section where Jhe opposite currents neutralize each other the pressure is zero, and as we move back from this neutral point against the neg- ative current we encounter an ever-increasing "negative " pressure, while in the opposite direction we meet an ever-ir creasing "positive" pressure. What we here call electrical pressure is called above tension or potential, and without attempting to give a theoretical conception of its nature, it is suffi- cient to say that it is a force measured at any point of the circuit by the ten- dency of the current to leave the conductor. Ohm's formula holds not only for the whole circuit, but also for any part of it ; but in such cases E stands, not for the whole electromotive force, but for the difference of tension between the two ends of the portion under consideration. 568 ELECTRICAL RELATIONS OF THE ATOMS. [ 504. Faraday, that the quantity of electricity which passes any point of a circuit, as measured by the amount of electrolysis, is proportional to the strength of the current and the time dur- ing which it flows. The fourth expresses an important law, first demonstrated experimentally by Joule, that the work done by a current (e. g. the quantity of heat generated) is proportional to the square of the current, to the time during which it acts, and to the resistance which it encounters. It should be remembered in this connection that the unit of force acting through one metre does the unit of work ; that the force of gravity acting on one gramme of matter through one metre does 9.8 units of work, equal to one metre-gramme, and that the unit of heat (12) is equivalent to 4157.25 units of work or 423.8 metre- grammes. The fifth is involved in the previous three, from which it is readily deduced, and expresses the fact that the work done in any portion of the circuit is proportional to the quantity of electricity which passes over it and to the difference of ten- sion between the two ends. 503. Kirchhoff's Laws. The following propositions may be deduced from the general theory of electrical currents : 1. The sum of the currents which approach any point is al- ways equal to those which recede from it. Or, if we distinguish the first by a plus and the second by a negative sign, we may say more generally : The sum of all the currents which meet at a point is equal to zero. 2. On any continuous line of conductors the sum of the pro- ducts of the resistances of the several parts by the strength of the current in each part is equal to the sum of the electromotive forces included in the same closed circuit. The last proposition holds true of every circuit which may be traced in any system of conductors and batteries, however complicated the maze ; only currents flowing in opposite direc- tions, with reference to the given circuit, must be distinguished by opposite signs. Moreover, the sum is equal to zero when there is no electromotive force on the line of conductors under consideration. 504. Electrical Units. In the following problems the val- 503.] ELECTRICAL RELATIONS OF THE ATOMS. 569 ties (7, R, or r and E of Ohm's formula are assumed to be measured in terms of the following units : First, the unit of current is that which would produce, by the electrolysis of wa- ter, 1 c. m. 8 of hydrogen and oxygen gas (measured under standard conditions) in one minute. Secondly, the unit of re- sistance is that offered by a pure silver or copper wire 1 m. long, and 1 m. m. in diameter at 0. Lastly, the unit of elec- tromotive force is that which transmits a unit current against a unit resistance in a unit of time. By means of the magnetic and thermal relations given by (1) and (4) above, it is possible to express the values of the three elements of an electrical current in terms of the funda- mental units of space, weight and time, the metre, the gramme, and the second. The following formulae in which L = length, M mass or weight, and T '= time, are easily deduced, in- volving only simple mechanical principles : Velocity = y=^. MV ML Force = F= -^- = -^ Work = W= FL = ^. Work in metre-grammes = --. r-r. J. 9*o Strength of pole * = m = . Strength of current 2 = C= T . Quantity of electricity = Q = CT = W Electro-motive force = E = -~- = Resistance = # = ?=:= K The values of C, R, and E, when the several factors in Jjie for- mulae expressing their values are each taken equal to unity, are called the electromagnetic units. Thus the unit of resist- 1 This value is readily obtained by considering that the force exerted between the two poles must be F = ^ or = ^, when the two poles are equal. Hence, m D V F. 2 Readily derived from value of C, (1). 570 ELECTRICAL RELATIONS OF THE ATOMS. [504. ance is a velocity of one metre a second. 1 These absolute units, however, are of an order of magnitude which is unsuit- able for ordinary measurements, but the following very small multiples or submultiples may be used to advantage : For R the Ohm equal to 107 absolute units of resistance. " " " Megohm '* '* lO 1 ^ " " " " " " Microhm " " 10 " " " " E " Volt " " 105 electromotive force. " " Megavolt " " 1QU " " " " " " Microvolt " " 10-1 u u " C " Farad " " 10- " " " quantity per second. " " " Megafarad " " 10~^ " " " " " " " " Microfarad " " 10-" " " " " The unit current is a current of one Farad a second. A pure copper or silver wire 1 m. m. in diameter and 48.61 metres long has a resistance of one Ohm at 65 F., and the Committee of the British Association on Electrical Standards have carefully constructed a standard Ohm of which copies are readily accessible. Further, we have a closely approximate standard of electromotive force in the Daniell's cell, which, ac- cording to Sir W. Thompson, is equal to 1.079 Volts, or 1 Volt = 0.9268 of force of Daniell's cell. One Volt equals about 500.6 of the old units, and a current of one Megafarad per second will yield during one minute by the electrolysis of water 10.3 c. m. 8 of gas very nearly. The admirable instruments now constructed for the purpose enable us to use the B. A. units, as they are called, with great facility, but in solving the following problems the older system will be found more convenient. The student, however, should familiarize himself with both ; but he should bear in mind that values in Ohm's Volts and Farads must be reduced to absolute units before they can be substituted for <7, 7?, or E in Ohm's formula. Questions and Problems. 1. What resistance does the current suffer in an iron wire 50 me- tres long and 5 m. m. diameter? Sp. R. of iron 7. + Ans. 14 units. 2. Assuming that the Sp. R. of copper is 1.3 and that of iron 7, what must be the diameter of an iron wire which will oppose no greater resistance to the current than a copper wire of 2 m. m. diam- eter? Ans. 4.64 m. m. 1 For the interpretation of this remarkable analytical result see pamphlet by the author on Absolute System of Electrical Measurements. ELECTRICAL RELATIONS OF THE ATOMS. 571 3. It is found by experiment that a wire of German silver, 7.201 m. long and 1.5 m. m. diameter, opposes the same resistance to the current as a wire of pure silver 10 m. long and \ m. m. diameter. What is the Sp. R. of German silver. Ans. 12.5. 4. It is required to make with 132.8 grammes of pure silver, a wire which will offer a resistance of 81 units. What must be its length and diameter ? Sp. Gr. of silver = 10.57. Solution. Representing by x the length in metres, and by y the diameter in millimetres, we deduce by [1] tf x 10.57 = 132.8 and by the laws of conduction ^ = 81. Whence x = 36 m. and y =' | m. m. 5. What is the length and diameter of an iron wire weighing 97.38 grammes, which offers a resistance of 9,072 units ? It is known that the Sp. Gr. of theJron = 7.75 and its Sp. R. = 7. Ans. Length, 144 m. Diameter, m. m. 6. From a given wire there are four branches, of which the re- sistance is respectively 10, 20, 30, and 40. Required the total resistance when the current passes simultaneously through the four branches. Solution. The resistance in the first branch may be represented by a normal silver wire 10 m. long and 1 m. m. diameter. If we call the area of a transverse section of this wire s, then the resist- ance in the other three branches will be represented by normal wires of the same length, but having on the cross sections the areas s, ^s and ^s respectively. If next we conceive of these wires as merged in one, having the common length 10m. and an area on the section equal to (1 -f- \ -\- % -f- J) s, it is evident that such a wire will represent the resistance required. Hence we easily deduce, Ans. 4.8. 7. A closed circuit has two branches through which the current passes simultaneously. In one branch r = 100. What length of copper wire 5 m. m. diameter must be used for the other that the total r = 50 ? ; Ans. 2,500 metres. 8. A conductor has two branches, one having r = 756, the other so adjusted that when the current passes at the same time through, both, the total resistance equals 540. Required the length of a Ger- man silver wire \ m. m. diameter and Sp. R. = 12.5, which, when inserted in the adjusted branch, will increase the total resistance to 630. Solution. By principle of last problem we easily find that the resistance in the adjusted branch before insertion equals 1,890, and after insertion, 3,780. The difference between these values, 1,890-,. is the resistance due to the inserted wire. Hence its length must ba 37.8 metres. 572 ELECTRICAL RELATIONS OF THE ATOMS. 9. We have a battery of six Daniells cells, in each of which .#=475, JK = 15, and the external resistance against which the battery is to work, r = 10. The cells may be arranged, 1st, as six single elements ; 2d, as three double elements ; l 3d, as two three-fold elements ; 4th, as one six-fold element. Required the current strength in each case. Ans. 28.5, 43.8, 47.5 and 38.0 respectively. 10. We have a battery of twelve Grove cells, in each of which E = 830, and .R =18, to work against an external resistance of r = 24. Required the strength of current when the cells are ar- ranged, 1st, as twelve single ; 2d, as six two-fold ; 3d, as four three- fold ; 4th, as three four-fold ; 5th, as two six-fold, and 6th, as one twelve-fold element. Ans. 41.5, 63.8, 69.2, 66.4, 55.3, and 32.5 respectively. 11. With a single cell, where E and R have a constant value, what is the maximum strength of current^tnd under what condi- tions would it be obtained ? TTI Ans. -^, when the external resistance is nothing. 12. With n cells in each of which E and R have the same value, what is the maximum strength of current, and under what condi- tions would it be obtained ? rr Ans. n , when the cells are arranged as one n-fold element, and work against no external resistance. 13. With n cells as above, working against a given external resist- ance r, how should they be arranged so as to obtain the maximum value of C ? Ans. So as to make the internal resistance equal to that of the external circuit. Solution. If x represents the number of compound elements formed with the n cells when C in Ohm's formula is a maximum, we should evidently have under this condition x compound elements, each formed f - cells. The electromotive force of such an arrangement would be x E. The internal resistance would be xR -=~ R ' x n (compare problems 8 and 9), and the strength of the maximum current required, o= XE * By double elements is meant a group of two cells coupled for quantity (89) and equivalent to a large cell having plates of twice the size. Six double elements are six such groups arranged for intensity, and the other terms have a similar meaning. ELECTRICAL RELATIONS OF THE ATOMS. 573 The first differential coefficient of this function of x when C is a maximum must be equal to zero. Hence, or r=- * R. n That is, the strength of the current is at its maximum when the in- ternal equals the external resistance, as stated above. Those who are not familiar with the elementary principles of the differential calculus may satisfy themselves of the truth of this result by com- paring the answers obtained to problems 8 and 9. 14. We have, in the first place, for a single cell of a given combi- r nation working against a feeble resistance, the value C = p ; in the second place, for n cells of the same combination working against n times the resistance, the identical value C = J 1 . - . In n H -\- nr "strength" the two currents are equal, but are they identical? 15. In a given cell E = 475 ; R = 15. The current passes through 30 metres pure copper wire 2 m. m. diameter. It is re- quired to arrange 8 cells so that C may be the greatest possible. Ans. They should be arranged as two four-fold elements. 16. We have a battery of four Bunsen cells (E = 800, R = 4 each), coupled as four single elements. The circuit is closed through 500 grammes of pure copper wire. Required the greatest strength of current, and the dimensions of the wire that this maximum may be obtained. 17. A simple Voltaic cell, whose electromotive force E is known, working against an unknown total resistance R' (both external and internal), produces a given effect upon a galvanometer. Another cell differently constructed, working against- a total resistance R", also unknown, produces the same effect upon the galvanometer. It is also observed that a measured length I of normal copper wire, in- serted in the first circuit, produces on the galvanometer the same difference of effect as a length I' inserted in the second circuit. Required the electromotive force E' of the second cell. Solution. We easily deduce from Ohm's formula the two equations = and -- = f whence we obtain, Ans. E' = E. 574 ELECTRICAL RELATIONS OF THE ATOMS. 18. In order to determine the electromotive force of a Bunsen's cell, it was compared, as in last problem, with a Daniell's cell whose electromotive force was known to be 470. After adjusting the ex- ternal resistances so that both produced the same effect upon the galvanometer, it was found that the insertion of 5.6 m. of copper wire into the first circuit caused the same change in the instrument as the insertion of 3.29 metres of the same wire in the circuit of the Daniells cell. What was the electromotive force sought ? Ans. 800. 19. A battery of 40 Bunsen's cells remains closed for an hour, and during that time furnishes a current whose strength C = 30. How much zinc will be consumed in this time, assuming that there is no local action ? Solution. Such a current would produce, by the electrolysis of water, 30 c. m. 8 of gas in one minute, or 1.8 litres in one hour. Of this gas 1.2 litres or 1.2 criths would be hydrogen. The chemical equivalent of zinc being 32.6, the amount of zinc dissolved in each cell must be 1.2 X 32.6 =; 39.12 criths, and in the forty cells 1564.8 criths, equal to 140 grammes, the answer required. 20. In an electrotype apparatus, Fig. 85, 16.36 grammes of cop- per were deposited on the negative mould in 24 hours. What was the strength of current ? Ans. 6 units. 21. In an electrotype apparatus the electromotive force of the single cell employed is 420, and the internal resistance 5. The ex- ternal resistance, including decomposing cell, is 0.25. How much copper will be deposited on the negative mould in one hour, and how much zinc will be dissolved in the battery during the same time ? Ans. 9.088 grammes copper and 9.346 grammes of zinc. 22. Thirty-two Grove cells (E = 830, R == 20 each) are con- nected as 4 eight-fold compound elements and the current employed to work an electro-silvering apparatus, in which the total resistance external to the battery was equivalent to 10. Required the number of grammes of silver deposited each hour, and the number of grammes of zinc dissolved during the same time in the battery. Ans. 64.24 grammes of silver and 77.56 grammes of zinc. 23. Assuming that the external resistance cannot be changed, could the same number of cells of the battery described in last problem be so arranged as to deposit more silver in the same time ? Ans. They could not. ^ Could they be so arranged as to deposit the same amount of silver with less expense of zinc ? What would be the most economical ar- rangement, and under these conditions how much silver would be deposited in one hour and how much zinc dissolved ? Answer to last question, 30.25 grammes silver, and 9.13 grammes of zinc. ELECTRICAL RELATIONS OF THE ATOMS. 575 K -&-^A 24. What is the current through 25 Ohm with a tension of 5 Volts? ft* ^ y 1 O^ Ans. C = jj = 0.5 X 10~* or 0.5 Megafarad. 25. What is the work done by a current of 5 Megafarads per sec- ond through a resistance of 10 Ohms? Ans. W = C^Rt = (5 X 10~ 2 ) 2 X 10 X 10 7 = 250,000 units per second. 26. What is the work done by one thousand Farads in falling in tension one Volt ? Ans. W=QE= 1000 X 10- 8 X 10 5 = 1000 X lO^ 5 = 1 unit of work. Hence, 9,800 Voltfarads equal one metregramme. 27. What would be the answers to Problem 10 in B. A. units? Assuming that nine tenths of the external resistance is in a coil of platinum wire surrounded by a kilogramme of water, how high would the temperature of the water be raised in ten minutes ? 28. Assuming that in the system of conductors represented in Fig. 3, E represents the electromotive force of the voltaic element, R the total resistance of the main conductor a E b, R l and R t the resistances of the two conductors into which the main stream divides, find the values of the three corresponding currents C, C v and C 2 in terms of E, R, R v and R y Prove also that C\ : C 2 = R 2 : R lt and further, that Cj = Cj: ^-75- or C a = Cj; ^~p- Lastly, show that the equiva- lent resistance of any number of branches may be found by adding together the reciprocals of each branch and taking the reciprocal of this sum. A conductor like 72,, which diverts a portion of the main current from R v is called a shunt, and if R l is the coil of a galva- nometer the galvanometer would be said to be shunted by R# and by adjusting the value of R^ to R^ we can cause a known fraction of the whole current to pass through the instrument. 29. In the system of conductors represented in Fig. 4, called Wheatstone's bridge, no current passes over the bridge between c and d when R l : R 2 = R 3 : R t . Prove the truth of this proposition, V Fio.3. ;>! -r>6' l^l? 576 ELECTRICAL KELATIONS OF THE ATOMS. and show how it may be applied for measuring resistances when we have a set of standard resistance coils. 30. In the system of conductors, represented in Fig. 5, prove that no current passes in the portion a E l b when = , and consider E H + /i how the system may be used for comparing the electromotive force of different cellg. TABLE I. FRENCH MEASURES. Measures of Length. 1 Kilometre = 1000 Metres. I Metre = 1.000 Metre. 1 Hectometre = 100 K 1 Decimetre = 0.100 it 1 Decametre = 10 tt 1 Centimetre = 0.010 1 Metre = 1 tt 1 Millimetre 0.001 M Ar. Co. Log. 0.2066 188 Logarithms. 1 Kilometre = 0.6214 Mile. 9.7933 712 1 Metre = 3.2809 Feet. 0.5159 930 9.4840 070 1 Centimetre = 0.3937 Inch. 9.5951 742 0.4048 258 The metre is one ten-millionth of a quadrant of the globe. Measures of Volume. 1 Cubic Metre m: 3 = 1000.000 Litres. 1 Cubic Decimetre dHn. 3 = 1.000 " 1 Cubic Centimetre cTm: 3 = 0.001 " Logarithms. Ar. Co. Log. Cubic Metre = 35.31660 Cubic Feet. 1.5479790 8.4520210 Cubic Decimetre = 61.02709 Cubic Inches. 1.7855226 8.2144774 Cubic Centimetre = 0.06103 " " 8.7855226 1.2144774 Litre = 0.22017 Gallon. 9.3427581 0.6572419 Litre = 0.88066 Quart. 9.9448 083 0.0551 917 Litre . = 1.76133 Pints. 0.2458 407 9.7541 593 FRENCH WEIGHTS. 1 Kilogramme = 1000 Grammes. 1 Hectogramme =100 " 1 Decagramme =10 " 1 Gramme =1 " 1 Gramme = 1.000 Gramme. 1 Decigramme =0.100 " 1 Centigramme = 0.010 " 1 Milligramme = 0.001 " Logarithms. Ar. Co. Log. 1 Kilogramme = 2.20462 Pounds Avoirdupois. 0.3433 337 9.6566 663 1 = 2.67922 " Troy. 0.4280083 9.5719917 1 Gramme = 15.43235 Grains. 1.1884321 8.8115679 1 Crith 0.089578 Grammes. 8.9522 014 1.0477 986 TABLE II. ELEMENTARY ATOMS. Perissad Elements. Atomic Weights. Symbols of Molecules. Quantiva- lence. Artiad Elements. Atomic Weights. 1"! * i Quanti va- lence. lydrogen 1.0 19.0 35.5 80.0 127.0 7.0 23.0 39.1 85.4 133.0 108.0 204.0 197.0 11.0 140 31.0 75.0 122.0 210.0 51.37 120.0 94.0 182.0 H-H F-F Cl-Cl Br-Br I-I Li-Li Na-Na K-K Rb-Rb Cs-Cs Ag-Ag? Tl-Tl? Au=Au? B=B? N=N M 2 As^Ast S6.J6V BiJBtf F=F? U=U? Cb^Cb? TalTa? I (i tt ft i i I or III III III or V u it (i n V Copper VIercury 63.4 200.0 40.0 87.6 137.0 207.0 24.0 65.2 72.0 112.0 9.3 61.7 112.6 92.0 93.6 95.0 588 58.8 55.0 56.0 52.2 27.4 104.4 199.2 104.4 196.0 106.6 197.4 50.0 118.0 89.6 231.4 28.0 12.0 Cu? Hg Ca? Sr? Ba? Pb? 21 In? Cd G? Y? E? Ce? La? D? Ni? Co? Mn? Fe? Cr? All Ru? Os? Rh lr? Pd? Pt? Ti? Sn? Zr? Th? Si? C? II tt a ti ft if ft tt ft ft n II or IV ft ft ft tt H tt tt ft IV ft t fluorine Chlorine Bromine Iodine Calcium Strontium Barium Lead Lithium Sodium Potassium Rubidium Ccesium Vlagnesium Zinc Indium Cadmium Silver Glucinum Yttrium Erbium Thallium Gtold ~ Boron Cerium Lanthanum Didymium Nitrogen Phosphorus Arsenic Antimonv Nickel Cobalt Bismuth Manganese Iron Vanadium Uranium Chromium Aluminum Columbium Tantalum Ruthenium Osmium Artiad Elements. 16.0 32.0 79.4 128.0 96.C 184.C 0-0 S--S Se=Se Te=Te Mo? W? II II or VI ( i< VI M Rhodium Iridium Palladium Platinum Titanium Tin Oxygen Sulphur Selenium Tellurium Zirconium Thorium Molybdenum Tungsten Silicon Carbon TABLE III. Specific Gravity of Gases and Vapors. Names. Symbols. Air = 1. Sp.Gr. H-H=l. Half Molecular Weight. Loga- rithms. Air 1.000 14.43 1.1593 Hydrogen H-H 0.0693 1.00 1.00 0.0000 Acetylic Hydride (Aldehyde) C 2 H 3 0-H 1.532 22.10 22.00 1.3424 Ace ty lie Chloride C 2 H^ O-Cl 2.87 41.42 39.25 1.5938 Acetic Anhydride (C 2 H 3 0) 2 =0 3.47 50.07 61.00 1.7076 Acetic Acid H-O-C 2 H 3 O 2.083 30.07 30.00 1.4771 Aluminic Chloride [Al 2 ]iCl 6 9.34 134.80 133.90 2.1268 Aluminic Bromide [Alo] l-Br 6 18.62 268.70 267.40 2.4272 Aluminic Iodide [A~1 2 ]\I 6 27. 389.60 408.40 2.6111 Antimonious Chloride sb=a a 7.8 112.70 114.20 2.0577 Triethylstibiue ( C 2 H 5 ) 3 =Sb 7.23 104.40 104.50 2.0191 Arsenic Ai^Aik 10.6 153.00 150.00 2.1761 Arseniuretted Hydrogen H 3 =As 2.695 38.90 39.00 1.5911 Triethylarsine ( C 2 H-) 3 =As 5.29 76.35 81.00 1.9085 Kakodyl ( CH 3 ). 2 As-( CH 3 ) 2 As 7.10 102.50 105.00 2.0212 Arsenious Chloride As = C1 3 6.3 90.90 90.75 1.9578 Arsenious Iodide As=2 3 16.1 232.40 228.00 2.3579 Bismuthous Chloride Bi = Cl a 11.35 163.90 158.25 2.1994 Boric Methide (CH 3 ) 3 =B 1.931 27.90 28.00 1.4472 Boric Ethide (C H-) -B 3.401 49.10 49.00 1.6902 Boric Fluoride JS=jP 3 2.37 34.20 34.00 1.5315 Boric Chloride B=Cl 3.942 56.85 58.75 1.7690 Boric Bromide B=Br 3 8.78 126.80 125.50 2.0986 Methylic Borate (CH 3 ) 3 = O^=B 3.59 51.80 52.00 1.7160 Ethylic Borate (C Z H 5 ) 3 =6 3 =B 5.14 74.20 73.00 1.8633 Bromine B>-Br 5.54 79.50 80.00 1.9031 Hydrobromic Acid H-Br 2.71 39.10 40.50 1.6075 Carbonic Tetrachloride C=Cl t 6.415 78.14 77.00 1.8865 Marsh Gas CH 0.5576 8.05 8.00 0.9031 Phosgene Gas CIO, C1 2 3.399 49.06 49.50 1.6946 Dicarbonic Hexachloride [C-C] = CI K 8.157 117.70 118.50 2.0737 Dicarbonic Tetrachloride [C=C]^Cl 1i 5.82 84.00 83.00 1.9191 Dicarbonic Bichloride [ C= C] = Cl t 47.50 1.6767 Carbonic Oxide c=o 0.967 13.95 14.00 1.1461 Carbonic Anhydride Carbonic Sulphide CiO, CIS, 1.529 2.645 22.06 38.17 22.00 38.00 13424 1.5798 Chlorine Cl-Cl 2.44 35.22 35.50 1.6502 Hydrochloric Acid H-Cl 1.27 18.32 18.25 1.2613 Chromic Oxychloride Cr = C7, 5.5 79.40 77.6 1.8935 Columbic Chloride CbiCl s 9.6 138.60 135.70 2.1326 Columbic Oxychloride C6|O, CZj 7.9 114.00 108.20 2.0342 Cyanogen CN-CN 1.806 26.06 26.00 1.4150 Hydrocyanic Acid H-CN 0.947 13.67 13.50 1.1303 Ethyl C H-C H 2.0 28.86 29.00 1.4624 Ethylic Chloride (C 2 H b )~Cl 2.219 32.02 32.25 '1.5085 Ethylic Oxide (Ether) Ethvlic Hydrate (Alcohol) <$$% 2.686 1.613 37.32 23.28 37.00 23.00 1.5682 1.3*517 TABLE III. (Continued.) Names. Symbols. ^p.(5r. Air =1. Sp.Gr. H-H=I. Half Molecular Weight. Loga- rithms. Ethylene (Olefiant Gas) C 2 H t 0.978 14.11 14.00 1.1461 " Chloride (Dutch Liq.) (C 2 H 4 ) = a a 3.443 49.69 49.50 1.6946 Ethylene Oxide (C 2 H t ) = 1.422 20.52 22.00 1.3424 Ethylene Hydrate (Glycol) (C 2 Ht) = O t =H a 31.00 1.4914 Ferric Chloride [Fe 2 ]lCl Q 11.39 164.40 162.60 2.2108 Iodine I-I 8.716 125.90 127.00 2.1038 Hydriodic Acid H-I 4.443 64.12 64.00 1.8062 Mercury Hg 6.976 100.70 100.00 2.0000 Mercuric Ethide (C 2 H K ) 2 =Hg 9.97 143.90 129.00 2.1106 Mercuric Methide (CH 3 ) 2 =Hg 8.29 119.60 115.00 2.0607 Mercuric Chloride Hg = Cl z 9.8 141.50 135.50 2.1319 Mercuric Bromide Hg=Br a 12.16 175.60 180.00 2.2553 Mercuric Iodide Hg=I z 15.9 229.60 227.00 2.3560 Mercurous Chloride (Hg 2 ] = Cl a 8.21 118.50 235.50 2.3720 Nitrogen N=N 0.971 14.00 14.00 1.1461 Ammonia H 3 =N 0.591 8.535 8.51 0.9294 Methylamine H S ,(CH 3 )=N 1.08 15.59 15.50 1.1903 Aniline H a ,(C 6 H B )=N 3.21 46.33 46.50 1.6675 Nitrous Oxide N Z O 1.527 22.04 22.00 1.3424 Nitric Oxide NO 1.038 14.97 15.00 1.1761 Nitric Peroxide JVO 2 1.72 24.82 23.00 1.3617 Osmic Tetroxide OsO 4 8.89 128.30 131.60 2.1193 Oxygen O=O 1.1056 15.95 16.00 1.2041 Aqueous Vapor H 2 =0 0.6235 8.998 9.00 0.9542 Phosphorus P 2 !P 2 4.42 63.78 62.00 1.7924 Phosphuretted Hydrogen H a =P 1.184 17.09 17.00 1.2304 Phosphorous Chloride P=Clg 4.742 68.44 68.75 1.8373 Phosphoric Oxychloride P10, C7 3 5.3 76.49 76.75 1.8851 Oxide of Triethylphosphine ((C a H 5 )^P) = 4.6 66.39 67.00 1.8261 Selenium, at 771 Se=Se 5.68 81.96 79.40 1.8998 Seleniuretted Hydrogen H a =Se 2.795 40.33 40.70 1.6096 Silicic Methide (CH s )t=Si 3.083 44.49 44.00 1.6435 Silicic Ethide (C 2 H 5 )i=Si 5.13 74.03 72.00 1.8573 Silicic Fluoride Si F 4 3.600 51.95 5200 1.7160 Silicic Chloride si=a 4 5.939 85.72 85.00 1.9294 Ethylic Silicate (C 2 H 5 ), = O t =Si 7.32 105.60 104.00 1.0170 Stannic Ethide (C 2 H 5 )t=Sn 8.021 115.80 117.00 2.0682 Stannic Dimethylo-diethide (CH^^C.H^Sn 6.838 98.68 103.00 2.0128 Stannic Chloro-triethide a,(C 2 H r ,)^Sn 8.430 121.70 120.20 2.0799 Stannic Dichloro-diethide C/ 2 , ( C^H^Sn 8.710 125.70 123.50 2.0917 Stannic Chloride Sn = Cl t 9.199 132.70 130.00 2.1139 Sulphur above 860 s=s 2.23 32.18 32.00 1.5051 Sulphur at 450 s 6.617 95.50 96.00 1.9823 Sulphuretted Hydrogen H^S 1.191 17.19 17.00 1.2304 Sulphurous Anhydride S=0 3 2.234 32.24 32.00 1.5051 Sulphuric Anhydride s=o 9 2.763 39.87 40.00 1.6021 Tantalic Chloride TaCl s 12.8 184.70 ' 179.70 2.2546 Titanic Chloride TiCl t 6.836 98.65 96.00 1.9823 Zinc Ethide (C 2 fl- 5 ) 2 =Z 4.259 61.46 61.60 1.7896 Zirconic Chloride Zr=Cl 4 8.15 117.60 115.80 2.0637 LOGARITHMS AND ANTILOGARITHMS. LOGARITHMS OF NUMBERS. -2 Proportional Parts, +* 1 4 , | 1 I H 1 2 a 4j5 67 8 9 ; 10 0000 0043 0086 0128 0170 0212 0253 0294 0334 0374 4 8 12 17 2 25 29 33 37 11 0414 0453 0492 0531 0569 0607 0645 0682 0719 0755 4 8 11 15 23 26 30 34 12 0792 0828 0864 0899 0934 0969 1004 1038 1072 1106 3 ~ 10 14 21 24 1 28 31 13 1139 1173 1206 1239 1271 1303 1335 1367 1399 1430 3 6 10 13 19 23 26 29 14 1461 1492 1523 1553 1584 1614 1644 1673 1703 1732 3 6 9 12 18 21 24 27 15 1761 1790 1818 1847 1875 1903 1931 1959 1987 2014 3 6 8 11 17 20 2-2 25 16 2041 2068 2095 2122 2148 2175 2201 2227 2253 2279 3 5 8 11 16 18 21 24 17 2304 2330 2355 2380 2405 2430 2455 2480 2504 2529 2 5 7 10 15 17 20 22 18 2553 2577 2601 2625 2648 2672 2695 2718 2742 2765 2, 5 7 9 14 16 19 21 19 2788 2810 2833 2856 2878 2900 2923 2945 296- 2989 \ 4 7 ( 13 16 18 20 20 3010 3032 3054 3075 3096 3118 3139 3160 318 3201 S t 6 8 13 15 17 19 21 3222 3243 3263 3284 3304 3324 3345 3365 3385 3404 2 4 6 8 12 14 16 18 22 3424 3444 3464 3483 3502 3522 3541 3560 3579 3598 2 4 6 8 o 12 14 15 17 23 3617 3636 3655 3674 3692 3711 3729 3747 3766 3784 2| 4 C ' 9 11 13 15 17 24 3802 3820 3838 3856 3874 3892 3909 3927 3945 3962 2 4 5 - 11! 12 14 16 25 3979 3997 4014 4031 4048 4065 4082 4099 4116 4133 2 3 5 7 10 12 14 15 26 4150 4166 4183 4200 4216 4232 4249 4265 428 4-298 2 3 5 7 8 10 11 13 15 27 4314 4330 4346 4362 4378 4393 4409 4425 4440 4456 2 3 5 6 8 9 11 13 14 28 4472 4487 4502 4518 4533 4548 4564 4579 4594 4609 2 3 5 b b 9, 11 12 14 29 4624 4639 4654 4669 4683 4698 4713 4728 4742 4757 1 3 4 6 ' 9; 10 12 13 30 4771 4786 4800 4814 4829 4843 4857 4871 4886 4900 | 4 6 - 10 11 13 31 4914 4928 4942 4955 4969 4983 4997 5011 5024 5038 3 4 6 7 8 10 11 12 32 5051 5065 5079 5092 5105 5119 5132 5145 5159 5172 3 4 5 7 8 9 11 12 33 34 5185 5315 5198 5328 9411 5340 pxx 5353 5237 5366 5250 5378 5263 5391 93 IV 5403 5289 5416 5302 5428 3 4 5 6 8 9 10 12 11 35 5441 5453 5465 5478 5490 5502 5514 5527 5539 5551 f 4 5 6 7 9 10 11 36 5563 5575 5587 5599 5611 5623 5635 5647 5658 5670 2 4 5 6 7 8 10 11 37 568-2 5694 5705 5717 5729 5740 5752 5763 5775 5786 ! c 3 5 6 7 8 9 10 38 5798 5809 5821 5832 5843 5855 5866 5877 5888 5899 2 3 5 6 7 8 9 10 39 Af\ 5911 5922 AAQ1 5933 i'A 1 -1 5944 flAfcO 5955 Gf\CA 5966 085 6191 ouuo 6201 i!07 6212 51 17 6222 2 3 4 5 6 7 8 IV 9 42 6232 6243 6253 6263 6274 6284 6294 6304 6314 6325 2 3 4 5 6 7 8 9 43 6335 6345 6355 6365 6375 6385 6395 6405 6415 6425 2 3 4 5 G 7 8 9 44 6435 6444 6454 6464 6474 6484 6493 6503 6513 6522 2 3 4 5 6 7 8 9 45 6532 6542 6551 6561 6571 6580 6590 6599 6609 6618 2 3 4 5 6 7 8 9 46 6628 6637 6646 6656 6665 6675 6684 6693 6702 671-2 2 3; 4 5 6 7 7 8 47 6721 6730 6739 6749 6758 6767 6776 6785 6794 6803 2 3 4 5 5 6 7 8 48 6812 6821 6830 6839 6848 6857 6866 6875 884 6893 a 3 ! 4 4 5 6 7 8 49 6902 6911 6920 6928 6937 6946 6955 6964 972 6981 2 3 ! 4 4 5 6 7 8 50 69906998 7007 7016 7024 7033 7042 7050 059 067 2 3 3 4 5 6 7 8 51 7076 7084 7093 7101 7110 7118 7126 7135 143 152 2 3 3 4 5 6 7 8 52 7160 7168 7177 7185 7193 7202 7210 7218 226 235 2 2 3 4 5 6 7 7 53 7243 7251 7259 7267 7275 7284 7292 7300 308 7316 2 2 3 4 5 6 6 7 54 7324 7332 7340 7348 7356 7364 7372 7380 388 7396 2 2 3 4 5 6 6 7 LOGARITHMS OF NUMBERS. 1 Natural Numbers. 1 2 3 4 5 6 7 8 Propcrt onal Parts. 9 1234 567; 9 55 7404 7415 S7419 7427 7435 7443 7451 745 7466 7474 1 2 2 45 56 7 56 748-J 7490 ! 7497 7505 7513 7520 7528 753 754 7551 1 2 2 45567 57 7559 7566 7574 7582 7589 7597 7604 761 761 7627 122 45567 58 7634 7642 7649 7657 7664 7672 7679 768 769 7701 1 1 2 44567 59 7709 7716 7723 7731 7738 7745 775:2 776 776 7774 1 1 2 44567 60 7782 7789 7796 7803 7810 7818 7825 783 783 7846 1 1 2 445 6 61 7853 7860 7868 7875 '7882 7889 7896 790 791 7917 1 1 2 4 4566 62 7924 7931 7938 7945 7952 7959 7966 797 798 7987 1 1 2 34666 1 63 ' 7S93 8000 8007 8014 8021 8028 8035 804 804 8055 1 1 2 34556 64 8062 8069' 8075 8082 8089 8096 8102 8109 811 8122 1 1 2 34666 65 812981368142 8149 8156 8162 81698176 818 8189 1 1 2 34566 66 8 195: 8-202 8209,8215 8222 8228 8235 8241 824 8254 1 1 2 34566 67^8261,8267 8274 82808287 8293 8299,8306 831 8319 1 1 2 34666 68 ' 832o;8331 8338 8344 8351 8357 8363 8*70 837 8382 1 1 2 34456 69 8388 8395 8401 8407 8414 8420 8426 8432 843 8445 1 1 2 34456 70 8451 8457 8463 8470 8476 8482 8488 8494 8500 8506 1 1 2 34456 71 ( 8513 8519 8525 8531 8537 8543 8549 8555 856 8567 Ij 1 2 ( 34455 72 ' 8573 8579 8585 8591 8597 8603 8609 8615 862 8627 1 1 2 34465 73 ; 8633 86398645 8651 8657 8663 86698675 868 8686 1 1 2 34456 74*8692 8698 8704 8710 8716 8722 8727 8733 8739 8745 li 1 2 34455 75 8751 8756 8762 8768 8774 8779 8785 8791 879~ 8802 1 1 2 33465 76*8808 8814 8820 8825 8831 8837 8842 8848 8854 8859 1 1 2 33465 77.8865 8871 8876 8882 8887 8893 8899 8904 8910 8915 1 1 2 3-3446 78^8921 8927 8932 8938 8943 8949 8954 8960 8965 8971 1 1 2 33445 79 8976 8982 8987 8993 8998 9004 9009 9015 9020 9025 1122 33446 80 9031 9036 9042 9047 9053 058 9063 9069 9074 9079 1122 33446 81 9085 9090 9096 9101 9106 9112 9117 9122 9128 )133 1122 33446 82 913S'9143 9149 9154 9159 165 9170 9175 180 9186 1122 33446 83 9191 9196 9201 9-206 9212 217 9222 9227 232 9238 1122 33445 84 9243 9248 9253 9258 9263 269 9274 9279 284 289 1122 33446 85 9294 9299 9304 9309 9315 320 9325 9330 335 340 1122 33446 86 9345 9350 9355 9360 9365 37Q 9375 9380 385 390 1122 33446 87 9395^400 9405 9410 9415 420 9425 9430 435 440 0112 93344 88 9445 9450 9455 ' 9460 ^465 469 9474 9479 484 489 0112 93344 89 9494 9499 9504 9509 9513 518 9523 9528 533 538 0112 23344 90 9542 9547 9552 9557 9562 566 9571 9576 581 586 12 23344 91 9590 9595 9600 9605^609 9614 9619 9624 628 ::!:< 2 2 3 3 4 4 92 96389643 9647 9652 9657 661 9666 9671 675 680 2 23344 93 9685 9689 9694 9699 9703 708 9713 9717 722 727 2 2 3344 94 9731 9736 9741 9745 9750 7549759 9763 768 )773 2 23344 95 9777 9782 9786 9791 9795 8009805 9809 -11 ' >818 9 23344 96 9823 9827 983298369841 845 9850 9854 859 < >863 9 23344 97 9868 9872 9877 988 l' 9886 890 9894 9899 )903< >908 19 2 8j 3 4 4 98 9912 9917 99-21 9926 9930 934 9939 9943 948 < U.v.' 1 9 23344 99 9956 9961! 9965 ! 9969 9974 978998319987 1991 < >996 1 1 9 93334 ANTILOGARITHMS. M 1 2 3 4 5 6 7 8 9 Proportional Parts, 2 3 4 a A 1 8 9 .00 000 1002 005 1007 009 012 014 016 019 021 1 1 i 1 2 2 2 .01 023 1026 028 1030 033 035 038 040 042 045 1 1 i 1 2 2 2 .02 047 1050 1052 1054 057 059 062 064 067 069 1 1 i 1 2 2 2 .03 072 1074 1076 1079 081 084 086 089 091 094 1 * i 1 2 2 2 .04 096 1099 1102 1104 107 109 112 114 117 119 1 1 1 i 2 2 2 2 .05 122 1125 1127 1130 132 1135 138 140 143 146 1 1 1 i 2 2 2 2 .06 148 1151 1153 1156 159 161 164 167 169 172 1 1 1 i 2 2 2 2 .07 175 1178 1180 1183 186 1189 191 194 197 199 1 1 1 i 2 2 2 2 .08 202 1205 120S 1211 213 216 219 222 225 227 1 1 1 i 2 2 2 3 .09 230 1233 1236 1239 242 245 247 1250 253 256 1 1 1 i 2 2 2 3 .10 259 1262 1265 1268 271 1274 276 279 282 285 1 1 1 i 2 2 2 3 .11 288 1291 1-294 1297 300 1303 306 1309 312 315 1 1 1 2 2 2 2 3 .12 318 1321 1324 1327 330 334 337 1340 343 346 1 1 ] 2 2 f\ 2 3 .13 349 1352 1355 1358 361 1365 368 1371 374 377 1 1 1 2 2 f 3 3 .14 380 1384 1387 1390 393 1396 400 1403 406 409 1 1 1 2 2 C 3 3 .15 413 1416 1419 1422 426 1429 432 1435 439 442 1 1 1 n 2 t 3 3 .16 445 1449 1452 1455 459 1462 466 1469 472 1476 1 1 1 2 2 2 3 3 .17 479 1483 1486 1489 493 1496 500 1503 507 510 1 1 ] 2 2 r 3 3 .18 514 1517 1521 1524 528 1531 535 1538 542 1545 1 1 1 2 2 3 3 .19 549 1552 1556 1560 563 1567 570 1574 578 1581 1 1 1 <\ 2 3 f 3 .20 585 1589 1592 1596 600 1603 607 1611 614 1618 1 1 1 ^) 3 3 3 .21 622 1626 1629 1633 637 1641 644 1648 1652 1656 1 1 2 B 2 3 3 3 .22 660 1663 1667 1671 675 1679 683 1687 1690 1694 1 1 2 2 2 3 f 3 .23 698 1702 1706 1710 714 1718 722 1726 1730 1734 1 1 2 o 2 3 3 4 .24 1738 1742 1746 1750 754 1758 762 1766 1770 1774 1 2 t) 2 3 3 4 .25 1778 1782 1786 1791 795 1799 803 1807 1811 1816 1 1 2 2 c 3 3 4 .26 1820 1824 1828 1832 1837 1841 1845 1849 1854 1858 1 <-) 2 3 3 3 4 .27 1862 1866 1871 1875 1879 1884 1888 1892 1897 1901 1 2 2 3 3 3 4 .28 1905 1910 1914 1919 1923 1928 1932 1936 1941 1945 1 2 2 3 3 4 4 .29 1950 1954 1959 1963 1968 1972 1977 1982 1986 1991 1 2 2 3 3 4 4 .30 1995 2000 2004 2009 2014 2018 2023 2028 2032 2037 1 o 2 3 3 4 4 .31 2042 2046 2051 2056 2061 2065 2070 2075 2080 2084 1 1 o 2 3 3 : 4 .32 2089 2094 2099 2104 2109 2113 2118 2123 2128 2133 1 1 2 2 3 3 4 4 .33 2138 2143 2148 2153 2158 2163 2168 2173 2178 2183 1 1 2 2 3 3 4 4 .34 2188 2193 2198 2203 2208 2213 2218 2223 2228 2234 1 2 2 3 | 4 4 5 .35 2239 2244 2249 2254 2259 2265 2270 2275 2280 2286 1 2 2 3 | 4 4 5 .36 2291 2296 2301 2307 2312 2317 2323 2328 2383 2339 1 2 2 3 3 4 4 5 .37 2344 2350 2356 2360 2366 237 2377 2382 2388 2393 1 2 2 3 3 4 4 5 .38 2399 2404 2410 2415 2421 2427 243- 2438 2443 2449 1 2 2 3 3 4 4 5 .39 2455 2460 2466 2472 2477 .2483 2489 2495 2500 2506 1 2 2 3 4 6 5 .40 2512 2518 2523 2529 2535 254 254 2553 255 2564 1 2 t 3 4 4 i 5 .41 2570 25762582 2588 2594 2600 260 261- 261 2624 1 2 i 3 4 4 5 5 .42 2630 2636 2642 2649 2655 266 2667 2673 267 2685 1 fl 2 3 4 4 5 6 .43 2692 2698 2704 2710 2716 272 2729 2735 274 2748 1 2 4 4 6 .44 2754 2761 2767 277 2780 278 2793 279 280 2812 1 9 3 4 4 6 .45 281 2825 2831 2838 2844 285 285 286 287 2877 1 r ] 5 6 .46 2884 2891 2897 290 291 291 2924 293 293 2944 1 c 5 6 .47 2951 2956 296 297 2979 298 2992 299 300 301 ] 2 3 5 6 .48 302( 3027 3034 304 3048 305 3062 306 307 308 ] 2 3 6 6 .4 309( ) 3097 3105 311 311 312 313S 314 314 315 ] 2 5 6 6 ANTILOGARITHMS. i 1 2 3 4 5 67 8 9 Proportional Parts. r 2 3 4*5 6 7 8 9 .50 3162 3170 3177 3184 3192 3199 3206J3214 3221 3228 i 1 2 3 4 4 5 6 7 .51 3236 3243 3251 3258 3266 3273 328 1! 3289 3296 3304 i 2 2l 3 4 6 5 6 7 .52 .53 3311 3319 3327 3334 3342 3388 auofi'a/in/i -a.iio QIOO 335033573365 3428 ^ A Qf? ' Q,4 A Q 3373 3451 3381 3459 1 2 2 3 O Q 4 5 5 6 7 .54 3467 3475 3483 3491 3499 3508 3516,3524 3532 3540 [ 2 11 4 5 6 ' 6 7 I .55 3548 3556 3565 3573 3581 35893597,3606 3614 3622 i 2 2 3 4 5 6 7 7 .56 3631 3639 3648 3656 3664 3673 3681,3690 3698 3707 i 2 3 3 4 56 7 8 .57 3715 3724 3733 3741J3750 3758 3767J3776 3784 3793 i 2 3 3 4 8 < 7 8 .58 380-2 38 li;3819 ;38-283837 3846 3855 3864 3873 3882 i 2 3 4 4 5 6 7 8 .59 3890 3899 3908 3917 3926 3936 3945,3954 3963 3972 > 2 3 4 5 ' 7 8 .60 3981 3990 3999 4009 4018 4027 40364046 4055 4064 i 2 3 4 5 6 6 7 8 .61 4074 40834093 4102 4111 4121 4130 4140 4150 4159 ! 2 3 4 5 8 9 .62 4169 4178 4138 4198 4207 4217 4227 4236 4246 4256 1 2 3 4 5 6 7 8 9 .63 4266 4276 4285 4295 4305 4315 4325 4335 4345 4356 1 2 3 4 5 6 7 8 9 .64 4365 4375 4385 4395 4406 4416 4426 4436 4446 4457 1 2 3 4 5 6 7 8 9 .65 4467 4477 4487 4498 4508 4519 4529 4539 4550 4560 1 2 3 4 5 6 7 8 9 .66 4571 4581 4592 4603 4613 4624 4634 4645 4656 4667 1 2 3 4 5 6 7 9 10 .67 4677 4688 4699 4710 4721 4732 4742 4753 4764 4775 1 2 3 4 5 7 8 9 '10 .68 4786 4797 4808 4819 4831 4842 4853 4864 4875 4887 ] c 3 4 6 7 8 9 10 .69 4898 4909 4920 4932 4943 4955 4966 4977 4989 5000 1 2 3 5 6 7 8 9 10 .70 5012 5023 5035 5047 5058 5070 5032 509'3 5105 5117 1 2 4 5 6 7 8 9 11 .71 5129 5140 5152 5164 5176 5188 5200 5212 5224 5236 1 2 4 5 6 7 8 10 11 .72 5248 5260 5272 5284 5297 5309 5321 5333 5346 5358 1 2 4 5 6 7 9 10 11 .73 5370 5383 5395 5408 5420 5433 5445 5458 5470 5483 1 3 4 5 6 8 9 10 '11 .74 5495 5508 5521 5534 5546 5559 5572 5585 5598 5610 1 3 4 5 6 8 9 10 12 .75 5623 5636 5649 5662 5675 5689 5702 5715 5728 5741 1 3 4 5 7 8 9 10 12 .76 5754 5768 5781 5794 5808 5821 5834 5848 5861 5875 I 3 4 5 7 ' 8 9 11 12 .77 5888 5902 5916 59-29 5943 5957 5970 5984 5998 6012 l 3 45 7 8 10 11 12 .78 6026 6039 6053 6067 6081 6095 6109 6124 6138 6152 I 3 4 6 7 8 10 11 13 .79 6166 6180 6194 6209 6223 6237 6252 6266 6281 6295 1 3 4 6 7 9 10 11 13 .80 6310 6324 6339 6353 6368 6383 6397 6412 6427 6442 1 3 4 6 7 9 10 1-2 13 .81 6457 6471 6486 6501 6516 6531 65466561 6577 6592 2 3 5 6 8 " 9 11 1-2 14 .82 6607 6622 6637 6653 6668 6683 6699 6714 6730 6743 2 3 5 6 8 9 11 12 14 .83 6761 6776 6792 6808 6823 6839 6855 6871 6887 6902 2 3 5 6 8 9 11 13 14 .84 6918 6934 6950 6966 6982 6998 7015 7031 7047" 7063 2 3 5 6 8 10 11 13 15 f .85 7079 7096 7112 7129 7145 7161 7178 7194 7211 7228 2 3 5 7 8 10 12 13 id .86 7244 7261 7278 7295 7311 7328 7345 7362 7379 7396 2 3 5 7 8 10 12 13 15 .87 7413 7430 7447 7464 748-2 7499 7516 7534 7551 7568 2 1 5 7 9 10 12 14 16 .88 7586 7603 7621 7638 7656 7674 7691 7709 7727 7745 2 4 5 7 9 11 1-2 14 16 .89 7762 7780 7798 7816 7834 7852 7870J7889 7907 7925 2 4 5 7 9 11 13 14 16 .90 7943 7962 7980 7998 8017 8035 80548072 8091 8110 2 4 6 7 9 11 13 15 17; .91 8128 8147 8166 8185 8204 8222 8241 ' 8260 8279 8299 2 4 6 B 9 11 13 15 17 .92 8318 8337 8356 8375 8395 8414 8433 ' 8453 8472 8492 2 4 6 B 10 1-2 14 15 17 .93 8511 8531 8551] 8570 8590 8610 86308650 8670 8690 2 4 6 B 10 1-2 14 16 18 .94 8710 8730 8750 8770 8790 8810 8831J8851 8872 8892 2 4 6 B 10 IS 14 16 18 .95 8913 8933 8954 8974 8995 9016 9036 9057 9078 9099 2 4 6 8 10 1-2 15 17 19 .96 9120 ! 9141 9162 9183 9204 9226 9247 9268 9290 9311 2 4 6 1 11 II 15 17 19 .97 9333 9354 9376 9397 9419 9441 9462 9484 9506 9528 2 4 7 9 11 II U 17 20 .98 9550,9572 9594 9616 9638 9661 9683 9705 9727 9750 2 4 7 9 11 II 16 18 20 .99 9772 9795 9817 98409863 9886 9908 ! 9931 9954 9977 2 5 7 9 11 14 16 18 20 CONSTANT LOGAKITHMS. Loga- Ar. Co. rithms. Log. Circumf. of circle when R = 1, (^ = 1.5708) 0.1961 9.8039 " " " D = 1, (TI = 3.1416) 0.4971 9.5028 Area of circle when 2?= 1, (n = 3.1416) 0.4971 9.5028 " " " " ZP=1, (~ = 0.7854) 9.8951 0.1049 " C"=l, Q^ = 0.0796) 8.9008 1.0992 Surface of sphere when # 2 = 1, (4^=12.5664) 1.0992 8.9008 " " " jD a =l, (TT = 3.1416) 0.4971 9.5028 " C 2 =l, (^ = 0.3183) 9.5028 0.4971 Solidity of sphere when 22 3 = 1, (|^= 4.1888) 0.6221 9.3779 " " D 8 =l, (^ = 0.5236) 9.7190 0.2810 " " " C=l, (g^a= 0.0169) 8.2275 1.7724 Weight of one litre of Hydrogen (0.0896 grammes) 8.9522 1.0478 " " 4< Air (1.293 " ) 0.1116 9.8884 " ". " " " " (14.43 criths ) 1.1594 8.8406 Per cent of Oxygen in air by weight (0.2318) 9.3651 0.6349 " "Nitrogen" " " " (0.7682) 9.8855 0.1145 Mean height of Barometer (76 c. m.) 1 .8808 8. 1 1 92 Coefficient of expansion of Air (0.00366) 7.5635 2.4365 Latent Heat of Water (79) 1.8976 8.1024 Free Steam (537) 2.7300 7.2700 To reduce 0p.(^r. to S P- Gr., or reverse, add to log. 1.1594 or 8.8406 " " Sp. Gr. toSp.Gr.," " " " " 5.9522 or 4.0478 " " 0p.(^r. to Sp. Gr., " " " " " 7.1 116 or 2.8884 <* grammes to criths, " " " " 1.0478 or 8.9522 INDEX. The numbers of this Index refer to pages ; those following dashes are references to reactions, into which the given substance enters as an important factor. To use the index with copies of the first edition, add ten to the number of all pages above the two hundredth. A. Acetamide, 243. 245. Acetic Acid, 74, 488, 493. 513. " Anhydride, 493. Ether, 492. - 61, 490. Acetine, 517- Ace to-lactic Acid, 510. Acetone, 495. Acetonyl, 484. Acetyl, 73, 484. " Chloride, 57, 496. Acetylene Series, 477, 480. Acidity of Bases, 94. Acids, Definition of, 83. Acid Radical?, 83. " Salts, 87. Aconitic Acid, 518. Acrolein,498. Acryl, 484. Acrylic Acid, 498. " Series, 498. " " Secondary Acids, 499. " " Tertiary Acids, 500. Adhesion, 12, 37. Adipic Acid, 512. Agalmatolite, 410. Agate, 445 Alabaster, 342. All bite, 409. Albumen, 524. Alcohol, 90, 485, 487. 38. 77, 358, 455, 491, 492, 509, 512. " Digly eerie, 517. Iso, 496. " Pseudo, 486, 496. " Radicals, 73 " Secondary, 496. " Tertiary, 497. " Tetratomic, 519. " Triatomic, 515. " Trigly eerie, 517. Aldehyde, 487, 494. 509. Alkali, Definition of, 81. " Fixed, 247. " Volatile, 247. Alkaline Sulphides, 312. " Sulphohydrates, 312. Allotropisra, 133. 251, 302, 308, 460. Allyl, 78, 477, 481. Allylic Alcohol, 497. " Iodide, 481,497. " Cyanide, 500. Allylene, 477. Altaite, 321. Alums, 319, 376, 400, 409, 412. Aluminates, 414. Aluminic Acetate, 413. Chloride, 414, 415. Aluminic Hydrate, 408, 414. Nitrate, 414. " Oxide, 415. " Sulphate, 409, 413. 414. " Sulphide, 415. Aluminite, 409. Aluminum, 408. 412. " Bronze, 411. Alum-stone, 409. Alunite, 409. Alunogen, 409. Amethyst, 445. Amides, 243. Amidogen, 39, 243. Amines, 242. Ammonia, 82, 240. 36, 38,82,233,246,494. Ammonic Carbonates, 248. 246, 341. " Chloride, 247. 38, 241. " Dichromate, 399. " Nitrate, 239. " Nitrite, 233. " Silico-fluoride, 452. " Sulphohydrate, 312. " Sulphide, 311, 312. 361. Ammonides, 242. Ammonio-cobalt Bases, 369. Ammonio-magnesic Phosphate, 356. Ammonio-manganous Salts, 374. Atnmonio-platinous Chloride. 427. Ammonio-platinic Chloride. 426. Ammonio-platinum Bases, 428. Ammonio-stannic Chloride, 435. Ammonium, 82, 246. Alum, 409. 413. " Bases, 248. " Compounds, 245. Ampere's Law, 17. Amygdaline, 522. Amylaceous Bodies, 521. Amylene, 477. Amyl, 72, 484. Amy lie Alcohol, 486. " Acetate, 492. 14 Glycerine, f>18. " Hydride, 477. ' Acid Sulphate, 492; Amyloses, 521. Analcime, 410, 456, 457. Analysis, 9. Analytical Reaction, 35 Anchoic Acid, 512. Andalusite. 409.- Andesine, 457. Angelic Acid, 498. Anglesite, 346. Anhydrides Acid, 85 " Basic, 82. " of Organic Acids, 493. Anhydrite, 342. INDEX. Aniline, 242, 482. 502. Animal Kingdom, Province of, 525. Ankerite, 378. Annabergite, 365. Anorthite, 409, 456. Antimoniate of Antimony, 270. Antimonic Acid, 269. " Anhydride, 270. " Chloride, 267. " Sulphochloride, 267. " Sulphide, 275. Antimonious Bromide, 267. Chloride, 266. 268,270. " Fluoride, 267. " Hydrate, 61. " Iodide, 267. H Oxide, 267. 264. *' Sulphate, 265. " Sulphide,272.-264,266,310. Antimoniuretted Hydrogen, 270. Antimony, 264. 265, 266. " Butter of, 266. " and Alcohol Radicals, 27L " " Chlorine, 266. " Hydrogen, 270. " " Oxygen, 267. " " Sulphur, 272. " * Zinc,27i. " Glance, 264, 272. " Oxychloride of, 266. Antozone, 304. Antozonides, 305. Apatite, 291, 343. Apjohnite, 409. Aqua Ammonia, 247. " Regia,224. Arachidic Acid, 488. Aragonite, 340. Argentic Bromide, 221. " Chloride, 221. " Iodide, 221. " Nitrate, 220. - 36, 38, 56, 236. [ " Oxalate, 465. ' " Oxide, 222. 249. " Peroxide, 222. " Sulphate, 54. " Sulphite, 315. Arsenic, 257. " Acid, 259. " and Alcohol Radicals, 261. " " Chlorine, 263. " " Hydrogen, 260. " " Iodine, 263. " " Sulphur, 263. " Anhydride, 260. " Compounds with Bromine, 263. Arsines, 261. Arsenide of Tin, 260. Arsenious Anhydride, 258. 257. " Bromide and Iodide , 263. Sulphide, 263. Arsenites, 259. Arseniuretted Hydrogen, 260. Artiad Elements, 300. Artiads, Definition of, 59. Atacamite, 331. Atmosphere, 114. Atomicity, 55. " of Acids, 93. 11 of Radicals, 59. Atomic Ratio, 448. " Weight, 25, 28. Atomic Weights, Relations of, 195. Atoms, Definition of, 24. " Negative, 168. " Positive, 168. Quantivalence of, 59, 132. " True Idea of, 70. Atom-fixing Power. 57. Augite, 356. Auric Salts, 224. Auriferous Quartz, 222. Aurous Salts, 224. Axinite, 228. Azurite, 330. Baric Chloride, 344. 36. ' Hydrate, 345. 82. Nitrate, 344. Oxide, 345. 35. Peroxide, 345. 203. Sulphide, 345. Bario-platinic Chloride, 426. Bario-stannous Chloride, 435. Barium, 344. Bases, Definition of, 80. Basic Ferric Hydrates, 386. " Radicals, 83. " Salts, 87. Basicity of Acids, 93, 465. Beauxite, 408. Behenic Acid, 488. Benzamide, 76, 243. Benzine, 482. Benzoic Acid, 501, 503. 482. " Alcohol, 601. " Ether, 493. Benzoin Gum, 603. Benzol, 477, 482. 235. Benzoyl, 503. Berthierite, 273. Beryl, 363, 456. Berzelianite, 320. Bismuth, 275. and Alcohol Radicals, 276. Basic Nitrate, 278. Compounds with Oxygen, 277. " " Sulphur, 278. Glance, 275. Magistery of, 278. Oxychloride of 276. Bismuthic Compounds, 277. Bismuthous Compounds, 276, 277, 278. Black Ball, 214. Blast Furnace, 380. Bleaching, 207, 314. " Powder, 341. Blende, 357. Bloom, 380. Bloomery Forge, 380. Blue Pill, 333. Blue Vitriol. 329. Bog Ore, 378. Bone Black, 458. Boracite, 232. Borax, 230. 229. Boric Acid, 229. 86. " Anhydride, 86, 229. 228, 231. " Bromide, 231. " Chloride, 231. " Fluoride, 231. , INDEX. Boric Sulphide, 232. Borofluoric Acid, 231. Boron, 228. Botryogen, 379. Bournonite, 273. Brackets, Use of, 74. Braunite, 373. Breithanphite, 365. Bricks, 411. Britannia Metal, 266. Brochantite, 330. Bromhydrine, 505. Bromine, 210. 499, 504. Bromoform, 494 Brookite, 430. Brown Clay Iron Stone, 378. Brown Hematite, 378. Brucite, 354. Brunswick Green, 331. Bunsenite, 365. Bunsen's Cell, 164. Burning, 114. Butyl, 4$4. Butylic Alcohol, 485. " Glycol, 505. " Hydride, 477. Butylene, 477. Butyric Acid, 488. " Anhydride, 493. " Ether, 492. " Butyryl, 484. 0. Cacoxenite, 379. Cadmio-Zirconic Fluoride, 440. Cadmium, 359. Caesium, 217. Calamine, 357. Calcareous Marl, 340. Calcic Acetate, 495. Carbonate, 340. 344. Chloride, 343. Chromate, 403. Fluoride, 343. 207, 452. Hydrate, 341. 82, 96, 313. Hyposulphite, 315. Nitrate, 344. Oxalate, 464. Oxide, 341. Peroxide, 342. Persulphide, 313. Phosphate, 343. 250. Silicate, 343- Sulphate, 342. 313. Sulphide, 313. Sulphite, 315. Calcined Magnesia, 354. Calcite, 340. Calcium, 340. Calomel, 334. Calorific Intensity, 119. " Power, 118, 122. Cane Sugar, 521. Capric Acid, 488. Caproic Acid, 488. Caprylic Acid, 488. Carbolic Acid, 502. Carbon 458. 115,467. Carbonic Acid, 462. " Anhydride, 461. 465. Carbonic Chloride 478. " Oxide, 462. 463. 44 Sulphide, 466. 478. CarbonyL, 39, 463, 484. Carnallite, 216. Carnelian, 445. Carre's Apparatus, 24L Cassiterite, 433. Caustic Potash, 216. " Soda, 214. Celestine, 344. Cementation, 382. Cerite, 364. Cerium, 364. Cerotene, 477. Cerotic Acid, 488. " Alcohol, 485. Cerusite, 346. Cervantite, 270. Cetene, 477. Cetylic Alcohol, 486. Chabaiite, 410. Chateostibite, 273. ' Chalcotrichite, 329. Chalcedony, 445. Chalk, 340. Chameleon Mineral, 377. Charcoal, 458. " Animal, 458. Chemical Change, Characteristics of; 3, 110- Chemistry, Definition of, 3 Chili Saltpetre, 215. Chinese Wax, 488. Chiolite, 408. Chloanthite, 365. Chloracatic Acid, 67. Chlorhydrines, 402, 504, 516. Chloric Acid, 209. " Peroxide, 209. Chlorine, 207. - 208, 231, 233, 341, 399, 452, 471, 493. " Compounds with Oxygen, 209. Chlorite, 356, 410. Chlorochromic Anhydride, 404. 399. Chloroform, 494. 38, 57. Chlorous Acid, 209. 44 Anhydride, 209. Choke Damp, 461. Chromates, 402. Chromatic Spectra, 176. Chrome Alum, 400. " Green. 399, 404. " Iron, 398. " Orange, 403- " Yellow, 403 Chromic Anhydride, 404. 44 Chlorhydrines, 402. 41 Chloride, 401. " Fluoride, 405 " Hydrates, 400, 82. " Nitrate, 401. " Oxalates, 401. 14 Oxides, 399. 14 Sulphates, 400. " Sulphides, 405. Chromite, 398. Chromium, 398. Chromous Chloride, 398. 44 Hydrate, 399. Chrysoberyl, 363, 408. Chrysolite, 356. Cinnabar, 332. IV INDEX. Cinnamene, 483. Cinnamic Acid, 503. Citraconic Acid, 514. Citric Acid, 519. Classification, Grounds of, 192. " Scheme of, 193. Clay Iron Stone, 378. Clays, 410. Cleavage, 152. " Eminent, 152. Coal, 458. Cobalt, 367. " Ammonio-Bases, 369. " and Oxygen, 368. " Bloom, 368. " Vitriol, 368. Cobalticyanides, 370. Cobaltine, 368. Coefficient of Expansion, 14. " M Absorption, 109. Cohesion, 12. 37. Coke, 459. Colcothar, 388. Colloids, 111. Color, 175. Columbite, 296. Columbium, 296. " Compounds of, 296, 297. Combustion, 114. " Heat of, 117. Common Salt, 213 Compound, Definition of, 7, 10. Radicals, 38, 83. Compounds, Classes of, 62, 80, 101. Conine, 249. Copiapite, 379. Copper, 328. " Ammouiated Compounds, 331. " Compounds with Oxygen, 329. " Fluohydrate, 331. " Glance, 330. " Pyrites. 328, 330. " Salts, 329. Coquimbite, 379. Corrosive Sublimate, 335. Corundum, 408. Covelline, 330. Cream of Tartar, 217. 214, 268. Creosote, 502. Cresylic Alcohol, 503. Crith, 2. Crocoite, 398. Crocus Martis, 388. Crotonic Acid, 498. Crotonylene, 477. Cryolite, 207, 408. Crystalline Axes, 138. " Form, 138. " " Identity of, 146. Structure, 152. Symmetry, 137. " Systems, 138. Crystalloids, 111. Crystals, Irregularities of, 148. " Modifications on, 143. " Twin, 150. Cumin, Essential Oil of, 501. Cuminic Acid, 501, 503. " Aldehyde, 501. Cumol, 477. Cumylic Alcohol, 501. Cupellation, 220. Cupric Carbonates, 330. " Chlorides, 331. Hydride, 331. Nitrates, 330. Oxide, 329. 84. Oxychloride, 331. Phosphate, 330. Silicate, 330. Silico-fluoride, 452. Sulphate, 329. 54. Sulphides, 330. Cuprous Chloride, 331. Current, Electric, Negative, 157. 4 " Positive, 157. 1 " Strength of, 160. ' " Unit of, 169. Cyanates, 472. Cyanetholine, 473. 77. Cyanhydrine, 505. Cyanic Acid, 471. 77- " Ethers, 472. 77. Cyanides, 468. Cyanite, 409. Cyanogen, 466. " Compounds with Chlorine, 471 Cyanuric Acid, 471. Cymol, 477. D. Danburite, 228. Dark Red Silver Ore, 220. Datholite, 228. Definite Proportions, Law of, 9. Dextrose, 522. Dialysis, 112. Diammonic-ferric Sulphate, 386. Diamond, 459. Diaspore, 408. Diatomic Acids. 93, 507 Dibasic Acids, 93, 268, 512. Dibromhydrine, 505. Dichlorhydrine, 516. Dicyanic Acid, 471. Didymium, 364. Diethoxalic Acid, 511. Diffusion Gaseous, 112. " Liquid, 110. Dimethoxalic Acid, 511. Dimetric System, 139. Dimorphism, 135, 252, 335. Dinitro-benzol, 482. Dioptase, 330. Diplumbic Chromate, 403- Disassociation, 128, 325 Prob. 38, 339 Prob. 30. Disinfectants, 207, 314. Dolomite, 355. Drummond Light, 341. Dufrenite, 379. Dufrenoysite, 263. Dutch Oil, 479. Earthen Ware, 411. Earthy Cobalt, 368. Electrical Conducting Power, 157. " Resistance, 157, 169. Electric Current, 156, 160, 169. Electricity, 155. " Intensity of, 161. INDEX. Electricity, Quantity of, 161. Electrolysis, 165. Electromotive Force, 159, 160, 169. " " Unit of, 169. Electroplating, 167, 221. Elements, 7 " Classes of, 192. " Distribution of, 8. " Individuality of, 70, 190. Emerald Nickel, 365. Emery, 408. Emplectite, 279. Enargite, 263. Epidote, 410, 456. Epsom Salts, 355. Equivalency, Chemical, 54. Equivalents, 54. Erbium, 363. Erubescite, 330. Erythrite, 368, 519. Etheric Acids, 508. " Secondary, 510. Etherification, 491. Ethers, 90, 491. 492. " Compound, 492. " Haloid, 493. u of Glycerine, 517. " Mixed, 492. Ethomethoxalic Acid, 511. Ethyl, 484. Ethylamine, 58, 242, 245, 472. Ethyl-glycollic Acid, 511. Ethyl-lactic Acid, 510. E thy lie Acetate, 491. " Alcohol, 485. Chloride, 492. Cyanide, 489. Glycol, 505. Hydride, 477. Iodide, 479, 494. Sulphate, 491. Ethylene, 477. 479, 480, 504, 508. Bromide, 479. 61, 480, 506. " Bromhydrine, 505. 506, 507. " Chloride, 479. Cyanhydrine, 505- - 609. ' Ether, 505. " Glycols, 506. " Iodide, 479. " Oxide, 505. Ethylidene Chloride, 509. " Cyanhydrine, 510. Ethyline, 517. Essential Oil of Cumin, 501. Oils, 477, 481. Eudialyte, 439. Euxenite, 296, 441. Exchanges, Theory of, 189. Expansion by Heat, 14. P. Fat Acids, 90, 487. " " Isomers of, 49L Fats, 518. Fayalite, 379. Feldspars, 409. Fergusonite, 296. Fermentation, 523. Ferrates, 389 Ferric Acetate, 3S6. " Arseniates, 379. Ferric Chloride, 386, 387. ~ 470. ' Ferrocyanide, 470. Hydrates, 378\ 386. Nitrate, 386. Oxalate, 386. Oxide, 378, 388. 469. Silicates, 379. Sulphate, 379, 386. Sulphides, 378, 388. Ferricyanides, 470. Ferrocyanides, 469. Ferrous Carbonate. 378, 384. " Chloride, 385, 387. 235, 470. " Ferric Oxide, 378, 388. " Hydrate, 385, 82. " Nitrate, 385. '* Oxalate, 385. " Oxide, 388. " Phosphate. 385. " Sulphate, 385. 226. " " JMpotassic, 393. " Sulphide, 388. 309, 469. Fibroferrite, 379. Fire Damp, 478. Flint, 445. Float Stone, 445. Fluorine, 207. Fluor Spar, 343, 207. Formic Acid, 488, 490. 464, 514. Formyl, 484. Forsterite, 457. Fowler's Solution, 259. Franklinite, 378. Freieslebenite, 273. Fumaric Acid, 514. " Series, 514. Fusible Alloy, 276. G. Gadolinite, 363, 441. Gahnite, 408. Galena, 346. Gallic Acid, 623. Galvanic Battery, 161. Garnet, 410, 448, 457. Gaseous State, 12. Gases, Molecular Condition of, 17. Gas, Illuminating, 478. Gay Lussac's Law, 48. Genthite, 365. German Silver, 366. Gibbsite, 408. Gilding, 226. Glass, 214, 216, 447. Glaucodot, 368. Glockerite, 379. Glucinnm, 363. Glucose, 521. 524. Glucoside, 522. Glyoeric Acid, 516. Glycerides, 518. Glycerine, 93, 515. 497. 498, 518. Chlorhydrines, 516. Ethers of, 617. Glyceryl, 484, 616. " Bromide, 618. Chloride, 61. Chlorhydrine, 516. 617. " Cyanide. 618. Glycide, 517. Glycocoll, 244, 77. INDEX. Glycol, 92, 504. " Condensed, 506. " Sulphur, 505. Glycollic Acid, 92, 505, 508, 509. Glycolyl, 484. Glyoxal, 511. - 512. Glyoxalic Acid. 611. 512. Gold, 222. " Bromide, 225. " Chloride, 224. 226. " Iodides, 225. " Oxides, 225. " and Sodium Hyposulphite, 225. " Sulphides, 225. Gbthite, 378. Granites, 411. Graphite, 459. Graphitic Acid, 459. Gray Iron, 381. Greenockite, 359. Green Stone, 411. " Vitriol, 379, 384. Grove's Cell, 163. Guano, 34a Gum, 521. Gun Cotton, 66, 522. Gunpowder, 216. Gypsum, 308, 342. H. Halloysite, 410. Halotrichite, 409. Hard Water, 340. Harmotome, 410, 456- Hauerite, 373. Hausmannite, 373. Heat, 13. 1 of Chemical Combination, 123. 1 of Combustion, 117. " Expansion by, 14. " Latent, 16. * Sources of, 16. " Specific, 16. " Unit of, 14. Heavy Spar, 344. Hematite, 378. Hemihedral Forms, 145. Hemitropes, 150. Hercynite, 408. Hessite, 321. Heulandite, 410, 457. Hexagonal System, 140. Hexatomic Organic Compounds, 620. Hexylene lode-hydride , 521. ' Hippuric Acid, 244, 77. Holohedral Forms, 146. Homologous Series, 475. Homologues, 475. Honey, 522. Hornblende, 356. Horn Silver, 220. " Stone, 445. Hydrates, 80, 230, 445. Hydric Oxide, 201. Peroxide, 202. Persulphide, 312. Selenide, 320. Sulphide, 309. 310, 311, 387. Tefluride, 320. Hydriodic Acid, 210. 84, 516, 520. Hydrobromic Acid, 210. 84. Hydrocarbon Radicals, 483. Hydrocarbons, 474. Hydrochloric Acid, 208. 84, 207, Hydrocyanic Acid, 468. - 40, 371, 469, 489. Hydrofluoboric Acid, 232. Hydrofluoric Acid, 207. Hydrogen, 201. - 202, 260, 478, 499. Alcoholic Atoms, 94, 244, 465. " Basic Atoms, 94, 244, 465. Hydrogenium, 425. Hydromagnesite, 355. Hydro-silicic Fluoride, 452. Hydro-titanic Fluoride, 431. Hydroxyl and its Analogues, 202, 302, Hypochlorous Acid, 209. 504. Hypochlorous Anhydride, 209. Hypophosphorous Acid, 252, 255. Hyposulphites, 315. Hyposulphurous Acid, 313, 315. Ignition, Point of, 122. Ilvaite, 379, 457. Imides, 245. Indelible Ink, 221. Indigo Copper, 330. Indium, 359. Ink, 523. lodic Acid, 314. Iodine, 210. 493. lodoform, 494. lolite, 456. Indium, 422. Iridium Compounds, 422. Iridosmine, 418. Iron, 377. 39. Cast, 380. Metallurgy of, 879. Olivine, 379. Passive Condition of, 384. Pyrites, 308, 378. Wrought, 380. Iso-acids, 491, 507. Isoamylic Alcohol, 497. Isohexylic Alcohol, 497. Isohexylic Iodide, 521. Isologne, 475. Isomaleic Acid, 514. Isomerism, 133. " in Lactic Family, 511. Isometric System, 138. Isomorphism, 68. Isomorphous Mixtures Notation for, 274. Isopropylic Alcohol, 496. Itaconic Acid, 514. Ivory, Black, 458. J. Jamesonite. 273. Jarosite, 379. Jasper, 445. Kakodyl, 261. Kaolinite, 410. Ketones, 495. Kieserite, 356. Kobellite, 279. Kupfernickel, 365, INDEX. vii Labradorite, 409. Lactaniide, 244, 245. Lactic Acid, 94, 509, 611. 524. Lactic Family, 507. " " Isomerism in, 511. " " Normal Acids, 508. " " Secondary Acids, 509. " " Tertiary Acids, 511. Lactimide, 245. Lac tme thane, 244. Lactyl, 484. Lakes, 412. Lamp Black, 458. Lanthanite, 364. Lanthanum, 364. Lapis Lazuli, 410. Laughing Gas, 239. Laurie Acid, 488. Lava, 411. Law of Ampere, 17. " Definite Proportions, 9. " Gay Lassac. 48. ' Mariotte, 12. " Multiple Proportions, 10. 41 Ohm, 159. Lazulite, 409. Lead, 346. " Soap, 515. Leucic Acid, 509. Leucite, 409, 456. Leukon, 454. Levulose, 522. Light, 174. Light Red Silver Ore, 220. Lime, 341. 81, 482. " Chloride of, 341. Limestone, 340.' Lime Water, 341. Lininite, 378. Limonite, 378. Linnaeite, 368. Liquation, 272. Liquid State, 12. Litharge, 347. Lithium, 217. Loadstone, 383. Lunar Caustic, 220. M. Magnesia Alba, 355. Magnesic Carbonate, 355 " Chloride, 356. 361. " Hydrate, 354. 81. " Oxide, 354. Silicates, 356. " Sulphate, 355. Magnesioferrite, 378. Magnesite, 355. Magnesium, 354. 61. Magnetic Pyrites, 378. Magnetite, 378. Malachite, 330. Malacone, 441. M.ileic Acid, 514. Malic Acid, 515, 520. Malonic Acid, 505, 512. Malonyl, 484. Manganblende, 373. Manganese, 373. Manganese, Brown , 374 " Red, Oxide of, 374. " Spar, 373. Manganic Chloride, 375. Dioxide, 375. 207, 300. " Hydrate, 375. Manganite, 373. Manganocalcite, 373. Manganous Compounds, 374. " Silico-fluoride, 452. Manna, 520. Mannite, 520. Mannitic Acid, 520. Marble, 340. Marcasite, 378. Margaric Acid, 488. Mariotte's Law, 12. Marsh Gas, 478. 486. " " Series, 477, 478. Massicot, 346. Melaconite,329. Melene, 477. Melissic Acid, 488. " Alcohol, 486. Menaccanite, 378. Meneghinite 27& Mercaptan, 487. Mercuramine, 336. Mercuric Chloride, 335 Cyanides. 467. Iodide, 335 Nitrate, 333. 334. Oxide, 333. Sulphate, 334. Sulphide. 334. 332. Mercurous Chloride, 334. Chromate. 399. Nitrate, 333. Oxide, 333. Sulphate, 333. Sulphide, 334. Mercury, 332. " Ammoniated Compounds, 335. Mesaconic Acid, 514. Mesitite,378. Metaphosphoric Acid, 253. Metastannic Hydrate, 436. Metathesis, Conditions of, 37. Metathetical Reaction, 36. Methyl, 72, 484. Methylamine, 242. Methyl-gly collie Acid, 510. Methyl-phenyl, 483. Methylic, Alcohol, 485. " Hydride, 477. Miargyrite, 273. Mica, 356, 410. Microcosmic Salt, 254. Millerite, 365. Mimetine, 348. 291. Minium, 347. Mispickel, 257, 378. Mixtures, Distinction from Compounds, 10. Molasses, 522. Molecular Condition of Gases, 17. " Compounds, 132. " Structure, 63, 76, 474, 476, 510, 525. Molecular Weight, 18. " " Determination of, 126. Molecules, Definition of, 11. 14 Constitution of, 131. Tin INDEX. Molecnles, Sum of Atomicities., 122. Molybdate of Ammonia, 321. Molybdenite, 321. Molybdenum, 321. Molybdic Anhydride, 321. Monatomic Organic Compounds, 485. Monazite, 441. Mono-acetine, 517. Monoclinic System, 141. Monometric System, 138. Mordants, 412, 442. Morphine, 249. Mortar, 341. Mosaic Gold, 438. Mucic Acid, 522. Multiple Proportions, Law of, 10. Mundic, 388. Muriatic Acid, 208. Myristic Acid, 488. Mysorin, 330. N. Nagyagite, 321. Names of Binary Compounds, 101. " of Elements, 101. " of Ternary Compounds, 104. Napthaline, 483. Natrolite, 410, 456. Natural Colors, 176. Naumannite, 320. Needle Ore, 279. Niccoliferous Smaltine, 365. Niccolous Chloride, 366 " Cyanide. 371. " Nitrate, 366. " Sulphate, 366. Nickel, 365. " and Oxygen, 366. " Glance, 365. " Green, 365. " Vitriol, 365. Nicotine, 249. Niobium, 296. Nitres, 215, 216. Nitric Acid, 234. - 236, 238, 239, 240, : 317, 347. Anhydride, 236. " Oxide, 238. 236. " Peroxide, 237. Nitriles, 245. Nitro-benzol, 66, 482. Nitrogen, 233. 467. Nitrogen , Bromide of, 250. " Chloride of, 250. " Iodide of, 250. " Oxides of, 234. Nitro-glycerine, 516. Nitrous Acid, 236. Anhydride, 236. Oxide, 239, 240. Nomenclature, 100. " Lavoiserian, 102. Notation, 33. 0. Octahedrite, 430. CEnanthylic Acid, 488. (Erstedite, 441. Ohm's Law, 159. Oil of Bitter Almonds, 501. 77. " Garlic, 498. " Meadow Sweet, 504. Oil of Mustard, 498. " Vitriol, 318. ** Winter Green, 504, Oils, Drying, 518. " Essential, 481, 501. Olefiant Gas, 479. 486. " Series, 477, 479. Olefines, 479. " Acid, 508. Oleic Acid, 498. Oleines, 618. Oligoclase, 409, 456. Olivine, 356. Onofrite, 320. Onyx, 445. Oolite, 340. Opal, Common. 444. " Varieties, 445. Optical Crystallography, 153. Orangeite, 441 Organic Chemistry, 473. " Compounds, 473. Oriental Amethyst, Ruby, and Topaz. 408. Orpiment, 263. Orthite, 441. Orthoacids, 229, 232, 235, 252. Orthoclase, 409. Orthophosphoric Acid, 252. Orthorhombic System, 141. Osmic Compounds, 420. Osmium, 420. Oxalic Acid, 464, 505. 463. Oxamethane, 77, 244. Oxamic Acid, 77, 244. Oxamide, 76, 243. Oxatyl, 465. Oxalic Ether. 499. Oxidation, 301. Oxides, Metallic, 82. Oxybutyric Acid, 509. Oxygen, 300. 115, 125, 325. Oxygenated Radicals, 484. u Water, 202. Oxygen Compounds, 301. " Ratio, 451. Oxygen Salts, 88. Ozone, 302. Ozonides, 303. P. Pachnolite, 408. Palladious Nitrate, 424. " Sulphate, 424. Palladium, 423. Palmitic Acid, 488. Palmitines, 518. Paracyanogen , 467. Paraffine, 477. Paralactic Acid, 505, 508. Paraleucic Acid, 508. Paraluminite, 409. Parentheses, use of, 34. Parisite, 364. Pearl White, 276. Pelargonic Acid, 488. Perchloric Acid, 209. Perchromic Acid, 405. Periclase, 354. Perissad Elements, 201. Perissads, 59. Permanganic Acid, 377. INDEX. Perofskite, 430. Petalite, 457. Petroleum, 458. Pewter, 434. Pharmacosederite, 379. Phenols, 501. Phenyl, 482. " Alcohol, 502. " Series, 477, 482, 501. " Series, Acids of, 503. Phenylene, 483. Phoenicochroite, 406. Phosgene Gas, 463. 508. Phosp nines, 256. Phosphoric Anhydride, 253. 86, 489. " Chloride, 256. 63,77,316,509. " Oxychloride, 257. " Sulphochloride, 257. Phosphorite, 343. Phosphorous Acid, 252, 257, 251. " Anhydride, 252. " Chloride, 256. 56, 493. " Iodide, 497. Phosphorus, 250. 255, 493. Red, 251. Phosphuretted Hydrogen, 255. Photography, 221. Physical Properties of Matter, 10. Physics, Definition of, 3. Pickeringite, 409. Picric Acid, 502. Pimelic Acid, 512. Pink Salt, 435. Pisanite, 379. Pitchblende, 293. Plaster of Paris, 342. Platinic Compounds, 426. Platinous Compounds, 427. Platinum, 425. Bases, 428. " Sponge, 418. Plumbates, 348. Plumbic Acetate, 347. 348, 349. " Carbonate, 348. " Chloride, 348. 349. " Chromate, 403. " Hydrates, 347. " Nitrate, 347. 40, 237, 240, 466. Oxide, 346. " Peroxide, 347. 305. " Phosphate, 348. " Sulphate, 348. " Sulphide, 346. " Sulphocarbonate, 466. Poles, Positive and Negative, 165. Polybasite, 273. Polymerism, 134. Polymorphism, 133. Porcelain, 411. Porphyry, 411. Potassic Aluminate, 216. " Acetate. 478, 489, 493, 494. " Bicarbonate, 216. " Carbonate, 215. 467. " Chlorate, 209. 300. " Chloride, 216. * Chromate. 403. 300. " Cobalticyanide, 370. " Cyanate, 472. Cyanide, 468. 371, 469, 472, 513. " Bichromate, 403. 399, 400. " Dioxide, 216. Potassic Ethylate, 472. " Ferricyanide, 470. 469. " Ferrocyanide, 469. 463, 469. " Fluoride, 232. " Fluotantalate, 298. " Hydrate, 216. - 82, 84, 209, 357, 376, 463, 472, 480, 499, 504, 510, 513. " Manganate, 376. Nitrate, 216. 238. " Nitrite, 233. Oxalates, 464. " Oxides, 216. u Permanganate, 376. 377. u Persulphide, 312. " Pyroantimoniate, 269. " Rutheniate, 419. " Stannate, 436. " Sulphate, 312. " Sulphide, 312, 466. " Sulphohydrate, 312, 487. " Sulphocarbonate, 89. 466. Tartrates, 217, 268. Tetroxide,216. " Trichromate, 403. Potassio-ferrous Sulphate, 319. Potassio-iridic Chloride, 422. Potassio-iridous Chloride, 422. Potassio-magnesic Sulphate, 356. Potassio-osmic Chloride, 421. Potassio-palladic Chloride, 424. Potassio-rhodic Chloride, 422. " " Sulphate, 422. Potassio-ruthenic Chloride, 420. Potassio-stannous Chloride, 435. Potassio-zirconic Fluoride, 440. Potassium, 215. 465. Alum, 409, 413. Precipitate, Definition of, 36. " How represented, 35. " When formed, 37. Printing Ink, 460. Propione, 495. Propionic Acid, 488. 510. " Anhydride, 493. Propionyl, 484. Propyl, 484. Propylene, 477. Propylic Alcohol, 485. " Glycerine, 518. " Glycol, 505. " Hydride, 477. Proustite, 220, 263. Prussian Blue, 470. Prussiates of Potash, 469, 471. Prussic Acid, 468. Psilomelane, 373. Puddling, 382. Purple of Cassius 225, 437. Pyrargyrite, 220, 273 Pyroantimonic Acid, 269. Pyrochlore, 296, 441. Pyrolusite, 373. Pyromorphite, 348, 291. Pyrope, 449. Pyrophosphoric Acid, 252, 254. Pyrophyllite, 410. Pyrotartaric Acid, 512. Pyroterbic Acid, 498. Pyroxene, 457. Pyruvic Acid, 611. 512. Series, 611. INDEX. Q. Quantivalence, 55. " of Radicals, 59. Quartation, 223. Quartz, 444. " Varieties, 445. Quick Lime. 341. Quinine, 249. R. Radical, Atomicity of, 60, 132. " Definition of, 83. " Substances, 38, 131. Radicals, Acid, 83. Alcoholic, 73. " Basic, 83. Compound, 38, 484. Raimondite, 379. Rammelsbergite, 365. Reaction, Definition of, 34. Realgar, 263. Red Hematite, 378. " Liquor, 414. " Ochre, 378. " Oxide of Zinc, 357. Reduction, 301. Remingtonite, 368. Rhodic Salts, 421, 422. Rhodium, 421. Rhodonite, 373. Rhombohedron, 140. Rinman's Green, 370, RoccelHc Acid, 512. Rochelle Salts, 214. Roman Alum, 413. Rouge, 388. Rubidium, 217. Ruby, 408. Ruthenium, 419. Rutile, 430. S. Saccharic Acid, 520. Saccharine Bodies, 521. Sal Ammoniac, 247. Saleratus, 214. Salicine, 523. Salicylic Acid, 504. 502. Saligenine, 523. Sal Prunelle, 216. Sal Soda, 213. Salts, 86. " Acid, 87, 105. " Basic, 87, 105. " Neutral, 87. " Oxygen, 88. " Sulphur, 89. Salt of Sorrel, 464. Sand, 445. Sandstone, 445. Saponification, 493, 515. Sapphire, 408. Sarcolite, 456, 457. Sartorite, 263. Scalenohedron, 140. Scapolite, 410. Scheele's Green, 259. Scheelite, 322. Scheeltine, 322. Schorlomite, 379. Scolecite, 410. Scorodite, 379. Sebacic Acid, 512. Selenic Acid, 820. Selenite, 342. Selenium, 319. Senarmontite, 268. Serpentine, 356. Siderite, 378. Siegenite, 368. Silica, 444. Silicates, 446. " Native, 448. 1 ' of Organic Radicals , 454. Siliceous Sinter, 445. Silicic Acid, 445. 86. " Anhydride, 444. " Bromide, 453. " Chloride, 452. 61, 455. " Ethers, 454. " Ethide, 454. " Fluoride, 451. " Hydrates, 445. " Hydride. 453. " Hydrochloride, 454. ' Iodide, 453. " Methide, 454. " Sulphide, 451. Silico-fluoric Acid, 452. Silico-fluorides, 452. Silicon, 444. Silver, 220. Silver Glance, 220. Slags, 380, 397, 447. Slate, 411. Smalt, 370. Smaltine, 368. Smithsonite, 357. Soap, 214, 216, 515. Soda-lime, 282. Sodic Alum, 413. " Aluminate, 414. " Arsenite, 263. " Bicarbonate, 214. " Carbonate, 213. 214. 361. " Chloride, 213. 208. " Disulphate, 319. 87, 316. " Ethide, 496. " Ethylate, 473, 492. " Hydrate, 214. 82,84,350,412. " Hyposulphite, 315. " Methide, 489. " Nitrate, 215. 234. " Oxide, 215. Peroxide, 215. " Phosphate, Common, 254. 361, " Stannate, 436. " Sulphates, 319. 35, 213. " Sulphide, 312. 213. " Sulphite, 315. Sodio-iridic Chloride, 422. Sodio-platinic Chloride, 426. Sodio-rhodic Chloride, 422. Sodio-zirconic Fluoride, 440. Sodium, 213. 481, 483, 492. Solder, 434. Solid State, 11. " " Symbol for, 35. Soluble Glass, 445. Solution, 107. " Curves of, 108. INDEX. Solution, Differs from Chem. Change, 110. " How indicated, 36. " of Gases, 109. Spathic Iron, 378. Specific Gravity, 1. " of Vapors, 21. " Heat, 16. Spectra by Absorption, 187. " Chromatic, 176. Spectroscope, 176. Spectrum Analysis, 181. Specular Iron, 378. Speiss, 365. Spermaceti, 488. Sphaerosiderite, 378. Sphene, 430. Spiegeleisen, 381. Spinel, 408. Spodumene, 457. Stannates, 433. Stannic Chloride, 435. " Hydrate, 436.* ' Oxide, 437. " Sulphides, 437. Stannous Chloride, 434. 208. " Hydrate, 436. " Oxide, 437. " Oxychloride, 434. " Sulphide, 437. Starch, 521. Stearic Acid, 488. Stearine, 516. Steel, 382. Stephanite, 273. Stibines, 271. Stiboniums, 271. Stilbite, 410, 456. Stochiometry, 41. " Rules of, 42, 47, 48, 49. Strontianite, 344 Strontic Sulphate, 345. " Sulphide, - 345. Strontium, 344. " Compounds of, 344, 345. Suberic Acid, 512. Substitution, 65. Succinamic Acid, 244. Succinamide, 243. 245. Succinic Acid, 92, 505, 612, 514. " Series, 612. Succinyl, 484. Sucroses, 521. 522. Cane, 521. " Fruit, 521. " Gripe, 521. 35. " of Lead, 347. of Milk, 521. Sulphantimonites, 273. Sulphates, 319. Sulphides, 309. 313. Sulphites, 314. Sulphoarseniatcs, 263. Sulphoaramites, 263. Sulpho-bismuthites, 279. Sulpho-carbonic Acid, 466. Sulphocyanates, 473. Sulphohydric Acid, 309. Sulphur, 308. 312, 314, 315, 316. " Anhydrides, 263. " Compounds with Oxygen, 313. " Flowers of, 309. Sulphur, Liver of, 312. Milk of, 309. Suits, 89, 263. Sulphuretted Hydrogen, 309 Sulphuric Acid, 316. 35, 36. 300, 314, 463, 486, 491, 493. " Nordhausen, 319. 316. " Anhydride. 315. 35, 40, 86. Chloride, 319. Sulphurous Acid, 314, 316. Anhydride, 313. 816. " Chloride, 319. Sulphurylic Chloride, 316. Sycocerylic Alcohol, 60L Syepoorite, 368. Sylvanite, 321. Symbols, 33. " Bracketed, 74. Empirical, 69. " Graphic, 70. " Rational, 69. Synaptase, 623. Synthesis, 9. Synthetical Reaction, 35. Systems of Crystals, 138. T. Tabular Spar, 343. Talc, 358. Tannic Acid, 523. Tannine, 523. Tanning, 523. Tantalic Acid, 298. " Anhydride, 298. " Chloride, 298. " Fluoride, 298. Tantalite, 297. Tantalum, 297. " Compounds of, 298. Tartar Emetic, 268. Tartaric Acid, 519, 268. 217. Tartronic Acid, 516. Telluric Acid, 320. Tellurium, 319. Tellurous Anhydride, 320. Temperature. 13. Tennantite, 263. Tension of Gases, 12. Tephroite, 373. Ternary Compounds, Names of, 104. Test Paper*,, 89. Tetradymite, 276. Tetragonal System, 139. Tetrahedrite, 273, 274, 330. Tetratomic Organic Compounds, 619. Thallium, 222. Thenard's Blue, 870. Theory of Exchanges, 189. Thiacetic Acid, 77. Thomsenolite. 408. Thomsonite, 410. Thoric Chloride, 441. Thoritv, 441. thorium, 441. Tin, 433. and Alcohol Radicals, 438.' Butter of, 434. Pyrites, 433. Salts, 4-'M 439. Stone, 433. Tincal, 230. INDEX. Titanic Iron, 378. Titanium, 430. " Compounds of, 430, 431, 432. Titanous Chloride, 430. " Oxide, 432. Toluol. 477. 501. Toluylic Acid, 503. Topaz, 409. Tourmaline, 228. Trachyte, 411. Travertine, 340. Triacetine, 517. Triatomic Organic Compounds, 515. Tribasic Acids, 85, 465, 518. Tricarballylic Acid, 518. Triclinic System, 142. Trie thy line, 517. Trimetric System, 141. Triphylite, 379. Triplite, 373. Tripoli, 445. Troilite, 378. Tufa, 340. Tungsten, 322. " Compounds of, 322. Tungstic Acid, 322. " Anhydride, 322. Turnbull's Blue, 471. Turpeth Mineral, 334. Turpentine, Oil of, 477, 481. Turquois, 409. Twin Crystals, 150. Type Metal, 265, 346. Types Chemical, 62, 69. " Condensed, 64. " Mixed, 65. U. Ultramarine, 410. Unit of Atomic Weight, 27. " Current, 169. " Electromotive Force, 169. ' Heat, 14. " Molecular Weight, 27. ' Quantivalence, 201. " Resistance, 169. " Specific Gravity, 2. Volume, 2. ' Weight, 2. Unitary Theory, 95, 132. Uranite, 293. Uranium, 293. Uranium and Oxygen, 295. Uranous Chloride, 294. Uranyl, 293. Chloride, 293. Fluoride, 293. Hydrate, 293. Nitrate, 293. Potassic Sulphate, 293. Urea, 243, 472, 473. V. Valentinite, 268. Valeramide, 245. Valerianic Anhydride, 493. Valeric Acid, 488. Valerolactic Acid, 509. Valeryl,484. Valerylene, 477. Vanadates, 292. Vanadic Anhydride, 292. Vanadinite, 291. Vanadium, 291. " Nitride of, 292. " Oxides of, 291. Vanadyl, 291. Vegetable Kingdom, Function of, 525. Vermilion, 334. Vesuvianite, 456. Vinyl, 484. ; Alcohol, 497. " Series, 497. Vitriols, 319. 329, 358, 379. Vivianite, 379. Voltaic Battery, 161. Voltaite, 379. Volume, 1. Vulcanized India Rubber, 309. W. Wad, 373 Water, 201. 80, 81, 202, 480. " of Crystallization, 94. " Glass, 445 Waves of Light, 176. Wavellite, 409. Weight, 1. White Iron, 381. " Lead, 348. " Vitriol, 358. Witherite, 344. Wittichenite, 279. Wolfram, 322. Wollastonite, 457. Woody Fibre, 521. Wulfenite, 321. X. Xanthosiderite, 378. Xylol, 477. Y. Yeast, 523. Yellow Ochre, 378. Yenite, 379. Yttrium, 363. Z. Zaratite, 365. Zeolites, 410. Zinc, 357. 35, 387, 479. and Alcohol Radicals, 358. Butter of, 358. Methide. 478, 496. Zincic Carbonate, 358 361. Chloride, 358. Hydrate, 357. Oxide, 357. 361. Sulphate, 358. 54. Sulphide, 361. Zinkenite, 273. Zircon, 440. Zirconia, 440. Zirconium, 439. " Compounds of, 439, 440. Zoisite, 457. THE HAMILTONIAN SYSTEM OF LOGIC AND METAPHYSICS. A TREATISE ON LOGIC; Or, The Laws of Pure Thought. Comprising both the Aristotelic and Hamiltonian Analyses of Logical Forms, and some Chapters on Applied Logic. By FRA.NCIS BOWEN, Alford Professor of Moral Philosophy in Harvard College. Sixth Thousand. 12mo. Cloth. 450 pp. $ 2.00. Extract from the Preface. " Among English authors, after Sir William Hamilton, I have been chiefly indebted to Prof. Mansel ; and have also derived much help from Thompson's excellent ' Outlines of the Laws of Thought ; but the work would not have been carried on in the same spirit in which my predecessors began it, if I had not ven- tured respectfully to dissent from some of their doctrines, and even to present some opinions which will very likely be found to have no other merit than that of origi- nality Throughout the work I have kept constantly in view the wants of learners, much of it having been first suggested while attempting to expound the science in my own class-room." From James Walker, D. D., LL.D., late President of Harvard University. It is, so far as I am able to judge, singularly complete, and yet is brought within reasonable limits. As an English text-book in this department of philoso- phy I have seen nothing to be compared with h." From E. O. Haven, LL.D., late President of Untverrity ofMichiffan. " I have examined the Treatise on Logic ' by Prof. Francis Bowen with great care, having, indeed, used it as a text-book, and have found it the most thorough and systematic text-book on the subject with which I am acquainted. I think it fully supplies the purpose for which it was written, and in the hands of a good teacher, it furnishes all the aid that he or his class will need." From Prof. W. D. Wilson, Hobart Cottr.gr, Geneva, JV. K. " It is, in my opinion, an admirable compend of what is now taupht as Losn'c ; presenting with great clearness and skill the rival systems of Aristotle and Ham- ilton, with a very full and fair exhibit of the thoughts and opinions of all others whose writings are of note on the subject." 2 BOWEN'S HAMILTON'S METAPHYSICS. THE METAPHYSICS OF SIR WILLIAM HAMILTON. Collected, Arranged, and Abridged for the Use of Colleges and Pri- vate Students. By FRANCIS BOWEN, A. M., Alford Professor of Moral Philosophy in Harvard College. Ninth Thousand. 12mo. Cloth. Price, $2.00. The publisher takes pleasure in stating that this work has met with great favor, and haa already been introduced as a text-book hi all the principal colleges and institutions of learning in the country. Extract from the Editor's Preface. " As any course of instruction in the Philosophy of Mind at the present day must be very imperfect which does not comprise a tolerably full view of Hamilton's Metaphysics, I have endeavored, in the present volume, to prepare a text-book which should contain, in his own language, the substance of all that he has written upon the subject. For this purpose, . the ' Lectures on Metaphysics ' have been taken as the basis of the work ; and I have freely abridged them by striking out the repetitions and redundancies in which they abound, and omitting also, in great part, the load of citations and references that they contain, as these are of inferior interest except to a student of the history of philosophy, or as marks of the stu- pendous erudition of the author." The Rev. Dr. Walker, late President of Harvard University, in a note to the editor, says of the book : " Having examined it with some care, I cannot refrain from congratulating you on the success of the undertaking. You have given the Metaphysics of Sir William Hamilton in his own words, and yet in a form admira- bly adapted to the recitation-room, and also to private students." Prof. J. Torrey, University of Vermont. " The editor has left scarcely anything to be desired. The work presents in short compass the Philosophy of Sir W. Hamilton, in his own language, more completely and satisfactorily than many students would find it done by the author himself in the whole series of his voluminous and scattered productions." From the North American Review. " Mr. Bowen's eminence as a scholar, thinker, and writer in this department, his large experience as a teacher, and his experimental use of the ' Lectures ' as a text- book, might have given the assurance, which he has fully verified, that so delicate an editorial task would be thoroughly, faithfully, and successfully performed. We cannot doubt that if Sir William were still living, the volume would have his cor- dial imprimatur ; ai/d the students of our colleges are to be congratulated that, the labors of the great master of Metaphysical Science are now rendered much more availing for their benefit, than they were made, perhaps than they could have been "s, by his own hand." 3