Chemistry

Front matter

WORKS ON CHEMICAL SCIENCE.

PUBLISHED BY BLANOHARD AND LEA.

A MANUAL OF ELEMENTARY CHEMISTRY; THEORETICAL AND PRACTICAL. By d-EORaE EoWNES, Ph. D. &c. Erom the seventh revised and corrected London edition. With one hundred and ninety-seven illustrations. Edited by Robert Bridges, M. B. In one large royal 12mo. volume of 600 pages. Price, in leather $1.65 ,• extra cloth $1.50.

Preface

The Student of Chemistry has already a large selection of books for his guidance. In the ^^ Fiest Step" of Mr. Galloway, of about ninety pageS; and in the translated "Handbook" of Grmelin; as 3^et incomplete, but filling, at the present date, fourteen octavo volumes, and covering nearly eight thousand pages — -we have the two extremes of English Chemical literature. There are numerous books on the Science, which occupy an intermediate position, some, under the title of "Elements," treating the subject so profoundly as to alarm a beginner; while others are so filled with symbols, formulse, and mystical language, as to conceal the great facts of Chemistry in a haze of technicality.

We see no reason for adopting an esoteric method of dealing with this Science. On the contrary, it appears to us, that without departing from the true objects of Chemistry, its facts admit of explanation, in a form to be intelligible to any educated man. It is not necessary to the progress of this Science, that its language should change with the opinions of every new theorist. The numerical value of atoms and volumes is not of so much importance to a student, as a correct description of the properties and uses of the substances which they represent. On this part of the subject, much labor appears to us to have been wasted by certain writers. They have apparently been engaged in working out an idea, and seeking for some Utopian standard of perfection, in a new system of notation : but in endeavoring to settle contested points on a firmer basis, they have incurred the risk of unsettling everything. Thus, instead of pursuing the inductive method, and fitting hypotheses to facts, they have introduced a deductive system, by which facts are made to bend to hypotheses ; and the elementary composition of bodies is altered, in order that they may correspond to certain artificial types. There is an old French proverb which it may be well to bear in mind, in reference to

PEEFACE.

While we do not undervalue the usefulness of a correct language to express the facts and theories of a Science, we have the strongest objection to frequent and capricious changes, in which the good is uncertain and prospective, while the evil is certain and immediate. Chemistry is not the Science of one nation, of one profession, or of one section of chemists. Among civilized nations it has now a community of language, and by this language, it is more closely linked to Arts, Manufactures, and Medicine, than any other branch of knowledge ; hence, changes, to be useful, should be such as are required by urgent necessity, and are likely to command general acceptance by their reasonableness and expediency. After all, it must be remembered that these changes are not in the/acfe, but in a supposed improvement in the mode of expressing them ; and if only partially adopted, they necessarily lead to confusion. Eeasoning from the past to the present, it is not too much to infer that a student of Chemistry must be prepared for a new crop of systematic names, and a new classification of elements and compounds, every ten years.

Our intention in the preparation of this volume has been, not to furnish a Treatise on the Science, but to provide the student, and general reader, with a plain introduction to the subject. With ample materials at our disposal to produce two volumes in place of one, we have studiously endeavored to compress within these pages, a selection of the more important facts and doctrines of Modern Chemistry. We have adopted for the explanation of these facts, that simple chemical language Avhich has found acceptance in the Schools and Colleges of Great Britain, France, and Germany, as well as in the best treatises on the Science.

In addition to the general properties of bodies, we have attached to the description of each substance, a summary of its most important characters, with an account of the special tests required for its detection. The student will thus have in this book a Manual of Practical Chemistry. As an adjunct to this branch of the Science, the subject of Practical Toxicology has been introduced in reference to the most important poisons, and the processes for their detection. We have also treated, as fully as our space would permit, the chemical principles on which Photography is based, and have given some practical rules for the guidance of those who wish to apply their chemical knowledge to this interesting art.

Having been engaged in teaching Chemistry in this Metropolis, the one for a period of forty, and the other for a period of thirty years, it

PREFACE. IX

"has appeared to ns that, in spite of the number of books already existing^ there was room for an additional volume; which should be specially adapted for the use of students. In preparing such a volume for the press, we have endeavored to bear in mind, that a student in the present day has much to learn, and but a short time at his disposal for the acquisition of this learning. An eminent writer has truly observed, that the whole circle of the Sciences is required to comprehend a single particle of matter; but ars longa, vita brevis. If a Medical Student has before him only a few years for acquiring a knowledge of at least eight sciences, the efforts of those who contribute to the literature of these sciences should be directed to the elucidation of the most important facts and principles, omitting altogether those details which are either of a controversial nature, or are not yet established on a satisfactory basis. In reference to this book, it may be considered by some, that we have assigned too little, and by otherS; too much, space to our subject. This, however, is a question of opinion, on which persons may reasonably differ. "We have taken that which seemed to us to be. the proper course ; and we trust we have so dealt with the principles and practice of Chemistry, that the contents of this book will prove useful to the general, as well as to the professional reader.

Note. — The limits of this work have not aUowed us to occupy our space with a separate essay on Physics. We have, however, described the more important Physical with the Chemical properties of bodies. For further details, we refer the reader either to Pesohel's Elements of Physics, translated by West, or to the Elements of Natural Philosophy of the late Dr. Golding Bird.

We have followed the example of the late Dr. Turner and other writers of repute, in excluding pictorial illustrations. Students of the present day are well acquainted with the shapes of air-pumps, gas-holders, flasks, and retorts. Those who require this aid to their studies, will find in the illustrated catalogues of dealers in Chemicals, more correct representations of apparatus, than those which are commonly met with in treatises on Chemistry.

Contents

CHAPTER PAGE

1. Matter and its Properties . . . , . . 17

2. Crystallization. DimorpMsm. Isomorphism . . . . 25

Chapter I. Matter And Its Properties

Chemistry as a science embraces the whole range of animate and inanimate nature. By its means, man acquires a knowledge of the special properties of bodies, and the laws which govern their combinations. By the application of its principles he can resolve substances into their elementary constituents, and out of old materials construct new compounds. It confers on him a species of creative power, by enabling him to unite elements or compounds, and thus to produce a large number of bodies which have no independent existence in nature. Either directly or indirectly, Chemistry as an art lends its aid to the great purposes of civilization. In qnqx-^ civilized country, mining and metallurgy, as well as most branches of manufacturing industry, owe their development and progress to the proper cultivation of Chemistry.

A chemist has to deal with matter, as well as with the forces which are inherent in and connected with it. Matter may be either simple or compound^ and the forces that control it may be either physical or chemical. Had the globe been constituted of only one kind of substance or matter, the laws of physics alone would have sufficed to explain the phenomena of nature. There are, however, sixty-five different kinds of matter now known to chemists, and as these are resolvable into no other bodies, they are called simple substances or elements. , But few of these are found in nature in their simple or elementary condition ; they are in general intimately combined with each other, constituting the large variety of compounds of which the crust of the earth is composed. These simple substances not only differ in properties, but their compounds also differ as much from each, other as from the elements which form them. It is the province of a chemist to define these differences, to determine the laws by v/hich they are brought about, and to establish the relations of this with other branches of science.

Chemistry teaches us that matter is in its nature unalterable and indestructible. It may change its state, and undergo a change in properties, as a result of the chemical force, but it may by the same force be restored to its original state with all its properties unimpaired. Iron and sulphur possess .well-marked characters by which they maybe easily known from each other; but when combined, as in iron pyrites or bisulphide of iron, these characters are entirely lost, and new properties are acquired. On again separating the two elements, each reassumes its original properties. Chemjstry, therefore, is not only a science of properties, but a science of metamorphoses or transformations.

Recent researches have shown that although elements are not resolvable •2

18 ALLOTROPIC STATE. ISOMERISM.

into other substances, tliey are in some instances so altered by chemical and physif ai forces, that they apparently lose their identity. We have an example of this metamorphosis of elementary matter, in that condition which is called allotropy {aTCko^ 'tpoTto^, change of state), and no substance presents it in so remarkable a degree as phosphorus. Common phosphorus is a waxy-looking solid, melting at or below lll^^ and taking fire a little above its melting point. It is dissolved by sulphide of carbon ; it is luminous in the dark, evolves an acid vapor in air, and is very poisonous. By exposure to a temperature of 460^, under certain conditions, this substance is so completely changed in its properties that it would no longer be recognized as phosphorus. It presents itself as a hard, brittle, red-colored solid, which may be heated to about 500° before it melts or takes fire, is insoluble in sulphide of carbon, does not evolve any luminous or acid vapors, and has no poisonous action on, 'animals. By the application of chemical reagents and heat, the same products are obtained from it as from common phosphorus ; and as no other matter or substance can be extracted from it, and each is convertible into the other, we are compelled to ascribe the difference in properties to molecular changes — a theory which will hardly account for the destruction of the poisonous effects of this element on the animal organism. Oxygen, sulphur, carbon, boron, and silicon, are bodies which may also exist in two or more states in which their properties are widely different. This difference is sometimes brought out by physical, and at other times by chemical agency. These facts show us that the elementary state of matter, is not so simple as has been hitherto supposed, and they point to the probability that many of the substances now regarded as elements, may hereafter be proved to be compounds. The allotropic state, however, is not confined to simple substances. Compound bodies, such as silicic acid, and the peroxides of iron and tin, present instances of this condition. The physical and chemical properties of these bodies are changed by heat, or vary with the mode of their production, v/hile their chemical composition remains unaltered.

When two compounds can be proved to be formed of the same elements in the same proportions by weight, it would appear to be a reasonable inference that their properties should be identical ; but chemistry teaches us that this condition may exist, and yet the substances be wholly different in chemical and physical properties. Bodies which thus resemble each other in atomic constitution are called isomeinc (lao^ equal, and ^cpo^ part), and isomerism is the name applied to this condition of matter. The fact is, the properties of the substance depend not only on the nature of the elements, and the number ©f atoms of each, but on the mode in which these elements are grouped or arranged. Gum, starch, and sugar are isomeric, or are constituted of a like number of atoms of the same elements, and the difference in their properties can therefore only be ascribed to a difference of arrangement among these atoms. Cases of isoirierism are much more numerous in organic than in mineral chemistry, for the reason that organic compounds are composed of a greater number of atoms of each element, and these admit of a greater variety of arrangement. In some instances, the atoms are in precisely the same number, but the bodies which they form are widely different. Thus, the hydrated cyanate of ammonia is represented by the formula NHgjC^ISrO,

110, while the organic compound urea is C^NgOyH^. The properties of these compounds are widely different. That the differences must depend on the arrangement of the atoms is proved by the discovery of Wohler, that on evaporating a solution of the hydrated cyanate of ammonia this salt disappeared, and the organic principle urea was produced. Oil of turpentine and oil of lemons present another instance of similarity of atomic composition

PHYSICAL rOROES. 19

with different properties. Each of these oils contains CgoH^^., but no method is known by which one can be converted into the other. There is a ^vhole group of hydrocarbons similarly constituted. Isomeric bodies in which the atoms are the same in number and relative proportion are called m.etameric, in oi'der to distinguish them from another class called polymeric, m which the relative proportions in 100 parts by w^eight are the same, Vv^hile the absolute number of atoms differs. Aldehyd and acetic ether are liquids remarkably different in properties, but they are polymeric. Aldehyd is represented by C^H^O^, and acetic ether by CgllgO^. Two atoms of aldehyd would therefore be equivalent to one of acetic ether; but 100 parts of each liquid would yield precisely the same relative weights of carbon and hydrogen. At the same time these liquids are not mutually convertible into each other. In mineral chemistry, a similar condition presents itself in reference to the compounds known as ferro and ferri-cyanogen. The former is FejCf-N.:,; the latter has exactly double the number of atoms, F^jC^gNg. In a state of combination, their crystalline forms, color, and chemical properties are v/hoUy different. These facts teach us that the grouping of the atoms, apart from the chemical composition of substances, has a material influence on their chemical and physical properties.

While physics relate to those changes, in masses as well as particles of matter, which result from the physical forces of gravitation, electricity, magnetism, light, and heat, chemistry roid^iQ^ to changes produced among the minute particles of bodies which are the result of one peculiar force— namely, chemical force, affinity, or attraction.

Physical Forces. — Physical forces are manifested on the same or on different kinds of matter. The chemical force can be manifested only between different kinds of matter. As a general rule physical forces produce no permanent change in the properties of bodies, w^hile it is the special character of the chemical force, and the leading feature of its existence, that the properties of the bodies on which it has been exerted are permanently altered. Sulphur and iro7i will serve to illustrate the differences here indicated. Gravitation affects both, but in different degrees. A cubic inch of iron gravitates with a force equal to that of three and a half cubic inches of sulphur. This is indicated by a comparison of their relative weights in the same volume or bulk (specific gravity). If the mass of iron is rubbed with a flannel, and held near a light substance, such as dry bran, there is no attraction ; when brought near to a suspended magnet, each end of the magnet is powerfully attracted ; when heated it does hot melt ; under reflected light it has a gray color and a metallic lustre. A small bar of it held in a flame, allows the heat rapidly to traverse its substance, and it becomes painfully hot, v/ithout undergoing, any further change. On the other hand, a mass of sulphur warmed and rubbed with dry flannel, powerfully attracts bran and all light substances. Until it has been rubbed it manifests no attraction for the magnet, and after rubbing, it attracts it only as a result of the frictional electricity produced in it ; when heated, it readily melts, takes fire, and burns with a blue flame ; under reflected light it has a peculiar yellow color v^ithout any metallic lustre. Here, then, we have a manifestation of dlE^YQui physical properties in these two bodies, and we learn that iron is of, greater specific gravity than sulphur ; that while iron is not rendered electric by frictioDj sulphur becomes highly electric ; that while, iron is powerfully magnetic, there is no magnetism in sulphur ; that as to the effect of heat, while one is infusible and incombustible at ordinary temperatures, the other readily melts and burns ; that the light reflected by the two is different, and that while iron allows heat to traverse its particles from end to end, sulphur does not. After having manifested all these phenomena as a result of physical forces brought

20 CHANGES IN MATTER BY THE CHEMICAL EORCE.

to bear upon them, the iron and the sulphur resume their original state and remain unchanged.

The chemical differences which exist between iron and sulphur are not less remarkable. If sulphur in fine powder is sprinkled in a jar inverted in a saucer of water, it may be kept for any length of time without undergoing any change. If iron-filings are sprinlded in another jar, also inverted in water, the iron will be oxidized or rusted, and the water will rise in the jar, showing that a part of its gaseous contents has been removed. The gas thus removed may be proved by experiment to be oxygen, which, at a low temperature, will combine with iron but not with sulphur.

If we mix together iron and sulphur in the finest powder, in the proportions in which we know they will chemically combine to form iron pyrites or bisulphide of iron, namely, forty-seven parts of iron and fifty-three of sulphur, they will remain as a mere mixture, each with'its physical properties unaltered. Owing to the presence of iron the powder will have magnetic properties, and when placed in water the iron will rust, and remove oxygen from a vessel of air. If a magnet be drawn over the powder the iron will be removed, and the sulphur remain.

Chemical Force. — When the sulphur and iron are, however, chemically united in the proportions above-mentioned, as in iron pyrites, they will be found to have lost their characteristic physical and chemical properties. This substance is seen in hard cubic crystals of a yellow color and of a metallic lustre. It has no magnetic properties ; it is not, like sulphur, rendered electric by slight friction, and in the state of fine powder it does not remove oxygen when placed in a jar of air over water. A magnet drawn over this powder produces no effect upon it, the iron is not separated from the sulphur. We have, in fact, an entire change of properties, and the new properties acquired are retained so long as the two elements are chemically combined. By aid of the chemical force, the two elements may be separated and procured in a pure state. The iron and sulphur will then be found to have re-acquired all the properties, physical and chemical, which they had lost as the result of their combination.

Physical forces, therefore, produce only temporary changes in bodies, while the chemical force entirely alters them ; and this alteration continues until the union of the elements is dissolved. Further, we learn that the properties of a chemical compound cannot be inferred from the properties of its constituents. Its physical condition as gas, liquid, or solid, and its chemical and physiological characters, can be determined only be experiment. Nitrogen and hydrogen are two comparatively inert gases, while carbon is an innoxious solid. The combination of these three elements produces a highly poisonous liquid, Prussic acid. Hydrogen has no smell, and sulphur only a slight smell on friction ; when combined these bodies produce a most offensively-smelling gas, sulphide of hydrogen. Carbon, oxygen, hydrogen, and nitrogen, are innoxious agents, and have no taste, but when combined in certain proportions they form strychnia, remarkable for its intensely bitter taste and highly poisonous properties. Iron manifests magnetism most powerfully, and oxygen is the most magnetic of gases, yet these two bodies, when combined in the proportions of two of iron to three of oxygen, produce a compound in which no trace of magnetism can be discovered.

The properties of substances which are referable to the senses in the form of taste, odor, color, or touch, are called by the French orga.noIepiic, to distinguish them from physical and chemical properties. They are of some importance in chemical analysis, as they often aid the inquirer in his search after minute traces of certain elements or compounds.

DIVISIBILITY OF MATTER. 21

DivisiMUty of Matter. — Matter, in the simple or compound, in the solid or liquid state, is divisible. Thus, a solid or liquid may, by various processes, be reduced into particles so fine that they are no longer perceptible to the eye. When reduced to the 1-500, 000th of an inch in diameter, the particle would be no longer visible under the most powerful microscope (Mitscherlich) ; but lines closer together than the 100,000th of an inch admit of no separation by the most powerful modern object-glass. The minute particles of fine precipitates, such as sulphate of baryta or chloride of silver, are individually imperceptible : they are only rendered visible to the eye by aggregation. So of all solids* in solution, the particles are so small that light traverses them. A small quantity of mercury shaken in a bottle with strong sulphuric acid, is temporarily split into myriads of minute globules- Mere pressure with the finger will divide this liquid into particles so small that they become gray and their bright lustre is lost to the eye. By subliming the metal in a tube, its particles may be so subdivided as to present only a gray tarnish on the glass. If a solution of chloride of tin is added to a solution of corrosive sublimate, a grayish-black precipitate is formed, which, when separated by filtration, appears on the filter in the form of microscopical globules, so minute that it would be difficult to assign a weight and size to each. Platinum, in the form of ammonio-chloride, is converted by sulphuric acid and zinc into a black powder (platinum-black) resembling charcoal.

All the physical characters of a metallic substance are lost by reason of the extreme tenuity of its particles. Gold admits of still finer subdivision. It has been reduced to such a state of tenuity that it does not sink in water, but allows light to traverse it as well as the liquid : its particles giving to the liquid a blue, green, or ruby color, according to the degree to which they have been divided by chemical agency. According to Paraday^s experiments, the ruby liquids present metallic gold in the finest state of division ; the blue liquids hold the gold in a more aggregated form. That they are finely diffused particles of the metal is proved by throwing a cone of sun-rays, either by a lens or mirror, into the midst of the liquid, when the illuminated cone clearly proves them to be undissolved bodies. He estimated that a particle in this state formed 1-500, 000th part of the volume of the fluid (Froc. Roy. Soc.,\^q\. 8, ISTo. 24, p. 361). Muncke has calculated, from the diffusion of a known weight of gold over silver wire, that one grain admits of subdivision into ninety-five thousand millions of visible parts, i. e. visible under a microscope magnifying 1000 i\mQ^.—{Handh. der Naturlehre, 43.) Pilms of gold, -finer than the finest leaves of the metal, may be* obtained by the following process. Place a thin slice of phosphorus on a surface of a very diluted solution of chloride of gold. Cover the vessel so as to prevent the access of light. In the course of twenty-four hours the gold will be reduced to the metallic state, for a considerable extent around the phosphorus. It will present the brilliant colors of the metal by reflected, but will appear bluish-green by transmitted light. The metallic film may be raised from the surface of the solution, by bringing into contact with it a clean surface of glass. It will adhere to, and may be dried and preserved upon the glass. Its tenuity is such, that by mere appearance it is scarcely possible to determine on .which side of the glass it is deposited. It is probably less than the millionth of an inch in thickness.

The divisibility of matter is of interest to the chemist, inasmuch as it enables him to speculate on the limits of chemical tests for the detection of substances. If half a grain of nitrate of silver is dissolved and diffused in 100 ounces of distilled water, the presence of the metallic silver throughout will be indicated by the liquid being rendered opaque, from the production of chloride of silver, by the addition of a few drops of a solution of common

22 COHESIVE FORCE OF MATTER.

salt. One grain of silver may here be proved to be split into 138,000 parts. But Malaguti found in sea-vv^ater taken off the French coast, that silver was dissolved in it as a chloride, in the proportion of one grain in 100,000,000 grains, so that each grain of water would contain only the 100,000,000th of a grain of metallic silver. No analysis could reveal its presence, except by an operation on a large quantity. {Quart. Jo urn. of Ghent. Soc. 1851, vol. 3, p. 69.) One quarter of a grain of acetate of lead dissolved and diffused in 100 ounces of water, will form a solution which is turned of a brown color by sulphuretted hydrogen, in parts as well as in the mass. The lead is here converted into sulphide ; and a grain of the metal is actually split into 336,000 parts. With indigo the divisibility may be carried still further. One-eighth of a grain of indigo dissolved in sulphuric acid will give a well-marked blue color to 300 ounces of water. This is in about the proportion of a millionth part of a grain in every drop of water. Muncke, who has ingeniously calculated the weight of the minutest visible particle of gold obtainable from the division of a grain of metal, has endeavored, in reference to indigo, to determine the size of the minutest particles of this substance from the dilution of a measured quantity of its solution. He estimates it at the five hundred billionth of a cubic inch. {Op. cit., p. 44.)

The divisibility of matter has of late acquired an additional interest in a chemical point of view, by reason of the discoveries of Kirchoff and Bunsen, in reference to the diffusion of metals. Their researches tend to show that sodiun], probably in the form of chloride, is a constituent of the atmosphere, and is diffused as a vapor over the whole of the globe. The divisibility of sodium to the extent in which it may be detected by prismatic analysis, utterly defies the balance and the microscope. They have tested the diffusion of the vapor of sodium from a minute quantity by weight in a room of known capacity, and they have detected its presence by the prism when the quantity examined could not have exceeded the 195,000,000th part of a grain in weight. — {Phil Mag., Aug. 1860, p. 95.) In reference to this mode of analysis they have also announced the presence of a metal (csesium) in a mineral water, of which it could not have formed more than the 100,000,000th part.

These results and calculations naturally suggest the question, wdiether there can be any limit to the divisibility of matter. Without going into the metaphysical part of this question, we may state that as bodies in masses can be proved to combine in definite weights, or weights which are fixed for each substance, it is probable that the same is true of the minutest particles of which they are composed. The view most consistent with chemical facts and theories is, that there is a limit to the divisibility of matter, and to this limit the terra atom {cLtofio^, undivided) is applied. It is believed that at this point matter is no longer divisible. What that limit is cannot be defined, and it is unnecessary for practical purposes to inquire. We can neither calculate nor estimate the size, shape, or absolute weight of atoms, but we can say that they are infinitely snialler than any particles which we can weigh in the most delicate balance, or measure in the field of the most powerful microscope.