^- ' r ^^ - CHEMISTRY LIBRARi BOUGHT WITH THE INCOME PROM THE SAGE ENDOWMENT FUND - THE GIFT OF Henrg W. Sage 1891 %Z,S.L,.\.S.:^ - -^.y.V^Al. 1357 Cornell University Library QD 35.087 Introduction to chemistry, 3 1924 004 364 224 if M^ B Cornell University The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924004364224 INTRODUCTION TO CHEMISTRY BY WILHELM OSTWALD AUTHORIZED TRANSLATION BY WILLIAM T. HALL and ROBERT S. WILLIAMS Department of Chemistry^ Masaachttsetta Institute of Technology WITH 74 FIGURES IN THE TEXT FIRST EDITION FIRST THOUSAND NEW YORK JOHN WILEY & SONS London: CHAPMAN & HALL, Limited 1911 COPIBtQHT, 1911 ET WILLIAM T. HALL AND ROBERT S. WILLIAMS Stanbope ipress I. GILSON COMPAMY BOSTON. U.S.A. PREFACE. The success both of the German edition and the numerous translations of the author's Schule der Chemie was a very welcome confirmation of the utility of the educational principles which are emphasized in that book. On the other hand, on account of the conversational form in which the work was written, it is not well adapted for use as a textbook. In the present instance the author has attempted to write a book which will be suitable to use as a text for beginning the study of chemistry, and yet it is based upon the same general principles as those adopted in the above-mentioned work. He has attempted to make it represent the sum of his wide experience in teaching. The greatest difficulty to overcome lies in the very large amount of material available. Most elementary textbooks attempt to cover so much ground that a student frequently gets the idea that there is nothing more to learn, and this false impression interferes greatly with his further development. If a student actually gets such an impression, it must surely be because so many isolated facts have been showered upon him that h? has had no time to learn how to analyze chemical phenomena thoughtfully. In this book, however, the author has tried to show from a few simple facts how it is possible, by carefully thinking over their causes and effects, to draw many wide and deep conclusions leading to new experiments and verifications, and he has thus sought to obtain, in elementary form, a practical introduction to scientific thought from chemical instruction. In this way the student does not get the impression that his knowledge of the subject is complete because he understands the book; but, rather, he will become more and more aware of the fact that far beyond the horizon which bounds his present view stretch fields that are open to him for further investigation. IV PREFACE More attention than usual is paid to the development of first principles. It was rather surprising to find how far the natural development of chemical conceptions coincides, on the one hand, with their historical development, and on the other hand, with the demands of rational pedagogics. The explanation of the fundamental conceptions — substance, solution, mixture, their properties and characteristics — not only forms the logical basis of chemical instruction, but makes possible, as well, the system- atic description of the more important chemical operations and methods of separation, which must be understood before a good knowledge of chemistry is acquired. The first third of the book contains a simple, experimental development of these general chemical relations, and the experiments chosen for illus- trating and demonstrating these relations are performed, for the most part, with well-known substances. They suffice, at the same time, to make the beginner so well acquainted with such phenomena that a sound empirical basis is obtained for the systematic study of chemistry, and thereby a feeling of progress is obtained. In this way, the student acquires a certain amount of thorough knowledge, which is more advantageous for future work than a much greater accumulation of half-digested fragments of isolated facts. Another point of view which the author has kept in mind more than in any other of his works, is the regard for the maturity of the class of students for whom this book is intended. The ability for abstract reasoning, and the joy therein, are just dawning, whereas the interest in the diverse nature of phenomena is already well developed. For this reason the contents have been arranged as far as possible in accordance with this natural development, and abstract analyses have been carried out only as far as the connection between experiment and hypothesis is clearly discernible. This again ought to be a source of pleasure to the student, for it is unnecessary for him to proceed with a half knowledge or with a badly developed intellectual con- sciousness. The subdivision of the text into sections, averaging about PREFACE V a page in length, serves the same purpose. In case a further limitation of the text seems desirable, the teacher will be able to leave out certain of these sections in the instruction of the class as a whole. It is very easy to follow the usual custom of taking miner- alogy into consideration and, in the description of the chemical geological reactions which take place on the earth's surface, a welcome opportunity is found for the introduction of general considerations. On the other hand, crystallography offers cer- tain difficulties which have been overcome in as simple a manner as possible. The customary enumeration of all the crystal forms has no educational value, although the knowl- edge of the elements of equal symmetry in the different forms of a system of crystals develops thought concerning spatial relations. The author feels as much justified in limiting such discussion, for the purpose of instruction, to the axes of sym- metry, and leaving out the other elements of symmetry, as in the usual limitation to seven principal systems in place of the thirty-two that actually exist. The experiments are partly new and all of them are so chosen that they can be performed easily by the beginner. Too often, in the attempt to base chemical instruction upon the results of experience, the student is called upon to witness such intricate experiments that he has neither time nor inclination to think them over carefully. Chemistry is an experimental science and it is just as much a matter of experiment as of science, which begins only with the application of experience to the formation of conceptions and conclusions. The author has tried, therefore, to give only such experiments as permit a direct scientific application, and this result is reached by the simplest conceiv- able means. Whenever possible, the student should perform the experiments himself. In fact, he will be able to carry out most of them at home, in case laboratory conveniences are not accessible. The experiments have been described briefly and it is intended that suggestions concerning many details not men- tioned in the text will be obtained from the drawings. NOTE. The translators wish to express their obligation to Messrs. J. W. Phelan and R. E. Gegenheimer of the Massachusetts Institute of Technology for much help and friendly criticism in reading and revising the proof sheets of the English text. W. T. H. R. S. W. Boston, March, 1911. VI TABLE OF CONTENTS. Page Preface iii CHAPTER I. SUBSTANCES AND MIXTURES. Sec. 1. Substances 1 2. Forms 6 3. Weight 8 4. Density 12 5. Homogeneous Substances and Mixtures 18 CHAPTER II. PHYSICAL TRANSFORMATIONS. Sec. 6. Fusion and Solidipication 27 7. Boiling and Liquefying 44 8. Sublimation 67 CHAPTER III. SOLUTIONS. Sec. 9. Pure Substances and Solutions 70 10. Saturation and Supbrsaturation 79 11. Gaseous Solutions 86 CHAPTER IV. CHEMICAL REACTIONS. Sec. 12. Chemical Combination 92 13. Chemical Separation 97 14. Elements 106 vii viii TABLE OF CONTENTS CHAPTER V. OXYGEN AND HYDROGEN. P^^e Sec. 15. Oxygen 112 16. Hydrogen 133 17. Water 144 CHAPTER VI. HALOGENS AND SALTS. Sec. 18. Chlorine 158 19. The Halogens 171 20. Sodium 175 21. Potassium 184 22. Magnesicm 189 CHAPTER VII. SULPHUR AND THE ALKALINE EARTH METALS. Sec. fs. Sulphur 195 24. The Alkaline Earth Metals 217 CHAPTER VIII. NITROGEN AND RELATED SUBSTANCES. Sec. 25. Nitrogen and Its Oxygen Compounds 225 26. Oxygen Compounds of the Halogens 238 27. Ammonia 244 CHAPTER IX. CARBON. Sec. 28. Carbon 250 29. Carbonic Acid 253 30. Hydrocarbons 272 31. The Law of Gas Volumes 286 CHAPTER X. THE EARTH'S CRUST. Sec. 32. Aluminium 294 33. Phosphorus 300 34. Silicon 304 TABLE OF CONTENTS ix CHAPTER XI. HEAVY METALS OF THE IRON GROUP. p^^^ Sec. 35. Zinc 313 36. Ikon 317 37. Manganese 324 CHAPTER XII. HEAVY METALS OF THE COPPER GROUP. Sec. 38. Lead 328 39. Copper 332 40. Mercukt 341 41. Silver 344 CHAPTER XIIL TIN, GOLD, AND PLATINUM. Sec. 42. Tin 351 43. Gold 353 44. Platinum 354 INTRODUCTION TO CHEMISTRY CHAPTER I. SUBSTANCES AND MIXTURES. § 1. Substances. 1. Chemistry is the study of substances. — Sugar, iron, sul- phur, coal, etc., are substances. Substances are the material from which bodies can be made. On the other hand, water and air are substances. What is the difference between a substance and a body? Both have weight and both occupy space. In the case of a body, however, the shape is taken into consideration, whereas it is not so with a substance. A body has some par- ticular shape and consists of some substance. Thus the knife is long and narrow and has a steel blade; steel is a substance and the knife is a body. A drop of water is globular in form and consists of water; water is the substance of the drop, and the drop itself is a spherical body. If the question is asked: Of what does this body consist? or Of what is it made? The answer is the name of a substance. 2. Different bodies may consist of the same substance. — Thus various tools for boring, cutting, punching, etc., are made of steel, and all sorts of different bodies from the large house to the small penholder and match are made of wood. Similar bodies can consist of different substances; thus dishes are made of clay, glass, iron, or tin, and coins consist of gold, silver, nickel, or copper. How is the substance recognized in the body? Why is it said that this bottle is made of glass? Because it is transparent and hard, not flexible but brittle since it is broken by a knock or a blow. Moreover, the pieces of broken glass have sharp edges 1 2 INTRODUCTION TO CHEMISTRY by which one's finger is easily cut and if a piece of common glass is heated it is likely to crack. All these characteristics are properties of glass; and glass, like any other substance,' is recognized by its properties. Name the properties of steel, of sulphur, of silver, copper, and wood. Describe, or characterize, the substances which you remember by their properties. 3. Is it possible to describe all substances? — This task proves to be an endless one. There are countless different substances, and among them many which you yourself have never heard of but of which the plumber, the mason, or the painter knows because he uses them at his own particular trade. It is the business of the chenjist to know all substances. But is this really possible? No, for there are at present more than sixty thousand different substances known, and if the chemist should become acquainted every day with ten new substances, it would take him twenty years of three hundred working days to know them all. In the meantime, other chem- ists would be discovering thousands of new substances, so that the work would never end. What, then, is to be done? Every time a chemist discovers, or makes, a new substance, he describes its properties. All these descriptions are collected in books (from which it is easy to find out also whether sev- eral people have described the same substance) and classified according to certain rules. When it is desired to know the properties of any particular substance, it is only necessary to look it up in some such book. Similarly, if a chemist thinks he has discovered a new substance, he examines the literature to see whether a substance with like properties has not been pre- pared by some one else. Only when he finds that this is not the case does he describe his substance as new and give it a correspondingly new name. Chemical literature thus replaces the human memory to a great extent, and retains all acquired knowledge independently of the life of the individual. 4. How many properties does a substance have? — It would be desirable to know all the properties of every substance, but this task is also an endless one because it cannot be stated just SUBSTANCES AND MIXTURES 6 how many properties every substance has. The properties of a substance are shown if it is looked at, felt, smelted, tasted, bent, pressed, hammered, heated, subjected to the action of an electric current, or brought into contact with other substances. There are, therefore, countless properties of a single sub- stance, and it is never wholly possible to describe or recognize every property of a substance. Large volumes have been pub- lished which deal solely with the properties of a single substance such as water, iron, or sugar, and every time a new edition of such a book is printed it is necessary to mention many new properties which have been discovered since the former edition appeared. It is therefore necessary in the course of the investigation and the description of the properties of substances to draw a line and describe only enough properties to characterize the substance. Often conditions change so that some special property which has not been previously studied becomes of importance. It is then necessary to carry out a new investiga- tion to establish this property. If such a work has been carried out once, it suffices for all time, because a definite substance always has definite properties no matter how or where it has been prepared. 5. The connection between properties. — It is very much the same with substances as with animals and plants. Each species has its own particular properties and characteristics which are duplicated in every single individual. If it has once been established that a raven has warm, red blood it is known for all time that ravens are warm-blooded birds, and up to the present time no raven has ever been found of which this is not true. In the same way, it is well known that iron will rust, and that it will be attracted by a magnet; a piece of iron has never been found which has not shown these two properties. With animals and plants there are always quite a number of characteristic properties which are all shown by a given species but are not shown in the same way by other species; and this is true of substances as well. The crow is black, has a large. 4 INTRODUCTION TO CHEMISTRY wedge-shaped bill, glistening feathers arranged in a definite manner, and a certain size and shape. When one is convinced that some of these properties are present, one may also expect to find certain other characteristics such as cleverness, cawing, etc. Similarly, in the case of a metal which rusts and is attracted by a magnet, the inference is that it will melt only at a very high temperature, that it is seven times as dense as water, that a polished surface will show a gray color and metallic luster, that it will dissolve in dilute hydrochloric acid, and, in fact, that it has all the properties of iron; these expec- tations will always be confirmed. 6. How many properties characterize a substance? — In the case of a given body it is often necessary to establish only a few properties in order to know of what substance it consists. The textbooks of chemistry, in which the different substances are described with respect to their properties, must contain, for every substance mentioned, at least enough statements concern- ing the properties to distinguish it with certainty from all other substances. To be sure the textbooks do not stop here, be- cause the numerous applications of the substance in commerce, medicine, the arts, or in any field of human activity, all depend upon its properties. It is necessary, therefore, to mention all such properties and their applications. Moreover, it is not known whether a property which up to the present time has never been utilized will in the future become valuable. Hence pure science, — in contrast to applied science, which makes use of the known properties, — is constantly trying to extend as far as possible the knowledge concerning the properties of substances. 7. The different kinds of properties. — There are two classes of properties: (1) those which are discernible from a study of the substance itself as it is, and (2) those which become evi- dent when we undertake to do something to the substance, i.e., change it from its ordinary condition to particular new conditions. Among the properties which are at once perceptible to our senses are, in the first place, those which are recognized by the SUBSTANCES AND MIXTURES 6 eye. In almost all cases it is the eye which first gives informa- tion concerning any substance. In this way are recognized (1) The Color, (2) The Transparency, (3) The Luster. (1) We distinguish between six principal colors, — red, orange, yellow, green, blue, and violet. Dark orange is called brown. Then there are white, gray, and black, which are not true colors in the sense used in physics, but are nevertheless used to designate the appearance of substances. White: chalk, common salt, sugar, etc. Gray: lead, iron, etc. Black: charcoal, asphalt, ink, etc. Red: minium, cinnabar, terra cotta, etc. Orange and brown: ocher, amber, lignite, etc. Yellow: sulphur, gold, brass, etc. Green: leaves, verdigris, emeralds, etc. Blue: lapis lazuli, ice in thick pieces, etc. Violet: amethysts. The colors white, black, and brown occur most frequently in natural substances. (2) There are three stages of transparency — -transparent, trans- luscent, and opaque. Glass is transparent, and it may be either colored or colorless. Thin milk is transluscent, as are ground glass and oiled paper. Most substances are, however, opaque. Transparent, translucent and opaque substances, more- over, may be of any color. (3) Finally, in the case of luster we distinguish the highest grade, called metallic luster, from all other ways in which sub- stances glisten. In mineralogy, the study of substances as they occur in the earth, a distinction is made between adamantine, vitreous, greasy, silky, and pearly lusters. Adamantine luster closely resembles metallic luster. It is shown by diamonds, which reflect a great deal of light and glisten brilliantly. Glass shows vitreous luster and fat has a greasy luster. Silky luster is produced when a number of glistening threads lie parallel to one another, each reflect- 6 INTRODUCTION TO CHEMISTRY ing the light in the shape of a line so that a peculiar shimmer is obtained. Pearly luster is caused by tiny, regular uneven- nesses on the shells of pearls and other bivalves, which so change the light that different colors are obtained in different directions. A substance like chalk, which has no luster, is called lusterless or dull. §2. Forms. A second, striking property of substances is the way they occupy space. A body is either solid, liquid, or gaseous, and correspond- ingly the substance of which it is composed is in the solid, liquid, or gaseous state. 8. Solid bodies are characterized by the fact that they have a definite shape which they retain unless acted upon by a force greater than gravity. Since all bodies are acted upon by gravity, the fact that a body has of itself a definite shape when not con- tained in a vessel, is sufficient to show that it is a solid. If it were a liquid the action of gravity would cause it to flow so that each particle would get as low as possible. The degree of solidity varies in different substances. Lead, for example, does not have much solidity, for a rod of lead can be changed in shape and torn much more readily than a rod of iron. A distinction is made between different kinds of solidity according to the way in which it is attempted to change the shape of a solid body. Thus the resistance towards crushing, towards tearing, and towards cutting may be measured. A solid substance which can be changed readily into small, inco- herent particles, for example by pounding it, is said to be brittle; one with the opposite qualities is said to be tenacious. A body which after being bent or twisted tends to revert to its original form is called elastic; if, on the contrary, it retains its new shape it is said to be inelastic or plastic. All these properties are capable of precise measurement, but in elementary chemistry and mineralogy it is sufficient to estimate them roughly. Thus substances are described in general as soft or hard, as tenacious or brittle, inelastic or elastic. India rubber SUBSTANCES AND MIXTURES T is soft, tenacious, and elastic; steel is hard, tenacious, and elastic and so on. 9. Liquids have no form of their own, but do possess a definite volume and consequently have a definite density. In the case of liquids so little work is required to make them assume a definite form that gravity itself does this work. Liquids, therefore, assume the shape of their solid surroundings, or the vessels con- taining them, as far as the bottom and sides are concerned. The surface of liquid in a vessel approaches the form of a horizontal plane which is perpendicular to the direction in which gravity acts. Under these conditions the center of gravity of the liquid is placed as low as the form of the vessel permits, and thus gravity has no further influence upon the form. There are transition stages between the liquid and solid states, for the mobility of liquids varies greatly. Benzin is more mobile than water, and the latter more than oil. Molasses, resin, and pitch are such viscous liquids that they respond but slowly to the action of gravity. This is particularly true of pitch, which may be broken quickly as if it were a solid, or by means of slow pressure it can be made to flow like a liquid. Soft and inelastic metals, such as lead, may be made to flow by means of great pressure, and threads or tubes may be pressed out. 10. Gases are the least conspicuous of all substances. For this reason it was a long time before the necessity was realized of describing them as a class along with the solids and liquids. Besides the atmosphere which surrounds us and in which we live, there are many other gases with different properties. For example there is illuminating gas, which is so commonly used as a source of light and heat, hydrogen gas with which balloons are filled, and carbonic-acid gas, which is used in soda water and in chemical fire extinguishers. All these gases are colorless, although other gases will be mentioned which have a perceptible color. It is likewise true that there are more colorless liquids than colored ones. Gases have neither a definite form nor a definite volume, but they completely fill any vessel in which they are placed. 8 INTRODUCTION TO CHEMISTRY Thereby they exert a certain amount of'pressure upon the walls of the vessel containing them, and the pressure can be made larger or smaller. This pressure depends upon the amount of the gas that is contained in the vessel, for it increases in pro- portion to the amount of gas that is introduced. This is evident on pumping up the tire of a bicycle; the more air pumped in, the harder the tire becomes. We live within an ocean of air, just as fish live in an ocean of water; and the air fills not only our lungs and the other cavities of the body but is also contained in every open vessel. If we say that a bottle is empty we mean that it contains nothing but air. Something is actually present in the bottle, as is evident from the fact that if it is inverted and placed in water, the latter penetrates only a little way. If the bottle is then turned right side up again, while completely immersed, air bubbles will escape through the water and the bottle will fill with water. From these experiments it is evident that the air is much less dense than water. The difference, in fact, is very great; water is, in round numbers, twelve hundred times as dense as the air which surrounds us. In other words, a gram of air under ordi- nary conditions will occupy a volume of about 1200 cc, or 1.2 liters. The density of air and that of all other gases vary greatly with the pressure. Since gases fill all vessels, and since, moreover, their density is so slight, they cannot usually be seen, especially if colorless. Their presence is most readily recognized when they are entirely or partly surrounded by water. If the bottom of a muddy pond be stirred with a stick, bubbles of gas will usually escape upward through the water. This gas may be collected by filling a glass cylinder with water and inverting it over the escaping bubbles. § 3. Weight. II. All bodies have weight. — Weight represents the force with which the body tends to fall, or to approach the center of the earth. The existence of weight is recognized if the attempt is made to lift a body; a certain amount of work is required, which of course varies greatly with different bodies. SUBSTANCES AND MIXTURES 9 A feather is so light that it is hard to realize that it actually has weight; on the other hand, a boulder is so heavy that we do not attempt to lift it because we know that it is beyond our power. In this way we learn to recognize that bodies have different weights and we learn to estimate whether two bodies have the same or different weights. Such estimations are always more or less indefinite and inaccurate. Accurate measurements of weight are made with a balance (Fig. 1). This consists of a lever which usually has two arms of equal length. For some purposes balances with unequal arms are used and there are even balances with only one Pig. 1. arm. If different bodies are placed in the scale pans which are suspended from the ends of the arms, usually one pan sinks and the other rises. In that case the body in the scale pan which drops is said to have the greater weight. If, however, the balance arm is not deflected in either direction, the bodies in the different scale pans are said to be of equal weight, and the balance is in equilibrium. Physics teaches that the force of gravity, or the absolute weight of bodies, varies at different places on the earth's surface and at different altitudes; but two bodies which have the same weight at any place will also be equally heavy at any other place. In other words, the absolute weight of every body changes at different places in the same proportion. If a balance is in equi- 10 INTRODUCTION TO CHEMISTRY librium at any place, it will remain in equilibrium at any other place. If, therefore, weights are compared with one another by means of a balance, it is not at all necessary to take the absolute weight into consideration. 12. The unit of weight. — To determine the weight of a body so that it will be known everywhere what is meant, a standard or normal weight has been chosen arbitrarily. This is the weight of a certain piece of platinum, which is one of the most unchangeable substances. This piece of metal is preserved with great care in Paris and is called the standard kilogram. Furthermore, there have been prepared about twenty other weights as nearly like it as possible, and which have been very carefully compared with the standard kilogram; these are preserved at the capitals of the different civilized countries. Other kilogram weights are compared with them and are kept in the various standardizing bureaus, and in the ofBces of the makers of weights, etc., so that they serve as a basis for all determinations of weight. The abbreviation kg. is commonly used for kilogram. The thousandth part of a kilogram is called a gram, abbrevi- ated g. This weight is the unit which is commonly used in science. There are other units of weight commonly used in commerce, but none of them is so convenient as the gram, which is the basis of the so-called metric system. The thousandth part of a gram is called a miUigram, mg., and a metric ton is equivalent to 1000 kilograms or about 2205 English pounds. The other names such as decagram-10 g., hectogram-100 g., decigram-0.1 g., and centigram-0.02 g., are not used very much; it is easier to say 10 g. than 1 decagram. To determine the weight of a given body, it is placed upon the left-hand pan of a balance and in the opposite pan enough weights are placed to restore equilibrium. Then the weights used are counted, and the sum is the weight of the body. Sets of Weights, Fig. 2, are readily obtainable. The weights in such a set are always so chosen that any weight between the smallest and largest can be obtained readily. The state of equilibrium is recognized not by the balance being at rest but by the fact that when the beam is made SUBSTANCES AND MIXTURES 11 to rest upon the central knife-edge the pointer will swing the same number of divisions to the left as to the right of the zero point, on the scale at the bottom.