Modern chemistry, with its practical applications

Front matter

Class

Book_

X*

Preface

In preparing this book for use in secondary schools, I have endeavored to look at the science from the viewpoint of the students themselves. The fault with many texts upon the same subject is that the position of the learner has been disregarded; the books have been encyclopsedic ; they have presented a great number of facts as a skeleton or framework, but this skeleton has not been clothed with muscle and animated with life. No more fascinating subject finds a place in the curricula of our secondary schools, yet to the average student chemistry is too often but an irksome task.

In the present work I have omitted much that is often given in an elementary text, while at the same time entering more into that detail which gives lively interest to the subject. It has been my aim to show, whenever possible, the practical application of the science to the everyday affairs of life; in other words, to emphasize industrial and commercial chemistry. At the same time the fundamental principles of the science have not been forgotten ;. on the contrary, they have been emphasized even more than is usual in an elementary chemistry. This has been rendered possible by the omission of much that can never be either of interest or of value to the beginner.

Eecognizing the fact that science must be taught inductively by experiment, some authors have assumed that the student must gain all his knowledge of chemistry in this way. No greater mistake could be made. The science has been hundreds of years in reaching its present development, and much must be accepted by the student without any effort to work it out for himself. In this text a large amount of experi-

4 PREFACE

mental work is given, sufficient to meet the requirements of all our best colleges. The experiment is always supplemented by notes and suggestions which enable the student to draw proper conclusions, and give him such information as he cannot hope in his limited time to gain for himself. It will be noticed also that the laboratory directions are largely in the form of questions, so as to compel even the least energetic students to secure the benefits of personal investigation. This plan is always followed except in cases where the student would be in danger of going astray.

To the pedagogical treatment of the difficult parts of the science I desire to call attention. The subject has been presented much in the same way as in my own classes, where the method has met with success. Beginning with the study of that most familiar of substances, Water, the text enters into a discussion of its composition and then proceeds to a detailed statement of its constituents. This work is prefaced merely by a short chapter connecting the science of Chemistry with that of Physics and by one chapter upon Valence. This somewhat difficult subject of Valence is introduced so early in the book in order to avoid many difficult questions that must arise when it is deferred. Although introduced early in the book, Valence is treated in so simple a way and with so many graphic illustrations that the student can hardly fail to grasp its meaning.

I recognize the demands, coming from all higher institutions of learning, for more quantitative work, and believe I have fully met all such requirements. The student of the subject, as taught hitherto, has been in danger of coming to the conclusion that very little in chemistry is exact; whereas nothing could be further from the truth. The pupil is shown this by the series of quantitative experiments which have been carefully worked out in the laboratory. For this work I have sought to make use of such apparatus only as may be or should be found in any secondary school.

PREFACE 5

To the regular text is appended detailed instruction for various laboratory manipulations, preparing solutions, etc. A chapter has also been added for the benefit of any who may desire to continue along qualitative lines the work introduced at various places in the text.

I desire to acknowledge, with gratitude, the valuable suggestions offered by Professor Irving P. Bishop, of the State Normal School, Buffalo, and Professor M. D. Sohon, of the Boys' High School, New York City, both of whom have read the book critically in manuscript ; furthermore, I wish to say that to many of my students of the past I am indebted for descriptions, original with them, and more appropriate than any I have found in any text. To Dr. Paul Schweitzer, for many years Professor of Chemistry in the Missouri State University, the true friend of the student, to whom I owe much for his great sympathy and encouragement, and his words of fatherly advice, I desire to express especial gratitude. Finally, I acknowledge with pleasure the help and inspiration I have gained in my private study and research from the writings of those who have been permitted to drink long and deep from this fountain of science.

TO THE TEACHER

It is not expected that everything given in the text will be demanded of the pupil, unless possibly in reviews. Some of the manufacturing processes, for example, I have deemed of sufficient importance and interest to be given; yet it may seem best in the judgment of the instructor to omit these.

The experiments, as a rule, may be performed by the students, and apparatus is suggested which most schools will be able to provide. The number of pupils will determine to some extent what experiments should be performed by the teacher and what by the students themselves. If the classes are small, so that the teacher can give very close personal attention, the pupils may attempt almost all; on the other hand, if the classes are large, it may be necessary for the teacher to perform some of the more difficult and dangerous experiments himself. On pages 355 to 380 will be found many useful suggestions to the student for the care and manipulation of apparatus, making up of solutions, etc. These should be read before the student begins his work in the laboratory, and frequent reference should afterward be made to them.

It is presumed that a school year of nine or ten months will be given to the work in this text, but by omitting some of the less important elements, much of the theory and many of the practical applications of chemical science may be obtained in five or six months. Besides the various chapters devoted to the fundamental laws of chemistry, special study should be given to the following elements and a few of their important compounds : hydrogen, oxygen, nitrogen, fluorine, chlorine, bromine, iodine, carbon, sulphur, sodium, calcium, zinc, lead, and iron.

Introduction

1. With what is Chemistry concerned ? — Nature presents herself in ever-changing forms, and to one who is not familiar with these variations she is a mystery. The untaught inhabitant of the tropics, who has never been beyond the confines of his native state, taken to a colder climate would see no relation between the snowflake or the icy covering of our northern rivers and the rain-drop as it falls upon his native hills. To him they are entirely different substances.

2. So the diamond, the filling of the ordinary " lead " pencil, and the coal that we burn in our furnaces seem altogether dissimilar, and yet they are practically the same thing. Likewise the emery with which the seamstress sharpens her needle and the mechanic his tools, and such valuable stones as the oriental emerald and the ruby, though seemingly so different, have really the same composition. The purpose of the science of chemistry is the investigation of the objects that lie all about us in nature, the study of their composition and of their relations to one another, the explanation of the various phenomena in connection with them, and the ability to apply this knowledge to practical uses.

3. Importance of the Subject. — A knowledge of chemistry adds a charm to many of the common things of life, clothing them with new beauty. Later it will be noticed that the science of chemistry enters into all or nearly all of the great manufacturing industries of the world, and that without the application of its laws and principles all such enterprises would result in failure. Whether studied, therefore, for its intellectual or for its practical value, it is of the greatest importance.

MATTER, THEORIES — PHYSICAL AND CHEMICAL CHANGES

4. Some Theories of Matter. — There have been men in .11 ages who believed that all substances .whatsoever might

be resolved back into one particular kind of matter; that )Y subjecting this matter to different conditions an endless variety of modifications would result. * To illustrate : here is a bar of steel ; by submitting it to varying processes it is made into saws, knives, needles, watch-springs, pens, md thousands of other articles. It is claimed that in the same manner the one elementary substance, in undergoing different treatments by the forces of nature, appears in :he endless variety of substances about us. It has never jeen possible, however, for those who hold this view to prove it by any experiments. Neither does it seem that the phenomena of nature require or even admit of any such explanation.

5. Elements. — What seems a more reasonable view, and one that has come nearer to demonstration, is that matter is composed of a large number of simple substances, and that these combined in different ways produce an infinite number of substances. According to this view there are about seventy-five simple substances, called elements, which cannot be, or at least never have been, divided into two or more simpler substances. Numerous experiments of every character, by means of the strongest

MOLECULES AND ATOMS 11

sisting of two elements, sodium and chlorine, always in the ratio of 46 to 71 by weight. Likewise, water is a compound, containing one part of hydrogen to eight of oxygen.

8. Divisibility of Matter. — Physics teaches us that matter is anything that occupies space, and that all matter is divisible. But where does this divisibility end? We do not know. A single costal of a dark purple solid known as potassium permanganate will very perceptibly color several gallons of water. To clo this, it must be divided up until its particles are diffused throughout the entire volume of the water, or into so many parts that the numbers are beyond our comprehension. Though we cannot fix an absolute limit to the division of matter, we assume it to be the molecule.

9. The Theory of Molecules. — A molecule is the smallest particle of matter that can exist alone, or in the case of a compound body, the smallest particle that can exist without destroying the identity of the substance. Thus, the smallest portion of common salt to be conceived of still contains the two elements mentioned, sodium and chlorine, and is a molecule. In the same way the smallest particle of water would contain both hydrogen and oxygen, and always in the same ratio. If, now, by any means we can break up these salt or water molecules into their two constituents, we no longer have a compound body, but two simpler substances or elements.

10. Atoms. — These constituent parts of a molecule we call atoms. Even the molecules of the elements may consist of two or more atoms ; in fact, they usually do. Thus, it will be seen later that a molecule of oxygen consists of two atoms ; a molecule of chlorine of two atoms, and so on. It may be said, therefore, that all matter is divisible into molecules, and that these molecules are composed of still smaller particles called atoms. From the above, it will be seen that the molecule of the compound body and its constituent atoms would be very different, while the molecule of an elementary body and its atoms would be exactly alike in properties. This is illustrated in Fig. 1.

Here, a represents a molecule of water consisting of two atoms of hydrogen and one of oxygen. If by electricity we decompose this molecule, we shall no longer have water, but two elementary substances, hydrogen and oxygen. Likewise, c represents a molecule of common salt, and if this be decomposed, we shall no longer have salt, but two substances, sodium and chlorine. On the other hand, b represents a molecule of oxygen, and if this be decomposed, we shall still have oxygen, but in the atomic form, possessing the same physical characteristics as before.

11. Physical Changes. — Matter exists in three conditions, solid, liquid, and gaseous, depending upon the relation to each other of the intermolecular forces. When the cohesion existing between the molecules is considerably greater than the repellant forces which tend to drive them apart, the substance exists in the form of a solid. When the converse of this is true, and the molecules tend to be driven farther and farther from each other, the substance is then in the form of a gas. When the repellant and attractive forces are about at an equilibrium, the substance exists as a liquid. It is with changes of molecular condition that physics deals, and the molecule is the basis of all physical phenomena.

Experiment 1. — Hold in the flame of the Bunsen burner a piece of tin foil, an aluminum wire, or a narrow strip of zinc; or put any one of them into a clean iron spoon and heat. What change takes

PHYSICAL CHANGES 13

place in the physical condition of the metal? Let it cool again and state what happens.

12. In this simple experiment two changes have taken place : one, the conversion of the solid into the liquid form; and second, the changing back again into the solid. We have changed the form of the substance and the arrangement of the molecules as regards one another, but the properties have remained the same.

13. Another Molecular Change. — Likewise, when a current of electricity is passed through an electro-magnet, the armature for the time being becomes a magnet ; that is, its molecules have been rearranged, or so affected that they present the well-knowui phenomenon of attraction. When the circuit is broken, the armature loses its magnetism ; in other words, its molecules have assumed their previous condition. When a body is heated, the molecules are set in more rapid vibration, and luminous bodies emit light because of this vibratory motion.

14. So throughout the domain of physics w^e find that all phenomena concern the molecule and molecular changes. We are all familiar with the different conditions under which water exists, and we are not surprised at the statement that fog, clouds, rain, snow, and other forms are modifications of the same substance, the only difference being in the greater or less amount of stored-up heat energy.

15. Substances exist in Three Forms. — At the same time we are not accustomed to think that nearly all substances may exist in the same three forms ; as liquids, solids, and gases. We are familiar with air in the gaseous condition only ; yet if we reduce the temperature of it to about 190° below zero Centigrade, it becomes a transparent liquid not very different in appearance from water, and

14 MODERN CHEMISTBY

at a still lower temperature it freezes or solidifies. In like manner carbon dioxide, an invisible gas thrown off from the lungs of all animals in breathing, if cooled, is first liquefied, and then by further reduction of temperature is converted into a beautiful white crystalline solid, very closely resembling snow.

16. Mercury and Carbon. — We are all familiar with mercury as a silvery white liquid, which may be boiled and converted into vapor at a moderately low temperature. On the other hand, in our most northern climates it frequently solidifies, and were the glacial epoch to return, under the rigors of that era we would know mercury, not as a liquid, but as a somewhat malleable solid closely resembling lead in its appearance and properties. To go still further, carbon, that we know best in the form of charcoal and coal, — one of the most refractory of substances — in an electrical furnace may be fused and made to boil, apparently like water, while in the intense heat of the sun it is converted into vapor and exists in the atmosphere surrounding that body just as water vapor does in our own.

17. All these are merely illustrations of changes in molecular condition, or are physical changes ; and the same substance in its different forms presents at all times essentially the same properties.

Experiment 2. — Put into a small test-tube a crystal of iodine and warm gently. What becomes of the crystal? Does anything deposit farther up the tube? When the colored vapors have disappeared, warm the tube higher up. What happens ?

From the above experiment we see what has been stated before, that heat converts many substances into vapors ; and further, that when this heat is removed, they condense again into their previous condition. We learn, too, that and

CHEMICAL CHANGES 15

the physical condition in which bodies exist is not an essential, but an incidental matter depending upon the ease or difficulty with which they are melted and vaporized.

18. Chemical Changes. — Chemical changes, on the other hand, involve, not the molecule, but the constituent parts of the molecule, the atoms. In every chemical change the molecule is broken up and its identity destroyed, while the atoms formerly composing it recombine to form ne^\ and different substances. Hence, when any substance i^

nged chemically, or when two or more substances react n one another and undergo a chemical change, new bducts are formed, differing altogether in properties from the original substances.

Experiment 3. — Put into a small test-tube a little mercuric oxide and heat, gently at first, then quite strongly. Continue this for several minutes. Thrust a pine splinter, having a spark upon the end, down into the tube. What happens? Is there any evidence of something present different from air? What seems to be forming upon the cooler portions of the tube ?

19. If we continue to heat long enough, the red oxide would entirely disappear, just as water does when boiled. In the latter case, however, the water might be condensed again as before, while in the present instance the mercuric oxide seems to be decomposed into two substances, — one, an invisible gas which caused the spark to burn brightly, the other a dark colored substance which condensed in small globules upon the cooler portion of the tube. Here we have a chemical change, one which caused the destruction of the original substance, and produced therefrom two, differing very strikingly in their properties.

20. Chemical changes are usually brought about by some physical agency, such as heat, electricity, light, percussion, etc. Innumerable instances of this kind of change might be given, but as such changes are to be studied throughout the science of chemistry, only a few will be noticed at present. As already seen, the substances produced are often very different from those used in obtaining them ; for example, two or more solids may unite in such a way as to form a gaseous body, or even a liquid ; two gases may form a solid or a liquid; while two liquids may combine to form a solid. Some of these will be illustrated below.

Experiment 4. — Rub vigorously together in a mortar a si crystal of potassium chlorate and an equal quantity of flowed sulphur. Into what are the two solids converted? How is i chemical union manifest?

fcW^I

21. A change similar to this is seen when gunpowder is exploded, causing the three substances, of which it is a mixture, to combine, with the formation of several gaseous products.

Experiment 5. — With a few small crystals of potassium chlorate

wrap in a piece of paper a bit of phosphorus ; fold the ends together

carefully and strike with a heavy weight as shown in

Fig. 2. What are the results? What is the nature of

the products formed?

CAUTION. — In preparing for this experiment, cut the phosphorus under water, dry quickly in the folds of a filter or blotting paper, and proceed as above. Small particles of the phosphorus often fly to some dis- FlG * 2t tance, and a board should be set up to protect

the clothing of the experimenter and of the members of the class.

Experiment 6. — Mix thoroughly a small quantity of granulated sugar with an equal amount of potassium chlorate, well powdered, and put the mixture into an iron saucer. Now by means of a pipette

CHEMICAL CHANGES or glass tube drop upon it a little strong sulphuric acid. Notice that the sugar is burned, a part is converted into gaseous products, and a part left as a black residue.

22. Chemical Change by Physical Agency. — In Experiments 3, 4, and 5, the different substances were caused to combine by friction, or percussion. That is, by physical force, the molecules of the different substances were brought so close together that the chemism, or chemical Affinity, of the atoms in the unlike substances w^as greater tliK the cohesion among the molecules, and as a result ^l^atoms rearranged themselves to form new compounds.

This may also be illustrated by the following experiment :

Experiment 7. — Put into a clean porcelain mortar a few crystals of potassium iodide, KI, and about the same amount of mercuric chloride, HgCl 2 . Rub them together for two or three minutes; notice that the two white compounds react with each other to form a bright red mixture.

23. By the friction, the molecules of the mercuric chloride and of potassium iodide are brought so close together, that the mercury and potassium atoms exchange places, forming mercuric iodide, which is bright red in color, and potassium chloride, which is a white compound. It is simply another striking illustration of the fact already stated that chemical action brings about a change in the atomic structure, and causes, therefore, the formation of substances very different from the original.

24. Chemical Change by Chemical Agent. — In Experiment 6, the same results were brought about by the use of a chemical reagent, sulphuric acid. In all of these instances, except Experiment 7, the solid substances used were largely converted into gaseous products, and in all entirely different from the original. To show that two gases may combine to form a solid, perform the following experiment : —

Experiment 8. — Pat into a beaker a few drops of hydroc acid, cover with a sheet of cardboard or glass, arid allow it to st; few minutes. Into another beaker put a few drops of strong ai nium hydroxide, and cover in the same way. Presently, inver first beaker over the second, then remove the cards, so that the two gases which have filled the beakers may come into contact with each other. Notice the heavy white fumes that form. These are a white solid compound, known as sal ammoniac.

Experiment 9. — To show that two liquids by reacting upon each other may produce a solid. Numerous instances of this will be seen from time to time. Powder a gram or two of alum and an equal amount of ferrous sulphate, put both into a test-tube and add about 10 cc. of water or just enough to dissolve them readily. You will now have a nearly colorless solution. To this add slowly a little strong ammonium hydroxide. You will obtain a greenish colored, jelly-like solid, with scarcely enough water present to enable the precipitates to be poured from the tube.

25. Mixtures. — We have had the term compound body defined, and we must be careful to distinguish between a compound and a mixture. In the latter, the two or more substances used are not necessarily in any definite proportion, nor are they united with each other. Furthermore, as a rule, mixtures may be very easily separated by purely mechanical means.

Thus, we may put together sand and common salt in any proportion whatsoever; they do not react with each other to form a new compound, but are still sand and salt hioric rt~cnw

I

MIXTURES 19

just as before being mixed. They may also be very easily separated and the salt recovered. Let the student suggest a method for doing this.

26. Gunpowder. — Gunpowder is a very familiar mixture, consisting of three substances which may be easily separated. Upon exploding, however, these three combine to form several compounds from which the original could be recovered only by difficult and expensive methods.

Experiment 10. — To separate gunpowder into its constituents. Put a gram or two of gunpowder into an evaporating dish and add a few cubic centimeters of water. After warming gently a few minutes, filter out as directed on page 00. Transfer the clear filtrate to an evaporating dish and boil slowly to dryness. While you are waiting for this, transfer the black residue upon the filter paper to a beaker and add a little carbon disulphide. Shake for a moment or two, and then decant or filter off this clear solution. Without heating, let it evaporate to dryness in a watch crystal or evaporating dish. What familiar substance is left? What was the appearance of the solid obtained by boiling down the solution in water? What colored residue was left after treating with carbon disulphide? Can you name the three substances?

Experiment 11. — To show the difference between a mixture and a compound of the same two elements. Put together in any proportion a small quantity of sulphur and of iron filings. Mix them thoroughly. What is the resulting color? See whether you can remove the filings by means of a magnet ; owing to the presence of some moisture a little sulphur may adhere to the filings. State your results. Put the filings back into the sulphur and again mix them well. Now add 1 or 2 cc. of carbon disulphide, shake for a moment or two, and decant thoroughly upon a watch crystal or into an evaporating dish. Let the clear solution dry without heating, as it is very inflammable. What do you obtain ? Have you effected a separation of the two ?

Again mix in about equal proportions by volume, or in the ratio of 32 to 56 by weight, sulphur and iron filings ; put them into the smallest test-tube you have and heat, first gently and then very strongly, until a bright red glow seems to go through the entire mass. After thus heating for two or three minutes, allow the tube to cool, and remove the contents ; if necessary, break the tube. How does the color differ from that of the mixture at the beginning? Powder the mass, and attempt to separate the filings from the sulphur by means of a magnet as before. Can you do this? Treat a part of the dark powdered mass with carbon disulphide and determine whether you can thus remove the sulphur as you did from the mixture. State your results. From this experiment we may note several differences between the mixture of iron and sulphur that we had before heating and the compound afterward. What are they?

Introduction.

Some theories of matter — Old — Illustration.

Present theory.

Definition of term element.

Compound bodies.

Definition.

Illustration.

Divisibility of matter. Chemical changes.

Difference between molecule How different from physical,

and atom. Several experiments to illustrate.

Illustration. Mixtures.

Physical changes. How different from elements and

Experiments to illustrate. compounds.

Name several others. Examples of mixtures.

What is a physical change ? Method of separating.

Chapter II Valence

1. What is Valence ? * — If we notice some of the common compounds of hydrogen, which we shall study, we shall see that different elements unite with a different number of hydrogen atoms. Thus, chlorine combines with one atom of hydrogen, oxygen with two, nitrogen with three, and carbon with four, as shown in the following compounds : —

Hydrochloric Acid .... HC1

Water H 2

Ammonia H 3 N

Marsh Gas ...... H 4 C

2. The four elements, chlorine, oxygen, nitrogen, and carbon, have the power of combining with one, two, three, and four atoms of hydrogen, respectively, and we speak of them as having a valence of one, two, three, and four.

I By valence or quantivalence we mean the power any element has ^ , , t

of holding in combination the N< • » ■

atoms of another element taken

as a standard. / This standard, primarily, as shown above,

* If in the judgment of the teacher the subject of valence can be more easily grasped by the student later in the course, this chapter may be deferred until after the study of carbon and its compounds.

is hydrogen, and by it the valence of other elements is measured or determined. It may be illustrated in this way : suppose the first line represents the combining power of hydrogen, which is our standard. Then with this " yard stick " we will measure the combining power of the other elements. In water, H 2 0, the valence of the oxygen atom is determined by applying the "yard stick," and is seen to be two ; in NH 3 the standard is used three times, and the valence of the nitrogen atom is three. In the same manner the valence of the carbon atom is determined as four.

3. Suppose, however, hydrogen did not combine with carbon, could we still determine its valence? We are familiar with the compound, carbon dioxide. In this molecule, C0 2 , the oxygen atom is used twice with the carbon atom, hence the latter must have twice the combining power of the oxygen. This has already been shown to be two, hence carbon would be four.