TEACHERS' HANDBOOK TO ACCOMPANY FOUNDATIONS OF CHEMISTRY BY ARTHUR A. BLANCHARD, PH.D. ASSOCIATE PROFESSOR OF INORUAMC CHEMISTRY AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY AND FRANK B. WADE, B.S. HEAD OF THE DEPARTMENT OF CHEMISTRY AT THE 8UORTRIUGE HIGH 9C1IOOL, INDIANAPOLIS, INDIANA AMERICAN BOOK COMPANY NEW YORK CINCINNATI CHICAGO TEACHERS' HANDBOOK TO ACCOMPANY FOUNDATIONS OF CHEMISTRY BY ARTHUR A. BLANCHARD, PH.D. ASSOCIATE PROFESSOR OF INORGANIC CHEMISTRY AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY AND FRANK B. WADE, B.S. HEAD OF THE DEPARTMENT OF CHEMISTRY AT THE 8HORTRIDGE HIGH SCHOOL, INDIANAPOLIS, INDIANA AMERICAN BOOK COMPANY NEW YORK CINCINNATI CHICAGO COPYRIGHT, 1915, BY ARTHUR A. BLANCHARD AND FRANK B. WADE ALL RIGHTS RESERVED TEACHERS' HANDBOOK w. P. i " PREFACE THIS" handbook has been prepared as a guide to the use of the authors' textbook, Foundations of Chemistry. Although it is obvious that the experienced teacher will find much of the detailed suggestion and answers to questions superfluous, nevertheless it is probable that even for such a teacher this handbook will be of value in showing the authors' point of view. Furthermore, it is to be hoped that maturer persons, who may be studying the main textbook from interest in the subject and without the advantage of class instruction, may derive a good deal of help from the use of the handbook. The authors realize that some matters are explained very fully in the textbook, much being stated that might be left to the pupils' imagination, or be brought out in classroom discussion. They believe, however, that it is better to treat few topics thoroughly than many superficially. The questions given at the end of each chapter will be of service in developing the pupils' imagination and suggesting lines of class discussion. Furthermore, countless facts and experiences of everyday life, of which the few treated in the book are fairly typical, may be studied in the light of the principles developed from the selected topics. The pupil may thus grow to a deeper realization that all happenings in the universe occur in obedience to natural law, and that the more fully he can understand the laws of nature, the better he will be able to apply the knowledge he possesses to the problems of his daily life. This handbook follows the order of the textbook, chapter by chap- ter. In many cases it is suggested that the teacher use extra matter to enrich the content of the course on the historical, the industrial, or other side of the subject. Trips to industrial plants are suggested at appropriate places. Such trips are profitable in increasing interest, in demonstrating the practical importance of chemistry, and espe- cially in securing better acquaintance between pupils and teacher. 33^476 4 PREFACE Excursions undertaken in school time are usually more profitable than those taken after school hours or on Saturday. A number of brief quotations from the original papers of men who have made great advances in chemistry have been given. Some of these have been translated from the less accessible originals. The answers to most of the questions are here given very fully. The authors hold that monosyllabic answers from the pupils should not be tolerated, but that the answers should show an appreciation of the purpose of the question. To this end they have given the answers in such a full and thoughtful manner as they would endeavor to have their pupils attain. In many instances they have gone be- yond the knowledge which the pupil could reasonably be supposed to possess in order to suggest elaborations of the topic which could serve, at the teacher's discretion, to make the classroom work of more value. In the solution of the numerical problems possibly an excess of detail in the steps of the process is given, but the authors believe it is better to err on this side. The mere numerical correctness of the answer from the pupil is of secondary importance to the understand- ing of the application to the problem, of scientific principles. If experiments precede the classroom and textbook work and embody in part at least the spirit of the discovery method, if class- room discussion follows, and lastly, if the use of the textbook sup- plements and arranges the material in orderly fashion, it is believed that good results will be obtained. TEACHERS' HANDBOOK CHAPTER I CHEMICAL AND PHYSICAL CHANGES Pages 9-14 As a first experiment in chemistry to give a concrete illustration of the nature of chemical change, something likely to be of intense interest to the pupil should be selected. The material used should be familiar to the pupil. We would suggest the lighting of a small pinch of black gunpowder placed on a piece of paper. This will show the principal features of chemical change and at the same time awaken interest in the pupils. The evolution of heat and light are obvious. The new products formed are easily seen and smelled, both those that are scattered in the smoke and those that remain on the paper. A word about the objectionable character of smoke from black gunpowder when used in war, and a hint to the effect that smokeless powder produces only invisible gases as new products, may add to the interest. A physical change can be illustrated by melting a bit of ice, boil- ing the water thus obtained, condensing some of the steam on the under side of a watch glass, and freezing the dew thus formed by rapidly evaporating ether in the watch glass. Use a current of air to assist the evaporation of the ether. Answers to Questions on Chapter I Page 14 1. Different chemical substances are distinguished by their different properties. Physical properties are evident to us through our senses of sight, feeling, smell, taste, and hearing. Chemical 6 CHEMICAL AND PHYSICAL CHANGES properties are shown in the ability of substances to undergo chemi- cal change, the latter always being accompanied by changes of physical properties. 2. Chemical changes differ from physical changes hi the follow- ing respects : (1) A chemical change involves a complete change of properties, that is, the disappearance of the properties of the substance or substances entering the change, and the appearance of new prop- erties which are the properties of the substance or substances pro- duced in the change. Physical changes do not involve a complete change of properties. The changes are caused by the application of some physical force, and when the force is removed the substances are free to return to their original condition. (2) Chemical changes are accompanied by a heat effect, often a very marked one accompanied by the evolution of light. Physical changes do not necessarily involve any heat effect. (3) Another distinction was hinted at in the statement on page 11 that the carbon dioxide produced by burning charcoal weighs 3f times as much as the charcoal. This statement in connection with the law of the conservation of matter shows that the same definite proportion must always exist between the weights of the substances entering this chemical change. If two substances are mixed physically, for example sugar and sand, they may be mixed in any proportion. 3. Five examples of physical change are: (1) Crushing of rock in a stone crusher. (2) Hammering of gold into gold leaf. (3) Compressing air in an automobile tire. (4) Careful mixing together of powdered charcoal, powdered sulphur, and powdered saltpeter, in making the mixture called gunpowder. (5) The shortening of a steel rail on a cold day and its lengthen- ing on a hot day. 4. Five instances of chemical change and points that distinguish them from physical changes are : (1) Sugar is scorched during cooking: The new properties of a PAGES 9-14 7 brown or black color and a burnt taste appear and remain perma- nently even after the sugar has cooled to ordinary temperature. (2) Bleaching of cloth : The property of color is changed, indi- cating that some highly colored substance in the cloth is changed chemically. (3) Ripening of fruit : Unripe fruit tastes sour ; ripe fruit tastes sweet, indicating that a sour substance has disappeared in the form- ing of a sweet substance. (4) Explosion of gunpowder: Heat and light are produced. A large quantity of gases is formed, and the solid substance left bears no resemblance to the original gunpowder. (5) The spoiling of eggs : During this process the eggs acquire a very offensive odor, a new property which indicates the formation of a new substance. 5. Three instances of chemical change in which the heat effect is so intense as to cause the emission of light : (1) Burning of wood. (2) Explosion of gunpowder. (3) Explosion of photographic flash-light powder. 6. Three instances of chemical change in which the heat effect is noticeable, but not so intense as to cause emission of light: (1) Slow combustion of food materials within the body. (2) Fermenting of a manure pile. (3) The action which results from mixing lime and water. 7. Three instances of chemical change in which the heat effect is not noticeable : (1) Rusting of iron. (2) Ripening of fruit. (3) The tarnishing of silver, as when a silver spoon is used in eating an egg. 8. A substance hotter than its surroundings cools off more or less rapidly because the heat escapes into the surroundings. When wood burns, so much heat is produced within a short time by the chemical change that it cannot all escape at once. Therefore the heat becomes very intense within the body of wood and amid the gases of the flame. If the same amount of wood decays completely, the same amount of heat is produced, but so slowly that it can escape 8 MIXTURES AND CHEMICAL SUBSTANCES just about as rapidly as it is produced, hence the heat within the body of wood cannot become much more intense than in the sur- roundings. 9. The material products of burning coal in a furnace are gases which pass up the chimney ; smoke, which consists of solid particles and globules of tarry matter ; and ashes, which consist of the incom- bustible residue from the coal. These products are of no use, and the ashes and smoke are difficult to dispose of without making a nui- sance. Hence the furnace is surely not run to obtain these sub- stances. 10. After a mason slakes lime, he allows the product to cool before he uses it mixed with sand and hair as mortar. In this reac- tion it is the material product and not the heat that is sought. CHAPTER II MIXTURES AND CHEMICAL SUBSTANCES Pages 15-19 To illustrate the separation of a mechanical mixture it may be well to have the pupils separate the constituents of black gunpowder, with which they are already familiar. To do this treat a pinch of powder with a few c.c. of carbon disulphide, filter into a watch glass, and allow the disulphide to evaporate. This will give sulphur by itself. Next use a few c.c. of water with the solid residue (first allow all the carbon disulphide to evaporate) and again filter on to a clean watch glass. On evaporating the water, they will now ob- tain saltpeter. The insoluble charcoal of the gunpowder will be left on the filter paper. As gunpowder is so excellently blended, few pupils would suspect at first that it is a mixture, and yet the simple physical means of separation above outlined will serve to show its character. PAGES 15-19 9 Answers to Questions on Chapter II Page 19 1. Matter is that of which any physical object or body is com- posed, whatever its form or condition, whether gaseous like air, liquid like water, or solid like stone. Anything which possesses mass is matter. In physics, the mass of a body of matter is measured by the force necessary to set the body in motion, or to bring the body to rest if it is already in motion. The mass-of a body is more con- veniently measured by its weight, that is, by the force with which it is attracted to the earth. Therefore matter is anything which pos- sesses mass or weight. Substance in its most general meaning is almost synonymous with matter. Anything which has substance is matter. A substance is, however, usually understood to be a particular kind of matter. A mixture consists of more than one kind of matter, that is, of more than a single substance. In its popular use, however, the term substance is often applied to mixtures. A body is a mass of matter considered separately from other matter. An object is a material thing of definite size and shape. 2. The word substance in its popular meaning may be applied to anything which is composed of matter, although it usually implies matter having special characteristics which readily distinguish it from other sorts of matter. In science, a pure substance is a definite kind of matter unmixed with other kinds of matter. Popularly gravel, garden soil, mortar, paper, wood, gunpowder, baking powder, coffee, leather, blood, flesh, etc., would be classed as substances, although chemically each of these is a mixture of several substances. The word material could properly be used in describing each of these mixtures. 3. Rain water is a pure substance. It is exactly the same sub- stance as pure water which comes from any other source than the clouds. Sea water is a mixture of water with small amounts of several other substances. The Atlantic Ocean is a body of sea water. 10 ELEMENTS AND COMPOUNDS Lake Superior is a body of water. Although the water of the lake is not absolutely free from other substances, it may in comparison with ocean water be classed as a pure substance. The block of ice is a body composed of a practically pure substance. Sugar is a substance. Mapk sugar would popularly be classed as a substance. Scientifi- cally, it is composed of the substance sugar mixed with small quan- tities of natural coloring and flavoring substances. Hash is a mixture. - A mince pie is an object formed from various materials, most of which are mixtures. The marble statue is an object composed of a nearly pure substance. The ledge of marble is a body consisting in the main of marble, although it is certain to contain much more foreign matter than the carefully selected block chosen for the statue. Iron is a substance, although practically all of what is ordinarily called iron contains a small amount of other chemical substances than iron. The old cannon is an object composed of iron. 4. By agitating a mixture of iron filings and powdered sulphur near a magnet, one allows the particles of iron to be drawn to the magnet while the sulphur is left behind. 6. A mixture of salt and sand may be stirred with water, where- upon the salt dissolves. The solution may be drained off from the sand and then, when the water is evaporated, dry salt is left. CHAPTER III ELEMENTS AND COMPOUNDS Pages 20-24 IT will be well in connection with this chapter to let the pupil actually perform the experiment with iron filings and sulphur which is described in the text. Most laboratory manuals give detailed instructions for this experiment. The separation of the experiment into parts is advisable with beginners. Let them first study the PAGES 20-24 11 mixture and separate the iron from the sulphur by various means, thus showing that no new substance results on merely mixing iron and sulphur. Then let them heat the mixture and study the residue as a separate experiment. There is then less likelihood of their be- coming confused as to what they are trying to prove. Answers to Questions on Chapter III Page 24 1. An elementary substance is a pure substance which cannot be decomposed chemically into other substances. A compound is a pure substance composed of two or more elements. An element is one of the eighty-three constituents of all known kinds of matter. An element by itself, that is, when not in combina- tion with other elements, has definite properties by which it is recognized as a definite substance. The physical properties of the element are completely changed when, through chemical combina- tion with other elements, it becomes a constituent of new sub- stances. The element itself, however, still exists, for it can always be separated by chemical means from the compound and obtained again undiminished in weight and exhibiting its original properties in every particular. The identity of the element then is not altered through chemical change, but the identity of the elementary sub- stance is lost. 2. For a list of elements see inside back cover of Foundations of Chemistry. 3. Salt, sugar, water, glass, and marble are compounds. 4. We cannot hope ever to be able to convert lead into gold, for, as a result of all the most painstaking experiments since chemistry has been studied as a science, it can be asserted that in no chemical change is there an increase or decrease in the weight of any element concerned large enough to be detected with the chemical balance. It is true that recent discoveries concerning radium, niton, and a few other elements have indicated very clearly that the elements are really complex and that some at least are constantly changing over into others. Yet the amounts involved in such changes are un- weighably small, and furthermore no force which human ingenuity 12 COMBUSTION has yet been able to bring to bear has had any effect in hastening or retarding such changes. We can therefore regard the mass of gold and that of lead in our earth as constant, at least for any period of time which will come within the limits of human observation. It has been found that radium is slowly but constantly changing into niton, but no indica- tion has ever been discovered that lead is changing into gold. Yet it is perfectly possible that such a change is taking place, only in- finitely slowly. No one would be rash enough to-day to assert that no force will ever be discovered which will hasten this change so that one will be able to see lead change into gold while he waits. But such a possibility is so contrary to all our experiences that we have no ground for hoping for its fulfillment. 5. See Law of Definite Proportions, Section 11, page 22. CHAPTER IV COMBUSTION Pages 25-37 IN this chapter we have a subject which is of the greatest inter- est to the chemist, as it was largely through the progress made in the knowledge of the true nature of combustion that modern chemis- try got its start. The lack of a true understanding of the problem on the part of Priestley, who discovered oxygen, yet never clearly understood the part it plays in combustion, should be pointed out to the class. Lavoisier's splendid demonstration of the nature of combustion should also receive attention. The phlogiston theory should be clearly presented, and it should be shown how natural was the error of those who believed in it, since the products of ordi- nary combustion are so often gaseous. The early discovery of the increase in weight of metals when heated in air should be brought out. In this connection the following quo- tation from the original paper of Jean Rey (1630) l may well be read 1 Rey, Jean, Essays on an Inquiry into the Cause wherefore Tin and Lead Increase in Weight on Calcination. Alembic Club Reprint, No. 11, page 36, Edinburgh. PAGES 25-37 13 to the class to show them that Rey was far ahead of his time and got no recognition from his contemporaries, who still continued to be- lieve in the phlogiston theory for over a hundred years. " Now I have made the preparations, nay, laid the foundations for my answer to the question of the Sieur Brun, which is, that hav- ing placed two pounds six ounces of fine English tin in an iron vessel and heated it strongly on an open furnace for the space of six hours with continual agitation and without adding anything to it, he recovered two pounds thirteen ounces of a white calx ; which filled him first with amazement, and with a desire to know whence the seven ounces of surplus had come. ... To this question, then, I respond and sustain proudly, resting on the foundations already laid, ' That this increase in weight comes from the air, which in the vessel has been rendered denser, heavier, and in some measure adhe- sive by the vehement and long- continued heat of the furnace; which air mixes with the calx (frequent agitation aiding) and be- comes attached to its most minute particles; not otherwise than water makes heavier sand which you throw into it and agitate, by moistening it and adhering to the smallest of its grains.' " Another original paper which will be of interest to pupils in con- nection with the subject of combustion is Priestley's paper on his discovery of oxygen. 1 After telling of his becoming possessed of a 12-inch burning lens, Priestley says, " With this apparatus, on the 1st of August, 1774, I endeavored to extract air from mer- curius calcinatus (red oxide of mercury) ; and I presently found that by means of this lens air was expelled from it very readily. Having got about three or four times as much as the bulk of my materials, I admitted water to it, and found that it was not imbibed by it. But what surprised me more than I can well express, was that a candle burned in this air with a remarkably vigorous flame, and a piece of red-hot wood sparkled in it, exactly like paper dipped in a solution of niter, and it consumed very fast." He says also that while hi Paris, " I frequently mentioned my surprise at the kind of air which I had got from this preparation to Mr. Lavoisier, Mr. le Roy, and several other philosophers, who honored me with their 1 Quotation from Alembic Club Reprints, No. 7, page 8. 14 COMBUSTION notice in that city ; and who I dare say cannot fail to recollect the circumstance." In this connection call attention to the fact that it was this same " Mr. Lavoisier " who finally made use of Priestley's discovery to straighten out the problem of the true nature of combustion. In connection with the study of the action of air on metals, it will be well to have all pupils heat bits of each of several common metals in the Bunsen flame. Iron and copper should of course be used by all. Magnesium may be used either by the instructor or, if plenty is at hand, by all pupils, to illustrate the case of a very active metal. In this connection some thermit; the well-known Gold- schmidt mixture of iron oxide and aluminium powder, may perhaps be used by the teacher. The iron oxide in it can be shown to be the same as the scale that the pupils get from the iron that they heat in air. Thus they may be shown how oxygen may be stored in com- bination and used later even more effectively than when in the free state. The term oxidizing agent may be introduced here for later use. Bits of pure gold, silver, and platinum might well be heated by pupils or teacher to show the lack of activity of the precious metals toward oxygen. Class discussion of the bearing of the facts learned in the above work on the practical uses of the several metals will be valuable. Tin roofs, copper roofs, the use of sheet lead and galvanized iron, and the use of the precious metals in jewelry may be mentioned. A classroom demonstration of the gain in weight when the prod- ucts of combustion of a candle are caught, weighed, and compared with the weight of the candle, is always of great interest to classes. The gain in weight of an oxidizing metal may well be proved by each pupil. For this purpose magnesium ribbon heated in a tared cruci- ble serves admirably because of the rapidity of the action and the marked gain in weight. If it is thought advisable to take the time for it, a comparison of the per cent gain of weight obtained by dif- ferent members of the class will illustrate roughly the definiteness of the proportions by weight existing between the metal and the oxygen which joins it. This example of definite combining proportions will be found valuable for reference on many later occasions. PAGES 25-37 15 With the first quantitative experiment performed by the pupils some little time will of course have to be taken in explanation of the proper use and care of the balance. The metric system should also receive some attention at this time. Pupils frequently find difficulty in understanding the denominations of weights, especially the frac- tional parts of the gram. If the box of weights is likened to a merchant's cash drawer and the weights themselves to pieces of money (i.e. 50 i piece, 20 i piece, 10?f piece, i piece, 2^ piece, and \i piece) pupils will readily learn the denomination of each weight from their familiarity with United States money. The counting of weights will then become as simple a matter as counting money. For the sake of the training in manipulation and in carefulness, it will pay to teach and to insist upon as careful handling of the bal- ance as though it had the accuracy of a fairly good chemical bal- ance. Few schools will have for the use of pupils balances that are accurate beyond the second decimal place, and pupils should not be held for results beyond the possibility of their apparatus. Where more than one or two balances are available, it will be found advantageous to assign each pupil to a definite balance and to hold pupils responsible for the loss of weights or for damage to the balance. By thus assessing minor losses against the pupils, the laboratory can afford to use more costly balances and to keep them in repair. For the sake of frequent subsequent reference, it will be found valuable to point out clearly to the pupils the origin of the gram. The fact that it is the weight of 1 c.c. of water (at 4 degrees C., to be exact) becomes useful later in calculating the volumes of liquids from the weight in grams and the specific gravity. In connection with the discussion of slow combustion in the body (Section 26) a little outline of the physiology of respiration will be valuable to the pupils, as many of them will not have had it in other courses, and others may later take physiology and thus have a bit of foundation laid for that work. The matter of proper ven- tilation may be touched upon here, and the fact that it is not the presence of carbon dioxide that makes the air of a room unsuitable in most cases should be brought out. Overheating, with too much or 16 COMBUSTION with too little moisture present, may be mentioned as more probable causes of discomfort in such cases. The topic of smoke prevention (Section 28, p. 33) is one of vast social significance, and, especially in the soft coal burning sections of the country, is deserving of considerable attention in the chemistry course. The principles back of complete combustion can easily be given at this time, and a visit to some progressive plant which is equipped with proper smoke-preventing devices should by all means be made. If it can be done in class time so that all pupils can go, so much the better. It will be worth more than the same amount of time spent in school. It will be necessary for the teacher to ex- plain the nature of destructive distillation and perhaps actually heat some soft coal in a test tube to put clearly before the pupil the principal cause of the formation of smoke. The procuring and maintaining of a temperature sufficiently high to kindle the smoke before it reaches the comparatively cold surfaces of the boiler, and the supplying of sufficient (but not excessive) air to unite with the smoke complete the chief requisites for complete combustion. Answers to Questions on Chapter IV Page 36 1. The strongest proof that something from the air is concerned in combustion lies in the fact that by allowing metals to act on a confined volume of air, the volume, as well as the weight, of the air diminishes. Metals like lead, iron, zinc, copper, and mercury thus lessen the volume of air if they are heated in it. Moist iron filings act in this way fairly rapidly even at ordinary temperature. Air which has thus been deprived of a part of its substance is no longer capable of causing the corrosion of metals or of supporting the active combustion of substances like wood and charcoal. Although the phlogistic chemists explained the gain in weight of metals when they changed to calces by the assumption that the phlogiston which escaped had a negative weight, their viewpoint becomes almost impossible to uphold when we consider the fact that the air into which the phlogiston is supposed to be escaping loses in volume as well as in weight. PAGES 25-37 17 2. Iron rust is porous and allows air to penetrate through to the metal underneath so that a piece of iron may in time become rusted completely through. On the other hand, the coatings formed by oxidation on the surface of copper, zinc, and lead are impervious and protect the metal underneath from further action of the air. 3. The paint used on iron bridges is impervious to the atmos- phere and thus prevents corrosion. The film of oxide (or basic car- bonate) which rapidly forms over the surface of copper exposed to the atmosphere renders the use of paint unnecessary. 4. In charcoal fires there are invariably parts in the interior of the incandescent mass where the amount of oxygen is deficient and carbon monoxide is therefore formed. This is very apt to escape and become cooled to below the kindling temperature, before it comes in contact with sufficient oxygen to burn it to carbon dioxide. On the other hand, a plentiful air supply has access to the hot gas flame from all sides, and although carbon monoxide probably exists in the interior of all such flames (in fact illuminating gas often contains a large proportion of carbon monoxide), it is impos- sible for it to get beyond the very hot part of the flame before it is completely burned. 5. The facts that the animal body is continually giving off heat and that carbon dioxide can be shown to be exhaled from the lungs prove that combustion is taking place within the body. 6. The rapid breathing of the runner and the use of the black- smith's bellows both supply a greater amount of oxygen, making more rapid oxidation possible. 7. Smoke consists of carbon and tarry matter. If these are burned, more heat is produced than if the smoke passes unburned up the chimney. 8. If we rake a lot of fresh leaves on top of a burning pile, the heat of the fire underneath decomposes the leaves, and some of the products of decomposition escape as smoke. This smoke consists largely of tarry matter which is combustible but is below its kindling temperature. When the layer of leaves is heated enough so that the flame can break through from below without being chilled, the nearest part of the smoke is raised to its kindling temperature, the combustion of the smoke particles produces the heat necessary to 18 COMBUSTION raise the temperature of the surrounding smoke particles to their kindling temperature, and so all of the smoke is consumed and its escape seems to cease as if by magic. 9. Soft coal is similar to leaves in that heat decomposes it into tarry matter and soot which pass off as smoke unless they are able to burn. If a stoker throws a large quantity of soft coal on a fire in a furnace, the surface is chilled and the decomposition products there- fore escape as smoke until the layer of fresh coal is heated through so that the smoke is heated to its kindling temperature. Of course even then smoke may continue to escape, if sufficient air for com- plete combustion is not admitted to the space above the fire. By shoveling in small amounts of coal frequently, but at no time enough to chill any large part of the surface of the fire, and by care- fully adjusting the drafts into the combustion chamber, a stoker can almost eliminate smoke even from the ordinary furnace. The design and manipulation of a furnace so as to prevent smoke are discussed in Section 28, p. 33. 10. The steaming of a pile of manure in winter indicates heat within the pile. This heat can be produced only by some chemical reaction which is probably in the nature of a slow combustion simi- lar to the decay of wood. This reaction, to produce so marked a steaming, must be considerably more rapid than the decay of wood. 11. A camper blows his fire when it gets low for the same reason that a blacksmith uses his bellows when he wishes a more intense heat. One might ask why blowing extinguishes a candle or a match in- stead of making it burn brighter in consequence of the increased supply of oxygen. The answer to this is that the candle or match as it ordinarily burns has ample oxygen supplied to burn the mate- rial as rapidly as it can be raised to its kindling temperature by the heat of the flame. Blowing forces the flame, that is the source of heat, away from the object which requires the heat. Furthermore the added amount of cold air cools the object, which then falls to be- low its kindling temperature. 12. The principal service of water in extinguishing a fire is that it cools the burning materials below their kindling temperatures. The exclusion of oxygen by the water, and more particularly by the steam formed from it, also plays a part. PAGES 38^19 19 CHAPTER V OXYGEN Pages 38-49 IN connection with the preparation of oxygen a modification of the historic experiment of Priestley may well be given. By using small closed tubes prepared by the pupils themselves from ordinary small glass tubing, only a small amount of the relatively costly mercuric oxide need be used. The Bunsen burner will of course take the place of Priestley's burning glass. By the use of leading questions, the pupils can be brought to reason out for themselves that the same gas which causes mercury to become covered with a red powder when heated in air also causes a pine splint to burn. Although the mercuric oxide used to-day is prob- ably never made by direct oxidation of mercury, it may be explained that the same product might be thus obtained, and by heating this product a gas is given off which does support ordinary combustion. The teacher cannot be too careful in connection with the use of potassium chlorate for the preparation of oxygen, as it makes a vio- lently explosive mixture with almost any combustible substance. Such mixtures frequently detonate on slight friction. Hence every precaution should be taken to see that the pupils do not obtain any quantity of the material, or use what is given to them except as directed. It is probably not advisable to tell them of the possibili- ties, but rather repeat the caution, doubtless already many times repeated, that they attempt nothing without specific direction from the teacher. The manganese dioxide used should first be tested by the teacher by heating a small sample with potassium chlorate in a test tube, and if any considerable amount of combustion is in evi- dence, the manganese dioxide should not be used for this purpose. Granular manganese dioxide is more likely to be free from carbon or other impurity than the powdered form, and having less surface it will not cause as rapid evolution of oxygen from the potassium chlo- rate. This is a real advantage in this case, as pupils frequently fail to collect the oxygen as fast as it is evolved. 20 OXYGEN For the preparation of oxygen on the lecture table the use of oxone (a commercial form of sodium peroxide) is' recommended on ac- count of its convenience and relatively low cost. By adding water from time to time in small amounts to a few small lumps of oxone in a flask, a free flow of oxygen may be kept up or renewed as needed. A thistle funnel, or better a small dropping funnel, through one of the two holes of the stopper will serve for the admission of the water, the other hole being provided with a delivery tube. In connection with the study of kindling points (Section 41) a simple lecture table experiment will serve to make the matter more real to the pupils. Bits of (a) yellow phosphorus, (6) sulphur, and (c) charcoal may be used. The charcoal can usually be ignited only by direct application of the flame to a projecting corner of the piece. The good heat conductivity of a copper plate will suffice to raise the temperature of the phosphorus and sulphur to the kindling point without contact with the flame. This should be pointed out to the class, as most pupils think that contact with an open flame is neces- sary for ignition. As a familiar example of differences in kindling point, cite the common match with sulphide of phosphorus l on the tip, an easily kindled gunpowder-like mixture next, and then paraf- fin and wood to progressively kindle from the heat of the burning substances first kindled. The safety match should also be ex- plained. The advantage of the higher kindling point and non-poi- sonous character of red phosphorus should be emphasized. Explain the ingenious placing of the red phosphorus on the lighting surface instead of on the tip of the match. In connection with the study of oxygen considerable class time should be given to relating active combustion with the slower forms such as combustion in the body, rusting of metals, and decay of organic matter. In connection with the paragraph on spontaneous combustion (Section 43, p. 46) the nature of the drying of paints can be explained. It consists in the oxidation of the liquid oil, usually linseed oil, to a solid resinous substance which adheres to the surface and binds 1 The use of yellow phosphorus, on account of its poisonous properties, is now prohibited by law in the United States. The sulphide of phosphorus kindles as easily but it is not poisonous. PAGES 38-49 21 together the coloring pigment. Of course this drying oxidation does not use as much oxygen as the rapid burning of the oil, which would yield carbon dioxide and water as products. The resinous substance is not especially subject to further slow oxidation, but of course if it were heated to its kindling temperature, it would burn like any resin to carbon dioxide and water. To facilitate the drying oxidation of the oils certain substances called driers, usually containing manganese dioxide or lead oxide, are added, but these driers do not themselves furnish oxygen to the oil ; they merely facilitate the addition of atmospheric oxygen. The driers act as catalyzers just as the manganese dioxide acted in the decomposition of potassium chlorate, although in one case the reaction is the addi- tion of oxygen and in the other case the breaking away of oxygen. The practical methods of preserving foods from decay (such as are briefly indicated in Question 12, p. 49) should be gone into in class and explained in some detail. The importance of decay as a means of removing organic matter that would otherwise become obnoxious should also be shown. This will lead naturally to the first topic of the next chapter. The kind of correlation between chemistry and daily life that is advocated in the above paragraph is very valuable and easily possible. It will be found far more worth while than the mere teaching of the facts without relating them to the general principles concerned. Answers to Questions on Chapter V Page 48 1. The most prominent chemical property of oxygen is its ability to react vigorously with many substances when they are heated in contact with it. It should be noted, however, that at ordinary tem- perature oxygen is practically without action in almost all cases if no moisture is present, but that it reacts slowly in many cases when water is present. 2. See answers to Questions 2 and 3, Chapter IV. 3. Gold does not unite directly with oxygen under any conditions. It must be that gold is much less active than most metals towards oxygen. 22 OXYGEN 4. The use of pure oxygen in the blacksmith's bellows would produce so violent a fire that even the iron put in the fire to be heated would be burned. 6. If the atmosphere consisted of pure oxygen, a fire once started would be so violent that it could not be checked. It would even consume iron and some other materials used in fireproof construc- tion. 6. The fire danger in wooden buildings is slight for the reason that the kindling temperature of wood is fairly high. 7. Conditions under which fires start without the application of flame are discussed under spontaneous combustion, Section 43, p. 46. 8. Oxygen is not lighter than air and hence would not be of use for filling balloons. 9. Fish breathe by withdrawing oxygen from water. Goldfish would probably die if they were placed in freshly distilled water. Before the water in a retort (see Fig. 1, p. 17) begins to distill actively, it must rise to 100 C., at which temperature practically all of the dis- solved oxygen is driven out, for the solubility of gases in water is less at higher temperatures (see top of p. 43). When steam begins to pass over into the condensing tube, the oxygen is driven out and the condensed water in trickling down the tube and falling into the receiver does not stay long enough in contact with the air to dis- solve sufficient oxygen to keep fish alive. 10. A fallen tree in the forest gradually disappears due to decay (Section 45, p. 47). 11. Water contaminated with sewage is unfit to drink on account of poisonous substances in the sewage and especially on account of the germs (bacteria, microscopic living organisms) of dangerous diseases which may be present if the sewage comes from infected persons. If the water runs for miles over rapids in a river, it be- comes thoroughly oxygenated, the poisonous materials are oxidized to harmless substances, and the bacteria are killed. 12. Although the spoiling of food products is similar to the decay of wood in that it takes place almost solely through the agency of microscopic life, it should be recognized that the most dangerous decompositions of foods occur in the absence of free oxygen and are PAGES 50-66 23 not oxidations. Nevertheless anything which kills these little or- ganisms will prevent the spoiling of food, as well as the decay of wood. (a) Canning excludes oxygen and also excludes bacteria. At the time the cans are sealed the contents are always hot so that no live bacteria are sealed up. Effective heating kills all living organisms. (6) The creosote in smoke kills bacteria. (c) Salt kills bacteria. (d) Bacteria cannot grow and multiply when cold, but simply lie dormant. Hence refrigeration retards the spoiling of food. (e) Bacteria can grow and multiply only in presence of water. If dry, they simply remain dormant. Hence drying prevents spoiling. (/) Neither can bacteria thrive in concentrated sugar solutions, although many organisms like yeasts live principally on sugars when the latter are diluted with water. Hence sirup, which is a highly concentrated solution of sugar, prevents the development of micro- scopic organisms. CHAPTER VI THE OXIDES OF CARBON Pages 50-66 THE carbon dioxide cycle in nature should receive more time in class than can be devoted to it in the textbook. Those pupils who have previously studied botany can be called upon to explain the necessary outlines of plant structure and plant physiology. The large part played by decay, brought about by bacteria, cannot be over-emphasized. Bacteria are to be classed as plants rather than as animals and it should be pointed out how extremely small a part in the great carbon dioxide cycle is played by animals, for animals and fires together produce only about three per cent of all the carbon dioxide returned to the air. In most classes all pupils will be given a chance to prepare carbon dioxide and to study it at first hand. All laboratory manuals con- tain full directions for this work. If a siphon of plain soda can be 24 THE OXIDES OF CARBON had, pupils can more readily learn the properties of the water solu- tion of carbon dioxide. Each pupil will need no more than a few c.c. of the solution. The effect of one drop of the solution on some lime water in a test tube and then the effect of adding a slight excess of the carbonated water, should be noted. The greater solubility of the calcium bicarbonate thus formed should be explained and the knowledge applied to the formation of limestone caves and the causation of one type of hard water (temporary hardness). This matter can then be gone into more thoroughly under calcium and its compounds (Sections 211-214, pp. 199-203), when the pupil has more chemistry at his command and can better understand the nature of the reactions involved. The preliminary approach to the subject in connection with this chapter will give something to which the more complete treatment later on can be attached. Because of the many valuable points of contact between some of the carbon dioxide chemistry and daily life, it is well to spend quite a little time on such topics as the chemical fire extinguisher, car- bonated waters, the use of yeast, and the use of baking powder. If a chemical extinguisher is available, it should by all means be taken apart in the presence of the pupils, and if practicable it should be discharged at a small fire built in the school yard. Such an ex- periment will arouse much interest and will be remembered long after most of the more theoretical parts of the course have been for- gotten. It has its practical value too, for every one should know what to do in case of fire and how to use extinguishers if they are available. The cooling effect of the water thrown by the carbon dioxide type of extinguisher should be emphasized. It is probably of more importance than the smothering effect, especially in outside fires, where the action of the wind prevents much smothering. In connection with the commercial manufacture of carbon dioxide (Section 61, p. 62), it may be added that much carbon dioxide for use in preparing soda water is being made at the present time by the combustion of coke. Such charged water does not carry any of the yeasty odor sometimes noted in the product from the breweries. The brief treatment of carbon monoxide (Section 62, p. 62 and Sec- tion 65, p. 63) serves to introduce the subject of multiple combining proportions and to give a slight acquaintance with the properties PAGES 67-78 25 of the lower oxide of carbon. This acquaintance can later be re- called when producer gas and water gas are to be studied (Sections 283-284, pp. 270-273). Answers to Questions on Chapter VI Page 65 In this chapter no question is asked except to recall or illustrate a practical use of information clearly given in the textbook. CHAPTER VII THE ATMOSPHERE AND NITROGEN Pages 67-78 THE experiments on air which make use of yellow phosphorus should be performed by the teacher on account of the danger of serious burns. The classroom discussion of the fixation of nitrogen affords a valuable means of correlating chemistry and daily life. A little volume, 1 which has recently been published, will be of value to the teacher in preparing himself for an up-to-date discussion of this subject. In performing the more accurate experiment on the volume of oxygen in air (Section 78, p. 74), it will be found advantageous to leave the apparatus standing overnight. The use of phosphorus rather than alkaline pyrogallate solution is recommended, as pupils can much more readily comprehend what is taking place in the former reaction. The above experiment leads naturally to the use of Boyle's and Charles' laws. It will be found that pupils will learn to use these laws much more readily when they thus have a real need for the application of them. 1 Knox, The Fixation of Atmospheric Nitrogen. D. Van Nostrand Com- pany. 26 THE ATMOSPHERE AND NITROGEN Answers to Questions on Chapter VII Page 78 1. It will be recalled that the chief characteristics of a chemical compoun^Las distinguished from a mixture are : (1) that its proper- ties are altogether different from the properties of its constituent elements when separate, (2) that heat is either given off or absorbed when it is formed from its constituents, (3) that the proportion of its constituents is always the same. The facts stated in Section 71, p. 69, in support of the assertion that air is a mixture rather than a chemical compound, show that air does not possess these characteristics of a compound. As additional facts may be mentioned : (1) Air may be separated by the physical process of distilling liquefied air (Section 33, p. 40). This, however, in itself is not a complete proof. We know, for example, when oxide of mercury, which is undeniably a compound, is subjected to the same sort of physical treatment, namely, heating, that it is decomposed and oxygen passes off first. But we know in the latter case that the two products bear no resemblance to the red mercuric oxide, and that the products are always yielded in the same proportion. When liquid air is distilled, nitrogen first passes off fairly pure, but the pro- portion of oxygen gradually increases, until towards the last nearly pure oxygen is passing off. The liquid left in the vessel shows no constant composition, but its proportion of oxygen increases steadily. Thus characteristics 1 and 3 of compounds are again shown not to be found with air. (2) Air is soluble in water, but air obtained from water which held it in solution has a different composition from the air originally dissolved. The oxygen and nitrogen of the air dissolve in water in the ratio of their solubilities, but this ratio is different from that in which they occur in normal air. If air were a compound, air ob- tained from solution would not vary in composition from that which was dissolved. (3) A more everyday argument is that air exhaled from the lungs contains a lesser proportion of oxygen than ordinary air. Yet this exhaled air is still practically air. This air can be passed through PAGES 67-78 27 a tube filled with caustic soda (see Fig. 2, p. 28) whereby the carbon dioxide is removed. The air then has practically the same proper- ties as ordinary air. It can support combustion and respiration almost as well as ordinary air. Yet the composition is different. Thus again it is shown that air does not possess characteristic 3 of compounds. 2. The gases present in the air are : Nitrogen, about 78 per cent by volume; oxygen, about 21 per cent; argon, about 1 per cent; carbon dioxide, about 0.04 per cent; minute quantities of helium, neon, krypton, and xenon; and water vapor in amounts varying from very little in desert regions to 2 per cent or even more in very warm and moist air. 3. Oxygen is the most important of these gases from the stand- point of its direct activity and the amount of it involved in processes which are vital to human life and welfare. The human being could not live many minutes without oxygen to breathe. Neither would fuels burn without oxygen. But water vapor, carbon dioxide, and nitrogen are also absolutely essential to the human race as it has become adapted through long ages to its present environment. Indeed we can hardly say that any one of these gases, not even excepting oxygen, is more important than any one of the others, for human life could not long continue if any one of these gases should disappear from the atmosphere. Water vapor, through occasional condensation as rain, supplies the land with the moisture necessary to the growth of crops. Car- bon dioxide also is necessary to the growth of plants (Section 48, p. 50). The direct service of nitrogen is in diluting the oxygen of the air, thus moderating the intensity of the combustion of fuels. Nevertheless without nitrogen it might be possible to dampen the combustion of fuels by redesigning our furnaces with smaller drafts. The vital service of nitrogen, however, is an indirect one. Through various means of fixation, some of which are mentioned in the chapter, the supply of combined nitrogen in the soil is maintained. This combined nitrogen is essential to the growth of plants, and thus if the nitrogen should disappear from the air, our crops would cease to grow after a period of years when the soil had become exhausted of its nitrogen compounds. 28 THE ATMOSPHERE AND NITROGEN Argon and the similar gases, helium, neon, krypton, and xenon, are of no known importance in the development of human life or of any other form of living matter. 4. The fixation of nitrogen is difficult because nitrogen is an inactive element, or in other words, it has little or no tendency to combine with the elements or substances with which it ordinarily comes in contact. Nitrogen once in combination, however, passes from one form of combination to another with considerable ease. Thus combined nitrogen can undergo the changes necessary to bring it into the forms required by the various kinds of plant and animal life. 6. In nature, atmospheric nitrogen is brought into combination mainly through the action of colonies of bacteria which live on the roots of the plants of the legume family. Electrical storms cause the combination of some nitrogen with oxygen in the air and subsequently nitric acid is formed and brought down to the soil with the rain. 6. See Section 75, p. 71. 7. Oxygen can be removed from the air by allowing any substance with which it will form a non-gaseous compound to act on the air. As stated in the textbook, phosphorus may be burned in the air, or better, wet phosphorus may be allowed to oxidize slowly. One of the best methods of removing oxygen from air is to pass the air through a tube containing copper turnings heated to redness. Iron turnings will serve as well if the air be free of water vapor, upon which the iron will also act, setting free hydrogen (see Section 100, p. 100). 8. In ordinary fires four volumes of nitrogen have to be heated to the temperature of the fire for every one volume of oxygen. This of course decreases the temperature of the fire and it provides a greater quantity of gas to carry unutilized heat up the chimney. If pure oxygen were used instead of air, the higher temperature of the fire would occasion a more rapid transfer of heat to the boiler tubes (see Fig. 4, p. 35) and there would be but approximately one fifth as much gas to carry waste heat up the chimney. The objections to such a use of oxygen are first its expense and second its effect on the furnace. Iron itself burns freely at tempera- tures above its kindling point. Its combustion in pure oxygen is, PAGES 67-78 29 as we know, self-sustaining. To use pure oxygen, the furnace would have to be redesigned. No iron could be used in the construction of the grate, dome, or even door. The water-cooled boiler tubes, however, could still be of iron because their temperature could not reach the kindling point since they are filled with water. Further- more, it would be very difficult to find a fire brick which would not melt under the heat of such a fire. 9. The following table taken from Woodman and Norton, Air, Water and Food, Wiley and Company, gives the per cent of nitroge- nous substance in some common kinds of food. The values are based on the weight of the food as bought, including in a number of cases a large proportion of water. The nitrogenous substance contains on an average 16 per cent of actual nitrogen. FOOD MATERIAL NITROGENOUS SUBSTANCE Beef (round) Per Cent 192 Beef (sirloin steak) . 165 Veal (breast) . 14 2 to 16 9 Fresh pork (ribs and shoulder) . Chicken (fowls) Medium fat mutton and beef . Salt cod (boneless) 13.7 to 14.5 11.5 to 16.0 11.4 to 12.9 277 Sardines (canned) 237 Herring (smoked) 20 5 Salmon (canned) 18 6 to 20 2 Salt mackerel . 163 Salmon (fresh) 12 6 to 15 Fish (fresh) 11 9 to 12 Eggs . 11 9 Milk 3 3 Cheese (American pale) . . . Cheese (Neuchatel) Butter 28.8 15.1 to 22.3 1 Peanut butter 293 30 THE GAS LAWS FOOD MATERIAL NITROGENOUS SUBSTANCE Peas (dried) Beans (dried) Peanuts Walnuts (shelled) . . . Oats Macaroni Wheat (entire) flour . . Wheat flour (white, bakers') Raisins . Per Cent 20.4 to 28.0 19.9 to 26.6 19.5 16.6 16.5 7.9 to 16.6 12.2 to 14.6 10.3 to 14.9 2.3 10. Clover and alfalfa are members of the legume family and are particularly suited for increasing the soil content of combined nitrogen. CHAPTER VIII THE GAS LAWS Pages 79-90 THE explanation of the gas law corrections has purposely been made in considerable detail, as experience has shown that what is obvious to the teacher is often far from obvious to the pupil. Where pupils have previously had work in physics on Boyle's and Charles' laws less time will be needed, but they, too, usually profit from a review of the work. It is difficult to teach how to correct for the presence of water vapor so that this subject will be really comprehended by the pupil. The authors deem it wiser to avoid the subject altogether than to teach it in a mere mechanical fashion, and particularly so since the refinement of any experiments likely to be undertaken will not be great enough to make the water vapor corrections of importance. Hence the subject of water vapor corrections has been omitted in the text. It is given in Sections I and II of the Appendix and it PAGES 79-90 31 is certainly well worth teaching if the teacher can take the time to teach it well. If it is well taught, the pupil not only will be able to use correctly aqueous tensions in calculating gas volumes to stand- ard conditions, but he will perceive their bearing on the subjects of relative humidity, evaporation, and precipitation. Answers to Questions on Chapter VIII Page 89 2 - 50x lfTfr 48 - 3c - c - 5. 100 X = 200 c.c. 6. 200 X - 194.7 c.c. 273 7oO 7. 100 X ^ = 102.6 c.c. 8. 40.1 X ^ = 38.0 c.c. 9. 20 X = 21.1 c.c. 10. 100 X = 50.0 c.c. 740 1520 13 55 x 15. New temp. = 273 X 2 = 546 Abs. = 273 C. New press. = 760 X 2 = 1520 mm. Ans. Final conditions are 273 C. and 1520 mm. 32 WATER CHAPTER IX WATER Pages 91-99 THIS preliminary chapter on water deals with it primarily from the side of its physical properties and its common uses. While not, strictly speaking, a chemical treatment of water, the chapter nevertheless deals with matters of the greatest importance, not only to chemists but to every one. A chemistry course can hardly afford to omit such a study of water. As most chemical reactions are conducted in water solution, the subject of solubility should receive even more attention than is given it in this chapter. It will be advisable to let the pupils make several simple experiments of a roughly quantitative character in order to determine for them- selves the simpler facts of solubility. The use of experiments which lead to practical applications will arouse more interest on the part of the pupils. For example, if gasoline is used by the pupil, together with grease, to show the solubility of the latter in gasoline, the pupil can then readily un- derstand why gasoline is used in cleaning clothing. It would be well to have the pupils remove grease spots from cloth by the use of gasoline. Some members of the class might use carbon tetrachlo- ride, ether, or benzol similarly and report to the class. The fact that all these solvents are in practical use for cleaning, or for extracting fats, should be brought out. The use of some of these solvents in extracting grease from garbage on a large scale may be men- tioned. The insolubility of grease in water should of course be first learned by actual test. Similarly the difference in solubility of sugar in hot and cold water may be shown experimentally, and related to candy making and to the crystallization of granulated sugar by the refineries. The slight solubility of some substances, as compared to others, may be shown by contrasting the ready solubility of sugar with the slight solubility of crystals of boric acid. The use of the saturated PAGES 91-99 33 solution of the latter as an eyewash may be mentioned. The very slight solubility of boric acid serves as a guide in making up the solution, for by shaking the crystals in cold water it is not possible to get too much for the purpose into solution. Supersaturation may be studied briefly in passing, in order to lead to a brief study of crystallization, which may well be made in connection with the solubility work. Chemists depend so largely on recrystallization to purify substances, that a few experiments in the forming of crystals will be well worth while. The use of common alum for this purpose is recommended and fine large perfect crystals can be obtained by the pupils if a little care is used. Perhaps the best way to proceed is to have each pu- pil prepare about 200 c.c. of hot alum solution containing about 25 g. of alum and to allow this to slowly cool. A wrapping of towels or aprons around the flasks will permit slow cooling, or a number of the flasks can be shut up in a fireless cooker, if one is available. The excess of material will form fairly perfect crystals during the cooling, and these may be used as seed crystals in the remain- ing saturated solution, which should be transferred to beakers or crystallizing dishes to permit evaporation of the water. The grow- ing crystals should be turned to lie on new sides each day, or they may be suspended in a noose of thread so as to grow symmetrically. In the latter case the thread will, of course, remain in the com- pleted crystal. Much interest will be aroused by such an experi- ment as above outlined, and no more than a few minutes each day will be required for it. A few of the pupils may use copper sulphate or nickel nitrate in small amounts to vary the experiment, and the beautiful blue or green crystals will prove very attractive to the class. The brief treatment of atmospheric moisture in Sections 94-95, pp. 93-95, although belonging more properly to another branch of science, has valuable practical applications which are so dependent on an important property of water, namely, its varying vapor ten- sions at different temperatures, that it deserves a place in this chapter. For those who teach the correction for aqueous tension in connection with gas law work, this matter of relative humidity 34 WATER has a direct application and may be used with the matter on page 426 in the Appendix (see footnote, p. 86). A visit to the local weather bureau station and the reading of the hygrometer will be of interest. As an additional classroom exercise, the effect on the mucous membranes of the respiratory tract of too low a relative humidity in over-heated air may well be taken up, and the use of various schemes for humidifying the air of public buildings should be men- tioned. The treatment of the subject of water purification given in Sections 96-98, pp. 95-97, is of course very brief and may well be supple- mented by class discussion. The difficult biological, chemical, and especially mechanical problems attendant upon the actual manage- ment of a public water supply cannot be more than touched upon in a high school course in chemistry. It would be unfair to the pupils to pretend that they can become expert in these difficult matters. A trip to the municipal filter plant and water laboratory is always of interest at this point. A brief hint at the general cause of the hardness of water is given in Section 99, p. 97, to establish a slight foothold for future progress, when hard water is studied more at length in Sections 213-214, p. 201. Answers to Questions on Chapter IX Page 98 1. A colorless liquid which appeared like water could be proved to be water if its specific gravity were found to be exactly one, or if it froze at exactly C., or boiled at exactly 100 C. 2. Ice could be most quickly distinguished from rock crystal (quartz) by its hardness. The former is easily scratched with a knife, the latter not at all. 3. We can prove that water vapor is present in the schoolroom by watching it condense on a cold surface, as the side of a dipper or tumbler filled with ice water or a mixture of salt and ice. 4. See Section 92, p. 92. 6. Nitrogen compounds, as well as compounds of potassium and PAGES 91-99 35 phosphorus, must be soluble, at least to some extent, to be available for plant nutrition. Hence if our western deserts had been subjected to rainfall during the last century, much of the soluble plant food would have been washed out, and the land would not show the fertility that it now does. 6. In the daytime, the sun warms the earth's surface and a good deal of water evaporates into the likewise warmed lower layer of the atmosphere. At night the lower layer of the atmosphere be- comes cooler and incapable of holding as much water vapor. Part of the latter therefore condenses and appears as dew (see Section 94, p. 93). If the subject of the pressure of saturated water vapor has been taught in connection with the corrections for gas volumes, it should also be applied in answering this question (see Appendix I and II, pp. 425-427). 7. See Section 95, p. 95. 8 and 9. See Sections 96, 97, pp. 95-96. 10. The human body requires a certain quantity of mineral salts for its nutrition, and these may be obtained from drinking water as well as from solid food. But mineral salts will remain as a solid scale in boiler tubes when the water is converted to steam, and they may interact with the soap used in laundries, thereby using up the soap and producing a troublesome precipitate. Bacteria, on the other hand, work no injury in most manufac- turing operations, for they find no fertile ground for multiplying. Even if they do by chance multiply, the poisons that they secrete have no effect on the inanimate objects with which they come in contact. Thus the same standards of purity do not apply to water for drinking and for industrial uses. 11. To obtain fresh water for drinking, one would be most likely to distill salt water. Lacking a still, however, one might take ad- vantage of a cold night or of an ice machine to freeze the water, for it is to be noted that pure ice separates from salt water unless the solution is saturated and sea water is not more than one tenth satu- rated with salt. 36 COMPOSITION OF WATER CHAPTER X COMPOSITION OF WATER Pages 100-110 THE teacher will note the pedagogical method involved in con- necting the investigation of the composition of water with the previous investigation as to the composition of air. If the matter is taken as a sort of interesting game, as a difficulty to be sur- mounted, the pupils will frequently apply themselves to the task with surprising eagerness. The material first used in the attack upon water is the well-known metal iron, which with the aid of heat succeeds in decomposing water. Draw from the pupils by suitable questions, the similarity between the product formed on the iron this time and that formed when iron was heated in air. In short, establish the identity of the two products by comparison of properties. Let this be done in connection with a classroom experiment, following the outline of that described in Section 100, p. 100, and let the use of the textbook by the pupils follow rather than precede the experiment. The use of the unfamiliar, but more active metal sodium, can then follow. (If the pupils use sodium, the usual precautions, as to using very small pieces and keeping at a respectful distance from the dish in which the reaction takes place, should be ob- served.) The teacher may use bits of potassium and calcium to illustrate the gradations in activity among the very active metals, and to amplify the evidence that water contains hydrogen, which it gives up when active metals react with it. The use of zinc dust with the residue, after water and sodium have reacted, gives another chance for the pupils to reason out the meaning of the reaction. It also enables them to show the double character of the hydrogen of water, and that part of the hydrogen is more readily dislodged than the rest of it. The electrolysis experiment adds to the evidence in regard to the composition of water the fact that oxygen is the other constituent, and also gives the volume composition. PAGES 100-110 37 The synthesis of water follows to confirm the volume composition and to show that two volumes of steam result from two volumes of hydrogen and one volume of oxygen. The weight composition is next calculated from the weight per liter of each gas and the volume composition. This fairly thorough study of the composition of water is given, to be later used as a basis for the presentation of the atomic theory and for showing how a formula may be deduced. Avogadro's hy- pothesis is also to be used in connection with the volume relations here brought out. The method is slow, but far surer to produce ultimate under- standing than a more rapid but superficial covering of the ground ; and there is surely more mental discipline to be had from the slow but more thorough method. The brief study of the other oxide of hydrogen, hydrogen perox- ide, comes naturally enough after the study of water. It affords an additional case of multiple proportions, the two oxides of carbon having previously been mentioned in Sections 62-65, pp. 62-64. Answers to Questions on Chapter X Page 109 1. We know that water cannot be an element because it can be decomposed into two substances, hydrogen and oxygen, the com- bined weights of which are just equal to the weight of the water. 2. The explosion of an oxygen-hydrogen mixture is due to the expansion caused by the high temperature produced during the re- action. Except for this expansion, the volume of the water vapor formed is less than the sum of the volumes of the oxygen and hydro- gen concerned. When there are just two volumes of hydrogen for each volume of oxygen, the gases combine completely, and the heat of the reaction goes solely to raising the temperature of, and thus ex- panding, the water vapor. If the proportions are other than two to one, the excess of either one gas or the other behaves like any inactive gas. Some of the heat of the reaction goes to heating this excess and so the temperature of the mixture does not rise so high, the ex- pansion is less sudden, and the explosion is not so sharp. 38 COMPOSITION OF WATER 3. See Table IV, p. 428, of Appendix. 4. The whole of the 30 c.c. of the hydrogen unites with 15 c.c. of the oxygen, leaving 15 c.c. of the oxygen unchanged. The volume of the water is negligible. Answer, 15 c.c. 6. 30 c.c. of hydrogen combine with 15 c.c. of oxygen, forming 30 c.c. of water vapor and leaving 15 c.c. of oxygen. Total volume is 45 c.c., consisting of 30 c.c. of water vapor and 15 c.c. of oxygen. 6. The volume of the tube being constant, the amounts of the gases are in proportion to, and can be measured by, the pressures they cause. Hence the 76 cm. of oxygen will combine with 2 x 76 = 152 cm. of hydrogen. 76 + 152 = 228 cm. = the total pressure of the mixture. Hence the tube contained the mixture in combining proportions. After the explosion, when room temperature is re- gained, there will be a few drops of liquid water collected on the walls of the tube, and the rest of the tube will be filled with water vapor at a low pressure. 7. At 100 C., 10 cm. of oxygen combine with 20 cm. of hydrogen, forming 20 cm. of water vapor and leaving 20 cm. of hydrogen. After explosion, the pressure is 40 cm. at 100 C. Cooled to C., the water vapor condenses to liquid, and we neg- lect the small pressure of the little water vapor that remains. The pressure of the hydrogen decreases in proportion to the absolute temperature : 20 X fit = 14.6 cm. = pressure at C. 8. Composition by weight : hydrogen, 2.75% ; chlorine, 97.25%. 9. A water chemist's business is to test the suitability of water for drinking supply or for industrial purposes. He knows, as does every chemist, the exact composition of pure water, hence there is no object in decomposing the water to find out how much hydrogen and how much oxygen will be obtained. His task is to examine the water for the dissolved and suspended substances it contains. 10. Water is used largely for power in turning mill wheels and turbines ; in mining it is used to carry gold or metal-bearing sands over plates that collect the metal ; in countless industries and in agriculture it is used as a solvent; and in all of these cases the water is not decomposed. It is decomposed in only a few practical industries, as, for example, where hydrogen is obtained by decompos- PAGES 111-120 39 ing water with hot iron, and where oxygen and hydrogen are obtained by decomposing water by the electric current. 11. See Section 108, p. 108. Other illustrations of the law of mul- tiple proportions are carbon monoxide and carbon dioxide, Section 66, p. 64, and in Section 71, p. 69, it is stated that there are several distinct compounds of nitrogen and oxygen. The law of multiple proportions as stated in Section 66 would embrace these oxides of nitrogen. 12. See Section 108, p. 108. 13. Hydrogen peroxide destroys germs because it oxidizes them. It is not a case of complete combustion, as for example when wood burns. But some of the many chemical substances within the little germ cell which are essential to its life processes are oxidized, and thus indirectly the germ is destroyed. The hydrogen peroxide is a poison for the germ, just as arsenic, prussic acid, or corrosive sublimate, are poisons for human beings. These poisons do not disintegrate the whole human body, but they do interact with some one or other of the chemical substances in the blood or tissues which is essential to the delicately balanced chemical processes of the body. 14. Hydrogen can hold oxygen very firmly bound in water, so that water is a very stable substance ; but the extra quantity of oxy- gen in hydrogen peroxide is just barely held there under favorable conditions. It is ready to break away on the least excuse, and it thus happens that readily oxidizable bodies like the skin and cotton are vigorously attacked by this oxygen from the hydrogen peroxide, even though they remain quite unaffected by the oxygen of the at- mosphere at ordinary temperatures. CHAPTER XI HYDROGEN Pages 111-120 As hydrogen was first discovered by the pupil while decom- posing water, it is a most natural thing to make next a study of its 40 HYDROGEN preparation, properties, and uses. This is done in Chapter XL After connecting the preparation of hydrogen with the displacing of the element from water by means of active metals, we next sug- gest a series of experiments to be performed by the pupils with various dilute acids and various metals capable of displacing hydro- gen from them. Iron, zinc, and then magnesium may be used with dilute sul- phuric acid, and then hydrochloric acid, in test tube quantities. The hydrogen produced can be lighted at the mouth of the tube. Various fruit acids, such as citric and tartaric, may be tested with bits of magnesium. Acetic acid, cream of tartar solution, and sour milk may be similarly tested by some of the pupils to show that all the common acids contain replaceable hydrogen, which is dis- placed by certain active metals. Copper, silver, gold, and plati- num may be briefly tried by members of the class to add the in- formation that certain metals fail to displace hydrogen from acids. In the classroom or in the laboratory, a brief study of the pro- portions of hydrogen and air which give the sharpest explosion, may be made. This work can be related to both the two to one vol- ume relation of hydrogen and oxygen in water and to the one to four relation of oxygen and nitrogen in air. Thus a mixture having two volumes hydrogen with five of air would have two volumes hydrogen to one volume oxygen and hence give the sharpest explosion. The practical bearing of this matter on explosions due to gas leaks should then be brought out and the danger of a relatively small leak shown. In the latter case, there will always be enough oxygen present to completely burn what gas is pres- ent, while in case of the presence of excess of gas a much milder explosion might result. The explosive character of a mixture of illuminating gas and air may be shown to a class by the teacher, us- ing a 250 c.c. Erlenmeyer flask with about one volume of gas to five or six volumes of air. The flask should be wrapped in a towel when the mixture is lighted. Usually the sharpest explosion that can be had with illuminating gas and air is very tame and cannot be shown in a test tube. It requires the confinement that a flask with wide body and narrow neck affords. The explosive character of gasoline vapor mixtures with air should be touched upon, and PAGES 111-120 41 pupils should be made acquainted with the necessary precautions for preventing such explosions. The oxyhydrogen and oxyacetylene blowpipes deserve some attention at this point, and the latter type is now so widely used that a visit may be made to some plant that makes use of it. The intense heat developed and the ease with which iron and other refractory materials may be melted, will interest pupils greatly. If no such place is available, the pupils can be given some under- standing of the principle involved by showing them a blast lamp or even a double tube blowpipe. If specimens of the scientific rubies and sapphires which are made with the oxyhydrogen blowpipe are available, much interest will be awakened in the pupils' minds. Any jeweler will probably lend a few specimens for class study. For a good account of the method of manufacture see the Outlook of March 22, 1913. The subject of reduction, especially the use of hydrogen as a re- ducing agent, should be dwelt upon sufficiently here, so that it may be recalled later when a deeper study of it must be made. See Sections 256, 387, and 391, pp. 241, 364, and 368. Gaseous fuels should also receive a bit of classroom attention, so that their nature and relation to hydrogen shall not be entirely un- known when taken up later in Sections 283, 284, and 285, pp. 270- 275. Answers to Questions on Chapter XI Page 119 1. See Section 109, p. 111. 2. Oxygen has a strong chemical attraction for hydrogen, as is evidenced by the violence with which the two elements unite in the formation of water. This chemical attraction has to be overcome to separate the hydrogen from water, and this may be accomplished by using some substance, for example, iron (Section 100, p. 100), sodium (Section 101, p. 102), or zinc (Section 102, p. 103), which has a still stronger chemical attraction for oxygen than has hydrogen. It may also be accomplished by bodily tearing apart the two elements by some force stronger than their force of attrac- 42 HYDROGEN tion. Such a force can be supplied by an electric current (Section 103, p. 103). 3. Since sodium can decompose water and liberate hydrogen, it is obvious that sodium must have the stronger attraction for the oxygen. 4. See Section 111, p. 112. 5. Hydrogen can be distinguished from the colorless, odorless gases oxygen and nitrogen in that it burns. It can be distinguished from carbon monoxide in that water can be condensed if the products of combustion pass over a cold surface. But there are numerous colorless, odorless gases composed of carbon and hydrogen which burn and yield water vapor. Their combustion products, however, would cloud lime water, due to the presence of the carbon dioxide. 6. See Section 115, p. 114. 7. The flame of hydrogen burning in air is less hot than that of hydrogen burning in oxygen, because of the inert nitrogen, which absorbs some of the heat and thus lowers the temperature. 8 and 9. See Section 124, p. 118. 10. In a properly adjusted gas stove the gaseous fuel comes into contact with a sufficient amount of air for complete combustion. Furthermore, the flame is very hot, and before any of the fuel can es- cape from the high temperature region of the flame, it has been com- pletely consumed. 11. The kindling temperature of gas is rather high, at least a temperature at which a solid substance would glow with a dull red color. The heat of the flame decomposes the hydrogen and carbon compounds into the free elements. The solid particles of carbon (soot) become incandescent and give luminosity to the flame. If any part of this mixture can escape from the hot part of the flame before it comes in contact with sufficient oxygen for its combustion, it will be chilled and produce smoke. As we know, it is not difficult to make a gas flame smoke if the supply of air is partially shut off. If one holds a piece of cold metal in an otherwise smokeless flame, soot is deposited on the metal, because some of the glowing carbon particles are cooled below their kindling temperature. 12. Since copper oxide is reduced to metallic copper (Section 123, p. 118) by heating in a current of hydrogen, it would not be unrea- sonable to suppose that rust (iron oxide) might also be reduced to PAGES 111-120 43 metallic iron by heating in hydrogen. This can actually be accom- plished. However, we may recall the process of obtaining hydro- gen by passing steam over hot iron (Section 100, p. 100). If it is possible for iron to withdraw oxygen from its compound with hydro- gen, is it not a contradiction if hydrogen can withdraw oxygen from iron oxide and leave metallic iron? This seeming discrepancy can be explained as follows : Hydrogen and iron have somewhere nearly the same attraction for oxygen. So if hydrogen is passed over hot iron oxide, it may wrest a little of the oxygen from the iron. The iron might perhaps be able to get back this oxygen from the water vapor except that .the latter is swept on out of the way by the current of fresh hydrogen passing through the tube. Thus the iron oxide can be reduced little by little until it is all reduced, because the water vapor as fast as formed is swept out of the way where it cannot reverse the reaction. But when steam is passed over heated iron, the latter can withdraw a little oxygen, and the hydrogen so liberated is swept out of the way by the current of steam. Thus gradually the metallic iron may all become changed to oxide, if the hydrogen formed is continually swept away and thus prevented from again reducing the iron oxide. 13. Weight of iron oxide ........ 5.8446 grams Weight of iron ...... .... 5.1300 grams Weight of oxygen combined ...... 0.7146 gram .Combining ratio by weight of oxygen to hydrogen = 7.94: 1.00 (see Section 107, p. 107). Let x = weight of hydrogen liberated. Then 0.7146 : x :: 7.94 : 1.00 x = 0.090 = weight of hydrogen in grams. But weight of one liter of hydrogen (standard conditions) = 0.09 gram (see Appendix, p. 428). OQO .*. Volume of hydrogen (standard conditions) = -~r = 1 00 liter. 14. 11.2 liters hydrogen (standard conditions) weigh 11.2 X 0.09 = 1.008 grams. 1.008 grams hydrogen combine with 7.94 X 1.008 = 8.004 grams of oxygen. Weight of water formed = 1.008 + 8.004 = 9.012 grams. 44 THE ATOMIC THEORY CHAPTER XII THE ATOMIC THEORY Pages 121-128 THE atomic theory is approached through the laws of definite and multiple proportions, which led Dalton to advance the theory. The presentation of the theory is made more vivid to the pupil by the use of a figurative example, that of the beans and peas. The pupil will usually be found quite eager to use his imagination in connection with chemical theory, if at all encouraged to do so. Some bright pupils will even devise an equivalent for Avogadro's theory, if led to consider matter from the standpoint of the kinetic theory. The children of to-day, like those early speculators in the childhood of the race, make very good " atomists." In order not to give too much of this sort of material at one time, and also in order to acquire more facts to be considered in the light of the atomic theory, the chapter on hydrogen chloride is next introduced. Answers to Questions on Chapter XII Page 128 1. Dalton's atomic theory was based on the two groups of facts which are summarized in the laws of definite and multiple propor- tions respectively. 2. See Section 126, p. 122. 3. See Section 127, p. 122. 4. Charcoal is a mass consisting of countless atoms of carbon which are held firmly together by some rather mysterious force of cohesion. Charcoal begins to burn in air or in oxygen only at a high temperature. We may suppose that the heat loosens the cohe- sion of the carbon atoms for each other, making it possible for two oxygen atoms to come into closer contact with each carbon atom. The attraction of oxygen atoms for carbon atoms is apparently far greater than the cohesion of the carbon atoms to each other. In fact, the attraction is so great that the atoms in flying together gen- PAGES 129-140 45 crate heat, thereby raising the temperature still more and making the reaction self-sustaining. In the molecules of carbon dioxide apparently nearly all of the cohesive force of the carbon atoms is used up in holding the oxygen atoms in combination. There is little cohesion among the molecules of carbon dioxide, and its molecules therefore remain widely separated as a gas. 5. It has been suggested that in water two hydrogen atoms are attached to one oxygen atom in the molecule (last paragraph, Sec- tion 128, p. 125). We know that hydrogen peroxide contains for a given weight of hydrogen exactly twice as much oxygen as does water (fourth paragraph, p. 109). Or in other words, for a given weight of oxygen, hydrogen peroxide contains only one half as much hydrogen as does water. If then the molecule of water contains two atoms of hydrogen and one of oxygen, the simplest supposition is that the molecule of hydrogen peroxide contains one atom of hy- drogen and one atom of oxygen. It may be stated here that there are good reasons for believing that the molecule of hydrogen peroxide contains two atoms each of hy- drogen and oxygen, although no reason has been brought forward yet in the textbook for holding such a view. 6. See Section 130, p. 126. CHAPTER XIII HYDROGEN CHLORIDE Pages 129-140 THE pupil will usually be given an opportunity to prepare both hydrogen chloride and its water solution, and to study the properties of both. The uses can best be taken up in the classroom after reference books have been consulted. The rather detailed explana- tion of methods for finding the volume composition of hydrogen chloride is intended to amplify the somewhat similar study of water in Chapter X, and to afford material for use in connection with the following chapter on Avogadro's hypothesis. It thus leads toward the establishing of the formula HC1. 46 HYDROGEN CHLORIDE Answers to Questions on Chapter XIII Page 140 1. See Sections 133, 134, and 137, pp. 129, 130, and 133. 2. See Section 140, p. 135. 3. See Section 141, p. 136. 4. See Sections 133, 135, and 136, pp. 129, 130, and 132. 6. See Section 136, p. 132. 6. See Section 138, p. 133. 7. Pressure of chlorine = 20 cm. Pressure of hydrogen = 76 - 20 = 56 cm. 20 cm. of chlorine react with 20 cm. of the hydrogen, forming hydrogen chloride, with a pressure of 40 cm., and leaving hydrogen with a pressure of 36 cm. After explosion total pressure is 40 + 36 = 76 cm. 8. If water enters the tube, all of the hydrogen chloride is dis- solved and only the hydrogen is left. The pressure of this gas in the 100 c.c. tube was 36 cm., or in other words at a pressure of 36 cm. the volume was 100 c.c. Now with the pressure increased to 76 cm., the volume decreases in inverse ratio : new volume = 100 X ^ = 47.4 c.c. 9. To solder metals, heat is necessary to melt the solder. At the higher temperature a film of oxide forms over the surfaces of the metals as well as of the solder. This prevents the solder from ad- hering. Muriatic acid reacts with and removes this film of oxide and so allows the solder to come into contact with the clean metal and adhere. 10. One reason that less hydrochloric acid than sulphuric acid is used in the arts is that it costs more. Another important reason is that the most concentrated solution of hydrochloric acid contains but 40 % of the acid, whereas concentrated sulphuric acid as prepared is about 98 % acid. In shipping the acid from the chemical works to the point where it is used, the. cost of freight on the 60 % of water in the hydrochloric acid is by no means a negligible item. For a number of purposes, the fact that sulphuric acid is non- volatile gives it the preference over hydrochloric acid. PAGES 141-146 47 CHAPTER XIV AVOGADRO'S THEORY Pages 141-146 FOLLOWING the historical order of events, Chapter XIV leads up to Avogadro's theory through Gay Lussac's law. It is strongly recom- mended that the teacher read to the class at this point the following translations from the original papers of Gay Lussac and Avogadro, as giving in a clearer fashion than most textbooks present them, the facts and deductions from the facts, of those great scientists. Quotation from the original memoirs of Gay Lussac upon the combining volumes of gases : * " Thus it appears to me evident that all gases in reacting with each other always combine in the simplest proportions; and we have indeed seen in the preceding examples that the proportion of combination is that of one to one, of one to two, or of one to three. "It is very important to observe that when one considers the weights there is no simple and finished proportion between the ele- ments of a primary combination : it is only when there is a second compound between the same two elements that the new proportion of the element which has been added is a multiple of the first amount. Gases, on the contrary, in whatever proportion they may combine, al- ways give rise to compounds of which the elements are multiples of each other in volume. " Not alone do gases combine among themselves in very simple proportions as we have just seen, but further, the apparent contrac- tion in volume which they experience as a result of the combination has also a simple relation with the volumes of the gases, or rather with that of one of them." Quotation from the original Essay of A. Avogadro : 2 " M. Gay 1 Memoirs de la Societe d'Orcueil, Vol. II, p. 207 (1809). Translated from a copy in Les Classiques de la Science, Librairie Armand Colin, Paris, 1913. 2 First published in the Journal de Physique de Delametherie in 1811. Translation made from Les Classiques de la Science, Librairie Armand Colin, Paris, 1913. 48 AVOGADRO'S THEORY Lussac has shown in a very interesting memoire that the combinations of gases among themselves always take place according to very simple volume relations and that when the product of the combina- tion is gaseous its volume is also in very simple relation with those of its constituents; but the proportions of the quantities of sub- stances entering into combinations would appear to depend only upon the relative numbers of the molecules which combine, and of the number of compound molecules which result from the combina- tion. " We must then admit that there are also very simple relations between the volumes of gaseous substances and the number of mole- cules, whether simple or compound, which go to make them up. " The first hypothesis which presents itself in this case, and indeed the only admissible one, is to suppose that the number of gas parti- cles in any gas whatever is always the same in equal volumes, or is always proportional to the volumes. In truth, if one should suppose that the number of particles in a given volume was different for different gases, it would scarcely be possible to conceive that the law which would then preside over the distance between the particles could give in every case relations as simple as the facts which we have just cited oblige us to admit between the volume and the num- ber of particles. "Starting with this hypothesis, we see that we have the means of very easily determining the relative masses of the molecules of bodies, which we may have in the gaseous condition, and the relative num- ber of molecules in compounds; for the relations of the masses of the molecules are then the same as those of the densities of the gases at like pressure and temperature, and the relative num- ber of molecules in a compound is given immediately by the rela- tion of the volumes of the gases which form it." The presentation of the argument based on Avogadro's theory and the facts of Gay Lussac's law, that the molecules of the com- mon elementary gases must be at least double, is given in some de- tail, as this argument, while simple enough to advanced students, is always difficult for the beginner to understand. It will pay to go over and over it with different examples until the pupils all really comprehend it. PAGES 141-146 49 The following questions may help to fix this work : 1. One volume of nitrogen unites with three volumes of hydrogen, yielding two volumes of ammonia gas. What are the relative num- bers (in lowest terms) of the particles of each of the gases according to Avogadro's hypothesis ? 2. In the above case show that each nitrogen particle must be at least double. 3. Explain why, in the above case, the argument as to the double- ness of hydrogen particles is not as direct. 4. Two volumes of nitrogen unite with one volume of oxygen, forming two volumes of nitrous oxide. Draw a graph (using the symbol Q for a nitrogen molecule and the symbol $ for an oxygen molecule) showing what must have taken place during the reaction. Answers to the above Questions 1. The relative numbers of particles are as follows : one nitrogen particle unites with three hydrogen particles to form two ammonia gas particles. This is true because of Avogadro's hypothesis which, in addition to asserting that equal volumes of all gases under like conditions have equal numbers of gas particles, also goes on to as- sert that where the volumes are not equal the numbers of particles are strictly proportional to the volumes. 2. In the case just discussed, the nitrogen gas particles must con- tain at least two atoms each for the following reasons : Let x = the number of gas particles per unit volume of any of the gases. Then we have x particles of nitrogen, and 2 x particles of ammonia. But every one of the 2 x particles of ammonia has at least one nitrogen atom in it (for all ammonia has nitrogen in it). Hence, as we have 2 x ammonia particles with at least 1 nitrogen atom each, we have at least 2 x nitrogen atoms in our ammonia. But we had only 1 x nitrogen gas particles to start with. Hence every one of these must have been at least double. 3. The same argument as to the doubleness of hydrogen gas particles cannot be made because the number of new (ammonia) 50 ATOMIC AND MOLECULAR WEIGHTS particles must be less (by Avogadro's hypotheses) than the number of hydrogen particles with which we started (since the volume is less). Hence we have no chance to show the presence of hydrogen in more particles than at first. There is indicated rather a condensation of hydrogen particles. However, it is true that 3 volumes of hydrogen disappear in the formation of 2 volumes of ammonia. If then we are sure that only a single new substance is formed, it is obvious that 3 atoms cannot be divided into two equal parts without splitting an atom, and we thus have proof that 3 molecules of hydrogen contain at least 6 atoms. 4. Indicating that during the reaction that forms nitrous oxide, each oxygen molecule must have divided into two atoms, one of which joined a molecule of N 2 and the other joined another N 2 molecule, thus forming 2 molecules of N 2 (nitrous oxide) . Sections 148-152, pp. 144-146, may perhaps be omitted with young pupils or where time is lacking. Older pupils will, however, appreciate the light that is shed on Boyle's and Charles' laws in these paragraphs. CHAPTER XV ATOMIC AND MOLECULAR WEIGHTS Pages 147-163 THE subject matter of this chapter is always difficult of compre- hension by high school pupils. No attempt has been made to handle the question of how atomic weights are obtained in any full fashion. One example has been made to suffice, that of the obtaining of the atomic weight of copper, and even here, the matter of hqw it is decided that copper and oxygen are present atom for atom has been passed over with the mere announcement that it has been so decided. PAGES 147-163 51 It is questionable whether it will pay to attempt to go more deeply into the subject with high school pupils than has been done in this chapter. In the case of gram-molecular volume, the explanation has been made more thorough. It is believed that, with the older pupils at least, it is possible by this complete treatment to make them under- stand why 22.4 liters were chosen and why it is that the weight of that volume of any gas at standard conditions is numerically equal to the molecular weight. Use is at once made of this method of finding molecular weights, and the weights thus found are at once applied in deciding final formulas, Section 168, p. 160. The weight significance of formulas is driven home, Sections 162, 163, 164, pp. 154-156, and the subject of equations is then studied. Many textbooks and many teachers have introduced equations far earlier than this in the chemistry course, but their use by pupils who do not and cannot comprehend their meaning or their origin is to be deprecated. It is better to wait until the right to use them has been earned. It will be well to give the class a good drill at this point in the balancing of equations. They should first of all be reminded that equations cannot be " made up " without experimental facts, and that in every case they are supposed to represent, in a species of shorthand, what has been found out to be true in the particular case under consideration. It may be announced, however, that so much experience has now ac- cumulated that we can in many cases tell in advance what is likely to be the result of putting together certain substances, and that one with a considerable knowledge of chemistry can write equations offhand with some likelihood of correctly expressing results. A preliminary hint as to the numerical combining habit of the atoms of the ele- ments as compared with the combining habit of hydrogen atoms (i.e. valence) may be given here. Pupils may then be given exer- cises, first in looking up, in the reference books, equations for reac- tions that have already become familiar to them, and second, in completing and balancing incomplete or unbalanced equations. From this point on, every pupil should be required to look up and write the equations for all reactions taking place in the laboratory and lecture table work, provided the reactions are well understood. 52 ATOMIC AND MOLECULAR WEIGHTS Too much time may easily be spent in balancing equations. The value of this species of exercise is frequently overestimated. Like the clerk in Chaucer's Prologue who " seemed busier than he was," the pupil who can readily complete or balance equations may really be accomplishing very little. An understanding of what equations are and how they are derived, and the ability to grasp the story conveyed by them is of far more value to the pupil than any artifi- cial facility in making the two sides balance. The introduction of the few paragraphs on ozone at the end of this chapter permits the practical application of what has just been gained, as the determination of the molecular formula of ozone de- pends upon the use of the molal volume method. Incidentally the properties of the substance are described and its uses touched upon. The extensive European use of ozone as a means of purifying munici- pal water supplies should be enlarged upon by the teacher. Pos- sibly a little ozone may be prepared by the teacher, using some freshly scraped yellow phosphorus. This should be placed in the bottom of a large wide-mouth bottle and half covered with water to prevent its ignition. Starch-iodide paper may then be moistened and lowered into the flask to show the oxidizing action of ozone, and a typical test for it, and the pupils should be allowed to smell of it. Degree of Precision in Problem Work In ordinary chemical arithmetic the accuracy obtained with a slide rule or a four-place logarithm table is sufficient. This gives the result with an accuracy of about one part in 1000. It is need- less to express atomic weights as used in calculations with any greater accuracy. For example : H = 1.008. To drop the 8 in the last place would be neglecting T^nnr, or nearly rihy of the whole, which would not be allowable. Therefore use atomic weight 1.008". Cl = 35.46. To round off this number to 35.5 would be adding Tr&tf, or approximately nfar, which is allowable. Therefore round off chlorine to 35.5. HC1 = 1.008 + 35.46 = 36.468. Round off to 36.5. Ba = 137.37. Round off to 137.4. PAGES 147-163 53 It should be remembered that a result is accurate only to the same extent as the least accurate quantity which is used in the multiplica- tions or divisions performed in obtaining the result. Thus, for example, if we weigh 10 grams of sodium chloride on a balance which may be in error by as much as 1 gram, we have a possible error of iV- If we calculate from this that by adding silver nitrate we can precipi- tate mol. wt. AgCl 107.88 + 35.46 X mol. wt. NaCl~ C 23.00 + 35.46 = 24.51899 grams of AgCl, we are not only doing needless work but we are giving a wrong im- pression, for we cannot know the true amount to nearer than yV, or 2.5 grams. Therefore round off the answer to 25 grams, or if it is wished to indicate clearly the possible error, write the answer 25 db 2.5 grams. It is very difficult to get the pupil to grasp the idea of the degree of precision of his measurements and results, and if the teacher were to insist strongly upon it, probably very little time would be left for anything else in the course. At least, however, the teacher may be careful to set a correct example in this regard. Provided the method of working the prob- lem is correct, answers should be accepted which do not vary from the average result by more than T7 % ? of the value of the result. Answers to Questions on Chapter XV Page 163 1. = 16.00 g. ; H = 1.008 g. ; 01= 35.46 g. ; Na = 23.00 g. ; Fe = 55.84 g. 2. H 2 = 18.02 g. ; HC1 = 36.47 g. ; NH 3 = 17.03 g. ; N 2 = 28.02 g. ; H 2 S0 4 = 98.09 g. 3. NaOH + HC1 -^ NaCl + H 2 23 + 16 + 1 1 +35.5 40 36.5 Let x = the weight of HC1 necessary. Then 40 : 36.5 : : 40 : x. x = 36.5. 54 ATOMIC AND MOLECULAR WEIGHTS Therefore 36.5 grams of HC1 are necessary. 4. 36.5 g. of HC1 = 1 mole. Volume of 1 mole of a gas (standard conditions) = 22.4 liters. 22.4 liters, answer. 5. From equation in No. 3 we see that one mole of NaOH yields one mole of NaCl. Since we started with 1 mole of NaOH, we ob- tain 1 mole of NaCl, or 23 + 35.5 = 58.5 grams. 6. BaCl 2 + H 2 S0 4 -> BaS0 4 + 2 HC1 137.4 + 2X35.5 137.4 + 32.1+4x16 208.4 233.5 Let x = weight of barium sulphate. Then 208.4 : 233.5 : : 100 : x. x = 111.9 111.9 grams = weight of BaS0 4 . 7. NaHC0 3 + HC1 -+ C0 2 + H 2 + NaCl 84 grams 22.4 liters 1 mole of NaHC0 3 yields 1 molal volume of C0 2 . Let x = volume of C0 2 . Then 84 : 22.4 : : 100 : x. x = 26.7 26.7 liters = weight of C0 2 . 8. 100 c.c. of ozonized oxygen becomes 102 c.c. when all changed to oxygen. Gain in volume due to change of ozone to oxygen = 2 c.c. In reaction 2 3 > 3 2 , the change of volume = ^ of the volume of the ozone. Volume of ozone = 2 x 2 = 4 = 4 % of 100. Therefore 4 % by volume of the original gas was ozone. 9. A mole of ozone = 3 X 16 = 48 grams. Volume of 1 mole of ozone under standard conditions = 22.4 liters. Volume of 1 gram of ozone under standard conditions = - g X 22.4 = 0.467 liter = 467 c.c. Answer, 467 c.c. of ozone. 10. 92% of 467 = 430 = c.c. of ozone changed. 8% of 467 = 37.4 = c.c. of ozone unchanged. 430 c.c. of ozone changes to f X 430 = 645 c.c. of oxygen. Final volume = 645 + 37 = 682 c.c. 11. Volume of oxygen changed to ozone = 3 % of 21 % of 100 c.c. = 0.63 c.c. This contracts by of its volume = 0.21 c.c. when changed to ozone. 100 c.c. of air contracts 0.21 c.c. 12. 15.88 parts by weight of oxygen are combined with 1 part by PAGES 164-176 55 weight of hydrogen in hydrogen peroxide. This is in the same ratio as 16.00 parts of oxygen and 1.008 parts of hydrogen. But these are the atomic weights. Therefore hydrogen peroxide must contain the same number of atoms of oxygen and hydrogen, and the simplest formula would be HO. 13. Hydrogen peroxide and ozone are similar in their properties in that they are both unstable and give off oxygen easily. They are capable of oxidizing substances even when dilute, and when pure are violent oxidizing agents, as well as being explosive. CHAPTER XVI CHLORINE Pages 164-176 UNLESS really effective down-draft gas hoods are available, it is probably wiser not to permit pupils to prepare chlorine for them- selves, on account of the exceedingly irritating and even dangerous character of this gas. Subsequent effects of the attack upon the mucous surfaces have probably been underestimated and no chances should be taken in such matters. Chlorine is, however, so typical a non-metal and so much chemistry can be learned through a study of it, and a comparison of it with oxygen, that classes should all be made acquainted with it. Where proper down-draft hoods are not available, a good way for the teacher to do in preparing chlorine is to set up a generator on a window sill where there is strong out draft. Then work with the window open and make most of the tests right where the chlorine is generated. The use of solid potassium permanganate in the generator as an oxidizing agent is recommended because of its convenience. Concentrated HC1 may be dropped upon it from a dropping funnel, or lacking the funnel, through a thistle tube arranged to dip beneath the contents of the generator. Chlorine can thus be had as desired, for the reaction begins promptly and is soon over. Some classroom discussion of the relative activity of oxygen and chlorine will be needed to make clear the fact that the ease with 56 CHLORINE which chlorine begins to react with certain elements at low tem- perature is not a fair measure of its activity. The practical uses of chlorine deserve considerable classroom discussion. Bleaching powder should be shown in its ordinary commercial form, and some may be used by each pupil in an actual bleaching experiment with ink spots or bits of brightly colored calico. The theory of chlorine bleaching can best be approached by way of the well-known reaction between chlorine and water. Let the pupils know of the actual formation of hypochlorous acid in this reaction and of its instability and the consequent loss of nascent oxygen, when it is heated, when the sun shines on it, or when any readily oxidized substance is present to take up the oxygen as fast as formed and thus prevent reversal of the reaction. The formation of hypo- chlorous acid from bleaching powder can then be explained and com- mercial bleaching thus connected with bleaching by means of chlo- rine water. Recent improvements in the commercial process eliminate the use of sulphuric acid to release hypochlorous acid. The bleacher prefers to depend upon the slower, but safer, action of carbonic acid formed from the C0 2 of the air. This reacts with the soluble hypochlorites, with which the goods are first moistened, and very slowly liberates the unstable hypochlorous acid. If possible, a steam laundry should be visited and the method of bleaching studied. Many laundries now electrolyze salt solution, thus getting sodium hypochlorite to use as a bleaching agent instead of calcium hypochlorite. The use of hypochlorites, or of chlorine, in treating suspected water supplies is so general in this country that it should be ex- plained. The chemistry is very similar to that of bleaching. Some of the newer plants use liquid chlorine for this purpose. The simi- larity between this use of chlorine and the use of ozone should be pointed out, both doing the work by the formation of nascent oxygen. Answers to Questions on Chapter XVI Page 176 1. Sodium chloride is the chief source of chlorine in nature. Free chlorine may be obtained from it by electrolysis, or by treatment PAGES 164-176 57 with an acid and an oxidizing agent, for example sulphuric acid and manganese dioxide. 2. See Section 169, p. 164. 3. See (1) Section 171, p. 166 and (2) Sections 139 and 166, pp. 134 and 156. 4. See Sections 173-176, 178, 180, pp. 167-171. 5. Three reasons why oxygen may be considered a more active non-metallic element than chlorine are : (1) In Deacon's process (Section 170, p. 165), oxygen can displace chlorine from hydro- gen chloride. (2) A mixture of hydrogen and oxygen explodes with more violence and evolves more heat than a similar mixture of hydrogen and chlorine (Section 176, p. 168). Note: The heat evolved in the respective reactions involving the molal quantities indicated is as follows : H 2 + ^ 2 > H 2 (vapor) + 58,100 calo- ries ; H 2 + C1 2 -> 2 HC1 (gas) + 44,000 calories. (3) The fact that charcoal and fuels containing carbon undergo, when once kindled, a rapid self-sustaining combustion in oxygen but not in chlorine can also be taken as an evidence of greater activity on the part of oxygen. Note : A number of facts point to a greater activity on the part of chlorine, e.g. several metals combine spontaneously with chlorine but only with difficulty, if at all, with oxygen. There thus does not seem to be a universal standard of activity for the various elements. The activity varies somewhat according to the other elements which are concerned, as well as to whether the system is in a dry, an aqueous, or other medium. It is of a good deal of teaching value, however, to arrange the non-metals in an order cor- responding to their activity and to note that the order is at least roughly the same against whatever metallic element that activity is being compared. The metals also may be arranged in the order of their activity (the order of the Electromotive Series, p. 329) and the order is practically the same against whatever non-metal the activity is being considered. 6. Chlorine is used practically for bleaching (Section 180, p. 170), as a germicidal agent (Section 184, p. 174), for dissolving gold (Section 178, p. 170). Note : A process formerly used to a consider- able extent in extracting gold from its ores was to treat the crushed ore with chlorine and then dissolve out the gold chloride with water. 58 SODIUM 7. See Sections 180-182, pp. 170-172. 8. 4 HC1 + Mn0 2 -> MnCl 2 + 2 H 2 + C1 2 4 x 36.5 54.9 + 32 146.0 86.9 100 kilograms of 36.5% HC1 contain 36.5 kg. of HC1. This is one kilogram mole of the substance. We see from the equation that 4 moles of HC1 require 1 mole of Mn0 2 . One kg. mole of HC1 then will require kg. mole or i X 86.9 = 21.73 kg. of Mn0 2 . 9. In equation in No. 8 it is seen that 4 moles of HC1 yield 1 mole of C1 2 . Therefore the 1 kg. mole actually used will yield J kg. mole = 1 X 71 = 17.75 kg. of C1 2 . 10. The I kg. mole of C1 2 obtained in No. 9 will occupy | X 22,400 = 5600 liters or 5.6 cubic meters. 11. 4 HC1 + Mn0 2 -> 2 H 2 + MnCl 2 + C1 2 MnCl 2 + H 2 S0 4 -> MnS0 4 + 2 HC1 Adding these equations, we get 2 HC1 + H 2 S0 4 + Mn0 2 -> 2 H 2 + MnS0 4 + Cl, We see that for 2 moles of HC1, 1 mole of C1 2 is obtained and 1 mole of H 2 S0 4 and 1 mole of Mn0 2 are needed. Therefore for 1 kg. mole of HC1 we obtain : i kg. mole of C1 2 = } X 71 = 35.5 kg. of C1 2 , 1 kg. mole of H 2 S0 4 = J x 98.1 = 49.05 kg. of H 2 S0 4 , i kg. mole of Mn0 2 = | X 86.9 = 43.45 kg. of Mn0 2 . 12. To obtain chlorine from bleaching powder treat it with sul- phuric acid, which first reacts to set free the two acids as shown : CaClOCl + H 2 S0 4 -+ CaS0 4 + HC1 + HC10 (Section 183, p. 172). These acids then react with each other, yielding chlorine (Section 180, p. 170). CHAPTER XVII SODIUM Pages 177-191 IF experiments are performed with sodium, it must be remembered that much of the sodium on the market has violently explosive PAGES 177-191 59 properties when reacting in any considerable quantity with water or acids. This seems to be due in part to the presence of an ex- plosive impurity in sodium which was made by the reaction of highly heated carbon with sodium hydroxide in the electric furnace. Teachers cannot be too careful in preventing the use, by pupils, of pieces of sodium larger than small peas ; and even with these small pieces, pupils should be warned to stand back when dropping them into water. Among the sodium salts which are studied in this chapter, two are especially worthy of detailed study on account of their extensive use in daily life. These are the bicarbonate and the carbonate of sodium. Pupils may well be allowed to prepare them individually in the laboratory. The bicarbonate may readily be made by a method very similar to the Solvay process as described, but not in detail, in Section 190, p. 180. The carbonate can then be made from the bicarbonate by heating the latter. The last experiment may be conducted as a quantita- tive experiment if desired. The first, if made quantitatively, illus- trates the difference between theoretical yield and actual yield in chemical processes for, owing to the relatively great solubility of the sodium bicarbonate, its precipitation is incomplete. If it is thought desirable, pupils can make baking powder from sodium bicarbonate together with cream of tartar, or some other suitable dry, solid acid. The enormous use of sodium carbonate in the arts and as a water softener and cleanser should be discussed in the classroom. The easily efflorescent character of the deca-hydrate of sodium carbonate affords an opportunity to study the subject of crystal hydrates, and this study may be made quantitative if time permits. Sodium hydroxide may be made by the reaction of sodium car- bonate and slaked lime, thereby bringing another commercial re- action of great importance to the attention of the pupils. The uses of the sodium hydroxide should then be studied, es- pecially its use in soap making. The study of sodium nitrate and of potassium salts in this chapter may be enlarged upon, in con- nection with their use in fertilizers. This is especially desirable in 60 SODIUM rural communities, where the information may later be of practical value to some of the pupils. Glass making should be discussed in class, while considering sodium and potassium compounds, and the broader fundamentals of its chemistry taken up. As glasses are usually very complex mixtures of the silicates of various metals, no very complete chemi- cal treatment can be made with elementary chemistry students. Answers to Questions on Chapter XVII Page 191 1. Common salt is the chief source of sodium compounds, not only on account of its abundance but also because it contains a high per cent of sodium, and, being soluble, it is easily purified. Other abundant materials containing sodium, such as soda feldspar, Na 2 A1 2 3 6 Si0 2 , mica, Na 2 3 A1 2 3 6 Si0 2 2 H 2 0, and cry- olite, A1F 3 . 3 NaF, are insoluble in water and require rather elabo- rate chemical treatment for their decomposition. 2. See Section 192, p. 183, and last paragraph of Section 60, p. 61. 3. See Section 193, p. 184. 4. See Section 193, p. 184. 6. See Section 195, p. 185. 6. Metallic sodium is protected from the action of the air by being immersed in kerosene, or a similar oil, which contains no com- bined oxygen and dissolves very little oxygen or water vapor from the air. 7. A bit of sodium exposed to the air becomes first covered with a dull film ; this soon becomes white and grows moist and little bub- bles are seen to puff it up. Gradually the surface grows more and more liquid and the lump seems to melt into a little puddle of rather viscous liquid with some solid white residue in the bottom. Finally the liquid dries up and a caked mass of white solid remains. First the metal reacts with the moisture of the air (which is far more abundant than carbon dioxide) 2 Na + 2 H 2 -+ 2 NaOH + H 2 The NaOH forms the white crust and the hydrogen gives rise to the PAGES 177-191 61 bubbles. The NaOH absorbs more water and dissolves in it, thus accounting for the wet surface and the viscous solution. The C0 2 of the air reacts with the NaOH. 2 NaOH + C0 2 -> Na 2 C0 3 + H 2 The Na 2 CO 3 is the white solid which separates from the NaOH solu- tion in which it is not very soluble. Finally, since Na 2 C0 3 does not have the attraction for water possessed by NaOH, the liquid evaporates and leaves dry sodium carbonate (see Section 195, p. 185). 8. The substance is sodium chloride. 9. Sodium hydroxide might be used to dry gases on account of its attraction for water vapor (see Section 195, p. 185). 10. See Section 192, p. 183. 11. Sodium bicarbonate is preferred to sodium carbonate in fire extinguishers because, for the same amount of sodium, it yields twice as much carbon dioxide, and for the same yield of carbon dioxide only one half as much acid is required ; 2 NaHCOs + H 2 S0 4 -> Na 2 S0 4 + H 2 + 2 C0 2 Na 2 C0 3 + H 2 S0 4 -> Na 2 S0 4 + H 2 + C0 2 12. 3 Na + A1C1 3 -> 3 NaCl + Al 3 X 23 27.1 Let x = weight of Al obtained. Then 69: 27.1:: 1000 :x. x = 392 g. of Al 13. Na 2 C0 3 + CaC0 3 + 6 Si0 2 -> Na 2 - CaO 6 Si0 2 + 2 C0 2 106 100.1 361.8 479.9 479.9 : 106 : : 1000 :x x = 220.9 kg. of Na 2 C0 3 | 479.9 : 100.1 : : 1000 : x x = 208.5 kg. of CaC0 3 | Answer 479.9 : 361.8 : : 1000 :x x = 754.5 kg. Si0 2 14. According to the equation, for each gram formula weight of glass produced, 2 moles of C0 2 gas escape = 2 x 22.4 = 44.8 liters. Since 1000 liters = 1 cubic meter, for each kilogram formula weight of glass there will be 44.8 cu.m. of C0 2 measured under stand- ard conditions. Then 479.9 : 44.8 : : 1000 : x, and x = 93.34 cubic meters C0 2 under standard conditions. 62 CALCIUM CHAPTER XVIII CALCIUM Pages 192-206 METALLIC calcium is deserving of wider use in the laboratory now that it is comparatively cheap. It is far safer for pupils to use than sodium or potassium, and being active enough to decompose water in the cold, it serves admirably to illustrate the properties of a very active metal. The use of calcium chloride as a drying agent and the general topic of deliquescence will naturally be enlarged upon in class in connection with the study of the calcium compounds. The use of concentrated sulphuric acid and of phosphorus pen- toxide as still more efficient drying agents for gases, may be men- tioned here. The lime industry is so important practically that the chemistry of limestone, lime, and slaked lime should be given considerable attention. The chemistry of the setting of mortar and plaster should then be taken up. Avoid giving the too common belief that the carbon dioxide reaction with the lime in the mortar is either prompt or complete, for it is said that considerable calcium hydroxide remains in the mortar for a long time. The drying out of the mortar is probably largely responsible for much of the first stiffness. The chemistry of calcium bicarbonate is vastly interesting be- cause of its connection with the temporary hardness of water and with cave formation. The chemistry of magnesium bicarbonate and ferrous bicarbonate is so similar, and all three bicarbonates are so likely to be present in hard waters, that they may be mentioned at this time. Calcium sulphate is briefly treated before going into the dis- cussion of hard water because it is mainly responsible for perma- nent hardness. Plaster of Paris is sufficiently important practically to deserve passing mention. The preparation and setting of this substance PAGES 192-206 63 can be explained by recalling what was learned about crystal hy- drates (see Section 194, p. 185). As the setting of cement depends largely on hydration of certain silicates, and as the concrete industry is of such vast importance, it may be worth while to digress at this point sufficiently to consider the general principles involved. Some cement can be secured and the classes can then construct a simple mold and secure gravel or crushed stone and make up some object, perhaps something that will be useful about the building. The practical side of this subject deserves more attention in rural schools than in city schools. Teachers will use their own judgment as to the amount of time they can afford to spend on such applications of chemistry to the affairs of daily life. Similarly, the amount of time to be spent in considering water softening and in experimenting with various water softeners, should depend upon the extent of the community interest in the subject. It is of little practical importance where pure soft water is used and of vast importance to the industries and to the home in those sec- tions of the country which are afflicted with hard water. In schools in places of the latter type, considerable interest will be found in testing some of the preparations sold under fanciful names as water softeners. Tests for sodium carbonate, tri-sodium phosphate, borax, sodium fluoride, or sodium aluminate may be made, as some one (or more) of these substances is usually present. The use of ammonia water in household water softening and the use of soap for the purpose should of course be explained. A visit to a laundry which softens the water used in washing clothes will be interesting and profitable. Having now studied oxygen, a bivalent non-metallic element, chlorine, which is monovalent toward hydrogen, and sodium and calcium, metals which are respectively mono- and divalent, a few paragraphs on the subject of valence can be introduced at this point with profit. The use of the idea in 'future chapters will gradually develop it, until in Chapter XXVII a much more complete discussion of the subject can be given after the hydrogen equiva- lents of sodium (monovalent), magnesium (divalent), and alu- minium (trivalent) have been determined. 64 CALCIUM Answers to Questions on Chapter XVIII Page 205 1. Metallic calcium is a very active substance, reacting at ordi- nary temperature with water and at elevated temperature com- bining vigorously with oxygen and even with nitrogen. Hence it is never found as free metal in nature. 2. See Sections 207 and 208, pp. 195 and 196. 3. See Sections 207, 208, 209, pp. 195-199. 4. See Section 209, p. 197. 6. See Section 211, p. 199. 6. Stalactites are icicle-like formations which hang from the roofs of caves. When carbonated water which on flowing through limestone beds has dissolved calcium carbonate hangs in drops from, the roof of the cave or trickles down the surface of the stalactites, some of the carbon dioxide escapes from the solution into the air of the cave. Thus the solvent power for calcium carbonate is diminished and some of this substance is deposited. If there is a constant trickle of the water and if the air is moving so as to carry away the carbon dioxide, large stalactites are gradually formed. 7. In the household, hard water can be softened by adding am- monia or sodium carbonate. Ammonia neutralizes the excess of carbonic acid in a temporary hard water, H 2 C0 3 + 2 NH 4 OH -+ (NH 4 ) 2 C0 3 + 2 H 2 O, and with the removal of carbonic acid, calcium carbonate precipi- tates. If the hardness is of the permanent variety, sodium carbon- ate will precipitate calcium or magnesium salts, CaCl 2 + Na 2 C0 3 -> CaC0 3 1 + 2 NaCl Ca(HC0 3 ) 2 + Na 2 C0 3 -> CaCO d + 2 NaHC0 3 It is to be noted from the last equation that temporary, as well as permanent, hardness is removed by the use of sodium carbonate. 8. In dry air only a thin superficial film of oxide or hydroxide forms over metallic calcium, and this excludes oxygen fairly well from the underlying layers. Hence the most satisfactory way to keep calcium is in dry stoppered bottles. The advantage of more completely excluding oxygen by using kerosene does not compensate for the inconvenience. PAGES 192-206 65 Sodium and potassium can likewise be kept in dry tight bottles which are infrequently opened, but the surface films of oxide or hydroxide have so great an attraction for water, that it is more difficult to keep them in this way. 9. Sea water may be softened for use in the boilers of a battle- ship by the addition of sodium carbonate, which removes the troublesome calcium and magnesium salts. But as the water is converted to steam much sodium salt is left and even this will soon begin to separate as a solid in spite of its considerable solubility, un- less the boilers are frequently " blown off." Distillation may also be resorted to, and of course this method would also furnish water fit for drinking. 10. See Section 206, p. 194. 11. See Section 212, p. 201. 12. CaO + H 2 -> Ca(OH) 2 56.1 18 56.1: 18:: 1000: a: x = 320.9 grams H 2 0. 13. CaO + H 2 -> Ca(OH) 2 Ca(OH) 2 + CO 2 -> CaC0 3 + H 2 O adding, " CaO + CO 2 -> CaCO 3 56.1 g. 22.4 1. 100.1 g. 56.1:22.4:: 1000 : x x = 399.3 liters CO 2 under standard conditions. 56.1:100.1:: 1000 :x x = 1784 grams air-slaked lime. 14. . 1 liter contains 0.5 g. CaS0 4 1000 liters contain 500 g. CaS0 4 CaS0 4 + Na 2 C0 3 -^ CaC0 3 + Na 2 SO 4 136.2 106 136.2 : 106 : : 500 : x x = 389.8 grams Na 2 C0 3 . 15. 2 NaC 18 H 35 2 + CaS0 4 -> Ca(Ci 8 H 35 2 ) 2 + Na 2 S0 4 612 136.2 612 : 136.2 : : x : 0.5 x = 2.25 grams of soap. 16. The pupil is expected in this question to consult the atomic 66 ACIDS AND BASES; NEUTRALIZATION weight table in order to be able to name the hitherto unfamiliar elements whose symbols are given. It is to be taken for granted that in such compounds, as for example Mn 2 7 all of the valences of the non-metal are held by the valences of the metallic element. Thus the two atoms of manganese must be exerting 14 metallic valences to hold the 7 X 2 = 14 non-metallic valences of the 7 oxygen atoms, and each atom of Mn is therefore exerting 7 valences. In other words, the valence of Mn is 7. The pupil should note that the valence of an element may be different in different compounds as that of tin in SnCl 2 and SnCl 4 . It should be emphasized that the kind of attraction exerted by metals is fundamentally opposite in character from that exerted by non-metals. One is called positive and the other negative. It may not be too soon to suggest the probable electrical nature of valence. CHAPTER XIX ACIDS AND BASES; NEUTRALIZATION Pages 207-219 SINCE the majority of inorganic substances can be classed either as acids or bases, or as salts, which are a product of the neutral- ization of acids and bases, it follows that a somewhat complete study of the fundamentals of the chemistry of these substances is necessary. After recalling the fact that hydrogen, in a peculiar state of com- bination, is a characteristic component of all acids (see Section 111, p. 1 12 , for a previous hint of this matter) the design of the chapter is to show, first that the non-metallic elements are essentially acid formers and that by oxidizing them and allowing the oxides to react with water, acids are produced. Several examples of this sort of behavior are given before it is announced that this type of reaction is general to the non-metals. It should be clearly pointed out that it is the hydrogen of the water that, under the influence of the non-metallic oxide, becomes the hydrogen of the acid. PAGES 207-219 67 After the nature of the formation of acids has been pointed out, a similar treatment of the bases follows, in which their metallic origin is -shown. Here the presence of the OH group as the characteristic group of all bases should be emphasized. The treatment of neutralization as a union of the characteristic hydrogen of an acid with the hydroxyl of a base to form water is then easy. That the other components of the acid and base yield a salt solution, which on evaporation of the water gives a salt, should be taught as an auxiliary reaction rather than as the prin- cipal reaction in neutralization. Answers to Questions on Chapter XIX Page 218 1. The sour taste of cream of tartar resembles the sour taste common to all acids, and it shows that cream of tartar must contain acid hydrogen. 2. The alkaline taste shows the presence of basic hydroxyl groups. 3. Chemically water is composed of the elements which would constitute the acid hydrogen and the basic hydroxyl group, yet water possesses none of the characteristic properties such as taste, or ef- fect on litmus, of either of these components. Hence, it is obvious that in water these two components are so bound to each other that they are unable to show their usual properties. When acid and base are brought together, then, it is very natural that these components should at once form water and thus disappear as distinct compo- nents. 4. See Sections 230, 231, p. 215. 6. Sodium sulphate may be made : (a) from sodium hydroxide by neutralizing it with sulphuric acid, 2 NaOH + H 2 S0 4 -> Na 2 S0 4 + 2 H 2 (6) from sodium chloride by adding sulphuric acid and heating to drive off the volatile hydrochloric acid (Section 139, p. 134), 2 NaCl + H 2 S0 4 -> Na 2 S0 4 + 2 HC1 * (c) from sodium carbonate by adding sulphuric acid, thus bring- ing together the components of the weak and unstable acid H 2 CO 3 . 68 . ACIDS AND BASES; NEUTRALIZATION This acid decomposes with the escape of C0 2 , and sodium sulphate is left, Na 2 C0 3 + H 2 S0 4 -> Na 2 S0 4 + H 2 C0 3 6. Ammonia water contains the weak and non-corrosive base NH 4 OH. It is used rather than sodium hydroxide to prevent sul- phuric acid eating holes in clothes because it is itself harmless, and yet it neutralizes the corrosive acid as effectively as does the even more corrosive base. Furthermore, all excess of ammonia not used in the neutralization is volatile and evaporates from the clothes. 7. If " sour " stomach is caused by too much acid it is obvious that lime water containing the base Ca(OH) 2 will neutralize the acid. 8. The 40 grams of NaOH = 1 mole. From the equations : NaOH + HC1 -> NaCl + H 2 O 2 NaOH + H 2 S0 4 -> Na 2 S0 4 + 2 H 2 it is obvious that 1 mole of HC1 or 36.5 grams, and mole of H 2 S0 4 or 49 grams are necessary to neutralize one mole of base. 9. 2 NaOH + C0 2 -> Na 2 C0 3 + H 2 80 g. 22.4 1. It is obvious that 40 grams of NaOH will require \ X 22.4 = 11.2 liters. 10. 2 NH 3 + H 2 S0 4 -> (NH 4 ) 2 S0 4 44.8 1. 98 g. If x = volume of ammonia gas Then 98 : 44.8 : : 1000 : x x = 457 liters of ammonia gas. 11. If 1 liter of the solution contains 200 g. of HC1, 100 c.c. of the solution will contain 20 g. of HC1. HC1 + KOH -* KC1 + H 2 36.5 56.1 Let x = weight of KOH required 36.5 : 56.1 : : 20 : x x = 30.74 g. of KOH. Since 1 liter of the KOH solution contains 100 g. of KOH, the volume which will contain 30.74 grams = ^i x 1000 = 307.4 c.c. 101) 12. See Sections 222, 223, 224, 226, 227, pp. 210-214. PAGES 220-224 69 CHAPTER XX NOMENCLATURE Pages 220-224 THIS brief chapter on nomenclature is naturally called for im- mediately after the discussion of acids, bases, and salts, as many opportunities for practice in the use of chemical names arise out of the latter subject. Future progress in the study of chemistry depends to some degree upon facility in the correct use of the names of chemical substances. In this work, methods such as are successful in the study of language should be used, and pupils will be found to have little diffi- culty with the subject, if given sufficient opportunity to practice it. After the first formal instruction from the textbook is over, much help will be had from a rapid drill upon the names of all the acids, bases, and salts present in the laboratory or classroom. The teacher can furnish in turn the names of the substances and require from the pupils the names of the related acid, base, or salt as the case may be. For example, if sodium nitrate be at hand, the teacher may ask, " From what acid may sodium nitrate be made? With what base? " Or, again, " This is a salt made by the union of sodium hydroxide with nitric acid. What is its name? " etc. Or, if a me- tallic oxide be at hand, " This is iron oxide. What should the prod- uct of its reaction with water be called? " etc. After sufficient drill with the names of familiar substances, the teacher may intro- duce names that are unfamiliar to the pupils in order to see if the pupils have really learned the scheme for the changes in endings of the names, or if they have merely memorized the particular names that have been employed. Citric acid and the citrates, tartaric acid and the tartrates, hypophosphorous acid and the hypophos- phites, permanganic acid and the permanganates, etc., may be used. Answers to Questions on Chapter XX Page 224 All answers are obvious from the rules given in the textbook. 70 THE METALS CHAPTER XXI THE METALS Pages 225-238 THE pupil already possesses at this point in his study some frag- mentary knowledge of the metals, for he has had to consider the metals in studying the way in which they form compounds with the non-metals. Instead of postponing a systematic study of the metals until a second part of the book and then giving a rather dry recital of the properties of the salts of each metal in turn, it is deemed better to give at this point a somewhat careful study of the main characteristics of the metals, and the differences among the broader groups of metals. This chapter leads up to the follow- ing chapter on metallurgy, which considers the occurrence, separa- tion from ores, and main uses of the more important metals. The next chapter thus illustrates and fixes more firmly in the mind some of the general principles brought out in this chapter. Nowhere in the book is an enumeration of the properties of the salts of each metal in turn undertaken. The pupil should learn to rely on his knowledge of the metal to know the character of the base that can be formed from it, and to rely on his knowledge of the acid and base and of salts in general to know approximately what a particular salt is like. Appendixes VI and VII on page 430 will be useful in finding the solubilities of salts, and whenever occasion arises to need exact information regarding a salt, reference should be made to a handbook, after first defining the general character of the salt from a consideration of the acid and the base. The electrical nature of the difference between metals and non- metals is here first suggested, and although this point may very well be kept in the background, it may, if followed up, lead to in- teresting deductions. If the electrical side of combination is to be considered at all, it should be emphasized that uncombined ele- ments are electrically neutral ; it" is only when they enter into the combined state that they acquire charges, the metals positive charges, the non-metals negative charges. On separating from the PAGES 225-238 71 state of combination elements part with whatever free electrical charges they possessed. Failure to appreciate this point accounts for the failure of the earlier chemists to develop a satisfactory elec- trochemical theory. Since, however, the electrification of constitu- ents of compounds, with the exception of acids, bases, and salts, is so well concealed that all chemists do not even admit its existence, it is not particularly recommended that the teacher go far in this line of argument, for the enthusiastic pupils are sure to carry the idea beyond where the teacher would willingly stop. In this chapter the metals are divided into three general classes, the alkali metals, the. earth-forming metals, and the heavy metals. The great chemical activity of the metals of the first two classes is brought out and the lack of practical usefulness because of this property should be emphasized by the teacher. Aluminium is the only metal of those in the first two groups that is largely in practical use, and its usefulness is possible, in spite of its great activity, because it acquires a protective coating of its own oxide. The preparation of aluminium illustrates again its great reactivity, requiring the use of electrolysis rather than the simple methods of reduction in use with the heavy metals. The similar preparation of sodium has already been discussed (Section 186, p. 177). The use of aluminium in aluminothermy (Section 434, p. 415) may be referred to here as further evidence of the great chemical activity of this member of the earth-forming metals. Leaving the more active metals, we come to the more familiar metals of the group which we have called the heavy metals. Be- fore entering upon a detailed study of the means of recovering these metals from their ores, a brief study of their relative degree of activ- ity is made. This in reality anticipates their positions in the elec- tromotive series (Section 347, p. 329) and should be made by the teacher to hark back to the displacement of hydrogen by zinc, iron, etc., but not by copper, silver, gold, etc. This study of relative activity gives the underlying explanation as to why some of the metals of this group are found free in the earth, while the others are found in combination with non-metals and re- quire the various treatments that are to be described in the follow- ing chapter on metallurgy. 72 THE METALS. Answers to Questions on Chapter XXI Page 238 1. See Sections 241, 242, pp. 225, 226. 2. See Section 243, p. 227. 3. See Section 246, p. 229. 4. See Section 245, p. 229. 5. See Section 247, p. 230. 6. See Section 248, p. 230. 7. See Section 249, p. 232. 8. See Section 250, p. 232. 9. Find the specific gravity of the metals in Appendix, p. 427. 10. See Section 253, p. 237. 11. See Section 251, p. 234. 12. Silver, platinum, and gold are the metals which can best be used for jewelry. 13. When zinc is exposed to the weather, its surface is quickly oxidized and a film consisting probably of hydroxide is formed on the surface. This film adheres firmly, and moreover is close in texture so that air and water are excluded from the metal beneath. On the other hand, the film of iron hydroxide formed by the action of the weather on iron is scaly and porous and does not exclude the weather. Hence, in spite of its greater activity, zinc is superior to iron for use on roofs. 14. The table on page 235 shows that tin is a less active metal than iron. Hence tin would be less quickly attacked by the acids present in food products. Furthermore, molten tin adheres well to a clean iron surface so that it is very easy to obtain a tinned surface on sheet iron. Tin is not a perfect metal for the purpose, because as seen from the table, tin is more active than hydrogen. It does displace hy- drogen slowly from hydrochloric acid, thus forming soluble tin chloride. It would also be able to displace hydrogen from the weak acids in canned goods, although of course more slowly, because the acids are weaker. Thus tin salts might get into the food. Tin salts in small amounts are not dangerously poisonous, although they are not desirable in food. PAGES 239-263 73 15. Structural iron is preserved from corrosion by painting or by surrounding with cement. Note : Cement is not impervious to air or water, but cement always contains sufficient calcium hydroxide to give a slight degree of alkalinity. This would neutralize any possible acid (as from smoke) which might get at the iron. Acidity is one of the most powerful factors in promoting the rusting of iron. CHAPTER XXII METALLURGY Pages 239-263 IN this very practical chapter the metallurgy of the commonest metal, iron, is first taken up and the principles as well as the prac- tice, dwelt upon quite extensively. The related subject, the nature and preparation of steel, is also given much space. Because of its practical importance, steel deserves a good deal of attention. Wherever possible, pupils should be given an opportunity to visit such iron or steel plants as the vicinity affords, even if it is only a trip to see a cupola in which cast iron is melted, or to a blacksmith's shop to see the heat treatment of steel in hardening and tempering. In connection with the metallurgy and the refining of copper, a small sample of powdered copper sulphide ore may be roasted in a porcelain crucible and then the resulting oxide reduced to metallic copper by passing hydrogen over the heated oxide, which may be placed in a hard glass tube. If current is available, the transfer of copper from a thick anode to a thin cathode of copper may be made to illustrate the electrolytic method of refining the crude metal. Pupils will be found to be much interested in the recovery of precious metals in copper and lead refining. If such refineries are within visiting distance, a trip to one, with a visit to the strong room where the gold and silver are kept, will afford a never-to-be- forgotten experience to the pupils.. Under the treatment of the recovery of gold, a description of the simple separation by means of differences in gravity in placer mining will interest pupils. 74 METALLURGY A recently patented improvement upon the amalgamation proc- ess l will also furnish a chance to apply a little physics and further interest pupils in the subject. It seems that gold as found in nature is sometimes coated over with iron oxide or other protective coating so that it is not dissolved by the mercury used to recover it from the concentrates. If 1 or 2 per cent of zinc be added to the mer- cury and a little sulphuric acid to the wash water, a " couple^ " is set up between the zinc and the gold, and hydrogen is released from the gold surfaces, thus loosening the scale-like coating so that the gold dissolves in the mercury. This method will probably make possible the working of vast deposits of low grade black sands in California which were impossible of profitable working before. The method of preparation of aluminium serves to illustrate the general method now in use for obtaining highly active metals from their ores. The general properties of the metal may be illustrated by reference to its large and increasing use in kitchen utensils. A little thermit may be fired off to illustrate the great activity of aluminium. Place not more than 50 grams of the thermit in a clay crucible and partly embed the latter in a large pan of sand. Make a depression in the middle of the thermit and place in it a little of a mixture of equal parts of photographic flashlight powder and powdered magnesium. Stick a piece of magnesium ribbon into this fuse powder and, when all is ready to set off the mixture, set fire with the burner to the upper end of the magnesium ribbon, and quickly retire. Caution : Stand at least ten feet from the crucible and protect with asbestos any woodwork near the reaction. Answers to Questions on Chapter XXII Page 262 1. Tin stone consists of tin dioxide, Sn0 2 . The most obvious method to obtain the metal therefrom is to heat the oxide with carbon. Since such a method suffices to reduce the oxides of zinc and iron, it must surely reduce the oxide of a metal that is less ac- tive than either zinc or iron. 2. The oxide of any metal less active chemically than zinc should 1 By Prof. R. H. Lyons of Indiana University. PAGES 239-263 75 be reducible with carbon. This would include iron, nickel, tin, lead, and copper, and of course mercury and the precious metals whose oxides can be decomposed by mere heating. On the other hand, it is unlikely that carbon will have any greater attraction for oxygen than the very active metals, aluminium, magnesium, cal- cium, barium, sodium, and potassium. In no case can the oxides of one of these latter be completely reduced to free metal by means of the action of carbon. Carbides ; however, can be obtained by in- tense heating of the oxides with carbon, for example A1 4 C 3 , CaC 2 , and by heating NaOH with carbon, Na 2 C0 3 and a part of the sodium in the metallic condition can be obtained, 6 NaOH + 2 C -> 2 Na 2 C0 3 + 3 H 2 + 2 Na. 3. The method of electrolyzing a melted compound of the metal is always available as a means of obtaining the free metal, when the oxide cannot be reduced with carbon. 4. Mercuric oxide decomposes into mercury and oxygen when heated. 6. See Section 274, p. 260. 6. See Section 265, p. 253. 7. Copper metal may be precipitated from copper sulphate solu- tion by hanging strips of iron in the solution. The iron is the more active metal and displaces the copper, Fe + CuS0 4 -> FeS0 4 + Cu |. 8. Fe 2 3 contains 70.0 per cent of Fe ; Fe 3 4 , 72.4 per cent ; FeC0 3 , 48.2 per cent ; Fe 2 3 3 H 2 0, 52.3 per cent. 9. (a) 2 Cu 2 + C -> 4 Cu + CO 2 2 x 143.2 12 286.4 : 12 : : 1000 : x x =41.9 kilos of carbon. (6) 2 CuO + C -> 2 Cu + C0 2 2 x 79.6 12 159.2 : 12 : : 1000 : x x = 75.4 kilos of carbon. 10. ZnO + C -> Zn + CO 81.4 12 81.4: 12:: 1000 :x x = 147.4 kilos of carbon. 76 COMPOUNDS OF CARBON CHAPTER XXIII COMPOUNDS OF CARBON Pages 264-281 THE study of carbon compounds is taken up in two sections in sepa- rate chapters. The division is made between what is called inor- ganic and organic chemistry, but care has been taken to point out that this division is purely one of convenience and that there is no essential difference between the chemistry of the laboratory and manufactory on the one hand and that of the living organism on the other. Teachers should further emphasize the unity of all chemis- try in this respect. Trips to municipal gas plants may be made with profit in connection with the study of this chapter. They will be found to be very valuable, both on account of the objective reality which they give to the subject matter and on account of the civic instruction which acquaintance with the workings of such public service corporations may afford. If the plant visited is not up to date and the charges on the community are high, the pupils ought to know it. In Indianapolis, Indiana, a modern by-product coke oven plant of the Solvay type permits the sale of gas to small con- sumers at 55 cents per 1000 cubic feet and to large users at con- siderably less, and at the same time pays generous dividends on all the stock of the company. Wherever possible, trips should be taken to factories where water gas or producer gas is made and here again there is value both in the subject matter itself and in the knowledge of the conditions under which many men have to make their living. Some very hot places to work in will be found in some of these plants, and the question of the hours of labor required in such places is of public interest. The teacher who teaches only chemistry will not teach chemistry itself so well as he who teaches it in all its relations to mankind and his welfare. Under the study of Welsbach mantles, the actual exhibition of one and a study of its brightness when held over a common Bunsen flame as compared with the brightness of other solids when made PAGES 264-281 77 equally hot in the same flame will prove instructive. Pupils will also be interested in the radioactivity of the thorium oxide of the mantle, and some who are interested in photography might be en- couraged to expose overnight a photographic plate, inclosed in a plate holder, to the action of a strip of broken mantle. If bits of metal of various shapes be laid between the mantle and the plate holder, their shadows will appear in the developed plate. Although they are aside from the main topic, such studies arouse consider- able interest in the subject on the part of pupils. The study of carborundum can be made more interesting if samples of the beautifully crystallized material, as it comes from the furnaces, are shown to the class. The exhibition of hones or grinding wheels made of the material will also add to the interest. In connection with the discussion of the great hardness of carbo- rundum, the popular notion that it is as hard as diamond should be corrected. It is really very much less hard. The slightest pres- sure will cause diamond to scratch carborundum deeply, while no amount of pressure can cause carborundum to attack diamond. However, carborundum is considerably harder than any precious stone other than diamond, and rubies and sapphires are easily cut by means of it. Pupils who are interested in art-metal work may be encouraged to use an ordinary coarse carborundum hone to shape pretty pebbles or rough semi-precious stones, which is easily done by rubbing them on the thoroughly wet stone until the desired shape is obtained. They may then be smoothed by the use of fine, and then finer, carborundum cloth, and polished by rubbing on a smooth board with well wet German tripoli. If the stone to be polished is cemented on to a penholder by means of a mixture of melted sealing wax and thoroughly dried plaster of Paris, the work can be more readily done. The cement should be melted over a flame when used. Lapidaries, of course, use rapidly rotating wheels of carborundum or metal wheels impregnated with powdered carborundum and water or oil. 78 COMPOUNDS OF CARBON Answers to Questions on Chapter XXIII Page 281 1. The most valuable form of carbon from the viewpoint of price is diamond. For economic reasons its price is high because of its scarcity and its remarkable hardness, which gives it a value for cer- tain instruments not possessed by any other substance. Its great hardness adds to its desirability as a gem stone, and added to this we have its crystal clearness and the beautiful play of colors given by a well-cut stone. But other stones possess considerable hardness, crystal clearness and beautiful play of colors, and we are obliged to conclude that the very high price paid for gem diamonds is fictitious value, and arises in large part from the human desire to possess the rare and expensive for the reason alone of the rareness and expense. Coal and charcoal are the most useful forms of carbon because they constitute our most valuable fuels. In the true sense, coal is more valuable than diamond because the latter is in no way essential to human welfare. Other substances of considerable hardness could be substituted for it in all important instruments. But if we were deprived of coal, a complete revolution in our industries and our household arrangements would be necessary before our lif e could be adjusted to the new conditions. Indeed, it seems very doubtful if satisfactory substitutes could be found for carbon in all of its varied uses in furnishing heat and power and in the metallurgical industries. 2 and 3. See Section 278, p. 266. 4. See Section 279, p. 268. 6. See Section 278, p. 266. 6. See Sections 283, 286 and 287, pp. 270, 275, and 276. Al- though the explanation of flame luminosity given in the textbook is a serviceable one, in that it would enable an intelligent person to find the cause of poor illumination and proceed to improve it, never- theless this explanation is not thorough, for it does not touch a num- ber of considerations which affect luminosity. 7. See Section 283, p. 270. For convenience in explaining the operation of the valves, number them 1 to 6 inclusive in going along the operating platform. Ability to thus explain the use of the valves is a test of the understanding of the statements in PAGES 264-281 79 the textbook. Beginning at the left of Fig. 55, p. 271, the first valve controls the admission of steam to the generator. The second valve, which is just to the right of the generator, con- trols the air blast to the generator. The third valve (beside the second) controls the admission of air to the carburetor during the passage of the producer gas, which is formed when air is being blown through the thick bed of coals in the generator. The com- bustion of this producer gas serves to help heat the carburetor and also the superheater. The fourth valve controls the admission of oil to the carburetor. It is immediately above the latter. The fifth valve serves to control the admission of air to the superheater, just as the third serves in the case of the carburetor. It is just to the right of the carburetor. The sixth valve is just to the right of the smoke stack. When closed (during the active combustion period) no gases can pass into the scrubber. When the stack is closed (during the admission of steam) this valve is opened so that the water gas may pass. Note that during the combustion period carbon monoxide (practically producer gas, see Section 284, p. 271) is produced in the generator and that it is the combustion of this producer gas in the carburetor and the superheater which serves to heat 'these to the required degree. 8. See Section 284, p. 271. The economizer serves to transfer the heat of the gases coming from the generator to the air entering the generator. The diagram represents only one of a great many modifications of gas producers. Often the economizer is not used at all, and the down draft arrangement of the generator is no more frequent than the up draft. 9. See Section 285, p. 273. 10. Water gas will give a hotter flame than producer gas, for the former contains practically nothing but fuel, whereas the latter contains much nitrogen, introduced with the air into the generator. The nitrogen cools -the producer gas flame. Following is a somewhat more exact treatment of the question if it seems wise to the teacher to take it up with the class. The average volume compositions of the gases in question are : Water gas: H 2 , 46; CH 4 , 2; CO, 46; C0 2 , 4; N ? , 2. Producer gas: H 2 , 12; CEU, 1; CO, 27; C0 2 , 3; N 2 , 57. 80 COMPOUNDS OF CARBON 100 volumes of water gas require the volumes of oxygen and yield the volumes of product as shown in the following table : VOLUME COMBUS- TIBLE COMPONENTS VOLUME OXYGEN REQUIRED VOLUME COMBUS- TION PRODUCTS H 2 46 23 46 CH4 2 4 6 CO 46 23 46 94 50 98 For simplicity, let us consider that air contains exactly one volume of 2 to four volumes of N 2 . The nitrogen in the air re- quired for the combustion of 100 volumes of water gas has a volume of 4 x 50 = 200. The non-combustible components of the gas amount to 6 volumes. The total volume of gases after combustion is thus 98 + 200 + 6 = 304. 100 volumes of producer gas require the volumes of oxygen and yield the volumes of products as shown in the following table : VOLUME COMBUS- TIBLE COMPONENTS VOLUME OXYGEN REQUIRED VOLUME COMBUS- TION PRODUCTS H 2 12 6 12 CH 4 1 2 3 CO 27 13.5 27 40 21.5 42 The nitrogen in the air required for combustion has a volume of 4 x 21.5 = 86.0. The non-combustible components of the gas amount to 60 volumes. The total volume of gases after combustion amounts to 42 + 86 + 60 = 188. If enough producer gas is taken to contain 94 instead of 40 volumes of combustible gas, thus giving as much combustible as contained in the 100 volumes of water gas, the total volume of gases after com- bustion would be f $ x 188 = 442. PAGES 282-298 81 Then, assuming what is nearly true, that the heating power of equal volumes of the combustibles in each gas is the same, we see that the same quantity of heat will have to raise 304 volumes of gas to the temperature of the flame in the case of water gas and 442 volumes of gas to the temperature of the flame in the case of producer gas. Hence the temperature attained in the water gas flame will be higher. We will make another assumption, which, although inaccurate, is sufficiently near the truth to serve in making a rough estimate ; namely, that the heat capacity of equal volumes of all the gases concerned is the same. With the same amount of heat available, then, the rise in temperature in the flame will be inversely propor- tional to the volume of gases that must be heated. If the feed gas and air are at C., the centigrade temperature of the water gas flame would be f |-f or 1.45 times as high as that of the producer gas flame. It is the common practice in metallurgical operations where producer gas is used, to preheat to a high temperature the feed gas and air before leading them into the combustion chamber. Thus a much higher flame temperature is attained. 11. See Section 290, p. 277, 12. See Section 291, p. 278. 13. See Section 294, p. 279. CHAPTER XXIV COMPOUNDS OF CARBON (Continued) Pages 282-298 THIS chapter on the fundamentals of what is called organic chemistry is especially important to those who may study domestic science later. Considerably more may be given by the teacher in special cases where the maturity and special needs of the pupil seem to justify it. A treatment of some member of the paraffin series, showing consecutively the hydrocarbon itself, its alcohol, its alde- hyde and its acid, will be useful later when various substances such 82 COMPOUNDS OF CARBON (Continued) as glycerine (an alcohol), the sugars (some have aldehyde struc- ture), acetic acid (having the COOH group), etc., are studied. While studying the chemistry of the paraffin series, it will be well to go a little more at length into the matter of the practical sepa- ration of petroleum products than is done in the textbook. The methods of the oil refineries illustrate splendidly the use of dis- tillation, of fractional distillation, and of destructive distillation. 1 The use of destructive distillation at increased pressure, in order to obtain products of different character from those to be had at ordi- nary pressure, may be brought out, and in this connection the matter of thus increasing the amount of gasoline-like product obtainable from a given crude oil is of great importance to the automobile industry. The teacher may take a little time in connection with the study of foodstuffs to inform the class as to the proper balance of each type of food in a well ordered diet, and also to take up the method of elimination of the resulting products after oxidation in the body. It should be shown that whereas the C0 2 and H 2 resulting from the oxidation of fats and carbohydrates are easily eliminated by lungs, skin, and kidneys, the protein is less completely oxidized in the body and the resulting complex substances are with difficulty eliminated by the body, principally through the kidneys. If excess of protein is habitually used over long periods, much harm may result at or after middle life. Boys who are in athletic training will be found especially interested in this matter. In connection with the discussion of alcohol, a valuable lesson may be had as to the economic waste involved in the chang- ing of grain products into alcoholic beverages. This view of the matter, as developed on page 292, may have more force with pupils than any attempt, along the usual lines, to teach them temperance. In studying soaps pupils may themselves make up small samples of very good soap or, better yet, the work may be done as a class project. 1 For detailed accounts of the methods in use, see : Molinari, Treatise on General and Industrial Chemistry, P. Blakiston's Son and Company ; or, Rogers and Aubert, Industrial Chemistry, D. Van Nostrand Company. PAGES 299-326 83 Answers to Questions on Chapter XXIV Page 298 1. See Section 295, p. 282, especially the second paragraph on page 283. 2. See Section 295, especially the third and fourth paragraphs on page 283. 3 and 4. See last paragraph on page 283. 5. The formulas are C 18 H 3 8, Ci H 22 , C 5 H 12 . 6. See Section 298, p. 286. 7. See Section 300, p. 288. 8. Glucose is a common name for a product consisting largely of grape sugar. 9. Assume that glucose is entirely grape sugar. C 6 H 12 6 -> 2 C0 2 + 2 C 2 H 5 OH 180 92.1 180:92.1:: 100 :x x =51.2 grams of alcohol. 10. See Section 304, p. 291. CHAPTERS XXV AND XXVI THE IONIC THEORY AND ELECTROLYSIS Pages 299-326 IT has for some time been a vexed question whether the subject of ionization should or should not be included in an elementary textbook in chemistry. It seems to the authors that this great extension of the atomic theory may now be taught to beginners in chemistry if the approach to it is made through familiar facts, and after considerable accumu- lation of matter that can be satisfactorily accounted for only by means of this theory. This would naturally throw the subject late hi the course. To secure thorough understanding of the matter every pupil 84 THE IONIC THEORY AND ELECTROLYSIS should, if possible, be given an opportunity to actually electrolyze various solutions. Where this is not possible a lecture table demon- stration of the results of electrolyzing, say, hydrochloric and sul- phuric acids, sodium hydroxide, and sodium sulphate solutions, should be made. Pupils will already be familiar with the results of the electrolysis of H 2 S0 4 (Section 103, p. 103) and of HC1 (Sec- tion 141, p. 136). Such objective demonstrations as that in which the concentra- tion of sulphate ion about the positive electrode is shown to be greater than elsewhere in the cell (Section 334, p. 316), are very valuable in impressing on the pupil the probable reality of the existence and migration of ions. The opportunity which these chapters on the ionic theory pre- sent, to introduce very briefly the modern view of the atomic structure of electricity, should not be neglected. Pupils will be found to be wonderfully receptive to the beautifully simple modern conception of the oneness of matter and of energy. The teacher who has been too busy to follow up the recent advances in the literature will find an excellent short summary of the matter in the little book Beyond the Atom. 1 The electrolysis of copper sul- phate -(Section 339, p. 320) affords an opportunity to give the class a glimpse of the principles underlying electroplating. If any of the class are interested in art-metal work, the actual plating of articles of copper, to cover the solder used in making them, will prove of interest. While copper sulphate solution can be made to serve for this purpose by properly regulating the current, an alka- line cyanide bath will be found easier to work with. On account of the very poisonous character of such cyanide solutions pupils should not be allowed to work with them unless under direct super- vision. Very slow deposition of the metal gives the best and most adherent coating, and the surfaces to be plated must of course be chemically clean. A caustic soda solution will remove grease, after which the articles should be rinsed and then not again handled before plating. Gold and silver may be substituted for copper if desired, the alkaline cyanides again being used. 1 Cox, Beyond the Atom, G. P. Putnam's Sons. PAGES 299-326 85 Answers to Questions on Chapter XXV Page 309 1. See Sections 217, 312, pp. 207, 299. 2. The OH~ ion is the component common to all bases. Hence it must be the component which turns litmus blue. Likewise it must be the H + ion, the common component of all acids, which turns litmus red. 3. At ordinary temperatures pure substances (other than un- combined metals) are not ionized, hence do not conduct the elec- tric current. Dissolved in water (also in a number of other sol- vents, among which alcohol and anhydrous liquid ammonia are conspicuous) acids, bases, and salts become in some way separated into ions and thus become conductive. Note. The theory as ordi- narily stated and used would convey the impression that ions were single atoms or radicals bearing electric charges. It is principally on account of our ignorance of the true magnitude of the ions, that we in a measure dodge the question by writing the simple formulas which we customarily use for the ions. As a matter of fact we have a good deal of evidence that ions have attached to them con- siderable amounts of the solvent, just as copper sulphate holds in combination five molecules of water of crystallization in blue vitriol, CuS0 4 5 H 2 0. Since we do not know much about the amount of water thus combined with the ions, we are prone to ignore it altogether and thus give a rather wrong impression to our pupils. It is well to discuss this matter in classroom, comparing the probable hydration of the ions with that of salts that crystallize with water. 4. See Section 325, p. 305. In solutions containing each one mole of acid in 10 liters of water only 0.1 per cent of the carbonic acid is ionized (H 2 C0 3 H + + HC0 3 ~) whereas 60 per cent of the sulphuric acid is ionized (H 2 S0 4 2 H + + SO 4 ). 6. See Section 323, p. 305. Note. Of course the teacher may here cite as proofs of the ionic theory the phenomena of vapor pres- sure lowering, osmotic pressure, freezing point lowering, and boil- ing point raising, all of which effects are proportional to the num- ber of moles of dissolved substance in the solution and altogether independent of the kind of substance. In ionized substances it 86 THE IONIC THEORY AND ELECTROLYSIS appears as if each separate ion produced just as much effect as an entire undissociated molecule. Hence by determining how much one of these effects produced by a dissolved electrolyte exceeds the effect that would be calculated on the assumption of there being no ionization, one has a means of estimating the number of ions present. These considerations if clearly presented are in no wise beyond the comprehension of the pupil, but they involve so many entirely new ideas that, if they are to be given well enough to be worth while, altogether too much time must be devoted to them. Furthermore their connection with the common experiences of the pupil or with the rest of the elementary study of chemistry is too remote to warrant the use of so much time. Hence in the textbook the development of the ionic theory is based entirely on the electrical conductivity and the great reactivity of electrolytes. 6. K+ + OH- + H+ + Cl- -> K+ + C1-+ H 2 2 Na + + 2 OH' + 2 H+ + S0 4 " -> 2 Na+ + S0 4 ~ + 2 H 2 2 K+ + 2 OH-+ 2 H+ + S0 4 ~ -> 2 K+ + SO 4 " + 2 H 2 Ca ++ + 2 OH' + 2 H+ + 2 Cl~ -* Ca ++ + 2Cl- + 2H 2 Ca ++ + 2 OH- + 2 H+ + S0 4 " -> Ca+ 4 + SO 4 "+ 2 H 2 and since CaS0 4 is only sparingly soluble, Ca++ + S0 4 ~ CaS0 4 |. In Section 233, NH 4 OH is characterized as a mild alkali, which would indicate that it gives comparatively few OH" ions. There- fore, before all of this base can be neutralized, it must progressively become ionized to keep resupplying the deficiency caused by the removal of OH" ions in the formation of water. This progressive ionization and neutralization takes place with extreme rapidity, and the neutralization of a weak base is thus not measurably slower than that of a strong base, 2 NH 4 OH ^ 2 NH 4 + + 2 OH~ S0 4 ~ + 2 H+ 2H 2 O NH 4 OH NH 4 + + OH- Cl- + H + [ 2 K+ + OH- + H+ + N0 3 ~ -> K+ + N0 3 ~ + H 2 PAGES 299-326 87 7. Ag+ + NOr + H+ + Cl- ->H+ + N0 3 - + AgClj 2 Ag+ + S0 4 ~ + 2 K+ + 2 Cl- ->2 K+ + S0 4 ~ + 2 AgCl| 8. Ba++ + 2 Cl- + 2 Na+ + S0 4 ~ -> 2 Na+ + 2 Cl~ + BaS0 4 1 :Ba++ + 2 OH- + 2 H+ + S0 4 ~ -> 2 H 2 + BaS0 4 t 9. Na+ + OH" + H+ + N(V -> Na+ + N0 3 - + H 2 NH 4 + + Cl- + Na + + N0 3 - -> no change K+ + NOr + Na+ + Cl- -> no change NH 4 + + Cl- + Na+ + OH" Na + + Cl~ + NH 4 OH (not entirely complete) NH 4 OH ^ NH 4 + + OH- Cl- + H+ H 2 The vertical reaction in this method of presentation is so com- plete that the OH" ion shown on the right hand side of the hori- zontal reaction has no chance to accumulate in the solution. With- out such an accumulation this reaction finds no opposition, and proceeds to completion towards the right, in spite of the fact that its tendency to proceed in this direction is small, corresponding to an ionization of NH 4 OH of only about 1 per cent in pure water. Note. It will be noted that the usage is adopted in the fore- going, of letting all salts and the strong acids and bases appear in reactions as completely ionized. This is an entirely justifiable practice. Nothing said in the textbook up to this point necessitates writing the reactions for NH 4 OH different from those for NaOH, and the teacher may prefer not to dwell on this difference. Answers to Questions on Chapter XXVI Page 326 1. See Sections 315, 320, pp. 301, 303. In electrolytic conduction, the electricity passes through the solution only as it is carried in definite amounts on the atoms and radicals which, with these charges, we call ions. In metallic conduction there is no move- ment of material atoms, but the electricity must pass from atom 88 THE IONIC THEORY AND ELECTROLYSIS to atom. Note. In Section 331, p. 314, it was stated that the negative electrons are known to exist independent of ordinary matter, whereas the positive electrons, if such exist at all, are never found separate from material atoms. It is easy to see that positive ions would result from atoms of metals if each lost these little nega- tive electrons, which must be able to escape more easily than posi- tive electrons. These negative electrons can pass to atoms of non- metals, like Cl, and attach themselves thereto, forming negative ions. In a metallic mass, the metal atoms can all part easily with nega- tive electrons, but there are no atoms of non-metals at hand to attach and hold these electrons. Hence negative electrons are free to pass from atom to atom or possibly around among the atoms in a mass of metal. Non-metals, on the other hand, cannot be con- ductors, because from their inability to form positive ions, we know that they are not able to part with any of their normal complement of negative electrons. It is true that their ability to form negative ions might be ascribed not to ability to attach extra negative elec- trons, but to ability to lose some of their normal complement of positive electrons. These positive electrons, however, we have just said are only known associated with material particles of the magnitude of the atoms ; hence, if they escaped from non-metal atoms, they would not be able to move around freely in the mass of non-metal as do the very small negative electrons in the mass of metal. 2. See Section 329, p. 312. 3. If dilute H 2 S0 4 were electrolyzed for a very long time, the solution would become more concentrated, since only water is de- composed, all the H 2 S0 4 being regenerated at the positive electrode. It should be noted that a very prolonged electrolysis would be necessary to produce much effect of this kind, for 96,600 coulombs are necessary to decompose 9 grams of water (a current of 1 ampere would have to flow 96,600 seconds, or 27 hours, to give this number of coulombs). 4. See Section 332, p. 315. If the S0 4 " ion is really discharged at the + electrode during electrolysis, the free S0 4 radical must at once react with water, regenerating H 2 S0 4 and liberating oxygen. Note. It is in some ways a simpler assumption and one which is PAGES 299-326 89 doubtless closer to the truth to say that the SO* ions do not dis- charge at all, but that water dissociates to an infinitesimal extent, (H 2 0^2H + +O~). The O~ ions nearest the electrodes dis- charge, leaving the H + ions balanced by the S0 4 ~~ ions brought up by the current. Since water can continue to ionize to an infinitesi- mal extent to make up for the 0" ions discharged, this process can continue indefinitely. 6. See Section 336, p. 318. Note. As with the SO 4 ~ ion, we do not need to suppose that the Na + ion is really discharged. The H + ions furnished by the slight dissociation of water, (H 2 0^ H + + OH~), can discharge instead, and the water in the immediate neighborhood of the electrode will continue to ionize always to a slight extent to make up for the H + ions discharged. The OH" ions which thus accumulate through the continuous dissociation of water, remain near the electrode balanced by the Na + ions which are brought up by the current. That it is possible to discharge Na + ions is shown in the electrolysis of molten NaOH (Section 336, p. 318), and also in the electrolysis of a Na salt solution with a mer- cury electrode in which latter the discharged Na dissolves to form an amalgam. 6. See Section 334, p. 316. 7. See Sections 337, 342, pp. 319, 322. It is of course obvious that the charges on 2 Na + ions are exactly equivalent to the charges on one S0 4 " ion, since the whole solution of Na 2 S0 4 shows no elec- trification. Likewise after the electrolysis has proceeded some time, since the solution shows still no electrification, it is obvious that just as much + electricity must have been discharged at the - electrode as of - electricity at the + electrode. Therefore 2 Na + ions must discharge for every S0 4 ion. A glance at the secondary reactions shows that 2 NaOH must result for every H 2 S0 4 formed, and these are quantities of the acid and base which will just neutralize each other. 8. Metals which stand high in the order of activity (see table on page 235, or the more complete table on page 329) would be unlikely to deposit on the - electrode during the electrolysis of solutions of their salts. Since H is less active and since even water contains some H+ ions, hydrogen will discharge by preference. Of course 90 THE ELECTROMOTIVE SERIES the metals like lead and tin, which are only a little more active than hydrogen, are more likely to be deposited than the metals higher up, and we must bear in mind that water furnishes but a small concen- tration of H + ions, whereas salts of Pb and Sn furnish a high con- centration of Pb ++ and Sn+ + ions. Metals standing below hydro- gen in the order of activity would always deposit in preference to hydrogen on the electrode. 9. Any metal standing below hydrogen in the order of activity can be electroplated on a conducting object which is made the electrode, when a solution of the salt of the metal is electrolyzed. (See Electroplating of Copper, Section 340, p. 321.) 10. A useful device for measuring the passage of the electric current is to make the circuit pass through a cell with two copper electrodes and a solution of a copper salt. For every 31.8 grams of copper deposited on the electrode and dissolved from the + elec- trode, the amount of electricity which has passed is 96,600 coulombs. Of course other metals and metal salts may be used, and we find for example that 108 grams of silver is equivalent to the 31.8 grams of copper. 11. From the formulas of the ions Cu ++ and Ag + it is seen that one copper ion is electrically equivalent to two silver ions. There- fore 63.6 grams of copper would be equivalent to 2x1 08 = 216 grams of silver and 6.36 grams of Cu would be equivalent to 21.6 grams of Ag = weight of silver which would be deposited. 12. 2 A1+++ is electrically equivalent to 3 Cu+ + . 2 X 27.1 g. Al are equivalent to 3 X 63.6 g. Cu. Therefore 27.1 g. Al are equivalent to f X 63.6 = 95.4 g. Cu. CHAPTER XXVII THE ELECTROMOTIVE SERIES Pages 327-332 THE order in which the metals stand according to the electro- motive series has already been hinted at several times, not only in the chapters on the ionic theory and on electrolysis, but also pre- PAGES 327-332 91 viously when the metals were rated in the order of their chemical activity (Section 252, p. 235). The fact that this difference in activity is related to the degree to which the metals possess elec- tropositive character can now be brought out. The Displacement of acid hydrogen by the more active metals can now also be related to the position of hydrogen in the electromotive series. The fact that hydrogen, when condensed on platinum, can displace copper from solution and cause it to be deposited on the platinum, may be advanced as further proof of hydrogen's title to a position above copper in the ranks of the metals. Answers to Questions on Chapter XXVII Page 332 1. In a mass of copper metal the atoms are electrically neutral and therefore possess no electrostatic repulsion or attraction for each other. The natural cohesion of the Cu atoms for each other has an opportunity to exert itself, and this accounts for the com- pactness and tenacity of a piece of copper. In a solution of a copper salt, on the other hand, every copper atom has negative electrical charges, and since like charges repel each other, there is no chance for the copper atoms to cohere. 2. Fe + Cu ++ + S0 4 ~-> Fe ++ + S0 4 ~ + Cu. The sign is used to draw attention to the fact that the atoms so designated bear no charges. 3. See Section 348, p. 329. 4. See Sections 242, 243, pp. 226, 227 and Section 348, first sen- tence, p. 329. The most important chemical characteristic of metals is their ability to form simple positive ions, and this characteristic is shown to a marked degree by hydrogen. 5. At ordinary temperatures chemical reactions among non- ionized substances are for the most part so slow that they can almost be said not to take place at all. Now water is ionized to a very slight extent, of a mole being ionized into H + and OH~ ions in every liter of pure water. Of course it is obvious that the more active a metal is, the more vigorously it will drive out 92 THE ELECTROMOTIVE SERIES even the few H + ions in pure water. Sodium, potassium, and cal- cium therefore, being among the most active metals, are the most able to set hydrogen free from water. Water has the ability, like all substances capable of ionization, of rapidly dissociating to re- supply any ions that are taken away, and so the displacement of ionic hydrogen may continue until the -active metal is all exhausted. Metals like magnesium, aluminium, and zinc, are active enough to displace hydrogen, but here the metal ions form insoluble hydroxides with the OH" ions likewise furnished by the dissociation of water. These hydroxides adhere to the metal surface and protect it from any continued action. 6. (1) Fe + Cu ++ -*Fe++ + Cu 55.8 63.6 (2) Zn + Cu++ -> Zn++ + Cu 65.4 63.6 (3) Mg + Cu ++ -> Mg ++ + Cu 24.3 63.6 (4) 2 Al + 3 Cu+ + -> 2 A1+++ + 3 Cu 2x27.1 3X63.6 (1) 55.8 : 63.6 : : 56 : x x = 63.8 grams of Cu (2) 65.4 : 63.6 : : 65 : x x = 63.2 grams of Cu (3) 24.3 : 63.6 : : 24 : x x = 62.8 grams of Cu (4) 54.2 : 190.8 : : 27 : x x = 95 grams of Cu ^~ 7. (a) Zn + 2 H+ + 2 Cl~ -> Zn++ + 2 Cl~ + H 2 (6) Zn + Cu++ + 2 Cl- -+ Zn++ + 2 Cl~ + Cu (c) Zn + 2 Ag+ + 2 NOr -> Zn++ + 2 NOr + 2 Ag (d) 2 Al + 3 Hg++ + 6 NOr -> 2 Al +++ + 6 N0 3 - + 3 Hg (e) Fe + AU+++ + 3 Cl- -* Fe +++ + 3 Cl~ + Au (/) Cu + Zn ++ + 2 Cl~ -> no change (g) Cu + 2 H+ + 2 Cl- -> no change (h) Cu + 2 Hg+ + 2 N0 3 - -> Cu ++ + 2 N0 3 - + 2 Hg (i) Cu + Hg + + + 2 NOr -> Cu ++ + 2 NOr + Hg (/) 2 Cu + Pt+ + ++ + 4 Cl- ->. 2 Cu ++ + 4 Cl- + Pt (A) 3 Ag + AU+++ + 3. CL- -> 3 AgCty + Au (0 4 Ag + R++++ -h 4 Cl- -> 4 AgCH + Pt c o PAGES 333-341 93 CHAPTER XXVIII HYDROGEN EQUIVALENTS AND VALENCE Pages 333-341 IF pupils are given an opportunity to actually perform the ex- periment which is described in Section 353, p. 333, especially if it is done for two different metals of different valences, as, for example, with magnesium and with aluminium, no difficulty should be ex- perienced in giving them thorough comprehension of the meaning of hydrogen equivalents. Through that comprehension, a much more real grasp of the significance of valence may be had than was possible when that topic was first introduced in Section 215, p. 203. The teacher should also perform a similar experiment with metallic sodium to illustrate the case of a monovalent element. Most pupils will need the triple repetition of the calculation before they will thoroughly understand just what they are after and just why they do the various things in the calculation. When the three hydrogen equivalents are before them, they can then compare them with the three atomic weights (Na, Mg, and Al). The facts that the two numbers are about the same for sodium, while the hydrogen equivalent of Mg is about ^ the atomic weight, and that of Al is about J, will at once appear. It is then easy to lead the pupil to see that the displacement of hydrogen by sodium must have been an atom for atom displacement, and that the valence of Na is I, whereas each atom of Mg must have displaced 2 atoms of hydrogen and each Al atom must have displaced 3 of hydrogen, making the valence of Mg II and that of Al III. Answers to Questions on Chapter XXVIII Page 341 1. See Section 352, p. 333. 2. Multiply the number of liters at standard conditions by .09. See Section 353, top of p. 335. 94 SULPHUR 070 740 3. 24.4 c.c. of H 2 at 20 and 740 mm. = 24.4 X .|g| X jjj- - 22.1 c.c. under standard conditions. 22 1 Weight of hydrogen = X 0.09 = 0.00199 gram. 0.112 gram of Cd is equivalent to 0.00199 gram of H. i oo Weight of Cd equivalent to 1 gram of H = Q X 0.112 = 56.3 grams. Hydrogen equivalent of cadmium = 56.3 grams. 4. The valence of cadmium is 2. 6. It would be well to plan to collect about 80 c.c. of the gas if the gas measuring tube has a volume of 100 c.c. The reaction would be Zn + 2HCl->ZnCl 2 + H 2 65 g. 22.4 1. 80 Weight of Zn necessary to yield 80 c.c. of H 2 = 22466 X 65 = 0.232 gram. CHAPTER XXIX SULPHUR Pages 342-357 THIS chapter, while hi its first part purely descriptive, leads to the consideration of the important practical application of chemistry in the manufacture of sulphuric acid. Teachers should emphasize the enormous commercial uses of sulphuric acid. The value of the annual output is almost unbe- lievable, $22,000,000 in 1913 in the United States alone. It has been said that there is no article used by civilized man which has not had sulphuric acid used, directly or indirectly, in connection with its making. Perhaps this statement will seem extravagant, but on being thought over carefully the statement will be found hard to contradict. Both the contact process and the chamber process are described, PAGES 342-357 95 as they are both likely to be used for many years, the chamber process appearing to be secure against the competition of its simpler rival where the manufacture of impure acid is concerned. The nature of the reactions in the chamber process has not of course been gone into extensively, as the possible reactions are too numerous and too complicated for discussion in an elementary textbook and many of them are still in dispute. The essential reactions are given. Wherever possible, pupils should be taken to see a sulphuric acid plant. Many large fertilizer companies have their own acid plants and use the acid in making phosphate fertilizers. Trips to such plants will afford interesting opportunities for the study of the practical application of chemistry. Stereopticon views may be made to serve where a trip is impossible. Answers to Questions on Chapter XXIX Page 356 1. Sulphur is distinctly a non-metal. The first and most im- portant classification of the elements is into metals and non- metals. 2. The oxides of sulphur yield acids on union with water. 3. See Section 363, p. 342. 4. See Section 367, p. 347, last paragraph. 5. Of the non-metallic elements, oxygen, chlorine, and sulphur, sulphur is the weakest, that is to say, it is the least active chemically towards the metals and hydrogen. Oxygen and chlorine combine with violence with hydrogen, sulphur with difficulty (Section 366, p. 346). Furthermore, both oxygen and chlorine displace sulphur from solutions of H 2 S or of the sulphides 2 H 2 S + 2 - 2 H 2 + 2 S|. Here the sulphur appears as a milky precipitate, Na 2 S + C1 2 -> 2 NaCl + S. In this case sulphur may stay in solution as a yellow polysulphide, Na 2 S S.C (x being any number between 1 and 4 inclusive), so long as excess of Na 2 S is present. After that a precipitate may be seen, but this disappears with excess of chlorine because it is oxidized to 96 SULPHUR sulphuric acid. The sulphides of the heavy metals can be changed to oxides or chlorides by roasting in air or roasting with salt (see Chap. XXII). 6. Sulphur dioxide and oxygen have a strong enough tendency to combine, but the reaction is extremely sluggish when no other sub- stance is present. With catalyzers, the reaction is facilitated and its natural tendency to take place exerts itself, (a) In the contact process, finely divided platinum acts as the catalyzer. (6) In the chamber process, oxides of nitrogen act as the catalyzer. 7. Concentrated sulphuric acid is appreciably heavier than concentrated hydrochloric acid, and it is a good deal more viscous, so by lifting the bottle and giving it a rocking motion one can decide which of these acids it contains. If the stopper is removed, HC1 gas escapes in the one case and can be perceived by the odor and by the mist if the breath is blown across the mouth. H 2 S0 4 is not volatile and gives no odor or mist. 8. In 1913, 3,000,000 tons of sulphuric acid, valued at $22,000,000, were manufactured in the United States. 9. Rhombic, monoclinic, and amorphous sulphur are different forms of pure sulphur, just as ordinary oxygen and ozone are differ- ent forms of pure oxygen. 10. See Sections 377 and 303, pp. 354 and 290. Concentrated sulphuric acid will give wood a charred appearance. 11. 4 FeS 2 + 11 2 -> 2 Fe 2 3 + 8 S0 2 8 S0 2 + 4 2 + 8 H 2 -* 8 H 2 S0 4 1 mole FeS 2 yields 2 moles H 2 S0 4 120 196.2 120 : 196.2 : : 1000 : x x = 1635 kilos H 2 S0 4 . 12. From the first equation under 11 we see that 4 moles of FeS 2 yield 8 moles of S0 2 , or 1 mole of FeS 2 yields 2 moles of S0 2 120 kilos (2 X 22.4 X 1000) liters =44.8 cubic meters 120 : 44.8 : : 1000 : x x = 373 cubic meters of SO 2 . 13. See Section 377, p. 354. 14. Ammonia combines with sulphuric acid to form a salt, PAGES 358-376 97 (NH 4 ) 2 S0 4 , hence ammonia gas cannot be dried by bubbling it through sulphuric acid. It can be dried with lumps of CaO or NaOH. CHAPTER XXX COMPOUNDS OF NITROGEN Pages 358-376 THE study of nitrogen compounds affords many very interesting and practical applications of chemistry, especially in connection with the fixing of atmospheric nitrogen by artificial means, and also in connection with the use of nitrogen compounds as explosives. The chemistry of nitric acid is more complicated than that of sulphuric acid, hence it is given only in this later part of the course. The fixing of nitrogen by active metals may be illustrated in the laboratory by the use of Mg powder in a crucible. On being heated, the surface material changes mainly to oxide, but much of the in- terior powder becomes nitride. The ammonia formed when the product is moistened can be detected by its odor. This experi- ment can be performed quantitatively, the ammonia being re- leased into HC1 solution to form the chloride. If standard HC1 be taken, the residue can be titrated with standardized NaOH and the amount of ammonia obtained can be calculated. In connection with the study of ammonia, visits to gas plants where ammonia is one of the by-products, should by all means be made wherever practicable. An artificial ice plant which uses ammonia should also be visited by the class if possible. Where such trips cannot be taken, the stereopticon will serve to help make the processes clear. The reactions of nitric acid with metals should be broadly ex- plained as in Section 390-391, pp. 366-370, which simplifies the other- wise seemingly complicated subject. The fact that sulphuric acid acts in a somewhat similar fashion when hot (Section 390, p. 368), illustrates the resemblance between the two acids in respect to their being oxidizing agents as well as acids. 98 COMPOUNDS OF NITROGEN Pupils will need some help in assimilating the idea that the addi- tion of H is reduction just as much as is the removal of a non-metal like oxygen or chlorine (Section 391, p. 368). The electrical ex- planation of the matter will help here if the teacher cares to develop that point of view: Increase of the positive valence of an element or, what is equivalent, decrease of the negative valence, consti- tutes oxidation. Decrease of positive valence, or increase of nega- tive valence, constitutes reduction. For example, when oxygen is removed from N 2 5 the nitrogen is reduced, for the positive valence is lowered from V to 0. When hydrogen is added to the nitrogen in forming NH 3 , the nitrogen is further reduced, for the negative valence is increased from to III, which is equivalent to lowering the positive valence from to III. Great interest is always manifested by pupils in the chemistry of explosive substances, and frequently teachers find it necessary to interfere tactfully with unwise experimentation on the part of pupils with dangerous substances. The nitrogen cycle in nature will require some classroom discus- sion, and specimens of sweet clover or other leguminous plants show- ing the nodules on the roots should be exhibited to the class. 1 Answers to Questions on Chapter XXX Page 375 1. When powdered magnesium is heated in a crucible, a chemical reaction with the air soon takes place ; the oxygen combines with the magnesium of the upper layers so that only the more abundant nitrogen penetrates to the lower layers. After the crucible has been heated one half to one hour, it is found that the upper one fifth of the contents is mostly magnesium oxide and approximately the lower four fifths is magnesium nitride. This reacts violently with water according to an equation similar to that at the top of p. 359. 2. See Section 382, p. 360. 1 See Knox, The Fixation of Atmospheric Nitrogen, D. Van Nostrand and Company. PAGES 358-376 99 3. A gas which by itself is colorless but turns brown on coming in contact with the air must be nitric oxide, NO. 4. Zinc stands above hydrogen in the electromotive series and it can set hydrogen free from hydrochloric acid. Copper stands below hydrogen in the series and cannot displace it from acids. Thus HC1 is without action on Cu (Section 348, p. 329). But HN0 3 is an oxidizing agent and oxidizes copper to CuO. The latter being a basic oxide reacts with more of the acid to form a salt. (See Sec- tions 387, 390, pp. 364, 366.) 6. 2 HN0 3 -> H 2 O + 2 NO + 3 3 + 6 Ag -> 3 Ag 2 3 Ag 2 + 6 HN0 3 -> 3 H 2 + 6 AgN0 8 adding 6 Ag + 8 HN0 3 -> 6 AgN0 3 + 4 H 2 O + 2 NO or 3 Ag + 4 HN0 3 -+ 3 AgN0 3 + 2 H 2 O + NO 6. Zn + 2 HN0 3 -> Zn(N0 3 ) 2 -f 2 H HN0 3 + 8 H -> 3 H 2 + NH 3 NH 3 + HN0 3 -> NH 4 N0 3 These reactions are not added to give a total reaction, because they represent only a part of the reactions that are taking place, and the proportion of the acid which acts as here shown varies very greatly according to conditions of temperature, concentration, and amount of resulting product. Hence the summation of these three equations could not be used to calculate the amount of product to be obtained from a given weight of material. Some of the nitric acid will be reduced only to NO, which escapes as a gas. Possibly some N 2 and free N 2 , and probably some free hydrogen will also escape. Which of the reaction products preponderates in a given case de- pends, as already said, on the conditions. 7. See Section 396, p. 371. 8. (NH 4 ) 2 S0 4 + Ca(OH) 2 -> CaS0 4 + 2 NH 3 *+ 2 H 2 O 132.2 74.1 132.2 : 74.1:: 100 ix x = 56.05 = no. of grams of Ca(OH) 2 . 9. From above equation it is seen that 132.2 grams of (NH 4 ) 2 S04 yield 2 moles or 2 X 22.4 liters of NH 3 . 132.2:44.8:: 100 :x x = 33.9 = no. of liters of NH 3 . 100 COMPOUNDS OF NITROGEN 10. From above equation, 132.2 grams of (NH 4 ) 2 S0 4 yield 2 X 17.03 grams of NH 3 . 132.2 : 34.06 : : 100 : x x = 25.76. 25.76 grams of pure NH 3 = ~ = 92.0 grams of 28% solu- .60 tion of NH 3 . no 11. 92 grams of NH 3 solution of sp. gr. 0.90 occupy -^ = 102.2 U. i7 c.c. 12. 3 Cu +8 HN0 8 -> 3 Cu(NO 3 ), + 2 NO + 4 H 2 O 3 X 63.6 8 X 63 190.8 : 504 : : 190.8 : x x = 504. KftA 504 grams of pure HN0 3 = ~ = 720 grains of 70% HN0 3 . 13. From above equation, 190.8 grams of Cu yield 2 X 22.4 liters = 44.8 liters of NO. 14. 2 NO + 2 -> 2 NO 2 44.8 1. 22.4 1. 22 4 22.4 liters of oxygen = -~ =112 liters of air. 16. The reaction of the explosion of gunpowder is expressed ap- proximately by the equation : 2 KN0 3 + 3 C + S -* 3 C0 2 + N 2 + K 2 S. The solid K 2 S is responsible for the smoke. Smokeless powder on exploding decomposes according to the equation : C 12 H 14 4 (N0 3 ) 6 -> 3 N 2 + 7 H 2 + 3 C0 2 + 9 CO which shows all the reaction products to be gaseous. 16. If heat is given off when N 2 O decomposes into nitrogen and oxygen, this heat is added to the heat of combustion of a substance burning in the N 2 0. This added heat would compensate partly or wholly for the heat absorbed by the inert N 2 produced by the reac- tion. Thus combustion in N 2 may be practically as vigorous as in pure oxygen. PAGES-377 T 39l 101 CHAPTER XXXI THE HALOGEN FAMILY; THE PERIODIC SYSTEM Pages 377-391 THE alert teacher will have already pointed out to pupils many family resemblances between elements ; as, for example, the chemical resemblance between oxygen and sulphur, where both were found to unite with iron in some of the earlier experiments, one making the oxide, the other the sulphide, and both causing the release of light and heat when the reaction was rapid enough. Again, when potassium and sodium were used to react with water, family resem- blance was doubtless pointed out. When the rare gases of the at- mosphere were mentioned, another chance to point out the close- ness of relationship in a natural family of the elements occurred, and this time chemical inactivity was the most striking resemblance. These family relationships may now be recalled to give a familiar setting to the advance work, and the pupil's knowledge of the proper- ties of chlorine should also be made use of in introducing him to fluo- rine, bromine, and iodine. With a fairly complete knowledge of the principal resemblances between the four members of the halogen family, the pupil may then be given some account of the marvelous regularity that exists among the atomic weights of the elements, and its relation to this matter of family resemblances may be shown. Pupils will always be found to be much interested in speculating as to what is back of this wonderful regularity ; and here again, as under the discussion of the probable atomic structure of electricity (Section 331, p. 314), the teacher may add a bit of the more recent theory, and briefly explain the modern conception of the atom as built up of electrons. 1 Answers to Questions on Chapter XXXI Page 391 1. The halogens resemble each other in that they all possess a most disagreeable odor ; they are all very active chemically, com- 1 See Cox, Beyond the Atom, G. P. Putnam's Sons. 102 THE HALOQEN FAMILY? THE PERIODIC SYSTEM bining spontaneously with nearly all the metals ; and their hydrogen compounds are all colorless and extremely soluble in water, in which solution they become strong acids. Their valence is always one towards hydrogen and the metals. 2. See Section 403, p. 379. 3. Fluorine decomposes water instantly, combining with the hy- drogen and driving out the oxygen. Mixed with hydrogen, fluorine combines explosively even in the dark. A mixture of chlorine and hydrogen does not combine chemically if it is kept from strong light, but exposed to intense light or touched with a flame or an electric spark it explodes with violence. Bromine can combine directly with hydrogen, but not with vio- lence, if a mixture of the two is passed through a heated tube. Iodine combines with hydrogen even less easily than does bromine, although the compound once formed remains undecomposed at ordi- nary temperature. We see that the halogens all form similar compounds with hydro- gen, but that the strength of the attraction decreases regularly in passing from the halogen of lightest atomic weight to that of heaviest atomic weight. 4. Free iodine gives an intense blue color with starch. Combined iodine does not give this color, but the addition of a little chlorine will liberate the iodine from combination and the blue color with starch will appear. 6. To demonstrate the presence of starch in a sweet potato, knead a little of the cooked potato in some water until a smooth thin emulsion is obtained, then add a little iodine solution and note the blue color, which is a test for starch. The color is so intense that it may appear black, in which case stir a little of the emulsion into a large volume of water. 6. See Section 411, p. 384. 7. A glance at the periodic arrangement of the elements on page 389 shows that an unknown element of atomic weight about 99, and another of atomic weight about 188 may be expected to exist and to fit into the same family with manganese; that two with atomic weights between 208 and 222.4 may be expected to be found and to fit respectively into the sulphur and halogen families. The PAGES 377-391 103 properties of these elements will, without doubt, prove to be what would be expected from their positions in their respective families. 8. K = 39.1; I = 127; KI = 166. 127 In 1000 grams of KI there are 7 - X 1000 = 765 grams of loo iodine. 9. 2KI + C1 2 ->2KC1 +I 2 332 g. 70.9 g. 332 : 70.9 : : 1000 : x x =213.6 grams of chlorine. 10. 2 KI + Clf -*2 KC1 + I 2 332 g. 22.4 1. 332 : 22.4 : : 1000 : x x = 67.5 liters of chlorine. 11. At 100 C. the molal volume is 273 l' Q 100 x 22.4 =30.6 liters. Zio Therefore 30.6 liters will be the volume occupied by 1 mole, or 160 grams of Br 2 vapor at atmospheric pressure and 100 C. 5c.c. of liquid bromine of sp. gr. 3.19 = 5 X 3.19 = 15.95 grams. As a gas at 100 C., this will occupy a volume of X 3,0.6 = 3.05 liters. 12. (a) CaF 2 + H 2 S0 4 -> CaS0 4 + 2 HF f (6) Mn0 2 + 4 HBr -+ MnBr 2 + 2 H 2 + Br a (c) Cu + Br 2 -> CuBr 2 (d) CuO + 2 HBr -> CuBr 2 + H 2 13. (a) 2 K+ + 2 r + Cl, -* 2 K+ + 2 Cl- + I 2 (6) K+ + Br- + Ag+ + N0 3 --^K++N0 3 -+AgBr| (c) Cu ++ + 2 Br~ + C1 2 -> Cu++ + 2 Cl~ + Br 2 (d) 2 H+ + 2 T + Zn -> Zn++ + 2 I~ + H 2 | (e) H+ -f Br- + Na+ + OH~ -> Na + + Br + H 2 (/) CuO + H 2 ^ Cu(OH) 2 ^ Cu++ + 2 OR- 2 Br + 2 H+ 2H 2 In pure water the horizontal reaction does not take place to a perceptible extent. In presence of HBr, the occurrence of the ver- 104 REVERSIBLE CHEMICAL REACTIONS tical reaction removes very completely one product of the horizontal reaction, and thereby the latter is enabled to run to completion, the copper oxide dissolving and ionized copper bromide being formed in the solution. CHAPTER XXXII REVERSIBLE CHEMICAL REACTIONS; CHEMICAL EQUILIBRIUM Pages 392-412 As was the case with the study of the periodic law, much pre- liminary material is available with which to introduce the formal study of reversible reactions on a familiar foundation. One of the earliest experiments performed by most classes makes use of mercuric oxide in obtaining oxygen by heating the oxide. While pupils seldom prepare their own mercuric oxide, they are always made familiar with the fact that it may be prepared by merely heating mercury in air or in oxygen, and they themselves prepare other oxides in that way. Thus, while the matter was perhaps not called to their attention at that time, it can now be made use of as a natural lead into the new topic of reversibility. Again, the fact that carbon dioxide reacts feebly with water to form an acid was early learned by the class (Section 57, p. 58), and the further fact that the carbonated water easily reverted to water and carbon dioxide was pointed out in connection with the fire extinguisher (Section 58, p. 58). This can now be recalled as an- other example of a reversible reaction. In connection with the study of crystal hydrates (Section 194, p. 185), it was shown that some substances readily react with water in definite proportion to form new products, and that these prod- ucts readily decompose on slight heating and yield water and the original anhydrous substance. Again (Section 219, p. 208), the reaction between sulphur dioxide and water was specifically shown to be reversible like that between PAGES 392^12 105 carbon dioxide and water. Thus there are many foundations on which to base an introduction to the study of reversible reactions. The mass law, in its simple, common sense form, without mathemat- ical complications, can readily be understood by pupils of high school age, and its use explains reactions that could not be un- derstood without it. The idea of chemical equilibrium is a valuable one to pupils who have progressed as far as this chapter. The study of the three general means of causing reversible re- actions to proceed to completion is also valuable. From a practical standpoint, the study of hydrolysis is a valuable application of the principles of this chapter. The extensive use of various salts such as sodium carbonate, borax, sodium phosphate (both the disodium and the trisodium salts), soap, and alum de- pends very largely on their hydrolysis, and their action cannot be understood without reference to hydrolysis. Answers to Questions on Chapter XXXII Page 412 1. Among the reversible reactions already studied are : (a) 2 HgO ^ 2 Hg + 0,. Sections 21, 414, pp. 29, 392. (6) 2 H 2 + 2 ^ 2 H 2 0. Sections 119, 414, pp. 117, 392. (c) 4 HC1 + 2 ^ 2 H 2 + 2 C1 2 . Sections 170, 181, pp. 165, 171. (d) 2 NaHCOa ^ Na 2 C0 3 + H 2 O + C0 2 . Section 192, p. 183. (e) CaC0 3 ^ CaO + C0 2 . Sections 207, 209, pp. 195, 197. (/) CaO + H 2 ^ Ca(OH) 2 . Section 226, p. 213. (g) H 2 C0 3 + CaC0 3 ^ Ca(HC0 3 ) 2 . Section 211, p. 199. (h) H 2 C0 3 ^ H 2 + C0 2 . Section 218, p. 208. (i) H 2 S0 3 ^ H 2 + S0 2 . Section 219, p. 208. (j) NH 3 + H 2 ^ NH 4 OH. Sections 233, 391, pp. 217, 368. (A;) Fe 2 3 + 3 CO ^ 2 Fe + 3 C0 2 . Section 256, p. 244. (0 All cases of ionization, Chapter XXV, p. 299. (m) H 2 + S ^ H 2 S. Section 366, p. 346. (n) H 2 S ^ 2 H+ + S~. Section 369, p. 348. 106 REVERSIBLE CHEMICAL REACTIONS (o) 2 BaO + 2 ^ 2 Ba0 2 . Section 415, p. 394. (p) 3 Fe + 4 H 2 ^ Fe 3 4 + 4 H 2 . Section 417, p. 396. (q) 2 NaCl + H 2 S0 4 ^t Na 2 S0 4 + 2 HC1. Section 420, p. 400. (r) Na 2 C0 3 + H 2 ^ NaHC0 3 + NaOH. Sections 423, 424, pp. 403, 405. 2. Elevating the temperature will cause many reactions to run in the opposite direction to that followed at lower temperature, as for example, in cases a, b, d, e, f, g, h, i, j, m, and o, above. Changes of concentration of substances entering into a reaction from one side or the other may cause a reaction to reverse, or to go at least a certain distance in the opposite direction, as, for example, in cases c, h, i, j, k, I, n, p, q, r, above. 3. See Sections 416, 417, pp. 395-398. 4. See Sections 419, 420, 421, pp. 399-401. 6. See Section 424, p. 405. 6. See Section 424, p. 405. 7. The use of alum in baking powders depends on its hydro- lyzing and yielding an acid. The use of sodium carbonate and of borax for washing depends on their hydrolyzing and yielding an alkali. 8. When sodium chloride is dissolved in water its molecules begin to dissociate into ions at a very rapid rate, and all would shortly exist in the ionized state except that Na + and Cl~ ions in solution are continually combining to form undissociated molecules. The reaction comes to equilibrium when as many molecules are being formed in a given interval of time by the reuniting of ions as are dissociated in the same time. The condition of equilibrium is reached with extreme rapidity. In solutions of moderate dilution about 80-90 per cent of the salt is ionized at this point of equilib- rium. NaCl ^ Na+ + Cl~ (o) By adding a solution of AgN0 3 , Cl~ ions will be removed through formation of the insoluble AgCl precipitate. This removal of Cl~ ions will displace the equilibrium toward the right until finally all of the NaCl has become ionized. (b) By evaporating the water, the whole concentration is in- creasing, but that of both the Na + and Cl~ on the right-hand side PAGES 413-424 107 increasing outweighs the increasing of only the NaCl on the left- hand side, so the equilibrium is displaced toward the left. Soon, however, the concentration of the NaCl has reached its saturation point and it begins to crystallize, or precipitate, out. This removal of NaCl still further displaces the equilibrium toward the left, and when finally the water has all been evaporated, the reaction has gone completely toward the left and only undissociated NaCl is left. 9. Guncotton does not exist in a state of chemical equilibrium. It has an extremely strong tendency to react in the direction of the formation of simpler compounds, but under ordinary conditions the reaction is so slow that it is negligible. Once provoke the reaction by concussion or local heating, and its own heat so hastens the reaction in adjacent portions, that the whole reaction completes itself in a brief interval of time. Thus to bring guncotton to a state of equilibrium, cause it to explode, whereupon the simpler com- pounds are formed which can exist together in a true state of equi- librium. The reaction is Ci 2 H 14 04(N0 3 )6 -V3 N 2 + 7 H 2 + 3C0 2 + 9 CO. This is not a reversible reaction. CHAPTER XXXIII CHEMICAL REACTIONS AND ENERGY TRANSFORMATIONS Pages 413-424 IN this, the final chapter of Foundations of Chemistry, an attempt is made to focus attention upon the energy side of chemistry. To be sure, the pupil's attention has many times been called to the fact that energy changes always accompany chemical changes, but before leaving the subject, either temporarily or permanently, it is well for the pupil to be reminded that chemistry, like physics, is con- cerned both with matter and with energy, and that although most of the reactions which are brought about by mankind in the affairs of daily life and in the laboratory are of the exothermic type, yet there are also many important reactions in which energy is absorbed. Most important of these are those changes brought about in green plants under the influence of sunlight, and the teacher should bring 108 ENERGY TRANSFORMATIONS in here the botany necessary to a clear explanation of such part of the mechanism of photosynthesis as is at present understood. Of artificial endothermic reactions, the preparation of nitric acid from atmospheric nitrogen and oxygen is perhaps one of the most important, and the teacher may add further information in this regard. (See Knox, The Fixation of Atmospheric Nitrogen, D. Van Nostrand Co.) In conclusion, the authors would make a final appeal to teachers to correlate everywhere what is being taught with what has pre- ceded, and also with the daily life of the pupil. Bring in and use the related sciences whenever and wherever possible, even at the risk of being charged with teaching general science, for it is only by teaching science as a whole, and not as consisting of isolated branches, that the true scientific spirit can be inculcated, and only thus can pupils be brought to realize the interrelation of all the sciences and the unity of nature. Answers to Questions on Chapter XXXIII Page 424 1. Some exothermic reactions which are used solely to obtain heat are : (a) The burning of fuels, Chapter IV ; (6) The thermit reaction, Section 434, p. 415 ; (c) The burning of hydrogen or acety- lene in the oxyhydrogen or oxyacetylene blowpipe, Sections 118- 119, 439, pp. 116, 117, 420; (d) All explosive reactions, since the violent expansion is caused quite as much by the enormous heating of the gases as by the production of the gaseous substances them- selves. Except for the use of the gases in producing the expan- sion, the material products of explosions are entirely waste. 2. Exothermic processes which yield energy in the form of an electric current are not discussed to any extent from this point of view in the textbook. Nevertheless, information given in Sec- tions 270, 342, 343, 346, 441, pp. 257, 322, 323, 328, 423, etc., has a bearing on the subject. It is obvious that all reactions in which the number of electric charges on the ions or atoms undergoes change are electro-chemical reactions; to make such reactions develop an electric current, it is necessary only to make them take PAGES 413^24 109 place in suitable cells. For example, in the Daniell cell the current is produced by the familiar reaction, Zn + Cu++ + S0 4 " -> Zn++ + S0 4 ~ + Cu| If, however, a strip of zinc is immersed directly hi a beaker of copper sulphate solution, the zinc is dissolved and the copper is precipitated, but no usable current is obtained, for the current simply flows through the metal strip from where the Cu ++ ions are precipitated to where the Zn +4 ions pass into the solution. But in the Daniell cell, the zinc strip is kept physically separated from the copper sulphate solution by means of a porous cup. The elec- tric charges deposited on the copper strip must flow as a current through the external wire, and can thus be made to ring bells or do other useful work, before they can get to the zinc rod to enter into the formation of Zn ++ ions. This is the secret of obtaining an elec- tric current from an electro-chemical reaction; viz., to keep the reacting substances physically separated, so that the interchange of electric charges will have to take place through an external conductor. It is a help in understanding such processes to consider separately the reactions at the two electrodes, treating the and electrons in the same way as material atoms in writing the equations (with the exception however that we may let the electrons drop out of, or appear in, the equations provided only that the number of and that appear or disappear is the same). For example, in the Daniell cell, the reaction at the copper electrode is : Cu ++ + S0 4 " -> Cu + SO" + 2; the reaction at the zinc electrode is: The S0 4 ~~ ions left unbalanced around the copper electrode have to pass through the wall of the porous cup to reach the locality where they can electrically balance the positive Zn ++ ions being formed. The separate reactions in the lead storage cell (Section 441, p. 423) may be written as follows. When discharged, both plates of the battery consist of PbS0 4 . The electrolyte is moderately con- centrated H 2 S0 4 . Charging, at + electrode : 2 + PbS0 4 + S0 4 ~ + 2 H 2 O -> PbO 2 + 4 H+ + 2 SO 4 ~ at the electrode : 20 + PbS0 4 -> Pb + S0 4 110 ENERGY TRANSFORMATIONS Adding to get the total charging reaction : 20 + 20 + 2 PbS0 4 + 2 H 2 -> Pb0 2 + Pb + 4 H+ + 2 S0 4 ". Discharging, at the Pb0 2 electrode : Pb0 2 + S0 4 - + 4 H+ -> PbS0 4 + 2 H 2 + 2 at the Pb electrode : Pb + S0 4 ~ -> PbS0 4 + 20 Adding to get the total discharging reaction : Pb + Pb0 2 + 2 H 2 S0 4 -> 2 PbS0 4 + 2 H 2 O + 20 + 20. In the Edison storage battery, in which the electrolyte is NaOH solution, Charging, at + electrode : 20+2 Ni(OH) 2 + 2 OH- -> 2 Ni(OH) 3 - Ni,0, + 3 H 2 at the - electrode : 20+ Fe(OH) 2 -> Fe + 2 OH~. Adding to get total charging reaction : 20 + 20 + 2 Ni(OH) 2 + Fe(OH) 2 -> Fe + Ni 2 3 + 3 H 2 O. Discharging, at Ni 2 3 electrode : 2 Ni(OH) 3 -> Ni(OH) 2 + 2 OIT + 2 at the Fe electrode: Fe + 2 OH- -> Fe(OH) 2 + 20 Adding to get the total discharging reaction : 2 Ni(OH) 3 + Fe -> 2 Ni(OH) 2 + Fe(OH) 2 + 20+20. 3. See Section 437, p. 418. 4. Two common explosives in which the power is developed by the decomposition of an endothermic substance are nitroglycerine and guncotton. Examples of other endothermic explosive sub- stances, which however are generally not used intentionally for such a purpose, are acetylene, ozone, and hydrogen peroxide. 6. Examples of explosive mixtures in which the power is de- veloped through the formation of an exothermic compound, are gunpowder, the oxyhydrogen mixture, the hydrogen chlorine mix- ture, a gasoline vapor-air mixture, etc. 6. The study of energy is usually considered as belonging to the study of physics rather more than to the study of chemistry. Physics deals with bodies of matter rather than with the sub- stances of which the matter is composed. The energy of motion of a body, the heat energy of a hot body, the light energy emitted PAGES 413^24 111 from a very hot body, the sound energy from a vibrating body, the transmission of mechanical energy by a belt, of electric energy through a wire, of sound energy through the air, all come within the scope of physics, as they are concerned only with bodies of matter and do not involve any change of substance. But chemical changes invariably involve the giving off or the absorption of heat energy, or of light or electrical energy, forms which in themselves would be classed as physical energy. Since chemical energy is thus convertible into physical as well as physical into chemical, it is clear that the sciences of physics and chemistry overlap. 7. Physiology is the science that deals with the vital phenomena of animals and plants. Since these vital phenomena depend on the chemical changes taking place in the animal and plant tissues, or upon the energy furnished by these chemical changes, chemistry must be fundamental to an understanding of physiology. Geology treats of the constitution and the structure of the earth and of the history of the development of the structure. The con- stitution involves a knowledge of chemical substances. The de- velopment of the structure involves chemical changes as well as physical. For example, deposits of limestone (Section 50, p. 51), of coal (Section 277, p. 266), of petroleum, and of sulphur, have very clearly resulted from chemical reactions. s o Hr ral Library ' 34 sity of Californn Berkeley UNIVERSITY OF CALIFORNIA LIBRARY