UC-NRLF 
 
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 A-V, 
 
 To "Te.c* cJn 
 
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UNIVERSITY OF CALIFORNIA. 
 
 GIFT OF 
 
 Accession - u j O r 
 
SUGGESTIONS TO TEACHERS 
 
 DESIGNED TO ACCOMPANY 
 
 THE ELEMENTARY PRINCIPLES 
 OF CHEMISTRY 
 
 BY 
 
 A. V. E. YOUNG 
 
 PROFESSOR OF CHEMISTRY IN NORTHWESTERN UNIVERSITY 
 
 NEW YORK 
 
 D. APPLETON AND COMPANY 
 1901 
 
TWENTIETH CENTURY TEXT-BOOKS 
 
 SUGGESTIONS TO TEACHERS 
 
 DESIGNED TO ACCOMPANY 
 
 THE ELEMENTARY PRINCIPLES 
 OF CHEMISTRY 
 
 BY 
 
 A. V. E. YOUNG 
 
 PROFESSOR OF CHEMISTRY IN NORTHWESTERN UNIVERSITY 
 
 NEW YORK 
 
 D. APPLETON AND COMPANY 
 1901 
 
COPYRIGHT, 1901 
 BY D. APPLETON AND COMPANY 
 
TO THE TEACHER OF CHEMISTRY 
 
 THE following suggestions are designed to accompany 
 the text-book of the writer. His desire is to assist the 
 teacher of a subject that draws heavily on time and 
 strength, not only for the work of instruction, but for 
 the preparation and care of material and for the man- 
 agement of the laboratory. As the intention, frankly 
 avowed, is to describe very informally my own methods, 
 I judge that I may be pardoned the use of the first 
 person singular. 
 
 184368 
 
 A. V. E. Y. 
 
 iii 
 
\ 
 
 Of THE 
 
 UNIVERSITY 
 
 THE ELEMENTARY PRINCIPLES OP 
 CHEMISTRY 
 
 SUGGESTIONS TO TEACHEES 
 
 i 
 INTRODUCTION 
 
 THE place of chemistry in education as a branch of 
 natural science is fairly well recognized. The value of its 
 training for close observation, clear thinking, and precise 
 expression is widely admitted, as is also the applicability 
 of much of its subject-matter to practical affairs. But I 
 sometimes think that those who stand as its advocates, and 
 perhaps its teachers also, do not sufficiently emphasize the 
 dignity and worth which pertain to it as a serious study of 
 nature, of nature in the broadest significance of the term ; 
 for surely that which elevates and ennobles should be 
 found, if it be sought, in the wonders of material creation, 
 the handiwork of infinite intelligence, as truly as in the 
 history of men's achievements in material things. 
 
 I am not so sure that the laboratory method for chem- 
 istry has received as general assent as has the claim in 
 behalf of the science for a place in the curriculum. For 
 my part, I almost think that in the interest of the pupils 
 their time may better be given to some other subject, unless 
 suitable laboratory study can be provided. I shall assume, 
 therefore, that the laboratory method is adopted. The 
 quantitative method in the laboratory is still further from 
 receiving universal approval, and to this, attention is here 
 
 84368 
 
2 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 invited since the course herewith offered is based upon it. 
 The quantitative method aims to bring the student into 
 direct contact, so to speak, with the relations of quantity as 
 well as with those of quality. It most distinctly does not 
 aim to present the systematic methods of quantitative analy- 
 sis. No more does it propose that the pupil shall prove to 
 his own mind the laws of quantity. Such laws are induc- 
 tions from a great many observations, arid the student 
 should be carefully guarded against the idea that his ex- 
 periments are to prove them, even to his own conviction. 
 His experimentation is simply to aid him by direct observa- 
 tion and by guided thought to get a clear notion of the 
 content and meaning of the laws. The relations of quan- 
 tity are absolutely fundamental to the science. No branch 
 of physical science has made any considerable progress 
 until it has been placed on a quantitative basis. There- 
 fore there is the same desirability to illustrate for the 
 student the quantitative aspect of things as there is to 
 illustrate their properties in descriptive experiments. 
 Moreover, it is desirable that quantity shall receive due 
 consideration and illustration at the moment when the logic 
 of the subject calls for the same, and that is early in the 
 course. I believe it also a positive advantage that the 
 careful manipulation which is necessary when attention is 
 given to quantity should come at the outset of the stu- 
 dent's experience rather than after he has formed the 
 habit of disregarding quantity. In addition, it may be 
 claimed that the quantitative method, speaking broadly, 
 contributes very considerably to the disciplinary value of 
 any branch of natural science. It is this which gives to 
 the subject of Physics its advantage over other branches. 
 
 But whatever may be said as to the desirability of these 
 things, the use of the method must be limited by its prac- 
 ticability. Probably the first objection to be urged is the 
 impracticability of providing the necessary equipment. Of 
 this the balance is the essential feature. If it were de- 
 
SUGGESTIONS TO TEACHERS 3 
 
 manded that this should be a balance capable of weighing 
 to one ten-thousandth of a gram, the impracticability of the 
 thing would be manifest. Not only this, but it would be 
 folly to try to use such a balance if it were provided. One 
 which weighs to the hundredth of a gram is all that is 
 called for, and this is surely within the range of the prac- 
 ticable. The rest of the equipment is hardly more than is 
 provided for the usual courses. 
 
 The next objection to be expected is that the beginning 
 pupil has not sufficient skill in manipulation to do the 
 work. This may be true, but it is equally true that he can 
 very quickly acquire that skill. No one, not even the most 
 advanced worker, has skill until he acquires it. And the 
 only way to get skill is to do, and of all doing there must 
 be a beginning. The pupil may just as well learn to use 
 the balance by using it the first day in the laboratory, as 
 by deferring its use until he has worked a year, if in the 
 meantime he never touches it. I have in mind, of course, 
 a balance like the one just specified, nothing finer. 
 
 Another objection is that quantitative experiments take 
 more time than do descriptive experiments. This is true, 
 but before the former are condemned for this reason, it 
 should be duly considered that they are used to lead the 
 student to a clear notion of fundamental laws which are 
 based on broad generalizations, and, if this is gained, it is 
 worth the greater expenditure of time. Suppose the pupil 
 could make a dozen experiments descriptive of some sub- 
 stance or substances in the time needed for the quanti- 
 tative experiment illustrating multiple proportions, does' it 
 follow that the time is spent to better advantage in the 
 former ? Indeed, there may be positive gain in the fact 
 that the student must work slowly and deliberately at the 
 outset, when he is getting the fundamental notions of the 
 subject. This, if not carried to excess, may help to make 
 the laboratory what it should be a place for thinking as 
 well as for seeing. Nor should it be overlooked that items 
 
4 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 of description also occur in the quantitative experiments, 
 although description is subordinate to the main idea. 
 
 Finally, it may be objected that with the limitations of 
 equipment and of manipulative skill already suggested, the 
 quantitative results obtainable are worthless. The truth 
 of this depends on how the results are used. If they are 
 used with any pretense to prove laws, they are worthless 
 for the purpose ; but if they suffice to bring to the stu- 
 dent's mind the relation of quantities within the limits of 
 his observational accuracy, the point is made. Therefore 
 it is reckoned essential to the satisfactory use of the quan- 
 titative method that the limits of accuracy be carefully 
 estimated for each experiment. The teacher is urged to 
 keep this constantly before his pupils. For a concrete ex- 
 ample, take the experiments Nos. 41/ 3 and 41/ 4 in which 
 the student determines the volume and mass of hydrogen 
 liberated by 2.4 grams of magnesium and 6.5 grams of zinc, 
 as illustration of equivalent proportions. If he makes two 
 determinations of the value for each metal, and finds that 
 the value for zinc does not differ from that for magnesium 
 more than one value for magnesium differs from the other 
 for the same, or one zinc from the other zinc, then the 
 experiment has served its purpose to bring to his observa- 
 tion and to impress upon his mind the relation of equiva- 
 lency within the limits of his observational accuracy. It 
 should not be forgotten that this careful consideration of 
 the limitations to accuracy is necessary in all experimental 
 results, even in those obtained by the most skillful experi- 
 menters and with the most refined apparatus. 
 
 TIME AND TOPICS 
 
 One of the first things to which a teacher must recon- 
 cile himself is the fact that he can not teach to beginners 
 in a course of one year the whole of the science. Even 
 if he were willing to make information the sole end of his 
 teaching, he could not present all the so-called useful in- 
 
SUGGESTIONS TO TEACHERS 5 
 
 formation of the subject of chemistry. But training is, 
 after all, a fundamental purpose of education, and it may 
 be reckoned as one of the peculiar advantages of our sub- 
 ject that training and useful information are so effectively 
 combined. In choosing topics, therefore, both these fea- 
 tures must be carefully considered as well as the limita- 
 tions of time. 
 
 I assume an aggregate time not less than four periods 
 a week through the academic year of thirty-eight or 
 forty weeks ; also that the quantitative method in the 
 laboratory is accepted. I also assume a maturity (with no 
 previous chemical instruction, however) on the part of the 
 student, which I estimate is attained by the average pupil 
 in the last year of his high school experience or the first 
 year of college ; and I must be permitted to decline sponsor- 
 ship for the course outside of these conditions. But four 
 periods a week may not always mean the same amount of 
 available time. Sessions limited to one hour or less are 
 very uneconomical of time for laboratory study, and make 
 it almost impracticable. Two, or at least one and a half, 
 hours of uninterrupted time should be provided, and two 
 hours of laboratory time should be reckoned as one of pre- 
 pared recitation. 
 
 In my own classes the time assignment is four hours 
 a week, but this is interpreted as allowing eight hours of 
 aggregate time to the subject, either in the class room or 
 in the laboratory. It is an advantage to have the time 
 assigned for class room work continuous with that for the 
 laboratory. This permits of adjustment according to the 
 demands of a particular topic. I therefore have three ses- 
 sions a week of two and a third hours each, thus taking 
 seven hours and allowing a margin of one hour for work 
 outside of the laboratory and of the class room. 
 
 If it is necessary to divide a class into sections for lab- 
 oratory work, there is advantage in having successive days 
 for each section e. g., Monday and Friday for one, and 
 
6 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 Tuesday, Wednesday, and Thursday for another as pupils 
 can thus suspend work on an unfinished experiment with 
 less inconvenience. However, this advantage may be over- 
 balanced by the difficulty of securing such allotment of 
 time. With the arrangement that has been indicated, I 
 allow thirty-five weeks, vacations not included, for complet- 
 ing the course offered in the text. But inasmuch as the 
 amount of work accomplished is likely to vary considerably, 
 even with the same time assignment, it may be helpful if I 
 give more in detail an estimate of the time needed for the 
 several portions of the course : 
 
 Chapter I, 6 weeks. 
 
 Chapter II, 6 weeks. 
 
 Chapters III and IV, 2 'weeks. 
 
 Chapter V, Law 1, 3 weeks ; Laws 2 and 3, 1 week ; Laws 
 4 and 5, 2 weeks. 
 
 Chapter VI and VII, 3 weeks. 
 
 Chapter VIII, 12 weeks. 
 
 If circumstances make it necessary to curtail the course, 
 the following expedients are suggested : 
 
 1. To waive the requirement of two good quantitative 
 results from each student. If this is done, care should be 
 taken to bring before the whole class a sufficient number 
 of the individual results to show the range of variation. 
 
 2. Under the law of equivalent proportions, Chapter II, 
 the four parts of the experiment might be assigned to dif- 
 ferent members of the class. Some could be asked to de- 
 termine the hydrogen with magnesium and the oxygen 
 with zinc ; others to determine the hydrogen with zinc and 
 the oxygen with magnesium some by the first method and 
 some by the second. In a similar manner the problem of 
 determining the vapor-density of carbon dioxide, Chapter 
 V, Law 1, might be divided, the determination of weight 
 being assigned to a part of the class and that of volume to 
 another part. An expedient of this kind is a sacrifice, for 
 it is very desirable that the student's work should be thor- 
 
SUGGESTIONS TO TEACHERS f 
 
 oughly individual. If it is used the teacher needs to see 
 that the class room discussion makes clear to each one how 
 his neighbor's observation supplements his own. 
 
 3. If curtailment of topics is necessary, it is suggested 
 that Chapter IV may be unnecessary in case the class has 
 previously studied these topics in physics. The same may 
 be said as to the experiments in specific heat (Chapter V, 
 Law 2), which, like the preceding, involve no chemical re- 
 actions. These experiments and the accompanying calcu- 
 lations are very helpful in clarifying the student's ideas. 
 Especially is this true as to the laws of Raoult (4 and 5, 
 Chapter Y), and it justifies the use of the latter experi- 
 ments, notwithstanding the crudeness of the quantitative 
 results which are attainable. 
 
 Chapter VI reinforces what has already been defined 
 and repeatedly discussed, and I judge the experiments are 
 worth the time given to them for this purpose, but they 
 might be omitted rather than sacrifice altogether some 
 other topic. 
 
 As to the last part of Chapter VII, beginning with 
 " Evidence as to structure," Xo. 181, its utility may be 
 doubted. I am in the habit of giving it to my classes with 
 the idea that they may get some impression from it. Many 
 probably would prefer to omit it altogether. For my part, 
 I would readily assent to having the whole of Chapter VII 
 dropped, although this would generally be regarded as too 
 radical a step. I believe that first-year courses of chem- 
 istry would be bettered if the conception of atoms and 
 molecules were not introduced at all, and that if teachers 
 would make their presentation of the science independent 
 of the atomic hypothesis as a basis they would come to 
 regard it as a genuine emancipation. 
 
 4. Finally, it is suggested that when the class reaches 
 Chapter V the teacher follow this plan if he is in doubt 
 about completing the course without curtailment, viz. : To 
 take up Chapter VIII either before entering on Chapter V 
 
8 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 or after completing Gay-Lussac's Law ; then after Chapter 
 VIII to No. 642 is finished, to turn back fco Chapter V and 
 present the remaining text with such curtailment as limit 
 of time may necessitate. It is difficult for a teacher to 
 foresee without actual trial how a text will adapt itself 
 to time. Some may prefer, aside from the question of 
 time limit, to introduce the descriptive matter before the 
 topics of Chapters V, VI, and VII ; and I see no serious 
 objection nor difficulty in so doing, although in my own 
 practice I prefer to follow the order of the text. There are 
 a few references in Chapter VIII to the matter of Chap- 
 ters V, VI, and VII, especially as to vapor-density, and over 
 these points the teacher might need to help the student 
 temporarily. Such references occur in Nos. 208/ 2 , 314, 323, 
 331, 434, 436, 461, 493, 494, and 640. I cite these so that 
 the teacher may judge for himself as to the practicability 
 of departing from the order of the text in the manner sug- 
 gested. In Chapter VIII the matter pertaining to indus- 
 trial applications and to other items not essential to the 
 unity of the course is set apart so that the teacher may 
 use it or not, at his discretion. Pupils are likely to read 
 such matter from general interest, and it does not call for 
 the time and effort of deliberate study. 
 
 Criticism is anticipated upon the fullness of treatment 
 in Chapter V, especially as to use of the tabulated data. 
 There is a distinct motive for this. Few, I judge, would 
 favor the omission of these topics ; and it is of prime impor- 
 tance that the student should realize that these laws are 
 inductions from observed data, and furthermore that they 
 are approximations of a very different order of exactness as 
 compared with that of the laws of proportion in Chapter 
 II. To present them as laws without this qualification is 
 to be false to fact, and leads the student naturally to infer 
 that which is not true. To avoid this error, therefore, the 
 data are presented, and not at all with the intention that 
 the student shall commit them to memory. Some, per- 
 
SUGGESTIONS TO TEACHERS 9 
 
 haps, would wish to include additional topics of similar 
 import, such as osmotic pressure and the electrical phe- 
 nomena of conductivity, etc., together with the theory of 
 ionization ; but I have judged it impracticable to illustrate 
 these phenomena experimentally without displacing other 
 matter or going beyond the reasonable scope of one year's 
 work ; and therefore I have deemed it best not to include 
 either them or the theory. 
 
 As TO TOPICS AND EXPERIMENTS IN DETAIL 
 
 References are to marginal numbers in Parts I and II of the text. 
 
 It is suggested that the teacher at the outset either 
 have the pupils read Numbers 1 to 6, Part I, or that he 
 give the class the substance of these paragraphs in an in- 
 formal talk immediately before they pass into the labora- 
 tory to begin work. In the laboratory it is well to begin 
 by naming over the articles of apparatus in the individual 
 equipment, letting the class identify each by the sample 
 shown from the instructor's table, then to direct attention 
 to the Recommendation as to Notes. I also emphasize in 
 this preliminary talk that the laboratory is a place for seri- 
 ous study and work and not for amusement. Then each 
 pupil being at his place with a sample of roll sulphur and 
 his directions before him, I call attention to each item 
 (Numbers 1 to 6), explaining that crystalline form is dif- 
 ferent from the chance shape of each fragment or the 
 form given by the mold. The commercial samples of roll 
 sulphur or brimstone do not often show crystalline forms 
 large enough to be apparent. The larger crystals are seen 
 in Number 12/j. 
 
 Number 7. This involves the first weighing, and atten- 
 tion is directed to the Appendix, 1. It is well for the 
 instructor to show from the demonstration table the ma- 
 nipulation of sorting the lumps, corking the test-tube 
 while holding it in the full palm to avoid the danger of 
 crushing, then of wiping and of weighing. 
 
10 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 It is recommended that pupils be called on in the class 
 room to read their experimental notes ; then that correc- 
 tions and additions be called for from the class ; and finally 
 that the instructor by questions, and perhaps added state- 
 ments, complete the discussion of the topic. My plan is 
 to have the pupils enter on the left-hand page such correc- 
 tions and additions as are brought out in this discussion. 
 After this reading and discussion of the observations fol- 
 lows the fuller presentation of Part I. 
 
 In calculating the specific gravity of sulphur, the error 
 is very commonly made of subtracting the weight of the 
 tube filled with water from the weight of the tube contain- 
 ing water and sulphur and calling the difference the weight 
 of the water displaced. Since the specific gravity of sul- 
 phur is 2, this error still gives a good numerical result, and 
 the, incident affords the opportunity to show the need, not 
 alone of a correct final result, but of correct reasoning and 
 method. Since this experiment involves quantitative meas- 
 urement, it is well to bring out an important matter, after 
 a record has been read, by questions somewhat like these : 
 You say your sulphur weighed 10 grams ; how do you know 
 that ? How do you know that the weight was not 10.001 
 grams? Do you know that it was not 10.01 ? How closely 
 did you measure the quantity you have called 10 grams ? 
 I do not generally give out the hundredth-gram weights 
 until later in the course, when they are specifically called 
 for in the directions, so only tenths are used here. With 
 these and the balance which is capable of indicating 
 hundredths, they estimate to .05 of a gram with an 
 uncertainty of 0.02 or 0.03. Well, then, I ask, if there 
 is an uncertainty of 0.02 in each weighing, how much 
 uncertainty attaches to the final result? (About 0.02 
 or 0.03.) This I let them figure out. I then explain that 
 similar estimates of uncertainty are involved in all obser- 
 vations of quantity, no matter how refined the methods. 
 Then I usually put the questions suggested in Num- 
 
SUGGESTIONS TO TEA 
 
 ber 8, and thus lead the way to the fuller statements of 
 Part I. 
 
 Numbers 10, 11, 12. The teacher should manipulate 
 this experiment before the class, by way of instruction. 
 Students will sometimes fail to get a good sample of the 
 plastic form, because they do not heat sufficiently before 
 pouring into water ; if so, I have them try again. As there 
 is no change in weight in passing from the plastic to the 
 brittle condition, it is, of course, important that the sam- 
 ple shall be well dried before it is weighed, hence the direc- 
 tion to string it out ; otherwise the drying is difficult. 
 
 Numbers 12/i and 12/ 2 , I do not allow the class to per- 
 form, but myself prepare the crystals from fusion shortly 
 before they are to be exhibited. For this purpose a Hessian 
 crucible is used. I prepare the solution in carbon disul- 
 phide at the lecture table and set it aside for crystalliza- 
 tion and later examination. 
 
 Number 13/ 1( The zinc must be the very fine powder 
 commercially called zinc dust, but this even does not always 
 react with equal readiness, because of the presence of oxide, 
 I infer. Nascent hydrogen with the sulphur forms some 
 hydrogen sulphide, hence the stain on the lead paper can- 
 not be satisfactorily used to discriminate between the mixed 
 zinc and sulphur and the zinc sulphide. This applies also 
 to the iron and sulphur in Number 13/ 2 . The hydrochloric 
 acid is supplied on the side table. It is of commercial 
 grade, specific gravity about 1.16, or 20 Baume. 
 
 Number 13/ 2 . The iron used here is iron dust, the 
 finest powder, designated in dealers' catalogues as " iron 
 by alcohol." Unfortunately, when treated with hydro- 
 chloric acid the gas often makes a stain on the lead paper. 
 
 Number 13/ 3 . The nitric acid is supplied on the side 
 table. The concentrated commercial article, specific grav- 
 ity 1.38, or 40 Baume, serves the purpose. The gas may 
 bubble quite rapidly through the acid and still give a good, 
 result. 
 
12 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 Number 15/j. In the pupil's hands this experiment 
 may fail of good result if the powder is too coarse. The 
 iodine may then sublime without much action on the lead. 
 I have had no trouble with the lead dust, but this is sup- 
 plied by the dealers only in the chemically pure grade. 
 This is much more expensive, and the purity is not needed. 
 In lieu of this, 100-mesh powder of commercial grade seems 
 to serve the purpose. Even the still coarser powder will 
 react if the heat is applied slowly and the mixture shaken. 
 
 Number 15/ 2 . I have found magnesium in the form of 
 ribbon preferable for this and similar experiments. 
 
 Number 15/ 4 . The oxidation of the lead is slow, espe- 
 cially if the powder is coarse, and its result is not as con- 
 spicuous as in the preceding illustrations. Still, the experi- 
 ment gives a useful observation to be recalled in the subse- 
 quent experiments with lead nitrate. 
 
 Number 16/ 2 . The zinc nitrate, being very deliquescent, 
 is best given out in small quantities. The main supply 
 should be kept well stoppered. 
 
 Number 17/ lt The zinc here and subsequently used 
 under the designation, granulated zinc, is chemically pure 
 (c. p.), Number 20, in the dealers' catalogues. It is about as 
 coarse as granulated sugar, and it is rather important in 
 some of the experiments that exactly this material be used. 
 
 Number 17/ 2 . The commercial strong sulphuric acid is 
 used. The dilute acid called for in the experiment is 
 made with one volume of acid to four of water, and I pre- 
 fer at this stage of the work to have only this dilute acid 
 supplied on the side table. If the pupils are to make the 
 dilution, they should be warned as to the manner of so 
 doing. (See Number 519, Part II.) 
 
 Number 18. This experiment as a whole takes a good 
 deal of time, although its several steps are not long. I 
 deem it well worth the time, for it is a difficult matter to 
 bring beginners to a fair understanding of the phenome- 
 non of exchange, because of the difficulty in tracing the 
 
SUGGESTIONS TO TEACHERS 13 
 
 several constituents by direct observation. In practice I 
 find that alkaline reaction is sometimes obtained in the 
 last part of (/), showing the presence of lime in the pre- 
 cipitate due, I suppose, to insufficient washing. 
 
 Number 22. Pupils are very likely to overlook the need 
 of having the water and the solute at the same ^temperature 
 before mixing. This condition is not specified in the direc- 
 tions, but if the student deliberates on his problem as he 
 should, his common sense will suggest the need. When I 
 find that this is overlooked, I like to suggest it by questions 
 like these : What is your problem ? (To get the effect of 
 solution simply.) Suppose you had some sand warmer than 
 the water and mixed it with the water, would it dissolve ? 
 What would be its effect on the temperature of the water ? 
 Suppose, then, that the salt is warmer than the water, what 
 would be its effect on temperature, if no solution took 
 place ? How, then, must you observe the effect of solution 
 simply ? I let them assume that the salt has the tempera- 
 ture of the room, or let them put the thermometer into the 
 bottle and thus observe it. 
 
 For thermometric experiments I use the so-called " chem- 
 ical thermometers " of the dealers' catalogues with the scale 
 up to 150 C. engraved on the stem. They vary a good deal 
 in their readings, and therefore it is useful to attach a num- 
 bered tag to each, in order that the student may use one 
 thermometer through his series of readings. If the scale 
 becomes dim, it is improved by rubbing over it a piece of 
 charcoal or a soft lead-pencil. 
 
 Number 34/!. The mercuric sulphocyanate I keep at my 
 table and give to each student his portion as he brings his 
 dish. The substance is not much in use, and there may be 
 some difficulty in getting it from the dealers, although I 
 have had no trouble. To omit the experiment would be no 
 serious matter ; it is introduced rather as a curiosity. This 
 substance is the material of the so-called Pharaoh's serpent, 
 It is also called sulphocyanide. 
 
14 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 Numbers 34/ 2 and 34/ 3 . The alternative form is some- 
 what simpler of construction, but the first has the advan- 
 tage that it gives the instructor opportunity to emphasize 
 the formation of two products of combustion. 
 
 Number 34/ 5 . The sodium hydroxide is supplied on the 
 side table, preferably as a solid. The sticks should be broken 
 in pieces about an inch long to avoid waste. Two or three 
 of these in a bottleful or beakerful of water are enough. 
 For counterpoising, clean gravel kept in a bottle on the 
 side table is convenient. 
 
 Number 34/ 6 . In quizzing on the law, I cite the several 
 reactions which have already occurred in the work, and ask 
 the application of the law to each one, calling for the spe- 
 cific naming of factors and products. 
 
 Number 37. It is important that the hydrochloric acid 
 be of the chemically pure (c. p.) grade. This is diluted 
 with an equal volume of water. It is well thus to prepare 
 at the start sufficient of the acid to serve all the class, 
 in order to insure uniformity of sample for the whole ex- 
 periment. The ammonium hydroxide is the commercial 
 article, "FFF,"16 Baume, or specific gravity 0.96, used 
 without dilution. Both substances leave but a slight stain 
 on evaporation. They are supplied on the side table. The 
 portions taken by the pupil to his own table should not be 
 allowed to stand long unstoppered, and it is best that resi- 
 dues be not returned to the side-table bottles. I use the 
 strips of paper made by cutting gummed labels, and the 
 measuring test-tubes thus marked should be preserved to 
 provide for repetition. If I see that two out of the three 
 results obtained are good, I direct repetition of only the 
 one. This may be made independently, provided the vol- 
 umes are preserved. It is best to use separate measuring 
 tubes, one for the acid and another for the hydroxide. 
 The pupils' ingenuity is taxed somewhat to " note carefully 
 the volume of acid used." If I find them blundering, I 
 suggest that they fill the tube to a marked strip, pour out 
 
SUGGESTIONS TO TEACHERS 15 
 
 what is needed, and mark the level of the residue by a 
 second strip. The directions are worded on the supposi- 
 tion that test-tubes with gummed strips are used for meas- 
 uring. About one half of a test-tubeful should be used 
 as the unit volume. 
 
 I have the class weigh only to tenths, and I hold them 
 to results that show a variation not exceeding 0.2 of a grain 
 from the ratio of. 2:1:2. A good proportion of the results 
 will show a smaller variation than this. 
 
 Number 37/ 5 . In quizzing on this law, as on Law 1, 
 I use the reactions already presented, and ask the applica- 
 tion of the law in both its forms to each one. 
 
 Number 37/ 7 . This paragraph usually puzzles the class 
 a good deal. In quizzing I follow a line like this : State 
 the converse of this law. Is this true ? Suppose you have 
 in hand two samples of matter, A and B\ suppose you 
 ascertain that both contain the same constituents, com- 
 bined in the same ratio as in the other one, does it follow 
 that A and B are samples of the same substance ? This 
 usually gives occasion to say, Learn the fact now ; the ex- 
 planation will come later. 
 
 Number 37/ 8 . Some may object to the alternative state- 
 ments as tending to confuse. The first is so commonly the 
 one given that I have not wished to omit it; and yet, it 
 seems to me, there is a distinct advantage in the broader 
 aspect of the second form. This is conveniently and force- 
 fully applied to any reactions, even those involving four or 
 more substances. 
 
 Numbers 40/a and 40/b. I find it a good plan to take off 
 altogether the metal pans of the balance and to substitute 
 glass crystals. In weighing out the mercury, pupils will be 
 awkward. I suggest that they put the weights on the right- 
 hand pan and pour from the bottle a little more mercury 
 than is necessary to counterpoise, then by means of a knife 
 or spatula blade separate a small globule and push it off the 
 pan and into the bottle. The use of the heavier balance, 
 
16 THE ELEMENTARY PRINCIPLES OP CHEMISTRY 
 
 in order to check the total weights, is not very material to 
 the problem, and may be omitted if it is not convenient to 
 provide the balance. It may occur once or twice in the 
 class that the reaction is spoiled by overheating. It is well 
 to emphasize from the desk the likelihood of this, and the 
 precaution of using a little alcohol. The heat of reaction 
 evaporates the alcohol if too much be not used. 
 
 In color the mercuric and the mercurous iodide are 
 somewhat variable, and they are sensitive to light. The 
 former sometimes responds well to the tests even if the 
 color is dull-red, and the odor of the iodine gives a good 
 indication as to the completeness of the reaction: The 
 latter often shows a brown tint. In both instances the first 
 test by alcohol sometimes shows the reaction incomplete ; 
 if so, the rubbing should be continued. Mercury and iodine 
 are both rather expensive, but I have been unable to find 
 cheaper practicable material which will illustrate the law as 
 clearly and as conspicuously as these do. I have had the 
 experiment long in use, and reckon it very serviceable. 
 
 Number 40/ 5 . To show that this law is not contra- 
 dictory to Law 2, gives a good opportunity for questions in 
 the class discussion. 
 
 Number 41. Magnesium in the form of ribbon is here 
 preferable, and, if it is tarnished, pieces of emery paper 
 should be supplied at the side table to be used in cleaning 
 the surface. It is important that the zinc be the granu- 
 lated, c. p., as already specified. The nitric acid is the com- 
 mercial article described in Number 13/ 3 . The crucible 
 should be of thin porcelain, Eoyal Berlin, or equally good, 
 and Number 1, diameter If inches, is recommended for size. 
 The evaporating dishes also, which are used in 41/#, should be 
 of the same material, 3^ or 3J inches in diameter, and glazed 
 inside and outside. These stand high heat with little break- 
 age, but the cheaper grades, in my experience, have not been 
 satisfactory for such experiments. The rod should be short 
 enough to lie in the dish without danger of spilling out. 
 
SUGGESTIONS TO TEACHERS 17 . 
 
 Of the two methods given in 41/j and 41/5, the first has 
 the advantage of directness and simplicity of reaction, but 
 there is sometimes difficulty in carrying the reaction to 
 completeness without loss of oxide or without prolonged 
 heating. Then, too, the porcelain is likely to be corroded 
 by reduction, and I have seen the nitride formed in some 
 instances. The product is often very dark-colored. On 
 the other hand, the second method gives a cleaner reaction, 
 although less direct to the beginner, but it involves the use 
 of iodine, is somewhat more difficult in manipulation, and 
 it uses smaller quantities. However, I have found the 
 two methods together very instructive, as one part of the 
 larger experiment. It is not necessary that the magnesium 
 should be entirely dissolved by the iodine, as small frag- 
 ments will be oxidized in the final heating. The mixture 
 does not become thoroughly dry on the water-bath. But 
 little alcohol is needed. The tendency is to use an excess, 
 which adds to the difficulty of evaporation. 
 
 I find that 75 per cent of the class results reach 1.59 
 0.04 grams of oxygen for 2.40 grams of magnesium. As an 
 error of 0.02 in the weight of oxygen is multiplied by 2.4 
 in the final result of the first method and by 4.8 in the sec- 
 ond, the range is fully as small as should be expected. In 
 the experiment with zinc about the same proportion of the 
 class reach 1.59 0.07. Since in this one the error of 
 0.02 in the weight of oxygen is multiplied by 3.3, a varia- 
 tion of 0.07 or even more is to be expected. The range of 
 variation in both cases should be made evident and be dis- 
 cussed in the class room. 
 
 Numbers 41/ 3 and 41/ 4 . The scale of these might be re- 
 duced with some economy of time, but the effect of error 
 in the final result would be thus increased. On the whole, 
 I prefer the quantities specified. For collecting bottles I use 
 the ordinary half-gallon packing bottles with glass stopper. 
 On these, both bottle and stopper, is placed a number 
 corresponding with the number of the individual equip- 
 
18 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 ment of which they are a part. Some such expedient is 
 important, in order to identify each bottle with its content. 
 
 For graduated flask, I have found latterly one of 1,200 
 c.c. capacity more convenient than one of 750 c.c. Com- 
 mon flasks of the right capacity are easily obtained, and 
 it is a small matter to graduate these with sufficient accu- 
 racy, using graduated flasks, and placing a mark with a file 
 or a diamond at the proper point of the neck. This effects 
 a considerable economy over the commercial graduated 
 flasks. Thus prepared they are distributed about the 
 laboratory on the side tables. The small residue of water 
 may be weighed as directed, or its volume may be measured 
 in the small cylinder. 
 
 About 75 per cent of the' class results come within 0.200 
 0.006 for the hydrogen by magnesium and by zinc. By 
 comparing the results for oxygen and for hydrogen in the 
 individual pupil's work, the practical equivalence often 
 appears even when the partial results are not satisfactory, 
 and this, indeed, is the main point at issue. It is espe- 
 cially recommended that there be thorough quizzing in all 
 the details of the manipulations, observations, and calcula- 
 tions before the corresponding text in Part I is taken up. 
 Then there should be thorough drilling on the law, the 
 corollaries, and the definitions, as they constitute the basis 
 of the whole system which is to follow. It may be sug- 
 gestive to recall the axiom, Two quantities equal to a third 
 are equal to each other. 
 
 Number 47/a, The dealers supply under the name of 
 " dissolving-tubes " what is preferable to the common test- 
 tube, being of a little heavier glass and of smaller diameter 
 for the length. The size 9 X f inches is used. The unit- 
 tube may, perhaps, be obtained of the proper size under the 
 name " specimen tube," but it is easily made to order if not 
 in stock. For rubber bands I use No. 8, getting them in 
 quarter-pound packages. It is a great convenience to get 
 the oxygen of dealers. If this source is not available, this 
 
SUGGESTIONS TO TEACHERS 19 
 
 part of the experiment might be omitted, although the 
 necessary quantity of oxygen could be made in the labora- 
 tory without much trouble. In generating the dioxide, 
 too much dilution of the nitric acid interferes with the 
 reaction. 
 
 Pupils, it is to be expected, will need some help in these 
 first gas manipulations. In the discussion they should be 
 guarded against the error of assuming that the residual 
 gas is the new product formed. It is recommended that 
 they be called upon to pick out illustrations, especially of 
 the fourth and fifth laws, from the data of Number 49, 
 Part I. 
 
 The volume measurements in this experiment are crude, 
 but I have found it useful, as it makes practicable some 
 illustration of volumetric proportions without the more ex- 
 pensive and complicated apparatus that would otherwise 
 be needed. If the Hofmann lecture apparatus is available, 
 it will be especially helpful to show the class experimen- 
 tally the volume ratio between hydrogen, oxygen, and water. 
 
 Number 50/ 3 . Believing that the energy relations of 
 chemical phenomena should not be ignored, even in an ele- 
 mentary course, I have introduced this experiment to illus- 
 trate heat of neutralization. u The oxalic acid is the crys- 
 tallized commercial article. In the conditions of the 
 experiment the rise of temperature is about 5, which gives 
 a neutralization heat of 25,000 cal. This is about the 
 book value. A variation of 0.5 in the reading makes a 
 difference of 2,500 in the final result. 
 
 Number 62/ 2 . Problems solved: 
 
 S = 31.8 = 50$ 
 = 31.8 = 
 
 S0 8 = 
 
 63.6 
 
 100 
 
 Fe = 
 
 55.6 = 
 
 63.6$ 
 
 S = 
 
 31.8 = 
 
 36.4$ 
 
 FeS = 
 
 87.4 = 
 
 100 
 
20 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 Zn 
 
 = 64.9 
 
 = 67.10 
 
 S 
 
 = 31.8 
 
 = 32.90 
 
 
 96.7 
 
 100 
 
 H 2 
 
 = 2. 
 
 = 5.90 
 
 S 
 
 = 31.8 
 
 = 94.10 
 
 
 33.8 
 
 100 
 
 Fe 
 
 = 55.6 
 
 = 44.10 
 
 C1 2 
 
 = 70.4 
 
 = 55.90 
 
 
 126.0 
 
 100 
 
 Fe 
 
 = . 55.6 
 
 = 34.50 
 
 C1 3 
 
 = 105.6 
 
 = 65.50 
 
 
 161.2 
 
 100 
 
 Pb 
 
 = 205.3 
 
 = 74.50 
 
 C1 2 
 
 = 70.4 
 
 = 25.50 
 
 
 275.7 
 
 100 
 
 Cu 
 
 = 63.1 
 
 = 39.80 
 
 S 
 
 = 31.8 
 
 = 20.10 
 
 4 
 
 = 63.6 
 
 = 40.10 
 
 
 158.5 
 
 100 
 
 A1 2 
 
 = 53.8 
 
 = 5.70 
 
 S 4 
 
 = 127.2 
 
 = 13.50 
 
 40 
 
 = 636.0 
 
 = 67.50 
 
 K 2 
 
 = 77.6 
 
 = 8.20 
 
 H48 
 
 = 48. 
 
 = 5.10 
 
 
 942.6 
 
 ioo~ 
 
 C 2 
 
 = 23.8 
 
 = 39.90 
 
 H 4 
 
 = 4. 
 
 = 6.70 
 
 2 
 
 = 31.8 
 
 = 53.40 
 
 
 59.6 
 
 100 
 
 C 2 
 
 = 23.8 
 
 = 92.20 
 
 H 2 
 
 = 2. 
 
 = 7.80 
 
 
 25.8 
 
 100 
 
SUGGESTIONS TO TEACHERS 21 
 
 C 6 = 71.4 = 92.2 
 H fi = 6. = 7.8 
 
 77.4 100 
 
 Number 65/ 6 . Problems solved : 
 
 1. Fe + S = FeS. 
 
 55.6 : 31.8 :: 75 : x = 42.9. 
 
 2. Zn + S = ZnS. 
 64.9 :31.8 : : x : 50. 
 
 x = 102.0. 
 
 3. Zn + 2HC1 = ZnCl 2 + 211. 
 64.9 : 135.3 : : x : 50. 
 
 x = 24.0. 
 
 4. 2XaOH + C0 2 = Na 2 C0 3 + H 2 0. 
 Na = 22.9 C =11.9 
 
 =15.9 8 = 31.8 
 
 H = 1.0 43?T 
 
 39.8 
 (2 X 39.8) : 43.7 : : 50 : x. 
 
 x = 27.45 grams C0 2 . 
 CaC0 3 + 2HC1 = C0 2 + CaCl 2 + H 2 0. 
 Ca = 39.7 C =11.9 
 
 C =11.9 8 = 31.8 
 
 3 =47.7 43?f 
 
 99.3 
 99.3 : 43.7 : : y : 27.45. 
 
 y = 62.4 grams CaC0 3 . 
 
 5. HgI 8 + Hg = 2HgI. 
 Hg = 198.5 
 
 I 8 = 251.8 
 
 450.3 
 450.3 : 198.5 : : 90 : x. 
 
 x = 39.7 grams Hg. 
 
 6. 2NaOH + C0 2 . 
 79.6 :43.7 :: 10 : x. 
 
 x = 5.49 grams C0 2 . 
 
22 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 CO + = C0 2 . 
 
 (11.9 + 15.9) :43.7 ny : 5.49. 
 
 y = 3.49 grams CO. 
 (11.9 + 15.9) : 15.9 :: 3.49 : z. 
 
 z = 1.996 grams 0. 
 
 ?4? = 2.79 + liters of CO. 
 
 = 1.395 liters of 0. 
 1.4o 
 
 2.79 :.1.395 ::2 : 1. 
 (Law of gas-volumetric proportions.) 
 
 7. Mg = 24.1. H = 1. 
 
 2 : 17.9 : : x : 10. 
 
 x 1.117 grams of H. 
 24.1 :2 n y : 1.117. 
 
 y = 13.46 grams Mg. 
 
 8. The first contraction is 12 vols., and in making this, 
 all the hydrogen has been combined ; therefore 
 
 3 : 2 : : 12 : x. 
 
 s= a 
 
 Q 
 
 X 100 = 80$ hydrogen. 
 
 The oxygen, however, is not all combined, since con- 
 traction follows the second addition of hydrogen. If the 
 total residual volume of 3 (RV) had been used and 6 of 
 hydrogen added, the residual would have been in the same 
 ratio as that observed that is, 7.5 vols. The total volume 
 would then have been 10 + 5 + 6, and, the residual being 
 7.5, the contraction would have been 13.5 vols., and in this, 
 all the oxygen is combined ; hence 
 3:1 ::13.5 : y. 
 
 y = 4.5 = 90$ oxygen. 
 
 27S I *>0 
 
 9 - 10 x x = lla34 c ' c ' = voL at 
 
 fare -- am vn '' 
 
 273 50 and 760 mm. 
 
 110.24 X ~ = 116.36 c.c. at 50 and 720 mm. 
 
SUGGESTIONS TO TEA 
 
 =15.9 |^ X 100 = 13.120 H. 
 
 45 ' 7 15.9 
 
 X 100 = 34.8$ 0. 
 
 
 
 
 "'=' 
 
 53.33 _ 3.354 
 
 1ST' 354- 
 
 Hence the coefficients are 1, 2, 1, and the formula is 
 CH 2 0. Pupils will need to be guarded against the error of 
 dropping the fractions in the first set of quotients, and 
 therefore calling the coefficients 3, 6, and 3. 
 
 Number 66. Possibly instructors may find other meth- 
 ods of illustrating Boyle's Law and Charles's Law conven- 
 iently accessible in the equipment of the physical laboratory, 
 and in some circumstances it may be thought unnecessary 
 to study them in detail ; or, to perform the experiments 
 before the class may be deemed sufficient. It is much 
 better, however, if practicable, to give every pupil the 
 chance to perform them for himself. If the apparatus de- 
 scribed in the text for Boyle's Law is used, it should be 
 prepared beforehand by the instructor in such number as 
 may be thought necessary. I use the gasometric tubes 
 therein described, and for jar a 50 c.c. cylinder ungradu- 
 ated. For linear measurement, a foot-rule is cheaply and 
 easily obtained. For economy they may be broken in two 
 and still serve. Pupils will often carelessly lift the tubes 
 too high and let the air out. It is quite a puzzle to them 
 to see how they are put into position. This is done by 
 pouring mercury into the gasometric tube until one half or 
 two thirds full, closing with the thumb, and inverting in a 
 
24 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 sufficiently wide and shallow dish of mercury. From this 
 the tuhe is transferred by dipping a deflagrating spoon 
 under its mouth and carrying it in this position to the 
 cylinder previously filled with mercury. After the tube is 
 in position the cylinder may be partly emptied for economy 
 of mercury. The cost of the latter is the chief objection 
 to this form of apparatus. 
 
 This experiment gives another good opportunity to dis- 
 cuss the limit of accuracy. Inasmuch as the reading of 
 volumes is limited to about 0.1 c.c., and this observed value 
 is multiplied by about 30, a constancy of product within 
 three or four units, or even better, is realized. 
 
 The barometer, if nqt already understood, should be 
 brought before the class and explained so that they may 
 realize how the relative pressures are measured in units of 
 length. 
 
 Number 67. The apparatus for Charles's Law should be 
 prepared beforehand. In Fig. 4 the supporting stand is 
 not shown. I use the ordinary iron stand, clamping the 
 tube A to the upright rod by means of a universal clamp, 
 and supporting the shallow dish of mercury as well as the 
 boiling flask on the iron rings. The tube S is best made 
 of rubber for flexibility. A smaller quantity of water than 
 indicated by the cut is better. The tube A is 12 inches 
 long and 1.5 inches in diameter. It can easily be obtained 
 of dealers. The upper stopper is cork, the lower one of 
 rubber. A foot-rule may be used for linear measurements. 
 The calculation of results I have not given in full, deeming 
 it better to let the pupil try, at least, to reason it out. It 
 involves, besides Boyle's Law, only the application of the 
 simplest arithmetical analysis, but it is surprising how 
 often even bright students stumble in such a matter. The 
 book value of the increment is 0.00367. The experiment 
 realizes 0.0037 0.0001. 
 
 The following results are taken from a student's note 
 book: 
 
SUGGESTIONS TO TEACHERS 25 
 
 Barometer = 30 in. 
 
 Initial length of column = 7 in. 
 
 Final length of column = 5.75 in. 
 Initial pressure =30 7 = 23 in. 
 Final pressure = 30 5.75 = 24.25 in. 
 
 Initial temperature = 18 
 
 Final temperature ,= 100 
 
 Rise in temperature = 82 
 
 Initial volume = 12.5 c.c. 
 
 Final volume = 15.3 c.c. 
 
 12.5 x 23 = 287.5 c.c. = Initial vol. at 1 in. and 18. 
 15.3 x 24.25 = 371.0 c.c. = Final vol. at 1 in. and 100. 
 371.0 287.5 = 83.5 c.c. = Increase of vol for 82. 
 83.5 -4-82 = 1.018 c.c. = Average increase of vol. for 1. 
 1.018 x 18 = 18.32 c.c. = Decrease in vol. for a decrease from 
 
 18 to 0. 
 287.5 18.32 = 269.18 c.c. = Initial vol. at and 1 in. 
 
 1.018 -r- 269.18 = 0.0038 c.c. = Average increase for 1 for unit vol. 
 
 at = coefficient of expansion. 
 
 Number 71/a. The ordinary test-tubes (9 X 1) are used. 
 It is recommended that they and also the rubber stoppers 
 and strips of asbestos board be prepared beforehand and 
 distributed as needed. The loose plug is quite essential to 
 prevent the fine dust being swept out of the tube by the 
 current of gas. A source of error is the loss of moisture in 
 addition to the oxygen. This comes chiefly from the oxide, 
 hence the preliminary ignition. I have found the chlorate 
 usually dry enough to serve. There is advantage in the 
 use of the oxide because of the lower temperature of reac- 
 tion, making unnecessary the employment of hard glass 
 ignition tubes. The directions call for the collection of 
 about two or two and a half liters of gas. Some would 
 prefer a smaller scale in order to economize time. But I 
 deem the larger scale preferable, as in 41/ 3 and 41/ 4 , because 
 the error in weighing has less effect on the final result. 
 
 The book value for the weight of the liter of oxygen is 
 1.43 and for the specific gravity 15.9. The students realize 
 for the latter about 16 0.5. 
 
 Number 81/ lt The pupils should get the plan of this 
 experiment, first and second steps, before beginning. Of 
 late I have been using the commercial precipitated chalk 
 instead of marble dust for the calcium carbonate, and, on 
 
26 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 the whole, I believe, like it better. Wrapping in paper (and 
 perhaps hi addition binding with a rubber band) serves to 
 reduce the danger of loss by spray. Kitric is preferable to 
 hydrochloric acid, because it gives a more soluble salt, all 
 of which remains in solution in the given conditions. The 
 intermediate bottles called for in 81/ 2 are two-gallon pack- 
 ing bottles. They are fitted beforehand with rubber stop- 
 pers and connecting tubes, and are supplied in considerable 
 number, serving from year to year. I have a few pairs of 
 common hand-bellows hung about the room during the 
 progress of this experiment. 
 
 The weight of carbon dioxide in the 5 grams of the car- 
 bonate, assuming the purity of the latter, is 2.20 grams. 
 The tendency is to get too large results. I judge that 75 
 per cent of the determinations will not exceed 2.25 grams, 
 which is as good as can be expected, since five weighings 
 are necessary. 
 
 The measurement of volume is not so close. The vol- 
 ume of the gas at and 760 mm., which weighs (2.20 X 2) 
 4.40 grams, is 2.226 liters. But the average class result is, 
 according to my experience, between 2.0 and 2.1 liters. 
 This brings the specific gravity nearer 24 than 22, which 
 can not be regarded a very satisfactory determination, and 
 yet I find that it serves the purpose of illustration help- 
 fully. 
 
 Numbers 72-92. This law of Gay-Lussac may perhaps 
 be called with propriety the keystone in the system of com- 
 bining weights, and therefore in the system of expressing 
 the quantitative relations of chemical phenomena. To 
 understand it is therefore very important for beginning 
 students. The reader will note that in the text the matter 
 is presented and discussed without using the conception of 
 atoms and molecules. Some teachers may think this too 
 radical a departure from prevailing methods, but my con- 
 viction grows with every year's experience that it is the 
 wiser method. It has been a satisfaction to me to realize 
 
SUGGESTIONS TO TEACHERS 27 
 
 that these fundamental laws may be clearly presented and, 
 may I say, assimilated by the student without once using 
 the words atom and molecule. I have maintained this plan 
 through the text, so that, as I have elsewhere said, Chapter 
 VII, with the whole conception of atoms and molecules, may 
 be omitted, and if I mistake not with no disadvantage to 
 the student. Some teachers, no doubt, will think that this 
 topic is discussed too fully and too early in the course. 
 I can only say that I do not agree with them. As to the 
 latter point it seems to me that the phenomenon and the 
 relation involve no serious difficulty, and that the student 
 can as well appreciate them at this stage as after more 
 extensive acquaintance with chemical substances. And 
 surely the matter is very fundamental. 
 
 Numbers 95/ 2 -95/ 5 . No. 8 shot is suitable. The zinc and 
 the tin are preferred in granular condition. The reading 
 of temperature makes the chief limitation in accuracy, since 
 it must be uncertain to one quarter of a degree at least, 
 and this is a large fraction of the quantity to be measured. 
 For the specific heat of lead I find the class results average 
 about 0.031 and for zinc between 0.1 and 0.09. 
 
 Numbers lll/j-lll/f. It has been a peculiar satisfaction 
 to devise an easily practicable means of illustrating experi- 
 mentally the phenomena involved in Eaoult's Laws. The 
 limitation in thermometric reading, as in the specific heat 
 experiment, prevents a good quantitative result. But when 
 the student can clearly see the cause of inaccuracy the 
 objection to such results is answered. Certainly these 
 experiments greatly help the student in understanding 
 Raoult's laws. The substances, common camphor and 
 paraffin and white crystallized naphthalene, are easily ob- 
 tainable of the dealers. The quantities of solute and sol- 
 vent are so chosen as to give depressions of 2 and 3 for 
 the 8- and 12-per-cent solutions of camphor, and 2 and 4 
 for the 6- and 12-per-cent solutions of naphthalene. These 
 proportions were ascertained by preliminary experiments 
 
28 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 with a thermometer reading to tenths. But even with the 
 finer thermometer and somewhat practiced skill the con- 
 stant obtained for camphor is 38 and for naphthalene 42. 
 Attention is called to the specification that the camphor be 
 dissolved quickly in the liquid paraffin. This lessens the 
 risk of loss by volatilizing. The class results can not do 
 more than give some notion of method and the opportunity 
 to make calculations. The data quoted in Part I, with per- 
 haps some additional, must be relied upon to give an ade- 
 quate idea of the phenomenon. Even the results of the 
 books give wide departures from the generalized law. And 
 it should be impressed upon the student that the approxi- 
 mations to the law in these matters are far different from 
 those of the laws of mass in Chapter II. 
 
 Numbers 127/ 1 -127/ 7 . The remarks in the preceding sec- 
 tion as to thermometric limitation apply here also. The 
 pumice is supplied in small lumps on the side table. The 
 sodium acetate is that designated by dealers as fused, 
 granular, pure. The potassium tartrate (not acid tartrate) 
 is granular or powdered, and pure. The potassium chlo- 
 ride and ammonium chloride are likewise used in granular 
 condition and pure. In 127/ 2 and 127/ 3 the quantities are 
 chosen to give elevations of 2 and 4 respectively; in 127/ 4 
 and 127/5 to give 1 and 2 respectively ; in 127/ 7 to give 2 
 and 4 for potassium chloride and the same for ammonium 
 chloride. These values give the following constants : So- 
 dium acetate, 10.9 ; potassium tartrate, 11.3 ; potassium 
 chloride, 9.6 ; and ammonium chloride, 9.6. It must be ex- 
 pected, however, that there will be a good deal of variation 
 in the class results. 
 
 Number 144. The tin foil should be pure. It is easily 
 obtainable. The white powder which appears as the first 
 product of the reaction with nitric acid is metastannic acid. 
 Its probable composition is 5Sn0 2 5H 2 0. The final product 
 is Sn0 2 . The reaction is sufficiently expressed by the equa- 
 tion ; 3Sn -f- 4HNOs = SSnOg + 4NO -f- 2H 8 0. 
 
SUGGESTIONS TO TEACHEHS 29 
 
 The quantitative result is very satisfactory. The value, 
 1.34 grams for the oxygen with 5 grams of tin, gives 29.6 
 for the equivalent weight and 118.4 for the combining 
 weight ; while the value 1.35 grams for the oxygen gives 
 29 A and 117.6 respectively. The book value for the latter 
 is 118.1. The class results come easily within the limits of 
 1.32 and 1.37, although a variation of 0.03 gram might be 
 allowed for the three weighings which are necessary. It 
 is important that evidence of constant weight should be 
 secured by repeated heating. 
 
 In quizzing it is well to recall the use of nitric acid with 
 hydrogen sulphide, Number 13/ 3 , and with ferrous sulphate, 
 Number 47/b, for the purpose of oxidation as in the tin ex- 
 periment, and to contrast this use with that in which sub- 
 stitution is the primary reaction, Numbers 17/ 3 and 41 / g ; 
 further, to bring out the fact that with lead and zinc, salts 
 are formed, but with tin no salt is formed, by the nitric 
 acid. 
 
 Additional questions like these are suggested : Defini- 
 tion of equivalent weight? of combining weight? What 
 would be the. formula of this oxide of tin, if 29.5 were 
 chosen as the combining weight of tin ? (Sn 2 0.) If 59.0 
 were chosen? (SnO.) If 88.5 were chosen? (Sn 2 3 .) 
 Would the percentage of tin expressed by these several 
 formulas be unchanged ? 
 
 Number 154. The sodium carbonate is designated as 
 dry and chemically pure in the dealers' catalogues. It is 
 first heated gently as a precaution, although probably dry 
 enough without heating. There is need of care that the 
 heating be not excessive, for the larger evaporating dishes 
 are easily cracked and the carbonate, if fused, attacks the 
 porcelain. The quantitative result for carbon dioxide is 
 not very satisfactory, being considerably too large, and that 
 for the sodium oxide too small. The weight of the former 
 should be 2.08 grams, but its determination involves five 
 weighings. The average is likely to be nearer 2.3, and this 
 8 
 
30 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 makes necessarily a large percentage variation. The weight 
 of sodium nitrate should be 8.02 grams and of sodium 
 oxide 2.92 grams. The average result is likely to be about 
 7.75 for the former and 2.82 for the latter. These values 
 reckoned as percentages give 46 for carbon dioxide and 56.4 
 for sodium oxide. The true percentages are 41.5 and 58.5. 
 
 Using the former percentages as basis for the formula 
 gives 46. -=- 44 = 1.05 
 
 56.4 -T- 62 = 0.91 
 whereas the ratio of these quotients should be 1 : 1. 
 
 Nitric acid is preferred in 154/5 because the nitrate is 
 evaporated to dryness a little more easily than the chloride. 
 Hydrochloric acid is specified in 154/a for variety in the 
 product. 
 
 In quizzing it should be made clear that more accurate 
 determinations would show results like these : 
 41.5 4- 43.7 = 0.9497 
 58.5 -r- 61.7 = 0.9481 
 
 Especially should the pupil be guarded against the error 
 of supposing that the coefficients 1 and 1 are chosen be- 
 cause these quotients approximate 1 sufficiently. The 
 choice is because their ratio is 1 : 1 ; and in this the ap- 
 proximation is much closer. Again, let it be made clear 
 that this ratio is a direct consequence of the corollaries of 
 Law 4 (Numbers 42 and 46). As a secondary line of 
 thought it is well to recall the experiments Numbers 34/ 5 , 
 81/j, and 81/ 2 , in which the decomposition of a carbonate 
 was studied from different standpoints. 
 
 Number 156. Solution of problems: 
 
 1. 92.30 -f- 11.9 7.76. 
 
 7.70 -T- 1 =7.70. Eatio 1 : 1 ; but (38 X 2) -r- 12.9 
 = 5.8 ; hence the multiple by six is chosen, C 6 H 6 . 
 
 2. 40. ^- 11.9 = 3.36. Eatio, 1:2:1. 
 
 6.67 -4- 1 = 6.67. CH 2 = 29.8. 
 53.33 -r- 15.9 = 3.35. (29 X 2) -r- 29.8 = 2 ; hence 
 
 formula is C 2 H 4 2 . 
 
SUGGESTIONS TO TEACHERS 31 
 
 3. 78.86 ^ 11.9 = 6.63. 
 
 10.60 -i- 1 = 10.60. Ratio, 10 : 16.01 : 1 ; hence 
 10.53 ^- 15.9 = 0.662. C 10 H 16 0. 
 
 4. 1.913 X r^ 7 = 0.520 grams carbon = 52.0$. 
 
 1.173 X JL = 0.131 grams hydrogen = 13.1$. 
 i/.y 
 
 1 _ (0.520 + 0.131) = 0.349 grams oxygen = 34.9$. 
 Formula is C 2 H 6 = combining weight 45.7. 
 
 5. 10.7 X 14.4 X 2 = 308 = approximate combining 
 
 weight of the chloride. 
 6.2 ^ 0.114 = 54 = approximate combining weight 
 
 of iron. 
 
 65.76 : 34.24 : : 35.2 : x 18.33 = exact equivalent 
 
 weight of iron. 
 
 18.33 X 3 = 55.99 = exact combining weight of iron. 
 65.76 -v- 35.2 = 1.87. 
 
 34.24 -T- 55.99 = 0.61. Ratio is 1 : 3 ; hence the sim- 
 plest formula is FeCl 3 , with the combining weight 
 161.59, but the chosen formula is Fe 2 Cl 6 , with com- 
 bining weight 323.2. 
 
 6. (35.2 X 100) -r- 53.1 = 66.29$. 
 
 7. (125.9 X 100) -5- 324.4 = 38.81$. 
 (125.9 X 2 X 100) -f- 450.3 = 55.91$. 
 
 8. 0.36 : 1 : : 10 : x = 27.8 = equivalent weight of iron 
 
 (in FeClg). 
 
 9. 121.7 : 47.7 : : 10 : x = 3.92 grams. 
 10. (43.7 X 100) -5- 99.3 = 44.0$. 
 
 Numbers 188-199. It should not be expected that stu- 
 dents will hold in mind much of these introductory para- 
 graphs. They will, however, gain useful impressions from 
 reading them, and it might be well to return to them as a 
 kind of review after the descriptions have been finished. 
 
 Number 202 (1). It is recommended that the experi- 
 ment indicated in Fig. 2 be exhibited to the class if the 
 apparatus is at hand. In the preparation of the hydrogen 
 
32 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 by the class, hydrochloric acid is the more convenient. If 
 sulphuric is used, the dilute (1 of acid to 4 of water) should 
 be supplied on the side table. For the metal I use nails. 
 
 Number 203/i. The tubes should be prepared before- 
 hand and supplied only for use in this experiment. They 
 serve from year to year. Convenient dimensions are 9 X f 
 inches. The plugs are about | inch thick. The phenome- 
 non is due to the fact that hydrogen and coal gas diffuse 
 through the porous partition more rapidly than air does. 
 
 Numbers 203/ 2 and 205, These make good experiments 
 for the lecture room. The platinum sponge is made by 
 dipping asbestos fiber in a solution of platinum chloride, 
 then drying and igniting it in the gas flame. It will serve 
 through many repetitions. It is best always to wrap a 
 towel about the generator. The phenomenon may be 
 shown also with coal gas thus : Hold the sponge in the 
 flame of a Bunsen burner, extinguish the flame, and let the 
 gas stream upon the sponge. The latter glows, and some- 
 times the flame is relighted. 
 
 Number 208. The hydrogen from common iron is so 
 impure that the gas from the generator decolorizes the 
 permanganate. 
 
 Number 210. It is recommended that lithium chloride 
 be exhibited and the color in the Bunsen flame be shown 
 from the lecture table. 
 
 Number 228/ 2 . Manganese in the oxidizing flame is vio- 
 let or amethyst, in the reducing flame it is colorless, but 
 persistent heating is necessary to remove the color. 
 
 Number 255/ 1 . An aniline dyestuff may be used in place 
 of the permanganate. The latter probably loses its color 
 in part by reduction. 
 
 Number 257/ 2 . The charcoal especially prepared for 
 blowpipe work is much preferable to the common article. 
 
 Number 237. It is interesting to exhibit glass models 
 of famous diamonds. These can be obtained of dealers, 
 although rather expensive. The catalogue price for a col- 
 
SUGGESTIONS TO TEACHERS 33 
 
 lection of twenty-one of the largest and most famous is 
 twenty-five dollars. 
 
 Number 243. Samples of graphite for exhibition can be 
 easily obtained. 
 
 Number 276. Use the same sodium acetate as directed 
 in Number 127/ 2 . This small scale of preparation is suffi- 
 cient. 
 
 Number 280. The calcium carbide is easily obtainable. 
 It should be supplied on the side table in only small quan- 
 tities, and the main supply should be carefully protected 
 from moisture. 
 
 Number 281. The mixing of acetylene in the test-tube 
 with varying quantities of air shows well the varying nature 
 of the combustion. With acetylene alone the flame is very 
 smoky and the action quiet, but with the suitable quantity 
 of air there is a flash of bright light and a sharp report. By 
 calculation the maximum effect should be when 2 volumes 
 of acetylene are mixed with 25 volumes of air, and the ex- 
 periment shows this fairly well. It is best not to ignite at 
 the generator. 
 
 Number 287. Pieces of wire gauze 5 or 6 inches square 
 are supplied at the side table only for this experiment. 
 
 Number 294. It is interesting to show samples of crude 
 petroleum and the commercial products obtained from it. 
 
 Number 308. There can not be too much caution in 
 using phosphorus. It is best that the instructor should 
 keep the supply at his own desk, himself cut suitable 
 pieces one quarter the size of a pea is more than enough 
 and give to each pupil, when he is ready to use it, only one 
 small portion at a time. 
 
 Number 312. A flask holding about 250 c.c. is recom- 
 mended "round, flat-bottom, 8 oz." in the dealers' cata- 
 logues. The ammonium nitrate is most convenient in the 
 crystallized granular form. 
 
 Number 354. An interesting experiment for the lec- 
 ture table to show reversed combustion is made as follows : 
 
34 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 An Argand chimney is suitably supported by a universal 
 clamp. The lower end of the chimney is fitted with a cork. 
 A disk of asbestos board with a hole in the middle covers 
 the upper end. Through the cork are passed two glass 
 tubes, one to remain fixed, the other to slide somewhat 
 easily up and down. By the first tube illuminating gas is 
 led to the interior of the chimney. The second tube is 
 attached to a piece of rubber hose. Fill the chimney with 
 gas and ignite the latter at the hole in the asbestos board, 
 so regulating that there is a small flame. Push up the 
 sliding tube until its open end is about one half inch from 
 the flame. Blow gently through this tube, and the stream 
 of air from the lungs ignites at the gas flame. Then gently 
 draw down the air tube, and the flame follows with it and 
 shows the air burning at the end of the tube. Call atten- 
 tion to the difference between the two flames. The air 
 flame is almost non-luminous, as there is no separation of 
 solid carbon. 
 
 Number 361. An experiment for the lecture table to 
 show the formation of ozone : A small bottle or beaker 
 covered with a glass plate ; into this is placed a piece of 
 phosphorus, a stick one or one and a half inches long, with 
 freshly cleaned surface ; also a little water, not enough of 
 course to cover the phosphorus. A strip of starch paper is 
 hung in the bottle over the phosphorus. The starch 
 paper is made by dipping filter paper into a fresh thin 
 starch paste to which a little solution of potassium iodide 
 has been added. It should be used in moist condition. 
 After an exposure of fifteen or twenty minutes the paper 
 shows the blue color. The ozone formed -by the oxidation 
 of the moist phosphorus liberates iodine, which gives the 
 blue color with the starch. 
 
 Number 366. A solution of hydrogen dioxide can be 
 obtained of the chemical dealers and usually of the retail 
 pharmacist. 
 
 A simple experiment is to show its decolorizing effect 
 
SUGGESTIONS TO TEACHERS 35 
 
 on permanganate acidulated with sulphuric acid ; also the 
 characteristic test by adding a few drops of the dioxide to 
 a very dilute solution of potassium dichromate acidulated 
 with sulphuric acid and shaking the mixture with a little 
 ether. The latter rises to the surface and shows a fine blue 
 color which is due to reaction between the dioxide and 
 chromic acid. 
 
 Numbers 371-377/ 5 . It is recommended that some of 
 the simple tests for impurities in water be exhibited on 
 the lecture table. For hardness, add soap dissolved in 
 water or alcohol, first to distilled water, then to distilled 
 water to which a little calcium or barium chloride has been 
 added, then to some sample of natural water. For chloride, 
 add a few drops of silver nitrate and of nitric acid first to 
 distilled water, then to water to which a few drops of salt 
 solution have been added, then to some sample of natural 
 water, then to a sample of water polluted with sewage. For 
 ammonia, test samples as in the preceding by adding potas- 
 sium mercuric iodide. For nitrite, a very sensitive test is 
 made by adding a solution of sulphanilic acid and of 
 naphthylamine chloride, if these reagents are at hand. Also, 
 by acidulating with sulphuric acid and adding potassium 
 permanganate, drop by drop, may be shown the test for 
 " oxygen consumed." These are the tests actually used in 
 the quantitative examination of water. 
 
 Number 378. It may be practicable to show some forms 
 of domestic filters and perhaps also of stills. 
 
 Number 406. Paraffin, powdered fluorspar, and sul- 
 phuric acid are supplied on the side table. The acid must 
 be concentrated, but the commercial grade serves the pur- 
 pose. The lead dishes also are supplied on the side table 
 for only this experiment. 
 
 Number 410. The sodium is best kept at the instruct- 
 or's table and by him given to each student as needed. 
 
 Number 420/j. It is deemed best in this first study of 
 reactions between salts in solution that each student should 
 
36 THE ELEMENTARY PRINCIPLES OP CHEMISTRY 
 
 prepare the several solutions from the solids supplied on 
 the side table. After he has some experience, it may be 
 expedient to supply the solutions previously prepared. 
 
 Number 420/ 3 . Equations completed : 
 2NaOH + CuS0 4 = Cu0 2 H 2 
 
 6NaOH + A1 2 (S0 4 ) 3 = A1 2 6 H 6 + 3Na 2 S0 4 . 
 NaOH +NH 4 N0 3 = XH 4 OH + NaNO s . 
 
 Number 441/ 1( Problems solved : 
 
 1. 22.9 : 1 : : 10 : x = 0.437 gram. 
 0.437 -T- 0.0899 = 4.86 liters. 
 
 2. 11.9 : 43.7 : : 10 : x = 36.72 grams. 
 
 36.72 -5- 1.98 = 18.55 liters of C0 2 and 18.55 liters of 0. 
 
 3. Vap. density = 7.95. 3 liters. 3.575 grams. 
 
 4. 1 liter of C0 2 and 1 liter of H. 
 
 5. Yap. density = 8.45, 1 liter NH 3 = 0.76 gram. 
 16.9 : 53.1 : : 0.76 : x = 2.39 grams XH 4 C1. 
 
 6. The ratio of combining weights 16.9 : 39.8. 
 
 7. 105.4 : (84.5 X 2) : : x : 10. 
 
 x = 6.237 grams Na 2 C0 3 . 
 (58.1 X 2) : 105.4 :: 10 : x = 9.07 grams Na 2 C0 3 . 
 
 8. 11.9 : 105.4 : : 1 : x = 8.857 grams Xa 2 C0 3 . 
 
 9. 11.9 : (40 X 2) : : 1 : x = 6.72 grams MgO. 
 
 10. Acetylene. C 2 H 2 + 50 = 2C0 2 + H 2 0. 
 
 CH 4 + 40 = C0 2 + 2H 2 0. 
 Combustion heat of acetylene (97000 X 2) -f- 
 
 68400 + 47600 = 310000 cal. 
 Combustion heat of methane = 97000 -f- (68400 X 2) 
 
 - 21800 = 212000 cal. 
 
 Equal volumes of the two gases therefore generate 
 heat in the ratio of 310 : 212. 
 
 11. CaC 2 + H 2 = C 2 H 2 + CaO. 
 63.5 : 25.8 :: l.ix. 
 
 x = 0.406 Ib. = 6.496 oz. = (6.496 -5- 1.17) cu. ft. = 
 
 5.55 cu. ft. of acetylene from 1 Ib. of CaC 2 . 
 1000 : x : : 310 : 212. 
 
SUGGESTIONS TO>^MCHl$g // 37 
 
 ^^[LlFOH^Jx^ 
 
 x = 684. . . 1000 cu. ft. of metBaioe"^684 cu. ft, 
 
 of acetylene in heating effect. 
 684 cu. ft. obtained from (684 -^ 5.55 =) 123.2 Ibs. 
 
 of CaC 2 . 
 50 -=- 123.2 = 0.406 cent per Ib. 
 
 Number 446/j. Ammonium hydroxide is always on the 
 side table. Ammonium chloride and carbonate and sodium 
 carbonate and phosphate may suitably be supplied in solu- 
 tion. 
 
 Equations completed : 
 
 Mg -f = MgO. 
 
 Mg + 2H 2 = MgOgH, + 2H. 
 
 Mg + 2HC1 = MgCl 2 + 2H. 
 
 Mg + H 2 S0 4 = MgS0 4 + 2H. 
 
 MgS0 4 + 2NaOH = Mg0 2 H 2 + NagSO* 
 
 MgS0 4 + Na 2 C0 3 = MgCQ 3 -f Na 2 S0 4 . 
 
 MgS0 4 + Na 2 HP0 4 = MgHP0 4 + Ka 2 S0 4 . 
 
 Number 451, The aluminium is most conveniently sup- 
 plied in the form of thin sheet or of wire. Equations for 
 aluminium : 
 
 A1 2 (S0 4 ) 3 + 6N"aOH = A1 2 6 H 6 -f 3Na 2 S0 4 . 
 A1 2 6 H 6 + 2NaOH = JS T a 2 -A1 2 3 + 4H 2 0. 
 A1 2 (S0 4 ) 3 + 6NH 4 OH = A1 2 6 H 6 + 3(NH 4 ) 2 S0 4 . 
 A1 2 (S0 4 ) 3 + 3Na 2 C0 3 + 3H 2 = AlAH 6 +3Na 2 S0 4 +3C0 2 . 
 A1 2 (S0 4 ) 3 + 3^ r a 2 HP0 4 = A1 2 (P0 4 ) 2 + 3Na 2 S0 4 + H 3 P0 4 . 
 
 Number 467. It is well to exhibit whatever is obtain- 
 able of the natural forms of silica and the silicates, also 
 a sample of alkaline silicate, the so-called soluble glass. 
 
 Number 474. To succeed in this experiment there must 
 be used a liberal proportion of the carbonate, and the heat- 
 ing must be persistent. The especially prepared charcoal 
 is preferable, as in other blowpipe experiments. 
 
 Number 485. Exhibit, if possible, samples of apatite or 
 other natural phosphate and of glacial phosphoric acid, 
 also of the phosphorus chlorides. 
 
38 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 Numbers 486 and 487. It is best that the instructor 
 himself give the small piece of phosphorus to each student 
 as it is called for. Some additional illustrations may be 
 made on the lecture table ; for example, a small fragment 
 of phosphorus covered with powdered charcoal or bone 
 black takes fire in a few minutes. If a small fragment is 
 dissolved in carbon disulphide and the solution is absorbed 
 by filter paper, the phosphorus on the latter takes fire by 
 brief exposure to the air. When brought in contact with 
 iodine, phosphorus inflames. 
 
 Number 507. It is perhaps well to exhibit samples of 
 roll sulphur, sulphur flowers, and precipitated sulphur, also 
 the crystallized form, on. the lecture table, although they 
 have been in frequent use. More important is it to show 
 some natural substances e. g., native sulphur, pyrites, and 
 gypsum. 
 
 Number 512. Equations completed: 
 (NH 4 ) 2 S + 2HC1 = H 2 S + 2NH 4 C1. 
 (NH 4 ) 2 S 8 + 2HC1 = S + H 2 S + 2NH 4 C1. 
 + NaXO 3 = 0. 
 + MgS0 4 = 0. 
 
 S + A1 8 (S0 4 ) S + 6H 2 = A1 2 6 H 6 + 3(NH 4 ) 8 S0 4 + 
 
 3H 2 S. 
 
 + FeS0 4 = FeS + (NH 4 ) 2 S0 4 . 
 (:\ T H 4 ) 2 S + CuS0 4 = CuS + (NH 4 ) 2 S0 4 . 
 
 Number 515. The sodium sulphite is of commercial 
 grade, and the dried and powdered condition is preferred, 
 although the crystallized probably would serve nearly as 
 well. 
 
 Number 517/ lt Equations completed: 
 S + 20 = S0 2 . 
 S0 2 + H 2 = H 2 S0 3 . 
 H 2 S0 3 + 2NaOH = Na 8 S0 8 + 2H 2 0. 
 Na 2 S0 3 + 2HC1 = S0 2 + H 2 
 S0 2 + = S0 3 . 
 
SUGGESTIONS TO TEACHERS 39 
 
 H 2 S0 3 + = H 2 S0 4 . 
 Na 2 S0 3 + = JS T a 2 S0 4 . 
 H 2 + 21 = 
 K 2 OMn 2 7 
 
 Number 52 1/ 2 . Equations completed : 
 S0 3 + H 2 = H 2 S0 4 . 
 H 2 S0 4 + NaOH = Na 2 S0 4 + 2H 2 0. 
 H 2 S0 4 + NaOH = NaHS0 4 + H 2 0. 
 Na 2 S0 4 + 20 = A T a 2 S + 2C0 2 . 
 H 2 S0 4 + Ba01 2 = BaS0 4 + 2HC1. 
 Na 8 S0 4 + SrCl 2 = SrS0 4 + fcNaCl. 
 JX T a 2 S0 4 + Pb(A) 2 = PbS0 4 + 2Na(A). 
 
 Number 531. To supplement the student's observations 
 it is recommended that the properties of chlorine be fur- 
 ther exhibited by experiments at the lecture table. The 
 following are suggested : Collect chlorine in four or five 
 glass jars, having one of extra depth. Exhibit with these 
 a bottle of bromine and of iodine to contrast the colors. 
 Into one jar, lower the lighted taper ; into another, drop a 
 piece of filter paper which has been dipped in turpentine ; 
 the latter should be heated nearly to boiling immediately 
 before the paper is immersed in it, in order that it shall 
 burst into flame when dropped in the chlorine. Sometimes 
 the paper only chars. In the third jar, show the bleaching 
 effect on some colored stuff e. g., some brightly colored 
 flower. Into the fourth jar, lower a piece of phosphorus 
 ignited in the deflagrating spoon. Into the fifth jar, the 
 deep one, shake some very finely pulverized antimony, pre- 
 viously somewhat heated on the spatula blade. In each 
 case the fumes are so irritating that the jars should be im- 
 mediately placed in the hood or otherwise disposed of. 
 
 Numbers 537 and 540. To show from the lecture table 
 some of the properties of the chlorine oxides : 
 
 1. Pulverize separately a little potassium chlorate and a 
 little white sugar. On a sheet of paper thoroughly mix 
 
40 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 about equal bulks of the powders. Place in an earthen dish 
 or suitable substitute a small quantity of the mixture, about 
 what could be heaped on a copper cent. Let a drop of 
 concentrated sulphuric acid fall upon this from a rod or 
 small pipette. The mixture bursts into flame. 
 
 2. Place in a mortar a small quantity of potassium chlo- 
 rate, hardly more than a pin-head in size, and shake on this 
 a little sulphur powder. Eub with the pestle under some 
 pressure, and the mixture explodes with considerable noise. 
 
 3. Wrap in tin foil a fragment of dry phosphorus, about 
 the size of a pin-head, and potassium chlorate in about 
 equal quantity. Place the package on a brick and explode 
 it by a sharp blow with a hammer. 
 
 4. Place some crystals of potassium chlorate in a pre- 
 cipitating glass or a small cylinder. Pour water on this to 
 some considerable depth. Drop into this several small 
 pieces of phosphorus ; then by means of a pipette let flow 
 upon the surface of the chlorate some concentrated sul- 
 phuric acid, a little at a time. The phosphorus burns with 
 flashes of light under the water. 
 
 Number 534/j, Equations completed : 
 
 NaCl + H 2 S0 4 = HC1 + NaHS0 4 . 
 
 2HC1 + Pb(C 2 H 3 2 ) 2 = PbCl 2 + 2HC 2 H 3 2 . 
 
 HOI + AgN0 3 = AgCl +HN 8 . 
 
 HC1 + HgN0 3 = HgCl + HN0 3 . 
 
 HOI + MgS0 4 = 0. 
 
 Number 567. It is easy to give some idea of the possible 
 explosion of dust in air by the following experiment for the 
 lecture table : A plain wood box, 6 X 6 X 12 inches, is pro- 
 vided. One of the long sides is open, but can be covered 
 by a piece of window glass. The box is placed on end and 
 a lighted taper supported by a flat cork is put inside, also 
 about a teaspoonful of flour or starch. The nozzle of a 
 pair of bellows is inserted through a hole in the side of the 
 box and the glass cover is put over the open side, which is 
 turned toward the class. A puff of air from the bellows 
 
SUGGESTIONS TO TEACHERS 41 
 
 raises a cloud of dust which is inflamed by the taper. A 
 flash of flame is seen, and often the glass lid is thrown off. 
 It is interesting to exhibit samples of black and of 
 smokeless gunpowders and of gun cotton, which are easily 
 obtainable. 
 
 Number 584. Equations completed: 
 CaO + H 2 = Ca0 2 H 2 . 
 Ca0 2 H 2 + C0 2 = CaC0 3 + H 2 0. 
 Ca0 2 H 2 + 2HC1 = CaCl 2 + 2H 2 0. 
 CaCl 2 + (NH 4 ) 2 C0 3 = CaCOg + 2NH 4 C1. 
 CaCl 2 + (NH 4 ) 8 C 8 4 = CaC 2 Q 4 + 2NH 4 C1. 
 Ca01 8 + Na 2 HP0 4 = CaHP0 4 
 CaCl 2 + Xa 2 S0 4 = CaS0 4 
 
 Number 5 88/i. Problems solved: 
 
 1. Mg : 21 : MgI 2 . 
 
 24.1 : (125.9 X 2) : 275.9. 
 
 2. Dissolve in dilute HC1, evaporate most of the excess 
 of acid, neutralize the rest with NH 4 OH, precipitate with 
 solution of Na 2 HP0 4 , filter, wash, ignite, and weigh the 
 precipitate. 
 
 3. Mg to Mg 2 P 2 7 . 
 
 (24.1 X 2) : 221.1 ::!:& = 4.587 grams. 
 
 4. Dissolve directly in water and proceed as before. 
 Mg to MgS0 4 . 
 
 24.1 : 119.5 ::l:x = 4.959 grams MgS0 4 . 
 
 5. NO. Dissolve in dilute HC1, precipitate with 
 NH 4 OH, filter, wash, ignite, and weigh the precipitate. 
 Al z to A1 2 3 (26.9 X 2) : 101.5 ::!:&= 1.887 grams A1 2 3 . 
 
 6. 24.1 : (26.9 X f). Same for oxygen. 
 
 7. 2NaOH to 21. 
 
 (39.8 X 2) : (125.9 X 2) : : 39.8 : x = 125.9 grams I. 
 
 8. NagS0 4 -10H 2 [to] BaCl 2 '2H 2 0. 
 
 320.2 : 242.6 : : 1 :x = 0.758 gram barium chloride. 
 
 9. NaCl to AgN0 3 . 
 
 58.1 : 168.7 ::!: = 2.90 grams AgN0 3 . 
 
42 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 10. 6C1 to 2HN0 3 . 
 
 211.2 : (62.6 X 2 =) 125.2. 
 
 11. NaN0 3 ; in ratio of combining weights i. e., 
 84.5:100.4, or 1 : 1.19. 
 
 12. MgO ; 40 : 55.6, or 1 : 1.39. 
 
 Number 601. Equations completed: 
 Fe + 2HC1 = FeCl 2 + 2R. 
 Fe + H 2 S0 4 = FeS0 4 + 2H. 
 
 6FeS0 4 +8HN0 3 = 2Fe 2 (S0 4 ) 3 +2NO + Fe 2 (N0 3 ) 6 + 4H 2 0. 
 FeCl 2 + 2NH 4 OH = Fe0 2 H 2 + 2NH 4 C1. 
 FeCl 2 + 2NH 4 HS = FeS + 2NH 4 C1 + H 2 S. 
 2FeCl 3 + 6NH 4 HS = SFeS + 6NH 4 C1 + 3H 2 S + S. 
 FeCl 3 + 3NH 4 OH = FeQ 3 H^ + 3NH 4 C1. 
 
 GENERAL EQUIPMENT 
 
 Lighting, ventilation, gas and water supply, and drainage are mat- 
 ters of first importance in the chemical laboratory; but to treat of 
 them is beyond the scope of this writing. 
 
 There is one item, however, in the furnishings which I am tempted 
 to urge because of its assistance in the work of instruction and over- 
 sight : this is an elevated platform, carrying, if possible, a small demon- 
 stration table, from which the instructor may see fairly well what is 
 going on at each table, and from which he may give explanations and 
 directions. This is extremely useful, especially when large sections 
 must be handled with little help. It would be useless to suggest 
 dimensions for the platform, since they must depend on the size and 
 shape of the room and other unknown conditions. 
 
 The items of apparatus and material called for in the text have 
 been already specified in the foregoing paragraphs, but for conven- 
 ience they are here summarized. Prices when given are taken from 
 American dealers' catalogues. 
 
 Balances. The balance of the type A, Fig. 5, in the Appendix, is 
 designated in the dealer's catalogue (Fairbanks's) as the Harvard Trip 
 Scale. The side beam which carries the sliding rider gives readings from 
 5 grams to 0.1 of a gram. Additional weights are of course necessary. 
 The catalogue price without weights is $7.50. This balance is called 
 for only three or four times in the course, and if economy is urgent 
 could be omitted from the equipment without serious interference. 
 The other balance is indispensable, and must weigh satisfactorily to 
 
SUGGESTIONS TO TEACHERS 43 
 
 0.01 of a gram. Of the type B, Fig. 6, Appendix, the cheapest I have 
 found now in the market, which is as good as I desire for my own 
 equipment, is designated (Fairbanks's catalogue) as the Jeweler's and 
 Broker's Scale ; pans 3 inches, beam 7 inches, length of box 12 inches ; 
 price without weights $8.50, and without pans $7.85. 1 prefer to sub- 
 stitute glass crystals for the metallic pans. These are marked in some 
 way (e. g., a gummed paper label) for identification and counterpoised 
 with wire or foil, and thus serve as well as the especially prepared 
 glass pans, which are much more expensive. 
 
 The balance of the type C, Fig. 7, Appendix, is very convenient, and 
 has the great advantage that the weights are attached. The one figured 
 is known as the Chaslin, and its cost is $15, which of course includes 
 weights. The hand scales with horn pans are recommended by some ; 
 they are much cheaper, but I have no experience in their use. 
 
 Thermometers, chemical, graduated up to 150 C., price $1.60 ; or a 
 cheaper grade with inclosed paper scale up to 150 C., for $1.10. 
 
 A barometer. 
 
 Distilling flasks, capacity about 200 c.c. (6 oz.), with rubber stop- 
 pers to fit, for Exps. 24 and 127. 
 
 Combustion apparatus, for Exp. 34/ 2 or 34/ 4 . 
 
 Graduated flasks, for Exp. 41/ 3 (a). See also Number 41/ 3 of this 
 pamphlet. 
 
 Apparatus for Boyle's Law, Number 66. 
 
 Apparatus for Charles's Law, Number 67. 
 
 Test-tubes, 8 or 9 inches x 1, with rubber stoppers (one hole) to fit, 
 and asbestos plug, for Exp. 71/A. 
 
 Intermediate bottles, 2 gal., acid packing bottles, fitted with rubber 
 stoppers and connecting tubes, for Exp. 81/ 2 . See Number 81/i, this 
 pamphlet. 
 
 Bellows, see Number 81/i, this pamphlet. 
 
 Diffusion tubes, glass tubes, 9 x f inches, with porous plug, for 
 Exp. 203/j. 
 
 Porous jar, for Exp. 203/ 2 . 
 
 Platinum sponge, for Exp. 205, see Number 203 X 2 of this pamphlet. 
 
 Wire gauze, in pieces about 6x6 inches, for Exps. 287-289. 
 
 Lead dishes, about 2 inches in diameter and f inch deep, for Exp. 
 406. 
 
 Files, three-edged, also round. 
 
 Cork-borers. 
 
 Gummed paper slips. 
 
 Rubber bands, No. 8. See Number 47/a. 
 
 Corks to fit smaller test-tubes. 
 
 Corks to fit flasks, Exp. 312. 
 
THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 SIDE-TABLE MATERIAL 
 
 Sulphur, roll, Exps. 1-13. 
 
 Sulphur flowers (sublimate), Exps. 12/,, 12/ a , 18/i, 13/ a , 18/B. 
 
 (Carbon disulphide, Exp. 12/ a ). 
 
 Zinc dust, Exps. 13/ a , 15/ 3 . 
 
 Iron dust (by alcohol), Exp. 13/ 2 . 
 
 Lead dust, or lead granulated, No. 100, commercial, Exps. 15/,, 15/, 
 and 17/3. 
 
 Zinc, granulated, c. p., No. 20, Exps. 17/i, 17/ 3 , 17/ 4 , 18/A, 41/ 2 , 41/ 4 , 
 95/4, and others. 
 
 Magnesium ribbon, Exps. 15/ 3 , 41/ l5 41/b, 41/ 3 , 263, 445, 446. 
 
 Iodine, resublimed, Exps. i5/j, 18/A, 20/,, 40/a, 41/b, and some 
 others. 
 
 Lead nitrate, crys. commercial, Exps. 16/i, 18/A(c), 18/C(e). 
 
 Zinc nitrate, crys., Exp. 16/ 2 '. 
 
 Copper sulphate, crys. commercial, Exps. 17/ 4 , 21/ 4 , 21/ 7 , 24/>. 
 
 Lime, Exp. 18/B, and others. 
 
 Alum, potassic, crys. commercial, Exps. 21/4, 21/ 7 , and others. 
 
 (Potassium bichromate, crys.); see Exp. 21/ 7 . 
 
 (Potassium nitrate, crys. pure) ; see Exp. 21/ 7 . 
 
 Sodium carbonate, crys., or sodium phosphate, crys., c. p., Exps. 21/ 8 , 
 and 496. 
 
 Sodium hydroxide (caustic), pure, sticks. 
 
 Sodium chloride, commercial, Exps. 22 and 24/ 8 . 
 
 Paraffin, white, hardest. 
 
 Mercury, Exps. 40/a and 40/b. 
 
 Mercuric sulphocyanate for Exp. 34/i. 
 
 Marble chips. 
 
 Iron sulphate, crude (copperas). 
 
 (Oxygen, Exp. 47/ a .) 
 
 Oxalic acid, crys. commercial, Exp. 50/ 3 . 
 
 Potassium chlorate, crys. or powd. commercial. 
 
 Manganese dioxide, powd. commercial. 
 
 Calcium carbonate, precipitated, commercial. 
 
 Shot, No. 8, for Exp. 95 A. 
 
 (Tin, granulated commercial), Exp. 95/ 5 . 
 
 Camphor, refined, Exps. lll/i and lll/ a . 
 
 Naphthalene, white crys., Exps. lll/ 8 and lll/ 4 . 
 
 Pumice in small pieces. 
 
 Sodium acetate, pure, fused, powd., Exps. 127/ a and 127/s. 
 
 Potassium tartrate, pure, powd., Exps. 127/ 4 and 127/j. 
 
SUGGESTIONS TO TEACHEKS 45 
 
 (Potassium chloride, c. p.), Exp. 127/ 7 . 
 (Ammonium chloride, c. p. crys.), Exp. 127/7. 
 Tin foil, pure, Exp. 144. 
 Sodium carbonate, c. p., dry, powd. 
 Litmus paper. 
 
 For the Descriptive Work of Chapter VIII. Nails ; borax, powd. ; 
 copper oxide, black, powd.; sugar; wood shavings; soft coal; char- 
 coal ; bone black ; iron sulphide ; lead oxide (litharge) ; calcium carbide ; 
 phosphorus, yellow ; phosphorus, red ; ammonium nitrate, gran, com- 
 mercial ; sodium nitrate, crys. commercial ; pieces of flannel or other 
 woolen stuff ; calcium fluoride, powd. (fluorspar) ; sodium, metallic ; 
 magnesium sulphate, crys. c. p. ; aluminium, sheet or wire ; sand ; sodium 
 sulphite, dried powd. ; sodium sulphate, dried commercial ; potassium 
 hydroxide (caustic), sticks, pure. 
 
 Solutions. Hydrochloric acid, commercial (muriatic) cone., 20 B, 
 or sp. gr. 1.16. 
 
 Nitric acid, commercial cone., 40 B, or sp. gr. 1.38. 
 
 Sulphuric acid, commercial dilute, 1 of cone, to 4 of water. 
 
 Sulphuric acid, cone, commercial. 
 
 Ammonium hydroxide, commercial, 16 B, FFF, sp. gr. 0.96. 
 
 Hydrochloric acid, c. p., dilute, 1 of cone, to 1 of water. For 
 Exp. 37. 
 
 Lead acetate, c. p., 1 of salt to 20 of water. 
 
 Alcohol. 
 
 Potassium permanganate, dilute. 
 
 Lime-water. 
 
 Ammonium chloride, c. p., 1 to 10. 
 
 Ammonium carbonate, c. p., 1 to 10. 
 
 Ammonium oxalate, c. p., 1 to 25. 
 
 Ammonium sulphide (yellow), 1 to 1. 
 
 Sodium phosphate, c. p., 1 to 20. 
 
 Silver nitrate, 1 to 40. 
 
 Barium chloride, c. p., 1 to 20. 
 
 Strontium chloride, c. p., 1 to 20. - 
 
 Mercurous nitrate, 1 to 30. 
 
 INDIVIDUAL EQUIPMENT 
 Iron stand, 3 rings. 
 Funnel support, wood bar. 
 Tongs, brass. 
 Burner and hose, 2. 
 Test-tube stand. 
 4 
 
46 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 Test-tubes, 10. 
 
 Evaporating dish, about 4 inches diameter. 
 
 Evaporating dish, Royal Berlin, 3 inches diameter, 2. 
 
 Crucible and lid, Royal Berlin, No. 1. 
 
 Beakers, 2. 
 
 Rods, 3. 
 
 Funnels, 2. 
 
 Test-tube brush. 
 
 Sponge. 
 
 Towel. 
 
 Asbestos board, 6 inches square. 
 
 Filter paper, common, 6 inches diameter. 
 
 Water-bath. A sauce-pan of granite or similar ware, about 5 inches 
 diameter and 2 deep, with two zinc covers, makes a cheap and service- 
 able water-bath. 
 
 Pneumatic trough. One of zinc, 5 x 11 x 15 inches, is recommended. 
 
 Spatula. A cheap kitchen knife can be obtained of hardware dealers, 
 which serves well and is much less expensive than the spatula of chem- 
 ical dealers. 
 
 Saucer, or shallow dish, of granite or earthenware, 4 or 5 inches 
 diameter e. g., the saucers made to sell with flower pots. 
 
 Gas 'generator, a suitable bottle e. g., a 5-oz. " quinine," fitted with 
 rubber stopper (2 holes). 
 
 Thistle-tube. 
 
 Rubber hose, 1 ft., pure gum, f in. diam. 
 
 Glass tubing. 
 
 Graduated cylinder, 50 or 100 c.c. 
 
 Collecting bottle, a ^-gal. " acid bottle," glass stopper. 
 
 Collecting bottle, small, about 5 oz., wide mouth, 2. 
 
 Glass covers, 2, squares of window glass about 4x4 inches. 
 
 Gasometric tubes, 2. See Number 47/a, this pamphlet. 
 
 Unit-tube. See Number 47/a, this pamphlet. 
 
 Mortar and pestle, about 3 in. diam. 
 
 Wire gauze, about 6x6 inches. The common iron-wire cloth, which 
 can be obtained of hardware dealers, serves the purpose, and is much 
 cheaper than brass or copper gauze. 
 
 Pipe-stem triangle. 
 
 For the descriptive work of Chapter VIII are needed in addition : 
 
 Flasks and corks. See Number 312, this pamphlet. 
 
 Blowpipe. 
 
 Platinum wire, 3 inches, fused into glass handle. 
 
 Combustion or deflagrating spoon. 
 
SUGGESTIONS TO TEACHERS 47 
 
 Crucible lid on flat cork. 
 Taper. 
 
 BOOKS OF REFERENCE 
 
 WATTS. Dictionary of Chemistry (Morley and Muir), 4 vols. 
 Longmans, Green & Company. 
 
 THORPE. Dictionary of Applied Chemistry, 3 vols. Longmans, 
 Green & Company. 
 
 ROSCOE and SCHORLEMMER. Treatise on Chemistry, 7 vols. (Inor- 
 ganic portion, 2 vols.) D. Appleton & Company. 
 
 RAMSAY. Inorganic Chemistry. P. Blakiston, Son & Company. 
 
 REMSEN. Inorganic Chemistry (Advanced). Henry Holt & Com- 
 pany. 
 
 RICHTER (SMITH). Inorganic Chemistry. P. Blakiston, Son & 
 Company. 
 
 MENDELEEFF. Principles of Chemistry. Longmans, Green & Com- 
 pany. 
 
 OSTWALD. Outlines of General Chemistry. Macmillan Company. 
 
 WALKER. Introduction to Physical Chemistry. Macmillan Com- 
 pany. 
 
 TILDEN. Introduction to Chemical Philosophy. Longmans, Green 
 & Company. 
 
 DOBBIN and WALKER. Chemical Theory for Beginners. Macmil- 
 lan Company. 
 
 COOKE. The New Chemistry. D. Appleton & Company. 
 
 LOTHAR MEYER. Modern Theories of Chemistry. Longmans, 
 Green & Company. 
 
 MUIR. Principles of Chemistry. 
 
 VON MEYER. History of Chemistry. Macmillan Company. 
 
 THORP, F. H. Outlines of Industrial Chemistry. Macmillan Com- 
 pany. 
 
 SADTLER. Handbook of Industrial Organic Chemistry. J. B. Lip- 
 pincott Company. 
 
 NEWTH. Chemical Section Experiments. Longmans, Green & 
 Company. 
 
 EMERGENCIES 
 
 Teachers of chemistry have a heavy responsibility in guarding 
 against serious accident by close and constant oversight of students' 
 work. Minor accidents, such as slight burns and cuts with glass, are 
 likely to occur, and it is recommended that some simple materials be 
 kept on hand for use in emergency : court-plaster, clean cotton, mus- 
 
48 THE ELEMENTARY PRINCIPLES OF CHEMISTRY 
 
 lin, and twine for bandaging : for burns, sodium bicarbonate, vase- 
 line, and emulsion of lime-water and sweet oil. The last is especially 
 effective, and should be applied liberally to the burned surface to protect 
 it from the air. In the case of acid burns, treatment with dilute 
 alkali carbonate or hydroxide should come first. Acid fumes, if in- 
 haled, should be counteracted by cautiously inhaling ammonia. The 
 irritation from inhaling chlorine is relieved by alcohol fumes. 
 
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